Solid electrolyte, solid electrolyte sheet, and modification method and production method for sulfide solid electrolyte

Abstract

A solid electrolyte according to the present invention includes lithium (Li), phosphorus (P), and sulfur (S). The solid electrolyte contains LixP (x being a number from 0 to 3, inclusive). It is preferable that the solid electrolyte also includes lithium sulfide. It is also preferable that the P2p spectrum measured by X-ray photoelectron spectroscopy has a peak at a binding energy of 124.5–129.0 eV. It is also preferable that the S2p spectrum measured by X-ray photoelectron spectroscopy has a peak at a binding energy of 159.0–160.8 eV.

Description

Solid electrolyte, solid electrolyte sheet, and sulfide solid electrolyte modification method and production method

[0001] The present invention relates to a solid electrolyte, a solid electrolyte sheet, and a method for modifying and producing a sulfide solid electrolyte.

[0002] In recent years, CO ２ Secondary batteries have been attracting attention as an approach to preventing global warming by reducing CO2 emissions. Among them, solid-state batteries are expected to be put into practical use as batteries that combine safety and high energy density. Solid-state batteries have a problem in that ionic conductivity decreases at the interface between the electrode active material and the solid electrolyte. To address this problem, for example, coating the surface of the active material with various metal compounds has been proposed.

[0003] For example, Patent Document 1 proposes an active material having a coating layer containing a compound containing Li, A (A is one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W, and Al), and O. This document states that the active material having such a coating layer has improved lithium ion mobility.

[0004] Japanese Patent Application Laid-Open No. 2020-135948

[0005] As described in Patent Document 1, coating an active material with a metal compound can improve ionic conductivity at the interface between the active material and a solid electrolyte. However, even with such a method, there are cases where ionic conductivity at the interface is still insufficient. Therefore, an object of the present invention is to provide a solid electrolyte having excellent ionic conductivity.

[0006] The present invention provides a solid electrolyte containing lithium (Li), phosphorus (P), and sulfur (S), comprising: ｘ The present invention provides a solid electrolyte containing P (x is a number of 0 or more and 3 or less).

[0007] The present invention also provides a method for modifying a sulfide solid electrolyte, comprising: preparing a cell comprising a solid electrolyte layer containing a sulfide solid electrolyte containing Li, P, and S elements; and electrodes disposed on each side of the solid electrolyte layer, at least one of the electrodes containing Li metal on a surface facing the solid electrolyte layer; and modifying the sulfide solid electrolyte by passing current through the cell.

[0008] The present invention also provides a method for producing a sulfide solid electrolyte by passing current through a cell including a sulfide layer containing a sulfide including Li, P, and S elements, and electrodes disposed on each side of the sulfide layer, wherein the surface of at least one of the electrodes facing the sulfide layer contains Li metal.

[0009] Fig. 1 shows P2p spectra obtained by X-ray photoelectron spectroscopy on the solid electrolytes produced in Example 2 and Comparative Example 1. Fig. 2 shows S2p ​​spectra obtained by X-ray photoelectron spectroscopy on the solid electrolytes produced in Example 2 and Comparative Example 1.

[0010] The present invention will be described below based on preferred embodiments. First, the solid electrolyte of the present invention will be described. The solid electrolyte of the present invention contains Li, P, and S elements. In one embodiment, the solid electrolyte of the present invention contains a sulfide containing Li, P, and S elements. The sulfide preferably has lithium ion conductivity. Examples of such sulfides include Li, P, and S. ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiX (where "X" represents one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ , Li ２ S-Li ３ P.O. ４ -P ２ S ５ , Li ３ P.S. ４ , Li ４P ２ S ６ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ , Li ａ P.S. ｂ X ｃ (Sulfides containing a crystalline phase having an argyrodite-type crystal structure, "X" represents one or more halogen elements.) Among them, sulfides containing a crystalline phase having an argyrodite-type crystal structure are preferably used because of their excellent ionic conductivity. Details of sulfides will be described later.

[0011] The solid electrolyte of the present invention has the composition formula: Li ｘ P (wherein x is a number greater than 0 and not greater than 3) (hereinafter simply referred to as "Li ｘ The solid electrolyte of the present invention contains Li ｘ By including P, when the solid electrolyte of the present invention is used in a solid battery, the lithium ion conductivity of the solid battery can be improved. From the viewpoint of further enhancing this effect, x is, for example, preferably 0.1 or more, more preferably 1.0 or more, and even more preferably 2.0 or more. On the other hand, x is preferably 3.0 or less. The value of x may not be constant. For example, Li ｘ P is x = x １ Compound of x = x ２ In this case, x may be a mixture of １ and x ２ are each preferably independently within the range of x described above.

