부산대학교 도서관

Vanadium oxyhydroxide has been recently investigated as a starting material to synthesize different phases of vanadium oxides by electrochemical or thermal conversion and has been used as an aqueous zinc-ion battery (AZIB) cathode. However, the low-valent vanadium oxides have poor phase stability under ambient conditions. So far, there is no study on understanding the phase evolution of such low-valent vanadium oxides and their effect on the electrochemical performance toward hosting the Zn2+ions. The primary goal of the work is to develop a high-performance AZIB cathode, and the highlight of the current work is the insight into the auto-oxidation-induced phase transition of VOOH to V10O24·nH2O under ambient conditions and Zn2+intercalation behavior thereon as an aqueous zinc-ion battery cathode. Herein, we demonstrate that hydrothermally synthesized VOOH undergoes a phase transition to V10O24·nH2O during both the electrochemical cycling and aerial aging over 38–45 days. However, continued aging till 150 days at room temperature in an open atmosphere exhibited an increased interlayer water content in the V10O24·nH2O, which was associated with a morphological change with different surface area/porosity characteristics and notably reduced charge transfer/diffusion resistance as an aqueous zinc-ion battery cathode. Although the fresh VOOH cathode had impressive specific capacity at rate performance, (326 mAh/g capacity at 0.1 A/g current and 104 mAh/g capacity at 4 A/g current) the cathode suffered from a continuous capacity decay. Interestingly, the aged VOOH electrodes showed gradually decreasing specific capacity with aging at low current and however followed the reverse order at high current. At a comparable specific power of ∼64–66 W/kg, the fresh VOOH and aged VOOH after 60, 120, and 150 days of aging showed the respective energy densities of 208.3, 281.2, 269.2, and 240.6 Wh/kg. Among all the VOOH materials, the 150 day-aged VOOH cathode exhibited the highest energy density at a power density beyond 1000 W/kg. Thanks to the improved kinetics, the 150 day-aged VOOH cathode delivered a considerable energy density of 39.7 Wh/kg with a high specific power of 4466 W/kg. Also, it showed excellent cycling performance with only 0.002% capacity loss per cycle over 20 300 cycles at 10 A/g.