Wound-type all-solid-state lithium-ion secondary battery and method for manufacturing the wound-type all-solid-state lithium-ion secondary battery

Abstract

The present invention provides a wound all-solid-state lithium ion secondary battery that is obtained by winding a multilayer body, in which a positive electrode layer, a solid electrolyte layer and a negative electrode layer are sequentially arranged in this order, around a core material, wherein: the solid electrolyte layer contains a solid electrolyte that is in an amorphous state, while containing a lithium salt and a lithium-containing oxide that contains Li, B and O; and the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte in an amorphous state is 0.001 to 1.5 in terms of the molar ratio. The present invention also provides a method for producing this wound all-solid-state lithium ion secondary battery.

Description

[Technical Field]

[0001] The present invention relates to a wound-type all-solid-state lithium ion secondary battery and a method for manufacturing the wound-type all-solid-state lithium ion secondary battery. [Background technology]

[0002] Conventionally, lithium-ion secondary batteries have used liquid electrolytes with high ionic conductivity. However, liquid electrolytes are flammable, posing safety concerns. Furthermore, the liquid nature of these electrolytes makes them difficult to compact, and as batteries become larger, limitations on capacity become an issue. On the other hand, all-solid-state lithium-ion secondary batteries are one of the next-generation batteries that can solve these problems. The basic structure of an all-solid-state lithium-ion secondary battery is shown in Figure 1. Viewed from the negative electrode side, an all-solid-state lithium-ion secondary battery 10 has 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. Each layer is in contact with each other and has an adjacent structure. By adopting such a structure, electrons (e - ) is supplied to the solid electrolyte layer 3, and lithium ions (Li + On the other hand, during discharge, the lithium ions (Li + ) passes through the solid electrolyte layer 3 and returns to the positive electrode side, supplying electrons to the operating part 6. In the illustrated example, a light bulb is used as a model for the operating part 6, and it is lit by discharge.

[0003] As described above, in all-solid-state lithium-ion secondary batteries, the solid electrolyte layer is required to have excellent lithium ion conductivity 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. Because sulfide-based solid electrolytes are soft and plastically deformable, the particles bond together simply by being pressed. Therefore, sulfide-based solid electrolytes have low interfacial resistance between particles and excellent ionic conductivity. However, sulfide-based solid electrolytes have the problem of reacting with water to produce toxic hydrogen sulfide. In contrast, oxide-based solid electrolytes have the advantage of being highly safe. However, oxide-based solid electrolytes are hard and resistant to plastic deformation. In order to increase the interparticle adhesion of oxide-based solid electrolytes, a high-temperature sintering process is required, which is constrained by factors such as battery production efficiency and energy costs. For example, Patent Document 1 discloses a solid electrolyte formed from a lithium-containing oxide with a specific elemental composition, and describes that this solid electrolyte exhibits high ionic conductivity. However, in order to use this lithium-containing oxide as a solid electrolyte sheet, a high-temperature sintering process is required. As a technique for addressing this problem, for example, Patent Document 2 discloses a technique for reducing the lithium ion conductivity at 25°C to 1.0 × 10 -6 Patent Document 2 describes a composite containing a lithium compound having a specific profile of the reduced pair distribution function G(r) obtained from X-ray total scattering measurement and lithium tetraborate. According to the technology described in Patent Document 2, although this composite is composed of a lithium-containing oxide, the lithium tetraborate plastically deforms between the lithium compounds to connect them, and therefore, this composite can be formed into a lithium ion conductor exhibiting good lithium ion conductivity by pressure treatment without being subjected to high-temperature sintering treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-052755 [Patent Document 2] International Publication No. 2021 / 193204 Summary of the Invention [Problem to be solved by the invention]

[0005] The composite described in Patent Document 2 is composed of a lithium-containing oxide, yet is soft, and can ensure interparticle bonding without being subjected to a sintering treatment or without incorporating a binder such as an organic polymer, thereby possessing properties that have not been achieved by previous oxide-based solid electrolytes. However, as the inventors continued their studies, they found that the lithium ion conductivity is currently insufficient for practical use as a solid electrolyte layer in all-solid-state lithium ion secondary batteries, and that there is room for improvement for practical use.

[0006] For practical use, all-solid-state lithium-ion secondary batteries usually need to conform to standardized shapes and volumes. To achieve high capacity or high output within these constraints, strip-shaped positive and negative electrodes are spirally wound with a solid electrolyte layer interposed between them to increase the electrode area. In such wound-type all-solid-state lithium-ion secondary batteries, the solid electrolyte layer is required to have high flexibility and adhesiveness.

[0007] An object of the present invention is to provide a wound-type all-solid-state lithium ion secondary battery that uses a lithium-containing oxide in a solid electrolyte layer, and that the solid electrolyte layer has excellent interparticle binding properties, high lithium ion conductivity, and excellent safety even without being subjected to high-temperature sintering treatment or even without incorporating a binder such as an organic polymer, and that is less likely to crack during the winding process or in the wound state, and a method for producing the same. [Means for solving the problem]

[0008] The object of the present invention has been achieved by the following means.

[0009] [1] A wound-type all-solid-state lithium ion secondary battery is formed by winding a laminate, which is formed by arranging a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order, around a core material, The solid electrolyte layer includes an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt, and in this amorphous solid electrolyte, the ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in terms of molar ratio. [2] [1] The wound all-solid-state lithium ion secondary battery according to [1], wherein the ratio of the water content to the lithium-containing oxide content in the amorphous solid electrolyte is 12 or less in molar ratio. [3] [3] The wound all-solid-state lithium ion secondary battery according to [2], wherein the ratio of the content of the water to the content of the lithium-containing oxide in the amorphous solid electrolyte is 1 to 12 in terms of molar ratio. [4] The lithium-containing oxide is Li 2+x B 4+y O 7+z The wound-type all-solid-state lithium-ion secondary battery according to any one of [1] to [3], comprising: However, -0.3 <x<0.3、-0.3<y<0.3、-0.3<z<0.3である。 [5] The wound-type all-solid-state lithium ion secondary battery according to any one of [1] to [4], wherein the lithium salt is represented by the following formula (1): Equation (1) LiN(R f1 SO2)(R f2 SO2) In the formula, R f1 and R f2 each independently represents a halogen atom or a perfluoroalkyl group. [6] [5] The wound-type all-solid-state lithium-ion secondary battery according to any one of [1] to [5], wherein, in the amorphous solid electrolyte, when the molar amount of B is 4.00, the molar amount of Li is 1.58 to 3.49, the molar amount of O is 6.23 to 25.00, and the molar amounts of elements other than B, Li, and O are each 0.001 to 10.00. [7] The wound-type all-solid-state lithium-ion secondary battery according to any one of [1] to [6], wherein the lithium-containing oxide is subjected to mechanical milling treatment. [8] A wound-type all-solid-state lithium ion secondary battery is formed by winding a laminate, which is formed by arranging a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order, around a core material, The solid electrolyte layer contains an amorphous solid electrolyte containing Li, B, and O, and when the molar amount of B in this amorphous solid electrolyte is 4.00, the molar amount of Li is 1.58 to 3.49, the molar amount of O is 6.23 to 25.00, and the molar amounts of elements other than Li, B, and O are each 0.001 to 10.00. [9] [9] The method for producing a wound-type all-solid-state lithium ion secondary battery according to any one of [1] to [8], comprising forming the laminate under conditions in which the solid electrolyte layer comes into contact with water.

[0010] In the present invention and the specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. [Effects of the Invention]

[0011] The wound-type all-solid-state lithium-ion secondary battery of the present invention is a wound-type all-solid-state lithium-ion secondary battery that uses a lithium-containing oxide in a solid electrolyte layer, and the solid electrolyte layer has excellent interparticle binding properties, high lithium ion conductivity, excellent safety, and is less likely to crack in a wound state, even without being subjected to high-temperature sintering treatment or even without incorporating a binder such as an organic polymer. Furthermore, the manufacturing method for the wound-type all-solid-state lithium-ion secondary battery of the present invention is a manufacturing method suitable for obtaining the wound-type all-solid-state lithium-ion secondary battery of the present invention. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the configuration of an all-solid-state lithium ion secondary battery. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a preferred embodiment of the wound-type all-solid-state lithium ion secondary battery of the present invention, and an enlarged cross-sectional view of part A in FIG. [Figure 3] FIG. 3 is a diagram showing an example of an X-ray diffraction pattern for illustrating the X-ray diffraction characteristics of the solid electrolyte (I) used in the present invention. [Figure 4] FIG. 4 is a diagram showing an example of the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement of the solid electrolyte (I) used in the present invention. [Figure 5] FIG. 5 shows an example of a spectrum obtained when solid-state 7Li-NMR measurement of the solid electrolyte (I) used in the present invention is carried out at 20° C. or 120° C. [Figure 6] FIG. 6 shows an example of a spectrum obtained when solid-state 7Li-NMR measurement of lithium tetraborate crystal is carried out at 20° C. or 120° C. [Figure 7] FIG. 7 is a diagram showing an example of a spectrum obtained when solid-state 7Li-NMR measurement of the solid electrolyte (I) used in the present invention is carried out at 20°C. [Figure 8] FIG. 8 is a diagram in which the peaks shown in FIG. 7 are separated into waveforms. [Figure 9] FIG. 9 is a diagram showing an example of the Raman spectrum of the solid electrolyte (I) used in the present invention. [Figure 10] FIG. 10 is a diagram showing the Raman spectrum of lithium tetraborate crystal. [Figure 11] FIG. 11 is a graph showing the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of the solid electrolyte (I)-1 prepared in Reference Example 1. [Figure 12] FIG. 12 shows the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of powdered Li2B4O7 crystal. [Figure 13] FIG. 13 shows the X-ray diffraction pattern of powdered Li2B4O7 crystals. [Figure 14] FIG. 14 is a diagram showing the X-ray diffraction pattern of the solid electrolyte (I)-2 prepared in Reference Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Wound-type all-solid-state lithium-ion secondary battery] The wound-type all-solid-state lithium ion secondary battery of the present invention (hereinafter also referred to as "secondary battery of the present invention") is a wound-type all-solid-state lithium ion secondary battery formed by winding a laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order around a core material. The solid electrolyte layer contains a solid electrolyte of a specific composition in an amorphous state, which will be described later. A preferred embodiment of the layer structure in the secondary battery of the present invention will be described with reference to the drawings. Note that the drawings show one example of an embodiment of the present invention, and the present invention is not limited to the embodiment shown in the drawings except as specified in the present invention. Furthermore, the drawings showing the battery structure are schematic diagrams for facilitating understanding of the present invention, and the arrangement, size, relative size, etc. of each component do not directly represent the actual relationship.

[0014] Fig. 2 is a cross-sectional view showing a preferred embodiment of the secondary battery of the present invention. As shown in Fig. 2, a wound (cylindrical) all-solid-state lithium-ion secondary battery 30 includes a laminate 21, which is formed by arranging a negative electrode current collector 21b, a negative electrode active material layer 21c, a solid electrolyte layer 21d, a positive electrode active material layer 21e, and a positive electrode current collector 21f in this order, and which is spirally wound around a core material (axial center) 22. In the embodiment shown in Fig. 2, the laminate 21 has a separator layer 21a on the side of the negative electrode current collector opposite to the solid electrolyte layer side. Therefore, when the laminate 21 is spirally wound around the core material 22, the separator 21a is also disposed on the outside of the positive electrode current collector 21f. That is, the configuration shown in FIG. 2 is a multi-layered configuration in which a battery element in which a negative electrode current collector 21b, a negative electrode active material layer 21c, a solid electrolyte layer 21d, a positive electrode active material layer 21e, and a positive electrode current collector 21f are stacked in this order is interposed between separator layers 21a. The wound-type all-solid-state lithium ion secondary battery 30 also includes a battery exterior body 23 that serves as a battery container into which the laminate 21 is inserted. In addition, the positive electrode current collector 21f of the laminate 21 is connected to the battery positive electrode 26 via an electrically connecting positive electrode tab 25, and the negative electrode current collector 21b is connected to the battery negative electrode 28 via an electrically connecting negative electrode tab 27. Therefore, based on the battery configuration shown in FIG. 2, the secondary battery of the present invention, including the separator layer, can be more specifically specified as follows, for example.

[0015] A wound-type all-solid-state lithium-ion secondary battery is obtained by winding a laminate around a core material, the laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order, and a separator layer arranged on the side of the positive electrode layer and / or the negative electrode layer opposite to the solid electrolyte layer side.

[0016] As described above, FIG. 2 shows a structure in which the battery element is multi-layered with the separator layer 21a interposed therebetween. However, the secondary battery of the present invention can also be configured without the separator layer 21a. In this case, the secondary battery of the present invention can function, for example, as a bipolar secondary battery. A bipolar secondary battery has a structure in which a positive electrode active material layer is disposed on one surface of a single current collector and a negative electrode active material layer is disposed on the side of the current collector opposite the positive electrode active material layer, and the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer are laminated in this order. This battery configuration allows for compact size and large current. In the present invention, when the term "a wound-type all-solid-state lithium ion secondary battery is simply used, which is obtained by winding a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order around a core material," it means that both a battery configuration in which a separator layer is not arranged (for example, a bipolar type) and a battery configuration in which a separator layer is arranged as shown in FIG. 2 are included.

[0017] The size of the secondary battery of the present invention is not particularly limited and is set appropriately depending on the type of device, vehicle, etc. in which the battery is installed. For example, the length L in the longitudinal direction of the cylindrical shape of the laminate 21 shown in Fig. 2 can be set to 2 to 50 cm. In addition, the diameter of the core material 22 (the diameter of a circle equivalent when the cross section of the core material 22 is not circular) is preferably set to 3 to 10 mm.

[0018] Next, each layer of the secondary battery of the present invention will be described.

