Realization of Aqueous Processed LiNi _0.5 Mn _1.5 O ₄ through the pH Optimization of Polyacrylate Binders

Abstract The transition to aqueous cathode processing is essential for achieving sustainable lithium‐ion battery production. Replacing the widely used solvent, N ‐methyl‐2‐pyrrolidone (NMP), with water poses challenges, particularly due to rapid pH increases during processing. This leads to aluminum corrosion and reduced performance. This study investigates the stability and performance of spinel LiNi _0.5 Mn _1.5 O ₄ (LNMO) electrodes processed with water‐based polyacrylate binders across a pH range. By partly neutralization with sodium or lithium, respectively, the pH is tuned from 5 to 8. The binders are assessed for their ability to stabilize slurry pH during processing and their electrochemical performance. Full cell cycling identifies pH5 as optimal condition for achieving on‐par performance and excellent cycling stability. Compared, electrodes processed at higher pH exhibit significantly reduced electrochemical performance. Electrochemical impedance spectroscopy reveals that higher slurry pH correlates with increased charge transfer resistance, while surface analyses using scanning electron microscopy and energy dispersive X‐ray spectroscopy indicate increased conductive carbon and binder agglomeration at higher pH, leading to an inhomogeneous electrode. Operando X‐ray diffraction confirms that poor conductive carbon/binder distribution in the cathodes processed at higher pH prevents complete (de)lithiation, while electrodes processed at pH5 demonstrate a uniform conductive network, resulting in superior performance comparable to conventionally processed counterparts.