Characterising the effects of vibration on the durability of electric vehicle batteries : innovation report

Vehicle electrification is a technology pathway being adopted by original equipment manufacturers (OEMs) to either reduce or eliminate tailpipe emissions. However, electric vehicles (EV’s) that employ a rechargeable energy storage system (RESS) still face significant barriers within the marketplace when compared to incumbent internal combustion engine (ICE) vehicle technology. One of these barriers is ensuring that the RESS lasts the life of the product or maintains customer satisfactory performance over a warranted life (such as 10 years or 100,000 miles of customer usage). There has been comparably little published research critically examining the effect of vibration on high voltage (HV) batteries within battery electric vehicles (BEV) and hybrid electric vehicles (HEV). Subsequently the effects of vibration on RESS components and subsystems are potentially a major cause of in market durability failures. The following thesis presents the findings from an International Engineering Doctorate (EngD (int.)) investigating factors influencing the vibration durability of HV batteries and components. This research programme has the objective of providing the underpinning knowledge that allows manufacturers to improve the mechanical durability and performance of EV battery assemblies with respect to vibration. This objective has been achieved through several novel studies within three primary areas of investigation. Firstly, the research focused on defining the “in-service” vibration environment of BEV components and assemblies through the analysis of vibration measurements from contemporary BEVs. This study was the first to synthesise a vibration profile that is representative of a durability life of 100,000 miles of UK customer usage from multiple real world BEV measurements. The presented profile can be employed by academics and engineers to underpin future vibration durability assessments of BEV battery components. The second avenue of investigation was to characterise the natural vibration and modal response of EV components and assemblies. This was to determine their susceptibility to vibration excitation, as identified from measurements of the in-service environment. It was also the first of its kind to fully characterise the natural vibration characteristics and mode shapes of lithium-ion pouch cells via modal analysis techniques. The final objective was to determine the durability behaviour of EV components and assemblies, by subjecting them to vibration, via state of the art single and multi-axis test techniques, which were the equivalent of a typical vehicle life (10 years) or customer mileage (100,000 miles). As well as defining the degradation characteristics of a contemporary BEV module and multiple EV cells, the impact of packaging variation and state of charge (SOC) on cell ageing was also determined. In conclusion, this research thesis defines innovative testing techniques and characterisation data, which can be employed by engineers to predict the warranty performance, with respect to the effects of in-service vibration, of future EV battery assemblies