Mechanistic understanding of CO 2 reduction and evolution reactions in Li-CO 2 batteries.

Rechargeable Li-CO 2 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-CO 2 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 CO 2 cathode has not yet been clear. In this review, various reaction mechanisms of CO 2 reduction and evolution at the cathode interface are discussed, including different reaction routes under mixed O 2 /CO 2 and pure CO 2 environments. Furthermore, the regulating strategies of different discharge products, including Li 2 CO 3 , Li 2 C 2 O 6 , and Li 2 C 2 O 4 , are summarized to decrease the polarization and improve the cycling performance of Li-CO 2 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-CO 2 batteries in the future.