WO2010058240A1

WO2010058240A1 - Low water loss battery

Info

Publication number: WO2010058240A1
Application number: PCT/IB2008/003212
Authority: WO
Inventors: Surendra Kumar Mittal; Basab Chakraborta
Original assignee: Exide Industries Ltd; Daramic, Llc
Priority date: 2008-11-19
Filing date: 2008-11-19
Publication date: 2010-05-27
Also published as: WO2010058240A8

Abstract

The invention discloses a low water loss battery, in particular lead-acid battery, with improved reduction in the rate of water loss, wherein a treated separator against antimony poisoning and an additive in conjunction with the treated separator are provided in the said battery. The separator is treated with chemical agents like water-soluble, non-ionic surfactants. The additive can be zinc or a zinc compound, e.g. zinc sulfate.

Description

LOW WATER LOSS BATTERY

BACKGROUND OF THE INVENTION

I. Field of the Invention

The invention relates in general to lead-acid storage batteries, and, more particularly, to a low water loss battery with improved reduction in the rate of water loss.

II. Description of the Prior Art

In automobile industry, the battery grid is formed of a lead-based alloy. Pb- Ca-Sn alloy is used for the negative electrode of a lead-acid battery. However, using said alloy for the positive grid of the battery makes the battery very sensitive and reduces the cycling ability. In heavy-duty applications, it poses a problem. To provide battery grids with sufficient mechanical strength and hardness, as well as with longer cycle life by causing improved electrical conductivity, a lead-antimony alloy containing from about 1 to 2% by weight of antimony has been used for the preparation of positive grid for lead-acid batteries. The antimony also improves the corrosion resistance of the positive plate against acid attack, and increases the ability of the battery for recovery from deep discharge cycles.

During the cycling of conventional batteries, which use antimony alloy grids, the decline of the voltage at the end of a recharge is recorded with progressing cycle life. The voltage decrease occurs mainly during the overcharge part of the recharge, that is, when only the gassing reactions are involved. It has been found that primarily the hydrogen evolution at the negative electrode that becomes facilitated and the reaction takes place at a lower voltage level. The reason for this behavior is that in the event of corrosion of the grid of hybrid batteries, the antimony comes out while charging. Due to corrosion, antimony releases from the alloy as antimony- (+V)-ions and is mostly adsorbed at the lead dioxide inside the positive electrode. Some of the antimony (+V)- ions diffuse through the separator, used as a distance-keeping component between the positive and the negative electrodes, and get into contact with the negative electrode, where they are reduced to antimony-(+lll)-ions, and are also finally reduced to metallic antimony. On subsequent charging, antimony gets deposited on the negative electrode, that is, the antimony plates out onto the negative electrode. This metallic antimony deposition is considered to be "poisonous", because, it allows for evolution of gaseous hydrogen to proceed more easily than what is achieved from pure lead, and consequently, such phenomenon results in the loss of water. It also facilitates the hydrogen evolution with all subsequent negative effects. Excess charge develops into electrolysis of water. The process of electrolysis starts prematurely, even at normal charging voltage. Thus, the major problem with the use of lead-antimony alloys in grids has been the transfer of the antimony to the negative plate during cycling where it increases the rate of gassing. Facilitated hydrogen evolution means a lower charging efficiency, resulting in higher water consumption, increased battery temperature and reduced shell life.

Conventional automotive batteries using lead-antimony grids typically containing up to 4.5% by weight of antimony, show a relatively high magnitude of float current at the completion of charging. The electrode plates in a maintenance-free battery, ideally, should accept only a small current during constant voltage overcharge so that only minimum gas generation occurs with the accompanying water loss being minimized.

