Aqueous Nickel-Ion Batteries with Long Lifetime, High Capacity, and High Rate Capability Based on K₂V₆O₁₆·1.64H₂O Cathodes

Aqueous nickel-ion batteries (NiIBs) featuring small ionic radius and high theoretical volumetric capacity hold great potential in novel aqueous battery systems. However, the further development of aqueous NiIBs is plagued, owing to the strong electrostatic repulsion between Ni2+ ions and the host electrode materials, leading to the limited capacity, poor cycling performance, and inferior rate capability. Herein, the novel K2V6O16·1.64H2O (KVO) nanobelts are synthesized and utilized as cathodes for aqueous NiIBs. The KVO cathode delivers a highly reversible specific capacity of ∼140.0 mA h g-1 after the initial activation process, and ∼70.8 mA h g-1 is achieved with the Coulombic efficiency close to 100% at 0.2 A g-1 after 1000 cycles. ∼40.5 mA h g-1 is still achieved at 1.0 A g-1 after 8000 cycles. Moreover, this battery possesses a remarkable rate capability with ∼137.4 mA h g-1 being regained when the current density is switched from 1.8 to 0.2 A g-1, which is ∼97% of that at 0.2 A g-1. The capacity, lifetime, and rate capability achieved all far exceed those of the reported aqueous NiIBs, arising from the layered structure and fast kinetics of the KVO cathode. This work paves the way toward the design of aqueous NiIBs with high electrochemical performances.