Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-06-05
2001-01-30
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S199000, C429S101000, C429S102000, C429S231400, C429S231700, C429S231800, C429S231950, C429S232000, C429S342000
Reexamination Certificate
active
06180284
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to electrochemical power cells (that is, batteries) and to a method for improving electrochemical power cell performance, and, more particularly, to electrochemical power cells having a cathode comprising a fluorine compound and to a method of improving electrochemical power cell performance comprising the step of adding a fluorine compound to the cell cathode and/or the electrolyte.
BACKGROUND OF THE INVENTION
A class of primary electrochemical power cells which incorporates lithium as the anode material and solid or liquid oxidizers as cathode materials is a commercially available source of power in a small, portable package. These lithium cells have theoretical output voltages in the range of 3 to 3.9 volts and theoretical specific energies in the range of 1000 to 2000 Wh/kg. These cells require nonaqueous electrolytes because of the reactivity of lithium in aqueous solutions. Examples of practical lithium cells are lithium carbon monofluoride (3.1 V), lithium sulfur dioxide (3.1 V), lithium manganese dioxide (3.5 V), lithium thionyl chloride (3.6 V) and lithium sulfuryl chloride (3.9 V). See U.S. Pat. Nos. 3,536,532, 3,567,515, and 4,400,453 The output voltage of 3.9 V for the lithium sulfuryl chloride cell is believed to be the highest output voltage achievable in small, portable commercially available electrochemical power cells.
The lithium anode is stable in these cells because a protective film forms on the lithium surface either by direct reaction with the electrolyte or with an additive in the electrolyte. See U.S. Pat. Nos. 3,567,515 and 4,400,453. In commercially available lithium/thionyl chloride and lithium/sulfural chloride electrochemical power cells, for example, the protective film produced by the reaction between the lithium and an oxyhalide electrolyte is lithium chloride. These films are typically good ionic conductors for lithium ions, but do not transport species present in the electrochemical power cell that could damage the lithium anode.
These lithium electrochemical power cells are commercially viable only because a mechanically stable electrode of blended carbon black and Teflon® was developed on which solid, liquid or soluble cathode materials could be efficiently reduced. A “solid” cathode material is incorporated into the blend of carbon black and Teflon®. A “liquid” cathode material may be the solvent component of the electrolyte. A “soluble” cathode material is dissolved in the electrolyte. The process of fabricating carbon black-Teflon® electrodes for commercial lithium cells is well established and is described, for example, in Turk, C.,
Modern Battery Technology
, p. 291 (1991).
For a number of uses, it is desirable to develop electrochemical power cells with output voltages and specific energies greater than possible with currently available electrochemical power cells.
SUMMARY OF THE INVENTION
The present invention provides generally an electrochemical power cell comprising an anode, a cathode comprising a fluorine compound and an electrolyte to maintain ionic conductivity between the anode and the cathode. Preferably, the water content of the fluorine compound is less than approximately 150 parts per million (ppm). More preferably, the water content of the fluorine compound is less than approximately 100 ppm. Most preferably, the water content of the fluorine compound is less than approximately 50 ppm. The fluorine compound is preferably present as a single phase with a purity of at least approximately 99%.
The present inventors have discovered that the small, portable electrochemical power cells of the present invention preferably provide a voltage of at least approximately 4.0 V. Indeed, voltages of over approximately 5.0 V are preferably achieved. Moreover, the electrochemical power cells of the present invention preferably provide a specific energy of the cathode material of at least approximately 1000 Wh/Kg (Watt·hours per Kilogram). Specific energy as used herein refers generally to the ratio of energy available from a cell to the weight of the cathodic material in a cell (that is, the weight of the fluorine compound).
Given the relatively high voltages achieved in the electrochemical power cells of the present invention, the electrolyte is preferably stable at voltages of at least approximately 4.0 V and, more preferably, at voltages of at least approximately 5.0 V. For example, alkyl carbonates such as ethylene carbonate and dimethyl carbonate are suitable as solvents (that is, electrolyte solvents) in the electrochemical power cells of the present invention.
Preferably, the cathode comprises a binder material, carbon and the fluorine compound. The binder material, the carbon and the fluorine compound are preferably ball milled and pressed to form the cathode under substantially dry conditions. Preferably, the water content of the binder material, the carbon and the fluorine compound is each less than 150 ppm. More preferably, the water content of the binder material, the carbon and the fluorine compound is each less than 100 ppm. Most preferably, the water content of the binder material, the carbon and the fluorine compound is each less than 50 ppm. The content of the binder material in the cathode preferably ranges between approximately 5 and approximately 10 weight percent. The content of the carbon in the cathode preferably ranges between approximately 10 and approximately 40 weight percent. The content of the fluorine compound in the cathode preferably ranges between approximately 50 and approximately 85 weight percent. The binder material preferably comprises polytetrafluorethylene. Preferably, the binder material is Teflon® 6C available from DuPont. The carbon is preferably acetylene black.
The binder material, the carbon, and the fluorine compound are preferably pressed onto a conductive current collector. The conductive current collector is preferably fabricated from aluminum, stainless steel or nickel. Other acceptable materials for the conductive current collector include titanium or vanadium.
The fluorine compounds of the present invention are typically very powerful oxidizing agents. The electrochemical power cells of the present invention, therefore, preferably further comprise at least one separator placed in the electrolyte between the cathode and the anode to reduce migration of cathodic material to the anode. Preferably, such separators are fabricated from a porous material such as Gore-Tex®, available from W. L. Gore & Associates, Celgard®, available from Hoechst Celanese, Corp. or Zircar®, available from Zircar Products Inc. Preferably, a first separator is provided adjacent the cathode and a second separator is provided adjacent the anode. The separator adjacent the cathode is preferably Gore-Tex® or Celgard®. The separator adjacent the anode is preferably Zircar®.
Preferably, a film is produced on the anode (for example, lithium) to provide kinetic stability (that is, to inhibit and/or slow down any reaction between the electrolyte components and/or soluble ions and the anode material). Any such film should be a good ionic conductor for the ions of the anode material as such ions must be transported through the film when the cell is discharged. The film should not transport other species that could react with the anode material or be deposited from the electrolyte onto the anode material. It is also desirable to provide for film repair (by an appropriate material soluble in the electrolyte) in the event that the film is disrupted, potentially resulting in an unprotected anode surface. In that regard, uninhibited reaction between the anode material and the electrolyte components or soluble oxidants leads to high parasitic capacity losses during storage.
An additive adapted to produce and/or repair a protective film on the anode is thus preferably added to the electrolyte. Additives suitable for use in the present invention include sulfuryl chloride, thionyl chloride, and iodine pentafluoride. Preferably, the additive comprises iodine pentafluoride.
A num
Bis Richard F.
Bytella Joseph J.
Kronenberg Marvin L.
Meshri Dayal T.
Shah Pinakin M.
Bartony, Jr. Henry E.
Mine Safety Appliances Company
Uber James G.
Weiner Laura
LandOfFree
Electrochemical power cells and method of improving... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrochemical power cells and method of improving..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrochemical power cells and method of improving... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2448164