Insight in to the defect model, Li+ diffusion mechanism and doping level dependency of Li+ doping BPO4 by first principles and molecular dynamics method

YT Xie and QY Wang and FP Gu and M Shui and J Shu, SOLID STATE IONICS, 357, 115465 (2020).

DOI: 10.1016/j.ssi.2020.115465

In this article, two defect models of LixB1-x/3PO4, Li-B '' + 2Li model and V-B''' + 3Li model, are fully evaluated by means of density function theory (DFT), bond-valence-energy-landscape mapping (BVEL) and molecular dynamics (MD). Li-B '' + 2Li model is more stable and is the dominant defect model at low temperatures. The Li+ diffusion mechanism for Li-B '' + 2Li model is revealed where Li-B '' 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 x 10(-9) cm(2).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.

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