Solid electrolyte, electrode, and secondary battery

Abstract

One aspect of the present disclosure provides a halide-based solid electrolyte that has an alkali metal element, a halogen element, nitrogen, and oxygen as constituent elements. In the halide-based solid electrolyte, the ratio of the molar amount of oxygen MO to the molar amount of nitrogen MN may be 5.0 or less.

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, Li ７ La ３ Zr ２ O １２ (LLZO) and other oxide-based solid electrolytes, and Li ３ InCl ６ , LiYBr ６ and other halide-based solid electrolytes 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 ion 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 Patent Application Laid-Open No. 2023-181158 International Publication No. 2020 / 137043 International Publication No. 2020 / 219846

[0006] Halide-based solid electrolytes containing nitrogen as a constituent element have the drawback of low resistance to oxidation. A halide-based solid electrolyte containing nitrogen as a constituent element that exhibits excellent oxidation resistance would be very useful.

[0007] This disclosure aims to provide a solid electrolyte having excellent ionic conductivity and oxidation resistance.

[0008] This disclosure provides the following [1] to

[10] .

[0009] [1] A halide-based solid electrolyte having alkali metal elements, halogen elements, N, and O as constituent elements. [2] The molar amount M of N. Ｎ The molar amount M of O relative to the above O Ｏ The halide-based solid electrolyte according to [1], wherein the ratio of is 5.0 or less. [3] Molar amount M of N Ｎ The molar amount M of O relative to the above O Ｏ A halide-based solid electrolyte according to [1] or [2], wherein the ratio of is 0.05 or more. [4] A halide-based solid electrolyte according to any one of [1] to [3], wherein the content of N is less than 25 mol% of the total number of atoms contained in the halide-based solid electrolyte. [5] The halide-based solid electrolyte is of general formula (1): A ａ N ｂ O ｃ M ｄ Z ｅ X ｆ H ｇA halide-based solid electrolyte according to any one of [1] to [4], having a composition represented by, where A represents an alkali metal element, M represents a metal element other than A, Z represents at least one selected from the group consisting of Si, B, Ge, S, Se, and P, X represents a halogen element, a is greater than 0 and 0.9 or less, b is greater than 0 and less than 0.25, c is greater than 0 and 0.30 or less, d is 0 or more and 0.1 or less, e is 0 or more and 0.25 or less, f is greater than 0 and 0.5 or less, g is 0 or more and 0.1 or less, and a + b + c + d + e + f + g = 1. [6] A halide-based solid electrolyte according to any one of [1] to [5], wherein the halogen element comprises at least Cl. [7] A molding density of 1.0 to 5.0 g / cm³ ３ A halide-based solid electrolyte according to any one of [1] to [6]. [8] An electrode comprising a solid electrolyte, wherein the solid electrolyte is a halide-based solid electrolyte according to any one of [1] to [7]. [9] A secondary battery comprising the electrode according to [8].

[10] A secondary battery comprising a solid electrolyte comprising a halide-based solid electrolyte according to any one of [1] to [9].

[0010] According to this disclosure, a solid electrolyte having excellent ionic conductivity and oxidation resistance can be provided.

[0011] The embodiments of this disclosure are described below. However, the embodiments described below are illustrative examples for the purpose of illustrating this disclosure and are not intended to limit this disclosure to the following.

[0012] Unless otherwise specified, the materials exemplified herein may be used individually or in combination of two or more. The content of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition.

[0013] One embodiment of a solid electrolyte is a halide-based solid electrolyte having alkali metal elements, halogen elements, nitrogen (N), and oxygen (O) as constituent elements.

[0014] The above-mentioned solid electrolyte is a halide-based solid electrolyte containing nitrogen as a constituent element, but also contains oxygen as a constituent element, resulting in an excellent balance between ionic conductivity and oxidation resistance. Although the reasons for this effect are not entirely clear, the inventors of the present invention hypothesize the following: By introducing oxygen beforehand, oxygen forms a strong bond with nitrogen, thereby improving oxidation resistance, and by weakening the bond between nitrogen and alkali metal elements, it is possible to improve ionic conductivity.

