Solid electrolyte composition, sheet for all-solid state secondary battery, all-solid state secondary battery, and methods for manufacturing sheet for all-solid state secondary battery and all-solid state secondary battery

A solid electrolyte composition comprising:

• a sulfide-based inorganic solid electrolyte having a conductivity of an ion of a metal belonging to Group I or II of the periodic table;
• a salt of a metal belonging to Group I or II of the periodic table;
• and
• a multibranched polymer,
• wherein the multibranched polymer has a core portion and at least three arm portions that bond to the core portion, and the arm portion dissolves a metal ion of the salt of the metal belonging to Group I or II of the periodic table,
• wherein the arm portion includes a polymer structure containing at least one repeating unit having an alkylene oxide group, a carbonate group, an ester group, an amide group, or a silicone group, and
• wherein the repeating unit is a repeating unit represented by Formula (A),
• in the formula, R1 represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group, an alkoxy group, or an aryl group, R2 represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group, an alkoxy group, or an aryl group, and L1 represents a divalent linking group including at least one of an alkylene oxide group, a carbonate group, an ester group, an amide group, or a silicone group.