IT8149424A1 - LEAD-ACID BATTERY FOR OCCASIONAL APPLICATIONS - Google Patents

Description

DOCUMENTATION

BOUND

SIB 82895

? ? M-ATJT-3007

DESCRIPTION of the industrial invention entitled: "Lead-acid battery for occasional applications" by the American company GOULD INC.

based in HOLDING MEABCWS, Illinois - U.S.A.

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.SUMMARY

A sealed, maintenance-free lead-acid battery is described in which the electrolyte is absorbed and immobilized in a porous separator. The battery delivers superior peak energy at relatively high discharge rates for the short periods of time encountered in various intermittent applications, has satisfactory performance characteristics, operates effectively at low internal pressures, and can utilize conventionally used thin-walled plastic containers.

DESCRIPTION

The present invention relates to lead-acid batteries and, more specifically, to sealed, maintenance-free lead-acid batteries suitable for use in occasional applications such as automobile starting, lighting and ignition.

For many applications, the focus of lead-acid battery technology is on providing maintenance-free batteries, that is, batteries that can be operated without water entering the electrolyte during their intended life. The life of such batteries is limited by water loss due to gassing, and therefore, excess electrolyte must be used to compensate for the resulting water loss in order to provide a satisfactory life.

Typically, water loss in such batteries has been minimized by using grid alloys with high hydrogen overpotential. Rigid, self-supporting, and sometimes structurally reinforced grids made from a variety of antimony-free or low-antimony lead alloys may be employed. Examples of grid alloy systems used include calcium-lead, calcium-tin-lead, cadmium-antimony-lead, seleniumantimony-tin-lead with various optional alloying ingredients such as silver and arsenic, as well as combinations of these alloys.

Furthermore, lead-acid batteries are known in which the electrolyte is immobilized in the form of a gel. Such batteries can provide not only maintenance-free but also spill-free characteristics, that is, the battery can be used in any position without loss of electrolyte. However, cracks that develop in the gel during charging, although essential for oxygen transport, give rise to conditions that can negatively affect the desired performance. Furthermore, such batteries invariably have a higher internal resistance and, therefore, cannot be used in applications where high-rate discharge capacity is a requirement, such as, for example, a car starter, lighting, and ignition battery.

To provide a sealed design while avoiding potential problems with gel-like electrolytes, sealed systems have been used in which the electrolyte is immobilized and absorbed in special separators. The separators are not completely saturated, and gases evolved during overcharging or at other times can diffuse rapidly from one electrode to another. Thus, under the right conditions, oxygen evolved at the positive electrode can diffuse to the negative electrode where it is rapidly reacted with active lead. Effectively, this reaction partially discharges the negative electrode, preventing the negative electrode from reaching its fully charged state, thus minimizing hydrogen evolution. This sequence gives rise to what has been called an "oxygen cycle." While the oxygen recombination rate is greater than the oxygen rate produced at the positive electrode, water loss and pressure development must be minimal.

Currently, sealed lead acid systems of this type have been commercially available only in small ampere-hour capacity sizes. Their use has therefore generally been confined to backup applications such as emergency lighting, alarm systems, and portable appliances with limited cycle life such as televisions, lanterns, and garden tools.

U.S. Patent 5,962,861 is an example of a cell configuration that recombines oxygen using relatively high internal pressures. It is believed that the cell increases the recombination rate by operating under increased pressure. For this reason, a blowdown valve is used that must be calibrated to blowdown at as high a pressure as possible. A Bunsen burner blowdown valve capable of retaining at least 15 lb (6.8 kg) of internal pressure is described. This type of battery may be used in intermittent applications and in deep-cycle applications where limited runtime is acceptable.

A battery having a prismatic container is described in Progress in Batteries and Solar Cells, volume 2, 1979, pp. 16-18, and is a type that apparently operates at relatively low internal pressures, the type being used primarily for occasional applications.

Another type of battery is reported in the International Symposium on Batteries, February 21-25, 1958. As described, in general terms, batteries are produced by forming a stack of rather soft, flat plates and separators, the stack, after compression, being inserted into a suitable container. In such a stack or block of plates and separators, the active material of the plates is completely supported by the separators. The block, after compression, must have a sufficiently high porosity to enable it to absorb and retain all the electrolyte necessary for efficient and economical operation. The separators are made of diatomaceous earth. Batteries suitable for automobile starting, lighting, and ignition applications are described, the advantages described being resistance to vibration, lack of spillage, and increased performance at high speeds at normal and low temperatures.

Although the report specifies that widespread market introduction has been limited by commercial considerations rather than performance or quality, it is believed that the performance characteristics do not meet current requirements for such applications. Furthermore, the battery type described has not achieved widespread use and has not enjoyed significant commercial success.

Furthermore, it has been suggested that a sealed lead-acid system can be scaled up to capacities of many ampere-hours more than those currently used commercially (Engineering, October, 1975* The Age of the sealed Battery, pp. 1020 - 1022).

It has, in fact, been argued that the characteristics of the sealed battery system should be particularly advantageous for an SLI application in automobiles (i.e. starting, lighting and ignition).

In addition, there are a number of applications that can be called "floating pulse" (i.e., a system capable of delivering relatively high peak energy at fairly high discharge rates for short periods of time) where the characteristics attributed to a sealed system would always make such a system desirable. Motorcycle batteries, outboard motor starters, and computer backups are examples that fall into this category. Applications requiring a relatively pure form of direct current also have similar needs. Batteries for such applications require capacities of at least 15 ampere-hours, or even 25 ampere-hours and substantially higher.

Yet, for whatever reason, sealed systems of such capacitive sizes have not become commercially available at all. This may well be simply because the necessary performance characteristics have not been achieved. It may therefore be argued that it has proven difficult to optimally achieve the capacity and durability required for such applications. Furthermore, it may be argued that a stronger, more rigid battery case is necessary to withstand the high internal pressures thought necessary to provide satisfactory oxygen recombination efficiency, and that this is particularly critical in batteries of relatively large capacitive sizes. The use of such stronger battery cases would naturally result in increased battery weight. This would be particularly detrimental in the automotive field since the present trend is to provide battery systems in which weight can be minimized as much as possible. The primary object of the present invention is therefore to provide a sealed, maintenance-free lead-acid battery that is suitable for use in automotive applications. designed to provide satisfactory performance characteristics for use in intermittent pulse applications.

Another and more specific object of the present invention is to provide a sealed lead acid battery capable of performance that equals or exceeds the characteristics required of batteries for automotive starting, lighting and ignition applications.

A further aim is to provide a sealed lead-acid battery with improved volumetric and gravimetric energy density.

A still further object of the present invention is to provide a sealed lead-acid battery that can be formed in sizes ranging from small to extremely high capacities.

Yet another purpose is found in the provision of a sealed lead-acid battery capable of being produced on standard equipment used for the production of conventional intermittent pulse batteries.

A still further object of the present invention is to provide a sealed lead-acid battery suitable for using the conventional thin-walled plastic containers often employed for intermittent pulse batteries.

Another object of the present invention is to provide a sealed lead-acid battery capable of operating at extremely low internal pressure while providing maintenance-free characteristics for extended life.

Further objects and advantages of the present invention will be apparent from the following description and drawings, in which:

Figure 1 is a perspective view of a battery formed in accordance with the present invention, with parts broken away to show the internal configuration;

Figure 2 is a side elevational view, in section, exploded, and illustrates the arrangement of the plates and separators of the battery of the present invention;

Figure 3 is a sectional view taken generally along the line 3-3 of Figure 1, and also showing the internal configuration of the battery;

Figure 4 is a voltage versus time plot showing the improved cold cranking performance of a sealed lead acid battery made in accordance with the present invention compared to a commercially available maintenance-free battery; and

Figure 5 is a diagram illustrating the performance of a sealed lead-acid battery of the present invention in an industrial cycle life test.

While the present invention is susceptible of various modifications and alternative structural forms, they will be shown in the drawings and described herein.

The preferred embodiments are described in detail. It should be understood, however, that it is not intended to limit the invention to the specific structural forms described. Rather, it is intended to encompass all modifications and alternative structural forms falling within the spirit and scope of the present invention. Therefore, while the present invention will be primarily described in connection with an automobile starting, lighting, and ignition application, it should be noted that the present invention can be utilized for any other intermittent pulse application. Furthermore, the invention is obviously equally applicable to a battery as to a single cell. Furthermore, while the present invention is described with reference to batteries of larger capacitive sizes, it should be noted that it is equally useful with small capacitive sizes. Likewise, while all the advantages of the present invention may not be achieved, a more rigid package than that required by the internal pressures developed in service may be employed, if desired.

