Highly efficient oxidation of single-walled carbon nanotubes in liquid crystalline phase and dispersion for applications in Li-ion batteries

Abstract

Single-walled carbon nanotubes (SWCNTs), which have high electrical conductivity, are promising candidates for enhancing the energy storage capability of lithium-ion batteries (LIBs). However, their usage in energy storage devices is limited due to the large bundle size and difficulties in dispersion. Here, we implement the debundling and mild oxidation of SWCNTs in the liquid crystalline phase paste (2 wt% solid content) with strong acid and co-intercalant (NaNO3). The thermal treatment successfully introduced carboxylic acid groups without requiring other oxidizing agents. The pretreated SWCNTs were dispersed in organic solvents such as N-methyl pyrrolidone (NMP) without dispersant molecules and were utilized as conductive additives for LIBs. Raman spectroscopy analysis showed that the D/G ratio of the SWCNT film changed from 0.012 to 0.023, implying that the oxidation method proposed herein is less defective and efficient. The filtrated 15 μm film of the SWCNTs exhibited a high electrical conductivity of 2384 S/cm. SWCNT dispersion in NMP was utilized to fabricate LIB cathode electrodes. Compared to the carbon black-applied electrodes, the SWCNT-applied LiNi0.8Co0.1Mn0.1O2 (NCM811) electrodes exhibited enhanced dispersity of conductive additive/binder networks, leading to improved electrode integrity. The capacity retention after 100 cycles for cells with SWCNTs was approximately 23.3 % better than that of the cells without SWCNTs.