Capacity enhancement of LaAl2Ag ternary alloy anode for fluoride-ion batteries

Abstract

The fluoride-ion battery (FIB) is considered a promising next-generation energy storage system due to the abundant fluorine resources and higher theoretical energy densities. Although the capacities of cathodes in FIBs have increased to near theoretical limits, the capacities of anodes in FIBs are still at most half of those in cathodes, and therefore it is a prerequisite to develop high-capacity anode materials for the practical application of FIBs. In typical pure metal fluoride anodes, it is difficult to simultaneously realize high F⁻ ion and high electron conductivities during the charging and discharging processes, which limits the practical capacities of anodes. Here, we propose the LaAl₂Ag ternary alloy for capacity enhancement of anodes in FIBs. Compared to pure Al metal and LaAl₃ binary alloy anodes, the LaAl₂Ag anode shows a high reversible capacity of more than 400 mA h g⁻¹. During the initial discharging process, the LaAl₂Ag anode is decomposed into LaF₃, AlF₃, and Ag nanocrystals, which form nanoscale fast conduction paths for F⁻ ions and electrons across the anode, and the capacity is significantly enhanced. The present strategy of alloying with electrochemically inactive Ag is effective in enhancing electron conductivity during cycling.