[0012] At least a portion of the surface of the solid electrolyte is Li ｘ It is preferable that the solid electrolyte is made of P. This allows the surface of the solid electrolyte to be free of Li ｘWhen a solid electrolyte is produced by bringing the part made of P into contact with the active material of the electrode, Li ｘ It is presumed that P exists at the interface between the solid electrolyte and the active material. This is thought to make the effect of increasing lithium ion conductivity even more remarkable. ｘ When the solid electrolyte is composed of P, the specific form of the solid electrolyte is, for example, Li ｘ A first layer containing P and Li ｘ In another example, a second layer containing Li and a second layer containing P are stacked in the thickness direction of the solid electrolyte. ｘ a first layer and a second layer containing P, and a second layer disposed between the two layers, ｘ An example of such a configuration is one in which a first layer and a third layer not containing P are laminated in the thickness direction of the solid electrolyte. Note that the boundaries between the first layer, the second layer, and the third layer described above do not need to be clearly observed.

[0013] At least a part of the surface of the solid electrolyte is Li ｘ The fact that the solid electrolyte is composed of P can be confirmed by, for example, X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS") measurement. Specifically, the solid electrolyte of the present invention preferably has a peak apex in the binding energy range of 124.5 eV to 129.0 eV in the P2p spectrum measured by XPS. Such a peak is due to Li that constitutes at least a part of the surface of the solid electrolyte. ｘ The peak is a peak derived from P. The apex of the peak more preferably has a binding energy of 128.0 eV or less, and even more preferably 127.0 eV or less. The apex of the peak more preferably has a binding energy of 125.5 eV or more.

[0014] The solid electrolyte of the present invention is ｘ It is preferable that the content of P is within a predetermined range. For example, when the solid electrolyte of the present invention contains a sulfide containing a crystalline phase having an argyrodite-type crystal structure, the content of Li, which is observed by XPS measurement, is ｘIt is preferable that the ratio of the peak intensity of the peak derived from P to the peak intensity of the peak derived from the sulfide containing a crystalline phase having an argyrodite-type crystal structure is within a predetermined range. Specifically, in the P2p spectrum measured by XPS, when the peak intensity of a peak having an apex in the binding energy range of 130.8 eV to 135.0 eV is defined as P1, and the peak intensity of a peak having an apex in the binding energy range of 124.5 eV to 129.0 eV is defined as P2, the ratio P2 / P1 of P2 to P1 is preferably 0.02 or more, more preferably 0.1 or more, and even more preferably 1.0 or more. Furthermore, P2 / P1 may be 100 or less, 10 or less, or 5.0 or less. Here, P1 corresponds to the peak intensity of the peak derived from phosphorus contained in the sulfide containing a crystalline phase having an argyrodite-type crystal structure, and P2 corresponds to the peak intensity of Li. ｘ This corresponds to the peak intensity of the peak derived from the phosphorus element contained in P.

[0015] By making P2 / P1 equal to or greater than the lower limit, a sufficient amount of Li ｘ Since P can be present in the solid electrolyte, Li ｘ The above-mentioned effects can be more reliably obtained by the presence of P. Furthermore, by making P2 / P1 equal to or less than the upper limit, the ionic conductivity of the solid electrolyte can be sufficiently ensured.

[0016] The solid electrolyte of the present invention preferably further contains lithium sulfide. When the solid electrolyte of the present invention contains lithium sulfide, sufficient electronic insulation can be ensured.

[0017] From the viewpoint of making the above-mentioned effect due to the presence of lithium sulfide more pronounced, it is preferable that at least a portion of the surface of the solid electrolyte is composed of lithium sulfide. The fact that at least a portion of the surface of the solid electrolyte is composed of lithium sulfide can be confirmed, for example, by XPS measurement. Specifically, the solid electrolyte of the present invention preferably has a peak apex in the S2p spectrum measured by XPS, in a binding energy range of 159.0 eV or more and 160.8 eV or less. This peak is a peak derived from the sulfur element contained in the lithium sulfide constituting at least a portion of the surface of the solid electrolyte. The binding energy of the apex of the peak is more preferably 159.6 eV or more, and even more preferably 159.8 eV or more. Furthermore, the binding energy of the apex of the peak is more preferably 160.4 eV or less, and even more preferably 160.2 eV or less.

[0018] When at least a part of the surface of the solid electrolyte is made of lithium sulfide, the specific form of the solid electrolyte can be, for example, a form in which a first layer containing lithium sulfide and a second layer not containing lithium sulfide are laminated in the thickness direction of the solid electrolyte. In this case, the first layer further contains Li ｘ P, and the second layer contains Li ｘ In another example, a first layer and a second layer containing lithium sulfide and a third layer not containing lithium sulfide disposed between the first and second layers may be stacked in the thickness direction of the solid electrolyte. In this case, the first and second layers may further contain Li ｘ The third layer contains Li ｘ It may or may not contain P. The boundaries between the first to third layers described above do not need to be clearly observed.

