Hybrid electrolyte-mediated nano-scaled γ-Fe2O3 cathode for emerging aqueous zinc battery

As a very promising energy storage device, aqueous Zn-ion battery (ZIB) has made great progress recently. However, the selection of cathode active material remains a major difficulty in this battery system. Here, a kind of low-cost, non-toxic, environmentally friendly, nano-scaled γ-Fe 2 O 3 with natural cation vacancies is demonstrated as an effective cathode material for aqueous zinc batteries. The electrochemical reaction mechanisms of the Zn/γ-Fe 2 O 3 system in two common electrolytes, 2 M ZnSO 4 aqueous solution and 3 M Zn(CF 3 SO 3 ) 2 aqueous solution, are explored. The H + insertion mechanism and H + /Zn 2+ co-insertion mechanism are defined in these two battery systems, respectively. Furthermore, it is found that the addition of highly concentrated magnesium ions in the electrolyte can effectively inhibit the formation of hydrated zinc hydroxide during the discharge process and improve the electrochemical performance of the battery. Whether in 1.5 M MgSO 4 + 0.5 M ZnSO 4 aqueous solution or in 2.5 M Mg(CF 3 SO 3 ) 2 + 0.5 M Zn(CF 3 SO 3 ) 2 aqueous solution, both of these two Zn/γ-Fe 2 O 3 battery systems exhibit good rate performance. This work provides more possibilities for the development of iron-based cathode materials.