FR2549298A1 - LEAD-ACID ELECTRIC STORAGE-FREE ELECTRIC BATTERY BATTERY WITH STORAGE-LOADED WET-LOADED CHARGE - Google Patents

Abstract

THE GRIDS ARE IN ANTIMONY-FREE LEAD ALLOY, IN PARTICULAR LEAD-CALCIUM-TIN, AND CONTAIN AN ACTIVE MATERIAL OBTAINED BY PASTA CONTAINING ORGANIC INHIBITORS, SUCH AS LIGNIN-SULFONIC ACIDS AND MINERALS, SUCH AS AS BARIUM SULPHATE AND ALKALINE OR ALKALINE-EARTH METAL SALTS AND ELECTROCHEMICALLY SHAPED INTO A MONOBLOC. THE BATTERIES HAVE TIGHTLY CLOSED CHIMNEYS BY MECHANICAL BLOCKING OR BY MEANS OF WELDING THERMOPLASTIC SHEETS OR BY DIRECT STAMPING, AS WELL AS THE COVER WITH THERMOSWELDING AFTER MOLDING, THE SAID SEALING CLOSURES IN THE MIDDLE OF PRESSURE EXACTLY IN PRESSURE. .

Description

The present invention relates to a lead acid battery

  preserved substantially by the single absorbed acid in the plates and in the separators, so as to be activated after a long storage time interval, by the simple addition of electrolyte. These types of batteries are obviously a convenient reserve for a first assembly or as spare parts for places that are not continuously replenished. We will briefly describe the situation of the

  technique that led to this discovery.

  It is known that lead-acid batteries are constituted, whatever their destination, by elements comprising negative and positive pairs of plates. Both the positive and negative plates have a conductive and support part called a grid, traditionally obtained by melting and most recently by

  cutting and mechanical drawing of lead alloys.

  The alloys for the fusion grids must be pre-20 to be melted, a certain flowability and for this purpose many alloys of lead have been studied with various metals, among which

  An historical view of antimony has taken a prominent place.

  In this regard, lead alloys with 11 to 13% anti-monkeys were used originally.

  In addition to the castability of the alloys, the grids, considered as a durable support element, must be considered as active ingredients. Consequently, they must be able to withstand the mechanical action due to the volume variation. active ingredient

  than electrochemical corrosion.

  For this purpose, lead-antimony binary alloys have been substituted with various ternary lead-antimoinuesenic alloys or lead-antimony-tin-arsenic quaternary alloys, in which the antimony content was 4 to 5%, with an arsenic content of 0 to 5%. , 1 to 0.3% and

in tin of 0.1 to 0.5%.

  In the electrochemical processes of formation of the active ingredient and especially during the life of the battery, the antimony, predominantly, but also the arsenic pass in solution in the electrolyte and will be deposited on the negative active matter which is consisting mainly of spongy metallic lead, since the potential for hydrogen of said lead is much more electro-negative than that

antimony and arsenic.

  Such deposition metals reduce the overvoltage of hydrogen, increasing the development, either when the battery is charging, or when it is in open circuit, that is to say at rest or store; This reduction is also due to the action of lead-antimony couples, lead-arsenic. To reduce these drawbacks, ever more advanced techniques have been introduced in the manufacture and conduction of grid matrices, so as to obtain alloys having a carbon content. in

antimony less than 2%.

  However, not all alloys are resistant to electrochemical corrosion if their microcrystalline and macro-crystalline structure does not have a particular morphology and for this purpose additives such as copper, tellurium, selenium, etc. have been experimentally introduced into the alloys. having for essential function

grain refining.

  With such alloys the development of hydrogen during charging and during the rest period of the batteries has been significantly reduced and thus it has been

  to the point of reduced maintenance batteries.

  However, another decisive step towards the reduction of hydrogen development and thus the elimination of maintenance has been accomplished when suitable alloys cured with calcium, strontium or other alkaline have been made. Recently, lead-calcium alloys, essentially alloyed with tin, have been obtained to obtain fusible alloys which are sufficiently resistant to tensile stress and corrosion at constant tension, as was necessary in batteries. stationary or starter With these alloys, we have arrived at batteries that have, at constant voltage, a minimum consumption of water that makes it possible not to have to fill the battery for its duration. In addition, in such batteries, it is possible, at rest, given the minimum self-discharge, to maintain the necessary starting power even

  after 12 months of shopping at 25 C.

