WO2025127115A1 - All-solid-state battery - Google Patents

Abstract

The battery internal resistance is reduced and the timewise increase in same is prevented in an all-solid-state battery that uses a sulfide-based solid electrolyte and that uses a conductive porous sheet for connection between an electrode and a conductive path of the exterior body.　The all-solid-state battery according to the present invention comprises: an electrode laminate having a positive electrode, a negative electrode, and a solid electrolyte layer; and an exterior body in which the electrode laminate is enclosed therein. This all-solid-state battery is characterized in that: the exterior body has a conductive path leading from the inside to the outside and has a porous metal substrate between the positive electrode and/or the negative electrode and the conductive path of the exterior body; at least one of the positive electrode, the negative electrode, and the solid electrolyte layer contains a sulfide-based solid electrolyte; and the porous metal substrate is composed of an alloy containing Ni and Cr wherein the Ni content in this alloy is at least 60 mass% and the Cr content in this alloy is 0.1-40 mass%.

Description

All solid state battery

The present invention relates to an all-solid-state battery that uses a sulfide-based solid electrolyte.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, there has been a demand for small, lightweight batteries with high capacity and high energy density.

Currently, lithium batteries, particularly lithium ion batteries, that can meet this demand use lithium-containing composite oxides such as lithium cobalt oxide ( _LiCoO2 ) and lithium nickel oxide ( _LiNiO2 ) as the positive electrode active material, graphite or the like as the negative electrode active material, and an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.

As devices that use lithium-ion batteries continue to develop, there is a demand for longer life, higher capacity, and higher energy density for lithium-ion batteries, as well as a high demand for the reliability of lithium-ion secondary batteries with longer life, higher capacity, and higher energy density.

However, the organic electrolyte used in lithium-ion batteries contains organic solvents, which are flammable substances, and so there is a possibility that the organic electrolyte may generate abnormal heat if an abnormality such as a short circuit occurs in the battery. Furthermore, with the recent trend toward higher energy density in lithium-ion batteries and an increasing amount of organic solvent in the organic electrolyte, there is a demand for even greater reliability in lithium-ion batteries.

In light of the above, all-solid-state lithium batteries that do not use organic solvents (all-solid-state batteries) are also being considered. All-solid-state lithium batteries use sheets or compacts of solid electrolytes that do not use organic solvents instead of the conventional organic solvent-based electrolytes, and are highly reliable with no risk of abnormal heat generation from the solid electrolyte.

As the solid electrolyte, sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, oxide-based solid electrolytes, etc. have been considered, but among them, the development of sulfide-based solid electrolytes has progressed rapidly due to their high lithium ion conductivity, and an all-solid-state battery using sulfide-based solid electrolytes in the positive electrode, negative electrode, and solid electrolyte layer has also been proposed (Patent Document 1).

On the other hand, in all-solid-state batteries, it has also been proposed to place a conductive porous member between the exterior body and the electrodes in order to alleviate the stress applied to the electrodes during sealing (Patent Document 2). Patent Document 2 gives an example of a conductive porous member such as a conductive porous sheet made of carbon fiber or graphite molded body, and shows that it is possible to maintain stable function even when a solid electrolyte that easily reacts with other constituent materials in the battery, such as a sulfide-based solid electrolyte, is used.

JP 2023-022836 A International Publication No. 2020/66323

However, when a conductive porous sheet made of the carbon material is interposed between an electrode inside an exterior body and a conductive path leading from the inside to the outside of the exterior body and used to electrically connect these two, it has been found that the electrical resistance becomes relatively high, resulting in a problem that the internal resistance of the battery cannot be reduced beyond a certain level. In addition, when a conductive foam base material made of copper or aluminum, as described in Patent Document 2, is used as the conductive porous sheet, it has been found that although the internal resistance of the battery can be reduced immediately after assembly, a problem arises in that the resistance gradually increases.

The present invention aims to reduce the internal resistance of a solid-state battery that uses a sulfide-based solid electrolyte and a conductive porous sheet for electrical connection between the electrodes and the conductive paths of the exterior body, and to prevent this resistance from increasing over time.

The all-solid-state battery of the present invention comprises an electrode laminate having a positive electrode, a negative electrode, and a solid electrolyte layer, and an exterior body enclosing the electrode laminate, the exterior body having a conductive path leading from the inside to the outside, a porous metal substrate between the positive electrode and/or the negative electrode and the conductive path of the exterior body, at least one of the positive electrode, the negative electrode, and the solid electrolyte layer contains a sulfide-based solid electrolyte, the porous metal substrate is made of an alloy containing Ni and Cr, the Ni content of the alloy is 60 mass% or more, and the Cr content of the alloy is 0.1 mass% or more and 40 mass% or less.

The present invention provides an all-solid-state battery that contains a sulfide-based solid electrolyte, has low internal resistance, and can suppress the increase in internal resistance over time.

FIG. 1 is a cross-sectional view illustrating a schematic diagram of an example of an all-solid-state battery of the present invention. FIG. 2 is a perspective view of a concave container of the all-solid-state battery of FIG. FIG. 2 is a perspective view of an elastic conductive member of the all-solid-state battery of FIG. 1 . 1 is a scanning electron microscope photograph for explaining the surface state of an electrode in the all-solid-state battery of the present invention.

The all-solid-state battery of the present invention comprises an electrode laminate having a positive electrode, a negative electrode, and a solid electrolyte layer, and an exterior body enclosing the electrode laminate, the exterior body having a conductive path leading from the inside to the outside, and at least one of the positive electrode, the negative electrode, and the solid electrolyte layer containing a sulfide-based solid electrolyte. The all-solid-state battery also has a porous metal substrate between at least one of the positive electrode and the negative electrode and the exterior body. In other words, the all-solid-state battery has a porous metal substrate as a conductive connecting member that electrically connects at least one of the positive electrode and the negative electrode to the conductive path of the exterior body.

In the all-solid-state battery, the porous metal substrate is made of an alloy containing Ni (nickel) and Cr (chromium) (hereinafter, sometimes referred to as a "Ni-Cr alloy"), in which the Ni content in the alloy is 60% by mass or more and the Cr content in the alloy is 0.1% by mass or more and 40% by mass or less.

Ni has high electrical conductivity, so by using a porous metal substrate made of this to connect the electrodes and the conductive paths of the exterior body, it is possible to lower the resistance between the electrodes and the conductive paths, thereby reducing the internal resistance of the solid-state battery.

In addition, since the porous metal substrate has pores and is made of metal, it is easy to ensure contact with the electrode by applying a force in the thickness direction, and gaps caused by variations in the thickness (height) of each component can be eliminated, making the conductive connection between the electrode and the conductive path more reliable. In particular, when a foamed metal substrate is used, it can be easily plastically deformed, so that when forming an all-solid-state battery, the electrode laminate can be inserted into the exterior body so as to be pressed against the porous metal substrate, or the electrode laminate can be pressed against the porous metal substrate by the pressing force of an elastic conductive member (described later), thereby compressing and deforming the porous metal substrate according to the degree of variation in the thickness (height) of each component (deviation from the design value). This improves the contact between the electrode pressed by the porous metal substrate in the electrode laminate, and also makes it possible to homogenize the degree of conduction between the porous metal substrate and the electrode laminate in each all-solid-state battery when a large number of all-solid-state batteries are manufactured. When a porous metal substrate, particularly a foamed metal substrate, is used in an all-solid-state battery, these actions make it possible to lower the internal resistance and reduce the variation in the individual internal resistances.

However, if the electrode mixture layer or solid electrolyte layer contains a sulfide-based solid electrolyte, sulfide gases such as hydrogen sulfide are generated inside the battery, and the porous metal substrate may corrode due to this gas or due to direct contact with the sulfide-based solid electrolyte, which may cause the internal resistance of the battery to increase over time.

Therefore, in the all-solid-state battery of the present invention, the electrodes and the conductive paths of the exterior body are electrically connected by a porous metal substrate made of an alloy containing Ni and Cr. The action of Cr in the porous metal substrate can suppress corrosion caused by contact with the sulfide-based solid electrolyte or contact with gas derived from the sulfide-based solid electrolyte.

On the other hand, in a porous metal substrate made of an alloy containing Ni and Cr, Cr also has the effect of reducing the electrical conductivity and increasing the resistance.

In the solid-state battery of the present invention, the Ni content and the Cr content in the Ni-Cr alloy that constitutes the porous metal substrate, which is the conductive connecting member, are each set within a specific range, thereby enabling good conductivity and suppression of corrosion caused by the sulfide-based solid electrolyte, lowering the initial internal resistance, and suppressing the increase in internal resistance over time.