[0019] <Solid electrolyte layer> The solid electrolyte layer constituting the secondary battery of the present invention is a layer formed by forming a solid electrolyte of a specific composition in an amorphous state (synonymous with a non-crystalline state or an amorphous state) or a mixture of this solid electrolyte with other components into a layer. This solid electrolyte of a specific composition in an amorphous state contains a lithium-containing oxide (hereinafter also referred to as a "lithium-containing oxide") containing Li, B, and O, and a lithium salt. In this solid electrolyte, the ratio of the content of the lithium salt to the content of the lithium-containing oxide (lithium salt / lithium-containing oxide) is 0.001 to 1.5 in molar ratio. Hereinafter, the solid electrolyte of a specific composition in an amorphous state will also be referred to as a "solid electrolyte (I)." The solid electrolyte (I) is usually an inorganic solid electrolyte.

[0020] The solid electrolyte (I) is in an amorphous state and exhibits elastic properties that allow for easy plastic deformation. As a result, in a solid electrolyte layer containing the solid electrolyte (I) formed by pressure treatment or the like, adhesion between the solid electrolytes (I) and / or between the solid electrolyte (I) and other ion conductors is improved, reducing interfacial resistance and providing better ion conductivity. By using this solid electrolyte (I), a lithium ion conductor that exhibits excellent lithium ion conductivity can be formed by pressure treatment or the like, even though it is a highly safe oxide-based solid electrolyte, without being subjected to high-temperature sintering treatment.

[0021] The solid electrolyte (I) also preferably contains at least bound water. In this case, the molar ratio of the water content to the lithium-containing oxide content in the solid electrolyte (I) is preferably 12 or less, more preferably 1 to 12, even more preferably 2 to 12, and still more preferably 3 to 11. The molar ratio is also preferably 2 to 10, also preferably 2 to 8, also preferably 2 to 7, and also preferably 3 to 7. The reason why the solid electrolyte (I) exhibits high lithium ion conductivity is not clear, but it is thought that in the amorphous solid electrolyte (I), a soft hydration layer is likely to form on the surface of the lithium-containing oxide, and this hydration layer contains a large amount of lithium derived from the lithium salt, resulting in higher ion conductivity. Here, in the present invention and the specification, "bound water" refers to water other than water present as free water or OH groups bound to a lithium-containing oxide. Even if the solid electrolyte (I) contains water, it is in the form of solid particles (including a state in which solid particles are bound together) and functions as a solid electrolyte for an all-solid-state lithium-ion secondary battery. That is, the solid electrolyte (I) may contain bound water that is not removed or is difficult to remove under normal drying conditions. In such a solid electrolyte (I), at least a portion of the water exists as bound water. When the solid electrolyte (I) contains water, it may contain free water as long as it functions as a solid electrolyte for an all-solid-state lithium-ion secondary battery in the form of solid particles (a state that can be handled as a powder). That is, in the present invention, the "all-solid-state lithium-ion secondary battery" also includes a form in which the solid electrolyte contains water, as long as it can be handled as solid particles (solid powder). The solid electrolyte used in the present invention, in which the ratio of the water content to the lithium-containing oxide content is 12 or less in molar ratio, is neither in a paste state nor a gel state, but in a solid particle (solid powder) state.

[0022] In the present invention, the solid electrolyte (I) being "in an amorphous state" means that it satisfies the following X-ray diffraction characteristics or the following requirement A-2 in the X-ray total scattering characteristics. That is, when at least one of the following X-ray diffraction characteristics and the following requirement A-2 in the X-ray total scattering characteristics is satisfied, the solid electrolyte (I) is in an "amorphous state."

[0023] (X-ray diffraction characteristics) In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, none of the following peaks is present: a first peak having a peak top in the diffraction angle 2θ range of 21.6 to 22.0° and a full width at half maximum of 0.65° or less, a second peak having a peak top in the diffraction angle 2θ range of 25.4 to 25.8° and a full width at half maximum of 0.65° or less, a third peak having a peak top in the diffraction angle 2θ range of 33.4 to 33.8° and a full width at half maximum of 0.65° or less, and a fourth peak having a peak top in the diffraction angle 2θ range of 34.4 to 34.8° and a full width at half maximum of 0.65° or less; or In the X-ray diffraction pattern, when at least one peak (hereinafter referred to as "peak X") among the first peak, second peak, third peak, and fourth peak is present, at least one peak among peak X has an intensity ratio of 5.0 or less as calculated by the intensity measurement method described below.

[0024] -Strength measurement method- An average intensity (Av1) is calculated over a range of +0.45° to +0.55° from the diffraction angle 2θ at the peak top of Peak X, and an average intensity (Av2) is calculated over a range of −0.55° to −0.45° from the diffraction angle 2θ at the peak top of Peak X, and an arithmetic average value of Av1 and Av2 is calculated. The ratio of the peak intensity at the peak top of Peak X to this arithmetic average value (peak intensity at the peak top of Peak X / arithmetic average value) is defined as the intensity ratio.

[0025] The X-ray diffraction characteristics will be explained in more detail. When none of the first, second, third, and fourth peaks is present in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, the solid electrolyte (I) satisfies the above X-ray diffraction characteristics and is in an amorphous state. Furthermore, when the above-mentioned peak X is present in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, if at least one peak of the peak X has an intensity ratio of 5.0 or less obtained by the above-mentioned intensity measurement method, the above-mentioned X-ray diffraction characteristics are also satisfied, and the solid electrolyte (I) is in an amorphous state. Here, the full width at half maximum (FWHM) of the peak means the peak width (°) at the point where the peak intensity is half the peak intensity at the peak top.

[0026] The above intensity measurement method will be explained in more detail with reference to FIG. FIG. 3 is a diagram showing an example of peak X appearing in a diffraction pattern obtained by X-ray diffraction measurement of solid electrolyte (I) using CuKα radiation. The diffraction pattern shown in FIG. 3 shows a specific peak whose peak top intensity is intensity 1. In the intensity measurement method, as shown in FIG. 3, the average intensity (Av1) of peak X in the range of +0.45° to +0.55° from the diffraction angle 2θ of the peak top is calculated, and the average intensity (Av2) in the range of −0.55° to −0.45° from the diffraction angle 2θ of the peak top of peak X is calculated. Next, the arithmetic mean values ​​of Av1 and Av2 are calculated, and the ratio of intensity 1 to the arithmetic mean value is determined as the intensity ratio. When the above X-ray diffraction characteristics are satisfied, this means that the solid electrolyte (I) has no or almost no crystalline structure and is in an amorphous state. In other words, the first to fourth peaks are mainly peaks derived from the crystalline structure in the solid electrolyte (e.g., the crystalline structure of lithium tetraborate), and the absence of these peaks indicates an amorphous state. Even if at least one of the first to fourth peaks is present, the intensity ratio of at least one of the peaks X present is 5.0 or less, which means that the solid electrolyte (I) is substantially free of a crystalline structure that would impair the effects of the present invention. For example, a peak derived from a specific component (e.g., a lithium salt) may overlap with any of the first to fourth peaks. However, in an amorphous solid electrolyte, all of the first to fourth peaks are usually reduced. Therefore, even if a peak derived from the specific component happens to overlap with any of the first to fourth peaks to produce a large peak, the presence of at least one peak X with an intensity ratio of a predetermined value or less indicates that the solid electrolyte (I) is in an amorphous state.

[0027] The X-ray diffraction measurement is carried out using CuKα radiation under measurement conditions of 0.01° / step and 3° / min.

[0028] In an X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, it is preferable that none of the first peak, second peak, third peak, and fourth peak is present, 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 peak X among the first peak, second peak, third peak, and fourth peak is 3.0 or less. Among these, it is more preferable that none of the first peak, second peak, third peak, and fourth peak is present, or that 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 peak among the peaks X is 2.0 or less.

[0029] 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 peak with the greatest diffracted X-ray intensity is selected as the first peak, and the above X-ray diffraction characteristics are determined. Furthermore, in the above X-ray diffraction pattern, if there are two or more peaks with a peak top in the range of 25.4 to 25.8° and a full width at half maximum of 0.65° or less, the peak with the greatest diffracted X-ray intensity is selected as the second peak, and the above X-ray diffraction characteristics are evaluated. Furthermore, in the above X-ray diffraction pattern, if there are two or more peaks with a peak top in the range of 33.4 to 33.8° and a full width at half maximum of 0.65° or less, the peak with the greatest diffracted X-ray intensity is selected as the third peak, and the above X-ray diffraction characteristics are evaluated. Furthermore, in the above X-ray diffraction pattern, if there are two or more peaks with a peak top in the range of 34.4 to 34.8° and a full width at half maximum of 0.65° or less, the peak with the greatest diffracted X-ray intensity is selected as the fourth peak, and the above X-ray diffraction characteristics are evaluated.

[0030] (X-ray total scattering characteristics) The solid electrolyte (I) preferably satisfies the following requirement A-1 in terms of X-ray total scattering characteristics. When the solid electrolyte (I) satisfies the above X-ray diffraction characteristics, the solid electrolyte (I) usually satisfies the following requirement A-2.

[0031] -Requirement A-1- In the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak whose peak top is located in the r range of 1.43±0.2 Å and a second peak whose peak top is located in the r range of 2.40±0.2 Å, and the G(r) at the peak top of the first peak exceeds 1.0, and the G(r) at the peak top of the second peak is 0.8 or more.

[0032] -Requirement A-2- In the reduced pair 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 when r is in the range of more than 5 Å and 10 Å or less.

[0033] 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 BO and BB, but has almost no long-range ordered structure, and therefore the oxide solid electrolyte itself is softer than conventional lithium-containing oxides and exhibits elastic properties that make it more susceptible to plastic deformation. As a result, it is presumed that in a layer containing the solid electrolyte (I) formed by pressure treatment or the like, adhesion between the solid electrolytes (I) and each other and / or adhesion between the solid electrolyte (I) and other ion conductors is improved, thereby reducing interfacial resistance and achieving better ion conductivity. Requirements A-1 and A-2 will be explained in more detail with reference to the drawings.

[0034] Figure 4 shows an example of the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of a solid electrolyte (I). The vertical axis of Figure 4 is the reduced pair distribution function obtained by Fourier transform of the X-ray scattering, which indicates the probability that an atom exists at a position of distance r. X-ray total scattering measurement can be performed at SPring-8 BL04B2 (accelerating voltage 61.4 keV, wavelength 0.2019 Å). The reduced pair distribution function G(r) can be obtained by converting the scattering intensity I obtained from the experiment using the following procedure. First, the scattering intensity I obs is expressed by the following formula (1). Also, the structure factor S(Q) is expressed by the following formula (2) as a function of the coherent scattering I coh is obtained by dividing by the number of atoms N and the square and product of the atomic scattering factor f. I obs =I coh +I incoh +I 蛍光 (1)

[0035]

number

[0036] The structure factor S(Q) is used for PDF (Pair Distribution Function) analysis. In the above equation (2), the required intensity is the coherent scattering I coh Incoherent scattering I incoh and X-ray fluorescence I 蛍光 is the scattering intensity I obtained by blank measurement, subtraction using the theoretical formula, and discriminator of the detector. obs can be deducted from Coherent Scattering I coh is expressed by Debye's scattering formula (Equation (3) below) (N: total number of atoms, f: atomic scattering factor, r ij :ij interatomic distance).

[0037]

number

[0038] If we focus on an arbitrary atom and the atomic density at a distance r is ρ(r), the number of atoms present within a sphere with a radius of r-r+d(r) is 4πr 2 Since the above equation (3) is expressed as the following equation (4), the above equation (3) is ρ(r)dr.

[0039]

number

[0040] If the average density of atoms is ρ0 and the above formula (4) is transformed, the following formula (5) is obtained.

[0041]

number

[0042] From the above formula (5) and formula (2), the following formula (6) is obtained.

[0043]

number

[0044] The pair distribution function g(r) is expressed by the following equation (7).

[0045]

number

[0046] From the above formulas (6) and (7), the following formula (8) is obtained.

[0047]

number

[0048] As described above, the pair distribution function can be obtained by Fourier transforming the structure factor S(Q). To facilitate observation of medium- and long-range order, the pair distribution function is transformed as G(r) = 4πr(g(r)-1) to obtain the reduced pair distribution function (Figure 4). g(r), which oscillates around 0, represents the density difference from the average density at each interatomic distance. If there is correlation at a specific interatomic distance, the average density will be higher than 1. Therefore, it reflects the element distance and coordination number corresponding to the local to medium distance. As order disappears, ρ(r) approaches the average density, and g(r) approaches 1. Therefore, in amorphous structures, as r increases, order decreases, and g(r) becomes 1, i.e., G(r) becomes 0.

[0049] In requirement A-1, as shown in FIG. 4, in the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak P1 whose peak top is located in an r range of 1.43±0.2 Å and a second peak P2 whose peak top is located in an r range of 2.40±0.2 Å, and the G(r) at the peak top of the first peak P1 is greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak P2 is 0.8 or greater (preferably greater than 1.0). In FIG. 4, 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 B (boron)-O (oxygen) interatomic distance. Also, at a position of 2.40 Å, there is a peak attributed to the B (boron)-B (boron) interatomic distance. In other words, the observation of the above two peaks (first peak and second peak) means that a periodic structure corresponding to the above two interatomic distances exists in the solid electrolyte (I).

[0050] Furthermore, in requirement A-2, the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å, as shown in Figure 4. The fact that the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å as described above means that there is almost no long-range ordered structure in the solid electrolyte (I).

[0051] In the reduced pair distribution function G(r), there may be a peak other than the first peak and the second peak in the range of r being 5 Å or less.

[0052] There is no particular limitation on the method for making the solid electrolyte (I) amorphous. For example, in preparing the solid electrolyte (I), a method is available in which a lithium-containing oxide used as a raw material is subjected to mechanical milling. This mechanical milling may be carried out in the presence of a lithium salt.

[0053] -Mechanical milling process- Mechanical milling is a process of pulverizing a sample while applying mechanical energy. Examples of mechanical milling include a ball mill, a vibration mill, a turbo mill, and a disk mill. From the viewpoint of obtaining an amorphous solid electrolyte (I) with high productivity, a ball mill is preferred. Examples of ball mills include a vibration ball mill, a rotary ball mill, and a planetary ball mill. A planetary ball mill is more preferred.

