Solid-state battery and method for manufacturing a solid-state battery

Abstract

To realize a solid state battery capable of suppressing deterioration in performance caused by a positive electrode layer.SOLUTION: A solid state battery includes a positive electrode layer, a negative electrode layer, and an electrolyte layer provided therebetween. In the solid state battery, the X-ray diffraction spectrum of the positive electrode layer measured using CuKα rays contains diffraction peaks attributed to LCPO and LAGP, and the ratio P / Q of the diffraction peak intensity P at the diffraction angle 2θ=13.0±0.2° to the diffraction peak intensity Q at the diffraction angle of 2θ=14.35±0.2° in the X-ray diffraction spectrum is in the range of 0.074<P / Q<5.744. According to the solid state battery having a positive electrode layer with a P / Q ratio within such a range, the positive electrode layer has a good crystal structure, and an increase in resistance and deterioration in charge / discharge characteristics due to the positive electrode layer can be suppressed. This results in a high performance solid state battery with a positive electrode layer with excellent properties.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a solid-state battery and a method for manufacturing the same.

Background Art

[0002] As one type of battery, a solid-state battery is known. For example, a solid-state battery is known in which a positive electrode layer containing a positive electrode active material and a solid electrolyte is provided on one surface side of an electrolyte layer using a solid electrolyte, and a negative electrode layer containing a negative electrode active material and a solid electrolyte is provided on the other surface side.

[0003] Regarding solid-state batteries, for example, as the positive electrode active material, a general formula LiMPO4 (M is at least one selected from the group consisting of Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel)) is used, and as the solid electrolyte, a general formula Li 1+z M III z Ti IV 2-z (PO4)3 (M III is at least one metal ion selected from the group consisting of Al (aluminum), Y (yttrium), Ga (gallium), In (indium), La (lanthanum), 0 ≦ z ≦ 0.6) is known. Also, a technique using amorphous LiFePO4 (lithium iron phosphate) as the positive electrode active material and LiPON (lithium phosphate oxynitride) or LiAl(PO4)(P2O7) (lithium aluminum pyrophosphate phosphate) as the solid electrolyte is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a solid-state battery, in addition to the olivine-type material as described above, a pyrophosphate-type material, for example, the general formula Li2Co 1-x M x P 2-y A y O7 (where M is any one of Ti (titanium), V (vanadium), Cr (chromium), Ni, Fe, and A is any one of B (boron), C (carbon), Al, Si (silicon), Ga, Ge (germanium), 0 ≦ x < 1, 0 ≦ y ≦ 0.07), such as LCPO-based materials such as Li2CoP2O7 (lithium cobalt pyrophosphate) may be used. Such LCPO-based materials are materials with relatively high average potential and capacity, and are considered effective in improving the energy density of solid-state batteries.

[0006] However, when an LCPO-based material is used as the positive electrode active material and a NASICON (Na super ionic conductor) type solid electrolyte, for example, the general formula Li 1+m Al m Ge 2-m (PO4)3 (0 < m < 1, referred to as "LAGP") is used for the solid electrolyte of the positive electrode layer, depending on the firing conditions during the manufacturing process of the solid-state battery, a positive electrode layer with a good crystal structure may not be obtained. If a positive electrode layer with a good crystal structure cannot be obtained, sufficient charge-discharge characteristics may not be obtained, and a high-performance solid-state battery may not be obtained.

[0007] On one side, the present invention aims to realize a solid-state battery capable of suppressing performance degradation caused by the positive electrode layer.

Means for Solving the Problems

[0008] In one aspect, it has a positive electrode layer, a negative electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, and the positive electrode Layer , Li2Co 1-x M x P 2-y Ay O7 (M is any one of Ti, V, Cr, Ni, Fe, A is any one of B, C, Al, Si, Ga, Ge, 0 ≦ x < 1, 0 ≦ y ≦ 0.07), and the first Li 1+m Al m Ge 2-m (PO4)3 (0 < m < 1), Li9Al3(P2O7)3(PO4)2, and The Li is included in the first X-ray diffraction spectrum of the positive electrode layer, measured using CuKα rays. 2 Co 1-x M x P 2-y A y O 7 And, Li of previous 1 1+m Al m Ge 2-m (PO 4 ) 3 And, the Li 9 Al 3 (P 2 O 7 ) 3 (PO 4 ) 2 and includes diffraction peaks attributable to, and at a diffraction angle 2θ = 13.0 ± 0.2° of the first X-ray diffraction spectrum, the diffraction peak attributable to (the (110) of Li2Co 1-x M x P 2-y A y O7 overlaps with the diffraction peak attributable to (the (002) of Li9Al3(P2O7)3(PO4)2) and appears, and at a diffraction angle 2θ = 14.35°, the diffraction peak attributable to (the (11-1) of Li2Co 1-x M x P 2-y A y O7 appears, and a solid battery is provided in which the ratio P / Q of the diffraction peak intensity P at the diffraction angle 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at the diffraction angle 2θ = 14.35 ± 0.2° is in the range of 0.074 < P / Q < 5.744.

[0009] In one aspect, a step of forming a laminate having a positive electrode layer, a negative electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, and a step of firing the laminate in an inert gas atmosphere are included. In the positive electrode layer of the laminate before firing, Li2Co 1-x M x P 2-y A y O7 (where M is any one of Ti, V, Cr, Ni, Fe; A is any one of B, C, Al, Si, Ga, Ge; 0 ≦ x < 1, 0 ≦ y ≦ 0.07), and the first Li 1+m Al m Ge 2-m (PO4)3 (0 < m < 1) are included, In the positive electrode layer of the laminate after firing, the Li 2 Co 1-x M x P 2-y A y O 7 And, Li of previous 1 1+m Al m Ge 2-m (PO 4 ) 3 And, Li 9 Al 3 (P 2 O 7 ) 3 (PO 4 ) 2 and are included, In the step of firing the laminate, the first X-ray diffraction spectrum of the positive electrode layer in the fired laminate measured using CuKα rays includes diffraction peaks attributed to the Li2Co 1-x M x P 2-y A y O7, the first Li 1+m Al m Ge 2-m (PO4)3, and The aforementioned Li9Al3(P2O7)3(PO4)2. At a diffraction angle 2θ = 13.0 ± 0.2° of the first X-ray diffraction spectrum, the Li2Co 1-x M x P 2-y A yThe diffraction peak attributed to (110) of O7 and the diffraction peak attributed to (002) of Li9Al3(P2O7)3(PO4)2 appear overlapping, and at a diffraction angle 2θ = 14.35°, the Li2Co 1-x M x P 2-y A y The diffraction peak attributed to (11-1) of O7 appears, and under the firing temperature condition where the ratio P / Q of the diffraction peak intensity P at the diffraction angle 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at the diffraction angle 2θ = 14.35 ± 0.2° is in the range of 0.074 < P / Q < 5.744, a method for manufacturing a solid battery for firing the laminate is provided.

Advantages of the Invention

[0010] On one side, it becomes possible to realize a solid battery capable of suppressing a decrease in performance caused by the positive electrode layer.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram showing an example of the manufacturing process flow of a solid battery. [Figure 2] It is a diagram for explaining the first example of the laminate formation process. [Figure 3] It is a diagram for explaining the second example of the laminate formation process. [Figure 4] It is a diagram for explaining an example of the degreasing and firing process. [Figure 5] It is a diagram for explaining an example of the current collector formation process. [Figure 6] It is a diagram showing an example of the XRD spectrum of the positive electrode layer. [Figure 7] It is a diagram showing an example of the relationship between the firing temperature and the ratio of a predetermined diffraction peak intensity of the positive electrode layer. [Figure 8] It is a diagram showing the first example of the relationship between the firing temperature and the discharge capacity and resistance. [Figure 9] It is a diagram showing the second example of the relationship between the firing temperature and the discharge capacity and resistance. [Figure 10] It is a diagram (part (1)) showing an example of the XRD spectrum of the negative electrode layer. [Figure 11] This is Figure (2) showing an example of the XRD spectrum of the negative electrode layer. [Figure 12] This figure shows an example of the relationship between firing temperature and a predetermined diffraction peak intensity ratio of the negative electrode layer. [Figure 13] This figure shows an example of the relationship between discharge capacity and a predetermined diffraction peak intensity ratio of the negative electrode layer. [Figure 14] This is a figure (part 1) showing an example of measurement results for the charge and discharge characteristics of a solid-state battery. [Figure 15] This is Figure (2) showing an example of measurement results for the charge and discharge characteristics of a solid-state battery. [Modes for carrying out the invention]

[0012] One type of battery known is a solid-state battery, which comprises a positive electrode layer containing a positive electrode active material and a solid electrolyte, a negative electrode layer containing a negative electrode active material and a solid electrolyte, and a solid electrolyte layer provided between the positive and negative electrode layers. Solid-state batteries do not use flammable organic electrolytes like lithium-ion secondary batteries, thus reducing risks such as leakage, combustion, explosion, and generation of toxic gases, thereby enhancing safety. They also have advantages such as being easy to handle in the atmosphere and maintaining performance under low and high temperature conditions.

