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A series of polyimides, which contain polyethylene glycol (PEG) segments with different molecular weight in the polymer chains, are synthesized through a facile one-pot method and characterized by Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy. The main part of polyimides is originated from trimellitic anhydride chloride (TMAC) and 4,4′-methylenedianiline, onto which PEG segments are introduced through an esterification reaction with TMAC. These obtained polyimides, which acquire excellent water solubility after being neutralized by triethylamine, are applied as water-soluble binders to silicon negative electrodes for lithium ion batteries, and significantly improve the electrochemical performance of silicon anodes. Specially, the PI-200 (polyimide copolymerized with PEG-200) based silicon electrode exhibits a high initial discharge capacity of 2989.7 mAh g −1 and remains about 2235.5 mAh g −1 after 200 cycles at the current density of 0.1 C (420 mA g −1 ). [ABSTRACT FROM AUTHOR]

Highly adhesive binders are developed to prolong the cycle life of silicon anodes and accelerate their practical application. A series of poly(N-methacryloyl-3,4-dihydroxy- l -phenylalanine) (PMDOPA) binders, containing ultra-high content of catechol groups, are synthesized through radical polymerization and applied to silicon anodes. The ultra-high content of catechol groups endows the PMDOPA binder superior adhesive strength compared to the carboxyl groups of the polyacrylic acid (PAA) binder. As the molecular weight increases, the flexibility, solvent resistance and adhesive strength of the PMDOPA binders are all enhanced, which effectively alleviates the electrode pulverization during long-term cycling and prolongs the cycle life of batteries. Especially, the PMDOPA-20 binder, which possesses the highest molecular weight of 208 kDa among all the PMDOPA samples, exhibits the longest cycle life of 665 cycles at the current density of 840 mA g−1, even though its molecular weight is lower than PAA. This work demonstrates that both the functional adhesive group and molecular weight are crucial for binder performance, which provides a valuable reference for the future development of high-performance binders. Image 1 • A series of binders containing ultra-high content of catechol groups are synthesized. • Silicon anode performance is improved as the binder molecular weight increases. • The silicon electrodes with catechol-based binders exhibit long cycle lives. • Both functional group and molecular weight are crucial for binder performance. [ABSTRACT FROM AUTHOR]

Abstract Silicon is one of the most promising anode materials for the next-generation high energy density lithium-ion batteries as its superior specific capacity and ultralow lithiation/delithiation voltage. Whereas, silicon suffers massive volume change during cycling, resulting in drastic pulverization of active material and iterative growth of solid electrolyte interphase, largely limiting their widely applications. To address the challenge, water-soluble glycinamide modified PAA (PAA-GA) is synthesized through a facile and low-cost coupling method as a polymer binder to assemble silicon anode for alleviating its huge volume change. The carboxyl and double amide groups of the PAA-GA can form hydrogen bonds with the hydration layer of silicon, and meanwhile the double amide groups of PAA-GA can form double hydrogen bonds via interchain cohesion. These strong supramolecular interactions are reversible and can recover the dissociated bonds more efficiently upon the elimination of the mechanical stress. The PAA-GA-based silicon electrodes exhibit excellent cycling stability and high coulombic efficiency, demonstrating the PAA-GA binder being great potential in fabricating high energy density silicon anodes for next-generation lithium-ion batteries. Graphical abstract Image 1 Highlights • Glycinamide-based binder was synthesized via a facile coupling method. • Water-soluble binders were used for silicon anodes in lithium ion batteries. • A high capacity and good cyclestability were achieved by using the modified binder. [ABSTRACT FROM AUTHOR]