Solid electrolyte, electrode, and secondary battery

Abstract

One aspect of the present disclosure provides a solid electrolyte that contains an alkali metal element, a non-metal element M and a halogen element X as constituent elements, and that has a band gap of 1.47 eV or more as calculated from an ultraviolet−visible absorption spectrum.

Description

Solid electrolyte, electrode, and secondary battery

[0001] The present disclosure relates to a solid electrolyte, an electrode, and a secondary battery.

[0002] In recent years, solid electrolytes have attracted attention as electrolytes used in electrochemical devices such as lithium-ion batteries. Solid electrolytes are considered useful for improving battery performance such as safety, high capacity, rapid charge and discharge, and pack energy density because they are superior to conventional electrolytic solutions in terms of high-temperature durability and high-voltage resistance.

[0003] As solid electrolytes, due to their high ionic conductivity close to that of electrolytic solutions and moderate flexibility, research has been conducted on sulfide-based solid electrolytes such as Li １０ GeP ２ S １２ etc. (for example, Patent Document 1). In addition, as solid electrolytes containing lithium, there are also oxide-based solid electrolytes such as Li ７ La ３ Zr ２ O １２ (LLZO), and halide-based solid electrolytes such as Li ３ InCl ６ , LiYBr ６ etc. are also known.

[0004] Halide-based solid electrolytes are highly oxidation-resistant, have low reactivity with moisture in the atmosphere and are stable, have a monovalent charge of halide ions and low activation energy in ionic conduction, and are considered useful because of their relatively high stability at high potentials. Patent Document 2 discloses a lithium-ion conductive solid electrolyte composed of Li, La, O, and X, where X is at least one element selected from the group consisting of Cl, Br, and I. Patent Document 3 discloses a solid electrolyte composed of Li, La, O, and I.

[0005] Japanese Unexamined Patent Application Publication No. 2023 - 181158 International Publication No. 2020 / 137043 International Publication No. 2020 / 219846

[0006] As described above, although halide-based solid electrolytes are excellent in oxidation resistance, there is room for improvement in terms of reduction resistance, and a solid electrolyte that is excellent in both reduction resistance and oxidation resistance would be useful.

[0007] An object of the present disclosure is to provide a solid electrolyte that is excellent in reduction resistance and oxidation resistance.

[0008] The present disclosure provides the following [1] to

[11] .

[0009] [1] A solid electrolyte having an alkali metal element, a non-metal element M, and a halogen element X as constituent elements, and having a band gap calculated from an ultraviolet-visible absorption spectrum of 1.47 eV or more. [2] The solid electrolyte according to [1], wherein the non-metal element M is at least one selected from the group consisting of N, P, O, Se, and S. [3] The solid electrolyte according to [1] or [2], wherein the non-metal element M is N. [4] The solid electrolyte according to [1], wherein the non-metal element M is two or more elements including N and at least one selected from the group consisting of P, O, Se, and S. [5] The solid electrolyte according to [1], comprising the alkali metal element, the non-metal element M, and the halogen element X. [6] The solid electrolyte according to any one of [1] to [5], wherein the content of the non-metal element M is less than 25 mol% with respect to the total number of atoms contained in the solid electrolyte. [7] The solid electrolyte according to any one of [1] to [6], wherein the halogen element contains at least Cl. [8] The molding density is 1.0 to 5.0 g / cm ３ The solid electrolyte according to any one of [1] to [7]. [9] An electrode containing a solid electrolyte, wherein the solid electrolyte is the solid electrolyte according to any one of [1] to [8].

[10] A secondary battery including the electrode according to [9].

[11] A secondary battery including a solid electrolyte containing the solid electrolyte according to any one of [1] to [8].

[0010] According to the present disclosure, a solid electrolyte excellent in reduction resistance and oxidation resistance can be provided.

[0011] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.

[0012] Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified.

