JP7702804B2 - Stacked solid-state battery unit and its manufacturing method - Google Patents

Description

The present invention relates to a laminated solid-state battery having a reference electrode and a method for manufacturing the same.

In recent years, solid-state batteries have been developed with the aim of achieving high energy density, but to achieve a high electrode utilization rate, it is necessary to accurately measure the potential of the positive and negative electrodes. Although it is possible to understand the performance of the electrodes by performing destructive testing of the battery after charging and discharging, it is also possible to measure the electrode potential and internal resistance of the electrode non-destructively by using a reference electrode.

In conventional liquid batteries, the potentials of the positive and negative electrodes can be measured separately by immersing a reference electrode in an electrolyte as in Patent Document 1. In solid-state battery systems, as in Patent Document 2, a separate solid electrolyte part is provided on the side of the solid electrolyte layer sandwiched between the positive and negative electrodes so as to connect to the solid electrolyte layer, the positive electrode, and the negative electrode, and a reference electrode is attached to this solid electrolyte part, making it possible to measure the potentials of the positive and negative electrodes separately.

Japanese Unexamined Patent Publication No. 56-1470 JP 2013-20915 A

In many sheet-laminated lithium batteries, the negative electrode is designed to be slightly larger than the positive electrode in order to avoid short circuits caused by current concentration at the ends of the sheets and concentrated lithium precipitation. However, in the cell structure of the solid-state battery disclosed in Patent Document 2, the solid electrolyte part is attached to the positive and negative electrodes of the same size, so this structure cannot be applied to cells in which the negative and positive electrodes are different sizes. In addition, in the cell structure disclosed in Patent Document 2, the positive electrode and the reference electrode do not face each other, and the negative electrode and the reference electrode also do not face each other, so there is a risk that potential separation and resistance separation will not be reliable.

The object of the present invention is to provide a sheet-stacked solid-state battery unit in which the negative electrode and positive electrode have different sizes, a reference electrode, and a stacked solid-state battery unit and solid-state battery in a structure in which potential separation or resistance separation is unlikely to occur between the reference electrode and the positive or negative electrode.

According to a first aspect of the present invention, there is provided a stacked solid-state battery, comprising:
A battery having a flat positive electrode layer, an electrolyte layer, and a negative electrode layer having a size larger than that of the positive electrode layer, in this order;
the electrolyte layer has a first electrolyte layer on the positive electrode layer side and a second electrolyte layer on the negative electrode side, and has a compression region where the first electrolyte layer and the second electrolyte layer are compressed and a non-compression region where they are not compressed,
In the stacked solid state battery, a reference electrode is provided between the first electrolyte layer and the second electrolyte layer in the non-bonded region so as to face the positive electrode layer and the negative electrode layer.

In the laminated solid-state battery, the non-bonded region may be a region that is sandwiched between the positive electrode layer and the negative electrode layer and that protrudes from the battery reaction region where the battery reaction occurs. In this case, the battery further includes a positive electrode collector layer that covers the positive electrode layer, a positive electrode terminal that extends from the positive electrode collector layer and is connected to the outside, a negative electrode collector layer that covers the negative electrode layer, and a negative electrode terminal that extends from the negative electrode collector layer and is connected to the outside, and the protruding region may be present on the positive electrode terminal.

According to a second aspect of the present invention, there is provided a stacked solid state battery according to the first aspect,
There is provided a stacked solid-state battery structure including the stacked solid-state battery and a plurality of stacked solid-state batteries stacked on the stacked solid-state battery.

According to a third aspect of the present invention, a method for manufacturing a semiconductor device comprising the steps of: forming a positive electrode layer including a positive electrode active material; and forming an anode layer having a size larger than that of the positive electrode layer and including an anode active material;
forming a first electrolyte layer on the positive electrode layer;
forming a second electrolyte layer on the negative electrode layer;
compressing the first electrolyte layer and the second electrolyte layer, except for a portion of an overlapping region of the first electrolyte layer and the second electrolyte layer facing each other;
and providing a reference electrode between the first electrolyte layer and the second electrolyte layer in the portion of the overlapping region so as to face the positive electrode layer and the negative electrode layer.

In the manufacturing method, a negative electrode current collector having a negative electrode terminal for external connection and a positive electrode current collector having a positive electrode terminal for external connection are prepared;
forming the negative electrode layer on the negative electrode current collector;
forming the positive electrode layer on the positive electrode current collector;
The positive electrode layer may be formed on the positive electrode terminal at least in a portion overlapping with the negative electrode layer.