[0013] For example, the positive electrode active material of a solid-state battery is Li2Co 1-x M x P 2-y A y An LCPO-based material represented as O7 (where M is one of Ti, V, Cr, Ni, Fe, and A is one of B, C, Al, Si, Ga, Ge, 0≦x<1, 0≦y≦0.07) can be used. For example, Li2CoP2O7, one such LCPO-based material, has an average potential (vsLi / Li +) is about 5V and the capacity (mass capacity density) is about 200 mAh / g, and it is considered effective for improving the energy density of solid-state batteries. In addition, for the solid electrolyte of solid-state batteries, oxide solid electrolytes can be used, for example, a LAGP-based material which is one type of NASICON-type oxide solid electrolytes. The LAGP-based material is an oxide solid electrolyte represented by the general formula Li 1+m Al m Ge 2-m (PO4)3 (0 < m < 1), and is also called aluminum-substituted lithium germanium phosphate, etc. For example, as the solid electrolyte of a solid-state battery, Li 1.5 Al 0.5 Ge 1.5 (PO4)3 can be used.

[0014] Here, when using an LCPO-based material as the positive electrode active material of the positive electrode layer of a solid-state battery and using a LAGP-based material as the solid electrolyte contained in the positive electrode layer together with it, during firing as described later in the manufacturing process of the solid-state battery, depending on the conditions, a positive electrode layer with a good crystal structure may not be obtained. For example, a good interface may not be formed between the LCPO-based material and the LAGP-based material, or another crystal phase that becomes a resistance layer between them may be formed due to the reaction between the LCPO-based material and the LAGP-based material. If a positive electrode layer with a good crystal structure cannot be obtained, sufficient charge-discharge characteristics may not be obtained, and it may happen that a high-performance solid-state battery cannot be obtained.

[0015] Regarding a solid-state battery that uses an LCPO-based material as the positive electrode active material of the positive electrode layer and a LAGP-based material as the solid electrolyte, in order to realize excellent charge-discharge characteristics and realize its high performance, it is desirable to obtain a positive electrode layer with a good crystal structure and manufacture the solid-state battery using firing conditions under which such a positive electrode layer can be obtained. Hereinafter, a solid-state battery capable of suppressing performance degradation caused by the positive electrode layer will be described.

[0016] In the following description, the LCPO-based material is simply referred to as "LCPO", and the case of using Li2CoP2O7 as LCPO will be taken as an example. Also, the LAGP-based material is simply referred to as "LAGP".

[0017] [Manufacturing of solid-state batteries] First, we will describe examples of materials used to form the positive electrode layer and negative electrode layer of a solid-state battery, as well as the electrolyte layer provided between them.

[0018] (LCPO powder) First, powders of Li, Co, and P are prepared in amounts based on the composition of LCPO. For example, Li2NO3 (lithium nitrate) is used as the Li powder. For example, Co(NO3)2 or Co(NO3)2·6H2O (cobalt nitrate) is used as the Co powder. For example, NH4H2PO4 (ammonium dihydrogen phosphate) is used as the P powder. These raw material powders are weighed and prepared so that they result in the composition of LCPO, in this case Li2CoP2O7, obtained by calcination described later.

[0019] The prepared Li, Co, and P raw materials, along with citric acid and pure water, are mixed in a container such as a beaker. The container is then heated using a hot plate or similar device to evaporate the water. The mixture obtained by the evaporation of water is ground using an agate mortar or similar device, and the ground mixture is calcined at a temperature of 600°C to 700°C for 2 to 6 hours. The calcined body obtained by calcination is ground using an agate mortar or similar device to obtain a powder with a predetermined average particle size (e.g., 7 μm), and the ground material is further ground using a ball mill or similar device. This yields LCPO powder adjusted to a predetermined average particle size (e.g., 1 μm).

[0020] For example, LCPO powder used as the positive electrode active material for the positive electrode layer of a solid-state battery is prepared by this method. Furthermore, other Li compounds such as Li2CO3 (lithium carbonate) may be used as the Li raw material for LCPO, and other Co compounds such as CoCO3 (cobalt carbonate) may be used as the Co raw material. In addition, other methods may be employed for the formation of LCPO, such as a wet process in which the Li raw materials, Co raw materials, and P raw materials are mixed in liquid with citric acid as described above, a wet process in which the Li raw materials, Co raw materials, and P raw materials are mixed while adding pure water to them without using citric acid, or a dry process that does not use citric acid or pure water.

[0021] (LAGP powder) LAGP can be formed using a solid-phase method. First, powders of Li2CO3, Al2O3 (aluminum oxide), GeO2 (germanium oxide), and NH4H2PO4, which are the raw materials for LAGP, are weighed and prepared in a predetermined composition ratio. These raw material powders are mixed using a magnetic mortar and pestle or a ball mill, and the resulting mixture is calcined at a temperature of 300°C to 400°C for 3 to 5 hours. The powder obtained from calcination is melted by heat treatment at a temperature of 1200°C to 1400°C for 1 to 2 hours. The material obtained from the melting is rapidly cooled and vitrified. This yields amorphous LAGP powder. Alternatively, the amorphous LAGP powder obtained in this way may be calcined, for example, under conditions of 600°C to 900°C. This yields crystalline LAGP powder. The obtained LAGP powder is pulverized to adjust to the desired particle size (average particle size D50).

[0022] For example, LAGP powder used in the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery is prepared by this method. Amorphous LAGP powder or crystalline LAGP powder may be used in the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery. Both amorphous and crystalline LAGP powder may be used in the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery.

[0023] (Electrolyte layer material) As an example, the LAGP powder obtained by the above method (either amorphous or crystalline LAGP powder, or both) is mixed with a binder, solvent, etc., and coated onto a carrier such as a polyethylene terephthalate (PET) film by the doctor blade method, etc., to form a green sheet for the electrolyte layer.

[0024] For example, LAGP powder is used as ceramic powder, and a certain amount of binder and a certain amount of anhydrous alcohol as a solvent are added to the ceramic powder to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like electrolyte layer material. The formed paste-like electrolyte layer material is degassed in a vacuum and then coated onto a PET film using a doctor blade method to form a sheet-like electrolyte layer material corresponding to the electrolyte layer. For example, one sheet-like electrolyte layer material formed in this way in a single coating can be used as an electrolyte layer green sheet. Alternatively, to adjust to the desired thickness, multiple sheets of electrolyte layer material formed in a single coating can be laminated and pressed together to form an electrolyte layer green sheet. An electrolyte layer green sheet containing one or more laminated sheets of electrolyte layer material may be cut to a predetermined planar size. For example, an electrolyte layer green sheet formed in this way can be used to form the electrolyte layer of a solid-state battery.

[0025] (Positive electrode layer material) As an example, LAGP powder obtained by the above method (either amorphous or crystalline LAGP powder, or both), a conductive additive, a positive electrode active material, a binder, a solvent, a plasticizer, etc. are mixed and coated onto a carrier such as a PET film using the doctor blade method to form a green sheet for the positive electrode layer. LCPO, in this case Li2CoP2O7, is used as the positive electrode active material. Conductive additives include, for example, carbon materials such as carbon nanofibers, carbon black, graphite, graphene, or carbon nanotubes, and conductive materials such as iron silicide.

[0026] For example, a ceramic powder is obtained by mixing LAGP powder and positive electrode active material in a mass ratio of 50:50. A certain amount of binder and a certain amount of anhydrous alcohol as a solvent are added to this ceramic powder to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like positive electrode layer material. After degassing the formed paste-like positive electrode layer material in a vacuum, it is coated onto a PET film using a doctor blade method to form a sheet-like positive electrode layer material corresponding to the positive electrode layer. For example, one sheet-like positive electrode layer material formed in this way in a single coating process can be used as a positive electrode layer green sheet. Alternatively, to adjust to the desired thickness and amount of positive electrode active material, multiple sheets of positive electrode layer material formed in a single coating process can be laminated and compressed to form a positive electrode layer green sheet. A positive electrode layer green sheet containing one or more laminated sheets of positive electrode layer material may be cut to a predetermined planar size. For example, the green sheet for the positive electrode layer formed in this way is used to form the positive electrode layer of a solid-state battery.

