Tuning surface reactivity towards high-performance hard carbon in Li/Na/K-ion batteries

The C–H functional groups play a crucial role in reducing electrolyte reduction reactivity and eliminating the trapping effects on Li/Na/K-ions, thereby enhancing the initial coulombic efficiency and reversible capacity. Controlling surface chemistry is critically important for improving the initial Coulombic efficiency (ICE) and adsorption capacity of hard carbon anode used in Li/Na/K-ion batteries. However, accurately identifying the types and concentrations of hydrogen/oxygen terminated functional groups (HTFG/OTFGs) and distinguishing their functionalities remain challenge. Herein, we quantitatively investigated the surface chemistry on hard carbon via ultra-high temperature programed desorption measurements, and uncovered the role of HTFG/OTFGs in influencing ICE and adsorption capacity in Li/Na/K-ions cells. The C–H group is found to be dominant species on the surface of hard carbon, and presents a positive correlation with ICE values and adsorption capacity. The low reactivity of C–H group with both electrolyte salt and solvent results in the formation of thinner and highly conducive solid electrolyte interphase (SEI) layer, which benefit for the enhanced ICE and improved Li/Na/K-ions diffusion across SEI layer. Additionally, the pimping trapping effect of C–H groups allows the adsorbed Li/Na/K-ions to migrate into graphitic interlayer quickly, enhancing the slope capacity. By fabricating a C–H group-rich surface chemistry on hard carbon, a high ICE value and satisfactory specific capacity have been realized. These findings enrich our understanding of the surface chemistry-induced interfacial reaction, which effectively guides the rational design of high-performance hard carbon.