In the solid-state battery of the present invention, the use of a reference electrode enables potential separation between the positive and negative electrodes even in a sheet-laminated solid-state battery in which the negative electrode has dimensions larger than the positive electrode. The reference electrode faces the positive and negative electrode layers, so the potentials of the positive and negative electrode layers can be measured independently and accurately. This makes it possible to detect abnormalities in the operation of the positive and negative electrodes and in the materials that make up these electrodes, and prevents short circuits in the battery unit and facilitates maintenance. In addition, since the reference electrode is located on the electrolyte that is connected on the same plane as the electrolyte in the reaction region where the battery reaction occurs, the battery has a simple structure and is easy to manufacture.

FIG. 1(a) is a schematic plan view of the solid-state battery unit of the first embodiment, FIG. 1(b) is a schematic cross-sectional view taken along line A-A in FIG. 1(a), and FIG. 1(c) is a schematic enlarged cross-sectional view taken along line B-B in FIG. 1(a). FIG. 2 is a schematic plan view of a solid-state battery unit according to the second embodiment. FIG. 3 is a schematic plan view of a solid-state battery unit according to the third embodiment. 4(a) to (e) are conceptual diagrams showing a method for manufacturing a solid-state battery unit. FIG. 5 is a schematic diagram showing the structure of a solid battery structure in which a solid battery unit having a reference electrode and a solid battery unit having no reference electrode are stacked. FIG. 6 shows charging curves obtained by measuring the voltage between the positive electrode and the negative electrode, between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode of the solid-state battery unit produced in the examples. FIG. 7 shows discharge curves obtained by measuring the voltage between the positive electrode and the negative electrode, between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode of the solid-state battery unit produced in the examples.

First Embodiment
A laminated solid-state battery according to an embodiment of the present invention will be described. Since a plurality of laminated solid-state batteries are laminated to form a solid-state battery structure or module as described later, the laminated solid-state battery unit will be referred to as a "solid-state battery unit" below. As shown in FIG. 1(a) to FIG. 1(c), the solid-state battery unit 10 includes a positive electrode sheet 1, a negative electrode sheet 3, and a solid electrolyte layer 5 sandwiched therebetween. The positive electrode sheet 1 includes a flat positive electrode layer 2 containing a positive electrode active material and a flat positive electrode current collector 6 provided so as to cover the surface of the positive electrode layer 2. The negative electrode sheet 3 includes a negative electrode layer 4 containing a flat negative electrode active material layer and a flat negative electrode current collector 8 provided so as to cover the surface of the negative electrode layer 4.

The positive electrode layer 2 and the negative electrode layer 4 both have a substantially rectangular shape, and the negative electrode layer 4 is wider than the positive electrode layer 2 and has a larger surface area. Therefore, as shown in FIG. 1(a), when the positive electrode layer 2 and the negative electrode layer 4 are stacked, there is a corresponding region (region where they overlap in the vertical direction) S1 where the positive electrode layer 2 and the negative electrode layer 4 face each other, and a non-facing region (region where they do not overlap in the vertical direction) S2 where they do not face each other. The positive electrode collector 6 and the negative electrode collector 8 each have a positive electrode terminal 12 and a negative electrode terminal 14 that protrude from the periphery for external connection. In this embodiment, as shown in FIG. 1(a), in the non-facing region S2 where the positive electrode layer 2 and the negative electrode layer 4 do not face each other, there is a portion S3 (positive electrode terminal/negative electrode layer facing portion) where the positive electrode terminal 12 and the negative electrode layer 4 face each other.

The electrolyte layer 5 is present between the positive electrode layer 2 and the negative electrode layer 4. In the manufacturing process of a solid-state battery, the electrolyte layer 5 is generally applied to either the positive electrode layer 2 or the negative electrode layer 4 and then pressed together, but in this application, the electrolyte layer is introduced in two separate layers on the positive electrode layer side and the negative electrode layer side. That is, as shown in FIG. 1(b), an electrolyte layer 51 (hereinafter referred to as the "first electrolyte layer") is provided on the positive electrode layer 2, and an electrolyte layer 52 (hereinafter referred to as the "second electrolyte layer") is formed on the negative electrode layer 4. Since the negative electrode layer 4 is larger than the positive electrode layer 2, the second electrolyte layer 52 also has a larger horizontal and vertical width than the first electrolyte layer 51.

The first electrolyte layer 51 and the second electrolyte layer 52 are pressed together in a pressing process for pressing the positive electrode layer 2 and the negative electrode layer 4 to the electrolyte layer 5. In this embodiment, the corresponding region S1 where the positive electrode layer 2 and the negative electrode layer 4 face each other is pressed to form the pressing region P. The portion where the first electrolyte layer 51 and the second electrolyte layer 52 are pressed together is called the "pressed electrolyte layer" or the "pressed region of the electrolyte layer". On the other hand, the region where the first electrolyte layer 51 and the second electrolyte layer 52 are not pressed together is called the "unpressed electrolyte layer" or the "non-pressed region of the electrolyte".

