KR102634600B1 - Metal-Carbon Composite Anode material for lithium secondary battery, method for manufacturing the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present disclosure includes the steps of spheronizing a plurality of silicon-based materials together with a crystalline carbon-based material to obtain spheroidized particles; Obtaining a composite by complexing the spherical particles with an amorphous carbon-based precursor material; and carbonizing the composite; wherein the silicon-based material includes silicon nanoparticles and silicon oxide, and the content of the silicon oxide is 25 parts by weight or less based on 100 parts by weight of the silicon-based material. It relates to anode active materials for secondary batteries and secondary batteries containing the same.

Description

Metal-carbon composite anode material for lithium ion secondary battery, manufacturing method thereof, and secondary battery comprising the same {Metal-Carbon Composite Anode material for lithium secondary battery, method for manufacturing the same and lithium secondary battery comprising the same}

The present invention relates to a negative electrode active material, a method of manufacturing the same, and a secondary battery containing the same. Specifically, the present invention relates to a metal-carbon composite negative electrode active material, a method of manufacturing the same, and a secondary battery containing the same.

Lithium-ion batteries are currently the most widely used secondary battery system in portable electronic communication devices, electric vehicles, and energy storage devices. These lithium-ion batteries have become the focus of attention because they have advantages such as high energy density, operating voltage, and relatively small self-discharge rate compared to commercial aqueous secondary batteries (Ni-Cd, Ni-MH, etc.). However, considering more efficient use time in portable devices and improved energy characteristics in electric vehicles, improvement in electrochemical properties still remains a technical problem that must be solved. For this reason, much research and development is currently underway across the four major raw materials such as anode, cathode, electrolyte, and separator.

Among these raw materials, graphite-based materials that exhibit excellent capacity preservation characteristics and efficiency are commercially available for cathodes. However, the relatively low theoretical capacity value (LiC6: 372 mAh/g) and low discharge capacity ratio of graphite-based materials are somewhat insufficient to meet the high energy and high power density characteristics of batteries required by the market. Therefore, many researchers are interested in group IV elements (Si, Ge, Sn) on the periodic table, especially silicon, which has a very high theoretical capacity (Li ₁₅ Si ₄ : 3600 mAh/g) and low operating voltage (~0.1 V). vs. Li/Li+), it is attracting attention as a very attractive material. However, general metallic anode materials have the disadvantage of being difficult to apply to actual batteries because they exhibit large volume changes and low discharge capacity ratio characteristics compared to existing graphite anode materials.

Recently, a metal-carbon composite anode material (composite, metal contained within the carbon template) that improves reversibility by combining a metal that can electrochemically react with lithium (e.g., silicon) and a conductive material (e.g., graphite or carbon). Research on this is actively underway, but in the case of these composites, there are problems in controlling the expansion of the metal system and achieving long lifespan, so research on this is necessary.

In providing a metal-carbon composite anode active material, the present invention seeks to achieve both high efficiency, high output, long life, and low expansion characteristics by controlling the metal components used. It is also intended to provide a manufacturing method and a secondary battery containing the same.

The anode active material for a lithium secondary battery according to an embodiment of the present invention is a carbonized silicon-carbon composite containing a carbon-based material and a plurality of silicon-based materials, wherein the silicon-based material includes silicon nanoparticles and silicon oxide, and the silicon-based material includes a plurality of silicon-based materials. The content of the silicon oxide is 25 parts by weight or less based on 100 parts by weight of the material.

The silicon nanoparticles are pulverized silicon nanoparticles or deposited silicon nanoparticles.

The pulverized silicon nanoparticles have a particle size D50 of 30 nm or more and 200 nm or less, and an aspect ratio of more than 90% by weight of the total weight of the pulverized silicon is greater than 3.

The deposited silicon nanoparticles have a particle size D50 of 30 nm or more and 100 nm or less, and an aspect ratio of 0.9 or more and 1.1 or less.

The silicon oxide is SiOx, and x is 0.6 or more and 1.1 or less.

The silicon oxide has a particle size D50 of 1 ㎛ or more and 10 ㎛ or less.

The negative electrode active material contains 50 parts by weight or more and 85 parts by weight or less of a silicon-based material based on 100 parts by weight of the carbon-based material.

