Constructing a BiF3/Bi7F11O5 multiple-phase composite as advanced cathode for room-temperature all-solid-state fluoride-ion batteries

Abstract

All-solid-state fluoride-ion batteries (FIBs) are deemed as promising candidates for post-lithium-ion technologies due to their high energy density and high security, and bismuth (III) fluoride (BiF3) is the most common cathode material for FIBs because of its desirable ionic conductivity. Nonetheless, the insufficient electronic conductivity of BiF3 still impedes its further development. Herein, intending to improve the performance of FIBs, we design and construct the BiF3/Bi7F11O5 multiple-phase composites as advanced cathode materials. It has been found that annealing treatment can induce the formation of the conductive Bi7F11O5 phase in BiF3 crystal, and the as-obtained BiF3/Bi7F11O5 multi-phase cathode material shows an enhanced electronic conductivity than the original BiF3 cathode. The electronic conductivity of BiF3/Bi7F11O5 can reach 1.6 × 10−4 S cm−1, which is almost 10 times higher than the pure BiF3 (2.9 × 10−5 S cm−1). Consequently, when BiF3/Bi7F11O5 cathode is used to assemble all solid-state FIB, FIB displays a reversible capacity of as high as 177.9 mAh/g and maintains 132.7 mA h g−1 after 50 cycles. Therefore, the multiple-phase construction of solid-state electrolyte through annealing treatment provides a meaningful exploration for the development of the high-performance fluoride cathode.