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

Abstract

A negative electrode active material according to the present invention contains graphite powder and Si / C powder containing Si-C composite particles composed of silicon and a carbon material. The graphite powder contains graphite powder (A) and graphite powder (B), which are two kinds of graphite powder having different median diameters D50 in a volume frequency particle size distribution by a laser diffraction scattering method. When the graphite powder (A) contains graphite particles containing amorphous carbon on the surface, and the median diameter D50 of the graphite powder (A) is DA and the median diameter D50 of the graphite powder (B) is DB, the value of DB / DA is 0.60 to 1.20.

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] As a negative electrode active material, Si / C powder is sometimes used. 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 a negative electrode active material containing graphite powder and Si / C powder may have poor press characteristics.

[0005] Furthermore, according to the investigations of the present inventors, it has become clear that lithium dendrites may be easily generated in lithium ion secondary batteries using a negative electrode active material containing graphite powder and Si / C powder.

[0006] The present invention provides a negative electrode active material that has good press characteristics and can suppress the generation of lithium dendrites in the resulting lithium ion secondary battery, a negative electrode that can suppress the generation of lithium dendrites in the resulting lithium ion secondary battery, and a lithium ion secondary battery and lithium ion secondary battery module that can suppress the generation of lithium dendrites.

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result, have discovered a method for producing a graphite powder having a median diameter D 1 / 2 in a volume frequency particle size distribution measured by a laser diffraction scattering method. ５０ The graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the graphite powder (A) has a median diameter D ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When this is done, D Ｂ / D Ａ The present inventors have found that a negative electrode active material having a value of 0.60 or more and 1.20 or less can suppress the formation of lithium dendrites in the resulting lithium ion secondary battery while having good pressing characteristics, and have completed the present invention.

[0008] 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.

[0009] [1] A method for producing a graphite powder having a Si / C powder containing Si-C composite particles containing silicon and a carbon material, wherein the graphite powder has a median diameter D ５０ The graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the graphite powder (A) has a median diameter D ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When this is done, D Ｂ / D Ａ [2] A negative electrode active material in which the value of D is 0.60 or more and 1.20 or less. Ａ [3] The negative electrode active material according to [1], wherein the D Ｂ [4] The negative electrode active material according to [1] or [2], wherein the median diameter D in a volume frequency particle size distribution of the graphite powder measured by a laser diffraction scattering method is 3.0 μm or more and 12.0 μm or less. ５０ [5] The negative electrode active material according to any one of [1] to [3], wherein the median diameter D in the volume frequency particle size distribution of the Si / C powder measured by a laser diffraction scattering method is 3.0 μm or more and 30.0 μm or less. ５０[6] The negative electrode active material according to any one of [1] to [5], wherein the graphite powder (B) comprises graphite particles whose surfaces do not contain amorphous carbon. [7] The negative electrode active material according to any one of [1] to [6], 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. [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] When the total amount of the negative electrode active material is 100.0 parts by mass, the content of the graphite powder in the negative electrode active material and the content of the Si / C powder in the negative electrode active material are each W １ and W ２ When W １ / W ２

[12] When the total amount of the graphite powder is 100.0 parts by mass, the content of the graphite powder (A) in the graphite powder and the content of the graphite powder (B) in the graphite powder are each W Ａ and W Ｂ When W Ｂ / W Ａ

[13] When a negative electrode laminate having a negative electrode current collector and a negative electrode active material layer is produced using the negative electrode active material by the following method, and the negative electrode laminate is pressed using a roll press, the density of the negative electrode active material layer after pressing is 1.6 g / cm ３ The required pressure P １．６The negative electrode active material according to any one of [1] to

[12] , wherein the initial charge capacity per unit area is 1.40 t / cm 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 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 having a thickness of 8 μm as the negative electrode current collector, and ... initial charge capacity per unit area is 4.3 mAh / cm. ２ and then drying to obtain the negative electrode laminate having the negative electrode current collector and the negative electrode active material layer.

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

[13] .

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

[14] .

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

[15] .

