Negative electrode layer

Abstract

To provide a negative electrode layer capable of implementing a satisfactory charging / discharging cycle characteristic of a solid-state battery.SOLUTION: There is provided a negative electrode layer for a solid-state battery. The negative electrode layer contains a negative electrode active material, a binding agent, a carbon fiber, and a ceramic fiber. 1.7 to 4.1 vol.% of the ceramic fiber is contained in the negative electrode layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode layer.

Background Art

[0002] With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones in recent years, the development of batteries used as their power sources has been emphasized. Also, in the automotive industry and the like, the development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles has been underway. In addition, solid-state batteries are attracting attention in that a solid electrolyte is used instead of an electrolytic solution containing an organic solvent as the electrolyte interposed between the positive electrode and the negative electrode.

[0003] Patent Document 1 discloses an all-solid-state battery including a fibrous carbon material having a carbon six-membered ring as a conductive material of the negative electrode.

[0004] Patent Document 2 discloses that carbon fiber is used as a conductive material of the positive electrode of an all-solid-state battery.

[0005] Patent Document 3 discloses that VGCF (vapor-grown carbon fiber) is used as a conductive aid as a conductive material of the positive electrode of an all-solid-state battery.

[0006] Patent Document 4 discloses that fine fibrous carbon and fibrous carbon having a diameter of 100 nm or more are used in combination.

[0007] Patent Document 5 discloses that carbon fiber and particulate carbon are used in combination.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] Conventional solid-state batteries containing carbon fibers have a problem of poor charge-discharge cycle characteristics.

[0010] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a negative electrode layer capable of improving the charge-discharge cycle characteristics of a solid-state battery.

Means for Solving the Problems

[0011] The negative electrode layer of the present disclosure is a negative electrode layer for a solid-state battery, The negative electrode layer includes a negative electrode active material, a binder, carbon fibers, and ceramic fibers, The ceramic fibers are characterized in that they are contained in the negative electrode layer in an amount of 1.7 to 4.1% by volume.

Effects of the Invention

[0012] The negative electrode layer for the solid-state battery of the present disclosure can improve the charge-discharge cycle characteristics of the solid-state battery.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0014] The negative electrode layer of the present disclosure is a negative electrode layer for a solid battery, and the negative electrode layer includes a negative electrode active material, a binder, carbon fibers, and ceramic fibers, and the ceramic fibers are characterized by being contained in the negative electrode layer in an amount of 1.7 to 4.1% by volume.

[0015] In the case of a solid battery using an active material such as Si-based or C-based that expands and contracts during charge and discharge for the negative electrode layer, peeling occurs at the interface between the negative electrode active material and the solid electrolyte due to the expansion and contraction of the negative electrode active material during charge and discharge, resulting in an increase in the internal resistance of the solid battery and a decrease in the capacity retention rate. In a conventional solid battery using carbon fibers, peeling at the interface between the negative electrode active material and the solid electrolyte cannot be suppressed. Since carbon fibers have high flexibility and cannot exhibit sufficient strength as fibers, it is considered that the ion conduction path and the electron conduction path of the negative electrode are interrupted due to the expansion and contraction of the negative electrode active material. The present researcher found that by adding ceramic fibers with low flexibility to the negative electrode layer, being arranged linearly in the negative electrode layer compared to carbon fibers, and increasing the immobilization by the binder, it is difficult for interface peeling to occur due to the expansion and contraction accompanying charge and discharge of the negative electrode active material, and the discharge capacity retention rate is improved. In addition, the present researcher found that when fine ceramic fibers are added, the increase in resistance is small in the region where the addition amount is small, and there is a region where the discharge capacity retention rate is improved. Usually, when a ceramic filler or the like is added into the electrode, the electron conduction path in the electrode is inhibited, and the resistance increases in a proportional relationship according to the addition amount. However, if a small amount of fine ceramic fibers are used, the electron conduction path by carbon fibers is not inhibited, and the binder strength is improved. Also, when the addition amount of the ceramic fibers is too large, the electron conduction path and the ion conduction path in the electrode are inhibited, a uniform charge and discharge reaction cannot occur in the electrode, local expansion and contraction occur, the negative electrode active material and the solid electrolyte are peeled off, and the discharge capacity retention rate is greatly reduced. Therefore, an appropriate addition amount is important.

