Catalyzing the Intercalation Storage Capacity of Aqueous Zinc-Ion Battery Constructed with Zn(II) Preinserted Organo-Vanadyl Hybrid Cathode

Abstract

This article reports the first instance of exploring a chemically Zn(II) preinserted organic-inorganic hybrid material [vanadyl ethylene glycolate or VEG, (VO(CH2O)2)] as an efficient cathode for rechargeable zinc-ion batteries (ZIBs). The control VEG electrode synthesized by a glycothermal process showed a modest specific capacity of 157 mAh/g at 0.1 A/g current density, however, suffered from poor rate capability and cycle stability due to structural dissolution. Chemically Zn(II) preinsertion into VEG (Zn-VEG) catalyzed the Zn2+ intercalation in the Zn-VEG cathode with a significantly decreased charge transfer resistance, resulting in high discharge capacity of 217 mAh/g (at 0.1 A/g) accompanied by excellent rate capability with ∼50% capacity retention on increasing the current by 50 times. A first-principles-based hybrid density-functional theory (DFT) study revealed that the electronic structure of the Zn-intercalated VEG is thermodynamically stable, indicating an energetically favorable Zn-ion intercalation process. The Zn(II) preinserted VEG cathode allowed faster ionic diffusion (DZn2+ in the order of 10-9 cm2/s), and the diffusion controlled process was the major contributor (∼66.9%) to the overall capacity at low scan rate (0.1 mV/s) and remained significant (43.8%) even at high scan rate of 0.8 mV/s. Furthermore, the Zn(II) preinsertion in the VEG could act as a bridge to hold the VEG layers firmly. This provides the desired structural stability to the Zn-VEG cathode during a continuous Zn2+ insertion/deinsertion process, resulting in excellent cycle stability with only ∼0.005% capacity loss per cycle over 2000 cycles (at 4 A/g) while maintaining a high columbic efficiency of 99.9% throughout the cycles. The high capacity accompanied by excellent rate capability and cycle stability supports the as-prepared Zn(II) preinserted organo-vanadyl hybrid electrode to be a potential cathode material for ZIBs. © 2020 American Chemical Society.