Impact of Formulation and Slurry Properties on Lithium‐ion Electrode Manufacturing

Abstract

The characteristics and performance of lithium‐ion batteries typically rely on the precise combination of materials in their component electrodes. Understanding the impact of this formulation and the interdependencies between each component is critical in optimising cell performance. Such optimisation is difficult as the cost and effort for the myriad of possible combinations is too high. This problem is addressed by combining a design of experiments (DoE) and advanced statistical machine learning approach with comprehensive experimental characterisation of electrode slurries and coatings. An industry relevant graphite anode system is used, and with the aid of DoE, less than 30 experiments are defined to map impact of different weight fractions of active material (80–96 wt%), conductive additive (Carbon Black at 1–10 wt%) and a two‐component binder system (Carboxymethyl Cellulose (CMC) at 1–3 wt% and Styrene Butadiene Rubber (SBR), at 1–7 wt%). Using Explainable Machine Learning (XML) methods, correlations between the formulation, slurry weight percentage (30–50 wt% in water) and coating speed (1–15 m/min) are quantified. Slurry viscosity, while known to depend on the CMC concentration, is also heavily influenced by carbon black and SBR when at high concentration, as is common in research. Viscosity increasing components also improve adhesion, by improving dispersion and hindering binder migration. Conductivity of the coating on current collector is sensitive to the current collector‐coating interface, which makes it a highly useful probe. Improvements in cell capacity are observed with higher viscosity formulations (High weight percentage, CMC content), attributed to reduction in migration and slumping of the slurry on the current collector. SBR had a negative impact at any concentration due to its insulating nature, and carbon black reduces gravimetric capacity when included at high concentrations. The insights from this study facilitate the formulation optimisation of electrodes providing improved slurry design rules for future high performance electrode manufacturing.

Robust Electrochemical Performance of LIBs Using a Polymethylene-Based High-Density Carboxylic Acid Binder in Graphite Anodes

“…At a shear rate of 3.75 s –1 , the viscosity of slurry containing PFA binder was 4.9 Pa·s, which is higher than PAA with 4.2 Pa·s and PVDF with 2.9 Pa·s (Figure S5). Higher viscosity slurry is reported to facilitate the production of uniform electrode material coating by enhancing binder dispersion and preventing binder migration. , The suspension properties can impact adhesion strength, which is a key factor in achieving high cyclability of the battery.…”

“…PFA, as a binder, significantly enhances cell performance by promoting Li + transport across the electrode domain and interfacial layer due to its dense and continuous polar carboxylic acid functional groups along the polymer chain. Its nonflexible backbone containing dense carboxylic acid prevents powder agglomeration, promoting strong bonds with the current collector and electrode material for improved capacity retention. , The polar carboxylic acid groups also influence SEI formation by facilitating inorganic species deposition and preventing continuous electrolyte degradation and crack formation. Table presents comparative studies of the electrochemical performance of PFA/Gr with various water-soluble binders containing −OH and −COOH functional groups for graphite anodes.…”

“…Higher viscosity slurry is reported to facilitate the production of uniform electrode material coating by enhancing binder dispersion and preventing binder migration. 59,60 The suspension properties can impact adhesion strength, which is a key factor in achieving high cyclability of the battery.…”

Continuous Anode Slurry Production in Twin-Screw Extruders: Effects of the Process Setup on the Dispersion

“…The mixing process in battery cell production has a major impact on the performance of the battery as it affects the microstructure in the cells by changing the particle size distribution and dispersion of the electrode components. It also has a major impact on the rheological properties of the electrode pastes, thus affecting the processability of the materials in downstream production steps [1][2][3][4][5][6][7][8]. The mixing step can be performed in either batch or continuous operation depending on the production scale.…”