AU706408B2 - Rechargeable positive electrode - Google Patents

Abstract

Disclosed are battery cells comprising a sulfur-based positive composite electrode. Preferably, said cells are secondary cells, and more preferably thin film secondary cells. In one aspect, the cells can be in a solid-state or gel-state format wherein either a solid-state or gel-state electrolyte separator is used. In another aspect of the invention, the cells are in a liquid format wherein the negative electrode comprises carbon, carbon inserted with lithium or sodium, or a mixture of carbon with lithium or sodium. The novel battery systems of this invention have a preferred operating temperature range of from -40 DEG C. to 145 DEG C. with demonstrated energies and powers far in excess of state-of-the-art high-temperature battery systems.

Description

RECHARGEABLE POSITIVE ELECTRODE This invention relates generally to positive electrodes characterized by activesulfur. The electrodes are preferably rechargeable, and in some preferred embodiments are constructed in a thin-film format. Various negative electrodes, such as, alkali metal, alkaline earth metal, transition metal, and carbon insertion electrodes, among others, can be coupled with the positive electrode to provide battery cells, preferably having high specific energy (Wh/kg) 1 0 and energy density (Wh/1).

The rapid proliferation of portable electronic devices in the international marketplace has led to a corresponding increase in the demand for advanced secondary batteries.

5 The miniaturization of such devices as, for example, cellular phones, laptop computers, etc., has naturally fueled the desire for rechargeable batteries having high specific energies (light weight).

At the same time, mounting concerns regarding the environmental impact of throwaway .technologies, has caused a discernible shift away from primary batteries and towards rechargeable systems.

0 In addition, heightened awareness concerning toxic waste has motivated, in part, efforts to replace toxic cadmium electrodes in nickel/cadmium batteries with the more benign hydrogen storage electrodes in nickel/metal hydride cells. For the above reasons, there is a strong market potential for environmentally benign secondary battery technologies.

Secondary batteries are in widespread use in modem society, particularly in applications where large amounts of energy are not required. However, it is desirable to use batteries in applications requiring considerable power, and much effort has been expended in developing batteries suitable for high specific energy, medium power applications, such as, for S) electric vehicles and load leveling. Of course, such batteries are also suitable for use in lower n power applications such as cameras or portable recording devices.

WO 96/16450 PCT/US95/12671 2 At this time, the most common secondary batteries are probably the lead-acid batteries used in automobiles. Those batteries have the advantage of being capable of operating for many charge cycles without significant loss of performance. However, such batteries have a low energy to weight ratio. Similar limitations are found in most other systems, such as Ni-Cd and nickel metal hydride systems.

Among the factors leading to the successful development of high specific energy batteries, is the fundamental need for high cell voltage and low equivalent weight electrode materials. Electrode materials must also fulfill the basic electrochemical requirements of sufficient electronic and ionic conductivity, high reversibility of the oxidation/reduction reaction, as well as excellent thermal and chemical stability within the temperature range for a particular application. Importantly, the electrode materials must be reasonably inexpensive, widely available, non-toxic, and easy to process.

Thus, a smaller, lighter, cheaper, non-toxic battery is sought for the next generation of batteries. The low equivalent weight of lithium renders it attractive as a battery electrode component for improving weight ratios. Lithium provides also greater energy per volume than do the traditional battery standards, nickel and cadmium.

