Hemicellulose-derived porous spherical micron-cage for advanced Zn²⁺ storage

Zinc ion capacitor (ZIC) is regarded as a new generation of energy storage device because of high redox potential of zinc anode, eco-friendly and safety. Herein, using hemicellulose as precursor and self-made cubic CaCO₃ as template, the porous carbon spherical micron-cage (MCs) were prepared by template method assisted physical activation method. The prepared MCs are mainly rich in mesopores and micropores. Simultaneously, the porous spherical cage also helps cathode to fully contact with electrolyte, which provides a shortcut for the rapid transport of ions in the porous channel. The MC4 obtained by optimizing the ratio of hemicellulose to CaCO₃ exhibits high specific capacity of 128.4 mAh g^-1 at 0.5 A g^-1 and remains 57.5 mAh g^-1 at 10 A g^-1. The energy density of 89.4 Wh kg^-1 and power density of 6916 W kg^-1 can be obtained. Besides, it can also achieve good cycle stability after 8000 cycles. The quasi-solid ZIC based on MC4 cathode and PVA/LiCl/ZnCl₂(gel) electrolyte is able to achieve high energy density up to 155.7 Wh kg^-1 at 0.1 A g^-1. This work may provide a novel idea for preparing advanced porous carbons for the cathode of ZIC.