Method for producing solid electrolyte

Abstract

The present invention addresses the problem of providing: a method for producing a modified sulfide solid electrolyte which is reduced in the generation amount of a hydrogen sulfide gas even if the sulfide solid electrolyte comes into contact with moisture and hydrogen sulfide is generated, while being suppressed in decrease in the ionic conductivity; this modified sulfide solid electrolyte; and an electrode mixture material and a lithium ion battery, each of which uses this modified sulfide solid electrolyte. A method for producing a modified sulfide solid electrolyte according to the present invention comprises mixing of a sulfide solid electrolyte with Li2S; and (100 – α) parts by mass of the sulfide solid electrolyte is used per α parts by mass of Li2S (meanwhile, α represents a number from 0.3 to 15.0).

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid electrolyte, a modified sulfide solid electrolyte, and an electrode mixture and a lithium ion battery using the same. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents, but by making batteries all-solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity are excellent. Therefore, batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] For the solid electrolyte layer, the use of sulfide solid electrolytes using lithium sulfide (Li2S) as a starting material is being considered. Although this sulfide solid electrolyte has high lithium ion conductivity (hereinafter simply referred to as ionic conductivity), it reacts easily with water (hereinafter including moisture) and oxygen, and in particular generates hydrogen sulfide (H2S) gas when it comes into contact with water, so there is a need to reduce the amount of H2S gas generated.

[0004] In order to reduce the generation of H2S gas, a method has been disclosed in which Li2S is used as a raw material and the Li2S remaining after the production of a sulfide solid electrolyte is completely eliminated (Patent Document 1). Methods of adding other compounds are also being considered. For example, an invention has been disclosed in which part of the Li2S in a sulfide solid electrolyte is replaced with the alkaline compound K2S as a method of neutralizing the generated H2S with an alkaline compound and suppressing its diffusion outside the system (Patent Document 2). In addition, an invention has been disclosed in which the surface of solid electrolyte particles is coated with an alkaline compound to suppress the generation of H2S gas (Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-129312 [Patent Document 2] Japanese Patent Application Publication No. 2019-160510 [Patent Document 3] Japanese Patent Application Publication No. 2017-120728 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-165650 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a modified sulfide solid electrolyte that reduces the cumulative amount of H2S gas generated over the medium to long term or over the entire period, even when the sulfide solid electrolyte comes into contact with water and H2S is generated, while suppressing a decrease in ionic conductivity, and a method for producing the modified sulfide solid electrolyte; and to provide a modified sulfide solid electrolyte, and an electrode composite and a lithium-ion battery using the same. [Means for solving the problem]

[0007] The method for producing a modified sulfide solid electrolyte according to the present invention includes mixing a sulfide solid electrolyte with LiS, and the sulfide solid electrolyte is used in an amount of (100-α) parts by mass per α parts by mass of LiS (α represents a number from 0.3 to 15.0), The modified sulfide solid electrolyte of the present invention is a mixture of Li2S and a sulfide solid electrolyte [(1-XY)(0.75Li2S / 0.25P2S5) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) and wherein α parts by mass of LiS (α represents a number of 0.3 to 15.0) per (100-α) parts by mass of the sulfide solid electrolyte, and the modified sulfide solid electrolyte, as well as an electrode composite and a lithium ion battery using the same. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a modified sulfide solid electrolyte that suppresses a decrease in ionic conductivity and reduces the cumulative amount of H2S gas generated over the medium to long term or over the entire period even when the sulfide solid electrolyte comes into contact with water and H2S is generated; a method for producing the modified sulfide solid electrolyte; and the modified sulfide solid electrolyte, as well as an electrode composite and a lithium-ion battery using the same. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart illustrating a preferred embodiment of the manufacturing method of the present embodiment. [Figure 2] FIG. 1 is a flow chart illustrating a preferred embodiment of the manufacturing method of the present embodiment. [Figure 3] FIG. 1 is a flow diagram illustrating an example of a preferred embodiment of a flow including a reaction vessel used in the production of an electrolyte precursor. [Figure 4] (2-1) Preparation of crystalline sulfide solid electrolyte (1) (liquid phase method) shows XRD patterns of the powdered electrolyte precursor, powdered amorphous solid electrolyte, and crystalline sulfide solid electrolyte (1). [Figure 5] This is an example of a preferred device for measuring the amount of H2S gas generated. [Figure 6] FIG. 1 is a schematic diagram illustrating a preferred method for determining breakthrough time. [Figure 7] 1 shows XRD patterns of crystalline sulfide solid electrolyte (2), amorphous sulfide solid electrolyte (3), and crystalline sulfide solid electrolyte (4) prepared in the examples. [Figure 8] 1 shows the measurement results of the amount of H2S gas generated in Example 1 and Comparative Example 1. [Figure 9] 1 shows the measurement results of the amount of H2S gas generated in Example 2 and Comparative Example 2. [Figure 10] 1 shows XRD patterns of the crystalline modified sulfide solid electrolytes produced in Examples 3 to 5. [Figure 11] 1 shows the measurement results of the amount of H2S gas generated in Examples 3 to 5 and Comparative Example 3. [Figure 12] 1 shows XRD patterns of the crystalline modified sulfide solid electrolytes prepared in Examples 7 and 8. [Figure 13] 1 shows the measurement results of the amount of H2S gas generated in Examples 6 to 9 and Comparative Example 3. [Figure 14] 1 shows X-ray diffraction spectra of the amorphous modified sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte prepared in Example 10. [Figure 15] 1 shows the measurement results of the amount of H2S gas generated in Example 10 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range of values ​​expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0011] (Findings gained by the inventors to arrive at the present invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention. The manufacturing method described in Patent Document 1 requires a first glass-forming step in which Li2S is completely consumed and a second glass-forming step in which Li2O is added as a bond-breaking compound to eliminate bridging sulfur, which tends to make the manufacturing process complicated and lengthy. Furthermore, the ionic conductivity of the manufactured sulfide solid electrolyte is not sufficiently high due to the addition of lithium oxide (Li2O), and furthermore, there is a need for improvement in suppressing the generation of H2S gas. In particular, there is a need for improvement in the process of manufacturing a lithium battery from a sulfide solid electrolyte and in suppressing the generation of H2S gas over the medium to long term or entire life of the lithium battery, as described below.

[0012] In the manufacturing method described in Patent Document 2, potassium sulfide (K2S) is present in the sulfide solid electrolyte, so the ionic conductivity is not sufficiently high. In addition, because K2S is dispersed in the sulfide solid electrolyte, the amount of K2S that contributes to neutralizing the generated H2S is insufficient, and there is a need for improvement in suppressing the generation of H2S gas over the medium to long term, and even over the entire period.

[0013] In the manufacturing methods described in Patent Documents 3 and 4, the sulfide solid electrolyte is coated with an alkaline compound, which has a certain effect in suppressing the generation of H2S. However, since the sulfide solid electrolyte is coated with a material other than its raw material, the ionic conductivity is reduced. The present inventors have found that a method for producing a modified sulfide solid electrolyte, which includes mixing a sulfide solid electrolyte with LiS, can provide a sulfide solid electrolyte that suppresses a decrease in ionic conductivity and reduces the amount of HS gas generated even when the sulfide solid electrolyte comes into contact with water and HS is generated, and a method for producing the sulfide solid electrolyte.

[0014] In this embodiment, it has been found that by mixing a sulfide solid electrolyte with LiS, it is possible to produce a modified sulfide solid electrolyte that suppresses a decrease in ionic conductivity and reduces the amount of HS gas generated even when the sulfide solid electrolyte comes into contact with water and HS is generated, without using any compounds other than the raw materials of the sulfide solid electrolyte described below and without significantly changing the conventional production process. The properties of the sulfide solid electrolyte can be modified by mixing the sulfide solid electrolyte with LiS, which will be described later. The modified sulfide solid electrolyte produced by modification can suppress a decrease in ionic conductivity, and can reduce the cumulative amount of HS gas generated over the medium to long term, even if the modified sulfide solid electrolyte comes into contact with water and HS is generated. Therefore, this embodiment is an extremely excellent production method. Furthermore, the modified sulfide solid electrolyte suppresses the decrease in ionic conductivity, and can reduce the cumulative amount of H2S gas generated over the medium to long term or over the entire period.

[0015] In conventional methods for producing sulfide solid electrolytes, as in the inventions described in Patent Documents 1 to 4, the ionic conductivity of the solid electrolyte is generally low, or the production process is complicated and does not sufficiently suppress the generation of H2S gas. In contrast, in this embodiment, by performing "modification," high ionic conductivity and suppression of the cumulative amount of H2S generation over the medium to long term, or even over the entire period, are both achieved. In this embodiment, attention is focused on Li2S, which is a raw material for the sulfide solid electrolyte. This method differs from conventional manufacturing methods in that the sulfide solid electrolyte is mixed with Li2S to "modify" the sulfide solid electrolyte to produce a "modified sulfide solid electrolyte."

[0016] The reason why this is possible is unclear, but it was previously thought that if Li2S remained, it would decompose and generate H2S gas, as described in Patent Document 1. However, one hypothesis is that by increasing the Li2S content on the surface of the sulfide solid electrolyte, although H2S gas generation associated with the decomposition of Li2S is observed initially, it is possible to efficiently capture the generated H2S over the medium to long term and throughout the entire period, thereby suppressing the generation of H2S gas.

[0017] In this specification, "initial period" means a period from 0 to 60 minutes in the method for measuring the amount of H2S gas generated described in the Examples, "mid- to long-term period" means a period from 60 to 240 minutes in the same manner, and "entire period" means a period from 0 to 360 minutes in the same manner. The initial generation of H2S gas is assumed to occur in the manufacturing process of modified sulfide solid electrolytes and lithium-ion batteries, etc.

[0018] The medium- to long-term generation of H2S gas corresponds to the period during which the produced modified sulfide solid electrolyte is stored, transported, and used in the manufacturing process of lithium-ion batteries, etc. In the medium to long term, it is important to extend the time until the generation of H2S gas, which initially increases and then decreases, suddenly increases again. Hereinafter, the time until the amount of H2S gas generation increases again is referred to as the "breakthrough time." A long breakthrough time reduces the amount of H2S gas generated in the medium to long term. A long breakthrough time reduces the generation of H2S gas during the storage and transportation of the modified sulfide solid electrolyte, or the manufacturing process of lithium-ion batteries, and is therefore preferable because it eliminates or simplifies the use of an H2S gas absorption device. The breakthrough time can be determined, for example, by the method described in the Examples.

[0019] The breakthrough time was measured in the examples, and was defined as the time required for 5 mL / g of H2S gas to be generated, based on the average cumulative amount of H2S gas generated over 60 and 120 minutes of flow. This 5 mL / g was determined in consideration of the impact of H2S gas generation on the storage and transportation environments.

[0020] The amount of H2S gas generated over the entire period includes the initial and mid- to long-term periods, and is assumed to be the cumulative amount of H2S gas generated over the entire period of use of lithium-ion batteries using modified sulfide solid electrolytes. Conventionally, attention has been focused only on the initial stage, and so studies have been conducted to reduce the content of Li2S, which contains sulfur atoms that constitute H2S, in order to reduce the generation of H2S gas, as in the aforementioned Patent Document 1. This is natural, since Li2S generates H2S when it reacts with water. In this invention, we focused on the generation of H2S gas over the mid- to long-term and entire period, and succeeded in suppressing the cumulative amount of H2S gas generated over the mid- to long-term and entire period by increasing the Li2S content. This is a surprising effect considering conventional technical common sense.

[0021] In the present invention, the Li2S content of the sulfide solid electrolyte as a whole is not increased, but rather the Li2S content on the surface of the sulfide solid electrolyte is increased. This reduces the Li2S content of the entire sulfide solid electrolyte, and although HS gas is generated initially, it can be suppressed to an acceptable range. In other words, in the present invention, after the initial HS gas generation, HS gas generation can be suppressed for a long period of time. By including Li2S on the surface, the time during which HS gas is not generated (breakthrough time) can be extended. Furthermore, the amount of HS gas generation can be suppressed over the entire period, and since only the content of Li2S, a raw material of the sulfide solid electrolyte, is increased, it is believed that high ionic conductivity can also be achieved.

[0022] The methods for producing modified sulfide solid electrolytes according to the first to tenth aspects of this embodiment will be described below. A method for producing a modified sulfide solid electrolyte according to a first aspect of the present embodiment includes: The method for producing a modified sulfide solid electrolyte includes mixing a sulfide solid electrolyte with Li2S, and using (100-α) parts by mass of the sulfide solid electrolyte for α parts by mass of Li2S (α represents a number from 0.3 to 15.0).