The low equivalent weight and low cost of sulfur and its nontoxicity renders it also an attractive candidate battery component. Successful lithium/organosulfur battery cells are known. (See, De Jonghe et al., U.S. patent Nos. 4,833,048 and 4,917,974; and Visco et al., U.S. Patent No. 5,162,175.) However, employing a positive electrode based on elemental sulfur in an alkali metal-sulfur battery system has been considered problematic. Although theoretically the reduction of sulfur to an alkali metal sulfide confers a large specific energy, sulfur is known to be an excellent insulator, and problems using it as an electrode have been noted. Such problems referred to by those in the art include the necessity of adjoining the sulfur to an inert electronic conductor, very low percentages of utilization of the bulk material, poor reversibility, and the formation of an insulating sulfur film on the carbon particles and current collector surface that electronically isolates the rest of the electrode components. (DeGott, "Polymere Carbone- WO 96/16450 PCT/US95/12671 3 Soufre Synth6se et Propridtes Electrochimiques," Doctoral Thesis at the Institut National Polytechnique de Grenoble (date of defense of thesis: 19 June 1986) at page 117.) Similarly, Rauh et al., "A Lithium/Dissolved Sulfur Battery with an Organic Electrolyte," J. Electrochem. Soc. 126 523 (April 1979) state at page 523: "Both S 8 and its ultimate discharge product, Li 2 S, are electrical insulators. Thus it is likely that insulation of the positive electrode material... led to the poor results for Li/S cells." Further, Peramunage and Licht, "A Solid Sulfur Cathode for Aqueous Batteries," Science, 261: 1029 (20 August 1993) state at page 1030: "At low (room) temperatures, elemental sulfur is a highly insoluble, insulating solid and is not expected to be a useful positive 1 0 electrode material." However, Peramunage and Licht found that interfacing sulfur with an aqueous sulfur-saturated polysulfide solution converts it from an insulator to an ionic conductor.

The use of sulfur and/or polysulfide electrodes in non-aqueous or aqueous liquidelectrolyte lithium batteries (that is, in liquid formats) is known. For example, Peled and Yamin, U.S. Patent No. 4,410,609, describe the use of a polysulfide positive electrode Li 2

S

x made by the direct reaction of Li and S in tetrahydrofuran (THF). Poor cycling efficiency typically occurs in such a cell because of the use of a liquid electrolyte with lithium metal foil, and the Peled and Yamin patent describes the system for primary batteries. Rauh et al., "Rechargeable Lithium-Sulfur Battery (Extended Abstract), J. Power Sources. 26: 269 (1989) also notes the poor cycling efficiency of such cells and states at page 270 that "most cells failed as a result of lithium depletion." Other references to lithium-sulfur battery systems in liquid formats include the following: Yamin et al., "Lithium Sulfur Battery," J. Electrochem. Soc.. 135(5): 1045 (May 1988); Yamin and Peled, "Electrochemistry of a Nonaqueous Lithium/Sulfur Cell," J. Power Sources 9: 281 (1983); Peled et al., "Lithium-Sulfur Battery: Evaluation of Dioxolane-Based Electrolytes," J. Electrochem. Soc., 136(6): 1621 (June 1989); Bennett et al., U.S. Patent No.

4,469,761; Farrington and Roth, U.S. Patent No. 3,953,231; Nole and Moss, U.S. Patent No.

3,532,543; Lauck, U.S. Patent Nos. 3,915,743 and 3,907,591; Societe des Accumulateurs Fixes et de Traction, "Lithium-sulfur battery," Chem. Abstracts, 66: Abstract No. 111055d at WO 96/16450 PCT/US95/12671 4 page 10360 (1967); and Lauck, H. "Electric storage battery with negative lithium electrode and positive sulfur electrode," Chem. Abstracts, 80: Abstract No. 9855 at pages 466-467 (1974).) DeGott, supr, notes at page 118 that alkali metal-sulfur battery systems have been studied in different formats, and then presents the problems with each of the studied formats. For example, he notes that an "all liquid" system had been rapidly abandoned for a number of reasons including among others, problems of corrosiveness of liquid lithium and sulfur, of lithium dissolving into the electrolyte provoking self-discharge of the system, and that lithium sulfide forming in the positive (electrode) reacts with the sulfur to give polysulfides Li 2

S

x that are soluble in the electrolyte.

