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

Abstract

Provided is a negative electrode active material comprising: graphite powder; and Si / C powder that includes Si-C composite particles which contain silicon and a carbon material, wherein the value of ID / IG of the graphite powder, as obtained by the following method 1, is 0.09-0.50. Method 1: In accordance with JIS K 0137:2010, a laser Raman spectrometer is used to irradiate the graphite powder with an argon laser and measure the Raman spectrum, wherein the excitation wavelength is 532 nm, entry slit width is 200 μm, exposure time is 15 seconds, the number of integrations is two, and a diffraction grating has 600 elements per mm. Next, ID and IG, which are the peak intensities at 1360 cm-1 and 1580 cm-1 are determined from the Raman spectrum. Then, the value of ID / IG is determined from ID and IG.

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]

[0005] In Patent Literature 1, for the purpose of providing a lithium ion secondary battery having a long life and a negative electrode material used therein, there is disclosed a negative electrode material for a lithium ion secondary battery, the negative electrode material being used for the negative electrode of the lithium ion secondary battery, the negative electrode material including: composite particles having a configuration in which scaly silicon particles are dispersed in a carbon material; and graphite-based particles, the carbon material being amorphous carbon or nanographene; and a content of the composite particles relative to the total amount of the composite particles and the graphite-based particles being 2% by mass or more and 50% by mass or less.

[0003] Japanese Patent Application Laid-Open No. 2019-067579

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

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

[0006] The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered a method for producing an I / C composite material comprising graphite powder and Si / C powder containing Si-C composite particles containing silicon and a carbon material, the I / C composite material being produced by a specific method using the graphite powder. Ｄ / I Ｇ The present inventors have found that a negative electrode active material having a value of 0.09 or more and 0.50 or less can improve the performance balance between the energy density and rapid chargeability 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 graphite powder is subjected to the following method 1: Ｄ / I Ｇ (Method 1) In accordance with JIS K 0137:2010, the graphite powder is irradiated with an argon laser using a laser Raman spectrometer under the conditions of an excitation wavelength of 532 nm, an entrance slit width of 200 μm, an exposure time of 15 seconds, an accumulation number of 2, and a diffraction grating of 600 lines / mm, and the Raman spectrum is measured. －１ and 1580 cm －１ I is the peak intensity of Ｄ and I Ｇ Next, the above I Ｄ and the above I Ｇ From the above I Ｄ / I Ｇ [2] The negative electrode active material according to [1], wherein the graphite powder contains graphite particles having amorphous carbon on the surface. [3] The median diameter D in a volume frequency particle size distribution of the graphite powder obtained by a laser diffraction scattering method is calculated. ５０ [4] The negative electrode active material according to [1] or [2], 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. ５０The negative electrode active material according to any one of [1] to [3], wherein the Si-C composite particles contain a porous carbon material, and the silicon is present in at least a portion of the pores of the porous carbon material. [5] The negative electrode active material according to any one of [1] to [4], wherein the carbon material in the Si-C composite particles contains a porous carbon material, and the silicon is present in at least a portion of the pores of the porous carbon material. [6] The negative electrode active material according to any one of [1] to [5], wherein the graphite powder contains artificial graphite particles. [7] The negative electrode active material according to any one of [1] to [6], 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, relative to 100 parts by mass of the total amount of the negative electrode active material. [8] The negative electrode active material according to any one of [1] to [7], wherein the content of the Si / C powder in the negative electrode active material is 1.0 parts by mass or more and 50.0 parts by mass or less, relative to 100 parts by mass of the total amount of the negative electrode active material. [9] When the total amount of the negative electrode active material is 100 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

[10] The negative electrode active material according to any one of [1] to [8], 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 D ５０ is the median diameter D of the graphite powder (B). ５０

[11] The negative electrode active material according to any one of [1] to [9], 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

[12] The negative electrode active material according to

[10] , wherein the value of is 0.40 or more and less than 1.00.

