Effect of TiC surface oxide overlayer on the control of Li O behavior in lithium-oxygen batteries: Implications for cathode catalyst design

TiC has attracted tremendous recent attention in lithium-oxygen batteries as a means of reducing the irreversible accumulation of by-products (i.e., Li2CO3) on the air cathode. However, TiC is intrinsically reactive to oxygen under ambient conditions, and its stability is completely determined by the surface overlayer. Herein, the catalytic effects of oxide overlayer (TiO) on adsorption mechanism, reaction path, and growth morphology of lithium oxides were comprehensively elucidated using periodic density functional theory calculations. The results indicate that the TiO overlayer on the surface of TiC(100)-TiO enhances the adsorption of lithium oxides. As compared to the disproportionation reaction, the lithiation reaction is the primary contributor to the formation of Li2O2 and Li2O on TiC(100) surface. Interestingly, the oxidized TiC(100)-TiO performs better in inhibiting the generation of undesirable Li2O. Analysis demonstrates that the discharge performance is not only related to the widely known morphology and size of product but also to the adsorption of (Li2O2)n clusters on the TiC(100) surface. The electronic structures of (Li2O2)n clusters on TiC(100)-TiC and TiC(100)-TiO surfaces have been examined to study the influence of TiO overlayer on the conductivity of accumulated products, which helps explain the innovative discovery of the experiment that TiC has excellent performance in improving the cycle ability of lithium-oxygen batteries. Our results promote the understanding of the ORR mechanism on TiC surface and provide theoretical guidance for the design of efficient and stable air cathodes for lithium-oxygen batteries.