Access Type
Open Access Embargo
Date of Award
January 2022
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Mechanical Engineering
First Advisor
Leela Arava
Second Advisor
Newaz Golam
Abstract
Battery safety studies of Li-ion batteries (LIBs) related to mechanical abusive loadinginvolving contact compression of hard objects, bending and nail penetration usually show that LIBs can withstand some mechanical deformation prior to internal short circuit (ISC). Stress or strain-based criteria has been suggested to understand local conditions between the anode, cathode and the separator due such abusive mechanical loading. A strain-based criterion has also been developed at Wayne State and reported in open literature (Newaz et al.) Focus of such work has been to determine strain levels that may rupture the separator putting in contact the anode and cathode leading to ISC. Much of the mechanical abusive studies have been confined to tracking voltage drop and temperature rise leading to ISC and there are good examples in literature where these two parameters have been monitored to capture ISC relatively easily. However, small mechanical damage due to indentation has received much less attention but is considered to be significantly more relevant and challenging as the long-term health of the LIB may have been compromised even with small mechanical deformation. Other researchers have reported that small scale deformation have reverted the original battery to behave like the undamaged original 102 battery and has referred to such LIBs as ‘silent heightened-risk cells’ (Jia et al.) In this investigation, we primarily focus in this area to develop better understanding and explore characterization techniques that may be used to sort out such defective cells which have undergone small scale deformation. We also employ advanced modeling technique to predict the voltage discharge curves and the temperature curves for C rates between for 1C, 2 C and 3C. We utilized cylindrical LIBs with dimension (?) having jelly roll architecture. The overall objective was to determine the characteristics of such undeformed and deformed cells where the deformation level was well below (6.2 mm) the ISC level (7-8 mm transverse deformation). Both thermal characteristics as well as voltage response were monitored for undeformed and deformed samples. It was found out that the small-scale deformation induced by (6.2mm depth of intrusion) LIB samples behaved better than undeformed samples initially. This is rationalized as tightening the gaps between the anode and cathode layers making the deformed samples more efficient but not enough damage to lower its capability. Under such circumstances, thermal cycling was employed for the 3C rate samples to determine if thermal response would accentuate the difference between the undeformed and deformed samples. We investigated the profiles of both temperatures and voltage at different discharge rates, which was applied to deformed and undeformed Lithium-ion batteries. Consequently, the results from the study show that as the discharge rate increased from 1C -2C- 3C in deformed Lithium-ion batteries, the surface temperature of the deformed sample showed a steady increase from 28 C TO 37.9 C (1C TO 3C). The major cause of the temperature rise was joule and entropic heating aided by internal damage. Hence, the choice of a minimum level of 6.2 mm proved more efficient since higher levels that fall into the category of 7- and 8-mm samples are completely damaged with no 103 guarantee of accomplishing a proper and authentic safety and performance evaluation as Jia et al., 2020 have pointed out as well. Besides, the focus on settling at a level of 6.2 mm was guided by the experimental observation that the spaces between the cell components would shrink as the load increases, which causes a slight drop in voltage level. As a result, the Lithium-ion batteries would be deemed effective and functional at this deformation level. MSMD-NTGK ANSYS Fluent Battery model was used in the experiment to simulate the deformed and undeformed samples of cells. The consideration of ANSYS was guided by the need to record the experimental data sets of voltage vs. time. The experiment used the temperature curves for both the deformed and undeformed samples to accurately predict performance using simulations. The experimental findings, mainly based on assessing voltage vs. time response curves, show that Lithium-ion batteries perform effectively due to the internal damage caused by deformation. The radial indentation of 6.2 mm showed an accurate correlation with modeling. However, the rise in temperature during the 125 cycles from 38 C to 45C at 3C rate of cycling outline the assessment of internal damage caused by deformation. An important of the investigation is that thermal cycling can be a powerful technique to determine the loss of capability of the small-scale deformed LIBs which initially seems to show similar response as undamaged cells. ANSYS based Fluent modeling can capture the voltage as well as thermal response of both the undamaged and small-scale damaged cells
Recommended Citation
Almohammedali, Maher A., "Assessment Of Small-Scale Mechanical Damage On Safety Performance Of Lithium-Ion Batteries" (2022). Wayne State University Dissertations. 3774.
https://digitalcommons.wayne.edu/oa_dissertations/3774