JP7795069B2 - Solid electrolyte material, its manufacturing method and battery - Google Patents

Description

This disclosure relates to a solid electrolyte material, a method for producing the same, and a battery.

There is a demand for safer all-solid-state lithium-ion secondary batteries that use solid electrolytes. Examples of solid electrolytes include oxide-based solid electrolytes containing lithium, metal elements, and oxygen; sulfide-based solid electrolytes containing lithium, phosphorus, and sulfur; and halogen-based solid electrolytes containing lithium, metal elements, and halogen. Among these, sulfides with an argyrodite structure have attracted attention as sulfide-based solid electrolytes due to their high ionic conductivity and low manufacturing costs.

For example, Patent Document 1 proposes a solid electrolyte material that has a peak corresponding to Li ₇ PS ₆ and a peak corresponding to Li ₃ PO ₄ in X-ray diffraction measurement, and that has high Li ion conductivity and high thermal stability.

JP 2017-33858 A

One aspect of the present disclosure aims to provide a solid electrolyte material that can reduce the resistance value in a battery and a method for producing the same.

The first aspect is a method for producing a solid electrolyte material, which includes obtaining a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate, and heat-treating the mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate. The lithium-containing compound used in the production method includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate. Furthermore, the mixture used in the production method has a metal phosphate content of less than 15.0% by mass.

A second aspect is a solid electrolyte material comprising a sulfide having an argyrodite-type crystal structure containing lithium, phosphorus, and sulfur, lithium phosphate, and sulfate ions. The solid electrolyte material has a sulfate ion content of 0.5% by mass or more. When measured in an X-ray diffraction pattern by the θ-2θ method using CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, the solid electrolyte material exhibits a first peak in the diffraction angle 2θ range of 21° or more and less than 23°, and a second peak in the diffraction angle 2θ range of 25° or more and less than 27°, with the ratio of the intensity of the first peak to the intensity of the second peak being 0.03 or more and less than 0.15.

One aspect of the present disclosure provides a solid electrolyte material that can reduce the resistance value in a battery, and a method for producing the same.

FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 1000. FIG. 2 is a cross-sectional view showing a schematic configuration of a measurement cell for evaluating battery characteristics. 1 shows X-ray diffraction (XRD) patterns of solid electrolyte materials according to Example 1 and Comparative Example 1. 1 shows XRD patterns of solid electrolyte materials according to Examples 2, 3, and 4. 1 shows XRD patterns of solid electrolyte materials according to Comparative Examples 2, 3, and 4.

As used herein, the term "process" refers not only to an independent process, but also to processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, when the composition contains multiple substances corresponding to each component, the content of each component in the composition refers to the total amount of those multiple substances present in the composition, unless otherwise specified. Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined. Below, embodiments of the present invention are described in detail. However, the embodiments described below are intended to exemplify solid electrolyte materials, manufacturing methods thereof, and batteries that embody the technical concepts of the present invention, and the present invention is not limited to the solid electrolyte materials, manufacturing methods thereof, and batteries described below.

1. Method for Producing Solid Electrolyte Material The method for producing a solid electrolyte material includes a preparation step of obtaining a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate, and a heat-treatment step of heat-treating the prepared mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate. The lithium-containing compound contained in the mixture includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate. The content of the metal phosphate in the mixture is less than 15.0 mass%.

When producing a solid electrolyte material containing a sulfide having an argyrodite-type crystal structure, adding a predetermined amount of metal sulfate in addition to metal phosphate reduces the resistance of a battery constructed using the produced solid electrolyte material. This can be attributed to, for example, the presence of a predetermined amount of sulfate ions and lithium phosphate in the solid electrolyte material, which improves the conductivity of lithium ions.

In the preparation step, a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate is obtained. The mixture may further contain a chlorine-containing compound. The mixture may be, for example, a raw material composition for a solid electrolyte material.

Examples of the lithium-containing compound include lithium sulfide (e.g., Li ₂ S), lithium oxide (e.g., Li ₂ O), and lithium carbonate (e.g., Li ₂ CO ₃ ). The lithium-containing compound may contain at least one selected from the group consisting of these compounds, and preferably contains at least lithium sulfide.

