WO1992009113A1

WO1992009113A1 - An alkaline battery

Info

Publication number: WO1992009113A1
Application number: PCT/DK1991/000336
Authority: WO
Inventors: Karen KÜMMEL
Original assignee: Gn Batteries As
Priority date: 1990-11-07
Filing date: 1991-11-07
Publication date: 1992-05-29
Also published as: DK167298B1; DK267290A; DK267290D0

Abstract

An alkaline battery, wherein the problems of a low content of Hg in the zinc anode have been resolved by means of an inhibitor complex comprising 1) inhibitors, being tensides having a HLB number higher than 10 and less than 20, and 2) inhibitors of the naphthylamin-sulphonic acid type and their radicals.

Description

An Alkaline Battβrv

Technical Field

The present invention relates to an alkaline battery, that is a battery comprising a manganese dioxide cathode, a zinc anode and an alkaline electrolyte. Such a battery has been known for more than 30 years as an all-round battery with a high rate capacity and a high capacity efficiency.

Background Art

However, zinc is chemically unstable in an alkaline solu- tion, since it dissolves under an H evolution, and in order to suppress this it is known to amalgamate the zinc with up to 15% mercury (estimated on the weight of the zinc). This amount of mercury is stabilized for a number of years at a rate of 7%, dependent upon the battery design and the field of application. Beyond suppressing the H2 evolution the Hg addition serves to improve the contact to the current collector, which also influences the capa¬ city and vibration stability. A mercury content of 3.6% in the zinc is the minimum amount necessary for maintaining an acceptable quality level of the battery as regards storage life, number of service hours, field of application and other properties without having to resort to other measures .

As environmental considerations dictate a steadily lower mercury content, attempts have been made to replace the toxic Hg with other inhibitors, for instance with metals such as In, Al , Pb , and Ga, alloyed with the zinc, or organic compounds, such as tensides ^"and compounds with polyethylen oxide chains used for surface treatment of the zinc or being added to the electrolyte. Hereby it has been possible to lower the mercury content considerably (down to 0.15% of the zinc weight) , but not without being at the expense of for instance the capacity, storage life, and the safety or vibration stability.

Besides, some of the metals used as inhibitor are undesir¬ able per se for environmental reasons, and for some of the organic inhibitors it can be said that although they suppress the H2 evolution, they reduce the^' closed circuit voltage at the same time.

Thus, a constant need exists for an alkaline battery with a low mercury content in the zinc, which meets the quality level displayed by a battery having a mercury content of 3.6% in the zinc.

Disclosure of the invention

The present invention relates to such a battery being characterised in that it contains an inhibitor complex comprising

1) inhibitors, being tensides having a HLB number higher than 10 and less than 20, and

2) inhibitors of the naphthylamin-sulphonic acid type and their radicals.

The first type of inhibitor has the effect of reducing the H2 evolution from the zinc anode, but the active quantity often results in a reduction of the closed circuit voltage of battery to the prejudice of the power of the battery. The other type of inhibitor has the effect of preventing the aforementioned inhibitor type from blocking the surface of the zinc to such an extent that the closed circuit voltage is influenced.

By means of such a battery according to the invention having a mercury content as low as 0.15% a satisfactory quality may be obtained without the drawbacks of the known batteries .

However, a battery according to the invention may present another problem as regards the contact to the current source because of the low mercury content of the anode.

The current collector in an alkaline manganese dioxide battery normally comprises a brass or brass plated nail or a copper pipe or a copper plated nail. The material required should have a certain strength, be weldable, and have an amalgamatable surface in order to avoid a differen¬ ce in potential to the anode, and in order to obtain a good contact with this at the same time.

Normally, the amalgamation of the current collector is effected by contact with the anode zinc and is completed in a short time.

The more the Hg content is reduced, the more difficult a sufficient amalgamation becomes, resulting in an increased U2 evolution due to the difference in potential between the anode and the collector. An incomplete amalgamation also results in a poor contact between the anode and the current collector and consequently in vibration sensitivity and low capacity.

According to the invention this problem is solved by the anode current collector being coated with a layer of zinc without pores and of same composition as the anode zinc .

The inhibitors used in the battery according to the inven¬ tion are added to the anode gel and^" used in quantities of the magnitude 25-100 ppm, and are thus causing negligi¬ ble environmental polution compared to the amount of mercury, they replace. Best Mode of Carrying Out the Invention

The invention is illustrated in detail by the following examples .