[0027] As another example, the LAGP powder obtained by the above method, a conductive additive, a positive electrode active material, a binder, a dispersant, a plasticizer, a non-aqueous solvent, etc., are mixed to form a paste-like positive electrode layer material called a positive electrode layer paste. For example, the positive electrode layer paste formed in this way is used to form the positive electrode layer of a solid-state battery by screen printing.

[0028] (Negative electrode layer material) As an example, LAGP powder obtained by the above method (either amorphous or crystalline LAGP powder or both), a conductive additive, anode active material, a binder, a solvent, a plasticizer, etc. are mixed and coated onto a carrier such as a PET film using the doctor blade method to form a green sheet for the anode layer. The anode active material can be TiO2 (titanium dioxide), Nb2O5 (niobium oxide), Li3V2(PO4)3 (lithium vanadium phosphate), or Li4Ti5O 12(Lithium titanate) and the like are used. Conductive additives include, for example, carbon materials such as carbon nanofibers, carbon black, graphite, graphene, or carbon nanotubes, and conductive materials such as iron silicide.

[0029] For example, a ceramic powder is obtained by mixing LAGP powder and negative electrode active material in a mass ratio of 50:50. A certain amount of binder and a certain amount of anhydrous alcohol as a solvent are added to this ceramic powder to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like negative electrode layer material. The formed paste-like negative electrode layer material is degassed in a vacuum and then coated onto a PET film using the doctor blade method to form a sheet-like negative electrode layer material corresponding to the negative electrode layer. For example, one sheet-like negative electrode layer material formed in this way in a single coating process can be used as a green sheet for the negative electrode layer. Alternatively, to adjust to the desired thickness and amount of negative electrode active material, multiple sheets of the single sheet-like negative electrode layer material formed in a single coating process can be laminated and pressed together to form a green sheet for the negative electrode layer. A green sheet for the negative electrode layer containing one or more laminated sheets of negative electrode layer material may be cut to a predetermined planar size. For example, the green sheet for the negative electrode layer formed in this way is used to form the negative electrode layer of a solid-state battery.

[0030] As another example, the LAGP powder obtained by the above method, a conductive additive, anode active material, binder, dispersant, plasticizer, non-aqueous solvent, etc., are mixed to form a paste-like anode layer material called anode layer paste. For example, the anode layer paste formed in this way is used to form the anode layer of a solid-state battery by screen printing.

[0031] Next, we will explain an example of a method for manufacturing solid-state batteries using the materials described above. Figure 1 shows an example of the manufacturing flow of a solid-state battery. In the manufacturing of solid-state batteries, first, a laminate of materials for the positive electrode layer, electrolyte layer, and negative electrode layer is formed (Step S1). The formed laminate is heat-treated to decompose any remaining binders, etc., and degreased (Step S2). After degreasing, the laminate is further fired to sinter the positive electrode layer, electrolyte layer, and negative electrode layer (Step S3). Then, after firing, current collectors are formed on the surfaces of the positive electrode layer and negative electrode layer, which sandwich the electrolyte layer, using metal or the like (Step S4). This forms the basic structure of the solid-state battery. Each step S1 to S4 shown in Figure 1 will be explained with reference to Figures 2 to 5.

[0032] (Laminate formation) Figure 2 illustrates a first example of the laminate formation process. Figure 2(A) schematically shows a cross-sectional view of the main part of an example of the crimping process for the green sheet groups for the positive electrode layer, electrolyte layer, and negative electrode layer, and Figure 2(B) schematically shows a cross-sectional view of the main part of an example of the crimped green sheet group.

[0033] In the laminate formation process shown in step S1 of Figure 1, for example, the method shown in Figures 2(A) and 2(B) is used. That is, as shown in Figure 2(A), the green sheet 11 for the positive electrode layer, the green sheet 31 for the electrolyte layer, and the green sheet 21 for the negative electrode layer, prepared using the above method, are laminated and pressed together such that the green sheet 31 for the electrolyte layer is sandwiched between the green sheet 11 for the positive electrode layer and the green sheet 21 for the negative electrode layer. This yields a laminate 2 as shown in Figure 2(B).

[0034] Furthermore, the green sheet 11 for the positive electrode layer and the green sheet 21 for the negative electrode layer may be made by laminating and pressing together multiple green sheets in advance to achieve a predetermined thickness and amount of active material, rather than using a single green sheet. Similarly, the green sheet 31 for the electrolyte layer may be made by laminating and pressing together multiple green sheets in advance to achieve a predetermined thickness, rather than using a single green sheet.

[0035] Figure 3 illustrates a second example of the laminate formation process. Figure 3(A) schematically shows a cross-sectional view of the main parts of an example of the coating process for the positive electrode layer paste, and Figure 3(B) schematically shows a cross-sectional view of the main parts of an example of the coating process for the negative electrode layer paste.

[0036] In forming the laminate shown in step S1 of Figure 1, for example, methods such as those shown in Figures 3(A) and 3(B) may be used. In this method, for example, as shown in Figure 3(A), a paste 12 for the positive electrode layer, prepared using the above method, is applied to one side of the green sheet 31 for the electrolyte layer, prepared using the above method, by screen printing. After application, drying is performed to remove the solvent in the paste 12 for the positive electrode layer. As shown in Figure 3(B), a paste 22 for the negative electrode layer, prepared using the above method, is applied to the other side of the green sheet 31 for the electrolyte layer, by screen printing. After application, drying is performed to remove the solvent in the paste 22 for the negative electrode layer. This yields a laminate 2 as shown in Figure 3(B).

[0037] Furthermore, the coating of the positive electrode layer paste 12 and the negative electrode layer paste 22 by screen printing may be performed multiple times to achieve the predetermined thickness and amount of active material. In this case, drying for solvent removal may be performed after each screen printing or all at once after multiple screen printings. In addition, the electrolyte layer green sheet 31 is not limited to a single green sheet, but may be made by laminating and pressing together multiple green sheets to achieve the predetermined thickness.

[0038] (Degreasing and firing) Figure 4 illustrates an example of the degreasing and firing process. Figure 4(A) schematically shows a cross-sectional view of the main parts of an example of the degreasing process, and Figure 4(B) schematically shows a cross-sectional view of the main parts of an example of the firing process.

[0039] In the degreasing step shown in step S2 of Figure 1, for example, as shown in Figure 4(A), the laminate 2 obtained in step S1 is heat-treated in an atmospheric environment at a temperature of approximately 300°C to 600°C to remove any binders remaining in the laminate 2 by thermal decomposition, i.e., degreasing is performed. The temperature of the heat treatment in the degreasing step can be set based on the thermal decomposition temperature of the binders contained in the positive electrode layer green sheet 11 or positive electrode layer paste 12, the electrolyte layer green sheet 31, and the negative electrode layer green sheet 21 or negative electrode layer paste 22 used to form the laminate 2.

[0040] Furthermore, during such degreasing, some of the LAGP and other materials contained in the positive electrode layer green sheet 11 or positive electrode layer paste 12, the electrolyte layer green sheet 31, and the negative electrode layer green sheet 21 or negative electrode layer paste 22 used to form the laminate 2 may be sintered. The heat treatment for degreasing may be carried out using a firing furnace 100 (Figure 4(B)) as described later.

[0041] In the firing process shown in step S3 of Figure 1, for example, as shown in Figure 4(B), the degreased laminate 2 obtained in step S2 is fed into the firing furnace 100. The fed laminate 2 is then fired in an inert gas atmosphere such as nitrogen, at a temperature higher than that of degreasing. This firing process sinters the LAGP and other materials contained in the degreased laminate 2.

[0042] (Current collector formation) Figure 5 illustrates an example of the current collector formation process. Figure 5(A) schematically shows a cross-sectional view of the main parts of an example before the current collector formation process. Figure 5(B) schematically shows a cross-sectional view of the main parts of an example of the current collector formation process.

