Li-ion batteries can still find useful applications after removal from their first use in electric vehicles, e.g. as low-cost energy storage media in conjunction with photovoltaic systems, but their uptake is hampered by the lack of accurate and cost-effective characterisation techniques. This project will develop a robust measurement procedure and the supporting metrological infrastructure to measure their residual capacity fast by using impedance based methods. Feasibility to predict premature failure will also be investigated. Such procedures are required to enable economical and ecologically reasonable use of large numbers of used Li-ion batteries available in the near future.
The specific objectives of the project are:
To develop protocols for life cycle testing (LCT) of different types of Li-ion battery cells and modules in terms of capacity, chemistry and geometry, at different temperatures, currents and cycling patterns in order to establish robust reproducibility conditions. Further, to perform a series of LCTs under these conditions.
To develop validated impedance based measurement procedures to measure the residual capacity of Li-ion battery cells and modules with a target relative uncertainty of better than 3 %. To this end various impedance based measurement and evaluation methods will be applied, such as such as the assessment of electrochemical impedance spectra (EIS), equivalent circuit (EC) fitting of impedance spectra, analysis of distributed relaxation times (DRT), physicochemical parameter fitting (based on Newman-type electrochemical models), nonlinear frequency response analysis (NFRA) and time domain measurements (TDM). In addition, to assess the feasibility of detecting the premature sudden death of Li-ion batteries using these methods.
To establish traceable impedance measurements in the mW and sub-mW range in the full complex plane in the frequency range between 10 mHz and 5 kHz, with a target relative uncertainty of 1 %. This should include the development of low impedance standards with arbitrary phase angles and a calibration method for impedance meters.