All-solid-state batteries

Abstract

The present invention provides a means for enabling a lithium deposition-type all-solid-state battery to be more reliably prevented from short circuit. The present invention provides an all-solid-state battery which is provided with a power generation element that comprises: a positive electrode having a positive electrode active material layer which contains a positive electrode active material; a negative electrode having a negative electrode collector on which lithium metal is deposited during the charging of the battery; a solid electrolyte layer which is interposed between the positive electrode and the negative electrode, and contains a solid electrolyte; and a negative electrode intermediate layer which is arranged adjacent to the negative electrode collector-side surface of the solid electrolyte layer, and contains at least one material that is selected from the group consisting of metal materials that can be alloyed with lithium and carbon materials that can absorb lithium ions. With respect to this all-solid-state battery, a surface of the negative electrode intermediate layer, the surface being adjacent to the solid electrolyte layer, has a surface roughness Rz of 2.5 µm or less.

Description

[Technical Field]

[0001] This invention relates to an all-solid-state battery. [Background technology]

[0002] In recent years, research and development on all-solid-state batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of ion conduction in a solid state. Therefore, all-solid-state batteries have the advantage of not, in principle, occurring in the way that conventional liquid-based batteries using non-aqueous electrolytes are caused by flammable organic electrolytes.

[0003] In all-solid-state batteries, a problem exists in which lithium dendrites deposited at the negative electrode penetrate the solid electrolyte layer and reach the positive electrode, causing a short circuit. Various technologies have been proposed to address this issue. For example, in International Publication No. 2018 / 186442, the porosity of the solid electrolyte layer is set to 10% or less, and the sum of the surface roughness Rz1 of the positive electrode layer and the surface roughness Rz2 of the negative electrode layer is set to 25 μm or less, thereby attempting to solve the above problem. [Overview of the Initiative]

[0004] Conventionally, a type of all-solid-state battery known is the so-called lithium-deposit type, in which lithium metal is deposited on the negative electrode current collector during the charging process. However, when the present inventors applied the technology described in International Publication No. 2018 / 186442 to a lithium-deposit type all-solid-state battery, it was found that short circuits could not be prevented in some cases.

[0005] Therefore, the present invention aims to provide a means that can more reliably suppress short circuits in lithium deposition type all-solid-state batteries.

[0006] The inventors diligently conducted research to solve the above problems. As a result, they discovered that the above problems can be solved by providing a negative electrode intermediate layer containing a metal that can alloy with lithium or a carbon material capable of adsorbing lithium ions between the negative electrode current collector and the solid electrolyte layer in an all-solid-state battery equipped with a lithium deposition type power generation element, and by controlling the surface roughness Rz of the surface of the negative electrode intermediate layer in contact with the solid electrolyte layer to a specific range, thus completing the present invention.

[0007] In other words, one embodiment of the present invention relates to an all-solid-state battery comprising a power generation element having a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging, a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and a negative electrode intermediate layer located adjacent to the negative electrode current collector side of the solid electrolyte layer and containing at least one selected from the group consisting of a metallic material that can alloy with lithium and a carbon material that can absorb lithium ions. In this all-solid-state battery, the surface roughness Rz of the surface of the negative electrode intermediate layer adjacent to the solid electrolyte layer is 2.5 μm or less. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (stacked secondary battery), which is one embodiment of the present invention. [Modes for carrying out the invention]

[0009] One embodiment of the present invention relates to an all-solid-state battery comprising a power generation element having a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging, a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and a negative electrode intermediate layer located adjacent to the negative electrode current collector side of the solid electrolyte layer and containing at least one selected from the group consisting of a metallic material that can alloy with lithium and a carbon material that can absorb lithium ions. In this all-solid-state battery, the surface roughness Rz of the surface of the negative electrode intermediate layer adjacent to the solid electrolyte layer is 2.5 μm or less. According to the all-solid-state battery of this embodiment, short circuits can be suppressed more reliably in a lithium deposition type all-solid-state battery.

