Negative electrode mixture for lithium ion secondary battery, and lithium ion secondary battery

Abstract

This negative electrode mixture for lithium-ion secondary batteries includes: a conductivity aid; and porous amorphous silicon particles containing an amorphous silicon phase. The porous amorphous silicon particles have: a lamellar structure comprising a lamellar-shaped protrusion having an average thickness in the range of 1–200 nm; a columnar structure comprising a columnar protrusion having an average diameter within the range of 1–100 nm; or a co-continuous structure comprising the lamellar-shaped protrusion and the columnar protrusion.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode mixture for a lithium ion secondary battery, and a lithium ion secondary battery. This application claims priority based on Japanese Patent Application No. 2020-160616, filed on September 25, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Lithium-ion secondary batteries are used as power sources for mobile devices and electric vehicles, and their production volume in the market is steadily increasing. Commonly used lithium-ion secondary batteries are non-aqueous electrolyte lithium-ion secondary batteries, which use a non-aqueous electrolyte, and solid electrolyte lithium-ion secondary batteries (all-solid-state batteries), which use a solid electrolyte.

[0003] Silicon has been investigated as an anode active material for lithium-ion secondary batteries. Silicon has the advantage of a theoretical mass capacity density of up to 4200 mAh / g, which is higher than that of graphite (mass capacity density: 372 mAh / g), which is commonly used as an anode active material in lithium-ion secondary batteries. However, silicon can expand in volume by approximately four times during charging due to alloying between silicon and lithium. Therefore, in lithium-ion batteries using silicon particles as the anode active material, the silicon particles tend to disintegrate and become finer due to the expansion of the silicon particles caused by the insertion of lithium ions during charging and the contraction of the silicon particles caused by the desorption of lithium ions during discharge. When silicon particles become finer, they can physically detach from the anode or the conductive path can be lost, reducing the electrical capacity of the anode and potentially degrading the charge / discharge cycle characteristics of lithium-ion batteries.

[0004] The use of porous silicon has been investigated with the aim of improving charge-discharge cycle characteristics (Non-Patent Document 1, Patent Document 1). Non-Patent Document 1 describes an all-solid-state battery using a porous amorphous silicon film with a thickness of 4.73 μm. The porous amorphous silicon film described in Non-Patent Document 1 is formed by a sputtering method. Patent Document 1 also describes porous silicon particles formed by bonding multiple silicon microparticles. The porous silicon particles described in Patent Document 1 have an average particle size of 0.1 μm to 1000 μm, and the silicon microparticles used as raw materials have an average particle size or average pillar diameter of 10 nm to 500 nm. The porous silicon particles described in Patent Document 1 are composed of single-crystal silicon produced by spinodal decomposition of a silicon alloy (precipitation of silicon from a silicon alloy in a molten metal) and dealloying. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5598861 [Non-patent literature]

[0006] [Non-Patent Document 1] Junichi Sakabe, Narumi Ohta, Tsuyoshi Ohnishi, Kazutaka Mitsuishi & Kazunori Takada, Porous amorphous silicon film anodes for highcapacity and stable all-solid-state lithium batteries, COMMUNICATIONS CHEMISTRY volume 1, Article number: 24 (2018) Summary of the Invention [Problem to be solved by the invention]

[0007] Lithium-ion secondary batteries are used in a variety of applications, including mobile devices and electric vehicles. Therefore, it is preferable that the electrode material for lithium-ion secondary batteries be adaptable to the size required for the battery's intended use. In particular, batteries with large electrical capacity are desired, with a thicker electrode material. However, the porous amorphous silicon film described in Non-Patent Document 1 is formed using a sputtering method, making it difficult to form a thick film. Furthermore, silicon itself has low electrical conductivity. Therefore, increasing the thickness of the porous amorphous silicon film reduces the conductivity of the porous amorphous silicon film, making it difficult for lithium ions to be inserted into the porous amorphous silicon film, potentially reducing the capacity of the porous amorphous silicon film.

[0008] Furthermore, the porous silicon particles described in Patent Document 1 are composed of single-crystal silicon. Therefore, repeated expansion of the porous silicon particles due to insertion of lithium ions during charging and contraction of the porous silicon particles due to release of lithium ions during discharging can cause fractures within the crystals, resulting in the loss of conductive paths within the crystals. When the conductive paths within the crystals are lost, the charge / discharge capacity of the porous silicon particles decreases.

[0009] The present invention has been made in light of these problems, and aims to provide a negative electrode mixture for a lithium ion secondary battery that has a high electric capacity even when the thickness of the negative electrode mixture layer is increased, and that is excellent in charge-discharge cycle characteristics and storage characteristics, and a lithium ion secondary battery that uses the negative electrode mixture. [Means for solving the problem]

[0010] To achieve the above object, the inventors conducted extensive research and found that by using a negative electrode mixture containing a conductive additive and porous amorphous silicon particles having a specific lamellar structure and / or columnar structure, it is possible to easily form a negative electrode mixture layer with no thickness restrictions. The inventors then confirmed that a lithium ion secondary battery using this negative electrode mixture layer has a high mass capacitance of the porous amorphous silicon particles and excellent charge / discharge cycle characteristics and storage characteristics, thereby completing the present invention.

[0011] That is, the negative electrode mixture for a lithium ion secondary battery according to the present invention comprises a conductive additive and a negative electrode active material, the negative electrode active material comprising porous amorphous silicon particles containing an amorphous silicon phase, the porous amorphous silicon particles having a lamellar structure comprising lamellar protrusions having an average thickness in the range of 1 nm to 200 nm, or a columnar structure comprising columnar protrusions having an average diameter in the range of 1 nm to 100 nm, or a bicontinuous structure comprising the lamellar protrusions and the columnar protrusions.

[0012] The porous amorphous silicon particles contained in the negative electrode mixture for lithium-ion secondary batteries according to the present invention have pores that absorb volume expansion during charging. This minimizes the apparent change in volume. Furthermore, amorphous silicon has higher strength and elasticity than crystalline silicon, making it less susceptible to collapse due to expansion / contraction during charging and discharging. Furthermore, amorphous silicon essentially lacks the dislocation defects found in crystalline materials. While fractures in general materials originate from dislocation defects that cause stress concentration, porous amorphous silicon particles lack dislocation defects, which prevent fractures due to stress concentration and thus prevent the loss of conduction paths within the particles. Therefore, the negative electrode mixture according to the present invention has excellent charge / discharge cycle characteristics and storage characteristics. Furthermore, the negative electrode mixture according to the present invention contains a conductive additive, resulting in high conductivity. Therefore, even when the thickness of the negative electrode mixture layer is increased, lithium can be easily inserted into the porous amorphous silicon particles, resulting in high electrical capacity.

[0013] In the negative electrode mixture for a lithium ion secondary battery or all-solid-state battery according to the present invention, when the porous amorphous silicon particles have the lamellar protrusions, the interval between adjacent lamellar protrusions is preferably in the range of 1 nm to 100 nm. The average thickness of the lamellar protrusions is preferably in the range of 1 nm to 50 nm. Meanwhile, when the porous amorphous silicon particles have the lamellar protrusions, the average thickness of the lamellar protrusions is preferably in the range of 1 nm to 50 nm. The interval between adjacent columnar protrusions is preferably in the range of 1 nm to 100 nm. The porous amorphous silicon particles have the above structure, and the expansion of the volume during charging can be efficiently absorbed by the pores between the lamellar or columnar protrusions, which means that the apparent change in volume of the porous amorphous silicon particles during charging and discharging is smaller.

[0014] In the negative electrode mixture for a lithium ion secondary battery according to the present invention, the porous amorphous silicon particles preferably have an average porosity in the range of 10% to 99%. Porous amorphous silicon particles with an average porosity within the above range can efficiently absorb the volume expansion during charging through their pores, thereby further reducing the apparent change in volume of the porous amorphous silicon particles during charging and discharging.

