‘Similar but compatible’ inspired functionalisation of different 4-substituted benzoic acid functionalised MWCNT to improve dispersibility in NMP solvent

Abstract

MWCNTs are frequently used as filler materials in lithium-ion battery anodes due to their excellent electrical conductivity, thermal conductivity, and mechanical properties. Achieving uniform dispersion of MWCNTs at high solid content in NMP while maintaining the conductive properties of the slurry is a prerequisite for preparing high-performance battery materials. However, the tendency of MWCNTs to intertwine and agglomerate, which increases proportionally with their solid content as fillers, currently hinders the effective dispersion of high-solid-content MWCNTs in solvents. This study uses NMP, a common solvent for lithium-ion battery anodes, as an example. Various functionalized benzoic acids with similar electrostatic potentials to NMP were selected to functionalize inert MWCNTs via electrophilic substitution reactions. This approach achieves uniform, ‘ink-like’ dispersion of functionalized multi-walled carbon nanotubes (X-MWCNTs) with 8 % solid content in NMP while minimizing conductivity loss. with stable dispersion lasting over 60 days. The effectively dispersed X-MWCNTs exceeded the solid content of conventional MWCNT fillers by fourfold. The experimental design drew inspiration from the chemical adage ‘like dissolves like,’ and DFT computational simulations confirmed this ‘like dissolves like’ characteristic. Both theoretical and experimental results indicate that MWCNTs modified with alkoxybenzoyl, aminobenzoic acid, hydroxybenzoyl groups whose polarity slightly exceeds that of NMP yields superior dispersion of X-MWCNTs in NMP compared to MWCNTs modified with halogenated or nitro groups, whose polarity is slightly lower than NMP.