[0054] The conditions for the ball mill treatment are adjusted appropriately depending on the object to be treated. The material of the milling 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 size of the milling balls is not particularly limited, and is preferably 1 to 10 mm, more preferably 3 to 7 mm, from the viewpoint of enabling the solid electrolyte (I) to be produced with good productivity. The average particle size is determined by measuring the diameters of 50 randomly selected milling balls and calculating the arithmetic mean. When the milling balls are not spherical, the major axis is taken as the diameter. The number of milling balls is not particularly limited.

[0055] The material of the grinding pot in the ball mill treatment is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred.

[0056] The rotation speed of the ball mill treatment is not particularly limited and can be, for example, 200 to 700 rpm, more preferably 350 to 550 rpm. The treatment time of the ball mill is not particularly limited and can be, for example, 10 to 200 hours, more preferably 20 to 140 hours. The ball mill treatment may be performed in air or in an inert gas (e.g., argon, helium, nitrogen, etc.) atmosphere.

[0057] In the production of the solid electrolyte (I), it is preferable to carry out the following steps 1, 2 and 3 in terms of mixing efficiency. Step 1: A step of subjecting a lithium-containing oxide to mechanical milling treatment. Step 2: A step of mixing the finely divided lithium-containing oxide obtained in step 1 with a lithium salt. Step 3: A step of further subjecting the mixture obtained in step 2 to mechanical milling.

[0058] In the above step 2, the lithium salt may be added all at once, or may be added in several divided portions while performing the mechanical milling treatment. In step 2, the amount of the lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.

[0059] When the solid electrolyte (I) contains at least water as bound water, it is preferable to carry out the following steps 1A to 3A in the production of the solid electrolyte (I). Step 1A: A step of subjecting a lithium-containing oxide to mechanical milling in the presence of a lithium salt Step 2A: Mixing the product obtained in Step 1A with water Step 3A: A step of removing water from the dispersion obtained in Step 2A to obtain a solid electrolyte (I).

[0060] In step 1A, the amount of the lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.

[0061] 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 mass, and more preferably 50 to 150 parts by mass, per 100 parts by mass of the product obtained in step 1A. The method for mixing the product obtained in step 1A with water is not particularly limited, and they may be mixed all at once, or water may be added stepwise to the product obtained in step 1A and mixed. When mixing, ultrasonic treatment may be performed as necessary. The ultrasonic treatment time is not particularly limited, and may be, for example, 10 minutes to 5 hours.

[0062] Step 3A is a step of removing water from the dispersion obtained in Step 2A to obtain a 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 a heat treatment or a vacuum drying treatment.

[0063] Before the above step 1A, step 0 may be carried out in which the lithium-containing oxide is subjected to mechanical milling treatment in an environment in which no lithium salt is present.

[0064] When the solid electrolyte (I) contains at least water as bound water, it is also preferable to carry out the following steps 1B to 3B in place of the above steps 1A to 3A in the production of the solid electrolyte (I). Step 1B: A step of subjecting the lithium-containing oxide to mechanical milling treatment Step 2B: Mixing the product obtained in Step 1B with water and a lithium salt. Step 3B: A step of removing water from the dispersion obtained in Step 2B to obtain a solid electrolyte (I).

[0065] The difference between Step 1B and Step 1A is that in Step 1A, mechanical milling is performed in the presence of a lithium salt, whereas in Step 1B, mechanical milling is performed without using a lithium salt. Therefore, in Step 2B, the product obtained in Step 1B is mixed with water and a lithium salt. The procedure of step 2B is not particularly limited, and may be a method (Method 1) in which the product obtained in step 1B, water, and a lithium salt are mixed all at once, a method (Method 2) in which the product obtained in step 1B is mixed with water to prepare a dispersion, and then the obtained dispersion is mixed with a lithium salt, or a method (Method 3) in which the product obtained in step 1B is mixed with water to prepare dispersion 1, a lithium salt is mixed with water to prepare solution 2, and dispersion 1 is mixed with solution 2. When mixing the product obtained in step 1B with water, a dispersion treatment such as ultrasonic treatment may be appropriately performed. In Method 2, when the dispersion liquid obtained by mixing the product obtained in Step 1B with water and a lithium salt is mixed, if the amount of lithium salt is too large, the resulting liquid is likely to gel, and the amount of lithium salt to be mixed is limited. In contrast, in Method 3, even when the product obtained in Step 1B and a lithium salt are mixed in approximately equimolar amounts, gelation of the liquid is unlikely to occur, and a larger amount of lithium salt can be mixed. From this perspective, Method 3 is preferred. The procedure of step 3B is the same as that of step 3A.

[0066] When the solid electrolyte (I) contains at least water as bound water, it is also preferable to carry out the following steps 1C to 3C in place of the above steps 1A to 3A in the production of the solid electrolyte (I). Step 1C: A step of subjecting the lithium-containing oxide to mechanical milling treatment Step 2C: Mixing the product obtained in Step 1C with water Step 3C: A step of removing water from the dispersion obtained in Step 2C and mixing the resulting product with a lithium salt to obtain a solid electrolyte (I).

[0067] The procedure of step 1C is the same as that of step 1B. The procedure of step 2C is the same as that of step 2A. Step 3C differs from Steps 3A and 3B in that the product obtained by removing water from the dispersion obtained in Step 2C is mixed with a lithium salt. In step 3C, the amount of the 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 for mixing the product obtained by removing water from the dispersion obtained in step 2C with the lithium salt is not particularly limited, and a method in which the product is impregnated with a solution in which the lithium salt is dissolved in water and the two are mixed may be used.

[0068] (Composition of solid electrolyte (I)) As described above, the solid electrolyte (I) used in the present invention is an amorphous solid electrolyte, and in this solid electrolyte (I), the ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in molar ratio. When the solid electrolyte (I) does not substantially contain water (for example, when water is not blended in addition to the lithium-containing oxide and the lithium salt in the preparation step of the solid electrolyte (I)), the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 0.002 to 1.4, and more preferably 0.005 to 1.3, in molar ratio. Furthermore, when the solid electrolyte (I) contains at least water as bound water (for example, when water is blended in addition to the lithium-containing oxide and the lithium salt in the preparation step of the solid electrolyte (I)), the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 0.001 to 1.2, more preferably 0.01 to 1.2, still more preferably 0.1 to 1.2, and particularly preferably 0.5 to 1.2, in molar ratio. Furthermore, when the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and lithium salt in the preparation step of the solid electrolyte (I)), the ratio of the water content to the lithium-containing oxide content in the solid electrolyte (I) is preferably 12 or less in molar ratio, more preferably 1 to 12, even more preferably 2 to 12, and still more preferably 3 to 11. Furthermore, this molar ratio is also preferably 2 to 10, also preferably 2 to 8, also preferably 2 to 7, and also preferably 3 to 7. The molar amounts of the lithium-containing oxide, the lithium salt, and the water in the solid electrolyte (I) can be determined based on elemental analysis.

[0069] When the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and lithium salt in the preparation step of the solid electrolyte (I)), the water content 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 even more preferably 35% by mass or less. The water content in the solid electrolyte (I) is also preferably 30% by mass or less, and also preferably 25% by mass or less. Furthermore, when the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and lithium salt in the preparation step of the solid electrolyte (I)), the water content 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, when the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and lithium salt in the preparation step of the solid electrolyte (I)), the water content 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, still more preferably 10 to 35% by mass, also preferably 10 to 30% by mass, also preferably 15 to 30% by mass, and also preferably 15 to 25% by mass. When the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and lithium salt in the preparation step of the solid electrolyte (I)), the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 20 to 80 mass%, more preferably 20 to 75 mass%, and still more preferably 25 to 70 mass%. Furthermore, when the solid electrolyte (I) contains at least bound water (for example, when water is blended in addition to the lithium-containing oxide and the lithium salt in the preparation step of the solid electrolyte (I)), the content of the lithium salt in the solid electrolyte (I) is preferably 0.5 to 60 mass%, more preferably 1.0 to 55 mass%, further preferably 2.0 to 50 mass%, and also preferably 5.0 to 50 mass%.

[0070] -Lithium-containing oxide- The lithium-containing oxide constituting the solid electrolyte (I) contains Li, B, and O as described above. The lithium-containing oxide is Li 2+x B 4+y O 7+zCompounds represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) are preferred. That is, 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 (i.e., 1.7×4 / 4.3 to 2.3×4 / 3.7), and the molar amount of O is preferably 6.23 to 7.89 (i.e., 6.7×4 / 4.3 to 7.3×4 / 3.7). In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of Li contained is 1.58 to 2.49, and the molar amount of O is preferably 6.23 to 7.89. As such a lithium-containing oxide, typically, lithium tetraborate (Li2B4O7) can be mentioned. Also, the above lithium-containing oxide is Li 1+x B 3+y O 5+z Compounds represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) are also preferred. As such a lithium-containing oxide, typically, lithium triborate (LiB3O5) can be mentioned. Also, the above lithium-containing oxide is Li 3+x B 11+y O 18+z Compounds represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) are also preferred. As such a lithium-containing oxide, typically, Li3B 11 O 18 can be mentioned. Also, the above lithium-containing oxide is Li 3+x B 7+y O 12+z Compounds represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) are also preferred. As such a lithium-containing oxide, typically, Li3B7O 12 can be mentioned. Therefore, the above lithium-containing oxide is 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+xB 7+y O 12+z It is preferable that the compound is at least one of the above. In addition, instead of the above-mentioned lithium-containing oxide, or together with the above-mentioned lithium-containing oxide, LiBO5, Li2BO 12 , LiB2O3(OH)H2O, and Li4B8O 13 At least one of (OH)2(H2O)3 and the like can also be used. In the solid electrolyte (I), the lithium-containing oxide is in an amorphous state. That is, so that the solid electrolyte (I) is in the above-mentioned amorphous state, the lithium-containing oxide is also in a desired amorphous state in the solid electrolyte (I). Among these, the lithium-containing oxide is preferably amorphous lithium tetraborate.

[0071] -Lithium salt- The lithium salt constituting the solid electrolyte (I) used in the present invention is not particularly limited, and Li + and an anion, Li + and an organic anion are preferred, and Li + and a salt composed of an organic anion having a halogen atom are more preferred. The lithium salt constituting the solid electrolyte (I) used in the present invention preferably contains two or more specific elements selected from the group consisting of elements of Group 3 of the periodic table, elements of Group 4 of the periodic table, elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic 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 formula (1) is preferred. Equation (1) LiN(R f1 SO2)(R f2 SO2) R f1 and R f2 each independently represents a halogen atom or a perfluoroalkyl group. R f1 and R f2When is a perfluoroalkyl group, the number of carbon atoms in the perfluoroalkyl group is not particularly limited. R f1 and R f2 is 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 even more preferably a halogen atom. When the volume of the terminal group increases, steric hindrance increases, which becomes a factor that inhibits ion conduction. f1 and R f2 When is a perfluoroalkyl group, it is preferable that the number of carbon atoms is small.

[0072] 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 the lithium salt that can be contained in the solid electrolyte (I) used in the present invention are shown below.

[0073] (L-1) Inorganic lithium salts: inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, and LiSbF6; perhalogenates such as LiClO4, LiBrO4, and LiIO4; inorganic chloride salts such as LiAlCl4.

[0074] (L-2) Fluorine-containing organic lithium salts: perfluoroalkanesulfonates such as LiCF3SO3; fluorosulfonylimide salts or perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2 (also referred to as Li(FSO2)2N in this specification), and LiN(CF3SO2)(C4F9SO2); perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3; fluoroalkyl fluorophosphates (preferably perfluoroalkyl fluorophosphates) such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], and Li[PF3(CF2CF2CF2CF3)3].

[0075] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate and lithium difluorooxalatoborate.

[0076] In addition to the above, examples include LiF, LiCl, LiBr, LiI, Li2SO4, LiNO3, Li2CO3, CH3COOLi, LiAsF6, LiSbF6, LiAlCl4, and LiB(C6H5)4. Among them, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f11 SO2), LiN(R f11 SO2)2, LiN(FSO2)2, or LiN(R f11 SO2)(R f12 SO2) are preferred, LiPF6, LiBF4, LiN(R f11 SO2)2, LiN(FSO2)2, or LiN(R f11 SO2)(R f12 SO2) is more preferred. In these examples, R f11 and R f12 each independently represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms, more preferably 1 to 4, and even more preferably 1 or 2. Furthermore, as the lithium salt, LiNO3 and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium are also preferred.

[0077] In the solid electrolyte (I) of the present invention, the ratio of the content of the lithium salt to the content of the lithium-containing oxide is preferably 0.001 to 1.2, more preferably 0.01 to 1.2, further preferably 0.1 to 1.2, and particularly preferably 0.5 to 1.2, in terms of molar ratio, from the viewpoint of further increasing lithium ion conductivity.

[0078] (Elemental composition of solid electrolyte (I)) The component composition of the solid electrolyte (I) has been described based on the compounds constituting the solid electrolyte (I). Next, the solid electrolyte (I) will be described from the viewpoint of a preferred elemental composition. In the solid electrolyte (I) used in the present invention, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amount of Li is preferably 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.80 to 3.00). When the molar amount of B in the solid electrolyte (I) is 4.00, the molar amount of O is preferably 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 8.00 to 23.00, and even more preferably 10.00 to 18.00). When the molar amount of B in the solid electrolyte (I) is 4.00, the molar amounts of elements other than B, Li, and O are preferably each 0.001 to 10.00 (preferably 0.005 to 6.00, more preferably 0.01 to 5.00).

[0079] The content of each element is determined by ordinary elemental analysis. For example, Li and B are analyzed by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry), N and the like are analyzed by inert gas fusion, and F and S are analyzed by combustion ion chromatography. O can be calculated by adding up the analyzed masses of elements other than O and subtracting them from the total powder amount. Note that the method for calculating the content of each element is not limited to the above, and the content of one element may be estimated from the analytical results of the content of another element, taking into account the structure of the compound used. From 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 set to 4.00.

