Non-aqueous electrolyte secondary batteries

Abstract

The problem to be solved by the present invention is to provide a non-aqueous electrolyte secondary battery that can suppress endurance degradation, improve energy density, and further suppress functional degradation of the non-aqueous electrolyte secondary battery unit. To solve the above problems, the non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode and a negative electrode, wherein the negative electrode comprises a current collector composed of a porous metal body and a negative electrode material disposed within the pores of the porous metal body, wherein the negative electrode material comprises a negative electrode active material composed of a silicon-based material, a skeleton-forming agent comprising a silicate having a siloxane bond, a conductive additive, and a binder, wherein the content of the skeleton-forming agent on the outer side of the negative electrode in the surface direction is greater than the content of the skeleton-forming agent on the inner side of the negative electrode in the surface direction.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. Background Art

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have increased in use in automobiles and the like due to their small size, light weight, and high output. The so-called non-aqueous electrolyte secondary battery is a general term for a battery system that uses an electrolyte that is not primarily composed of water and is capable of charging and discharging. For example, lithium ion batteries, lithium polymer batteries, lithium all-solid-state batteries, lithium-air batteries, lithium-sulfur batteries, sodium ion batteries, potassium ion batteries, multivalent ion batteries, fluoride batteries, sodium-sulfur batteries, etc. are known. This non-aqueous electrolyte secondary battery is mainly composed of a positive electrode, a negative electrode, and an electrolyte. Moreover, when the electrolyte has fluidity, a separator is inserted between the positive electrode and the negative electrode.

[0003] For example, a technology is disclosed for the purpose of improving battery life, in which a skeleton-forming agent comprising a silicate having a siloxane bond is present at least on the surface of the active material, and the skeleton-forming agent is allowed to penetrate from the surface to the interior (for example, see Patent Document 1). It is generally believed that according to this technology, since a strong skeleton can be formed in the active material, the battery life can be improved. In addition, a technology is also disclosed in which the above-mentioned skeleton-forming agent is applied to a negative electrode comprising a silicon (Si)-based active material (for example, see Patent Document 2).

[0004] [Prior Art Literature]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent No. 6369818

[0007] Patent Document 2: Japanese Patent No. 6149147 Summary of the Invention

[0008] [Problems to be solved by the invention]

[0009] However, in the above-mentioned non-aqueous electrolyte secondary battery, it is required to improve the energy density. In order to improve the energy density, it is generally believed that increasing the thickness of the negative electrode or densifying the amount of the negative electrode active material is effective. However, in the prior art, there is a limit to the thickness of the negative electrode in the production of the negative electrode. Specifically, the practical thickness of the electrode mixture layer that can be applied on the collector foil is less than 100 μm. If the film thickness is more than 100 μm, problems such as uneven coating, cracks, and peeling will occur, making it difficult to produce a high-precision negative electrode.

[0010] Furthermore, in order to balance the binding force of the binder with the expansion and contraction of the negative electrode active material, there is a limit to the amount of negative electrode active material per unit area from the perspective of durability. Specifically, the capacity of the negative electrode active material per unit area is limited to 4 mAh / cm 2 (film thickness 50μm) is the limit, above which sufficient cycle performance cannot be maintained. On the other hand, if the active material capacity is less than 4mAh / cm 2 , then no improvement in energy density can be expected.

[0011] In order to solve the above problems, it is considered to apply a porous metal body to the current collector of the negative electrode of the non-aqueous electrolyte secondary battery, and to fill the electrode mixture into the porous metal body. In a non-aqueous electrolyte secondary battery, when a current collector composed of a porous metal body and a negative electrode active material composed of a silicon-based material are applied to the negative electrode, the current collector composed of the porous metal body on the negative electrode side will follow the expansion and contraction of the negative electrode active material composed of the silicon-based material during charging and discharging, so the negative electrode as a whole will expand and contract. It is known that the expansion and contraction of the negative electrode as a whole sometimes causes unexpected deformation of the negative electrode and displacement of the position of the positive electrode in the non-aqueous electrolyte secondary battery cell, which can also reduce the function of the non-aqueous electrolyte secondary battery cell.

[0012] Therefore, a negative electrode for a nonaqueous electrolyte secondary battery, a positive electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery having the same are desired, which can suppress durability degradation, increase energy density, and further suppress functional degradation of the nonaqueous electrolyte secondary battery unit.

[0013] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery that can suppress durability degradation, improve energy density, and further suppress functional degradation of a single cell of the non-aqueous electrolyte secondary battery.

[0014] [Technical means to solve the problem]

[0015] (1) In order to achieve the above-mentioned object, the present invention provides a non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode, wherein the negative electrode has a current collector composed of a porous metal body and a negative electrode material arranged in the pores of the porous current collector, the negative electrode material comprises a negative electrode active material composed of a silicon-based material, a skeleton former comprising a silicate having a siloxane bond, a conductive auxiliary agent and a binder, and the content of the skeleton former on the outside of the surface direction of the negative electrode is greater than the content of the skeleton former on the inside of the surface direction of the negative electrode.

[0016] (2) A nonaqueous electrolyte secondary battery is also provided, wherein in the nonaqueous electrolyte secondary battery of (1), the positive electrode has a buffer layer in a region facing the negative electrode that is more easily deformed by external force than other regions of the positive electrode.

[0017] (3) In the non-aqueous electrolyte secondary battery of (2), the buffer layer may include at least one of a carbon-based material and an organic conductive polymer.

[0018] (4) In any of the nonaqueous electrolyte secondary batteries of (1) to (3), the negative electrode may have a non-deformable layer in a region facing the positive electrode that is less susceptible to deformation due to external force than other regions of the negative electrode.

[0019] (5) In the non-aqueous electrolyte secondary battery of (4), the non-deformable layer may be an active material layer containing at least one of a carbon-based material and lithium titanate.

[0020] (6) In any one of the non-aqueous electrolyte secondary batteries (1) to (5), the skeleton-forming agent may include a silicate represented by the following general formula (1):

[0021] [Chemistry 1]

[0022] A2O·nSiO2 formula (1)

[0023] [In the above general formula (1), A represents an alkali metal].

[0024] (6) In any one of the nonaqueous electrolyte secondary batteries (1) to (6), the porous metal body may be a foamed metal body.

[0025] (Effects of the Invention)

[0026] According to the present invention, a nonaqueous electrolyte secondary battery can be provided which can suppress durability degradation and improve energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram schematically showing a cross section of a conventional non-aqueous electrolyte secondary battery.

[0028] Figure 2 It is a cross-sectional view schematically showing the structure of a non-aqueous electrolyte secondary battery according to the first embodiment of the present invention.

[0029] Figure 3 It is a cross-sectional view schematically showing the structure of a non-aqueous electrolyte secondary battery according to a second embodiment of the present invention.

[0030] Figure 4 It is a cross-sectional view schematically showing the structure of a non-aqueous electrolyte secondary battery according to a third embodiment of the present invention.

[0031] Figure 5 This is a diagram schematically showing the structure inside the negative electrode of the non-aqueous electrolyte secondary battery of the present invention.

[0032] Figure 6 It is a graph showing the relationship between the number of cycles and the capacity retention rate of each Example and Comparative Example. DETAILED DESCRIPTION

[0033] Hereinafter, a first embodiment of the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to the accompanying drawings.

