Compositions – Electrically conductive or emissive compositions
Reexamination Certificate
2001-03-09
2002-11-19
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Reexamination Certificate
active
06482334
ABSTRACT:
TECHNICAL FIELD
The present invention pertains generally to the fields of conductive organic polymers and electroactive cathode materials for electrochemical cells. More particularly, the present invention pertains to methods of preparing non-corrosive, electroactive, conductive organic polymers, wherein the non-corrosive polymers are formed by treatment of electroactive, conductive organic polymers, comprising corrosive anions, with sulfide anions and to the polymers prepared by such methods. The present invention also pertains to composite cathodes comprising such polymers, electrochemical cells comprising such cathodes, and to methods of making such composite cathodes and cells.
BACKGROUND
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the evolution of batteries continues, and particularly as lithium batteries become more widely accepted for a variety of uses, the need for safe, long lasting high energy batteries becomes more important. There has been considerable interest in recent years in developing high energy density cathode-active materials for use in high energy primary and secondary batteries with alkali-metal anode materials. Various types of cathode materials for the manufacture of thin film alkali-metal batteries are known in the art. Of considerable interest are cathode materials comprising sulfur-sulfur bonds, wherein high energy capacity and rechargeability are achieved by the electrochemical cleavage (via reduction) and reformation (via oxidation) of these bonds. For example, in combination with a lithium anode, elemental sulfur has a specific capacity of 1680 mAh/g, and sulfur-containing polymers with trisulfide and longer polysulfide groups in the polymers have shown specific capacities of more than 800 mAh/g. Examples of sulfur containing cathode materials disclosed for use in lithium and sodium batteries include, for example, elemental sulfur, organo-sulfur, and carbon-sulfur polymer compositions.
Elemental sulfur is an attractive cathode material in alkali-metal batteries owing to its low equivalent weight, low cost, and low toxicity. Many alkali-metal/sulfur battery cells have been described, as for example, in U.S. Pat. No. 3,532,543 to Nole et al., U.S. Pat. No. 3,953,231 to Farrington, and U.S. Pat. No. 4,469,761 to Bennett; Rauh et al.,
J. Electrochem. Soc.,
1979, 126, 523-527; Yamin et al.,
J. Electrochem. Soc.,
1988, 135, 1045-1048; and Peled et al.,
J. Power Sources,
1989, 26, 269-271. However, problems with alkali metal/elemental sulfur battery cells have been reported. One problem is that alkali-metal sulfides once reoxidized on cell charge may lead to the formation of an insulating layer on the positive electrode surface which electrochemically and ionically isolates it from the electroactive elements in the cell, resulting in poor cell reversibility and loss of capacity. The electrically and ionically non-conductive properties of sulfur are an obstacle to overcome in cells comprising elemental sulfur.
Attempts have been made to improve the electrochemical accessibility of elemental sulfur by complexing at least one polysulfurated chain with one dimensional electron conducting polymers as described in U.S. Pat. No. 4,664,991 to Perichaud et al.
Electroactive, conjugated polymers have been suggested as additives or components for electrochemical cells, capacitors, and other devices, such as electroluminescent displays, sensors, photovoltaic cells and the like. U.S. Pat. Nos. 5,460,905 and 5,462,566, to Skotheim describe an electrochemical cell which contains a composite cathode comprising carbon-sulfur compounds in combination with a conjugated polymer. U.S. Pat. Nos. 5,529,860, 5,601,947, 5,690,702, and 6,117,590 to Skotheim et al. describe sulfur-containing organic polymer materials which undergo oxidation and reduction with the formation and breaking, respectively, of many sulfur-sulfur bonds which are attached to conjugated structures. The conjugated polymer structures provide good electron transport and fast electrochemical kinetics at ambient temperatures and below. Novak et al. in
Chem. Rev.,
1997, 97, 207-281, review electroactive conductive polymers, including polymers comprising sulfur, for electrochemical cells.
In the preparation of electroactive, conductive organic polymers, a variety of oxidants and other reagents are used. For example, oxidants such as inorganic ferric salts and alkali metal persulfates, dichromates, periodates, and permanganates, are used as polymerization initiators. In addition, mineral acids such as HCl and H
2
SO
4
and other reagents are used in conjunction with the oxidants. Residual amounts of these oxidants or reagents or by-products of these materials formed in the polymerization process may remain in the electroactive, conductive organic polymers isolated.
In the fabrication of electrochemical cells, one problem encountered is that of corrosion of the current collectors by cell components, for example, by the electrolyte, by reduction or oxidation products of the electrodes, or by impurities or process residuals present in cell components, such as cathode materials. For example, Braithwaite et al., in
J. Electrochem. Soc.,
1999, 146, 448-456, describe, in lithium ion batteries, degradation of aluminum current collectors by pitting corrosion and degradation of copper current collectors by corrosion cracking. Another example of aluminum current collector corrosion is described by Behl et al., in
J. Power Sources,
1998, 72, 132-135.
One approach to reduce the corrosion of aluminum current collectors is described in U.S. Pat. No. 5,518,839, to Olsen, in which a layer of corrosion resistant metal, such as nickel, copper, chromium, titanium, or mixtures thereof, is applied to an etched aluminum current collector surface. Such an approach, however, adds an additional process step and adds weight and cost to the cell.
It is therefore an object of the present invention to provide electroactive, conductive organic polymer materials and composite cathodes which show reduced corrosion of current collectors.
It is a further object of the present invention to provide methods for making electroactive, conductive organic polymer materials and composite cathodes which show reduced corrosion of current collectors.
SUMMARY OF THE INVENTION
The present invention pertains to a method for preparing an electroactive, conductive organic polymer in its oxidized state, wherein the electroactive, conductive organic polymer comprises a positively charged polymer and one or more sulfide anions. The electroactive, conductive organic polymer in its oxidized state, prepared by the methods of the present invention, comprises (i) a positively charged polymer selected from the group consisting of positively charged polypyrroles, positively charged polyanilines, positively charged polythiophenes, positively charged [M″(S
m
)
x−
n
]
y
polymers, and positively charged [M′]
p
[{M″(S
m
)
x−
n
}
y
]
z
polymers, and (ii) one or more sulfide anions; wherein: M′ is a non-conductive repeating unit of the polymer and is the same or different at each occurrence; M″ is a conductive repeating unit of the polymer and is the same or different at each occurrence; n is an integer from 0 to 3 and is the same or different at each occurrence, with the proviso that the number of (S
m
)
x−
moieties in the positively charged polymer is equal to or greater than 1; y is an integer from 8 to 1000; m is an integer from 3 to 200 and is the same or different at each occurrence; x is an integer from 0 to 2 and is the same or different at each occurrence; p is an integer from 2 to 20,000; and z is an integer from 1 to 100,
Kovalev Igor P.
Sloane Dawn M.
Trofimov Boris A.
Kopec Mark
Moltech Corporation
Nicol Jacqueline M.
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