The solid electrolyte-carbon composites were made by ball milling of the solid electrolytes with Super C45 and carbon nanofibers in the weight ratio of 0.85: 0.10: 0.05 for 2 hours at 300 rpm. This mixture was tested for both oxidation and reduction stability. Depending on the reaction, either a lithium source or drain is needed as the counter electrode with a known, constant potential. Lithium titanate (Li4Ti5O12, from altair nano) was used as a lithium drain.