Stabilized solid garnet electrolyte and methods thereof

A method of making a solid garnet electrolyte membrane for use in an energy storage device, the method comprising:

• contacting opposite faces of the solid garnet electrolyte membrane with a protic acid, the contacting transforms the solid garnet electrolyte from an air sensitive, lithium-containing garnet to form a protonated garnet surface composition at the opposite faces while a bulk of the solid garnet electrolyte membrane comprises a bulk solid garnet composition,
• wherein the method further comprises forming the solid garnet electrolyte membrane before the contacting.