[0015] In the negative electrode mixture for a lithium ion secondary battery according to the present invention, the conductive additive preferably contains a carbon material. In this case, the carbon material has excellent electrical conductivity, which improves the electrical conductivity of the negative electrode mixture, making it easier for lithium ions to be inserted into the porous amorphous silicon particles.

[0016] The negative electrode mixture for a lithium ion secondary battery according to the present invention preferably further contains a solid electrolyte. In this case, the lithium ion conductivity of the negative electrode mixture is improved. Also, when the negative electrode mixture layer is incorporated into an all-solid-state battery, the affinity with the solid electrolyte layer is increased. Therefore, the negative electrode mixture containing the solid electrolyte can be advantageously used for the all-solid-state battery.

[0017] The lithium ion secondary battery according to the present invention includes a negative electrode containing the above-described negative electrode mixture for lithium ion secondary batteries. The lithium ion secondary battery according to the present invention includes the above-described negative electrode mixture for lithium ion secondary batteries, and therefore has a high electric capacity even when the thickness of the negative electrode mixture layer is increased, and is excellent in charge / discharge cycle characteristics and storage characteristics. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a negative electrode mixture for a lithium ion secondary battery that has a high electric capacity even when the thickness of the negative electrode mixture layer is increased, and that has excellent charge / discharge cycle characteristics and storage characteristics, and a lithium ion secondary battery that uses the negative electrode mixture. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an all-solid-state battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a nonaqueous electrolyte lithium ion secondary battery according to one embodiment of the present invention. [Figure 3A] FIG. 3A is a scanning electron microscope (SEM) photograph of the porous amorphous silicon particles obtained in Example 1. [Figure 3B] FIG. 3B is an enlarged SEM photograph of FIG. 3A. [Figure 3C] FIG. 3C is a magnified SEM of FIG. 3B. [Figure 3D] FIG. 3D is a magnified SEM of FIG. 3C. [Figure 4A] FIG. 4A is an XRD spectrum of the porous amorphous silicon particles obtained in Example 1. [Figure 4B]FIG. 4B is an XRD spectrum of crystalline silicon prepared as a reference sample in the example. [Figure 5] FIG. 5 shows the energy spectrum of the porous amorphous silicon particles obtained in Example 1 measured by EDX. [Figure 6A] FIG. 6A is a graph showing the charge-discharge characteristics of an all-solid-state battery using the porous amorphous silicon particles obtained in Example 1 as a negative electrode active material. [Figure 6B] FIG. 6B is a graph showing the cycle characteristics of an all-solid-state battery using the porous amorphous silicon particles obtained in Example 1 as a negative electrode active material. [Figure 7A] FIG. 7A is an SEM photograph of the porous amorphous silicon particles (ribbon-shaped) obtained in Example 2. [Figure 7B] FIG. 7B is an enlarged SEM photograph of FIG. 7A. [Figure 7C] FIG. 7C is an enlarged SEM photograph of FIG. 7B. [Figure 8] FIG. 8 is an XRD spectrum of the porous amorphous silicon particles obtained in Example 2. [Figure 9A] FIG. 9A is an SEM photograph of the negative electrode mixture layer obtained in Example 3. [Figure 9B] FIG. 9B is an enlarged SEM photograph of FIG. 9A. [Figure 10] FIG. 10 is a graph showing the results of evaluation of the charge-discharge cycle of a non-aqueous electrolyte lithium ion secondary battery using the porous amorphous silicon particles obtained in Example 3 as the negative electrode active material. [Figure 11] FIG. 11 is a graph showing the results of evaluation of the charge-discharge cycle of a non-aqueous electrolyte lithium ion secondary battery using the porous amorphous silicon particles obtained in Example 4 as the negative electrode active material. [Figure 12] FIG. 12 is a graph showing the results of evaluation of the charge-discharge cycle of a non-aqueous electrolyte lithium ion secondary battery using the porous amorphous silicon particles obtained in Example 5 as the negative electrode active material. [Figure 13]FIG. 13 is a graph showing the results of evaluation of the charge-discharge cycle of a non-aqueous electrolyte lithium ion secondary battery using the porous amorphous silicon particles obtained in Example 6 as the negative electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0020] Embodiments of the negative electrode mixture for a lithium-ion secondary battery and the all-solid-state battery of the present invention will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the present invention.

[0021] FIG. 1 is a cross-sectional view showing an example of an all-solid-state battery according to one embodiment of the present invention. As shown in FIG. 1 , the all-solid-state battery 10 is a laminate in which an anode 11, a solid electrolyte layer 14, and a cathode 15 are laminated in this order. The anode 11 includes an anode current collector 12 and an anode mixture layer 13. The cathode 15 includes a cathode mixture layer 16 and a cathode current collector 17. The anode mixture layer 13 and the cathode mixture layer 16 are located on the solid electrolyte layer 14 side. That is, the solid electrolyte layer 14 is located between the anode mixture layer 13 and the cathode mixture layer 16.

[0022] There are no particular limitations on the shape or material of the negative electrode current collector 12. The shape of the negative electrode current collector 12 may be, for example, a foil, a plate, a mesh, a lattice, etc. The material of the negative electrode current collector 12 may be, for example, stainless steel, copper, nickel, titanium, platinum, etc.

[0023] The negative electrode mixture layer 13 is formed from a negative electrode mixture containing a conductive additive and a negative electrode active material. The negative electrode mixture may further contain a solid electrolyte.

[0024] The conductive additive has the function of improving the conductivity of the negative electrode mixture layer 13. For example, a carbon material or a metal material can be used as the conductive additive. Examples of carbon materials include carbon black, acetylene black, ketjen black, furnace black, activated carbon, graphite, carbon fiber, carbon nanotubes, graphene, and fullerene. Examples of metal materials include gold, silver, copper, and platinum. One type of conductive additive may be used alone, or two or more types may be used in combination. The conductive additive preferably contains a carbon material.

[0025] The negative electrode active material includes porous amorphous silicon particles. The porous amorphous silicon particles have an amorphous silicon phase. The porous amorphous silicon particles included in the negative electrode active material may be a single particle containing only an amorphous silicon phase, or a composite particle containing an amorphous silicon phase and a crystalline silicon phase. The negative electrode active material may also include crystalline silicon particles. When the negative electrode active material includes a crystalline silicon component (a crystalline silicon phase or crystalline silicon particles), the content of the crystalline silicon component in the negative electrode active material may be, for example, an amount such that the ratio A / B of the maximum peak value A attributable to crystalline silicon in the XRD spectrum of the negative electrode active material to the maximum peak value B in the XRD spectrum of a crystalline silicon reference sample is 0.5 or less. The content of the crystalline silicon component in the negative electrode active material may be, for example, an amount such that the ratio C / D of the half-width C of the maximum peak value attributable to crystalline silicon in the XRD spectrum of the negative electrode active material to the half-width D of the maximum peak value in the XRD spectrum of a crystalline silicon reference sample is 2.0 or more. As a reference sample of crystalline silicon, silicon particles manufactured by Kojundo Chemical Laboratory Co., Ltd., having an average particle size of 5 μm and a purity of 3N, may be used.

[0026] Furthermore, when the negative electrode active material contains crystalline silicon particles, the crystalline silicon particles may have an average particle diameter of 0.5 μm or more and 1.5 μm or less and may be attached to the surface of the porous amorphous silicon particles. Crystalline silicon particles and porous amorphous silicon particles can be distinguished by the presence or absence of facets and the presence or absence of Kikuchi lines in EBSD (electron backscatter diffraction). That is, crystalline silicon particles have facets, and Kikuchi lines appear in EBSD. Porous amorphous silicon particles do not have facets, and Kikuchi lines do not appear in EBSD. The crystalline silicon particle content of the negative electrode active material may be 10% or less, as a volume ratio of crystalline silicon to porous amorphous silicon particles. The method for measuring the crystalline silicon particle content will be described later.

