First-principles investigation of Li ion diffusion in Li sub(2)FeSiO sub(4)

We have studied the Li-ion migration and the electrochemical performance of Li sub(2)FeSiO sub(4) in the monodinic crystal structure with P2 sub(1) symmetry and the related delithiated system LiFeSiO sub(4). For this purpose, the framework of the density functional theory within the generalized gradient approximation in conjunction with the climbing image nudged elastic band method was used. Addition of the Hubbard term was also considered in the Kohn-Sham Hamiltonian to better model the d electrons of the metal ions in this material. The calculated activation energies for Li ion migration are found to decrease by around 20% with the Hubbard term inclusion in the chosen diffusion pathways of Li sub(2)FeSiO sub(4). Regarding the delithiated structure, the activation energies were found to be sensitive to the Hubbard term addition, however no general behavior such as in the lithiated structure was found. Furthermore, the diffusion coefficients were calculated considering temperatures of 300 K, 500 K, and 700 K.