[0019] As described above, the solid electrolyte of the present invention contains Li, P, and S elements, but the solid electrolyte of the present invention may also contain elements other than these. For example, it is preferable that the solid electrolyte of the present invention further contains a halogen (X) element from the viewpoint of further improving ion conductivity. Examples of the X element include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The X element may be one of these elements, or a combination of two or more of them. Among these, the X element is preferably one or more selected from the group consisting of Cl, Br, and I. In one embodiment, the solid electrolyte of the present invention comprises a sulfide containing Li, P, S, and X elements, and Li ｘ P.

[0020] The solid electrolyte of the present invention more preferably contains the X element at a predetermined content. Specifically, the solid electrolyte of the present invention preferably contains the X element at 1.4 atm% or more, more preferably at 5.7 atm% or more, and even more preferably at 8.6 atm% or more. The solid electrolyte of the present invention also preferably contains the X element at 14.3 atm% or less, and more preferably at 11.4 atm% or less. The content of the X element in the solid electrolyte can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy) or X-ray photoelectron spectroscopy.

[0021] As described above, the solid electrolyte of the present invention preferably contains a sulfide containing a crystalline phase having an argyrodite-type crystal structure. The argyrodite-type crystal structure has the chemical formula: Ag ８ GeS ６This is the crystalline structure possessed by a group of compounds derived from minerals represented by the formula: Whether or not a sulfide has a crystalline phase with an argyrodite-type crystalline structure can be confirmed by measurement using X-ray diffraction (hereinafter also referred to as "XRD"). For example, in a diffraction pattern measured by XRD using CuKα1 radiation, a crystalline phase with an argyrodite-type crystalline structure shows characteristic diffraction peaks at 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. Depending on the element species constituting the sulfide, in addition to the diffraction peaks, characteristic diffraction peaks may also be observed at 2θ = 15.3 ° ± 1.0 °, 18.0 ° ± 1.0 °, 44.3 ° ± 1.0 °, 47.2 ° ± 1.0 °, 51.7 ° ± 1.0 °, 58.3 ° ± 1.0 °, 60.7 ° ± 1.0 °, 61.5 ° ± 1.0 °, 70.4 ° ± 1.0 °, and 72.6 ° ± 1.0 °. To identify the diffraction peaks derived from the argyrodite-type crystal structure, for example, data from PDF number 00-034-0688 is used.

[0022] When the sulfide has a crystal structure having a crystal phase of an argyrodite-type crystal structure, the sulfide has a composition formula (I): Li ａ P.S. ｂ X ｃ (X is at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)) is preferred from the viewpoint of improving lithium ion conductivity.

[0023] In composition formula (I), a, which indicates the molar ratio of Li element, is preferably, for example, 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. On the other hand, a is preferably, for example, 6.5 or less, more preferably 5.9 or less, and particularly preferably 5.6 or less. When a is in this range, the cubic argyrodite-type crystal structure at around room temperature (25°C) becomes more stable, allowing lithium ion vacancies to be sufficiently introduced into the structure, resulting in effectively increasing lithium ion conductivity.

[0024] In composition formula (I), b is preferably, for example, 3.5 or more, more preferably 4.0 or more, and particularly preferably 4.2 or more. On the other hand, b is preferably, for example, 5.5 or less, more preferably 4.9 or less, and particularly preferably 4.7 or less. When b is within the above range, the argyrodite-type crystal structure becomes more stable at around room temperature (25°C), and lithium ion conductivity is effectively increased.

[0025] In composition formula (I), c is preferably, for example, 0.1 or more, more preferably 1.1 or more, and particularly preferably 1.4 or more, while c is preferably, for example, 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0026] The sulfide has the composition formula (II): Li ７－ｄ P.S. ６－ｄ X ｄ The composition represented by composition formula (II) is a stoichiometric composition of an argyrodite-type crystal phase. In composition formula (II), X has the same meaning as in composition formula (I).

[0027] In composition formula (II), d is preferably, for example, 0.4 or more, more preferably 0.8 or more, and particularly preferably 1.2 or more, while d is preferably, for example, 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0028] The sulfide has the composition formula (III): Li ７－ｄ－２ｅ P.S. ６－ｄ－ｅ X ｄ The argyrodite-type crystalline phase having the composition represented by the composition formula (III) may be, for example, a mixture of an argyrodite-type crystalline phase having the composition represented by the composition formula (II) and P ２ S ５ It is produced by reaction with diphosphorus pentasulfide.

[0029] In the composition formula (III), e is the Li from the stoichiometric composition represented by the composition formula (II). ２e is a value indicating the deviation of the S component. e is, for example, preferably −0.9 or more, more preferably −0.6 or more, and particularly preferably −0.3 or more. On the other hand, e is, for example, preferably (−d+2) or less, more preferably (−d+1.6) or less, and particularly preferably (−d+1.0) or less.

