KR102568786B1 - Cathode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

A positive electrode of a lithium ion secondary battery and a lithium ion secondary battery are provided. The positive electrode of the lithium ion secondary battery includes coated particles having positive electrode active material particles and a coating layer covering the positive electrode active material particles, and sulfide-based solid electrolyte particles in contact with the coated particles, and the coating layer is a positive electrode active material of elements other than lithium and oxygen. A reactive element having a higher reactivity with sulfide-based solid electrolyte particles than a transition metal element in the particles is included, and the ratio of the layer thickness of the coating layer to the diameter of the positive electrode active material particle is 0.0010 to 0.25. The positive electrode may further suppress a reaction at an interface between positive electrode active material particles and sulfide-based solid electrolyte particles in a lithium ion secondary battery including a sulfide-based solid electrolyte.

Description

Cathode for lithium ion secondary battery, and lithium ion secondary battery}

The present invention relates to a positive electrode of a lithium ion secondary battery and a lithium ion secondary battery.

Lithium-ion secondary batteries have large charge-discharge capacity, high operating potential, and excellent charge-discharge cycle characteristics, so they can be used in portable information terminals, portable electronic devices, household small power storage devices, motorcycles powered by motors, electric vehicles, and hybrid electric vehicles. Demand for such uses is increasing. A lithium ion battery uses a non-aqueous electrolyte in which lithium salt is dissolved in an organic solvent as an electrolyte, but safety of such a non-aqueous electrolyte is concerned about ignitability and leakage of the electrolyte. Therefore, recently, for the purpose of improving the safety of lithium ion batteries, research on all-solid lithium ion secondary batteries (hereinafter also referred to as "all-solid secondary batteries") using solid electrolytes made of inorganic materials that are non-combustible materials has been actively conducted.

Although sulfides and oxides can be used as solid electrolytes for all-solid-state secondary batteries, sulfide-based solid electrolytes are the most promising materials in terms of lithium ion conductivity. However, when a sulfide-based solid electrolyte is used, a reaction occurs at the interface between the positive electrode active material particles and the solid electrolyte particles during charging, and this interface resistance component is generated, so that when lithium ions move through the interface between the positive electrode active material particles and the solid electrolyte particles, resistance (hereinafter also referred to as “interfacial resistance”) tends to increase. Since the lithium ion conductivity decreases due to the increase in interface resistance, there is a problem in that the output of the lithium ion battery decreases.

In response to these problems, it has been studied to reduce the interfacial resistance by coating the surface of positive electrode active material particles such as LiCoO ₂ (hereinafter also referred to as “LCO”) with another material.

However, coating the surface of the positive electrode active material particle with an oxide such as SiO ₂ or providing a buffer layer or intermediate layer between the positive electrode layer and the solid electrolyte layer is insufficient to suppress the reaction at the interface between the positive electrode active material particle and the solid electrolyte particle. In addition, further reduction of the resistance component is required.

The present invention has been made in view of the above phenomenon, and an object of the present invention is to provide a positive electrode capable of further suppressing the reaction at the interface between particles of a positive electrode active material and particles of a sulfide-based solid electrolyte and a lithium ion secondary battery employing the same.

According to one aspect,

coated particles having positive electrode active material particles and a coating layer covering the positive electrode active material particles; and sulfide-based solid electrolyte particles in contact with the coated particles, wherein the coating layer contains a highly reactive element having a higher reactivity with the sulfide-based solid electrolyte particles than a transition metal element in the positive electrode active material particle among elements other than lithium and oxygen, The ratio of the layer thickness of the coating layer and the diameter of the positive electrode active material particles (a value obtained by dividing the layer thickness of the coating layer by the diameter of the positive electrode active material particles) is 0.0010 to 0.25.

Here, the ratio of the layer thickness of the coating layer and the diameter of the positive electrode active material particles may be, for example, 0.0016 to 0.1, and more specifically, 0.0016 to 0.01.

In the positive electrode, since the highly reactive element in the coating layer preferentially reacts with the elemental sulfur in the sulfide-based solid electrolyte particles, the reaction (side reaction) between the transition metal element and the elemental sulfur in the positive electrode active material particles can be suppressed. That is, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the highly reactive element may have a lower standard enthalpy of sulfide formation than the transition metal element in the positive electrode active material particle. Accordingly, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the sulfide standard formation enthalpy of the highly reactive element may be less than -80 kJ/mol. Within the above range, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to an embodiment, a first DSC test is conducted in which the coated particles and the sulfide-based solid electrolyte particles are mixed at a mass ratio of 1:1 and heated, while the positive electrode active material particles not covered with a coating layer and the sulfide-based solid electrolyte particles are mixed and heated. In the case of conducting the second DSC test in which the mixture is heated by mixing in a mass ratio of 1: 1, the initiation temperature of the exothermic reaction in the first DSC test may be higher than the initiation temperature of the exothermic reaction in the second DSC test. . Accordingly, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the onset temperature of the exothermic reaction in the first DSC test may be higher than 250°C. Within the above range, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the temperature at which the calorific value in the first DSC test is maximized may be higher than 330°C. Within the above range, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, some of the highly reactive elements may be dissolved in the positive electrode active material particles. Accordingly, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the highly reactive element is aluminum (Al), magnesium (Mg), zirconium (Zr), titanium (Ti), tantalum (Ta), sodium (Na), potassium (K), calcium (Ca ), strontium (Sr), barium (Ba), indium (In), molybdenum (Mo), lanthanum (La), cobalt (Co), and manganese (Mn). For example, the highly reactive element may be at least one selected from the group consisting of aluminum (Al), cobalt (Co), manganese (Mn), and magnesium (Mg). Accordingly, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to one embodiment, the sulfide-based solid electrolyte particles may include phosphorus (P). Accordingly, the reaction at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte particles can be further suppressed.

According to another aspect,

an anode as described above;

a negative electrode including a negative electrode active material; and

a solid electrolyte layer disposed between the positive electrode and the negative electrode and including sulfide-based solid electrolyte particles;

A lithium ion secondary battery comprising a is provided.

In a lithium ion secondary battery having a sulfide-based solid electrolyte, the positive electrode according to one aspect may further suppress a reaction at an interface between positive electrode active material particles and sulfide-based solid electrolyte particles.