A method of manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention includes the steps of spheroidizing a plurality of silicon-based materials together with a crystalline carbon-based material to obtain spherical particles; Obtaining a composite by complexing the spherical particles with an amorphous carbon-based precursor material; and carbonizing the composite, wherein the silicon-based material includes silicon nanoparticles and silicon oxide, and the content of the silicon oxide may be 25 parts by weight or less based on 100 parts by weight of the silicon-based material.

In the step of obtaining spherical particles, the plurality of silicon-based materials are in a state in which silicon nanoparticles and silicon oxide are dispersed.

The step of obtaining spherical particles is a step of spheroidizing a silicon-based material by immersing it in a solvent with a crystalline carbon-based material and then drying it.

Obtaining a composite is a step of mixing and binding spherical particles and an amorphous carbon-based precursor material by a dry method or a wet method.

In the step of obtaining the composite, the amorphous carbon-based precursor material contains 50 to 80% by weight of fixed carbon and has a softening point of 300°C or less.

The amorphous carbon-based precursor material is a highly graphitizable carbon precursor material, a non-graphitizable carbon precursor material, or a combination thereof.

Carbonizing the composite is a step of carbonizing the composite at a temperature of 800°C or higher and 1000°C or higher for 0.5 hours or more and 2 hours or less.

The lithium secondary battery of one embodiment of the present invention includes a positive electrode; cathode; and an electrolyte, and the negative electrode includes the negative electrode active material for a lithium secondary battery described above.

According to one embodiment of the present invention, it is possible to provide a metal-carbon based composite anode active material containing both silicon nanoparticles and silicon oxide as a metal base, a method for manufacturing the same, and a secondary battery containing the same.

According to one embodiment of the present invention, it is possible to provide a metal-carbon composite anode active material having both the high efficiency and high output characteristics of silicon nanoparticles and the long life and low expansion characteristics of silicon oxide, a method of manufacturing the same, and a secondary battery containing the same. there is.

1 illustrates a metal-carbon-based composite anode active material according to an embodiment of the present disclosure.
Figure 2 illustrates a metal-carbon-based composite anode active material of a comparative example of the present disclosure.

Terms such as first, second, and third are used to describe, but are not limited to, various parts, components, regions, layers, and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, the first part, component, region, layer or section described below may be referred to as the second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is only intended to refer to specific embodiments and is not intended to limit the invention. As used herein, singular forms include plural forms unless phrases clearly indicate the contrary. As used in the specification, the meaning of "comprising" refers to specifying a particular characteristic, area, integer, step, operation, element and/or ingredient, and the presence or presence of another characteristic, area, integer, step, operation, element and/or ingredient. This does not exclude addition.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part or may be accompanied by another part in between. In contrast, when a part is said to be "directly on top" of another part, there is no intervening part between them.

Additionally, unless specifically stated, % means weight%, and 1ppm is 0.0001% by weight.

Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

Below, we will look at each step in detail.

The present invention sought to use as a metal material a material capable of electrochemical alloying reaction with lithium, which has a high capacity effect, in constructing a metal-carbon composite. Candidate metal materials capable of alloying with lithium include silicon, tin, and aluminum. The present invention uses silicon nanoparticles and silicon oxide as metal-based materials capable of alloying with lithium.

A method of manufacturing a negative active material for a lithium secondary battery according to an embodiment of the present invention includes the steps of spheroidizing a plurality of silicon-based materials together with a crystalline carbon-based material to obtain spherical particles; Obtaining a composite by complexing the spherical particles with an amorphous carbon-based precursor material; and carbonizing the composite, wherein the silicon-based material includes silicon nanoparticles and silicon oxide.

In the step of obtaining spherical particles, the plurality of silicon-based materials are in a state in which silicon nanoparticles and silicon oxide are dispersed. That is, dried silicon nanoparticles and silicon oxide can be uniformly mixed and dispersed at a predetermined weight ratio to be used as a silicon-based material. This is to ensure that silicon nanoparticles and silicon oxide, which are silicon-based materials, are evenly dispersed within the conductive matrix formed by the carbon-based material in the composite obtained in the subsequent step.

