Solid secondary battery

Abstract

To provide a solid secondary battery including an intermediate layer, capable of quick charging and having preferred charging and discharging efficiency.SOLUTION: A solid secondary battery includes a positive electrode layer, a negative electrode layer including at least a negative electrode current collector, a solid electrolyte layer including a solid electrolyte material, and an intermediate layer provided between the negative electrode layer and the solid electrolyte layer. A buffer material that restricts an electrode assembly in which the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are joined is provided. The 25%-compression load of the buffer material is more than 0.5 MPa and the extension thereof is less than 100%.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0003] As such secondary batteries, solid secondary batteries such as lithium metal batteries and lithium-ion secondary batteries in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer are known. An intermediate layer may be disposed between the negative electrode layer and the solid electrolyte layer for the purpose of making the deposition of lithium or the like uniform and stabilizing the interface.

[0004] In solid secondary batteries, improvement in charge / discharge efficiency is required. For example, Patent Document 1 discloses a technique for achieving both charge / discharge efficiency and discharge capacity.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 proposes an electrode material including a first active material containing Li, Ti, and O, a second active material containing Mo and O, and a solid electrolyte, in response to the problem that lithium titanate used for the negative electrode has a small capacity per unit mass. On the other hand, in a solid secondary battery having an intermediate layer, when rapid charging is performed, the current density distribution becomes non-uniform, resulting in an increase in the resistance of the battery or a short circuit.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a solid secondary battery having an intermediate layer that enables rapid charging and obtains favorable charge and discharge efficiency.

Means for Solving the Problems

[0008] (1) The present invention has a positive electrode layer, a negative electrode layer including at least a negative electrode current collector, a solid electrolyte layer including a solid electrolyte material, and an intermediate layer provided between the negative electrode layer and the solid electrolyte layer, and has a buffer material that restrains an electrode assembly in which the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are joined. The buffer material relates to a solid secondary battery in which a 25% compression load is greater than 0.5 MPa and elongation is less than 100%.

[0009] According to the invention of (1), it is possible to provide a solid secondary battery having an intermediate layer that enables rapid charging and obtains favorable charge and discharge efficiency.

[0010] (2) The material constituting the intermediate layer and the solid electrolyte material are in a particulate state, and the particle size of the particles constituting the intermediate layer is smaller than the particle size of the solid electrolyte material. The solid secondary battery according to (1).

[0011] According to the invention of (2), it is possible to increase the contact area between the intermediate layer and the solid electrolyte layer and improve the adhesion between these layers.

[0012] (3) The porosity of the intermediate layer is 40 to 70%. The solid secondary battery according to (1) or (2).

[0013] According to the invention of (3), even when charge and discharge are repeated, the interfacial adhesion can be maintained and the durability of the solid secondary battery can be improved.

[0014] (4) The complex elastic modulus of the intermediate layer is less than 1 GPa. The solid secondary battery according to any one of (1) to (3).

[0015] According to the invention of (4), since the intermediate layer can follow the change in the thickness of the solid-state secondary battery associated with charge and discharge, the interfacial adhesion can be maintained and the durability of the solid-state secondary battery can be improved.

[0016] (5) The solid-state secondary battery according to any one of (1) to (4), wherein the intermediate layer contains amorphous carbon.

[0017] According to the invention of (5), the formation of dendrites can be suppressed and the cycle characteristics of the solid-state secondary battery can be improved.

[0018] (6) The solid-state secondary battery according to any one of (1) to (5), wherein the compression residual strain of the buffer material is 6% or more.

[0019] According to the invention of (6), the buffer material can easily follow the change in the thickness of the solid-state secondary battery during charge and discharge, and the reaction distribution can be made uniform.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0021] [Solid-state secondary battery] As shown in Fig. 1, the solid secondary battery 1 has an electrode assembly in which a negative electrode layer 20, an intermediate layer 50, a solid electrolyte layer 40, and a positive electrode layer 30 are laminated and joined in this order. In the present embodiment, the structure in which the negative electrode layer 20, intermediate layer 50, solid electrolyte layer 40, positive electrode layer 30, solid electrolyte layer 40, intermediate layer 50, and negative electrode layer 20 shown in Fig. 1 are laminated in this order will be described as the structure of the electrode assembly of the solid secondary battery 1. However, the structure of the electrode assembly is not limited to the above, and it may have a negative electrode layer 20, a solid electrolyte layer 40, and a positive electrode layer 30, and an intermediate layer 50 provided between the negative electrode layer 20 and the solid electrolyte layer 40. The solid secondary battery 1 has a buffer material 70 that constrains the above electrode assembly. The buffer material 70 can appropriately constrain the above electrode assembly.