The content of the lithium-containing compound in the mixture may be, for example, 3 to 7 moles, preferably 3.1 to 5 moles, and more preferably 3.3 to 4.3 moles, per mole of the phosphorus- and sulfur-containing compound. The content of the lithium-containing compound does not include metal sulfates, metal phosphates, and chlorine-containing compounds, which will be described later.

The compound containing phosphorus and sulfur may be, for example, a compound having a phosphorus-sulfur bond. Examples of the compound containing phosphorus and sulfur include diphosphorus trisulfide (e.g., P ₂ S ₃ ), diphosphorus pentasulfide (e.g., P ₂ S ₅ ), etc., and the compound may contain at least one selected from the group consisting of these, and preferably may contain at least diphosphorus pentasulfide.

The metal sulfate may be, for example _, an alkali metal sulfate. Examples of the metal sulfate include lithium sulfate (e.g., _Li2SO4 ), sodium sulfate ( _Na2SO4 ), _etc. , and the metal sulfate may contain at least one selected from the group consisting of these, and preferably contains at least lithium sulfate.

The content of the metal sulfate in the mixture may be, for example, 1.0% by mass or less, and preferably 0.7% by mass or less, 0.6% by mass or less, or 0.55% by mass or less, relative to the mixture. The lower limit of the metal sulfate content may be, for example, 0.01% by mass or more, and preferably 0.1% by mass or more, 0.2% by mass or more, or 0.4% by mass or more, relative to the mixture. Having the metal sulfate content within the above range tends to further improve the lithium ion conductivity of the produced solid electrolyte material, further reduce battery resistance, and further improve battery characteristics.

The metal phosphate may be, for example _, an alkali metal phosphate. Examples of the metal phosphate include lithium phosphate (e.g., _Li3PO4 ), sodium phosphate ( _Na3PO4 ), _etc. , and the metal phosphate may contain at least one selected from the group consisting of these, and preferably contains at least lithium phosphate.

The content of the metal phosphate in the mixture may be, for example, 15.0% by mass or less, and preferably 10.0% by mass or less, 7.0% by mass or less, 5.0% by mass or less, or 3.0% by mass or less, relative to the mixture. The lower limit of the metal phosphate content may be, for example, 0.1% by mass or more, and preferably 0.5% by mass or more, or 1.0% by mass or more, relative to the mixture. When the metal phosphate content is within the above range, the battery resistance of the produced solid electrolyte material tends to be further reduced.

The chlorine-containing compound may be, for example, a metal chloride, preferably an alkali metal chloride. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Specific examples of chlorine-containing compounds include lithium chloride (e.g., LiCl), sodium chloride (e.g., NaCl), and potassium chloride (e.g., KCl). The compound may contain at least one selected from the group consisting of these, and preferably contains at least lithium chloride.

The content of the chlorine-containing compound in the mixture may be, for example, 0 to 3.9 moles, preferably 1 to 3.7 moles, and more preferably 2.9 to 3.5 moles, per mole of the phosphorus- and sulfur-containing compound. When the content of the chlorine-containing compound in the mixture is within the above range, the effect of reducing internal resistance, described below, tends to be greater.

A portion of the chlorine-containing compound may be replaced with a bromine-containing compound. The bromine-containing compound may be, for example, a metal bromide, preferably an alkali metal bromide. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Specific examples of the bromine-containing compound include lithium bromide (e.g., LiBr), sodium bromide (e.g., NaBr), and potassium bromide (e.g., KBr). The compound may contain at least one selected from the group consisting of these, preferably lithium bromide. When a portion of the chlorine-containing compound is replaced with a bromine-containing compound, the content of the bromine-containing compound may be greater than 0 moles and less than 1 mole per mole of the chlorine-containing compound, preferably 0.5 moles or less, and more preferably 0.1 moles or less. The lower limit of the content of the bromine-containing compound relative to the chlorine-containing compound may be, for example, 0.001 moles or more. Furthermore, when a portion of the chlorine-containing compound is replaced with a bromine-containing compound, the total amount of the chlorine-containing compound and the bromine-containing compound may be 0 to 3.9 moles, preferably 1 to 3.7 moles, and more preferably 2.9 to 3.5 moles, per mole of the phosphorus- and sulfur-containing compound.

