WO2023234351A1

WO2023234351A1 - All-solid-state lithium ion secondary battery and method for producing all-solid-state lithium ion secondary battery

Info

Publication number: WO2023234351A1
Application number: PCT/JP2023/020287
Authority: WO
Inventors: 洋介白鳥; 健吾齋藤; 健太渡辺; 伸太郎安井; 雅俊東海林
Original assignee: 富士フイルム株式会社; 国立大学法人東京工業大学
Priority date: 2022-06-01
Filing date: 2023-05-31
Publication date: 2023-12-07

Abstract

The present invention provides an all-solid-state lithium ion secondary battery which is obtained by sequentially arranging a positive electrode layer, a solid electrolyte layer and a negative electrode layer in this order, wherein: the solid electrolyte layer contains a solid electrolyte which contains a lithium-containing oxide that contains Li, B and O, a lithium salt and water; relative to the content of the lithium-containing oxide, the ratio of the content of the lithium salt is 0.001 to 1.5 in terms of the molar ratio and the ratio of the content of water is 1 to 12 in terms of the molar ratio in the solid electrolyte; and the discharge potential difference between a positive electrode active material in the positive electrode layer and a negative electrode active material in the negative electrode layer is 1.3 V or more based on Li. The present invention also provides a method for producing this all-solid-state lithium ion secondary battery.

Description

All-solid-state lithium-ion secondary battery and method for manufacturing an all-solid-state lithium-ion secondary battery

The present invention relates to an all-solid lithium ion secondary battery and a method for manufacturing an all-solid lithium ion secondary battery.

Conventionally, organic solvents with high ionic conductivity have been used as electrolytes in lithium ion secondary batteries. However, since organic solvents are flammable, there is a safety problem. Furthermore, since it is in a liquid state, it is difficult to make it compact, and when the battery becomes larger, capacity limitations become a problem. On the other hand, although water is nonflammable, it has a narrow potential window; under the condition of pH=7, it is oxidatively decomposed above 3.8 V (Li standard), reductively decomposed below 2.5 V (Li standard), and the potential window is 1. It is less than 3V. For this reason, lithium ion secondary batteries that use an aqueous solution as an electrolyte have not been put into practical use because they cannot have a high capacity.
In contrast, all-solid-state lithium ion secondary batteries are one of the next generation batteries that can solve these problems. Figure 1 shows the basic configuration of an all-solid-state lithium-ion secondary battery. The all-solid-state lithium ion secondary battery 10 includes a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5 in this order when viewed from the negative electrode side. The layers are in contact with each other and have an adjacent structure. By adopting such a structure, during charging, electrons (e ⁻ ) are supplied to the negative electrode side, and lithium ions (Li ⁺ ) that have migrated through the solid electrolyte layer 3 are accumulated there. On the other hand, during discharging, lithium ions (Li ⁺ ) accumulated in the negative electrode are returned to the positive electrode side through the solid electrolyte layer 3, and electrons are supplied to the operating region 6. In the illustrated example, a light bulb is used as a model for the operating portion 6, and the light bulb is lit by discharge.

As mentioned above, in an all-solid-state lithium ion secondary battery, excellent lithium ion conductivity is required in the solid electrolyte layer in order to obtain desired charge/discharge characteristics.
As the solid electrolyte constituting the solid electrolyte layer, a sulfide-based solid electrolyte or an oxide-based solid electrolyte is mainly used.
Sulfide-based solid electrolytes are soft and deform plastically, so the particles are bound together just by pressure molding. Therefore, sulfide-based solid electrolytes have low interparticle interfacial resistance and excellent ionic conductivity. However, sulfide-based solid electrolytes have the problem of reacting with water and generating toxic hydrogen sulfide.
In contrast, oxide-based solid electrolytes have the advantage of high safety. However, oxide-based solid electrolytes are hard and difficult to undergo plastic deformation. In order to improve the binding between particles of an oxide-based solid electrolyte, a high-temperature sintering process is required, and there are restrictions in terms of battery production efficiency and energy cost. For example, Patent Document 1 discloses a solid electrolyte formed of a lithium-containing oxide having a specific elemental composition, and describes that this solid electrolyte exhibits high ionic conductivity. However, in order to use the lithium-containing oxide described in Patent Document 1 as a solid electrolyte sheet, high-temperature sintering treatment is required.
As a technique to deal with this problem, for example, Patent Document 2 describes a lithium compound whose lithium ion conductivity at 25°C is 1.0 × 10 ^-6 S/cm or more and a lithium compound obtained from X-ray total scattering measurement. A complex with lithium tetraborate is described whose reduced two-body distribution function G(r) exhibits a particular profile. According to the technology described in Patent Document 2, although this composite is composed of a lithium-containing oxide, lithium tetraborate plastically deforms between the lithium compounds and plays the role of connecting the lithium compounds, so this It is said that the composite can form a lithium ion conductor exhibiting good lithium ion conductivity by pressure treatment without being subjected to high temperature sintering treatment.

JP2018-052755A International Publication No. 2021/193204

Although the composite described in Patent Document 2 is composed of a lithium-containing oxide, it is soft and can be used between particles without being subjected to sintering treatment or without adding a binder such as an organic polymer. It can ensure binding, and has properties that conventional oxide-based solid electrolytes have not been able to achieve. However, as the inventors proceeded with their studies, they found that the conductivity of lithium ions is not currently sufficient for practical use as a solid electrolyte layer in all-solid-state lithium-ion secondary batteries, and that It has become clear that there is room for improvement.

The present invention is an all-solid-state lithium ion secondary battery using a lithium-containing oxide as a solid electrolyte layer, wherein the solid electrolyte layer can be formed using organic polymers, for example, without being subjected to high-temperature sintering treatment. An all-solid-state lithium ion secondary battery that has excellent interparticle binding properties, higher lithium ion conductivity, and excellent safety even when a binder is not blended, and a method for manufacturing the same. The challenge is to provide the following.

The problem of the present invention was solved by the following means.

[1]
An all-solid lithium ion secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order,
The solid electrolyte layer includes a solid electrolyte containing a lithium-containing oxide containing Li, B, and O, a lithium salt, and water, and the lithium salt The value of the ratio of the content of is 0.001 to 1.5 in molar ratio, the value of the ratio of the content of water is 1 to 12 in molar ratio,
An all-solid-state lithium ion secondary battery, wherein the difference in discharge potential based on Li between the positive electrode active material contained in the positive electrode layer and the negative electrode active material contained in the negative electrode layer is 1.3 V or more.
[2]
The all-solid lithium ion secondary battery according to [1], wherein the lithium-containing oxide includes Li _2+x B _4+y O _7+z .
However, -0.3<x<0.3, -0.3<y<0.3, and -0.3<z<0.3.
[3]
The positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , Li ₂ MnO ₃ -LiNiMnCoO ₂ , Containing _at least _one of _LiMn2O4 _, _{LiNi0.5Mn1.5O4} _, _LiFePO4 , _LiMnPO4 , _LiCoPO4 , _Li2CoP2O7 _and _LiNiPO4 ,
The negative electrode active material contains at least one of Li ₄ Ti ₅ O ₁₂ , TiNb ₂ O ₇ , Fe ₃ O ₄ , graphite, hard carbon, Si, SiO, Sn, Al, and metal Li,
The all-solid lithium ion secondary battery according to [1] or [2], wherein the difference in discharge potential between the positive electrode active material and the negative electrode active material based on Li is 1.3 V or more.
[4]
The all-solid-state lithium ion secondary battery according to any one of [1] to [3], wherein the negative electrode active material has a discharge potential of 2.5 V or less based on Li.
[5]
[4] The negative electrode active material is at least one of Li ₄ Ti ₅ O ₁₂ , TiNb ₂ O ₇ , Fe ₃ O ₄ , graphite, hard carbon, Si, SiO, Sn, Al, and metallic Li. The all-solid-state lithium ion secondary battery described in .
[6]
The all-solid-state lithium ion secondary battery according to any one of [1] to [5], wherein the positive electrode active material has a discharge potential of 3.8 V or more based on Li.
[7]
The positive electrode active material is selected from LiCoO ₂ , Li ₂ MnO ₃ -LiNiMnCoO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiMnPO ₄ , LiCoPO ₄ , Li ₂ CoP ₂ O ₇ and LiNiPO ₄ . The all-solid-state lithium ion secondary battery according to [6], which is at least one of the above.
[8]
The all-solid-state according to any one of [1] to [7], wherein the production of the all-solid lithium ion secondary battery includes forming the solid electrolyte layer by applying a dispersion of the solid electrolyte. A method for manufacturing a lithium ion secondary battery.
[9]
The production of the all-solid lithium ion secondary battery according to any one of [1] to [7], including forming the solid electrolyte layer by applying pressure to the powder of the solid electrolyte. A method for manufacturing a solid lithium ion secondary battery.

In the present invention or the specification, when a numerical range is indicated and explained, when an upper limit value and a lower limit value of the numerical range are explained separately, either the upper limit value or the lower limit value is appropriately combined to specify a specific numerical range. It can be done. On the other hand, when setting and explaining multiple numerical ranges expressed using "~", the upper and lower limit values forming the numerical range are specified as specific numerical ranges written before and after "~". The numerical ranges are not limited to the above combinations, and may be a numerical range that is an appropriate combination of the upper limit and lower limit of each numerical range. In the present invention and the specification, a numerical range expressed using "-" means a range that includes the numerical values written before and after "-" as lower and upper limits.

The all-solid-state lithium ion secondary battery of the present invention uses a lithium-containing oxide in the solid electrolyte layer, and the solid electrolyte layer can be made of, for example, an organic polymer without being subjected to high-temperature sintering treatment. Even when such a binder is not blended, it has excellent binding properties between particles, higher lithium ion conductivity, and excellent safety. Further, the method for manufacturing an all-solid lithium ion secondary battery of the present invention is a suitable manufacturing method for obtaining the above-mentioned all-solid lithium ion secondary battery of the present invention.

FIG. 1 is a cross-sectional view schematically showing an example of the configuration of an all-solid-state lithium ion secondary battery. FIG. 2 is a diagram showing an example of an X-ray diffraction pattern for explaining the X-ray diffraction characteristics of a preferred embodiment of the solid electrolyte (I) used in the present invention. FIG. 3 is a diagram showing an example of the reduced two-body distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I) used in the present invention. FIG. 4 is a diagram showing an example of a spectrum obtained when solid-state ⁷ Li-NMR measurement is performed at 20° C. or 120° C. for a preferable form of the solid electrolyte (I) used in the present invention. FIG. 5 is a diagram showing an example of a spectrum obtained when solid ⁷ Li-NMR measurement of lithium tetraborate crystal is performed at 20°C or 120°C. FIG. 6 is a diagram showing an example of a spectrum obtained when solid-state ⁷ Li-NMR measurement is performed at 20° C. for a preferred form of the solid electrolyte (I) used in the present invention. FIG. 7 is a diagram in which the peaks shown in FIG. 6 are separated into waveforms. FIG. 8 is a diagram showing an example of a Raman spectrum of a preferable form of the solid electrolyte (I) used in the present invention. FIG. 9 is a diagram showing a Raman spectrum of a lithium tetraborate crystal. FIG. 10 is a diagram showing the reduced two-body distribution function G(r) obtained by X-ray total scattering measurement of powdered Li ₂ B ₄ O ₇ crystal. FIG. 11 is a diagram showing an X-ray diffraction pattern of powdered Li ₂ B ₄ O ₇ crystal.

[All-solid-state lithium ion secondary battery]
The all-solid lithium ion secondary battery of the present invention (hereinafter also referred to as "the secondary battery of the present invention") is an all-solid lithium ion secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order. The difference in discharge potential between the positive electrode active material contained in the positive electrode layer and the negative electrode active material contained in the negative electrode layer is 1.3 V or more based on Li. The solid electrolyte layer contains a solid electrolyte (I) having a specific composition described below.
Since the solid electrolyte layer in the secondary battery of the present invention contains the solid electrolyte (I) with a specific composition, it can be used without being subjected to high-temperature sintering treatment, as will be described later. Even when it is not blended, it has excellent binding properties between particles, higher lithium ion conductivity, and excellent safety.
Furthermore, the solid electrolyte (I) having a specific composition contains two types of water: "free water" and "bound water". This "bound water" interacts with the lithium-containing oxide and/or lithium salt, and the potential window of the solid electrolyte (I) becomes wider than the potential window of water, and it is no longer decomposed by redox even if the potential difference is 1.3 V or more. As a combination of a positive electrode active material and a negative electrode active material, a combination in which the difference in discharge potential based on Li is 1.3 V or more can be adopted, and a secondary battery with increased capacity can be provided. . As mentioned above, in conventional liquid-based lithium ion secondary batteries that use an aqueous solution as the electrolyte, water undergoes redox decomposition at a potential difference of 1.3 V or more, so the positive electrode active material and negative electrode active material used are However, in the secondary battery of the present invention, this problem is solved even though the solid electrolyte (I) contains water. I can do it.

The structure of the secondary battery of the present invention is not particularly limited as long as the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are arranged in this order, and there is no solid state between these layers and the adjacent positive electrode layer and negative electrode layer. This includes a structure in which a plurality of electrolyte layers are stacked (a structure of a small stacked battery). Each constituent layer (including a current collector, etc.) constituting the secondary battery of the present invention may have a single-layer structure or a multi-layer structure.
Among the configurations of the above-mentioned small stacked battery, the solid electrolyte layer is a solid electrolyte (I) with a specific composition, and the difference in discharge potential based on Li between the positive electrode active material contained in the positive electrode layer and the negative electrode active material contained in the negative electrode layer For configurations other than the configuration in which is set to 1.3 V or more, for example, the solid battery configurations described in paragraphs [0021] to [0046] of JP 2016-001602 A can be referred to and applied to the present invention.
Each layer of the secondary battery of the present invention will be explained below.

<Solid electrolyte layer>
The solid electrolyte layer constituting the secondary battery of the present invention is a layer formed of a solid electrolyte having a specific composition or a mixture of this solid electrolyte and other components. This solid electrolyte with a specific composition includes a lithium-containing oxide containing Li, B, and O (hereinafter also referred to as a "lithium-containing oxide"), water, and a lithium salt.
In the solid electrolyte having this specific composition, the ratio of the content of lithium salt to the content of lithium-containing oxide (lithium salt/lithium-containing oxide) is 0.001 to 1.5 in terms of molar ratio. Further, in the solid electrolyte having this specific composition, the ratio of the water content to the lithium-containing oxide content (water/lithium-containing oxide) is 1 to 12 in terms of molar ratio.
Hereinafter, a solid electrolyte with a specific composition in which the ratio of the lithium salt content and water content to the lithium-containing oxide content satisfies the above-mentioned specific molar ratio will be referred to as a "solid electrolyte ( Also referred to as ``I)''. The solid electrolyte (I) is usually an inorganic solid electrolyte.

The solid electrolyte (I) exhibits elastic properties that allow it to easily undergo plastic deformation. As a result, in a constituent layer such as a solid electrolyte layer containing solid electrolyte (I) formed by pressure treatment etc., the adhesion between solid electrolytes (I) and/or the composition with solid electrolyte (I) Adhesion with other components present in the layer is improved, interfacial resistance can be reduced, and better ionic conductivity can be obtained. By using this solid electrolyte (I), although it is a highly safe oxide-based solid electrolyte, it can achieve excellent lithium ion conductivity through pressure treatment, etc., without having to undergo high-temperature sintering treatment. Constituent layers such as the solid electrolyte layer shown can be formed.

The water contained in the solid electrolyte (I) includes at least bound water. It is not clear why the solid electrolyte (I) exhibits high lithium ion conductivity, but in the solid electrolyte (I), a soft hydration layer is likely to be formed on the surface of the lithium-containing oxide, and in this hydration layer, It is thought that a large amount of lithium derived from lithium salt is contained, and as a result, the ionic conductivity is further enhanced.
Here, in the present invention and the specification, "bound water" means water other than water existing as free water, or an OH group bonded to a lithium-containing oxide. Even if the solid electrolyte (I) contains water in the above content ratio, it remains in the state of solid particles (including a state in which solid particles are bound together), and can be used as a solid electrolyte of an all-solid lithium ion secondary battery. It's something that works. That is, the solid electrolyte (I) contains bound water that is not removed or difficult to remove under normal drying conditions. Note that, as long as the solid electrolyte (I) functions as a solid electrolyte of an all-solid lithium ion secondary battery in the state of solid particles (a state that can be handled as a powder), the solid electrolyte (I) may contain free water. That is, in the present invention, the "all-solid lithium ion secondary battery" includes a form in which the solid electrolyte contains water, as long as the solid electrolyte can be handled as solid particles (solid powder). The solid electrolyte (I) used in the present invention, in which the ratio of the water content to the lithium-containing oxide content is 12 or less in terms of molar ratio, is neither in a paste-like nor gel-like state, but in a solid particle state. (solid powder) state.

In the present invention, it is preferable that the solid electrolyte (I) be in an amorphous state (synonymous with an amorphous state or an amorphous state) from the viewpoint of more easily exhibiting elastic properties that are more likely to be plastically deformed. The solid electrolyte (I) being in an "amorphous state" means that it satisfies the following X-ray diffraction characteristics.

(X-ray diffraction characteristics)
In the X-ray diffraction pattern obtained from X-ray diffraction measurement using CuKα rays of solid electrolyte (I), the peak top is located in the range of diffraction angle 2θ of 21.6 to 22.0°, and the full width at half maximum is 0. The first peak is .65° or less, the peak top is located in the range of 25.4 to 25.8° with a diffraction angle 2θ, the second peak is with a full width at half maximum of 0.65° or less, and the diffraction angle 2θ is 33.4 The peak top is located in the range of ~33.8°, the third peak has a full width at half maximum of 0.65° or less, and the peak top is located in the range of the diffraction angle 2θ of 34.4 to 34.8°, There is no fourth peak with a full width at half maximum of 0.65° or less, or
In the X-ray diffraction pattern, if at least one peak (hereinafter referred to as "peak X") among the first peak, second peak, third peak, and fourth peak is present, the peak At least one of the peaks has an intensity ratio of 5.0 or less as calculated by the intensity measurement method described below.

-Strength measurement method-
The average intensity (Av1) in the range of +0.45° to +0.55° is calculated from the diffraction angle 2θ of the peak top of peak X, and the average intensity (Av1) in the range of −0.55° to −0. The average intensity (Av2) in the range of 45° is calculated, and the additive average value of the above Av1 and Av2 is calculated. The value of the ratio of the peak intensity at the peak top of peak X to this additive average value (peak intensity at the peak top of peak X/additive average value) is defined as the intensity ratio.

