WO1995015587A1

WO1995015587A1 - Improved grid alloy for lead-acid battery

Info

Publication number: WO1995015587A1
Application number: PCT/AU1994/000737
Authority: WO
Inventors: Shi Xue Dou; You Xiao Chen; Ben Li Luan; Hui Jun Zhao; Hua Kun Liu
Original assignee: Shi Xue Dou; You Xiao Chen; Ben Li Luan; Hui Jun Zhao; Hua Kun Liu
Priority date: 1993-11-30
Filing date: 1994-11-30
Publication date: 1995-06-08

Abstract

A grid alloy for use particularly, but not exclusively, ensealed, maintenance free lead-acid batteries is defined. The grid alloy includes a component or components which preferably improve mechanical strength of the grid and/or prevent or at least reduce the formation of lead sulphate as a corrosion product and/or which improves the surface state of the grid material and/or which inhibit the deposition of various metals on crystalline boundaries of the alloy. In particular, the grid alloy can include group 1A and/or group 5A metallic elements and/or Ag, more particularly As and/or Bi, K and/or Na and optionally Ca and/or Li, Sn and/or Cu, Al and/or Mg and/or Zn.

Description

IMPROVED GRID ALLOY FOR LEAD-ACID BATTERY

Technical Field The present invention relates to improvements in lead-acid batteries and, in particular, to improvements in composition of the grids used in lead-acid batteries.

Background Art Lead storage cells, or lead-acid batteries, have been known for many years. A lead storage cell consists essentially of two lead gratings, one impregnated with lead to provide abundant surface area for reaction and the other impregnated with lead dioxide Pb0₂. The grids are inserted in a solution of sulphuric acid, H₂S0₄, and, when the grids are connected together by a conductor, an electric current will flow due to anodic and cathodic reactions on the grids. The reactions are totally reversible, which enables the battery to be charged and discharged. The well-known electrolytic reaction can be summarised as follows: discharge Pb + Pb0₂ + 2S0₄ ^2" + 4H⁺ ► 2PbS0₄ + 2H₂0

Charge

Due to inefficiencies in this type of cell, regular maintenance is required, in particular regular addition of water to the solution of electrolyte is required, due to some "side" reactions generating hydrogen and oxygen and other paths by which water is lost. Further, lead sulphate is generated by the discharge reaction and is deposited on both grids in the form of crystals. This may cause the storage cell to "go dead" if the crystals grow too large or cover the entire electrode.

To overcome these problems, in particular the problem of required regular maintenance, sealed, maintenance free, lead-acid batteries have been developed. Much research has concentrated on the development of grid alloys for these batteries. At present a grid alloy of composition Pb-Ca-Sn-Al is widely adopted. There are a number of major problems with this type of grid, however.

Firstly, the grid material has low mechanical strength, making it difficult to fabricate large batteries. Secondly, if the hydrogen evolution over-potential is not high enough, the following reaction will take place at the cathode: 2H⁺ + 2e^_ ^ H₂

This will result in the lead of the cathode being corroded to lead sulphate as a corrosion product. This is a problem with Pb-Ca-Sn-Al grid alloys and may result in deformation of the grid and expansion, due to the formation of lead sulphate on the surface of the cathode, which may give rise to short-circuit and battery failure. Further, the formation of lead sulphate as a corrosion product leads to the early capacity decay of the battery.

Disclosure Of The Invention The present invention provides grid alloys for use particularly, but not exclusively, in sealed, maintenance free lead-acid batteries. In particular, the grid alloy of the present invention includes a component or components which preferably improve mechanical strength of the grid and also include a component or components which preferably prevent or at least reduce the formation of lead sulphate as a corrosion product, preferably by maintaining a high hydrogen evolution over- potential.