[0034] <First embodiment>

[0035] [negative electrode]

[0036] Figure 2 Schematically illustrates the structure of the non-aqueous electrolyte secondary battery of this embodiment. Figure 5 : This is a diagram schematically illustrating the structure of the negative electrode of the non-aqueous electrolyte secondary battery of the present invention. The negative electrode 1 of the non-aqueous electrolyte secondary battery of this embodiment has a current collector 11 composed of a porous metal body and a negative electrode material 12 arranged in the pores of the porous metal body. In addition, the negative electrode material 12 includes a negative electrode active material 13 composed of a silicon-based material, a skeleton forming agent 14 comprising a silicate having a siloxane bond, a conductive additive 15, and a binder 16. In addition, the content of the aforementioned skeleton forming agent in the outer side 17 of the surface direction of the negative electrode is greater than the content of the aforementioned skeleton forming agent in the inner side 18 of the surface direction of the aforementioned negative electrode 1. For example, by applying this embodiment to a lithium-ion secondary battery, a lithium-ion secondary battery can be provided that can suppress endurance degradation, increase energy density, and further suppress the functional decline of the non-aqueous electrolyte secondary battery monomer. Below, an example of applying this embodiment to a lithium-ion secondary battery is described in detail. Various additions, changes, or deletions can be made without departing from the scope of the present invention.

[0037] The current collector 11 is made of a porous metal. Examples thereof include mesh, woven fabric, non-woven fabric, embossed material, punched material, expanded material, and foamed material. A foamed metal is preferably used. Among these, a foamed metal having a three-dimensional mesh structure with continuous pores is preferably used. For example, Celmet (registered trademark) (manufactured by Sumitomo Electric Industries, Ltd.) can be used.

[0038] The material of the porous metal body is not particularly limited as long as it has electron conductivity and can conduct electricity to the electrode material held therein. For example, conductive metals such as Al, Al alloys, Ni, Ni-Cr alloys, Fe, Cu, Ti, Cr, Au, Mo, W, Ta, Pt, Ru, and Rh, and conductive alloys containing two or more of these conductive metals (stainless steel (SUS304, SUS316, SUS316L, YUS270, etc.)) can be used. Furthermore, when materials other than the above-mentioned conductive metals or conductive alloys are used, for example, a multilayer structure in which Fe is coated with a dissimilar metal such as Cu or Ni may be used. Among them, Ni or a Ni alloy is preferably used due to its excellent electron conductivity and reduction resistance.

[0039] The thickness of the porous metal body is preferably 10 μm or more, more preferably 50 μm or more. The thickness of the porous metal body is preferably 1 mm or less, more preferably 500 μm or less.

[0040] The average pore diameter of the porous metal body is preferably 500 μm or less. By ensuring that the average pore diameter of the porous metal body is within this range, the distance between the negative electrode active material 13 filled within the porous metal body and the metal skeleton is stabilized, improving electron conductivity and suppressing increases in the battery's internal resistance. Furthermore, even if volume changes occur during charging and discharging, the electrode mixture can be prevented from falling out.

[0041] The specific surface area of the porous metal body is preferably 200 to 10,000 m 2 / m 3 This is 2 to 10 times the specific surface area of conventional collector foils. By keeping the specific surface area of the porous metal body within this range, the contact between the electrode mixture and the collector 11 is improved, and the increase in the internal resistance of the battery is suppressed. A more preferred specific surface area is 500 to 7000 m 2 / m 3 .

[0042] The porosity of the porous metal body is preferably 90 to 99%. By making the porosity of the porous metal body within this range, it is possible to increase the filling amount of the electrode mixture, thereby improving the energy density of the battery. Specifically, when the porosity exceeds 99%, the mechanical strength of the porous metal body decreases significantly, and it is easy to be damaged due to the volume change of the electrode caused by charging and discharging. On the contrary, if it is less than 90%, not only the filling amount of the electrode mixture decreases, but also the ion conductivity of the electrode decreases, making it difficult to obtain sufficient input and output characteristics. From these viewpoints, the more preferred porosity is 93 to 98%.

[0043] The electrode weight per unit area of the porous metal body is preferably 1 to 100 mg / cm 2By making the electrode weight per unit area of the porous metal body within this range, the active material capacity can be fully demonstrated, thereby showing the capacity designed as an electrode. A more preferred electrode weight per unit area is 5 to 60 mg / cm 2 .

[0044] As the negative electrode active material 13, a substance that can reversibly absorb and release lithium ions is used. Specifically, a negative electrode active material 13 composed of a high-capacity silicon-based material is used. As the silicon-based material, silicon monomer, silicon alloy, silicon oxide, silicon compound, etc. are suitable. Here, the so-called silicon monomer refers to crystalline or amorphous silicon with a purity of 95% by mass or more. The so-called silicon alloy refers to a Si-M alloy containing silicon and other transition elements M. M can be, for example, Al, Mg, La, Ag, Sn, Ti, Y, Cr, Ni, Zr, V, Nb, Mo, etc., and can also be a complete solid solution alloy, eutectic alloy, hypoeutectic alloy, hypereutectic alloy, or peritectic alloy. The so-called silicon oxide refers to silicon oxide, or a complex containing silicon monomer and SiO2. The element ratio of Si to O is as long as Si is 1 and O is 1.7 or less. The so-called silicon compound is a substance formed by chemically bonding silicon with two or more other elements. Among them, silicon monomer is preferred because it can form the interface layer described later well. Alternatively, a material obtained by mixing or compositely combining a carbon-based material with a silicon-based material may be used.

[0045] The shape of the silicon-based material is not particularly limited and may be spherical, elliptical, square with bald corners, ribbon, fiber, flake, donut, or hollow powder. These may be single particles or granules.

[0046] The negative electrode active material 13 made of silicon has an expansion rate of 10% or more during charge and discharge. This means that the negative electrode active material 13 significantly expands and contracts during charge and discharge. However, the use of the skeleton-forming agent 14, described below, can suppress the durability degradation caused by this expansion and contraction.

[0047] From the viewpoint of achieving excellent cycle characteristics of the electrode and high input-output characteristics, the particle size of the silicon-based material is preferably 0.01 μm to 10 μm.

[0048] Furthermore, the negative electrode active material 13 may be configured to include a carbon-based material (graphite, hard carbon, soft carbon, etc.) in addition to the above-mentioned silicon-based material.

[0049] As the skeleton forming agent 14, a skeleton forming agent 14 containing a silicate having a siloxane bond is used. More specifically, the skeleton forming agent 14 preferably contains a silicate represented by the following general formula (1):

[0050] [Chemistry 2]

[0051] A2O·nSiO2 formula (1).

[0052] In the general formula (1), A represents an alkali metal. A is preferably at least one of lithium (Li), sodium (Na), and potassium (K). By using an alkali metal salt of silicate having a siloxane bond as a skeleton-forming agent, a lithium-ion secondary battery having high strength, excellent heat resistance, and excellent cycle life can be obtained.

[0053] Moreover, in the above general formula (1), n is preferably 1.6 or more and 3.9 or less. By making n within this range, when the skeleton forming agent 14 and water are mixed to form a skeleton forming agent liquid, suitable viscosity can be obtained, and when applied to a negative electrode comprising silicon as a negative electrode active material 13 as described later, the skeleton forming agent 14 easily penetrates into the negative electrode material 12. Therefore, a lithium ion secondary battery with high strength, excellent heat resistance and excellent cycle life can be obtained more effectively. A more preferred n is 2.0 or more and 3.5 or less.

[0054] The silicate is preferably amorphous. Amorphous silicates are composed of disordered molecular arrangements and therefore do not break in specific directions like crystals. Therefore, using an amorphous silicate as the framework-forming agent 14 improves cycle life characteristics.

[0055] For example, by applying the above-mentioned skeleton forming agent liquid on the negative electrode containing silicon as the negative electrode active material 13, the skeleton forming agent 14 penetrates into the negative electrode active material 13. It is speculated that the silicon constituting the negative electrode active material 13 and the above-mentioned silicate constituting the skeleton forming agent 14 are fused, for example, the hydrolyzed silicate undergoes a dehydration reaction (condensation reaction of the silanol group) due to heating, thereby forming a siloxane bond (-Si-O-Si-). That is, in the negative electrode 1 for lithium-ion secondary batteries of this embodiment, an interface layer composed of inorganic substances is formed at the interface between the negative electrode active material 13 and the skeleton forming agent 14. This interface layer contains silicon derived from the siloxane bond and an alkali metal generated by the hydrolysis of the silicate. It is speculated that, due to the presence of this interface layer, the negative electrode active material 13 and the skeleton forming agent 14 are firmly bonded, resulting in excellent cycle life characteristics.

