Solid-state battery

Abstract

The present disclosure addresses the problem of providing a solid battery capable of suppressing the occurrence of abnormal electrodeposition and having favorable battery performance. One embodiment of the present invention that solves the problem is a solid-state battery having a structure in which a negative electrode layer, a solid electrolyte layer, and a positive electrode layer are laminated in that order, wherein: the solid electrolyte layer includes a first solid electrolyte layer disposed on the negative electrode layer side, and a second solid electrolyte layer disposed adjacent to the first solid electrolyte layer; and the density of the first solid electrolyte layer is higher than the density of the second solid electrolyte layer.

Description

solid state battery

[0001] The present invention relates to a solid-state battery.

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Known examples of such secondary batteries include solid-state batteries such as lithium metal batteries and lithium ion secondary batteries, in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer.

[0004] Known technologies relating to solid-state batteries include technologies relating to all-solid-state batteries that have a first solid electrolyte layer adjacent to a negative electrode and a second solid electrolyte layer located between the first solid electrolyte layer and a positive electrode, in which the first solid electrolyte layer has a smaller Young's modulus than the second solid electrolyte layer (see, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2022-108202

[0006] The technology disclosed in Patent Document 1 aims to suppress deterioration of the interfacial contact between the solid electrolyte layer and the positive and negative electrode layers and suppress voltage drop during self-discharge. One method for reducing the Young's modulus of the first solid electrolyte layer is to relatively increase the binder content of the first solid electrolyte layer. However, because the binder acts as a resistor during the operation of the solid-state battery, it is not desirable to increase the binder content of the solid electrolyte layer.

[0007] One method for fabricating such a solid-state battery is to press the positive electrode layer and the negative electrode layer separately, and then sandwich the solid electrolyte layer between them and press them together to integrate them. However, if the pressing pressure during integration is too high, each layer may be damaged, so there is a practical upper limit to the pressing pressure during integration. As a result, the solid electrolyte layer may not be sufficiently densified at the interface between the negative electrode layer and the solid electrolyte layer. Furthermore, the negative electrode layer and the solid electrolyte layer may not be sufficiently adhered to each other. If the degree of densification and adhesion is insufficient, abnormal electrodeposition occurs, resulting in the problem of not being able to achieve the required battery performance.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid-state battery that can suppress the occurrence of abnormal electrodeposition and has favorable battery performance.

[0009] (1) The present invention relates to a solid-state battery having a structure in which an anode layer, a solid electrolyte layer, and a cathode layer are stacked in this order, the solid electrolyte layer having a first solid electrolyte layer disposed on the anode layer side and a second solid electrolyte layer disposed adjacent to the first solid electrolyte layer, and the density of the first solid electrolyte layer is higher than the density of the second solid electrolyte layer.

[0010] According to the invention (1), the occurrence of abnormal electrodeposition can be suppressed, and a solid-state battery having favorable battery performance can be provided.

[0011] (2) The solid-state battery according to (1), further comprising a third solid electrolyte layer disposed on the positive electrode layer side, the third solid electrolyte layer being disposed adjacent to the second solid electrolyte layer.

[0012] According to the invention (2), a solid-state battery having more preferable battery performance can be provided.

[0013] (3) The solid-state battery according to (1) or (2), wherein the particle size of the solid electrolyte material constituting the first solid electrolyte layer is 1 μm or less in D50.

[0014] According to the invention (3), the first solid electrolyte layer can be easily densified.

[0015] (4) The solid-state battery according to any one of (1) to (3), wherein the thickness of the first solid electrolyte layer is 7 μm or less.

[0016] According to the invention (4), the first solid electrolyte layer can be easily densified.

[0017] (5) The solid-state battery according to any one of (1) to (4), wherein the porosity of the first solid electrolyte layer is 7% or less.

[0018] According to the fifth aspect of the present invention, the first solid electrolyte layer can be said to be highly densified, and the efficiency of ion migration within the first solid electrolyte layer is improved.

[0019] (6) The density of the first solid electrolyte layer is 1.65 g / cm ３ The solid state battery according to any one of (1) to (5).

[0020] According to the invention (6), the occurrence of abnormal electrodeposition can be more reliably suppressed.

[0021] (7) The solid state battery according to any one of (1) to (6), wherein the content of the binder contained in the first solid electrolyte layer is 0% by mass or more and 25% by mass or less.

[0022] According to the seventh aspect of the present invention, the density of the first solid electrolyte layer can be easily increased, and the energy density of the solid-state battery can be improved.