[0016] In the present disclosure, unless otherwise specified, the average particle size of the particles is the value of the volume-based median diameter (D50) measured by laser diffraction / scattering particle size distribution measurement. Further, in the present disclosure, the median diameter (D50) is the diameter (volume average diameter) at which the cumulative volume of the particles becomes half (50%) of the total volume when the particles are arranged in order of increasing particle size.

[0017] FIG. 1 is a schematic cross-sectional view showing an example of the negative electrode layer of the present disclosure. As shown in FIG. 1, the negative electrode layer 100 includes a negative electrode active material 11, a binder 12, a solid electrolyte 13, carbon fibers 14, and ceramic fibers 15. The ceramic fibers 15 are present in the binder 12 existing between the particles of the negative electrode active material 11 and the solid electrolyte 13.

[0018] [Negative electrode layer] The negative electrode layer of the present disclosure includes at least a negative electrode active material, a binder, carbon fibers, and ceramic fibers, and may contain a solid electrolyte or the like as necessary. The thickness of the negative electrode layer is not particularly limited, and may be, for example, 10 to 100 μm.

[0019] Examples of the negative electrode active material include graphite, mesocarbon microbeads (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, soft carbon, lithium alloy, Si single crystal, Si alloy, and Li4Ti5O 12 and the like. As the lithium alloy and the Si alloy, the same ones as those exemplified for the positive electrode active material can be used. The shape of the negative electrode active material is not particularly limited, and examples include particulate and plate-like shapes. When the negative electrode active material is particulate, it may be primary particles or secondary particles. The content of the negative electrode active material in the negative electrode layer is not particularly limited, and may be, for example, 20% by mass to 90% by mass.

[0020] Examples of the binder include acrylonitrile butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), etc. The content of the binder in the negative electrode layer is not particularly limited, and may be 1 to 5% by mass.

[0021] The carbon fiber may be any one or a mixture of two or more selected from the group consisting of vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and carbon nanofiber (CNF). The wire length of the carbon fiber is not particularly limited, but may be longer than the wire length of the ceramic fiber. The content of the carbon fiber in the negative electrode layer is not particularly limited, and may be 1.0 to 20.0% by mass. The volume ratio of the carbon fiber in the negative electrode layer is not particularly limited, and may be 1.0 to 20.0% by volume.

[0022] The ceramic fiber may be a substance with lower flexibility compared to the carbon fiber and low reactivity that does not deteriorate other battery components. The wire length of the ceramic fiber is not particularly limited, and may be 200 nm or more, may be 400 nm or more, and may be shorter than the wire length of the carbon fiber. The wire diameter of the ceramic fiber is not particularly limited, and may be 1 to 10 nm, or may be 2 to 6 nm. From the perspective of strengthening the negative electrode layer, the ceramic fibers in the negative electrode layer need to be arranged linearly. Since the probability of bending increases as the fiber becomes longer, from the perspective of arranging the ceramic fiber more linearly than the carbon fiber, the ceramic fiber may be a fiber shorter and less flexible than the carbon fiber. The ceramic fiber may be any one or a mixture of two or more selected from the group consisting of oxides, carbides, nitrides, and borides, or may be fibrous aluminum oxide. The ceramic fiber may have an aspect ratio (fiber length / diameter) of 100 or more with respect to the wire diameter. The ceramic fiber may be present in a binder existing between particles of the negative electrode active material and the solid electrolyte. From the viewpoint of making the ceramic fiber present in the binder, the wire diameter may be sufficiently thinner than that of the negative electrode active material and the solid electrolyte, and the aspect ratio (fiber length / diameter) with respect to the wire diameter may be 100 or more. The ceramic fiber may be contained in the negative electrode layer in a volume ratio of 0.24 or more and 0.59 or less with respect to the carbon fiber. The content of the ceramic fiber in the negative electrode layer is not particularly limited, and may be 1.0 to 5.5% by mass, or may be 1.9 to 4.8% by mass. The ceramic fiber may be contained in the negative electrode layer in an amount of 1.7 to 4.1% by volume.

