Fast potassium storage in porous CoV2O6 nanosphere@graphene oxide towards high-performance potassium-ion capacitors

The increasing demand to develop sustainable energy storage equipment has aroused interest for potassium-ion capacitors (PICs), owing to their high abundance and low cost of potassium sources. Nevertheless, the practical application of PICs is impeded by the lack of suitable anode materials with high performance. Here we demonstrate a solvothermal-assisted synthesis of porous CoV2O6 nanosphere@graphene oxide (GO) composites as the anode material of PICs for the first time. Benefiting from the well-designed porous nanostructure and high-conductivity carbon incorporation, the hybrid composite delivers an initial high discharge capacity (264 mAh g(-1), 1 A g(-1)) and superior rate capability (97 mAh g(-1), 10 A g(-1)). Moreover, the electrochemical reaction mechanism of CoV2O6 involving an intercalation followed by conversion reaction is comprehensively revealed by first-principles calculations (DFT), ex-situ X-ray photoelectron spectroscopy as well as ex-situ high-resolution transmission electron microscopy. Meanwhile, the DFT also indicates that CoV2O6 possesses high electron/K-ion conductivity and low diffusion barriers for K+ intercalation. Consequently, PICs coupling the CoV2O6 @GO anode and activated carbon cathode display a high energy/power density (78.2 Wh kg(-1) and 22,500 W kg(-1)) as well as an ultralong lifespan over 3000 cycles. The work delves metal vanadate as high-performance anode for PICs and may provide innovative insight into electrode structure building in rechargeable metal-ions chemistry.

Automated summary

This study demonstrates the use of porous CoV2O6 nanosphere@graphene oxide composites as an anode material for potassium-ion capacitors (PICs) for the first time, showing high performance in terms of discharge capacity and rate capability. The electrochemical reaction mechanism of CoV2O6 and its high electron/K-ion conductivity are comprehensively revealed through various experiments. The PICs based on this anode and activated carbon cathode exhibit high energy/power density and an ultralong lifespan.