WO2000067339A1

WO2000067339A1 - Electroactive sulfur containing, conductive, highly branched polymeric materials for use in electrochemical cells

Info

Publication number: WO2000067339A1
Application number: PCT/US2000/012076
Authority: WO
Inventors: Tatyana I. Movchan; Terje A. Skotheim; Alexei B. Gavrilov; Boris A. Trofimov
Original assignee: Moltech Corporation
Priority date: 1999-05-04
Filing date: 2000-05-03
Publication date: 2000-11-09
Also published as: AU5125700A

Abstract

Provided is an electroactive, highly branched, conductive organic polymer for use in electrochemical cells, wherein the polymer comprises a plurality of repeating units, which repeating units are bonded to polysulfide chains, and the polysulfide chains comprise a moiety selected from the group consisting of -(Sm)-, -(Sm)-, and (S¿m)?2-; where m is an integer from 3 to 200 and is the same or different at each occurrence. Also provided are composite cathodes comprising such polymers, electrochemical cells comprising such cathodes, and methods of preparing such polymers, composite cathodes, and cells.

Description

ELECTRO ACTIVE SULFUR CONTAINING, CONDUCTIVE, HIGHLY BRANCHED POLYMERIC MATERIALS FOR USE IN ELECTROCHEMICAL

CELLS

TECHNICAL FIELD The present invention pertains generally to the field of electroactive cathode materials for electrochemical cells. More particularly, the present invention pertains to an electroactive, highly branched, conductive organic polymer, wherein the polymer comprises a plurality of repeating units, which repeating units are bonded to polysulfide chains, and each of the polysulfide chains comprises a moiety selected from the group consisting of -(S_m)-, -(S_m)^", and (S_m)"^"; 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 rechargeabihty 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. 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. 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 conducting 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 found by Ye et al. , J. Phys. Chem., 1996, 100, 15848-15855, 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. Pat. Application Ser. No. 09/033,218 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-sulfur 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 sulfur-containing electroactive cathode materials and the corresponding electrochemical 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 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, highly branched, conductive organic polymers, wherein the polymers, in their oxidized state, comprise a plurality of repeating units, wherein one or more of the repeating units are bonded to polysulfide chains; and, further wherein the polysulfide chains comprise one or more moieties selected from the group consisting of -(S_m)-, -(S_m)^", and (S_m) ^"; where m is an integer from 3 to 200 and is the same or different at each occurrence. In one embodiment, the repeating units comprise one or more moieties selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives. In one embodiment, the one or more repeating units comprise pyrrole. In one embodiment, the one or more repeating units comprise aniline. In one embodiment, the electroactive, highly branched, conductive organic polymer comprises a polymer backbone and the polysulfide chains comprise covalent moieties, -(S_m)-, which covalent moieties are covalently bonded by one or both of their terminal sulfur atoms as a side group to the polymer backbone. In one embodiment, the polysulfide chains comprise polysulfide anion moieties, -(S_m)^", which anion moieties are covalently bonded by a terminal sulfur atom to the polymer. In one embodiment, the polysulfide chains comprise polysulfide dianion moieties, (S_m) ^", and the polymer repeating units comprise positively charged atoms; wherein the dianion moieties are ionically bonded to one or more of the positively charged atoms. In one embodiment, m of the moieties, -(S_m)-, -(S_m) , and (S_m) ^", is an integer from 9 to 200 and is the same or different at each occurrence. In one embodiment, m of the moieties, -(S_m)-, -(S_m)^", and (S_m) ^", is an integer from 24 to 100 and is the same or different at each occurrence.

In another embodiment of the present invention, the electroactive, highly branched, conductive organic polymer, in its oxidized state, is of the formula: 5

[M (S_m)^χ-_n]_y wherein:

M is a repeating unit; 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 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; and, x is an integer from 0 to 2 and is the same or different at each occurrence. In one embodiment, M comprises one or more repeating units selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives. In one embodiment, M is pyrrole. In one embodiment, M is aniline.

In a preferred embodiment, y is an integer from 20 to 400. In one embodiment, the polymer comprises greater than 50% by weight of sulfur. In a preferred embodiment, the polymer comprises greater than 75% by weight of sulfur. Another aspect of the present invention pertains to a method of making an electroactive, highly branched, conductive organic polymer of this invention, the method comprising the steps of: (a) providing a dispersion of elemental sulfur in a liquid medium; (b) adding to the dispersion of step (a) one or more monomers and a polymerization initiator comprising an oxidant; (c) stirring the mixture of step (b) thereby forming an electroactive, highly branched, conductive organic polymer; and (d) separating the polymer from the reaction medium of step (c).

In one embodiment, the one or more monomers is selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives.

In one embodiment, the particle size of the elemental sulfur is from 0.01 microns to 100 microns. In one embodiment, the weight ratio of the monomer to elemental sulfur is from 1 :1 to 1 :15.

In one embodiment, the polymerization initiator comprises an oxidant selected from the group consisting of FeCl₃, Fe(NO₃)₃, CuCl₂, H₂O₂, (NH₄)₂S₂O₈, KIO₃, 1₂, KMnO₄, and K₂Cr₂O₇.

In one embodiment, the liquid medium comprises water. 6

In one embodiment, the method further comprises after step (d), one or more steps of: (e) purifying the polymer after separation; and (f) drying the polymer.

A further aspect of the present invention pertains to an electroactive, highly branched, organic polymer prepared by the method as described herein. In one embodiment, the polymer comprises greater than 50% by weight of sulfur. In a preferred embodiment, the polymer comprises greater than 75% by weight of sulfur.

Another aspect of the present invention pertains to composite cathodes comprising the electroactive, highly branched, conductive organic polymers of this invention for use in electrochemical cells. In one embodiment, the composite cathode comprises: (a) an electroactive, highly branched, conductive organic polymer of this invention, as described herein; and (b) one or more conductive fillers selected from the group consisting of conductive carbons, graphites, activated carbon fibers, non-activated carbon nanofibers, metal flakes, metal powders, metal fibers, carbon fabrics, metal mesh, electrically conductive polymers, and electrically conductive metal chalcogenides. In one embodiment, the composite cathode further comprises elemental sulfur.

Another aspect of the present invention pertains to a method of preparing a composite cathode comprising the electroactive, highly branched, conductive organic polymers of the present invention, as described herein, which method comprises the steps of: (a) dispersing or suspending in a liquid medium the electroactive polymer; (b) optionally adding to the mixture of step (a) a conductive filler; (c) mixing the composition resulting from step (b) to disperse the electroactive polymer; (d) casting the composition resulting from step (c) onto a suitable substrate; and (e) removing some or all of the liquid from the composition resulting from step (d) to provide a composite cathode.

In one embodiment, the method further comprises, subsequent to step (e), step (f) of heating the composite cathode structure to a temperature of 120 °C or greater.

In one embodiment, the method further comprises the addition to any or all of the steps (a), (b), or (c) of one or more materials selected from the group consisting of binders, electrolytes, non-electroactive metal oxides, and electroactive transition metal chalcogenides. Another aspect of the present invention pertains to an electrochemical cell. The cell of this invention comprises an anode, a composite cathode comprising an electroactive, highly branched, conductive organic polymer of the present invention, as described herein, and an electrolyte interposed between the anode and the cathode. In one 7 embodiment, the anode comprises one or more materials selected from the group consisting of lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium- intercalated carbons, and lithium-intercalated graphites. In one embodiment, the electrolyte is an organic electrolyte comprising one or more materials selected from the group consisting of liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes.

Another aspect of the present invention pertains to methods of forming an electrochemical cell. The methods comprise the steps of providing an anode, providing a cathode comprising an electroactive, highly branched, conductive organic polymer of the present invention, as described herein, and interposing an electrolyte between the anode and the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the conductivity of a physical mixture of polypyrrole and sulfur (+) and the conductivity of highly branched pyrrole/sulfur polymers (•), prepared as described herein, as a function of sulfur content.

Figure 2 shows cyclic voltametry of Example 22, using as electrolyte 0.5 M lithium bis(trifluoromethylsulfonyl) imide in a mixture of 1,2-dimethoxy ethane (DME) and 1,3- dioxolane (DOL) at a scan rate of 10 mV/sec. Figure 3 shows cyclic voltametry of Example 23, using as electrolyte 0.5 M lithium bis(trifluoromethylsulfonyl) imide in a mixture of DME and DOL at a scan rate of 10 mV/sec.

