Negative electrode active material, non-aqueous electrolyte secondary battery, and method for producing a negative electrode active material

Abstract

To provide a negative electrode active material capable of reducing deterioration of battery capacity, a non-aqueous electrolyte secondary battery including the negative electrode active material, and a manufacturing method of the negative electrode active material.SOLUTION: A negative electrode active material 5 includes graphite, low crystalline carbon, and carbon black. The graphite forms secondary particles 2. The secondary particles 2 include multiple primary particles 1. Inside the secondary particle 2, low-crystalline carbon 3 is attached to the surface of the primary particle 1. Carbon black 4 is surrounded by multiple primary particles 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode active material, a non-aqueous electrolyte secondary battery, and a method for producing a negative electrode active material. [Background technology]

[0002] Japanese Patent Publication No. 2020-043069 (Patent Document 1) discloses natural graphite containing secondary particles assembled from a plurality of primary particles, amorphous carbon present on the surface of the primary particles, and a coating layer containing amorphous carbon surrounding the secondary particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-043069 [Overview of the project] [Problems that the invention aims to solve]

[0004] Graphite is widely used as the negative electrode active material in non-aqueous electrolyte secondary batteries (hereinafter sometimes abbreviated as "batteries"). Battery capacity gradually decreases with use (repeated charging and discharging). One possible cause of capacity degradation is graphite degradation. To mitigate graphite degradation, a method of coating graphite with amorphous carbon has been proposed. It is expected that amorphous carbon will reduce graphite degradation by inhibiting direct contact between graphite and the electrolyte.

[0005] Generally, graphite forms secondary particles. Secondary particles are aggregates of primary particles. Amorphous carbon coats the outer surface of the secondary particles. During charging and discharging, graphite repeatedly expands and contracts. Due to the volume change of secondary particles, open pores leading to the interior of the secondary particles can be formed. For example, cracks can occur due to grain boundary delamination between primary particles. Open pores can be formed when cracks occur on the surface of secondary particles. The inner walls of open pores are not coated with amorphous carbon. In open pores, contact between the inner wall (new surface) and the electrolyte can lead to capacity degradation.

[0006] Therefore, this disclosure aims to mitigate capacity degradation. [Means for solving the problem]

[0007] The technical configuration and effects of this disclosure are described below. However, the mechanisms of action described herein include assumptions. The mechanisms of action do not limit the technical scope of this disclosure.

[0008] 1. The negative electrode active material contains graphite, low-crystalline carbon, and carbon black. The graphite forms secondary particles. The secondary particles contain multiple primary particles. Within the secondary particles, low-crystalline carbon adheres to the surface of the primary particles. Carbon black is surrounded by multiple primary particles.

[0009] In the negative electrode active material described in "1" above, carbon black is arranged inside the secondary particles. The presence of carbon black inside the secondary particles can increase the compressive modulus of the secondary particles. In other words, the secondary particles can become harder. This hardening of the secondary particles can reduce the volume change of the secondary particles associated with charging and discharging. This reduction in volume change of the secondary particles is expected to reduce cracking.

[0010] Furthermore, even within the secondary particles, low-crystalline carbon adheres to the surface of the primary particles. Therefore, even if cracks (open pores) occur, it is thought that new surfaces are less likely to form. The synergistic effect of these factors is expected to reduce capacity degradation.

[0011] 2. The negative electrode active material described in "1" above includes secondary particles. In the cross-sectional image of the secondary particles, the secondary particles consist of a central region and a surface region. The surface region surrounds the central region. The surface region extends 0.25D from the surface of the secondary particle in the depth direction of the secondary particle. max It extends to a distant location. 0.25D max This represents 0.25 times the maximum diameter. The maximum diameter represents the distance between the two furthest points on the contour line of the secondary particle. In the central region, low-crystalline carbon is attached to the surface of primary particles. Carbon black is surrounded by multiple primary particles.

[0012] The internal structure of secondary particles can be observed in cross-sectional images of the secondary particles. These cross-sectional images may be, for example, SEM (Scanning Electron Microscope) images.

[0013] Conventionally, carbon black and low-crystalline carbon are mixed after the formation of secondary particles. Hereafter, this manufacturing method will also be referred to as the "conventional method." In the conventional method, it is difficult to place carbon black in the central region of the secondary particles. In the conventional method, it is also difficult to protect the surface of the primary particles with low-crystalline carbon in the central region of the secondary particles.

[0014] The method for producing the negative electrode active material described in "8" below allows for the placement of carbon black and low-crystalline carbon in the central region of the secondary particles. The placement of carbon black in the central region of the secondary particles tends to make the secondary particles harder. Due to the presence of low-crystalline carbon on the surface of the primary particles in the central region, it is expected that capacity degradation will be less likely to occur when cracks occur.

[0015] 3. In the negative electrode active material described in "2" above, closed pores may be formed in at least one of the central region and the surface region. Carbon black may be disposed in the closed pores.

[0016] A "closed pore" refers to a void within a secondary particle that does not lead to the outside of the particle. A void that leads to the outside is called an "open pore." Whether or not a void leads to the outside can be confirmed in a cross-sectional image of the secondary particle. Closed pores are isolated within the secondary particle. In conventional methods, it is difficult to place carbon black in closed pores.

[0017] 4. In the negative electrode active material described in "1" above, closed pores may be formed within the secondary particles. Carbon black may be placed in the closed pores.

[0018] 5. The negative electrode active material described in any one of items "1" to "4" above may contain, for example, 0.1 to 5% carbon black by mass fraction.

[0019] 6. The negative electrode active material described in any one of items "1" to "5" above may contain, for example, 1 to 5% by mass fraction of low-crystalline carbon.

[0020] 7. The non-aqueous electrolyte secondary battery contains the negative electrode active material described in any one of items "1" to "6" above.

[0021] 8. The method for producing the negative electrode active material includes the following (a) and (b). (a) Secondary particles are formed by mixing primary particles containing graphite, a precursor, and carbon black. (b) The precursor is transformed into low-crystalline carbon by heat treatment of the secondary particles.

[0022] During the formation of secondary particles (during the aggregation of primary particles), a precursor of low-crystalline carbon and carbon black are mixed, thereby allowing low-crystalline carbon and carbon black to be arranged inside the secondary particles.

[0023] 9. In the method for producing the negative electrode active material described in "8" above, "a" may include shaping the secondary particles into spheres.

[0024] It is expected that the spheroidization of secondary particles will make it easier for them to encapsulate low-crystalline carbon and carbon black.

[0025] 10. In the method for producing the negative electrode active material described in "8" or "9" above, the primary particles may be, for example, in the form of flakes.

[0026] The flaky nature of the primary particles is expected to facilitate the inclusion of low-crystalline carbon and carbon black in the secondary particles.

[0027] 11. In the method for producing a negative electrode active material described in any one of items "8" to "10" above, the precursor may include, for example, coal tar pitch.

[0028] 12. In the method for producing a negative electrode active material described in any one of items "8" to "11" above, the precursor may have, for example, a softening point of 180°C or lower.

[0029] Because the precursor has a softening point of 180°C or lower, it is expected to exhibit good wettability during heat treatment. During heat treatment, it is expected that the deposition area of ​​low-crystalline carbon will increase as the precursor wets and spreads across the surface of the primary particles.