[0023] As the solid electrolyte to be contained in the negative electrode layer, known solid electrolytes usable in a solid battery can be appropriately used, and examples thereof include oxide-based solid electrolytes and sulfide-based solid electrolytes. Examples of the sulfide-based solid electrolyte include Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4. The description of "Li2S-P2S5" means a material obtained by using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions. Further, "X" in the above LiX represents a halogen element. LiX may be contained in the raw material composition containing LiX in one kind or two or more kinds. When two or more kinds of LiX are contained, the mixing ratio of the two or more kinds is not particularly limited. The molar ratio of each element in the sulfide-based solid electrolyte can be controlled by adjusting the content of each element in the raw material. Further, the molar ratio and composition of each element in the sulfide-based solid electrolyte can be measured, for example, by ICP emission spectrometry.

[0024] The sulfide-based solid electrolyte may be a sulfide glass, a crystallized sulfide glass (glass-ceramics), or a crystalline material obtained by a solid-phase reaction treatment of a raw material composition. The crystalline state of the sulfide-based solid electrolyte can be confirmed, for example, by performing powder X-ray diffraction measurement using CuKα rays on the sulfide-based solid electrolyte.

[0025] The sulfide glass can be obtained by subjecting a raw material composition (for example, a mixture of Li2S and P2S5) to an amorphous treatment. Examples of the amorphous treatment include mechanical milling.

[0026] The glass-ceramics can be obtained, for example, by heat-treating a sulfide glass. The heat treatment temperature may be higher than the crystallization temperature (Tc) observed by thermal analysis measurement of the sulfide glass, and is usually 195°C or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited. The crystallization temperature (Tc) of the sulfide glass can be measured by differential thermal analysis (DTA). The heat treatment time is not particularly limited as long as the desired crystallinity of the glass-ceramics is obtained, but is, for example, in the range of 1 minute to 24 hours, and among them, the range of 1 minute to 10 hours can be mentioned. The method of heat treatment is not particularly limited, and examples thereof include a method using a firing furnace.

[0027] Examples of the oxide-based solid electrolyte include substances having a garnet-type crystal structure containing an Li element, a La element, an A element (A is at least one of Zr, Nb, Ta, and Al), and an O element. Examples of the oxide-based solid electrolyte include Li 3+x PO 4-x N x (1 ≦ x ≦ 3) or the like may also be used.

[0028] From the viewpoint of good handleability, the shape of the solid electrolyte may be particulate. The solid electrolyte can be used alone or in combination of two or more. When using two or more solid electrolytes, they may be mixed. The proportion of the solid electrolyte in the negative electrode layer is not particularly limited, but when the total mass of the negative electrode layer is 100% by mass, it may be, for example, in the range of 1% to 80% by mass.

[0029] The method for manufacturing the negative electrode layer is as follows, for example. Particles of the negative electrode active material, particles of the solid electrolyte, carbon fiber, ceramic fiber, and binder are mixed with an organic solvent (dispersion medium) such as N-methylpyrrolidone to form a slurry (or paste). The slurry (or paste) for the negative electrode layer is applied onto one surface of a support such as a current collector, and the negative electrode layer is formed on the support by drying the slurry for the negative electrode layer. The method for applying the slurry for the negative electrode layer is not particularly limited, and examples include the doctor blade method, the metal mask printing method, the electrostatic coating method, the dip coating method, the spray coating method, the roll coating method, the gravure coating method, and the screen printing method. As the support, one having self-supporting properties can be appropriately selected and used, and there is no particular limitation. For example, metal foils such as Cu and Al can be used.