[13] The negative electrode active material according to

[10] or

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

[14] When the total amount of the graphite powder is taken as 100 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

[10] to

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

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

[13] , wherein the energy density E measured by the following method 2 is 900 Wh / L or more in terms of a cell. (Method 2) 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 6.5 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)

[15] 2C / 1C cycle capacity retention rate C according to Method 3 below ＱＣ The negative electrode active material according to any one of [1] to

[14] , wherein the content of the negative electrode active material is 86% or more. (Method 3) A suitable amount of water is 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 is applied to a copper foil negative electrode current collector so that the initial charge capacity per unit area is 6.5 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 ０．９Co ０．０５ Mn ０．０５ A lithium ion secondary battery is fabricated by placing an electrode laminate, in which a positive electrode including a 2.0 C charge / discharge electrode and a positive electrode including a 2.0 C charge / discharge electrode are disposed opposite each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film, connecting a positive electrode tab and a negative electrode tab to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. Next, a charge / discharge cycle test (charge rate: 2.0 C, discharge rate: 1.0 C, temperature: 25°C, upper limit voltage: 4.25 V, lower limit voltage: 2.5 V, number of cycles: 300) is performed on the lithium ion secondary battery. Next, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle of the lithium ion secondary battery is calculated, and the 2C / 1C cycle capacity retention rate C ＱＣ (%).

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

[15] , wherein the charging time T according to the following method 4 is 20 minutes or less. (Method 4) 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 6.5 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 is fabricated by placing an electrode laminate, in which a positive electrode containing a cation exchanger (C1) and a positive electrode containing a cation exchanger (C2) are arranged opposite each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab are connected to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. Next, the lithium ion secondary battery is placed in a thermostatic chamber at 25°C. Next, the lithium ion secondary battery is charged according to the following (charging procedure), and the time from the start of charging to the end of charging is measured and defined as the charging time T (min). (Charging procedure) The lithium ion secondary battery is subjected to constant current charging at a charging current of 5C up to an SOC of 50%. After reaching an SOC of 50%, constant voltage charging is performed until the current value drops to 0.05C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 4C up to an SOC of 65%. After reaching an SOC of 65%, constant voltage charging is performed until the current value drops to 0.05C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 3 C up to an SOC of 70%. After reaching an SOC of 70%, constant voltage charging is performed until the current value drops to 0.05 C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 2 C up to an SOC of 80%. After reaching an SOC of 80%, constant voltage charging is performed until the current value drops to 0.05 C.

[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 obtain a lithium ion secondary battery with an improved performance balance between energy density and rapid chargeability, as well as a lithium ion secondary battery and a lithium ion secondary battery module with an improved performance balance between energy density and rapid chargeability.

[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. In this specification, SOC stands for "State of Charge." In this specification, current C stands for C rate.

[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 graphite powder is subjected to the following method 1: Ｄ / I Ｇ (Method 1) In accordance with JIS K 0137:2010, a laser Raman spectrometer is used to irradiate graphite powder with an argon laser under the conditions of an excitation wavelength of 532 nm, an entrance slit width of 200 μm, an exposure time of 15 seconds, an accumulation number of 2, and a diffraction grating of 600 lines / mm, and the Raman spectrum is measured. －１ and 1580 cm －１ I is the peak intensity of Ｄ and I Ｇ Next, I Ｄ and I Ｇ From I Ｄ / I Ｇ Find the value of .

[0014] According to the investigations of 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 I of the graphite powder Ｄ / I Ｇ We have found that there is a relationship between the value of γ and the performance balance between the energy density and rapid charging capability 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 graphite powder can be subjected to I by the above method 1. Ｄ / I Ｇ The present inventors have found that by adjusting the value of (a) to 0.09 or more and 0.50 or less, the performance balance between the energy density and the rapid chargeability of the resulting lithium ion secondary battery can be improved, and have completed the present invention.

[0016] The graphite powder of this embodiment is prepared by the above method 1. Ｄ / I Ｇ From the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery, the value of is 0.09 or more and 0.50 or less, preferably 0.09 or more and 0.48 or less, more preferably 0.09 or more and 0.46 or less, even more preferably 0.10 or more and 0.44 or less, and still more preferably 0.10 or more and 0.42 or less.