In the mixture, some of the chlorine-containing compounds may be replaced with compounds containing halogen atoms other than chlorine and bromine. Examples of halogen atoms contained in compounds containing halogen atoms other than chlorine and bromine include fluorine and iodine, and the mixture may contain at least one of these. The compound containing halogen atoms other than chlorine and bromine may contain, for example, a metal halide, preferably an alkali metal halide, and may contain at least a lithium halide.

When the mixture contains compounds containing halogen atoms other than chlorine and bromine, the content of the compounds containing halogen atoms other than chlorine and bromine in the mixture may be, for example, greater than 0 mol and less than 0.1 mol, and preferably greater than 0 mol and less than 0.05 mol, per 1 mol of the chlorine-containing compound.

The mixture can be prepared by weighing and mixing the lithium-containing compound, phosphorus- and sulfur-containing compound, metal sulfate, metal phosphate, and, if necessary, chlorine-containing compound to the desired content. For example, the total molar ratio of the lithium-containing compound and chlorine-containing compound to the phosphorus- and sulfur-containing compound in the mixture may be, for example, 3 or more and 8 or less, preferably 5 or more and 7.8 or less, and more preferably 6 or more and 7.5 or less.

Examples of mixing methods for mixing the raw materials include mixing methods that can apply mechanical stress, such as a high-speed shear mixer, ball mill, bead mill, vibration mill, or planetary ball mill.

In the heat treatment step, the prepared mixture is heat-treated to obtain a heat-treated product containing sulfate ions and lithium phosphate. The heat-treated product may contain a sulfide having an argyrodite-type crystal structure that contains lithium, phosphorus, and sulfur in its composition, and the sulfide having the argyrodite-type crystal structure may contain a crystalline phase. When the sulfide contains a crystalline phase, it may contain a crystalline phase having a composition represented _{by Li7PS6} .

The heat treatment temperature of the mixture may be, for example, 400°C or higher, preferably 450°C or higher, or 500°C or higher. The upper limit of the heat treatment temperature may be, for example, 1000°C or lower, preferably 800°C or lower, or 600°C or lower. The heat treatment time may be, for example, 1 hour to 20 hours, preferably 5 hours to 15 hours. The heat treatment atmosphere may be, for example, an inert gas atmosphere such as nitrogen gas or a rare gas, or the heat treatment may be performed under reduced pressure.

Solid Electrolyte Material The solid electrolyte material contains a sulfide having an argyrodite-type crystal structure containing lithium, phosphorus, and sulfur, lithium phosphate, and sulfate ions. When the X-ray diffraction pattern of the solid electrolyte material is measured by the θ-2θ method using CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, a first peak is observed in a diffraction angle 2θ range of 21° or more and less than 23°, and a second peak is observed in a diffraction angle 2θ range of 25° or more and less than 27°. Furthermore, the ratio of the intensity of the first peak to the intensity of the second peak may be, for example, 0.03 or more and less than 0.15. The content of sulfate ions contained in the solid electrolyte material may be, for example, 0.5% by mass or more relative to the solid electrolyte material.

When a solid electrolyte material contains lithium phosphate and sulfate ions in addition to a sulfide having an argyrodite-type crystal structure, the conductivity of lithium ions is improved. Furthermore, when a battery is constructed, the internal resistance is reduced, resulting in excellent battery characteristics. This can be explained, for example, as follows: When a sulfide having an argyrodite-type crystal structure is used as a solid electrolyte, the presence of lithium phosphate, which has a higher lithium concentration than the sulfide having an argyrodite-type crystal structure, on the particle surface of the solid electrolyte is thought to improve the diffusibility of lithium ions and improve battery resistance. Furthermore, the argyrodite-type crystal structure is composed of a structure of Li ₂ S—Li ₃ PS ₄ —Li ₂ S. It is thought that when lithium sulfate is present nearby, a portion of it is replaced with Li ₃ PS ₄ to form a solid solution. This causes lithium deficiency in the solid electrolyte, creating vacant lithium sites, which is thought to facilitate lithium migration within the solid electrolyte. It is considered that when the solid electrolyte material contains lithium chloride, a portion of the lithium chloride is replaced with _Li2S to form a solid solution, causing lithium deficiency and forming vacant lithium sites. This replacement of the _Li2S and _{Li3PS4 units} is considered to synergistically improve the lithium ion conductivity.