Generally, only silicon nanoparticles are used by complexing them with a conductive material such as carbon, and silicon oxide is not complexed but is mixed into the negative electrode active material as a separate particle. However, the present invention mixes silicon nanoparticles and silicon oxide at the beginning of the manufacturing method and composites them all into a conductive material to complement each other's strengths and weaknesses as a final material. In other words, it is characterized by providing a negative electrode active material that exhibits both the high efficiency and high power, which are the advantages of silicon nanoparticles, and the long life and low expansion characteristics, which are the advantages of silicon oxide.

The step of obtaining spherical particles is a step of obtaining spherical particles by immersing the dispersed silicon-based material in a solvent with a crystalline carbon-based material and drying it. At this time, the solvent may preferably be ethanol, and the drying method may preferably be spray drying.

The step of obtaining a composite is a step of combining spherical particles and an amorphous carbon-based precursor material. In other words, this is the step of mixing spherical particles and an amorphous carbon-based precursor material together and applying shear force to bind them together to form a composite.

The step of obtaining the composite may be performed by a dry method or a wet method. Specifically, selected from the group consisting of planetary mixer, 3D-mixer, V-mixer, Meccano-Fusion, Hybridizer, Nobilta, Homo mixer, Henschel mixer, inline mixer, and spray dryer. 1 It can be compounded using any method on paper.

Specifically, when a silicon-based material is attached and bonded to an amorphous carbon-based precursor material through the above complexing step and then carbonized to obtain a negative electrode active material, the nano-silicon particles are different despite volume expansion and contraction due to cycling when applied to a battery. It can maintain electrical contact with the material. In other words, the amorphous carbon-based raw material can control the expansion of nano-silicon particles.

The step of carbonizing the composite is a step in which an amorphous carbon-based precursor material is immersed and carbonized into the spherical particles included in the composite to obtain a negative electrode active material. The carbonizing step is a step of carbonizing the composite in an inert atmosphere at a temperature of 800°C or more and 1000°C or less for 0.5 hours or more and 2 hours or less.

Specifically, heat treatment under the above conditions prevents Si oxidation, removes the volatile matter (VM) of the amorphous carbon-based precursor material, converts it into a better quality amorphous carbon-based material, and simultaneously performs a spheroidization step. This is to create an amorphous carbon-based material densely inside the particles composed of silicon and graphite through the spray drying process.

A step of carbonizing the composite; It may further include the step of molding the composite before. Preferably, the step of obtaining a molded body by pressure molding the composite may be further included. That is, the step of carbonizing the composite may be a step of carbonizing a molded body obtained by pressure molding the composite.

carbonizing the composite; Thereafter, the step of pulverizing and classifying the carbonized molded body may be further included. Preferably, the carbonized molded body may be pulverized and classified so that the D50 is 9 ㎛ or more and 15 ㎛ or less.

The silicon-based material may include silicon nanoparticles and silicon oxide, and the mixing ratio is as follows. The content of the silicon oxide may be 25 parts by weight or less based on 100 parts by weight of the silicon-based material. Specifically, with respect to 100 parts by weight of the silicon-based material, the content of the silicon oxide may be more than 0 and 25 parts by weight or less, or more than 0 and 20 parts by weight or less, or more than 0 and 15 parts by weight or less. More specifically, the content of the silicon oxide may be 10 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the silicon-based material.

When the silicon nanoparticles are pulverized silicon nanoparticles, the amount of silicon oxide may be 25 parts by weight or less based on 100 parts by weight of the silicon-based material. Specifically, it may be more than 0 to 25 parts by weight or less, or more than 0 to 20 parts by weight or less, or more preferably more than 10 to 25 parts by weight.

When the silicon nanoparticles are vapor-deposited silicon nanoparticles, the amount of silicon oxide may be 20 parts by weight or less based on 100 parts by weight of the silicon-based material. Specifically, it may be more than 0 and 20 parts by weight or less, or more specifically, more than 0 and 18 parts by weight or less.

Among the silicon-based materials, silicon nanoparticles may be pulverized silicon nanoparticles or deposited silicon nanoparticles. Deposited silicon is nano-sized silicon that is synthesized in a bottom-up manner using dry methods including thermal evaporation, chemical vapor deposition (CVD), physical vapor deposition (PVD), electromagnetic melting, and co-volatilization, and does not require a separate grinding process. It may be a particle. Pulverized silicon may be nano-sized silicon particles obtained by a top-down method of milling large silicon particles. The step of milling large silicon particles to obtain pulverized silicon nanoparticles may be performed wet, and during this process, oxidation of 10% by weight on the surface of the pulverized silicon nanoparticles may be achieved due to moisture in the wet milling solution.