[0030] In the sulfide, the atomic ratio X / P of the X element to the P element is, for example, preferably greater than 1.0, more preferably 1.1 or more, even more preferably 1.2 or more, and even more preferably 1.4 or more. On the other hand, the atomic ratio X / P is, for example, preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.2 or less. When the atomic ratio X / P is within the above range, the lithium ion conductivity is further improved. The atomic ratio X / P can be measured, for example, by ICP emission spectroscopy or SEM-EDS analysis.

[0031] In particular, when the X element includes at least Cl and Br, the atomic ratio (Cl + Br) / P of the total of Cl and Br to P is preferably greater than 1.0, more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.4 or greater. On the other hand, the atomic ratio (Cl + Br) / P is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less. The atomic ratio (Cl + Br) / P within the above range is preferable because it further improves lithium ion conductivity. The atomic ratio (Cl + Br) / P can be measured, for example, by elemental analysis using ICP emission spectroscopy or a scanning electron microscope equipped with EDS (SEM-EDS).

[0032] The sulfide is particularly represented by the composition formula (IV) Li ７－ｄ P.S. ６－ｄ Cl ｄ１ Br ｄ２In the composition formula (IV), the total molar ratio d (= d1 + d2) of Cl and Br is preferably greater than 1.0, more preferably 1.2 or more, and particularly preferably 1.4 or more. On the other hand, the total molar ratio d is preferably less than 2.5, more preferably less than 2.0, particularly preferably 1.8 or less, and even more preferably 1.7 or less. When the total molar ratio d is within the above range, the formation of heterophases can be sufficiently controlled, and the decrease in ionic conductivity can be effectively suppressed.

[0033] In the composition formula, the ratio of the molar ratio of Br to the molar ratio of Cl (d2 / d1) is, for example, preferably 0.1 or more, more preferably 0.3 or more, and particularly preferably 0.5 or more. On the other hand, the molar ratio is, for example, preferably 10 or less, more preferably 5 or less, and particularly preferably 3 or less. When the molar ratio is within the above-mentioned range, lithium ion conductivity can be further improved.

[0034] In the composition formula, d1, which indicates the molar ratio of Cl, is preferably, for example, 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d1 is preferably, for example, 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. When d1 is equal to or greater than the lower limit, lithium ion conductivity can be further increased. On the other hand, when d1 is equal to or less than the upper limit, the sulfide can be more easily obtained.

[0035] In the composition formula, d2, which indicates the molar ratio of Br, is preferably, for example, 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d2 is, for example, preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. When d2 is equal to or greater than the lower limit, sulfides are easily obtained. On the other hand, when d2 is equal to or less than the upper limit, lithium ion conductivity can be further increased.

[0036] In any case where the sulfide is represented by any of the composition formulas (I), (II), (III) and (IV), it is preferable that the X element contains Br, since this further improves the lithium ion conductivity.

[0037] The solid electrolyte of the present invention can be used as a battery comprising a solid electrolyte layer containing the solid electrolyte, a positive electrode, and a negative electrode. The battery may be a primary battery or a secondary battery. Examples of the battery include, but are not limited to, lithium ion batteries and sodium ion batteries. As the positive electrode and negative electrode constituting the battery, those commonly used as electrodes for solid-state batteries can be used as appropriate. In particular, it is preferable that the active material of the electrode has a coating layer containing, for example, lithium niobate, lithium phosphate, or lithium sulfate, from the viewpoint of further enhancing ionic conductivity at the interface between the active material and the solid electrolyte. The solid electrolyte layer may contain additives such as a binder in addition to the solid electrolyte of the present invention.

[0038] The solid electrolyte of the present invention can also be used as a solid electrolyte sheet in which the solid electrolyte of the present invention is supported on a porous support. By supporting the solid electrolyte of the present invention on a porous support, the self-supporting property of the solid electrolyte layer containing the solid electrolyte of the present invention can be improved.

[0039] The term "porous" in the context of a porous support refers to a state in which a large number of pores are present. The porous support may be made of a plurality of fibrous materials, as long as it has pores that allow the particles constituting the solid electrolyte to be filled and in contact with each other when a solid electrolyte sheet is formed. The porous support preferably has pores that extend from one surface to the other surface of the porous support. The size of the pores may be such that the particles constituting the solid electrolyte can be filled when a solid electrolyte sheet is formed. The pores in the porous support may be, for example, micropores, mesopores, or macropores. The pores may be interconnected.

[0040] The porous support is preferably a fiber sheet, since it can provide the solid electrolyte sheet with sufficient self-supporting properties and appropriate flexibility. Examples of the fiber sheet include nonwoven fabric, woven fabric, and knitted fabric, and nonwoven fabric is particularly preferred. When the porous support is a fiber sheet, the term "porous" refers to a state in which voids are generated in the gaps between the fibers.

