Valve-regulated Batteries Research Articles

The use of activated carbon and graphite for the development of lead-acid batteries for hybrid vehicle applications

Future vehicle applications require the development of reliable and long life batteries operating under high-rate partial-state-of-charge (HRPSoC) working conditions. This paper updates work carried out to develop spiral wound valve-regulated batteries for vehicles with different hybridisation degrees, ranging from stop–start to mild hybrid applications. In order to develop a battery that can withstand the hard operating conditions that the work at High Rate Partial-State-of-Charge (HRPSoC) implies, it is necessary to modify the negative AM formulation by using special, additives like carbon and graphite that reduce lead sulphate accumulation during HRPSoC cycling within in the negative plate. Several batches of negative active material (NAM) with the addition of graphites of different types, as well as combinations of graphite and activated carbons, have been made on 6 V 24 Ah Spiral wound modules. Electrical results show a dramatic increase of the charge acceptance at different SoC's that for some combinations approach 200%. On the other hand, on cycle life according to EUCAR Power Assist cycling, values in the range 200,000–220,000 cycles have been obtain in most part of the batch. This represents a capacity turnover of 5000–5500 times the nominal capacity. The paper is divided into three parts. The first part is devoted to identify the cause of failure of the negative plate on Power Assist Cycle Life, that turned to be the development of high amounts of lead sulphate and its accumulation on the surface of the plate. The second part covers the addition of carbon and graphite of low SSA to NAM and finally the third part is dedicated to the test of additions of medium/high SSA carbon to NAM with the specific objective of trying to implement the supercapacitor effect inside the battery.

The influence of fast charging on the performance of VRLA batteries

A valve regulated battery (VRLA) with thin tubular electrodes combines the endurance of robust positive tubular electrodes and the enhanced power properties of very thin electrodes. Fast charging is essential for many applications and it can compensate the lower energy density of lead-acid batteries. Thin tubular electrodes VRLA batteries were cycle life tested and influences of two charging regimes were investigated. A comparison is made between a newly developed fast charging regime with current step-down and a conventional charging regime as regards battery life and performance. The fast charging procedure was beneficial for the cycle life; however, associated beneficial effects were reduced by certain drawbacks. A measuring method was developed for analysing the current distribution over the electrodes at high and low currents and results are presented in this paper. Post-mortem battery analyses were carried out to determine the dominating degradation effects. The differences in the degradation effects caused by the charging regimes are discussed. The paper concentrates on the newly developed fast charging regime and compares the influence of the charging regime on ageing mechanisms of the VRLA batteries with tubular electrodes as opposed to a conventional charging regime.

Amersorb: a new high-performance polymeric separator for lead–acid batteries

Given the recent improvements in valve-regulated batteries, lead-acid technology is nowadays considered to be well-suited for stationary power applications. Gel and absorptive glass mat (AGM) valve-regulated lead-acid (VRLA) batteries are complementary technologies and provide reliability and efficiency due to progressive optimization of the design and components. Special attention has been paid to the separation system, as its influence on the battery performance has been fully demonstrated. Polymeric calendered ribbed separators are traditionally used in gel VRLA batteries. For this technology, the separator is required to have high pore volume, optimized pore size, low acid displacement and low electrical resistance. It must also support efficient and controlled oxygen transfer. Glass–microfibre separators are presently the preferred material for AGM batteries. In addition to the properties listed for the polymeric type, glass–microfibre separators must not allow any drainage or stratification of the liquid electrolyte, and be able to retain their initial thickness after filling and during the battery life in order to sustain the initial compression in each cell. The Amersorb separator is well adapted to both technologies, for example: (i) the ribbed and corrugated patterns provide improved porosity (pore volume and pore-size distribution); (ii) the flat membrane is not only able to wick and retain the acid, but has also optimal compression properties (low compressibility and excellent springiness).

