The excellent stability of sulfide solid electrolyte with solvate ionic liquids Li(triethylene glycol dimethyl ether)bis(trifluoromethanesulfonyl)imide (Li(G3)TFSI) and their application in high-performance all-solid-state lithium-ion batteries are successfully demonstrated. The addition of a small amount of Li(G3)TFSI gives an alternative ionic pathway through normally poor solid-solid contacts, leading to a dramatic increase in capacity of LiFePO4 composite electrode.