The solid electrolyte material includes a sulfide containing lithium, phosphorus, and sulfur and having an argyrodite-type crystal structure. The sulfide constituting the solid electrolyte material may include, for example, a crystalline phase having a composition represented by Li ₇ PS _6. The presence of the crystalline phase having a composition represented by Li ₇ PS ₆ in the sulfide can be confirmed, for example, by X-ray diffraction (XRD) measurement. Specifically, when XRD measurement of the solid electrolyte material is performed by the θ-2θ method using CuKα rays with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, peaks corresponding to the crystalline phase having a composition represented by Li ₇ PS ₆ typically appear at 2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, and 52.7°.

The lithium content in the sulfide composition may be, for example, 4 to 7 moles, and preferably 5 to 6 moles, per mole of phosphorus. The sulfur content in the sulfide composition may be, for example, 3 to 6 moles, and preferably 4 to 5 moles, per mole of phosphorus.

Sulfides having an argyrodite-type crystal structure may contain a halogen in their composition. The inclusion of a halogen tends to further improve lithium ion conductivity. Examples of halogens include chlorine, bromine, and iodine. The sulfide may contain at least one selected from the group consisting of these, may contain either chlorine or bromine, or may contain at least chlorine. The inclusion of chlorine tends to result in a sulfide solid electrolyte with higher chemical stability.

When a sulfide having an argyrodite-type crystal structure contains a halogen in its composition, the halogen content in the sulfide composition may be, for example, greater than 0 mol and not more than 2 mols per mol of phosphorus, preferably 1 mol to 2 mols, and more preferably 1.4 mol to 1.8 mols. When the halogen content in the composition of a sulfide having an argyrodite-type crystal structure is within the above range, the lithium ion conductivity of the sulfide tends to be more easily improved.

The solid electrolyte material contains lithium phosphate in addition to a sulfide having an argyrodite-type crystal structure. The presence of lithium phosphate in the solid electrolyte material can be evaluated using an X-ray diffraction pattern. Specifically, when XRD measurement of the solid electrolyte material is performed using the θ-2θ method with CuKα radiation having wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, peaks corresponding to lithium phosphate (e.g., Li ₃ PO ₄ ) typically appear at 2θ=22.3°, 23.2°, 24.8°, 33.9°, and 36.6°.

A solid electrolyte material containing lithium phosphate in addition to a sulfide having an argyrodite-type crystal structure may _have , in an X-ray diffraction pattern using CuKα radiation as an X-ray source, a first peak corresponding to lithium phosphate (e.g., _Li3PO4 ) and a second peak corresponding to a crystalline phase having a composition represented _{by Li7PS6} . The first peak may have a diffraction angle 2θ value of 21° or more and less than 23°, for example, about 22.3°. The second peak may have a diffraction angle 2θ value of 25° or more and less than 27°, for example, about 25.7°.

The lithium phosphate content of a solid electrolyte material can be evaluated, for example, using an X-ray diffraction pattern. Specifically, it can be evaluated by the ratio of the intensity of the first peak to the intensity of the second peak (hereinafter simply referred to as the "peak intensity ratio"). The ratio of the intensity of the first peak to the intensity of the second peak of the solid electrolyte material may be, for example, 0.03 or more and less than 0.15, preferably 0.04 or more or 0.045 or more, and preferably 0.10 or less or 0.06 or less. When the peak intensity ratio corresponding to the lithium phosphate content is within the above range, battery resistance tends to be further reduced.

The solid electrolyte material contains sulfate ions. The content of sulfate ions contained in the solid electrolyte material may be, for example, 0.5 mass% or more, and preferably 0.54 mass% or more, relative to the solid electrolyte material. The upper limit of the sulfate ion content may be, for example, 1.0 mass% or less, and preferably 0.8 mass% or less, relative to the solid electrolyte material. When sulfate ions are present at a content within the above range, lithium ion conductivity is further improved, battery resistance is further reduced, and battery characteristics tend to be further improved.

