A Thermodynamic Model for the Insertion Electrochemistry of Battery Cathodes

Abstract

Abstract The transition to Ni‐based battery cathodes enhances the energy density and reduces the cost of batteries. However, this comes at the expense of losing energy efficiency which could be a consequence of charge–discharge hysteresis. Here, a thermodynamic model is developed to understand the extent and origin of charge–discharge hysteresis in battery cathodes based on their cyclic voltammograms (CVs). This was possible by defining a Gibbs energy function that weights random ion insertion/expulsion, i. e., a solid solution pathway, against selective ion insertion/expulsion, i. e., a phase separation route. The model was verified experimentally by the CVs of CoOOH and Ni(OH)2 as solid‐solution and phase‐separating cathodes, respectively. Finally, a microscopic view reveals that phase separation and hysteresis are a consequence of large ionic radii difference of the reduced and oxidized central metal atoms.

Keywords

• Cobalt
• Hysteresis
• Ion insertion
• Nickel
• Phase transition