Absorptive Glass Mat Separators Research Articles

Fabrication and characterisation of proton exchange membrane from sulfonated natural rubber for possible use as an alternative separator in AGM battery

Proton Exchange Membrane was fabricated from sulfonated natural rubber (NR) as an alternative to absorptive glass mat (AGM) separator for AGM battery. The separator was fabricated using chlorosulphuric acid as the sulfonating agent at 0 °C under continuous stirring. Water uptake at 25 °C ranges from 0 to 58% while at 60 °C the range is from 4 to 38%, which suggest a strong attraction between the water molecules and sulfonate moiety. The acid uptake ranges from 18 to 83% for all three membranes (A, B and C) fabricated, which proves excellent electrolyte uptake, resistance to oxidation and acid attack. The FTIR analyses, water uptake, acid uptake and Carbon-Sulphur analysis confirm that the sulfonation occurred in NR through substitution reaction on the alpha carbons. The incorporation of ZnO and SiO2, caused increase in cell size, which indicate the porous and spongy structure throughout the surface area of each membrane, which indicate promising materials for application in AGM battery.

Probing the three-dimensional porous and tortuous nature of absorptive glass mat (AGM) separators

Abstract The valve regulated lead acid (VRLA) battery is a predominant electrochemical storage system that stores energy in a cheap, reliable and recyclable manner for innumerable applications. The absorptive glass mat (AGM) separator is a key component, which is pivotal for the successful functioning of the VRLA battery. Herein, the intricate three-dimensional (3D) porous structure of AGM separators has been unveiled using X-ray micro-computed tomography (microCT) analysis. X-ray microCT has quantified a variety of fiber and structural parameters including fiber orientation, porosity, tortuosity, pore size distribution, pore interconnectivity and pore volume distribution. A predictive model of hydraulic tortuosity has been developed based upon some of these fiber and structural parameters. Moreover, the pore size distribution extracted via X-ray microCT analysis has served as a benchmark for making a comparison with the existing analytical model of the pore size distribution of AGM separators. Pore size distributions obtained via the existing analytical model and through X-ray microCT analysis are in close agreement.

Optimal design of absorptive glass mat (AGM) separator with fastest electrolyte uptake using X-ray micro-computed tomography

Abstract Valve regulated lead acid (VRLA) batteries are traditionally classified on the basis of gel and absorptive glass mat (AGM) separators. To fulfill the desired functions of AGM batteries, a key design feature of the separator relies on the uptake of the electrolyte in shortest transport time. Herein, we present a three-dimensional (3D) analytical model to predict the fastest electrolyte uptake in AGM separators based upon the optimal set of fiber and structural parameters. The predictive model has utilized 3D data of fiber orientation in AGM separators, obtained via X-ray micro-computed tomography analysis. Such realistic structural information of AGM has assisted in simulating the separators made up of cheaper coarser glass fibers, which was subsequently benchmarked with the experimental samples consisting of finer fibers for attaining the fastest electrolyte uptake. Through theoretical modeling, a design criterion has successfully evolved for the fastest electrolyte uptake by mapping the key effects of the fiber diameter, 3D fiber orientation distribution and porosity of AGM separators. In general, high-density AGM separators comprising of preferentially aligned coarser fibers tend to attain the fastest electrolyte uptake.

Deconstructing three-dimensional (3D) structure of absorptive glass mat (AGM) separator to tailor pore dimensions and amplify electrolyte uptake

Absorptive glass mat (AGM) separator is a vital technical component in valve regulated lead acid (VRLA) batteries that can be tailored for a desired application. To selectively design and tailor the AGM separator, the intricate three-dimensional (3D) structure needs to be unraveled. Herein, a toolkit of 3D analytical models of pore size distribution and electrolyte uptake expressed via wicking characteristics of AGM separators under unconfined and confined states is presented. 3D data of fiber orientation distributions obtained previously through X-ray micro-computed tomography (microCT) analysis are used as key set of input parameters. The predictive ability of pore size distribution model is assessed through the commonly used experimental set-up that usually apply high level of compressive stresses. Further, the existing analytical model of wicking characteristics of AGM separators has been extended to account for 3D characteristics, and subsequently, compared with the experimental results. A good agreement between the theory and experiments pave the way to simulate the realistic charge-discharge modes of the battery by applying cyclic loading condition. A threshold criterion describing the invariant behavior of pore size and wicking characteristics in terms of maximum permissible limit of key structural parameters during charge-discharge mode of the battery has also been proposed.

