Lithium ion secondary battery and lithium ion secondary battery module

Abstract

This lithium ion secondary battery comprises a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and an electrolytic solution, wherein: the negative electrode active material layer includes a mixed negative electrode active material including graphite powder and Si / C powder containing Si-C composite particles containing silicon and a carbon material; and in an X-ray diffraction spectrum of the mixed negative electrode active material, measured using an X-ray diffraction device in accordance with JIS K 0131:1996 under the conditions of a tube voltage of 40 kV and a tube current of 40 mA, using CuKα radiation having a wavelength of 1.5406 Å as a radiation source, a value of (ISi / IC)×100 (%) is 0.20% or more and 2.00% or less, where IC is the peak intensity of a maximum diffraction peak existing in a range in which a diffraction angle 2θ is 25.5° or more and less than 27.5°, and ISi is the peak intensity of a maximum diffraction peak existing in a range in which the diffraction angle 2θ is 27.5° or more and 29.5° or less.

Description

Lithium-ion secondary battery and lithium-ion secondary battery module

[0001] The present invention relates to 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 in a lithium ion secondary battery using a negative electrode active material layer containing graphite powder and Si / C powder, the cycle characteristics and rapid chargeability may be reduced.

[0005] The present invention provides a lithium ion secondary battery and a lithium ion secondary battery module with improved cycle characteristics and rapid chargeability.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have discovered a lithium ion secondary battery comprising a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and an electrolyte, wherein the negative electrode active material layer includes a negative electrode active material including graphite powder and Si / C powder including Si-C composite particles containing silicon and a carbon material, and wherein an X-ray diffraction spectrum of the negative electrode active material is measured in accordance with JIS K 0131:1996 using CuKα radiation having a wavelength of 1.5406 Å as a radiation source with an X-ray diffractometer under conditions of a tube voltage of 40 kV and a tube current of 40 mA, and the peak intensity of a maximum diffraction peak present in a diffraction angle 2θ range of 25.5° or more and less than 27.5° is I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When this is done, (I Ｓｉ / I Ｃ The present inventors have found that a lithium ion secondary battery in which the value of (%) × 100(%) is 0.20% or more and 2.00% or less can improve cycle characteristics and rapid chargeability, and have completed the present invention.

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

[0008] [1] A lithium ion secondary battery comprising: a negative electrode including a negative electrode active material layer; a positive electrode including a positive electrode active material layer; a separator; and an electrolyte; wherein the negative electrode active material layer includes a negative electrode active material including graphite powder and Si / C powder including Si-C composite particles containing silicon and a carbon material; and wherein, in an X-ray diffraction spectrum of the negative electrode active material measured in accordance with JIS K 0131:1996 using CuKα radiation having a wavelength of 1.5406 Å as a radiation source with an X-ray diffractometer under conditions of a tube voltage of 40 kV and a tube current of 40 mA, the peak intensity of a maximum diffraction peak present in a diffraction angle 2θ range of 25.5° or more and less than 27.5° is defined as I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When this is done, (I Ｓｉ / I Ｃ [2] A lithium ion secondary battery in which the value of I by the following method 1 is 0.20% or more and 2.00% or less. Ｄ / I Ｇ The lithium ion secondary battery according to [1], wherein the value of is 0.080 or more and 0.300 or less. (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. Next, from the Raman spectrum, －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 [3] The median diameter D in the volume frequency particle size distribution of the Si / C powder by the laser diffraction scattering method is calculated. ５０[4] The lithium ion secondary battery according to any one of [1] to [3], wherein the carbon material in the Si-C composite particles contains a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material. [5] The lithium ion secondary battery according to [1] or [2], wherein the content of the graphite powder in the negative electrode active material layer is W Ｃ , the content of the Si / C powder in the negative electrode active material layer is W ＳｉＣ When W Ｃ / W ＳｉＣ The lithium ion secondary battery according to any one of [1] to [4], wherein the value of is 1.0 or more and 20.0 or less. [6] The lithium ion secondary battery according to any one of [1] to [5], wherein the electrolytic solution contains a lithium salt / halogen-containing EC-based electrolytic solution. [7] The lithium ion secondary battery according to [6], wherein the lithium salt / halogen-containing EC-based electrolytic solution contains one or more halogen-containing ethylene carbonates selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, and trichloroethylene carbonate. [8] The lithium ion secondary battery according to any one of [1] to [7], wherein the graphite powder contains graphite particles having amorphous carbon on the surface. [9] The lithium ion secondary battery according to any one of [1] to [8], wherein the graphite powder contains artificial graphite particles.

[10] The lithium ion secondary battery according to any one of [1] to [8], wherein the graphite powder has a median diameter D 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 lithium ion secondary battery according to any one of [1] to [9], wherein the graphite powder (A) comprises graphite particles containing amorphous carbon on their surfaces, and the graphite powder (B) comprises graphite particles not containing amorphous carbon on their surfaces.