[0017] In this embodiment, the graphite powder I Ｄ / I Ｇ As a method for adjusting the value of I, for example, Ｄ / I Ｇ A method using commercially available graphite powders with different I values, or a method adjusting the manufacturing conditions of graphite powder such as surface treatment and heat treatment, Ｄ / I Ｇ In addition, there is a method for producing graphite powders with different I values. Ｄ / I Ｇ Two or more types of graphite powders with different values ​​of I are mixed to obtain the graphite powder Ｄ / I Ｇ You may adjust the value of .

[0018] <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.

[0019] 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.

[0020] 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.

[0021] 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 3.0 μm or more and 17.0 μm or less, even more preferably 5.0 μm or more and 14.0 μm or less, even more preferably 7.0 μm or more and 12.0 μm or less, and even more preferably 8.0 μm or more and 10.0 μm or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0022] 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.

[0023] From the viewpoint of further improving the performance balance between the energy density and rapid chargeability 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 10.0 parts by mass or more and 40.0 parts by mass or less, even more preferably 14.0 parts by mass or more and 35.0 parts by mass or less, and even more preferably 17.0 parts by mass or more and 30.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0024] 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.

[0025] <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 9.0 μm or more and 15.0 μm or less, and even more preferably 10.0 μm or more and 12.0 μm or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0026] 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.

[0027] The graphite powder of this embodiment preferably contains graphite particles containing amorphous carbon on the surface, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0028] 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.

[0029] 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 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.

[0030] From the viewpoint of further improving the performance balance between the energy density and rapid chargeability of 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 55.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 60.0 parts by mass or more and 90.0 parts by mass or less, even more preferably 65.0 parts by mass or more and 86.0 parts by mass or less, and even more preferably 70.0 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.

[0031] 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 ２From the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery, the value of is preferably 0.1 or more and 10.0 or less, more preferably 0.5 or more and 7.0 or less, even more preferably 0.8 or more and 5.0 or less, even more preferably 1.0 or more and 3.0 or less, and still more preferably 1.1 or more and 1.5 or less.

[0032] In the negative electrode active material of this embodiment, when the total amount of the negative electrode active material is 100 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 ２ From the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery, the value of is preferably 1.0 or more and 20.0 or less, more preferably 1.5 or more and 15.0 or less, even more preferably 2.0 or more and 10.0 or less, even more preferably 2.4 or more and 7.0 or less, and even more preferably 2.7 or more and 5.0 or less.

[0033] From the viewpoint of further improving the performance balance between the energy density and rapid chargeability 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.

[0034] <Graphite Powder (A), Graphite Powder (B)> From the viewpoint of further improving the performance balance between the energy density and the rapid chargeability 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) ５０The negative electrode active material of the present embodiment contains two types of graphite powder, that is, graphite powder (A) and graphite powder (B), and therefore can achieve a better balance of energy density and rapid chargeability compared to a case where only one type of graphite powder is contained.

[0035] 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) measured by a laser diffraction scattering method is 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 energy density and rapid chargeability 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.

[0036] 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 is preferably 3.0 μm or more and 30.0 μm or less, more preferably 7.0 μm or more and 25.0 μm or less, even more preferably 10.0 μm or more and 20.0 μm or less, even more preferably 12.0 μm or more and 17.0 μm or less, and even more preferably 13.0 μm or more and 15.0 μm or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0037] 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 is preferably 1.0 μm or more and 20.0 μm or less, more preferably 3.0 μm or more and 17.0 μm or less, even more preferably 5.0 μm or more and 15.0 μm or less, even more preferably 7.0 μm or more and 13.0 μm or less, and even more preferably 9.0 μm or more and 11.0 μm or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0038] When the graphite powder of the present embodiment contains graphite powder (A) and graphite powder (B), from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery, preferably, the graphite powder (A) contains graphite particles containing amorphous carbon on the surface, and the graphite powder (B) contains graphite particles not containing amorphous carbon on the surface.

[0039] 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 and the content of graphite powder (B) in the graphite powder are respectively expressed as W and W, where the total amount of the graphite powder is 100 parts by mass. Ａ and W Ｂ When W Ｂ / W Ａ From the viewpoint of further improving the performance balance between the energy density and the rapid chargeability of the resulting lithium ion secondary battery, the value of is preferably 0.1 or more and 10.0 or less, more preferably 0.3 or more and 7.0 or less, even more preferably 0.5 or more and 4.0 or less, and still more preferably 0.7 or more and 2.0 or less.