[0030] Embodiments of the present disclosure (which may be abbreviated as "Embodiments") and examples of the present disclosure (which may be abbreviated as "Examples") are described below. However, these embodiments and examples do not limit the technical scope of the present disclosure. These embodiments and examples are illustrative in all respects. These embodiments and examples are non-limiting. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from these embodiments and examples and combined in any way. [Brief explanation of the drawing]

[0031] [Figure 1] Figure 1 is a conceptual diagram showing the negative electrode active material in this embodiment. [Figure 2] Figure 2 is a conceptual diagram showing the central and surface regions of a secondary particle. [Figure 3] Figure 3 is a schematic flowchart of the method for producing the negative electrode active material in this embodiment. [Figure 4] Figure 4 is a conceptual diagram showing a non-aqueous electrolyte secondary battery in this embodiment. [Figure 5] Figure 5 is a table showing the configuration of the first battery. [Figure 6] Figure 6 is a table showing the configuration of the second battery. [Figure 7] Figure 7 is a table showing the configuration of the third battery. [Figure 8] Figure 8 is a table showing the sample composition and evaluation results. [Modes for carrying out the invention]

[0032] <<Terms and Definitions>> The phrases “compose,” “include,” “have,” and variations thereof (e.g., “composed of,” etc.) are open-ended. Open-ended descriptions may or may not include additional elements in addition to the required elements. The phrase “consist of” is closed-ended. However, even in closed-ended descriptions, additional elements that are usually incidental or irrelevant to the disclosed technology are not excluded. The phrase “substantially consists of…” is semi-closed. Semi-closed descriptions allow for the addition of elements that do not substantially affect the fundamental and novel characteristics of the disclosed technology.

[0033] Expressions such as "may do" and "may be" are used in a permissive sense, meaning "there is a possibility," rather than in an obligatory sense, meaning "it must be done."

[0034] Unless otherwise specified, the order in which the various steps, actions, and operations included in each method are executed is not limited to the order in which they are described. For example, multiple steps may occur simultaneously. For example, multiple steps may occur one after the other.

[0035] "At least one of A and B" includes "A or B" and "A and B". "At least one of A and B" can also be written as "A and / or B".

[0036] Elements expressed in the singular form also include the plural form unless otherwise specified. For example, "particle" includes not only "a single particle" but also "multiple particles (groups of particles)" and "a collection of particles (powder, fine powder)."

[0037] Geometric terms (e.g., "parallel," "perpendicular," "orthogonal," etc.) should not be interpreted strictly. For example, "parallel" may deviate slightly from its strict meaning. Geometric terms may include tolerances, errors, etc., in design, operation, and manufacturing. Dimensional relationships in each diagram may not match actual dimensions. Dimensional relationships (length, width, thickness, etc.) in each diagram may be altered to aid the reader's understanding. Furthermore, some components may be omitted.

[0038] Numerical ranges such as "m~n%" include upper and lower limits unless otherwise specified. That is, "m~n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". Furthermore, a number arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0039] All numerical values ​​are modified by the term "approximately." The term "approximately" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that vary depending on how the disclosed technology is used. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be the average of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. Generally, the reliability of the average value is expected to improve with a larger number of measurements. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors such as those associated with the detection limit of the measuring device.

[0040] The stoichiometric compositional formula shows a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to compounds with a molar ratio of "Al / O = 2 / 3". Unless otherwise specified, "Al2O3" refers to a compound containing Al and O in any compositional ratio. Furthermore, for example, the compound may be doped with trace elements, or some of the Al and O may be substituted with other elements.

[0041] A "derivative" refers to a compound in which a part of the parent compound has been modified by at least one of the following chemical reactions: introduction of substituents, substitution of atoms, oxidation, reduction, and other chemical reactions. The modification may be at one location or multiple locations. The "substituents" may include at least one selected from the group consisting of, for example, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (F, Cl, Br, I, etc.), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphate amide groups, sulfo groups, carboxyl groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. If there are two or more substituents, the substituents may be the same or different. Multiple substituents may be bonded to each other to form a ring.

[0042] The term "copolymer" includes at least one selected from the group consisting of unspecified type, statistical type, random type, alternating type, periodic type, block type, and graft type.

[0043] The crystallinity of the carbon material may be evaluated by the "R value". The R value is obtained by the following formula (F-1). R = I 1360 / I 1580 …(F-1) In the formula, I 1360 represents the intensity of the peak (D band) near 1360 cm -1 in the Raman spectrum of the carbon material. I 1580 represents the intensity of the peak (G band) near 1580 cm -1 in the Raman spectrum of the carbon material. The smaller the R value, the higher the crystallinity is considered to be. "Graphite" may have, for example, an R value less than 0.20, or may have an R value of 0 to 0.15. "Low-crystalline carbon" may have, for example, an R value of 0.20 to 1.00, or may have an R value of 0.40 to 0.80. "Carbon black" may have, for example, an R value exceeding 1.00, or may have an R value of 1.10 to 1.50.

[0044] The crystallinity of the carbon material may be evaluated by the "d 002 value". The d 002 value indicates the average spacing of the (002) plane. The d 002 value can be measured in accordance with "JIS R7651: Method for Measuring Lattice Constant and Crystallite Size of Carbon Materials". "Graphite" may have, for example, a d 002 value of 0.3354 to 0.3385 nm. "Low-crystalline carbon" may have, for example, a d 002 value of 0.3386 to 0.3450 nm. "Carbon black" may have, for example, a d 002 value of 0.3451 to 0.3550 nm.

[0045] The "softening point" of the precursor can be measured by the Metler softening point method (ASTM D3104).

[0046] Regarding other terms, they can be appropriately defined in the following description.

[0047] <<Negative electrode active material>> The negative electrode active material undergoes a negative electrode reaction. The negative electrode active material may be in powder form. The negative electrode active material may have a D50 of, for example, 1-50 μm, 5-30 μm, or 10-25 μm. "D50" indicates the particle size at which the cumulative frequency from the smaller particle size reaches 50% in the volume-based particle size distribution. D50 can be measured by laser diffraction. The sample to be measured is a powder. The negative electrode active material may be, for example, 0.5-5 μm 2 / g, 1-4m 2 / g, or 1.5-3m 2 It may have a BET specific surface area of ​​1 / g. The "BET specific surface area" can be measured by the gas adsorption method (BET single-point method).

[0048] Figure 1 is a conceptual diagram showing the negative electrode active material in this embodiment. The negative electrode active material 5 includes graphite, low-crystalline carbon 3, and carbon black 4. The graphite forms secondary particles 2. The secondary particles 2 contain a plurality of primary particles 1. Inside the secondary particles 2, the low-crystalline carbon 3 is attached to the surface of the primary particles 1. Inside the secondary particles 2, the carbon black 4 is surrounded by the plurality of primary particles 1. The distribution of each carbon material inside the secondary particles 2 can be determined, for example, by TEM (Transmission Electron Microscope) electron diffraction mapping.

[0049] The presence of carbon black 4 inside secondary particle 2 is expected to reduce the volume change of secondary particle 2. This is thought to be because the compressive modulus of secondary particle 2 increases. By reducing the volume change of secondary particle 2, cracks may be reduced. Furthermore, because low-crystallinity carbon 3 adheres to primary particle 1 inside secondary particle 2, even if cracks occur, it is thought that new surfaces are less likely to form.

[0050] Figure 2 is a conceptual diagram showing the central and surface regions of a secondary particle. In a cross-sectional image of secondary particle 2 (e.g., a cross-sectional SEM image), secondary particle 2 consists of a central region 2c and a surface region 2s. The central region 2c and surface region 2s are defined as follows: Maximum diameter (D) of secondary particle 2 max ) is identified. D max D is the distance between the two furthest points on the contour line of secondary particle 2. max The midpoint of the line segment forming the line is considered to be the center (o) of secondary particle 2. The direction from the surface of secondary particle 2 toward the center (o) is the depth direction of secondary particle 2. From the surface of secondary particle 2, the depth direction is 0.25D max The region extending to a distant location is the surface region 2s. 0.25D max D max This represents a 0.25x ratio. The central region 2c is the remainder after removing the surface region 2s from the whole.

[0051] In the central region 2c, low-crystallinity carbon 3 may be attached to the surface of the primary particle 1. In the central region 2c, carbon black 4 may be surrounded by the primary particle 1. The arrangement of low-crystallinity carbon 3 and carbon black 4 in the central region 2c is expected to reduce capacity degradation.

[0052] A "pore" refers to a gap between primary particles 1. Pores may be cavities. Pores may be filled with, for example, low-crystallinity carbon 3 and carbon black 4. The negative electrode active material 5 may have a porosity of, for example, 1-15%, 5-15%, or 10-13%. The "porosity" can be measured by the mercury intrusion method.