1 is an explanatory diagram schematically illustrating a configuration of a lithium ion secondary battery according to an exemplary embodiment.
2 is a graph obtained by differential scanning calorimetry (DSC) measurement of a mixture of positive electrode active material particles and sulfide-based solid electrolyte particles.
3 is a graph showing impedance evaluation results of Examples and Comparative Examples.
Fig. 4 is an explanatory view showing an increase in interface resistance in a typical all-solid-state lithium ion secondary battery.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail, referring an accompanying drawing. In addition, in this specification and drawings, the same reference numerals are assigned to components having substantially the same functional configuration, thereby omitting redundant description.

<1. Problems in the case of using a solid electrolyte>

First, with reference to FIG. 4 , before describing a lithium ion battery according to a preferred embodiment of the present invention, problems in the case of using a solid electrolyte will be described. 4 is an explanatory diagram showing a schematic configuration of a typical lithium ion secondary battery 100. As shown in FIG.

The lithium ion secondary battery 100 has a structure in which a positive electrode layer 110 , a negative electrode layer 120 and a solid electrolyte layer 130 are stacked. The positive electrode layer 110 is composed of mixed particles in which positive electrode active material particles 111 and sulfide-based solid electrolyte particles 131 (hereinafter also referred to as "solid electrolyte particles 131") are mixed. Similarly, the negative electrode layer 120 is composed of mixed particles in which negative electrode active material particles 121 and solid electrolyte particles 131 are mixed. The solid electrolyte layer 130 is installed between the anode layer 110 and the cathode layer 120 . The solid electrolyte layer 130 is composed of solid electrolyte particles 131 .

In the lithium ion secondary battery 100 using a sulfide-based solid electrolyte, since the positive electrode active material and the electrolyte are solid, the electrolyte is more difficult to penetrate into the positive electrode active material than when an organic electrolyte solution is used as the electrolyte, and the interface between the positive electrode active material and the electrolyte is difficult to penetrate. Since the area tends to decrease, it is difficult to sufficiently secure a path for movement of lithium ions and electrons. Therefore, as shown in FIG. 4, the positive electrode layer 110 is composed of mixed particles of the positive electrode active material particles 111 and the sulfide-based solid electrolyte particles 131, and the negative electrode active material particles 121 and the sulfide-based solid electrolyte particles 131 ) is used to form the negative electrode layer 120 with mixed particles. Through this, the area of the interface between the active material and the solid electrolyte is increased.

However, as described above, during charging, a reaction occurs at the interface between the positive electrode active material particles 111 and the solid electrolyte particles 131 to form the high resistance layer 150 . Specifically, the high resistance layer 150 is formed by reacting a transition metal element present on the surface of the positive electrode active material particle 111 with a sulfur element present on the surface of the solid electrolyte particle 131 . Here, the "high resistance layer 150" is a layer made of a resistance component formed on the interface between the positive electrode active material particles 111 and the solid electrolyte particles 131, and the inside of the positive electrode active material particles 111 or sulfide-based solid electrolyte particles (131) means a layer in which the resistance when moving lithium ions becomes larger than that of (131). Accordingly, the interface resistance between the positive electrode active material particles 111 and the solid electrolyte particles 131 is easily increased. In addition, when the area of the interface between the positive electrode active material particles 111 and the solid electrolyte particles 131 is increased, the movement path of lithium ions and electrons can be secured, while the high resistance layer 150 is easily formed. For this reason, the movement of lithium ions from the positive electrode active material particles 111 to the solid electrolyte particles 131 is inhibited by the high resistance layer 150 . As a result, since the lithium ion conductivity is lowered, the output of the lithium ion secondary battery 100 is lowered.

<2. Review by the present inventors>

It was thought that the high resistance layer 150 was created by a difference in chemical potential between lithium ions in the positive electrode active material particles 111 and lithium ions in the solid electrolyte particles 131 . However, no technology capable of sufficiently suppressing the generation of the high-resistance layer 150 has been established so far.

Accordingly, the present inventors considered that factors affecting the formation of the high-resistance layer 150 may exist other than the difference in chemical potential of lithium ions, and investigated thermodynamic data of various metal sulfides. As a result, the present inventors found that the reactivity between the metal element included in the positive electrode active material particle 111 and the sulfur element included in the solid electrolyte particle 131 greatly affects the formation of the high resistance layer 150 .

In addition, the present inventors have a higher reactivity with elemental sulfur included in the solid electrolyte particles 131 (hereinafter also referred to as "reactivity with the solid electrolyte particles 131") than the transition metal element in the positive electrode active material particle 111 (metal element ( Hereinafter, it has been found that formation of the high resistance layer 150 is greatly suppressed by coating the positive electrode active material particles 111 with such a metal element (also referred to as “highly reactive element”).

Regarding this phenomenon, the present inventors believe that the highly reactive element preferentially reacts with the sulfur element in the solid electrolyte particles 131 rather than the transition metal element in the positive electrode active material particle 111, so that the reaction between the transition metal element and the sulfur element is suppressed. are doing

In addition, as a result of examining an index for classifying a metal element having high reactivity with the solid electrolyte particle 131 (ie, a highly reactive element) and a metal element having low reactivity, the present inventors found that the standard enthalpy of sulfide formation of the metal element is an index. Found. That is, the present inventors found that the higher the metal element's sulfide standard formation enthalpy (larger in the negative direction), the higher the reactivity between the metal element and the sulfide-based solid electrolyte particles 131.

According to the above research results, the present inventors have come to the idea of a lithium ion secondary battery according to the present embodiment. As shown in FIG. 1 , in the lithium ion secondary battery 1 according to the present embodiment, the formation of a high resistance layer can be suppressed by covering the positive electrode active material particles 11 with the coating layer 12 containing a highly reactive element. . Hereinafter, the lithium ion secondary battery 1 according to the present embodiment will be described in detail.

<3. Configuration of Lithium Ion Secondary Battery>

Subsequently, the configuration of a lithium ion secondary battery according to a preferred embodiment of the present invention will be described in detail with reference to FIG. 1 . 1 is an explanatory diagram schematically showing the configuration of a lithium ion secondary battery 1 according to the present embodiment.

As shown in FIG. 1, the lithium ion secondary battery 1 according to the present embodiment is an all-solid-state lithium ion secondary battery, and includes a positive electrode layer 10, a negative electrode layer 20, a positive electrode layer 10, and a negative electrode layer 20. ) has a structure in which the solid electrolyte layer 30 installed between them is stacked.