[0056] In this embodiment, the ratio of alkali metal atoms to all constituent atoms of the interface layer is preferably higher than the ratio of alkali metal atoms to all constituent atoms of the skeleton-forming agent 14. More specifically, the ratio of alkali metal atoms to all constituent atoms of the interface layer is preferably at least five times the ratio of alkali metal atoms to all constituent atoms of the skeleton-forming agent 14. This strengthens the bond between the negative electrode active material 13 and the skeleton-forming agent 14, further suppresses delamination caused by expansion and contraction of the negative electrode active material 13 during charge and discharge, and prevents wrinkles or cracks in the current collector 11, thereby further improving the cycle life.

[0057] The thickness of the interface layer is preferably 3 nm to 30 nm. By setting the thickness of the interface layer within this range, the bond between the negative electrode active material 13 and the skeleton-forming agent 14 becomes stronger, and the delamination caused by the expansion and contraction of the negative electrode active material 13 during charge and discharge, as well as the wrinkling or cracking of the current collector 11, is further suppressed, thereby further improving the cycle life.

[0058] The skeleton-forming agent 14 of this embodiment may also contain a surfactant. This improves the lyophilicity of the skeleton-forming agent 14 within the negative electrode material 12, allowing the skeleton-forming agent 14 to evenly penetrate the negative electrode material 12. Consequently, a uniform skeleton is formed between the negative electrode active materials 13 within the negative electrode material 12, further improving cycle life characteristics.

[0059] Moreover, in the negative electrode 1 of the present embodiment, the skeleton former 14 is arranged at least on the interface between the negative electrode material 12 and the current collector 11. In more detail, the skeleton former 14 is dispersed between the negative electrode active materials 13 not only on the interface between the current collector 11 and the negative electrode material 12, but also on the entire negative electrode material 12. Moreover, in the present embodiment, the content (density) of the skeleton former in the outer side 17 of the surface direction of the negative electrode 1 is greater than the content of the skeleton former in the inner side 18 of the surface direction of the negative electrode 1. Thus, the expansion and contraction from the inner side of the surface direction of the negative electrode toward the outer side of the surface direction of the negative electrode during the charge and discharge of the non-aqueous electrolyte secondary battery, that is, the unexpected deformation and positional displacement of the negative electrode can be suppressed. Therefore, the functional decline of the non-aqueous electrolyte secondary battery monomer can be suppressed.

[0060] The outer side 17 of the negative electrode 1 in the plane direction refers to the region extending from the outer periphery of the negative electrode inward to 10% of the longitudinal and lateral widths of the electrode, and the remaining region is referred to as the inner side 18 in the plane direction.

[0061] The content (density) of the skeleton forming agent 14 relative to the negative electrode material 12 is preferably 2.0 to 5.0 mg / cm2 on the outer side 17 of the negative electrode 1. 2The content (density) of the skeleton forming agent 14 relative to the negative electrode material 12 is preferably 1.0 to 2.0 mg / cm2 on the inner side 18 of the negative electrode 1 in the surface direction. 2 If the content of the skeleton forming agent 14 relative to the negative electrode material 12 is within this range, the effect of using the skeleton forming agent 14 will be more effectively exerted. A more preferred content of the skeleton forming agent is 2.0 mg / cm 2 , 1.0 mg / cm in the inner side 18 of the surface direction 2 .

[0062] When the total solid content of the negative electrode active material 13, the skeleton former 14, the conductive aid 15 and the binder 16 is set to 100% by mass, the content of the skeleton former 14 in the entire negative electrode is preferably 3.0% by mass to 40.0% by mass. If the content of the skeleton former 14 in the entire negative electrode is within this range, the effect brought about by the use of the above-mentioned skeleton former 14 will be more effectively exerted. By setting the content of the skeleton former 14 in the negative electrode material 12 to 3.0% by mass or more, the function of the skeleton former 14 can be more fully obtained. Moreover, by setting the content of the skeleton former 14 to 40.0% by mass or less, the decrease in energy density can be further prevented. The more preferred content of the skeleton former 14 in the entire negative electrode is 5.0% by mass to 30.0% by mass.

[0063] Furthermore, the negative electrode 1 for lithium ion secondary batteries of this embodiment includes a conductive auxiliary agent 15. As the conductive auxiliary agent 15, there is no particular limitation as long as it has electronic conductivity, and metals, carbon materials, conductive polymers, conductive glass, etc. can be used. Specifically, examples include: acetylene black (AB), Ketchen black (KB), furnace black (FB), thermal cracking black, lamp black, slot black, roller black, disk black, carbon black (CB), carbon fiber (for example, vapor-grown carbon fiber VGCF (registered trademark)), carbon nanotubes (CNT), carbon nanohorns, graphite, graphene, glassy carbon, amorphous carbon, etc., and one or more of these can be used.

[0064] When the total of the negative electrode active material 13, the conductive aid 15, and the binder 16 contained in the negative electrode material 12 is taken as 100 mass%, the content of the conductive aid 15 is preferably 0 to 20.0 mass%. Within this range, the conductive aid 15 content improves conductivity without reducing the negative electrode capacity density, and sufficient voids for retaining the skeleton-forming agent 14 in liquid form can be formed within the negative electrode material 12. A more preferred content of the conductive aid 15 is 8.8 to 25.0 mass%.

[0065] The conductive additive 15 of this embodiment preferably has a volume density of 0.04 mg / cm 3 ~0.25mg / cm 3 By setting the bulk density of the conductive agent 15 within this range, the skeleton forming agent 14 can be fully impregnated, thereby fully exerting the effect of the skeleton forming agent 14. A more preferred bulk density of the conductive agent 15 is 0.04 mg / cm 3 ~0.15mg / cm 3 .

[0066] Furthermore, the negative electrode 1 of this embodiment includes a binder 16. As the binder 16, for example, one of the following organic materials may be used alone, or two or more thereof may be used in combination: polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aromatic polyamide, polyacryl, styrene butadiene rubber (SBR), ethylene-vinylacetate copolymer (EVA), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), and the like. cellulose, CMC), xanthan gum, polyvinyl alcohol (PVA), ethylene vinyl alcohol, polyvinyl butyral (PVB), ethylene vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylamide, polyacrylate, epoxy resin, polyethylene terephthalate (PET), polybutylene terephthalate (polybuthylene terephthalate) Polyurethane (PTFE), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea resin, melamine resin, phenol resin, latex, polyurethane, silanized polyurethane, nitrocellulose, dextrin, polyvinyl pyrrolidone, vinyl acetate, polystyrene, allyl chloride, resorcinol resin, polyaromatic hydrocarbon, modified silicone, methacrylic resin, polybutene, butyl rubber, 2-acrylic acid, cyanoacrylate, methyl methacrylate, glycidyl methacrylate, acrylic acid oligomer, 2-hydroxyethyl acrylate, alginic acid, starch, lacquer, sucrose, animal glue, casein, cellulose nanofiber, etc.

