Maximizing ionic transport of Li1+xAlxTi2-xP3O12 electrolytes for all-solid-state lithium-ion storage: A theoretical study

Abstract

The concept of all-solid-state batteries provides an efficient solution towards highly safe and long-life energy storage, while the electrolyte-related challenges impede their practical application. Li1+xAlxTi2-xP3O12 (0 ≤ x ≤ 1) with superior Li ionic conductivity holds the promise as an ideal solid-state electrolyte. The intrinsic mechanism to reach the most optimum ionic conductivity in Al-doped Li1+xAlxTi2-xP3O12, however, is unclear to date. Herein, this work intends to provide an atomic scale study on the Li-ion transport in Li1+xAlxTi2-xP3O12 electrolyte to rationalize how Al-dopant initiates interstitial Li activity and facilitate their easy mobility combining Density Functional Theory (DFT) and ab initio Molecular dynamics (AIMD) simulations. It is discovered that the interstitial Li ions introduced by Al dopants can effectively activate the neighboring occupied intrinsic Li-ions to induce a long-range mobility in the lattice and the maximum Li ionic conductivity is achieved at 0.50 Al doping concentration. The Li- ion migration paths in Li1+xAlxTi2-xP3O12 have investigated as the degree of distortion of [PO4] tetrahedra and [TiO6] octahedra resulted by different Al doping concentrations. The asymmetry of the surrounding distorted [PO4] and [TiO6] polyhedrons play a critical role in reducing the migration barrier of Li ions in Li1+xAlxTi2-xP3O12. The flexible [TiO6] polyhedrons with a capacity to accommodate the structural distortion govern the Li ionic conductivity in Li1+xAlxTi2-xP3O12. This work rationalizes the mechanism for the most optimum Li ionic conductivity in Al-doped LiTi2P3O12 electrolyte and, more importantly, paves a road for exploring novel all-solid-state lithium battery electrolytes.