Solid-state battery

Abstract

To provide a solid-state battery in which a solid electrolyte layer is appropriately designed according to a function and which can improve the energy density.SOLUTION: A solid-state battery has a structure in which an anode layer, a solid electrolyte layer, and a cathode layer are laminated in this order, the solid electrolyte layer consists of a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer arranged in this order from the cathode layer side, the first solid electrolyte layer has a thickness of 3 to 8.5 μm, the second solid electrolyte layer has a thickness of 10 to 20 μm, the third solid electrolyte layer has a thickness of 3 to 8.5 μm, and the total thickness of the solid electrolyte layers is 17 to 26 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid-state 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.

[0003] Known examples of such secondary batteries include solid-state batteries such as lithium metal batteries and lithium ion secondary batteries, in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer.

[0004] Known technology relating to solid-state batteries includes technology relating to all-solid-state batteries having a first solid electrolyte layer adjacent to a negative electrode and a second solid electrolyte layer located between the first solid electrolyte layer and a positive electrode, where the first solid electrolyte layer has a smaller Young's modulus than the second solid electrolyte layer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-108202 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology disclosed in Patent Document 1 aims to suppress deterioration of the interfacial contact between the solid electrolyte layer and the positive and negative electrode layers, and to suppress voltage drop during self-discharge. However, simply multiplying the solid electrolyte layer increases the overall thickness of the solid electrolyte layer, resulting in a decrease in the energy density of the solid battery. Another problem is that interfaces between the multilayered solid electrolyte layers increase battery resistance. Furthermore, it is necessary to design the thickness of the solid electrolyte layer appropriately according to the functions required for each multilayered solid electrolyte layer.

[0007] The present invention has been made in view of the above, and has an object to provide a solid-state battery in which a solid electrolyte layer is appropriately designed according to the function and in which the energy density can be improved. [Means for solving the problem]

[0008] (1) A solid-state battery having a structure in which an anode layer, a solid electrolyte layer, and a cathode layer are stacked in this order, the solid electrolyte layer comprising a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer, which are arranged in this order from the cathode layer side, the first solid electrolyte layer having a thickness of 3 to 8.5 μm, the second solid electrolyte layer having a thickness of 10 to 20 μm, the third solid electrolyte layer having a thickness of 3 to 8.5 μm, and the total thickness of the solid electrolyte layers having a thickness of 17 to 26 μm.

[0009] According to the invention (1), it is possible to provide a solid-state battery in which the solid electrolyte layer is appropriately designed according to the function and the energy density can be improved.

[0010] (2) The solid state battery according to (1), wherein the binder content (vol %) in the third solid electrolyte layer is equal to or less than the binder content (vol %) in the first solid electrolyte layer and equal to or less than the binder content (vol %) in the second solid electrolyte layer.

[0011] According to the invention of (2), the first solid electrolyte layer can be pressed under high pressure together with the positive electrode layer when the positive electrode layer is densified, so that the first solid electrolyte layer can be stretched to follow the positive electrode layer, thereby improving the bonding of the second solid electrolyte layer to other solid electrolyte layers.

[0012] (3) The solid state battery according to (1) or (2), wherein the content of the binder in the first solid electrolyte layer is 5% by volume or more and 25% by volume or less.

[0013] According to the invention of (3), the first solid electrolyte layer can be preferably stretched to conform to the positive electrode layer by pressing the positive electrode layer together with the first solid electrolyte layer at a high pressure when the positive electrode layer is densified.

[0014] (4) The solid state battery according to any one of (1) to (3), wherein the first solid electrolyte layer contains a fluorine-based binder.

[0015] According to the invention of (4), the first solid electrolyte layer can be preferably stretched to conform to the positive electrode layer by pressing the positive electrode layer together with the first solid electrolyte layer at a high pressure when the positive electrode layer is densified.

[0016] (5) The solid state battery according to any one of (1) to (4), wherein the content of the binder in the second solid electrolyte layer is 5% by volume or more and 25% by volume or less.

[0017] According to the fifth aspect of the present invention, the bonding strength of the second solid electrolyte layer to other solid electrolyte layers can be improved.

[0018] (6) The solid state battery according to any one of (1) to (5), wherein the second solid electrolyte layer contains at least one of a fluorine-based binder and a styrene-based binder.

[0019] According to the sixth aspect of the present invention, the bonding strength between the second solid electrolyte layer and other layers can be improved, or the ionic conductivity can be improved.

[0020] (7) The solid state battery according to any one of (1) to (6), wherein the binder content in the third solid electrolyte layer is 2.7% by volume or more and 10% by volume or less.