[0023] In Patent Document 3, the sulfide solid electrolyte is coated with Li2O or lithium carbonate (Li2CO3). In contrast, in the first embodiment, Li2S, a raw material for the sulfide solid electrolyte, is mixed with the sulfide solid electrolyte. In this way, the modified sulfide solid electrolyte produced in the first embodiment can be modified by the raw material Li2S. Furthermore, by setting the content of Li2S within a specific range, the effect on the composition of the sulfide solid electrolyte itself is extremely small. Therefore, high ionic conductivity can be maintained.

[0024] As previously described in Patent Document 1, it has been considered preferable for Li2S not to be contained in a sulfide solid electrolyte because it decomposes to generate H2S gas. In contrast, in the first embodiment, a layer with a high Li2S content is formed near the surface of the modified sulfide solid electrolyte. Although H2S is generated initially by decomposition of Li2S present on the surface, the amount of H2S generated can be kept to an acceptable level. Furthermore, since H2S is efficiently absorbed by the layer throughout the entire period, the generation of H2S gas can be suppressed.

[0025] The mechanism by which the generation of H2S gas can be suppressed is unclear, but when Li2S is present on the surface of the sulfide solid electrolyte, it reacts with moisture in the atmosphere, generating H2S, but also simultaneously generating alkaline lithium compounds. The H2S generated in this process is thought to correspond to the initial generation of H2S gas. However, the alkaline lithium compounds generated are deliquesced by the moisture in the atmosphere, essentially coating the surface of the sulfide solid electrolyte. It is speculated that even if H2S is subsequently generated from within the sulfide solid electrolyte, neutralization occurs, preventing the H2S from being released as a gas outside the system.

[0026] In the first embodiment, the sulfide solid electrolyte and Li2S are mixed, allowing for easy adjustment of the amount of Li2S used. By using (100-α) parts by mass of the sulfide solid electrolyte for α parts by mass of Li2S (α represents a number between 0.3 and 15.0), it is possible to suppress the amount of H2S gas generated initially while extending the breakthrough time, thereby enabling the suppression of H2S gas generation throughout the entire period. In Patent Document 2, the solid electrolyte contains K2S, and the K2S dispersed within the solid electrolyte suppresses H2S generation. However, in the first embodiment, by increasing the Li2S content on the surface of the sulfide solid electrolyte as described above, it is possible to efficiently suppress H2S gas generation without increasing the amount of Li2S in the entire solid electrolyte. Limiting the amount of Li2S used in this way allows for an optimized balance between the initial H2S gas generation, the extension of the breakthrough time, and the H2S gas generation throughout the entire period.

[0027] A method for producing a modified sulfide solid electrolyte according to a second aspect of the present embodiment includes: The sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms.

[0028] It is preferable that the sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms as in the second embodiment, since the ionic conductivity of the modified sulfide solid electrolyte is increased.

[0029] A method for producing a modified sulfide solid electrolyte according to a third aspect of the present embodiment includes: The method for producing a modified sulfide solid electrolyte is such that the sulfide solid electrolyte further contains a halogen atom.

[0030] As will be described later, it is preferable that the sulfide solid electrolyte further contains a halogen atom, since this can improve the ionic conductivity of the modified sulfide solid electrolyte.

[0031] A method for producing a modified sulfide solid electrolyte according to a fourth aspect of the present embodiment includes: The sulfide solid electrolyte is [(1-XY)(0.75Li2S / 0.25P2S5) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, Y represents a number from 0 to 0.2, P2S5 represents diphosphorus pentasulfide, LiBr represents lithium bromide, and LiI represents lithium iodide.) The present invention relates to a method for producing a modified sulfide solid electrolyte, which is a solid electrolyte represented by the formula:

[0032] As will be described later, it is preferable that the sulfide solid electrolyte has a specific composition, since this can improve the ionic conductivity of the modified sulfide solid electrolyte.

[0033] A method for producing a modified sulfide solid electrolyte according to a fifth aspect of the present embodiment includes: In the method for producing a modified sulfide solid electrolyte, the mixing is carried out using a pulverizer.

[0034] By carrying out the mixing using a pulverizer, conventional solid electrolyte production equipment can be utilized, and a more uniform modified sulfide solid electrolyte can be produced, which is preferable.

[0035] A method for producing a modified sulfide solid electrolyte according to a sixth aspect of the present embodiment includes: The method for producing a modified sulfide solid electrolyte is such that the sulfide solid electrolyte is an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0036] This is preferable because it can suppress the decrease in ionic conductivity.

[0037] A method for producing a modified sulfide solid electrolyte according to a seventh aspect of the present embodiment includes: The method for producing a modified sulfide solid electrolyte further includes mixing a raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain the sulfide solid electrolyte.

[0038] The use of a raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms is preferred because it allows for the production of a modified sulfide solid electrolyte with high ionic conductivity. Furthermore, the use of a complexing agent, as described below, is preferred because it reduces the amount of energy required for production. Furthermore, the use of a complexing agent is preferred because it allows for the production of a homogeneous modified sulfide solid electrolyte.

[0039] A method for producing a modified sulfide solid electrolyte according to an eighth aspect of the present embodiment includes: The modified sulfide solid electrolyte includes a thiolisine region II crystal structure.

[0040] The production method of the present invention is particularly suitable for producing a crystalline sulfide solid electrolyte containing a thiolicon region II type crystal structure, and is preferable from the viewpoint of improving ionic conductivity.

[0041] A method for producing a crystalline modified sulfide solid electrolyte according to a ninth aspect of this embodiment includes: and further crystallizing the modified sulfide solid electrolyte.

[0042] Further crystallization of the modified sulfide solid electrolyte is preferable because it improves the ionic conductivity.

[0043] The modified sulfide solid electrolyte according to a tenth aspect of this embodiment is Li2S and sulfide solid electrolyte [(1-XY)(0.75Li2S / 0.25P2S5) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) and Li2S is α parts by mass (α represents a number from 0.3 to 15.0) relative to (100-α) parts by mass of the sulfide solid electrolyte. The modified sulfide solid electrolyte is

[0044] The modified sulfide solid electrolyte having the above composition is preferable because it can suppress a decrease in ionic conductivity and reduce the amount of H2S gas generated even when the sulfide solid electrolyte comes into contact with water and H2S is generated.

[0045] The modified sulfide solid electrolyte according to an eleventh aspect of the present embodiment comprises: The modified sulfide solid electrolyte has a pH value of 9.0 or higher when the aqueous solution contains 1% by mass of the modified sulfide solid electrolyte.

[0046] The pH value reflects the amount of Li2S contained in the modified sulfide solid electrolyte. When the modified sulfide solid electrolyte has the pH value, the decrease in ionic conductivity can be suppressed, and even if the sulfide solid electrolyte comes into contact with water and H2S is generated, the amount of H2S gas generated can be reduced, which is preferable. The pH value can be determined, for example, by the method described in the Examples.

[0047] The electrode mixture according to the twelfth aspect of this embodiment is The electrode mixture includes the modified sulfide solid electrolyte and an electrode active material. An electrode composite containing the modified sulfide solid electrolyte exhibits high ionic conductivity, and when in contact with moisture, reduces the cumulative amount of H2S gas generated over the medium to long term or over the entire period.

[0048] A lithium ion battery according to a thirteenth aspect of the present embodiment is a lithium ion battery including at least one of the modified sulfide solid electrolyte and the electrode mixture. The modified sulfide solid electrolyte and / or an electrode composite containing the modified sulfide solid electrolyte exhibits high ionic conductivity, and when in contact with moisture, the cumulative amount of H2S gas generated is reduced over the medium to long term or over the entire period. Furthermore, the electrode mixture exhibits excellent battery characteristics over a long period of time, and it is expected that a lithium ion battery using this will exhibit excellent battery characteristics over a long period of time.

[0049] The manufacturing method and modified solid electrolyte of this embodiment will be described in more detail below in accordance with the above-described embodiment.

[0050] [Method for producing modified sulfide solid electrolyte] The method for producing the modified sulfide solid electrolyte of this embodiment includes mixing the sulfide solid electrolyte with LiS, as shown in FIG. 1, and requires that the sulfide solid electrolyte be used in an amount of (100-α) parts by mass per α parts by mass of LiS (α is a number between 0.3 and 15.0). The method for producing a modified sulfide solid electrolyte of this embodiment preferably further includes crystallizing the modified sulfide solid electrolyte, as described below. When crystallization is further included, preferred methods include methods (1) and (2) as shown in FIG. 2, depending on the order of mixing and crystallization. (1) in FIG. 2 is a production method in which a sulfide solid electrolyte is crystallized to form a crystalline sulfide solid electrolyte, which is then mixed with LiS to form a crystalline modified sulfide solid electrolyte. (2) in FIG. 2 is a production method in which a sulfide solid electrolyte is mixed with LiS to form a (crystalline or amorphous) modified sulfide solid electrolyte, which is then crystallized to form a crystalline sulfide solid electrolyte.

[0051] <Mixed> There are no particular limitations on the mixing (sometimes referred to as "modification" in this specification) of the sulfide solid electrolyte and LiS. The mixing may be performed using a pulverizer, a stirrer, or a mixer, but it is preferable to use a pulverizer, as this produces a homogeneous modified sulfide solid electrolyte that suppresses a decrease in ionic conductivity and reduces the amount of HS gas generated.

[0052] (Mixing using a grinder) The mixing using a pulverizer is a method that has been conventionally adopted as a mechanical milling method. As the pulverizer, for example, a media type pulverizer using a pulverizing medium can be used. Media-type mills are broadly classified into vessel-driven mills and media-agitation mills. Examples of vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Examples of media-agitation mills include impact mills such as cutter mills, hammer mills, and pin mills; tower mills and other tower-type mills; agitation tank mills such as attritors, aquamizers, and sand grinders; flow-through tank mills such as Viscomill and pearl mills; flow-through pipe mills; annular mills such as Coball mills; continuous dynamic mills; and single- or multi-shaft kneaders. Among these, considering the ease of adjusting the particle size of the resulting sulfide, the ball mill or bead mill exemplified as a vessel-driven mill is preferred.

[0053] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0054] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mm or more, preferably 0.1 mm or more, more preferably 0.2 mm or more, with the upper limit being usually 5.0 mm or less, preferably 3.0 mm or less, more preferably 2.0 mm or less. The diameter of the balls is usually 2.0 mm or more, preferably 2.5 mm or more, more preferably 3.0 mm or more, with the upper limit being usually 30.0 mm or less, preferably 20.0 mm or less, more preferably 15.0 mm or less.

[0055] The amount of beads or balls used varies depending on the scale of processing and cannot be generalized, but is usually 100 g or more, preferably 200 g or more, and more preferably 300 g or more, with the upper limit being 5.0 kg or less, more preferably 3.0 kg or less, and even more preferably 1.0 kg or less. Examples of materials include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0056] Regarding the peripheral speed of the rotating body, low and high peripheral speeds cannot be generally defined because they can vary depending on, for example, the particle size, material, and amount of the media used in the mill. For example, in the case of a device that does not use ball or bead milling media, such as a high-speed rotating thin-film mixer, even at relatively high peripheral speeds, mainly crushing occurs and granulation is difficult to occur. On the other hand, in the case of a device that uses milling media, such as a ball mill or bead mill, crushing can be performed at low peripheral speeds and granulation can be performed at high peripheral speeds, as described above. Therefore, if the specified conditions of the milling device, milling media, etc. are the same, the peripheral speed at which crushing is possible is lower than the peripheral speed at which granulation is possible. Therefore, for example, in the conditions under which granulation is possible at a peripheral speed of 6 m / s, a low peripheral speed means less than 6 m / s, and a high peripheral speed means 6 m / s or higher.

[0057] The peripheral speed may be appropriately selected depending on the modified sulfide solid electrolyte to be produced, and may be either low or high as long as the sulfide solid electrolyte can be coated with LiS and a sulfide solid electrolyte having high ionic conductivity and reducing the amount of HS gas generated is obtained. The reforming time varies depending on the scale of the treatment and cannot be generalized, but is usually 10 minutes or more, preferably 20 minutes or more, more preferably 30 minutes or more, and even more preferably 45 minutes or more, and the upper limit is usually 72 hours or less, preferably 65 hours or less, and more preferably 52 hours or less. This range is preferable because reforming proceeds and H2S generation is suppressed.

[0058] By selecting the size and material of the media (beads, balls) used, the rotor rotation speed, time, etc., mixing, stirring, crushing, and combinations of these processes can be performed, and the particle size, etc. of the resulting sulfide can be adjusted.

[0059] (Mixing using a stirrer or mixer) Examples of the stirrer and mixer include a mechanical stirring mixer that is equipped with stirring blades in a reaction vessel and can stir (also referred to as mixing by stirring or stirring mixing). Examples of the mechanical stirring mixer include a high-speed stirring mixer and a double-arm mixer. Examples of the high-speed stirring mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0060] Examples of the shape of the stirring blade used in a mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-type blade type, etc. From the viewpoint of more efficiently promoting the reaction of the raw materials, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, and the anchor type, paddle type, and full zone type are more preferred. When performing on a small scale, it is also preferable to use a Schlenk bottle with a stirring bar or a separable flask equipped with a rotor blade.

