CA2212507C

CA2212507C - Cobaltous oxide containing metallic cobalt, methods for producing the same and use thereof

Info

Publication number: CA2212507C
Application number: CA002212507A
Authority: CA
Inventors: Astrid Gorge; Katrin Plaga; Armin Olbrich
Original assignee: HC Starck GmbH
Current assignee: HC Starck GmbH
Priority date: 1995-02-10
Filing date: 1996-01-29
Publication date: 2009-02-24
Anticipated expiration: 2016-01-29
Also published as: JP4007612B2; CA2212507A1; CN1094903C; FI973276A0; JPH10513430A; CN1173855A; FI973276L; KR100405288B1; EP0808294B1; FI114311B; DE19504320C1; AU4714896A; ZA961054B; KR19980702107A; DE59601074D1; US6096424A; EP0808294A1; TW396145B; US5972306A; WO1996024557A1

Abstract

The present invention relates to cobalt(II) oxide containing metallic cobalt, to a process for producing it and to its use as an electrode material in a secondary cell. The process comprises: (i) reacting a crystallised basic cobalt compound of general formula:

Co[(OH)2]a[O]b[CO3]c wherein the sum of a+b+c is >= 1 and <= 1.5, with an aqueous or alcoholic solution of a carboxylic acid containing at least one carboxyl group; and (ii) separating and calcining the solid thus obtained.

Description

COBALTOUS OXIDE CONTAiNING METALLIC COBALT, METHODS
FOR PRODUCING THE SAME AND USE THEREOF

The present invention relates to cobalt(II) oxide containing metallic cobalt, to a process for producing it and to its use.

Cobalt(II) oxide is used in admixture with metallic cobait as an additive in the positive paste material of rechameable alkaline Ni batteries based on Ni/Cd or Ni/NiH. For this purpose Ni(OI~)~ is processed with the Co(II) oxide-metal ; C) mixture and aux.iliary materials to form pastes which are subsequently incorpor ated in an electrically conductive electrode support. The electrodes produced by this route are further processed by dr,,,ing and/or sintering in order thus to produce batteries of various designs.

Thus for the production of round button cells, for example, the electrochemically active electrode consti'LUents are compacted togetller with auxiliary materials, predominantly graphite or nickel powder, to form tablets of various sizes. The content of cobalt in the electrode compositions is between 2 and 10 % by -weight in this application.

According to EP-A 353 837, the main effect of cobalt metal is due to the fact that during the first charging cycles (forming cycles) the cobalt metal first is ox idi.sed, corresponding to its potential, to divalent cobalt, and is thus able to dissolve in alkaline electrolytes. The Co2' ions which are thus obtained and those which may already be present tilen diffuse to=wards the surface of the nickel hydroxide.
On further charging of th.e battery, they are oxidised here to Co'' ions in the form of 25, CoO(OH). This in turn is formed as a layer on the surface of the ni.ckel hvdro-xide particles and gives rise to the electrical conductivity of the electrode material durin- the follov~ing charg:ng and discharain, c~~cles.

However, Coc+ ions can also enter the layer lattice. of the nicl:el hydro7.ide and can modif}= the properties of the hydroxide the. c- so that a higher charging efficiency of the electrode material is obtained. In addition to the properties which have already been mentioned, the cobalt used in the eiectrode paste material can act as a safety ;eser .'e 1f d]scliaralnL? is t00 irliensl",'e. In t"he cou;sE Of this procedure, Co'`+ ions are eiectrochemically reduced again and thus prevent the evolution of hydrogen. Cobalt compounds with the aforementioned properties are also disclosed in US Patent Specifications US-A 5 032 475 and US-A 5 053 292, and in European Patent Application EP-A 523 284.

Only up to about 50 % of the cobalt in the electrode can be utili.sed for the cllarging and discharaing cycles on electrochemical oxidation, since the pre-dominant fraction of the cobalt is coated with a stable oxide layer. This protective layer in turn prevents the formation of Co`'+ ions which are necessar-y for the activation of the electrode, as mentioned above. In order to circumvent this difficulty, soiuble cobalt compounds such as cobalt hydroxide or monoxide have hitherto been incorporated in the electrode paste material. The effect of this has been that Co2T ions are present in dissolved form in the electrolyte even before electrochemical forming, and can already separate out at the surface of the nickel hydroxide (Matsumo et al.: The 162nd ECS Fall r~Ieeting Detroit, i 8(1982).

