Composite particles for negative electrode material, and secondary battery

Abstract

This composite particle (10) for a negative electrode material is provided with a carbon phase (1) and silicon particles (2) dispersed in the carbon phase (1), and in an X-ray diffraction pattern obtained by X-ray diffraction measurement using a Cu-K alpha ray, the half-value width of an X-ray diffraction peak from the (111) plane of Si is 0.1 DEG or more and less than 0.75 DEG, and the average value of the aspect ratio of the silicon particles (2) is 1.0 or more and 1.6 or less.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a composite particle for a negative electrode material and a secondary battery. BACKGROUND

[0002] As a negative electrode material for high-capacity lithium ion batteries, a composite material containing silicon and a carbon material has been studied. Patent Literature 1 discloses a negative electrode active material for a lithium secondary battery, which is a porous silicon-carbon composite body having a plurality of nano-silicon particles embedded in a carbon-based substance and containing a plurality of pores.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 2022-501787 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In the prior art, it is desired to improve the initial charge-discharge efficiency of a battery using a composite material containing silicon and a carbon material as an active material.

[0008] SOLUTION TO PROBLEM

[0009] The composite particle for a negative electrode material of the present disclosure contains a carbon phase and silicon particles dispersed in the carbon phase, and in an X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα rays, a half-value width of an X-ray diffraction peak from a (111) plane of Si is 0.1° or more and less than 0.75°, and an average value of an aspect ratio of the silicon particles is 1.0 or more and 1.6 or less.

[0010] EFFECT OF THE INVENTION

[0011] According to the technology of the present disclosure, it is possible to provide a composite particle for a negative electrode material capable of improving the initial charge-discharge efficiency of a battery. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a cross-sectional view showing a schematic configuration of an example of a composite particle for a negative electrode material of Embodiment 1.

[0013] Figure 2 is a cross-sectional view showing a schematic configuration of a secondary battery of Embodiment 2. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0015] (Embodiment 1)

[0016] Figure 1 This is a cross-sectional view showing a schematic configuration of an example of composite particles for anode material according to Embodiment 1. Composite particles 10 comprise a carbon phase 1 and silicon particles 2. Silicon particles 2 are dispersed in the carbon phase 1. In the X-ray diffraction pattern of composite particles 10 obtained by X-ray diffraction using Cu-Kα rays, the half-width of the X-ray diffraction peaks from the (111) plane of Si is 0.1° or more and less than 0.75°. The average aspect ratio of the silicon particles 2 is 1.0 or more and 1.6 or less.

[0017] In this disclosure, the aspect ratio of silicon particle 2 refers to the ratio of the longest diameter (i.e., the length of the major axis) of silicon particle 2 to the shortest diameter (i.e., the length of the minor axis) of silicon particle 2 (length of the major axis / length of the minor axis).

[0018] The aspect ratio of silicon particle 2 can be determined from the SEM image of composite particle 10 obtained by scanning electron microscopy (SEM). Specifically, the shortest and longest diameters of silicon particle 2 are determined from the SEM image of the cross-section of composite particle 10 exposed by silicon particle 2, and the aspect ratio is calculated. The average aspect ratio can be obtained by calculating the aspect ratios of 500 silicon particles 2 arbitrarily extracted from the SEM image of composite particle 10 and calculating the median value of their number reference.

[0019] The X-ray diffraction pattern of composite particle 10 can be obtained using a wavelength of 1.5405 nm. and 1.5444 The Cu-Kα rays with wavelengths of 0.15405 nm and 0.15444 nm were obtained by X-ray diffraction using the θ-2θ method.

[0020] The diffraction angle of a peak in an X-ray diffraction pattern is defined as the angle representing the maximum intensity of the mountain-shaped portion with a signal-to-noise ratio (S / N ratio, i.e., the ratio of signal S to background noise N) greater than 1.3 and a half-width of less than 10°. The half-width refers to the angle at which the maximum intensity of the X-ray diffraction peak is set to I. MAX When, the intensity becomes I MAX The width is represented by the difference between two diffraction angles, which is half the value of the diffraction angle.

[0021] For X-ray diffraction peaks from the (111) plane of Si, for example, the X-ray diffraction peaks with the highest intensity in the range of diffraction angle 2θ above 28.1° and below 28.7°, for example, the X-ray diffraction peak at a diffraction angle 2θ at 28.4°.

[0022] In the composite particles 10, crystalline silicon particles 2 with a small aspect ratio are dispersed in the carbon phase 1. In other words, the carbon phase 1, containing carbonaceous material, covers the crystalline silicon particles 2 with a small aspect ratio. Due to the small aspect ratio of the silicon particles 2, the pore volume of the composite particles 10 can be reduced based on the improved coverage of the carbon phase 1. Therefore, in the battery using the composite particles 10, side reactions between the electrolyte and the composite particles 10 can be suppressed, thus improving the initial charge-discharge efficiency. Furthermore, due to the small aspect ratio of the silicon particles 2, the expansion of the silicon particles 2 during battery charge-discharge can also be reduced, thus suppressing the formation of cracks in the composite particles 10, which is a major cause of side reactions with the electrolyte. Therefore, with the above configuration, the initial charge-discharge efficiency of the battery using the composite particles 10 can be improved.

