JP7113513B2 - Inorganic sulfide and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inorganic sulfide and a method for producing the same.

Lithium-ion secondary batteries are attracting attention as high-energy-density batteries, and their applications are expanding not only in mobile devices (small consumer applications) but also in stationary applications such as vehicles and social infrastructure. One of the requirements for these large-sized lithium ion secondary batteries is an improvement in safety. Ordinary lithium-ion secondary batteries (hereafter abbreviated as liquid systems) use an organic electrolyte, and a flammable low-boiling-point solvent (carbonic acid dimethyl, diethyl carbonate, ethyl methyl carbonate, etc.), there is concern that batteries may ignite or emit smoke. Although corporate efforts are being made to improve safety, it would be great if we could change the components, that is, change the electrolytic solution to a less flammable solid electrolyte, and dramatically improve safety in terms of material composition. , the cost can be reduced for safety consideration, and it is very useful in industry.

There are two types of solid electrolytes: polymer-based and inorganic-based. Currently, polymer-based electrolytes have low ionic conductivity at room temperature or below, and sufficient battery operation similar to that of liquid-based electrolytes cannot be expected unless the temperature is above 60°C. On the other hand, inorganic materials include oxides and sulfides. Although oxides have high ionic conductivity, they have low formability and are brittle, making it difficult to construct batteries only by pressing.

By the way, sulfide solid electrolytes composed of lithium sulfide (Li ₂ S), phosphorus sulfide (P ₂ S ₅ ), germanium sulfide (GeS ₂ ), etc. have high ionic conductivity approaching that of organic electrolytes even at room temperature. However, it is one of the most promising solid electrolytes due to its low grain boundary resistance and high moldability compared to oxides.

An example is a Li ₂ SP ₂ S ₅ based solid electrolyte. Unlike the general sulfide solid electrolyte synthesis methods such as the sealed tube method and the hydrogen sulfide sintering method, this electrolyte is easily prepared by mechanical milling (hereinafter referred to as MM) at room temperature using a milling device. It is the only sulfide solid electrolyte that can be synthesized. It is known that the MM method yields a solid electrolyte composed of sulfide glass that does not contain a crystalline phase and has excellent formability. However, the solid electrolyte obtained in this way has the drawback of being inferior in rate characteristics due to its low ionic conductivity. We have obtained a solid electrolyte called ceramics. Although this glass-ceramic-based solid electrolyte is excellent in rate characteristics, there is a problem that it is inferior in cycle characteristics unless a glass solid electrolyte obtained only by the MM method is mixed (see, for example, Patent Document 1). That is, the glass-ceramic solid electrolyte cannot be used alone. For this reason, there is a demand for solid electrolytes that are excellent in formability (in particular, have a low Young's modulus) and excellent in ionic conductivity. If such a solid electrolyte can be provided, it is promising not only as a solid electrolyte and a binder material for electrolyte layers, but also as a binder material for electrodes.

By the way, in the xLi2S-(1-x) _{P2S5 -} based solid electrolyte, the _xLi2S- ( ₁ -x) _{P2S5 -} based solid electrolyte must have an x value of 0.75 or more, otherwise it will cause the generation of toxic hydrogen sulfide. P ₂ S ₇ groups, P ₂ S ₆ groups, etc. are generated. In this composition, the ionic conductivity is not sufficient when synthesized only by the MM method. On the other hand, it has been reported that when the x value is 0.80 or more, the raw material Li ₂ S remains when synthesized only by the MM method, and hydrogen sulfide is likely to be generated (for example, see Non-Patent Document 1). It cannot be handled and the work becomes complicated. On the other hand, in the case of the xLi ₂ S-(1-x)GeS ₂ -based solid electrolyte containing Li ₂ S and GeS ₂ , it is necessary to make only GeS ₄ ^4- ions by setting x to 0.667 or more.

Furthermore, Li2S _- GeS2 _- P2S5 _- based solid electrolytes containing _GeS2 in addition to _Li2S and _P2S5 , and _{Li2S - GeS2 -} based solid electrolytes containing _Li2S and _GeS2 are Li ₂ S and GeS ₂ and, if necessary, P ₂ S ₅ are enclosed in a quartz glass tube, and the final product is obtained by a sealed tube method in which heat treatment is performed at a high temperature (eg, 700 ° C.) (see, for example, Non-Patent Document 2 and 3). However, according to this manufacturing method, a solid electrolyte having a large Young's modulus and excellent moldability cannot be obtained. In general, when the sealed tube method is used, mass synthesis is difficult, so there is a need to establish a method for producing a solid electrolyte that has high lithium ion conductivity, is easy to manufacture batteries, and can be mass synthesized. . Moreover, if such a solid electrolyte can be produced, it will be possible to improve moldability by forming a composite with an oxide-based or phosphate-based solid electrolyte having low moldability.

Japanese Patent Application Laid-Open No. 2008-103281

A. Hayashi et al., Electrochemistry Communications, 5, 111-114 (2003). R. Kanno et al, Journal of Electrochemical Society, 148 A742-A746 (2001). M. Murayama et al, Solid State Ionics, 154, 789-794 (2002).

The present invention has been made in view of the current state of the prior art described above, and the main object thereof is to provide a solid electrolyte that is excellent in moldability (particularly having a low Young's modulus) and excellent in ionic conductivity. and

The present inventors have made intensive studies to achieve the above-described object. As a result, inorganic sulfides (especially solid electrolytes) having a specific composition and having a crystal phase and a glass phase coexist have excellent formability (especially low Young's modulus) and ion conductivity. found to be superior to The inventors also found that the inorganic sulfide can be obtained by milling a predetermined raw material powder at a high rotational speed and then milling it at a low rotational speed. Based on such knowledge, the present inventors have further studied and completed the present invention. That is, the present invention includes the following configurations.
Section 1. General formula (1):
xLi2S _- yGeS2-( ₁ -xy) _{P2S5 (} 1)
[In the formula, x and y represent 0.667≦x≦0.860, 0≦y≦0.333, and 0.667≦x+y≦1. ]
Inorganic sulfide in which a crystal phase and a glass phase coexist.
Section 2. Item _2. The inorganic sulfide according to Item ₁ , wherein the crystal phase is at least one crystal phase _selected from the group _consisting of _Li3PS4 , _{Li7PS6 , Li4GeS4} and _Li10GeP2S12 .
Item 3. General formula (2):
dLi2S _- eMS2 _- fLiX-(1-def) _P2S5 ( ₂ )
[In the formula, X represents at least one selected from the group consisting of Cl, Br and I. M represents at least one selected from the group consisting of Ge, Sn and Ti. d, e and f are 0.600≦d≦0.860, 0≦e≦0.333, 0<f≦0.300, and 0.600≦d+e+f≦1. ]
Inorganic sulfide in which a crystal phase and a glass phase coexist.
Section 4. The crystal phase is at least one selected from the group consisting of β-Li ₃ PS ₄ , cubic ajarodite, Li ₁₀ MP ₂ S ₁₂ (M is Ge or Sn), and Li ₄ PS ₄ I Item 4. The inorganic sulfide according to Item 3, which is in a crystalline phase.
Item 5. Item 5. The inorganic sulfide according to any one of Items 1 to 4, which does not contain a crystal phase consisting of Li ₂ S.
Item 6. Item 6. The inorganic sulfide according to any one of Items 1 to 5, which has a Young's modulus of 3.0 GPa or less.
Item 7. Item 7. The inorganic sulfide according to any one of Items 1 to 6, which has an ionic conductivity of 1.00×10 ⁻⁴ S·cm ⁻¹ or more.
Item 8. A method for producing an inorganic sulfide according to any one of Items 1 to 7,
A production method comprising a step of subjecting a raw material powder containing Li ₂ S to milling at a high rotation speed and then to milling at a low rotation speed.
Item 9. Item 9. The manufacturing method according to Item 8, wherein the rotation speed in the high rotation speed milling treatment is 800 rpm or more, and the rotation speed in the low rotation speed milling treatment is 600 rpm or less.
Item 10. Item 10. The production method according to Item 8 or 9, wherein the raw material powder further contains at _least one selected from the group consisting of _GeS2 , _SnS2 , _TiS2 , LiX and _P2S5 .
Item 11. A solid electrolyte for a lithium ion secondary battery, comprising the inorganic sulfide according to any one of items 1 to 7.
Item 12. A binder material for an electrolyte layer of a lithium ion secondary battery, comprising the inorganic sulfide according to any one of Items 1 to 7.
Item 13. A binder material for lithium ion secondary battery electrodes, comprising the inorganic sulfide according to any one of items 1 to 7.
Item 14. An electrolyte layer containing the solid electrolyte for a lithium ion secondary battery according to Item 11 or a binder material for an electrolyte layer of a lithium ion secondary battery according to Item 12, and an electrode for a lithium ion secondary battery according to Item 13. and at least one electrode containing a binder material.

