Negative electrode active material and secondary battery

Abstract

A negative electrode active material 10 according to the present disclosure contains a carbon phase 1 and Si-Ni-containing particles 2 dispersed in the carbon phase 1. The ratio of Ni in the Si-Ni-containing particles 2 may be 0.01% by mass to 5.0% by mass inclusive. A secondary battery according to the present disclosure comprises a negative electrode including the negative electrode active material according to the present disclosure, a positive electrode and a nonaqueous electrolyte.

Description

Negative electrode active material and secondary battery

[0001] The present disclosure relates to a negative electrode active material and a secondary battery.

[0002] In recent years, the use of silicon-containing composite materials as negative electrode materials for increasing the capacity of lithium-ion batteries has been expected, and for example, negative electrode active materials in which silicon is dispersed in a Li2Si2O5 matrix have been studied. To meet the demand for even higher capacity, efficiency, and durability of lithium-ion batteries, composite materials containing silicon and carbon materials have been studied. Patent Document 1 discloses a silicon / graphite / carbon composite containing graphite and non-aggregated nanoscale silicon particles, with the silicon particles embedded in a carbon matrix.

[0003] Special table 2017-506413 publication

[0004] In the prior art, it is desirable to improve the initial charge-discharge efficiency of a battery that uses a composite material containing silicon and a carbon material as an active material.

[0005] The negative electrode active material of the present disclosure includes: a carbon phase; and Si—Ni-containing particles dispersed in the carbon phase.

[0006] According to the technology of the present disclosure, it is possible to provide a negative electrode active material that can improve the initial charge / discharge efficiency of a battery.

[0007] Fig. 1 is a cross-sectional view showing a schematic configuration of one example of a negative electrode active material according to Embodiment 1. Fig. 2 is a cross-sectional view showing a schematic configuration of another example of a negative electrode active material according to Embodiment 1. Fig. 3 is a cross-sectional view showing a schematic configuration of a secondary battery according to Embodiment 2. Fig. 4 is a graph showing X-ray diffraction patterns of the negative electrode active materials of Example 1 and Comparative Example 1.

[0008] 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.

[0009] 1 is a cross-sectional view showing a schematic configuration of an example of a negative electrode active material according to Embodiment 1. The negative electrode active material 10 includes a carbon phase 1 and Si—Ni-containing particles 2 dispersed in the carbon phase 1.

[0010] The negative electrode active material 10 is a composite particle comprising a carbon phase 1 and Si—Ni-containing particles 2 .

[0011] The Si—Ni-containing particles 2 are particles containing Si and Ni elements. The inclusion of Ni in the Si—Ni-containing particles 2 improves electronic conductivity compared to silicon particles. That is, in the negative electrode active material 10, particles with improved electronic conductivity are dispersed in the carbon phase 1. With the above configuration, the initial charge / discharge efficiency of a battery using the negative electrode active material 10 can be improved.

[0012] The carbon phase 1 is a matrix containing carbon, and includes, for example, a carbonaceous material. The carbonaceous material is not particularly limited as long as it is a carbonaceous material that can absorb lithium ions. The carbonaceous material may be amorphous. The carbon phase 1 may be composed of an amorphous carbonaceous material. Examples of the carbonaceous material include pitch-derived materials, amorphous carbon, carbon black, and organic polymer-derived materials. Examples of pitch include coal pitch and petroleum pitch, and the coal pitch is, for example, coal tar pitch. This can further stabilize the electrical connection between the Si—Ni-containing particles 2 in the negative electrode active material 10 and the electrical connection between the Si—Ni-containing particles 2 and the carbonaceous material. The carbon phase 1 may include multiple types of carbonaceous materials.

[0013] The ratio of carbon (C) in the negative electrode active material 10 may be 40% by mass or more and 80% by mass or less, 40% by mass or more and 60% by mass or less, or 40% by mass or more and 50% by mass or less.

[0014] The proportion of C in the negative electrode active material 10 can be measured by a combustion-infrared absorption method using a carbon / sulfur analyzer.