[0022] The solid secondary battery 1 is not particularly limited, and may be a lithium-ion solid secondary battery or a lithium metal secondary battery.

[0023] (Negative electrode layer) The negative electrode layer 20 has at least a negative electrode current collector layer 22. The negative electrode layer 20 may further have a negative electrode active material layer 21.

[0024] The negative electrode current collector layer 22 is not particularly limited, and can be made of copper, nickel, stainless steel, or the like. Examples of the shape of the negative electrode current collector layer 22 include a foil shape, a plate shape, a mesh shape, a non-woven fabric shape, and a foamed shape.

[0025] The negative electrode active material layer 21 is not particularly limited and can be composed of a material that can be used as a negative electrode active material for a solid battery. The negative electrode active material layer 21 is preferably a lithium metal layer in which the negative electrode active material is lithium metal. This is because the solid secondary battery 1 according to the present invention can adhere to the solid electrolyte layer 40 with high adhesion even when the negative electrode active material layer 21 is a hard metal. The above lithium metal includes lithium alloys and the like in addition to lithium metal alone. In addition to the above, the negative electrode active material layer 21 is a silicon-based active material such as Si or Si alloy, lithium titanate (Li4Ti5O 12)It may be composed of lithium transition metal oxides such as [], transition metal oxides such as TiO2, Nb2O3 and WO3, metal sulfides, metal nitrides, carbon materials such as graphite, soft carbon and hard carbon, metal indium, etc.

[0026] The negative electrode active material layer 21 may contain materials other than those described above that can be contained in the negative electrode active material layer of the solid battery. Examples of the above materials include solid electrolytes, conductive aids, binders, etc. Examples of the solid electrolyte include the same ones as those contained in the solid electrolyte layer 40 described later. Examples of the conductive aid include carbon black, natural graphite, carbon fiber, carbon nanotube, etc. Examples of the binder include nitrile-based polymers, polyester-based polymers, acrylic acid-based polymers, cellulose-based polymers, styrene-based polymers, styrene-butadiene-based polymers, vinyl acetate-based polymers, urethane-based polymers, fluoroethylene-based polymers, etc.

[0027] When the solid secondary battery 1 is a lithium metal secondary battery using metallic lithium as the negative electrode active material, the solid secondary battery 1 may be an anode-free battery in which the negative electrode active material layer 21 does not exist during the first charging. In this case, a lithium metal layer as the negative electrode active material layer 21 is formed after the first charge and discharge.

[0028] The lithium deposition layer 21a is a layer generated during charging of the solid secondary battery 1 when the solid secondary battery 1 is a lithium metal secondary battery using metallic lithium as the negative electrode active material. The lithium deposition layer 21a is generated when lithium ions released from the positive electrode active material layer 31 are deposited on the surface of the negative electrode active material layer 21 during charging of the solid secondary battery 1. On the other hand, during discharge, lithium ions are released from the lithium deposition layer 21a and occluded in the positive electrode active material layer 31. Therefore, the lithium deposition layer 21a may become thinner or disappear during discharge of the solid secondary battery.

[0029] (Intermediate layer) The intermediate layer 50 is disposed between the negative electrode layer 20 and the solid electrolyte layer 40. The intermediate layer 50 has voids through which metal ions (e.g., lithium ions), which are charge carriers in the solid secondary battery 1, can pass. When the solid secondary battery 1 is, for example, a lithium metal battery, lithium ions can pass through the intermediate layer 50 to uniformly deposit lithium metal. Further, since the intermediate layer 50 has voids and is flexible, it can follow the change in the thickness of the solid secondary battery 1 accompanying charge and discharge. Therefore, even when the charge and discharge of the solid secondary battery 1 are repeated, the interfacial adhesion can be maintained and the durability of the solid secondary battery 1 can be improved.

