Solid Electrolyte of Lithium Secondary Battery and Sulfide Compound for Said Solid Electrolyte

Abstract

As a novel sulfide compound having a low elastic modulus while retaining 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.

1 . A solid electrolyte for a lithium secondary battery, comprising a sulfide compound, the sulfide compound 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 the sulfide compound having an average particle diameter (D50) of from 0.1 μm to 10 μm, where the average particle diameter (D50) is obtained by the laser diffractive scattering particle size distribution measurement method. 
     
     
         2 . The solid electrolyte for a lithium secondary battery 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 . The solid electrolyte for a lithium secondary battery according to  claim 1 , wherein the solid electrolyte comprises a single phase constituted by a crystal phase of a cubic argyrodite type crystal structure. 
     
     
         4 . The solid electrolyte for a lithium secondary battery according to  claim 1 , wherein the sulfide compound has an average particle diameter (D50) of from 0.3 μm to 7 μm, where the average particle diameter (D50) is obtained by the laser diffractive scattering particle size distribution measurement method. 
     
     
         5 . The solid electrolyte for a lithium secondary battery according to  claim 1 , wherein the content of the sulfide compound is 90% by mass or more. 
     
     
         6 . A method for producing the solid electrolyte according to  claim 1 , 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 a material temperature from 450 to 600° C. 
     
     
         7 . A negative electrode for a lithium secondary battery, comprising the solid electrolyte according to  claim 1 , and a negative electrode active material. 
     
     
         8 . The negative electrode for a lithium secondary battery according to  claim 7 , wherein the negative electrode comprises a negative electrode active material comprising carbon or silicon. 
     
     
         9 . A positive electrode for a lithium secondary battery, comprising the solid electrolyte according to  claim 1 , and a positive electrode active material. 
     
     
         10 . A lithium secondary battery comprising the solid electrolyte according to  claim 1 .