WO2011113903A1

WO2011113903A1 - Galvanic element, in particular mercury-free silver oxide battery

Info

Publication number: WO2011113903A1
Application number: PCT/EP2011/054070
Authority: WO
Inventors: Pascal Haering; Beat Steiger
Original assignee: Renata Ag
Priority date: 2010-03-17
Filing date: 2011-03-17
Publication date: 2011-09-22
Also published as: DE112011100911A5; CH704941B1

Abstract

The aim of the invention is to provide a silver oxide battery that is free of mercury, lead, and cadmium but still has the desired properties of previously known silver oxide batteries, in particular with respect to electromagnetic electricity generation. According to the invention, this is achieved by a galvanic element, in particular by a mercury-free silver oxide battery that has a metal anode, an electrolyte, and a silver oxide electrode, said metal anode comprising zinc as the main component with possible additives of indium and bismuth in a mercury-, cadmium-, and lead-free manner. The electrolyte contains additives that prevent undesired secondary reactions in combination and coordination with a coated current conductor on the anode side. In this manner, it is possible to reduce the self-discharge of zinc in alkaline electrolytes and therefore adjust a controlled and long-term linear oxidation of the zinc and thus the desired stability of the electromagnetic energy generation.

Description

Galvanic element, especially mercury

Si l beroxidbatterie

The present invention relates to a galvanic cell, in particular to a mercury-free silver oxide battery.

Silver oxide batteries are typically used to generate electrical energy by means of the electrochemical reaction voltage and current and thus to provide energy to electronic or electrical equipment.

Common silver oxide batteries usually work as silver oxide zinc batteries. In this case, in an electrochemical reaction at the anode, metallic zinc is oxidized in an alkaline electrolyte to the doubly positively charged zinc ion (Zn ++) and the silver oxide is reduced to silver at the cathode by a reduction reaction. The cathode may also consist of a mixture containing silver oxide. Typically, additives such as manganese oxide, carbon and polymers (eg as a binder) are added. As the silver oxide, both Ag ₂ O (silver (I) oxide) and Ag ₂ O ₂ (silver (I / III) oxide, often referred to as Slilber (II) oxide, AgO) can be used. Today, these electrochemical silver oxide batteries are usually built up with mercury-containing zinc powder. The mercury serves as corrosion protection for a current collector on the negative metallic zinc-providing battery side (anode side on discharge) and also contributes to reducing the unwanted hydrogen evolution by self-corrosion of zinc, which otherwise unwanted spontaneous hydrogen evolution on the zinc-containing anode by a alkaline zinc corrosion or by forming a local electrochemical element with the surface of the current collector would set. The content of mercury in existing Zn / alkali electrolyte / silver oxide silver oxide batteries based on the total metal content in the zinc powder is about 1 to 8%. In addition to this level of mercury, such silver oxide batteries may also contain minor components of lead and cadmium. These admixtures are typically also in the range of 0.5 to 6%.

Due to the toxicity of the metals mercury, lead and cadmium in the course of strict legal requirements for a replacement of these substances by less toxic metals or non-metallic additives worked or mandatory the use of less toxic metals with simultaneous ban on mercury, lead and cadmium. However, traces of Hg, Cd, and Pb may still occur. At this point, it is necessary to point out the omission of Hg, Cd, Pb additives or the non-necessity of the declaration of these metals in the sense of the EU battery directive. Article 21 (3) of the EU Battery Directive 2006/66 / EC says that for the purposes of this Directive, it is possible to speak of mercury, cadmium and lead free if the corresponding content is less than 5 ppm Hg for Hg, less for Cd is 20 ppm and for Pb less than 40 ppm, based on the total weight of the product.

The present invention is therefore based on the object to provide a silver oxide battery that is free of mercury, lead and cadmium and yet has the desired properties, in particular with regard to the electrochemical electricity generation, previously known silver oxide batteries.

