Improving the Cycle Performances of Si Anode Using Water-Soluble Polyimide Binders for Lithium-Ion Batteries

With increasing demands for high-energy storage in electric vehicles and various applications, lithium-ion batteries (LIBs) are faced with the crucial need for both high energy density and long cycle life. Silicon is one of the most promising anode materials due to its high theoretical capacity and abundant resources. However, the enormous volume change during charging and discharging cycles results in repeatedly formed solid electrolyte interfaces, pulverization of electrodes, and continuous capacity fading. Although binders possess a small portion in the Si anode, they have a significant influence on the cycle performance. Polyimides are well-known engineering polymers due to their excellent properties, including superior mechanical, remarkable thermal, and chemical properties. Besides, its excellent properties can be modified by selecting monomers with desirable functional moieties.
In this work, we designed and synthesized water-soluble polyimide (W-PI) binders for eco-friendly and high-performance silicon anodes. The two types of diamine structures were designed to enhance cycling stability. The carboxylic acid (-COOH) group in one diamine provides strong adhesion sites to silicon (Si) particles, effectively mitigating damage caused by volume expansion. Additionally, the ether (-O-) group in the other diamine contributes to the flexibility of the polyimide (PI) structure and facilitates rapid ionic transport during the charge-discharge process. The structural and thermal properties of the synthesized W-PI were confirmed through NMR, FT-IR, and TGA analyses, demonstrating its robust thermal stability and adaptability. Cyclic voltammetry and galvanostatic charge/discharge tests were conducted to evaluate the electrochemical performance of the silicon anodes. We demonstrated that the engineered W-PI binders enhance the cycling stability and performance of silicon anodes, enabling more efficient and sustainable energy storage solutions.