Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV) are seen as solutions to meet the rising demand of consumers whilst overcoming challenges such as dependency on fossil fuels and carbon dioxide emissions. The success of these vehicles is highly dependent on reliable and efficient Energy Storage Systems (ESS). In order to build a reliable and efficient ESS system, a cylindrical lithium-ion cell is the most prominent choice since it has good energy density and favourable charging and discharging properties. Arrays of lithium-ion cells are connected in series and parallel to build the high power ESS system. These connections are realised by Battery Tab Joints. The durability and performance of the ESS system depends on the battery tab joint. Hence, the battery tab joint should be capable of enduring the static and dynamic mechanical loads as well as the electrical load. In order to understand battery tab joint behaviour, the performance (both mechanical and electrical properties) of battery tab joints were investigated under mechanical and electrical load. Resistance Spot Welding (RSW) was selected as the joining technique. RSW process parameters were optimised to achieve consistent nugget size and weld quality. The materials selected for investigation were nickel plated steel and nickel plated copper. In order to understand the mechanical and electrical behaviour of spot welded joints under mechanical and electrical load a test environment was designed to allow quasi-static and dynamic (fatigue) testing of tensile coupons and lap-shear welded specimens under electrical load. Temperature change and electrical properties were recorded during the tests. During fatigue test of lap-shear joints for different electric current load, it was found that the change in electric contact resistance (ECR) ratio up to the point of fatigue failure of joints was 0.1 and 0.2 for steel and copper respectively. Importantly, it was suggested that the change in ECR could act as a prediction mechanism for joint failure in a real ESS. It was found that electric current load has no observable effect on fatigue life of the battery tab joints. A computer-based model was developed to simulate weld damage and it was found to be in good agreement with experimental results. The effect of preload arising during battery pack manufacture was investigated. It was found that preload (without electric current load) had significant impact on fatigue performance of the battery tab joints.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:731452 |
| Date | January 2017 |
| Creators | Kumar, Prabhanjan |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/98040/ |
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