[12] The lithium ion secondary battery according to any one of [1] to

[11] , wherein the negative electrode active material layer further comprises one or more conductive additives selected from the group consisting of carbon nanotubes, carbon nanohorns, graphene, carbon nanobrushes, and carbon black.

[13] The lithium ion secondary battery according to any one of [1] to

[12] , wherein the capacity retention rate C measured by Method 2 below is 85% or higher. (Method 2) The lithium ion secondary battery is placed in a thermostatic chamber at 45°C and charged at 30 mA. After the upper limit voltage reaches 4.2 V, the battery is charged at a constant voltage until the total charging time reaches 2.5 hours. The battery is then discharged at a constant current of 30 mA until the lower limit voltage reaches 2.5 V. Next, this charge / discharge cycle is repeated 300 times, and the ratio of the 300th discharge capacity to the 1st discharge capacity is calculated, which is defined as the capacity retention rate C (%).

[14] 2C / 1C cycle capacity retention rate C according to the following method 3 ＱＣ The lithium ion secondary battery according to any one of [1] to

[13] , wherein the 2C / 1C cycle capacity retention ratio C is 88% or more. (Method 3) 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 1st cycle of the lithium ion secondary battery is calculated, and the 2C / 1C cycle capacity retention ratio C ＱＣ (%).

[15] A lithium ion secondary battery module comprising the lithium ion secondary battery according to any one of [1] to

[14] .

[0009] According to the present invention, it is possible to provide a lithium ion secondary battery and a lithium ion secondary battery module with improved cycle characteristics 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.

[0013] <Lithium-ion secondary battery> The lithium-ion secondary battery of the present embodiment is a lithium-ion secondary battery including a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and an electrolyte solution, in which the negative electrode active material layer includes a negative electrode active material including graphite powder and Si / C powder including Si—C composite particles containing silicon and a carbon material, and in an X-ray diffraction spectrum of the negative electrode active material measured in accordance with JIS K 0131:1996 using CuKα radiation having a wavelength of 1.5406 Å as a radiation source with an X-ray diffractometer under conditions of a tube voltage of 40 kV and a tube current of 40 mA, the peak intensity of a maximum diffraction peak present in a diffraction angle 2θ range of 25.5° or more and less than 27.5° is I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When this is done, (I Ｓｉ / I Ｃ ) × 100(%) is 0.20% or more and 2.00% or less.

[0014] According to studies by the present inventors, in a lithium ion secondary battery comprising a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and an electrolyte, wherein the negative electrode active material layer contains a negative electrode active material including graphite powder and Si / C powder containing Si—C composite particles containing silicon and a carbon material, it has been found that there is a correlation between the ratio of the peak intensity of the diffraction peak derived from silicon to the peak intensity of the diffraction peak derived from graphite in the X-ray diffraction spectrum of the negative electrode active material and the cycle characteristics and rapid chargeability of the lithium ion secondary battery.

[0015] As a result of further investigations by the present inventors based on the above findings, they have found that a lithium ion secondary battery includes a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and an electrolyte, wherein the negative electrode active material layer includes a negative electrode active material including Si / C powder containing graphite powder and Si-C composite particles containing silicon and a carbon material, and in the lithium ion secondary battery, the peak intensity of a maximum diffraction peak present in a diffraction angle 2θ range of 25.5° or more and less than 27.5° is I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When Ｓｉ / I Ｃ The present inventors have found that the cycle characteristics and rapid chargeability can be improved by adjusting the value of (%)×100(%) to 0.20% or more and 2.00% or less, and have completed the present invention.

[0016] In the X-ray diffraction spectrum of a negative electrode active material containing graphite powder and Si / C powder containing Si-C composite particles containing silicon and a carbon material, the maximum diffraction peak present in the range of a diffraction angle 2θ of 25.5° or more and less than 27.5° corresponds to the peak derived from the 002 plane of graphite, and the maximum diffraction peak present in the range of a diffraction angle 2θ of 27.5° or more and 29.5° or less corresponds to the peak derived from the 111 plane of silicon.

[0017] In the X-ray diffraction spectrum of the negative electrode active material of this embodiment, measured in accordance with JIS K 0131:1996 using CuKα radiation having a wavelength of 1.5406 Å as a radiation source under conditions of a tube voltage of 40 kV and a tube current of 40 mA using an X-ray diffractometer, the peak intensity of the maximum diffraction peak present in the range of a diffraction angle 2θ of 25.5° or more and less than 27.5° is defined as I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When this is done, (I Ｓｉ / I ＣFrom the viewpoint of further improving the cycle characteristics and the rapid chargeability, the value of (%) is 0.20% or more and 2.00% or less, preferably 0.20% or more and 1.50% or less, more preferably 0.20% or more and 1.20% or less, even more preferably 0.20% or more and 1.00% or less, even more preferably 0.30% or more and 0.90% or less, even more preferably 0.40% or more and 0.80% or less, and even more preferably 0.50% or more and 0.70% or less.