[0061] When a mechanically agitated mixer is used, the rotation speed of the agitator blades can be adjusted appropriately depending on the volume of the fluid in the reaction tank, the temperature, the shape of the agitator blades, etc., and is not particularly limited. However, it is usually set to about 5 rpm or more and 400 rpm or less. From the viewpoint of more efficiently promoting the reaction of the raw materials, the rotation speed is preferably 10 rpm or more and 300 rpm or less, more preferably 15 rpm or more and 250 rpm or less, and even more preferably 20 rpm or more and 230 rpm or less.

[0062] The temperature conditions when mixing using a mixer are not particularly limited, and are, for example, usually -30 to 120°C, preferably -10 to 100°C, more preferably 0 to 80°C, and even more preferably 10 to 60°C. Mixing without external temperature control is also preferred. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of more uniform dispersion of the raw materials and accelerating the reaction, it is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and even more preferably 30 to 300 hours.

[0063] <li2s> The Li2S to be mixed with the sulfide solid electrolyte can be the same as the raw material contents described below. The amount of sulfide solid electrolyte used should be (100-α) parts by mass for α parts by mass of Li2S. Since α can extend the breakthrough time, it must be a number from 0.3 to 15.0. If it is equal to or greater than the lower limit, the amount of H2S gas generated over the entire period can be suppressed, and if it is equal to or less than the upper limit, the initial generation of H2S gas can be suppressed and further, a decrease in the ionic conductivity of the modified sulfide solid electrolyte can be suppressed. Therefore, a is more preferably a number from 0.5 to 8.0, more preferably a number from 0.8 to 6.5, and even more preferably a number from 1.0 to 6.0.

[0064] <Sulfide solid electrolyte> The sulfide solid electrolyte of this embodiment is a solid electrolyte that contains at least sulfur atoms and has ionic conductivity due to conductive species that exhibit ionic conductivity, such as alkali metals such as lithium, sodium, potassium, rubidium, cesium, and francium. From the viewpoint of improving ionic conductivity, lithium atoms are preferred as the conductive species, and from the same viewpoint, phosphorus atoms and halogen atoms are preferred. As used herein, the term "solid electrolyte" refers to an electrolyte that remains solid at 25°C under a nitrogen atmosphere.

[0065] The term "solid electrolyte" as used herein includes both crystalline solid electrolytes having a crystalline structure and amorphous solid electrolytes. Therefore, the sulfide solid electrolyte is preferably an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte. In this specification, a crystalline sulfide solid electrolyte refers to a solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, the crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as the crystalline sulfide solid electrolyte has the X-ray diffraction pattern described above, it may also include an amorphous solid electrolyte in part. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than the crystallization temperature.

[0066] In addition, in this specification, an amorphous solid electrolyte refers to an amorphous solid electrolyte that has a halo pattern in which peaks other than those derived from the material are substantially not observed in an X-ray diffraction pattern obtained by X-ray diffraction measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0067] The sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms from the viewpoint of increasing ion conductivity. It is preferable that the compound contains a halogen atom, because the ionic conductivity is further increased by the inclusion of a halogen atom.

[0068] More specifically, the sulfide solid electrolyte is [(1-XY)(0.75Li2S / 0.25P2S5) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) A solid electrolyte represented by the formula (I) is preferred because it has high ionic conductivity. In this embodiment, the generation of H2S gas can be suppressed by the modification. However, the ionic conductivity of the modified sulfide solid electrolyte is significantly affected by the ionic conductivity of the sulfide solid electrolyte used. Therefore, it is preferable that the ionic conductivity of the sulfide solid electrolyte be high.

[0069] From the viewpoint of increasing the ionic conductivity of the sulfide solid electrolyte, X is preferably 0 to 0.15, more preferably 0 to 0.13, and even more preferably 0 to 0.12, and Y is preferably 0 to 0.15, more preferably 0 to 0.13, and even more preferably 0 to 0.12. When the sulfide solid electrolyte contains both LiBr and LiI, X is preferably 0.01 to 0.15, more preferably 0.05 to 0.13, and still more preferably 0.08 to 0.12, and Y is preferably 0.01 to 0.15, more preferably 0.05 to 0.13, and still more preferably 0.08 to 0.12. This is also true after modification.

[0070] (Method of manufacturing sulfide solid electrolyte) Methods for producing sulfide solid electrolytes can be broadly divided into solid-phase and liquid-phase methods. Liquid-phase methods include homogeneous methods, in which the solid electrolyte material is completely dissolved in a solvent, and heterogeneous methods, in which the solid electrolyte material is not completely dissolved but is instead a solid-liquid coexistence suspension. For example, a known solid-phase method involves mechanically milling raw materials such as LiS and P2S5 using a device such as a ball mill or a bead mill, followed by heat treatment as needed to produce an amorphous or crystalline solid electrolyte (see, for example, International Publication No. 2017 / 159667). This method produces a solid electrolyte by applying mechanical stress to raw materials such as LiS to promote solid-solid reactions.

[0071] On the other hand, among the liquid-phase methods, a homogeneous method in which a solid electrolyte is dissolved in a solvent and then reprecipitated is known (see, for example, JP 2014-191899 A), and a heterogeneous method in which a solid electrolyte raw material such as Li2S is reacted in a solvent containing a polar aprotic solvent (see WO 2014 / 192309, WO 2018 / 054709, and "CHEMISTRY OF MATERIALS," Vol. 29, pp. 1830-1835, 2017). For example, a method for producing a solid electrolyte with a Li4PS4I structure has been disclosed, which includes a step of using dimethoxyethane (DME) to combine with a Li3PS4 structure to obtain Li3PS4·DME.

[0072] In the present embodiment, the method for producing the sulfide solid electrolyte may be either a solid phase method or a liquid phase method. However, the liquid phase method is preferred because it allows simple and large-scale synthesis and enables the production of a homogeneous sulfide solid electrolyte.

[0073] In the solid phase method, it is preferable to obtain a sulfide solid electrolyte by mixing raw material ingredients described below, and in the liquid phase method, it is preferable to obtain a sulfide solid electrolyte by mixing raw material ingredients described below and a complexing agent, optionally together with a solvent, which is a so-called heterogeneous method.

[0074] (Raw material content) The raw material ingredients used in this embodiment preferably contain a conductive species that exhibits ionic conductivity, such as lithium, and sulfur atoms, and preferably further contain phosphorus atoms. Furthermore, the raw material ingredients used in this embodiment may also contain halogen atoms as needed, from the viewpoint of forming a sulfide solid electrolyte having a specific crystal system, which will be described later, and improving ionic conductivity.

[0075] More specifically, lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); phosphorus halides such as various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PCl5, P2Cl4), various phosphorus bromides (PBr3, PBr5), and various phosphorus iodides (PI3, P2I4); thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (P Representative examples include raw materials consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides such as thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F); and elemental halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), with bromine (Br2) and iodine (I2) being preferred.

[0076] Examples of materials that can be used as raw materials other than those mentioned above include raw materials that contain at least one atom selected from the above four types of atoms and also contain atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS), aluminum sulfide, and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium, such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides, and bismuth halides; and phosphorus oxyhalides such as phosphorus oxychloride (POCl) and phosphorus oxybromide (POBr).

[0077] Among the above, preferred are lithium sulfide, phosphorus sulfides such as diphosphorus trisulfide (PS) and diphosphorus pentasulfide (PS), halogen elements such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. Furthermore, when oxygen atoms are introduced into the solid electrolyte, preferred are phosphate compounds such as lithium oxide, lithium hydroxide, and lithium phosphate. Preferred combinations of raw materials include lithium sulfide, diphosphorus pentasulfide, and lithium halides, and lithium sulfide, diphosphorus pentasulfide, and halogen elements. Preferred lithium halides are lithium bromide and lithium iodide, and preferred halogen elements are bromine and iodine.

[0078] In this embodiment, Li3PS4 containing the PS4 structure can be used as part of the raw material. Specifically, Li3PS4 is prepared in advance by manufacturing or the like, and then used as the raw material. The content of Li3PS4 relative to the total of the raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%.

[0079] When Li3PS4 and a simple halogen are used, the content of the simple halogen relative to Li3PS4 is preferably 1 to 50 mol %, more preferably 10 to 40 mol %, even more preferably 20 to 30 mol %, and even more preferably 22 to 28 mol %.

[0080] The lithium sulfide used in this embodiment is preferably in the form of particles. The average particle size of lithium sulfide particles (D 50 ) is preferably 10 μm or more and 2000 μm or less, more preferably 30 μm or more and 1500 μm or less, and even more preferably 50 μm or more and 1000 μm or less. 50 ) is the particle size at which 50% of the total particle size is obtained by accumulating the particle size distribution curve from the smallest particle size, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution analyzer. Furthermore, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, i.e., within the same range as that of the lithium sulfide particles.

[0081] When lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 70 to 80 mol%, more preferably 72 to 78 mol%, and even more preferably 74 to 78 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity. When lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as needed are used, the content of lithium sulfide and diphosphorus pentasulfide relative to the total of these is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%. Furthermore, when lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of improving ionic conductivity, the proportion of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, still more preferably 30 to 70 mol%, and particularly preferably 40 to 60 mol%.

[0082] When lithium sulfide, diphosphorus pentasulfide, lithium bromide, and lithium iodide are used, the proportion of lithium sulfide to the total of lithium sulfide, diphosphorus pentasulfide, lithium bromide, and lithium iodide is preferably 30 to 90 mol%, more preferably 40 to 80 mol%, even more preferably 50 to 70 mol%, and still more preferably 55 to 65 mol%.

[0083] When a halogen element is used as a raw material, and lithium sulfide and diphosphorus pentasulfide are used, the ratio of the number of moles of lithium sulfide excluding the same number of moles of lithium sulfide as the halogen element to the total number of moles of lithium sulfide and diphosphorus pentasulfide excluding the same number of moles of lithium sulfide as the halogen element is preferably within the range of 60 to 90%, more preferably within the range of 65 to 85%, even more preferably within the range of 68 to 82%, even more preferably within the range of 72 to 78%, and particularly preferably within the range of 73 to 77%. This is because higher ionic conductivity can be obtained at these ratios. From the same viewpoint, when lithium sulfide, diphosphorus pentasulfide, and a halogen element are used, the content of the halogen element relative to the total amount of lithium sulfide, diphosphorus pentasulfide, and the halogen element is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 25 mol%, and even more preferably 3 to 15 mol%.

[0084] When lithium sulfide, diphosphorus pentasulfide, an elemental halogen, and a lithium halide are used, the content of the elemental halogen (β mol %) and the content of the lithium halide (γ mol %) relative to the total amount of these preferably satisfy the following formula (2), more preferably satisfy the following formula (3), even more preferably satisfy the following formula (4), and even more preferably satisfy the following formula (5). 2≦2β+γ≦100…(2) 4≦2β+γ≦80 …(3) 6≦2β+γ≦50 …(4) 6≦2β+γ≦30 …(5)

[0085] When two types of halogens are used as simple substances, the molar number of one halogen atom in the substance is A1, and the molar number of the other halogen atom in the substance is A2. The ratio A1:A2 is preferably 1 to 99:99 to 1, more preferably 10:90 to 90:10, even more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0086] Furthermore, when the two types of halogen atoms are bromine and iodine, where the number of moles of bromine is B1 and the number of moles of iodine is B2, the ratio B1:B2 is preferably 1 to 99:99 to 1, more preferably 15:85 to 90:10, even more preferably 20:80 to 80:20, still more preferably 30:70 to 75:25, and particularly preferably 35:65 to 75:25.

[0087] When mixing the raw material ingredients with a complexing agent described below, it is preferable to mix the raw material ingredients with a solvent described below to form a slurry, since this will result in the raw material ingredients becoming a uniform complex.

[0088] (Mixing of raw material contents) The mixing in the solid phase method is preferably the same as the mixing of Li2S and the sulfide solid electrolyte described above. In the liquid phase method, the raw material ingredients and a complexing agent described below are preferably mixed together to form an electrolyte precursor. By mixing the raw material ingredients with a complexing agent and complexing the raw material ingredients, a complex containing lithium atoms, phosphorus atoms, sulfur atoms, etc., such as Li3PS4, is formed, which prevents separation of specific components and allows a homogeneous solid electrolyte to be obtained, even in the liquid phase method or heterogeneous method.

[0089] The mixing in the liquid phase method may be carried out in the same manner as the above-mentioned mixing, but is preferably carried out without using the above-mentioned pulverizer, and is preferably carried out using a stirrer or mixer. This allows production using simple production equipment without using a large-scale device for pulverization, which is preferable from the viewpoint of simplifying the production process and reducing the energy input during production.