Preferably, the present invention provides a grid material which incorporates sodium and/or lithium and/or potassium for improving the strength of the grid material and Cu and/or Zn and/or Mg and/or Bi and/or As, for metamorphosing of Pb-Ca alloy, maintaining a high hydrogen evolution over-potential and preventing or reducing the production of lead sulphate as a corrosion product. Preferred components that can be incorporated into the lead grid are from group 5A of the periodic table and group 1A of the periodic table, and most preferably are Bi and Na.

In one aspect the present invention provides a grid alloy for a sealed lead-acid battery, the alloy composition including a proportion of at least one of the elements from group 5A of the periodic table and a proportion of at least one of the elements from group 1A of the periodic table.

Preferably the at least one element from group 5A is As and/or Bi and the at least one element from group 1A of the periodic table is K and/or Na.

Most preferably the at least one element from group 5A is Bi and the at least one element from group 1A is Na.

The grid alloy preferably further includes a proportion of Ca and/or Li, a proportion of Sn and/or Cu and a proportion of Al and/or Mg and/or Zn.

The present invention further provides a grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula: Pb-Ax-By-Cz-Du-Ev, wherein:

A = Ca and/or Li and 0 < x ≤ 1% ; B = Sn and/or Cu and 0 < y ≤ 1.8% ; C = Al and/or Mg and/or Zn and 0 < z ≤ 1% ; D = Bi and/or As and 0 < u ≤ 0.5% ; and E = Na and/or K and 0 < v ≤ 0.5% .

It should be noted that "%" used throughout the present specification is weight %.

Preferably, A = Ca; B = Sn; C = Al; D = Bi; E = Na. Preferably, 0 < x ≤ 0.2% ; 0 < y ≤ 0.8% ; 0 < z ≤ 0.6% ; 0 < u ≤ 0.2% ; 0 < v ≤ 0.2% .

The present invention also provides a grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula: Pb-Ax-Cz-Du, wherein: A = Ca and x = 0.08% ; C = Sn and z = 0.4% ; and D = Bi and u = 0.08% .

The present invention further provides a grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula Pb-Ax-By-Cz-Du-Ev, wherein:

A = Li and 0 < x ≤ 0.1% ; B = Cu and 0 < y ≤ 1.8% ; C = Zn and 0 < z ≤ 1% ; D = Sn and 0 < u ≤ 0.05% ; E = K and 0 < v ≤ 0.02% . The present invention also provides a grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula Pb-By-Cz-Du-Ev, wherein: B = Sn and y = 0.6% ; C = Al and z = 0.02% ; D = Bi and u = 0.1% ; E = Na and v = 0.01% . In a second aspect the present invention provides a process for manufacturing a grid alloy for a lead-acid battery, including the steps of adding Sn, Bi and Al to melted lead and stirring, and adding Ca and Na.

Preferably the Sn, Bi and Al are added at a temperature of 480°C and the Ca and Na are added at a temperature of 500°C.

Preferably the additions of Ca and Na are 120% as much as required for the final alloy composition.

The present invention further provides a process for the manufacture of Pb-Ca-Al-Sn-Bi-Na alloy, comprising the steps of forming an intermediate alloy of Sn, Bi and Na by melting the components together and adding these to Pb-Ca-Al.

Another traditional alloy material for lead-acid battery plate grids is Pb-Sb alloy. The main advantage of an alloy material containing Sb is that lead oxide is formed between the plate grid and active material, significantly improving the cycling performance of the battery. Unfortunately, introducing Sb into Pb-Ca type alloys results in the formation of an intermetallic compound between Ca and Sb which tends to deposit out as it possesses a very high melting point. The positive effect of Ca in the alloy is therefore eliminated and also the corrosion resistance of the alloy is seriously decreased.

Another disadvantage of present sealed lead-acid battery alloys is that it is difficult to get the battery incorporating such alloy grids to work at super low temperatures (i.e. minus 10°C and less) . When used as a car battery, this means that cars have difficultly starting in such low temperatures.

