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Electrolyte Additives for Enhancing the Cycle-Life of Automotive Lead-Acid Batteries

A wide range of inorganic and organic materials are used as additives to the electrolyte or/and to the negative and positive electrodes of leadacid cells to improve, for example, their conductivity, enhance battery capacity and cycle-life, suppress hydrogen and oxygen evolution reactions on the negative and positive electrodes, retard electrode corrosion. The major factors contributing to the decline in capacity of the positive plates during chargedischarge cycling are progressive deterioration of the electrical contact between the PbO2 particles of the positive active-mass and the grid, and formation of a layer of PbSO4 crystals on the electrode surface that isolates a fraction of the active mass and thus reduces its utilization. During charging a leadacid battery, the positive grid is oxidized and a boundary layer forms between the grid and the active mass.

The main goal of the present study is to improve the cycling performance of positive plates by adding inorganic or organic surfactants to the H2SO4 solution. The surfactants under test are organic compounds (anionic or cationic) or inorganic phosphate material. This research is aimed at understanding how the tested surfactants influence the morphology of PbSO4 and PbO2 crystals. The basic effects of the different surfactants added to the electrolyte on the electrochemical reactions that proceed on a lead or lead alloy (PbSb, PbCaSn) electrode are evaluated by cyclic voltammetry. The morphology of PbO2 or PbSO4 crystals formed on the surface of the investigated electrodes is also examined. Scanning electron micrographs demonstrate that the surfactants cause the formation of PbO2 particles of different size, as compared with the PbO2 formed with blank electrolyte.

Experimental data from an initial capacity test and a 17.5% DoD cycling test for start-stop leadacid batteries show that cells with organic additives give about 20% improvement in cycle-life. Furthermore, the cycle- life of cells with an inorganic phosphate material is beyond 2000 cycles, which is twice that of obtained from the control cell.

Maria Matrakova

Research Associate , Institute of Electrochemistry and Energy Systems ”Acad. Evgeni Budevski”- Bulgarian Academy of Sciences, Sofia, Bulgaria

Maria Matrakova has a PhD degree in Electrochemistry from the Institute of Electrochemistry and Energy Systems of the Bulgarian Academy of Sciences. Her scientific interests are focused on studying the impact of new additives on the phase composition, structure and electrochemical properties of leadacid battery electrodes by employing various techniques for characterizing the materials.