Compression-recovery model of absorptive glass mat (AGM) separator guided by X-ray micro-computed tomography analysis

Absorptive glass mat (AGM) separators play a key role in enhancing the cycle life of the valve regulated lead acid (VRLA) batteries by maintaining the elastic characteristics under a defined level of compression force with the plates of the electrodes. Inevitably, there are inherent challenges to maintain the required level of compression characteristics of AGM separators during the charge and discharge of the battery. Herein, we report a three-dimensional (3D) analytical model for predicting the compression-recovery behavior of AGM separators by formulating a direct relationship with the constituent fiber and structural parameters. The analytical model of compression-recovery behavior of AGM separators has successfully included the fiber slippage criterion and internal friction losses. The presented work uses, for the first time, 3D data of fiber orientation from X-ray micro-computed tomography, for predicting the compression-recovery behavior of AGM separators. A comparison has been made between the theoretical and experimental results of compression-recovery behavior of AGM samples with defined fiber orientation characteristics. In general, the theory agreed reasonably well with the experimental results of AGM samples in both dry and wet states. Through theoretical modeling, fiber volume fraction was established as one of the key structural parameters that modulates the compression hysteresis of an AGM separator.

Amplification of electrolyte uptake in the absorptive glass mat (AGM) separator for valve regulated lead acid (VRLA) batteries

Absorptive glass mat (AGM) separators are widely used for valve regulated lead acid (VRLA) batteries due to their remarkable fiber and structural characteristics. Discharge performance and recharge ...

Pressure influence on the structural characteristics of modified absorptive glass mat separators: A standard contact porosimetry study

The article presents a comparative analysis of the structural characteristics of absorptive glass mats manufactured by “Hollingsworth & Vose” (a 2.8 mm thickness) and “Bernard Dumas” (a 3.0 mm thickness) modified by impregnation with polymeric emulsions based on polyvinylidene fluoride, a polyvinylpyrrolidone styrene copolymer, and polytetrafluoroethylene, by means of standard contact porosimetry. The key study is influence of features of the porous structure on the compression properties, the rate of wicking, and the oxygen cycle efficiency in lead-acid battery mock-ups under several plate-group compression pressures. It is found that the treatment of the absorptive glass mat separators with polymeric emulsions leads to redistribution of their pores by size. An increased pressure in the electrode unit insignificantly changes the pore structure of the modified absorptive glass mat separators, and the oxygen cycle efficiency rises in comparison with unmodified separators.

Investigation of lead dendrite growth in the formation of valve-regulated lead-acid batteries for electric bicycle applications

The battery temperature, H2SO4 distribution, Pb2+ ion concentration and composition of the plates during the plate soaking of the 12 V 12 Ah valve-regulated lead-acid (VRLA) battery are studied. A simulated cell composed by two pure Pb plates and the absorptive glass mat (AGM) separator is used to investigate the growth of the lead dendrite in the separator, which is verified by analyzing the faulty batteries after the formation and the failure batteries after the usage. It is found that the H2SO4 is exhausted very quickly after filling and the separator near the plates can become neutral during soaking. Low acidity, high temperature and small PbSO4 particle size will increase the Pb2+ ion concentration. Higher Pb2+ ion concentration makes more PbSO4 tend to deposit on the coarse glass fibers, develop along them and even enwrap the entire fiber. And the fine PbSO4 crystals are continually transformed into large PbSO4 crystals via dissolution-deposition. In the subsequent charge, these PbSO4 crystals will be reduced to the club-shaped lead dendrites and may lead to short circuit of the battery.

Absorptive glass mat separator surface modification and its influence on the heat generation in valve-regulated lead-acid battery

This paper presents the results from a comparative study between two types of valve-regulated lead-acid battery cells, with uncoated and polymer composite coated absorptive glass mat (AGM) separators. The volt-ampere characteristics of the studied cells, recorded at different ambient temperatures, show that the cells with polymer coated separators have significantly lower overcharge (recombinant) current than the cells with conventional untreated AGM separator. During overcharge, the higher recombinant current in the cells with plain separator leads to higher cell temperature than that of the cells with polymer coated AGM separator.The possibility to avoid thermal runaway (TR) is also illustrated during polarization of the cells at 2.65 V. After 320 h, a conventional cell has C/4 current (trend to TR), while the cells with composite coating sustain low (C/26) constant current for long period of time (at least 650 h). The cycle life test indicates stable operation of the cells with coated separator, while the conventional cell reaches high recombinant current and thus, it is susceptible to thermal runaway phenomena.