[0023] FIG. 1 is a conceptual cross-sectional view showing the configuration of a solid state battery according to an embodiment of the present invention. FIG. 2 is a view showing part of a process in a method for manufacturing a solid state battery according to a first embodiment of the present invention. FIG. 3 is a view showing part of a process in a method for manufacturing a solid state battery according to each embodiment of the present invention. FIG. 4 is a view showing part of a process in a method for manufacturing a solid state battery according to the first embodiment of the present invention. FIG. 5 is a view showing part of a process in a method for manufacturing a solid state battery according to a second embodiment of the present invention. FIG. 6 is a view showing part of a process in a method for manufacturing a solid state battery according to the second embodiment of the present invention. FIG. 7 is a graph showing charge / discharge curves of a solid state battery according to an example of the present invention. FIG. 8 is a graph showing a self-discharge curve of a solid state battery according to an example of the present invention. FIG. 9 is a graph showing measurement results of the internal resistance of a solid state battery according to an example of the present invention. FIG. 10 is a graph showing charge / discharge curves of a solid state battery according to an example of the present invention. FIG. 11 is a graph showing charge / discharge curves of a solid state battery according to an example of the present invention. FIG. 12 is a graph showing charge / discharge curves of a solid state battery according to a comparative example of the present invention. FIG. 13 is a graph showing the cross-sectional porosity of a solid electrolyte layer of a solid state battery according to an example of the present invention. FIG. 14 is a graph showing the average cross-sectional void size of a solid electrolyte layer of a solid state battery according to an example of the present invention.

[0024] [Solid-State Battery] As shown in Fig. 1, the solid-state battery 1 has an electrode laminate in which an anode layer 2, a solid electrolyte layer 4, and a cathode layer 3 are laminated in this order. In this embodiment, the structure in which the anode layer 2, the solid electrolyte layer 4, the cathode layer 3, the solid electrolyte layer 4, and the anode layer 2 are laminated in this order as shown in Fig. 1 will be described as the laminate structure of the solid-state battery 1. However, the structure of the solid-state battery 1 is not limited to the above, and it is sufficient if the solid-state battery 1 has a structure in which the solid electrolyte layer 4 is laminated between the anode layer 2 and the cathode layer 3.

[0025] The solid electrolyte layer 4 in the solid battery 1 has at least a first solid electrolyte layer 41 disposed on the anode layer 2 side and a second solid electrolyte layer 42 disposed adjacent to the first solid electrolyte layer 41. An intermediate layer 5 may be optionally disposed between the anode layer 2 and the solid electrolyte layer 4. The solid electrolyte layer 4 may optionally have a third solid electrolyte layer 43. In the following description, the solid battery 1 will be described as having the intermediate layer 5 and the third solid electrolyte layer 43.

[0026] The solid state battery 1 is not particularly limited, but may be a lithium ion solid state secondary battery or a lithium metal secondary battery.

[0027] (Negative Electrode Layer) The negative electrode layer 2 has an anode active material layer 21 and an anode current collector layer 22. The anode active material layer 21 is not particularly limited and can be made of a material that can be used as an anode active material for a solid-state battery. The anode active material layer 21 is preferably a lithium metal layer in which the anode active material is lithium metal. This is because the solid-state battery 1 according to the present invention can adhere to the solid electrolyte layer 4 with high adhesion strength even when the anode active material layer 21 is made of a hard metal. The lithium metal includes not only lithium metal but also lithium alloys. The anode active material layer 21 can also be made of silicon-based active materials such as Si and Si alloys, lithium titanate (Li ４ Ti ５ O １２ ), lithium transition metal oxides such as TiO ２ , Nb ２ O ３ and W.O. ３The conductive material may be composed of transition metal oxides such as those mentioned above, metal sulfides, metal nitrides, carbon materials such as graphite, soft carbon and hard carbon, metallic indium, or the like.

[0028] The negative electrode active material layer 21 may contain materials that can be contained in a negative electrode active material layer of a solid-state battery in addition to the above. Examples of such materials include a solid electrolyte, a conductive additive, a binder, etc. Examples of the solid electrolyte include the same solid electrolyte contained in the solid electrolyte layer 4 described below. Examples of the conductive additive include carbon black, natural graphite, carbon fiber, and carbon nanotubes. Examples of the binder include a fluorine-based polymer, a nitrile-based polymer, a polyester-based polymer, an acrylic acid-based polymer, a cellulose-based polymer, a styrene-based polymer, a styrene-butadiene-based polymer, a vinyl acetate-based polymer, a urethane-based polymer, and a fluoroethylene-based polymer.

[0029] The negative electrode current collector layer 22 is not particularly limited, but may be made of copper, nickel, stainless steel, etc. Examples of the shape of the negative electrode current collector layer 22 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the negative electrode current collector layer 22 extends in a predetermined direction to form a negative electrode current collector tab 22a.

[0030] (Solid Electrolyte Layer) The solid electrolyte layer 4 is formed between the anode layer 2 and the cathode layer 3. In this embodiment, the solid electrolyte layer 4 has a structure in which a first solid electrolyte layer 41 disposed on the anode layer side, a second solid electrolyte layer 42, and a third solid electrolyte layer 43 disposed on the cathode side are stacked in this order.

