A New Method to Model the Thickness Change of a Commercial Pouch Cell during Discharge

Self Cite

The safety, performance and lifetime of lithium-ion cells are critical for the acceptance of electric vehicles (EVs) but the detection of cell quality issues non-destructively is difficult. In this work, we demonstrate the use of a multi-dimensional laser scanning method to detect local inhomogeneities. Commercially available cells with Nickel Cobalt Manganese (NMC) cathode are cycled at various charge and discharge rates, while 2D battery displacement measurements are taken using the laser scanning system. Significant local swelling points are found on the cell during the discharge phase, the magnitude of swelling can be up to 2% of the cell thickness. The results show that the swelling can be aggravated by a combination of slow charge rate and fast discharge rate. Disassembly of the cells shows that the swelling points are matched with the location of 'adhesive-like' material found on the electrode surfaces. Scanning Electron Microscope (SEM) images show that the material is potentially blocking the electrodes and separators at these locations. We therefore present laser-scanning displacement as a valuable tool for defect/inhomogeneity detection.

Section: Resultsmentioning

confidence: 87%

Localized Swelling Inhomogeneity Detection in Lithium Ion Cells Using Multi-Dimensional Laser Scanning

Zhao

Spingler

Patel

et al. 2019

Self Cite

“…Consequently the lithiation range of both electrodes during a full cycle is narrowed and the overall reversible cell displacement, which is directly related to the lithiation stages of the electrodes, is reduced in the same amount. Again, the reader is referred to the work of Rieger et al 67 for more information about the lithiation induced volume change of the LiCO 2 /graphite electrodes.…”

Section: Resultsmentioning

confidence: 99%

“…However, the deintercalation induced volume expansion of LiCO 2 electrodes was determined to be around 2.3% 67 , referring to the fully intercalated state. More information about the intercalation induced volume expansion is given in previous work 67 . The intercalation induced thickness change of lithium-ion cells is strongly related to intercalation stages of lithium in graphite.…”

mentioning

confidence: 99%

Non-Destructive Detection of Local Aging in Lithium-Ion Pouch Cells by Multi-Directional Laser Scanning

Sturm

Spingler

Rieger

et al. 2017

Self Cite

Understanding the mechanical activity of lithium-ion cells during cycling and its connection with aging phenomena is essential to improve cell design and operation strategies. Previous studies of lithium-ion pouch cells [B. Rieger et al., Journal of Energy Storage, 8, 1 (2016)] have shown non-uniform swelling with local displacement overshoots during charging. In this experimental work, a novel three-dimensional laser scanning method is used to investigate local reversible and irreversible thickness changes of six commercial LiCoO 2 /graphite cells during a cyclic aging experiment. Three cycle scenarios were included and two cells each were exposed to a specific temperature and charging rate. The cells showing local displacement overshoots also exhibit non-uniform distributions of irreversible thickness change. Post-mortem analysis showed largely inhomogenously degraded surfaces of the single anode layers. It is shown that the cells' irreversible thickness change correlates with capacity fade and internal resistance increase monitored via electrochemical impedance spectroscopy. Lithium-ion batteries have become the most promising energy storage technology for small electronic devices such as smartphones or laptops as well as for battery packs in electric vehicles. Although their relatively high density in power and energy make Li-ion batteries the technology of choice for many applications, its aging and degradation behavior likewise limits their use in applications that require extreme safety standards and cycle life.2 In order to quantify the decay of batteries, the state of health (SOH) 3 is used which refers to the capacity fade by relating the current capacity of the cell to its initial capacity. This relation can be seen as an overall concept introducing a measurable quantity of aging effects occurring during battery lifetime.Detecting the cell's SOH by measuring external stress and strain on the surface of the cell's housing 2,4 is a recent method based on the mechanical behavior of Li-ion batteries in form of volume change effects during charge and discharge processes. These are largely caused by electrode swelling, 5-8 polymer deformation 5,9 and film growth. 10,11Estimating the cell's SOH by a single point measurement implies a homogeneous stress and strain distribution over the housing of the cell. Hence, the utilization of the cell would need to be homogeneous. Local variations in current density and electrode potential occurring during cell operation along the current collector foils 12-15 object this assumption. Considering an inhomogeneous utilization of the electrodes described by local variations in state of charge (SOC), 15 an overall estimation of SOH seems inappropriate to gain a deeper understanding of aging mechanisms occurring in commercial Li-ion cells. Consequently, there is a need for local detection of aging mechanisms to account for design specific inhomogeneous load across the cell.As already presented in previous work, 1 extending the measurement of strain or stress to a local re...

“…al. 23 Awarke et al 24 studied the variation of porosity in microscale computations on representative volume elements by assuming a porosity expression involving the local state of charge and volumetric strain. Then, with a homogenized model at the macroscopic, electrode scale, they imposed spatial profiles for the state of charge and studied how the porosity and conductivity varied.…”

Section: Introductionmentioning

confidence: 99%

Intercalation Driven Porosity Effects in Coupled Continuum Models for the Electrical, Chemical, Thermal and Mechanical Response of Battery Electrode Materials

Wang

Siegel

Garikipati

2017

We present a coupled continuum formulation for the electrostatic, chemical, thermal and mechanical processes in battery materials. Our treatment applies on the macroscopic scale, at which electrodes can be modelled as porous materials made up of active particles held together by binders and perfused by the electrolyte. Starting with the description common to the field, in terms of reaction-transport partial differential equations for ions, variants of the classical Poisson equation for electrostatics, and the heat equation, we add mechanics to the problem. Our main contribution is to model the evolution of porosity as a consequence of strains induced by intercalation, thermal expansion and mechanical stresses. Recognizing the potential for large local deformations, we have settled on the finite strain framework. We present a detailed computational study of the influence of the dynamically evolving porosity, upon ion distribution, electrostatic potential fields, charge-discharge cycles and mechanical force generated in the cell.