The all-solid-state battery of the present invention includes secondary batteries (all-solid-state secondary batteries) and primary batteries (all-solid-state primary batteries).

FIG. 1 shows a schematic longitudinal cross-sectional view of an example of an all-solid-state battery of the present invention. The all-solid-state battery 100 shown in FIG. 1 has an electrode laminate 110 having a positive electrode 120, a negative electrode 130, and a solid electrolyte layer 140 interposed between them, and this electrode laminate 110 is enclosed in a battery container (exterior body) formed of a recessed container 150 and a sealing body 160.

FIG. 2 is a perspective view showing a schematic representation of the concave container 150 constituting the battery container of the all-solid-state battery 100 shown in FIG. 1. As shown in FIG. 2, the concave container 150 is composed of a bottom surface portion 151 and a side wall portion 152, has an opening portion that opens to the upper side in the figure, and has a concave cross-section.

The battery 100 shown in FIG. 1 is an example having a positive electrode 120 having a sheet-shaped metal substrate 122 as a current collector and a negative electrode 130 having a sheet-shaped metal substrate 132 as a current collector. That is, the positive electrode 120 has a positive electrode mixture layer 121 and a foamed metal substrate 122 similar to that used as the conductive connection member, and the entire foamed metal substrate 122, including the end on the positive electrode mixture layer 121 side, is embedded in the surface layer of the positive electrode mixture layer 121. That is, the entire location of the metal substrate 122 corresponds to the area where the positive electrode mixture layer and the metal substrate coexist. Furthermore, in the positive electrode 120, the end of the foamed metal substrate 122 on the opposite side to the positive electrode mixture layer 121 side (the lower end in FIG. 1) is exposed. The dotted line in the positive electrode 120 indicates the boundary between the region in the positive electrode mixture layer 121 where the metal substrate does not coexist and the region where the positive electrode mixture layer and the metal substrate coexist, and corresponds to the end of the metal substrate 122 on the positive electrode mixture layer 121 side.

The negative electrode 130, like the positive electrode 120, has a negative electrode mixture layer 131 and a foamed metal substrate 132, and the entire foamed metal substrate 132, including the end on the negative electrode mixture layer 131 side, is embedded in the surface layer of the negative electrode mixture layer 131. That is, the entire location of the metal substrate 132 corresponds to the area where the negative electrode mixture layer and the metal substrate coexist. Furthermore, in the negative electrode 130, the end of the foamed metal substrate 132 on the opposite side to the negative electrode mixture layer 131 side (the upper end in FIG. 1) is exposed. Note that the dotted line in the negative electrode 130 indicates the boundary between the area in the negative electrode mixture layer 131 where the metal substrate does not coexist and the area where the negative electrode mixture layer and the metal substrate coexist, and corresponds to the end of the metal substrate 132 on the negative electrode mixture layer 131 side.

The lower side of the recessed container 150 in the figure is provided with connection terminals 170, 180 for electrically connecting the all-solid-state battery 100 to a device in which it is used. The connection terminal 170 is conductively connected to a conductive path 171 that runs from the inside of the recessed container 150 to the external connection terminal 170. The conductive path 171 is conductively connected to the positive electrode 120 of the electrode stack 110 contained in the recessed container 150, thereby providing electrical continuity between the positive electrode 120 of the electrode stack 110 and the connection terminal 170. In the all-solid-state battery 100 of FIG. 1, a porous metal substrate 190, which is a conductive connection member, is interposed between the positive electrode 120 of the electrode stack 110 and the conductive path 171. As described above, in the all-solid-state battery 100, the action of the porous metal substrate 190 increases the conductivity between the positive electrode 120 and the conductive path 171, and also suppresses the occurrence of variations in the internal resistance of individual batteries when a large number of all-solid-state batteries are produced.

The connection terminal 180 is conductively connected to a conductive path 181 that runs from the inside of the recessed container 150 to the external connection terminal 180, and this conductive path 181 is disposed at the top of the electrode stack 110 in the figure, and is conductively connected to the negative electrode 130 via an elastic conductive member 210 that contacts the negative electrode 130 of the electrode stack 110. This provides electrical continuity between the negative electrode 130 of the electrode stack 110 and the connection terminal 180.

The side wall portion 152 of the recessed container 150 has a support portion 153 that supports the elastic conductive member 210. In the all-solid-state battery 100, as shown in FIG. 2, the support portion 153 is formed at the upper end of the inner circumferential surface of the side wall portion 152 and is a protruding portion that protrudes in the radial direction, but the support portion for holding the elastic conductive member of the all-solid-state battery may have another shape as long as it can support the elastic conductive member 210.

FIG. 3 is a perspective view showing a schematic representation of the elastic conductive member 210 of the all-solid-state battery 100 shown in FIG. 1. The elastic conductive member 210 is made of, for example, a thin metal plate, and as shown in FIG. 3, has a rectangular shape in plan view, but can have a shape corresponding to the plan view shape of the electrode laminate or concave container of the all-solid-state battery.

The recessed container 150 of the all-solid-state battery 100 shown in FIG. 1 has a number of support portions 153 for supporting the elastic conductive member 210 at the upper end of the side wall portion 152. The support portions 153 are formed as protruding portions that protrude in the circumferential direction of the inner surface of the side wall portion 152. More specifically, the support portions 153 are the top walls of a number of recesses formed radially outward on the inner surface of the side wall portion 152. A part of the conductive path 181 is exposed on the lower surface and side surface of the top wall. At least the number of support portions 153 is formed corresponding to the number of supported portions 211 of the elastic conductive member 210 described later.

The elastic conductive member 210 has a supported portion 211 and a flat portion 212. A plurality of supported portions 211 are provided at locations on the radially outer side in a plan view of the electrode laminate 110 of the all-solid-state battery 101, corresponding to the positions of the support portions 153. The supported portions 211 are hook-shaped engaging pieces that are engaged with the lower surface of the top wall of the support portion 153, and extend from the edge of the elastic conductive member 210 toward the support portion 153 (downward in FIG. 1). The supported portions 211 also have a tip that is folded back toward the support portion 153, i.e., the lower surface of the top wall. The tip of the supported portion 211 is in contact with the conductive path 181 exposed on the lower surface and side surface of the top wall of the support portion 153. As a result, the elastic conductive member 210 functions as a current collector and forms part of the conductive path that electrically connects the negative electrode 130 and the connection terminal portion 180.

The elastic conductive member 210 is supported by a support portion 153 formed on the inner circumferential surface of the side wall portion 152 of the recessed container 150, and covers a part of the opening of the recessed container 150. The area of the elastic conductive member 210 in a plan view is smaller than the area of the opening of the recessed container 150. Note that even if the hook-shaped engaging piece of the elastic conductive member 210 is not engaged with the underside of the top wall of the support portion 153, as long as the elastic conductive member 210 can be fixed in place with the hook-shaped engaging piece pressed into a recess formed on the inner circumferential surface of the side wall portion 152, the elastic conductive member 210 is considered to be engaged with the side wall portion 152 of the recessed container 150.

As shown in Figures 1 and 3, the elastic conductive member 210 has a spring portion 213 that rises from the flat portion 212 toward the negative electrode 130 of the electrode laminate 110, and this spring portion 213 comes into contact with the upper surface of the negative electrode 130 of the electrode laminate 110 (its current collector, the foamed metal substrate 132) in the figure, pressing the electrode laminate 110 toward the inner bottom surface of the recessed container 150.

In an elastic conductive member having a spring portion, the shape of the spring portion is not particularly limited as long as it can press the electrode laminate toward the inner bottom surface of the concave container. The spring portion 213 of the elastic conductive member 210 shown in FIG. 1 and FIG. 3 is a spring piece that is inclined from the planar portion 212 toward the negative electrode 130 of the electrode laminate 110 (hereinafter, the spring portion 213 may be referred to as the spring piece 213). As shown in FIG. 3, the spring piece 213 is formed by cutting out a part of the planar portion 212 in a U-shape and is supported by the planar portion 212 in a cantilever manner. In other words, the spring piece 213 in the elastic conductive member 210 shown in FIG. 1 and FIG. 3 is a leaf spring. With such a form of the elastic conductive member 210, it is only necessary to form the spring piece 213 on a part of the planar portion 212, so that the manufacture of the elastic conductive member and therefore the manufacture of the all-solid-state battery can be more easily performed. Furthermore, by cutting out the flat surface portion 212 to form the spring piece 213, it is possible to further facilitate the manufacture of the elastic conductive member, and therefore the manufacture of the all-solid-state battery.

