Intercalation Pseudocapacitance of Cation-Exchanged Molybdenum-Based Polyoxometalate for the Fast and Stable Zinc-Ion Storage
Hwi Jung Kim, Jeong Yeon, Hye Rin Park, Hye Rin Park, Sang Joon Lee, Won Il Kim, Gun Jang, Ho Seok Park, Ho Seok Park
Abstract
Recently, intercalation pseudocapacitance has received significant interest as an abnormal charge storage mechanism owing to the battery-like intercalation energy storage into the bulk electrodes and the fast charge storage kinetics of electrochemical capacitors. However, intercalation pseudocapacitance of molybdenum-based polyoxometalates (POMs) for high-performance Zn ion battery (ZIB) cathodes is yet to be exploited. Herein, we demonstrate the fast and reversible intercalation pseudocapacitance of vanadium-substituted Keggin-type molybdenum-based POMs (XPMoV), where H of HPMoV is replaced by X cations (X = Li, Na, K, or Rb). This cation exchange allows cation-exchanged XPMoV to exhibit the morphological evolution into an anisotropic rodlike structure and to achieve a pillar effect on the improved chemical and structural integrity. Despite the micron-size rod morphology and the contracted lattice of (100) plane, the intercalation pseudocapacitance kinetics of XPMoV was dominated by the fast surface-confined electrochemistry and became highly reversible after the 1st cycle activation process by co-intercalation of Li + and Zn 2+ ions. Therefore, the ZIB with the KPMoV cathode delivered a high rate capability of 74.0 mAh g –1 at 20,000 mA g –1 and 87% capacity retention over 2000 cycles at 1000 mA g –1, far exceeding HPMoV and other Mo-based cathodes. This study paves the way to design the fast and reversible intercalation pseudocapacitance of POMs and the cation exchange chemistry into the improved (electro)chemical and structural integrity.