One of the major research targets of our Department is to diclose the phenomena that occur during operation of VRLA batteries. When the lead-antimony grids in lead-acid batteries were substituted by lead-calcium ones battery cycle life was dramatically shortened. This phenomenon was called first “antimony-free effect” and later “premature capacity loss” (PCL).
Parameters and conditions influencing PCL. Reviewing the abundant literature data D. Pavlov has summarized the basic parameters that exert the strongest influence on PLC as follows:
Alloying additives to grid alloys (Sb, Sn, Ca)
Active mass density
Amount and concentration of H2SO4
Modes of charge and discharge
High utilization coefficient of positive active mass and great depth-of-discharge
No stack pressure in the cell
Location of PCL effect. It has been established that PLC effect is a result of changes in the structure and electrical properties (formation of PbSO4 barrier layer) of the corrosion layer during cycling. There are a few models proposed in the literature that describe the structure and properties of the corrosion layer (CL). D. Pavlov suggests a new concept for the phenomena that occur in the corrosion layer, based on the theory of gel-crystal structure of PAM.
Corrosion layer. It has been established that CL comprises two sublayers: a dense (inner) and a porous (outer) sublayer. The inner layer is composed of PbO1.2 and the outer layer of PbO1.8 lead oxides, which results in different conductivities of the sublayers. The gel-crystal approach is applied to describe corrosion layer properties. According to the above-mentioned properties of the hydrated gel zones the “bridges-islands” mechanism of electron transfer is proposed. The composition and structure of the CL depend on the rate of the reactions that take place at the grid and on grid alloy composition. Alloying additives could affect CL conductivity in two ways. First, they can act as electrocatalysts or inhibitors of the reactions in the CL and thus change its stoichiometric coefficient. The second mode is to altering the semi-conductor properties of the oxides in CL - formation of mixed oxides. The effect of Sb, Sn, As, Bi on the structure and properties of CL and its influence on PCL has been investigated in our laboratory.
A new theoretical approach to the grid/PAM interface is proposed. It assumes that the interface between grid and PAM has the following structure: grid/CL/AMCL/PAM, where AMCL means Active Mass Collecting Layer. The main function of AMCL is to collect current generated by PAM. The structure, composition and conductivity of AMCL have been reviewed. Clear experimental verification of the proposed theory has been searched.
Methods for suppressing PCL effect. On grounds of the theoretical and experimental data obtained from the fundamental investigations methods have been proposed to prevent failure caused by PCL. D. Pavlov has suggested methods for suppressing the PCL phenomena. These methods can be divided in two groups, the first group being related to the production technology and the second group to cell design parameters.
Select appropriate additives to grid alloys (Sb, Sn) that would interconnect the polymer chains of gel zones of PAM in a network with high conductivity.
Select appropriate dopants to grid alloys that maintain high stoichiometric coefficient and high conductivity of CL
Improve the contact between grid and PAM through formation of thick CL (high temperature curing of positive plates)
Restrict plate pulsation to about 10-15% during charge–discharge cycling
Limit amount of H2SO4 reaching the grid/PAM interface by increasing PAM density
- D. Pavlov, B. Monakhov, M. Maja, N. Penazzi, Mechanism of action of Sn on the passivation phenomena in the lead-acid battery positive plate (Sn-free effect), J. Electrochem. Soc., 136 (1989) 27
- D. Pavlov, B. Monakhov, M. Maja, N. Penazzi, Sn-Free Effect at the Positive Lead Acid Battery Plates, Revue Roumaine de Chimie, 34 (1989) 551
- T. Laitinen, K. Salmi, G. Sundholm, B. Monahov, D. Pavlov, The Effect of Antimony on the Anodic Behaviour of Lead in Sulphuric Acid Solution. 1. The Behaviour of Lead-Antimony Alloys During the Early Stage of Oxidation, Electrochim. Acta, 36 (1991) 605-614
- D. Pavlov, B. Monahov, G. Sundholm, T. Laitinen, The Effect of Antimony on the Anodic Behaviour of Lead in Sulphuric Acid Solution. 2. Phase Composition of the Anodic Layer in Dependence of the Oxidation Potential, J. Electroanalyt. Chem., 305 (1991) 57-72
- D. Pavlov, A. Dakhouche, T. Rogachev, Influence of Arsenic, Antimony and Bismuth on the Properties of Lead/Acid Battery Positive Plates, J. Power Sources, 30 (1990) 117
- D. Pavlov, Effect of Dopants (Group V) on the Performance of the Positive Lead-Acid Battery Plate, J. Power Sources, 33 (1991) 221
- D. Pavlov, A. Dakhouche, T. Rogachev, Influence of Antimony on the Electrochemical Behaviour and the Structure of the Lead Dioxide Active Mass of Lead-Acid Batteries, J. Power Sources, 42 (1993) 71
- B. Monahov, D. Pavlov, Influence of Antimony on the Structure and Degree of Hydration of the Anodic PbO2 Layer Formed on Pb-Sb Electrodes, J. Electrochem. Soc., 141 (1994) 2316
- D. Pavlov, Premature Capacity Loss (PCL) of the Positive Lead/Acid Battery Plate: Phenomena. New Concept., J. Power Sources, 42 (1993) 345
- D. Pavlov, Suppression of premature capacity loss by methods based on the gel-crystal concept of the PbO2 electrode, J. Power Sources, 46 (1993) 171
- D. Pavlov, Effect of the corrosion layer on the phenomena causing premature capacity loss (PCL), J. Power Sources, 48 (1994) 179
- M.K. Dimitrov, D. Pavlov, Location of the phenomena of premature capacity loss during cycling of lead/acid batteries with lead grids, J. Power Sources, 46 (1993) 203
- D. Pavlov, Methods for Suppressing the Phenomena Causing Premature Capacity Loss (PCL) Based on the Gel-Crystal Concept of the PbO2 Electrode, Proceedings of the International Conference LABAT'93, 7-11 June 1993, Varna, Bulgaria, p. 11
- D. Pavlov, A theory of the grid/positive active mass (PAM) interface and possible methods to improve PAM utilization and cycle life of lead/acid batteries, J. Power Sources, 53 (1995) 9
- D. Pavlov, A. Dakhouche, T. Rogachev, Influence of antimony ions and PbSO4 content in the corrosion layer on the properties of the interface grid/active mass in positive lead-acid battery plates, J. Applied Electrochem., 27 (1997) 720
- T. Rogachev, D. Pavlov, Influence of CaSO4 on the properties of the positive lead-acid battery plates, Proceedings of extended Abstracts, LABAT’96 International conference, p.29, Varna, June 1996
- T. Rogachev, D. Pavlov, Influence of cycling on the nature of the positive active mass of lead-acid batteries and effect of CaSO4 on the behaviour of the positive plates, J. Power Sources, 64 (1997) 51
Keywords: antimony-free effect, premature capacity loss, PCL, gel-crystal concept, corrosion layer in LAB, suppress PCL