It would be desirable to reduce the amount of antimony in the positive grid alloy in order to reduce antimony poisoning and to improve the end-of-charge voltage characteristics. Using lead-calcium-tin alloy for the positive grid helps to make for water loss, but, in such cases, the battery becomes very sensitive, cycling ability comes down, and in heavy-duty applications, it poses a problem. Lead-calcium alloys containing traces of arsenic, selenium, tellurium or manganese and tin exhibit good cycling capabilities, but cause an increase in current and consequently result in an increase in water loss. Antimony alloys, on the other hand, give good cycling duty. Hence, substantial advantages being achieved from lead-antimony alloys in positive grids, there should be some technical solution for counteracting the undesirable effect of antimony "poisoning", to yield a "foolproof" result.

Studies have shown that antimony does not deposit uniformly on the negative grid surface. Rather, it deposits in the form of clusters or peaks. It is also found that the hydrogen evolution rate and the amount of antimony are proportional. Antimony, which grows as dendrites or whiskers, allows for easy hydrogen generation at the tip of the dendrites. It has, therefore, been observed that the antimony dendrites cause higher degree of water loss.

Several ideas have been proposed in an attempt to overcome the aforesaid difficulty/ problem. Prior art teachings on low water loss technologies suggest that various battery separator types retard the antimony poisoning of the negative plate and thereby reduce the hydrogen evolution and, consequently, water loss of lead acid batteries. The basic principle is that organic molecules released from the separator are adsorbed on the antimony sites of the negative electrode and thereby inhibit the catalytic effect of the antimony on the hydrogen evolution [W. Boehnstedt, Journal of Power Sources (1993) 211 -220].

It is well known that the effects of antimony poisoning can be retarded by the use of rubber (natural rubber being a cis- 1 ,4-polyisoprene) separators. This is caused due to a chemical interaction, whereby, in the presence of extracts from rubber separators, antimony is deposited on the negative electrode in a different modification, which is relatively less poisonous, and which in a way, reduces the hydrogen evolution reaction. This results in comparatively less total antimony deposition. However, rubber separators are quite brittle and difficult to handle and also have other weak points.

In car batteries, cellulosic separators were the most commonly used battery separators for decades. One of their advantages over other car battery separators (e.g. sinter-PVC separators, glass fiber separators) is the reduction of the battery water loss by retardation of the antimony poisoning effect.

Polyethylene separators, on the other hand, are superior to cellulosic separators, in most of the aspects, and offer favorable property characteristics, such as, minimized electrical resistance, low acid displacement, high oxidation stability, excellent processability, excellent mechanical properties, except lack of significant antimony poisoning retardation. Because of the inherent limitations of cellulosic separators, several approaches were tried in order to modify the polyethylene separators, until a new polyethylene separator, provided with "chemical agent(s)", such as water-soluble, non-ionic surfactants (said separators, so modified, being hereinafter referred to as "treated separator", and described, in detail, hereinafter), was developed with similar effect with regard to antimony poisoning retardation of cellulosic separators, while maintaining all other superior performance properties of polyethylene separators. Antimony was found to be deposited on the negative electrode in a far less dangerous form. The afore-mentioned "treated separator" was found to exhibit the ability to retard antimony transfer to the negative plates and to reduce the water loss to the level of batteries assembled with cellulosic separators.

The aforesaid "treated separator" is made from filled polyolefins and is provided with "chemical agent(s)", formed of one or more water soluble surfactants, such as herein described. The surfactants used are non-ionic surfactants, which consist of a non-polar and a polar part and are applied either on the surfaces of the separators, or on the side of the separator turned towards the negative electrode, or on the side turned towards the positive electrode or on both the sides of the separator, or these can be added to the mixture for the production of filled poly-olefin separators. Examples of said surfactants, among others, are oleylaminooxethylate, stearylaminooxethylate, tallow fatty aminoxethylate, coconut oil aminooxethylate, coconut oil acid diethanol amidoxethylate, coconut oil acid monoethanol amidoxethylate, dodecanedioic-acid-N,N-diethylamide, fatty alcohol oxethylate such as decylalcohol oxethylate, octylalcohol-oxethylate, coconut oil alcohol oxethylate, tallow fatty alcohol oxethylate, stearyl alcohol oxethylate and oleyl alcohol oxethylate, oleic acid amideoxethylate, fatty acid oxethylate such as tallow fatty acid oxethylate and tall oil fatty acid oxethylate, oxoalcoholoxethylate with 8 to 20 carbon atoms in the alcohol residue, fatty acid glycerinesteroxethylate such as polyoxethylene glycerine monolaurate, - stearate, oleate or palmitate and castor oil oxethylate as well as fatty acid sorbitan ester oxethylate of the Tween type. The surfactant concentration which is used, in reference to the accumulator electrolyte, is chosen to be greater than 0.03 g/l, preferably greater than 0.08 g/l and in particular greater than 0.16 g/l. In reference to the separator surface, the surfactant concentration is chosen to be greater than 0.1 g/m², preferably greater than 0.25 g/m² and in particular greater than 0.5 g/m².