[0027] The porous amorphous silicon particles have a lamellar or columnar structure or a co-continuous structure. Porous amorphous silicon particles with a lamellar structure have lamellar projections (lamellar projections) protruding from the particle surface. The lamellar projections are usually arranged in layers. In porous amorphous silicon particles with a lamellar structure, the gaps between the lamellar projections form pores. The lamellar projections have an average thickness in the range of 1 nm to 100 nm, preferably in the range of 1 nm to 50 nm. The spacing between adjacent lamellar projections is preferably in the range of 1 nm to 100 nm. The average thickness and spacing of the lamellar projections can be measured, for example, using a scanning electron microscope (SEM).

[0028] Porous amorphous silicon particles with a columnar structure have convex portions (columnar convex portions) that protrude in a columnar shape from the particle surface. The columnar convex portions are usually arranged continuously. In porous amorphous silicon particles with a columnar structure, the gaps between the columnar convex portions form pores. The columnar convex portions have an average diameter in the range of 1 nm to 100 nm, preferably in the range of 1 nm to 50 nm. The average aspect ratio of the columnar convex portions (average length / average diameter of the columnar convex portions) is preferably in the range of 1 to 50. The distance between adjacent columnar convex portions is preferably in the range of 1 nm to 100 nm. The average diameter, average aspect ratio, and distance of the columnar convex portions can be measured using, for example, an SEM.

[0029] The bicontinuous structure refers to a structure in which a lamellar structure and a columnar structure are mixed. A porous amorphous silicon particle having a bicontinuous structure has lamellar protrusions and columnar protrusions. The structure of the porous amorphous silicon particles can be confirmed by observing the porous amorphous silicon particles using, for example, an SEM. Furthermore, the porous amorphous silicon particles preferably have a continuous three-dimensional network structure of amorphous silicon and also have continuous voids. Furthermore, the porous amorphous silicon particles preferably have a silicon content of 90 at.% or more (atomic percent), in terms of atomic percentage of elements excluding oxygen.

[0030] The porous amorphous silicon particles preferably have an average porosity in the range of 10% to 99%. When the porous amorphous silicon particles are produced by selectively eluting components other than silicon from a eutectic alloy containing silicon and components other than silicon, the porosity here refers to the atomic percentage content of the components selectively eluted from the eutectic alloy, i.e., the atomic percentage content of the components selectively eluted from the eutectic alloy relative to all components in the eutectic alloy. For example, when all components other than silicon are eluted from the eutectic alloy, porosity (%) = atomic percentage content (at.%) of the components eluted from the eutectic alloy relative to all components in the eutectic alloy = 100 (at.%) - atomic percentage content (at.%) of silicon in the eutectic alloy.

[0031] The shape of the porous amorphous silicon particles is not particularly limited. The shape of the porous amorphous silicon particles may be, for example, ribbon-like, spherical, elliptical, cylindrical, prismatic, or irregular. The size of the porous amorphous silicon particles is preferably such that the major axis length is in the range of 1 nm to 100 μm, more preferably in the range of 0.1 μm to 100 μm, and particularly preferably in the range of 10 μm to 100 μm.

[0032] The porous amorphous silicon particles can be produced, for example, as follows. First, a molten metal containing metal and silicon is poured into a 10 6The eutectic alloy is formed by cooling the metal and silicon at a cooling rate of 1000 K / sec or more. Next, the metal (components other than silicon) is selectively eluted from the eutectic alloy using an acid or alkali. This results in porous amorphous silicon particles. The remaining metal may be 10 at.% or less. Alternatively, the remaining metal may be 2 at.% or more. Here, the crystalline silicon particles contained in the negative electrode active material may be crystalline silicon attached to the eutectic alloy, which is an intermediate product of the porous amorphous silicon particles. In this case, the content of crystalline silicon particles in the negative electrode active material is the amount of crystalline silicon attached to the eutectic alloy. The amount of crystalline silicon attached to the eutectic alloy can be measured, for example, as follows. A cross-section of the eutectic alloy is observed using a scanning transmission electron microscope with an energy dispersive X-ray analyzer (STEM-EDX) to measure the areas of the eutectic alloy portion where metals other than silicon are detected and the silicon portion where only silicon is detected. Next, the ratio of the area of ​​the silicon portion to the area of ​​the eutectic alloy portion (area of ​​silicon portion / area of ​​eutectic alloy portion × 100) is calculated. The area ratio is measured for 10 eutectic alloys, and the average value is taken as the amount of crystalline silicon attached to the eutectic alloy (content of crystalline silicon particles in the negative electrode active material).

[0033] In the above-described method for producing porous amorphous silicon particles, the eutectic alloy may be produced by, for example, a single-roll liquid quenching method or a twin-roll liquid quenching method. In this case, the produced eutectic alloy may be in the form of a ribbon or foil with an average thickness ranging from 0.1 μm to 1 mm. The eutectic alloy may also be produced by a gas atomization method or a water atomization method. In this case, the produced eutectic alloy may be in the form of particles with an average particle size ranging from 10 nm to 100 μm. Furthermore, the domain size of the silicon phase in the eutectic alloy structure is preferably in the range of 1 nm to 100 nm, more preferably in the range of 1 nm to 50 nm. When using a gas atomization method to produce eutectic alloy powder, the metal powder production apparatus described in Japanese Patent No. 6544836 can be used as the atomization apparatus.

[0034] In the method for producing porous amorphous silicon, the eutectic alloy may be, for example, an Al-Si alloy. In this case, it is preferable that the Si content be in the range of 1 at.% to 50 at.% inclusive, in atomic percentage. This allows the production of porous amorphous silicon with an average porosity of 50% to 99% inclusive. The eutectic alloy may be an Fe-Si alloy, a Ni-Si alloy, a Cr-Si alloy, an Ag-Si alloy, or a Cu-Si alloy. In this case, it is preferable that the Si content be in the range of 50 at.% to 90 at.% inclusive, in atomic percentage. This allows the production of porous amorphous silicon with an average porosity of 10% to 50% inclusive.

[0035] The eutectic alloy may be a binary or multi-component eutectic alloy represented by M1-Si (M1 is one or more elements selected from Al, Ag, As, Au, Be, Ca, Cr, Cu, Mg, Pd, Pt, Y, Co, Fe, Mn, Ti, and Zr), or a ternary or multi-component eutectic alloy represented by M2-Al-Si (M2 is one or more elements selected from Ca, Cu, Ge, P, Mn, Na, Sb, Sn, Sc, Sr, and Ti). The eutectic alloy may also be an amorphous alloy.

[0036] The solid electrolyte has a function of improving the lithium ion conductivity of the anode mixture layer 13. The solid electrolyte also has a function of improving the affinity between the anode mixture layer 13 and the solid electrolyte layer 14, thereby improving the ionic conductivity of lithium ions between the anode mixture layer 13 and the solid electrolyte layer 14. The material of the solid electrolyte can be the same as the material of the solid electrolyte layer 14. The material of the solid electrolyte layer 14 will be described later.

[0037] The ratio of the conductive additive to the negative electrode active material contained in the negative electrode mixture layer 13 is preferably in the range of 2 to 8 parts by mass, more preferably in the range of 3 to 7 parts by mass, and particularly preferably in the range of 4 to 6 parts by mass, based on 1 part by mass of the negative electrode active material. Furthermore, the ratio of the solid electrolyte to the negative electrode active material contained in the negative electrode mixture layer 13 is preferably in the range of 0.1 to 3 parts by mass, more preferably in the range of 0.2 to 2.5 parts by mass, and particularly preferably in the range of 0.5 to 2 parts by mass, based on 1 part by mass of the negative electrode active material.

[0038] The solid electrolyte layer 14 includes a solid electrolyte. The solid electrolyte is preferably lithium ion conductive. For example, sulfide-based solid electrolytes and oxide-based solid electrolytes can be used as the solid electrolyte. Examples of sulfide-based solid electrolytes include Li2S-P2S5 and LiI-Li2S-P2S5. Examples of oxide-based solid electrolytes include Nasicon-type oxides and garnet-type oxides. Examples of Nasicon-type oxides include Li 1.4 Al 0.4 Ti 1.6 (PO4)3, etc. Examples of garnet-type oxides include Li7La3Zr2O 12 The following can be mentioned:

[0039] The positive electrode mixture layer 16 contains a positive electrode active material. The positive electrode mixture layer 16 may contain a conductive additive. The positive electrode mixture layer 16 may further contain a solid electrolyte.