ADVANTAGE OF THE INVENTION According to this invention, the solid electrolyte which is excellent in moldability (it has especially low Young's modulus) and is excellent in ion conductivity can be provided by a simple method.

1 shows an X-ray diffraction pattern of a sample obtained in Example 1. FIG. For reference, the peaks of the known 70Li ₂ S-30P ₂ S ₅ phase (glass phase) and Li ₃ PS ₄ phase (crystalline phase) are also shown. 1 shows the measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 1 that was calcined at 500°C. 1 shows X-ray diffraction patterns of samples obtained in Examples 2 and 3. FIG. For reference, the peaks of the known 70Li ₂ S-30P ₂ S ₅ phase (glass phase), Li ₃ PS ₄ phase (crystalline phase) and Li ₇ PS ₆ phase (crystalline phase) are also shown. 1 shows X-ray diffraction patterns of samples obtained in Examples 4 and 5. FIG. For reference, the peaks of the known 70Li ₂ S-30P ₂ S ₅ phase (glass phase) and Li ₇ PS ₆ phase (crystalline phase) are also shown. 4 shows the X-ray diffraction pattern of the sample obtained in Example 6. FIG. For reference, the peaks of the known 70Li ₂ S-30P ₂ S ₅ phase (glass phase), Li ₃ PS ₄ phase (crystalline phase) and Li ₁₀ GeP ₂ S ₁₂ phase (crystalline phase; LGPS phase) are also shown. Fig. 2 shows the measured (+) and calculated (solid line) X-ray diffraction patterns of the sample obtained in Example 6 which was calcined at 500°C. 1 shows X-ray diffraction patterns of samples obtained in Examples 7 and 8. FIG. As a reference, the known _{70Li2S - 30P2S5} phase (glass phase), _Li3PS4 phase (crystal phase), _{Li10GeP2S12 phase (} crystal phase; _LGPS phase), _{Li4GeS4 (} crystal phase) and Li ₆ PS ₇ phase (crystalline phase) are also shown. 1 shows an X-ray diffraction pattern of a sample obtained in Example 9. FIG. 1 shows the X-ray diffraction pattern of the sample obtained in Example 10. FIG. Numerical values in the figure indicate indices corresponding to the peak positions of the corresponding crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 11, the glass phase, and the constituent crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 12, the glass phase, and the constituent crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 13, the glass phase, and the constituent crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 14, the glass phase, and the constituent crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 15, the glass phase, and the constituent crystal phases. 1 shows the X-ray diffraction patterns of the sample obtained in Example 16, the glass phase, and the constituent crystal phases. 1 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid-state lithium-ion secondary battery using the sample obtained in Example 1. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material. 4 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid lithium ion secondary battery using the sample obtained in Example 5. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material. 4 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid lithium ion secondary battery using the sample obtained in Example 13. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material. 4 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid lithium ion secondary battery using the sample obtained in Example 15. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material. 4 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid lithium ion secondary battery using the sample obtained in Example 16. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material. 4 shows the results of charge-discharge characteristics evaluation at 30° C. of an all-solid-state lithium-ion secondary battery using the sample obtained in Example 6. FIG. The charge/discharge capacity is standardized by the amount of positive electrode active material.

In this specification, when a numerical range is expressed as "A to B", it means A or more and B or less.

1. inorganic sulfide (1)
The inorganic sulfide (1) of the present invention has the general formula (1):
xLi2S _- yGeS2-( ₁ -xy) _{P2S5 (} 1)
[In the formula, x and y represent 0.667≦x≦0.860, 0≦y≦0.333, and 0.667≦x+y≦1. ]
and the crystal phase and the glass phase coexist.

In the inorganic sulfide (1) of the present invention, P and Ge are present as PS ₄ ^3- and GeS ₄ ^4- ions with respect to Li ions acting as charge carriers, and glass phase forming or crystal lattice forming ions work as

In the inorganic sulfide (1) of the present invention, in the general formula (1), the Li ₂ S content x is 0.667 to 0.860, and the GeS ₂ content y is 0 to 0.333. is important. This can be summed up in the following two points. (1) Since ionic conductivity is proportional to the product of charge carrier concentration and mobility, increasing the Li ₂ S concentration can increase the charge carrier (Li ion) concentration. Since all Li ₂ S cannot be introduced into the glass structure, Li ₂ S remains as an impurity in the inorganic sulfide (there is a crystal phase composed of Li ₂ S), and it becomes a hydrogen sulfide (H ₂ S) generation source. Become. For this reason, x is 0.750 to 0.860, preferably 0.760 to 0.850, more preferably 0.770 to 0.830 in one preferred embodiment (embodiment containing P ₂ S ₅ ), and in another preferred embodiment (embodiment containing P ₂ S ₅ ) 0.667 to 0.800, preferably 0.680 to 0.770, more preferably 0.700 to 0.750. (2) On the other hand, y, which is the content of _GeS2 , can increase the ionic conductivity and widen the potential window on the high potential side as necessary, but if y exceeds 0.333, a large amount of expensive Ge is used. cost increase due to the need for For this reason, y is 0 to 0.200, preferably 0.050 to 0.20, more preferably 0.080 to 0.150 in one preferred embodiment (embodiment containing P ₂ S ₅ ), and in another preferred embodiment (embodiment containing P ₂ S ₅ ) In the embodiment not containing it), it is 0 to 0.333, preferably 0.050 to 0.30, more preferably 0.080 to 0.250. Such x and y are numerical values satisfying 0.667≦x+y≦1.

The crystal phase of the inorganic sulfide (1) of the present invention is not particularly limited, but preferably does not include a crystal phase composed of raw material powders such as Li ₂ S, GeS ₂ and P ₂ S ₅ . In particular, by not including a crystal phase composed of Li ₂ S, generation of hydrogen sulfide can be suppressed, so an inorganic sulfide that is easy to handle even in a low-humidity environment can be obtained.

In addition, in the inorganic sulfide (1) of the present invention, the abundance ratio of each crystal phase can be quantitatively analyzed, for example, by analyzing the X-ray diffraction pattern by the Rietveld method. The abundance ratio of each crystal phase can be changed by, for example, the composition of the raw material powder, the milling conditions in the manufacturing method described later, the heat treatment conditions after the milling treatment, and the like. In the inorganic sulfide (1) of the present invention, although each crystal phase exhibits good lithium ion conductivity, the total content of Li ₃ PS ₄ or Li ₇ PS ₆ is 40% by mass or more (40 to 100 mass %) is preferably included.

