In situ growth of δ-MnO2/C fibers as binder-free and free-standing cathode for advanced aqueous Zn-ions batteries

Manganese dioxide (MnO2) has been extensively studied in aqueous zinc ion batteries (AZIBs) due to its high redox potential, high theoretical capacity and low cost. However, its low capacity and poor structural stability result in poor performance. In this study, we propose a novel approach where δ-MnO2 is grown in situ on carbon fibers derived from coal (δ-MnO2@CCFs). The unform anchoring of δ-MnO2 on the carbon fibers allow for good flexibility and keep structural stability during cycling. The doping of heteroatoms (N) directly forms chemical bonds with δ-MnO2 and reduces electrostatic repulsion within the δ-MnO2@CCFs material, while facilitating the insertion and extraction of Zn2+ and H+ ions. Moreover, the flexible AZIBs exhibit excellent electrochemical reversibility even under bending and folding conditions. The δ-MnO2@CCFs electrode material exhibits a capacity of 352 mAh g-1 at a current density of 0.5 A g-1 after 100 cycles. Furthermore, the assembled flexible Zn//δ-MnO2@CCFs AZIBs maintain a capacity of 293.7 mAh g-1 after 50 cycles at a current density of 0.1 A g-1.