  However, lead-calcium-tin alloys make difficult the automatic melting of thin grids. Moreover, the easy variability of the molten alloys by oxidation of the components renders unreliable the uniformity of the production. For this reason, one has studied and put in 20 a technology of continuous production of lead-calcium-tin alloy grids obtained by rolling, stretching and cutting of the alloy strip, which is carefully controllable. This has led to a continuous cycle production of qualitatively uniform grids, with a reducible thickness. practically at will, and with

  reproducible physical and chemical characteristics.

  In conclusion, with lead-calcium-tin alloys, obtained by fusion as well as by the process of

  When stretched, the antimony and arsenic were completely removed from the grids.

  So far we've talked about the support conductor or grid It is now appropriate to make a brief presentation

  the state of the art relating to the active ingredient.

  It is known that on the grids, it is necessary to postpone the active substance, essentially Pb O 2 for the positive plate 2549298 i and Pb spongy for the negative plate The two electrodes (plates) are both reversible in sulfuric acid solution, for the density of which there are

  particular limits of convenience according to the uses.

  In practice, the density value at a fine load is between 1.210 and 1.300 per second of the application

drums.

  The reaction which is at the base of the lead acid battery, as we know, is the following: Pb O 2 + H 25 04 10 + Pb = 2 Pb SO 4 + 2 H 20 The two electrodes have an electromotive force EO = 2.04 volts and the voltages of the two electrodes with respect to hydrogen are respectively Eo Pb = -0.31 volts and Eo Pb O 2 = + 1.73 volts Given the significantly negative voltage of the Pb with respect to the hydro-gene, it is obvious that, if there is not some passivation, lead can move hydrogen from sulfuric acid. It is also known, however, that the Pb SO 4 that is formed by displacement of Hydrogen has a very low solubility in water and its solubility decreases rapidly with increasing sulfuric acid content. For this reason, a pure solution of H 25 O 4 in the presence of uncontaminated spongy lead is practically stable and so we have a minimum development

  of hydrogen by chemical displacement.

  However, the equilibrium changes rapidly, if it appears on the lead, by direct displacement or by galvanic deposit, traces of elements having a potential less

electro-negative than lead.

  These traces are small local couples, in which lead is sulphate while on the metal more

  Electro-negative, the hydrogen is discharged.

  The presence of these impurities determines the well-known self-discharge, which leads to a capacity loss of 1% per day in the presence of the pollution that occurred in the batteries with the old high-grade alloys.

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  antimony, but which can be reduced to 0.03% per day in the presence of antimony-free alloys

  and in particular lead-calcium-tin alloys.

  It is known that the loss of capacity is approximately proportional to the amount of hydrogen whose development

  is therefore reduced by about 30 times.

  This result has been achieved through the use of inhibitors or organic extenders such as certain lignosulfonic acids and their application to the active ingredient via their sodium salts, and also inorganic inhibitors such as barium sulphate and sodium sulphate, etc. By these methods applied simultaneously to the grids and to the active masses, it is

  arrived at batteries called "maintenance free".

  All this is not enough to keep very long, beyond 12 months, with the initial efficiency,

a complete battery with acid.

  Then, having noted that the fastest degradation is obtained for the self-discharge of the negative plate in the acid, the storage system was introduced.

  batteries in the dry charged state.

  There are many systems for converting the lead from the negative, soaked acid solution plate, first to lead soaked with water only by means of a wash and then to lead completely free of water (less than 0, 05%) by allowing it to oxidize as little as possible (Pb OC 2%) and this with drying in an oxygen-free atmosphere and with a protection of the material

  activated by slight inhibitory layers (mineral oils, stearic acid, or stearate, boric acid, etc.).

