Li-ion transport in solid-state electrolyte of Li_1–xAl_1–xSi_2+xO₆:an ab initio study

All-solid-state batteries are considered as next-generation technology for energy storage due to their high energy density and excellent safety. However, only a few solid electrolytes exhibit ionic conductivities comparable to liquid electrolytes. Finding low-cost solid electrolytes with high Li-ion conductivity is in high demand. Based on the ab initio molecular dynamic simulations, the Li⁺ diffusion in β-LiAlSi₂O₆, a type of cost-effective and naturally-available mineral, and its disordered systems Li_1–xAl_1–xSi_2+xO₆ with −1.0 ≤ x ≤ 0.5 was studied. Our calculations show that the phases of Li_1–xAl_1–xSi_2+xO₆ with nonzero x all possess much lower diffusion energy barriers than pristine LiAlSi₂O₆. When x is positive, increased concentration of lithium vacancies accelerates the diffusion of Li-ions. When x is negative, additional Li-ions are inserted into structures and co-migration is stimulated among these Li-ions. In particular, the maximal ionic conductivity at 300 K (1.92 × 10^–6 S·cm⁻¹) is obtained in Li₂Al₂SiO₆ (x = −1.0), which is five orders of magnitude larger than that of pristine β-LiAlSi₂O₆. In addition, the diffusion barrier can be further reduced to 0.38 eV by replacing Si with Ge, and the ionic conductivity for Li₂Al₂GeO₆ can reach 3.08 × 10^–5 S·cm⁻¹ at 300 K. Our work facilitates the understanding of Li⁺ conduction mechanisms in silicate-based electrolytes and the development of cost-effective and high-performance solid-sate electrolytes. Graphical abstract: [Figure not available: see fulltext.]