[0023] The average aspect ratio of silicon particles 2 can be greater than 1.1 and less than 1.6.

[0024] In the X-ray diffraction pattern of the composite particle 10 obtained by X-ray diffraction using Cu-Kα rays, the half-width of the X-ray diffraction peak from the (111) plane of Si can be greater than 0.2° and less than 0.4°.

[0025] Carbon phase 1 is a matrix composed of carbonaceous materials. There are no particular limitations on the carbonaceous materials, as long as they are capable of absorbing and storing lithium ions. The carbonaceous materials can be amorphous. Carbon phase 1 can be composed of amorphous carbonaceous materials. Examples of carbonaceous materials include materials derived from pitch, amorphous carbon, and carbon black. Pitch examples include coal tar pitch and petroleum pitch. This allows for more stable electrical connections between silicon particles 2 within the composite particles, as well as between silicon particles 2 and the carbonaceous materials.

[0026] In the X-ray diffraction pattern of the composite particle 10 obtained by X-ray diffraction using Cu-Kα rays, the half-width of the X-ray diffraction peak from the (002) plane of C within the range of diffraction angle 2θ of 23.0° to 26.0° can be 4.0° to 9.5° or less. Here, the X-ray diffraction peak from the (002) plane of C is, for example, the X-ray diffraction peak with the highest intensity within the range of diffraction angle 2θ of 23.0° to 26.0°.

[0027] Silicon particles 2 are, for example, nano-sized silicon particles. The average particle size of silicon particles 2 can be 10 nm or more and 110 nm or less, or 10 nm or more and 100 nm or less. The average particle size of silicon particles 2 can be 25 nm or more and 65 nm or less. Based on the above configuration, the initial charge and discharge efficiency of the battery can be improved.

[0028] The average particle size of silicon particles 2 can be determined from the SEM image of the composite particles 10 obtained by SEM. That is, the average particle size of silicon particles 2 can be determined from the SEM image of the cross-section of the composite particles 10 exposed by the cross-section of silicon particles 2. The average particle size can be obtained by measuring the particle size of 500 silicon particles 2 randomly extracted from the SEM image of the composite particles 10 and calculating their median particle size (D50). Here, the maximum Ferrette diameter of silicon particles 2 in the obtained SEM image can be considered as the particle size of silicon particles 2. The "maximum Ferrette diameter" is the maximum length of the perpendicular line formed by two parallel lines sandwiching the particle.

[0029] The median particle size of silicon particle 2 is considered as the median particle size of 500 silicon particles 2 as measured by SEM observation.

[0030] The average particle size of composite particles 10 can be greater than 1 μm and less than 10 μm. The average particle size of composite particles 10 can be measured, for example, in the same way as the average particle size of silicon particles 2.

[0031] The pore volume of composite particles 10 can be less than 0.10 cc / g. Alternatively, the pore volume of composite particles 10 can be greater than 0.01 cc / g. Or, the pore volume of composite particles 10 can be greater than 0.01 cc / g and less than 0.08 cc / g, or greater than 0.01 cc / g and less than 0.05 cc / g. The carbon phase 1 is a dense carbonaceous material, and the silicon particles 2 are covered by the dense carbon phase 1, thus improving the initial charge and discharge efficiency of the battery.

[0032] The pore volume of the composite particle 10 is determined, for example, using a nitrogen adsorption apparatus by the BJH (Barrett-Joyner-Halenda) method.

[0033] The specific surface area of ​​composite particles 10 can be 15.0 m². 2 Below / g, it can also be 11.0m 2 / g or less. In this disclosure, specific surface area is the BET specific surface area that can be determined by the BET method. The specific surface area of ​​composite particles 10 can be 2.0 m². 2 / g or more and 11.0m 2 Below / g, it can be 5.0m 2 / g or more and 11.0m 2 Below / g, it can be 6.0m 2 / g or more and 11.0m 2 Below / g, it can also be 6.0m 2 / g or more and 9.0m 2 / g or less. This configuration improves the initial charge and discharge efficiency of the battery.

[0034] The true density of composite particles 10 can be less than 2.2 g / cc. Alternatively, the true density of composite particles 10 can be greater than 2.0 g / cc and less than 2.2 g / cc. Based on the above composition, the silicon particles 2 are densely covered by the carbon phase 1, which can improve the initial charge-discharge efficiency of the battery. The true density of composite particles 10 can be determined, for example, using the He gas specific gravity bottle method.

[0035] The Si content in the composite particles 10 can be 35.0% by mass or more and 60.0% by mass or less. Alternatively, the Si content in the composite particles 10 can be 38.0% by mass or more and 60.0% by mass or less, or 38.9% by mass or more and 50.0% by mass or less. Based on the above configuration, the initial charge-discharge efficiency of the battery can be improved.

