Solid state battery and manufacturing method thereof

Abstract

Provided are: a solid-state battery which can be applied even to a solid-state battery using an oxide-based solid-state electrolyte and which can improve cycle characteristics without requiring an additional structure such as a conductive resin layer; and a method for manufacturing the solid-state battery. The present invention for solving the problem relates to a solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid-state electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the ratio of the designed capacity of the negative electrode layer to the designed capacity of the positive electrode layer (negative electrode capacity / positive electrode capacity) is from 0.74 to 0.96 (inclusive).

Description

Technical Field

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

[0002] In recent years, with the rapid development of technologies related to information-related devices and communication devices, such as computers, mobile phones (smartphones), and electric vehicles, and transportation-related devices, the development of batteries as their power sources has been emphasized. Furthermore, as batteries used in these applications, lithium-ion secondary batteries and solid-state batteries with high safety and high energy density have attracted attention.

[0003] Among these batteries, a lithium-ion secondary battery that uses a flammable organic electrolyte solution in the electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer requires safety measures for suppressing liquid leakage and resulting fire, short circuit, etc., and overcharging. In particular, if the battery is made to have a high capacity or high energy density, these risks also increase, so further safety measures are required. In contrast, a solid-state battery that does not use an organic electrolyte solution and uses a solid electrolyte in the electrolyte layer is less likely to have the above problems and has higher safety. Therefore, the development of solid-state batteries is being promoted.

[0004] Regarding these secondary batteries, an improvement in so-called cycle characteristics in which the capacity is not easily reduced even when repeatedly used is also required. Regarding solid-state batteries, various methods for improving cycle characteristics have also been explored.

[0005] For example, Patent Document 1 discloses an all-solid-state lithium-ion battery that contains a carbon-based material as a negative electrode active material, and the BET specific surface area of the particles of the negative electrode active material is 27.4 m 2 / g or less. In this solid-state battery, the ratio (X / Y) of the theoretical capacity (X) of the positive electrode active material layer to the theoretical capacity (Y) of the negative electrode active material layer in the portion where the positive electrode and the negative electrode overlap is set to 1.03 or more and 1.20 or less, and the ratio (A / B) of the area (A) of the positive electrode active material layer to the area (B) of the negative electrode active material layer is set to 1 or more and 1.24 or less.

[0006] According to Patent Document 1, conventionally, by setting the theoretical capacitance ratio of the negative electrode to the positive electrode to 1.2 or more, a decrease in the capacity retention rate has been suppressed. However, if the capacitance ratio of the negative electrode is increased, the total surface area of the negative electrode active material increases, and a reaction between moisture and Li ions occurs on the surface of the particles of the negative electrode active material, resulting in a decrease in the amount of Li ions that can contribute to charge and discharge. In response to this, in Patent Document 1, by reducing the amount of the negative electrode active material (increasing X / Y), the reaction between moisture and Li ions on the surface of the particles of the negative electrode active material is suppressed, and the decrease in the amount of Li ions is suppressed, thereby achieving an improvement in the capacity retention rate (cycle characteristics).

[0007] In addition, Patent Document 2 discloses an electrode for an all-solid-state lithium-ion battery in which an electrode active material layer is fixed to a current collector layer via a conductive resin layer. According to Patent Document 2, by bonding the electrode active material layer with the conductive resin layer, even if there is a volume change of the electrode active material accompanying charge and discharge, the conductive resin layer and the current collector layer are not easily separated. Further, thereby, particles such as the electrode active material and the conductive additive are not easily separated from each other, and thus charge and discharge characteristics such as discharge capacity density and cycle characteristics are improved.

[0008] In addition, Patent Document 3 discloses a thin-film solid-state secondary battery in which, when the ratio of the reciprocals of the maximum charge and discharge capacities per unit volume of the positive electrode active material layer and the negative electrode active material layer is set as R, the film thickness ratio X of the positive electrode active material layer and the negative electrode active material layer satisfies the conditional expression of 0.2R ≤ X ≤ 10R. In Patent Document 3, it is preferred that X = R, that is, the positive electrode film thickness / negative electrode film thickness (X) is equal to the maximum charge and discharge capacity per unit volume of the negative electrode / the maximum charge and discharge capacity per unit volume of the positive electrode (Y). At this time, the amounts of lithium ions that can be inserted and detached in the positive electrode layer and the negative electrode layer are substantially equal, so that Li ions can be inserted into / detached from the positive electrode and the negative electrode in an appropriate amount, and thus the battery capacity per unit volume is maximized. Further, Patent Document 3 discloses that no serious problems occur in the cycle characteristics at this time.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-6055

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-93156

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2007-103130 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] As described in Patent Documents 1 to 3, various attempts have been made to improve the cycle characteristics of solid-state batteries.

[0016] However, the negative electrode using a carbon-based material as the negative electrode active material described in Patent Document 1 reduces and decomposes a solid electrolyte such as LAGP during charge and discharge or disappears during calcination, and thus cannot be used in a solid-state battery using a calcined oxide-based solid electrolyte during manufacturing. The technology described in Patent Document 1 is basically limited to being used in a battery using a sulfide-based electrolyte as the solid electrolyte.

[0017] In addition, in the electrode having a conductive resin layer described in Patent Document 2, the electrical output efficiency from the electrode active material to the current collector is reduced due to the conductive resin layer, making it difficult to increase the energy density of the battery.

[0018] Furthermore, in Patent Document 3, ultimately only the capacities of the positive electrode and the negative electrode are set to be approximately the same, and there is no technological improvement for conventional solid-state batteries.

[0019] The present invention has been made in view of the above problems, and an object thereof is to provide a solid-state battery and a method for manufacturing the same, which can also be applied to a solid-state battery using an oxide-based solid electrolyte, and can improve the cycle characteristics without an additional structure such as a conductive resin layer.