In general, the present invention is based on the discovery that a sealed, maintenance-free lead-acid battery suitable for various intermittent applications, such as automobile starting, lighting, and ignition, can be provided by storing the electrolyte in highly absorbent separators, operating at extremely low internal pressures that permit the use of conventional thin-walled containers. The battery of the present invention will provide higher peak energy at relatively high discharge rates compared to conventionally used electrolyte-filled batteries, while meeting other required performance characteristics.

Referring now to the drawings, Figures 1 and 2 show the battery 10 according to the present invention. The battery 10 has a case 12, separated into individual cells by internal dividers 1^. In each cell, numerous positive electrodes 16 and negative electrodes 18 are separated by absorbent separators 20.

The necessary electrical connections may be made by any of several methods known in the art. The particular technique employed does not form part of the present invention. As shown, conducting strips 22 connect the electrodes to each other, and the connections between cells are shown in FIG. 3. The terminal cell strips 22 are connected to external terminals 24 by conventional means. As seen in FIGS. 1 and 3, exhaust venting is provided through manifolds 26 via automatic low-pressure exhaust valves, such as Bunsen burners 38. Although exhaust through one manifold is illustrated, individual cells could each be provided with an exhaust valve if desired. On the other hand, a single manifold could be used for the six cells shown, or more than two manifolds could be used.

The electrodes 16 and 13 and the separators 20 must fit precisely in the cells, that is, the electrodes and separators must remain in an assembled condition when the container is inverted. The electrodes may therefore be sized up to approximately the internal dimensions of the cells. To eliminate the possibility of short circuits, however, it is desirable to size the separators used so that the edges extend slightly beyond all edges of the electrodes, as shown in Figure 2. One means of achieving this at the bottom of the electrodes is to fold the separators around the electrode in a U-shaped fold as shown in Figure 2.

This clearly demonstrates the effective use of the container's interior. However, if desired, spacers, such as shims, could be used if the cells used are oversized for any reason.

Considering the present invention in more detail, the grids used as positive and negative grids may be made of any of several known grid alloys used for conventional maintenance-free batteries. As an example, it is therefore convenient to use a calcium-tin alloy in which the calcium content is from about 0.06 to 0.20 percent and the tin is in the range of 0.1 to 80.5 percent (preferably 0.2-0.3 percent), both percentages being based on the total weight of the alloy. The alloys used must be capable of providing self-supporting grids. The grids may be formed by any of the known techniques, such as direct casting or expanded metal.

There are several difficulties associated with providing a satisfactory internal structure for a sealed system. One such difficulty arises from the need to provide sufficient system absorptive capacity to ensure that sufficient electrolyte will be retained to provide the desired capacity. This can be achieved to some extent by using thicker separators than would be necessary for a filled system. However, this will not generally provide a complete answer as the internal resistance will increase as the plate spacing increases. There is therefore a practical limit to the alternation of performance characteristics that will occur. Some benefits may be obtained by using an electrolyte with a somewhat higher specific gravity than that of conventional filled systems; but even here there is a practical upper limit due to factors such as the occurrence of decreased conductivity. Another possibility is, of course,

to reduce the density of the active material pastes. Since mold formation on the negative active material and flaking of the positive active material must be avoided, or at least substantially minimized, reducing the density of the active paste material should be conceptually possible by precisely matching the electrodes in the absorbent separators used. However, even here, there are limitations due to the processing problems that arise with such reduced densities when conventional kneading machines are used, as in an automotive application.

Another difficulty arises from the shrinkage of the negative active material that occurs in batteries exposed to fluctuating conditions, as is well known. This can be a major failure mode, significantly reducing the useful life of an Ef battery. For this reason, battery manufacturers have conventionally used various expanders to maintain the desired porosity and surface area of the active material on the negative plates. This difficulty has been found to be particularly severe in sealed systems for occasional applications.

Accordingly, to achieve the full advantages of the present invention, it is preferred to utilize active material pastes that have increased absorbency and that can be readily processed with conventional equipment and provide a system with satisfactory durability and performance characteristics. To this end, the paste densities of the positive active materials are lower than the paste densities used for conventional electrolyte-filled lead-acid batteries employing long-lasting lead oxide materials, such as those obtained from a Barton crucible. It has thus been found desirable to utilize plate densities in the range of about 2.9 to 4.1 g/cm5 for the unformed, cured positive active material. Over the densities range of 3.0 to 7.0 g/cm5,

at 4.2 g/cm" for the formed and cured positive active material is acceptable.

To provide the desired electrolyte holding properties, it is preferred to incorporate

An electrolyte-retaining agent such as colloidal silica in the paste. An incorporation of colloidal silica in an amount of about 0.05 to 1.0%, based on the weight of the unformed positive active material, has been found suitable. Other electrolyte-retaining materials are known that can similarly be used as substitutes, in whole or in part, for silica. Desirably, the electrolyte-retaining agent should also function as a bulking agent, i.e., increase the consistency of the wet paste to improve handling. Colloidal silica fulfills this function.

According to a further preferred aspect of the present invention, the characteristics of the negative active material are improved not only to increase absorbency but also to compensate for shallow cycling effects to provide satisfactory durability and performance characteristics. To this end, the negative active paste preferably includes a combination of conventionally used paste additives above the levels typically used.

As the first component, it is preferred to use a conventional organic expander at a level of about 0.5 to about 1.4%, based on the weight of the dry unformed pulp. Various lignosulfonates, such as sodium lignosulfonate, are known and suitable. Furthermore, it is preferred to use an additive that serves to minimize the physical consolidation of the lead sulfate crystals formed during the cycle into larger crystals and ultimately into an essentially solid layer with minimal porosity that would result in battery failure. Staple cellulose serves this purpose and can be used at a level of about 0.3 to about 1.0% by weight.

It is believed that the maximum benefits will be achieved by using only one type of expander when the functions are considered different. In some way, the organic expander influences the morphology of the lead sulfate structure in a way that retards the loss of porosity. The additive that retards consolidation is believed to effectively serve as a means of physical distancing.

Preferably, the pulp additives used should also function as bulking agents. Both staple cellulose and sodium lignosulfonate perform this function.

A mixture of 0.75% sodium lignosulfonate and 0.6% staple cellulose is preferred, both percentages being based on the weight of the dry unformed pulp. The use of such a mixture appears to provide the desired cycle life.

The density of hardened, but unformed, paste for the negative active material should desirably be in the range of about 3.5 to 4.4 g/cm3. A density range of about 3.2 to 4.1 g/cm3 for the hardened and formed negative active material is satisfactory. Although the negative paste additives described above serve to retard the loss of porosity and thus maintain absorbency, it is also preferred to incorporate an electrolyte-retaining agent such as colloidal silica into the negative paste. Amounts in the range of about 0.05 to 10%, based on the weight of the dry unformed paste, are suitable.

Typically, it has been found essential, as set forth in U.S. Pat. No. 5,862,861, to utilize in a sealed system an excess of negative active material relative to positive active material in order to achieve the required oxygen cycling. In accordance with one aspect of the present invention, it has been found that a satisfactory oxygen cycling can be achieved even if the amount of negative active material is less than that of positive active material. It is accordingly preferred to utilize a weight ratio of negative active material to positive active material of from about 0.75 to about 0.92 or the like. The result is not only reduced weight but also reduced expense without detrimental effects on performance.

The separator material 20 must be stable in the sulfuric acid electrolyte employed, resistant to oxidation by FbO2, and not release materials into the electrolyte that could adversely affect battery performance. Furthermore, the material should be highly porous, such as at least 70-75%? preferably up to 90% or similar, and should be sufficiently compressible to conform at least substantially to the varying shapes of the electrodes during assembly and service. Furthermore, the average pore diameter should be small enough to prevent the propagation of dendrites from the negative plate and shield the active material from the positive plate. The average pore diameter, however, should be large enough to be easily wetted by the electrolyte and not so small as to result in an unduly high internal impedance. The separator material must also be capable of retaining the electrolyte over the desired height of the separator.