[0010] Embodiments of the present invention will be described below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery"), which is one embodiment of the present invention. Figure 1 shows a cross-section of the stacked secondary battery during charging. The stacked secondary battery 10a shown in Figure 1 has a structure in which a roughly rectangular power generation element 21, where the charge and discharge reaction actually proceeds, is sealed inside a laminate film 29, which is the battery casing. Here, the power generation element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are stacked. A negative electrode intermediate layer 14 is arranged adjacent to the surface of the negative electrode active material layer 13 that faces the solid electrolyte layer 17. The positive electrode has a structure in which a positive electrode active material layer 15 is arranged on the surface of the positive electrode current collector 11''. The negative electrode, solid electrolyte layer, and positive electrode are stacked in this order, with the negative electrode intermediate layer 14 and the positive electrode active material layer 15 facing each other via a solid electrolyte layer 17. As a result, adjacent negative electrodes, solid electrolyte layers, and positive electrodes constitute one single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel. The negative electrode current collector 11' and the positive electrode current collector 11'' are fitted with a negative electrode current collector plate 25 and a positive electrode current collector plate 27, respectively, which are electrically connected to the respective electrodes (negative electrode and positive electrode), and have a structure in which they are led out to the outside of the laminate film 29 by being sandwiched between the edges of the laminate film 29. The stacked secondary battery 10a is subjected to restraining pressure in the stacking direction of the power generation element 21 by a pressurizing member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

[0012] The main components of the all-solid-state battery according to this embodiment will be described below.

[0013] [Current collector] Current collectors (negative electrode current collector, positive electrode current collector) have the function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials that make up the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but one example is 10 to 100 μm.

[0014] [Negative electrode active material layer] The all-solid-state battery according to this embodiment is a so-called lithium-depositing type, in which lithium metal is deposited on the negative electrode current collector during the charging process. The layer of lithium metal deposited on the negative electrode current collector during this charging process is the negative electrode active material layer of the all-solid-state battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharge process progresses. The negative electrode active material layer does not need to be present during complete discharge, but in some cases, a negative electrode active material layer consisting of a certain amount of lithium metal may be present during complete discharge. Furthermore, there are no particular restrictions on the thickness of the negative electrode active material layer (lithium metal layer) during complete charge, but it is usually 0.1 to 1000 μm.

[0015] [Negative electrode intermediate layer] The negative electrode intermediate layer is a layer adjacent to the negative electrode current collector side of the solid electrolyte layer, and contains at least one material selected from the group consisting of a metallic material that can alloy with lithium and a carbon material that can absorb lithium ions. Since the metallic material and the carbon material have high electronic conductivity, the negative electrode intermediate layer as a whole is conductive. The volume resistivity of the negative electrode intermediate layer is not particularly limited, but is preferably 10 2 The resistivity is Ω·cm or less, and more preferably 10Ω·cm or less. In this specification, the volume resistivity of the negative electrode intermediate layer is the value measured using an electrode resistance measurement system (HIOKI E.E. CORPORATION, product name: RM2610).

[0016] The negative electrode intermediate layer preferably contains at least one material selected from the group consisting of metallic materials that can be alloyed with lithium. By containing a metallic material that can be alloyed with lithium in the negative electrode intermediate layer, the lithium metal can be deposited more uniformly on the surface of the current collector. Specific examples of metallic materials that can be alloyed with lithium include, for example, indium (In), aluminum (Al), silicon (Si), tin (Sn), magnesium (Mg), gold (Au), silver (Ag), zinc (Zn), nickel (Ni), and alloys containing at least one of these. In particular, the metallic material preferably contains at least one material selected from the group consisting of In, Al, Si, Sn, Mg, Au, Ag, Zn, and Ni, more preferably at least one material selected from the group consisting of Ag, Mg, Zn, Ni, and Al, even more preferably at least one material selected from the group consisting of Ag, Mg, and Zn, and particularly preferably contains Ag.

