KR20240129487A - Silicon carbon composite anode materials, manufacturing method thereof and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a silicon carbon composite negative electrode active material, a method for producing the same, and a secondary battery including the same. In one specific example, the negative electrode active material includes a primary particle including a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion; and a secondary particle including a second hollow core having a second hollow portion formed therein and one or more of the primary particles filled in the second hollow portion; wherein the second hollow core has a harder surface than the first hollow core.

Description

Silicon carbon composite anode materials, manufacturing method thereof and secondary battery comprising the same {Silicon carbon composite anode materials, manufacturing method thereof and secondary battery comprising the same}

The present invention relates to a silicon carbon composite negative electrode active material, a method for producing the same, and a secondary battery including the same.

Currently, the problem of greenhouse gases such as carbon dioxide and rising global temperatures due to fossil fuel use is serious. Carbon dioxide emission regulations are being strengthened in countries around the world, and the introduction of electric vehicles that use electricity as a power source is rapidly increasing to replace internal combustion engine vehicles that use fossil fuels as a power source.

Secondary batteries, which are used to supply electricity to electric vehicles, are a key component of electric vehicles that can be reused through charging, unlike primary batteries that are used once and discarded. In addition to electric vehicles, secondary batteries are used in various fields such as notebook PCs, mobile devices, vertical takeoff and landing aircraft used as urban air mobility (UAM) means, and electric storage systems. Recently, with the development of industry, the demand for high-capacity, low-weight, and high-efficiency secondary batteries is increasing, and research on this is actively being conducted.

Representative secondary batteries include lead-acid batteries, nickel-cadmium batteries, and lithium-ion batteries. Among these, lithium secondary batteries produce electrical energy through the intercalation and deintercalation reactions of lithium ions (Li+) during charging and discharging. They are lightweight and have high energy density, so they are used in various fields such as electric vehicles.

A lithium secondary battery includes a positive electrode and a negative electrode; an electrolyte disposed between the positive electrode and the negative electrode; and a separator impregnated with the electrolyte; wherein the positive electrode and the negative electrode each include an active material formed on a current collector. The positive electrode active material of the lithium secondary battery includes a lithium transition metal oxide, etc., and determines the capacity and average voltage of the lithium ion battery as a lithium ion source, and the negative electrode active material can store and release lithium ions released from the positive electrode and cause current to flow through an external circuit. The electrolyte acts as a medium to allow lithium ions to move between the positive electrode and the negative electrode inside the battery.

Conventionally, crystalline carbon materials such as natural graphite or artificial graphite or amorphous carbon materials have been used as negative electrode active materials for lithium-ion batteries.

Recently, silicon (Si) has been attracting attention as an anode material instead of carbon. While graphite, which is used as a conventional anode material, stores one lithium ion per six carbon atoms, silicon (Si) can store 4.4 lithium ions per atom, which is higher in energy density than conventional graphite, and has a theoretical capacity of approximately 4,200 mAh/g, and has the advantage of very fast charge/discharge speed, drawing attention.

However, silicon anode active materials have the problem of low structural stability. When lithium ions are stored in the anode material, the volume of the anode increases (lithiation). While graphite increases in volume by about 10-20%, in silicon (Si), 4.4 lithium ions react per silicon to form a Li ₂₂ Si ₅ alloy, resulting in a large volume expansion of 4-5 times. In particular, silicon anode active materials have high crystal brittleness, which causes pulverization (cracks and destruction of particles) of silicon-based anode active materials when lithium-ion batteries are repeatedly charged and discharged, and electrical separation from the current collector (Cu electrode plate) occurs, resulting in a rapid decrease in energy capacity (capacity decay) and a shortened lifespan.

In order to prevent breakage of the negative electrode active material due to such silicon volume expansion, optimization of the negative electrode active material size and control of the optimal number of silicon particles included in the negative electrode active material are required.

In addition, silicon anode active materials have a problem in that their efficiency rapidly decreases due to changes in the interface state between the anode material (anode active material) and the electrolyte and electrode during charge and discharge. This is because when the anode material expands during battery charging, numerous lithium traps are generated when the silicon particles break. More specifically, when the silicon particles expand, the SEI (Solid Electrolyte Interphase) layer is easily destroyed by mechanical stress, and when the destruction and regeneration of the SEI layer are repeated during charge and discharge, the amount of SEI layer generated on the outer surface of the silicon increases, which reduces the gap between the particles, weakening the electrical contact between the particles and causing the lithium trap phenomenon. The SEI layer is a protective film formed on the outer surface of the active material when the electrolyte reacts with the active material of the electrode, and has low electron mobility but high lithium ion conductivity, acting as a passage through which lithium ions move between the electrolyte and the anode material. Graphite has a small volume change, so there is no problem with the SEI layer, but silicon expands to the point where it destroys the SEI layer when charging, so lithium is consumed by lithiation of silicon particles and gas is generated, and the SEI layer gradually hardens and thickens, preventing lithium ions from approaching the electrode and limiting the redox reaction of lithium, which shortens the battery life.

Therefore, active research is being conducted to improve the structural stability of silicon negative electrode active materials and prevent breakage of the negative electrode active materials due to silicon volume expansion during charging and discharging of secondary batteries.

In addition, in order to prevent destruction of the negative electrode active material and reduction in capacity due to volume expansion of silicon during charge and discharge, optimization of the size of the negative electrode active material is required, and research is being conducted to control the optimal number of silicon particles included in the negative electrode active material.

Background technology related to the present invention is disclosed in Korean Patent Publication No. 10-2185490 (published on December 2, 2020, title of the invention: Negative active material for non-aqueous electrolyte secondary battery containing silicon oxide composite and method for producing the same).

One object of the present invention is to provide a silicon carbon composite negative electrode active material having excellent durability and structural stability.

Another object of the present invention is to provide a silicon carbon composite negative electrode active material that prevents destruction of the negative electrode active material and minimizes capacity reduction due to volume expansion of nanosilicon particles caused by lithium ion insertion during charge and discharge.

Another object of the present invention is to provide a silicon carbon composite negative electrode active material having excellent electrical properties, by optimizing the number of primary particles filled inside the secondary particles of the negative electrode active material and the number of nano-silicon particles filled inside the primary particles, thereby preventing destruction of the negative electrode active material due to volume expansion of the nano-silicon particles.

Another object of the present invention is to provide a silicon carbon composite negative electrode active material having high capacity, high output and long life characteristics and excellent reversibility and initial efficiency.

Another object of the present invention is to provide a silicon carbon composite negative electrode active material that can be included in a high content when manufacturing a secondary battery negative electrode.

Another object of the present invention is to provide a silicon carbon composite negative electrode active material having excellent productivity and economic efficiency.

Another object of the present invention is to provide a method for producing the silicon carbon composite negative electrode active material.

Another object of the present invention is to provide a secondary battery including the silicon carbon composite negative electrode active material.

One aspect of the present invention relates to a silicon carbon composite negative electrode material. In one specific example, the silicon carbon composite negative electrode material comprises: a primary particle comprising a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion; and a secondary particle comprising a second hollow core having a second hollow portion formed therein and one or more of the primary particles filled in the second hollow portion; wherein the second hollow core has a harder surface than the first hollow core.

In one specific example, the number of nanosilicon particles filled in the first hollow portion may be set such that the total volume of expanded nanosilicon particles formed by inserting lithium ions into the nanosilicon particles is less than or equal to the volume of the first hollow portion, and the number of primary particles filled in the second hollow portion may be set such that the total volume of the primary particles is less than or equal to the volume of the second hollow portion.

In one specific example, the primary particle comprises first and second nanosilicon particles having radii of r ₁ and r ₂ , respectively, wherein the number of the first and second nanosilicon particles filled in the first hollow space can satisfy the condition of the following equation 1:

[Formula 1]

(In the above formula 1, the r ₁ ' is the radius and the number of the first expanded nano-silicon particles, the r ₂ ' is the radius of the second expanded nano-silicon particles, the R is the radius of the first hollow part, and the r ₁ ' and r ₂ ' are 1.5874*r ₁ and 1.5874*r ₂ , respectively).

In one specific example, the secondary particles include primary particles (1) and (2) having radii of a ₁ and a ₂ , respectively, wherein the number of primary particles (1) and (2) filled in the second hollow space can satisfy the condition of the following equation 2:

[Formula 2]

(In the above formula 2, a ₁ and n ₃ are the radius and number of primary particles (1), a ₂ and n ₄ are the radius and number of primary particles (2), and b is the radius of the second hollow part).

In one specific example, the first hollow core may have a pencil hardness of less than 4H as measured according to ISO 15184, and the second hollow core may have a pencil hardness of 4H or greater.

In one specific example, the first hollow core may have a thickness of 5 to 300 nm, the first hollow portion may have a diameter of 1 to 8 μm, the nanosilicon particles may have an average particle diameter of 50 to 500 nm, and the number of nanosilicon particles filled in the first hollow portion may be 50 to 10,000.

In one specific example, the second hollow core may have a thickness of 5 to 500 nm, the second hollow portion may have a diameter of 3 to 25 μm, and the number of primary particles filled in the second hollow portion may be 5 to 500.

In one specific example, the negative electrode active material may include 25 to 80 wt% of the nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core, based on the total weight of the negative electrode active material.

In one specific example, the negative electrode active material may include the second hollow core and the first hollow core in a weight ratio of 1:0.5 to 1:6.

In one specific example, the negative electrode active material further includes a first coating layer formed on an outer surface of the second hollow core, and the first coating layer may include at least one of a soft coating layer and a medium coating layer.

In one specific example, the primary particles may have a packing density of 75% or less of the nanosilicon particles.

In one specific example, the first coating layer may include the soft coating layer and the medium coating layer in a weight ratio of 1:0.5 to 1:3.

Another aspect of the present invention relates to a method for producing the silicon carbon composite negative electrode active material. In one specific example, the method for producing the silicon carbon composite negative electrode active material includes: a step of drying a mixed slurry including a nano-silicon slurry and a soft coating material to produce a dry powder; a step of producing a first mixture including the dry powder and the soft coating material; and a step of sintering the first mixture and the second mixture including the hard coating material to produce a first intermediate; wherein the first intermediate includes primary particles including a first hollow core having a first hollow portion formed and nano-silicon particles filled in the first hollow portion, and secondary particles including a second hollow core having a second hollow portion formed and one or more of the primary particles filled in the second hollow portion, wherein the second hollow core has a harderness than the first hollow core.

In one specific example, the nanosilicon slurry is manufactured including the steps of adding and dispersing a silicon raw material powder and a dispersant into a first solvent to manufacture a dispersion; and pulverizing the dispersion; wherein the first solvent may include at least one of water, ethanol, isopropyl alcohol, and potassium hydroxide (KOH).

In one specific example, the first hollow core may have a pencil hardness of less than 4H as measured according to ISO 15184, and the second hollow core may have a pencil hardness of 4H or greater.

In one specific example, the second mixture can be calcined at 850 to 1050°C.

In one specific example, the step of manufacturing the first intermediate may be performed including the steps of first firing the first mixture at 850 to 950°C, and second firing the second mixture including the first-fired first mixture and the soft coating material at a temperature higher than 950°C and lower than 1050°C.

In one specific example, after the step of manufacturing the first intermediate, the method further includes the step of forming a first coating layer on an outer surface of the first intermediate, wherein the first coating layer includes at least one of a soft coating layer and a medium coating layer, wherein the soft coating layer is formed by including the step of mixing and firing the first intermediate and a soft coating material, and the medium coating layer can be formed by including the step of heat-treating the first intermediate in a hydrocarbon gas atmosphere.

Another aspect of the present invention relates to a secondary battery including the silicon carbon composite negative electrode active material. In one specific example, the secondary battery includes a positive electrode; a negative electrode; and an electrolyte formed between the positive electrode and the negative electrode; wherein the negative electrode includes the negative electrode active material.

The negative electrode active material according to the present invention has excellent durability and structural stability, prevents destruction of the negative electrode active material due to silicon volume expansion when lithium ions are inserted during charge and discharge, minimizes capacity decrease, optimizes the number of primary particles filled inside the secondary particles of the negative electrode active material and the number of nano-silicon particles filled inside the primary particles, thereby preventing destruction of the negative electrode active material due to nano-silicon particle volume expansion during charging, has excellent electrical characteristics, can be included in a high content when manufacturing a secondary battery negative electrode, and has high capacity, high energy density, high output, and long life characteristics, and can have excellent reversibility and initial efficiency, and excellent productivity and economy.

Figure 1 illustrates a negative electrode active material according to one specific example of the present invention.
Figure 2 illustrates a negative active material according to another specific example of the present invention.
Figure 3 is an XRD analysis graph of the negative electrode active material of Example 1.

In describing the present invention, if it is determined that a detailed description of a related known technology or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

In addition, the terms described below are terms defined in consideration of their functions in the present invention, and may vary depending on the intention or custom of the user or operator, and therefore, their definitions should be made based on the contents of the entire specification explaining the present invention.

Silicon carbon composite cathode active material

One aspect of the present invention relates to a silicon carbon composite negative electrode active material. FIG. 1 illustrates a negative electrode active material according to one specific example of the present invention. Referring to FIG. 1, the silicon carbon composite negative electrode active material (100) includes a first hollow core (14) in which a first hollow portion (16) is formed and a primary particle (10) including nanosilicon particles (12) filled in the first hollow portion (16); and a second hollow core (22) in which a second hollow portion (24) is formed and a secondary particle (20) including one or more primary particles (10) filled in the second hollow portion (24); wherein the second hollow core (22) has a harder surface than the first hollow core (14).

In one specific example, the negative electrode active material may include 25 to 80 wt% of the nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core, based on the total weight of the negative electrode active material.