The X-ray diffraction characteristics will be explained in more detail.
In the X-ray diffraction pattern obtained from X-ray diffraction measurement using CuKα rays of the solid electrolyte (I), when none of the above first peak, second peak, third peak, and fourth peak is present. The solid electrolyte (I) satisfies the above-mentioned X-ray diffraction characteristics and is in an amorphous state.
In addition, in the X-ray diffraction pattern obtained from the X-ray diffraction measurement using CuKα rays of the solid electrolyte (I), if the above-mentioned peak Even when the obtained intensity ratio satisfies 5.0 or less, the above-mentioned X-ray diffraction characteristics are satisfied and the solid electrolyte (I) is in an amorphous state.
Here, the full width at half maximum (FWHM) of a peak means the peak width (°) at 1/2 point of the peak intensity at the peak top.

The above intensity measuring method will be explained in more detail with reference to FIG. 2.
FIG. 2 is a diagram showing an example of a peak X appearing in a diffraction pattern obtained from X-ray diffraction measurement using CuKα rays of solid electrolyte (I). In the X-ray diffraction pattern shown in FIG. 2, a specific peak whose peak top intensity is 1 is shown. In the intensity measurement method, the average intensity (Av1) in the range of +0.45° to +0.55° is calculated from the diffraction angle 2θ at the peak top of peak The average intensity (Av2) in the range of -0.55° to -0.45° from the top diffraction angle 2θ is calculated. Next, the average value of Av1 and Av2 is calculated, and the ratio of intensity 1 to the average value is determined as the intensity ratio. When the above X-ray diffraction characteristics are satisfied, it means that the solid electrolyte (I) has no or almost no crystal structure and is in an amorphous state.
In other words, the first to fourth peaks above are mainly peaks derived from the crystal structure in the solid electrolyte (for example, the crystal structure of lithium tetraborate), and if these peaks do not exist, it is in an amorphous state. It means something. Further, even if at least one of the first to fourth peaks is present, the fact that the intensity ratio of at least one of the peaks X is 5.0 or less means that the solid electrolyte (I) is This means that there is almost no crystal structure that would impede the effects of the invention. Note that, for example, a peak derived from a specific component (eg, lithium salt) may overlap with any of the first to fourth peaks described above. However, in an amorphous solid electrolyte, usually all of the first to fourth peaks decrease, so if the peak due to the above-mentioned specific component happens to overlap with any of the first to fourth peaks, Even if one large peak appears, the presence of at least one peak X with an intensity ratio below a predetermined value can be said to indicate that the solid electrolyte (I) is in an amorphous state.

The above X-ray diffraction measurement is performed using CuKα radiation under measurement conditions of 0.01°/step and 3°/min.

In the X-ray diffraction pattern obtained from X-ray diffraction measurement using CuKα rays of the solid electrolyte (I), none of the above first peak, second peak, third peak and fourth peak exist, or , Even if at least one peak X among the first peak, second peak, third peak, and fourth peak is present, the intensity ratio of at least one of the peaks X is 3.0 or less. is preferred.
Among them, none of the first peak, second peak, third peak and fourth peak are present, or at least one of the first peak, second peak, third peak and fourth peak is present. Even if two peaks X exist, it is more preferable that the intensity ratio of at least one of the peaks X is 2.0 or less.

In addition, in the above X-ray diffraction pattern, if the peak top is located in the range of 21.6 to 22.0° and there are two or more peaks with a full width at half maximum of 0.65° or less, the diffraction X-ray intensity is the highest. A large peak is selected as the first peak, and the above-mentioned X-ray diffraction characteristics are determined.
In addition, in the above X-ray diffraction pattern, if the peak top is located in the range of 25.4 to 25.8° and there are two or more peaks with a full width at half maximum of 0.65° or less, the diffracted X-ray intensity is the highest. A large peak is selected as the second peak, and the above-mentioned X-ray diffraction characteristics are determined.
In addition, in the above X-ray diffraction pattern, if the peak top is located in the range of 33.4 to 33.8° and there are two or more peaks with a full width at half maximum of 0.65° or less, the diffracted X-ray intensity is the highest. A large peak is selected as the third peak, and the above-mentioned X-ray diffraction characteristics are determined.
In addition, in the above X-ray diffraction pattern, if the peak top is located in the range of 34.4 to 34.8° and there are two or more peaks with a full width at half maximum of 0.65° or less, the diffracted X-ray intensity is the highest. A large peak is selected as the fourth peak, and the above-mentioned X-ray diffraction characteristics are determined.

(X-ray total scattering characteristics)
The solid electrolyte (I) preferably satisfies the following requirement A-1 in terms of total X-ray scattering properties. Further, when the solid electrolyte (I) satisfies the above-mentioned X-ray diffraction characteristics, this solid electrolyte (I) usually satisfies the following requirement A-2.

-Requirement A-1-
In the reduced two-body distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), a first peak whose peak top is located in a range where r is 1.43 ± 0.2 Å, and r There is a second peak whose peak top is located in a range of 2.40 ± 0.2 Å, G(r) at the top of the first peak is more than 1.0, and G(r) at the top of the second peak is (r) indicates 0.8 or more.

-Requirement A-2-
In the reduced two-body distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), the absolute value of G(r) is less than 1.0 in the range where r is more than 5 Å and less than 10 Å.

When the solid electrolyte (I) satisfies requirements A-1 and A-2, it has a short-range ordered structure related to the interatomic distances of B-O and B-B, but has almost no long-range ordered structure. Therefore, the oxide solid electrolyte itself is softer than conventional lithium-containing oxides and exhibits elastic properties that make it easier to plastically deform. As a result, in the layer containing the solid electrolyte (I) formed by pressure treatment etc., the adhesion between the solid electrolytes (I) and/or the constituent layers such as the solid electrolyte (I) and the solid electrolyte layer etc. It is presumed that adhesion with other components present therein is improved, interfacial resistance can be reduced, and better ionic conductivity can be obtained.
Requirement A-1 and Requirement A-2 will be explained in more detail with reference to the drawings.

FIG. 3 shows an example of the reduced two-body distribution function G(r) obtained by X-ray total scattering measurement of the solid electrolyte (I). The vertical axis in FIG. 3 is a reduced two-body distribution function obtained by Fourier transforming X-ray scattering, and indicates the probability that an atom exists at a position at a distance r. X-ray total scattering measurement can be performed with SPring-8 BL04B2 (acceleration voltage 61.4 keV, wavelength 0.2019 Å). The reduced two-body distribution function G(r) is obtained by converting the scattering intensity I _obs obtained by experiment according to the following procedure.
First, the scattering intensity I _obs is expressed by the following formula (1). Further, the structure factor S(Q) can be obtained by dividing the coherent scattering I _coh by the product of the number N of atoms and the square of the atomic scattering factor f, as expressed by the following formula (2).

I _obs = I _coh + I _{in coh} + I _fluorescence (1)

A structure factor S(Q) is used for PDF (Pair Distribution Function) analysis. In the above equation (2), the only required intensity is the coherent scattering I _coh . Incoherent scattering I _incoh and X-ray fluorescence I _fluorescence can be subtracted from the scattering intensity I _obs by blank measurements, subtraction using theoretical formulas, and detector discriminators.
The coherent scattering I _coh is expressed by Debye's scattering formula (formula (3) below) (N: total number of atoms, f: atomic scattering factor, r _ij : interatomic distance between ij).

Focusing on an arbitrary atom, if the atomic density at a distance r is ρ(r), then the number of atoms existing in a sphere with radius r−r+d(r) is 4πr ² ρ(r)dr, so the above Formula (3) is expressed by the following formula (4).

If the average density of atoms is set to ρ ₀ and the above formula (4) is modified, the following formula (5) is obtained.

From the above formula (5) and formula (2), the following formula (6) is obtained.

The two-body distribution function g(r) is expressed by the following formula (7).

From the above formulas (6) and (7), the following formula (8) is obtained.

As described above, the two-body distribution function can be obtained by Fourier transformation of the structure factor S(Q). To make it easier to observe medium/long-range order, the two-body distribution function g(r) is transformed into the formula: G(r)=4πr(g(r)-1), which gives the reduced two-body distribution function G( r) (Figure 3). g(r), which oscillates around 0, represents the density difference from the average density at each interatomic distance, and if there is a correlation at a specific interatomic distance, the average density will be higher than 1. Therefore, it reflects the distance and coordination number of elements corresponding to local to intermediate distances. When orderliness disappears, ρ(r) approaches the average density, so g(r) approaches 1. Therefore, in an amorphous structure, the larger r becomes, the less order there is, so g(r) becomes 1, that is, G(r) becomes 0.

In requirement A-1, as shown in Figure 3, in the reduced two-body distribution function G(r) obtained from the X-ray total scattering measurement of the solid electrolyte (I), r is 1.43 ± 0.2 Å. There is a first peak P1 whose peak top is located within the range, and a second peak P2 whose peak top is located within the range where r is 2.40±0.2 Å. ) is more than 1.0 (preferably 1.2 or more), and G(r) at the top of the second peak P2 is 0.8 or more (preferably more than 1.0).
In addition, in FIG. 3, the peak top of the first peak P1 is located at 1.43 Å, and the peak top of the second peak P2 is located at 2.40 Å.
At a position of 1.43 Å, there is a peak attributed to the interatomic distance of B (boron)—O (oxygen). Further, at a position of 2.40 Å, there is a peak attributed to the interatomic distance of B (boron)-B (boron). That is, the observation of the two peaks (first peak and second peak) means that a periodic structure corresponding to the two interatomic distances exists in the solid electrolyte (I).

Further, in requirement A-2, as shown in FIG. 3, the absolute value of G(r) is less than 1.0 in the range of more than 5 Å and less than 10 Å. As mentioned above, the fact that the absolute value of G(r) is less than 1.0 in the range where r is more than 5 Å and less than 10 Å means that there is almost no long-range ordered structure in the solid electrolyte (I). .

Note that in the reduced two-body distribution function G(r), there may be a peak other than the first peak and other than the second peak in the range where r is 5 Å or less.

There is no particular restriction on the method for bringing the solid electrolyte (I) into an amorphous state. For example, in preparing the solid electrolyte (I), there is a method of using a mechanically milled lithium-containing oxide as a raw material. This mechanical milling process may be performed in the presence of a lithium salt.

-Mechanical milling process-
Mechanical milling is a process in which a sample is ground while applying mechanical energy. Examples of the mechanical milling treatment include milling treatment using a ball mill, vibration mill, turbo mill, or disk mill, and from the viewpoint of obtaining the solid electrolyte (I) in an amorphous state with high productivity, the milling treatment using a ball mill is preferred. Examples of ball mills include vibrating ball mills, rotary ball mills, and planetary ball mills, with planetary ball mills being more preferred.

Conditions for milling using a ball mill (hereinafter referred to as ball milling) are adjusted as appropriate depending on the object to be processed. The material of the grinding balls (media) is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred. The average particle diameter of the grinding balls is not particularly limited, and is preferably 1 to 10 mm, more preferably 3 to 7 mm, from the standpoint of producing solid electrolyte (I) with good productivity. The above average particle diameter is determined by randomly measuring the diameters of 50 grinding balls and taking the arithmetic average of the diameters. If the crushing ball is not perfectly spherical, the major axis is the diameter. The number of grinding balls is not particularly limited.

The material of the grinding pot in the ball milling process is also not particularly limited. Examples include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred.

The rotation speed of the ball milling process is not particularly limited, and can be, for example, 200 to 700 rpm, preferably 350 to 550 rpm. The processing time of the ball milling process is not particularly limited, and can be, for example, 10 to 200 hours, preferably 20 to 140 hours. The atmosphere of the ball milling process may be the atmosphere or an inert gas (eg, argon gas, helium gas, nitrogen gas, etc.) atmosphere.

As a method for producing solid electrolyte (I) using a lithium-containing oxide subjected to mechanical milling treatment, it is preferable to perform the following steps 1A to 3A.
Step 1A: Mechanically milling the lithium-containing oxide in the presence of a lithium salt Step 2A: Mixing the product obtained in Step 1A with water Step 3A: Dispersion obtained in Step 2A Step of obtaining solid electrolyte (I) by removing water from

In Step 1A, the amount of lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.

In the above step 2A, the amount of water used is not particularly limited. For example, the amount of water used can be 10 to 200 parts by weight, and preferably 50 to 150 parts by weight, relative to 100 parts by weight of the product obtained in step 1A.
The method of mixing the product obtained in Step 1A and water is not particularly limited, and may be mixed all at once, or may be mixed by adding water stepwise to the product obtained in Step 1A. good. When mixing, ultrasonic treatment may be performed as necessary. The time for ultrasonication is not particularly limited, and can be, for example, 10 minutes to 5 hours.

Step 3A is a step of removing water from the dispersion obtained in Step 2A to obtain solid electrolyte (I). The method for removing water from the dispersion obtained in step 2A is not particularly limited, and water may be removed by heat treatment or vacuum drying treatment.
The drying conditions are not particularly limited, and, for example, normal drying conditions applied to general drying processes can be appropriately applied, and examples thereof include the drying conditions applied in Examples. Typical drying conditions include, for example, natural drying (<30% RH), drying in a desiccator (<5% RH), and drying by heating up to 100° C. for 30 minutes to 2 hours.

Before the above step 1A, step 0 may be performed in which the lithium-containing oxide is mechanically milled in an environment where no lithium salt is present.

As a method for producing the solid electrolyte (I), it is also preferable to perform the following steps 1B to 3B instead of the above steps 1A to 3A.
Step 1B: Mechanically milling the lithium-containing oxide Step 2B: Mixing the product obtained in Step 1B with water and lithium salt Step 3B: Remove water from the dispersion obtained in Step 2B Step of obtaining solid electrolyte (I)

The method for performing steps 1B to 3B differs from the method for performing steps 1A to 3A above in that a lithium salt is mixed in the lithium-containing oxide subjected to mechanical milling treatment in the presence of water. Therefore, the difference between Process 1B and Process 1A is that in Process 1A, mechanical milling is performed in the presence of lithium salt, whereas in Process 1B, mechanical milling is performed without using lithium salt. The point is that Therefore, in Step 2B, the product obtained in Step 1B, water, and lithium salt are mixed.
The procedure of Step 2B is not particularly limited, and it may be a method (method 1) of mixing the product obtained in Step 1B, water, and lithium salt all at once, or a method of mixing the product obtained in Step 1B with water and lithium salt at once, or and water to prepare a dispersion, and then the resulting dispersion and lithium salt may be mixed (Method 2), or the product obtained in Step 1B and water may be mixed. A method (method 3) may be used in which dispersion 1 is prepared by mixing, solution 2 is prepared by mixing the lithium salt and water, and dispersion 1 and solution 2 are mixed. When mixing the product obtained in step 1B with water, a dispersion treatment such as ultrasonication may be appropriately performed.
In Method 2, when mixing a dispersion of the product obtained in Step 1B and water with a lithium salt, if there is too much lithium salt, the resulting liquid tends to gel, and the mixing of the lithium salt is difficult. Quantity is limited. On the other hand, in method 3, even if the product obtained in step 1B and the lithium salt are mixed in equimolar amounts, gelation of the liquid is unlikely to occur, and the amount of lithium salt mixed can be increased. . From this point of view, method 3 is preferred.
The procedures of Step 3B and Step 3A are the same.

As a method for producing the solid electrolyte (I), it is also preferable to perform the following steps 1C to 3C instead of the above steps 1A to 3A.
Step 1C: A step of mechanically milling the lithium-containing oxide Step 2C: A step of mixing the product obtained in Step 1C with water Step 3C: A process of removing water from the dispersion obtained in Step 2C. A step of mixing the obtained product and lithium salt to obtain solid electrolyte (I)

The procedures of Step 1C and Step 1B are the same.
The procedures of Step 2C and Step 2A are the same.
Step 3C differs from Steps 3A and 3B in that a product obtained by removing water from the dispersion obtained in Step 2C is mixed with a lithium salt.
In step 3C, the amount of lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.
The method of mixing the product obtained by removing water from the dispersion obtained in step 2C with the lithium salt is not particularly limited, and the above product is impregnated with a solution of the lithium salt dissolved in water. A method of mixing both may be used.

(Component composition of solid electrolyte (I))
In the solid electrolyte (I) used in the present invention, the molar ratio of the lithium salt content to the lithium-containing oxide content is 0.001 to 1.5, and the water content is The value of the ratio is 1 to 12 in terms of molar ratio.
The value of the ratio of the content of lithium salt to the content of lithium-containing oxide in solid electrolyte (I) is preferably 0.001 to 1.2 in molar ratio, more preferably 0.01 to 1.2, More preferably 0.1 to 1.2, particularly preferably 0.5 to 1.2.
Furthermore, the molar ratio of the water content to the lithium-containing oxide content in the solid electrolyte (I) is more preferably 2 to 12, and even more preferably 3 to 11. Further, this molar ratio is also preferably 2 to 10, preferably 2 to 8, preferably 2 to 7, and also preferably 3 to 7.
The molar amounts of the lithium-containing oxide, lithium salt, and water in the solid electrolyte (I) can be determined based on elemental analysis. Examples of the elemental analysis include the elemental analysis method described in the elemental composition of the solid electrolyte (I) below. Moreover, the molar amount of water can also be determined by the Karl Fischer method.

The content of water in the solid electrolyte (I) is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. Further, the content of water in the solid electrolyte (I) is also preferably 30% by mass or less, and preferably 25% by mass or less.
Further, the content of water in the solid electrolyte (I) is usually 5% by mass or more, preferably 10% by mass or more, and also preferably 15% by mass or more. Therefore, the content of water in the solid electrolyte (I) is preferably 5 to 50% by mass, more preferably 5 to 45% by mass, even more preferably 10 to 40% by mass, particularly preferably 10 to 35% by mass, It is also preferably 10 to 30% by weight, preferably 15 to 30% by weight, and preferably 15 to 25% by weight.
The content of the lithium-containing oxide in the solid electrolyte (I) is preferably 20 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 25 to 70% by mass.
Further, the content of the lithium salt in the solid electrolyte (I) is preferably 0.5 to 60% by mass, more preferably 1.0 to 55% by mass, even more preferably 2.0 to 50% by mass, and 5. It is also preferably 0 to 50% by mass.

