FR2491684A1 - LEAD-CAPACITABLE ACID BATTERY FOR BUFFER APPLICATIONS - Google Patents

Abstract

THE INVENTION RELATES TO LEAD-ACID BATTERY BATTERY TECHNOLOGY. AN ACCUMULATOR BATTERY ESSENTIALLY CONTAINS A TRAY 12 CONTAINING POSITIVE AND NEGATIVE PLATES 16, 18 BETWEEN A POROUS SEPARATOR 20. THE ELECTROLYTE IS ABSORBED AND IMMOBILIZED IN THE SEPARATOR. THE BATTERY OFFERS EXCELLENT PERFORMANCE AT HIGH DISCHARGE FOR SHORT TIMES, IT OPERATES UNDER LOW INTERNAL PRESSURES AND CAN USE THE USUAL THIN-WALL PLASTIC CONTAINERS. APPLICATION TO AUTOMOTIVE BATTERIES.

Description

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  The present invention relates to lead-acid batteries

  and more particularly, it relates to sealed, maintenance-free, lead-acid batteries for use in buffering applications, such as starter, lighting and ignition applications for automobiles. For many applications, the trend in lead-acid technology is to make batteries that are maintenance-free, that is, a type of battery that can be operated without adding water to the electrolyte for a period of time. the recommended life of the battery. The life of such batteries is limited by the loss of water due to the release of gas and, therefore, an excess of electrolyte must be used to compensate for the loss of water that occurs.

  product, in order to achieve a satisfactory service life.

  The loss of water from such batteries is typically reduced by using gate alloys having a high limiting potential for hydrogen. Rigid, self-supporting and sometimes structural reinforcing grids can be employed using various alloys of antimony-free or relatively low antimony lead. Among the grilled alloys used, the following systems can be mentioned as examples: calcium-lead,

  calcium-tin-lead, cadmium-antimony-pomb, selenium-antimony-

  tin-lead, with various optional alloying ingredients, such as silver and arsenic, as well as combinations of these alloys. In addition, lead-acid batteries are known in which the electrolyte is immobilized in the form of a

  gel. These batteries can offer not only

  lack of maintenance, but also the characteristics of no flow, that is to say that the

  batteries in any attitude without electrolyte leakage.

  However, cracks that occur in the gel during charging, although essential to the transport of oxygen, lead to conditions that may have an adverse effect on the desired performance. In addition, these batteries are invariably characterized by a higher internal resistance and therefore can not be used in applications in which the possibility of high-speed discharge is required, as for example in the case of a starter battery, lighting and ignition for automobiles. To achieve a watertight structure while avoiding the potential problems that accompany the electrolytes in gel form, sealed structures have been used in which the electrolyte is immobilized and absorbed in special separators. The separators are not completely saturated and the gases released during the overload or at other

  moments can quickly diffuse from one electrode to the other.

  Thus, under the appropriate conditions, the oxygen that is

  released at the positive electrode can diffuse to the electrode-

  negative where it reacts quickly with active lead. This reaction in fact partially discharges the negative electrode, which prevents the negative electrode from reaching its fully charged state, so as to minimize the evolution of hydrogen. This sequence leads to what has been called an "oxygen cycle". When the recombination rate of oxygen is greater than the rate at which oxygen is produced on the positive electrode, the

  Water loss and pressure elevation must be minimal.

  At present, sealed lead-acid structures of this type exist in the trade-only for sizes

  corresponding to a low capacity, expressed in amperes-

  hours. As a result, the use has been generally limited to applications in which the battery does not occasionally discharge, such as emergency lighting and alarm systems, and to applications for portable equipment in which the service life is limited. of the battery corresponds to a number of cycleslimited, the receivers

  television, portable lamps and garden tools.

  U.S. Patent No. 3,862,861 shows an example of an elemental configuration in which the recombination of oxygen takes place using relatively high internal pressures. It is said in this patent that the operation of the element under increased pressure increases the rate of recombination. For this reason, a relief valve is used which must be tared so as to open at as high a pressure as possible. The aforesaid patent discloses a Bunsen type relief valve capable of retaining an internal overpressure of at least 0.7 x 10 Pa at 1 x 10 Pa. This type of element can be used in buffer and deep cycle cycle applications in which a limited lifetime

is acceptable.

