Sulfide solid electrolyte, and electrode mixture and lithium-ion battery using same

Abstract

Provided are: a sulfide solid electrolyte that exhibits excellent battery characteristics by having deformability when processed and having excellent formability of interfaces between solid electrolytes and between the solid electrolyte and an electrode active material; and an electrode mixture and a lithium-ion battery using the sulfide solid electrolyte. The sulfide solid electrolyte has a deformation rate measured by a predetermined method of more than 2.4 GPa and less than 3.2 GPa. The electrode mixture uses the sulfide solid electrolyte. The lithium-ion battery uses the sulfide solid electrolyte and the electrode mixture.

Description

Sulfide solid electrolyte, electrode mixture using the same, and lithium ion battery

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

[0002] In recent years, with the rapid popularization of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, development of batteries used as their power sources has been regarded as important. Conventionally, electrolytes containing flammable organic solvents have been used in batteries for such applications. However, since the electrolyte is liquid and flammable, there are concerns about safety related to leakage, ignition, and the like when used as a battery. Particularly, in automotive applications, higher capacity and higher output are required, and concerns about safety in batteries using conventional electrolytes are increasing. Therefore, development of all-solid-state batteries, in which the electrolyte is replaced with a solid electrolyte layer, has been underway. By making the battery all-solid, no flammable organic solvent is used in the battery, the safety device can be simplified, and the battery is excellent in manufacturing cost and productivity. In addition, all-solid-state batteries are advantageous due to their high energy density, especially in automotive applications where higher capacity and higher output are required.

[0003] As a solid electrolyte used for lithium ion batteries, sulfide solid electrolytes are known. Various crystal structures of sulfide solid electrolytes are known, and one of them is the argyrodite-type crystal structure. It is known that a sulfide solid electrolyte having an argyrodite-type crystal structure has high stability and high ionic conductivity (for example, Patent Documents 1 and 2).

[0004] In addition, Patent Document 3 discloses, as a sulfide solid electrolyte having high ionic conductivity, a sulfide solid electrolyte glass-ceramic which has a peak having a predetermined intensity at a predetermined diffraction angle in X-ray diffraction measurement and has a crystallite diameter of 30 nm or more.

[0005] International Publication No. WO 2022 / 190940, International Publication No. WO 2018 / 164224, International Publication No. WO 2023 / 190862

[0006] This invention has been made in view of the above circumstances, and aims to provide a sulfide solid electrolyte that exhibits excellent battery characteristics by having deformability when processed and excellent interface formation between solid electrolytes and between solid electrolytes and electrode active materials, an electrode composite material using the same, and a lithium-ion battery.

[0007] The solid electrolyte according to the present invention is a sulfide solid electrolyte whose deformation rate, as measured by the following method, is greater than 2.4 GPa and less than 3.2 GPa. (Method for measuring deformation rate) 0.15 g of the sample to be measured was filled into a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm, and a compression test was performed using a compression testing machine to compress the sample at a speed of 0.2 mm / min until the stress reached 550 MPa. A stress-strain curve was prepared using the thickness of the sample at a stress of 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate.

[0008] The electrode composite material according to the present invention is an electrode composite material comprising the above-mentioned sulfide solid electrolyte and electrode active material, and the lithium-ion battery according to the present invention is a lithium-ion battery comprising at least one of the above-mentioned sulfide solid electrolyte and electrode composite material.

[0009] According to the present invention, a sulfide solid electrolyte that exhibits excellent battery characteristics due to its deformability when processed and its excellent interface formation properties between solid electrolytes and between solid electrolytes and electrode active materials, an electrode composite material using the same, and a lithium-ion battery can be provided.

[0010] This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 1.

[0011] The embodiments of the present invention (hereinafter sometimes referred to as "these embodiments") will be described below. In this specification, the upper and lower limit values ​​related to numerical ranges such as "greater than or equal to," "less than or equal to," and "~" can be arbitrarily combined, and the values ​​of the examples can also be used as the upper and lower limit values. Furthermore, any provisions that are considered preferable can be adopted arbitrarily. That is, one provision that is considered preferable can be adopted in combination with one or more other provisions that are considered preferable. Combinations of preferred provisions are considered even more preferable.

[0012] (Knowledge gained by the inventors to arrive at the present invention) The inventors diligently studied to solve the above problems and, as a result, discovered the following, and completed the present invention.

[0013] To improve the battery characteristics of lithium-ion batteries using solid electrolytes, especially all-solid-state batteries, it is important that the solid electrolyte itself has high ionic conductivity. However, it is also important to focus on the state of the solid electrolyte when it is used in the solid electrolyte layer, positive electrode, and negative electrode. One of the battery characteristics required of all-solid-state batteries is improved input / output. To achieve high input / output, it is essential to reduce the resistance inside the battery. This is achieved by forming interfaces between particles (solids), that is, by bringing the solid electrolyte particles into close contact with each other in the solid electrolyte layer, and the solid electrolyte and electrode active material particles into close contact with each other in the positive and negative electrodes, thereby forming junctions and junction surfaces between particles (these can be collectively called "interfaces"). It is effective to have many junctions and junction surfaces (interfaces) between particles. By having many junctions and junction surfaces (interfaces) between particles, it is possible to secure many ion conduction paths, which makes it possible to improve battery characteristics such as high input / output.

[0014] The interface between the particles of the solid electrolyte and the electrode active material is crucial for improving battery performance because it directly handles ion storage and release. Electrode active materials include positive electrode active materials and negative electrode active materials. Transition metal oxides, widely used as positive electrode active materials, are extremely hard particles that are difficult to deform. Therefore, the deformability of the solid electrolyte during processing is important for forming the interface between the solid electrolyte and the positive electrode active material. Thus, to improve battery performance, the solid electrolyte must have excellent deformability during processing, and consequently, excellent interface formation properties, including ease of interface formation between solid electrolytes and between the solid electrolyte and the electrode active material.

[0015] Therefore, the inventors focused on the deformability of sulfide solid electrolytes. As they proceeded with their investigation into evaluating deformability, they found that sulfide solid electrolytes consist of extremely small particles with particle sizes on the order of micrometers, and that when attempting to measure them at the individual particle level, problems such as particle aggregation and particle heterogeneity (for example, heterogeneity in composition, crystal orientation, etc.) arise, making it extremely difficult to accurately evaluate deformability. Next, they investigated the evaluation of deformability in aggregates (bulk) of sulfide solid electrolyte particles and found that compaction property evaluation (stress-density evaluation) could be adopted, and that when stress is applied to aggregates of sulfide solid electrolyte particles, densification progresses due to particle rearrangement in the low-pressure region, while movement due to deformation of the particles themselves becomes dominant in the high-pressure region. Furthermore, we discovered that sulfide solid electrolytes whose deformation rate, measured using the stressed state just before particle deformation becomes dominant as a reference, falls within a specific range, exhibit superior interface formation capabilities (hereinafter also simply referred to as "interface formation capabilities") between solid electrolytes and between solid electrolytes and electrode active materials, thereby enabling them to exhibit superior battery characteristics.