Additionally, the silicon nanoparticles may have a particle size D50 of 30 to 200 nm. Specifically, when the silicon nanoparticles are pulverized silicon nanoparticles, D50 is 30 to 200 nm based on the long side, and in addition, the aspect ratio of the pulverized silicon nanoparticles is 90% by weight or more based on the total weight of the pulverized silicon nanoparticles and exceeds 3, Preferably it may be greater than 1.5. That is, the pulverized silicon nanoparticles may be needle-shaped. On the other hand, when the silicon nanoparticles are deposited silicon nanoparticles, D50 is 30 to 100 nm based on diameter, and additionally, the aspect ratio of the deposited silicon nanoparticles is 0.9 to 1.1, which is closer to a spherical shape than the pulverized type.

Among the silicon-based materials, silicon oxide may be expressed as SiO _x , and x may be 0.6 to 1.1. Specifically, x may be 0.7 to 1.1. Additionally, the particle size D50 of the silicon oxide may be 1 to 10 μm.

Silicon oxide can inherently exhibit long life and low expansion characteristics. However, in relation to silicon nanoparticles, if more is added than the above mixing ratio, not only the initial efficiency may be deteriorated, but the lifespan characteristics and expansion rate characteristics may also be deteriorated. On the other hand, if there is too little silicon oxide, the long life and low expansion effects that can be achieved by adding silicon oxide cannot be achieved.

The crystalline carbon-based material that is spheroidized together with the silicon-based material may be graphite, and the amorphous carbon-based material that is carbonized by complexing with the spheroidized particles may be soft carbon, hard carbon, or a combination thereof. It can be.

Specifically, the crystalline carbon-based material may be graphite, in which case long-life characteristics can be supplemented due to graphite's excellent reversibility. Additionally, the particle size (D50) of the graphite may be 10 μm or more and 40 μm or less. Specifically, it may be flaky graphite sieved on a #635 mesh (20㎛).

Among the amorphous carbon-based materials, soft carbon may be due to coal-based or petroleum-based pitch among the amorphous carbon-based precursor materials described later. Accordingly, when using a graphitized carbon-based precursor material, structural stability can be strengthened after carbonization through heat treatment.

Among the amorphous carbon-based materials, hard carbon is an amorphous carbon-based precursor such as polyimide resin, furan resin, phenol resin, polyvinyl alcohol resin, cellulose resin, epoxy resin, and polystyrene resin that can be used additionally. It may be caused by a substance. Non-graphitizable carbon-based precursor materials can also enhance structural stability after carbonization through heat treatment.

Specifically, the amorphous carbon-based precursor material may contain 50 to 80% by weight of fixed carbon and have a softening point of 300°C or lower. In the amorphous carbon-based precursor material that satisfies these characteristics, low molecules such as VM are volatilized and removed during the carbonization step, and after carbonization, it becomes carbon with more than 95% fixed carbon. This amorphous carbon-based material can prevent the structure of the silicon-carbon-based composite of the negative electrode active material from collapsing even if the lithium secondary battery is repeatedly charged and discharged. In addition, as the fixed carbon value of the amorphous carbon-based material increases, capacity and efficiency can be increased by creating a conductive path with Si, which has low self-conductivity. Additionally, when the fixed carbon value satisfies the above range, the internal pores of the negative electrode active material of this embodiment can be reduced. Accordingly, side reactions with the electrolyte can also be reduced, contributing to increasing the initial efficiency of the battery.

The negative electrode active material of one embodiment of the present disclosure is a negative electrode active material for a lithium secondary battery, and is a carbonized silicon-carbon-based composite containing a carbon-based material and a plurality of silicon-based materials, wherein the silicon-based material includes silicon nanoparticles and silicon oxide, The content of the silicon oxide is 25 parts by weight or less based on 100 parts by weight of the silicon-based material.

The negative electrode active material may be a negative electrode active material manufactured using the manufacturing method described above.

