Revisiting the Role of Discharge Products in Li-CO2 Batteries

Rechargeable lithium-carbon dioxide (Li-CO2) batteries are promising devices for CO2 recycling and energy storage. However, thermodynamically stable and electrically insulating discharge products (DPs) (e.g., Li2CO3) deposited at cathodes require rigorous conditions for completed decomposition, resulting in large recharge polarization and poor battery reversibility. Although progress has been achieved in cathode design and electrolyte optimization, the significance of DPs is generally underestimated. Therefore, it is necessary to revisit the role of DPs in Li-CO2 batteries to boost overall battery performance. Here, a critical and systematic review of DPs in Li-CO2 batteries is reported for the first time. Fundamentals of reactions for formation and decomposition of DPs are appraised; impacts on battery performance including overpotential, capacity, and stability are demonstrated; and the necessity of discharge product management is highlighted. Practical in situ/operando technologies are assessed to characterize reaction intermediates and the corresponding DPs for mechanism investigation. Additionally, achievable control measures to boost the decomposition of DPs are evidenced to provide battery design principles and improve the battery performance. Findings from this work will deepen the understanding of electrochemistry of Li-CO2 batteries and promote practical applications.