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Role of divalent cation (Ba) substitution in the Li+ ion conductor LiTi2(PO4)3: a molecular dynamics study

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Abstract

The derivatives of LiTi2(PO4)3 are promising electrolytes for solid-state batteries. An extensive molecular dynamics study is performed employing a refined set of potential parameters to understand the influence of Ba substitution on Li+ ion conductivity in Bax/2Li1−xTi2(PO4)3 (0.0 ≤ x ≤ 0.83). The refined set of potential parameters reveals the structural and dynamical properties of Bax/2Li1−xTi2(PO4)3 which are consistent with experimental results. In the presence of Ba2+, the system endures a persistent competition between the generation of vacant Li-sites and blocking of Li+ ion paths. The diffusivity of Li+ ions enhances with x and increases one order of magnitude higher at x = 0.67, where the creation of vacant Li-sites mainly drives the diffusion. This trend is similar to the experimental report. However, for x > 0.67 compositions, the blocking of the Li+ ion path dominates in the presence of immobile Ba2+ ions, resulting in a reduction of Li+ ion diffusion. The present study also proposes an ordered substitution of Ba2+ ions at crystallographically identified Li1-sites, where an extra Li-site generation is identified at higher compositions. In this case, the vacancy strongly dominates over Li+ ion path blocking, resulting in the possibility to achieve even higher Li+ ion diffusion. The creation of extra Li-sites and mechanism of Li+-ion transport are studied systematically with varying compositions. Further insight into Li+ ion transport is gained by constructing a three-dimensional density map and determining the free energy barrier and clustering of Li+ ion probability density. And the factors affecting the cation diffusion are also systematically investigated.

Graphical abstract: Role of divalent cation (Ba) substitution in the Li+ ion conductor LiTi2(PO4)3: a molecular dynamics study

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Article information


Submitted
25 Feb 2020
Accepted
15 Apr 2020
First published
15 Apr 2020

Phys. Chem. Chem. Phys., 2020, Advance Article
Article type
Paper

Role of divalent cation (Ba) substitution in the Li+ ion conductor LiTi2(PO4)3: a molecular dynamics study

K. Sau, T. Ikeshoji and S. Roy, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/D0CP01053G

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