[0043] Through the firing process described above, a solid-state battery body 1a having a positive electrode layer 10, an electrolyte layer 30, and a negative electrode layer 20 after firing is formed, as shown in Figure 5(A). Current collectors 40 and 50 are formed on the surfaces of the positive electrode layer 10 and the negative electrode layer 20 of the solid-state battery body 1a, respectively, as shown in Figure 5(B). For example, a thin film of metal such as Au (gold) is formed on the surfaces of the positive electrode layer 10 and the negative electrode layer 20, respectively, by sputtering or vapor deposition, as the current collectors 40 and 50. Alternatively, current collectors 40 and 50 may be obtained by coating and firing a conductive paste containing various metal particles such as Au or Ag (silver), or conductive particles such as carbon particles.

[0044] Using the method described above, a solid battery 1 is obtained, comprising a solid battery body 1a having a positive electrode layer 10 and a negative electrode layer 20 and an electrolyte layer 30 provided between them, and current collectors 40 and 50 connected to the positive electrode layer 10 and the negative electrode layer 20, respectively.

[0045] During charging, lithium ions are conducted from the positive electrode layer 10 to the negative electrode layer 20 via the electrolyte layer 30 and absorbed into the solid-state battery 1. During discharging, lithium ions are conducted from the negative electrode layer 20 to the positive electrode layer 10 via the electrolyte layer 30 and absorbed into the solid-state battery 1. The charging and discharging operation of the solid-state battery 1 is achieved by this lithium ion conduction.

[0046] In this example, a solid-state battery 1 is used, in which a solid-state battery body 1a, comprising one electrolyte layer 30, one positive electrode layer 10, and one negative electrode layer 20, has current collectors 40 and 50 connected to the positive electrode layer 10 and negative electrode layer 20, respectively. Alternatively, a stacked solid-state battery can be obtained by alternately stacking multiple positive electrode layers 10 and multiple negative electrode layers 20 with an electrolyte layer 30 in between, degreasing and firing the stacked

[0047] [Evaluation of Solid-State Batteries] Next, we will describe the results of evaluating the solid-state battery 1 formed using various conditions according to the method described above. Here, the following samples of solid-state battery 1 were prepared for evaluation.

[0048] (Positive electrode layer) For the positive electrode active material of the positive electrode layer 10, LCPO, specifically Li2CoP2O7, was used. For the LCPO of the positive electrode layer 10, Li2NO3 was used as the Li raw material, Co(NO3)2·6H2O as the Co raw material, and NH4H2PO4 as the P raw material. These were mixed with citric acid in pure water, and after the water evaporated, the mixture was pulverized in a ball mill to an average particle size of 0.5 μm.

[0049] LAGP was used as the solid electrolyte for the positive electrode layer 10. For the LAGP of the positive electrode layer 10, Li2CO3, Al2O3, GeO2, and NH4H2PO4 were used as raw materials. These were mixed in a magnetic mortar and then a ball mill. The mixture was placed in an aluminium vessel and calcined at 300°C for 5 hours, then melted and rapidly cooled by heat treatment at 1300°C for 2 hours (melt-and-quench method). The amorphous LAGP obtained by this method was then ground in a ball mill to an average particle size of 1.0 μm. The LAGP used as the solid electrolyte for the positive electrode layer 10 had an average particle size D of 50 [μm] and a BET specific surface area [m²] as shown in Table 1. 2 Two different types of LAGP with different values ​​[ / g] were used.

[0050] [Table 1]

[0051] Carbon nanotubes (CNTs) were used as the conductive additive in the positive electrode layer 10. LCPO, LAGP, and CNT were mixed in a weight ratio of LCPO:LAGP:CNT = 3.88:5.82:0.3, and a binder, dispersant, plasticizer, and non-aqueous solvent were added in predetermined proportions and kneaded to form a paste 12 for the positive electrode layer used in screen printing.

[0052] (electrolyte layer) LAGP was used as the solid electrolyte for the electrolyte layer 30. For the LAGP in the electrolyte layer 30, amorphous LAGP obtained by the same melt-quenching method as for the positive electrode layer 10 was pulverized to an average particle size of 1.0 μm using a ball mill. A binder, dispersant, plasticizer, and non-aqueous solvent were added to this in predetermined ratios and kneaded, and a green sheet 31 for the electrolyte layer with a thickness of 200 μm was formed by the doctor blade method.

[0053] (Negative electrode layer) TiO2 with an average particle size of 1.0 μm was used as the negative electrode active material for the negative electrode layer 20. The same solid electrolyte and conductive additive as those used in the positive electrode layer 10 were used for the negative electrode layer 20, and the negative electrode layer paste 22 for screen printing was formed in the same manner as for the positive electrode layer 10.

[0054] Furthermore, a negative electrode layer paste 22 was also formed using Nb2O5 with an average particle size of 1.0 μm as the negative electrode active material, and the same solid electrolyte and conductive additive as the positive electrode layer 10. (Lamination, degreasing, and firing) A paste 12 for the positive electrode layer was screen printed onto one side of the green sheet 31 for the electrolyte layer, and a paste 22 for the negative electrode layer was screen printed onto the other side of the green sheet 31 for the electrolyte layer to form a laminate 2.

[0055] The formed laminate 2 was degreased and fired under the following conditions. For degreasing, the following conditions were used: heating in an air-flow atmosphere at a rate of 50°C / hour, holding at 500°C for 5 hours, and then allowing natural cooling.

[0056] For the firing process, the temperature was increased at a rate of 50°C / hour in a nitrogen flow atmosphere, and the temperature was maintained for 5 hours at a predetermined temperature in the range of 525°C to 650°C (one of the following temperatures: 525°C, 537°C, 550°C, 563°C, 575°C, 587°C, 600°C, 612°C, 625°C, 637°C, or 650°C), followed by natural cooling.

[0057] Multiple solid battery bodies 1a, each having an electrolyte layer 30 and a positive electrode layer 10 and a negative electrode layer 20 sandwiching it, were formed on the laminate 2 by degreasing and firing in the same manner, with different firing temperatures after degreasing.

[0058] (Current collector) After degreasing, the positive electrode layer 10 and negative electrode layer 20 of each solid battery body 1a were formed by sputtering gold onto their surfaces, respectively, to create current collectors 40 and 50. This completed the formation of the solid battery 1.

[0059] Multiple solid-state battery 1 samples were prepared as described above. The combinations of positive electrode active material, negative electrode active material, solid electrolyte, and firing temperature for the prepared samples are summarized in Table 2.

[0060] [Table 2]

[0061] In the following, samples such as samples No. 1 to 7, which use LCPO (Li2CoP2O7) as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 (Table 1) as the solid electrolyte, will also be referred to as "LCPO / TiO2 / LAGP-1". Samples such as samples No. 8 to 14, which use LCPO (Li2CoP2O7) as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 (Table 1) as the solid electrolyte, will also be referred to as "LCPO / TiO2 / LAGP-2". Samples such as samples No. 15 to 22, which use LCPO (Li2CoP2O7) as the positive electrode active material, Nb2O5 as the negative electrode active material, and LAGP-1 (Table 1) as the solid electrolyte, will also be referred to as "LCPO / Nb2O5 / LAGP-1".

[0062] (Charge / discharge characteristics) Multiple solid-state battery 1 samples prepared as described above, i.e., samples No. 1 to 22 in Table 2, were charged and discharged under the following conditions, and their capacity (cell capacity) and voltage (cell voltage) were measured. Here, for charging, a constant current charge was performed at a rate of 1 / 20C at room temperature until the battery voltage reached 3.6V. For discharging, a constant current discharge was performed at a rate of 1 / 20C at room temperature until the battery voltage reached 0.5V.

[0063] (X-ray diffraction measurement) For the multiple solid-state battery 1 samples obtained as described above, X-ray diffraction (XRD) measurements were performed on the exposed positive electrode layer 10 (thickness 5 μm). From the XRD spectra obtained by the XRD measurements, the intensity ratio (also simply called the "ratio") of predetermined diffraction peaks was determined. The XRD measurements were performed by setting each solid-state battery 1 sample so that the positive electrode layer 10 was the outermost surface (exposed), using Cu (copper) Kα rays (CuKα rays), with a slit width of 5 mm, a tube voltage of 40 kV, a tube current of 30 mA, and a diffraction angle 2θ = 5° to 20° at a speed of 0.1° / min.

[0064] Furthermore, for the multiple solid-state battery 1 samples obtained as described above, XRD measurements were performed on the exposed negative electrode layer 20 within a predetermined diffraction angle range 2θ. <Relationship between post-firing positive electrode layer characteristics and solid-state battery performance> First, we will describe an example of the relationship between the characteristics of the positive electrode layer 10 after firing and the performance of the solid-state battery 1.