Example 1

A 6 LF 22 battery is produced having the following con¬ struction.

A 6 battery consists of six cells connected in series, which are identical as to the inner construction and contains an anode gel comprising 0.79 g zinc powder alloyed with 0.15% Hg and 0.62 g K0H solution (40%) gelled with CMC and to which 50 ppm alkylphenolethylene oxide has been added as inhibitor of type 1) and 50 ppm (or 25 ppm) 2-naphthylamin-1-sulphonic acid has been added as inhibitor of type 2), a cathode consisting of 2.19 g electrolytic Mnθ2 and 0.29 g carbon to which a binding agent of 1.8-2% has been added.

The electrodes are separated by three layers of separator.

Without the addition of an inhibitor a battery with 0.15% Hg in the zinc would generate more hydrogen than accep¬ table, which can result in an unstable function and a possible disruption of the battery.

The magnitude of the H2 evolution appears from the table below, wherein the battery according to the invention is compared with similar batteries having no inhibitor or having only one of the two types of inhibitors, respec¬ tively, and with a battery, wherein the^" anode zinc contains 3.6% Hg but no inhibitor. The measuring has been made on the zinc gel only. Tab l e 1

Evolution of hydrogen in 25 g zinc anode after 8 days at 40^βC.

Thus it appears that the inhibitor of type 2) alone has no influence on the H2 evolution, but that the use of both types of inhibitor results in a reduction of the H2 evolu¬ tion of the same order of magnitude as that obtained by a battery, wherein the anode zinc contains 3.6.% Hg. The use of inhibitor 1) alone gives a result slightly better than when using both inhibitor types, but both inhibitor types are necessary taking the closed circuit voltage of the battery into account, as it appears from the following table 2. Table 2

Closed circuit voltage (CCV) of 6 LF 22 alkaline batteries at 900 Ohm and 180 Ohm.

30

Example 2

The battery is of the same construction as in example 1, the only difference being the inhibitor complex, which in 35 this case is 50 ppm polyethylene glycol (the HBL number is approximately 13) (inhibitor 1) and 50 ppm (or 25 ppm) 2- naphthylamin-1-sulphonic acid (inhibitor 2).

Tab l e 3

Evolution of hydrogen in 25 g zinc anode after 8 days at 40°C.

As it appears a reduction of the hydrogen evolution is obtained by the battery according to the invention, wherein the zinc anode only contains 0.15% Hg, said reduction 5 being of the same order of magnitude as that obtained by a battery, wherein the zinc anode contains 3.6% Hg . Also in this example the use of inhibitor 1) alone gives a slightly better result than the use of the inhibitor complex, but both inhibitor types are necessary taking the 0 closed circuit voltage of the battery into consideration, as it appears from the following table 4. Table 4

Closed circuit voltage of 6 LF 22 alkaline batteries at

900 Ohm and 180 Ohm

When the zinc anode comes into contact with the current collector in the battery, the hydrogen evolution in the zinc anode with a low Hg content is intensified. Acco¬ rding to the invention, this problem may be solved by coating the current collector with a layer of zinc without pores and of the same composition as the anode zinc, as shown in the following example.

Example 3

A battery is produced as shown in example 2 , wherein the anode is zinc + 0.15% Hg and the inhibitor is 50 ppm polyethylenglycol (inhibitor 1) . The hydrogen evolution is measured in 13 g zinc anode at 40°C after 9 days without a current collector; with the normal current collector coated with brass; and with a current collector coated with zinc powder containing 0.15% Hg. The results are as shown in the following table 5

Table 5

As it appears the use of a normal current collector coated with brass results in an considerably increased hydrogen evolution, whereas the use of a current collector coated 35 with zinc of the same composition as the anode does not result in an increased hydrogen evolution.

Claims

1. An alkaline battery comprising a manganese dioxide cathode, a zinc anode and an alkaline electrolyte c h a- r a c t e r i s e d in that the battery having a low Hg contents in the zinc anode contains an inhibitor complex comprising

2) inhibitors of the naphthylamin-sulphonic acid type and their radicals.

2. An alkaline battery according to claim 1, c h r a c¬ t e r i s e d in that the inhibitors are present in an amount of the magnitude 25-100 ppm.

3. An alkaline battery according to claim 1 or 2, c h a- r a c t e r i s e d in that the anode current collector is coated with a layer of zinc without pores of the same composition as the zinc anode.