Self-supporting oxygen vacancy-rich α-MnO2 nanowire/few-layer graphite/SWNT bundle composite film for high-performance flexible aqueous zinc-ion battery cathode

The increasing demand for flexible and wearable electronic devices has led to widespread interest in flexible electrochemical energy storage devices. However, the transformation of the battery structure from conventional to flexible presents a great challenge to the battery design. Herein, we developed a facile method for the preparation of a self-supporting composite film consisting of oxygen-vacancy rich MnO2 nanowires (NWs), few-layer graphite nanosheets (FLGs), and single-walled carbon nanotube (SWNT) bundles as the cathode of flexible zinc-ion batteries. This ternary interwoven interconnection 3D structure enhances the electrochemical performance of the battery and realizes fast charge transfer; oxygen vacancies in the MnO2 NWs caused by heat treatment (300 °C in Ar) allow for rapid intercalation and diffusion of Zn2+. The interwoven FLGs and SWNT bundles improve the electrical conductivity, and the robust interactions between the two carbon nanomaterials and the MnO2 NWs effectively make the composite film with excellent mechanical properties. This self-supporting flexible electrode exhibits a high specific capacity of 374 mAh/g at 0.4 A/g, maintains a Coulombic efficiency of ∼ 100 % after 1600 cycles at 2 A/g, and has a high energy density of 651.5 Wh kg−1 at 65.2 W kg−1. Moreover, the flexible zinc ion batteries assembled with the electrode demonstrate good mechanical properties and a high reversible specific capacity of 343 mAh/g after 75 bending cycles. Based on these findings, we believe that this composite film holds great promise as a cathode material in flexible energy storage applications.