Ultra-fast and high-stable near-pseudocapacitance intercalation cathode for aqueous potassium-ion storage

The intrinsically limited rate capability of batteries by the diffusion-controlled ionic storage mechanism is still existing, and long-service batteries are always required for low-cost grid-scale energy storage. Herein, we design and construct a series of NixZnyHCF (x + y = 3, x = 1, 1.5 or 2) bimetallic Prussian blue analogues as cathode materials for aqueous potassium-ion batteries. On the basis of electrochemical and structural analysis, a synergistic effect between stable Ni2+ and high-voltage Zn2+ in Ni2Zn1HCF is demonstrated, which simultaneously promises ultrafast near-pseudocapacitance intercalation and super-stable potassium storage. As presented, Ni2Zn1HCF cathode shows an extraordinary high-rate capability of 1000C with a capacity retention of 66% and a high capacity recovery of 95.3%, which derives from the large sufeace area and fast near-pseudocapacitive intercalation mechanism. When cycled at 1000C for 80,000 times, a negligible capacity decay of 0.000385% per cycle further proves this cathode to be high-rate and ultra-stable. In addition, the highly reversible solid-solution K+ intercalation/extraction mechanism in the Ni2Zn1HCF cathode is illustrated by the in-situ X-ray diffraction. This work presents a promising cathode for building ultrafast and long-service aqueous potassium-ion batteries.