Solid secondary battery

Abstract

To provide a solid secondary battery that is resistant to deposition of metal ions at an end of a solid electrolyte layer or an intermediate layer even after repeated charging and discharging and has excellent cycle characteristics.SOLUTION: A solid secondary battery includes an electrode laminate and an exterior body that houses the electrode laminate. The electrode laminate 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. The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer. The solid electrolyte layer has a positive electrode facing region that faces the positive electrode active material layer and a positive electrode non-facing region that does not face the positive electrode layer. The porosity of the positive electrode non-facing region is less than 5%.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Among secondary batteries, solid-state secondary batteries using solid electrolytes have attracted particular attention because of their superiority in terms of improved safety due to the non-flammability of the solid electrolyte and higher energy density.

[0003] In a solid-state secondary battery, repeated charging and discharging may cause the precipitation of metal ions such as lithium ions used as a charge transfer medium between the solid electrolyte layer and the negative electrode layer. The precipitation of the metal may cause a decrease in the adhesion of the interface, which may result in a decrease in the performance of the solid-state secondary battery. In response to this problem, a technology is known in which a layer on which lithium metal can be precipitated is provided to cover the negative electrode current collector, and the lithium metal is precipitated approximately uniformly on the surface of the coating layer, thereby making it difficult for dead lithium to be generated (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-129159 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in solid secondary batteries, improving cycle characteristics is an issue. In particular, in solid secondary batteries, when the dimensions, structural design, and process conditions are inappropriate, metal ions, which are charge transfer media, may be easily precipitated at the end of the solid electrolyte layer. In addition, when an intermediate layer is provided between the solid electrolyte layer and the negative electrode current collector, metal ions may also be easily precipitated at the end of the intermediate layer. When metal ions are precipitated at the end of the solid electrolyte layer or the intermediate layer, the precipitated metal may accumulate, causing a short circuit between the positive electrode layer and the negative electrode layer, or a side reaction may occur locally, causing an increase in resistance, which may result in a decrease in cycle characteristics.

[0006] The present invention has been made in view of the above, and aims to provide a solid secondary battery that is less likely to cause deposition of metal ions at the ends of a solid electrolyte layer or an intermediate layer even after repeated charging and discharging, and has excellent cycle characteristics, which in turn contributes to improved energy efficiency. [Means for solving the problem]

[0007] The present inventors have found that it is possible to solve the above problems by providing a non-positive electrode facing region in the solid electrolyte layer that does not face the positive electrode layer and making the non-positive electrode facing region into a dense solid electrolyte layer with low porosity, and have thus completed the present invention.

[0008] (1) A solid secondary battery comprising: an electrode laminate; and an exterior body that houses the electrode laminate, the electrode laminate having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the positive electrode layer including a positive electrode current collector and a positive electrode active material layer, the solid electrolyte layer having a positive electrode facing region that faces the positive electrode active material layer and a positive electrode non-facing region that does not face the positive electrode layer, and a porosity of the positive electrode non-facing region is less than 5%.

[0009] In the solid secondary battery of (1), the non-positive electrode facing region has a low porosity of 5% or less and is dense, so that metal ions released from the positive electrode layer and the negative electrode layer do not easily move in the non-positive electrode facing region during charging and discharging. Therefore, metal ions are less likely to deposit at the end of the solid electrolyte layer. Therefore, the solid secondary battery of (1) has excellent cycle characteristics.

[0010] (2) The solid secondary battery according to (1), wherein, when the apparent density of the positive electrode facing region is D1 and the apparent density of the positive electrode non-facing region is D2, −3%≦(D1−D2) / D1×100≦+3% is satisfied.

[0011] In the solid secondary battery (2), the ratio [(D1-D2) / D1×100] of the difference (D1-D2) between the apparent density of the positive electrode facing region and the apparent density of the non-positive electrode facing region to the apparent density D1 of the positive electrode facing region is low, and the difference in apparent density between the positive electrode facing region and the non-positive electrode facing region is small. Therefore, metal ions released from the positive electrode layer or the negative electrode layer and supplied to the positive electrode facing region are less likely to move to the non-positive electrode facing region, and the metal ions are less likely to precipitate at the end of the solid electrolyte layer.

[0012] (3) The solid secondary battery according to (1) or (2), wherein the adhesion strength within the layer of the non-positive electrode facing region of the solid electrolyte layer is greater than 0.3 kN / m.

[0013] According to the solid secondary battery of (3), the adhesion strength within the layer of the non-positive electrode facing region of the solid electrolyte layer is greater than 0.3 kN / m, and the shape stability of the non-positive electrode facing region is increased. As a result, metal ions are less likely to precipitate on the end portion of the solid electrolyte layer over a long period of time.

[0014] (4) The solid secondary battery according to any one of (1) to (3), wherein, when a composite elastic modulus of the positive electrode facing region of the solid electrolyte layer is E1 and a composite elastic modulus of the positive electrode non-facing region is E2, (E1-E2) / E1×100≦15% is satisfied.

[0015] According to the solid secondary battery of (4), the ratio [(E1-E2) / E1×100] of the difference (E1-E2) between the composite elastic modulus of the positive electrode facing region and the composite elastic modulus of the non-positive electrode facing region to the composite elastic modulus E1 of the positive electrode facing region is low at 15% or less, and the difference in the composite elastic modulus of the positive electrode facing region and the non-positive electrode facing region is small. Therefore, the variation in the thickness of the positive electrode facing region and the non-positive electrode facing region when a restraining force is applied to the solid secondary battery is small. Therefore, even if a restraining force is applied to the solid secondary battery, the interface and structure of each member in the solid secondary battery can be maintained, and local reactions and current concentration can be suppressed.

[0016] (5) The solid secondary battery according to any one of (1) to (4), wherein the solid electrolyte layer contains a sulfide solid electrolyte material.

