Efficient Transformation of Bituminous Grade Noncoking Coal into Hard Carbon for High-Performance Sodium-Ion Battery Anodes: A Sustainable and Cost-Effective Energy Storage Solution

Hard carbon, characterized by its low surface area and optimized pore structure, is considered one of the most promising anode materials for sodium-ion batteries due to its high capacity in the low-voltage plateau. Progenitors are crucial to both the final cost and yield of synthesized hard carbon. So, in this context, cost-effective bituminous grade noncoking coal is used as a precursor for hard carbon. Interestingly, this coal has ∼40% ash, negatively impacting the final product’s electrochemical performance. However, this study’s chemical and physical processes remove all kinds of ashes/impurities from the raw coal. Finally, the hard carbon is synthesized at ∼1500 °C and ∼55% yield of the final product is obtained, consisting of micro- and mesopores, a disordered structure with a low surface area of ∼4.2 m 2 g –1 . The hard carbon exhibits a specific capacity of ∼259 mAh g –1 with an extended plateau region when cycled at a specific current of ∼80 mA g –1 . Due to extended layer spacing and generation of micro- and mesopores, it shows a sound diffusion of Na + ions of ∼3.6004 × 10 –15 cm 2 s –1 . Upon long cycling, this material shows a cyclic stability of ∼76% up to 100 cycles, proving its effectiveness. When applied to the full cell, against the NVP@C cathode, it exhibits an energy density of ∼165 Wh kg –1 .