Analysis for performance degradation mechanisms of the retired LiFePO4/graphite power cells

• Published in: Ionics Vol. 26; no. 9; pp. 4443 - 4454
• Main Authors: Li, Shoutao, Meng, Qinghan, Fan, Maosong, Yang, Kai, Tian, Guiying
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2020; Springer Nature B.V
• Subjects: Anodes; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Energy Storage; Graphite; Inorganic salts; Lithium fluoride; Lithium ions; Optical and Electronic Materials; Original Paper; Performance degradation; Renewable and Green Energy; Storage systems; LiFePO; Retired cell; Degradation mechanism; Lithium loss; Electrochemical stability
• ISSN: 0947-7047; 1862-0760
• DOI: 10.1007/s11581-020-03590-w

In this work, the performance degradation mechanism of the retired power cells is investigated after 400 and 800 cycles at 25 °C and 45 °C to determine whether they satisfy the secondary utilization requirement under the simulated energy storage systems. The results confirm that the capacity of retired cells show a linear relationship with cycle number. When the cycle numbers are more than 2400 times (at 25 °C), the capacity of the retired cells is decreased to less than 80% of initial capacity, which means the retired cells have the value of secondary utilization. In contrast to stable capacity delivering of LiFePO 4 , graphite anode shows obvious capacity fading. Further, the lithium loss at the LiFePO 4 cathode accounts for more than 70% of the retired cells capacity loss, and exceeding 85% of the consumed lithium-ion can be found at the graphite anode, leading to the formation of SEI film consisting of Li 2 CO 3 and LiF inorganic salts.