According to the invention, the object is achieved by a mercury-free galvanic element comprising a metal anode (10), an electrolyte (14) and a silver oxide electrode (20), wherein the metal anode (10) comprises zinc as the main constituent and is characterized in that the electrolyte (14) has a substance or a mixture of substances which have the following effects simultaneously:

a) corrosion inhibition

b) surface-active effect

c) Viscosity formation with thixotropic properties

with a composition of:

a) 5 mol ppm to 300 mol ppm corrosion inhibitor

b) 1 mol ppm to 100 mol ppm surfactants

c) 0.5 mol ppm to 1000 mol ppm viscosity builder with thixotropic

Properties;

B) an inner surface of a current collector (6) directed towards the metal anode (10) has an at least partially two-layered coating (9), wherein the first layer serves as a barrier layer and adhesion layer and through a layer with Sn and / or Cu / Zn and / or a Cu / Sn and / or a Cu / Zn / Sn alloy is superimposed.

An embodiment of the invention is shown on the single FIGURE.

In contrast to the known additives for electrolytes 3 different effects are achieved here simultaneously, but without negative mutual side effects. The amounts and / or mixing ratios in the composition are optimized with respect to these effects to the material properties of zinc and anode inner surface, ie the composition is balanced so that a similar electrochemical electricity generation as in a conventional silver oxide battery is still achieved. Preferably, a balanced blend was achieved by a mole ratio of a: b: c at 10: 2: 1, adjusting the absolute levels to the absolute effects in the interactions with the zinc used and the surface material of the anode inner surface; and (c) preferably consists of one or more high molecular mass (> 10000 g / mol) viscosity formers. Preferably Mixing conditions, which lead to dispersions, however, to avoid.

These substances contribute to further reduction of zinc self-discharge and spontaneous and uncontrolled hydrogen evolution. Furthermore, these additives can lead to a passivation of the metallic surfaces in the anode, which reduces unwanted reactions of local elements and the flow properties of the electrolyte are favorably influenced. By way of example, the addition of inorganic and organic acids such as phosphoric acid, tartaric acid, succinic acid and citric acid to the electrolyte can be cited, whereby the hydrogen overvoltage of the electroactive surfaces can be improved. These additives are more typically added to a NaOH / KOH electrolyte containing about 0.3 to 0.6 moles of ZnO.

The arrangement of a two-layer coating, with the first

Layer which serves as a barrier and adhesive layer further allows on the one hand to reduce the diffusion of metal atoms, which also contributes to reducing the self-discharge of the battery, and on the other hand to increase the mechanical robustness against damage. This also improves the electrochemical properties with respect to corrosion.

In an advantageous embodiment of the present invention, the zinc is added as additives indium and / or bismuth. In this way, it is possible with the additives indium and / or bismuth to reduce the zinc self-discharge in alkaline electrolytes and thus to set a controlled and long-term linear oxidation of the zinc and thus the desired stability of hydrogen evolution. These additives avoid the use of mercury, cadmium and lead, so that in the sense of the above-mentioned EU Regulation can be spoken of a mercury-free, cadmium and lead-free silver oxide battery, because the limits set by the EU Regulation for these metals are below and the so constructed Silver oxide battery so that is no longer notifiable. Of course, technically, traces of these metals can still be present and even desired, but the content of these metals can now be kept well below the specified limits due to the additives.

The anode consists mainly of Zn and ZnO, although it can also contain additional fibers, these can be present as cellulose fibers but also consist of durable polymer fibers and can serve as internal Feuchteleiter and filler. These fibers form internal electrolyte channels, which keep the electrode wet and porous over a long period of operation.

Wherever electrically insulating and / or material-separating materials are required, polyamides (PA) can be used. Polyepoxides, polyvinyl alcohol (PVA), poly-acrylic acid (PAA), polyethylene (PE) and polypropylene (PP) can be used.

In an advantageous development of these insulating components are constructed in two layers of the above materials, thereby the sealing properties, insulation properties and / or

Improved material separation properties; In addition, surfaces bordering on these electrically insulating and / or material-separating materials may also be coated with the above-mentioned substances, thereby providing an additional improvement of the abovementioned properties.

Sulfur salts, polyethylene glycols (PEGs), PEG diacid, polyfluoro alcohol ethoxylate, alkyl are, for example, surfactants which are considered as wetting agents and can be used on the surface of the zinc and / or the anode inner surface for electrochemical partial passivation Polyethylene oxide, polyethylene ether, diaminopyridine, phenyldiamine, aminophenol sulfonic acid, 2,4-di-nitrophenols, benzidine, fluorosurfactants, hydroxyethyl quinoline and quaternary ammonium phenates. The surface-active substances are present in the electrolyte at a concentration of 0.01-2% by weight, the concentration preferably being between 0.1-0.8%.

