Solid electrolyte of lithium secondary battery and sulfide compound for said solid electrolyte
As a novel sulfide compound having a low elastic modulus while retaining the high ion conductivity, a sulfide compound for a solid electrolyte of a lithium secondary battery that includes a crystal phase of a cubic argyrodite type crystal structure, and is represented by the compositional formula: Li 7−x PS 6−x Cl y Br z , wherein x in the compositional formula satisfies x=y+z and 1.0<x≤1.8, and a ratio (z/y) of the molar ratio of Br to the molar ratio of Cl is from 0.1 to 10.0 is proposed.
1. A sulfide compound for a solid electrolyte of a lithium secondary battery, comprising a crystal phase of a cubic argyrodite type crystal structure, and being represented by the compositional formula: Li 7−x PS 6−x Cl y Br z , wherein x in the compositional formula satisfies x=y+z and 1.0<x≤1.8, and a ratio (z/y) of the molar ratio of Br to the molar ratio of Cl is from 0.1 to 10.0, and wherein a Young's modulus of the sulfide compound is 1 GPa to 32 GPa.
2. The sulfide compound according to claim 1 , wherein in the compositional formula, y satisfies 0.3≤y≤1.5, and z satisfies 0.3≤z≤1.5.
3. A solid electrolyte of a lithium secondary battery, comprising the sulfide compound according to claim 1 .
4. The solid electrolyte of a lithium secondary battery according to claim 3 , wherein the solid electrolyte comprises a single phase constituted by a crystal phase of a cubic argyrodite type crystal structure.
5. The solid electrolyte of a lithium secondary battery according to claim 3 , wherein the solid electrolyte has an average particle diameter (D50) of from 0.1 μm to 10 μm.
6. A method for producing the solid electrolyte according to claim 3 , comprising mixing a compound containing lithium (Li), a compound containing phosphorus (P), a compound containing sulfur (S), a chlorine-containing compound, and a bromine-containing compound, and calcining the compounds under a stream of hydrogen sulfide gas (H 2 S) at from 450 to 600° C. (material temperature).
7. A negative electrode for a lithium secondary battery, comprising the solid electrolyte according to claim 3 , and a negative electrode active material.
8. The negative electrode for a lithium secondary battery according to claim 7 , wherein the negative electrode comprises the negative electrode active material comprising carbon or silicon.
9. A positive electrode for a lithium secondary battery, comprising the solid electrolyte according to claim 3 , and a positive electrode active material.
10. A lithium secondary battery comprising the solid electrolyte according to claim 3 .
11. The negative electrode according to claim 7 , wherein the solid electrolyte comprises a single phase constituted by a crystal phase of a cubic argyrodite type crystal structure.
12. A positive electrode for a lithium secondary battery, comprising the solid electrolyte according to claim 5 , and a positive electrode active material.
13. A lithium secondary battery comprising the solid electrolyte according to claim 5 .
14. The sulfide compound for a solid electrolyte of a lithium secondary battery according to claim 1 or 2 , wherein the Young's modulus is 10 GPa to 32 GPa.
15. The sulfide compound for a solid electrolyte of a lithium secondary battery according to claim 1 or 2 , wherein the Young's modulus is 18 GPa to 32 GPa.