Ultrasonic characterisation of lithium-ion battery cathode slurries: Monitoring post-mixing evolution and structural recovery

Achieving consistent slurry quality is critical for reliable electrode manufacturing in lithium-ion batteries, yet many aspects of slurry evolution during and post mixing remain difficult to examine with currently available characterisation methods. In this work, we investigate the use of ultrasonic technology characterisation as a complementary metrology technique capable of revealing subtle changes in structural dynamics during slurry recovery and ageing. NMC – 622 cathode slurries with solid contents of 63%, 65%, and 67% were monitored acoustically under static conditions, with their recovery tracked through signal amplitude measurement. A 69% solid content formulation was also examined. However, the backwall echo reduced below the system noise floor due to strong acoustic attenuation, defining the upper detectability limit of the current pulse – echo configuration. For the first time, ultrasonic signals are employed to characterise the multi – stage post – mixing process the slurries transition through. This includes rapid early restructuring, slow consolidation and a stable plateau across the measurable solid content range. Slurries with lower solid content (i.e. 63%) demonstrated lower overall change, while higher solid content slurries (i.e. 67% and above) showed a stronger and faster recovery. Ultrasonic testing shows potential to improve our understanding of mixing quality, structural stability, and coating readiness. It can be positioned as a specialised and valuable method for improving process understanding and quality control assisting with the eventual digitalisation of electrode manufacture due to its continuous, quantitative outputs.