The spring piece 213 has a boundary 213a with the flat portion 212 and a tip portion 213b, and is bent at the boundary 213a and inclined from the boundary 213a to the tip portion 213b toward the electrode laminate 110 in order to contact the negative electrode 130 of the electrode laminate 110. However, if the tip portion 213b of the spring piece 213 is brought into contact with the negative electrode 130 of the electrode laminate 110, there is a risk that the negative electrode 130 may be damaged by the tip portion 213b. Therefore, in the elastic conductive member 210 shown in Figures 1 and 3, the spring piece 213 is bent so that the tip portion 213b faces upward in Figure 2, and the spring piece 213 contacts the negative electrode 130 at a location other than the tip portion 213b.

In the elastic conductive member 210 before the all-solid-state battery 100 is assembled, the height from the bottom surface of the flat portion 212 to the point where the spring piece 213 contacts the negative electrode 130 (the height of the spring piece 213) is greater than the height from the bottom surface of the flat portion 212 to the point where the spring piece 213 contacts the negative electrode 130 in the elastic conductive member 210 after the all-solid-state battery 100 is assembled. This allows the spring piece 213 to press against the electrode laminate 110, and a good electrical connection between the elastic conductive member 210 and the negative electrode 130 of the electrode laminate 110 can be maintained.

Furthermore, by forming the spring portion 213 of the elastic conductive member 210 with a spring piece, the thickness of the elastic conductive member 210 excluding the supported portion 211 can be reduced. For example, before assembling the all-solid-state battery 100, the thickness (overall height) of the elastic conductive member 210 excluding the supported portion 211 can be the sum of the thickness of the plate material constituting the planar portion 212 and the height of the spring piece 213. Specifically, the thickness of the plate material: 0.2 mm and the height of the spring piece: 0.5 mm can be combined to make the thickness of the elastic conductive member 210 excluding the supported portion 211 0.7 mm.

The length (length from the boundary 213a to the tip 213b) of the spring piece 213 can be 3 mm or the like, and the width (length in the direction perpendicular to the length direction) can be 1.5 mm or the like. An elastic conductive member having spring pieces may have multiple spring pieces. In that case, the shape of the spring pieces, including the width and length, may be different from each other for reasons such as preventing resonance. The thickness of the elastic conductive member 210 excluding the supported portion 211 is preferably 1.2 mm or less, more preferably 1 mm or less, and particularly preferably 0.8 mm or less. On the other hand, in order to generate a pressing force in the spring portion 213 well, the thickness of the elastic conductive member 210 excluding the supported portion 211 is preferably 0.3 mm or more, more preferably 0.4 mm or more, and particularly preferably 0.5 mm or more.

Furthermore, the edge of the elastic conductive member 210, i.e., the position of the supported portion 211, can be freely set in the height direction (thickness direction of the elastic conductive member 210), so even if a gap is formed between the sealing body 160 and the elastic conductive member 210, the distance between the sealing body 160 and the part where the spring piece 213 contacts the negative electrode 130 does not increase. As a result, the gap between the sealing body 160 and the electrode laminate 110 can be prevented from increasing, so that the capacity of the all-solid-state battery 100 can be increased. The thickness direction of the elastic conductive member 210 is the vertical direction in FIG. 1 (height direction of the all-solid-state battery 100), and can also be said to be the direction perpendicular to the bottom surface of the flat portion 212.

The overall thickness of the elastic conductive member 210, including the supported portion 211, can be set appropriately depending on the height from the bottom surface portion 151 of the side wall portion 152 of the concave container 150. Furthermore, the supported portion 211 only needs to have a height necessary for engaging with the supporting portion 153. The overall thickness of the elastic conductive member 210, including the supported portion 211, can be, for example, 3 mm or less, preferably 2.7 mm or less, and more preferably 2.5 mm or less.

In the elastic conductive member 210, the spring piece 213 may be formed by cutting out the flat portion 212 as described above, or may be attached by welding the spring piece 213 separately to the bottom surface of the flat flat portion 212. Also, a base for attaching the spring piece 213 may be provided in advance separately from the flat portion 212, and the spring piece 213 may be attached to the base to form the entire spring portion. That is, the spring piece 213 may rise directly from the flat portion 212, or may rise from the flat portion 213 via another element such as a base. Furthermore, the spring piece 213 may be in a form in which both ends of the spring piece 213 are supported by the flat portion 212 so that it has a convex shape toward the electrode stack 110.

In the all-solid-state battery 100 shown in FIG. 1, when installing the elastic conductive member 210, first, the electrode laminate 110 is accommodated inside the concave container 150, and then the elastic conductive member 210 is placed on the upper surface of the electrode laminate 110. With the elastic conductive member 210 placed on the upper surface of the electrode laminate 110, the tip of the supported portion 211 is positioned between the upper surface of the electrode laminate 110 and the support portion 153, i.e., the lower surface of the top wall, in the axial direction of the electrode laminate 110 (the up-down direction in FIG. 1). Then, while pushing the supported portion 211 of the elastic conductive member 210 toward the bottom portion 151 of the concave container 150, the supported portion 211 is supported by the support portion 153. More specifically, the tip of the supported portion 211 is engaged with the support portion 153, i.e., the lower surface of the top wall. Because the supported portion 211 is pressed downward, the spring piece 213 of the elastic conductive member 210 is pressed in the opposite direction to the negative electrode 130 while in contact with the electrode stack 110. At this time, the spring piece 213 presses the electrode stack 110 toward the bottom portion 151 of the recessed container 150 by its elastic force. This allows the elastic conductive member 210 to make more stable contact with the electrode stack 110, and maintain a good electrical connection without misalignment due to vibration or the like.

In the all-solid-state battery 100 shown in FIG. 1, the concave container 150 has two support parts 153, 153, but the number of support parts 153 may be three or more. The supported parts 211 of the elastic conductive member 210 may be formed according to the number of support parts 153.

An example of a method for fixing the edge (supported portion 211) of the elastic conductive member 210 to the inner peripheral surface of the side wall portion 152 of the recessed container 150 is to glue the edge of the elastic conductive member 210 to the inner peripheral surface of the side wall portion 152 of the recessed container 150.

As shown in FIG. 1, it is preferable that a gap is formed between the elastic conductive member 210 and the sealing body 160. In other words, it is preferable that the elastic conductive member 210 and the sealing body 160 are not in contact with each other. This makes it possible to avoid contact between the elastic conductive member 210 and the sealing body 160 even if the elastic conductive member 210 is pushed toward the sealing body 160 due to a volume change in the electrode stack 110.

In the all-solid-state battery 100 shown in FIG. 1, the electrode laminate 110 is arranged so that the positive electrode 120 is located on the inner bottom surface side of the recessed container 150 and the negative electrode 130 is located on the sealing body 160 side (elastic conductive member 210 side), but an all-solid-state battery can also be constructed by arranging the electrode laminate so that the negative electrode is located on the inner bottom surface side of the recessed container and the positive electrode is located on the sealing body side (elastic conductive member side).

<Porous metal base material>
The porous metal substrate may be disposed either between the conductive path for the positive electrode in the outer casing and the positive electrode, or between the conductive path for the negative electrode in the outer casing and the negative electrode, or may be disposed in both of these locations.

As described above, the porous metal substrate is pressed against the electrode laminate and pressed against the conductive path on the inner surface of the exterior body, thereby making the conductive connection between the electrode and the conductive path more reliable. Furthermore, in the case of a foamed metal substrate, since it is easily plastically deformed, it is possible to more effectively exert the effect of lowering the internal resistance of the battery and the effect of suppressing the variation in internal resistance among a plurality of batteries. In this case, as in the all-solid-state battery shown in FIG. 1, it is preferable to arrange a means (elastic conductive member in FIG. 1) for pressing the electrode laminate toward the inner surface of the exterior body (concave container) on either side of the positive electrode or negative electrode of the electrode laminate, so that the porous metal substrate is usually arranged between either one of the outermost electrodes (positive electrode and negative electrode) of the electrode laminate and the conductive path of the exterior body. However, depending on the selection of the internal structure of the all-solid-state battery, the porous metal substrate can also be arranged both between the conductive path for the positive electrode of the exterior body and the positive electrode, and between the conductive path for the negative electrode of the exterior body and the negative electrode.

The porous metal substrate is composed of an alloy containing Ni and Cr. The Ni content in the alloy is 60% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more, from the viewpoint of improving the conductivity of the porous metal substrate, lowering the resistance in the conductive connection between the conductive path of the exterior body and the electrodes, and lowering the internal resistance of the all-solid-state battery.

