A pH Buffer Additive for Aqueous Processing of Spinel and Layered Li‐Ion Positive Electrodes

Aqueous processing of cathodes offers a lower‐cost, greener alternative to poly(vinylidene fluoride)/N‐methyl‐2‐pyrrolidone routes, but contact with water elevates slurry pH and drives metal leaching, causing Al current‐collector corrosion and electrode voids. Strong acids (e.g., H 3 PO 4 ) can curb corrosion yet often disrupt rheology, increase leaching, and weaken adhesion. Herein, lithium dihydrogen phosphate (LiH 2 PO 4 ) is introduced as a lithium‐containing pH buffer (H 2 PO 4 − /HPO 4 2− near‐neutral pH) for water‐based processing of LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NMC622) and Li[Ni 0.5 Mn 1.45 Al 0.05 ]O 4 (LNMO). Slurry pH evolution and transition‐metal dissolution under H 3 PO 4 versus LiH 2 PO 4 dosing are quantified and showing that LiH 2 PO 4 more effectively stabilizes pH and suppresses leaching. Electrodes cast with LiH 2 PO 4 additives display reduced Al pitting, crack‐free coatings with good adhesion, and improved cycling stability. X‐ray photoelectron spectroscopy detects surface phosphorus species consistent with a thin phosphate passivation layer. These results establish LiH 2 PO 4 as a simple, scalable additive that enables robust aqueous processing of high‐voltage cathodes without the side effects associated with strong acids.