In the literature, mechanical deformation of Li-ion batteries (LIB) is characterized in terms of global or volumetric strain of the entire cell to develop load vs. strain plots. In characterizing the mechano-electrical–thermal–chemical interaction of the battery in relation to internal short circuit (ISC) due to mechanical load, these estimated strains are “indirect strains” at best. Direct evaluation of “internal local strains” between the layers, particularly, in the first separator layer should be a critical material parameter as it relates to separator rupture and should be the key link in ISC in LIBs. We make an effort to assess “internal local strains” which is not reported elsewhere, first by using the Oak Ridge National Laboratory (ORNL) approach to use plastic deformation of aluminum casing to “freeze” deformation states of the LIBs followed by microscopy to image undeformed and deformed cells. An image analysis procedure is developed to estimate transverse compression strains in the cells, e.g., in Cu anode, Al cathode, and the polymeric separator. The local strain experienced by the polymeric separator nearest to ball indentation is found to be close to 65–70% and this strain level is much higher than 40–50% maximum average strains estimated for the same sample.
Though lithium-ion batteries (LIB) are becoming prevalent energy storage systems for electrifying vehicles, their high energy density often makes them susceptible to various thermal instability problems. Also, due to the battery abuse that can barely be avoided and as LIBs are exposed to many accidents, mechanical damage of different intensities often facilitates internal short-circuiting of the components and leads to thermal runaway events. Herein, we demonstrate resistance measurement by electrochemical impedance spectroscopy (EIS) as a tool for the detection of an internal short circuit (ISC) and health monitoring in LIBs. The changes in the EIS at different mechanical deformation levels are evaluated through a proper equivalent circuit model. The fitted results reveal that the cathode-electrolyte interface resistance can be used to predict the onset of ISC due to the mechanical abusive conditions. Changes in the EIS are traced to the battery deformation levels or local strain changes due to the internal damage leading to ISC. The obtained results demonstrate that impedance spectroscopy provides information about the emergence of ISC and battery health.
Due to the high energy density and long lifetime, lithium-ion batteries (LIB) become ubiquitous energy storage systems for electric vehicle operations1. However, a higher energy density frequently results in a developed risk of thermal instability issues, where a series of heat-producing reactions can quickly occur, leading to fire and even explosions2. Due to the prevalent utilization in electric vehicles, battery abuse can hardly be avoided as LIB is exposed to many accidents, and mechanical abuse of various degrees of intensity often paves the way for internal short-circuiting of components through rupturing of separators3-4. Such battery failure induced by mechanical damage can lead to electrical and chemical hazards together with fire, which can result in danger to life, the environment, and the infrastructure and should therefore not occur in the field. The origin of such thermal-induced battery degradation certainly caused by short-circuiting of battery components mostly by direct contact of anode and cathode electrodes. To mitigate these issues and caution the electric vehicle drivers about thermal runaway events, the development of a diagnostic method to identify the damage mechanism under mechanical deformation and corresponding electrical behavior is essential. The onset of short circuits often characterized by a sharp increase in current, temperature, and rapid drop in voltage and set pass criteria as the absence of these potentially dangerous events as which may be enough for regular safety testing. Such events detected by a range of techniques including electrochemical impedance, incremental capacity-differential voltage, infra-red, tomography, etc5-7. However, it is challenging to design repeatable experiments that can emulate early-stage incubation of field ISC failure. Herein, we demonstrate resistance measurement by electrochemical impedance spectroscopy as an indicator for the detection of an internal short circuit of LIBs. The occurrence of ISC at different mechanical deformative conditions is evaluated through proper equivalent circuit model with multi-frequency and alternating voltage or current signal. The fitted results reveal that cathode-electrolyte interface resistance can be used to predict the onset of ISC due to mechanical abusive conditions. The obtained results demonstrate that impedance spectroscopy, together with a precise modeling parameter, provides information about the emergence of ISC and battery lifetime. Scrosati, B.; Garche, J., Lithium batteries: Status, prospects and future. Journal of power sources 2010, 195 (9), 2419-2430. Feng, X.; Ouyang, M.; Liu, X.; Lu, L.; Xia, Y.; He, X., Thermal runaway mechanism of lithium ion battery for electric vehicles: A review. Energy Storage Materials 2018, 10, 246-267. Wang, Q.; Ping, P.; Zhao, X.; Chu, G.; Sun, J.; Chen, C., Thermal runaway caused fire and explosion of lithium ion battery. Journal of Power Sources 2012, 208, 210-224. Zhu, X.; Wang, H.; Wang, X.; Gao, Y.; Allu, S.; Cakmak, E.; Wang, Z., Internal short circuit and failure mechanisms of lithium-ion pouch cells under mechanical indentation abuse conditions:An experimental study. Journal of Power Sources 2020, 455, 227939. Xiong, R.; Ma, S.; Li, H.; Sun, F.; Li, J., Toward a Safer Battery Management System: A Critical Review on Diagnosis and Prognosis of Battery Short Circuit. iScience 2020, 23 (4), 101010. Spielbauer, M.; Berg, P.; Ringat, M.; Bohlen, O.; Jossen, A., Experimental study of the impedance behavior of 18650 lithium-ion battery cells under deforming mechanical abuse. Journal of Energy Storage 2019, 26, 101039. Barai, A.; Uddin, K.; Dubarry, M.; Somerville, L.; McGordon, A.; Jennings, P.; Bloom, I., A comparison of methodologies for the non-invasive characterisation of commercial Li-ion cells. Progress in Energy and Combustion Science 2019, 72, 1-31.
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