In regard to alkali metal-sulfur systems wherein the electrodes are molten or dissolved, and the electrolyte is solid, which function in exemplary temperature ranges of 130 0

C

to 180 0 C and 300 0 C to 350 0 C, DeGott states at page 118 that such batteries have problems, such as, progressive diminution of the cell's capacity, appearance of electronic conductivity in the electrolyte, and problems of safety and corrosion. DeGott then lists problems encountered with alkali metal-sulfur battery systems wherein the electrodes are solid and the electrolyte is an organic liquid, and by extension wherein the negative electrode is solid, the electrolyte is solid, and the positive electrode is liquid. Such problems include incomplete reduction of sulfur, mediocre reversibility, weak maximum specific power (performance limited to slow discharge regimes), destruction of the passivating layer of Li 2 S as a result of its reaction with dissolved sulfur leading to the formation of soluble polysulfides, and problems with the stability of the solvent in the presence of lithium.

DeGott also describes on page 117 a fundamental barrier to good reversibility as follows. As alkali metal sulfides are ionic conductors, they permit, to the degree that a current collector is adjacent to sulfur, the propagation of a reduction reaction. By contrast, their reoxidation leads to the formation of an insulating sulfur layer on the positive electrode that ionically insulates the rest of the composite, resulting in poor reversibility.

DeGott concludes on page 119 that it is clear that whatever format is adopted for an alkali metal-sulfur battery system that the insulating character of sulfur is a major obstacle that is difficult to overcome. He then describes preliminary electrochemical experiments with a WO 96/16450 PCTJUS95/12671 r composite sulfur electrode prepared from a slurry. The slurry was prepared by mixing the following components in acetonitrile: 46% sulfur; 16% acetylene black; and 38% (PEO)8/LiC104 (polyethylene oxide/lithium perchlorate). The resulting slurry was then deposited on a stainless steel substrate by "capillary action." From those preliminary experiments, DeGott concludes on page 128 that it is clear that, even when optimizing the efficiency of the composite electrode (that is, by multiplying the triple point contacts) that elemental sulfur cannot be considered to constitute an electrode for a secondary battery, in an "all solid" format.

Present solid-state lithium secondary battery systems are limited to a specific energy of about 120 Wh/kg. It would be highly desirable to have a battery system characterized by higher specific energy values.

It would be even more desirable if solid-state batteries having practical specific energy values greater than about 150 Wh/kg could operate at room temperature. It would be additionally advantageous if solid-state batteries having high specific energy and operation at room temperature could be reliably fabricated into units with reproducible performance values.

In lithium cells wherein a liquid electrolyte is used, leakage of the electrolyte can leave lithium exposed to the air, where it rapidly reacts with water vapor and oxygen.

Substantial casing can prevent such reactions and protect users and the environment from exposure to hazardous, corrosive, flammable or toxic solvents but adds unwanted weight to the battery. A solid-state battery would greatly reduce such problems of electrolyte leakage and exposure of lithium, and would allow reducing the weight of the battery.

Furthermore, a battery formulation that overcomes the problem of lithium depletion described in the prior art, for example, Rauh et al., supra, would have many advantages.

In summary, disadvantages in currently available metal-sulfur battery systems include poor cycling efficiency, poor reversibility, lithium depletion, or operating temperatures above 200'C, among other problems. Practitioners in the battery art have long sought a solidstate or gel-state metal-sulfur battery system that would overcome these limitations.

P OPER 3WS.95 047 4 99 According to the present invention there is provided a positive electrode comprising a mixture of a) active-sulfur; b) an electronic conductor mixed with the active-sulfur so that electrons can move between the active-sulfur and the electronic conductor; and c) an ionic conductor mixed with the active-sulfur so that ions can move between the ionic conductor and the active-sulfur, wherein the mixture has between and 100% of the active-sulfur available for electrochemical reaction.

According to the present invention there is further provided a battery cell which comprises: a) a positive electrode comprising a mixture of i) between 20% to 80% active-sulfur in percent by weight; ii) a gel-state or solid-state ionic conductor in percent by weight between 15 15% to 75%; and iii) an electronic conductor in a percent by weight between 5% and b) a current collector electrically connected to the positive electrode; c) a negative electrode; and d) an electrolyte separator; 20 wherein the mixture has between 10% and 100% of the active-sulfur available for electrochemical reaction.