In the solid-state battery of this embodiment, the attached positive electrode layer 2a and the attached first electrolyte layer 51a are formed on the positive electrode terminal 12, and they are continuous with the positive electrode layer 2 and the first electrolyte layer 51 on the positive electrode collector layer 6. Therefore, as shown in FIG. 1(c), the positive electrode terminal/negative electrode layer facing portion S3 has a laminated structure of the positive electrode terminal 12: the attached positive electrode layer 2a: the attached first electrolyte layer 51a: the second electrolyte layer 52: the negative electrode layer 4: the negative electrode collector 8. However, in the positive electrode terminal/negative electrode layer facing portion S3, the attached first electrolyte layer 51a and the attached second electrolyte layer 52a are not crimped, and become the non-crimped region NP of the electrolyte. The reason for providing the non-crimped region NP in this manner is as follows. In the solid-state battery unit of the present invention, a reference electrode is inserted into the electrolyte layer, but since the electrolyte layer is, for example, about 50 μm, the distance between the reference electrode and the positive electrode or the negative electrode is about half that, that is, about 25 μm. If such a thin electrolyte layer is pressed together with the reference electrode and the positive or negative electrode, a short circuit may occur between the reference electrode and the positive or negative electrode layer. To prevent such a short circuit, the region of the electrolyte where the reference electrode is provided is designated as a non-pressed region. In addition, since the reference electrode is provided in a region different from the region intended for the battery reaction in the solid-state battery, the operation of the solid-state battery is not affected even if this region is not pressed.

In the non-bonded region NP of the electrolyte layer, the first electrolyte layer 51a and the second electrolyte layer 52a are not bonded, so the boundary between them is clear and the two layers can be easily separated, whereas in the bonded region P of the electrolyte layer, the first electrolyte layer 51 and the second electrolyte layer 52 cannot be separated or the boundary between them cannot be physically recognized. Therefore, it can be said that the bonded region P of the electrolyte is a layer with a uniform layer structure, and the non-bonded region NP is an electrolyte layer having a boundary or two layers. Furthermore, it has been observed that the layer thickness of the bonded region P is about 1/3 to 1/2 thinner than that of the non-bonded region NP. These structural differences make it possible to distinguish the bonded region P and the non-bonded region NP of the electrolyte layer. In addition, the resistance is high in the non-bonded region NP, making it difficult for a sufficient battery reaction to occur between the positive electrode and the negative electrode. That is, in the solid-state battery unit 10, the originally planned battery reaction occurs between the positive electrode layer 2 and the negative electrode layer 4 in the bonded region P of the electrolyte layer 51 (the opposing region in FIG. 1(a)).

As shown in FIG. 1(c), a flat or foil-shaped reference electrode 16 is inserted between the first electrolyte layer 51a and the second electrolyte layer 52, and faces the associated positive electrode layer 2 and negative electrode layer 4 in approximately parallel relation. A terminal (reference electrode current collector) 18 is connected to the reference electrode 16 for external extraction.

By connecting the positive electrode terminal 12 and the reference electrode 16 of the solid-state battery having the above structure with a voltage meter, the potential of the positive electrode layer 2 can be measured through the positive electrode layer 2a. Also, by connecting the negative electrode current collector 16 and the reference electrode 16 with a voltage meter, the potential of the negative electrode layer 4 can be measured. As described above, the positive electrode layer 2a and the reference electrode 16 face each other, and the negative electrode layer 4 also faces the reference electrode 6, so that the potentials of the positive electrode layer 2 and the negative electrode layer 4 are reliably separated, and the potentials of each can be accurately measured. Even if a negative electrode layer 4 having a larger area than the positive electrode layer 2 is used, the reference electrode 6 can be provided using the area where the positive electrode terminal 12 and the negative electrode layer 4 face each other, so that the potentials of the positive electrode layer 2 and the negative electrode layer 4 can be measured independently and accurately, even with a simple structure.

Second Embodiment
In the solid-state battery unit 20 of the second embodiment, as shown in FIG. 2, the reference electrode 16 is provided in the opposing region S1 where the positive electrode layer 2 and the negative electrode layer 4 oppose each other, that is, in the portion protruding from the battery reaction region. The positive electrode current collector 6 has a shape having a protruding portion 6p where a part of the periphery of the rectangle protrudes, and an additional positive electrode layer and an additional first electrolyte layer are formed on the protruding portion 6p. The protruding portion 6p overlaps with the negative electrode layer 4 and extends to the outer edge of the negative electrode layer 4. In the specific example shown in FIG. 2, the protruding portion 6p opposes the negative electrode layer 4 and the second electrolyte layer thereon, and extends to the outer edge of the negative electrode layer 4, but is not limited thereto, and may not reach the periphery of the negative electrode layer 4, or may protrude so as to extend beyond the negative electrode layer 4.