[0018] In this embodiment, the X-ray diffraction spectrum of the negative electrode active material (I Ｓｉ / I Ｃ ) × 100, for example, can be obtained by using commercially available graphite powders and Si / C powders with different crystallinity, or by adjusting the manufacturing conditions of the graphite powders and Si / C powders, such as raw materials and heat treatment conditions, to manufacture graphite powders and Si / C powders with different crystallinity. Ｓｉ / I Ｃ ) × 100 may be adjusted, and two or more Si / C powders with different crystallinity may be mixed to adjust the value of (I Ｓｉ / I Ｃ ) × 100 may be adjusted.

[0019] <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 cycle characteristics and rapid chargeability, 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.

[0020] 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.

[0021] 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.

[0022] The median diameter D in the volume frequency particle size distribution of the Si / C powder of this embodiment measured by the laser diffraction scattering method ５０ From the viewpoint of further improving cycle characteristics and rapid chargeability, the average particle size is preferably 6.0 μm or more and less than 10.0 μm, more preferably 6.5 μm or more and 9.5 μm or less, even more preferably 7.0 μm or more and 9.0 μm or less, and still more preferably 8.0 μm or more and 9.0 μm or less.

[0023] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the Si / C powder according to this embodiment, as determined by the laser diffraction scattering method, is ９０ From the viewpoint of further improving cycle characteristics and rapid chargeability, the average particle diameter is preferably 10.5 μm or more and 16.0 μm or less, more preferably 11.0 μm or more and 15.5 μm or less, even more preferably 11.5 μm or more and 15.0 μm or less, even more preferably 13.0 μm or more and 15.0 μm or less, and even more preferably 14.0 μm or more and 15.0 μm or less.

[0024] 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.

[0025] The specific surface area of ​​the Si / C powder of this embodiment, determined by the BET flow method and the single-point method in accordance with JIS Z 8830:2013, is preferably 5.0 m from the viewpoint of further improving cycle characteristics and rapid chargeability. ２ / g or less, more preferably 4.5m ２ / g or less, more preferably 3.5m ２ / g or less, more preferably 2.5m ２ The lower limit of the specific surface area of ​​the Si / C powder of this embodiment, determined by the BET flow method and the single-point method in accordance with JIS Z 8830:2013, is not particularly limited, but is, for example, 0.1 m ２ / g or more, and ２ / g or more, and ２ / g or more.

[0026] The specific surface area of ​​the Si / C powder of this embodiment, determined by the BET flow method and the single-point method in accordance with JIS Z 8830:2013, is preferably 0.1 m from the viewpoint of further improving cycle characteristics and rapid chargeability. ２ / g or more 5.0m ２ / g or less, more preferably 0.1m ２ / g or more 4.5m ２ / g or less, more preferably 0.5m ２ / g or more 3.5m ２ / g or less, more preferably 1.0m ２ / g or more 2.5m ２ / g or less.

[0027] From the viewpoint of further improving cycle characteristics and rapid chargeability, 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 10.0 parts by mass or more and 30.0 parts by mass or less, even more preferably 13.0 parts by mass or more and 25.0 parts by mass or less, and even more preferably 18.0 parts by mass or more and 22.0 parts by mass or less, when the total amount of the negative electrode active material is taken as 100.0 parts by mass.

[0028] 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 12.0 μm and a specific surface area of ​​1000 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 mixture is treated under conditions of 400 to 550°C, 700 to 800 Torr, and 60 to 150 minutes.

[0029] Here, the above I Ｓｉ In order to produce a Si / C powder that can yield a negative electrode active material with a small crystallinity, i.e., a Si / C powder in which the silicon crystallinity is low and the peak intensity of the diffraction peak derived from the silicon 111 plane in the X-ray diffraction spectrum is small, it is preferable to produce the powder under conditions where the treatment temperature is 480°C or higher and the treatment time is 100 minutes or longer.

[0030] <Graphite powder> Graphite powder I of this embodiment Ｄ / I Ｇ From the viewpoint of further improving cycle characteristics and rapid chargeability, the value of I is preferably 0.080 or more and 0.300 or less, more preferably 0.085 or more and 0.250 or less, even more preferably 0.090 or more and 0.200 or less, and still more preferably 0.120 or more and 0.180 or less. Ｄ / I Ｇ By setting the value of within the above range, the cycle characteristics and rapid chargeability can be further improved.

[0031] In this embodiment, the graphite powder I Ｄ / I Ｇ The following method can be used to determine the value of

[0000] . First, 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. Next, the Raman spectrum is obtained by determining the peak at 1360 cm －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 .

