Negative electrode active material, negative electrode, lithium-ion secondary battery, and lithium-ion secondary battery module

Abstract

A negative electrode active material comprising a graphite powder and a Si / C powder that includes Si-C composite particles including silicon and a carbon material, wherein the value of CS1 / CS2 is 0.32 or less, where CS1 and CS2 are the respective fracture strengths of the graphite powder and the Si / C powder as measured in accordance with JIS R 1639-5:2007.

Description

Anode active material, anode, lithium ion secondary battery, and lithium ion secondary battery module

[0001] The present invention relates to a negative electrode active material, a negative electrode, a lithium ion secondary battery, and a lithium ion secondary battery module.

[0002] Si / C powder is sometimes used as a negative electrode active material. Patent Document 1 describes composite particles made of a Si-C composite material, which have an object to provide composite particles that achieve a high silicon utilization rate in a lithium ion secondary battery and are resistant to oxidation when dispersed in water, and which contain a carbon material and silicon, and have a silicon content of 30% by mass or more and 80% by mass or less, and a true density of 1.80 g / cm as determined by dry density measurement using helium gas. ３ 1.99g / cm or more ３ or less, and in the Raman spectrum of the composite particle, a peak is 450 to 495 cm －１ and the intensity of the peak is I Ｓｉ and the G band intensity (1580 cm －１ (peak intensity around Ｇ Then, I Ｓｉ / I Ｇ is 1.3 or less, and the atomic ratios of Si, O and C in the narrow spectrum of the composite particle by X-ray photoelectron spectroscopy are Ｓｉ , A Ｏ , and A Ｃ In the Si species ratio by Si2p spectrum state analysis, SiO ２ and SiO ratios are B ＳｉＯ２ , B ＳｉＯ Then, A Ｓｉ is 0.05 or more, and at least one of the following formulas (1) and (2) is satisfied: Y≧0.75 (1) Y≧−0.32X+0.81 (2) (wherein X=I Ｓｉ / I Ｇ and Y=A Ｃ / (A Ｃ +A Ｓｉ × (B ＳｉＯ２ +B ＳｉＯ ))

[0003] JP 2023-059283 A

[0004] According to the investigations of the present inventors, it has become clear that the energy density of a lithium ion secondary battery using a negative electrode active material containing graphite powder and Si / C powder may be low.

[0005] The present invention provides a negative electrode active material and a negative electrode that can provide a lithium ion secondary battery with improved energy density, as well as a lithium ion secondary battery and a lithium ion secondary battery module with improved energy density.

[0006] The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered a method for producing a composite material comprising graphite powder and Si / C powder containing Si-C composite particles containing silicon and a carbon material, the fracture strengths of which are measured in accordance with JIS R 1639-5:2007 and CS. １ and C.S. ２ When this is done, CS １ / CS ２ The present inventors have found that a negative electrode active material having a value of 0.32 or less can improve the energy density of the resulting lithium ion secondary battery, and have completed the present invention.

[0007] According to the present invention, there are provided the following negative electrode active material, negative electrode, lithium ion secondary battery, and lithium ion secondary battery module.

[0008] [1] A graphite powder and a Si / C powder containing Si-C composite particles containing silicon and a carbon material, wherein the fracture strength of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 is CS １ and C.S. ２ When this is done, CS １ / CS ２ [2] The negative electrode active material having a value of 0.32 or less. １ [3] The negative electrode active material according to [1], wherein the median diameter D in a volume frequency particle size distribution of the graphite powder measured by a laser diffraction scattering method is 10 MPa or more and 90 MPa or less. ５０[4] The negative electrode active material according to [1] or [2], wherein the particle diameter D at which the cumulative value reaches 10% in a volume frequency particle size distribution measured by a laser diffraction scattering method of the graphite powder is 3.0 μm or more and 30.0 μm or less. １０ , 90% particle diameter D ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ [5] The negative electrode active material according to any one of [1] to [3], wherein the value of is 0.50 or more and 3.00 or less. ５０ [6] The negative electrode active material according to any one of [1] to [4], wherein the carbon material in the Si—C composite particles comprises a porous carbon material, and the silicon is present in at least a portion of the pores of the porous carbon material. [7] The negative electrode active material according to any one of [1] to [6], wherein the graphite powder comprises graphite particles having amorphous carbon on the surface thereof. [8] The negative electrode active material according to any one of [1] to [7], wherein the graphite powder comprises artificial graphite particles. [9] The negative electrode active material according to any one of [1] to [8], wherein the content of the graphite powder in the negative electrode active material is 50.0 parts by mass or more and 99.0 parts by mass or less, when the total amount of the negative electrode active material is 100.0 parts by mass.

[10] The negative electrode active material according to any one of [1] to [9], wherein the content of the Si / C powder in the negative electrode active material is 1.0 part by mass or more and 50.0 parts by mass or less when the total amount of the negative electrode active material is 100.0 parts by mass.

[11] The content of the graphite powder in the negative electrode active material is W １ , the content of the Si / C powder in the negative electrode active material is W ２ When W １ / W ２

[12] The negative electrode active material according to any one of [1] to

[10] , wherein the value of the median diameter D in a volume frequency particle size distribution measured by a laser diffraction scattering method is 1.0 or more and 20.0 or less. ５０ The graphite powder (A) and the graphite powder (B) are two kinds of graphite powders having different median diameters D５０ is the median diameter D of the graphite powder (B). ５０

[13] The negative electrode active material according to any one of [1] to

[11] , wherein the median diameter D of the graphite powder (A) is larger than ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When this is done, D Ｂ / D Ａ

[14] The negative electrode active material according to

[12] , wherein the graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the graphite powder (B) contains graphite particles not containing amorphous carbon on the surface thereof.

[15] The negative electrode active material according to

[12] or

[13] , wherein the content of the graphite powder (A) in the graphite powder is W Ａ The content of the graphite powder (B) in the graphite powder is W Ｂ When W Ａ / W Ｂ The negative electrode active material according to any one of

[12] to

[14] , wherein the value of is 0.1 or more and 10.0 or less.

