A solid electrolyte for a lithium battery includes Li.sub.3+xGe.sub.xAs.sub.1-xS.sub.4 where x=0 to 0.50. The value of x can be a range of any high value and any lower value from 0 to 0.50. For example, x can be 0.25 to 0.50, and x can be 0.3 to 0.4, among many other possible ranges. In one embodiment x=0.33 such that the solid electrolyte is Li.sub.3.334Ge.sub.0.334As.sub.0.666S.sub.4. A solid electrolyte for a lithium battery can include LiAsS.sub.4 wherein 1/2 to 2/3 of the As is substituted with Ge. A lithium battery and a method for making a lithium battery are also disclosed.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 This invention was made with government support under contract No. DE-AC05-000R22725 awarded by the United States Department of Energy. The government has certain rights in this invention.