[0065] Figure 6 shows an example of the XRD spectrum of the positive electrode layer. Figure 6 shows the XRD spectra of the positive electrode layer 10 of samples No. 15 to 21 shown in Table 2 above, i.e., samples No. 15 to 21 (LCPO / Nb2O5 / LAGP-1) which used LCPO as the positive electrode active material, Nb2O5 as the negative electrode active material, and LAGP-1 as the solid electrolyte, and were fired at temperatures of 563°C to 637°C.

[0066] From the XRD spectrum of the positive electrode layer 10 shown in Figure 6, when the firing temperature is 637°C (sample No. 21), in addition to the diffraction peaks attributed to LCPO and LAGP, a diffraction peak that is thought to be attributed to Li9Al3(P2O7)3(PO4)2 (referred to as "LAPP") appears.

[0067] From the XRD spectrum of the positive electrode layer 10 shown in Figure 6, when the firing temperature is 587°C to 625°C (samples No. 17 to 20), diffraction peaks attributed to LCPO and LAGP appear. Alternatively, when the firing temperature is 587°C to 625°C (samples No. 17 to 20), in addition to diffraction peaks attributed to LCPO and LAGP, diffraction peaks thought to be attributed to LAPP appear.

[0068] From the XRD spectrum of the positive electrode layer 10 shown in Figure 6, no diffraction peaks attributable to LAPP appear when the firing temperature is 575°C or lower (samples No. 15, 16). Furthermore, the XRD spectrum of the positive electrode layer 10 may sometimes show diffraction peaks that are thought to belong to LiAlP2O7 (lithium aluminum pyrophosphate).

[0069] Based on the findings obtained from the XRD spectra of the positive electrode layer 10 as shown in Figure 6, the intensity ratio of diffraction peaks appearing at a predetermined diffraction angle 2θ is determined from the XRD spectra of the positive electrode layer 10 obtained for the sample groups shown in Table 2 above. That is, the ratio P / Q[-] of the diffraction peak intensity P at a diffraction angle 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at a diffraction angle 2θ = 14.35 ± 0.2° is determined.

[0070] Here, at diffraction angle 2θ = 12.9°, a diffraction peak attributed to LCPO(110) appears, and at diffraction angle 2θ = 13.1°, a diffraction peak attributed to LAPP(002) appears. At diffraction angle 2θ = 13.0 ± 0.2°, it is inferred that the diffraction peak attributed to LCPO(110) and the diffraction peak attributed to LAPP(002) appear to overlap. Furthermore, at diffraction angle 2θ = 14.35°, a diffraction peak attributed to LCPO(11-1) appears.

[0071] In the case of an XRD spectrum obtained for a sample containing only LCPO, the ratio P / Q is the ratio of the diffraction peak intensity of LCPO(110) to the diffraction peak intensity of LCPO(11-1), i.e., the theoretical intensity ratio. If the ratio P / Q of the XRD spectrum of the positive electrode layer 10 containing the positive electrode active material LCPO and the solid electrolyte LAGP after firing is greater than the theoretical intensity ratio, it is presumed that the diffraction peak of LAPP(002) with a diffraction angle of 2θ = 13.1° is superimposed on the diffraction peak of LCPO(110) with a diffraction angle of 2θ = 12.9°. It is presumed that information regarding the presence of a crystalline phase considered to be LAPP in the positive electrode layer 10 after firing of the solid-state battery 1 can be obtained from the value of the ratio P / Q.

[0072] Figure 7 shows an example of the relationship between firing temperature and a predetermined diffraction peak intensity ratio of the positive electrode layer. In Figure 7, for some of the sample groups shown in Table 2 above, the predetermined diffraction peak intensity ratio, i.e., the ratio P / Q[-] of the diffraction peak intensity P at a diffraction angle of 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at a diffraction angle of 2θ = 14.35 ± 0.2°, is plotted against firing temperature [°C].

[0073] In samples No. 3, 4, 5, 6, and 7 (LCPO / TiO2 / LAGP-1), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, a tendency for the P / Q ratio to increase was observed as the firing temperature increased from 550°C, 563°C, 600°C, 637°C, to 650°C.

[0074] Similarly, in samples No. 9, 11, 12, 13, and 14 (LCPO / TiO2 / LAGP-2), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, a tendency for the ratio P / Q to increase was observed as the firing temperature increased to 537°C, 563°C, 600°C, 637°C, and 650°C.

[0075] Similarly, in samples No. 15, 16, 17, 18, 19, 20, and 21 (LCPO / Nb2O5 / LAGP-1), which used LCPO as the positive electrode active material, Nb2O5 as the negative electrode active material, and LAGP-1 as the solid electrolyte, a tendency for the ratio P / Q to increase was observed as the firing temperature increased to 563°C, 575°C, 587°C, 600°C, 612°C, 625°C, and 637°C.

[0076] As shown in Figure 7, when the ratio P / Q is plotted against the firing temperature, a tendency for the ratio P / Q to increase as the firing temperature increases is observed, and a relatively steep increase in the ratio P / Q is observed from around 600°C.

[0077] Figure 8 shows the first example of the relationship between firing temperature, discharge capacity, and resistance. In Figure 8, for several samples from the sample group shown in Table 2 above, using TiO2 as the negative electrode active material, the discharge capacity after 3 charge-discharge cycles (3rd discharge capacity (2V)) [mAh / g-LCPO] and the resistance estimated from the IR drop after charging (3rd charge resistance) [kΩ] are plotted against firing temperature [°C].

[0078] In samples No. 3, 4, 5, 6, and 7 (LCPO / TiO2 / LAGP-1), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, a tendency was observed for the discharge capacity to decrease with increasing resistance when the firing temperature was below 563°C. At firing temperatures of 563°C, 600°C, and 637°C, the resistance was relatively low and the discharge capacity was relatively high at 30 mAh / g or more.

[0079] In samples No. 8, 9, 10, 11, 12, 13, and 14 (LCPO / TiO2 / LAGP-2), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, a tendency was observed for the discharge capacity to decrease with increasing resistance when the firing temperature was below 550°C and above 637°C. At firing temperatures of 550°C, 563°C, 600°C, and 637°C, the resistance was relatively low and the discharge capacity was relatively high at 30 mAh / g or more.

[0080] As shown in Figure 8, in samples using TiO2 as the negative electrode active material, depending on the type, there is a tendency for the resistance to be relatively low and the discharge capacity to be relatively high within a certain firing temperature range.

[0081] Figure 9 shows a second example of the relationship between firing temperature, discharge capacity, and resistance. In Figure 9, for a sample using Nb2O5 as the negative electrode active material from the sample group shown in Table 2 above, the discharge capacity after 5 charge-discharge cycles (5th discharge capacity (2V)) [mAh / g-LCPO] and the resistance estimated from the IR drop after charging (resistance after 5th charge) [kΩ] are plotted against firing temperature [°C].

[0082] In samples No. 15, 16, 17, 18, 19, 20, 21, and 22 (LCPO / Nb2O5 / LAGP-1), which used LCPO as the positive electrode active material, Nb2O5 as the negative electrode active material, and LAGP-1 as the solid electrolyte, a tendency for the discharge capacity to decrease with increasing resistance was observed when the firing temperature was below 587°C and above 625°C. At firing temperatures of 587°C, 600°C, 612°C, and 625°C, the resistance was relatively low and the discharge capacity was relatively high at 70 mAh / g or more.

[0083] As shown in Figure 9, even in samples using Nb2O5 as the negative electrode active material, a tendency for relatively low resistance and relatively high discharge capacity is observed within a certain firing temperature range, similar to Figure 8 above.

[0084] Based on the results shown in Figures 7 to 9 above, Table 3 summarizes the values ​​of the ratio P / Q[-] relative to the firing temperature [°C], discharge capacity [mAh / g-LCPO], and resistance [kΩ] obtained for samples No. 3 to 7 of the samples No. 1 to 7 that used TiO2 as the negative electrode active material.

[0085] [Table 3]

[0086] Furthermore, Table 4 summarizes the values ​​obtained for samples No. 8 to 14, which used TiO2 as the negative electrode active material, including the ratio P / Q[-] relative to the firing temperature [°C], discharge capacity [mAh / g-LCPO], and resistance [kΩ].

[0087] [Table 4]

[0088] Furthermore, Table 5 summarizes the values ​​obtained for samples No. 15 to 22, which used Nb2O5 as the negative electrode active material, including the ratio P / Q[-] relative to the firing temperature [°C], discharge capacity [mAh / g-LCPO], and resistance [kΩ].

