In Situ Formation of Tungsten Nitride among Porous Carbon Polyhedra for High Performance Zinc–Iodine Batteries

To address the low capacity and poor stability of aqueous zinc–iodine batteries owing to the insulating nature of iodine and the shuttle effect of polyiodide, herein, tungsten nitride-modified porous carbon polyhedron (W2N/N-C) was prepared via the pyrolysis of ZIF-8 injected with phosphotungstic acid (PTA@ZIF-8). During the thermal treatment process, the self-nitridation enabled the in situ formation of tungsten nitride nanoparticles in hierarchical porous carbon with nitrogen doping for favorable loading of iodine. When used as the electrode material, the zinc–iodine battery exhibited the low polarization during the charge/discharge process with improved reversibility and good cycling stability for 2000 cycles. The improved electrochemical performance would be attributed to the confinement effect of W2N/N-C for the reversible conversion between iodine and polyiodide, thus enhancing the redox reversibility and utilization of active materials. The present work demonstrates an efficient strategy to prepare porous carbon with metal nitrides via the combination of carbonization and self-nitridation process for high-performing zinc–iodine battery.