[0013] One embodiment of the solid electrolyte has an alkali metal element, a non-metal element M, and a halogen element X as constituent elements. The solid electrolyte has a band gap calculated from the ultraviolet-visible absorption spectrum of 1.47 eV or more.

[0014] The solid electrolyte is a halogen-based solid electrolyte having an alkali metal element, a non-metal element M, and a halogen element X as constituent elements, has excellent reduction resistance, has a band gap of a predetermined value or more, and is so-called highest occupied molecular orbital (HOMO). The difference (energy gap) between the energy levels of the lowest unoccupied molecular orbital (LUMO) is large, and it also has excellent oxidation resistance.

[0015] The alkali metal element in the solid electrolyte may be, for example, at least one selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), preferably includes at least one of Li and Na, preferably includes Li, and may be Li.

[0016] The non-metal element M in the solid electrolyte may be, for example, at least one selected from the group consisting of nitrogen (N), phosphorus (P), oxygen (O), selenium (Se), and sulfur (S). Although the solid electrolyte having a halogen as a constituent element has a relatively high energy level of its LUMO, when the non-metal element M contains N, the energy level of the LUMO of the solid electrolyte is higher, and it is easier to widen the above-mentioned band gap. Therefore, it is likely to become a solid electrolyte with more excellent oxidation resistance. The non-metal element M may be N.

[0017] When the nonmetal element M contains two or more elements, it is preferable that it contains N, for example, N and at least one element selected from the group consisting of P, O, Se, and S.

[0018] The upper limit of the content of nonmetal element M relative to the total number of atoms in the solid electrolyte may be, for example, less than 25 mol%, 24.5 mol% or less, 24 mol% or less, or 23.8 mol% or less. If the upper limit of the content of nonmetal element M is within the above range, the oxidation resistance of the resulting solid electrolyte can be further improved. The lower limit of the content of nonmetal element M relative to the total number of atoms in the solid electrolyte may be, for example, 1 mol% or more, 3 mol% or more, 5 mol% or more, or 7 mol% or more. If the lower limit of the content of nonmetal element M is within the above range, the reduction resistance of the resulting solid electrolyte can be further improved. The content of nonmetal element M relative to the total number of atoms in the solid electrolyte may be adjusted within the above range, for example, 1 mol% or more and less than 25 mol%, or 1 to 24.5 mol%.

[0019] The halogen element X in the above solid electrolyte may be at least one selected from the group consisting of, for example, fluorine (F), bromine (Br), chlorine (Cl), and iodine (I). From the viewpoint of achieving a higher level of both ionic conductivity and oxidation resistance, it is preferable that it contains at least Cl, and may be Cl.

[0020] The above solid electrolyte contains an alkali metal element, a nonmetal element M, and a halogen element X as constituent elements. Other metal elements may be included as constituent elements, to the extent that they do not impair the spirit of this disclosure, and preferably, other metal elements are not included as constituent elements. In halogen-based solid electrolytes containing the above metal elements, the reductive decomposition of metal ions in the electrolyte at the negative electrode interface generates conductive metal elements, and the decomposition of the electrolyte tends to proceed continuously. For this reason, the reduction resistance of the solid electrolyte can be further improved by not including metal elements other than the alkali metal elements as constituent elements.

[0021] The above solid electrolyte may be a compound comprising the alkali metal element, the nonmetal element M, and the halogen element X.

[0022] The above solid electrolyte is based on the general formula: A ａ M ｂ X ｃ Z ｄ The composition may be represented as follows: A represents an alkali metal element, M represents a nonmetal element, X represents a halogen element, and Z represents a metallic element.

[0023] In this specification, the elemental composition ratios of solid electrolytes refer to values ​​measured by the following methods: The proportion of alkali metal element A refers to the value determined by inductively coupled plasma atomic emission spectroscopy (ICP), the proportion of halogen element X refers to the value determined by ion chromatography, and the proportion of nonmetallic element M refers to the value determined by non-dispersive infrared absorption spectroscopy. These values ​​are used to calculate the above composition ratios. The content of nonmetallic element M is calculated from the above composition ratios. When preparing solid electrolytes oneself, the composition ratios can be calculated from the elemental composition ratios of the raw materials.