[0089] [Table 5]

[0090] From Tables 3 to 5, obtain the range of the ratio P / Q when the resistance is below a certain value with relatively low resistance, and the range of the ratio P / Q when the discharge capacity is above a certain value with relatively high discharge capacity. For example, obtain the range of the ratio P / Q when the resistance is below 3.8 kΩ, and the range of the ratio P / Q such that the discharge capacity is above 30 mAh / g (the range of the ratio P / Q within the thick frames in Tables 3 to 5), then 0.074 < P / Q < 5.744. In Table 4, the ratio P / Q at the firing temperature of 550°C is estimated to be a value (>0.074) between the ratio P / Q = 0.077 at the firing temperature of 537°C and the ratio P / Q = 0.083 at the firing temperature of 563°C, based on the tendency shown in Fig. 7 above (the tendency that the ratio P / Q increases with the increase in the firing temperature). Also, in view of the findings obtained from the measurement results of charge-discharge characteristics as described later (Figs. 15, 16 and Tables 8, 9), the data of the sample with the firing temperature of 650°C is excluded in setting the range of the ratio P / Q.

[0091] Here, from Tables 3 to 5, in the range of 0.074 < P / Q < 0.083, there may be a possibility that a stable low resistance and high discharge capacity cannot be achieved. From this, it is also possible to obtain the range of 0.083 < P / Q < 5.744 as the range of the ratio P / Q for more stable low resistance and high discharge capacity. If the ratio P / Q obtained from the XRD spectrum of the positive electrode layer 10 after firing is within the range of 0.074 < P / Q < 5.744 as described above, or within the range of 0.083 < P / Q < 5.744, it can be said that it is possible to obtain the solid-state battery 1 with relatively low resistance and the solid-state battery 1 with relatively high discharge capacity.

[0092] In other words, when firing is performed under firing temperature conditions such that the ratio P / Q obtained from the XRD spectrum of the positive electrode layer 10 after firing falls within the range of 0.074 < P / Q < 5.744 or the range of 0.083 < P / Q < 5.744, it can also be said that it becomes possible to obtain the solid-state battery 1 with a relatively low resistance and the solid-state battery 1 with a relatively high discharge capacity. That is, when the positive electrode active material is LCPO, the negative electrode active material is TiO2, and the solid electrolyte is LAGP-1 (LCPO / TiO2 / LAGP-1; Table 3), the firing temperature is preferably in the range of 563°C to 637°C or the range of 600°C to 637°C. Further, when the positive electrode active material is LCPO, the negative electrode active material is TiO2, and the solid electrolyte is LAGP-2 (LCPO / TiO2 / LAGP-2; Table 4), the firing temperature is preferably in the range of 537°C to 637°C or the range of 563°C to 637°C. Also, when the positive electrode active material is LCPO, the negative electrode active material is Nb2O5, and the solid electrolyte is LAGP-1 (LCPO / Nb2O5 / LAGP-1; Table 5), the firing temperature is preferably in the range of 575°C to 625°C or the range of 587°C to 625°C.

[0093] As described above, P is the diffraction peak intensity at a diffraction angle 2θ = 13.0 ± 0.2° in the XRD spectrum of the positive electrode layer 10 after firing, and Q is the diffraction peak intensity at a diffraction angle 2θ = 14.35 ± 0.2° in the XRD spectrum of the positive electrode layer 10 after firing. A diffraction peak attributed to LCPO(110) appears at a diffraction angle 2θ = 12.9°, and a diffraction peak attributed to LAPP(002) appears at a diffraction angle 2θ = 13.1°. It is presumed that at a diffraction angle 2θ = 13.0 ± 0.2°, diffraction peaks presumably attributed to LCPO(110) and LAPP(002) overlap and appear. Also, a diffraction peak attributed to LCPO(11-1) appears at a diffraction angle 2θ = 14.35°.

[0094] From FIG. 7, as the firing temperature increases, a tendency for the ratio P / Q to increase is recognized. Therefore, it is considered that as the firing temperature increases, LAPP is more likely to be generated in the positive electrode layer 10.

[0095] When the firing temperature exceeds a certain temperature, in addition to LCPO and LAGP, excessive LAPP is generated, which is considered to become a resistance layer and reduce the discharge capacity. On the other hand, when the firing temperature is lower than a certain temperature, the ionic conductivity of LAGP cannot be enhanced, and a good particle interface state cannot be formed between LCPO and LAGP, which is considered to reduce the discharge capacity.

[0096] When the firing temperature is within an appropriate range, excessive generation of LAPP can be suppressed, and a good particle interface state can be formed between LCPO and LAGP, and it is considered that a sufficient discharge capacity can be obtained.

[0097] For example, in the case of LCPO / Nb2O5 / LAGP-1, when the firing temperature is 587°C to 625°C (Sample Nos. 17 to 20), excessive generation of LAPP can be suppressed, and a good particle interface state can be formed between LCPO and LAGP. On the other hand, when the firing temperature is 575°C or lower (Sample Nos. 15, 16), compared with the case where the firing temperature is 587°C to 625°C (Sample Nos. 17 to 20), the generation of LAPP may be further suppressed, and it is considered that it may be difficult to form a good particle interface state between LCPO and LAGP.

[0098] When the ratio P / Q obtained from the XRD spectrum of the positive electrode layer 10 after firing is in the range of 0.074 < P / Q < 5.744 or 0.083 < P / Q < 5.744 as described above, a solid battery 1 with a relatively low resistance and a solid battery 1 with a relatively high discharge capacity can be obtained. Depending on the material used for the positive electrode layer 10, when firing is performed under firing temperature conditions such that the ratio P / Q obtained from the XRD spectrum of the positive electrode layer 10 after firing is in the range of 0.074 < P / Q < 5.744 or 0.083 < P / Q < 5.744, a solid battery 1 with a relatively low resistance and a solid battery 1 with a relatively high discharge capacity can be obtained.

[0099] According to the solid-state battery 1 obtained within a predetermined firing temperature range set based on the material used for the positive electrode layer 10, where the ratio P / Q in the XRD spectrum of the positive electrode layer 10 is in the range of 0.074 < P / Q < 5.744 or 0.083 < P / Q < 5.744, a positive electrode layer 10 having a good crystal structure is formed, and an increase in resistance and a decrease in charge / discharge characteristics due to the positive electrode layer 10 are suppressed. Thereby, a high-performance solid-state battery 1 equipped with a positive electrode layer 10 having excellent characteristics is realized.

[0100] <Relationship between the characteristics of the negative electrode layer after firing and the performance of the solid-state battery> Next, an example of the relationship between the characteristics of the negative electrode layer 20 after firing and the performance of the solid-state battery 1 will be described. FIGS. 10 and 11 are diagrams showing examples of XRD spectra of the negative electrode layer. FIG. 10 shows the XRD spectra of the negative electrode layer 20 of Samples No. 3 to 7 (positive electrode active material LCPO / negative electrode active material TiO2 / solid electrolyte LAGP-1 / firing temperature 550° C. to 650° C.) shown in Table 2 above. FIG. 11 shows the XRD spectra of the negative electrode layer 20 of Samples No. 10 to 14 (positive electrode active material LCPO / negative electrode active material TiO2 / solid electrolyte LAGP-2 / firing temperature 550° C. to 650° C.) shown in Table 2 above.

[0101] From the XRD spectra of the negative electrode layer 20 as shown in FIGS. 10 and 11, the intensity ratio of the diffraction peaks that appear at the following predetermined diffraction angles 2θ is obtained. That is, the ratio R / S [-] of the diffraction peak intensity R at the diffraction angle 2θ = 48.0 ± 0.2° to the diffraction peak intensity S at the diffraction angle 2θ = 48.7 ± 0.2° is obtained. Here, a diffraction peak attributed to TiO2(200) appears at the diffraction angle 2θ = 48.0°. A diffraction peak attributed to LAGP(128) appears at the diffraction angle 2θ = 48.7°.

[0102] Figure 12 shows an example of the relationship between firing temperature and a predetermined diffraction peak intensity ratio of the negative electrode layer. In Figure 12, for some of the sample groups shown in Table 2 above, the predetermined diffraction peak intensity ratio, i.e., the ratio R / S[-] of the diffraction peak intensity R at a diffraction angle of 2θ = 48.0 ± 0.2° to the diffraction peak intensity S at a diffraction angle of 2θ = 48.7 ± 0.2°, is plotted against firing temperature [°C].