[0016] Patent Document 1 focuses on a specific diffraction peak measured by X-ray diffraction, sets the relationship between the peak intensities of two peaks separated by waveform separation of the diffraction peak within a predetermined range, and attempts to suppress the generation of hydrogen sulfide by adjusting the balance between the argyrodite-type crystal structure and other crystal structures. Patent Document 2 attempts to obtain a sulfide solid electrolyte with a small particle size and high ionic conductivity by setting the intensity ratio of diffraction peaks within a predetermined range measured by X-ray diffraction within a specific range in a sulfide solid electrolyte having a predetermined average particle size. However, these patent documents do not focus at all on deformability during processing, and do not consider the formation of interfaces between solid electrolytes obtained with excellent deformability, or between the solid electrolyte and electrode active material, nor do they consider excellent battery characteristics.

[0017] Furthermore, Patent Document 3 focuses on the crystallite size when improving ionic conductivity, and also focuses on improving water resistance. However, similar to Patent Documents 1 and 2, it does not focus on deformability when processed, the ability to form interfaces between solid electrolytes and between solid electrolytes and electrode active materials obtained through excellent deformability, nor on excellent battery characteristics.

[0018] Based on the above considerations, the inventors have found that a sulfide solid electrolyte having a specific deformation rate exhibits excellent interface formation between solid electrolytes and between the solid electrolyte and the electrode active material, and as a result, can exhibit excellent battery characteristics.

[0019] (Regarding various embodiments of this embodiment) The sulfide solid electrolyte according to the first embodiment of this embodiment is a sulfide solid electrolyte whose deformation rate, as measured by the method described below, is greater than 2.4 GPa and less than 3.2 GPa. (Method for measuring deformation rate) 0.15 g of the object to be measured was filled into a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm, and a compression test was performed using a compression testing machine to compress the sample at a speed of 0.2 mm / min until the stress reached 550 MPa. A stress-strain curve was prepared using the thickness of the sample at the point when the stress was 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate.

[0020] The sulfide solid electrolyte of this embodiment, when the deformation rate measured by the above measurement method has a range within the predetermined range, that is, when the deformation rate measured based on the stressed state just before the movement due to the deformation of the particles themselves becomes dominant has a deformation rate within the predetermined range, exhibits excellent interface formation between solid electrolytes and between the solid electrolyte and the electrode active material, and as a result can exhibit excellent battery characteristics.

[0021] When stress is applied to a sulfide solid electrolyte using a compression tester, it exhibits critical behavior near 100 MPa. This suggests that densification occurs through particle rearrangement up to 100 MPa, and that above 100 MPa, particle movement due to deformation becomes dominant. The compression test is continued by gradually increasing the stress up to 550 MPa to promote particle movement due to deformation. Here, the stress-strain curves from 100 MPa to 550 MPa, with 100 MPa being the baseline at which particle movement due to deformation becomes dominant, are considered to represent the behavior of the sulfide solid electrolyte when particle movement due to deformation becomes dominant.

[0022] The inventors conducted a detailed study of stress-strain curves from 100 MPa to 550 MPa and found that the stress gradient with respect to strain when the stress is between 400 and 550 MPa correlates with the ability to form interfaces between solid electrolytes and between solid electrolytes and electrode active materials. They also found that sulfide solid electrolytes with a deformation rate of more than 2.4 GPa and less than 3.2 GPa exhibit particularly excellent interface formation, resulting in superior battery characteristics. This led to the development of the sulfide solid electrolyte of this embodiment.

[0023] The sulfide solid electrolyte according to the second embodiment of this model is characterized in that, in the sulfide solid electrolyte of the first embodiment described above, the average particle diameter (D50) based on volume is 0.1 μm or more and 10.0 μm or less.

[0024] When the average particle size (D50) based on volume is within the above range, the ability to form interfaces between solid electrolytes and between solid electrolytes and electrode active materials is improved, making it easier to exhibit excellent battery characteristics.

[0025] The third embodiment of this invention is a sulfide solid electrolyte that, in the first or second embodiment, contains lithium atoms, phosphorus atoms, and sulfur atoms as constituent atoms, and the fourth embodiment of this invention is a sulfide solid electrolyte that, in the third embodiment, further contains halogen atoms.

[0026] The sulfide solid electrolyte of this embodiment, by containing lithium atoms, phosphorus atoms, and sulfur atoms as constituent atoms, easily improves ionic conductivity, and by further containing halogen atoms, the ionic conductivity can be further improved.

[0027] The sulfide solid electrolyte according to the fifth embodiment of this embodiment contains an organic solvent in any one of the first to fourth embodiments described above; the sulfide solid electrolyte according to the sixth embodiment of this embodiment is characterized in that, in the fifth embodiment described above, the organic solvent is at least one selected from aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; and the sulfide solid electrolyte according to the seventh embodiment of this embodiment is characterized in that, in the fifth or sixth embodiment described above, the content of the organic solvent is 0.1% by mass or more and 5.0% by mass or less.

[0028] The sulfide solid electrolyte of this embodiment may contain organic solvents derived from the manufacturing process, if which is used in the manufacturing process. The sulfide solid electrolyte of this embodiment tends to have the predetermined deformation rate described above if an organic solvent is used in any operation of the manufacturing process. Therefore, the sulfide solid electrolyte containing an organic solvent tends to have excellent interface formation properties, and as a result tends to exhibit excellent battery characteristics.

[0029] The solid electrolyte according to the eighth embodiment of this embodiment is characterized in that, in any one of the first to seventh embodiments described above, the ionic conductivity is 3.5 mS / cm or higher, and the solid electrolyte according to the ninth embodiment of this embodiment is characterized in that, in any one of the first to eighth embodiments described above, it has an argyrodite-type crystal structure.

[0030] The sulfide solid electrolyte of this embodiment, by having the predetermined deformation rate described above, not only exhibits excellent interfacial moldability but also high ionic conductivity. Furthermore, the sulfide solid electrolyte of this embodiment has high ionic conductivity due to its argyrodite crystal structure. Sulfide solid electrolytes having an argyrodite crystal structure are known to have high ionic conductivity but are inherently poor in interfacial moldability due to their hard properties. However, the sulfide solid electrolyte of this embodiment, even with an argyrodite crystal structure, exhibits excellent interfacial formation and can also possess the inherently high ionic conductivity. Therefore, it can exhibit extremely excellent battery characteristics.

[0031] The electrode composite material according to the tenth embodiment of this embodiment is an electrode composite material comprising a sulfide solid electrolyte according to any one of the first to ninth embodiments described above, and an electrode active material.

