Sustainable biowaste conversion into microporous carbons for efficient energy storage solutions in sodium-ion batteries

Sodium-ion batteries (SIBs) are prospective candidates for renewable energy storage technologies. However, SIB systems are still emerging, creating a demand for innovative, practical, and affordable active materials. Biomass-based hard carbons are promising anode materials for SIBs due to their easy accessibility, sustainability, and low cost.This study offers a novel, simple, and cost-effective method to produce microporous carbons from waste cotton using hydrothermal carbonization (HTC), KOH activation, and pyrolysis. Unlike previous studies on cotton-based carbons, the waste cotton-based microporous carbons were synthesized by the combination of HTC and KOH activation for the first time to be utilized as an anode in SIBs. Moreover, the influence of varying KOH concentrations on the structural and electrochemical properties of carbons was examined. The microporous carbon with a carbon/KOH ratio of 1/3, MC3, displayed a large surface area of 808 m2/g, abundant microporosity, and achieved a high reversible capacity of 330 mAh/g at 0.1 A/g, and good cyclability with a reversible capacity of 280 mAh/g at 1 A/g after 400 cycles. These results demonstrated that the microporous structure of MC3 provides fast and efficient ion transfer and an increased contact area between the electrode and electrolyte. In addition, the integration of hydrothermal carbonization and KOH activation improves electrochemical performance and offers substantial economic benefits, while incorporating wastewater treatment and KOH recovery strategies into the process can enhance scalability and environmental sustainability for industrial-scale production. Therefore, this research presents a cost-effective and scalable approach using a sustainable source to produce microporous carbon anode materials for SIBs, significantly benefiting the energy sector.