[0103] In samples No. 3, 4, 5, 6, and 7 (LCPO / TiO2 / LAGP-1), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, a tendency for the specific R / S ratio to decrease was observed as the firing temperature increased from 550°C, 563°C, 600°C, 637°C, to 650°C. Similarly, in samples No. 9, 10, 11, 12, 13, and 14 (LCPO / TiO2 / LAGP-2), which used LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, a tendency for the specific R / S ratio to decrease was observed as the firing temperature increased from 537°C, 550°C, 563°C, 600°C, 637°C, to 650°C. As shown in Figure 12, when the ratio R / S is plotted against the firing temperature, a tendency for the ratio R / S to decrease as the firing temperature increases is observed, and a relatively steep decrease in the ratio R / S is observed around a firing temperature of 550°C.

[0104] As shown in Figure 12, in the range where the firing temperature exceeds 550°C, the diffraction peak intensity R of TiO2(200) and the diffraction peak intensity S of LAGP(128) are approximately the same (ratio R / S is about 1), suggesting that a good particle interface state is formed between TiO2 and LAGP.

[0105] Figure 13 shows an example of the relationship between discharge capacity and a predetermined diffraction peak intensity ratio of the negative electrode layer. In Figure 13, for several samples from the sample group shown in Table 2 above, using TiO2 as the negative electrode active material, the ratio R / S obtained from the XRD spectrum of the negative electrode layer 20 is plotted against the discharge capacity after 3 charge-discharge cycles (3rd discharge capacity (2V)) [mAh / g-TiO2].

[0106] Figure 13 shows that when the diffraction peak intensity R of TiO2(200) and the diffraction peak intensity S of LAGP(128) are approximately the same (ratio R / S is about 1), a relatively high discharge capacity of 40 mAh / g or more tends to be obtained.

[0107] Based on the results shown in Figures 10 to 13 above, Table 6 summarizes the values ​​of the ratio R / S [-] relative to the firing temperature [°C], discharge capacity [mAh / g-TiO2], and resistance [kΩ] obtained for samples No. 3 to 7 using TiO2 as the negative electrode active material.

[0108] [Table 6]

[0109] Furthermore, Table 7 summarizes the values ​​obtained for samples No. 8 to 14, which used TiO2 as the negative electrode active material, including the ratio R / S [-] relative to the firing temperature [°C], discharge capacity [mAh / g-TiO2], and resistance [kΩ].

[0110] [Table 7]

[0111] From Tables 6 and 7, the range of the ratio R / S when the resistance is below a certain relatively low value and the range of the ratio R / S when the discharge capacity is above a certain relatively high value are determined. For example, when determining the range of the ratio R / S when the resistance is 1.7 kΩ or less and the range of the ratio R / S when the discharge capacity is 10 mAh / g or more (the range of the ratio R / S within the thick frames in Tables 6 and 7), it is 0.958 < R / S < 4.340. Also, for example, when determining the range of the ratio R / S when the resistance is 1 kΩ or less and the range of the ratio R / S when the discharge capacity is 50 mAh / g or more, it is 0.958 < R / S < 1.575. In view of the findings obtained from the measurement results of the charge-discharge characteristics as described later (Figs. 15, 16 and Tables 8, 9), in setting the range of the ratio R / S, the data of the sample with a firing temperature of 650°C is excluded. When the ratio R / S obtained from the XRD spectrum of the negative electrode layer 20 after firing is within the range of 0.958 < R / S < 4.340 or 0.958 < R / S < 1.575, it can be said that it is possible to obtain a solid battery 1 with a relatively low resistance and a solid battery 1 with a relatively high discharge capacity.

[0112] In other words, when firing is carried out under firing temperature conditions such that the ratio R / S obtained from the XRD spectrum of the negative electrode layer 20 after firing is within the range of 0.958 < R / S < 4.340 or 0.958 < R / S < 1.575, it can also be said that it is possible to obtain a solid battery 1 with a relatively low resistance and a solid battery 1 with a relatively high discharge capacity. That is, when the positive electrode active material is LCPO, the negative electrode active material is TiO2, and the solid electrolyte is LAGP-1 (LCPO / TiO2 / LAGP-1; Table 6), the firing temperature is preferably in the range of 563°C to 637°C. Also, when the positive electrode active material is LCPO, the negative electrode active material is TiO2, and the solid electrolyte is LAGP-2 (LCPO / TiO2 / LAGP-2; Table 7), the firing temperature is preferably in the range of 537°C to 637°C or 550°C to 637°C.

[0113] According to the solid-state battery 1 obtained within a predetermined firing temperature range set based on the material used for the negative electrode layer 20, where the ratio R / S in the XRD spectrum of the negative electrode layer 20 is in the range of 0.958 < R / S < 4.340 or 0.958 < R / S < 1.575, a negative electrode layer 20 having a good crystal structure is formed, and an increase in resistance and a decrease in charge / discharge characteristics due to the negative electrode layer 20 are suppressed. Thereby, a high-performance solid-state battery 1 equipped with a negative electrode layer 20 having excellent characteristics is realized.

[0114] <Volume energy density of the solid-state battery> Next, the results of evaluating the volume energy density of the solid-state battery 1 will be described. FIG. 14 and FIG. 15 are diagrams showing examples of measurement results of the charge / discharge characteristics of the solid-state battery.

[0115] FIG. 14 shows the measurement results of the charge / discharge characteristics of Samples No. 3 to 7 (LCPO / TiO2 / LAGP-1) using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte. Here, FIG. 14(A) is an example of the measurement results of the charge / discharge characteristics of Sample No. 3 (firing temperature 550°C), FIG. 14(B) is an example of the measurement results of the charge / discharge characteristics of Sample No. 4 (firing temperature 563°C), FIG. 14(C) is an example of the measurement results of the charge / discharge characteristics of Sample No. 5 (firing temperature 600°C), FIG. 14(D) is an example of the measurement results of the charge / discharge characteristics of Sample No. 6 (firing temperature 637°C), and FIG. 14(E) is an example of the measurement results of the charge / discharge characteristics of Sample No. 7 (firing temperature 650°C).

[0116] Figure 15 also shows the measurement results of the charge-discharge characteristics of samples No. 10 to 14 (LCPO / TiO2 / LAGP-2), which use LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte. Here, Figure 15(A) is an example of the measurement results of the charge-discharge characteristics of sample No. 10 (firing temperature 550°C), Figure 15(B) is an example of the measurement results of the charge-discharge characteristics of sample No. 11 (firing temperature 563°C), Figure 15(C) is an example of the measurement results of the charge-discharge characteristics of sample No. 12 (firing temperature 600°C), Figure 15(D) is an example of the measurement results of the charge-discharge characteristics of sample No. 13 (firing temperature 637°C), and Figure 15(E) is an example of the measurement results of the charge-discharge characteristics of sample No. 14 (firing temperature 650°C).

[0117] Table 8 summarizes the average discharge voltage [V], discharge capacity [mAh], cell energy [mWh], and volumetric energy density [mWh / L] of solid-state battery 1, which are determined based on the measurement results of the charge and discharge characteristics shown in Figure 14.

[0118] [Table 8]

[0119] Furthermore, Table 9 summarizes the average discharge voltage [V], discharge capacity [mAh], cell energy [mWh], and volumetric energy density [mWh / L] of solid-state battery 1, which are determined based on the measurement results of the charge and discharge characteristics shown in Figure 15.

[0120] [Table 9]

[0121] Figures 14 and 15 show that in solid-state battery 1 (Figures 14(E) and 15(E)) fired at a firing temperature of 650°C (or above 650°C), a larger cell capacity is required to increase the voltage to 3.5V. Therefore, charging under the same conditions as for other firing temperatures results in insufficient charge and a reduced discharge capacity. In light of these findings, data from samples fired at 650°C were excluded when setting the ranges for the ratio P / Q and ratio R / S.

[0122] From Table 8, for Samples No. 3 to 7 (LCPO / TiO2 / LAGP-1) using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, when the firing temperature is 563 °C, 600 °C, and 637 °C, a volume energy density exceeding 40 mWh / L (within the thick frames in Table 8) can be obtained. When the firing temperature is 563 °C, 600 °C, and 637 °C, as shown in Table 3 (within the thick frames) above, a positive electrode layer 10 that can realize a solid battery 1 with a relatively low resistance and a relatively high discharge capacity can be obtained. Also, as shown in Table 6 (within the thick frames) above, a negative electrode layer 20 that can realize a solid battery 1 with a relatively low resistance and a relatively high discharge capacity can be obtained.

