O2-boosted Li-CO2 battery performance via microscopic regulation

[Display omitted] •The link between product growth, reaction mechanism, and battery performance is built.•The tendency of discharge performance and reaction kinetics are mismatched.•Li2CO3 evolves from aggregated spheres to loosely structured flakes.•O2– is dominant rather than other intermediate competitors.•O2 activates the solution pathway and transforms 2D into 3D of Li2CO3 growth mode. The development of Li-CO2 batteries is limited by poor discharge capacity and low output plateau. O2 can boost Li-CO2 battery performance via altering reaction pathways, while the role of solid product is missing. Herein, we innovatively unravel discharge process from a microscopic viewpoint and build a link among product growth, reaction mechanism, and battery performance. At an oxygen content range of 0–100%, the highest discharge capacity of up to 6345 mAh g-1 is achieved at 50% oxygen. Surprisingly, the tendency of discharge performance and reaction kinetics are mismatched. Morphology exploration confirms Li2CO3 evolution from aggregated spheres to flocculent shapes, and then to loosely-structured flakes. Through replacing the rapid combination of Li+, the powerful O2– is dominant during discharge rather than other intermediate competitors, simulating a disproportionation reaction to expedite CO2 conversion. In situ evolution of Li2O2 demonstrates O2-boosted CO2 reduction involving synchronous reactions of Li2O2 to Li2CO3. Surprisingly, O2 excites the CO2 reduction pathway in vertical spatial dimension of Li2CO3 growth. Verified by further limited-capacity results, the Li2CO3 growth theory from 2D to 3D thoroughly illustrates the achievement of high-performance O2-boosted Li-CO2 batteries. This work breaks previous knowledge of O2-boosted Li-CO2 electrochemistry and provides direction to advance next-generation Li-CO2 batteries.