Negative electrode composite material and lithium secondary battery

Abstract

A negative electrode composite material and a lithium secondary battery are provided. This negative electrode composite material contains a plurality of carbon particles and a plurality of Si-based particles. The plurality of carbon particles include a plurality of scaly graphite particles doped with boron. The content of the plurality of Si-based particles relative to the plurality of carbon particles is 5% by mass to 60% by mass. The content of the plurality of scaly graphite particles relative to the plurality of carbon particles is 1.5 mass% or more.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode composite material and a lithium secondary battery. Background Technology

[0002] Lithium secondary batteries are used in information and communication technology (such as personal computers, smartphones, etc.), in vehicles, and for power storage.

[0003] Japanese Patent Publication No. 2004-103391 discloses a non-aqueous electrolyte lithium secondary battery. The non-aqueous electrolyte lithium secondary battery comprises a negative electrode, a specific positive electrode and a non-aqueous electrolyte. The negative electrode contains a carbon material capable of lithium doping / dedoping. The carbon material is composed of a specific graphite that does not contain boron and a specific graphite that contains boron. SUMMARY OF THE INVENTION

[0004] However, the non-aqueous electrolyte lithium secondary battery disclosed in Japanese Patent Application Laid-Open No. 2004-103391 has room for improvement in capacity retention.

[0005] The present disclosure is completed in view of the above circumstances.

[0006] An embodiment of the present disclosure aims to provide a negative electrode composite material capable of improving the capacity retention rate of a lithium secondary battery and a lithium secondary battery having an excellent capacity retention rate.

[0007] Means for solving the above-mentioned problems include the following implementation methods.

[0008] <1>A negative electrode composite material, comprising a plurality of carbon particles (A) and a plurality of Si-based particles (B), wherein the plurality of carbon particles (A) include a plurality of flaky graphite particles (A1) doped with boron, the content (B / A) of the plurality of Si-based particles (B) relative to the plurality of carbon particles (A) is 5% to 60% by mass, and the content (A1 / A) of the plurality of flaky graphite particles (A1) relative to the plurality of carbon particles (A) is 1.5% by mass or more.

[0009] <2> According to the negative electrode composite material described in <1> above, the content (A1 / A) is 8.0 mass % or more.

[0010] <3> According to the negative electrode composite material described in <1> or <2> above, the content (A1 / A) is 15.0 mass % or less.

[0011] <4> According to any one of <1> to <3>, the plurality of carbon particles (A) further include a plurality of spherical graphite particles (A2), and the boron doping amount of the scaly graphite particles (A1) is 0.2 atm% or more.

[0012] <5>A lithium secondary battery includes a negative electrode including the negative electrode composite material according to any one of <1> to <4>.

[0013] According to the present disclosure, there are provided a negative electrode composite material capable of improving the capacity retention rate of a lithium secondary battery and a lithium secondary battery having excellent capacity retention rate. Detailed Description

[0014] In the present disclosure, a numerical range represented by "to" means a range including the numerical values described before and after "to" as the minimum value and the maximum value, respectively. In a numerical range described stepwise in the present disclosure, an upper limit value or a lower limit value described in a certain numerical range may also be replaced with an upper limit value or a lower limit value of another numerically described stepwise range. In the numerical range described in the present disclosure, an upper limit value or a lower limit value described in a certain numerical range may also be replaced with the value shown in the examples. In the present disclosure, a combination of two or more preferred modes is a more preferred mode. In the present disclosure, when there are a plurality of substances belonging to each component, unless otherwise specified, the amount of each component means the total amount of the plurality of substances. In the present disclosure, the term "process" includes not only an independent process, but also a process included in this term even when it cannot be clearly distinguished from other processes as long as the desired purpose of the process is achieved. (1) Negative Electrode Composite Material

[0015] The negative electrode composite material of the present disclosure contains a plurality of carbon particles (A) and a plurality of Si-based particles (B). The plurality of carbon particles (A) include a plurality of flaky graphite particles (A1) doped with boron. The content of the plurality of Si-based particles (B) relative to the plurality of carbon particles (A) (hereinafter, also simply referred to as "content (B / A)") is 5% by mass to 60% by mass. The content of the plurality of flaky graphite particles (A1) relative to the plurality of carbon particles (A) (hereinafter also simply referred to as "content (A1 / A)") is 1.5% by mass or more.

