JP7128624B2 - All-solid secondary battery, laminated all-solid secondary battery, and method for manufacturing all-solid secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an all-solid secondary battery, a stacked all-solid secondary battery, and a method for manufacturing an all-solid secondary battery.

In recent years, attention has been focused on all-solid secondary batteries. An all-solid secondary battery has a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer arranged between these active material layers. In an all-solid secondary battery, a medium that conducts lithium ions is a solid electrolyte.

An all-solid secondary battery using such a solid electrolyte is expected to have an improved energy density compared to a conventional lithium-ion battery using an electrolytic solution. Moreover, as one of the methods for further improving the energy density of the all-solid secondary battery, there is a method of stacking a plurality of unit cells of the all-solid secondary battery to reduce the exterior body occupying the entire battery. For example, Patent Literature 1 discloses a method of obtaining a stacked all-solid secondary battery by pressing a pair of temporary battery bodies having roughened positive electrode current collectors.

JP 2017-157271 A

By the way, when the inventors of the present invention conducted studies, they faced a situation in which simply stacking a plurality of single cells of all-solid-state secondary batteries does not sufficiently exhibit battery characteristics. Specifically, in a laminated all-solid-state secondary battery, we faced a situation in which a short circuit occurred or good cycle characteristics could not be obtained, especially during charging.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved all-solid secondary battery that can be laminated in multiple layers without deteriorating battery characteristics. , to provide a laminated all-solid secondary battery in which the all-solid secondary batteries are laminated and a method for manufacturing the all-solid secondary battery.

In order to solve the above problems, according to one aspect of the present invention,
a first current collector;
a pair of first active material layers arranged on both sides of the first current collector;
a pair of solid electrolyte layers disposed on the surface of the pair of first active material layers opposite to the first current collector;
a pair of second active material layers disposed on the surface of the pair of solid electrolyte layers opposite to the first active material layer;
a pair of second current collectors disposed on the surface of the pair of second active material layers opposite to the solid electrolyte layer;
Among the pair of second current collectors, there is no convex portion having a height of more than 5.0 μm on the surface opposite to the second active material layer of one of the second current collectors, 0 or more and 1.0 or less projections having a height of more than 8.0 μm per 1 cm ² on the surface of the other second current collector opposite to the second active material layer, all solid A secondary battery is provided.

According to this aspect, it is possible to stack a plurality of all-solid secondary batteries without deteriorating battery characteristics.

Here, there may be no projections having a height of more than 5.0 μm on the surface of the one second current collector opposite to the second active material layer.
From this point of view, deterioration of the characteristics of the all-solid secondary battery during stacking can be more reliably suppressed.

Here, the surface of the other second current collector opposite to the second active material layer may not have a convex portion having a height of more than 5.0 μm.
From this point of view, deterioration of the characteristics of the all-solid secondary battery during stacking can be more reliably suppressed.

Further, the first active material layer is a positive electrode active material layer,
The second active material layer may be a negative electrode active material layer.
From this point of view, it is possible to stack a plurality of all-solid secondary batteries without deteriorating battery characteristics.

In addition, the second active material layer includes at least one of a negative electrode active material that forms an alloy with lithium and a negative electrode active material that forms a compound with lithium,
During charging, metallic lithium may be deposited in the second active material layer through the negative electrode active material.
From this point of view, the battery characteristics of the all-solid secondary battery are improved. In addition, such a second active material layer is relatively thin and easily affected by the shape of the adjacent second current collector, but such an influence is prevented in the present invention.

Further, charging of the first active material layer and the second active material layer when the first active material layer is a positive electrode active material layer and the second active material layer is a negative electrode active material layer The capacity ratio is given by the following formula (1)
0.002<b/a<0.5 (1)
where a is the charge capacity (mAh) of the first active material layer, and b is the charge capacity (mAh) of the second active material layer.
may be satisfied.
From this point of view, the battery characteristics of the all-solid secondary battery are improved. In addition, such a second active material layer is relatively thin and easily affected by the shape of the adjacent second current collector, but such an influence is prevented in the present invention.

Further, the second active material layer may contain at least one selected from the group consisting of amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc. good.
From this point of view, the battery characteristics of the all-solid secondary battery are improved.

According to another aspect of the invention, at least one insulating layer;
a plurality of all-solid-state secondary batteries stacked via the insulating layer,
The one second current collector of the all-solid-state secondary battery is arranged to face the other second current collector of the other adjacent all-solid-state secondary battery, and the stacked all-solid-state A secondary battery is provided.
According to this aspect, it is possible to stack a plurality of all-solid secondary batteries without deteriorating battery characteristics.

According to another aspect of the present invention, a first current collector, a pair of first active material layers disposed on both sides of the first current collector, and the pair of first active material layers A pair of solid electrolyte layers arranged on the surface of the layer opposite to the first current collector, and a pair of solid electrolyte layers arranged on the surface of the pair of solid electrolyte layers opposite to the first active material layer. Manufacture of an all-solid secondary battery comprising a second active material layer and a pair of second current collectors arranged on the surface of the pair of second active material layers opposite to the solid electrolyte layer a method,
forming the solid electrolyte layer on the first active material layer or the second active material layer by screen printing;
Regarding the laminate obtained by laminating the first current collector, the pair of first active material layers, the pair of solid electrolyte layers, the pair of second active material layers, and the pair of second current collectors , a step of placing a support material on one side of the laminate and isostatically pressing;
A method for manufacturing an all-solid secondary battery is provided.
According to this aspect, it is possible to stack a plurality of all-solid secondary batteries without deteriorating battery characteristics.

As described above, according to the present invention, a novel and improved all-solid secondary battery that can be stacked in multiple layers without degrading battery characteristics, and a laminated all-solid secondary battery obtained by stacking the all-solid secondary batteries A battery and a method for manufacturing the all-solid secondary battery can be provided.

A cross-sectional schematic diagram illustrating an all-solid secondary battery according to one embodiment of the present invention, 4 is a current collector plate cross-sectional analysis chart for explaining a method for evaluating unevenness in a current collector plate. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the laminated all solid state secondary battery which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the manufacturing method of the laminated all-solid-state secondary battery which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the manufacturing method of the laminated all-solid-state secondary battery which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the manufacturing method of the laminated all-solid-state secondary battery which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the all-solid secondary battery which the present inventors used for examination. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the laminated all-solid secondary battery which the present inventors used for examination. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the laminated all-solid secondary battery which the present inventors used for examination.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description. Also, each component in the drawing is enlarged or reduced as appropriate for ease of explanation, and the size and ratio of each component in the drawing differ from the actual ones.

<1. Study by the present inventors>
The present inventors first investigated the reason why the battery characteristics of each single cell are not sufficiently exhibited when a plurality of all-solid-state secondary batteries are stacked as single cells (single cells), as shown in FIG. A study was conducted using an all-solid-state secondary battery 200 .

The all-solid secondary battery 200 shown in FIG. , a pair of negative electrode active material layers 240 formed on the solid electrolyte layer 230, and a pair of negative electrode current collectors 250A and 250B arranged on the negative electrode active material layer 240.

Note that in manufacturing the all-solid secondary battery 200, a sheet-like solid electrolyte layer 230 formed on a non-woven fabric was used. A laminate obtained by laminating each layer as shown in FIG. 7 was placed on a support plate so that the negative electrode current collector 250A was in contact with the support plate, and isotropic pressing was performed to manufacture an all-solid secondary battery 200 .

