 Ceramic solid electrolytes (CSEs) of the NASICON family (e.g., Li1−xAxM2−x(PO4)3 with A ∈ [Al, Sc, Y] and M ∈ [Ti, Ge]) has been studied.Compatible with water at alkaline pH and having a large electrochemical window (see Figs.3,4), their low Li+ ion conductivity near room temperature (< 0.005 S/cm, >85 Ω cm2) makes them unsuitable for automotive and stationary energy storage applications that demand low cost (i.e., operating current densities over 100 mA/cm2).