“…PbSnF 4 is the best superionic conductor, exhibiting fluoride ion conduction, while BaSnF 4 is the most commonly used solid electrolyte known for RT FIB applications. 15,16,[19][20][21] Unlike MSnF 4 materials, only a few reports are available on MSn 2 F 5 (M: Na, K, Rb, Cs, NH 4 , Cs) materials. [22][23][24] Recently, Yu et al reported the application of KSn 2 F 5 solid electrolyte in a FIB, exhibiting a specific capacity of 150 mA h g −1 for more than 70 cycles.…”