(2.1. anode layer (10))

The positive electrode layer 10 includes mixed particles obtained by mixing coated particles 10a and sulfide-based solid electrolyte particles 31 (hereinafter, also referred to as "solid electrolyte particles 31"). The coated particle 10a includes the positive electrode active material particle 11 and the coating layer 12 covering the surface of the positive electrode active material particle 11 . Thus, the coating layer 12 contacts the solid electrolyte particles 31 . As described above, in the lithium ion secondary battery 100 using the solid electrolyte particles 131, the interface resistance increases due to the reaction at the interface between the positive electrode active material particles 111 and the solid electrolyte particles 131, so that the output of the battery increases. There is a problem with deterioration. However, according to the all-solid-state lithium ion battery 1 according to the present embodiment, the surface of the positive electrode active material particle 11 is coated with the coating layer 12 containing a highly reactive element, so that the coating layer 12 is a solid electrolyte particle The reaction (side effect) between the sulfur element in (31) and the transition metal element in the positive electrode active material particles 11 can be prevented. Accordingly, it is difficult to generate a resistance component (high resistance layer) at the interface between the positive electrode active material particles 11 and the solid electrolyte particles 31 .

In addition, at least a part of the surface of the positive electrode active material particle 11 should just be covered with the coating layer 12. That is, the entire surface of the positive electrode active material particles 11 may be covered with the coating layer 12, or the surface of the positive electrode active material particles 11 may be partially covered with the coating layer 12.

In addition, the fact that the coating layer 12 containing a highly reactive element is formed on the particle surface of the positive electrode active material particles 11 is, for example, contrast due to the difference in structure between the positive electrode active material particles 11 and the coating layer 12. It can be confirmed by a method such as microscopic image (field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) image) analysis using the difference in . Hereinafter, the positive electrode active material particles 11 and the coating layer 12 included in the positive electrode layer 10 will be described in detail.

(Cathode Active Material Particles 11)

The positive electrode active material constituting the positive electrode active material particles 11 is not particularly limited as long as it can reversibly occlude and release lithium ions.

For example, Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1 and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α F _α (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO 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); A compound represented by any of the chemical formulas of LiFePO ₄ may be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B 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; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or combinations thereof.

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include a coating element compound of an oxide, a hydroxide, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. Compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. In the process of forming the coating layer, any coating method may be used as long as the compound can be coated in a method (eg, spray coating, dipping method, etc.) that does not adversely affect the physical properties of the positive electrode active material by using these elements. Since it is a content that can be well understood by those skilled in the art, a detailed description thereof will be omitted.

Specific examples of the positive electrode active material include lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminate (hereinafter sometimes referred to as “NCA”), and lithium nickel cobalt manganate (hereinafter referred to as “NCA”). Sometimes referred to as "NCM"), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide, and the like. These cathode active materials may be used alone or in combination of two or more.

Among the above-mentioned examples of the positive electrode active material, the positive electrode active material particle 11 may include, in particular, a lithium salt of a transition metal oxide having a layered rock salt structure. "Layered" as used herein means a thin sheet-like shape, and "rock salt structure" is a sodium chloride type structure, which is a type of crystal structure, and the face-centered cubic lattice formed by each of the cation and anion is 1/1 of the corner of the unit cell. Indicates a structure that is displaced by 2. Lithium salts of transition metal oxides having such a layered rock salt structure include, for example, Li _2-xyz Ni _x Co _y Al _z O ₂ (NCA) or Li _2-xyz Ni _x Co _y Mn _z O ₂ (NCM ) (0<x<1, 0<y<1, 0<z<1, and x + y + z is 1 or less).

In this way, by using the lithium salt of the ternary transition metal oxide as the positive electrode active material particle 11, an all-solid-state lithium ion battery having excellent energy density and thermal stability can be obtained. In addition, lithium salt particles of ternary transition metal oxides such as NCA and NCM (existing as aggregates of primary particles) have a smaller particle size and larger specific surface area than, for example, LCO particles (about 10 times). . Therefore, since the contact area between the positive electrode active material particles 11 and the solid electrolyte particles 31 is increased and lithium ion conductivity is improved, the output of the battery increases. In addition, by including Ni as a constituent element of the positive electrode active material particle 11, the capacity density of the lithium ion secondary battery 1 is increased, and since metal elution in the charged state is small, the lithium ion secondary battery in the charged state (1 ) can improve the long-term reliability.

( coating layer (12))

As described above, the coating layer 12 is a layer containing a highly reactive element. The coating layer 12 may be composed of only highly reactive elements. Among elements other than lithium and oxygen, the highly reactive element has a higher reactivity with the sulfur element in the solid electrolyte particle 31 than the transition metal element in the positive electrode active material particle 11 (hereinafter, also referred to simply as “reactivity with the solid electrolyte particle 31”). ) is a high element. More specifically, the highly reactive element is an element other than lithium and oxygen that has a lower standard enthalpy of sulfide formation than the transition metal element in the positive electrode active material particle 11 . When the positive electrode active material particles 11 include several types of transition metal elements, the highly reactive elements are all transition metal elements included in the positive electrode active material particles 11 (when the positive electrode active material particles 11 include highly reactive elements) , excluding highly reactive elements) has a lower enthalpy of sulfide standard formation. In addition, when several types of sulfides can be formed from highly reactive elements, it is preferable that the standard enthalpies of formation of all sulfides satisfy the above condition. In addition, several types of highly reactive elements may be included in the coating layer 12 .

Specifically, the sulfide standard formation enthalpy value of the highly reactive element may be -80.0 kJ/mol or less, specifically -250 kJ/mol. When the sulfide standard formation enthalpy value of the highly reactive element becomes a value within this range, the formation of the high resistance layer can be more reliably suppressed. In addition, as described above, the highly reactive element requires a lower sulfide standard formation enthalpy than all transition metal elements included in the positive electrode active material particle 11 . Therefore, it is preferable that the enthalpy of sulfide standard formation of the highly reactive element is a value within the above numerical range while satisfying this condition.

By covering the positive electrode active material particles 11 with such a coating layer 12, the reaction between the positive electrode active material particles 11 and the sulfide solid electrolyte particles 31 is suppressed. Inhibition of the above reaction can be confirmed, for example, through a DSC test described below. That is to say, whether or not a metal element is a highly reactive element can be judged according to the results of the following DSC test.

