Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-05-06
2004-07-06
Ryan, Patrick J. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S220000, C429S229000, C429S232000
Reexamination Certificate
active
06759166
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an aqueous alkaline cell with a cathode mixture comprising silver copper oxide comprising silver copper oxide AgCuO
2
or Ag
2
Cu
2
O
3
or mixtures thereof, also mixtures of such silver copper oxide with manganese dioxide.
BACKGROUND OF THE INVENTION
Conventional alkaline electrochemical cells have an anode comprising zinc and a cathode comprising manganese dioxide. The cell is typically formed of a cylindrical casing. The casing is initially formed with an enlarged open end and opposing closed end. After the cell contents are supplied, an end cap with insulating plug is inserted into the open end. The cell is closed by crimping the casing edge over an edge of the insulating plug and radially compressing the casing around the insulating plug to provide a tight seal. A portion of the cell casing at the closed end forms the positive terminal.
Primary alkaline electrochemical cells typically include a zinc anode active material, an alkaline electrolyte, a manganese dioxide cathode active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers. (The term “anode active material” or “cathode active material” as used herein shall be understood to mean material in the anode or cathode, respectively, which is capable of under going electrochemical reaction during cell discharge.) The anode active material can include for example, zinc particles admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and an electrolyte. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Typically, a conductive metal nail inserted into the anode active material serves as the anode current collector, which is electrically connected to the negative terminal end cap. The electrolyte can be an aqueous solution of an alkali metal hydroxide for example, potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material admixed with an electrically conductive additive, typically graphite material, to enhance electrical conductivity. Optionally, polymeric binders, and other additives, such as titanium-containing compounds can be added to the cathode.
The manganese dioxide used in the cathode is preferably electrolytic manganese dioxide (EMD) which is made by direct electrolysis of a bath of manganese sulfate and sulfuric acid. The EMD is desirable since it has a high density and high purity. The resistivity of EMD is fairly low. An electrically conductive material is added to the cathode mixture to improve the electric conductivity between individual manganese dioxide particles. Such electrically conductive additive also improves electric conductivity between the manganese dioxide particles and the cell housing, which also serves as cathode current collector. Suitable electrically conductive additives can include, for example, conductive carbon powders, such as carbon blacks, including acetylene blacks, flaky crystalline natural graphite, flaky crystalline synthetic graphite, including expanded or exfoliated graphite. The resistivity of graphites such as flaky natural or expanded graphites can typically be between about 3×10
−3
ohm-cm and 4×−10
−3
ohm-cm.
It is desirable for a primary alkaline battery to have a high discharge capacity (i.e., long service life). Since commercial cell sizes have been fixed, it is known that the useful service life of a cell can be enhanced by packing greater amounts of the electrode active materials into the cell. However, such approach has practical limitations such as, for example, if the electrode active material is packed too densely in the cell, the rates of electrochemical reactions during cell discharge can be reduced, in turn reducing service life. Other deleterious effects such as cell polarization can occur as well. Polarization limits the mobility of ions within both the electrolyte and the electrodes, which in turn degrades cell performance and service life. Although the amount of active material included in the cathode typically can be increased by decreasing the amount of non-electrochemically active materials such as polymeric binder or conductive additive, a sufficient quantity of conductive additive must be maintained to ensure an adequate level of bulk conductivity in the cathode. Thus, the total active cathode material is effectively limited by the amount of conductive additive required to provide an adequate level of conductivity.
It is desirable that the cell have high service life under normal drain rates, for example, between about 50 milliAmp and 500 milliAmp and also perform well in higher power application, at current rates between about 0.5 and 2.0 Amp, for example, between about 0.5 Amp and 1.5 Amp. Such high power application corresponds to a power output between about 0.5 and 1.5 Watt or even higher up to about 2.0 Watt. In conventional zinc/MnO
2
cells the utilization of anode/cathode active materials falls off as the current drain or power output requirements move into the high power regime.
Although such alkaline cells are in widespread commercial use there is a need to improve the cell or develop a new type of cell that exhibits reliable performance and longer service life for normal applications such as flashlight, radio, audio recorders and portable CD players and desirably also performs even better than conventional zinc/MnO
2
cells in high power applications.
SUMMARY OF THE INVENTION
The invention is directed to a primary (nonrechargeable) electrochemical alkaline cell having an anode comprising zinc and a cathode mixture comprising silver copper oxide selected from the compounds AgCuO
2
or Ag
2
Cu
2
O
3
or any mixture of AgCuO
2
and Ag
2
Cu
2
O
3
. The invention is also specifically directed to a primary (nonrechargeable) electrochemical alkaline cell having an anode comprising zinc and a cathode mixture comprising silver copper oxide selected from the compounds AgCuO
2
or Ag
2
Cu
2
O
3
or any mixture of AgCuO
2
and Ag
2
Cu
2
O
3
wherein said silver copper oxide is admixed with manganese dioxide, preferably electrolytic manganese dixoide (EMD). The term “silver copper oxide” as used herein, unless otherwise specified shall be understood to mean the compounds AgCuO
2
, Ag
2
Cu
2
O
3
or mixtures thereof. The anode and cathode include an aqueous alkaline solution, preferably aqueous KOH solution. Such cell of the invention can be conveniently referenced herein as a Zn/Silver copper oxide alkaline cell.
The silver copper oxide (AgCuO
2
or Ag
2
Cu
2
O
3
or mixtures thereof) employed in the cathode is preferably in the form of a powder having an average particle size between about 1 and 100 micron. The cathode mixture includes a conductive material such as flaky crystalline natural graphite or flaky crystalline synthetic graphite including expanded graphite and graphitic carbon nanofibers. The term graphitic carbon nanofibers as used herein shall mean graphitic carbon fibers having a mean average diameter less than 1000 nanometers (less than 1000×10
9
meter). The term “average” or “mean average” as used herein shall mean the “arithmetic mean average” unless otherwise specified.) Preferably, the graphitic carbon nanofibers have a mean average diameter less than 500 nanometer, more preferably less than 300 nanometers. Desirably the graphitic carbon nanofibers have a mean average diameter between about 50 and 300 nanometers, typically between about 50 and 250 nanometers. The cathode mixture includes an aqueous KOH solution, desirably having a concentration of between about 30 and 40 percent by weight, preferably between 35 and 45 percent weight KOH in water.
It has been determined that in the Zn/Silver copper oxide alkaline cell of the invention the anode can comprise conventional gelled zinc anode compositions as in commercial use in conventional zinc/MnO
2
alkaline c
Eylem Cahit
Nanjundaswamy Kirakodu S.
Rozelle James
Wang Francis
Xue Jiayu Simon
Douglas Paul I.
Dove Tracy
Josephs Barry D.
Krivulka Thomas G.
Ryan Patrick J.
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