[0040] When the graphite powder of the present embodiment contains graphite powder (A) and graphite powder (B), the content of graphite powder (A) in the graphite powder is preferably 10.0 parts by mass or more and 80.0 parts by mass or less, more preferably 20.0 parts by mass or more and 70.0 parts by mass or less, even more preferably 25.0 parts by mass or more and 60.0 parts by mass or less, even more preferably 30.0 parts by mass or more and 50.0 parts by mass or less, and even more preferably 35.0 parts by mass or more and 45.0 parts by mass or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0041] When the graphite powder of the present embodiment contains graphite powder (A) and graphite powder (B), the content of graphite powder (B) in the graphite powder is preferably 10.0 parts by mass or more and 80.0 parts by mass or less, more preferably 20.0 parts by mass or more and 70.0 parts by mass or less, even more preferably 25.0 parts by mass or more and 60.0 parts by mass or less, even more preferably 30.0 parts by mass or more and 50.0 parts by mass or less, and even more preferably 35.0 parts by mass or more and 45.0 parts by mass or less, from the viewpoint of further improving the performance balance between the energy density and rapid chargeability of the resulting lithium ion secondary battery.

[0042] <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.

[0043] <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 following Method 2 of this embodiment is preferably 900 Wh / L or more, more preferably 910 Wh / L or more, even more preferably 920 Wh / L or more, and even more preferably 930 Wh / L or more, in terms of cell conversion. The upper limit of the energy density E obtained by the following Method 2 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 2) An appropriate 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 negative electrode current collector so that the initial charge capacity per unit area is 6.5 mAh / cm. ２ The negative electrode laminate is then coated with the coating solution 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 The negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９Co 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, 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)

[0044] From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the energy density E by the above-described method 2 of the present embodiment is, in terms of a cell, preferably 900 Wh / L or more and 1500 Wh / L or less, more preferably 910 Wh / L or more and 1500 Wh / L or less, even more preferably 920 Wh / L or more and 1200 Wh / L or less, and still more preferably 930 Wh / L or more and 1000 Wh / L or less.

[0045] <2C / 1C cycle capacity retention rate C ＱＣ > 2C / 1C cycle capacity retention rate C according to the following method 3 of this embodiment ＱＣFrom the viewpoint of further improving the rapid chargeability of the resulting lithium ion secondary battery, the 2C / 1C cycle capacity retention rate C according to the following method 3 of this embodiment is preferably 86% or more, more preferably 88% or more, even more preferably 90% or more, even more preferably 91% or more, and even more preferably 92% or more. ＱＣ is not particularly limited, and may be, for example, 100% or less, or 99% or less. (Method 3) 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 negative electrode current collector so that the initial charge capacity per unit area is 6.5 mAh / cm. ２ The negative electrode laminate is then coated with the coating solution 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 The negative electrode is then pressed with a pressure so that the negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５ A lithium ion secondary battery is fabricated by placing an electrode laminate, in which a positive electrode including a 1.0-dichloro-2-propanediol (1.0-dichloro-2-propanediol) and a positive electrode including a 1.0-dichloro-2-propanediol (1.0-dichloro-2-propanediol) are disposed opposite each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film, connecting a positive electrode tab and a negative electrode tab to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. Next, the lithium ion secondary battery is subjected to a charge-discharge cycle test (charge rate: 2.0 C, discharge rate: 1.0 C, temperature: 25°C, upper limit voltage: 4.25 V, lower limit voltage: 2.5 V, number of cycles: 300). Next, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle of the lithium ion secondary battery is calculated, and the 2C / 1C cycle capacity retention rate C ＱＣ (%).

[0046] 2C / 1C cycle capacity retention rate C according to the above method 3 of this embodiment ＱＣis preferably 86% or more and 100% or less, more preferably 88% or more and 100% or less, even more preferably 90% or more and 100% or less, even more preferably 91% or more and 99% or less, and even more preferably 92% or more and 99% or less, from the viewpoint of further improving the rapid chargeability of the resulting lithium ion secondary battery.