[0036] The composite particles 10 may also contain nitrogen (N). This configuration improves the conductivity of the composite particles 10 and suppresses silicon oxidation. Consequently, the initial charge / discharge efficiency of the battery is improved. The N content in the composite particles 10 can be 0.02% by mass or more and 2.0% by mass or less, or 0.05% by mass or more and 1.0% by mass or less. Alternatively, the N content in the composite particles 10 can be 0.05% by mass or more and 0.7% by mass or less, or 0.05% by mass or more and 0.5% by mass or less. Based on this configuration, the initial charge / discharge efficiency of the battery is improved. The N contained in the composite particles 10 may come from a binder used in the manufacturing process of the composite particles 10. This configuration improves the conductivity of the interface between the carbon phase 1 and the silicon particles 2 and suppresses silicon oxidation during manufacturing.

[0037] The composite particles 10 may also contain oxygen (O). The percentage of O in the composite particles 10 can be less than 7% by mass, less than 6.8% by mass, or less than 6.3% by mass. Alternatively, the percentage of O in the composite particles 10 can be more than 1% by mass and less than 7% by mass, more than 4% by mass and less than 6.8% by mass, or more than 5% by mass and less than 6.25% by mass. Based on the above configuration, the initial charge and discharge efficiency of the battery can be improved.

[0038] The C content in the composite particles 10 can be 35% by mass or more and 60% by mass or less, or 35% by mass or more and 55% by mass or less. Based on this configuration, the initial charge and discharge efficiency of the battery can be improved.

[0039] The mass ratio of Si in composite particles 10 can be determined using Si-NMR. The mass ratio of C in composite particles 10 can be determined using combustion-infrared absorption spectrometry with a carbon-sulfur analyzer. The mass ratio of N in composite particles 10 can be determined, for example, using inert gas melting-thermal conductivity (TCD) spectrometry with an oxygen-nitrogen-hydrogen analyzer. The mass ratio of O in composite particles 10 can be determined, for example, using inert gas melting-nondispersive infrared absorption spectrometry (NDIR) with an oxygen-nitrogen-hydrogen analyzer.

[0040] In addition to the above-mentioned components, the composite granules 10 may also contain other components. The composite granules 10 may contain other components in a proportion of more than 0% by mass and less than 20% by mass, in a proportion of more than 0% by mass and less than 10% by mass, in a proportion of more than 0% by mass and less than 5% by mass, or in a proportion of more than 0% by mass and less than 2% by mass.

[0041] Composite particles 10 are used, for example, as a negative electrode active material.

[0042] (Manufacturing method of composite particles for negative electrode materials)

[0043] An example of a method for manufacturing composite particles for anode materials according to Embodiment 1 will be described. The method for manufacturing composite particles for anode materials according to Embodiment 1 includes: mixing silicon particles and a carbon source; pressing the resulting mixture into shape; heat-treating the resulting molded body; and coating the heat-treated molded body with carbon.

[0044] When mixing silicon particles with a carbon source, a binder may also be mixed in. That is, the method for manufacturing composite particles for anode materials according to Embodiment 1 may include: mixing silicon particles, a carbon source and a binder; pressing the resulting mixture into shape; heat-treating the resulting molded body; and covering the heat-treated molded body with carbon.

[0045] The same silicon particles as silicon particle 2 described above can be used as silicon particles.

[0046] As a carbon source, for example, bitumen, tar, thermoplastic resins, and thermosetting resins can be used. The carbon source can be bitumen, which can be coal tar or petroleum bitumen.

[0047] Examples of binders include ammonium polycarboxylate, polyvinylpyrrolidone, ammonium polyacrylate, carboxymethyl cellulose ammonium salt, polyalkylene polyamine, polyacrylamide, polyethyleneimine, and polyethylene glycol. The binder can be a polymer that has been amorphously carbonized under heat treatment of the molded body. With the above configuration, the electrical connections between silicon particles in the composite particles for the negative electrode material, or between silicon particles and carbonaceous materials, are stabilized. The binder can have a structure containing nitrogen (N). With the above configuration, composite particles for the negative electrode material that improve the initial charge-discharge efficiency of the battery can be manufactured. The binder can be polyvinylpyrrolidone.

[0048] There are no particular limitations on the mixing method of silicon particles, carbon source and binder; for example, a gyratory mill can be used for mixing.

[0049] Next, the mixture is pressurized, for example, using cold isostatic pressing (CIP). Alternatively, pressurization can be performed using a uniaxial press.

[0050] Next, the carbon source and binder are carbonized by heat treatment of the resulting molded body. The carbon source and binder can be carbonized into amorphous carbon. Thus, composite particles of silicon and carbon are obtained.

[0051] The temperature for heat treatment of the molded body is, for example, 700°C or higher and 1000°C or lower. The heat treatment time is, for example, 1 hour or higher and 10 hours or lower, and can be 5 hours or lower. The heat treatment can be carried out in a non-reactive atmosphere.