[16] The negative electrode active material according to any one of [1] to

[15] , wherein the energy density E measured by the following method is 800 Wh / L or more in terms of cell conversion. (Method) A negative electrode active material slurry is prepared by adding an appropriate amount of water to a solid content consisting of 96.9 parts by mass of the negative electrode active material, 0.1 parts by mass of single-walled carbon nanotubes, and 3.0 parts by mass of polyacrylic acid. Next, the negative electrode active material slurry is applied to a copper foil negative electrode current collector so that the initial charge capacity per unit area is 4.3 mAh / cm. ２ The negative electrode laminate is then coated in an amount such that the density of the negative electrode active material layer becomes 1.65 g / cm using a roll press machine. ３ Then, the negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５A lithium-ion secondary battery was fabricated by placing an electrode laminate, in which a positive electrode containing a cellulose acylate (C1) and a positive electrode containing a cellulose acylate (C2) facing each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate outer casing formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab were connected to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate outer casing. The lithium-ion secondary battery was then charged at 7.2 mA, and after the upper voltage reached 4.2 V, it was charged at a constant voltage until the total charge time was 12 hours. It was then discharged at a constant current of 7.2 mA until the lower voltage reached 2.5 V. It was then charged again under the same conditions, left in a thermostatic chamber at 45°C for 3 days, and discharged again under the same conditions. The capacity and average voltage at the final discharge were measured. After the final discharge, the thickness of the lithium-ion secondary battery was measured. Next, the energy density E (Wh / L) converted into a cell is calculated using the following formula based on the above measured values, the electrode area of ​​the electrode laminate, the thickness of the laminate exterior body, the thickness of the negative electrode current collector, and the thickness of the positive electrode current collector in the positive electrode. (Energy density E) = (Capacity at final discharge) x (Average voltage at final discharge) / (Electrode area of ​​electrode laminate) / ((Thickness of lithium ion secondary battery) - (Thickness of laminate exterior body) - (Thickness of positive electrode current collector) / 2 - (Thickness of negative electrode current collector) / 2)

[17] A negative electrode comprising the negative electrode active material according to any one of [1] to

[16] .

[18] A lithium ion secondary battery comprising the negative electrode according to

[17] .

[19] A lithium ion secondary battery module comprising the lithium ion secondary battery according to

[18] .

[0009] According to the present invention, it is possible to provide a negative electrode active material and a negative electrode that can provide a lithium ion secondary battery with improved energy density, as well as a lithium ion secondary battery and a lithium ion secondary battery module with improved energy density.

[0010] 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to an embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. To avoid complexity, when multiple identical components appear in the same drawing, only one of the components may be labeled with a reference symbol, and not all of the components may be labeled with a reference symbol. The drawings are for illustrative purposes only. The shapes and dimensional ratios of each component in the drawings do not necessarily correspond to actual objects.

[0012] In this embodiment, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0013] <Negative Electrode Active Material> The negative electrode active material of this embodiment includes graphite powder and Si / C powder including Si-C composite particles containing silicon and a carbon material, and the breaking strength of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 is CS. １ and C.S. ２ When this is done, CS １ / CS ２ The value of is 0.32 or less.

[0014] According to the investigations of the present inventors, it has been found that in a negative electrode active material containing graphite powder and Si / C powder including Si-C composite particles containing silicon and a carbon material, there is a correlation between the ratio of the fracture strengths of the graphite powder and the Si / C powder and the energy density of the resulting lithium ion secondary battery.

[0015] As a result of further investigations by the present inventors based on the above findings, it has been found that in a negative electrode active material containing graphite powder and Si / C powder containing Si-C composite particles containing silicon and a carbon material, the fracture strengths of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 are respectively CS １ and C.S. ２ When this is done, CS １ / CS ２ The inventors have found that the energy density of the resulting lithium ion secondary battery can be improved by adjusting the value of 0.32 or less, and have completed the present invention.

[0016] In the negative electrode active material of this embodiment, the fracture strength of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 is CS １and C.S. ２ When this is done, CS １ / CS ２ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of CS is 0.32 or less, preferably 0.31 or less, more preferably 0.30 or less, even more preferably 0.29 or less, even more preferably 0.28 or less, even more preferably 0.27 or less, even more preferably 0.26 or less, even more preferably 0.25 or less, and even more preferably 0.24 or less. １ / CS ２ The lower limit of the value is not particularly limited, and may be, for example, 0.01 or more, 0.05 or more, 0.10 or more, 0.13 or more, 0.15 or more, or 0.18 or more.

[0017] In the negative electrode active material of this embodiment, the fracture strength of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 is CS １ and C.S. ２ When this is done, CS １ / CS ２ From the viewpoint of further improving the energy density of the obtained lithium ion secondary battery, the value of is preferably 0.01 or more and 0.32 or less, more preferably 0.01 or more and 0.31 or less, even more preferably 0.01 or more and 0.30 or less, even more preferably 0.01 or more and 0.29 or less, even more preferably 0.05 or more and 0.28 or less, even more preferably 0.10 or more and 0.27 or less, even more preferably 0.13 or more and 0.26 or less, even more preferably 0.15 or more and 0.25 or less, and even more preferably 0.18 or more and 0.24 or less.

[0018] In the negative electrode active material of this embodiment, the breaking strength CS of the graphite powder measured in accordance with JIS R 1639-5:2007 １ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the pressure is preferably 10 MPa or more and 90 MPa or less, more preferably 30 MPa or more and 85 MPa or less, even more preferably 40 MPa or more and 80 MPa or less, and even more preferably 50 MPa or more and 78 MPa or less.

[0019] In the negative electrode active material of this embodiment, the breaking strength CS of the Si / C powder measured in accordance with JIS R 1639-5:2007 ２ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the pressure is preferably 50 MPa or more and 500 MPa or less, more preferably 100 MPa or more and 450 MPa or less, even more preferably 130 MPa or more and 420 MPa or less, even more preferably 150 MPa or more and 370 MPa or less, even more preferably 180 MPa or more and 330 MPa or less, and even more preferably 200 MPa or more and 300 MPa or less.

[0020] In this embodiment, the breaking strength of graphite powder or Si / C powder can be measured, for example, by the following method. First, a micro-compression tester is used to measure the test force P (N) of graphite powder or Si / C powder when the powder particles break using an indenter. That is, after scattering a very small amount of powder on a sample stage, 100 random particles are compressed one by one using an indenter to determine the test force P (N) when the powder particles break. In addition, the particle diameter d (mm) of each particle is measured in two orthogonal directions (X direction and Y direction in the observation image of the micro-compression tester) and the average value thereof is used. Next, the breaking strength CS of each particle is calculated from the test force P (N), particle diameter d (mm), and pi (π) using the following formula, and the average value of the breaking strengths CS for the 100 particles is used as the breaking strength of the powder. CS = 2.48 × P / (π × d ２ )

[0021] In this embodiment, examples of methods for adjusting the breaking strength of the graphite powder and Si / C powder include a method using commercially available graphite powder and Si / C powder with different breaking strengths, and a method for producing graphite powder and Si / C powder with different breaking strengths by adjusting the production conditions of the graphite powder and Si / C powder, such as surface treatment, heat treatment, etc. Alternatively, the breaking strength of the graphite powder may be adjusted by mixing two or more types of graphite powder with different breaking strengths, or the breaking strength of the Si / C powder may be adjusted by mixing two or more types of Si / C powder with different breaking strengths.

