Solid secondary battery and manufacturing method for coating solution for forming intermediate layer in the same

Abstract

To provide a solid secondary battery with improved output characteristics and a coating solution for forming an intermediate layer that can improve the output characteristics of the same.SOLUTION: The solid secondary battery has a positive electrode layer, a negative electrode layer, a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer. The intermediate layer includes carbon, silicon particles, and a binder, and the composite elastic modulus of the intermediate layer is 200 MPa or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid secondary battery and a method for producing a coating liquid for forming an intermediate layer of the 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 due to their superior safety as a result of the solid electrolyte's non-flammability and their higher energy density.

[0003] A solid-state secondary battery is a battery in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer. A known example of a solid-state battery is a solid-state lithium secondary battery that uses lithium ions as a charge transfer medium. In this solid-state lithium secondary battery, in order to suppress uneven deposition of lithium at the interface of the negative electrode layer, it has been investigated to dispose an intermediate layer containing carbon and metal nanoparticles between the negative electrode layer and the solid electrolyte layer (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023-189892 Summary of the Invention [Problem to be solved by the invention]

[0005] In secondary battery technology, improving output characteristics that enable discharge at high current densities is one of the challenges. To improve the output characteristics of solid-state secondary batteries, an effective approach is to place an intermediate layer with high charge transfer medium conductivity between the anode layer and the solid electrolyte layer. However, solid-state lithium secondary batteries have been studied that use lithium or a lithium alloy as the material for the anode active material layer of the anode layer. During charging, lithium ions are deposited on the surface of the anode active material layer to form a lithium metal layer, and during discharging, the lithium ions released from the lithium metal layer are absorbed by the cathode. In solid-state lithium secondary batteries with such a configuration, changes in the thickness of the anode layer due to charging and discharging can reduce the adhesion between the anode layer and the intermediate layer, thereby degrading the output characteristics of the solid-state secondary battery.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a solid secondary battery having improved output characteristics and a coating liquid for forming an intermediate layer that can improve the output characteristics of the solid secondary battery, which in turn contributes to energy efficiency. [Means for solving the problem]

[0007] The present inventors have found that, in order to solve the above problems, it is effective to form an intermediate layer from a composition containing carbon, silicon particles, and a binder so that the composite elastic modulus is 200 MPa or less, and have completed the present invention. Accordingly, the present invention provides the following.

[0008] (1) A solid secondary battery comprising: a positive electrode layer; a negative electrode layer; a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; and an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer, wherein the intermediate layer contains carbon, silicon particles, and a binder, and the intermediate layer has a composite elastic modulus of 200 MPa or less.

[0009] In the solid-state secondary battery (1), the intermediate layer contains carbon, silicon particles, and a binder, which increases the conductivity of the charge carrier transport medium between the solid electrolyte and the negative electrode. Furthermore, the intermediate layer has a low composite elastic modulus of 200 MPa or less, making it easily deformable. Therefore, even if the negative electrode active material layer contains lithium or a lithium alloy and the thickness of the negative electrode layer changes during charging and discharging, the negative electrode layer and the intermediate layer remain in a stable, tightly adhered state. This improves the output characteristics of the solid-state secondary battery.

[0010] (2) The solid secondary battery according to (1), wherein the carbon content is in the range of 50% by mass or more and 90% by mass or less, the silicon particle content is in the range of 7% by mass or more and 45% by mass or less, and the binder content is in the range of 3% by mass or more and 8% by mass or less, relative to the total amount of the carbon, the silicon particles, and the binder.

[0011] According to the solid secondary battery (2), since the contents of the carbon and silicon particles and binder in the intermediate layer are within the above ranges, the conductivity of the charge carrier transport medium in the intermediate layer is high and the composite elastic modulus is low.

[0012] (3) The solid secondary battery according to (2), wherein the content of the binder is in the range of 3% by mass to 4% by mass.

[0013] According to the solid secondary battery of (3), since the binder content is within the above range, the conductivity of the charge carrier transport medium in the intermediate layer becomes higher.

[0014] (4) The solid secondary battery according to (2) or (3), wherein the ratio of the content of the silicon particles to the content of the carbon is in the range of 0.30 to 0.35.

[0015] In the solid secondary battery of (4), the ratio of the content of silicon particles to the content of carbon is within the above range, so that the conductivity of the charge carrier transport medium in the intermediate layer is further increased.

