Density functional theory (DFT) was also implemented to analyze the molecular electrostatic potential (MESP) and identify the redox-active sites. As shown in Fig. , the equivalent minima of the electrostatic potential (ESP) regions located around the nitrogen of the imine linkage acted as redox-active centres for Li⁺ storage in COF@bio. Additionally, the oxygen in the furan structure and the centre of the benzene ring also exhibited negative ESP values, suggesting these sites may serve as potential lithium storage sites. In addition, the ex-situ X-ray photoelectron spectroscopy (XPS) analysis was conducted to investigate the reaction mechanisms of the COF composites-based electrode. For COF@bio-40 based anode, the high-resolution C 1s XPS peaks of the initial state at about 284.2, 284.8, 285.9, 287.6, and 290.0 eV correspond to C=C, C-C, C-O/C-N, C=N, and C-Li, respectively (Fig. ). The N 1s spectra of the initial COF@bio-40 anode shown two peaks at 398.6 (N=C) and 399.5 eV (N-C) (Fig. ). In contrast, the O 1s spectrum of the starting state of the electrode exhibited three characteristic peaks attributed to O-C, C-O-C, and O-Li (Fig. ).