[0016] In the present disclosure, the "negative electrode composite material" means the solid component of the negative electrode composite material layer included in the negative electrode of a lithium secondary battery. The lithium secondary battery may be a battery having a solid electrolyte or a battery including a non-aqueous electrolyte.

[0017] "Carbon particle" means a particle containing carbon. "Graphite particle" means a particle containing graphite. "Flaky" means a shape having an aspect ratio of 2.1 or more. "Aspect ratio" means the ratio of the major axis of a particle to the minor axis of the particle.

[0018] "Si-based particle" means a particle containing silicon (Si).

[0019] Since the negative electrode composite material of the present disclosure has the above configuration, the capacity retention rate of the lithium secondary battery can be improved.

[0020] This effect is speculated based on the following reasons, but is not limited thereto.

[0021] If boron is doped into the flaky graphite particles, the electronic conductivity is improved. Therefore, it is easy to form a conductive path for the Si-based particles. As a result, it is speculated that the negative electrode composite material of the present disclosure can improve the capacity retention rate of the lithium secondary battery. (1.1) Carbon particles (A)

[0022] The negative electrode composite material of the present disclosure contains a plurality of carbon particles (A). The plurality of carbon particles (A) function as a negative electrode active material. Examples of the material constituting the carbon particles (A) include graphite, hard carbon, soft carbon, etc. Among them, graphite is preferred. The graphite can be natural graphite or artificial graphite. The carbon particles (A) can be coated with an amorphous carbon material. (1.1.1) Flaky graphite particles (A1)

[0023] The plurality of carbon particles (A) include a plurality of flaky graphite particles (A1) doped with boron. The graphite constituting the flaky graphite particles (A1) can be natural graphite or artificial graphite.

[0024] The doping amount of boron in the flaky graphite particles (A1) is not particularly limited, and can be 0.2 atm% or more, can be 1.0 atm% or more, and can also be 2.0 atm% or more. The doping amount of boron in the flaky graphite particles (A1) can be 3.6 atm% or less, and can also be 3.5 atm% or less.

[0025] The aspect ratio of the flaky graphite particles (A1) is 2.1 or more, can be 3.0 or more, and can also be 3.4 or more. The aspect ratio of the flaky graphite particles (A1) can be 10.0 or less, can also be 4.0 or less, and can also be 3.8 or less.

[0026] The average particle size of the plurality of flaky graphite particles (A1) is not particularly limited, and can be 2 μm to 40 μm, and can also be 4 μm to 26 μm. "Average particle size" means the particle size (median particle size) corresponding to a cumulative frequency of 50% by volume from the side of fine particles with a small particle size in the particle size distribution based on the volume basis of the laser diffraction / light scattering method.

[0027] The content (A1 / A) is 1.5% by mass or more, preferably 8.0% by mass or more. By the content (A1 / A) being 8.0% by mass or more, the negative electrode composite material can further improve the capacity retention rate of the lithium secondary battery. The content (A1 / A) can be 10.0% by mass or more.

[0028] The content (A1 / A) may be 40.0 mass % or less, may be 25.0 mass % or less, and preferably 15.0 mass % or less. By setting the content (A1 / A) to 15.0 mass % or less, even if the content of the plurality of flaky graphite particles (A1) is relatively small, the negative electrode composite material can efficiently improve the capacity retention rate of the lithium secondary battery. (1.1.2) Spherical graphite particles (A2)

[0029] The plurality of carbon particles (A) may further include spherical graphite particles (A2). "Spherical" means a shape having an aspect ratio of less than 2.1. The graphite constituting the spherical graphite particles (A2) may be natural graphite or artificial graphite.

[0030] The spherical graphite particles (A2) may or may not be doped with boron. When the spherical graphite particles (A2) are doped with boron, the amount of boron doped in the spherical graphite particles (A2) may be the same as that exemplified as the amount of boron doped in the spherical graphite particles (A1).

[0031] The aspect ratio of the spherical graphite particles (A2) is less than 2.1, and may be less than 1.9 or greater than 1.7. The aspect ratio of the spherical graphite particles (A2) may be greater than 1.0.