[0017] The negative electrode intermediate layer preferably contains, instead of containing at least one material selected from the group consisting of metallic materials that can alloy with lithium, or, in addition to containing at least one material selected from the group consisting of metallic materials that can alloy with lithium, it preferably contains at least one material selected from the group consisting of carbon materials that can absorb lithium ions. By containing a carbon material that can absorb lithium ions in the negative electrode intermediate layer, the deposition and growth of lithium dendrites can be suppressed. Specific examples of carbon materials that can absorb lithium ions include carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNTs), graphite, hard carbon, etc. Among these, it is preferable that the carbon material contains at least one material selected from the group consisting of carbon black, and more preferably at least one material selected from the group consisting of acetylene black, Ketjenblack®, furnace black, channel black, and thermal lamp black.

[0018] In one preferred embodiment, the negative electrode intermediate layer comprises a mixture of at least one metal particle containing a lithium-alloyable metallic material and at least one carbon particle containing a lithium-ion-adsorbable carbon material. By constructing the negative electrode intermediate layer using a mixture of metal and carbon particles, short circuits can be further suppressed.

[0019] The average particle diameter of the metal particles is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and particularly preferably 100 nm or less. There is no particular lower limit to the average particle diameter of the metal particles, but it is preferably 20 nm or more. The average particle diameter of the carbon particles is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. There is no particular lower limit to the average particle diameter of the carbon particles, but it is preferably 10 nm or more. When the average particle diameters of the metal particles and carbon particles are within the above ranges, it becomes easy to control the surface roughness Rz of the surface adjacent to the solid electrolyte layer in the negative electrode intermediate layer (hereinafter also simply referred to as "surface roughness Rz of the negative electrode intermediate layer" or "surface roughness Rz") within a predetermined range. In this specification, the average particle diameter refers to the 50% cumulative diameter (D50) of the particle diameter observed within several to tens of fields of view when a cross-section of the layer containing the particle is observed using a scanning electron microscope (SEM) (the maximum distance between any two points on the contour line of the observed particle).

[0020] The mass ratio (metal particles:carbon particles) of metal particles to carbon particles in the mixture is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1. The volume ratio (metal particles:carbon particles) is preferably 1:99 to 30:70, and more preferably 5:95 to 25:75. When the mixing ratio (mass ratio or volume ratio) of metal particles to carbon particles is within the above range, short circuits can be further suppressed.

[0021] When the negative electrode intermediate layer is composed of a mixture of metal particles and carbon particles, it is preferable that the negative electrode intermediate layer further contains a binder. The type of the binder is not particularly limited, and those known in the art can be appropriately adopted. As an example of the binder, polyvinylidene fluoride (PVDF), a compound in which a hydrogen atom of PVDF is substituted with another halogen element, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) can be mentioned. Among them, from the viewpoint of controlling the surface roughness Rz and the thickness d of the negative electrode intermediate layer described later within a predetermined range, it is preferable that the binder contains polyvinylidene fluoride (PVDF), and it is more preferable that it is polyvinylidene fluoride (PVDF).

[0022] When the negative electrode intermediate layer contains a binder, the content of the binder is preferably more than 10 parts by mass, more preferably 12 parts by mass or more, based on 100 parts by mass of the mixture of metal particles and carbon particles. When the content of the binder is within the above range, it becomes easy to control the surface roughness Rz of the surface adjacent to the solid electrolyte layer in the negative electrode intermediate layer described later (hereinafter, also simply referred to as "the surface roughness Rz of the negative electrode intermediate layer" or "the surface roughness Rz") within a predetermined range. The upper limit of the content of the binder is not particularly limited, but from the viewpoint of suppressing the increase in resistance, it is preferably 20 parts by mass or less.

[0023] The ratio of the total mass of the metal material, the carbon material, and the binder to the total mass of the negative electrode intermediate layer is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 98% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass.