The crystal phase of the inorganic sulfide ( ₁ ) of the present invention includes at least _{one selected} from the group _consisting of _{Li3PS4 , Li7PS6} , _Li4GeS4 and _Li10GeP2S12 . Crystalline phases are preferred. Specifically, in general formula (1), when 0.750 ≤ x ≤ 0.775 under the condition of y = 0, a crystal phase composed of Li ₃ PS ₄ (β-type orthorhombic crystal of space group Pnma phase) is easily formed, and when 0.755 ≤ x ≤ 0.860 in general formula (1), a crystal phase composed of Li ₇ PS ₆ (especially a space group composed of Li ₇ PS ₆

cubic ajarodite crystal phase) is likely to be formed. On the other hand, when y is other than 0 in general formula (1) (0 < y ≤ 0.333, especially 0.050 ≤ y ≤ 0.200), the crystal phase composed of Li ₁₀ GeP ₂ S ₁₂ (especially Li ₁₀ GeP ₂ S ₁₂ tetragonal crystal phase of space group P42/nmc) and Li ₄ GeS ₄ (orthorhombic crystal phase of space group Pnma) when y is large (e.g. 0.200<y≦0.333, e.g. y=0.333). easy to form.

By having such a crystal phase, the inorganic sulfide (1) of the present invention can have high ion conductivity (especially lithium ion conductivity). Specifically, the inorganic sulfide (1) of the present invention has an ionic conductivity of 1.00×10 ⁻⁴ S·cm ⁻¹ or more, particularly 1.50×10 ⁻⁴ to 5.00×10 ⁻⁴ S·cm ⁻¹ . It is possible. The ionic conductivity is measured by the AC impedance method after tableting the obtained powder.

On the other hand, the glass phase possessed by the inorganic sulfide (1) of the present invention means a phase having a broad peak similar to the glass phase generated in a conventionally known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. . By having such a glass phase, the inorganic sulfide (1) of the present invention can be made into a soft material with improved moldability and a low Young's modulus. Specifically, the Young's modulus of the inorganic sulfide (1) of the present invention can be 3.0 GPa or less, particularly 0.2 to 2.8 GPa. Young's modulus is measured using a microcompression tester.

In the inorganic sulfide (1) of the present invention, the abundance ratio between the crystal phase and the glass phase can be quantitatively analyzed by solid-state ³¹ P-NMR described in JP-A-2014-093262. . The abundance ratio of the crystal phase and the glass phase can be changed by, for example, milling conditions in the manufacturing method described below, heat treatment conditions after the milling treatment, and the like. In the inorganic sulfide (1) of the present invention, the existence ratio of the crystal phase and the glass phase is preferably 10:90 to 90:10 (mass ratio) from the viewpoint of the balance between moldability and ionic conductivity. 20:80 to 80:20 (mass ratio) is more preferable.

On the other hand, the inorganic sulfide (1) of the present invention only needs to contain the above crystal phase and glass phase, and may contain other impurity phases within a range that does not seriously affect the charge/discharge characteristics. Such impurity phases include elemental sulfur, phosphorus sulfide, germanium sulfide, and lithium sulfide. However, in the present invention, the crystalline phase improves the ion conductivity and the glass phase improves the formability and lowers the Young's modulus, so the content of the impurity phase is preferably low. From this point of view, when the inorganic sulfide (1) of the present invention has an impurity phase, the impurity phase is usually 0.1 to 10% by mass with the total amount of the inorganic sulfide (1) of the present invention being 100% by mass. (especially 0.2 to 5% by mass) is preferred.

The shape of the inorganic sulfide (1) of the present invention that satisfies the above conditions is not particularly limited, and any shape such as powder, granules, pellets, and fibers can be used. In addition, according to the manufacturing method described later, powdery inorganic sulfide is likely to be generated.

The inorganic sulfide (1) of the present invention, which satisfies the above conditions, has excellent moldability (in particular, it has a low Young's modulus) and excellent ion conductivity. Therefore, it is useful as a solid electrolyte constituting an electrolyte layer for lithium ion secondary batteries, and is also useful as a binder material for solid electrolytes (especially solid electrolytes with poor moldability) constituting electrolyte layers for lithium ion secondary batteries. Useful. It is also useful as a binder material for electrodes of lithium ion secondary batteries.

2. Inorganic sulfide (2)
The inorganic sulfide (2) of the present invention has the general formula (2):
dLi2S _- eMS2 _- fLiX-(1-def) _P2S5 ( ₂ )
[In the formula, X represents at least one selected from the group consisting of Cl, Br and I. M represents at least one selected from the group consisting of Ge, Sn and Ti. d, e and f are 0.600≦d≦0.860, 0≦e≦0.333, 0<f≦0.300, and 0.600≦d+e+f≦1. ]
and the crystal phase and the glass phase coexist.

In general formula (2), X is at least one selected from the group consisting of Cl, Br and I, preferably Cl and Br from the viewpoint of charge/discharge characteristics.

In general formula (2), M is at least one selected from the group consisting of Ge, Sn and Ti, and it is preferable to use a mixture of Ge and Ti from the viewpoint of charge/discharge characteristics.

In the inorganic sulfide (2) of the present invention, P, Ge, Sn and Ti exist as PS ₄ ^3- and MS ₄ ^4- ions and X as X ^- ions for Li ions acting as charge carriers. Both act as glass-phase-forming or crystal-lattice-forming ions.

In the inorganic sulfide (2) of the present invention, in the general formula (2), the Li ₂ S content d is 0.600 to 0.860, the MS ₂ content e is 0 to 0.333, and LiX It is important that the content of f is between 0 and 0.300. This can be summed up in the following two points. (1) Since ionic conductivity is proportional to the product of charge carrier concentration and mobility, increasing the _Li2S and LiX concentrations can increase the charge carrier (Li ion) concentration, while d is 0.860. , when f exceeds 0.300, not all Li ₂ S and LiX can be introduced into the glass structure, so Li ₂ S and LiX remain as impurities in the inorganic sulfide (crystal phases composed of Li ₂ S and LiX exist). ) and become a source of hydrogen sulfide (H ₂ S). For this reason, d is 0.750 to 0.860, preferably 0.760 to 0.850, more preferably 0.770 to 0.830 in one preferred embodiment (embodiment containing P ₂ S ₅ ), and in another preferred embodiment (embodiment containing P ₂ S ₅ ) 0.667 to 0.800, preferably 0.680 to 0.770, more preferably 0.700 to 0.750. Also, f is 0.050 to 0.300, preferably 0.100 to 0.250 in a preferred embodiment (an embodiment containing P ₂ S ₅ ). ( ₂ ) On the other hand, e, which is the content of MS2, can increase the ionic conductivity and widen the potential window on the high potential side as necessary, but when e exceeds 0.333, M = Ge , a large amount of expensive Ge is required, leading to an increase in cost. For this reason, e is 0 to 0.200, preferably 0.050 to 0.20, more preferably 0.080 to 0.150 in one preferred embodiment (embodiment containing P ₂ S ₅ ), and in another preferred embodiment (embodiment containing P ₂ S ₅ ) In the embodiment not including), it is 0 to 0.333, preferably 0.050 to 0.30, more preferably 0.080 to 0.250. Such d, e, and f are numerical values satisfying 0.600≦d+e+f≦1.