In one specific example, the negative electrode active material may have a particle density of 1 to 3 g/cm ³ . Under the above conditions, light weight and output may be excellent.

In one specific example, the negative electrode active material may have an average particle size of 5 to 30 μm. Under the above conditions, the negative electrode active material may have excellent high-capacity, high-output characteristics and structural stability under the above average particle size conditions, may prevent destruction of the negative electrode active material due to volume expansion of the nano-silicon particles during charge and discharge, and may have excellent long-life characteristics. For example, the negative electrode active material may have an average particle size of 3 to 30 μm, 3 to 25 μm, 3 to 20 μm, 5 to 20 μm, 5 to 15 μm, 5 to 18 μm, or 6 to 12 μm.

Primary particle

The above primary particle includes a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion.

In one specific example, the primary particles may have an average particle size (d50) (or diameter) of 1 to 8.5 μm. Under the above conditions, the primary particles may be prevented from being destroyed due to volume expansion of the nanosilicon particles during charging and discharging, and may have excellent long-life characteristics. For example, the diameter may be 1 to 6 μm, 1 to 5.5 μm, 1 to 4.5 μm, or 2 to 3 μm.

The above first hollow core may be spherical or elliptical, for example, it may be spherical.

In one specific example, the first hollow core is formed by firing a soft coating material to be described later. When the first hollow core is formed by firing the soft coating material, when lithium ions are inserted into the nano-silicon particles during the secondary battery charging process and expand, the first hollow core (or negative electrode active material) is prevented from being broken or damaged, thereby preventing capacity reduction and providing excellent long-life characteristics.

In one specific example, the soft coating material may include one or more of carbon precursors formed from pitch, coke, and other organic materials. For example, the pitch may include one or more of pyrolysis fuel oil pitch and coal tar pitch.

In one specific example, the first hollow portion may have an average diameter of 1 to 8 μm. Under the above conditions, the destruction of the primary particles due to volume expansion of the nano-silicon particles during charging and discharging may be prevented, and long-life characteristics may be excellent. For example, the diameter may be 1 to 6 μm, 1 to 5 μm, 1 to 4 μm, or 2 to 3 μm.

For example, the first hollow portion may have a radius of 0.5 to 4 μm or 1 to 1.5 μm.

In one specific example, the first hollow core may have a thickness of 5 to 300 nm. Under the above conditions, the hardness and mechanical strength are excellent, so that the cathode active material can be prevented from being broken or damaged even when the nanosilicon particles expand. For example, the thickness may be 5 to 250 nm, 10 to 300 nm, or 10 to 50 nm.

In one specific example, the first hollow core may have a density of 1.5 g/cm ³ or less. Under the above conditions, the light weight and structural stability may be excellent. For example, the first hollow core may have a density of 0.3 to 1.5 g/cm ³ .

In one specific example, the first hollow core may have a surface area (BET) of 300 m ² /g or more. Under the above conditions, the structural stability may be excellent. For example, the surface area (BET) may be 300 to 2500 m ² /g.

In one specific example, the first hollow core may have a purity (impurity content) of 1000 ppm or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, it may be 1000 to 5000 ppm.

In one specific example, the first hollow core may have an electrical conductivity (resistivity) of 50 μΩ·m or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, the electrical conductivity (resistivity) may be 50 to 300 μΩ·m.

In one specific example, the first hollow core may have a pencil hardness of less than 4H as measured according to ISO 15184. Under the above conditions, the effect of buffering the expansion of the first hollow core due to the volume expansion of the nanosilicon particles is excellent, thereby preventing destruction of the negative electrode active material and providing excellent long-life characteristics. For example, the pencil hardness may be B to 3H, or B to 1H.

In one specific example, the first hollow core may be included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material. When included in the above range, the durability and structural stability of the negative electrode active material may be excellent, and the electrical characteristics may be excellent. For example, it may be included in an amount of 1 to 30 wt%, 1 to 25 wt%, 1 to 20 wt%, 1 to 15 wt%, 2 to 15 wt%, 3 to 15 wt%, or 5 to 15 wt%.

Nanosilicon particles

The above nanosilicon particles are included to secure high capacity and high output characteristics. In one specific example, the nanosilicon particles may be spherical, polyhedral, ellipsoidal or irregularly shaped. For example, it may be spherical.

In the past, in order to suppress the destruction of the negative active material when the silicon expands due to lithium ion insertion, graphite was added and pulverized and calcined to manufacture the negative active material. However, in the process of pulverizing the silicon and graphite, oxidation of the silicon occurred, and there was a problem that the capacity significantly decreased to less than 1,400 mAh/g when manufacturing the negative active material.

On the other hand, the negative electrode active material of the present invention prevents destruction of the negative electrode active material due to expansion of nano-silicon particles without containing flake graphite by applying a specific structure of primary particles and secondary particles, thereby enabling the production of a long-life negative electrode active material, and can implement high-capacity characteristics of 2,000 mAh/g or more.

In one specific example, the number of nanosilicon particles filled in the first hollow portion may be set such that the total volume of the expanded nanosilicon particles formed when lithium ions are inserted into the nanosilicon particles is less than or equal to the volume of the first hollow portion. When the number of nanosilicon particles is set as described above, the first hollow core (or negative electrode active material) can be prevented from being broken or destroyed due to the expansion of the nanosilicon particles.

In one specific example, the nanosilicon particles may exhibit relatively high crystalline properties.

In one specific example, the nanosilicon particles may have effective peaks in one or more regions of 2θ values of 26 to 30˚, 47 to 50˚, 53 to 58˚, 68 to 72˚, 74 to 78˚, and 88 to 90˚ in an X-ray diffraction (XRD) spectrum. Under the above conditions, high-capacity and high-power characteristics of the nanosilicon particles are secured, and the breakage of the silicon particles during charge and discharge can be significantly reduced.

For example, the nano-silicon particles may have effective peaks in the X-ray diffraction spectrum at diffraction angles (2θ) of 27.5 to 28.5˚, 47.5 to 48.5˚, 56 to 57˚, 68 to 69.5˚, 75 to 76˚, and 88 to 90˚, respectively, and the effective peaks may represent crystal planes (111), (220), (311), (400), (331), and (442), respectively. Under the above conditions, the high-capacity and high-power characteristics of the nano-silicon particles can be secured, and the breakage of the silicon particles during charge and discharge can be significantly reduced.

For example, the nanosilicon particles may have effective peaks in the range of 26 to 30˚ for the diffraction angle (2θ) value at the (111) plane and in the range of 47 to 50˚ for the diffraction angle (2θ) value at the (220) plane in an X-ray diffraction (XRD) spectrum using CuKα rays of 1.54 to 2.0 Å.

For example, in an X-ray diffraction (XRD) spectrum measured at 2θ of 10-70° with a step size of 0.01° using CuKα radiation of 1.54178 Å, the nanosilicon particles may have effective peaks in the range of 26 to 30° for the diffraction angle (2θ) value at the (111) plane and in the range of 47 to 50° for the diffraction angle (2θ) value at the (220) plane, respectively.

In one specific example, the nano silicon particles may have an FWHM (Full width at half maximum) of an X-ray diffraction angle (2θ) using CuKα rays of 1.54 to 2.0 Å at the (111) plane and the (220) plane in the range of 0.40° to 0.80°, more preferably in the range of 0.52° to 0.68° or 0.59° to 0.71°. Under the above conditions, the high-capacity and high-power characteristics of the nano silicon particles can be secured, and the breakage phenomenon of the silicon particles during charge and discharge can be significantly reduced.

In one specific example, the nanosilicon particles may have an average particle diameter of 50 to 500 nm. In another specific example, the nanosilicon particles may have an average particle diameter (50) of 500 nm or less, more preferably 160 nm to 260 nm, 180 nm to 230 nm, 190 nm to 220 nm, or 200 nm to 220 nm. In addition, the control of the maximum value (Dmax) of the average particle diameter of the nanosilicon particles is also very important. For example, the Dmax particle diameter may be 380 nm or less, preferably 320 nm to 360 nm. More preferably, it may be 300 nm to 340 nm. The lower the Dmax value, the higher the viscosity of the nanosilicon slurry. The viscosity of the nanosilicon slurry can be controlled to 6500 cps or less (25° C.).

1.5874*r).For example, an expanded nanosilicon particle whose volume is expanded four times that of a spherical nanosilicon particle with a radius r may have a radius r' of 1.5874*r. The radius r' of the expanded nanosilicon particle can be derived using the relationship (4/3)*π*(r') ³ = 4*(4/3)*π*(r) ³ (r' = ( ³ √4)*r

1.5874*r).

0.7405)을 고려하여 도출될 수 있다.In addition, the number of nanosilicon particles filled inside the first hollow space is the particle filling ratio (π*(√3/2)) in the hexagonal close-packed or face-centered cubic structure.

It can be derived by considering 0.7405).

In one specific example, a nanosilicon particle having a radius (r) of 100 nm can have a radius of about 158 nm (158.74 nm) when expanded four-fold to a radius (r'). In another specific example, a nanosilicon particle having a radius (r) of 150 nm can have a radius of about 238 nm (238.11 nm) when expanded four-fold to a radius (r').

In one specific example, the primary particle may include first and second nanosilicon particles having radii of r ₁ and r ₂ , respectively. The r ₁ and r ₂ may be the same or different, respectively.

In one specific example, the number of the first and second nanosilicon particles filled in the first hollow portion of the first particle may satisfy the condition of the following equation 1:

[Formula 1]

(In the above Equation 1, the r ₁ ' is the radius of the first expanded nano-silicon particle, the r ₂ ' is the radius of the second nano-silicon particle, the R is the radius of the first hollow part, and the r ₁ ' and r ₂ ' are 1.5874*r ₁ and 1.5874*r ₂ , respectively).

When the number of first and second nano-silicon particles filled in the first hollow portion is set under the condition of the above formula 1, the first hollow core (or negative electrode active material) of the first particle can be prevented from being broken or destroyed due to expansion of the nano-silicon particles.

In one specific example, the number of nanosilicon particles filled in the first hollow portion of the primary particle may be 50 to 10,000. Under the above conditions, it is easy to control the number of nanosilicon particles, prevent destruction of the first hollow core due to expansion of the nanosilicon particles, and excellent high-capacity and high-output characteristics of the negative electrode active material may be achieved. For example, the number of nanosilicon particles filled in the first hollow portion of the primary particle may be 150 to 10,000. For example, it may be 150 to 8,000. For other examples, it may be 150 to 6,000, 200 to 2,000, or 200 to 1,600.

As another example, the first hollow portion may have an average diameter of 2 to 4 μm (or a radius of 1 to 2 μm), and the total number of first nano-silicon particles having an average particle diameter (d50) of 180 to 220 nm (a radius of 90 to 110 nm) and second nano-silicon particles having an average particle diameter (d50) of 280 to 320 nm (a radius of 140 to 160 nm) filled in the first hollow portion may be 150 to 5,000. Under the above conditions, it is easy to control the number of nano-silicon particles, prevent destruction of the first hollow core due to expansion of the nano-silicon particles, and provide excellent high-capacity and high-output characteristics of the negative electrode active material. For example, the total number of first nano-silicon particles having a radius of 100 nm (average particle diameter (d50) of 200 nm) and second nano-silicon particles having a radius of 150 nm (average particle diameter (d50) of 300 nm) filled in the first hollow space may be 150 to 2,000, 200 to 2,000, or 200 to 1,600.

For example, the first hollow portion having the above average diameter of 2 to 4 μm (or radius of 1 to 2 μm) may contain 140 to 1,300 first nano-silicon particles (radius of 90 to 110 nm), and the second nano-silicon particles (radius of 140 to 160 nm) may contain 30 to 360. Under the above conditions, it is easy to control the number of nano-silicon particles, prevent destruction of the first hollow core due to expansion of the nano-silicon particles, and provide excellent high-capacity and high-output characteristics of the negative electrode active material.

In one specific example, the primary particle may have a packing density of 75% or less of the nanosilicon particles. The packing density of the nanosilicon particles may mean the number of nanosilicon particles actually filled with respect to the maximum number of nanosilicon particles filled in the first hollow space. Under the packing density condition, the negative electrode active material may be prevented from being destroyed by expansion of the nanosilicon particles, while exhibiting excellent high-capacity and high-output characteristics. For example, the packing density may be 20 to 50%. In another example, the packing density may be 20 to 25%.

In one specific example, the secondary particles may have a packing density of 75% or less of the primary particles. The packing density of the secondary particles may mean the number of primary particles actually packed relative to the maximum number of primary particles that can be packed in the second hollow space. Under the packing density conditions, the negative electrode active material may be prevented from being destroyed by expansion of the primary particles, while exhibiting excellent high-capacity and high-output characteristics. For example, the packing density may be 20 to 60%. In another example, the packing density may be 20 to 35%.

In one specific example, the nano-silicon particles may be included in an amount of 25 to 80 wt% based on the total weight of the negative electrode active material. In the above content range, the negative electrode active material may have excellent mixing and durability, as well as excellent high-capacity and high-output characteristics. For example, the negative electrode active material may be included in an amount of 25 to 70 wt%. In another specific example, the negative electrode active material may be included in an amount of 25 to 65 wt%, 25 to 60 wt%, or 30 to 50 wt%.

secondary particle

The above secondary particle includes a second hollow core having a second hollow portion formed therein and one or more of the above primary particles filled in the second hollow portion.

The above second hollow core may be spherical or elliptical, for example, it may be spherical.

The above second hollow core may exhibit relatively high crystalline characteristics. Under the above conditions, the strength and durability may be excellent.

