solid secondary battery

Abstract

To provide a solid secondary battery having guaranteed recyclability.SOLUTION: A solid secondary battery includes an active material layer that has a plurality of active material particles in a layer thickness direction, an electrolyte layer that delivers and receives active material ions to and from the active material particles, and a collector layer that delivers and receives electrons to and from the active material particles. The active material layer has, in the layer thickness direction, a first area where the specific surface area of the active material particles is lower than the other area in the layer thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Generally, secondary batteries are composed of electrodes (positive and negative electrodes) and an electrolyte, and charge and discharge occur through the movement of ions between the electrodes via the electrolyte. Such secondary batteries are used in a wide range of applications, from small devices such as mobile phones to large devices such as electric vehicles. Therefore, further improvement in the performance of secondary batteries is required. In order to improve the charge and discharge characteristics of secondary batteries, it is generally important to increase the interface between the active material in the electrode and the electrolyte. Here, active material refers to a substance that is involved in the reaction that generates electricity.

[0003] One known method for improving charge-discharge characteristics is to use an active material with fine protrusions as the positive electrode of a solid secondary battery. Patent Document 1 discloses a technique for forming a pattern of lithium cobalt oxide, with a specific surface area increased to 1.1 to 2, on a current collector by a flux method in which a plating layer containing cobalt is brought into contact with a raw active material containing lithium and heated.

[0004] On the other hand, when secondary batteries are discarded due to the end of their service life or the life of the electrical appliances in which they are installed, it is necessary to increase the recycling rate and facilitate separation of each material from an environmental perspective. Patent Document 2 discloses that a pressure-sensitive adhesive that is plastic at room temperature is provided between the active material layer and the current collector layer in a solid-state secondary battery (all-solid-state battery) to ensure the peelability of the active material layer and the current collector layer. The pressure-sensitive adhesive described in Patent Document 2 is provided in a portion of the gap between the active material layer and the current collector layer, such as the four corners, during assembly, and in the remaining portion, i.e., the portion where the pressure-sensitive adhesive is not provided, the active material layer and the current collector layer are arranged so that they can be adhered by compression bonding during the cell assembly process. It discloses that conductivity between the active material layer and the current collector layer is ensured after cell assembly, and the two layers can be easily separated as needed.

[0005] Patent Document 2 further discloses that by discarding only the active material layer and current collector layer associated with a portion identified as having a defect due to a short circuit or the like, parts that can be used again in all-solid-state batteries are left, thereby improving the yield of parts. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-220080 [Patent Document 2] Japanese Patent Publication No. 2020-129157 Summary of the Invention [Problem to be solved by the invention]

[0007] It was feared that all-solid-state batteries (solid-state secondary batteries) manufactured using an active material layer containing active material particles with protrusions obtained by the method of Patent Document 1 may have the following problems that make recyclability difficult when attempting to recycle them after disposal. This problem occurred when asymmetric separation occurred between different components adjacent in the layer direction between the solid electrolyte layer and the active material layer, or between the active material layer and the current collector layer, in which at least a portion of one component remained on the other, as shown in Figure 5. It was presumed that this asymmetric separation was due to the anchoring effect of the multiple protrusions provided to ensure ionic conductivity between adjacent particles or layers.

[0008] As a result of investigations by the present inventors, it was predicted that the problem of asymmetric separation would occur more significantly between materials with similar physical properties related to deformation, such as elasticity and plasticity, because regions of stress concentration tend to develop in multiple directions. Structurally, asymmetric separation occurs more significantly at solid-solid interfaces than at solid-liquid interfaces, and therefore there was a need to provide a solid secondary battery in which the problem of asymmetric separation described above is less likely to occur.

[0009] Furthermore, there has been a demand for a solid secondary battery that improves the separability at the interface between an electrolyte layer containing materials such as Li and Co, which are highly valuable resources and for which a high recovery rate is desired, and an active material layer, where asymmetric separation is more likely to occur than at the interface between a current collector layer and an active material layer, where a relatively soft material can be selected.

