The role of transition metal interfaces on the electronic transport in lithium–air batteries

Low electronic conduction is expected to be a main limiting factor in the performance of reversible lithium–air, Li–O2, batteries. Here, we apply density functional theory and non-equilibrium Green's function calculations to determine the electronic transport through lithium peroxide, Li2O2, formed at the cathode during battery discharge. We find the transport to depend on the orientation and lattice matching of the insulator–metal interface in the presence of Au and Pt catalysts. Bulk lithium vacancies are found to be available and mobile under battery charging conditions, and found to pin the Fermi level at the top of the anti bonding peroxide π*(2px) and π*(2py) levels in the Li2O2 valence band. Under an applied bias, this can result in a reduced transmission, since the anti bonding σ*(2pz) level in the Li2O2 conduction band is found to couple strongly to the metal substrate and create localized interface states with poor coupling to the Li2O2 bulk states. These observations provide a possible explanation for the higher overpotential observed for charging than discharge.

The calculated electronic conduction through transition metal–Li2O2 interfaces in Li–air batteries as a function of the applied bias voltage.Figure optionsDownload high-quality image (95 K)Download as PowerPoint slideResearch highlights▶ DFT calculations of the electronic conduction at Li–air electrode interfaces. ▶ The conduction is sensitive to the lattice matching of the metal–insulator interface. ▶ Lithium vacancies may lower the electronic transport during charging. ▶ Limited electronic conduction can contribute to the asymmetry of the overpotentials.