W-doped VO2 for high-performance aqueous Zn-ion batteries.

Aqueous Zn-ion batteries (AZIBs) have become one of the most promising energy storage devices due to their high safety and low cost. However, the development of stable cathodes with fast kinetics and high energy density is the key to achieving large-scale application of AZIBs. In this work, W-doped VO2 (W-VO2) is developed by a one-step hydrothermal method. Benefiting from the pre-insertion of W6+ and the introduction of the W-O bond, accomplishing an expanded lattice spacing and a stable structure, both improved kinetics and long cycle life are achieved. The W-VO2 delivers a specific capacity of 340.2 mA h g-1 at 0.2 A g-1, an excellent high-rate capability with a discharge capacity of 186.9 mA h g-1 at 10 A g-1, and long-term cycling stability with a capacity retention of 76.5% after 2000 cycles. The electrochemical performance of the W-VO2 has been greatly improved, compared with the pure VO2. The W doping strategy proposed here also presents an encouraging pathway for developing other high-energy and stable cathodes.