[0017] According to the solid secondary battery of (5), since the solid electrolyte layer contains a sulfide solid electrolyte material, it is easy to form a dense positive electrode non-facing region with low porosity.

[0018] (6) The solid secondary battery according to any one of (1) to (53), further comprising an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer, the intermediate layer having a porosity greater than the porosity of the solid electrolyte layer.

[0019] In the solid secondary battery of (6), since the solid electrolyte layer has the above-mentioned non-positive electrode facing region, even if an intermediate layer is provided, metal ions are unlikely to deposit at the end of the intermediate layer. In addition, since the porosity of the intermediate layer is larger than that of the solid electrolyte layer, non-uniform metal deposition at the negative electrode layer interface can be suppressed, and cycle characteristics can be further improved.

[0020] (7) The solid secondary battery according to (6), wherein the intermediate layer has a thickness of 5 μm or less in the stacking direction of the electrode stack.

[0021] According to the solid-state secondary battery of (7), since the thickness of the intermediate layer is 5 μm or less, the deposition position of the metal, which is the charge transfer medium during charging, can be between the intermediate layer and the negative electrode layer. This significantly reduces the frequency of direct contact between the electrolyte layer and the deposited metal, suppresses local deterioration of the electrolyte layer and current concentration, and improves cycle characteristics and storage characteristics. In addition, a relatively elastic intermediate layer can be arranged between the hard electrolyte layer and the deposited metal, making it easier to follow the expansion and contraction caused by the deposition and dissolution of the metal, allowing for a uniform reaction in the in-plane and thickness directions, resulting in reduced resistance and improved cycle characteristics.

[0022] (8) The solid secondary battery according to (64) or (75), wherein the intermediate layer contains metal nanoparticles and amorphous carbon.

[0023] According to the solid-state secondary battery (8), the electronic conductivity of the intermediate layer can be ensured, and even when molded under high pressure, voids that allow the charge transfer medium to move within the intermediate layer can be maintained, thereby achieving the effect of reducing resistance.

[0024] (9) The solid secondary battery according to any one of (1) to (86), wherein the outer periphery of the positive electrode active material layer is surrounded by an insulating frame.

[0025] In the solid secondary battery of (9), the outer periphery of the positive electrode active material layer is surrounded by an insulating frame, and the non-positive electrode facing region can be supported by the insulating frame, improving the strength of the non-positive electrode facing region. In addition, even if metal accumulates at the ends of the solid electrolyte layer and the intermediate layer, the metal is unlikely to flow into the positive electrode active material layer. As a result, the positive electrode layer and the negative electrode layer are even less likely to short-circuit, and the cycle characteristics are even more improved. Effect of the Invention

[0026] According to the present invention, it is possible to provide a solid secondary battery that is less susceptible to deposition of metal ions at the ends of a solid electrolyte layer or an intermediate layer even after repeated charging and discharging and has excellent cycle characteristics. [Brief description of the drawings]

[0027] [Figure 1]FIG. 2 is a top view of an electrode stack of a solid secondary battery according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] 3 is a cross-sectional view showing a charged state of the electrode stack shown in FIG. 2. [Figure 4] FIG. 1 is a cross-sectional view of a solid secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0029] Fig. 1 is a top view of an electrode laminate of a solid secondary battery according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, and Fig. 3 is a cross-sectional view showing the charged state of the electrode laminate shown in Fig. 2. Fig. 4 is a cross-sectional view of a solid secondary battery having the electrode laminate shown in Figs. 1 to 3. In Figs. 1 to 4, the X direction indicated by the arrow X is a direction parallel to the upper surface of the electrode laminate when viewed from above. The Y direction indicated by the arrow Y is a direction parallel to the upper surface of the electrode laminate when viewed from above and perpendicular to the X direction. The Z direction indicated by the arrow Z is the stacking direction of the electrode laminate.

[0030] The solid secondary battery 100 of this embodiment includes an electrode laminate 1, as shown in FIG. As shown in Figs. 1 to 3, the electrode laminate 1 is a laminate in which a positive electrode layer 10, a solid electrolyte layer 20, an intermediate layer 30, and a negative electrode layer 40 are laminated in this order. The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The outer periphery of the positive electrode active material layer 12 is surrounded by an insulating frame 15. The negative electrode layer 40 includes a negative electrode current collector 41. The electrode laminate 1 shown in Figs. 1 and 2 is in a discharged state, and the electrode laminate 1 shown in Fig. 3 is in a charged state. The negative electrode layer 40 in a charged state has a metal precipitate layer 42 formed by precipitation of metal ions, which are a charged negative electrode active material, on the surface of the negative electrode current collector 41 on the intermediate layer 30 side. The metal precipitate layer 42 acts as a negative electrode active material layer and releases metal ions during discharge. The thickness of the negative electrode layer 40 of the electrode laminate 1 changes with charging and discharging.

[0031] 1, the electrode laminate 1 has a rectangular shape in which the X direction is longer than the Y direction when viewed from above. The electrode laminate 1 may have a square or circular shape when viewed from above.

