Evaluation of the Cycle Profile Effect on the Degradation of Commercial Lithium Ion Batteries

Radhakrishnan, Karthik Narayanan

Evaluation of the Cycle Profile Effect on the Degradation of Commercial Lithium Ion Batteries

dc.contributor.author	Radhakrishnan, Karthik Narayanan	en
dc.contributor.committeechair	Ellis, Michael W.	en
dc.contributor.committeemember	Nelson, Douglas J.	en
dc.contributor.committeemember	von Spakovsky, Michael R.	en
dc.contributor.committeemember	Moore, Robert Bowen	en
dc.contributor.committeemember	Mukherjee, Partha P.	en
dc.contributor.department	Mechanical Engineering	en
dc.date.accessioned	2018-07-27T13:04:24Z	en
dc.date.available	2018-07-27T13:04:24Z	en
dc.date.issued	2017-09-14	en
dc.description.abstract	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.	en
dc.description.abstractgeneral	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.	en
dc.description.degree	Ph. D.	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:12462	en
dc.identifier.uri	http://hdl.handle.net/10919/84420	en
dc.language.iso	en_US	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	Lithium ion batteries	en
dc.subject	capacity degradation	en
dc.subject	cycle profile	en
dc.title	Evaluation of the Cycle Profile Effect on the Degradation of Commercial Lithium Ion Batteries	en
dc.type	Dissertation	en
thesis.degree.discipline	Mechanical Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en