Aging mechanisms and service life of lead–acid batteries

Abstract In lead–acid batteries, major aging processes, leading to gradual loss of performance, and eventually to the end of service life, are: • Anodic corrosion (of grids, plate-lugs, straps or posts). • Positive active mass degradation and loss of adherence to the grid (shedding, sludging). • Irreversible formation of lead sulfate in the active mass (crystallization, sulfation). • Short-circuits. • Loss of water. Aging mechanisms are often inter-dependent. For example, corrosion of the grids will lead to increased resistance to current flow, which will in turn impede proper charge of certain parts of the active mass, resulting in sulfation. Active mass degradation may lead to short-circuits. Sulfation may be the result of a loss of water, and so forth. The rates of the different aging processes strongly depend on the type of use (or misuse) of the battery. Over-charge will lead to accelerated corrosion and also to accelerated loss of water. With increasing depth-of-discharge during cycling, positive active mass degradation is accelerated. Some aging mechanisms are occurring only upon misuse. Short-circuits across the separators, due to the formation of metallic lead dendrites, for example, are usually formed only after (excessively) deep discharge. Stationary batteries, operated under float-charge conditions, will age typically by corrosion of the positive grids. On the other hand, service life of batteries subject to cycling regimes, will typically age by degradation of the structure of the positive active mass. Starter batteries are usually aging by grid corrosion, for instance in normal passenger car use. However, starter batteries of city buses, making frequent stops, may age (prematurely) by positive active mass degradation, because the batteries are subject to numerous shallow discharge cycles. Valve-regulated batteries often fail as a result of negative active mass sulfation, or water loss. For each battery design, and type of use, there is usually a characteristic, dominant aging mechanism, determining the achievable service life. Temperature has a strong influence on aging. Grid corrosion rates, and rates of water loss due to evaporation or hydrogen evolution at the negative plates (self-discharge), increase with increasing temperature. On the other hand, a (moderate) temperature increase may improve service life in applications involving severe cycling. Aging also depends on acid concentration (and concentration variations, for instance due to acid stratification). In general, very low acid concentrations, as prevailing in the discharged state, are harmful to the grids. On the other hand, at very high acid concentrations, service life also decreases, in particular due to higher rates of self-discharge, due to gas evolution, and increased danger of sulfation of the active material.

A novel cureless paste for positive plates in valve-regulated batteries

Abstract A new manufacturing technique for positive plates for valve-regulated lead–acid batteries has been developed. This involves a novel paste-preparation method which employs hydrogen peroxide to replace the traditionally used sulfuric acid. After pasting, the plates can be assembled into groups and placed directly into a battery case. Formation can then be performed without the plates undergoing the conventional curing process. Such a non-curing process could reduce production time and costs. More importantly, the resulting plates provide good flexibility which is particularly suitable for spirally-wound battery designs.

Silver–silver sulfate reference electrodes for use in lead-acid batteries

Electrochemical properties of silver–silver sulfate reference electrodes for lead-acid batteries are described, and the following possible applications discussed:•Determination of individual capacities of positive and negative plates.•Monitoring individual electrode behavior during deep discharge and cell reversal.•Optimization charge or discharge parameters, by controlling the current such that pre-determined limits of positive or negative half-cell potential are respected.•Observation of acid concentration differences, for example due to acid stratification, by measuring diffusion potentials (concentration-cell voltages).•Detection of defective cells, and defective plate sets, in a string of cells, at the end of their service life.Silver–silver sulfate reference electrodes, permanently installed in lead-acid cells, may be a means to improve battery management, and therewith to improve reliability and service life. In vented batteries, reference electrodes may be used to limit positive plate polarization during charge, or float-charge. Limiting the positive half-cell potential to an upper, pre-set value would permit to keep anodic corrosion as low as possible. During cycling, discharge could be terminated when the half-cell potential of the positive electrode has dropped to a pre-set limit. This would prevent excessive discharge of the positive electrodes, which could result in an improvement of cycle life. In valve-regulated batteries, reference electrodes may be used to adjust float-charge conditions such as to assure sufficient cathodic polarization of the negative electrodes, in order to avoid sulfation. The use of such reference electrodes could be beneficial particularly in multi-cell batteries, with overall voltages above 12V, operated in a partial-state-of-charge.

Manufacturing and operational issues with lead-acid batteries

An expert panel replies to questions on lead-acid technology and performance asked by delegates to the Ninth Asian Battery Conference. The subjects are as follows. Grid alloys: effects of calcium and tin levels on microstructure, corrosion, mechanical and electrochemical properties; effect of alloy-fabrication process on mechanical strength and corrosion resistance; low dross-make during casting of lead–calcium–tin alloys; future of book-mould casting; effect of increasing levels of silver; stability of continuously processed grids at high temperature. Negative-plate expanders: function of lignosulfonates and barium sulfate; benefits of pre-blended expanders; optimum expander formulations. Valve-regulated batteries: effect of oxygen cycle; optimum methods for float charging; charging and deep-cycle lifetimes; reliability testing.