[0032] The sulfide solid electrolyte of this embodiment exhibits excellent interface formation properties, increasing the number of interparticle bonding points and bonding surfaces through close contact with the electrode active material. This ensures ion conduction paths and results in superior battery characteristics. Furthermore, since the sulfide solid electrolyte of this embodiment has high ionic conductivity, the electrode composite material containing it also exhibits high ionic conductivity. As a result, using the electrode composite material of this embodiment in a lithium-ion battery yields superior battery characteristics.

[0033] The lithium-ion battery according to the eleventh embodiment of this embodiment is a battery comprising at least one of the sulfide solid electrolyte according to any one of the first to ninth embodiments and the electrode composite material according to the tenth embodiment.

[0034] The sulfide solid electrolyte of this embodiment exhibits excellent interface formation properties and high ion conductivity. Therefore, by employing the sulfide solid electrolyte and the electrode composite material using it in a lithium-ion battery, excellent battery characteristics can be achieved.

[0035] The solid electrolyte of this embodiment will be described in more detail below, following the embodiments described above.

[0036] In this specification, "solid electrolyte" means an electrolyte that remains solid at 25°C under a nitrogen atmosphere. The sulfide solid electrolyte in this embodiment is a solid electrolyte containing at least sulfur atoms, and it is preferable to further contain lithium atoms in order to have a higher ionic conductivity. The ionic conductivity due to lithium atoms, which is exhibited by using lithium atoms as a conductive species, will be higher.

[0037] The term "solid electrolyte" includes both crystalline solid electrolytes and amorphous solid electrolytes. In this specification, a crystalline solid electrolyte is a solid electrolyte in which peaks originating from the solid electrolyte are observed in the X-ray diffraction pattern in X-ray diffraction measurements, regardless of whether or not peaks originating from the raw materials of the solid electrolyte are present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and may be partially or entirely derived from the solid electrolyte. Furthermore, a crystalline solid electrolyte may contain an amorphous solid electrolyte as long as it has the above-described X-ray diffraction pattern. Therefore, crystalline solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte above its crystallization temperature. In this specification, an amorphous solid electrolyte is a solid electrolyte in which, in the X-ray diffraction pattern in X-ray diffraction measurements, substantially no peaks other than those originating from the material are observed, regardless of whether or not peaks originating from the raw materials of the solid electrolyte are present.

[0038] [Sulfide Solid Electrolyte] The sulfide solid electrolyte of this embodiment is a sulfide solid electrolyte whose deformation rate, as measured by the method described below, is greater than 2.4 GPa and less than 3.2 GPa. (Method for measuring deformation rate) 0.15 g of the sample to be measured was filled into a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm, and a compression test was performed using a compression testing machine to compress the sample at a speed of 0.2 mm / min until the stress reached 550 MPa. A stress-strain curve was prepared using the thickness of the sample at the point when the stress was 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate. The thickness of the sample to be measured after the above compression test was approximately 1 mm.

[0039] If the deformation rate measured by the above method is 2.4 GPa or less, the sulfide solid electrolyte particles become too easily deformed, damaging the structure of the sulfide solid electrolyte and resulting in poor battery performance. On the other hand, if the deformation rate is 3.2 GPa or higher, the sulfide solid electrolyte particles become too difficult to deform, reducing the ability to form interfaces and preventing the acquisition of good battery performance.

[0040] From the viewpoint of obtaining better battery characteristics by obtaining better interface formation, the deformation rate of the sulfide solid electrolyte is preferably 2.5 GPa or more, more preferably 2.7 GPa or more, even more preferably 2.9 GPa or more, and preferably 3.1 GPa or less as the upper limit.

[0041] (Average particle size (D50)) The average particle size of the sulfide solid electrolyte in this embodiment is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, as a volume-based average particle size (D50), and the upper limit is preferably 10.0 μm or less, more preferably 8.0 μm or less, and even more preferably 5.0 μm or less. When the average particle size of the sulfide solid electrolyte in this embodiment is within the above range, as described above, the ability to form interfaces between solid electrolytes and between the solid electrolyte and the electrode active material is improved, making it easier to exhibit excellent battery characteristics. Furthermore, the ability to form interfaces with the positive electrode active material is improved, making it particularly suitable as a positive electrode composite material that is a mixture with the positive electrode active material.

[0042] In this specification, the average particle diameter (D50) is the particle diameter at which the sum of the particle diameters, starting from the smallest particle, reaches 50% of the total when plotting a particle diameter distribution integration curve, and the volume distribution is the average particle size that can be measured, for example, using a laser diffraction / scattering particle diameter distribution analyzer.

[0043] (Constituent Atoms) The sulfide solid electrolyte of this embodiment is a solid electrolyte containing sulfur atoms as described above, and more preferably contains lithium atoms. From the viewpoint of improving ionic conductivity, the sulfide solid electrolyte of this embodiment preferably contains lithium atoms, phosphorus atoms and sulfur atoms, and more preferably further contains halogen atoms. Preferred halogen atoms include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms, more preferably chlorine atoms, bromine atoms and iodine atoms, and even more preferably chlorine atoms and bromine atoms. In the solid electrolyte of this embodiment, the halogen atoms may be the above halogen atoms alone or in combination of several types.

[0044] In the sulfide solid electrolyte of this embodiment, when lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms are included, the composition ratio (molar ratio) of these atoms is preferably 1.0 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.6, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.08 to 0.4.

[0045] When bromine and chlorine are used in combination as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and chlorine is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.3:0.01 to 0.3, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.02 to 0.25:0.02 to 0.25, even more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.03 to 0.2:0.03 to 0.2, and even more preferably 1.35 to 1.45:0.3 to 0.45:1.4 to 1.7:0.04 to 0.18:0.04 to 0.18.

[0046] In the sulfide solid electrolyte of the present embodiment, by setting the composition ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms and halogen atoms within the above ranges, the sulfide solid electrolyte is likely to have an argyrodite-type crystal structure described later, and can be formed into a solid electrolyte having higher ionic conductivity. In addition, excellent interface formability is also easily obtained. The types and composition ratios (molar ratios) of the atoms constituting the solid electrolyte of the present embodiment can be confirmed, for example, by an ICP emission spectroscopy analyzer.

[0047] (Ionic Conductivity) The ionic conductivity of the sulfide solid electrolyte of the present embodiment is 3.5 mS / cm or more, 4.0 mS / cm or more, further 4.2 mS / cm or more, 4.4 mS / cm or more, 4.5 mS / cm or more, 4.8 mS / cm or more, 5.0 mS / cm or more, and the upper limit is usually 12.5 mS / cm or less, further 12.0 mS / cm or less, 11.5 mS / cm or less, 11.0 mS / cm or less. As described above, the sulfide solid electrolyte of the present embodiment has high ionic conductivity.

