ELECTROLYTE SEPARATOR FOR A SOLID STATE BATTERY

A solid electrolyte separator for an electrochemical storage device is described. The solid electrolyte separator comprises: an electrolyte comprising a lithium-ion conductive compound; and a binder comprising a copolymer, wherein the lithium-ion conductive compound comprises sulfur, and the copolymer has a repeating unit comprising a carboxylic acid group or a conjugate base thereof. Also described is a masterbatch product, a method of manufacturing the solid electrolyte separator and an electrochemical storage device.