Improved oxides for production of lead/acid battery plates

For many years, the plates of lead/acid batteries have been produced from leady oxide, a mixture of finely divided lead (`free-lead') and lead monoxide. Although this material is generally satisfactory, it suffers from the disadvantages that it is variable in composition and requires complicated and lengthy processing after pasting to remove the residual free-lead. Plates made from leady oxide also require cycling before they achieve their full performance, and this can result in either depressed initial capacity or additional processing cost. There is a growing trend towards the use of pure lead monoxide (β-PbO) for the production of positive plates. This material is particularly valuable in valve-regulated batteries where cell-to-cell uniformity is essential for proper control of battery performance. It also reduces processing cost since it does not require time-consuming curing to remove free-lead. Red lead (Pb3O4) is also being more widely used in industrial batteries since it reduces formation time, and improves initial and high-rate performance. The methods of production of leady oxide, β-PbO and red lead are briefly reviewed and the characteristics of battery-grade materials are described. Particular emphasis is placed on optimum particle-size distribution, and how this can affect the battery performance. The benefits in processing and performance are described together with information on how pure litharge and red lead are used in battery plates.

Innovative valve-regulated battery designs rekindle excitement inlead/acid battery technology

Recent innovative approaches to the extension of valve-regulated lead/acid (VRLA) technology have led to thedevelopment of several unique products that possess performance attributes not previously achieved in lead/acid technologies, namely: (i)starting, lighting, ignition (SLI) VRLA batteries; (ii) StackPack ™ foil batteries, and (iii) spiral-wound Thin Metal Film (TMF ™) batteries.TheVRLA automotive product has been demonstrated to be capable of improving on the durability of conventional flooded designs in extreme high-temperature climate and extreme drive-cycle operating conditions. In uninterruptible power supply (UPS) applications, the StackPack ™ battery, at a 15-min discharge rate has delivered 23.3 Wh kg −1 and 1090 Wh 1 −1 as compared with 16.0 Wh kg −1 and 595 Wh 1 −1 for traditional designs. TMF ™ prototypes have exhibited power capability of an order of magnitude higher than conventional VRLA designs and have been utilized successfully in a vehicle for seven months and over 31 000 km (19 200 miles).

Rapid partial charging of lead/acid batteries

Rapid partial-charge cycling tests, in which the battery received only 5 or 15 min of high-current charge in each cycle, were carried out for a number of commercial lead/acid batteries. It was found that valve-regulated batteries retained their capacity well, and their full discharge capacity was usually recovered in an extended recharge following five to ten rapid partial-charge cycles. Flooded batteries, tested under stationary conditions, did not perform as well as the valve-regulated batteries, which may have been caused by electrolyte stratification. The experimental data indicated that rapid charging was beneficial to the cycle life of a battery. Heat analysis indicated that the ohmic heat was the major contributor to the total heat generated in the rapid partial-charging process.

Lead/acid battery technology

Following the schedule of previous Asian Battery Conferences, the Proceedings closed with an expert panel of battery scientists and technologists who answered questions put by the assembled delegates. The subjects under consideration were as follows. Grid alloys: grain structure of lead-calcium and lead-calcium-tin alloys; dross problems; control of calcium content; cast-on-strap; terminal-post attack; porosity/acid-wicking problems; effect of silver; lead-cadmium alloys. Leady oxide: α-PbO:β-PbO ratio; influence on plate-processing and battery performance. Paste-mixing and curing: influence of amorphous material. Plate formation: black/powdery plates; effect of acid concentration; charge level. Valve-regulated batteries: mass balances; grid thickness; shelf life. Battery charging: overcharge effects; fast charging; temperature effects; string configurations; sodium sulfate additive.

Review of factors that affect the deep cycling performance of valve-regulated lead/acid batteries

The effects of compression, positive-grid growth, electrolyte stratification and uniformity across a series string of cells during deep-cycling service of valve-regulated lead/acid batteries are considered. Without adequate control, each of these will cause premature failure. Although substantial improvements in cycleability have been made in recent years, more understanding and optimization of these factors is necessary for further improvements. In particular, little is known about the changes in the properties of separators during service that effect compressive forces on the positive plate, and more knowledge is required on the influence of grid growth and on the influence of cell design on electrolyte stratification in valve-regulated batteries. In addition, the paper considers the progressive variation between cells in long series strings, which is a major cause of early failure of these designs.