[0030] The porosity of the intermediate layer 50 is preferably 40 to 70%. The porosity of the intermediate layer 50 can be obtained, for example, by the following formula (1). In formula (1), "filling rate" means the percentage of the density of the intermediate layer after molding with respect to the true density. Porosity (%) = (100 - filling rate (%))...(1)

[0031] From the viewpoint of obtaining the above-mentioned preferable flexibility, the complex elastic modulus of the intermediate layer 50 is preferably less than 1 GPa. The complex elastic modulus of the intermediate layer 50 may be in the range of 600 to 800 MPa.

[0032] The material constituting the intermediate layer 50 is not particularly limited, and examples thereof include amorphous carbon and metals that can be alloyed with lithium. The intermediate layer 50 preferably contains amorphous carbon. The intermediate layer 50 may contain a binder in addition to the above substances.

[0033] Amorphous carbon, unlike, for example, graphite, is difficult to react with metals such as lithium and alloy, so it can suppress the formation of dendrites and improve the cycle characteristics of the solid secondary battery 1. The amorphous carbon may be easily graphitizable carbon (soft carbon) or hardly graphitizable carbon (hard carbon). The amorphous carbon only needs to be one that does not show a distinct crystalline state among the allotropes of carbon, and may be an aggregate of fine graphite crystals. Specific examples of the amorphous carbon include carbon blacks such as acetylene black, furnace black, and ketjen black, coke, activated carbon, CNT (carbon nanotube), fullerene, and graphene.

[0034] Examples of metals that can alloy with lithium include tin (Sn), silicon (Si), zinc (Zn), magnesium (Mg), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), antimony (Sb), etc. The metal that can alloy with lithium may be nanoparticles.

[0035] As the material constituting the intermediate layer 50, a plurality of the above-mentioned types of materials may be used in combination.

[0036] The material constituting the intermediate layer 50 is in particle form, and its particle size is preferably smaller than the particle size of the solid electrolyte material constituting the solid electrolyte layer 40. Thereby, the particles constituting the intermediate layer 50 can enter between the solid electrolyte materials constituting the interface between the intermediate layer 50 and the solid electrolyte layer 40. Therefore, the contact area between the intermediate layer 50 and the solid electrolyte layer 40 can be increased, and the adhesion between these layers can be improved. The particle size of the amorphous carbon may be, for example, in the range of 0.02 μm to 0.06 μm in terms of median diameter (D50). The particle size of the metal nanoparticles may be, for example, in the range of 0.06 μm to 0.1 μm or less in terms of median diameter (D50).

[0037] (Solid electrolyte layer) The solid electrolyte layer 40 is provided between the intermediate layer 50 and the positive electrode layer 30. The solid electrolyte material constituting the solid electrolyte layer 40 is not particularly limited as long as it is a material that can be used as the electrolyte of a solid secondary battery. For example, sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, halide solid electrolyte materials, etc. can be mentioned.

[0038] Examples of sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiI, etc. The description of "Li2S-P2S5" means a sulfide solid electrolyte material formed using a raw material composition containing Li2S and P2S5, and the same applies to other similar descriptions. The sulfide solid electrolyte material may have an argyrodite-type crystal structure.

[0039] Examples of oxide solid electrolyte materials include NASICON-type oxides, garnet-type oxides, perovskite-type oxides, etc. Examples of NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (for example, Li 1.5 Al 0.5 Ti 1.5 (PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (for example, Li7La3Zr2O 12 ). Examples of perovskite-type oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0040] The solid electrolyte material constituting the solid electrolyte layer 40 is preferably in particulate form. The particle diameter of the solid electrolyte material is, for example, 0.5 to 10 μm in terms of median diameter (D50), and is preferably larger than the particles constituting the intermediate layer 50.

[0041] In addition to the solid electrolyte material, the solid electrolyte layer 40 may contain materials that can be used in the solid electrolyte layer of a solid secondary battery. For example, the solid electrolyte layer 40 may contain a binder. As the binder, the same substances as those that can be contained in the negative electrode active material layer 21 can be used.

[0042] The solid electrolyte layer 40 may have a porous base material inside. As the porous base material, for example, woven fabric or non-woven fabric can be used. By having the porous base material in the solid electrolyte layer 40, the strength of the solid electrolyte layer 40 is improved.

[0043] (Positive electrode layer) The positive electrode layer 30 has a positive electrode active material layer 31 and a positive electrode current collector layer 32. In the present embodiment, the positive electrode layer 30 has a configuration in which two positive electrode active material layers 31 are laminated on both sides of one positive electrode current collector layer 32. On the other hand, the configuration of the positive electrode layer 30 is not limited to the above, and may have a configuration in which one positive electrode active material layer 31 is laminated on one side of one positive electrode current collector layer 32.