First, as shown in FIG. 8, the all-solid secondary battery 200 is laminated and pressed with the insulating layer 310 interposed so that the negative electrode current collectors 250A face each other, and two all-solid secondary batteries 200 are obtained. A laminated all-solid secondary battery 300A was manufactured. Furthermore, as shown in FIG. 9, the negative electrode current collector 250A of one all-solid secondary battery 200 and the negative electrode current collector 250B of the other all-solid secondary battery 200 are laminated so as to face each other. A laminated all-solid secondary battery 300B having the all-solid secondary battery 200 was manufactured.

Battery characteristics were evaluated for the laminated all-solid secondary batteries 300A and 300B described above. As a result, in the stacked all-solid secondary battery 300A, the battery characteristics of the individual all-solid secondary batteries 200 were not impaired, sufficiently excellent cycle characteristics were obtained, and no short circuit occurred. On the other hand, the laminated all-solid-state secondary battery 300B did not have sufficiently excellent cycle characteristics, and a short circuit occurred early.

The present inventors focused on the lamination direction of the all-solid secondary battery 200 and the surface state of the negative electrode current collectors 250A and 250B as the cause of the difference in the battery characteristics of the laminated all-solid secondary batteries 300A and 300B. That is, the all-solid secondary battery 200 is manufactured by isostatic pressing, and in this case, the surface shapes of the negative electrode current collectors 250A and 250B may differ. Specifically, the negative electrode current collector 250A supported by the support plate tends to become smooth along the shape of the support plate. On the other hand, since the negative electrode current collector 250B is not supported by the support plate, the metal foil that constitutes the negative electrode current collector 250B does not form the negative electrode active material layer 240 and the solid electrolyte layer 230 inside the all-solid secondary battery 200. Unevenness is likely to occur due to the shape of

Therefore, with respect to the stacked all-solid secondary battery 300B, when the all-solid-state secondary batteries 200 are stacked, the negative electrode current collector 250B with many irregularities is placed in the other all-solid-state secondary battery 200B. , and the unevenness of the negative electrode current collector 250B physically affected the adjacent all-solid secondary battery 200. On the other hand, the inventors of the present invention have found that in the laminated all-solid secondary battery 300A, as a result of laminating the smooth negative electrode current collectors 250A facing each other, the influence on the adjacent all-solid secondary battery 200 is suppressed. , the battery characteristics of each all-solid secondary battery 200 were considered to be sufficiently maintained.

However, when the all-solid secondary battery 200 is manufactured by isostatic pressing, only one flat negative electrode current collector 250A is formed by the supporting plate. Therefore, when three or more all-solid secondary batteries 200 are stacked, the negative electrode current collector 250B with large unevenness faces the adjacent all-solid secondary battery 200 via the insulating layer 310 . Therefore, it has been difficult to simply stack three or more of the all-solid-state secondary batteries 200 that have been used so far.

A method of smoothing both surfaces of the all-solid secondary battery 200 by arranging support plates on both surfaces is also conceivable. However, when the support plates are arranged on both sides, the support plates can only be used once by the isostatic pressing, so such a method is not realistic in terms of cost.

In view of the above situation, the present inventors have proposed a shape of a current collector and a method for manufacturing an all-solid secondary battery having such a current collector so that three or more all-solid-state secondary batteries can be stacked. was investigated, and the present invention was achieved.

<2. Configuration of All-Solid-State Secondary Battery and Laminated All-Solid-State Secondary Battery>
Next, an all-solid secondary battery and a stacked all-solid secondary battery according to the present embodiment will be described. FIG. 1 is a cross-sectional schematic diagram for explaining an all-solid secondary battery according to the present embodiment, FIG. 2 is a current collector plate cross-sectional analysis chart for explaining a method for evaluating unevenness in a current collector plate, and FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram explaining the laminated all-solid-state secondary battery which concerns on embodiment.

[2.1. All-solid secondary battery]
As shown in FIG. 1 , the all-solid secondary battery 1 according to the present embodiment includes a positive electrode current collector (first current collector) 10 and a pair of positive electrode current collectors 10 formed on both sides of the positive electrode current collector 10 . A material layer (first active material layer) 20, a pair of solid electrolyte layers 30 formed on the positive electrode active material layer 20, and a pair of negative electrode active material layers (second active material layer) formed on the solid electrolyte layer 30. active material layer) 40 and a pair of negative electrode current collectors (second current collectors) 50A and 50B arranged on the negative electrode active material layer 40 . That is, the positive electrode active material layer 20, the solid electrolyte layer 30, the negative electrode active material layer 40, and the negative electrode current collector 50A (or the negative electrode current collector 50B) are laminated in this order on both sides of the positive electrode current collector 210. there is The all-solid secondary battery 1 is a so-called all-solid lithium ion secondary battery in which lithium ions move between the positive electrode active material layer 20 and the negative electrode active material layer 40 .

In the present embodiment, the negative electrode current collector 50A does not have protrusions having a height of more than 8.0 μm on the surface opposite to the adjacent negative electrode active material layer 40 . On the other hand, the negative electrode current collector 50B has only 0 or more and 1.0 or less protrusions having a height of more than 8.0 μm per 1 cm ² on the surface opposite to the adjacent negative electrode active material layer 40. That is, it is 1.0 or less.

As a result, when the stacked all-solid secondary battery 100 is obtained by stacking a plurality of all-solid-state secondary batteries 1, the battery characteristics of the stacked all-solid-state secondary battery 100 are excellent. That is, even when a plurality of, for example, three or more all-solid-state secondary batteries 1 are stacked, the battery characteristics of each all-solid-state secondary battery 1 in the stacked all-solid-state secondary battery 100 are prevented from deteriorating. .

Specifically, when one all-solid-state secondary battery 1 is stacked on the other all-solid-state secondary battery 1, the negative electrode current collector 50B having relatively large unevenness is placed on the smooth surface of the other all-solid-state secondary battery 1. Even when arranged on the negative electrode current collector 50A, the battery characteristics of each all-solid-state secondary battery 1 in the obtained laminated all-solid-state secondary battery 100 do not deteriorate. Therefore, in adjacent all-solid secondary batteries 1, by stacking the negative electrode current collector 50A and the negative electrode current collector 50B so as to face each other, deterioration of the battery characteristics of each all-solid secondary battery 1 is prevented. , three or more all-solid secondary batteries 1 can be stacked.

In contrast, in the conventional all-solid secondary battery 200, one negative electrode current collector 250A is smooth, but the other negative electrode current collector 250B has large irregularities. Therefore, if the negative electrode current collector 250A and the negative electrode current collector 250B face each other when stacking a plurality of all-solid-state secondary batteries 200, the battery characteristics are degraded. On the other hand, when the all-solid secondary batteries 200 are stacked so that the negative electrode current collectors 250A face each other, deterioration of battery characteristics can be prevented. However, it is impossible to stack three or more all-solid secondary batteries 200 such that the negative electrode current collectors 250A face each other.

The present inventors realized the negative electrode current collectors 50A and 50B having the predetermined surface conditions as described above by a method to be described later. In a conventional general all-solid secondary battery, it is difficult to realize a negative electrode current collector having the above-described predetermined surface state when isotropic pressing is performed.

As described above, in the present embodiment, the negative electrode current collector 50A should not have protrusions having a height of more than 8.0 μm on the surface opposite to the adjacent negative electrode active material layer 40. Preferably there are no protrusions with a height greater than 5.0 μm. As a result, when the all-solid secondary batteries 1 are stacked, the battery characteristics of the all-solid secondary batteries 1 are exhibited more reliably.

