Regeneration of Lithium-Ion Cells

Examensarbete för masterexamen
Master's Thesis
Sustainable energy systems (MPSES), MSc
Rasmussen, Marcus
Dufvenius Esping, Elin
Electric Vehicles (EVs) are a key factor in the vision of reaching the goal of net-zero emission by 2050, and Lithium-Ion Batteries (LIBs) are one of the most promising technologies for EVs in this pursuit. However, as the demand for LIBs increase, the waste generated by the spent batteries also increases. From a material supply shortage perspective, as well as a waste management perspective, further improvements are needed to achieve a more sustainable approach. While recycling is an important aspect, regeneration could provide a more efficient solution by extending the LIB lifecycle. In this work, a study to investigate the potential for capacity regeneration of lithium-ion cells was initiated. The aim was to develop and validate a general non-invasive regenerative approach which in the long run could be implemented into the Volvo battery management system. Lithium-ion cells were aged with two different charging rates during a two-month period, after ageing, three different regenerative approaches were investigated. The cells consisted of an NMC cathode. Performance tests and Electrochemical Impedance Spectroscopy (EIS) were performed before ageing, after ageing and after regeneration to quantify the effects of ageing as well as regeneration. Differential Analysis and EIS were used to identify the different modes of degradation occurring in the cells, meaning Loss of Active Material (LAM) and Loss of Lithium Inventory (LLI). The cells were cycled for 365 cycles and displayed a maximum capacity fade of 3.18 %, reaching around 97 % State of Health (SoH). Furthermore, LAM, LLI and internal resistance increase were identified as plausible causes for capacity fade. Three different regeneration approaches were investigated based on crystal spatial movement, current pulses and a combination if spatial and current pulses. Electrochemical characterization suggested additional capacity fade after the end of regeneration for all approaches. However, an indication towards regained active anode material was observed for all regenerated cells. The combination of crystal spatial movement and current pulses showed indications of regained lithium inventory. Further investigations and results validation are required to confirm those results.
lithium-ion batteries , battery degradation , loss of active material , loss of lithium inventory , capacity regeneration
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