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 next-generation 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 two-dimensional 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.