[0080] In a preferred embodiment of the solid electrolyte (I), in addition to Li, B, and O, the solid electrolyte (I) further contains one or more, more preferably two or more, elements (E) selected from Group 4 elements of the periodic table, Group 15 elements of the periodic table, Group 16 elements of the periodic table, Group 17 elements of the periodic table, Si, C, Sc, and Y. Among these, the solid electrolyte (I) preferably contains one or more, more preferably two or more, elements (E) selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N. Examples of Group 4 elements in the periodic table include Ti, Zr, Hf, and Rf. Examples of Group 15 elements in the periodic table include N, P, As, Sb, Bi, and Mc. Examples of Group 16 elements in the periodic table include S, Se, Te, Po, and Lv. Examples of Group 17 elements in the periodic table include F, Cl, Br, I, At, and Ts. The number of types of element (E) contained in the solid electrolyte (I) may be three or more, preferably two to five, and more preferably two to four. The second embodiment of the solid electrolyte (I) preferably contains two or more elements (E) selected from F, S, N, P, and C, more preferably contains two or more elements (E) selected from F, S, C, and N, and further preferably contains three elements (E) of F, S, and N.

[0081] In the solid electrolyte (I) containing one or more (preferably two or more) of the above elements (E), when the molar amount of B in the solid electrolyte (I) is taken as 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.49. In other words, when the molar amount of B contained is taken as 4.00, the relative value of the molar amount of Li contained is preferably 1.58 to 3.49. In particular, when the molar amount of B contained in the solid electrolyte (I) is taken as 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.00, and more preferably 1.80 to 3.00.

[0082] In the solid electrolyte (I) containing one or more (preferably two or more) of the above elements (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.23 to 25.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of O contained is preferably 6.23 to 25.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and even more preferably 10.00 to 18.00.

[0083] In the solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned elements (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.001 to 10.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of each element (E) contained is preferably 0.001 to 10.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.005 to 6.00, and more preferably 0.01 to 5.00.

[0084] One preferred embodiment of the elemental composition of the solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned element (E) is a composition containing Li, B, O, F, S, and N, in which, 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 1.80 to 3.00), and the molar amount of O is 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably is 8.00 to 23.00, more preferably 10.00 to 23.00, and still more preferably 10.00 to 18.00), the molar amount of F is 0.001 to 10.00 (preferably 0.01 to 10.00), the molar amount of S is 0.001 to 2.00 (preferably 0.01 to 2.00), and the molar amount of N is 0.001 to 2.00 (preferably 0.005 to 1.00).

[0085] Here, in the solid electrolyte (I), the atoms constituting the lithium salt may be present in a form doped in the lithium-containing oxide. For example, this is the case when the solid electrolyte (I) is obtained through the above steps 1, 2, and 3. In this case, the lithium salt blended in the preparation of the solid electrolyte (I) may contain a lithium salt that is no longer present in the solid electrolyte (I) in the form of a lithium salt, and such a solid electrolyte is also included in the solid electrolyte (I). In other words, in one embodiment, the secondary battery of the present invention does not have a "lithium-containing oxide" or a "lithium salt" as a matter specifying the invention, and can be specified by its elemental composition, for example, as follows:

[0086] A wound-type all-solid-state lithium ion secondary battery is formed by winding a laminate, which is formed by arranging a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order, around a core material, The solid electrolyte layer comprises an amorphous solid electrolyte containing Li, B, and O, and when the molar amount of B in this amorphous solid electrolyte is taken as 4.00, the molar amount of Li is 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.80 to 3.00), 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, still more preferably 10.00 to 18.00), and the molar amounts of elements other than Li, B, and O are each 0.001 to 10.00 (preferably 0.005 to 6.00, more preferably 0.01 to 5.00). In the wound-type all-solid-state lithium-ion secondary battery specified by the above elemental composition, as described above, the "elements other than Li, B, and O" preferably include one or more, and more preferably two or more, elements (E) selected from Group 4 elements of the periodic table, Group 15 elements of the periodic table, Group 16 elements of the periodic table, Group 17 elements of the periodic table, Si, C, Sc, Y, and H. In particular, the element (E) preferably includes one or more, and more preferably two or more, elements selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N. Therefore, a more preferred embodiment of the wound-type all-solid-state lithium ion secondary battery specified by the above elemental composition can be specified as follows.

[0087] The solid electrolyte layer includes an amorphous solid electrolyte that contains Li, B, and O, and also contains, as an element other than Li, B, and O, one or more (preferably two or more) elements (E) selected from Group 4 elements of the periodic table, Group 15 elements of the periodic table, Group 16 elements of the periodic table, Group 17 elements of the periodic table, Si, C, Sc, and Y, and when the molar amount of B in this amorphous solid electrolyte is 4.00, the molar amount of Li is 1.58 to 3.49 (preferably 1. a molar amount of O of 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, and still more preferably 10.00 to 18.00), and a molar amount of element (E) of 0.001 to 10.00 (preferably 0.005 to 6.00, more preferably 0.01 to 5.00). Furthermore, a more preferred embodiment can be specified as follows.

[0088] The solid electrolyte layer includes an amorphous solid electrolyte containing Li, B, and O, and also containing one or more (preferably two or more) elements (E) selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N, and the molar amount of Li in this amorphous solid electrolyte is 1.58 to 3.49 (preferably 1.58 to 3.00, and more preferably 1.58 to 3.00) when the molar amount of B in the amorphous solid electrolyte is 4.00. a molar amount of O of 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, and still more preferably 10.00 to 18.00), and a molar amount of element (E) of 0.001 to 10.00 (preferably 0.005 to 6.00, and more preferably 0.01 to 5.00).

[0089] The solid electrolyte (I) used in the present invention is in the amorphous state described above, and as a result, the solid electrolyte (I) preferably exhibits the following properties in addition to the above X-ray diffraction properties.

[0090] (solid 7 Li-NMR spectral characteristics) The solid electrolyte (I) is a solid 7 Li-NMR measurements are performed at 20°C and 120°C, and the full width at half maximum ratio calculated from the obtained spectrum by the following method is preferably 70% or less, more preferably 60% or less, even more preferably 50% or less, even more preferably 40% or less, and even more preferably 35% or less. There is no particular lower limit, but it is often 10% or more. The above full width at half maximum ratio is the solid electrolyte (I) 7Li-NMR measurements are performed at 20°C and 120°C, and the full width at half maximum (FWHM 1) of the peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained from the measurement at 20°C and the full width at half maximum (FWHM 2) of the peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained from the measurement at 120°C are determined. The full width at half maximum (FWHM) of a peak is then calculated as a percentage {(FWHM 2 / FWHM 1) × 100}. The full width at half maximum (FWHM) of a peak refers to the width (ppm) at half the peak height (H) (H / 2). The above characteristics will be explained below with reference to FIG. 5. In FIG. 5, the solid electrolyte (I) 7 The solid line spectrum shown at the bottom of Figure 5 shows an example of the spectrum obtained when Li-NMR measurement was performed at 20°C or 120°C. 7 The spectrum obtained when Li-NMR measurement was performed at 20°C, and the dashed line at the top of Figure 5 is the spectrum of the solid 7 This is the spectrum obtained when Li-NMR measurement was performed at 120°C. Generally, solid 7 In Li-NMR measurements, Li + When the mobility of Li is high, the peak obtained is sharper. In the embodiment shown in FIG. 5, when the spectrum at 20°C is compared with the spectrum at 120°C, the spectrum at 120°C is sharper. In other words, in the embodiment shown in FIG. 5, due to the presence of Li defects, etc., + This shows that the mobility of Li is high. Such a solid electrolyte (I) is prone to plastic deformation due to the defect structure described above, and + It is thought that the hopping ability is excellent. For reference, the solid state of a typical lithium tetraborate crystal is 7When Li-NMR measurements are performed at 20°C or 120°C, the spectrum measured at 20°C, represented by the solid line in the lower part of Fig. 6, and the spectrum measured at 120°C, represented by the dashed line in the upper part of Fig. 6, tend to have approximately the same shape. In other words, lithium tetraborate crystals are free of Li defects, and as a result, have a high elastic modulus and are not prone to plastic deformation.

[0091] The above solid 7 The Li-NMR measurement conditions are as follows: Measurements are performed using a 4 mm HX CP-MAS probe with the 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, and MAS rotation speed: 0 Hz.

[0092] The solid electrolyte (I) used in the present invention is a solid 7 When a spectrum obtained by Li-NMR measurement at 20°C is subjected to waveform separation of a first peak appearing in the range of -100 to +100 ppm, it is preferable that a second peak having a chemical shift in the range of -3 to 3 ppm and a full width at half maximum of 5 ppm or less is present, 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 ratio of the area intensity is more preferably 2% or more, more preferably 5% or more, even more preferably 10% or more, and even more preferably 15% or more. When the solid electrolyte (I) contains at least water as bound water, the solid electrolyte (I) 7 It is preferable that the Li-NMR spectrum characteristics are as described above. There is no particular upper limit to the ratio of the area intensity, but it is often 50% or less.

[0093] The above characteristics will be explained below with reference to FIGS. In FIG. 7, the solid electrolyte (I) 7An example of a spectrum obtained when Li-NMR measurement was performed at 20°C is shown in Figure 7. As shown in Figure 7, a peak (corresponding to the first peak) is observed in the range of -100 to +100 ppm for the solid electrolyte (I), and within this first peak, a small peak is observed near the chemical shift of 0 ppm, as enclosed by a dashed line. As described above, Li + When the mobility of the molecule is high, the peak is observed sharply, which is thought to be the influence of the molecule. Next, the waveform separation of the first peak is shown in Figure 8. As shown in Figure 8, the first peak is separated into a small peak (corresponding to the second peak) represented by a solid line and a large peak represented by a dashed line. The second peak appears in the chemical shift range of -3 to 3 ppm and has a full width at half maximum of 5 ppm or less. In the solid electrolyte (I), the ratio of the area intensity of the second peak represented by the solid line in FIG. 8 to the area intensity of the first peak (peak before waveform separation) represented by the solid line in FIG. 7 {(area intensity of the second peak / area intensity of the first peak)×100} is preferably within the above range. Methods for waveform separation include methods using known software, such as graph processing software Igor Pro from WaveMetrics.

[0094] (Raman spectrum characteristics) The solid electrolyte (I) is characterized by the Raman spectrum of 600-850 cm -1 The coefficient of determination obtained by linear regression analysis by the least squares method in the wavenumber region is preferably 0.9400 or more, more preferably 0.9600 or more, and also preferably 0.9800 or more. There is no particular upper limit, but it is usually 1.0000 or less.

[0095] The above Raman spectrum characteristics will be described with reference to FIG. First, the Raman spectrum of the solid electrolyte (I) is obtained. Raman imaging is used to measure the Raman spectrum. Raman imaging is a microspectroscopic technique that combines Raman spectroscopy with microscopy. Specifically, it is a technique in which excitation light is scanned over the sample to detect measurement light containing Raman scattered light, and the distribution of components is visualized based on the intensity of the measurement light. The measurement conditions for Raman imaging were as follows: 27°C, atmospheric air, excitation light of 532 nm, objective lens of 100x magnification, point scanning by mapping method, 1 μm steps, exposure time per point of 1 second, number of accumulations of 1, and measurement range of 70 μm x 50 μm. Furthermore, the Raman spectrum data is subjected to principal component analysis (PCA) to remove noise. Specifically, in the PCA process, spectra are recombined using components with autocorrelation coefficients of 0.6 or higher.

[0096] An example of the Raman spectrum of the solid electrolyte (I) is shown in Fig. 9. In the graph shown in Fig. 9, the vertical axis represents the Raman intensity and the horizontal axis represents the Raman shift. -1 The coefficient of determination (R) obtained by linear regression analysis using the least squares method in the wavenumber region of 2 ) is calculated from 600 to 850 cm of the Raman spectrum in Figure 9. -1 In the wavenumber region, the regression line (thick line in Figure 9) is calculated by the least squares method, and the coefficient of determination R 2 The coefficient of determination takes a value between 0 (no linear correlation) and 1 (perfect linear correlation of the measurements) depending on the linear correlation of the measurements. In the solid electrolyte (I), as shown in FIG. -1 Almost no peaks are observed in the wavenumber region, resulting in a high coefficient of determination. The coefficient of determination R 2 corresponds to the square of the correlation coefficient (Pearson's product-moment correlation coefficient). More specifically, in this specification, the coefficient of determination R 2is calculated by the following formula: In the formula, x1 and y1 represent the wavenumber in the Raman spectrum and the Raman intensity corresponding to that wavenumber, x2 represents the (arithmetic) average of the wavenumbers, and y2 represents the (arithmetic) average of the Raman intensity.

[0097]

number

[0098] On the other hand, for reference, the Raman spectrum of a typical lithium tetraborate crystal is shown in Figure 10. As shown in Figure 10, in the case of a typical lithium tetraborate crystal, the peak at 716 to 726 cm originating from its structure is observed. -1 , and 771~785cm -1 When such a peak is present, a peak is observed in the wavenumber region of 600-850 cm. -1 When linear regression analysis is performed using the least squares method in the wavenumber region of , the coefficient of determination is calculated to be less than 0.9400. In other words, the above coefficient of determination being 0.9400 or more indicates that the solid electrolyte (I) contains almost no crystalline structure. As a result, the solid electrolyte (I) has the property of being easily plastically deformed and the property of Li + It is believed that the compound has excellent hopping properties.

