Battery manufacturing method and battery

Abstract

A battery manufacturing method according to the present disclosure includes: (A) performing charge / discharge processing for a power generation element provided with a positive electrode layer, a negative electrode layer, and an electrolyte layer positioned between the positive electrode layer and the negative electrode layer, in a state where the power generation element is restrained in the lamination direction; and (B) reducing a restraint pressure for the power generation element after the charge / discharge processing in (A). At least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer includes an electrode active material in which the volume expansion in the charge state is 2-14% of that in the discharge state.

Description

Battery manufacturing method and battery

[0001] The present disclosure relates to a method for manufacturing a battery and the battery.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as power sources for these devices has become increasingly important. In addition, the automotive industry is promoting the development of high-output, high-capacity batteries for electric vehicles and hybrid vehicles, and in particular, the development of lithium batteries with high energy density has been progressing.

[0003] As electrode active materials for such batteries, it is expected that materials with high theoretical capacity will be used. For example, in the case of the negative electrode, it is expected that materials with high theoretical capacity and high negative electrode potential, especially at the end of charging, which reduces the possibility of lithium deposition during charging, will be used as the negative electrode active material.

[0004] Furthermore, the use of flammable organic electrolyte in the battery simplifies safety devices and improves manufacturing costs and productivity. From this perspective, development is also underway to replace organic electrolyte with a solid electrolyte layer to create an all-solid-state battery.

[0005] As with liquid-based batteries using organic electrolytes, which have been developed and commercialized, the negative electrode active material for all-solid-state batteries is expected to provide a higher battery capacity. For example, in the case of negative electrodes, materials that provide a higher battery capacity and have a high negative electrode potential at the end of charging, which reduces the possibility of lithium precipitation during charging, are expected to be used as negative electrode active materials. In addition to carbon-based materials, oxide-based materials are also expected to be used as negative electrode active materials for all-solid-state batteries. However, many of the new materials expected to be used as electrode active materials expand and contract during charging and discharging. The expansion and contraction of such electrode active materials during charging and discharging can cause cracks in the solid electrolyte contained in the electrode, reducing battery performance.

[0006] As a battery capable of solving the above-described problems caused by the expansion and contraction of electrode active materials during charge and discharge, for example, Patent Document 1 discloses a battery including a restraining member that restrains a power generating element having a positive electrode, a negative electrode, and a solid electrolyte in the stacking direction in order to solve problems caused by the expansion and contraction of the positive electrode active material in particular.

[0007] Japanese Patent Application Laid-Open No. 2022-110345

[0008] The present disclosure aims to suppress cracks that occur in electrodes during charging and discharging, and thereby suppress a decrease in discharge capacity, in a battery that uses an electrode active material that expands and contracts during charging and discharging, using a method that is simpler than conventional methods.

[0009] The method for manufacturing an electrode according to the present disclosure includes: (A) performing a charge / discharge process on a power generating element including a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer, while the power generating element is constrained in a stacking direction; and (B) reducing the constraining pressure on the power generating element after the charge / discharge process in (A), wherein at least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer includes a negative electrode active material having a volume expansion rate upon charge / discharge of 2% or more and 14% or less.

[0010] According to the manufacturing method of the present disclosure, in a battery that uses an electrode active material that expands and contracts during charging and discharging, it is possible to suppress cracks that occur in the electrode during charging and discharging and to suppress a decrease in discharge capacity in a manner that is simpler than conventional methods.

[0011] Fig. 1 is a flowchart showing a method for manufacturing a battery according to embodiment 1. Fig. 2 is a cross-sectional view showing an example of a power generating element used in the method for manufacturing a battery according to embodiment 1. Fig. 3 is a schematic view showing an example of how the power generating element shown in Fig. 2 is constrained in the stacking direction. Fig. 4 is a cross-sectional view showing an example of a battery according to embodiment 2. Fig. 5 is a schematic view showing a cross section along the thickness direction of the negative electrode layer in the battery according to embodiment 2.

[0012] (Knowledge forming the basis of the present disclosure) The battery disclosed in Patent Document 1 listed in the [Background Art] section requires a restraining member for restraining the power generating element having the positive electrode, negative electrode, and solid electrolyte in the stacking direction in the completed battery in order to suppress the occurrence of cracks caused by expansion and contraction of the electrode active material, particularly the positive electrode active material, during charge and discharge.

[0013] Among the electrode active materials selected to achieve high capacity are some that exhibit large amounts of expansion and contraction during charge and discharge. Through intensive research, the present inventors have discovered that in electrodes containing such electrode active materials with large amounts of expansion and contraction, cracks that occur not only between the solid electrolyte but also between the electrode active material and the solid electrolyte are the main cause of a decrease in discharge capacity.

[0014] In view of the above circumstances, the present inventors have further conducted intensive research into a technology that can effectively suppress cracks that occur between the electrode active material and the solid electrolyte after charge and discharge, thereby suppressing a decrease in discharge capacity, in a battery that uses an electrode active material that expands and contracts during charge and discharge, in a manner that is simpler than conventional methods. As a result, the present inventors have arrived at the battery manufacturing method and battery described below in the present disclosure.

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0016] First Embodiment FIG. 1 is a flowchart showing a method for manufacturing a battery according to a first embodiment.

[0017] 1 , the method for manufacturing a battery according to the first embodiment includes: (A) performing a charge / discharge process on a power generating element including a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer while the power generating element is constrained in the stacking direction (S11); and (B) reducing the constraining pressure on the power generating element after the charge / discharge process in (A) (S12). At least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer includes an electrode active material having a volume expansion coefficient associated with charge / discharge of 2% to 14%.

[0018] In the manufacturing method according to the first embodiment, a power generating element having a positive electrode layer, an electrolyte layer, and a negative electrode layer arranged in this order is constrained in the stacking direction, and then a charge / discharge process is performed while the constraining pressure is reduced to complete the battery. Note that, in the present disclosure, "stacking direction" refers to the direction in which the positive electrode layer, the electrolyte layer, and the negative electrode layer are stacked. The manufacturing method according to the first embodiment does not require the completed battery to be continuously constrained as in conventional batteries, and therefore can effectively suppress cracks that occur between the electrode active material and the solid electrolyte after charge / discharge, thereby suppressing a decrease in discharge capacity, in a simpler manner than conventional batteries.

[0019] Here, in the battery according to embodiment 1, the "volume expansion coefficient associated with charge and discharge" of the electrode active material refers to the volume expansion coefficient between the charged and discharged states of the electrode active material. When the electrode active material is, for example, a negative electrode active material, the volume expansion coefficient between the charged and discharged states refers to the volume expansion coefficient in the charged state relative to the volume in the discharged state. When the electrode active material is, for example, a positive electrode active material, the volume expansion coefficient between the charged and discharged states refers to the volume expansion coefficient in the discharged state relative to the volume in the charged state. Hereinafter, in this specification, a positive electrode layer and / or a negative electrode layer containing an electrode active material having a volume expansion coefficient associated with charge and discharge of 2% to 14% is referred to as an "electrode layer."

