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 nextgeneration technology for energy storage due to their high energy density and excellent safety. However, only a fewsolid electrolytes exhibit ionic conductivities comparable to liquid electrolytes. Finding low-cost solid electrolytes with high Liion conductivity is in high demand. Based on the ab initio molecular dynamic simulations, the Li? diffusion in b-LiAlSi2O6, a type of cost-effective and naturally-available mineral, and its disordered systems Li1-xAl1-xSi(2)?xO(6) with -1.0 B x B 0.5 was studied. Our calculations show that the phases of Li1-xAl1-xSi(2)?xO(6) 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 9 10(-6) S-cm(-1)) is obtained in Li2Al2SiO6 (x = -1.0), which is five orders of magnitude larger than that of pristine b-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 9 10(-5) Scm(-1) at 300 K. Our work facilitates the understanding of Li+ conduction mechanisms in silicatebased electrolytes and the development of cost-effective and high-performance solid-sate electrolytes.