[0021] According to the seventh aspect of the present invention, the third solid electrolyte layer easily expands in accordance with the negative electrode.

[0022] (8) The solid state battery according to any one of (1) to (7), wherein at least one of the first solid electrolyte layer, the second solid electrolyte layer, and the third solid electrolyte layer contains a support.

[0023] According to the invention of (8), the strength of the solid electrolyte layer is improved, so that the solid electrolyte layer can be made thinner and the energy density of the solid battery can be improved.

[0024] (9) The solid state battery according to any one of (1) to (8), wherein the particle diameter (D50) of the solid electrolyte layer particles contained in the solid electrolyte layer is 0.1 μm or more and 3 μm or less.

[0025] According to the invention (9), it is possible to achieve both a thin solid electrolyte layer and favorable ionic conductivity. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view showing a solid-state battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] [Solid battery] As shown in Fig. 1, the solid-state battery 1 has an electrode laminate in which an anode layer 2, a solid electrolyte layer 4, and a cathode layer 3 are laminated in this order. In this embodiment, the structure in which the anode layer 2, the solid electrolyte layer 4, the cathode layer 3, the solid electrolyte layer 4, and the anode layer 2 are laminated in this order as shown in Fig. 1 will be described as the laminate structure of the solid-state battery 1. However, the structure of the solid-state battery 1 is not limited to the above, and it is sufficient that the solid-state battery 1 has a structure in which the solid electrolyte layer 4 is laminated between the anode layer 2 and the cathode layer 3.

[0028] The solid electrolyte layer 4 in the solid battery 1 includes at least a first solid electrolyte layer 43 disposed on the positive electrode layer 3 side, a third solid electrolyte layer 41 disposed on the negative electrode layer 2 side, and a second solid electrolyte layer 42 disposed between the first solid electrolyte layer 43 and the third solid electrolyte layer 41. An intermediate layer 5 may be optionally disposed between the negative electrode layer 2 and the solid electrolyte layer 4. In the following description, the solid battery 1 will be described as including the intermediate layer 5.

[0029] The solid state battery 1 is not particularly limited, but may be a lithium ion solid state secondary battery or a lithium metal secondary battery.

[0030] (solid electrolyte layer) The solid electrolyte layer 4 is formed between the negative electrode layer 2 and the positive electrode layer 3 .

[0031] The first solid electrolyte layer 43 is disposed on the positive electrode layer 3 side. In this embodiment, the first solid electrolyte layer 43 is disposed adjacent to the positive electrode active material layer 31 in the positive electrode layer 3. The first solid electrolyte layer 43 is disposed adjacent to the second solid electrolyte layer 42. That is, in this embodiment, the first solid electrolyte layer 43 is disposed between the positive electrode active material layer 31 and the second solid electrolyte layer 42.

[0032] The first solid electrolyte layer 43 is high-pressure pressed together with the positive electrode layer 3 during high-pressure pressing to densify the positive electrode layer 3. Therefore, the first solid electrolyte layer 43 preferably has the property of expanding in accordance with the positive electrode layer 3 during the high-pressure pressing.

[0033] The solid electrolyte material constituting the first solid electrolyte layer 43 is not particularly limited, and may be any material that can be used as an electrolyte in a solid-state battery. Examples include inorganic solid electrolytes such as sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, and lithium-containing salts, and polymer solid electrolytes such as polyethylene oxide. The above solid electrolytes may be used alone or in combination of two or more.

[0034] In addition to the solid electrolyte material, the first solid electrolyte layer 43 may contain a material that can be used in a solid electrolyte layer of a solid-state battery. For example, the first solid electrolyte layer 43 preferably contains a binder. Examples of binders include fluorine-based polymers, nitrile-based polymers, polyester-based polymers, acrylic acid-based polymers, cellulose-based polymers, styrene-based polymers, styrene-butadiene (SBR)-based polymers, vinyl acetate-based polymers, and urethane-based polymers.

[0035] The first solid electrolyte layer 43 preferably contains a fluorine-based binder. Examples of the fluorine-based binder include PVdF (polyvinylidene fluoride). This can improve the elongation of the first solid electrolyte layer 43. The binder content in the first solid electrolyte layer 43 is preferably 5% by volume or more and 25% by volume or less.

[0036] The first solid electrolyte layer 43 may include a support. The support may be a three-dimensional structure such as a mesh, a woven fabric, a nonwoven fabric, an embossed body, a punched body, an expanded body, or a foam. The first solid electrolyte layer 43 may not include the support.