[0024] The above solid electrolyte is, for example, Li １３．５ N ３．５ ClO, Li ９ N ２ ClO, Li ７ N ２ Cl ２ The compound may have a composition represented by, for example, the above.

[0025] The lower limit of the band gap calculated from the above ultraviolet-visible absorption spectrum may be, for example, 1.47 eV or higher, 1.50 eV or higher, 1.55 eV or higher, or 1.60 eV or higher. By having the lower limit of the band gap within the above range, the oxidation resistance of the solid electrolyte can be further improved. The upper limit of the band gap calculated from the above ultraviolet-visible absorption spectrum may be, for example, 5.00 eV or lower, 4.90 eV or lower, 4.80 eV or lower, or 4.70 eV or lower. The band gap calculated from the above ultraviolet-visible absorption spectrum may be adjusted within the above range, for example, 1.47 to 5.00 eV, 1.50 to 4.90 eV, 1.55 to 4.80 eV, or 1.60 to 4.70 eV. The aforementioned band gap is not necessarily determined solely by the elemental species and compositional ratios constituting the solid electrolyte; it can also be adjusted by factors such as crystallinity and the proportion of crystal defects. For example, it can be adjusted by the mixing conditions and annealing treatment during the manufacturing of the solid electrolyte.

[0026] In this specification, the band gap is understood to mean the difference (energy gap) between the energy level of the highest occupied orbital (HOMO) and the energy level of the lowest unoccupied orbital (LUMO). In this specification, the band gap can be determined by measuring the diffuse reflectance spectrum using an integrating sphere unit with a UV-Vis spectrophotometer. For example, a UV-2600 (product name) manufactured by Shimadzu Corporation can be used as the UV-Vis spectrophotometer. Specifically, it shall be determined by the method described in the examples of this application.

[0027] The shape of the solid electrolyte described above is not particularly limited and may be a powder consisting of an aggregate of polycrystalline particles.

[0028] The molding density of the above solid electrolyte is, for example, 1.0 to 5.0 g / cm³. ３ , 1.05-4.9g / cm ３ , 1.1-4.7g / cm ３ , or 1.15 to 4.5 g / cm³ ３ That's fine.

[0029] In this specification, the molding density of the solid electrolyte refers to the value calculated by preparing a sample by filling an insulating cylinder with an inner diameter of 10 mm with 100 mg of the solid electrolyte and applying a pressure of 370 MPa, measuring the volume of the sample, and specifically determining it by the method described in the examples of this application.

[0030] One example of a method for producing a solid electrolyte involves altering a raw material composition containing a compound having an alkali metal element as a constituent element, a compound having a nonmetal element M as a constituent element, and a compound having a halogen element as a constituent element, by a mechanochemical method. The alteration of the raw material composition by mixing is carried out using a ball mill, by repeatedly switching between forward and reverse rotation more than five times. The raw material composition described above does not necessarily have to contain three types of compounds: a compound having an alkali metal element as a constituent element, a compound having a nonmetal element M as a constituent element, and a compound having a halogen element as a constituent element. For example, lithium halide is a compound having both an alkali metal element and a halogen element as a constituent element, so it is sufficient to include at least two types: lithium halide and a compound having a nonmetal element M as a constituent element.

[0031] Examples of alkali metal element sources include halides, nitrides, and oxides. Examples of compounds containing nonmetallic elements M include oxides, nitrides, phosphoric acid compounds, halides, and compounds containing ammonia ions of alkali metal elements. Examples of compounds containing halogen elements include halogen compounds of alkali metal elements, halogen compounds of nonmetallic elements, and halogen compounds of metallic elements.