[0022] <Si / C Powder> The Si / C powder of this embodiment includes Si-C composite particles containing silicon and a carbon material. From the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery, the Si / C powder of this embodiment preferably has the carbon material in the Si-C composite particles containing a porous carbon material, and silicon present in at least part of the pores of the porous carbon material.

[0023] In this embodiment, a method for confirming that the Si-C composite particles in the Si / C powder contain silicon and a carbon material and that the silicon in the Si-C composite particles is present in at least a portion of the pores of the porous carbon material can be, for example, a method of observing a cross section of a Si-C composite particle in the Si / C powder by using a scanning electron microscope, an energy dispersive X-ray spectroscopic detector, and image analysis software, selecting secondary electrons as the detection target, and performing elemental mapping of silicon and carbon under conditions of an acceleration voltage of 3 kV, a mapping accumulation number of 20, and a magnification of 3000x.

[0024] Examples of porous carbon materials that make up the Si-C composite particles include activated carbon, aggregates of carbon fibers, aggregates of carbon nanotubes, carbon obtained by heat treating resins or organic materials, hard carbon, etc. Porous carbon materials can be produced by methods for producing activated carbon or known production methods involving heat treatment of polymers, but commercially available products may also be purchased, and are not limited to these, as long as silicon can be produced or incorporated into the pores of the porous carbon.

[0025] The median diameter D in the volume frequency particle size distribution of the Si / C powder of this embodiment measured by the laser diffraction scattering method ５０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle size is preferably 1.0 μm or more and 20.0 μm or less, more preferably 2.0 μm or more and 17.0 μm or less, even more preferably 3.0 μm or more and 14.0 μm or less, even more preferably 3.5 μm or more and 12.0 μm or less, and even more preferably 4.0 μm or more and 10.0 μm or less.

[0026] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the Si / C powder according to this embodiment, as determined by the laser diffraction scattering method, is １０From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle size is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.5 μm or more and 8.0 μm or less, even more preferably 1.0 μm or more and 6.0 μm or less, and still more preferably 1.5 μm or more and 5.0 μm or less.

[0027] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the Si / C powder according to this embodiment, as determined by the laser diffraction scattering method, is ９０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle diameter is preferably 3.0 μm or more and 30.0 μm or less, more preferably 5.0 μm or more and 25.0 μm or less, even more preferably 6.0 μm or more and 20.0 μm or less, even more preferably 7.0 μm or more and 17.0 μm or less, and even more preferably 8.0 μm or more and 15.0 μm or less.

[0028] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the Si / C powder according to this embodiment, as determined by the laser diffraction scattering method, is １０ , 90% particle diameter D ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 0.50 or more and 3.00 or less, more preferably 0.70 or more and 2.50 or less, even more preferably 0.90 or more and 2.00 or less, even more preferably 1.00 or more and 1.80 or less, and still more preferably 1.05 or more and 1.60 or less.

[0029] In this embodiment, the volume frequency particle size distribution of the Si / C powder can be measured, for example, by the following method. First, the Si / C powder is suspended in a dispersion medium and ultrasonically dispersed. Next, the volume frequency particle size distribution of the Si / C powder is measured by a laser diffraction scattering method using a laser diffraction particle size distribution analyzer. The measurement is performed five times, and the average value can be used.

[0030] From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the content of the Si / C powder in the negative electrode active material of this embodiment is preferably 1.0 part by mass or more and 50.0 parts by mass or less, more preferably 5.0 parts by mass or more and 45.0 parts by mass or less, even more preferably 8.0 parts by mass or more and 42.0 parts by mass or less, even more preferably 15.0 parts by mass or more and 40.0 parts by mass or less, and even more preferably 18.0 parts by mass or more and 37.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0031] In this embodiment, the method for producing the Si / C powder is not particularly limited. For example, the Si / C powder may have a median diameter of 4.0 to 10.0 μm and a specific surface area of ​​1600 to 1800 m. ２ / g of porous carbon material is placed in a tubular furnace, the atmosphere inside the furnace is replaced with argon gas, and then a mixed gas of silane gas and nitrogen gas, in which the silane gas is 1 to 3 mol %, is flowed into the tubular furnace at a flow rate of 250 to 350 sccm, and the furnace is maintained under conditions of 450 to 550°C, 700 to 800 Torr, and 90 to 150 minutes for treatment.

[0032] <Graphite Powder> The median diameter D in the volume frequency particle size distribution of the graphite powder of this embodiment measured by the laser diffraction scattering method ５０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle diameter is preferably 3.0 μm or more and 30.0 μm or less, more preferably 5.0 μm or more and 25.0 μm or less, even more preferably 7.0 μm or more and 20.0 μm or less, even more preferably 8.0 μm or more and 16.0 μm or less, and even more preferably 9.0 μm or more and 14.0 μm or less.

[0033] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder of this embodiment as determined by the laser diffraction scattering method １０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle size is preferably 1.0 μm or more and 10.0 μm or less, more preferably 2.0 μm or more and 9.0 μm or less, even more preferably 2.5 μm or more and 8.5 μm or less, and still more preferably 3.0 μm or more and 8.0 μm or less.

[0034] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the graphite powder of this embodiment as determined by the laser diffraction scattering method ９０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the average particle diameter is preferably 5.0 μm or more and 40.0 μm or less, more preferably 10.0 μm or more and 35.0 μm or less, even more preferably 12.0 μm or more and 30.0 μm or less, even more preferably 14.0 μm or more and 27.0 μm or less, and even more preferably 16.0 μm or more and 24.0 μm or less.

[0035] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder of this embodiment as determined by the laser diffraction scattering method １０ , 90% particle diameter D ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 0.50 or more and 3.00 or less, more preferably 0.70 or more and 2.50 or less, even more preferably 0.80 or more and 2.00 or less, even more preferably 0.90 or more and 1.70 or less, and even more preferably 1.00 or more and 1.50 or less.

[0036] In this embodiment, the volume frequency particle size distribution of the graphite powder can be measured, for example, by the following method. First, the graphite powder is suspended in a dispersion medium and ultrasonically dispersed. Next, the volume frequency particle size distribution of the graphite powder is measured by a laser diffraction scattering method using a laser diffraction particle size distribution analyzer. The measurement is performed five times, and the average value can be used.