[0052] The heat-treated molded body can be pulverized. It can also be pulverized to adjust the particle size to the target size.

[0053] Next, carbon is coated onto the pulverized molded body. For example, carbon can be coated by covering the pulverized molded body with a carbon source and then heat-treating it under the conditions described above. The pulverization of the molded body and the coating with carbon can be repeated multiple times. Pulverization can be performed, for example, using a cutting-type pulverizer.

[0054] As described above, composite particles for the negative electrode material of Embodiment 1 are obtained.

[0055] (Implementation Method 2)

[0056] The secondary battery of Embodiment 2 includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode comprises a negative electrode material containing composite particles for negative electrode material of Embodiment 1. That is, the negative electrode of the secondary battery of Embodiment 2 comprises composite particles for negative electrode material of Embodiment 1.

[0057] Figure 2This is a cross-sectional view showing the schematic configuration of the secondary battery according to Embodiment 2. The secondary battery 100 includes a positive electrode 23, a negative electrode 26, a separator 27, a non-aqueous electrolyte 29, and a casing 28. The positive electrode 23, negative electrode 26, non-aqueous electrolyte 29, and separator 27 are housed in the casing 28. A separator 27 is disposed between the positive electrode 23 and the negative electrode 26. The positive electrode 23 and the negative electrode 26 are opposite to each other with respect to the separator 27. The positive electrode 23 includes a positive electrode flux layer 22 and a positive electrode current collector 21. The positive electrode flux layer 22 is disposed between the positive electrode current collector 21 and the separator 27. The negative electrode 26 includes a negative electrode flux layer 25 and a negative electrode current collector 24. The negative electrode flux layer 25 is disposed between the negative electrode current collector 24 and the separator 27.

[0058] The positive electrode layer 22 contains a positive electrode active material capable of absorbing, storing, and releasing lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using lithium-containing transition metal oxides or lithium-containing transition metal phosphates as positive electrode active materials can reduce battery manufacturing costs and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. At least one of these positive electrode active materials can be used.

[0059] The positive electrode binder layer 22 may contain conductive additives, ionic conductors and binders as needed.

[0060] Conductive additives and ionic conductors are used to reduce the resistance of electrodes. Examples of conductive additives include carbon materials and conductive polymers. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymers include polyaniline, polypyrrole, and polythiophene. At least one of these conductive additives may be used.

[0061] Adhesives are used to improve the adhesion of materials constituting electrodes. Examples of adhesives include polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene copolymer, polytetrafluoroethylene (PTFE), carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one adhesive selected from these can be used.

[0062] The positive current collector 21 is a sheet or film made of a metal material such as aluminum, aluminum alloy, stainless steel, titanium, or titanium alloy. The sheet or film can be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. Carbon material can be coated on the surface of the positive current collector 21 as a conductive auxiliary material.

[0063] The negative electrode compound layer 25 contains a negative electrode material. The negative electrode material contains composite particles for the negative electrode material according to Embodiment 1. The negative electrode material (negative electrode compound layer 25) may contain conductive additives, ionic conductors, and binders as needed. As conductive additives, ionic conductors, and binders, materials that can be used in the positive electrode compound layer 22 may also be used in the negative electrode compound layer 25.

[0064] The negative current collector 24 is a sheet or film made of a metal material such as stainless steel, nickel, nickel alloy, copper, or copper alloy. The sheet or film can be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. Carbon material can be coated on the surface of the negative current collector 24 as a conductive auxiliary material.

[0065] The separator 27 is an electrolyte layer with lithium-ion conductivity. The material of the separator 27 is not particularly limited, as long as lithium ions can pass through. The material of the separator 27 can be at least one selected from the group consisting of solid electrolytes, gel electrolytes, ion exchange resin membranes, semi-permeable membranes, and porous membranes. If the separator 27 is made of these materials, the safety of the secondary battery 100 can be sufficiently ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li₂S-P₂S₅ and Li₇La₃Zr₂O. 12 (LLZ) and other oxide solid electrolytes, etc. Gel electrolytes include those containing fluorinated resins such as PVdF. Ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Porous membranes include porous membranes made of polyolefin resins and porous membranes made of cellophane obtained by weaving glass fibers into nonwoven fabric.

[0066] The non-aqueous electrolyte 29 can be immersed in the positive electrode 23, the negative electrode 26, and the separator 27. The non-aqueous electrolyte 29 can fill the internal space of the casing 28. Through the action of the non-aqueous electrolyte 29, lithium ions can move between the positive electrode 23 and the negative electrode 26. The non-aqueous electrolyte 29 can contain a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid.

[0067] Non-aqueous electrolytes may contain non-aqueous solvents and lithium salts.

[0068] As a non-aqueous solvent, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorinated solvents, nitriles, etc., can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butyl carbonate. Examples of chain carbonates include dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic esters include γ-butyrolactone. Examples of chain esters include methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, methyl ethyl fluorocarbonate, and dimethyl fluorocarbonate. Examples of nitriles include acetonitrile. At least one of these non-aqueous solvents can be used.