The crystal phase of the inorganic sulfide ( ₂ ) of the present invention is not particularly limited, but preferably does not include a crystal phase composed of raw material powders such as _Li2S , _LiX , MS2 and _P2S5 . . In particular, by not including a crystal phase composed of Li ₂ S, generation of hydrogen sulfide can be suppressed, so an inorganic sulfide that is easy to handle even in a low-humidity environment can be obtained.

In addition, in the inorganic sulfide (2) of the present invention, the abundance ratio of each crystal phase can be quantitatively analyzed by, for example, analysis of the X-ray diffraction pattern by the Rietveld method. The abundance ratio of each crystal phase can be changed by, for example, the composition of the raw material powder, the milling conditions in the manufacturing method described later, the heat treatment conditions after the milling treatment, and the like. In the inorganic sulfide (1) of the present invention, although each crystal phase exhibits good lithium ion conductivity, the β-Li ₃ PS ₄ or ajarodite phase (Li ₇ PS ₆ or Li ₆ PS ₅ X) is preferably contained in a total amount of 40% by mass or more (40 to 100% by mass).

The crystal phase of the inorganic sulfide (2) of the present invention is selected from the group consisting of β-Li ₃ PS ₄ , cubic ajarodite, and Li ₁₀ MP ₂ S ₁₂ and Li ₄ PS ₄ I. At least one crystalline phase is preferred. Specifically, in general formula (2), when 0.750 ≤ d ≤ 0.775 under the condition of e = 0, the crystal phase composed of β-Li ₃ PS ₄ (orthorhombic crystal phase of space group Pnma ) is likely to be formed, and when 0.755 ≤ d ≤ 0.860 in general formula (2), the crystal phase composed of Li ₇ PS ₆ (especially the space group composed of Li ₇ PS ₆

cubic ajarodite crystal phase) is likely to be formed. When X is an iodide ion, a crystal phase composed of Li ₄ PS ₄ I (space group P4/nmm) is also likely to be formed. On the other hand, when e is other than 0 in general formula (2) (0 < e ≤ 0.333, especially 0.050 ≤ e ≤ 0.200), the crystal phase composed of Li ₁₀ MP ₂ S ₁₂ (especially Li ₁₀ MP ₂ S ₁₂ A tetragonal crystal phase of space group P42/nmc) is also easily formed. When d is 0.222 and e is close to 0, the cubic ajarodite phase composed of Li ₆ PS ₅ X is likely to be formed.

By having such a crystal phase, the inorganic sulfide (2) of the present invention can have high ion conductivity (especially lithium ion conductivity). Specifically, the inorganic sulfide (2) of the present invention has an ionic conductivity of 1.00×10 ⁻⁴ S·cm ⁻¹ or more, particularly 1.50×10 ⁻⁴ to 5.00×10 ⁻⁴ S·cm ⁻¹ . It is possible. The ionic conductivity is measured by the AC impedance method after tableting the obtained powder.

On the other hand, the glass phase possessed by the inorganic sulfide (2) of the present invention means a phase having a broad peak similar to the glass phase generated in a conventionally known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. . By having such a glass phase, the inorganic sulfide (2) of the present invention can improve moldability as a soft material and lower Young's modulus. Specifically, the Young's modulus of the inorganic sulfide (2) of the present invention can be 3.0 GPa or less, particularly 0.2 to 2.8 GPa. Young's modulus is measured using a microcompression tester.

In the inorganic sulfide (2) of the present invention, the abundance ratio between the crystal phase and the glass phase can be quantitatively analyzed by solid-state ³¹ P-NMR described in JP-A-2014-093262. . The abundance ratio of the crystal phase and the glass phase can be changed by, for example, milling conditions in the manufacturing method described below, heat treatment conditions after the milling treatment, and the like. In the inorganic sulfide (2) of the present invention, the existence ratio of the crystal phase and the glass phase is preferably 10:90 to 90:10 (mass ratio) from the viewpoint of the balance between moldability and ionic conductivity. 20:80 to 80:20 (mass ratio) is more preferable.

On the other hand, the inorganic sulfide (2) of the present invention only needs to contain the above crystal phase and glass phase, and may contain other impurity phases within a range that does not seriously affect the charge/discharge characteristics. Such impurity phases include elemental sulfur, phosphorus sulfide, germanium sulfide, titanium sulfide, tin sulfide, lithium sulfide, lithium chloride, lithium bromide, and lithium iodide. However, in the present invention, the crystalline phase improves the ion conductivity and the glass phase improves the formability and lowers the Young's modulus, so the content of the impurity phase is preferably low. From this point of view, when the inorganic sulfide (2) of the present invention has an impurity phase, the impurity phase is usually 0.1 to 10% by mass with the total amount of the inorganic sulfide (2) of the present invention being 100% by mass. (especially 0.2 to 5% by mass) is preferred.

The shape of the inorganic sulfide (2) of the present invention that satisfies the above conditions is not particularly limited, and any shape such as powder, granules, pellets, and fibers can be employed. In addition, according to the manufacturing method described later, powdery inorganic sulfide is likely to be generated.

The inorganic sulfide (2) of the present invention that satisfies the above conditions is excellent in moldability (in particular, it has a low Young's modulus) and is excellent in ionic conductivity. Therefore, it is useful as a solid electrolyte constituting an electrolyte layer for lithium ion secondary batteries, and is also useful as a binder material for solid electrolytes (especially solid electrolytes with poor moldability) constituting electrolyte layers for lithium ion secondary batteries. Useful. It is also useful as a binder material for electrodes of lithium ion secondary batteries.

3. Method for Producing Inorganic Sulfide The inorganic sulfide of the present invention is produced by, for example, milling a raw material powder containing Li ₂ S at a high rotational speed and then milling the powder at a low rotational speed. method.

The raw material powder can be appropriately selected according to the composition of the inorganic sulfide to be finally obtained. For example, when trying to obtain a _{Li2SP2S5 -} based solid electrolyte, _Li2S and _P2S5 can be used as raw material powders, and a _{Li2S - MS2 ( GeS2} , etc.)-based solid electrolyte Li ₂ S and MS ₂ (GeS ₂ etc.) can be used as raw material powders to obtain a Li ₂ S-MS ₂ (GeS ₂ etc.)-P ₂ S ₅ system solid electrolyte. Li ₂ S, MS _{2 ( GeS 2} etc.) and _{P 2} S ₅ can be used as raw material powders when _Li2S , _LiX and _P2S5 can be used as raw material powders.

In the present invention, for example in the case of the Li ₂ SP ₂ S ₅ system, high Li ₂ S content x or d (x≧0.667, especially x≧0.750; d≧0.600, especially d≧0.750) in the resulting inorganic sulfide ), it is necessary to perform high-rotation milling first, and then perform low-rotation milling after this high-rotation milling. By performing such a treatment, it is possible to obtain an inorganic sulfide of high purity and high ionic conductivity that does not contain Li ₂ S as an impurity (does not contain a crystal phase composed of Li ₂ S). It should be noted that a crystal phase composed of Li ₂ S is included as an impurity in the inorganic sulfide only by milling at a high rotational speed. In addition, the Li ₂ S content of the inorganic sulfide cannot be increased only by milling at a low rotational speed, and a crystalline phase composed of Li ₂ S is included as an impurity.

