Faradaically selective membrane for liquid metal displacement batteries

Abstract

In the realm of stationary energy storage, a plurality of candidate chemistries continues to vie for acceptance, among them the Na–NiCl2 displacement battery, which has eluded widespread adoption owing to the fragility of the β″-Al2O3 membrane. Here we report a porous electronically conductive membrane, which achieves chemical selectivity by preferred faradaic reaction instead of by regulated ionic conduction. Fitted with a porous membrane of TiN, a displacement cell comprising a liquid Pb positive electrode, a liquid Li–Pb negative electrode and a molten-salt electrolyte of PbCl2 dissolved in LiCl–KCl eutectic was cycled at a current density of 150 mA cm−2 at a temperature of 410 °C and exhibited a coulombic efficiency of 92% and a round-trip energy efficiency of 71%. As an indication of industrial scalability, we show comparable performance in a cell fitted with a faradaic membrane fashioned out of porous metal. Molten-salt batteries such as Na–NiCl2 are promising candidates for grid storage, but suffer from fragility of ion-selective ceramic membranes. Here the authors report the operation of a Li–Pb||PbCl2 battery fitted with a robust TiN mesh membrane that functions by protective faradaic reaction.