Enable reversible conversion reaction of copper fluoride batteries by hydroxyl solution and anion acceptor

Metal fluorides as conversion-reaction cathodes are attracting more attentions due to their advantages of low cost, environmentally friendly and high energy density. Among CuF2 enables the high theoretical energy density (1874 Wh/kg) and conversion reaction potential (3.55 V vs. Li+/Li), but its poor reversibility is always criticized due to the dissolution of Cu species occurring in delithiation process. In response to this conundrum, here we propose a hydroxyl‑rich copper fluoride (Cu2(OH)3F) as conversion cathode coupled with an electrolyte additive engineering to address the reversibility bottleneck. The presence of OH enables the effective suppression of Cu+ dissolution and imparts Cu2(OH)3F a phase-division conversion mechanism, resulting in the better reaction reversibility and kinetics. Combing with the electrolyte formulation based on boron-based anion acceptor with mild Lewis acidity, the dissociation and conversion of anions from Cu2(OH)3F lattices are promoted and hence the cycling performance is further upgraded, with a reversible capacity over 200 mA h/g after 50 cycles.