[0020] In the present disclosure, the volume expansion rate of an electrode active material during charge and discharge is a theoretical value. Specifically, the theoretical volume expansion rate is calculated using the unit cell volume in a fully lithiated state, i.e., a state in which lithium ions are absorbed (e.g., a fully charged state for a negative electrode active material), and the unit cell volume in a fully delithiated state, i.e., a state in which lithium ions are released (e.g., a fully discharged state for a negative electrode active material). For example, Figure 1j in the literature "J. Deng et al., "Selective Doping to Controllably Tailor Maximum Unit-Cell-Volume Change of Intercalating Li+-Storage Materials: A Case Study of γ Phase Li3VO4," Advanced Science, 2022, 9, 2106003" shows theoretical values ​​of the volume expansion rate between the charged and discharged states for example electrode active materials.

[0021] Fig. 2 is a cross-sectional view showing an example of a power generating element used in the manufacturing method of a battery according to embodiment 1. Fig. 3 is a schematic view showing an example of how the power generating element shown in Fig. 2 is constrained in the stacking direction.

[0022] 2 , the power generating element 1000 includes a positive electrode layer 101, a negative electrode layer 102, and an electrolyte layer 103. The electrolyte layer 103 is disposed between the positive electrode layer 101 and the negative electrode layer 102. The electrolyte layer 103 is, for example, a solid electrolyte layer. The power generating element 1000 used in the manufacturing method according to the first embodiment constitutes, for example, an all-solid-state battery.

[0023] The positive electrode layer 101 includes, for example, a positive electrode active material layer 104 and a positive electrode current collector 105. The positive electrode layer 101 is disposed so that the positive electrode active material layer 104 faces the electrolyte layer 103. The negative electrode layer 102 includes, for example, a negative electrode active material layer 106 and a negative electrode current collector 107. The negative electrode layer 102 is disposed so that the negative electrode active material layer 106 faces the electrolyte layer 103.

[0024] In the manufacturing method according to the first embodiment, the charge / discharge treatment of the power generating element 1000 in (A) above is performed with the power generating element 1000 restrained in the stacking direction. The member (restraining member) used to restrain the power generating element 1000 is not particularly limited as long as it is a member capable of applying a restraining pressure to the power generating element 1000 in the stacking direction. For example, a known restraining member that can be used as a restraining member for an all-solid-state battery can be used. For example, as shown in FIG. 3 , one example of a restraining member includes a lower pressure plate 110a, which is a plate-shaped portion that presses the lower surface of the power generating element 1000, an upper pressure plate 110b, which is a plate-shaped portion that presses the upper surface, a rod-shaped portion 120 that connects the lower pressure plate 110a and the upper pressure plate 110b, and an adjustment portion 130 that is connected to the rod-shaped portion 120 and adjusts the restraining pressure applied to the power generating element 1000 by a screw structure or the like. In the example shown in Fig. 3, the adjustment unit 130 adjusts the position of the upper pressure plate 110b relative to the lower pressure plate 110a, thereby applying a desired restraint pressure to the power-generating element 1000. The power-generating element 1000 during restraint may be enclosed in an exterior body, for example. In this case, as shown in Fig. 3, exterior bodies 140 are present between the power-generating element 1000 and the lower pressure plate 110a and between the power-generating element 1000 and the upper pressure plate 110b, respectively.

[0025] In the above (A), the power generating element 1000 may be constrained, for example, at a confinement pressure of 1 MPa or more. By performing a charge / discharge process while the power generating element 1000 is constrained at such a constraining pressure, even if the completed battery is charged / discharged in an unconstrained state, cracks that occur between the negative electrode active material and the solid electrolyte after charge / discharge can be effectively suppressed, thereby further suppressing a decrease in discharge capacity. In order to more effectively suppress the occurrence of cracks in the negative electrode layer due to charge / discharge and further suppress a decrease in discharge capacity, the constraining pressure may be 5 MPa or more. Increasing the constraining pressure has the advantage of making it easier to improve the contact between the layers. On the other hand, the constraining pressure may be, for example, 100 MPa or less, 50 MPa or less, 20 MPa or less, or 14 MPa or less. This is because if the constraining pressure is too high, the constraining member is required to have high rigidity, which may increase the size of the constraining member.

[0026] The charge / discharge treatment in (A) above is not particularly limited as long as the target design capacity can be achieved. For example, constant current charging (CC charging) may be performed within a range of 2C to 1 / 20C of the positive electrode capacity. Alternatively, for example, CCCV charging may be performed, in which CC charging is performed within a range of 2C to 1 / 20C of the positive electrode capacity, and then constant voltage charging (CV charging) is performed when the battery voltage reaches a specified value.

[0027] In the above (B), after the charge / discharge treatment in the above (A), the restraint pressure on the power-generating element 1000 is reduced. In the above (B), the restraint pressure on the power-generating element 1000 may be reduced by, for example, 90% or more, 95% or more, or 98% or more. In the above (B), the restraint on the power-generating element 1000 may be released. That is, the restraint pressure on the power-generating element 1000 may be reduced by 100%.

[0028] The following provides a detailed description of the power generating element used in the manufacturing method according to embodiment 1. Hereinafter, the "power generating element used in the manufacturing method according to embodiment 1" will be referred to as the "power generating element according to embodiment 1."

[0029] [Power-generating element] The power-generating element 1000 according to the first embodiment includes a positive electrode layer 101, a negative electrode layer 102, and an electrolyte layer 103. The electrolyte layer 103 is disposed between the positive electrode layer 101 and the negative electrode layer 102. The electrolyte layer 103 is, for example, a solid electrolyte layer. The power-generating element 1000 according to the first embodiment may be an all-solid-state battery.

[0030] [Positive Electrode Layer] The positive electrode layer 101 includes, for example, a positive electrode active material layer 104 and a positive electrode current collector 105 .

[0031] [Positive Electrode Active Material Layer] The positive electrode active material layer 104 contains a positive electrode active material. The positive electrode active material layer 104 may contain optional components such as a solid electrolyte, a conductive material, and a binder.

[0032] The positive electrode active material layer 104 may include a positive electrode active material having a volume expansion rate associated with charging and discharging, i.e., a volume expansion rate in a discharged state relative to a charged state, of 2% or more and 14% or less.

[0033] Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions and fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using lithium-containing transition metal oxides as the positive electrode active material can reduce manufacturing costs and increase average discharge voltage. Examples of lithium-containing transition metal oxides include Li(NiCoAl)O, Li(NiCoMn)O, and LiCoO.