[0067] Moreover, a mixture of the various organic binders and inorganic binders mentioned above can also be used. As the inorganic binder, silicate system, phosphate system, sol system, cement system and the like can be cited. For example, one of the following inorganic materials can be used alone, or two or more thereof can be used in combination. The inorganic materials are: lithium silicate, sodium silicate, potassium silicate, cesium silicate, guanidine silicate, ammonium silicate, silicofluoride salt, borate, lithium aluminate, sodium aluminate, potassium aluminate, aluminosilicate, lithium aluminate, sodium aluminate, potassium aluminate, polyaluminum chloride, polyaluminum sulfate, polyaluminum sulfate silicate, aluminum sulfate, aluminum nitrate, ammonium alum, lithium alum, sodium alum, potassium alum, chrome alum, iron alum, manganese alum, nickel ammonium sulfate, diatomaceous earth, polyzirconium oxane, polytitanium oxane, mullite, white carbon, silica sol, colloidal silica, fumed dioxide, Silica, alumina sol, colloidal alumina, fumed alumina, zirconia sol, colloidal zirconia, fumed zirconia, magnesia sol, colloidal magnesia, fumed magnesia, calcium oxide sol, colloidal calcium oxide, fumed calcium oxide, titania sol, colloidal titanium dioxide, fumed titanium dioxide, zeolite, silicoaluminophosphate zeolite, sepiolite, montmorillonite, kaolin, saponite, aluminum phosphate, magnesium phosphate, calcium phosphate, iron phosphate, copper phosphate, zinc phosphate, titanium phosphate, manganese phosphate, barium phosphate, tin phosphate, low-melting-point glass, plaster, gypsum, magnesium cement, lead monoxide cement, Portland cement, blast furnace cement, fly ash cement, silica cement, phosphate cement, concrete, solid electrolyte, etc.

[0068] In addition, in this embodiment, since the above-mentioned interface layer formed by using the skeleton forming agent 14 firmly bonds the negative electrode active material 13 and the skeleton forming agent 14, all of the above-mentioned binders 16 can be used. When the total amount of the negative electrode active material 13, the conductive auxiliary agent 15 and the binder 16 contained in the negative electrode material 12 is set to 100 mass%, the content of the binder 16 is preferably 0.1 mass% to 60 mass%. By making the content of the binder 16 within this range, the ion conductivity can be improved without reducing the negative electrode capacity density, and high mechanical strength can be obtained, thereby obtaining excellent cycle life characteristics. A more preferred content of the binder 16 is 0.5 mass% to 30 mass%.

[0069] The thickness of the negative electrode 1 of this embodiment, constructed as described above, is preferably 50 μm to 1000 μm. When the thickness of the negative electrode 1 is within this range, degradation over time can be suppressed and energy density can be increased compared to conventional methods. A more preferred thickness of the negative electrode 1 is 80 μm to 800 μm.

[0070] Furthermore, in the negative electrode 1 of this embodiment, the distance between the current collector 11 composed of a porous metal body and the negative electrode active material 13 is preferably 50 μm or less. When the distance between the current collector 11 composed of a porous metal body and the negative electrode active material 13 is 50 μm or less, long-term degradation can be suppressed. More preferably, the distance between the current collector 11 composed of a porous metal body and the negative electrode active material 13 is 30 μm or less.

[0071] [positive electrode]

[0072] Next, a description will be given of a positive electrode when a lithium ion secondary battery is constructed using the above-described negative electrode.

[0073] As the positive electrode active material, there is no particular limitation as long as it is a positive electrode active material commonly used in lithium ion secondary batteries. For example, positive electrode active materials such as alkali metal transition metal oxides, vanadium, sulfur, solid solution systems (lithium excess system, sodium excess system, potassium excess system), carbon, and organic systems can be used.

[0074] The positive electrode of this embodiment may also contain a skeleton forming agent, similarly to the negative electrode described above. As the skeleton forming agent, the same skeleton forming agent as that of the negative electrode described above can be used, and the preferred content of the skeleton forming agent is also the same as that of the negative electrode.

[0075] The positive electrode of this embodiment may also contain a conductive additive. As the conductive additive, the various conductive additives that can be used in the negative electrode can be used. The preferred content of the conductive additive is the same as that of the negative electrode.

[0076] The positive electrode of this embodiment may also include a binder. As the binder, for example, one of the following organic materials may be used alone, or two or more may be used in combination. The organic materials include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), hexafluoropropylene, tetrafluoroethylene, polypropylene, alginic acid, etc. Furthermore, a mixture of these organic binders and an inorganic binder may also be used. Examples of the inorganic binder include silicate-based, phosphate-based, sol-based, and cement-based binders.

[0077] As the material of the current collector used in the positive electrode, as long as it is a material with electronic conductivity that can be energized to the positive electrode active material maintained, there is no particular limitation. For example, conductive materials such as C, Ti, Cr, Ni, Ni-Cr alloy, Cu, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al, and alloys containing two or more of these conductive materials (for example, stainless steel or Al-Fe alloy) can be used. When using materials other than the above-mentioned conductive materials, for example, a multilayer structure of a heterogeneous metal such as Al coated on Fe or a heterogeneous element such as C coated on Al can also be used. With respect to the viewpoint of high electrical conductivity and high stability in the electrolyte, the current collector is preferably C, Ti, Cr, Au, Al, stainless steel, etc., and further with respect to the viewpoint of oxidation resistance and material cost, it is preferably C, Al, stainless steel, etc. More preferably, Al or Al alloy coated with carbon, stainless steel coated with carbon. Even when the current collector used in the positive electrode is composed of a porous metal body, the material of the current collector used in the positive electrode is not particularly limited as long as it is the material described above.

[0078] The current collector used in the positive electrode can be in the form of a wire, rod, plate, foil, or porous. A porous shape is also possible because it can increase the packing density and facilitate the penetration of the skeleton-forming agent into the active material layer. Examples of porous shapes include mesh, woven fabric, non-woven fabric, embossed body, punched body, expanded body, or foamed body. The same porous metal body as that used for the negative electrode can also be used.

[0079] [Diaphragm]

[0080] In the lithium-ion secondary battery of this embodiment, a separator commonly used in lithium-ion secondary batteries can be used. For example, a polyethylene microporous membrane, a polypropylene microporous membrane, a glass non-woven fabric, an aramid non-woven fabric, a polyimide microporous membrane, a polyolefin microporous membrane, or the like can be used as the separator.

[0081] [Electrolytes]

[0082] In the lithium-ion secondary battery of this embodiment, the electrolyte commonly used in lithium-ion secondary batteries can be used. Examples include electrolyte solutions formed by dissolving an electrolyte in a solvent, gel electrolytes, solid electrolytes, ionic liquids, and molten salts. Here, the electrolyte solution refers to an electrolyte dissolved in a solvent.

[0083] The electrolyte of a lithium-ion secondary battery needs to contain lithium ions as a carrier responsible for conductivity. Therefore, the electrolyte salt thereof is not particularly limited as long as it can be used in a lithium-ion secondary battery, but lithium salts are preferred. As such a lithium salt, at least one selected from the group consisting of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO4), lithium bistrifluoromethanesulfonimide (LiN(SO2CF3)2), lithium bispentafluoroethanesulfonimide (LiN(SO2C2F5)2), lithium bis(oxalatoborate) (LiBC4O8), etc. can be used, or two or more can be used in combination.

[0084] The solvent for the electrolyte is not particularly limited as long as it can be used in lithium-ion secondary batteries. For example, at least one solvent selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma-butyrolactone (GBL), methyl-gamma-butyrolactone, dimethoxymethane (DMM), dimethoxyethane (DME), vinylene carbonate (VC), vinyl ethylene carbonate (EVC), fluoroethylene carbonate (FEC), and ethylene sulfite (ES) can be used, or two or more solvents can be used in combination.

[0085] The concentration of the electrolyte solution (the concentration of the salt in the solvent) is not particularly limited, but is preferably 0.1 mol / L to 3.0 mol / L, and more preferably 0.8 mol / L to 2.0 mol / L.

[0086] Ionic liquids or molten salts are classified according to the type of cation, such as pyridinium, alicyclic amine, and aliphatic amine. A variety of ionic liquids or molten salts can be synthesized by selecting the type of anion to be combined with them. Examples of cations include ammonium ions such as imidazolium salts and pyridinium salts, phosphonium ions, and inorganic ions. Examples of anions include halogen ions such as bromide and trifluoromethanesulfonate, boron ions such as tetraphenylborate, and phosphorus ions such as hexafluorophosphate.

