Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1995-05-31
2001-06-19
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S206000, C429S220000, C429S221000, C429S224000, C429S229000
Reexamination Certificate
active
06248478
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electrochemical cells.
Batteries are a type of electrochemical cell containing an anode, a cathode, and an electrolyte in which the anode and cathode are permanently contained within the cell. Batteries containing a metal anode, metal oxide cathode, and an electrolyte are known. Because metal oxides generally are poor electrical conductors (their conductivities are in the semiconducting to insulating range), an electrically conductive material is added to the metal oxide to render the cathode electrically conductive.
Carbon microfibers (i.e. fibers having diameters less than 1 micron) are also known. Microfibers having diameters less than 0.5 micron are referred to as fibrils.
SUMMARY OF THE INVENTION
In general, the invention features an improved battery having an anode, a cathode that includes a chemically reducible material into which is incorporated an amount of electrically conductive carbon microfibers sufficient to enhance the electrical conductivity of the chemically reducible material, and an electrolyte.
In preferred embodiments, the microfibers have diameters no greater than 0.1 micron and length to diameter ratios of at least 5. Even more preferred are carbon microfibers that are tubes having graphitic layers that are substantially parallel to the microfiber axis and diameters between 3.5 and 75 nanometers, inclusive, as described in Tennent, U.S. Pat. No. 4,663,230 (“Carbon Fibrils, Method for Producing Same and Compositions Containing Same”), Tennent et al., U.S. Ser. No. 871,676 filed Jun. 6, 1986 (“Novel Carbon Fibrils, Method for Producing Same and Compositions Containing Same”), Tennent et al., U.S. Ser. No. 871,675 filed Jun. 6, 1986 (“Novel Carbon Fibrils, Method for Producing Same and Encapsulated Catalyst”), Snyder et al., U.S. Ser. No. 149,573 filed Jan. 28, 1988 (“Carbon Fibrils”), Mandeville et al., U.S. Ser. No. 285,817 filed Dec. 16, 1988 (“Fibrils”), and McCarthy et al., U.S. Ser. No. 351,967 filed May 15, 1989 (“Surface Treatment of Carbon Microfibers”), all of which are assigned to the same assignee as the present application and are hereby incorporated by reference. One aspect of substantial parallelism is that the projection of the graphite layers on the microfiber axis extends for a relatively long distance in terms of the external diameter of the microfiber (e.g., at least two microfiber diameters, preferably at least five diameters), as described in Snyder et al., U.S. Ser. No. 149,573. These microfibers preferably are also substantially free of a continuous thermal carbon overcoat (i.e. pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the microfibers). These microfibers also are preferably in the form of aggregates in which individual microfibers are randomly entangled with each other or oriented substantially parallel to each other.
Preferred batteries include both primary (i.e. non-rechargeable) batteries and secondary (i.e. rechargeable) batteries. Examples of preferred batteries include reserve batteries, alkaline batteries (e.g., alkaline zinc-manganese dioxide batteries), and Leclanche batteries. The chemically reducible material for the cathode preferably includes a metal oxide (e.g., MnO
2
, HgO, Ag
2
O, AgO, PbO
2
, or NiOOH), a metal chloride (e.g., CuCl), a metal sulfide (e.g., FeS), or sulfur. The anode preferably includes Zn, Li, Cd, Ag, Mg, Fe, Na, Li—Al alloy, or Pb metal.
In the case of a Leclanche or alkaline zinc-manganese dioxide battery, the amount of microfibers incorporated into the cathode preferably is less than 0.5 grams per gram of chemically reducible material, more preferably less than 0.2 grams.
The invention also features a method for preparing the battery. Preferably, the microfibers are milled or co-milled with the chemically reducible material. Preferred milling methods include mechanical and chemical milling (by exposure to a chemical reagent that decreases the microfiber length, e.g., by chopping the microfiber). A preferred method for preparing the battery involves growing the chemically reducible material in situ within the electrically conductive network formed by the carbon microfibers.
The invention provides a battery having high energy density. The battery exhibits a long discharge lifetime and high utilization of the chemically reducible material. The microfibers enable the cathode to retain an effective amount of electrolyte for efficient operation. This ability is maintained even after vigorously mixing the microfibers and chemically reducible material to form the cathode. Moreover, high amounts of the chemically reducible material can be incorporated in the cathode.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
Description of the Preferred Embodiments
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Atkins Jaspard Harvey
Friend Stephen O.
Hausslein Robert
Tennent Howard G.
Hyperion Catalysis International Inc.
Kramer Levin Naftalis & Frankel LLP
Maples John S.
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