Super-Reversible CuF 2 Cathodes Enabled by Cu 2+ -Coordinated Alginate.

Copper fluoride (CuF 2 ) 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, CuF 2  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 Cu 2+ -coordinated sodium alginate (Cu-SA) on the surface of CuF 2  particles during the electrode fabrication process, by using water as a slurry solvent and sodium alginate (SA) as a binder. The trace dissolved Cu 2+ in water from CuF 2  can in situ cross-link with SA binder forming a conformal Cu-SA layer on CuF 2  surface. After water evaporation during the electrode dry process, the Cu-SA layer is Li-ion conductor but Cu 2+ insulator, which can effectively suppress the dissolution of Cu-ions in the organic 4 m LiClO 4 /ethylene carbonate/propylene carbonate electrolyte, enhancing the reversibility of CuF 2 . CuF 2  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 . Cu 2+ cross-link polymer coating on CuF 2  opens the door for stabilizing the high-energy and low-cost CuF 2  cathode for next-generation Li-ion batteries.