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Chapter 17: Maintenance-Free Lead Batteries with Immobilized Electrolyte

Since the maintenance-free sealed nickel/cadmium accumulator became of high importance in the market, in the middle of the 1950s (Figure 17.1), the German battery company Sonnenschein has invented the first maintenance-free portable lead-acid batteries in small sizes in modules of 2 to 12 V between 1 and about 30 Ah. These batteries have been absolutely maintenance free and because of their immobilized electrolyte they could be used in any position without leakage. | 17 Maintenance-Free Lead Batteries with Immobilized Electrolyte H. TUPHORN 17.1 INTRODUCTION Since the maintenance-free sealed nickel cadmium accumulator became of high importance in the market in the middle of the 1950s Figure 17.1 the German battery company Sonnenschein has invented the first maintenance-free portable lead-acid batteries in small sizes in modules of 2 to 12 V between 1 and about 30 Ah. These batteries have been absolutely maintenance free and because of their immobilized electrolyte they could be used in any position without leakage. Applications for these batteries were electronic flashlights portable TVs tape recorders and electric lawn mowers. Also for emergency power supply and in alarm equipment these batteries in valve-regulated construction are used still today. Important for the maintenance-free properties of these batteries was the possibility to use antimony-free grid alloys instead of the conventional leadantimony alloys which were used only at this time. Because antimony in the grid alloys provides a high cycle life for the battery it was necessary to develop more sophisticated methods in battery manufacturing in order to achieve the required product properties. Copyright 2003 by Expert Verlag. All Rights Reserved. Figure 17.1 Valve-regulated maintenance-free gel batteries from the 1950s. 17.2 FUNDAMENTALS The basis for charging lead-acid batteries is the redox reaction of lead 1. PbSO4 2H2O PbO2 H2SO4 2H 2e 2. PbSO4 2H 2e- Pb H2SO4 Besides this main reaction an additional reaction takes place at the electrodes during charging which generates hydrogen and oxygen 1a. H2O 2H 1 2 O2 2e 2a. 2H 2e H2 This water decomposition during charging which requires the maintenance of topping up of water to the electrolyte generally takes place in lead-acid batteries if charging is not stopped after full charge of the active masses because no more lead ions for reactions 1 and 2 are available. This basically takes place during charging with constant