[0032] The positive electrode layer 10, the solid electrolyte layer 20, the intermediate layer 30, and the negative electrode layer 40 are laminated such that their centers C overlap. When the area of the positive electrode active material layer 12 as viewed from above is Sp, the area of the solid electrolyte layer 20 as viewed from above is Ss, the area of the intermediate layer 30 as viewed from above is Sm, and the area of the negative electrode layer 40 as viewed from above is Sn, the relationship Sp < Sn ≤ Sm ≤ Ss may be satisfied. In this embodiment, the relationship between the areas of the respective layers is Sp < Sn = Sm < Ss. The relationship between the areas of the respective layers may be Sp < Sn < Sm = Ss, or Sp < Sn = Sm = Ss, or Sp < Sn < Sm < Ss. By having the areas of the respective layers satisfy the above relationship, in the electrode laminate 1, when viewed from above, the end portion of the positive electrode active material layer 12 is located most inward, and the end portions of the other layers (solid electrolyte layer 20, intermediate layer 30, negative electrode layer 40) are located outside the end portion of the positive electrode active material layer 12. In the electrode laminate 1 having such a configuration, since the end portion of the positive electrode active material layer 12 and the end portions of the other layers are at separated positions, metal ions (charge transfer medium) released from the positive electrode active material layer 12 during charging are less likely to precipitate on the end portions of the other layers. The ratio Sn / Sp of the area Sn of the negative electrode layer 40 to the area Sp of the positive electrode active material layer 12 may be, for example, within the range of 1.05 to 1.45. The ratio Sm / Sp of the area Sm of the intermediate layer 30 to the area Sp of the positive electrode active material layer 12 may be, for example, within the range of 1.10 to 1.45. The ratio Ss / Sp of the area Ss of the solid electrolyte layer 20 to the area Sp of the positive electrode active material layer 12 may be, for example, within the range of 1.25 to 2.00.

[0033] The positive electrode current collector 11 is not particularly limited in terms of material or shape as long as it has the function of collecting current of the positive electrode layer 10. The area of the positive electrode current collector 11 as viewed from above is preferably the same as or larger than that of the positive electrode active material layer 12. Examples of the material of the positive electrode current collector 11 include aluminum, aluminum alloy, stainless steel, nickel, iron, and titanium, among which aluminum, aluminum alloy, and stainless steel are preferable. Examples of the shape of the positive electrode current collector 11 include a foil shape and a plate shape.

[0034] The positive electrode active material layer 12 contains at least one type of positive electrode active material. There are no particular limitations on the positive electrode active material, and any material that is used in the positive electrode layers of general solid-state secondary batteries can be used. As the positive electrode active material, for example, a layered active material containing lithium, a spinel type active material, an olivine type active material, etc. can be used. 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 manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y Examples of such materials include Li-Mn spinel substituted with different elements represented by MO4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni).

[0035] The positive electrode active material layer 12 may optionally contain a solid electrolyte in order to improve the charge transfer medium conductivity. It may also optionally contain a conductive assistant in order to improve the conductivity. Furthermore, it may also optionally contain a binder in order to achieve flexibility. There are no particular limitations on the solid electrolyte, conductive assistant, and binder, and those used in the positive electrode layer of a general solid secondary battery may be used.

[0036] The solid electrolyte layer 20 is a layer laminated between the positive electrode layer 10 and the negative electrode layer 40. The solid electrolyte layer 20 has a positive electrode facing region 21 facing the positive electrode layer 10, and a positive electrode non-facing region 22 not facing the positive electrode layer 10. The positive electrode non-facing region 22 is a portion that exceeds the edge of the positive electrode active material layer 12 in a top view. The end of the positive electrode non-facing region 22 may be located, for example, 1.0 mm or more away from the end of the positive electrode facing region 21, or may be located within a range of 0.5 to 5.0 mm from the end of the positive electrode facing region 21.

[0037] The solid electrolyte layer 20 contains at least one type of solid electrolyte material. The positive electrode facing region 21 and the positive electrode non-facing region 22 of the solid electrolyte layer 20 may contain the same solid electrolyte material. The solid electrolyte layer 20 can conduct a charge transfer medium between the positive electrode layer 10 and the negative electrode layer 40 via the solid electrolyte material contained in the solid electrolyte layer 20.

[0038] The solid electrolyte material is not particularly limited as long as it has charge transfer medium conductivity. For example, a sulfide solid electrolyte material, an oxide solid electrolyte material, a nitride solid electrolyte material, a halide solid electrolyte material, etc. can be used.

[0039] Examples of sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiI, etc. The above description of "Li2S-P2S5" means a sulfide solid electrolyte material made 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.

[0040] 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 (e.g., Li 1.5 Al 0.5 Ti 1.5 (PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li7La3Zr2O 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0041] The particle size of the solid electrolyte material constituting the solid electrolyte layer 20 is, for example, 0.5 to 10 μm in terms of median size (D50), and is preferably larger than the particles constituting the intermediate layer 30 described below.

[0042] The positive electrode facing region 21 and the positive electrode non-facing region 22 may have a gap. The porosity of the positive electrode non-facing region 22 is less than 5%. The porosity of the positive electrode facing region 21 is not particularly limited and may be lower than the porosity of the intermediate layer 30, for example, less than 10%. The porosity of the positive electrode facing region 21 and the porosity of the positive electrode non-facing region 22 may be the same, or the porosity of the positive electrode facing region 21 may be lower, or the porosity of the positive electrode non-facing region 22 may be lower.

[0043] The porosity of the positive electrode facing region 21 and the positive electrode non-facing region 22 can be calculated, for example, by the following formula (1). In formula (1), the "filling rate" refers to the percentage of the apparent density to the true density of the positive electrode facing region 21 and the positive electrode non-facing region 22. Porosity (%)=100-Filling rate (%) …(1)

[0044] The positive electrode facing region 21 and the positive electrode non-facing region 22 may satisfy -3%≦(D1-D2) / D1×100≦+3%, where D1 is the apparent density of the positive electrode facing region 21 and D2 is the apparent density of the positive electrode non-facing region 22. (D1-D2) / D1×100 may be -3% or more and less than 0%, or may be more than 0% and 3% or less.

[0045] Furthermore, the positive electrode facing region 21 and the positive electrode non-facing region 22 may satisfy (E1-E2) / E1×100≦15%, where the composite elastic modulus of the positive electrode facing region 21 is E1 and the composite elastic modulus of the positive electrode non-facing region 22 is E2.