  Treatments that are less complex, but still attentive enough, must also be applied to the drying of positive plaques so as not to be in danger.

  presence of charged Pb O 2, but separated from the conductive grid by thin layers of basic sulphates.

  After these treatments, the battery must be hermetically sealed and can retain the charge for a very long time in a dry state. However, for the well-known phenomena of local passivation on the positive plate, and because of the slow oxidation of the negative active ingredient, the charged batteries dry, especially in cold diets, and require a fairly long

moment of activation.

  In addition, the washing of sulfuric acid results in significant installation and pollution problems.

  Finally, chemical conditioning and drying of

  plates require significant energy consumption.

  Therefore, when the production of antimony-reduced batteries (less than 3%) has been increased, it has been found that said batteries formed in monobloc and emptied of acid could retain their own charge with the only quantities of acid retained in the plates and in the separators, by developing a reduced quantity of hydrogen, if the access of the air and therefore of the oxygen on the plates was prevented

negative remained wet.

  To this end, it was necessary to create, in addition to the corresponding production cycle, various types of semi-waterproof plugs, that is to say capable of allowing the hydrogen to escape and not allowing access to the oxygen. In this way, batteries were kept moist in charge for 6 to 12 months, even with medium-antimony alloys. However, negative active ingredients were obtained which, in the period of 6 to 12 months, transformed into lead sulphate. a quantity of active ingredient corresponding to 5 to 10% of

the nominal capacity.

  In addition, the rapid dilution of the acid in the active ingredient gave rise to the formation of layers of

2549298,

  basic sulphates and localized corrosion, especially

on the positive grids.

  It has also been noted in the meantime that a certain amount of hydrogen and oxygen is recombinable if the electrode is sufficiently exposed. All of the foregoing summarizes the progressive development of batteries in general and particularly those to be kept wet as well, which, as mentioned above, are not produced for extended storage since they can not be used. The object of the present invention is to provide a conservable moist charged battery in which the active material does not degrade, because of the rapid development of hydrogen and the consequent degradation of the active material and grids. the grids are not corroded and in which there is no gas development beyond the amount compatible with the tight closure of the cells, so as to

  to be able to keep the battery itself, ready for immediate activation after a period of time which may extend beyond 24 months.

  According to the invention, when the technique of charge batteries with a reduced acid is applied, and the conditioning introduced for maintenance-free batteries, that is to say alloys without antimony, the material is also applied with care. With the inhibitor active, a reduced hydrogen development is achieved, and for this reason an exhaust for the gas is not necessary and even the element must remain sealed to absolutely prevent the access of oxygen which would cause slow degradation of the negative plate and consumption of absorbed acid. Inside a battery made according to these concepts, it was noted the pace of the internal pressure P as a function of the storage time t expressed in months and it was found

2549298 '

  under the assumption of conservation in an environment of + 5 C and with a density of fine formation 1,280, which

  is shown in the diagram of Figure 1.

  From the observation of the curve of the diagram, it is evident that the battery sealed immediately after the formation and emptying of the free acid has a first period with a speed of combination of the oxygen of the air present in the cell, greater than the speed

  developing hydrogen produced by the chemical displacement and local couples on the negative plate.

  As a result, sealing according to a main feature of the invention is not only possible but necessary because, otherwise,

  we would have a continuous reminder of the outside air.

  With sealing, we limit the formation of Pb O which, at the beginning, lowers the H 2 SO 4 content on the surface

of the negative active ingredient.

  This phase being exhausted, a second occurs in which a small amount of oxygen is released on the active ingredient Pb O 2 which had absorbed

during the training.

  Finally, a state of equilibrium close to the atmospheric pressure is reached in which, thanks to the characteristics of the grids and the active ingredient illustrated above, the development of hydrogen is maintained at a speed which is equal to that of recombination on

the positive plate.

  The practical consequence is that the battery according to the invention exhausts with extreme slowness the sulphuric ions present in the negative plate while retaining for a long time the potential, and consequently by losing only a minimal amount of the capacitance even beyond the 24 In addition, on the positive electrode, the acidity of fine formation is kept practically intact, and the

  local corrosion phenomena of the grid.