[0048] (Crystal Structure) The sulfide solid electrolyte of the present embodiment preferably has an argyrodite-type crystal structure. The argyrodite-type crystal structure is represented by the space group F-43m, and Li ７ PS ６ is a cubic crystal structure that basically has the above structural skeleton. Examples of the composition formula of the argyrodite-type crystal structure include Li ７－ｘ P １－ｙ Si ｙ S ６ , Li ７＋ｘ P １－ｙ Si ｙ S ６ (where x is -0.6 to 0.6, and y is 0.1 to 0.6). The argyrodite-type crystal structure represented by these composition formulas is cubic crystal or orthorhombic crystal, preferably cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has a peak appearing mainly at 2θ=25.4°, and also has a peak appearing at at least any one of positions 2θ=15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°.

[0049] As the composition formula of the argyrodite-type crystal structure, Li ７－ｘ－２ｙ PS６－ｘ－ｙ Cl ｘ Examples include (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5). The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, peaks appear mainly at 2θ = 25.4°, as well as at least one of 2θ = 15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0050] Furthermore, the compositional formula for the argyrodite type crystal structure is Li ７－ｘ PS ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8) is also an example. The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, it has peaks that appear mainly at 2θ = 25.4°, as well as at least one of 2θ = 15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°.

[0051] Here, the sulfide solid electrolyte of this embodiment preferably contains sulfur atoms, more preferably contains sulfur atoms and lithium atoms, even more preferably contains lithium atoms, phosphorus atoms and sulfur atoms, and even more preferably contains halogen atoms. Therefore, the above "Li ７－ｘ P １－ｙ Si ｙ S ６ Li ７＋ｘ P １－ｙ Si ｙ S ６ In the empirical formula (where x is -0.6 to 0.6 and y is 0.1 to 0.6), if an atom other than a chlorine atom is used as the halogen atom, then "Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘThe composition formula (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) may not always be applicable. However, if the solid electrolyte of this embodiment has the same diffraction peak as the diffraction peak described above as being present in the "argyrodite-type crystal structure," then it can be said that the solid electrolyte of this embodiment has an argyrodite-type crystal structure formed by the preferably included atoms described above.

[0052] (Organic solvent) The sulfide solid electrolyte of this embodiment may contain an organic solvent. As previously described, the organic solvent may be included if it is used in the manufacturing process of the sulfide solid electrolyte of this embodiment. The use of an organic solvent in any operation of the manufacturing process tends to result in the above-mentioned predetermined deformation rate. The inclusion of an organic solvent in the sulfide solid electrolyte of this embodiment results in excellent interface formation and tends to exhibit excellent battery characteristics.

[0053] As the organic solvent, hydrocarbon solvents are preferred. Examples of hydrocarbon solvents include saturated or unsaturated aliphatic hydrocarbons such as hexane, hexene, pentane, 2-ethylhexane, heptane, heptene, octane, decane, undecane, dodecane, and tridecane; saturated or unsaturated alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclohexene; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene. Among these, aromatic hydrocarbon solvents are preferred, and toluene and xylene are more preferably used.

[0054] When the sulfide solid electrolyte of this embodiment contains an organic solvent, the organic solvent content is preferably as low as possible, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and even more preferably 1.5% by mass or less. There is no particular lower limit, and it is usually 0.1% by mass or more.

[0055] (Method for producing sulfide solid electrolyte) There are no particular restrictions on the method for producing the sulfide solid electrolyte of this embodiment, as long as a product having the configuration required for the sulfide solid electrolyte of this embodiment is obtained. Various production methods such as conventional solid-phase methods and liquid-phase methods (for example, methods using complexing agents) can be employed. However, a preferred production method includes, for example, heat-treating a raw material-containing material in a solvent using a pressure vessel or under reflux, removing the solvent, and calcining the heat-treated product obtained by the heat-treating process. This production method makes it possible to produce the sulfide solid electrolyte of this embodiment more efficiently.

[0056] (Heat treatment) This manufacturing method includes heat treatment of the raw material-containing material in a solvent using a pressure vessel or under reflux. The raw material-containing material may contain solid electrolyte raw materials selected according to the solid electrolyte to be obtained, preferably a material containing multiple types of solid electrolyte raw materials containing at least one atom selected from lithium atoms, phosphorus atoms and sulfur atoms, and more preferably a material containing multiple types of solid electrolyte raw materials containing at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms.

[0057] (Materials contained in raw materials) Examples of solid electrolyte materials contained in raw materials include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and phosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ A raw material containing at least two atoms selected from the above atoms, such as phosphorus sulfide (F), and fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Typical examples include halogen molecules such as phosphorus molecules and sulfur molecules, and raw materials consisting of one type of atom selected from the above atoms.

[0058] Among the above, solid electrolyte raw materials containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Phosphorus sulfides such as ) are preferred, and among phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0059] Among the above, lithium sulfide and phosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) Phosphorus sulfide, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Halogen molecules such as ) and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. Furthermore, when introducing oxygen atoms into a sulfide solid electrolyte, phosphorus compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred.

[0060] Among the above, halogen molecules and lithium halides can be preferably used as solid electrolyte raw materials containing halogen atoms. The halogen atoms contained in the raw material are as described above as halogen atoms that the sulfide solid electrolyte of this embodiment may contain, with fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms being preferred, chlorine atoms, bromine atoms, and iodine atoms being more preferred, and chlorine atoms and bromine atoms being even more preferred. Therefore, it is preferable to use solid electrolyte raw materials containing such halogen atoms. By including halogen atoms, not only can the ionic conductivity of the sulfide solid electrolyte be improved, but an argyrodite-type crystal structure can also be easily formed. As a result, the resulting sulfide solid electrolyte tends to have high ionic conductivity and excellent interface formation properties can be easily obtained.

[0061] Lithium chloride, lithium bromide, and lithium iodide are more preferred as lithium halides, and it is preferable to use at least one of lithium chloride and lithium bromide, and it is even more preferable to use lithium chloride and lithium bromide in combination. As halogen molecules, chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) is more preferable, and it is preferable to use at least one of chlorine and bromine, and it is even more preferable to use chlorine and bromine in combination.

[0062] Preferred combinations of solid electrolyte raw materials to be included in the raw material include, for example, combinations of lithium sulfide and phosphorus sulfide, combinations of lithium sulfide, phosphorus sulfide and lithium halide, combinations of lithium sulfide, phosphorus sulfide and halogen molecules, and combinations of lithium sulfide, phosphorus sulfide, lithium halide and halogen molecules. More preferably, combinations of lithium sulfide, diphosphorus pentasulfide and lithium halide, and combinations of lithium sulfide, diphosphorus pentasulfide and halogen molecules are mentioned. In the above combinations, lithium chloride, lithium bromide, and lithium iodide are preferred as lithium halides, and chlorine, bromine, and iodine are preferred as halogen molecules. By using such solid electrolyte raw materials, the ability to form interfaces can be improved. Furthermore, the resulting sulfide solid electrolyte tends to have an argyrodite-type crystal structure, thus improving ionic conductivity.