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

[0016] Molar amount M in the above text Ｎ The molar amount M of O relative to the above O Ｏ The ratio (M Ｏ / M Ｎ The upper limit of the value of may be, for example, 5.0 or less, 3.0 or less, 1.5 or less, or 0.9 or less. Ｏ / M Ｎ By keeping the upper limit of the value within the above range, the ionic conductivity of the resulting halide-based solid electrolyte can be further improved. Ｏ / M Ｎ The lower limit of the value may be, for example, 0.05 or greater, 0.1 or greater, 0.15 or greater, or 0.20 or greater. Ｏ / M Ｎ The lower limit of the value of N is within the above range, which further improves the oxidation resistance of the resulting halide-based solid electrolyte. Ｎ The molar amount M of O relative to the above O Ｏ The ratio (M Ｏ / M Ｎ The value of ( ) may be adjusted within the above range, for example, between 0.05 and 5.0.

[0017] The upper limit of the N content relative to the total number of atoms in the above halide-based solid electrolyte may be, for example, less than 25 mol%, 23 mol% or less, 21 mol% or less, or 19 mol% or less. When the upper limit of the N content is within the above range, the oxidation resistance of the resulting halide-based solid electrolyte can be further improved, and a higher level of both ionic conductivity and oxidation resistance can be achieved. The lower limit of the N content relative to the total number of atoms in the above halide-based solid electrolyte may be, for example, 1 mol% or more, 3 mol% or more, 5 mol% or more, 7 mol% or more, or 10 mol% or more. When the lower limit of the N content is within the above range, the ionic conductivity of the resulting halide-based solid electrolyte can be further improved. The N content relative to the total number of atoms in the above halide-based solid electrolyte may be adjusted within the above range, for example, 1 mol% or more and less than 25 mol%, or 1 to 23 mol%.

[0018] The halogen element X in the above halide-based 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 at least Cl is included, and may be Cl.

[0019] The above-mentioned halide-based solid electrolyte contains alkali metal elements, halogen elements, N, and O as constituent elements. Other metal elements may be included as constituent elements as long as they do not impair the spirit of the present invention, and preferably, other metal elements are not included as constituent elements. In a halide-based solid electrolyte containing the above-mentioned 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 improved by not including metal elements other than the above-mentioned alkali metal elements as constituent elements.

[0020] The above halide-based solid electrolyte is, for example, a general formula (1): A ａ N ｂ O ｃ M ｄ Z ｅ X ｆ Hｇ The compound may have a composition represented by the above general formula (1). In the above general formula (1), A represents an alkali metal element, N represents nitrogen, O represents oxygen, M represents a metal element other than A, Z represents at least one selected from the group consisting of Si, B, Ge, S, Se, and P, X represents a halogen element, and H represents hydrogen. The alkali metal element may be any of the elements listed as alkali metal elements in the above description of halide solid electrolytes. The halogen element may be any of the elements listed as halogen elements in the above description of halide solid electrolytes.

[0021] In the above general formula (1), a is greater than 0 and less than or equal to 0.9, b is greater than 0 and less than 0.25, c is greater than 0 and less than or equal to 0.30, d is 0 or greater and less than or equal to 0.1, e is 0 or greater and less than or equal to 0.25, f is greater than 0 and less than or equal to 0.5, and g is 0 or greater and less than or equal to 0.1, satisfying a + b + c + d + e + f + g = 1.

[0022] The above value a may be, for example, 0.1 to 0.85, 0.2 to 0.8, or 0.3 to less than 0.75. It is believed that when the upper limit of the value of a is within the above range, cation defects are more likely to occur in the crystal structure, and the ionic conductivity is more likely to improve. It is believed that when the lower limit of the value of a is within the above range, the carrier concentration of cations increases, and the ionic conductivity is more likely to improve.