[0010] According to the present invention, it is possible to provide a negative electrode active material that has good press characteristics and is capable of suppressing the generation of lithium dendrites in the resulting lithium ion secondary battery, a negative electrode that is capable of suppressing the generation of lithium dendrites in the resulting lithium ion secondary battery, and a lithium ion secondary battery and lithium ion secondary battery module that are capable of suppressing the generation of lithium dendrites.

[0011] 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to an embodiment of the present invention.

[0012] 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.

[0013] In this embodiment, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0014] <Negative Electrode Active Material> The negative electrode active material of the present embodiment includes graphite powder and Si / C powder including Si—C composite particles containing silicon and a carbon material, and the graphite powder has a median diameter D５０ The graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the median diameter D of the graphite powder (A) is ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When this is done, D Ｂ / D Ａ The value is 0.60 or more and 1.20 or less.

[0015] According to the study by the present inventors, 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 graphite powder has a median diameter D ５０ When two different graphite powders are included, the median diameter D of the two graphite powders is ５０ It has been found that there is a relationship between the ratio of 0.01 to 0.1 and the performance balance between the pressing characteristics and the suppression of lithium dendrite formation in the resulting lithium ion secondary battery.

[0016] 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 graphite powder has a median diameter D ５０ The graphite powder (A) contains graphite particles containing amorphous carbon on the surface thereof, and the median diameter D of the graphite powder (A) is ５０ D Ａ , the median diameter D of the graphite powder (B) ５０ D Ｂ When Ｂ / D Ａ The present inventors have found that by adjusting the value of (a) to 0.60 or more and 1.20 or less, it is possible to improve the balance of performance between the pressing characteristics and the suppression of lithium dendrite formation in the resulting lithium ion secondary battery, and have completed the present invention.

[0017] In the negative electrode active material of this embodiment, the median diameter D in the volume frequency particle size distribution of the graphite powder (A) measured by the laser diffraction scattering method ５０ D Ａ, the median diameter D in the volume frequency particle size distribution of the graphite powder (B) measured by the laser diffraction scattering method ５０ D Ｂ When this is done, D Ｂ / D Ａ From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the value of is 0.60 or more and 1.20 or less, preferably 0.61 or more and 1.15 or less, more preferably 0.62 or more and 1.10 or less, even more preferably 0.63 or more and 1.05 or less, even more preferably 0.64 or more and 1.00 or less, and still more preferably 0.65 or more and 0.98 or less.

[0018] The median diameter D in the volume frequency particle size distribution of the graphite powder (A) of this embodiment measured by the laser diffraction scattering method ５０ D is Ａ is preferably 5.0 μm or more and 20.0 μm or less, more preferably 6.0 μm or more and 19.0 μm or less, even more preferably 7.0 μm or more and 18.0 μm or less, even more preferably 8.0 μm or more and 17.0 μm or less, and even more preferably 9.0 μm or more and 16.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0019] The median diameter D in the volume frequency particle size distribution of the graphite powder (B) of this embodiment measured by the laser diffraction scattering method ５０ D is Ｂ is preferably 3.0 μm or more and 12.0 μm or less, more preferably 5.0 μm or more and 11.0 μm or less, even more preferably 7.0 μm or more and 10.5 μm or less, and still more preferably 9.0 μm or more and 10.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0020] 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.

[0021] In this embodiment, the median diameter D of the graphite powder (A) and the graphite powder (B) ５０ As a method for adjusting the median diameter D ５０ A method of using commercially available graphite powders with different median diameters, or a method of adjusting the manufacturing conditions of graphite powders such as heat treatment, pulverization treatment, or classification treatment to obtain a median diameter D ５０ In addition, a method for producing graphite powder (A) and graphite powder (B) having different median diameters D ５０ Two or more kinds of graphite powders having different median diameters D of graphite powder (A) and graphite powder (B) are mixed together. ５０ may be adjusted.