[0041] There are various types of nonwoven fabrics depending on the type of fibers (fiber length, fiber diameter, fiber material, etc.) used in the production of the nonwoven fabric, the type of production method (e.g., web formation method, web fiber bonding method, etc.), etc. The nonwoven fabric used as the porous support is not particularly limited as long as a desired solid electrolyte sheet can be obtained. Examples of nonwoven fabrics include orthogonal fiber nonwoven fabrics, long fiber nonwoven fabrics, short fiber nonwoven fabrics, wet-laid nonwoven fabrics, dry-laid nonwoven fabrics, air-laid nonwoven fabrics, carded nonwoven fabrics, parallel nonwoven fabrics, cross-laid nonwoven fabrics, random nonwoven fabrics, spunbonded nonwoven fabrics, meltblown nonwoven fabrics, flash-spun nonwoven fabrics, chemically bonded nonwoven fabrics, hydroentangled nonwoven fabrics, needle-punched nonwoven fabrics, stitch-bonded nonwoven fabrics, thermally bonded nonwoven fabrics, burst fiber nonwoven fabrics, tow-opened nonwoven fabrics, split fiber nonwoven fabrics, composite nonwoven fabrics, laminated nonwoven fabrics, coated nonwoven fabrics, and laminated nonwoven fabrics. Of these, cross-laid nonwoven fabrics are preferred. Cross-laid nonwoven fabrics are preferred because the strength ratio in the length direction X and the width direction Y, the basis weight, etc. can be easily adjusted. It is preferable to adjust the strength ratio in the length direction X and the width direction Y of a cross-laid nonwoven fabric uniformly. The basis weight of the cross-type nonwoven fabric may be low or high. An example of a cross-type nonwoven fabric is polyolefin mesh cloth (see JP 2007-259734 A). Note that the specific basis weight of the nonwoven fabric can be the same as that described in, for example, JP 2018-129307 A, and therefore will not be described here.

[0042] The material, porosity, air permeability, thickness, etc. constituting the porous support may be the same as those of the porous support used in a general solid electrolyte sheet, for example, the porous support described in JP 2018-129307 A, and therefore description thereof will be omitted here.

[0043] Next, a preferred method for producing the solid electrolyte of the present invention will be described. The solid electrolyte of the present invention (hereinafter also referred to as "sulfide solid electrolyte") can be produced by passing current through a cell including a sulfide layer containing sulfides including Li, P, and S elements, and electrodes disposed on each side of the sulfide layer.

[0044] The sulfide layer may contain components other than sulfides. Examples of such components include binders. The sulfide layer may also contain a porous support. The thickness of the sulfide layer is, for example, preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less. On the other hand, the thickness of the sulfide layer may be, for example, 5 μm or more, or 10 μm or more.

[0045] The sulfide layer can be produced, for example, by dropping a slurry composed of a sulfide, a binder, and a solvent onto a substrate and scraping it off with a doctor blade or the like, by contacting the substrate with the slurry and then cutting it with an air knife, or by forming a coating film by screen printing or the like and then removing the solvent through heat drying. Alternatively, the sulfide can be produced by compacting a powdered sulfide by pressing or the like and then processing it appropriately. Furthermore, when the solid electrolyte of the present invention is produced in the form of a solid electrolyte sheet in which the solid electrolyte is supported on a porous support, for example, the solid electrolyte of the present invention can be supported on a porous support according to the method described in JP 2021-163759 A, and this can be used as the sulfide layer.

[0046] At least one of the electrodes disposed on each side of the sulfide layer contains Li metal on the surface of the sulfide layer. When the cell is energized, the sulfide contained in the sulfide layer reacts with the Li metal on the electrode, resulting in Li ｘP and lithium sulfide are generated on the surface of the sulfide layer facing the electrode. Regarding the electrodes disposed on each side of the sulfide layer, one of the electrodes may contain Li metal on the surface facing the sulfide layer, or both of the electrodes may contain Li metal on the surfaces facing the sulfide layer. When the surface facing the sulfide layer of one electrode contains Li metal, the surface facing the sulfide layer of the other electrode may contain a metal such as aluminum or indium. Furthermore, in the present invention, it is preferable that the surface facing the sulfide layer of one electrode is made of Li metal. The same applies to the surface facing the sulfide layer of the other electrode.

[0047] After preparing the positive electrode, negative electrode, and sulfide layer, the sulfide layer is then placed between the positive electrode and negative electrode, and these three components are sealed in a container. This results in a cell before energization. The three components may be subjected to a pressure treatment before, while, or after being placed in the container. This increases the adhesion between the three components, and the Li ｘ The production efficiency of P and lithium sulfide can be improved. The pressure applied in the pressure treatment is, for example, preferably 300 MPa or more, more preferably 400 MPa or more, and even more preferably 500 MPa or more. On the other hand, the pressure is, for example, preferably 1000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less.