[0031] The first solid electrolyte layer 41 is disposed on the anode layer side. The first solid electrolyte layer 41 may be disposed adjacent to the anode layer 2. When the solid battery 1 has an intermediate layer 5 as shown in FIG. 1 , the first solid electrolyte layer 41 may be disposed adjacent to the intermediate layer 5. The first solid electrolyte layer 41 has a higher density than the second solid electrolyte layer 42 and is densified. During the densification process, the first solid electrolyte layer 41 adheres closely to the intermediate layer 5 or the anode layer 2. By densifying the first solid electrolyte layer 41 and adhering closely to the intermediate layer 5 or the anode layer 2, the occurrence of abnormal electrodeposition can be suppressed. Furthermore, favorable battery performance can be obtained.

[0032] The density of the first solid electrolyte layer 41 is 1.65 g / cm ３ It is preferable that the density is 1.80 / cm or more. ３ The density of the first solid electrolyte layer 41 is not particularly limited, but is preferably 2.00 / cm ３ It may be the following:

[0033] The solid electrolyte material constituting the first solid electrolyte layer 41 is not particularly limited, and may be any material that can be used as an electrolyte in a solid-state battery. Examples include inorganic solid electrolytes such as sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, and lithium-containing salts, and polymer solid electrolytes such as polyethylene oxide. The above solid electrolytes may be used alone or in combination of two or more.

[0034] The solid electrolyte material constituting the first solid electrolyte layer 41 is preferably in a particulate form. The particle size (D50, median diameter) of the solid electrolyte material constituting the first solid electrolyte layer 41 is preferably 1 μm or less. This allows the first solid electrolyte layer 41 to be easily densified. The particle size of the solid electrolyte material is more preferably 0.7 μm or less. The particle size of the solid electrolyte material is not particularly limited, but may be 50 nm or more.

[0035] The first solid electrolyte layer 41 may contain, in addition to the solid electrolyte material, a material that can be used in a solid electrolyte layer of a solid-state battery. For example, the first solid electrolyte layer 41 may contain a binder. The binder may be the same material as the binder that can be contained in the negative electrode active material layer 21. When the first solid electrolyte layer 41 contains a binder, the upper limit of the binder content is 25 mass% with respect to the total mass of the first solid electrolyte layer 41. The binder content is preferably 10 mass% or less, and more preferably 1.3 mass% or less. This allows for easy densification of the first solid electrolyte layer 41 and improved energy density of the solid-state battery 1. The binder content may be 0 mass%.

[0036] The thickness of the first solid electrolyte layer 41 (the length of each layer in the stacking direction) is preferably 7 μm or less. This allows the first solid electrolyte layer 41 to be easily densified. The thickness of the first solid electrolyte layer 41 is more preferably 3 μm or less. The thickness of the first solid electrolyte layer 41 is not particularly limited, but may be 1 μm or more.

[0037] The porosity of the first solid electrolyte layer 41 is preferably 7% or less. This can be said to increase the density of the first solid electrolyte layer 41. Furthermore, the efficiency of charge transfer within the first solid electrolyte layer 41 is improved. The porosity of the first solid electrolyte layer 41 is more preferably 4% or less. The porosity of the first solid electrolyte layer 41 is not particularly limited, but may be 1% or more.

[0038] The second solid electrolyte layer 42 is disposed adjacent to the first solid electrolyte layer 41. The second solid electrolyte layer 42 has a lower density than the first solid electrolyte layer 41. The solid electrolyte material constituting the second solid electrolyte layer 42 is not particularly limited and may be the same as the solid electrolyte material constituting the first solid electrolyte layer 41. The particle size of the solid electrolyte material constituting the second solid electrolyte layer 42 may be the same as or larger than that of the solid electrolyte material constituting the first solid electrolyte layer 41. Alternatively, a solid electrolyte material having a particle size equivalent to that of the solid electrolyte material constituting the first solid electrolyte layer 41 may be combined with a solid electrolyte material having a larger particle size. This allows the second solid electrolyte layer 42 to be densified.

[0039] Like the first solid electrolyte layer 41, the second solid electrolyte layer 42 may contain a binder or the like in addition to the solid electrolyte material. The second solid electrolyte layer 42 may also contain a support. The support may be a three-dimensional structure such as a mesh, a woven fabric, a nonwoven fabric, an embossed body, a punched body, an expanded body, or a foamed body. The second solid electrolyte layer 42 may not contain the support.

[0040] The thickness of the second solid electrolyte layer 42 (the length of each layer in the stacking direction) is not particularly limited, but can be, for example, 5 to 50 μm.

[0041] The third solid electrolyte layer 43 is disposed on the positive electrode layer side. In the present embodiment, the third solid electrolyte layer 43 is disposed adjacent to the positive electrode active material layer 31 in the positive electrode layer 3. The third solid electrolyte layer 43 is disposed adjacent to the second solid electrolyte layer 42. That is, in the present embodiment, the third solid electrolyte layer 43 is disposed between the positive electrode active material layer 31 and the second solid electrolyte layer 42.

