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1 PROSPECTS FOR MnO2-BASED AQUEOUS Zn-ION BATTERYrnAqueous rechargeable zinc-ion batteries (AZIBs) have been considered as promising altatives to lithium-ion batteries for electrochemical energy storage.There are two typical overwhelming advantages that make AZIBs stand out among the various electrochemical energy storage systems (organic alkaline ion batteries,e.g.,Na+ and K+,and aqueous batteries,e.g.,Na+,K+,Mg2+,and Al3+).Firstly,some advantages come from the utilization of aqueous electrolyte.The aqueous electrolytes could deliver 2 orders of magnitude higher ionic conductivities (～1 S·cm-1) than the non-aqueous electrolytes (～1-10 mS·cm-1)[1].Moreover,aqueous electrolyte reduces the fabrication cost comparing with the usage of organic solvents.In addition,it is an important point that the high operational safety and environmental friendliness derived from aqueous electrolyte endows AZIBs with strong competitiveness.Secondly,zinc metal can directly be used as the anode in the AZIBs,which makes the AZIBs more promising than other aqueous batteries (Al3+,Mg2+,Na+,K+).Zn anode features the low oxidation-reduction potential of Zn2+/Zn (-0.76 V vs.standard 2H+/H2 potential),which can deliver higher energy density[2].Moreover,the low-cost Zn metal can decrease the manufacturing cost.