[0037] The solid electrolyte material constituting the first solid electrolyte layer 43 is preferably in a particulate form. The particle size (D50, median diameter) of the solid electrolyte material constituting the first solid electrolyte layer 43 is preferably 0.1 μm or more and 3 μm or less.

[0038] The thickness of the first solid electrolyte layer 43 is 3 to 8.5 μm, which allows the first solid electrolyte layer 43 to be sufficiently thin and still be able to perform its functions.

[0039] The second solid electrolyte layer 42 is disposed between the first solid electrolyte layer 43 and the third solid electrolyte layer 41. The second solid electrolyte layer 42 is required to have good adhesion to the first solid electrolyte layer 43 and the third solid electrolyte layer 41. The type of material constituting the second solid electrolyte layer 42 may be the same as that of the first solid electrolyte layer.

[0040] The second solid electrolyte layer 42 preferably contains at least one of a fluorine-based binder and a styrene-based binder (SBR, etc.). By containing a fluorine-based binder in the second solid electrolyte layer 42, the bonding strength between the second solid electrolyte layer 42 and other solid electrolyte layers can be improved. By containing a styrene-based binder in the second solid electrolyte layer 42, the ion conductivity can be improved. The binder content in the second solid electrolyte layer 42 is preferably 5% by volume or more and 25% by volume or less.

[0041] The second solid electrolyte layer 42 may include a support, similar to the first solid electrolyte layer 43. The second solid electrolyte layer 42 may not include a support.

[0042] The thickness of the second solid electrolyte layer 42 is 10 to 20 μm. This allows the second solid electrolyte layer 42 to be sufficiently thin and still be able to perform its functions. When the second solid electrolyte layer 42 includes a support, the lower limit of the thickness of the second solid electrolyte layer 42 may be the thickness of the support plus 1 μm (a layer of 0.5 μm or more is formed on each of the stacking surfaces of the support). Therefore, depending on the thickness of the support, the lower limit of the thickness of the second solid electrolyte layer 42 may be further reduced.

[0043] The third solid electrolyte layer 41 is disposed on the anode layer 2 side. In this embodiment, the third solid electrolyte layer 41 is disposed adjacent to the intermediate layer 5 on the anode layer 2 side. The third solid electrolyte layer 41 preferably has the property of expanding in accordance with the expansion of the anode layer 2 when pressed. The type of material constituting the third solid electrolyte layer 41 may be the same as that of the first solid electrolyte layer 43.

[0044] The amount of binder contained in the third solid electrolyte layer 41 is less than that contained in the first solid electrolyte layer 43 and the second solid electrolyte layer 42. The amount of binder contained in the third solid electrolyte layer 41 is preferably 2.7% by volume or more and 10% by volume or less.

[0045] The third solid electrolyte layer 41 may include a support, similar to the first solid electrolyte layer 43. The third solid electrolyte layer 41 may not include a support.

[0046] The thickness of the third solid electrolyte layer 41 is 3 to 8.5 μm, which allows the third solid electrolyte layer 41 to be sufficiently thin and still be able to perform its functions.

[0047] (negative electrode layer) The anode layer 2 has an anode active material layer 21 and an anode current collector layer 22. The anode active material layer 21 is not particularly limited and can be made of a material that can be used as an anode active material for a solid-state battery. The anode active material layer 21 is preferably a lithium metal layer in which the anode active material is lithium metal. This is because, in the solid-state battery 1 according to the present invention, even if the anode active material layer 21 is made of a hard metal, it can adhere to the solid electrolyte layer 4 with high adhesion. The lithium metal includes not only elemental lithium metal but also lithium alloys, etc. The anode active material layer 21 can also be made of silicon-based active materials such as Si and Si alloys, lithium titanate (Li4Ti5O 12 The electrode may be composed of lithium transition metal oxides such as TiO2, Nb2O3 and WO3, metal sulfides, metal nitrides, carbon materials such as graphite, soft carbon and hard carbon, metallic indium, etc.

[0048] The negative electrode active material layer 21 may contain materials that can be contained in a negative electrode active material layer of a solid-state battery, in addition to the above. Examples of such materials include a solid electrolyte, a conductive additive, and a binder. Examples of the solid electrolyte include the same solid electrolyte as that contained in the solid electrolyte layer 4. Examples of the conductive additive include carbon black, natural graphite, carbon fiber, and carbon nanotubes. Examples of the binder include a fluorine-based polymer, a nitrile-based polymer, a polyester-based polymer, an acrylic acid-based polymer, a cellulose-based polymer, a styrene-based polymer such as a styrene-butadiene-based polymer, a vinyl acetate-based polymer, a urethane-based polymer, and a fluoroethylene-based polymer.