  From what has been noted above with surprise experimentally, it is clear the new possibility to produce maintenance-free batteries 5 formed in monobloc, acid-drained, sealed and able to keep charged ready for immediate activation for periods longer than 24 months In fact, the lead sulphate which forms on the negative plate increases in an extremely slow manner and for this reason it does not tend to spread in the separators, avoiding thus the well-known danger of its reduction in metallic lead, with the unavoidable possibilities of short circuits For the same reason, there is no reabsorption of the acid from the positive plate to the negative plate, thus the positive grid stays in an environment that is certainly acidic so as not to be subject to local corrosions

  and this gives the advantage of the duration of the battery.

  Before illustrating some embodiments of the sealed closure of the battery, the

  conditions which it must satisfy, according to the invention, so that such closures can be realized.

  The conditions are as follows: (a) the alloys of the grids and the various conductors are made up of lead at a level greater than 99.97% alloyed with calcium at a content of 0.06 to 0.1%; tin, at least in the positive grids with a content of 0.1 to 0.5%; b) the positive active ingredient after monoblock formation must contain more than 90% Pb O 2, while the negative active ingredient must contain more than 95% Pb and sulphonated organic inhibitors or additives of between 0.1 and 1 % with a sodium content equivalent to the sodium released from the salts of the organic acids mentioned above; (c) the residual acid after pouring the formation acid, with a final density of between 1,150 and 1,300 must not exceed 12% of the active ingredient and 15% in the separators and in the aggregate it must not be greater than 25% of the acid required at nominal capacity. With elements thus packaged and mounted in the particular cells, it is possible to realize some particular types of waterproof closures whose choice depends mainly on the tools available and the diversity of the presentation modes of the battery.

in activation.

  In all cases, it is necessary and sufficient that the sealing is performed by a shutter capable of supporting, without losing its functional character,

  from 0 to 0.1 atm in depression and from 0 to 0.35 atm in pressure.

  Practical embodiments of sealing are illustrated by way of example in the accompanying drawings, in which: Figure 2 schematically shows a sealed closure of a stack of a battery element partially in section, by means of mechanical locking a lid in the chimney; Figure 2A shows, on an enlarged scale, the lid inserted in the chimney; Figure 3 shows, in section, the closure of a chimney with a strip of plastic material welded to the edges; Figure 4 shows the same closure of Figure 3 but with a plastic strip combined with a metal top layer; Figure 5 shows, in perspective, the metal closure and plastic with a tab provided for tearing; and Figure 6 shows, in section, the application of a lid with closing diaphragm, obtained by stamping on the chimneys and in which the lid is welded to the monobloc after formation and emptying of the battery

while the monoblock is open.

  According to FIG. 2, a group of plates 1, constructed according to the rules indicated above, is mounted in a monobloc cell or container 2 made of thermoplastic material (preferably polypropylene), with the connectors 3 passing through the partitions 4 towards the Next element After the operations described above, the lid 5 is heat-sealed on the partitions and on the edge of the container according to the conventional methods. The operation of forming and emptying the acid once finished, is immediately forced into the chimney 6 a stopper 7

  polypropylene with a diameter equal to that of the chimney.

  The plug has a final conical course 8 which facilitates its introduction into the chimney and a ring 9 which holds

  the plug in the chimney once inserted.

  A tongue 10 connects the various small covers 7 '20 of the cap 7 which can be extracted with a considerable force of tearing, because it must withstand up to an internal pressure of 0.35 atm, which is ensured by the interference of the ring 9 against the lower part

of the chimney 6.

  In FIG. 3, the groups 11 are mounted in the usual container 12 and are connected to each other by polarity.

  opposite, with the connector 13 through the partition 14.

  The lid 15 is heat-sealed as usual, but it is provided with a stack 16 with two concentric seats 17 30 and 18 whose lower seat 18 is of a diameter slightly smaller than that of the upper seat 17 and constitutes the seat of the conventional final plug mounted after the usual activation The upper seat 17 of reduced height is of a slightly increased diameter in order to prevent interference with the final plug of the burrs

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  possible welding of the thermoplastic band 19

  welded along the groove 20 at the edge of the chimney.

