Ultrasonic Calendering for Lithium-ion Battery Electrodes

The goal of high energy density and high power density lithium-ion batteries necessitates optimised electrode architectures with an efficient pore network. While calendering is the current industry standard for adjusting electrode porosity, the process offers limited control over the resulting microstructure. This thesis introduces a novel mechanical technique, termed ultrasonic calendering, as an alternative to traditional calendering. Inspired by ultrasonic welding technology, this method employs ultrasonic vibration to compact dry electrodes for the first time. The ultrasonic calendering of nickel cobalt manganese (NMC) cathodes resulted in enhanced electrochemical performance at high C-rates without compromising specific capacity. This improvement is attributed to a reduced tortuosity attained from alterations in pore size distribution, and the emergence of a unique carbon binder domain (CBD) morphology induced by the ultrasonic compaction. Conducted on industrially relevant film loadings, the performance of the ultrasonically calendered cathode was extrapolated to pouch cell format and demonstrated greater energy density and greater energy density at high rate. Whilst this work presents a technology in its infancy, a mechanistic understanding is proposed, and the process is demonstrated in detail. Valuable insights are provided towards the potential of ultrasonic calendering as it offers a new versatile platform to increase electrochemical performance through tuning both the pore structure and CBD phase. The results also support the prospects of harnessing mechanical processes for next-generation lithium-ion battery manufacturing.