And last but not least, the separator material should preferably provide in service a substantially uniform void volume throughout the separator.* The separator thus preferably provides a void volume sufficient to accommodate the oxygen transport rate required for the desired internal pressure of the battery. It is believed that the void volume is achieved by some of the pores having their walls covered with a film of electrolyte while the central portion of the hole is free of electrolyte. Satisfactory oxygen recombination efficiency for some applications can also be achieved when the separator is completely wetted with electrolyte. Suitability in this respect can be determined by weight (water) loss measurements taken during cycling. If the material is suitable, excessively high water loss should not occur. The thickness of the separator will generally be determined by the capacity of the battery and the expected cooperative rate for the particular application. From this point of view, the separator thickness used does not have to practically refer to those found suitable for other types of lead-acid batteries used for the particular end-use application.

It has been found suitable to use a borosilicate glass material consisting of glass microfibers and cut strands. Materials of this type are commercially available and have previously been used for sealed lead-acid batteries. One such material (C.H. Dexter, Division, The Dexter Corporation, Windsor Locks, Connecticut, "Grade 225B"), which has been found satisfactory, exhibits the following characteristic properties: nominal thickness of 300 ?, air permeability (ASTKD

2

737-75) of 15.1 liters/min/100 cm at 12.7 mm of water ? P (Prazier Permeometer), an average pore size of 16.6 ? and a porosity (by mercury infiltration) of 1.2 m /g. It is preferred to use at least one layer of borosilicate glass material adjacent to the electrodes. Additional layers of other materials may be used, for example, as reinforcement to improve handling during processing. As an illustrative example, commercially available non-woven sheets of polyethylene, polypropylene and polyester can be advantageously used. These materials possess the desired electrolyte retention and also reduce costs as well as improve mechanical strength. Such a laminar separator system can be be used to provide the necessary mechanical strength for relatively easy introduction of pocket-type and U-bent separators in the conventionally employed high-power SLI battery assembly techniques.

For a given application, the required fully charged specific gravity of the electrolyte can be easily calculated. In particular, fully charged specific gravities in the range of 1.255-1.320 may be satisfactory; the range of 1.285-1.220 is preferred. Particular applications may require the use of slightly higher or lower acid specific gravities.

The formation of the kneaded electrodes can be performed using known techniques. Thus, before assembly in the container, the electrodes can be provided by conventional vacuum forming. When this technique is used, the formed electrodes should be dried to remove residual electrolyte.

Conveniently, the unformed electrodes and

The separators are placed in the container, the necessary electrical connections are made, the lid is sealed to the container, the necessary electrolyte is added through the opening in the lid for the vent valve, and the valve is then placed in the service position. The formation is then carried out using conditions suitable for conventional formation in a single

lead-acid battery phase. However, it may be useful to use slightly less severe forming finishing conditions than conventionally used. It may also be appropriate to initially cool the forming electrolyte to a certain degree.

It should also be noted that when the formation is used in situ, the onset of formation should occur within 1/2 to 1 hour or so after the electrolyte is introduced. Longer delays may result in conditions that will ultimately create internal short circuits.

The amount of electrolyte used should preferably ensure that the battery's absorbent materials are completely saturated, i.e., the battery should be in an electrolyte-starved condition. While the battery is self-regulating in service, a fully saturated condition could result in undesirable gas formation during the initial stages of charging during cycling. Furthermore, the operation will reach an equilibrium state in which an efficient oxygen recombination cycle is achieved. The rather higher gas formation that occurs during the initial stages can be substantially eliminated by determining the specific void volume required for efficient oxygen recombination. However, it has been found advisable to add sufficient electrolyte to saturate the system's absorbent capacity to a level of approximately 90%.

Care must be taken to avoid free electrolyte in the system. Large amounts of free electrolyte (i.e., not immobilized in the electrolyte and separators) can have adverse effects on performance. In accordance with one aspect of the present invention, venting is provided by means of a self-sealing vent valve that breaks the seal at extremely low internal pressures. For this purpose, a valve is used that breaks the seal at internal pressures of approximately 0.035 kg/cm

2

up to approximately 0.21 kg/cm . In fact it is preferable to use internal operating pressures not exceeding

. 2

about 0.07 or perhaps 0.14 kg/cm so that the thin-walled plastic containers commonly used can be used. The following examples further illustrate the present invention but are not a limitation thereof. Unless otherwise specified, all percentages are by weight.

EXAMPLE 1

This example illustrates the performance of the sealed lead-acid battery of the present invention compared to a conventional maintenance-free flooded battery.

Batteries with a nominal capacity of approximately 71 ampere-hours were assembled in ebonite containers. Each battery contained 17 plates per cell. The alloys used for the grids of both batteries were calcium-tin-lead with a nominal composition of 0.09% calcium, 0.3% tin, and the remainder lead. The densities were 0.05 to 0.15. of the paste used were 4.0 g/cm" for the positive and 4.4 for the negative, both based on the dry weight of the unformed paste. The pastes were treated by exposure to 60°C for about 16 hours in a 100% relative humidity atmosphere, and subsequently by exposure to 60°C in a 0% relative humidity atmosphere for a period of about 48 hours or so. Each electrode of the battery of the present invention was wrapped with a two-layer separator comprising an inner layer of a nominal 0.35 mm borosilicate glass material as described above and an outer layer of 0.33 mm of a point-bonded non-woven polypropylene material folded in a U-shape around the electrode as shown in FIG. 2. A conventional polyvinyl chloride separator having a nominal thickness of 0.94 mm with a backing film of 0.3 mm It was used for the conventional maintenance-free battery.

Other construction details are shown in the table below.

TABLE 1

Battery Parameter Conventional sealed battery Positive grid thickness, mm 1.05 1.05 Negative grid thickness, mm 0.99 0.99 Dry weight of positive paste

per plate, g 110 110 Dry weight of negative paste

per plate, g 101 101 Weight ratio of positive paste/grid 70/40 70/40 Weight ratio of negative paste/grid, g 62.5/38.5 62.5/58.5 Specific gravity of electrolyte 1.285 1.285 Inter-plate spacing, mm 0.56 0.94 Other details of the batteries as a whole are shown in Table 2.

TABLE 2

Battery Parameter Conventional sealed battery Total weight, positive paste, kg 3>35 3.35 Total weight, negative paste, kg 3.37 3.37 Total weight, positive grids, kg 1.92 1.92 Total weight, negative grids, kg 2.08 2.08 Total weight, lead within cell, kg 10.73 10.73 Total weight of electrolyte, kg 2.61 6.94

The plates and separators have been arranged

The necessary electrical connections were made in the containers and the formation acid of specific gravity 1.200 was added and cooled to -17.8°C. A charging rate of 7 amps for 16.5 hours was used, followed by 4 amps for 5 hours and 2 amps for 2 hours. The lids were then placed in place. The sealed battery included a standard Bunsen burner vent that released the seal at 0.035

2

kg/cm . The batteries were then checked and the performance is shown in table 3:

TABLE 3

Battery Test Conventional sealed battery. Cold start at -17.8?C,

voltage after 30 seconds, 550 A 8.05 7.60 Relative electrical resistance,

-17.8?C 9.9 11.2 Reserve capacity, discharge at

25 amps, 78 124 minutes

As can be seen, the sealed battery of the present invention exhibits improved cold cranking performance over the conventional maintenance-free battery. Figure 4 also shows this improved performance over the 60-second discharge to which each battery was subjected, with the curve marked 1 for the sealed system and curve 2 for the conventional maintenance-free battery.

However, as can be seen from Table 3, the reserve capacity of the sealed battery of the present invention was substantially lower than that of the conventional maintenance-free battery. It will be noted that the active material pastes have not been modified as previously described, and the results thus clarify the need for appropriate modification to achieve the full advantages of the present invention.

The sealed battery was subjected to a 12-minute SLI unified cycle, J240 regime, and failed at approximately 4500 cycles, which is substantially lower than the performance typically achieved by commercially available maintenance-free batteries. However, the failure is believed to be due to a design flaw in the special positive grids used.

EXAMPLE 2

This example illustrates the performance that can be achieved by a sealed battery constructed in accordance with the present invention.

A test battery having a nominal ampere-hour capacity of approximately 67 amps was assembled and containing 13 plates per cell. The alloys used had the same composition as set forth in Example 1. The densities of the hardened, unformed paste were approximately 4.4 g/cm^ for the negative active material and approximately 3.9 g/cm^ for the positive active material. The negative paste was made from a formulation that included, in parts, 1200 g of lead-acid litharge, 50 g of a conventional expander mixture, and approximately 0.3% colloidal silica based on the dry, unformed weight of the paste.

The pastes were cured as described in Example 1. The positive plates were wrapped with two layers of the borosilicate material as described previously and the negative plates were wrapped with one layer of that material.