[0087] Ionic liquids or molten salts can be obtained, for example, by the following known synthesis method: cations such as imidazolium and Br - 、Cl - , BF 4- PF 6- 、(CF3SO2)2N - CF3SO 3- 、FeCl 4- If it is an ionic liquid or molten salt, it can function as an electrolyte even without adding an electrolyte.

[0088] Solid electrolytes are categorized into sulfide, oxide, hydride, and organic polymer types. Most are amorphous or crystalline, consisting of salts and inorganic derivatives as carriers. Because they eliminate the need for flammable aprotic organic solvents, as with electrolytes, they are less susceptible to gas or liquid leakage, leading to the potential for safety-enhancing secondary batteries.

[0089] [Manufacturing method]

[0090] Next, a method for manufacturing the lithium ion secondary battery of this embodiment will be described.

[0091] The method for manufacturing the negative electrode of the lithium-ion secondary battery of this embodiment has a first step, in which a negative electrode material comprising a negative electrode active material, a conductive additive, and a binder is applied to the current collector and dried to form a negative electrode layer precursor. For example, a nickel porous material having a thickness of 1000 μm is prepared by preparing a nickel porous body pre-wound into a roll. On the other hand, as the negative electrode material, a paste slurry is prepared by mixing the negative electrode active material, a binder, a conductive additive, etc. . Subsequently, the slurry-like negative electrode material is filled and applied inside the nickel porous body, dried, and then subjected to a voltage regulation treatment to obtain a negative electrode layer precursor. Moreover, the negative electrode layer precursor may not be subjected to a voltage regulation treatment.

[0092] In addition, as mentioned above, the negative electrode layer precursor may also be kept in a wet state without being dried. In addition, in addition to the above-mentioned slurry coating, for example, it can also be listed: using chemical plating or sputtering, evaporation, gas deposition, impregnation, pressing, etc., the negative electrode active material (precursor) is formed into a negative electrode active material layer inside the porous current collector and the like. However, from the perspective of the lyophilicity of the skeleton forming agent and the cost of electrode manufacturing, a slurry filling coating method or an impregnation method is preferred.

[0093] For example, a silicate having a siloxane bond or a phosphate having a phosphate bond is purified by a dry or wet process and then water is added to the purified solution to prepare a skeleton forming agent liquid containing a skeleton forming agent. A surfactant may also be mixed at this time. As a dry process, for example, alkali metal silicates can be produced by adding SiO2 to water in which an alkali metal hydroxide is dissolved and treating the mixture in an autoclave at 150°C to 250°C. As a wet process, for example, a mixture of an alkali metal carbonate and SiO2 can be calcined at 1000°C to 2000°C and then dissolved in hot water.

[0094] Furthermore, the method for manufacturing a negative electrode for a lithium-ion secondary battery of this embodiment includes a second step in which the negative electrode layer precursor formed in the first step is impregnated with a skeleton-forming agent comprising a silicate having a siloxane bond or a phosphate having a phosphate bond and dried, thereby forming the negative electrode layer. In this case, by first impregnating the entire negative electrode layer precursor formed in the first step with the skeleton-forming agent and curing it, and then re-impregnating only the outer side of the surface with the skeleton-forming agent and curing it, a negative electrode can be manufactured in which the content of the skeleton-forming agent on the outer side of the surface of the negative electrode is greater than the content of the skeleton-forming agent on the inner side of the surface of the negative electrode.

[0095] Then, a skeleton forming agent is applied to the entire surface of the negative electrode layer precursor and a negative electrode active material is applied. In addition to the method of impregnating the negative electrode precursor in a tank storing a skeleton forming agent liquid, the skeleton forming agent can also be applied by dripping the skeleton forming agent onto the surface of the negative electrode precursor, applying the skeleton forming agent, spray coating, screen printing, curtain coating, spin coating, gravure coating, die coating, etc. The skeleton forming agent applied to the surface of the negative electrode layer precursor penetrates into the interior of the negative electrode and enters the gaps between the negative electrode active material or the conductive additive. Then, after drying by heat treatment to harden the skeleton forming agent, the skeleton forming agent is further applied again only on the outside of the surface direction of the negative electrode layer precursor. At this time, a masking treatment can also be performed on the inside of the surface direction with tape or the like. In this way, a negative electrode can be manufactured in which the skeleton forming agent forms the skeleton of the negative electrode active material layer, and the content of the skeleton forming agent on the outside of the surface direction of the negative electrode is greater than the content of the skeleton forming agent on the inside of the surface direction of the negative electrode.

[0096] In the above-mentioned drying treatment, if the temperature becomes high temperature, the heat treatment time can be shortened, and the strength of the skeleton forming agent is improved, so it is preferably 80°C or more, more preferably 100°C or more, and ideally 110°C or more. In addition, as the upper limit temperature of the heat treatment, there is no particular limitation as long as the collector does not melt. For example, it can also be increased to the melting point of copper, that is, about 1000°C. In the case of a conventional electrode, the binder sometimes carbonizes or the collector softens, so it is estimated that the upper limit temperature is much lower than 1000°C. However, in this embodiment, by using a skeleton forming agent, the skeleton forming agent shows excellent heat resistance and is stronger than the strength of the collector. Therefore, the upper limit of the temperature is 1000°C.

[0097] The drying time can be maintained for 0.5 to 100 hours. The heat treatment can be performed in air, but is preferably performed in a non-oxidizing atmosphere to prevent oxidation of the current collector.

[0098] Here, in the method for manufacturing the negative electrode of the lithium ion secondary battery of this embodiment, the ratio of the density B of the entire negative electrode layer formed in the second step to the density A of the entire negative electrode layer precursor formed in the first step, that is, B / A, is controlled to be 0.9.

[0099] In the method for producing the negative electrode of the lithium ion secondary battery of this embodiment, the density A of the entire negative electrode layer precursor formed in the first step is set to 0.5 g / cm 3 ~2.0g / cm 3 As a result, the ratio B / A (i.e., density increase ratio) of the overall density B of the negative electrode layer to the density A of the negative electrode layer precursor can be more reliably within the above range, thereby enhancing the effect of the above-mentioned skeleton forming agent. The more preferred range of the overall density A of the negative electrode layer precursor is 0.6 g / cm 3 ~1.5g / cm 3 By setting the density A of the negative electrode layer precursor to 0.6 g / cm 3 As mentioned above, the decrease in energy density caused by the decrease in electrode density can be suppressed, and by setting the electrode density to 1.5 g / cm 3 Hereafter, the decrease in capacity can be suppressed.

[0100] ​The method for manufacturing a positive electrode for a lithium-ion secondary battery of the present invention comprises the following steps: applying a positive electrode material comprising a positive electrode active material, a conductive additive, and a binder to a current collector, drying the material, and rolling the material to produce the positive electrode. For example, to produce a rolled aluminum foil having a thickness of 10 μm, the aluminum foil is pre-wound into a roll. Separately, a paste-like slurry is prepared by mixing the positive electrode active material, a binder, a conductive additive, and the like as the positive electrode material. The slurry-like positive electrode material is then applied to the surface of the aluminum, dried, and then subjected to a rolling process to produce the positive electrode. Furthermore, a foamed porous body composed of a metal may also be used as the current collector. The current collector is characterized in that the current collector is filled with an electrode composite material. The method for filling the current collector with the electrode composite material is not particularly limited; for example, a method can be used in which a slurry comprising the electrode composite material is filled into the mesh structure of the current collector by applying pressure using a press-in method. After filling with the electrode composite material, the filled current collector is dried and then pressed to increase the density of the electrode composite material, thereby adjusting the density to the desired value.