[0037] The graphite powder of this embodiment preferably contains graphite particles containing amorphous carbon on the surface thereof, from the viewpoint of further improving the energy density of the resulting lithium ion secondary battery.

[0038] The graphite powder of this embodiment preferably contains artificial graphite particles from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery.

[0039] These graphite powders can be obtained by, for example, classifying commercially available graphite powders using a sieve with an appropriate opening ratio and wire diameter, thereby obtaining a median diameter D ５０ , cumulative 10% diameter D １０ and cumulative 90% diameter D ９０ can be obtained by adjusting the thickness of the coating layer. Graphite powder containing graphite particles with amorphous carbon on the surface can be obtained, for example, by coating 2 to 5 parts by weight of amorphous carbon with 100 parts by weight of commercially available graphite powder by a method such as arc ion plating, sputtering, or plasma CVD. In this case, the breaking strength of the graphite powder can be adjusted by adjusting the thickness of the amorphous carbon coating layer. Examples of commercially available graphite powder include graphite powder manufactured by Nippon Graphite Industries Co., Ltd. and graphite powder manufactured by JFE Chemical Corporation.

[0040] From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the content of the graphite powder in the negative electrode active material of this embodiment, when the total amount of the negative electrode active material is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 99.0 parts by mass or less, more preferably 55.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 58.0 parts by mass or more and 92.0 parts by mass or less, even more preferably 60.0 parts by mass or more and 85.0 parts by mass or less, and still more preferably 63.0 parts by mass or more and 82.0 parts by mass or less.

[0041] The median diameter D in the volume frequency particle size distribution of the graphite powder and Si / C powder of this embodiment measured by the laser diffraction scattering method ５０ D respectively １ and D ２ When this is done, D １ / D ２ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 0.5 or more and 10.0 or less, more preferably 0.8 or more and 7.0 or less, even more preferably 1.0 or more and 5.0 or less, even more preferably 1.4 or more and 4.0 or less, and still more preferably 1.8 or more and 3.0 or less.

[0042] In the negative electrode active material of this embodiment, the content of graphite powder in the negative electrode active material is W １ , the content of Si / C powder in the negative electrode active material is W２ When W １ / W ２ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 1.0 or more and 20.0 or less, more preferably 1.2 or more and 15.0 or less, even more preferably 1.4 or more and 10.0 or less, even more preferably 1.6 or more and 7.0 or less, and still more preferably 1.8 or more and 5.0 or less.

[0043] From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the total content of the graphite powder and Si / C powder in the negative electrode active material of this embodiment is preferably 80.0 parts by mass or more and 100.0 parts by mass or less, more preferably 90.0 parts by mass or more and 100.0 parts by mass or less, even more preferably 95.0 parts by mass or more and 100.0 parts by mass or less, and still more preferably 99.0 parts by mass or more and 100.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0044] <Graphite Powder (A), Graphite Powder (B)> From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the graphite powder of the present embodiment preferably has a median diameter D in a volume frequency particle size distribution measured by a laser diffraction scattering method. ５０ The graphite powder (A) and the graphite powder (B) are two kinds of graphite powders having different median diameters D ５０ is the median diameter D of the graphite powder (B) ５０ Greater than.

[0045] When the graphite powder of this embodiment contains graphite powder (A) and graphite powder (B), the median diameter D in the volume frequency particle size distribution of the graphite powder (A) and the graphite powder (B) by the laser diffraction scattering method is ５０ D respectively Ａ and D Ｂ When this is done, D Ｂ / D Ａ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 0.40 or more and less than 1.00, more preferably 0.50 or more and 0.95 or less, even more preferably 0.55 or more and 0.90 or less, and still more preferably 0.60 or more and 0.85 or less.

[0046] When the graphite powder of the present embodiment contains graphite powder (A) and graphite powder (B), from the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, preferably, the graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the graphite powder (B) contains graphite particles not containing amorphous carbon on the surface thereof.

[0047] When the graphite powder of this embodiment contains graphite powder (A) and graphite powder (B), the content of graphite powder (A) in the graphite powder is W Ａ , the content of graphite powder (B) in the graphite powder is W Ｂ When W Ａ / W Ｂ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the value of is preferably 0.1 or more and 10.0 or less, more preferably 0.1 or more and 8.0 or less, even more preferably 0.2 or more and 6.0 or less, and still more preferably 0.2 or more and 5.0 or less.

[0048] <Method for Producing Negative Electrode Active Material> As a method for producing the negative electrode active material of this embodiment, for example, a method of dry-mixing the raw materials, graphite powder and Si / C powder, using a mixer, such as a small mill mixer, a V-type mixer, a rocking mixer, a ball mill, or a vibration mill, can be used.

[0049] <Energy Density E> From the viewpoint of further improving the energy density of the resulting lithium-ion secondary battery, the energy density E obtained by the method described below of this embodiment is preferably 800 Wh / L or more, more preferably 810 Wh / L or more, even more preferably 820 Wh / L or more, even more preferably 830 Wh / L or more, even more preferably 840 Wh / L or more, even more preferably 855 Wh / L or more, even more preferably 865 Wh / L or more, and even more preferably 875 Wh / L or more, in terms of cell conversion. The upper limit of the energy density E obtained by the method described below of this embodiment is not particularly limited, but may be, for example, 1500 Wh / L or less, 1200 Wh / L or less, or 1000 Wh / L or less. (Method) A negative electrode active material slurry is prepared by adding an appropriate amount of water to a solid content consisting of 96.9 parts by mass of a negative electrode active material, 0.1 parts by mass of single-walled carbon nanotubes, and 3.0 parts by mass of polyacrylic acid. Next, the negative electrode active material slurry was applied to a copper foil negative electrode current collector so that the initial charge capacity per unit area was 4.3 mAh / cm ２ The negative electrode laminate is then coated in an amount such that the density of the negative electrode active material layer becomes 1.65 g / cm using a roll press. ３ The negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５A lithium-ion secondary battery was fabricated by placing an electrode laminate, in which a positive electrode containing a cellulose acylate (C1) and a positive electrode containing a cellulose acylate (C2) facing each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate outer casing formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab were connected to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate outer casing. The lithium-ion secondary battery was then charged at 7.2 mA, and after the upper voltage reached 4.2 V, it was charged at a constant voltage until the total charge time was 12 hours. It was then discharged at a constant current of 7.2 mA until the lower voltage reached 2.5 V. It was then charged again under the same conditions, left in a thermostatic chamber at 45°C for 3 days, and discharged again under the same conditions. The capacity and average voltage at the final discharge were measured. After the final discharge, the thickness of the lithium-ion secondary battery was measured. Next, based on the above measured values, the electrode area of ​​the electrode laminate, the thickness of the laminate exterior body, the thickness of the negative electrode current collector, and the thickness of the positive electrode current collector in the positive electrode, the cell-equivalent energy density E (Wh / L) is calculated using the following formula: (Energy density E) = (Capacity at final discharge) x (Average voltage at final discharge) / (Electrode area of ​​electrode laminate) / ((Thickness of lithium ion secondary battery) - (Thickness of laminate exterior body) - (Thickness of positive electrode current collector) / 2 - (Thickness of negative electrode current collector) / 2)

