Calcium-antimony alloys as electrodes for liquid metal batteries

The performance of a calcium-antimony (Ca-Sb) alloy serving as the positive electrode in a Ca∥Sb liquid metal battery was investigated in an electrochemical cell, Ca(in Bi) | LiCl-NaCl-CaCl₂ | Ca(in Sb). The equilibrium potential of the Ca-Sb electrode was found to lie on the interval, 1.2-0.95 V versus Ca, in good agreement with electromotive force (emf) measurements in the literature. During both alloying and dealloying of Ca at the Sb electrode, the charge transfer and mass transport at the interface are facile enough that the electrode potential varies linearly from 0.95 to 0.75 V vs Ca(s) as current density varies from 50 to 500 mA cm^-2. The discharge capacity of the Ca∥Sb cells increases as the operating temperature increases due to the higher solubility and diffusivity of Ca in Sb. The cell was successfully cycled with high coulombic efficiency (∼100%) and small fade rate (<0.01% cycle^-1). These data combined with the favorable costs of these metals and salts make the Ca∥Sb liquid metal battery attractive for grid-scale energy storage.