[0015] The Si—Ni-containing particles 2 are particles containing Si and Ni.

[0016] The Si—Ni-containing particles 2 may contain crystalline silicon, that is, the Si element in the Si—Ni-containing particles 2 may be crystalline silicon.

[0017] In the Si—Ni-containing particle 2, Ni may be located inside the Si—Ni-containing particle 2 or on the surface of the Si—Ni-containing particle 2. For example, Ni may be dispersed within the silicon particle or may be located on the surface of the silicon particle.

[0018] The Si—Ni-containing particle 2 may contain crystalline silicon with Ni atoms in solid solution, that is, in the Si—Ni-containing particle 2, Ni may be Ni atoms in solid solution in crystalline silicon.

[0019] The Si—Ni-containing particle 2 may contain a nickel material. In this specification, the nickel material is a material containing Ni, and includes metallic Ni and Ni-containing compounds. In this specification, metallic Ni means elemental nickel. The Ni element in the Si—Ni-containing particle 2 may be Ni contained in a nickel material. The Si—Ni-containing particle 2 may be a composite particle of silicon and a nickel material.

[0020] The nickel material may include at least one selected from the group consisting of metallic Ni, Ni oxide, and Ni carbide. That is, the Si—Ni-containing particle 2 may include at least one selected from the group consisting of metallic Ni, Ni oxide, and Ni carbide. The Si—Ni-containing particle 2 may include metallic Ni.

[0021] The nickel material may be dispersed within the silicon particles or may be located on the surface of the silicon particles.

[0022] The Si—Ni containing particles 2 may contain nickel material and Ni atoms dissolved in crystalline silicon.

[0023] The average particle diameter of the Si—Ni-containing particles 2 may be 1 nm or more and 1000 nm or less, 1 nm or more and 100 nm or less, or 25 nm or more and 65 nm or less. With the above configuration, the initial charge / discharge efficiency of the battery can be improved.

[0024] The average particle diameter of the Si—Ni-containing particles 2 can be determined from an SEM image of the negative electrode active material 10 obtained by a scanning electron microscope (SEM). That is, the average particle diameter of the Si—Ni-containing particles 2 can be measured from an SEM image of the cross section of the negative electrode active material 10 in which the cross sections of the Si—Ni-containing particles 2 are exposed. The average particle diameter can be determined by measuring the particle diameters of 500 Si—Ni-containing particles 2 randomly extracted from the SEM image of the negative electrode active material 10 and calculating their median diameter (D50). Here, the maximum Feret diameter of the Si—Ni-containing particles 2 in the obtained SEM image can be considered as the particle diameter of the Si—Ni-containing particles 2. The "maximum Feret diameter" is the maximum length of the perpendicular line obtained by sandwiching a particle between two parallel lines.

[0025] The median value based on the number of particle diameters of 500 Si—Ni-containing particles 2 measured by SEM observation is regarded as the median diameter of the Si—Ni-containing particles 2.

[0026] The ratio of Si in the negative electrode active material 10 may be 20% by mass or more and 60% by mass or less, 30% by mass or more and 60% by mass or less, 40% by mass or more and 60% by mass or less, or 50% by mass or more and 60% by mass or less.

[0027] The proportion of Si in the negative electrode active material 10 can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0028] The ratio of Ni in the Si—Ni-containing particles 2 may be 0.01% by mass or more and 5.0% by mass or less, 0.01% by mass or more and 3.0% by mass or less, or 0.01% by mass or more and 1.0% by mass or less. The ratio of Ni in the Si—Ni-containing particles 2 may be 0.05% by mass or more, 0.1% by mass or more, or 1% by mass or more.

[0029] The mass ratio of Ni in the Si—Ni-containing particles 2 can be measured, for example, by removing the Si—Ni-containing particles 2 from the negative electrode active material 10 and then quantifying the Si amount and Ni amount by ICP.