[0090] Furthermore, mixing in the liquid phase method may be performed by circulating agitation, in which a fluid in the reaction vessel is withdrawn from an outlet provided in the reaction vessel to the outside and the withdrawn fluid is returned to the reaction vessel from a return port provided in the reaction vessel, as shown in Fig. 3. Mixing by circulating agitation is preferred because it can promote the reaction of the raw materials without pulverization, and it prevents raw materials with a high specific gravity, such as lithium halide, from settling and stagnating at the bottom of the reaction vessel, particularly immediately below the rotating shaft of the stirring blade, without requiring strong agitation that would cause the fluid to splash and adhere to the inner wall of the reaction vessel, thereby suppressing compositional deviations in the sulfide solid electrolyte due to non-contribution to the reaction, efficiently promoting the reaction, and producing a sulfide solid electrolyte with high ionic conductivity.

[0091] (complexing agent) The sulfide solid electrolyte is preferably obtained by mixing a raw material containing at least one selected from the group consisting of lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent. The complexing agent is a substance capable of forming a complex with lithium element, and has the property of reacting with sulfides, halides, etc. containing lithium element contained in the raw material to promote the formation of an electrolyte precursor.

[0092] The complexing agent can be any agent having the above properties, and is preferably a compound containing an element having a high affinity with lithium, such as a hetero element such as nitrogen, oxygen, or chlorine, and more preferably a compound having a group containing such a hetero element, because such a hetero element or group containing such a hetero element can coordinate (bond) with lithium. The complexing agent is believed to have a high affinity for lithium due to the heteroatom in its molecule. This property allows it to easily bond with lithium-containing structures, such as Li3PS4, which typically contain a PS4 structure and are present as the main structure in the solid electrolyte obtained by this production method, as well as with lithium-containing raw materials, such as lithium halides, to form aggregates. Therefore, by mixing the raw material components with the complexing agent, lithium-containing structures, such as PS4 structures, or aggregates mediated by the complexing agent, and lithium-containing raw materials, such as lithium halides, or aggregates mediated by the complexing agent, are uniformly present, resulting in an electrolyte precursor in which the halogen elements are more dispersed and fixed. This results in a solid electrolyte with high ionic conductivity and reduced H2S generation. It is also believed that the desired average particle size and specific surface area can be easily achieved.

[0093] Therefore, it is preferable to have at least two heteroatoms capable of coordinating (bonding) in the molecule, and more preferably to have a group containing at least two heteroatoms in the molecule. By having a group containing at least two heteroatoms in the molecule, a lithium-containing structure such as Li3PS4 containing a PS4 structure can be bonded to a lithium-containing raw material such as lithium halide via at least two heteroatoms in the molecule. This allows the halogen elements to be more dispersed and fixed in the electrolyte precursor, resulting in a solid electrolyte having a predetermined average particle size and specific surface area, high ionic conductivity, and reduced H2S generation. Furthermore, among heteroatoms, nitrogen is preferred, and the nitrogen-containing group is preferably an amino group. In other words, an amine compound is preferred as the complexing agent.

[0094] The amine compound is not particularly limited as long as it has an amino group in the molecule, as long as it can promote the formation of the electrolyte precursor, but a compound having at least two amino groups in the molecule is preferred. By having such a structure, a lithium-containing structure such as Li3PS4 containing a PS4 structure can be bonded to a lithium-containing raw material such as lithium halide via at least two nitrogen elements in the molecule, so that the halogen elements are more dispersed and fixed in the electrolyte precursor, resulting in a solid electrolyte having a predetermined average particle size and specific surface area and high ionic conductivity.

[0095] Examples of such amine compounds include aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination.

[0096] More specifically, typical and preferred examples of the aliphatic amine include aliphatic primary diamines such as ethylenediamine, diaminopropane, and diaminobutane; aliphatic secondary diamines such as N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyldiaminopropane, and N,N'-diethyldiaminopropane; and aliphatic tertiary diamines such as N,N,N',N'-tetramethyldiaminomethane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyldiaminopropane, N,N,N',N'-tetraethyldiaminopropane, N,N,N',N'-tetramethyldiaminobutane, N,N,N',N'-tetramethyldiaminopentane, and N,N,N',N'-tetramethyldiaminohexane. In the examples given in this specification, for example, in the case of diaminobutane, unless otherwise specified, all isomers of butane, such as linear and branched isomers, are included, in addition to isomers relating to the position of the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and 1,4-diaminobutane. The number of carbon atoms in the aliphatic amine is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the hydrocarbon group of the aliphatic hydrocarbon group in the aliphatic amine is preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0097] Typical preferred examples of the alicyclic amine include alicyclic primary diamines such as cyclopropanediamine and cyclohexanediamine; alicyclic secondary diamines such as bisaminomethylcyclohexane; and alicyclic tertiary diamines such as N,N,N',N'-tetramethyl-cyclohexanediamine and bis(ethylmethylamino)cyclohexane. Typical preferred examples of the heterocyclic amine include heterocyclic primary diamines such as isophoronediamine; heterocyclic secondary diamines such as piperazine and dipiperidylpropane; and heterocyclic tertiary diamines such as N,N-dimethylpiperazine and bismethylpiperidylpropane. The number of carbon atoms in the alicyclic amine and heterocyclic amine is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0098] Representative preferred examples of the aromatic amine include aromatic primary diamines such as phenyldiamine, tolylenediamine, and naphthalenediamine; aromatic secondary diamines such as N-methylphenylenediamine, N,N'-dimethylphenylenediamine, N,N'-bismethylphenylphenylenediamine, N,N'-dimethylnaphthalenediamine, and N-naphthylethylenediamine; and aromatic tertiary diamines such as N,N-dimethylphenylenediamine, N,N,N',N'-tetramethylphenylenediamine, N,N,N',N'-tetramethyldiaminodiphenylmethane, and N,N,N',N'-tetramethylnaphthalenediamine. The aromatic amine preferably has 6 or more carbon atoms, more preferably 7 or more carbon atoms, and even more preferably 8 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0099] The amine compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom. Although diamines have been given as specific examples, it goes without saying that the amine compounds that can be used in this embodiment are not limited to diamines, and examples thereof include aliphatic monoamines corresponding to various diamines such as trimethylamine, triethylamine, ethyldimethylamine, and the above-mentioned aliphatic diamines, piperidine compounds such as piperidine, methylpiperidine, and tetramethylpiperidine, pyridine compounds such as pyridine and picoline, morpholine compounds such as morpholine, methylmorpholine, and thiomorpholine, imidazole compounds such as imidazole and methylimidazole, and the above-mentioned alicyclic diamines. In addition to monoamines such as alicyclic monoamines such as the corresponding monoamines, heterocyclic monoamines corresponding to the above heterocyclic diamines, and aromatic monoamines corresponding to the above aromatic diamines, polyamines having three or more amino groups, such as diethylenetriamine, N,N',N''-trimethyldiethylenetriamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, triethylenetetramine, N,N'-bis[(dimethylamino)ethyl]-N,N'-dimethylethylenediamine, hexamethylenetetramine, and tetraethylenepentamine, can also be used.

[0100] Among the above, from the viewpoint of obtaining a predetermined average particle size and specific surface area as well as higher ionic conductivity, a tertiary amine having a tertiary amino group as the amino group is preferred, a tertiary diamine having two tertiary amino groups is more preferred, a tertiary diamine having two tertiary amino groups at both ends is even more preferred, and an aliphatic tertiary diamine having tertiary amino groups at both ends is even more preferred. Among the above amine compounds, the aliphatic tertiary diamine having tertiary amino groups at both ends is preferably tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, or tetraethyldiaminopropane, and in consideration of ease of availability, etc., tetramethylethylenediamine or tetramethyldiaminopropane is preferred.

[0101] Examples of complexing agents other than amine compounds include compounds having a group containing a hetero element such as oxygen, chlorine, or other halogen element, which have a high affinity with lithium. Compounds having a group other than an amino group that contains nitrogen as a hetero element, such as a nitro group or an amide group, also have similar effects.

[0102] Examples of the other complexing agents include alcohol solvents such as ethanol and butanol; ester solvents such as ethyl acetate and butyl acetate; aldehyde solvents such as formaldehyde, acetaldehyde, and dimethylformamide; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as diethyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole; halogen-containing aromatic hydrocarbon solvents such as trifluoromethylbenzene, nitrobenzene, chlorobenzene, chlorotoluene, and bromobenzene; and solvents containing carbon atoms and heteroatoms such as acetonitrile, dimethyl sulfoxide, and carbon disulfide. Among these, ether solvents are preferred, with diethyl ether, diisopropyl ether, dibutyl ether, and tetrahydrofuran being more preferred, and diethyl ether, diisopropyl ether, and dibutyl ether being even more preferred.

[0103] By mixing the raw material inclusions with a complexing agent, the lithium, sulfur, phosphorus, and halogen atoms contained in the raw material inclusions interact with the complexing agent to form a complex in which these atoms are directly bonded to one another with or without the complexing agent. That is, in the method for producing a solid electrolyte of this embodiment, the complex obtained by mixing the raw material inclusions with the complexing agent is composed of the complexing agent, lithium, sulfur, phosphorus, and halogen atoms. The complex obtained in this embodiment is not completely soluble in the liquid complexing agent and is typically solid. Therefore, in this embodiment, a suspension in which the complex is suspended in the complex and a solvent added as needed is obtained. Therefore, the method for producing a solid electrolyte of this embodiment corresponds to a heterogeneous system in a so-called liquid-phase method.

[0104] (solvent) In this embodiment, a solvent may be further added when the raw material ingredients and the complexing agent are mixed. When a solid complex is formed in a liquid complexing agent, if the complex is easily soluble in the complexing agent, separation of the components may occur. Therefore, by using a solvent in which the complex is insoluble, the elution of components in the electrolyte precursor can be suppressed. Furthermore, by mixing the raw material ingredients and the complexing agent using a solvent, complex formation is promoted, allowing each main component to be more evenly present, and an electrolyte precursor in which halogen atoms are more dispersed and fixed can be obtained, which makes it easier to achieve the effect of obtaining high ionic conductivity.

[0105] The method for producing a sulfide solid electrolyte according to this embodiment is a so-called heterogeneous method, and it is preferable that the complex does not completely dissolve in the liquid complexing agent but precipitates. The solubility of the complex can be adjusted by adding a solvent. Halogen atoms, in particular, tend to dissolve from the complex, so adding a solvent suppresses the dissolution of halogen atoms and produces a desired complex. As a result, a crystalline sulfide solid electrolyte with high ionic conductivity can be obtained via an electrolyte precursor in which components such as halogens are dispersed, which is preferable.

[0106] A preferred example of a solvent having such properties is a solvent having a solubility parameter of 10 or less. In this specification, the solubility parameter is a value δ ((cal / cm)) calculated by the following formula (1), which is described in various documents, such as "Chemical Handbook" (published in 2004, 5th revised edition, Maruzen Co., Ltd.). 3 ) 1 / 2 ) and is also called the Hildebrand parameter or SP value.

[0107]

number

[0108] By using a solvent with a solubility parameter of 10 or less, halogen atoms, halogen-containing raw materials such as lithium halide, and even halogen-containing components constituting the co-crystal contained in the complex (e.g., an aggregate formed by bonding lithium halide and the complexing agent) can be made relatively less soluble compared to the complexing agent. This facilitates the fixation of halogen atoms in the complex, resulting in well-dispersed halogen atoms in the resulting electrolyte precursor and solid electrolyte, making it easier to obtain a solid electrolyte with high ionic conductivity. In other words, the solvent used in this embodiment preferably has the property of not dissolving the complex. From the same perspective, the solubility parameter of the solvent is preferably 9.5 or less, more preferably 9.0 or less, and even more preferably 8.5 or less.

[0109] More specifically, the solvent used in this embodiment can be a wide variety of solvents that have conventionally been used in the production of solid electrolytes. The solvent is preferably at least one selected from nonpolar solvents and aprotic polar solvents. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used. Examples of the solvent include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; solvents containing carbon atoms such as alcohol-based solvents, ester-based solvents, aldehyde-based solvents, ketone-based solvents, ether-based solvents having 4 or more carbon atoms on one side, and solvents containing carbon atoms and heteroatoms. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used.