[0034] The shape of the positive electrode active material is not particularly limited, and may be particulate. When the positive electrode active material is particulate, the positive electrode active material may be primary particles or secondary particles.

[0035] A coating layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material, because this can suppress the reaction between the positive electrode active material and the solid electrolyte.

[0036] Examples of Li ion conductive oxides include LiNbO3 and Li4Ti5O 12 , and Li3PO4. 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 coating layer may cover, for example, 70% or more, or may cover 90% or more of the surface of the positive electrode active material.

[0037] Examples of the solid electrolyte include the same ones as those exemplified for the electrolyte layer 103 .

[0038] The content of the solid electrolyte in the positive electrode active material layer 104 is not particularly limited, but may be, for example, in the range of 1 mass % to 80 mass % when the total mass of the positive electrode active material layer is 100 mass %.

[0039] Known conductive materials can be used, such as carbon materials and metal particles. Examples of the carbon material include at least one selected from the group consisting of acetylene black, furnace black, vapor-grown carbon fiber (VGCF), carbon nanotubes, and carbon nanofibers. From the viewpoint of electronic conductivity, at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Examples of metal particles include particles of Ni, Cu, Fe, and SUS.

[0040] The content of the conductive material in the positive electrode active material layer 104 is not particularly limited.

[0041] 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 positive electrode layer is not particularly limited.

[0042] The thickness of the positive electrode active material layer 104 is not particularly limited, but may be, for example, 10 μm or more and 100 μm or less, or 10 μm or more and 20 μm or less.

[0043] The positive electrode active material layer 104 can be formed by a known method.

[0044] 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 active material layer, and the slurry for the positive electrode active material layer is applied to one surface of a support and dried to obtain the positive electrode active material layer 104.

[0045] Examples of the solvent include butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP).

[0046] The method for applying the slurry for the positive electrode active material layer onto one surface of the support is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic application method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method.

[0047] The support can be appropriately selected from those having self-supporting properties and is not particularly limited, and examples thereof include metal foils such as Cu and Al foils.

[0048] As another method for forming the positive electrode active material layer 104, a powder of a positive electrode mixture containing a positive electrode active material and, if necessary, other components may be pressure-molded to form the positive electrode active material layer 104. When pressure-molding the powder of the positive electrode mixture, a pressing pressure of about 1 MPa or more and 2000 MPa or less is typically applied.

[0049] The method of applying pressure is not particularly limited, but examples thereof include a method of applying pressure using a plate press, a roll press, or the like.

[0050] [Positive Electrode Current Collector] For example, a known metal that can be used as a current collector for an all-solid-state battery can be used as the positive electrode current collector 105. Examples of such metals include metal materials containing at least one element 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 105 include SUS, aluminum, nickel, iron, titanium, and carbon.

[0051] The shape of the positive electrode current collector 105 is not particularly limited, and may be various shapes such as a foil shape, a mesh shape, etc. The thickness of the positive electrode current collector 105 varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0052] [Negative Electrode Layer] The negative electrode layer 102 includes, for example, a negative electrode active material layer 106 and a negative electrode current collector 107 .

[0053] [Negative Electrode Active Material Layer] The negative electrode active material layer 106 contains at least a negative electrode active material, and optionally contains a solid electrolyte, a conductive material, a binder, and the like.

[0054] The negative electrode active material layer 106 includes, for example, a negative electrode active material whose volume expansion rate during charging and discharging, i.e., the volume expansion rate in the charged state relative to the discharged state, is 2% or more and 14% or less. Examples of such a negative electrode active material include graphite, mesocarbon microbeads (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, soft carbon, elemental lithium, lithium alloys, and oxide-based materials.

[0055] 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, Examples include 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.

[0056] Examples of oxide-based materials include compounds containing Ti, Nb, and O. By using such compounds as the negative electrode active material, a high battery capacity can be obtained.

[0057] The compound containing Ti, Nb, and O may be represented by the following composition formula (1), for example: TiNb x O y In the composition formula (1), x satisfies 1.5≦x≦2.5, and y satisfies 6.5≦y≦7.5.

[0058] By using the compound represented by the above composition formula (1) as the negative electrode active material, a higher battery capacity can be obtained.

[0059] The compound represented by the above composition formula (1) may be, for example, TiNb2O7. By using TiNb2O7 as the negative electrode active material, a higher battery capacity can be obtained.

[0060] The negative electrode active material layer 106 may contain multiple types of negative electrode active materials. For example, in addition to a negative electrode active material (first negative electrode active material) whose volume expansion coefficient in a charged state relative to a discharged state is 2% or more and 14% or less, the layer may further contain a negative electrode active material (second negative electrode active material) whose volume expansion coefficient does not satisfy the above range. The proportion of the first negative electrode active material in the entire negative electrode active material may be, for example, 80% by mass or more. The proportion of the first negative electrode active material in the entire negative electrode active material may be 100%.

[0061] The shape of the negative electrode active material is not particularly limited, and examples thereof include particulate and plate-like shapes. When the negative electrode active material is particulate, the negative electrode active material may be primary particles or secondary particles.

[0062] The conductive material and binder used in the negative electrode active material layer 106 may be the same as those exemplified for the positive electrode active material layer 104. The solid electrolyte used in the negative electrode active material layer 106 may be the same as those exemplified for the electrolyte layer 103.

[0063] The thickness of the negative electrode active material layer 106 is not particularly limited, but may be, for example, 10 μm or more and 100 μm or less, or 10 μm or more and 20 μm or less.

[0064] The content of the negative electrode active material in the negative electrode active material layer 106 is not particularly limited, but may be, for example, 20% by mass or more and 90% by mass or less.

[0065] The negative electrode active material layer 106 may be formed, for example, so that the specific charge capacity of the negative electrode is 1.0 to 2.0 times the specific charge capacity of the positive electrode, or may be formed so that the specific charge capacity is 1.0 to 1.2 times the specific charge capacity of the positive electrode.

[0066] [Negative Electrode Current Collector] The material of the negative electrode current collector 107 may be a material that does not alloy with Li, such as SUS, copper, or nickel. Furthermore, even materials that alloy with Li can be used as long as the operating potential of the negative electrode active material is within a range in which they do not alloy with Li. For example, when Al is used as the negative electrode current collector, it can be used as long as the operating range of the negative electrode is 0.3 V or higher. Examples of the shape of the negative electrode current collector 107 include foil and plate shapes. The planar shape of the negative electrode current collector 107 is not particularly limited, but examples include circular, elliptical, rectangular, and any polygonal shape. The thickness of the negative electrode current collector 107 varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0067] [Electrolyte Layer] The electrolyte layer contains a solid electrolyte.