[0069] Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalate-containing)borate. At least one of these lithium salts may be used.

[0070] Gel electrolytes can be materials obtained by impregnating a non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polymers containing ethylene oxide bonds.

[0071] Examples of cations constituting ionic liquids include aliphatic chain quaternary cations, aliphatic cyclic ammonium cations, and nitrogen-containing heterocyclic aromatic cations. Examples of aliphatic chain quaternary cations include tetraalkylammonium and tetraalkylphosphonium. Examples of aliphatic cyclic ammonium cations include pyrrolidine-onium, morpholinium-onium, imidazoline-onium, tetrahydropyrimidine-onium, piperazine-onium, and piperidinium-onium. Examples of nitrogen-containing heterocyclic aromatic cations include pyridinium and imidazoline-onium. Examples of anions constituting ionic liquids include PF6. - BF4 - SbF6 - AsF6 - SO3CF3 - N(SO2F)2 - N(SO2CF3)2 - N(SO2C2F5)2 - N(SO2CF3)(SO2C4F9) - C(SO2CF3)3 - Etc. Ionic liquids can contain lithium salts.

[0072] The outer casing 28 is made of a material, for example, obtained by laminating a metal foil, such as aluminum foil, with a resin film, such as PET film. The outer casing 28 may also be a container made of resin or metal.

[0073] The shape of the secondary battery 100 is not limited to a stacked type. Other shapes of the secondary battery 100 include coin type, cylindrical type, square type, sheet type, button type, flat type, etc.

[0074] The secondary battery of Embodiment 2 improves the initial charge-discharge efficiency by including composite particles of the negative electrode material of Embodiment 1 in the negative electrode.

[0075] (Other implementation methods)

[0076] (Postscript)

[0077] Based on the description of the above embodiments, the following technology is disclosed.

[0078] (Technology 1)

[0079] A composite particle for anode material, comprising:

[0080] carbon phase, and

[0081] Silicon particles dispersed in the aforementioned carbon phase,

[0082] In the X-ray diffraction pattern obtained by using Cu-Kα X-ray diffraction, the half-width of the X-ray diffraction peak from the (111) plane of Si is greater than 0.1° and less than 0.75°.

[0083] The average aspect ratio of the aforementioned silicon particles is greater than 1.0 and less than 1.6.

[0084] This configuration can improve the initial charge and discharge efficiency of the battery.

[0085] (Technology 2)

[0086] According to the composite particles for the negative electrode material described in Technology 1, the half-width is 0.2° or more and 0.4° or less. This configuration improves the initial charge / discharge efficiency of the battery.

[0087] (Technology 3)

[0088] According to the composite particles for the negative electrode material described in technique 1 or 2, the average particle size of the silicon particles is 10 nm or more and 100 nm or less. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0089] (Technology 4)

[0090] According to the composite particles for the negative electrode material described in Technology 3, the average particle size is 25 nm or more and 65 nm or less. This configuration improves the initial charge-discharge efficiency of the battery.

[0091] (Technology 5)

[0092] The composite particles for the negative electrode material according to any one of techniques 1 to 4 have a pore volume of 0.10 cc / g or less. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0093] (Technology 6)

[0094] The composite particles for the negative electrode material according to any one of techniques 1 to 5 have a pore volume of 0.01 cc / g or more and 0.08 cc / g or less. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0095] (Technology 7)

[0096] The composite particles for negative electrode materials according to any one of techniques 1 to 6, wherein the Si ratio in the composite particles for negative electrode materials is 35.0% by mass or more and 60.0% by mass or less. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0097] (Technology 8)

[0098] The composite particles for negative electrode materials according to any one of techniques 1 to 7, wherein the N ratio in the composite particles for negative electrode materials is 0.05% by mass or more and 1.0% by mass or less. With this configuration, the charge and discharge efficiency of the battery can be further improved.

[0099] (Technology 9)

[0100] The composite particles for negative electrode materials according to any one of techniques 1 to 8, wherein the O ratio in the composite particles for negative electrode materials is less than 6.3% by mass. With this configuration, the initial charge-discharge efficiency of the battery can be further improved.

[0101] (Technology 10)

[0102] The composite particles for the negative electrode material according to any one of techniques 1 to 9, wherein the carbon phase is composed of an amorphous carbonaceous material. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0103] (Technology 11)

[0104] According to any one of the composite particles for negative electrode materials in art 1 to 10, in an X-ray diffraction pattern obtained by measuring using Cu-Kα rays, the half-width of the X-ray diffraction peaks from the (002) plane of C in the range of diffraction angle 2θ of 23.0° or more and 26.0° or less is 4.0° or more and 9.5° or less. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0105] (Technology 12)

[0106] The composite particles for the negative electrode material according to any one of techniques 1 to 11 have a true density of 2.0 g / cc or more and 2.2 g / cc or less. With this configuration, the silicon particles are densely covered by a carbon phase, which improves the initial charge-discharge efficiency of the battery.