[0049] The negative electrode current collector layer 22 is not particularly limited, and can be made of copper, nickel, stainless steel, aluminum (Al), or the like. Examples of the shape of the negative electrode current collector layer 22 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the negative electrode current collector layer 22 extends in a predetermined direction to form a negative electrode current collector tab 22a.

[0050] (positive electrode layer) The positive electrode layer 3 has a positive electrode active material layer 31 and a positive electrode current collector layer 32. In this embodiment, the positive electrode layer 3 has a configuration in which two positive electrode active material layers 31 are stacked on both sides of one positive electrode current collector layer 32. However, the configuration of the positive electrode layer 3 is not limited to the above, and the positive electrode layer 3 may have a configuration in which one positive electrode active material layer 31 is stacked on one side of one positive electrode current collector layer 32.

[0051] The positive electrode active material layer 31 is not particularly limited and can be made of a material that can be used as a positive electrode active material for a solid-state battery. Examples of the positive electrode active material that makes up the positive electrode active material layer 31 include LiCoO2, LiNiO2, LiCo x Ni y Mn z O2 (x+y+z=1), LiVO2, LiCrO2, etc., layered positive electrode active material particles, LiMn2O4, Li(Ni 0.25 Mn 0.75 Examples of such positive electrode active materials include spinel-type positive electrode active materials such as LiCoPO, LiMnPO, and LiFePO; solid solution oxides (LiMnO-LiMO (M=Co, Ni, etc.)); conductive polymers such as polyaniline and polypyrrole; sulfides such as LiS, CuS, Li-Cu-S compounds, TiS, FeS, MoS, and Li-Mo-S compounds; and mixtures of sulfur and carbon. The positive electrode active material may be one of the above materials, or may be composed of two or more of the above materials.

[0052] An insulating frame 6 may be provided around the outer periphery of the positive electrode active material layer 31. The insulating frame 6 can prevent short circuits in the solid state battery 1 and improve its strength. In this embodiment, the insulating frame 6 is disposed so as to cover the side surfaces of the two positive electrode active material layers 31 formed on both sides of the positive electrode current collector layer 32. The insulating frame 6 also abuts against a portion of the stacking surface of the positive electrode current collector layer 32, and has a gap through which a positive electrode current collector tab 32a (described later) extends. The material for the insulating frame 6 is not particularly limited, but examples thereof include insulating oxides such as alumina, resins such as polyvinylidene fluoride (PVDF), and rubbers such as styrene-butadiene rubber (SBR).

[0053] The positive electrode current collector layer 32 is not particularly limited, and can be made of, for example, aluminum, stainless steel, conductive carbon (graphite, carbon nanotubes, etc.), etc. Examples of the shape of the positive electrode current collector layer 32 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the positive electrode current collector layer 32 extends in a predetermined direction to form a positive electrode current collector tab 32a.

[0054] (middle class) The intermediate layer 5 is optionally disposed between the anode layer 2 and the solid electrolyte layer 4. For example, when the solid battery 1 is a lithium metal battery, the intermediate layer 5 has the function of uniformly depositing lithium metal. Therefore, the interface between the intermediate layer 5 and the solid electrolyte layer 4 is stabilized. When the solid battery 1 is a lithium metal secondary battery having the intermediate layer 5, the solid battery 1 may be an anode-free battery in which the anode active material layer 21 is not present during the initial charge. In this case, a lithium metal layer is formed as the anode active material layer 21 after the initial charge / discharge. Note that the solid battery 1 does not necessarily have to have the intermediate layer 5.

[0055] The material constituting the intermediate layer 5 is not particularly limited, and examples thereof include metals capable of forming an alloy with lithium and amorphous carbon. Examples of metals capable of forming an alloy with lithium include tin (Sn), silicon (Si), zinc (Zn), magnesium (Mg), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), antimony (Sb), and indium (In). The metal capable of forming an alloy with lithium may be nanoparticles. Examples of amorphous carbon include carbon blacks such as acetylene black, furnace black, and ketjen black, coke, and activated carbon. The amorphous carbon may be graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), CNT (carbon nanotube), fullerene, or graphene. The intermediate layer may contain a binder in addition to the above materials.

[0056] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. The solid-state battery 1 may have a configuration that can be used in a solid-state battery, such as an exterior body, in addition to the electrode laminate shown in FIG.