  An element having a prismatic tray is described in "Progress in Batteries & Solar Cells", Vol. 2, 1979, pages 167-170, and this element is of a type that apparently operates under relatively low internal pressures. This type of element is used essentially for

applications in buffer.

  Another type of battery is described in the document

  "International Symposium on Batteries", 21-23 October 1958.

  As stated in this document, and in general terms, batteries of this type are constructed by forming a stack of flat and relatively soft plates and separators, and the battery is then inserted into an appropriate container after being compressed. . In this stack or block of plates and separators, the active material of the plates is fully supported by the separators. The block must have, after compression, a sufficiently high porosity to allow it to absorb and retain all the electrolyte necessary for efficient and economical operation. The separators are made from infusorial earth. This document describes batteries suitable for automotive start-up, lighting and ignition applications, and the advantages indicated are vibration resistance, inability to flow, and better performance in fast discharge conditions. normal and low temperatures. Although the document indicates that it is commercial considerations rather than performance or quality that are opposed to wide distribution of this type of battery, it is believed that the performance characteristics do not meet the current requirements for such applications. In any case, the type of battery described in this document has not been widely used and has not been commercially successful. It has furthermore been suggested that it is possible to increase the size of the battery. a lead-acid tight structure, up to capacity values (amperes-hours) higher than those currently found in the trade (Engineering,

  October 1978, The Age of the Sealed Battery, pages 1020-22).

  This article indeed indicates that the characteristics of the sealed battery structure would be particularly advantageous for an application concerning the starting, lighting and ignition of automobiles, In addition to this application, there are a number of applications that may be called "pulse buffer" applications (ie it is an installation capable of providing relatively high peak power with relatively high discharge rates, for short periods of time) , in which the characteristics attributed to a tight structure seem to militate in favor of the use of such a structure. Batteries for motorcycles, for starting outboard motors and for back-up power for computers 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 a capacity of at least 15 Aoh, or even 25 Ah and much more. However, whatever the reasons, structures such capabilities have not been the subject of significant commercial production. This may very well be due to the fact that we have not been able to

  to obtain the necessary performance characteristics.

  It can thus be deduced that it has proved to be difficult at least to obtain the capacity and the lifetime required for such applications. It may also be thought that a more robust and rigid battery tray is necessary to support the high internal pressures that are thought necessary to obtain a satisfactory oxygen recombination yield, and. This would be particularly important in batteries of relatively high capacity. The use of such more robust battery bins would obviously increase the weight of the battery. This would be particularly disadvantageous in the field of automobiles, since the current trend is to produce batteries whose weight is the

weaker possible.

  A main object of the invention is therefore to provide a sealed and maintenance-free lead acid battery which is capable of offering satisfactory performance characteristics for buffered applications.

pulse regime.

  Another more specific object of the invention is to provide a sealed lead-acid battery having performance at a level equal to or greater than the characteristics required for batteries intended for start-up applications.

  lighting and ignition for automobiles.

  The invention also aims to provide a sealed lead-acid battery characterized by a better

  energy density, by volume and by weight.

  Another object of the invention is to provide a sealed lead-acid battery which can be designed with sizes ranging from low capacitances to extremely high capacitances. The invention also aims to provide a sealed lead-acid battery which can be manufactured with conventional equipment that is used for the manufacture of common batteries operating in buffering mode

pulse.

  Another object of the invention is to provide a sealed lead-acid battery capable of using the usual thin-walled plastic containers which are often used for buffer batteries.

in-pulse mode.

  The invention also aims to provide a sealed lead-acid battery capable of operating with an extremely low internal pressure, while not requiring

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  no maintenance for a long life.

  The invention will be better understood when reading

  the following description of embodiments and in

  Referring to the accompanying drawings in which: Figure 1 is a perspective view of a battery made in accordance with the invention, partially broken away to show the internal configuration; Figure 2 is an elevation, side, and exploded showing the arrangement of the plates and separators of the battery of the invention; Figure 3 is a section corresponding generally to the line 3-3 of the figure also showing the internal configuration of the battery; FIG. 4 is a graph of the voltage as a function of time and shows the best behavior at cold start of a lead-acid sealed battery produced according to the invention, in comparison with a battery of coamerce not requiring 'interview; and FIG. 5 is a graph showing the performance of a sealed lead-acid battery according to the invention in a lifetime test involving

industrial type cycles.

