Improved synthesis enables assessment of the electrochemical window of monocarborate solid state electrolytes.

We synthesized Li and Na monocarborate salts with minimal protic impurities and reassessed their electrochemical windows. Na salts display higher efficiency for metal deposition/stripping and are more oxidatively stable than Li salts. This strong cation effect is rationalized in terms of differences in charge density between Li + and Na + cations.