[0030] The ratio of the total mass of Si and Ni to the mass of the negative electrode active material 10 may be 20 mass% or more and 60 mass% or less, 30 mass% or more and 60 mass% or less, or 40 mass% or more and 60 mass% or less.

[0031] The mass ratio of Si may be smaller near the surface of the negative electrode active material 10 than in portions other than the near surface of the negative electrode active material 10. Here, the near surface refers to a region extending to a depth of 5 nm from the surface of the negative electrode active material 10. The amount of Si in the depth direction can be measured by X-ray photoelectron spectroscopy (XPS).

[0032] The amount of Ni near the surface of the negative electrode active material 10 may be smaller than that of portions other than the surface of the negative electrode active material 10. The amount of Ni in the depth direction can be measured by X-ray photoelectron spectroscopy (XPS).

[0033] The Si—Ni-containing particles 2 may include a crystalline phase. For example, as described above, the Si—Ni-containing particles 2 may include crystalline silicon. In this specification, the phrase "the Si—Ni-containing particles 2 include crystalline silicon" means that a peak derived from the Si (111) plane is observed in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material 10 using Cu—Kα radiation. The X-ray diffraction peak derived from the Si (111) plane is, for example, an X-ray diffraction peak having the highest intensity within a diffraction angle 2θ range of 28.0° or more and 28.7° or less.

[0034] The X-ray diffraction pattern of the negative electrode active material 10 can be obtained by X-ray diffraction measurement by the θ-2θ method using Cu-Kα rays with wavelengths of 1.5405 Å and 1.5444 Å, that is, wavelengths of 0.15405 nm and 0.15444 nm.

[0035] In this specification, a peak is a mountain-shaped portion having an S / N ratio (i.e., the ratio of signal S to background noise N) of 1.3 or more and a half-width of 10° or less.

[0036] In an X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material 10 using Cu-Kα radiation, an X-ray diffraction peak derived from the Si (111) plane may be present within a diffraction angle 2θ range of 28.30° or more and 28.40° or less. "An X-ray diffraction peak derived from the Si (111) plane is present within a diffraction angle 2θ range of 28.30° or more and 28.40° or less" means that the peak top of the X-ray diffraction peak derived from the Si (111) plane is observed within a diffraction angle 2θ range of 28.30° or more and 28.40° or less. In an X-ray diffraction pattern obtained by X-ray diffraction measurement of the negative electrode active material 10 using Cu-Kα radiation, an X-ray diffraction peak derived from the Si (111) plane may be present within a diffraction angle 2θ range of 28.30° or more and 28.35° or less.

[0037] The diffraction angle of a peak in an X-ray diffraction pattern is defined as the angle at which the S / N ratio is 1.3 or more and the peak width at half maximum is 10° or less, showing the maximum intensity. MAX When the intensity is I MAX The width is the difference between the two diffraction angles that are half the value of the square root of the diffraction angle.

[0038] The Si—Ni-containing particle 2 may include an amorphous phase. The amorphous phase may include Ni.

[0039] When a lattice image of the Si—Ni-containing particle 2 in the negative electrode active material 10 is observed using a transmission electron microscope (TEM), a crystalline portion and an amorphous portion may be confirmed, and the amorphous portion may be derived from Ni.

[0040] The average particle diameter of the negative electrode active material 10 may be 1 μm or more and 20 μm or less, or may be 1 μm or more and 10 μm or less. The average particle diameter of the negative electrode active material 10 can be measured, for example, in the same manner as the average particle diameter of the Si—Ni-containing particles 2.

[0041] 2 is a cross-sectional view showing a schematic configuration of another example of the negative electrode active material according to Embodiment 1. The negative electrode active material 20 further includes a coating layer 3 that coats the surface of the carbon phase 1, and the coating layer 3 contains carbon.

[0042] The coating layer 3 is made of, for example, a carbonaceous material. Examples of the carbonaceous material include those described above for the carbon phase 1. The carbonaceous material contained in the coating layer 3 may be the same material as the carbonaceous material contained in the carbon phase 1. The coating layer 3 may be made of a carbonaceous material made of a pitch-derived material.