Specifically, a first DSC test is conducted in which coated particles 10a and solid electrolyte particles 31 are mixed and heated in a mass ratio of 1:1. Similarly, a second DSC test is performed in which the positive electrode active material particles 11 not coated with the coating layer 12 and the sulfide-based solid electrolyte particles 31 are mixed in a mass ratio of 1:1 and heated. As a result, the initiation temperature of the exothermic reaction in the first DSC is higher than the initiation temperature of the exothermic reaction in the second DSC test.

That is, the exothermic reaction is a reaction between the transition metal element of the positive electrode active material particle 11 and the sulfur element of the solid electrolyte particle 31, that is, a side effect. Therefore, it can be said that the higher the starting temperature of this exothermic reaction, the more difficult the side reaction occurs. The onset temperature of the exothermic reaction in the first DSC test may be higher than 250°C. When the starting temperature of the exothermic reaction becomes a value within this range, the formation of the high-resistance layer can be suppressed more reliably.

In addition, the temperature at which the calorific value (calorific value of exothermic reaction) in the first DSC test is maximized, the so-called peak temperature of exothermic reaction, may be higher than 330°C, specifically higher than 350°C. When the peak temperature of the exothermic reaction becomes a value within this range, the formation of the high-resistance layer can be suppressed more reliably. Table 1 shows examples of highly reactive elements, sulfides of highly reactive elements, and enthalpies of standard formation of sulfides. For reference, the standard formation enthalpy of sulfide of elemental nickel is -53 kJ/mol. Therefore, all of the elements listed in Table 1 have higher reactivity with the solid electrolyte particles 31 than elemental nickel.

highly reactive element sulfide Enthalpy of sulfide standard formation
(kJ/mol) Al Al ₂ S ₃ -724 Mg MaS -346 Zr ZrS -566 Ti TiS -407 Ta TaS ₂ -464 Na _Na2S -364.8 K _K2S -380.7 Ca CaS -482 Sr SrS -472 Ba BaS -460 In In ₂ S ₃ -427 Mo MoS ₂ -276 Mo ₂ S ₃ -407 La La ₂ S ₃ -1209 Co CoS -82.8 Co ₂ S ₃ -147.2 Mn MnS -214.2

The coating layer 12 is not effective even if it is too thick or too thin with respect to the diameter of the positive electrode active material particle 11 . The ratio of the layer thickness of the coating layer 12 to the diameter of the positive electrode active material particles 11 (equivalent sphere diameter of primary particles) (hereinafter also referred to as “diameter layer thickness ratio”) may be 0.0010 to 0.25. Specifically, it may be 0.0016 to 0.1. More specifically, it may be 0.0016 to 0.01. The diameter-layer-thickness ratio can be obtained, for example, by dividing the arithmetic average value of the layer thicknesses of the coating layer 12 by D50 (median diameter) of the positive electrode active material particles 11. The arithmetic mean value of the layer thickness is calculated as follows. That is, a portion of the coated particles 10a is sampled. Then, the layer thickness of the coated layer 12 is calculated for each sampled coated particle 10a. Specifically, a certain measurement point is set on the covering layer 12, and the layer thickness at this measurement point is measured. And the layer thickness of the coating layer 12 is measured by carrying out the arithmetic average of the layer thickness at each measurement point. Then, the arithmetic mean value of the layer thickness of the coating layer 12 is calculated (measured) by arithmetic averaging the measured layer thickness for each coated particle 10a. In Examples described later, the arithmetic average value of the layer thickness was measured by this method. In addition, the layer thickness at each measurement point is measured by observing the cross-section of the coated particle 10a with a field emission scanning electron microscope (for example, S-4800 manufactured by Hitachi High Technologies) and by energy dispersive X-ray analysis (for example, , EMAX ENERGY E-350 manufactured by Horiba Manufacturing Co., Ltd.) can be measured based on the results of elemental analysis. In addition, D50 of the positive electrode active material particles 11 can be measured by a laser diffraction/scattering type particle size distribution measuring device (for example, Nikkiso Co., Ltd. Microtrac MT-3000II).

In addition, some of the highly reactive elements may be dissolved in the positive electrode active material particles 11 . That is, the highly reactive element may be a constituent element of the positive electrode active material particle 11 . However, the concentration of the highly reactive element in the coating layer 12 is greater than that in the positive electrode active material particles 11 . In addition, whether a highly reactive element is dissolved in the positive electrode active material particles 11 and the concentration of the highly reactive element can be measured by X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectrometry (SIMS). When the highly reactive element is dissolved in the positive electrode active material particle 11, the coated particle 10a is sequentially formed from the surface of the coated particle 10a to the coating layer 12, the layer in which the highly reactive element is dissolved in the positive electrode active material, and the positive electrode active material It is composed of layers (particles) made of Therefore, elements highly reactive with sulfides can be disposed at high concentration on the surface side.

In this way, the highly reactive element may be dissolved in the positive electrode active material particle 11, but it is necessary to be unevenly distributed on the surface of the positive electrode active material particle 11 without fail. In the all-solid-state lithium ion secondary battery 1, since the electrolyte is solid, that is, the electrolyte particles 31, it does not penetrate into the positive electrode active material particles 11. Therefore, a side reaction between the electrolyte particles 31 and the positive electrode active material particles 11 occurs at the interface between the solid electrolyte particles 31 and the positive electrode active material particles 11 , that is, on the surface of the positive electrode active material particles 11 . Therefore, it is necessary to manage the surface of the positive electrode active material particle 11 . Therefore, when the highly reactive element is dissolved in the positive electrode active material particle 11, the highly reactive element is unevenly distributed on the surface of the positive electrode active material particle 11 (specifically, the surface of the positive electrode active material particle 11 is treated as a highly reactive element). cover).

(other additives)

In addition to the coated particles 10a, the positive electrode layer 10 may contain appropriately selected additives such as a conductive agent, a binder, an electrolyte, a filler, a dispersant, and an ion-conductive agent.

Examples of the conductive agent include graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. etc. can be mentioned. Examples of the electrolyte include a sulfide-based solid electrolyte described later. In addition, as the filler, the dispersant, the ion-conducting agent, etc., known materials commonly used in electrodes of lithium ion batteries can be used.