According to this prior art, the Co(II) oxide used for the purposes of application described above is produced commercially by the thermal decomposition of cobalt carbonate, cobalt hydroxide or higher oxides of cobalt. In accordance with thermodynamic equilibrium considerations, however, these always contain an excess of oxygen and thus have residual contents of Co(III), However, slight traces of Co(III) in Co(II)oxide catalyse the oxidation of divalent cobalt to trivalent cobalt. The latter does not form compounds which are soluble in the electrolyte, however, so that the formation of the conductive layer according to the meciianism described above is not possible. The result of this is that a high utitisability of the electrode can only be obtained if the Co(III) content of the starting material is as low as possible.

The present invention provides a Co(II) oxide containinc-, cobalt metal which does not have the disadvantages described above.

It has now proved possible to obtain correspondinQ Co(IIj oxides bv a process for producing Co(II) oxide containin, metallic cobalt, wherein crvstallised basic cobalt ~0 conlpounds of ;eneral formula STA 106-Foreign CountiCAo22i2so7 1997 os o7 Co[(OH)21a [Olb [C03L, where the sum of a+b+c is ? 1<_ 1.5, are reacted with aqueous and/or alcoholic solutions of an organic compound containing at least one carboxyl group and the solids thus obtained are separated from the suspension and calcined. The present invention relates to such a process.
Carboxylic acids can preferably be used as the organic compound containing at least one carboxyl group in the process according to the invention. In this respect, particularly suitable substances from the group comprising carboxylic acids are - linear or branched, saturated or unsaturated monocarboxylic acids having a number of C atoms from 1 to 9, and/or - linear or branched, saturated or unsaturated polycarboxylic acids having a number of C atoms from 2 to 10, and/or - cyclic or heterocyclic, saturated or unsaturated mono- and polycarboxylic acids having a number of C atoms from 4 to 14, and/or - linear or branched, saturated or unsaturated mono- and polyhydroxycarb-oxylic acids having a number of C atoms from 2 to 7, and/or - aromatic hydroxycarboxylic acids having a number of C atoms from 7 to 11, and/or - cyclic or aliphatic, saturated or unsaturated ketocarboxylic acids having a number of C atoms from 2 to 14.

Adipic acid, succinic acid, glutaric acid, glyoxylic acid, maleic acid, malonic acid, lactic acid, oxalic acid, phthalic acids, mucic acid, sorbic acid, racemic acid, versatic acid, tartaric acid and/or citric acid can be used just as advantageously.

STA 106-Foreign Countnes In a further advantageous embodiment of the process according to the invention, the carboxylic acids may also be used in partially esterified form, as long as they still contain at least one active carboxyl group.

Crystallised basic cobalt compounds in the sense of this invention have the formula Co[(OH)21a [Olb [C031c' where the sum of a+ b+ c is _ 1<_ 1.5. The values of a, b and c may each be any values between 0 and 1.5. They can thus be used both as pure crystals and as mixed crystals, wherein the cobalt may be present in oxidation states between and 3. Compounds which are particularly suitable are those having particle sizes in the region of 0.5 m, preferably 2 to 20 m. They are most preferably present within a narrow particle size distribution.

The external shape of the crystallised basic cobalt compounds also determines the shape of the final products according to the invention. Those exhibiting a spherical morphology are most preferably used.

The calcination step which completes the process is advantageously effected under an inert gas atmosphere at temperatures between 200 and 1000 C, preferably 500 to 800 C.

Depending on the control of the process, the process according to the invention permits both a selective conversion of the external surface of the particles, and a conversion of the internal surface in addition.

In order to obtain Co(II) oxide wherein the metallic cobalt is situated pre-dominantly on the external surface of the Co(II) oxide, the reaction according to the invention is conducted within a temperature range from 50 to 100 C, pref-erably 70 to 90 C. This invention relates to correspondingly obtainable Co(II) oxides. A scanning electron microscope photograph of microsections of corre-sponding Co(II) oxides is illustrated in Figure 2. Metallic cobalt particles in the submicron range, which are concentrated in discrete form in the external surface, are typical of these oxides.

