Hydrothermal modification of natural graphite with KCl: different roles of K⁺ and Cl⁻ in promoting the electrochemical performance of Li-ion batteries

The poor structural stability and cyclability restrict the wide application of natural graphite (NG) in Li-ion batteries (LIBs). Herein, NG was hydrothermally modified with KCl at 200 °C for 12 h. The NG modified with 1.0 wt% KCl exhibits excellent rate performance (revealing average lithiation capacities of 407.7 mAh g⁻¹ at 0.1 C and 341.2 mAh g⁻¹ at 0.5 C) and cyclability. The roles of K⁺ and Cl⁻ in promoting the electrochemical performance of NG was revealed via systematic characterizations. In the hydrothermal process, K⁺ entered into graphene interlayers to enhance electronic conductivity and introduce lattice distortion in NG to facilitate Li-ion transport during lithiation and delithiation, while Cl⁻ interacted with the NG surface to create C‒Cl bonds which are partially converted into Li-conductive LiCl during lithiation to function as the component of solid electrolyte interphase. Both the residual C‒Cl bonds and in situ formed LiCl with high stability could stabilize the structure and performance of the NG anode. This simple hydrothermal modification with KCl might promote the wide utilization of the NG anode in LIBs.