[0042] The configuration of the third solid electrolyte layer 43 can be the same as the configuration of the first solid electrolyte layer 41. The third solid electrolyte layer 43 is densified and closely adheres to the positive electrode active material layer 31, thereby achieving favorable battery performance. For example, low resistance is an example of the favorable battery performance.

[0043] (Positive Electrode Layer) The positive electrode layer 3 has a positive electrode active material layer 31 and a positive electrode current collector layer 32. In this embodiment, the positive electrode layer 3 has a configuration in which two positive electrode active material layers 31 are stacked on both sides of one positive electrode current collector layer 32. However, the configuration of the positive electrode layer 3 is not limited to the above, and the positive electrode layer 3 may have a configuration in which one positive electrode active material layer 31 is stacked on one side of one positive electrode current collector layer 32.

[0044] The positive electrode active material layer 31 is not particularly limited and can be made of a material that can be used as a positive electrode active material for a solid-state battery. Examples of the positive electrode active material that can be used to make the positive electrode active material layer 31 include LiCoO ２ , LiNiO ２ , LiCo ｘ Ni ｙ Mn ｚ O ２ (x+y+z=1), LiVO ２ , LiCrO ２ Layered positive electrode active material particles such as LiMn ２ O ４ , Li(Ni ０．２５ Mn ０．７５ ) ２ O ４ , LiCoMnO ４ , Li ２ NiMn ３ O ８ Spinel-type positive electrode active materials such as LiCoPO ４ , LiMnPO ４ , LiFePO ４ Olivine-type positive electrode active materials such as solid solution oxides (Li ２ MnO ３ -LiMO ２ (M=Co, Ni, etc.), conductive polymers such as polyaniline and polypyrrole, Li ２ S, CuS, Li-Cu-S compound, TiS ２ , FeS, MoS ２ , sulfides such as Li—Mo—S compounds, mixtures of sulfur and carbon, etc. The positive electrode active material may be one of the above materials, or may be composed of two or more of the above materials.

[0045] An insulating frame 6 may be provided on the outer periphery of the positive electrode active material layer 31. The insulating frame 6 can prevent short-circuiting of the solid state battery 1 and improve its strength. In this embodiment, the insulating frame 6 is arranged so as to cover the side surfaces of the two positive electrode active material layers 31 formed on both sides of the positive electrode current collector layer 32. The insulating frame 6 also abuts against a portion of the stacking surface of the positive electrode current collector layer 32, and has a gap through which a positive electrode current collector tab 32a (described later) extends. The material constituting the insulating frame 6 is not particularly limited, but examples thereof include insulating oxides such as alumina, resins such as polyvinylidene fluoride (PVDF), and rubbers such as styrene-butadiene rubber (SBR).

[0046] The positive electrode current collector layer 32 is not particularly limited, and can be made of, for example, aluminum, stainless steel, conductive carbon (graphite, carbon nanotubes, etc.), etc. Examples of the shape of the positive electrode current collector layer 32 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the positive electrode current collector layer 32 extends in a predetermined direction to form a positive electrode current collector tab 32a.

[0047] (Intermediate Layer) The intermediate layer 5 is disposed between the anode layer 2 and the solid electrolyte layer 4. For example, when the solid battery 1 is a lithium metal battery, the intermediate layer 5 has the function of uniformly depositing lithium metal. Therefore, the interface between the intermediate layer 5 and the first solid electrolyte layer 41 is stabilized. When the solid battery 1 is a lithium metal secondary battery having the intermediate layer 5, the solid battery 1 may be an anode-free battery in which the anode active material layer 21 is not present during the initial charge. In this case, a lithium metal layer is formed as the anode active material layer 21 after the initial charge / discharge.

[0048] The material constituting the intermediate layer 5 is not particularly limited, but examples thereof include metals capable of alloying with lithium and amorphous carbon. Examples of metals capable of alloying with lithium include tin (Sn), silicon (Si), zinc (Zn), magnesium (Mg), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), and antimony (Sb). The metal capable of alloying with lithium may be nanoparticles. Examples of amorphous carbon include carbon blacks such as acetylene black, furnace black, and ketjen black, coke, and activated carbon. The amorphous carbon may be easily graphitized carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), CNT (carbon nanotube), fullerene, or graphene. The intermediate layer may contain a binder in addition to the above materials.

[0049] [Method for Manufacturing a Solid-State Battery] <First Embodiment> A method for manufacturing a solid-state battery according to this embodiment will be described below with reference to FIGS. 2A to 2D. The method for manufacturing a solid-state battery according to this embodiment is a method for manufacturing a solid-state battery having an electrode stack La in which an anode layer, an intermediate layer, a solid electrolyte layer, and a cathode layer are stacked in this order. The method for manufacturing a solid-state battery according to this embodiment includes Step 1, Step 2A, Step 3, and Step 4A, which will be described below. The order in which the steps are performed can be any order, except that Step 2A is performed after Step 1, and Step 4A is performed after Steps 2A and 3.