[0043] The thickness of the coating layer 3 may be 0.1 nm or more and 10 nm or less, or may be 5 nm or less.

[0044] The negative electrode active material 10 may further contain other components in addition to the components described above. The negative electrode active material 10 may contain the other components in a proportion of more than 0% by mass and not more than 20% by mass, more than 0% by mass and not more than 10% by mass, more than 0% by mass and not more than 5% by mass, or more than 0% by mass and not more than 2% by mass. The other components may be, for example, components derived from an organic polymer described below.

[0045] (Method for Producing Negative Electrode Active Material) A description will be given of an example of a method for producing the negative electrode active material according to embodiment 1. The example of the method for producing the negative electrode active material according to embodiment 1 includes obtaining Si—Ni-containing particles containing Si and Ni, mixing the Si—Ni-containing particles with a carbon source, and firing the obtained mixture.

[0046] The method for producing a negative electrode active material according to the first embodiment may include granulating the Si—Ni-containing particles between obtaining the Si—Ni-containing particles and mixing the Si—Ni-containing particles with a carbon source. That is, the method for producing a negative electrode active material according to the first embodiment may include obtaining the Si—Ni-containing particles, granulating the Si—Ni-containing particles, mixing the Si—Ni-containing particles with a carbon source, and firing the resulting mixture.

[0047] The method for obtaining the Si—Ni-containing particles is not particularly limited, and the Si—Ni-containing particles can be obtained, for example, by mixing a solution containing a Ni source with silicon particles and heat treating the mixture.

[0048] The Ni source is, for example, nickel formate, nickel nitrate, or nickel acetate. The Ni source may be nickel formate.

[0049] The mixing time is, for example, 10 minutes or more and 5 hours or less, and may be 3 hours or less.

[0050] The temperature of the heat treatment is, for example, 200°C or higher and 600°C or lower, and may be 500°C or lower.

[0051] The heat treatment may be carried out in an inert atmosphere.

[0052] Granulation of the Si—Ni-containing particles is carried out, for example, by dispersing the Si—Ni-containing particles in an aqueous solution containing a water-soluble organic polymer, and then spray-drying the dispersion.

[0053] Examples of the water-soluble organic polymer include carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, polyvinyl alcohol, starch, sodium polyacrylate, polyvinylpyrrolidone, casein, and gelatin, and may be carboxymethyl cellulose.

[0054] The means for mixing the Si—Ni-containing particles and the carbon source is not particularly limited, and for example, they may be mixed using a rocking mill.

[0055] Examples of the carbon source that can be used include pitch, tar, thermoplastic resin, and thermosetting resin. The carbon source may be pitch. Examples of the pitch include coal pitch and petroleum pitch, and examples of the coal pitch include coal tar pitch.

[0056] The calcination can carbonize the carbon source and the water-soluble organic polymer used for granulation. The carbon source and the water-soluble organic polymer can be carbonized to amorphous carbon. In this way, a negative electrode active material that is composite particles of Si—Ni-containing particles and carbon is obtained.

[0057] The firing temperature is, for example, 700° C. or more and 1000° C. or less, and may be 750° C. or more and 850° C. or less. The firing time is, for example, 1 hour or more and 10 hours or less, and may be 5 hours or less. The firing may be performed in an inert atmosphere.

[0058] In this manner, the negative electrode active material according to the first embodiment is obtained.

[0059] (Embodiment 2) A secondary battery according to embodiment 2 includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode contains a negative electrode material including the negative electrode active material according to embodiment 1. That is, in the secondary battery according to embodiment 2, the negative electrode contains the negative electrode active material according to embodiment 1.