[0016] (5) The carbon has a BET specific surface area of ​​50 m 2 / g or more 80m2 The solid secondary battery according to any one of (1) to (4), wherein the carbon black has a densitometric value in the range of 0.1 to 0.25 wt %.

[0017] According to the solid secondary battery of (5), by binding high-surface-area carbon black and silicon particles with a binder, the conductivity of the charge carrier transport medium in the intermediate layer becomes higher and the composite elastic modulus becomes lower.

[0018] (6) The solid secondary battery according to any one of (1) to (5), wherein the intermediate layer has a composite elastic modulus of 80 MPa or less.

[0019] According to the solid secondary battery of (6), the composite elastic modulus is low at 80 MPa or less, and the shape is deformable, so that even if the negative electrode layer is deformed, the negative electrode layer and the intermediate layer remain in a stable state of even higher adhesion.

[0020] (7) A method for producing a coating liquid for forming an intermediate layer of a solid secondary battery, comprising mixing a silicon particle dispersion obtained by stirring silicon particles in a solvent at a stirring speed of 20 m / sec or more and 40 m / sec or less for 60 seconds or more with carbon and a binder.

[0021] According to the method for producing a coating solution for forming an intermediate layer of a solid secondary battery described in (7), a coating solution in which silicon particles are dispersed as primary particles or fine aggregated particles close to primary particles can be obtained industrially advantageously, and by using this coating solution, an intermediate layer can be formed that has high conductivity of the charge carrier transport medium, a low composite elastic modulus, and is easily deformable. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a solid state secondary battery with improved output characteristics and a coating liquid for forming an intermediate layer that can improve the output characteristics of a solid state secondary battery. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic cross-sectional view of a solid secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] Fig. 1 is a schematic cross-sectional view of a solid secondary battery according to one embodiment of the present invention. As shown in Fig. 1, the solid secondary battery 1 according to this embodiment includes a positive electrode layer 10, a negative electrode layer 20, a solid electrolyte layer 30 disposed between the positive electrode layer 10 and the negative electrode layer 20, and an intermediate layer 40 disposed between the negative electrode layer 20 and the solid electrolyte layer 30.

[0026] The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 laminated on the surface of the positive electrode current collector 11. Examples of materials for the positive electrode current collector 11 include aluminum, aluminum alloy, stainless steel, nickel, iron, and titanium.

[0027] The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material is a lithium compound that releases lithium ions during discharge and absorbs lithium ions during charge. Examples of the lithium compound that can be used include layered active materials, spinel-type active materials, and olivine-type active materials. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium-nickel-manganese cobalt oxide (NMC: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-yExamples of such an element-substituted Li-Mn spinel are 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). The positive electrode active material layer 12 may further contain a solid electrolyte, a conductive additive, and a binder.

[0028] The negative electrode layer 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 laminated on the surface of the negative electrode current collector 21. Examples of materials for the negative electrode current collector 21 include copper, copper alloy, nickel, and stainless steel.

[0029] The negative electrode active material contained in the negative electrode active material layer 22 can be appropriately selected from known materials capable of absorbing lithium ions during charging and releasing lithium ions during discharging. Examples of the negative electrode active material include metals such as metallic lithium and lithium alloys, lithium transition metal oxides such as lithium titanate, transition metal oxides such as TiO2, Nb2O3, and WO3, Si, SiO2, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon, and hard carbon. Examples of metals contained in lithium alloys include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The negative electrode active material layer 22 may further contain a solid electrolyte, a conductive additive, and a binder.

[0030] The solid electrolyte layer 30 includes a solid electrolyte. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Examples of sulfide solid electrolytes include Li2S-P2S5 and Li2S-P2S5-LiI. The sulfide solid electrolyte may have an argyrodite-type crystal structure. Examples of oxide solid electrolytes include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides. Examples of NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 Al0.5 Ti 1.5 Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., LiLaZrO 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0031] The intermediate layer 40 includes carbon, silicon particles, and a binder. The intermediate layer 40 may be formed from only three components: carbon, silicon particles, and a binder. The carbon content relative to the total amount of carbon, silicon particles, and a binder may be, for example, in the range of 50% by mass to 90% by mass, or in the range of 60% by mass to 80% by mass. The silicon particle content may be, for example, in the range of 7% by mass to 45% by mass, or in the range of 10% by mass to 40% by mass. The binder content may be in the range of 3% by mass to 8% by mass, or in the range of 3% by mass to 4% by mass. The ratio of the silicon particle content to the carbon content (silicon particles / carbon) may be in the range of 0.30 to 0.35.