[0030] The negative electrode layer of the present disclosure is for a solid battery. The solid battery may include a positive electrode including a positive electrode layer, a solid electrolyte layer, and a negative electrode including a negative electrode layer.

[0031] [Positive electrode] The positive electrode includes a positive electrode layer and, if necessary, a positive electrode current collector.

[0032] [Positive electrode layer] The positive electrode layer includes a positive electrode active material, and may include, as optional components, a solid electrolyte, a conductive material, a binder, and the like.

[0033] There is no particular limitation on the type of the positive electrode active material, and any material that can be used as the active material of the solid battery can be adopted. The positive electrode active material is, for example, metallic lithium (Li), a lithium alloy, LiCoO2, LiNi 0.8 Co0.15 Al 0.05 O2, LiNi x Co 1-x O2(0 < x < 1), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, hetero-element substituted Li-Mn spinel, lithium titanate, metal lithium phosphate, LiCoN, Li2SiO3, and Li4SiO4, transition metal oxides, TiS2, Si, SiO2, Si alloys, and lithium storage intermetallic compounds, etc. can be mentioned. Hetero-element substituted Li-Mn spinel is, for example, LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4, and LiMn 1.5 Zn 0.5 O4, etc. Lithium titanate is, for example, Li4Ti5O 12 etc. Metal lithium phosphate is, for example, LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, etc. Transition metal oxides are, for example, V2O5, and MoO3, etc. Lithium storage intermetallic compounds are, for example, Mg2Sn, Mg2Ge, Mg2Sb, and Cu3Sb, etc. Examples of lithium alloys include Li-Au, Li-Mg, Li-Sn, Li-Si, Li-Al, Li-B, Li-C, Li-Ca, Li-Ga, Li-Ge, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-In, Li-Sb, Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, and Li-At, etc. Examples of Si alloys include alloys with metals such as Li, etc., and may also be alloys with at least one metal selected from the group consisting of Sn, Ge, and Al. The shape of the positive electrode active material is not particularly limited, and it may be particulate. When the positive electrode active material is particulate, the positive electrode active material may be primary particles or secondary particles. A coating layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material. This is because it can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of the Li ion conductive oxide include LiNbO3, Li4Ti5O 12 , and Li3PO4, etc. The thickness of the coating layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coating layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage rate of the coating layer on the surface of the positive electrode active material is, for example, 70% or more, and may be 90% or more.

[0034] Examples of the solid electrolyte that can be exemplified are the same as those exemplified in the negative electrode layer. The content of the solid electrolyte in the positive electrode layer is not particularly limited, but when the total mass of the positive electrode layer is 100% by mass, it may be, for example, in the range of 1% to 80% by mass.

[0035] As the conductive material, known materials can be used, and examples include carbon materials and metal particles. Examples of the carbon material include at least one selected from the group consisting of acetylene black, furnace black, VGCF, carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, it may be at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers. Examples of the metal particles include particles such as Ni, Cu, Fe, and SUS. The content of the conductive material in the positive electrode layer is not particularly limited.

[0036] Examples of the binder that can be exemplified are the same as those exemplified in the negative electrode layer.

[0037] The thickness of the positive electrode layer is not particularly limited.

[0038] The positive electrode layer can be formed by a conventionally known method. For example, a positive electrode active material and, if necessary, other components are put into a solvent and stirred to prepare a slurry for the positive electrode layer. The positive electrode layer is obtained by applying the slurry for the positive electrode layer onto one surface of a support such as a positive electrode current collector and drying it. Examples of the solvent include butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP). The method of applying the slurry for the positive electrode layer onto one surface of a support such as a positive electrode current collector is not particularly limited, and the same methods as those for applying the slurry for the negative electrode layer can be exemplified.