[0060] 3 is a cross-sectional view showing a schematic configuration of a 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 an exterior casing 28. The positive electrode 23, the negative electrode 26, the non-aqueous electrolyte 29, and the separator 27 are housed in the exterior casing 28. The separator 27 is disposed between the positive electrode 23 and the negative electrode 26. The positive electrode 23 and the negative electrode 26 face each other with the separator 27 interposed therebetween. The positive electrode 23 includes a positive electrode mixture layer 22 and a positive electrode current collector 21. The positive electrode mixture layer 22 is disposed between the positive electrode current collector 21 and the separator 27. The negative electrode 26 includes a negative electrode mixture layer 25 and a negative electrode current collector 24. The negative electrode mixture layer 25 is disposed between the negative electrode current collector 24 and the separator 27.

[0061] The positive electrode mixture layer 22 includes a positive electrode active material capable of absorbing and releasing lithium ions. Examples of the positive electrode active material 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 a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce the manufacturing cost of the battery 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 selected from these positive electrode active materials can be used.

[0062] The positive electrode mixture layer 22 may contain a conductive additive, an ion conductor, and a binder as needed.

[0063] Conductive additives and ion conductors are used to reduce the resistance of the electrodes. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives can be used.

[0064] Examples of ionic conductors include gel electrolytes such as polymethyl methacrylate and polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, and Li7La3Zr2O 12 At least one selected from these ion conductors can be used.

[0065] Binders are used to improve the binding properties of the materials that make up the electrode. Examples of binders include polymeric materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one selected from these binders can be used.

[0066] The positive electrode current collector 21 is a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be applied to the surface of the positive electrode current collector 21 as a conductive auxiliary material.

[0067] The negative electrode mixture layer 25 includes a negative electrode material. The negative electrode material includes the negative electrode active material according to embodiment 1. The negative electrode material (negative electrode mixture layer 25) may include a conductive additive, an ion conductor, and a binder, as necessary. Materials that can be used for the positive electrode mixture layer 22 as the conductive additive, ion conductor, and binder can also be used for the negative electrode mixture layer 25.

[0068] The negative electrode current collector 24 is a sheet or film made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be applied to the surface of the negative electrode current collector 24 as a conductive auxiliary material.

[0069] The separator 27 is an electrolyte layer having lithium ion conductivity. There are no particular limitations on the material of the separator 27 as long as it allows the passage of lithium ions. 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, semipermeable 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, Li7La3Zr2O 12 Examples of the electrolyte include oxide solid electrolytes such as LLZ. Examples of the gel electrolyte include gel electrolytes containing fluororesins such as PVdF. Examples of the ion exchange resin membrane include cation exchange membranes and anion exchange membranes. Examples of the porous membrane include porous membranes made of polyolefin resins and porous membranes made of glass paper obtained by weaving glass fibers into nonwoven fabric.

[0070] The non-aqueous electrolyte 29 may be impregnated into the positive electrode 23, the negative electrode 26, and the separator 27. The non-aqueous electrolyte 29 may fill the internal space of the exterior casing 28. The non-aqueous electrolyte 29 functions to allow lithium ions to travel between the positive electrode 23 and the negative electrode 26. The non-aqueous electrolyte 29 may include a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid.

[0071] The non-aqueous electrolyte solution contains, for example, a non-aqueous solvent and a lithium salt.

[0072] Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorine-containing solvents, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonates include dimethyl carbonate, ethyl methyl 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 fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. Examples of nitriles include acetonitrile. At least one selected from these non-aqueous solvents can be used.

[0073] Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. At least one selected from these lithium salts can be used.

[0074] The gel electrolyte can be a material obtained by impregnating a polymer material with a non-aqueous electrolyte solution, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0075] Examples of cations constituting ionic liquids include aliphatic chain quaternary cations, aliphatic cyclic ammonium, and nitrogen-containing heterocyclic aromatic cations. Examples of aliphatic chain quaternary cations include tetraalkylammonium and tetraalkylphosphonium. Examples of aliphatic cyclic ammonium include pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, and piperidiniums. Examples of nitrogen-containing heterocyclic aromatic cations include pyridiniums and imidazoliums. 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 - The ionic liquid may contain a lithium salt.

[0076] The exterior 28 is made of a material obtained by laminating a metal foil such as an aluminum foil with a resin film such as a PET film, for example. The exterior 28 may also be a container made of resin or metal.

