Altering Thermal Transformation Pathway to Create Closed Pores in Coal‐Derived Hard Carbon and Boosting of Na+ Plateau Storage for High‐Performance Sodium‐Ion Battery and Sodium‐Ion Capacitor

Abstract Coal features low‐cost and high carbon yield and is considered as a promising precursor for carbon anode of sodium‐ion batteries (SIBs) and sodium‐ion capacitors (SICs). Regulation of microcrystalline state and pore configuration of coal structure during thermal transformation is key to boost Na + storage behavior. Herein, a facile strategy is reported to create abundant closed pores in anthracite‐derived carbon that greatly improves Na + plateau storage. An altered thermal transformation pathway of chemical activation followed by high‐temperature carbonization is adopted to achieve the conversion of open nanopores and ordered carbon crystallite into closed pores surrounded by short‐range carbon structures. The optimized sample delivers a large reversible capacity of 308 mAh g –1 that is dominantly contributed by the low‐voltage plateau process. Experimental results reveal the enhanced pore‐filling mechanism in the developed closed pores. Benefitting from the improved plateau behavior, the constructed SIB delivers a high‐energy density of 231.2 Wh kg –1 with an average voltage of 3.22 V; the assembled full‐carbon SIC shows high energy and power densities (101.8 Wh kg –1 and 2.9 kW kg –1 ). This work provides a universal thermal transformation approach for designing high‐performance carbon anode with closed porosity from low‐cost and highly aromatic precursors.