The plates and separators were placed in a thin-walled plastic container conforming to SLI standards used for commercial maintenance-free batteries, modified to significantly reduce the weight of the supports at the bottom of the container. Assembly and formation were performed as generally described in Example 1, with the specific formation regime requiring charging at 7 amps for 18 hours, followed by 4 amps for 6 hours, and 2 amps for 2 hours.

Further construction details are shown in Table 4, having included for comparison the specifications for a conventional maintenance-free battery:

TABLE 4

Battery Parameter Specification Sealed Conventional

Positive grid thickness, mm 1.9 1.62 Negative grid thickness, mm 1.5 1.2 Dry weight of positive plate, g 148 149 Dry weight of negative plate, g 104 106 Weight ratio of positive/negative paste

grid, g 89.8/58.5 87/62 Weight ratio negative paste/

grid, g 63.5/40.2 66/41 Specific gravity of electrolyte 1.290 1.265 Table 5 shows the details of the assembled battery, the specifications for the conventional battery are given in conjunction with table 4

that is, included here:

Battery Parameter Specification Sealed Conventional _ _____ naie Total weight? positive paste, kg 3.23 3.13 Total weight, negative paste, kg 2.6? 2.7? Total weight, positive grids, kg 2.46 2.23 Total weight, negative grids, kg 1.69 1.71 Total weight within cells, kg 10.05 9.85 Total weight of electrolyte, kg approx. approx. 3.13 5.26 Total weight of "battery", kg 14.6 17.14? The sealed battery has been tested and Table 6 shows the results in comparison to the specifications for the conventional battery described here.

TABLE 6

Test Battery Specifi sealed conventional AC Cold start at -17*8?C,

Volts at 30 sec.? Discharged at 500 A 7*84- 7.2 Reserve capacity, 25 A, minutes 91 102 As can be seen from Table 6, the sealed battery of the present invention provides the same improved cold starting performance as shown in Example 1. So while not the same as the conventional battery, the modification to the negative grids along with increased plate spacing has given an improvement in relation

compared to example 1. A further improvement in this respect can be achieved by further modifying the active material pastes, as described above*

The sealed battery was subjected to the J240 endurance test, described in Example 1, and performed approximately 8,000 cycles. During this test regime, the battery was discharged to 500 amperes; the 5-second and 30-second voltages were determined. Figure 5 shows the results, with curve 3 being the 5-second voltages and curve R being the 30-second voltages. Failure occurred as a result of corrosion on the positive grids; this is believed to be a design flaw in those grids.

Significantly, over the duration of the J240 test the sealed battery of the present invention lost only 0.07 kg of water (+.0.05 measurement accuracy) which is considered to be around an order of magnitude less than that expected from a conventional battery.

maintenance-free.

As seen, the battery of the present invention thus provides all the advantages of a sealed system and in particular achieves improved peak power at relatively high speeds for short durations encountered in a wide variety of intermittent applications. In engine starting, ignition and lighting applications, this invention thus provides significantly superior cold starting power. This performance is achieved while maintaining other required performance characteristics. The efficient oxygen recosabination rate even at extremely low internal pressures provides superior maintenance-free product characteristics. The use of low internal pressures similarly permits the use of conventional thin-walled plastic containers, an aspect of great utility in automotive applications where low weight is becoming increasingly important. Indeed, the relatively high energy density per volume that can be achieved may permit the use of even smaller container sizes without sacrificing performance.

1. Maintenance-free lead-acid battery having characteristics suitable for use in non-continuous applications, comprising:

a sealed container divided into numerous internal subdivision cells; numerous positive plates contained within each cell, each of said plates comprising a self-supporting grid and positive active material bonded onto said grid,

numerous negative plates contained in each cell, each of said plates comprising a self-supporting grid and negative active material kneaded onto said grid,

at least one layer of a separator material absorbing and retaining the electrolyte intimately in contact and separation in said positive and negative plates,

sulfuric acid electrolyte absorbed in said plates and separators, said plates and separators being sufficiently porous to retain sufficient electrolyte to provide a capacity of at least about 25 ampere hours, and

said container having at least one normally closed vent valve capable of venting gas from the container to the atmosphere when the pressure within said container is in the range of about

2

0.035 up to 0.2l kg/cm .

2. The battery of claim 1, wherein at least one of the positive and negative grids is made of a calcium-tin-lead alloy.

5. The battery of claim 1, wherein the positive active material has a density of from about 5.0 to 4.2 g/cm².

4. The battery of claim 1, wherein the positive active material contains about 0.05 to 1?(?? by weight of an electrolyte retaining agent.

5. The battery of claim 4, wherein said electrolyte-holding agent is colloidal silica.

6. The battery of claim 1, wherein the negative active material has a density of about 3.0 to 4.1 g/cm3.

7. The battery of claim 1, wherein the negative active material contains about 0.05 to !,(?? by weight of an electrolyte retaining agent.

8. The battery of claim 7 wherein said electrolyte holding agent is colloidal silica.

9. The battery of claim 1, wherein said negative active material contains an organic expander present in an amount of about 0.5 to about 1.0% by weight.

10. The battery of claim 1, wherein said negative active material contains an additive which minimizes the consolidation of lead sulfate crystals during cycling operation and is present in an amount of about 0.3 to about 1% by weight.

11. The battery of claim 1, wherein the weight ratio of negative active material to positive active material is less than 1.0.

12. The battery of claim 10, wherein said weight ratio is in the range of about 0.75 to 0.92.

13- The battery of claim 1, wherein said electrolyte-retaining and absorbing separator material is a borosilicate glass material.

14? The battery of claim 12, wherein there are at least two layers of said electrolyte holding and absorbing material and the layer adjacent to said plates is a borosilicate glass material.

15- The battery of claim 1, wherein a common collector connects a plurality of said cells,l *1

the said vent valve.

16. . Battery as substantially described herein,

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Serial Number Filing Date Patent Number 195569 5/10/80

Date number ai Class Sub-class i?Technical unit Examination series deosite ! ai group tore 6/195-569 5/10/80 429

Applicants: PURUSHOTHAMA RAO, EAGAN, MN; FREDERICK L. MARSH,

FRIDLEY, MN.

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xx Foreign Questions/P'CT verification The

Do you claim high priority? And- ? as shown in tables 1 rev. r?v. tax pr si i_jno positato?o cor-dise- tot_a indi'dep. doc. stere.Adem ? yes One peri tea, reception number of patients with M-AUT-ditions 35 MN 16

USC 119 2 / 87 8007

Augustus J. Hipp

Address

Gould Ine. PAT. DEPT.

P.O. Box 43140

St. Paul, MN 55164

Title: "Lead-acid batteries, sealed, maintenance-free

for occasional applications"

This is to certify that the attached is a true copy of the United States Patent Office Records of the application as originally filed.

seal again and which is indicated above.

By permission of the Commissioner of Patents and March 1 -to: C.W. Smitt.

Date September 17, 1981 Certifying Officer

o-o-o meoo?

H-AUT?3007

/ E?SC.R1?IQI?~ of the invention?is indicated by the title ?Sectario al piombo? "por -opplioozioni aslbuoria"? from the ?luta-otatunitc-noc? GQL3? IMO?

een aedo o ?QU.51ffS- KBAJOWS , Illinoio , U.&?*.

o-o -o-o-o-o-o-o

CLiQ-t*- ?-??t-'iVS- >0>^e- d,?? 1^ ^

A sealed, maintenance-free lead-acid battery in which the electrolyte is absorbed and immobilized in a porous separator is described. The battery provides superior peak energy at relatively high discharge rates for the short periods of time encountered in various intermittent applications, has satisfactory performance characteristics, operates effectively at low internal pressures, and can utilize conventionally used thin-walled plastic containers.

The present invention relates to lead-acid batteries and, more particularly, to sealed, maintenance-free lead-acid batteries suitable for use in occasional applications such as automobile starting, lighting and ignition. For many applications, the orientation of the

While the aim of lead-acid battery technology is to provide batteries that are maintenance-free, that is, a type of battery that can be operated without water entering the electrolyte during its intended life, the life of such batteries is limited by water loss due to gassing, and therefore excess electrolyte must be used to compensate for the water loss that occurs in order to provide satisfactory life.

Typically, water loss in such batteries has been minimized by using grid alloys with high hydrogen overpotential. Rigid, self-supporting, and sometimes structurally reinforced grids made from a variety of antimony-free or low-antimony lead alloys may be employed. Examples of grid alloy systems used include calcium-lead, calcium-tin-lead, cadmium-antimony-lead, selenium-antimony-tin-lead with various optional alloying ingredients such as silver and arsenic, as well as combinations of these alloys.