[0053] For example, closed pores may be formed in at least one of the central region 2c and the surface region 2s. For example, closed pores may be formed so as to span both the central region 2c and the surface region 2s. Carbon black 4 may be placed in the closed pores. Low-crystalline carbon 3 may be filled in the closed pores. Carbon black 4 and low-crystalline carbon 3 may be filled in the closed pores. Carbon black 4 and low-crystalline carbon 3 may be filled in the closed pores belonging to the surface region 2s. Carbon black 4 and low-crystalline carbon 3 may be filled in the closed pores belonging to the central region 2c. Part of the closed pores may belong to the central region 2c, or all of the closed pores may belong to the central region 2c.

[0054] <Graphite> Graphite is crystalline carbon. Graphite can reversibly store Li in the gaps between its hexagonal carbon network faces. Graphite may include, for example, at least one selected from the group consisting of natural graphite and artificial graphite. Natural graphite may include, for example, at least one selected from the group consisting of flake graphite, massive graphite, and earthy graphite.

[0055] <Carbon Black> Carbon black 4 is amorphous carbon. Carbon black 4 is surrounded by multiple primary particles 1. For example, carbon black 4 may be located at the grain boundary of two primary particles 1. Carbon black 4 may be located in a closed pore surrounded by three or more primary particles 1, or in an open pore surrounded by three or more primary particles 1. Carbon black 4 may adhere to the surface of the primary particles 1. Carbon black 4 may form aggregates or agglomerates. Carbon black 4 has a size smaller than the primary particles 1. The maximum Ferret diameter of carbon black 4 may be, for example, 0.01 to 1 μm, or 0.1 to 1 μm.

[0056] Carbon black 4 can be formed by any method. Carbon black 4 may include, for example, at least one selected from the group consisting of acetylene black, lamp black, thermal black, furnace black, and channel black.

[0057] The negative electrode active material 5 may contain, for example, 0.1 to 5% carbon black 4 by mass fraction. The mass fraction of carbon black 4 may be, for example, 0.5% or more, 1% or more, or 2% or more. The mass fraction of carbon black 4 may be, for example, 4% or less, 3% or less, or 2% or less. When the mass fraction of carbon black 4 is 2 to 5%, capacity degradation tends to be small.

[0058] <Low-crystalline carbon> Low-crystallinity carbon 3 exhibits crystallinity between graphite and amorphous carbon (carbon black 4). Low-crystallinity carbon 3 is attached to the surface of primary particles 1. Low-crystallinity carbon 3 may be in the form of a film. Low-crystallinity carbon 3 may coat the surface of primary particles 1. Low-crystallinity carbon 3 may coat a part of primary particles 1 or the entire primary particles 1. Low-crystallinity carbon 3 may also coat the outer surface of secondary particles 2. Low-crystallinity carbon 3 may coat a part of the outer surface or the entire outer surface. Low-crystallinity carbon 3 may be derived from at least one selected from the group consisting of coal tar pitch, mesophase pitch, and petroleum pitch, for example.

[0059] <Other ingredients> The negative electrode active material 5 may contain a dopant. The dopant may contain, for example, at least one selected from the group consisting of B, N, P, Li, and Ca. The amount added may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in mole fraction.

[0060] A dissimilar material may be attached to the outer surface of the secondary particle 2. The outer surface of the secondary particle 2 may be coated with a dissimilar material. The dissimilar material may include, for example, at least one selected from the group consisting of P, W, Al, and O. Examples of dissimilar materials include Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO3. 3、 It may also include at least one selected from the group consisting of Li3PO4.

[0061] <<Method for manufacturing negative electrode active material>> Figure 3 is a schematic flowchart of the method for producing the negative electrode active material in this embodiment. Hereinafter, "the method for producing the negative electrode active material in this embodiment" may be abbreviated as "this manufacturing method". This manufacturing method includes "(a) formation of secondary particles" and "(b) heat treatment".

[0062] <(a) Formation of secondary particles> This manufacturing method involves forming secondary particles by mixing primary particles, a precursor, and carbon black.

[0063] In this manufacturing method, any mixing apparatus, particle compounding apparatus, etc., can be used. For example, secondary particles may be sphericalized at the same time as their formation. For example, secondary particles may be sphericalized by a high-speed airflow impact method, etc. During the process of spheroidizing the secondary particles, it is expected that low-crystallinity carbon and carbon black will be incorporated into the secondary particles. For example, the formation of secondary particles and the spheroidizing of secondary particles may proceed substantially simultaneously. For example, the spheroidizing treatment may be performed after the formation of secondary particles.

[0064] The primary particles contain graphite. The primary particles may contain, for example, flaky graphite. The flaky nature of the primary particles is expected to facilitate the encapsulation of carbon black within the primary particles during the formation of secondary particles. By being encapsulated within the primary particles, the carbon black can be arranged in closed pores. The primary particles may have, for example, any particle size. The primary particles may have a D50 of 1 to 50 μm, a D50 of 5 to 25 μm, or a D50 of 10 to 20 μm.

[0065] When the precursor is heated, crystallization may proceed, and low-crystalline carbon may be formed. The precursor may adhere to the surface of primary particles. The precursor may coat the surface of primary particles. The precursor may include at least one selected from the group consisting of coal tar pitch, mesophase pitch, and petroleum pitch. The precursor may have a softening point of, for example, 250°C or less, 180°C or less, or 120°C or less. When the softening point is 180°C or less, the wettability of the precursor tends to be good during heat treatment. The softening point may be, for example, 50°C or more, or 100°C or more.

[0066] Carbon black has catalytic properties. The catalytic action of carbon black can accelerate the crystallization of precursors. The carbon black may have an oil absorption capacity of, for example, 20-200 ml / 100g. Oil absorption capacity is an indicator of the structure size. "Oil absorption capacity" can be measured in accordance with "JIS K6217-4: Basic properties of carbon black for rubber, Part 4: Method for determining oil absorption capacity". Dibutyl phthalate (DBP) is used as the oil. The carbon black may have an oil absorption capacity of, for example, 50-150 ml / 100g, or 50-100 ml / 100g.

[0067] (b) Heat treatment This manufacturing method involves heat-treating secondary particles to transform the precursor into low-crystalline carbon. The negative electrode active material can be completed by generating low-crystalline carbon.

[0068] The heat treatment may be carried out, for example, under an inert atmosphere. For example, the heat treatment may be carried out under an argon atmosphere. The treatment temperature may be, for example, 500-1500°C, 800-1200°C, or 900-1100°C. The treatment time may be, for example, 0.5-5 hours, 0.5-3 hours, or 0.5-1 hour.

[0069] <<Nonaqueous electrolyte secondary battery>> Figure 4 is a conceptual diagram showing a non-aqueous electrolyte secondary battery in this embodiment. The battery 100 includes a power generation element 50 and an electrolyte (not shown).

[0070] <Exterior> The battery 100 may include an outer casing (not shown). The outer casing may house the power generation element 50 and the electrolyte. The outer casing can have any form. For example, the outer casing may be a metal case, or a pouch made of metal foil laminate film, etc. The case may have any shape. For example, the case may be cylindrical, rectangular, flat, coin-shaped, etc. The outer casing may contain, for example, Al. The outer casing may house, for example, one power generation element 50, or multiple power generation elements 50. The multiple power generation elements 50 may form, for example, a series circuit or a parallel circuit. Within the outer casing, the multiple power generation elements 50 may be stacked in the thickness direction of the battery 100.

[0071] <Power generation elements> The power generation element 50 may also be referred to as an "electrode group," "electrode body," etc. The power generation element 50 includes a positive electrode 10 and a negative electrode 20. The power generation element 50 may further include a separator 30. The separator 30 is placed between the positive electrode 10 and the negative electrode 20. The power generation element 50 can have any form. The power generation element 50 may be, for example, a laminated type. For example, the power generation element 50 may be formed by alternately stacking the positive electrode 10 and the negative electrode 20 with a separator 30 in between. The power generation element 50 may be, for example, a wound type. For example, a laminate may be formed by stacking a strip-shaped positive electrode 10, a strip-shaped separator 30, and a strip-shaped negative electrode 20. The power generation element 50 may be formed by winding the laminate in a spiral shape. The wound type power generation element 50 may be formed into a flat shape after winding.