In one specific example, the second hollow core is formed by firing a hard coating material to be described later. When the second hollow core is formed by firing the hard coating material, the crystallinity of the second hollow core is excellent, and electrical conductivity, hardness, and mechanical strength are excellent. In addition, when lithium ions are inserted into the nano-silicon particles and expand during the secondary battery charging process, the second hollow core (or negative electrode active material) is prevented from being broken or damaged due to primary particle expansion, thereby preventing capacity reduction and having excellent long-life characteristics.

The diameter of the second hollow portion is larger than the diameter of the first hollow portion.

In one specific example, the second hollow portion may have an average diameter of 3 to 25 μm. Under the above conditions, the destruction of the negative electrode active material due to expansion of the primary particles may be prevented, and long-life characteristics may be excellent. For example, the second hollow portion may have an average diameter of 5 to 20 μm, 6 to 20 μm, 10 to 20 μm, 6 to 18 μm, 12 to 18 μm, or 14 to 18 μm.

In one specific example, the second hollow core may have a thickness of 5 to 500 nm. Under the above conditions, the hardness and mechanical strength are excellent, so that the cathode active material can be prevented from being broken or damaged even when the nanosilicon particles expand. For example, the thickness may be 5 to 250 nm, 10 to 300 nm, or 10 to 50 nm.

In one specific example, the second hollow core may have a density of 1.8 to 2.5 g/cm ³ . Under the above conditions, the light weight and structural stability may be excellent. For example, the second hollow core may have a density of 1.8 to 2.1 g/cm ³ .

In one specific example, the second hollow core may have a BET surface area of 100 m ² /g or less. Under the above conditions, the structural stability may be excellent.

In one specific example, the second hollow core may have a purity (impurity content) of 100 ppm or less. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the second hollow core may have an electrical conductivity (resistivity) of 3 to 5 μΩ·m. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the second hollow core may have a pencil hardness of 4H or higher as measured according to ISO 15184. Under the above conditions, the durability and strength of the second hollow core are excellent, and even when the primary particles expand due to the insertion of lithium ions into the nanosilicon particles, the effect of preventing breakage or damage to the second hollow core (or the negative electrode active material) may be excellent. For example, the second hollow core may have a pencil hardness of 4H to 6H.

In one specific example, the second hollow core may be included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material. When included in the above range, the durability and structural stability of the negative electrode active material may be excellent, and the electrical characteristics may be excellent. For example, it may be included in an amount of 1 to 35 wt%, 1 to 30 wt%, 1 to 25 wt%, 1 to 20 wt%, 1 to 15 wt%, 1 to 10 wt%, or 5 to 15 wt%.

In one specific example, the negative electrode active material may include the second hollow core and the first hollow core in a weight ratio of 1:0.5 to 1:6. When included in the above weight ratio, the durability and structural stability of the negative electrode active material may be excellent, while long life, high output, and electrical characteristics may be excellent. For example, the negative electrode active material may include the second hollow core and the first hollow core in a weight ratio of 1:1 to 1:5, 1:1.5 to 1:5, 1:2 to 1:4, or 1:2 to 1:3.

In one specific example, the secondary particles may include primary particles (1) and (2) having radii a ₁ and a ₂ , respectively. The radii a ₁ and a ₂ of the primary particles (1) and (2) may be the same or different.

In one specific example, the number of primary particles (1) and (2) filled in the second hollow portion may satisfy the condition of the following equation 2:

[Formula 2]

(In the above formula 2, a ₁ and n ₃ are the radius and number of primary particles (1), a ₂ and n ₄ are the radius and number of primary particles (2), and b is the radius of the second hollow part).

When the number of primary particles (1) and (2) filled in the second hollow portion of the secondary particle is derived under the condition of the above equation 2, the breakage or destruction of the second hollow core (or negative electrode active material) due to expansion of the primary particle can be prevented.

In one specific example, the number of primary particles charged into the second hollow portion may be 5 to 500. Under the above conditions, high output, long life, and excellent electrical characteristics may be achieved. For example, the number of primary particles may be 5 to 300, for example, 100 to 300.

In one specific example, the second hollow portion may have an average diameter of 6 to 18 μm, and the second hollow portion may contain 13 to 445 primary particles (1) having an average particle diameter (d50) of 2 to 3 μm (or a radius of 1.0 to 1.5 μm) and 1 to 125 primary particles (2) having an average particle diameter (d50) of 3 to 4 μm (or a radius of 1.5 to 2.0 μm). Under the above conditions, it is easy to control the number of primary particles, prevent destruction of the second hollow core due to expansion of the primary particles (or nanosilicon particles), and excellent high-capacity and high-output characteristics of the negative electrode active material may be achieved.

1st coating layer

Figure 2 illustrates a negative electrode active material according to another specific example of the present invention. Referring to Figure 2, the negative electrode active material (200) (or secondary particle (20)) may further include a first coating layer (30) formed on the outer surface of the second hollow core (22).

In one specific example, the first coating layer may include at least one of a soft coating layer and a medium coating layer.

The above medium coating layer has a harder texture than the soft coating layer.

In one specific example, the first coating layer may have a thickness of 5 to 100 nm. Under the above conditions, the second hollow core (or negative electrode active material) may be prevented from being broken or destroyed due to expansion, and may have excellent high output and long life characteristics. For example, the thickness may be 5 to 90 nm, 5 to 50 nm, 10 to 80 nm, or 10 to 40 nm.

Soft coating layer

In one specific embodiment, the soft coating layer can be manufactured by firing a soft coating material. In one specific embodiment, the soft coating material can include one or more of a carbon precursor formed from pitch, coke, and other organic materials. For example, the pitch can include one or more of a pyrolysis fuel oil pitch and a coal tar pitch.

In one specific example, the soft coating layer may have a pencil hardness of B to 3H as measured according to ISO 15184. Under the above conditions, the destruction of the negative electrode active material due to volume expansion of the nanosilicon particles may be prevented, thereby providing excellent long-life characteristics. For example, the pencil hardness may be B to 1H.

In one specific example, the soft coating layer may have a thickness of 5 to 100 nm. Under the above conditions, the effect of buffering the expansion of the second hollow core due to the expansion of the primary particle (or nanosilicon particle) is excellent, thereby preventing breakage or damage. For example, the thickness may be 5 to 80 nm, 5 to 60 nm, 5 to 30 nm, or 5 to 20 nm.

In one specific example, the soft coating layer may have a density of 1.5 g/cm ³ or less. Under the above conditions, the light weight and structural stability may be excellent. For example, the soft coating layer may have a density of 0.3 to 1.5 g/cm ³ .

In one specific example, the soft coating layer may have a surface area (BET) of 300 m ² /g or more. Under the above conditions, the structural stability may be excellent. For example, the surface area (BET) may be 300 to 2500 m ² /g.

In one specific example, the soft coating layer may have a purity (impurity content) of 1000 ppm or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, it may be 1000 to 5000 ppm.

In one specific example, the soft coating layer may have an electrical conductivity (resistivity) of 50 μΩ·m or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, the electrical conductivity (resistivity) may be 50 to 300 μΩ·m.

In one specific example, the soft coating layer may be included in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material. When included in the above range, the second hollow core may be prevented from being broken or destroyed due to the expansion of the primary particles (or nano-silicon particles), and capacity reduction may be minimized, thereby providing excellent long-life characteristics. For example, the soft coating layer may be included in an amount of 1 to 15 wt%, 1 to 10 wt%, 2 to 8 wt%, or 2 to 5 wt%.

Medium coating layer

In one specific example, the medium coating layer may be formed by heat treating at least one of a hydrocarbon gas and carbon black. For example, the hydrocarbon gas may include at least one of methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), and pentane (C ₅ H ₁₂ ).

The above medium coating layer may be amorphous or crystalline. Under the above conditions, the strength and durability may be excellent.

The above medium coating layer has a harder surface than the above soft coating layer.

In one specific example, the medium coating layer may have a pencil hardness of 2H or more and less than 4H as measured according to ISO 15184. Under the above conditions, the destruction of the second hollow core due to volume expansion of the primary particles (or nanosilicon particles) may be prevented, thereby providing excellent long-life characteristics.

In one specific example, the medium coating layer may have a thickness of 5 to 100 nm. Under the above conditions, the effect of buffering the expansion of the second hollow core due to the expansion of the primary particle (or nanosilicon particle) is excellent, thereby preventing breakage or damage. For example, the thickness may be 5 to 60 nm, 5 to 30 nm, or 5 to 20 nm.

In one specific example, the medium coating layer may have a density of less than 1.8 g/cm ³ . Under the above conditions, the light weight and structural stability may be excellent. For example, the medium coating layer may have a density of greater than 1.5 and less than or equal to 1.7 g/cm ³ .

In one specific example, the medium coating layer may have a BET surface area of 100 to 200 m ² /g or less. Under the above conditions, the structural stability may be excellent.

In one specific example, the medium coating layer may have a purity (impurity content) of 500 ppm or less. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the medium coating layer may have an electrical conductivity (resistivity) of 20 to 40 μΩ·m. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the medium coating layer may be included in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material. When included in the above range, the electrical conductivity may be excellent, and the second hollow core may be prevented from being broken or destroyed due to the expansion of the primary particles (or nano-silicon particles), and the capacity reduction may be minimized, thereby providing excellent long-life characteristics. For example, the medium coating layer may be included in an amount of 1 to 15 wt%, 1 to 10 wt%, 2 to 8 wt%, or 2 to 5 wt%. In another specific example, the first coating layer may include a hard coating layer or a medium coating layer.

Also, referring to the above-described FIG. 2, the first coating layer (30) of the negative electrode active material (200) may include a soft coating layer (32) and a medium coating layer (34) that are formed sequentially.

In one specific example, the second hollow core may have higher crystallinity than the first hollow core, the soft coating layer, and the medium coating layer. The crystallinity can be confirmed through a conventional XRD (X-ray diffraction) analysis. Under the above conditions, the electrical conductivity, strength, and high-power characteristics of the negative electrode active material may be excellent.

In one specific example, the medium coating layer may have a higher crystallinity than the first hollow core and the soft coating layer.

In one specific example, the first coating layer may include a soft coating layer and a medium coating layer in a weight ratio of 1:0.5 to 1:3. When included in the above range, the electrical conductivity is excellent, and the second hollow core may be prevented from being broken or destroyed due to the expansion of the primary particles (or nano-silicon particles), and the capacity reduction may be minimized, so that the long-life characteristics may be excellent. For example, the weight ratio may be 1:1 to 1:3 or 1:1.5 to 1:2.5.

Method for manufacturing silicon carbon composite cathode active material

Another aspect of the present invention relates to a method for producing the silicon carbon composite negative electrode active material. In one specific example, the method for producing the negative electrode active material includes: (S10) a step of producing a dry powder; (S20) a step of producing a first mixture; and (S30) a step of producing a first intermediate. More specifically, the method for producing the negative electrode active material includes: (S10) a step of drying a mixed slurry including a nano-silicon slurry and a soft coating material to produce a dry powder; (S20) a step of producing a first mixture including the dry powder and the soft coating material; and (S30) a step of firing a second mixture including the first mixture and the hard coating material to produce a first intermediate.

The first intermediate body includes a first hollow core having a first hollow portion formed therein and a primary particle including nanosilicon particles filled in the first hollow portion, and a second hollow core having a second hollow portion formed therein and a secondary particle including one or more of the first particles filled in the second hollow portion, wherein the second hollow core has a harderness than the first hollow core.

(S10) Dry powder manufacturing step

The above step is a step of manufacturing a dry powder by drying a mixed slurry containing nanosilicon slurry and a soft coating material.

In one specific example, the nanosilicon slurry may include nanosilicon particles. In one specific example, the nanosilicon slurry may be manufactured by including the steps of adding and dispersing a silicon raw material powder and a dispersant into a first solvent to manufacture a dispersion; and then pulverizing the dispersion to manufacture nanosilicon particles.

In one specific example, the first solvent may include one or more of water, ethanol, isopropyl alcohol, and potassium hydroxide (KOH). When the first solvent is included, the silicon raw material powder may have excellent mixing and dispersibility without being oxidized.

In one specific example, the dispersant may include one or more of polyvinylpyrrolidone, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, stearic acid, palmitic acid, oleic acid, and lauric acid. In another example, the dispersant may include one or more of stearic acid, petroleum pitch, coal pitch, coal tar, glucose, sucrose, polyimide, polyacrylic acid (PAA), and polyvinyl alcohol (PVA). When the dispersant is included, the dispersibility of the silicon powder is excellent, so that a nanosilicon slurry including nanosilicon particles can be easily prepared. For example, it may include stearic acid. For example, the dispersant can be used by mixing stearic acid and N-methylpyrrolidone (NMP).

In one specific example, the nanosilicon slurry may include 100 parts by weight of a silicon raw material powder, 5 to 1,500 parts by weight of a first solvent, and 0.1 to 30 parts by weight of a dispersant. Under the above conditions, the mixing and dispersibility of the nanosilicon particles are excellent, and the nanosilicon slurry may be easily manufactured. For example, the nanosilicon slurry may include 100 parts by weight of a silicon raw material powder, 800 to 1,000 parts by weight of a first solvent, and 0.5 to 25 parts by weight of a dispersant.

For example, a dispersant may be added to the first solvent in the above-mentioned amount and mixed, then the silicon raw material powder may be added and mixed to prepare a dispersion, and the dispersion may be pulverized to prepare a nanosilicon slurry.

In one specific example, the grinding may be performed by milling. In one specific example, the milling may be performed using a beads mill, a ball mill, a high energy ball mill, a planetary mill, a stirred ball mill, a vibration mill, or the like.