[0046] The solid electrolyte layer 20 having the porosity and apparent density of the positive electrode facing region 21 and the positive electrode non-facing region 22 within the above range is dense and does not easily adsorb moisture. The solid electrolyte layer 20 may have a moisture content of 700 mass ppm or less, or 500 mass ppm or less after drying at 110° C. for 1 hour in a vacuum state of less than 100 Pa. By using a solid electrolyte layer 20 with a low moisture content, it is possible to suppress the decrease in the ion conductivity of the solid electrolyte layer, and also to suppress the deterioration of the positive electrode layer 10, the intermediate layer 30, and the negative electrode layer 40 due to moisture, thereby further improving the cycle characteristics of the solid secondary battery 100. The moisture content of the solid electrolyte layer 20 after drying can be measured using the Karl Fischer method.

[0047] The volume resistivity (20° C.) of the positive electrode non-facing region 22 is, for example, 1×10 7 ~1×10 9 In the case where the positive electrode non-facing region 22 contains a sulfide solid electrolyte material, the volume resistivity (20° C.) may be within a range of 1×10 7 ~1×10 8 The volume resistivity (20°C) of the oxide solid electrolyte material may be within the range of 1×10 8 ~1×10 9 may be in the range.

[0048] The strength at which the positive electrode non-facing region 22 peels off in layers (intralayer adhesion strength) measured by the SAICAS method may be greater than 0.3 kN / m. The intralayer adhesion strength is an index of the shape stability of the positive electrode non-facing region 22. When the intralayer adhesion strength is high, layer-like cracks and chips are less likely to occur in the positive electrode non-facing region 22, and shape stability is improved.

[0049] The intermediate layer 30 is a layer laminated between the solid electrolyte layer 20 and the negative electrode layer 40. The intermediate layer 30 has the function of suppressing non-uniform deposition of metal ions at the interface of the negative electrode layer 40 and improving the interface adhesion.

[0050] The intermediate layer 30 preferably has electron conductivity and voids through which metal ions (e.g., lithium ions) serving as a charge transfer medium can pass. When the intermediate layer 30 has voids, when the solid secondary battery 100 is charged, the metal ions moving from the solid electrolyte layer 20 toward the negative electrode layer 40 pass through the intermediate layer 30 and are precipitated on the surface of the negative electrode current collector 41 of the negative electrode layer 40 on the intermediate layer 30 side, forming a metal precipitate layer 42 (a layer of metallic lithium). By passing through the intermediate layer 30, the metal precipitate layer 42 can be uniformly formed on the surface of the negative electrode current collector 41. In addition, by having voids, the intermediate layer 30 has flexibility capable of following the change in thickness of the negative electrode layer 40 accompanying charging and discharging. Therefore, even when the solid secondary battery 100 is repeatedly charged and discharged, the interfacial adhesion can be maintained, and the durability of the solid secondary battery 100 can be improved.

[0051] The porosity of the intermediate layer 30 is preferably higher than that of the solid electrolyte layer 20. This allows many voids through which metal ions can pass to be formed inside the intermediate layer 30, so that the metal deposit layer 42 can be more uniformly formed on the surface of the negative electrode current collector 41. In addition, the intermediate layer 30 becomes more flexible, so that the ability to follow changes in the thickness of the negative electrode layer 40 is improved. The porosity of the intermediate layer 30 can be, for example, 40 to 70%. The porosity of the intermediate layer 30 can be calculated in the same manner as the porosity of the solid electrolyte layer 20.

[0052] The thickness of the intermediate layer 30 may be 5 μm or less. By making the thickness of the intermediate layer 30 5 μm or less, the deposition position of the metal, which is the charge transfer medium during charging, can be between the intermediate layer 30 and the negative electrode layer 40. This can greatly reduce the frequency of direct contact between the solid electrolyte layer 20 and the deposited metal, suppressing local deterioration and current concentration of the solid electrolyte layer 20, and improving cycle characteristics and storage characteristics. In addition, the relatively elastic intermediate layer 30 can be disposed between the hard solid electrolyte layer 20 and the deposited metal, making it easier to follow the expansion and contraction caused by the deposition and dissolution of the metal, allowing a uniform reaction in the in-plane and thickness directions, thereby obtaining the effects of reducing resistance and improving cycle characteristics. In order to obtain the effects of further reducing resistance and improving cycle characteristics, the thickness of the intermediate layer may be 3 μm or less, or may be within the range of 1 to 3 μm.

[0053] The intermediate layer 30 preferably contains amorphous carbon and metal nanoparticles. By containing amorphous carbon and metal nanoparticles, the electronic conductivity of the intermediate layer 30 can be ensured, and even in a state where it is molded under high pressure, voids through which the charge transfer medium can move can be maintained within the intermediate layer 30, thereby obtaining the effect of reducing resistance. The intermediate layer 30 may further contain a binder as a binding material to maintain the structure.

[0054] Unlike graphite, amorphous carbon is less likely to react with metals such as lithium and form an alloy, and therefore can suppress the formation of dendrites and improve the cycle characteristics of solid secondary batteries. The amorphous carbon may be either easily graphitized carbon (soft carbon) or difficultly graphitized carbon (hard carbon). In addition, the amorphous carbon may be any carbon allotrope that does not show a clear crystalline state, and may be an aggregate of fine graphite crystals. Specific examples of amorphous carbon include carbon blacks such as acetylene black, furnace black, and ketjen black, coke, activated carbon, CNT (carbon nanotube), fullerene, and graphene.

[0055] Examples of metal nanoparticles include metal nanoparticles of tin (Sn), silicon (Si), zinc (Zn), magnesium (Mg), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), and antimony (Sb). The content of the metal nanoparticles in the intermediate layer 30 is preferably more than 0 mass% and 30 mass% or less. When the intermediate layer 30 contains metal nanoparticles, the electronic conductivity of the intermediate layer 30 can be increased, and the metal precipitate layer 42 can be generated more uniformly. In addition, since the metal nanoparticles have a high Young's modulus compared to amorphous carbon, the structure of the intermediate layer 30 can be maintained even when high-pressure pressing is performed when manufacturing the solid secondary battery 100.