The grid alloy of the present invention preferably also includes a component which preferably improves the surface state of the grid material so that the active material of at least the negative electrode can discharge at super low temperatures. In particular, the alloy of the present invention preferably includes a proportion of Ag.

The present invention in a third aspect provides a grid alloy for a lead-acid battery, the alloy including a proportion of Bi, a proportion of Al, and a proportion of Ag. Preferably, the alloy also includes a proportion of Ca.

The present invention further provides a grid alloy for a lead-acid battery, the alloy having the formula Pb-Ax-By, wherein: A=Ca, and 0.01%≤x≤0.5%;

B=Ag + Bi + Al, and 0 < y ≤ 2% .

Preferably the proportions of Ag, Bi and Al relative to each other range as follows: Ag = 5 - 85% ; Bi = 8 - 85% ; Al = 4 - 84% . More preferably the proportions of Ag, Bi and Al relative to each other are as follows: Ag = 20% , Bi = 40% and Al = 40% .

Preferably the grid alloy has a formula of A=Ca and 0.01% ≤x≤ 0.2% ; B=Ag + Bi + Al and 0 < y ≤ 0.8%.

The present invention yet further provides a grid alloy for a lead-acid battery of formula Pb- (0.08%-0.1%)Ca- (0.05%-0.1%)Bi_χAl_yAg_z , wherein: x=0.8-0.85, y=0.05-0.15 and 2=0.05-0.1 . The present invention yet further provides a grid alloy for a lead-acid battery, having a composition, Pb-0.08%Ca-0.5% (Al+Bi+Ag) , wherein the proportions of Al:Bi:Ag relative to each other are 40:40:20. The addition of Ag preferably improves the surface state of the grid material so that it connects well with the active material and enables the battery to function even at low temperatures. The addition of Bi preferably increases the hydrogen evolution over potential of the alloy, so as to improve performance of the battery and the surface state of the alloy and to reduce the amount of lead sulphate in the corrosion product. Al is a fine surfactant which preferably modifies the surface state of the alloy and inhibits the formation of lead sulphate.

The addition of Ag to the alloy preferably also inhibits the deposition of Ca, Al and Bi on crystalline boundaries and can therefore produce an alloy possessing excellent anti-corrosion performance.

In a fourth aspect the present invention provides a process for manufacturing a grid alloy for a lead-acid battery, the alloy having a composition of formula Pb-Ca-Bi-Al-Ag, comprising the steps of adding Bi-Al-Ag ternary alloy to Pb-Ca alloy.

Preferably, in the ternary alloy, Ag, Bi, Al are in the proportions Ag=5-85% ; Bi=8-85% and Al=4-84% ; the ternary alloy is made up at melting temperature and the ternary alloy is then added to melted Pb-Ca alloy. Preferably, the Bi is initially melted then Ag and Al are added at 500°C, the mixture and temperature being maintained for 20 minutes, the resultant ternary alloy is then added to melted lead at 500 to 520°C with stirring, Ca then being added to the melted lead in a proportion greater than that required for the final composition.

Preferably Ca is added in an amount 120% of the desired amount of Ca in the final composition. Modes For Carrying Out The Invention Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described in a non-limiting way, with reference to a number of examples. In one process for the manufacture of grid alloys in accordance with the present invention, the alloy components were taken (any combination of components given above may be taken in any of the proportions given above) and melted together at 480 to 500°C, stirred and cast into a grid with the temperature of the grid mould being maintained at 140 to 160°C. Additional standard components of a grid for the sealed battery were added to form a pasted plate, within the period of 17 to 19 hours after formation of the grid, and were then aged for 3 days. The electrode could then be used in the fabrication of batteries. Example 1

This is an example of a process for manufacturing an alloy containing Pb, Ca, Sn, Al, Na and Bi.