Figure 4 shows cyclic voltametry of Example 24, using as electrolyte 0.5 M lithium bis(trifluoromethylsulfonyl) imide in a mixture of DME and DOL at a scan rate of 10 mV/sec.

DETAILED DESCRIPTION OF THE INVENTION

Cathode Active Polymers One aspect of the present invention pertains to cathode active polymers which are electroactive, highly branched, conductive organic polymers and which comprise a plurality of conjugated repeating units bonded to polysulfide chains. 8

The term "branched polymer" is used herein in the conventional sense to refer to polymers which are characterized by the presence of branch points, i.e., atoms or small groups from which more than two long chains emanate or by the presence of more than two end groups. The term "highly branched polymer", as used herein, pertains to branched polymers characterized by multiple end groups, such as from 5 to 500 end groups.

The terms "conductive polymer" and "conductive organic polymer", as used herein, refer, respectively, to polymers and organic polymers having conjugated π-electron polymeric segments which can be oxidized and reduced reversibly and which have electrically conductive properties in at least one of their oxidation states.

The term "monomer" is used herein to describe moieties that are capable of reacting to form polymers.

The term "repeating unit", as used herein, refers to one or more moieties in a polymer derived from the polymerization of one or more monomers. For example, the term "aniline repeating units" refers to those aniline repeating units present in polyaniline (I) and to any of the various forms of the aniline repeating units in polyaniline such as, for example, leuco emeraldine (y=l), emeraldine (y=0.5), and pernigraniline (y=0), as shown below, (I).

(i)

The term "polysulfide chain", as used herein, relates to a divalent chemical moiety, -(Sm)-, -(S_m) , or (S_m)^2", in its oxidized state, which moiety is bonded covalently, covalently and ionically, or ionically to repeating units of a polymer, where m is equal to or greater than 3. Typically, m of the polysulfide chain is an integer from 3 to 200 and is the same or different at each occurrence. In one embodiment, m is an integer from 9 to 200 and is the same or different at each occurrence. In another embodiment, m is an integer from 24 to 100 and is the same or different at each occurrence. Electroactive, highly branched, conductive organic polymers of the present invention may be described by the following formula:

[M (S_m)^X-n]y wherein:

M is a repeating unit 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 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; and x is an integer from 0 to 2 and is the same or different at each occurrence.

In one embodiment, the repeating unit, M, is derived from the oxidative polymerization of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives. Suitable derivatives include, but are not limited to, alkyl derivatives, amine derivatives, and benzo derivatives. Examples of alkyl derivatives include methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, octyl, and decyl, such as N-methyl pyrrole, 3 -methyl pyrrole, and 2-methyl aniline. Suitable monomers include, but are not limited to:

( ) so ndole,

(e) thiophene,

(f) alkylthiophene,

(g) carbazole,

(h) furan,

(i) para-phenylene diamine,

(j) meta-phenylene diamine,

(k) ortho-phenylene diamine,

Other suitable repeating units include, but are not limited to, phenylene, acetylene, thienylene-vinylene, and phenylene-vinylene. The repeating units, M, may comprise more than one type of repeating unit as one of the options to obtain the highly branched conductive polymers of the present invention. For example, polymers derived from aniline will be more highly branched when also incorporating phenylene diamine repeating units.

In one embodiment, the ratio of aniline to phenylene diamine is from about 5 to 1 to about

100 to 1. In a preferred embodiment, the number of polymer repeating units, y, is from 20 to

400.

In one embodiment, the electroactive, highly branched, conductive organic polymers of the present invention comprise at least 50% by weight of sulfur. In a preferred embodiment, the electroactive, highly branched, conductive polymers of the present invention comprise at least 75% by weight of sulfur.

Repeating units of the electroactive, highly branched, conductive organic polymer of this invention are bonded to polysulfide chains, wherein the polysulfide chains comprise one or more moieties selected from the group consisting of -(S_m)-, -(S_m)^", and (S_m) ^"; where m is an integer from 3 to 200 and is the same or different at each occurrence. In one embodiment, m is an integer from 9 to 200 and is the same or different at each occurrence. In one embodiment, m is from 24 to 100 and is the same or different at each occurrence. In one embodiment, the electroactive, highly branched, conductive organic polymer comprises a polymer backbone and the polysulfide chains comprise covalent moieties, - (S_m)-, which covalent moieties are covalently bonded by one or both of their terminal sulfur atoms as a side group to the polymer backbone. In one embodiment, the polysulfide chains comprise polysulfide anion moieties,-(S_m)^", which anion moieties are covalently bonded by a terminal sulfur atom to the polymer. In one embodiment, the polysulfide chains comprise polysulfide dianion moieties, (S_m) ^", and the polymer repeating units comprise positively charged atoms; wherein the dianion moieties are ionically bonded to one or more of the positively charged atoms. In other words, the bonding of the polysulfide chains to repeating units of the highly branched, conductive polymer may be ionic or covalent or both covalent and ionic. Covalent bonding of polysulfide chains, - (S_m)-, or -(S_m)^", may be, for example, through C-S bonds or N-S bonds to the repeating units. Ionic bonding of polysulfide chains, -(S_m)^", and (S_m) ^", may be, for example, to N, S, or C positively charged atoms in the repeating units.

The highly branched, conductive organic polymers of the present invention typically have 5 to 10% of the repeating units as branch points. In other words, for polymers with y = 100, there are typically 7 to 12 end groups or 5 to 10 branches for each polymer molecule. For polymers of higher molecular weight, such as, for example, where y = 500, there are typically 27 to 52 end groups or 25 to 50 branches for each polymer molecule. In one embodiment, the highly branched polymer is characterized by more than 4 end groups comprising the repeating units, preferably by more than 6 end groups comprising the repeating units, and more preferably by more than 25 end groups comprising the repeating units. In one embodiment, the highly branched polymer is characterized by 7 to 100 end groups comprising the repeating units, and preferably by 26 to 100 end groups comprising the repeating units. Methods For Making Cathode Active Polymers

Another aspect of the present invention pertains to processes for making the electroactive, highly branched, conductive organic polymers of this invention.

In one embodiment of the methods of the present invention for preparing an electroactive, highly branched, conductive organic polymer, the method comprises the steps of (a) providing a dispersion of elemental sulfur in a liquid medium; (b) adding to the dispersion of step (a) one or more monomers and a polymerization initiator comprising an oxidant; (c) stirring the mixture of step (b) thereby forming an electroactive material comprising the electroactive, highly branched, conductive organic polymer; and (d) separating the electroactive material from the reaction medium.

Dispersion or suspension of elemental sulfur in the liquid medium can be carried out by methods known in the art for dispersing or suspending solids in liquids. For example, the elemental sulfur, such as flowers of sulfur, can be added to the liquid medium with stirring to provide the dispersion or suspension. In one embodiment, the particle size of the elemental sulfur dispersed in the liquid medium is from about 0.01 microns to 100 microns.

In an alternative method, the dispersion of elemental sulfur may be made in situ from reduced sulfur moieties such as, for example, sulfide anions, polysulfide anions, or polysulfanes by oxidation. Examples of suitable reduced sulfur moieties include, but are not limited to, M₂ (S_r), and H₂(S_r), where M is Li, Na, K, or NH₄, and r is an integer from 1 to 8. For example, the polymerization initiator comprising an oxidant may both initiate polymerization and oxidize reduced sulfur moieties. An electroactive, highly branched, conductive organic polymer of the present invention may be formed from a mixture of one or more monomers, reduced sulfur moieties and a polymerization initiator comprising an oxidant in a liquid medium.

The liquid medium for providing the elemental sulfur dispersion must be compatible with the oxidant polymerization initiator and may be aqueous or non-aqueous and may be a single solvent or a multi-component solvent. In a preferred embodiment of the invention, the liquid medium comprises water. Additional liquids may be used in the liquid medium to enhance the dispersion of the hydrophobic sulfur. For example, water miscible liquids such as alcohols may be used in volume ratios of alcohol to water of from about T.5 to about 1 :20. It is well known that surfactants can aid the dispersion or suspension of solids in liquid media, such as water. Surfactants may optionally be added to the liquid medium for dispersing or suspending the elemental sulfur in the methods of the present invention. Suitable surfactants include anionic, cationic, and non-ionic surfactants. Examples of suitable surfactants include, but are not limited to, alkylbenzene sulfonates, alkyl sulfonates, alkyl sulfates, alkyl phosphates, dialkyl sulfosuccinates, ethoxylated alcohols, ethoxylated alkylphenols, acetylenic alcohols, trimethylalkyl ammonium halides, benzyl trimethyl ammonium halides, alkyl pyridinium halides, and alkylamine N-oxides.