[0072] <Negative electrode> The negative electrode 20 may be, for example, in the form of a sheet. The negative electrode 20 may include, for example, a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 is conductive. The negative electrode current collector 21 supports the negative electrode active material layer 22. The negative electrode current collector 21 may be, for example, in the form of a sheet. The negative electrode current collector 21 may have a thickness of, for example, 5 to 50 μm. The negative electrode current collector 21 may include, for example, a metal foil. The negative electrode current collector 21 may include, for example, at least one selected from the group consisting of Cu, Ni, Fe, Zn, Pb, Ag, and Au. The negative electrode current collector 21 may include, for example, a Cu foil, a Cu alloy foil, etc.

[0073] The negative electrode active material layer 22 is located on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be located on only one side of the negative electrode current collector 21. The negative electrode active material layer 22 may be located on both the front and back surfaces of the negative electrode current collector 21. The negative electrode active material layer 22 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The negative electrode active material layer 22 contains negative electrode active material. The negative electrode active material layer 22 may further contain, for example, a conductive material and a binder.

[0074] Conductive materials The conductive material can form electron conduction paths within the negative electrode active material layer 22. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of negative electrode active material. The conductive material may contain any components. For example, the conductive material may contain at least one selected from the group consisting of acetylene black (AB), Ketjenblack (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), and graphene flakes (GF). The CNTs may contain at least one selected from the group consisting of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0075] Binder The binder can fix the negative electrode active material layer 22 to the negative electrode current collector 21. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of negative electrode active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of styrene-butadiene rubber (SBR), acrylate-butadiene rubber (ABR), sodium alginate, carboxymethylcellulose (CMC-H, CMC-Na, CMC-Li, CMC-NH4, etc.), polyacrylic acid (PAA-H, PAA-Na, PAA-Li, etc.), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), acrylic resin (acrylic acid ester copolymer), methacrylic resin (methacrylic acid ester copolymer), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and derivatives thereof. For example, "CMC-Na" indicates the sodium salt of CMC. For example, "CMC-H" indicates the acidic form of CMC. The same applies to "PAA-Na," etc.

[0076] Other ingredients The negative electrode active material layer 22 may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, or the like. The negative electrode active material layer 22 may contain, for example, a layered silicate (smectite, montmorillonite, bentonite, hectorite, etc.), an inorganic filler (solid alumina, hollow silica, boehmite, etc.), a polysiloxane compound, or the like.

[0077] 《Second Negative Electrode Active Material》 The negative electrode active material layer 22 contains the negative electrode active material according to this embodiment. Hereinafter, for convenience, the negative electrode active material according to this embodiment is referred to as the "first negative electrode active material". The negative electrode active material layer 22 may further contain a second negative electrode active material in addition to the first negative electrode active material. The mixing ratio (mass ratio) of the first negative electrode active material and the second negative electrode active material may be, for example, "first negative electrode active material / second negative electrode active material = 1 / 9 to 9 / 1", "first negative electrode active material / second negative electrode active material = 2 / 8 to 8 / 2", or "first negative electrode active material / second negative electrode active material = 3 / 7 to 7 / 3".

[0078] 〈Carbon-Based Active Material〉 The second negative electrode active material may contain a carbon-based active material. The second negative electrode active material may contain, for example, at least one selected from the group consisting of soft carbon and hard carbon.

[0079] 〈Alloy-Based Active Material〉 The second negative electrode active material may contain an alloy-based active material. The second negative electrode active material may contain, for example, at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloy, Sn, SnO, and Sn-based alloy.

[0080] SiO may be represented, for example, by the following formula (A-1).

[0081] SiO x …(A-1) In the formula, the relationship of 0 < x < 2 is satisfied.

[0082] In equation (A-1) above, x may satisfy, for example, 0.5 ≤ x ≤ 1.5 or 0.8 ≤ x ≤ 1.2.

[0083] The Li silicate may include, for example, at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The second negative electrode active material may include, for example, a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1", "Si / Li silicate = 2 / 8 to 8 / 2", "Si / Li silicate = 3 / 7 to 7 / 3", or "Si / Li silicate = 4 / 6 to 6 / 4".

[0084] The alloying active material (Si, SiO, etc.) may contain additives. The additives may be, for example, substitutional solid solution atoms or interstitial solid solution atoms. The additives may also be deposits that adhere to the surface of the alloying active material. The deposits may be, for example, elements, oxides, carbides, nitrides, halides, etc. The amount of additive may be, for example, 0.01-5%, 0.1-3%, or 0.1-1% in mole fraction. The additives may include, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg and Na. For example, Mg silicate, Na silicate, etc. may be formed. For example, SiO may have boron oxide (e.g., B2O3) or yttrium oxide (e.g., Y2O3) added to it.

[0085] <Si-C composite material> The second negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be called a "Si-C composite material". For example, Si nanoparticles may be dispersed within carbon particles. For example, Si nanoparticles may be dispersed within graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon).

[0086] <Other active materials> The second negative electrode active material is, for example, Li metal, Li-based alloy, and Li4Ti5O 12 It may include at least one selected from the group consisting of the following.

[0087] <Positive electrode> The positive electrode 10 may be, for example, in the form of a sheet. The positive electrode 10 may include, for example, a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 is conductive. The positive electrode current collector 11 supports the positive electrode active material layer 12. The positive electrode current collector 11 may be, for example, in the form of a sheet. The positive electrode current collector 11 may have a thickness of, for example, 5 to 50 μm. The positive electrode current collector 11 may include, for example, a metal foil. The positive electrode current collector 11 may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The positive electrode current collector 11 may include, for example, Al foil, Al alloy foil, Ti foil, stainless steel (SUS) foil, etc.

[0088] An intermediate layer (not shown) may be formed between the positive electrode current collector 11 and the positive electrode active material layer 12. The intermediate layer does not contain positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, a binder, etc. The conductive material may contain, for example, carbon black. The insulating material may contain, for example, alumina, boehmite, aluminum hydroxide, etc. The binder may contain, for example, PVdF, etc.

[0089] The positive electrode active material layer 12 is located on the surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be located on only one side of the positive electrode current collector 11. The positive electrode active material layer 12 may be located on both the front and back surfaces of the positive electrode current collector 11. The positive electrode active material layer 12 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer 12 contains positive electrode active material. The positive electrode active material layer 12 may further contain, for example, a conductive material and a binder.

[0090] Conductive materials The conductive material can form electron conduction paths within the positive electrode active material layer 12. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The conductive material may contain any components. For example, the conductive material may contain at least one selected from the group consisting of graphite, AB, Ketjenblack, VGCF, CNT, and GF.

[0091] Binder The binder can fix the positive electrode active material layer 12 to the positive electrode current collector 11. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of positive electrode active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of PVdF, vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), PTFE, CMC, PAA, PVA, PVP, polyoxyethylene alkyl ether, and derivatives thereof.

[0092] Other ingredients The positive electrode active material layer 12 may further contain, for example, inorganic fillers, organic fillers, solid electrolytes, surface modifiers, dispersants, lubricants, flame retardants, protective agents, fluxes, coupling agents, adsorbents, etc. The positive electrode active material layer 12 may also contain, for example, polyoxyethylene allylphenyl ether phosphate, zeolite, silane coupling agents, MoS2, WO3, etc.

[0093] 《Cathode active material》 The positive electrode active material may be, for example, particulate. The positive electrode active material may have a D50 of, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm. The positive electrode active material may contain any component. The positive electrode active material may contain, for example, a transition metal oxide, a polyanion compound, or the like. Within one particle (positive electrode active material), the composition may be uniform or non-uniform. For example, the composition may vary from the surface to the center of the particle. The composition may change continuously or discontinuously (stepwise).

