Effect of Addition of Thermally Annealed Graphene in Tender Coconut-Derived Hard Carbon for Potassium Ion Battery

To fulfill the rising demand for large-scale energy storage devices, potassium ion batteries (KIB) are forecasted to play a critical role in replacing lithium-ion batteries (LIB). Herein, we have synthesized hard carbon derived from tender coconut (THC) with thermally reduced GO sheets (trGO@THC) using a two-step precarbonization and pyrolysis method. The synthesized hard carbon possesses a low specific surface area of about 20 m2 g–1. The CR2032-type coin cells with the synthesized material as anode and 0.8 M KPF6 in EC:DEC (1:1 v/v) electrolyte, and K-metal as counter/reference electrode were assembled for further electrochemical characterizations. The addition of rGO sheets in the THC improved the initial reversible capacity, showing a value of 217.6 mAhg–1 compared to 166.2 mAhg–1 of pristine hard carbon coin cells at a current density of 200 mAg–1. The Coulombic efficiency improved to 76.5% from 69.6%. However, the composite electrode exhibited lower reversible capacity at higher current densities, indicating a poor rate capability. Furthermore, the composite electrode retained only 76.5% of the original capacity compared to 98.3% THC after 100 cycles. The FESEM images of cycled electrodes show the formation of dendrites caused by electrolyte degradation. This interplay of material characteristics leading to a change in electrochemical behavior can be helpful for the futuristic development of KIBs.