A Refined Stepwise Carbonation Strategy for Controllable Synthesis of Porous Carbon for High-Performance Zinc-Ion Hybrid Capacitors

The precise tailoring of the composition and structure of porous carbon is crucial for its application in capacitors. Herein, a refined stepwise carbonization strategy, involving holding the material at the melting temperature of metal salts for controlled carbonization, is proposed to precisely design coal tar pitch (CTP)-based porous carbon. The stepwise carbonization effectively modulates the yield, pore structure, and defect level of the porous carbon. Dwelling at the melting point promotes the dehydration-condensation of CTP and stabilizes the carbon skeleton, yielding a high carbon content. Theoretical calculations elucidate the interaction between metal salts and hydroxyl oxygen in CTP, and the energy barrier as a metric to evaluate the ability of metal salts to regulate the microcrystalline structure of carbon is proposed. Meanwhile, sodium alginate gels induced by the aforementioned metal salts are prepared, and the zinc-ion hybrid capacitor assembled with the prepared porous carbon and gel exhibits superior specific capacity (219 mAh g −1 ), high energy density (176.2 Wh kg −1 ), and broad temperature range applicability (−40–75 °C). This study proposes a universal method for controlling the yield, microcrystalline structure, and capacitance properties of CTP-based porous carbon. It holds promise for broadening the application scope in the preparation of other carbon materials.