(2.2. cathode layer (20))

(negative electrode active material particle 21)

The negative electrode active material particles 21 included in the negative electrode layer 20 according to the present embodiment are not particularly limited as long as they are alloyed with lithium or capable of reversibly occluding and releasing lithium.

The negative electrode active material particle 21 is, for example, one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, a material capable of doping and undoping lithium, and a carbon-based material. may contain more than

The metal alloyable with lithium is, for example, Si, Sn, Al, In, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal) , a rare earth element or a combination thereof, but not Si), a Sn—Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and Sn is not), etc. The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be Se, Te, Po, or a combination thereof.

The transition metal oxide may be, for example, tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, or lithium vanadium oxide.

The non-transition metal oxide may be, for example, SnO ₂ or SiO _x (0<x<2).

The material capable of doping and undoping the lithium is, for example, Si, SiO ₂ , Si—Y alloy, Sn, SnO ₂ , Sn—Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 11 element, a group 12 element, a group 13 element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, or a combination thereof, but not Sn). The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be Se, Te, Po, or a combination thereof.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. Examples of the carbon-based material include natural graphite, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis gas-phase growth carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, Vapor-phase growth carbon fiber, soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, or the like may be used. These may be used alone as the negative electrode active material 201 or may be used in combination of two or more.

The carbon-based material may be amorphous, plate-like, flake-like, spherical, fibrous, or a combination thereof.

These negative electrode active material particles 21 may be used alone or two or more types may be used together.

(other additives)

In addition to the negative electrode active material particles 21, the negative electrode layer 20 may contain, for example, a conductive agent, a binder, an electrolyte, a filler, a dispersant, an ion conductive agent, and other additives that are appropriately selected. A specific example of this may be the same material as the anode layer 10 described above.

(2.3 solid electrolyte layer (30))

The solid electrolyte layer 30 according to the present embodiment includes solid electrolyte particles 31 . The solid electrolyte particles 31 are not particularly limited as long as they are sulfide-based solid electrolyte particles. The solid electrolyte particles 31 may be sulfide-based solid electrolyte particles containing at least Li, P, and S. This sulfide-based solid electrolyte is known to have higher lithium ion conductivity than other inorganic compounds, and may include sulfides such as SiS ₂ , GeS ₂ , and B ₂ S ₃ in addition to Li ₂ S and P ₂ S ₅ . Further, Li ₃ PO ₄ , a halogen, a halogen compound, or the like may be appropriately added to the solid electrolyte particles 31 .

(3. Manufacturing method of lithium ion battery)

Above, the configuration of the lithium ion secondary battery 1 according to the preferred embodiment of the present invention has been described in detail. Next, a method for manufacturing the lithium ion secondary battery 1 having the above configuration will be described. The lithium ion secondary battery 1 can be manufactured by forming the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, and then laminating each of these layers. Hereinafter, each process is explained in detail.

(3.1 Production of coated particles 10a)

First, the manufacturing method of the coated particle 10a is demonstrated. In this example, the coated particles 10a are produced by a so-called coprecipitation method. Of course, the manufacturing method of the coated particles 10a is not limited to this example, and any method may be used as long as the positive electrode active material particles can be coated with a highly reactive element.

First, an aqueous solution of urea is added to an aqueous solution of nitrate of a highly reactive element, and a transition metal hydroxide, which is a raw material for a cathode active material, is dispersed in this solution.

Subsequently, the transition metal dispersion is maintained at 100° C. under a nitrogen atmosphere to decompose urea. Because of this, since the pH in the transition metal dispersion liquid rises, a hydroxide of a highly reactive element precipitates on the surface of the transition metal oxide particle.

The obtained sample is dried, and then the sample is mixed with lithium hydroxide powder. The mixture is then calcined in air. The firing temperature is not particularly limited, but may be, for example, about 1000°C. Through the above process, the coated particle 10a is manufactured. Here, the layer thickness of the coating layer 12 is adjusted by fixing the concentration of the nitrate aqueous solution of the highly reactive element and adjusting at least one of the mass and reaction time of the transition metal oxide introduced into the nitric acid aqueous solution or by adjusting the firing time. . Both the firing time and at least one of the mass of the transition metal oxide and the reaction time may be adjusted. In addition, in some cases, a part of the highly reactive element in the coating layer 10a is dissolved into the positive electrode active material particle 11 by firing. The higher the firing temperature and the longer the firing time, the more highly reactive elements are dissolved in the positive electrode active material particles 11 . However, in this manufacturing method, since the coating layer 12 is composed only of highly reactive elements, the concentration of the highly reactive elements in the coating layer 12 is higher than the concentration of the highly reactive elements in the positive electrode active material particles 11 .

(3.2 Preparation of Solid Electrolyte Particles 31)

The manufacturing method of the solid electrolyte particles 31 is not particularly limited, and conventional methods are arbitrarily applicable. For example, the solid electrolyte particles 31 can be produced by a melt quenching method or a mechanical milling method (MM method). Hereinafter, as an example of a method for manufacturing the solid electrolyte particles 31, a method for manufacturing the solid electrolyte particles 31 containing Li ₂ S and P ₂ S ₅ will be described.

In the case of the melt quenching method, a sulfide-based solid electrolyte can be obtained by mixing a predetermined amount of Li ₂ S and P ₂ S ₅ and reacting them in the form of pellets at a predetermined reaction temperature in a vacuum state and then rapidly cooling. The reaction temperature at this time may be, for example, 400 ° C to 1000 ° C, more specifically 800 ° C to 900 ° C. In addition, the reaction time may be, for example, 0.1 hour to 12 hours, more specifically 1 to 12 hours. In addition, the quenching temperature of the reactant may be usually 10 ° C or less, specifically 0 ° C or less, and the cooling rate may be usually about 1 to 10000 K / sec, specifically 1 to 1000 K / sec.

In the case of the MM method, a sulfide-based solid electrolyte can be obtained by mixing a predetermined amount of Li ₂ S and P ₂ S ₅ and reacting for a predetermined time by a mechanical milling method. The mechanical milling method using the raw material has the advantage of being able to carry out the reaction at room temperature. According to the MM method, since a solid electrolyte can be produced at room temperature, thermal decomposition of raw materials does not occur, and a solid electrolyte of charged components can be obtained. The rotation speed and rotation time of the MM method are not particularly limited, but the faster the rotation speed, the faster the production rate of the solid electrolyte, and the longer the rotation time, the higher the conversion rate of the raw material into the solid electrolyte.