STA 106-Foreign Countries This invention also relates to Co(II) oxides in which the metallic cobalt exists in an concentrated state in both the internal and in the external surface. A
photograph of a corresponding Co(II) oxide is likewise illustrated as a micro-section in Figure 3. It can be obtained by the process according to the invention, wherein the reaction is firstly conducted for 0.1 to 3 hours, preferably 0.5 to 1.5 hours, at room temperature, and is subsequently conducted for 0.1 to 3 hours at 50 to 100 C, preferably 70 to 90 C. A three-dimensional network of finely divided metallic cobalt is typical of these Co(II) oxides.

The content of metallic cobalt in the Co(II) oxide according to the invention can be adjusted to any desired ratio by means of the ratio of the corresponding re-duction equivalents. Contents of metallic cobalt from 2 to 50 % by weight, most.
preferably 3 to 20 % by weight, are preferred.

The Co(II) oxides according to the invention are characterised by a high resistance to atmospheric oxygen. Another merit of the material, for example, is its high flowability when spherical particles are used, since the habit of the materials are maintained during the entire course of the reaction.

Another advantage is manifested in that, compared with materials produced according to the prior art, the metallic and oxide fractions cannot segregate, which facilitates uniform processing of the cobalt in the paste preparation operation which is necessary for the production of electrodes.

This invention also relates to the use of the Co(II) oxides according to the invention as an electrode material in electrochemical secondary cells.

The invention is explained below by means of examples, without being seen as being restricted thereto.

STA 106-Foreign CountrC~ 02212507 1997 08 07 Example 1 (external coating) 200 g of spherical basic cobalt carbonate, produced by the reaction of CoC12 with Na2CO31 were slurried in 1.5 litres of water and this suspension was heated to 85 C with stirring. Metered additions of 100 g of solid tartaric acid were made uniformly to this suspension over 30 minutes, the temperature being maintained at 85 C. The reaction mixture was subsequently stirred for 15 minutes at T = 85 C
and then filtered hot. The filter cake was subsequently washed with 500 ml of water and dried to constant weight at T= 70 C.

260 g of basic cobalt tartrate/carbonate were obtained as an intermediate product.
100 g of this product were calcined in a quartz boat at T = 700 C for 3 hours under argon.

67 g of Co(II) oxide containing cobalt metal, which had a cobalt content of 79.72 %, were obtained as the calcination product.

Example 2 (external coating) 200 g of spherical basic cobalt carbonate, produced as in Example 1, were slurried in 1000 ml of methanol. 20 g of citric acid monohydrate - dissolved in 50 ml of methanol - were added thereto with stirring. The suspension was subsequently heated for 4 hours under reflux, filtered, and washed with 1000 ml of methanol.
The filter cake was dried to constant weight at T = 70 C.

212 g of basic cobalt citrate/carbonate were obtained as an intermediate product, which was calcined at T = 700 C for 2 hours in an argon atmosphere. The Co(II) oxide containing cobalt metal which was obtained (27 g) had a cobalt content of 79.3 %.

A correspondingly produced powder is illustrated in Figure 1(magnification .,i 5000X).

STA 106-Foreign CountrCA 02212507 1997 08 07 Examples 3 to 6(external coating) 200 g of spherical basic cobalt carbonate, produced as described in Example 1, were suspended in water and heated to T = 80 C. This was followed by the addition of oxalic acid in the amounts given in Table 1. After the reaction was complete, the suspension was stirred for 1 hour, filtered, and dried to constant weight at T = 70 C.

The materials obtained by this route were subsequently subjected to calcination at 700 C under an inert gas.

Table 1 Starting material: spherical Co carbonate Co content: 54.5 %
amount originally weighed in: 200 g Example No. Amount of oxalic acid Cobalt content in weighed in final product 3 46g 81.5%

4 70 g 83.1 %
5 81g 83.8%
6 93g 85.0%
A powder produced according to Example 5 is illustrated in the form of a microsection in Figure 2 (magnification 4000X).
Example 7 (external and internal coating) 200 g of spherical basic cobalt carbonate, produced as described in Example l, were slurried in 1.5 litres of water and 100 g of tartaric acid were added.
The suspension was stirred for 1 hour at room temperature and subsequently heated to 53 C for 2.5 hours. It was subsequently filtered and washed with 500 ml of STA 106-Foreign CountrCA 02212507 1997-08-07 water. After drying to constant weight the residue on the filter gave 261 g of basic cobalt tartrate/carbonate as an intermediate product.

This was calcined at T = 700 C for 3 hours under an argon atmosphere. 137 g of Co(II) oxide containing cobalt metal, which had a cobalt content of 91.4 %, were obtained as the calcination product.