[0077] The shape of the secondary battery 100 is not limited to the laminated type. Other shapes of the secondary battery 100 include a coin type, a cylindrical type, a square type, a sheet type, a button type, and a flat type.

[0078] In the secondary battery according to the second embodiment, the negative electrode contains the negative electrode active material according to the first embodiment, and therefore the initial charge-discharge efficiency is improved.

[0079] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0080] (Technology 1) A negative electrode active material comprising: a carbon phase; and Si—Ni-containing particles dispersed in the carbon phase.

[0081] This configuration can improve the initial charge / discharge efficiency of the battery.

[0082] (Technology 2) The negative electrode active material according to Technology 1, wherein the ratio of Ni in the Si—Ni-containing particles is 0.01 mass % or more and 5.0 mass % or less. With this configuration, the initial charge / discharge efficiency of the battery can be improved.

[0083] (Technology 3) The negative electrode active material according to Technology 1 or 2, wherein the Si—Ni-containing particles contain at least one selected from the group consisting of metallic Ni, Ni oxide, and Ni carbide. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0084] (Technology 4) The negative electrode active material according to any one of Technologies 1 to 3, wherein the Si—Ni-containing particles contain metallic Ni. With this configuration, the initial charge / discharge efficiency of the battery can be improved.

[0085] (Technology 5) The negative electrode active material according to any one of Technologies 1 to 4, wherein the Si—Ni-containing particles contain crystalline silicon in which Ni atoms are solid-dissolved. With this configuration, the initial charge / discharge efficiency of the battery can be improved.

[0086] (Technology 6) The negative electrode active material according to any one of Technologies 1 to 5, wherein the Si—Ni-containing particles contain an amorphous phase. With this configuration, the initial charge / discharge efficiency of the battery can be improved.

[0087] (Technology 7) The negative electrode active material according to any one of Technologies 1 to 6, wherein an X-ray diffraction peak derived from the Si (111) plane is present within a diffraction angle 2θ range of 28.30° or more and 28.40° or less in an X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα radiation. With this configuration, the initial charge-discharge efficiency of the battery can be improved.

[0088] (Technology 8) The negative electrode active material according to any one of Technologies 1 to 7, wherein the Si—Ni-containing particles have an average particle size of 1 nm or more and 1000 nm or less. With this configuration, the initial charge / discharge efficiency of the battery can be improved.

[0089] (Technology 9) The negative electrode active material according to any one of Technologies 1 to 8, further comprising a coating layer that coats a surface of the carbon phase, the coating layer containing carbon. With this configuration, the initial charge / discharge efficiency of the battery can be further improved.

[0090] (Technology 10) A secondary battery comprising: a negative electrode containing the negative electrode active material according to any one of Technologies 1 to 9; a positive electrode; and an electrolyte.

[0091] With this configuration, the effect of improving the initial charge / discharge efficiency can be obtained.

[0092] The present disclosure will be described in more detail below using examples. The following examples are merely examples of embodiments, and are not intended to limit the scope of the present disclosure.

[0093] [Preparation of Negative Electrode Active Material] (Example 1) 0.2 g of nickel formate as a Ni source was dissolved in 20 mL of ethanol to obtain a Ni source solution. The obtained Ni source solution was mixed with 6 g of silicon particles with an average particle size of 20 nm for 30 minutes. After mixing, the mixture was heat-treated at 400°C for 1 hour in an argon atmosphere. In this way, the Ni source was introduced into the silicon particles to prepare Si—Ni-containing particles.

[0094] The Ni ratio in the obtained Si—Ni-containing particles was measured by ICP-AES. Specifically, the sample was weighed into a nickel crucible, and then alkali-fused by adding sodium peroxide and heating in an electric furnace. The resulting melt was dissolved in acid and diluted with pure water, and then evaluated by ICP analysis. The measurement results are shown in Table 1.

