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EXAMINATION OF LITHIUM-ION BATTERY PERFORMANCE DEGRADATION UNDER DYNAMIC ENVIRONMENT AND EARLY DETECTION OF THERMAL RUNAWAY WITH INTERNAL SENSOR MEASUREMENT
thesisposted on 15.12.2020, 22:18 by Bing Li
Performance degradation of lithium-ion batteries (LIBs) from in-service abuse was analyzed using novel dynamic abuse tests and sensor-based in-situ monitoring of battery state of health (SOH). The relation between dynamic impact and structure changes of LiCoO2 (LCO) electrode was analyzed through a nano-impact test directly applied to the electrode and Raman imaging. After the electrode structure damage induced by the dynamic loading was analyzed, the performance of the LIBs with the abused electrodes was evaluated to establish the relation between the number of impact cycles and LIB performance degradation. The mechanism of impact related LIB capacity decrease was analyzed, and the capacity change can be predicted based on the impact abuse history using this approach. In order to provide more detailed information on the battery performance degradation caused by the in-service dynamic loads, a dynamic aging testing platform was designed to simulate in-service vibration and impact experienced by the LIBs. Based on the lessons learned, a sensor network was constructed to provide a comprehensive in-situ evaluation of the SOH of commercial batteries. Mechanisms of LIB capacity fade, temperature increase, and cell deformation from cycling in representative dynamic environments were analyzed and correlated with theoretical predictions. Difference between the aging of a battery pack and that of a single cell was also investigated, which presented the influence of current imbalance on the SOH decay of battery packs. SEM imaging, Raman imaging, and electrochemical impedance spectroscopy (EIS) analysis were also applied to support the sensor network measurements.
In order to provide an early detection of catastrophic LIB failure such as thermal runaway, an internal resistance temperature detector (RTD) based electrode temperature monitoring approach was developed. By embedding the RTD into LIBs with 3D printing technique, electrode temperature can be collected during ordinary cycling and electrical abuse of LIBs, such as external short circuit and overcharge. The internal RTD presented high measuring efficiency, while there was no interference between the sensor measurement and battery operation. The internal RTD detected the short circuit event and overcharge failure prior of time: the efficiency of the internal RTD was 6-10 times higher than the external RTD in the short circuit test. This provided the chance for early detection and prevention of catastrophic LIB failures. Besides, with the detailed information on electrode temperature evolution during LIB thermal runaway available, the internal RTD also provided the chance to enhance the understanding of the thermal runaway mechanism.