[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 includes a carbon material in the Si-C composite particles that contains a porous carbon material, and silicon is present in at least some 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 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, even more preferably 4.0 μm or more and 10.0 μm or less, and even more preferably 4.5 μm or more and 5.5 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[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 １０ 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, even more preferably 1.5 μm or more and 4.5 μm or less, and even more preferably 1.7 μm or more and 2.5 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[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 ９０From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the thickness 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, even more preferably 8.0 μm or more and 15.0 μm or less, and even more preferably 8.5 μm or more and 10.0 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 performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained 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 performance balance between the pressing characteristics and the suppression of lithium dendrite generation in 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 40.0 parts by mass or less, even more preferably 8.0 parts by mass or more and 35.0 parts by mass or less, even more preferably 15.0 parts by mass or more and 30.0 parts by mass or less, and even more preferably 18.0 parts by mass or more and 25.0 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 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 15.0 μm or less, and even more preferably 9.0 μm or more and 13.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[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 １０is 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 3.0 μm or more and 8.5 μm or less, and still more preferably 4.0 μm or more and 8.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[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 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 25.0 μm or less, and even more preferably 16.0 μm or more and 23.5 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[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 , the particle diameter D at which the cumulative value reaches 90% ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained 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] 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.

[0037] 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 D１０ and cumulative 90% diameter D ９０ The graphite powder containing graphite particles having amorphous carbon on the surface thereof 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. Examples of commercially available graphite powder include graphite powder manufactured by Nippon Graphite Industries Co., Ltd. and graphite powder manufactured by JFE Chemical Corporation.

[0038] From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the content of the graphite powder in the negative electrode active material of this embodiment is preferably 50.0 parts by mass or more and 99.0 parts by mass or less, more preferably 60.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 65.0 parts by mass or more and 92.0 parts by mass or less, still more preferably 70.0 parts by mass or more and 86.0 parts by mass or less, and still more preferably 75.0 parts by mass or more and 83.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0039] 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 performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery, the value of is preferably 0.10 or more and 10.00 or less, more preferably 0.50 or more and 7.00 or less, even more preferably 0.80 or more and 5.00 or less, even more preferably 1.00 or more and 4.00 or less, and still more preferably 1.10 or more and 3.00 or less.

[0040] When the total amount of the negative electrode active material of this embodiment is 100.0 parts by mass, the content of the graphite powder in the negative electrode active material and the content of the Si / C powder in the negative electrode active material are W １ and W ２ When W １ / W ２From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery, the value of is preferably 1.00 or more and 20.00 or less, more preferably 2.00 or more and 15.00 or less, even more preferably 3.00 or more and 10.00 or less, and still more preferably 3.50 or more and 9.50 or less.

[0041] From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in 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.

[0042] <Graphite powder (A)> The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder (A) of this embodiment measured by the laser diffraction scattering method １０ is preferably 1.0 μm or more and 15.0 μm or less, more preferably 2.0 μm or more and 13.0 μm or less, even more preferably 3.0 μm or more and 11.0 μm or less, and still more preferably 4.0 μm or more and 10.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0043] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the graphite powder (A) of this embodiment as measured by the laser diffraction scattering method ９０ is preferably 5.0 μm or more and 50.0 μm or less, more preferably 10.0 μm or more and 45.0 μm or less, even more preferably 12.0 μm or more and 42.0 μm or less, even more preferably 14.0 μm or more and 40.0 μm or less, and even more preferably 16.0 μm or more and 38.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0044] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder (A) of this embodiment as measured by the laser diffraction scattering method １０ , the particle diameter D at which the cumulative value reaches 90% ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery, the value of is preferably 0.50 or more and 3.00 or less, more preferably 0.60 or more and 2.50 or less, even more preferably 0.70 or more and 2.20 or less, even more preferably 0.80 or more and 2.00 or less, and still more preferably 0.90 or more and 1.90 or less.

[0045] The graphite powder (A) of the present embodiment preferably contains artificial graphite particles from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery.

