Factors Contributing to Path Hysteresis of Displacement and Conversion Reactions in Li Ion Batteries

Abstract

We investigate the thermodynamic and kinetic attributes of electrode materials that are necessary to suppress path hysteresis during displacement and conversion reactions in Li ion batteries. We focus on compounds in the Li–Cu–Sb ternary composition space, as the displacement reaction between Li1+ϵCu1+δSb and Li3Sb can be cycled reversibly. A first-principles analysis of migration barriers indicates that Cu, while not as mobile as Li in the discharged phase (Li3Sb), nevertheless should exhibit mobilities similar to that of Li in common intercalation compounds. A calculation of phase stability in the ternary Li–Cu–Sb system predicts that the intermediate phases along the reversible charge/discharge path are stable in a large Cu chemical potential window. This ensures that intermediate phases are not bypassed upon Li extraction even when large thermodynamic driving forces are needed to reinsert Cu into the discharged electrode. Our study suggests that the suppression of path hysteresis during displacement reactions requires (i) a high mobility of the displaced metal and (ii) the thermodynamic stability of intermediate phases along the reversible path in a wide metal chemical potential window. Even in the absence of path hysteresis, displacement and conversion reactions suffer from polarization needed to set up thermodynamic driving forces for metal extrusion and reinsertion. This polarization can be estimated with a Clausius–Clapeyron analysis.