[0044] The positive electrode active material layer 31 is not particularly limited and can be composed of a material that can be used as a positive electrode active material of a solid battery. Examples of the positive electrode active material constituting the positive electrode active material layer 31 include, for example, a layered active material containing lithium, a spinel-type active material, an olivine-type active material, etc. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi p Mn q Co r O2 (p + q + r = 1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganate (LiMn2O4), Li 1+x Mn 2-x-y MO4 (x + y = 2, M = at least one selected from Al, Mg, Co, Fe, Ni, and Zn) represented by a hetero-element substituted Li-Mn spinel, lithium titanate (oxide containing Li and Ti), lithium metal phosphate (LiMPO4, M = at least one selected from Fe, Mn, Co, and Ni), etc. can be mentioned.

[0045] The positive electrode active material layer 31 may optionally contain a solid electrolyte and a conductive assistant. Further, from the viewpoint of exhibiting flexibility, etc., it may optionally contain a binder. The solid electrolyte, the conductive assistant, and the binder are not particularly limited, and those that can be used for the positive electrode layer of the solid secondary battery can be used.

[0046] The positive electrode current collector layer 32 is not particularly limited, and for example, it can be composed of aluminum, an aluminum alloy, stainless steel, nickel, iron, titanium, conductive carbon (graphite, carbon nanotube, etc.), etc. Examples of the shape of the positive electrode current collector layer 32 include a foil shape, a plate shape, a mesh shape, a non-woven fabric shape, a foamed shape, etc.

[0047] The electrode assembly composed of the above layers is housed in the exterior body 60. The exterior body 60 can expand and contract along with the change in the thickness of the electrode assembly due to charge and discharge. As the material constituting the exterior body 60, for example, a laminate film can be used. As the laminate film, a laminated film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are laminated in this order from the inside can be used. The outer resin layer is, for example, a polyamide (nylon) layer or a polyethylene terephthalate (PET) layer, the metal layer is, for example, an aluminum layer, and the inner resin layer may be, for example, a polyethylene layer or a polypropylene layer.

[0048] (Buffer material) The buffer material 70 is a member that restrains the solid secondary battery 1. In the present embodiment, the solid secondary battery 1 abuts against the buffer material 70 at both ends in the stacking direction (the vertical direction in FIG. 1). The solid secondary battery 1 is restrained in a state of being pressurized from both ends in the stacking direction toward the central position in this state. By appropriately restraining the solid secondary battery 1 by the buffer material 70, rapid charging of the solid secondary battery 1 becomes possible. Further, the occurrence of short circuits, etc., is suppressed, and favorable charge and discharge efficiency can be obtained.

[0049] The buffer material 70 has a 25% compression load greater than 0.5 MPa. Thereby, the surface pressure distribution with respect to the solid secondary battery 1 can be made uniform, and the deposition thickness of the lithium metal is made uniform. The 25% compression load of the buffer material 70 can be measured by a method conforming to JIS K 6254. The 25% compression load of the buffer material 70 may be greater than 1.0 MPa.

[0050] The buffer material 70 has an elongation less than 100%. Thereby, it can be made easier to follow the thickness change of the solid secondary battery 1 during charge and discharge. The elongation of the buffer material 70 can be measured by a method conforming to the measurement method of "elongation at break" defined in JIS K 6251. Specifically, the elongation at break (%) can be calculated by the formula "(distance between gauge marks at break - distance between gauge marks before test) ÷ distance between gauge marks before test × 100".

[0051] The buffer material 70 preferably has a compression residual strain of 6% or more. Thereby, the buffer material 70 can be made easier to follow the thickness change of the solid secondary battery 1 during charge and discharge. The compression residual strain of the buffer material 70 can be measured by a method conforming to JIS K 6401.

[0052] The restraint pressure for restraining the solid secondary battery 1 by the buffer material 70 can be 3 MPa or less at 25°C, and can also be 1 MPa or less. With the buffer material 70, preferable followability with respect to the thickness change of the solid secondary battery 1 during charge and discharge is obtained. Therefore, even if the restraint pressure of the solid secondary battery 1 is set to the above conditions, an effective reaction area can be maintained and rapid charging becomes possible.