The composition purity of the starting materials was as follows: Pb (Fe<0.002%, Sb<0.002% impurities); Ca>99%; Sn, 99.9%; Al, 99.9%, Na>99%; Bi>99%

The final alloy composition was: Pb-0.08%Ca-0.12%Bi-0.05%Na-0.27%Sn-0.03%A1

The process for manufacture of this alloy composition was as follows: The lead was melted and Sn, Bi, and Al were added at a temperature of 480°C with stirring for 10 minutes. Stirring was maintained and then Ca and Na were added at a temperature of 500°C. The proportions of Sn, Al and Bi added to the mix were the same as shown in the final alloy composition above. Additions of Ca and Na were 120% as much as shown in the formula.

The final alloy composition was analysed either by atomic absorption analysis or titration analysis to determine composition. A generalised method for formation of an alloy with components Pb, Ca, Al, Sn, Bi and Na, was as follows. The components were taken in their desired proportion and an intermediate alloy was first made using Sn, Bi and Na, melting the components together to form the intermediate alloy. The dispersion of Sn and Bi on the surface of the Pb-Ca-Al alloy, preferably greatly increased the surface activation energy, and hence prevented Pb0₂ from transforming to PbS0₄. The addition of Na was very effective for the further strengthening of the alloy.

The alloy of example 1 possessed good mechanical properties with a Brinell Hardness HB = 14.8kg/cm² and a tensile strength σb of 5.12kg/cm², had excellent corrosion resistance and a high hydrogen evolution over- potential as well. The anodic corrosion product of the positive grid was Pb0₂. Because of the low electric resistance, the forming time was shortened by 3 to 4 hours, and the manufacture technique was simple and could be put into effect by use of common facilities. All the technical data of a sealed battery manufactured with the alloy in accordance with the present invention reached Japanese industry standards . The following example alloy compositions were also formed using similar techniques as for example 1. The subscripted numbers are percentages of total composition. Example 2. PbCa_{0 09}Sn₀_₂Al₀_₀₂Bi_{0 1}Na_0-02 3. PbCa₀_ - B→L_Q_₁ Li₀_₀₁

4 . PbCa_{0 1}Bi₀ _ ₁₄Cu_{0 05}

5 . PbCa_{0 08}Sn_{0 4}Bi_{0 08}

6 . PbLi₀ _ _gCu₀ _ ₈Zn₀ _ ₅Sb₀ _ ₀₂K₀ _ ₀₂ 7 . PbSn₀ _ _gAl₀ _ ₀₂Bi_{0 1}Na₀ _ ₀₁

In each further example excellent strength improvement and increases in surface activation energy were observed. Furthermore, the alloys showed excellent corrosion resistance and high hydrogen evolution over-potential.

The performance of preferred compositions of the first aspect of the invention against the Japanese standard for battery performance parameters for (1) a small sealed maintenance free battery; and (2) a large scale industrial battery; are shwon respectively in the following tables 1 and 2 : Table 1. Small Sealed Maintenance Free Battery

Performance Japanese Standard Preferred Parameter SBA-2101-88 Compositions of First Aspect

capacity ≥95% (3rd cycle) ≥100% (1st cycle) high rate ≥27 mins (1CA) , ≥35mins (1CA) , discharge OCA not >5 mins OCA) required) overcharge C≥95% C=100% seal reaction ≥90% ≥99% efficiency safety no leakage no leakage storage property ≥60% (stored for ≥78% (stored for 6 months) 6 months) cycle life 200 cycles (80% >600 cycles discharge) (80% discharge)

Table 2. Comparisons Of Large Scale Stationary Battery

Performance Japanese Standard Preferred Parameters SBA 3018-82 Compositions Of First Aspect

capacity ≥95% (5th cycle) 100% (2nd cycle) maximum discharge lmin, (3CA) , 5 qualified current seconds (6CA) , terminal not melted self discharge >0.2%/day <0.1%/day Performance Japanese Standard Preferred Parameters SBA 3018-82 Compositions Of First Aspect

seal reaction ≥90% ≥98% efficiency over charge C≥95% C=100% constant voltage 600 days > 5 years charge life safety no leakage and qualified deformation

This battery has already been applied in the areas of power supply system, communication, UPS, vehicles, miner's lamps etc. Example 9

Preferably, the composition purity of the starting materials was as follows: Pb>99.8% (Fe<0.002% Sb<0.002%) ; Ca>99% ; Ag>99% ; Bi>99% .

