A mesoporous tungsten carbide nanostructure as a promising cathode catalyst decreases overpotential in Li-O2 batteries

Lithium-oxygen (Li-O-2) batteries as promising energy storage devices possess high gravimetric energy density and low emission. However, poor reversibility of electrochemical reactions at the cathode significantly affects the electrochemical properties of nonaqueous Li-O-2 batteries, and low charge-discharge efficiency also results in short cycle-life. In this work, functional air cathodes containing mesoporous tungsten carbide nanoparticles for improving the reversibility of positive reactions in Li-O-2 cells are designed. Mesoporous tungsten carbides are synthesized with mesoporous carbon nitride as the reactive template and carbon source. And mesoporous tungsten carbides in cathode materials display better electrochemical performance in Li-O-2 cells in comparison with mesoporous carbon nitride and hard carbon. Tungsten carbide-1 (WC-1) with larger specific surface area promotes reversible formation and decomposition of Li2O2 at the cathode and lower charge overpotential (about 0.93 V) at 100 mA g(-1), which allows the Li-O-2 cell to run up to 100 cycles. In addition, synergistic interaction between WC-1 and LiI could further decrease the charging overpotentials of Li-O-2 cells and improve the charge-discharge performances of the Li-O-2 cells. These results indicate that mesoporous electrocatalysts can be utilized as promising functional materials for Li-O-2 cells to decrease overpotentials.