  Although the invention is susceptible to various modifications and various forms of

  realization, the drawings and the detailed description that follows

  relate to the preferred modes of M'alization. It should be noted, however, that the invention is not intended to be limited to the particular forms described; On the contrary, it is desired to encompass all modifications and variants within the scope of the invention, as defined by the

  appended claims. Thus, although the invention is

  Essentially described by considering a starter, lighting and ignition application for automobiles, it should be noted that the invention can also be used for any other pulse buffer applications. In addition, the invention naturally applies equally well to a battery or a single element. Moreover, although the invention is described in relation to high capacity batteries, it should be noted that it is all

  also useful for the realization of low capacity batteries.

  Similarly, it is possible to use if desired a more rigid tray than that required by the internal pressures that appear during use, although this does not allow to obtain

all the advantages of the invention.

  The invention is generally based on the discovery that a sealed and maintenance-free lead-acid battery can be produced which is suitable for various buffer applications, such as starting, lighting and lighting. ignition of automobiles, by immobilizing the electrolyte in highly absorbent separators, while operating with extremely low internal pressures,

  which allows the use of conventional thin-walled bins.

  The battery of the invention has a higher peak power at relatively high discharge rates, compared to the free liquid electrolyte type batteries commonly used while satisfying the others.

  performance characteristics required.

  We will now consider the drawings in which Figures 1 and 2 show the battery 10 which corresponds to the invention. The battery 10 comprises a tray 12, separated into individual elements by internal partitions 14. In each element, several positive electrodes 16 and several negative electrodes 18 are separated by separators

absorbents 20.

  The necessary electrical connections can be

  established by any of the various known techniques.

  The particular technique that is employed is not part of the invention. As shown, conductive strips 22 connect the electrodes together and the interconnections between elements are shown in FIG. 3. The bars 22 of the end elements are connected.

  at external terminals 24 by conventional means.

  As shown in the figures. and 3, placing in communication with the atmosphere from a certain internal pressure is provided by collectors 26 which communicate with low-pressure discharge valves and t2491684 automatic reclosing, such as Bunsen valves 28. Well Since a communication with the atmosphere has been shown by means of a collector, each individual element may be equipped with a discharge valve, if desired. On the other hand, one could use a single collector

  for the six elements represented, or more than two collectors.

  The electrodes 16 and 18, and the separators 20 must be set without play inside the elements, i.e. the electrodes and separators must remain in the assembled state when the trough is overturned. The electrodes can thus be dimensioned so as to

  practically correspond to the internal dimensions of the elements.

  To avoid the possibility of short circuits, however, it is desirable to size the separators used so that the edges extend slightly beyond the edges of the electrodes, as shown in Figure 2. A way to achieve this at the bottom of electrodes is to fold the separators into

  U around the electrode, as shown in Figure 2.

  Thus, of course, an excellent use of the internal volume of the baco is obtained. However, if desired, spacing means such as wedges may be employed if the elements employed are oversized for any reason. The invention will now be considered in more detail, noting that the positive and negative grids used may be made with any of the various known gate alloys that are used for conventional maintenance-free batteries. By way of example, it is possible to use an alloy containing calcium and tin in which the calcium content is from about 0.06% to 0.20% and the tin content is in the range of 0.1% to 0.5% (preferably 0.2% to 0.3%), all percentages being based on the total weight of the alloy. The alloys used must be able to form self-supporting grids. Grids can be formed by any known techniques, such as by direct molding or by use

expanded metal.

  Achieving a satisfactory internal structure for a sealed battery raises several difficulties. One of these difficulties results from the need to give the structure an absorption capacity to ensure that it retains a sufficient quantity of electrolyte to give the desired capacity. This can be achieved to some extent by using thicker separators than would be

  required in a free liquid electrolyte structure.

  However, this is not generally a complete solution because the internal resistance increases as the gap between plates increases. There is therefore a practical limit in the compromise on the resulting performance characteristics. A certain advantage can be obtained by using an electrolyte with a density slightly higher than the density used in conventional structures with free electrolyte. However, there is still a higher practical limit here because of factors such as the consequent decrease in conductivity.-Another possibility is

  obviously to decrease the density of the active ingredient pastes.

