Elucidating the Chemical Pre‐Lithiation Mechanism of Hard Carbon Anodes for Ultra‐high Stability Lithium‐Ion Batteries

The hard carbon (HC) anode materials demonstrate high capacity and excellent rate performance in lithium-ion batteries. However, HC anodes suffer from excessive loss of Li⁺ ions during the formation of the solid electrolyte interphase (SEI) film, leading to poor cycling stability, which hinders their large-scale applications. Herein, a facile pre-lithiation strategy is proposed to achieve multi-functional precompensation of carbon nanofibers (CNFs) anodes. Both experimental and density functional theory (DFT) calculation results revealed that the strategy compensated for the loss of Li⁺ ions and reacted with four structures of CNFs during pre-lithiation, including tiny graphite domains, CO-containing functional groups, defects, and micropores. Furthermore, the lithium in pre-lithiated carbon nanofibers (pCNFs) existed in various forms, consisting of LiC₂₄ and LiC₁₈, Li─O─C, quasi-metallic lithium, and Li⁺ ions. Moreover, the uniformly distributed lithium on the surface of pCNFs induced the formation of denser and more robust LiF/Li₂CO₃-rich SEI film, which promoted Li⁺ ions transport. As a result, pCNFs showed more stable cycling performance (369.8 mAh g^-1, almost no decay for 1500 cycles). This work provides deeper insight into chemical pre-lithiation and offers a simple and mild strategy for highly stable batteries.