[0032] The average particle size of the plurality of spherical graphite particles (A2) is not particularly limited and may be 2 μm to 30 μm or 4 μm to 26 μm. The method for measuring the average particle size is the same as the method for measuring the average particle size of the scaly graphite particles (A1).

[0033] The content (A2 / A) of the plurality of spherical graphite particles (A2) relative to the plurality of carbon particles (A) may be 60.0% by mass or more, 75.0% by mass or more, or 85.0% by mass or more. The content (A2 / A) may be 98.5% by mass or less, 92.0% by mass or less, or 90.0% by mass or less. (1.1.3) Preferred method

[0034] Preferably, the plurality of carbon particles (A) further include a plurality of spherical graphite particles (A2), and the boron doping amount of the flaky graphite particles (A1) is 0.2 atm% or more. Thus, the negative electrode composite material can further improve the capacity retention rate of the lithium secondary battery. (1.2) Si-based particles (B)

[0035] The negative electrode composite material disclosed herein contains a plurality of Si-based particles (B). The plurality of Si-based particles (B) function as negative electrode active materials. Examples of materials constituting the Si-based particles (B) include Si single substance (silicon), Si alloys, silicon monoxide (SiO), silicon dioxide (SiO2 ), etc. The Si alloy preferably has Si as the main component.

[0036] The aspect ratio of the Si-based particles (B) is not particularly limited, and can be less than 2.1, can be 1.9 or less, or can be 1.7 or more. The aspect ratio of the Si-based particles (B) can be 1.0 or more.

[0037] The average particle size of the plurality of Si-based particles (B) is not particularly limited, and can be 0.01 μm to 10.0 μm, or can be 0.5 μm to 8.0 μm. The measurement method of the average particle size is the same as that of the average particle size of the flaky graphite particles (A1).

[0038] The content (B / A) is 5% by mass to 60% by mass. The content (B / A) can be 10% by mass or more, or can be 15% by mass or more. The content (B / A) can be 40% by mass or less, can be 30% by mass or less, or can be 25% by mass or less. (1.3) Binder

[0039] The negative electrode composite material may further contain a binder. Examples of the binder include polyvinylidene fluoride (PVDF), carboxymethyl cellulose, rubber-based binders (such as butadiene rubber, hydrogenated butadiene rubber, etc.), fluoride-based binders (such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), etc.), polyolefin-based thermoplastic resins (such as polyethylene, polypropylene, polystyrene, etc.), etc. The content of the binder relative to the total amount of the negative electrode composite material can be 0.1% by mass to 10% by mass. (1.4) Conductive additive

[0040] The negative electrode composite material may further contain a conductive additive. Examples of the conductive additive include carbon nanotubes (CNT), carbon black (such as acetylene black, furnace black, Ketjen black, etc.), etc. The content of the conductive additive relative to the total amount of the negative electrode composite material can be 0.1% by mass to 10% by mass. (2) Lithium secondary battery

[0041] The lithium secondary battery of the present disclosure includes a negative electrode. The negative electrode contains the negative electrode composite material of the present disclosure. Thus, the capacity retention rate of the lithium secondary battery of the present disclosure is excellent.

[0042] The lithium secondary battery of the present disclosure generally includes a positive electrode and an ion conduction medium in addition to the negative electrode. The ion conduction medium is interposed between the positive electrode and the negative electrode and conducts carrier ions. Examples of the ion conduction medium include non-aqueous electrolytes, non-aqueous gel electrolytes, solid ion-conductive polymers, inorganic solid electrolytes, etc.

[0043] Hereinafter, a lithium secondary battery using a non-aqueous electrolyte (hereinafter also referred to as a "non-aqueous battery") will be described. (2.1) Non-aqueous battery

[0044] The non-aqueous battery includes the negative electrode, positive electrode, separator disposed between the positive electrode and the negative electrode, and non-aqueous electrolyte of the present disclosure. (2.1.1) Negative electrode

[0045] The negative electrode has a negative electrode composite material layer and may further have a negative electrode current collector (such as a copper foil, etc.). The negative electrode composite material layer is laminated on at least one main surface of the negative electrode current collector. The negative electrode composite material layer contains the negative electrode composite material of the present disclosure. (2.1.2) Positive electrode

[0046] The positive electrode has a positive electrode composite material layer and may further have a positive electrode current collector (such as an aluminum foil, etc.). The positive electrode composite material layer is laminated on at least one main surface of the positive electrode current collector.