[0020] Solution to the problem

[0021] The above problems can be solved by the following solid-state battery and method for manufacturing a solid-state battery.

[0022] The solid-state battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and the ratio (negative electrode capacity / positive electrode capacity) of the design capacity of the negative electrode layer to the design capacity of the positive electrode layer is 0.74 or more and 0.96 or less.

[0023] The method for manufacturing a solid-state battery of the present invention includes: a step of forming a laminate including a positive electrode mixture layer, a negative electrode mixture layer, and an electrolyte mixture layer disposed between the positive electrode mixture layer and the negative electrode mixture layer; and a step of calcining the laminate, and the ratio (negative electrode capacity / positive electrode capacity) of the design capacity of the negative electrode mixture layer to the design capacity of the positive electrode mixture layer in the laminate after the calcination is 0.74 or more and 0.96 or less.

[0024] Advantages of the invention

[0025] According to the present invention, it is possible to provide a solid-state battery and a method for manufacturing the same, which can also be applied to a solid-state battery using an oxide-based solid electrolyte, and can improve the cycle characteristics without an additional structure such as a conductive resin layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figures 1A - 1C is a schematic diagram showing the structure of the solid-state battery of the present embodiment.

[0027] Figures 2A - 2E is a schematic diagram showing an example of a preparation process of a positive electrode mixture layer portion.

[0028] Figures 3A - 3C is a schematic diagram showing an example of the prepared positive electrode mixture layer portion.

[0029] Figures 4A - 4C This is a schematic diagram showing an example of a prepared negative electrode mixture layer portion.

[0030] Figures 5A - 5C This is a schematic diagram showing an example of a process for preparing a solid-state battery main body.

[0031] Figures 6A - 6C This is a schematic diagram showing an example of a process for preparing a solid-state battery main body.

[0032] Figure 7 This is a graph showing the cycle characteristics of the examples and comparative examples. Detailed implementation manners

[0033] 1. Solid-state battery

[0034] Figures 1A - 1C This is a schematic diagram showing the structure of the solid-state battery 1 of this embodiment. Among them, Figure 1A This is a schematic perspective view of the main part of the solid-state battery, Figure 1B This is along Figure 1A A schematic cross-sectional view taken along line 1B of Figure 1C This is along Figure 1A A schematic cross-sectional view taken along line 1C of

[0035] As Figures 1A - 1C shown, the solid-state battery 1 includes a solid-state battery main body 10, a protective layer 20, and external electrodes 31 and 32.

[0036] 1-1. Solid-state battery main body 10

[0037] The solid-state battery main body 10 has a positive electrode layer 11, a negative electrode layer 12, and a solid electrolyte layer 13 disposed therebetween. In this embodiment, a plurality of positive electrode layers 11, a plurality of negative electrode layers 12, and a plurality of solid electrolyte layers 13 are stacked such that the solid electrolyte layer 13 is interposed between a pair of positive electrode layer 11 and negative electrode layer 12. That is, the solid-state battery main body 10 of this embodiment has a structure in which a negative electrode layer 12, a solid electrolyte layer 13, a positive electrode layer 11, a solid electrolyte layer 13, a negative electrode layer 12, a solid electrolyte layer 13, and a positive electrode layer 11 are sequentially stacked from the bottom.

[0038] (Positive electrode layer 11)

[0039] The positive electrode layer 11 is disposed on a part of one surface 13a of the solid electrolyte layer 13.

[0040] The positive electrode layer 11 contains a positive electrode active material. Examples of the positive electrode active material include layered oxides such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), compounds having an olivine structure such as lithium cobalt pyrophosphate (Li2CoP2O7, hereinafter also referred to as "LCPO") and lithium cobalt phosphate (LiCoPO4), lithium manganese oxide having a spinel structure such as LiMO2 (M is one or more of Ni, Mn, Co), lithium titanate, and phosphate compounds such as lithium vanadium phosphate (Li3V2(PO4)3, hereinafter also referred to as "LVP"), Li2FeP2O7, Li2CoP2O7, Li2NiP2O7, Li2MnP2O7, etc.

[0041] The positive electrode layer 11 may further contain a solid electrolyte and a conductive additive as needed. Examples of the solid electrolyte that the positive electrode layer 11 may contain include the same materials as the solid electrolyte used in the solid electrolyte layer 13 described later, and preferably an oxide solid electrolyte such as LAGP described later is used. Examples of the conductive additive include carbon materials such as carbon fiber, carbon black, graphite, graphene, and carbon nanotubes.

[0042] The thickness of the positive electrode layer 11 is not particularly limited, for example, it is 1 μm or more and 35 μm or less, preferably 6 μm or more and 25 μm or less. If the thickness of the positive electrode layer 11 is above the above lower limit value, it is easier to further increase the discharge capacity.

[0043] (Negative electrode layer 12)

[0044] The negative electrode layer 12 is provided on a part of the other surface 13b of the solid electrolyte layer 13. As Figure 1B shown, the paired positive electrode layer 11 and negative electrode layer 12 are arranged so as to partially overlap each other with the solid electrolyte layer 13 interposed therebetween.

[0045] The negative electrode layer 12 contains a negative electrode active material. Examples of the negative electrode active material include carbon materials such as natural graphite, artificial graphite, and graphite carbon fiber, anatase-type titanium oxide, LATP, LVP, metal oxides such as lithium titanate (Li4Ti5O 12 ) etc., metals such as silicon (Si) and tin (Sn), niobium oxide (Nb2O5), and silicides of metals such as nickel (Ni). Among them, anatase-type titanium oxide is preferred. The negative electrode active material may be one kind or a combination of two or more kinds.

[0046] The negative electrode layer 12 may further contain a solid electrolyte and a conductive additive as needed. The solid electrolyte and conductive additive used in the negative electrode layer 12 may be the same materials as the solid electrolyte and conductive additive used in the positive electrode layer 11. The negative electrode layer 12 preferably contains the same kind of solid electrolyte as the positive electrode layer 11.