  Since it is necessary to avoid foaming of the negative active material and the disintegration of the positive active material, or at least to significantly reduce them, by a tight fit of the electrodes in the absorbent separators used, it would be theoretically possible to reduce the density. pasta of active ingredient. However, here again, there are limitations because of manufacturing problems that occur with such reduced densities, when using conventional mashing machines, as in applications

for automobiles.

  An additional difficulty results from the retraction of the negative active material that occurs as is known in batteries subjected to buffer operating conditions. This can be a predominant fault mode,

  significantly reducing the useful life of a battery.

  It is for this reason that battery manufacturers conventionally use various blowing agents to maintain the desired porosity and the desired contact area for the active material of the negative plates. Or has found that this difficulty is manifested with particular acuity

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  in sealed batteries for buffer applications.

  Therefore, to obtain all the advantages of the invention, it is preferable to use active ingredient pastes which have an increased absorption capacity, while being able to be processed by conventional equipment, and leading to a structure which satisfies the characteristics of service life and performance. For this purpose, the pulp densities for the active active ingredients are lower than the pulp densities used for lead-acid batteries with conventional free-liquid electrolyte, employing oxide and lead-based materials, such as those we get from a Barton tank. Thus, it has been found possible to employ plate densities in the range of about 2.9 to 4.1 g / cm 3 for the cured and unformed positive active material. A density range of 3.0 to 4.2 g / em 3

  is acceptable for the hardened and formed positive active material.

  To obtain the desired properties of electrolyte retention, it is preferable to incorporate into the dough a

  an electrolyte retention agent such as colloidal silica.

  Incorporation of colloidal silica in a proportion of about 0.05% - 1.0%, based on the weight of the unformed positive active material, has been found to be appropriate. Other electrolyte retention materials are known and can be

  use to replace the silica, in whole or in part.

  It is desirable that the electrolyte retention agent also function as a thickener, i.e. it increases the consistency of the wet paste so as to facilitate its implementation. Colloidal silica fills

this function.

  According to a further and preferred aspect of the invention, the characteristics of the negative active material are improved not only to increase its absorption capacity, but also to compensate for the effects of operation with shallow discharge cycles, in order to obtain satisfactory characteristics of service life and performance. For this purpose, the negative active paste preferably comprises a combination of paste additives usually used, with levels higher than those

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  it is used in a characteristic way. For one of the components, it is preferable to use a conventional organic blowing agent, at a level of about 0.3% to about 1.0%, based on the weight of the unformed paste. Various lignosulphonates, for example sodium lignosulphonate, are known and can be used. It is further preferable to use an additive for the purpose of minimizing the physical agglomeration of the lead sulphate crystals formed during the cyclic operation, to give larger crystals and finally a substantially solid layer with minimal porosity, resulting in the putting out of use of the battery. The cellulose wad fulfills this function and we can use a

  level from about 0.3% to about 1.0% by weight.

  It is not thought that maximum benefits can be achieved by employing only one type of blowing agent,

  because we consider that the functions are different.

  In a way, the organic blowing agent affects the morphology of the lead sulphate structure so as to retard the loss of porosity. It is believed that the additive that delays agglomeration actually functions to define

physical means of spacing.

  It is preferred that the additives used for the dough simultaneously act as thickening agents for the dough. Cellulose wad and lignosulfonate

  both serve this function.

  It is preferable to use a mixture of 0.75% sodium lignosulfonate and 0.6% cellulose wad, both percentages being based on the weight of the dried and unformed pulp. It appears that the use of this mixture gives the desired life in cyclic operation. The density of the hardened but unformed pulp for the negative active material should preferably be in the range of about 3.5 to 4, 4 g / cm 3 A density range of about 3.2 to 4.1 g / cm 3 for the cured and foraged negative active material is satisfactory. Although the negative paste additives described above have the function of delaying the loss of porosity and thus of preserving the absorption capacity, it is preferable also to incorporate in the negative paste an electrolyte retention agent, such as silica. colloid. Proportions in the range of about 0.05% to 1.0% based on the weight of the dried and unformed pulp are suitable. It was typically thought that it was essential, as indicated by US Pat. No. 3,862,861, to use in an airtight structure an excess of negative active material relative to the positive active material, so as to achieve the necessary bone. According to one aspect of the invention, it has been found that a satisfactory oxygen cycle can be achieved even if the amount of the negative active material is less than that of the positive active material. It is therefore preferable to use a weight ratio of about 0.75 to about 0.92, or of this order of magnitude between the negative active material and the positive active material. This leads not only to a lower weight, but also to a lower cost, without any adverse effect on

performances.

