Engineering the microstructures of Terminalia catappa fruit shell-derived carbon as a potential anode for potassium-ion batteries

A low-cost, highly abundant, and environmentally friendly Terminalia catappa (TC) fruit shell-derived carbon with engineered microstructures is used for K-ion storage. The treatment with HCl and FeCl 3 catalyst controls the number of active sites and the degree of graphitization in the TC carbon in a facile single-step procedure before high-temperature pyrolysis. XRD and Raman analysis classify the prepared samples as amorphous, pseudo-graphitic, or graphite-like based on the pre-treatment. The HR-TEM and SAED images visually confirm the local (dis)order of the engineered structures. The electrochemical performance of the effectively altered TC carbon demonstrates that the increase in the number of lateral graphene sheets in FTC (FeCl 3 -treated) and HFTC (HCl and FeCl 3 -treated) results in high discharge capacities of 272 and 350 mAh g -1 , respectively, compared to the pristine electrode (220 mAh g -1 at 20 mA g -1 ). FTC and HFTC show better long-term cyclic stability, with specific capacities of 71 and 83 mAh g -1 , respectively, after 700 cycles at 200 mA g -1 . In addition, a potential-dependent ex-situ EIS study with DRT analysis reveals K-ion kinetics through the engineered graphite-like structures during charge-discharge. The systematic investigation of the engineered microstructure helps to pave the way for practical K-ion batteries.