[0023] The above value b may be, for example, 0.01 or more and 0.23 or less, 0.05 or more and 0.21 or less, or 0.1 or more and 0.19 or less. The upper limit of the value of b being within the above range increases the distance between N atoms in the crystal structure, and N ２ This makes it more difficult for the material to detach, and thus the oxidation resistance is likely to improve. Since the lower limit of the value of b is within the above range, it is thought that weak bonds between N and alkali metal ions are more easily formed in the crystal structure, and the ionic conductivity is likely to improve further.

[0024] The above value c may be, for example, 0.01 to 0.20, 0.02 to 0.18, or 0.03 to 0.15. When the upper limit of the value of c is within the above range, it is thought that strong bonds between O and alkali metal ions are less likely to form in the crystal structure, and ionic conductivity is more likely to improve. When the lower limit of the value of c is within the above range, it is thought that bonds between N and O are more likely to form in the crystal structure, and oxidation resistance is more likely to improve.

[0025] The above value d may be, for example, 0 or more and 0.08 or less, 0 or more and 0.05 or less, or 0 or more and 0.03 or less.

[0026] The above value e may be, for example, 0 or more and 0.10 or less, 0 or more and 0.05 or less, or 0 or more and 0.01 or more.

[0027] The above value of f may be, for example, 0.05 to 0.45, 0.07 to 0.4, or 0.1 to 0.35. When the upper limit of the value of f is within the above range, it is thought that strong bonds between Cl and alkali metal ions are less likely to form in the crystal structure, and ionic conductivity is more likely to improve. When the lower limit of the value of f is within the above range, it is thought that bonds between N and Cl are more likely to form in the crystal structure, and oxidation resistance is more likely to improve.

[0028] The above value of g may be, for example, 0 to 0.05, 0 to 0.04, or 0 to 0.03. It is believed that by keeping the upper limit of the value of g within the above range, the influence of proton conduction in the crystal structure is less likely to occur, the transportity of alkali metal ions increases, and the battery is more likely to operate stably.

[0029] The above halide-based solid electrolyte may be a compound comprising the alkali metal element, the halogen element, N, and O.

[0030] In this specification, the elemental composition ratios of halide-based solid electrolytes refer to values ​​measured by the following methods: The proportions of alkali metal element A, metal element M, and Z refer to values ​​determined by inductively coupled plasma atomic emission spectroscopy (ICP); the proportion of halogen element X refers to values ​​determined by ion chromatography; and the proportions of N and O refer to values ​​determined by non-dispersive infrared absorption spectroscopy. These values ​​are used to calculate the above composition ratios. Note that when preparing halide-based solid electrolytes oneself, the composition ratios can be calculated from the elemental composition ratios of the raw materials.

[0031] The above halide-based solid electrolyte is, for example, Li １３．５ N ３．５ ClO, Li ９ N ２ ClO, Li ７ NClin ２ The compound may have a composition represented by O, etc.

[0032] The ionic conductivity of the above halide-based solid electrolyte is, for example, 1.4 × 10⁻⁶. －３ mS / cm or more, 1.6×10 －３ mS / cm or more, 1.8×10 －３ mS / cm or more, 2.0×10 －３ mS / cm or more, 3.0×10 －３ mS / cm or more, 4.0×10 －３ mS / cm or more, 5.0×10 －３ mS / cm or higher, or 10.0 × 10⁻⁶ －３ It can be set to mS / cm or higher.

[0033] In this specification, ionic conductivity refers to a value calculated from the results of AC impedance measurements taken under the conditions of 25°C, a frequency range of 0.1 Hz to 1 MHz, and an applied voltage of 100 mV (vs. open-circuit voltage), and specifically shall be determined by the method described in the embodiments of this application.