The effect of said organic chemical compounds provided on the separator, as surfactants, on the performance of the lead-acid battery was assessed by means of a water-loss test, in which, automotive batteries were fully charged before an overcharge at a constant voltage of 14.4 V, started for several weeks. The current was recorded, as shown in Fig. 1 of the accompanying drawings, which illustrates a graph showing the water loss test carried out on a lead-acid battery having a "treated separator", when compared to a standard polyethylene (PE) separator. The higher current level at the start is due to residual lead conversion, that is, as compensation for some prior self- discharge. The current increases slightly with time due to poisoning of the negative plates by antimony or other elements that are more noble than lead. In the case of lead-calcium alloys, traces of nickel, selenium, tellurium or manganese and tin can cause an increase in current. When using the aforesaid "treated separator", made of porous polyethylene containing the aforesaid "chemical agent(s)", the current flow was found to be reduced, as illustrated by the lower curve in Fig. 1.

The weight loss that these batteries exhibit, due to decomposition of water by electrolysis, is proportional to the total overcharge, that is, the integral of current over time, in accordance with Faraday's law. The said "chemical agent(s)", provided on/ in the "treated separator" cause(s) to reduce the water loss to an extent of 30- 40%. However, this reduction is not good enough.

The details of the aforesaid "treated separator" have been provided in U.S. Patent specification No. 5,246,798, which is mentioned herein by way of reference.

Water loss reducing effect is also known to be caused by additives in the battery. One such additive and its use for the purpose of minimizing water dissipation in an electrolytic cell has been described in U.S. Patent specification No. 3,928,066A. The additive used is a quaternary ammonium compound wherein there has been substituted for all the hydrogen atoms an aliphatic and/or aromatic group. As a general reference, such or other additives, described hereinafter, are denoted as "additive".

Zinc has been shown to be a beneficial element as "additive" in reducing the float current of lead acid batteries. U.S. Patent No. 4,086,392 issued to Mao and Rao, discloses that the addition of elemental zinc or a zinc affording compound to Pb-Ca-Sn and Pb-Cd-Sb batteries in certain levels, diminishes the required float current. Mao and Rao have shown that the addition of a small amount of zinc to the electrolyte (for example, 6 grams of ZnSO4.7H2O per battery) decreases the float current of SLI batteries by almost 50% when floated at 51.60 C and 2.35 V. Addition of zinc to the electrolyte diminished the required float current, and consequently the water consumption in voltage regulated charging modes. In another example, zinc was added to the positive and negative active material in an amount of 340 ppm. The float current at 51.60° C was reduced by 49% at the hgh float voltage of 2.76 V per cell. Smaller amounts were less effective but still reduced the oxygen and hydrogen evolution float currents.

Zinc has been shown to reduce gassing, and, thus, the zinc leached into the electrolyte reduces gassing and enhances stability of the potentials. Zinc is the only element other than bismuth, which is effective in reducing both the positive and negative gassing currents. Based on the amount of zinc added to the active material in the Mao and Rao work, the reduction in gassing currents is achieved. Zinc stabilizes the plate potentials upon float and reduces the effects of other impurities which might be present particularly on the negative active material. Zinc can stabilize the potential of the active material, and reduce the float currents, which cause gassing, and reduce water usage when added to the active material in amounts of 350 ppm or more. The stabilized currents permit improved recharge and ultimately higher capacity and longer life. The addition of zinc as an additive can give the maintenance-free battery a low water usage than that which could be attained with lead-calcium-tin alloy grids. Zinc was believed to deposit on or plate out on the negative electrodes during voltage regulated overcharge.