[0094] 〈Transition metal oxide: Space group R-3m〉 The transition metal oxide may have any crystal structure. The transition metal oxide may contain, for example, a crystal structure belonging to the space group R-3m or the like. For example, a compound represented by the general formula "LiMO2" may have a crystal structure belonging to the space group R-3m. The transition metal oxide may be represented, for example, by the following formula (C-1).

[0095] Li 1-a Ni x M 1-x O2…(C-1) In the formula, the relationship of -0.5 ≦ a ≦ 0.5 and ≦ x ≦ 1 is satisfied. M may contain at least one selected from the group consisting of Co, Mn, and Al, for example.

[0096] In the above formula (C-1), x may satisfy the relationship of, for example, 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1. a may satisfy the relationship of, for example, -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1.

[0097] The transition metal oxide is, for example, LiCoO2, LiMnO2, LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn0.1 It may contain at least one selected from the group consisting of O2 and LiNiO2.

[0098] 〈NCM〉 The transition metal oxide may be represented, for example, by the following formula (C-2). The compound represented by the following formula (C-2) may also be referred to as "NCM".

[0099] Li 1-a Ni x Co y Mn z O2…(C-2) In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0100] In the above formula (C-2), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1.

[0101] In the above formula (C-2), y may satisfy, for example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1.

[0102] In the above formula (C-2), z may satisfy, for example, the relationship of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦?0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1.

[0103] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0104] 〈NCA〉 The transition metal oxide may be represented, for example, by the following formula (C-3). The compound represented by the following formula (C-3) may also be referred to as "NCA".

[0105] Li 1-a Ni x Co y Al z O2…(C-3) In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0106] In the above formula (C-3), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1.

[0107] In the above formula (C-3), y may satisfy, for example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1.

[0108] In the above formula (C-3), z may satisfy, for example, the relationship of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1.

[0109] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O², LiNi 0.8 Co 0.1 Al 0.1 O², LiNi 0.8 Co 0.17 Al 0.03 O², LiNi 0.8 Co 0.15 Al 0.05 O², and, LiNi 0.9 Co 0.05 Al 0.05 may include at least one selected from the group consisting of O².

[0110] 〈Multi-component system〉 The positive electrode active material may contain, for example, two or more NCMs. The positive electrode active material may contain, for example, NCM(0.6≦x) and NCM(x<0.6). "NCM(0.6≦x)" refers to a compound in formula (C-2) above where x (Ni ratio) is 0.6 or more. NCM(0.6≦x) may also be called, for example, "high nickel material". NCM(0.6≦x) is, for example, LiNi 0.8 Co 0.1 Mn 0.1 Contains O2, etc. "NCM(x<0.6)" indicates a compound in the above formula (C-2) where x (Ni ratio) is less than 0.6. NCM(x<0.6) is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Contains O2, etc. The mixing ratio (mass ratio) of NCM (0.6≦x) and NCM (x<0.6) may be, for example, "NCM(0.6≦x) / NCM(x<0.6)=9 / 1~1 / 9", "NCM(0.6≦x) / NCM(x<0.6)=9 / 1~4 / 6", or "NCM(0.6≦x) / NCM(x<0.6)=9 / 1~3 / 7".

[0111] The positive electrode active material may contain, for example, NCA and NCM. The mixing ratio (mass ratio) of NCA to NCM may be, for example, "NCA / NCM = 9 / 1 to 1 / 9", "NCA / NCM = 9 / 1 to 4 / 6", or "NCA / NCM = 9 / 1 to 3 / 7". The Ni ratio between NCA and NCM may be the same or different. The Ni ratio of NCA may be higher than that of NCM. The Ni ratio of NCA may be lower than that of NCM.

[0112] <Transition metal oxides: space group C2 / m> The transition metal oxide may include, for example, a crystal structure belonging to the space group C2 / m. The transition metal oxide may also be represented by, for example, the following formula (C-4).

[0113] Li2MO3…(C-4) In the formula, M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0114] The positive electrode active material may include, for example, a mixture of LiMO2 (space group R-3m) and Li2MO3 (space group C2 / m). The positive electrode active material may also include, for example, a solid solution of LiMO2 and Li2MO3 (Li2MO3-LiMO2).

[0115] <Transition metal oxides: space group Fd-3m> The transition metal oxide may include, for example, a crystal structure belonging to the space group Fd-3m. The transition metal oxide may also be represented by, for example, the following formula (C-5). LiMn 2-x M x O4…(C-5) The relationship 0 ≤ x ≤ 2 is satisfied in the equation. M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn.

[0116] LiM2O4 (space group Fd-3m) is, for example, LiMn2O4 and LiMn 1.5 Ni 0.5 The positive electrode active material may contain at least one selected from the group consisting of O4. The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m) may be, for example, "LiMO2 / LiM2O4 = 9 / 1 to 9 / 1", "LiMO2 / LiM2O4 = 9 / 1 to 5 / 5", or "LiMO2 / LiM2O4 = 9 / 1 to 7 / 3".

[0117] <Polyanionic compounds> The polyanionic compound may contain, for example, phosphates (e.g., LiFePO4), silicates, borates, etc. The polyanionic compound may also be represented by, for example, the following formulas (C-6) to (C-9).

[0118] LiMPO4…(C-6) Li 2-xMPO4F …(C-7) Li2MSiO4…(C-8) LiMBO3…(C-9) In equations (C-6) to (C-9) above, M may include at least one selected from the group consisting of, for example, Fe, Mn, and Co. In equation (C-7) above, for example, the relationship 0 ≤ x ≤ 2 may be satisfied.

[0119] The positive electrode active material may, for example, contain a mixture of LiMO2 (space group R-3m) and a polyanionic compound. The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and the polyanionic compound may be, for example, "LiMO2 / polyanionic compound = 9 / 1 to 9 / 1", "LiMO2 / polyanionic compound = 9 / 1 to 5 / 5", or "LiMO2 / polyanionic compound = 9 / 1 to 7 / 3".

[0120] <Dopant> A dopant may be added to the positive electrode active material. The dopant may be diffused throughout the particle or distributed locally. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The amount of dopant added (mole fraction relative to the total positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One type of dopant may be added, or two or more types of dopants may be added. Two or more types of dopants may form a complex.

[0121] The dopant may include, for example, at least one selected from the group consisting of B, C, N, halogens, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0122] For example, NCA may contain the following combinations: "Zr, Mg, W, Sm", "Ti, Mn, Nb, Si, Mo", or "Er, Mg".

[0123] For example, Ti may be added to NCM. For example, the combination of "Zr, W", the combination of "Si, W", or the combination of "Zr, W, Al, Ti, Co" may be added to NCM.

[0124] <Surface coating> The positive electrode 10 may contain composite particles. The composite particles include core particles and a coating layer. The core particles contain a positive electrode active material. The coating layer covers at least a portion of the surface of the core particles. The coating layer may have a thickness of, for example, 1-3000 nm, 5-2000 nm, 10-1000 nm, 10-100 nm, or 10-50 nm. The thickness of the coating layer can be measured, for example, in an SEM image of the particle cross-section. That is, the sample is prepared by embedding the composite particles in a resin material. The sample is cross-sectionalized using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, "Product Name ArBlade(Registered Trademark) 5000" (or an equivalent product) may be used. The cross-section of the sample is observed by SEM. For example, an SEM device manufactured by Hitachi High-Technologies Corporation, "Product Name SU8030" (or an equivalent product) may be used. For each of the 10 composite particles, the thickness of the coating layer is measured in 20 fields of view. The arithmetic mean of the thicknesses at a total of 200 locations is used.

[0125] The percentage of the core particle surface covered by the coating layer is also called the "coverage rate." The coverage rate may be, for example, 1% or more, 10% or more, 30% or more, 50% or more, or 70% or more. The coverage rate may also be, for example, 100% or less, 90% or less, or 80% or less.