[0053] [Method for manufacturing a solid secondary battery] The method for manufacturing the above solid secondary battery 1 is not particularly limited, and a general method for manufacturing a solid secondary battery can be used. For example, a method of laminating the above layers, press-bonding them with a roll press device, a flat plate press device, etc. to produce an electrode assembly, then housing it in an exterior body, and restraining it with the buffer material 70 can be mentioned.

[0054] [Constraint Fixture for Solid-State Secondary Battery] As a method of disposing buffer materials 70 on both laminated end faces of the solid-state secondary battery 1 and applying pressure to constrain the solid-state secondary battery 1, a method using a constraint fixture 100 shown in FIG. 2 can be mentioned. The constraint fixture 100 has, for example, a pedestal 81, a pressing portion 82, a base portion 83, and a housing portion 84, as shown in FIG. 2.

[0055] As shown in FIGS. 1 and 2, buffer materials 70 are disposed on both laminated end faces of the solid-state secondary battery 1 disposed on the pedestal 81. In this state, pressure is applied to the solid-state secondary battery 1 by the pressing portion 82 from above the solid-state secondary battery 1. The pedestal 81 and the base portion 83 that abuts against the installation surface of the constraint fixture 100 are connected by a spring S. Therefore, a uniform pressure is applied to the solid-state secondary battery 1 in the lamination direction from both laminated end faces by the pressure applied by the pressing portion 82 and the reaction force of the spring S. By fixing the pressing portion 82 in a state where a predetermined pressure is applied to the solid-state secondary battery 1, the solid-state secondary battery 1 can be constrained under a predetermined pressure. The pressing portion 82 has a pressing surface larger than the laminated surface of the solid-state secondary battery. A part of the pressing portion 82 extends outward from the housing portion 84 that houses the solid-state secondary battery 1 and is configured to be slidable in the vertical direction. The pressing portion 82 is fixed to the housing portion 84, for example, in a state where a predetermined constraint pressure is applied to the solid-state secondary battery 1.

[0056] The above is an example of a specific method of constraining the solid-state secondary battery 1, and the method of constraining the solid-state secondary battery 1 is not limited to the above.

[0057] As described above, the preferred embodiments of the present invention have been explained. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, it has been described that the buffer materials 70 are arranged on both laminated surfaces of the solid secondary battery 1. However, the buffer materials 70 may be arranged on only one laminated surface of the solid secondary battery 1. As an example where such a configuration is possible, for example, the case where the solid secondary battery 1 has a positive electrode layer 30 in which one positive electrode active material layer 31 is laminated on one side of one positive electrode current collector layer 32 can be cited. In the above configuration, for example, a solid electrolyte layer for bag-sealing may be arranged between the positive electrode current collector layer 32 and the exterior body 60. Thus, when a material having a buffering action is arranged between the positive electrode current collector layer 32 and the exterior body 60, the arrangement of the buffer materials 70 on the positive electrode layer 30 side can be omitted.

[0058] Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the contents of the following examples.

Examples

[0059] <Example 1> [Fabrication of positive electrode layer] An aluminum foil with a thickness of 15 μm was prepared as the positive electrode current collector. 80 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) was used as the positive electrode active material, 17 parts by mass of an argyrodite-type sulfide solid electrolyte was used as the solid electrolyte, 2 parts by mass of carbon black was used as the conductive assistant, and 1 part by mass of an SBR (styrene-butadiene rubber) - based binder was used as the binder, and they were mixed at a ratio. The obtained mixture was dispersed in 43 parts by mass of butyl butyrate to prepare a positive electrode active material layer slurry. The obtained positive electrode active material layer slurry was applied to both sides of the positive electrode current collector using a bar coater so that the basis weight after drying was 27 mg / cm 2 and dried to form a positive electrode active material layer with a thickness of 80 μm, thereby fabricating a positive electrode layer.

[0060] [Fabrication of solid electrolyte layer transfer sheet] 97 parts by mass of an argyrodite-type sulfide solid electrolyte (median diameter: 3.0 μm) and 3 parts by mass of a binder were mixed. The resulting mixture was dispersed in a solvent to prepare a solid electrolyte slurry. The obtained solid electrolyte slurry was dried to produce a solid electrolyte layer transfer sheet.