[0047] The thickness of the negative electrode layer 12 is not particularly limited. For example, it is 1 μm or more and 25 μm or less, preferably 6 μm or more and 20 μm or less. If the thickness of the negative electrode layer 12 is at least the above lower limit value, it is easier to further improve the discharge capacity.

[0048] (Solid electrolyte layer 13)

[0049] The solid electrolyte layer 13 contains a solid electrolyte. Examples of the solid electrolyte include oxide solid electrolytes, sulfide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc. Among them, oxide solid electrolytes are preferred. Examples of the oxide solid electrolyte include the NASICON type (Na superionic conductor type, also referred to as "sodium superionic conductor type") oxide solid electrolyte represented by the general formula Li 1+y Al y M 2-y (PO4)3. In the above general formula, the composition ratio y is 0 < y ≤ 1, and M is one or both of germanium (Ge) and titanium (Ti). The NASICON type oxide solid electrolyte is preferably LAGP. LAGP is an oxide solid electrolyte represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 < x ≤ 1), also referred to as lithium aluminum germanium phosphate, etc. For example, as LAGP of the solid electrolyte layer 13, Li with a composition ratio x = 0.5 is preferred 1.5 Al 0.5 Ge 1.5 (PO4)3. In addition, as LAGP, it is not limited to the composition of Li 1.5 Al 0.5 Ge 1.5 (PO4)3, and NASICON type LAGP with other compositions such as Li 1.4 Al 0.4 Ge 1.6 (PO4)3 can also be used. LAGP can be amorphous LAGP, crystalline LAGP, or LAGP obtained by combining them.

[0050] The thickness of the solid electrolyte layer 13 is not particularly limited. For example, it is 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 10 μm or less. If the thickness of the solid electrolyte layer 13 is at least the lower limit value, it is easier to further improve the insulation between the positive electrode layer 11 and the negative electrode layer 12. If it is at most the upper limit value, the diffusion distance of Li ions becomes smaller, so the internal resistance of the solid-state battery 1 can be further reduced.

[0051] In the solid-state battery body 10 configured as described above, during charging, lithium ions are conducted from the positive electrode layer 11 through the solid electrolyte layer 13 and enter the negative electrode layer 12. During discharging, lithium ions are conducted from the negative electrode layer 12 through the solid electrolyte layer 13 and enter the positive electrode layer 11. Through such lithium ion conduction, charge and discharge operations are achieved.

[0052] (Design capacity ratio)

[0053] The ratio (negative electrode capacity / positive electrode capacity) of the design capacity of the negative electrode layer 12 to the design capacity of the positive electrode layer 11 of the solid-state battery body 10 of the present embodiment is 0.7 or more and 1.0 or less.

[0054] Here, the design capacity of the positive electrode layer 11 and the design capacity of the negative electrode layer 12 refer to the amount of electricity (unit: μAh) that the positive electrode layer 11 and the negative electrode layer 12 can charge and discharge. The design capacity of the positive electrode layer 11 and the design capacity of the negative electrode layer 12 can be set as values obtained by multiplying the theoretical capacity (unit: μAh / g) of each active material contained in the positive electrode layer 11 and the negative electrode layer 12 by the amount of incorporation (unit: g) of each active material.

[0055] The theoretical capacity of the active material used in the above calculation can be a reference value. In addition, the type of active material can be obtained by X-ray diffraction (XRD) or the like, and the amount of the active material (obtained from the composition ratio of the positive electrode layer 11 and the negative electrode layer 12) can be obtained by energy dispersive X-ray analysis (EDX) or the like. Using these measurement results and the theoretical capacity of each active material, the design capacity of the positive electrode layer 11 and the design capacity of the negative electrode layer 12 are obtained.

[0056] For reasons such as sufficiently accommodating lithium ions in the negative electrode to suppress the precipitation of lithium and maintaining the charge and discharge capacity of the battery even when the negative electrode active material deteriorates due to over-discharge, conventional lithium ion secondary batteries have been designed such that the design capacity of the negative electrode is more than that of the positive electrode. In contrast, according to the opinion of the present inventor, different from conventional lithium ion secondary batteries using a liquid electrolyte, in a solid-state battery, the positive electrode active material is a material that deteriorates more easily than the negative electrode active material, and has a tendency to deteriorate in crystal structure at a high potential. Therefore, the positive electrode active material is likely to deteriorate first. Therefore, it is considered that in a solid-state battery, by making the design capacity of the positive electrode more than that of the negative electrode, the cycle characteristics (reduction in battery capacity during repeated use) caused by the deterioration of the positive electrode active material can be suppressed.

[0057] According to the opinion of the present inventor, the deterioration of the above positive electrode active material is likely to occur when using lithium metal phosphate as the positive electrode active material. Therefore, the effect of improving the cycle characteristics brought about by making the design capacity of the positive electrode more than that of the negative electrode is significantly exerted when using lithium metal phosphate as the positive electrode active material.

[0058] It should be noted that if the design capacity of the positive electrode is excessive relative to the design capacity of the negative electrode (if the ratio of the above design capacities is too small), the cycle characteristics of the battery will instead deteriorate due to over-discharge. Therefore, in the present embodiment, the ratio of the above design capacities is set to 0.7 or more and 1.0 or less. From the viewpoint of obtaining their balance, the ratio of the above design capacities is preferably 0.74 or more and 0.96 or less, more preferably 0.74 or more and 0.78 or less, or 0.90 or more and 0.96 or less.