[0032] In the mechanochemical method, for example, a ball mill can be used to supply mechanical energy such as collision, shearing, and friction between the solid raw materials. The ball milling process may be performed dry. Before the ball milling process, the raw material composition may be mixed (pre-mixed) in a mortar and pestle for one minute or more. By performing such pre-mixing, the raw material composition introduced into the container during the ball milling process becomes more uniform, resulting in a more uniform solid electrolyte obtained by the ball milling process, and thus improving oxidation resistance.

[0033] Zirconia balls can be used for the ball mill. The diameter of the balls may be, for example, 1 to 15 mm, 2 to 10 mm, or 2 to 5 mm.

[0034] The ball filling rate in the container during the ball milling process may be adjusted by the amount of raw material composition filled. The ratio of the mass of the raw material composition to the mass of the balls (100 [total mass of raw material composition] / [total mass of balls]) may be, for example, 5.0% by mass or less, 4.5% by mass or less, 3.0% by mass or less, 2.8% by mass or less, 2.6% by mass or less, or 2.5% by mass or less. When the above ratio is within the above range, the impact of the balls can be supplied more sufficiently to the raw material composition. The ratio of the mass of the raw material composition to the mass of the balls may be, for example, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, or 1.8% by mass or more. When the lower limit of the above ratio is within the above range, the contamination of the solid electrolyte with impurities due to collisions between balls can be further reduced, the occurrence of crystal defects due to impurity contamination can be suppressed, and oxidation resistance can be further improved. The ratio of the mass of the raw material composition to the mass of the balls may be adjusted within the above range, for example, 0.3 to 5.0% by mass or less.

[0035] The rotational speed of the ball mill may be, for example, 200 to 700 rpm, 200 to 500 rpm, or 250 to 350 rpm.

[0036] The processing time using the ball mill may be, for example, 24 hours or more, 24 to 72 hours, or 36 to 60 hours. By having the ball mill processing time within the above range, each raw material solid is more thoroughly mixed, elemental substitution by the mechanochemical method is more sufficient, and the oxidation resistance of the resulting solid electrolyte can be further improved.

[0037] In ball milling, it is preferable to switch between forward rotation and reverse rotation multiple times. The number of rotation direction switches during ball milling may be, for example, 10 or more, 50 or more, or 100 or more. By having the number of rotation direction switches during ball milling within the above range, each raw material solid is more thoroughly mixed, elemental substitution by the mechanochemical method is more sufficient, and the oxidation resistance of the resulting solid electrolyte can be further improved.

[0038] The above method for producing a solid electrolyte may further include a step of heat-treating the solid obtained by the mechanochemical method at 150 to 500°C (annealing step). By including the annealing step, it is possible to reduce crystal defects in the obtained solid electrolyte and improve its crystallinity, thereby lowering the LUMO energy level and further widening the band gap.

[0039] The heating time in the annealing process may be, for example, 1 to 24 hours, 2 to 15 hours, or 5 to 10 hours.

[0040] Because the above-mentioned solid electrolyte possesses both reduction and oxidation resistance, it is useful as a material for forming solid electrolyte layers and electrodes in batteries. Furthermore, because the above-mentioned solid electrolyte can exhibit excellent reduction and oxidation resistance, it is useful as a constituent material for secondary batteries such as lithium-ion secondary batteries.

[0041] One embodiment of an electrode is an electrode comprising a solid electrolyte. The solid electrolyte is composed of the solid electrolyte according to this disclosure. The electrode comprises an electrode active material (positive electrode active material or negative electrode active material). One embodiment of a secondary battery comprises the electrode described above. Another embodiment of a secondary battery comprises a solid electrolyte comprising the solid electrolyte according to this disclosure. Hereinafter, a lithium-ion secondary battery will be described as an example.

[0042] One embodiment of a lithium-ion secondary battery includes the above-mentioned electrodes. The electrodes may be either a positive electrode or a negative electrode.