For example, the ball mill may be made of a chemically inert material that does not react with the silicon powder and other organic components. For example, it may include zirconia (ZrO ₂ ). In one specific example, the ball mill may have an average particle diameter of 0.1 to 1 mm. Under the above conditions, nanosilicon particles can be easily manufactured.

For example, the ratio of zirconia beads to silicon raw material powder (Ball Per Ratio) may be in the range of silicon raw material powder/zirconia beads = 1/3.5 to 1/10 in weight ratio. In addition, when dispersing the dispersion, the rotation speed of the rotor inside the grinder may be in the range of 2200 rpm to 2600 rpm.

In one specific example, the silicon raw material powder may have an average particle size (D50) of 0.3 to 3.5 μm. Under the above conditions, mixing and grinding are easy, and nanosilicon particles having a desired average particle size can be easily manufactured. For example, the silicon raw material powder may have an average particle size (D50) of 0.5 to 2.5 μm. In another example, it may be 0.3 to 1.8 μm.

In one specific example, the silicon raw material powder may have a maximum particle size (Dmax) of 10㎛ or less. Under the above conditions, nanosilicon particles having a desired average particle size can be easily manufactured.

In one specific example, the silicon raw material powder in the nanosilicon slurry may be included in an amount of 6.5 to 17.8 wt% based on the solid content. Under the above conditions, the mixing property and workability may be excellent.

In one specific example, the nanosilicon slurry may have a viscosity of 2000 to 6500 cps (25°C). Under the above conditions, the mixing and dispersibility of the nanosilicon powder is excellent, and the number of nanosilicon particles filled inside the hollow portion can be easily controlled.

In one specific example, the nanosilicon particles may have an average particle diameter of 50 to 500 nm. In another specific example, the nanosilicon particles may have an average particle diameter (50) of 500 nm or less, more preferably 160 nm to 260 nm, 180 nm to 230 nm, 190 nm to 220 nm, or 200 nm to 220 nm. In addition, the control of the maximum value (Dmax) of the average particle diameter of the nanosilicon particles is also very important. For example, the Dmax particle diameter may be 380 nm or less, preferably 320 nm to 360 nm. More preferably, it may be 300 nm to 340 nm. The lower the Dmax value, the higher the viscosity of the nanosilicon slurry. The viscosity of the nanosilicon slurry can be controlled to 6500 cps or less (25° C.).

In one specific example, the nanosilicon particles may be spherical, polyhedral, ellipsoidal or irregularly shaped. For example, they may be spherical.

The soft coating material may be the same as that described above. In one specific example, the soft coating material may include at least one of pitch, coke, and carbon precursors formed from other organic substances. For example, the pitch may include at least one of pyrolysis fuel oil pitch and coal tar pitch.

The above soft coating material forms the first hollow core and can have excellent electrical characteristics while preventing destruction of the negative electrode active material when the nanosilicon particles expand.

In one specific example, the mixed slurry may contain 70 to 99.9 wt% of the nanosilicon slurry and 0.1 to 30 wt% of the soft coating material. When included within the above weight range, the mixing and dispersibility of the components of the mixed slurry may be excellent.

In one specific example, the soft coating material may have an average particle size (d50) of 3 nm to 2.5 μm. Under the above conditions, the first hollow core may be easily formed during the firing described below. For example, the average particle size may be 5 to 1000 nm, 10 to 500 nm, or 15 to 200 nm.

The powder size of the negative electrode active material can be easily controlled by drying the above-mentioned mixed slurry. For example, the drying can be performed using a spray dryer or the like. For example, the drying can be performed by spray drying using a spray dryer equipped with a one-fluid nozzle, a two-fluid nozzle, or a four-fluid nozzle.

In one specific example, the dry powder may be spherical, polyhedral or ellipsoidal, for example spherical.

In one specific example, the dry powder may have an average particle diameter (or size) of 0.1 to 15 μm. Under the above conditions, the mixing and molding properties may be excellent.

In one specific example, when the mixed slurry is spray-dried using a one-fluid nozzle, the spray dryer can be set to an outlet temperature of 70 to 130°C and an air flow rate of 650 to 850 sccm to manufacture a dry powder, and the dry powder can have an average particle size of 7 to 14 μm. In another specific example, the mixed slurry can be spray-dried using a four-fluid nozzle to manufacture a dry powder, and the dry powder can have an average particle size of 0.1 to 8 μm.

(S20) First mixture manufacturing step

The above step is a step of preparing a first mixture including the above dry powder and a soft coating material.

The above soft coating material forms the first hollow core and can have excellent electrical characteristics while preventing destruction of the negative electrode active material when the nanosilicon particles expand.

In one specific example, the soft coating material may include one or more of carbon precursors formed from pitch, coke, and other organic materials. For example, the pitch may include one or more of pyrolysis fuel oil pitch and coal tar pitch.

In one specific example, the soft coating material can be applied in the form of a soft coating liquid containing the soft coating material and a solvent.

In one specific example, the solvent may include at least one of water, an ethanol solvent, an amide solvent, an ester solvent, and a hydrocarbon solvent. When the solvent is included, the mixing property and workability may be excellent. The alcohol solvent may include at least one of methanol, ethanol, isopropanol, and butanol. The amide solvent may include at least one of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF). The hydrocarbon solvent may include at least one of toluene and xylene.

In one specific example, the average particle size (d50) of the soft coating material may be 5 nm to 10 μm. Under the above conditions, the mixing and dispersibility of the first mixture is excellent, and the first hollow core can be easily formed during sintering. For example, it may be 10 nm to 5 μm, 10 nm to 1 μm, 10 to 500 nm, or 30 nm to 3 μm.

In one specific example, the first mixture may include 80 to 99 wt% of the dry powder and 1 to 20 wt% of the soft coating material. When included under the above content conditions, a first hollow core having a first hollow portion formed therein and a primary particle structure including nanosilicon particles filled in the first hollow portion may be easily formed.

In one specific example, after the step of preparing the first mixture, the step of compressing the first mixture may be further included. For example, the first mixture may be pressurized (or uniaxially compressed) in one direction at a pressure of 10 to 60 atm to prepare a compressed product. When preparing a compressed product under the pressurizing conditions, the internal void volume of the negative electrode active material may be controlled, thereby improving the electrical characteristics, long life, and capacity characteristics of the negative electrode active material.

(S30) First intermediate manufacturing step

The above step is a step of producing a first intermediate by firing a second mixture including the first mixture and a hard coating material.

For example, the hard coating material may include a carbon-based material.

In one specific example, the hard coating material may have a pencil hardness of 4H or higher as measured according to ISO 15184. Under the above conditions, the nanosilicon particles may have excellent high output characteristics and electrical characteristics while preventing destruction of the negative electrode active material when expanded. For example, the pencil hardness may be 4H to 6H. For example, the hard coating material may include a carbon-based material having the pencil hardness of 4H to 6H.

For example, NanoMollisAdamas from Lemon Energy can be used as the hard coating material.

The above hard coating material may be amorphous. In addition, the above hard coating material is formed through self-assembly, has excellent isotropy and excellent thermal stability, so that no structural change occurs even at high temperatures (approximately 3000°C).

The hard coating material may have high gas impermeability and excellent chemical resistance and electrical conductivity. In addition, the hard coating material may be dust-free and have a purity (impurity content) of 5 ppm or less or 2 ppm or less. Under the above conditions, the strength and electrical properties may be excellent, and the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the hard coating material can be applied in the form of a hard coating liquid containing the hard coating material and a solvent.

In one specific example, the solvent may include at least one of water, an ethanol solvent, an amide solvent, an ester solvent, and a hydrocarbon solvent. When the solvent is included, the mixing property and workability may be excellent. The alcohol solvent may include at least one of methanol, ethanol, isopropanol, and butanol. The amide solvent may include at least one of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF). The hydrocarbon solvent may include at least one of toluene and xylene.

In one specific example, the hard coating material may have an electrical conductivity (resistivity) of 3 to 5 μΩ·m. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the hard coating material may have an average particle size (d50) of 3 nm to 2.5 μm. Under the above conditions, a first intermediate body including a second hollow core can be easily formed during the firing described below. For example, it may be 5 to 1000 nm, 10 to 500 nm, or 15 to 200 nm.

In one specific example, the second mixture may include 70 to 99 wt% of the first mixture and 1 to 30 wt% of the hard coating material. When included under the above conditions, a first intermediate body including a second hollow core in which a second hollow portion is formed and a secondary particle including one or more of the primary particles filled in the second hollow portion can be easily formed.

The hard coating material described above can be the same as that described above.

In one specific example, the second mixture can be fired at 850 to 1050°C. When fired under the above conditions, the first intermediate is easily formed, and durability and long-life characteristics can be excellent. For example, the firing can be performed at 850 to 1050°C, 870 to 1050°C, 900 to 1000°C, 930 to 975°C, or 930 to 960°C.

For example, the calcination of the second mixture can be performed in an inert gas atmosphere. The inert gas can include nitrogen. For example, the calcined calcined material can be classified after being subjected to a general dry grinding process such as an attrition mill, an air classifier mill (ACM), a jet mill, and a pin mill to produce a first intermediate.

In one specific example, the step of manufacturing the first intermediate may be performed including the steps of first firing the first mixture at 850 to 950° C., and then mixing the first mixture that has been first fired with a hard coating material and second firing the mixture at a temperature exceeding 950° C. and lower than 1050° C. Under the above conditions, the first intermediate having a structure including a second hollow core in which a second hollow portion is formed and secondary particles including one or more of the first particles filled in the second hollow portion can be easily formed.

For example, the first firing and the second firing can be performed in an inert gas atmosphere. The inert gas can include nitrogen.

For example, a primary particle structure including a first hollow core in which a first hollow portion is formed during the first sintering and nanosilicon particles filled in the first hollow portion can be formed, and a secondary particle structure including a second hollow core in which a second hollow portion is formed during the second sintering and one or more of the primary particles filled in the second hollow portion can be formed.

In one specific example, the secondary firing may be performed at a higher temperature than the primary firing. Under the above conditions, the primary particles and secondary particles may be formed with higher strength, so that the durability, electrical characteristics, long-life characteristics, and capacity characteristics of the negative electrode active material may be excellent.

In one specific example, a second mixture may be prepared by mixing the compressed material produced by pressurizing the first mixture that has been first fired with a hard coating material, and the second mixture may be fired for the second time.

For example, the first mixture that has been firstly calcined can be pressurized (or uniaxially compressed) in one direction at a pressure of 10 to 60 atm to produce a compressed product. When producing a compressed product under the pressurization conditions, the internal void volume of the negative electrode active material can be controlled, so that the electrical characteristics, long life, and capacity characteristics of the negative electrode active material can be excellent.

In one specific example, the first intermediate body comprises a primary particle including a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion, and a secondary particle including a second hollow core having a second hollow portion formed therein and one or more of the primary particles filled in the second hollow portion.

The above second hollow core has a harder surface than the first hollow core.

In one specific example, the number of nanosilicon particles filled in the first hollow portion may be set such that the total volume of the expanded nanosilicon particles formed when lithium ions are inserted into the nanosilicon particles is less than or equal to the volume of the first hollow portion. When the number of nanosilicon particles is set as described above, the first hollow core (or negative electrode active material) can be prevented from being broken or destroyed when the nanosilicon particles expand.

In one specific example, the nanosilicon particles may exhibit relatively high crystalline properties.

In one specific example, the nanosilicon particles may have effective peaks in one or more regions of 2θ values of 26 to 30˚, 47 to 50˚, 53 to 58˚, 68 to 72˚, 74 to 78˚, and 88 to 90˚ in an X-ray diffraction (XRD) spectrum. Under the above conditions, high-capacity and high-power characteristics of the nanosilicon particles are secured, and the breakage of the silicon particles during charge and discharge can be significantly reduced.

For example, the nano-silicon particles may have effective peaks in the X-ray diffraction spectrum at diffraction angles (2θ) of 27.5 to 28.5˚, 47.5 to 48.5˚, 56 to 57˚, 68 to 69.5˚, 75 to 76˚, and 88 to 90˚, respectively, and the effective peaks may represent crystal planes (111), (220), (311), (400), (331), and (442), respectively. Under the above conditions, the high-capacity and high-power characteristics of the nano-silicon particles can be secured, and the breakage of the silicon particles during charge and discharge can be significantly reduced.

For example, the nanosilicon particles may have effective peaks in the range of 26 to 30˚ for the diffraction angle (2θ) value at the (111) plane and in the range of 47 to 50˚ for the diffraction angle (2θ) value at the (220) plane in an X-ray diffraction (XRD) spectrum using CuKα rays of 1.54 to 2.0 Å.

For example, in an X-ray diffraction (XRD) spectrum measured at 2θ of 10-70° with a step size of 0.01° using CuKα radiation of 1.54178 Å, the nanosilicon particles may have effective peaks in the range of 26 to 30° for the diffraction angle (2θ) value at the (111) plane and in the range of 47 to 50° for the diffraction angle (2θ) value at the (220) plane, respectively.

In one specific example, the nano silicon particles may have an FWHM (Full width at half maximum) of an X-ray diffraction angle (2θ) using CuKα rays of 1.54 to 2.0 Å at the (111) plane and the (220) plane in the range of 0.40° to 0.80°, more preferably in the range of 0.52° to 0.68° or 0.59° to 0.71°. Under the above conditions, the high-capacity and high-power characteristics of the nano silicon particles can be secured, and the breakage phenomenon of the silicon particles during charge and discharge can be significantly reduced.