[0039] As another method for forming the positive electrode layer, the positive electrode layer may be formed by pressure-molding a powder of a positive electrode mixture containing a positive electrode active material and, if necessary, other components. When pressure-molding the powder of the positive electrode mixture, usually, a pressing pressure of about 1 MPa or more and 2000 MPa or less is applied. The pressing method is not particularly limited, and examples thereof include methods of applying pressure using a flat press, a roll press, etc.

[0040] [Positive Electrode Current Collector] As the positive electrode current collector, a known metal that can be used as a current collector of a solid battery can be used. Examples of such a metal include a metal material containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Examples of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The form of the positive electrode current collector is not particularly limited, and various forms such as foil shape and mesh shape can be adopted. The thickness of the positive electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or may be in the range of 5 μm to 20 μm.

[0041] [Negative Electrode] The negative electrode includes the negative electrode layer of the present disclosure and, optionally, a negative electrode current collector.

[0042] [Negative electrode current collector] The material of the negative electrode current collector may be a material that does not alloy with Li, and examples thereof include SUS, copper, nickel, etc. Examples of the form of the negative electrode current collector include foil shape, plate shape, etc. The planar shape of the negative electrode current collector is not particularly limited, and examples thereof include circular shape, elliptical shape, rectangular shape, any polygonal shape, etc. Also, the thickness of the negative electrode current collector varies depending on the shape, but may be, for example, within the range of 1 μm to 50 μm, or may be within the range of 5 μm to 20 μm.

[0043] [Solid electrolyte layer] The solid electrolyte layer includes at least a solid electrolyte. Examples of the solid electrolyte can be the same as those exemplified in the negative electrode layer. The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, 50% by mass or more, and may be within the range of 60% by mass or more and 100% by mass or less, may be within the range of 70% by mass or more and 100% by mass or less, or may be 100% by mass.

[0044] From the viewpoint of expressing plasticity, etc., the solid electrolyte layer can also contain a binder. Examples of such a binder can be the materials exemplified as the binder used in the negative electrode layer. However, from the viewpoint of facilitating high output and forming a solid electrolyte layer having a solid electrolyte that prevents excessive aggregation and is uniformly dispersed, the binder contained in the solid electrolyte layer may be 5% by mass or less.

[0045] The thickness of the solid electrolyte layer is not particularly limited and is usually 0.1 μm or more and 1 mm or less. As a method for forming the solid electrolyte layer, there may be mentioned a method of pressure-molding a powder of a solid electrolyte material containing a solid electrolyte. When pressure-molding the powder of the solid electrolyte material, usually, a press pressure of about 1 MPa or more and 2000 MPa or less is applied. The pressing method is not particularly limited, and examples thereof include the pressing methods exemplified in the formation of the positive electrode layer.

[0046] The solid battery may include, as necessary, an exterior body that houses a laminate including a positive electrode current collector, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector in this order, a restraining member, and the like. The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin. The restraining member only needs to be able to apply a restraining pressure in the stacking direction to the laminate, and a known restraining member that can be used as the restraining member of the solid battery can be used. For example, there may be mentioned a restraining member having a plate-like portion that sandwiches both surfaces of the laminate, a rod-like portion that connects the two plate-like portions, and an adjustment portion that is connected to the rod-like portion and adjusts the restraining pressure by a screw structure or the like. By the adjustment portion, a desired restraining pressure can be applied to the laminate. The restraining pressure is not particularly limited. For example, it may be 0.1 MPa or more, may be 1 MPa or more, or may be 5 MPa or more. This is because increasing the restraining pressure has the advantage of easily improving the contact between the layers. On the other hand, the restraining pressure may be, for example, 100 MPa or less, may be 50 MPa or less, or may be 20 MPa or less. This is because if the restraining pressure is too large, high rigidity is required for the restraining member, and the restraining member may be enlarged.