[0043] Examples of positive electrode active materials include lithium-containing composite metal oxides comprising lithium (Li) and at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, and Cu. Examples of such lithium composite metal oxides include LiCoO ２ LiNiO ２ LiMn ２ O ４ Li ２ MnO ３ LiNi ｘ Mn ｙ Co １－ｘ－ｙ O ２ [0<x+y<1], LiNi ｘ Co ｙ Al １－ｘ－ｙ O ２ [0<x+y<1], LiCr ０．５ Mn ０．５ O ２ LiFePO ４ Li ２ FeP ２ O ７ LiMnPO ４ LiFeBO ３ Li ３ V ２ (PO ４ ) ３ Li ２ CuO ２ Li ２ FeSiO ４ , and Li ２ MnSiO ４ These are some examples.

[0044] Examples of negative electrode active materials include metals such as Li, Si, Sn, Si-Mn, Si-Co, Si-Ni, In, and Au, as well as alloys containing these metals, carbon materials such as graphite, and materials in which lithium ions are inserted between layers of the carbon material.

[0045] The above electrode may contain other components in addition to the above-mentioned solid electrolyte and electrode active material. Examples of other components include solid electrolyte compounds other than the above-mentioned solid electrolyte, conductive additives, and binders.

[0046] The conductive additive may be, for example, a carbon material. Examples of carbon materials include graphene, graphite, carbon black, fullerene, carbon nanotubes, and carbon fibers. Examples of graphite include natural graphite (such as flaky graphite) and artificial graphite. Examples of carbon black include acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Examples of carbon fibers include carbon fibers such as vapor-grown carbon fibers (VGCF).

[0047] Examples of binders include fluororesins and synthetic rubbers. Fluorine resins are preferably those having a carbon chain as their main chain. The carbon chain may be formed by radical polymerization of a compound having an ethylenically unsaturated group. Examples of fluororesins include poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and polyvinylidene fluoride (PVDF). Examples of synthetic rubbers include SBR (styrene-butadiene rubber).

[0048] The electrode may have a configuration in which a layer of the composition containing the above-mentioned solid electrolyte and electrode active material is provided on the current collector. The material of the current collector is not particularly limited and may be a single metal or an alloy of metals such as Cu, Mg, Ti, Fe, Co, Ni, Zn, Al, Ge, In, Au, Pt, Ag, and Pd.

[0049] Another embodiment of the lithium-ion secondary battery includes a solid electrolyte containing the solid electrolyte described above. The lithium-ion secondary battery may have a laminated structure comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in that order. In the lithium-ion secondary battery according to this embodiment, since the solid electrolyte layer contains the solid electrolyte described above, even if the solid electrolyte layers containing the solid electrolyte are arranged in contact with each other so as to be in direct contact with the negative electrode, metal deposition due to reductive decomposition is suppressed, and stable operation can be expected.

[0050] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other.

[0051] The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the examples described below.

[0052] (Example 1) In an argon atmosphere having a dew point of -70°C or lower (hereinafter referred to as a dry argon atmosphere), LiCl, Li ３ N, and Li ２ O was weighed to the proportions shown in Table 1 to prepare the raw material composition. The raw material composition was mixed for 1 minute using a mortar and pestle in a dry argon atmosphere. 1.6 g of the mixed raw material composition was placed in a zirconia pot, and then 80 g of zirconia balls with a diameter of 4 mm were added to the pot. Subsequently, a solid electrolyte was obtained by ball milling using a planetary ball mill at 300 rpm for 24 hours, with a total of 144 rotations of forward and reverse rotation. The planetary ball mill used was the "PM 400" (product name) manufactured by Verder Scientific Co., Ltd.

[0053] (Example 2) LiCl, Li ３ N, and Li ２ A solid electrolyte was obtained in the same manner as in Example 1, except that O was weighed to the amount shown in Table 1.

[0054] (Example 3) LiCl and Li ３ A solid electrolyte was obtained in the same manner as in Example 1, except that N was weighed to the amount shown in Table 1.

[0055] (Comparative Example 1) Li as the raw material composition ３ A solid electrolyte was obtained in the same manner as in Example 1, except that 1.6 g of N was weighed out.

