Mechanistic Understanding of CO2 Reduction and Evolution Reaction in Li-CO2 batteries

Abstract

Rechargeable Li-CO2 batteries have garnered extensive attention due to their high theoretical energy density (1876 W h Kg-1). However, their practical application is hindered by large polarization, low Coulombic efficiency, and cathode degradation. The electrochemical performance of Li-CO2 batteries is significantly affected by the thermodynamic stability and reaction kinetics of discharge products. Although advances have been achieved on cathode design and electrolyte optimization over the past decade, the reaction mechanism of CO2 cathode is not yet clear. In this review, various reaction mechanisms of CO2 reduction and evolution at the cathode interface are discussed, involving different reaction routes under mixed O2/CO2 and pure CO2 environments. Furthermore, the regulating strategies of different discharge products, including Li2CO3, Li2C2O6, and Li2C2O4, have been summarized to decrease the polarization and improve the cycle performance of Li-CO2 batteries. Finally, the challenges and perspectives are proposed from three aspects: reaction mechanisms, cathode catalysts, and electrolyte engineering, offering insights for the development of Li-CO2 batteries in the future.