The oxidative polymerization of pyrrole and aniline in the presence of inorganic powders and granular materials has been described, for example, in U.S. Pat. No. 4,937,060, to Kathirgamanathan et al, in which talc, mica, wollastonite, calcium carbonate, aluminum hydroxide or hydroxyapatite were coated with conductive polymer. Various methods may be used to develop an understanding of the composition of conductive polymers, such as those of the present invention. Electrical conductivity measurements on examples of highly branched conductive polymers of the present invention prepared from pyrrole and sulfur and electrical conductivity measurements on mixtures of polypyrrole with elemental sulfur show significant differences. The conductivity of the polymers of the present invention is much higher compared with the conductivity of physical mixtures of polypyrrole and sulfur with the same sulfur content, from about 80% to 95%), as can be seen in Figure 1. The composition of the conductive polymer is supported by additional experiments.

For example, the polymer of Example 21 was treated with carbon disulfide as described in Example 22 in a process which removes elemental sulfur. The polymer product of Example 22 was treated with an aqueous solution of sodium chloride as described in Example 23. The polymer product of Example 22 was also treated with sodium borohydride in a reduction process as described in Example 24. Sodium borohydride reduction of polysulfide materials, R(Sι)R', where R is an organic group and R¹ is an organic group or H and 1 is > 2, is a standard method which produces RSH compounds. This method is described by Cardone in The Analytical Chemistry of Sulfur and its Compounds, Part II, pp. 363-365, Wiley, New York (1972). Elemental analysis of the polymers of Examples 21, 22, 23, and 24 is compiled in

Table 3. Figures 2, 3, and 4 summarize cyclic voltametry measurements on the polymers of Examples 22, 23, and 24, respectively. The experimental data summarized in Examples 21, 22, 23, and 24 and in Table 3 and Figures 2, 3, and 4 provide support for the composition of one example of the highly branched conductive polymers of this invention derived from pyrrole and sulfur. The polymer of Example 22, obtained by carbon disulfide extraction of the polymer of Example 21 to remove elemental sulfur, is essentially free of elemental sulfur as shown by infrared spectroscopy and Differential Scanning Calorimetry (DSC). Sodium borohydride reduction of the polymer of Example 22 yields a material containing sulfur and pyrrole units. From the elemental analysis of Example 24, as shown in Table 3, it is clear that there are approximately 8-9 pyrrole units for each sulfur. From the solubility properties and thermal analysis, the product of Example 24 must be polymeric. The reduction in sulfur content from 30.88 % to 4.62 % in the conversion of the polymer of Example 22 to the polymer of Example 24 comes from removal of all S-S bonds by the sodium borohydride treatment. The cyclic voltametry data shown in Figure 2 indicates the absence of S-S bonds in the polymer of Example 24. The average sulfide chain length in the polymer of Example 22 must be approximately 8-10 sulfur atoms. The polymer of Example 23, formed by washing the polymer of Example 22 with sodium chloride to liberate ionically bound polysulfides, shows a reduction of sulfur content by elemental analysis. A comparison of the cyclic voltametry scans of Examples 22 and 23, shown in Figure 2 and Figure 3, indicate a presence of readily reducible anionic polysulfides in the polymer of Example 22 by the broad peak at 1.8 V which is removed in the chloride washing step.

In summary, the examples support a composition for the conductive polymers of the present invention which possesses both ionically and covalently bonded polysulfide moieties. While not wishing to be bound by any theory, the polymerization of the monomers in the presence of finely dispersed sulfur particles in the present invention may be viewed as a simultaneous coating process and chemical bonding process. In other words, as the polymerization of the monomers proceeds, the sulfur particles are coated by the developing polymer and at the same time chemical bonding of the polymer takes place to the sulfur particles which react to form polysulfide chains. No specific mechanism can be ascribed but oxidative polymerization of pyrrole or aniline in presence of sulfur particles may create highly branched conductive polymers with bonded polysulfide chains in a number of ways. For example, pyrrole or aniline may undergo polymerization by reaction with the initiating oxidant to form a growing polymer which is subsequently terminated by reaction at the surface of sulfur particles with the formation of the polysulfide chains bonded to a repeat unit of the polymer. Alternatively, the oxidant or its reduced form may react with sulfur to create reactive sites from which the polymer chains are built, e.g., of pyrrole or of aniline, or the oxidant may be adsorbed on the sulfur surface and create initiation sites. Polymerization of pyrrole or aniline initiated by oxidants is believed to involve radical cation species. It is known that the S₈ rings in elemental sulfur are readily opened by such radical cation species to form polysulfide chains (Voronkov et al. , Reactions of Sulfur with Organic Compounds, 1987, 40-44, Consultants Bureau, New York; and Pryor, Mechanisms of Sulfur Reactions, 1962, 7-15, McGraw-Hill, New York). An additional alternative is that a combination of the above mechanisms operates simultaneously. In other words, the elemental sulfur participates in the formation of the highly branched conductive polymer with bonded polysulfide chains in both terminator and initiator roles. In one embodiment of the methods of this invention, the weight ratio of the monomer to elemental sulfur is from about 1 :1 to 1 :15.

Many oxidants are known to induce polymerization of the monomer repeat units useful in the methods of this invention. The choice of oxidant will depend upon the monomer which is to be polymerized, the degree of branching desired, the molecular weight desired, and other factors. For example, reaction conditions for the preparation of two-dimensional, branched polypyrroles and their electronic and magnetic properties have been described by Schmeisser et al, Synthetic Metals, 1998, 93, 43-58. The polymerization of aniline by electrochemical methods, in the presence of additives, is described by Wei et al, J. Phys. Chem., 1990, 94, 7716-7721. Also noted by these authors are cross-linking or branching reactions of aniline from oxidative polymerization with strong chemical oxidants, by electrochemical oxidation of aniline at high applied potential, and by incorporation of difunctional additives. U.S. Pat. No. 5,958,301 to Angelopolous et al. describes a method for the preparation of branched electrically conductive polymers by the incorporation of multifunctional monomers in the process. Suitable oxidants for use as the polymerization initiators in the methods of the present invention include, but are not limited to, FeCl₃, Fe(NO₃)₃, CuCl₂, H₂O₂, (NH₄)₂S₂O₈, KIO₃, 1₂, KMnO₄, (NH₄)₂Cr₂O₇, and K₂Cr₂O₇. The concentration of the oxidant for the polymerization in the methods of this invention is typically close to that required by the stoichiometry of the oxidative process. Concentrations higher or lower than that required by the stoichiometry, such as from 85% to 150%, may be used. It is generally preferred to use a concentration from 100%) to 120%) of the amount required by the stoichiometry to obtain an acceptable reaction rate. Furthermore, excess oxidant may add cost without a commensurate improvement in rate.

The oxidative polymerization of the monomers can be carried out at temperatures from -30 °C to about 80 °C. It is preferred to use a temperature at or above ambient temperature to enhance the degree of the branching in the conductive polymer formed. Preferred temperatures are from about 20 °C to about 50 °C. The oxidant, in addition to initiating the formation of branched polymer bonded polysulfide chains, may directly oxidize the elemental sulfur introducing S-O bonds. These S-O species, such as for example, -(S_m)-SO₃ ^" or -(S_m)-SO ^", where m is an integer equal to or greater than 3, may be present in various concentrations in the polymers of the present invention. Certain of the oxidative polymerization initiators are more powerful oxidants and may generate a higher concentration of these S-O species. Likewise, more vigorous reaction conditions, such as a higher temperature, may generate a higher concentration of S-O species. These S-O species are thiophiles which would also readily react with and open elemental sulfur S₈ rings to further promote the polymerization process to form the polymers of the present invention. In one embodiment, the highly branched polymer of this invention further comprises one or more moieties selected from the group consisting of -(S_m)-SO₃ ^" and -(S_m)-SO₂\

X-ray photoelectron spectroscopy (XPS) is a technique which measures the binding energy of electrons in chemical species. The binding energy is sensitive to the specific environment of the atom. For example, the binding energy of the 2 p electrons of sulfur atoms in elemental sulfur differs from that in species with S-O bonds or in polysulfides. The measurements on the polymers of Examples 21, 22, 23, and 24 by XPS show the presence of different sulfur species, including the presence of S-O species in addition to polysulfides and elemental sulfur.