[0047] The positive electrode composite material layer contains a positive electrode active material. The positive electrode active material releases lithium ions to the non-aqueous electrolyte or occludes lithium ions from the electrolyte. The positive electrode active material is a known positive electrode active material (such as LiNiO 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , etc.). The positive electrode composite material layer may further contain a known conductive material (such as carbon black, etc.), lithium phosphate, and a binder (such as polyvinylidene fluoride, etc.). (2.1.3) Separator

[0048] The separator maintains the interval between the positive electrode and the negative electrode to prevent the occurrence of contact short circuit and allows lithium ions to pass through. As the separator, for example, a porous resin sheet or non-woven fabric can be cited. As the material of the porous resin sheet, for example, polyolefins (such as polypropylene, polyethylene, etc.) can be cited. As the material of the non-woven fabric, for example, polypropylene, polyethylene terephthalate, methyl cellulose, etc. can be cited. The separator can be a known structure. (2.1.4) Non-aqueous electrolyte

[0049] The non-aqueous electrolyte may contain a non-aqueous solvent and a lithium salt. As the lithium salt, for example, LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN(FSO 2 ), 2 , LiN(CF 3 SO2 ) 2 etc. As non-aqueous solvents, cyclic carbonates (such as ethylene carbonate, etc.), chain carbonates (such as dimethyl carbonate, methyl ethyl carbonate, etc.), cyclic esters (such as γ-butyrolactone, γ-valerolactone, etc.), chain esters (such as methyl formate, methyl acetate, etc.), ethers (such as 1,2-dimethoxyethane, ethoxymethoxyethane, etc.) can be cited. The non-aqueous electrolyte can contain additives (such as vinylene carbonate, lithium bis(oxalato)borate, etc.). (2.1.5) Housing

[0050] Non-aqueous batteries usually have a housing. The housing houses a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. As the housing, there is no particular limitation, and laminated films (such as aluminum sheets, etc.), battery cans (such as cylindrical, square, coin-shaped, etc.) can be cited.

[0051] Hereinafter, the present disclosure will be described in more detail by way of examples, but the invention of the present disclosure is not limited to these examples only. [1] Examples and Comparative Examples [1.1] Raw Materials

[0052] As raw materials for the negative electrode composite material, the following materials were prepared. [1.1.1] Flaky Graphite Particles (A1) [1.1.1.1] Flaky Graphite Particles (A1-1)

[0053] As flaky graphite particles (A1) doped with boron (negative electrode active material), flaky graphite particles (A1-1) were prepared. Specifically, boron carbide (B 4 C) and a plurality of flaky graphite particles (particle material: graphite, particle aspect ratio: 3.5) were mixed to obtain a mixture. The mixing ratio of boron carbide (B 4 C) was 3.0% by mass relative to the plurality of flaky graphite particles. The mixture was fired in an argon atmosphere at 2800 °C for 2 hours. Thus, a plurality of flaky graphite particles (A1-1) were obtained.

[0054] The boron doping amount of the plurality of flaky graphite particles (A1-1) was measured using XPS (X-ray photoelectron spectroscopy). Specifically, the boron doping amount was calculated from the peak at 188 eV (attributed to the B-C bond). The measurement result of the boron doping amount of the plurality of flaky graphite particles (A1-1) was 1.4 atm%. [1.1.1.2] Flaky Graphite Particles (A1-2)

[0055] As flaky graphite particles (A1) doped with boron (negative electrode active material), flaky graphite particles (A1-2) were prepared. Specifically, boron carbide (B4 The mixing ratio of (C) was changed to 0.5% by mass relative to a plurality of flaky graphite particles. Except for this, a plurality of flaky graphite particles (A1-2) were obtained in the same manner as the production of the flaky graphite particles (A1-1). The measurement result of the boron doping amount of the flaky graphite particles (A1-2) was 0.2 atm%. [1.1.1.3]Flaky graphite particles (A1-3)

