Optimizing NMP-Slurry Gelation in High-Solid Content Systems for NMC622 Electrodes: Advances in Roll-to-Roll Processes and Electrochemical Efficiency

N-methyl-2-pyrrolidone (NMP) is crucial for processing solvent-borne electrodes but significantly increases manufacturing costs due to its evaporation, recovery, and treatment. While green solvents like water are being explored, they are not yet practical for large-scale production due to undesired reactions with active materials. Super high solid content (SC) slurries are essential to reduce the use of harmful, expensive, and polluting solvents. However, high SC in Li(Ni0.6Mn0.2Co0.2)O2 (NMC622) slurries is typically associated with strong gelation, a poorly understood phenomenon. Casting slurries with high SC can be problematic due to high viscosity and gelation, resulting in poor-quality coatings. An initial strategy integrating the advantages of both slurry and electrolyte additives is introduced in this thesis. Electrolyte additives/salts, commonly employed to boost cell performance when dissolved in the electrolyte, were instead pre-added during slurry preparation to tune rheology and enable processing of NMC622 suspensions at high solid loadings. These additives are chosen to avoid unknown interactions within the complex battery system. ... mehrIndeed, NMC622 materials bear basic surface compounds that destabilize the NMP slurry, causing its gelation. This work reveals, for the first time, that such additives delay slurry gelation by modulating PVdF adsorption via neutralization and complexation on NMC622. The application of H3PO4 and of three Li electrolyte salts, namely lithium trifluoroacetate (LiTFA), lithium bis(trifluoromethane)sulfonimide (LiTFSI) and lithium difluoro(oxalato)borate (LiODFB), as slurry cathode additives is at first examined1. These additives effectively tune gelation, enabling the processing of high 75 wt.% SC slurries, thus surpassing the regular limits attainable without additive of 70 wt.% SC. Li salts, even in very low concentrations, are more effective than H3PO4, which requires higher loadings for a comparable delay of slurry gelation. Long-term cycling in NMC-graphite pouch cells up to 1000 cycles showed that H3PO4 led to deteriorated performance at high C-rates and severe capacity fading due to side reactions with the graphite anode. In contrast, Li-salts containing cathodes demonstrated comparable rate-capability performance to a reference electrode without additives. LiTFSI exhibited the best capacity retention among Li-salts containing cathodes, with long-term capacity close to the best-performing additive-free sample. Other Li-salts containing electrodes showed faster degradation compared to the reference. A second approach to enable slurry processing at high SC is demonstrated by means of an improved slurry mixing scheme coupled with formulations characterized by reduced (1wt.%) carbon black loadings. This strategy allowed casting of NMC622-NMP slurries within the 80 wt.% to 85 wt.% SC range. Additionally, the impact of extremely reduced carbon black content (0.5wt.%) on rheology was examined at 85 wt.% SC. Enhanced carbon black deagglomeration enables a more favorable PVdF binder conformation onto the carbon black surface, thus resulting in impaired bridging flocculation and reduced physical slurry gelation. Moreover, the reduced carbon black content in the slurry formulation did not compromise the electrode cycling performance and allowed the production of coatings with higher active material loadings of up to 98% and reduced porosities of 15%. The high-power and long-term cycling performances of the resulting high energy density cathodes were tested in NMC-graphite full-cells, where they demonstrated comparable performance to the standard reference electrode. The standard electrode was produced with standard mixing and higher additive amounts and showed optimal cycling performance at higher porosities. Industrially relevant materials and compositions are used in the roll-to-roll manufacturing process, with special focus on commercial high Mw PVdF binders. Therefore, the manufacturing processes investigated in this thesis show an intrinsic potential for positive economic benefit and upscaling.