Freestanding vanadium oxides/carbon hybrid cathode with long-term cyclability at low current density for flexible aqueous zinc ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are identified as a serious contender for flexible energy storage devices on account of their safety and low cost. Nevertheless, the rapid capacity decay attributed to the structural deterioration and by-product formation of active materials has hindered their further development, which is more evident at low current density. Herein, we prepared a flexible self-supported hybrid cathode material VGS-811, composed of V₂O₅·1.6H₂O (VOH), graphene oxide (GO), and single-walled carbon nanotubes (SWCNTs), which delivers extremely high specific capacity of 443.6 mAh g⁻¹ at 0.1 A g⁻¹ and exhibits remarkable cycle stability with a capacity retention of 86.7 % after 5000 cycles at 0.5 A g⁻¹. In this cathode, GO matrix prevents direct VOH-electrolyte contact, effectively mitigating its dissolution. Simultaneously, SWCNTs facilitate by-product decomposition and enhance electrochemical kinetics through their superior conductivity. For the active material VOH, Zn²⁺ is embedded into the interlayers to form Zn-O bonds through in-situ electrochemical reaction in the first cycle, which act as pillars between adjacent [VO] layers to maintain structural stability. In addition, due to the high conductivity and flexibility of VGS-811, the assembled flexible soft-packaged AZIBs display stable electrochemical performances at different deformation states. This work provides insights on the combination of active materials with carbon materials and in-situ electrochemical conversion.