Computational and Experimental Investigation of the Electrochemical Stability and Li-Ion Conduction Mechanism of LiZr₂(PO₄)₃

Abstract

Solid electrolytes possessing sufficient ionic conductivity and electrochemical stability are urgently needed for the fabrication of all-solid-state Li-ion batteries (LIBs). In this study, we focus on a solid-state oxide electrolyte LiZr2(PO4)3 (LZP), which has NASICON structure and electrochemically stable Zr4+ ions. Using density functional theory (DFT) to calculate the electrochemical window of LZP, we find that it is unstable against Li metal, in accordance with our experimental results. The Li-ion transport is investigated using first-principles molecular dynamics (FPMD) simulations. The calculated Li-ion conductivity at room temperature (5.0 × 10–6 S/cm) and the activation energy for Li-ion diffusion (0.43 eV) are in fair agreement with experimental results. The mechanism of Li-ion conduction in LZP is revealed by analyzing the Li-ion trajectories in the FPMD simulations. It is found that each Li ion migrates between 6b sites as it is pushed out or repelled by other Li ions around these 6b sites. Hence, the high Li-ion conductivity is attributed to a migration mechanism driven by Frenkel-like defect.