High ICE Hard Carbon Anodes for Lithium-Ion Batteries Enabled by a High Work Function

Hard carbons (HC) derived from biomass material are most promising anodes for lithium-ion batteries (LIBs) because of their cost effectiveness and environmental friendliness. However, the low initial Coulombic efficiency (ICE) of HC anodes reduces the energy density of full cells, which seriously impedes their practical applications. Herein, we demonstrate that the ICE of HC anodes can be significantly improved by modulating the work function of a model HC derived from cotton and deliberately treated to form C-Cl bonds on its surface. By X-ray absorption near-edge structure and density functional theory (DFT) calculation studies, it is verified that the introduction of the C-Cl bond leads to the electron transfer from C to Cl and enhances the work function of the system. In addition, this Cl-doped HC anode can inhibit the reduction of solvent molecules in the electrolyte and reduce the formation of a solid electrolyte interface (SEI) film. Consequently, the ICE is improved from 64.8 to 78.1%. This study provides an effective route to reduce the formation of the SEI film and improve the ICE of hard carbon anodes for LIBs.