The
electrode drying process is a crucial step in the manufacturing
of lithium-ion batteries and can significantly affect the performance
of an electrode once stacked in a cell. High drying rates may induce
binder migration, which is largely governed by the temperature. Additionally,
elevated drying rates will result in a heterogeneous distribution
of the soluble and dispersed binder throughout the electrode, potentially
accumulating at the surface. The optimized drying rate during the
electrode manufacturing process will promote balanced homogeneous
binder distribution throughout the electrode film; however, there
is a need to develop more informative in situ metrologies
to better understand the dynamics of the drying process. Here, ultrasound
acoustic-based techniques were developed as an in situ tool to study the electrode drying process using NMC622-based cathodes
and graphite-based anodes. The drying dynamic evolution for cathodes
dried at 40 and 60 °C and anodes dried at 60 °C were investigated,
with the attenuation of the reflective acoustic signals used to indicate
the evolution of the physical properties of the electrode-coating
film. The drying-induced acoustic signal shifts were discussed critically
and correlated to the reported three-stage drying mechanism, offering
a new mode for investigating the dynamic drying process. Ultrasound
acoustic-based measurements have been successfully shown to be a novel in situ metrology to acquire dynamic drying profiles of
lithium-ion battery electrodes. The findings would potentially fulfil
the research gaps between acquiring dynamic data continuously for
a drying mechanism study and the existing research metrology, as most
of the published drying mechanism research studies are based on simulated
drying processes. It shows great potential for further development
and understanding of the drying process to achieve a more controllable
electrode manufacturing process.
Highlights A CFD model is developed to simulate microwave heating in a millifluidic channel. The effect of process parameters on the temperature profile are investigated. Satisfactory agreement between modelling and experiments is obtained.
A highly-reproducible, high-yield flow synthesis of gold nanoparticles is developed based on synthesis kinetics from a high-pH gold precursor solution.
Over the last decade, acoustic methods, including acoustic emission (AE) and ultrasonic testing (UT), have been increasingly deployed for process diagnostics and health monitoring of electrochemical power devices, including batteries, fuel cells, and water electrolysers. These techniques are non-invasive, highly sensitive, and low-cost, providing a high level of spatial and temporal resolution and practicality. Their application in electrochemical devices is based on identifying changes in acoustic signals emitted from or propagated through materials as a result of physical, structural, and electrochemical changes within the material. These changes in acoustic signals are then correlated to critical processes and the health status of these devices. This review summarises progress in the use of acoustic methods for the process and health monitoring of major electrochemical energy conversion and storage devices. First, the fundamental principles of AE and UT are introduced, and then the application of these acoustic techniques to electrochemical power devices are discussed. Conclusions and perspectives on some of the key challenges and potential commercial and academic applications of the devices are highlighted. It is expected that, with further developments, acoustic techniques will form a key part of the suite of diagnostic techniques routinely used to monitor electrochemical devices across various processes, including fabrication, post-mortem examination and recycle decision support to aid the deployment of these devices in increasingly demanding applications.
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