[0024] The all-solid-state battery according to this embodiment is characterized in that the surface roughness Rz of the surface adjacent to the solid electrolyte layer in the negative electrode intermediate layer is 2.5 μm or less. If the surface roughness Rz exceeds 2.5 μm, the deposition and growth of lithium dendrites cannot be sufficiently suppressed, and a short circuit may occur. Also, if the surface roughness Rz exceeds 2.5 μm, the solid electrolyte contained in the solid electrolyte layer may penetrate close to the negative electrode active material layer (metallic lithium deposited on the negative electrode current collector), and the solid electrolyte may be decomposed by the deposited metallic lithium and deteriorate. Furthermore, if the surface roughness Rz exceeds 2.5 μm, the strength of the negative electrode intermediate layer may decrease and cracking may occur. From a similar viewpoint, the surface roughness Rz is more preferably 2.0 μm or less, and even more preferably 1.0 μm or less. On the other hand, from the viewpoint of ensuring contact area with the solid electrolyte layer and preventing delamination between the negative electrode intermediate layer and the solid electrolyte layer, the surface roughness Rz is preferably 0.5 μm or more. In other words, according to a preferred embodiment of the present invention, the surface roughness Rz is 0.5 μm or more and 2.0 μm or less. According to a more preferred embodiment of the present invention, the surface roughness Rz is 0.5 μm or more and 1.0 μm or less. In this specification, the surface roughness Rz (maximum height roughness) is the value measured by the method described in the examples below.

[0025] The method for controlling the surface roughness Rz of the negative electrode intermediate layer within a predetermined range is not particularly limited, but in the manufacture of an all-solid-state battery, a two-stage pressing process may be employed, in which the solid electrolyte layer is pressed at a predetermined pressure, and then the solid electrolyte layer and the negative electrode intermediate layer are laminated and pressed at a predetermined pressure. More specifically, a solid electrolyte slurry containing a solid electrolyte is coated onto the surface of a support (e.g., metal foil), and the coating is dried to obtain a solid electrolyte layer formed on the surface of the support. Then, the solid electrolyte layer formed on the surface of the support is pressed at a predetermined pressure (first pressing step). This arranges the solid electrolyte particles on the surface of the solid electrolyte layer adjacent to the support and reduces unevenness. After peeling off the support used to form the solid electrolyte layer, pressing may be performed using another metal foil or the like. Alternatively, before the first pressing step, the exposed surface of a separately manufactured positive electrode active material layer may be placed on the exposed surface of the solid electrolyte layer, and the first pressing step may be performed with the solid electrolyte layer and the positive electrode active material layer stacked together. On the other hand, a negative electrode active material slurry containing the materials included in the negative electrode intermediate layer (metal particles and / or carbon particles, and optionally added binders) is coated onto the surface of a negative electrode current collector (e.g., stainless steel foil), and the coating is dried to obtain a negative electrode intermediate layer formed on the surface of the negative electrode current collector. Then, the support (metal foil) used in the first pressing step is peeled off to expose the solid electrolyte layer, and the exposed surface of the solid electrolyte layer and the exposed surface of the negative electrode intermediate layer are placed on top of each other and pressed at a predetermined pressure (second pressing step). This adjusts the surface roughness of the surface of the negative electrode intermediate layer adjacent to the solid electrolyte layer. Cold isostatic pressing (CIP) is preferred for the pressing in the first and second pressing steps, but is not limited thereto.

[0026] In the above manufacturing method, it is preferable not to apply a press treatment to only the negative electrode intermediate layer before the second pressing step. This is because if only the negative electrode intermediate layer is pressed, even if the negative electrode intermediate layer and the solid electrolyte layer are stacked and pressed together in the subsequent second pressing step, the negative electrode intermediate layer and the solid electrolyte layer will not adhere well to each other, and delamination at the interface may occur.

[0027] The pressing pressure in the first pressing step and the pressing pressure in the second pressing step vary depending on the materials contained in the solid electrolyte layer and the negative electrode intermediate layer, and can be appropriately set by those skilled in the art. For example, the pressing pressure in the first pressing step is preferably 300 MPa to 1000 MPa, more preferably 300 MPa to 800 MPa, and even more preferably 500 MPa to 700 MPa. The pressing pressure in the second pressing step is preferably 100 MPa to 700 MPa, more preferably 300 MPa to 500 MPa, and even more preferably 400 MPa to 500 MPa. In particular, if the pressing pressure in the first pressing step is too low (around 100 MPa), the unevenness caused by the solid electrolyte particles will increase, and the surface roughness Rz of the negative electrode intermediate layer may exceed 2.5 μm.

