Carbon composited zinc ion doped vanadium dioxide synthesized by the hydrothermal method based on surfactant regulation as the cathode material for aqueous zinc ion batteries

Abstract

Aqueous zinc-ion batteries are regarded as having the potential for large-scale application owing to their low cost and inherent safety. However, due to the slow kinetics of cathode materials and the suboptimal microstructure, AZIBs often exhibit unsatisfactory stability during actual cycling. The rational design and development of cathode materials possessing high specific capacity and long-cycling stability hold significant importance for the progress of AZIBs. Here, carbon-nanosphere-composited zinc-ion-doped VO₂ (SZVO@C) electrode materials were fabricated through a hydrothermal process with the assistance of sodium dodecyl sulfonate. Under the modulation of surfactants, the SZVO@C electrode exhibits a rose-like cluster structure composed of nanosheets, this confers a more extensive specific surface area, measuring 40.2 m² g⁻¹. Under a current density of 0.5 A g⁻¹, the SZVO@C electrode exhibits an outstanding specific capacity of 360 mA h g⁻¹. Moreover, it showcases exceptional cycling stability at 5 A g⁻¹, retaining an impressive 98% of its capacity even after 2000 cycles. The SZVO@C electrode's remarkable cycling performance can be attributed to two key factors. First, it has an outstanding specific surface area. Second, there is a morphological alteration that occurs during the first charge. The tight bonding between the cathode material and conductive carbon improves electron transfer efficiency and effectively reduces charge transfer resistance. GITT tests show that the SZVO@C electrode has an excellent Zn²⁺ diffusion coefficient of 1.3 × 10⁻¹⁰ to 1.52 × 10⁻⁸ cm² s⁻¹, which provides a strong guarantee for its excellent cycling performance. The ex situ XPS and XRD examinations unveil the storage mechanism of Zn²⁺. During the initial cycle, the SZVO@C electrode forms the new phase Zn_xV₂O₅·nH₂O, and the pristine Zn_yVO₂ engages in a subsequent reversible cycle along with the new phase. This research work clearly demonstrates that employing surfactants to regulate the microstructure of cathode materials and incorporating carbon materials constitute a potent strategy to enhance the performance.