[0063] A solid electrolyte raw material containing at least two atoms selected from the above atoms, wherein the raw material contains various phosphorus fluorides (PF ３ , PF ５ ), various phosphorus chlorides (PCL ３ , PCL ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and other phosphorus halides; thiophosphoryl fluoride (PSF ３), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), dibromide fluoride thiophosphoryl (PSBr ２ Examples include halogenated thiophosphoryls such as F).

[0064] Other solid electrolyte raw materials contained in the raw material include, for example, solid electrolyte raw materials containing at least one atom selected from the above atoms and also containing atoms other than said 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; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ ), metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; alkali metal halides other than lithium, such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; metal halides such as aluminum halide, silicon halide, germanium halide, arsenic halide, selenium halide, tin halide, antimony halide, tellurium halide, and bismuth halide; phosphorus oxychloride (POCl) ３ ), phosphorus oxybromide (POBr ３ Examples include phosphorus oxyhalogenates such as ) and others. Furthermore, when introducing oxygen atoms into a solid electrolyte, phosphorus compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred.

[0065] In this embodiment, PS ４ Li including structure ３ PS ４ It can also be used as a solid electrolyte raw material. Specifically, Li ３ PS ４ It is possible to prepare this by manufacturing it, and then use it as a raw material. In this case, the combination of solid electrolyte raw materials contained in the raw material is Li ３ PS４ and the above lithium halogen combination, Li ３ PS ４ and the above halogen molecule combination, Li ３ PS ４ A preferred combination is the lithium halide and halogen molecule described above.

[0066] The ratio of solid electrolyte raw materials used should be within the range of the atomic composition ratio (molar ratio) that the sulfide solid electrolyte of this embodiment may contain. For example, when lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as solid electrolyte raw materials, the mixing ratio (molar ratio) of these compounds is preferably 30-60:10-25:15-50, more preferably 45-55:10-15:30-50, even more preferably 45-50:11-14:35-45, and even more preferably 46-49:11-13:38-42.

[0067] The raw material (solid electrolyte raw material) is preferably pulverized to an average particle size (D50) of 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. By pulverizing the solid electrolyte raw material, the average particle size (D50) of the resulting sulfide solid electrolyte tends to fall within the range described above as the average particle size (D50) that the sulfide solid electrolyte of this embodiment may have.

[0068] A grinder can be used to grind solid electrolyte raw materials. Examples of grinders include medium-type grinders such as container-driven grinders and medium-agitated grinders. Examples of container-driven grinders include agitated tanks, grinding tanks, or combinations thereof such as ball mills and bead mills. Examples of medium-agitated grinders include impact grinders such as cutter mills, hammer mills and pin mills; tower-type grinders such as tower mills; agitated tank-type grinders such as attritors, aquamizers and sand grinders; flow-tank type grinders such as visco mills and pearl mills; flow-pipe type grinders; annular-type grinders such as coball mills; continuous dynamic grinders; and various grinders such as single-shaft or multi-shaft kneaders. Pin mills are also preferred because they have a short processing time and allow for continuous grinding operations.

[0069] It is preferable to pre-mix the raw materials. Suitable mixers for pre-mixing include, for example, mechanical agitator mixers equipped with stirring blades in the reaction vessel to perform stirring (also referred to as stirring or agitation mixing). Examples of mechanical agitator mixers include high-speed agitator mixers and dual-arm mixers. Examples of high-speed agitator mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used. Other preferred mixers include, for example, container-rotating mixers and container-fixed mixers, as well as conical screw mixers such as the Nauta mixer and high-speed agitator mixers such as the FM mixer.

[0070] In this manufacturing method, it is preferable to heat-treat the material obtained by mixing and grinding the above-mentioned raw material in a solvent. As the solvent used during mixing and grinding, nonpolar solvents such as hydrocarbon solvents and polar solvents such as solvents containing heteroatoms are preferably used, and it is preferable to use a combination of nonpolar and polar solvents.

[0071] As hydrocarbon solvents, those described above as organic solvents that the sulfide solid electrolyte of this embodiment may contain are preferred.

[0072] Furthermore, as solvents containing heteroatoms, polar solvents containing heteroatoms such as nitrogen atoms and oxygen atoms are also preferred, and it is preferable to use a solvent containing at least one atom selected from nitrogen atoms and oxygen atoms. Examples of such solvents include solvents containing oxygen atoms such as ether solvents, ester solvents, alcohol solvents, aldehyde solvents, and ketone solvents; and as solvents containing nitrogen atoms, solvents having groups containing nitrogen atoms such as amino groups, amide groups, nitro groups, and nitrile groups are preferred. Among these, ether solvents and nitrile solvents are preferably used.

[0073] Preferred ether solvents include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, with aliphatic ethers and alicyclic ethers being particularly preferred. Preferred aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; and polyethers having three or more ether groups, such as diethylene glycol dimethyl ether (diglym) and triethylene oxide glycol dimethyl ether (trilym). Among these, monoethers are preferred.

[0074] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, and dioxolane. Among the above aliphatic ethers and alicyclic ethers, diethyl ether and tetrahydrofuran are preferred.

[0075] Preferred nitrile solvents include aliphatic nitrile solvents such as acetonitrile, acrylonitrile, propionitrile, chloropropionitrile, isobutyronitrile, tert-butyronitrile, capronitrile, isocapronitrile, malononitrile, and fumanitrile; alicyclic nitrile solvents such as cyclohexylnitrile; and aromatic nitrile solvents such as benzonitrile and fluorobenzonitrile. Among these, aliphatic nitrile solvents are preferred, with propionitrile, isobutyronitrile, and isocapronitrile being more preferred.

[0076] When using a combination of a nonpolar solvent and a polar solvent, aromatic hydrocarbon solvents, particularly toluene and ethylbenzene, are preferred as the nonpolar solvent, and nitrile solvents, which have azeotropic properties with aromatic hydrocarbon solvents such as toluene and are easily removed together with aromatic hydrocarbon solvents such as toluene, are preferred as the polar solvent.

[0077] The content of the nonpolar solvent in the solvent is preferably 95% by mass or more. When a nonpolar solvent and a polar solvent are used in combination, the content of the polar solvent in the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, with an upper limit of preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0078] As for the equipment used for mixing and grinding the raw material components, the grinders exemplified as grinders that can be used for grinding the raw material components mentioned above are preferred, among which planetary ball mills, vibratory mills, rolling mills, and bead mills are preferred. As for the grinder, a grinder that circulates the slurry between the grinder (grinding mixer) that grinds the slurry and the temperature-holding tank (reaction vessel) can also be used. In addition, kneaders such as single-screw kneaders and multi-screw kneaders may be used.