The carbonized silicon-carbon composite may be one in which a plurality of silicon-based materials are embedded in a carbon-based material. The carbon-based material included in the carbonized silicon-carbon-based composite may be derived from a crystalline carbon-based material, an amorphous carbon-based material, or a combination thereof during the manufacturing method. The amorphous carbon-based material may be carbonized from an amorphous carbon-based precursor material.

The negative electrode active material may include 50 parts by weight or more and 85 parts by weight or less of a silicon-based material based on 100 parts by weight of the carbon-based material. Preferably, the silicone-based material may be included in an amount of 50 parts by weight or more and 75 parts by weight or less, or 50 parts by weight or more and 65 parts by weight or less, or more than 50 parts by weight and 55 parts by weight or less.

Detailed information about each silicon-based material, carbon-based material, etc. that constitute the negative electrode active material is the same as the description of the manufacturing method described above, and is therefore omitted here. In particular, silicon nanoparticles and silicon oxide, which are silicon-based materials, do not change their material properties such as mixing ratio, size, and aspect ratio even if they go through the carbonization step.

The obtained negative electrode active material can be usefully used in the negative electrode of a lithium secondary battery. That is, the lithium secondary battery according to one embodiment includes a positive electrode, a negative electrode containing the above-described negative electrode active material, and an electrolyte.

A lithium secondary battery according to one embodiment may include an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. This electrode assembly is wound or folded and accommodated in a case to form a lithium secondary battery.

At this time, the case may have a cylindrical, prismatic, or thin-film shape, and may be appropriately modified depending on the type of device to be applied.

The negative electrode may be manufactured by mixing a negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then applying the composition to a negative electrode current collector.

The negative electrode current collector may be, for example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

The binder includes polyvinyl alcohol, carboxymethyl cellulose/styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or Polypropylene, etc. may be used, but are not limited thereto. The binder may be mixed in an amount of 1% to 30% by weight based on the total amount of the composition for forming the negative electrode active material layer.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and specifically includes graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be mixed in an amount of 0.1% to 30% by weight based on the total amount of the composition for forming the negative electrode active material layer.

Next, the positive electrode can be manufactured by mixing a positive electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a positive active material layer, and then applying this composition to a positive electrode current collector. At this time, the binder and conductive material are used in the same way as in the case of the above-mentioned cathode.

The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc.

The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound).

The positive electrode active material may be one or more types of complex oxides of metals such as cobalt, manganese, nickel, or a combination thereof, and lithium. As a specific example, a compound represented by any of the following chemical formulas may be used. Li _a A _1-b R _b D ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li _a E _1-b R _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE _2-b R _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b R _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li _a Ni _1-bc Co _b R _c O _2-α Z _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _1-bc Co _b R _c O _2-α Z ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _1-bc Mn _b R _c D _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li _a Ni _1-bc Mn _b R _c O _2-α Z _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _1-bc Mn _b R _c O _2-α Z ₂ (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LITO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); and LiFePO ₄ .

In the above formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

The electrolyte filled in the lithium secondary battery can be a non-aqueous electrolyte or a known solid electrolyte, and one in which lithium salt is dissolved can be used.

The lithium salt is, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO One or more types selected from the group consisting of ₄ , LiAlCl ₄ , LiCl, and LiI may be used.

Examples of solvents for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide may be used, but are not limited thereto. These can be used individually or in combination of more than one. In particular, a mixed solvent of cyclic carbonate and linear carbonate can be preferably used.

Additionally, as the electrolyte, a gel-like polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte solution, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The separator may include an olefin-based polymer such as chemical-resistant and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fiber, polyethylene, etc. can be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Manufacturing of negative electrode active material and half cells

(1) Manufacturing of negative electrode active material

An amorphous carbon precursor was used as the carbon-based material, and silicon oxide and pulverized silicon nanoparticles or vapor-deposited silicon nanoparticles were used as the silicon-based material. The mixing ratio of silicone-based materials is shown in Table 1 below.

The pitch used had 70% by weight of fixed carbon and a softening point of 250°C.

The pulverized silicon nanoparticles used were needle-shaped, had a long side D50 of 110 nm, and had an aspect ratio of 3 or more, which was 90% by weight or more of the total weight of the silicon nanoparticles.

The deposited silicon nanoparticles used were spherical, had a diameter D50 of 70 nm, and an aspect ratio of 1.01.

