Ultra-Long Cycle Life in Lithium-Carbon Dioxide Batteries via Synergistic Solution Pathway Regulation and Redox-Mediating Effect of Mo/Co Species.

During the CO2 reduction reaction (CO2RR) process in Li-CO2 batteries, molybdenum carbide (Mo2C) catalysts have attracted wide attention owing to the 2-electron lithium oxalate (Li2C2O4) route, while the formation of lithium carbonate (Li2CO3) is often inevitable due to the disproportionation of C2O4 2-. In this study, benefit from the introduction of Co to Mon+C catalyst, a rapid diffusion of Li2C2O4 has been realized with a solution-mediated dissolution process, leading to heterostructure products with mixed growth of Li2CO3 and C. Furthermore, in this Co-loaded Mon+C catalyst, the Mo+2/+3C serves as a solid redox mediator and facilitate electron transfer from Mo+2/+3C to the CO2 molecule through the formation of C─O─Mo bond, then they achieved an ultrahigh discharge voltage of 3.1 V in the CO2RR process. Through the regulation of the CO2 - and Li2CO3 absorbing of Mo2C, the synchronous decomposition of both discharge products, Li2CO3 and C is achieved, avoiding the irreversible accumulation of carbon that leads to capacity decay. This enables Li-CO2 batteries to achieve an ultra-long cycle life exceeding 4800 h. This design provides new insights for the future optimization of charge/discharge pathways, especially the synchronous decomposition of two solid-phase products Li2CO3 and C in Li-CO2 batteries.