[0126] Coverage can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). For example, an XPS instrument manufactured by ULVAC-PHI, "product name PHI X-tool" (or equivalent) may be used. A sample powder consisting of composite particles is placed in the XPS. Narrow scan analysis is performed. The measurement data is processed by analysis software. For example, analysis software manufactured by ULVAC-PHI, "product name MulTiPak" (or equivalent) may be used. By analyzing the measurement data, multiple elements are detected. The ratio of each detected element is determined from the area of ​​each peak. Coverage is calculated using the following formula (F-2).

[0127] θ = {I1 / (I0+I1)} × 100 …(F-2) θ: Coverage rate [%] I0: Ratio of elements derived from core particles I1: Ratio of elements derived from the coating layer For example, if the core particles contain NCM, I0 represents the total elemental ratio of "Ni, Co, Mn". For example, if the core particles contain NCA, I0 represents the total elemental ratio of "Ni, Co, Al". For example, if the coating layer contains P and B, I1 represents the total elemental ratio of "P, B".

[0128] The coating layer may contain any components. For example, the coating layer may contain elements, organic substances, inorganic acid salts, organic acid salts, hydroxides, oxides, carbides, nitrides, sulfides, halides, etc. The coating layer may contain, for example, B, Al, W, Zr, Ti, Co, F, lithium compounds (e.g., Li2CO3, LiHCO3, LiOH, Li2O, etc.), tungsten oxide (e.g., WO3, etc.), titanium oxide (e.g., TiO2, etc.), zirconium oxide (e.g., ZrO2), boron oxide, boron phosphate (e.g., BPO4, etc.), aluminum oxide (e.g., Al2O3, etc.), boehmite, aluminum hydroxide, phosphates (e.g., Li3PO4, etc.). 4、(NH4)3PO4, AlPO4), borates (e.g., Li2B4O7, LiBO3, etc.), polyacrylates (Li salts, Na salts, NH4 salts, etc.), acetates (e.g., Li salts, etc.), CMC (CMC-Na, CMC-Li, CMC-NH4, etc.), LiNbO 3、 It may also contain Li2TiO3 and at least one selected from the group consisting of Li-containing halides (e.g., LiAlCl4, LiTiAlF6, LiYBr6, LiYCl6, etc.).

[0129] <Hollow particles / Solid particles> "Hollow particles" refer to secondary particles in which, in a cross-sectional image, the area of ​​the central cavity accounts for 30% or more of the total cross-sectional area of ​​the particle. The proportion of the cavity in hollow particles may be, for example, 40% or more, 50% or more, or 60% or more. "Solid particles" refer to secondary particles in which, in a cross-sectional image of the particle, the area of ​​the central cavity accounts for less than 30% of the total cross-sectional area of ​​the particle. The proportion of the cavity in solid particles may be, for example, 20% or less, 10% or less, or 5% or less. The positive electrode active material may be hollow particles or solid particles. A mixture of hollow particles and solid particles may be used. The mixing ratio (mass ratio) of hollow particles to solid particles may be, for example, "hollow particles / solid particles = 1 / 9 to 9 / 1", "hollow particles / solid particles = 2 / 8 to 8 / 2", "hollow particles / solid particles = 3 / 7 to 7 / 3", or "hollow particles / solid particles = 4 / 6 to 6 / 4".

[0130] <Large particles / Small particles> "Electrode active material" is a general term for positive electrode active material and negative electrode active material. The electrode active material may, for example, have a unimodal particle size distribution (number-based). The electrode active material may, for example, have a multimodal particle size distribution. The electrode active material may, for example, have a bimodal particle size distribution. That is, the electrode active material may contain large particles and small particles. When the particle size distribution is bimodal, the particle size corresponding to the peak top of the larger particle size is the particle size of the large particle (d L ) is considered to be the particle size of the smallest particle (d S ) is considered to be the particle size ratio (dL / d S ) may be, for example, 2-10, 2-5, or 2-4. d L For example, it may be 8-20 μm or 8-15 μm. S For example, the thickness may be 1 to 10 μm, or 1 to 5 μm.

[0131] For example, the particle size distribution may be subjected to peak separation processing using waveform analysis software. Peak area (S) originating from large particles. L ) and the peak area (S) originating from small particles S The ratio to ) is, for example, "S L / S S =1 / 9~9 / 1", S L / S S =5 / 5~9 / 1" or "S L / S S It could also be "=7 / 3~9 / 1".

[0132] The particle size distribution based on particle count is measured by microscopy. Multiple cross-sectional samples are taken from the electrode active material layer. The cross-sectional samples may include, for example, a cross-section perpendicular to the surface of the electrode active material layer. The surface to be observed is cleaned, for example, by ion milling. The cross-sectional samples are observed using a scanning electron microscope (SEM). The observation magnification is adjusted so that 10 to 100 particles are contained within the observation field. The Ferret diameter of all particles in the image is measured. The "Ferret diameter" indicates the distance between the two furthest points on the contour line of the particle. By observing multiple cross-sectional samples, a total of 1000 or more Ferret diameters are obtained. From these 1000 or more Ferret diameters, a particle size distribution based on particle count is created.

[0133] A bimodal particle size distribution can be formed by mixing two types of particles. The two types of particles have different particle size distributions. For example, the two types of particles may have different D50s. "D50" refers to the particle size at which the cumulative frequency from the smaller particle size side reaches 50% in the volume-based particle size distribution. D50 can be measured by laser diffraction. The sample to be measured is a powder. For example, the large particles may have a D50 of 8-20 μm or 8-15 μm. For example, the small particles may have a D50 of 1-10 μm or 1-5 μm. The ratio of the D50 of the large particles to the D50 of the small particles may be, for example, 2-10, 2-5, or 2-4. The mixing ratio (mass ratio) of large particles to small particles may be, for example, "large particles / small particles = 1 / 9 to 9 / 1", "large particles / small particles = 5 / 5 to 9 / 1", or "large particles / small particles = 7 / 3 to 9 / 1".

[0134] The large particles and small particles may have the same composition or different compositions. For example, the large particles may be NCA and the small particles may be NCM. For example, the large particles may be NCM (0.6 ≤ x) and the small particles may be NCM (x < 0.6).

[0135] <Electrolyte> The electrolyte is a Li-ion conductor. The electrolyte may be a liquid electrolyte, a gel electrolyte, or a solid electrolyte.

[0136] 《Liquid electrolyte》 A liquid electrolyte may, for example, include an electrolyte solution. The electrolyte solution contains a solvent and a solute.

[0137] <Solute> The concentration of the solute may be, for example, 0.5-1 mol / L, 1-1.5 mol / L, 1.5-2 mol / L, 2-2.5 mol / L, or 2.5-3 mol / L. The solute contains a supporting salt (Li salt). The solute may also contain, for example, inorganic acid salts, imide salts, oxalate complexes, halides, etc. The solute may also contain, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0138] <Carbonate-based solvents> The electrolyte may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, cyclic carbonates, linear carbonates, fluorinated carbonates, etc. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0139] The solvent may contain cyclic carbonates (EC, PC, FEC, etc.) and linear carbonates (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to linear carbonates may be, for example, "cyclic carbonate / linear carbonate = 1 / 9 to 4 / 6", "cyclic carbonate / linear carbonate = 2 / 8 to 3 / 7", or "cyclic carbonate / linear carbonate = 3 / 7 to 4 / 6".

[0140] The solvent may contain cyclic carbonates (EC, PC, etc.) and fluorinated cyclic carbonates (FEC, etc.). The mixing ratio (volume ratio) of cyclic carbonates to fluorinated cyclic carbonates may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3", or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9".

[0141] The solvent may include, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy the relationship expressed by, for example, the following formula (E-1).

[0142] V EC +V FEC +V EMC +V DMC +V DEC =10 …(E-1) In the formula, V EC , V FEC , V EMC , V DMC , V DEC These represent the volume ratios of EC, FEC, EMC, DMC, and DEC, respectively. 1 ≤ V EC ≤4, 0 ≤V FEC ≤3,V EC +V FEC ≤4, 0≦V EMC ≤9, 0 ≤V DMC ≤9, 0 ≤V DEC ≤9,6≦V EMC +V DMC +V DEC ≤9 The relationship is satisfied.

