Bismuth and Fluorine Dual‐Doping of Lithium Argyrodite toward High‐Performance All‐Solid‐State Lithium Metal Batteries

Chlorine-rich lithium argyrodite is considered as a promising superionic conductor electrolyte, but its practical application is limited due to poor air stability and instability toward lithium metal. In this work, BiF₃ is proposed as a multi-functional dopant for electrolyte modification, and the effects on the ionic conductivity, air stability, critical current density, and electrolyte/Li metal interfacial stability are studied. The results show that the doped electrolyte Li_5.54P_0.98Bi_0.02S_4.5Cl_1.44F_0.06 (LPBiSClF_0.06) still maintains a relatively high ionic conductivity of 5.37 mS cm^-1. Additionally, the formation of BiS₄ ^5- unit and LiBiS₂ phase provides high air/moisture resistibility. Meanwhile, the critical current density of the Li/LPBiSClF_0.06/Li cell is increased two-fold (2.1 mA cm^-2). The in-situ formation of LiF and Li-Bi alloy at the lithium metal/electrolyte interface plays a key role in achieving high performance. As a result, the assembled LCO@LNO/LPBiSClF_0.06/Li battery retains 78.4 % of its capacity after 100 cycles at 0.2C.