Thereafter, the obtained solid electrolyte is subjected to heat treatment at a predetermined temperature and then pulverized to obtain solid electrolyte particles 31 . The mixing ratio of the sulfide containing Li ₂ S and P ₂ S ₅ is usually 50:50 to 80:20, specifically 60:40 to 75:25 in terms of molar ratio.

(3.3. of the anode layer 10 manufacturing)

A mixture of the coated particles 10a, the solid electrolyte particles 31, and various additives is added to a solvent to prepare a slurry or paste-like positive electrode mixture. Here, the solvent is not particularly limited as long as it can be used for producing the positive electrode mixture, but a non-polar solvent is particularly preferred. This is because non-polar solvents are difficult to react with the solid electrolyte particles 31 . Next, the obtained positive electrode mixture is applied to the current collector using a doctor blade or the like and dried. Then, the current collector and the positive electrode mixture layer are compacted with a rolling roll or the like to obtain the positive electrode layer 10 .

Examples of the current collector that can be used at this time include a plate-like body or a thin body made of stainless steel, titanium, aluminum, or an alloy thereof. Alternatively, the positive electrode layer 10 may be obtained by compacting and molding the positive electrode mixture into a pellet form without using a current collector.

(3.4. of the cathode layer 20 manufacturing)

A manufacturing method of the cathode layer 20 is as follows. For example, a slurry or paste-type negative electrode mixture is prepared by adding a mixture of the negative electrode active material particles 21, the solid electrolyte particles 31, and various additives to a solvent. Here, the solvent is not particularly limited as long as it can be used for preparing the negative electrode mixture, but a non-polar solvent can be particularly used. This is because non-polar solvents are difficult to react with the solid electrolyte particles 31 . Next, the obtained negative electrode mixture is applied to the current collector using a doctor blade or the like and dried. Subsequently, the negative electrode layer 20 is obtained by compacting the current collector and the negative electrode mixture layer with a rolling roll or the like.

As the current collector that can be used at this time, for example, a plate-shaped body or a thin body made of copper, stainless steel, nickel, or alloys thereof, and the like are exemplified. In addition, the negative electrode layer 20 may be obtained by compacting and molding a mixture of the negative electrode active material particles 21 and various additives in a pellet form without using a current collector. In addition, when using a metal or its alloy as the negative electrode active material particle 21, you may use a metal sheet (foil) as it is.

(3.5. Solid of the electrolyte layer 30 produce)

The manufacturing method of the solid electrolyte layer 30 is as follows. The solid electrolyte layer 30 is formed by forming the solid electrolyte particles 31 into a film using a known film forming method such as, for example, a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a vapor deposition method (CVD), and a thermal spray method. can be manufactured Alternatively, a method may be used in which a solution in which the solid electrolyte particles 31 are mixed with a solvent and a binder (a binder and a polymer compound) is applied, and then the solvent is removed to form a film. In addition, the strength of the solid electrolyte particles 31 themselves, the solid electrolyte particles 31, binders (binders or polymer compounds, etc.) or supports (solid electrolyte layer 30 are reinforced, and the solid electrolyte particles 31 themselves are short-circuited. A film can be formed by pressing an electrolyte mixed with materials and compounds for preventing

(3.6. Lamination of each layer)

The lithium ion secondary battery 1 according to the present embodiment can be manufactured by laminating the positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20 obtained as described above in this order and pressing or the like. there is.

[ Example ]

Next, examples of this embodiment will be described. Of course, the present invention is not limited only to the following examples.

(1. of coated particles manufacturing example One)

In Production Example 1 of Coated Particles, coated particles 10a were manufactured in the following process. 100 ml of 0.16 mol/L urea solution was added to 100 ml of 0.15 mol/L aluminum nitrate aqueous solution. Subsequently, 60 g of a transition metal hydroxide ((Mn, Co, Ni) _1/3 (OH) ₂ ) serving as a raw material for an active material was dispersed in this aqueous solution.

Then, this dispersion is maintained at 100°C under a nitrogen atmosphere. This resulted in decomposition of urea. As a result, the pH in the dispersion increased, and aluminum hydroxide precipitated on the surface of the transition metal hydroxide particles.

The obtained sample was dried, mixed with lithium hydroxide powder, and calcined at 1000°C for 10 hours in the air. Thus, coated particles 10a according to Production Example 1 (hereinafter also referred to as "covered particles 10a-1") were obtained. The positive active material particles 11 of the coated particles 10a-1 are composed of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM333), and the coated layer 12 of the coated particles 10a-1 is aluminum. It consists of

As a result of measuring D50 (median diameter) of the positive electrode active material particles 11 using Nikkiso Co., Ltd. Microtrac MT-3000II, it was 5.0 μm. In addition, as a result of measuring the arithmetic average value of the layer thickness of the coated particles 10a by the method described above, it was 8.0 nm. Here, the layer thickness at each measuring point is measured by observing the cross-section of the coated particle 10a with a field emission scanning electron microscope (S-4800 manufactured by Hitachi High-Technology Co., Ltd.) and by energy dispersive X-ray analysis (EMAX ENERGY E manufactured by Horiba Manufacturing Co., Ltd.). -350) was measured based on the result of elemental analysis. Therefore, the diameter layer thickness ratio was 0.0016. In addition, whether a part of the coating layer 12 was dissolved in the positive electrode active material particles 11 was confirmed by XPS.

(2. Covered Particles manufacturing example 2)

Coated particles 10a according to Production Example 2 (hereinafter referred to as “coated particles 10a-2 )”) was prepared. Further, as a result of measuring the diameter-to-thickness ratio of the coated particles 10a-2 in the same manner as in Production Example 1, it was found to be 0.01.

(3. Covered Particles manufacturing example 3)

Coated particles 10a according to Production Example 3 (hereinafter referred to as "coated particles 10a-3 )”) was prepared. In addition, the result of measuring the diameter-to-layer thickness ratio in the same manner as in Production Example 1 was 0.10.

(4. Covered Particles manufacturing example 4)

Coated particles 10a according to Production Example 4 ( Hereinafter, also referred to as "covered particles 10a-4") was manufactured. In addition, the result of measuring the diameter-to-layer thickness ratio in the same manner as in Production Example 1 was 0.25.