In one specific example, the nanosilicon particles may have an average particle diameter of 50 to 500 nm. In another specific example, the nanosilicon particles may have an average particle diameter (50) of 500 nm or less, more preferably 160 nm to 260 nm, 180 nm to 230 nm, 190 nm to 220 nm, or 200 nm to 220 nm. In addition, the control of the maximum value (Dmax) of the average particle diameter of the nanosilicon particles is also very important. For example, the Dmax particle diameter may be 380 nm or less, preferably 320 nm to 360 nm. More preferably, it may be 300 nm to 340 nm. The lower the Dmax value, the higher the viscosity of the nanosilicon slurry. The viscosity of the nanosilicon slurry can be controlled to 6500 cps or less (25° C.).

1.5874*r).For example, an expanded nanosilicon particle whose volume is expanded four times that of a spherical nanosilicon particle with a radius r may have a radius r' of 1.5874*r. The radius r' of the expanded nanosilicon particle can be derived using the relationship (4/3)*π*(r') ³ = 4*(4/3)*π*(r) ³ (r' = ( ³ √4)*r

1.5874*r).

0.7405)을 고려하여 도출될 수 있다.In addition, the number of nanosilicon particles filled inside the hollow space is the particle filling ratio (π*(√3/2)) in the hexagonal close-packed or face-centered cubic structure.

It can be derived by considering 0.7405).

In one specific example, a nanosilicon particle having a radius (r) of 100 nm can have a radius of about 158 nm (158.74 nm) when expanded four-fold to a radius (r'). In another specific example, a nanosilicon particle having a radius (r) of 150 nm can have a radius of about 238 nm (238.11 nm) when expanded four-fold to a radius (r').

In one specific example, the primary particle may include first and second nanosilicon particles having radii of r ₁ and r ₂ , respectively. The r ₁ and r ₂ may be the same or different, respectively.

In one specific example, the number of the first and second nanosilicon particles filled in the first hollow portion of the first particle may satisfy the condition of the following equation 1:

[Formula 1]

(In the above Equation 1, the r ₁ ' is the radius of the first expanded nano-silicon particle, the r ₂ ' is the radius of the second nano-silicon particle, the R is the radius of the first hollow part, and the r ₁ ' and r ₂ ' are 1.5874*r ₁ and 1.5874*r ₂ , respectively).

When the number of first and second nano-silicon particles filled in the first hollow portion is set under the condition of the above formula 1, the first hollow core (or negative electrode active material) of the primary particle can be prevented from being broken or destroyed due to expansion of the nano-silicon particles.

In one specific example, the number of nanosilicon particles filled in the first hollow portion of the primary particle may be 50 to 10,000. Under the above conditions, it is easy to control the number of nanosilicon particles, prevent destruction of the first hollow core due to expansion of the nanosilicon particles, and excellent high-capacity and high-output characteristics of the negative electrode active material may be achieved. For example, the number of nanosilicon particles filled in the first hollow portion of the primary particle may be 150 to 10,000. For example, it may be 150 to 8,000. For other examples, it may be 150 to 6,000, 200 to 2,000, or 200 to 1,600.

As another example, the first hollow portion may have an average diameter of 2 to 4 μm (or a radius of 1 to 2 μm), and the total number of first nano-silicon particles having an average particle diameter (d50) of 180 to 220 nm (a radius of 90 to 110 nm) and second nano-silicon particles having an average particle diameter (d50) of 280 to 320 nm (a radius of 140 to 160 nm) filled in the first hollow portion may be 150 to 5,000. Under the above conditions, it is easy to control the number of nano-silicon particles, prevent destruction of the first hollow core due to expansion of the nano-silicon particles, and provide excellent high-capacity and high-output characteristics of the negative electrode active material. For example, the total number of first nano-silicon particles having a radius of 100 nm (average particle diameter (d50) of 200 nm) and second nano-silicon particles having a radius of 150 nm (average particle diameter (d50) of 300 nm) filled in the first hollow space may be 150 to 2,000, 200 to 2,000, or 200 to 1,600.

For example, the first hollow portion having the average diameter of 2 to 4 μm (or radius of 1 to 2 μm) may contain 140 to 1,300 first nano-silicon particles (radius of 90 to 110 nm, average particle diameter (d50) of 180 to 220 nm), and the second nano-silicon particles (radius of 140 to 160 nm, average particle diameter (d50) of 280 to 320 nm) may contain 30 to 360. Under the above conditions, it is easy to control the number of nano-silicon particles, prevent destruction of the first hollow core due to expansion of the nano-silicon particles, and provide excellent high-capacity and high-output characteristics of the negative electrode active material.

In one specific example, the first hollow core may be included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material (or the first intermediate). When included in the above range, the durability and structural stability of the negative electrode active material may be excellent, and the electrical characteristics may be excellent. For example, it may be included in an amount of 1 to 30 wt%, 1 to 25 wt%, 1 to 20 wt%, 1 to 15 wt%, 2 to 15 wt%, 3 to 15 wt%, or 5 to 15 wt%.

In one specific example, the nano-silicon particles may be included in an amount of 25 to 80 wt% based on the total weight of the negative active material (or the first intermediate). In the above content range, the negative active material may have excellent mixing and durability, as well as excellent high-capacity and high-output characteristics. For example, the amount may be included in an amount of 25 to 70 wt%. In another specific example, the nano-silicon particles may be included in an amount of 25 to 65 wt%, 25 to 60 wt%, or 30 to 50 wt%.

In one specific example, the primary particle may have a packing density of 75% or less of the nanosilicon particles. The packing density of the nanosilicon particles may mean the number of nanosilicon particles actually filled with respect to the maximum number of nanosilicon particles filled in the first hollow space. Under the packing density condition, the negative electrode active material may be prevented from being destroyed by expansion of the nanosilicon particles, while exhibiting excellent high-capacity and high-output characteristics. For example, the packing density may be 20 to 50%. In another example, the packing density may be 20 to 25%.

In one specific example, the secondary particles may have a packing density of 75% or less of the primary particles. The packing density of the primary particles may mean the number of primary particles actually packed with respect to the maximum number of primary particles packed in the second hollow portion of the secondary particles. Under the packing density conditions, the negative electrode active material may be prevented from being destroyed by expansion of the primary particles, while exhibiting excellent high-capacity and high-output characteristics. For example, the packing density may be 20 to 60%. In another example, the packing density may be 20 to 35%.

The above secondary particle includes a second hollow core having a second hollow portion formed therein and one or more of the above primary particles filled in the second hollow portion.

The above second hollow core may be spherical or elliptical, for example, it may be spherical.

The above first hollow core is formed by firing a soft coating material to be described later.

In one specific example, the soft coating material may include one or more of carbon precursors formed from pitch, coke, and other organic materials. For example, the pitch may include one or more of pyrolysis fuel oil pitch and coal tar pitch.

In one specific example, the first hollow core may have a pencil hardness of less than 4H as measured according to ISO 15184. Under the above conditions, the first hollow core (or negative electrode active material) may be prevented from being destroyed due to volume expansion of the primary particles (or nanosilicon particles), thereby providing excellent long-life characteristics. For example, the pencil hardness may be B to 3H, or B to 1H.

In one specific example, the first hollow core may have a surface area (BET) of 300 m ² /g or more. Under the above conditions, the structural stability may be excellent. For example, the surface area (BET) may be 300 to 2500 m ² /g.

In one specific example, the first hollow core may have a purity (impurity content) of 1000 ppm or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, it may be 1000 to 5000 ppm.

In one specific example, the first hollow core may have an electrical conductivity (resistivity) of 50 μΩ·m or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, the electrical conductivity (resistivity) may be 50 to 300 μΩ·m.

The diameter of the second hollow portion is larger than the diameter of the first hollow portion.

In one specific example, the second hollow portion may have an average diameter of 3 to 25 μm. Under the above conditions, the destruction of the negative electrode active material due to expansion of the primary particles may be prevented, and long-life characteristics may be excellent. For example, the second hollow portion may have an average diameter of 5 to 20 μm, 6 to 20 μm, 10 to 20 μm, 6 to 18 μm, 12 to 18 μm, or 14 to 18 μm.

For example, the second hollow portion may have a radius of 1.5 to 12.5 μm, 2 to 10 μm, 3 to 9 μm, or 7 to 9 μm.

In one specific example, the second hollow core may have a thickness of 5 to 500 nm. Under the above conditions, the hardness and mechanical strength are excellent, so that the negative electrode active material can be prevented from being broken or damaged due to the expansion of the primary particles. For example, the thickness may be 5 to 250 nm, 10 to 300 nm, or 10 to 50 nm.

In one specific example, the second hollow core may have a pencil hardness of 4H or higher as measured according to ISO 15184. Under the above conditions, the durability and strength of the second hollow core are excellent, and even when the primary particles expand due to the insertion of lithium ions into the nanosilicon particles, the effect of preventing breakage or damage to the second hollow core (or the negative electrode active material) may be excellent. For example, the second hollow core may have a pencil hardness of 4H to 6H.

In one specific example, the second hollow core may have a density of 1.8 to 2.5 g/cm ³ . Under the above conditions, the light weight and structural stability may be excellent. For example, the second hollow core may have a density of 1.8 to 2.1 g/cm ³ .

In one specific example, the second hollow core may have a BET surface area of 100 m ² /g or less. Under the above conditions, the structural stability may be excellent.

In one specific example, the second hollow core may have a purity (impurity content) of 100 ppm or less. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the second hollow core may have an electrical conductivity (resistivity) of 3 to 5 μΩ·m. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the second hollow core may be included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material (or the first intermediate). When included in the above range, the durability and structural stability of the negative electrode active material may be excellent, and the electrical characteristics may be excellent. For example, it may be included in an amount of 1 to 35 wt%, 1 to 30 wt%, 1 to 25 wt%, 1 to 20 wt%, 1 to 15 wt%, 1 to 10 wt%, or 5 to 15 wt%.

In one specific example, the negative electrode active material (or the first intermediate) may include the second hollow core and the first hollow core in a weight ratio of 1:0.5 to 1:6. When included in the weight ratio, the durability and structural stability of the negative electrode active material may be excellent, while long life, high output, and electrical characteristics may be excellent. For example, the negative electrode active material may include the second hollow core and the first hollow core in a weight ratio of 1:1 to 1:5, 1:1.5 to 1:5, 1:2 to 1:4, or 1:2 to 1:3.

In one specific example, the secondary particles may include primary particles (1) and (2) having radii a ₁ and a ₂ , respectively. The radii a ₁ and a ₂ of the primary particles (1) and (2) may be the same or different.

In one specific example, the number of primary particles (1) and (2) filled in the second hollow portion may satisfy the condition of the following equation 2:

[Formula 2]

(In the above formula 2, a ₁ and n ₃ are the radius and number of primary particles (1), a ₂ and n ₄ are the radius and number of primary particles (2), and b is the radius of the second hollow part).

When the number of primary particles (1) and (2) filled in the second hollow portion of the secondary particle is derived under the condition of the above equation 2, the breakage or destruction of the second hollow core (or negative electrode active material) due to expansion of the primary particle can be prevented.

In one specific example, the number of primary particles charged into the second hollow portion may be 5 to 500. Under the above conditions, high output, long life, and excellent electrical characteristics may be achieved. For example, the number of primary particles may be 5 to 300, for example, 100 to 300.

In one specific example, the second hollow portion may have a diameter of 6 to 18 μm (radius 3 to 9 μm), and the second hollow portion may contain 13 to 445 primary particles (1) having an average particle diameter (d50) of 2 to 3 μm (or a radius of 1 to 1.5 μm) and 1 to 125 primary particles (2) having an average particle diameter (d50) of 3 to 4 μm (or a radius of 1.5 to 2.0 μm). Under the above conditions, it is easy to control the number of primary particles, the destruction of the second hollow core due to expansion of the primary particles is prevented, and the high-capacity and high-output characteristics of the negative electrode active material may be excellent.

(S40) First coating layer formation step

In one specific example, after the step (S30) of manufacturing the first intermediate, the method may further include the step (S40) of forming a first coating layer on the outer surface of the first intermediate.

In one specific example, the first coating layer may include at least one of a soft coating layer and a medium coating layer.

In one specific example, the soft coating layer may be formed by including a step of mixing and firing the first intermediate and the soft coating material.

In one specific example, the firing can be performed at 850 to 975°C. Under the above conditions, the soft coating layer can be easily formed on the outer surface of the first intermediate. For example, the firing can be performed at 860 to 975°C or 900 to 960°C.

In one specific example, the soft coating material may include one or more of carbon precursors formed from pitch, coke, and other organic materials. For example, the pitch may include one or more of pyrolysis fuel oil pitch and coal tar pitch.

In one specific example, the soft coating layer can be formed by applying and firing a soft coating liquid containing a soft coating material and a solvent.

In one specific example, the solvent may include at least one of water, an ethanol solvent, an amide solvent, an ester solvent, and a hydrocarbon solvent. When the solvent is included, the mixing property and workability may be excellent. The alcohol solvent may include at least one of methanol, ethanol, isopropanol, and butanol. The amide solvent may include at least one of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF). The hydrocarbon solvent may include at least one of toluene and xylene.

In one specific example, the soft coating layer may have a pencil hardness of B to 3H as measured according to ISO 15184. Under the above conditions, the effect of buffering the volume expansion of the negative electrode active material due to the volume expansion of the nanosilicon particles is excellent, and the destruction of the hard hollow core is prevented, so that the long-life characteristics may be excellent. For example, the pencil hardness may be B to 1H.

In one specific example, the soft coating layer may have a density of 1.5 g/cm ³ or less. Under the above conditions, the light weight and structural stability may be excellent. For example, the soft coating layer may have a density of 0.3 to 1.5 g/cm ³ .