[0047] <Charging Time T> The charging time T according to the following Method 4 of this embodiment is preferably 20 min or less, more preferably 19 min or less, and even more preferably 18 min or less, from the viewpoint of further improving the rapid chargeability of the resulting lithium-ion secondary battery. The lower limit of the charging time T according to the following Method 4 of this embodiment is not particularly limited, but may be, for example, 1 min or more. (Method 4) An appropriate 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 negative electrode current collector so that the initial charge capacity per unit area is 6.5 mAh / cm. ２ The negative electrode laminate is then coated with the coating solution 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 The negative electrode is then pressed with a pressure so that the negative electrode and lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５A lithium-ion secondary battery is fabricated by placing an electrode laminate, in which a positive electrode containing a cation exchanger (C1) and a positive electrode (C2) are arranged opposite each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film. A positive electrode tab and a negative electrode tab are connected to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. The lithium-ion secondary battery is then placed in a thermostatic chamber at 25°C. The lithium-ion secondary battery is then charged according to the following (charging procedure), and the time from the start of charging to the end of charging is measured and defined as the charging time T (min). (Charging Procedure) The lithium-ion secondary battery is subjected to constant-current charging at a charging current of 5C up to an SOC of 50%. After reaching an SOC of 50%, constant-voltage charging is performed until the current value drops to 0.05C. The lithium-ion secondary battery is then subjected to constant-current charging at a charging current of 4C up to an SOC of 65%. After reaching an SOC of 65%, constant-voltage charging is performed until the current value drops to 0.05C. Next, the lithium-ion secondary battery is subjected to constant current charging at a charging current of 3 C up to an SOC of 70%. After reaching an SOC of 70%, constant voltage charging is performed until the current value drops to 0.05 C. Next, the lithium-ion secondary battery is subjected to constant current charging at a charging current of 2 C up to an SOC of 80%. After reaching an SOC of 80%, constant voltage charging is performed until the current value drops to 0.05 C.

[0048] The charging time T by the above-described method 4 of this embodiment is preferably 1 min or more and 20 min or less, more preferably 1 min or more and 19 min or less, and even more preferably 1 min or more and 18 min or less, from the viewpoint of further improving the rapid chargeability of the resulting lithium ion secondary battery.

[0049] <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.

[0050] From the viewpoint of further improving the performance balance between the energy density and rapid chargeability 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] <Lithium-ion secondary battery> The lithium-ion secondary battery of this embodiment includes the negative electrode of this embodiment. Since the lithium-ion secondary battery of this embodiment includes the negative electrode containing the negative electrode active material of this embodiment, the performance balance between energy density and rapid chargeability is improved.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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 fluoroborate (LiBF ４ ), LiFSI, lithium perchlorate (LiClO ４ The organic solvent may be used alone or in combination of two or more kinds.

[0068] 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.

[0069] 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.

[0070] <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 an improved performance balance between energy density and rapid chargeability, the lithium-ion secondary battery module of this embodiment also has an improved performance balance between energy density and rapid chargeability.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In preparing the negative electrode active material, the following graphite powder was used.

[0076] <Graphite powder (A)> Graphite powder 1 (artificial graphite containing amorphous carbon on the surface, D ５０ Graphite powder 2 (artificial graphite containing amorphous carbon on the surface, D ５０ Graphite powder 3 (artificial graphite containing amorphous carbon on the surface, D ５０ Graphite powder 4 (artificial graphite containing amorphous carbon on the surface, D５０ Graphite powder 5 (artificial graphite containing amorphous carbon on the surface, D ５０ : 13.3 μm)

[0077] <Graphite powder (B)> Graphite powder 6 (artificial graphite not containing amorphous carbon on the surface, D ５０ : 9.9 μm)

[0078] <Preparation of Si / C Powder 1> Porous Carbon Material 1 (D ５０ :9.0μm, specific surface area: 1635m ２ The Si / C powder (1 / g) was placed in a tubular furnace, and the inside of 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 conditions of 500°C, 760 Torr, and 120 minutes. The product was then cooled to room temperature, and Si / C powder 1 was obtained.

