Revealing the phase evolution and lithium diffusion in the liquid Sn-Sb electrode

Abstract Understanding the phase evolution and mass transfer kinetics at the liquid metal/molten salt interface is of significance for developing liquid metal electrodes, but it is very challenging due to the involving harsh experimental conditions of high temperature and active metals. Herein, an in-situ observation device is set up to monitor the phase evolution of liquid Sn-Sb alloy during its alloying with Li under electrochemical polarization at 550 oC, and a thermodynamic model is used to describe the growth process of solid Li3Sb layer in the Sn-Sb alloy and reveal the correlation of the phase evolution with the discharge equilibrium potential. Using the coulombic titration method, the diffusion coefficient of Li in liquid Sn-Sb alloy is calculated. The diffusion coefficient of Li in liquid Sn-Sb alloy at 550 oC decreases from 13.9 × 10-4 to 1.02 × 10-4 cm2/s when the Li concentration ranges from 0.8 to 20.5 mol.% vs. Sb. Overall, this paper reveals the phase evolution of liquid Sb-Sn electrode during the lithiation process and provides a general method to measure metal diffusion coefficients in liquid metal electrodes.