The rotation speed in the high rotation speed milling treatment is 800 rpm or more from the viewpoint of further suppressing the generation of the crystal phase composed of Li ₂ S while increasing the Li ₂ S content x or d in the inorganic sulfide obtained. Preferably, 900-2000 rpm is more preferred. Moreover, the treatment time in this case is not particularly limited, and is preferably 30 minutes to 3 hours, more preferably 40 minutes to 2 hours. Moreover, the treatment temperature is not particularly limited, and the treatment can be carried out at 0 to 50° C. (for example, room temperature). Such a high rotation speed milling process can be performed by, for example, a vibration mill or the like.

The rotation speed in the low rotation speed milling treatment is preferably 600 rpm or less, more preferably 300 to 550 rpm, from the viewpoint of further suppressing the generation of the crystal phase composed of Li ₂ S. Moreover, the treatment time at this time is not particularly limited, and is preferably 10 to 100 hours, more preferably 20 to 80 hours. Moreover, the treatment temperature is not particularly limited, and the treatment can be carried out at 0 to 50° C. (for example, room temperature). Such a low-rotation-speed milling process can be performed, for example, by a planetary ball mill or the like.

As a specific manufacturing method, first, for example, milling at high rotation speed in a closed container (glove box, dry room, open dry chamber, etc.) under an ultra-low humidity (dew point of -60 ° C or less) environment. The raw material powder is filled in the container of the device to be processed. The container that can be used at this time is not particularly limited, and materials such as agate, alumina, and zirconia can be used. At this time, the amount of raw material to be filled is not particularly limited, and can be about 1 to 100 g. It is preferable to add pulverizing media to this raw material powder, if necessary, take it out of the glove box after sealing, and set it in a milling device. After milling, the product may strongly adhere to the container, so if necessary, reintroduce the container into an ultra-low humidity (dew point of -60 ° C or less) environment (glove box, etc.) and remove the product from the container. After scraping off the wall of the wall, the same process can be performed again.

After that, the container is opened, for example, in an ultra-low humidity (dew point of -60°C or lower) environment (glove box, etc.), the powder is transferred to a container for a low-rotation milling apparatus, and milled at a low rotation speed. After treatment, the product should be taken out in an ultra-low humidity (dew point of -60°C or lower) environment (glove box, etc.), sealed in a sealed container, and subjected to various evaluations such as X-ray diffraction measurement and ion conductivity measurement. can be done.

In this way, the inorganic sulfide of the present invention is obtained, after which heat treatment can be applied as necessary. As a result, it is possible to increase the crystalline phase and further increase the ionic conductivity, so that it is possible to adjust the existence ratio of the crystalline phase and the glass phase according to the required properties. In this case, the heating temperature is not particularly limited, preferably 100 to 500°C, more preferably 200 to 400°C. The heating time is also not particularly limited, preferably 0.5 to 100 hours, more preferably 1 to 50 hours.

4. Lithium Ion Secondary Battery A lithium ion secondary battery using the inorganic sulfide of the present invention can be produced by a known method.

For example, when the inorganic sulfide of the present invention is used as a binder material for a positive electrode, a known lithium-manganese-based composite oxide or the like is used as a positive electrode material, and the inorganic sulfide of the present invention is used as a binder material to obtain a known The positive electrode can be manufactured by the technique. In other words, the inorganic sulfide of the present invention can be used as a substitute material for PTFE or the like, which is usually used as a binder material, to produce a positive electrode. When the inorganic sulfide of the present invention is not used as a binder material for the positive electrode, conventionally known positive electrodes can be employed.

Further, when the inorganic sulfide of the present invention is used as a binder material for a negative electrode, metallic lithium known as a negative electrode material, carbon-based materials (activated carbon, graphite, etc.), silicon, silicon oxide, Si—SiO-based materials, lithium Using a titanium oxide or the like and using the inorganic sulfide of the present invention as a binder material, a negative electrode can be produced by a known method. That is, the negative electrode can be produced using the inorganic sulfide of the present invention as a substitute material for PTFE or the like, which is usually used as a binder material. When the inorganic sulfide of the present invention is not used as a binder material for the negative electrode, conventionally known negative electrodes can be employed.

Further, when the inorganic sulfide of the present invention is used as the solid electrolyte of the electrolyte layer, the inorganic sulfide of the present invention can be formed into a layer by a conventional method and used as the electrolyte layer. When the inorganic sulfide of the present invention is used as the binder material for the electrolyte layer, the solid electrolyte is used as the solid electrolyte, the inorganic sulfide of the present invention is used as the binder material, and the electrolyte layer is produced by a known method. can be done. That is, the inorganic sulfide of the present invention can be used as a substitute material for PTFE or the like, which is usually used as a binder material, to produce an electrolyte layer.

In addition, other known battery components can be used to assemble the lithium ion secondary battery according to conventional methods. In the present invention, the term "lithium ion secondary battery" is a concept that also includes a "lithium secondary battery" using metallic lithium as a negative electrode material.

Examples and comparative examples are shown below to further clarify the features of the present invention, but the present invention is not limited to the following examples.

[Example 1]
Li ₂ S and P ₂ S ₅ were weighed in a glove box (GB) at a molar ratio of 75:25 and then mixed in a mortar. The total amount was adjusted to 2 g. This was filled in an agate container for a vibration mill (rotation speed 1000 rpm), filled with disk-shaped grinding media, sealed, taken out of the GB, and set in the vibration mill. After pulverizing with a vibration mill for 1 hour, the powder was scraped off from the walls of the container and media in the GB, and pulverized again for 1 hour. After pulverization, the mixture was transferred to a container for a low-speed planetary ball mill in the GB, sealed, taken out of the GB, and pulverized for 30 hours with a low-speed planetary ball mill (500 rpm). After pulverization, the powder was recovered from the container in the GB and subjected to X-ray diffraction evaluation (XRD evaluation) and the like.

FIG. 1 shows the X-ray diffraction pattern of the obtained sample.

From the obtained X-ray diffraction pattern and its Rietveld analysis result, the sample obtained in Example 1 is said to have high lithium ion conductivity (non-patent literature, Homma et al., Solid State Ionics 182 53-58 (2011).) High-temperature phase β-Li ₃ PS ₄ crystal phase (orthorhombic system, space group Pnma, a = 12.624(6) Å, b = 8.056(3) Å, c = 6.041(3) Å ) and a glass-ceramic powder having a broad peak similar to the glass phase generated in a known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. Ion conductivity was measured to be 4.6×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature with a maximum load of 1000 mN under an Ar atmosphere and a low dew point (-55 ° C) using a microcompression tester, and the Poisson's ratio = 0.5. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

In a previous report (A. Hayashi et al., Electrochemistry Communications 5 111-114 (2003).), samples of the same composition were synthesized only by milling at a low rotational speed (370 rpm). Only a glassy phase without crystals was obtained, and a crystalline phase was obtained for the first time after heat treatment at 230°C. The crystal phase is assigned to the monoclinic crystal phase thiolysicon III shown in another document (R. Kanno et al., J. Electrochem. Soc., 148 A742-A746 (2001)), and the present invention It can be seen that the crystal phase is different from that of

FIG. 2 shows the X-ray diffraction pattern of the sample obtained in Example 1 which was heated (baked) at 500° C. in vacuum. As is clear from FIG. 2, the obtained X-ray diffraction pattern is orthorhombic β-Li ₃ PS ₄ (space group Pnma, a= 12.8924(8) Å, b= 8.1490(5) Å, c= 6.1441 Only the unit cell of (4) Å) could be fitted, and the glassy phase changed to the crystalline phase. The ionic conductivity of this baked product was 5.33×10 ⁻⁴ S·cm. It is clear from this that the obtained sample of Example 1 can also be utilized as a raw material for a baked product having high ionic conductivity.