Separating the electroactive, highly branched, conductive organic polymer from the reaction medium can be performed by procedures known in the art for the separation of solids from liquids. The polymers, which are typically insoluble in the liquid medium, can, for example, be separated by filtration, by centrifugation, or by simply decantation. After separation, the polymer may be further purified by washing with liquids which will remove impurities but will not dissolve the polymer, such as with water or organic liquids. After separation and any purification, it is normally desirable to dry the polymer. Drying can be performed by any of the drying methods known in the art.

Cathodes Comprising Electroactive. Highly Branched. Conductive Organic

Polymers

One embodiment of the present invention pertains to a composite cathode for use in an electrochemical cell, wherein said cathode comprises: (a) an electroactive, highly branched, conductive organic polymer; which polymer, in its oxidized state, comprises a plurality of repeating units, which repeating units are bonded to polysulfide chains; wherein said 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; and (b) one or more conductive fillers selected from the group consisting of conductive carbons, graphites, activated carbon fibers, non-activated carbon nano fibers, metal flakes, metal powders, metal fibers, carbon fabrics, metal mesh, electrically conductive polymers, and electrically conductive transition metal chalcogenides.

In one embodiment, the highly branched polymer may also function both as an electrically conductive filler and an electroactive, conductive polymer. The excellent electrical conductivity of the highly branched polymer as, for example, described in Example 20, may be advantageous in significantly reducing the amount of additional conductive filler, such as conductive carbons, in the composite cathode. For example, as described in Examples 17 and 18, only 5.5 weight % of a conductive carbon, instead of a typical loading of about 20 to 35 weight % of a conductive carbon, needed to be included in the composite cathode containing 50 weight % of the highly branched polymer of this invention.

Methods Of Making Cathodes Comprising Electroactive. Highly Branched. Conductive Organic Polymers One aspect of the present invention pertains to methods for fabricating composite cathodes comprising the electroactive, highly branched, conductive organic polymers of the present invention. In one embodiment of the method for preparing a composite cathode of the present invention, the method comprises the steps of: (a) dispersing or suspending in a liquid medium the electroactive, highly branched, conductive organic polymer, as described herein; (b) optionally adding to the mixture of step (a) a conductive filler; (c) mixing the composition resulting from step (b) to disperse the electroactive polymer; (d) casting the composition resulting from step (c) onto a suitable substrate; and (e) removing some or all of the liquid from the composition resulting from step (d) to provide a composite cathode. Examples of liquid media suitable for use in the methods of the present invention include aqueous liquids, non-aqueous liquids, and mixtures thereof. Especially preferred liquids are non-aqueous liquids such as methanol, ethanol, isopropanol, propanol, butanol, tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene, acetonitrile, and cyclohexane.

Mixing of the various components can be accomplished using any of a variety of methods so long as the desired dissolution or dispersion of the components is obtained. Suitable methods of mixing include, but are not limited to, mechanical agitation, grinding, ultrasonication, ball milling, sand milling, and impingement milling.

The formulated dispersions can be applied to substrates by any of a variety of well- known coating methods and dried using conventional techniques. Suitable hand coating techniques include, but are not limited to, the use of a coating rod or gap coating bar. Suitable machine coating methods include, but are not limited to, the use of roller coating, gravure coating, slot extrusion coating, curtain coating, and bead coating. Removal of some or all of the liquid from the mixture can be accomplished by any of a variety of conventional means. Examples of suitable methods for the removal of liquid from the mixture include, but are not limited to, hot air convection, heat, infrared radiation, flowing gases, vacuum, reduced pressure, extraction, and by simply air drying if convenient.

Rechargeable Battery Cells and Methods of Making Same One aspect of the present invention pertains to a rechargeable electrochemical cell which comprises: (a) an anode; (b) the composite cathode comprising an electroactive highly branched, conductive organic polymer of the present invention, as described herein; and (c) an electrolyte interposed between said anode and said cathode.

The cells comprising the polysulfide-containing, highly branched, conductive organic polymers of the present invention possess properties which are advantageous in several respects. The highly branched, conductive polymer structures enhance the 19 electrochemical cycling capability, for example, in relation to non-branched one- dimensional conductive polymer materials. In addition, the highly branched conductive structures typically exhibit advantageous thermal stability, oxidative stability, and mechanical properties of benefit in the fabrication of the cathode materials. The highly branched conductive polymers also typically possess higher electrical conductivity which is, furthermore, maintained over a wide temperature range in comparison to one dimensional conductive polymers. This is particularly useful for good low temperature and ambient temperature performance when the electroactive, highly branched polymers of this invention are utilized in electrochemical cells. The highly branched, conductive polymer structure has a potential disadvantage of reducing the number of possible bonding sites for polysulfide chains in the presence of multiple branching points, in comparison to a non-branched, one dimensional conductive polymer. However, if desired, this can be readily compensated for in the highly branched, conductive polymers of this invention by increasing the length of the polysulfide chains, while retaining the positive features of the highly branched, conductive polymer structure. For example, suitable methods to increase the length of the polysulfide chains in the highly branched, conductive polymers of the present invention include, but are not limited to, increasing the weight ratio of elemental sulfur to the one or more monomers during preparation of the polymer, adjusting the polarity and amount of liquid medium during preparation of the polymer, and adjusting the type, polarity, and amount of electrolyte solvents present during electrochemical cycling of the polymers in an electrochemical cell.

Another aspect of the present invention pertains to methods of forming rechargeable electrochemical cells, said methods comprising the steps of: (a) providing an anode; (b) providing a composite cathode of the present invention, as described herein; and (c) interposing an electrolyte between the anode and the cathode.

Suitable anode materials for the electrochemical cells of the present invention include, but are not limited to, lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium-intercalated carbons, and lithium-intercalated graphites.

The electrolytes used in battery cells function as a medium for the storage and transport of ions, and in the special case of solid electrolytes and gel electrolytes, these materials may additionally function as separator materials between the anode and the cathode. Any liquid, solid, or gel material capable of storing and transporting ions may be used, so long as the material is electrochemically and chemically unreactive with respect to the anode and the cathode, and the material facilitates the transport of ions between the anode and the cathode. The electrolyte must also be electronically non-conductive to prevent short circuiting between the anode and the cathode.

Examples of suitable electrolytes for use in the present invention include, but are not limited to, organic electrolytes comprising one or more materials selected from the group consisting of liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes.

Examples of useful liquid electrolytes include, but are not limited to, liquid electrolyte solvents, such as, for example, N-methyl acetamide, acetonitrile, carbonates, sulfones, sulfolanes, aliphatic ethers, cyclic ethers, glymes, siloxanes, dioxolanes, N- alkylpyrrolidones, substituted forms of the foregoing, and blends thereof; to which is added an appropriate ionic electrolyte salt.

These liquid electrolyte solvents are themselves useful as plasticizers for gel polymer electrolytes. Examples of useful gel polymer electrolytes include, but are not limited to, those comprising polymers selected from the group consisting of polyethylene oxides, polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes, polyethers, sulfonated polyimides, perfluorinated membranes, such as, for example, NAFION™ resins, polydivinyl polyethylene glycols, polyethylene glycol diacrylates, polyethylene glycol dimethacrylates, derivatives of the foregoing, copolymers of the foregoing, crosslinked and network structures of the foregoing, and blends of the foregoing; to which is added an appropriate ionic electrolyte salt.

Examples of useful solid polymer electrolytes include, but are not limited to, those comprising polymers selected from the group consisting of polyethers, polyethylene oxides, polypropylene oxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes, derivatives of the foregoing, copolymers of the foregoing, crosslinked and network structures of the foregoing, and blends of the foregoing; to which is added an appropriate ionic electrolyte salt.