[0061] [Fabrication of negative electrode layer] As a negative electrode current collector, a copper foil with a thickness of 10 μm was prepared. A metal lithium foil with a thickness of 40 μm was roll-laminated on the surface of the copper foil to fabricate a negative electrode layer.

[0062] [Fabrication of intermediate layer transfer sheet] A total of 95 parts by mass of Sn particles (average particle diameter: 0.07 μm) as metal particles and acetylene black (average particle diameter: 0.05 μm) as amorphous carbon particles were mixed with 5 parts by mass of a PVDF-based binder as a binder. The resulting mixture was dispersed in 1000 parts by mass of NMP (N-methyl-2-pyrrolidone) to prepare an intermediate layer slurry. The obtained intermediate layer slurry was applied to a support sheet and dried to produce an intermediate layer transfer sheet with a final thickness of 3.0 μm.

[0063] [Fabrication of solid secondary battery] The solid electrolyte layer of the solid electrolyte layer transfer sheet was overlaid on the surface of the positive electrode active material layer of the positive electrode layer, and they were joined under the joining conditions of a joining pressure of 90 MPa, a joining time of 3 minutes, and a joining temperature of room temperature using a uniaxial forming press device. Then, the support sheet of the solid electrolyte layer transfer sheet was peeled off to obtain a positive electrode layer-solid electrolyte layer joined body. Next, the intermediate layer of the intermediate layer transfer sheet was overlaid on the surface of the solid electrolyte layer of the positive electrode layer-solid electrolyte layer laminate, and they were joined under the joining conditions of a joining pressure of 290 MPa, a joining time of 5 minutes, and a joining temperature of room temperature using a uniaxial forming press device. Then, the support sheet of the intermediate layer transfer sheet was peeled off to obtain a positive electrode layer-solid electrolyte layer-intermediate layer joined body. Next, using an isostatic pressing press device, the integrated body of the positive electrode layer-solid electrolyte layer-intermediate layer joined body was subjected to a densification treatment at a joining pressure of 980 MPa, a joining time of 5 minutes, and a joining temperature of 120°C. Next, the metal lithium foil of the negative electrode layer was overlaid on the surface of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer joined body, and they were joined under the conditions of a joining pressure of 180 MPa, a joining time of 2 minutes, and a joining temperature of room temperature using a uniaxial forming press device. Thus, an electrode laminate was obtained. The above electrode joined body was housed in an aluminum laminate film exterior body, and a polyurethane foam (PORON MX-48HF, manufactured by Rogers Inoaak Co., Ltd.) as a buffer material was disposed on the negative electrode layer side and constrained at a constraint pressure of 3 MPa.

[0064] <Example 2> A solid secondary battery according to Example 2 was fabricated in the same manner as in Example 1, except that the constraint pressure of the solid secondary battery was 1 MPa.

[0065] <Comparative Example 1> A solid secondary battery according to Comparative Example 1 was fabricated in the same manner as in Example 1, except that a polyurethane foam (PORON CH-48EG, manufactured by Rogers Inoaak Co., Ltd.) was used as the buffer material.

[0066] <Comparative Example 2> A solid secondary battery according to Comparative Example 2 was fabricated in the same manner as in Example 1, except that a polyurethane foam (PORON SA-30, manufactured by Rogers Inoaak Co., Ltd.) was used as the buffer material.

[0067] <Comparative Example 3> A solid secondary battery according to Comparative Example 3 was fabricated in the same manner as in Example 1, except that the intermediate layer was not disposed.

[0068] <Comparative Example 4> A solid secondary battery according to Comparative Example 4 was fabricated in the same manner as in Example 2, except that the intermediate layer was not disposed.

[0069] [Measurement of Physical Properties of Buffer Material] The elongation at break (%), 25% compression load (MPa), and compression residual strain (%) which are the physical properties of the buffer material used in each Example and Comparative Example were measured respectively. The measurement of the elongation at break (%) was carried out by a method in accordance with JIS K 6251. The measurement of the 25% compression load (MPa) was carried out by a method in accordance with JIS K 6254. The measurement of the compression residual strain (%) was carried out by a method in accordance with JIS K 6401. The results are shown in Table 1.

