Jiuwei Liu1 Yuan Huang1 Hang Zhou1

1, Shenzhen Key Lab of Thin Film Transistor and Advanced Display, Peking University Shenzhen Graduate School, Peking University, Shenzhen, People's Republic of China, Shenzhen, , China

Aqueous zinc ion batteries (ZIBs) have received incremental attention because of cost effectiveness and abundance of Zn source. MnO2 is a most promising cathode material for ZIBs due to its high capacity, abundant material supply, and excellent safety. However, it suffers from low electronic conductivity, which results in sacrificed capacity and low rate performance of the cathode. Conventionally, introducing conducting additives (such as carbon black, super P, carbon nanotube, or poly(3,4-ethylenedioxythiophene) with mass ratio ranging from 20%-33%) would help to improve the electronic conductivity of the MnO2-based electrode. On the other hand, binders (such as polyvinylidene fluoride or carboxymethyl cellulose with mass ratio around 10%) are required to construct a workable cell. Finding efficient additives that enhances the electronic conductivity of MnO2, while at the same time minimizing the content of both additives and binders, become a tempting goal as it would lead to high performance electrode with high packing density. In the present work, we demonstrate a binder free composite electrode of MnO2/reduced graphene oxide (rGO) with high MnO2 mass ratio (80 wt% of MnO2) using vacuum filtration. No additional additives (other than rGO) is introduced. The MnO2 nanosheets are homogeneously distributed on the surface of rGO sheets. Enhanced capacity, improved rate capability and cyclability are achieved in the MnO2/rGO composite electrodes, when compared to the conventional MnO2 electrodes. The MnO2/rGO composite electrodes have manifested the merits of an ideal electrode material: high capacity (301.4 mAh g-1 at 0.15 A g-1), fantastic rate capability (172.3 mAh g-1 at 6 A g-1), and cycling stability (the capacity retention remains 97.8% after 500 charge/discharge cycles at 6 A g-1). Our work demonstrates that the MnO2/rGO composite electrodes are one of the most attractive cathodes in zinc storage applications.