  Any bands 19 'connect in series the different strips 19 of the soldered shutters so that tearing can be done in a single operation. FIG. 4 represents the possible external reinforcement of the shutters by a metal strip 21, for example of aluminum, integral with the rolling of the thermoplastic strip 19, the rest being identical to that

which is shown in Figure 3.

  FIG. 5 shows a method for more easily removing the closure, made with the aid of a metallo-plastic layer, while keeping everywhere the arrangement of FIGS. 3 and 4, and having only as a characteristic variant that the metal part in steel 21 applied to the welded thermoplastic strip 19 can be interrupted by a new tear-off system 22 along the perimeter corresponding to the outside diameter of the chimney, thanks to which the closure is very safe

and opening very easy.

  Finally, in FIG. 6, the usual groups 41 are mounted in the monoblock 42 and are connected to each other through partitions 43 by means of a weld 44. In this case, the monobloc with the groups formed and emptied of acid free before closing comes immediately after such a emptying operation, sealed by means of a heat seal with the cover 45 carried by the chimney 46, and closed by stamping by a thin disc 47 which can be removed at the moment of activation of the battery by a

  cut along a groove 48 provided during the stamping.

  By this operation, the chimney 46 releases the seat 49 on which will be placed the usual plug of operation

after activating the battery.

  In the various drawings, the heights of the chimneys have been generically indicated in accordance with the plug structures that the various manufacturers will adopt, having no effect on the characteristics of the battery, as well as have none of the diameters of the chimneys other than that they condition the thicknesses of the plastic diaphragms of the weld or the compression seal sealing rings Variations and modifications with regard to the forms of realization of the chimneys 10 and Illustrated lids are possible without departing from the scope of the present invention provided that it is always a "maintenance-free" type battery kept charged with only the acid absorbed in the plates and separators, with absolutely sealed closure at the air inlet, the elimination of hydrogen gas remaining limited by the permeability of the material plastic and by recombination with the active ingredient completely exposed to the electrolyte always saturated

by the gases.

Claims (4)

  1 Maintenance-free type lead-acid battery, kept charged after formation and substantially with only acid absorbed by plates and separators, characterized by the fact that: a) it is contained within a monobloc or thermoplastic container with lid welded to it by fusion of the edges; (b) the grids and conductors are of antimony lead alloy, particularly of lead-calcium tin; c) the active substance electrochemically formed in monoblock is constituted by Pb O 2 in an amount greater than 90% of the active active material and by Pb in an amount greater than 95% of the negative active material, which also comprises sulfonated compounds organic compounds in an amount of not more than 1% and alkali metal salts in the amount which results from the displacement of the alkalis of the salts of said organic sulfonated compounds; (d) the formation acid is removed so that not more than 12% of the active ingredient remains and in the separators not more than 15% and overall not more than 25% of the active ingredient total acid required to provide the nominal capacity; e) the density of the residual acid at the beginning of the storage of the battery is between 1,150 and 1,300;   f) the various chimneys practiced by stamping   on the cover mentioned above are hermetically closed by welding the corresponding plugs or plugs or in any case fixed thereto without any escape.   Storage battery according to Claim 1, characterized in that each shutter or plug, which is sealed, resists a negative pressure of 0 to 0.1 atm and a positive pressure generated at   the interior by the development of gases from 0 to 0.35 atm.   3 battery according to claims 1 and 2, characterized in that the various chimneys are closed   by single or multiple thermoplastic strips welded to their edges directly or by an intermediate adhesive.   4 battery according to claim 3, characterized in that the various chimneys are closed by means of a heat-sealing of a composite strip consisting of a thermoplastic layer and a metal upper layer. Battery according to Claim 4, characterized in that the metal upper layer of the composite strip is provided with a tear-off device. 6. Battery according to claim 1, characterized in that the various chimneys are closed by a diaphragm made to be stamped at the same time as the lid and that said lid is heat-sealed on the   monoblock containing the elements, after electrochemical formation of the plates and emptying of the acid not absorbed by the plates, and by the separators; said shutter diaphragms being cut off at the time of battery activation.