In one specific example, the soft coating layer may have a surface area (BET) of 300 m ² /g or more. Under the above conditions, the structural stability may be excellent. For example, the surface area (BET) may be 300 to 2500 m ² /g.

In one specific example, the soft coating layer may have a purity (impurity content) of 1000 ppm or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, it may be 1000 to 5000 ppm.

In one specific example, the soft coating layer may have an electrical conductivity (resistivity) of 50 μΩ·m or more. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent. For example, the electrical conductivity (resistivity) may be 50 to 300 μΩ·m.

In one specific example, the soft coating layer may have a thickness of 5 to 100 nm. Under the above conditions, the effect of buffering the volume expansion of the negative electrode active material due to the expansion of the nanosilicon particles is excellent, and the breakage or damage of the negative electrode active material can be prevented.

In one specific example, the soft coating layer may be included in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material. When included in the above range, the electrical conductivity is excellent, the effect of buffering the volume expansion of the negative electrode active material due to the expansion of nano-silicon particles is excellent, the breakage and destruction of the negative electrode active material is prevented, and capacity reduction is minimized, so that the long-life characteristics can be excellent. For example, it may be included in an amount of 1 to 15 wt%, 1 to 10 wt%, 1 to 7 wt%, 1 to 6 wt%, 1 to 5 wt%, or 2 to 5 wt%.

In one specific example, the medium coating layer may be formed including a step of heat treating the first intermediate in a hydrocarbon gas atmosphere.

In one specific example, the medium coating layer may be formed by heat treating at least one of a hydrocarbon gas and carbon black. For example, the hydrocarbon gas may include at least one of methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), and pentane (C ₅ H ₁₂ ).

For example, the above heat treatment can be performed at 850 to 970°C. Under the above conditions, a medium coating layer can be easily formed. For example, it can be 890 to 910°C.

In one specific example, the heat treatment may be performed under vacuum conditions. Under the conditions, the hydrocarbon gas can easily diffuse, thereby forming a uniform medium coating layer. For example, the heat treatment may be performed under vacuum conditions of 10 ^-1 to 10 ^-6 torr.

In one specific example, the medium coating layer may have a pencil hardness of 2H or more and less than 4H as measured according to ISO 15184. Under the above conditions, the effect of buffering the volume expansion of the negative electrode active material due to the volume expansion of the nanosilicon particles is excellent, and the destruction of the hard hollow core is prevented, so that the long-life characteristics can be excellent.

In one specific example, the medium coating layer may have a thickness of 5 to 100 nm. Under the above conditions, the cathode active material may be prevented from being broken or damaged even when the nanosilicon particles expand.

In one specific example, the medium coating layer may have a density of less than 1.8 g/cm ³ . Under the above conditions, the light weight and structural stability may be excellent. For example, the medium coating layer may have a density of greater than 1.5 and less than or equal to 1.7 g/cm ³ .

In one specific example, the medium coating layer may have a BET surface area of 100 to 200 m ² /g or less. Under the above conditions, the structural stability may be excellent.

In one specific example, the medium coating layer may have a purity (impurity content) of 500 ppm or less. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the medium coating layer may have an electrical conductivity (resistivity) of 20 to 40 μΩ·m. Under the above conditions, the electrical conductivity of the negative electrode active material may be excellent.

In one specific example, the medium coating layer may be included in an amount of 1 to 20 wt% based on the total weight of the negative electrode active material. When included in the above range, the electrical conductivity is excellent, and the negative electrode active material may be prevented from being broken or destroyed when the nanosilicon particles expand, and the capacity reduction may be minimized, thereby providing excellent long-life characteristics. For example, the medium coating layer may be included in an amount of 1 to 15 wt%, 2 to 10 wt%, 1 to 5 wt%, or 3 to 5 wt%.

For example, the first coating layer may be formed by including the steps of forming a soft (or medium) coating layer on the outer surface of the first intermediate body; and forming a medium (or soft) coating layer on the outer surface of the soft (or medium) coating layer.

In one specific example, the first coating layer may include a soft coating layer and a medium coating layer in a weight ratio of 1:0.5 to 1:3. When included in the above range, the electrical conductivity is excellent, and the cathode active material may be prevented from breaking and breaking when the nanosilicon particles expand, and the capacity reduction may be minimized, so that the long-life characteristics may be excellent. For example, the weight ratio may be 1:1 to 1:3 or 1:1.5 to 1:2.5.

In one specific example, the first coating layer may include a soft coating layer and a medium coating layer that are formed sequentially.

Secondary battery containing silicon carbon composite negative electrode material

Another aspect of the present invention relates to a secondary battery including the silicon carbon composite negative electrode active material. In one specific example, the secondary battery includes a positive electrode; a negative electrode; and an electrolyte formed between the positive electrode and the negative electrode; wherein the negative electrode includes the negative electrode active material.

The secondary battery may include a lithium secondary battery. In one specific example, the lithium secondary battery may include a cathode including a cathode active material; an anode spaced apart from the cathode and including the anode active material; an electrolyte disposed between the cathode and the anode; and a separator disposed between the cathode and the anode to prevent electrical short-circuiting between the cathode and the anode.

In one specific example, the positive and negative electrodes can be manufactured by applying a mixture including an active material, a conductive material, and a binder to one surface of each electrode plate (current collector), and then drying and pressing.

In one specific example, the positive electrode plate and the negative electrode plate may each include one or more of copper, stainless steel, aluminum, nickel, and titanium.

As another example, the cathode electrode plate may be nickel foam, copper foam, a polyimide film coated with a conductive metal, or a combination thereof.

As another example, the cathode electrode plate may include a copper foil, a carbon-coated copper foil, a copper foil having a surface roughness of 5 nm or more, a nickel foil, a stainless steel foil, a nickel-coated iron (Fe) foil, and a copper foil having holes formed therein with a size of 1 to 50 μm.

In one specific example, the cathode active material may include a composite oxide of a metal and lithium. The metal may include at least one of cobalt (Co), manganese (Mn), aluminum (Al), and nickel (Ni). For example, it may include at least one of lithium-nickel oxide, lithium-nickel-cobalt oxide, lithium-nickel-cobalt-manganese oxide, and lithium-nickel-cobalt-aluminum oxide.

In one specific example, the conductive material may include one or more of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, carbon fibers, metal fibers, fluorinated carbon, aluminum, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene compounds.

In one specific example, the binder may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrenic rubber, and fluorine rubber.

In one specific example, the separator may be a conventional one. For example, the separator may include one or more of polyester, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE). The separator may be in the form of a nonwoven fabric or a woven fabric. The separator is porous with an average pore diameter of 0.01 to 10 μm, and the separator may have a thickness of 5 to 500 μm.

In one specific example, the electrolyte may include a non-aqueous organic solvent and a lithium salt. For example, the non-aqueous organic solvent may include one or more of a carbonate-based, ester-based, ether-based, and ketone-based solvent. The carbonate-based solvent may include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylmethyl carbonate (EMC), ethylpropyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

The ester solvent may include at least one of butyrolactone, decanolide, valerolactone, caprolactone, n-methyl acetate, n-ethyl acetate, and n-propyl acetate. The ether solvent may include dibutyl ether, etc. The ketone solvent may include polymethylvinyl ketone.

The above lithium salt can act as a source of lithium ions in the battery. For example, the lithium salt may include, but is not limited to, one or more of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , and LiAlCl ₄ .

In one specific example, the electrolyte may further include one or more of vinylene carbonate, vinyl ethylene carbonate, monofluoroethylene carbonate, difluoroethylene carbonate, succinic anhydride, and 1,3-propane sultone.

In one specific example, the lithium secondary battery may include a square battery, a cylindrical battery, and a pouch-type battery.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and cannot be interpreted as limiting the present invention in any way. Contents not described herein can be sufficiently technically inferred by those skilled in the art, so their description will be omitted.

Examples and Comparative Examples

Example 1

(1) Preparation of nanosilicon slurry: A dispersion containing 100 parts by weight of silicon raw material powder, 0.1 parts by weight of dispersant (stearic acid), and 900 parts by weight of first solvent (ethanol) was prepared, and the dispersion was milled to prepare a nanosilicon slurry (viscosity at 25°C of 4320 cPs) having an average particle size (d50) of 200 nm (radius of 100 nm).

(2) Preparation of mixed slurry and dry powder: A mixed slurry containing the above nano-silicon slurry and a soft coating material (including a pitch with an average particle size (d50) of 0.01 to 0.5 μm) was prepared. Then, the mixed slurry was dried using a rotary spray dryer at a disk rotation speed (20,000 to 30,000 rpm) to prepare a dry powder.

(3) Preparation of first mixture: A first mixture containing the above dry powder and soft coating material (including a pitch having an average particle size (d50) of 0.01 to 0.5 ㎛) was prepared.

(4) Preparation of first intermediate and negative electrode active material: The first mixture was first fired at 850 to 950°C. Then, the first mixture that was first fired was pressurized in one direction at 10 to 30 atm (or uniaxially compressed) to prepare a compressed material. Then, a second mixture including the compressed material and a hard coating material (carbon material having a pencil hardness of 4 to 6H and an average particle size (d50) of 0.05 to 0.5 μm (NanoMollisAdamas of Lemon Energy Co., Ltd.) according to ISO 15184) was prepared, and the second mixture was secondarily fired at 960 to 1050°C to prepare a first intermediate. Then, the first intermediate was pulverized and classified to prepare a negative electrode active material.

The above negative active material includes a first hollow core (thickness 20 nm, pencil hardness B to 1H according to ISO 15184, and density 1.3 g/cm ³ ) in which a first hollow portion is formed and a primary particle including nanosilicon particles filled in the first hollow portion; and a second hollow core (thickness 20 nm, pencil hardness 4H to 6H according to ISO 15184, and density 1.8 to 2.1 g/cm ³ ) in which a second hollow portion is formed and a secondary particle including one or more of the above primary particles filled in the second hollow portion.

The above nanosilicon particles included first nanosilicon particles having an average particle diameter (d50) of 200 nm (radius 100 nm) and second nanosilicon particles having an average particle diameter (d50) of 300 nm (radius 150 nm).

The above primary particles included a primary particle (1) having a first hollow portion with a radius of 1 µm (1000 nm, average diameter 2 µm) and a primary particle (2) having a first hollow portion with a radius of 1.5 µm (1500 nm). In addition, the primary particle (1) had a radius (a ₁ ) of 1020 nm, the primary particle (2) had a radius (a ₂ ) of 1520 nm, and the secondary particle had a second hollow portion with a radius (b) of 3 µm (average diameter 6 µm).

The above negative active material contained 25 to 80 wt% of nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core.

Example 2

The first mixture of the above Example 1 was first fired at 850 to 945°C, and the second mixture containing the first-fired first mixture and a hard coating material (carbon-based material having an ISO 15184 pencil hardness of 4 to 6H and an average particle size (d50) of 0.05 to 0.5 μm (NanoMollisAdamas of Lemon Energy Co., Ltd.)) was secondarily fired at 955 to 1050°C to produce a first intermediate, and the first intermediate was pulverized and classified to produce a negative electrode active material.

The above negative active material includes a first hollow core (thickness 20 nm, pencil hardness B to 1H according to ISO 15184, and density 1.3 g/cm ³ ) in which a first hollow portion is formed and a primary particle including nanosilicon particles filled in the first hollow portion; and a second hollow core (thickness 20 nm, pencil hardness 4H to 6H according to ISO 15184, and density 1.8 to 2.1 g/cm ³ ) in which a second hollow portion is formed and a secondary particle including one or more of the above primary particles filled in the second hollow portion.

The above nanosilicon particles included first nanosilicon particles having an average particle diameter (d50) of 200 nm (radius 100 nm) and second nanosilicon particles having an average particle diameter (d50) of 300 nm (radius 150 nm).

The above primary particles included a primary particle (1) having a first hollow portion with a radius of 1 µm (1000 nm, average diameter 2 µm) and a primary particle (2) having a first hollow portion with a radius of 1.5 µm (1500 nm). In addition, the primary particle (1) had a radius (a ₁ ) of 1020 nm, the primary particle (2) had a radius (a ₂ ) of 1520 nm, and the secondary particle had a second hollow portion with a radius (b) of 5 µm (average diameter 10 µm).

The above negative active material contained 25 to 80 wt% of nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core.

Example 3

The first mixture of the above Example 1 was compressed in one direction at a pressure of 20 atm to produce a compressed material. Then, a second mixture including the compressed material and a hard coating material (carbon material having a pencil hardness of 4 to 6H and an average particle size (d50) of 0.05 to 0.5 ㎛ (NanoMollisAdamas, Lemon Energy Co., Ltd.) according to ISO 15184) was calcined at 900 to 1050°C to produce a first intermediate, and the first intermediate was pulverized and classified to produce a negative electrode active material.

The above negative active material includes a first hollow core (thickness 20 nm, pencil hardness B to 1H according to ISO 15184, and density 1.3 g/cm ³ ) in which a first hollow portion is formed and a primary particle including nanosilicon particles filled in the first hollow portion; and a second hollow core (thickness 20 nm, pencil hardness 4H to 6H according to ISO 15184, and density 1.8 to 2.1 g/cm ³ ) in which a second hollow portion is formed and a secondary particle including one or more of the above primary particles filled in the second hollow portion.

The above nanosilicon particles included first nanosilicon particles having an average particle diameter (d50) of 200 nm (radius 100 nm) and second nanosilicon particles having an average particle diameter (d50) of 300 nm (radius 150 nm).

The above primary particles included a primary particle (1) having a first hollow portion with a radius of 1 µm (1000 nm, average diameter 2 µm) and a primary particle (2) having a first hollow portion with a radius of 1.5 µm (1500 nm). In addition, the primary particle (1) had a radius (a ₁ ) of 1020 nm, the primary particle (2) had a radius (a ₂ ) of 1520 nm, and the secondary particle had a second hollow portion with a radius (b) of 7 µm (average diameter 14 µm).