[0099] (Infrared absorption spectrum characteristics) When the solid electrolyte (I) contains at least water as bound water, it has a peak in the infrared absorption spectrum of 800 to 1600 cm -1 3000-3500 cm for the maximum absorption intensity in the wavenumber region -1 The ratio of the maximum absorption intensity in the wavenumber region (3000-3500 cm -1 Maximum absorption intensity in the wavenumber region / 800-1600cm -1 It is preferable that the ratio (maximum absorption intensity in the wave number region of 1 / 5 or more) is 1 / 5 or more (0.2 or more). In particular, the ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more. There is no particular upper limit, but it is preferably 1 or less. Infrared absorption spectrum 3000-3500 cm -1 The OH stretching vibration mode is observed in the wavenumber region of 800–1600 cm -1 The BO stretching vibration mode is observed in the wavenumber region. In the solid electrolyte (I), a strong absorption intensity due to the OH stretching vibration mode is observed, indicating that the solid electrolyte (I) contains many OH groups and a large amount of water. In such a solid electrolyte (I), lithium ions tend to move more easily, resulting in improved ionic conductivity. In addition, 800~1600cm -1 In the wavenumber region, vibrational modes originating from lithium salts can also be observed.

[0100] The infrared absorption spectrum measurement conditions can be as follows. Objective lens: 32x Cassegrain type (NA 0.65), Detector: MCT-A, Measurement range: 650-4000 cm -1 , resolution: 4cm -1 , Sample cell: Measurement is performed using a diamond cell. The obtained infrared absorption spectrum is corrected to remove signals from atmospheric water and CO2, and then offset correction is applied to the background to set the absorption intensity to 0. In addition, measurements are performed under atmospheric pressure after drying in a vacuum at 40°C for 2 hours.

[0101] 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 -8 S / cm or more is preferable, and 1.0×10 -7 In addition, when the solid electrolyte (I) contains at least water as bound water, the ionic conductivity (27°C) is preferably 1.0 × 10 -5 S / cm or more is preferable, and 1.0×10 -4 S / cm or more is more preferable, and 1.0×10 -3 S / cm or more is more preferable, and 3.0×10 -3 The upper limit is not particularly limited, but is preferably 1.0 × 10 -2 It is often below S / cm.

[0102] Furthermore, it is also preferable that the solid electrolyte (I) exhibits the following characteristics or physical properties.

[0103] (mass reduction rate) When the solid electrolyte (I) contains at least water as bound water, the mass loss rate when the solid electrolyte (I) is heated to 800°C is preferably 20 to 40 mass%, more preferably 25 to 35 mass%. The mass loss caused by heating is considered to be due to the removal of at least the water contained in the solid electrolyte (I). When the solid electrolyte (I) contains such water, the lithium ion conductivity can be further improved. In the heat treatment, the sample is heated at a temperature rising rate of 20°C / sec in the range of 25°C to 800°C. A known thermogravimetric differential thermal analyzer (TG-DTA) can be used to measure the mass loss. The mass loss rate is {(mass at 25°C - mass at 800°C) / mass at 25°C} x 100 It is calculated as follows. Before measuring the mass loss rate, the solid electrolyte (I) is vacuum dried at 40° C. for 2 hours. The mass loss rate is measured in the atmosphere.

[0104] (bulk modulus) The bulk modulus of the solid electrolyte (I) is not particularly limited, and is preferably 45 GPa or less, more preferably 40 GPa or less. The lower limit is not particularly limited, but is preferably 5 GPa or more.

[0105] (particle size) The median diameter (D50) of the solid electrolyte (I) is not particularly limited, but is preferably 0.01 to 20 μm, more preferably 0.1 to 2.0 μm.

[0106] 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 may contain a binder made of an organic polymer. The organic polymer constituting the binder may be particulate or non-particulate. By including a binder, it becomes possible to more reliably prevent cracks and the like from occurring in the solid electrolyte layer or electrode layer when a wound-type secondary battery is formed. The solid electrolyte layer may also contain a solid electrolyte other than the solid electrolyte (I). The other solid electrolyte refers to a solid electrolyte capable of transferring lithium ions therein. The solid electrolyte is preferably an inorganic solid electrolyte. Examples of the other solid electrolyte include sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes. In consideration of safety, at least one of oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes is preferred, with oxide-based solid electrolytes being more preferred. The content of the solid electrolyte (I) in the solid electrolyte layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, also preferably 80% by mass or more, and also preferably 90% by mass.

[0107] There are no particular limitations on the thickness of the solid electrolyte layer constituting the secondary battery of the present invention, and it can be, for example, 10 to 1000 μm, preferably 50 to 400 μm.

[0108] <Positive electrode layer> The positive electrode layer is generally composed of a positive electrode current collector and a positive electrode active material layer. However, when the positive electrode current collector also functions as the positive electrode active material layer (in other words, when the positive electrode active material layer also functions as the positive electrode current collector), it does not need to be composed of two layers, i.e., a positive electrode current collector and a positive electrode active material layer, and may be composed of a single layer. Furthermore, 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 does not have to contain a solid electrolyte. The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, preferably 80% by mass or more, and even preferably 90% by mass.

[0109] 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 prioritizing flexibility, a sulfide-based solid electrolyte can be used, and from the viewpoint of prioritizing 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 above-mentioned solid electrolyte (I). In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the positive electrode layer, making the positive electrode layer more flexible. As a result, in the production of a wound-type lithium-ion secondary battery, the occurrence of cracks can be effectively suppressed when the positive electrode layer is wound.

[0110] The positive electrode active material itself used in the positive electrode layer can be any positive electrode active material that can be used in ordinary lithium ion secondary batteries. Preferred forms of the positive electrode active material are described below.

[0111] (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, but a transition metal oxide is preferred, and a transition metal oxide containing a transition metal element Ma (one or more elements selected from Co, Ni, Fe, Mn, Cu, and V) is more preferred. Furthermore, this transition metal oxide may be mixed with an element Mb (a metal element in Group 1 (Ia) of the periodic table other than lithium, an element in Group 2 (IIa), an element such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B). The amount of Mb mixed is preferably 0 to 30 mol% relative to the amount of the transition metal element Ma (100 mol%). A material synthesized by mixing so that the Li / Ma molar ratio is 0.3 to 2.2 is more preferred. 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 phosphate compounds, and (ME) lithium-containing transition metal silicate compounds. Among these, (MA) transition metal oxides having a layered rock salt structure are preferred, and LiCoO2 or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is more preferred.

[0112] (MA) Examples of transition metal oxides with a layered rock salt structure include LiCoO2 (lithium cobalt oxide [LCO]), LiNiO2 (lithium nickel oxide), and LiNi 0.85 Co 0.10 Al 0.05 O2 (nickel cobalt lithium aluminate [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (lithium nickel manganese cobalt oxide [NMC]) and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide).

[0113] (MB) Transition metal oxides with spinel structure include, for example, LiMn2O4 (LMO), LiNi 0.5 Mn 1.5 O4([LNMO]), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8.

[0114] (MC) Examples of lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as Li2CoP2O7(LCP) and LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic NASICON-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate).

[0115] (MD) Examples of lithium-containing transition metal halide phosphate compounds include iron fluorophosphates such as Li2FePO4F, manganese fluorophosphates such as Li2MnPO4F, and cobalt fluorophosphates such as Li2CoPO4F.

[0116] (ME) Examples of lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4.

[0117] 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 particles can be determined in the same manner as the volume average particle diameter of the negative electrode active material described below. The positive electrode active material obtained by the baking method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0118] The positive electrode active material may be surface-coated with a surface coating agent, sulfur or phosphorus, or further with actinic rays, in the same manner as the negative electrode active material described below.

[0119] The positive electrode active material may be used alone or in combination of two or more kinds.

[0120] (Positive electrode current collector) The current collector constituting the positive electrode layer is an electron conductor, and is usually in the form of a film sheet. Examples of materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, and titanium, and aluminum or aluminum alloys are preferred. Examples of the positive electrode current collector include aluminum or stainless steel surfaces treated with carbon, nickel, titanium, or silver (thin films formed thereon).

[0121] There are no particular limitations on the thickness of the positive electrode active material layer constituting the secondary battery of the present invention, and it can be, for example, 5 to 500 μm, preferably 20 to 200 μm. 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.

[0122] <Negative electrode layer> The negative electrode layer is generally composed of a negative electrode current collector and a negative electrode active material layer. However, when the negative electrode current collector also functions as the negative electrode active material layer (in other words, when the negative electrode active material layer also functions as the negative electrode current collector), it does not need to be composed of two layers, i.e., a negative electrode current collector and a negative electrode active material layer, and may be composed of a single layer. Furthermore, 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 does not have to contain a solid electrolyte. The content of the negative electrode active material in the negative electrode active material layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, preferably 80% by mass or more, and even preferably 90% by mass.

[0123] 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 prioritizing flexibility, a sulfide-based solid electrolyte can be used, and from the viewpoint of prioritizing 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 above-mentioned solid electrolyte (I). In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the negative electrode layer, thereby imparting greater flexibility to the negative electrode layer. As a result, in the production of a wound-type lithium-ion secondary battery, the occurrence of cracks can be effectively suppressed when the negative electrode layer is wound.

[0124] The negative electrode active material itself used in the negative electrode layer can be any negative electrode active material that can be used in ordinary lithium ion secondary batteries. Preferred forms of the negative electrode active material are described below.

[0125] (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, and examples thereof include carbonaceous materials, oxides of metals or semimetals, lithium alone, lithium alloys, and negative electrode active materials that can form alloys with lithium.

[0126] The carbonaceous material used as the negative electrode active material is a material substantially composed of carbon, such as petroleum pitch, carbon black such as acetylene black (AB), graphite (natural graphite and artificial graphite such as vapor-grown graphite), and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins and furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, mesophase microspheres, graphite whiskers, and plate-like graphite. These carbonaceous materials can be divided into non-graphitizable carbonaceous materials (also called hard carbon) and graphite-based carbonaceous materials depending on the degree of graphitization. The carbonaceous material preferably has the interplanar spacing, density, or crystallite size described in JP-A-62-022066, JP-A-2-006856, and JP-A-3-045473. The carbonaceous material does not need to be a single material, and a mixture of natural graphite and artificial graphite described in JP-A-5-090844 and graphite having a coating layer described in JP-A-6-004516 can also be used. The carbonaceous material is preferably hard carbon or graphite, and more preferably graphite.

[0127] The oxide of a metal element or a metalloid element used as the negative electrode active material is not particularly limited as long as it is an oxide that can absorb and release lithium, and examples thereof include oxides of metal elements (metal oxides), 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 also collectively referred to as metal composite oxides. As these oxides, iron oxides such as Fe3O4 are preferred, amorphous oxides are also preferred, and chalcogenides which are reaction products of metal elements and elements of Group 16 of the periodic table are also preferred. In the present invention, the term "metalloid elements" refers to elements that exhibit properties intermediate between those of metallic elements and non-metallic elements, and generally includes six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and further includes three elements: selenium, polonium, and astatine. Furthermore, "amorphous" means a substance that has a broad scattering band with a peak in the 2θ range of 20 to 40° when measured by X-ray diffraction using CuKα radiation, and may have crystalline diffraction lines. The strongest intensity of the crystalline diffraction lines observed in the 2θ range of 40 to 70° is preferably 100 times or less, more preferably 5 times or less, the intensity of the diffraction line at the peak of the broad scattering band observed in the 2θ range of 20 to 40°, and even more preferably no crystalline diffraction lines.

[0128] Among the compound group consisting of the above amorphous oxides and chalcogenides, amorphous oxides or the above chalcogenides of metalloid elements are more preferred, and (composite) oxides or chalcogenides consisting of one element selected from Groups 13 (IIIB) to 15 (VB) of the periodic table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) or a combination of two or more elements thereof are even more preferred. As the amorphous oxide and chalcogenide, Ga2O3, GeO, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O8Bi2O3, Sb2O8Si2O3, Sb2O5, Bi2O3, Bi2O4, GeS, PbS, PbS2, Sb2S3 or Sb2S5 are preferred. As a negative electrode active material that can be used in combination with the amorphous oxide negative electrode active material mainly composed of Sn, Si, or Ge, a carbonaceous material that can occlude and / or release lithium ions or lithium metal, lithium alone, a lithium alloy, or a negative electrode active material that can be alloyed with lithium is preferred.

[0129] The oxides of metal elements or semimetal elements (particularly metal (composite) oxides) and the chalcogenides preferably contain at least one of titanium and lithium as a constituent component in terms 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 above metal oxides, metal composite oxides, or chalcogenides. More specifically, Li2SnO2 is exemplified. The negative electrode active material (for example, a metal oxide) preferably contains titanium (titanium oxide). Specifically, Li4Ti5O 12 Lithium titanate (LTO) is preferred because it has excellent rapid charge / discharge characteristics due to its small volumetric fluctuation during absorption and desorption of lithium ions, and because it can suppress electrode deterioration and improve the lifespan of all-solid-state lithium-ion secondary batteries.

[0130] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is commonly used as a negative electrode active material for all-solid-state lithium ion secondary batteries, and examples thereof include lithium aluminum alloys.

[0131] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one that is commonly used as a negative electrode active material for all-solid-state lithium-ion secondary batteries. Examples of the negative electrode active material include negative electrode active materials (alloys) containing silicon or tin, and metals such as Al and In. A negative electrode active material containing silicon (silicon-containing active material) that enables higher battery capacity is preferred, and a silicon-containing active material in which the silicon content of all constituent elements is 50 mol % or more is more preferred. Generally, negative electrodes containing these negative electrode active materials (for example, Si negative electrodes containing silicon element-containing active materials, Sn negative electrodes containing active materials containing tin elements) can occlude more Li ions than carbon negative electrodes (such as graphite and acetylene black). That is, the amount of Li ions occluded per unit mass increases. Therefore, the battery capacity can be increased. As a result, there is an advantage that the battery driving time can be lengthened.

[0132] Examples of the silicon element-containing active material include silicon materials such as Si and SiOx (0 < x ≤ 1), and further silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (for example, LaSi2, VSi2, La-Si, Gd-Si, and Ni-Si), or organized active materials (for example, LaSi2 / Si). In addition, active materials containing silicon elements and tin elements such as SnSiO3 and SnSiS3 can be mentioned. Note that SiOx can be used as a negative electrode active material (semimetal oxide) by itself, and can also be used as a negative electrode active material (its precursor material) that can be alloyed with lithium to generate Si by the operation of an all-solid-state lithium-ion secondary battery. Examples of the negative electrode active material having a tin element include Sn, SnO, SnO2, SnS, SnS2, and the active materials containing the above silicon elements and tin elements.

