The present invention relates to an aluminium- and/or lithium-bearing zinc powder for alkaline batteries.

Aluminium-bearing zinc powders are known from EP-A-0427315. In this document protection is asked for a zinc base powder for alkaline batteries, characterized in that it contains 0.005-2% aluminium as well as either 0.0001-0.01 % REM, RE being a rare earth metal or a mixture of rare earth metals ; or, besides zinc and unavoidable impurities, only 0.0001-2% of at least one of the elements indium and REM ; or, besides zinc and unavoidable impurities, only 0.003-2% bismuth and 0.0001-2% of at least one of the elements indium and REM ; or, besides zinc and unavoidable impurities, only 0.005-2% lead and 0.0001-2% of at least one of the elements indium and REM ; or, besides zinc and unavoidable impurities, only 0.005-2% lead, 0.003-2% bismuth and 0.0001-2% of at least one of the elements indium and REM. The first example in this document relates to a powder that is made by atomizing a molten bath with the following composition : 220 ppm Al, 5 ppm La, 12 ppm Ce, 500 ppm Pb, 54 ppm In, the rest being thermally refined zinc. The second example relates to a powder made by atomizing a molten bath with the following composition : 600 ppm Al, 500 ppm Pb, 500 ppm Bi, 100 ppm In, the rest being thermally refined zinc. All other given examples concern powders having aluminium contents going from 0.03 up to 0.06% (all percents given herebefore and hereafter are percents by weight).

The powders according to these examples have in common with each other that they contain at least about 220 ppm Al and that they have a good resistance to corrosion in the electrolyte of the battery before and after partial discharging of the battery. However, they have a drawback in that they may cause a short circuit in certain types of batteries, among others the LR6-type and smaller types.

The aim of the present invention is to provide an aluminium- and/or lithium-bearing zinc powder for alkaline batteries, which does not cause, or causes to a much lesser extent than the powders according to the examples of EP-A-0427315, a short circuit and which nevertheless has a sufficient resistance to corrosion.

The powder according to the invention is characterized in that it consists of either (1), 1-95 ppm Al, one of 0.001-2% Bi, 0.005-2% In and 0.003-2% Pb, and optionally

0.003-2% Ca ; or (2), 1-95 ppm Al, 0.001-2% Bi, 0.005-2% In and optionally 0.003-2% Pb ; or (3), 1-95 ppm Al, one of 0.001-2% Bi and 0.005-2% In, 0.003-2% Pb and optionally

0.003-2% Ca ; or (4), 1-1000 ppm Li, at least one of 0.001-2% Bi and 0.005-2% In, and optionally 0.003

2% Ca ; or (5), 1-1000 ppm Li, 0.003-2% Pb, 0.003-2% Ca and optionally 0.005-2% In ; or (6), 1-1000 ppm Li, 0.001-2% Bi, 0.003-2% Pb and optionally at least one of 0.005-2

In and 0.003-2% Ca ; or (7), 1-95 ppm Al, 1-1000 ppm Li, at least one of 0.001-2% Bi, 0.005-2% In and 0.003-

2% Pb, and optionally 0.003-2% Ca ; and for the rest of zinc and the unavoidable impurities present in the aforesaid metals, being excluded indium-bearing powders with 50 ppm Al according to the combinations (1) and (3) unless these powders contain calcium.

Indeed, regarding the aluminium in the powder according to the invention, the applicant has found that powder with a low Al content, in contrast to the powders according to the example of EP-A-0427315, does not cause or seldom causes, a short circuit in the battery in which it i used. Likewise, the applicant has found, as will be proved further, that a very low Al content suffices to give the powder an adequate resistance to corrosion, particularly after partial or complete discharging of the battery. The other alloying elements (Bi and/or Pb and/or In) gi the powder a sufficient resistance to corrosion before discharging. Therefore, the powder is suited to any type of alkaline battery such as LR6, LR14, LR20 and others.

Likewise, the applicant has found that the influence of lithium on the gas evolution after parti or complete discharging is similar with that of aluminium. Both elements can therefore be u separately or together.