[0040] The positive electrode active material is preferably a lithium-containing compound that releases lithium during charging and inserts lithium during discharging. Examples of the positive electrode active material include layered rock salt oxides, spinel oxides, olivine phosphates, silicates, etc. Examples of layered rock salt oxides include LiCoO2, LiMnO2, LiNiO2, and Li(Ni x Co y Mn z)O2(x+y+z=1), etc. Examples of spinel oxides include LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, etc. Examples of olivine-type phosphates include LiFePO4, LiMnPO4, LiNiPO4, LiCuPO4, etc. Examples of silicates include Li2FeSiO4, Li2MnSiO4, etc.

[0041] The conductive additive has the function of improving the conductivity of the positive electrode mixture layer 16. For example, a carbon material or a metal material can be used as the conductive additive. Examples of the carbon material and the metal material are the same as the examples of the conductive additive contained in the negative electrode mixture layer 13.

[0042] The solid electrolyte has a function of improving the lithium ion conductivity of the positive electrode mixture layer 16. The solid electrolyte also has a function of improving the affinity between the positive electrode mixture layer 16 and the solid electrolyte layer 14, thereby improving the ionic conductivity of lithium ions between the positive electrode mixture layer 16 and the solid electrolyte layer 14. The material of the solid electrolyte can be the same as the material of the solid electrolyte layer 14.

[0043] The ratio of the conductive additive to the positive electrode active material contained in the positive electrode mixture layer 16 is preferably in the range of 0.02 to 1.00 parts by mass, more preferably 0.04 to 0.50 parts by mass, and particularly preferably 0.08 to 0.25 parts by mass, based on 1 part by mass of the positive electrode active material. The ratio of the solid electrolyte to the positive electrode active material contained in the positive electrode mixture layer 16 is preferably in the range of 0.1 to 3.0 parts by mass, more preferably 0.2 to 1.5 parts by mass, and particularly preferably 0.4 to 0.8 parts by mass, based on 1 part by mass of the positive electrode active material.

[0044] There are no particular limitations on the shape or material of the positive electrode current collector 17. The shape of the positive electrode current collector 17 may be, for example, a foil, a plate, a mesh, a lattice, etc. The material of the positive electrode current collector 17 may be, for example, stainless steel, copper, aluminum, nickel, titanium, platinum, etc.

[0045] The all-solid-state battery 10 of this embodiment is used by being housed in an outer container. The shape of the outer container is not particularly limited. Examples of the shape of the outer container include a coin shape, a button shape, a sheet shape, a cylindrical shape, and a square shape.

[0046] Next, a method for manufacturing the all-solid-state battery 10 of this embodiment will be described. The all-solid-state battery 10 can be manufactured, for example, as follows. First, the negative electrode and the positive electrode are fabricated, and then they are laminated so that the negative electrode mixture layer of the negative electrode and the positive electrode mixture layer of the positive electrode face each other with the solid electrolyte layer interposed therebetween.

[0047] For example, the negative electrode is prepared by dispersing a negative electrode mixture in a solvent to prepare a negative electrode mixture paste. The negative electrode mixture paste is then applied to a negative electrode current collector to form a coating layer. The application method is not particularly limited, and examples thereof include spin coating, dipping, die coating, spray coating, and gravure printing. The coating layer is then dried to form a negative electrode mixture layer. The positive electrode can be produced in the same manner as the negative electrode, except that a positive electrode mixture is used instead of the negative electrode mixture.

[0048] The all-solid-state battery 10 can also be manufactured by stacking a negative electrode current collector, a negative electrode mixture pellet, a solid electrolyte pellet, a positive electrode mixture pellet, and a positive electrode current collector, and then pressing the resulting stack. The negative electrode mixture pellet, the solid electrolyte pellet, and the positive electrode mixture pellet can be manufactured by, for example, a press molding method.

[0049] FIG. 2 is a cross-sectional view showing an example of a nonaqueous electrolyte lithium ion secondary battery according to one embodiment of the present invention. 2, the nonaqueous electrolyte lithium-ion secondary battery 20 includes a laminate in which a negative electrode 21, a separator 24, and a positive electrode 25 are laminated in this order, and a nonaqueous electrolyte (not shown). The negative electrode 21 includes a negative electrode current collector 22 and a negative electrode mixture layer 23. The positive electrode 25 includes a positive electrode mixture layer 26 and a positive electrode current collector 27. The negative electrode mixture layer 23 and the positive electrode mixture layer 26 are located on the separator 24 side. That is, the separator 24 is located between the negative electrode mixture layer 23 and the positive electrode mixture layer 26.

[0050] There are no particular limitations on the shape or material of the negative electrode current collector 22. The negative electrode current collector 22 may be the same as the negative electrode current collector 12 of the above-described all-solid-state battery 10.

[0051] The negative electrode mixture layer 23 is formed from a negative electrode mixture containing a conductive additive and porous amorphous silicon particles. The negative electrode mixture may further contain a binder. The conductive additive and porous amorphous silicon particles can be the same as those that can be used in the negative electrode mixture layer 13 of the above-described all-solid-state battery 10.

[0052] The binder adheres the conductive additive and the porous amorphous silicon particles to improve the electrical conductivity and lithium ion conductivity of the negative electrode mixture layer 13, and also improves the adhesion between the negative electrode mixture layer 23 and the negative electrode current collector 22. Examples of the binder that can be used include polymers such as polyimide, polyamide, polyamideimide, polyvinylidene fluoride, and polytetrafluoroethylene, and rubbers such as styrene butadiene rubber and fluororubber.

[0053] The ratio of the conductive additive to the negative electrode active material contained in the negative electrode mixture layer 23 is preferably in the range of 0.1 parts by mass to 1 part by mass, more preferably 0.2 parts by mass to 0.8 parts by mass, and particularly preferably 0.2 parts by mass to 0.6 parts by mass, based on 1 part by mass of the negative electrode active material. The ratio of the binder to the negative electrode active material contained in the negative electrode mixture layer 23 is preferably in the range of 0.05 parts by mass to 1 part by mass, more preferably 0.05 parts by mass to 0.5 parts by mass, and particularly preferably 0.05 parts by mass to 0.3 parts by mass, based on 1 part by mass of the negative electrode active material.

[0054] A porous film can be used as the separator 24. Materials that can be used for the porous film include polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, and polyesters such as polyethylene terephthalate.

[0055] The positive electrode mixture layer 26 contains a positive electrode active material. The positive electrode mixture layer 26 may contain a conductive additive. The positive electrode mixture layer 26 may further contain a binder.

[0056] The positive electrode active material and the conductive additive can be the same as those that can be used in the positive electrode mixture layer 16 of the above-described all-solid-state battery 10. The binder brings the conductive additive and the positive electrode active material into close contact with each other, thereby improving the electrical conductivity and lithium ion conductivity of the positive electrode mixture layer 26 and also improving the adhesion between the positive electrode mixture layer 26 and the positive electrode current collector 27. The binder may be the same as that which can be used in the negative electrode mixture layer 23.

[0057] The ratio of the conductive additive to the positive electrode active material contained in the positive electrode mixture layer 26 is preferably in the range of 0.1 parts by mass to 1 part by mass, more preferably 0.2 parts by mass to 0.8 parts by mass, and particularly preferably 0.2 parts by mass to 0.6 parts by mass, based on 1 part by mass of the positive electrode active material. The ratio of the binder to the positive electrode active material contained in the positive electrode mixture layer 26 is preferably in the range of 0.05 parts by mass to 1 part by mass, more preferably 0.05 parts by mass to 0.5 parts by mass, and particularly preferably 0.05 parts by mass to 0.3 parts by mass, based on 1 part by mass of the positive electrode active material.