[0133] In terms of battery capacity, a negative electrode active material that can be alloyed with lithium is preferable as the negative electrode active material, the above silicon material or silicon-containing alloy (alloy containing silicon element) is more preferable, and silicon (Si) or silicon-containing alloy is even more preferable.

[0134] It is also preferable to use a titanium niobium composite oxide as the negative electrode active material. The titanium niobium composite oxide is expected to have a high theoretical volume capacity density, long life, and be capable of rapid charging. Examples of the titanium niobium composite oxide include TiNb2O7 and the like.

[0135] The shape of the negative electrode active material is not particularly limited, but is preferably particulate. The volume average particle size 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 size is measured by the following procedure. The negative electrode active material is diluted with water (or heptane if the material is unstable in water) to prepare a 1% by mass dispersion in a 20 mL sample bottle. The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and then used for testing immediately thereafter. Using this dispersion sample, a laser diffraction / scattering particle size analyzer is used to collect data 50 times at 25°C using a quartz measurement cell to obtain the volume average particle size. For other detailed conditions, refer to JIS Z 8828:2013 "Particle size analysis - dynamic light scattering method" as necessary. Five samples are prepared for each level, and the average value is used.

[0136] The negative electrode active material may be used alone or in combination of two or more kinds.

[0137] The surface of the negative electrode active material may be coated with another metal oxide. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds, such as Li4Ti5O 12 , Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, and Li3AlF6. The surface of the electrode containing the negative electrode active material may be surface-treated with sulfur or phosphorus. Furthermore, the particle surfaces of the negative electrode active material may be subjected to a surface treatment with actinic rays or an active gas (for example, plasma) before or after the above surface coating.

[0138] (Negative electrode current collector) The current collector constituting the negative electrode layer is an electron conductor, and is usually in the form of a film sheet. Examples of materials for the negative electrode current collector include aluminum, copper, a copper alloy, stainless steel, nickel, and titanium, and aluminum, copper, a copper alloy, or stainless steel is preferred. Examples of the negative electrode current collector include aluminum, copper, a copper alloy, or stainless steel whose surface is treated with carbon, nickel, titanium, or silver.

[0139] There are no particular limitations on the thickness of the negative electrode active material layer that constitutes the secondary battery of the present invention, and it can be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the negative 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.

[0140] The positive electrode layer and the negative electrode layer may contain components (other components) other than the solid electrolyte and the active material in their active material layers, such as a conductive additive. As the conductive additive, a commonly known conductive additive can be used. Examples of the conductive additive include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, and furnace black, amorphous carbon such as needle coke, fibrous carbon such as vapor-grown carbon fiber and carbon nanotubes, and carbonaceous materials such as graphene and fullerene. In addition, conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may also be used. In addition to the above-mentioned conductive additives, ordinary conductive additives that do not contain carbon atoms, such as metal powder or metal fibers, may also be used. A conductive additive is one that does not insert or release Li when the battery is charged or discharged, and does not function as an active material. Therefore, among conductive additives, those that can function as an active material in the active material layer when the battery is charged or discharged are classified as active materials rather than conductive additives. Whether or not a conductive additive functions as an active material when the battery is charged or discharged is not uniquely determined, but is determined by its combination with the active material.

[0141] Other components include the binder and lithium salts described above.

[0142] <Separator layer> In the present invention, the separator layer is a layer for insulating between current collectors in a wound-type secondary battery. Therefore, there are no particular limitations on the insulating film, and a wide range of separators commonly used for insulating between current collectors can be used. There are also no particular limitations on the thickness of the separator layer, and it can be, for example, 10 to 100 μm. Examples of insulating films include fluororesin films.

[0143] <Manufacturing wound-type all-solid-state lithium-ion secondary batteries> The secondary battery of the present invention can be produced by referring to a method for producing a conventional wound-type all-solid-state secondary battery, except that the solid electrolyte (I) is used for at least the solid electrolyte layer. That is, the method for producing a secondary battery of the present invention includes winding a laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order around a core material. For example, a cathode-forming composition (slurry) containing a cathode active material is applied to a metal foil cathode current collector to form a cathode active material layer, a solid electrolyte layer-forming dispersion (slurry) containing a solid electrolyte is applied to the cathode active material layer to form a solid electrolyte layer, and a cathode-forming composition (slurry) containing a negative electrode active material is applied to the solid electrolyte layer to form a negative electrode active material layer. An anode current collector (metal foil) is then superimposed on the negative electrode active material layer, and if necessary, a separator layer is disposed on the outside of the cathode current collector and / or the negative electrode current collector. The entire assembly is subjected to a pressure treatment, and the resulting laminate is wound around a core material to obtain a wound-type all-solid-state lithium-ion secondary battery as shown in FIG. Alternatively, the method for forming each layer may be reversed, such that a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer are formed on a negative electrode current collector, and then a positive electrode current collector is placed on top of the negative electrode current collector. If necessary, a separator layer is disposed on the outside of the positive electrode current collector and / or the negative electrode current collector. The entire assembly is subjected to a pressure treatment, and the resulting laminate is wound around a core material to produce a wound-type all-solid-state lithium-ion secondary battery.

[0144] Alternatively, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer may be separately prepared, stacked, and optionally a separator layer may be disposed on the outside of the positive electrode current collector and / or the negative electrode current collector, and optionally pressurized, and the resulting stack may be wound around a core material to produce a wound-type all-solid-state lithium-ion secondary battery. In this case, when forming each layer, a support such as a nonwoven fabric may be disposed as necessary, so that each layer can be made into a self-supporting film.

[0145] The direction in which the laminate is wound around the core material is not particularly limited, and the laminate may be wound with the positive electrode side on the inside and the negative electrode side on the outside, or may be wound with the negative electrode side on the inside and the positive electrode side on the outside.

[0146] In the production of the secondary battery of the present invention, even without using a sulfide-based solid electrolyte as the solid electrolyte, the oxide-based solid electrolyte (I) can be easily plastically deformed by pressure, allowing for the formation of layers with reduced interfacial resistance between solid particles or layers. Therefore, even when the secondary battery is produced in the presence of moisture (e.g., in the atmosphere), the generation of harmful substances such as hydrogen sulfide can be avoided, resulting in excellent productivity. Note that producing a secondary battery in the presence of moisture means producing the secondary battery of the present invention under conditions in which the solid electrolyte layer comes into contact with moisture (e.g., in the atmosphere). A typical example is a form in which the formation of a laminate including the formation of the solid electrolyte layer of the secondary battery of the present invention is carried out under conditions in which moisture comes into contact with the solid electrolyte layer (e.g., in the atmosphere). Furthermore, since the solid electrolyte (I) itself is soft and plastically deformable, and acts as a binder, contributing to improving the binding between solid particles or between layers, it is also possible to form layers without using a binder such as an organic polymer.

[0147] The secondary battery of the present invention is preferably initialized after manufacture or before use.

[0148] <Applications of wound-type all-solid-state lithium-ion secondary batteries> The secondary battery of the present invention can be used in a variety of applications. While there are no particular limitations on the application, examples of applications include notebook computers, pen-input PCs, mobile PCs, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video camcorders, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, and backup power supplies. Other consumer applications include automobiles, electric vehicles, motors, lighting fixtures, toys, game consoles, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, the battery can be used for various military and space applications. It can also be combined with solar cells. [Example]

[0149] The present invention will be described in more detail with reference to examples, but the present invention is not to be construed as being limited thereto. Furthermore, the production of the solid electrolyte and the production of the secondary battery described below were carried out in the atmosphere containing moisture.

[0150] [Reference example 1] <Preparation of solid electrolyte (I)> Powdered Li2B4O7 crystals (LBO powder) (made by Rare Metallic) were ball-milled using a ball mill (P-7 manufactured by Fritsch) under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), milling balls: YSZ (average particle diameter: 5 mm, number: 50), rotation speed: 370 rpm (revolutions per minute), amount of LBO powder: 1 g, atmosphere: air, and ball mill treatment time: 100 hours, to obtain a finely divided lithium-containing oxide (hereinafter also referred to as "fine lithium-containing oxide"). To 1.0 g of the obtained fine particles of lithium-containing oxide, 0.02 g of LiFSI (chemical formula: Li(FSO2)2N) was added as a lithium salt (2 mass % relative to the fine particles of lithium-containing oxide), and the mixture was further ball milled for 100 hours to obtain a powdered solid electrolyte (I)-1. The molar ratio of the lithium-containing oxide to the lithium salt in the solid electrolyte shown in the table below is calculated from the amounts charged.

[0151] The powdered solid electrolyte (I)-1 was subjected to elemental analysis, and the composition of the solid electrolyte (I)-1 was found to be Li 1.98 B 4.00 O 6.83 F 0.08 S 0.07 N 0.04 Of the elements contained in this solid electrolyte (I), elemental analysis was performed on Li and B by ICP-OES, on F and S by combustion ion chromatography, and on N by inert gas fusion. The mass of O was calculated by adding up the analyzed masses of elements other than O and subtracting it from the total powder mass.

[0152] <Production and evaluation of solid electrolyte compacts> The powdered solid electrolyte (I)-1 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compacted body of the solid electrolyte (compacted body 1). The compacted body 1 had a cylindrical shape with a diameter of 10 mm and a thickness of 0.5 to 1 mm. The ionic conductivity of the obtained compacted body 1 was measured, and the ionic conductivity of the compacted body 1 at 27°C was found to be 2.8 x 10 -7 S / cm at 60°C, and 1.6 × 10-6 S / cm.

[0153] The ionic conductivity of the solid electrolyte (I)-1 was calculated by placing two electrodes made of In foil so as to sandwich the powder compact 1, measuring the AC impedance between the two In electrodes in a measurement frequency range of 1 Hz to 1 MHz under conditions of a measurement temperature of 27°C or 60°C and an applied voltage of 100 mV, and analyzing the arc diameter of the obtained Cole-Cole plot.

[0154] The particle size distribution of the solid electrolyte (I)-1 obtained above was approximately several hundred nanometers to 10 μm, with an average particle size of 1.6 μm and a median diameter (D50) of 1.5 μm. The particle size distribution of the solid electrolyte was calculated by obtaining particle images using a flow particle image analysis method and creating a histogram (particle size distribution) of the particle size of the solid electrolyte. The particle size corresponds to the circle equivalent diameter.

[0155] The bulk modulus of the solid electrolyte (I)-1 obtained above was 36 GPa. The bulk modulus of the LBO powder before ball milling was 47 GPa. The bulk modulus of the solid electrolyte was measured using an ultrasonic attenuation method. Specifically, the solid electrolyte was first suspended in pure water to prepare a suspension. The solid electrolyte content in the suspension was 1.2 mass% relative to the total mass of the suspension. The ultrasonic attenuation spectrum of the suspension was then measured, and the bulk modulus (GPa) of the solid electrolyte was calculated by fitting using the scattering attenuation theory. The bulk modulus was calculated using equations (7), (12), and (13) described in Kohjiro Kubo et al., Ultrasonics 62 (2015), pp. 186-194.

[0156] Using the solid electrolyte (I)-1 obtained above, X-ray total scattering measurements were performed at SPring-8BL04B2 (accelerating voltage: 61.4 keV, wavelength: 0.2019 Å). The sample was sealed in a 2 mm or 1 mm Kapton capillary, and the experiment was performed under vacuum. The obtained data were Fourier transformed as described above to obtain the reduced pair distribution function G(r). Figure 11 shows the reduced pair distribution function G(r) obtained from solid electrolyte (I)-1. As a result of the analysis, in the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement, a first peak with a peak top of G(r) exceeding 1.0 and located at 1.43 Å in the r range of 1 to 5 Å, and a second peak with a peak top of G(r) exceeding 1.0 and located at 2.40 Å, were confirmed, and it was also confirmed that in the reduced pair distribution function G(r), the absolute value of G(r) in the r range of more than 5 Å and 10 Å or less was less than 1.0.

[0157] The absolute value of the reduced pair distribution function G(r) is less than 1.0 when r is greater than 5 Å and less than 10 Å. This indicates that the solid electrolyte (I) obtained above has almost no long-range order, and solid electrolyte (I)-1 is in an amorphous state. Meanwhile, this solid electrolyte (I)-1 maintains the peaks attributable to the B-O and B-B distances observed in typical lithium tetraborate crystals. Typical lithium tetraborate crystals have a structure in which BO tetrahedra and BO triangles exist in a 1:1 ratio (diborate structure), and it was estimated that this structure is maintained in the solid electrolyte (I)-1.

[0158] In contrast to the above solid electrolyte (I)-1, 7Li-NMR measurements were carried out at 20°C and 120°C, respectively, and the full width at half maximum (FWHM 1) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 20°C and the full width at half maximum (FWHM 2) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 120°C were determined. From the obtained FWHM 1 and FWHM 2, the FWHM ratio (%) of the solid electrolyte (I), which is the percentage ratio of FWHM 2 to FWHM 1 {(FWHM 2 / FWHM 1) × 100}, was calculated to be 65%.

[0159] Raman imaging measurements were performed on powder compact 1. The measurement conditions were: excitation light 532 nm, objective lens 100x magnification, mapping method point scanning, 1 μm steps, exposure time per point 1 second, number of integrations 1, and measurement range 70 μm x 50 μm. Noise was removed from the obtained data by PCA processing. In the Raman spectrum obtained in this way, -1 The coefficient of determination for the obtained powder compact 1 was 0.9952.

[0160] [Reference example 2] A powdered solid electrolyte (I)-2 was prepared in the same manner as in Reference Example 1, except that 0.05 g of LiFSI was added as a lithium salt to 1.0 g of the fine particles of the lithium-containing oxide prepared in Reference Example 1 (5 mass% relative to the fine particles of the lithium-containing oxide). As a result of elemental analysis, the composition of the obtained solid electrolyte (I)-2 was 2.01 B 4.00 O 7.47 F 0.12 S 0.12 N 0.07 It was. Next, the powdered solid electrolyte (I)-2 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compact of the solid electrolyte (compact 2) similar to that of Reference Example 1. The ionic conductivity of the obtained compact 2 at 27°C was 3.0 × 10 -7 S / cm and 1.7 × 10 at 60°C.-6 S / cm.