Here, the following should be noted :

EP-A-0457354 relates among others to zinc powders for alkaline batteries containing 0.01-1 In, 0.005-0.5% in total of one or two of Pb and Bi and 0.005-0.2% in total of one or more of Ca and Al. Many examples of compositions of powders are given : powders without Al, powders with Al > 0.01% and also powders with 25 ppm Al, which however differ from the powder of the invention in that they contain Ca, In and Bi and optionally Pb. No example is given of a lithium bearing powder. However, it is stated that lithium has the same effect as aluminium. Nothing in this document suggests that there is a short circuit problem with heig

RECTIFIED SHEET (RULE 91) ISA/EP

Al contents and that this problem can be solved, without impairing substantially the corrosion resistance of the powder, by limiting the Al content to 1-95 ppm.

JP-A-62176053 describes amalgamated zinc powders containing 0.001-0.5% In, 0.005-0.5% f Pb, 0.005-0.5% Al, 0.005-0.5% of one or more of Tl, Sn, Cd and Ga, 0.0001-0.5% of one or

5 more of Li, Na, K, Rb and Ce and 0.005-0.5% of one or more of Ni, Co and Te. Thus these powders contain at least 6 alloying elements and are moreover amalgamated. From EP-A-0384975 lithium bearing zinc alloys are known which are used for cups for Leclanche batteries. Lithium is added in order to improve the mechanical strength, a feature which has no significance in the case of zinc powders for alkaline batteries. 10

The preferred compositions of the powder according to the invention are subject of the enclosed claims 2-22.

An easy way to produce the powder of the invention consists in adding all additives, which 15 should be present in the powder to be produced (Al and for instance In and Bi), to the molten zinc and to atomize the thereby obtained alloy with gas, water or a mixture of both.

One can also atomize molten zinc containing already a part of the additives (for instance Al and Bi), whereafter the remaining additives (for instance In) are deposited on the atomized powder, either by cementation from an aqueous solution, or by physical deposition from a 20 gaseous phase ("Physical Vapour Deposition" or PVD), or by chemical deposition from a gaseous phase ("Chemical Vapour Deposition" or CVD). It is clear that the cementation technique can only be applied if the additives are more electropositive than zinc. When more additives have to be deposited on the atomized powder, they can be deposited simultaneously or separately. 25 One can also atomize molten zinc as such and then deposit all additives on the atomized powder.

It is also possible to introduce a specific additive partly by alloying with the molten zinc and the remainder by deposition on the atomized powder.

Instead of atomization with gas, water or a mixture of both, any technique which is appropriate 30 to convert a molten metal into a powder can be applied, such as for instance centrifugal atomization or casting and grinding of the casted metal.

In case the desired powder contains additives which can be cemented (for instance In), then , still another way to produce the powder consists in preparing a powder with the additives which cannot be cemented and optionally with a part of the additives which can be cemented 35 according to one of the abovementioned methods and making an anode from the thus obtained powder. That anode is introduced in the battery and the additives which can be cemented are added to the electrolyte of the battery, from which they cement on the powder of the anode.

This invention relates therefore not only to a powder such as it is introduced in the battery, but also to a powder such as it is present in the battery.

Example 1

This example proves that zinc base powders according to the invention have a good resistance to corrosion in the electrolyte of the battery after partial discharging of the battery.

There are prepared 7 powders with the following composition : Zn, 500 ppm Pb, 500 ppm Bi, 500 ppm In and respectively 0, 5 ,7 ,16 ,21 ,70 en 280 ppm Al. To this end one starts from thermally refined zinc in molten state to which one adds the alloying elements in the desired amounts.

The thus obtained molten bath is homogenized at 450°C by stirring. The molten alloy is made to flow in a jet of compressed air, thereby producing an alloy powder, the particles of which have substantially the same homogeneous composition as that of the homogeneous molten bath.

The alloy powder is sifted so as to separate thereof the fraction over 500 μm and, as far as possible, the fraction below 104 μm. In this way an alloy powder with a particle size of 104 to 500 μm is obtained.