  The material used for the separators 20 must be stable in the electrolyte used, consisting of sulfuric acid, it must resist oxidation by PbO 2 and it must not release into the electrolyte any material which is susceptible to

  to have a detrimental effect on the performance of the element.

  In addition, the material must be very porous ie it must have a porosity of at least 70 to 75%, and preferably up to about 90%. and it must be sufficiently compressible to at least substantially conform to the variable shapes of the electrodes during mounting and use. In addition, the average pore diameter must be small enough to prevent the spread of dendrites from the surface. negative plate and the disintegration of the active material of the positive plate. The average pore diameter, however, must be large enough for the pores to be easily wetted by the electrolyte and not so weak as to lead to excessively high internal impedance. The material of the separators must also be able to suck the electrolyte by a

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  wick, on the desired height of the separator.

  Finally, an important point is that the material of the separator should preferably establish, during use, a substantially uniform void volume throughout the separator. The separator should thus preferably establish a void volume sufficient to allow the transport of oxygen at the rate necessary for the desired internal pressure for the element. This volume of voids is thought to be obtained by the fact that the walls of some of the pores are covered with a film of electrolyte, while

  that the central part of these pores is free of electrolyte.

  Satisfactory oxygen uptake can be obtained for some applications even when the separator is fully wetted with the electrolyte. It can be determined whether the separator is suitable for this purpose by making weight loss determinations (loss of water) during cyclic operation. If the material is suitable, the loss of water should not be excessively high.

  The thickness of the separator is generally determined by the capacity of the element and the operating regime provided for the particular application under consideration. In this respect, the separator thickness used does not differ significantly from those suitable for other types of elements.

  lead-acid used for the same particular end use.

  It was found that it was appropriate to use a

  borosilicate glass material formed from micro-

  glass fibers and chopped glass threads. Such materials are commercially available and have been used previously for sealed lead-acid elements. A material of this type (manufactured by The Dexter Corporation, CH Dexter Division, Windsor Locks, Connecticut, under the reference "Grade 225B") which has proved satisfactory has the following characteristic properties: 300 μm nominal thickness, permeability to the air (according to the ASTMD 737-75 standard) of 0.151 l.mn1.cM 2 under a differential pressure of 12.7 mm of water (value measured with an instrument of the Frazier Permeometer type), an average pore size 12.6 pm, and one

  porosity (by mercury penetration) of 1.2 m 2 / g.

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  It is preferred to use at least one layer of the borosilicate glass material adjacent the electrodes. Additional layers of other materials may be used, for example for reinforcing purposes to improve handling ability during manufacture. For example, commercially available nonwoven sheets of polyethylene, polypropylene and polyester may be employed. Such materials have the desired property of electrolyte retention but all provide reduced cost as well as improved strength. Such a laminated separator structure can be used to provide the necessary strength for relatively easy insertion of the pocket type and the U-fold type separators in the high fill mounting techniques which are conventionally used for battery packs. automotive start, lighting and ignition applications. The full load density required for the electrolyte can be easily calculated for a given application. Typically, full charge densities in the range of 1.255 to 1.320 are satisfactory, with the range of 1.285 to 1.320 being preferred. For particular applications, it may be desirable to use densities

  acid slightly higher or lower.

  The formation of the pasted electrodes can be accomplished by known techniques. Thus, before mounting in the tray, the electrodes can be formed by conventional vat formation. When using this technique, one must dry

  the electrodes formed to remove the residual electrolyte.

  It is however preferable to place the unformed electrodes and the separator in the tank, to establish the necessary electrical connections, to put the lid on the tank and to close it, to add the necessary electrolyte through the opening formed in the cover for the relief valve, and then place the valve in the service position. The formation is then carried out by employing conventional one-step conventional training conditions, lead-acid batteries. he can

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  however, it is useful to use a slightly less severe training finishing condition than is usually used. It may also be desirable to cool

  initially to some extent the formation electrolyte.