[0010] The present application aims to provide a solid secondary battery including an active material layer in which peelability between an active material layer and a current collector layer, and between the active material layer and the current collector layer, is guaranteed, and recyclability is guaranteed. [Means for solving the problem]

[0011] A solid secondary battery according to an embodiment of the present invention is a solid secondary battery including: an active material layer in which a plurality of active material particles, each having a particle portion and a plurality of protrusions protruding in multiple directions from the particle portion, are stacked in a layer thickness direction; a solid electrolyte layer that transfers active material ions between itself and the active material particles; and a current collector layer that transfers electrons between itself and the active material particles, the active material layer has a first region in the layer thickness direction in which the specific surface area of ​​the active material particles is lower than that of other regions in the layer thickness direction, the solid electrolyte layer includes an oxide-based solid electrolyte including a metal oxide, The first region has a tensile stress along the thickness direction of the layer, Active material layer Corresponding to a region where at least one of the shear stresses along the layer direction is concentrated higher than other regions in the layer thickness direction, The first region is a region in which the active material particles are solid The electrode is characterized by including a position in contact with the electrolyte layer or the current collector layer. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a solid secondary battery including an active material layer in which peelability between an active material layer and a current collector layer, and between an active material layer and a current collector layer, is ensured, and recyclability is ensured. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1A is a schematic cross-sectional view of a solid secondary battery according to a first embodiment; FIG. 1B is a partially enlarged view including a positive electrode active material layer; FIG. 1C is a diagram showing the distribution of the specific surface area of ​​the positive electrode active material particles in the layer thickness direction; and FIG. 1D is a schematic diagram showing the general shape and cross section. [Figure 2] 1A is a flowchart showing a method for manufacturing a solid secondary battery according to a first embodiment, and FIGS. 1B and 1C are flowcharts showing manufacturing methods of modified embodiments. [Figure 3] 1 is a flowchart showing a method for manufacturing a positive electrode active material layer according to a first embodiment (a) and a modified embodiment (b). [Figure 4] 10A, 10B, and 10C show the layer thickness direction profiles of the specific surface area of ​​the positive electrode active material layers according to the second, third, and fourth embodiments. [Figure 5] 10(a) and 10(b) are enlarged partial views including a positive electrode active material layer according to the fifth and sixth embodiments. [Figure 6] 1 shows the holding state of specimens for shear tests (a) and (c) and uniaxial tensile test (b). [Figure 7] 10B and 10C show the layer thickness direction profiles of the specific surface area of ​​the positive electrode active material particles according to the first and second reference embodiments. [Figure 8] 1 shows specimens of the solid secondary batteries according to the first practical embodiment (a) and the first reference embodiment (b) after shear stress testing. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, shapes, relative positions, and other details of the components described in these embodiments are not intended to limit the scope of the present invention.

[0015] (First embodiment) <Structure of secondary battery and positive electrode active material layer> A solid secondary battery 100 having a positive electrode current collector layer 10, a positive electrode active material layer 20, and a solid electrolyte layer 40 according to the first embodiment will be described with reference to Figures 1(a) to 1(d). Figure 1 shows a schematic cross-sectional view of the solid secondary battery according to the first embodiment (a), a partially enlarged view including the positive electrode active material layer (b), a profile of the specific surface area of ​​the positive electrode active material particles in the layer thickness direction (c), and a schematic diagram of the particle shape and cross section (d). This shows that.

[0016] FIG. 1(a) is a schematic cross-sectional view of a solid secondary battery 100 to which the positive electrode active material layer 20 of this embodiment is applied. The solid secondary battery 100 includes a solid electrolyte layer 40 on the surface opposite to the side of the positive electrode current collector layer 10 in contact with the positive electrode active material layer 20. The solid secondary battery 100 includes a negative electrode 70 on the side opposite to the side where the electrolyte layer 40 is in contact with the active material layer 20. The negative electrode 70 includes a negative electrode active material layer 50 on the surface of the solid electrolyte layer 40 opposite to the surface where the positive electrode active material layer 20 is in contact with the positive electrode active material layer 20. The negative electrode 70 includes a negative electrode current collector layer 60 on the surface opposite to the surface where the negative electrode active material layer 50 is in contact with the electrolyte layer 40. In other words, the solid secondary battery 100 includes the negative electrode 70, the electrolyte layer 40, and the positive electrode 30 in the stacking direction 200.

[0017] Hereinafter, for simplicity, in this specification, the positive electrode current collector layer 10, the positive electrode active material layer 20, the solid electrolyte layer 40, and the positive electrode active material particles 22 may be referred to as the current collector layer 10, the active material layer 20, the electrolyte layer 40, and the active material particles 22. Furthermore, although the term "solid secondary battery" is used to refer to a secondary battery having at least a non-aqueous solid electrolyte, it may also be referred to as a secondary battery or an all-solid-state battery.

