Critical Role of Interfacial Charge Transfer in Reducing Charge Potential of Li–O2 Battery

Rechargeable Li–O2 batteries promise high gravimetric energy densities but suffer from a high overpotential, low energy conversion efficiency, and side reactions. A rational design of cathode materials is an important step toward addressing these issues but faces a large challenge of simultaneous optimization for many design parameters such as Li2O2 decomposition reaction kinetics and charge transfer rate in different regions. In this work, two typical materials TiC and TiN are taken as examples to study the energy profiles of Li2O2 decomposition and charge transfer energies from Li2O2 to cathode based on first-principles calculations and an electronic structure analysis. The electrochemical decomposition energies of Li2O2 on O-covered TiC and TiN surfaces make similar contributions to charge potentials (1.17–1.48 and 1.14–1.33 V), respectively. In contrast, interfacial charge transfer energies of 1.98 and 3.04 eV from Li2O2 to TiC and TiN, respectively, are significantly different. The calculated charge potentials of TiC (3.30–3.61 V) and TiN (4.33–4.52 V) are well consistent with experimentally measured values (3.5 and 4.5 V). The present study shows that interfacial charge transfer plays the key role in reducing charge overpotentials and should be considered in the calculation of charge potentials by the use of surface models.