  It should be noted in a similar way that, when the formation on site is used, the beginning of the formation must take place in a period not exceeding about half an hour to one hour after the addition of electrolyte. Longer waiting times can lead to conditions that

  to finally create internal shorts.

  The amount of electrolyte employed should preferably not lead to complete saturation of the battery's absorbent materials, ie the battery must be in a state of lack of electrolyte. Although the battery in use is self-regulating, a full saturation condition can lead to excessive gas evolution during the initial phases of charging, during cyclic operation. Continued operation leads to an equilibrium state in which an efficient oxygen recombination cycle is achieved. The slightly higher gas evolution that occurs during the initial phases can be virtually eliminated by determining the particular void volume that

  is necessary for efficient recombination of oxygen.

  However, it has been found that it is appropriate to add sufficient electrolyte to saturate the capacity

  absorption of the system to a level of about 90%.

  Care must be taken to avoid the presence of free electrolyte in the battery. Significant amounts of free electrolyte (i.e., not immobilized in the plates and

  separators) may have adverse effects on performance.

  According to one aspect of the invention, communication with the outside atmosphere from a certain internal pressure is provided by an automatically closing relief valve which opens for extremely low internal pressures. For this purpose a valve is used which opens for internal pressure pressures of about 0.03 x 105 Pa to 0.2 x 105 Pa. In fact, it is preferable to use gauge pressures.

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  internal, in operation, not exceeding 0.07 x 10 5 Pa, or perhaps 0.14 x 10-5 Pa, so as to allow the use of thin-walled plastic containers usually used. The following examples further illustrate the invention but are in no way limiting. All percentages are by weight unless otherwise stated0

EXEMPLE 1

  This example shows the performance of the plonmb-acid-tight battery of the invention, compared to a conventional battery with free liquid electrolyte, not requiring

no maintenance.

  Hard batteries have a nominal capacity of about 71 Ache. Each battery contains 17 plates per element. The alloys used for the grids of the two batteries are calcium-lead lead type, with a nominal composition of 0.09% calcium, 0.3% tin, and the remainder in lead. The pulp densities used are 4, 0 g / cm: for positive electrodes and 4.4 g / cm3 for negative electrodes, both values

  being based on the weight of the dried and unformed pulp.

  The straws are cured by exposure to 60 C for about 16 hours in an atmosphere having

  relative humidity of 100%, followed by exposure to 600C.

  in an atmosphere having a relative humidity of 0% for a duration of the order of 48 hours. Each electrode of the battery of the invention is enveloped by a separator having two layers comprising a net layer with a nominal thickness of 0.33 May of the borosilicate glass material described above, and an outer layer of 033 am of polypropylene material, non-woven and spot welded, this separator being bent at a U-shape around the electrode as shown in FIG. FIG. 2 uses conventional maintenance-free battery a conventional polyvinyl chloride separators having a nominal thickness of 0.94 mm with a reinforcement sheet of 0.30 mm. Table 1 gives further construction details. : TaLleau 1 Parameter Battery Standard Waterproof Battery Positive Grid Thickness (mm) 1.04 1.04 Negative Grid Thickness (mm) 0.99 0.99 Dry Positive Dough Weight per Plate (g) 110 110 Weight of the dry dough, per plate (g) 101 101 Ratio: weight of the positive dough / weight of the grid (g) 70/40 70/40 Ratio: weight of the negative dough / weight of the grid ( g) 62.5 / 38.5 62.5 / 38.5 Electrolyte density 1.285 1.285 Plate spacing- (mm) o0.56 0.94 Table 2 shows additional details

  concerning batteries considered globally.

  Table 2 Parameter Total positive dough weight (kg) Total negative dough weight (kg) Total positive grid weight (kg) Total negative grid weight (kg) Total weight of lead in 1 1 ment (ki) Total weight Electrolyte (kg) Waterproof Battery 3,36 3,38 1,92 2,08, 74 2,61 Classic Battery 3,36 3,38 1,92 2,08, 74 6,95 Plates and separators in the tanks, necessary electrical connections are established and formation acid having a density of 1, 200 and cooled to -180C. A load regime of 7 A is used for 16.5 hours followed by a 4 A diet for 3 hours and a 2 A diet that loses 2 hours. The lids are then put in place. The sealed battery features a conventional Bunsen relief valve that opens for

  pressure of 0.035 x 10-5 Pa.