The above negative active material contained 25 to 80 wt% of nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core.

Example 4

A soft coating material (including a pitch having an average particle diameter (d50) of 0.01 to 0.5 μm) was mixed into the first intermediate of the above Example 1, and calcined at 850 to 975°C in an inert gas atmosphere to form a first coating layer (soft coating layer) on the outer surface of the first intermediate (or the second hollow core), thereby manufacturing a negative electrode active material.

The above negative active material includes a first hollow core (thickness 20 nm, ISO 15184 standard pencil hardness B to 1H, and density 1.3 g/cm ³ ) in which a first hollow portion is formed and a primary particle including nano-silicon particles filled in the first hollow portion; and a second hollow core (thickness 20 nm, ISO 15184 standard pencil hardness 4H to 6H, and density 1.8 to 2.1 g/cm ³ ) in which a second hollow portion is formed and a secondary particle including one or more of the first particles filled in the second hollow portion, and a first coating layer (soft coating layer having a thickness of 10 to 25 nm, ISO 15184 standard pencil hardness B to 1H, and density 0.3 to 1.5 g/cm ³ ) formed on an outer surface of the second hollow core.

The above nanosilicon particles included first nanosilicon particles having an average particle diameter (d50) of 200 nm (radius 100 nm) and second nanosilicon particles having an average particle diameter (d50) of 300 nm (radius 150 nm).

The above primary particles included a primary particle (1) having a first hollow portion with a radius of 1 µm (1000 nm, average diameter 2 µm) and a primary particle (2) having a first hollow portion with a radius of 1.5 µm (1500 nm). In addition, the primary particle (1) had a radius (a ₁ ) of 1020 nm, the primary particle (2) had a radius (a ₂ ) of 1520 nm, and the secondary particle had a second hollow portion with a radius (b) of 9 µm (average diameter 18 µm).

The above negative active material contained 25 to 80 wt% of nanosilicon particles, 1 to 40 wt% of the first hollow core, 1 to 40 wt% of the second hollow core, and 1 to 20 wt% of the first coating layer (soft coating layer).

Example 5

A soft coating material (including a pitch with an average particle diameter (d50) of 0.01 to 0.5 μm) was mixed into the first intermediate of the above Example 1, and calcined at 850 to 975°C in an inert gas atmosphere to form a soft coating layer on the outer surface of the first intermediate (or the second hollow core).

Next, the first intermediate having the soft coating layer formed thereon was introduced into a chamber and heat-treated at 900°C while supplying hydrocarbon gas (CH ₄ ) at a flow rate of 0.2 L/cc for 20 minutes under vacuum conditions of ¹⁰ -2 to ^{10 -6} torr, thereby forming a medium coating layer on the outer surface of the soft coating layer by thermal decomposition of the hydrocarbon gas, thereby manufacturing a negative electrode active material.

The above negative active material comprises a first hollow core (thickness 20 nm, pencil hardness B~1H and density 1.3 g/cm ³ according to ISO 15184) in which a first hollow portion is formed, and a primary particle including nanosilicon particles filled in the first hollow portion; And a second hollow core (thickness 20 nm, ISO 15184 standard pencil hardness 4H to 6H, and density 1.8 to 2.1 g/cm ³ ) in which a second hollow portion is formed, and one or more of the first particles filled in the second hollow portion, and a second particle including a first coating layer formed on an outer surface of the second hollow core (a soft coating layer having a thickness of 10 to 25 nm, ISO 15184 standard pencil hardness B to 1H, and density 0.3 to 1.5 g/cm ³ , and a medium coating layer having a thickness of 5 to 20 nm, ISO 15184 standard pencil hardness 2H to 3H, and density 1.5 to 1.7 g/cm ³ are sequentially formed).

The above nanosilicon particles included first nanosilicon particles having an average particle diameter (d50) of 200 nm (radius 100 nm) and second nanosilicon particles having an average particle diameter (d50) of 300 nm (radius 150 nm).

The above primary particles included a primary particle (1) having a first hollow portion with a radius of 1 µm (1000 nm, average diameter 2 µm) and a primary particle (2) having a first hollow portion with a radius of 1.5 µm (1500 nm). In addition, the primary particle (1) had a radius (a ₁ ) of 1020 nm, the primary particle (2) had a radius (a ₂ ) of 1520 nm, and the secondary particle had a second hollow portion with a radius (b) of 3 µm (average diameter 6 µm).

The above negative electrode active material contained 25 to 80 wt% of nanosilicon particles, 1 to 40 wt% of a first hollow core, 1 to 40 wt% of a second hollow core, and a first coating layer (1 to 10 wt% of a soft coating layer and 1 to 10 wt% of a medium coating layer).

(1) Derivation of the number of particles of first and second nanosilicon charged to the primary particle

Meanwhile, in the above examples 1 to 5, the number (n ₁ , n ₂ ) of the first nano-silicon particles and the second nano-silicon particles filled in the first hollow space of the first particle satisfied the condition of the following equation 1:

[Formula 1]

(In the above formula 1, the r ₁ ' is the radius of the first expanded nano-silicon particle, the r ₂ ' is the radius of the second expanded nano-silicon particle, the R is the radius of the first hollow part, and the r ₁ ' and r ₂ ' are 1.5874*r ₁ and 1.5874*r ₂ , respectively).

Manufacturing examples 1-3

According to the above Equation 1, when the first hollow radius (R) of the primary particle is applied as 1 ㎛, 1.5 ㎛, and 2 ㎛, respectively, the number (n ₁ ) of the first nanosilicon particles having a radius (r ₁ ) of 100 nm (radius (r ₁ ') upon expansion is 158 nm) filled in the primary particle, and the number (n ₂ ) of the second nanosilicon particles having a radius (r ₂ ) of 150 nm (radius (r ₂ ') upon expansion is 238 nm) are shown in Table 1 below.

Referring to the results in Table 1 above, it was found that when the first hollow core primary particle having a radius (R) of 1 to 2 μm (diameter of 2 to 4 μm) is filled with 126 to 1,014 first nano-silicon particles having a radius of 100 nm and 37 to 296 second nano-silicon particles having a radius of 150 nm (total of 163 to 1,310 particles), the primary particle (first hollow core) does not break or break even when the nano-silicon particles expand four times.

Through this, it was found that in the above Examples 1 to 5, when the primary particle (1) having a first hollow portion with a radius of 1 ㎛ (1000 nm) is filled with 126 first nano-silicon particles (radius 100 nm) and 37 second nano-silicon particles (radius 150 nm) (total of 163 particles), and the primary particle (2) having a first hollow portion with a radius of 1.5 ㎛ (1500 nm) is filled with 427 first nano-silicon particles (radius 100 nm) and 125 second nano-silicon particles (radius 150 nm) (total of 552 particles), no breakage or destruction of the primary particle (first hollow core) occurs even when the nano-silicon particles expand four times.

(2) Derivation of the number of primary particles (1) and (2) charged into the second cavity

In the above examples 1 to 5, the number of primary particles (1) and (2) filled in the second hollow space of the secondary particles satisfied the condition of the following equation 2:

[Formula 2]

(In the above formula 2, a ₁ and n ₃ are the radius and number of primary particles (1), a ₂ and n ₄ are the radius and number of primary particles (2), and b is the radius of the second hollow part).

According to the above formula 2, the number of primary particles ( ₁ ) having a radius (a 1 ) of 1020 nm and the number of primary particles (2) having a radius (a ₂ ) of 1520 nm included in the secondary particles of Examples 1 to 5 are shown in Table 2 below. In Table 2 above, the PNR is a packing density (packing number raito) and was derived by the following calculation formula:

[Calculation formula]

PNR = n ₁ *(a ₁ /b) ³ + n ₂ *(a ₂ /b) ³

(In the above calculation formula, b is the radius of the second hollow part).

Referring to the results in Table 2 above, it was found that when the secondary particles of Examples 1 to 5 having a radius of the second hollow core of 3 to 9 ㎛ were filled with 7 to 221 primary particles (1) having a radius (a ₁ ) of 1020 nm and 2 to 61 primary particles ( ₂ ) having a radius (a 2 ) of 1520 nm (a total of 9 to 281 primary particles), the secondary particles (second hollow cores) did not break or break even when the nanosilicon particles expanded four times.

Comparative Example 1

Only the dry powder of the above Example 1 was calcined at 900 to 1050°C in an inert gas atmosphere to produce calcined powder. Then, the calcined powder and a soft coating material (including a pitch having an average particle diameter (d50) of 3 to 5 μm) were mixed and calcined at 850 to 975°C to form a first coating layer (soft coating layer), thereby producing an intermediate molded body (negative electrode active material), and the intermediate molded body was pulverized and classified.

The above negative active material includes a core portion including nano-silicon particles and a first coating layer (a soft coating layer having a thickness of 10 to 20 nm, a pencil hardness of B according to ISO 15184, and a density of 1.5 g/cm ³ ) formed on an outer surface of the core portion.

The above negative active material contained 25 to 80 wt% of nanosilicon particles and 20 to 75 wt% of the first coating layer.

Experimental example

(1) Measurement of the (111) plane crystal grain value, oxidation rate, and specific surface area of nanosilicon particles: The crystal grain value, oxidation rate, and specific surface area of the (111) plane of the nanosilicon particles among the negative electrode materials of the examples and comparative examples were measured. Specifically, the crystal grain value was calculated using the crystal grain calculation value (K=9, Sherrer equation) using the full width at half maximum (FWMH) of the (111) plane diffraction peak during X-ray diffraction analysis using CuKα rays for the nanosilicon particles of the examples and comparative examples. The oxidation rate of the nanosilicon particles was measured using a measuring device (LECO, 0NH 836 series) to measure the oxygen ratio, and the specific surface area was measured using a BET measuring device (Micromeritics, Tristar II 3920). The results are shown in Table 3 below.

Referring to the results in Table 3 above, it was found that Examples 1 to 5 had higher crystallinity of nano silicon particles and lower oxidation levels than Comparative Example 1, resulting in superior high output and long life characteristics.

In addition, in order for reversible physical expansion and contraction to occur in nano silicon particles upon binding and debinding of lithium ions, the smaller the size of the silicon particles, the better (if the size of the silicon particles is smaller, the full width at half maximum in the Si 111 direction in the 2θ data of XRD becomes larger, and the calculated crystal grain size when K = 9 in Shererr's crystal calculation formula becomes smaller). However, as the size of the silicon decreases, the grinding time of the silicon raw material increases, which may lead to a problem in that the oxidation degree of the silicon increases. Therefore, it is important to appropriately determine the size of the nano silicon particles and proceed with manufacturing to control the oxidation degree range of the nano silicon.

That is, in the present invention, the average particle diameter (d50) of the nano silicon particles is determined to satisfy the oxidation range of the silicon anode. In addition, in this case, the shrinkage/expansion of the nano silicon particles becomes reversible. Therefore, in the evaluation of a lithium ion secondary battery using the anode active material of the embodiment, stable electrochemical characteristics can be secured.

The above nano silicon particles may have an FWMH of an X-ray diffraction angle (2θ) using CuKα rays on the (111) plane in the range of 0.40° to 0.80°, more preferably in the range of 0.52° to 0.68° or 0.59° to 0.71°.

In the present invention, when the FWMH of the nano silicon particles after high-temperature sintering satisfies the above-set range, the new exposed surface of the nano silicon particles is sufficiently suppressed, so that the phenomenon of silicon particle breakage during charge and discharge is significantly reduced. However, it was found that the embodiment enabled high charge/discharge efficiency to proceed, and thus the life characteristics of the silicon anode were greatly improved. In addition, it was found that the capacity of the silicon/carbon composite using the nano silicon particles as described above can produce a high-capacity silicon anode exceeding the range of 1,300 to 1,400 mAh/g, that is, an anode active material for a lithium ion secondary battery.

(2) Analysis of XRD peaks of negative electrode active material: Among the above examples and comparative examples, XRD peaks were analyzed for the hollow core and soft coating layer of the negative electrode active material of Example 1, and the results are shown in Figure 3 below.

The above FIG. 3 shows the XRD analysis results of the first hollow core and the second hollow core of the negative electrode active material of Example 1. Referring to the above FIG. 3, in the first peak intensity of the XRD graph, the first peak of the first hollow core of Example 1 is formed at 2θ = 23˚ on the C (002) crystal plane, whereas the first peak of the second hollow core of Example 1 is formed at around 2θ = 25˚, which is a value close to graphite. Through this, it was found that the second hollow core has higher crystallinity than the first hollow core.

In addition, in the second peak intensity in the above Fig. 3, the second peak appears at around 2θ = 43˚ on the C(100) crystal plane, and it was found that the second hollow core has higher crystallinity than the first hollow core. Through this, it was found that the second hollow core with higher crystallinity has higher hardness, a more solid film, and higher electrical conductivity of carbon than the first hollow core.

(3) Electrochemical evaluation (1)

(3-1) Manufacturing of lithium ion battery (half coin-type battery): Half CR2032 coin cells were manufactured using the negative electrode active materials of the examples and comparative examples. Specifically, 96.99 wt% of the negative electrode active materials of the examples and comparative examples, 0.11 wt% of a conductive material (Oscial, Tuball, Graphene carbon nanotube), 1.65 wt% of CMC (carboxy methyl cellulose), and 1.25 wt% of styrene butadiene rubber (SBR) were mixed to prepare a mixture. Then, 10.1 wt% of the manufactured mixture and 89.9 wt% of commercial natural graphite having a capacity of 364 mAh/g were mixed to prepare a negative electrode slurry having a capacity of about 450 mAh/g. Then, the manufactured slurry was coated/dried on a negative electrode current collector, and then rolled to manufacture a negative electrode. The above cathode had a loading of 6.5±0.5 mg/cm ² and an electrode density of 1.60 to 1.65 g/cc.

