Enhanced Li-Ion Diffusivity of LiFePO4 by Ru Doping: Ab Initio and Machine Learning Force Field Results

Ionic diffusivity plays a central role in battery performance. A cathode material for lithium-ion (Li-ion) batteries, LiFePO4 (LFP), performs poorly at high current rates due to low Li-ion diffusivity. An increase in ionic diffusivity is essential to enhance battery performance for high-power-density applications such as hybrid and electric vehicles. Here, we use molecular dynamics simulations with machine learning force field and climbing-image nudged elastic band calculations to show that Li-ion diffusivity in LFP increases when doped with the transition-metal dopant ruthenium. This increase is associated with a reduction in Li-diffusion energy barrier, diffusion length, and Li-vacancy formation energy, and it is accompanied by changes in the electronic band structure, specifically the appearance of electronic states in the middle of the band gap and vicinity of the conduction band.