[0059] The design capacity of the positive electrode layer 11 and the design capacity of the negative electrode layer 12 can be adjusted within the above range by changing the type or combination of the positive electrode active material or the negative electrode active material to change the theoretical capacity, or by changing the thicknesses of the positive electrode layer 11 and the negative electrode layer 12. It should be noted that in the present embodiment, the solid-state battery body 10 has a plurality of positive electrode layers 11 and a plurality of negative electrode layers 12. In this case, the design capacity of the positive electrode layer 11 and the design capacity of the negative electrode layer 12 are respectively the sum of the design capacities of the plurality of positive electrode layers 11 and the sum of the design capacities of the plurality of negative electrode layers 12. In addition, the thickness of the positive electrode layer 11 and the thickness of the negative electrode layer 12 are respectively the sum of the thicknesses of the plurality of positive electrode layers 11 and the sum of the thicknesses of the plurality of negative electrode layers 12.

[0060] In addition, from the same viewpoint, the ratio of the thickness of the negative electrode layer 12 to the thickness of the positive electrode layer 11 (negative electrode thickness / positive electrode thickness) is preferably 0.7 or more and 1.0 or less, more preferably 0.7 or more and 0.9 or less, and further preferably 0.7 or more and 0.8 or less.

[0061] 1-2. Protective layer 20

[0062] The protective layer 20 covers the solid-state battery body 10 in such a manner that the end faces 11a of the positive electrode layer 11 and the end faces 12a of the negative electrode layer 12 of the solid-state battery body 10 are exposed (refer to Figure 1B ). The surface of the solid-state battery body 10 from which the end face 11a of the positive electrode layer 11 is exposed from the protective layer 20 becomes the positive electrode lead-out surface 1a, and the surface from which the end face 12a of the negative electrode layer 12 is exposed from the protective layer 20 becomes the negative electrode lead-out surface 1b. In this way, by covering the periphery of the solid-state battery body 10 with the protective layer 20, the solid-state battery body 10 can be protected from external forces or the external environment.

[0063] The protective layer 20 only needs to have electronic insulation, but a protective layer with low water or gas permeability and good airtightness is preferred. Among them, a protective layer having the same degree of thermal expansion coefficient as each layer constituting the solid-state battery body 10 or a protective layer having good adhesion to each layer is preferred. As the material constituting the protective layer 20, for example, the solid electrolyte used in the solid electrolyte layer 13, glass, or ceramic can be used.

[0064] 1-3. External electrodes 31 and 32

[0065] The external electrode 31 is provided on the positive electrode lead-out surface 1a of the solid-state battery 1 and is connected to the end face 11a of the positive electrode layer 11 exposed from the positive electrode lead-out surface 1a (see Figure 1B ). The external electrode 32 is provided on the negative electrode lead-out surface 1b of the solid-state battery 1 and is connected to the end face 12a of the negative electrode layer 12 exposed from the negative electrode lead-out surface 1b (see Figure 1B ).

[0066] Various conductor materials can be used for the external electrode 31 and the external electrode 32. For example, materials obtained by drying and curing a conductive paste containing conductive particles such as metal particles containing silver (Ag) or carbon particles, or materials formed by various metal depositions using a sputtering method or a plating method can be used for the external electrode 31 and the external electrode 32.

[0067] 1-4. Function

[0068] In the solid-state battery 1 of the above-described embodiment, the ratio (negative electrode capacity / positive electrode capacity) of the design capacity of the negative electrode layer 12 to the design capacity of the positive electrode layer 11 is 0.7 or more and 1.0 or less. Thereby, the cycle characteristics of the solid-state battery 1 can be improved.

[0069] 2. Manufacturing method of solid-state battery

[0070] The solid-state battery 1 of the present embodiment can be manufactured through the following steps: 1) a step of preparing a negative electrode paste (negative electrode mixture), a positive electrode paste (positive electrode mixture), an electrolyte paste (electrolyte mixture), and a protective paste (protective material); 2) a step of forming a laminate including a negative electrode mixture layer, a positive electrode mixture layer, and an electrolyte mixture layer obtained from the negative electrode paste; and 3) a step of firing the laminate.

[0071] 1) Step of preparing negative electrode paste, etc.

[0072] First, a negative electrode paste is prepared. The negative electrode paste contains a negative electrode active material and may further contain a solid-state electrolyte and a conductive auxiliary agent, a binder, a dispersant, a plasticizer, a diluent, etc. as needed. For example, the negative electrode paste can contain anatase-type titanium oxide particles as the negative electrode active material, an oxide solid-state electrolyte (preferably LAGP) as the solid-state electrolyte, a conductive auxiliary agent, a binder, a dispersant, and a diluent (organic solvent).

[0073] Furthermore, the positive electrode paste (positive electrode mixture), the electrolyte paste (electrolyte mixture), and the protective paste (protective material) are prepared in the same manner.

[0074] (Positive electrode paste)

[0075] The positive electrode paste contains positive electrode active materials, and may further contain a solid electrolyte, a conductive aid, a binder, a dispersant, a plasticizer, a diluent, etc. as required. For example, the positive electrode paste may contain positive electrode active materials such as LCPO, oxide solid electrolytes such as LAGP, conductive aids such as carbon nanofibers, a binder, and a diluent.

[0076] (Electrolyte paste)

[0077] The electrolyte paste contains a solid electrolyte, and may further contain a solid electrolyte, a conductive aid, a binder, a dispersant, a plasticizer, a diluent, etc. as required. For example, the electrolyte paste may contain a solid electrolyte such as LAGP and a diluent.

[0078] (Protection paste)

[0079] As the protection paste, an electrolyte paste may be used, or a paste containing a glass component or a ceramic component such as Al2O3 may be used.

[0080] 2) Process of forming a laminate

[0081] Next, using the above-mentioned pastes, a laminate 44 including a positive electrode mixture layer 41, a negative electrode mixture layer 42, an electrolyte mixture layer 43, a protective material layer 21, and a protective sheet 22 is formed. In the present embodiment, a positive electrode mixture layer portion and a negative electrode mixture layer portion are prepared, and these are laminated to form the laminate 44.