-Lithium-containing oxide-
The lithium-containing oxide constituting the solid electrolyte (I) contains Li, B, and O, as described above.
The above lithium-containing oxide is represented by Li _2+x B _4+y O _7+z (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3). Compounds such as In other words, when the molar amount of B is 4.00 and the molar amount of Li is expressed, the molar amount of Li is 1.58 to 2.49 (that is, 1.7×4/4.3 to 2.3× 4/3.7), and the molar amount of O is preferably 6.23 to 7.89 (ie, 6.7×4/4.3 to 7.3×4/3.7). In other words, when the molar amount of B is 4.00, the relative value of the molar amount of Li is 1.58 to 2.49, and the molar amount of O is 6.23 to 7.89. is preferred. Such a lithium-containing oxide typically includes lithium tetraborate (Li ₂ B ₄ O ₇ ).
Further, the above lithium-containing oxide has Li _1+x B _3+y O _5+z (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3). Also preferred are the compounds represented. Such a lithium-containing oxide typically includes lithium triborate (LiB ₃ O ₅ ).
Further, the above lithium-containing oxide has Li _3+x B _11+y O _18+z (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3). Also preferred are the compounds represented. A typical example of such a lithium-containing oxide is Li ₃ B ₁₁ O ₁₈ .
Further, the above lithium-containing oxide has Li _3+x B _7+y O _12+z (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3). Also preferred are the compounds represented. A typical example of such a lithium-containing oxide is Li ₃ B ₇ O ₁₂ .
Therefore, the lithium-containing oxide is preferably at least one of the above Li _2+x B _4+y O _7+z , the above Li _1+x B _3+y O _5+z , Li _3+x B _11+y O 18+ _z , and Li _3+x B _7+y O _12+z .
In addition, in place of or together with the above lithium-containing oxide, lithium-containing oxides such as LiBO ₅ , Li ₂ B ₇ O ₁₂ , LiB ₂ O ₃ (OH)H ₂ O, and Li ₄ B ₈ O ₁₃ (OH) ₂ (H ₂ O) ₃ and the like can also be used.
In the solid electrolyte (I), the lithium-containing oxide is preferably in an amorphous state. That is, it is preferable that the lithium-containing oxide in the solid electrolyte (I) is also in the desired amorphous state so that the solid electrolyte (I) is in the above-mentioned amorphous state.
Among these, the lithium-containing oxide is preferably amorphous lithium tetraborate.

-Lithium salt-
The lithium salt constituting the solid electrolyte (I) used in the present invention is not particularly limited, and examples include salts composed of Li ⁺ and anions, preferably salts composed of Li ⁺ and organic anions, More preferred is a salt composed of Li ⁺ and an organic anion having a halogen atom.
The lithium salt constituting the solid electrolyte (I) used in the present invention is an element of group 3 of the periodic table, an element of group 4 of the periodic table, an element of group 13 of the periodic table, an element of group 14 of the periodic table, an element of group 14 of the periodic table, or an element of group 14 of the periodic table. It is preferable to contain two or more specific elements selected from the group consisting of elements of group 15 of the table, elements of group 16 of the periodic table, elements of group 17 of the periodic table, and H.
As the lithium salt constituting the solid electrolyte (I) used in the present invention, for example, a compound represented by the following formula (1) is preferable.

Formula (1) LiN(R _f1 SO ₂ ) (R _f2 SO ₂ )

R _f1 and R _f2 each independently represent a halogen atom or a perfluoroalkyl group. R _f1 and R _f2 may be the same or different.
When R _f1 and R _f2 are perfluoroalkyl groups, the number of carbon atoms in the perfluoroalkyl group is not particularly limited.
R _f1 and R _f2 are preferably a halogen atom or a perfluoroalkyl group having 1 to 6 carbon atoms, more preferably a halogen atom or a perfluoroalkyl group having 1 to 2 carbon atoms, and are halogen atoms. It is even more preferable. When the volume of the terminal group increases, steric hindrance increases, which becomes a factor that inhibits ion conduction. Therefore, when R _f1 and R _f2 are perfluoroalkyl groups, it is preferable that the number of carbon atoms is small.

The lithium salt that can be contained in the solid electrolyte (I) used in the present invention is not limited to the compound represented by the above formula (1). Examples of lithium salts that can be included in the solid electrolyte (I) used in the present invention are shown below.

(L-1) Inorganic lithium salts: Inorganic fluoride salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiSbF ₆ ; Perhalates such as LiClO ₄ , LiBrO ₄ and LiIO ₄ ; LiAlCl ₄ etc. Inorganic chloride salt.

(L-2) Fluorine-containing organic lithium salt: perfluoroalkanesulfonate such as LiCF ₃ SO ₃ ; LiN(CF ₃ SO ₂ ) ₂ (also referred to herein as Li(FSO ₂ ) ₂ N). , LiN( _CF3CF2SO2 ₎ ₂ , _LiN ₍ _FSO2 ₎ ₂ _, and LiN(CF3SO2)( _C4F9SO2 ₎ ; Perfluoroalkanesulfonyl methide salts such as LiC(CF ₃ SO ₂ ) ₃ ; Li[PF ₅ (CF ₂ CF ₂ CF ₃ )], Li[PF ₄ (CF ₂ CF ₂ CF ₃ ) ₂ ], Li[PF ₃ (CF ₂ CF ₂ CF ₃ ) ₃ ], Li[PF ₅ (CF ₂ CF ₂ CF ₂ CF ₃ )], Li[PF ₄ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₂ ], and Li[PF ₃ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₃ ] and the like (preferably perfluoroalkyl fluorophosphates).

(L-3) Oxalatoborate salts: lithium bis(oxalato)borate and lithium difluorooxalatoborate.

In addition to the above, examples of lithium salts include LiF, LiCl, LiBr, LiI, Li ₂ SO ₄ , LiNO ₃ , Li ₂ CO ₃ , CH ₃ COOLi, LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , and LiB(C ₆ H ₅ ) ₄ and the like.
Among them, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , Li(R _f11 SO ₂ ), LiN(R _f11 SO ₂ ) ₂ , LiN(FSO ₂ ) ₂ , or LiN(R _f11 SO ₂ )(R _f12 SO ₂ ) is preferable, and LiPF ₆ , LiBF ₄ , LiN(R _f11 SO ₂ ) ₂ , LiN(FSO ₂ ) ₂ or LiN(R _f11 SO ₂ )(R _f12 SO ₂ ) is more preferable. . In these examples, R _f11 and R _f12 each independently represent a perfluoroalkyl group, and the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, and 1 to 2. It is even more preferable. Note that R _f11 and R _f12 may be the same or different. Also preferred as the lithium salt are LiNO ₃ and

lithium

1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide.

(Elemental composition of solid electrolyte (I))
The component composition of the solid electrolyte (I) has been explained based on the compounds constituting the solid electrolyte (I). Next, solid electrolyte (I) will be explained from the viewpoint of preferred elemental composition. That is, in one form of the secondary battery of the present invention, the solid electrolyte (I) does not include "lithium-containing oxide" and "lithium salt" as invention-specific matters, but has the following elemental composition, for example: can be specified.
The solid electrolyte (I) used in the present invention has a molar amount of Li of 1.58 to 3.49 (preferably 1.58 to 3.49), when the molar amount of B in the solid electrolyte (I) is 4.00. 3.00, more preferably 1.90 to 3.00, even more preferably 2.00 to 3.00). Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amount of O is 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably 8.00 to 25.00). 00 to 23.00, more preferably 10.00 to 23.00, particularly preferably 10.00 to 18.00). Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amounts of elements other than B, other than Li, and other than O are each 0.001 to 10.00 (preferably 0.001 ~6.00, more preferably 0.01~5.00).

The content of each element is determined by ordinary elemental analysis. For elemental analysis, for example, Li and B are analyzed using ICP-OES (inductively coupled plasma optical emission spectrometry), N, etc. are analyzed using an inert gas melting method, and for example, F and S are analyzed using combustion ion analysis. Analyze by chromatography. Regarding O, it can be calculated as a difference from the total amount of powder by adding up the analyzed masses of elements other than O. Note that the method for calculating the content of each element is not limited to the above, and the content of other elements may be estimated from the analysis result of the content of one element, taking into consideration the structure of the compound used.
Based on the content of each element calculated by elemental analysis, the molar amounts of Li, O, and other elements are calculated when the molar amount of B is 4.00.

In a preferred embodiment of the solid electrolyte (I), in addition to Li, B, and O, the solid electrolyte (I) further contains an element of group 4 of the periodic table, an element of group 15 of the periodic table, and an element of group 16 of the periodic table. , Group 17 elements of the periodic table, Si, C, Sc, and Y.
Examples of Group 4 elements of the periodic table include Ti, Zr, Hf, and Rf. Group 15 elements of the periodic table include N, P, As, Sb, Bi, and Mc. Group 16 elements of the periodic table include S, Se, Te, Po, and Lv. Group 17 elements of the periodic table include F, Cl, Br, I, At, and Ts.
Among them, an element (E) selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N It is preferable to include more than one type, and more preferably two or more types.
The solid electrolyte (I) may contain three or more types of element (E), preferably 2 to 5 types, and more preferably 2 to 4 types.
A preferred embodiment of the solid electrolyte (I) preferably contains two or more elements (E) selected from F, S, N, P, and C; It is more preferable that two or more selected elements (E) are included, and it is even more preferable that three types of elements (E), F, S, and N are included.

In the solid electrolyte (I) containing one or more (preferably two or more) of the above elements (E), when the molar amount of Li is expressed with the molar amount of B in the solid electrolyte (I) being 4.00. , the molar amount of Li is preferably 1.58 to 3.49. That is, when the molar amount of B is 4.00, the relative value of the molar amount of Li is preferably 1.58 to 3.49. Among these, when the molar amount of Li is expressed with the molar amount of B in the solid electrolyte (I) being 4.00, the molar amount of Li is preferably 1.58 to 3.00, and preferably 1.90 to 3.00. 00 is more preferable, and 2.00 to 3.00 is even more preferable.

In the solid electrolyte (I) containing one or more (preferably two or more) of the above elements (E), when the molar amount of O is expressed with the molar amount of B in the solid electrolyte (I) being 4.00. , the molar amount of O is preferably 6.23 to 25.00. That is, when the molar amount of B is 4.00, the relative value of the molar amount of O is preferably 6.23 to 25.00. Among these, when the molar amount of O in the solid electrolyte (I) is expressed as 4.00, the molar amount of O is preferably 6.50 to 23.00, and preferably 8.00 to 23.00. 00 is more preferable, 10.00 to 23.00 is more preferable, and 10.00 to 18.00 is particularly preferable.

In the solid electrolyte (I) containing one or more types (preferably two or more types) of the above element (E), the molar amount of B in the solid electrolyte (I) is 4.00, and the molar amount of element (E) is When expressed, the molar amount of each element (E) is preferably 0.001 to 10.00. That is, when the molar content of B is 4.00, the relative value of the molar content of each element (E) is preferably 0.001 to 10.00. In particular, when the molar amount of B in solid electrolyte (I) is 4.00 and the molar amount of element (E) is expressed, the molar amount of each element (E) is 0.001 to 6.00. Preferably, 0.01 to 5.00 is more preferable.

One preferred embodiment of the elemental composition of the solid electrolyte (I) containing one or more (preferably two or more) of the above elements (E) includes Li, B, O, F, S, and N. , when the molar amount of B is 4.00, the molar amount of Li is 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.90 to 3.00, even more preferably 2.00 to 3.00), and the molar amount of O is 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10. 00 to 23.00, particularly preferably 10.00 to 18.00), the molar amount of F is 0.001 to 10.00 (preferably 0.01 to 10.00), and the molar amount of S is is 0.001 to 2.00 (preferably 0.01 to 2.00), and the molar amount of N is 0.001 to 1.00 (preferably 0.005 to 1.00). Can be mentioned.

The solid electrolyte (I) used in the present invention is preferably in the above-mentioned amorphous state, and as a result, this solid electrolyte (I) has the following properties in addition to the above-mentioned X-ray diffraction properties. It is preferable to indicate.

(Solid ⁷ Li-NMR spectral characteristics)
The solid electrolyte (I) shall have a full width at half maximum ratio of 50% or less, which is calculated by the following method from the spectrum obtained by performing solid ⁷ Li-NMR measurements of the solid electrolyte (I) at 20°C and 120°C. is preferable, more preferably 40% or less, and even more preferably 35% or less. The lower limit is not particularly limited, but is often 10% or more.
The above full width at half maximum ratio is determined by performing solid ⁷ Li-NMR measurements of the solid electrolyte (I) at 20°C and 120°C, respectively, and the chemical shift in the spectrum obtained by measurement at 20°C is in the range of -100 to +100 ppm. After determining the full width at half maximum of the peak that appears (full width at half maximum 1) and the full width at half maximum (full width at half maximum 2) of the peak that appears in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 120°C, It is obtained by calculating the percentage of the full width at half maximum 2 to the full width 1 {(full width at half maximum 2/full width at half maximum 1)×100(%)}. The full width at half maximum (FWHM) of a peak means the width (ppm) at 1/2 point (H/2) of the peak height (H).
The above characteristics will be explained below using FIG. 4. FIG. 4 shows an example of a spectrum obtained when solid ⁷ Li-NMR measurement of solid electrolyte (I) is performed at 20°C or 120°C. The solid line spectrum shown on the lower side of FIG. 4 is the spectrum obtained when solid-state ⁷ Li-NMR measurement was performed at 20°C, and the broken line spectrum shown on the upper side of FIG. 4 is the spectrum obtained when solid-state ⁷ Li-NMR measurement was performed. This is a spectrum obtained when the test was carried out at 120°C.
Generally, in solid-state ⁷ Li-NMR measurements, when the mobility of Li ⁺ is high, the peaks obtained are sharper. In the embodiment shown in FIG. 4, when the spectrum at 20°C and the spectrum at 120°C are compared, the spectrum at 120°C is sharper. In other words, in the embodiment shown in FIG. 4, the mobility of Li ⁺ is high due to the presence of Li defects. Such a solid electrolyte (I) is considered to be easily plastically deformed due to the defect structure as described above, and to have excellent Li ⁺ hopping properties.
For reference, when solid-state ⁷ Li-NMR measurements are performed at 20°C or 120°C for a general lithium tetraborate crystal, the solid line shown at the bottom of Figure 5 is The spectrum measured at 20° C. and the spectrum measured at 120° C. shown by the broken line shown in the upper part of FIG. 5 tend to have substantially the same shape. That is, the lithium tetraborate crystal has no Li defects, and as a result has a high elastic modulus and is difficult to undergo plastic deformation.

The Li-NMR measurement conditions for the above solid ⁷ are as follows.
Using a 4 mm HX CP-MAS probe, single pulse method, 90° pulse width: 3.2 μs, observation frequency: 155.546 MHz, observation width: 1397.6 ppm, repetition time: 15 sec, integration: 1 time, MAS rotation number: Measure at 0Hz.

In addition, the solid electrolyte (I) used in the present invention shows that when the waveform of the first peak appearing in the range of -100 to +100 ppm is separated in the spectrum obtained when solid-state ⁷ Li-NMR measurement is performed at 20°C, the chemical It is preferable that the shift has a second peak with a full width at half maximum of 5 ppm or less in the range of -3 to +3 ppm, and the ratio of the area intensity of the second peak to the area intensity of the first peak is 0.5% or more. The area strength ratio is more preferably 2% or more, further preferably 5% or more, particularly preferably 10% or more, and most preferably 15% or more. In the embodiment of the present invention in which the solid electrolyte (I) contains water, the solid state ⁷ Li-NMR spectral characteristics of the solid electrolyte (I) tend to be as described above. The upper limit of the area strength ratio is not particularly limited, but is often 50% or less.

The above characteristics will be explained below using FIGS. 6 and 7.
FIG. 6 shows an example of a spectrum obtained when solid ⁷ Li-NMR measurement of solid electrolyte (I) is performed at 20°C. As shown in Figure 6, solid electrolyte (I) has a peak (corresponding to the first peak) observed in the range of -100 to +100 ppm, and in this first peak, the chemical shift is around 0 ppm as shown by the broken line. A small peak is observed. As mentioned above, when the mobility of Li ⁺ is high, the peak is observed sharply, so this is considered to be an influence.
Next, FIG. 7 shows the waveform of the first peak separated. As shown in FIG. 7, the first peak is waveform-separated into a small peak (corresponding to the second peak) represented by a solid line and a large peak represented by a broken line. The second peak appears in a chemical shift range of -3 to +3 ppm, and has a full width at half maximum of 5 ppm or less.
The solid electrolyte (I) has a ratio of the area intensity of the second peak shown by the solid line in FIG. 7 to the area intensity of the first peak (the peak before waveform separation) shown in FIG. Area intensity/area intensity of first peak)×100(%)} is preferably within the above range.
As a method for waveform separation, a method using known software can be mentioned, and an example of the software is Igor Pro, a graph processing software manufactured by WaveMetrics.

(Raman spectrum characteristics)
The solid electrolyte (I) has a coefficient of determination of 0.9400 or more obtained by linear regression analysis using the least squares method in the wave number region of 600 to 850 cm ^-1 of the Raman spectrum of the solid electrolyte (I). It is preferably 0.9600 or more, more preferably 0.9800 or more. The upper limit is not particularly limited, but is usually 1.0000 or less.

The above Raman spectral characteristics will be explained with reference to FIG. 8.
First, a Raman spectrum of the solid electrolyte (I) is obtained. Raman imaging is performed as a method for measuring the Raman spectrum. Raman imaging is a microscopic spectroscopic technique that combines Raman spectroscopy with microscopic technology. Specifically, this is a method in which measurement light including Raman scattered light is detected by scanning excitation light over a sample, and the distribution of components is visualized based on the intensity of the measurement light.
The measurement conditions for Raman imaging are as follows: 27°C in the atmosphere, excitation light at 532 nm, objective lens at 100x, mapping method point scanning, 1 μm steps, exposure time per point for 1 second, and integration once. , the measurement range is 70 μm×50 μm. However, depending on the film thickness of the sample, the measurement range may become narrower.
Further, principal component analysis (PCA) processing is performed on the Raman spectrum data to remove noise. Specifically, in the principal component analysis process, spectra are recombined using components with an autocorrelation coefficient of 0.6 or more.

