Lightweight lead acid batteries for hybrid electric vehicle applications

Abstract

This report presents architectures, designs and chemistries for novel static soluble lead acid batteries, with the objective of producing a lightweight lead acid battery for improved specific energy. The demands for lightweight lead-acid batteries come from an expanding hybrid electric vehicle market demanding improved battery specific energy. There are several avenues for improving battery specific energy; the main two are improved active material utilisation efficiency and grid weight reduction. Both of these have been focuses of this project. Two approaches have been taken in this project, the first is focussed on the electrode design. Design modifications have been achieved by using novel grid materials to reduce weight and novel electrode designs to improve active material utilisation. Battery electrodes were built from titanium and the active material was applied as a thin film of lead. Characterisation of lead coatings on several material geometries under different plating regimes was conducted. A novel thin-film active material battery was designed, built and tested satisfactorily to industrial standards. The second battery system being investigated has the active materials solvated in the methanesulphonic acid electrolyte during the discharged state. Due to the high solubility of lead in this Pb-CH3SO3H electrolyte, lead-acid batteries with this chemistry have a theoretical specific energy of 35.7 Ah l-1. This compares favourably with the specific energy for a conventional spiral wound VRLA battery at 44.4 Ah l-1. These soluble lead acid batteries operate by a mechanism whereby cycling is stripping and plating lead and lead dioxide onto the electrodes. Active material utilisation in this type of lead-acid battery is not limited in the same way as conventional lead-acid batteries, as the discharge product is not electrically insulating, as is lead sulphate. The operation mechanism was improved by using additives in the electrolyte to maintain a quality deposit and preserve charge efficiency, voltage efficiency and active mass utilisation. In addition, the use of a separator membrane and novel carbon-polymer electrodes improved battery performance further. The behaviour of a static soluble lead acid battery during cycling with and without additives and a cell membrane is characterised and the results are used to develop a 6 V battery. The results of the 6 V battery cycling under HEV simulated cycling are presented and discussed.

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ORCID for Richard Wills: orcid.org/0000-0002-4805-7589

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