[0056] The particle diameter of the amorphous carbon and metal nanoparticles is preferably smaller than that of the solid electrolyte material. This allows the intermediate layer 30 to enter the gap between the solid electrolyte materials constituting the interface of the solid electrolyte layer 20, thereby increasing the contact area between the solid electrolyte layer 20 and the intermediate layer 30 and improving the adhesion. The particle diameter of the amorphous carbon may be, for example, in the range of 0.02 to 0.10 μm in terms of median diameter (D50). The particle diameter of the metal nanoparticles may be, for example, in the range of 0.02 to 0.20 μm in terms of median diameter (D50).

[0057] The binder is preferably one that can improve the adhesion between the particles constituting the intermediate layer 30 and between the intermediate layer 30 and the solid electrolyte layer 20. There are no particular limitations on the binder, and it is possible to use binders that are generally used in solid secondary batteries. Examples of binders include acrylic acid-based polymers, cellulose-based polymers, styrene-based polymers, vinyl acetate-based polymers, urethane-based polymers, fluoroethylene-based polymers, and PVDF-based polymers.

[0058] The negative electrode current collector 41 is a laminate having a current collecting substrate 41a and a metal layer 41b laminated on the surface of the current collecting substrate 41a. There are no particular limitations on the material or shape of the current collecting substrate 41a as long as it has the function of collecting current from the negative electrode layer 40. Examples of materials for the current collecting substrate 41a include nickel, copper, and stainless steel. Examples of the shape of the current collecting substrate 41a include a foil shape, a plate shape, and the like.

[0059] The metal layer 41b is not particularly limited in material or shape as long as it has a function of densely precipitating a charge transfer medium such as lithium ions. When the charge transfer medium is lithium ions, the material of the metal layer 41b can be metallic lithium or a metal that forms an alloy with lithium. Examples of metals that form an alloy with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The metal that forms the metal layer 41b may be in the form of a powder or a thin film. By using the negative electrode current collector 41 having this metal layer 41b, a uniform metal deposition layer 42 can be formed on the surface of the negative electrode current collector 41. The metal layer 41b may be omitted and lithium ions may be directly deposited on the current collector substrate 41a.

[0060] 4, the electrode laminate 1 is housed in an exterior body 50. A pair of restraining members 60 for applying a restraining force to the electrode laminate 1 are disposed on the outer surface of the exterior body 50. The solid secondary battery 100 has a positive electrode tab (not shown) having one end connected to the positive electrode current collector 11 and the other end protruding outward, and a negative electrode tab (not shown) having one end connected to the negative electrode current collector 41 and the other end protruding outward.

[0061] The exterior body 50 is expandable and contractable in accordance with the change in thickness of the negative electrode due to charging and discharging. A laminate film can be used as the material of the exterior body 50. As the laminate film, a laminate 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 may be, for example, a polyamide (nylon) layer or a polyethylene terephthalate (PET) layer, the metal layer may be, for example, an aluminum layer, and the inner resin layer may be, for example, a polyethylene layer or a polypropylene layer. In addition, an adhesive layer may be included between each layer, and the layers may be integrated by heat, pressure, or the like.

[0062] In order to ensure clearance inside the exterior body 50, the ratio of the thickness of the positive electrode layer 10 to the thickness of the negative electrode layer 40 (the thickness of the negative electrode current collector 41) in a discharged state (thickness of the positive electrode layer 10 / thickness of the negative electrode layer 40) may be 1.9 or more.

[0063] The restraining member 60 is intended to apply a restraining force in the stacking direction of the electrode laminate 1. When the area of ​​the restraining member 60 in a top view is Sr and the area of ​​the negative electrode layer 40 in a top view is Sn, it is preferable that the relationship Sn≦Sr is satisfied. When the area Sr of the restraining member 60 satisfies this relationship, the restraining force acts uniformly on the surface of the negative electrode layer 40. Therefore, during charging, metal ions can be uniformly precipitated on the surface of the negative electrode layer 40, so that metal is less likely to accumulate at the ends of the solid electrolyte layer 20 and the intermediate layer 30. There is no particular restriction on the material of the restraining member 60, and a material generally used for solid-state batteries can be used. The restraining force of the restraining member 60 on the electrode laminate 1 may be within the range of, for example, 0.1 to 10 MPa.

[0064] Next, a method for manufacturing the solid secondary battery 100 of this embodiment will be described. The electrode laminate 1 can be produced, for example, by a method including a positive electrode layer preparation step, a solid electrolyte layer formation step, an intermediate layer formation step, and a negative electrode layer formation step.

[0065] The positive electrode layer preparation step is a step of preparing a positive electrode layer 10. The positive electrode layer 10 can be prepared, for example, by forming a positive electrode active material layer 12 on the surface of a positive electrode current collector 11. The positive electrode active material layer 12 can be formed by applying a positive electrode active material layer slurry and drying it. The positive electrode active material layer slurry can be a dispersion of a positive electrode active material containing a solvent, a positive electrode active material, and optionally a conductive assistant and a binder. In the positive electrode layer preparation step, it is preferable to arrange an insulating frame 15 so as to surround the outer periphery of the positive electrode active material layer 12.

[0066] The solid electrolyte layer forming step is a step of forming a solid electrolyte layer 20 on the surface of the positive electrode active material layer 12 of the positive electrode layer 10. As a method of forming the solid electrolyte layer 20, a method of directly applying a solid electrolyte layer slurry to the surface of the positive electrode active material layer 12 and drying it, or a method of applying a solid electrolyte layer slurry to the surface of a separately prepared support sheet and drying it to form a solid electrolyte layer 20, and transferring the solid electrolyte layer 20 to the surface of the positive electrode active material layer 12 at a predetermined pressure can be used. As the solid electrolyte layer slurry, for example, a dispersion liquid of a solid electrolyte containing a solvent, a solid electrolyte, and an optional binder can be used. As a method of forming the solid electrolyte layer 20, a method of integrating a solid electrolyte layer with a substrate, making it independent, and then arranging it on the positive electrode layer can be used. As the substrate, for example, a nonwoven fabric or a woven fabric can be used. As the material of the substrate, a polyester resin such as PET can be used.