The Cr content in the alloy is 0.1% by mass or more, preferably 3% by mass or more, and more preferably 10% by mass or more, from the viewpoint of suppressing corrosion of the porous metal substrate due to reactions with the sulfide-based solid electrolyte and gas generated from the sulfide-based solid electrolyte, and suppressing an increase in the internal resistance of the all-solid-state battery over time. However, if the Cr content in the alloy is too high, the conductivity of the porous metal substrate decreases, increasing the internal resistance of the battery. In addition, the hardness of the porous metal substrate increases, making it difficult to plastically deform, making it difficult to adjust the variation in thickness (height) of each component. Therefore, the Cr content in the alloy is 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less.

As can be seen from the Ni content and Cr content in the alloy constituting the current collector, the composition of the alloy constituting the porous metal substrate typically contains Cr in the above-mentioned content, with the remainder being Ni, but it may contain, for example, elements other than Ni and Cr (e.g., Sn, Fe, Co, Ti, Al, Mo, etc.) in a total content of 39.9 mass% or less. In other words, the composition of the alloy constituting the porous metal substrate may contain a total content of Ni and Cr of 60.1 mass% or more, and elements other than Ni and Cr in a range of 39.9 mass% or less.

Examples of porous metal substrates include punched metal, netting, and expanded metal, but it is preferable to use a foamed metal substrate made of an alloy of the above composition (such as "Celmet (registered trademark)" manufactured by Sumitomo Electric Industries, Ltd.) because it is relatively easy to plastically deform it.

The thickness of the porous metal substrate after assembly of the all-solid-state battery is preferably 20 μm or more, and more preferably 100 μm or more, from the viewpoint of ensuring the function of the all-solid-state battery better. There is no particular upper limit on the thickness of the porous metal substrate after assembly of the all-solid-state battery, but from the viewpoint of suppressing the volume of components not involved in power generation inside the exterior body, it is preferably 500 μm or less, and more preferably 300 μm or less.

The thickness of the porous metal substrate is determined from the maximum width in the thickness direction in an image of a cross section of the substrate observed with a scanning electron microscope (SEM) at a magnification of 50 to 1000 times (the values in the examples described below are determined by these methods).

As mentioned above, the foamed metal substrate is preferably stored inside the battery (inside the exterior body) in a state compressed in the thickness direction, and the thickness inside the battery is preferably 90% or less, and more preferably 80% or less, of the thickness before use (thickness before compression). Therefore, the thickness of the foamed metal substrate before use in the battery (before compression) is preferably 100 to 3000 μm.

In addition, the porosity of the foamed metal substrate before use in a battery (before compression) is preferably 99.5% or less, more preferably 99% or less, and even more preferably 98.5% or less, from the viewpoint of making it easier to perform plastic deformation by pressing the electrode laminate against it and better ensuring the effect of reducing the internal resistance of the all-solid-state battery and the effect of suppressing its variation, and from the viewpoint of ensuring sufficient strength for use, it is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more.

In addition, if the basis weight (weight per unit area) of the porous metal substrate (particularly the foamed metal substrate) is too large, the resistance or hardness increases, making it difficult to plastically deform, and there is a risk that the effect of reducing the internal resistance of the battery will be reduced. Therefore, from the viewpoint of better ensuring the effect of reducing the internal resistance of the battery, the basis weight is preferably 600 g/m ² or less, and more preferably 400 g/m ² or less. In addition, if the basis weight of the porous metal substrate (particularly the foamed metal substrate) is too small, the electrical resistance of the substrate will increase and the internal resistance of the battery will increase, so the basis weight is preferably 200 g/m ² or more.

<Electrode laminate>
The electrode stack of the all-solid-state battery has a positive electrode, a negative electrode, and a solid electrolyte layer, with the solid electrolyte layer being interposed between the positive electrode and the negative electrode.

(positive electrode)
The positive electrode can be, for example, a molded body (such as a pellet) made by molding a positive electrode mixture containing a positive electrode active material, or a structure having a layer formed of a positive electrode mixture (positive electrode mixture layer) on one or both sides of a current collector.

When the all-solid-state battery is a primary battery, the positive electrode active material can be the same as the positive electrode active material used in conventionally known non-aqueous electrolyte primary batteries. Specifically, for example, manganese dioxide, lithium-containing manganese oxide (e.g., LiMn ₃ O ₆ , or a composite oxide having the same crystal structure as manganese dioxide (β-type, γ-type, or a structure in which β-type and γ-type are mixed, etc.) and a Li content of 3.5 mass% or less, preferably 2 mass% or less, more preferably 1.5 mass% or less, particularly preferably 1 mass% or less), lithium-containing composite oxide such as Li _a Ti _5/3 O ₄ (4/3≦a<7/3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag ₂ S; nickel oxides such as NiO ₂ ; and the like.

When the all-solid-state battery is a secondary battery, the positive electrode active material may be the same as the positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries. Specifically, the spinel-type lithium manganese composite oxide represented by Li _1-x M _r Mn _2-r O ₄ (wherein M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0≦x≦1, 0≦r≦1), Li _r Mn _(1-s-t) Ni _s M _t O _(2-u) F _v a layered compound represented by Li 1-x Co 1-r M r O 2 (wherein M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, and 0≦r≦1.2, 0<s<0.5, 0≦t≦0.5, u+v<1, -0.1≦u≦0.2, 0≦v≦0.1); a lithium cobalt composite oxide represented by Li _1-x Ni _1-r M _r O ₂ (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦ _x ≦1 _{, 0} ≦ _r ≦ _0.5); a lithium nickel composite oxide represented by Li 1+s-x M 1-r N r PO 4 F s (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦1, 0≦r≦0.5); an olivine type composite oxide represented by Li _2-x M _{1-r N r} P ₂ O ₇ (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦x≦ ₁ , 0≦r≦0.5, ₀ ≦ _s ≦1 _{) ;} (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦x≦2, 0≦r≦0.5), and the like can be exemplified. Among these, only one type may be used, or two or more types may be used in combination.

When the all-solid-state battery is a secondary battery, the average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, and preferably 10 μm or less, more preferably 8 μm or less. The positive electrode active material may be either primary particles or secondary particles formed by agglomeration of primary particles. When a positive electrode active material with an average particle size in the above range is used, a large interface with the solid electrolyte contained in the positive electrode can be obtained, thereby further improving the output characteristics of the battery.

The average particle diameter of various particles (such as positive electrode active material and solid electrolyte) referred to in this specification means the 50% diameter value ( _D50 ) in the volume-based integrated fraction when the integrated volume is calculated from particles with small particle sizes using a particle size distribution measurement device (such as the Microtrack particle size distribution measurement device "HRA9320" manufactured by Nikkiso Co., Ltd.).

When the all-solid-state battery is a secondary battery, it is preferable that the positive electrode active material has a reaction suppression layer on its surface to suppress reaction with the solid electrolyte contained in the electrode.

If the positive electrode active material comes into direct contact with the solid electrolyte in the positive electrode mixture molded body or in the positive electrode mixture layer, the solid electrolyte may oxidize and form a resistance layer, which may reduce the ionic conductivity in the positive electrode mixture molded body or in the positive electrode mixture layer. By providing a reaction suppression layer on the surface of the positive electrode active material that suppresses reaction with the solid electrolyte and preventing direct contact between the positive electrode active material and the solid electrolyte, it is possible to suppress the reduction in ionic conductivity in the positive electrode mixture molded body or in the positive electrode mixture layer due to oxidation of the solid electrolyte.

The reaction suppression layer may be made of a material that has ion conductivity and can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can form the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti and Zr, more specifically, Nb-containing oxides such as LiNbO ₃ , Li ₃ PO ₄ , Li ₃ BO ₃ , Li ₂ SO ₄ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , LiTiO ₃ , LiZrO ₃ , Li ₂ WO ₄ and the like. The reaction suppression layer may contain only one of these oxides, or may contain two or more of them, and further, a plurality of these oxides may form a composite compound. Among these oxides, it is preferable to use an Nb-containing oxide, and it is more preferable to use LiNbO ₃ .

The reaction suppression layer is preferably present on the surface in an amount of 0.1 to 1.0 parts by mass per 100 parts by mass of the positive electrode active material. This range allows for good suppression of the reaction between the positive electrode active material and the solid electrolyte.

Methods for forming a reaction suppression layer on the surface of the positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 85 mass % from the viewpoint of increasing the energy density of the all-solid-state battery in which the electrode is used as the positive electrode.

The positive electrode mixture can contain a conductive assistant. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes. For example, when Ag ₂ S is used as the active material, conductive Ag is generated during the discharge reaction, so the conductive assistant does not need to be contained. When the conductive assistant is contained in the positive electrode mixture, the content is preferably 1.0 parts by mass or more, preferably 7.0 parts by mass or less, and more preferably 6.5 parts by mass or less, when the content of the positive electrode active material is 100 parts by mass.

