Journal of Power Sources, 41 (1993) 231-238 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Mechanism of Pb02 formation positive plates L. Zerroual* and F. Tedjar 231 in lead/acid battery Unit6 de Recherche Electrochimie, Universitt! de S&G 19000 S&f (Algeria) J. Guitton Laboratoire d’lonique et d’Electrochimie des Solides de Grenoble (LIESG), Dornaine Universitaire, BP 75, 38402 Saint-Martin d’H&es (France) A. Mousser Dt’partement Mat&&x Ino?ganiques, Universitk de Constantine, 25000 Constantine (Algeria) (Received September 24, 1991; in revised form August 27, 1992) Abstract The processes which take place in the paste during preparation and formation of lead/ acid battery positive plates in H,SO, (sp.gr. 1.05) were studied using wet chemical analysis and X-ray diffraction. It was found that basic lead sulfate was obtained in two stages. During the first stage, free lead reacts in a basic character paste with HzS04 added to the lead powder and gives lead sulfate with an overall stoichiometry equivalent to PbS04.Hz0. During the second period, PbO undergoes an acid/base reaction to 3Pb0.PbS04.Hz0. When soaking and forming in free H,SO,, lead oxide (free PbO plus PbO in the basic sulfate) reacts with H,SO, and gives lead sulfate PbSO+ The X-ray diffraction data showed that PbS04*Hz0 is converted to a-Pb02, while PbSO., leads to the /3-PbOz form. zyxwvutsrqponm Introduction Two forms of Pb02 are present in positive plates material: cr-PbOz and p-Pb02 [l, 21. The former is the orthorhombic and the latter is the tetragonal modification. It has been shown previously that the amounts of (Y- and /3-Pb02 that are formed in the positive plate material vary with: (i) the density of the paste, i.e. the H2S0.JPb0 ratio; (ii) the specific gravity of the forming acid; (iii) the rate, and (iv) the temperature of the formation [3-141. On the other hand, the capacity and the life of the positive plate are determined by the ratio of the two polyrnorphs. The mechanism of the processes of cu-PbOz formation in lead/acid battery positive plate has been subject of continuing interest these last years. Two schools of thought are found in the literature. According to the first one, solid state reactions within the basic lead sulfate crystals take place and yield cu-PbOz [4, 61. According to the second one, the solution in the pores of the paste, which is locally alkalinized, leads to a-PbOz crystals [3, 71. Other mechanisms have been proposed such as anodic oxidation of grid lead [l], of PbO in the paste [14], and tetrabasic lead sulfate (4Pb0.PbS04) [15]. *Author to whom correspondence should be addressed. 0378-7753/93/.%X@ 0 1993 - Elsevier Sequoia. All rights reserved