[0082] (Preparation of positive electrode mixture layer portion)

[0083] Figures 2A - 2E It is a schematic diagram showing an example of the process of preparing the positive electrode mixture layer portion. Figures 3A - 3C It is a schematic diagram showing an example of the prepared positive electrode mixture layer portion. Among them, Figure 3A is a schematic perspective view of the positive electrode mixture layer portion, Figure 3B is along Figure 3A a schematic cross-sectional view taken along line 4B, Figure 3C is along Figure 3A a schematic cross-sectional view taken along line 4C.

[0084] First, on a part of the support 40, for example, after coating the positive electrode paste by screen printing, it is dried to form the positive electrode mixture layer 41 ( Figure 2A and 2B ). Next, around the positive electrode mixture layer 41 formed on a part of the support 40, for example, the protection paste is coated by screen printing and dried to form the protective material layer 21 (embedded layer) (refer to Figure 2C ).

[0085] In order to adjust the thickness and the amount of active material of the positive electrode mixture layer 41, etc., the coating of the positive electrode paste and the coating of the protective paste around it can be alternately repeated multiple times. In this case, the drying of the positive electrode paste and the protective paste can be carried out after each coating is completed, or can be carried out together after multiple coatings of the positive electrode paste and the protective paste.

[0086] Next, on the positive electrode mixture layer 41 and on a part of the protective material layer 21 formed around it, for example, an electrolyte paste is coated by a screen printing method and dried to form an electrolyte mixture layer 43 (refer to Figure 2D ). After forming the electrolyte mixture layer 43, on a part of the protective material layer 21 not covered by it, for example, a protective paste is coated by a screen printing method and dried to form a protective material layer 21 (embedded layer) (refer to Figure 2E ). Thus, a positive electrode mixture layer part is obtained (refer to Figure 3A ).

[0087] In order to adjust the thickness of the electrolyte mixture layer 43, etc., the coating of the electrolyte paste and the coating of the protective paste outside it can be alternately repeated multiple times. In this case, the drying of the electrolyte paste and the protective paste can be carried out after each coating is completed, or can be carried out together after multiple coatings of the electrolyte paste and the protective paste.

[0088] It should be noted that the material obtained by peeling the support 40 from the positive electrode mixture layer part shown in Figures 3A - 3C can also be used as the positive electrode mixture layer part. In addition, the part shown in Figure 2C before forming the electrolyte mixture layer 43 or the material obtained by peeling the support 40 from this part can also be used as the positive electrode mixture layer part.

[0089] In addition, although an example is shown in which the electrolyte mixture layer 43 and the protective material layer 21 outside it are formed after forming the positive electrode mixture layer 41 and the protective material layer 21 around it on the support 40, the order can also be reversed. That is, the positive electrode mixture layer 41 and the protective material layer 21 around it can also be formed after forming the electrolyte mixture layer 43 and the protective material layer 21 outside it on the support 40.

[0090] In addition, each layer can be directly coated on the support 40, but it can also be formed by transferring it onto the support 40 after coating on other release films (such as PET films).

[0091] (Preparation of the negative electrode mixture layer part)

[0092] Figures 4A - 4C is a schematic diagram showing an example of the prepared negative electrode mixture layer part. Among them, Figure 4A is a schematic three-dimensional view of the negative electrode mixture layer part,Figure 4B is a schematic cross-sectional view along Figure 4A the 5B line of Figure 4C and is a schematic cross-sectional view along Figure 4A the 5C line of

[0093] The preparation of the negative electrode mixture layer portion can be carried out in the same manner as the preparation method of the above-mentioned positive electrode mixture layer portion. Thus, a negative electrode mixture layer portion in which a support 40, a negative electrode mixture layer 42 and a protective material layer 21 around it, and an electrolyte mixture layer 43 and a protective material layer 21 outside it are laminated in sequence can be obtained ( Figures 4A - 4C ).

[0094] (Formation of the laminate)

[0095] Figures 5A - 5C and Figures 6A - 6C is a schematic diagram showing an example of the process for preparing the solid-state battery body 10.

[0096] Laminating the above-prepared positive electrode mixture layer portion and negative electrode mixture layer portion. For example, on the negative electrode mixture layer portion with the support 40 in Figure 4B , the material after peeling off the support 40 from the positive electrode mixture layer portion in Figure 3B is laminated, and on it, the material after peeling off the support 40 from the negative electrode mixture layer portion shown in Figure 4B is laminated, and on it, the material after peeling off the support 40 from the positive electrode mixture layer portion shown in Figure 2C is laminated (refer to Figure 5A ). Further, the support 40 is peeled off from the obtained laminate, protective sheets 22 are laminated on the lower side and the upper side, and these are thermocompression bonded under specified pressure and temperature conditions to form a laminate 44 (refer to Figure 5B ).

[0097] The positive electrode mixture layer portion and the negative electrode mixture layer portion are laminated in such a manner that the negative electrode mixture layer 42 facing each other across the electrolyte mixture layer 43 partially overlaps with the positive electrode mixture layer 41. In addition, the number of laminations can be set according to the required performance (such as the capacity of the battery, etc.).

[0098] Thus, a laminate 44 including a positive electrode mixture layer 41, a negative electrode mixture layer 42, an electrolyte mixture layer 43 between them, a protective material layer 21, and a protective sheet 22 is formed (refer to Figure 5B ).

[0099] (Adjustment of the capacity ratio)

[0100] In the present embodiment, in this process, the laminate after calcination in the next process is formed such that the ratio of the design capacity of the negative electrode mixture layer 42 to the design capacity of the positive electrode mixture layer 41 (negative electrode capacity / positive electrode capacity) is 0.7 or more and 1.0 or less. It should be noted that the discharge capacities of the calcined positive electrode layer and negative electrode layer are consistent with the above-mentioned design capacities. For example, based on the theoretical capacity and its content of the positive electrode active material contained in the positive electrode paste (positive electrode mixture layer portion) and the theoretical capacity and its content of the negative electrode active material contained in the negative electrode paste (negative electrode mixture layer portion), the thickness of each positive electrode mixture layer portion and negative electrode mixture layer portion or the number of layers of each positive electrode mixture layer portion and negative electrode mixture layer portion can be adjusted so that the above ratio is 0.7 or more and 1.0 or less.