The sulfate ion content of the solid electrolyte material is measured using inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy).

The composition of the solid electrolyte material may be such that the lithium atom composition ratio is, for example, 4 to 7 moles per mole of phosphorus, and preferably 5 to 6 moles. The sulfur atom composition ratio may be, for example, 3 to 6 moles per mole of phosphorus, and preferably 4 to 5 moles. The oxygen atom composition ratio may be, for example, 0 to 4 moles per mole of phosphorus, and preferably 0.1 to 2.0 moles. The halogen atom composition ratio may be, for example, 0 to less than 2 moles per mole of phosphorus, and preferably 1.4 to 1.8 moles.

The solid electrolyte material may have a composition represented by the following formula (I), for example.
Li _r PS _s O _t X _u (I)
In formula (I), r, s, t, and u are each 4≦r≦7, 3≦s≦6, 0≦t≦4, and 0≦u<2, and X may be at least one selected from the group consisting of F, Cl, Br, and I. Preferably, 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8 are satisfied, and X may be at least one of Br and Cl.

Battery The battery is configured to include an electrolyte containing the above-described solid electrolyte material, a positive electrode, and a negative electrode. The electrolyte may form an electrolyte layer disposed between the positive electrode and the negative electrode. An example of the battery configuration will now be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 1000. The battery 1000 includes a positive electrode 201, a negative electrode 203, and an electrolyte layer 202 disposed between the positive electrode 201 and the negative electrode 203. The positive electrode 201 includes a positive electrode active material layer containing a positive electrode active material 204. The positive electrode active material layer constituting the positive electrode 201 may contain, in addition to the positive electrode active material 204, a conductive additive, the solid electrolyte material 100, and the like. The positive electrode 201 may also include a current collector and a lead connected to the current collector. The negative electrode 203 includes a negative electrode active material layer containing a negative electrode active material 205. The negative electrode active material layer constituting the negative electrode 203 may contain, in addition to the negative electrode active material 205, a conductive additive, the solid electrolyte material 100, and the like. The negative electrode 203 may include a current collector and a lead connected to the current collector. The electrolyte layer 202 includes a solid electrolyte material. An example of the battery is a lithium ion battery, which may be an all-solid-state secondary battery.

The lithium-ion battery referred to in this specification includes lithium-ion secondary batteries that use a lithium transition metal composite oxide in the positive electrode and lithium-sulfur batteries that use a material that absorbs and releases lithium in the negative electrode. For specific examples of lithium transition metal composite oxides, see, for example, paragraph 0066 of WO 2017/141735 (paragraphs 0152 to 0156 of U.S. Patent Publication No. 2018/0309167). For examples of materials that absorb and release lithium, see, for example, paragraph 0058 of WO 2015/056564 (paragraph 0070 of U.S. Patent Publication No. 2016/0254529).

For example, a lithium transition metal composite oxide is used for the positive electrode active material 204. Examples of suitable materials include transition metal oxides having a layered rock salt structure and transition metal oxides having a spinel structure, as described in the above-mentioned publications. In addition to lithium-containing transition metal phosphate compounds, lithium-containing transition metal halide phosphate compounds, and lithium-containing transition metal silicate compounds, the positive electrode active material 204 may also include transition metal fluorides, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, and transition metal oxynitrides. In the case of lithium-sulfur batteries, elemental sulfur can be used as the positive electrode active material.

The average particle size of the positive electrode active material 204 may be, for example, 0.1 μm or more and 30 μm or less. If the average particle size of the positive electrode active material 204 is 30 μm or less, lithium diffusion within the positive electrode active material 204 will not be too slow, which may make it easier for the battery to operate at high power. The thickness of the positive electrode active material layer may be, for example, 10 μm or more and 500 μm or less. If the thickness of the positive electrode active material layer is 10 μm or more, it may be easier to ensure sufficient battery energy density. Furthermore, if the thickness of the positive electrode active material layer is 500 μm or less, it may make it easier for the battery to operate at high power.