[0079] 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) under conditions of an acceleration voltage of 3 kV, 20 mapping accumulations and 3000x magnification, with secondary electrons selected as the detection target. It was confirmed that silicon was present in at least a portion of the pores of the porous carbon material in the Si-C composite particle.

[0080] The median diameter D of the obtained Si / C powder 1 was determined from the volume frequency particle size distribution measured by a laser diffraction scattering method using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation). ５０ The 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 measurement. The results are shown in Table 1. A 0.1 mass % aqueous solution of sodium hexametaphosphate was used as the dispersion medium.

[0081] (Examples 1 to 4, Comparative Examples 1 to 3) <Preparation of Graphite Powder> Graphite powder (A) and graphite powder (B) were mixed in the compounding ratios shown in Table 1 to obtain graphite powders of Examples 1 to 4 and Comparative Examples 1 to 3.

[0082] For the graphite powders of each Example and Comparative Example, Raman spectra were measured in accordance with JIS K 0137:2010 using a triple laser Raman spectrometer (RAMANOR T64000, manufactured by HORIBA Jobin Yvon) under the conditions of an excitation wavelength of 532 nm, an entrance slit width of 200 μm, an exposure time of 15 seconds, an accumulation number of 2, and a diffraction grating of 600 lines / mm. －１ and 1580 cm －１ I is the peak intensity of Ｄ and I Ｇ were calculated respectively. Ｄ and I Ｇ From I Ｄ / I Ｇ The results are shown in Table 1.

[0083] The graphite powders of each example and each comparative example were measured for median diameter D ５０ The 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 measurement. The results are shown in Table 1. A 0.1% by mass aqueous solution of sodium hexametaphosphate was used as the dispersion medium.

[0084] <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 4 and Comparative Examples 1 to 3.

[0085] <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 6.5 mAh / cm. ２The 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 0.1 to 1.0.

[0086] <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 positive electrode current collector so that the initial charge capacity per unit area was 6.2 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.

[0087] <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.

[0088] <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.

[0089] <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)

[0090] <2C / 1C cycle capacity retention rate C ＱＣA charge-discharge cycle test (charge rate: 2.0 C, discharge rate: 1.0 C, temperature: 25° C., upper limit voltage: 4.25 V, lower limit voltage: 2.5 V, number of cycles: 300) was carried out on the lithium ion secondary batteries of each Example and Comparative Example. Next, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle of the lithium ion secondary batteries of each Example and Comparative Example was calculated, and the 2C / 1C cycle capacity retention ratio C ＱＣ The results are shown in Table 1.

[0091] <Charging Time T> For each example and comparative example, the lithium-ion secondary battery was placed in a thermostatic chamber at 25°C. The lithium-ion secondary battery was then charged according to the following (charging procedure), and the time from the start of charging to the end of charging was measured and defined as the charging time T (min). The results are shown in Table 1. (Charging Procedure) The lithium-ion secondary battery was subjected to constant current charging at a charging current of 5C to an SOC of 50%. After reaching SOC 50%, constant voltage charging was performed until the current value dropped to 0.05C. The lithium-ion secondary battery was then subjected to constant current charging at a charging current of 4C to an SOC of 65%. After reaching SOC 65%, constant voltage charging was performed until the current value dropped to 0.05C. The lithium-ion secondary battery was then subjected to constant current charging at a charging current of 3C to an SOC of 70%. After reaching SOC 70%, constant voltage charging was performed until the current value dropped to 0.05C. The lithium-ion secondary battery was then subjected to constant current charging at a charging current of 2C to an SOC of 80%. After the SOC reached 80%, constant voltage charging was carried out until the current value decreased to 0.05C.

[0092]

[0093] This application claims priority based on Japanese Patent Application No. 2024-056825, filed March 29, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0094] 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 comprising: forming a graphite powder; and a Si / C powder containing Si-C composite particles containing silicon and a carbon material, the method comprising: forming the graphite powder by the following method 1. Ｄ / I Ｇ (Method 1) In accordance with JIS K 0137:2010, the graphite powder is irradiated with an argon laser using a laser Raman spectrometer under the conditions of an excitation wavelength of 532 nm, an entrance slit width of 200 μm, an exposure time of 15 seconds, an accumulation number of 2, and a diffraction grating of 600 lines / mm, and the Raman spectrum is measured. －１ and 1580 cm －１ I is the peak intensity of Ｄ and I Ｇ Next, the above I Ｄ and the above I Ｇ From the above I Ｄ / I Ｇ Find the value of .