[0161] [Reference example 3] A powdered solid electrolyte (I)-3 was prepared in the same manner as in Reference Example 1, except that 0.05 g of lithium iodide (LiI) was added as a lithium salt to 1.0 g of the fine particles of the lithium-containing oxide prepared in Reference Example 1 (5 mass% relative to the fine particles of the lithium-containing oxide). As a result of elemental analysis, the composition of the obtained solid electrolyte (I)-3 was Li 2.05 B 4.00 O 9.28 I 0.07 The elemental analysis of iodine was carried out by combustion IC. Next, the powdered solid electrolyte (I)-3 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compact of the solid electrolyte (compacted powder 3). The ionic conductivity of the obtained compacted powder 3 at 27°C was 3.1 x 10 -5 S / cm and 9.4 × 10 at 60°C. -5 S / cm.

[0162] [Reference example 4] A powdered solid electrolyte (I)-4 was prepared in the same manner as in Reference Example 1, except that 0.02 g of lithium chloride (LiCl) was added as a lithium salt to 1.0 g of the fine particles of the lithium-containing oxide used in Reference Example 1 (2 mass % relative to the fine particles of the lithium-containing oxide). As a result of elemental analysis, the composition of the obtained solid electrolyte (I)-4 was 2.03 B 4.00 O 9.80 Cl 0.06 The elemental analysis of chlorine was carried out by combustion IC. Next, the powdered solid electrolyte (I)-4 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compacted body of the solid electrolyte (compacted body 4). The ionic conductivity of the obtained compacted body 4 at 27°C was 2.3 × 10 -5 S / cm and 3.6 × 10 at 60 °C. -5 S / cm.

[0163] [Comparative Reference Example 1] The LBO powder used in Reference Example 1 (powdered Li2B4O7 crystals that were not ball-milled) was subjected to elemental analysis. As a result, the composition of the obtained LBO powder was 1.96 B 4.00 O 6.80 The LBO powder was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a comparative green compact C1. The ionic conductivity of the obtained green compact C1 was undetectable. Furthermore, X-ray total scattering measurement was performed using LBO powder to obtain the reduced pair distribution function G(r) in the same manner as in Reference Example 1. Figure 12 shows the reduced pair distribution function G(r) obtained from the LBO powder. Analysis revealed that the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of LBO powder contained a first peak with a peak top at 1.40 Å (corresponding to the B-O proximity) and a second peak with a peak top at 2.40 Å (corresponding to the B-B proximity), with G(r) values ​​at the peak tops of the first and second peaks being 1.0 or greater (see Figure 12). Furthermore, peaks with peak tops at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å were also present, and the absolute values ​​of G(r) at the peak tops of each of these peaks clearly exceeded 1.0 (see Figure 12).

[0164] [Comparative Reference Example 2] As a result of performing elemental analysis on the fine particles of lithium-containing oxide prepared in Reference Example 1 (powdered Li2B4O7 crystals ball-milled), the composition of the fine particles of lithium-containing oxide was 1.94 B 4.00 O 6.80 It was. Next, the fine particles of the lithium-containing oxide were compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a reference compact (compacted powder R1). The ionic conductivity of the obtained compacted powder R1 was 7.5 x 10 at 27°C. -9 S / cm and 7.5 × 10 at 60 °C. -8 S / cm.

[0165] The particle size distribution of the fine lithium-containing oxide particles of the solid electrolytes (I)-2, (I)-3, and (I)-4 obtained in Reference Examples 2 to 4 and Comparative Reference Example 2 was approximately several hundred nanometers to 10 μm, with an average particle diameter of approximately 1.6 μm and a median diameter (D50) of approximately 1.5 μm. The bulk modulus, reduced pair distribution function G(r), and ratio of full width at half maximum 2 to full width at half maximum 1 were determined for the solid electrolytes (I)-2, (I)-3, and (I)-4 obtained in Reference Examples 2 to 4, the LBO powder used in Comparative Reference Example 1, and the fine lithium-containing oxide particles used in Comparative Reference Example 2, respectively, in the same manner as in Reference Example 1. The coefficient of determination was determined for each of the compacts obtained in Reference Examples 2 to 4 and Comparative Reference Examples 1 and 2, respectively, in the same manner as in Reference Example 1. The evaluation results based on each measurement are summarized in Tables 1-1, 1-2, and 2.

[0166] In Table 2, in the "Requirement A-1" column, cases where requirement A-1 is met are indicated as "A," and cases where requirement A-1 is not met are indicated as "B." In the "Requirement A-2" column, cases where requirement A-2 is met are indicated as "A," and cases where requirement A-2 is not met are indicated as "B." In Table 2, the "full width at half maximum ratio (%)" and "coefficient of determination" are as explained in the above description of Reference Example 1.

[0167] [Table 1-1]

[0168] [Table 1-2]

[0169] [Table 2]

[0170] As shown in the above table, the solid electrolytes of Reference Examples 1 to 4 have superior ionic conductivity compared to the LBO powder (Li2B4O7 crystal) of Comparative Reference Example 1 and compared to the fine lithium-containing oxide (ball-milled powdered Li2B4O7 crystal) of Comparative Reference Example 2.

[0171] (X-ray diffraction measurement) Using CuKα radiation, X-ray diffraction measurements were performed on the solid electrolyte (I)-2 prepared in Reference Example 2 and the LBO powder used in Comparative Reference Example 1. The measurement conditions were 0.01° / step, 3° / min. Figure 13 shows the X-ray diffraction pattern of the LBO powder of Comparative Reference Example 1. As shown in Figure 13, the LBO powder used in Comparative Reference Example 1 exhibited multiple narrow peaks. More specifically, the strongest peak corresponding to the (1,1,2) plane was observed at a 2θ value of 21.78°. Other major diffraction peaks included a peak corresponding to the (2,0,2) plane at 25.54°, a peak corresponding to the (2,1,3) plane at 33.58°, and a peak corresponding to the (3,1,2) plane at 34.62°, and the intensities of these three peaks were approximately equal. These peaks were derived from crystalline components. FIG. 14 shows the X-ray diffraction pattern of solid electrolyte (I)-2. As shown in FIG. 14, solid electrolyte (I)-2 exhibited the desired X-ray diffraction characteristics described above. It can be seen from FIG. 13 that the crystalline components present were amorphized by the mechanical milling treatment, and the sharp peaks derived from lithium tetraborate crystals disappeared and broadened. X-ray diffraction measurements were also performed on solid electrolytes (I)-1, (I)-3, and (I)-4 prepared in Reference Examples 1, 3, and 4. Similar to solid electrolyte (I)-2, these electrolytes exhibited the desired X-ray diffraction characteristics described above, confirming their amorphous state.

[0172] [Reference example 5] To 1 g of the fine particles of the lithium-containing oxide used in Reference Example 1, 0.05 g of LiFSI (chemical formula: Li(FSO2)2N) was added as a lithium salt (5 mass % relative to the fine particles of the lithium-containing oxide), and the mixture was further ball milled for 100 hours. The obtained powder was added to water so that the powder concentration was 42 mass %, and ultrasonically dispersed for 30 minutes. Subsequently, the obtained dispersion was transferred to a glass petri dish and dried in the atmosphere at 120°C for 2 hours to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain a powdered solid electrolyte (I)-5.

[0173] X-ray diffraction measurement of solid electrolyte (I)-5 was performed using CuKα radiation. The measurement conditions were 0.01° / step, 3° / min. As a result, it was found that the X-ray diffraction characteristics described above were satisfied, and solid electrolyte (I)-5 was found to be in an amorphous state.

[0174] Using the solid electrolyte (I)-5 obtained above, X-ray total scattering measurements were performed at SPring-8L04B2 (accelerating voltage: 61.4 keV, wavelength: 0.2019 Å). The sample was sealed in a 2 mm or 1 mm Kapton capillary and the experiment was performed. The obtained data were Fourier transformed as described above to obtain the reduced pair distribution function. As a result of the analysis, the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement showed a first peak with a peak top of 1.43 Å and a G(r) of 1.0 or more in the range of r from 1 to 5 Å, and a second peak with a peak top of 2.40 Å and a G(r) of 1.0 or more in the range of r from 1 to 5 Å. On the other hand, in solid electrolyte (I)-5, the peaks assigned to the BO and BB distances observed in typical lithium tetraborate crystals were maintained. Typical lithium tetraborate crystals have a structure in which BO4 tetrahedra and BO3 triangles exist in a 1:1 ratio (diborate structure), and it was presumed that this structure was maintained in solid electrolyte (I)-5.

[0175] The solid electrolyte (I)-5 obtained above 7The solid electrolyte (I)-5 is measured at 20°C using Li-NMR, and the chemical shift of the peak appears in the range of -100 to +100 ppm (FWHM 1). 7 The ratio of the full width at half maximum (FWHM2) of the peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by Li-NMR measurement at 120°C {(FWHM2 / FWHM1) × 100} was 33%. Also, solid 7 When the spectrum obtained by Li-NMR measurement at 20°C was subjected to waveform separation of the first peak appearing in the range of -100 to +100 ppm, a second peak with a chemical shift in the range of -3 to 3 ppm and a full width at half maximum of 5 ppm or less was found, and the ratio of the area intensity of the second peak to the area intensity of the first peak was 4%.

[0176] The solid electrolyte (I)-5 obtained above was subjected to infrared absorption spectroscopy under the conditions described above. In the obtained infrared absorption spectrum, -1 3000-3500 cm for the maximum absorption intensity in the wavenumber region -1 The ratio of the maximum absorption intensities in the wavenumber region of 0.72 was found to be 0.72.

[0177] In the Raman spectrum of the solid electrolyte (I)-5 obtained above, -1 The coefficient of determination obtained by linear regression analysis using the least squares method in the wavenumber region was 0.9974. When the solid electrolyte (I)-5 was heated from 25° C. to 800° C. as described above, the mass loss rate was 29.8%.

[0178] Regarding the analysis of each element in the obtained solid electrolyte (I)-5, lithium and boron were quantitatively analyzed by ICP-OES, and fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated by adding up the analyzed masses of elements other than O and subtracting it from the total powder mass. The results are shown in the table below.

[0179] [Reference example 6] 1 g of the fine lithium-containing oxide particles used in Reference Example 1 was added to water so that the concentration of the fine particles was 42 mass %, and ultrasonic dispersion was performed for 30 minutes. 0.05 g of LiFSI (chemical formula: Li(FSO2)2N) was added as a lithium salt to the obtained dispersion (5 mass % relative to the fine lithium-containing oxide particles), and ultrasonic dispersion was performed for another 30 minutes. The resulting dispersion was transferred to a glass petri dish and dried at 120°C for 2 hours in the atmosphere to obtain a solid electrolyte film. The resulting film was then peeled off to obtain powdered solid electrolyte (I)-6. Various evaluations were performed on solid electrolyte (I)-6 in the atmosphere in the same manner as in Reference Example 5. The results are summarized in the table below.

[0180] [Reference example 7] Powdered Li2B4O7 (LBO powder) (Rare Metallic) was ball milled using a ball mill (Fritsch P-7) under the following conditions: pot: YSZ (45 ml), milling balls: 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 mill treatment time: 100 hours, to obtain fine lithium-containing oxide. The obtained fine particles of lithium-containing oxide were added to water so that the concentration of the fine particles was 42 mass %, and the mixture was subjected to ultrasonic treatment for 60 minutes, whereby dispersion liquid 1 was obtained. Next, 3.25 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water to a concentration of 87 mass %, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 2. The obtained dispersion 1 and solution 2 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then 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 carried out in the atmosphere using solid electrolyte (I)-7 in the same manner as in Reference Example 5. The results are summarized in the table below.

[0181] [Reference example 8] Dispersion 3 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 7. Next, 2.32 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water at a concentration of 87 mass % and subjected to ultrasonic treatment for 60 minutes to obtain solution 4. The obtained dispersion 3 and solution 4 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-8. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-8 in the same manner as in Reference Example 5. The results are summarized in the table below.

[0182] [Reference example 9] Dispersion 5 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 7. Next, 4.65 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water at a concentration of 87 mass % and subjected to ultrasonic treatment for 60 minutes to obtain Solution 6. The obtained dispersion 5 and solution 6 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum dried at 40°C and 10 Pa for 15 hours to obtain a powdered solid electrolyte (I)-9. The obtained powder was immediately subjected to various evaluations in the atmosphere in the same manner as in Reference Example 5. The results are summarized in the table below.

[0183] [Reference example 10] Dispersion 7 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 7. Next, 7.13 g of LiTFSI (chemical formula: Li(F3CSO2)2N) as a lithium salt was added to water at a concentration of 87 mass %, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain a solution 8. The obtained dispersion 7 and solution 8 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-10. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-10 in the same manner as in Reference Example 5. The results are summarized in the table below. In Reference Example 10, the carbon amounts shown in Table 3 below were estimated from the analyzed mass of sulfur, taking into account the weight of each atom in the lithium salt.

[0184] [Comparative Reference Example 3] As in Comparative Reference Example 1, the LBO powder was used as Comparative Reference Example 3, and various evaluations were carried out in the same manner as in Reference Example 5.

[0185] [Comparative Reference Example 4] As in Comparative Reference Example 2, the fine particles of the lithium-containing oxide were used as Comparative Reference Example 4, and various evaluations were carried out in the same manner as in Reference Example 5.

