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

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.