Superoxide Radical Capture Agent for a Stable and Efficient Li-CO2 Battery: Experimental and Density Functional Theory Studies

The lithium carbon dioxide (Li-CO2) battery is regarded as an attractive electrochemical energy storage system on account of its high energy density (∼1876 Wh kg–1) and utilization of "greenhouse gas" CO2. The main discharge product lithium carbonate (Li2CO3) is decomposed along with the inevitable formation of superoxide radicals (O2•–), and it results in irreversible side reactions, such as the deterioration of electrolytes and oxidation of the carbon cathode, which lead to unfavorable cycle life. Herein, sodium lignosulfonate (LSS) is introduced as a radical capture agent to reduce the reactivity of generated O2•– in the Li-CO2 battery. Combined with the results of adsorption energy calculation, it is found that O2•– can be preferentially adsorbed with LSS. It favors suppression of the side reactions between O2•– and the carbon cathode/electrolyte during charge. The discharge/charge voltage gap of the Li-CO2 battery is significantly reduced by 0.23 V with a long lifespan of over 200 cycles. This investigation demonstrates that the reactivity manipulation of the O2•– is essential to construct a stable and efficient Li-CO2 battery.