The positive electrode layer and the first electrolyte layer on the protruding portion 6p are continuous with the positive electrode layer 2 and the first electrolyte layer 51 present in the facing region S1, respectively. The first electrolyte layer and the second electrolyte layer in the protruding portion 6p are not pressed and form a non-pressed region. A flat reference electrode 16 is inserted between the attached first electrolyte layer 51a and the second electrolyte layer 52, and the reference electrode 16 faces the positive electrode layer 2a and the negative electrode layer 4 in parallel in the protruding region 6p.

In the solid-state battery unit of this structure, as in the first embodiment, the potential of the positive electrode layer 2 can be measured by connecting the protruding portion 6p of the positive electrode collector to the reference electrode 16 with a voltage meter, and the potential of the negative electrode layer 4 can be measured by connecting the negative electrode collector 8 to the reference electrode 16 with a voltage meter. As in the first embodiment, the battery reaction in the solid-state battery unit occurs between the positive electrode layer 2 and the negative electrode layer 4 in the compression region P of the electrolyte layer, i.e., in the opposing region S1.

Third Embodiment
In the first and second embodiments, the reference electrode is provided outside the range of the positive electrode collector and the positive electrode layer, that is, outside the facing region S1, but in this embodiment, it is provided within the facing region S1. As shown in FIG. 3, only the first electrolyte layer and the second electrolyte layer in the region 2b of the rectangular positive electrode collector 6 and the positive electrode layer 2 are pressed to form the pressed region P, and the first electrolyte layer 51 and the second electrolyte layer 52 in the region 2c along the width direction of the lower edge of the positive electrode layer 2 are not pressed and become the non-pressed region NP. That is, in this solid battery unit 30, the pressed region P is smaller than the facing region S1 and exists inside the non-pressed region NP. The reference electrode 16 exists between the first electrolyte layer 51 and the second electrolyte layer 52 in the non-pressed region NP.

In this embodiment of the solid-state battery unit 30, the potential of the positive electrode layer 2 can be measured by connecting the positive electrode collector 6 in the non-bonded region NP to the reference electrode 16 with a voltage meter, and the potential of the negative electrode layer 4 can be measured by connecting the negative electrode collector 8 to the reference electrode 16 with a voltage meter. Note that in the solid-state battery unit 30, the battery reaction also occurs between the positive electrode layer 2 and the negative electrode layer 4 in the bonded region P of the electrolyte layer 5.

The solid-state battery unit having the reference electrode of the above embodiment can accurately measure the potential of the positive electrode layer 2 and the potential of the negative electrode layer 4 independently, and therefore can detect the operation of the positive electrode or negative electrode and the deterioration of the materials constituting those electrodes. For example, in a positive electrode made of NCA, the crystal structure may change at 4.2 V or higher, which may cause the battery performance to decrease. However, by detecting an abnormality by measuring the potential of the reference electrode-positive electrode layer, it becomes possible to maintain the battery operation at 4.2 V or lower. In addition, in the negative electrode, for example, in an active material such as graphite, whose voltage drops close to the Li deposition potential, by detecting an abnormality by measuring the potential of the reference electrode-negative electrode layer, it becomes possible to operate the battery without reaching the Li deposition potential, and it becomes possible to prevent a short circuit due to Li electrolytic deposition.

The materials that make up the solid-state battery unit of the above embodiment are described below.

[Positive electrode current collector and negative electrode current collector]
The positive electrode current collector can be made of any material having electrical conductivity, for example, stainless steel such as SUS, conductive metal materials such as Ni, Ti, Fe, Cu, Al or alloys thereof, or carbon materials. The shape of the positive electrode current collector is not particularly limited, and can be, for example, foil, approximately flat plate, or mesh. The negative electrode current collector can be made of the same material and shape as the positive electrode current collector.

[Solid electrolyte layer]
The solid electrolyte layers, such as the first and second electrolyte layers, include a solid electrolyte, such as a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte. The sulfide solid electrolyte contains at least lithium and sulfur, and examples thereof include Li ₂ S-P ₂ S ₅ system (Li ₇ P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₈ P ₂ S ₉ , etc.), Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ S ₅ , LiI-LiBr-Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -GeS ₂ (Li ₁₃ GeP ₃ S ₁₆ , Li ₁₀ GeP ₂ S _12, etc.), LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li _7-x PS _6-x Cl _x, etc. can be used.