Additionally, lead-acid batteries are known in which the electrolyte is immobilized in the form of a gel. These batteries can provide not only maintenance-free but also spill-free characteristics, meaning the battery can be used in any position without loss of electrolyte. However, cracks that develop in the gel during charging, although essential for oxygen transport, give rise to conditions that can negatively affect the desired performance. Furthermore, these batteries invariably have a higher internal resistance and, therefore, cannot be used in applications where the capacity is limited. high-rate discharge is a requirement, such as, for example, an automobile starter, lighting and ignition battery. To provide a sealed design and at the same time avoid potential problems with electrolytes in the form of gei, sealed systems have been used in which the electrolyte is immobilized and absorbed in special separators. The separators are not fully saturated and the gases evolved during overcharging or at other times can diffuse rapidly from one electrode to the other. Thus, under the right conditions, oxygen evolved at the positive electrode can diffuse to the negative electrode where it is rapidly reacted with active lead. Effectively, this reaction partially discharges the negative electrode while preventing the negative electrode from reaching its fully charged condition so that hydrogen evolution is minimized. This sequence gives rise to what has been called an "oxygen cycle". While the oxygen recombination regime ? greater than the oxygen regime produced at the positive electrode? Water losses and pressure development must be minimal.

Currently, sealed lead-acid systems of this type have been commercially available only in small ampere-hour capacity sizes. Their use has therefore generally been confined to backup applications such as emergency lighting, alarm systems, and portable appliances with limited cycle times such as televisions, lanterns, and garden tools.

U.S. Patent* 862-861 is an example of a cell configuration that recombines oxygen using relatively high internal pressures. It is believed that the cell thus increases the recombination rate by operating under increased pressure. For this reason, a blow-off valve is used, which must be calibrated to aca-vi. "??<?*???? rd?? 3jv?s.??.tv'.je ou.v.nvw> more cita possibi-:s:- '?'v - vivivi tvu? 'rivoli di spherical d? type toaaexx atua *s vraitensre s?lf?eso 4,> l'ino a StP ?rg il pratica?ne .Ir.*;?.!*?* .i?la type ai battery can be used 'in ^.pplice'/i-orvi eaictiax?e and in app.l-?.a?ions to pre-cycle in which it is acceptable ans aurata licitata*

A battery having a prismatic container? See Progress in Batteries and Colors, vol. 2, 1979, pp. 167-171. Is it a type that operates like a file at very low pressures?? The 1K type is used for occasional applications.?

? the other type ? the batteries ? reported sealed

Intornat io 1 Sysposium ou Bat?orlas? October 21 - 22, 1??63. As described in general terms, batteries are produced by making a stack of plates and flat, rather soft separators. The stack, after compression, is inserted into a suitable container. In this stack or block are the plates and separators, made of active material, and fully supported by these separators. The block, after compression, must have a sufficiently high porosity to allow it to absorb and treat all the electrolyte necessary for effective and economical operation. The separators are made of diatomaceous earth. Batteries suitable for automotive warning, lighting and ignition applications are described, the advantages described being resistance to vibration, lack of spillage, and increased performance at high speeds at normal and low temperatures.

Although the report specifies that widespread market introduction has been limited by commercial considerations rather than performance or quality, it is believed that the performance characteristics do not meet the current requirements for such applications. Regardless, the type of battery described has not achieved widespread use and has not had much commercial success.

Furthermore, it has been suggested that a sealed lead-acid system can be scaled up to capacities of more than a few ampere-hours than are currently used commercially (Engineering, October, 1975, 3?h? Age of the sealed Battery, pp. 1020 ~ 1022).

It has, in fact, been argued that the characteristics of the sealed battery system should be particularly advantageous for an SLI application in automobiles (i.e. starting, lighting and ignition)?

In addition, there are a number of applications that can be called "floating pulse" (i.e., a system capable of delivering relatively high peak energy at fairly high discharge rates for short periods of time) where the characteristics attributed to a sealed system would always make such a system desirable for use. Batteries for motorcycles, outboard motor starters, and computer backup power are examples that fall into this category. Applications requiring a relatively pure form of direct current also have similar requirements. Batteries for such applications require capacities of at least 15 ampere-hours, or even 25 ampere-hours and substantially greater.

Yet, for whatever reason, sealed systems of such capacitive sizes have not become commercially available at all. This may well be simply because the necessary performance characteristics have not been achieved. It can therefore be argued that it has proven difficult to optimally achieve the capacity, city, and endurance required for such applications. Furthermore, it may be argued that a more robust, more rigid battery case is necessary to withstand the high internal pressures thought necessary to provide satisfactory oxygen recombination efficiency, and that this is particularly critical in batteries of relatively large capacitive sizes. Would the use of such more robust battery cases naturally result in increased battery weight? This would be particularly detrimental in the automotive field, since the current trend is to provide battery systems in which weight can be reduced as much as possible.

It is therefore a primary object of the present invention to provide a sealed* maintenance-free* lead-acid battery which is capable of providing satisfactory performance characteristics for use in intermittent pulse applications.

Another and more specific object of the present invention is to provide a lead acid battery si-

* Sealed for performance that equals or exceeds the characteristics required for batteries for automotive starting, lighting and ignition applications.

A further aim is to provide a sealed lead-acid battery with improved volumetric and gravimetric energy density.

It is a still further object of the present invention to provide a sealed lead-acid battery that can be formed in sizes ranging from small to extremely high capacities. Yet another object is to provide a sealed lead-acid battery that can be produced on standard equipment used for the production of conventional intermittent pulse batteries.

A still further object of the present invention is to provide a sealed lead-acid battery suitable for using the conventional thin-walled plastic containers often employed for intermittent pulse batteries.

Another object of the present invention is to provide a sealed lead acid battery capable of operating at extremely low internal pressure while providing maintenance-free characteristics for extended life.

Other objects and advantages of the present invention will be apparent from the following description and drawings, in which:

Figure 1 is a perspective view of a battery formed in accordance with the present invention, with parts broken away to show the internal configuration;

Figure 2 is an exploded, sectional, side elevational view illustrating the arrangement of the battery separator plates of the present invention;

Figure ? is a cross-sectional view taken primarily along line 3-3 of Figure 1, and also showing the internal configuration of the battery;

Figure 4 is a voltage versus time plot showing the improved cold cranking performance of a sealed lead acid battery made in accordance with the present invention compared to a commercially available maintenance-free battery; and

Figure 5 is a diagram illustrating the performance of a sealed lead-acid battery of the present invention in an industrial cycle life test.

While the present invention is susceptible to various modifications and alternative constructions, the preferred embodiments will be shown in the six drawings and described in detail herein. It should be understood, however, that it is not intended to limit the invention to the specific constructions disclosed. Rather, it is intended to encompass all modifications and alternative constructions falling within the spirit and scope of the present invention. Therefore, while the present invention will be primarily described in connection with an automobile starting, lighting, and ignition application, it should be noted that the present invention can be utilized for any other intermittent pulse application.

Furthermore, the invention is obviously equally applicable to a battery or a single cell. Furthermore, although the present invention is described with reference to batteries of larger capacitances, it has been found that it is equally useful with smaller capacitances. Likewise, although not all the advantages of the present invention can be achieved, a more rigid container than that required by the internal pressures developed in service can be used, if desired.

In general, the present invention is based on the discovery that a sealed, maintenance-free lead-acid battery suitable for various intermittent applications, such as automobile starting, lighting, and ignition, can be provided by immobilizing the electrolyte in highly absorbent separators, operating at extremely low internal pressures that permit the use of conventional thin-walled containers. The battery of the present invention will provide higher peak energy at relatively high discharge rates compared to conventionally used electrolyte-filled batteries, while meeting other required performance characteristics.

Referring now to the drawings, FIGS. 1 and 2 show the battery 10 according to the present invention. The battery 10 has a case 12, separated into individual cells by internal dividers ?A. In each cell, numerous positive electrodes 16 and negative electrodes 18 are separated by absorbent separators 20.

The necessary electrical connections may be made by any of several methods known in the art. The particular technique employed herein forms part of the present invention. As shown, conducting strips 22 connect the electrodes to each other, and the connections between cells are shown in FIG. 3. The terminal cell strips 22 are connected to external terminals 25 by conventional means. As seen in FIGS. 1 and 3, exhaust venting is provided through manifolds 26 via automatic low-pressure exhaust valves, such as Bunsen burners 38. Although exhaust through one manifold is illustrated, the individual cells could each be provided with an exhaust valve if desired. On the other hand, a single manifold could be used for the six cells shown, or more than two manifolds could be used.