FIG. 8 shows an example of the Raman spectrum of the solid electrolyte (I). In the graph shown in FIG. 8, the vertical axis shows Raman intensity and the horizontal axis shows Raman shift. In the wave number region of 600 to 850 cm ⁻¹ of the Raman spectrum shown in FIG. 8, a coefficient of determination (coefficient of determination R ² ) obtained by performing linear regression analysis using the least squares method is calculated. That is, in the wave number region of 600 to 850 cm ⁻¹ of the Raman spectrum in FIG. 8, a regression line (thick line in FIG. 8) is found by the least squares method, and the coefficient of determination R ² of the regression line is calculated. Note that the coefficient of determination takes a value between 0 (no linear correlation) and 1 (perfect linear correlation of the measured values) depending on the linear correlation of the measured values.
In the solid electrolyte (I), as shown in FIG. 8, almost no peak is observed in the wave number region of 600 to 850 cm ⁻¹ , and as a result, it exhibits a high coefficient of determination.
Note that the determination coefficient ^R2 corresponds to the square of the correlation coefficient (Pearson's product moment correlation coefficient). More specifically, in this specification, the coefficient of determination ^R2 is calculated by the following formula. In the formula, x ₁ and y ₁ represent the wave number in the Raman spectrum and the Raman intensity corresponding to that wave number, x ₂ is the (additive) average of the wave numbers, and y ₂ is the (additive) Raman intensity. Represents the average.

On the other hand, for reference, FIG. 9 shows a Raman spectrum of a general lithium tetraborate crystal. As shown in FIG. 9, in the case of a general lithium tetraborate crystal, peaks are observed in the wave number regions of 716 to 726 cm ⁻¹ and 771 to 785 cm ⁻¹ , which are derived from its structure. When such a peak exists, the coefficient of determination is less than 0.9400 when linear regression analysis is performed using the least squares method in the wave number region of 600 to 850 cm ⁻¹ to calculate the coefficient of determination.
In other words, the fact that the coefficient of determination is 0.9400 or more indicates that the solid electrolyte (I) contains almost no crystal structure. Therefore, as a result, it is considered that the solid electrolyte (I) has the property of being easily plastically deformed and the property of being excellent in Li ⁺ hopping property.

(Infrared absorption spectrum characteristics)
In the infrared absorption spectrum, the solid electrolyte ^{(I) has a value of the ratio of the maximum absorption intensity in the wavenumber region of 3000 to 3500 cm −1} ^to the maximum absorption intensity in the wavenumber region of 800 to 1600 cm −1 (3000 to 3500 cm ⁻¹ The ratio (maximum absorption intensity in the wave number region/maximum absorption intensity in the wave number region from 800 to 1600 cm ⁻¹ ) is preferably 1/5 or more (0.2 or more). Among these, the ratio is preferably 3/10 or more, more preferably 2/5 or more. The upper limit is not particularly limited, but is preferably 1 or less.
An OH stretching vibration mode is observed in the wave number region of 3000 to 3500 cm ⁻¹ in the infrared absorption spectrum, and a B—O stretching vibration mode is observed in the wave number region of 800 to 1600 cm ⁻¹ . In the solid electrolyte (I), a strong absorption intensity derived from the OH stretching vibration mode is observed, indicating that it contains a large number of OH groups and/or a large amount of water. In such a solid electrolyte (I), lithium ions tend to move easily, and as a result, ion conductivity tends to improve.
Note that in the wave number region of 800 to 1600 cm ⁻¹ , a vibration mode derived from lithium salt can also be observed.

The above infrared absorption spectrum measurement conditions can be as follows.
Objective lens: 32x Cassegrain type (NA 0.65), detector: MCT-A, measurement range: 650 to 4000 cm ⁻¹ , resolution: 4 cm ⁻¹ , sample cell: Measurement is performed using a diamond cell.
The obtained infrared absorption spectrum is corrected to remove signals derived from atmospheric water and CO ₂ , and then offset correction is applied to the background to make the absorption intensity 0. Further, after vacuum drying at 40° C. for 2 hours, measurement is performed in the atmosphere.

The ionic conductivity (27° C.) of the solid electrolyte (I) is not particularly limited, and from the viewpoint of application to various uses, it is preferably 1.0×10 ⁻⁵ S/cm or more, and 1.0×10 ⁻⁴ S /cm or more is more preferable, 1.0×10 ⁻³ S/cm or more is even more preferable, and 3.0×10 ⁻³ S/cm or more is particularly preferable. The upper limit is not particularly limited, but is often 1.0×10 ⁻² S/cm or less.

Furthermore, it is also preferable that the solid electrolyte (I) exhibits the following characteristics or physical properties.

(mass reduction rate)
The mass reduction rate when solid electrolyte (I) is heated to 800° C. is preferably 20 to 40% by mass, more preferably 25 to 35% by mass. The mass reduction caused by the heating is considered to be due to the removal of water contained in the solid electrolyte (I). When the solid electrolyte (I) contains such water, the conductivity of lithium ions can be further improved.
In the above heat treatment, heating is performed at a temperature increase rate of 20°C/sec in the range from 25°C to 800°C. A known thermogravimetric differential thermal analysis (TG-DTA) device can be used to measure the amount of mass loss. The above mass reduction rate is
{(mass at 25°C - mass at 800°C)/mass at 25°C} x 100
Calculated by
In measuring the mass reduction rate, the solid electrolyte (I) was previously subjected to vacuum drying at 40° C. for 2 hours. Furthermore, the mass reduction rate is measured in the atmosphere.

The solid electrolyte layer constituting the secondary battery of the present invention may contain other components in addition to the solid electrolyte (I).
For example, the solid electrolyte layer can include a binder made of an organic polymer. The organic polymer constituting the binder may be particulate or non-particulate. By including the binder, it becomes possible to more reliably prevent cracks from occurring in the solid electrolyte layer or the electrode layer.
Further, the solid electrolyte layer may contain another solid electrolyte other than the solid electrolyte (I). Other solid electrolyte means a solid electrolyte in which lithium ions can be moved. As the solid electrolyte, an inorganic solid electrolyte is preferable. Other solid electrolytes include oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes, with oxide-based solid electrolytes being more preferred.

In the secondary battery of the present invention, it is also preferable that the solid electrolyte layer contains other components such as an ionic liquid and a surfactant.
By adding an ionic liquid, it is possible to further improve the charge/discharge cycle characteristics of the secondary battery of the present invention. An ionic liquid is a liquid "salt" composed only of ions (anions, cations), and has a higher viscosity than water (equivalent to free water in the present invention), so its ionic conductivity is lower than that of water. On the other hand, since the potential window is wide, depending on the type of ionic liquid and the amount added, it is possible to achieve both ionic conductivity and potential window at a better level by using water and an ionic liquid in combination.
The cation structures constituting the ionic liquid include pyrrolidinium cations such as 1-butyl-1-methylpyrrolidinium cation (BMP ⁺ ), n-methyl-n-pentylpyrrolidinium cation (PYR15 ⁺ ), and 1-butyl cation. Imidazolium cations such as -3-methylimidazolium cation (BMI ⁺ ), 1-ethyl-3-methylimidazolium cation (EMI ⁺ ), n-methyl-n-propylpiperidinium cation (PIP ⁺ ), etc. Examples include sulfonium cations such as piperidinium cations and triethylsulfonium cations (TES ⁺ ).
The anion structures constituting the ionic liquid include N(FSO ₂ ) ₂ ⁻ [FSI ⁻ ], N(CF ₃ SO ₂ ) ₂ ⁻ [TFSI ⁻ ], N(CF ₃ CF ₂ SO ₂ ) ₂ ⁻ [LIBETI ⁻ ] and other perfluoroalkanesulfonylimide anions, perfluoroalkanesulfonate anions such as CF ₃ SO ₃ ^- , inorganic fluoride anions such as PF ₆ ^- and BF ₄ ^- , and perhalogen acid ions such as ClO ₄ ^- . .
Further, by adding a surfactant, it is possible to further improve the charge/discharge cycle characteristics of the secondary battery of the present invention. By adding a surfactant, it is possible to improve the dispersibility of the solid electrolyte (I) in the solid electrolyte layer, the dispersibility of the lithium salt in the solid electrolyte (I), and the like.
As the surfactant, compounds commonly used as surfactants can be used within a range that does not impair the effects of the present invention.

The thickness of the solid electrolyte layer constituting the secondary battery of the present invention is not particularly limited, and can be, for example, 10 to 1000 μm, preferably 50 to 400 μm.

<Positive electrode layer>
Although the positive electrode layer is generally composed of a positive electrode current collector and a positive electrode active material layer, it may be composed of a positive electrode active material layer and not include a positive electrode current collector. In other words, when the positive electrode active material layer also functions as a positive electrode current collector, it does not need to be composed of two layers, the positive electrode current collector and the positive electrode active material layer, and may be a single layer structure. .
Further, the positive electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) together with the positive electrode active material, but it may not contain a solid electrolyte.

When the positive electrode active material layer contains a solid electrolyte, the type of the solid electrolyte is not particularly limited. From the viewpoint of emphasizing higher safety, an oxide-based solid electrolyte can be used.
From the viewpoint of achieving both flexibility and safety at a high level, it is preferable to use the solid electrolyte (I) described above. By doing so, the solid electrolyte (I) also acts like a binder for the solid particles contained in the positive electrode layer, and the positive electrode layer can be made more flexible.
The positive electrode active material layer may contain one or more solid electrolytes.
The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, and the total content with the positive electrode active material is preferably 50 to 99.9% by mass, more preferably 70 to 99.5% by mass. More preferably 90 to 99% by mass.

The positive electrode active material itself used in the positive electrode layer is not particularly limited as long as the difference in discharge potential with respect to the Li standard satisfies 1.3 V or more with the negative electrode active material, and it can be used in ordinary lithium ion secondary batteries. A wide variety of positive electrode active materials can be used. A preferred form of the positive electrode active material will be explained below.

(Cathode active material)
The positive electrode active material is preferably one that can reversibly insert and/or release lithium ions. The positive electrode active material is not particularly limited as long as the difference in discharge potential between it and the negative electrode active material based on Li satisfies 1.3 V or more, and transition metal oxides are preferable, and transition metal elements Ma (Co, Ni, A transition metal oxide containing one or more elements selected from Fe, Mn, Cu, and V is more preferable. In addition, this transition metal oxide contains element Mb (metal elements of group 1 (Ia) of the periodic table other than lithium, elements of group 2 (IIa) of the periodic table, Al, Ga, In, Ge, Sn, Pb, Sb , Bi, Si, P, and B) may be mixed. The mixing amount of element Mb is preferably 0 to 30 mol% with respect to the amount of transition metal element Ma (100 mol%). More preferably, it is synthesized by mixing Li/Ma at a molar ratio of 0.3 to 2.2.
Specific examples of transition metal oxides include (MA) transition metal oxides having a layered rock salt structure, (MB) transition metal oxides having a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD ) Lithium-containing transition metal halide phosphoric acid compounds, (ME) lithium-containing transition metal silicate compounds, and the like.

(MA) Examples of transition metal oxides having a layered rock salt structure include LiCoO ₂ (lithium cobalt oxide [LCO]), LiNiO ₂ (lithium nickel oxide [LNO]), LiNi _0.85 Co _0.10 Al _{0. 05} O ₂ (nickel cobalt lithium aluminate [NCA]), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (nickel manganese cobalt lithium [NMC]), LiNi _0.5 Mn _0.5 O ₂ ( lithium manganese nickelate), and Li ₂ MnO ₃ -LiNiMnCoO ₂ .

(MB) Examples of transition metal oxides having a spinel structure include LiMn ₂ O ₄ (LMO), LiNi _0.5 Mn _1.5 O ₄ ([LNMO]), LiCoMnO ₄ , Li ₂ FeMn ₃ O ₈ , Examples include Li ₂ CuMn ₃ O ₈ , Li ₂ CrMn ₃ O ₈ and Li ₂ NiMn ₃ O ₈ .

(MC) Lithium-containing transition metal phosphate compounds include, for example, olivine-type iron phosphates such as LiFePO ₄ ([LFP]) and Li ₃ Fe ₂ (PO ₄ ) ₃ , and iron pyrophosphates such as LiFeP ₂ O ₇ . salts, olivine-type manganese phosphate salts such as LiMnPO ₄ [(LMP)], olivine-type nickel phosphate salts such as LiNiPO ₄ [(LNP)], olivine-type cobalt phosphate salts such as LiCoPO ₄ [(LCP)], Examples include olivine-type cobalt pyrophosphate salts such as Li ₂ CoP ₂ O ₇ and monoclinic NASICON-type vanadium phosphate salts such as Li ₃ V ₂ (PO ₄ ) ₃ (lithium vanadium phosphate).

(MD) Examples of lithium-containing transition metal halide phosphate compounds include iron fluorophosphates such as Li ₂ FePO ₄ F, manganese fluorophosphates such as Li ₂ MnPO ₄ F, and Li ₂ CoPO Examples include cobalt fluorophosphate salts such as _4F .

(ME) Examples of the lithium-containing transition metal silicate compound include Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoSiO ₄ .

The shape of the positive electrode active material is not particularly limited, and is usually particulate. The volume average particle diameter of the positive electrode active material is not particularly limited, and is preferably, for example, 0.1 to 50 μm. The volume average particle diameter of the positive electrode active material can be determined in the same manner as the volume average particle diameter of the negative electrode active material, which will be described later.
The positive electrode active material obtained by the calcination method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

Similar to the negative electrode active material described below, the surface of the positive electrode active material may be coated with a surface coating agent described later, sulfur or phosphorus, or even with actinic light.
The surface coating material (also referred to as coating material) for the positive electrode active material can suppress contact between the positive electrode active material and water, and can also suppress Li deficiency at the interface between the positive electrode active material and the solid electrolyte. It is considered that the charge/discharge cycle characteristics of the all-solid-state lithium ion secondary battery can be further improved. From this point of view, the coating material for the positive electrode active material is preferably a Li ion conductive oxide, such as LiNbO ₃ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , LiAlO ₂ , Li ₄ SiO ₄ , Li ₂ SiO ₃ , More preferred than Li ₃ PO ₄ , Li ₂ SO ₄ , Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , Li ₂ ZrO ₃ , Li ₂ MoO ₄ , Li ₂ WO ₄ or Li ₃ AlF ₆ Can be mentioned.

The positive electrode active materials may be used alone or in combination of two or more.
The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, and is preferably 10 to 97% by mass, more preferably 30 to 95% by mass, even more preferably 40 to 93% by mass, and 50 to 90% by mass. % is particularly preferred.

Among these, the positive electrode active material preferably has a discharge potential of 3.5 V or more based on Li, more preferably 3.7 V or more, even more preferably 3.8 V or more, and 4. It is particularly preferable that the voltage is .2V or more.
Note that when the positive electrode active material has a coat layer described below, and this coat layer is made of a material that can reversibly insert and release lithium ions, the discharge potential of the positive electrode active material based on Li is , means the discharge potential of a material with a lower potential based on Li.
As mentioned above, in the secondary battery of the present invention, of the two types of water, "free water" and "bound water" contained in the solid electrolyte (I) having a specific composition, "bound water" is composed of lithium-containing oxide and / or interacts with the lithium salt, and the potential window of the solid electrolyte (I) becomes wider than that of water. For this reason, the solid electrolyte (I) decomposes even above 3.8 V (Li standard, pH = 7), which causes oxidative decomposition of water in conventional liquid-based lithium ion secondary batteries that use an aqueous solution as the electrolyte. Instead, a positive electrode active material having a discharge potential of 3.8 V or more based on Li can be used.
Examples of positive electrode active materials having a discharge potential of 3.8 V or higher based on Li include LiCoO ₂ (LCO, 3.9 V), Li ₂ MnO ₃ -LiNiMnCoO ₂ (3.9 V), and LiMn ₂ O ₄ (LMO). , 3.8V), _{LiNi0.5Mn1.5O4} (LNMO, 4.7V ₎ , _LiMnPO4 ₍ LMP, 4.1V), _LiCoPO4 ₍ LCP _, 4.8V), _Li2CoP2O7 (5V) and LiNiPO ₄ (LNP, 5.1V), and at least one of these is preferred. Note that the value written in parentheses after each positive electrode active material is the discharge potential based on Li. LCO can provide better cycle characteristics, and LNMO can provide a wider potential difference.
In addition, it is also preferable to coat these with an interfacial resistance stabilizing layer such as an oxide or a carbon-based material, which will be described later.

(Positive electrode current collector)
The current collector that constitutes the positive electrode layer is an electron conductor. Further, the positive electrode current collector is usually in the form of a film sheet.
Constituent materials of the positive electrode current collector include aluminum (Al), aluminum alloy (Al alloy), stainless steel, nickel, copper, platinum, carbon, and titanium (Ti), including aluminum, copper, platinum, and carbon. Or titanium is preferable, and aluminum or titanium is more preferable.
In addition, the positive electrode current collector has a coating layer (thin film) of aluminum, carbon, nickel, titanium, copper, platinum, or silver on the surface of a metal base material such as aluminum, copper, platinum, carbon, titanium, or stainless steel. Those having a coating layer of aluminum, copper, platinum, carbon or titanium on the surface of a metal base material of aluminum, copper, platinum, carbon or titanium are preferred, and metals of aluminum, copper, platinum, carbon or titanium are preferably used. It is more preferable to have an aluminum or titanium coating layer on the surface of the base material.
and those having a coating layer (thin film) of aluminum, copper, platinum, carbon, or titanium on the surface of a metal base material such as copper (Cu).

Among these, from the viewpoint of further improving charge-discharge cycle characteristics, the positive electrode current collector is preferably Al, Ti, or a metal coated with Al or Ti; Alternatively, Cu coated with Ti is more preferable.
In addition to originally having a strong oxide film on the surface, when a fluorine-containing lithium salt is contained in the electrode layer, this fluorine reacts with the surface of the oxide film to form a highly corrosion-resistant fluoride film. Al is formed. After the formation of Al fluoride, the reaction between Al and the lithium salt does not proceed any further and the lithium salt is not consumed, so it is presumed that the charge/discharge cycle characteristics are improved.
In addition, since Ti has low reactivity, when it contains materials in the electrode layer (for example, active material, conductive agent, solid electrolyte (I), lithium-containing oxide, lithium It is presumed that this material is less likely to react with salt (salt, water) and improves charge/discharge cycle characteristics.

The thickness of the positive electrode active material layer constituting the secondary battery of the present invention is not particularly limited, and can be, for example, 5 to 500 μm, preferably 20 to 200 μm.
Further, the thickness of the positive electrode current collector constituting the secondary battery of the present invention is not particularly limited, and can be, for example, 10 to 100 μm, preferably 10 to 50 μm.

<Negative electrode layer>
Although the negative electrode layer is generally composed of a negative electrode current collector and a negative electrode active material layer, it may be composed of a negative electrode active material layer and not include a negative electrode current collector. In other words, if the negative electrode active material layer also functions as a negative electrode current collector, it does not need to be composed of two layers, the negative electrode current collector and the negative electrode active material layer, and may be a single layer structure. .
Further, the negative electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) together with the negative electrode active material, but it may not contain a solid electrolyte.

