Iron phosphate hydroxide hydrate as a novel anode material for advanced aqueous full potassium-ion batteries.

The development of aqueous potassium-ion batteries is limited by the lack of suitable anode materials. Here, a novel anode material, iron phosphate hydroxide hydrate Fe 1.19 PO 4 (OH) 0.18 (H 2 O) 0.3 , was introduced and synthesized, which delivers considerable reversible capacities of 80 mA h g -1 at 0.05 A g -1 . An aqueous full potassium-ion battery assembled with the K 2 Zn 3 (Fe(CN) 6 ) 2 cathode exhibits 80% capacity retention after 1000 cycles.