With the alloy powder one produces batteries of the LR14-type. These batteries are discharged at 2.2 Ohm for 2h. Subsequently on determines at 45°C the quantity of hydrogen which is evolved for 7 days. The results are summarized in the table below.

These results prove that minor additions of Al reduce already considerably the gassing rate.

Example 2

This example proves that zinc base powders according to the invention have a good resistance to corrosion in the electrolyte of the battery after partial discharging of the battery.

Three powders are prepared with the following composition : Zn, 500 ppm In, 500 ppm Bi and respectively 0, 35 and 70 ppm Al. To this end one proceeds like in example 1.

Batteries of the LR14-type are made with the alloy powder. The batteries are discharged at 2.2 Ohm for 9h. Subsequently one determines at 71 °C the hydrogen which is evolved for 7 days. One obtains respectively : 165, 101 and 73 μl/g day.

Example 3

This example proves that zinc base powder according to the invention does not cause any short circuit in the LR6-type battery.

Three powders are prepared with the following composition : Zn, 500 ppm In, 500 ppm Bi and respectively 30, 70 and 325 ppm Al. To this end one proceeds like in example 1.

These powders were supplied to battery-makers for use in batteries of the LR6-type. They have told the applicant that the powder with 325 ppm Al is not suited to that type of battery because it can cause short circuits, whereas the powders with 30 and 70 ppm are suited because they do not cause any short circuit in the same type of battery.

Other typical examples of powder according to the invention have the following composition :

Zn - 30 ppm Al - 250 ppm Bi

Zn - 40 ppm Al - 250 ppm Bi Zn - 70 ppm Al - 250 ppm Bi

Zn - 85 ppm Al - 250 ppm Bi

Zn - 30 ppm Al - 250 ppm Bi - 180 ppm Ca

Zn - 70 ppm Al - 250 ppm Bi - 250 ppm Ca

Zr, - 30 ppm Al - 250 ppm Bi - 45 ppm Ca Zn - 70 ppm Al - 250 ppm Bi - 100 ppm Ca