[0067] The intermediate layer forming step is a step of forming an intermediate layer 30 on the surface of the solid electrolyte layer 20 opposite to the positive electrode active material layer 12 side. The intermediate layer 30 can be formed by directly applying an intermediate layer slurry to the surface of the solid electrolyte layer 20 and drying it, or by applying the intermediate layer slurry to the surface of a separately prepared support sheet, drying it, and transferring the intermediate layer 30 to the surface of the solid electrolyte layer 20 at a predetermined pressure. The intermediate layer slurry can be a dispersion of an intermediate layer forming material containing a solvent, metal nanoparticles, amorphous carbon, and an optional binder.

[0068] The negative electrode layer forming step is a step of forming the negative electrode layer 40 on the surface of the intermediate layer 30 opposite to the solid electrolyte layer 20. As a method for forming the negative electrode layer 40, a method in which a previously prepared negative electrode current collector 41 is disposed on the surface of the intermediate layer 30 can be used.

[0069] The intermediate layer forming step and the negative electrode layer forming step may be performed simultaneously. For example, the intermediate layer 30 of an intermediate layer-negative electrode layer laminate in which the intermediate layer 30 and the negative electrode layer 40 are integrated and made independent in advance may be disposed on the surface of the solid electrolyte layer 20. The intermediate layer-negative electrode layer laminate can be obtained, for example, by applying an intermediate layer slurry to the surface of the negative electrode current collector 41 and drying it to form the intermediate layer 30.

[0070] In this manner, an electrode laminate 1 is obtained in which the positive electrode layer 10, the solid electrolyte layer 20, the intermediate layer 30, and the negative electrode layer 40 are laminated in this order. The obtained electrode laminate 1 may be optionally pressed to be integrated.

[0071] The solid secondary battery 100 can be fabricated as follows. One end of the positive electrode tab is connected to the positive electrode current collector 11 of the obtained electrode laminate 1, and one end of the negative electrode tab is connected to the negative electrode current collector 41. Next, the electrode laminate 1 is housed in an exterior body 50 so that the other ends of the positive electrode tab and the negative electrode tab protrude, and the exterior body 50 is sealed. Then, a restraining member 60 is disposed on the outer surface of the exterior body 50, and the electrode laminate 1 is restrained with a predetermined restraining force.

[0072] According to the solid secondary battery 100 of this embodiment configured as described above, the non-positive electrode facing region 22 of the solid electrolyte layer 20 has a low porosity of 5% or less and is dense, so that metal ions released from the positive electrode layer 10 and the negative electrode layer 40 do not easily move within the non-positive electrode facing region during charging and discharging. This makes it difficult for metal ions to precipitate at the end of the solid electrolyte layer 20. Therefore, the solid secondary battery 100 of this embodiment has excellent cycle characteristics.

[0073] In the solid secondary battery 100 of this embodiment, when the ratio [(D1-D2) / D1×100] of the difference (D1-D2) between the apparent density of the positive electrode facing region 21 and the apparent density of the non-positive electrode facing region 22 to the apparent density D1 of the positive electrode facing region 21 of the solid electrolyte layer 20 is within the above range, the difference in apparent density between the positive electrode facing region 21 and the non-positive electrode facing region 22 is small. Therefore, metal ions released from the positive electrode layer 10 or the negative electrode layer 40 and supplied to the positive electrode facing region 21 are less likely to move to the non-positive electrode facing region 22 side, and the metal ions are less likely to precipitate at the end of the solid electrolyte layer 20.

[0074] In the solid secondary battery 100 of the present embodiment, when the adhesion strength within the layer of the non-positive electrode facing region 22 of the solid electrolyte layer 20 satisfies the above value, the shape stability of the non-positive electrode facing region 22 is improved. Therefore, metal ions are less likely to precipitate at the end portion of the solid electrolyte layer 20 for a long period of time.

[0075] In addition, in the solid secondary battery 100 of this embodiment, when the ratio [(D1-D2) / D1×100] of the difference (E1-E2) between the composite elastic modulus of the positive electrode facing region 21 and the composite elastic modulus of the positive electrode non-facing region 22 to the composite elastic modulus E1 of the positive electrode facing region 21 of the solid electrolyte layer 20 satisfies the above value, the difference in the composite elastic modulus of the positive electrode facing region 21 and the positive electrode non-facing region 22 is small. Therefore, the variation in the thickness of the positive electrode facing region 21 and the positive electrode non-facing region 22 when a restraining force is applied to the solid secondary battery 100 is small. Therefore, even if a restraining force is applied to the solid secondary battery 100, the interface and structure of each member in the solid secondary battery can be maintained, and local reactions and current concentration can be suppressed. Furthermore, in the solid secondary battery 100 of this embodiment, when the solid electrolyte layer 20 contains a sulfide solid electrolyte material, it is easy to form a dense positive electrode non-facing region 22 with a low porosity.

[0076] According to the solid secondary battery 100 of this embodiment, even if the intermediate layer 30 is provided between the solid electrolyte layer 20 and the negative electrode layer 40, the solid electrolyte layer 20 has the positive electrode non-facing region 22, so that metal ions are less likely to precipitate at the end of the intermediate layer 30. Furthermore, when the porosity of the intermediate layer 30 is larger than the porosity of the solid electrolyte layer 20, non-uniform metal precipitation at the interface with the negative electrode layer 40 of the solid secondary battery 100 can be suppressed, and therefore the cycle characteristics can be further improved.