[0028] The ratio of the press pressure of the first pressing step to the press pressure of the second pressing step (press pressure of the first pressing step / press pressure of the second pressing step) is preferably 0.5 to 10, more preferably 1 to 5, even more preferably 1 to 2, and particularly preferably 1.25 to 1.75. When this ratio is within the above range, the surface roughness Rz of the negative electrode intermediate layer can be controlled to 2.5 μm or less, and cracking of the negative electrode intermediate layer can be prevented.

[0029] From the viewpoint of improving the energy density of the all-solid-state battery, a smaller thickness d of the negative electrode intermediate layer is preferable. Specifically, the thickness d of the negative electrode intermediate layer is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 4.5 μm or less. The lower limit of the thickness d of the negative electrode intermediate layer is not particularly limited, but from the viewpoint of ensuring the strength of the negative electrode intermediate layer, it is preferably 3 μm or more, and more preferably 3.5 μm or more. In this specification, the thickness d of the negative electrode intermediate layer is the value obtained by the method described in the examples below.

[0030] The ratio of surface roughness Rz to the thickness d of the negative electrode intermediate layer (percentage: (Rz / d) × 100 (%)) is preferably 1% to 65%, more preferably 5% to 50%, even more preferably 10% to 30%, and particularly preferably 12.5% ​​to 25.0%. When this ratio is within the above range, short circuits can be further suppressed.

[0031] [Solid electrolyte layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as the main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any known in the art can be used as appropriate. Examples include LPS (Li2S-P2S5), Li6PS5X (where X is Cl, Br, or I), and Li7P3S 11 Li 3.2 P 0.96 Examples of sulfide solid electrolytes include s and Li3PS4. These sulfide solid electrolytes are preferred because they have excellent lithium-ion conductivity and a low bulk modulus, which allows them to follow the volume changes of the electrode active material during charging and discharging.

[0032] The ionic conductivity of a sulfide solid electrolyte at room temperature (25°C) (for example, the Li ion conductivity) is, for example, 1 × 10⁻⁶. -5 Preferably, S / cm or more, 1 × 10 -4 A value of S / cm or higher is more preferable. The ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

[0033] Examples of solid electrolyte shapes include spherical, ellipsoidal, and other particulate forms, as well as thin films. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 0.01 μm to 40 μm, more preferably 0.1 μm to 20 μm, and even more preferably 0.5 μm to 10 μm.

[0034] The content of the solid electrolyte in the solid electrolyte layer is preferably 50 to 100% by mass, more preferably 90 to 100% by mass.

[0035] In addition to the solid electrolyte, the solid electrolyte layer may further contain a binder.

[0036] The thickness of the solid electrolyte layer varies depending on the configuration of the target all-solid-state battery, but is usually 0.1 to 1000 μm, preferably 10 to 40 μm.

[0037] [Positive electrode active material layer] The positive electrode active material layer essentially contains a positive electrode active material and may contain a binder and a conductive aid as required.

[0038] The type of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but includes layered rock salt type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, Li(Ni-Mn-Co)O2, spinel type active materials such as LiMn2O4, LiNi 0.5 Mn 1.5 O4, olivine type active materials such as LiFePO4, LiMnPO4, Si-containing active materials such as Li2FeSiO4, Li2MnSiO4, etc. In addition, examples of oxide active materials other than the above include, for example, Li4Ti5O 12 Among them, Li(Ni-Mn-Co)O2 and those in which a part of these transition metals is substituted by other elements (hereinafter, also simply referred to as "NMC composite oxide") are preferably used as the positive electrode active material.

[0039] Also, it is one of the preferred embodiments that a sulfur-based positive electrode active material is used. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material that can utilize the oxidation-reduction reaction of sulfur to release lithium ions during charging and occlude lithium ions during discharging may be used.