[0050] 2A, the first step is a step of press-bonding the negative electrode layer 2 and the intermediate layer 5 to obtain an intermediate layer-negative electrode layer laminate L1. A specific method for disposing the intermediate layer 5 on the surface of the negative electrode layer 2 on the negative electrode active material layer 21 side, which is the lamination surface, is a method of transferring the intermediate layer using an intermediate layer transfer sheet. The intermediate layer transfer sheet can be obtained, for example, by dispersing the material constituting the intermediate layer 5 in a solvent, applying a slurry to a support sheet, and drying the slurry.

[0051] The pressure for pressing the negative electrode layer 2 and the intermediate layer 5 together in the first step is not particularly limited as long as the pressure does not excessively deform the negative electrode layer 2 and the intermediate layer 5 and allows them to be bonded together without peeling in a subsequent step. The pressing pressure in the first step is, for example, in the range of 300 MPa or more and 600 MPa or less.

[0052] Step 2A is a step of placing a material constituting the first solid electrolyte layer 41 on the lamination surface of the intermediate layer 5 in the intermediate layer-anode layer laminate L1 and press-bonding them to obtain a solid electrolyte layer-intermediate layer-anode layer laminate L2, as shown in FIG. 2B . The method of placing the first solid electrolyte layer 41 on the lamination surface of the intermediate layer 5 may be a method using a solid electrolyte layer transfer sheet, or a method using a solid electrolyte sheet formed in advance in a sheet shape. The solid electrolyte layer transfer sheet has the same configuration as the intermediate layer transfer sheet.

[0053] The pressure used to press the intermediate layer-negative electrode layer laminate L1 and the first solid electrolyte layer 41 in Step 2A is preferably higher than the pressure used in Step 4A to integrate the layers. This allows the first solid electrolyte layer 41 to be densified. The pressure used in Step 2A is, for example, in the range of more than 500 MPa and not more than 700 MPa. The pressure is preferably in the range of not less than 600 MPa and not more than 700 MPa.

[0054] 2C , the third step is a step of placing a material constituting the third solid electrolyte layer 43 on the stacking surface of the positive electrode layer 3 and press-bonding them to obtain a solid electrolyte layer-positive electrode layer stack L3. In this embodiment, the positive electrode layer 3 has positive electrode active material layers 31 formed on both sides of the positive electrode current collector layer 32, and the third solid electrolyte layer 43 is placed on both positive electrode active material layers 31. If the positive electrode layer 3 has a positive electrode active material layer 31 formed on only one side of the positive electrode current collector layer 32, the third solid electrolyte layer 43 can be placed on a single positive electrode active material layer 31. The method of placing the third solid electrolyte layer 43 can be the same as in step 2A.

[0055] The pressure used to press the positive electrode layer 3 and the third solid electrolyte layer 43 in the third step is preferably higher than the pressure used in step 4A to integrate the layers, thereby increasing the density of the third solid electrolyte layer 43. The pressure used in the third step is, for example, in the range of 700 MPa to 1200 MPa.

[0056] As shown in FIG. 2D , step 4A is a step of obtaining an electrode laminate La by placing a second solid electrolyte layer 42 between the solid electrolyte layer-intermediate layer-anode layer laminate L2 and the solid electrolyte layer-cathode layer laminate L3 so as to face each solid electrolyte layer, and then press-bonding the layers together. The second solid electrolyte layer 42 may be, for example, a pre-formed sheet. In this embodiment, the solid electrolyte layer-cathode layer laminate L3 has a third solid electrolyte layer 43 on both sides. Therefore, two second solid electrolyte layers 42 are placed so as to face both sides of the solid electrolyte layer-cathode layer laminate L3, and each layer is further placed so as to be sandwiched between two solid electrolyte layer-intermediate layer-anode layer laminates L2. If the solid electrolyte layer-cathode layer laminate L3 has the third solid electrolyte layer 43 on only one side, one second solid electrolyte layer 42 can be arranged to face the third solid electrolyte layer 43, and one solid electrolyte layer-intermediate layer-anode layer laminate L2 can also be arranged.

[0057] Since Step 4A is a step of integrating the layers, it is preferable to apply a pressing pressure that does not excessively deform the layers. The pressing pressure in Step 4A is, for example, in the range of 300 MPa to 500 MPa. Even if the pressing pressure in Step 4A is within the above range, the first solid electrolyte layer 41 has already been sufficiently densified by Step 2A. Therefore, abnormal electrodeposition can be suppressed, and favorable battery performance can be obtained.

[0058] In each of the above steps, the press bonding apparatus is not particularly limited, and a roll press, a plate press, or an isostatic press (CIP, WIP) apparatus can be used. When press bonding is performed using a roll press, the conveying directions of the objects to be press-bonded to the roll press may be the same or different. For example, the conveying direction of the objects to the roll press in steps 2A and 3 may be different from or perpendicular to the conveying direction of the objects to the roll press in step 4A. This allows the layers with a low Young's modulus to extend in one direction, thereby pulling the solid electrolyte layer 4 and making it less likely that defects will occur in the solid electrolyte layer 4.

