Oxygen vacancies confined in porous Co3V2O8 sheets for durable and high-energy aqueous sodium-ion capacitors
Anchun Tang, ChuBin Wan, Xianhe Meng, Xiangcao Li, Xiaoyu Hu, Miaofeng Huang, Xin Ju
Abstract
Sodium-ion capacitors have the potential to deliver high energy, power density, and excellent cycling stability. In this study, ultrathin Co 3 V 2 O 8 nanosheets are successfully synthesized through an one-pot hydrothermal reaction and a subsequent doping reconfiguration-induced vacancy-forming process. Abundant oxygen vacancies and high porosity are observed in the Co 3 V 2 O 8 electrode and result in excellent electrochemical performance in 1 M NaOH and Na 2 SO 4 electrolytes. The cathode has a large specific capacity (@NaOH), high-rate capability (@NaOH), wide voltage window (@Na 2 SO 4 ), and favorable long-cycle stability. Ex-situ X-ray diffraction and X-ray photoelectron spectroscopy show that the Co 3 V 2 O 8 electrode displays a battery-like behavior related to OH − ions in the alkaline NaOH electrolyte. By contrast, in the neutral Na 2 SO 4 electrolyte, Co 3 V 2 O 8 mainly shows an intercalation/extraction behavior with Na + ions. Density functional theory calculation suggests that oxygen vacancy leads to a new state located in the bandgap, which greatly improves the electron transfer efficiency and reduces the sodiation energy barrier of Co 3 V 2 O 8 in the neutral Na 2 SO 4 electrolyte. Moreover, when paired with a high-voltage activated carbon (AC) anode, full-cell Co 3 V 2 O 8 //Na 2 SO 4 //AC delivers high energy/power densities (89.6 Wh·kg −1 /330 W·kg −1 ).