In Situ Development of Elastic Solid Electrolyte Interphase via Nanoregulation and Self-Polymerization of Sodium Itaconate on Graphite Surface

The regulation of solid electrolyte interface (SEI) on electrode material surface is one of the most crucial fundamental issues in lithium ion batteries. A desired SEI film is characterized by high homogeneity, flexibility and ductility, which is able to stand up with the volume change of the active material during repeated electrochemical cycles. More than 10% volume change of graphite particle is easy to cause brittle fracture and rearrangement of the SEI film, resulting in continuous consumption of the active Li ion and capacity decline of the cell. Herein, we proposed an in situ development of elastic SEI film via nanoregulation and self-polymerization of sodium itaconate (SI) on graphite surface. The nanotuned uniform SI nanolayer on the graphite surface, as a template for SEI film, contributes to a polymer-reinforced SEI film through self-polymerization between the carbon double bonds. With 20 nm of the SI nanolayer template, the overall electrochemical performances including the first Coulombic efficiency, rate capability, cycling stability, and even, the high temperature performance are remarkably improved. Moreover, the impedance rise of the electrode with electrochemical cycles is effectively suppressed. As the result, cycle-life of the full cell based on LiFePO₄ cathode and the SI-decorated graphite anode is greatly enhanced.