[0058] The positive electrode current collector 27 can be the same as the positive electrode current collector 17 of the above-mentioned all-solid-state battery 10.

[0059] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt. Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, ethers, lactones, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and dipropyl carbonate. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of lactones include γ-butyrolactone. Examples of nitriles include acetonitrile. These non-aqueous solvents may be used alone or in combination of two or more. In addition, some or all of the hydrogen atoms in the non-aqueous solvent may be substituted with fluorine.

[0060] Examples of the electrolyte salt that can be used include lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bis(trifluoromethylsulfonylimide) (LiN(CFSO)). The concentration of the electrolyte salt in the nonaqueous electrolyte may be, for example, in the range of 0.5 mol / liter to 2.0 mol / liter.

[0061] The nonaqueous electrolyte lithium-ion secondary battery 20 of this embodiment is used housed in an outer container. The shape of the outer container is not particularly limited. Examples of the shape of the outer container include a coin shape, a button shape, a sheet shape, a cylindrical shape, and a rectangular shape.

[0062] Next, a method for manufacturing the nonaqueous electrolyte lithium-ion secondary battery 20 of this embodiment will be described. The nonaqueous electrolyte lithium-ion secondary battery 20 can be manufactured, for example, as follows. First, a negative electrode and a positive electrode are each prepared. Next, they are stacked with a separator between them so that the negative electrode mixture layer of the negative electrode and the positive electrode mixture layer of the positive electrode face each other to obtain a laminate. Next, a nonaqueous electrolyte is injected into the obtained laminate.

[0063] The negative electrode can be manufactured, for example, as follows. First, a negative electrode mixture paste is prepared by dispersing a negative electrode mixture in a solvent. Next, the negative electrode mixture paste is applied to a negative electrode current collector to form a coating layer. The application method is not particularly limited, and examples that can be used include spin coating, dipping, die coating, spray coating, and gravure printing. Next, the coating layer is dried to form a negative electrode mixture layer. The positive electrode can be produced in the same manner as the negative electrode, except that a positive electrode mixture is used instead of the negative electrode mixture.

[0064] The nonaqueous electrolyte lithium-ion secondary battery 20 can also be produced by stacking a negative electrode current collector, a negative electrode mixture pellet, a separator, a positive electrode mixture pellet, and a positive electrode current collector, and then pressing the resulting stack. The negative electrode mixture pellet and the positive electrode mixture pellet can be produced, for example, by a press molding method.

[0065] In the lithium ion secondary batteries (all-solid-state battery 10, non-aqueous electrolyte lithium ion secondary battery 20) according to the present embodiment configured as described above, the porous amorphous silicon particles contained in the negative electrode mixture layers 13, 23 have pores that absorb the volumetric expansion during charging. This reduces the apparent change in volume. Furthermore, amorphous silicon has higher strength and elasticity than crystalline silicon, making it less susceptible to collapse due to expansion / contraction during charging and discharging. Furthermore, amorphous silicon essentially does not have the dislocation defects found in crystalline silicon. Therefore, the porous amorphous silicon particles are less susceptible to fracture due to dislocation defects, and the conductive paths within the particles are less likely to be lost. Therefore, the all-solid-state battery 10 and the non-aqueous electrolyte lithium ion secondary battery 20 have improved charge / discharge cycle characteristics and storage characteristics. Furthermore, the negative electrode mixture layers 13, 23 contain a conductive additive, which increases the electrical conductivity of the negative electrode mixture layers 13, 23. Therefore, in the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20 according to the present embodiment, lithium can be easily inserted into the porous amorphous silicon particles even if the thickness of the negative electrode mixture layer 13, 23 is increased, resulting in a high electrical capacity.

[0066] Furthermore, in the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20 according to this embodiment, when the porous amorphous silicon particles contained in the negative electrode mixture layer 13, 23 have lamellar protrusions, the spacing between adjacent lamellar protrusions is in the range of 1 nm to 100 nm, and the average thickness of the lamellar protrusions is in the range of 1 nm to 50 nm, thereby allowing the pores between the lamellar protrusions to efficiently absorb volume expansion during charging. Therefore, the porous amorphous silicon particles exhibit less apparent volume change during charging and discharging. This further improves the charge / discharge cycle characteristics and storage characteristics of the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20.

[0067] Furthermore, in the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20 according to this embodiment, when the porous amorphous silicon particles contained in the negative electrode mixture layer 13, 23 have columnar protrusions, the spacing between adjacent columnar protrusions is within the range of 1 nm to 100 nm, and the average diameter of the columnar protrusions is within the range of 1 nm to 50 nm, so that the pores between the columnar protrusions can efficiently absorb the volume expansion during charging. Therefore, the porous amorphous silicon particles exhibit less apparent volume change during charging and discharging. This further improves the charge / discharge cycle characteristics and storage characteristics of the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20.

[0068] Furthermore, in the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20 according to this embodiment, when the average porosity of the porous amorphous silicon particles contained in the negative electrode mixture layer 13, 23 is in the range of 10% to 99%, the pores can efficiently absorb the volume expansion during charging. Therefore, the porous amorphous silicon particles exhibit a smaller apparent change in volume due to charging and discharging. This further improves the charge-discharge cycle characteristics and storage characteristics of the all-solid-state battery 10 and the nonaqueous electrolyte lithium-ion secondary battery 20.

[0069] Furthermore, in the all-solid-state battery 10 and the non-aqueous electrolyte lithium-ion secondary battery 20 according to this embodiment, when the conductive assistant contained in the negative electrode mixture layers 13, 23 contains a carbon material, the carbon material has excellent electrical conductivity, and therefore the electrical conductivity of the negative electrode mixture layers 13, 23 is improved. This makes it easier for lithium ions to be inserted into the porous amorphous silicon particles, and therefore the electrical capacity of the all-solid-state battery 10 and the non-aqueous electrolyte lithium-ion secondary battery 20 is improved.

[0070] Furthermore, in the all-solid-state battery 10 according to this embodiment, when the anode mixture layer 13 further contains a solid electrolyte, the lithium ion conductivity of the anode mixture layer 13 is improved. Also, the affinity between the anode mixture layer 13 and the solid electrolyte layer 14 is increased. Therefore, the all-solid-state battery 10 has high lithium ion conductivity, and therefore improves charge-discharge cycle characteristics at high current density.

[0071] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as set forth in the claims.

[0072] [Example 1] (1) Production of porous amorphous silicon particles Silicon (lump, purity 99.9% or higher) and aluminum (pellet, purity 99.999%) were mixed in a ratio of Si:Al = 12:88 (at.%). The resulting mixture was arc-melted in a vacuum furnace under argon gas to produce an Al-Si master alloy. The Al-Si master alloy was heated to 1400°C, and the resulting molten metal was pulverized and refined using a gas atomizer with a high-speed jet of 10 MPa argon gas. The resulting powder was then solidified to produce an Al-Si alloy powder with a particle size of 63 μm or less. This Al-Si alloy powder is a eutectic alloy composed of Al and Si. The Al-Si alloy powder was immersed in a 2N hydrochloric acid solution at 50°C for 12 hours to dissolve the Al in the Al-Si alloy powder and produce silicon particles.

[0073] The obtained silicon particles were observed using a scanning electron microscope equipped with an electron backscatter diffraction (SEM-EBSD). The obtained SEM images are shown in Figure 3. As shown in Figures 3(a) and 3(b), the silicon particles were confirmed to be spherical. The average particle diameter of these silicon particles was 50 μm. Furthermore, it was confirmed that the amorphous silicon particles were porous with a bicontinuous structure comprising multiple lamellar protrusions and multiple columnar protrusions (see Figure 3(c)). EBSD analysis of the lamellar protrusions and columnar protrusions did not reveal any Kikuchi lines. Therefore, the silicon particles were confirmed to be porous amorphous silicon particles. Furthermore, it was confirmed that the silicon particles contained fine crystalline silicon particles (see Figure 3(d)). The crystalline silicon particles had facets, and EBSD analysis confirmed the Kikuchi lines. The crystalline silicon particles had an average particle diameter of 1.0 μm and tended to be present in the surface layer of the porous amorphous silicon particles. The content of crystalline silicon particles in the silicon particles was less than 10%.