[0123] That is, in solid battery 1 using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, when the firing temperature is 563 °C, 600 °C, and 637 °C, for the positive electrode layer 10, the ratio P / Q is in the range of 0.074 < P / Q < 5.744, and for the negative electrode layer 20, the ratio R / S is in the range of 0.958 < R / S < 4.340, and a volume energy density exceeding 40 mWh / L can be obtained.

[0124] Therefore, when using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-1 as the solid electrolyte, it can be said that when the firing temperature is 563 °C, 600 °C, and 637 °C, a high-performance solid battery 1 with low resistance, high discharge capacity, and even higher volume energy density is realized.

[0125] Also, from Table 9, in Samples No. 10 to 14 (LCPO / TiO2 / LAGP-2) using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, when the firing temperatures are 550 °C, 563 °C, 600 °C, and 637 °C, a volume energy density exceeding 39 mWh / L, generally exceeding 40 mWh / L (within the thick frame in Table 9) is obtained. When the firing temperatures are 550 °C, 563 °C, 600 °C, and 637 °C, as shown in Table 4 (within the thick frame) above, a positive electrode layer 10 capable of realizing a solid battery 1 with a relatively low resistance and a relatively high discharge capacity can be obtained. Also, as shown in Table 7 (within the thick frame) above, a negative electrode layer 20 capable of realizing a solid battery 1 with a relatively low resistance and a relatively high discharge capacity can be obtained.

[0126] That is, in the solid battery 1 using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, when the firing temperatures are 550 °C, 563 °C, 600 °C, and 637 °C, for the positive electrode layer 10, the ratio P / Q is in the range of 0.074 < P / Q < 5.744, and for the negative electrode layer 20, the ratio R / S is in the range of 0.958 < R / S < 4.340, and a volume energy density exceeding 39 mWh / L is obtained. Incidentally, based on the tendency shown in FIG. 7 above (the tendency for the ratio P / Q to increase as the firing temperature increases), the ratio P / Q at a firing temperature of 550 °C is estimated to be a value (>0.074) between the ratio P / Q = 0.077 at a firing temperature of 537 °C and the ratio P / Q = 0.083 at a firing temperature of 563 °C.

[0127] Therefore, when using LCPO as the positive electrode active material, TiO2 as the negative electrode active material, and LAGP-2 as the solid electrolyte, it can be said that a high-performance solid battery 1 with low resistance, high discharge capacity, and even higher volume energy density is realized when the firing temperatures are 550 °C, 563 °C, 600 °C, and 637 °C.

[0128] In the above description, the case of using Li2CoP2O7 as LCPO is taken as an example. However, it is not limited to Li2CoP2O7, and the general formula is Li2Co 1-x M x P 2-y A yThe same effect as above can be obtained when using LCPO represented as O7 (where M is one of Ti, V, Cr, Ni, and Fe, and A is one of B, C, Al, Si, Ga, and Ge, with 0≦x<1 and 0≦y≦0.07). [Explanation of Symbols]

[0129] 1 solid state battery 1a solid battery body 2 Laminate 10 Positive electrode layer 11. Green sheet for positive electrode layer 12. Paste for the positive electrode layer 20 Negative electrode layer 21. Green sheet for negative electrode layer 22 Paste for the negative electrode layer 30 Electrolyte layer 31 Green sheet for electrolyte layer 40, 50 Current collector 100 firing furnaces

Claims

1. It has a positive electrode layer, a negative electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer. The positive electrode layer, Li ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ (M is one of Ti, V, Cr, Ni, Fe; A is one of B, C, Al, Si, Ga, Ge; 0 ≤ x < 1, 0 ≤ y ≤ 0.07) The first Li １＋ｍ Al ｍ Ge ２－ｍ (PO ４ ) ３ (0 < m < 1), and fi) ９ B. ３ (). ２ . ７ ) ３ (?) ４ ) ２ と It includes, The first X-ray diffraction spectrum of the positive electrode layer, measured using CuKα rays, The aforementioned Li 2 Co 1-x M x P 2-y A y O 7, The first Li 1+m Al m Ge 2-m (PO 4) 3 and, The aforementioned Li₇Al₃(P₂O₇)₃(PO₄)₂ and It includes diffraction peaks that belong to, At the diffraction angle 2θ = 13.0 ± 0.2° of the first X-ray diffraction spectrum, the Li ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ The diffraction peaks attributed to (110) and the Li ９ Al ３ (P ２ O ７ ) ３ (PO ４ ) ２ The diffraction peak attributed to (002) appears to overlap with the diffraction peak, and at the diffraction angle 2θ = 14.35°, the Li ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ A diffraction peak attributed to (11-1) appears, The ratio P / Q of the diffraction peak intensity P at a diffraction angle 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at a diffraction angle 2θ = 14.35 ± 0.2° is: 0.074<P / Q<5.744 A solid-state battery characterized by being within a certain range.

2. The second X-ray diffraction spectrum of the negative electrode layer, measured using CuKα rays, TiO ２ and, Second Li １＋ｎ Al ｎ Ge ２－ｎ (PO ４ ) ３ (0 < n < 1) It includes diffraction peaks that belong to, The ratio R / S of the diffraction peak intensity R at diffraction angle 2θ = 48.0 ± 0.2° to the diffraction peak intensity S at diffraction angle 2θ = 48.7 ± 0.2° of the second X-ray diffraction spectrum is: 0.958<R / S<4.340 The solid battery according to claim 1, characterized in that it is within the range.

3. The solid-state battery according to claim 2, characterized in that its volumetric energy density is greater than 39 mWh / L.

4. A step of forming a laminate having a positive electrode layer, a negative electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, A step of firing the laminate in an inert gas atmosphere Includes, In the positive electrode layer of the laminate before firing, Li ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ (M is one of Ti, V, Cr, Ni, Fe; A is one of B, C, Al, Si, Ga, Ge; 0 ≤ x < 1, 0 ≤ y ≤ 0.07) First Li １＋ｍ Al ｍ Ge ２－ｍ (PO ４ ) ３ (0 < m < 1) It includes, In the positive electrode layer of the laminate after firing, The aforementioned Li 2 Co 1-x M x P 2-y A y O 7, The first Li 1+m Al m Ge 2-m (PO 4) 3 and, Li 9 Al 3 (P 2 O 7 ) 3 (PO 4 ) 2 and It includes, In the process of firing the laminate, The first X-ray diffraction spectrum of the positive electrode layer in the laminate after firing, measured using CuKα rays, The Li ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ and, The first Li １＋ｍ Al ｍ Ge ２－ｍ (PO ４ ) ３ and, The Li ９ Al ３ (P ２ O ７ ) ３ (PO ４ ) ２ and It includes diffraction peaks that belong to, In the first X-ray diffraction spectrum, at a diffraction angle 2θ = 13.0 ± 0.2°, the ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ diffraction peak attributed to (110) of ９ Al ３ (P ２ O ７ ) ３ (PO ４ ) ２ attributed to (002) of ２ Co １－ｘ M ｘ P ２－ｙ A ｙ O ７ appears overlappingly, and at a diffraction angle 2θ = 14.35°, the diffraction peak attributed to (11-1) of The ratio P / Q of the diffraction peak intensity P at a diffraction angle 2θ = 13.0 ± 0.2° to the diffraction peak intensity Q at a diffraction angle 2θ = 14.35 ± 0.2° is: 0.074<P / Q<5.744 A method for manufacturing a solid battery, characterized by firing the laminate under firing temperature conditions within the range of [specified range].

5. In the negative electrode layer of the laminate before firing, TiO ２ and, Second Li １＋ｎ Al ｎ Ge ２－ｎ (PO ４ ) ３ (0 < n < 1) and It includes, In the process of firing the laminate, The second X-ray diffraction spectrum of the negative electrode layer in the laminate after firing, measured using CuKα rays, The TiO ２ and, The second Li １＋ｎ Al ｎ Ge ２－ｎ (PO ４ ) ３ and It includes diffraction peaks that belong to, The ratio R / S of the diffraction peak intensity R at diffraction angle 2θ = 48.0 ± 0.2° to the diffraction peak intensity S at diffraction angle 2θ = 48.7 ± 0.2° of the second X-ray diffraction spectrum is: 0.958<R / S<4.340 The method for manufacturing a solid battery according to claim 4, characterized in that the laminate is fired under firing temperature conditions within the range of .

6. The method for manufacturing a solid battery according to claim 5, characterized in that the volumetric energy density of the solid battery manufactured using the laminate is greater than 39 mWh / L.

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