To find and understand the influence DC ripple current has on lithium-ion cells in automotive applications

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The battery cell is probably the most critical component of an EV and electrification, especially in passenger cars is key to more sustainable transport solutions. Currently, most battery testing is performed using very "clean" DC test currents whereas in real world situations there is significant amounts of noise introduced by the switching of power inverters as well as motor characteristics. These AC components are of various frequencies, and it is crucial to understand how they affect the performance of the battery in the long run, for which current literature offers differing opinions. To characterise how Li-ion cells react to ripple current, the project aims to conduct experiments applying various types of ripple to various lithium-ion cells with electrochemical modelling used to inform decisions on the design of experiment. Additionally, if this modelling provides different results to those eventually found experimentally, it will serve to highlight the limitations of that model and aid any future work done to improve the model. The experimental stage will then be conducted, varying the chosen variables (e.g. waveform, frequency, cell chemistry, cell format etc.) whilst concurrently recording chosen indicators (e.g. EIS, capacity/power fade) before performing post-cycling characterization. This characterisation is expected to include various scanning and dissection, so as the specific type of degradation can be determined. This will aid in the final objective of the project which will be to seek an explanation for the experimental results in electrochemical theory. This is crucial as the ripple current may enhance or emphasise specific type of degradations and so imply methods to negate this deterioration, and any further understanding of the working of lithium-ion cells is a valuable addition to literature. This work will not only add to the lithium-ion knowledge base, but the project will also look to exploit the results found to inform best practice in the design of battery management systems, such as removal of power filters or modifications of switching frequencies. Hence this work has the potential to not only improve battery lifetime by reducing degradation, but also impact the way power electronic subsystems are designed. This potential simplification or improvement of performance of battery management systems shows the relevance to both AVL and UKRI is significant.