[0068] The solid electrolyte contained in the electrolyte layer may be any known solid electrolyte that can be used in all-solid-state batteries. Examples of inorganic solid electrolytes include sulfide-based solid electrolytes, oxide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and nitride-based solid electrolytes. The sulfide-based solid electrolyte may contain sulfur (S) as the main anion element. The oxide-based solid electrolyte may contain oxygen (O) as the main anion element. The hydride-based solid electrolyte may contain hydrogen (H) as the main anion element. The halide-based solid electrolyte may contain halogen (X) as the main anion element. The nitride-based solid electrolyte may contain nitrogen (N) as the main anion element.

[0069] The sulfide-based solid electrolyte may be sulfide glass, crystallized sulfide glass (glass ceramics), or a crystalline material obtained by a solid-phase reaction treatment of a raw material composition.

[0070] The crystalline state of the sulfide-based solid electrolyte can be confirmed, for example, by subjecting the sulfide-based solid electrolyte to powder X-ray diffraction measurement using CuKα rays.

[0071] Sulfide glass can be obtained by subjecting a raw material composition (e.g., a mixture of LiS and P2S5) to amorphous processing, such as mechanical milling.

[0072] Glass ceramics can be obtained, for example, by heat treating sulfide glass.

[0073] The heat treatment temperature may be any temperature higher than the crystallization temperature (Tc) of the sulfide glass observed by thermal analysis, and is usually 195° C. or higher. On the other hand, there is no particular upper limit to the heat treatment temperature.

[0074] The crystallization temperature (Tc) of the sulfide glass can be measured by differential thermal analysis (DTA).

[0075] The heat treatment time is not particularly limited as long as it is a time that allows the desired crystallinity of the glass ceramic to be obtained, but is, for example, in the range of 1 minute to 24 hours, and particularly, in the range of 1 minute to 10 hours.

[0076] The heat treatment method is not particularly limited, but may be, for example, a method using a firing furnace.

[0077] Examples of oxide-based solid electrolytes include solid electrolytes containing Li, Y (wherein Y is at least one selected from the group consisting of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. A specific example of an oxide-based solid electrolyte is LiLaZrO. 12 , Li 7-x La3(Zr 2-x Nb x ) O 12 (0≦x≦2), Li5La3Nb2O 12perovskite-type solid electrolytes such as (Li,La)TiO3, (Li,La)NbO3, and (Li,Sr)(Ta,Zr)O3; Nasicon-type solid electrolytes such as Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3; Li-P-O-based solid electrolytes such as Li3PO4 and LIPON (a compound in which part of the O in Li3PO4 is substituted with N); and Li-B-O-based solid electrolytes such as Li3BO3 and a compound in which part of the O in Li3BO3 is substituted with C.

[0078] The hydride-based solid electrolyte contains, for example, Li and a complex anion containing hydrogen. The complex anion may be, for example, (BH4). - , (NH2) - , (AlH4) - , and (AlH6)3 - etc.

[0079] Examples of halide-based solid electrolytes include Li 6-3z Y z X6 (X is at least one of Cl and Br, and z satisfies 0<z<2).

[0080] An example of the nitride-based solid electrolyte is Li3N.

[0081] The solid electrolyte may be in the form of particles from the viewpoint of ease of handling.

[0082] The average particle size of the solid electrolyte particles is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more, while the average particle size of the solid electrolyte particles is, for example, 25 μm or less, or 10 μm or less.

[0083] In this disclosure, unless otherwise specified, the average particle size of particles is the volume-based median diameter (D50) value measured by laser diffraction / scattering particle size distribution measurement. Furthermore, in this disclosure, the median diameter (D50) is the diameter (volume average diameter) at which the cumulative volume of particles is half (50%) of the total volume when the particles are arranged in order from smallest to largest particle size.

[0084] The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure.

[0085] The proportion of the solid electrolyte in the electrolyte layer 103 is not particularly limited, but may be, for example, 50% by mass or more, or may be in the range of 60% by mass or more and 100% by mass or less, or may be in the range of 70% by mass or more and 100% by mass or less, or may be 100% by mass.

[0086] The electrolyte layer 103 may contain a binder from the viewpoint of exhibiting plasticity, etc. Examples of such binders include the materials exemplified as binders used in the positive electrode active material layer 104. However, in order to facilitate achieving high output, the binder content in the electrolyte layer 103 may be 5 mass % or less from the viewpoint of preventing excessive aggregation of the solid electrolyte and enabling the formation of a solid electrolyte layer having a uniformly dispersed solid electrolyte.

[0087] The thickness of the electrolyte layer 103 is not particularly limited, but is usually 0.1 μm or more and 1 mm or less.

[0088] Examples of methods for forming the electrolyte layer 103 include a method of applying a slurry for the solid electrolyte layer containing a solid electrolyte onto a support and drying it, and a method of press-molding a powder of a solid electrolyte material containing a solid electrolyte. Examples of the support include the same supports as those exemplified for the positive electrode active material layer 104. When press-molding the powder of the solid electrolyte material, a pressing pressure of about 1 MPa or more and 2000 MPa or less is typically applied.

[0089] The pressing method is not particularly limited, but may be any of the pressing methods exemplified in the formation of the positive electrode active material layer.

[0090] The battery manufactured by the manufacturing method according to the first embodiment includes a power generating element 1000 that has undergone charge and discharge treatment in (A) above and then had its restraining pressure reduced in (B) above.

[0091] The battery manufactured by the manufacturing method according to the first embodiment may, as necessary, include an exterior body that houses a laminate having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector arranged in this order.

[0092] The material of the exterior body is not particularly limited as long as it is stable against the electrolyte used in the battery, and examples thereof include polypropylene, polyethylene, and resins such as acrylic resin. The exterior body may be, for example, a laminate exterior body.

[0093] The battery manufactured by the manufacturing method according to the first embodiment can suppress cracks that occur between the electrode active material and the solid electrolyte after charge and discharge. For example, in a scanning electron microscope image of a cross section of a battery manufactured by the manufacturing method according to the first embodiment, when the layer direction of the electrode layer (i.e., the surface direction of the electrode layer) is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, the average value Lx (ave) of the x-axis projected lengths Lx, obtained by projecting the length L of a line segment connecting the start point and end point of a crack present in the cross section in the x-axis direction, can be, for example, 15% or less of the length in the x-axis direction of the image. In this way, the battery manufactured by the manufacturing method according to the first embodiment can satisfy the requirement that the average value Lx (ave) of the x-axis projected lengths Lx is 15% or less of the length in the x-axis direction of the image, even after charge and discharge. That is, the battery manufactured by the manufacturing method according to the first embodiment can maintain high continuity between the electrode active material and the solid electrolyte in the thickness direction of the electrode layer, even after charge and discharge. Therefore, the battery manufactured by the manufacturing method according to the first embodiment can suppress the decrease in discharge capacity due to charge and discharge, and can achieve a large discharge capacity. The electrode layer having such a configuration may be, for example, a negative electrode layer.