In addition to solvents, gelling agents, and ionically conductive polymers as known in the art for non-aqueous electrolytes, the non-aqueous electrolyte further comprises one or more ionic electrolyte salts, also as known in the art, to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the present invention include, but are not limited to, MSCN, MBr, MI, MClO₄, MAsF₆, MSO₃CF₃, MSO₃CH₃, MBF₄, MB(Ph)₄,

MPF₆, MC(SO₂CF₃)₃, MN(SO₂CF₃)₂, ^MN — S0₂CF₂CF₂CF₂CF₂— SO-^

, ₅ and the like, where M is Li or Na.

Other electrolyte salts useful in the practice of this invention are lithium polysulfides, lithium salts of organic ionic polysulfides, and those disclosed in U.S. Pat. No. 5,538,812 to Lee et al Preferred ionic electrolyte salts are Lil, LiSCN, LiSO₃CF₃ (lithium triflate), LiN(SO₂CF₃)₂ (lithium imide), and LiC(SO₂CF₃)₃ (lithium methide).

EXAMPLES

Several embodiments of the present invention are described in the following examples, which are offered by way of illustration and not by way of limitation.

Example 1

To 5L of deionized water stirred in a 22L flask was added anhydrous FeC (680 g). To this stirred solution was added sulfur (1090 g) through a dry powder funnel followed by ethanol (300 mL). Pyrrole (255.8 g) was added dropwise during 15 minutes at ambient temperature, and the reaction mixture was stirred for an additional 2 hours. Additional deionized water (10L) was added, and stirring was continued for 2 hours. The resultant black solid was recovered by filtration and washed with deionized water and then with acetone. The solid was washed again with water and then dried under vacuum at room temperature for 18 hours. Analysis of the polymer gave the following results: C, 7.17%; N, 1.93%; S, 87.0%.

Example 2

Powdered sulfur (10 g, 310 mmol) was added in portions, during 10 minutes, to a solution of (NH₄)₂S₂O₈ (5 g, 22 mmol) in 12.5 mL of IN aqueous HCl. The mixture was stirred for an additional 40 minutes at ambient temperature, and aniline (4.1 g, 44 mmol) was added. The color of the reaction mixture changed from yellow to black, and the temperature rose to 45 °C. Stirring was continued at ambient temperature for 2.5 hours, and the mixture was diluted with water (10 mL) and allowed to stir overnight. The black solid was filtered, washed with water to remove chloride ion, and dried under vacuum at 20-25 °C for 12 hours. The yield of solid, highly branched, polymer was 11.5 g, melting point 116-118 °C. Additional washing of the polymer with acetone and diethyl ether yielded a purified polymer of melting point 108-120 °C. Analysis of the purified polymer gave the following results: C, 4.74%; H, 0.22%; N, 1.12%; S, 89.22%.

Example 3

Powdered sulfur (6.4 g, 200 mmol) was added in portions, during 30 minutes, to 33% H₂O₂ (0.36 g, 3.4 mmol) in 10 mL of 2N aqueous HCl. After stirring for 20 minutes, aniline (0.62 g, 6.7 mmol) was added in portions. The yellow reaction mixture turned black, and the temperature rose to 30 °C. The reaction mixture was stirred for 9 hours and then allowed to stand overnight. The black solid was filtered, washed with water and dried under vacuum at 20-25 °C for 6 hours to yield 6.68 g of solid polymer, melting point 122- 126 °C. Analysis of the highly branched polymer gave the following results: C, 4.86%; H, 0.25%; N, 0.69%; S, 86.96%.

Example 4

To a stirred solution of aniline (2.05 g, 22 mmol) in 2.5 mL of IN aqueous HCl was added sulfur (5 g, 156 mmol) in portions over 10 minutes The mixture was stirred for an additional 40 minutes at 20 °C, and a solution of KIO₃ (2.35 g, 11 mmol) in 50 mL of 0.5 N HCl was added over 10 minutes After stirring for 5 hours, the mixture was allowed to sit overnight. The resulting black solid was filtered, washed successively with a 10% solution of sodium sulfide in water (10 mL), water, ethanol, and diethyl ether. After drying under vacuum at 50-60 °C, 6.6 g of highly branched polymer was obtained, melting point 116-180 °C. The following analysis results were obtained: C, 12.28%; H, 1.80%; N, 3.91%; S, 70.22%.

Example 5

Elemental sulfur (5 g, 156 mmol) was added in portions over 15 minutes to a solution of K₂Cr₂O₇ (0.82 g, 2.8 mmol) in 19.6 mL of 2M aqueous HCl. After stirring for 10 minutes, aniline (0.5 g, 5.4 mmol) was added in portions. The color of the reaction mixture changed from yellow to black, and the temperature rose to 32 °C. The mixture was stirred for 3.5 hours and then allowed to stand overnight. The solid product was filtered, washed with water, and dried in vacuum at 20-25 °C for 6 hours to yield 6.16 g of polymer, melting point 127-138 °C. The highly branched polymer gave the following analysis: C, 6.44%; H, 0.49%; N, 1.13%; S, 89.42%.

Example 6 Elemental sulfur (6 g, 188 mmol) was added to a stirred solution of (NH₄)₂S₂O₈

(3.5 g, 15 mmol) in 4 mL of ethanol and 6 mL of 2N HCl. To this mixture at 30 °C was added a solution of pyrrole (1 g, 15 mmol) in ethanol (4 mL) and water (6 mL). A black solid was formed which was filtered, washed successively with water, ethanol, and diethyl ether, and dried in vacuum to yield 6.68 g of polymer. Analysis of the solid gave a sulfur content of 92.09%.

Example 7

To a solution of (NH₄)₂S₂O₈ (5 g, 22 mmol) in 8.7 mL of 2N HCl containing polyethylene glycol (0.1 g) was added a solution of sulfur (4 g, 125 mmol) in carbon disulfide (10 mL) and pyrrole (0.5 g, 7 mmol) over a period of 2 hours. After stirring an additional 1 hour at ambient temperature, the resulting black solid was filtered, washed successively with water, ethanol and diethyl ether, and dried in vacuum. The polymer obtained, 3.23 g, had a sulfur content of 93.7%>.

Example 8

Pyrrole (0.97 g) and triethyl benzyl ammonium chloride (0.2 g) were added to a solution of FeC (5 g) in water (20 mL). After stirring at ambient temperature for 1 hour, a dark solid was formed which was filtered, washed successively with water, ethanol and diethyl ether, and dried under vacuum. The yield of polymer was 0.83 g.

Example 9

To a solution of (NH )₂S O₈ (5 g, 22 mmol) in 8.7 mL of 2N HCl containing polyethylene glycol (0.1 g) was added a solution of sulfur (4 g, 125 mmol) in carbon disulfide (10 mL) and N-methyl pyrrole (1 g, 12 mmol) over a period of 2 hours. After stirring an additional 1 hour at ambient temperature, the resulting black solid was filtered, washed successively with water, ethanol and diethyl ether, and dried in vacuum. The polymer, 2.5 g, gave the following analysis: C, 6.73%; H, 0.57%; N, 2.7%; S, 84.95%. Example 10

Sulfur (6 g, 188 mmol) was dispersed in a solution of (NH₄)₂S₂O₈ (1 g, 4 mmol) in ethanol (4 mL) and aqueous 2 M H₂SO₄ (6 mL) by stirring. After stirring the dispersion at 30 °C for 1 hour, a solution of indole (0.5 g, 4 mmol) in ethanol (10 mL) was added in portions. The reaction was completed by stirring at 20-25 °C for an additional 1 hour, and the resulting black solid was filtered, and washed successively with water, ethanol, and diethyl ether. After drying under vacuum, 5.88 g of polymer was obtained which gave the following analysis: C, 3.64%; H, 0.27%; N, 0.55%; S, 95.18%.

Example 11

Powdered sulfur (2 g, 62.5 mmol) was dispersed in a stirred solution of FeCl₃»6H₂O (4.6 g, 17 mmol) in a mixture of methanol (20 mL) and water (20 mL). After stirring the dispersion for 3 hours, a solution of pyrrole (0.47 g, 7 mmol) and m-phenylene diamine (0.2 g, 1.8 mmol) in methanol (10 mL) was added during 3 hours. After stirring the reaction mixture for an additional 3 hours, the mixture was held overnight before filtration of the bluish-black solid. The filtered solid was washed with water and dried under vacuum to yield a solid highly branched polymer, 2.43 g. Analysis of the solid gave the following results: C, 15.09%; H, 1.27%; N, 2.58%; S, 80.45%.