The electrodes 16 and 13 and the separators 20 must fit precisely in the cells—that is, the electrodes and separators must remain in an assembled condition when the container is inverted. The electrodes may therefore be sized up to approximately the internal dimensions of the cells. To eliminate the possibility of short circuits, however, it is desirable to size the separators used so that the edges extend slightly beyond all edges of the electrodes—as shown in Figure 2. One means of achieving this at the bottom of the electrodes is to fold the separators around the electrode in a U-shaped fold as shown in Figure 2.

This clearly demonstrates the highly effective use of the container interior. However, if desired, spacers, such as shims, could be used if the cells used are oversized for any reason.

Considering the present invention in more detail, the grids used as positive and negative grids may be made of any of several known grid alloys used for conventional maintenance-free batteries. As an example, it is therefore convenient to use a calcium-tin alloy in which the calcium content is from about 0.06 to 1.5% and the tin is in the range of 0.1 to 0.5% (preferably 0.2-0.3%), both percentages being based on the total weight of the alloy. The alloys used must be capable of providing self-supporting grids. The grids may be formed by any of several known techniques, such as direct casting or expanded metal.

There are several difficulties associated with providing a satisfactory internal structure for a sealed system. One such difficulty arises from the need to provide sufficient system absorptive capacity to ensure that sufficient electrolyte will be retained to provide the desired capacity. This can be achieved to some extent by using thicker separators than would be necessary for a packed system. However, this will not generally be a complete answer as the internal resistance will increase as the plate spacing increases. There is therefore a practical limit to the alternation of performance characteristics that will occur. Some benefits may be obtained by using an electrolyte with a somewhat higher specific gravity than that of conventional packed systems; but even here there is a practical upper limit due to factors such as the occurrence of decreased conductivity. Another possibility is, of course, the possibility of using a more compact electrolyte.

to reduce the density of the active material pastes. Since mold formation on the negative active material and flaking of the positive active material must be avoided or at least substantially minimized, should reducing the density of the active paste material be conceptually possible by precisely matching the electrodes in the absorbent separators used? However, even here, there are limitations due to the processing problems that arise with such reduced densities when conventional kneading machines are used, as in an automotive application.

Another difficulty arises from the shrinkage of the negative active material that is known to occur in batteries exposed to fluctuating conditions. This can be a major failure mode, significantly reducing the useful life of a battery. For this reason, battery manufacturers have conventionally used various expanders to maintain the desired porosity and active material surface area of the negative plates.

This difficulty has been found to be particularly serious in sealed systems for occasional applications.

Accordingly, to achieve the full advantages of the present invention, it is preferred to use active material pastes that have increased absorbency and that can be readily processed with conventional equipment and provide a system with satisfactory durability and performance characteristics. To this end, the paste densities of the positive active materials are lower than the paste densities used for conventional electrolyte-filled lead-acid batteries employing long-lasting lead oxide materials, such as those obtained from a Barton crucible. It has thus been found desirable to use plate densities in the range of about 2.9 to 4.1 g/cm² for the unformed, cured positive active material, while a densities range of 3.0 to 4.2 g/cm² for the formed, cured positive active material is acceptable.

To provide the desired electrolyte holding properties, it is preferable to incorporate

An electrolyte-retaining agent such as colloidal silica in the paste? A rare incorporation of colloidal silica in an amount of about 0.05 to 1.0%, based on the weight of the unformed positive active material, has been found suitable. Other electrolyte-retaining materials are known that can similarly be used as substitutes, in whole or in part, for silica. Desirably, the electrolyte-retaining agent should also function as a bulking agent, i.e., increase the consistency of the wet paste so as to improve handling. Colloidal silica fulfills this function.

According to a further preferred aspect of the present invention, the characteristics of the negative active material are improved not only to increase absorbency but also to compensate for shallow cycling effects to provide satisfactory durability and performance characteristics. To this end, the negative active paste preferably includes a combination of conventionally used paste additives above typically used levels.

As the first component, it is preferred to use a conventional organic expander at a level of about 0.5 to about 1.4 in, based on the weight of the dried unformed pulp. Various lignosulphonates, such as sodium lignosulphonate, are known and suitable. Furthermore, it is preferred to use an additive that serves to minimize the physical consolidation of the lead sulfate crystals formed during the cycle into larger crystals and ultimately into an essentially solid layer with minimal porosity that would result in battery failure. Staple cellulose serves this purpose and can be used.

19

to a level of about 0.3 up to about 1.0% by weight.

It is believed that the maximum benefits will be achieved by using only one type of expander when the functions are considered different. In some way, the organic expander influences the morphology of the lead sulfate structure in a way that delays the loss of porosity. The additive that retards consolidation is believed to effectively serve as a means of physical distancing.

Preferably, the pulp additives used should also function as bulking agents for the pulp. Both staple cellulose and sodium lignosulfuron serve this function.

A mixture of 0.75% sodium hydroxide and 0.6% flake cellulose is preferred, both percentages being based on the weight of the dry unformed pulp. The use of such a mixture appears to provide the desired cycle life. The density of the cured, unformed pulp for the negative active material should preferably be in the range of about 3.5 to 4.4 g/cm*. A density range of about 3.2 to 4.5 g/cm for the cured and formed negative active material is recommended. "satisfactory" Although the negative paste additives described above serve to retard the loss of porosity and thus maintain the adsorptive capacity, it is also preferred to incorporate an electrolyte-retaining agent such as colloidal silica into the negative paste. Amounts in the range of approximately 0.05 to 1.0%, based on the weight of the unformed, dry paste, are suitable.

Typically, it has been found essential* as set forth in U.S. Pat. No. 5,862,861, to utilize in a sealed system an excess of negative active material over positive active material in order to achieve the required oxygen cycling. In accordance with one aspect of the present invention, it has been found that a satisfactory oxygen cycling can be achieved even if the amount of negative active material is less than that of positive active material. It is accordingly preferred to utilize a weight ratio of negative active material to positive active material of from about 0.75 to about 0.92 or the like. The result is not only reduced weight but also reduced expense without detrimental effects on performance.

The material used for the separators 20 must be stable in the sulfuric acid electrolyte employed, resistant to oxidation by PbO2, and not release materials into the electrolyte that could adversely affect battery performance. Furthermore, the material should be highly porous, e.g., at least 70-75%*, preferably up to 9% or similar, and should be sufficiently compressible to conform at least substantially to the varying shapes of the electrodes during assembly and service. Furthermore, the mean pore diameter should be sufficiently small to prevent the propagation of dendrites from the negative plate and shield the active material from the positive plate. The mean pore diameter, however, should be large enough to be easily wetted by the electrolyte and not so small as to result in an unduly high internal impedance. The separator material must also be capable of retaining the electrolyte to the desired height of the separator. And last but not least, the separator material should, if possible, provide a substantially uniform void volume throughout the separator in service. The separator thus preferably provides sufficient void volume to accommodate the oxygen transport rate required for the desired internal pressure of the battery. The void volume is believed to be achieved by some of the pores having their walls covered with a film of electrolyte while the central portion of the hole is free of electrolyte. Satisfactory oxygen recombination efficiency for some applications can also be achieved when the separator is completely wetted with electrolyte. Suitability in this respect can be determined by weight (water) loss measurements taken during cycling. If the material is suitable, excessively high water loss should not occur. The thickness of the separator will generally be determined by the battery capacity and the expected co-operation rate for the particular application. From this point of view, the separator thickness used should in practice not refer to those found suitable for other types of lead-acid batteries used for the particular end-use application.

It has been found suitable to use a borosilicate glass material consisting of glass fibers and cut braids. Materials of this type are commercially available and have previously been used for sealed lead-acid batteries. One such material (C.H. Dexter, Bivision, The Dexter Corporation, Windsor Locks, Connecticut, Grade 225B) which has been found satisfactory has the following characteristic properties: nominal thickness of 300 μm, air permeability (ASTMD 757-75) of 15 μm liters/min/100 cm^ at 12.7 M water - P (Fraeier Permeometer), a mean pore size of 16.6 μm, and a porosity (for infiltration of - ?i\ _

mercury) of 1.2 m /g. It is preferred to use at least one layer of borosilicate glass material adjacent to the electrodes. Additional layers of other materials may be used as reinforcement to improve handling during processing. As an illustrative example, commercially available non-woven sheets of polyethylene, polypropylene, and polyester may be advantageously used. These materials possess the desired electrolyte retention and also reduce costs as well as improve mechanical strength. Such a laminar separator system can be used to provide the necessary mechanical strength for relatively easy introduction of pocket-type and U-bent separators in conventionally employed high-power SLI battery assembly techniques.