[0032] The intermediate layer 40 has a composite elastic modulus of 200 MPa or less. The intermediate layer 40 has a low composite elastic modulus and is easily deformed. For example, even if the thickness of the negative electrode layer 20 changes, the intermediate layer 40 deforms in accordance with the change. This allows the intermediate layer 40 and the negative electrode layer 20 to be in a stable state of close contact. This improves the output characteristics of the solid secondary battery 1 of this embodiment. The composite elastic modulus of the intermediate layer 40 may be 150 MPa or less, 100 MPa or less, or 80 MPa or less. From the viewpoint of maintaining the shape of the intermediate layer 40, the composite elastic modulus of the intermediate layer 40 may be 10 MPa or more.

[0033] The carbon contained in the intermediate layer 40 may be amorphous carbon. 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 easily graphitized carbon (soft carbon), or may be difficult to graphitize carbon (hard carbon), CNT (carbon nanotube), fullerene, or graphene.

[0034] The carbon contained in the intermediate layer 40 is preferably carbon black, and has a BET specific surface area of, for example, 50 m 2 / g or more 80m 2 / g or less. By binding high-specific surface area carbon black and silicon particles with a binder, it is possible to obtain an intermediate layer 40 with high lithium ion conductivity and a low composite elastic modulus.

[0035] Examples of binders contained in the intermediate layer 40 include acrylic acid polymers, cellulose polymers, styrene polymers, vinyl acetate polymers, urethane polymers, fluoroethylene polymers, and PVDF (polyvinylidene fluoride) polymers.

[0036] The intermediate layer 40 can be formed by, for example, a coating method, in which a coating liquid for forming the intermediate layer containing the material of the intermediate layer 40 is applied and dried.

[0037] The coating solution for forming the intermediate layer can be produced, for example, by mixing a silicon particle dispersion obtained by stirring silicon particles in a solvent at a stirring speed of 20 m / s to 40 m / s for 60 seconds or more with carbon and a binder. The silicon particle dispersion may contain silicon particles dispersed in the form of primary particles or fine aggregated particles similar to primary particles. A high-speed stirrer can be used as a stirring device for dispersing the silicon particles.

[0038] The solid secondary battery 1 is manufactured by stacking a positive electrode layer 10, a solid electrolyte layer 30, an intermediate layer 40, and a negative electrode layer 20 in the order shown in Fig. 1. After the stacking, the layers may be optionally pressed together to form a single unit. Furthermore, a plurality of the structural units shown in Fig. 1 may be stacked as unit batteries.

[0039] In the solid secondary battery 1 of this embodiment configured as described above, the intermediate layer 40 contains carbon, silicon particles, and a binder, which increases the conductivity of the charge carrier transfer medium between the solid electrolyte and the negative electrode. Furthermore, the intermediate layer 40 has a low composite elastic modulus of 200 MPa or less, making it easily deformable. Therefore, even if the negative electrode active material layer 22 contains lithium or a lithium alloy and the thickness of the negative electrode layer 20 changes during charge and discharge, the negative electrode layer 20 and the intermediate layer 40 remain in a stable, tightly adhered state. This improves the output characteristics of the solid secondary battery 1.

[0040] According to the method for producing a coating solution for forming an intermediate layer of a solid secondary battery of this embodiment, a coating solution in which silicon particles are dispersed as primary particles or fine aggregated particles similar to primary particles can be obtained industrially advantageously, and by using this coating solution, an intermediate layer 40 can be formed that has high conductivity of the charge carrier transport medium, a low composite elastic modulus, and is easily deformed. [Example]

[0041] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0042] Example 1 [Preparation of coating liquid for forming intermediate layer] Five parts by mass of silicon particles were added to NMP (N-methyl-2-pyrrolidone) and stirred using a high-speed mixer (Filmix, manufactured by Primix Corporation) at a stirring speed of 30 m / s and a stirring time of 150 seconds to prepare a silicon particle dispersion. Next, carbon A (BET specific surface area 62 m) was added to the silicon particle dispersion. 271 parts by mass of carbon black (1 / g) and 5 parts by mass of a PVDF binder were added, and the mixture was stirred and mixed using a high-speed stirrer (Filmix, manufactured by Primix Corporation). In this way, a coating liquid for forming an intermediate layer was prepared.

