Effects of Stack Pressure on High Performance Lithium-Ion Batteries

With the rapid acceleration of electrification in the automotive industry, the development of control systems and pack design must continue to keep pace. Pouch cells are a commonly used geometry in electric vehicles due to their high packing efficiency and therefore high volumetric energy density; however, the non-rigid casing provides an additional design parameter to consider. Previous works have shown that applying mechanical pressure to the through-plane surface of pouch cells can have both beneficial and detrimental effects on cell perfor- mance and lifetime. Despite this, there is little work exploring the implications of this performance difference when discussing battery models. Equivalent circuit models (ECMs) are a well-documented and frequently used battery modelling approach for lithium-ion cells due to their minimal parameterisation requirement, low computational complexity and flexibility compared to physics-based counter- parts. This thesis presents experimental results of two lithium cobalt oxide cells at different pressures. The experimental setup is presented alongside the considera- tions when designing the tests for pouch cells. The results for pressure variation, capacity measurements and resistance measurements are evaluated with a clear pressure dependency across all tests. The thesis then investigates the addition of pressure dependence to an ECM. The results presented show an improvement in fidelity of up to 68% when utilising a pressure-informed fitting method when compared to field standard implementation of the ECM that does not consider operating stack pressure. A single-RC model and a two-RC model are presented and compared, with the two-RC model showing improvement in fidelity, at the cost of computational cost, and execution time. Overall, this work provides justification that it it critical to consider the operating stack pressure when utilising equivalent circuit models for lithium-ion pouch cells.

Grantor dc:publisher

Oxford Brookes University

Author dc:creator

• Lukow, Katie

Contributors dc:contributor

• Morrey, Denise

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/35t2-4a13

OAI identifier oai:identifier

tle:28d01c63-5253-4db7-976b-eecdc5daaee4:d6bd9758-527a-46cd-bfe2-c433766e8fca:1