Accelerating Li-ion diffusion in β-eucryptite by tuning Li–Li correlation

Abstract

Solid-state Li-ion batteries are emerging as promising next-generation energy storage devices, but new solid-state Li-ion conductors or electrolytes, a critical component of such devices, are highly demanded to meet the conductivity and stability requirements. In this study, one of the cost-effective and stable silicate-based solid Li-ion conductors, β-eucryptite LiAlSiO4, was studied via ab initio molecular dynamics simulations. The Si/Al ratio from 0 to 7 corresponding to x in Li1+xAl1+xSi1-xO4 from 1 (Li-rich) to −0.75 (Li-poor) was adjusted to investigate its impact on Li-ion diffusion. The results show that the Li-ion diffusion barrier can be greatly decreased from 0.61 eV in β-eucryptite LiAlSiO4 (x = 0) to 0.20 eV in Li0.5Al0.5Si1.5O4 (x = −0.5; Si/Al = 3) and 0.24 eV in Li1.25Al1.25Si0.75O4 (x = 0.25; Si/Al = 0.6). The predicted Li-ion conductivity is 6.976 mS/cm in Li0.5Al0.5Si1.5O4 and 3.773 mS/cm in Li1.25Al1.25Si0.75O4 at 25 °C, both allowing room-temperature operation of solid-state batteries. The modulation of Li–Li correlation at these two distinctive Si/Al ratios results in significantly lower diffusion barrier and higher Li-ion conductivity than those of the parent composition. Our work facilitates the design of low-cost silicate-based Li-ion conductors with high Li conductivity.