[0048] The cell is then energized. ｘ From the viewpoint of successfully producing P, the temperature when current is applied to the cell is preferably 25° C. or higher, more preferably 45° C. or higher, and even more preferably 60° C. or higher. From the same viewpoint, the temperature when current is applied to the cell is preferably 90° C. or lower, more preferably 80° C. or lower, and even more preferably 70° C. or lower. Note that, depending on the current application conditions, heat may be generated, and the battery may reach a temperature different from the ambient temperature. However, the temperature when current is applied in this step refers to the ambient temperature where the cell is placed.

[0049] Li ｘ In order to successfully generate P, the present manufacturing method requires the cell to have a current of 0.01 mAh / cm ２It is preferable to apply a current at a current density of 0.03 mAh / cm or more. ２ It is more preferable to apply a current at a current density of 0.05 mAh / cm or more. ２ From the same viewpoint, it is more preferable to apply a current at a current density of 1.0 mAh / cm or more to the cell. ２ It is preferable to apply current at a current density of 0.5 mAh / cm or less. ２ It is more preferable to apply current at a current density of 0.3 mAh / cm or less. ２ It is more preferable to pass current at the following current density. The current density may be constant or may vary within the above range. The applied voltage may be adjusted so that the current density falls within the above range. The current is preferably passed using an electrode made of Li metal as the anode.

[0050] Li ｘ From the viewpoint of successfully generating P, the energization time is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more. The energization time is preferably 20 hours or less, more preferably 15 hours or less, and even more preferably 12 hours or less.

[0051] This manufacturing method can produce a cell comprising the solid electrolyte of the present invention and electrodes disposed on each side of the solid electrolyte. Such a cell can be used as a solid-state battery as is, or the solid electrolyte of the present invention can be extracted from the cell. When the solid electrolyte of the present invention is extracted from the cell, for example, electrodes made of a different material from the electrodes used when applying current can be placed on each side of the solid electrolyte, and the solid electrolyte can be used as a solid-state battery.

[0052] Next, a method for reforming a sulfide solid electrolyte (hereinafter also referred to as "the reforming method of the present invention") will be described. The reforming method of the present invention is a method for reforming a sulfide solid electrolyte containing Li, P, and S elements. In the reforming method of the present invention, first, a cell is prepared, which includes a solid electrolyte layer containing the sulfide solid electrolyte to be reformed and electrodes arranged on each side of the solid electrolyte layer. Here, of the electrodes arranged on each side of the solid electrolyte layer, at least one side facing the solid electrolyte layer contains Li metal. In the present invention, it is preferable that at least one side of the above-mentioned electrode facing the solid electrolyte layer is made of Li metal. As a result, when current is applied to the cell, sulfides contained in the sulfide layer react with Li metal on the electrode, resulting in Li ｘ P and lithium sulfide are generated at the contact surface of the sulfide layer with the electrode. In other words, by passing current through the cell, the sulfide solid electrolyte is modified. Of the electrodes disposed on each side of the solid electrolyte layer, at least one of the electrodes may contain Li metal on the surface facing the solid electrolyte layer, or both of the electrodes may contain Li metal on the surfaces facing the solid electrolyte layer.

[0053] The above-described explanations regarding the sulfide, sulfide layer, cell preparation method, and current application conditions in the preferred method for producing a solid electrolyte of the present invention also apply to the modification method of the present invention. In this case, the terms "sulfide" and "sulfide layer" described in the production method should be read as "sulfide solid electrolyte" and "sulfide solid electrolyte layer," respectively.

[0054] By using the modification method of the present invention, a cell can be obtained that includes a solid electrolyte layer containing a modified sulfide solid electrolyte and electrodes disposed on each side of the layer. Such a cell can be used as a solid-state battery as is, or the solid electrolyte layer can be removed from the cell. When the solid electrolyte layer is removed from the cell, for example, electrodes made of a different material from the electrodes used during current application can be disposed on each side of the solid electrolyte layer, and the cell can be used as a solid-state battery.

[0055] The above-described embodiments of the present invention encompass the following technical concepts: [1] A solid electrolyte containing Li, P, and S elements, wherein Li ｘA solid electrolyte comprising P (x is a number greater than 0 and equal to or less than 3). [2] The solid electrolyte according to [1], further comprising lithium sulfide. [3] The solid electrolyte according to [1] or [2], having a peak apex in a binding energy range of 124.5 eV or more and 129.0 eV or less in a P2p spectrum measured by X-ray photoelectron spectroscopy. [4] The solid electrolyte according to any one of [1] to [3], having a peak apex in a binding energy range of 159.0 eV or more and 160.8 eV or less in an S2p spectrum measured by X-ray photoelectron spectroscopy. [5] The solid electrolyte according to any one of [1] to [4], containing a sulfide including a crystalline phase having an argyrodite-type crystal structure. [6] The solid electrolyte according to [5], wherein, in a P2p spectrum measured by X-ray photoelectron spectroscopy, the peak intensity of a peak having an apex in the binding energy range of 130.8 eV to 135.0 eV is defined as P1, and the peak intensity of a peak having an apex in the binding energy range of 124.5 eV to 129.0 eV is defined as P2, and the ratio P2 / P1 of P2 to P1 is 0.02 or more. [7] The solid electrolyte according to any one of [1] to [6], further comprising a halogen element. [8] The solid electrolyte according to [7], wherein the halogen element is one or more selected from the group consisting of Cl, Br, and I. [9] The solid electrolyte according to [7] or [8], comprising a halogen element in an amount of 1.4 atm % to 14.3 atm %.

