In-situ gas analysis as a tool to understand battery degradation triggered by low/high temperatures and electrode laser cutting.

Abstract

The aim of this study was to ascertain the impact of cycling conditions and electrode production on the electrochemical performance of lithium-ion cells. Initial tests were carried out to determine baseline electrochemical performance. Graphite and lithium iron phosphate electrodes were used due to the present understanding of their cycling and gas evolution processes in literature. Two measurement techniques were optimised for utilisation for investigating lithium-ion cell performance. The first technique was a highly sensitive operando pressure measurement cell. The suitability of the operando pressure measurement technique was determined with a clear correlation observed between electrode volume changes and the measured pressure. Standard gas evolution volumes corresponding to solid electrolyte formation was obtained for graphite versus lithium iron phosphate cells. The second technique was a 3-electrode cell design. This technique facilitated the ability to monitor individual electrode potentials as well as the cell voltage. To optimise the combination of both the 3-electrode cell and operando pressure measurement techniques, minimal reactivity of the reference electrode was imperative. The applicability of a Li0.5FePO4 reference electrode was demonstrated. The impact of temperature and current on electrochemical performance and gas evolution volume was studied. Cells were cycled at temperatures ranging from 10 °C to 60 ° C and current rates of C/20 to C/3. An increasing temperature was shown to improve cycling performance, for the limited cycling that was carried out. Both an increasing temperature and decreasing current rate resulted in an increase volume of gas evolution during formation cycling of graphite versus lithium iron phosphate cells. Finally, an alternative electrode cutting methodology was tested. Graphite electrodes were laser cut, with additional holes cut across the surface to facilitate operando pressure measurements. The extent of the laser cutting was determined to impact both electrochemical performance and gas evolution volume. Electrochemical data and analysis via optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy identified copper contaminants as the cause.

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Identifiers

ORCID for Nuria Garcia-Araez: orcid.org/0000-0001-9095-2379

ORCID for Philip Bartlett: orcid.org/0000-0002-7300-6900

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