[0059] Second Embodiment A method for manufacturing a solid-state battery according to this embodiment is a method for manufacturing a solid-state battery having an electrode stack Lb in which an anode layer, a solid electrolyte layer, and a cathode layer are stacked in this order. Unlike the first embodiment, the electrode stack Lb does not have an intermediate layer 5. Therefore, the method for manufacturing a solid-state battery according to this embodiment does not include the first step.

[0060] The method for manufacturing a solid-state battery according to this embodiment includes the following steps 2B, 3, and 4B. The steps may be performed in any order except that step 4B is performed after steps 2B and 3. In the following description, the same reference numerals are used in the drawings to designate the same components as those in the first embodiment, and the description thereof may be omitted.

[0061] 2E, Step 2B is a step of arranging and press-bonding a material constituting the first solid electrolyte layer 41 on the surface of the anode layer 2 that faces the anode active material layer 21, thereby obtaining a solid electrolyte layer-anode layer laminate L2a. The method of arranging the first solid electrolyte layer 41 on the surface of the anode layer 2 can be the same as in Step 2A.

[0062] The pressure used to press the anode layer 2 and the first solid electrolyte layer 41 in step 2B is preferably higher than the pressure used in step 4B, in which the layers are integrated. This allows the first solid electrolyte layer 41 to be densified. The pressure used in step 2B is, for example, in the range of more than 500 MPa and not more than 700 MPa. The pressure is preferably in the range of not less than 600 MPa and not more than 700 MPa.

[0063] The third step can be the same step as in the first embodiment.

[0064] In Step 4B, as shown in FIG. 2F , a second solid electrolyte layer 42 is disposed between the solid electrolyte layer-anode layer laminate L2a and the solid electrolyte layer-cathode layer laminate L3 so as to face the respective solid electrolyte layers, and then press-bonded to obtain an electrode laminate Lb. The remaining configuration of Step 4B can be the same as Step 4A in the first embodiment. The pressing pressure in Step 4B is, for example, in the range of 300 MPa or more and 500 MPa or less. In this embodiment, since the first solid electrolyte layer 41 is densified in advance in Step 2B, the same effects as in the first embodiment can be obtained.

[0065] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. The solid-state battery 1 may have a configuration that can be used in solid-state batteries, such as an exterior body, in addition to the electrode stack shown in FIG. 1. The manufacturing methods of the solid-state batteries according to the first and second embodiments may include any steps other than those described above.

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the contents of the following examples.

[0067] Example 1 An electrode laminate having a negative electrode layer, a solid electrolyte layer, and a positive electrode layer laminated in this order and no intermediate layer was produced by the following procedure.

[0068] [Preparation of Positive Electrode Layer] A 12.0 μm thick aluminum foil was prepared as a positive electrode current collector. 60.0 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) was used as the positive electrode active material, 35.8 parts by mass of a sulfide solid electrolyte was used as the solid electrolyte, 2.9 parts by mass of acetylene black (DENKA BLACK Li-100, manufactured by Denka Co., Ltd.) was used as the conductive additive, and 1.3 parts by mass of an SBR (styrene butadiene rubber) binder were mixed together. The resulting mixture was dispersed in a solvent to prepare a positive electrode active material slurry. The resulting positive electrode active material slurry was applied to both sides of the positive electrode current collector so that the basis weight after drying was 27.4 mg / cm. ２ The solution was applied using a bar coater so as to form a positive electrode layer, and then dried.

[0069] [Preparation of Solid Electrolyte Transfer Sheet for First and Third Solid Electrolyte Layers] A dispersion of a sulfide solid electrolyte (median diameter: 0.7 μm) was applied to a support sheet and dried to prepare a solid electrolyte transfer sheet.

[0070] [Preparation of Second Solid Electrolyte Layer] As the sulfide solid electrolyte, one with a median diameter of 3 μm (A) and one with a median diameter of 0.7 μm (B) were used in a mixing ratio of 8:2. An SBR (styrene butadiene rubber) binder was used as the binder. 94.5 parts by mass of the above solid electrolyte and 5.5 parts by mass of the binder were mixed. The resulting mixture was dispersed in a solvent to prepare a solid electrolyte slurry. The resulting solid electrolyte slurry was impregnated into a nonwoven fabric substrate and dried to prepare a second solid electrolyte layer.

[0071] [Preparation of Negative Electrode Layer] A copper foil having a thickness of 10 μm was prepared as a negative electrode current collector. A metallic lithium foil having a thickness of 6.5 μm was laminated on the surface of the copper foil to prepare a negative electrode layer.

