A first-principle investigation of the Li diffusion mechanism in the super-ionic conductor lithium orthothioborate Li 3 BS 3 structure. F. Bianchini ∗ , H. Fjellv˚ ag, P. Vajeeston Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, Norway, Box 1033 Blindern, N-0315 Oslo, Norway Abstract The research of superior ionic conductors is a very active field. Identify- ing such materials would allow for the design of improved solid-state Li-ion batteries, solving the safety hazard posed by the liquid electrolytes and im- proving the electrochemical stability and thus the energy efficiency. In this work, we study lithium orthothioborate Li 3 BS 3 by means of fist-principle atomistic calculations based on Density Functional Theory. This material is a very promising super ion conductor candidate, as it is a layered compound based on a deformed body-centred structure of the anion sublattice. The minimum energy paths for the diffusion of the lithium ions are identified, and the activation energy are evaluated using the nudged elastic band method. A very fast 1D diffusive channel is found, contained in a Li-rich layer, with an activation energy below 0.1 eV. The other paths connecting these layers and extending the mobility of lithium to the whole structure are found to have activation barriers of 0.25 eV or lower. This bottleneck corresponds to a diffusive coefficients of the order of 10 −6 cm 2 s −1 , thus characterising lithium orthothioborate as an excellent ionic conductor. Keywords: Li-ion battery, ionic conductivity, solid-state electrolyte, DFT ∗ Corresponding author Email address: federico.bianchini@smn.uio.no (F. Bianchini) Preprint submitted to Materials Letters January 15, 2018