However, the above prior art approach of reducing the float currents in batteries by addition of zinc and its compound(s) does not cover the normal hybrid batteries (1.6% Sb, Positive electrode, and Pb-Ca, Negative electrode), where its effect is minimal due to the morphology of antimony deposition on the negative plate surface.

Water loss is a concern area in tropical countries. Life of lead-acid batteries in tropical zones is appreciably lower than that obtained in the cold temperature climates. In the tropical countries, the challenge is to make the battery last under severe operating conditions which may include in addition to high ambient temperatures, sluggish vehicle movement in the city centers, frequent stops/ starts, rough road conditions, excessive running of the utility vehicles and less dependable charging system. These operating conditions do entail an element of cycling together with occasional deep discharges as well as high propensity of positive grid corrosion and more importantly, greater water loss. This seems to be an area of genuine concern for those operating in the tropical part of the world.

Despite the advances made in the art for dealing with the problem of reducing the water loss in the batteries, there is a continued need to address the said problem of further minimizing water loss in batteries, particularly for use in the tropical climates. The principal object of the present invention is to achieve a substantial reduction in the rate of water loss in a battery of the type as herein described, which had not yet been possible by adopting various means/ techniques, as mentioned hereinbefore.

SUMMARY OF THE INVENTION

To achieve the object of the invention, it is proposed to provide a low water loss battery having a "treated separator" and an "additive" in conjunction with the treated separator.

Accordingly, in one embodiment, the invention provides a low water loss battery such as a lead-acid storage battery, with improved reduction in the rate of water loss, characterized in that a separator, treated to retard antimony poisioning of the negative plate is used, in conjunction with an additive in the said battery.

Preferably, the separator used in the above low water loss battery is a polyethylene separator containing "chemical agent(s)", e.g. water-soluble, non-ionic surfactants, while the additive used in conjunction with the treated separator is zinc and its compound(s), and in particular, zinc sulphate ZnSO4.7H2O.

According to the invention, the objects are achieved by the features of the low water loss batery, as described hereinafter. Advantageous refinements of the invention are specified in the following detailed description of the invention.

BRIEF DESCRIPTION QF THE DRAWINGS

The above features of an embodiment of the present invention and their relative advantages will be apparent to those having ordinary skill in the art upon reading the following detailed description of the preferred embodiment of the invention with reference to the accompanying drawings, in which : Fig. 1 is a graph showing the float, current for the water loss test carried out on a lead-acid battery having a "treated separator",, when compared to a standard PE separator, according to prior art ;

Figures 2A₅ 2B and 2C are graphs respectively showing the equilibrium float currents of hybrid battery with "additive" only (Battery A)₁ hybrid battery with "treated separator" (Battery B) and hybrid battery with both "additive" and "treated separator" according to an embodiment of the invention (Battery C), when compared to a (reference) normal hybrid battery (X1), each of the batteries being floated at a temperature of 60^e C for a period of first 21 days ;

Figures 3A, 3B and 3C are graphs respectively showing the equilibrium float currents of the aforesaid Battery A₁ Battery B and Battery C, when compared to the (reference) normal hybrid battery (X1), each of the batteries being floated at a temperature of 60³ C, subsequently, for a period of second 21 days ;

Fig. 4 is a graph comprising histograms showing the comparative water loss characteristics of the aforesaid Battery A, Battery B and Battery C, with reference to the (reference) normal hybrid battery (X1 ) ;

Figures 5A and 5B are graphs showing the relationships between water loss and the "additive" concentration, in the Battery C, according to the present invention, the battery being floated at a temperature of 60^s C, for periods of first 21 days and the following second 21 days, respectively ;