Zn - 30 ppm Al - 250 ppm Bi - 180 ppm Pb

Zn - 70 ppm Al - 250 ppm Bi - 250 ppm Pb

Zn - 30 ppm Al - 500 ppm Bi

Zn - 40 ppm Al - 500 ppm Bi

Zn - 70 ppm Al - 500 ppm Bi

Zn - 30 ppm Al - 500 ppm Bi - 180 ppm Ca

Zn - 30 ppm Al - 1000 ppm Bi

Zn - 40 ppm Al - 1000 ppm Bi

Zn - 70 ppm Al - 1000 ppm Bi

Zn - 30 ppm Al - 1000 ppm Bi - 180 ppm Ca

Zn - 40 ppm Al - 2300 ppm Bi

Zn - 70 ppm Al - 2300 ppm Bi

Zn - 70 ppm Al - 3000 ppm Bi

Zn - 40 ppm Al - 250 ppm In

Zn - 70 ppm Al - 250 ppm In

Zn - 40 ppm Al - 500 ppm In

Zn - 70 ppm Al - 500 ppm In

Zn - 40 ppm Al - 250 ppm In - 200 ppm Ca

Zn - - 70 ppm Al - 250 ppm In - 200 ppm Ca

Zn - - 40 ppm Al - 500 ppm In - 200 ppm Ca

Zn - - 70 ppm Al - 500 ppm In - 200 ppm Ca

Zn - - 30 ppm Al - 2300 ppm Bi - 180 ppm Ca

Zn - - 30 ppm Al - 3000 ppm Bi - 180 ppm Ca

Zn - - 30 ppm Al - 250 ppm In - 250 ppm Bi

Zn - - 40 ppm Al - 250 ppm In - 250 ppm Bi

Zn - - 70 ppm Al - 250 ppm In - 250 ppm Bi

Zn - - 30 ppm Al - 500 ppm In - 250 ppm Bi

Zn - - 40 ppm Al - 500 ppm In - 250 ppm Bi

Zn - - 70 ppm Al - 500 ppm In - 250 ppm Bi

Zn - - 30 ppm Al - 500 ppm In - 500 ppm Bi

Zn - 40 ppm Al - 500 ppm In - 500 ppm Bi

Zn - 70 ppm Al - 500 ppm In - 500 ppm Bi

Zn - 30 ppm Al - 500 ppm In - 1000 ppm Bi

Zn - 40 ppm Al - 500 ppm In - 1000 ppm Bi

Zn - 70 ppm Al - 500 ppm In - 1000 ppm Bi

Zn - 40 ppm Al - 500 ppm In - 2300 ppm Bi

Zn - 70 ppm Al - 500 ppm In - 2300 ppm Bi

Zn - 70 ppm Al - 500 ppm In - 3000 ppm Bi

Zn - 20 ppm Al - 500 ppm In - 1000 ppm Bi

Zn - 40 ppm Al - 500 ppm In - 1000 ppm Bi - 50 ppm Pb

Zn - 70 ppm Al - 500 ppm In - 1000 ppm Bi - 50 ppm Pb

Zn - 40 ppm Al - 500 ppm In - 500 ppm Bi - 50 ppm Pb Zn - 70 ppm Al - 500 ppm In - 500 ppm Bi - 50 ppm Pb Zn - 40 ppm Al - 250 ppm In - 250 ppm Bi - 100 ppm Pb Zn - 250 ppm Li - 250 ppm Bi Zn - 430 ppm Li - 250 ppm Bi

Zn - 30 ppm Li - 250 ppm Bi - 100 ppm Pb Zn - 50 ppm Li - 250 ppm Bi - 250 ppm Pb Zn - 30 ppm Li - 500 ppm Bi Zn - 50 ppm Li - 500 ppm Bi Zn - 250 ppm Li - 500 ppm Bi Zn - 430 ppm Li - 500 ppm Bi Zn - 50 ppm Li - 500 ppm Bi - 200 ppm Ca Zn - 250 ppm Li - 500 ppm Bi - 100 ppm Ca Zn - 30 ppm Li - 500 ppm In Zn - 50 ppm Li - 500 ppm In Zn - 250 ppm Li - 500 ppm In Zn - 430 ppm Li - 500 ppm In Zn - 50 ppm Li - 500 ppm In - 200 ppm Ca Zn - 250 ppm Li - 500 ppm In - 100 ppm Ca Zn - 250 ppm Li - 1000 ppm In Zn - 430 ppm Li - 1000 ppm In Zn - 50 ppm Li - 1000 ppm In - 200 ppm Ca Zn - 250 ppm Li - 2300 ppm Bi Zn - 430 ppm Li - 2300 ppm Bi Zn - 50 ppm Li - 3000 ppm Bi Zn - 30 ppm Li - 3000 ppm Bi Zn - 50 ppm Li - 2300 ppm Bi - 200 ppm Ca Zn - 250 ppm Li - 250 ppm Bi - 500 ppm In Zn - 430 ppm Li - 250 ppm Bi - 500 ppm In Zn - 30 ppm Li - 250 ppm Bi - 500 ppm In - 100 ppm Pb Zn - 50 ppm Li - 250 ppm Bi - 500 ppm In - 250 ppm Pb Zn - 30 ppm Li - 500 ppm Bi - 500 ppm In Zn - 50 ppm Li - 500 ppm Bi - 500 ppm In Zn - 250 ppm Li - 500 ppm Bi - 500 ppm In Zn - 430 ppm Li - 500 ppm Bi - 500 ppm In

Zn - 50 ppm Li - 500 ppm Bi - 500 ppm In - 200 ppm Ca Zn - 250 ppm Li - 500 ppm Bi - 500 ppm In - 100 ppm Ca Zn - 30 ppm Li - 1000 ppm Bi - 500 ppm In

