Block Copolymer-Derived Porous Carbon Fibers Enable High MnO2 Loading and Fast Charging in Aqueous Zinc-Ion Battery

Rechargeable aqueous Zn MnO2 batteries are promising for stationary energy storage because of their high energy density, safety, environmental benignity, and low cost. Conventional gravel MnO2 cathodes have low electrical conductivity, slow ion (de-)insertion, and poor cycle stability, resulting in poor recharging performance and severe capacity fading. To improve the rechargeability of MnO2, strategies have been devised such as depositing micrometer-thick MnO2 on carbon cloth and blending nanostructured MnO2 with additives and binders. The low electrical conductivity of binders and sluggish ion (de)insertion in micrometer-thick MnO2, however, still limit the fastcharging performance. Herein, we have prepared porous carbon fiber (PCF) supported MnO2 cathodes (PCF@MnO2), comprised of nanometer-thick MnO2 uniformly deposited on electrospun block copolymer-derived PCF that have abundant uniform mesopores. The high electrical conductivity of PCF, fast electrochemical reactions in nanometer-thick MnO2, and fast ion transport through porous nonwoven fibers contribute to a high rate capability at high loadings. PCF@MnO2, at a MnO2 loading of 59.1 wt%, achieves a MnO2-based specific capacity of 326 and 184 mAhg(-1) at a current density of 0.1 and 1.0 Ag-1, respectively. Our approach of block copolymer-based PCF as a support for zinc-ion cathode inspires future designs of fastcharging electrodes with other active materials.