As described above, in the present embodiment, the negative electrode current collector 50A has 0 or more protrusions having a height of more than 8.0 μm per 1 cm ² on the surface opposite to the adjacent negative electrode active material layer 40 . There are only 0.0 or less, but preferably there are no protrusions with a height greater than 10.0 μm. As a result, when the all-solid secondary batteries 1 are stacked, the battery characteristics of the all-solid secondary batteries 1 are exhibited more reliably.

The height of the protrusions on the surfaces of the negative electrode current collectors 50A and 50B can be measured as follows. First, the three-dimensional shapes of the surfaces of the negative electrode current collectors 50A and 50B are measured to obtain measurement data. A three-dimensional shape can be measured by an optical three-dimensional shape measuring machine.
Next, a reference plane is set using the three-dimensional shape information obtained from the three-dimensional shape measurement data. A reference plane is set by estimating a plane by the least-squares method from the shape of the height image for which the area is specified.

Next, the projections are identified and the heights of the projections are detected in the three-dimensional shape measurement data for which the reference plane is set. A convex portion can be defined, for example, from the top of a cross-sectional curve in three-dimensional shape measurement data as shown in FIG. Then, for example, as shown in FIG. 3, the difference in height from the position of the apex to the lowest point of the points where the monotonically decreasing height is negative can be taken as the height of the convex portion. Since the surfaces of the negative electrode current collectors 50A and 50B are two-dimensional in the surface direction, the point where the monotonically decreasing width of the height from the top is negative exists as a closed curve. In this case, the lowest point on the closed curve can be used as the reference point for measuring the height of the apex.
The configuration of each layer will be described below.

(Positive electrode current collector)
The positive electrode current collector 10 is composed of a sheet-like conductor. Examples of the positive electrode current collector 10 include plate-shaped bodies or foil-shaped bodies made of stainless steel, titanium (Ti), nickel (Ni), aluminum (Al), or alloys thereof. The positive electrode current collector 10 is connected to wiring via a terminal (electrode tab) (not shown) when the all-solid secondary battery 1 is used.

(Positive electrode active material layer)
The positive electrode active material layers 20 are arranged on both sides of the positive electrode current collector 10 . The cathode active material layer 20 usually contains a cathode active material and a solid electrolyte. The solid electrolyte contained in the positive electrode active material layer 20 may or may not be of the same type as the solid electrolyte contained in the solid electrolyte layer 30 . Details of the solid electrolyte will be described in detail in the section of the solid electrolyte layer 30 .

The positive electrode active material may be any positive electrode active material capable of reversibly intercalating and deintercalating lithium ions.

For example, the positive electrode active material includes lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, and lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA). , nickel cobalt lithium manganate (hereinafter referred to as NCM), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide (Vanadium oxide) or the like. These positive electrode active materials may be used alone, or two or more of them may be used in combination.

Moreover, it is preferable that the positive electrode active material is formed by including a lithium salt of a transition metal oxide having a layered rock salt structure among the lithium salts described above. Here, "layered" represents a thin sheet-like shape. The term "rock salt structure" refers to a sodium chloride structure, which is a type of crystal structure. Represents structures that are offset by 1/2 of an edge.

Lithium salts of transition metal oxides having such a layered _rocksalt structure include, for example, _{LiNixCoyAlzO2 ( NCA} ) or _{LiNixCoyMnzO2 ( NCM} ) (where ₀ <x<1,0<y<1,0<z<1, and x+y+z=1), and lithium salts of ternary transition metal oxides.

When the positive electrode active material contains the lithium salt of the ternary transition metal oxide having the layered rock salt structure, the energy density and thermal stability of the all-solid secondary battery 1 can be improved.

The positive electrode active material may be covered with a coating layer. Here, the coating layer of the present embodiment may be of any type as long as it is known as a coating layer of a positive electrode active material for an all-solid secondary battery. Examples of coating layers include Li ₂ O—ZrO ₂ and the like.

Further, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM and contains nickel (Ni) as the positive electrode active material, the capacity density of the all-solid secondary battery 1 can be increased, and metal elution from the positive electrode active material in a charged state can be reduced. Thereby, the all-solid secondary battery 1 according to the present embodiment can improve long-term reliability and cycle characteristics in a charged state.

Here, examples of the shape of the positive electrode active material include particle shapes such as spherical and elliptical. Moreover, the particle size of the positive electrode active material is not particularly limited as long as it is within a range applicable to the positive electrode active material of conventional all-solid secondary batteries. The content of the positive electrode active material in the positive electrode active material layer 20 is not particularly limited as long as it is within the range applicable to the positive electrode layer of the conventional all-solid secondary battery.

Further, in the positive electrode active material layer 20, in addition to the positive electrode active material and the solid electrolyte described above, additives such as a conductive aid, a binder, a filler, a dispersant, and an ion conductive aid are appropriately added. may be blended.

Examples of conductive aids that can be incorporated into the positive electrode active material layer 20 include graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder. Examples of binders that can be blended in the positive electrode active material layer 20 include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. ) etc. can be mentioned. Further, as fillers, dispersants, ion-conducting aids, etc. that can be blended in the positive electrode active material layer 20, known materials that are generally used for electrodes of all-solid secondary batteries can be used.

(Solid electrolyte layer)
The solid electrolyte layer 30 is formed between the positive electrode active material layer 20 and the negative electrode active material layer 40 and contains a solid electrolyte.

The solid electrolyte is composed of, for example, a sulfide-based solid electrolyte material. Sulfide-based solid electrolyte materials include, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element, such as I, Cl), Li ₂ SP ₂ S ₅ -Li2O, _{Li2SP2S5 -} Li2O _- LiI, _{Li2S - SiS2} , _{Li2S -} SiS2 _- LiI, Li2S _- SiS2-LiBr, _{Li2S - SiS2 -LiCl} , _{Li2S - SiS2 -} B2S3 _- LiI, Li2S _- SiS2 _{- P2S5 -} LiI, Li2S _{- B2S3} , _{Li2SP2S5 -} Z _m S _n (m and n are positive numbers, Z is either Ge, Zn or Ga), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ — Li _p MO _q (p and q are positive numbers; M is any one of P, Si, Ge, B, Al, Ga and In). Here, the sulfide-based solid electrolyte material is produced by processing a starting material (for example, Li ₂ S, P ₂ S ₅ , etc.) by a melt quenching method, a mechanical milling method, or the like. Further, heat treatment may be performed after these treatments. The solid electrolyte may be amorphous, crystalline, or a mixture of both.

As the solid electrolyte, it is preferable to use a material containing sulfur and at least one element selected from the group consisting of silicon, phosphorus and boron among the sulfide solid electrolyte materials described above. Thereby, the lithium conductivity of the solid electrolyte layer is improved, and the battery characteristics of the all-solid secondary battery 1 are improved. In particular, it is preferable to use a solid electrolyte containing at least sulfur (S), phosphorus (P) and lithium (Li) as constituent elements, and it is particularly preferable to use a solid electrolyte containing Li ₂ SP ₂ S ₅ . .

Here, when a material containing Li ₂ S—P ₂ S ₅ is used as the sulfide-based solid electrolyte material forming the solid electrolyte, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S :P ₂ S ₅ =50:50 to 90:10. Moreover, the solid electrolyte layer 30 may further contain a binder. Examples of the binder contained in the solid electrolyte layer 30 include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene oxide. The binder in the solid electrolyte layer 30 may be the same as or different from the binder in the positive electrode active material layer 20 .