[0040] The content of the positive electrode active material in the positive electrode active material layer is preferably 50 to 100% by mass, more preferably 55 to 95% by mass, and even more preferably 60 to 90% by mass.

[0041] The thickness of the positive electrode active material layer varies depending on the configuration of the intended all-solid-state battery, but is usually 0.1 to 1000 μm, and preferably 10 to 40 μm.

[0042] Although one embodiment of the all-solid-state battery of the present invention has been described above, the present invention is not limited to the configuration described in the above-mentioned embodiment, and can be modified as appropriate based on the description of the claims.

[0043] The following embodiments are also included in the scope of the present invention: a solid-state battery according to claim 1 having the features of claim 2; a solid-state battery according to claim 1 having the features of claim 3; a solid-state battery according to any one of claims 1 to 3 having the features of claim 4; a solid-state battery according to any one of claims 1 to 4 having the features of claim 5; a solid-state battery according to any one of claims 1 to 5 having the features of claim 6; a solid-state battery according to claim 6 having the features of claim 7; a solid-state battery according to claim 6 or 7 having the features of claim 8; a solid-state battery according to any one of claims 6 to 8 having the features of claim 9; a solid-state battery according to claim 9 having the features of claim 10. [Examples]

[0044] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following examples, the instruments and devices used inside the glove box were thoroughly dried beforehand.

[0045] <Example of creating evaluation cells> [Example 1] (Fabrication of the positive electrode) In a glove box with an argon atmosphere and a dew point of -68°C or lower, NMC composite oxide (LiNi) is used as the positive electrode active material. 0.8 Mn 0.1 Co0.1 O2, carbon fiber as a conductive additive, and argyrodite-type sulfide solid electrolyte (Li6PS5Cl) as a solid electrolyte were weighed in a mass ratio of 50:30:20. These were mixed using an agate mortar and then further stirred and mixed using a planetary ball mill. To 100 parts by mass of the resulting mixed powder, 2 parts by mass of polytetrafluoroethylene (PTFE) as a binder were added and mixed. The resulting mixture was layered with aluminum foil as a positive electrode current collector and subjected to a pressing process to obtain a positive electrode having a positive electrode active material layer (thickness 50 μm) on the surface of the positive electrode current collector.

[0046] (Preparation of a solid electrolyte layer) A solid electrolyte slurry was prepared by adding 2 parts by mass of SBR as a binder to 100 parts by mass of argyrodite-type sulfide solid electrolyte (Li6PS5Cl, average particle size (D50): 0.8 μm) as a solid electrolyte in a glove box with an argon atmosphere with a dew point of -68°C or lower, and then adding mesitylene as a solvent and mixing. A solid electrolyte layer (thickness 30 μm) was obtained by coating the surface of stainless steel foil as a support with the solid electrolyte slurry and drying it.

[0047] (Fabrication of the negative electrode intermediate layer) Silver nanoparticles (average particle size (D50): 60 nm) and carbon black (average particle size (D50): 12 nm) were weighed in a mass ratio of Ag:C = 1:3 and mixed. To 88 parts by mass of the resulting mixture, 12 parts by mass of polyvinylidene fluoride (PVDF) as a binder was added, and mesitylene was added as a solvent and mixed to prepare a negative electrode intermediate layer slurry. The negative electrode intermediate layer slurry was coated onto the surface of stainless steel foil, which was used as the negative electrode current collector, and dried to obtain a negative electrode intermediate layer (thickness before pressing: 10 μm).