Wrought lead-calcium-tin alloys for tubular lead/acid battery grids

Lead/acid batteries with tubular grids for the positive electrodes give flatter discharge curves and higher cycle life than batteries using flat plates. Most tubular grids for motive-power batteries contain 9–11 wt.% antimony. Recently, alloys with 1–6 wt.% antimony have been used for reduced maintenance batteries. Sealed, valve-regulated batteries with tubular positive grids for motive power, telecommunications, and UPS service are produced from cast lead-calcium-tin alloys. While these alloys permit the construction of such batteries, cast PbCaSn alloys are significantly inferior to cast PbSb alloys in mechanical properties. Wrought PbCaSn alloys, when used for tubular grids, permit the application of maintenance-free alloys with mechanical properties comparable with, or higher than, those of high-antimony alloys. Wrought materials increase life due to the absence of casting defects. Wrought lead-calcium alloys also offer a dramatic improvement in creep and corrosion resistance compared with conventional cast, tubular, PbCaSn alloys, as well as superior conductivity to cast PbSb. Wrought PbCaSn alloys permit the production of tubular grids at high speed in shapes and forms that are difficult to produce from cast materials. These grid shapes can lead to higher performance, higher discharge-rate, tubular plates. This paper discusses the mechanical properties, grain structure, and corrosion behaviour of cast and wrought PbCaSn and PbSb alloys for tubular grids. It also suggests manufacturing techniques for high performance, wrought, tubular plates.

Eight years of experience with valve-regulated batteries for automotive use

In 1985, Matsushita developed a valve-regulated lead/acid (VRLA) battery with an expanded grid for automotive use. Since 1989, these batteries have been adopted as original equipment for cars. To take full advantage of their benefits, the batteries are installed away from the engine compartment, for example, in the boot of the car. Despite a steady market for automotive VRLA batteries, there are still a few problems that accompany their use. These must be solved in order to enhance reliability and improve customer satisfaction. The major areas of concern are life at high temperature, and recovery after over-discharge and long standing. Work in these areas is reported here.

Failure modes of valve-regulated lead/acid batteries in different applications

Failure modes of valve-regulated lead/acid batteries are discussed and methods are suggested to overcome the problems. Many of the failures are associated with the positive plate, i.e., grid corrosion, and softening or sulfation of the active mass. Other failures include drying out, thermal runaway, and corrosion at the negative grid/top-bar connection. This work does not give a complete list of all failures that can occur, but it shows a summary of experiences gained from the practical use of valve-regulated batteries in different applications.

Battery performance enhancement with additions of bismuth

Automotive and valve-regulated batteries (VRBs) of typical commercial design have been constructed using positive and negative plates produced from leady oxide that is doped with 0.06 wt.% bismuth. The doping is performed by adding bismuth (III) oxide powder during the paste-mixing stage. Both battery designs have been subjected to endurance tests (automotive batteries: JIS cycle-life test; VRBs: repetitive 3-h discharge) in parallel with batteries that are similar in all respects but do not contain bismuth. A strategy and necessary hardware have been developed to measure the gassing properties of the VRBs during both charge and discharge. The procedure involves monitoring the internal pressure with high-precision pressure transducers. For automotive batteries, doping with bismuth produces no significant differences in JIS cycle life. By contrast, both the endurance and the capacity of VRBs are found to be enhanced by the presence of bismuth. Furthermore, bismuth reduces the build-up in gas pressure (mainly oxygen) in VRBs during constant-current charging. These results suggest that future specifications for leady oxide should include a minimum — rather than a maximum — bismuth content. In this respect, although studies performed to date show that significant advantages can be achieved with 0.06 wt.% bismuth in the active material, the optimum bismuth level has yet to be established.

Effects of fast charging on hybrid lead/acid battery temperature

The effects of very fast charging on two types of deep-cycling hybrid lead/acid batteries were determined using a MINITCHARGER TM to control the charging current. One of the hybrid batteries was flooded and contained Pb-4.7wt.%Sb positive grids, the other was a valve-regulated battery with Pb-1.5wt.%Sb-0.3wt.%Sn positive grids. Results are presented and discussed in relation to these battery types, but many of the conclusions are more generally applicable. It was found that both 5-min/50%-recharge and 15-min/80%-recharge rates could be achieved, in the case of the flooded battery, with a quite acceptable temperature increase. Following an 80% depth-of-discharge, the dominant source of heat was ohmic during the first 40% of the charge returned at very high rates. The temperatures were distributed non-uniformly within the battery. After this, non-ohmic polarization became progressively more important. For the hybrid recombination battery, the oxygen cycle is a substantial source of heat during the latter stages of the charge, particularly in comparison with previous non-antimonial batteries that have been investigated.

