Harvesters
Reexamination Certificate
2000-05-03
2003-11-25
Choi, Ling-Siu (Department: 1713)
Harvesters
C525S279000, C525S280000, C525S281000, C525S540000
Reexamination Certificate
active
06652440
ABSTRACT:
TECHNICAL FIELD
The present invention pertains generally to the field of electroactive cathode materials for electrochemical cells. More particularly, the present invention pertains to cathode materials which comprise an electroactive, organic polymer, wherein the polymer comprises conductive segments and non-conductive segments, which polymer segments are bonded to polysulfide chains, and wherein the polysulfide chains comprise one or more moieties selected from the group consisting of: —(S
m
)—, —(S
m
)
−
, and (S
m
)
2−
, where m is an integer from 3 to 200 and is the same or different at each occurrence. The present invention also pertains to composite cathodes comprising such polymers, to electrochemical cells comprising such cathodes, and to methods of making such polymers, 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 1200 mAh/g. 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. Nos. 3,532,543, 3,953,231, and 4,469,761; 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.
Many problems with alkali metal/elemental sulfur battery cells have been reported. One pertains to alkali-metal sulfides, formed at the positive electrode on discharge, reacting with elemental sulfur to produce polysulfides that are soluble in the electrolyte causing self-discharge and loss of cell capacity. Another 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 in cathodes by adsorbing sulfur onto conductive carbons, as extensively reviewed by Kavan et al.,
Electrochimica Acta
, 1988, 33, 1605-1612, or by complexing at least one polysulfurated chain with one dimensional electron conductive polymers as described in U.S. Pat. No. 4,664,991 to Perichaud et al. Polycarbon sulfide compounds are described in U.S. Pat. No. 4,739,018 to Armand et al. Novak et al. in
Chem. Rev
., 1997, 97, 207-281, extensively review electroactive conductive polymers, including polymers comprising sulfur, for electrochemical cells.
A number of investigations of the electrochemical behavior of organo-sulfur materials, such as for example, in the presence of conductive polymers have been reported. For example, the redox process of disulfide compounds, such as dimercaptothiadiazole, has been shown by Naoi et al.,
J. Electroanal. Chem
., 1991, 318, 395-398, to be enhanced on polyaniline films. Composite cathodes consisting of the same dimercaptan and polyaniline powder showed similar enhanced performance as reported by Sotomura et al.,
Denki Kagaku
, 1993, 61, 1366-1372. In an attempt to improve the redox kinetics of dimercaptothiadiazole by the use of a polypyrrole film, it was reported by Ye et al.,
J. Electrochem. Soc
., 1994, 141, L49-L50, that a new composite electrode material is formed when a polypyrrole film is cycled .in an aqueous solution containing dimercaptothiadiazole.
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. 5,529,905, 5,601,947 and 5,690,702 to Skotheim et al. and copending U.S. Patent application Ser. No. 09/033,218, now U.S. Pat. No. 6,117,590, to Skotheim et al. of the common assignee 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. The incorporation of large fractions of polysulfur components in the carbon-sulfide polymer materials provides the exceptionally high storage capacity per unit weight of material. Upon reduction and oxidation, these materials need not lead to de-polymerization and re-polymerization of the polymer backbone.
U.S. Pat. No. 5,723,230 to Naoi et al describes sulfur-containing electrode materials for secondary batteries which contain from 2 but not more than 6 continuous S—S bonds.
Despite the various approaches proposed for the fabrication of high energy density alkali metal rechargeable cells containing elemental sulfur, organo-sulfur, and carbon-sulfur polymer cathode materials, there remains a need for materials that improve the utilization of electroactive cathode materials and the cell efficiencies and provide rechargeable cells with high sustainable capacities over many cycles.
It is therefore an object of the present invention to provide composite cathodes containing electroactive sulfur-containing cathode materials that exhibit a high utilization of the available electrochemical energy and retain this energy capacity without significant loss over many charge-discharge cycles.
It is another object of the present invention to provide high sulfur content polymers useful as cathode materials with high surface areas and structures that exhibit high charge and discharge rates, and to provide processes for making such high sulfur content polymers.
It is a further object of this invention to provide methods for fabricating cathode elements comprising the high sulfur content polymers of the present invention.
It is yet a further objective of this invention to provide energy storing rechargeable battery cells which incorporate such composite cathodes, and which exhibit much improved self-discharge characteristics, long shelf life, improved capacity, and high manufacturing reliability.
SUMMARY OF THE INVENTION
The present invention pertains to electroactive organic polymers, wherein the polymers, in their oxidized state, comprise conductive polymer segments and non-conductive polymer segments, wherein one or more of the conductive and non-conductive polymer segments are bonded to polysulfide chains; and
Annenkov Vadim V.
Carlson Steven A.
Kovalev Igor P.
Trofimov Boris A.
Ching Alexander B.
Choi Ling-Siu
Moltech Corporation
Nicol Jacqueline M.
Squire Sanders & Dempsey L.L.P.
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