Real-Time Operando SEM Investigation into Lithium Ion Battery Degradation
Authors: Patel Anisha N. , Maddar Faduma M. , Loveridge Melanie J. 
Published: February 2020

Lithium ion batteries (LIBs) are the preferred rechargeable battery choice for a range of electric technologies, and have increasingly become an integral part of our lives due to their high energy density, low memory effect, low self-discharge and good cycle life during operation. However, they are complicated by a variety of chemical, electrochemical and physical processes that take place within dynamic microstructures (anodes and cathodes). Hence, extensive research efforts are being invested in improving existing battery components, but greater fundamental understanding within these processes remains critical for optimising the battery design and addressing issues such as safety, long cycle life and efficiency. An attractive approach is to couple a powerful microscopic characterisation technique with electrochemical operation, enabling critical studies with direct real-time monitoring around capacity fading issues, such as dendrite formation and physical degradation under realistic conditions to be carried out. These studies enable correlations between physical and chemical processes to the electrochemical responses of a battery, producing powerful information, leading to a better understanding of LIB degradation processes.

One effective example is the coupling of scanning electron microscopy (SEM) with electrochemistry, enabling information on structure, morphology, composition and performance to be acquired at electrode surfaces, under operando conditions, during the course of experiment and down to μm resolution. In recent years, several studies have reported on attempts to investigate degradation in real-time employing SEM coupled with electrochemistry. However, these studies have either exposed battery material to atmospheric moisture or have required the use of alternative electrolytes to that generally employed in real battery systems, e.g. ionic liquids or the use of polymeric electrolytes. In order to simulate real conditions, a bespoke in situ coin cell design has been designed in order to visualise electrode/electrolyte interfaces and capture morphological changes at μm resolution. The fabrication steps protect the battery material (particularly important for the nickel-rich cathode) from exposure to moisture in the air, and during cycling to avoid degradation of typical battery electrolytes. This ensures maximum investigation possibilities including dendrite growth, where the morphology variations and growth extent can be characterised and correlated with electrochemical data. The electrochemical activity of the bespoke coin cell is compared to that of a conventionally fabricated coin cell battery. The degradation processes under a range of operando conditions is explored by varying the temperature of the sample stage or the pressure of the SEM chamber.

This study gathers information by characterising electrode structures in order to compare microstructural architecture with performance. The results are expected to enhance our understanding of the processes taking place that lead to electrode degradation and failure, therefore contribute to improvements in the design of LIB materials and their processing, which in turn will positively impact cell performance.