17IND10 LiBforSecUse: Quality assessment of electric vehicle Li-ion batteries for second use applications

• Forschungsstelle: METAS
• Projektnummer: F-5212.30100

Schlüsselwörter (Englisch)

Li-ion batteries, second life batteries, electric vehicles, impedance spectroscopy, nonlinear frequency response analysis, distributed relaxation times

Kurzbeschreibung (Englisch)

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 using fast and non-destructive impedance based methods and the 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.

Li-ion batteries can still be used for many years in a range of other applications after their end of life in an electric vehicle (EV), for instance as reserve power in electricity grids or for local energy storage in conjunction with photovoltaic systems. Such batteries are called second use (or second life) batteries. Forecasts estimate that up to 200 GWh of energy storage capacity will already be available by 2020 in terms of second use batteries, which could significantly reduce the cost of second use applications compared to the purchase of new batteries. Therefore, resale of re-purposed batteries opens great economic opportunities for a European second use market.

However, to this end optimisation of battery reprocessing is urgently required, otherwise the application of second use batteries will be too expensive to be economically viable. In particular, validated impedance based procedures to measure the residual capacity needs to be significantly faster and more accurate compared to existing methods. Furthermore, a robust measurement procedure to assess the risk of premature failure, at least qualitatively, does not yet exist. Impedance based measurement and evaluation methods could serve this purpose but the underpinning metrological framework, including traceability, quantified measurement uncertainties and defined measurement procedures in order to guarantee comparability of the results, is currently lacking. Consequently, standardised protocols for life cycle testing and impedance measurements as well as practical calibration concepts and standards for impedance measurement devices must be developed.

In the broader, environmental context, the EU has declared the need to reduce greenhouse gas emissions on several occasions. Hence, actions to implement second use batteries in conjunction with renewable energy sources need to be supported, instead of wasting enormous amounts of storage capacity and buying new storage systems, primarily imported from Asia, for that purpose.

This is a joint research project carried out in the framework of the European Metrology Programme for Innovation and Research (EMPIR) (see:http://www.euramet.org/research-innovation/empir/). The EMPIR initiative is co-funded by the European Unions's Horizon 2020 research and innovation programme and the participating states. METAS is one of the project partners in the project.

Projektziele (Englisch)

The specific objectives of the research are:

1. To develop protocols for life cycle testing of different types of Li-ion battery cells and modules in terms of capacity, chemistry and geometry, at different temperatures, currents and cycling patterns. The life cycle tests will include both impedance based methods (e.g. EIS, EC, DRT, NFRA and TDM) and conventional methods e.g. open circuit voltage (OCV) measurement and current integration.
2. 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 %. In addition, to assess the feasibility of detecting the premature sudden death of Li-ion batteries based on impedance based measurements.
3. To establish traceable impedance measurements in the m? and sub-m? range in the full complex plane in the frequency range between 10 mHz and 5 kHz, with a target relative uncertainty of 1 %. This will include the development of low impedance standards with arbitrary phase angles and a calibration method for impedance meters.
4. To develop a validated protocol for the application to Li-ion battery modules of the traceable impedance measurements in the m? and sub-m? range in the full complex plane in the frequency range between 10 mHz and 5 kHz.
5. To facilitate the take up of the technology and measurement infrastructure developed in the project by the measurement supply chain (e.g. batteries manufacturers and the automotive industry) standards developing organisations (e.g. IEC-TC21 and input to IEC 62660 1) and end users (e.g. the transport sector).

METAS contributes to WPs 1, 2 and 5.