Binder-Free α-MnO2 Nanowires on Carbon Cloth as Cathode Material for Zinc-ion Batteries.

Recently, rechargeable zinc-ion batteries (ZIBs) have gained a considerable amount of attention due to their high safety, low toxicity, abundance, and low cost. Traditionally, a composite manganese oxide (MnO2) and a conductive carbon having a polymeric binder are used as a positive electrode. In general, a binder is employed to bond all materials together and to prevent detachment and dissolution of the active materials. Herein, the synthesis of α-MnO2 nanowires on carbon cloth via a simple one-step hydrothermal process and its electrochemical performance, as a binder-free cathode in aqueous and nonaqueous-based ZIBs, is duly reported. Morphological and elemental analyses reveal a single crystal α-MnO2 having homogeneous nanowire morphology with preferential growth along {001}. It is significant that analysis of the electrochemical performance of the α-MnO2 nanowires demonstrates more stable capacity and superior cyclability in a dimethyl sulfoxide (DMSO) electrolyte ZIB than in an aqueous electrolyte system. This is because DMSO can prevent irreversible proton insertion as well as unfavorable dendritic zinc deposition. The application of the binder-free α-MnO2 nanowires cathode in DMSO can promote follow-up research on the high cyclability of ZIBs.

Annealing induced a well-ordered single crystal δ-MnO2 and its electrochemical performance in zinc-ion battery.

Herein, the formation and electrochemical performance of a novel binder-free turbostratic stacked/ well-ordered stacked δ-MnO2-carbon fiber composite cathodes in deep eutectic solvent (DES) based zinc-ion battery (ZIB) is reported. Results of morphological, elemental, and structural analyses revealed directly grown and interconnected δ-MnO2 crumpled nanosheets on a carbon fiber substrate. Moreover, an improvement via a simple annealing strategy in the stacking, surface area and conductivity of the δ-MnO2 sheets was observed. Annealing induces the rearrangement of δ-MnO2 sheets resulting in the transformation from turbostratic stacking to a well-ordered stacking of [Formula: see text]-MnO2 sheets, as indicated by the selected area electron diffraction (SAED) hexagonal single crystal pattern. Besides, the formation of the well-ordered stacking of [Formula: see text]-MnO2 sheets exhibited improved electrochemical performance and cyclability, as cathode material for ZIB. The novel strategy described in this study is an essential step for the development of binder-free δ-MnO2-C fiber composite with a well-ordered stacking of δ-MnO2 sheets. This study also demonstrated comparable electrochemical performance between the turbostratic [Formula: see text]-MnO2 sheets and the well-ordered stacked δ-MnO2 sheets.