The silicon oxide (SiOx) used had an x of 0.85 and a particle size D50 of 1.5㎛.

A composite was obtained by dispersing and complexing 52.8 parts by weight of the silicon-based material with respect to 100 parts by weight of the carbon-based material, which was carbonized in an inert atmosphere at a temperature of 900° C. for 1 hour to obtain a negative electrode active material.

(2) Manufacturing of lithium secondary battery (half-cell)

Prepare the negative electrode active material, binder (SBR-CMC), and conductive material (Super P) of (1) so that the weight ratio of negative electrode active material:binder:conductive material is 95.8:3.2:1, add them to distilled water, and mix evenly to form a slurry. was manufactured.

The above slurry was uniformly applied to a copper (Cu) current collector, compressed in a roll press, and then dried to produce a negative electrode. Specifically, the loading amount was 5 mg/cm ² and the electrode density was 1.2 to 1.3 g/cc.

Lithium metal (Li-metal) is used as the counter electrode, and as the electrolyte, 1 mole of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is mixed in a mixed solvent with a volume ratio of 3:7. A dissolved LiPF6 solution was used.

A CR 2032 half coin cell was manufactured according to a conventional manufacturing method using the cathode, lithium metal, and electrolyte.

Electrochemical property measurement

(1) Initial efficiency measurement

Negative active materials prepared with the compositions shown in Table 1 below were applied to each half battery and tested.

Specifically, the initial efficiency was measured by driving the battery under the conditions of 0.1C, 0.005V, 0.05C cut-off charging and 0.1C, 1.5V cut-off discharging, and is listed in Table 1 below.

(2) 50 ^th life span

Lifespan was measured by manufacturing half cells.

Specifically, after measuring the initial efficiency, long-term lifespan was measured through charging and discharging 50 times under 0.5C (0.005V, 0.05C cut off charging)/0.5C (1.5V cut-off discharging) conditions, and the results are presented. It is described in 1. The loading amount of the electrode was 5 mg/cm ² and the electrode density was 1.2 to 1.3 g/cc, and the electrolyte for the long-term life test was EC:EMC = 3:7 (1.0M LiPF ₆ ).

(3) Expansion rate

The expansion rate was calculated using the formula below, and the results are listed in Table 1.

yes A substance that undergoes an electrochemical alloy reaction with lithium.
(wt%) Electrochemical evaluation results Initial efficiency* 50 ^th lifespan** Expansion rate*** More than 85% More than 60% 105% or less Example 1 Crushed silicon nanoparticles 85 + silicon oxide 15 86.8 67.2 98.7 Example 2 Crushed silicon nanoparticles 80 + silicon oxide 20 85.7 71.1 95.2 Example 3 Deposited silicon nanoparticles 85 + silicon oxide 15 85.3 61.1 101.1 Example 4 Crushed silicon nanoparticles 90 + silicon oxide 10 87.1 73.5 100.3 Example 5 Deposited silicon nanoparticles 90 + silicon oxide 10 86.4 69.7 102.5 Comparative Example 1 Crushed Silicon Nanoparticles 100 88.1 56.2 110.5 Comparative example 2 Deposited silicon nanoparticles 100 86.2 45.5 120.3 Comparative example 3 Silicon Oxide 100 78.6 83.3 90.9 Comparative example 4 Crushed silicon nanoparticles 70 + silicon oxide 30 84.6 59.5 102.1 Comparative Example 5 Deposited silicon nanoparticles 70 + silicon oxide 30 83.5 54.2 112.2 Comparative Example 6 Pulverized silicon nanoparticles 70 + Deposited silicon nanoparticles 30 87.4 51.1 111.9 Comparative example 7 Deposited silicon nanoparticles 70 + pulverized silicon nanoparticles 30 86.7 45.2 115.7 Comparative example 8 Silicon nanoparticles (crushed type: deposition type 5:5) 85 + silicon oxide 15 85.9 55.5 109.8

As can be seen from Table 1, Comparative Example 3 containing only silicon oxide cannot take advantage of silicon nanoparticles and has inferior initial efficiency characteristics, and in the case of Comparative Examples 1, 2, 6, and 7 containing only silicon nanoparticles, It was confirmed that the long-term life characteristics and expansion rate characteristics were inferior because the advantages of silicon oxide could not be taken.