2. The negative electrode active material according to claim 1, wherein the graphite powder comprises graphite particles having amorphous carbon on the surface thereof.

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 size is 3.0 μm or more and 30.0 μm or less.

4. 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 3, wherein the average particle size is 1.0 µm or more and 20.0 µm or less.

5. The negative electrode active material according to any one of claims 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 some of the pores of the porous carbon material.

6. The negative electrode active material according to any one of claims 1 to 5, wherein the graphite powder contains artificial graphite particles.

7. The negative electrode active material according to any one of claims 1 to 6, 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 parts by mass.

8. The negative electrode active material according to any one of claims 1 to 7, 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 parts by mass.

9. When the total amount of the negative electrode active material is 100 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 8, wherein the value of is 1.0 or more and 20.0 or less.

10. 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 9, wherein the negative electrode active material has a molecular weight of 1.0 or more.

11. 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 10 , wherein the value of 12. The negative electrode active material according to claim 10 or 11, 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.

13. When the total amount of the graphite powder is 100 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 The negative electrode active material according to any one of claims 10 to 12, wherein the value of is 0.1 or more and 10.0 or less.

14. The negative electrode active material according to any one of claims 1 to 13, having an energy density E of 900 Wh / L or more in terms of a cell, as measured by Method 2 below. (Method 2) 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 6.5 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) 15. 2C / 1C cycle capacity retention rate C according to method 3 below ＱＣ The negative electrode active material according to any one of claims 1 to 14, wherein the content of the negative electrode active material is 86% or more. (Method 3) 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 as to have an initial charge capacity per unit area of ​​6.5 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 is fabricated by placing an electrode laminate, in which a positive electrode including a 2.0 C charge / discharge electrode and a positive electrode including a 2.0 C charge / discharge electrode are disposed opposite each other via a polyethylene separator, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film, connecting a positive electrode tab and a negative electrode tab to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. Next, a charge / discharge cycle test (charge rate: 2.0 C, discharge rate: 1.0 C, temperature: 25°C, upper limit voltage: 4.25 V, lower limit voltage: 2.5 V, number of cycles: 300) is performed on the lithium ion secondary battery. Next, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle of the lithium ion secondary battery is calculated, and the 2C / 1C cycle capacity retention rate C ＱＣ (%).

16. The negative electrode active material according to any one of claims 1 to 15, wherein the charging time T according to Method 4 below is 20 minutes or less. (Method 4) A suitable amount of water is 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. Then, 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 6.5 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 is fabricated by placing an electrode laminate, in which a positive electrode containing a cation exchange resin (A) and a positive electrode containing a cation exchange resin (B) are arranged opposite each other with a polyethylene separator interposed therebetween, and a nonaqueous electrolyte solution in a laminate exterior body formed by processing an aluminum-based film, connecting a positive electrode tab and a negative electrode tab to the negative electrode and the positive electrode, respectively, and sealing the periphery of the laminate exterior body. Next, the lithium ion secondary battery is placed in a thermostatic chamber at 25°C. Next, the lithium ion secondary battery is charged according to the following (charging procedure), and the time from the start of charging to the end of charging is measured, and this is defined as the charging time T (min). (Charging Procedure) The lithium ion secondary battery is subjected to constant current charging at a charging current of 5C up to an SOC of 50%. After reaching SOC 50%, constant voltage charging is performed until the current value drops to 0.05C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 4C up to an SOC of 65%. After reaching SOC 65%, constant voltage charging is performed until the current value drops to 0.05C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 3C up to an SOC of 70%. After reaching SOC 70%, constant voltage charging is performed until the current value drops to 0.05C. Next, the lithium ion secondary battery is subjected to constant current charging at a charging current of 2C up to an SOC of 80%. After the SOC reaches 80%, constant voltage charging is performed until the current value drops to 0.05C.

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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