Fig. 6 is a graph showing the relationship between water loss and the "additive" concentration, in the Battery C, according to the present invention, the battery being floated at a temperature of 80^s C ;

Fig. 7 is a graph comprising histograms showing the comparative water loss characteristics of the hybrid Battery C according to one embodiment of the present invention, a lead-calcium battery (Y) with both "additive" and "treated separator", according to another embodiment of the invention, as compared to a (reference) normal hybrid battery (X1) ; and Fig. 8 is a graph comprising histograms showing the water loss characteristics of a lead-calcium battery (Y) with both "additive" and "treated separator", according to an embodiment of the present invention, as compared to a (reference) normal calcium battery (X2).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To achieve the objective of the invention, a low water loss lead/ sulphuric acid storage battery is disclosed. In the said embodiment of the low water loss battery, according to the invention, a combination of a polyethylene separator containing "chemical agent(s)" formed of one or more of water-soluble, non- ionic surfactants (referred to as a "treated separator") and an "additive" in conjunction with the treated separator are provided.

The nature of the "chemical agent(s)" of the "treated separator" has been described in U.S. Patent No. 5,246,798, as mentioned hereinbefore. Provision of the "chemical agent(s)", e.g. organic surfactant(s) on/ in the "treated separator" effectively changes the morphology of antimony deposition on the negative plate. It helps in finer distribution by making the antimony distribution more uniform by suppressing the antimony peaks [W. Boehnstedt, The Battery Man, June 2005].

The "additive" which is used in conjunction with the "treated separator" is, preferably, ZnSO4.7H2O, which is known from the prior art described in the U.S. Patent No. 4,086,392, as mentioned hereinbefore, and which is also incorporated herein by reference. Although the effect of reducing the float current by addition of zinc and its compound in a hybrid battery is minimal due to the morphology of antimony deposition on the negative plate surface, but, in presence of the "treated separator", the morphology of antimony deposition is appreciably altered and hence this additive becomes very effective. On the contrary, common additives when used alone, are found to be less effective due to the presence of antimony peaks.

Both the "treated separator" with the specific "chemical agent(s)", as aforesaid, and the particular additive of ZnSO4.7H2O are known per se, and further detailed explanations of these are therefore not necessary in view of the disclosures made in U.S. Patent specifications Nos. 5,246,798 and 4,086,392 respectively.

It has been surprisingly found that the low water loss battery of the present invention having the aforementioned combination of the "treated separator" and the particular "additive", such as herein described, provides, due to a synergistic effect, a substantial improvement in the suppression of the evolution of gaseous hydrogen and the retention of water, as compared to a similar battery not having the said "combination". A convenient method of measuring water loss is to measure the quantity of gas emitted at the anode due to the breakdown of water.

To evaluate the effectiveness of using the combination of the "treated separator" and the "additive" in the lead-acid storage battery, according to the invention, water-loss tests were carried out on the battery. The sample (reference) battery used in the tests is a Normal Hybrid Battery. Hybrid battery is constructed to comprise a positive electrode having a grid made of a lead- antimony alloy containing anywhere from about 1 to 2.5 per cent by weight antimony and more preferably 1.6 to 1.7 per cent by weight antimony and a negative electrode having a grid made of a lead-based alloy comprising lead- calcium/ lead-calcium-tin.

One such normal Hybrid battery was taken for reference purpose (referred to herein as 'Battery X1'). Also, three more Hybrid Batteries were arranged with the following combinations :

(A) Hybrid Battery having an "additive" only (hereinafter referred to as 'Battery A') ;

(B) Hybrid Battery having "treated separator" (hereinafter referred to as 'Battery B') and

(C) Hybrid Battery having both "additive" and "treated separator" (hereinafter referred to as 'Battery C). To prepare the Hybrid Battery of (A) type, containing the zinc additive, the free electrolyte from the Hybrid battery was removed by inverting and draining and then adding a measured amount of the zinc additive of ZnSO4.7H2O to the drained electrolyte and then refilling the battery with the modified electrolyte to the same level and charging to ensure thorough electrolyte mixing.