[0070] [Table 1]

[0071] [Charge and Discharge Test] A charge and discharge test was carried out using the solid secondary batteries according to each Example and Comparative Example. The test conditions were five conditions of 60 °C and 0.1C, 45 °C and 0.1C, 45 °C and 1 / 3C, 25 °C and 1 / 3C, 25 °C and 1.97C. The voltage range was an upper limit voltage of 4.3V and a lower limit voltage of 2.65V. The charge was carried out by constant current - constant voltage (CCCV), and the discharge was carried out by constant current (CC) for the charge and discharge test. The charge and discharge evaluation results are shown in Table 2, and the charge and discharge efficiency is shown in Table 3 respectively.

[0072] [Table 2]

[0073] The charge and discharge evaluation criteria in Table 2 are as follows. 2: Charge and discharge are possible without short - circuit 1. Overcharging, abnormal charging, or short circuit occurred.

[0074]

Table 3

[0075] In Table 3, the ratio of the discharge capacity to the charge capacity (discharge capacity / charge capacity × 100) under each test condition for the first charge capacity was defined as the charge-discharge efficiency.

[0076] From the results of Table 2 and Table 3, it is clear that for the solid secondary batteries according to each example, even when the charge rate is increased to 1 / 3C or higher, no problems such as short circuits occur, and charge and discharge can be performed with high charge-discharge efficiency. In contrast, for the solid secondary batteries according to each comparative example, especially when the charge rate is increased to 1 / 3C or higher, problems such as short circuits occur, and accordingly, the charge-discharge efficiency also decreases.

[0077] [Charge characteristics at 25°C] Regarding the solid secondary batteries according to each example and comparative example, as the charge characteristics at 25°C, the maximum allowable charge current density (mA / cm 2 ), and the maximum allowable charge rate (C) were respectively determined. The results are shown in Table 4. At 25°C, from the charge current values at which the charge-discharge efficiency is 98% or higher and overcharging, abnormal charging, or short circuit does not occur, the maximum allowable charge current density (mA / cm 2 ), and the maximum allowable charge rate (C) were determined.

[0078]

Table 4

[0079] As shown in Table 4, it is clear that for the solid secondary batteries according to each example, both the maximum allowable charge current density (mA / cm 2 ), and the maximum allowable charge rate (C) are higher than those of the solid secondary batteries according to each comparative example.

[0080] Figure 3 is a graph showing the results of charge-discharge tests performed at 25°C with the charge rate varied using the solid secondary battery cell of Example 1. The vertical axis in Figure 3 represents voltage (V), and the horizontal axis represents capacity (mAh / g). After the start of charging, charging was performed at a constant current (CC: Constant Current) at each charge rate. When the voltage reached 4.3 V, the control was switched to a constant voltage (CV: Constant Voltage) to continue charging. Charging was carried out at each charge rate, and charging could be performed without occurrence of short circuit or the like.

[0081] Figure 4 is a graph showing the SOC (%) when charging is performed at a charge rate of 1.97C and an upper limit voltage of 4.3V CCCV at 25°C using the solid secondary battery cell of Example 1. In Figure 4, the full charge capacity when charging is performed at a charge rate of 0.1C at 25°C is set to 100%. It is clear from Figure 4 that as a result of charging for 30 minutes at a charge rate of 1.97C, charging can be performed up to SOC 68.7%.

Explanation of Reference Signs

[0082] 1 Solid secondary battery 20 Negative electrode layer 30 Positive electrode layer 40 Solid electrolyte layer 50 Intermediate layer 60 Outer package 70 Buffer material

Claims

1. A solid secondary battery having a positive electrode layer, a negative electrode layer including at least a negative electrode current collector, a solid electrolyte layer including a solid electrolyte material, and an intermediate layer provided between the negative electrode layer and the solid electrolyte layer, having a buffer material that constrains an electrode assembly in which the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are joined together, wherein the buffer material has a 25% compression load greater than 0.5 MPa and an elongation less than 100%.

2. The material constituting the intermediate layer and the solid electrolyte material are in particle form, and the particle size of the particles constituting the intermediate layer is smaller than the particle size of the solid electrolyte material. The solid secondary battery according to Claim 1.

3. The porosity of the intermediate layer is 40 to 70%. The solid secondary battery according to Claim 1 or 2.

4. The complex elastic modulus of the intermediate layer is less than 1 GPa. The solid secondary battery according to Claim 1 or 2.

5. The intermediate layer contains amorphous carbon. The solid secondary battery according to Claim 1 or 2.

6. The compression residual strain of the buffer material is 6% or more. The solid secondary battery according to Claim 1 or 2.

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