(5. Covered Particles manufacturing example 5)

Coated particles 10a according to Production Example 5 (hereinafter referred to as "coated particles 10a-5) by treating the rest in the same manner as in Production Example 1 of coated particles, except that the amount of transition metal hydroxide used in Production Example 1 of coated particles was 80 g. Also referred to as ") was prepared. In addition, as a result of measuring the diameter-to-layer thickness ratio in the same manner as in Production Example 1, it was 0.0010.

(6. Covered Particles manufacturing example 6)

The 0.15 mol/L aluminum nitrate solution was a mixed solution in which both aluminum nitrate and magnesium nitrate were dissolved at 0.075 mol/L, and the amount of the transition metal hydroxide was set to 10 g, and the remainder was treated in the same manner as in Production Example 1 of coated particles, Coated particles 10a according to Production Example 6 (hereinafter also referred to as "covered particles 10a-6") were manufactured. The coating layer 12 of Production Example 6 of the coated particles is composed of only aluminum and magnesium. The molar ratio of aluminum and magnesium constituting the coating layer 12 is 1:1. As a result of measuring the diameter-to-layer thickness ratio in the same manner as in Preparation Example 1, it was 0.010.

(7. Covered Particles manufacturing example 7)

In Production Example 1 of coated particles, the 0.15 mol/L aqueous solution of aluminum nitrate was changed to 0.15 mol/L aqueous solution of cobalt nitrate, the transition metal hydroxide was changed to nickel hydroxide, the amount of transition metal hydroxide was changed to 10 g, and the remainder was coated. By processing the particles in the same manner as in Production Example 1, coated particles 10a according to Production Example 7 (hereinafter also referred to as "covered particles 10a-7") were produced. The positive electrode active material particles 11 are composed of lithium nickelate, and the coating layer 12 is composed of cobalt. As a result of measuring the diameter-to-layer thickness ratio in the same manner as in Preparation Example 1, it was 0.009.

(8. Covered Particles manufacturing example 8)

Coated particles 10a according to Production Example 8 (hereinafter Also referred to as "covered particles 10a-8") was manufactured. In addition, as a result of measuring the diameter-to-layer thickness ratio in the same manner as in Production Example 1, it was a value smaller than 0.0010.

(9. Covered Particles manufacturing example 9)

Coated particles 10a according to Production Example 9 ( Hereinafter, also referred to as “covered particles 10a-9”) were manufactured. In addition, as a result of measuring the diameter-to-layer thickness ratio in the same manner as in Production Example 1, it was a value greater than 0.25.

(8.DSC evaluation)

(8.1 manufacturing example 1, DSC test of 6)

Next, in order to evaluate the reactivity between the coated particles 10a-1 and 10a-6 and the solid electrolyte particles 31, a DSC test described below was conducted. That is, as the solid electrolyte particles 31, Li ₂ SP ₂ S ₅ (80-20 mol%) mechanically milled (MM treated) was prepared. Then, the coated particles 10a-1 and the solid electrolyte particles 31 were mixed at a mass ratio of 1:1 in a glove box. Then, the temperature at which the exothermic reaction of the mixture starts was evaluated using a differential scanning calorimeter (THERMO plus EVO II / DSC8230 manufactured by Rigaku Co., Ltd.). The same evaluation was performed also on the coated particle 10a-6. In addition, NCM333 particles (positive electrode active material particles 11) not covered with the coating layer 12 were prepared and the same evaluation was performed. Results are shown in FIG. 2 . In Fig. 2, the horizontal axis represents the temperature, and the vertical axis represents the heat flow. "Li(Ni, Mn, Co)O ₂ + Al" in FIG. 2 represents the covered particle 10a-1, and "Li(Ni, Mn, Co)O ₂ + Al/Mg" represents the coated particle 10a-6 "Li(Ni, Mn, Co)O ₂ " represents NCM333 (positive electrode active material particles 11 not covered with the coating layer 12).

As can be seen from FIG. 2 , the initiation temperature of the exothermic reaction of the coated particles 10a-1 and 10a-6 was higher than that of the NCM333 particles. Specifically, the starting temperature of the exothermic reaction of the coated particles 10a-1 and 10a-6 was about 290°C, whereas the starting temperature of the exothermic reaction of the NCM333 particles was about 210°C. In addition, the highest temperature of the exothermic reaction of the coated particles 10a-1 and 10a-6 was about 350 to 380°C, whereas the highest temperature of the exothermic reaction of the NCM333 particles was 310°C.

In addition, the exothermic reaction is a reaction between the transition metal of the positive electrode active material particle 11 and the sulfur element in the solid electrolyte particle 31, that is, a side effect. Therefore, the coated particles 10a-1 and 10a-6 are less likely to cause a side reaction than the positive electrode active material particles 11 (i.e., NCM333 particles) not covered with the coated layer 12. As a result, it was confirmed that by covering the positive electrode active material particles 11 with the coating layer 12 made of a highly reactive element, side reactions are less likely to occur (ie, generation of a high resistance layer is suppressed).

(8.2 manufacturing example 2-5 DSC test)

8.1. The same DSC test was conducted by changing the coated particle 10a-1 to the coated particle 10a-2 to 10a-5. As a result, the same results as in 8.1.

(8.3. Preparation Example 7 DSC evaluation)

The coated particles 10a-7 and the solid electrolyte particles 31 prepared in 8.1. were mixed at a weight ratio of 1:1. Then, the same evaluation as in 8.1. was performed. In addition, lithium nickelate particles (positive electrode active material particles 11) not covered with the coating layer 12 were prepared and evaluated in the same manner as in 8.1. As a result, the same results as in 8.1.

(9. Example One)

An all-solid-state lithium ion secondary battery 1 was manufactured through the following steps. A Li foil (thickness: 0.03 mm) used as the negative electrode layer 20 was punched into ?13 (mm), and set in a cell container. On top of that, 80 mg of the solid electrolyte particles 31 prepared in 8.1. were laminated, and the surface was lightly prepared with a molding machine. Thus, the electrolyte layer 30 was formed. Subsequently, a mixture of the coated particles 10a-1, the solid electrolyte particles 31 prepared in 8.1., and vapor grown carbon fiber (VGCF) as a conductive agent at a ratio of 60/35/5% by weight was used as a positive electrode mixture in the SE phase. laminated on. Subsequently, the laminate was pressurized at a pressure of 3 t/cm ² to prepare pellets. That is, a test cell according to Example 1 was obtained.