[0018] In this specification, the electrode structures in which active material ions are exchanged with the solid electrolyte layer 40 are referred to as the positive electrode and the negative electrode, and therefore the positive electrode active material layer 20 obtained by removing the positive electrode current collector layer 10 from the positive electrode 30 in FIG. 1(a) may be referred to as the positive electrode 30. Also, the negative electrode active material layer 50 obtained by removing the negative electrode current collector layer 60 from the negative electrode 70 in FIG. 1(a) may be referred to as the negative electrode 70.

[0019] The positive electrode current collector layer 10 is a conductor that conducts electrons between an external circuit (not shown) and the active material layer. The positive electrode current collector layer 10 may be a free-standing film (foil) of a metal such as stainless steel (sometimes referred to as SUS) or aluminum, or a laminated layer supported by a resin. The negative electrode current collector layer 60 may be a free-standing film (foil) of a metal such as silver or copper, or a laminated layer supported by a resin.

[0020] As shown in FIG. 1(b), the positive electrode active material layer 20 includes positive electrode active material layers 20a, 20b, and 20c as sublayers. The positive electrode active material layers 20a, 20b, and 20c are distinguished by stacking sublayers each including active material particles 22. The stacking direction 200 of the positive electrode active material layers 20a, 20b, and 20c, which are sublayers, is parallel to the layer thickness direction, and may therefore be referred to as the layer thickness direction 200. The positive electrode active material layer 20 may include active material particles 22 containing an oxide-based solid electrolyte such as LiCoO (lithium cobalt oxide, hereinafter sometimes abbreviated as LCO) or CoLiOP (lithium cobalt phosphate). Materials applicable to each layer will be described later. As shown in FIG. 1(d), the positive electrode active material particle 22 according to this embodiment includes particle portions 22b and protrusions 22p that protrude radially in multiple directions from the outer surface of the particle portions 22b. In FIG. 1(c), the particle portions 22b and the protrusions 22p are omitted.

[0021] The specific surface area Srv (m -4 )=S(m 2 ) / V(m 3 )×σ(m -3 ) is controlled. By stacking the sublayers 20a, 20b, and 20c with controlled specific surface areas, it is possible to provide a bonding force between particles and an anchoring effect between layers in the stacking direction 200. In this specification, the specific surface area Srv is defined as the surface area per unit volume. The specific surface area of ​​the sublayer 20i is calculated by multiplying the average specific surface area Srp (m -1 )=S(m 2 ) / V(m 3 ) and particle number density per unit volume σv(m -3 ) and the volume V of one layer.

[0022] When the active material layer 20 has a particle number density σv per unit volume that does not have a significant distribution in the layer thickness direction, the increase ΔSrv in the specific surface area Srv when the active material particles 22 have protrusions 22p is proportional to the number n (dimensionless) of protrusions 22p per particle of the active material particle 22. Similarly, when the active material layer 20 has no significant distribution in the layer thickness direction in the number of protrusions 22p per particle, the increase ΔSrv in the specific surface area Srv when the active material particles 22 have protrusions 22p is proportional to the particle number density σv (m -3 ). That is, the increase ΔSrv(i) in the specific surface area Srv(i) due to the presence of the protruding portion 22p of the sublayer 20i of the active material layer 20 is proportional to the particle number density σv(m -3 ) and the number n (dimensionless) of protrusions per particle of the active material particle 22. Therefore, the specific surface area Srv(i) of the sublayer 20(i) of the active material layer 20 having the protrusions 22p is proportional to the particle number density σv(m -3 In other words, the change is positively correlated with the product of the number of protrusions per particle of the active material particle 22 (dimensionless) and the number of protrusions per particle of the active material particle 22.

[0023] In each layer constituting the solid secondary battery 100, the interlayer bonding strength between the positive electrode active material layer 20 and the solid electrolyte layer 40 may be stronger than the interlayer bonding strength between other components due to the correlation between the material affinity and structure. When the interlayer bonding strength between the positive electrode active material layer 20 and the positive electrode current collector layer 10 is stronger than the interlayer bonding strength between the positive electrode active material layer 20 and the solid electrolyte layer 40, the solid electrolyte layer 40 in the following description may be replaced with the positive electrode current collector layer 10. Hereinafter, the solid secondary battery 100 of this embodiment will be described as including a positive electrode active material layer 20 containing lithium cobalt oxide and a solid electrolyte layer 40 containing lithium borate (hereinafter, sometimes referred to as LBO).