The final alloy composition was as follows: Pb-0.08%Ca-0.5% (Ag + Bi + Al) , wherein Ag, Bi and Al were in the proportions 20:40:40. As a first step, Bi was melted in a crucible, then Ag and Al were added at 500°C and maintained for 20 minutes. The resultant ternary Ag, Bi, Al alloy was added to the melted lead at 500 to 520°C with stirring, then Ca was added with an amount of 120% of that required for Ca in the final formula.

Additional standard components of a grid for the sealed battery were added to form pasted plates, within a period of 17 to 19 hours after formation of the grids, and were then aged for 3 days. The electrode grid could then be used in the fabrication of batteries. Example 10

Pb-0.08%Ca alloy was made up in a common melting furnace at a temperature of between 500-510°C and a 80%Bi-15% Al-5%Ag ternary alloy was made up in a crucible furnace at 400°C. The ternary alloy was then added according to the proportion of 0.05% to the Pb-0.08% Ca alloy. Then electrode plate grids for sealed battery in 12V38Ah were casted at temperature of 500°C±10°C. Example 11

Pb-0.1% Ca alloy was made up at 510°C 80%Bi-10%Al-10%Ag ternary alloy was made up. The ternary alloy was then added according to the proportion of 0.1% to Pb-0.1%Ca alloy. Then electrode plate grids of sealed lead-acid battery in 12V100Ah were casted at 500°C with the alloy.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A grid alloy for a sealed lead-acid battery, the alloy composition including a proportion of at least one of the elements from group 5A of the periodic table and a proportion of at least one of the elements from group 1A of the periodic table.

2. A grid alloy in accordance with claim 1, the at least one element from group 5A being As and/or Bi and the at least one element from group 1A of the periodic table being K and/or Na.

3. A grid alloy in accordance with claim 2, the at least one element from group 5A being Bi and the at least one element from group 1A being Na.

4. A grid alloy in accordance with any one of claims 1, 2 or 3, further including a proportion of Ca and/or Li, a proportion of Sn and/or Cu and a proportion of Al and/or Mg and/or Zn.

5. A grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula: Pb-Ax-By-Cz-Du-Ev, wherein:

A = Ca and/or Li and 0 < x ≤ 1% ;

B = Sn and/or Cu and 0 < y ≤ 1.8% ;

C = Al and/or Mg and/or Zn and 0 < z ≤ 1% ;

D = Bi and/or As and 0 < u ≤ 0.5% ; and E = Na and/or K and 0 < v ≤ 0.5% .

6. A grid alloy in accordance with claim 5, wherein A = Ca; B = Sn; C = Al; D = Bi; E = Na.

7. A grid alloy in accordance with claim 6, wherein: 0 < x ≤ 0.2% ; 0 < y ≤ 0.8% ; 0 < z ≤ 0.6% ;

0 < u ≤ 0.2% ; 0 < v ≤ 0.2% .

8. A grid alloy in accordance with claim 6, wherein: x = 0.08%; y = 0.27%; z = 0.03%; u = 0.12%; v = 0.05%.

9. A grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula: Pb-Ax-Cz-Du, wherein: A = Ca and x = 0.08% ; C = Sn and z = 0.04% ; and D = Bi and u = 0 . 08% .

10. A grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula Pb-Ax-By-Cz-Du-Ev, wherein:

A = Li and 0 < x ≤ 0.1% ; B = Cu and 0 < y ≤ 1.8% ; C = Zn and 0 < z ≤ 1% ; D = Sn and 0 < u ≤ 0.05% ; E = K and 0 < v ≤ 0.02% .

