Performance Evaluation of Retired Lithium-ion Batteries for Echelon Utilization

Abstract

With the rapid growth of the electric vehicle (EV) market, the number of Lithium-ion (Li-ion) batteries that reach their end of life (EOL) is increasing rapidly. Given the stringent capacity fading threshold of EV batteries, tools are required for better understanding and evaluating the health condition of large volume EV batteries that have reached EOL. In this paper, four modules from the same battery pack of a hybrid electric vehicle have been evaluated in terms of their current capacity and performance of the cells within each module. The results have been analyzed to find an affordable method for performance assessment of the retired batteries for echelon utilization. Electrochemical impedance spectroscopy (EIS) as an accurate and powerful technique has been used as a benchmark for the measurement to show the reliability of the tests. Experimental results are obtained from different test approaches on both modules and cell levels and show a different ageing degradation pattern for the cells inside the modules. The result shows that even for the modules with the same range of state of health, any non-uniformity of the cells inside the modules will affect the reliability of the modules for a second life. We also show there is a meaningful dependency between the voltage monitoring of the cells and other test approaches to determine the uniformity of a module.

Empowering Electric Vehicles Batteries: A Comprehensive Look at the Application and Challenges of Second-Life Batteries

“…On the other hand, this method strongly depends on accurate measurements, generally leading to limited accuracy. Also, the applicability of the method at the module and pack level is very dependent on the thermal management system (TMS) of the battery pack; as was mentioned above, the location of the cell inside the module and the location of the module inside the battery pack seriously affects the reliability of this method [87].…”

“…Charging happens for LiBs in constant current-constant voltage mode (CC-CV), which means that when the voltage reaches the cut-off limit, the constant current in the first charging part is decreased and charging is continued in a CV mode. Based on our initial work [87] and the infrared image of Figure 12, the location to monitor the surface temperature was chosen in the middle of the cell. There is an almost 2 °C temperature discrepancy between cell number 2 and cell number 6 in this aged module that underlines the necessity for a proper TMS in an SLB.…”

An Integrated Approach to Lithium-Ion Battery Cell Management through Accurate Voltage Measurement and Cell Balancing

“…Conventional voltage measurement involves installing a voltage sensor for each cell within the battery pack. This method is the widely used voltage measurement technique in today's applications, where Individual voltage sensors or monitoring integrated circuits (ICs) are used to monitor the voltage values of individual cells [13]. This method has been adopted this paper to achieve accurate balancing of cells connected in series.…”

T-Type Based Cascaded H-bridge Converter Operating as a Split AC Battery and Modified State-of-Charging Hierarchical Balancing Method

“…Due to manufacturing complexity, the battery cells commonly have different intrinsic characteristics like self-discharge rates, internal resistance and impedance, and thermal performances leading to different state-of-charges (SoCs) during operation in battery packs. These disparities between the cells become wider especially when the battery ages [1], [2]. This can result in reduced battery capacity, shorter battery lifetime, and in extreme cases, safety hazards leading to battery fires and explosions [3].…”