[Example 2]
After weighing Li ₂ S and P ₂ S ₅ in GB so that the molar ratio was 76:24, synthesis was carried out under the same conditions as in Example 1. FIG. 3 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis results, the sample obtained in Example 2 is β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 12.857 (3) Å, b = 8.127(2)Å, c= 6.1068(15)Å) and the high temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.915(5) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It was found to be a glass-ceramic powder consisting of _In the crystal phase, the mass ratio of _Li3PS4 and _Li7PS6 was _88:12 . Ion conductivity was measured to be 4.79×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 3]
After Li ₂ S and P ₂ S ₅ were weighed in the GB so that the molar ratio was 77:23, synthesis was carried out under the same conditions as in Example 1. FIG. 3 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis results, the sample obtained in Example 3 is β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 12.692 (5) Å, b = 8.185(3)Å, c= 6.120(2)Å) and high temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.899(2) Å) and a glassy phase with a broad peak similar to the glassy phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It was found to be a glass-ceramic powder consisting of _In the crystal phase, the mass ratio of _Li3PS4 and _Li7PS6 was _83:17 . Ion conductivity was measured to be 4.17×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 4]
After weighing Li ₂ S and P ₂ S ₅ in GB so that the molar ratio was 78:22, synthesis was carried out under the same conditions as in Example 1. FIG. 4 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis result, the sample obtained in Example 4 has a high-temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.985(5) Å) and a glassy phase with a broad peak similar to the glassy phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It was found to be a glass-ceramic powder of Ion conductivity was measured to be 3.9×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 5]
After weighing Li ₂ S and P ₂ S ₅ in GB so that the molar ratio was 80:20, synthesis was carried out under the same conditions as in Example 1. FIG. 4 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis result, the sample obtained in Example 5 has a high-temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.9024(17) Å) and a glassy phase with a broad peak similar to the glassy phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It was found to be a glass-ceramic powder of Ion conductivity was measured to be 4.5×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. This result differs from the previous report (A. Hayashi et al., Electrochemistry Communications 5 111-114 (2003).). In the report, samples _were synthesized with the same composition only by milling at a low rotation speed (370 rpm). However, Li ₂ S also remained. If Li ₂ S remains, it tends to generate H ₂ S gas, which is a weak point in that it cannot be handled in a dry room. Since the inorganic sulfide of the present invention does not contain _Li2S , it is clear that a Li2S _- free solid electrolyte was obtained. In addition, Young's modulus was measured at room temperature under an Ar atmosphere with a low dew point (-55°C) under a low dew point (-55°C) under a maximum load of 1000 mN using a microcompression tester. 2) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 6]
After weighing Li ₂ S, GeS ₂ and P ₂ S ₅ in the GB so that the molar ratio was 5: 1: 1 (71.4: 14.3: 14.3), synthesis was performed under the same conditions as in Example 1. rice field. FIG. 5 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis results, the sample obtained in Example 6 has β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 13.068 (6) Å, b = 7.934(4)Å, c = 6.057(3)Å) and _{Li10GeP2S12 ( LGPS} ; tetragonal, space group P42/nmc, a = 8.537(9)Å, c = 12.877(18 )Å) peak and a glass phase having a broad peak similar to the glass phase produced in a known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. One thing became clear. _In the crystal phase, the mass _ratio of _Li3PS4 and _Li10GeP2S12 was _73:27 . Ion conductivity was measured to be 5.1×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature under an Ar atmosphere with a low dew point (-55°C) under a low dew point (-55°C) under a maximum load of 1000 mN using a microcompression tester. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

FIG. 6 shows the X-ray diffraction pattern of the sample obtained in Example 6 which was heated (baked) at 500° C. in vacuum. As is clear from FIG. 6, the obtained X-ray diffraction pattern is that of tetragonal _{Li10GeP2S12 ( LGPS} ; tetragonal system, space group P42/nmc, a=8.6731(3) Å, c=12.5906( 5) Only the unit cell of Å) could be fitted, and the glassy phase changed to the crystalline phase. The ionic conductivity of this baked product was 1.5×10 ⁻³ S·cm. It is clear from this that the obtained sample of Example 6 can also be utilized as a raw material for a fired product having high ionic conductivity.

[Example 7]
After weighing Li ₂ S, GeS ₂ and P ₂ S ₅ in the GB so that the molar ratio was 6: 1: 1 (75.0: 12.5: 12.5), synthesis was performed under the same conditions as in Example 1. rice field. FIG. 7 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis results, the sample obtained in Example 7 has β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 13.171 (4) Å, b = 7.979(3)Å, c = 6.1095(19)Å) and _{Li10GeP2S12 ( LGPS} ; tetragonal, space group P42/nmc, a = 9.138(7)Å, c = 13.250(15 )Å) and a high-temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.9678(9) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It turned out to be a glass-ceramic powder. _In the crystal phase, the mass _ratio of _{Li3PS4 , Li10GeP2S12} and _Li7PS6 was _51:25:24 . Ion conductivity was measured to be 7.4×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 8]
After weighing Li ₂ S, GeS ₂ and P ₂ S ₅ in the GB so that the molar ratio is 7: 1: 1 (77.8: 11.1: 11.1), the same conditions as in Example 1 (but at low rotation One additional milling for 30 hours in a planetary ball mill (500 rpm) was performed.). FIG. 7 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis results, the sample obtained in Example 8 has β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 13.212 (9) Å, b = 7.991( ₁₀ )Å, c = 6.123(6)Å) and _Li10GeP2S12 ( _LGPS ; tetragonal, space group P42/nmc, a = 9.159(13)Å, c = 12.77(2 )Å) and a high-temperature phase Li ₇ PS ₆ (cubic system (cubic ajarodite), space group

, a = 9.9765(7) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It turned out to be a glass-ceramic powder. _In the crystal phase, the mass _ratio of _{Li3PS4 , Li10GeP2S12} and _Li7PS6 was _39:16:45 . Ion conductivity was measured to be 9.46×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature with a maximum load of 1000 mN under an Ar atmosphere and a low dew point (-55 ° C) using a microcompression tester, and the Poisson's ratio = 0.5. 2) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 9]
After weighing Li ₂ S and GeS ₂ in the GB so that the molar ratio was 2:1 (66.7:33.3), synthesis was carried out under the same conditions as in Example 1. FIG. 8 shows the X-ray diffraction pattern of the obtained sample. From the obtained X-ray diffraction pattern and its Rietveld analysis result, the sample obtained in Example 9 is Li ₄ GeS ₄ (orthorhombic system, space group Pnma, a = 13.928 (6) Å, b = 7.816 (4) Å, c = 6.192 (3) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It was found to be a two-phase glass-ceramic powder. Ion conductivity was measured to be 1.1×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 10]
After weighing Li ₂ S, LiI and P ₂ S ₅ in a molar ratio of 2: 3: 1 (0.333: 0.500: 0.167, Li ₇ P ₂ S ₈ I composition) in a glove box (GB), Mixed. The total amount was adjusted to 2 g. This was filled in an agate container for a vibration mill (rotation speed 1000 rpm), filled with disk-shaped grinding media, sealed, taken out of the GB, and set in the vibration mill. Grinding was carried out for 0.5 hours in a vibrating mill four times with breaks of about 10 minutes, for a total of 2 hours. After pulverization, the mixture was transferred to a container for a low-speed planetary ball mill in the GB, sealed, taken out of the GB, and pulverized for 30 hours with a low-speed planetary ball mill (500 rpm). After pulverization, the powder was recovered from the container in the GB and subjected to X-ray diffraction evaluation (XRD evaluation) and the like. FIG. 9 shows the X-ray diffraction pattern of the obtained sample. From FIG. 9, the tetragonal Li ₄ PS ₄ I crystal phase (space group P4/nmm, lattice constant a = 8.4761 (10) Å, c = 5.9602 (9) Å can be indexed and has the same space group , Li ₄ PS ₄ I solid electrolyte (SJ Sedlmaier et al., Chem. Mater., 29 1830-1835 (2017). Literature values a=8.48284(12) Å, c=5.93013(11) Å).This crystal In addition to the phase, a glass phase with a broad peak similar to the glass phase generated in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte coexisted at the position indicated by the arrow in the figure. When the temperature was measured, it was 5.8×10 ^-4 S cm ^-1 , and it is clear that it has sufficient characteristics as a solid electrolyte. Young's modulus was measured at room temperature under a maximum load of 1000 mN at (-55°C), and calculated as Poisson's ratio = 0.5. GPa), and it is clear that it is a solid electrolyte with excellent moldability.

