Regulating Crystal Orientation in VO₂ for Aqueous Zinc Batteries with Enhanced Pseudocapacitance

Although aqueous zinc batteries have attracted extensive interest, they are limited by relatively low rate capabilities and poor cyclic stability of cathodes. The crystal orientation of the cathode is one important factor influencing electrochemical properties. However, it has rarely been investigated. Herein, VO₂ cathodes with different crystal orientations are developed via tuning the number of hydroxyl groups in polyol, such as using glycerol, erythritol, xylitol, or mannitol. The polyols serve as a reductant as well as a structure-directing agent through a hydrothermal reaction. Xylitol-derived VO₂ shows a (110)-orientated crystalline structure and ultrathin nanosheet morphology. Such features greatly enhance the pseudocapacitance to 76.1% at a scan rate of 1.0 mV s^-1, which is significantly larger than that (61.6%) of the (001)-oriented VO₂ derived from glycerol. The corresponding aqueous zinc batteries exhibit a high energy storage performance with a reversible specific capacity of 317 mAh g^-1 at 0.5 A g^-1, rate ability of 220 mAh g^-1 at 10 A g^-1, and capacity retention of 81.0% at 10 A g^-1 over 2000 cycles. This work demonstrates a facile method for tailoring VO₂ crystal orientations, offers an understanding of the Zn²⁺ storage mechanism upon different VO₂ facets, and provides a novel method to develop cathode materials toward advanced aqueous zinc batteries.