Gamma(ɣ)-MnO2/rGO Fibered Cathode Fabrication from Wet Spinning and Dip Coating Techniques for Cable-Shaped Zn-Ion Batteries

Cable/fiber-shaped Zn-ion batteries are designed to power wearable electronics that require high flexibility to operate on human body. However, one of technical challenges of these devices is the complexity and high cost for manufacturing fibered cathode. In this work, we demonstrated gamma manganese oxide (ɣ-MnO2)/reduced graphene oxide (rGO) fibered cathode fabrication using facile and cost-effective fiber production and active material coating techniques. Specifically, rGO fibers were fabricated via wet spinning, followed by chemical reduction with hydroiodic acid (HI). The synthesized rGO fiber bundle was then dip-coated with a mixture of ɣ-MnO2, carbon black or multi-walled carbon nanotubes, and xanthan gum or polyvinylidene fluoride binder to obtain ɣ-MnO2/rGO fibered cathode. We studied the effect of binders and conductive materials on physical properties and electrochemical performance of the fibered cathode. It was found that hydrophobic binder had more benefits than hydrophilic binder by providing higher active material loading, better coating layer homogeneity, and more stable electrochemical performance. Cable-shaped Zn-ion batteries (CSZIBs) were then assembled by using the ɣ-MnO2/rGO fibered cathode, Zn wire anode, and xanthan gum polymeric gel electrolyte with 2 M ZnSO4 and 0.2 M MnSO4 salts without a separator. We investigated the battery assembling procedure on a glass slide (prototype ZIB) and in a plastic tube (cable-shaped ZIB), and evaluated their electrochemical performance. The CSZIB showed promising maximum capacity of ~ 230 mAh/g with moderate cycling stability (80% capacity retention after 200 cycles) and high flexibility by maintaining the potential after consecutive pressing for 200 times under controlled pressing distance, duration, and testing speed. Finally, we explored ion intercalation behaviours and proposed a H+/Zn2+ co-intercalation mechanism in ZIB with ɣ-MnO2 active material.Graphical abstract