When the negative electrode active material layer contains a solid electrolyte, the type of the solid electrolyte is not particularly limited. From the viewpoint of both flexibility and safety, an oxide-based solid electrolyte can be used.
From the viewpoint of achieving both flexibility and safety at a higher level, it is preferable to use the solid electrolyte (I) described above. By doing so, the solid electrolyte (I) also acts like a binder for the solid particles contained in the negative electrode layer, and the negative electrode layer can be made more flexible.
The negative electrode active material layer may contain one or more solid electrolytes.
The content of the solid electrolyte in the negative electrode active material layer is not particularly limited, and the total content with the negative electrode active material is preferably 50 to 99.9% by mass, more preferably 70 to 99.5% by mass, More preferably 90 to 99% by mass.

The negative electrode active material itself used in the negative electrode layer is not particularly limited as long as the difference in discharge potential on Li basis satisfies 1.3 V or more between it and the positive electrode active material, and it can be used in ordinary lithium ion secondary batteries. A wide variety of negative electrode active materials can be used. A preferred form of the negative electrode active material will be explained below.

(Negative electrode active material)
The negative electrode active material is preferably one that can reversibly insert and release lithium ions. The negative electrode active material is not particularly limited as long as the difference in discharge potential based on Li with the positive electrode active material satisfies 1.3 V or more, and examples thereof include carbonaceous materials, oxides of metal elements or semimetal elements, Examples include simple lithium (also referred to as metal Li), lithium alloys, and negative electrode active materials that can form alloys with lithium.

The carbonaceous material used as the negative electrode active material is a material consisting essentially of carbon. For example, petroleum pitch, carbon black such as acetylene black (AB), graphite (natural graphite and artificial graphite such as vapor-grown graphite), and various types such as PAN (polyacrylonitrile) resin or furfuryl alcohol resin. Examples include carbonaceous materials made by firing synthetic resins.
Furthermore, various carbon fibers such as PAN carbon fiber, cellulose carbon fiber, pitch carbon fiber, vapor grown carbon fiber, dehydrated PVA (polyvinyl alcohol) carbon fiber, lignin carbon fiber, glassy carbon fiber, and activated carbon fiber. Also mentioned are graphite, mesophase microspheres, graphite whiskers, and tabular graphite.
These carbonaceous materials can also be divided into non-graphitizable carbonaceous materials (also referred to as hard carbon) and graphite-based carbonaceous materials depending on the degree of graphitization.
In addition, carbonaceous materials have the lattice spacing, density, or crystallite size described in JP-A-62-022066, JP-A-2-006856, and JP-A-3-045473. It is preferable to have. The carbonaceous material does not need to be a single material, and may include a mixture of natural graphite and artificial graphite described in JP-A-5-090844, and graphite with a coating layer as described in JP-A-6-004516. You can also use
As the carbonaceous material, hard carbon or graphite is preferable, and graphite is more preferable.

The oxide of a metal element or metalloid element to be applied as a negative electrode active material is not particularly limited as long as it is an oxide that can occlude and release lithium, and oxides of metal elements (metal oxides, etc.) such as Fe ₃ O ₄ can be used. oxides of metal elements), composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and oxides of metalloid elements (metalloid oxides). Note that composite oxides of metal elements and composite oxides of metal elements and metalloid elements are collectively referred to as metal composite oxides.
As these oxides, amorphous oxides are preferable, and chalcogenides, which are reaction products of metal elements and elements of group 16 of the periodic table, are also preferable.
In the present invention, a metalloid element refers to an element that exhibits intermediate properties between metallic elements and nonmetallic elements, and usually includes six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and further includes selenium, Contains three elements: polonium and astatine.
In addition, amorphous means a substance that has a broad scattering band with an apex in the 2θ value range of 20 to 40 degrees when measured by X-ray diffraction using CuKα rays, and has a crystalline diffraction line. You may. The strongest intensity among the crystalline diffraction lines seen between 40 and 70 degrees in 2θ values is less than 100 times the diffraction line intensity at the top of the broad scattering band seen at 20 to 40 degrees in 2θ values. It is preferably 5 times or less, more preferably 5 times or less, and even more preferably not having any crystalline diffraction lines.

Among the compound group consisting of the above-mentioned amorphous oxides and chalcogenides, amorphous oxides of metalloid elements or the above-mentioned chalcogenides are more preferable, and elements of groups 13 (IIIB) to 15 (VB) of the periodic table (e.g. , Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) or a (composite) oxide or chalcogenide consisting of one type selected from the group consisting of one type alone or a combination of two or more types thereof is more preferable.
Amorphous oxides and chalcogenides include Ga ₂ O ₃ , GeO, PbO, PbO ₂ , Pb 2 O ₃ , Pb ₂ O ₄ , Pb ₃ O ₄ , Sb ₂ O ₃ , _{Sb 2} _O ₄ , Sb ₂ O ₈ Bi ₂ O ₃ , Sb ₂ O ₈ Si ₂ O ₃ , Sb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ O ₄ , GeS, PbS, PbS ₂ , Sb ₂ S ₃ or Sb ₂ S ₅ are preferred.
Examples of negative electrode active materials that can be used in conjunction with amorphous oxide negative electrode active materials mainly containing Sn, Si, or Ge include carbonaceous materials that can absorb and/or release lithium ions or lithium metal, and lithium alone. , a lithium alloy, or a negative electrode active material that can be alloyed with lithium.

The oxide of a metal element or metalloid element (particularly a metal (composite) oxide) and the chalcogenide preferably contain at least one of titanium and lithium as a constituent from the viewpoint of high current density charge/discharge characteristics.
Examples of metal composite oxides containing lithium (lithium composite metal oxides) include composite oxides of lithium oxide and the aforementioned metal oxides, the aforementioned metal composite oxides, or the aforementioned chalcogenides. More specifically, Li ₂ SnO ₂ is mentioned.
It is also preferable that the negative electrode active material (eg, metal oxide) contains a titanium element (titanium oxide). Specifically, Li ₄ Ti ₅ O ₁₂ (lithium titanate [LTO]) has excellent rapid charging and discharging characteristics due to small volume fluctuations when lithium ions are intercalated and released, suppresses electrode deterioration, and is an all-solid lithium oxide. This is preferable in that it is possible to improve the life of the ion secondary battery.

The lithium alloy as a negative electrode active material is not particularly limited as long as it is an alloy commonly used as a negative electrode active material of all-solid-state lithium ion secondary batteries, and examples thereof include lithium aluminum alloys.

The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is commonly used as a negative electrode active material of all-solid-state lithium ion secondary batteries. Examples of the negative electrode active material include negative electrode active materials (alloys) containing silicon element or tin element, and various metals such as Al and In. (element-containing active material) is preferable, and a silicon element-containing active material in which the content of silicon element is 50 mol % or more of all constituent elements is more preferable.
In general, negative electrodes containing these negative electrode active materials (e.g., Si negative electrodes containing silicon element-containing active materials, Sn negative electrodes containing tin element-containing active materials) are more expensive than carbon negative electrodes (such as graphite and acetylene black). , more Li ions can be stored. That is, the amount of Li ions stored per unit mass increases. Therefore, battery capacity can be increased. As a result, there is an advantage that the battery operating time can be extended.

Examples of silicon element-containing active materials include silicon materials such as Si and SiOx (0<x≦1), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (e.g. , LaSi ₂ , VSi ₂ , La-Si, Gd-Si, and Ni-Si), or structured active materials (eg, LaSi ₂ /Si). Other examples include active materials containing silicon and tin elements, such as SnSiO ₃ and SnSiS ₃ . Note that SiOx itself can be used as a negative electrode active material (semi-metal oxide), and since SiOx generates Si when an all-solid-state lithium ion secondary battery is operated, it is a negative electrode active material that can be alloyed with lithium. (precursor substance thereof).
Examples of the negative electrode active material containing the tin element include Sn, SnO, SnO ₂ , SnS, SnS ₂ , and active materials containing the silicon element and tin element described above.

In terms of battery capacity, the negative electrode active material is preferably a negative electrode active material that can be alloyed with lithium, more preferably the silicon material or silicon-containing alloy (alloy containing silicon element), and silicon (Si) or a silicon-containing alloy. More preferred.

It is also preferable to use titanium niobium composite oxide as the negative electrode active material. Titanium niobium composite oxide has a high theoretical volume capacity density, and is expected to have a long life and be capable of rapid charging. An example of the titanium niobium composite oxide is TiNb ₂ O ₇ ([TNO]).

Although the shape of the negative electrode active material is not particularly limited, a particulate shape is preferable. The volume average particle diameter of the negative electrode active material is not particularly limited, but is preferably 0.1 to 60 μm, more preferably 0.5 to 20 μm, and even more preferably 1.0 to 15 μm.
The volume average particle diameter is measured by the following procedure.
A 1% by mass dispersion of the negative electrode active material is prepared by diluting it with water (heptane in the case of a substance unstable in water) in a 20 mL sample bottle. The diluted dispersion sample is irradiated with 1 kHz ultrasonic waves for 10 minutes, and immediately thereafter used for the test. Using this dispersion sample, data is acquired 50 times using a quartz cell for measurement at a temperature of 25° C. using a laser diffraction/scattering particle size distribution measuring device to obtain the volume average particle diameter. For other detailed conditions, refer to the description of JIS Z 8828:2013 "Particle size analysis - dynamic light scattering method" if necessary. Five samples are prepared for each level and the average value is used.

One type of negative electrode active material may be used alone, or two or more types may be used in combination.
The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, and is preferably 10 to 90% by mass, more preferably 20 to 85% by mass, and even more preferably 30 to 80% by mass. It is preferably 35 to 75% by weight, particularly preferably 35 to 75% by weight.

The surface of the negative electrode active material may be coated with another oxide such as a metal oxide, a carbon-based material, or the like. These surface coating layers can function as interfacial resistance stabilizing layers.
Surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si or Li. Specific examples include spinel titanate, tantalum oxides, niobium oxides, and lithium niobate compounds, such as Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , LiTaO ₃ , LiNbO ₃ _, _LiAlO2 , _Li2ZrO3 _, _Li2WO4 _, _Li2TiO3 _, _Li2B4O7 , _Li3PO4 _, _Li2MoO4 _, _Li3BO3 _, _LiBO2 _, _Li2CO3 _, Examples include Li ₂ SiO ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , B ₂ O ₃ and Li ₃ AlF ₆ . Further, carbon-based materials such as C, SiC, and SiOC (carbon-added silicon oxide) can also be used as the surface coating material.
Further, the surface of the negative electrode active material may be surface-treated with sulfur or phosphorus.
Furthermore, the surface of the negative electrode active material may be subjected to surface treatment using active light or active gas (for example, plasma) before and after the surface coating.
The surface coating material (also referred to as coating material) for the negative electrode active material can suppress contact between the negative electrode active material and water, and can also suppress Li deficiency at the interface between the negative electrode active material and the solid electrolyte. It is considered that the charge/discharge cycle characteristics of the all-solid-state lithium ion secondary battery can be further improved. From this point of view, the coating material for the negative electrode active material is preferably carbon.

Among these, the negative electrode active material preferably has a discharge potential of 2.5 V or less based on Li, more preferably 1.7 V or less, even more preferably 1.55 V or less, and 1. It is particularly preferable that the voltage is .0V or less.
Note that when the negative electrode active material has the above-mentioned coat layer and this coat layer is made of a material that can reversibly insert and release lithium ions, the discharge potential of the negative electrode active material based on Li is , means the discharge potential of a material with a higher potential based on Li.
As mentioned above, in the secondary battery of the present invention, of the two types of water, "free water" and "bound water" contained in the solid electrolyte (I) having a specific composition, "bound water" is composed of lithium-containing oxide and / or interacts with the lithium salt, and the potential window of the solid electrolyte (I) becomes wider than that of water. For this reason, the solid electrolyte (I) decomposes even below 2.5 V (Li standard, pH = 7), where water reductive decomposition occurs in conventional liquid-based lithium ion secondary batteries that use an aqueous solution as the electrolyte. Instead, a negative electrode active material having a discharge potential of 2.5 V or less based on Li can be used.
Examples of negative electrode active materials whose discharge potential is 2.5 V or less based on Li include Li ₄ Ti ₅ O ₁₂ (LTO, 1.55 V), TiNb ₂ O ₇ (TNO, 1.55 V), and Fe ₃ O. ₄ (1.0V), graphite [for example, artificial graphite (0-0.25V), natural graphite (0-0.25V)], hard carbon (0-0.8V), Si (0-0.8V) , SiO (0 to 0.8V), Sn (0 to 0.8V), Al (0 to 0.8V), and metal Li (0V), and at least one of these is preferred. Note that the value written in parentheses after each negative electrode active material is the discharge potential based on Li.
In addition, it is also preferable to coat these with an interfacial resistance stabilizing layer such as the above-mentioned oxide or carbon-based material.

(Negative electrode current collector)
The current collector that constitutes the negative electrode layer is an electron conductor. Further, the negative electrode current collector is usually in the form of a film sheet.
Examples of the constituent material of the negative electrode current collector include aluminum, copper, copper alloy, stainless steel, nickel, zinc, and titanium (Ti), with aluminum, copper, zinc, or titanium being preferred, and aluminum or titanium being more preferred.
In addition, as a negative electrode current collector, a coating layer (thin film) of carbon, nickel, aluminum, copper, zinc, titanium, or silver is applied to the surface of a metal base material such as aluminum, copper, copper alloy, zinc, titanium, or stainless steel. It is preferable to have a coating layer of aluminum, copper, zinc or titanium on the surface of the metal base material of aluminum, copper, zinc or titanium. It is more preferable to use an aluminum or titanium coating layer.

Among these, from the viewpoint of further improving charge-discharge cycle characteristics, the negative electrode current collector is preferably Al, Ti, or a metal coated with Al or Ti; Alternatively, Cu coated with Ti is more preferable.
In addition to originally having a strong oxide film on its surface, when a fluorine-containing lithium salt is contained in the electrode layer, this fluorine reacts with the surface of the oxide film to form a highly corrosion-resistant fluoride film. Al is formed. After the formation of Al fluoride, the reaction between Al and the lithium salt does not proceed any further and the lithium salt is not consumed, so it is presumed that the charge/discharge cycle characteristics are improved.
In addition, since Ti has low reactivity, when it contains materials in the electrode layer (for example, active material, conductive agent, solid electrolyte (I), lithium-containing oxide, lithium It is presumed that this material is less likely to react with salt (salt, water) and improves charge/discharge cycle characteristics.

The thickness of the negative electrode active material layer constituting the secondary battery of the present invention is not particularly limited, and can be, for example, 5 to 500 μm, preferably 20 to 200 μm.
Further, the thickness of the negative electrode current collector constituting the secondary battery of the present invention is not particularly limited, and may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

(Active material in the secondary battery of the present invention)
In the secondary battery of the present invention, the difference in discharge potential based on Li between the positive electrode active material contained in the positive electrode layer and the negative electrode active material contained in the negative electrode layer, that is, the Li standard of the positive electrode active material contained in the positive electrode layer The value obtained by subtracting the Li-based discharge potential of the negative electrode active material contained in the negative electrode layer from the discharge potential at is 1.3 V or more, and the positive electrode active material and the negative electrode active material are used in combination so as to satisfy this value.
In the present invention, the discharge potential of the positive electrode active material and the negative electrode active material refers to the intercalation reaction of lithium into the negative electrode active material or the positive electrode active material (a phenomenon in which lithium ions are inserted into the negative electrode active material or the positive electrode active material). The Li standard means the electric potential energy that occurs, and the Li standard means that the potential at which the oxidation-reduction reaction of lithium occurs is set as the standard, that is, 0V.
In the present invention, the discharge potential of the positive electrode active material and the negative electrode active material based on Li is determined, for example, by using Li metal as a reference electrode, sandwiching an electrochemically stable electrolyte layer within the range of the measured potential, and measuring the positive electrode active material layer. Alternatively, it can be measured by cyclic voltammetry (sweep voltage 0.5 mV/s with a potentiostat) using the negative electrode active material layer as a working electrode.
In addition, when two or more types of positive electrode active materials are included and/or when two or more types of negative electrode active materials are included, the Li of the positive electrode active material showing the lowest discharge potential and the negative electrode active material showing the highest discharge potential is This means that the difference in discharge potential with reference is 1.3V or more.
In the present invention, the positive electrode active material is LiCoO ₂ (LCO, 3.9V), LiNiO ₂ ( LNO, 3.5V), LiNi _0.85 Co _0.10 Al _0.05 O ₂ (NCA, 3.6V), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC, 3.9V) , Li ₂ MnO ₃ -LiNiMnCoO ₂ (3.9 V), LiMn ₂ O ₄ (LMO, 3.8 V), LiNi _0.5 Mn _1.5 O ₄ (LNMO, 4.7 V), LiFePO ₄ (LFP, 3 .2-3.4V), LiMnPO ₄ (LMP, 4.1V), LiCoPO ₄ (LCP, 4.8V), Li ₂ CoP ₂ O ₇ (5V) and LiNiPO ₄ (LNP, 5.1V). The negative electrode active material contains at least one of Li ₄ Ti ₅ O ₁₂ (LTO, 1.55V), TiNb ₂ O ₇ (TNO, 1.55V), Fe ₃ O ₄ (1.0V), graphite [e.g. , artificial graphite (0-0.25V), natural graphite (0-0.25V)], hard carbon (0-0.8V), Si (0-0.8V), SiO (0-0.8V), It is preferable to use a combination containing at least one of Sn (0 to 0.8V), Al (0 to 0.8V), and metal Li (0V). Note that the value written in parentheses after each active material is the discharge potential based on Li.

The positive electrode layer and the negative electrode layer may contain components other than the solid electrolyte and other than the active material (other components) in their active material layers. For example, a conductive additive may be included.
As the conductive aid, those known as general conductive aids can be used. Examples of conductive aids include electron conductive materials such as graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, Ketjen black, and furnace black, and amorphous materials such as needle coke. Examples include fibrous carbon such as carbon, vapor-grown carbon fiber, and carbon nanotubes, and carbonaceous materials such as graphene and fullerene. Further, conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may also be used.
In addition to the above conductive aids, ordinary conductive aids that do not contain carbon atoms, such as metal powder or metal fibers, may be used.
A conductive additive is one that does not insert or release Li when a battery is charged or discharged, and does not function as an active material. Therefore, among conductive aids, those that can function as active materials in the active material layer when the battery is charged and discharged are classified as active materials rather than conductive aids. Whether or not it functions as an active material when charging and discharging a battery is not unique, but is determined by the combination with the active material.
The content of the conductive additive in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass, and more preferably 1 to 5% by mass.
The content of the conductive additive in the negative electrode active material layer is not particularly limited, but is preferably, for example, 0 to 10% by mass, more preferably 1 to 5% by mass.

