Performance assessment of retired EV battery modules for echelon use

The performance of retired EV battery modules was tested in order to learn their attenuation states and different capacity test protocols of retired modules are compared in order to strike a balance between calibration accuracy and test time. The results show that most modules have no serious capacity fading while a minority of modules whose capacity is less than 80% SOH will bring about the capacity of the whole battery system down to below 80% SOH. Echelon use of EV battery from aspect of modules has more value than that from aspect of packs. The capacity fading of Pack 2 is more than that of Pack 1 due to a rise in temperature because the cold air enters the side of Pack 1 and exits from the side of Pack 2. High capacity is not always related to small resistance, showing that different modules have experienced different ageing processes. The retired modules still have good discharge ability at 25%-200% of rated power, implying that a retired battery energy storage system can be employed to satisfy power demand of electricity grid. The capacity test protocol of 1/3 C constant current process without constant voltage process is proposed for retired modules. (C) 2019 Published by Elsevier Ltd.