For conducting the comparative water-loss tests, the aforementioned batteries (A, B, C and X1) were fully charged before an overcharge at a constant voltage of 14.4 V. Each of the batteries (A, B and C) alongwith the reference battery (X1) was floated at a temperature of 60^s C for a period of first 21 days, and subsequently, for a period of following second 21 days. The current was recorded for each case. The current was found to increase slightly with time due to poisoning of the negative plates by antimony. After carrying out the tests, the results were evaluated. The average values of these evaluations were then compared with each other. The comparative analysis of the float current and water loss characteristics of the tree types of batteries, namely, Battery A, Battery B and Battery C₁ in relation to the reference Battery X1 , are presented in Figures 2A, 2B, 2C, 3A, 3B, 3C and 4 of the accompanying drawings.

As shown, when floated at the temperature of 60^s C, at the end of the second 21 days, the equilibrium float current, as recorded, was found to be reduced significantly for the Hybrid Battery C, which was provided with both "additive" and "treated separator". Clearly, the Battery C, with the combination of the particular "additive" and the "treated separator" yields substantially improved efficacy due to the synergistic effect of the combination, that being significantly better than the Hybrid Battery A having "additive" only or the

Hybrid Battery B, having the "treated separator" only. This is also evident from

Figure 4, which illustrates a schematic comparison of the water loss tests, based on Battery X1 (reference Hybrid battery) vis-a-vis Battery A with

"additive" in electrolyte vis-a-vis Battery B with "treated separator" vis-a-vis Battery C (according to the invention) with combination of "treated separator" and "additive" being provided in the electrolyte. From the comparative analysis data, as presented, lead-acid performance is found to have been improved substantially by the use of the combination of the "treated separator" and the "additive", that being significantly better than what is achieved from the reference Hybrid battery (X1).

It is clear that provision of the said combination of the "treated separator" and the "additive" in the low water loss battery, according to the invention, gives the battery significantly lower water usage. The said combination has been found to inhibit the evolution of gaseous hydrogen effectively and thereby attenuating the loss of water significantly. Thus, important synergistic effects are found in using the said combination in the lead-acid batteries.

The amount of the additive of ZnSO4.7H2O used in the battery of the invention should be such that it is sufficient to decrease the float current during constant voltage overcharge and result in lower water losses. The reduction in water loss as a function of zinc sulphate added to the electrolyte, is shown in figures 5A and 5b, where the battery is floated at a temperature of 60^s C, and in Fig. 6, where the battery is floated at a temperature of 80^B C. While the amount of zinc sulphate required may vary depending upon the manner in which it is added to the battery, it has been found suitable to use the additive concentration in the range of from about 0.3 to about 2.0 gm/l in electrolyte. However, for optimization of the concentration of the "additive" and for achieving the desired result of the invention, it is preferable to use the amount of zinc sulphate in the range of 0.5 to 1.1 gm/l in electrolyte, and more preferably 0.6 to 0.9 gm/l in electrolyte.

According to preferred embodiments of the invention, although it is desirable to add the additive of ZnSO4.7H2O into the battery electrolyte, it can also be . applied on the electrode, or it can be added to the active material paste used for the electrodes.

It is to be understood that, apart from using the combination of the "treated separator" and the "additive", the low water loss battery according to the invention, also encompasses ordinary lead sulphuric acid storage battery with conventional electrodes and sulphuric acid as electrolyte. Preferably, the battery is a starter battery for motor vehicles. The low water loss battery according to the invention works successfully in case of Lead Acid batteries used in cars. However, the battery according to the invention, as described herein, is not limited to the battery for a vehicle, but, it is general. Hence, the invention can be used in varying operating conditions and for different types of batteries.