[0024] Here, the manner in which a specimen is held when a separation test is performed on the solid secondary battery 100 including the positive electrode active material layer 20 of this embodiment will be described with reference to FIGS. 6(a) to 6(c).

[0025] 6(a) and 6(b) are schematic diagrams showing the arrangement for a shear test in the layer direction and a tensile test in the layer thickness direction 200 for a specimen taken from a solid secondary battery 100, in which the portion where the solid electrolyte 40 and the positive electrode active material layer 20 are bonded together. FIG. 6(c) is a schematic diagram showing the arrangement for a shear test in the layer direction, similarly, using the solid secondary battery 100 as the specimen. FIG. 6(c) can be used to identify or separate interlayers (interfaces) with weak bonding strength. In this specification, bonding strength may also be referred to as adhesive strength, fixing strength, or anchoring force.

[0026] The destructive testing machine (not shown) is configured so that one of the test holders 640a, 640b is fixed and a shear force Fshear or a tensile force Ftensile can be applied to the other. The test holders 640a, 640b shown in Figures 6(a) to 6(c) and the destructive testing machine (not shown) are configured so that a shear force Fshear or a tensile force Ftensile can be applied coaxially so as not to generate a rotational moment on the specimen. Any known device capable of acquiring stress-strain characteristics and a precursory state to fracture can be used as the destructive testing machine.

[0027] The test holders 640a and 640b are configured to hold test jigs 660a and 660b, which are bonded to the cathode active material layer 10 and solid electrolyte layer 40 to be peeled via adhesive layers 680a and 680b, respectively. The adhesive layers 680a and 680b can be made of an adhesive that ensures adhesion between the material of the bonded surface of the specimen and the material of the test jigs 660a and 660b. Examples of adhesives include epoxy adhesives and thermosetting adhesives. The test jigs 660a and 660b are disk-shaped metal members with tapered flanges. Aluminum materials are also available for the test jigs 660a and 660b. The test holders 640a and 640b have recesses that allow the test jigs 660a and 660b to be inserted with a predetermined gap. Metals such as brass and stainless steel are suitable for the test holders.

[0028] As shown in FIG. 1( c), in the positive electrode active material layer 20 according to the first embodiment, the active material layer 20c in contact with the solid electrolyte 40 has a minimum number density σv of active material particles per unit volume lower than the other active material layers 20b and 20a located on the positive electrode current collector layer 10 side. As a result, the specific surface area Srv of the active material layer 20c in contact with the solid electrolyte 40 is lower than the other sublayers and has a minimum value. As a result, the interlayer bonding strength between the solid electrolyte 40 and the positive electrode active material layer 20c is weaker than the interlayer bonding strength between the other positive electrode active material layers 20c and 20b, and between 20b and 20a. As a result, the interface between the solid electrolyte 40 and the positive electrode active material layer 20c serves as a stress concentration surface where stress is concentrated to cause preferential peeling over other regions when subjected to tensile stress parallel to the stacking direction 200 or shear stress parallel to the layer direction.

[0029] In the active material layer 20, the region where the specific surface area is the smallest extends parallel to the center of gravity plane of the sublayer 20c. In other words, in the active material layer 20, the region where the specific surface area is the smallest extends in the complementary direction or parallel to a plane perpendicular to the layer thickness direction. When the region of the active material layer 20 where the specific surface area is the smallest is defined as a first region, in other words, the positive electrode active material layer 20 has a first region in which the specific surface area per particle of the positive electrode active material particles 22 is lower in the layer thickness direction 200 than in other regions in the layer thickness direction.

[0030] A specimen including the positive electrode active material layer 20 and the solid electrolyte layer 40 taken out of the solid secondary battery 100 of this embodiment was subjected to a shear fracture test using the test jig arrangement shown in FIG. 6(a). Separated specimens 800A and 800B were selected, as shown in FIG. 8(a). The separated specimens 800A and 800B were cleanly separated at the layer interface (interlayer) between the sublayer 20c of the positive electrode active material layer 20 and the solid electrolyte layer 40. In this specification, the state in which a pair of specimens separated as a result of the fracture test retain part of each other's structure may be referred to as "uneven separation," "irregular separation," or "irregular peeling." The solid electrolyte 40 and the positive electrode active material layer 20 of the solid secondary battery 100 of this embodiment were separated at the layer interface between the sublayer 20c and the solid electrolyte layer 40 without irregular separation.