[0095] The obtained Si—Ni-containing particles were dispersed in an aqueous solution of carboxymethyl cellulose (CMC) at a mass ratio of 10:1. The resulting dispersion was then granulated using a spray dryer to obtain a granulated powder.

[0096] The obtained granulated powder and coal tar pitch were charged into a rocking mill and mixed at 50 Hz for 1 minute, and the obtained mixture was heat-treated at 800°C for 5 hours in an argon atmosphere.

[0097] In this manner, the negative electrode active material of Example 1 was obtained.

[0098] Here, in a preliminary experiment, it was confirmed by X-ray diffraction measurement that metallic Ni was produced by heat treating nickel formate at 800° C. Therefore, it is presumed that metallic Ni was produced from nickel formate, which is the Ni source in the Si—Ni-containing particles, by the heat treatment at 800° C.

[0099] Comparative Example 1 A negative electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1, except that silicon particles having an average particle size of 20 nm were dispersed in a CMC aqueous solution so that the mass ratio of the silicon particles to the CMC was 10:1 to obtain a granulated powder. That is, in Comparative Example 1, Ni was not introduced into the silicon particles, and silicon particles were used instead of Si—Ni-containing particles.

[0100] [X-ray Diffraction] X-ray diffraction patterns of the negative electrode active materials of Example 1 and Comparative Example 1 were obtained by powder X-ray diffraction measurement. An X-ray diffractometer (MiniFlex 600, manufactured by RIGAKU Corporation) was used for the measurement. Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) was used as the X-ray source. FIG. 4 is a graph showing the X-ray diffraction patterns of the negative electrode active materials of Example 1 and Comparative Example 1. Table 1 shows the diffraction angles at which the peak tops of the peaks derived from the Si (111) plane were observed for Example 1 and Comparative Example 1. In the X-ray diffraction pattern of the negative electrode active material of Example 1, a peak derived from the Si (111) plane was observed at a diffraction angle 2θ of 28.34°. On the other hand, in the X-ray diffraction pattern of the negative electrode active material of Comparative Example 1, a peak derived from the Si (111) plane was observed at a diffraction angle 2θ of 28.41°. It is generally known that the peak shifts to a lower angle when an atom with a larger atomic radius than the atoms constituting the crystal lattice is introduced into the crystal lattice. Therefore, from the above results, it can be confirmed that Ni is introduced into the silicon crystal lattice in the negative electrode active material of Example 1.

[0101] [Lattice Image Observation] Lattice image observation was performed by cross-sectional transmission electron microscope observation (cross-sectional TEM) of the negative electrode active material of Example 1. As a result, crystalline material derived from Si was confirmed in the Si—Ni-containing particles and the surrounding observation region. Furthermore, amorphous material was confirmed in the portion of the Si—Ni-containing particles presumed to be derived from Ni.

[0102] [Fabrication of Battery] Using the negative electrode active materials of Example 1 and Comparative Example 1, evaluation cells of Example 1 and Comparative Example 1 were fabricated as follows.

[0103] (Preparation of Negative Electrode) A mixture was obtained by mixing a negative electrode active material and graphite in a mass ratio of 20:80. This mixture, sodium carboxymethyl cellulose (CMCNa), styrene-butadiene rubber (SBR), and lithium polyacrylate were mixed in a mass ratio of the mixture of the negative electrode active material and graphite:CMCNa:SBR:lithium polyacrylate = 96.5:1:1.5:1. Water was added to the negative electrode mixture, and the mixture was stirred using a mixer to prepare a negative electrode slurry. Next, a 1 m thick layer was applied to the surface of a copper foil. 2 The negative electrode slurry was applied to both sides of the copper foil so that the mass of the negative electrode mixture per sheet was 190 g, and the coating was dried and then rolled to form a negative electrode mixture with a density of 1.5 g / cm 3 A negative electrode having the negative electrode mixture layer formed thereon was fabricated.

[0104] The negative electrode was cut into a 20 mm × 20 mm shape with a 5 mm × 5 mm protrusion, and the negative electrode mixture layer at the protrusion was peeled off to expose the copper foil. A negative electrode tab lead was then connected to the exposed copper foil, and a predetermined region around the periphery of the negative electrode tab lead was covered with an insulating film.

