Improved working voltage and high rate performance of sodium vanadate cathode materials for aqueous zinc ion batteries by altering synthetic solution pH guiding the structure change

Aqueous zinc ion batteries (ZIBs) are considered as potential candidates for large-scale energy storage systems due to low cost, safety and environmental friendliness. However, the low voltage platform is one of the factors that limit the application of vanadium-based cathode materials for ZIBs. In this paper, the NaV6O15.0.61H(2)O, NaV6O15.0.51H(2)O and Na2V6O16.1.66H(2)O with rod-shaped structure were obtained by adjusting the pH of the solution in a simple hydrothermal process. Different pH value of the solution results in the formation of different phase samples and effectively improves the discharge voltage platform of material electrode. The stable discharge voltage platform of Na(2)V(6)O16.1.66H(2)O with the solution pH of 7 increased 0.17 V than that of NaV(6)O15.0.61H(2)O and NaV(6)O15.0.51H(2)O. Meanwhile, Na(2)V(6)O16.1.66H(2)O showed improved electrochemical properties. The reversible capacities of 371 mAh g(-1) for Na(2)V(6)O16.1.66H(2)O were acquired after 50 cycles charging/discharging at a current density of 500 mA g(-1), and a high rate capability and remarkable cycling stability with capacity retention of 90% were displayed over 1800 cycles at 5 A g(-1). Furthermore, the Na(2)V(6)O16.1.66H(2)O showed high capacitance contribution and Zn2+ diffusion coefficient.