[0050] From the viewpoint of further improving the energy density of the obtained lithium-ion secondary battery, the energy density E by the above method of the present embodiment is, in cell conversion, preferably 800 Wh / L to 1500 Wh / L, more preferably 810 Wh / L to 1500 Wh / L, even more preferably 820 Wh / L to 1500 Wh / L, even more preferably 830 Wh / L to 1500 Wh / L, even more preferably 840 Wh / L to 1200 Wh / L, even more preferably 855 Wh / L to 1200 Wh / L, even more preferably 865 Wh / L to 1000 Wh / L, and even more preferably 875 Wh / L to 1000 Wh / L.

[0051] <Negative electrode> The negative electrode of this embodiment includes the negative electrode active material of this embodiment. From the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery, the negative electrode of this embodiment preferably includes a negative electrode active material layer including the negative electrode active material of this embodiment and a negative electrode current collector. From the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery, the negative electrode active material layer of this embodiment preferably includes the negative electrode active material and a binder of this embodiment, and more preferably includes the negative electrode active material, a binder, and a conductive additive of this embodiment.

[0052] From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the content of the negative electrode active material of this embodiment in the negative electrode active material layer of this embodiment is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 75.0 parts by mass or more and 99.9 parts by mass or less, even more preferably 85.0 parts by mass or more and 99.5 parts by mass or less, still more preferably 90.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 95.0 parts by mass or more and 98.5 parts by mass or less, and still more preferably 96.0 parts by mass or more and 98.0 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0053] Examples of the conductive additive in the negative electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and ketjen black; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination. Among these, the conductive additive in the negative electrode active material layer of this embodiment preferably contains a carbon material, more preferably contains carbon nanotubes, and even more preferably contains single-walled carbon nanotubes, from the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery.

[0054] From the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery, the content of the conductive additive in the negative electrode active material layer of this embodiment is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably 0.03 parts by mass or more and 1.0 parts by mass or less, even more preferably 0.05 parts by mass or more and 0.5 parts by mass or less, and still more preferably 0.07 parts by mass or more and 0.3 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0055] Examples of the binder in the negative electrode active material layer of this embodiment include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); polycarboxylic acid-based polymers such as poly(meth)acrylic acid; conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery, the binder in the negative electrode active material layer of the present embodiment preferably contains one or more selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more selected from the group consisting of polyvinylidene fluoride, polycarboxylic acid polymer, and styrene butadiene rubber, even more preferably contains a polycarboxylic acid polymer, and even more preferably contains poly(meth)acrylic acid.

[0056] From the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery, the content of the binder in the negative electrode active material layer of this embodiment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0057] From the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery, the thickness of the negative electrode active material layer of this embodiment is preferably 10 μm or more and 250 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 50 μm or more and 150 μm or less.

[0058] The density of the negative electrode active material layer of this embodiment is preferably 0.50 g / cm from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery. ３ 3.00g / cm or more ３ or less, more preferably 1.00 g / cm ３ 2.50g / cm or more ３ More preferably, 1.30 g / cm or less ３ 2.00g / cm or more ３ The following is the result.

[0059] The negative electrode current collector of this embodiment may be formed of, for example, copper, stainless steel, nickel, titanium, or an alloy thereof. The shape of the negative electrode current collector may be, for example, a foil, a flat plate, or a mesh. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0060] <Lithium-ion secondary battery> The lithium-ion secondary battery of this embodiment includes the negative electrode of this embodiment. The lithium-ion secondary battery of this embodiment includes the negative electrode containing the negative electrode active material of this embodiment, and therefore has improved energy density.

[0061] The lithium ion secondary battery of this embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the lithium ion secondary battery of this embodiment. As shown in FIG. 1, the lithium ion secondary battery 10 includes the negative electrode of this embodiment, an electrolyte, and a positive electrode. A separator 5 can be provided between the positive electrode and the negative electrode. A plurality of electrode pairs of a positive electrode and a negative electrode can be provided.

[0062] The lithium-ion secondary battery 10 includes a positive electrode including a positive electrode current collector 3 made of a metal such as aluminum foil and a positive electrode active material layer 1 containing a positive electrode active material disposed thereon, and a negative electrode including a negative electrode current collector 4 made of a metal such as copper foil and a negative electrode active material layer 2 containing a negative electrode active material disposed thereon. The positive electrode and negative electrode are stacked, for example, with a separator 5 interposed between them, such as a nonwoven fabric or a microporous polypropylene film, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. This electrode pair is housed in a container formed of exterior bodies 6 and 7 made of, for example, aluminum laminate film. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4, with these tabs extending outside the container. An electrolyte solution is poured into the container and sealed. Alternatively, a container may contain an electrode group in which multiple electrode pairs are stacked.

[0063] The lithium ion secondary battery 10 can be fabricated according to a known method. The electrodes can be, for example, laminates or wound bodies. The exterior can be a metal exterior or an aluminum laminate exterior. The battery can be in any shape, such as a coin, button, sheet, cylindrical, rectangular, or flat shape.

[0064] In the lithium-ion secondary battery of this embodiment, the positive electrode preferably includes a positive electrode active material layer containing a positive electrode active material and a positive electrode current collector. The positive electrode active material layer of this embodiment preferably includes a positive electrode active material and a binder, and more preferably includes a positive electrode active material, a binder, and a conductive additive.

[0065] Examples of the positive electrode active material in the positive electrode active material layer of this embodiment include composite oxides of lithium and transition metals such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt composite oxide, lithium-nickel-aluminum composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-manganese-cobalt composite oxide, lithium-nickel-manganese-aluminum composite oxide, and lithium-nickel-cobalt-manganese-aluminum composite oxide; TiS２ , FeS, MoS ２ transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２ and transition metal oxides such as olivine-type lithium phosphate; and the like. One of these may be used alone, or two or more may be used in combination.