[0143] In the above formula (E-1), For example, 1 ≤ V EC ≤ 2, or 2 ≤ V EC The condition ≤ 3 may also be satisfied. For example, 1 ≤ V FEC≤ 2, or 2 ≤ V FEC The condition ≤ 4 may also be satisfied. For example, 3 ≤ V EMC ≤4, or 6 ≤V EMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DMC ≤4, or 6 ≤V DMC The condition ≤ 8 may also be satisfied. For example, 3 ≤ V DEC ≤4, or 6 ≤V DEC The condition ≤ 8 may also be satisfied.

[0144] The solvent may have compositions such as "EC / EMC=3 / 7", "EC / DMC=3 / 7", "EC / FEC / DEC=1 / 2 / 7", "EC / DMC / EMC=3 / 4 / 3", "EC / DMC / EMC=3 / 3 / 4", "EC / FEC / DMC / EMC=2 / 1 / 4 / 3", "EC / FEC / DMC / EMC=1 / 2 / 4 / 3", "EC / FEC / DMC / EMC=2 / 1 / 3 / 4", and "EC / FEC / DMC / EMC=1 / 2 / 3 / 4" in volume ratio.

[0145] <Ether-based solvents> The electrolyte may contain an ether-based solvent. The electrolyte may contain, for example, at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylglycyle, triglycyle, tetraglycyle, and derivatives thereof.

[0146] <Additives> The electrolyte may contain any additives. The amount of additive (mass fraction of the total electrolyte) may be, for example, 0.01-5%, 0.05-3%, or 0.1-1%. The additives may include, for example, SEI (Solid Electrolyte Interphase) formation promoters, SEI formation inhibitors, gas generators, overcharge inhibitors, flame retardants, antioxidants, electrode protectants, surfactants, etc.

[0147] Additives include, for example, vinylene carbonate (VC), vinylethylene carbonate (VEC), 1,3-propanesultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propanesultone (PS), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters [e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.], fluorobenzenes [e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluene (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methyl benzothiazole) It may contain at least one selected from the group consisting of nzothiazole, tetrathiafluban, etc., nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0148] The components mentioned above may be used as solutes and solvents, or as trace components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0149] <Ionic liquid> The liquid electrolyte may include an ionic liquid. The liquid electrolyte may include, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0150] Gel electrolytes The gel electrolyte may contain a liquid electrolyte and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, PAN, PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0151] 《Solid electrolyte》 The solid electrolyte may be, for example, particulate. The solid electrolyte may have a D50 of, for example, 0.1 to 3 μm. The D50 of the solid electrolyte may be, for example, 1 μm or less, or 0.5 μm or less. The solid electrolyte may include, for example, at least one selected from the group consisting of sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and hydride solid electrolytes. The sulfide solid electrolyte may be, for example, glass ceramics or argyrodite. Examples of sulfide solid electrolytes include LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, Li4P2S6, and Li7P3S. 11 It may contain at least one selected from the group consisting of Li3PS4 and Li6PS5X (X = Cl, Br, I). For example, "LiI-LiBr-Li3PS4" refers to a substance synthesized by mixing LiI, LiBr, and Li3PS4 in any molar ratio (amount of substance ratio).

[0152] If the battery 100 is an all-solid-state battery, a solid electrolyte layer may be placed in place of the separator 30 (described later). The solid electrolyte layer may contain, for example, a solid electrolyte and a binder. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of solid electrolyte. The binder may contain, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, ABR, and SBR. The solid electrolyte layer may have a single-layer structure or a multilayer structure. In a multilayer structure, the solid electrolytes contained in each layer may be different from each other.

[0153] <Separator> The separator 30 can separate the positive electrode 10 from the negative electrode 20. The separator 30 has electrical insulating properties. The separator 30 may include at least one selected from the group consisting of, for example, a resin film, an inorganic particle layer, and an organic particle layer. For example, the separator 30 may include a resin film and an inorganic particle layer.

[0154] 《Resin film》 The resin film is porous. The resin film may include, for example, a microporous membrane, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a mesh-like manner. Pores are formed in the gaps of the resin skeleton. The resin film can permeate electrolytes. The resin film may have, for example, an average pore diameter of 1 μm or less. The resin film may have, for example, an average pore diameter of 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore diameter" can be measured by the mercury intrusion method. The resin film is subjected to, for example, 50 to 250 s / 100 cm. 3 It may have a Gaulle value. The "Garle value" can be measured by the Gaulle test method.

[0155] The resin film may contain at least one selected from the group consisting of, for example, olefin resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, acrylic resins, and polyester resins. The resin film may also contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamide-imide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film can be formed, for example, by a stretching method, a phase separation method, or the like. The resin film may have a thickness of, for example, 5 to 50 μm or 10 to 25 μm.

[0156] The resin film may have, for example, a single-layer structure. The resin film may consist of, for example, a PE layer. The framework of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multilayer structure. The resin film may include, for example, a PP layer and a PE layer. The framework of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0157] 《Inorganic particle layer》 The inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film, or on both the front and back surfaces. The inorganic particle layer may be formed on the surface facing the positive electrode 10, or on the surface facing the negative electrode 20. The inorganic particle layer may be formed on the surface of the positive electrode 10, or on the surface of the negative electrode 20.

[0158] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles may also be called "inorganic fillers". Pores are formed in the gaps between the inorganic particles. The inorganic particle layer may have a thickness of, for example, 0.5 to 10 μm or 1 to 5 μm. The inorganic particles may contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also called an "HRL (Heat Resistance Layer)". The inorganic particles may contain at least one selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, and silica. The inorganic particles may have any shape. For example, the inorganic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The inorganic particles may have a D50 of, for example, 0.1 to 10 μm or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may include, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluororesins, aromatic polyether resins, and liquid crystal polyester resins.

[0159] 《Organic particle layer》 The separator 30 may include, for example, an organic particle layer. The separator 30 may include, for example, an organic particle layer instead of a resin film. The separator 30 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 30 may include both a resin film and an organic particle layer. The separator 30 may include both an inorganic particle layer and an organic particle layer. The separator 30 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0160] The organic particle layer may have a thickness of, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer contains organic particles. The organic particles may also be called "organic fillers". The organic particles may contain heat-resistant materials. The organic particles may contain at least one selected from the group consisting of, for example, PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be spherical, rod-shaped, plate-shaped, fibrous, etc. The organic particles may have a D50 of, for example, 0.1 to 10 μm or 0.5 to 3 μm.

[0161] The separator 30 may include, for example, a mixed layer. The mixed layer may contain both inorganic and organic particles.

[0162] <Battery configuration> Figure 5 is a table showing the first battery configuration. Figure 6 is a table showing the second battery configuration. Figure 7 is a table showing the third battery configuration. In each table, if multiple types of materials are listed in a cell, the description includes each material individually and in combination thereof. For example, if the materials "α, β, γ" are listed in a cell, the description indicates "at least one selected from the group consisting of α, β, and γ". Any elements may be extracted from the first to third battery configurations and combined in any way.

[0163] This embodiment may be incorporated, for example, into the first to third battery configurations. The "graphite," "natural graphite," and "synthetic graphite" in the first to third battery configurations may be replaced with the negative electrode active material of this embodiment. By combining the first to third battery configurations with this embodiment, etc., battery performance may be improved. [Examples]

[0164] <<Sample Preparation>> Figure 8 is a table showing the sample configuration and evaluation results. The negative electrode active materials and batteries corresponding to No. 1 to 10 were manufactured as follows. Hereafter, for example, the negative electrode active material corresponding to No. 1 may simply be referred to as "No. 1".

[0165] <No.1> (a) Formation of secondary particles The following materials were prepared. Primary particles: Flecked graphite (D50, 15μm class) Carbon Black: Acetylene Black Precursor: Coal tar pitch (softening point 250°C)

[0166] The above materials were fed into an MP mixer (product name, manufactured by Nippon Coke Industries Co., Ltd., hereinafter the same). In the MP mixer, a spheroidizing process was carried out at a rotation speed of 5000 rpm for 1 hour, thereby forming secondary particles.