Example 12

To a mixture of aniline (0.306 g, 3.7 mmol) in 15 mL of 2N aqueous HCl and a solution of sulfur (3.2 g, 100 mmol) in CS₂ (10 mL) was added (NH₄)₂S₂O₈ (2 g, 8.8 mmol) in 15 mL of 2N aqueous HCl in small portions. After stirring at 20-25 °C for 5 hours, the mixture was allowed to stand overnight. The mixture was then heated to remove CS₂ and cooled. The black precipitate was filtered, washed with water, and dried under vacuum. The solid polymer obtained, 3.34 g, gave the following analysis: C, 6.68%>; H, 0.21%; N, 2.11%; S, 90.03%. Example 13

Powdered sulfur (6.4 g, 200 mmol) was added to a solution of K Cr₂O₇ (0.82 g, 2.8 mmol) in 24.5 mL of 2N aqueous HCl and stirred vigorously for 3 hours. To this dispersion, a mixture of aniline (0.5 g, 5.4 mmol) and m-phenylene diamine ( 0.06 g, 0.5 mmol) was introduced portionwise. The mixture changed color from yellow to black, and the temperature increased to 45 °C. After continuing stirring for 3 hours, the mixture was allowed to stand overnight. The black solid was filtered, washed with water and dried under vacuum at 20-25 °C for 6 hours to yield 6.96 g of polymer with a melting point range of 116-170 °C. Analysis of the branched polymer gave the following results: C, 3.48%; H, 0.15%; N, 1.06%; S, 94.11%.

Example 14

Elemental sulfur (70 g, 2.19 mol) was dispersed in a solution of FeCl₃ (22.2 g,

0.137 mol) in deionized water (600 mL), at a pH of 1.5 by adjustment with 10% HCl. Pyrrole (9 g, 0.134 mol) was added to the dispersion, and stirring was continued for 3 hours. The molar ratio of reactants (pyrrole: FeC : sulfur) was 1 :1 :16. After addition of 1 L of water, the mixture was allowed to stand overnight. The black solid which had formed was collected by filtration and successively washed with water, 5% HCl, water, and ethanol, and then dried under vacuum overnight at room temperature. Elemental analysis of the solid gave: C, 3.8%; H, 0.03%; N, 0.93%; S, 95.87%.

Example 15

To a solution of FeC^ (125 g, 0.77 mol) in deionized water (1.3 L) and ethanol (200 mL) was added elemental sulfur (200 g, 6.25 mol) with vigorous stirring to form a dispersion. To the dispersion, pyrrole (29.1 g, 0.434 mol) was added, and stirring was continued for 2 hours. At this time an additional 1.5 L of water was added, and the mixture was allowed to stand overnight. The black solid which formed was separated by filtration and successively washed with water, 5% HCl, water, and ethanol, and finally dried overnight under vacuum. The dried polymer had a mean particle size of 9.2 microns with 100% of the sample of particle size less than 25 microns. The resulting polymer gave the following analysis: C, 9.23%; H, 0.17%; N, 2.66%; S, 88.09%. Example 16

By the procedure of Example 14, pyrrole was polymerized by FeC-₃ in presence of sulfur in the molar ratio of pyrrole:FeCl₃: sulfur of 1 :1:4. The resulting polymer gave the following analysis: C, 12.42%; H, 0.82%; N, 3.51%; S, 76.72%.

Example 17

A solid composite cathode comprising the polymer of Example 14 and a particulate carbon material was fabricated and evaluated in AA cells in the following way. A cathode slurry formulation of 50 wt. %> polymer of Example 14, 38 wt. % elemental sulfur, 5.5 wt. % carbon SAB-50 (available from Chevron Corporation, Baytown, TX), and 6.5 wt. % polyethylene oxide binder (5,000,000 molecular weight, available from Polysciences Inc., Warrington, PA), using an ethanol/water mixture (14/1) as the solvent, was prepared by conventional techniques. The slurry was cast by hand coating using a gap coater bar onto a two side coated conductive carbon coated aluminum foil substrate (Product No. 60303 available from Rexam Graphics, South Hadley, MA) as a current collector and dried in a laboratory hood with exhaust of the ambient air to provide flowing air over the coating to provide a dry cathode coating thickness of about 25 microns. The coating and drying process was repeated for the second side of the substrate. The solid composite cathode was then wound into a AA cell with a 50 micron lithium foil anode and a 25 micron E 25 SETELA separator (a trademark for a polyolefin separator available from Tonen Chemical Corporation, Tokyo, Japan, and also available from Mobil Chemical Company, Films Division, Pittsford, NY) and filled with a liquid electrolyte (50% 1,3-dioxolane, 45% 1,2- dimethoxyethane, and 5% o-xylene by volume with 1.3 M lithium triflate salt).

Cells were tested at 165 mA discharge and 100 mA charge. The average discharge capacity of three cells at the 10^th cycle showed a specific capacity of 732 mAh/g (based on total sulfur content) and, at the 40^l cycle, the average specific capacity was 600 mAh/g (based on total sulfur content).

Example 18 Following the procedure of Example 17, composite cathodes were prepared from the polymer of Example 15 by substitution for the polymer of Example 14 in the cathode formulation and then fabricated into AA cells. Following the cell test procedure of Example 17, the average specific capacity of three cells at the 1^st cycle was 841 mAh/g (based on total sulfur content), and at the 10^th cycle, the average specific capacity was 707 mAh/g (based on total sulfur content).

Comparative Example 1

FeCl_3, (81.2 g, 0.50 mol), was dissolved in 500 mL of water with stirring and allowed to stand for 20 minutes To the stirred solution, pyrrole, (32.9 g, 0.49 mol), was slowly added at ambient temperature. The solution immediately turned black, and solid began to separate. After stirring for 1 hour, the black solid which had formed was separated by filtration and washed successively with water, 5% HCl, water, and acetone. The black solid was dried overnight at 80 °C. Analysis of the polypyrrole, (PPy), gave the following results: C, 56.95%; H, 2.30%; N, 16.43%; CI, 10.44%; Fe, 0.42%.

Comparative Example 2 Following the procedures of Example 17, composite cathodes were prepared from a cathode slurry formulation of 10 wt. % polypyrrole of Comparative Example 1 (PPy), 78 wt. % elemental sulfur, 5.5 wt. %> carbon SAB-50, and 6.5 wt. % polyethylene oxide binder (5,000,000 molecular weight), using an ethanol/water mixture (14/1) as the solvent. The composite cathode was then fabricated into AA cells by the procedures of Example 17.

Following the cell test procedures of Example 17, the specific capacity of three cells at the 1^st cycle was 741 mAh/g (based on total sulfur content), at the 10^th cycle the average specific capacity was 466 mAh/g (based on total sulfur content), and at the 50^th cycle the average specific capacity was 394 mAh/g (based on total sulfur content).

Example 19

Table 1 summarizes performance of highly branched polymers in cathode formulations by cyclic voltammetry in button cells. Cathodes were prepared by coating 50 wt. % of the highly branched conductive polymer, 35 wt. % of conductive carbon, (SAB- 50), and 15 wt. % polyethylene oxide (PEO) (5,000,000 molecular weight) in acetonitrile as the solvent onto a conductive carbon coated aluminum foil (Product No. 60303) to provide a dry cathode coating thickness of about 25 microns. The anode was lithium foil of about 175 microns thickness. The electrolyte was a 1 M solution of lithium triflate in 28 dimethoxyethane (glyme). The porous separator used was CELGARD 2500 (a trademark for a polyolefin separator available from Hoechst Celanese Corp., Charlotte, NC).

The above components were combined into a layered structure of cathode/separator/anode with the liquid electrolyte filling the void areas of the separator and cathode to form disc-shaped CR2032 button cells of 2 cm² in area. Cycling of the cells was performed between 1.25 V and 2.8 V at 1 mV/s.

Example 20 Electronic conductivity measurements were performed on highly branched conductive polymers of the present invention and for comparison on intimate mixtures of polypyrrole (PPy) of Comparative Example 1 and sulfur with the same overall sulfur content.

The measurements of electronic conductivity were made by the two-electrode galvanostatic method. The pellet of material under investigation was placed between stainless steel electrodes and polarized by a constant current of 0.1 mA/cm². Voltage response was monitored with time until a steady-state condition was reached. The steady- state voltage was used to calculate the resistance of the investigated pellet. Under the assumption that the stainless steel electrode is ionically blocking and electronically 29 conducting, the electronic conductivity was derived after measuring the thickness and diameter of the pellet. The conductivities were calculated without making any iR correction. The conductivity results obtained, therefore, represent a lower limit for the electronic conductivity.

