Scalable In Situ Reactive Assembly of Polypyrrole-Coated MnO2 Nanowire and Carbon Nanotube Composite as Freestanding Cathodes for High Performance Aqueous Zn-Ion Batteries

Flexible aqueous zinc-ion batteries are attracting increasing interest owing to high theoretical capacity, low cost and high safety, however, it is highly challenging to design and fabricate suitable cathodes with superior Zn2+ storage as well as high flexibility. Herein, a free-standing flexible film composed of carbon nanotubes and polypyrrole (PPy)-coated MnO2 nanowires is prepared via a facile in situ reactive self-assembly and following vacuum filtration. The unique hierarchically porous 3D architecture of uniformly dispersed MnO2 nanowires with PPy coating in highly electrically conductive and interconnected CNTs networks not only improve the reaction kinetics and structural stability of the electrodes during repeated cycling, but also provides abundant sites for Zn2+ and H+ adsorption, giving rise to additional pseudocapacitive charge storage. When the free-standing flexible film is used as a freestanding cathode for an aqueous zinc ion battery, the electrode shows a good storage capacity of H+ and Zn2+ ions and a superior durability with a good capacity retention rate of 87.4 % after 1000 times at 1 A/g. And the energy density of the flexible device is about 341.6 Wh/kg (based on the mass of MnO2).The results provide a feasible strategy of constructing high-performance cathodes for flexible aqueous zinc-ion batteries.