For a given application, the required full-charge specific gravity of the electrolyte can be easily calculated. In particular, full-charge specific gravities in the range of 1.255-1.320 may be satisfactory; the range of 1.285-1.220 is preferred. Particular applications may require the use of acid specific gravities - <r'5

a little higher or lower.

The formation of kneaded electrodes can be performed using known techniques. Thus, before assembly in the container, the electrodes can be formed using conventional vat formation. When this technique is used, the formed electrodes should be dried to remove residual electrolyte.

Conveniently, the unformed electrodes and

The separators are placed in the container, the necessary electrical connections are made, the lid is sealed to the container, the required electrolyte is added through the opening in the lid for the vent valve, and the valve is then placed in the service position. The formation is then carried out using conditions suitable for conventional formation in a single

lead-acid battery stage. However, it may be useful to use slightly less severe forming finishing conditions than those conventionally employed. It may also be appropriate to initially cool the forming electrolyte to a certain degree.

It should also be noted that when the formation is used in situ, the onset of formation should occur within 1/2 to 1 hour or so after the electrolyte is introduced. Longer delays may result in conditions that will ultimately create internal short circuits.

The amount of electrolyte used should preferably ensure that the battery's absorbent materials are completely saturated, i.e., the battery should be in an electrolyte-starved condition. While the battery is self-regulating in service, a fully saturated condition could result in undesirable gas formation during the initial stages of charging during cycling. Furthermore, the operation will reach an equilibrium state where efficient oxygen recombination cycling is achieved. The somewhat higher gas formation that occurs during the initial stages can be substantially eliminated by determining the particular void volume required for efficient oxygen recombination. However, it has been found advisable to add sufficient electrolyte to saturate the system's absorbent capacity to a level of approximately 90%.

Care must be taken to avoid free electrolyte in the system. Large amounts of free electrolyte (i.e., not immobilized in the electrolyte and separators) can have negative effects on performance.

In one aspect of the present invention, venting is provided by means of a self-sealing vent valve which breaks the seal at extremely low internal pressures. For this purpose, a valve is employed which breaks the seal at internal pressures of approximately 0.035 kg/cm

2

up to approximately 0.2l kg/cm . In fact it is preferable to use internal operating pressures not exceeding

2

to about 0.07 or perhaps 0.14 kg/cm so that commonly used thin-walled plastic containers can be used. The following examples further illustrate the present invention but are not a limitation thereof. Unless otherwise specified, all percentages are by weight.

EXAMPLE 1

This example illustrates the performance of the sealed lead-acid battery of the present invention compared to a conventional maintenance-free flooded battery.

Batteries with a nominal capacity of approximately 71 ampere hours were assembled in ebonite containers. Each battery contained 17 plates per cell. The alloys used for the grids of both

28

The batteries were calcium-tin-pyrophosphate having a nominal composition of 0.09% calcium, 0.3% tin, and the remainder lead. The densities of the paste used were 4.0 g/cm³ for the positive and 4.4 for the negative, both based on the dry weight of unformed paste. The pastes were treated by exposure to 60°C for about 16 hours in an atmosphere of 100% relative humidity, and subsequently by exposure to 60°C in an atmosphere of 0% relative humidity for a period of about 48 hours or so. Each electrode of the battery of the present invention is was wrapped with a two-layer separator comprising an inner layer of a nominal 0.33 mm borosilicate glass material as described above and an outer layer of 0.33 mm of a point-bonded non-woven polypropylene material folded in a U-shape around the electrode as shown in Figure 2. A conventional polyvinyl chloride separator having a nominal thickness of 0.94 mm with a 0.3 mm backing film was employed for the conventional maintenance-free battery.

Other construction details are shown in Table 1:

29

TABLE 1

Battery Parameter Conventional Battery Positive grid thickness, mm 1.05 1.05 Negative grid thickness, mm 0.99 0.99 Dry weight of positive paste

per plate, g 110 110

Dry weight of negative paste

per plate, g 101 101 Weight ratio of positive paste/grid 70/40 70/40 Weight ratio of negative paste/grid, g 62.5/38.5 62.5/58.5 Specific gravity of electrolyte 1.285 1.285 Interspace spacing, mm 0.56 0.94 Other details of the batteries as a whole are shown in table 2,

TABLE 2

Battery Parameter Conventional sealed battery Total weight, positive paste, kg 5.35 3.35 Total weight, negative paste, kg 3.37 3.37 Total weight, positive grids, kg 1.92 1.92 Total weight, negative grids, kg 2.08 2.08 Total weight, lead within cell, kg 10.73 10.73 Total weight of electrolyte, kg 2.61 6.94

The plates and separators have been arranged

The containers were filled with the necessary electrical connections and the formation acid of specific gravity 1.200 was added and cooled to ~7s8°C. A charging rate of 7 amps for 16.5 hours was used, followed by 4 amps for 3 hours and 2 amps for 2 hours. The lids were then placed in place.* The sealed battery included a standard Bunsen burner vent that vented at 0.035 kg/cm². The batteries were then tested and the performance is shown in Table 5:

TABLE 3

Battery Test Conventional sealed battery Cold start at -17.8?C,

voltage after 30 seconds, 550 A 8.05 7? 60 Relative electrical resistance,

-17.8?C 9.9 11.2 Reserve capacity, discharge at

2nd amp, minutes 78 124?

As can be seen, the sealed battery of the present invention exhibits improved cold cranking power over the conventional maintenance-free battery. Figure 4 also shows this improved performance over the 60-second discharge to which each battery was subjected, the curve marked 1 being the sealed system.

31

side and curve 2 valid for the conventional maintenance-free battery?

However, as can be seen from Table 3, the reserve capacity of the sealed battery of the present invention was substantially lower than that of the conventional maintenance-free battery. It will be noted that the active material pastes have not been modified as previously described, and the results thus clarify the need for appropriate modification to achieve the full advantages of the present invention.

The sealed battery was subjected to a 12-minute SLI unified cycle, J240 regime, and failed at approximately 4500 cycles, which is substantially lower than the performance typically achieved by commercially available maintenance-free batteries. However, the failure is believed to be due to a design flaw in the special positive grids used.

EXAMPLE 2

This example illustrates the performance that can be achieved by a sealed battery constructed in accordance with the present invention.

A test battery has been assembled

- 32 -

had a nominal ampere-hour capacity of about 67 ampere-hours and contained 13 plates per cell. The alloys used had the same composition as shown in Example 1. The densities of the hardened paste,

3

The unformed paste was about 4.4 g/cm3 for the negative active material and about 3.9 g/cm3 for the positive active material. The negative paste was made from a formulation that included, in parts, 120g g of lead litharge, 50 g of a conventional expander mixture, and about 0.3% colloidal silica based on the unformed dry weight of the paste.

The pastes were cured as described in Example 1. The positive plates were wrapped with two layers of the horosilicate material as described previously and the negative plates were wrapped with one layer of that material.

The plates and separators were placed in a thin-walled SLI-compliant plastic container used for commercial maintenance-free batteries, modified to significantly reduce the weight of the supports at the bottom of the container. Assembly and formation were performed as generically described in Example 1, with the specific formation regime requiring a 7-amp charge for 18 hours, followed by 4 amps for 6 hours, and

33

2 amps for 2 hours.

Further construction details are shown in Table 4, including for comparison the specifications for a conventional maintenance-free battery:

TABLE 4

Battery Parameter Specification Sealed Conventional

Positive grid thickness, mm 1.9 1.62 Negative grid thickness, ram 1.3 1.2 Dry weight of positive plate, g 148 149 Dry weight of negative plate, g 104 106 Weight ratio of positive/negative paste

grid, g 89 s8/58.5 87/62 Weight ratio negative paste/

grid, g 63.5A 0.2 66/41 Specific gravity of electrolyte 1.290 1.265 Table 5 shows the details of the assembled battery, the specifications for the conventional battery are given in conjunction with table 4

that is, included here:

Battery Parameter Specification Sealed Total weight, positive cell, kg 3.23 3.13 Total weight, negative cell, kg 2.67 2.77 Total weight, positive grids, kg 2.46 2.23 Total weight, negative grids, kg 1.69 1.71 Total weight within cells, kg 10.03 9.85 Total weight of electrolyte, kg approx. approx. 3.13 5.26 Total weight of battery, kg 14.6 17.14 The sealed battery was tested and Table 6 shows the results in comparison to the specifications for the conventional battery described here.

