Abstract
First-principle calculations are carried out to study the diffusion of Li ions in rutile structure RuO2, a material for positive electrodes in rechargeable Li ion batteries. The calculations focus on migration pathways and energy barriers for diffusion in Li-poor and Li-rich phases using the Nudged Elastic Band Method. Diffusion coefficients estimated based on calculated energy barriers are in good agreement with experimental values reported in the literature. The results confirm the anisotropic nature of diffusion of Li ions in one-dimensional c channels along the [001] crystalline direction of rutile RuO2 and show that Li diffusion in the Li-poor phase is faster than in the Li-rich phase. The findings of fast Li diffusion and feasible Li insertion at low temperatures in the host rutile RuO2 suggest this material is a good ionic conductor for Li transport. The finding also suggests possible means for enhancing the performance of RuO2-based electrode materials.
Highlights
As demand for lithium ion batteries increases, extensive experimental and theoretical research on promising electrode materials has been conducted
First-principle calculations are carried out to study the diffusion of Li ions in rutile structure RuO2, a material for positive electrodes in rechargeable Li ion batteries
The first-principle calculations carried out are based on the density functional theory (DFT) and use the Vienna Ab-initio Simulation Package (VASP)[12] with the projector augmented-wave (PAW)[13,14] approach and generalized gradient approximation (GGA) exchange correlation functional of Perdew-Wang 1991.15 The pseudopotential deals with all three electrons of Li (Li_sv) with the 1s shell being treated as valence states, and the standard potentials of Ru and O are used
Summary
As demand for lithium ion batteries increases, extensive experimental and theoretical research on promising electrode materials has been conducted. Ideal electrodes should have flexible structures, large reversible capacities, low cost, high and consistent voltages, structural integrity, non-toxicity, ionic bonding, and good electronic conductivity. Transition metal oxides possess many of these attributes and are promising candidates for high-performance electrode materials. Lithium cobalt oxide (LiCoO2) is the most commercialized cathode material and LiFePO4 has received attention as a generation material. RuO2, one of the transition metal oxides having the rutile structure, has been recently attracting interest for its unusual characteristics in lithium insertion. It has an extremely high total capacity of 1130 mAg−1 and high first-cycle Coulombic efficiency of above 98%.1
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