Imperial College London 

Supervisors: Dr Bo Lan and Dr Fred Cegla 

Net zero carbon emission targets are rapidly transforming the mix of technologies for energy supply in the UK. As an integral part of renewable energy movement, Lithium-ion batteries are filling the place of fossil fuels to become the energy storage devices of choice for transportation and beyond. While the production of batteries has been ramped up quickly, limited work has been done on non-destructive evaluation (NDE) of them. Most in-production NDE work has been performed with x-ray, which is time consuming and costly and not feasible to be performed at scale. Ultrasound has been used to track the evolution of through-package parameters such as the time-of-flight and attenuation in the battery, which are then correlated with the overall state of charge of the battery. However, these are mostly based on crude through-thickness averages, and there has been a lack of accurate physical model to reveal more detail about the internal structure and its changes during cycling.  

The Imperial NDE group has recently developed a technique to characterise the properties (such as the state of charge, and the porosity of the electrodes) and track the locations of individual layers within a pouch cell battery. This was based on ultrasonic resonances formed between the repetitive units of the layered structures of a LIB, and we have established a theoretical framework to model the wave physics from the ground up.  

This PhD project will be dedicated to investigating the application of this resonance-based technique to gain a better insight into NDE for batteries. 

  • We will adapt and quantify the performance of the technique in identifying defects in the layering process, i.e. folds and tab welding defects. These are important defects to be picked up during the manufacturing process. 

  • While to date, the above has been done with contact transducers, we will also study the use of non-contact air coupled transducers to inspect the batteries. We already have a simple setup that measures the ultrasonic signals at ~1 MHz. In this project we aim to further increase the frequency range to obtain better resolution in both the lateral and depth directions.  

  • We will study the use of the technique to monitor the evolution of the different layer properties during the charging and discharging process, and develop a methodology for the determination of the states. 

  • To date we have considered cuboid-shaped pouch cells. Many cells are of the cylindrical shape, and we will explore how the current approaches can be adapted to also inspect cylindrical cells.