[0046] From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the content of the graphite powder (A) in the negative electrode active material of this embodiment is preferably 5.0 parts by mass or more and 80.0 parts by mass or less, more preferably 10.0 parts by mass or more and 75.0 parts by mass or less, even more preferably 13.0 parts by mass or more and 70.0 parts by mass or less, still more preferably 20.0 parts by mass or more and 60.0 parts by mass or less, even more preferably 30.0 parts by mass or more and 50 parts by mass or less, and still more preferably 35.0 parts by mass or more and 45.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0047] <Graphite powder (B)> The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder (B) of this embodiment by the laser diffraction scattering method １０ is preferably 1.0 μm or more and 10.0 μm or less, more preferably 2.0 μm or more and 8.0 μm or less, even more preferably 3.0 μm or more and 7.0 μm or less, and still more preferably 4.0 μm or more and 6.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0048] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the graphite powder (B) of this embodiment measured by the laser diffraction scattering method ９０ is preferably 5.0 μm or more and 40.0 μm or less, more preferably 10.0 μm or more and 30.0 μm or less, even more preferably 13.0 μm or more and 25.0 μm or less, even more preferably 15.0 μm or more and 20.0 μm or less, and even more preferably 17.0 μm or more and 18.0 μm or less, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery.

[0049] The particle diameter D at which the cumulative value reaches 10% in the volume frequency particle size distribution of the graphite powder (B) of this embodiment measured by the laser diffraction scattering method １０ , the particle diameter D at which the cumulative value reaches 90% ９０ and median diameter D ５０ (D ９０ -D １０ ) / D ５０ From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the obtained lithium ion secondary battery, the value of is preferably 0.50 or more and 3.00 or less, more preferably 0.80 or more and 2.50 or less, even more preferably 1.00 or more and 2.00 or less, even more preferably 1.15 or more and 1.70 or less, and still more preferably 1.25 or more and 1.40 or less.

[0050] The graphite powder (B) of the present embodiment preferably contains graphite particles that do not contain amorphous carbon on the surface, from the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite formation in the resulting lithium ion secondary battery.

[0051] The graphite powder (B) of the present embodiment preferably contains artificial graphite particles from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery.

[0052] From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the content of the graphite powder (B) in the negative electrode active material of this embodiment is preferably 5.0 parts by mass or more and 80.0 parts by mass or less, more preferably 10.0 parts by mass or more and 75.0 parts by mass or less, even more preferably 13.0 parts by mass or more and 70.0 parts by mass or less, still more preferably 20.0 parts by mass or more and 60.0 parts by mass or less, even more preferably 30.0 parts by mass or more and 50 parts by mass or less, and still more preferably 35.0 parts by mass or more and 45.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0053] When the total amount of the graphite powder of this embodiment is 100.0 parts by mass, the content of the graphite powder (A) in the graphite powder and the content of the graphite powder (B) in the graphite powder are respectively W Ａ and W Ｂ When W Ｂ / W Ａ From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the value of is preferably 0.05 or more and 20.00 or less, more preferably 0.10 or more and 15.00 or less, even more preferably 0.15 or more and 10.00 or less, even more preferably 0.20 or more and 5.00 or less, even more preferably 0.30 or more and 3.00 or less, even more preferably 0.50 or more and 2.00 or less, and even more preferably 0.70 or more and 1.50 or less.

[0054] From the viewpoint of further improving the performance balance between the pressing characteristics and the suppression of lithium dendrite generation in the resulting lithium ion secondary battery, the total content of graphite powder (A) and graphite powder (B) in the graphite powder 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 graphite powder is taken as 100.0 parts by mass.

[0055] <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.

[0056] A negative electrode laminate having a negative electrode current collector and a negative electrode active material layer was produced by the following method using the negative electrode active material of this embodiment, and when the negative electrode laminate was pressed using a roll press, the density of the negative electrode active material layer after pressing was 1.6 g / cm ３ The required pressure P １．６ From the viewpoint of further improving the pressing characteristics, the density of the negative electrode active material layer after pressing is preferably 1.40 t / cm or less, more preferably 1.30 t / cm or less, even more preferably 1.20 t / cm or less, even more preferably 1.10 t / cm or less, even more preferably 1.00 t / cm or less, even more preferably 0.90 t / cm or less, and even more preferably 0.80 t / cm or less. When the negative electrode laminate is pressed using a roll press, the density of the negative electrode active material layer after pressing is 1.6 g / cm ３ The required pressure P １．６ The lower limit of the density is not particularly limited, but may be, for example, 0.01 t / cm or more, 0.10 t / cm or more, or 0.30 t / cm or more. (Method) A suitable amount of water is added 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 to prepare a negative electrode active material slurry. Next, the negative electrode active material slurry is applied to a copper foil having a thickness of 8 μm as a negative electrode current collector so as to obtain a negative electrode current collector having an initial charge capacity per unit area of ​​4.3 mAh / cm. ２ After coating in such an amount that the coating amount becomes 100%, the coating is dried to obtain a negative electrode laminate having a negative electrode current collector and a negative electrode active material layer.