[0110] More specifically, aliphatic hydrocarbon solvents such as hexane (7.3), pentane (7.0), 2-ethylhexane, heptane (7.4), octane (7.5), decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane (8.2) and methylcyclohexane; benzene, toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8), tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene (9.5), chlorotoluene (8.8), and bromobenzene. Examples of the solvents include aromatic hydrocarbon solvents such as ethanol (12.7) and butanol (11.4); aldehyde solvents such as formaldehyde, acetaldehyde (10.3), and dimethylformamide (12.1); ketone solvents such as acetone (9.9) and methyl ethyl ketone; ether solvents such as dibutyl ether, cyclopentyl methyl ether (8.4), tert-butyl methyl ether, and anisole; and solvents containing carbon atoms and heteroatoms such as acetonitrile (11.9), dimethyl sulfoxide, and carbon disulfide. Note that the numbers in parentheses in the above examples are SP values.

[0111] Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether-based solvents are preferred, and from the viewpoint of obtaining more stable and high ionic conductivity, heptane, cyclohexane, toluene, ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole are more preferred, diethyl ether, diisopropyl ether, and dibutyl ether are even more preferred, and diisopropyl ether and dibutyl ether are even more preferred, and cyclohexane is particularly preferred. The solvent used in this embodiment is preferably an organic solvent exemplified above, and is an organic solvent different from the complexing agent. In this embodiment, these solvents may be used alone or in combination.

[0112] (Dry) In this embodiment, since the electrolyte precursor is often a suspension, a drying step may be included. This results in a powder of the electrolyte precursor. Drying before heating, which will be described later, is preferable because it allows for efficient heating. Note that drying and subsequent heating may be performed in the same step.

[0113] Drying can be performed at a temperature depending on the type of complexing agent and solvent remaining in the electrolyte precursor. For example, drying can be performed at a temperature equal to or higher than the boiling point of the complexing agent or solvent. Drying can be performed under reduced pressure (vacuum drying) using a vacuum pump or the like at typically 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably about room temperature (23°C) (for example, about room temperature ±5°C), to volatilize the complexing agent and solvent. Unlike the complexing agent, the solvent is not easily incorporated into the complex, and therefore the amount of the solvent that can be contained in the complex is usually 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

[0114] The drying may be performed by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge, etc. In this embodiment, after the solid-liquid separation, drying may be performed under the above-mentioned temperature conditions. Specifically, solid-liquid separation can be easily performed by decantation, in which the suspension is transferred to a container, and after the solid has settled, the supernatant complexing agent and the solvent added as needed are removed, or by filtration using, for example, a glass filter with a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

[0115] The complex is composed of a complexing agent, lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and is characterized in that, in X-ray diffraction measurement, peaks distinct from those derived from the raw materials are observed in the X-ray diffraction pattern. Preferably, the complex includes a cocrystal composed of a complexing agent, lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Simply mixing the raw materials results in peaks derived from the raw materials, whereas mixing the raw materials with a complexing agent results in peaks distinct from those derived from the raw materials. Therefore, the complex clearly has a structure distinct from the raw materials themselves. This is specifically confirmed in the Examples. (2-1) Preparation of Crystalline Sulfide Solid Electrolyte (1) Examples of X-ray diffraction patterns of the electrolyte precursor, amorphous solid electrolyte, and crystalline sulfide solid electrolyte (1) prepared by the liquid-phase method are shown in Figure 4. The X-ray diffraction pattern indicates that the electrolyte precursor has a predetermined crystalline structure. Furthermore, the diffraction pattern does not include the diffraction patterns of any of the raw materials, such as lithium sulfide, indicating that the electrolyte precursor has a crystalline structure distinct from those of the raw materials.

[0116] The electrolyte precursor is also characterized by having a structure different from that of the crystalline sulfide solid electrolyte. This is also specifically confirmed in the Examples. Figure 4 also shows the X-ray diffraction pattern of the crystalline sulfide solid electrolyte (1) prepared by (2-1) Preparation of crystalline sulfide solid electrolyte (1) (liquid phase method), which shows that it differs from the diffraction pattern of the electrolyte precursor. Note that the electrolyte precursor has a specific crystalline structure and is different from the amorphous solid electrolyte having a broad pattern shown in Figure 4.

[0117] The content of the complexing agent in the electrolyte precursor varies depending on the molecular weight of the complexing agent, but is usually about 10% by mass to 70% by mass, preferably 15% by mass to 65% by mass.

[0118] (heating) The method for producing the sulfide solid electrolyte of this embodiment preferably includes heating an electrolyte precursor to obtain a (amorphous or crystalline) sulfide solid electrolyte (decomplex decomposition product). By including a step of heating the electrolyte precursor, the complexing agent in the electrolyte precursor is removed, and a complex decomposition product containing lithium atoms, sulfur atoms, phosphorus atoms, and, if necessary, halogen atoms is obtained. Here, the removal of the complexing agent in the electrolyte precursor is supported by the fact that the results of X-ray diffraction patterns, gas chromatography analysis, etc. show that the complexing agent forms a co-crystal with the electrolyte precursor, and also by the fact that the solid electrolyte obtained by removing the complexing agent by heating the electrolyte precursor has the same X-ray diffraction pattern as a solid electrolyte obtained by a conventional method without using a complexing agent.

[0119] In this embodiment, the sulfide solid electrolyte is obtained by heating an electrolyte precursor to remove the complexing agent from the electrolyte precursor. The less complexing agent in the sulfide solid electrolyte, the better, but the sulfide solid electrolyte may contain a complexing agent to the extent that it does not impair the performance of the sulfide solid electrolyte. The content of the complexing agent in the sulfide solid electrolyte is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. Specifically, when the electrolyte precursor is subjected to differential thermal analysis (DTA) at a temperature increase rate of 10°C / min using a differential thermal analyzer (DTA), the heating temperature is preferably set to 5°C or lower, more preferably 10°C or lower, and even more preferably 20°C or lower, starting from the temperature at the lowest temperature where the exothermic peak is observed. The lower limit is not particularly limited, but may be set to about 40°C or higher than the temperature at the lowest temperature where the exothermic peak is observed. By setting the temperature in this range, the sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining a sulfide solid electrolyte cannot be generally defined because it varies depending on the structure of the sulfide solid electrolyte to be obtained. However, it is generally preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. There is no particular lower limit, but the temperature is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher.

[0120] The heating time is not particularly limited as long as the desired sulfide solid electrolyte is obtained, but is preferably, for example, 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0121] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum), as this can prevent deterioration (e.g., oxidation) of the sulfide solid electrolyte. The heating method is not particularly limited, and examples thereof include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a calcination furnace. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of heat to be processed.

[0122] (crystallization) In this embodiment, the amorphous sulfide solid electrolyte or the amorphous modified sulfide solid electrolyte described below may be crystallized to form a crystalline sulfide solid electrolyte or the crystalline modified sulfide solid electrolyte described below, as needed. Crystallization is preferable because it increases ionic conductivity. When an amorphous sulfide solid electrolyte or an amorphous-modified sulfide solid electrolyte is heated (crystallized) to obtain a crystalline sulfide solid electrolyte or a crystalline-modified sulfide solid electrolyte, the heating temperature can be determined depending on the structure of the crystalline sulfide solid electrolyte or the crystalline-modified sulfide solid electrolyte. It is preferably higher than the heating temperature for obtaining a sulfide solid electrolyte by decomplexation. Specifically, the amorphous sulfide solid electrolyte or the amorphous-modified sulfide solid electrolyte is subjected to differential thermal analysis (DTA) at a heating rate of 10 ° C. / min using a differential thermal analyzer (DTA). The temperature is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher, starting from the peak top temperature of the exothermic peak observed at the lowest temperature. The upper limit is not particularly limited, but it should be about 40 ° C. or lower. By using such a temperature range, a crystalline sulfide solid electrolyte or a crystalline-modified sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining a crystalline sulfide solid electrolyte or a crystalline modified sulfide solid electrolyte cannot be generally specified because it varies depending on the structure of the crystalline sulfide solid electrolyte or crystalline modified sulfide solid electrolyte to be obtained. However, it is generally preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher. There is no particular upper limit, but it is preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower. (to crush) This embodiment preferably includes pulverizing the electrolyte precursor, sulfide solid electrolyte, or modified sulfide solid electrolyte as needed. By pulverizing the electrolyte precursor, sulfide solid electrolyte, or modified sulfide solid electrolyte, a solid electrolyte with small particle size can be obtained. Furthermore, a decrease in ionic conductivity can be suppressed.

[0123] The pulverizer used to pulverize the electrolyte precursor, sulfide solid electrolyte, or modified sulfide solid electrolyte is not particularly limited as long as it can pulverize particles, and for example, a media-type pulverizer using a pulverizing medium can be used. When the electrolyte precursor is in a liquid state containing mainly liquids such as a complexing agent and a solvent, or in a slurry state, a wet pulverizer that can handle wet pulverization is preferred. Representative examples of wet mills include wet bead mills, wet ball mills, and wet vibration mills, with wet bead mills using beads as milling media being preferred because they allow for flexible adjustment of milling conditions and are suitable for smaller particle sizes. Alternatively, dry mills such as dry media mills (e.g., dry bead mills, dry ball mills, and dry vibration mills) and dry non-media mills (e.g., jet mills) can also be used.

[0124] Furthermore, the electrolyte precursor to be pulverized in the pulverizer is usually supplied as an electrolyte precursor-containing material obtained by mixing a raw material containing material and a complexing agent, and is supplied mainly in a liquid or slurry state. That is, the object to be pulverized in the pulverizer is mainly an electrolyte precursor-containing liquid or an electrolyte precursor-containing slurry. Therefore, the pulverizer used in this embodiment is preferably a flow-through pulverizer capable of circulating the electrolyte precursor-containing liquid or the electrolyte precursor-containing slurry as needed. More specifically, it is preferable to use a pulverizer in a form that circulates the slurry between a pulverizer (pulverizer mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel), as described in JP 2010-140893 A.

[0125] The size of the beads used in the above-mentioned grinder may be selected appropriately depending on the desired particle size, processing amount, etc. For example, the diameter of the beads may be approximately 0.05 mmφ or more and 5.0 mmφ or less, preferably 0.1 mmφ or more and 3.0 mmφ or less, and more preferably 0.3 mmφ or more and 1.5 mmφ or less.

[0126] As the crusher used for crushing, a machine capable of crushing an object using ultrasonic waves, such as a machine called an ultrasonic crusher, ultrasonic homogenizer, or probe ultrasonic crusher, can be used. In this case, various conditions such as the frequency of the ultrasonic waves may be appropriately selected depending on the average particle size of the desired electrolyte precursor, and the frequency may be, for example, about 1 kHz or more and 100 kHz or less, and from the viewpoint of more efficiently pulverizing the electrolyte precursor, the frequency is preferably 3 kHz or more and 50 kHz or less, more preferably 5 kHz or more and 40 kHz or less, and even more preferably 10 kHz or more and 30 kHz or less. The output of the ultrasonic crusher is usually about 500 to 16,000W, preferably 600 to 10,000W, more preferably 750 to 5,000W, and even more preferably 900 to 1,500W.

[0127] The average particle size (D 50 ) is determined appropriately as desired, but is usually 0.01 μm or more and 50 μm or less, preferably 0.03 μm or more and 5 μm or less, and more preferably 0.05 μm or more and 3 μm or less. By setting the average particle size in this range, it is possible to meet the demand for a solid electrolyte with a small average particle size of 3 μm or less.

[0128] The pulverization time is not particularly limited as long as it is a time that allows each solid electrolyte to have a desired average particle size, and is usually from 0.1 hours to 100 hours. From the viewpoint of efficiently achieving a desired particle size, the pulverization time is preferably from 0.3 hours to 72 hours, more preferably from 0.5 hours to 48 hours, and even more preferably from 1 hour to 24 hours.

[0129] In this specification, the average particle diameter (D 50 ) is a value measured by a laser diffraction particle size distribution measurement method, and can be measured, for example, by the method described in the Examples.

[0130] [Modified sulfide solid electrolyte] The modified sulfide solid electrolyte of this embodiment has: α parts by mass of Li2S and (100-α) parts by mass of sulfide solid electrolyte [(1-XY)(0.75Li2S / 0.25P2S5) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) It is preferred that the compound contains: The shape of the sulfide solid electrolyte is preferably particulate, and a layer with a high LiS content (sometimes referred to as a coating layer in this specification) is preferably present on the particle surface. The "layer" may be in a form that completely covers the particle surface of the sulfide solid electrolyte (sometimes referred to as a coating in this specification), or may be in a form that partially covers the particle surface, or may be distributed in an island-like manner on the particle surface of the sulfide solid electrolyte, or particulate LiS may be attached to the surface of the sulfide solid electrolyte. Furthermore, the sulfide solid electrolyte and LiS may be physically adsorbed or may be partially mixed together, or a layer having a higher LiS content than the composition of the sulfide solid electrolyte may be formed on the surface of the sulfide solid electrolyte.

