Enabling Aqueous Processing of Ni-Rich Layered Oxide Cathodes via Systematic Modification of Biopolymer (Polysaccharide)-Based Binders

Abstract

Aqueous processing of lithium (ion) battery cathodes based on Ni-rich layered oxides like LiNi_0.83Co_0.12Mn_0.05O₂ (NCM) can reduce costs, increase sustainability, and pave the way for F-free, e.g., biopolymeric binders, however, the degradation of water-sensitive Ni-rich NCM remains a challenge. Besides strategies like NCM coatings and processing additives, customized binders can be performance-decisive via impacting both, electrode processing aspects (paste viscosity, particle dispersibility, etc.) and chemical interactions with NCM surface, though, a distinction between these two impacting factors is difficult given their mutual influences. For this reason, a bifunctional binder system is chosen in this work, i.e., highly viscous xanthan and low viscous pullulan, both polysaccharides known from the food industry, which realize constant viscosity and processing, finally enabling systematic investigation of binder modifications (here pullulan) with various side groups. In fact, while the rate performance remains constant, suggesting a similar composite network with comparable electronic and ionic conductivities, the modified binders affect the NCM||graphite cycle life, where a higher substitution degree of carboxymethylated pullulan can even compete with N-methyl-2-pyrrolidone/polyvinylidene difluoride state-of-the-art system at conventional upper charge voltage (4.2 V); while at 4.5 V water-reasoned NCM damages get obvious, as seen by enhanced electrode cross-talk via transition metal deposition on anode.