Table 2 summarizes the results.

Example 21

To 5L of deionized water stirred in a 22L flask was added anhydrous FeCl₃ (680 g). To this stirred solution was added sulfur (1090 g) through a dry powder funnel followed by ethanol (600 mL). Pyrrole (255.8 g) was added dropwise during 15 minutes at ambient temperature, and the reaction mixture was stirred for an additional 2 hours. Additional deionized water (10L) was added, and stirring was continued for 2.5 hours. The resultant black solid was recovered by filtration and washed with acetone (5L). The solid was washed again with water (5L). The wet solid was added to a solution of Na₂S»9H₂O (500 g) in water (5.4L) and stirred for 15 minutes. The black solid was filtered and washed with deionized water until the filtrate was colorless. After washing with acetone, the solid was dried under vacuum at room temperature for 18 hours. The infrared spectrum of the solid showed a peak at 468 cm^" showing the presence of elemental sulfur. Differential Scanning Calorimetry (DSC) of the solid showed peaks at 108.3 °C and 119.3 °C consistent with the presence of elemental sulfur. X-ray photoelectron spectra (XPS) were obtained with x-rays generated by an Al K-_α source with an energy of 1486.6 eV. Binding energies for sulfur 2p of 163.69 eV (elemental sulfur), 30

164.84 eV (polysulfide), and 168.12 eV and 169.30 eV (both for S-O species) were measured. Elemental analysis of the polymer is shown in Table 3.

Example 22

The polymer of Example 21 (200 g) was extracted with carbon disulfide (6 successive extractions with IL each) to remove elemental sulfur. The resulting solid material was dried in vacuum. DSC of the solid shows the absence of peaks at 108.3 °C and 119.3 °C present in elemental sulfur. In the infrared spectrum, a peak at 468 cm^"1 attributable to elemental sulfur, present in the polymer of Example 21, was also absent. Cyclic voltametry, using as electrolyte 0.5 M lithium bis(trifluoromethylsulfonyl) imide in a mixture of dimethoxyethane and dioxolane at a scan rate of 10 mV/sec, showed a broad reduction peak at approximately 1.8 volts as shown in Figure 2. XPS measured as in Example 21 gave binding energies for sulfur 2p of 164.8 eV (polysulfide), and 167.5 eV and 168.6 eV (both for S-O species). XPS also gave a doublet structure for the nitrogen Is level which is characteristic of two-dimensional or branched polypyrroles and is not observed for one-dimensional or linear polypyrroles, as, for example, described by Schmeisser et al. in Synthetic Metals, 1993, 59211-221.

Example 23

The polymer of Example 22 (5 g) was stirred at under mild heating for 2 hours with sodium chloride (15 g) dissolved in water (1 L). The solid was filtered, washed with deionized water, and dried in vacuum. Cyclic voltametry by the method of Example 22 showed the absence of the broad reduction peak at approximately 1.8 V and a new peak at 1.2 V as shown in Figure 3. XPS measured as in Example 21 gave binding energies for sulfur 2p of 164.85 eV (polysulfide), and 167.36 eV and 168.56 eV (both for S-O species). XPS also gave a doublet structure for the nitrogen Is level which is characteristic of two- dimensional or branched polypyrroles and is not observed for one-dimensional or linear polypyrroles.

Example 24

To the polymer of Example 22 (1 g) dispersed in dimethoxyethane (100 mL) was added sodium borohydride (1 g) at room temperature. The mixture was heated to 60 °C and held at this temperature for 2 hours. After cooling the mixture was diluted with water and the solid filtered. After washing with water and acetone, the solid was dried in vacuum. Cyclic voltametry by the method of Example 22 showed the essential absence of oxidation or reduction peaks as depicted in Figure 4. XPS measured as in Example 21 gave binding energies for sulfur 2p of 164.64 eV (polysulfide), and 167.58 eV and 168.69 eV (both for S-O species). XPS also gave a doublet structure for the nitrogen 1 s level which is characteristic of two-dimensional or branched polypyrroles and is not observed for one-dimensional or linear polypyrroles.

Examples 21-24 show that the electroactive polymer is branched and that the structure includes ionic and covalent polysulfide moieties -(S_m)-, -(S_m)^", and (S_m)^2" in which m is greater than 8. These same examples also show that elemental sulfur may be present in the polymer as formed and that there is approximately one covalent sulfur attachment for each 8 pyrrole units.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made without departing from the spirit and scope thereof.

Claims

32CLAIMS

1. An electroactive, highly branched, conductive organic polymer for use in an electrochemical cell, wherein said polymer, in its oxidized state, comprises a plurality of repeating units, wherein one or more of said repeating units are bonded to polysulfide chains; and further wherein said 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.

2. The polymer according to claim 1, wherein said highly branched polymer is characterized by more than 4 end groups comprising said repeating units.

3. The polymer according to claim 1 , wherein said highly branched polymer is characterized by more than 6 end groups comprising said repeating units.

4. The polymer according to claim 1 , wherein said highly branched polymer is characterized by 7 to 100 end groups comprising said repeating units.

5. The polymer according to claim 1, wherein said highly branched polymer is characterized by more than 25 end groups comprising said repeating units.

6. The polymer according to claim 1 , wherein said highly branched polymer is characterized by 26 to 100 end groups comprising said repeating units.

7. The polymer according to any one of claims 1-6, wherein said polysulfide chains further comprise one or more moieties selected from the group consisting of -(Sm)-SO₂- and -(S_m)-SO₃ ^".

8. The polymer according to any one of claims 1-7, wherein said repeating units comprise one or more moieties selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives.

. The polymer according to any one of claims 1 -7, wherein one or more of said repeating units bonded to said polysulfide chains comprise pyrrole.

10. The polymer according to any one of claims 1-7, wherein one or more of said repeating units bonded to said polysulfide chains comprise aniline.

11. The polymer according to any one of claims 1-10, wherein the bonding of said polysulfide chains comprising one or more -(S_m)- moieties to one or more of said repeating units is covalent.

12. The polymer according to any one of claims 1-11, wherein said polymer comprises a polymer backbone and said polysulfide chains comprise covalent moieties, -(S_m)-, which covalent moieties are covalently bonded by one or both of their terminal sulfur atoms as a side group to said polymer backbone chain.

13. The polymer according to any one of claims 1-12, wherein said polysulfide chains comprise polysulfide anion moieties, -(S_m)^", which anion moieties are covalently bonded by a terminal sulfur atom to said polymer.

14. The polymer according to any one of claims 1-13, wherein said polysulfide chains comprise polysulfide dianion moieties, (S_m)^2", and said repeating units comprise positively charged atoms, wherein said dianion moieties are ionically bonded to one or more of said positively charged atoms of said repeating units.

15. The polymer according to any one of claims 1-14, wherein m of said moieties,

-(S_m)-, -(S_m) , and (S_m) ^", is an integer from 9 to 200 and is the same or different at each occurrence.

16. The polymer according to any one of claims 1-14, wherein m of said moieties, -(S_m)-, -(S_m)^", and (S_m) ^", is an integer from 24 to 100 and is the same or different at each occurrence. 34

17. An electroactive, highly branched, conductive organic polymer for use in an electrochemical cell, wherein said polymer, in its oxidized state, comprises a plurality of repeating units, wherein one or more of said repeating units are bonded to polysulfide chains; and further wherein said polysulfide chains comprise -(S_m)-, -(S_m) , and (S_m)^2" moieties; where m is an integer from 3 to 200 and is the same or different at each occurrence.

18. An electroactive, highly branched, conductive organic polymer for use in an electrochemical cell, wherein said polymer, in its oxidized state, is of the formula: [M (Sm)^X"n]y wherein:

M is a repeating unit; 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 said polymer is equal to or greater than l; 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; and x is an integer from 0 to 2 and is the same or different at each occurrence.

19. The polymer according to claim 18, wherein said highly branched polymer is characterized by more than 4 end groups comprising said repeating units.

20. The polymer according to claim 18, wherein said highly branched polymer is characterized by more than 6 end groups comprising said repeating units.

21. The polymer according to claim 18, wherein said highly branched polymer is characterized by 7 to 100 end groups comprising said repeating units.