[0034] The oxidation resistance of the above halide-based solid electrolyte can be such that, for example, the maximum peak current value in linear sweep voltammetry up to a voltage of 3.0 V relative to Li metal is 5.00 μA or less, 3.00 μA or less, 1.00 μA or less, 0.80 μA or less, and 0.50 μA or less.

[0035] In this specification, oxidation resistance refers to the maximum value of the peak current in a linear sweep voltammetry measurement taken at 25°C and a sweep rate of 1 mV / s, in the range from the open-circuit voltage to a voltage relative to Li metal of 3.0 V, and is specifically determined by the method described in the examples of this application.

[0036] The shape of the above-mentioned halide-based solid electrolyte is not particularly limited, but for example, it may be in the form of a powder.

[0037] The molding density of the above halide-based 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.

[0038] In this specification, the molding density of the solid electrolyte refers to the value calculated by preparing a measurement sample by filling an insulating cylinder with an inner diameter of 10 mm with 100 mg of the above halide-based solid electrolyte and applying a pressure of 370 MPa, and then measuring the volume of the measurement sample. Specifically, it shall be determined by the method described in the examples of this application.

[0039] One example of a method for producing a halide-based solid electrolyte involves altering a raw material composition containing an alkali metal element, a nitrogen (N) element, and a halogen element by a mechanochemical method. In the above raw material composition, at least one of the alkali metal element, nitrogen (N) element, and halogen element is an oxide or hydroxide. For example, lithium halide is a compound that contains both an alkali metal element and a halogen element.

[0040] Examples of alkali metal element sources include halides, nitrides, oxides, and hydroxides. Examples of compounds containing N as a constituent element include alkali metal element nitrides and compounds containing ammonium ions. Examples of compounds containing halogen elements include alkali metal element halides, nonmetal element halides, and metallic element halides.

[0041] In the mechanochemical method, for example, a ball mill can be used to supply mechanical energy such as collision, shearing, and friction between the raw material solids. 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 halide-based solid electrolyte obtained by the ball milling process, and thus improving oxidation resistance.

[0042] 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.

[0043] 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 halide-based 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 ball may be adjusted within the range described above, for example, 0.3 to 5.0% by mass.

[0044] The rotational speed of the ball mill may be, for example, 200 to 700 rpm, 200 to 500 rpm, or 250 to 350 rpm.

[0045] 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 halide-based solid electrolyte can be further improved.

[0046] The above-described method for producing a halide-based solid electrolyte may further include a step of heat-treating the solid obtained by the mechanochemical method at 150 to 500°C (annealing step).

[0047] The heating time in the annealing process may be, for example, 1 to 24 hours, 2 to 20 hours, or 5 to 15 hours.

[0048] The above-mentioned halide-based solid electrolytes are useful as materials for forming solid electrolyte layers and electrodes in batteries due to their high ionic conductivity and oxidation resistance. Furthermore, because the above-mentioned halide-based solid electrolytes can exhibit excellent ionic conductivity and oxidation resistance, they are useful as constituent materials for secondary batteries such as lithium-ion secondary batteries.

[0049] One embodiment of an electrode is an electrode comprising a solid electrolyte. The solid electrolyte is composed of a halide-based 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 above electrode. Another embodiment of a secondary battery comprises a solid electrolyte including a halide-based solid electrolyte according to this disclosure. The following description will use a lithium-ion secondary battery as an example.

[0050] 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.

[0051] 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 etc. can be mentioned.

[0052] The negative electrode active material can include, for example, metals such as Li, Si, Sn, Si-Mn, Si-Co, Si-Ni, In, Au, and alloys containing these metals, carbon materials such as graphite, and substances in which lithium ions are inserted between the layers of the carbon material.

[0053] In addition to the halide-based solid electrolyte and the electrode active material, the above electrode may contain other components. Examples of the other components include solid electrolyte compounds other than the halide-based solid electrolyte, conductive aids, and binders.

