The critical challenges for fluoride conversion cathodes lie in the absence of built-in Li source, poor capacity retention, and rate performance. For lithiated fluorides, the reason to limit their competitiveness is rooted in the facile coarsing of insulating LiF (as built-in Li source) and its insufficient splitting kinetics during charging. Previous efforts on blending LiF nanodomains with reductive metal, metal oxide, or fluoride by ball-milling method still face the problems of large overpotential and low current density. Herein we propose a strategy of dual-metal (Fe-Cu) driven LiF splitting to activate the conversion reaction of fluoride cathode. This lithiated heterostructure (LiF/Fe/Cu) with compact nanodomain contact enables a substantial charge process with considerable capacity release (300 mAh g-1) and low charge overpotential. Its reversible capacity is as high as 375-400 mAh g-1 with high energy efficiency (76%), substantial pseudocapacitance contribution (>50%), and satisfactory capacity retention (at least 200 cycles). The addition of Cu nanodomains greatly catalyzes the kinetics of Fe-Cu-F formation and decomposition compared with the redox process of Fe-F, which lead to the energy and power densities exceeding 1000 Wh kg-1 and 1500 W kg-1, respectively. These results indicate that LiF-driven cathode is promising as long as its intrinsic conductive network is elegantly designed.
Keywords: Li-ion batteries; LiF splitting; conversion reaction; fluoride cathode; thin film.