[0056] As the flaky graphite particles (A1) (negative electrode active material) doped with boron, a plurality of flaky graphite particles (A1-3) were prepared. Specifically, the mixing ratio of boron carbide (B 4 C) was changed to 10.0% by mass relative to a plurality of flaky graphite particles. Except for this, a plurality of flaky graphite particles (A1-3) were obtained in the same manner as the production of the flaky graphite particles (A1-1). The measurement result of the boron doping amount of the flaky graphite particles (A1-3) was 3.5 atm%. [1.1.2]Flaky graphite particles (X)

[0057] As the flaky graphite particles (X) not doped with boron, a plurality of flaky graphite particles (X-1) (particle material: graphite, particle aspect ratio: 3.3) were prepared. [1.1.3]Spherical graphite particles (A2)

[0058] As the spherical graphite particles (A2) (negative electrode active material) not doped with boron, a plurality of spherical graphite particles (A2-1) (particle material: artificial graphite) were prepared. [1.1.4]Si-based particles (B)

[0059] As the Si-based particles (B) (negative electrode active material), a plurality of silicon particles (B-1) (particle material: silicon) were prepared. [1.2]Comparative Example 1

[0060] A plurality of flaky graphite particles (X-1) and a plurality of spherical graphite particles (A2-1) were mixed to obtain a plurality of carbon particles (A). The ratio (X / A) of the plurality of flaky graphite particles (X-1) to the total of the plurality of flaky graphite particles (X-1) and the plurality of spherical graphite particles (A2-1) (i.e., the plurality of carbon particles (A)) was 10.0% by mass. A plurality of carbon particles (A) and a plurality of Si-based particles (B-1) were mixed to obtain a negative electrode composite material. The content (B / A) of the plurality of Si-based particles (B-1) relative to the plurality of carbon particles (A) was 20% by mass. [1.3]Examples 1 to 8 and Comparative Examples 2 to 4

[0061] A plurality of flaky graphite particles (A1) and a plurality of spherical graphite particles (A2-1) shown in Table 1 were mixed to obtain a plurality of carbon particles (A). The ratio (A1 / A) of the plurality of flaky graphite particles (A1) to the total of the plurality of flaky graphite particles (A1) and the plurality of spherical graphite particles (A2-1) (i.e., the plurality of carbon particles (A)) was the ratio shown in Table 1. The plurality of carbon particles (A) and a plurality of Si-based particles (B-1) were mixed to obtain a negative electrode composite material. The content (B / A) of the plurality of Si-based particles (B-1) relative to the plurality of carbon particles (A) was 20% by mass. [2] Evaluation of capacity retention rate [2.1] Fabrication of lithium secondary battery

[0062] A lithium secondary battery was fabricated as follows. [2.1.1] Positive electrode

[0063] As the positive electrode active material, LiNiCoMnO was prepared. 2 As the conductive additive, acetylene black (AB) was prepared. As the binder, polyvinylidene fluoride (PVdF) was prepared.

[0064] The positive electrode active material, the conductive additive, the binder, and the solvent were mixed to prepare a positive electrode composite material paste. The mass ratio of the positive electrode composite material paste (positive electrode active material: conductive additive: binder) was 92:5:3. The positive electrode composite material paste was coated on an aluminum foil (thickness: 15 μm), dried, and pressed. Thus, a positive electrode was obtained. The thickness of the positive electrode active material layer of the positive electrode was the specified thickness. [2.1.2] Negative electrode

[0065] As binder A, carboxymethyl cellulose (CMC) was prepared. As binder B, styrene-butadiene rubber (SBR) was prepared.

[0066] The obtained negative electrode composite material, the conductive additive, binder A, binder B, and the solvent were mixed to prepare a negative electrode composite material paste. The mass ratio of the negative electrode composite material paste (negative electrode active material: conductive additive: binder A: binder B) was 97:1:1:1. In addition, insoluble CMC was calculated as the active material weight. The negative electrode composite material paste was coated on a copper foil (thickness: 10 μm), dried, and pressed. Thus, a negative electrode was obtained. The thickness of the negative electrode active material layer of the negative electrode was the specified thickness. [2.1.3] Separator

[0067] As the separator, a three-layered porous sheet (thickness: 24 μm) was prepared. The porous sheet was formed by sequentially laminating a polypropylene (PP) layer, a polyethylene (PE) layer, and a PP layer. A layer (4 μm) of ceramic (aluminum oxide, boehmite, etc.) was coated on one side of the separator. [2.1.4] Non-aqueous electrolyte