[Example 11]
_Li2S , _GeS2 , _TiS2 and P2S5 _were prepared in a glove box (GB) at a _Li2S :MS2 _{( GeS2} and _TiS2 ): _P2S5 molar ratio of ₅ : ₁ :1 ( 0.714: 0.143: 0.143, the molar ratio of GeS ₂ and TiS ₂ in MS ₂ was 9: 1, the composition formula: Li ₁₀ Ge _0.9 Ti _0.1 P ₂ S ₁₂ ), and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 10 shows the X-ray diffraction pattern of the obtained sample. From FIG. 10, the peak of β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a= 13.235(3) Å, b= 7.9758(19) Å, c= 6.1047(14) Å) and Li ₁₀ GeP A crystal phase having a peak of ₂ S ₁₂ (LGPS; tetragonal system, space group P42/nmc, a=8.712(7) Å, c=12.701(13) Å) was confirmed. The mass ratio of the β-Li ₃ PS4 phase and the _LGPS phase was 69:31. In addition to this crystal phase, a glass phase with a broad peak similar to the glass phase generated in a known 70Li ₂ S _- 30P ₂ S5 solid electrolyte coexisted at the position indicated by the arrow in the figure. Ion conductivity was measured to be 4.0×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature with a maximum load of 1000 mN under an Ar atmosphere and a low dew point (-55 ° C) using a microcompression tester, and the Poisson's ratio was calculated as 0.5. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 12]
Li ₂ S, SnS ₂ and P ₂ S ₅ were weighed in a glove box (GB) at a molar ratio of 5:1:1 (0.714:0.143:0.143) and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 11 shows the X-ray diffraction pattern of the obtained sample. From FIG. 11, the peak of β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a = 13.381(5) Å, b = 8.009(3) Å, c = 6.1192(2) Å) and Li ₁₀ SnP ₂ S ₁₂ (LSPS; tetragonal system, space group P42/nmc, a=8.736(2) Å, c=12.828(4) Å) was confirmed. The mass ratio of β-Li ₃ PS ₄ phase and LSPS phase was 69:31. In addition to this crystal phase, a glass phase with a broad peak similar to the glass phase generated in a known 70Li ₂ S _- 30P ₂ S5 solid electrolyte coexisted at the position indicated by the arrow in the figure. Ion conductivity was measured to be 4.0×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature under an Ar atmosphere with a low dew point (-55°C) under a low dew point (-55°C) under a maximum load of 1000 mN using a microcompression tester. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 13]
Li ₂ S, SnS ₂ and P ₂ S ₅ were weighed in a glove box (GB) at a molar ratio of 6:1:1 (0.750:0.125:0.125) and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 12 shows the X-ray diffraction pattern of the obtained sample. From FIG. 12, the peak of β-Li ₃ PS ₄ (orthorhombic system, space group Pnma, a= 13.577(6) Å, b= 7.991(3) Å, c= 6.221(2) Å) and Li ₁₀ SnP ₂ S ₁₂ (LSPS; tetragonal system, space group P42/nmc, a = 8.487(12) Å, c = 13.51(3) Å) and cubic ajarodite Li ₇ PS ₆ (cubic system, space group group

, a=9.9940(17)) was confirmed. The mass ratio of β-Li ₃ PS4 phase to _LSPS phase and cubic ajarodite phase was 57:23:20, respectively. In addition to this crystal phase, a glass phase with a broad peak similar to the glass phase generated in a known 70Li ₂ S _- 30P ₂ S5 solid electrolyte coexisted at the position indicated by the arrow in the figure. Ion conductivity was measured to be 4.7×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature with a maximum load of 1000 mN under an Ar atmosphere and a low dew point (-55 ° C) using a microcompression tester, and the Poisson's ratio was calculated as 0.5. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 14]
Li ₂ S, P ₂ S ₅ and LiI were weighed in a glove box (GB) at a molar ratio of 6:1:2 (0.667:0.111:0.222) and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 13 shows the X-ray diffraction pattern of the obtained sample. From FIG. 13, Li ₆ PS ₅ I (cubic ajarodite), space group

, a = 10.0705(8) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It turned out to be a glass-ceramic powder. Ion conductivity was measured to be 1.5×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. The obtained sample was a soft sample similar to Example 1 and had excellent moldability.

[Example 15]
Li ₂ S, P ₂ S ₅ and LiCl were weighed in a glove box (GB) at a molar ratio of 6:1:2 (0.667:0.111:0.222) and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 14 shows the X-ray diffraction pattern of the obtained sample. From FIG. 14, Li ₆ PS ₅ Cl (cubic arjarodite), space group

, a = 9.8466(9) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It turned out to be a glass-ceramic powder. Ion conductivity was measured to be 10.8×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature under an Ar atmosphere with a low dew point (-55°C) under a low dew point (-55°C) under a maximum load of 1000 mN using a microcompression tester. 1) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

[Example 16]
Li ₂ S, P ₂ S ₅ and LiBr were weighed in a glove box (GB) at a molar ratio of 6:1:2 (0.667:0.111:0.222) and mixed in a mortar. The total amount was adjusted to 2 g. Thereafter, samples were prepared in the same manner as in Example 10. FIG. 15 shows the X-ray diffraction pattern of the obtained sample. From FIG. 15, Li ₆ PS ₅ Br (cubic ajarodite), space group

, a = 9.9389(8) Å) and a glass phase with a broad peak similar to the glass phase produced in the known 70Li ₂ S-30P ₂ S ₅ solid electrolyte. It turned out to be a glass-ceramic powder. Ion conductivity was measured to be 4.8×10 ⁻⁴ S·cm ⁻¹ , and it is clear that the material has sufficient properties as a solid electrolyte. In addition, Young's modulus was measured at room temperature with a maximum load of 1000 mN under an Ar atmosphere and a low dew point (-55 ° C) using a micro compression tester, and the Poisson's ratio = 0.5. 8) GPa, which is close to polytetrafluoroethylene (0.5 GPa), which is a binder material, and is clearly a solid electrolyte with excellent moldability.