[0167] (b) Heat treatment The precursor was converted to low-crystalline carbon by heat treatment of secondary particles under an argon atmosphere. The treatment temperature was 1000°C and the treatment time was 1 hour. Thus, the anode active material was produced. The anode active material consisted of 0.1% carbon black, 3% low-crystalline carbon, and the remainder graphite, by mass fraction.

[0168] In No. 1, carbon black and precursors are added during "(a) Formation of secondary particles." In the "Addition Timing" section of Figure 8, "a" indicates that the substances (carbon black and precursors) were added during the secondary particle formation stage (see Figure 3).

[0169] <No.2~4> The negative electrode active material was manufactured in the same manner as in No. 1, except that the amount of carbon black added was changed so that the mass fraction of carbon black in the negative electrode active material matched the value shown in Figure 8.

[0170] <No.5、6> The anode active material was manufactured in the same manner as in No. 1, except that the amount of precursor added was changed so that the mass fraction of low-crystalline carbon in the anode active material matched the value shown in Figure 8.

[0171] <No.7、8> The negative electrode active material was manufactured in the same manner as in No. 1, except that a precursor with the softening point shown in Figure 8 was used.

[0172] <No.9> The negative electrode active material was manufactured in the same way as in No. 1, except that carbon black was not used.

[0173] <No.10> (a) Formation of secondary particles Primary particles (flaky graphite) and a precursor (coal tar pitch) were introduced into an MP mixer. In the MP mixer, a spheroidizing process was carried out at a rotation speed of 5000 rpm for 1 hour, thereby forming secondary particles.

[0174] (b) Heat treatment A mixture was formed by mixing secondary particles and carbon black. The mixture was heat-treated under an argon atmosphere, converting the precursor into low-crystalline carbon. The treatment temperature was 1000°C and the treatment time was 1 hour. Thus, the negative electrode active material was produced. The negative electrode active material consisted of 2% carbon black, 3% low-crystalline carbon, and the remainder graphite, by mass fraction. The carbon black is thought to be attached to the outer surface of the secondary particles.

[0175] In No. 10, carbon black is added during "(b) heat treatment." In the "Addition Timing" section of Figure 8, "b" indicates that the substance (carbon black) was added during the heat treatment stage (see Figure 3).

[0176] <<Rating>> Evaluation batteries containing negative electrode active materials No. 1 to 10 were manufactured. Capacity degradation was evaluated through charge-discharge cycle testing.

[0177] <Battery configuration> The configuration of the evaluation battery is as follows:

[0178] 《Positive electrode》 Composition of the positive electrode active material layer: NCM / AB / PVdF = 92 / 5 / 3 (mass ratio) Positive electrode current collector: Al foil (thickness 15 μm)

[0179] 《Negative electrode》 Composition of the negative electrode active material layer: Negative electrode active material / CMC / SBR = 98 / 1 / 1 (mass ratio) Negative electrode current collector: Cu foil (thickness 10 μm)

[0180] 《Separator》 Resin film: 3-layer structure (PP layer / PE layer / PP layer), thickness 24 μm Inorganic particle layer (HRL): one side (opposite side of positive electrode), thickness 4 μm

[0181] 《Electrolyte (electrolytic solution)》 Solvent: EC / DMC / EMC = 3 / 3 / 4 (volume ratio) Solute: LiPF6 (1mol / L) Additive: LiBOB (0.5 ml / L)

[0182] <Assembly Instructions> A positive electrode paste is applied to the surface of the positive electrode current collector to form a positive electrode active material layer. The positive electrode is then manufactured by pressing the positive electrode active material layer.

[0183] A negative electrode paste is applied to the surface of the negative electrode current collector to form a negative electrode active material layer. The negative electrode is then manufactured by pressing the negative electrode active material layer.

[0184] A laminate is formed by stacking a positive electrode, a separator, and a negative electrode in that order. The power generation element (electrode group) is formed by winding the laminate in a spiral shape.

[0185] A rectangular case is prepared as the outer casing. The power generation element is housed in the outer casing. The power generation element and terminals are electrically connected.

[0186] The electrolyte is injected into the casing. After the electrolyte is injected, the casing is sealed.

[0187] After the electrolyte is impregnated, the battery is charged with a predetermined amount. After charging, the battery is stored for a predetermined time in an environment of 60°C.

[0188] <Charge and Discharge Cycle Test> The charge and discharge cycle test was carried out under the following conditions. Ambient temperature: 60°C SOC range: 0 to 100% Current time rate: 2C (the time rate for discharging the rated capacity in 0.5 hours) Number of cycles: 300

[0189] Before and after the charge and discharge cycle test, the discharge capacity was measured. The discharge capacity before the charge and discharge cycle test is the initial capacity. The discharge capacity after the charge and discharge cycle test is the capacity after cycling. By dividing the capacity after cycling by the initial capacity, the capacity retention rate was obtained. The capacity retention rate is expressed as a percentage. The higher the capacity retention rate, the more the capacity degradation is considered to be reduced.

[0190] <<Results>> No. 1 to 8 have a higher capacity retention rate compared to No. 9 (see Fig. 8). No. 9 does not contain carbon black.

[0191] No. 1 to 8 have a higher capacity retention rate compared to No. 10 (see Fig. 8). In No. 10, it is considered that carbon black is not arranged inside the secondary particles. <​​​​​​​​​​​​​​

[0195] 1 Primary particles, 2 Secondary particles, 2c Central region, 2s Surface region, 3 Low-crystallinity carbon, 4 Carbon black, 5 Negative electrode active material, 10 Positive electrode, 11 Positive electrode current collector, 12 Positive electrode active material layer, 20 Negative electrode, 21 Negative electrode current collector, 22 Negative electrode active material layer, 30 Separator, 50 Power generation element, 100 Battery (non-aqueous electrolyte secondary battery).

Claims

1. It contains graphite, low-crystalline carbon, and carbon black. The crystallinity of the low-crystallinity carbon is lower than that of the graphite and higher than that of the carbon black. The R value of the aforementioned low-crystalline carbon is 0.20 to 1.

00. The aforementioned graphite forms secondary particles, The aforementioned secondary particle includes a plurality of primary particles, The primary particles are flaky, In the cross-sectional image of the secondary particle, The aforementioned secondary particle consists of a central region and a surface region. The aforementioned surface region surrounds the aforementioned central region, The aforementioned surface region extends 0.25D from the surface of the secondary particle in the depth direction of the secondary particle. max It extends to distant locations. The aforementioned 0.25D max This represents 0.25 times the maximum diameter. The aforementioned maximum diameter indicates the distance between the two furthest points on the contour line of the secondary particle. In the aforementioned central region, The low-crystalline carbon is attached to the surface of the primary particles, The carbon black is surrounded by a plurality of primary particles. Negative electrode active material.

2. A closed pore is formed in at least one of the central region and the surface region. The carbon black is disposed in the closed pore. The negative electrode active material according to claim 1.

3. A carbon black comprising 0.1 to 5% by mass fraction, The negative electrode active material according to claim 1 or claim 2.

4. The low-crystalline carbon is present in a mass fraction of 1 to 5%. The negative electrode active material according to claim 1 or claim 2.

5. The negative electrode active material comprises the material described in claim 1, Nonaqueous electrolyte secondary battery.

6. (a) By mixing primary particles containing graphite, a precursor, and carbon black, Forming secondary particles, and (b) Heat treatment of the secondary particles to change the precursor into low-crystalline carbon, Includes, The primary particles are flaky, The crystallinity of the low-crystallinity carbon is lower than that of the graphite and higher than that of the carbon black. The R value of the aforementioned low-crystalline carbon is 0.20 to 1.

00. A method for producing a negative electrode active material.

7. (a) above includes shaping the secondary particles into spheres, A method for producing a negative electrode active material according to claim 6.

8. The precursor includes coal tar pitch. A method for producing a negative electrode active material according to claim 6 or claim 7.

9. The precursor has a softening point of 180°C or lower. A method for producing a negative electrode active material according to claim 6 or claim 7.

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