[0131] The modified sulfide solid electrolyte of this embodiment preferably has a pH value of 9.0 or higher when the modified sulfide solid electrolyte is in a 1 mass % aqueous solution. The pH value is preferably 9.0 or more, more preferably 10.00 or more, and even more preferably 10.50 or more, from the viewpoint of being able to reduce the amount of H2S gas generated even when the sulfide solid electrolyte comes into contact with water and H2S is generated, while suppressing a decrease in ionic conductivity. The upper limit is not particularly limited, and may be greater than 14.00 or equal to or less than 14.00, or may be equal to or less than 13.00, or may be equal to or less than 12.00.

[0132] The modified sulfide solid electrolyte of this embodiment may be a crystalline modified sulfide solid electrolyte or an amorphous modified sulfide solid electrolyte, but in order to achieve high ionic conductivity, it is preferable that the modified sulfide solid electrolyte be a crystalline modified sulfide solid electrolyte that has been crystallized at some stage. A crystalline modified sulfide solid electrolyte may be obtained by modifying a crystalline sulfide solid electrolyte according to the present embodiment, or a crystalline modified sulfide solid electrolyte may be obtained by crystallizing an amorphous modified sulfide solid electrolyte.

[0133] The crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte may be a so-called glass ceramic, and the crystal structure thereof may be Li3PS4 crystal structure, Li4P2S6 crystal structure, Li7PS6 crystal structure, Li7P3S 11 Examples of such a crystal structure include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A). The modified sulfide solid electrolyte preferably contains a thiolisiconregion II type crystal structure, since this increases the ionic conductivity.

[0134] Also, Li 4-x Ge 1-x P x S4-type thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li 4-x Ge 1-x P x Examples of such a crystal structure include a crystal structure similar to the S4-based thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). The crystal structure of the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte obtained by this production method is preferably the thio-LISICON Region II type crystal structure among the above, since it provides higher ionic conductivity. Here, the "thio-LISICON Region II type crystal structure" refers to a structure in which Li 4-x Ge 1-x P x S4-type thio-LISICON Region II crystal structure, Li 4-x Ge 1-x P x This indicates that the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte obtained by this production method preferably contain the above-mentioned thio-LISICON Region II type crystal structure. The crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte obtained by this production method preferably contain the above-mentioned thio-LISICON Region II type crystal structure. While they may have the thio-LISICON Region II type crystal structure as the main crystal, it is preferable that they have the thio-LISICON Region II type crystal structure as the main crystal from the viewpoint of obtaining higher ionic conductivity. In this specification, "having the thio-LISICON Region II type crystal structure as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte obtained by this production method preferably do not contain crystalline Li3PS4 (β-Li3PS4) from the viewpoint of obtaining higher ionic conductivity.

[0135] In X-ray diffraction measurements using CuKα radiation, the diffraction peaks of the Li3PS4 crystal structure appear, for example, at 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, the diffraction peaks of the Li4P2S6 crystal structure appear, for example, at 2θ = 16.9°, 27.1°, and 32.5°, and the diffraction peaks of the Li7PS6 crystal structure appear, for example, at 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and the diffraction peaks of the Li7P3S 11 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°. 4-x Ge 1-x P x The diffraction peaks of the S4 thio-LISICON Region II crystal structure appear, for example, at 2θ = 20.1°, 23.9°, and 29.5°. 4-x Ge 1-x P x Diffraction peaks of a crystal structure similar to the S4 thio-LISICON Region II type appear, for example, at 2θ = 20.2 and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0136] As described above, when a thiolic region II-type crystal structure is obtained in this embodiment, it is preferably free of crystalline Li3PS4 (β-Li3PS4). Fig. 10 shows an example of X-ray diffraction measurement of the crystalline modified sulfide solid electrolyte obtained by this manufacturing method. As can be understood from Figs. 4 and 10, the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte of this embodiment do not have diffraction peaks at 2θ = 17.5° and 26.1° found in crystalline Li3PS4, or even if they have such peaks, the detected peaks are extremely small compared to the diffraction peaks of the thiolic region II-type crystal structure. Note that for the crystalline modified sulfide solid electrolyte, a peak at 2θ = 27.45° for Li2S can be confirmed due to the modification.

[0137] Having the above-mentioned structural framework of Li7PS6 and substituting part of P with Si, the crystal structure represented by the composition formula Li 7-x P 1-y Si y S6 and Li 7+x P 1-y Si y S6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6) is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα radiation, mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The above composition formula Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Also, the above composition formula Li 7-x PS 6-x Ha x The crystal structure represented by the formula (where Ha is Cl or Br, and x is preferably 0.2 to 1.8) is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. These peak positions may vary within a range of ±0.5°.

[0138] Furthermore, the crystalline sulfide solid electrolyte and crystalline modified sulfide solid electrolyte obtained by this production method preferably have a half-width of the maximum peak, including the background at 2θ=10 to 40°, of Δ2θ=0.32 or less in X-ray diffraction measurement using CuKα radiation. Such properties result in higher ionic conductivity and improved battery performance. From the same perspective, the half-width of the maximum peak is more preferably Δ2θ=0.30 or less, and even more preferably Δ2θ=0.28 or less. Typical examples of crystalline sulfide solid electrolytes and crystalline modified sulfide solid electrolytes having such properties include those having a thiolicon region II type crystal structure.

[0139] For example, Figure 10 shows an example of X-ray diffraction measurement of the crystalline modified sulfide solid electrolyte having a thiolicon region II crystal structure obtained in Example 3. It can be seen that the maximum peak, including the background from 2θ = 10 to 40°, is at 20.1° and has a sharp half-width of Δ2θ = 0.25. Because the maximum peak has a sharp half-width of 0.32 or less, the crystalline modified sulfide solid electrolyte exhibits extremely high ionic conductivity and is expected to improve battery performance. Such a half-width indicates good crystallinity. This allows for crushing with little energy, making it less likely to experience a decrease in ionic conductivity due to vitrification (amorphization). Furthermore, the precursor for mechanical treatment of this embodiment has a porous structure with a relatively large specific surface area and good crystallinity. Therefore, even if the precursor is partially or completely vitrified by crushing and granulation, changes in morphology during recrystallization are relatively suppressed, allowing for easy adjustment of the morphology by mechanical treatment.

[0140] The half width can be calculated as follows. Use a range of ±2° from the maximum peak. Let A be the Lorentzian function ratio (0≦A≦1), B be the peak intensity correction value, C be the 2θ maximum peak, D be the peak position in the range used for calculation (C±2°), E be the half-width, F be the background, and G be the intensity of each peak in the peak range used for calculation. When the variables are A, B, C, D, E, and F, calculate the following for each peak position. H=G-{B×{A / (1+(DC) 2 / E 2 )+(1-A)×exp(-1×(DC) 2 / E 2 )}+F} The half-width can be calculated by summing up H within the range of ±2° of the above peak C and minimizing the total value with GRG nonlinearity using the solver function of the spreadsheet software Excel (Microsoft).

[0141] The shape of the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D 50 ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0142] The volume-based average particle size of the crystalline sulfide solid electrolyte and crystalline modified sulfide solid electrolyte obtained by this production method is 3 μm or more, the same as the average particle size of the modified sulfide solid electrolyte of this embodiment described above. The specific surface area of ​​the crystalline sulfide solid electrolyte and the crystalline modified sulfide solid electrolyte obtained by this production method, as measured by the BET method, is 20 m, which is the same as the specific surface area of ​​the modified sulfide solid electrolyte of the present embodiment. 2 / g or more.

[0143] (Applications of modified sulfide solid electrolytes) The modified sulfide solid electrolyte of the present embodiment has a predetermined average particle size and specific surface area, as well as high ionic conductivity and excellent battery performance. In addition, it is unlikely to generate H2S, and therefore is suitable for use as an electrode composite for lithium ion batteries and in lithium ion batteries. It is particularly preferable to use lithium element as the conductive species. The modified sulfide solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer.

[0144] The battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the modified sulfide solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used.

[0145] [Electrode composite material] The electrode mixture of this embodiment is required to contain the modified sulfide solid electrolyte and an electrode active material described below.

[0146] (electrode active material) As the electrode active material, a positive electrode active material or a negative electrode active material is adopted depending on whether the electrode mixture is used for the positive electrode or the negative electrode.

[0147] The positive electrode active material can be any material that can promote a battery chemical reaction involving the movement of lithium ions due to atoms that are used to exhibit ionic conductivity, preferably lithium atoms, in relation to the negative electrode active material. Examples of such positive electrode active materials that can insert and extract lithium ions include oxide-based positive electrode active materials and sulfide-based positive electrode active materials.

[0148] Preferred examples of oxide-based positive electrode active materials include lithium-containing transition metal composite oxides such as LMO (lithium manganese oxide), LCO (lithium cobalt oxide), NMC (lithium nickel manganese cobalt oxide), NCA (lithium nickel cobalt aluminate), LNCO (lithium nickel cobalt oxide), and olivine-type compounds (LiMeNPO4, Me=Fe, Co, Ni, Mn). Examples of sulfide-based positive electrode active materials include titanium sulfide (TiS2), molybdenum sulfide (MoS2), iron sulfide (FeS, FeS2), copper sulfide (CuS), and nickel sulfide (Ni3S2). In addition to the above positive electrode active materials, niobium selenide (NbSe3) and the like can also be used. The positive electrode active material can be used alone or in combination of two or more kinds.

[0149] The negative electrode active material can be any material that can promote a battery chemical reaction involving the movement of lithium ions originating from lithium atoms, such as an atom that is used as an atom to exhibit ionic conductivity, preferably a metal that can form an alloy with lithium atoms, an oxide thereof, an alloy of the metal with lithium atoms, etc. As such a negative electrode active material capable of inserting and extracting lithium ions, any material known in the field of batteries as a negative electrode active material can be used without any limitation. Examples of such negative electrode active materials include metallic lithium, metallic indium, metallic aluminum, metallic silicon, metallic tin, and other metallic lithium or metals capable of forming alloys with metallic lithium, oxides of these metals, and alloys of these metals with metallic lithium.

[0150] The electrode active material used in this embodiment may have a coating layer on its surface. The material for forming the coating layer is an ion conductor such as an atom that exhibits ionic conductivity in the sulfide solid electrolyte, preferably a nitride or oxide of lithium atoms, or a composite thereof. Specifically, lithium nitride (Li3N), Li4GeO4, and the like, which have a main structure, for example, Li 4-2x Zn x Conductors with a lithiated crystal structure such as GeO4, and those with a Li3PO4-type framework structure such as Li 4-x Ge 1-x P x Conductors with thiolicon-type crystal structures such as S4, La 2 / 3-x Li 3x Examples include conductors having a perovskite crystal structure such as TiO3, and conductors having a NASICON crystal structure such as LiTi2(PO4)3. Also, Li y Ti 3-y O4(0 <y<3)、Li4Ti5O 12 Examples include lithium titanates such as (LTO), lithium metal oxides of metals belonging to Group 5 of the periodic table such as LiNbO3 and LiTaO3, and oxide-based conductors such as Li2O-B2O3-P2O5, Li2O-B2O3-ZnO, and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0151] An electrode active material having a coating layer can be obtained, for example, by applying a solution containing various atoms constituting the material that forms the coating layer to the surface of the electrode active material, and then firing the electrode active material after application at a temperature preferably between 200°C and 400°C. Here, the solution containing various atoms may be a solution containing alkoxides of various metals such as lithium ethoxide, titanium isopropoxide, niobium isopropoxide, tantalum isopropoxide, etc. In this case, the solvent may be an alcoholic solvent such as ethanol or butanol, an aliphatic hydrocarbon solvent such as hexane, heptane or octane, or an aromatic hydrocarbon solvent such as benzene, toluene or xylene. The above-mentioned attachment may be carried out by immersion, spray coating or the like.

[0152] From the viewpoint of improving production efficiency and battery performance, the firing temperature is preferably 200°C or higher and 400°C or lower, more preferably 250°C or higher and 390°C or lower, and the firing time is usually about 1 minute to 10 hours, preferably 10 minutes to 4 hours.

[0153] The coverage of the coating layer is preferably 90% or more, more preferably 95% or more, and even more preferably 100% of the surface area of ​​the electrode active material, i.e., the entire surface is covered. The thickness of the coating layer is preferably 1 nm or more, more preferably 2 nm or more, and the upper limit is preferably 30 nm or less, more preferably 25 nm or less. The thickness of the coating layer can be measured by cross-sectional observation using a transmission electron microscope (TEM), and the coverage rate can be calculated from the thickness of the coating layer, elemental analysis values, and BET specific surface area.

[0154] (Other ingredients) The electrode mixture of this embodiment may contain, in addition to the modified sulfide solid electrolyte and electrode active material, other components such as a conductive material, a binder, etc. That is, the method for producing an electrode mixture of this embodiment may use, in addition to the modified sulfide solid electrolyte and electrode active material, other components such as a conductive material, a binder, etc. The conductive material, binder, etc. may be added to and mixed with the modified sulfide solid electrolyte and electrode active material when mixing the modified sulfide solid electrolyte and electrode active material. Examples of the conductive material, from the viewpoint of improving battery performance by improving electronic conductivity, include carbon-based materials such as artificial graphite, graphite carbon fiber, resin-baked carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads, furfuryl alcohol resin-baked carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon.