Test Example 1: Battery production (1)
In order to confirm whether the obtained inorganic sulfide powder (solid electrolyte powder) can actually operate as a lithium-ion secondary battery, a battery was fabricated in GB. The solid electrolyte powder obtained in Examples 1 to 6 and the positive electrode active material (NMC: LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) were mixed at a mass ratio of 3:7 to obtain a positive electrode mixture. On the other hand, the negative electrode mixture was prepared by mixing the solid electrolyte powders obtained in Examples 1 to 6 with the negative electrode active material (LTO: Li ₄ Ti ₅ O ₁₂ ) at a mass ratio of 4:6. First, a metal jig was put in one side of the metal tube, and after the solid electrolyte powders of Examples 1 to 6 were put in, a metal jig was put in the other side and pressed to form an electrolyte layer. After the positive electrode mixture was put into one side of the press and pressed to produce a positive electrode, the negative electrode mixture was put into the opposite side and pressed to produce a negative electrode. The three-layer integrated tablet is removed from the mold, put into a PET (polyethylene terephthalate) tube with a metal jig on one side of the battery lower part, put a metal jig on the other side and press, then place the battery upper part, An all-solid lithium ion secondary battery was fabricated by fixing with a thumbscrew and tightening the upper portion with a wrench.

FIG. 16 shows the charging/discharging characteristics evaluation results at 30° C. of the all-solid lithium ion secondary battery using the sample obtained in Example 1. As shown in FIG. It works without problems as a battery, and the inorganic sulfide (solid electrolyte) of the present invention is used as a positive electrode binder material for lithium ion secondary batteries, a negative electrode binder material for lithium ion secondary batteries, and a solid electrolyte for lithium ion secondary batteries. It is clear that we can.

Next, FIG. 17 shows the charge-discharge characteristic evaluation results at 30° C. of the all-solid lithium ion secondary battery using the sample obtained in Example 5. As shown in FIG. It works without problems as a battery, and the inorganic sulfide (solid electrolyte) of the present invention is used as a positive electrode binder material for lithium ion secondary batteries, a negative electrode binder material for lithium ion secondary batteries, and a solid electrolyte for lithium ion secondary batteries. It is clear that we can.

Test Example 2: Battery production (2)
In Test Example 1 above, a battery was fabricated in the same manner as described above, except that NCA (LiNi _0.85 Co _0.10 Al _0.05 O ₂ ) was used as the positive electrode active material and In was used as the negative electrode.

FIG. 18 shows charge-discharge characteristics when the sample obtained in Example 13 is used for the positive electrode mixture and the solid electrolyte for the electrolyte. From FIG. 18, the sample obtained in Example 13 operated without problems as a lithium ion secondary battery, and the inorganic sulfide (solid electrolyte) of the present invention was used as a positive electrode binder material for a lithium ion secondary battery and a lithium ion secondary battery. It is clear that it can be used as a negative electrode binder material for batteries and a solid electrolyte for lithium ion secondary batteries.

FIG. 19 shows charge-discharge characteristics when the sample obtained in Example 15 is used for the positive electrode mixture and the solid electrolyte for the electrolyte. From FIG. 19, the sample obtained in Example 15 operates as a lithium ion secondary battery without problems, and the inorganic sulfide (solid electrolyte) of the present invention is a positive electrode binder material for a lithium ion secondary battery and a lithium ion secondary battery. It is clear that it can be used as a negative electrode binder material for batteries and a solid electrolyte for lithium ion secondary batteries.

FIG. 20 shows charge-discharge characteristics when the sample obtained in Example 16 is used for the positive electrode mixture and the solid electrolyte for the electrolyte. From FIG. 20, the sample obtained in Example 16 operated without problems as a lithium ion secondary battery, and the inorganic sulfide (solid electrolyte) of the present invention was used as a positive electrode binder material for a lithium ion secondary battery and a lithium ion secondary battery. It is clear that it can be used as a negative electrode binder material for batteries and a solid electrolyte for lithium ion secondary batteries.

FIG. 21 shows charge-discharge characteristics when the sample obtained in Example 6 is used for the positive electrode mixture and the solid electrolyte for the electrolyte. From FIG. 21, the sample obtained in Example 6 operates as a lithium ion secondary battery without any problem, and the inorganic sulfide (solid electrolyte) of the present invention is a positive electrode binder material for a lithium ion secondary battery and a lithium ion secondary battery. It is clear that it can be used as a negative electrode binder material for batteries and a solid electrolyte for lithium ion secondary batteries.

From the above, the inorganic sulfide (solid electrolyte) of the present invention can be used as a positive electrode binder material for lithium ion secondary batteries, a negative electrode binder material for lithium ion secondary batteries, a solid electrolyte for lithium ion secondary batteries, a lithium ion secondary It is clear that it can be utilized as an electrolyte layer binder material for batteries.

The inorganic sulfide of the present invention can be used, for example, as a solid electrolyte for large lithium-ion secondary batteries such as those for vehicle use and stationary use where safety is required, a binder material for solid electrolytes, a binder material for solid battery electrodes, and the like. It is possible.

Claims (11)

General formula (1):
xLi2S _- yGeS2-( ₁ -xy) _{P2S5 (} 1)
[In the formula, x and y represent 0.667≦x≦0.860, 0≦y≦0.333, and 0.667≦x+y≦1. ]
wherein a crystal phase and a glass phase _coexist , and the crystal phase is at least one _{selected from the group} consisting of _Li3PS4 , Li7PS6 _, Li4GeS4 _{and Li10GeP2S12} is a seed crystalline phase, and
under the condition of y=0, the crystalline phase is Li3PS4 for x ≦ 0.775 and _Li7PS6 for _0.755 ≦ _{x ;}
Inorganic sulfide , wherein under the condition that y is non-zero, the crystalline _{phase is Li4GeS4 and /} or Li10GeP2S12 . General formula (2):
dLi2S _- eMS2 _- fLiX-(1-def) _P2S5 ( ₂ )
[In the formula, X represents at least one selected from the group consisting of Cl, Br and I. M represents at least one selected from the group consisting of Ge, Sn and Ti. d, e and f are 0.600≦d≦0.860, 0≦e≦0.333, 0<f≦0.300, and 0.600≦d+e+f≦1. ]
and a crystal phase and a glass phase coexist, and the crystal phase includes β-Li ₃ PS ₄ , cubic ajarodite, Li ₁₀ MP ₂ S ₁₂ (M is Ge or Sn), and an inorganic sulfide which is at least one crystal phase selected from the group consisting _of Li4PS4I _{. 3.} The inorganic sulfide according to claim 1 , which does not contain a crystalline phase consisting of Li2S. The inorganic sulfide according to any one of claims 1 to 3 , which has a Young's modulus of 3.0 GPa or less. The inorganic sulfide according to any one of claims 1 to 4 , which has an ionic conductivity of 1.00 × 10 ^-4 S·cm ^-1 or more. A method for producing an inorganic sulfide according to any one of claims 1 to 5 ,
A production method comprising a step of milling a raw material powder containing Li ₂ S with a vibration mill at a rotation speed of 800 rpm or more, and then milling with a planetary ball mill at a rotation speed of 600 rpm or less . 7. The manufacturing method according to claim 6 , wherein said raw material powder further contains at _least one selected from the group consisting of _GeS2 , _SnS2 , _TiS2 , LiX and _P2S5 . A solid electrolyte for a lithium ion secondary battery, comprising the inorganic sulfide according to any one of claims 1 to 5 . A binder material for an electrolyte layer of a lithium ion secondary battery, comprising the inorganic sulfide according to any one of claims 1 to 5 . A binder material for an electrode of a lithium ion secondary battery, comprising the inorganic sulfide according to any one of claims 1 to 5 . The solid electrolyte for a lithium ion secondary battery according to claim 8 or the electrolyte layer containing the binder material for the electrolyte layer of the lithium ion secondary battery according to claim 9 , and the lithium ion secondary battery according to claim 10 . and an electrode containing a binder material for the electrode of the lithium ion secondary battery.

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