Ionic Liquid-Decorated Copolymer Binders for Silicon/Graphite Anodes with Enhanced Rate Capability and Excellent Cycle Stability

Ionic liquid (IL)-decorated copolymers based on poly­((ethylene glycol) methyl ether methacrylate)-co-(acrylic acid)-co-(1-vinyl-3-ethylimidazolium hexafluorophosphate) were prepared and used as binders for Si/Gr anodes in lithium-ion batteries. The IL-decorated copolymer-bonded Si/Gr anodes showed a higher rate capability and better cycle stability than poly­(vinylidene fluoride) (PVDF)-bonded and poly­(acrylic acid) (PAA)-bonded Si/Gr anodes. In particular, the Si/Gr@CP1 anode exhibited an initial charge/discharge capacity of 1053/1286 mAh g^–1 during the first formation cycle and retained 93.1% of its specific capacity after 100 cycles at a current density of 0.6 A g^–1. Measurements from electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy demonstrated the quick formation of a well-structured solid–electrolyte interphase (SEI) layer on the IL-decorated copolymer-bonded Si/Gr anodes, which led to the excellent electrochemical performance of Si/Gr@CP1. The quick formation of this SEI layer was attributed to the introduction of IL into the polymer binder, which accumulated a large number of PF₆^– anions on the anode surface and facilitated SEI formation through in situ decomposition. The success of this work provides a promising avenue for pursuing high-capacity lithium-ion batteries (LIBs) with an extended cycle life.