Advanced aqueous binders for sustainable lithium-ion battery cathodes
- Autores: Ana Clara Rolandi
- Directores de la Tesis: Cristina Pozo Gonzalo (dir. tes.), David Mecerreyes Molero (dir. tes.)
- Lectura: En la Universidad del País Vasco - Euskal Herriko Unibertsitatea ( España ) en 2025
- Idioma: inglés
- Programa de doctorado: Programa de Doctorado en Química Aplicada y Materiales Poliméricos por la Universidad del País Vasco/Euskal Herriko Unibertsitatea
- Calificación: Sobresaliente Cum Laude
- Materias:
- Enlaces
- Tesis en acceso abierto en: ADDI
- Resumen
The increasing demand for sustainable and high-performance energy storage systems has driven significant advancements in lithium-ion batteries (LIBs). This thesis investigates the development of novel and advanced aqueous binders for high-energy cathodes in LIBs, aiming to address the limitations associated with traditional polyvinylidene fluoride (PVDF) binders and toxic solvents like N-methyl-2-pyrrolidone (NMP). Replacing NMP with water offers environmental and economic benefits, such as cost reductions, faster drying times, and facilitated recyclability of battery components.Notably, sodium carboxymethyl cellulose (Na-CMC) and styrene butadiene rubber (SBR) blends have been successfully utilized for anodes and LiFePO4 (LFP) electrodes that benefit from their inherent stability in water. However, high-voltage cathodes have been less explored due to their sensitivity to water. To address this gap, the developed aqueous binders were applied to high-nickel content cathodes, which are particularly challenging due to their susceptibility in aqueous solutions.Based on the binder classification from the literature review, this thesis introduces three types of polymer binders: a latex with high biocontent, a functional poly(ionic liquid) binder, and a biopolymer. The firstapproach focused on developing latexes with properties similar to commercial latexes but with high bio-content, reducing reliance on petroleum resources. Two biobased monomers, isobornyl methacrylate (IBOMA) and 2-octyl acrylate (2OA), were selected. The strategic combination of IBOMA and 2OA optimizes the mechanical properties of the binders, balancing rigidity and flexibility to enhance the electrochemical performance and mechanical integrity of the NMC 811 cathodes, delivering superior adhesion and reduced electrode cracking.The second approach focuses on developing a new family of poly (ionic liquid)s (PILs), which are widely used in battery applications due to their high ionic conductivity, wide electrochemical stability window, and good mechanical properties. However, most PILs investigated are not water-soluble. Therefore, the synthesis of water-soluble PILs was explored based on poly(diallyldimethylammonium) (PDADMA) with two phosphate anions; diethyl phosphate (DEP) and dibutyl phosphate (DBP). These PILs are fluorine-free, contributing to the reduced environmental impact of the binder. The PDADMA-phosphate binders delivered excellent electrochemical stability, low charge-transfer resistance, and enhanced cycling performance.The third binder under study is based on carrageenan biopolymers, which are biocompatible and used in the food industry, demonstrating their large availability and low cost. Three distinct types of carrageenan-kappa, iota, and lambda-are evaluated with 1, 2 or 3 sulfonate groups, respectively. Lambda carrageenan, with the highest sulfonate content, exhibits remarkable dispersion properties, strong adhesion to the current collector, and excellent electrochemical stability. The binder content was optimized by reducing it, given that the binder is an electrochemically inactive component, making minimization advantageous. Remarkably, the reduction in binder content preserved the mechanical properties and enhanced the electrochemical performance.Finally, the PDADMA-DEP PIL was evaluated with LiMn2O4 (LMO) cathodes and lithium anodes, whereas the previous studies focused on using graphite anodes. Additionally, its compatibility with less flammable ionic liquid electrolyte was examined, offering a safer alternative to conventional organic liquid electrolytes. PDADMA-DEP demonstrated exceptional rate capability without the need for high-temperature calendaring, thereby reducing energy consumption and processing costs. Moreover, using PDADMA-DEP as a binder significantly enhanced the stability of LMO|lithium cells, particularly when combined with an ionic liquid (IL) electrolyte composed of N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide (N1113) and 50 wt% LiFSI. X-ray photoelectron spectroscopy (XPS) analysis revealed a robust interaction between PDADMA-DEP and LMO, which appears to mitigate degradation and enhance electrochemical performance. Nevertheless, when using IL electrolyte, cells with the PDADMA-DEP binder exhibited higher polarization and charge transfer resistances compared to those utilizing a PVDF binder. This increased resistance may be attributed to the larger swelling of the ionic liquid (IL) by the PDADMA-DEP coating surrounding the LMO active particles, which potentially impedes lithium-ion kinetics.In summary, this thesis highlights the potential of various water-soluble polymers as effective binders for cathodes in LIBs. It presents viable approaches to lower the environmental impact of LIB production while potentially improving or maintaining key performance metrics of the batteries. Furthermore, by integrating water-soluble binders with innovative ionic liquid electrolytes, safer energy storage solutions can be achieved. This will accelerate the shift from PVDF to aqueous binders, advancing the development of environmentally friendly lithium-ion batteries.
