Boosting proton storage in layered vanadium oxides for aqueous zinc−ion batteries

• Kinetic properties associated with Zn 2+ and H + were systematically investigated. • Distinctive porous structures can be achieved by introducing Co 2+ ions. • Co 2+ preinserted V 2 O 5 samples exhibit enhanced apparent ion diffusion coefficient. • Promoted proton storage in CoVO samples leads to superior battery performance. Aqueous zinc−ion batteries have received increasing attention due to the merits of low cost and high safety. In addition to Zn 2+ , protons can also serve as charge carriers in aqueous electrolytes for realizing energy storage. This work utilizes three electrolyte components, including 3 M ZnSO 4 /H 2 O, 1.5 M H 2 SO 4 /H 2 O, and 3 M ZnSO 4 /ethylene glycol (EG), to investigate kinetic properties of layered vanadium cathodes. As studied by CV and EIS analyses, the ion diffusion coefficient associated with Zn 2+ /H + in Co 2+ preinserted V 2 O 5 (CoVO) samples are higher than that in V 2 O 5 . Interestingly, H + diffusivity in Co 0.17 V 2 O 5 •0.83H 2 O (CoVO−2) is greatly promoted by a factor of ∼26 times in comparison with V 2 O 5 (1.19 × 10 −12 vs. 4.49 × 10 −14 cm 2 s −1 ) in 1.5 M H 2 SO 4 /H 2 O, while Zn 2+ diffusivities in these two cathodes are comparable in 3 M ZnSO 4 /EG (1.48 × 10 −14 vs. 9.80 × 10 −15 cm 2 s −1 ). The boosted proton diffusion coefficient renders superior battery performance of CoVO−2. As a result, high discharge capacity (393 mAh g −1 at 0.5 A g −1 ), good rate performance (148 mAh g −1 at 8 A g −1 ), and stable cycle retention (89 % after 2,000 cycles at 4 A g −1 ) can be achieved. By contrast, V 2 O 5 exhibits inferior battery performance (185 and 57 mAh g −1 at 0.5 and 8 A g −1 , respectively) due to sluggish kinetics of H + transport in the host.