Characterization of polymeric binders for silicon anodes in next-generation lithium-ion batteries

This doctoral research focuses on the development, characterization, and industrial transfer of advanced polymeric binders for silicon-based composite anodes in next-generation lithium-ion batteries. Silicon offers a theoretical capacity far exceeding that of graphite, yet its practical use is limited by the severe volume expansion occurring during lithiation and delithiation, which leads to particle fracture, unstable SEI formation, loss of electrical contact, and rapid degradation. The thesis addresses these challenges by analysing how the molecular design of polymeric binders can stabilize silicon-composite electrodes and enable reliable large-scale manufacturing. The work investigates SiOx@C and Si/C composites, materials in which oxide matrices and carbon coatings help buffer mechanical stress and improve interfacial stability. Li-doped and Mg-doped SiOx@C are examined for their enhanced robustness, improved processability, and compatibility with water-based formulations. A central contribution is the comprehensive evaluation of poly(acrylic acid)-based terpolymer binders developed by Syensqo Specialty Polymers S.p.A.. Their acidity, monomer composition, and architecture are tailored to strengthen interactions with silicon-oxide surfaces, improve adhesion to the current collector, and maintain mechanical integrity throughout cycling. The research establishes direct correlations between binder chemistry, slurry rheology, coating uniformity, mechanical properties, and electrochemical performance. Laboratory studies are complemented by pilot-scale validation. Issues such as gas evolution from Li-containing oxides during aqueous processing are identified, motivating the adoption of Mg-doped SiOx@C as a more stable and industrially scalable active material. Full-cell testing confirms that the most advanced binder generation provides superior cycling stability, reduced impedance growth, and improved thermal dimensional stability compared with conventional systems. Overall, the thesis demonstrates that rational binder design is crucial for enabling robust, manufacturable silicon-composite anodes and outlines a practical route toward their integration into high-energy lithium-ion battery technologies.