[0094] The battery manufactured by the manufacturing method according to the first embodiment may have only one power generating element 1000, or may have a plurality of power generating elements 1000 stacked on top of each other.

[0095] The battery manufactured by the manufacturing method according to the first embodiment is, for example, an all-solid-state battery, and may be an all-solid-state lithium secondary battery, an all-solid-state lithium ion secondary battery, or the like.

[0096] The shape of the battery manufactured by the manufacturing method according to the first embodiment can be, for example, a coin type, a laminate type, a cylindrical type, a prismatic type, or the like.

[0097] The use of the battery manufactured by the manufacturing method according to the first embodiment is not particularly limited, and examples thereof include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. Furthermore, the battery manufactured by the manufacturing method according to the first embodiment may be used as a power source for mobile objects other than vehicles (e.g., railways, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0098] (Embodiment 2) Fig. 4 is a cross-sectional view showing an example of a battery according to embodiment 2. Fig. 5 is a schematic diagram showing a cross section of the battery according to embodiment 2 taken along the thickness direction of the negative electrode layer.

[0099] 4 , the battery 2000 according to the second embodiment includes a positive electrode layer 201, a negative electrode layer 202, and an electrolyte layer 203 located between the positive electrode layer 201 and the negative electrode layer 202. The positive electrode layer 201 includes, for example, a positive electrode active material layer 204 and a positive electrode current collector 205. The negative electrode layer 202 includes, for example, a negative electrode active material layer 206 and a negative electrode current collector 207.

[0100] In a scanning electron microscope image of a cross section along the thickness direction of at least one electrode layer selected from the group consisting of positive electrode layer 201 and negative electrode layer 202 in battery 2000 according to embodiment 2, when the layer direction of the electrode layer is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, the average value Lx (ave) of x-axis projection lengths Lx obtained by projecting the length L of a line segment connecting the start point and end point of a crack present in the cross section along the x-axis direction is 15% or less of the length along the x-axis direction of the image. Hereinafter, battery 2000 according to embodiment 2 will be specifically described using an example in which the electrode layer is negative electrode layer 202.

[0101] As shown in FIG. 5 , in a scanning electron microscope image of a cross section of the battery 2000 according to the second embodiment taken along the thickness direction of the anode layer 202, when the layer direction of the anode layer 202 is the x-axis direction and the thickness direction of the anode layer 202 is the y-axis direction, an average value Lx (ave) of x-axis projection lengths Lx obtained by projecting the length L of a line segment connecting the start point and the end point of a crack 210 present in the cross section onto the x-axis direction is 15% or less of the length in the x-axis direction of the image.

[0102] In the battery 2000 according to the second embodiment, the average value Lx(ave) of the x-axis projected length Lx is 15% or less of the length in the x-axis direction of the image. The battery 2000 according to the second embodiment can maintain high continuity between the negative electrode active material 211 and the solid electrolyte 212 in the thickness direction (y-axis direction) of the negative electrode layer 202 even after charging and discharging. Therefore, the battery 2000 according to the first embodiment can maintain the interface between the negative electrode active material 211 and the solid electrolyte 212 even after charging and discharging, and the movement of Li is not inhibited. Therefore, the battery 2000 according to the second embodiment can suppress a decrease in discharge capacity and achieve a large discharge capacity.

[0103] The image can be obtained, for example, by exposing a cross section of the battery 2000 along its thickness direction by ion milling or the like, and then capturing an image of the exposed cross section of the negative electrode layer 202 using a scanning electron microscope. For example, an image at 5000x magnification is used as the image. A crack 210 in the negative electrode layer 202 that is visually confirmed in the captured image is traced using, for example, a broken line tool in ImageJ to obtain a broken line of the crack 210. The length L of the line segment connecting the start point and end point of the broken line of the crack 210 is projected in the x-axis direction, which is the layer direction of the negative electrode layer 202, to obtain an x-axis projected length Lx. Specifically, for example, the angle θ is defined as the angle formed between the x-axis and the line segment L connecting the start point and end point of the broken line of the crack 210. The x-axis projected length Lx can be calculated using this angle θ and the length L of the line segment connecting the start point and end point of the broken line of the crack using the following formula (a): Lx=L×cosθ...(a)

[0104] Furthermore, the top 10 longest x-axis projection lengths Lx within the same field of view are selected, and the average of these 10 is taken as the average value Lx(ave) within that field of view. The ratio of the obtained average value Lx(ave) to the length of the image in the x-axis direction is calculated as a percentage.

[0105] In battery 2000 according to embodiment 2, average value Lx(ave) may be equal to or less than 3.84 μm. This configuration can suppress cracks that occur in the negative electrode during charge and discharge, thereby suppressing a decrease in discharge capacity.

[0106] Battery 2000 according to Embodiment 2 can be manufactured by the battery manufacturing method according to Embodiment 1. In battery 2000 according to Embodiment 2, positive electrode layer 201, negative electrode layer 202, electrolyte layer 203, positive electrode active material layer 204, positive electrode current collector 205, negative electrode active material layer 206, and negative electrode current collector 207 correspond to positive electrode layer 101, negative electrode layer 102, electrolyte layer 103, positive electrode active material layer 104, positive electrode current collector 105, negative electrode active material layer 106, and negative electrode current collector 107, respectively, described in Embodiment 1. Therefore, in Embodiment 2, detailed description of each of the above components will be omitted.

[0107] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0108] (Technology 1) A method for manufacturing a battery, the method comprising: (A) performing a charge / discharge process on a power generating element including a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer, while constraining the power generating element in a stacking direction; and (B) reducing a constraining pressure on the power generating element after the charge / discharge process in (A), wherein at least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer contains a negative electrode active material whose volume expansion rate upon charge / discharge is 2% or more and 14% or less.

[0109] According to the above manufacturing method, there is no need to continue restraining the completed battery as in the conventional method, and therefore it is possible to effectively suppress cracks that occur between the electrode active material and the solid electrolyte after charge and discharge, thereby suppressing a decrease in discharge capacity, in a simpler manner than in the conventional batteries.

[0110] (Technical 2) The method for producing a battery according to Technical 1, wherein in (A), the power generating element is constrained at a constraining pressure of 1 MPa or more.

[0111] According to the above manufacturing method, even when the completed battery is charged and discharged in an unconstrained state, cracks that occur between the electrode active material and the solid electrolyte after charging and discharging can be effectively suppressed, and a decrease in discharge capacity can be further suppressed.

[0112] (Technology 3) The method for producing a battery according to Technology 1 or 2, wherein the negative electrode layer contains a negative electrode active material having a volume expansion rate during charging and discharging of 2% or more and 14% or less.

[0113] According to the above manufacturing method, cracks that occur between the negative electrode active material and the solid electrolyte after charge and discharge can be effectively suppressed, and a decrease in discharge capacity can be suppressed, using a method that is simpler than that of conventional batteries.