[0074] It was confirmed that the lamellar protrusions of the porous amorphous particles had an average thickness of 100 nm, with the spacing between adjacent lamellar protrusions ranging from 1 nm to 100 nm, and that the columnar protrusions had an average diameter of 100 nm, with the spacing between adjacent columnar protrusions ranging from 1 nm to 100 nm (see Figure 3(c)). The columnar protrusions shown in Figure 3(c) also had an average length of 1 μm and an average aspect ratio (average length / average diameter) of 10.

[0075] The XRD spectrum of the obtained silicon particles was measured by X-ray diffraction (XRD) using Cu-Kα radiation. The results are shown in Figure 4(a). As a reference example, Figure 4(b) shows the XRD spectrum of a crystalline silicon reference sample (silicon particles with an average particle size of 5 μm and a purity of 3N, manufactured by Kojundo Chemical Laboratory Co., Ltd.). The measurement conditions for the XRD spectra in Figures 4(a) and (b) were the same. The diffraction peaks due to crystalline silicon in the XRD spectrum of Figure 4(a) show reduced peak intensity and broadened half-widths compared to those in the XRD spectrum of Figure 4(b). This confirms that the silicon particles obtained contain a small amount of crystalline phase and are mostly amorphous. The ratio A / B of the maximum peak value A due to crystalline silicon in the XRD spectrum of Figure 4(a) to the maximum peak value B in the XRD spectrum of Figure 4(b) was 0.43. The ratio C / D of the maximum peak value C due to crystalline silicon in the XRD spectrum of Figure 4(a) to the maximum peak value D in the XRD spectrum of Figure 4(b) was 2.44.

[0076] The composition of the obtained silicon particles was analyzed using a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX). The energy spectrum measured by EDX is shown in Figure 5. From the energy spectrum in Figure 5, the composition of the silicon particles was calculated in mass percentage (mass%) and atomic percentage (at.%). The results are shown in Table 1. From the composition shown in Table 1, it was confirmed that the silicon particles were composed of 93 at.% or more (94 mass% or more) silicon element. It was also confirmed that 3.33 at.% aluminum remained in the silicon particles. Furthermore, the silicon particles contained approximately 4 at.% oxygen. This oxygen is believed to be present on the surface of the silicon.

[0077] [Table 1]

[0078] (2) Production of solid electrolyte particles Li2S (Sigma-Aldrich) and P2S5 (Sigma-Aldrich) were mixed in a molar ratio of 75:25 using a ball mill, and the resulting mixture was vacuum dried in a glove box at room temperature to produce Li2S-P2S5 solid electrolyte particles.

[0079] (3) Manufacturing of negative electrode mixture pellets The porous amorphous silicon particles obtained in (1) above, the Li2S-P2S5 solid electrolyte particles obtained in (2) above, and a conductive additive were placed in a ball mill in a mass ratio of 1:1:5. Next, ball milling was performed using alumina balls (diameter: 3 mm) to obtain a negative electrode mixture. Carbon black (Super-P, manufactured by MTI) was used as the conductive additive. The obtained negative electrode mixture was placed in a mold and pressure-molded under conditions of a molding load of 20 kN and a pressure time of 3 minutes to produce a disk-shaped negative electrode mixture pellet with a diameter of 10 mm and a thickness of 12 μm.

[0080] (4) Manufacturing solid electrolyte pellets The Li2S-P2S5 solid electrolyte particles obtained in (2) above were placed in a mold and press-molded under conditions of a molding load of 20 kN and a pressing time of 3 minutes to produce disk-shaped solid electrolyte pellets with a diameter of 10 mm and a thickness of 0.6 mm.

[0081] (5) Manufacturing of all-solid-state batteries The negative electrode mixture pellets obtained in (3) above and the solid electrolyte pellets obtained in (4) above were stacked in this order on a stainless steel current collector. Next, In foil (thickness: 100 μm), Li foil (thickness: 100 μm), and a stainless steel current collector were stacked in this order on the solid electrolyte pellets. Then, by applying pressure under a condition of 100 MPa, an all-solid-state battery was produced in which the stainless steel current collector, negative electrode mixture pellets, solid electrolyte pellets, In foil, Li foil, and stainless steel current collector were stacked in this order. The In foil was used to bond the solid electrolyte pellets and Li foil.

[0082] (6) Evaluation of all-solid-state batteries For the all-solid-state battery obtained in (5) above, the porous amorphous silicon particles in the negative electrode mixture layer were charged at 0.05 C (1 C is 3579 mA / g: the composition of the porous amorphous silicon particles in the fully charged state was Li 15A charge-discharge cycle test was performed 10 times, with one cycle consisting of charging to -0.615 V at a charge rate of 0.05 C (values ​​when using Si4) and then discharging to 0.38 V at a discharge rate of 0.05 C. The charge-discharge cycle test was performed in an environment at a temperature of 25°C. The results are shown in Figures 6A and 6B. In the graph of Figure 6A, the horizontal axis represents capacity, and the vertical axis represents potential. In the graph of Figure 6B, the horizontal axis represents the number of cycles, and the vertical axis represents the mass capacity density (capacity) and charge-discharge efficiency (coulombic efficiency) of the porous amorphous silicon particles during charge and discharge.

[0083] 6A and 6B, the mass capacity density of the all-solid-state battery obtained in Example 1 during discharge at the first cycle was 3398 mAh / g, which is a high value of 95% of the theoretical mass capacity density of silicon (3579 mAh / g). Furthermore, when the mass discharge capacity at the 10th cycle (2876 mAh / g) is compared with the mass discharge capacity at the first cycle, the capacity retention rate at the 10th cycle was 85%, indicating that the decrease in discharge capacity due to charge / discharge cycles was small and the battery had excellent charge / discharge cycle characteristics.

[0084] [Example 2] (1) Production of porous amorphous silicon ribbons First, silicon (lump, purity 99.999% or higher) and aluminum (pellet, purity 99.999%) were mixed in a ratio of Si:Al = 12:88 (at.%). The resulting mixture was arc-melted in a vacuum furnace with the atmosphere purged with argon gas to produce a molten metal. The molten metal was quenched using a single-roll liquid quenching method with a single-roll casting machine to produce a ribbon-shaped Al-Si alloy with a thickness of approximately 20 μm. This Al-Si alloy is a eutectic alloy composed of Al and Si. The Al-Si alloy was immersed in a 5N hydrochloric acid solution at 60°C for 24 hours to dissolve the Al, producing a ribbon-shaped silicon.

[0085] Scanning electron microscope (SEM) photographs of the obtained silicon ribbon are shown in Figures 7A, 7B, and 7C. As shown in Figures 7A to 7C, it was confirmed that the obtained silicon ribbon was porous and had a lamellar structure with a plurality of lamellar protrusions inside (see Figures 7A and 7B). It was confirmed that the lamellar protrusions had an average thickness of 20 nm, and the spacing between adjacent lamellar protrusions was 1 nm or more and 20 nm or less (see Figure 7C).

[0086] The results of measurement of the obtained ribbon-shaped silicon by X-ray diffraction (XRD) are shown in Figure 8. As shown in Figure 8, the XRD spectrum has a gentle shape without any sharp peaks, and it was therefore confirmed that the obtained ribbon-shaped silicon does not contain crystalline silicon and is a single substance containing only an amorphous silicon phase. From the above results, it was confirmed that the ribbon-shaped silicon obtained in Example 2 is porous amorphous silicon having a lamellar structure.

[0087] [Example 3] (1) Production of porous amorphous silicon ribbons A ribbon-shaped silicon was produced in the same manner as in Example 2(1), except that the Si:Al ratio was set to 20:80 (at. %).