[0031] Meanwhile, FIG. 7(a) shows the thickness-wise distribution of the specific surface area of ​​the active material layer of a solid secondary battery including a positive electrode active material layer 27 (not shown) according to the first embodiment. The positive electrode active material layer 27 has sublayers 27a to 27c, in this order, from the positive electrode current collector layer side toward the solid electrolyte layer side. The solid secondary battery according to this embodiment has a uniform thickness-wise distribution of the specific surface area of ​​the positive electrode active material layer. Therefore, when tensile stress or shear stress is applied to a test piece of the positive electrode active material layer and the solid electrolyte layer of a solid secondary battery including the positive electrode active material layer according to this embodiment, the stress concentration region does not align to a specific height region, resulting in an inconsistent stress distribution. As a result, when a test piece according to this embodiment is fractured by applying shear stress, the crack propagates by repeatedly meandering and branching, forming multiple fragments 860A to 860D, as shown in FIG. 8(b). The fragments of the solid secondary battery separated by such irregular breaking include fragments 860B and 860C, which are a mixture of multiple components 40-i and 27-i, and thus have reduced recyclability. Similarly, the fragments of the solid secondary battery separated by such irregular breaking include fragments, such as fragment 860D, which are too small and require separate analytical testing for sorting, and thus have reduced recyclability. The recyclability issues include a decrease in the recovery rate, an increase in the number of steps required for recovery, an increase in the time required for recovery, etc.

[0032] 7(b) shows the layer thickness direction distribution of the specific surface area of ​​the active material layer of a solid secondary battery including a positive electrode active material layer 27 according to the second embodiment. The positive electrode active material layer 27 (not shown) has sublayers 27a to 27c in this order from the positive electrode current collector layer side toward the solid electrolyte layer side.

[0033] Because the distribution of the specific surface area in the layer thickness direction 200 is uniform, when tensile stress or shear stress is applied to a test piece of the positive electrode active material layer and the solid electrolyte layer, the stress concentration does not occur in a specific area, and the stress distribution is inconstant. In the solid secondary battery according to this reference embodiment, the sublayer 20c on the solid electrolyte side exhibits the maximum values ​​in the number of protrusions per particle and the specific surface area. As a result, the solid electrolyte layer and the sublayer 27c of the positive electrode current collector layer are firmly bonded. On the other hand, because the interlayer spacing between the sublayers 27a and 27b is uniform, when tensile stress or shear stress is applied to a test piece of the positive electrode active material layer and the solid electrolyte layer in the solid secondary battery according to this reference embodiment, the stress distribution is inconstant, as in the first reference embodiment. As a result, when a shear stress is applied to the test piece of the second reference embodiment to cause it to fracture, the crack propagates by repeatedly meandering and branching, forming multiple fragments, and the recyclability is low, similar to that of the test piece of the first reference embodiment. The solid secondary batteries having the positive electrode active material layer according to the first and second reference embodiments correspond to the solid secondary batteries of the prior art.

[0034] Next, a process for manufacturing the solid secondary battery 100 of this embodiment will be described with reference to the flowchart in Fig. 2(a). The solid secondary battery 100 according to the first embodiment can be manufactured by a manufacturing method S2000 shown in the flowchart in Fig. 2(a). The manufacturing method S2000 includes a step S200 of disposing a positive electrode current collector layer, a step S210 of disposing a positive electrode active material layer, a step S220 of disposing a solid electrolyte layer, a step S240 of disposing a negative electrode active material layer, and a step S260 of disposing a negative electrode current collector layer, and each step is performed in this order.

[0035] 2(b) is a flowchart showing a method S2100 for manufacturing a solid secondary battery, which is a variation of the manufacturing method S2000 of the first embodiment. This variation differs from the first embodiment in that the order in which the positive electrode current collector layer 10, the positive electrode active material layer 20, and the electrolyte layer 40 are stacked is reversed. That is, the order in which the elements constituting the solid secondary battery 100 are stacked with other adjacent elements can be interchanged as long as the other elements are not damaged, and the steps can be performed simultaneously.

[0036] 2(c) is a flowchart showing a method S8200 for manufacturing a secondary battery according to another modification of the manufacturing method S2000 of the first embodiment. The method S8200 for manufacturing a secondary battery according to this modification differs from S2000 of the first embodiment and its modification S2100 in that the positive electrode 30 and the negative electrode 70 are manufactured in advance before laminating them with the solid electrolyte layer 40.

