Hybrid Ionically Covalently Cross-Linked Network Binder for High-Performance Silicon Anodes in Lithium-Ion Batteries

Abstract

Silicon has gained considerable attention as an anode material in lithium-ion batteries due to its high theoretical capacity. However, the significant volume changes that occur during lithiation/delithiation processes often result in poor cycling stability of silicon anodes. In this study, a hybrid ionically covalently cross-linked network binder carboxymethylcellulose-hyperbranched polyethyleneimine (CMC-HBPEI) is successfully constructed by “switching” ionic bonds and partially “converting” them to covalent bonds to buffer the volume variation of silicon anodes. In this hybrid cross-linked network, the covalently cross-linked network is responsible for maintaining the structural integrity of the anode, while the ionically cross-linked network utilizes the bonding reversibility to sustainably dissipative the mechanical stress and self-heal the structural breakages generated from the lithiation expansion of silicon. By changing the drying temperature of the anode, the ratio of covalent and ionic bonds in the hybrid cross-linked network can be adjusted to balance the mechanical stability and bonding reversibility of the CMC-HBPEI binder. Even after 300 cycles of charging/discharging under a current density of 500 mAg−1, the specific capacity of the optimized Si/CMC-HBPEI anode remains at 1545 mAhg−1.

Keywords

• carboxymethylcellulose
• hyperbranched polyethyleneimine
• hybrid cross-linked network
• silicon anode
• lithium-ion battery