Enhancing power density and cycle life of NMC811 battery cathodes via combined dense calendering and laser patterning

Abstract

The charging time of Li-ion batteries is an important bottleneck in the wider adoption of electric vehicles (EVs). A common strategy to improve the rate performance is improving ion transport by patterning the electrode. However, these patterning methods usually increase the electrode porosity, thereby decreasing the volumetric energy density. In this work, we leverage the ability of Single Crystal LiNi_0.8Mn_0.1Co_0.1O₂ (SC-NMC811) electrodes to be calendered to higher packing densities than traditional cathodes, which then allows to offset additional porosity introduced by electrode patterning. We calendar SC-NMC811 electrodes to a 25% porosity and then introduce hole patterns spaced 100 to 600 µm apart using laser processing with a goal to maintain average porosities below 30%. As expected, we found systematic improvements in the rate performance with increasing hole density and used operando charge photometry to explore the limits of mass transport in the regions surrounding the holes but interestingly, we also observe improved capacity retention when using patterned electrodes. We found that there is less cathode lattice oxygen loss when using patterned cathodes, this in turn reduces transition metal shuttling reduces anode solid electrolyte interphase (SEI) impedance growth. We demonstrated a reduction in oxygen loss by both electron energy loss spectroscopy (EELS) mapping, X-ray diffraction (XRD) mapping and X-ray diffraction computed tomography (XRD-CT). Overall, SC-NMC811 electrode's ability to withstand over-calendering offers the opportunity to introduce laser patterned holes while maintaining the average porosity below 30%. This increases both the rate performance and longevity of the electrodes.