[0072] [Preparation of Electrode Stack] A solid electrolyte from a solid electrolyte transfer sheet was transferred onto the surface of the metallic lithium foil of the negative electrode layer to form a first solid electrolyte layer. The negative electrode layer and the first solid electrolyte layer were then press-bonded at 25°C under a bonding pressure of 600 MPa to produce a solid electrolyte layer-negative electrode layer stack. A solid electrolyte from a solid electrolyte transfer sheet was transferred onto the surfaces of two positive electrode active material layers of the positive electrode layer to form a third solid electrolyte layer. The positive electrode layer and the third solid electrolyte layer were then press-bonded at 25°C under a bonding pressure of 800 MPa to produce a solid electrolyte layer-cathode layer stack. Next, two second solid electrolyte layers were arranged to sandwich the solid electrolyte layer-cathode layer stack from both sides, and two more solid electrolyte layer-negative electrode layer stacks were arranged on the outside. These layers were press-bonded at 25°C under a bonding pressure of 300 MPa. A roll press was used for the pressing method. In this way, the electrode stack according to Example 1 was produced.

[0073] Example 2 An electrode laminate in which an anode layer, an intermediate layer, a solid electrolyte layer, and a cathode layer were stacked in this order was produced by the following procedure: The anode layer, the solid electrolyte layer transfer sheet, the second solid electrolyte layer, and the cathode layer were produced by the same procedures as in Example 1.

[0074] [Preparation of Intermediate Layer Transfer Sheet] Sn particles (median diameter: 0.07 μm) were used as the metal nanoparticles, and acetylene black (median diameter: 0.05 μm) was used as the amorphous carbon. A total of 95 parts by mass of the above mixture was mixed with 5 parts by mass of a PVDF binder. The resulting mixture was dispersed in a solvent to prepare an intermediate layer slurry. The resulting intermediate layer slurry was applied to a support sheet and dried to prepare an intermediate layer transfer sheet with a final thickness of 4 to 10 μm.

[0075] [Preparation of Electrode Stack] An intermediate layer from an intermediate layer transfer sheet was transferred onto the surface of the metallic lithium foil of the negative electrode layer to form an intermediate layer, and the layers were press-bonded at 25°C under a bonding pressure of 400 MPa to prepare an intermediate layer-negative electrode layer stack. Next, a solid electrolyte from a solid electrolyte transfer sheet was transferred onto the surface of the intermediate layer of the intermediate layer-negative electrode layer stack to form a first solid electrolyte layer. Next, the intermediate layer-negative electrode layer stack and the first solid electrolyte layer were press-bonded at 25°C under a bonding pressure of 600 MPa to prepare a solid electrolyte layer-intermediate layer-negative electrode layer stack. A solid electrolyte layer-cathode layer stack was prepared in the same manner as in Example 1. Next, two second solid electrolyte layers were placed so as to sandwich the solid electrolyte layer-cathode layer stack from both sides, and two solid electrolyte layer-intermediate layer-negative electrode layer stacks were placed on the outside, and these three stacks were press-bonded at 25°C under a bonding pressure of 500 MPa. A roll press was used for the pressing method. In this way, the electrode stack according to Example 2 was prepared.

[0076] Example 3 An electrode laminate according to Example 3 was produced in the same manner as in Example 2, except that only acetylene black was used as the intermediate layer transfer sheet.

[0077] Comparative Example 1 An electrode laminate according to Comparative Example 1 was produced in the same manner as in Example 2, except that a first solid electrolyte layer was not formed. That is, instead of producing a solid electrolyte layer-intermediate layer-anode layer laminate, two second solid electrolyte layers were arranged to sandwich the solid electrolyte layer-cathode layer laminate from both sides, and two intermediate layer-anode layer laminates were further arranged on the outside, and these three laminates were press-bonded at 25°C with a bonding pressure of 500 MPa. A roll press device was used as the pressing method. In this way, an electrode laminate according to Comparative Example 1 was produced.

[0078] [Charge / Discharge Test] Solid-state battery cells were constructed using the electrode laminates according to each Example and Comparative Example, and a charge / discharge test was conducted. FIG. 3A is a graph showing the results of the charge / discharge test for the solid-state battery according to Example 1. In the graph of FIG. 3A, the vertical axis represents voltage (V) and the horizontal axis represents capacity (mAh). The test was conducted at 60°C with N=3, and the respective results are shown as Example 1a, Example 1b, and Example 1c. The charge / discharge efficiencies calculated from FIG. 3A were 98.6% for Example 1a, 98.5% for Example 1b, and 98.7% for Example 1c, clearly demonstrating favorable charge / discharge efficiencies. The charge / discharge efficiencies were calculated using the formula: discharge capacity / charge capacity = charge / discharge efficiency.

[0079] FIG. 4A shows the results of a charge-discharge test of the solid-state battery according to Example 3. Similarly, FIG. 4B shows the results of a charge-discharge test of the solid-state battery according to Example 2. The test conditions are the same as those in FIG. 3A. Example 2 was performed with N=2, and the respective results are shown as Example 2a and Example 2b. The charge-discharge efficiencies calculated from FIGS. 4A and 4B were 100.4% for Example 2a, 97.2% for Example 2b, and 98.5% for Example 3, which clearly shows that favorable charge-discharge efficiencies were obtained.

