Effect of Nanostructured and Open-Porous Particle Morphology on Electrode Processing and Electrochemical Performance of Li-Ion Batteries

A nanostructured, porous NCM cathode material is investigated regarding its behavior during electrode processing and electrochemical performance. The results are related to the densely packed NCM original material from which the nanostructure has been derived. Chemical composition and structural parameters are not affected by the nanostructuring process; changes are limited to the particle morphology in terms of primary particle size, specific surface area, and porosity. Electrodes containing a porous NCM material deliver lower adhesion strength values when adding identical amounts of PVDF binder. Increasing the binder fraction from four to six parts increases also the adhesion strength to an acceptable level without deteriorating the cell capacity. Despite initially high electrode porosities of 65–70%, electrodes with nanostructured NCM are capable of withstanding calendering to 40% porosity without destroying the porous particles. Full-cell tests with 50 mAh pouch cells and graphite anodes reveal substantially improved C-rate capabilities for the nanostructured material in relation to the commercial original NCM. The advantage increases with increasing C-rate and corresponds to shorter diffusion pathways in nanostructured NCM. Remarkably, even at low C-rates (C/20) where diffusion effects are considered secondary, porous NCM lies ahead of the original material. This can be explained by the higher surface area and thereby enlarged interface to the electrolyte, which eases delithiation. Long-term cycling up to 1100 cycles displayed further benefits for the nanostructured active material as one of the most prominent degradation factors, that is, crack formation and particle fragmentation, does not occur throughout the complete cycling procedure—in contrast to the bulk particles of original NCM.