[0056] (Comparative Example 2) In an argon atmosphere having a dew point of -70°C or lower (hereinafter referred to as a dry argon atmosphere), LiCl and InCl ３ The raw materials were weighed to a mass ratio of 16.1% and 83.9%, respectively, to prepare the raw material composition. The raw material composition was mixed for 1 minute using a mortar and pestle in a dry argon atmosphere. 1.6 g of the mixed raw material composition was placed in a zirconia pot, and then 80 g of zirconia balls with a diameter of 4 mm were added to the pot. Subsequently, the mixture was ball-milled using a planetary ball mill at 300 rpm for 24 hours, with a total of 144 rotations of forward and reverse rotation, to obtain the crude product. The obtained crude composition was heat-treated at 230°C for 5 hours in an argon atmosphere to prepare a solid electrolyte material. The planetary ball mill used was the "PM 400" (product name) manufactured by Verder Scientific Co., Ltd.

[0057] (Comparative Example 3) A solid electrolyte was obtained in the same manner as in Example 3, except that the ball milling process was performed so that the total number of times the forward rotation and reverse rotation were switched was five.

[0058]

[0059] <Evaluation of Solid Electrolyte Properties> For each of the solid electrolytes prepared in the examples and comparative examples, the composition formula, band gap, content of nonmetallic element M, and molding density were evaluated using the method described below. The results are shown in Table 2.

[0060] [Determination of Compositional Formula] The compositional formulas of the solid electrolytes prepared in the examples and comparative examples were determined from the elemental composition ratios in the raw material compositions.

[0061] [Calculation of Band Gap] The band gap was calculated for the solid electrolytes prepared in the examples and comparative examples by measuring the diffuse reflectance spectrum using a Shimadzu UV-Vis spectrophotometer (UV-2600). Specifically, baseline correction was performed using silicon dioxide, and the diffuse reflectance spectrum was measured at wavelengths from 220 nm to 1400 nm. The solid electrolyte was packed into the measurement cell in a dry argon atmosphere. The reflectance (R) for the obtained wavelength was given by f(∞) = (1-R). ２ The function was converted to the Kubelka-Munk function f(∞) using / 2R.

[0062] Next, let the horizontal axis be energy (hν) and the vertical axis be (hνα). （１／ｎ） A Tauc plot was created as follows: Here, h is Planck's constant and ν is the frequency. The energy on the horizontal axis was calculated from the relationship hν = 1239.7 / λ, where λ is the wavelength. α is the absorption coefficient, and the Kubelka-Munk function f(∞) was used as a substitute. Furthermore, 1 / 2 of the indirect transition was used for n. The intersection points of the slope of the Tauc plot (the slope at the inflection point of the graph) and the horizontal axis were calculated, and the value on the horizontal axis at the intersection point was taken as the band gap described above. If there were multiple slopes, the smallest value among the intersection points on the horizontal axis was adopted as the band gap described above.

[0063] [Determination of Nonmetallic Element M Content] For the solid electrolytes prepared in the examples and comparative examples, the content of nonmetallic element M was determined from the elemental composition ratio in the raw material composition.

[0064] [Measurement of Molding Density of Solid Electrolytes] For each of the solid electrolytes prepared in the examples and comparative examples, 100 mg of the solid electrolyte was filled into an insulating cylinder with an inner diameter of 10 mm, and a pressure of 370 MPa was applied to prepare a measurement sample. The volume of the measurement sample was measured, and the density was calculated.

[0065] <Evaluation of Solid Electrolytes> For each of the solid electrolytes prepared in the examples and comparative examples, the reduction resistance and oxidation resistance were evaluated by cyclic voltammetry as shown below.

