Study on the performance evaluation and echelon utilization of retired LiFePO_4 power battery for smart grid

摘要

Lithium ion batteries (LIBs), with LiFePO4 (LFP) cathodes, are being widely used in hybrid and full electric vehicles (EVs). To reduce the cost of LIBs, it is necessary to estimate the capacity of retired LFP power batteries (RLFPPBs) and investigate their echelon application. Herein, we analyze the electrochemical performance of RLFPPBs and research the echelon features in different applications according to the simulated working conditions. The results reveal that the capacities of most of the as-obtained RLFPPBs retained 77% of initial capacity, the capacity retention rate and capacity recovery rate are approximate 97% and 99% after pause for 28 days, respectively. This suggests that these RLFPPBs can be used to study the echelon utilization. Three working conditions, including back-up power, energy storage and grid frequency modulation, are simulated in this work. As a back-up power, the RLFPPBs have a longer service life of 8 years due to their excellent self-discharge performance. In energy storage application, the RLFPPBs can be used for 5667 cycles under low current density and large discharge depth. In the case of grid frequency modulation, it may be able to work for only about 1 year at 1C rate, but the depth of discharge is only 10%. Such a shorter service life, resulting from the increased electrochemical impedance, suggests that the RLFPPBs may not be suitable in grid frequency modulation. Potentially, this work presents an effective and efficient route to recycle the retired power LIBs by using the echelon utilization. (C) 2018 Elsevier Ltd. All rights reserved.