The resulting test cell was charged at a constant current of 0.02C to an upper limit voltage of 4.0V at a temperature of 25°C and discharged at 0.1C to a discharge end voltage of 2.5V, and 30 cycles were performed. Then, the impedance of the lithium ion secondary battery 1 was measured, and interface resistance was calculated from the result. Impedance was measured by the alternating current impedance method.

(10. Example 2-7)

The same treatment as in Example 1 was performed except that the coated particles 10a-1 of Example 1 were replaced with the coated particles 10a-2 to 10a-7.

(11. comparative example 1 to 4)

The same treatment as in Example 1 was carried out except that the coated particles 10a-1 of Example 1 were replaced with coated particles 10a-8, coated particles 10a-9, NCM333 particles, and lithium nickelate particles.

(12. Evaluation of interfacial resistance)

Table 2 summarizes the diameter-to-layer thickness ratio and interfacial resistance of Examples 1-7 and Comparative Examples 1 to 4.

Production example of coated particles Diameter layer thickness ratio interfacial resistance Example 1 Preparation Example 1 0.0016 250 Example 2 Preparation Example 2 0.010 230 Example 3 Preparation Example 3 0.10 380 Example 4 Production Example 4 0.25 500 Example 5 Preparation Example 5 0.0010 480 Example 6 Preparation Example 6 0.010 202 Example 7 Preparation Example 7 0.0090 300 Comparative Example 1 Preparation Example 8 <0.0010 650 Comparative Example 2 Preparation Example 9 >0.25 >1000 Comparative Example 3 660 Comparative Example 4 >1000

According to Table 2, the interfacial resistances of Examples 1 to 6 are all lower than those of Comparative Examples 1 to 3. Accordingly, it was confirmed that in Examples 1 to 6, the formation of a higher resistive layer was suppressed than in Comparative Examples 1 to 3. 3 shows the impedance of Example 6 (indicated as “Li(Ni, Mn, Co)O ₂ + Al/Mg”) and the impedance of Comparative Example 3 (indicated as “Li(Ni, Mn, Co)O ₂ ”) show against 3, the horizontal axis represents the real part of the impedance, and the vertical axis represents the imaginary part. That is, FIG. 3 is a complex impedance plot diagram (Nyquist diagram). As is evident from FIG. 3, the interfacial resistance of Example 6 is lower than that of Comparative Example 3. Further, comparing Examples 1 and 2 with Examples 3 to 5, the interfacial resistances of Examples 1 and 2 are lower than those of Examples 3 to 5. Further, when Example 3 is compared with Examples 4 and 5, the interfacial resistance of Example 3 is smaller than that of Examples 4 and 5. Therefore, it was found that a preferred range of the diameter-to-layer thickness ratio is 0.0016 to 0.1, and a more preferred range is 0.0016 to 0.01.

Further, as a result of comparing the impedance of Example 7 with the impedance of Comparative Example 4, the impedance of Example 7 is lower than that of Comparative Example 4. Therefore, it was confirmed that the formation of the high-resistance layer was suppressed in Example 7 compared to Comparative Example 4.

Although preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention belongs can conceive of various changes or modifications within the scope of the technical idea described in the claims, and this also naturally falls within the technical scope of the present invention. It is understood that

One… ion battery
10... anode layer
10a... coated particles
11... Cathode Active Material Particles
12... coating layer
20... cathode layer
21... negative active material particles
30... electrolyte layer
31... solid electrolyte particles

Claims (11)

It includes coated particles including positive electrode active material particles and a coating layer covering the positive electrode active material particles, and sulfide-based solid electrolyte particles in contact with the coated particles,
The coating layer is made of a highly reactive element having a higher reactivity with sulfur in the sulfide-based solid electrolyte particles than with a transition metal element in the positive electrode active material particle, among elements other than lithium and oxygen,
The highly reactive element is aluminum (Al), magnesium (Mg), zirconium (Zr), titanium (Ti), tantalum (Ta), sodium (Na), potassium (K), calcium (Ca), strontium (Sr) , At least one selected from the group consisting of barium (Ba), indium (In), molybdenum (Mo), lanthanum (La), cobalt (Co), and manganese (Mn),
The ratio of the layer thickness of the coating layer to the diameter of the positive electrode active material particles is 0.0010 to 0.25,
A first DSC test was conducted in which the coated particles and the sulfide-based solid electrolyte particles were mixed at a weight ratio of 1:1 and heated, while the positive electrode active material particles not covered with the coating layer and the sulfide-based solid electrolyte particles were mixed at a weight ratio of 1:1. When the second DSC test of mixing and heating at a weight ratio of 1 is performed, the onset temperature of the exothermic reaction in the first DSC test is higher than the onset temperature of the exothermic reaction in the second DSC test. a positive electrode of a lithium ion secondary battery. According to claim 1,
The positive electrode of the lithium ion secondary battery of According to claim 2,
The positive electrode of a lithium ion secondary battery wherein the sulfide standard formation enthalpy of the highly reactive element is less than -80 kJ / mol. delete According to claim 1,
The positive electrode of the lithium ion secondary battery in which the onset temperature of the exothermic reaction in the first DSC test is higher than 250 ° C. According to claim 5,
A positive electrode of a lithium ion secondary battery in which the temperature at which the calorific value in the first DSC test is maximized is higher than 330 ° C. According to claim 1,
A positive electrode of a lithium ion secondary battery in which a portion of the highly reactive element is dissolved in the positive electrode active material particles. delete According to claim 1,
The positive electrode of a lithium ion secondary battery, wherein the highly reactive element is at least one selected from the group consisting of aluminum (Al), cobalt (Co), manganese (Mn), and magnesium (Mg). According to claim 1,
The positive electrode of a lithium ion secondary battery in which the sulfide-based solid electrolyte particles include phosphorus. The anode according to any one of claims 1 to 3, 5 to 7, 9 and 10;
a negative electrode including a negative electrode active material; and
a solid electrolyte layer disposed between the positive electrode and the negative electrode and including sulfide-based solid electrolyte particles;
A lithium ion secondary battery comprising a.

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