[0032] The median diameter D in the volume frequency particle size distribution of the graphite powder of this embodiment measured by the laser diffraction scattering method ５０ From the viewpoint of further improving the cycle characteristics and rapid chargeability, the average particle diameter is preferably 3.0 μm or more and 16.0 μm or less, more preferably 5.0 μm or more and 15.0 μm or less, even more preferably 7.0 μm or more and 14.0 μm or less, even more preferably 8.0 μm or more and 13.0 μm or less, even more preferably 9.0 μm or more and 12.0 μm or less, and even more preferably 10.0 μm or more and 11.0 μm or less.

[0033] The particle diameter D at which the cumulative value reaches 90% in the volume frequency particle size distribution of the graphite powder of this embodiment as determined by the laser diffraction scattering method ９０ From the viewpoint of further improving cycle characteristics and rapid chargeability, the average particle size is preferably 5.0 μm or more and 30.0 μm or less, more preferably 8.0 μm or more and 27.0 μm or less, even more preferably 10.0 μm or more and 24.0 μm or less, even more preferably 13.0 μm or more and 20.0 μm or less, and even more preferably 16.0 μm or more and 18.0 μm or less.

[0034] 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.

[0035] The graphite powder of this embodiment preferably contains graphite particles containing amorphous carbon on the surface thereof, from the viewpoint of further improving cycle characteristics and rapid chargeability.

[0036] The graphite powder of this embodiment preferably contains artificial graphite particles from the viewpoint of further improving cycle characteristics and rapid chargeability.

[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 D １０and 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 cycle characteristics and rapid chargeability, the content of graphite powder in the negative electrode active material of this embodiment, when the total amount of the negative electrode active material is taken as 100.0 parts by mass, is preferably 50.0 parts by mass or more and 99.0 parts by mass or less, more preferably 60.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 70.0 parts by mass or more and 90.0 parts by mass or less, even more preferably 75.0 parts by mass or more and 87.0 parts by mass or less, and still more preferably 77.0 parts by mass or more and 83.0 parts by mass or less.

[0039] In the negative electrode active material of this embodiment, the content of graphite powder in the negative electrode active material is W Ｃ , the content of Si / C powder in the negative electrode active material is W ＳｉＣ When W Ｃ / W ＳｉＣ From the viewpoint of further improving the cycle characteristics and rapid chargeability, the value of is preferably 1.0 or more and 20.0 or less, more preferably 2.0 or more and 15.0 or less, even more preferably 2.5 or more and 10.0 or less, even more preferably 3.0 or more and 7.0 or less, and still more preferably 3.5 or more and 5.0 or less.

[0040] From the viewpoint of further improving cycle characteristics and rapid chargeability, 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.

[0041] <Graphite Powder (A), Graphite Powder (B)> From the viewpoint of further improving cycle characteristics and rapid chargeability, the graphite powder of the present embodiment preferably has a median diameter D in a volume frequency particle size distribution measured by a laser diffraction scattering method. ５０ The graphite powder (A) and the graphite powder (B) are two kinds of graphite powders having different median diameters D ５０ is the median diameter D of the graphite powder (B) ５０ Greater than.

[0042] When the graphite powder of this embodiment contains graphite powder (A) and graphite powder (B), the median diameter D in the volume frequency particle size distribution of the graphite powder (A) and the graphite powder (B) by the laser diffraction scattering method is ５０ D respectively Ａ and D Ｂ When this is done, D Ｂ / D Ａ From the viewpoint of further improving cycle characteristics and rapid chargeability, 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 0.60 or more and 0.90 or less, and still more preferably 0.70 or more and 0.85 or less.

[0043] When the graphite powder of the present embodiment contains graphite powder (A) and graphite powder (B), from the viewpoint of further improving cycle characteristics and rapid chargeability, preferably, graphite powder (A) contains graphite particles containing amorphous carbon on the surface, and graphite powder (B) contains graphite particles not containing amorphous carbon on the surface.

[0044] When the graphite powder of this embodiment contains graphite powder (A) and graphite powder (B), the content of graphite powder (A) in the graphite powder is W Ａ , the content of graphite powder (B) in the graphite powder is W Ｂ When W Ａ / W Ｂ From the viewpoint of further improving the cycle characteristics and rapid chargeability, the value of is preferably 0.1 or more and 10.0 or less, more preferably 0.3 or more and 5.0 or less, even more preferably 0.5 or more and 3.0 or less, even more preferably 0.7 or more and 2.0 or less, and still more preferably 0.8 or more and 1.5 or less.

[0045] <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.

[0046] <Negative Electrode> The negative electrode of this embodiment includes a negative electrode active material layer containing the negative electrode active material of this embodiment, and preferably includes a negative electrode active material layer containing the negative electrode active material of this embodiment and a negative electrode current collector, from the viewpoint of further improving the cycle characteristics and rapid chargeability. The negative electrode active material layer of this embodiment preferably includes the negative electrode active material of this embodiment and a binder, and more preferably includes the negative electrode active material of this embodiment, a binder, and a conductive additive, from the viewpoint of further improving the cycle characteristics and rapid chargeability.

[0047] From the viewpoint of further improving cycle characteristics and rapid chargeability, 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 100.0 parts by mass.

