Investigation of the effect of F-doping on the solid-electrolyte property of Li₃InCl₆

The effect of F-doping in Li₃InCl₆ is theoretically investigated using the first-principle methods. The simulations for the ionic transport property show that the energy barrier for Li-ion migration decreases near the position of the F ion in F-doped Li₃InCl₆, which improves Li-ion diffusivity by generating Li vacancies and promoting the vacancy diffusion mechanism. However, the F ion imposes a correlation effect on the Li-ion movement, which restricts the long-term travel range of the Li ions that are located near the F ion. These positive and negative effects of F-doping suggest that the F concentration should be precisely controlled for the optimum Li-ion conductivity of Li₃InCl₆. The thermodynamic study indicates that F-doping in Li₃InCl₆ is energetically unfavorable, but a kinetic possibility exists for the formation of the F-doped Li₃InCl₆ phase. However, the thermodynamic driving force for the segregation of F via the formation of a LiF phase still exists, which seems to be the origin of the LiF-based stable solid-electrolyte interphase layer formation when an F-doped Li₃InCl₆ is used as the electrolyte for all-solid-state Li batteries.