(Negative electrode active material layer)
The negative electrode active material layers 40 are respectively arranged on the solid electrolyte layers 30 . In the present embodiment, the negative electrode active material layer 40 includes, for example, at least one of a negative electrode active material that forms an alloy with lithium and a negative electrode active material that forms a compound with lithium. The negative electrode active material layer 40 contains such a negative electrode active material so that metallic lithium can be deposited on one or both surfaces of the negative electrode active material layer 40 as follows. may

First, at the initial stage of charging, the negative electrode active material that forms an alloy or compound with lithium in the negative electrode active material layer 40 forms an alloy or compound with lithium ions, whereby lithium is occluded in the negative electrode active material layer 40. be done. After that, after the capacity of the negative electrode active material layer 40 is exceeded, metallic lithium is deposited on one or both surfaces of the negative electrode active material layer 40 . A metal layer is formed by this metallic lithium. Since metallic lithium is formed while diffusing through the negative electrode active material capable of forming an alloy or compound, it is formed uniformly along the surface of the negative electrode active material layer 40 instead of in a dendrite shape. It becomes what was done. During discharge, metallic lithium in the negative electrode active material layer 40 and the metal layer is ionized and moves toward the positive electrode active material layer 20 side. Therefore, as a result, metallic lithium can be used as a negative electrode active material, thereby improving energy density.

Furthermore, when a metal layer is formed between the negative electrode active material layer 40 and the negative electrode current collector 50, the negative electrode active material layer 40 covers the metal layer. Thereby, the negative electrode active material layer 40 functions as a protective layer for the metal layer. As a result, the short circuit and capacity reduction of the all-solid secondary battery 1 are suppressed, and the characteristics of the all-solid secondary battery are improved.

As a method for enabling deposition of metallic lithium in the negative electrode active material layer 40 , for example, there is a method of making the charge capacity of the positive electrode active material layer 20 larger than the charge capacity of the negative electrode active material layer 40 . Specifically, the ratio (capacity ratio) between the charge capacity a (mAh) of the positive electrode active material layer 20 and the charge capacity b (mAh) of the negative electrode active material layer 40 is expressed by the following formula (1):
0.002<b/a<0.5 (1)
It is preferable to satisfy the relationship of

When the capacity ratio represented by the formula (1) is 0.002 or less, depending on the configuration of the negative electrode active material layer 40, the negative electrode active material layer 40 cannot sufficiently mediate the deposition of metallic lithium from lithium ions. Layer formation may not occur properly. Further, when a metal layer is formed between the negative electrode active material layer 40 and the negative electrode current collectors 50A and 50B, the negative electrode active material layer 40 may not sufficiently function as a protective layer. The capacity ratio is preferably 0.01 or more, more preferably 0.03 or more.

If the capacity ratio is 0.5 or more, most of the lithium is stored in the negative electrode active material layer 40 during charging, and depending on the structure of the negative electrode active material layer 40, the metal layer may not be uniformly formed. There is The capacity ratio is preferably 0.2 or less, more preferably 0.1 or less.

Examples of negative electrode active materials for realizing the functions described above include amorphous carbon, gold, platinum, palladium (Pd), silicon (Si), silver, aluminum (Al), bismuth (Bi), tin, antimony, and zinc. Examples of amorphous carbon include carbon black (acetylene black, furnace black, ketjen black ((acetylene black, furnace black, ketjen black), etc.), graphene, and the like.

The shape of the negative electrode active material is not particularly limited. In the former case, lithium ions pass through the gaps between the granular negative electrode active materials and can form lithium metal layers between the negative electrode active material layer 40 and the negative electrode current collectors 50A and 50B. On the other hand, in the latter case, a metal layer is deposited between the negative electrode active material layer 40 and the solid electrolyte layer 30 .

Among the above, the negative electrode active material layer 40 includes, as amorphous carbon, a low specific surface area amorphous carbon having a specific surface area of 100 m ² /g or less measured by a nitrogen gas adsorption method, and a low specific surface area amorphous carbon measured by a nitrogen gas adsorption method. It preferably contains a mixture with high specific surface area amorphous carbon having a specific surface area of 300 m ² /g or more.

The negative electrode active material layer 40 may contain only one of these negative electrode active materials, or may contain two or more types of negative electrode active materials. For example, the negative electrode active material layer 40 may contain only amorphous carbon as the negative electrode active material, and may be selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc. may contain any one or more. Further, the negative electrode active material layer 40 is a mixture of amorphous carbon and at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, antimony, and zinc. May contain. The mixing ratio (mass ratio) of the mixture of amorphous carbon and metal such as gold is preferably about 1:1 to 1:3. By forming the negative electrode active material from these materials, the characteristics of the all-solid secondary battery 1 are further improved.

Here, when one or more of gold, platinum, palladium, antimony, silicon, silver, aluminum, bismuth, tin, and zinc are used together with amorphous carbon as the negative electrode active material, the particle size of these negative electrode active materials is preferably 4 μm or less. In this case, the characteristics of the all-solid secondary battery 1 are further improved.

Further, when using a material capable of forming an alloy with lithium as the negative electrode active material, for example, any one or more of gold, platinum, palladium, antimony, silicon, silver, aluminum, bismuth, tin, and zinc, The active material layer 40 may be these metal layers. For example, the metal layer can be a plated layer.

Here, the charge capacity of the positive electrode active material layer 20 is obtained by multiplying the charge capacity density (mAh/g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode active material layer 20 . When a plurality of types of positive electrode active materials are used, the value of charge capacity density×mass is calculated for each positive electrode active material, and the sum of these values is used as the charge capacity of the positive electrode active material layer 20 . The charge capacity of the negative electrode active material layer 40 is also calculated in a similar manner. That is, the charge capacity of the negative electrode active material layer 40 is obtained by multiplying the charge capacity density (mAh/g) of the negative electrode active material by the mass of the negative electrode active material in the negative electrode active material layer 40 . When multiple kinds of negative electrode active materials are used, the value of charged capacity density×mass is calculated for each negative electrode active material, and the sum of these values is used as the capacity of the negative electrode active material layer 40 . Here, the charge capacity densities of the positive electrode and negative electrode active materials are capacities estimated using an all-solid-state half-cell using lithium metal as the counter electrode. In practice, the charge capacities of the positive electrode active material layer 20 and the negative electrode active material layer 40 are directly measured by measurement using an all-solid half-cell. By dividing this charge capacity by the mass of each active material, the charge capacity density is calculated.

Furthermore, the negative electrode active material layer 40 may contain a binder as needed. Such binders include, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, and the like. The binder may be composed of one of these, or may be composed of two or more. By including the binder in the negative electrode active material layer 40 in this way, separation of the negative electrode active material can be prevented, particularly when the negative electrode active material is granular. When the negative electrode active material layer 40 contains a binder, the content of the binder is, for example, 0.3 to 20% by mass, preferably 1.0 to 15% by mass, more preferably 1.0 to 15% by mass, based on the total mass of the negative electrode active material layer 40. 3.0 to 15% by mass.

In addition, the negative electrode active material layer 40 may appropriately contain additives used in conventional all-solid secondary batteries, such as fillers, dispersants, and ion conductive agents.

The thickness of the negative electrode active material layer 40 is not particularly limited when the negative electrode active material is granular, but is, for example, 1.0 to 20 μm, preferably 1.0 to 10 μm. As a result, the resistance value of the negative electrode active material layer 40 can be sufficiently reduced while the above-described effects of the negative electrode active material layer 40 can be sufficiently obtained, and the characteristics of the all-solid secondary battery 1 can be sufficiently improved.
On the other hand, the thickness of the negative electrode active material layer 40 is, for example, 1.0 to 100 nm when the negative electrode active material forms a uniform layer. In this case, the upper limit of the thickness of the negative electrode active material layer 40 is preferably 95 nm, more preferably 90 nm, still more preferably 50 nm.

