High S-doped amorphous carbon/carbon quantum dots coupled micro-frame for highly efficient potassium storage

Anode materials with excellent rate capability, capacity, and cycle life have been a challenge in obtaining cost-effective K-ion batteries (KIBs). Based on the concept of waste recycling, we prepared the S-doped (21.5%) amorphous carbon/carbon quantum dots coupled micro-frame (SCMF) by combining chemical exfoliation and S/Se-assisted carbonization. SCMF exhibited the advantages of integrating amorphous carbon and carbon quantum dots (CQDs). The CQDs serve as fast electron channels, while amorphous carbon can accommodate more large-size K-ions and mitigate volume expansion. In KIBs, SCMF maintained a high reversible capacity (414.0 mAh g⁻¹, after 100 cycles at 100 mA g⁻¹), a good rate capability (224.0 mAh g⁻¹, 2000 mA g⁻¹), and excellent capacity retention (208.9 mAh g⁻¹, after 2000 cycles at 1000 mA g⁻¹). The molecular dynamic simulation revealed that CQDs provided fast electron transport channels and that C, O and S atoms had suitable interactions with K, facilitating potassium storage. Moreover, the potassium-ion capacitor (PIC) assembled from SCMF and activated carbon exhibited stable electrochemical performance, proving its potential for application. The research provided valuable insights into the reuse of biomass waste in new secondary batteries.