Electrode Degradation Analysis in Li-Ion Batteries

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This study investigates modes of degradation in composite silicon (Si) anodes for Li-ion batteries, with emphasis on the electrode architecture. In recent years, considerable studies have shown that crystalline Si is a promising negative electrode candidate, with a specific capacity of 3579 mAh/g which is ca. 10 times the specific capacity of graphite. However, Si still has major performance issues associated with it, predominantly the volume expansion (up to 280%) which can result in cracking and pulverisation of active particles. Additionally the surface of the Si reacts with the electrolyte at lower voltages to form the solid-electrolyte interphase (SEI) – a major source of continued irreversible Li loss. Subsequent charge-discharge cycling causes repeated disruption of the SEI layer where it continues to form and grow. These phenomena culminate in conductivity loss and capacity fade. Despite the numerous studies and evolution of sophisticated in-situ characterisation techniques, relatively little is understood still about the microstructural evolution and its impact and relation to the cell performance during operation and failure. Therefore, a more detailed study is required to fully characterise types of crystalline Si as well as the importance of electrode architectures for high capacity lithium-ion storage materials. It is imperative to comprehensively understand the fundamental degradation mechanisms inside anode microstructures and at their interfaces. X-ray computed tomography (CT), in conjunction with impedance spectroscopy and associated physical characterization, will be employed to capture and quantify key aspects of the evolution of internal morphology and resistance build up. This includes characterisation of SEI growth, porosity changes and conductive network breakdown during charge-discharge operation. The study will also include in-situ and operando tomography, and diffraction experiments for clearer insights into key degradation processes, such as delamination, initiation and propagation of particle cracking as well as time-resolved identification of phase transformations. X-ray CT has been proven to be an effective tool to explore the hierarchical structure of battery electrodes and for diagnosing battery failure mechanisms at multiple- length scales. This approach will enable us to observe and quantify failures in Li-ion batteries at the electrode level, and thus facilitate construction of better electrode architectures. This study aims to characterise electrode structures to be able to develop and compare microstructural architecture with performance. It is anticipated that this study will influence major improvements in the design of Li-ion battery materials and their processing which in turn positively impact cell performance. Figure 1