Abstract
Building a lithium-ion cell with a third reference electrode which is stable and does not disturb the cell characteristics promises deep insights into the cell performance and aging behavior. In this study, a lithium titanium oxide coated aluminum mesh is introduced into lab size 28 mAh pouch cells, which allows the cells to be braced as usual. The influence of inserting the coated mesh together with an additional separator is analyzed using electrochemical impedance spectroscopy and cyclic aging tests. Cells with this reference electrode show small deviations in the Nyquist plot and an increased capacity fade compared to the standard cells. Nonetheless, these 3-electrode cells already allowed C-rate performance tests in a fresh and aged cell state. According to this, the charge current profiles for fresh and aged cells are optimized as step wise protocols to improve the utilization of the anode overpotential reserve while avoiding lithium plating. In order to realize this, the aged cells require a 60% slower protocol. This work shows that the overpotentials on the anode side increase during aging, which makes the cells more susceptible to lithium plating. However, compared to a constant current charge, a reduction in charging time of 30% is possible.
Highlights
To cite this article: Bernd Epding et al 2019 J
If the lithium plating appears in the form of dendrites which pierce through the separator, it can lead to electrical shorts inside the battery causing an accelerated self-discharge or even thermal runaway.[3]
The results indicate that the onset of lithium plating is heavily influenced by the aging of the electrode materials as it was predicted by Yang et al and observed by others.[22,23,24]
Summary
Development of Durable 3-Electrode Lithium-Ion Pouch Cells with LTO Reference Mesh: Aging and Performance Studies. Due to the fact that the anode potential falls below 0 V vs Li/Li+ before lithium plating occurs, a reference electrode can be used to detect its onset during a charge period.[3,4,5] it gives the opportunity to stop a charge step if the anode potential reaches a critical value and limits the damage to the test cell. This way a single cell can be used to test a whole range of operating conditions. After 10 min rest time the cells were discharged with 3C to 3.0 V without CV phase followed again by 10 min rest time
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