[0107] (Technology 13)

[0108] The composite particles for the negative electrode material according to any one of techniques 1 to 12 have a specific surface area of ​​11.0 m². 2 Below / g. This configuration improves the initial charge / discharge efficiency of the battery.

[0109] (Technology 14)

[0110] A secondary battery, comprising:

[0111] A negative electrode comprising composite particles for negative electrode materials as described in any one of techniques 1 to 13,

[0112] Positive electrode, and

[0113] Electrolytes.

[0114] This configuration can improve the initial charge and discharge efficiency.

[0115] Example

[0116] The present disclosure will now be described in more detail using examples. These examples are merely illustrative and are not intended to limit the scope of the disclosure.

[0117] [Fabrication of Composite Particles for Anode Materials]

[0118] (Example 1)

[0119] Silicon particles with an average particle size of 40 nm and an aspect ratio of 1.3 were prepared. The average particle size and aspect ratio of the silicon particles were calculated from SEM images of the silicon particles obtained using a scanning electron microscope. Specifically, the median particle size (D50) and the median of the number of arbitrary 500 particles selected from the SEM images of the silicon particles were used as the average particle size and aspect ratio, respectively.

[0120] Add 50g of silica particles, 10g of polyvinylpyrrolidone as a binder, and 50g of zirconia balls as a mixing medium to a gyratory mill and mix at 60Hz for 1 minute. After mixing, add 55g of petroleum asphalt to the gyratory mill and mix at 60Hz for 1 minute.

[0121] The resulting mixture was then subjected to cold isostatic pressing (CIP) at 190 MPa for 5 minutes to form a molded body.

[0122] The resulting molded body was heat-treated at 800°C for 5 hours under an argon atmosphere at a heating rate of 100°C / min to obtain silicon-carbon composite particles.

[0123] The resulting composite particles were pulverized using a cutting pulverizer at 18,000 rpm for 5 minutes. 3.25 g of petroleum asphalt was added to 50 g of the pulverized composite particles, and the mixture was then heat-treated and pulverized again under the same conditions.

[0124] The heat treatment and pulverization processes described above were each repeated once. This yielded the composite particles for the negative electrode material of Example 1.

[0125] (Example 2)

[0126] Using silicon particles with an average particle size of 25 nm and an aspect ratio of 1.2, the composite particles for the anode material of Example 2 were obtained in the same manner as in Example 1.

[0127] (Example 3)

[0128] Using silicon particles with an average particle size of 50 nm and an aspect ratio of 1.2, the composite particles for the negative electrode material of Example 3 were obtained in the same manner as in Example 1.

[0129] (Example 4)

[0130] Using silicon particles with an average particle size of 65 nm and an aspect ratio of 1.2, the composite particles for the anode material of Example 4 were obtained in the same manner as in Example 1.

[0131] (Example 5)

[0132] Using silicon particles with an average particle size of 110 nm and an aspect ratio of 1.2, the composite particles for the anode material of Example 5 were obtained in the same manner as in Example 1.

[0133] (Example 6)

[0134] Using silicon particles with different crystallinity than those used in Example 1 and an aspect ratio of 1.2, the composite particles for the negative electrode material of Example 6 were obtained in the same manner as in Example 1.

[0135] (Example 7)

[0136] Using silicon particles with different crystallinity than those used in Example 1 and Example 6, the composite particles for the negative electrode material of Example 7 were obtained in the same manner as in Example 6.

[0137] (Example 8)

[0138] Using silicon particles with an aspect ratio of 1.0, the composite particles for the negative electrode material of Example 8 were obtained in the same manner as in Example 1.

[0139] (Example 9)

[0140] Using silicon particles with an aspect ratio of 1.6, the composite particles for the negative electrode material of Example 9 were obtained in the same manner as in Example 1.

[0141] (Example 10)

[0142] The amount of petroleum asphalt added to the oscillating mill was set to 32.5g. Otherwise, the composite particles for the negative electrode material of Example 10 were obtained in the same manner as in Example 1.

[0143] (Example 11)

[0144] The amount of petroleum asphalt fed into the oscillating mill was set to 85g. Otherwise, the composite particles for the negative electrode material of Example 11 were obtained in the same manner as in Example 1.

[0145] (Example 12)

[0146] The amount of binder added to the oscillating mill was set to 16.5g. Otherwise, the composite particles for the negative electrode material of Example 12 were obtained in the same manner as in Example 1.

[0147] (Example 13)

[0148] The amount of binder added to the oscillating mill was set to 1.65g. Otherwise, the composite particles for the negative electrode material of Example 13 were obtained in the same manner as in Example 1.

[0149] (Example 14)

[0150] The binder added to the oscillating mill was set to 1.65 g of polyethylene glycol. Otherwise, the composite particles for the negative electrode material of Example 14 were obtained in the same manner as in Example 1.