Example 8(external and internal coating) 200 g of spherical basic cobalt(II, III) hydroxide-oxide with a Co content of 49 %
by weight of cobalt were slurried with 1.5 litres of water, and 15 g of solid tartaric acid were added. The suspension formed was stirred for 1.5 hours at room temperature and subsequently heated to 70 C for 2 hours. Thereafter it was filtered, washed, and dried to constant weight. The 212 g of basic cobalt tartrate/(II, III) hydroxide-oxide obtained from the reaction was subjected to calcination at T = 700 C for 3 hours under an inert gas.

117 g of Co(II) oxide containing cobalt, which had a cobalt content of 80.8 %, were obtained as the product.

A correspondingly produced powder is illustrated in the form of a microsection in Figure 3 (magnification 5000X).

Claims

CLAIMS:

1. A process for producing Co(II) oxide containing metallic cobalt, comprising: (i) reacting a crystallised basic cobalt compound of general formula:

Co[(CH)2]a[O]b[CO]c wherein the sum of a+b+c is >= 1 and <= 1.5, with an aqueous or alcoholic solution of a carboxylic acid containing at least one carboxyl group; and (ii) separating and calcining the solid thus obtained.

2. A process according to claim 1, wherein the carboxylic acid is:

(a) a linear or branched, saturated or unsaturated monocarboxylic acid having 1 to 9 carbon atoms;

(b) a linear or branched, saturated or unsaturated polycarboxylic acid having 2 to 10 carbon atoms;

(c) a cyclic or heterocylic, saturated or unsaturated mono-or polycarboxylic acid having 4 to 14 carbon atoms;

(d) a linear or branched, saturated or unsaturated mono- or polyhydroxycarboxylic acid having 2 to 7 carbon atoms;

(e) an aromatic hydroxycarboxylic acid having 7 to 11 carbon atoms;

(f) a cyclic or aliphatic, saturated or unsaturated ketocarboxylic acid having 2 to 14 carbon atoms; or (g) a mixture of (a) to (f).

3. A process according to claim 1, wherein the carboxylic acid is adipic acid, succinic acid, glutaric acid, glyoxylic acid, maleic acid, malonic acid, lactic acid, oxalic acid, a phthalic acid, mucic acid, sorbic acid, racemic acid, versatic acid, tartaric acid, citric acid or a mixutre thereof.

4. A process according to claim 2 or 3, wherein the carboxylic acid is a partially esterified carboxylic acid.

5. A process according to any one of claims 1 to 4, wherein the crystallised basic Co compound has a particle size within the range of 0.5 µm to 50 µm.

6. A process according to claim 5, wherein the particle size is within the range of 2 to 20 µm.

7. A process according to any one of claims 1 to 6, wherein the crystallised basic Co compound has a spherical morphology.

8. A process according to any one of claims 1 to 7, wherein the calcination is effected in an inert gas atmosphere at a temperature between 200 and 1000°C.

9. A process according to claim 8, wherein the temperature is between 500 and 800°C.

10. A process according to any one of claims 1 to 9, wherein the reaction (i) is conducted within a temperature range of 50 to 100°C, and wherein on subsequent calcination metallic cobalt is predominantly formed on the external surface of the Co(II) oxide.

11. A process according to claim 10, wherein the reaction (i) is conducted within a temperature range of 70 to 90°C.

12. A process according to any one of claims 1 to 9, wherein the reaction (i) is first conducted for 0.1 to 3 hours, at room temperature, and subsequently for 0.1 to 3 hours at 50 to 100°C, and wherein after the completion of calicination both the internal and external surfaces of the Co(II) oxide are covered with metallic cobalt.

13. A process according to claim 12, wherein the reaction (i) is first conducted for 0.5 to 1.5 hours at room temperature, and subsequently for 0.1 to 3 hours at 70 to 90°C.

14. Co(II) oxide containing metallic cobalt, wherein the metallic cobalt is predominantly present on the external surface of the Co(II) oxide, obtained according to the process of any one of claims 1 to 11.

15. Co(II) oxide containing metallic cobalt, wherein the metallic cobalt is present both on the external and on the internal surfaces of the Co(II) oxide, obtained according to the process of claim 12 or 13.

16. Use of the Co(II) oxide containing metallic cobalt obtained according to the process of any one of claims 1 to 8, 12 and 13, as an electrode material in a secondary cell.