[10] A solid electrolyte sheet comprising the solid electrolyte according to any one of [1] to [9] supported on a porous support.

[11] A battery comprising a solid electrolyte layer containing the solid electrolyte according to [1] to [9], a positive electrode, and a negative electrode.

[12] A method for reforming a sulfide solid electrolyte, comprising: preparing a cell comprising a solid electrolyte layer containing a sulfide solid electrolyte containing Li, P, and S elements, and electrodes disposed on each side of the solid electrolyte layer, at least one of the electrodes containing Li metal on a surface facing the solid electrolyte layer; and reforming the sulfide solid electrolyte by passing current through the cell.

[13] The method according to

[12] , wherein current is passed at a temperature of 25°C or higher and 90°C or lower.

[14] 0.01mAh / cm. ２

[14] The method for producing a sulfide solid electrolyte by passing current through a cell including a sulfide layer containing a sulfide containing Li, P, and S elements, and electrodes disposed on each side of the sulfide layer, wherein the surface of at least one of the electrodes facing the sulfide layer contains Li metal.

[0056] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0057] [Example 1] (Cell manufacturing process) Composition formula Li ５．４ P.S. ４．４ C ｌ０．８ Br ０．８ A sulfide containing a crystalline phase with an argyrodite-type crystal structure, represented by the formula (containing 11.4 atm% halogen elements), was used as the sulfide solid electrolyte. The lower opening of a cylindrical container (MACOR®, opening diameter 10.5 mm, height 18 mm) with open top and bottom was blocked with a lower electrode (made of SUS), 0.1 g of the sulfide solid electrolyte powder was placed on top of it, and the container was blocked with an upper electrode (made of SUS). A solid electrolyte layer was then formed by uniaxial pressing at 540 MPa. The upper electrode was temporarily removed, and a 100 μm-thick lithium metal foil was placed on top of the solid electrolyte layer and blocked with the upper electrode. The cylindrical container was then inverted, the lower electrode was temporarily removed, and a 100 μm-thick lithium metal foil was placed on top of the solid electrolyte layer and blocked again with the lower electrode. The upper and lower electrodes were then restrained at a pressure of 60 MPa. This resulted in the production of a cell in which an electrode made of lithium metal was disposed on each side of the solid electrolyte layer. The cell was fabricated in a glove box filled with thoroughly dried argon gas (dew point of −60° C. or less).

[0058] (Electrification step) The cell was energized at a temperature of 25°C and a current density of 0.1 mAh / cm ２A cell containing a modified sulfide solid electrolyte was obtained by passing a current through the cell under the above conditions for 12 hours.

[0059] Example 2 A cell containing a modified sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the temperature in the current application step was changed to 60°C.

[0060] Comparative Example 1 A cell containing a sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the current-passing step was not carried out.

[0061] [Evaluation] (XPS Measurement) The solid electrolyte layers were removed from the cells produced in Example 2 and Comparative Example 1, and their surfaces were measured using a VersaProbe III XPS device manufactured by ULVAC-PHI, Inc. The XPS measurement conditions were as follows: Excitation X-ray: Monochrome AlKα ray (1486.7 eV) Output: 50 W X-ray diameter: 200 μm Pass energy: 26 eV Photoelectron escape angle: 45° The obtained XPS spectra are shown in Figures 1 and 2.

[0062] In the P2p spectrum obtained under the above measurement conditions, whether or not a peak apex was observed in the binding energy range of 124.5 eV or more and 129.0 eV or less was recorded in Table 1. Similarly, in the S2p spectrum obtained under the above measurement conditions, whether or not a peak apex was observed in the binding energy range of 159.0 eV or more and 160.8 eV or less was recorded in Table 1. Furthermore, in the P2p spectrum obtained under the above measurement conditions, the ratio P2 / P1 of the peak intensity P1 of the peak having an apex in the binding energy range of 130.8 eV or more and 135.0 eV or less to the peak intensity P2 of the peak having an apex in the binding energy range of 124.5 eV or more and 129.0 eV or less was calculated, and the value is recorded in Table 1.