In addition, even though both silicon nanoparticles and silicon oxide were included, in Comparative Examples 4 and 5, where the amount of silicon oxide was not controlled, it was confirmed that the initial efficiency, long-term life characteristics, and expansion rate characteristics were all inferior to those of the Example. .

Additionally, even if the silicon oxide content range was 25 parts by weight or less, it was confirmed that the lifespan characteristics and expansion rate characteristics of Comparative Example 8, which included both pulverized and vapor-deposited silicon nanoparticles, were inferior. This is due to non-uniform contact between nanoparticles with different aspect ratios or between nanoparticles and carbon-based materials.

The present invention is not limited to the embodiments, but can be manufactured in various different forms, and a person skilled in the art will understand that the present invention can be manufactured in other specific forms without changing the technical idea or essential features of the present invention. You will understand that it can be done. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive.

Claims (15)

As a negative electrode active material for lithium secondary batteries,
It is a carbonized silicon-carbon-based composite containing a plurality of silicon-based materials in a carbon-based material,
The silicon-based material consists of silicon nanoparticles and silicon oxide,
The silicon nanoparticles and the silicon oxide form an evenly dispersed structure within the matrix formed by the carbon-based material,
The content of the silicon oxide is 20 parts by weight or less with respect to 100 parts by weight of the silicon-based material,
The silicon nanoparticles are pulverized silicon nanoparticles, a negative electrode active material for a lithium secondary battery. delete According to paragraph 1,
The pulverized silicon nanoparticles have a particle size D50 of 30 nm or more and 200 nm or less,
A negative electrode active material for a lithium secondary battery comprising at least 90% by weight of the total weight of pulverized silicon and having an aspect ratio greater than 3. delete According to paragraph 1,
The silicon oxide is SiOx, and x is 0.6 or more and 1.1 or less. According to paragraph 1,
The silicon oxide is a negative electrode active material for a lithium secondary battery having a particle size D50 of 1 ㎛ or more and 10 ㎛ or less. According to paragraph 1,
The negative active material is,
A negative electrode active material for a lithium secondary battery, comprising 50 parts by weight or more and 85 parts by weight or less of a silicon-based material based on 100 parts by weight of the carbon-based material. Spheroidizing a plurality of silicon-based materials together with a crystalline carbon-based material to obtain spherical particles;
Obtaining a composite by complexing the spherical particles with an amorphous carbon-based precursor material; and
Comprising: carbonizing the composite,
The silicon-based material is a simple mixture containing silicon nanoparticles and silicon oxide,
A method for producing a negative electrode active material for a lithium secondary battery, wherein the content of the silicon oxide is 25 parts by weight or less based on 100 parts by weight of the silicon-based material. According to clause 8,
Obtaining spheronized particles;
A method of manufacturing a negative electrode active material for a lithium secondary battery, wherein the plurality of silicon-based materials are dispersed silicon nanoparticles and silicon oxide. According to clause 8,
Obtaining spheronized particles;
A method of manufacturing a negative electrode active material for a lithium secondary battery, which involves immersing a silicon-based material in a solvent with a crystalline carbon-based material and drying it to make it spherical. According to clause 8,
Obtaining the complex;
A method of producing a negative electrode active material for a lithium secondary battery, comprising mixing and bonding spherical particles and an amorphous carbon-based precursor material by a dry method or a wet method. According to clause 8,
Obtaining the complex;
A method of producing a negative electrode active material for a lithium secondary battery, wherein the amorphous carbon-based precursor material contains 50 to 80% by weight of fixed carbon and has a softening point of 300° C. or lower. According to clause 12,
The amorphous carbon-based precursor material is a highly graphitizable carbon precursor material, a non-graphitizable carbon precursor material, or a combination thereof, and a method of producing a negative electrode active material for a lithium secondary battery. According to clause 8,
Carbonizing the composite;
A method of producing a negative electrode active material for a lithium secondary battery, which involves carbonizing at a temperature of 800°C or higher and 1000°C or higher for 0.5 hours or more and 2 hours or less. anode;
cathode; and
Contains electrolytes,
The negative electrode is a lithium secondary battery comprising the negative electrode active material for a lithium secondary battery of any one of claims 1, 3, and 5 to 7.