SELIBA. SEcond LIfe Program for Lithium Ion BAtteries. Final report

In the SeLiBa project, different "second-life" applications (reuse) of used lithium-ion traction batteries are ecologically and economically evaluated with the help of life cycle analyses (LCA) and business assessment methods such as life cycle costing (LCC) and the total cost of ownership (TCO) method in order to identify potential savings. This also includes a comparison to the alternative "end-of-life" option of recycling. The project partners are Esslingen University of Applied Sciences with the Institute for Sustainable Energy Technology and Mobility (INEM) and the Faculty of Fundamentals as well as the medium-sized company CTC cartech company GmbH with headquarters in Böblingen. Seliba's goal is to develop processes and test rigs that can be used to determine the recyclability of used vehicle batteries in terms of function and safety. For this purpose, conventional internal resistance and (residual) capacity measurements are combined with impedance spectroscopy and measurement of the voltage curve after current pulses. Load profiles are analysed in parallel to determine the external ageing factors. The correlations between ageing factors, electrochemical processes and external measured variables are combined in the form of a physical-empirical ageing model. Based on this, statements on both the residual value and possible fields of application in suitable "second life" (SL) applications will be determined. In addition, these will be ecologically and economically evaluated with the help of LCA and business assessment methods in order to determine possible savings potential. To characterise the battery, battery models will be developed within the project that determine meaningful parameters to describe the current electrochemical state of the battery. The research work focuses on determining the relaxation times of the electrochemical processes. In combination with "grey box models" (for example equivalent circuit models), the state of the battery can be described in detail. In the laboratory, batteries are loaded by means of statistically planned ageing cycles and measured during their ageing by impedance spectroscopy and pulse measurements. The measurement results are used to determine electrochemical parameters using the models described above. This is followed by the creation of a model that describes the dependence of the electrochemical parameters on the external ageing factors. A linear regression is used. The aim of the described procedure is to create a long-term model for the change in the battery's state of health due to its application-dependent load. This model can be used to determine the optimal application location of each battery and its residual value and remaining lifetime. Economically identified SL applications are the provision of primary control power, home storage system in combination with a photovoltaic system, microgrid, deferring grid investments and ensuring power quality. Furthermore, a potential economic value for the use of SL batteries (SLB) compared to new batteries could be identified. Identified success factors are a high share of SLB costs in the total investment costs, a long useful life of the SLB and low absolute SLB costs. An average TCO reduction potential of 3.4 percent as well as a comparable reduction of the purchase costs of a BEV between 6.2 and 7.3 percent were determined for the economically evaluated SL applications. Compared to recycling, economic SL applications are to be preferred, as recycling is currently not economically feasible. In order to be able to exploit the existing economic potentials, the legal framework as well as a technical standardisation must be specified. The commercial exploitation of the project results is carried out by integrating the battery models into the products of the "Lion family" of CTC cartech company GmbH.