Coral-like directional porosity lithium ion battery cathodes by ice templating

Abstract

Thick electrodes (>500 μm) that minimize the proportion of inactive components (current collectors, separators, etc.) are attractive for high energy density lithium ion battery (LIB) cell-stacks. However, the tortuous porosity inside the electrodes usually restricts the use of these more cost-effective thick electrodes, because lithium ion diffusion becomes restricted and capacity reduces to impractical levels. To overcome this problem, we manufacture 900 μm thick cathodes with aligned pore arrays in the predominant ion transport direction using a scalable ice templating technique without the need for post-processing sintering. The aligned porosity combined with a coral-like electrode structure exhibited high areal and gravimetric capacities (14 mA h cm⁻² and 142 mA h g⁻¹ at 0.1C) as well as a sustained rate capability at faster (dis)charge rates (e.g. 12 mA h cm⁻² and 124 mA h g⁻¹ at 1C) that outperformed the capacities (0.5 mA h cm⁻² and 141 mA h g⁻¹ at 0.1C) and rate capability (e.g. 0.4 mA h cm⁻² and 103 mA h g⁻¹ at 1C) of conventional LIB electrodes containing the same materials and with a random microstructure fabricated by standard slurry casting. X-ray tomography and numerical modelling were used to quantify and confirm the aligned porosity benefits, which were preserved after many cycles of operation, along with robust mechanical integrity of the electrodes.