[0048] (Creation of evaluation cells) The positive electrode active material layer formed on the surface of the aluminum foil (positive electrode current collector) and the solid electrolyte layer formed on the surface of the stainless steel foil were stacked so that the exposed surfaces of the positive electrode active material layer and the exposed surfaces of the solid electrolyte layer faced each other, and pressed at 700 MPa for 1 minute using a cold isostatic press (CIP) (first pressing step). This transferred the solid electrolyte layer to the exposed surface of the positive electrode active material layer and aligned the solid electrolyte particles on the surface of the solid electrolyte layer adjacent to the stainless steel foil, reducing the unevenness. After peeling off the stainless steel foil adjacent to the solid electrolyte layer, the solid electrolyte layer and the negative electrode intermediate layer formed on the surface of the stainless steel foil (negative electrode current collector) were stacked so that the exposed surfaces of the solid electrolyte layer and the exposed surfaces of the negative electrode intermediate layer faced each other, and pressed at 100 MPa for 1 minute using a cold isostatic press (CIP) (second pressing step). This transferred the negative electrode intermediate layer to the exposed surface of the solid electrolyte layer and adjusted the surface roughness of the surface of the negative electrode intermediate layer adjacent to the solid electrolyte layer. Finally, an aluminum positive electrode tab and a nickel negative electrode tab were joined to the aluminum foil (positive electrode current collector) and stainless steel foil (negative electrode current collector) respectively using an ultrasonic welding machine. The resulting laminate was then placed inside an aluminum laminate film and vacuum-sealed to obtain an evaluation cell, which is a lithium deposition type all-solid-state battery of this embodiment.

[0049] [Example 2] In the above (preparation of evaluation cells), the evaluation cells for this embodiment were prepared using the same method as in Example 1, except that the press pressure in the second pressing process was changed to 400 MPa.

[0050] [Example 3] In the above (preparation of evaluation cells), the evaluation cells for this embodiment were prepared using the same method as in Example 1, except that the press pressure in the second pressing process was changed to 500 MPa.

[0051] [Example 4] Except for changing the press pressure in the first pressing step to 600 MPa, the evaluation cell for this embodiment was manufactured using the same method as in Example 3 (for the preparation of the evaluation cell).

[0052] [Example 5] In the above (preparation of evaluation cells), the evaluation cells for this embodiment were prepared using the same method as in Example 3, except that the press pressure in the first pressing step was changed to 500 MPa.

[0053] [Example 6] In the above (preparation of evaluation cells), the evaluation cells for this embodiment were prepared using the same method as in Example 3, except that the press pressure in the first pressing process was changed to 300 MPa.

[0054] [Comparative Example 1] Except for changing the press pressure in the first pressing step to 100 MPa, the evaluation cell for this comparative example was prepared using the same method as in Example 3 (preparation of the evaluation cell).

[0055] <Measurement of surface roughness Rz and thicknessd> From the evaluation cell (before initial charging) prepared as described above, the power generation element was removed, and a cross-section perpendicular to the surface direction (parallel to the stacking direction) was exposed by ion milling. The cross-section was observed using a scanning electron microscope (SEM), and an image (field of view: 200 μm × 200 μm) of the interface between the negative electrode intermediate layer and the solid electrolyte layer was captured. The surface roughness Rz of the negative electrode intermediate layer at the interface between the negative electrode intermediate layer and the solid electrolyte layer (surface roughness Rz of the surface adjacent to the solid electrolyte layer in the negative electrode intermediate layer) was measured using image analysis software (WinROOF2021, manufactured by Mitani Corporation). In addition, the above cross-section was observed using SEM, and the thickness was measured at several to several dozen different locations in the negative electrode intermediate layer, and the arithmetic mean of these measurements was taken as the thickness d of the negative electrode intermediate layer. The ratio of the surface roughness Rz to the thickness d of the negative electrode intermediate layer (percentage: (Rz / d) × 100 (%)) was then calculated. The obtained values ​​are shown in Table 1 below.

[0056] Furthermore, when the surface roughness Rz of the evaluation cell after the charge-discharge test described later was measured using the same method as above, it was confirmed that it was the same value as the surface roughness Rz of the evaluation cell before the initial charge.

[0057] <Charge / Discharge Test> The positive electrode lead and negative electrode lead were connected to the positive electrode current collector and negative electrode current collector, respectively, of the evaluation cell (before initial charging) prepared as described above, and charging and discharging were performed according to the following charge / discharge test conditions. During this process, a constraining pressure of 3 MPa was applied in the stacking direction of the evaluation cell using a pressurizing member, while performing the following charge / discharge test.