[0151] (Refer to Example 1)

[0152] 50g of silicon particles with an average particle size of 10μm and 2kg of zirconia beads were pulverized using a ball mill at 1000rpm for 5 hours. The resulting silicon particles had an average particle size of 150nm and an aspect ratio of 2. Using the silicon particles thus obtained, composite particles for the negative electrode material of Reference Example 1 were obtained in the same manner as in Example 1.

[0153] (See Example 2 for reference)

[0154] 50g of silicon particles with an average particle size of 10μm and 2kg of zirconia beads were pulverized using a ball mill at 1000rpm for 15 hours. The resulting silicon particles had an average particle size of 40nm and an aspect ratio of 2.5. Using the silicon particles thus obtained, composite particles for the negative electrode material of Reference Example 2 were obtained in the same manner as in Example 1.

[0155] [Cross-section SEM observation]

[0156] Cross-sectional SEM images of the composite particles for anode materials from Examples 1-14 and Reference Examples 1-2 were used to confirm the average aspect ratio and average particle size of the silicon particles. The results are shown in Table 1.

[0157] [BET specific surface area]

[0158] The BET specific surface area of ​​the composite particles used as negative electrode materials in Examples 1-14 and Reference Examples 1-2 was determined using a nitrogen adsorption apparatus (Microtrac BEL, BEL SOAP Mini X) via the BET multi-point method. The values ​​calculated with relative pressure ratios between 0.1 and 0.3 were used as the surface area. The measurement results are shown in Table 1.

[0159] [Kong Rong]

[0160] The pore volumes of the composite particles used as anode materials in Examples 1-14 and Reference Examples 1-2 were determined using the BJH method with a nitrogen adsorption apparatus (Microtrac BEL Corporation, BEL SOAP Mini X). The results are shown in Table 1.

[0161] X-ray diffraction

[0162] X-ray diffraction patterns of the composite particles used as anode materials in Examples 1-14 and Reference Examples 1-2 were obtained by powder X-ray diffraction. The measurements were performed using an X-ray diffraction apparatus (Spectris, ENPYREAN). Cu-Kα rays (wavelength 1.5405 nm) were used as the X-ray source. and 1.5444 In the X-ray diffraction pattern, the half-width of the peak from the (111) plane of Si is shown in Table 1.

[0163] [Component analysis]

[0164] The mass ratios of Si, C, N, and O in the composite particles used as the negative electrode materials in Examples 1 to 14 and Comparative Examples 1 to 2 were measured as follows. The measurement results are shown in Table 1.

[0165] The mass ratio of Si in the composite particles was determined by quantifying Si using Si-NMR under the conditions shown below.

[0166] [Si-NMR measurement conditions]

[0167] Measurement device: Solid nuclear magnetic resonance spectrometer (INOVA-400) manufactured by Varian

[0168] Probe: Varian 7mm CPMAS-2

[0169] MAS: 4.2 kHz

[0170] MAS speed: 4 kHz

[0171] Pulse: DD (45° pulse + signal acquisition time 1H decoupling)

[0172] Repetition time: 1200 seconds to 3000 seconds

[0173] Observation width: 100 kHz

[0174] Observation center: around -100 ppm

[0175] Signal acquisition time: 0.05 seconds

[0176] Number of accumulations: 560

[0177] Sample amount: 207.6 mg

[0178] The mass ratio of C in the composite particles was measured by combustion-infrared absorption method using a high-frequency induction heating furnace of a carbon and sulfur analyzer (EMIA-520 manufactured by Horiba, Ltd.). The sample was weighed on a magnetic plate, a combustion aid was added, and it was inserted into a combustion furnace heated to 1350 °C (carrier gas: oxygen). The amount of carbon dioxide gas generated during combustion was detected by infrared absorption. A standard curve was made using carbon steel (carbon content 0.49%) manufactured by Bureau of Analysed Samples.Ltd, and the carbon content of the sample was calculated to quantify C.

[0179] The mass ratios of N and O in the composite particles were determined using an oxygen-nitrogen-hydrogen analyzer (Horiba Manufacturing Co., Ltd., EGMA-830). The sample was placed in a Ni capsule and, together with Sn and Ni particles used as flux, was added to a carbon crucible heated to 5.75 kW. The released carbon dioxide, carbon monoxide, and nitrogen gases were measured. The quantification of O was performed by calculating the oxygen content of the sample using a standard curve prepared with NS-16-2 (steel standard sample). The quantification of N was performed by calculating the nitrogen content of the sample using a standard curve prepared with SS-2-115 (steel standard sample).

[0180] [Evaluation of battery cell fabrication]

[0181] Using the composite particles for negative electrode materials from Examples 1-14 and Reference Examples 1-2, the evaluation battery cells of Examples 1-14 and Reference Examples 1-2 were fabricated as follows.