Other components include the above-mentioned binder and lithium salt.

In the secondary battery of the present invention, it is also preferable that at least one of the positive electrode active material layer and the negative electrode active material layer contains other components such as an ionic liquid and a surfactant.
When the positive electrode active material layer and/or the negative electrode active material layer contains the solid electrolyte (I), the second aspect of the present invention can be achieved by including the ionic liquid in the same manner as in the case where the solid electrolyte (I) is included in the solid electrolyte layer described above. It is possible to further improve the charge/discharge cycle characteristics of the next battery. The ionic liquid is as described above.
By adding a surfactant, it is possible to further improve the charge/discharge cycle characteristics of the secondary battery of the present invention. By adding a surfactant, the dispersibility of the active material, conductive agent, and solid electrolyte in the positive electrode active material layer and/or negative electrode active material layer, and the solid electrolyte (I) in the positive electrode active material layer and/or negative electrode active material layer When containing, it is possible to improve the dispersibility of the lithium salt in the solid electrolyte (I). The surfactant is as described above.

(Solid electrolyte (I) protective agent)
If the solid electrolyte (I) contains free water and/or weakly bound water, it may be decomposed by a battery operating voltage higher than the electrolysis voltage of water. In order to prevent and suppress this decomposition, the secondary battery of the present invention may be impregnated with a solid electrolyte (I) protective agent. Note that weakly bound water refers to bound water that has a narrow potential window.
In the form of impregnating the solid electrolyte (I) protective agent into the secondary battery of the present invention, at least one of the solid electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer is impregnated with the solid electrolyte (I) protective agent. Preferably, at least one layer including the solid electrolyte layer is impregnated with the solid electrolyte (I) protective agent. More preferred is a form in which it is invasive. Impregnation with the solid electrolyte (I) protective agent may be performed at any stage, for example, impregnation at the stage of forming each layer, or at the stage of forming the solid electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer. impregnation in the state.
Examples of the solid electrolyte (I) protective agent include preferably ester compounds, phosphate ester compounds, phosphite ester compounds, and carbonate compounds among organic compounds. Specifically, preferred examples include isodecyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, and isopropyl palmitate.
Further, from the viewpoint of safety, the solid electrolyte (I) protective agent preferably has a flash point of 150° C. or higher.

<Manufacture of all-solid-state lithium ion secondary battery>
The secondary battery of the present invention uses a solid electrolyte (I) in at least the solid electrolyte layer, and the difference in discharge potential between the positive electrode active material contained in the positive electrode layer and the negative electrode active material contained in the negative electrode layer on a Li basis is 1. The battery can be manufactured by referring to a normal method for manufacturing an all-solid-state secondary battery, except for using a positive electrode layer and a negative electrode layer that have a voltage of .3V or more. That is, the method for manufacturing a secondary battery of the present invention can be manufactured including the step of obtaining a laminate in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are arranged in this order. Here, the amount of water in the solid electrolyte (I) used may or may not satisfy the amount specified in the present invention. In the method for manufacturing an all-solid-state secondary battery, regardless of the amount of water in the solid electrolyte (I) used, the amount of water in the solid electrolyte (I) contained in the constituent layers such as the solid electrolyte layer can be adjusted according to the present invention. In order to set the amount to a specified value, manufacturing the secondary battery of the present invention can also include a step of subjecting the formed solid electrolyte layer to a drying process, if necessary. This step of drying the constituent layers such as the solid electrolyte layer can be carried out if the solid electrolyte (I) in the constituent layers such as the solid electrolyte layer in the obtained secondary battery can be set to the amount of water specified in the present invention. It may be performed at any stage after forming the layer. In order to more reliably set the water amount to the amount specified in the present invention, it is possible to subject the laminate in which at least a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are arranged in this order to a drying treatment while being arranged in a battery cell. preferable. The drying method is not particularly limited, and for example, the amount of water in the solid electrolyte (I) in the solid electrolyte layer can be reduced by using a desiccator, vacuum drying, freeze vacuum drying, or heat treatment. can be reduced to within the range defined by the present invention.
The secondary battery of the present invention is preferably formed by sealing a laminate in which the above-described positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in this order. By sealing, it is possible to more reliably prevent moisture from entering the solid electrolyte layer after the drying step, and the cycle characteristics can be further improved. The sealing method is not particularly limited as long as it can block or suppress the ingress of moisture (atmosphere). For example, the laminate is sealed by closing the lid of the casing (battery cell) that houses the laminate in which the above-mentioned positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in this order through a gasket such as an O-ring. For example, how to stop it. Furthermore, cell resistance can also be improved by heating the obtained laminate (for example, at 80° C. for 2 hours).

Furthermore, the method for forming a laminate in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are arranged in this order is not particularly limited, and methods for forming each layer include forming by coating a dispersion, compacting powder, etc. Can be mentioned.
One form of the method for manufacturing a secondary battery of the present invention includes a method for manufacturing a secondary battery that includes forming a solid electrolyte layer by applying a dispersion of solid electrolyte (I). This method can be adopted because an aqueous dispersion (slurry) of the solid electrolyte (I) can be easily prepared. Note that the dispersion liquid of solid electrolyte (I) may contain, in addition to solid electrolyte (I), other components that may be contained in the solid electrolyte layer.
Regarding the positive electrode active material layer and the negative electrode active material layer, the positive electrode active material layer and the negative electrode active material layer can be formed, respectively, by applying a dispersion of the active material. When other components other than the active material, such as a conductive aid and a solid electrolyte, are included, a dispersion liquid in which these components are also dispersed is used.
The dispersion medium in the solid electrolyte (I) dispersion liquid and the active material dispersion liquid can be appropriately selected in consideration of reactivity with the components contained in the dispersion liquid. For example, when solid electrolyte (I) is included, it is preferable to use an aqueous dispersion, and when a sulfide-based solid electrolyte is included, it is preferable to use an organic solvent dispersion.
As a manufacturing method for an all-solid-state secondary battery, for example, a positive electrode forming composition (positive electrode slurry) containing a positive electrode active material is applied onto a metal foil serving as a positive electrode current collector to form a positive electrode active material layer, and then a positive electrode active material layer is formed. Next, a solid electrolyte layer forming dispersion containing a solid electrolyte (solid electrolyte slurry) is applied onto the positive electrode active material layer to form a solid electrolyte layer, and a negative electrode active material is further applied onto the solid electrolyte layer. An example of a method is to form a negative electrode active material layer by applying a negative electrode forming composition (negative electrode slurry) containing the negative electrode active material layer, and to stack a negative electrode current collector (metal foil) on the negative electrode active material layer. If necessary, the whole can be subjected to pressure treatment to obtain an all-solid lithium ion secondary battery as shown in FIG. 1.
In addition, by reversing the formation method of each layer, a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer are formed on the negative electrode current collector, and a positive electrode current collector (metal foil) is formed on the positive electrode active material layer. An all-solid-state lithium ion secondary battery can also be manufactured by stacking the two and subjecting the whole to pressure treatment if necessary.

Another method is to prepare a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer separately, and place them between a positive electrode current collector and a negative electrode current collector (a metal foil), a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector (metal foil) are laminated in this order and pressurized if necessary to produce an all-solid-state lithium ion secondary battery. You can also do it.
In this case, in forming each layer, a support such as a nonwoven fabric may be provided as necessary to make each layer a self-supporting film. Note that it is preferable that the support in the self-supporting membrane is usually removed when laminating each layer to produce an all-solid-state lithium ion secondary battery.

Another form of the method for manufacturing a secondary battery of the present invention includes a method for manufacturing a secondary battery that includes applying pressure to powder of solid electrolyte (I) to form a solid electrolyte layer. The solid electrolyte (I) can be easily plastically deformed by pressure, and it itself is soft and plastically deformed, acting like a binder and contributing to improving the cohesion between solid particles or layers. A solid electrolyte layer exhibiting high ionic conductivity can be obtained without undergoing a high-temperature sintering process (in other words, without sintering). In addition, when the solid electrolyte layer contains other components that may be contained in the solid electrolyte layer as components other than the powder of the solid electrolyte (I), by applying pressure to the mixture containing the powder of the solid electrolyte (I), the solid An electrolyte layer can also be formed.
The positive electrode active material layer and the negative electrode active material layer can also be formed by pressure molding the powders constituting each layer. When other components other than the active material include conductive aids, solid electrolytes, etc., especially when the solid electrolyte is solid electrolyte (I) and/or sulfide-based solid electrolyte, pressure is not applied to the powder mixture. By applying this, it is possible to obtain a solid electrolyte layer that exhibits high ionic conductivity without undergoing a high-temperature sintering process (in other words, without sintering).
Specifically, the powder constituting the positive electrode active material layer (hereinafter referred to as positive electrode composite powder), the powder constituting the solid electrolyte layer (hereinafter referred to as solid electrolyte powder), and the negative electrode active material. Using the powder constituting the layers (hereinafter referred to as negative electrode composite powder), the powder constituting each layer is pressurized and shaped into a predetermined shape to form pellets of each layer, and the pellets of the positive electrode or negative electrode are assembled. An all-solid-state lithium ion secondary battery can also be manufactured by stacking it with an electric body and applying pressure.
For example, solid electrolyte powder is filled into a predetermined mold, pressure molded to form solid electrolyte pellets, and negative electrode composite powder is filled on one side of the obtained solid electrolyte pellets. Pellets of negative electrode composite material are formed by pressure molding, and pellets of positive electrode composite material are formed by filling powder of positive electrode composite material on the other side of the obtained solid electrolyte pellets and press molding. A compact is obtained in which pellets of the positive electrode composite material, pellets of the solid electrolyte, and pellets of the negative electrode composite material are laminated in this order. Next, the negative electrode composite pellets of the obtained compacted powder are stacked on the negative electrode current collector (metal foil) with the pellets facing downward, and then the positive electrode collector is placed on top of the positive electrode composite pellets. An all-solid-state lithium ion secondary battery as shown in FIG. 1 can be obtained by stacking electric bodies (metal foils) and subjecting the whole body to pressure treatment.
There are no particular limitations on the method for preparing solid electrolyte powder, and for example, it can be prepared by freeze-vacuum drying a solid electrolyte layer-forming dispersion (solid electrolyte slurry) containing a solid electrolyte.
There is no particular restriction on the method for preparing the powder of the negative electrode composite material, and for example, it can be prepared by mixing a solid electrolyte powder prepared in advance and a component for forming a negative electrode active material layer including the negative electrode active material. can.
There is no particular restriction on the method for preparing the powder of the positive electrode composite material. For example, it can be prepared by mixing a solid electrolyte powder prepared in advance and a component for forming a positive electrode active material layer including the positive electrode active material. can.
There are no particular restrictions on the pressurizing conditions when producing pellets of negative electrode composite material, pellets of solid electrolyte material, and pellets of positive electrode composite material. It can be made.
Further, the pellets of the negative electrode composite material and the negative electrode current collector, and the pellets of the positive electrode composite material and the positive electrode current collector can also be crimped by applying a pressure of about 60 MPa.
Note that there is no particular restriction on the order in which the pellets of each layer are formed; for example, the pellets may be formed in the order of negative electrode composite material pellets, solid electrolyte pellets, and positive electrode composite material pellets.
Another method is to separately produce pellets of the negative electrode composite material, pellets of the solid electrolyte material, and pellets of the positive electrode composite material, stack the obtained pellets, and stack the stacked pellets with the current collectors of the positive electrode and negative electrode. An all-solid-state lithium ion secondary battery can also be manufactured by sandwiching and stacking them and applying pressure.

In addition, a method for manufacturing a small stacked battery in which a plurality of positive electrode layers, solid electrolyte layers, and negative electrode layers are stacked, with a solid electrolyte layer disposed between adjacent positive electrode layers and negative electrode layers, is described, for example. It can be manufactured by referring to the lamination method described in paragraphs [0033] to [0046] of JP-A No. 2016-001602. Note that each layer of the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer can be manufactured based on the manufacturing method of the present invention described above.

Note that the manufacturing method of the secondary battery of the present invention is not limited to that described above as long as the secondary battery defined by the present invention can be obtained.

In manufacturing the secondary battery of the present invention, without using a sulfide-based solid electrolyte as a solid electrolyte, the action of the oxide-based solid electrolyte (I), which can be easily plastically deformed under pressure, can be applied between solid particles or between layers. It is possible to form a layer with reduced interfacial resistance.
The solid electrolyte (I) itself is soft and plastically deformable, acts like a binder, and contributes to improving the binding between solid particles or layers, so layer formation is possible without using a binder such as an organic polymer. It is also possible to do so.

The secondary battery of the present invention is preferably initialized after manufacture or before use. The method of initialization is not particularly limited, and for example, initial charging and discharging may be carried out under a high press pressure, and then the pressure may be released until the pressure falls within the range of pressure conditions during use of the secondary battery. I can do it.

<Applications of all-solid-state lithium ion secondary batteries>
The secondary battery of the present invention can be applied to various uses. There are no particular restrictions on how it can be applied, but for example, when installed in electronic devices, it can be used in notebook computers, pen input computers, mobile computers, e-book players, mobile phones, cordless phone handsets, pagers, handy terminals, mobile fax machines, mobile phones, etc. Examples include photocopiers, portable printers, headphone stereos, video movies, LCD televisions, handy cleaners, portable CDs, mini discs, electric shavers, walkie talkies, electronic organizers, calculators, memory cards, portable tape recorders, radios, and backup power supplies. Other consumer products include automobiles, electric vehicles, motors, lighting equipment, toys, game equipment, road conditioners, watches, strobes, cameras, and medical equipment (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, it can be used for various military purposes and for space purposes. It can also be combined with solar cells.

The present invention will be explained in more detail based on Examples, but the present invention is not to be construed as being limited thereto. In the present invention, room temperature means 27°C. Further, the production of the solid electrolyte and the production of the secondary battery described below were performed in an atmosphere where moisture was present in the atmosphere.

[Reference Example 1: Production according to the above steps 0, 1A to 3A]
Using a ball mill (manufactured by Fritsch, planetary ball mill P-7), powdered Li ₂ B ₄ O ₇ crystals (LBO powder) (manufactured by Rare Metallic) were placed in a pot of stabilized zirconia (YSZ) (45 mL). , Grinding balls: YSZ (average particle diameter: 5 mm, number: 50 pieces), rotation speed: 370 rpm (revolutions per minute), LBO powder amount: 1 g, atmosphere: air, ball mill processing time: 100 hours. , and ball milled to obtain a finely divided lithium-containing oxide (hereinafter also referred to as "fine lithium-containing oxide").
To 1 g of the obtained lithium-containing oxide fines, 0.05 g of LiFSI (chemical formula: Li(FSO ₂ ) ₂ N) was added as a lithium salt (5% by mass based on the lithium-containing oxide fines). ) and further ball milled for 100 hours. The obtained powder was added to water so that the powder concentration was 42% by mass, and ultrasonically dispersed for 30 minutes. Subsequently, the obtained dispersion liquid was transferred to a glass Petri dish and dried at 120° C. for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powdered solid electrolyte (I)-1.

<Preparation and evaluation of solid electrolyte molded body>
The powdered solid electrolyte (I)-1 obtained above was compacted at 27° C. (room temperature) and an effective pressure of 220 MPa to obtain a solid electrolyte compact (compact 1). The powder compact 1 has a cylindrical shape with a diameter of 10 mm and a thickness of 0.5 to 1 mm. As a result of measuring the ionic conductivity of the obtained compact 1, the ionic conductivity of the compact 1 was 1.5×10 ⁻⁴ S/cm at 27°C and 4.0×10 at 60°C. ^-4 S/cm.

The ionic conductivity of the solid electrolyte (I)-1 was measured at 1 Hz under the conditions of a measurement temperature of 27°C or 60°C and an applied voltage of 50 mV, with two In foil electrodes placed to sandwich the powder compact 1. It was calculated by measuring the AC impedance between both In electrodes in a measurement frequency range of ~1 MHz and analyzing the arc diameter of the obtained Cole-Cole plot (Nyquist plot).

X-ray diffraction measurement of solid electrolyte (I)-1 was performed as described above using CuKα radiation. The measurement conditions were 0.01°/step and 3°/min. As a result, it was revealed that the above-mentioned X-ray diffraction characteristics were satisfied, and solid electrolyte (I)-1 was found to be in an amorphous state.

Using the solid electrolyte (I)-1 obtained above, X-ray total scattering measurement was performed with SPring-8L04B2 (acceleration voltage: 61.4 keV, wavelength: 0.2019 Å). The sample was sealed in a 2 mmφ or 1 mmφ Kapton capillary, and experiments were conducted. The obtained data was Fourier transformed as described above to obtain a reduced two-body distribution function.
As a result of the analysis, in the reduced two-body distribution function G(r) obtained from X-ray total scattering measurement, G(r) at the peak top exceeded 1.0 in the range of r from 1 to 5 Å, and the peak A first peak whose top was located at 1.43 Å, and a second peak whose peak top G(r) exceeded 1.0 and whose peak top was located at 2.40 Å were confirmed.
On the other hand, in solid electrolyte (I)-1, the peaks attributed to the BO distance and the BB distance observed in general lithium tetraborate crystals were maintained. A typical lithium tetraborate crystal has a structure in which BO ₄ tetrahedrons and BO ₃ triangles exist in a 1:1 ratio (diborate structure), and it is assumed that this structure is maintained in solid electrolyte (I)-1. .

The full width at half maximum (full width at half maximum ¹ ) of the solid ^electrolyte (I)-1 at 120°C. The ratio {(full width at half maximum 2/full width at half maximum 1)×100} was 33%.
In addition, when the first peak appearing in the range of -100 to +100 ppm in the spectrum obtained when solid-state ⁷ Li-NMR measurement was performed at 20 °C was separated into waveforms, the chemical shift was found to be in the range of -3 to 3 ppm, with a full width at half maximum. It had a second peak of 5 ppm or less, and the ratio of the area intensity of the second peak to the area intensity of the first peak was 4%.

Using the solid electrolyte (I)-1 obtained above, an infrared absorption spectrum was measured under the above conditions, and in the obtained infrared absorption spectrum, the maximum absorption intensity in the wave number region of 800 to 1600 ^cm , the value of the ratio of maximum absorption intensity in the wave number region of 3000 to 3500 cm ⁻¹ was 0.72.