[0114] (Technology 4) The method for producing a battery according to Technology 3, wherein the negative electrode active material contains a compound containing Ti, Nb, and O.

[0115] According to the above manufacturing method, a high battery capacity can be obtained.

[0116] (Technology 5) The compound is represented by the following composition formula (1): TiNb x O y 5. The method for producing a battery according to claim 4, wherein in the composition formula (1), the x satisfies 1.5≦x≦2.5, and the y satisfies 6.5≦y≦7.5.

[0117] According to the above manufacturing method, a high battery capacity can be obtained.

[0118] (Technology 6) The method for manufacturing a battery according to claim 5, wherein the compound includes TiNb2O7.

[0119] According to the above manufacturing method, a higher battery capacity can be obtained.

[0120] (Technology 7) The method for manufacturing a battery according to any one of Technologies 1 to 6, wherein, in a scanning electron microscope image of a cross section along a thickness direction of the electrode layer, when the layer direction of the electrode layer is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, an average value Lx (ave) of x-axis projection lengths Lx obtained by projecting length L of a line segment connecting a start point and an end point of a crack present in the cross section in the x-axis direction is 15% or less of the length in the x-axis direction of the image.

[0121] The battery manufactured by the above manufacturing method can suppress the decrease in discharge capacity that occurs during charging and discharging, and can achieve a large discharge capacity.

[0122] (Technology 8) The method for producing a battery according to Technology 7, wherein the electrode layer is the negative electrode layer.

[0123] The battery manufactured by the above manufacturing method can suppress the decrease in discharge capacity that occurs during charging and discharging, and can achieve a large discharge capacity.

[0124] (Technology 9) A battery comprising: a positive electrode layer; a negative electrode layer; and an electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein in a scanning electron microscope image of a cross section along a thickness direction of at least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer, when the layer direction of the electrode layer is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, an average value Lx (ave) of x-axis projected lengths Lx obtained by projecting length L of a line segment connecting a start point and an end point of a crack present in the cross section along the x-axis direction is 15% or less of the length in the x-axis direction of the image.

[0125] According to the above configuration, cracks occurring in the electrodes due to charging and discharging can be suppressed, and a decrease in discharge capacity can be suppressed.

[0126] (Technology 10) The method for manufacturing a battery according to Technology 9, wherein the electrode layer is the negative electrode layer.

[0127] According to the above configuration, cracks occurring in the negative electrode due to charge and discharge can be suppressed, and a decrease in discharge capacity can be suppressed.

[0128] (Technology 11) The battery according to Technology 9 or 10, wherein the average value Lx(ave) is 3.84 μm or less.

[0129] According to the above configuration, cracks occurring in the negative electrode due to charge and discharge can be suppressed, and a decrease in discharge capacity can be suppressed.

[0130] [Preparation of sulfide solid electrolyte] In a glove box with an Ar atmosphere having a dew point of -60°C or less, Li2S and PS5 were weighed out so that the molar ratio of Li2S:PS5 was 75:25. These were pulverized and mixed in a mortar. Then, a planetary ball mill (Fritsche, P-7 model) was used to mill the mixture at 510 rpm for 10 hours, yielding a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated at 270°C for 2 hours in an inert atmosphere. This yielded a glass-ceramic solid electrolyte, Li2S-PS5.

[0131] [Preparation of paste for positive electrode active material layer] As the positive electrode active material, LiNi 0.8 Co 0.15 Al 0.05 LiNbO2 (density 4.65 g / cc, average particle size 5 μm) was used. The positive electrode active material was surface-treated with LiNbO3 using a tumbling fluidized bed granulation coating device. 4.0 g of this surface-treated positive electrode active material, 0.094 g of VGCF as a conductive material, 1.024 g of the sulfide solid electrolyte Li2S-P2S5 prepared by the above method, 0.017 g of a butadiene rubber binder, and 2.77 g of tetralin were weighed and mixed using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation) to form a paste for the positive electrode active material layer.

[0132] [Preparation of TiNbO] 30 g of niobium oxide (NbO) powder and 18 g of titanium oxide (TiO) powder were premixed in a planetary mixer. Then, the resulting mixture was loaded into a pod (zirconia, volume 45 mL) of a planetary ball mill (Fritsche, P-7) with ethanol added as an auxiliary agent. 45 g of zirconia balls (diameter 5 mm) were placed in the pod, the lid was closed, and the mixture was milled and mixed at 400 rpm for 50 hours.

[0133] The resulting pulverized mixture was placed in an alumina tray and calcined in an electric furnace (treatment temperature: 1100° C., treatment time: 5 hours).

[0134] The obtained fired product was coarsely pulverized in a power mill until it passed through a 1 mm mesh. Then, 30 g of the coarsely pulverized powder was added to a pod (zirconia, volume 45 mL) of a planetary ball mill (manufactured by Fritsche, P-7) and filled with water. 45 g of zirconia balls (diameter 1 mm) were placed in the pod, the lid was closed, and the wet pulverization was carried out at 400 rpm for 50 hours. The wet pulverization was stopped when the median diameter (D50) became 2 μm or less while measuring the particle size of the pulverized slurry over time with a laser diffraction particle sizer.

[0135] The resulting pulverized slurry was dried in a vacuum drying furnace to obtain a titanium-niobium composite oxide powder. The resulting titanium-niobium composite oxide powder was mainly composed of TiNbO. The theoretical value of the volume expansion rate of TiNbO during charge and discharge is 7.22%.

[0136] The capacity of the obtained TiNb2O7 alone was measured using a Li counter electrode, and was found to be 250 mAh / g at 1.5 V-0.5 V.

[0137] [Preparation of Negative Electrode Active Material Layer Paste] As the negative electrode active material, 3.0 g of TiNbO particles (density 3.54 g / cc) prepared by the above method, 0.033 g of conductive carbon (density 2 g / cc), 0.039 g of butadiene rubber binder (density 0.9 g / cc), and 3.71 g of tetralin were weighed and mixed for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation). Then, 1.0 g of the sulfide solid electrolyte LiS-PS prepared by the above method was added to the slurry obtained by mixing, and the mixture was mixed again for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation). The resulting mixture was used as a negative electrode active material layer paste.

[0138] [Preparation of Paste for Solid Electrolyte Layer] Heptane, a heptane solution containing 5% by mass of a butadiene rubber binder, and the sulfide solid electrolyte LiS-PS prepared as the solid electrolyte by the method described above were added to a polypropylene container and mixed for 30 seconds using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation). Next, the container was shaken for 3 minutes using a shaker to obtain a paste for the solid electrolyte layer.