The negative electrode active material layer 40 having the structure described above greatly contributes to the improvement of battery characteristics. easy to receive. Therefore, even during stacking, the shapes of the outer surfaces of the adjacent all-solid secondary batteries 1, specifically, the surface shapes of the negative electrode current collectors 50A and 50B, are likely to affect. However, in the all-solid secondary battery 1 according to the present embodiment, by adopting the negative electrode current collectors 50A and 50B in which unevenness is suppressed as described above, the influence of the adjacent all-solid secondary battery 1 during stacking is reduced. can be prevented.

The present invention is not limited to the above-described embodiments, and the negative electrode active material layer 40 can employ any configuration that can be used as a negative electrode active material layer of an all-solid secondary battery.
For example, the negative electrode active material layer 40 can be a layer containing a negative electrode active material, a solid electrolyte, and a negative electrode layer conductive aid.

In this case, for example, a metal active material, carbon active material, or the like can be used as the negative electrode active material. As the metal active material, for example, metals such as lithium (Li), indium (In), aluminum (Al), tin (Sn), and silicon (Si), alloys thereof, and the like can be used. Carbon active materials include, for example, artificial graphite, graphite carbon fiber, resin calcined carbon, pyrolytic vapor growth carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin calcined Carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, non-graphitizable carbon, and the like can be used. These negative electrode active materials may be used alone, or two or more of them may be used in combination.

The same compound as the conductive agent and solid electrolyte contained in the positive electrode active material layer 20 can be used for the negative electrode layer conductive aid and the solid electrolyte. Therefore, description of these configurations is omitted here.

(Negative electrode current collector)
The negative electrode current collectors 50A and 50B are the outermost layers of the laminate of the all-solid secondary battery 1, which are arranged on the negative electrode active material layer 40, respectively. The negative electrode current collectors 50A and 50B have surface shapes as described above.

The negative electrode current collectors 50A and 50B include, for example, plate-shaped bodies or foil-shaped bodies made of copper (Cu), stainless steel, titanium (Ti), nickel (Ni), or alloys thereof.

[2.2. Laminated all-solid-state secondary battery]
Next, the laminated all-solid secondary battery 100 according to this embodiment will be described. The stacked all-solid secondary battery 100 has one or more insulating layers 110 and a plurality of all-solid secondary batteries 1 stacked with the insulating layers 110 interposed therebetween.

In the stacked all-solid secondary battery 100, a plurality of all-solid secondary batteries 1 are arranged such that the negative electrode current collector 50A of a certain all-solid secondary battery 1 faces the adjacent negative electrode current collector 50B. Laminated. Thereby, lamination can be performed without impairing the battery characteristics of each all-solid secondary battery 1 . In addition, even if the all-solid secondary battery 1 is stacked so that the negative electrode current collector 50A of a certain all-solid secondary battery 1 faces the adjacent negative electrode current collector 50B, the battery characteristics are not impaired. It becomes possible to stack three or more all-solid secondary batteries 1 .

The insulating layer 110 is not particularly limited as long as it can insulate adjacent all-solid secondary batteries 1 from each other. Resin sheets, thermosetting resin sheets such as phenol resin, epoxy resin, melamine resin, and urethane resin; engineering plastics such as polyethylene terephthalate, polyamide, and polycarbonate; synthetic rubber sheets such as silicone rubber and urethane rubber; Alternatively, the all-solid-state battery 1 may be coated with a resin.

Moreover, the thickness of the insulating layer 110 is not particularly limited as long as it can insulate adjacent all-solid secondary batteries 1, and can be, for example, 0.1 μm or more and 100 μm or less.

<3. Method for manufacturing all-solid secondary battery and stacked all-solid secondary battery>
Next, an example of a method for manufacturing the all-solid secondary battery and the stacked all-solid secondary battery according to the present embodiment will be described.

[3.1. Production of all-solid secondary battery]
First, an example of a method for manufacturing an all-solid secondary battery according to this embodiment will be described. 4 to 6 are schematic diagrams for explaining the manufacturing method of the all-solid secondary battery according to this embodiment.
The method for manufacturing the all-solid secondary battery 1 according to the present embodiment includes a step of forming the solid electrolyte layer 30 on the negative electrode active material layer 40 by screen printing;
For a laminate obtained by laminating the positive electrode current collector 10, the pair of positive electrode active material layers 20, the pair of solid electrolyte layers 30, the pair of negative electrode active material layers 40, and the pair of negative electrode current collectors 50, at least one of the laminate and a step of placing a support member (support plate) 140 on the surface side and performing isostatic pressing.

Further, in the present embodiment, specifically, the positive electrode structure 120 including the positive electrode current collector 10 and the positive electrode active material layer 20 and the solid state structure including the negative electrode current collector 50, the negative electrode active material layer 40, and the solid electrolyte layer 30 are described. The following description will be given assuming that the electrolyte-negative electrode composite 130 is prepared separately and laminated.

(Preparation of positive electrode structure)
The positive electrode structure 120 can be manufactured by first preparing the positive electrode current collector 10 (S-510) and forming the positive electrode active material layers 20 on both sides of the positive electrode current collector 10 (S-520). .

The positive electrode active material layer 20 can be formed by preparing a slurry or paste containing the material of the positive electrode active material layer 20, applying it, and drying it. Specifically, a material for the positive electrode active material layer 20, such as a positive electrode active material, a solid electrolyte prepared by a method described later, and various additives are mixed and added to a nonpolar solvent to prepare a slurry or paste. Furthermore, the positive electrode structure 120 can be obtained by applying the obtained slurry or paste onto the positive electrode current collector 10, drying it, and rolling it. Alternatively, the positive electrode structure can be obtained only by rolling the obtained paste without coating it on the positive electrode current collector 10 , and then integrated with the positive electrode current collector 10 . In addition, in order to increase the density of the positive electrode active material layer 20, a pressing process such as roll pressing can be performed as necessary.

(Preparation of Solid Electrolyte Negative Electrode Composite)
Solid electrolyte/negative electrode composite 130 first prepares negative electrode current collector 50 (S-610), and sequentially forms negative electrode active material layer 40 and solid electrolyte layer 30 on one side of negative electrode current collector 50 (S-610). 620, S-630).

As the negative electrode current collector 50, the same material as the negative electrode current collectors 50A and 50B described above can be used.

The negative electrode active material layer 40 can be formed by preparing a slurry or paste containing the material of the negative electrode active material layer 40, applying it, and drying it (S-620). Specifically, materials for the negative electrode active material layer 40, such as a negative electrode active material, a binder, and various additives, are mixed and added to a nonpolar solvent to prepare slurry or paste. Furthermore, the resulting slurry or paste is applied onto the negative electrode current collector 50 and dried to form the negative electrode active material layer 40 .
Alternatively, the negative electrode active material layer 40 may be formed by applying a negative electrode active material onto the negative electrode current collector 50 by sputtering or the like. Furthermore, a metal foil for forming the negative electrode active material layer 40 may be arranged on the negative electrode current collector 50 .

Next, the solid electrolyte layer 30 is formed on the negative electrode active material layer 40 by screen printing (S-620). Thereby, coarse particles of the solid electrolyte can be removed, and the surface of the formed solid electrolyte layer 30 can be smoothed. Therefore, it is possible to prevent large irregularities from occurring in the negative electrode current collectors 50A and 50B formed by isostatic pressing, which will be described later.