[0068] As the non-aqueous electrolyte, a mixed solution of a mixed solvent and LiPF 6 as a supporting salt was prepared. The mixed solvent consists of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The volume ratio of the mixed solvent (EC:DMC:EMC) is 3:3:4. The concentration of LiPF 6 is 1 mol / L. [2.1.5] Assembly

[0069] The positive electrode and the negative electrode were wound with a separator in between to form an electrode assembly. The ceramic layer of the separator faces the positive electrode. Collector plates with covers were welded to both ends of the electrode assembly, the electrode assembly was inserted into a housing, and the cover plate was welded to the housing. A predetermined amount of non-aqueous electrolyte was injected through the liquid injection hole of the housing, and a screw for sealing was fastened to the liquid injection hole. After injecting the non-aqueous electrolyte, the electrode assembly was left for an appropriate time to allow the non-aqueous electrolyte to impregnate the electrode assembly, and the electrode assembly was charged and aged at 60°C. Thus, a lithium secondary battery was obtained. [2.2] Evaluation of life (cycle) characteristics

[0070] For the lithium-ion lithium secondary battery, charge and discharge were performed at a rate load of 2C in an atmosphere of 60°C. The SOC range was from 0% to 100%, and 300 cycles were carried out. The battery capacity at the first discharge (hereinafter also referred to as "initial capacity") and the battery capacity after 300 cycles (hereinafter also referred to as "capacity after 300 cycles") were measured. The capacity retention rate was calculated by the following formula (A). The results are shown in Table 1. The higher the capacity retention rate, the better the battery characteristics can be evaluated. The allowable range of the capacity retention rate is 77% or more. Formula (A): Capacity retention rate (%) = (Capacity after 300 cycles / Initial capacity) × 100

[0071] [3] Results

[0072] The negative electrode composite material of Comparative Example 1 does not contain multiple flaky graphite particles (A1). Therefore, the capacity retention rate of Comparative Example 1 is not 77% or more.

[0073] In the negative electrode composite material of Comparative Example 2, the content (A1 / A) is not 1.5 mass% or more. Therefore, the capacity retention rate of Comparative Example 2 is not 77% or more.

[0074] In Comparative Examples 3 and 4, the content (B / A) is not 5 mass% to 60 mass%. Therefore, the capacity retention rates of Comparative Examples 3 and 4 are not 77% or more.

[0075] From these results, it can be seen that the negative electrode composite materials of Comparative Examples 1 to 4 are not "negative electrode composite materials capable of improving the capacity retention rate of lithium secondary batteries".

[0076] The negative electrode composite materials of Examples 1 to 8 contain a plurality of carbon particles (A) and a plurality of Si-based particles (B). The plurality of carbon particles (A) include flaky graphite particles (A1). The content (B / A) is 5% by mass to 60% by mass. The content (A1 / A) is 1.5% by mass or more. Therefore, the capacity retention rate of Examples 1 to 5 is 77% or more.

[0077] From these results, it can be seen that the negative electrode composite materials of Examples 1 to 8 are "negative electrode composite materials capable of improving the capacity retention rate of lithium secondary batteries".

Claims

1. A negative electrode composite material comprising a plurality of carbon particles and a plurality of Si-based particles, The plurality of carbon particles include a plurality of flaky graphite particles doped with boron, The content of the plurality of Si-based particles relative to the plurality of carbon particles is 5 mass % to 60 mass %, The content of the plurality of flaky graphite particles relative to the plurality of carbon particles is 1.5 mass % or more.

2. The negative electrode composite material according to claim 1, wherein The content of the plurality of flaky graphite particles relative to the plurality of carbon particles is 8.0 mass % or more.

3. The negative electrode composite material according to claim 2, wherein: The content of the plurality of flaky graphite particles relative to the plurality of carbon particles is 15.0 mass % or less.

4. The negative electrode composite material according to claim 1, wherein The plurality of carbon particles further include a plurality of spherical graphite particles, The boron doping amount of the flaky graphite particles is 0.2 atm % or more. 5 . A lithium secondary battery comprising a negative electrode comprising the negative electrode composite material according to claim 1 .

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