Effect of Microstructure on the Cycling Behavior of Li–In Alloy Anodes for Solid-State Batteries

Indium–lithium alloys operating in the two-phase region of indium metal and the InLi intermetallic are the counter and reference electrodes of choice in two-electrode solid-state batteries. At high current densities on both charge and discharge, they offer low polarization, good accessible capacity, and good cycle life. By synthesizing a phase pure InLi intermetallic and measuring its diffusion and mechanical properties, it is clear that the electrochemical performance is attributable to measured fast diffusion kinetics in the InLi intermetallic, D_Li^298K = 5.5 × 10^–7 cm² s^–1. The indium metal phase is essentially ion-blocking, so the performance is tied to the microstructure, which evolves with cycling. A simple two-layer microstructure is proposed, based on the fundamental understanding established, which maximizes performance. Despite the limitations of indium-based alloys in commercial applications, the lessons learned can be extended to other fast-conducting lithium intermetallics.