The average particle size of the positive electrode active material 204 may be larger than the average particle size of the solid electrolyte material 100. This allows the positive electrode active material 204 and the solid electrolyte material to be well dispersed in the positive electrode active material layer.

The volume ratio of the positive electrode active material 204 to the total volume of the positive electrode active material 204 and the solid electrolyte material 100 contained in the positive electrode active material layer may be, for example, 30% or more and 95% or less. A volume ratio of 30% or more ensures sufficient energy density for the battery. Furthermore, a volume ratio of 95% or less may make it easier to operate at high power.

The electrolyte layer 202 may be a solid electrolyte layer containing the above-mentioned solid electrolyte material. The thickness of the solid electrolyte layer may be, for example, 1 μm or more and 100 μm or less. If the thickness of the solid electrolyte layer is 1 μm or more, short-circuiting between the positive electrode 201 and the negative electrode 203 can be suppressed. Furthermore, if the thickness of the solid electrolyte layer is 100 μm or less, high-power operation may be easier.

The negative electrode active material 205 is composed of a material capable of absorbing and releasing metal ions such as lithium ions. Specific examples of the negative electrode active material 205 include metal materials and carbon materials. The metal material may be a simple metal or an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon.

The average particle size of the negative electrode active material 205 may be, for example, 0.1 μm or more and 100 μm or less. If the average particle size of the negative electrode active material 205 is 0.1 μm or more, it is possible that the negative electrode active material 205 and the solid electrolyte material 100 can form a well-dispersed state in the negative electrode active material layer. This can prevent a deterioration in the charge/discharge characteristics of the battery. Furthermore, if the average particle size of the negative electrode active material 205 is 100 μm or less, lithium diffusion within the negative electrode active material 205 will not be too slow, which may make it easier for the battery to operate at high power.

The average particle size of the negative electrode active material 205 may be larger than the average particle size of the solid electrolyte material 100. This allows the negative electrode active material 205 and the solid electrolyte material to be well dispersed in the negative electrode active material layer.

The volume ratio of the negative electrode active material 205 to the total volume of the negative electrode active material 205 and the solid electrolyte material 100 contained in the negative electrode active material layer may be, for example, 30% or more and 95% or less. A volume ratio of 30% or more ensures sufficient energy density for the battery. Furthermore, a volume ratio of 95% or less may make it easier to operate at high power.

At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive, if necessary. The conductive additive is used to reduce the electrical resistance of the battery. Examples of conductive additives include graphites such as natural graphite and artificial graphite, and carbons such as acetylene black and ketjen black.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

Example 1
In a dry atmosphere with _a dew point of -50°C or lower, _the raw materials _Li2S , _P2S5 , _LiCl , _Li2SO4 , _{and Li3PO4 were} weighed out in a molar ratio of _Li2S : _P2S5 : _LiCl : _Li2SO4 : _Li3PO4 = _3.74 :1:3.28:0.03:0.05. These were ground and mixed in an absolute mill to obtain a mixture. The resulting mixture was filled into a crucible and placed in a sealed quartz container. A carbon packing was placed in the sealed container and tightened with a torque of _{3.4 Nm} . The sealed container was heat-treated at 500°C for 8 hours in a nitrogen atmosphere to obtain a powder of the solid electrolyte material of Example 1. The solid electrolyte material of Example 1 had a composition expressed as _{Li5.5PS4.2O0.1Cl1.7 .} Table 1 also shows the content (mass%) of Li ₂ SO ₄ in the mixture.

Example 2
A powder of the solid electrolyte material of _{Example 2} was obtained in the same manner as in Example 1, except that the raw materials were weighed out so that the molar ratio of the mixture was _Li2S : _P2S5 :LiCl: _Li2SO4 : _Li3PO4 = 3.76: ₁ : _3.43 : _0.03 : _0.14 . The solid electrolyte material of Example 2 had a composition expressed as _{Li5.5PS4.0O0.5Cl1.6} .

