Ionic conductivity and interfacial stability of Li6PS5Cl–Li6.5La3Zr1.5Ta0.5O12 composite electrolyte

Solid electrolytes which possess excellent lithium-ion conductivity and chemical compatibility with electrode materials are necessary for the commercialization of all-solid-state lithium batteries. However, a single solid electrolyte meeting above requirements is difficult. Consequently, the composite electrolytes have attracted more attention. In this paper, Li6PS5Cl–xLi6.5La3Zr1.5Ta0.5O12 (LLZTO) (x = 0, 2.5 wt%, 5 wt%, 10 wt%) composite electrolytes are prepared by a simple planetary grinding process. It has been found that adding an appropriate amount of LLZTO can increase the lithium-ion conductivity. At 30 °C, the lithium-ion conductivity increases from 2.6 × 10−4 S/cm (Li6PS5Cl) to 5.4 × 10−4 S/cm (Li6PS5Cl-5 wt% LLZTO). Besides, the addition of LLZTO to the Li6PS5Cl can influence the growth rate of the SEI. It has been shown that the SEI growth rate obeys a parabolic rate law, and the growth rates of Li6PS5Cl, Li6PS5Cl-2.5 wt% LLZTO, Li6PS5Cl-5 wt% LLZTO, and Li6PS5Cl-10 wt% LLZTO are 8.62, 3.53, 3.33, and 3.38 Ω/h1/2 at 60 °C, respectively. In lithium plating and stripping experiment, the voltage of symmetrical Li/Li6PS5Cl/Li cell suddenly drops to 0 V after cycling 39 h at 0.103 mA/cm2 (0.097 mAh/cm2). On the contrary, the Li/Li6PS5Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%)/Li symmetrical cell exhibits a stable voltage profile over 100 h at the same test conditions. The corresponding interfacial impedance of Li/Li6PS5Cl–xLLZTO (x = 2.5 wt%, 5 wt%, 10 wt%) remains stable after 10, 30, and 50 charge/discharge cycles.