[0058] (Charge / discharge test conditions) Evaluation temperature: 333K (60℃) Voltage range: 2.5~4.3V Charging process: CCCV (0.02C cutoff) Charging rate: 3.5C Discharge process:CC Discharge rate: 0.1C After charging and discharging, let it rest for 30 minutes.

[0059] The evaluation cells were charged using a charge / discharge tester in a constant temperature bath set to the evaluation temperature. During the charging process (deposition of lithium metal on the negative electrode current collector), the cells were charged in constant current / constant voltage (CCCV) mode at 3.5C to 4.3V (0.02C cutoff). Subsequently, during the discharging process (dissolution of lithium metal on the negative electrode current collector), the cells were discharged in constant current (CC) mode at 0.1C to 2.5V. Here, 1C is the current value at which charging for one hour results in the battery being fully charged (100% charged). Ten evaluation cells were prepared, and the number of cells that did not experience a short circuit during the above charge / discharge process was determined. The presence or absence of a short circuit was determined by checking whether the ratio of discharge capacity to charge capacity was less than 99%. Cells with a ratio of less than 99% were judged to have a short circuit, and those with a ratio of 99% or more were judged to not have a short circuit. Then, out of 10 evaluation cells, we evaluated the number of cells without short circuits as follows: ◎ (excellent) if 9 or more cells were short-circuit-free, ○ (good) if 7 or more were short-circuit-free, △ (satisfactory) if 5 or more were short-circuit-free, and × (poor) if 4 or fewer were short-circuit-free. The results are shown in Table 1 below.

[0060] [Table 1]

[0061] The results in Table 1 show that, according to the present invention, short circuits can be suppressed more reliably in lithium deposition type all-solid-state batteries. [Explanation of Symbols]

[0062] 10A stacked secondary battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 14. Negative electrode intermediate layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layers, 21 Power generation elements, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29. Laminating film.

Claims

1. A positive electrode having a positive electrode active material layer containing positive electrode active material, A negative electrode having a negative electrode current collector, wherein lithium metal is deposited on the negative electrode current collector during charging, A solid electrolyte layer containing a solid electrolyte is interposed between the positive electrode and the negative electrode, A negative electrode intermediate layer is located adjacent to the negative electrode current collector side surface of the solid electrolyte layer and contains at least one selected from the group consisting of a metallic material that can be alloyed with lithium and a carbon material that can absorb lithium ions, A solid-state battery comprising a power generation element having, The surface roughness Rz of the surface adjacent to the solid electrolyte layer in the negative electrode intermediate layer is 2.5 μm or less. An all-solid-state battery in which the negative electrode intermediate layer comprises a mixture of at least one metal particle containing a metallic material that can be alloyed with lithium, and at least one carbon particle containing a carbon material that can absorb lithium ions.

2. The all-solid-state battery according to claim 1, wherein the surface roughness Rz is 0.5 μm or more and 2.0 μm or less.

3. The all-solid-state battery according to claim 1, wherein the surface roughness Rz is 0.5 μm or more and 1.0 μm or less.

4. The all-solid-state battery according to claim 1 or 2, wherein the thickness d of the negative electrode intermediate layer is 10 μm or less.

5. The all-solid-state battery according to claim 1 or 2, wherein the ratio of the surface roughness Rz to the thickness d of the negative electrode intermediate layer is 1% or more and 65% or less.

6. The all-solid-state battery according to claim 1 or 2, wherein the metal material comprises at least one selected from the group consisting of indium, aluminum, silicon, tin, magnesium, gold, silver, zinc, and nickel, and the carbon material comprises at least one selected from the group consisting of carbon black, carbon nanotubes, graphite, and hard carbon.

7. The all-solid-state battery according to claim 1 or 2, wherein the mass ratio (metal particles:carbon particles) of the metal particles to the carbon particles in the mixture is 10:1 to 1:

1.

8. The all-solid-state battery according to claim 1 or 2, wherein the negative electrode intermediate layer further contains a binder in an amount exceeding 10 parts by mass per 100 parts by mass of the mixture.

9. The all-solid-state battery according to claim 8, wherein the binder comprises polyvinylidene fluoride.

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