11. A grid alloy for a sealed lead-acid battery, the alloy having a composition of general formula Pb-By-Cz-Du-Ev, wherein:

B = Sn and y = 0.6% ; C = Al and z = 0.02% ;

D = Bi and u = 0.1% ; E = Na and v = 0.01% .

12. A process for manufacturing a grid alloy for a lead-acid battery, comprising adding Sn, Bi and Al to melted lead and stirring, adding Ca and Na.

13. A process in accordance with claim 12, wherein the Sn, Bi and Al are added at a temperature of 480°C and the Ca and Na are added at a temperature of 500°C.

14. A process in accordance with claim 12 or 13, additions of Ca and Na being 120% as much as required for the final alloy composition.

15. A process for the manufacture of Pb-Ca-Al-Sn-Bi-Na alloy, comprising the steps of forming an intermediate alloy of Sn, Bi and Na by melting the components together and adding these to Pb-Ca-Al.

16. A grid alloy for a lead-acid battery, the alloy composition including a proportion of Bi, a proportion of Al, and a proportion of Ag.

17. A grid alloy in accordance with claim 16, the composition of the alloy further including a proportion of Ca.

18. A grid alloy for a lead-acid battery, the alloy having the formula Pb-Ax-By, wherein:

A=Ca, and 0.01%≤x≤0.5%;

B=Ag + Bi + Al, and 0 < y ≤ 2% .

19. A grid alloy according to claim 18, wherein the proportions of Ag, Bi and Al relative to each other range as follows:

Ag = 5 - 85% ; Bi = 8 - 85% ; Al = 4 - 84% .

20. A grid alloy according to claim 19, wherein the proportions of Ag, Bi and Al relative to each other are as follows:

Ag = 20% , Bi = 40% and Al = 40% .

21. A grid alloy according to any one of claims 18 to 20, wherein: A=Ca and 0.01% ≤x≤ 0.2% ; B=Ag + Bi + Al and 0 < y ≤ 0.8% .

22. A grid alloy for a lead-acid battery of formula Pb- (0.08%-0.1%) Ca- (0.05%-0.l%)Bi_xAl_yAg_z , wherein: x=0.8-0.85, y=0.05-0.15 and z=0.05-0.1 .

23. A grid alloy according to claim 21, wherein A = Ca and x = 0.08% ; B = Ag + Bi + Al and y = 0.05% ; and the proportion of Ag, Bi, Al in B is 5%, 80%, 15% respectively.

24. A grid alloy according to claim 21, wherein A = Ca and x = 0.1%; B = Ag + Bi + Al and y = 0.1% ; and the proportion of Ag, Bi, Al in B is 10%, 80%, 10% respectively.

25. A grid alloy for a lead-acid battery, having a composition, Pb-0.08% Ca-0.5% (Al+Bi+Ag) , wherein the proportions of Al:Bi:Ag relative to each other are 40:40:20.

26. A process for manufacturing a grid alloy for a lead-acid battery, the alloy having a composition of formula Pb-Ca-Bi-Al-Ag, comprising the steps of adding Bi-Al-Ag ternary alloy to Pb-Ca alloy.

27. A process according to claim 26, wherein in the ternary alloy Ag, Bi, Al are in the proportions Ag=5-85% ; Bi=8-85% and Al=4-84%, and the ternary alloy is made up at melting temperature and then added to melted Pb-Ca alloy.

28. A process according to claim 27, wherein Bi is initially melted then Ag and Al are added at 500°C, the mixture and temperature being maintained for 20 minutes, the resultant ternary alloy is then added to melted lead at 500 to 520°C with stirring, Ca then being added to the melted lead in a proportion greater than that required for the final composition.

29. A process according to claim 27 or 28, wherein the Ca is added in a proportion of 120% of that required in the final formula.