Major vehicle manufacturers are committed to expand their electrified vehicle fleet in upcoming years to meet fuel efficiency goals. Understanding the effect of the charge/discharge cycle profiles on battery durability is important to the implementation of batteries in electrified vehicles and to the design of appropriate battery testing protocols. In this work, commercial high-power prismatic lithium ion cells were cycled using a pulse-heavy profile and a simple square-wave profile to investigate the effect of cycle profile on the capacity fade of the battery. The pulse-heavy profile was designed to simulate on-road conditions for a typical hybrid electric vehicle, while the simplified square-wave profile was designed to have the same charge throughput as the pulse-heavy profile, but with lower peak currents. The batteries were cycled until each battery achieved a combined throughput of 100 kAh. Reference Performance Tests were conducted periodically to monitor the state of the batteries through the course of the testing. The results indicate that, for the batteries tested, the capacity fade for the two profiles was very similar and was 11 % ± 0.5 % compared to beginning of life. The change in internal resistance of the batteries over the course of the testing was also monitored and found to increase 21% and 12% compared to beginning of life for the pulse-heavy and square-wave profiles respectively. Cycling tests on coin cells with similar electrode chemistries as well as development of a first principles, physics based model were done in order to understand the underlying cause of the observed degradation. The results from the coin cells and the model suggest that the loss of active material in the electrodes due to the charge transfer process is the primary cause of degradation while the loss of cyclable lithium due to side reactions plays a secondary role. These results also indicate that for high power cells, the capacity degradation associated with the charge-sustaining mode of operation can be studied with relatively simple approximations of complex drive cycles. / Ph. D. / Major vehicle manufacturers are committed to expand their electrified vehicle fleet in upcoming years to meet fuel efficiency goals. Understanding the effect of the charge/discharge cycle profiles on battery durability is important to the implementation of batteries in electrified vehicles and to the design of appropriate battery testing protocols. In this work, commercial lithium ion cells were tested using two profiles with the same energy transfer; a pulse-heavy profile to simulate on-road conditions for a typical hybrid electric vehicle, and a simplified square-wave profile with the same charge flow as the pulse-heavy profile, but with lower currents. Cycling tests on coin cells with similar electrode chemistries as well as development of a first principles, physics based model were done in order to understand the underlying cause of the degradation. The results suggest that the degradation observed is not dependent on the type of profile used. These results also indicate that for high power cells, the capacity degradation associated with the charge-sustaining mode of operation can be studied with relatively simple approximations of complex drive cycles.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/84420 |
| Date | 14 September 2017 |
| Creators | Radhakrishnan, Karthik Narayanan |
| Contributors | Mechanical Engineering, Ellis, Michael W., Nelson, Douglas J., von Spakovsky, Michael R., Moore, Robert Bowen, Mukherjee, Partha P. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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