[0037] Next, step S210 of disposing the positive electrode active material layer 20 of this embodiment will be described using the flowcharts of Figures 3(a) and 3(b). The positive electrode active material layer 20 according to the first embodiment can be manufactured by a manufacturing method S3000 shown in the flowchart of Figure 3(a). The manufacturing method S3000 of this embodiment includes step S200 of disposing a positive electrode current collector layer, step S300 of classifying positive electrode active material particles, step S320 of stacking positive electrode active material layers, and step S220 of disposing a solid electrolyte layer, and each step is performed in this order.

[0038] The step S300 of classifying the positive electrode active material particles includes a step of screening the positive electrode active material layer 20i (i=a, b, c, etc.) for the average particle size, the number of protrusions per particle, shape variation, etc. The step S300 of classifying the positive electrode active material particles can also be performed in parallel with the step S200 of arranging the positive electrode current collector layer.

[0039] Positive electrode active material particles selected from the group of positive electrode active material particles classified in step S300 of classifying positive electrode active material particles are used for each sublayer 20i to be laminated in the next step, step S320 of laminating positive electrode active material layers, to adjust the specific surface area Svr(i) of the sublayer 20i. This step S320 can be performed using known patterning and deposition methods such as inkjet printing, sand painting, and mask CVD.

[0040] In the positive electrode active material layer 20 of this embodiment, the distribution of the specific surface area Svr in the layer thickness direction is formed by utilizing the lamination process of the sublayers 20i, but post-treatment for reducing the specific surface area of ​​a predetermined region may be performed after disposing the positive electrode active material layer 20. As the post-treatment, known surface modification methods including milling, FIB processing, blasting, buffing, etc. can be applied.

[0041] FIG. 3(b) is a flowchart showing a manufacturing method S3100 for a cathode active material layer 20, which is a variation of the manufacturing method S3000 of the first embodiment. This variation differs from the first embodiment in that the order in which the cathode current collector layer 10, the cathode active material layer 20, and the electrolyte layer 40 are stacked and arranged is reversed. Steps S300 and S310 of the manufacturing method S3000 for a cathode active material layer 20 in FIG. 3(a) correspond to step S210 of arranging a cathode active material layer in the manufacturing method S2000 for a solid secondary battery 100 in FIG. 2(a). Similarly, steps S300 and S310 of the manufacturing method S3100 for a cathode active material layer in FIG. 3(b) correspond to step S210 of arranging a cathode active material layer in the manufacturing method S2100 for a solid secondary battery in FIG. 2(a).

[0042] (Negative electrode) A known method can be applied to the manufacturing method of the negative electrode. As in the modified example of the fourth embodiment of the present application, the manufacturing method of the positive electrode 30 of the first embodiment may be applied to the manufacturing of the negative electrode. As with the positive electrode 30, particles containing a negative electrode active material may be formed, or a metal such as metallic Li or In-Li may be formed as a film.

[0043] solid electrolyte Examples of solid electrolytes that can be used in the solid electrolyte layer 40 include oxide-based solid electrolytes, sulfide-based solid electrolytes, and complex hydride-based solid electrolytes. The oxide-based solid electrolyte is a Li 1.5 Al 0.5 Ge 1.5 (PO4)3 and Li 1.3 Al 0.3 Ti 1.7 Nasicon-type compounds such as (PO4)3, Li 6.25 La3Zr2Al 0.25 O 12In addition, oxide-based solid electrolytes include garnet-type compounds such as Li 0.33 Li 0.55 Perovskite-type compounds such as TiO3 are also included. Oxide-based solid electrolytes include Li 14 Examples of sulfide-based solid electrolytes include silicon-type compounds such as Zn(GeO) and acid compounds such as LiPO, LiSiO, and LiBO. Specific examples of sulfide-based solid electrolytes include LiS-SiS, LiI-LiS-SiS, LiI-LiS-P2S, LiI-LiS-P2O, LiI-LiPO-P2S, and LiS-P2S. The solid electrolyte may be crystalline or amorphous, or may be glass ceramics. The term "LiS-P2S" refers to a sulfide-based solid electrolyte made from raw materials containing LiS and P2S.