[0048] From the viewpoint of further improving cycle characteristics and rapid chargeability, the negative electrode active material layer of the present embodiment preferably contains one or more conductive additives selected from the group consisting of carbon nanotubes, carbon nanohorns, graphene, carbon nanobrushes, and carbon black, more preferably contains carbon nanotubes, and even more preferably contains single-walled carbon nanotubes.

[0049] When the negative electrode active material layer of this embodiment contains carbon nanotubes, the average fiber length of the carbon nanotubes is preferably 1.0 μm or more and 5.0 μm or less, more preferably 2.0 μm or more and 4.0 μm or less, and even more preferably 2.5 μm or more and 3.5 μm or less, from the viewpoint of further improving cycle characteristics and rapid chargeability.

[0050] From the viewpoint of further improving the cycle characteristics and rapid chargeability, 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.

[0051] 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 battery performance, 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.

[0052] From the viewpoint of further improving battery performance, 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.

[0053] From the viewpoint of further improving battery performance, 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.

[0054] 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. ３ 3.00g / cm or more ３ or less, more preferably 1.00 g / cm ３ 2.50g / cm or more ３ More preferably, 1.30 g / cm or less ３ 2.00g / cm or more ３ The following is the result.

[0055] 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.

[0056] <Positive Electrode> The positive electrode of this embodiment includes a positive electrode active material layer, and from the viewpoint of further improving battery performance, preferably includes a positive electrode active material layer and a positive electrode current collector. From the viewpoint of further improving battery performance, the positive electrode active material layer of this embodiment preferably includes a positive electrode active material, more preferably includes a positive electrode active material and a binder, and even more preferably includes a positive electrode active material, a binder, and a conductive additive.

[0057] 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; TiS ２ , 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 lithium phosphate, olivine-type lithium phosphate, etc., and one of these may be used alone or two or more may be used in combination. Among these, from the viewpoint of further improving battery performance, the positive electrode active material in the positive electrode active material layer of this embodiment preferably contains a composite oxide of lithium and a transition metal, more preferably contains a lithium-nickel-manganese-cobalt composite oxide, and even more preferably contains lithium nickel cobalt manganese oxide.

[0058] From the viewpoint of further improving battery performance, the content of the positive electrode active material in the positive 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 100.0 parts by mass or less, even more preferably 85.0 parts by mass or more and 100.0 parts by mass or less, even more preferably 90.0 parts by mass or more and 100.0 parts by mass or less, and still more preferably 95.0 parts by mass or more and 100.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

[0059] 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. Among these, the conductive additive in the positive 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 battery performance.

[0060] From the viewpoint of further improving battery performance, the content of the conductive additive in the positive 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 0.3 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.5 parts by mass or more and 3.0 parts by mass or less, and still more preferably 0.7 parts by mass or more and 1.5 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

[0061] 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. Among these, the binder in the positive electrode active material layer of this embodiment preferably contains a fluorine-based binder, more preferably polyvinylidene fluoride, from the viewpoint of further improving battery performance.

[0062] From the viewpoint of further improving battery performance, the content of the binder in the positive 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 0.5 parts by mass or more and 5.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 3.0 parts by mass or less, and still more preferably 1.2 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

[0063] 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.

[0064] <Electrolyte Solution> The electrolyte solution of the present embodiment preferably contains a lithium salt and an organic solvent, from the viewpoint of further improving battery performance.

[0065] Examples of the lithium salt in the electrolytic solution of this embodiment include lithium salts such as lithium hexafluorophosphate, lithium tetrafluorophosphate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium bis(fluoroethylsulfonyl)imide, and one of these may be used alone or two or more may be used in combination. Among these, the lithium salt of this embodiment preferably contains lithium hexafluorophosphate from the viewpoint of further improving battery performance.

[0066] From the viewpoint of further improving battery performance, the content of the lithium salt in the electrolytic solution of the present embodiment is preferably 1.0 parts by mass or more and 30.0 parts by mass or less, more preferably 5.0 parts by mass or more and 20.0 parts by mass or less, and even more preferably 10.0 parts by mass or more and 15.0 parts by mass or less, when the total amount of the electrolytic solution is 100.0 parts by mass.

[0067] Examples of organic solvents in the electrolyte solution of this embodiment include 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 organic solvents such as cyclic ethers. One of these may be used alone, or two or more may be used in combination. Among these, the organic solvent in the electrolyte solution of this embodiment, from the viewpoint of further improving battery performance, preferably contains one or more selected from the group consisting of cyclic carbonates and chain carbonates, and more preferably contains one or more selected from the group consisting of ethylene carbonate, vinylene carbonate, and ethyl methyl carbonate. The electrolyte solution of the present embodiment may contain the above-mentioned compound as an organic solvent or as an additive.

