Super‐Reversible CuF₂ Cathodes Enabled by Cu²⁺‐Coordinated Alginate

Abstract Copper fluoride (CuF₂) has the highest energy density among all metal fluoride cathodes owing to its high theoretical potential (3.55 V) and high capacity (528 mAh g⁻¹). However, CuF₂ can only survive for less than five cycles, mainly due to serious Cu‐ion dissolution during charge/discharge cycles. Herein, copper dissolution is successfully suppressed by forming Cu²⁺‐coordinated sodium alginate (Cu‐SA) on the surface of CuF₂ particles during the electrode fabrication process, by using water as a slurry solvent and sodium alginate (SA) as a binder. The trace dissolved Cu²⁺ in water from CuF₂ can in situ cross‐link with SA binder forming a conformal Cu‐SA layer on CuF₂ surface. After water evaporation during the electrode dry process, the Cu‐SA layer is Li‐ion conductor but Cu²⁺ insulator, which can effectively suppress the dissolution of Cu‐ions in the organic 4 m LiClO₄/ethylene carbonate/propylene carbonate electrolyte, enhancing the reversibility of CuF₂. CuF₂ electrode with SA binder delivers a reversible capacity of 420.4 mAh g^‐1 after 50 cycles at 0.05 C, reaching an energy density of 1009.1 Wh kg^‐1. Cu²⁺ cross‐link polymer coating on CuF₂ opens the door for stabilizing the high‐energy and low‐cost CuF₂ cathode for next‐generation Li‐ion batteries.