[0047] The solid battery may have only one of the above laminates, or may be formed by laminating a plurality of laminates. The solid battery may be a primary battery or a secondary battery, and among them, a secondary battery is also acceptable. The secondary battery can be repeatedly charged and discharged. The secondary battery is useful, for example, as a vehicle-mounted battery. Further, the solid battery may be a solid lithium secondary battery or a solid lithium ion secondary battery. Examples of the shape of the solid battery include a coin type, a laminate type, a cylindrical type, and a rectangular type. In the present disclosure, the solid battery may be any battery that uses a solid electrolyte instead of an electrolytic solution containing an organic solvent as the electrolyte of the electrolyte layer interposed between the positive electrode and the negative electrode, and may be an all-solid battery in which the positive electrode, the negative electrode, and the electrolyte layer are all composed of solid materials.

[0048] The method for manufacturing the solid battery of the present disclosure is, for example, first, forming a solid electrolyte layer by pressure molding a powder of a solid electrolyte material. Then, a positive electrode layer is obtained by pressure molding a powder of a positive electrode material containing a positive electrode active material on one surface of the solid electrolyte layer. Thereafter, a negative electrode layer is obtained by pressure molding a powder of a negative electrode material on one surface of a negative electrode current collector. A negative electrode current collector-negative electrode layer laminate is attached so that the negative electrode layer is in contact with the solid electrolyte layer on the surface of the solid electrolyte layer opposite to the surface on which the positive electrode layer is formed. Then, a positive electrode current collector is attached to the surface of the positive electrode layer opposite to the solid electrolyte layer. Thereby, it may be the solid battery of the present disclosure. In this case, the pressing pressure when pressure molding the powder of the negative electrode material, the powder of the solid electrolyte material, and the powder of the positive electrode material is usually about 1 MPa or more and 2000 MPa or less. The pressing method is not particularly limited, and examples thereof include the pressing methods exemplified in the formation of the positive electrode layer.

Examples

[0049] (Example 1) [Fabrication of Positive Electrode] A positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (average particle size: 10 μm), sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size: 0.5 μm), conductive material (VGCF-H), and binder (PVDF) were weighed so that the weight ratio of cathode active material: sulfide-based solid electrolyte: conductive material: binder = 85.4:12.7:1.3:0.6, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a slurry for the cathode layer. The obtained slurry for the cathode layer was coated on a cathode current collector (Al foil, thickness: 15 μm) by the blade coating method using an applicator and dried at 100 °C for 30 minutes. Then, it was punched into a size of 1 cm 2 to obtain a cathode having a cathode layer and a cathode current collector. [Fabrication of Anode] Anode active material (Si particles, average particle size: 2.5 μm), sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size: 0.5 μm), carbon fiber (VGCF-H), binder (SBR), and ceramic fiber (aluminum oxide manufactured by Sigma-Aldrich, product number: 551643) were weighed so that the weight ratio of anode active material: sulfide-based solid electrolyte: carbon fiber: binder: aluminum oxide = 45.7:43.3:6.4:1.4:2.7, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using a thin-film swirling high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the anode layer. The obtained slurry for the anode layer was coated on an anode current collector (Ni foil, thickness: 22 μm) by the blade coating method using an applicator and dried at 100 °C for 30 minutes. The gap of the applicator at this time was adjusted so that the weight of the anode active material per 1 cm 2 would result in a ratio of anode capacity / cathode capacity of 3 when the cathode active material capacity was 207 mAh / g and the anode active material capacity was 3579 mAh / g. Then, 1 cm 2By punching out to the size of , a negative electrode having a negative electrode layer and a negative electrode current collector was obtained. When the volume of the negative electrode layer was 100% by volume, the ceramic fiber was 2% by volume. In the negative electrode layer, the ceramic fiber was contained at a volume ratio of 0.28 with respect to the carbon fiber. [Fabrication of Solid Electrolyte Layer] A sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)(mol%), average particle size 2.0 μm) and a binder (SBR) were weighed so that the weight ratio of the sulfide solid electrolyte:binder = 99.6:0.4, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a slurry for the solid electrolyte layer. The obtained slurry for the solid electrolyte layer was coated on a support (Al foil, thickness 15 μm) by a blade coating method using an applicator, and dried at 100 °C for 30 minutes. Then, by punching out to the size of 1 cm 2 a solid electrolyte layer having an Al foil was obtained. [Fabrication of Solid State Battery] The obtained solid electrolyte layer was opposed to the positive electrode, and the solid electrolyte layer and the positive electrode layer were overlapped and pressed by a roll press method at a linear pressure of 1.6 t / cm. Then, the Al foil was peeled off from the solid electrolyte layer to transfer the solid electrolyte layer onto the positive electrode layer. The solid electrolyte layer transferred onto the positive electrode layer was opposed to the negative electrode, and the solid electrolyte layer and the negative electrode layer were overlapped and pressed by a uniaxial press at a surface pressure of 5.0 t / cm 2 After pressing, tabs for current collection were placed on the positive and negative electrode current collector foils, and laminated and sealed to obtain a solid state battery.