[0101] Finally, the obtained negative electrode and positive electrode are cut into the desired size, joined with a separator, and sealed while immersed in an electrolyte to obtain a lithium-ion secondary battery. The structure of the lithium-ion secondary battery can be applied to existing battery forms or structures such as stacked batteries or wound batteries.

[0102] [Effect]

[0103] According to the first embodiment of the nonaqueous electrolyte secondary battery of the present invention, the following effects are achieved.

[0104] In a first embodiment, a non-aqueous electrolyte secondary battery 3 having a positive electrode 2 and a negative electrode 1 is provided with a current collector 11 composed of a porous metal body and a negative electrode material 12 arranged in the pores of the aforementioned porous metal body. In the negative electrode 1, the negative electrode material 12 is constructed to include a negative electrode active material 13 composed of a silicon-based material, a skeleton former 14 containing a silicate having a siloxane bond, a conductive additive 15 and a binder 16, and the content of the skeleton former 14 on the outer side 17 in the surface direction of the negative electrode 1 is greater than the content of the skeleton former 14 on the inner side 18 in the surface direction of the negative electrode 1.

[0105] First, by using a porous metal body as the current collector 11 , the negative electrode material 12 can be fixed in a micrometer-sized region by the porous metal skeleton, thereby suppressing separation and cracking of the negative electrode.

[0106] Furthermore, by using the framework-forming agent 14 as the negative electrode material 12, the negative electrode material 12 can be fixed in the nanometer-scale region. More specifically, by forming a third phase composed of the framework-forming agent 14 at the interface between the current collector 11 composed of a porous metal body and the negative electrode active material 13, the negative electrode active material 13 can be firmly bonded within the negative electrode material 12, thereby suppressing its shedding during expansion and contraction, thereby suppressing its durability degradation.

[0107] Furthermore, by making the content of the skeleton forming agent 14 on the outside of the surface direction of the negative electrode 1 greater than the content of the skeleton forming agent 14 on the inside of the surface direction of the negative electrode 1, the unexpected deformation and position displacement of the negative electrode from the inside to the outside of the surface direction during expansion and contraction can be suppressed.

[0108] Therefore, by filling the foamed metal body with the negative electrode material 12 containing this skeleton-forming agent 14 to form a multi-skeleton structure, even when using the negative electrode active material 13 composed of a high-capacity silicon-based material with a very high expansion and contraction rate, unexpected deformation and positional shifting of the negative electrode can be suppressed during full charge and discharge cycles with a state of charge (SOC) of 0 to 100, thereby maintaining the negative electrode structure. Furthermore, the thicker the negative electrode, the higher the capacity and the higher the weight per unit area, which can lead to shedding and breakage of the conductive path, can be suppressed, thus achieving high cyclability and achieving an absolutely high energy density.

[0109] In addition, the present invention is not limited to the above-mentioned embodiments, and modifications and improvements within the scope of achieving the purpose of the present invention are included in the present invention. For example, a non-aqueous electrolyte secondary battery is a secondary battery (electricity storage device) in which an organic solvent or other non-aqueous electrolyte is used as the electrolyte. In addition to lithium-ion secondary batteries, it also includes sodium-ion secondary batteries, potassium-ion secondary batteries, magnesium-ion secondary batteries, calcium-ion secondary batteries, etc. Moreover, the so-called lithium-ion secondary battery refers to a secondary battery with a non-aqueous electrolyte that is not mainly composed of water, and is a battery containing lithium ions in a carrier responsible for conductivity. For example, lithium-ion secondary batteries, metal lithium batteries, lithium polymer batteries, all-solid-state lithium batteries, air lithium-ion batteries, etc. meet the requirements. Moreover, other secondary batteries are also the same. Here, the so-called non-aqueous electrolyte that is not mainly composed of water refers to an electrolyte in which the main component is not water. That is, it is a well-known electrolyte used in non-aqueous electrolyte secondary batteries. Even if this electrolyte contains a small amount of water, it can still function as a secondary battery. However, since it will have an adverse effect on the cycle characteristics, storage characteristics, and input-output characteristics of the secondary battery, it is ideal to use an electrolyte that is as free of water as possible. In reality, the water content in the electrolyte is preferably below 5000ppm.

[0110] <Second embodiment>

[0111] [positive electrode]

[0112] Hereinafter, as yet another embodiment of the present invention, a description will be given in detail with reference to the accompanying drawings of a positive electrode that constitutes a non-aqueous electrolyte secondary battery together with the negative electrode of the first embodiment, and in which a buffer layer is provided in the region of the positive electrode that is opposite to the negative electrode and is more easily deformed by external force than other regions of the positive electrode (hereinafter also referred to as a second embodiment).

[0113] [Buffer layer]

[0114] Figure 3 Schematically depicts the structure of a non-aqueous electrolyte secondary battery of the second embodiment. The positive electrode 2 of the non-aqueous electrolyte secondary battery has a buffer layer 27 in the area opposite to the negative electrode 1, which is more easily deformed by external force than other areas of the positive electrode. For example, by applying this embodiment to a lithium-ion secondary battery, a lithium-ion secondary battery can be provided that can suppress durable degradation and improve energy density. The buffer layer can further be used to suppress or absorb unexpected deformation of the negative electrode and positional displacement with the positive electrode, thereby further suppressing the functional degradation of the non-aqueous electrolyte secondary battery monomer. The following will be described in detail, but various additions, changes or deletions can be made without departing from the scope of the present invention.

[0115] The buffer layer 27 has the property of being compressed following the expansion of the negative electrode 1 and returning to its original shape due to the contraction of the negative electrode 1 .

[0116] The buffer layer preferably comprises at least one of a carbon-based material and an organic conductive polymer. When a carbon-based material is used in the buffer layer, a material with a high bulk density, such as conductive furnace carbon, is preferred. When an organic conductive polymer is used in the buffer layer, an elastomer or resin with lithium conductivity is preferred.

[0117] From the perspective of not reducing the energy density of the non-aqueous electrolyte secondary battery, the thickness of the buffer layer is preferably 10 μm or less, and more preferably 5 μm.

[0118] [Method for Manufacturing a Positive Electrode Having a Buffer Layer]

[0119] The second embodiment of the method for manufacturing a positive electrode for a lithium-ion secondary battery comprises the following steps: applying a mixture comprising at least one of a carbon-based material and an organic conductive polymer to the positive electrode obtained by the steps described in the first embodiment and drying the mixture, thereby providing a buffer layer on the positive electrode. For example, the buffer layer can be provided on the positive electrode layer by applying a slurry comprising at least one of a carbon-based material and an organic conductive polymer to the positive electrode layer and drying the mixture.

[0120] [Effect]

[0121] According to the second embodiment of the present invention, the following effects are achieved.

[0122] In this embodiment, the nonaqueous electrolyte secondary battery is configured such that, in addition to the negative electrode of the first embodiment, a buffer layer 27 is provided on the positive electrode in a region of the positive electrode 2 facing the negative electrode, which is more easily deformed than other regions of the positive electrode.

[0123] By having a buffer layer 27 in the area of the positive electrode 2 that is opposite to the negative electrode, which is more easily deformed than other areas of the positive electrode, in addition to the unexpected deformation and positional displacement of the negative electrode from the inner side of the surface direction to the outer side of the surface direction of the negative electrode during charging and discharging, the expansion and contraction of the negative electrode generated from the negative electrode toward the positive electrode can also be followed, thereby further suppressing or absorbing the unexpected deformation and positional displacement of the negative electrode.

[0124] Therefore, by including a buffer layer 27 in the region of the positive electrode 2 facing the negative electrode, which is more easily deformed than other regions of the positive electrode, even though the negative electrode uses a negative electrode active material 13 composed of a high-capacity silicon-based material with a significant expansion and contraction rate, during full charge and discharge cycles with an SOC of 0 to 100, unexpected deformation and positional shift of the negative electrode, in addition to any shift occurring from the inside to the outside of the negative electrode's surface, can be effectively suppressed or absorbed, thereby maintaining the negative electrode structure. Furthermore, this further suppresses the risk of detachment and conductive path breakage caused by increased capacity and high weight per unit area due to thicker negative electrodes, thereby achieving high cyclability and even higher energy density.