[0044] negative electrode active material Examples of negative electrode active materials that can be used in the negative electrode active material layer 50 are as follows. Examples of negative electrode active materials include metals, metal fibers, carbon materials, oxides, nitrides, silicon, silicon compounds, tin, tin compounds, and various alloy materials. Among these, metals, oxides, carbon materials, silicon, silicon compounds, tin, tin compounds, and the like are preferred from the viewpoint of capacity density. Examples of metals include metallic Li and In-Li, and examples of oxides include Li4Ti5O 12 Examples of carbon materials include various natural graphites, coke, partially graphitized carbon, carbon fiber, spherical carbon, various artificial graphites, and amorphous carbon. Examples of silicon compounds include silicon-containing alloys, silicon-containing inorganic compounds, silicon-containing organic compounds, and solid solutions. Examples of tin compounds include SnO b(0 < b < 2), SnO2, SnSiO3, Ni2Sn4, Mg2Sn, etc. may be mentioned. Further, the negative electrode material may contain a conductive assistant. Examples of the conductive assistant include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. The conductive assistant may include conductive fibers such as carbon fiber, carbon nanotube, and metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene dielectric.

[0045] Current collector layer The current collector applied to the current collector layers 10 and 60 is a conductive member containing a metal such as SUS, aluminum, or copper. The metal is adopted in the form of a metal foil, a self-supporting film, or a thin film supported on a substrate.

[0046] <Second Embodiment> Next, a solid secondary battery 100 including a cathode active material layer 20 according to a second embodiment will be described with reference to FIG. 4(a). The cathode active material layer 20 according to this embodiment differs from the cathode active material layer 20 according to the first embodiment in that the specific surface area Srv is adjusted for each sublayer by changing the number n of protrusions per particle and in that the cathode active material layer 20 has four sublayers 20a to 20d. The cathode active material layer 20 according to this embodiment also differs from the cathode active material layer 20 according to the first embodiment in that the surface area Svr gradually decreases from the sublayer 20b to the sublayer 20c, and then to the sublayer 20d. In the solid secondary battery 100 according to this embodiment, the interlayer bonding strength between the sublayer 20d of the cathode active material layer 20 and the solid electrolyte layer 40 is weaker than the interlayer bonding strength between the other sublayers of the cathode active material layer 20. Therefore, in the cathode active material layer 20 according to this embodiment, like the cathode active material layer 20 of the first embodiment, the space between the cathode active material layer 20 and the solid electrolyte layer 40 forms a stress concentration surface against shear force in the layer direction and tensile force in the layer thickness direction. In the solid secondary battery 100 including the cathode active material layer 20 of this embodiment, like the first embodiment, the recyclability of the cathode active material material and the solid electrolyte material is ensured.

[0047] <Third embodiment> Next, a solid secondary battery 100 including a positive electrode active material layer 20 according to a third embodiment will be described with reference to FIG. 4(b). The positive electrode active material layer 20 according to this embodiment differs from the first embodiment in that the specific surface area Srv is adjusted for each sublayer by changing the number n of protrusions per particle, and that the specific surface area Svr of the sublayer 20a located on the positive electrode current collector layer 10 side is the smallest. In the solid secondary battery 100 including the positive electrode active material layer 20 according to this embodiment, the bonding strength between the sublayer 20a of the positive electrode active material layer 20 and the positive electrode current collector layer 10 is weaker than the bonding strength between the other sublayers of the positive electrode active material layer 20. Therefore, in the positive electrode active material layer 20 according to this embodiment, the interface between the positive electrode current collector layer 10 and the sublayer 20a forms a stress concentration surface against shear force in the layer direction and tensile force in the layer thickness direction. In the solid secondary battery 100 including the positive electrode active material layer 20 of this embodiment, the recyclability of the positive electrode active material and the positive electrode current collector material is ensured.

[0048] <Fourth embodiment> Next, a solid secondary battery 100 including a cathode active material layer 20 according to a fourth embodiment will be described with reference to FIG. 4(a). The cathode active material layer 20 according to this embodiment differs from the cathode active material layer 20 according to the second embodiment in that the sublayer 20c has the smallest specific surface area Srv and the sublayer 20d has the second smallest specific surface area Sv. In the solid secondary battery 100 including the cathode active material layer 20 according to this embodiment, the bonding strength between the sublayers 20c and 20d of the cathode active material layer 20 is weaker than the bonding strength between the other sublayers of the cathode active material layer 20 and the bonding strength between the sublayer 20d and the solid electrolyte layer 40. Therefore, in the cathode active material layer 20 according to this embodiment, the space between the sublayers 20c and 20d forms a stress concentration surface against shear force in the layer direction and tensile force in the layer thickness direction. The solid secondary battery 100 including the positive electrode active material layer 20 of this embodiment is different from the first and second reference embodiments in that the positive electrode active material layer including the sublayers 20a to 20c of the positive electrode active material layer 20 is easily separated, ensuring the recyclability of the positive electrode active material material. Furthermore, in the solid secondary battery 100 including the positive electrode active material layer 20 of this embodiment, the fracture surface formed by receiving a shearing force or a tensile force becomes a separation surface with a clean cleavage plane, and therefore the recovery rate of the solid electrolyte 40 is expected to be improved compared to the first and second reference embodiments.