Minor elements in lead materials used for lead/acid batteries 1. Hydrogen- and oxygen-gassing characteristics

Minor elements are commonly present in the raw lead materials that are used to manufacture lead/acid batteries. Although certain of these elements are known to exert, individually, a marked influence on the gassing characteristics during charging, less is understood of their collective effect. As the first stage in an experimental campaign to obtain such information, the evolution of hydrogen and oxygen has been examined on both bare (grid) and doped/pasted electrodes. With the latter electrodes, different dopants (Ag, Bi, Cd, Cr, Ni, Sb, Se, Sn, Zn) have been introduced at a level of 0.1 wt.%. The subsequent gassing rates have been determined by application of either a potential-scan or a potential-step procedure. The latter has been conducted together with gas collection. The hydrogen-evolution characteristics on bare electrodes are dependent on the chosen lead alloy. The rate increases in the order: Pb<Pb−0.09Ca<Pb−0.07Bi<Pb−0.09Ca−0.4Sn< Pb−0.09Ca−0.3Sn<Pb−0.09Ca−0.7Sn<Pb−2.2Sb<Pb−1.7Sb<Pb−5.7Sb. By comparison, the oxygen-gassing rate does not exhibit such a clear relationship with alloy composition. In general, oxygen evolution above 1.7 V increases in the order: Pb< Pb−0.09Ca−0.3Sn<Pb−2.2Sb<Pb−0.09Ca≈Pb−5.7Sb<Pb−0.09Ca−Ca−0.7Sn<Pb−0.07Bi<Pb− 0.09Ca−0.4Sn<Pb−1.7Sb. The Pb−0.09Ca−0.4Sn and Pb−1.7Sb electrodes exhibit abnormal hydrogen- and oxygen-evolution rates. This is probably due to the fact that these two alloys were made by a different manufacturer. The degree of hydrogen evolution on untreated and doped negative-material (pasted) electrodes can be classified in terms of a low, a medium or a high rate. For elements that give a low rate, gassing increases in the order: Ag<Zn<untreated<Cd<Bi≈Cr. The Sn- and Se-doped electrodes exhibit a medium evolution rate. Finaly, Sb- and Ni-doped electrodes display the highest rate of hydrogen evolution; of these, nickel exerts the stronger effect. All the dopants enhance oxygen evolution. The gassing rate increases in the order: untreated ≈Cd<Se<Sn<Bi≈Cr< Ni≈Zn<Sb<Ag. The hydrogen- and oxygen-gassing behaviour of the doped electrodes is discussed in terms of the operating characteristics of valve-regulated batteries.

Glass-fibre separators for valve-regulated batteries

Recombining battery mat separators for valve-regulated lead/acid batteries must: (i) prevent shedding of active material from positive plates; (ii) retain the whole of the electrolyte for flexibility of battery positioning; (iii) have fine pores to eliminate the need for maintenance. The relationship between these requirements and the diameter of glass microfibres are discussed with respect to the design of a new cost-effective recombinant battery mat separator, brand name: M Sepa. M Sepa products have been introduced to the market to meet the special requirements of valve-regulated lead/acid batteries.

Ten minutes-rechargeable, valve-regulated, lead/acid battery after deep discharge and stand

Ten minutes-rechargeable, valve-regulated batteries for headphone steroes were released on to the market in 1990. These were very thin batteries, i.e., the PF2V0.28 (2 V, 0.28 Ah) unit was 6 mm thick and the PF2V0.55 (2 V, 0.55 Ah) unit was 8.5 mm thick. The systems were well accepted for normal operation, but the batteries could not be recharged rapidly after overdischarge and long stand. Therefore, batteries have been developed that can be recharged quickly, even after being subjected to the most severe operating conditions experienced with portable electronic appliances. In order to simulate the operational problem, the batteries were evaluated in an overdischarge condition that consisted of one-week discharge through a resistor and long-term standing at open-circuit at high temperature. The batteries have now been improved to accept charge current in a few minutes, even under the most severe of overdischarge conditions. The improved batteries also display good performance with respect to storage, overcharge and cycle life.