  The batteries are then tested and Table 3 shows the performances:

Board

  Battery Test Waterproof Classic Cold start at -18C; voltage after 30 s, at 550 A 8.05 V 7.60 V Relative electrical resistance

at -180C 9.9 11.2

  Capacity in reserve, discharge at 25 A (min) 78 124 As can be seen, the sealed battery of the invention offers better cold start performance than the conventional battery without maintenance. FIG. 4 also shows these improved performances on the 60 s discharge to which each battery has been subjected, the marked curve 1 being that of the sealed battery and the curve 2

  that of the conventional battery without maintenance.

  However, as shown in Table 3, the reserve capacity of the sealed battery of the invention is significantly

  lower than that of the conventional battery, without maintenance.

  It should be noted that active ingredient pastes have not been modified as previously described and the results thus highlight the need for modification.

  suitable for obtaining all the advantages of the invention.

  The sealed battery was subjected to a standard test for batteries for start-up, lighting and ignition applications, with the J240 and 12-minute cycles, and became defective at around 4500 cycles. which is noticeably less than what is typically achieved with the maintenance-free batteries found in the marketplace. However, the fault mode is considered to be a design error

  in the particular positive grids used.

EXAMPLE 2

  This example shows the lifetime performance that can be achieved with a sealed battery

according to the invention.

  A test battery with capacity is built

  nominal about 67 A.h, holding 13 plates per element.

  The alloys used have the same composition as in Example 1. The density of the hardened and unformed paste is about 4.4 g / cm 3 for the negative active material and about 3.9 g / cm 3 for the positive active ingredient. The negative paste is made from a composition comprising, in part, 1200 g of a mixture of litharge and lead, 50 g of a conventional expansion mixture and about 003% of colloidal silica.

  being based on the weight of the dry and unformed pulp.

  The pastes were cured in the manner described in Example 1. The positive plates were wrapped with two layers of the previously described borosilicate glass material and the negative plates were wrapped with

only layer of this material.

  Plates and separators are placed in a thin-walled plastic tray of the conventional type used for starting, lighting and ignition applications, for conventional maintenance-free batteries. This tray is modified to significantly reduce the height of the litters formed at the bottom of the tank. The assembly and formation of the general procedure described in Example 1 is carried out and the particular formation regime involves charging at 7 A for 18 hours, followed by charging at 4 A for 6 hours.

  and a charge at 2 A for 2 hours.

  Other construction details are shown in Table 4 which also indicates, for general purposes of comparison, the specifications for a conventional maintenance-free battery.

Table 4

  Battery Parameter Classical Waterproof Specifications Positive Grid Thickness (mm) 1.91 1.63 Negative Grid Thickness (mm) 1.30 1.19 Positive Dry Plate Weight (g) 148 149 Negative Dry Plate Weight (g) 10o4 107 Ratio: weight of the positive dough / weight of the grid (g) 89.8 / 58.5 87/62 Ratio: weight of the negative dough / weight of the grid (g) 6395 / 40.2 66/41 Electrolyte Density 1,290 1,265 Table 5 gives details of the assembled battery and also the specifications for the standard battery mentioned in connection with Table 4 Table Battery Parameter Watertight Classi fi cations Total Positive Dough Weight (kg ) 3, 23 3,13 Total weight of the negative pulp (kg) 2,67 2,77 Total weight of the positive grids (kg) 2,46 2,23 Total weight of the negative grids (kg) 1,69 1.71 Total weight in the elements (kg) 10.06 9.86 Total electrolyte weight (kg) approximately

3.10 5.30

  Total weight of the battery (kg) 14.6 17.2 The waterproof battery is tested and Table 6 presents the results, compared to the specifications for the conventional battery described here:

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Table 6

  Battery Test Standard waterproof specifications Cold start at -180C, voltage after 30s of discharge at 500A 7.84V 7.2V Capacity in reserve, at 25A (min) 91 102 As shown in Table 6, the battery In addition, the present invention provides the same improved cold start performance as in Example 1. In addition, without allowing the performance of the conventional battery to be equalized, the modification of the negative grids together with the increase in spacing between plates provides an improvement over the comparison presented in Example 1. It is possible to obtain an additional improvement in this respect by a further modification of the pulps of active ingredient,

  the way previously described.