In the Raman spectrum of solid electrolyte (I)-1 obtained above, the coefficient of determination obtained by linear regression analysis using the least squares method in the wave number region of 600 to 850 cm ^-1 was 0.9974.
The mass reduction rate when solid electrolyte (I)-1 was heated from 25° C. to 800° C. as described above was 29.8%.

Regarding the analysis of each element in the obtained solid electrolyte (I)-1, lithium and boron were quantitatively analyzed by ICP-OES, fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC), and N was analyzed quantitatively by ICP-OES. It was estimated from the analytical mass of sulfur in consideration of each atomic weight in the salt, and O was calculated as the difference from the total amount of powder by adding up the analytical masses of elements other than O. The results are shown in the table below.

[Reference example 2: Production according to the above steps 1B to 3B and method 2]
1 g of the lithium-containing oxide fines used in Reference Example 1 were added to water so that the concentration of the fines was 42% by mass, and the mixture was ultrasonically dispersed for 30 minutes. To the resulting dispersion, 0.05 g of LiFSI (chemical formula: Li(FSO ₂ ) ₂ N) was added as a lithium salt (5% by mass based on the fine particles of the lithium-containing oxide), and an additional 30 Ultrasonic dispersion was carried out for a minute.
The obtained dispersion liquid was transferred to a glass Petri dish and dried at 120° C. for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powdered solid electrolyte (I)-2. Solid electrolyte (I)-2 was subjected to various evaluations in the same manner as in Reference Example 1 under atmospheric conditions. The results are summarized in the table below.

[Reference example 3: Production according to the above steps 1B to 3B and method 3]
Using a ball mill (manufactured by Fritsch, planetary ball mill P-7), powdered Li ₂ B ₄ O ₇ (LBO powder) (manufactured by Rare Metallic) was ground using a pot: YSZ (45 ml), a grinding ball: YSZ (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm (revolutions per minute), amount of LBO powder: 4.2 g, atmosphere: air, ball milling time: 100 hours. Fine particles of lithium-containing oxide were obtained.
The obtained lithium-containing oxide fines were added to water so that the concentration of the fines was 42% by mass, and subjected to ultrasonic treatment for 60 minutes to obtain Dispersion 1.
Next, 3.25 g of LiFSI (chemical formula: Li(FSO ₂ ) ₂ N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 2. .
The obtained dispersion liquid 1 and solution 2 were mixed and stirred and mixed using a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum dried at 40° C. and 10 Pa for 15 hours to obtain powdery solid electrolyte (I)-3. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were conducted in the atmosphere in the same manner as in Reference Example 1 using solid electrolyte (I)-3. The results are summarized in the table below.

[Reference example 4: Production according to the above steps 1B to 3B and method 3]
Dispersion 3 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3.
Next, 2.32 g of LiFSI (chemical formula: Li(FSO ₂ ) ₂ N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 4.
The obtained dispersion liquid 3 and solution 4 were mixed and stirred and mixed using a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum dried at 40° C. and 10 Pa for 15 hours to obtain a powdery solid electrolyte (I)-4. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were conducted in the atmosphere in the same manner as in Reference Example 1 using solid electrolyte (I)-4. The results are summarized in the table below.

[Reference Example 5: Production according to the above steps 1B to 3B and method 3]
Dispersion 5 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3.
Next, 4.65 g of LiFSI (chemical formula: Li(FSO ₂ ) ₂ N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 6.
The obtained dispersion liquid 5 and solution 6 were mixed and stirred and mixed using a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum dried at 40° C. and 10 Pa for 15 hours to obtain powdery solid electrolyte (I)-5. The obtained powdered solid electrolyte (I)-5 was immediately used to perform various evaluations in the same manner as in Reference Example 1 in the atmosphere. The results are summarized in the table below.

[Reference Example 6: Production according to the above steps 1B to 3B and method 3]
Dispersion 7 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3.
Next, 7.13 g of LiTFSI (chemical formula: Li(F ₃ CSO ₂ ) ₂ N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 8.
The obtained dispersion liquid 7 and solution 8 were mixed and stirred and mixed using a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum dried at 40° C. and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-6. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were conducted in the atmosphere in the same manner as in Reference Example 1 using solid electrolyte (I)-6. The results are summarized in the table below.
In addition, in Reference Example 6, the carbon content shown in Table 1 below was estimated from the analytical mass of sulfur in consideration of each atomic weight in the lithium salt.

[Comparative reference example 1]
As a result of elemental analysis of the LBO powder (powdered Li ₂ B ₄ O ₇ crystals not ball milled) used in Reference Example 1, the composition of the obtained LBO powder was Li _1.96 B _4.00 O It was _6.80 . The LBO powder was compacted at 27° C. (room temperature) and an effective pressure of 220 MPa to obtain a compact C1 for comparative reference. The ionic conductivity of the obtained green compact C1 could not be detected.
Further, in the same manner as in Reference Example 1, X-ray total scattering measurement was performed using LBO powder to obtain the reduced two-body distribution function G(r). FIG. 10 shows the reduced two-body distribution function G(r) obtained from the LBO powder.
As a result of the analysis, in the reduced two-body distribution function G(r) obtained from the X-ray total scattering measurement of LBO powder, the peak top is the first peak located at 1.40 Å (corresponding to the BO proximity), the peak There was a second peak whose top was located at 2.40 Å (corresponding to B-B proximity), and the G(r) at the peak tops of the first and second peaks were both 1.0 or more (Fig. 10). In addition, there are other peaks with peak tops located at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å, and the absolute value of G(r) at the peak top of each peak is 1. It clearly exceeded 0 (see Figure 10).

X-ray diffraction measurement was performed on the LBO powder of Comparative Reference Example 1 using CuKα radiation. The measurement conditions were 0.01°/step and 3°/min.
FIG. 11 shows the X-ray diffraction pattern of the LBO powder of Comparative Reference Example 1. As shown in FIG. 11, a plurality of narrow peaks were observed in the LBO powder used in Comparative Reference Example 1. More specifically, the strongest peak corresponding to the (1,1,2) plane was observed at a 2θ value of 21.78°. Other main diffraction peaks include a peak corresponding to the (2,0,2) plane at the position of 25.54°, a peak corresponding to the (2,1,3) plane at the position of 33.58°, 34. A peak corresponding to the (3,1,2) plane appeared at the 62° position, and the intensities of these three peaks were almost equal. These peaks are derived from crystalline components.

[Comparative reference example 2]
As a result of elemental analysis of the lithium-containing oxide fines prepared in Reference Example 1 (ball-milled powdered Li ₂ B ₄ O ₇ crystals), the composition of the lithium-containing oxide fines was as follows: Li _1.94 B _4.00 O _6.80 .
Next, the fine particles of the lithium-containing oxide were compacted at 27° C. (room temperature) and an effective pressure of 220 MPa to obtain a compact for comparative reference (compact R1). The ionic conductivity of the obtained green compact R1 was 7.5×10 ⁻⁹ S/cm at 27° C. and 7.5×10 ⁻⁸ S/cm at 60° C.

In the table below, in the reduced two-body distribution function G(r) obtained from the X-ray total scattering measurement as described above, the first peak whose peak top is located in the range where r is 1.43 ± 0.2 Å, and , there is a second peak whose peak top is located in a range where r is 2.40±0.2 Å, and G(r) at the peak top of the first peak and G(r) at the peak top of the second peak are 1. When the value exceeds .0, the "Short distance G(r)" column is marked as "A", and in other cases, it is marked as "B".
In addition, in Reference Examples 1 to 5 and Reference Examples 9 to 13 shown in the table below, the value of G(r) at the top of the first peak was 1.2 or more.
In addition, in the above reduced two-body distribution function G(r), if the absolute value of G(r) is less than 1.0 in the range where r is more than 5 Å and less than or equal to 10 Å, then )” column was designated as “A”, and cases where the absolute value of G(r) did not satisfy less than 1.0 were designated as “B”.
Further, as a result of the X-ray diffraction measurement using the CuKα rays described above, the case where the above-mentioned X-ray diffraction characteristics were satisfied was rated as “A”, and the case where the above-mentioned X-ray diffraction characteristics were not satisfied was rated as “B”. In addition, in Reference Examples 1 to 6 shown in the table below and Reference Examples 7 to 13 described below, none of the first peak, second peak, third peak, and fourth peak are present in the X-ray diffraction pattern. Or, the intensity ratio of at least one peak among the first peak, second peak, third peak, and fourth peak was 2.0 or less.

In the table below, the "Elemental analysis" column shows the relative values of the composition of the solid electrolyte (I) obtained in each reference example and the lithium-containing oxide in each comparative reference example, with the B content being "4.00". represents the molar amount of each element.
In the table below, a blank column means that the corresponding element is not contained.

In the table below, "percentage of full width at half maximum (%)", "coefficient of determination", and "mass reduction rate (%)" are as explained in the above description of Reference Example 1.

In the table below, "area intensity ratio" is the ratio of the area intensity of the second peak to the area intensity of the first peak in the solid-state ⁷ Li-NMR measurement described above, and the evaluation results based on the following criteria are described. <Standard for ratio of area intensity>
A: When the area intensity ratio is 15% or more B: When the area intensity ratio is 0.5% or more and less than 15% C: When the area intensity ratio is less than 0.5%

In the table below, the "maximum absorption intensity ratio" column indicates whether the above-mentioned infrared absorption spectrum characteristics are satisfied, and is [maximum absorption intensity in the wave number region of 3000 to 3500 cm ^-1 ]/[800 to 1600 cm ^-1 wave number region] is 0.20 or more, it is shown as "A", and less than 0.20 is shown as "B".
In the table below, "-" means that no measured value is shown.

As shown in the table above, solid electrolytes (I)-1, (I)-2, (I)-3, (I)-4, (I)-5 and (I)-6 of Reference Examples 1 to 6 It can be seen that it has desired characteristics or physical properties and is excellent in ionic conductivity. Furthermore, from the results of elemental analysis, it was confirmed that in Reference Examples 3 to 6, the content of Li in the solid electrolyte was higher. In Reference Examples 3 to 6, an aqueous dispersion containing a mechanically milled lithium-containing oxide and an aqueous solution containing a lithium salt were mixed (method 3 in step 2B described above), and the lithium salt was mixed with an aqueous solution containing a lithium salt. It is presumed that more Li could be mixed, and as a result, the amount of Li incorporated into the solid electrolyte increased. It was also found that in Reference Examples 3, 4, and 5 in which LiFSI was used as the lithium salt, the ionic conductivity was further improved. This is presumed to be because Li with high mobility is included in the increased Li.

<Effect of water in solid electrolyte>
The green compact (pellet) of solid electrolyte (I)-3 obtained in Reference Example 3 (10 mmφ, 0.9 mmt (thickness)) was vacuum-dried at 27°C under 60 MPa restraint, and the pressure relative to the vacuum drying time was The changes and ionic conductivity were investigated. Note that the method for producing the green compact and the evaluation of ionic conductivity were as described above, except that the In electrode was changed to a Ti electrode. The results are shown in Table 3.

Solid electrolyte (I)-3 of Reference Example 3 has a strong absorption intensity derived from the O-H stretching peak in the wave number region of 3000 to 3500 cm ^-1 in the infrared absorption spectrum, so it contains a large number of OH groups and water. is thought to exist. Regarding water, the existence of free water and bound water is presumed. In the above, by vacuum drying, the pellets were first dried under conditions that are considered to volatilize from free water, and then the pellets were further dried under strict drying conditions, and the ionic conductivity at each stage was evaluated.

As shown in the table above, the drying time was 5 minutes, the pressure was 200 Pa, and the free water was considered to be in a vaporized state, but the ionic conductivity was a high value of 3.8 × 10 ^-3 S/cm. Even at a drying time of 1080 minutes and a pressure of 15 Pa, the ionic conductivity was 5.7×10 ⁻⁴ S/cm. This result indicates that bound water other than free water exists and contributes to ionic conductivity.

[Reference Example 7: Production according to the above steps 1B to 3B and method 3]
In the same manner as in the preparation of Dispersion 1 in Reference Example 3 above, Dispersion 9 having a concentration of lithium-containing oxide fines of 42% by mass was obtained.
Next, 7.12 g of LiTFSI (chemical formula: Li(F ₃ CSO ₂ ) 2 ) ₂ N as a lithium salt was added to water to a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 10. Ta.
The obtained dispersion liquid 9 and solution 10 were mixed and stirred and mixed using a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum dried at 40° C. and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-7. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were conducted in the atmosphere in the same manner as in Reference Example 1 using solid electrolyte (I)-7. The results are summarized in the table below.

[Reference example 8]
Solid electrolyte (I)-8 was obtained in the same manner as in Reference Example 7, except that the contents of water and LiTFSI in the obtained solid electrolyte (I) were changed to the amounts listed in the table below. In the same manner as Reference Example 1, various evaluations were carried out under the atmosphere. The results are summarized in the table below.

[Reference Examples 9 to 13]
A solid electrolyte (I) was prepared in the same manner as in Reference Example 7, except that LiTFSI was changed to LiFSI, and the contents of water and LiFSI in the obtained solid electrolyte (I) were changed to the amounts listed in the table below. )-9 to (I)-13 were obtained, and various evaluations were conducted in the same manner as in Reference Example 1 under air. The results are summarized in the table below. However, in Reference Example 13, the powder obtained by vacuum drying was immediately used and the evaluation was conducted in the atmosphere.

In the table below, the "Lithium-containing oxide fines" column, the "Lithium salt" column, and the "Water" column represent relative molar ratios. For example, in Reference Example 7, the molar ratio of the lithium salt to the fine lithium-containing oxide is 1, and the molar ratio of water to the fine lithium-containing oxide is 11. In addition, the said molar ratio was calculated by the following method.
For the analysis of each element, lithium and boron were quantitatively analyzed by ICP-OES, fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC), and for N, the analytical mass of sulfur was determined by considering the atomic weight of each element in Li salt. Regarding O, the analyzed mass of elements other than O was added up and calculated as the difference from the total amount of solid electrolyte. In addition, in Reference Examples 7 and 8, the carbon content was estimated from the analytical mass of sulfur in consideration of each atomic weight in the lithium salt. The molar ratio between the lithium-containing oxide fines and the lithium salt in the solid electrolyte was calculated from the molar ratio of an element (for example, B) found only in the lithium-containing oxide fines and an element found only in the lithium salt. In addition, the molar ratio of lithium-containing oxide fines to water is calculated by subtracting the molar ratio of O contained in lithium-containing oxide fines and lithium salt from the molar ratio of O in the solid electrolyte. The molar amount of derived O was calculated and calculated using the obtained molar amount of O derived from water and the molar amount of fine particles of the lithium-containing oxide.

Furthermore, based on the molar amounts and molecular weights listed in Table 4, the content (mass %) of each component in the solid electrolyte (I) was calculated. The results are shown in Table A below.

As shown in the table above, the solid electrolyte of each reference example satisfied the composition specified in Claim 1 of the present application, had desired characteristics or physical properties, and exhibited excellent ionic conductivity.

[Production Example 1] Production of a coated secondary battery <Preparation of fine particles of lithium-containing oxide>
Put 45 g of powdered Li ₂ B ₄ O ₇ crystals (LBO powder) (manufactured by Rare Metallic), 770 g of zirconia beads, and 3 mL of water into a 500 mL zirconia pot, and add a Teflon (registered trademark) ring and a zirconia pot. It was sealed with a lid. This was ball milled at 300 rpm (revolutions per minute) for 45 hours using a planetary ball milling device (P-7, manufactured by Fritsch) to pulverize the LBO powder and obtain fine particles of lithium-containing oxide. Ta.

<Preparation of solid electrolyte slurry 1: Preparation of solid electrolyte (I) by the above steps 1B to 3B and method 1>
10 g of the above lithium-containing oxide fines, 15 g of water, and 11 g of LiFSI were mixed in a beaker and subjected to ultrasonic treatment for 30 minutes using an ultrasonic cleaner to obtain a dispersion. This dispersion was further stirred for 30 minutes using a magnetic stirrer to obtain solid electrolyte slurry 1.
This solid electrolyte slurry 1 was vacuum dried at 40° C. and 20 Pa for 15 hours to obtain a powder. When the obtained powder was stored in a desiccator (humidity 5%) for several days and then analyzed in the atmosphere, it was confirmed that it had the above-mentioned X-ray diffraction characteristics and was in an amorphous state. Further, when the ionic conductivity was measured using the method described above, it was found to be 4.5×10 ⁻³ S/cm. Further, the ratio of the LiFSI content to the content of the lithium-containing oxide was 1 in molar ratio, and the ratio of the water content was 9 in molar ratio. Regarding the elemental composition, Li=3, B=4, O=20, F=2, S=2, and N=1.

<Preparation of solid electrolyte slurry 2: Preparation of solid electrolyte (I) by the above steps 1B to 3B and method 1>
10 g of the above lithium-containing oxide fines, 15 g of water, and 17 g of LiTFSI were mixed in a beaker and subjected to ultrasonic treatment for 30 minutes using an ultrasonic cleaner to obtain a dispersion. This dispersion was further stirred for 30 minutes using a magnetic stirrer to obtain solid electrolyte slurry 2.
This solid electrolyte slurry 2 was vacuum dried at 40° C. and 20 Pa for 15 hours to obtain a powder. When the obtained powder was stored in a desiccator (humidity 5%) for several days and then analyzed in the atmosphere, it was confirmed that it had the above-mentioned X-ray diffraction characteristics and was in an amorphous state. Further, when the ionic conductivity was measured using the method described above, it was found to be 7.0×10 ⁻⁴ S/cm. Further, the ratio of the LiTFSI content to the content of the lithium-containing oxide was 1 in molar ratio, and the ratio of the water content was 10 in molar ratio. Regarding the elemental composition, Li=3, B=4, O=21, F=6, S=2, N=1, and C=2.

<Preparation of positive electrode slurry 1>
To 5.2 g of the above solid electrolyte slurry 1, 5.0 g of the positive electrode active material and 4.8 g of a 6% by mass aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Special Paper Co., Ltd.) as a conductive agent were added. The mixture was stirred using a magnetic stirrer for 30 minutes to obtain positive electrode slurry 1.

<Preparation of positive electrode slurry 2>
To 4.6 g of the above solid electrolyte slurry 2, 5.0 g of the positive electrode active material and 4.8 g of a 6% by mass aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Special Paper Co., Ltd.) as a conductive agent were added. The mixture was stirred using a magnetic stirrer for 30 minutes to obtain positive electrode slurry 2.