As the viscosity builders, natural substances such as polyalcohols, cellulose or cellulose derivatives such as e.g. Carboxymethyl cellulose (CMC) and agar. As polymers also polyvinyl alcohol, polyglycols, Teflon (PTFE) and polyacrylic acids are suitable. The viscosity formers are present in the electrolyte at a concentration of 0.01-5% by weight, the concentration preferably being between 1 -3%.

Benzotriazole, tolyltriazole, tolyltriazole solution and benzimidazole, for example, may be mentioned as corrosion inhibitors, the corrosion inhibitors having a concentration of 0.01-3% by weight in the electrolyte, and the concentration preferably being between 0.2-1%.

The current collector on the cathode side often has a three-metal nature of Ni / SS304 / CU band, with copper inside the cover, whereby the copper layer can also be replaced by a Cu / Sn or Cu / Zn / Sn alloy. If the inner side of this band consists of pure copper, an additional metal coating consisting of tin can be applied to this copper surface. The layer thickness of this tin layer may be 0.2 to 10 μηπ and may be applied by different techniques, such as applied by electroless plating, electrochemical or vapor deposition). This additional tin layer may have minor defects, such as small pores or cracks, which may cause the copper layer of the current collector to be exposed to the aggressive alkaline electrolyte. Therefore, the addition of additives is required to reduce the side reactions due to the electrical properties of the copper / electrolyte / zinc system. To improve the uniformity of the tin coating, the coated film can be heated to a temperature close to the melting point for tin, whereby possible defects can be repaired. This leads to a disappearance of the small pores and to a faster spontaneous alloying of the tin layer with the copper atoms. This temperature treatment may also be combined with a mechanical treatment.

For the positive electrode stainless steel or another deep-drawing steel can be used, which is ev. Subsequently to the forming process additionally refined by a nickel coating.

A further advantageous development of the present invention results when an inner surface of a current collector directed toward the metal anode is at least partially coated with a Cu / Zn and / or a Cu / Sn and / or a Cu / Zn / Sn alloy. This metal layer may additionally contain indium and / or bismuth. The at least partial coating makes it possible to increase the hydrogen overvoltage of the surface, to improve the corrosion properties of the current collector and to stabilize the contact resistance between the electroactive metal anode and the current collector.

A particularly safe and uniform function of the silver oxide electrochemical battery is obtained when the concentration of indium and bismuth in the range of 50 to 2000 ppm, preferably in the range of 100 to 1000 ppm. Such a concentration has been found to be sufficient to offset the effects attributable to the absence of the toxic metals mercury, lead and cadmium.

In order to achieve these desired effects, it is particularly expedient if the particle sizes of indium and bismuth-containing zinc granules are in the range from 0.5 to 1000 μηπ, preferably from 1 to 500 μηπ. A further improvement of the sealing effect may be the additional coating of the sealing surfaces (contact surfaces between the seal, lid sealing surface and cup sealing surface with an alkaline electrolyte resistant polymer.) Polymers or polymer blends which provide an adhesive force to the surfaces to be wetted are preferably used Hot melt adhesives, epoxy adhesives, acrylate adhesives, various elastomeric polymers and also fluorinated polymers, etc. Advantageous also a water-unfriendly surface finish of these polymers, therefore, water-friendly polymers are rather less suitable.

Preferred embodiments of the present invention are explained below with reference to a drawing. The figure shows a schematic view of the structure of an inventive silver oxide battery. The silver oxide battery comprises a cup 4 and a lid 6, which together with a seal 8 form the housing of the silver oxide battery. The bottom of the lid 6 additionally carries on its inside a coating 9 of a Cu / Zn alloy, which increases the hydrogen overvoltage of the surface of the electroactive material, improves the corrosion properties of a zinc anode 10 and the contact resistance between the zinc anode 10 and the lid bottom, the serves as a current collector, can be stabilized. This coating 9 can also consist of a Cu / Sn or a Cu / Zn / Sn alloy or also of any combination of the above alloys.