[0057] When a negative electrode laminate was produced by the above method using the negative electrode active material of this embodiment and the negative electrode laminate was pressed using a roll press, the density of the negative electrode active material layer after pressing was 1.6 g / cm ３ The required pressure P １．６From the viewpoint of further improving the press characteristics, is preferably 0.01 t / cm or more and 1.40 t / cm or less, more preferably 0.01 t / cm or more and 1.30 t / cm or less, even more preferably 0.01 t / cm or more and 1.20 t / cm or less, even more preferably 0.10 t / cm or more and 1.10 t / cm or less, even more preferably 0.10 t / cm or more and 1.00 t / cm or less, even more preferably 0.30 t / cm or more and 0.90 t / cm or less, and even more preferably 0.30 t / cm or more and 0.80 t / cm or less.

[0058] <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.

[0059] From the viewpoint of further suppressing the generation of lithium dendrites in 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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. ３3.00g / 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.

[0066] 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.

[0067] <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 can suppress the generation of lithium dendrites.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] <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 can suppress the generation of lithium dendrites, the lithium-ion secondary battery module of this embodiment can suppress the generation of lithium dendrites.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In preparing the negative electrode active material, the following graphite powder was used.

[0085] <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 : 5.0 μm, D ５０ : 10.0 μm, D ９０ : 17.0 μm, (D ９０ -D １０ ) / D ５０ : 1.20) Graphite powder 4 (artificial graphite containing amorphous carbon on the surface, D １０ : 12.0 μm, D ５０ : 22.5 μm, D ９０ : 38.2 μm, (D ９０ -D １０ ) / D ５０ 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)

[0086] <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 Graphite powder 7 (artificial graphite not containing amorphous carbon on the surface, D １０ : 7.0 μm, D ５０ : 12.5 μm, D ９０ : 22.0 μm, (D ９０ -D １０ ) / D ５０ : 1.20)

[0087] <Preparation of Si / C Powder 1> Porous Carbon Material 1 (D ５０ : 4.8 μm, specific surface area: 1678 m ２The 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.

[0088] 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.

[0089] 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 ５０ The 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.

[0090] <Preparation of Si / C Powder 2> Instead of the porous carbon material 1, the porous carbon material 2 (D ５０ :9.0μm, specific surface area: 1635m ２ Si / C powder 2 was obtained in the same manner as Si / C powder 1, except that Si / C powder 1 (1 / g) was used.

[0091] Elemental mapping of the cross section of the Si-C composite particle contained in the obtained Si / C powder 2 was performed in the same manner as for the above-mentioned Si / C powder 1. 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.

[0092] The obtained Si / C powder 2 was subjected to the same method as the Si / C powder 1 to measure the 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.

[0093] (Examples 1 to 8, Comparative Examples 1 to 4) <Preparation of Graphite Powder> Graphite powder (A) and graphite powder (B) were mixed in the blending ratios shown in Table 1 to obtain graphite powders of Examples 1 to 8 and Comparative Examples 1 to 4.

[0094] The graphite powders of each example and each comparative example were measured for the cumulative 10% diameter D １０ , cumulative 90% diameter D ９０ , median diameter D ５０ and (D ９０ -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.

[0095] <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 8 and Comparative Examples 1 to 4.

[0096] For the negative electrode active materials of each Example and Comparative Example, the median diameter D of the graphite powder (A), graphite powder (B), and Si / C powder used was ５０ and content, median diameter D of graphite powder ５０ and the content, each D Ｂ / D Ａ , W Ｂ / WＡ , D １ / D ２ and W １ / W ２ The results are shown in Table 1.

