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

Graphical Bi−F dual-doped Li 5.5 PS 4.5 Cl 1.5 electrolyte is synthesized and exhibits significant compatibility for bare lithium metal, directs uniform Li + deposition/stripping by forming a Li−Bi alloy, and forms a robust LiF phase to inhibit the growth of lithium dendrites. In addition, the formation of BiS 4 ⁵ − unit and LiBiS 2 phase gives it a high air/moisture resistance. 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, BiF 3 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 5.54 P 0.98 Bi 0.02 S 4.5 Cl 1.44 F 0.06 (LPBiSClF 0.06 ) still maintains a relatively high ionic conductivity of 5.37 mS cm −1 . Additionally, the formation of BiS 4 5− unit and LiBiS 2 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.