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The Use of Elevated Temperature Storage Experiments to Learn about Parasitic Reactions in Wound LiCoO2/Graphite Cells

The Use of Elevated Temperature Storage Experiments to Learn about Parasitic Reactions in Wound... Twenty seven LiCoO2/graphite wound prismatic cells containing a variety of electrolyte additives as well as high or low surface area LiCoO2 were studied during high temperature storage using an automated storage system. The same cells had been previously studied using high precision coulometry. Cells were initially cycled to measure the capacity, charged and then stored for one month at either 40 or 60 °C, then cycled again to measure the reversible and irreversible capacity loss. The process was then repeated. During storage, the open circuit potential was automatically measured every 6 hours. The mechanisms responsible for the voltage drop which occurred during storage and the capacity loss after storage were analysed using a Li inventory model. The voltage drop during storage is caused primarily by parasitic reactions (electrolyte oxidation, transition metal dissolution, etc.) that insert Li into the positive electrode, because the potential of the LixC6 electrode is virtually constant on the stage-2/stage-1 plateau even if its Li content changes due to solid electrolyte interface (SEI) growth. The experimental results show that the combination of the electrolyte additive, vinylene carbonate, and low surface area LiCoO2 minimizes the voltage drop and capacity loss during storage presumably by reducing the amount of electrolyte oxidation occurring at the positive electrode. The same cells had charge endpoint capacity slippages that were closest to 0.00%/cycle during cycling tests monitored with high precision coulometry. Storage experiments, in concert with precision coulometry, allow a clear picture of the effect of additives to be determined. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Electrochemical Society IOP Publishing

The Use of Elevated Temperature Storage Experiments to Learn about Parasitic Reactions in Wound LiCoO2/Graphite Cells

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Copyright
Copyright ©2011 ECS - The Electrochemical Society
ISSN
0013-4651
eISSN
1945-7111
DOI
10.1149/2.007111jes
Publisher site
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Abstract

Twenty seven LiCoO2/graphite wound prismatic cells containing a variety of electrolyte additives as well as high or low surface area LiCoO2 were studied during high temperature storage using an automated storage system. The same cells had been previously studied using high precision coulometry. Cells were initially cycled to measure the capacity, charged and then stored for one month at either 40 or 60 °C, then cycled again to measure the reversible and irreversible capacity loss. The process was then repeated. During storage, the open circuit potential was automatically measured every 6 hours. The mechanisms responsible for the voltage drop which occurred during storage and the capacity loss after storage were analysed using a Li inventory model. The voltage drop during storage is caused primarily by parasitic reactions (electrolyte oxidation, transition metal dissolution, etc.) that insert Li into the positive electrode, because the potential of the LixC6 electrode is virtually constant on the stage-2/stage-1 plateau even if its Li content changes due to solid electrolyte interface (SEI) growth. The experimental results show that the combination of the electrolyte additive, vinylene carbonate, and low surface area LiCoO2 minimizes the voltage drop and capacity loss during storage presumably by reducing the amount of electrolyte oxidation occurring at the positive electrode. The same cells had charge endpoint capacity slippages that were closest to 0.00%/cycle during cycling tests monitored with high precision coulometry. Storage experiments, in concert with precision coulometry, allow a clear picture of the effect of additives to be determined.

Journal

Journal of the Electrochemical Society – IOP Publishing

Published: Oct 5, 2011

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