[0054] The conductive aid can be, for example, a carbon material. Examples of the carbon material include graphene, graphite, carbon black, fullerene, carbon nanotube, and carbon fiber. 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 fiber include carbon fibers such as vapor-grown carbon fiber (VGCF).

[0055] Examples of the binder include fluorine-based resins and synthetic rubbers. The fluorine-based resin is preferably a resin having a carbon chain as the main chain. The carbon chain may be formed by radical polymerization of a compound having an ethylenically unsaturated group. Examples of the fluorine-based resin include poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and polyvinylidene fluoride (PVDF). Examples of the synthetic rubber include SBR (styrene-butadiene rubber).

[0056] The electrode may have a structure in which a layer of a composition containing the above solid electrolyte and electrode active material is provided on a current collector. The material of the current collector is not particularly limited, and may be, for example, a single metal or an alloy such as Cu, Mg, Ti, Fe, Co, Ni, Zn, Al, Ge, In, Au, Pt, Ag, and Pd.

[0057] Another embodiment of the lithium-ion secondary battery includes a solid electrolyte containing the above-described halide-based solid electrolyte. The lithium-ion secondary battery may have a laminated structure including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order.

[0058] As described above, several embodiments have been described, but the present disclosure is not limited to the above embodiments at all. Also, the description contents of the above-described embodiments can be applied to each other.

[0059] Hereinafter, the content of the present disclosure will be described in more detail with reference to Examples and Comparative Examples. However, the present disclosure is not limited to the following Examples.

[0060] (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 were weighed so as to have the blending amounts shown in Table 1, and a raw material composition was prepared. In a dry argon atmosphere, the raw material composition was mixed using a mortar for 1 minute. 1.6 g of the mixed raw material composition was placed in a zirconia pot, and further, 80 g of zirconia balls having a diameter of 4 mm were charged into the pot. Then, a solid electrolyte was obtained by performing a ball milling treatment for 24 hours under the condition of 300 rpm using a planetary ball mill. The planetary ball mill used was "PM 400" (product name) manufactured by Vorder Scientific Co., Ltd.

[0061] (Example 2) A solid electrolyte was obtained in the same manner as in Example 1, except that LiCl, Li ３ N, and Li ２ O were weighed so as to have the blending amounts shown in Table 1.

[0062] (Example 3) LiCl, and Li ３ N, and Li ２A solid electrolyte was obtained in the same manner as in Example 1, except that O was weighed to the amount shown in Table 1.

[0063] (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.

[0064] (Comparative Example 2) 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.

[0065]

[0066] <Evaluation of Solid Electrolytes> For each of the solid electrolytes prepared in the examples and comparative examples, the composition formula, N content, and molar amount of N M were evaluated using the method shown below. Ｎ Molar amount M of O relative to O Ｏ The ratio and molding density were evaluated. The results are shown in Table 2.

[0067] [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.

[0068] [N content and molar amount M of N] Ｎ Molar amount M of O relative to O Ｏ [Determination of the ratio] For the solid electrolytes prepared in the examples and comparative examples, the N content and the molar amount M of N were determined from the elemental composition ratio in the raw material composition. Ｎ Molar amount M of O relative to O Ｏ The ratio was identified.

[0069] [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.

[0070] <Evaluation of Solid Electrolytes> For each of the solid electrolytes prepared in the examples and comparative examples, AC impedance measurements and linear sweep voltammetry measurements were performed using the methods described below, and the ionic conductivity and oxidation resistance were evaluated from the results.

[0071] [Evaluation of Ionic Conductivity: AC Impedance Measurement] (Preparation of Evaluation Cell X) The following steps for preparing evaluation cell X were all carried out in a glove box purged with an inert gas. First, 100 mg of the above solid electrolyte material was filled into an insulating cylinder with an inner diameter of 10 mm, and a solid electrolyte layer was formed by applying a pressure of 370 MPa. Next, current collectors made of stainless steel were attached to both sides of the solid electrolyte layer, and lead wires were attached to each current collector to prepare evaluation cell X.