[0080] 5 shows the results of a charge-discharge test of the solid-state battery according to Comparative Example 1. The test conditions were the same as those in FIG. 3A. As shown in FIG. 5, the voltage during charging did not increase relative to the discharge capacity, and it is clear that an overcharged state occurred.

[0081] [Self-Discharge Measurement] Figure 3B is a graph showing the results of measuring the self-discharge state of the solid-state battery according to Example 1. In the graph of Figure 3B, the vertical axis represents voltage (V) and the horizontal axis represents time (h). N = 3 tests were conducted, and the respective results are shown as Example 1a, Example 1b, and Example 1c. The self-discharge calculated from Figure 3B was 1.025 (mV / h) for Example 1a, 0.875 (mV / h) for Example 1b, and 1.025 (mV / h) for Example 1c. It is clear that the self-discharge was sufficiently low, being 1.5 (mV / h) or less, and favorable results were obtained.

[0082] [DCR Resistance Measurement] Fig. 3C is a graph showing the results of measuring the DCR resistance of the solid state battery according to Example 1. In the graph of Fig. 3C, the vertical axis represents the DCR resistance (Ωcm ２ ) is shown. First, the SOC of the solid-state battery according to Example 1 was adjusted to 50%. Next, it was discharged at 3.8 C for 10 seconds, and the DCR resistance value during discharge was measured. The test was performed with N=3, and the respective results are shown as Example 1a, Example 1b, and Example 1c. As shown in FIG. 3C, the degree of variation in the DCR resistance value of each Example was low, and batteries with stable performance were fabricated.

[0083] [Cross-sectional porosity measurement] FIG. 6 is a graph comparing the cross-sectional porosity near the interface between the intermediate layer and the solid electrolyte layer of the electrode stacks according to Comparative Example 1, Example 2, and Reference Example. The porosity (%) was measured as follows. First, an SEM cross-sectional photograph of the target solid-state battery was obtained, and voids were extracted by image processing within the relevant area (the solid electrolyte layer near the interface between the intermediate layer and the solid electrolyte of the electrode stack). Next, the total area of ​​the calculated void portions was calculated, and the value obtained by dividing this by the total area of ​​the relevant area was determined as the porosity (%). Note that the Reference Example is an example in which an electrode stack was fabricated in the same manner as Example 2, except that a water-insulating press (WIP) machine was used instead of the roll press machine. As shown in FIG. 6, the cross-sectional porosity of the electrode stack according to Example 2, while not as high as that of the Reference Example, was lower than that of the electrode stack according to Comparative Example 1, clearly demonstrating the densification of the first solid electrolyte layer.

[0084] [Measurement of Average Cross-Sectional Void Size] Fig. 7 is a graph comparing the average cross-sectional void size near the interface between the intermediate layer and the solid electrolyte layer of the electrode laminates according to Comparative Example 1, Example 2, and Reference Example. The average cross-sectional void size was calculated by aggregating the size of the void portion calculated when calculating the porosity (%). As shown in Fig. 7, the average cross-sectional void size of the electrode laminate according to Example 2 is lower than the average cross-sectional void size of the electrode laminates according to Reference Example and Comparative Example 1, clearly indicating that the first solid electrolyte layer is densified.

[0085] REFERENCE SIGNS LIST 1 Solid-state battery 2 Anode layer 3 Cathode layer 4 Solid electrolyte layer 41 First solid electrolyte layer 42 Second solid electrolyte layer 43 Third solid electrolyte layer

Claims

1. A solid-state battery having a structure in which an anode layer, a solid electrolyte layer, and a cathode layer are stacked in this order, wherein the solid electrolyte layer has a first solid electrolyte layer disposed on the anode layer side and a second solid electrolyte layer disposed adjacent to the first solid electrolyte layer, and the density of the first solid electrolyte layer is higher than the density of the second solid electrolyte layer.

2. The solid-state battery according to claim 1, further comprising a third solid electrolyte layer disposed on the positive electrode layer side, the third solid electrolyte layer being disposed adjacent to the second solid electrolyte layer.

3. The solid state battery according to claim 1 or 2, wherein the particle size of the solid electrolyte material constituting the first solid electrolyte layer is 1 μm or less in D50.

4. The solid-state battery according to claim 1 or 2, wherein the thickness of the first solid electrolyte layer is 7 μm or less.

5. The solid-state battery according to claim 1 or 2, wherein the porosity of the first solid electrolyte layer is 7% or less.

6. The density of the first solid electrolyte layer is 1.65 g / cm ３ The solid state battery according to claim 1 or 2.

7. The solid state battery according to claim 1 or 2, wherein the content of the binder contained in the first solid electrolyte layer is 0% by mass or more and 25% by mass or less.

Images