Example 3
A powder of the solid electrolyte material of Example ₃ was obtained in the same manner as in Example 1, except that the raw materials were weighed out so that the molar ratio of the mixture was _Li2S : _P2S5 :LiCl: _Li2SO4 : _Li3PO4 = _3.90 : ₁ : _3.68 : _0.025 : _0.25 . The solid electrolyte material of Example 3 had a composition expressed as _{Li5.4PS3.6O0.9Cl1.6} .

Example 4
A powder of the solid electrolyte material of _{Example 4} was obtained in the same manner as in Example 1, except that the raw materials were weighed out so that the molar ratio of the mixture was _Li2S : _P2S5 :LiCl: _Li2SO4 : _Li3PO4 = 3.65: ₁ : _3.43 : _0.04 : _0.14 . The solid electrolyte material of Example 4 had a composition expressed as _{Li5.2PS3.9O0.6Cl1.6} .

Comparative Example 1
_A powder of a solid electrolyte material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed out so that the molar ratio of _Li2S : _P2S5 :LiCl in the mixture was _3.8 :1: _3.2 . The solid electrolyte material of Comparative Example 1 had a composition expressed as _{Li5.4PS4.4Cl1.6} .

Comparative Example 2
_A powder of a solid electrolyte material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the raw materials were weighed so that the molar ratio of the mixture was _Li2S : _P2S5 :LiCl: _Li2SO4 = 3.84: ₁ : _3.22 : _0.03 . The solid electrolyte material of Comparative Example 2 had a composition expressed as _{Li5.3PS4.35O0.05Cl1.6 .}

Comparative Example 3
_A powder of the solid electrolyte material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the raw materials were weighed so that the molar ratio in the mixture was _Li2S : _P2S5 :LiCl: _Li3PO4 = 3.92: ₁ : _3.23 : _0.30 . The solid electrolyte material of Comparative Example 3 had a composition expressed as _{Li5.2PS3.9O0.5Cl1.4 .}

Comparative Example 4
A powder of the solid electrolyte material of Comparative Example ₄ was obtained in the same manner as in Example ₁ , except that the raw materials were weighed out so that the molar ratio in the mixture was _Li2S : _P2S5 :LiCl: _Li2SO4 : _Li3PO4 = 3.85: ₁ :3.99: _0.03 : _0.5 . The solid electrolyte material of Comparative Example 4 had a composition expressed _{as Li5.0PS3.1O1.4Cl1.4} .

Analysis of the crystal structure of the solid electrolyte material was carried out by measuring the X-ray diffraction pattern of a sample packed in a sealed cell at a dew point of −50° C. using an X-ray diffractometer (Rigaku Corporation, SmartLab). CuKα rays with wavelengths of 0.15405 nm and 0.15444 nm were used as the X-ray source.

In _the obtained X-ray diffraction pattern, the peak at 2θ = 22.3° was _selected as the first peak corresponding to _Li3PO4 , and the peak at 2θ = 25.7° was selected as the second peak corresponding to _Li7PS6 , and the ratio of the intensity of the first peak to the intensity of the second peak (peak intensity ratio) was calculated. The results are shown in Table 1.

Figure 3 shows the XRD patterns of the solid electrolyte materials obtained in Example 1 and Comparative Example 1. As shown in Figure 3, peaks corresponding to _{Li7PS6 (} 2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) were confirmed in the solid electrolyte materials of Example 1 and Comparative Example _1. Furthermore, peaks corresponding to _Li3PO4 (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°) were confirmed in the solid electrolyte material of Example 1.

The XRD patterns of the solid electrolyte materials obtained in Examples 2, 3, and 4 are shown in Figure 4. As shown in Figure 4, the solid electrolyte materials of Examples 2, 3, and ₄ had peaks corresponding to _Li7PS6 (2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) and peaks corresponding _{to Li3PO4} (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°).

Figure 5 shows the XRD patterns of the solid electrolyte materials obtained in Comparative Examples 2, 3, and 4. As shown in Figure 5, peaks corresponding to _Li7PS6 (2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) were confirmed in the solid electrolyte materials of Comparative Examples 2, 3, and 4, and peaks corresponding to _Li3PO4 (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°) were also confirmed in the XRD patterns of the solid electrolyte materials obtained in Comparative Examples ₃ and ₄ .

