Wet Spinning of Graphene Oxide Fibers with Different MnO 2 Additives.

We present the fabrication of graphene oxide (GO) and manganese dioxide (MnO 2 ) composite fibers via wet spinning processes, which entails the effects of MnO 2 micromorphology and mass loading on the extrudability of GO/MnO 2 spinning dope and on the properties of resulted composite fibers. Various sizes of rod and sea-urchin shaped MnO 2 microparticles have been synthesized via hydrothermal reactions with different oxidants and hydrothermal conditions. Both the microparticle morphology and mass loading significantly affect the extrudability of the GO/MnO 2 mixture. In addition, the orientation of MnO 2 microparticles within the fibers is largely affected by their microscopic surface areas. The composite fibers have been made electrically conductive via chemical or thermal treatments and then applied as fiber cathodes in Zn-ion battery prototypes. Thermal annealing under an argon atmosphere turns out to be an appropriate method to avoid MnO 2 dissolution and leaching, which have been observed in the chemical treatments. These rGO/MnO 2 fiber cathodes have been assembled into prototype Zn-ion batteries with Zn wire as the anode and xanthan-gum gel containing ZnSO 4 and MnSO 4 salts as the electrolyte. The resulted electrochemical output depends on the annealing temperature and MnO 2 distribution within the fiber cathodes, while the best performer shows stable cycling stability at a maximum capacity of ca. 80 mA h/g.