[0139] [Preparation of Positive Electrode Layer and Negative Electrode Layer] The paste for the positive electrode active material layer was applied to a positive electrode current collector (Al foil, 15 μm thick) using an applicator by the blade method. After application, the paste was dried on a hot press at 100 ° C for 30 minutes to obtain a positive electrode layer having a positive electrode active material layer on the surface of the aluminum foil. Similarly, the paste for the negative electrode active material layer was applied to a negative electrode current collector (Ni foil, 22 μm thick) and dried to obtain a negative electrode layer having a negative electrode active material layer on the surface of the Ni foil. In all of the examples and comparative examples, the basis weight of the negative electrode active material layer was adjusted so that the negative electrode charge specific capacity was 1.1 times that of the positive electrode charge specific capacity of 200 mAh / g.

[0140] [Fabrication of Solid Electrolyte Layer] [Coating of Solid Electrolyte Layer Paste (Positive Electrode Layer Side)] The positive electrode layer was pre-pressed. After pre-pressing, the positive electrode layer was coated with the solid electrolyte layer paste using a die coater on the surface of the positive electrode active material layer, and dried on a hot plate at 100°C for 30 minutes.

[0141] Then, 2 ton / cm 2 The laminate was roll-pressed at 800° C. to obtain a positive electrode-side laminate having a solid electrolyte layer on the surface of the positive electrode active material layer in the positive electrode layer.

[0142] [Coating of solid electrolyte layer paste (negative electrode layer side)] The negative electrode layer was pre-pressed. After pre-pressing, the solid electrolyte layer paste was coated on the surface of the negative electrode active material layer using a die coater, and the coated negative electrode layer was dried on a hot plate at 100°C for 30 minutes.

[0143] Then, 2 ton / cm 2 The laminate was roll-pressed at 800° C. to obtain a negative electrode-side laminate having a solid electrolyte layer on the surface of the negative electrode active material layer in the negative electrode layer.

[0144] [Fabrication of All-Solid-State Lithium-Ion Secondary Battery] The positive electrode side laminate and the negative electrode side laminate were each punched and then laminated together so that the solid electrolyte layers were bonded together. Here, the laminate was laminated in a state in which an unpressed solid electrolyte layer (solid electrolyte layer paste) was transferred between the solid electrolyte layer of the positive electrode side laminate and the solid electrolyte layer of the negative electrode side laminate. Thereafter, the laminate was laminated at 160°C with a pressure of 2 ton / cm.2 The resulting power generating element was laminated and sealed to form an all-solid-state lithium ion secondary battery for evaluation.

[0145] [Charge-discharge treatment of the power generating element in a restrained state] The charge-discharge treatment of the power generating element in a restrained state was carried out as follows.

[0146] Example 1 The restraining member used for restraining the power generating element enclosed in the laminate exterior body was the restraining member described as an example with reference to Fig. 3. That is, a restraining member was used that had plate-shaped portions that sandwiched both surfaces of the power generating element, rod-shaped portions that connected the two plate-shaped portions, and an adjustment portion that was connected to the rod-shaped portions and adjusted the restraining pressure by a screw structure or the like. The adjustment portion adjusted the restraining pressure applied to the power generating element.

[0147] A confining pressure was applied to the power generating element enclosed in the laminate exterior body under conditions such that the confining pressure, as confirmed in advance by prescaling, was 8 MPa. That is, in Example 1, the power generating element was confined in the stacking direction at a confining pressure of 8 MPa.

[0148] The battery was then placed in a constant temperature bath at 25°C.

[0149] The battery was charged at a constant current of 0.05 C rate (20-hour rate) to a positive electrode capacity of 200 mAh / g calculated from the active material ratio in the positive electrode layer of the power generating element, and charging was terminated after 20 hours.

[0150] After a further 20-minute rest, the power generating element was discharged at a constant current value of 0.05 C rate (20-hour rate), and the discharge was completed at 1.5 V.

[0151] Next, the voltage when charging was completed 20 hours after the initial charge was set as the end voltage, and the battery was charged at a constant current of 0.05 C rate (20-hour rate). Charging was terminated at the end voltage described above, and after a 20-minute pause, the battery was discharged at a constant current of 0.05 C rate (20-hour rate). Discharge was terminated at 1.5 V.

[0152] After the above charge / discharge treatment, the restraints on the power generating element were released, and the battery of Example 1 was completed.

[0153] Example 2 A battery of Example 2 was completed in the same manner as in Example 1, except that the restraining pressure during the charge-discharge treatment was changed to 1 MPa.

[0154] Comparative Example 1 A battery of Comparative Example 1 was completed in the same manner as in Example 1, except that the power generating element was not constrained during the charge / discharge treatment, that is, the constraining pressure was changed to 0 MPa.

[0155] Comparative Example 2: LiTiO was used instead of TiNbO as the negative electrode active material. 12 A battery of Comparative Example 2 was completed in the same manner as in Example 1, except that a power generating element was prepared using Li4Ti5O particles (density 3.5 g / cc) and the power generating element was not constrained during charge / discharge treatment, i.e., the constraining pressure was changed to 0 MPa. 12 The capacity of the single electrode was measured using a Li counter electrode and was found to be 175 mAh / g at 1.5 V-0.5 V. 12 The theoretical value of the volume expansion rate associated with charging and discharging is 0.2%.

[0156] [Evaluation of Initial Negative Electrode Weight Energy Density of All-Solid-State Lithium-Ion Secondary Batteries] The batteries fabricated in Examples 1 and 2 and Comparative Examples 1 and 2 had the same configuration as battery 2000 shown in Fig. 4. Using the batteries of Examples 1 and 2 and Comparative Examples 1 and 2, evaluation of the initial negative electrode weight energy density was carried out by the following charge / discharge test.

[0157] The unrestrained battery was placed in a constant temperature bath at 25°C.

[0158] The battery was charged at a constant current of 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, and charging was terminated at the voltage at which charging was terminated 20 hours after the initial charging of each battery.

[0159] Next, the battery was discharged at a constant current value of 0.05C rate (20 hour rate), and the discharge was completed at a voltage of 1.5V.

[0160] The discharge capacity was divided by the amount of negative electrode active material used in the battery to obtain the initial negative electrode weight energy density.

[0161] [Evaluation of Crack Length in Negative Electrode of All-Solid-State Lithium-Ion Secondary Battery] After the evaluation of the initial negative electrode weight energy density, the battery was disassembled, the laminate outer casing was removed, and a cross section in the thickness direction of the battery consisting of only the positive electrode layer, the solid electrolyte layer, and the negative electrode layer was exposed using an ion milling device (ArBlade R5000, manufactured by Hitachi High-Technologies Corporation).

