Ionically Conductive Self-Healing Polymer Binders with Poly(ether-thioureas) Segments for High-Performance Silicon Anodes in Lithium-Ion Batteries

During repeated discharging and charging processes, the large volume change of Si causes the anode structure to break, resulting in poor cycle performance. The binder plays a vital role in reducing the volume expansion of Si. Herein, by grafting poly(ether-thioureas) (TUEG) on poly(acrylic acid) (PAA) through an amidation reaction, a self-healing polymer binder (PAA–TUEG) was designed and synthesized, which is beneficial for the fast Li ionic conduction and self-healing ability. Specifically, PAA–TUEG gel samples achieved 81% healing efficiency at room temperature without any external intervention. The Li-ion diffusion coefficient of the Si anode with PAA–TUEG as a binder reached 8.80 × 10–5 cm2 s–1. Half batteries consisting of Si anodes using the PAA–TUEG polymer as a binder and lithium metal anodes exhibited an initial discharge capacity as high as 3676.1 mAh g–1 with a Coulombic efficiency of 87.2%. A stable reversible capacity of 2744.3 mAh g–1 with a capacity retention rate of 82% after 300 cycles was also realized. It indicates that the electrochemical performance of Si anodes with this polymer binder is significantly improved compared with that using conventional binders. Furthermore, the full cell composed of LiFePO4 cathodes and Si anodes with PAA–TUEG as a binder exhibits superior electrochemical performance. This concept of the polymeric binder, combining high Li-ion conductivity and self-healing ability, should be used to improve the cycle life of next-generation batteries using high-capacity materials that undergo huge volume changes during cycling.