The oxide solid electrolyte contains at least lithium and oxygen, and can be classified into Nasicon type, perovskite type, garnet type, etc. according to the crystal structure. For example, Li1 _{+ xAlxTi2 -x(PO4)3, Li1+xAlxGe2-x(PO4)3, Li3xLa2/3- xTiO3 , Li7La3Zr2O12 , Li7 - xLa3Zr1 - xNbxO12 , Li7-3xLa3Zr2AlxO12 , Li3PO4 , or Li3 + xPO4 - xNx ( LiPON ) or the like can be used} . Among these, oxide solid electrolytes having a garnet-type structure or a garnet-like structure containing at least Li, La, _Zr , _and O are preferred. In particular, _Li7La3Zr2O12 (hereinafter referred to as "LLZ") and _LLZ substituted with at least one of Mg and A (wherein "A" is Ca, Sr, Ba, or a combination thereof) (hereinafter referred to as "substituted LLZ") are preferred. Powder consisting of LLZ or substituted LLZ electrolyte is referred to as "LLZ-based powder".

When an LLZ-based powder is used as the solid electrolyte of the solid electrolyte layer, it is preferable to further include a lithium ion conductive assistant. The lithium ion conductive assistant includes an ionic liquid having lithium ion conductivity. The ionic liquid having lithium ion conductivity is, for example, an ionic liquid in which a lithium salt is dissolved. The ionic liquid is composed of only cations and anions, and is a liquid substance at room temperature. Examples of the lithium salt that can be used include lithium tetrafluoroborate ( _LiBF4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (Li( _{SO3CF3 )} ), lithium bis(trifluoromethanesulfonyl)imide (LiN( _{SO2CF3 ) 2} ), _lithium bis(fluorosulfonyl)imide (LiN( _SO2F ) ₂ ) (hereinafter referred to as "LiFSI"), and lithium bis( _{pentafluoroethanesulfonyl} )imide (LiN( _SO2C2F5 ) ₂ ) _.

The above-mentioned ionic liquids may have cations such as ammonium-based cations, such as butyltrimethylammonium and trimethylpropylammonium, imidazolium-based cations, such as 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium, piperidinium-based cations, such as 1-butyl-1-methylpiperidinium and 1-methyl-1-propylpiperidinium, pyridinium-based cations, such as 1-butyl-4-methylpyridinium and 1-ethylpyridinium, pyrrolidinium-based cations, such as 1-butyl-1-methylpyrrolidinium and 1-methyl-1-propylpyrrolidinium, sulfonium-based cations, such as trimethylsulfonium and triethylsulfonium, phosphonium-based cations, morpholinium-based cations, etc.

The ionic liquid may have, as an anion, a halide such as Cl- ^{or Br-} _{, a boron compound such as BF4-, an amine such as (NC)2N-, (CF3SO2)2N-, or (FSO2} ^)2N- _, ^{a sulfate} _{or sulfonate such as} ^CH3SO4- _{or CF3SO3-} ^, _or a phosphate such _{as PF6-} ^, or _the ^like .

More specifically, the ionic liquid may be butyltrimethylammonium bis(trifluoromethanesulfonyl)imide, trimethylpropylammonium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, or the like. By including a lithium ion conductive assistant, when the LLZ powder is in a pressure-molded state, it is present at the grain boundaries of the LLZ powder, improving the lithium ion conductivity at the grain boundaries.

The solid electrolyte layer may contain a binder. Examples of binders that can be used include polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene, polyimide, polyamide, silicone, styrene-butadiene rubber, acrylic resin, and polyethylene oxide. Examples of additives such as the above-mentioned LLZ-based powder (ion conductive powder), ionic liquid, and binder are disclosed in, for example, Japanese Patent No. 6682708, and they can be used in the solid battery unit of the present invention.

The thickness of the first electrolyte layer and the second electrolyte layer is 5 μm to 50 μm, preferably 5 μm to 15 μm, and the thickness of the entire electrolyte layer is 10 μm to 100 μm, preferably 10 μm to 30 μm.

[Positive electrode layer]
The positive electrode layer includes a positive electrode active material, and may further include additives such as a solid electrolyte constituting the above-mentioned solid electrolyte layer, a lithium ion conductive assistant, an electron conductive assistant, and a binder. Examples of the positive electrode active material include S, TiS ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _1-x-y Co _x Al _y O ₂ , LiNi _1-x-y Co _x Mn _y O ₂ , LiMn ₂ O ₄ , and LiFePO _4. The above-mentioned ionic liquid having lithium ion conductivity may be included as a lithium ion conductive assistant. The solid electrolyte also functions as a lithium ion conductive assistant. As the electron conductive assistant, an electron conductive assistant such as conductive carbon, Ni, Pt, or Ag may be used. As the binder, a binder similar to the binder that may be included in the solid electrolyte layer may be used. The thickness of the positive electrode layer may be, for example, from 20 μm to 60 μm.

