Enabling High Performance Bismuth Trifluoride Cathode by Engineering the Cathode/Electrolyte Interface in Sulfide‐Based All Solid State Batteries

Abstract Metal fluorides are conversion‐type cathodes that have the potential to boost the energy densities of next generation lithium‐ion batteries (LIBs). However, the study of non‐transitional metal fluorides (NTMFs) such as bismuth trifluoride (BiF 3 ) is limited due to the challenges on the construction of a stable electrochemical reaction interfaces with liquid electrolyte, although it shows advantages on high electrochemical potential, moderately high theoretical capacity and low voltage hysteresis. Moreover, the performance of BiF 3 in all solid state batteries (ASSBs) has not been explored. In this contribution, the micro‐sized commercial BiF 3 is successfully coated with a cyclic polyacrylonitrile (cPAN) and refined its size to nanoscale. The refined nano‐sized BiF 3 @cPAN uniformly disperses in the solid electrode and delivers an initial discharge capacity of 330 and 200 mAh g −1 after 250 cycles in sulfide electrolyte based ASSBs. Furthermore, the voltage hysteresis of the ASSBs reaches a record low value of 180 mV. Postmortem analysis shows that the elastic coating hindered the undesirable interface side reaction and rendered the BiF 3 with excellent cycle reversibility. This work demonstrates the crucial role of stable interfaces for BiF 3 in preventing electrolyte decomposition, which promotes the practical adoption of BiF 3 cathode with higher specific energy for LIBs.