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the contents of the following examples. [Example]

[0058] [Fabrication of solid electrolyte sheets] A dispersion of sulfide solid electrolyte (D50: 0.1 to 3 μm) was applied and dried to prepare a solid electrolyte sheet. In addition to the solid electrolyte, the dispersion contained the binder in the amount shown in Table 1 below. A nonwoven fabric substrate with a thickness of 9 μm was used as the support (substrate). When an attempt was made to prepare a solid electrolyte sheet with a thickness less than that of the substrate using the nonwoven fabric substrate, tears occurred and it was not possible to prepare it.

[0059] [Preparation of positive electrode layer] A 12.0 μm thick aluminum foil was prepared as a positive electrode current collector. 60.0 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) was used as the positive electrode active material, 35.8 parts by mass of a sulfide solid electrolyte was used as the solid electrolyte, 2.9 parts by mass of acetylene black (DENKA BLACK Li-100, manufactured by Denka Co., Ltd.) was used as the conductive additive, and 1.3 parts by mass of an SBR (styrene butadiene rubber) binder were mixed together. The resulting mixture was dispersed in a solvent to prepare a positive electrode active material slurry. The resulting positive electrode active material slurry was applied to both sides of the positive electrode current collector so that the basis weight after drying was 27.4 mg / cm. 2 The solution was applied using a bar coater so as to form a positive electrode layer, and then dried.

[0060] [Creating the negative electrode layer] A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector, and a metallic lithium foil with a thickness of 6.5 μm was laminated on the surface of the copper foil to prepare a negative electrode layer.

[0061] [Fabrication of solid-state battery cells] The cathode layer, solid electrolyte layer, and anode layer obtained above were stacked and press-bonded to produce an electrode laminate. A test solid-state battery cell was fabricated using the electrode laminate thus fabricated.

[0062] [Cell charge / discharge test] Using the test solid-state battery cells obtained as described above, a charge-discharge test was carried out in a voltage range of 2.65 to 4.3 V. A test cell in which the second charge-discharge capacity was 95% or more of the first charge-discharge capacity was rated as pass "2". A test cell in which the second charge-discharge capacity was less than 95% was rated as fail "1". The results are shown in Table 1.

[0063] [Voltage measurement] The test solid-state battery cell obtained as described above was fully charged and then left for 24 hours, and the voltage was measured after 20 hours and after 24 hours. A voltage difference (ΔV / h) of 1.5 mV or less was rated as pass "2", and a voltage difference of more than 1.5 mV was rated as fail "1". The results are shown in Table 1.

[0064] [Table 1] [Explanation of symbols]

[0065] 1 solid state battery 2. Negative electrode layer 3 Positive electrode layer 4 Solid electrolyte layer 41 Third solid electrolyte layer 42 Second solid electrolyte layer 43 First solid electrolyte layer

Claims

1. A solid-state battery having a structure in which an anode layer, a solid electrolyte layer, and a cathode layer are stacked in this order, the solid electrolyte layer includes a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer, which are arranged in this order from the positive electrode layer side; the thickness of the first solid electrolyte layer is 3 to 8.5 μm; the second solid electrolyte layer has a thickness of 10 to 20 μm; the thickness of the third solid electrolyte layer is 3 to 8.5 μm; The solid-state battery, wherein the total thickness of the solid electrolyte layer is 17 to 26 μm.

2. 2. The solid state battery according to claim 1, wherein a binder content (vol %) in the third solid electrolyte layer is equal to or less than a binder content (vol %) in the first solid electrolyte layer and is equal to or less than a binder content (vol %) in the second solid electrolyte layer.

3. 3. The solid state battery according to claim 2, wherein the content of the binder in the first solid electrolyte layer is 5% by volume or more and 25% by volume or less.

4. The solid state battery according to claim 2 or 3, wherein the first solid electrolyte layer contains a fluorine-based binder.

5. 3. The solid state battery according to claim 2, wherein the content of the binder in the second solid electrolyte layer is 5% by volume or more and 25% by volume or less.

6. The solid state battery according to claim 5 , wherein the second solid electrolyte layer contains at least one of a fluorine-based binder and a styrene-based binder.

7. 3. The solid state battery according to claim 2, wherein the content of the binder in the third solid electrolyte layer is 2.7% by volume or more and 10% by volume or less.

8. 2. The solid-state battery according to claim 1, wherein at least one of the first solid electrolyte layer, the second solid electrolyte layer, and the third solid electrolyte layer contains a support.

9. 2. The solid state battery according to claim 1, wherein the particle diameter (D50) of the solid electrolyte layer particles contained in the solid electrolyte layer is 0.1 μm or more and 3 μm or less.

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