The positive electrode mixture may contain a binder. A specific example of such a binder is a fluororesin such as polyvinylidene fluoride (PVDF). Note that, as in the case of containing a sulfide-based solid electrolyte in the positive electrode mixture, if good moldability can be ensured in forming the positive electrode mixture molded body and the positive electrode mixture layer without using a binder, the positive electrode mixture does not need to contain a binder.

If the positive electrode mixture requires a binder, its content is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, if the positive electrode mixture can obtain moldability without requiring a binder, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

The positive electrode mixture may contain a solid electrolyte. There are no particular limitations on the solid electrolyte contained in the positive electrode mixture as long as it has lithium ion conductivity. For example, sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, oxide-based solid electrolytes, etc. can be used, but it is preferable to contain a sulfide-based solid electrolyte in the positive electrode mixture because of its high lithium ion conductivity.

Examples of sulfide-based solid electrolytes include particles of Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-P ₂ S ₅ -GeS ₂ , and Li ₂ S-B ₂ S ₃ based glass. In addition, thio-LISICON type electrolytes, which have been attracting attention in recent years for their high Li ion conductivity, are exemplified by Li ₁₀ GeP ₂ S ₁₂ , Li _9.54 Si _1.74 P _1.44 S _11.7 Cl _0.3 , and have the general formula Li _{12-12a-b+c+6d-e} M ¹ _3+a-b-c-d M ² _b M ³ _c M ⁴ _d M ⁵ _12-e X _e (wherein M ¹ is Si, Ge, or Sn, and M ^M2 is P or V, ^M3 is Al, Ga, Y or Sb, ^M4 is Zn, Ca, or Ba, ^M5 is S or either S and O, and X is F, Cl, Br or I, 0≦a<3, 0≦b+c+d≦3, 0≦e≦3) or one having an argyrodite-type crystal structure (argyrodite-type solid electrolyte) can also be used.

Examples of hydride-based solid electrolytes include LiBH ₄ , solid solutions of LiBH ₄ and the following alkali metal compounds (for example, those in which the molar ratio of LiBH ₄ to the alkali metal compound is 1:1 to 20:1), etc. Examples of the alkali metal compounds in the solid solutions include at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

Examples of halide-based solid electrolytes include monoclinic LiAlCl ₄ , defective spinel or layered structure LiInBr ₄ , and monoclinic Li _6-3m Y _m X ₆ (wherein 0<m<2 and X=Cl or Br). Other known solid electrolytes that can be used include those described in, for example, WO 2020/070958 and WO 2020/070955.

Examples of oxide-based solid electrolytes include garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ , NASICON-type Li _1+O Al _1+O Ti _2-O (PO ₄ ) ₃ and Li _1+p Al _1+p Ge _2-p (PO ₄ ) ₃ , and perovskite-type Li _3q La _2/3-q TiO ₃ .

Among these solid electrolytes, sulfide-based solid electrolytes containing Li and P are more preferred due to their high lithium ion conductivity, and argyrodite-type solid electrolytes are even more preferred due to their high lithium ion conductivity and chemical stability.

As the argyrodite-type crystalline solid electrolyte, for example, one represented by the following general composition formula (1), the following general composition formula (2) or the following general composition formula (3), such as Li ₆ PS ₅ Cl, is particularly preferred.

Li _7-k PS _6-k X _k (1)

In the general composition formula (1), X represents one or more halogen elements, and 0.2<k<2.0.

Li _7-x+y PS _6-x Cl _x+y (2)

In the general composition formula (2), 0.05≦y≦0.9 and -3.0x+1.8≦y≦-3.0x+5.7.

Li _7-a PS _6-a Cl _b Br _c (3)

In the general composition formula (3), a = b + c, 0 < a ≦ 1.8, and 0.1 ≦ b/c ≦ 10.0.

The average particle size of the solid electrolyte is preferably 0.1 μm or more, and more preferably 0.2 μm or more, from the viewpoint of reducing grain boundary resistance, while from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte, it is preferably 10 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.

From the viewpoint of further increasing the ionic conductivity in the positive electrode and further improving the output characteristics of the all-solid-state battery, the content of the solid electrolyte in the positive electrode mixture is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more, when the content of the positive electrode active material is 100 parts by mass. However, if the amount of solid electrolyte in the positive electrode mixture is too large, the amounts of other components may be reduced, and the effects of these components may be reduced. Therefore, the content of solid electrolyte in the positive electrode mixture is preferably 65 parts by mass or less, and more preferably 60 parts by mass or less, when the content of the positive electrode active material is 100 parts by mass.

The thickness of the positive electrode mixture molded body or the positive electrode mixture layer is preferably 0.2 mm or more, more preferably 0.5 mm or more, and even more preferably 0.7 mm or more, while it is preferably 2 mm or less, more preferably 1.7 mm or less, and even more preferably 1.5 mm or less.

A current collector can be used for the positive electrode. Positive electrode current collectors include metal substrates such as metal foil, punched metal, net, expanded metal, and foamed metal substrates; carbon sheets such as carbon nonwoven fabric; and the like. The thickness of the positive electrode current collector is preferably 50 to 1500 μm. When the positive electrode current collector is made of metal, it is preferable that the metal does not react or corrode within the battery, and an alloy (Ni-Cr alloy) with the same composition as that described above for constituting the porous metal substrate is more preferable.

Among these current collectors, it is preferable to use a foamed metal substrate because it has a higher current collection efficiency. As mentioned above, examples of foamed metal substrates that can be used for the current collector include "Celmet (registered trademark)" manufactured by Sumitomo Electric Industries, Ltd. When the current collector is made of a foamed metal substrate, at least a portion of the positive electrode mixture (positive electrode mixture layer) penetrates into the pores, which increases the contact area between the current collector and the positive electrode mixture layer, making it possible to lower the resistance of the positive electrode.

In other words, it is preferable that the positive electrode has a foamed metal substrate as a current collector, and at least a portion of the positive electrode mixture is filled into the pores of the foamed metal substrate. More specifically, it is preferable that at least a portion of the foamed metal substrate, which is the positive electrode current collector, including the end portion on the positive electrode mixture layer side, is embedded in the surface layer of the positive electrode mixture layer and is integrated with the positive electrode mixture layer.

Incidentally, such metal substrates are usually compressed and reduced in thickness when preparing a positive electrode together with the positive electrode mixture, so that the thickness before use in the positive electrode is greater than the thickness in the positive electrode. For example, the thickness of the foamed metal substrate before compression is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more, while it is preferably 3 mm or less, more preferably 2 mm or less, and particularly preferably 1.5 mm or less. For example, in the method of producing an electrode laminate described below, when a positive electrode is produced through a process of pressing the positive electrode mixture and the metal substrate, the foamed metal substrate is compressed in the thickness direction, and its thickness becomes the value described below.

The porosity and area density of the foamed metal substrate before compression may be in the same range as those of the conductive connecting member described above.

In the case of a positive electrode having a foamed metal substrate as a current collector, at least a portion of which, including the end portion on the side of the positive electrode mixture layer, is embedded in the surface layer of the positive electrode mixture layer and integrated with the positive electrode mixture layer, the thickness of the portion of the metal substrate embedded in the positive electrode mixture layer is preferably 10% or more, and more preferably 20% or more, of the thickness of the metal substrate (the thickness of the entire metal substrate, including the thickness of the portion where the positive electrode mixture layer coexists. Unless otherwise specified, the same applies below to the thickness of the foamed metal substrate of the positive electrode) from the viewpoint of more reliably integrating the metal substrate and the positive electrode mixture layer.

In a positive electrode having a foamed metal substrate as a current collector, at least a portion of which, including the end on the positive electrode mixture layer side, is embedded in the surface layer of the positive electrode mixture layer and integrated with the positive electrode mixture layer, in order to reduce the resistance when the metal substrate is brought into contact with a conductive path (or conductive connection member) in the exterior body of the all-solid-state battery, it is desirable that the end of the metal substrate opposite the positive electrode mixture layer side (hereinafter sometimes referred to as the surface side end) is not embedded in the positive electrode mixture layer, and the end of the positive electrode (the surface of the positive electrode) is composed only of the metal substrate. That is, for example, in the manufacturing method of the electrode laminate described below, when the positive electrode is manufactured through a process of pressurizing the positive electrode mixture and the metal substrate, it is desirable that the metal substrate is compressed in the thickness direction, the pores in the surface side end of the metal substrate are crushed and eliminated, and only the metal substrate is exposed on the surface of the positive electrode. However, some of the pores at the surface end of the metal substrate may not be crushed and may remain as pores or may be filled with the positive electrode mixture. As long as the contact resistance with the conductive path is not significantly affected, a part of the mixture may be exposed to the surface of the positive electrode together with the surface end of the metal substrate. In other words, as long as the surface end of the foamed metal substrate can be exposed to the electrode surface, the entire metal substrate (100% of the thickness of the metal substrate) may be embedded in the surface layer of the positive electrode mixture layer. By filling the pores of the metal substrate up to the surface of the positive electrode with the positive electrode mixture, the integration of the positive electrode mixture layer and the metal substrate can be more reliably achieved.