[0066] Examples of the conductive additive in the positive electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and ketjen black; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination.

[0067] Examples of the binder in the positive electrode active material layer of this embodiment include fluorine-based binders such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); and aqueous binders such as styrene-butadiene rubber. One of these may be used alone, or two or more may be used in combination.

[0068] The positive electrode current collector of this embodiment may be formed of, for example, aluminum, stainless steel, nickel, titanium, or an alloy thereof. The positive electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh. The thickness of the positive electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0069] The electrolyte solution of this embodiment may be, for example, a solution of lithium hexafluorophosphate (LiPF) in an organic solvent such as cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and butylene carbonate (BC); chain carbonates such as ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters; γ-lactones such as γ-butyrolactone; chain ethers; and cyclic ethers. ６), lithium fluoride (LiBF ４ ), LiFSI, lithium perchlorate (LiClO ４ The organic solvent may be used alone or in combination of two or more kinds.

[0070] The separator of this embodiment is made of, for example, a porous film, woven fabric, nonwoven fabric, etc., mainly made of resin, and the resin component can be, for example, a polyolefin resin such as polypropylene or polyethylene, a polyester resin, an acrylic resin, a styrene resin, a nylon resin, etc. If necessary, the separator may be formed with a layer containing inorganic particles, and examples of the inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc.

[0071] The exterior body of this embodiment can be, for example, a case or a can case made of a flexible film, and from the viewpoint of reducing the weight of the battery, it is preferable to use a flexible film. The flexible film can be a metal layer serving as a base material, with resin layers provided on both sides. The metal layer can be selected from those having barrier properties, such as preventing leakage of the electrolyte solution and infiltration of moisture from the outside, and aluminum, stainless steel, etc. can be used. A heat-sealable resin layer, such as a modified polyolefin, is provided on at least one side of the metal layer. The heat-sealable resin layers of the flexible films are placed opposite each other, and the periphery of the portion housing the electrode stack is heat-sealed to form the exterior body. A resin layer, such as a nylon film or a polyester film, can be provided on the surface of the exterior body opposite the side on which the heat-sealable resin layer is formed.

[0072] <Lithium-ion secondary battery module> The lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment. Since the lithium-ion secondary battery of this embodiment has improved energy density, the lithium-ion secondary battery module of this embodiment also has improved energy density.

[0073] The lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment more preferably includes a housing capable of accommodating two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment further preferably includes one or more components selected from the group consisting of a protection circuit that protects the lithium-ion secondary batteries from overcurrent, a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary batteries, a controller that controls the lithium-ion secondary batteries, a cooler that can cool the lithium-ion secondary batteries, and a heater that can heat the lithium-ion secondary batteries.

[0074] The lithium-ion secondary battery module of this embodiment can be used in a battery system including a plurality of electrically connected lithium-ion secondary battery modules and a battery control system. Examples of battery systems include battery packs, stationary storage battery systems, automotive power storage battery systems, automotive auxiliary storage battery systems, and emergency power storage battery systems.

[0075] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0076] The embodiments of the present invention will be described in detail based on examples and comparative examples, but the present invention is not limited to the examples.

[0077] In preparing the negative electrode active material, the following graphite powder was used.

[0078] <Graphite powder (A)> Graphite powder 1 (artificial graphite containing amorphous carbon on the surface, D １０ : 8.4 μm, D ５０ : 13.6 μm, D ９０ : 21.1 μm, (D ９０ -D １０ ) / D ５０ : 0.93) Graphite powder 2 (artificial graphite containing amorphous carbon on the surface, D１０ : 9.0 μm, D ５０ : 14.5 μm, D ９０ : 36.0 μm, (D ９０ -D １０ ) / D ５０ Graphite powder 3 (artificial graphite containing amorphous carbon on the surface, D １０ : 6.0 μm, D ５０ : 12.0 μm, D ９０ : 19.0 μm, (D ９０ -D １０ ) / D ５０ Graphite powder 4 (artificial graphite containing amorphous carbon on the surface, D １０ : 6.0 μm, D ５０ : 12.0 μm, D ９０ : 20.0 μm, (D ９０ -D １０ ) / D ５０ : 1.17) Graphite powder 5 (artificial graphite containing amorphous carbon on the surface, D １０ : 10.0 μm, D ５０ : 30.0 μm, D ９０ : 36.0 μm, (D ９０ -D １０ ) / D ５０ : 0.87)

[0079] <Graphite powder (B)> Graphite powder 6 (artificial graphite not containing amorphous carbon on the surface, D １０ : 4.9 μm, D ５０ : 9.6 μm, D ９０ : 17.6 μm, (D ９０ -D １０ ) / D ５０ : 1.32)

[0080] <Preparation of Si / C Powder 1> Porous Carbon Material 1 (D ５０ : 4.8 μm, specific surface area: 1678 m ２ The Si / C powder (1 / g) was placed in a tubular furnace, and the atmosphere inside the furnace was replaced with argon gas. Then, a mixed gas of 2 mol % silane gas and 98 mol % nitrogen gas was flowed into the furnace at a flow rate of 300 sccm, and the treatment was carried out by holding the product under the conditions of 500°C, 760 Torr, and 120 minutes. The product was then cooled to room temperature, and Si / C powder 1 was obtained.

[0081] A cross section of the Si-C composite particle contained in the obtained Si / C powder 1 was subjected to elemental mapping of silicon and carbon using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), an energy dispersive X-ray spectroscopic detector (Ultim Max 40, manufactured by Oxford Instruments) and image analysis software (Aztec, manufactured by Oxford Instruments) with secondary electrons selected as the detection target under conditions of an acceleration voltage of 3 kV, 20 mapping accumulations and 3000x magnification, and it was confirmed that the Si-C composite particle contained silicon and that the silicon in the Si-C composite particle was present in at least a portion of the pores of the porous carbon material.

