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At present battery capacity is conventionally measured by integrating the current of a charging (or discharging) process or measuring battery voltage curves under defined conditions. These methods do not fulfil the requirements for quality assessment of second use batteries since they are either too slow or too inaccurate for economically viable reprocessing of Li ion batteries. Hence, an adequate measurement procedure is lacking at present. Measurement procedures to assess the risk of premature failure do not exist at all. In general, this project will investigate impedance-based measurement and evaluation methods to establish an adequate battery testing method for this purpose. The project has five major objectives:

Objective 1: Metrologically sound life cycle test and impedance measurement procedures.

Impedance based measurement methods depend sensitively from the applied test and measurement conditions. A lot of life cycle tests, including impedance-based measurements, have been performed in the past to investigate Li-ion batteries. Unfortunately, those tests were lacking a common metrological basis to ensure reproducibility and comparability of the results. As a consequence, results were often deemed inconsistent or insignificant. To overcome this shortcoming agreed measurement procedures for life cycle tests and impedance measurement methods, as well as for conventional methods will be established for the first time with associated target uncertainties around 1 %.

Objective 2: Development and characterisation of impedance-based procedures to measure the residual capacity and detect premature sudden death

Using these protocols, an extensive database of metrologically consistent impedance-based measurement results will be established from life cycle tests of different types of Li ion battery cells and modules under various cycling conditions for the first time. The results will be investigated with the various impedance-based evaluation methods mentioned above. Based on this investigation, new impedance-based measurement procedures to measure the residual capacity of high energy Li ion battery cells and modules with a target relative uncertainty of better than 3 % will be developed and the feasibility of using them to detect premature sudden death of Li ion batteries will be investigated.

Objective 3: Low impedance standards and calibration procedures

Moreover, there is no metrological basis for the calibration of impedance measurement devices in the low impedance (m) range at present. Adequate impedance standards and associated measurement uncertainties, as well as calibration procedures and the required metrological calibration infrastructure, are missing. Therefore, this project will go beyond the state of the art by establishing 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 will include the development of low impedance standards with arbitrary phase angles and a calibration method for impedance meters.

Objective 4: Validated test protocol to characterise modules based on impedance measurements

The activities above will result in new, readily applicable, impedance-based procedures for the application to Li-ion battery cells and modules. The procedures will be scientifically validated with a physical battery model and by conducting inter laboratory comparison measurements on second use batteries provided by industrial partners and, if possible, by stakeholders in order to meet the requirements of economical quality assessment of second use batteries.

Objective 5: Standardisation and up take

Finally, characterisation of Li-ion battery cells for second use application by means of impedance-based methods has neither been considered in standardisation nor have the related metrological principles been realised in corresponding industrial measurements. Hence, up take 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, IEC 62660-1) and end users (e.g. the transport sector) will be facilitated. The consortium includes partners that are members of relevant standardisation boards or have contacts to them. It includes partners from related industry, universities and research facilities and has contacts to a variety of relevant stakeholders. Taking advantage of these links, the consortium will promote up take of the project’s outcomes by informing stakeholders regularly on the progress, by introducing measurement guides to standardisation, by publishing the results and by organising workshops and on-site trainings.