FIG. 4 shows an SEM photograph to explain the surface state of an electrode having a metal substrate as a current collector (note that the SEM photograph shown in FIG. 4 is not of the surface of the positive electrode in the all-solid-state battery of the present invention, but of a positive electrode having a surface state similar to that of the positive electrode in the all-solid-state battery of the present invention, and is shown only for the purpose of explaining the surface state of the positive electrode in the all-solid-state battery of the present invention). On the surface of the positive electrode shown in FIG. 4, the end of the metal substrate 122 of the positive electrode is exposed, but part of the positive electrode mixture 121a is also exposed on the surface of the electrode by entering pores present at the end of the metal substrate.

However, since the contact resistance between the metal substrate and the conductive path (or conductive connection member) of the exterior body increases as the proportion (area ratio) of the positive electrode mixture exposed on the surface of the positive electrode increases, the proportion of the exposed area of the positive electrode mixture on the positive electrode surface is preferably 50% or less in a plan view, more preferably 25% or less, even more preferably 15% or less, and particularly preferably 10% or less.

In a positive electrode having a metal substrate as a current collector, when at least a portion of the metal substrate is embedded in the surface layer of the positive electrode mixture layer, from the viewpoint of more reliably integrating the metal substrate and the positive electrode mixture layer, the thickness of the metal substrate is preferably 1% or more, more preferably 2% or more, and particularly preferably 3% or more of the total thickness of the positive electrode mixture layer (including the thickness of the portion coexisting with the metal substrate. Unless otherwise specified, the "thickness of the positive electrode mixture layer" referred to below means the "total thickness of the positive electrode mixture layer" here). Also, from the viewpoint of increasing the filling property of the positive electrode mixture layer in the positive electrode, the thickness of the metal substrate is preferably 30% or less, more preferably 20% or less, and particularly preferably 10% or less of the thickness of the positive electrode mixture layer.

In addition, in a positive electrode having a metal substrate as a current collector, the thickness of the metal substrate is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more, while it is preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less.

In the electrodes (positive and negative electrodes) referred to in this specification, the thickness of the metal substrate and the thickness of the mixture layer (positive and negative mixture layers) are determined from the maximum width in the thickness direction of the area in which the metal substrate can be confirmed and the area in which the mixture (positive and negative mixture layers) can be confirmed in an image of a cross section of the electrode in the thickness direction observed with an SEM at a magnification of 50 to 1000 times. The thickness of the part of the metal substrate embedded in the mixture layer (positive and negative mixture layers) is determined from the maximum width in the thickness direction of the part where the area in which the metal substrate can be confirmed overlaps with the area in which the mixture can be confirmed (the values in the examples described later are determined by these methods).

The proportion (area ratio) of the positive electrode mixture exposed on the surface of the positive electrode can be determined by the ratio (A/B) of the total area of the exposed positive electrode mixture (A) to the area of the entire positive electrode (B) in an image of the positive electrode surface observed with an SEM at a magnification of 50 to 200 times (the values in the examples described below were determined using this method).

The positive electrode can be manufactured by pressing the positive electrode mixture to form a molded body (such as a pellet) of the positive electrode mixture, and bonding this to a current collector as necessary, by pressing the positive electrode mixture and current collector together to simultaneously mold the positive electrode mixture and integrate it with the current collector, or by applying a positive electrode mixture-containing composition, in which the positive electrode mixture is dispersed in a solvent, to a current collector, drying it, and then applying pressure as necessary.

The solvent for the positive electrode mixture-containing composition is preferably one that does not easily deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with trace amounts of water, so it is preferable to use non-polar aprotic solvents such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. In particular, it is more preferable to use ultra-dehydrated solvents with a water content of 0.001 mass% (10 ppm) or less. In addition, fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by Mitsui DuPont Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Nippon Zeon Co., Ltd., and "Novec (registered trademark)" manufactured by Sumitomo 3M Co., Ltd., as well as non-aqueous organic solvents such as dichloromethane and diethyl ether can also be used.

(Negative electrode)
The negative electrode constituting the electrode laminate may be, for example, a molded body (such as a pellet) obtained by molding a negative electrode mixture containing a negative electrode active material, or a structure having a layer (negative electrode mixture layer) formed of a negative electrode mixture on one or both sides of a current collector. In addition, a negative electrode using metallic lithium or lithium-aluminum alloy foil as is, or a negative electrode having metallic lithium or lithium-aluminum alloy foil and a current collector may also be used.

Anode active materials in anodes having anode mixtures include, for example, carbon materials such as graphite, lithium titanium oxides (lithium titanate, etc.), simple substances containing elements such as Si and Sn, compounds (oxides, etc.), and alloys thereof. Lithium metal and lithium alloys (lithium-aluminum alloys, lithium-indium alloys, etc.) can also be used as anode active materials.

The content of the negative electrode active material in the negative electrode mixture is preferably 40 to 80 mass % from the viewpoint of increasing the energy density of the all-solid-state battery in which the electrode is used as the negative electrode.

The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives as those exemplified above as those that may be contained in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 10 to 30 parts by mass when the content of the negative electrode active material is 100 parts by mass.

The negative electrode mixture may contain a binder. Specific examples include the same binders as those exemplified above as those that may be contained in the positive electrode mixture. Note that, as in the case of containing a sulfide-based solid electrolyte in the negative electrode mixture, if good moldability can be ensured in forming the negative electrode mixture molded body and the negative electrode mixture layer without using a binder, the negative electrode mixture does not need to contain a binder.

If the negative electrode mixture requires a binder, its content is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, if the negative electrode mixture can obtain moldability without requiring a binder, its content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

The negative electrode mixture can contain a solid electrolyte. Examples of the solid electrolyte to be contained in the negative electrode mixture include the various sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes exemplified above as the solid electrolytes that can be contained in the positive electrode mixture. Among these solid electrolytes, sulfide-based solid electrolytes are preferred because of their high lithium ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type solid electrolytes are even more preferred because of their high lithium ion conductivity and high chemical stability, and those represented by the general composition formula (1), the general composition formula (2), or the general composition formula (3) are particularly preferred.

For the same reasons as in the case of the positive electrode mixture, the average particle size of the solid electrolyte in the negative electrode mixture is preferably 0.1 μm or more, more preferably 0.2 μm or more, and is preferably 10 μm or less, more preferably 5 μm or less.

From the viewpoint of further increasing ionic conductivity in the negative electrode and further improving the output characteristics of the all-solid-state battery, the content of the solid electrolyte in the negative electrode mixture is preferably 30 parts by mass or more, and more preferably 35 parts by mass or more, when the content of the negative electrode active material is 100 parts by mass. However, if the amount of solid electrolyte in the negative electrode mixture is too large, the amount of other components may decrease, and the effects of these components may become smaller. Therefore, the content of solid electrolyte in the negative electrode mixture is preferably 130 parts by mass or less, and more preferably 110 parts by mass or less, when the content of the negative electrode active material is 100 parts by mass.

The thickness of the negative electrode mixture molded body or negative electrode mixture layer in the negative electrode is preferably 0.2 mm or more, more preferably 0.5 mm or more, and even more preferably 0.7 mm or more, while it is preferably 2 mm or less, more preferably 1.7 mm or less, and even more preferably 1.5 mm or less.

A current collector can be used for the negative electrode. Examples of the negative electrode current collector include metal substrates such as metal foil, punched metal, net, expanded metal, and foamed metal substrates; and carbon sheets such as carbon nonwoven fabric. The thickness of the negative electrode current collector is preferably 50 to 1500 μm. When the negative electrode current collector is made of metal, it is preferable that the metal does not react or corrode in the battery, and an alloy of the same composition as that described above for constituting the porous metal substrate (an alloy containing Ni and Cr) is more preferable.

The negative electrode current collector and the negative electrode can be fabricated in the same manner as the positive electrode current collector and the positive electrode described above, so a detailed explanation will be omitted.