[0088] The obtained ribbon-shaped silicon was subjected to surface observation by SEM and XRD pattern measurement. As a result of the surface observation by SEM, it was confirmed that the obtained ribbon-shaped silicon was porous and had a lamellar structure in which the average thickness of the lamellar convex portions was 20 nm and the spacing between adjacent lamellar convex portions was 1 nm or more and 20 nm or less. Furthermore, the XRD pattern confirmed that the obtained ribbon-shaped silicon was a single substance containing only an amorphous silicon phase. From these results, it was confirmed that the ribbon-shaped silicon obtained in Example 3 was porous amorphous silicon having a lamellar structure.

[0089] (2) Manufacturing of non-aqueous electrolyte lithium-ion secondary batteries A non-aqueous electrolyte lithium-ion secondary battery was manufactured using the amorphous-phase-containing porous silicon ribbon obtained in (1) above as the negative electrode material. First, the amorphous-phase-containing porous silicon ribbon, a conductive additive, and a polyimide binder were placed in a ball mill in a mass ratio of 60:25:15. Next, ball milling was performed using alumina balls (diameter: 3 mm) to obtain a negative electrode mixture. Carbon black (Super-P, manufactured by MTI) was used as the conductive additive. The obtained negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a uniform negative electrode mixture slurry. The obtained negative electrode mixture slurry was applied to a rolled copper foil at a concentration of 1.5 mg / cm. 2 The coating was then heated to 450°C in a vacuum and dried to obtain a copper foil with a negative electrode mixture layer. The coating was then solidified. A separator and pure lithium foil were laminated on the negative electrode mixture layer of the copper foil with a negative electrode mixture layer, and a non-aqueous electrolyte solution was injected into the resulting laminate to produce a 2023mm coin-type half-cell. The non-aqueous electrolyte solution used was a non-aqueous electrolyte solution prepared by dissolving lithium hexafluorophosphate in fluoroethylene carbonate at a concentration of 1 mol / L.

[0090] (3) Observation of the negative electrode Scanning electron microscope (SEM) photographs of the resulting negative electrode are shown in Figures 9A and 9B. Figure 9A is a low-magnification SEM image, which confirms that the porous amorphous silicon particles, observed as white, and the conductive additive (carbon black), observed as gray, are evenly mixed. Figure 9B is a high-magnification SEM image, which confirms that the porous amorphous silicon particles maintain their lamellar structure even after being formed into the negative electrode mixture layer.

[0091] (4) Evaluation of non-aqueous electrolyte lithium-ion secondary batteries The nonaqueous electrolyte lithium-ion secondary battery obtained in (2) above was subjected to 160 charge-discharge cycle tests, with one cycle consisting of charging the porous amorphous silicon particles in the negative electrode mixture layer to 0.005 V at a charge rate of 0.5 C (1 C is 3579 mA / g) and then discharging to 1 V at a discharge rate of 0.5 C. The measurement results are shown in the graph of FIG. 10. In the graph of FIG. 10, the horizontal axis represents the number of cycles, and the vertical axis represents the mass capacity density and charge-discharge efficiency of the porous amorphous silicon particles during charge and discharge. As shown in the graph of FIG. 10, at the 20th cycle when charge and discharge became stable, the mass capacity density during discharge was 1571 mAh / g. Furthermore, when comparing the mass discharge capacity at the 160th cycle (1353 mAh / g) with the mass discharge capacity at the 20th cycle, the capacity retention rate at the 160th cycle was 86%, indicating that there was little decrease in discharge capacity due to charge / discharge cycling and that the charge / discharge cycle characteristics were excellent.

[0092] [Example 4] (1) Production of porous amorphous silicon particles Silicon (lump, purity 99.9% or higher) and aluminum (pellet, purity 99.999%) were mixed in a ratio of Si:Al = 80:20 (at.%). The resulting mixture was arc-melted in a vacuum furnace under argon gas. The Al-Si master alloy was then heated to 1400°C. The resulting molten metal was then pulverized using a gas atomizer with a high-speed jet of 10 MPa helium gas to produce Al-Si alloy powder with a particle size of approximately 10 μm. This Al-Si alloy powder is a hypereutectic alloy of Al and Si. The resulting Al-Si alloy powder was then immersed in 5N hydrochloric acid at 60°C for 24 hours to dissolve the Al, producing silicon particles.

[0093] The resulting silicon particles were observed using SEM-EBSD. Shape observation by SEM and confirmation of crystallinity by EBSD confirmed that the resulting silicon particles consisted of a mixture of relatively large spherical amorphous silicon particles and crystalline silicon particles appearing on the surface layers of the amorphous silicon particles. The average particle size of the amorphous silicon particles was 50 μm. The average particle size of the crystalline silicon particles was 1.0 μm, and the crystalline silicon content of the silicon particles was 10% or less. The amorphous silicon particles were also confirmed to be porous with a bicontinuous structure comprising multiple lamellar protrusions and multiple columnar protrusions. The lamellar protrusions had an average thickness of 100 nm, and the spacing between adjacent lamellar protrusions was between 1 nm and 100 nm. The columnar protrusions had an average length of 1.0 μm, an average aspect ratio of 10, and the spacing between adjacent columnar protrusions was between 1 nm and 100 nm.

[0094] The XRD spectrum of the obtained silicon particles was measured using the XRD method with Cu-Kα radiation. The ratio A / B of the maximum peak value A attributable to crystalline silicon in the XRD spectrum of the obtained silicon particles to the maximum peak value B in the XRD spectrum of a crystalline silicon reference sample was 0.5 or less. The ratio C / D of the half-width C of the maximum peak value attributable to crystalline silicon in the XRD spectrum of the porous amorphous silicon particles to the half-width D of the maximum peak value in the XRD spectrum of a crystalline silicon reference sample was 2.0 or more.

[0095] (2) Manufacturing of non-aqueous electrolyte lithium-ion secondary batteries A coin-type half cell having a size of 2023 mm was produced in the same manner as in Example 3(2), except that the porous amorphous silicon particles obtained in (1) above were used as the negative electrode material.

[0096] (3) Evaluation of non-aqueous electrolyte lithium-ion secondary batteries The lithium-ion battery obtained in (2) above was subjected to a charge-discharge cycle test for 143 cycles in the same manner as in Example 3(4). The measurement results are shown in the graph in FIG. 11. In the graph in FIG. 11, the horizontal axis represents the number of cycles, and the vertical axis represents the mass capacity density and charge-discharge efficiency of the porous amorphous silicon particles during charge and discharge. As shown in the graph in FIG. 11, at the 10th cycle at which charge and discharge became stable, the mass capacity density during discharge was 1770 mAh / g. Furthermore, comparing the mass discharge capacity at the 143rd cycle (1506 mAh / g) with the mass discharge capacity at the 10th cycle, the capacity retention rate at the 143rd cycle was 85%, indicating little decrease in discharge capacity due to charge-discharge cycles and excellent charge-discharge cycle characteristics.

[0097] [Example 5] (1) Production of porous amorphous silicon particles Silicon particles were produced in the same manner as in Example 4(1), except that Si:Al=70:30 (at. %).

[0098] The resulting silicon particles were observed using SEM-EBSD. Shape observation by SEM and confirmation of crystallinity by EBSD confirmed that the resulting silicon particles consisted of a mixture of relatively large spherical amorphous silicon particles and crystalline silicon particles appearing on the surface of the amorphous silicon particles. The average particle size of the amorphous silicon particles was 50 μm. The average particle size of the crystalline silicon particles was 1.0 μm, and the crystalline silicon content of the silicon particles was 10% or less. The amorphous silicon particles were confirmed to be porous with a bicontinuous structure comprising multiple lamellar protrusions and multiple columnar protrusions. The lamellar protrusions had an average thickness of 100 nm, and the spacing between adjacent lamellar protrusions was between 1 nm and 100 nm. The columnar protrusions had an average length of 1.0 μm, an average aspect ratio of 10, and the spacing between adjacent columnar protrusions was between 1 nm and 100 nm. Furthermore, the XRD pattern confirmed that the obtained silicon particles were porous amorphous silicon particles.