[0186] In the table below, if the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement as described above has a first peak whose peak top is located in the range of r 1.43±0.2 Å and a second peak whose peak top is located in the range of r 2.40±0.2 Å, and if the G(r) at the peak top of the first peak and the G(r) at the peak top of the second peak are greater than 1.0, the column for "short-range G(r)" is marked with "A," and otherwise it is marked with "B." In Reference Examples 5 to 8 and 13 to 16 shown in the table below, the G(r) value at the peak top of the first peak was 1.2 or more. In addition, in the above-mentioned reduced pair distribution function G(r), when the absolute value of G(r) is less than 1.0 in the range of r greater than 5 Å and not more than 10 Å, the column "Long-distance G(r)" in the table below is marked with "A", and when the absolute value of G(r) is not less than 1.0, it is marked with "B". Furthermore, as a result of the X-ray diffraction measurement using the above-mentioned CuKα ray, cases where the above-mentioned X-ray diffraction characteristics were satisfied were rated as "A", and cases where the above-mentioned X-ray diffraction characteristics were not satisfied were rated as "B". Note that in Reference Examples 5 to 10 and Reference Examples 11 to 17 shown in the table below, none of the first peak, second peak, third peak, and fourth peak was present in the X-ray diffraction pattern, or the intensity ratio of at least one of the first peak, second peak, third peak, and fourth peak was 2.0 or less.

[0187] In the table below, the "Elemental Analysis" column shows the composition of the solid electrolyte (I) obtained in each Reference Example and the lithium-containing oxide in each Comparative Reference Example as a molar amount of each element, with the content of B being set to "4.00" as a relative value. In the table below, the "full width at half maximum ratio (%)," "coefficient of determination," and "mass reduction rate (%)" are as explained in the above description of Reference Example 1.

[0188] In the table below, the "area intensity ratio" is the solid 7 In Li-NMR measurement, this is the ratio of the area intensity of the second peak to the area intensity of the first peak, and the evaluation results are listed based on the following criteria. <Standards for area intensity ratio> 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%

[0189] In the table below, the "maximum absorption intensity ratio" column indicates whether or not the above-mentioned infrared absorption spectrum characteristics are satisfied. -1 Maximum absorption intensity in the wavenumber region of 800-1600cm -1 The maximum absorption intensity in the wavenumber region of [A] is 0.20 or more and is indicated as "A", and the maximum absorption intensity in the wavenumber region of [B] is less than 0.20. In the table below, "-" means that no measured value is shown.

[0190] [Table 3]

[0191] [Table 4]

[0192] As shown in the table above, the solid electrolytes (I)-5, (I)-6, (I)-7, (I)-8, (I)-9, and (I)-10 of Reference Examples 5 to 10 were found to have excellent ionic conductivity. Furthermore, the results of elemental analysis confirmed that the solid electrolytes in Reference Examples 7 to 10 had a higher Li content. In Reference Examples 7 to 10, an aqueous dispersion containing a lithium-containing oxide subjected to mechanical milling was mixed with an aqueous solution containing a lithium salt (Method 3 in Step 2B described above). This allowed for a larger amount of lithium salt to be mixed, which is presumably responsible for the increased amount of Li incorporated into the solid electrolyte. Furthermore, Reference Examples 7, 8, and 9, which used LiFSI as the lithium salt, were found to have improved ionic conductivity. This is presumably due to the presence of highly mobile Li in the increased Li.

[0193] <Effect of water in solid electrolyte> A compact (pellet) (10 mm diameter, 0.9 mm thickness) of the solid electrolyte (I)-7 obtained in Reference Example 7 was vacuum-dried at 27°C under a restraint of 60 MPa, and the pressure change and ionic conductivity with respect to the vacuum drying time were investigated. The method for producing the compact and the evaluation of ionic conductivity were the same as those described above, except that the In electrode was replaced with a Ti electrode. The results are shown in Table 5.

[0194] [Table 5]

[0195] The solid electrolyte (I)-7 of Reference Example 7 has a peak in the infrared absorption spectrum of 3000 to 3500 cm -1 The OH stretching peak increases, suggesting the presence of numerous OH groups and water. Furthermore, the presence of free and bound water is suspected. In the above study, the pellets were first dried under vacuum conditions that would volatilize the free water, and then under more severe drying conditions, and the ionic conductivity at each stage was evaluated.

[0196] As shown in the table above, the pressure was 200 Pa after 5 minutes of drying, and the free water was considered to have evaporated. However, the ionic conductivity was 3.8 × 10 -3 Even with a drying time of 1080 minutes and a pressure of 15 Pa, the ionic conductivity was 5.7 × 10 -4 This result indicates that bound water exists in addition to free water, and that this contributes to the ionic conductivity.

[0197] [Reference example 11] Dispersion 9 having a concentration of fine lithium-containing oxide particles of 42 mass % was obtained in the same manner as in the preparation of dispersion 1 in Reference Example 7 above. Next, 7.12 g of LiTFSI (chemical formula: Li(F3CSO2)2N) as a lithium salt was added to water to a concentration of 87 mass %, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 10. The obtained dispersion 9 and solution 10 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-11. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were carried out in the atmosphere using solid electrolyte (I)-11 in the same manner as in Reference Example 5. The results are summarized in the table below.

[0198] [Reference example 12] A solid electrolyte (I)-12 was obtained in the same manner as in Reference Example 11, except that the contents of water and LiTFSI in the obtained solid electrolyte (I) were changed to the amounts shown in the table below, and various evaluations were carried out under air in the same manner as in Reference Example 5. The results are summarized in the table below.

[0199] [Reference examples 13~17] Solid electrolytes (I)-13 to (I)-17 were obtained in the same manner as in Reference Example 11, 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 shown in the table below, and various evaluations were carried out in the atmosphere in the same manner as in Reference Example 5. The results are summarized in the table below. However, in Reference Example 17, the powder obtained after vacuum drying was immediately evaluated in the atmosphere.

[0200] In the table below, the columns "fine particles of lithium-containing oxide", "lithium salt", and "water" indicate relative molar ratios. For example, in Reference Example 11, the molar ratio of lithium salt to fine particles of lithium-containing oxide is 1, and the molar ratio of water to fine particles of lithium-containing oxide is 11. The molar ratios were calculated by the following method. For the analysis of each element, lithium and boron were quantitatively analyzed by ICP-OES, and fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated as the difference from the total amount of the solid electrolyte by adding up the analyzed masses of elements other than O. In Reference Examples 11 and 12, the carbon amount was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the lithium salt. The molar ratio of the fine particles of the lithium-containing oxide to the lithium salt in the solid electrolyte was calculated from the molar ratio of an element (e.g., B) present only in the fine particles of the lithium-containing oxide to the element present only in the lithium salt. The molar ratio of the fine particles of the lithium-containing oxide to water was calculated by subtracting the molar ratio of O contained in the fine particles of the lithium-containing oxide and the lithium salt from the molar ratio of O in the solid electrolyte to calculate the molar amount of O derived from water, and then using the resulting molar amount of O derived from water and the molar amount of the fine particles of the lithium-containing oxide.

[0201] [Table 6]

[0202] The content (mass %) of each component in the solid electrolyte (I) was calculated based on the molar amount and molecular weight shown in Table 6. The results are shown in the table below.

[0203] [Table 7]

[0204] [Table 8]

[0205] As shown in the above table, the solid electrolytes of each Reference Example had the desired characteristics or properties and exhibited excellent ionic conductivity.

[0206] [Test Example 1] <Rolling durability test> (Preparation of fine particles of lithium-containing oxide) 45 g of powdered Li2B4O7 crystals (LBO powder) (manufactured by Rare Metallic), 770 g of zirconia beads, and 3 mL of water were placed in a 500 mL zirconia pot and sealed with a Teflon (registered trademark) ring and a zirconia lid. The LBO powder was milled in a planetary ball mill at 300 rpm for 45 hours to obtain fine particles of lithium-containing oxide.

[0207] (Preparation of solid electrolyte slurry) 10 g of the fine particles of the lithium-containing oxide, 15 g of water, and 11 g of LiFSI were mixed in a beaker and subjected to ultrasonic treatment using an ultrasonic cleaner for 30 minutes to obtain a dispersion liquid, which was further stirred with a magnetic stirrer for 30 minutes 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. The obtained powder was stored in a desiccator (5%) for several days and then analyzed under atmospheric conditions. It was confirmed that the powder had the above-mentioned X-ray diffraction characteristics and was in an amorphous state. Furthermore, the ionic conductivity was measured by the above-mentioned method and was 4.5 x 10 -3The molar ratio of the LiFSI content to the lithium-containing oxide content was 1, and the molar ratio of the water content was 9. The elemental composition (molar ratio) was approximately as follows: Li:B:O:F:S:N=3:4:20:2:2:1.

[0208] (Preparation of Positive Electrode Slurry) To 5.2 g of the above solid electrolyte slurry 1, 5.0 g of the positive electrode active material LiCoO2 and 4.8 g of a 6 mass % aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain positive electrode slurry 1.

[0209] (Preparation of negative electrode slurry) To 7.6 g of the above solid electrolyte slurry 1, 5.0 g of the negative electrode active material TiNb2O7 and 9.8 g of a 6% aqueous dispersion of CNT (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain negative electrode slurry 1.

[0210] (Preparation of positive electrode laminate [solid electrolyte layer / positive electrode active material layer / Al current collector]) The positive electrode slurry 1 was applied to a 50 μm thick A4-size aluminum foil using a desktop coater with an applicator gap of 100 μm and a coating speed of 30 mm / s. After leaving the mixture at room temperature for 1 hour, the solid electrolyte slurry 1 was applied to the positive electrode slurry coating in a multilayer fashion using a desktop coater with an applicator gap of 200 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, yielding a positive electrode laminate (solid electrolyte layer / positive electrode active material layer / Al current collector). The thickness of the solid electrolyte layer was approximately 60 μm.

[0211] (Preparation of negative electrode laminate [solid electrolyte layer / negative electrode active material layer / Al current collector]) The above-mentioned negative electrode slurry 1 was applied to a 50 μm-thick A4-size Al foil using a desktop coater with an applicator gap of 200 μm and a coating speed of 30 mm / s. After leaving it at room temperature for 1 hour, the above-mentioned solid electrolyte slurry 1 was applied in a multilayer on the negative electrode slurry coating using a desktop coater with an applicator gap of 300 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, yielding a negative electrode laminate (solid electrolyte layer / negative electrode material layer / Al current collector). The thickness of the solid electrolyte layer was approximately 60 μm.

[0212] (Rolling durability test) The positive electrode laminate and the negative electrode laminate are bonded together to form a battery element, and the negative electrode laminate is A 50 μm thick Teflon (registered trademark) film was laminated as a separator layer, and pressed to obtain a battery element laminate. The battery element laminate was wound around a core material having a diameter of 3 mm, with the separator layer side facing inward, four times in a spiral fashion so that the battery elements were in four layers. Next, the solid electrolyte layer was unwound and stretched out, and visually inspected. No cracks were found in the solid electrolyte layer. Furthermore, when the above battery element laminate was wound around a core material to produce a wound secondary battery as shown in FIG. 2, it was confirmed that the battery was capable of charging and discharging and functioned as a secondary battery. As described above, it has been confirmed that the secondary battery of the present invention, while using an oxide-based solid electrolyte, has excellent interparticle bonding properties, is highly flexible and is less likely to crack even when wound around a core material, and does not produce harmful substances, making it highly safe.

[0213] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0214] This application claims priority based on Japanese Patent Application No. 2022-089963, filed in Japan on June 1, 2022, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0215] 1 Negative electrode current collector 2 Negative electrode active material layer 3 Solid electrolyte layer 4 Cathode active material layer 5 Positive electrode current collector 6. Operating parts 10 All-solid-state lithium-ion secondary battery 21 Laminate 21a Separator layer 21b Negative electrode current collector 21c Negative electrode active material layer 21d Solid electrolyte layer 21e Cathode active material layer 21f Positive electrode current collector 23 Battery casing 25 Positive electrode tab 26 Battery positive electrode 27 Negative electrode tab 28 Battery negative electrode 30 Wound-type all-solid-state lithium-ion secondary battery

Claims

1. A wound-type all-solid-state lithium ion secondary battery is formed by winding a laminate, which is formed by arranging a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order, around a core material, the solid electrolyte layer includes an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt, and in the amorphous solid electrolyte, a ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in terms of molar ratio.

2. 2. The wound-type all-solid-state lithium ion secondary battery according to claim 1, wherein the ratio of the content of water to the content of the lithium-containing oxide in the amorphous solid electrolyte is 12 or less in molar ratio.

3. 3. The wound all-solid-state lithium ion secondary battery according to claim 2, wherein the ratio of the content of the water to the content of the lithium-containing oxide in the amorphous solid electrolyte is 1 to 12 in terms of molar ratio.

4. The lithium-containing oxide is Li ２＋ｘ B ４＋ｙ O ７＋ｚ The wound type all-solid-state lithium ion secondary battery according to any one of claims 1 to 3, comprising: However, −0.3<x<0.3, −0.3<y<0.3, and −0.3<z<0.

3.

5. The wound-type all-solid-state lithium ion secondary battery according to any one of claims 1 to 3, wherein the lithium salt is represented by the following formula (1): Formula (1) LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) In the formula, R ｆ１ and R ｆ２ each independently represents a halogen atom or a perfluoroalkyl group.

6. 4. The wound all-solid-state lithium ion secondary battery according to claim 1, wherein, in the amorphous solid electrolyte, when the molar amount of B is 4.00, the molar amount of Li is 1.58 to 3.49, the molar amount of O is 6.23 to 25.00, and the molar amounts of elements other than B, Li, and O are each 0.001 to 10.

00.

7. A wound-type all-solid-state lithium ion secondary battery is formed by winding a laminate, which is formed by arranging a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order, around a core material, the solid electrolyte layer comprises an amorphous solid electrolyte containing Li, B, and O, and when the molar amount of B in the amorphous solid electrolyte is 4.00, the molar amount of Li is 1.58 to 3.49, the molar amount of O is 6.23 to 25.00, and the molar amounts of elements other than Li, B, and O are each 0.001 to 10.

00.

8. 8. The method for producing the wound all-solid-state lithium ion secondary battery according to claim 1, further comprising forming the laminate under conditions in which the solid electrolyte layer is in contact with water.

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