[0101] 3) Process of calcining the laminate

[0102] Next, if necessary, the obtained laminate 44 is cut at the specified positions C1 and C2 (refer to Figure 5B ). Further, the obtained laminate 44 is calcined at a specified temperature (refer to Figure 6A and 6B ).

[0103] (Debinding / calcination)

[0104] The laminate 44 is heat-treated under conditions of a specified atmosphere, temperature, and time. The heat treatment can be performed, for example, in a heat treatment furnace 45. Specifically, a heat treatment mainly for debinding to burn off organic components such as binders and a heat treatment mainly for calcining the solid electrolyte and protective materials are performed.

[0105] The heat treatment for debinding can be performed, for example, in an atmosphere containing oxygen, maintained at 200 - 500 °C for 1 - 30 hours, preferably maintained at 500 °C for 10 hours. The heat treatment for calcination can be performed, for example, in an atmosphere containing nitrogen or oxygen, maintained at 500 - 700 °C for 0.5 - 10 hours, preferably maintained at 600 °C for 2 hours.

[0106] By the heat treatment for calcination, the solid electrolytes in the electrolyte mixture layer 43, the solid electrolytes in the positive electrode mixture layer 41 and the negative electrode mixture layer 42 contained in the laminate 44 are sintered. In addition, by the heat treatment for calcination, the protective material layer 21 and the protective sheet 22 contained in the laminate 44 are sintered and integrated with each other. Thus, a sintered body of the laminate 44 having a positive electrode layer 11, a negative electrode layer 12, a solid electrolyte layer 13, and a protective layer 20 is formed (refer to Figure 6B ).

[0107] The cut surface of the sintered body of the laminate 44 at position C1 becomes the positive electrode lead-out surface 1a, and the end face 11a of the positive electrode layer 11 exposed from the positive electrode lead-out surface 1a is connected to the external electrode 31. The cut surface of the sintered body of the laminate 44 at position C2 becomes the negative electrode lead-out surface 1b, and the end face 12a of the negative electrode layer 12 exposed from the negative electrode lead-out surface 1b is connected to the external electrode 32. Thus, the solid-state battery main body 10 (reference Figure 6B ) can be obtained.

[0108] (Formation of External Electrodes)

[0109] An external electrode 31 is formed on the positive electrode lead-out surface 1a of the sintered body of the obtained laminate 44, and an external electrode 32 is formed on the negative electrode lead-out surface 1b. The external electrode 31 and the external electrode 32 are formed, for example, by the following methods: a method of coating, drying, and curing a conductive paste; and a method of depositing a metal by sputtering or plating. Thus, the solid-state battery 1 (reference Figure 6C ) can be obtained.

[0110] 3. Modification Example

[0111] It should be noted that in the above embodiment, the positive electrode layer 11, the negative electrode layer 12, and the solid electrolyte layer 13 constituting the solid-state battery main body 10 are each plural, but it is not limited thereto, and each may be one. In addition, the number of the positive electrode layer 11, the negative electrode layer 12, and the solid electrolyte layer 13 is not limited to the above embodiment and can be appropriately set according to the required characteristics.

[0112] In addition, in the above embodiment, an oxide solid electrolyte is used as the solid electrolyte of the solid electrolyte layer 13, the positive electrode layer 11, and the negative electrode layer 12, and LAGP is preferably used. LAGP can be amorphous LAGP, crystalline LAGP, or LAGP obtained by combining them.

[0113] In addition, in addition to LAGP, NASICON-type LATP (general formula Li 1+z Al z Ti 2-z (PO4)3, 0 < z ≤ 1) of Li 1.3 Al 0.3 Ti 1.7 (PO4)3, garnet-type lithium lanthanum zirconate (Li7La3Zr2O 12 , hereinafter referred to as "LLZ"), perovskite-type lithium lanthanum titanate (Li 0.5 La 0.5 TiO3, hereinafter referred to as "LLT"), partially nitrided γ-lithium phosphate (γ-Li3PO4, hereinafter referred to as "LiPON") and other oxide solid electrolytes can also be used.

[0114] In the solid electrolyte layer 13, the positive electrode layer 11, and the negative electrode layer 12, the same type of oxide solid electrolyte can be used, or different types of oxide solid electrolytes can be used. In the solid electrolyte layer 13, the positive electrode layer 11, and the negative electrode layer 12, one type of oxide solid electrolyte can be used respectively, or two or more types of oxide solid electrolytes can be used.

[0115] In addition, in the above-described embodiment, the protective material layer 21 serving as the buried layer and the protective sheets 22 disposed on the lower side and the upper side of the laminate 44 may be formed of a protective paste having the same composition, or may be formed of protective pastes having different compositions.

[0116] Examples

[0117] Hereinafter, the present invention will be further described with reference to examples. It should be noted that the technical scope of the present invention is not limited by these examples.

[0118] 1. Preparation of Solid State Battery

[0119] [Example 1]

[0120] 1-1. Preparation of Slurry

[0121] 1-1-1. Preparation of Positive Electrode Slurry

[0122] 11.8 parts by mass of Li2CoP2O7 powder (LCPO powder) as a positive electrode active material, amorphous Li 1.5 Al 0.5 Ge 1.5 (PO4)3 powder (LAGPg powder) 17.7 parts by mass as a solid electrolyte, 2.7 parts by mass of vapor-grown carbon fiber powder (VGCF powder) as a conductive aid, 7.8 parts by mass of polyvinyl butyral as an adhesive, 0.3 parts by mass of triethylene glycol bis(2-ethylhexanoate) (manufactured by Sumitomo Chemical Co., Ltd., G-260) as a plasticizer, 0.6 parts by mass of HIPLAAD ED350 (registered trademark of the company) manufactured by Kusumoto Chemical Co., Ltd. as a dispersant, and 59.1 parts by mass of terpineol as a diluent were used in the following proportions. After mixing them with a ball mill for 72 hours, they were mixed and dispersed with a three-roll mill, and the material aggregates were dispersed to 1 μm or less using a particle size meter to obtain a positive electrode slurry.