[0099] The XRD spectrum of the obtained silicon particles was measured using the XRD method with Cu-Kα radiation. The ratio A / B of the maximum peak value A attributable to crystalline silicon in the XRD spectrum of the obtained silicon particles to the maximum peak value B in the XRD spectrum of a crystalline silicon reference sample was 0.5 or less. The ratio C / D of the half-width C of the maximum peak value attributable to crystalline silicon in the XRD spectrum of the porous amorphous silicon particles to the half-width D of the maximum peak value in the XRD spectrum of a crystalline silicon reference sample was 2.0 or more.

[0100] (2) Manufacturing of non-aqueous electrolyte lithium-ion secondary batteries A coin-type half cell having a size of 2023 mm was produced in the same manner as in Example 3(2), except that the porous amorphous silicon particles obtained in (1) above were used as the negative electrode material.

[0101] (3) Evaluation of non-aqueous electrolyte lithium-ion secondary batteries The lithium-ion battery obtained in (2) above was subjected to a charge-discharge cycle test for 143 cycles in the same manner as in Example 3(4). The measurement results are shown in the graph of FIG. 12. In the graph of FIG. 12, the horizontal axis represents the number of cycles, and the vertical axis represents the mass capacity density and charge-discharge efficiency of the porous amorphous silicon particles during charge and discharge. As shown in the graph of FIG. 12, at the 10th cycle at which charge and discharge became stable, the mass capacity density during discharge was 1811 mAh / g. Furthermore, comparing the mass discharge capacity at the 138th cycle (1536 mAh / g) with the mass discharge capacity at the 10th cycle, the capacity retention rate at the 138th cycle was 85%, indicating little decrease in discharge capacity due to charge-discharge cycles and excellent charge-discharge cycle characteristics.

[0102] [Example 6] (1) Production of porous amorphous silicon particles Silicon (block, purity ≥99.9%), aluminum (pellet, purity 99.999%), and titanium (granule, purity 99.999%) were mixed in a ratio of Si:Al:Ti = 19.5:79.5:1.0 (at.%). The resulting mixture was arc-melted in a vacuum furnace under argon gas. The Al-Ti-Si master alloy was heated to 1400°C, and the resulting molten metal was pulverized using a gas atomizer with a high-velocity jet of 10 MPa helium gas. The resulting molten metal was then pulverized and solidified to produce Al-Si-Ti alloy powder with a particle size of approximately 10 μm or less. This Al-Si-Ti alloy powder is a hypereutectic alloy of Al and Si with the addition of Ti. The Al-Si-Ti alloy powder was immersed in 5N hydrochloric acid at 60°C for 24 hours to dissolve the Al and Ti, producing silicon particles.

[0103] The resulting silicon particles were observed using SEM-EBSD. Shape observation by SEM and confirmation of crystallinity by EBSD confirmed that the resulting silicon particles were a mixture of relatively large spherical amorphous silicon particles and crystalline silicon particles attached to the surfaces of the amorphous silicon particles. The average particle size of the amorphous silicon particles was 50 μm. The average particle size of the crystalline silicon particles was 1.0 μm, and the crystalline silicon content of the silicon particles was 10% or less. The amorphous silicon particles were also confirmed to be porous with a bicontinuous structure comprising multiple lamellar protrusions and multiple columnar protrusions. The lamellar protrusions had an average thickness of 100 nm, and the spacing between adjacent lamellar protrusions was between 1 nm and 100 nm. The columnar protrusions had an average length of 1 μm, an average aspect ratio of 10, and the spacing between adjacent columnar protrusions was between 1 nm and 100 nm.

[0104] The XRD spectrum of the obtained silicon particles was measured using the XRD method with Cu-Kα radiation. The ratio A / B of the maximum peak value A attributable to crystalline silicon in the XRD spectrum of the obtained silicon particles to the maximum peak value B in the XRD spectrum of a crystalline silicon reference sample was 0.5 or less. The ratio C / D of the half-width C of the maximum peak value attributable to crystalline silicon in the XRD spectrum of the porous amorphous silicon particles to the half-width D of the maximum peak value in the XRD spectrum of a crystalline silicon reference sample was 2.0 or more.

[0105] (2) Manufacturing of non-aqueous electrolyte lithium-ion batteries A coin-type half cell having a size of 2023 mm was produced in the same manner as in Example 3(2), except that the porous amorphous silicon particles obtained in (1) above were used as the negative electrode material.

[0106] (3) Evaluation of non-aqueous electrolyte lithium-ion batteries The lithium-ion battery obtained in (2) above was subjected to a charge-discharge cycle test for 205 cycles in the same manner as in Example 3(4). The measurement results are shown in the graph in FIG. 13. In the graph in FIG. 13, the horizontal axis represents the cycle number, and the vertical axis represents the mass capacity density and charge-discharge efficiency of the porous amorphous silicon particles during charge and discharge. As shown in the graph in FIG. 11, at the 20th cycle, at which charge and discharge became stable, the mass capacity density during discharge was 1097 mAh / g. Furthermore, comparing the mass discharge capacity at the 205th cycle (1040 mAh / g) with the mass discharge capacity at the 20th cycle, the capacity retention rate at the 205th cycle was 95%, indicating extremely little decrease in discharge capacity due to charge-discharge cycles and excellent charge-discharge cycle characteristics. [Explanation of symbols]

[0107] 10 All-solid-state battery 11 Negative electrode 12 Negative electrode current collector 13 Negative electrode mixture layer 14 Solid electrolyte layer 15 Positive electrode 16 Positive electrode mixture layer 17 Positive electrode current collector 20. Non-aqueous electrolyte lithium-ion secondary battery 21 Negative electrode 22 Negative electrode current collector 23 Negative electrode mixture layer 24 Separator 25 Positive electrode 26 Positive electrode mixture layer 27 Positive electrode current collector

Claims

1. a conductive additive and a negative electrode active material, the negative electrode active material includes porous amorphous silicon particles containing an amorphous silicon phase, The porous amorphous silicon particles have, on their surfaces, a lamellar structure including lamellar protrusions having an average thickness in the range of 1 nm to 200 nm, a columnar structure including columnar protrusions having an average diameter in the range of 1 nm to 100 nm, or a bicontinuous structure including the lamellar protrusions and the columnar protrusions.

2. 2. The negative electrode mixture for a lithium ion secondary battery according to claim 1, wherein the porous amorphous silicon particles have the lamellar protrusions, and the interval between adjacent lamellar protrusions is in the range of 1 nm to 100 nm.

3. 3. The negative electrode mixture for a lithium ion secondary battery according to claim 1, wherein the porous amorphous silicon particles have the lamellar protrusions, and the lamellar protrusions have an average thickness in the range of 1 nm to 50 nm.

4. 3. The negative electrode mixture for a lithium ion secondary battery according to claim 1, wherein the porous amorphous silicon particles have the columnar protrusions, and the interval between adjacent columnar protrusions is in the range of 1 nm to 100 nm.

5. 3. The negative electrode mixture for a lithium ion secondary battery according to claim 1, wherein the porous amorphous silicon particles have the columnar protrusions, and the columnar protrusions have an average diameter in the range of 1 nm to 50 nm.

6. 6. The negative electrode mixture for a lithium ion secondary battery according to claim 1, wherein the porous amorphous silicon particles have an average porosity in the range of 10% to 99%.

7. The negative electrode mixture for a lithium ion secondary battery according to claim 1 , wherein the conductive additive comprises a carbon material.

8. The negative electrode mixture for a lithium ion secondary battery according to claim 1 , further comprising a solid electrolyte.

9. A lithium ion secondary battery comprising a negative electrode containing the negative electrode mixture for lithium ion secondary batteries according to any one of claims 1 to 8.

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