[0105] (Preparation of Counter Electrode) A tab was prepared by welding a small piece of Ni mesh to the end thereof. The tab was cut to a predetermined size, and the mesh portion was pressed against a lithium metal foil having a thickness of 300 μm to prepare a counter electrode.

[0106] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by dissolving LiPF in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 4:1:15. The LiPF concentration was 1.3 mol / L.

[0107] (Cell Fabrication) Using the above-mentioned negative electrode and two counter electrodes, a cell for evaluating negative electrode regulation was fabricated as follows. The cell was fabricated in a dry air atmosphere with a dew point of −60° C. or less. An electrode group was fabricated by sandwiching the negative electrode between a pair of counter electrodes and arranging the negative electrode mixture layer and lithium metal foil opposite each other via a separator. Next, an Al laminate film cut into a rectangle was folded in half, and the two long edge portions were heat-sealed to form a cylinder. Thereafter, the fabricated electrode group was placed into the cylinder from one of the short edge portions of the Al laminate film, and the end face of the Al laminate film was aligned with the insulating film of each tab lead and heat-sealed. Next, 0.3 cm of electrolyte was poured into the cylinder from the short edge portion of the cylinder that was not heat-sealed. 3 After the injection, the negative electrode mixture layer was impregnated with the nonaqueous electrolyte by leaving the negative electrode mixture layer under a reduced pressure of 0.02 MPa for 3 minutes and then returning the pressure to atmospheric pressure twice. Finally, the end face of the cylindrical Al laminate film on the injected side was heat-sealed while reducing the pressure to obtain an evaluation cell.

[0108] [Evaluation of Charge / Discharge Efficiency] The evaluation cells of Example 1 and Comparative Example 1 were charged at a constant current of 0.1 C at an ambient temperature of 25° C. until the voltage reached 1.0 V. Thereafter, constant current discharge was performed at a current of 0.1 C until the voltage reached 0.005 V. In this manner, the initial charge / discharge efficiencies of the evaluation cells of Example 1 and Comparative Example 1 were evaluated. Table 1 shows the relative values ​​when the charge / discharge efficiency of Comparative Example 1 was set to 100%.

[0109]

[0110] (Discussion) The battery using the negative electrode active material of Example 1 had improved initial charge-discharge efficiency compared to Comparative Example 1.

[0111] The technology of the present disclosure can be used in batteries such as lithium ion secondary batteries.

Claims

1. An anode active material comprising: a carbon phase; and Si-Ni containing particles dispersed in the carbon phase.

2. The negative electrode active material according to claim 1, wherein the ratio of Ni in the Si-Ni containing particles is 0.01% by mass or more and 5.0% by mass or less.

3. The negative electrode active material according to claim 1, wherein the Si-Ni-containing particles include at least one selected from the group consisting of metallic Ni, Ni oxide, and Ni carbide.

4. The negative electrode active material according to claim 3, wherein the Si-Ni containing particles contain metallic Ni.

5. The negative electrode active material according to claim 1, wherein the Si-Ni containing particles contain crystalline silicon in which Ni atoms are dissolved.

6. The negative electrode active material according to claim 1, wherein the Si-Ni containing particles include an amorphous phase.

7. The negative electrode active material according to claim 1, wherein an X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-Kα radiation has an X-ray diffraction peak derived from the (111) plane of Si within a diffraction angle 2θ range of 28.30° or more and 28.40° or less.

8. The negative electrode active material according to claim 1, wherein the average particle size of the Si-Ni containing particles is 1 nm or more and 1000 nm or less.

9. The negative electrode active material according to claim 1, further comprising a coating layer that coats a surface of the carbon phase, the coating layer containing carbon.

10. A secondary battery comprising: a negative electrode containing the negative electrode active material according to any one of claims 1 to 9; a positive electrode; and an electrolyte.

Images