[0066] [Preparation of evaluation cell] The following steps for preparing the evaluation cell were all carried out in a glove box purged with an inert gas. First, 100 mg of the above solid electrolyte was filled into an insulating cylinder with an inner diameter of 10 mm, and a pressure of 123 MPa was applied to form the first solid electrolyte layer. Next, Li, which is a sulfide solid electrolyte... ６ PS ５ 60 mg of Cl is measured out and packed into contact with the first solid electrolyte layer, and a pressure of 123 MPa is applied to form the second solid electrolyte layer (Li ６ PS ５ A Cl layer was formed.

[0067] Next, 37 parts by mass of SUS powder and 63 parts by mass of the above solid electrolyte were weighed and mixed in an agate mortar to prepare a mixture. 30 mg of the above mixture was packed into the surface of the first solid electrolyte layer opposite to the second solid electrolyte layer, and a working electrode layer was formed by applying a pressure of 370 MPa. In addition, 6 mg of Li foil was placed in contact with and covering the surface of the second solid electrolyte layer opposite to the first solid electrolyte layer, and a reference electrode layer was formed by applying a pressure of 50 MPa.

[0068] As described above, current collectors made of stainless steel were attached to the working electrode layer and the reference electrode layer on the side opposite to the solid electrolyte side, and lead wires were attached to each current collector to create an evaluation cell.

[0069] [Measurement of Cyclic Voltammetry] Using the evaluation cell prepared as described above, lead wires electrically connected to the current collector in contact with the working electrode layer and lead wires electrically connected to the current collector in contact with the reference electrode layer were electrically connected to an impedance analyzer (Solatron Analytical, product name: SL1260) and a potentiostat (Solatron Analytical, product name: SL1287A), and a cyclic voltammetry test was performed under the following conditions.

[0070] In the cyclic voltammetry test, the sweep rate was set to 1 mV / s, and the current flowing when the potential of the working electrode was changed relative to the reference electrode (Li+ / Li) was measured. More specifically, the potential of the working electrode relative to the reference electrode (Li) was first increased to 3.0 V starting from the open-circuit voltage, and then decreased back down to 0 V. The maximum value of the peak current in the range from the open-circuit voltage to 3.0 V relative to the Li metal was determined as an evaluation index for oxidation resistance, and the peak current value when the voltage relative to the Li metal became 0 V was determined as an evaluation index for reduction resistance. The results are shown in Table 2.

[0071]

[0072] As shown in Table 2, it was confirmed that the solid electrolyte of the example satisfying the requirements for a solid electrolyte according to this disclosure exhibits superior reduction resistance and oxidation resistance compared to the solid electrolyte of the comparative example.

[0073] According to this disclosure, a solid electrolyte with excellent reduction resistance and oxidation resistance can be provided.

Claims

1. A solid electrolyte having alkali metal elements, nonmetal element M, and halogen element X as constituent elements, and having a band gap of 1.47 eV or greater as calculated from its ultraviolet-visible absorption spectrum.

2. The solid electrolyte according to claim 1, wherein the nonmetallic element M is at least one selected from the group consisting of N, P, O, Se, and S.

3. The solid electrolyte according to claim 1, wherein the nonmetal element M is N.

4. The solid electrolyte according to claim 1, wherein the nonmetallic element M is two or more elements, including N and at least one selected from the group consisting of P, O, Se, and S.

5. The solid electrolyte according to claim 1, comprising the alkali metal element, the nonmetal element M, and the halogen element X.

6. The solid electrolyte according to any one of claims 1 to 5, wherein the content of the nonmetal element M is less than 25 mol% with respect to the total number of atoms contained in the solid electrolyte.

7. The solid electrolyte according to any one of claims 1 to 5, wherein the halogen element comprises at least Cl.

8. Molding density is 1.0 to 5.0 g / cm³ ３ The solid electrolyte according to any one of claims 1 to 5.

9. An electrode comprising a solid electrolyte, wherein the solid electrolyte is the solid electrolyte described in claim 1 or 2.

10. A secondary battery comprising the electrode described in claim 9.

11. A secondary battery comprising a solid electrolyte containing the solid electrolyte described in claim 1 or 2.

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