More specifically, the inventors of the present invention have studied how to suppress the formation of protrusions on the negative electrode current collectors 50A and 50B. It was found that the shape, particularly the surface shape of the negative electrode current collector 50B that is not in contact with the support plate 140 described later, is greatly affected. Furthermore, as a result of further investigation to flatten the shape of the solid electrolyte layer 30, it was found that the method of forming the solid electrolyte layer alone in the form of a non-woven fabric sheet causes the unevenness of the solid electrolyte layer to increase. The present inventors have found that by forming the solid electrolyte layer 30 directly on the negative electrode active material layer 40 by screen printing, the solid electrolyte layer 30 can be flattened, and the surfaces of the negative electrode current collectors 50A and 50B can be flattened. It was found that the influence of the solid electrolyte layer 30 on the shape can be suppressed.

In forming the solid electrolyte layer 30, first, a solid electrolyte is prepared. For this purpose, a solid electrolyte is obtained by processing the starting material of the solid electrolyte, for example, by a melt quenching method or a mechanical milling method.

For example, when a melt quenching method is used, a predetermined amount of starting materials (e.g., Li ₂ S, P ₂ S ₅ , etc.) are mixed, pelletized, reacted at a predetermined reaction temperature in vacuum, and then quenched. By doing so, a sulfide-based solid electrolyte material can be produced. The reaction temperature of the mixture of Li ₂ S and P ₂ S ₅ is preferably 400°C to 1000°C, more preferably 800°C to 900°C. The reaction time is preferably 0.1 hour to 12 hours, more preferably 1 hour to 12 hours. Furthermore, the quenching temperature of the reactant is usually 10° C. or less, preferably 0° C. or less, and the quenching rate is usually about 1° C./sec to 10000° C./sec, preferably 1° C./sec to 1000° C. C./sec.

Further, when using a mechanical milling method, a sulfide-based solid electrolyte material can be produced by stirring and reacting starting materials (for example, Li ₂ S, P ₂ S ₅ , etc.) using a ball mill or the like. . The stirring speed and stirring time in the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the sulfide-based solid electrolyte material can be generated. can increase the conversion rate of the raw material.

After that, the mixed raw material obtained by the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature, and then pulverized to produce a particulate solid electrolyte. If the solid electrolyte has a glass transition point, it may change from amorphous to crystalline by heat treatment.

Subsequently, a slurry or paste liquid composition containing the solid electrolyte obtained by the above method, other additives such as a binder, and a dispersion medium is prepared. General-purpose nonpolar solvents such as xylene and diethylbenzene can be used as the dispersion medium. The concentrations of the solid electrolyte and other additives can be appropriately adjusted according to the composition of the solid electrolyte layer 30 to be formed, the viscosity of the liquid composition, and the like.

Next, using a liquid composition containing a solid electrolyte, the composition is applied onto the negative electrode active material layer 40 by screen printing, and dried to form the solid electrolyte layer 30 . In screen printing, the mesh number of the screen can be 60-300. If the mesh is coarse, coarse particles cannot be removed. On the other hand, depending on the particle size of the solid electrolyte used and the viscosity of the liquid composition, if the mesh is too fine, a good solid electrolyte layer cannot be coated. .

As described above, the solid electrolyte negative electrode composite 130 can be produced. In addition, the solid electrolyte negative electrode composite 130 can also be subjected to a pressing process such as roll pressing, if necessary.

(Lamination)
Next, the obtained positive electrode structure 120 and the solid electrolyte negative electrode composite 130 are laminated (S-710). As shown in FIG. 6, the stacking can be performed by arranging the solid electrolyte/negative composite 130 such that the solid electrolyte layers 30 face the positive electrode active material layers 20 on both sides of the positive electrode structure 120 . At this time, a support plate 140 for isotropic pressing is placed on one side of the negative electrode current collector 50A.

(Isostatic press)
Next, the support plate 140 is placed on at least one side of the obtained laminate, and isostatic pressing is performed (S-710). Thereby, the all-solid secondary battery 1 is obtained. In the isostatic pressing, the negative electrode current collector 50 becomes negative electrode current collectors 50A and 50B reflecting the surface shape of each layer.

Isostatic pressing is advantageous from the viewpoint of suppressing cracking of each layer in the all-solid secondary battery 1 and preventing the all-solid secondary battery 1 from warping, as compared with other pressing methods such as roll pressing. Therefore, the battery performance of the all-solid secondary battery 1 is improved. On the other hand, on the surface where the support plate 140 is not arranged, the surface shapes of the negative electrode active material layer 40 and the solid electrolyte layer 30, particularly the solid electrolyte layer 30, are likely to be reflected on the negative electrode current collector 50 (50B). However, in the present embodiment, the surface shape of the solid electrolyte layer 30 is flattened by forming the solid electrolyte layer 30 directly on the negative electrode active material layer 40 by screen printing. Therefore, the negative electrode current collector 50B to be formed is prevented from having large unevenness.

Examples of the pressure medium for isostatic pressing include liquids such as water and oil, powders, and the like. It is more preferable to use a liquid as the pressure medium.

The pressure in the isostatic press is not particularly limited, but can be, for example, 10 to 1000 MPa, preferably 100 to 500 MPa. Also, the pressurization time is not particularly limited, and can be, for example, 1 to 120 minutes, preferably 5 to 30 minutes. Furthermore, the temperature of the pressure medium during pressurization is not particularly limited, and can be, for example, 20 to 200.degree. C., preferably 50 to 100.degree.

During isostatic pressing, it is preferable that the laminate constituting the all-solid-state secondary battery 1 is laminated together with the support plate 140 with a resin film or the like so as to be isolated from the external atmosphere.

[3.2. Production of laminated all-solid-state secondary battery]
Next, a plurality of all-solid secondary batteries 1 are stacked to obtain a stacked all-solid secondary battery 100 . At the time of stacking, the negative electrode current collector 50A and the negative electrode current collector 50B of the other all-solid secondary battery 1 are arranged to face each other with the insulating layer 110 interposed therebetween. This makes it possible to stack a relatively large number of, for example, three or more, all-solid secondary batteries 1 .

The all-solid secondary battery 1 and the stacked all-solid secondary battery 100 according to the present embodiment and the manufacturing methods thereof have been described above in detail. However, the invention is not limited to the embodiments described above.

For example, in the above-described embodiments, the first active material layer, the first current collector, the second active material layer, and the second current collector are respectively the positive electrode active material layer, the positive electrode current collector, and the negative electrode. Although the active material layer and the negative electrode current collector have been described, the present invention is not limited to this. For example, the first active material layer may be the negative electrode active material layer, and the second active material layer may be the positive electrode active material layer. In this case, the first current collector is the negative electrode current collector, and the second current collector is the positive electrode current collector.

In the above-described embodiment, the positive electrode structure and the solid electrolyte/negative composite are separately produced and laminated to produce an all-solid secondary battery, but the present invention is not limited to this. For example, centering on a positive electrode current collector (first current collector), a positive electrode active material layer (first active material layer), a solid electrolyte layer, a negative electrode active material layer (second active material layer) and a negative electrode collector An all-solid secondary battery may be manufactured by laminating current bodies (second current collectors) on both sides in this order.

The present invention will be described in more detail below with reference to examples. In addition, an Example is an example to the last, and does not limit this invention.

[1. Production of all-solid secondary battery and laminated all-solid secondary battery]
<Example 1>
(Preparation of positive electrode structure)
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) ternary powder as a positive electrode active material and Li ₂ SP ₂ S ₅ (80:20 mol %) as a sulfide-based solid electrolyte Amorphous powder and vapor-grown carbon fiber powder as a positive electrode layer conductive material (conductive aid) were weighed at a mass ratio of 60:35:5 and mixed using a rotation-revolution mixer.