  The sealed battery was subjected to the J240 life test described in Example 1 and reached about 8000 cycles. During this test regime, the

  battery at 500 A and the voltages are determined at 5 s and 30 s.

  Figure 5 shows the results and curve 3 corresponds to the voltage at 5 s while curve 4 corresponds to the voltage at 30 s. The decommissioning results from the corrosion of the positive grid, which is considered to be a design defect

in these grids.

  It is important to note that over the lifetime corresponding to the J240 test, the sealed battery of the invention lost only about 68 g of water (with a measurement accuracy of + 0.05 4%) , which is considered to be an order of magnitude lower than expected for a conventional maintenance-free battery. It can thus be seen that the battery of the invention offers all the advantages of a sealed battery and, in particular, provides a higher peak power for the relatively high regimes, for short periods of time, encountered in many buffer applications. In a starter, lighting and ignition application for automobiles, the invention thus offers greater cold starting power. These performances are obtained while retaining the other performance characteristics required. The high rate of recombination of oxygen, even with pressures

  extremely low internal

  the lack of maintenance. Also, the use of low internal pressures makes it possible to use conventional thin-walled plastic containers, which is an extremely attractive feature for automotive applications in which reduced weight becomes more and more important. In fact, the relatively high volume energy density that can be achieved allows the use of even smaller sized bins without

no sacrifice of performances.

  It goes without saying that many modifications can be made to the device described and shown, without leaving

of the scope of the invention.

Claims (6)

  1 Lead-acid battery that is maintenance-free and has characteristics that are suitable for use in applications in. buffer, characterized in that it comprises: a sealed tank (12) divided into several elements by internal partitions (14); a plurality of positive plates (16) housed in each element, each of these plates comprising a self-supporting grid and a positive active material in the form of a paste deposited on this grid; a plurality of negative plates (18) housed in each element, each of these plates comprising a self-supporting grid and a negative active material in the form of a paste deposited on the grid; at least one layer of an electrolyte absorbing and separating separator material (20) which is in intimate contact with the positive and negative plates and separates these plates; an electrolyte consisting of sulfuric acid absorbed in the plates and separators, these plates and separators being sufficiently porous to retain a sufficient amount of electrolyte to give a capacity of at least 25Ah; and at least one discharge valve (28), closed at rest, which equips the tank and which is capable of discharging into the atmosphere the gases contained in the tank when the gauge pressure inside the tank is in the range from about 0.03 x 105 Pa to 0.2 X 10-5 Pa 2. Battery according to claim 1, characterized in that the positive grids or the negative grids, or both, consist of a calcium-tin-lead alloy. 3. Battery according to claim 1, characterized in that the positive active material has a density of about 3.0 to 4.2 g / cm3.   4. Battery according to claim 1, characterized in that the positive active material contains approximately   0.05 to 1.0% by weight of an electrolyte retention agent.   5. Battery according to claim 4, characterized in that the electrolyte retention agent is colloidal silica. 6. Battery according to claim 1, characterized in that the negative active material has a density of about 3.2 to 4.1 g / cm3.   Battery according to Claim 1, characterized in that the negative active material contains approximately   0.05% to 1.0% by weight of an electrolyte retention agent.   8..battery according to claim 7, characterized in that the electrolyte retention agent is colloidal silica. 9. Battery according to claim 1, characterized in that the negative active material contains an organic blowing agent present in a proportion of about 0.3 to about 1.0% by weight.   10. Battery according to claim 1, characterized in that the negative active material contains an additive which minimizes the agglomeration of lead sulfate crystals during cyclic operation and which is present in a proportion of about 0.3% to about 1.0% by weight 11. Battery according to claim 1, characterized in that the weight ratio of the negative active ingredient   relative to the positive active ingredient is less than 1.0.   12. Battery according to claim 11, characterized in that the weight ratio is in the range of about 0.75 at 0.92.   13. Battery according to claim 1, characterized in that the absorbent and retaining separator material   the electrolyte is a borosilicate glass.   14. Battery according to claim 12, characterized in that it comprises at least two layers of the absorbent material and retaining the electrolyte, and the layer adjacent to the plates is a borosilicateo glass material 15. The battery according to claim 1, characterized in that a common manifold connects a plurality of elements to the discharge valve (28)