[0050] [Example 2] Negative electrode active material (Si particles, average particle size 2.5 μm), sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), carbon fiber (VGCF-H), binder (SBR), and ceramic fiber (aluminum oxide manufactured by Sigma-Aldrich, product number: 551643) were weighed in a weight ratio of negative electrode active material:sulfide-based solid electrolyte:carbon fiber:binder:aluminum oxide = 45.1:42.8:6.3:1.4:4.1 and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using a thin-film rotary high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the negative electrode layer. Other preparation methods were the same as in Example 1. The ceramic fiber was 3% by volume when the volume of the negative electrode layer was 100% by volume. In the negative electrode layer, the ceramic fiber was contained at a volume ratio of 0.42 with respect to the carbon fiber.

[0051] [Example 3] Negative electrode active material (Si particles, average particle size 2.5 μm), sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), carbon fiber (VGCF-H), binder (SBR), and ceramic fiber (aluminum oxide manufactured by Sigma-Aldrich, product number: 551643) were weighed in a weight ratio of negative electrode active material:sulfide-based solid electrolyte:carbon fiber:binder:aluminum oxide = 44.4:42.1:6.2:1.3:5.5 and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using a thin-film rotary high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the negative electrode layer. Other preparation methods were the same as in Example 1. The ceramic fiber was 4.1% by volume when the volume of the negative electrode layer was 100% by volume. In the negative electrode layer, the ceramic fiber was contained at a volume ratio of 0.59 with respect to the carbon fiber.

[0052] [Comparative Example 1] The negative electrode active material (Si particles, average particle diameter 2.5 μm), the sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)(mol%), average particle diameter 0.5 μm), carbon fiber (VGCF-H), and binder (SBR) were weighed so that the weight ratio of the negative electrode active material:sulfide-based solid electrolyte:carbon fiber:binder = 47.0:44.6:6.6:1.4, and mixed with a dispersion medium (diisobutyl ketone). That is, no ceramic fiber was added. The obtained mixture was dispersed using a thin-film swirling high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the negative electrode layer. Other production methods were the same as in Example 1.

[0053] [Example 4] The negative electrode active material (Si particles, average particle diameter 2.5 μm), the sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)(mol%), average particle diameter 0.5 μm), carbon fiber (VGCF-H), binder (SBR), and ceramic fiber (aluminum oxide manufactured by Sigma-Aldrich, product number: 551643) were weighed so that the weight ratio of the negative electrode active material:sulfide-based solid electrolyte:carbon fiber:binder:aluminum oxide = 45.9:43.5:6.4:1.4:2.3, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using a thin-film swirling high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the negative electrode layer. Other production methods were the same as in Example 1. When the volume of the negative electrode layer was 100% by volume, the ceramic fiber was 1.7% by volume. In the negative electrode layer, the ceramic fiber was contained at a volume ratio of 0.24 with respect to the carbon fiber.