[0082] For the obtained Si / C powder 1, a micro-compression tester (MCT-510, manufactured by Shimadzu Corporation) was used to measure the test force P (N) at which the particles of Si / C powder 1 broke using an indenter. That is, after scattering a very small amount of Si / C powder 1 on a sample stage, 100 random particles were compressed one by one using an indenter, and the test force P (N) at which the particles of Si / C powder 1 broke was determined. In addition, the particle diameter d (mm) of each particle was measured in two orthogonal directions (X direction and Y direction in the observation image of the micro-compression tester) and the average value thereof was used. Next, the breaking strength CS of each particle was calculated from the test force P (N), particle diameter d (mm), and pi using the following formula, and the average value of the breaking strengths CS for the 100 particles was taken as the breaking strength CS of Si / C powder 1. ２ The results are shown in Table 1. CS = 2.48 × P / (π × d ２ )

[0083] The obtained Si / C powder 1 was measured by a laser diffraction scattering method using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) to determine the particle diameter D at which the cumulative value reached 10%. １０ , the particle diameter D at which the cumulative value reaches 90% ９０ , median diameter D ５０ and (D ９０ -D １０ ) / D ５０The value of was determined. Here, Si / C powder 1 was suspended in a dispersion medium and ultrasonically dispersed, and then the measurement was performed. The measurement was performed five times, and the average value was used for each. The results are shown in Table 1. A 0.1 mass % aqueous solution of sodium hexametaphosphate was used as the dispersion medium.

[0084] <Preparation of Si / C Powder 2 and Si / C Powder 3> Instead of the porous carbon material 1, the porous carbon material 2 (D ５０ : 4.4μm, specific surface area: 1750m ２ / g) and porous carbon material 3 (D ５０ :9.0μm, specific surface area: 1635m ２ Si / C powder 2 and Si / C powder 3 were obtained in the same manner as in the production of Si / C powder 1, except that Si / C powder 2 (1 / g) was used instead.

[0085] Cross sections of the Si-C composite particles contained in the obtained Si / C powder 2 and Si / C powder 3 were subjected to elemental mapping using the same method as for the above-mentioned Si / C powder 1. As a result, it was confirmed that the Si-C composite particles in both cases contained silicon, and that the silicon in the Si-C composite particles was present in at least some of the pores of the porous carbon material.

[0086] The resulting Si / C powder 2 and Si / C powder 3 were subjected to the same fracture strength CS as that of the Si / C powder 1. ２ , cumulative 10% diameter D １０ , cumulative 90% diameter D ９０ , median diameter D ５０ and (D ９０ -D １０ ) / D ５０ The results are shown in Table 1.

[0087] Examples 1 to 13, Comparative Examples 1 and 2 <Preparation of Graphite Powder> Graphite powder (A) and graphite powder (B) were mixed in the blending ratio shown in Table 1 to obtain graphite powders of Examples 1 to 13 and Comparative Examples 1 and 2.

[0088] The graphite powders of each example and each comparative example were subjected to the same method as the Si / C powder 1 to measure the breaking strength CS １ , cumulative 10% diameter D １０ , cumulative 90% diameter D ９０ , median diameter D ５０ , (D９０ -D １０ ) / D ５０ The value of was measured. Here, graphite powder was suspended in a dispersion medium and ultrasonically dispersed, and then the measurement was performed. The measurement was performed five times, and the average value was used for each. The results are shown in Table 1. A 0.1 mass % aqueous solution of sodium hexametaphosphate was used as the dispersion medium.

[0089] <Preparation of Negative Electrode Active Material> Graphite powder and Si / C powder were mixed in the compounding ratios shown in Table 1 to obtain negative electrode active materials of Examples 1 to 13 and Comparative Examples 1 and 2.

[0090] <Preparation of Negative Electrode> For the negative electrode active materials of each Example and Comparative Example, a suitable amount of water was added to a solid content consisting of 96.9 parts by mass of the negative electrode active material, 0.1 parts by mass of single-walled carbon nanotubes, and 3.0 parts by mass of polyacrylic acid to prepare a negative electrode active material slurry. Next, the negative electrode active material slurry was applied to a copper foil having a thickness of 8 μm as a negative electrode current collector, so that the initial charge capacity per unit area was 4.3 mAh / cm. ２ The negative electrode laminate was then coated in an amount such that the density of the negative electrode active material layer was 1.65 g / cm using a roll press. ３ The negative electrodes of the examples and comparative examples were obtained by pressing the negative electrodes with a pressure of 1000 kJ / cm.sup.2 or less.

[0091] <Preparation of Positive Electrode> Lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ A suitable amount of N-methyl-2-pyrrolidone was added to a solid content consisting of 97.5 parts by mass of ethylenediamine fluoride, 1.5 parts by mass of polyvinylidene fluoride, and 1.0 part by mass of single-walled carbon nanotubes to prepare a positive electrode active material slurry. Next, the positive electrode active material slurry was applied to a 12 μm thick aluminum foil as a positive electrode current collector so that the initial charge capacity per unit area was 4.0 mAh / cm. ２ The positive electrode laminate was then coated in an amount such that the density of the positive electrode active material layer was 3.5 g / cm using a roll press. ３ The positive electrode was obtained by pressing the positive electrode with a pressure of 0.015.

[0092] <Preparation of Non-Aqueous Electrolyte> The non-aqueous electrolyte was prepared by mixing an organic solvent and a supporting salt. The volume ratio of ethylene carbonate, which is a cyclic carbonate, to ethyl methyl carbonate, which is a chain carbonate, was adjusted to 3 / 7, and lithium hexafluorophosphate (LiPF ) was further added as a supporting salt. ６ ) (concentration: 1.2 mol / L) and fluoroethylene carbonate (concentration relative to the organic solvent: 6% by mass) as an additive.

[0093] <Fabrication of Lithium-Ion Secondary Batteries> The positive electrode and the negative electrode of each Example and Comparative Example were cut into 3 cm x 3 cm pieces and placed opposite each other with a separator interposed therebetween to fabricate an electrode laminate. The separator used was a 10 μm-thick microporous polyethylene film with ceramic coating on both sides. The electrode laminate and nonaqueous electrolyte were then placed in a laminate outer casing formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab were connected to the negative electrode and the positive electrode, respectively, and the periphery of the laminate outer casing was sealed to fabricate the lithium-ion secondary batteries of each Example and Comparative Example. One end of the positive electrode tab was connected to the positive electrode and the other end was extended outside the outer casing, and one end of the negative electrode tab was connected to the negative electrode and the other end was extended outside the outer casing.