[0123] 1-1-2. Preparation of Negative Electrode Slurry

[0124] A negative electrode slurry was obtained in the same manner as the preparation of the positive electrode slurry, except that anatase titanium oxide was used in an equal amount as the negative electrode active material instead of the positive electrode active material.

[0125] 1-1-3. Preparation of Electrolyte Slurry

[0126] Use amorphous Li as a solid electrolyte in the following ratio 1.5 Al 0.5 Ge 1.5 (PO4)3 powder (LAGPg powder) 29.0 parts by mass and crystalline Li 1.5 Al 0.5 Ge 1.5 (PO4)3 powder (LAGPc powder) 3.2 parts by mass, polyvinyl butyral as a binder 6.2 parts by mass, triethylene glycol bis(2-ethylhexanoate) (manufactured by Sumitomo Chemical Co., Ltd., G-260) as a plasticizer 2.2 parts by mass, HIPLAAD ED350 manufactured by Kusumoto Chemical Co., Ltd. as a dispersant 0.3 parts by mass, and terpineol as a diluent 59.1 parts by mass. After mixing them with a ball mill for 72 hours, they were mixed and dispersed with a three-roll mill, and the material aggregates were dispersed to 1 μm or less using a particle size meter to obtain an electrolyte slurry.

[0127] 1-2. Preparation of the solid-state battery

[0128] 1-2-1. Preparation of the positive electrode mixture layer part

[0129] The above electrolyte slurry was pattern-printed on a PET film by screen printing and dried at 90 °C for 5 minutes. The above positive electrode slurry was pattern-printed thereon by screen printing and dried at 90 °C for 5 minutes. Then, the above electrolyte slurry (buried slurry) was printed around the pattern-printed positive electrode slurry by screen printing and dried at 90 °C for 5 minutes. These operations were repeated until a specified thickness was reached. Thus, a positive electrode mixture layer part having a laminated structure of a PET film / electrolyte mixture layer / positive electrode mixture layer and an electrolyte mixture layer around it was prepared.

[0130] 1-2-2. Preparation of the negative electrode mixture layer part

[0131] Except for using the above negative electrode slurry in place of the above positive electrode slurry, the negative electrode mixture layer part was prepared in the same manner as the positive electrode mixture layer part. Thus, a negative electrode mixture layer part having a laminated structure of a PET film / electrolyte mixture layer / negative electrode mixture layer and an electrolyte mixture layer around it was prepared.

[0132] 1-2-3. Preparation of the upper cover and the lower cover

[0133] The above electrolyte slurry was printed (full-surface printing) on a PET film so as to cover it and then dried. Thus, an upper cover and a lower cover having a laminated structure of a PET film / electrolyte mixture layer were respectively prepared.

[0134] 1-2-4. Preparation of the laminate

[0135] The thus-prepared positive electrode mixture layer is partially laminated on the electrolyte mixture layer of the thus-prepared lower cover in such a manner that the positive electrode mixture layer is in contact with the electrolyte mixture layer of the lower cover, and then they are thermocompression bonded to transfer the positive electrode mixture layer / electrolyte mixture layer.

[0136] Next, the negative electrode mixture layer is partially laminated on the transferred electrolyte mixture layer in such a manner that the negative electrode mixture layer is in contact with the electrolyte mixture layer, and then they are thermocompression bonded to transfer the negative electrode mixture layer / electrolyte mixture layer.

[0137] The transfer of the positive electrode mixture layer part and the negative electrode mixture layer part described above is repeated until the specified number of laminated layers (10 layers) is reached. Finally, the upper cover is laminated in the same manner, and then thermocompression bonding and transfer are performed.

[0138] The thermocompression bonding conditions are all set to 20 MPa and 70 °C. Thus, a laminate having a laminated structure as shown in Figure 1B and 1C is obtained.

[0139] After cutting the laminate into a planar size of 4.5 mm × 3.2 mm, it is placed horizontally on a porous ceramic plate and heated at 500 °C for 1 hour in an air atmosphere to remove the binder component. Then, it is heated at 600 °C for 2 hours in a nitrogen atmosphere. Thus, the laminate is calcined. The thickness of the calcined positive electrode layer is 18 μm, and the thickness of the negative electrode layer is 12 μm.

[0140] An external electrode is formed so as to cover the lead-out part of the obtained calcined laminate. The external electrode is formed by applying a main material containing silver and then performing Ni plating and Sn plating on its surface. Thus, the solid-state battery shown in Fig. 1 is prepared.

[0141] [Example 2]

[0142] A solid-state battery is prepared in the same manner as in Example 1 except that the thicknesses of the positive electrode mixture layer part and the negative electrode mixture layer part are changed respectively. The thickness of the calcined positive electrode layer is 14.3 μm, and the thickness of the negative electrode layer is 11 μm.

[0143] [Example 3]

[0144] A solid-state battery is prepared in the same manner as in Example 1 except that the thicknesses of the positive electrode mixture layer part and the negative electrode mixture layer part are changed respectively. The thickness of the calcined positive electrode layer is 20 μm, and the thickness of the negative electrode layer is 16 μm.

[0145] [Example 4]

[0146] A solid-state battery was prepared in the same manner as in Example 1, except that the amount of the negative active material (anatase titanium oxide) incorporated when formulating the negative electrode paste was set to 9.38 parts by mass, the amount of LAGPg powder incorporated in the solid electrolyte was set to 20.12 parts by mass, and the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 18.3 μm, and the thickness of the negative electrode layer was 14.5 μm.

