High-performance bismuth-gallium positive electrode for liquid metal battery

Abstract

Liquid metal battery (LMB) with three-liquid-layer configuration is a promising large-scale energy storage technology due to its facile cell fabrication, low cost and long cycle life. The solid discharge product located at electrolyte/electrode interface seriously impedes the electrode reaction kinetics and so causes large polarization voltage, which limits LMB development. In this work, a novel bismuth-gallium alloy (70:30 mol%) positive electrode is designed to address this issue. Bi provides lower operating temperature and high energy density. Ga with low melting point and low density forms Ga-rich Li–Bi-Ga melt (Ga-rich phase), which coexists in the same layer with solid discharge product Li3Bi. The liquid Ga-rich phase offers a fast lithium diffusion path for further lithiation reaction, and so enables an accelerated electrode reaction kinetics, endowing the Li||Bi–Ga system with high discharge voltage (0.67 V at 200 mA cm−2), and high energy efficiency (45% at 1200 mA cm−2), almost twice that of the Li||Bi system. Moreover, the Li||Bi–Ga system demonstrates excellent reversibility and cycle stability with a small fade rate of 0.08% per cycle after 300 charge/discharge cycles. These superior electrochemical performances make the designed Bi–Ga alloy an attractive positive electrode material of LMB for high efficiency large-scale energy storage.