[0125] <Third embodiment>

[0126] As a further embodiment of the non-aqueous electrolyte secondary battery of the present invention, a non-deformable layer is provided in the region of the negative electrode facing the positive electrode, which is less susceptible to deformation due to external forces than other regions of the negative electrode (hereinafter also referred to as the third embodiment), which will be described in detail with reference to the accompanying drawings.

[0127] [Non-deformation layer]

[0128] Figure 4It is a cross-sectional view schematically illustrating the structure of a non-aqueous electrolyte secondary battery of the third embodiment. In addition to the structure of the first embodiment, the negative electrode 1 of the non-aqueous electrolyte secondary battery of this embodiment has a non-deformation layer 19 in the area of the negative electrode 1 facing the positive electrode, which is less likely to be deformed by external force than other areas of the negative electrode. Furthermore, in this embodiment, the above-mentioned buffer layer 27 can also be provided on the positive electrode. For example, by applying this embodiment to a lithium-ion secondary battery, a lithium-ion secondary battery can be provided, which can suppress durable degradation, improve energy density, further suppress accidental deformation of the negative electrode and positional displacement with the positive electrode, and further suppress the functional decline of the non-aqueous electrolyte secondary battery monomer. Below, an example of applying this embodiment to a lithium-ion secondary battery is also described in detail, and various additions, changes or deletions can be made without departing from the scope of the main purpose of the present invention.

[0129] Electrode active materials that do not expand or contract with charge and discharge, or that expand and contract only slightly, can be used in the non-deformable layer 19. Examples of such electrode active materials include carbon-based materials and lithium titanate (LTO). When using a carbon-based material, hard carbon is preferably used.

[0130] The coating amount of the non-deformable layer can be set within a range that does not affect the energy density of the non-aqueous electrolyte secondary battery, and is preferably 7 mg / cm 2 A more preferred coating amount of the non-deformable layer is 2.5 mg / cm 2 .

[0131] Furthermore, from the viewpoint of energy density, the thickness of the non-deformable layer is preferably 15 μm or less, and more preferably 10 μm or less.

[0132] In addition, regarding other structures of the negative electrode in this embodiment, the structure of the first embodiment can be preferably used.

[0133] [Method for Manufacturing Negative Electrode Having Non-Deformable Layer]

[0134] The method for manufacturing the negative electrode of a lithium-ion secondary battery of the third embodiment has a third step, wherein the third step is to further provide a non-deformable layer on the negative electrode formed in the second step of the first embodiment. For example, a non-deformable layer can be provided on the negative electrode layer by applying a slurry containing an electrode active material that does not expand or contracts or expands and contracts little due to charge and discharge to the negative electrode layer and drying it. In addition to the above-mentioned slurry coating, for example, methods can also be listed: using a chemical plating method or sputtering method, a vapor deposition method, a gas deposition method, an immersion method, etc., to form an electrode active material layer on the negative electrode layer with the above-mentioned electrode active material (precursor) that does not expand or contracts or expands and contracts little, and a method of integrating the negative electrode layer with the non-deformable layer.

[0135] [Effect]

[0136] According to the third embodiment, the following effects are achieved.

[0137] In the third embodiment, in addition to the negative electrode structure of the first embodiment, the nonaqueous electrolyte secondary battery has a non-deformable layer 19 in the region of the negative electrode 1 facing the positive electrode, which is less likely to deform due to external force than other regions of the negative electrode.

[0138] By providing a non-deformable layer 19 in the area of the negative electrode 1 that is less susceptible to deformation due to external forces than other areas of the negative electrode, in addition to unexpected deformation and positional shifts of the negative electrode from the inside of the surface direction of the negative electrode to the outside of the surface direction during expansion and contraction, unexpected deformation and positional shifts of the negative electrode from the inside of the surface direction of the negative electrode toward the non-deformable layer can also be suppressed.

[0139] Therefore, by including a non-deformable layer 19 in the region of the negative electrode 1 facing the positive electrode, which is less susceptible to deformation due to external forces than other regions of the negative electrode, even though the negative electrode uses a negative electrode active material 13 composed of a high-capacity silicon-based material with a significant expansion and contraction coefficient, during full charge and discharge cycles with an SOC of 0 to 100, unintended deformation and positional shift of the negative electrode from the inside of the negative electrode's surface toward the non-deformable layer are suppressed, maintaining the negative electrode structure. Furthermore, the potential for shedding and conductive path breakage associated with increased capacity and high weight per unit area due to thicker negative electrodes is further suppressed, enabling high cyclability and achieving a more substantial energy density.

[0140] Furthermore, according to the embodiment in which the positive electrode is provided with the buffer layer 27 in addition to the structure having the non-deformation layer 19, the following effects are obtained.

[0141] By providing a buffer layer 27 that is more easily deformed than other areas of the positive electrode in the area of the positive electrode 2 facing the negative electrode, and providing a non-deformable layer 19 that is less likely to deform due to external forces than other areas of the negative electrode in the area of the negative electrode 1 facing the positive electrode, the expansion and contraction of the negative electrode during charging and discharging from the inside of the surface of the negative electrode toward the outside of the surface, toward the positive electrode, and toward the non-deformable layer can be followed, thereby further suppressing or absorbing unexpected deformation and positional displacement of the negative electrode.

[0142] Therefore, by including a buffer layer 27, which is more easily deformed than other areas of the positive electrode, in the region of the positive electrode 2 facing the negative electrode, and a non-deformable layer 19, which is less susceptible to deformation due to external forces than other areas of the negative electrode, in the region of the negative electrode 1 facing the positive electrode, the negative electrode active material 13, composed of a high-capacity silicon-based material with a significant expansion and contraction coefficient, can further suppress or absorb unintended deformation and positional shift of the negative electrode from the inward direction of the negative electrode toward the outward direction, toward the positive electrode, and toward the non-deformable layer, respectively, during full charge and discharge cycles with an SOC of 0 to 100, thereby maintaining the negative electrode structure. Furthermore, the occurrence of dropout and conductive path breakage caused by increased capacity and high weight per unit area due to thicker negative electrode films can be further suppressed, thereby achieving high cyclability and even higher energy density.

[0143] [Example]

[0144] Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[0145] <Example 1>

[0146] [Production of negative electrode]

[0147] A slurry containing silicon (average particle size 1 μm to 10 μm) as the negative electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder was prepared. The prepared slurry was then filled into a "Nickel Celmet" (registered trademark) manufactured by Sumitomo Electric Industries, Ltd., as a current collector and dried to obtain a negative electrode layer precursor.

[0148] Separately, a 10% by mass aqueous solution of Na2O·3SiO2 was prepared as a skeleton-forming agent solution containing a skeleton-forming agent and water. The negative electrode layer precursor obtained above was immersed in the prepared skeleton-forming agent solution. After immersion, the negative electrode precursor was heated at 160°C and dried to obtain a negative electrode having a negative electrode layer formed thereon (first step).

[0149] Next, the negative electrode obtained in the first step was masked on both its front and back surfaces with chemical-resistant tape, leaving a margin of 10% of its vertical and horizontal width. The negative electrode was immersed in a 10% by mass aqueous solution of Na₂O·3SiO₂, heated at 160°C, and dried, yielding the first-form negative electrode (second step).

