Passivation effect for current collectors enables high-voltage aqueous sodium ion batteries

Abstract

The narrow electrochemical stability window (1.23 V) of electrolyte has hindered the development of aqueous sodium ion batteries greatly, especially the choice of electrode materials. Here, through theoretical calculation and experimental proof, it's found that the deposition of oxide films on both Al cathode and Ti anode current collectors exhibits strong passivation effect. When the thickness of Al2O3 film on Al is about 3 nm and the thickness of TiO2 film on Ti is about 5 nm, the electrochemical stability window of aqueous electrolyte can be expanded to 3.5 V. Therefore, TiS2 with low working potential (1.5 V versus Na+/Na) can be used as anode material in aqueous sodium-ion battery for the first time. We assembled a full cell coupling TiS2 anode with Prussian blue cathode in 15 M NaClO4 aqueous electrolyte. The full cell of 2.6 V demonstrates cycle life up to 1000 times with high energy density (100 Wh kg−1) and high rate capability (30 C).