[0077] According to the solid secondary battery 100 of this embodiment, the outer periphery of the positive electrode active material layer 12 is surrounded by the insulating frame 15, and the positive electrode non-facing region 22 is supported by the insulating frame 15, so that the strength of the positive electrode non-facing region 22 is improved. Furthermore, even if metal accumulates at the ends of the solid electrolyte layer 20 and the intermediate layer 30, the metal is less likely to find its way into the positive electrode active material layer 12. As a result, the positive electrode layer 10 and the negative electrode layer 40 are even less likely to short-circuit, and the cycle characteristics are further improved.

[0078] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the solid secondary battery 100 of this embodiment, the outer periphery of the positive electrode active material layer 12 is surrounded by the insulating frame 15, but the insulating frame 15 may be omitted. In this case, it is preferable to cover the outer periphery of the negative electrode layer 40 with an insulating frame and support the positive electrode non-facing region 22 of the solid electrolyte layer 20 with the insulating frame.

[0079] In addition, in the solid secondary battery 100 of this embodiment, the metal precipitate layer 42 is used as the negative electrode active material layer, but the negative electrode active material layer is not limited thereto. The negative electrode active material layer may be a layer containing a negative electrode active material capable of absorbing and releasing a charge transfer medium such as lithium ions. In this case, the negative electrode active material layer may be disposed on the surface of the current collecting substrate 41a. As the negative electrode active material, a material used in the negative electrode of a general solid secondary battery can be used. When the charge transfer medium is lithium ions, examples of the negative electrode active material include lithium transition metal oxides such as lithium titanate, transition metal oxides such as TiO2, Nb2O3 and WO3, Si, SiO, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon and hard carbon. The negative electrode active material layer may optionally contain a solid electrolyte from the viewpoint of improving the conductivity of the charge transfer medium. In addition, it may optionally contain a conductive assistant to improve the conductivity. Furthermore, it may optionally contain a binder from the viewpoint of expressing flexibility. As for the solid electrolyte, the conductive assistant, and the binder, those generally used in solid-state batteries can be used. EXAMPLES

[0080] The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

[0081] <Example 1> [Preparation of positive electrode layer] As a positive electrode current collector, a rectangular aluminum foil having a length of 30.0 mm in the X direction, a length of 30.0 mm in the Y direction, and a thickness of 15.0 μm was prepared. A mixture of 80 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) as the positive electrode active material, 17 parts by mass of an argyrodite-type sulfide solid electrolyte as the solid electrolyte, 2 parts by mass of carbon black as the conductive assistant, and 1 part by mass of an SBR (styrene butadiene rubber) binder as the binder was used. The 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 the center of the positive electrode current collector in a size of 20.0 mm in the X direction, 20.0 mm in the Y direction, and 27 mg / cm2 in weight per unit area after drying. 2 The positive electrode layer was thus produced by applying the positive electrode active material thereto using a bar coater so as to obtain a positive electrode active material layer.

[0082] [Installation of insulating frame] An insulating sheet having a length of 30.0 mm in the X direction, a length of 30.0 mm in the Y direction, and a thickness of 80.0 μm was prepared. An opening having a length of 20.0 mm in the X direction and a length of 20.0 mm in the Y direction was formed in the center of the insulating sheet to prepare an insulating frame. The obtained insulating frame was placed around the positive electrode active material layer.

[0083] [Preparation of solid electrolyte layer] A dispersion of an argyrodite-type sulfide solid electrolyte (median diameter: 3.0 μm) was applied to a support sheet and dried to obtain a sheet having a length of 27.0 mm in the X direction, a length of 27.0 mm in the Y direction, and a drying weight of 20 mg / cm. 2 The argyrodite-type sulfide solid electrolyte layer was formed. The argyrodite-type sulfide layer formed on the support sheet was transferred to the center of the positive electrode active material layer to prepare a solid electrolyte layer.

[0084] [Creation of intermediate layer] A total of 95 parts by mass of Sn particles (median diameter: 0.07 μm) as metal nanoparticles, acetylene black (median diameter: 0.05 μm) as amorphous carbon, and 5 parts by mass of a PVDF-based binder as a binder were mixed. 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 the center of the solid electrolyte layer in a size of 22.0 mm in the X direction × 22.0 mm in the Y direction × 0.4 mg / cm2 after drying. 2 The resulting mixture was applied using a gravure coater so that the intermediate layer had a thickness of 100 μm and then dried to produce a positive electrode layer-solid electrolyte layer-intermediate layer laminate in which the positive electrode layer, the solid electrolyte layer, and the intermediate layer were laminated in this order.

[0085] [Preparation of negative electrode current collector] A laminated metal foil (total thickness: 50 μm) was prepared by laminating a copper foil having a thickness of 10 μm and a lithium foil having a thickness of 40 μm. This laminated metal foil was cut into a size of 21.0 mm in the X direction × 21.0 mm in the Y direction to prepare a negative electrode current collector.

[0086] [Preparation of electrode laminate] The cathode layer-solid electrolyte layer-intermediate layer laminate obtained above was densified by isostatic pressing. The pressing conditions were a heating temperature of 120°C, a pressurizing pressure of 980MPa, and a holding time of 5 minutes. Next, the anode current collector obtained above was arranged so that the lithium foil was in contact with the surface of the intermediate layer of the cathode layer-solid electrolyte layer-intermediate layer laminate, and then pressed to produce an electrode laminate in which the cathode layer, solid electrolyte layer, intermediate layer, and anode current collector were laminated in this order. After densification pressing, the thickness of the cathode layer was 78 μm, the thickness of the solid electrolyte layer was 100 μm, and the thickness of the intermediate layer was 3 μm.

[0087] [Preparation of solid-state secondary batteries] After tabs were attached to the positive and negative current collectors of the electrode laminate obtained above, the electrode laminate was housed in a bag-shaped laminate pack, and the laminate pack was then sealed in an argon atmosphere.