[0043] [Fabrication of Intermediate Layer / Pellet-shaped Solid Electrolyte Substrate / Intermediate Layer Laminate] The argyrodite-type sulfide solid electrolyte was pressure-molded to prepare a pellet-shaped solid electrolyte substrate with flat upper and lower surfaces. An intermediate layer coating liquid was applied to each of the upper and lower surfaces of the obtained solid electrolyte substrate, followed by drying to prepare an intermediate layer / pellet-shaped solid electrolyte substrate / intermediate layer laminate.

[0044] [evaluation] (Measurement of composite elastic modulus) The composite elastic modulus of one of the resulting intermediate layers was measured, and the results are shown in Table 1 below.

[0045] (Measurement of limiting current density) A laminated electrode was prepared by laminating a metallic lithium foil on one surface of a copper foil. The metallic lithium foil of the laminated electrode was then placed on each surface of the intermediate layer of the intermediate layer / solid electrolyte layer / intermediate layer laminate to prepare an evaluation cell consisting of laminated electrode / intermediate layer / pellet-shaped solid electrolyte substrate / intermediate layer / laminated electrode. The limiting current density of the obtained evaluation cell was measured. The results are shown in Table 1 below.

[0046] <Examples 2 to 4, Comparative Example 1>

[0047] The coating solution for forming an intermediate layer was prepared in the same manner as in Example 1, except that the type of carbon, the amounts of carbon, silicon particles, and binder blended, and the dispersion conditions for the silicon particles were changed to those shown in Table 1 below. Carbon A had a BET specific surface area of ​​62 m 2 / g of carbon black, and Carbon B has a BET specific surface area of ​​39 m 2 / g of carbon black. Using the obtained coating liquid for forming an intermediate layer, an intermediate layer / pellet-shaped solid electrolyte substrate / intermediate layer laminate was produced in the same manner as in Example 1, and the composite elastic modulus and limiting current density were measured. The results are shown in Table 1 below.

[0048] [Table 1]

[0049] The results of Examples 1 to 4 shown in Table 1 demonstrate that, according to the present invention, an intermediate layer having a composite modulus of elasticity of 200 MPa or less can be obtained by using a coating solution for forming an intermediate layer obtained by mixing a silicon particle dispersion in which silicon particles are dispersed with carbon and a binder. Furthermore, the evaluation cells using such intermediate layers exhibit a high limiting current density, demonstrating that the output characteristics of solid secondary batteries using such intermediate layers are improved. On the other hand, the evaluation cells using intermediate layers made from the silicon particle dispersion of Comparative Example 1, in which the silicon particles were dispersed for a short time, exhibited a low limiting current density. [Explanation of symbols]

[0050] 1 Solid state secondary battery 10 Positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 20 negative electrode layer 21 Negative electrode current collector 22 Negative electrode active material layer 30 Solid electrolyte layer 40 Middle Class

Claims

1. a positive electrode layer, a negative electrode layer, a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer; the intermediate layer contains carbon, silicon particles, and a binder; A solid secondary battery, wherein the intermediate layer has a composite elastic modulus of 200 MPa or less.

2. 2. The solid secondary battery according to claim 1, wherein the carbon content is in the range of 50% by mass or more and 90% by mass or less, the silicon particle content is in the range of 7% by mass or more and 45% by mass or less, and the binder content is in the range of 3% by mass or more and 8% by mass or less, relative to the total amount of the carbon, the silicon particles, and the binder.

3. The solid secondary battery according to claim 2 , wherein the content of the binder is in the range of 3% by mass to 4% by mass.

4. 4. The solid secondary battery according to claim 2, wherein the ratio of the content of said silicon particles to the content of said carbon is in the range of 0.30 to 0.

35.

5. The carbon has a BET specific surface area of ​​50 m ２ / g or more 80m ２ The solid secondary battery according to claim 1 or 2, wherein the carbon black has a surface area of ​​1 / g or less.

6. The solid secondary battery according to claim 1 or 2, wherein the intermediate layer has a composite elastic modulus of 80 MPa or less.

7. A method for producing a coating liquid for forming an intermediate layer of a solid secondary battery, comprising: stirring silicon particles in a solvent at a stirring speed of 20 m / sec or more and 40 m / sec or less for 60 seconds or more to obtain a silicon particle dispersion; and mixing the silicon particle dispersion with carbon and a binder.

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