A CR2032 half coin cell was manufactured by a conventional method using a lithium metal anode (thickness 300 μm, MTI) as a counter electrode of the manufactured negative electrode, an electrolyte, and a separator (including polypropylene and polyethylene). The electrolyte was manufactured by dissolving 1 M LiPF ₆ in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) (EMC and EC = 5:5 by volume ratio), and then adding vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (containing 94.5 wt% of the mixed solvent, 0.5 wt% of vinylene carbonate, and 5 wt% of fluoroethylene carbonate).

(3-2) Charge/discharge characteristic evaluation: After aging the half coin cell manufactured in (3-1) at room temperature (25°C) for more than 20 hours, an electrochemical evaluation was performed. The reference capacity of the negative active material of the electrode plate was 450 mAh/g, and the measurement temperature was 45°C. One cycle of the formation process was performed in the operating voltage range of 0.005 V to 1.5 V, and the current during charge/discharge was measured at 0.1 C in the first cycle. Then, two cycles were performed based on the 0.2 C capacity, and a current of 0.5 C was applied during charge/discharge based on the 0.2 C capacity of the second cycle to measure the lifespan after 50 cycles. At this time, the charge cut-off current was set to 0.005 C, and the discharge cut-off voltage was set to 1.0 V.

Through the above electrochemical evaluation, the capacity (mAh/g) of the negative electrode of the above examples and comparative examples, the capacity (mAh/g) of the negative electrode plate, the charge/discharge efficiency (%), and the capacity retention rate were evaluated to evaluate the lifespan (%), and the results are shown in Table 4 below.

(3-3) Evaluation of expansion characteristics: For the half coin cells of examples and comparative examples manufactured in (3-1) above, the expansion rate of the negative electrode active material according to charge and discharge was evaluated. The evaluation of the expansion rate was based on the initial electrode thickness of the negative electrode of the half coin cell. The half coin cell was charged/discharged at 0.5 C current for 50 cycles, and then charged at 0.5 C current. Then, the thickness of the negative electrode was measured, and the thickness increase rate based on the initial negative electrode thickness was measured, and the results are shown in Table 4.

The above thickness measurement was performed using a measuring device (micrometer) after disassembling the coin cell after completing the cycle and sufficiently cleaning the electrode surface foreign substances including salt using DMC solvent.

Referring to the results in Table 4 above, it was found that Examples 1 to 5 had better charge/discharge efficiency and longer life characteristics than Comparative Example 1. In addition, the negative active materials of Examples 1 to 5 had lower volume changes during charge/discharge than Comparative Example 1, and through this, it was found that the negative active materials were prevented from breaking and destruction during lithium ion insertion/desorption reactions, and capacity reduction was minimized, resulting in better long life characteristics.

(3-4) Impedance evaluation: The half cells of the examples and comparative examples manufactured in (3-1) above were charged and discharged under the conditions of 0.5 C/0.01 C cutoff (cutoff charge), 1.5 V discharge, and 100% SOC (state of charge), and the impedance (charge transfer resistance (Rct) value) was measured using the EIS (electrochemical impedance spectroscopy) method. The results are shown in Table 5 below.

Referring to Table 5 above, it was found that the negative electrode active material impedance values of Examples 1 to 5 were lower than those of Comparative Example 1, and in particular, the charge transfer resistance (Rct) values were significantly lower.

(4) Electrochemical evaluation (2)

(4-1) Manufacturing of lithium secondary battery (1.0 Ah pouch-type full cell): A pouch-type full cell was manufactured using the negative electrode active materials of the examples and comparative examples. Specifically, 96.99 wt% of the negative electrode active materials of the examples and comparative examples, 0.11 wt% of a conductive material (Oscial, Tuball, Graphene carbon nanotube), 1.65 wt% of CMC (carboxy methyl cellulose), and 1.25 wt% of styrene-butadiene rubber (SBR) were mixed to manufacture a mixture. Then, 10.1 wt% of the manufactured mixture and 89.9 wt% of commercial natural graphite having a capacity of 364 mAh/g were mixed to manufacture a negative electrode slurry having a capacity of about 550 mAh/g. Then, the manufactured slurry was coated/dried on a negative electrode current collector, and then rolled to manufacture a negative electrode. The loading amount of the above cathode was 6.5±0.5 mg/cm ² and the electrode density was 1.55 to 1.60 g/cc.

Next, a pouch cell with a capacity of 1.0 Ah was manufactured using a cathode (NCM811) as a counter electrode of the manufactured cathode, an electrolyte, and a separator (including polypropylene and polyethylene) in a conventional manner.

The above electrolyte was prepared by dissolving 1 M LiPF ₆ in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) (EMC and EC = 5:5 by volume ratio), and then adding vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (containing 96.5 wt% of the mixed solvent, 0.5 wt% of vinylene carbonate, and 3 wt% of fluoroethylene carbonate).

(4-2) Charge/discharge characteristic evaluation: After aging the full cell manufactured in (4-1) above at room temperature (25°C) for more than 20 hours, an electrochemical evaluation was performed at room temperature. Specifically, for the full cells of the examples and comparative examples, a formation process of 0.1C charge/0.1C discharge for one cycle was performed in the operating voltage range of 2.75 V to 4.25 V. The current during charging was measured as 0.1C and the cut-off current was 0.005C for one cycle. Then, two cycles were performed based on the standard process of 0.2C charge, cut-off 0.01C/0.1C discharge, and then a charge current of 0.5C/cut-off 0.02C was applied during charging based on the 0.2C discharge capacity of the two cycles, and the 250-cycle life (capacity retention rate) was measured under the condition of 1.0C/4.2V cutoff. The results are shown in Table 6 below.

Referring to the results in Table 6 above, it was found that the full cells of Examples 1 to 5 had superior charge/discharge efficiency and longer life characteristics than Comparative Example 1.

(5) Evaluation of expansion characteristics of single-electrode plate cell: For the above examples and comparative examples, the expansion rate of the negative electrode active material according to charge and discharge was evaluated. Specifically, a positive electrode plate was manufactured using NCM622, and a negative electrode plate was manufactured using the negative electrode active materials manufactured in Examples 1 to 5 and Comparative Example 1 under the conditions of a current density of 3.2 mA/cm ² and a rolling density of 1.55 g/cc. Then, a single-electrode plate cell in which the positive and negative electrodes are in contact with each other on one side was manufactured using these.

Next, the single-pole plate cell was charged/discharged once with a current of 0.1C/0.1C, and then subjected to the formation process and standard process by performing one 0.25C/0.25C process. Then, the process of charging at 0.6C, 2.65V cutoff and discharging at 0.6C, 4.2V cutoff was performed as one cycle, and operation was performed up to 50 cycles.

Next, the initial thickness of the negative electrode of the single-electrode plate cells of Examples 1 to 5 and Comparative Example 1 and the thickness of the negative electrode after 1 cycle, 30 cycles and 50 cycles of operation were measured, respectively, and then the thickness increase rate during 1 cycle, 30 cycles and 50 cycles of operation was measured based on the initial negative electrode thickness. In addition, the charge/discharge efficiency (%) during 1 cycle of operation of the single-electrode plate cells was measured, and the results are shown in Table 7 below.

Referring to the results in Table 7 above, it was found that the thickness (volume) change during charge and discharge of the single-electrode cell in Examples 1 to 5 was lower than that in Comparative Example 1.

The present invention has been described with reference to embodiments. Those skilled in the art will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a restrictive perspective. The scope of the present invention is indicated by the claims, not the foregoing description, and all differences within the scope equivalent thereto should be interpreted as being included in the present invention.

10: Primary particle 12: Nanosilicon particle
14: 1st hollow core 16: 1st hollow part
20: Secondary particle 22: Secondary hollow core
24: Second hollow section 30: First coating layer
32: Hard coating layer 34: Medium coating layer
100, 200: Negative active material

Claims (19)

A primary particle comprising a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion; and
A second hollow core having a second hollow portion formed therein and a secondary particle including one or more of the primary particles filled in the second hollow portion;
A negative electrode active material, wherein the second hollow core has a harder surface than the first hollow core.
In the first paragraph, the number of nanosilicon particles filled in the first hollow portion is set so that the total volume of the expanded nanosilicon particles formed by inserting lithium ions into the nanosilicon particles is less than or equal to the volume of the first hollow portion, and
A negative electrode active material, characterized in that the number of primary particles filled in the second hollow portion is set so that the total volume of the primary particles is less than or equal to the volume of the second hollow portion.
In the second paragraph, the primary particle comprises first and second nanosilicon particles having radii of r ₁ and r ₂ , respectively,
The number of the first and second nano-silicon particles (n ₁ , n ₂ ) filled in the first hollow space is a negative electrode active material satisfying the condition of the following equation 1:
[Formula 1]

(In the above formula 1, the r ₁ ' is the radius of the first expanded nanosilicon particle, the r ₂ ' is the radius of the second expanded nanosilicon particle, and the R is the radius of the first hollow part,
The above r ₁ 'and r ₂ ' are 1.5874*r ₁ and 1.5874*r ₂ , respectively.
In the third paragraph, the secondary particles include primary particles (1) and (2) having radii of a ₁ and a ₂ , respectively,
The number of primary particles (1) and (2) charged in the second hollow space is a negative electrode active material satisfying the condition of the following equation 2:
[Formula 2]

(In the above formula 2, a ₁ and n ₃ are the radius and number of primary particles (1), a ₂ and n ₄ are the radius and number of primary particles (2), and b is the radius of the second hollow part).
In the first paragraph, the first hollow core has a pencil hardness of less than 4H as measured according to ISO 15184, and
The above second hollow core is a negative electrode active material having a pencil hardness of 4H or higher.
In the first paragraph, the first hollow core has a thickness of 5 to 300 nm, and the first hollow portion has a diameter of 1 to 8 μm.
The above nano-silicon particles have an average particle diameter of 50 to 500 nm, and the number of nano-silicon particles filled in the first hollow space is 50 to 10,000, which is a negative electrode active material.
In the first paragraph, the second hollow core has a thickness of 5 to 500 nm, and the second hollow portion has a diameter of 3 to 25 μm.
A negative electrode active material, wherein the number of primary particles charged in the second hollow space is 5 to 500.
In the first paragraph, a negative electrode active material comprising 25 to 80 wt% of the nanosilicon particles, 1 to 40 wt% of the first hollow core, and 1 to 40 wt% of the second hollow core relative to the total weight of the negative electrode active material.
In the first paragraph, the negative electrode active material is a negative electrode active material comprising the second hollow core and the first hollow core in a weight ratio of 1:0.5 to 1:6.
In the first paragraph, the negative active material further includes a first coating layer formed on the outer surface of the second hollow core,
A negative electrode active material, wherein the first coating layer comprises at least one of a soft coating layer and a medium coating layer.
In the first paragraph, the primary particle is a negative electrode active material having a packing density of the nanosilicon particles of 75% or less.
In claim 10, the first coating layer is a negative electrode active material comprising the soft coating layer and the medium coating layer in a weight ratio of 1:0.5 to 1:3.
A step of manufacturing a dry powder by drying a mixed slurry containing nanosilicon slurry and a soft coating material;
A step of preparing a first mixture comprising the above dry powder and a soft coating material; and
A method for producing a negative electrode active material, comprising: a step of producing a first intermediate by firing a second mixture including the first mixture and a hard coating material;
The first intermediate body comprises a primary particle including a first hollow core having a first hollow portion formed therein and nanosilicon particles filled in the first hollow portion, and a secondary particle including a second hollow core having a second hollow portion formed therein and one or more of the first particles filled in the second hollow portion.
A method for manufacturing a negative electrode active material, wherein the second hollow core has a harder surface than the first hollow core.
In the 13th paragraph, the nanosilicon slurry is prepared by adding and dispersing silicon raw material powder and a dispersant into a first solvent to prepare a dispersion; and
It is manufactured including the step of crushing the above dispersion;
A method for producing a negative electrode active material, wherein the first solvent comprises at least one of water, ethanol, isopropyl alcohol, and potassium hydroxide (KOH).
In claim 13, the first hollow core has a pencil hardness of less than 4H as measured according to ISO 15184, and
A method for manufacturing a negative electrode active material, wherein the second hollow core has a pencil hardness of 4H or higher.
A method for manufacturing a negative electrode active material in claim 13, wherein the second mixture is calcined at 850 to 1050°C.
In the 13th paragraph, the step of manufacturing the first intermediate is,
The above second mixture is first calcined at 850 to 950°C, and then
A method for manufacturing a negative electrode active material, comprising: a step of mixing the first-fired second mixture and a hard coating material and firing the second mixture at a temperature exceeding 950°C and lower than 1050°C.
In the 13th paragraph, after the step of manufacturing the first intermediate, a step of forming a first coating layer on the outer surface of the first intermediate is further included;
The above first coating layer comprises at least one of a soft coating layer and a medium coating layer,
The above soft coating layer is formed by including a step of mixing and firing the first intermediate and the soft coating material; and
A method for manufacturing a negative electrode active material, wherein the above medium coating layer is formed, including a step of heat-treating the first intermediate in a hydrocarbon gas atmosphere.
anode;
cathode; and
An electrolyte formed between the positive and negative electrodes;
A secondary battery, characterized in that the negative electrode comprises a negative electrode active material according to any one of claims 1 to 12.

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