[Negative electrode layer]
The negative electrode layer includes a negative electrode active material, and may further include additives such as a solid electrolyte constituting the above-mentioned solid electrolyte layer, a lithium ion conductive assistant, an electronic conductive assistant, and a binder. Examples of the negative electrode active material include Li metal, Li-Al alloy, Li ₄ Ti ₅ O ₁₂ , carbon, Si, and SiO. The lithium ion conductive assistant may include an ionic liquid having the above-mentioned lithium ion conductivity. The solid electrolyte also functions as a lithium ion conductive assistant. The electronic conductive assistant may be conductive carbon, Ni, Pt, or Ag. The binder may be the same as the binder that may be included in the solid electrolyte layer. The thickness of the negative electrode layer may be, for example, 20 μm to 70 μm.

[Reference pole]
The reference electrode may be formed, for example, from a lithium alloy or an oxide containing lithium. The size of the reference electrode 16 is not important, but a flat plate with a thickness of about 10 to 50 μm is preferable from the viewpoint of being inserted between the electrolyte layers. The terminal for external connection connected to the reference electrode may be made of copper tape, copper foil, or the same material as the positive electrode current collector.

<Method of manufacturing a solid-state battery unit>
The manufacturing method of the solid-state battery unit will be described by taking the manufacturing method of the solid-state battery unit of the first embodiment as an example. First, a rectangular positive electrode current collector and a negative electrode current collector having a width longer than that of the positive electrode current collector are prepared as shown in the left and right of FIG. 4(a). Next, a mixture is prepared in which a positive electrode mixture containing a positive electrode active material and a solid electrolyte is dispersed in a solvent, and the mixture is applied to the entire surface of the positive electrode current collector by wet coating or the like as shown in the left side of FIG. 4(b), and after drying, a positive electrode sheet is obtained in which a positive electrode layer is formed on the positive electrode current collector. Also, a mixture is prepared in which a negative electrode mixture containing a negative electrode active material and a solid electrolyte is dispersed in a solvent, and the mixture is wet coated on the surface of the negative electrode current collector except for the upper part as shown in the right side of the figure, and after drying, a negative electrode sheet is obtained in which a negative electrode layer is formed on the negative electrode current collector.

Next, as shown on the left side of FIG. 4(c), an electrolyte layer mixture containing a solid electrolyte is applied onto the positive electrode layer of the positive electrode sheet to form a first electrolyte layer. The positive electrode sheet provided with the positive electrode layer and the first electrolyte layer is called the "positive electrode electrolyte sheet." An electrolyte layer mixture having the same components and composition as the first electrolyte layer is applied onto the negative electrode layer of the negative electrode sheet to form a second electrolyte layer, as shown on the right side of the figure. The negative electrode sheet provided with the negative electrode layer and the second electrolyte layer is called the "negative electrode electrolyte sheet."

Next, as shown in FIG. 4(d), the positive electrode electrolyte sheet and the negative electrode electrolyte sheet are punched out so that the positive electrode terminal (positive electrode lead portion) and the negative electrode terminal (negative electrode lead portion) protrude partially from the sheet surface. After punching, the positive electrode terminal is composed of the positive electrode layer and the first electrolyte layer on the Al foil, and the negative electrode terminal is composed of only the negative electrode current collector.

Next, as shown in FIG. 4(e), the punched positive electrode electrolyte sheet and the negative electrode electrolyte sheet are overlapped so that the first electrolyte faces the second electrolyte. At this time, a reference electrode is inserted into the overlapping portion of the first electrolyte layer on the positive electrode terminal and the second electrolyte layer of the negative electrode sheet. After this, the overlapped positive electrode electrolyte sheet and the negative electrode electrolyte sheet are pressed together. A press machine heated to about 60°C is used for pressing. The area to be pressed is the area excluding the positive electrode terminal, that is, only the area where the rectangular first electrolyte and the second electrolyte overlap (battery reaction area). As long as only a partial area can be pressed, any pressing method can be used, not limited to a press machine. Also, the reference electrode can be inserted after the pressing process. In this way, a solid-state battery unit having a structure as shown in FIG. 1(a) to (c) can be manufactured.

A solid-state battery structure 100 (or a solid-state battery module) is completed by stacking a plurality of solid-state battery units without a reference electrode on the solid-state battery unit manufactured as described above as shown in FIG. 5 and connecting the positive electrode terminals to each other and the negative electrode terminals to each other in parallel. The solid-state battery structure can be placed in a case such as a laminate film made of a thermoplastic resin and sealed by thermocompression or the like. The welded positive electrode terminal and negative electrode terminal can be extended outside the case as a positive electrode tab and a negative electrode tab, respectively.