(Solid electrolyte layer)
Specific examples of the solid electrolyte constituting the solid electrolyte layer of the electrode laminate include the same solid electrolytes as those exemplified above as those that can be contained in the positive electrode mixture. Among the above-mentioned solid electrolytes, it is preferable to use a sulfide-based solid electrolyte because it has high lithium ion conductivity and also has a function of improving moldability, and it is more preferable to use a sulfide-based solid electrolyte having an argyrodite-type crystal structure, and it is even more preferable to use one represented by the general composition formula (1), the general composition formula (2), or the general composition formula (3).

The solid electrolyte layer can be formed by a method of compressing the solid electrolyte by pressure molding or the like; a method of dispersing the solid electrolyte in a solvent to prepare a composition for forming the solid electrolyte layer, applying it to the substrate, positive electrode, or negative electrode, drying it, and, if necessary, performing pressure molding such as pressing.

The solid electrolyte layer may contain a binder such as acrylic resin or fluororesin to maintain its shape.

The solid electrolyte layer may also have a porous body such as a resin nonwoven fabric as a support. In this case, a solid electrolyte sheet having the support is obtained.

As with the solvent used in the positive electrode mixture-containing composition, it is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte for use in the composition for forming the solid electrolyte layer. It is preferable to use the various solvents listed above as examples of solvents for the positive electrode mixture-containing composition, and it is particularly preferable to use an ultra-dehydrated solvent with a moisture content of 0.001% by mass (10 ppm) or less.

The thickness of the solid electrolyte layer is preferably 10 to 200 μm.

(Method of manufacturing electrode laminate)
The method for producing the electrode laminate is not particularly limited, but it can be produced, for example, by a production method including the following steps 1 to 3. Note that the steps will be described below in relation to the case where a foamed metal substrate is used as the current collector.

In the first step, the mixture (positive electrode mixture or negative electrode mixture) is poured into a mold and pressure molded. The surface pressure for pressure molding in the first step is preferably, for example, 30 to 500 MPa.

In the next step, a foamed metal substrate is placed on the mixture formed in the first step, and then in the next step, a pressure is applied to the mixture and the metal substrate. The pressure applied in the third step further compresses the mixture while embedding the metal substrate in the mixture from the end on the mixture side, and compresses the metal substrate in the thickness direction, integrating the mixture layer (positive electrode mixture layer or negative electrode mixture layer) with the metal substrate to form an electrode (positive electrode or negative electrode).

As described above, in this third step, the metal substrate is compressed in the thickness direction, and the degree of compression is preferably such that the thickness of the metal substrate after compression is 30% or less of the thickness before compression, more preferably 20% or less, and particularly preferably 10% or less, from the viewpoint of ensuring a more reliable bond between the metal substrate and the composite layer. Also, from the viewpoint of retaining a certain amount or more of the composite in the voids of the metal substrate and increasing the bond strength between the metal substrate and the composite layer, the thickness of the metal substrate after compression in the third step is preferably 1% or more of the thickness before compression, and more preferably 2% or more.

The surface pressure during the third step is preferably 800 MPa or more, more preferably 1000 MPa or more, and particularly preferably 1200 MPa or more, in order to compress and mold the mixture and sufficiently increase the density of the mixture layer. There is no particular upper limit to the surface pressure during the third step, but in a typical pressurizing device, the upper limit is usually around 2000 MPa.

By going through the first to third steps, it is possible to obtain an electrode (positive or negative electrode) in which at least a portion of the metal substrate, including the end on the mixture layer side (a certain range in the thickness direction from the end of the metal substrate), is embedded in the surface layer of the mixture layer and is integrated with the mixture layer, and the other end of the metal substrate is exposed on the surface of the electrode.

If the surface pressure during the application of pressure in the third step becomes too high, it may cause cracks when the metal base material is compressed. However, even if the metal base material breaks into pieces, this can contribute to reducing the contact resistance if the ends are exposed on the surface of the electrode.

The positive and negative electrodes are produced through the first, second and third steps described above, and are then arranged on both sides of the solid electrolyte layer, and if necessary, pressurized to form an electrode laminate.

Furthermore, before the first step, a preliminary step is performed in which the solid electrolyte is placed in a mold and pressure-molded, and a mixture (positive electrode mixture or negative electrode mixture) is placed on the solid electrolyte that has been pressure-molded in this preliminary step. Then, the first, second, and third steps are performed in sequence to produce an integrated product of the solid electrolyte layer and the electrode (positive electrode or negative electrode), which can be used in the electrode laminate.

The surface pressure during pressure molding in the preliminary process is preferably, for example, 30 to 120 MPa.

Also, an electrode stack can be manufactured by forming one of the positive and negative electrodes on one side of a solid electrolyte layer through a preliminary process, followed by the first, second and third processes, and then sequentially carrying out the first, second and third processes on the other side of the solid electrolyte layer to form the other electrode (negative or positive electrode).

<Exterior body>
For the exterior body of the all-solid-state battery, a battery container having a concave container (exterior container) and a sealing body (lid) as shown in FIG. 1; a flat (coin-shaped, button-shaped, etc.) or tubular (cylindrical, rectangular, etc.) battery container having a metal exterior can and a metal sealing body; a battery container made of a laminate film exterior body composed of a metal laminate film such as an aluminum laminate film; and the like can be used.

In the case of a battery container having a concave container and a sealing body as shown in Figure 1, the concave container can be made of ceramics or resin. The sealing body can be made of ceramics, resin, or metal (iron-nickel alloy, iron-based alloy such as iron-nickel-cobalt alloy, etc.).

In the concave container, the connection terminal portion and the conductive path connecting the electrode of the electrode stack and the connection terminal portion can be made of metals such as manganese, cobalt, nickel, copper, molybdenum, silver, palladium, tungsten, platinum, and gold, or alloys containing these metals.

The concave container and the sealing body can be sealed by bonding them together with an adhesive, or when using a metal sealing body, as shown in FIG. 1, a seal ring 200 made of metal (such as an iron-nickel alloy or an iron-based alloy such as an iron-nickel-cobalt alloy) can be placed on the sealing body 160 side of the side wall 152 of the concave container 150 (the upper side in the figure) to make the sealing body side of the side wall out of metal, and the concave container and the sealing body can be welded together to seal.

The shape of the exterior body in a plan view may be circular or polygonal, such as a quadrilateral (square or rectangle). If it is polygonal, the corners may be curved.

(Elastic conductive member)
The elastic conductive member is not particularly limited as long as it functions as a leaf spring that presses the electrode stack toward the inner bottom surface of the concave container. Specifically, for example, as shown in Figures 1 and 3, an elastic conductive member having a shape including a supported portion 211 shaped according to the support portion 153 of the concave container 150 and a flat portion 212 including a spring portion (spring piece) 213; an elastic conductive member having a cross-sectional shape including a locking portion shaped according to the support portion of the concave container and a recess that presses the electrode stack; etc.

The elastic conductive member can be formed from a plate made of nickel, iron, copper, chromium, cobalt, titanium, aluminum, or an alloy of these. Of the above examples, the metal constituting the elastic conductive member is preferably a stainless steel plate or a stainless steel plate plated with nickel, and in order to facilitate the function of the plate spring, stainless steel for springs such as SUS301-CSP, SUS304-CSP, SUS316-CSP, SUS420J2-CSP, SUS631-CSP, and SUS632J1-CSP are more preferable.

The thickness of the metal plate constituting the elastic conductive member is preferably 0.05 mm or more, more preferably 0.07 mm or more, and even more preferably 0.1 mm or more, in order to ensure a certain level of pressing force on the electrode laminate. On the other hand, in order to prevent the elastic conductive member from becoming too thick, which would increase the storage volume inside the battery container, and to make the elastic conductive member easily deformable so that it can be easily engaged with the side wall portion of the concave container, the thickness of the metal plate constituting the elastic conductive member is preferably 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.3 mm or less.

The present invention will be described in detail below based on examples. However, the following examples do not limit the present invention.

Example 1
A negative electrode mixture was prepared by mixing lithium titanate (Li ₄ Ti ₅ O ₁₂ , negative electrode active material) having an average particle size of 2 μm, a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an average particle size of 0.7 μm, and graphene (conductive additive) in a mass ratio of 50:41:9.

In addition, LiCoO ₂ (positive electrode active material) having an average particle size of 5 μm and having a LiNbO ₃ coating layer formed on the surface, a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an average particle size of 0.7 μm, and graphene were mixed in a mass ratio of 65:30.7:4.3 to prepare a positive electrode mixture.

