Journal of Power Sources, 50 (1994) 67-79 67 zyxwvuts Effect of gelling on the electrode kinetics of the Pb/ PbS04 and hydrogen-electrode reactions in maintenance-free lead/ acid batteries M.P. Vinod and K. Vijayamohanan* Materials Chemistry Division, National Chemical Laboratory, Pune-III 008 zyxwvutsrqponmlkjihgfedcb (India) (Received July 13, 1993; accepted November 17, 1993) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Abstract The electrode kinetics of the PbffbSO, and the hydrogen-evolution reactions on porous lead electrodes in sulfuric acid has been studied using a quantitative analysis of galvanostatic transients in the linear polarization domain. Significant changes are observed in the kinetics with the addition of thixotropic agents (e.g., sodium silicate) that are often employed in the manufacture of maintenance-free lead/acid batteries. The effects of these thixotropic agents on the charge-transfer and ohmic components of the Pb/PbS04 reaction and charge- transfer components of hydrogen-electrode reaction are analysed with the help of a ‘pore- plugging’ model. This study allows a non-destructive determination of the electrode kinetic parameters and the internal resistance contribution from pore-plugging. This is useful when designing maintenance-free lead/acid batteries. Introduction The advent of sealed maintenance-free batteries in recent years has resulted increasingly in the use of immobilized and absorbed electrolytes [l-3], with or without catalytic recombination plugs. In the former, the loss of oxygen and hydrogen (produced during charge or overcharge of the respective positive and negative electrode) is minimized either by oxygen/hydrogen recombination on a suitable catalyst in the vent plug, or by oxygen reduction on the porous lead of the negative electrode. In the latter, immobilization of the electrolyte is necessary and is achieved by adding a thixotropic agent, such as sodium silicate, to the electrolyte. Addition of a thixotropic agent will, however, have ,other implications, such as: increased ohmic resistance; changes in the interfacial kinetics due to adsorption of silicate ions; formation of cracks in the electrolyte, and gas entrapment. Furthermore, a progressive loss of hydrogen from the cell can cause drying out of the gel and results in electrolyte imbalance followed by eventual cell or battery failure. Although pressure-regulated valve cells with gelled electrolyte are commonly used for several float applications, none of the above problems have been systematically analysed, except for the effect of thixotropic agents on the kinetics of hydrogen evolution [4]. More importantly, recent studies [5, 61 indicate tpat the lead/acid system is amenable to pulsed discharge. Such operation demands a careful analysis of the effect of gelling on the ohmic drop (IR), especially if maintenance-free gelled systems are to be used for these and other *Author to whom correspondence should be addressed. 037%7753/94/$07.00 0 1994 Elsevier Sequoia. All rights reserved SSDI 0378-7753(93)01883-J