When stacking the solid-state battery units, the negative electrode current collectors and the positive electrode current collectors may be stacked together as shown in FIG. 5, or the negative electrode current collector of the solid-state battery unit may be stacked with a separator interposed between them, so that the positive electrode current collector of the solid-state battery unit stacked on top of the negative electrode current collector faces the negative electrode current collector of the solid-state battery unit stacked on top of the negative electrode current collector. In the example shown in FIG. 5, only one solid-state battery unit of the solid-state battery structure has a reference electrode, but multiple or all of the battery units constituting the solid-state battery structure may have a reference electrode. Alternatively, a solid-state battery unit in which a reference electrode is provided for each battery unit of a different manufacturing lot may be introduced into the solid-state battery structure. A solid-state battery unit not provided with a reference electrode may use a single-layer electrolyte layer instead of the electrolyte layer being divided into the first and second electrolyte layers and compressed as described above, or may be a solid-state battery unit manufactured by another known method.

The method for manufacturing the solid-state battery unit has been described using the method for manufacturing the solid-state battery of the first embodiment as an example, but the solid-state batteries of the second and third embodiments can also be manufactured in the same manner by changing the insertion position and crimping position of the reference electrode. The solid-state battery structure composed of multiple solid-state battery units may also include a battery control circuit, a voltage measurement unit, and other detectors and elements.

The solid-state battery unit and its manufacturing method will be specifically described below using examples, but the present invention is not limited to these examples.

The positive electrode active material was lithium nickel oxide (NCA), the electron conductive additive was carbon nanofiber (VGCF (vapor grown carbon fiber)), the solid electrolyte was LLZ, the lithium ion conductive additive was LiFSI, and the binder was PVDF-HFP. These were dispersed in an organic solvent to prepare a positive electrode mixture. This positive electrode mixture was wet coated to a thickness of approximately 30 μm on an Al foil measuring 78 mm x 46 mm x 15 μm (thickness) as a positive electrode current collector to prepare a positive electrode sheet having a positive electrode layer (see Figures 4 (a) and (b)).

The negative electrode active material was natural graphite, the electron conductive additive was carbon nanofiber (VGCF (vapor grown carbon fiber)), the solid electrolyte was LLZ, the lithium conductive additive was LiFSI, and the binder was PVDF-HFP. These were mixed and dispersed in an organic solvent to prepare a negative electrode mixture. This negative electrode mixture was wet coated to a thickness of approximately 40 μm on a Cu foil measuring 80 mm x 50 mm x 12 μm (thickness) as a negative electrode current collector to produce a negative electrode sheet with a negative electrode layer (see Figures 4 (a) and (b)).

LLZ was used as the solid electrolyte, LiFSI (P13FSI) as the lithium conductive assistant, and PVDF-HFP as the binder, and these were mixed to prepare a paste-like electrolyte layer mixture. The electrolyte layer mixture was wet-coated to a thickness of approximately 25 μm on the positive electrode layer of the positive electrode sheet and the negative electrode layer of the negative electrode sheet, respectively, to prepare a positive electrode electrolyte sheet and a negative electrode electrolyte sheet (see Figure 4 (c)).

The upper rectangular portions (positive electrode sheet: 32 mm x 36 mm, negative electrode sheet: 30 mm x 40 mm) of the positive electrode electrolyte sheet and the negative electrode electrolyte sheet were punched out so that the positive electrode terminal and the negative electrode terminal protruded (see FIG. 4(d)). Next, the positive electrode electrolyte sheet and the negative electrode electrolyte sheet were stacked so that the electrolytes faced each other, and a Li metal reference electrode measuring 5 mm x 15 mm x (thickness) 50 μm was inserted at the boundary between the electrolyte on the positive electrode terminal and the electrolyte on the negative electrode electrolyte sheet (see FIG. 4(e)). In this state, the positive electrode electrolyte sheet and the negative electrode electrolyte sheet were pressed together. The pressing was performed by heating the pressing portion to about 60°C using a roll press, and only the portion excluding the positive electrode terminal and the negative electrode terminal (battery reaction portion) was pressed together.