[0079] When the above-mentioned raw material-containing material is mixed and ground, the raw material-containing material obtained by mixing and grinding forms a slurry with the solvent. Therefore, after mixing and grinding, the solvent contained in the slurry can be dried and removed. There are no particular restrictions on the drying method as long as the solvent can be removed. For example, it can usually be done by reduced-pressure drying (vacuum drying) using a vacuum pump or the like at around 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at room temperature (e.g., 23°C) (e.g., room temperature ± 5°C). The slurry may also be separated by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge or the like. Alternatively, solid-liquid separation may be performed first, followed by the drying described above. Furthermore, it is preferable to use the same solvent used during heat treatment as the solvent used during the mixing and grinding of the raw material-containing material. This is because drying of the solvent becomes unnecessary.

[0080] Heat treatment in a solvent is carried out using a pressure vessel or under reflux. Performing heat treatment in a solvent, that is, without removing the solvent, prevents aggregation of the treated materials and makes it possible to reduce the size of secondary particles of the sulfide solid electrolyte.

[0081] The solvent used during the heat treatment can be appropriately selected from the non-polar and polar solvents described above as the solvents used during the mixed grinding process. Therefore, the same solvent used during mixed grinding may be used, or a different solvent may be used. Using the same solvent is preferable because, as mentioned earlier, drying is unnecessary. Among the above solvents, aromatic hydrocarbon solvents are preferred.

[0082] The heating temperature in the heat treatment can be appropriately selected depending on the type of solid electrolyte raw material used, for example, preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and even more preferably 180°C or higher, with an upper limit of preferably 300°C or lower, more preferably 280°C or lower, even more preferably 270°C or lower, and even more preferably 260°C or lower. The heating time is preferably 10 minutes to 6 hours, more preferably 10 minutes to 3 hours, and even more preferably 30 minutes to 2 hours. By using the above conditions, PS ４ The structure is formed, making it easier for halogens to be incorporated into the crystal, and thus improving ionic conductivity. Furthermore, since the raw material mixture of fine crystals is heat-treated in a solvent, PS can be produced at relatively low temperatures. ４ This facilitates the formation of crystalline structures containing the structure. As a result, the interfacial formation properties of the resulting sulfide solid electrolyte can be improved, and the ionic conductivity can also be enhanced.

[0083] When heat treatment is performed using a pressure vessel, if the heating temperature exceeds the boiling point of the solvent used, it is preferable to use an autoclave. When heat treatment is performed with reflux of the solvent, the method is not particularly limited, and for example, a condenser (e.g., a Dieblot condenser) that cools the vapor and returns it to the solvent can be used.

[0084] (Removal of solvent) This manufacturing method includes removing the solvent after performing heat treatment in the above solvent. The heat-treated product is obtained by removing the solvent from the slurry containing the solvent and the heat-treated product obtained by the above heat treatment.

[0085] As for the method of removing the solvent from the slurry, there are no particular restrictions as long as the solvent can be removed. For example, it can be dried using the same method as the drying method used to remove the solvent during the mixing and grinding process described above.

[0086] (Castration) This manufacturing method includes calcining the heat-treated product obtained by removing the solvent. This makes it easier to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure, thereby improving the ionic conductivity of the obtained sulfide solid electrolyte. It also improves the ability to form interfaces.

[0087] The heating temperature in the firing of the heat-treated material is preferably 300°C or higher, more preferably over 300°C, even more preferably 320°C or higher, even more preferably 350°C or higher, and particularly preferably 380°C or higher, with an upper limit of preferably 470°C or lower, more preferably 460°C or lower, even more preferably 450°C or lower, even more preferably 440°C or lower, and particularly preferably 430°C or lower. The heating time is preferably 1 minute to 6 hours, more preferably 1 minute to 2 hours, and even more preferably 5 minutes to 1 hour. When the heating temperature in firing is within the above range, the ionic conductivity of the obtained sulfide solid electrolyte is improved, and the interface formation ability is also improved.

[0088] The firing process is preferably carried out in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) or a reduced-pressure atmosphere (especially in a vacuum). Furthermore, the firing process can be carried out using a firing furnace such as a stationary hearth kiln or a rotary kiln.

[0089] (Grinding) The manufacturing method preferably includes further grinding of the calcined material obtained by the above calcination. By grinding, the calcined material can be made finer and adjusted to an average particle size suitable for the application. Furthermore, grinding makes it easier to adjust the deformation rate within the above predetermined range. Thus, by grinding the calcined material, not only can the particle size be adjusted, but the structure of the resulting sulfide solid electrolyte, i.e., the deformation rate, can be adjusted within the predetermined range, thereby improving the interface formation and ionic conductivity of the resulting sulfide solid electrolyte. The grinding is preferably carried out by wet grinding (also called "wet micronization"). When wet grinding is performed, the object to be ground is preferably a fluid containing the above calcined material and a solvent.

[0090] When wet atomization is performed, suitable solvents include, for example, hydrocarbon solvents as exemplified above as nonpolar solvents, more preferably aromatic hydrocarbon solvents, and among these, toluene and xylene are more preferably used. When using a solvent, the amount of solvent used is adjusted so that the content of the calcined product in the fluid used for wet atomization is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, with an upper limit of preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0091] Furthermore, the fluid that is the target of wet atomization preferably contains a dispersant. Examples of preferred dispersants include nitrile solvents, ether solvents, and ester solvents. The nitrile solvent and ether solvent can be appropriately selected from the nitrile solvents and ether solvents exemplified as solvents used during the mixed grinding of the raw material-containing material.

[0092] Preferred ester solvents include, for example, aliphatic esters such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, and dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, acetolactone, propiolactone, butyrolactone, and valerolactone; and aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, and triethyl trimellitate.

[0093] When a dispersant is used, the amount of dispersant used is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, with an upper limit of preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, relative to the content of the calcined product contained in the above fluid.

[0094] The calcined material can be crushed using a crushing machine. The crushing machine can be appropriately selected from the examples of crushing machines that can be used for crushing the above raw materials, and container-driven crushing machines such as ball mills and bead mills are preferably used.

[0095] The grinding energy can vary depending on the amount of material to be ground, the size of the grinder, etc., and therefore cannot be stated definitively, but it is preferably greater than 0.3 kWh / kg, more preferably 0.5 kWh / kg or more, even more preferably 0.8 kWh / kg or more, with an upper limit of preferably less than 3.8 kWh / kg, more preferably 3.5 kWh / kg or less, even more preferably 3.0 kWh / kg or less, and even more preferably 2.5 kWh / kg or less. When the grinding energy is within the above range, not only can particle size adjustment be performed efficiently, but the structure of the resulting sulfide solid electrolyte, i.e., the deformation rate, can be easily adjusted within a predetermined range, thereby improving the interfacial formation and ionic conductivity of the resulting sulfide solid electrolyte.

[0096] (Applications) The sulfide solid electrolyte of this embodiment exhibits excellent battery characteristics due to its superior interface formation properties. Therefore, it is suitably used in electrode composites and in batteries, particularly lithium-ion batteries, and especially in all-solid-state batteries. The solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer can be manufactured by known methods.