[0088] A restraining member having a length of 21.0 mm in the X direction and a length of 21.0 mm in the Y direction was prepared. This restraining member was placed so as to face the negative electrode current collector of the electrode laminate from the surface of the laminate pack, and a restraining force of 3 MPa was applied to the electrode laminate to produce a solid secondary battery.

[0089] <Examples 2 to 3, Comparative Examples 1 to 3> A solid secondary battery was produced in the same manner as in Example 1, except that in the preparation of the electrode laminate, the conditions (method, heating temperature, and pressurizing pressure) of the densification treatment of the positive electrode layer-solid electrolyte layer-intermediate layer laminate were set to the temperatures and pressures shown in Table 1 below.

[0090] [Table 1]

[0091] <Physical properties of solid electrolyte layer> A solid electrolyte layer was taken out from the electrode laminate produced in Examples 1 to 3 and Comparative Examples 1 to 3. The obtained solid electrolyte layer was separated into a positive electrode facing region and a positive electrode non-facing region. The weight and size of the positive electrode facing region and the positive electrode non-facing region were measured to obtain the apparent density. (D1-D2) / D1×100 was calculated from the obtained apparent density (D1) of the positive electrode facing region and the apparent density (D2) of the positive electrode non-facing region. In addition, the volume resistivity (20° C.) and true density of the positive electrode non-facing region were measured. The packing rate was obtained from the obtained true density and apparent density, and the porosity of the positive electrode non-facing region was calculated. In addition, the adhesion strength within the layer of the positive electrode non-facing region was measured using a surface and interface physical properties analyzer (SAICAS). Furthermore, the composite elastic modulus was measured for the positive electrode facing region and the non-positive electrode facing region, and (E1-E2) / E2 x 100 was calculated from the composite elastic modulus (E1) of the positive electrode facing region and the composite elastic modulus (E2) of the non-positive electrode facing region. The results are shown in Table 2.

[0092] <Physical properties of the intermediate layer> An intermediate layer was taken out from the electrode laminate produced in Examples 1 to 3 and Comparative Examples 1 to 3. The weight and size of the obtained intermediate layer were measured to determine the apparent density. The true density of the intermediate layer was also measured. The packing ratio was determined from the obtained true density and apparent density, and the porosity of the intermediate layer was calculated. The results are shown in Table 2.

[0093] <Battery characteristics> For the solid secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 3, cycle tests were conducted in which charging and discharging were repeated at a charging upper limit voltage of 4.3V, a discharging lower limit voltage of 2.65V, and a C rate of 1 / 3C. The ratio of the discharge capacity to the first charging capacity (discharging capacity / charging capacity×100) was taken as the initial charging and discharging efficiency. In addition, when the ratio of the second discharging capacity to the first charging capacity (second charging capacity / first discharging capacity×100) exceeded 105%, the short circuit behavior during the second charging was considered to be "present", and when the ratio of the second discharging capacity to the first charging capacity was 105% or less, the short circuit behavior during the second charging was considered to be "absent". The results are shown in Table 2.

[0094] [Table 2]

[0095] From the results shown in Table 2, it was confirmed that the solid secondary batteries obtained in Examples 1 to 3, in which the solid electrolyte layer had a non-positive electrode facing region with a porosity of less than 5%, had high initial charge / discharge efficiency and were less likely to short circuit. In contrast, the solid secondary batteries obtained in Comparative Examples 1 to 3, in which the porosity of the non-positive electrode facing region was 5% or more, had low initial charge / discharge efficiency and short circuited during the second charge. This is because lithium was precipitated in the pores in the non-positive electrode facing region during charging in the solid secondary batteries of Comparative Examples 1 to 3. [Explanation of symbols]

[0096] 1 Electrode laminate 10 Positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 15 Insulation frame 20 Solid electrolyte layer 21 Positive electrode facing area 22 Positive electrode non-facing area 30 Middle Class 40 Negative electrode layer 41 Negative electrode current collector 41a Current collector substrate 41b Metal layer 42 Metal deposit layer 50 Exterior body 60 Restraint member 100 Solid state secondary battery

Claims

1. The electrode stack includes an electrode laminate and an exterior body that houses the electrode laminate. the electrode stack 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; the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer, the solid electrolyte layer has a positive electrode facing region that faces the positive electrode active material layer and a positive electrode non-facing region that does not face the positive electrode layer, A solid-state secondary battery, wherein the porosity of a region not facing a positive electrode is less than 5%.

2. 2. The solid secondary battery according to claim 1, wherein the apparent density of the positive electrode facing region is D1 and the apparent density of the positive electrode non-facing region is D2, and -3%≦(D1−D2) / D1×100≦+3% is satisfied.

3. The solid secondary battery according to claim 1 , wherein the adhesion strength within the layer of the non-positive electrode facing region of the solid electrolyte layer is greater than 0.3 kN / m.

4. 2. The solid secondary battery according to claim 1, wherein, when the composite elastic modulus of the positive electrode facing region of the solid electrolyte layer is E1 and the composite elastic modulus of the positive electrode non-facing region is E2, (E1-E2) / E1×100≦15% is satisfied.

5. The solid state secondary battery according to claim 1 , wherein the solid electrolyte layer comprises a sulfide solid electrolyte material.

6. an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer; The solid secondary battery according to claim 1 , wherein the porosity of the intermediate layer is greater than the porosity of the solid electrolyte layer.

7. The solid secondary battery according to claim 6 , wherein the intermediate layer has a thickness of 5 μm or less in the stacking direction of the electrode stack.

8. The solid state secondary battery according to claim 6 , wherein the intermediate layer comprises metal nanoparticles and amorphous carbon.

9. The solid secondary battery according to claim 1 , wherein an outer periphery of the positive electrode active material layer is surrounded by an insulating frame.

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