[0155] By using a binder, the strength of the positive electrode and the negative electrode when they are fabricated is improved. The binder is not particularly limited as long as it can impart functions such as binding property and flexibility, and examples thereof include fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride, thermoplastic elastomers such as butylene rubber and styrene-butadiene rubber, and various resins such as acrylic resin, acrylic polyol resin, polyvinyl acetal resin, polyvinyl butyral resin, and silicone resin.

[0156] The compounding ratio (mass ratio) of the electrode active material to the modified sulfide solid electrolyte in the electrode mixture is preferably 99.5:0.5 to 40:60, more preferably 99:1 to 50:50, and even more preferably 98:2 to 60:40, in order to improve battery performance and in consideration of production efficiency.

[0157] When a conductive material is contained, the content of the conductive material in the electrode mixture is not particularly limited, but in consideration of improving battery performance and production efficiency, the content is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 1.5 mass% or more, and the upper limit is preferably 10 mass% or less, preferably 8 mass% or less, and even more preferably 5 mass% or less. Furthermore, when a binder is contained, the content of the binder in the electrode mixture is not particularly limited, but in consideration of improving battery performance and production efficiency, the content is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, with the upper limit being preferably 20 mass % or less, preferably 15 mass % or less, and even more preferably 10 mass % or less.

[0158] [Lithium-ion battery] The lithium ion battery of this embodiment is a lithium ion battery that includes at least one selected from the modified sulfide solid electrolyte of this embodiment and the electrode composite, and also includes at least one selected from the modified sulfide solid electrolyte of another form and the electrode composite.

[0159] The lithium ion battery of this embodiment is not particularly limited in its configuration as long as it contains either the modified sulfide solid electrolyte of this embodiment, an electrode composite containing the same, or a different form of modified sulfide solid electrolyte or an electrode composite containing the same, and may have the configuration of a commonly used lithium ion battery.

[0160] The lithium ion battery of this embodiment preferably includes, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. The positive electrode layer and the negative electrode layer preferably use the electrode mixture of this embodiment, and the electrolyte layer preferably uses the modified sulfide solid electrolyte of this embodiment.

[0161] The current collector may be a known material, for example, a layer of Au or the like coated with a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu. [Example]

[0162] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0163] (1) Measurement method (1-1) Measurement of H2S gas generation rate The amount of H2S gas generated was measured over time using the device shown in Figure 5. As described above, evaluation was made based on the amount of H2S gas generated initially and over the entire period. First, the test equipment (exposure test equipment 1) used in the exposure test will be described with reference to FIG. The exposure test apparatus 80 mainly comprises a flask 21 for humidifying air, a static mixer 20 for mixing humidified air and non-humidified air, a dew-point meter 30 (M170 / DMT152 manufactured by VAISALA) for measuring the moisture content of the mixed air, a double reaction tube 40 in which a measurement sample is placed, a dew-point meter 50 for measuring the moisture content of the air discharged from the double reaction tube 40, and a hydrogen sulfide meter 60 (Model 3000RS manufactured by AMI) for measuring the H2S concentration in the discharged nitrogen, all of which are connected by pipes (not shown). The temperature of the flask 10 is set to 20°C by a cooling bath 22. The tubes connecting the components were made of 6 mm diameter Teflon (registered trademark) tubes. In this diagram, the tubes are not shown, and instead the flow of nitrogen is indicated by arrows. The evaluation procedure was as follows.

[0164] In a nitrogen glove box with a dew point of −80° C., about 0.15 g of powder sample (solid electrolyte) 41 was weighed out, placed between quartz wool 42, and sealed in a reaction tube 40. The evaluation was carried out at room temperature (20° C.). Dry air adjusted to a dew point of -55°C at 0.02 MPa was supplied into the apparatus 1 from an air source (not shown). The supplied air passed through a bifurcated pipe BP, and a portion of it was supplied to the flask 21 where it was humidified. The remainder was supplied directly to the static mixer 20 as unhumidified air. The amount of air supplied to the flask 21 was adjusted by a needle valve V.

[0165] The dew point was controlled by adjusting the flow rate of the unhumidified nitrogen and humidified air using a flow meter FM with a needle valve. Specifically, the unhumidified air was supplied to the static mixer 20 at a flow rate of 100 mL / min and the humidified air at a flow rate of 733 mL / min, and mixed. The dew point of the mixed gas (a mixture of unhumidified air and humidified air) was confirmed using a dew point meter 30. After adjusting the dew point to 18°C, the time when the three-way stopcock 43 was rotated was set to 0 minutes, and the mixed gas was allowed to flow through the reaction tube 40 for the time shown in Table 1. The amount of H2S contained in the mixed gas that passed through the sample 41 was measured using a hydrogen sulfide meter 60. The amount of H2S was recorded at 1-second intervals and integrated to measure the cumulative amount generated per 1 g of solid electrolyte (mL / g). For reference, the dew point of the mixed gas after exposure was also measured using a dew point meter 50. The cumulative amount of H2S generated between 0 and 60 minutes was defined as the initial amount, and the cumulative amount of H2S generated between 0 and the end of the measurement was defined as the total amount. The standard measurement time was 360 minutes, but it was extended as necessary. After the measurement, the air was passed through an alkaline trap 70 to remove H2S.

[0166] (1-2) Breakthrough time (1-1) The breakthrough time was determined from the result 100 obtained from the measurement of the amount of H2S gas generated (see Figure 6). From the average value 120 of the cumulative amount generated at flow times of 60 and 120 minutes, the flow time 140 at point 110, when 5 mL / g of H2S gas (equivalent to 130) was generated, was taken as the breakthrough time (min). If breakthrough was not confirmed by the end of the measurement, for example, if the breakthrough time exceeded 360 minutes, it was recorded as 360<.

[0167] (1-3) Volume-based average particle diameter (D 50 ) Measurements were made using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950 (model number), manufactured by Horiba, Ltd.). Dehydrated 2-ethyl-1-hexanol (Wako Pure Chemical Industries, special grade) was used as the dispersion medium. 50 mL of dispersion medium was injected into the flow cell of the instrument, circulated, and then the measurement target was added and ultrasonicated, after which the particle size distribution was measured. The amount of measurement target added was adjusted so that the red light transmittance (R) corresponding to the particle concentration on the measurement screen specified by the instrument was 80-90% and the blue light transmittance (B) was 70-90%. The calculation conditions used were 1.81 for the refractive index of the measurement target and 1.43 for the refractive index of the dispersion medium. The number of iterations was fixed at 15 for the distribution configuration, and particle size calculations were performed.

[0168] (1-4) Ionic conductivity measurement In this example, the ionic conductivity was measured as follows. From the sulfide solid electrolyte, a 10 mm diameter (cross-sectional area S: 0.785 cm 2 ) and a height (L) of 0.1 to 0.3 cm were molded into circular pellets to serve as samples. Electrode terminals were attached to the top and bottom of the samples, and measurements were made at 25°C using the AC impedance method (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following equation: R=ρ(L / S) σ=1 / ρ

[0169] (1-5) X-ray diffraction (XRD) measurement (XRD pattern) The resulting crystalline product was determined by XRD measurement. The precursor or solid electrolyte powder prepared in each example was filled into a groove 20 mm in diameter and 0.2 mm deep, and the groove was smoothed with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured without being exposed to air. The powder X-ray diffraction measurement was carried out using a D2 PHASER powder diffraction measurement device manufactured by BRUKER Corporation under the following conditions.

[0170] Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: 4°sollar slit (both incident and receiving sides), 1mm divergence slit, Kβ filter (0.5% Ni plate), 3mm air scatter screen) Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.05deg, 0.05deg / sec

[0171] (1-6)pH measurement In this example, pH measurement was carried out as follows. The powder of the solid electrolyte produced in each example was dissolved in ion-exchanged water to a concentration of 1 mass %, and the solution was stirred for 1 minute until the solution became homogeneous and transparent. The pH of the resulting aqueous solution was measured using a pH meter (model number: AS600) manufactured by AS ONE Corporation.

[0172] (2) Production of sulfide solid electrolyte (2-1) Preparation of crystalline sulfide solid electrolyte (1) (liquid phase method) A 1-L reactor equipped with a stirring blade was charged with 13.19 g of lithium sulfide, 21.26 g of diphosphorus pentasulfide, 4.15 g of lithium bromide, and 6.40 g of lithium iodide under a nitrogen atmosphere. 100 mL of tetramethylethylenediamine (TMEDA) as a complexing agent and 800 mL of cyclohexane as a solvent were added, and the mixture was stirred with the stirring blade activated. A circulation-operated bead mill ("Star Mill LMZ015" manufactured by Ashizawa Finetech Co., Ltd.) was charged with 456 g of zirconia balls (0.5 mm diameter) (bead filling rate in the milling chamber: 80%). The mixture was milled for 60 minutes while circulating between the reactor and the milling chamber at a pump flow rate of 550 mL / min, a peripheral speed of 8 m / s, and a mill jacket temperature of 20 °C to obtain an electrolyte precursor slurry. Next, the obtained electrolyte precursor slurry was immediately dried under reduced pressure (vacuum degree 300 Pa or less) at room temperature (23° C.) to obtain a powdery electrolyte precursor.

[0173] 30 g of the obtained powdered electrolyte precursor was loaded into a vibration dryer can (volume: 150 ml) in a glove box. The vacuum was adjusted to 100 Pa or less, and the powder temperature was gradually increased until it reached 110 °C. Heating was performed by circulating a heat medium heated to a predetermined temperature in a heat medium unit through the vibration dryer jacket. During the heating process, the heat medium circulation rate was adjusted so that the vacuum did not exceed 100 Pa. The completion of complexation was determined when at least one hour had elapsed since the powder temperature exceeded 110 °C and the vacuum had returned to the value before heating began. The obtained powdered amorphous solid electrolyte was heated at 200 °C under reduced pressure (vacuum level 300 Pa or less) for 2 hours to obtain a powdered crystalline sulfide solid electrolyte (1). The XRD pattern of the crystalline sulfide solid electrolyte (1) is shown in Figure 4, confirming that it contained a thiolithiregion II crystal structure. The ionic conductivity was 3.5 mS / cm (listed as Comparative Example 1 in Table 1).

[0174] (2-2) Preparation of crystalline sulfide solid electrolyte (2) (solid-phase method) The bead mill used was a "Bead Mill LMZ015" (manufactured by Ashizawa Finetech Co., Ltd.) and was charged with 485 g of zirconia balls with a diameter of 0.5 mm. A 2.0-liter glass reactor equipped with a stirrer was used as the reaction vessel. 13.19 g of lithium sulfide, 21.26 g of diphosphorus pentasulfide, 4.15 g of lithium bromide, and 6.40 g of lithium iodide ([(1-XY)(0.75LiS / 0.25P5S) / XLiBr / YLiI], where X = 0.1 and Y = 0.1) were charged into a reaction vessel, and 1000 mL of dehydrated toluene was added to form a slurry.

[0175] The slurry introduced into the reaction vessel was circulated at a flow rate of 600 mL / min using the pump in the bead mill. The peripheral speed of the bead mill was set to 12 m / s, and hot water (HW) was passed through an external circulation system, allowing the reaction to proceed while maintaining the pump discharge temperature at 70 °C. After removing the supernatant from the resulting slurry, the slurry was placed on a hot plate and dried at 80 °C to obtain a powdered amorphous sulfide solid electrolyte. The resulting powdered amorphous sulfide solid electrolyte was heated at 195 °C for 3 hours using a hot plate installed in a glove box to obtain a powdered crystalline sulfide solid electrolyte (2). The XRD pattern of the crystalline sulfide solid electrolyte (2) is shown in Figure 7, confirming that it contains a thiolithicomplex II crystal structure. The ionic conductivity was 5.2 mS / cm (listed as Comparative Example 2 in Table 1).

[0176] (2-3) Particle size control of crystalline sulfide solid electrolyte (1) The bead mill used was a "Bead Mill LMZ015" (manufactured by Ashizawa Finetech Co., Ltd.) and was charged with 456 g of zirconia balls with a diameter of 0.5 mm. A 2.0-liter glass reactor equipped with a stirrer was used as the reaction vessel. 100 g of the crystalline sulfide solid electrolyte (1) prepared in (2-1) was placed in a reaction vessel, and 790 mL of dehydrated toluene and 65 mL of dibutyl ether were added in that order to form a slurry.