[0054] [Comparative Example 2] Negative electrode active material (Si particles, average particle diameter 2.5 μm), sulfide-based solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)(mol%), average particle diameter 0.5 μm), carbon fiber (VGCF-H), binder (SBR) and ceramic fiber (aluminum oxide manufactured by Sigma-Aldrich, product number: 551643) were weighed in a weight ratio of negative electrode active material:sulfide-based solid electrolyte:carbon fiber:binder:aluminum oxide = 44.0:41.7:6.2:1.3:6.4 and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed using a thin-film swirling type high-speed mixer (Filmix 30-L type, manufactured by Primix Corporation) to obtain a slurry for the negative electrode layer. Other production methods were the same as in Example 1. The ceramic fiber was 4.7% by volume when the volume of the negative electrode layer was 100% by volume. In the negative electrode layer, the ceramic fiber was contained at a volume ratio of 0.68 with respect to the carbon fiber.

[0055] [Charge and discharge evaluation] The fabricated solid-state batteries of Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to constant current charging at 0.364 mAh up to 4.05 V in a thermostat at 25°C, then constant voltage charging at 4.05 V until the current value reached 0.036 mAh, constant current discharging at 0.364 mAh down to 2.5 V, and then constant voltage discharging at 2.5 V until the current value reached 0.036 mAh. This was repeated 3 times. For the cycle performance evaluation, constant current charging was performed at 3.64 mAh up to 4.05 V in a thermostat at 60°C, then constant voltage charging at 4.05 V until the current value reached 1.21 mAh, constant current discharging at 3.64 mAh down to 2.5 V, and then constant voltage discharging at 2.5 V until the current value reached 1.21 mAh. This was repeated 30 times, and the discharge capacity retention rate after 30 cycles was evaluated. The discharge capacity retention rate after 30 cycles was calculated from the following formula. The results are shown in Table 1. Also, the initial resistivity and the resistance increase rate after 30 cycles with respect to the addition of 0% by volume (vol%) of ceramic fiber were calculated. The results are shown in Figure 2. Discharge capacity retention rate after 30 cycles (%) = (Discharge capacity after 30 cycles / Discharge capacity at the first cycle) × 100

[0056]

Table 1

[0057] Figure 2 is a diagram showing the initial resistivity and the resistance increase rate after 30 cycles for 0% volume addition of ceramic fibers. As shown in Figure 2, compared with Comparative Example 1 without addition of ceramic fibers, the initial resistivity of Examples 1 to 4 and Comparative Example 2 increases, but the resistance increase rate after 30 cycles of Examples 1 to 4 decreases due to the addition of ceramic fibers. As shown in Table 1, the discharge capacity retention rate is improved by the addition of ceramic fibers in Examples 1 to 4 compared with Comparative Example 1 without addition of ceramic fibers. From this, it is considered that the difference in the discharge capacity retention rate will appear more significantly when the number of cycles is further increased. Therefore, it has been demonstrated that by using a negative electrode layer containing 1.7 to 4.1% by volume of ceramic fibers in a solid battery, the charge and discharge cycle characteristics of the solid battery can be improved.

Explanation of Reference Numerals

[0058] 11 Negative electrode active material 12 Binder 13 Solid electrolyte 14 Carbon fiber 15 Ceramic fiber 100 Negative electrode layer

Claims

【Claim 1】 A negative electrode layer for a solid battery, wherein the negative electrode layer contains a negative electrode active material, a binder, carbon fibers, and ceramic fibers, the ceramic fibers are contained in the negative electrode layer at 3 to 4.1% by volume, and the ceramic fibers are contained in the negative electrode layer at a volume ratio of 0.42 or more and 0.59 or less with respect to the carbon fibers, characterized by the negative electrode layer.

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