Insight in to the defect model, Li+ diffusion mechanism and doping level dependency of Li+ doping BPO4 by first principles and molecular dynamics method
Abstract In this article, two defect models of LixB1-x/3PO4, LiB″ + 2Li model and VB‴ + 3Li model, are fully evaluated by means of density function theory (DFT), bond-valence-energy-landscape mapping (BVEL) and molecular dynamics (MD). LiB″ + 2Li model is more stable and is the dominant defect model at low temperatures. The Li+ diffusion mechanism for LiB″ + 2Li model is revealed where LiB′′ mediated diffusion along a/b axis owns the lowest energy barrier of 0.35 eV. Li+ doping level dependency of Li+ diffusion coefficient is obtained by molecular dynamics simulation of LixB1-x/3PO4 with multiple doping levels, which exhibits better ionic conductivities within the range of 0.093–0.28, with the highest DLi+ of 1.45 × 10−9 cm2∙s−1 at x = 0.187. Basically, all the activation energy components increase slowly with the augmentation of Li+ doping level except the lowest doping level 0.049 and they reach their respective minimum at x = 0.093.