Next, a dehydrated xylene solution in which styrene-butadiene rubber (SBR) as a binder is dissolved is added to the mixed powder so that the SBR is 5.0% by mass with respect to the total mass of the mixed powder. A mixture was prepared. Furthermore, a secondary liquid mixture was prepared by adding an appropriate amount of dehydrated xylene to the primary liquid mixture for viscosity adjustment. Furthermore, in order to improve the dispersibility of the mixed powder, zirconia balls with a diameter of 5 mm were added to the secondary mixed liquid so that the space, the mixed powder, and the zirconia balls each accounted for 1/3 of the total volume of the kneading container. put in. The tertiary mixed solution thus produced was put into a rotation-revolution mixer and stirred at 3000 rpm for 3 minutes to prepare a positive electrode active material layer coating solution.

Next, an aluminum foil current collector having a thickness of 20 μm was prepared as a positive electrode current collector, the positive electrode current collector was placed on a desktop screen printer, and a metal mask having a hole diameter of 2.0 cm × 2.0 cm and a thickness of 150 µm was used. The positive electrode active material layer coating solution is applied onto the aluminum foil current collector using a hot plate at 60 ° C. for 30 minutes. dried. Next, the positive electrode active material layer coating liquid was applied to the back surface of the aluminum foil current collector, and dried on a hot plate at 60° C. for 30 minutes. Then, the coated aluminum foil current collector was further vacuum-dried at 80° C. for 12 hours. As a result, positive electrode active material layers were formed on both surfaces of the positive electrode current collector to obtain a positive electrode structure. The total thickness of the positive electrode structure after drying was around 330 μm.

(Preparation of negative electrode structure)
A nickel foil current collector having a thickness of 10 μm was prepared as a negative electrode current collector. In addition, as the negative electrode active material, CB1 manufactured by Asahi Carbon Co., Ltd. (amorphous carbon, nitrogen adsorption specific surface area is about 339 m ² /g, DBP oil supply amount is about 193 ml / 100 g), CB2 manufactured by Asahi Carbon Co., Ltd. (amorphous carbon, nitrogen adsorption Silver particles having a specific surface area of about 52 m ² /g, a DBP oil supply amount of about 193 ml/100 g), and a particle size of 3 μm (the particle size was measured by the method described above) were prepared.

Next, 1.5 g of CB1, 1.5 g of CB2, and 1 g of silver particles were placed in a container, and 4 g of an N-methylpyrrolidone (NMP) solution containing 5% by mass of a binder (#9300 manufactured by Kureha Co., Ltd.) was added. A mixed solution was obtained. Next, a slurry was prepared by stirring the mixed solution while adding a total of 30 g of NMP little by little to the mixed solution. This slurry was applied to a nickel foil current collector using a blade coater and dried in the air at 80° C. for about 20 minutes. The laminate thus obtained was vacuum-dried at 100° C. for about 12 hours. Through the steps described above, a negative electrode structure in which a negative electrode active material layer was laminated on a negative electrode current collector was produced.

(Preparation of Solid Electrolyte Negative Electrode Composite)
An SBR binder dissolved in dehydrated xylene was added to Li ₂ SP ₂ S ₅ (80:20 mol %) amorphous powder as a sulfide-based solid electrolyte so as to be 1% by mass with respect to the solid electrolyte. to produce a primary mixed slurry. Furthermore, a secondary mixed slurry was produced by adding appropriate amounts of dehydrated xylene and dehydrated diethylbenzene for viscosity adjustment to this primary mixed slurry. Furthermore, in order to improve the dispersibility of the mixed powder, zirconia balls with a diameter of 5 mm were added to the tertiary mixed slurry so that the space, the mixed powder, and the zirconia balls each accounted for 1/3 of the total volume of the kneading vessel. put in. The tertiary mixed liquid thus prepared was put into a rotation-revolution mixer and stirred at 3000 rpm for 3 minutes to prepare an electrolyte layer coating slurry.

The negative electrode structure was placed on a desktop screen printer, and the solid electrolyte slurry was applied onto the negative electrode structure using a metal screen (80 mesh, wire diameter of 50 μm, thickness of about 100 μm). After that, it was dried on a hot plate at 50° C. for 10 minutes, and then vacuum-dried at 40° C. for 12 hours to form a solid electrolyte layer. The total thickness of the electrolyte layer after drying was around 90 μm. As described above, a solid electrolyte negative electrode composite having a solid electrolyte layer formed on the negative electrode structure was obtained.

(Fabrication of all-solid secondary battery)
After the sheet-like solid electrolyte negative electrode composite and the sheet-like positive electrode structure having the positive electrode active material layers formed on both sides thereof were punched out with a Thomson blade, the solid electrolyte layers were in contact with both sides of the positive electrode structure. The solid electrolyte negative electrode composite, the positive electrode structure, and the solid electrolyte negative electrode structure were stacked in this order. In this state, it was placed in an aluminum laminate film, evacuated to 100 Pa by a vacuum machine, and laminated-packed.

Then, it was placed on an aluminum plate (supporting plate) having a thickness of 3 mm, and vacuum lamination packing was carried out including the supporting plate. This was submerged in a pressurized medium and subjected to isotropic pressure treatment (consolidation step) at 490 MPa. The temperature of the pressurized medium during the isostatic treatment was 80° C. and the treatment time was 30 minutes. Thus, an all-solid secondary battery was produced as a single cell. At this time, the negative electrode current collector foil of the solid electrolyte negative electrode composite on the side in contact with the aluminum plate side is called the A side, and the opposite negative electrode current collector foil is called the B side.

In the obtained all-solid secondary battery, the initial charge capacity of the positive electrode active material layer was 778 mAh, and the initial charge capacity of the negative electrode active material layer was 99 mAh. Therefore, b/a in formula (1) was 0.13.

(Production of laminated all-solid secondary battery)
Insulate between the two single cells of the produced all-solid-state secondary battery, overlap so that the A-side of one all-solid-state secondary battery and the B-side of the other all-solid-state secondary battery face each other, and connect the terminals. The laminated all-solid-state secondary battery according to Example 1 was produced by putting it in the attached aluminum laminate film, evacuating it to 100 Pa with a vacuum machine, heat-sealing it, and packing it.

<Comparative Example 1>
In the same manner as in Example 1, except that the solid electrolyte slurry was applied onto the negative electrode structure using a squeegee and a metal mask (thickness: 60 μm) instead of screen printing during the formation of the solid electrolyte layer, comparison was performed. A laminated all-solid secondary battery according to Example 1 was produced.

<Comparative Example 2>
First, in the same manner as in Example 1, a positive electrode structure and a negative electrode structure were produced.
Next, the solid electrolyte slurry obtained in the same manner as in Example 1 was applied onto a 10 μm polyethylene terephthalate nonwoven fabric fixed on a 75 μm polyethylene substrate, dried on a hot plate at 50° C. for 10 minutes, and dried for 40 minutes. C. for 12 hours to obtain a solid electrolyte layer.

Next, the solid electrolyte layer, the negative electrode composite, and the positive electrode structure were each punched out with a Thomson blade. After that, the solid electrolyte layer and the negative electrode structure were laminated in this order on both sides of the positive electrode structure. The negative electrode structure was laminated so that the negative electrode active material layer was in contact with the solid electrolyte layer.