[0097] <Press line pressure P １．６ In each example and each comparative example, a negative electrode laminate having a negative electrode current collector and a negative electrode active material layer was produced by the following method using a negative electrode active material, and when the negative electrode laminate was pressed using a roll press, the density of the negative electrode active material layer after pressing was 1.6 g / cm ３ The required pressure P １．６ The surface area (t / cm) of the negative electrode active material was measured. The results are shown in Table 1. (Method) A negative electrode active material slurry was prepared by adding an appropriate amount of water to a solid content consisting of 96.9 parts by mass of 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 having a thickness of 8 μm as a negative electrode current collector so as to obtain an initial charge capacity per unit area of ​​4.3 mAh / cm. ２ After coating in an amount such that the coating amount was as follows, the coating was dried to obtain a negative electrode laminate having a negative electrode current collector and a negative electrode active material layer.

[0098] <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.

[0099] <Preparation of Positive Electrode> Lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２A 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.

[0100] <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.

[0101] <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.

[0102] <Suppression of Lithium Dendrite Generation> The lithium ion secondary batteries of each Example and Comparative Example were charged to an SOC (state of charge) of 35% or 50% at a temperature of 25°C and a charge rate of 2.0C, and then discharged to an SOC of 0% at a temperature of 25°C and a discharge rate of 0.1C. Next, the lithium ion secondary batteries of each Example and Comparative Example that had been charged and discharged under each condition were disassembled, and visually inspected to see if lithium had precipitated on the surface of the negative electrode. Next, the suppression of lithium dendrite generation of the lithium ion secondary batteries of each Example and Comparative Example was evaluated based on the following criteria. The results are shown in Table 1. A: When charged to an SOC of 50%, lithium did not precipitate on the surface of the negative electrode. B: When charged to an SOC of 50%, lithium precipitated on the surface of the negative electrode, but when charged to an SOC of 35%, lithium did not precipitate on the surface of the negative electrode. C: When charged to an SOC of 35%, lithium precipitated on the surface of the negative electrode.

[0103]

[0104] This application claims priority based on Japanese Patent Application No. 2024-056826, filed March 29, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0105] 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 method for producing a graphite powder having a Si / C powder containing Si-C composite particles containing silicon and a carbon material, wherein 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) contains graphite particles containing amorphous carbon on the surface thereof, and the graphite powder (A) has a median diameter D 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 has a value of 0.60 or more and 1.20 or less.

2. The above D Ａ The negative electrode active material according to claim 1 , wherein the average particle diameter is 5.0 μm or more and 20.0 μm or less.

3. The above D Ｂ The negative electrode active material according to claim 1 or 2, wherein the average particle size is 3.0 μm or more and 12.0 μm or less.

4. 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 any one of claims 1 to 3, wherein the average particle size is 3.0 µm or more and 30.0 µm 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 graphite powder (B) contains graphite particles whose surfaces do not contain amorphous carbon.

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

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. When the total amount of the negative electrode active material is 100.0 parts by mass, the content of the graphite powder in the negative electrode active material and the content of the Si / C powder in the negative electrode active material are each expressed as W １ and 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 1.00 or more and 20.00 or less.

12. When the total amount of the graphite powder is 100.0 parts by mass, the content of the graphite powder (A) in the graphite powder and the content of the graphite powder (B) in the graphite powder are each W Ａ and W Ｂ When W Ｂ / W Ａ The negative electrode active material according to any one of claims 1 to 11, wherein the value of is 0.05 or more and 20.00 or less.

13. Using the negative electrode active material, a negative electrode laminate having a negative electrode current collector and a negative electrode active material layer is produced by the following method. When the negative electrode laminate is pressed using a roll press, the density of the negative electrode active material layer after pressing is 1.6 g / cm ３ The required pressure P １．６ The negative electrode active material according to any one of claims 1 to 12, wherein the initial charge capacity per unit area is 1.40 t / cm 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 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 having a thickness of 8 μm as the negative electrode current collector, and ... initial charge capacity per unit area is 4.3 mAh / cm. ２ After coating in an amount such that the coating amount satisfies the above formula (1), the coating is dried to obtain the negative electrode laminate having the negative electrode current collector and the negative electrode active material layer.

14. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 13.

15. A lithium ion secondary battery comprising the negative electrode according to claim 14.

16. A lithium ion secondary battery module comprising the lithium ion secondary battery according to claim 15.

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