Carbon honeycomb grids for advanced lead-acid batteries. Part II: Operation of the negative plates

The article presents the recent progress in the carbon honeycomb grid technology for valve-regulated lead-acid batteries with absorptive glass-mat separators (AGM-VRLAB). The work is focused on the development of negative current collectors using industrial grade composite honeycomb precursors. The developed model AGM-VRLA cells comprised of one prototype honeycomb negative electrode and two conventional traction positive counter-electrodes show high utilisation of the negative active material and long cycle life both in high-rate partial state of charge (HRPSoC) cycling mode and in deep cycling mode. The analysis of the results from the cycle-life tests and the tear-down analysis indicate that the benefits delivered by the novel grids can be related to the low mesh size of the grid, low γ-coefficient, as well as the use of milled carbon fibre additive. The combination of the three, results in the reversibility of the negative active material sulfation process when the electrolyte concentration in the cells is lower than the one traditionally used in the AGM-VRLAB technology. The negative plates show no signs of irreversible degradation after more than 900 cycles in deep cycling mode and more than 2000 capacity turnovers (equivalent cycles) in HRPSoC cycling mode.

Three-layered absorptive glass mat separator with membrane for application in valve-regulated lead-acid batteries

Abstract During charge and discharge of the lead-acid cell equal amounts of H 2 SO 4 participate in the reactions at the two types of plates (electrodes). However, the charge and discharge reactions at the positive plates involve also 2 mol of water per every mole of reacted PbO 2 . Consequently, a concentration difference appears in the electrolyte between the two electrodes (horizontal stratification), which affects the reversibility of the processes at the two electrodes and thus the cycle life of the battery. The present paper proposes the use of a three-layered absorptive glass mat (AGM) separator, the middle layer playing the role of a membrane that divides (separates) the anodic and cathodic electrolyte spaces, and controls the exchange rates of H 2 SO 4 , H + ions, O 2 and H 2 O flows between the two electrode spaces. To be able to perform this membrane function, the thinner middle AGM layer (0.2 mm) is processed with an appropriate polymeric emulsion to acquire balanced hydrophobic/hydrophilic properties, which sustain constant H 2 SO 4 concentration in the two electrode spaces during cycling. Three types of polymeric emulsions have been used for treatment of the membrane: (a) polyvinylpyrollidonestyrene (MPVS), (b) polyvinylpyrrolidone “Luviskol” (MPVP), or (c) polytetrafluorethylene modified with Luviskol (MMAGM). It is established experimentally that the MMAGM membrane maintains equal acid concentration in the anodic and cathodic spaces (no horizontal stratification) during battery cycling and hence ensures longer cycle life performance.

Influence of float and charge voltage adjustment on the service life of AGM VRLA batteries depending on the conditions of use

Valve-regulated lead–acid (VRLA) batteries with absorptive glass mat (AGM) separators have been in use for over 20 years in different standby applications. These applications are increasingly varied, especially regarding environmental conditions. Standby batteries are not only for use in applications where conditions are strictly defined and controlled (air conditioning) and it is therefore necessary to review and clarify the key parameters for the use of VRLA batteries with respect to the optimum conditions. Several series of chemical and electrochemical reactions occur in VRLA batteries particularly when in a charge or float charge condition. These reactions give specific properties such as minimal water loss (low maintenance) but also create specific precautions for use. VRLA battery functioning is limited by four main phenomena that are positive grid corrosion, irreversible active mass sulfation, active mass degradation by cycling and dry-out by loss of water. Positive grid corrosion is the usual failure mode in float operation or due to persistent overcharge. Irreversible active mass sulfation occurs due to lack of charge. In cycling, dependent upon the frequency and depth of discharge, the active mass undergoes numerous structural changes that cause degradation. These four limiting phenomena define a framework inside which several parameters determine the service life of VRLA batteries. These parameters are commissioning, temperature, and frequency and depth of discharge. Commissioning is necessary to equalise and fully charge the cells before use. Temperature, and temperature dispersion, is the main factor determining the rate of corrosion. The frequency and depth of discharge determine how the active mass is utilised. This paper, by considering these parameters both qualitatively and quantitatively, attempts to indicate how and why to adjust the charge and float voltages to optimise the use of AGM VRLA batteries according to the environmental conditions.

