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

Abstract

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...

A Review of State of Health Estimation of Energy Storage Systems: Challenges and Possible Solutions for Futuristic Applications of Li-Ion Battery Packs in Electric Vehicles

“…For example, a light optical system can be used for determining the damage of separator; X-ray computed tomography for analysing microstructural properties, short circuits, or even to analyze thermal runway; multidirectional laser scanning for aging; etc. Multidirectional laser scanning investigates local reversible and irreversible thickness change of the cell and establishes corelation with capacity fade and impedance [140]. Furthermore, the use of signal features made up the elements of statistical analysis; pattern vectors can be inputted to pattern recognition paradigms (ANN, SVM, and K-nearest-neighbor) for decision making on battery damage characterization.…”

A review of thermal physics and management inside lithium-ion batteries for high energy density and fast charging

“…At low temperatures, the main concern is the risk of lithium plating due to sluggish battery kinetics [6,15,[17][18][19]. On the other hand, the accelerated side reactions at high temperatures, e.g., severe solid electrolyte interphase (SEI) formation, cause fast capacity degradation [19][20][21][22][23][24][25]. Based on prior studies of LIBs with relatively low energy density and at slow and moderate charge rates, a balance between these two dominant aging mechanisms, i.e., lithium plating and SEI formation, is typically reached around RT.…”

“…They observed a thick surface layer of SEI on the anode in the aged cells in a post-mortem study and lithium plating was estimated to be the failure mechanism for the operation around or below RT. Further, Sturm et al cycled cells with similar areal loadings and found that the cycle life at 25 °C was greatly improved when the charge rate was reduced from 1C to 0.5C [24]. That indicated lithium plating as the dominant aging mechanism in high areal-loading cells even at a moderate charge rate (1C).…”

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

“…Local resolution of cell dilation has been achieved by 3-D image correlation 25 and laser triangulation. [26][27][28] Other non-touching measurements include X-ray tomography 29 and neutron diffraction. 15 Dilation measurements have been used to detect lithium plating 22 and, by making use of local resolution across the cell surface, to investigate inhomogeneous aging.…”

“…15 Dilation measurements have been used to detect lithium plating 22 and, by making use of local resolution across the cell surface, to investigate inhomogeneous aging. 27,30 Here, we investigate and discuss the relationship of macroscopic inhomogeneities observable in fresh cells to anomalous local volume expansion and local deposits on the electrodes found post-mortem.…”