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

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-x) 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^-1, a capacity of 825.2 mAh g^-1 was achieved with a retention of 93.1%. At 2.0 A g^-1, the electrode maintained a high capacity of 701.6 mAh g^-1. Full cells assembled with a LiNi_0.5Co_0.2Mn_0.3O₂ cathode demonstrated a capacity of 150.4 mAh g^-1, 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.