Reversible manganese dioxide electrode, method for the production thereof, the use thereof, and rechargeable alkaline-manganese battery containing said electrode

Abstract

The invention relates to a reversible manganese dioxide electrode, comprising an electrically conductive carrier material having a nickel surface, a nickel layer made of spherical nickel particles adhering to each other and having an inner pore structure applied to the carrier material, and a manganese dioxide layer applied to the nickel particles, wherein the manganese dioxide layer is also present in the inner pore structure of the nickel particle. The invention also relates to a method for producing such a manganese dioxide electrode, the use thereof in rechargeable alkaline-manganese batteries, and a rechargeable alkaline-manganese battery containing a manganese dioxide electrode according to the invention.

Claims

1. A method for the production of a reversible manganese dioxide electrode, comprising the following steps: a) providing an electrode structure made of an electrically conductive carrier material having a nickel surface and a nickel layer made of spherical, porous nickel particles adhering to each other and having an inner pore structure, the nickel layer being applied to the electrically conductive carrier material; b) depositing a manganese(II)-hydroxide layer onto the spherical, porous nickel particles of the nickel layer from a manganese(II)-salt solution; and c) oxidizing the manganese(II)-hydroxide layer to a manganese dioxide layer, wherein the manganese dioxide layer is present in the inner pore structure of the nickel layer.

2. The method according to claim 1, wherein the deposition of a manganese(II)-hydroxide layer in step b) is carried out electrochemically.

3. The method according to claim 1, wherein in step b) a manganese nitrate solution is used as the manganese(II)-salt solution.

4. The method according to claim 1, wherein in step c) an oxidizing agent is used, selected from the group of hydrogen peroxide, potassium peroxodisulfate, potassium permanganate, sodium hypochlorite, dichloroxide, oxygen, and ozone.

5. The method of claim 4, wherein the oxidation in step c) is carried out by means of an alkaline solution of hydrogen peroxide.

6. The method of claim 5, wherein an aqueous solution of potassium hydroxide and hydrogen peroxide is used as the alkaline solution of hydrogen peroxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a SEM image of the surface of a nickel electrode used as the basic electrode structure for producing a manganese dioxide electrode according to the invention at a magnification of five hundred times;

(2) FIG. 2 shows an SEM image of the nickel electrode shown in FIG. 1 at a magnification of ten thousand times;

(3) FIG. 3 shows an SEM image of the surface of a manganese dioxide electrode according to the invention having a 5 μm-thick manganese dioxide layer at a magnification of five hundred times;

(4) FIG. 4 shows an SEM image of the manganese dioxide electrode shown in FIG. 3 at a magnification of three thousand times;

(5) FIG. 5 shows a SEM image of the surface of a manganese dioxide electrode according to the invention having a 10 μm-thick manganese dioxide layer at a magnification of five hundred times;

(6) FIG. 6 shows an SEM image of the manganese dioxide electrode shown in FIG. 5 at a magnification of three thousand times;

(7) FIG. 7 shows discharge diagrams of manganese dioxide electrodes according to the invention having a manganese dioxide layer thickness of approximately 5 μm;

(8) FIG. 8 shows discharge diagrams of manganese dioxide electrodes according to the invention having a manganese dioxide layer thickness of approximately 10 μm.

PREFERRED EMBODIMENTS AND EXEMPLARY EMBODIMENTS

Example 1 (Production of a Manganese Dioxide Electrode Having a MnO.SUB.2 .Layer Thickness of Approximately 5 μm)

(9) In the first step, an approximately 5 μm Mn(OH).sub.2 layer is electrochemically deposited on nanostructured nickel electrodes by potentiostatic deposition at −1.1 V against the Ag/AgCl reference electrode from a freshly prepared, aqueous 1M Mn(NO.sub.3).sub.2 solution. The amount of current for the deposition of 2.54 mg Mn(OH).sub.2 per 1 cm.sup.2 electrode area results according to Faraday's law in 1.567 mAh. After the Mn(OH).sub.2 layer has been produced, the electrode is rinsed thoroughly with deionized water.

(10) In the second step, the electrode thus produced is oxidized to MnO.sub.2 with a 1:1 solution of 0.1 M KOH and 0.1 MH.sub.2O.sub.2 for 10 to 12 hours at room temperature. Mathematically, this results in 2.48 mg MnO.sub.2 per 1 cm.sup.2. With a density of 5.03 g/cm.sup.3 for MnO.sub.2, this results in an equivalent layer thickness of 4.93 μm MnO.sub.2 and approximately 5 μm rounded. After the MnO.sub.2 layer has been produced, the electrode is rinsed thoroughly with deionized water and then dried at 40° C. for 5 hours.

Example 2 (Production of a Manganese Dioxide Electrode with MnO.SUB.2 .Layer Thickness of about 10 μm)

(11) In the first step, an approximately 10 μm Mn(OH).sub.2 layer is electrochemically deposited on nanostructured nickel electrodes by potentiostatic deposition at −1.1 V against the Ag/AgCl reference electrode from a freshly prepared, aqueous 1M Mn(NO.sub.3).sub.2 solution. The amount of current for the deposition of 5.08 mg Mn(OH).sub.2 per 1 cm.sup.2 electrode area results according to Faraday's law in 3.134 mAh. After the Mn(OH).sub.2 layer has been produced, the electrode is rinsed thoroughly with deionized water.

(12) In the second step, the electrode thus produced is oxidized to MnO.sub.2 with a 1:1 solution of 0.1 M KOH and 0.1 MH.sub.2O.sub.2 for 10 to 12 hours at room temperature. Mathematically, this results in 4.96 mg MnO.sub.2 per 1 cm.sup.2. This results in an equivalent layer thickness of 9.86 μm MnO.sub.2 and approximately 10 μm rounded. After the MnO.sub.2 layer has been produced, the electrode is rinsed thoroughly with deionized water and then dried at 40° C. for 5 hours.

Example 3 (Cyclization and Discharge of the Electrodes According to the Invention)

(13) Three samples each of the electrodes produced in Example 1 (layer thickness approximately 5 μm) and Example 2 (layer thickness approximately 10 μm) were discharged with different current densities up to 400 mA/cm.sup.2. The discharge diagrams obtained in this way are shown in FIGS. 7 and 8.

(14) It can be seen that the electrodes produced undergo an initial formation reaction of approximately 30 cycles before they reach their full capacity.

(15) The MnO.sub.2 electrodes with a coating thickness of 5 μm (example 1 and FIG. 7) have a maximum capacity of 1.27 mAh/cm.sup.2 and can be discharged up to 200 mA/cm.sup.2 or 157 C without significant loss of capacity (FIG. 7).

(16) The MnO.sub.2 electrodes with a coating thickness of 10 μm (example 2 and FIG. 8) have a maximum capacity of 1.92 mAh/cm.sup.2 and can be discharged up to 50 mA/cm.sup.2 or 26 C without significant loss of capacity (FIG. 8).

(17) The fact that doubling the MnO.sub.2 layer thickness does not lead to doubling the surface capacity is due to the fact that the nickel electrodes used as the base electrode structure already have their own capacity of approximately 0.55 mAh/cm.sup.2. Taking this capacity of the nickel electrode into account results in a rounded capacity for the manganese dioxide layer of approximately 1.4 mAh per 10 μm layer thickness.

(18) The discharges were each carried out on a 1 cm.sup.2 electrode in 6.0 M KOH.