[0147] [Comparative Example 1]

[0148] A solid-state battery was prepared in the same manner as in Example 1, except that the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 22 μm, and the thickness of the negative electrode layer was 12 μm.

[0149] [Comparative Example 2]

[0150] A solid-state battery was prepared in the same manner as in Example 1, except that the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 10.3 μm, and the thickness of the negative electrode layer was 11 μm.

[0151] [Comparative Example 3]

[0152] A solid-state battery was prepared in the same manner as in Example 1, except that the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 11 μm, and the thickness of the negative electrode layer was 16 μm.

[0153] [Comparative Example 4]

[0154] A solid-state battery was prepared in the same manner as in Example 1, except that the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 10.8 μm, and the thickness of the negative electrode layer was 15.8 μm.

[0155] [Comparative Example 5]

[0156] A solid-state battery was prepared in the same manner as in Example 1, except that the thicknesses of the positive electrode mixture layer portion and the negative electrode mixture layer portion were changed respectively. The thickness of the positive electrode layer after calcination was 18.5 μm, and the thickness of the negative electrode layer was 13.8 μm.

[0157] The thicknesses of the positive electrode layer and the negative electrode layer after calcination, the ratio of the thickness of the negative electrode layer to the thickness of the positive electrode layer (negative electrode thickness / positive electrode thickness), the total design capacity of the positive electrode layer and the negative electrode layer, and the ratio of the design capacity of the negative electrode layer to the design capacity of the positive electrode layer (negative electrode capacity / positive electrode capacity) of each solid-state battery are shown in Table 1.

[0158] Table 1

[0159]

[0160] 2. Evaluation (Charge and Discharge Cycle Test)

[0161] For the fabricated solid-state battery, charge and discharge are performed for 60 cycles under the following conditions.

[0162] (Charging Conditions)

[0163] Charging is performed in the CC-CV charging mode (Constant Current-Constant Voltage). The maximum current rate in the CC charging mode is set to 1C, and the end condition of the CV charging mode is set to 3 hours from the start of the CV mode. The upper limit voltage during CV charging is set to 3.4V.

[0164] (Discharging Conditions)

[0165] Discharging is performed in the CC discharging mode. The current rate is set to 0.2C, and the end is set to 1V. The charge and discharge test is carried out at 85°C.

[0166] Calculate the ratio of the discharge capacity in each cycle to the initial discharge capacity (μAh) as the discharge capacity retention rate in each cycle. The relationship between the number of cycles and the discharge capacity retention rate of each solid-state battery is as Figure 7 shown.

[0167] From Figure 7 it can be seen that a solid-state battery with a ratio of the designed capacity of the negative electrode layer to the designed capacity of the positive electrode layer (negative electrode capacity / positive electrode capacity) of 0.74 or more and 0.96 or less has good charge and discharge cycle characteristics.

[0168] This application claims the priority of Japanese Patent Application No. 2022-156663 filed on September 29, 2022. The matters described in the specification, claims, and drawings of the original application of this application are incorporated herein by reference.

[0169] Industrial Applicability

[0170] According to the present invention, it is possible to provide a solid-state battery and a method for manufacturing the same, and the solid-state battery can also be applied to a solid-state battery using an oxide-based solid electrolyte, and can improve the cycle characteristics without an additional structure such as a conductive resin layer.

[0171] Explanation of Reference Numerals

[0172] 1: Solid-state battery;

[0173] 1a: Positive electrode lead-out surface;

[0174] 1b: Negative electrode lead-out surface;

[0175] 10: Solid-state battery main body;

[0176] 11: Positive electrode layer;

[0177] 12: Negative electrode layer;

[0178] 13: Solid electrolyte layer;

[0179] 11a, 12a: End faces;

[0180] 13a: One face;

[0181] 13b: The other face;

[0182] 20: Protective layer;

[0183] 21: Protective material layer;

[0184] 22: Protective sheet;

[0185] 31, 32: External electrodes;

[0186] 40: Support;

[0187] 41: Positive electrode mixture layer;

[0188] 42: Negative electrode mixture layer;

[0189] 43: Electrolyte mixture layer;

[0190] 44: Stacked body.

Claims

1. A solid-state battery, comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. In the solid-state battery, the ratio of the designed capacity of the negative electrode layer to the designed capacity of the positive electrode layer, i.e., negative electrode capacity / positive electrode capacity, is 0.74 or more and 0.96 or less.

2. The solid-state battery according to claim 1, wherein the ratio of the thickness of the negative electrode layer to the thickness of the positive electrode layer, i.e., negative electrode thickness / positive electrode thickness, is 0.7 or more and 0.8 or less.

3. The solid-state battery according to claim 1, wherein the positive electrode layer contains an oxide solid electrolyte.

4. The solid-state battery according to claim 1, wherein the positive electrode layer contains lithium metal phosphate.

5. A method for manufacturing a solid-state battery, comprising: a step of forming a laminate including a positive electrode mixture layer, a negative electrode mixture layer, and an electrolyte mixture layer disposed between the positive electrode mixture layer and the negative electrode mixture layer; and a step of calcining the laminate, wherein the ratio of the designed capacity of the negative electrode mixture layer to the designed capacity of the positive electrode mixture layer in the laminate after the calcination, i.e., negative electrode capacity / positive electrode capacity, is 0.74 or more and 0.96 or less.

6. The method for manufacturing a solid-state battery according to claim 5, wherein the ratio of the thickness of the negative electrode mixture layer to the thickness of the positive electrode mixture layer in the laminate after the calcination, i.e., negative electrode thickness / positive electrode thickness, is 0.7 or more and 0.8 or less.

7. The method for manufacturing a solid-state battery according to claim 5, wherein the positive electrode mixture layer contains an oxide solid electrolyte.

8. The method for manufacturing a solid-state battery according to claim 5, wherein the positive electrode mixture layer contains lithium metal phosphate.

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