After that, in the same manner as in Example 1, a laminate pack, an isotropic pressure treatment, and a laminated all-solid secondary battery were produced, and a laminated all-solid secondary battery according to Comparative Example 2 was obtained.

<Reference example 1>
The procedure was the same as in Comparative Example 2 except that the two single cells of the all-solid secondary battery were insulated and the A-side of one all-solid-state secondary battery and the A-side of the other all-solid-state secondary battery faced each other. Thus, a laminated all-solid secondary battery according to Reference Example 1 was produced.

[2. evaluation]
(Surface properties of negative electrode current collector)
The surface properties of the negative electrode current collectors of the all-solid-state secondary batteries constituting the laminated all-solid-state secondary batteries according to Example 1, Comparative Examples 1 and 2, and Reference Example 1 were measured using a curved surface fine shape measurement system VR-manufactured by KEYENCE. 3200 was used and evaluated as follows.

Using a 25x lens, after observing arbitrary five points of the negative electrode current collector of the all-solid secondary battery in a field of view of 12 mm × 9 mm (1.08 cm ² ), from the measurement data of the three-dimensional shape A reference plane was set using the obtained three-dimensional shape information. A reference plane was set by estimating a plane by the least-squares method from the shape of the height image for which the area was specified. After correcting the reference surface, confirm the unevenness in the cross-sectional direction. The number of protrusions with height was detected respectively. As for the height of the convex portion, the difference in height from the top of the convex portion to the lowest point among the points where the monotonically decreasing height is negative was taken as the height of the convex portion.

(Battery performance evaluation)
The laminated all-solid secondary batteries according to Example 1, Comparative Examples 1 and 2, and Reference Example 1 were evaluated for short circuits and cycle characteristics as follows. First, the laminated all-solid-state secondary battery is sandwiched between two upper and lower metal plates, a screw with a disk spring inserted is passed through a hole drilled in advance in the metal plate, and the screw is tightened so that the pressure applied to the battery is 3.0 MPa. rice field.
Next, after charging to the upper limit voltage of 4.25 V at a constant current of 0.1 C at 60° C., constant voltage charging (0.1 C CCCV charging) is performed until the current value reaches 33% of the constant current value, The battery was discharged at 0.1C to a final discharge voltage of 2.0V. Next, it was charged at 0.1C CCCV, discharged at 0.33C, further charged at 0.1C CCCV, and discharged at 1C. Subsequently, at a constant current of 0.5 C, charging to an upper limit voltage of 4.25 V (0.5 C CC charging) and discharging by 0.5 C to a discharge end voltage of 2.0 V were repeated. It was measured by TOSCAT-3100 (Toyo System Co., Ltd.).

A short circuit is defined as “A” when the cutoff voltage is reached during 0.1C CCCV charging and the charge/discharge efficiency is 0.90 or higher, and when the cutoff voltage is not reached during 0.1C CCCV charging and charging When the discharge efficiency was less than 0.90, it was evaluated as "B".
In addition, the cycle characteristics are "A" when the discharge capacity retention rate after 10 cycles after 0.5C charging and discharging is 95% or more, and the discharge capacity retention rate after 10 cycles is less than 95%. In the case of , it was evaluated as "B".
Table 1 shows the above results.

As is clear from Table 1, the laminated all-solid-state secondary battery according to Example 1 was excellent in cycle characteristics as in Reference Example 1, and short-circuiting was prevented. On the other hand, unlike Reference Example 1, since it is possible to laminate with the A side facing the support plate and the B side not facing the support plate during isotropic pressing, it is possible to laminate three or more layers. It was suggested that stacking all-solid secondary batteries is possible. In addition, on the A side of the all-solid secondary battery according to Example 1, no protrusion having a height of more than 5.0 μm was observed.

On the other hand, the all-solid secondary battery according to Comparative Example 1 had a short circuit and was inferior in cycle characteristics, and the all-solid secondary battery according to Comparative Example 2 had a short circuit.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

1 All-solid secondary battery 10 Positive electrode current collector 20 Positive electrode active material layer 30 Solid electrolyte layer 40 Negative electrode active material layers 50, 50A, 50B Negative electrode current collector 100 Laminated all-solid secondary battery 110 Insulating layer 120 Positive electrode structure 130 Solid Electrolyte-negative composite 140 Support plate 200 All-solid secondary battery 210 Positive electrode current collector 220 Positive electrode active material layer 230 Solid electrolyte layer 240 Negative electrode active material layers 250A and 250B Negative electrode current collectors 300A and 300B Laminated all-solid secondary battery 310 Insulation layer

Claims (9)

a first current collector;
a pair of first active material layers arranged on both sides of the first current collector;
a pair of solid electrolyte layers disposed on the surface of the pair of first active material layers opposite to the first current collector;
a pair of second active material layers disposed on the surface of the pair of solid electrolyte layers opposite to the first active material layer;
a pair of second current collectors disposed on the surface of the pair of second active material layers opposite to the solid electrolyte layer;
There is no protrusion having a height of more than 8.0 μm on the surface of one of the pair of second current collectors opposite to the second active material layer, 0 or more and 1.0 or less protrusions having a height of more than 8.0 μm are present per 1 cm on the surface opposite to the second active material layer of the other second current collector, next battery. 2. The all-solid secondary battery according to claim 1, wherein no convex portion having a height of more than 5.0 [mu]m is present on the surface of said one second current collector opposite said second active material layer. 3. The all-solid secondary according to claim 1 or 2, wherein no protrusions having a height of more than 10.0 μm are present on the surface of the other second current collector opposite to the second active material layer. battery. The first active material layer is a positive electrode active material layer,
The all-solid secondary battery according to any one of claims 1 to 3, wherein the second active material layer is a negative electrode active material layer. The second active material layer includes at least one of a negative electrode active material that forms an alloy with lithium and a negative electrode active material that forms a compound with lithium,
5. The all-solid secondary battery according to claim 4, wherein metallic lithium can be deposited in said second active material layer through said negative electrode active material during charging. The ratio between the charge capacity of the first active material layer and the charge capacity of the second active material layer is expressed by the following formula (1)
0.002<b/a<0.5 (1)
where a is the charge capacity (mAh) of the first active material layer, and b is the charge capacity (mAh) of the second active material layer.
The all-solid secondary battery according to claim 5, which satisfies: wherein the second active material layer contains at least one selected from the group consisting of amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc; 7. The all-solid secondary battery according to any one of 6. one or more insulating layers;
and a plurality of all-solid secondary batteries according to any one of claims 1 to 7 stacked in layers via the insulating layer,
The one second current collector of the all-solid-state secondary battery is arranged to face the other second current collector of the other adjacent all-solid-state secondary battery, and the stacked all-solid-state secondary battery. A first current collector, a pair of first active material layers disposed on both sides of the first current collector, and the pair of first active material layers opposite the first current collector a pair of solid electrolyte layers arranged on the side surface, a pair of second active material layers arranged on the surface of the pair of solid electrolyte layers opposite to the first active material layer, and the pair of A method for manufacturing an all-solid secondary battery, comprising: a pair of second current collectors arranged on a surface of a second active material layer opposite to the solid electrolyte layer,
forming the solid electrolyte layer on the first active material layer or the second active material layer by screen printing;
Regarding the laminate obtained by laminating the first current collector, the pair of first active material layers, the pair of solid electrolyte layers, the pair of second active material layers, and the pair of second current collectors , placing a support material on one side of the laminate and isostatically pressing it,
A method for producing an all-solid secondary battery, wherein the screen used for the screen printing has a mesh size of 60 to 300 mesh .

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