The zinc anode 10 is inserted in the lid 6. It consists in the present case of zinc powder with additives of indium and bismuth. The concentration of indium and bismuth is about 300 ppm each. However, this concentration can be on the whole of the range of about 50 to 2000 ppm. The grain sizes of the indium and bismuth admixtures correspond to the grain sizes of the zinc powder, which are in the range of 1 to 500 μηπ. These grain sizes can also be in the range of 0.5 to 1000 μηι lie. The zinc anode 10 formed in this way is free of additives which contain mercury, lead or cadmium. However, these elements may still be present as trace contaminants, but do not exceed the values of 0.0005% Hg, 0.002% Cd and 0.004% Pb, calculated on the total weight of the electrochemical cell. The cell is therefore not subject to declarations according to the European battery directive 2006/66 / EC for these elements. If these impurity concentrations are not exceeded, this is generally interpreted as mercury-free, lead-free and cadmium-free. At the bottom of the lid 6, a porous, compressible body 12 can be arranged, which can provide additional electrolyte solution. On the side facing away from the bottom of the lid 6 side of the zinc anode 10, an electrolyte-impregnated non-woven 15 is arranged. The electrolyte itself comprises about 20 to 40% potassium hydroxide solution. In addition, the electrolyte contains corrosion inhibitors and viscosity builders, as well as optionally surfactants, which altogether help to further improve the system. The choice of this electrolyte with its additives mentioned above promotes the reduction of zinc self-discharge, the spontaneous and uncontrolled evolution of hydrogen and the potential difference of local elements.

The electrolyte flow is covered on the cathode side by a separator film 16. The Separatorfolie 1 6 is a typical porous polymer membrane, as used for example in batteries with alkaline electrolyte. The Separatorfolie 1 6 is held by a support ring 18 in position. The separator foil 16 is followed by a silver oxide cathode 20, which as a rule consists of a polymer-bound powder layer. The metallic support ring 18 contacts the silver oxide electrode 20 and connects it electrically to the cup 4. Between the silver oxide electrode 20 and the bottom of the cup 4 may still be a coarse-pored metallic mesh 22 is inserted, which serves to better contact with the cup to create.

Claims

claims

1 . A mercury-free galvanic cell comprising a metal anode (10), an electrolyte (14) and a silver oxide electrode (20), the metal anode (10) comprising zinc as the main constituent, characterized in that

A) the electrolyte (14) has a substance or a mixture of substances which have the following effects simultaneously:

a) corrosion inhibition

b) surface-active effect

c) Viscosity formation with thixotropic properties

with a composition of:

a) 5 mol ppm to 300 mol ppm corrosion inhibitor

b) 1 mol ppm to 100 mol ppm surfactants

c) 0.5 mol ppm to 1000 mol ppm viscosity builder with thixotropic properties;

B) an inner surface of a current collector (6) directed towards the metal anode (10) has an at least partially two-layered coating

(9), wherein the first layer serves as a barrier layer and adhesion layer and is superposed by a layer with Sn and / or Cu / Zn and / or a Cu / Sn and / or a Cu / Zn / Sn alloy.

2. Galvanic element, comprising a metal anode (10), an electrolyte (14) and a silver oxide electrode (20), wherein the metal anode

(10) comprises as its main component zinc and characterized in that the substance or the mixture of substances contains indium and / or bismuth.

3. Galvanic element, according to claim 1, characterized in that the sealing contact surfaces and the seal (8), additionally coated on the lid and / or on the cup with a hydrophobic and / or adhesive polymer or polymer mixture.

4. Galvanic element according to one of claims 1 to 3, characterized in that the concentration of indium and bismuth in the anode (10) in the range of 50 to 2000 ppm, preferably from 100 to 1000 ppm, is located.

5. Galvanic element, according to one of claims 1 to 4, characterized in that

the grain sizes of indium and bismuth in the range of 0.5 to 1000 μηπ, preferably from 1 to 500 μηπ lie.

6. Galvanic element according to one of claims 1 to 5, characterized in that the electrolyte is corrosion inhibitor with a concentration of 0.01 -3% by weight in the electrolyte, wherein the concentration is preferably between 0.2-1%.

7. Galvanic element according to one of claims 1 to 6 characterized in that the surface-active substances with a concentration of 0.01 -2% by weight in the electrolyte, wherein the concentration is preferably between 0.1 -0.8%.

8. Galvanic element according to one of claims 1 to 7, characterized in that the viscosity-forming agent with a concentration of 0.01 -5% by weight in the electrolyte, wherein the concentration is preferably between 1 -3%.