Cross‐Linked Acrylate Binder for High‐Rate Graphite Anodes

ABSTRACT Sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) are state‐of‐the‐art binders in aqueous‐processed anodes for lithium‐ion batteries. Binders act as dispersing agents and rheology modifiers in aqueous slurries, while also providing mechanical integrity of dry electrodes during battery fabrication and operation. However, despite their low concentration, they may have detrimental effects on the conductivity and electrochemical performance of batteries, for example, due to their adsorption on active material particles, which is supposed to limit Li + insertion and extraction, but also affect electrode microstructure and adhesion to the current collector. Here, a commercially available, cross‐linked acrylate binder (Carbopol® Ultrez10, x‐PAA) with high thickening efficiency is applied for graphite anodes. At lower polymer content, anode slurries based on x‐PAA exhibit high‐shear viscosities similar to those of the CMC reference and provide a yield stress, which is advantageous for slurry stability. Furthermore, SBR content could be reduced without loss of adhesion strength compared to the CMC reference, since x‐PAA does not adsorb onto graphite. Thus, the total binder content could be lowered by about 40% in comparison to reference anodes comprising CMC. The substantial reduction in total binder amount resulted in slightly lower long‐term stability compared to the reference cell including CMC. Cells incorporating x‐PAA, however, outperformed references under fast‐charging conditions (up to 5C) presumably since x‐PAA does not adsorb on graphite, thus enabling more effective Li + insertion and extraction. Further refinement of crosslinking microstructure may enable fabrication of electrodes with higher energy density and higher capacity retention during cycling, irrespective of cycling rate.