[0063] (Measurement of Lithium Ion Conductivity) The cells produced in each Example and Comparative Example were used as measurement samples, and the lithium ion conductivity σ was measured using a potentio / galvanostat SP-200 manufactured by Bio-Logic Science Instruments. The measurement was carried out at a temperature of 25°C, and the conductivity was within ±0.5 mAh / cm. ２ and ±1.0 mAh / cm２ The overvoltage (V) versus the current (I) was linearly approximated, and the cell resistance and, in turn, the ionic conductivity σ were calculated from the slope of the linear approximation. The results are shown in Table 1.

[0064]

[0065] As shown in Table 1, in Example 2, the apex of the peak was observed in the binding energy range of 124.5 eV or more and 129.0 eV or less in the P2p spectrum. Therefore, it was found that Li was not present on the surface of the sulfide solid electrolyte produced (modified) in Example 2. ｘ Similarly, in the S2p spectrum of Example 2, the apex of the peak was observed in the range of binding energy of 159.0 eV to 160.8 eV, which indicates that lithium sulfide is present on the surface of the sulfide solid electrolyte produced (modified) in Example 2. On the other hand, in Comparative Example 1 in which no current was applied, the apex of the peak was not observed in either range, which indicates that Li is present on the surface of the sulfide solid electrolyte. ｘ It can be seen that P and lithium sulfide are not present. The ionic conductivity σ measured using the cell of Example 2 as a measurement sample was significantly higher than that of the cell of Comparative Example 1, which was not electrified. This indicates that Li generated on the surface of the sulfide solid electrolyte by electrification. ｘ It can be seen that the ionic conductivity of the sulfide solid electrolyte was improved by P and lithium sulfide. Furthermore, an improvement in ionic conductivity σ was confirmed for the cell of Example 1, similar to the cell of Example 2. From this, it can be seen that in Example 1 as well, Li was deposited on the surface of the sulfide solid electrolyte by applying current. ｘ It is presumed that P and lithium sulfide are produced.

[0066] According to the present invention, a solid electrolyte having excellent ionic conductivity is provided.

Claims

1. A solid electrolyte containing lithium (Li), phosphorus (P) and sulfur (S), wherein Li ｘ A solid electrolyte containing P (x is a number greater than 0 and equal to or less than 3).

2. The solid electrolyte of claim 1, further comprising lithium sulfide.

3. The solid electrolyte according to claim 1 or 2, which has a peak apex in the binding energy range of 124.5 eV to 129.0 eV in a P2p spectrum measured by X-ray photoelectron spectroscopy.

4. The solid electrolyte according to claim 1 or 2, wherein the S2p spectrum measured by X-ray photoelectron spectroscopy has a peak apex in the binding energy range of 159.0 eV to 160.8 eV.

5. The solid electrolyte according to claim 1 or 2, which contains a sulfide containing a crystalline phase having an argyrodite-type crystal structure.

6. A solid electrolyte according to claim 5, wherein, when P1 is the peak intensity of a peak having an apex in the binding energy range of 130.8 eV or more and 135.0 eV or less in a P2p spectrum measured by X-ray photoelectron spectroscopy, and P2 is the peak intensity of a peak having an apex in the binding energy range of 124.5 eV or more and 129.0 eV or less in a P2p spectrum measured by X-ray photoelectron spectroscopy, the ratio P2 / P1 of P2 to P1 is 0.02 or more.

7. The solid electrolyte according to claim 1, further comprising a halogen element.

8. The solid electrolyte according to claim 7, wherein the halogen element is at least one element selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I).

9. The solid electrolyte according to claim 7 or 8, which contains the halogen element in an amount of 1.4 atm % or more and 14.3 atm % or less.

10. A solid electrolyte sheet comprising the solid electrolyte according to claim 1 or 2 supported on a porous support.

11. A battery comprising a solid electrolyte layer containing the solid electrolyte according to claim 1 or 2, a positive electrode, and a negative electrode.

12. A method for modifying a sulfide solid electrolyte, comprising: preparing a cell comprising a solid electrolyte layer containing a sulfide solid electrolyte containing lithium (Li), phosphorus (P), and sulfur (S); and electrodes disposed on each side of the solid electrolyte layer, at least one of the electrodes containing lithium (Li) metal on the side facing the solid electrolyte layer; and modifying the sulfide solid electrolyte by passing current through the cell.

13. The reforming method according to claim 12, wherein the current is applied at a temperature of 25°C or higher and 90°C or lower. 14.0.01mAh / cm ２ The method according to claim 12 or 13, wherein the current is applied at a current density equal to or greater than the above.

15. The method of claim 12 or 13, wherein the current is applied for one hour or longer.

16. A method for producing a sulfide solid electrolyte by passing current through a cell including a sulfide layer containing a sulfide containing lithium (Li), phosphorus (P), and sulfur (S), and electrodes disposed on each side of the sulfide layer, wherein the surface of at least one of the electrodes facing the sulfide layer contains lithium (Li) metal.

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