Multi-electron redox mediation for ultra-stable Li-O2 and Li-CO2 batteries

초록

Li-O2 and Li-CO2 batteries are promising high-energy-density electrochemical systems but suffer from severe overpotentials and rapid degradation due to the accumulation of insulating Li2O2 and Li2CO3 discharge products. Redox mediators (RMs) can mitigate these limitations, but securing molecules with both high activity and longterm stability remains challenging. Here, we unveil the catalytic mechanism of 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (spiroOMeTAD), a it-conjugated molecule with multiple accessible oxidation states, as a multi-electron RM for both Li-O2 and Li-CO2 batteries. Spectroelectrochemical analysis reveals distinct redox transitions corresponding to multi-electron oxidation. In O2-purged cells, spiroOMeTAD maintains stable ORR/OER voltages and extends cycle life to over 2200 h, about five-fold longer than pristine cells. Furthermore, CO2-purged cell tests indicate that spiroOMeTAD also facilitates lithium carbonate decomposition, supporting its role as a dual-function mediator. These results establish spiroOMeTAD as a highly stable and active RM capable of enabling long-life, dual-gas Li-O2 and Li-CO2 battery operation.

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