Zn - 50 ppm Li - 1000 ppm Bi - 500 ppm In Zn - 250 ppm Li - 1000 ppm Bi - 500 ppm In Zn - 430 ppm Li - 1000 ppm Bi - 500 ppm In Zn - 30 ppm Al - 30 ppm Li - 250 ppm Bi Zn - 30 ppm Al - 50 ppm Li - 250 ppm Bi Zn - 70 ppm Al - 30 ppm Li - 250 ppm Bi Zn - 70 ppm Al - 50 ppm Li - 250 ppm Bi Zn - 30 ppm Al - 30 ppm Li - 250 ppm Bi - 180 ppm Ca Zn - 70 ppm Al - 30 ppm Li - 250 ppm Bi - 250 ppm Ca Zn - 30 ppm Al - 250 ppm Li - 250 ppm Bi Zn - 70 ppm Al - 250 ppm Li - 250 ppm Bi Zn - 30 ppm Al - 50 ppm Li - 250 ppm Bi - 180 ppm Pb Zn - 70 ppm Al - 30 ppm Li - 250 ppm Bi - 250 ppm Pb Zn - 30 ppm Al - 30 ppm Li - 500 ppm Bi Zn - 30 ppm Al - 50 ppm Li - 500 ppm Bi Zn - 70 ppm Al - 50 ppm Li - 500 ppm Bi Zn - 30 ppm Al - 250 ppm Li - 500 ppm Bi Zn - 30 ppm Al - 30 ppm Li - 1000 ppm Bi Zn - 30 ppm Al - 250 ppm Li - 1000 ppm Bi Zn - 70 ppm Al - 30 ppm Li - 1000 ppm Bi Zn - 30 ppm Al - 250 ppm Li - 2300 ppm Bi Zn - 70 ppm Al - 30 ppm Li - 2300 ppm Bi Zn - 70 ppm Al - 50 ppm Li - 3000 ppm Bi

Zn - 30 ppm Al - 50 ppm Li - 250 ppm In Zn - 70 ppm Al - 50 ppm Li - 250 ppm In Znn -- 330U ppppmm A Ali - ■ 330U ppppmm L Lii -- 5 tj0u0u ppppmm I inn Zn - 70 ppm Al ■ 30 ppm Li - 500 ppm In Zn - 30 ppm Al ■ 30 ppm Li - 250 ppm In - 250 ppm Bi Zn - 30 ppm Al ■ 50 ppm Li - 250 ppm In - 250 ppm Bi Zn - 70 ppm Al ■ 30 ppm Li - 250 ppm In - 250 ppm Bi Zn - 30 ppm Al ■ 250 ppm Li - 250 ppm In - 250 ppm Bi Zn - 30 ppm Al • 30 ppm Li - 500 ppm In - 250 ppm Bi Zn - 30 ppm Al • 50 ppm Li - 500 ppm In - 250 ppm Bi

Zn - 70 ppm Al - 30 ppm Li i - 5 —00 p _r p _r m In - 250 p _r p _x m Bi

Zn - 30 ppm Al - 250 ppm Li - 500 ppm In - 250 ppm Bi Zn - 30 ppm Al - 50 ppm Li - 500 ppm In - 500 ppm Bi Zn - 30 ppm Al - 250 ppm Li - 500 ppm In - 500 ppm B Zn - 70 ppm Al - 50 ppm Li - 500 ppm In - 500 ppm Bi

Zn - 30 ppm Al - 30 ppm Li - 500 ppm In - 1000 ppm Bi

Zn - 30 ppm Al - 250 ppm Li - 500 ppm In - 1000 ppm Bi

Zn - 70 ppm Al - 30 ppm Li - 500 ppm In - 1000 ppm Bi

Zn - 70 ppm Al - 50 ppm Li - 500 ppm In - 1000 ppm Bi

Zn - 30 ppm Al - 50 ppm Li - 500 ppm In - 2300 ppm Bi

Zn - 70 ppm Al - 30 ppm Li - 500 ppm In - 2300 ppm Bi

Zn - 70 ppm Al - 30 ppm Li - 500 ppm In - 3000 ppm Bi

These powders contain, besides zinc and unavoidable impurities, only the given additives.

Unavoidable impurities are the impurities which are present in the zinc and in the additives.