Unraveling the potassium storage performance of carbon nanosheets derived from heavy oils

As by-products of petroleum refining, heavy oils are characterized by high content of carbon, low cost, and tunability, making them competitive precursors for constructing anodes for potassium ion batteries (PIBs). However, the correlation between heavy oil composition and potassium storage performance remains unclear. Here, by employing heavy oils with distinct group compositions as carbon sources, namely fluid catalytic cracking slurry (FCCs), petroleum asphalt (PA), and deoiled asphalt (DOA), three carbon nanosheets (CNS) were prepared through a molten salt method as anodes for PIBs. The four-component composition of heavy oils can effectively tailor the lamellar thicknesses, sp³-C/sp²-C ratios, and defect levels, thereby affecting the potassium storage performance. Notably, with a high content of aromatic hydrocarbons and moderate heavy component moieties, the FCCs-derived carbon nanosheets (CNS-FCCs) exhibit a smaller layer thickness, enlarged interlayer spacing (0.372 nm), and increased folding defects, which show enhanced charge/ion transfer, potassium storage sites, and reaction kinetics. The CNS-FCCs deliver a remarkable K⁺ storage capacity (248.7 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹), long cycle lifespan (190.8 mAh g⁻¹ after 800 cycles at 1.0 A g⁻¹), and excellent rate capability, ranking among the top echelons. This work sheds light on the influence of heavy oil composition on carbon structure and electrochemical performance, providing guidance for the design and development of advanced heavy oil-derived carbon electrodes for PIBs.