Highly conductive NMP-free carbon-coated nano-lithium titanate/carbon composite electrodes via SBR-assisted electrophoretic deposition

Li-ion storage electrodes are manufactured through the conventional cast process involving the use of a toxic solvent (n-methyl-2-pyrrolidone, NMP) and the binder polyvinylidene fluoride (PVDF). This process can be problematic for nanosized materials as they form viscous suspensions that prevent the formation of uniformly dense coatings. Additionally, the NMP solvent is very hazardous. Herein lies the viability of using electrophoretic deposition (EPD) as an alternative manufacturing process that would both eliminate the need for a toxic solvent and improve electrode properties is presented. In particular, it is shown that styrene-butadiene rubber (SBR) enables the assembly of carbon-coated LTO and carbon nanoparticles into bridged hetero-aggregates that render themselves to fast growth of adherent highly performing LIB electrodes. The electrodes are built by suspending C-coated LTO, carbon, and SBR at 80/10/10 wt% ratio in a medium consisting of 90/10 vol% acetonitrile and water, performing 3-5 stages of 15-s constant current deposition cycles followed by pressing at 4 MPa and drying in a vacuum oven. Raman spectroscopy, thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDS) with SEM were performed to examine carbon/LTO composite film homogeneity and compared to conventional PVDF-based electrodes. More importantly, photoemission electron microscopy (PEEM) and X-ray absorption near edge structure (XANES) were used to probe the presence/distribution of the SBR binder in the coating. The EPD-based electrode exhibits superior rate capability when compared to the PVDF-based electrodes. The conductivity, as shown by EIS, of the pressed EPD electrodes was 15 times higher than that of the pressed PVDF electrodes demonstrating the superiority of EPD in fabricating highly conductive electrodes for high-power LIB application. (C) 2019 Elsevier Ltd. All rights reserved.