Molecular Modularized Co-Polyimide as a Water-Processable Multifunctional Binder for High-Performance Si/C Anodes in Lithium-Ion Batteries.

Micrometer-sized silicon-carbon (Si/C) anode materials with high capacity represent one of the most promising alternatives for achieving a high energy density in lithium-ion batteries. The development of binders that effectively interact with Si/C active materials is crucial for ensuring the stability of the Si/C electrodes. In this study, a water-processable multifunctional copolyimide binder (denoted as SPI-) comprising three molecular modules was designed. The adenine modules within the molecular chain serve to facilitate hydrogen bonding with the silicon surface of Si/C as well as promote π-π interactions with the carbon surface. These dual interfacial interactions contribute significantly to the stability of the electrode structure. Furthermore, lithium sulfonate groups (Li transport module) and flexible segments (entropic elasticity module) enhance lithium ion transport and accommodate volume expansion, respectively. Electrodes incorporating this multifunctional binder exhibited excellent cycling stability and rate performance: after 400 cycles at 0.5 A g, a capacity of 825.2 mAh g was achieved with a retention of 93.1%. At 2.0 A g, the electrode maintained a high capacity of 701.6 mAh g. Full cells assembled with a LiNiCoMnO cathode demonstrated a capacity of 150.4 mAh g, with a retention of 92.7% after 300 cycles. This work provides key insights into the development of multifunctional binders for high-energy, long-life lithium-ion batteries.