[0049] <Fifth embodiment> Next, a solid secondary battery 100 including a cathode active material layer 20 according to a fifth embodiment will be described with reference to FIG. 5(a). The cathode active material layer 20 of this embodiment differs from the cathode active material layer 20 of the first embodiment in that it includes an intra-cathode active material 24 mixed with the cathode active material particles 22. The mixture ratio of the cathode active material particles 22 to the intra-cathode active material 24 in each of the sublayers 20a to 20c can be adjusted by the step S300 of classifying the cathode active material particles and the step S320 of stacking the cathode active material layers, as shown in FIG. 3(b). The intra-cathode electrolyte 24 is provided in the cathode active material layer 20 so as to have a portion in contact with the cathode active material particles 22 in order to increase ionic conductivity between the cathode active material layer 20 and the solid electrolyte layer 40. The sublayers 20a, 20b, and 20c of the positive electrode active material layer may form a distribution in the layer thickness direction not only in the mixture ratio (volume fraction) of the active material particles 22 and the electrolyte 24 in the positive electrode, but also in the conductive additive (not shown), porosity, etc.

[0050] The positive electrode active material particles 22 and the positive electrode electrolyte 24 may have different particle sizes and particle size distributions. Furthermore, the positive electrode electrolyte 24 and the electrolyte particles (not shown) contained in the solid electrolyte layer 40 may have different particle sizes, particle size distributions, compositions, and the like.

[0051] Sixth Embodiment Next, a solid secondary battery 100 including a cathode active material layer 20 according to a sixth embodiment will be described with reference to Fig. 5(b). The cathode active material layer 20 of this embodiment differs from the cathode active material layer 20 of the first embodiment in that the cathode active material layer 20 includes an intra-cathode active material 24 mixed with the cathode active material particles 22, and that the intra-cathode active material 24 and the cathode active material particles 22 are arranged in a predetermined arrangement pattern within the layer. The cathode active material layer 20 of this embodiment also differs from the cathode active material layer 20 of the fifth embodiment in that the intra-cathode active material 24 and the cathode active material particles 22 form a predetermined arrangement pattern and that the patterns of the sublayers 20a to 20c are aligned in phase. [Explanation of symbols]

[0052] 10 Positive electrode current collector layer 20 Cathode active material layer 30 positive electrode 40 electrolyte layer 50 Negative electrode active material layer 60 Negative electrode collector layer 70 negative electrode 100 Solid Secondary Batteries

Claims

1. A solid secondary battery comprising: an active material layer in which a plurality of active material particles, each having a particle portion and a plurality of protrusions protruding in multiple directions from the particle portion, are stacked in a layer thickness direction; a solid electrolyte layer that transfers active material ions between itself and the active material particles; and a current collector layer that transfers electrons between itself and the active material particles, the active material layer has a first region in the layer thickness direction in which the specific surface area of ​​the active material particles is lower than that of other regions in the layer thickness direction, the solid electrolyte layer includes an oxide-based solid electrolyte including a metal oxide, the first region corresponds to a region in which at least one of a tensile stress along the layer thickness direction and a shear stress along the layer direction of the active material layer is concentrated to a higher level than other regions in the layer thickness direction; The solid secondary battery, wherein the first region includes a position where the active material particle is in contact with the solid electrolyte layer or the current collector layer.

2. The solid secondary battery according to claim 1 , wherein the first region extends along a layer direction of the active material layer.

3. 3. The solid secondary battery according to claim 1, wherein the active material layer has a first region in the layer thickness direction in which the specific surface area per particle of the active material particles is lower than that of other regions in the layer thickness direction.

4. 4. The solid secondary battery according to claim 1, wherein the active material particles contain at least one of lithium cobalt oxide and lithium cobalt phosphate.

Images