Next, a powder of sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an average particle size of 0.7 μm was placed in a powder molding die, and pressure molding was performed at a surface pressure of 70 MPa using a press machine to form a provisionally molded layer of the solid electrolyte layer. Furthermore, the negative electrode mixture was placed on the upper surface of the provisionally molded layer of the solid electrolyte layer and pressure molding was performed at a surface pressure of 50 MPa, and a provisionally molded layer of the negative electrode was further formed on the provisionally molded layer of the solid electrolyte layer.

Next, a foamed metal substrate (Celmet (registered trademark) from Sumitomo Electric Industries, Ltd., made of a Ni-Cr alloy with Ni and Cr contents of 95% by mass and 5% by mass, respectively) cut to a diameter of 7.25 mm (thickness: 1.1 mm, porosity: 98%, basis weight: 347 g/m ² ) was placed on the provisionally molded layer of the negative electrode formed on the provisionally molded layer of the solid electrolyte layer as a current collector, and pressure molding was performed at a surface pressure of 300 MPa to form an integrated product of the solid electrolyte layer and the negative electrode.

Furthermore, after the mold was turned upside down, the positive electrode mixture was placed on the upper surface of the solid electrolyte layer in the mold (the surface opposite to the surface having the negative electrode) and pressure molding was performed with a surface pressure of 50 MPa, forming a provisionally molded layer of the positive electrode on the solid electrolyte layer.

Next, a cut foamed metal substrate made of Ni-Cr alloy with the same composition as that used for the negative electrode was placed as a current collector on the provisionally molded layer of the positive electrode formed on the solid electrolyte layer, and pressure molding was performed with a surface pressure of 1400 MPa to obtain an electrode laminate.

In the obtained electrode laminate, the thickness of the negative electrode mixture layer of the negative electrode, the thickness of the metal substrate, and the thickness of the portion of the metal substrate embedded in the negative electrode mixture layer were 1400 μm, 60 μm (5% of the thickness of the metal substrate before use in the negative electrode), and 60 μm (100% of the total thickness of the metal substrate), respectively. In addition, the area ratio of the portion of the negative electrode mixture exposed on the surface of the negative electrode was 7%.

In addition, in the obtained electrode laminate, the thickness of the positive electrode mixture layer of the positive electrode, the thickness of the metal substrate, and the thickness of the portion of the metal substrate embedded in the positive electrode mixture layer were 800 μm and 60 μm (5% of the thickness of the metal substrate before use in the positive electrode), and 60 μm (100% of the total thickness of the metal substrate), respectively. In addition, the area ratio of the portion of the positive electrode mixture exposed on the surface of the positive electrode was 7%.

　A foamed metal substrate made of Ni-Cr alloy (i.e., Ni and Cr contents of 95% and 5% by mass, respectively) with the same composition as that used for the positive and negative electrodes was cut to a diameter of 7.25 mm and placed on the inner bottom surface of a concave container (ceramic depth 2.5 mm) with a structure similar to that shown in Figures 1 and 2, with a seal ring made of an iron-nickel-cobalt alloy arranged on the upper part of the side wall. The metal substrate was brought into contact with the conductive path of the positive electrode as a conductive connecting member, and the electrode stack was placed on top of it with the positive electrode facing down. Furthermore, an elastic conductive member made of a stainless steel plate (thickness 0.2 mm) with a shape similar to that shown in Figures 1 and 3 was placed on top of the negative electrode of the electrode stack, with its supported portion engaged with the support portion of the concave container. Then, the spring piece of the elastic conductive member was bent toward the negative electrode side of the electrode laminate, and the tip was bent toward the flat portion side, and the spring piece was brought into contact with the negative electrode of the electrode laminate at a location on the boundary side with the flat portion from the tip portion so as to press the electrode laminate toward the inner bottom surface of the concave container. After that, a sealing body made of an iron-nickel-cobalt alloy plate (thickness 0.1 mm) was placed on the seal ring of the concave container, and the sealing body and the concave container (seal ring) were welded to seal the battery container, thereby obtaining an all-solid-state secondary battery. In the obtained all-solid-state secondary battery, as described above, the elastic conductive member pressed the electrode laminate toward the inner bottom surface of the concave container, and as a result, the electrode laminate pressed the conductive connection member made of the foamed metal substrate. In addition, the thickness of the conductive connection member (foamed metal substrate) in the assembled all-solid-state secondary battery was 200 μm.

(Comparative Example 1)
An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the conductive connecting member placed on the inner bottom surface of the concave container was changed to a foamed metal substrate (weight: 330 g/ ^m2 ) made of pure Ni containing no Cr.

(Comparative Example 2)
An all-solid-state secondary battery was produced in the same manner as in Comparative Example 1, except that the foamed metal substrate used as the current collectors of the positive and negative electrodes was changed to a substrate made of the same pure Ni as that used as the conductive connecting member in Comparative Example 1.

The all-solid-state secondary batteries of the examples and comparative examples were charged at a constant current of 4 mA until the voltage reached 2.6 V, then charged at a constant voltage of 2.6 V until the current reached 0.05 mA, and then discharged at a constant current of 0.4 mA until the voltage reached 1.0 V.

Then, each battery was stored in a thermostatic chamber at 115°C for 28 days, removed and cooled to room temperature, after which it was charged at a constant current, charged at a constant voltage, and discharged at a constant current under the same conditions as above, and the discharge capacity after storage was measured.

The batteries whose resistance was measured after storage were also disassembled, and the presence or absence of corrosion of the porous metal substrate placed between the positive electrode of the electrode laminate and the exterior body, and of the current collector, was confirmed using an SEM.

These results are shown in Table 1.

The battery of Example 1, in which the conductive connection members and current collectors are both made of Ni-Cr alloy, suppresses the increase in resistance due to corrosion of the base material, and is able to increase the discharge capacity after storage compared to the battery of Comparative Example 1, in which the conductive connection members are made of Ni, and the battery of Comparative Example 2, in which both the conductive connection members and current collectors are made of Ni.

In addition, in addition to the above, when the base material for the conductive connection member was changed to an alloy with a composition of Ni 85% by mass - Cr 15% by mass, Ni 75% by mass - Cr 25% by mass, and Ni 65% by mass - Cr 35% by mass, all-solid-state secondary batteries were fabricated in the same manner as above and stored at 115°C for 28 days, and it was confirmed that no corrosion of the conductive connection member occurred.

In addition, the resistance value of the substrate for each of the alloy compositions (resistance value of the substrate alone before the battery is assembled) is shown in Table 2. From the viewpoint of reducing the internal resistance of the battery, it is clear that the Cr content is preferably 30 mass% or less, more preferably 20 mass% or less, and particularly preferably 10 mass% or less.

The present invention can be implemented in forms other than those described above without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the description of the appended claims rather than the description of the above specification, and all modifications within the scope of the claims are included in the scope of the claims.

The all-solid-state battery of the present invention can be used in the same applications as conventionally known primary and secondary batteries, but because it has a solid electrolyte instead of an organic electrolyte, it has excellent heat resistance and can be preferably used in applications where it is exposed to high temperatures.

REFERENCE SIGNS LIST 100 All-solid-state battery 110 Electrode laminate 120 Positive electrode 121 Positive electrode mixture layer 122 Positive electrode current collector 130 Negative electrode 131 Negative electrode mixture layer 132 Negative electrode current collector 140 Solid electrolyte layer 150 Concave container 151 Bottom surface portion 152 Side wall portion 153 Support portion 160 Sealing body 170 Connection terminal portion 171 Conductive path 180 Connection terminal portion 181 Conductive path 190 Porous metal substrate 200 Seal ring 210 Elastic conductive member 211 Supported portion 212 Planar portion 213 Spring portion (spring piece)
213a Boundary 213b Tip

Claims (5)

An all-solid-state battery comprising an electrode stack having a positive electrode, a negative electrode, and a solid electrolyte layer, and an exterior body enclosing the electrode stack,
The exterior body has a conductive path leading from the inside to the outside,
A porous metal substrate is provided between the positive electrode and/or the negative electrode and the conductive path of the exterior body,
At least one of the positive electrode, the negative electrode, and the solid electrolyte layer contains a sulfide-based solid electrolyte;
The porous metal substrate is made of an alloy containing Ni and Cr,
The Ni content in the alloy is 60% by mass or more,
The alloy has a Cr content of 0.1% by mass or more and 40% by mass or less. The solid-state battery according to claim 1, wherein the Ni content in the alloy is 70 mass% or more. The solid-state battery according to claim 1, wherein the Cr content in the alloy is 30 mass% or less. The all-solid-state battery according to claim 1, wherein the sulfide-based solid electrolyte contains an argyrodite-type solid electrolyte. The all-solid-state battery according to claim 1 , wherein the porous metal substrate has a basis weight of 600 g/m ² or less.

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