Developments in absorptive glass mat separators for cycling applications and 36 V lead−acid batteries

The major markets for valve-regulated lead−acid (VRLA) batteries are undergoing a radical upheaval. In particular, the telecommunications industry requires more reliable power supplies, and the familiar 12 V electrical system in cars will probably be soon replaced by a 36/42 V system, or by other electrical systems if part of the automotive market is taken over by hybrid electrical vehicles (HEVs). In order to meet these new challenges and enable VRLA batteries to provide a satisfactory life in float and cycling applications in the telecommunication field, or in the high-rate-partial-state-of-charge service required by both 36/42 V automobiles and HEVs, the lead−acid battery industry has to improve substantially the quality of present VRLA batteries based on absorptive glass mat (AGM) technology. Therefore, manufacturing steps and cell components have to be optimized, especially AGM separators as these are key components for better production yields and battery performance. This paper shows how the optimal segregation of the coarse and fine fibres in an AGM separator structure can improve greatly the properties of the material. The superior capillarity, springiness and mechanical properties of the 100% glass Amerglass multilayer separator compared with commercial monolayer counterparts with the same specific surface-area is highlighted.

Advanced separator construction for long life valve-regulated lead-acid batteries

The performance of absorptive glass mat separators in valve-regulated lead-acid (VRLA) batteries is strongly influenced by the diameter of the fibres from which they are made. Coarser diameter fibres are beneficial for the compressive properties of separators while finer fibres maintain the uniform distribution of the electrolyte. Studies of cell compression and electrolyte stratification are reported using separators manufactured with segregated layers of fine and coarse fibres incorporated into a single sheet. This construction locates the different classes of fibre at their location of maximum effectiveness. Improvements in battery life in both cyclic and float charge applications are recorded, and compared with single layer separators.

High integrity VRLA batteries for telecommunications service

Telecommunications power requirements continue to evolve and to meet new patterns of use, new battery configurations have been developed to maximise energy density, optimise space utilisation and provide for ease of installation and maintenance. Front-access terminal batteries are well-matched to these requirements and are now widely applied in rack-mounted power supplies for telecommunications.A new range of sealed lead–acid batteries are described which embody front-access terminals but adopt a somewhat different approach where applications issues have been brought into sharper prominence rather than established design and manufacturing criteria. This range uses absorptive glass mat separators and state-of-the-art electrochemical designs to produce a range of batteries that has strong user benefits and enhanced performance.The technical characteristics of these batteries are described and compared to other constructions to demonstrate their behaviour under a wide range of operational conditions.

Micro-structural design and function of an improved absorptive glass mat (AGM) separator for valve-regulated lead–acid batteries

Two important properties of absorptive glass mat (AGM) separators are examined in order to design optimum separators for advanced valve-regulated lead–acid (VRLA) batteries. Acid stratification in the separator depends on its micro-glass-fibre diameter, and it is found that the extent of stratification can be estimated based on hydrodynamics theory. Decreasing the plate-group pressure of the separator in the wetted state is also investigated, and it is considered that the phenomenon is caused by the balance between the fibre strength and the surface tension of acid solution. Given these results, the way to design AGM separators according to purpose has been identified. Accordingly, a new AGM separator has been developed and this functions both to suppress stratification and to maintain plate-group pressure.

The Behavior of Oxygen Transport in Valve-Regulated Lead-Acid Batteries with Absorptive Glass Mat Separator

In the oxygen cycle of valve-regulated lead-acid (VRLA) batteries, there are two ways in which oxygen can move from the positive to the negative plates, namely, either horizontally to penetrate the absorptive glass mat (AGM) separator, and/or transport vertically via the gas space. It is found that the oxygen transport depends on the passageway with big void space in the AGM separator and its rate is proportional to the oxygen partial pressure. The rate constant of vertical transport is about three orders higher than that of horizontal transport because of the large void space between the AGM separator and plates. However, in the horizontal direction, the area is very large and the transport path is very short. So the way and the rate of oxygen transport actually depend on the level of saturation in VRLA batteries. The horizontal transport is dominant when the saturation is less than 93%, while the vertical transport becomes dominant when it is higher than 93%. The experiments also indicate that with decreasing saturation, the recombination of more oxygen at the negative plate may oxidize more active atoms and therefore, the overpotential of hydrogen evolution increases obviously. © 2001 The Electrochemical Society. All rights reserved.

00/01359 A study of the effects of compression on the performance of the positive active mass in lead-acid cells using absorptive glass mat separators

00/01359 A study of the effects of compression on the performance of the positive active mass in lead-acid cells using absorptive glass mat separators

00/00840 Synthetic fibre reinforcement of absorptive glassmat separators for valve-regulated lead-acid batteries

00/00840 Synthetic fibre reinforcement of absorptive glassmat separators for valve-regulated lead-acid batteries

00/00818 A multi-layered approach for absorptive glass-mat separators

00/00818 A multi-layered approach for absorptive glass-mat separators