[0150] [Production of positive electrode]

[0151] As the positive electrode active material, prepare LiNi 0.5Co 0.2 Mn 0.3 O2 (particle size 5μm to 15μm). 94% by mass of positive electrode active material, 4% by mass of carbon black as a conductive additive, and 2% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and the obtained mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidinone (NMP) to prepare a positive electrode composite material slurry. As a current collector, a thickness of 1.0mm, a porosity of 95%, a pore (cell) number of 46 / inch to 50 / inch, a pore diameter of 0.5mm, and a specific surface area of 5000m 2 / m 3 The prepared positive electrode composite material slurry was pressed into the surface of the substrate with a coating amount of 90 mg / cm 2 The mixture was dried at 120° C. for 12 hours in a vacuum and then roll-pressed at a pressure of 15 tons to produce a positive electrode for a lithium ion secondary battery in which the pores of the aluminum foam were filled with the electrode composite material.

[0152] [Manufacturing of lithium-ion secondary batteries]

[0153] As a separator, a 25 μm-thick microporous membrane of a three-layer laminate of polypropylene / polyethylene / polypropylene was prepared and punched into a size of 100 mm long by 90 mm wide. The lithium-ion secondary battery positive electrode and lithium-ion secondary battery negative electrode obtained above were stacked in the order of positive electrode / separator / negative electrode / separator / positive electrode / negative electrode to produce an electrode stack.

[0154] Afterwards, the tab leads were attached to the current collecting areas of each electrode using ultrasonic welding. The aluminum laminate for the secondary battery was heat-sealed and processed into a bag shape, and the electrode stack with the tab leads welded to it was inserted into the bag to create a laminated unit. As an electrolyte, a solution of 1.2 mol of LiPF6 dissolved in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 3:4:3 was prepared. This solution was then injected into the laminated unit to create a lithium-ion secondary battery.

[0155] Comparative Example 1

[0156] The negative electrode was prepared in the same manner as in Example 1 except that no skeleton-forming agent was used.

[0157] Comparative Example 2

[0158] The negative electrode was produced in the same manner as in Example 1 except that the second step was not performed.

[0159] <Example 2>

[0160] [Production of negative electrode]

[0161] The same method as in Example 1 was carried out to produce the product.

[0162] [Production of positive electrode]

[0163] As the positive electrode active material, prepare LiNi 0.5 Co 0.2 Mn 0.3 O2 (particle size 5μm to 15μm). 94% by mass of positive electrode active material, 4% by mass of carbon black as a conductive additive, and 2% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and the obtained mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material slurry. As a current collector, a thickness of 1.0mm, a porosity of 95%, a pore (cell) number of 46 / inch to 50 / inch, a pore diameter of 0.5mm, and a specific surface area of 5000m 2 / m 3 The prepared positive electrode composite material slurry was pressed into the surface of the substrate with a coating amount of 90 mg / cm 2 The positive electrode layer was prepared by applying a furnace black solution of 20% by mass to the surface of the positive electrode layer by blade coating. The positive electrode layer was dried at 120°C for 1 hour. The surface was dried at 120°C in a vacuum for 1 hour. The positive electrode was then rolled at a pressure of 15 tons to prepare a positive electrode for a lithium-ion secondary battery having a buffer layer. The thickness of the positive electrode layer was 350 μm, and the buffer layer was 5 μm.

[0164] [Manufacturing of lithium-ion secondary batteries]

[0165] The same method as in Example 1 was carried out to produce the product.

[0166] <Example 3>

[0167] [Production of negative electrode]

[0168] A slurry containing silicon (average particle size 1 μm to 10 μm) as the negative electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder was prepared. The prepared slurry was then filled into a "Nickel Celmet" (registered trademark) manufactured by Sumitomo Electric Industries, Ltd., as a current collector and dried to obtain a negative electrode layer precursor.

[0169] Separately, a 10% by mass aqueous solution of Na2O·3SiO2 was prepared as a skeleton-forming agent solution containing a skeleton-forming agent and water. The negative electrode layer precursor obtained above was immersed in the prepared skeleton-forming agent solution. After immersion, the negative electrode precursor was heated at 160°C and dried to obtain a negative electrode having a negative electrode layer formed thereon (first step).

[0170] Next, the negative electrode obtained in the first step was masked on both its front and back surfaces with chemical-resistant tape, leaving a margin of 10% of its vertical and horizontal width. The negative electrode was immersed in a 10% by mass aqueous solution of Na₂O·3SiO₂, heated at 160°C, and dried, yielding the first-form negative electrode (second step).

[0171] Hard carbon was used as the active material for the non-deformation layer. 96% by mass of hard carbon and 4% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and the resulting mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a hard carbon slurry. Next, the hard carbon slurry was applied to one side of the negative electrode using a doctor blade. Drying was performed at 120°C in a vacuum for 1 hour. Subsequently, roller pressing was performed at a pressure of 1 ton to prepare a negative electrode for a lithium-ion secondary battery having a non-deformation layer. The thickness of the positive electrode layer prepared was 500 μm, and the buffer layer was 10 μm.

[0172] [Manufacturing of lithium-ion secondary batteries]

[0173] The same method as in Example 1 was carried out to produce the product.

[0174] <Evaluation>

[0175] [Durability test]

[0176] The lithium ion secondary batteries of the examples and comparative examples were subjected to a cycle life test at a test environment temperature of 25° C., a current density of 0.2 C-rate, and a cutoff potential of 2.5 V to 4.2 V.

[0177] Figure 6 : It is a graph showing the relationship between the number of cycles and the capacity retention rate of each embodiment and comparative example. The capacity retention rate is calculated as the ratio of the discharge capacity after each cycle test relative to the initial value of the discharge capacity (mAh / g). The following results can be seen, namely: the lithium ion secondary battery of the embodiment has a suppressed decrease in the capacity retention rate compared with the lithium ion secondary battery of the comparative example. Therefore, it is confirmed that a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery having the same can be obtained, and the negative electrode for the non-aqueous electrolyte secondary battery can suppress durable degradation and improve energy density.

[0178] Reference numerals

[0179] 1: Negative electrode

[0180] 2: Positive electrode

[0181] 3: Non-aqueous electrolyte secondary battery

[0182] 4: Diaphragm

[0183] 5: Exterior body

[0184] 11, 21: Current collector

[0185] 12: Anode material

[0186] 22: Positive electrode materials

[0187] 13: Negative electrode active material

[0188] 23: Positive electrode active material

[0189] 14, 24: skeleton forming agent

[0190] 15, 25: Conductive additives

[0191] 16, 26: Adhesive

[0192] 17: Outer side of the negative electrode

[0193] 18: Inner side of the negative electrode

[0194] 19: Non-deformable layer (active material layer)

[0195] 27: Buffer layer

Claims

1. A non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode, The negative electrode comprises a current collector composed of a porous metal body and a negative electrode material arranged in the pores of the porous metal body. The negative electrode material comprises a negative electrode active material composed of a silicon-based material, a skeleton forming agent comprising an alkali metal silicate having a siloxane bond, a conductive auxiliary agent, and a binder. The content of the skeleton-forming agent on the outside of the surface direction of the negative electrode is greater than the content of the skeleton-forming agent on the inside of the surface direction of the negative electrode, the outside of the surface direction is the area from the outer periphery of the negative electrode to the inside of the electrode to 10% of the length of the longitudinal and transverse widths of the electrode, and the inside of the surface direction is the area other than the outside of the surface direction. in, The positive electrode has a buffer layer in a region facing the negative electrode that is more easily deformed by external force than other regions of the positive electrode. The buffer layer includes at least one of a carbon-based material and an organic conductive polymer.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The negative electrode includes a non-deformable layer in a region opposite to the positive electrode, which is less likely to be deformed by an external force than other regions of the negative electrode.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein The non-deformable layer is an active material layer containing at least one of a carbon-based material and lithium titanate.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein The skeleton-forming agent comprises an alkali metal silicate represented by the following formula (1): A2O·nSiO2 formula (1) In the above formula (1), A represents an alkali metal, and n represents 1.6 or more and 3.9 or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein The porous metal body is a foamed metal body.

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