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

Aqueous zinc -ion batteries have received increasing attention due to the merits of low cost and high safety. In addition to Zn2+, protons can also serve as charge carriers in aqueous electrolytes for real-izing energy storage. This work utilizes three electrolyte components, including 3 M ZnSO4/H2O, 1.5 M H2SO4/H2O, and 3 M ZnSO4/ethylene glycol (EG), to investigate kinetic properties of layered vana-dium cathodes. As studied by CV and EIS analyses, the ion diffusion coefficient associated with Zn2+/H+ in Co2+ preinserted V2O5 (CoVO) samples are higher than that in V2O5. Interestingly, H+ diffusivity in Co0.17V2O5 center dot 0.83H2O (CoVO-2) is greatly promoted by a factor of similar to 26 times in comparison with V2O5 (1.19 x 10(-12) vs. 4.49 x 10(-14) cm(2) s(-1)) in 1.5 M H2SO4/H2O, while Zn2+ diffusivities in these two cath-odes are comparable in 3 M ZnSO4/EG (1.48 x 10 -14 vs. 9.80 x 10(-15) cm(2) s(-1)). The boosted proton dif-fusion 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 2,0 0 0 cycles at 4 A g(-1)) can be achieved. By contrast, V2O5 exhibits inferior battery perfor-mance (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. (C) 2021 Elsevier Ltd. All rights reserved.