[0068] From the viewpoint of further improving battery performance, the content of the organic solvent in the electrolytic solution of the present embodiment is preferably 70.0 parts by mass or more and 99.0 parts by mass or less, more preferably 80.0 parts by mass or more and 95.0 parts by mass or less, and even more preferably 83.0 parts by mass or more and 90.0 parts by mass or less, when the total amount of the electrolytic solution is 100.0 parts by mass.

[0069] From the viewpoint of further improving battery performance, the electrolyte solution of the present embodiment preferably contains a lithium salt / halogen-containing EC-based electrolyte solution, which is a nonaqueous electrolyte solution containing a lithium salt, an organic solvent, and halogen-containing ethylene carbonate.

[0070] From the viewpoint of further improving battery performance, the lithium salt / halogen-containing EC-based electrolyte solution of the present embodiment preferably contains one or more halogen-containing ethylene carbonates selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, and trichloroethylene carbonate, and more preferably contains fluoroethylene carbonate.

[0071] From the viewpoint of further improving battery performance, the content of the halogen-containing ethylene carbonate in the electrolytic solution of the present embodiment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 0.5 parts by mass or more and 5.0 parts by mass or less, and even more preferably 1.0 parts by mass or more and 3.0 parts by mass or less, when the total amount of the electrolytic solution is 100.0 parts by mass.

[0072] <Separator> The separator of this embodiment is mainly made of, for example, a porous film, woven fabric, nonwoven fabric, etc. 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 have a layer containing inorganic particles, and examples of the inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc.

[0073] <Exterior Body> The lithium-ion secondary battery of this embodiment may further include an exterior body. For example, a case or a can made of a flexible film can be used as the exterior body of this embodiment, and from the viewpoint of reducing the weight of the battery, a flexible film is preferably used. 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 arranged 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.

[0074] 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.

[0075] 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 the positive electrode active material layer 1 and the negative electrode active material layer 2 facing each other, via a separator 5 made of a nonwoven fabric, a polypropylene microporous film, or the like. This electrode pair is housed in a container formed by 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.

[0076] 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.

[0077] <Capacity Retention Rate C> From the viewpoint of further improving the cycle characteristics, the capacity retention rate C of the lithium ion secondary battery of this embodiment is preferably 85% or more, more preferably 88% or more, even more preferably 90% or more, even more preferably 92% or more, even more preferably 94% or more, and even more preferably 96% or more. The upper limit of the capacity retention rate C of the lithium ion secondary battery of this embodiment is not particularly limited, and may be, for example, 100% or less. In this embodiment, the cycle characteristics of the lithium ion secondary battery can be evaluated using the capacity retention rate C as an index.

[0078] From the viewpoint of further improving the cycle characteristics, the capacity retention rate C of the lithium ion secondary battery of the present embodiment is preferably 85% 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, still more preferably 92% or more and 100% or less, even more preferably 94% or more and 100% or less, and still more preferably 96% or more and 100% or less.

[0079] In this embodiment, the capacity retention rate C of a lithium ion secondary battery can be measured, for example, by the following method. First, the lithium ion secondary battery is placed in a thermostatic chamber at 45°C and charged at 30 mA. After the upper limit voltage reaches 4.2 V, the battery is charged at a constant voltage until the total charging time reaches 2.5 hours. Next, the battery is discharged at a constant current of 30 mA until the lower limit voltage reaches 2.5 V. Next, this charge / discharge cycle is repeated 300 times, and the ratio of the 300th discharge capacity to the first discharge capacity is calculated, which is defined as the capacity retention rate C (%).

[0080] <2C / 1C cycle capacity retention rate C ＱＣ > 2C / 1C cycle capacity retention rate C of the lithium ion secondary battery of this embodiment ＱＣ From the viewpoint of further improving the rapid chargeability, the 2C / 1C cycle capacity retention rate C of the lithium ion secondary battery of this embodiment is preferably 88% or more, more preferably 89% or more, even more preferably 90% or more, and still more preferably 93% or more. ＱＣ The upper limit of the 2C / 1C cycle capacity retention rate C is not particularly limited, but may be, for example, 100% or less. ＱＣ The rapid chargeability of a lithium ion secondary battery can be evaluated using this as an index.

[0081] 2C / 1C cycle capacity retention rate C of the lithium ion secondary battery of this embodiment ＱＣ From the viewpoint of further improving the rapid charging property, the charge capacity is preferably 88% or more and 100% or less, more preferably 89% or more and 100% or less, even more preferably 90% or more and 100% or less, and even more preferably 93% or more and 100% or less.

[0082] In this embodiment, the 2C / 1C cycle capacity retention rate C of the lithium ion secondary batteryＱＣ The following method can be used to measure the 2C / 1C cycle capacity retention ratio C. First, 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 ratio C is calculated. ＱＣ (%).

[0083] <Lithium-ion secondary battery module> The lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment. Since the lithium-ion secondary battery of this embodiment has improved cycle characteristics and rapid chargeability, the lithium-ion secondary battery module of this embodiment also has improved cycle characteristics and rapid chargeability.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] In preparing the negative electrode active material, the following graphite powder was used.