[0182] (Making the negative electrode)

[0183] The negative electrode material was prepared by mixing composite particles and graphite at a mass ratio of 5:95 to serve as the negative electrode active material. Water was added to a negative electrode mixture containing the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) at a mass ratio of negative electrode active material:CMC-Na:SBR=97.5:1:1.5, and the mixture was stirred to prepare a negative electrode slurry. Then, the slurry was applied to both sides of the copper foil at a ratio of 1m... 2 The negative electrode mixture, weighing 190g, is coated with a negative electrode slurry. After drying, the coating is calendered to form a film with a density of 1.5g / cm³ on both sides of the copper foil. 3 The negative electrode of the negative electrode compound layer.

[0184] (The production of the positive electrode)

[0185] Prepare a cathode active material with a mass ratio of AB:PVDF = 95:2.5:2.5, containing LiNi. 0.88 Co 0.09 Al 0.03 A positive electrode mixture of O2, acetylene black (AB), and polyvinylidene fluoride (PVDF) was prepared. N-methyl-2-pyrrolidone (NMP) was added to the positive electrode mixture and stirred to prepare a positive electrode slurry. Next, the positive electrode slurry was coated onto both sides of an aluminum foil. After the coating was dried, it was calendered to form a film with a density of 3.6 g / cm³ on both sides of the aluminum foil. 3 The positive electrode of the positive electrode compound layer.

[0186] (Preparation of electrolyte)

[0187] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7.

[0188] (Making a secondary battery)

[0189] A tab is attached to the positive and negative electrodes, and the electrodes are wound into a spiral shape with the tabs at the outermost periphery, separated by a separator, to create an electrode assembly. The electrode assembly is inserted into an aluminum laminate casing, vacuum dried at 105°C for 2 hours, and then injected with a non-aqueous electrolyte. The opening of the casing is sealed to obtain a secondary battery for evaluation purposes.

[0190] [Evaluation of charge / discharge efficiency]

[0191] For the evaluation battery cells of Examples 1-14 and Reference Examples 1-2, at an ambient temperature of 25°C, they were charged with a constant current of 1 It (800 mA) until the voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current reached 1 / 20 It (40 mA). After a 10-minute rest period, they were discharged with a constant current of 1 It (800 mA) until the voltage reached 2.5V. The initial charge-discharge efficiency of the evaluation battery cells of Examples 1-14 and Reference Examples 1-2 was thus evaluated. The relative values ​​when the charge-discharge efficiency of Reference Example 2 was set to 100% are shown in Table 1.

[0192] [Table 1]

[0193]

[0194] (Inspection)

[0195] The batteries using composite particles of negative electrode materials from Examples 1-14 showed improved initial charge-discharge efficiency compared to Reference Examples 1 and 2.

[0196] Industrial availability

[0197] The technology disclosed herein is useful for batteries such as lithium-ion secondary batteries.

Claims

1. A composite particle for anode materials, comprising: carbon phase, and Silicon particles dispersed in the carbon phase, In the X-ray diffraction pattern obtained by using Cu-Kα X-ray diffraction, the half-width of the X-ray diffraction peak from the (111) plane of Si is greater than 0.1° and less than 0.75°. The average aspect ratio of the silicon particles is greater than 1.0 and less than 1.

6.

2. The composite particles for the negative electrode material according to claim 1, wherein, The half-value width is greater than 0.2° and less than 0.4°.

3. The composite particles for the negative electrode material according to claim 1, wherein, The average particle size of the silicon particles is greater than 10 nm and less than 100 nm.

4. The composite particles for the negative electrode material according to claim 3, wherein, The average particle size is above 25 nm and below 65 nm.

5. The composite particles for negative electrode materials according to claim 1, wherein the pore volume is less than 0.10 cc / g.

6. The composite particles for the negative electrode material according to claim 5, wherein, The pore volume is above 0.01cc / g and below 0.08cc / g.

7. The composite particles for the negative electrode material according to claim 1, wherein, The Si ratio in the composite particles used for the negative electrode material is 35.0% by mass or more and 60.0% by mass or less.

8. The composite particles for the negative electrode material according to claim 1, wherein, The N ratio in the composite particles used for the negative electrode material is 0.05% by mass or more and 1.0% by mass or less.

9. The composite particles for negative electrode materials according to claim 1, wherein, The O ratio in the composite particles used for the negative electrode material is less than 6.3% by mass.

10. The composite particles for the negative electrode material according to claim 1, wherein, The carbon phase is composed of amorphous carbonaceous materials.

11. The composite particles for the negative electrode material according to claim 1, wherein, In the X-ray diffraction pattern obtained by using Cu-Kα X-ray diffraction, the half-width of the X-ray diffraction peaks from the (002) plane of C in the range of diffraction angle 2θ above 23.0° and below 26.0° is above 4.0° and below 9.5°.

12. The composite particles for negative electrode materials according to claim 1, wherein the true density is above 2.0 g / cc and below 2.2 g / cc.

13. The composite particles for the negative electrode material according to claim 1, having a specific surface area of ​​11.0 m². 2 / g or less.

14. A secondary battery, comprising: A negative electrode comprising the composite particles for negative electrode material as described in any one of claims 1 to 13, Positive electrode, and Electrolytes.

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