[0162] For cracks in the negative electrode layer, a scanning electron microscope (Regulus 8230 manufactured by Hitachi High-Tech Corporation) was used to take an image of the negative electrode layer of the battery with the cross section exposed at 5000x magnification. The cracks in the negative electrode layer that were visually confirmed in the captured image were traced with the ImageJ line tool to obtain a crack line. The layer direction of the negative electrode layer was defined as the x-axis direction, and the thickness direction of the negative electrode layer was defined as the y-axis direction. The length L of the line segment connecting the start and end points of the crack line was projected onto the x-axis direction, which is the planar direction of the negative electrode layer, to obtain the X-axis projection length Lx. Specifically, the angle θ formed between the line segment L connecting the start and end points of the crack line and the x-axis was defined, and the x-axis projection length Lx was calculated using this angle θ and the length L of the line segment connecting the start and end points of the crack line using the following formula (a): Lx = L × cos θ (a)

[0163] Furthermore, the top 10 longest x-axis projected lengths Lx were selected within the same field of view, and the average of these 10 was taken as the average Lx (ave) within that field of view. The crack evaluation criterion Lx (%) was calculated as the percentage of the obtained average Lx (ave) relative to the x-axis length of the 5000x image (equivalent to 25.6 μm in this case).

[0164] The initial negative electrode weight energy densities and crack evaluation criteria Lx (%) of the batteries of Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in Table 1.

[0165]

[0166] <<Discussion>> The initial negative electrode weight energy density (mAh / g) of the battery of Example 1 was higher than that of the battery of Comparative Example 1. The battery of Example 1 was subjected to charge / discharge processing with the power-generating element constrained during manufacture. This is thought to be because the interface between the TiNbO particles, which theoretically would expand by 7.22% during charge, and the solid electrolyte in the negative electrode layer was maintained in an unconstrained state during evaluation of the initial negative electrode weight energy density after the battery was completed. This is thought to be because the expansion volume of the negative electrode active material during charge was constrained in the stacking direction of the power-generating element, i.e., the thickness direction of the electrode, and this expansion volume was absorbed by voids within the electrode, suppressing movement of the interface between the negative electrode active material and the solid electrolyte. Furthermore, the battery of Example 1 exhibited a smaller crack evaluation criterion Lx than the battery of Comparative Example 1. A smaller crack evaluation criterion Lx indicates high continuity between the negative electrode active material and the solid electrolyte in the thickness direction of the negative electrode layer. Therefore, the movement of Li was not inhibited, and it is believed that the TiNb2O7 particles contributed to charge and discharge.

[0167] As with the battery of Example 1, the battery of Example 2 also had a larger initial negative electrode weight energy density (mAh / g) than the battery of Comparative Example 1, and a smaller crack evaluation criterion Lx than the battery of Comparative Example 1.

[0168] In the battery of Comparative Example 1 using TiNb2O7, the power generating element was not constrained during the charge / discharge process during manufacture. As a result, the battery of Comparative Example 1 had a small initial negative electrode weight energy density (mAh / g) and a large crack evaluation criterion Lx. This is thought to be because cracks occurred between TiNb2O7 and the solid electrolyte due to contraction during discharge, and Li absorbed in the active material during charge was not released from the active material during discharge, resulting in a small initial negative electrode weight energy density. Furthermore, the crack evaluation criterion Lx was also thought to be large because crack generation was not suppressed.

[0169] In Comparative Example 2, Li4Ti5O was used as the negative electrode active material. 12In theory, the active material in a battery using Li4Ti5O particles hardly expands or contracts during charging and discharging, and the theoretical volume expansion rate during charging is 0.2%. Therefore, even without restraints during charging and discharging as in the manufacturing method of the present disclosure, the battery discharges almost the theoretical capacity. 12 The capacity measured using a Li counter electrode alone was 175 mAh / g at 1.5 V - 0.5 V, which is smaller than the 250 mAh / g of TiNb2O7. Therefore, when a similar positive electrode is used, the irreversible capacity of the positive electrode is the same (the irreversible capacity of the positive electrode used in this case is 17.6%), so the initial negative electrode weight energy density is small. 12 Since Li4Ti5O has almost no volume change during charging and discharging, it is an excellent negative electrode active material in terms of volume change during charging and discharging, but it is not preferable as a negative electrode active material for batteries where high capacity is desired. 12 In theory, there is almost no expansion or contraction during charging and discharging, and therefore the crack evaluation criterion Lx was very small.

[0170] The battery manufacturing method of the present disclosure can be used, for example, for all-solid-state lithium secondary batteries as well as nonaqueous lithium ion batteries.

Claims

1. A method for manufacturing a battery, comprising: The manufacturing method includes: (A) performing a charge / discharge process on a power generating element including a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer while the power generating element is constrained in a stacking direction; (B) reducing the restraining pressure on the power generating element after the charge / discharge treatment in (A); and Including, At least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer contains an electrode active material having a volume expansion rate during charge and discharge of 2% or more and 14% or less. How batteries are manufactured.

2. In the above (A), the power generating element is constrained at a constraining pressure of 1 MPa or more. A method for manufacturing the battery according to claim 1.

3. the negative electrode layer contains a negative electrode active material having a volume expansion rate during charge and discharge of 2% or more and 14% or less; A method for manufacturing the battery according to claim 1.

4. The negative electrode active material includes a compound containing Ti, Nb, and O, The method for manufacturing the battery according to claim 3 .

5. The compound is represented by the following composition formula (1): TiNb x O y ・・・(1) In the composition formula (1), The x satisfies 1.5≦x≦2.5, The y satisfies 6.5≦y≦7.5, The method for manufacturing the battery according to claim 4 .

6. The compound is TiNb 2 O 7 Including, The method for manufacturing the battery according to claim 5 .

7. In a scanning electron microscope image of a cross section along the thickness direction of the electrode layer, when the layer direction of the electrode layer is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, an average value Lx (ave) of x-axis projection lengths Lx obtained by projecting a line segment length L connecting a start point and an end point of a crack present in the cross section in the x-axis direction is 15% or less of the length in the x-axis direction of the image. A method for manufacturing the battery according to claim 1.

8. The electrode layer is the negative electrode layer. The method for manufacturing the battery according to claim 7 .

9. a positive electrode layer; a negative electrode layer; an electrolyte layer located between the positive electrode layer and the negative electrode layer; Equipped with In a scanning electron microscope image of a cross section along a thickness direction of at least one electrode layer selected from the group consisting of the positive electrode layer and the negative electrode layer, when the layer direction of the electrode layer is the x-axis direction and the thickness direction of the electrode layer is the y-axis direction, an average value Lx (ave) of x-axis projection lengths Lx obtained by projecting length L of a line segment connecting a start point and an end point of a crack present in the cross section in the x-axis direction is 15% or less of the length in the x-axis direction of the image. battery.

10. The electrode layer is the negative electrode layer.

10. The battery of claim 9.

11. The average value Lx(ave) is 3.84 μm or less.

10. The battery of claim 9.