The solid-state battery unit thus obtained was subjected to the following measurements. The battery was charged to 20 mAh between the positive and negative electrodes at a current density of 0.08 mA/ ^cm2 , and discharged to 2.5 V. At this time, a voltage measuring device was connected between the positive and reference electrodes and between the negative and reference electrodes, respectively, to measure the voltage. Voltage measurements were also performed in the same manner between the positive and negative electrodes. The charge and discharge curves of the measurement results are shown in Figs. 6 and 7, respectively. From these figures, it can be seen that the potentials of the positive and negative electrodes can be measured, and that the potentials of the positive and negative electrodes are sufficiently ionized and separated for measurement. It is noted that the potential of the reference electrode is a constant 0 V (vs Li/Li ⁺ ) from a comparison with the voltage measurement curve using a half cell consisting of Li and a positive electrode.

Although the solid-state battery and its manufacturing method of the present invention have been described above using embodiments and examples, the technical scope of the present invention is not limited to the above. It is clear to those skilled in the art that various modifications or improvements can be made to the above embodiments and examples, and it is also clear from the claims that such modifications or improvements can be included in the technical scope of the present invention. For example, in the manufacturing process of the solid-state battery unit with reference to FIG. 4, the negative electrode layer and the second electrolyte layer were not formed on the negative electrode terminal, but the negative electrode layer and the second electrolyte layer may also be provided on the negative electrode terminal. In addition, the positive electrode layer and the first electrolyte layer were formed on the entire area of the positive electrode current collector before punching, but the positive electrode layer and the first electrolyte layer may be formed only in a part of the area that defines the positive electrode terminal, and it is sufficient that a reference electrode is inserted between that part and the second electrolyte layer.

The order in which each process in the manufacturing method shown in the specification and drawings is performed is not specifically stated, and the processes may be performed in any order unless the output of a previous process is used in a subsequent process. For convenience, even if the description uses "first," "next," etc., it does not mean that the processes must be performed in that order.

10, 20, 30 Solid-state battery unit 2 Positive electrode layer, 3 Negative electrode sheet, 4 Negative electrode layer 5 Electrolyte layer, 6 Positive electrode current collector, 8 Negative electrode current collector, 12 Positive electrode terminal 14 Negative electrode terminal, 16 Reference electrode, 18 Reference electrode terminal 51 First electrolyte layer, 52 Second electrolyte layer 100 Solid-state battery structure P Pressure-bonded region, NP Non-pressed region S1 Facing region, S2 Non-facing region, S3 Positive electrode/positive electrode terminal/negative electrode layer facing portion

Claims (6)

A laminated solid-state battery,
A battery having a flat positive electrode layer, an electrolyte layer, and a negative electrode layer having a size larger than that of the positive electrode layer, in this order;
the electrolyte layer has a first electrolyte layer on the positive electrode layer side and a second electrolyte layer on the negative electrode side, and has a compression region where the first electrolyte layer and the second electrolyte layer are compressed and a non-compression region where they are not compressed,
a reference electrode is provided between the first electrolyte layer and the second electrolyte layer in the non-bonded region so as to face the positive electrode layer and the negative electrode layer ;
The laminated solid-state battery , wherein the reference electrode is not pressed against either the first electrolyte layer or the second electrolyte layer . The stacked solid-state battery according to claim 1, characterized in that the non-bonded region is a region that is sandwiched between the positive electrode layer and the negative electrode layer and extends outside the battery reaction region where the battery reaction occurs. The stacked solid-state battery according to claim 2 further comprises a positive electrode current collector layer covering the positive electrode layer, a positive electrode terminal extending from the positive electrode current collector layer and connected to the outside, a negative electrode current collector layer covering the negative electrode layer, and a negative electrode terminal extending from the negative electrode current collector layer and connected to the outside, and the protruding region is present on the positive electrode terminal. A stacked solid-state battery structure comprising the stacked solid-state battery according to claim 1 and a plurality of stacked solid-state batteries stacked on the stacked solid-state battery. forming a positive electrode layer including a positive electrode active material and a negative electrode layer having a size larger than the positive electrode layer and including a negative electrode active material;
forming a first electrolyte layer on the positive electrode layer;
forming a second electrolyte layer on the negative electrode layer;
compressing the first electrolyte layer and the second electrolyte layer, except for a portion of an overlapping region of the first electrolyte layer and the second electrolyte layer facing each other;
providing a reference electrode between the first electrolyte layer and the second electrolyte layer in the portion of the overlapping region so as to face the positive electrode layer and the negative electrode layer;
In the part, the first electrolyte layer and the second electrolyte layer are not compressed together with the reference electrode sandwiched therebetween . providing a negative electrode current collector having a negative electrode terminal for external connection and a positive electrode current collector having a positive electrode terminal for external connection;
forming the negative electrode layer on the negative electrode current collector;
forming the positive electrode layer on the positive electrode current collector;
The method according to claim 5 , further comprising forming the positive electrode layer on at least a portion of the positive electrode terminal that overlaps with the negative electrode layer.

Images