[0089] <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 : 30.0 μm)

[0090] <Graphite powder (B)> Graphite powder 4 (artificial graphite not containing amorphous carbon on the surface, D ５０ : 9.6 μm)

[0091] <Preparation of Si / C Powder 1> Porous Carbon Material 1 (D ５０ :8.5μm, specific surface area: 1566m 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.

[0092] 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.

[0093] The specific surface area of ​​the obtained Si / C powder 1 was measured by the BET flow method and the single-point method in accordance with JIS Z 8830:2013 using a fully automatic specific surface area measuring device (Macsorb HM-1208, manufactured by Mountech Co., Ltd.). Furthermore, the particle diameter D at which the cumulative value reaches 90% was determined from the volume frequency particle size distribution measured by the laser diffraction scattering method using a laser diffraction particle size distribution measuring device (SALD-2300, manufactured by Shimadzu Corporation). ９０ and median diameter D 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.

[0094] <Si / C powder 2> Porous carbon material 2 (D ５０ :7.5μm, specific surface area: 1675m 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.

[0095] <Preparation of Si / C Powder 3 and Si / C Powder 4> Instead of the porous carbon material 1, the porous carbon material 3 (D ５０ :5.5μm, specific surface area: 1756m ２ / g) and porous carbon material 4 (D ５０ : 10.0μm, specific surface area: 1655m ２Si / C powders 3 and 4 were obtained in the same manner as in the production of Si / C powder 1, except that Si / C powders 3 and 4 (1 / g) were used, the treatment temperature of the porous carbon material in the tubular furnace was changed to 450°C, and the treatment time of the porous carbon material in the tubular furnace was changed to 90 minutes.

[0096] Elemental mapping was performed on the cross sections of the Si-C composite particles contained in the obtained Si / C powders 2, 3, and 4 by the same method as for the Si / C powder 1. It was confirmed that the Si-C composite particles in all cases contained silicon, and that the silicon in the Si-C composite particles was present in at least some of the pores of the porous carbon material.

[0097] The specific surface area, cumulative 90% diameter D of the obtained Si / C powder 2, Si / C powder 3, and Si / C powder 4 were measured in the same manner as for the Si / C powder 1. ９０ and median diameter D ５０ The results are shown in Table 1.

[0098] Examples 1 to 3, Comparative Examples 1 and 2 <Preparation of Graphite Powder> Graphite powder (A) and graphite powder (B) were mixed in the blending ratio shown in Table 1 to obtain graphite powders of Examples 1 to 3 and Comparative Examples 1 and 2.

[0099] 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 the graphite powders of each example and each comparative example, Ｄ / I Ｇ The results are shown in Table 1.

[0100] The graphite powders of each example and each comparative example were measured for the cumulative 90% diameter D ９０ and 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.

[0101] <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 3 and Comparative Examples 1 and 2.

[0102] For the negative electrode active materials of each Example and Comparative Example, the X-ray diffraction spectrum was measured in accordance with JIS K 0131:1996 using CuKα radiation of wavelength 1.5406 Å as a radiation source with a fully automatic multipurpose X-ray diffractometer (Rigaku Corporation, SmartLab 3kW) under conditions of a tube voltage of 40 kV and a tube current of 40 mA. The peak intensity of the maximum diffraction peak present in the range of a diffraction angle 2θ of 25.5° or more and less than 27.5° was determined as I. Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When Ｓｉ / I Ｃ The results are shown in Table 1.

[0103] <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 (average fiber length: 3.0 μm), 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.

[0104] <Preparation of Positive Electrode> Lithium nickel cobalt manganese oxide (Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ A suitable amount of N-methyl-2-pyrrolidone was added to a solid content consisting of 97.5 parts by mass of ethylenediamine fluoride, 1.5 parts by mass of polyvinylidene fluoride, and 1.0 part by mass of single-walled carbon nanotubes to prepare a positive electrode active material slurry. Next, the positive electrode active material slurry was applied to a 12 μm thick aluminum foil as a positive electrode current collector so that the initial charge capacity per unit area was 4.0 mAh / cm. ２ The positive electrode laminate was then coated in an amount such that the density of the positive electrode active material layer was 3.5 g / cm using a roll press. ３ The positive electrode was obtained by pressing the positive electrode with a pressure of 0.015.

[0105] <Preparation of Non-Aqueous Electrolyte> A non-aqueous electrolyte was prepared by mixing an organic solvent, a lithium salt, and an additive. The organic solvent was prepared by mixing ethylene carbonate, a cyclic carbonate, and ethyl methyl carbonate, a chain carbonate, in a volume ratio of 3 / 7. Next, 12 parts by mass of lithium hexafluorophosphate as a lithium salt and 2 parts by mass of fluoroethylene carbonate and 2 parts by mass of vinylene carbonate as additives were added to 84 parts by mass of the prepared organic solvent and mixed to obtain a non-aqueous electrolyte.