Sulfate Ion Content The powders of the solid electrolyte materials obtained in the examples and comparative examples were treated with zinc acetate to remove sulfur as zinc sulfide, and then the content of sulfate ions (SO ₄ ²⁻ ) was measured using high-frequency inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy). The results are shown in Table 1.

Evaluation of Battery Characteristics: Charge/Discharge Characteristics: In a dry atmosphere with a dew point of -50°C or less, the solid electrolyte materials obtained in the Examples and Comparative Examples were pressed at 310 MPa using the jig shown in Figure 2. The upper punch 303 was then removed, and a mixture of the cathode material, the above-mentioned solid electrolyte material, and a conductive additive was packed inside, followed by a pressure of 310 MPa. The lower punch 302 was then removed, and a Li negative electrode was packed inside, followed by a pressure of 310 MPa to fabricate a battery. The fabricated battery was connected to a potentiostat, and the charge capacity and discharge capacity were measured. The efficiency (%) was calculated by dividing the discharge capacity by the measured charge capacity. The results are shown in Table 1.

Battery Resistance The battery resistance (Ω) of the battery prepared above was measured at frequencies ranging from 20 Hz to 120 MHz using an impedance measuring device (Keysight Impedance Analyzer E4990A). The results are shown in Table 1.

As shown in Table 1, the batteries fabricated using the solid electrolyte materials of Examples 1 to 4 had reduced battery resistance.

1000 Battery 100 Solid electrolyte material 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Positive electrode active material 205 Negative electrode active material 300 Pressure molding die 301 Frame mold 302 Lower punch 303 Upper punch

Claims (12)

obtaining a mixture comprising a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate;
and heat-treating the mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate,
the lithium-containing compound includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate,
the mixture has a content of the metal phosphate of less than 15.0 mass%,
The solid electrolyte material has a composition represented by the following formula (I):
Li _r PS _s O _t X _u (I)
(In formula (I), r, s, t, and u satisfy the following conditions: 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8, respectively. X is at least one of Cl and Br.) The manufacturing method described in claim 1, wherein the mixture further contains a compound containing chlorine. The manufacturing method described in claim 1 or 2, wherein the compound containing phosphorus and sulfur includes at least one of diphosphorus trisulfide and diphosphorus pentasulfide. The manufacturing method described in claim 2, wherein the lithium-containing compound includes lithium sulfide, the phosphorus and sulfur-containing compound includes diphosphorus pentasulfide, the chlorine-containing compound includes lithium chloride, the metal sulfate includes lithium sulfate, and the metal phosphate includes lithium phosphate. The manufacturing method described in any one of claims 1 to 4, wherein the mixture contains 1.0 mass% or less of the metal sulfate. The manufacturing method described in any one of claims 1 to 5, wherein the mixture contains 0.7 mass% or less of the metal sulfate. The manufacturing method described in any one of claims 1 to 6, wherein the mixture contains 10.0% by mass or less of the metal phosphate. The manufacturing method described in any one of claims 1 to 7, wherein the mixture is heat-treated at a temperature of 400°C or higher. The composition includes a sulfide having an argyrodite-type crystal structure and containing lithium, phosphorus, and sulfur, lithium phosphate, and sulfate ions;
The content of the sulfate ions is 0.5% by mass or more,
In an X-ray diffraction pattern, when measured by the θ-2θ method using CuKα rays having wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, a first peak is observed in a diffraction angle 2θ value range of 21° or more and less than 23°, and a second peak is observed in a diffraction angle 2θ value range of 25° or more and less than 27°, and the ratio of the intensity of the first peak to the intensity of the second peak is 0.03 or more and less than 0.15, and the solid electrolyte material has a composition represented by the following formula (I) :
Li _r PS _s O _t X _u (I)
(In formula (I), r, s, t, and u satisfy the following conditions: 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8, respectively. X is at least one of Cl and Br.) The solid electrolyte material according to claim 9, wherein the sulfate ion content is 1.0 mass% or less. The solid electrolyte material according to claim 9 or 10, wherein the sulfide further contains chlorine. A battery comprising a solid electrolyte containing the solid electrolyte material according to any one of claims 9 to 11, a positive electrode, and a negative electrode.