Accordingly, while the invention has been described using a hybrid battery for reference, those skilled in the art will appreciate that the experiment can be conducted with a lead calcium battery, or a lead antimony battery (e.g. with 1 to 2.5 % by weight of antimony in the grids of the positive and negative electrodes), even though a less significant reduction in water loss may be obtained. This can be better understood from Figure 7, which shows the comparative analysis of the water loss test carried on the low water loss battery according to the invention (Battery C), vis-a-vis lead calcium battery with both "additive" and "treated separator" (Battery Y), when compared to the reference Hybrid battery (Battery X1). All the batteries, namely, Battery C, Battery Y and Battery X1 were floated at a temperature of 60^s C and at a constant voltage of 14.4 V for a period of first 21 days, and subsequently, for a period of following second 21 days. Clearly, Hybrid battery having the "additive" and the "treated separator" (Battery C) was found to exhibit a greater reduction in water loss, compared to that of the lead-calcium battery having the "additive" and the "treated separator" (Battery Y).

Figure 8 illustrates a comparative analysis of the water loss test carried on the lead-calcium battery with both Additive and treated separator (Battery Y), as compared to a reference calcium battery (' Battery X2' ), and the corresponding experimental result obtained thereby.

Several battery applications demand superior and better cycle-life characteristics, particularly at medium and higher depth of discharge as well as battery ability to withstand higher operating temperatures, that is high temperature endurance. For heavy-duty applications, lead-calcium grid is not preferred. The calcium presents difficulties in the manufacture of lead acid batteries because of the attendant need for precise control of impurities and the tendency of calcium to oxidize on contact with air. As a consequence, the manufacture of lead acid batteries utilizing calcium is more difficult and more costly than the manufacture of the aforementioned antimony lead batteries. Addition of calcium also results in an increase in the corrosion rate of the positive grid and deformation by elongation of the grid, that is, generation of "growth". The growth tends to impair the electrical connection between the grid and the active material so as to give rise to serious defects such as a decrease in the battery capacity and short-circuiting caused by the deformation of the plate. Lead-Antimony batteries give good cycle life.

The foregoing is to be considered as illustrative only of the principles of the present invention. Depending on the battery under test, the value of equilibrium float current and the water loss, as measured, will vary and can be experimented with. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact embodiment shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the true spirit and scope of the invention in the appended claims, and their equivalents.

Claims

1. A low water loss battery such as a lead-acid storage battery, with improved reduction in the rate of water loss, characterized in that a separator, treated to retard antimony poisioning of the negative plate is used, in conjunction with an additive in the said battery.

2. The low water loss battery according to claim 1 , wherein the treated separator is a polyethylene separator treated with chemical agent(s) like water-soluble, non-ionic surfactants.

3. The low water loss battery according to claims 1 or 2, wherein the additive used in conjunction with the treated separator is zinc and its compound(s).

4. The low water loss battery, according to claim 3, wherein the zinc compound used is zinc sulphate ZnSO4.7H2O.

5. The low water loss battery, according to claim 4 wherein the concentration of the zinc sulphate used in the battery is in the range of 0.3 to 2.0 gm/l in electrolyte.

6. The low water loss battery, according to claim 5, wherein the concentration of the zinc sulphate is in the range of 0.5 to 1.1 gm/l in electrolyte, and more preferably 0.6 to 0.9 gm/l in electrolyte.

7. The low water loss battery, according to any one of claims 1 to 6, wherein the additive is added to the electrolyte.

8. The low water loss battery, according to any one of claims 1 to 6, wherein the additive is added to the active material paste, used for the battery electrodes.

9. The low water loss battery, according to any one of the preceding claims, wherein the battery is a normal Hybrid battery with a positive electrode having a grid made of a lead-antimony alloy containing 1 to 2.5 per cent by weight antimony, and more preferably 1.6 to 1.7 per cent by weight antimony, and a negative electrode having a grid made of a lead-based alloy comprising lead- calcium/ lead-calcium-tin.

10. The low water loss battery, according to any one of the preceding claims, wherein the battery is a lead-calcium battery or a lead-antimony battery.