[0106] <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.

[0107] <Capacity Retention Rate C> The lithium ion secondary batteries of each Example and Comparative Example were placed in a thermostatic chamber at 45°C and charged at 30 mA. After the upper limit voltage reached 4.2 V, they were charged at a constant voltage until the total charging time reached 2.5 hours. They were then discharged at a constant current of 30 mA until the lower limit voltage reached 2.5 V. This charge / discharge cycle was then repeated 300 times, and the ratio of the 300th discharge capacity to the first discharge capacity was calculated, giving the capacity retention rate C (%). The results are shown in Table 1.

[0108] <2C / 1C cycle capacity retention rate C ＱＣ 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) 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.

[0109]

[0110] This application claims priority based on Japanese Patent Application No. 2024-056829, filed March 29, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0111] 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 lithium ion secondary battery comprising: a negative electrode including a negative electrode active material layer; a positive electrode including a positive electrode active material layer; a separator; and an electrolyte; wherein the negative electrode active material layer includes a negative electrode active material including graphite powder and Si / C powder including Si-C composite particles containing silicon and a carbon material; and wherein, in an X-ray diffraction spectrum of the negative electrode active material measured in accordance with JIS K 0131:1996 using CuKα radiation having a wavelength of 1.5406 Å as a radiation source with an X-ray diffractometer under conditions of a tube voltage of 40 kV and a tube current of 40 mA, the peak intensity of the maximum diffraction peak present in the diffraction angle 2θ range of 25.5° or more and less than 27.5° is defined as I Ｃ , the peak intensity of the maximum diffraction peak present in the range of the diffraction angle 2θ of 27.5° to 29.5° is defined as I Ｓｉ When this is done, (I Ｓｉ / I Ｃ ) × 100(%) is 0.20% or more and 2.00% or less.

2. The graphite powder is subjected to the following method 1. Ｄ / I Ｇ The lithium ion secondary battery according to claim 1, wherein the value of is 0.080 or more and 0.300 or less. (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. Next, from the Raman spectrum, －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 .

3. The median diameter D in the volume frequency particle size distribution of the Si / C powder measured by the laser diffraction scattering method ５０ The lithium ion secondary battery according to claim 1 or 2, wherein the average particle diameter is 6.0 μm or more and less than 10.0 μm.

4. A lithium ion secondary battery according to any one of claims 1 to 3, 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.

5. The content of the graphite powder in the negative electrode active material is W Ｃ , the content of the Si / C powder in the negative electrode active material is W ＳｉＣ When W Ｃ / W ＳｉＣ The lithium ion secondary battery according to any one of claims 1 to 4, wherein the value of is 1.0 or more and 20.0 or less.

6. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the electrolyte solution comprises a lithium salt / halogen-containing EC-based electrolyte solution.

7. The lithium ion secondary battery according to claim 6, wherein the lithium salt / halogen-containing EC-based electrolyte solution contains one or more halogen-containing ethylene carbonates selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, and trichloroethylene carbonate.

8. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the graphite powder contains graphite particles having amorphous carbon on the surface thereof.

9. The lithium ion secondary battery according to any one of claims 1 to 8, wherein the graphite powder contains artificial graphite particles.

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 lithium ion secondary battery according to any one of claims 1 to 9, 11. The lithium ion secondary battery according to claim 10, wherein the graphite powder (A) contains graphite particles having amorphous carbon on the surface thereof, and the graphite powder (B) contains graphite particles having no amorphous carbon on the surface thereof.

12. The lithium ion secondary battery according to any one of claims 1 to 11, wherein the negative electrode active material layer further contains one or more conductive additives selected from the group consisting of carbon nanotubes, carbon nanohorns, graphene, carbon nanobrushes, and carbon black.

13. A lithium ion secondary battery according to any one of claims 1 to 12, wherein the capacity retention rate C measured by the following method 2 is 85% or higher. (Method 2) The lithium ion secondary battery is placed in a thermostatic chamber at 45°C, charged at 30 mA, and after the upper limit voltage reaches 4.2 V, charged at a constant voltage until the total charging time reaches 2.5 hours. Next, the battery is discharged at a constant current of 30 mA until the lower limit voltage reaches 2.5 V. Next, this charge / discharge cycle is repeated 300 times, and the ratio of the discharge capacity at the 300th time to the discharge capacity at the first time is calculated, and this is defined as the capacity retention rate C (%).

14. 2C / 1C cycle capacity retention rate C according to method 3 below ＱＣ The lithium ion secondary battery according to any one of claims 1 to 13, wherein the 2C / 1C cycle capacity retention ratio C is 88% or more. (Method 3) 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 1st cycle of the lithium ion secondary battery is calculated, and the 2C / 1C cycle capacity retention ratio C ＱＣ (%).

15. A lithium ion secondary battery module comprising the lithium ion secondary battery according to any one of claims 1 to 14.

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