22. The polymer according to claim 18, wherein said highly branched polymer is characterized by more than 25 end groups comprising said repeating units.

23. The polymer according to claim 18, wherein said highly branched polymer is characterized by 26 to 100 end groups comprising said repeating units.

24. The polymer according to any one of claims 18-23, wherein said polysulfide chains further comprise one or more moieties selected from the group consisting of

-(Sm)-SO₂- and -(S_m)-SO₃ ^".

25. The polymer according to any one of claims 18-24, wherein the repeating unit, M, comprises one or more repeating units selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives.

26. The polymer according to any one of claims 18-24, wherein the repeating unit, M, is pyrrole.

27. The polymer according to any one of claims 18-24, wherein the repeating unit, M, is aniline.

28. The polymer according to any one of claims 18-27, wherein y is an integer from 20 to 400.

29. The polymer according to any one of claims 18-28, wherein said polymer comprises greater than 50% by weight of sulfur.

30. The polymer according to any one of claims 18-28, wherein said polymer comprises greater than 75% by weight of sulfur.

31. A method for preparing an electroactive, highly branched, conductive organic polymer, wherein said polymer, in its oxidized state, comprises a plurality of repeating units, wherein one or more of said repeating units are bonded to polysulfide chains; and further wherein said polysulfide chains comprise one or more moieties selected from the group consisting of -(S_m)-, -(S_m)^", and (S_m) ^"; 36 where m is an integer from 3 to 200 and is the same or different at each occurrence, said method comprising the steps of:

(a) providing a dispersion of elemental sulfur in a liquid medium;

(b) adding to the dispersion of step (a) one or more monomers and a polymerization initiator comprising an oxidant;

(c) stirring the mixture of step (b) thereby forming an electroactive material comprising said electroactive, highly branched, conductive organic polymer comprising said polymer repeating units; and

(d) separating said electroactive material from the reaction medium of step (c).

32. The method according to claim 31 , wherein said one or more monomers of step (b) is selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives.

33. The method according to claims 31 or 32, wherein the particle size of said elemental sulfur in step (a) is from 0.01 micron to 100 microns.

34. The method according to any one of claims 31-33, wherein the weight ratio of said one or more monomers to elemental sulfur in the mixture of step (b) is from 1 : 1 to

1:15.

35. The method according to any one of claims 31-34, wherein said polymerization initiator comprises an oxidant selected from the group consisting of FeCl₃, Fe(NO₃)₃, CuCl₂, H₂O₂, (NH₄)₂S₂O₈, KIO₃, 1₂, KMnO₄, and K₂Cr₂O₇.

36. The method according to any one of claims 31-35, wherein said liquid medium comprises water.

37. The method according to any one of claims 31-36, wherein said method further comprises after step (d), one or more steps of:

(e) purifying the polymer after separation; and

(f) drying the polymer. 37

38. An electroactive, highly branched, conductive organic polymer, wherein said polymer, in its oxidized state, comprises a plurality of repeating units, wherein one or more of said repeating units are bonded to polysulfide chains; and further wherein said polysulfide chains comprise one or more moieties selected from the group consisting of -(S_m)-, -(S_m)\ and (S_m) ^"; where m is an integer from 3 to 200 and is the same or different at each occurrence, said polymer prepared by a method comprising the steps of:

(a) providing a dispersion of elemental sulfur in a liquid medium; (b) adding to the dispersion of step (a) one or more monomers and a polymerization initiator comprising an oxidant;

(c) stirring the mixture of step (b) thereby forming an electroactive material comprising said electroactive, highly branched, conductive organic polymer; and

39. The polymer according to claim 38, wherein said polymer comprises greater than 50% by weight of sulfur.

40. The polymer according to claim 38, wherein said polymer comprises greater than 75%> by weight of sulfur.

41. A composite cathode for use in an electrochemical cell, said composite cathode comprising:

(a) an electroactive, highly branched, conductive organic polymer; wherein said polymer, in its oxidized state, comprises a plurality of repeating units, wherein one or more of said repeating units are bonded to polysulfide chains; and further wherein said 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; and (b) one or more conductive fillers selected from the group consisting of conductive carbons, graphites, activated carbon fibers, carbon nanofibers, metal flakes, metal powders, metal fibers, carbon fabrics, metal mesh, electrically conductive polymers, and electrically conductive metal chalcogenides. 38

42. The cathode according to claim 41, wherein said highly branched polymer is characterized by more than 4 end groups comprising said repeating units.

43. The cathode according to claim 41, wherein said highly branched polymer is characterized by more than 6 end groups comprising said repeating units.

44. The cathode according to claim 41, wherein said highly branched polymer is characterized by 7 to 100 end groups comprising said repeating units.

45. The cathode according to claim 41, wherein said highly branched polymer is characterized by more than 25 end groups comprising said repeating units.

46. The cathode according to claim 41, wherein said highly branched polymer is characterized by 26 to 100 end groups comprising said repeating units.

47. The cathode according to any one of claims 41-46, wherein said polysulfide chains further comprise one or more moieties selected from the group consisting of -(S_m)-SO₂- and -(S_m)-SO₃-.

48. The cathode according to any one of claims 41-47, wherein said cathode further comprises one or more materials selected from the group consisting of binders, electrolytes, non-electroactive metal oxides, and electroactive transition metal chalcogenides.

49. The cathode according to any one of claims 41-48, wherein said electroactive, highly branched, conductive organic polymer comprises one or more repeating units formed by the polymerization of one or more monomers selected from the group consisting of pyrrole, aniline, indole, phenylene diamines, thiophene, acetylene, phenylene, vinyl phenylene, vinyl thienylene; and their substituted derivatives.

50. The cathode according to any one of claims 41-49, wherein said cathode further comprises elemental sulfur. 39

51. A method for preparing a composite cathode, wherein said method comprises the steps of:

(a) dispersing or suspending in a liquid medium an electroactive material comprising the electroactive polymer according to any one of claims 1-30;

(b) optionally adding to the mixture of step (a) a conductive filler;

(c) mixing the composition resulting from step (b) to disperse said electroactive polymer;

(d) casting the composition resulting from step (c) onto a substrate; and (e) removing some or all of the liquid from the composition resulting from step

(d) to provide said composite cathode.

52. The method according to claim 51 , wherein said electroactive material further comprises elemental sulfur.

53. The method according to claims 51 or 52, wherein said method further comprises, subsequent to step (e), a step (f) of heating said composite cathode to a temperature of 120 °C or greater.

54. The method according to any one of claims 51 -53, wherein said method further comprises the addition to any or all of the steps (a), (b), or (c) of one or more materials selected from the group consisting of binders, electrolytes, non- electroactive metal oxides, and electroactive transition metal chalcogenides.

55. A method for preparing a composite cathode, wherein said method comprises the steps of:

(a) dispersing or suspending in a liquid medium an electroactive material comprising an electroactive, highly branched, conductive organic polymer, wherein said polymer, in its oxidized state, is of the formula: [M (S_m)^X"n]y wherein:

M is a repeating unit; 40 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 said 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; and x is an integer from 0 to 2 and is the same or different at each occurrence;

(b) optionally adding to the mixture of step (a) a conductive filler;

(d) casting the composition resulting from step (c) onto a suitable substrate; and

(e) removing some or all of the liquid from the composition resulting from step (d) to provide a composite cathode.

56. The method according to claim 55, wherein said electroactive material further comprises elemental sulfur.

57. An electrochemical cell comprising:

(a) an anode, (b) the composite cathode according to any one of claims 41-50; and

(c) an electrolyte interposed between said anode and said composite cathode.

58. The cell according to claim 57, wherein said anode comprises one or more materials selected from the group consisting of lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium-intercalated carbons, and lithium-intercalated graphites.

59. The cell according to claims 57 or 58, wherein said electrolyte comprises one or more materials selected from the group consisting of liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes.

60. A method of forming an electrochemical cell, said method comprising the steps of:

(a) providing an anode; 41

(b) providing the composite cathode according to any one of claims 41-50; and

(c) interposing an electrolyte between said anode and said cathode.

61. The method according to claim 60, wherein said anode comprises one or more materials selected from the group consisting of lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium-intercalated carbons, and lithium-intercalated graphites.

62. The method according to claims 60 or 61, wherein said electrolyte comprises one or more materials selected from the group consisting of liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes.