Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-03-30
2002-02-19
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S324000, C428S328000, C428S330000, C429S224000, C429S232000
Reexamination Certificate
active
06348259
ABSTRACT:
The invention relates to novel manganese dioxide electrodes comprising modified, electrochemically active manganese dioxide, a method for producing said novel manganese dioxide electrodes, and also their use in primary electrochemical cells.
Typical constituents of an alkaline primary cell are a cathode consisting of manganese dioxide, an anode, preferably of zinc, an alkaline electrolyte and an electrolyte-permeable separator material.
The zinc electrode consists, as a rule, of large-area zinc powder and a gelling agent, for example carboxymethylcellulose, as stabilizer. Also known, however, are zinc powder electrodes pressed or sintered cold or hot with or without binder. In addition to amalgamated zinc anodes, mercury-free zinc anodes are being used to an increased extent.
The alkaline electrolyte generally consists of an aqueous potassium hydroxide solution. It may, however, also be solutions of other hydroxides, such as sodium hydroxide or lithium hydroxide solutions and also their mixtures.
The separator material situated between the electrodes has the purpose of electronically isolating the two electrodes.
An electrolyte comprising pyrolusite, a manganese dioxide having &ggr;-structure, which has a very high electrochemical activity is frequently used as cathode material. To increase the electrical conductivity, carbon particles, soot particles or graphite particles are usually added to such manganese dioxide electrodes. Organic or inorganic additives are used as binders.
U.S. Pat. No. 5,342,712 describes cell discharge times prolonged by 5 to 15% at high and at medium discharge currents as a result of adding titanium dioxide having anatase structure to the active mass of the manganese dioxide cathode. At the same time, such cells have a cell voltage which is increased by about 60 mV during the discharge. At low discharge currents, however, a negative effect is exhibited. The mode of operation of the titanium dioxide of this structure is explained by an increased ion mobility in this material during the discharge and a reduction in the polarization associated therewith, which results in turn in a longer discharge time. This effect is not achieved, according to this publication, by adding titanium oxide having rutile structure.
U.S. Pat. No. 5,532,085 describes the addition of CaWO
4
, MgTiO
3
, BaTiO
3
, CaTiO
3
, ZnMn
2
O
4
and Bi
12
TiO
20
and combinations of these oxides to the manganese dioxide cathode. Under various discharge conditions, up to 10% longer discharge times were measured on primary cells as a result of these additives.
These known processes for prolonging the limited discharge time of primary electrochemical cells by adding titanium dioxide have, however, substantial disadvantages for large-scale industrial use. As already stated in connection with U.S. Pat. No. 5,342,712, good cell characteristics can be achieved by adding anatase TiO
2
only for high and medium discharge currents. At low discharge rates, this effect cannot be detected. Furthermore, the specified improvements can be achieved only by using high-purity titanium dioxide particles. The prolonged discharge times described in U.S. Pat. No. 5,532,085 are not clearly comprehensible.
SUMMARY OF THE INVENTION
The object of the present invention was therefore to provide manganese dioxide electrodes whose use in galvanic cells, electrochemical cells, in particular in primary cells result in products having improved properties, in particular having prolonged discharge times and increased cell voltages during the discharge, and to be specific, both at high and at low discharge rates. It was also the object to provide an inexpensive, readily performed process for producing these modified manganese dioxide electrodes.
The object is achieved by manganese dioxide electrodes which comprise inorganic particles. These particles may be either plain or coated inorganic particles. Suitable as plain inorganic particles are, in particular, mica particles. Surprisingly, it was found by experiments that by blending the manganese dioxide normally used as cathode material with commercially obtainable mica particles, a starting material is obtained for producing manganese dioxide electrodes from which cathodes can be produced which have considerably improved properties.
The present invention therefore relates also to a manganese dioxide electrode which contains mica.
In this connection, the generally known and commercially obtainable mica types can be used. In a particularly preferred embodiment of this invention, the mica is used in ground form, mica particles having certain particle sizes being present. Preferably, mica particles having a particle size of 5-50 &mgr;m are used. Obtainable commercially, for example, are various micas of certain particle sizes, such as, for example, the F-mica (Merck KGaA, Darmstadt) having a particle size of 5-25 &mgr;m, the M-mica (Merck KGaA, Darmstadt) having a particle size of <15 &mgr;m or also the N-mica (Merck KGaA, Darmstadt) having a particle size of 10-50 &mgr;m. It goes without saying, however, that micas can also be used which have not been previously subjected to a specific treatment.
The coated particles can be those whose support particles consist of a material selected from the group consisting of mica, SiO
2
, Al
2
O
3
, ZrO
2
and ZnO. Single or multiple coatings of said particles can be built up of dielectric and, in particular, of ferroelectric, piezoelectric or pyroelectric substances. Such coatings may consist of titanates, stannates, tungstates, niobates or zirconates; in addition, however, silicate coatings are also possible, depending on the type of basic particle selected. Particles having coatings consisting of mixtures of said substances are also suitable. Suitable inorganic particles may also have coatings consisting of metal oxides from the group consisting of Fe
2
O
3
, NiO, CoO, ZrO
2
, SnO
2
, TiO
2
, Sb
2
O
3
, PbO, Pb
3
O
4
or Bi
2
O
3
and mixtures of the latter. The single coatings consisting per se of one substance may be doped with foreign ions, such as, for example, SnO
2
coatings doped with foreign ions.
The manganese dioxide used as basic material can be present in a structure comprising water of crystallization.
The abovementioned object is achieved, in particular, by manganese dioxide electrodes which comprise coated inorganic particles in an amount of 0.01 to 20% by weight, relative to the amount of manganese dioxide comprised in the electrode.
The manganese dioxide electrodes are produced by
a) homogenizing the manganese dioxide powder with an inorganic powder consisting of plain or singly or multiply coated inorganic particles,
b) optionally blending the mixture with an organic or inorganic binder and a conductive additive (preferably graphite), and
c) making the product obtained into an electrode.
The invention likewise relates to this production process.
Manganese dioxide electrodes according to the invention can be used to produce galvanic cells, electrochemical cells, primary batteries and in the latter case, 8 button-cell batteries, in particular.
Surprisingly, it was found by experiments that, as a result of blending the manganese dioxide conventionally used as cathode material with inorganic coated particles, so-called pearlescent pigments, obtainable commercially, a starting material is obtained for the production of manganese dioxide electrodes from which cathodes can be produced which have substantially improved properties. These pigments are inorganic particles which may be coated with a very wide variety of substances.
The experiments performed have shown that cathodes having prolonged discharge times are obtained by adding plain inorganic particles, such as, for example, mica, or inorganic coated particles if such inorganic particles are added in the form of mica or of coated mica particles, SiO
2
particles, Al
2
O
3
particles, ZrO
2
particles or coated ZnO particles to the manganese dioxide in an amount of 0.01 to 20% by weight, relative to the amount of manganese dioxide. The amount added in each case depends
Glausch Ralf
Hilarius Volker
Kloss Matthias
Pfaff Gerhard
Plieth Waldfried
Le Hoa T.
Merck Patent Gesellschaft mit
Millen White Zelano & Branigan P.C.
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