TABLE 6

Battery Test Specified sealed AC conc_ _ _ __ conventional Cold start at -17?8?C,

Volts at 30 see., discharge at 500 A 7.84 7.2 Reserve capacity, ?5 A, minutes 91 102 As can be seen from Table 6, the sealed battery of the present invention provides the same improved cold cranking as shown in Example 1. So while not the same as the conventional battery - the modification to the negative grids along with increased inter-plane spacing has given an improvement in relation

compared to example 1. A further improvement in this respect can be achieved by further modifying the active material pastes, as described above*

The sealed battery was subjected to the J240 endurance test, described in Example 1, and performed approximately 8,000 cycles. During this test regime, the battery was discharged at 500 amperes; the 5-second and 30-second voltages were determined. Figure 5 shows the results, with curve 3 being the 5-second voltages and curve 4 being the 30-second voltages. Failure occurred as a result of corrosion on the positive grids, which is believed to be a design flaw in those grids.

Significantly, over the duration of the J240 test the sealed battery of the present invention lost only 0.0? kg of water (+ 0.05 measurement accuracy) which is considered to be around an order of magnitude less than that expected from a conventional battery.

maintenance-free.

As seen, the battery of the present invention thus provides all the advantages of a sealed system and in particular achieves improved peak power at relatively high speeds for short durations encountered in a wide variety of intermittent applications. In engine starting, ignition and lighting applications, this invention thus provides significantly superior cold starting power. This performance is achieved while maintaining the other required performance characteristics. The efficient oxygen recombination rate even at extremely low internal pressures offers superior maintenance-free product characteristics. The use of low internal pressures similarly permits the use of conventional thin-walled plastic containers, an aspect of great utility in automotive applications where low weight is becoming increasingly important. Indeed, the relatively high energy density per volume that can be achieved may permit the use of even smaller container sizes without any sacrifice in performance.

???? ?gfrEHDI0A2ieg?-1. Maintenance-free lead-acid battery having characteristics suitable for use in non-continuous applications, comprising:

a sealed container divided into numerous internally dividing cells; numerous positive plates contained within each cell, each of said plates comprising a self-supporting grid and positive active material kneaded onto said grid!?

numerous negative plates contained in each cell, each of said plates comprising a self-supporting grid and negative active material kneaded onto said grid,

at least one layer of a separator material absorbing and retaining the electrolyte intimately in contact and separation in said positive and negative plates,

sulfuric acid electrolyte absorbed in said plates and separators, said plates and separators being sufficiently porous to retain sufficient electrolyte to provide a capacity of at least about 25 ampere hours, and

said container having at least one normally closed vent valve capable of venting gas from the container to the atmosphere when the pressure within said container is in the range of about

2

0.035 up to 0.2l lvg/cm .

2. The battery of claim 1, wherein at least one of the positive and negative grids are made of a calcium-tin-lead alloy.

3? The battery of claim 1, wherein the positive active material has a density of about 3*0 to z

4.2 g/em''.

4* The battery of claim 1, wherein the positive active material contains about 0.05 to 1.0% by weight of an electrolyte holding agent. 5V Battery of claim 4, wherein said electrolyte holding agent is colloidal silica.

6. The battery of claim 1, wherein the negative active material has a density of about 3*^ to 4.1 g/cm".

7- The battery of claim 1, wherein the negative active material contains about 0.05 to 1.0% by weight of an electrolyte retaining agent.

8. The battery of claim 7, wherein said electrolyte-holding agent is colloidal silica.

9. Battery of claim 1, wherein said but

39

The active ingredient in the negative compound contains an organic expander present in an amount of about 0.3 to about 1.0% by weight.

10. The battery of claim 1, wherein said negative active material contains an additive which minimizes the consolidation of lead sulfate crystals during cycling operation and is present in an amount of about 0.3 to about 1% by weight.

11. The battery of claim 1, wherein the weight ratio of negative active material to positive active material is less than 1.0.

12. The battery of claim 10, wherein said weight ratio is in the range of about 0.75 to 0.92.

13. The battery of claim 1, wherein said electrolyte-retaining and absorbing separator material is a borosilicate glass material? 14. The battery of claim 12, wherein there are at least two layers of said electrolyte-retaining and absorbing material and the layer adjacent to said plates is a borosilicate glass material?

15* The battery of claim 1, wherein a common collector connects a plurality of said cells^ vQ -

the said vent valve.

16. Battery as substantially described herein. ^ V-_ ?W.r\TTTT>_ TT.T^r_

djtsu. a ^ ' \> i

STATEMENT AND POWER OF ATTORNEY - No. of ine.

Original question from the agent

As the inventor hereinafter named, I hereby declare that:

my residence, postal address and citizenship are as indicated below after my name;

I indeed believe myself to be the original, first and only inventor (if only one name is listed below in 201) or a joint inventor (if several inventors are named below in 201-203) of the invention entitled: "Maintenance-free, sealed lead-acid batteries for occasional applications"; which is described and claimed in the attached specification;

I am not aware of, and do not believe, that the invention was ever known or used in the United States of America prior to my or our invention of it;

I am not aware of and do not believe that the invention has ever been patented or described in

* any publication printed in any country

before my or our invention of it and more than a year before this question;

I am not aware and do not believe that the invention has been in public use or on sale.

in the United States of America more than a year before

this question;

I know my duty to provide information that I am aware of and that is important.

for the examination of this application;

the invention has not been patented or the subject of an inventor's certificate issued before the date of this application in any country

outside the United States of America pursuant to an application filed by me or my attorneys or representatives or assigns more than twelve months prior to this

question; and

as regards applications for: patents or inventor's certificate on the invention filed in

any country outside the United States of America

before this question by me or my legal representatives or assignees,

? no such application has been filed or

Q such applications were filed as follows:

?previous foreign applications, if any, filed within 12 months prior to this application

COUNTRY Application No. Filing Date Priority Date Release Reseller-(day, month, year) month, year) to 35 U.S.C. 119

YES NO YES NO

All foreign applications, if any, filed more than twelve months prior to this application

Power of Attorney: As the named inventor, I hereby instruct the following attorney(s) and/or agent(s) to prosecute this application and handle all matters connected therewith in the Patent and Trademark Office (list and registration no.):

Augustus J. Hipp, Reg. n? 25093 e

Edward E. Sachs, Reg.n? 204-57

Please direct correspondence to: August J. Hipp. Telephone calls to:

Gould Ine., Patent Dept. Augustus J. Hipp

BIT. Box 4-314-0 (612) 681-54-17 or

ST. Paul, Minnesota 55164-681-5000

Inventor's full name

Surname J First Name Given Middle Name Given RAO ? PURUSHOTHAMA

Residence and city:Lnanza

City? State or Country of Citizenship Foreign Country

Eagan Minnesota U.S.A.

Postal Address

Postal Address City, State, and Zip Code/

Village

1210 Carlson I^ake jane Eagan MN 55123/U.S.A.

44

Rome complete with the inventor

Surname First name given Middle name given

with MARSH FREDERICK LEON Residence and citizenship

City? State or Country of Citizenship Foreign Country

FRIDLEY MINNESOTA U.S.A.

Postal Address

Postal Address City, State, and Postal Code State/Country

1523 Windemere Drive Fridley Mn 55421/U.S.A.

Inventor's full name

Surname First name given Middle name given ??

Residence and citizenship

Or City? State or Country Country of foreign citizenship

Postal Address and Code Po-C\J

Postal Address City/Country

I hereby declare that all the statements

made here for my own knowledge are true and that

all statements made following information

neither and convention are believed to be true; furthermore

that these statements are made with knowledge

Claims (2)

that willful false statements and the like so made are punishable by fine or imprisonment or both, under section 1001 of title 18 of the United States Code, and that such willful false statements may impair the validity of the application or of any patent issued therefor Signature of the inventor Signature of the inventor 201 inventor 202 inventor 205 PURUSHOTHAMA RAO FREDERICK MARSH Date: Date: Date: October 2, 1980 October 2, 1980 (for compliant translation) Affi*? Uxm, 3>. 00 $4 ?v ?5 ? *5 XP The Rotating Officer *~3 > ? ? ir> S. ol