Abstract: It is a big challenge to tune the structure and composition of carbon-based anode materials to increase the active sites by a green synthesis strategy for potassium ion batteries (PIBs). Herein, the N/F/S co-doped three-dimensional (3D) interconnected carbon nanosheets (NFS-CNSs) were synthesized from coal tar pitch (CTP) through a green and low-temperature treatment process for the first time. The as-obtained NFS-CNS₆₀₀ features 3D interconnected ultra-thin carbon nanosheets with abundant active sites, tunable N/F/S species, and enlarged carbon interlayer spacing. The density functional theory calculation results demonstrate that NFS-CNSs exhibit the highest electron density and most negative K⁺ adsorption energy (-0.59 eV) compared to single or double-atom doping, thereby enhancing the storage performance of K⁺. As an anode for PIBs, the NFS-CNS₆₀₀ exhibits good cycle stability (98.2 % capacity retention after 200 cycles at 0.2 A g^-1), high capacity (409.1 mAh g^-1 at 0.05 A g^-1) and rate performance (179.5 mAh g^-1 at 5 A g^-1). Besides, the NFS-CNS₆₀₀ anode also displays outstanding sodium storage performance. This work offers a green strategy to synthesize CTP-based anode materials from coal chemical by-products for high-performance PIBs.

Key words: Potassium ion batteries, Green synthesis, Heteroatom doping, Carbon nanosheets, Coal tar pitch, Density functional theory