Committee Members:
Dr. Gleb Yushin, Advisor (MSE)
Dr. Faisal Alamgir (MSE)
Dr. Ting Zhu (MSE/ME)
Dr. Alexander Alexeev (ME)
Dr. Seung Woo Lee (ME
“Enhancing Ion Transport in Thick Li-ion Battery Electrodes by Pore Engineering”
Abstract:
The development of lithium-ion batteries (LIBs) has been the driving force behind the use of mobile electronic devices and the enabler of electric vehicles (EVs) and most energy storage systems (ESSs). Despite their relatively high energy and power densities, reliability and cost efficiency, the current performance limitations of conventional LIB materials highlight the need for further improvements. To achieve volumetric and gravimetric energy densities beyond 600-700 Wh/L and 250 Wh/kg, increasing the areal capacity loading of the electrode from 3-4 mAh/ cm2 to 5-7 mAh/cm2 while maintaining volumetric electrode capacity and fast charge and discharge capabilities is critical, especially for the widespread adoption of electric vehicles. However, thicker and denser electrodes with higher areal capacities and lower porosity (<20%) can compromise ion transport, reduce rate performance and lower capacity utilization, especially at fast C-rates, due to highly tortuous ion paths that impede ion transport and introduce unwanted internal resistance.
To address the drawbacks of dense electrodes, our study investigated the tradeoff between laser patterning material loss and electrochemical performance of commercially produced thick and dense high-nickel NCA, graphite, and silicon-blended graphite anodes using high-nickel NCA, graphite, and silicon-blended graphite electrodes with areal capacities of 4.8 and 6 mAh/ cm2 and porosities of less than 20%. The study revealed that laser patterning of straight, tapered channels in these electrodes decreased electrode tortuosity and accelerated ion diffusion. This resulted in a substantial improvement in rate performance compared to conventional thick electrodes. Despite these improvements, this approach typically resulted in significant electrode material loss of 1 to 8% by weight, which reduced the volumetric capacity of the electrodes, compromised energy density, and increased the overall cost of the battery.
In response to these challenges, an innovative, cost-effective one-step electrode patterning method has been developed. This novel approach forms a hexagonal array of channels in highly areal loading graphite anodes as part of an advanced electrode architecture engineering process. Not only does it prevent active material loss, but it's also suitable for a continuous, roll-to-roll process. Although these introduced channels represent a minimal volume fraction, they significantly improve battery performance by accelerating electrolyte infiltration and subsequently increasing battery rate performance.
Another alternative approach involving the use of aqueous processed electrodes with inhomogeneous randomly distributed pores of different channel sizes was also explored. This strategy not only addresses the kinetic limitations associated with thick, high-mass LIB battery electrodes, but also responds to environmental and health concerns associated with the use of N-methyl-2-pyrrolidone (NMP) in the battery industry. Despite the random distribution of these channels, they significantly improve the overall performance of the battery by facilitating ion transport.