Mechanistic understanding of CO₂ reduction and evolution reactions in Li-CO₂ batteries

Rechargeable Li-CO₂ batteries have attracted extensive attention owing 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 in cathode design and electrolyte optimization over the past decade, the reaction mechanism of the CO₂ cathode has not yet been clear. In this review, various reaction mechanisms of CO₂ reduction and evolution at the cathode interface are discussed, including different reaction routes under mixed O₂/CO₂ and pure CO₂ environments. Furthermore, the regulating strategies of different discharge products, including Li₂CO₃, Li₂C₂O₆, and Li₂C₂O₄, are summarized to decrease the polarization and improve the cycling performance of Li-CO₂ batteries. Finally, the challenges and perspectives are discussed from three aspects: reaction mechanisms, cathode catalysts, and electrolyte engineering, offering insights for the development of Li-CO₂ batteries in the future.