Systematic Screening of New Additives for Lead–Acid Technology –The Role of Porosity and Electrode Surface-Area
Additives play a key role in improving the electrical performance and durability of lead-acid battery technology. For instance, customized expander mixes, containing different expander types, barium sulfate and functional carbon types are used to improve and stabilize the surface-area of the negative electrode. On the other hand, only a limited number of additives have been adopted for the positive active-mass.
The AddESun project, a public research project between Fraunhofer ICS, Exide Technologies, Evonik Resource Efficiency GmbH, RWTH Aachen University, SGL Carbon Group, and PENOX, is undertaking a systematic screening programme for new and improved additive classes, as well as for synergistic interactions between different additives. PENOX is responsible for both the paste preparation and pasting process and the characterization of the electrodes. The project was established in late 2017 and will run for three years. The main target is to review and benchmark established (state-of-the-art) additives and better understand their functional mechanism(s), as well to search for new additives. Since battery additives are likely to show functional interactions which impact their effectiveness, the overall number of variables in such as screening is rather large. A Design of Experiment Approach (DOE) is therefore been devised. The latter action, which is still uncommon in battery-related research, is very powerful and enables a rapid check for interactions between components without the need for numerous parallel trials.
This paper provides a review of the general approach used in the AddESun project and offers insight into the screening strategy and the first (non-confidential) results. Several challenges, such as controlling the test conditions and identifying relevant response levels are discussed. The research is backed up by structural analysis of electrodes using a high-resolution SEM and element mapping techniques to correlate electrical performance with structural aspects of the active mass.
At present, controlling the porosity of the active masses is a main topic of focus. It has been demonstrated that several additives lead to an improvement in the porosity of the positive active-mass. TBLS+ (a tetrabasic seeding material) is among the prospective additives that have demonstrated a significant improvement in porosity and initial capacity. Other additives based on nanostructured fumed metal oxides (AEROXIDE® grades from Evonik) have also been identified as improving the porosity of the active mass. Early results indicate sufficient chemical stability under cycling conditions.
As the Battery Additives Manager of PENOX Rainer Bussar is responsible for the development of new battery additives, scientific collaborations and technical support for the battery Industry. Prior to joining PENOX in March 2018, he was served as the Director of R&D at EXIDE Technologies in Europe. Rainer holds a PhD in chemistry and between 2001 and 2009 conducted research and at the University of Bonn, the Technical University of Munich, and the Bavarian Center of Applied Energy Research.