[0072] (AC Impedance Measurement) An impedance measuring device is used to measure under the following conditions: 25°C, frequency range 0.1 Hz to 1 MHz, applied voltage 100 mV (vs. open circuit voltage). The ionic conductivity σ can be calculated using the following formula: σ(S・cm) －１ )=t(cm) / (R(Ω)×A(cm ２ In the formula, R represents the impedance value, A represents the sample area, and t represents the sample thickness. The results are shown in Table 2.

[0073] [Evaluation of oxidation resistance: Linear sweep voltammetry measurement] (Preparation of evaluation cell Y) The following steps for preparing evaluation cell Y were all carried out in a glove box purged with 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.

[0074] 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.

[0075] 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 Y.

[0076] (Measurement of Linear Sweep Voltammetry) Using the evaluation cell Y 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 linear sweep voltammetry test was performed under the following conditions.

[0077] In the linear sweep voltammetry test, the sweep speed 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 increased from the open-circuit voltage to 3.0 V. The maximum value of the peak current in the range from the open-circuit voltage to the voltage relative to the Li metal of 3.0 V was determined as an evaluation index for oxidation resistance. The results are shown in Table 2.

[0078]

[0079] As shown in Table 2, the solid electrolytes of the examples that satisfy the requirements for halide-based solid electrolytes according to this disclosure were found to be superior to the solid electrolytes of the comparative examples in terms of the balance between ionic conductivity and oxidation resistance. In particular, the solid electrolytes of the examples were found to maintain high oxidation resistance despite being compounds that contain N as a constituent element.

[0080] This disclosure aims to provide a solid electrolyte having excellent ionic conductivity and oxidation resistance.

Claims

A halide-type solid electrolyte having alkali metal elements, halogen elements, N, and O as constituent elements. 　 The molar amount M of N Ｎ The molar amount M of O relative to the above O Ｏ The halide-based solid electrolyte according to claim 1, wherein the ratio of is 5.0 or less. 　 The molar amount M of N Ｎ The molar amount M of O relative to the above O Ｏ The halide-based solid electrolyte according to claim 2, wherein the ratio of is 0.05 or more. 　 The halide-based solid electrolyte according to claim 1, wherein the content of N is less than 25 mol% relative to the total number of atoms contained in the halide-based solid electrolyte. 　 The halide-based solid electrolyte has a composition represented by the general formula (1): A ａ N ｂ O ｃ M ｄ Z ｅ X ｆ H ｇ and has a composition represented by the formula, A above represents an alkali metal element, The above M represents a metal element other than A, The aforementioned Z represents at least one selected from the group consisting of Si, B, Ge, S, Se, and P. The aforementioned X represents a halogen element, The above a is greater than 0 and less than or equal to 0.

9. The aforementioned b is greater than 0 and less than 0.

25. The aforementioned c is greater than 0 and less than or equal to 0.

30. The aforementioned d is 0 or greater and 0.1 or less. The aforementioned e is 0 or greater and 0.25 or less. The aforementioned f is greater than 0 and less than or equal to 0.

5. The aforementioned g is 0 or greater and 0.1 or less. A halide-based solid electrolyte according to claim 1, satisfying a + b + c + d + e + f + g = 1. 　 The halide-based solid electrolyte according to any one of claims 1 to 5, wherein the halogen element comprises at least Cl. 　 The molding density is 1.0 to 5.0 g / cm³. ３ The halide-based solid electrolyte according to any one of claims 1 to 5. 　 An electrode containing a solid electrolyte, An electrode in which the solid electrolyte is the halide-based solid electrolyte described in claim 1 or 2. 　 A secondary battery comprising the electrode described in claim 8. 　 A secondary battery comprising a solid electrolyte containing the halide-based solid electrolyte described in claim 1 or 2.

Images