Exploration of the zinc storage mechanism and kinetics of vanadium sulfides/reduced graphene oxide composites for aqueous zinc-ion battery cathodes

초록

Aqueous zinc-ion batteries (AZIBs) are considered suitable devices for large-scale energy storage systems. Vanadium sulfides have gained wide attention as AZIB cathode materials owing to their low cost, high specific capacity, and fast Zn-ion insertion/extraction ability. However, a thorough examination of their actual operation as AZIB cathodes remains lacking. In this study, we synthesized three types of vanadium sulfides/reduced graphene oxide (VxS8/rGO, x = 2, 5, and 6), fabricated electrodes from these materials, and systemically explored their Zn-ion storage mechanisms and kinetics. All three VxS8/rGO electrodes required an electrochemical activation step, which involved charging over 1.8 V (vs. Zn/Zn2+), to obtain high reversible discharging-charging capacity. The V5S8/rGO and V6S8/rGO electrodes exhibited structural and morphological evolution during electrochemical activation and maintained 70% of their capacities for 700 cycles at a current density of 5 A g-1. The V2S8/rGO electrode maintained its initial state during repeated discharge-charge cycling and, thus, exhibited exceptional long-term cycling stability with 99% capacity retention for 700 cycles at the same current density. These findings highlight the importance of an in-depth study of vanadium sulfide materials requiring electrochemical activation to achieve high-power- and energy-density AZIBs.

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