Electronic structure and lithium ion diffusion in nitrogen-doped Li₂FeSiO₄: First-principles study

As a typical orthosilicate material, Li₂FeSiO₄ has become a potential candidate for the cathode materials of nextgeneration advanced lithium-ion batteries. However, low electronic/ionic conductivity and slow diffusion rate of lithium ions limit its practical application in the field of lithium-ion batteries. Element doping is an effective and simple strategy to improve the electrical and electrochemical performance of Li₂FeSiO₄. In this work, electronic structure and lithium ion diffusion of nitrogen doped Li₂FeSiO₄ were studied by first-principles calculations. The band gap of Li₁₆Fe₈Si₈O₃₁N (0.331 eV) is smaller than that of Li₁₆Fe₈Si₈O₃₀N₂ (0.712 eV), which indicates a better electronic conductivity. Results of mean square displacement confirm that lithium ion could diffuse in twodimensional path in Li₂FeSiO₄ along the a-axis and c-axis. Additionally, nitrogen doping reduces the energy barrier and improves the diffusion of lithium ions. Diffusion coefficient of lithium ion and the ionic conductivity is 4 and 5 orders of magnitude larger than that of intrinsic system, respectively.