[0177] The mixture was circulated between the reaction vessel and the milling chamber at a pump flow rate of 550 mL / min, a peripheral speed of 12 m / s, and a mill jacket temperature of 40°C while being milled for 60 minutes. The mixture was then circulated at a pump flow rate of 550 mL / min, a peripheral speed of 12 m / s, and a mill jacket temperature of 20°C while being milled for 120 minutes, yielding a solid electrolyte slurry. The resulting slurry was immediately dried under reduced pressure (vacuum level of 300 Pa or less) at room temperature (23°C) to yield a powdered amorphous sulfide solid electrolyte (3). The XRD pattern of the amorphous sulfide solid electrolyte (3) is shown in FIG. 7.

[0178] (2-4) Crystallization of amorphous sulfide solid electrolyte (3) The amorphous sulfide solid electrolyte (3) prepared in (2-3) was placed in a 1 L glass Schlenk vessel in a glove box and heated to 190 °C under reduced pressure (vacuum degree 100 Pa or less) using an oil bath to obtain a powdered crystalline solid electrolyte (4). The XRD pattern is shown in Figure 7, and it was confirmed that the solid electrolyte contained a thiolithium region II crystal structure. The volume-based average particle size was 1.2 μm, and the ionic conductivity was 4.6 mS / cm (listed as Comparative Example 3 in Table 1).

[0179] (Example 1 and Comparative Example 1) A crystalline modified sulfide solid electrolyte was produced by mixing 0.99 g of the crystalline sulfide solid electrolyte (1) prepared in (2-1) and 0.01 g of Li2S using a mortar and pestle in a nitrogen glove box with a dew point of -80 °C. The ionic conductivity of the crystalline modified sulfide solid electrolyte is shown in Table 1. The measured amount of H2S gas generated is shown in Figure 8. The initial and overall amount of H2S gas generated, the breakthrough time, and the pH value are shown in Table 2. For comparison, the crystalline sulfide solid electrolyte (1) was used as Comparative Example 1.

[0180] A total of 100 mg of the crystalline modified sulfide solid electrolyte obtained in Example 1 and SUS powder (sulfide solid electrolyte:SUS powder = 50:50 (volume ratio)) was mixed in a mortar for 10 minutes to obtain a measurement powder (1) (electrode mixture). 60 mg of electrolyte for the separator layer was added to a 10 mm diameter battery cell, and the cell was pressurized in a stainless steel mold at 10 MPa / cm 2 After pressing three times while rotating by 120° at a pressure of 20 MPa / cm, 3.5 mg of powder (1) was added. 2 Then, the powder (1) was pressed three times with a pressure of 20 MPa / cm from the opposite side of the powder (1). 2 The press was performed three times, rotating the press by 120° each time. The electrolyte for the separator layer was synthesized under the following conditions.

[0181] A 1-L reactor equipped with an impeller was charged with 20.5 g of L2S, 33.1 g of P2S5, 10.0 g of LiI, and 6.5 g of LiBr under a nitrogen atmosphere. After rotating the impeller, 630 g of toluene was added, and the resulting slurry was stirred for 10 minutes. The reactor was connected to a recirculating bead mill ("Star Mill LMZ015" (product name), manufactured by Ashizawa Finetech Co., Ltd., zirconia bead material: zirconia, bead diameter: 0.5 mm, bead amount: 456 g), and milling was performed for 45 hours (pump flow rate: 650 mL / min, bead mill peripheral speed: 12 m / s, mill jacket temperature: 45 °C). The obtained slurry was dried under vacuum at room temperature (25°C) and then heated (80°C) to obtain a white powder of amorphous solid electrolyte. The obtained white powder was further heated under vacuum at 195°C for 2 hours to obtain a white powder of crystalline solid electrolyte. In the XRD spectrum of the crystalline solid electrolyte, crystallization peaks were detected at 2θ = 20.2° and 23.6°, confirming that it had a thiolicon region II crystal structure. In addition, the average particle size (D 50 ) was 4.5 μm and the ionic conductivity was 5.0 mS / cm.

[0182] An InLi foil (having a layered structure, " / " indicates the space between each layer. In: 10mmφ×0.1mm / Li: 9mmφ×0.08mm / SUS: 10mmφ×0.1mm) was placed on the opposite side of the electrolyte measurement powder (1) for the separator layer, and a pressure of 6 MPa / cm was applied. 2 The cell was fixed with four screws sandwiching an insulator to prevent a short circuit between the test powder (1) and the InLi foil, and the screws were fastened with a torque of 8 N m to obtain a lithium-ion battery.

[0183] [Table 1]

[0184] [Table 2]

[0185] (Example 2 and Comparative Example 2) A crystalline modified sulfide solid electrolyte was produced in the same manner as in Example 1, except that the amounts of the sulfide solid electrolyte and LiS used were changed as shown in Table 1. The ionic conductivity of the crystalline modified sulfide solid electrolyte is shown in Table 1. The measured amount of H2S gas generated is shown in Figure 9. The amount of H2S gas generated initially and over the entire period, the breakthrough time, and the pH value are shown in Table 3. For comparison, the crystalline sulfide solid electrolyte (2) was used as Comparative Example 2.

[0186] [Table 3]

[0187] (Examples 3 to 5 and Comparative Example 3) A crystalline modified sulfide solid electrolyte was produced in the same manner as in Example 1, except that the amounts of the sulfide solid electrolyte and LiS used were changed as shown in Table 1. The ionic conductivity of the crystalline modified sulfide solid electrolyte is shown in Table 1, and the XRD pattern is shown in Figure 10. The measured amount of H2S gas generated is shown in Figure 11. The amount of H2S gas generated initially and over the entire period, the breakthrough time, and the pH value are shown in Table 4. For comparison, the crystalline sulfide solid electrolyte (4) was used as Comparative Example 3.

[0188] [Table 4]

[0189] Example 6 In a nitrogen glove box with a dew point of −80°C, 0.99 g of the amorphous sulfide solid electrolyte (3) prepared in (2-3) and 0.01 g of Li2S were mixed using a mortar and pestle to obtain an amorphous-modified sulfide solid electrolyte. The obtained amorphous modified sulfide solid electrolyte was placed in a 1 L glass Schlenk vessel in a glove box and heated to 190°C under reduced pressure (vacuum degree 100 Pa or less) using an oil bath to produce a crystalline modified sulfide solid electrolyte. The ionic conductivity of the crystalline modified sulfide solid electrolyte is shown in Table 1. The measured amount of H2S gas generated is shown in Figure 13. The amount of H2S gas generated initially and over the entire period, the breakthrough time, and the pH value are shown in Table 5. For comparison, the crystalline sulfide solid electrolyte (4) was used as Comparative Example 3.

[0190] [Table 5]

[0191] Examples 7 to 9 Crystalline-modified sulfide solid electrolytes were produced in the same manner as in Example 6, except that the amount of LiS used was changed as shown in Table 1. The ionic conductivities of the crystalline-modified sulfide solid electrolytes are shown in Table 1. The XRD patterns of the crystalline-modified sulfide solid electrolytes produced in Examples 7 and 8 are shown in Figure 12. The measured amount of H2S gas generated is shown in Figure 13. The amount of H2S gas generated initially and over the entire period, the breakthrough time, and the pH value are shown in Table 5. For comparison, the crystalline sulfide solid electrolyte (4) was used as Comparative Example 3.

[0192] Example 10 The bead mill used was a "Bead Mill LMZ015" (manufactured by Ashizawa Finetech Co., Ltd.) and was charged with 456 g of zirconia balls with a diameter of 0.5 mm. A 2.0-liter glass reactor equipped with a stirrer was used as the reaction vessel. 98 g of the sulfide solid electrolyte prepared in (2-1) was placed in a reaction vessel, and 790 mL of dehydrated toluene and 65 mL of dibutyl ether were added in that order to form a slurry.

[0193] The slurry was pulverized for 60 minutes while circulating between the reaction vessel and the pulverization chamber under conditions of a pump flow rate of 550 mL / min, a peripheral speed of 12 m / s, and a mill jacket temperature of 40°C. Next, 2 g of LiS was added to the slurry, and the slurry was pulverized for 120 minutes while circulating under conditions of a pump flow rate of 550 mL / min, a peripheral speed of 12 m / s, and a mill jacket temperature of 20°C, yielding a solid electrolyte slurry. The resulting slurry was immediately dried under reduced pressure (vacuum level of 300 Pa or less) at room temperature (23°C) to yield a powdered amorphous modified solid electrolyte.

[0194] The obtained amorphous-modified sulfide solid electrolyte was placed in a 1 L glass Schlenk vessel in a glove box and heated at 190°C under reduced pressure (vacuum degree 100 Pa or less) using an oil bath to obtain a crystalline-modified sulfide solid electrolyte. The XRD patterns of the amorphous-modified solid electrolyte and the crystalline-modified solid electrolyte are shown in Figure 14. The measured initial and overall H2S gas generation rates, breakthrough times, and pH values ​​are shown in Figure 15 and Table 6, as in Example 1. For comparison, a crystalline sulfide solid electrolyte (4) is listed as Comparative Example 3.

[0195] [Table 6]

[0196] Comparisons between Example 1 and Comparative Example 1, and Example 3 and Comparative Example 3 confirmed that the crystalline sulfide solid electrolyte (1) prepared by a liquid phase method and the crystalline sulfide solid electrolyte (1) prepared using the same are effective in reducing the amount of H2S generated while suppressing a decrease in ionic conductivity through modification, regardless of the manufacturing method or particle size. Comparisons between Example 2 and Comparative Example 2 confirmed that even when a crystalline sulfide solid electrolyte (4) prepared by a solid phase method is used, modification is effective in reducing the amount of H2S generated, and that the effect of modification is manifested regardless of the manufacturing method of the sulfide solid electrolyte. Examples 3 to 5 confirmed that although the initial amount of H2S generated increases with the addition of Li2S, the amount generated over the entire period can be suppressed and the decrease in ionic conductivity can be minimized. Examples 6 to 9 confirmed that the same modification effect can be obtained for amorphous solid electrolytes. Example 10 confirmed that the same effect can be obtained when the modification method is a wet bead mill, i.e., when modification is performed in a micronization process. The results of pH measurements show that the unmodified solid electrolyte has a nearly neutral pH (pH = 6 to 8), whereas modification with Li2S makes it alkaline (pH = 10 to 12). This prevents H2S from being released from the system as H2S gas, extends the breakthrough time, and is presumed to have an effect on suppressing the amount of H2S generated over the entire period. [Industrial Applicability]

[0197] According to this embodiment, a modified sulfide solid electrolyte can be produced that suppresses a decrease in ionic conductivity and reduces the cumulative amount of H2S gas generated over the medium to long term or over the entire period, even when the sulfide solid electrolyte comes into contact with water and H2S is generated. The modified sulfide solid electrolyte obtained by the production method of this embodiment is suitable for use in batteries, particularly lithium-ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. Sulfide solid electrolyte and Li ２ and S, α parts by mass of Li ２ A method for producing a modified sulfide solid electrolyte, wherein (100-α) parts by mass of the sulfide solid electrolyte is used relative to S (α represents a number of 0.3 to 15.0).

2. 2. The method for producing a modified sulfide solid electrolyte according to claim 1, wherein the sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms.

3. The method for producing a modified sulfide solid electrolyte according to claim 2 , wherein the sulfide solid electrolyte further contains a halogen atom.

4. The sulfide solid electrolyte is [(1-X-Y)(0.75Li ２ S / 0.25P ２ S ５ ) / XLiBr / YLiI] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) The method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 3, wherein the solid electrolyte is represented by:

5. The method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 4, wherein the mixing is performed using a pulverizer.

6. The method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 5, wherein the sulfide solid electrolyte is an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

7. The method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 6, further comprising mixing a raw material containing at least one selected from the group consisting of lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain the sulfide solid electrolyte.

8. The method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 7, wherein the modified sulfide solid electrolyte comprises a thiolicon region II crystal structure.

9. A method for producing a crystalline modified sulfide solid electrolyte, comprising further crystallizing the modified sulfide solid electrolyte according to any one of claims 1 to 8.

10. Li ２ S and sulfide solid electrolyte [(1-X-Y)(0.75Li ２ S / 0.25P ２ S ５ ) / XLiBr / YLi] (In the formula, X represents a number from 0 to 0.2, and Y represents a number from 0 to 0.2.) and Li relative to the mass part of the sulfide solid electrolyte (100-α). ２ S is α parts by mass (α represents a number from 0.3 to 15.0). Modified sulfide solid electrolyte.

11. The modified sulfide solid electrolyte according to claim 10, wherein a pH value of a 1 mass % aqueous solution of the modified sulfide solid electrolyte is 9.0 or more.

12. An electrode mixture comprising the modified sulfide solid electrolyte according to claim 10 or 11 and an electrode active material.

13. A lithium ion battery comprising at least one of the modified sulfide solid electrolyte according to claim 10 or 11 and the electrode mixture according to claim 12.

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