[0097] [Electrode mixture] The electrode mixture of this embodiment is an electrode mixture comprising the sulfide solid electrolyte of this embodiment described above and an electrode active material.

[0098] As electrode active materials, positive electrode active materials and negative electrode active materials are selected depending on whether the electrode composite material is used as the positive electrode or the negative electrode. Conventional materials that have been used as such for the positive and negative electrode active materials can be used.

[0099] In electrode composite materials, the mixing ratio (mass ratio) of electrode active material and sulfide solid electrolyte 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, considering both improved battery performance and manufacturing efficiency.

[0100] The electrode composite material of this embodiment may also contain other components in addition to the sulfide solid electrolyte of this embodiment and the electrode active material described above, such as conductive materials like carbon-based materials, binders like thermoplastic elastomers and resins.

[0101] [Lithium-ion battery] The lithium-ion battery of this embodiment includes at least one of the sulfide solid electrolyte of this embodiment and the electrode composite material of this embodiment.

[0102] The lithium-ion battery of this embodiment is not particularly limited in its configuration as long as it contains either the sulfide solid electrolyte of this embodiment or the electrode mixture containing it, and for example, a different form of sulfide solid electrolyte or electrode mixture containing it may be used. Furthermore, the configuration of the lithium-ion battery may be that of a commonly used lithium-ion battery.

[0103] The lithium-ion battery of this embodiment preferably comprises, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. Preferably, the electrode composite material of this embodiment is used for the positive electrode layer and the negative electrode layer, and preferably, the sulfide solid electrolyte of this embodiment is used for the electrolyte layer. A lithium-ion battery in which a solid electrolyte is used as the electrolyte layer is also called an all-solid-state battery.

[0104] The sulfide solid electrolyte used in the lithium-ion battery of this embodiment exhibits excellent interface formation properties between solid electrolytes and between the solid electrolyte and the electrode active material, and in particular, the interface formation properties with the positive electrode active material are easily improved. For this reason, it is preferable to use it as a positive electrode composite material used in forming the solid electrolyte layer and the positive electrode layer.

[0105] In addition to the positive electrode layer, electrolyte layer, and negative electrode layer, the above-mentioned battery preferably uses a current collector, and known current collectors can be used. For example, a layer coated with Au or the like, which reacts with the above-mentioned solid electrolyte, can be used.

[0106] The present invention will now be specifically described with reference to examples, but the present invention is not limited in any way by these examples.

[0107] (Measurement by Powder X-ray Diffraction (XRD)) Powder X-ray diffraction (XRD) measurements were performed as follows. The samples obtained from the examples and comparative examples (powder) were packed into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the samples. These samples were sealed with Kapton film for XRD and measured under the following conditions without exposure to air. Measurement device: D2 Phaser (Bruker Co., Ltd.) Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: Focused method Slit configuration: Solar slit 4°, divergent slit 1 mm, Kβ filter (Ni plate) used Detector: Semiconductor detector Measurement range: 2θ = 10⁻⁶⁰ deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0108] (Measurement of Deformation Rate) 0.15 g of the sample obtained in the examples and comparative examples was placed in a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm. A compression test was performed using a compression testing machine ("AGX-50kNVD (model number)", manufactured by Shimadzu Corporation) at a speed of 0.2 mm / min until the stress reached 550 MPa. A stress-strain curve was created using the thickness of the sample at a stress of 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate. The thickness of the sample after compression in the above compression test was approximately 1 mm.

[0109] (Evaluation of Battery Characteristics) For the samples obtained in the Examples and Comparative Examples, compacted coin batteries were prepared as follows. First, an NCM-based positive electrode material, a solid electrolyte obtained in the Examples and Comparative Examples, and acetylene black as a conductive additive were blended in a ratio of 97 parts by mass (75 parts by mass of NCM / 25 parts by mass of solid electrolyte) and 3 parts by mass to obtain 30 mg of positive electrode mixture. For the solid electrolyte layer, 100 mg of the solid electrolyte obtained in the Examples and Comparative Examples was used, and for the negative electrode material, metallic Li foil (thickness: 100 μm) was used. 100 mg of the solid electrolyte used for the solid electrolyte layer was pressed using a compaction jig (φ10 mm) at a press pressure of 180 MPa, then 30 mg of the positive electrode mixture was filled and pressed at a press pressure of 550 MPa to form the positive electrode layer. Furthermore, the negative electrode material was placed on the opposite side of the solid electrolyte layer from the positive electrode layer and pressed at a press pressure of 40 MPa to obtain a laminate in which the positive electrode / solid electrolyte layer / negative electrode were stacked in order. This was then restrained with a bolt and nut under a pressure of 15 MPa to create a compacted coin cell.

[0110] Using the above-mentioned compacted coin cell battery, initial charge and discharge cycles were performed at a temperature of 45°C using an electrochemical measuring device ("VMP-3 (model number)", manufactured by Bio-Logic Co., Ltd.), repeating 10-hour charge and discharge cycles twice. Next, the capacity retention rate was calculated after 10 hours of charging followed by 1 hour of discharge. The battery was evaluated as passing if the discharge capacity after 1 hour of discharge was 85% or more of the charge capacity after 10 hours of charging, and failing if it was less than 85%.

[0111] (Measurement of Ionic Conductivity) The ionic conductivity was measured as follows: For the objects obtained in the examples and comparative examples, a diameter of 10 mm (cross-sectional area S: 0.785 cm²) was measured. ２ A 0.3 g sample of the material to be measured was placed in a 3 cm high measuring cell and subjected to uniaxial compression molding at a molding pressure of 400 MPa using a uniaxial molding machine ("Single-Acting Cylinder MS2 (model number)", manufactured by Riken Kiki Co., Ltd.) to obtain a sample for measurement (thickness (L) 1-2 mm). 10 mg of conductive carbon powder was placed above and below the sample, and after pressure molding, electrode terminals were taken from the top and bottom, and measurements were taken at 25°C using the AC impedance method (frequency range: 1 MHz to 0.1 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. Near the right end of the arc observed in the high-frequency region, the real part Z' (Ω) at the point where -Z'' (Ω) is minimized was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula. Here, if it is not an arc, the intercept of the axis of the real part Z' (Ω) is taken as the bulk resistance R (Ω). R = ρ (L / S) σ = 1 / ρ

[0112] (Example 1) Lithium sulfide (manufactured by Idemitsu Kosan Co., Ltd.), phosphorus pentasulfide (manufactured by Thermophos Inc.), lithium chloride (manufactured by Honjo Chemical Co., Ltd.), and lithium bromide (manufactured by Honjo Chemical Co., Ltd.) were coarsely ground in a nitrogen atmosphere using a pin mill equipped with a quantitative feeder ("100UPZ (model number)", manufactured by Hosokawa Micron Corporation).