[0094] <Energy Density E> The lithium-ion secondary batteries of each Example and Comparative Example were charged at 7.2 mA. After the upper limit voltage reached 4.2 V, they were charged at a constant voltage until the total charge time reached 12 hours. They were then discharged at a constant current of 7.2 mA until the lower limit voltage reached 2.5 V. They were then charged again under the same conditions, left in a thermostatic chamber at 45°C for 3 days, and discharged again under the same conditions. They were then charged and discharged once more. The capacity and average voltage at the final discharge were measured. After the final discharge, the thickness of the lithium-ion secondary battery was measured. The cell-equivalent energy density E (Wh / L) was calculated using the following formula based on the above measurements, the electrode area of ​​the electrode laminate, the thickness of the laminate exterior body, the thickness of the negative electrode current collector, and the thickness of the positive electrode current collector. The results are shown in Table 1. (Energy density E) = (Capacity at final discharge) × (Average voltage at final discharge) / (Electrode area of ​​electrode laminate) / ((Thickness of lithium ion secondary battery) - (Thickness of laminate exterior body) - (Thickness of positive electrode current collector) / 2 - (Thickness of negative electrode current collector) / 2)

[0095]

[0096] This application claims priority based on Japanese Patent Application No. 2024-056822, filed March 29, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0097] REFERENCE SIGNS LIST 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode current collector 4 Negative electrode current collector 5 Separator 6 Exterior body 7 Exterior body 8 Negative electrode tab 9 Positive electrode tab 10 Lithium ion secondary battery

Claims

1. A graphite powder and a Si / C powder containing Si-C composite particles containing silicon and a carbon material, wherein the fracture strength of the graphite powder and the Si / C powder measured in accordance with JIS R 1639-5:2007 is CS. １ and C.S. ２ When this is done, CS １ / CS ２ The negative electrode active material has a value of 0.32 or less.

2. Said CS １ The negative electrode active material according to claim 1 , wherein the stress is 10 MPa or more and 90 MPa or less.

3. Median diameter D in the volume frequency particle size distribution of the graphite powder measured by laser diffraction scattering method ５０ The negative electrode active material according to claim 1 or 2, wherein the average particle diameter is 3.0 μm or more and 30.0 μm or less.

4. The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder by the laser diffraction scattering method １０ , 90% particle diameter D ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ 4. The negative electrode active material according to claim 1, wherein the value of is 0.50 or more and 3.00 or less.

5. Median diameter D in the volume frequency particle size distribution of the Si / C powder measured by laser diffraction scattering method ５０ The negative electrode active material according to any one of claims 1 to 4, wherein the average particle size is 1.0 µm or more and 20.0 µm or less.

6. The negative electrode active material according to any one of claims 1 to 5, wherein the carbon material in the Si-C composite particles comprises a porous carbon material, and the silicon is present in at least part of the pores of the porous carbon material.

7. The negative electrode active material according to any one of claims 1 to 6, wherein the graphite powder contains graphite particles having amorphous carbon on the surface thereof.

8. The negative electrode active material according to any one of claims 1 to 7, wherein the graphite powder contains artificial graphite particles.

9. The negative electrode active material according to any one of claims 1 to 8, wherein the content of the graphite powder in the negative electrode active material is 50.0 parts by mass or more and 99.0 parts by mass or less, when the total amount of the negative electrode active material is 100.0 parts by mass.

10. The negative electrode active material according to any one of claims 1 to 9, wherein the content of the Si / C powder in the negative electrode active material is 1.0 part by mass or more and 50.0 parts by mass or less, when the total amount of the negative electrode active material is 100.0 parts by mass.

11. The content of the graphite powder in the negative electrode active material is W １ , the content of the Si / C powder in the negative electrode active material is W ２ When W １ / W ２ The negative electrode active material according to any one of claims 1 to 10, wherein the value of is 1.0 or more and 20.0 or less.

12. The graphite powder has a median diameter D in a volume frequency particle size distribution measured by a laser diffraction scattering method. ５０ The graphite powder (A) and the graphite powder (B) are two kinds of graphite powders having different median diameters D ５０ is the median diameter D of the graphite powder (B). ５０ The negative electrode active material according to any one of claims 1 to 11, wherein the negative electrode active material has a molecular weight of 1.0 or more.

13. Median diameter D of the graphite powder (A) ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When this is done, D Ｂ / D Ａ The negative electrode active material according to claim 12 , wherein the value of 14. The negative electrode active material according to claim 12 or 13, wherein the graphite powder (A) contains graphite particles having amorphous carbon on their surfaces, and the graphite powder (B) contains graphite particles having no amorphous carbon on their surfaces.

15. The content of the graphite powder (A) in the graphite powder is W Ａ The content of the graphite powder (B) in the graphite powder is W Ｂ When W Ａ / W Ｂ The negative electrode active material according to any one of claims 12 to 14, wherein the value of is 0.1 or more and 10.0 or less.

16. The negative electrode active material according to any one of claims 1 to 15, having an energy density E of 800 Wh / L or more in terms of a cell, as measured by the following method: (Method) A negative electrode active material slurry is prepared by adding an appropriate amount of water to a solid content consisting of 96.9 parts by mass of the negative electrode active material, 0.1 parts by mass of single-walled carbon nanotubes, and 3.0 parts by mass of polyacrylic acid. Next, the negative electrode active material slurry is applied to a copper foil negative electrode current collector so that the initial charge capacity per unit area is 4.3 mAh / cm. ２ The negative electrode laminate is then coated in an amount such that the density of the negative electrode active material layer becomes 1.65 g / cm using a roll press machine. ３ Then, the negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５ A lithium-ion secondary battery was fabricated by placing an electrode laminate, in which a positive electrode containing a cellulose acylate (C1) and a positive electrode containing a cellulose acylate (C2) facing each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate outer casing formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab were connected to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate outer casing. The lithium-ion secondary battery was then charged at 7.2 mA, and after the upper voltage reached 4.2 V, it was charged at a constant voltage until the total charge time was 12 hours. It was then discharged at a constant current of 7.2 mA until the lower voltage reached 2.5 V. It was then charged again under the same conditions, left in a thermostatic chamber at 45°C for 3 days, and discharged again under the same conditions. The capacity and average voltage at the final discharge were measured. After the final discharge, the thickness of the lithium-ion secondary battery was measured. Next, the energy density E (Wh / L) converted into a cell is calculated using the following formula based on the above measured values, the electrode area of ​​the electrode laminate, the thickness of the laminate exterior body, the thickness of the negative electrode current collector, and the thickness of the positive electrode current collector in the positive electrode: (Energy density E) = (Capacity at final discharge) x (Average voltage at final discharge) / (Electrode area of ​​electrode laminate) / ((Thickness of lithium ion secondary battery) - (Thickness of laminate exterior body) - (Thickness of positive electrode current collector) / 2 - (Thickness of negative electrode current collector) / 2) 17. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 16.

18. A lithium ion secondary battery comprising the negative electrode according to claim 17.

19. A lithium ion secondary battery module comprising the lithium ion secondary battery according to claim 18.

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