<Preparation of negative electrode slurry 1>
To 7.6 g of the above solid electrolyte slurry 1, 5.0 g of the negative electrode active material and 9.8 g of a 6% by mass aqueous dispersion of CNT (manufactured by KJ Special Paper Co., Ltd.) as a conductive agent were added, and the mixture was stirred with a magnetic stirrer. After stirring for 30 minutes, negative electrode slurry 1 was obtained.

<Preparation of negative electrode slurry 2>
To 7.0 g of the solid electrolyte slurry 2 above, 5.0 g of the negative electrode active material and 9.8 g of a 6% by mass aqueous dispersion of CNT (manufactured by KJ Special Paper Co., Ltd.) as a conductive agent were added, and the mixture was stirred with a magnetic stirrer. After stirring for 30 minutes, negative electrode slurry 2 was obtained.

<Preparation of positive electrode side laminate [solid electrolyte layer/positive electrode active material layer/Al or Ti current collector]>
The above

positive electrode slurry

1 or 2 was applied onto a 50 μm thick A4 size Al or Ti foil using a tabletop coater with an applicator gap of 100 μm and a coating speed of 30 mm/s. After being left at room temperature for 1 hour, the above

solid electrolyte slurry

1 or 2 was coated in multiple layers on the positive electrode slurry coating using a tabletop coater at an applicator gap of 200 μm and a coating speed of 90 mm/s. The multilayer coating film was dried by storing it in a desiccator at a relative humidity of 5% or less for 12 hours, and punched out into a 10 mm diameter piece using a hand punch to form a positive electrode side laminate (solid electrolyte layer/positive electrode active material layer/Al or Ti current collector). ) was obtained. Note that the thickness of the solid electrolyte layer was approximately 60 μm.

<Preparation of negative electrode side laminate [solid electrolyte layer/negative electrode active material layer/Al or Ti current collector]>
The above

negative electrode slurry

1 or 2 was applied onto a 50 μm thick A4 size Al or Ti foil using a tabletop coater with an applicator gap of 200 μm and a coating speed of 30 mm/s. After being left at room temperature for 1 hour, the

solid electrolyte slurry

1 or 2 described above was coated in multiple layers on the negative electrode slurry coating using a desktop coater at an applicator gap of 300 μm and a coating speed of 90 mm/s. The multi-layer coating film was dried by storing it in a desiccator at a relative humidity of 5% or less for 12 hours, and punched out to a diameter of 10 mm using a hand punch to form a negative electrode side laminate (solid electrolyte layer/negative electrode material layer/Al or Ti current collector). I got it. Note that the thickness of the solid electrolyte layer was approximately 60 μm.

<Production of coating type secondary battery>
Place the negative electrode side laminate obtained above on a 10 mm diameter SUS stand of an all-solid battery evaluation cell manufactured by Hosensha (product name: KP-SolidCell) with the solid electrolyte layer side facing upward, and then The positive electrode side laminate obtained above was placed on top with the solid electrolyte layer side facing down.
Next, a tube made of Teflon (registered trademark) with an inner diameter of 10.2 mm (hereinafter referred to as a Teflon tube) is inserted from the upper side (positive electrode side laminate side) of Cell A, which is made by stacking the positive electrode side laminate/negative electrode side laminate in this order. A polished Ti plate with a diameter of 10 mm and a thickness of 2 mm was inserted into the hole at the top of the Teflon tube and placed on top of the positive electrode stack, and a Ti rod with a diameter of 10 mm and a height of 2 cm was inserted and placed on the Ti plate. .
Next, a drop of silica gel for water removal was placed in the cavity of the KP-SolidCell, and the upper casing of the KP-SolidCell was fitted and sealed using a double O-ring, four-point bolts, and a wing nut. Cell A was restrained from above and below with a torque of 5 Nm (equivalent to 30 MPa) using a restraining pressure applying mechanism installed on the top of the KP-SolidCell.
Next, once open the KP-SolidCell and take out the cell A, wipe off the excess liquid component that seeped out due to the application of confining pressure, and then set the cell A in the KP-SolidCell again in the same manner as above. A confining pressure was applied with a torque of 5 Nm (equivalent to 30 MPa).
Thereafter, the moisture inside the cell A was sufficiently removed by freeze-vacuum drying for 2 hours with the upper lid open. After taking out the KP-SolidCell from the vacuum dryer, the upper lid was closed and sealed via a double O-ring. After leaving it at room temperature for 40 hours, the whole cell was heated at 80° C. for 2 hours to produce a coated secondary battery. In this coating type secondary battery, the thickness of the positive electrode active material layer was 80 μm, the thickness of the solid electrolyte layer was 120 μm, and the thickness of the negative electrode active material layer was 100 μm.
Table 6 summarizes the configuration of the secondary battery and the evaluation results of the charge/discharge test.

(Charge/discharge test)
A confining pressure (30 MPa) was applied to the coated secondary battery obtained above, and the following procedure was carried out under a temperature condition of 27°C using 580-NOHFR (trade name) manufactured by Toyo Technica as a charging/discharging device. Charging and discharging were repeated under the following conditions.
Charging is performed at a constant current value I _β until the desired battery voltage E _α is reached, and after the desired battery voltage E _α is reached, the voltage is kept constant (E _α ) and the current value becomes 2.4C. I went to In addition, the battery voltage E _α is determined according to the value of the average battery voltage listed in the table below. When the average battery voltage is 1.85V, E _α is set to 2.3V, and when the average battery voltage is 2.35V, E α is set to 2.3V. E _α was set to 2.8V, and E _α was set to 3.4V when the average battery voltage was 3.15V.
After charging, the circuit was opened and left for 10 minutes, and then discharged at a constant current value _Iβ until the battery voltage reached 1.5V.
The charging and discharging up to this point was defined as one cycle.
After discharging, the circuit was opened and left for 10 minutes, and then the next charge was started, and charging and discharging were repeated under the same conditions.
In addition, in the above charging and discharging, the current value I _β is set to 0.2C in the first charging and discharging cycle as battery initialization, and is set to 3C in the subsequent charging and discharging. A cycle test was conducted.

Further, the discharge capacity retention rate (%) was calculated by the following formula and evaluated based on the following evaluation criteria.
Discharge capacity retention rate (%) = (discharge capacity after 50 cycles of 3C charge/discharge/discharge capacity after 10 cycles of 3C charge/discharge) x 100

- Evaluation criteria -
A: The discharge capacity retention rate is 90% or more.
B: The discharge capacity retention rate is 80% or more and less than 90%.
C: The discharge capacity retention rate is 70% or more and less than 80%.
D: Discharge capacity retention rate is less than 70%.

<Table notes>
In the following description, the value written after each active material is the discharge potential on a Li basis.
(Cathode active material)
LFP: LiFePO ₄ , 3.4V, volume average particle diameter: 10 μm
LCO: LiCoO ₂ , 3.9V, volume average particle diameter: 12 μm
NMC: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , 3.9V, volume average particle diameter: 10 μm
LNLCO: LCO with ₃ coated layers of LiNbO, 3.9V, volume average particle size: 12 μm
LNMO: LiNi _0.5 Mn _1.5 O ₄ , 4.7 V, volume average particle diameter: 5 μm
(Negative electrode active material)
LTO: Li ₄ Ti ₅ O ₁₂ , 1.55V, volume average particle diameter: 7 μm
cLTO: LTO with carbon coat layer, 1.55V, volume average particle diameter: 10 μm
TNO: TiNb ₂ O ₇ , 1.55V, volume average particle diameter: 10 μm

The

number

1 or 2 in the column of positive electrode, negative electrode, and SE layer (solid electrolyte layer) of the slurry indicates the

number

1 or 2 of the positive electrode slurry, negative electrode slurry, and solid electrolyte slurry, respectively, used to form each layer.
The active materials described in the positive electrode and negative electrode columns indicate the types of active materials used in the positive electrode slurry and negative electrode slurry used to form each layer, respectively.
The average battery voltage (unit: V) is a value obtained by subtracting the Li-based discharge potential of the negative electrode active material from the Li-based discharge potential of the positive electrode active material.
The theoretical capacity (unit: mAh/g) is a value calculated from the theoretical discharge capacity of the active material.

From Table 6 above, it was found that the secondary battery of the present invention having a solid electrolyte layer containing solid electrolyte (I) achieved a wide potential window of 1.3 V or more and exhibited excellent charge-discharge cycle characteristics.

[Production Example 2] Production of a compacted powder type secondary battery <Preparation of solid electrolyte powder 1: Production of solid electrolyte (I) by the above steps 1B to 3B and method 1>
10 g of the lithium-containing oxide fines prepared in Production Example 1 above, 15 g of water, and 11 g of LiFSI were mixed in a beaker, and the mixture was sonicated (dispersed) for 30 minutes using an ultrasonic cleaner. After that, the mixture was further stirred and dispersed using a magnetic stirrer for 30 minutes to obtain a solid electrolyte slurry. Solid electrolyte powder 1 was obtained by freeze-vacuum drying the obtained slurry at 40° C. and 10 Pa for 12 hours.

<Preparation of positive electrode composite powder 1>
100 mg of the solid electrolyte powder 1, 150 mg of the positive electrode active material, and 3 mg of the conductive agent carbon black (manufactured by Denka Corporation) were mixed in a mortar to obtain a positive electrode composite powder 1.

<Preparation of negative electrode composite powder 1>
60 mg of the solid electrolyte powder 1, 120 mg of the negative electrode active material, and 3 mg of the conductive agent carbon black (manufactured by Denka Corporation) were mixed in a mortar to obtain negative electrode composite powder 1.

<Manufacture of compacted powder body>
A 10 mm diameter SUS punch (short length) was inserted into the hole at the bottom of a SUS tube for powder compaction (inner diameter 10 mm), and the solid electrolyte powder 1 was poured into the hole at the top of the SUS tube and leveled. A SUS punch (long length) was inserted through the upper hole, pressurized at 50 MPa for 10 seconds using a hydraulic press, the pressure was released, and the SUS punch (long length) was pulled out from the SUS pipe.
Subsequently, negative electrode composite powder 1 was introduced through the hole at the top of the SUS tube and leveled on the compacted powder layer of solid electrolyte powder 1. Insert the SUS punch (long) through the hole at the top, apply pressure at 50 MPa for 10 seconds using a hydraulic press, release the pressure, and then insert the SUS punch (long) / SUS pipe / SUS punch (short) into the upper part. ) was on the bottom side, and then turned it upside down so that the SUS punch (short length) was on the top side, and then the SUS punch (short length) was removed from the SUS tube.
Positive electrode composite powder 1 was put into the hole at the top of the SUS tube and leveled on the compacted powder layer of solid electrolyte powder 1. Insert a SUS punch (short length) into the upper hole, apply pressure at 200 MPa for 10 seconds using a hydraulic press, release the pressure, and use a puncher to remove the compacted powder layer of negative electrode composite powder 1. The compacted powder body in which the compacted powder layer of solid electrolyte powder 1/the compacted powder layer of positive electrode composite powder 1 were laminated in this order was taken out, and the excess liquid component that had seeped out was wiped off.

<Production of powder-type secondary battery>
Place a 50 μm thick Al foil (negative electrode side current collector) punched to a diameter of 10 mm on a 10 mm diameter SUS stand of an all-solid battery evaluation cell (product name: KP-SolidCell) manufactured by Hosensha, and place it on top of it. The powder compact obtained above was placed with the negative electrode side facing down. Insert a Teflon tube with an inner diameter of 10.2 mm, insert a 50 μm thick Al foil (positive electrode side current collector) punched to a diameter of 10 mm through the hole at the top of the Teflon tube, and place a polished Ti plate with a diameter of 10 mm and a thickness of 2 mm on top of it. A Ti rod with a diameter of 10 mm and a height of 2 cm was further inserted and placed on the Ti plate.
Next, a drop of silica gel for water removal was placed in the cavity of the KP-SolidCell, and the upper casing of the KP-SolidCell was fitted and sealed using a double O-ring, four-point bolts, and a wing nut. Cell B was restrained from above and below with a torque of 9 Nm (equivalent to 60 MPa) using a restraining pressure applying mechanism installed on the top of the KP-SolidCell. Here, the cell B means a cell formed by stacking a negative electrode side current collector/a compacted powder body/a positive electrode side current collector in this order.
Next, once open the KP-SolidCell and take out the cell B, wipe off the excess liquid component that seeped out due to the application of confining pressure, and then set the cell B in the KP-SolidCell again in the same manner as above. A confining pressure was applied with a torque of 9 Nm (equivalent to 60 MPa).
Thereafter, with the upper lid open, the cell B was subjected to freeze-vacuum drying for 2 hours to sufficiently remove moisture inside the cell B. After taking out the KP-SolidCell from the vacuum dryer, the upper lid was closed and sealed via a double O-ring. After leaving it at room temperature for 40 hours, the whole cell was heated at 80° C. for 2 hours to produce a powder-type secondary battery. In this compacted powder type secondary battery, the thickness of the positive electrode active material layer was 100 μm, the thickness of the solid electrolyte layer was 200 μm, and the thickness of the negative electrode active material layer was 100 μm.
Table 7 summarizes the configuration of the secondary battery and the evaluation results of the charge/discharge test.

(Charge/discharge test)
A confining pressure (60 MPa) was applied to the powder-type secondary battery obtained above, and the following procedure was performed under the temperature condition of 27°C using 580-NOHFR (trade name) manufactured by Toyo Technica as a charging/discharging device. Charging and discharging were repeated under these conditions.
Charging was performed at a constant current value _Iβ until the battery voltage reached 2.8V, and after reaching 2.8V, the voltage was kept constant (2.8V) and continued until the current value reached 2.4C. Ta.
After charging, the circuit was opened and left for 10 minutes, and then discharged at a constant current value _Iβ until the battery voltage reached 1.5V.
The charging and discharging up to this point was defined as one cycle.
After discharging, the circuit was opened and left for 10 minutes, and then the next charge was started, and charging and discharging were repeated under the same conditions.
In addition, in the above charging and discharging, the current value I _β is set to 0.2C in the first charging and discharging cycle as battery initialization, and is set to 3C in the subsequent charging and discharging. A cycle test was conducted.

Further, the discharge capacity retention rate (%) was calculated by the following formula and evaluated based on the following evaluation criteria.
Discharge capacity retention rate (%) = (discharge capacity after 50 cycles of 3C charge/discharge/discharge capacity after 10 cycles of 3C charge/discharge)

- Evaluation criteria -
A: The discharge capacity retention rate is 90% or more.
B: The discharge capacity retention rate is 80% or more and less than 90%.
C: The discharge capacity retention rate is 70% or more and less than 80%.
D: Discharge capacity retention rate is less than 70%.

<Table notes>
Each active material, average battery voltage, and theoretical capacity are as described in the notes of Table 6 above.

From Table 7 above, it was found that the secondary battery of the present invention having a solid electrolyte layer containing solid electrolyte (I) achieved a wide potential window of 1.3 V or more and exhibited excellent charge-discharge cycle characteristics.

Although the invention has been described in conjunction with embodiments thereof, we do not intend to limit our invention in any detail in the description unless otherwise specified and contrary to the spirit and scope of the invention as set forth in the appended claims. I believe that it should be interpreted broadly without any restrictions.

This application claims priority based on Japanese Patent Application No. 2022-089964, which was filed in Japan on June 1, 2022, and the contents thereof are incorporated herein by reference. Incorporate it as a part.

1 Negative electrode current collector 2 Negative electrode active material layer 3 Solid electrolyte layer 4 Positive electrode active material layer 5 Positive electrode current collector 6 Operating part 10 All-solid-state lithium ion secondary battery

Claims

An all-solid lithium ion secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order,
The solid electrolyte layer includes a solid electrolyte containing a lithium-containing oxide containing Li, B, and O, a lithium salt, and water, and in the solid electrolyte, the lithium salt is The value of the ratio of the content of is 0.001 to 1.5 in molar ratio, the value of the ratio of the content of water is 1 to 12 in molar ratio,
An all-solid-state lithium ion secondary battery, wherein a difference in discharge potential based on Li between a positive electrode active material contained in the positive electrode layer and a negative electrode active material contained in the negative electrode layer is 1.3 V or more.
The all-solid-state lithium ion secondary battery according to claim 1, wherein the lithium-containing oxide includes Li2 +xB4 + yO7+z .
However, -0.3<x<0.3, -0.3<y<0.3, and -0.3<z<0.3.
The positive electrode active material is LiCoO 2 , LiNiO 2 , LiNi 0.85 Co 0.10 Al 0.05 O 2 , LiNi 1/3 Mn 1/3 Co 1/3 O 2 , Li 2 MnO 3 -LiNiMnCoO 2 , Containing at least one of LiMn2O4 , LiNi0.5Mn1.5O4 , LiFePO4 , LiMnPO4 , LiCoPO4 , Li2CoP2O7 and LiNiPO4 ,
The negative electrode active material contains at least one of Li 4 Ti 5 O 12 , TiNb 2 O 7 , Fe 3 O 4 , graphite, hard carbon, Si, SiO, Sn, Al, and metal Li,
The all-solid-state lithium ion secondary battery according to claim 1 or 2, wherein a difference in discharge potential between the positive electrode active material and the negative electrode active material based on Li is 1.3 V or more.
The all-solid-state lithium ion secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material has a discharge potential of 2.5 V or less based on Li.
4 . The negative electrode active material is at least one of Li 4 Ti 5 O 12 , TiNb 2 O 7 , Fe 3 O 4 , graphite, hard carbon, Si, SiO, Sn, Al, and metal Li. The all-solid-state lithium ion secondary battery described in .
The all-solid-state lithium ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material has a discharge potential of 3.8 V or more based on Li.
The positive electrode active material is selected from LiCoO 2 , Li 2 MnO 3 -LiNiMnCoO 2 , LiMn 2 O 4 , LiNi 0.5 Mn 1.5 O 4 , LiMnPO 4 , LiCoPO 4 , Li 2 CoP 2 O 7 and LiNiPO 4 . The all-solid-state lithium ion secondary battery according to claim 6, which is at least one type of.
The all-solid lithium ion battery according to any one of claims 1 to 7, wherein the manufacturing of the all-solid lithium ion secondary battery includes forming the solid electrolyte layer by applying a dispersion of the solid electrolyte. A method for manufacturing a secondary battery.
The all-solid lithium according to any one of claims 1 to 7, wherein the manufacturing of the all-solid lithium ion secondary battery includes forming the solid electrolyte layer by applying pressure to the solid electrolyte powder. A method for manufacturing an ion secondary battery.