[0113] In a glove box under a nitrogen atmosphere, lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide, which are the raw materials for the solid electrolyte, were weighed in a molar ratio of 47.5:12.5:25.0:15.0, totaling 110 g. These were placed in a glass container and roughly mixed by shaking the container. The roughly mixed raw material-containing material was dispersed under a nitrogen atmosphere in a mixed solvent of 1140 mL of dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 7 mL of dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) to obtain a slurry (containing approximately 10% by mass of the raw material components). Next, the slurry was operated for 1 hour using a bead mill ("LMZ015 (model number)," manufactured by Ashizawa Finetech Co., Ltd.) to mix and grind the material, obtaining a slurry containing the ground raw materials.

[0114] Next, the slurry containing the pulverized raw materials was placed in an autoclave (capacity: 2000 mL, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200°C for 2 hours while stirring (rotation speed: 200 rpm). After heat treatment in the solvent, the slurry was transferred to a Schlenk bottle purged with nitrogen, and the solvent was removed by vacuum drying to obtain the heat-treated product.

[0115] The resulting heat-treated material was fired in an electric furnace (model number F-1404-A, manufactured by Tokyo Glass Machinery Co., Ltd.) inside a glove box under a nitrogen atmosphere. Specifically, while maintaining the temperature inside the electric furnace at 430°C, the door of the electric furnace was opened and 50g of the heat-treated material was quickly placed in a sagger (model number 999-60S, Al) ２ O ３ The sagger (manufactured by Tokyo Glass Machinery Co., Ltd.) was placed inside, the door was closed, and firing was carried out for 30 minutes. After that, the sagger was removed from the electric furnace, allowed to cool slowly, and then granulated using a sieve with a mesh size of 300 μm to obtain the powder.

[0116] The obtained powder, dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in an amount such that the powder content relative to the total amount of powder, dehydrated toluene, and dispersant was 10% by mass), and dispersant (dehydrated isobutyronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in an amount of 20% by mass relative to the powder) were subjected to wet micronization. Specifically, a slurry containing the above powder, dehydrated toluene, and dispersant was operated using a bead mill ("LMZ015 (model number)", manufactured by Ashizawa Finetech Co., Ltd.) at a peripheral speed of 8 m / s, and wet micronization was carried out until the grinding energy was 2.2 kWh / kg. The obtained slurry was transferred to a Schlenk bottle purged with nitrogen, the solvent was removed by distillation, and it was vacuum dried at room temperature until dry, and then dried at 80°C for 1 hour to obtain the powder.

[0117] When the obtained powder was subjected to powder XRD diffraction measurements using the method described above, diffraction peaks originating from the argyrodite crystal structure were confirmed at 2θ = 25.5° and 29.9°, confirming that it is a sulfide solid electrolyte having an argyrodite crystal structure. The X-ray diffraction spectrum obtained from the powder XRD diffraction measurement is shown in Figure 1.

[0118] When the deformation rate was measured using the method described above, it was found to be 2.9 GPa, confirming excellent interface formation properties. When the ionic conductivity was measured using the method described above, it was found to have a high ionic conductivity of 4.4 mS / cm.

[0119] (Examples 2-5 and Comparative Examples 1 and 2) Powder was obtained in the same manner as in Example 1, except that the grinding energy in wet pulverization and the drying temperature after wet pulverization were as shown in Table 1. When the obtained powder was measured by powder XRD diffraction using the method described above, diffraction peaks originating from the argyrodite crystal structure were confirmed at 2θ = 25.5° and 29.9° for all powders, thus confirming that it is a sulfide solid electrolyte having an argyrodite crystal structure. Furthermore, the deformation rate, capacity retention rate and its evaluation, ionic conductivity, and average particle size (D50) measured by the method described above are shown in Table 1.

[0120]

[0121] As shown in Table 1, the sulfide solid electrolyte of this embodiment exhibits excellent battery performance, as its deformation rate is within the range of 2.9 to 3.1, between 2.4 GPa and 3.2 GPa, and its capacity retention rate evaluation is good in all cases. It was also confirmed that the ionic conductivity is high, at 4.4 to 5.7 mS / cm. Furthermore, the average particle size (D50) is 0.7 to 0.8 μm, confirming that it has a particle size suitable for the solid electrolyte layer and the positive electrode.

[0122] On the other hand, the solid electrolytes of Comparative Examples 1 and 2 had deformation rates outside the range of greater than 2.4 GPa and less than 3.2 GPa, resulting in low capacity retention and confirming that they cannot be considered solid electrolytes that exhibit excellent battery performance. Although the ionic conductivity of the solid electrolyte of Comparative Example 1 was high at 6.2 mS / cm, its large deformation rate, meaning that the particles of the solid electrolyte were difficult to deform, reduced interface formation, and thus prevented the acquisition of excellent battery characteristics.

[0123] The sulfide solid electrolyte of this embodiment exhibits excellent deformability during processing and superior interface formation between solid electrolytes and between the solid electrolyte and the electrode active material, thereby resulting in excellent battery characteristics. For this reason, the sulfide solid electrolyte and electrode composite of this embodiment are suitably used in lithium-ion batteries, particularly in lithium-ion batteries used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as in automotive applications, and especially in all-solid-state batteries.

Claims

1. A sulfide solid electrolyte whose deformation rate, as measured by the method described below, is greater than 2.4 GPa and less than 3.2 GPa. (Method for measuring deformation rate) 0.15 g of the sample to be measured was placed in a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm, and a compression test was performed using a compression testing machine to compress the sample at a speed of 0.2 mm / min until the stress reached 550 MPa. A stress-strain curve was prepared using the thickness of the sample at a stress of 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate.

2. The sulfide solid electrolyte according to claim 1, wherein the average particle size (D50) based on volume is 0.1 μm or more and 10.0 μm or less.

3. The sulfide solid electrolyte according to claim 1 or 2, comprising a lithium atom, a phosphorus atom, and a sulfur atom as constituent atoms.

4. The sulfide solid electrolyte according to claim 3, further comprising a halogen atom.

5. A sulfide solid electrolyte according to any one of claims 1 to 4, comprising an organic solvent.

6. The sulfide solid electrolyte according to claim 5, wherein the organic solvent is at least one selected from aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

7. The sulfide solid electrolyte according to claim 5 or 6, wherein the content of the organic solvent is 0.1% by mass or more and 5.0% by mass or less.

8. A sulfide solid electrolyte according to any one of claims 1 to 7, wherein the ionic conductivity is 3.5 mS / cm or more.

9. A sulfide solid electrolyte according to any one of claims 1 to 8, having an argyrodite-type crystal structure.

10. An electrode mixture comprising a sulfide solid electrolyte according to any one of claims 1 to 9 and an electrode active material.

11. A lithium-ion battery comprising at least one of the sulfide solid electrolyte described in any one of claims 1 to 9 and the electrode composite material described in claim 10.

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