According to the present invention there is further provided a battery cell which comprises: a positive composite electrode comprising active-sulfur in a percentage by weight from 20% to 80%, an ionic conductor in a percentage by weight from 15% to and an electronic conductor in a percentage by weight from 5% to a negative electrode; and a solid-state electrolyte separator or a gel-state electrolyte separator; 0NVX0 wherein the positive electrode has between 10% and 100% of the active-sulfur P (IP \11% (2 4' 1 4 5B available for electrochemical reaction.

According to the present invention there is further provided a battery cell which comprises: a negative electrode which comprises carbon, carbon inserted with lithium or sodium, or a mixture of carbon with lithium or sodium; and a positive composite electrode comprising active-sulfur in a percentage by weight of from 20% to 80%, an ionic conductor in a percentage weight of from 15% to and an electronic conductor in a percentage by weight from 5 to wherein the positive electrode has between 10% and 100% of the active-sulfur available for electrochemical reaction.

In another aspect, the present invention provides A positive electrode comprising: a) an electrochemically active material selected from the group consisting of S 15 elemental sulfur, a metal sulfide, a metal polysulfide, and combinations thereof, wherein said metal is selected from the group consisting of alkali metals, alkaline earth metals, and :o mixtures of alkali and alkaline earth metals; b) an electronically conductive material mixed with the electrochemically active material so that electrons move between the electrochemically active material and the electronically conductive material; and an ionically conductive material mixed with the electrochemically active material so that ions move between the ionically conductive material and the electrochemically active material, wherein at least 10% of the electrochemically active material is accessible to electrons and ionic charge carriers, and wherein the ionically conductive material is a 25 solid or gel state material and is not a sulfide or polysulfide.

According to the present invention there is further provided a battery cell comprising: a) a positive electrode comprising a mixture of i) an electrochemically active material, ii) a gel-state or solid-state ionically conductive material, and P' O(I' NII..A iii) an electronically conductive material, the mixture having between 10% and 100% of the electrochemically active material accessible to electrons and ionic charge carriers; b) a current collector electrically connected to the positive electrode c) a negative electrode including a metal or metal ion; and d) an electrolyte separator; wherein electrochemically active material is selected from the group consisting of elemental sulfur, sulfides of the metal, polysulfides of the metal, and combinations thereof.

According to the present invention there is further provided a battery cell comprising: a) a negative electrode including a metal or an ion of the metal; 1 b) a positive electrode comprising 15 i) in electrochemically active material comprising sulfur in the form of at :least one of elemental sulfur, a sulfide of the metal, and a polysulfide of the metal, and ii) an electronically conductive material; and c) a gel-state or polymeric solid-state electrolyte separator electronically separating the positive and negative electrodes, 20 d) wherein at least 10 of the sulfur is accessible to electrons and ionic charge S carriers.

According to the present invention there is further provided a method of forming an active-sulfur-containing electrode, the method comprising the following steps: combining active-sulfur, an electronic conductor, and an ionic conductor to form a mixture; homogenizing the mixture to form a homogenous mixture; and forming the active-sulfur-containing electrode from said homogenous mixture, wherein said active-sulfur-containing electrode has at least 10% of its active-sulfur R- 0O available for electrochemical reaction.

-M

Certain embodiments of this invention may provide a positive electrode for a battery cell that has low equivalent weight and high cell voltage and consequently a high specific energy, and operates in a wide range of temperatures including ambient and subambient temperatures. An exemplary operating temperature range for the batteries of this invention is from -40°C to 145°C. The batteries of this invention are preferably rechargeable. Thin film type battery cells are preferred embodiments.

The positive electrode of this invention comprises an active-sulfur-based material having a relatively low equivalent weight. Said electrode is a composite comprising, in the 1 0 theoretically fully charged state, elemental sulfur, preferably an ionically conductive material, and an electronically conductive material. Upon discharge, the active-sulfur of the positive electrode reacts with the metal of the negative electrode, and metal sulfides and polysulfides form. For example, where M is the metal of the negative electrode, the overall cell reaction can be S. described as follows: Sx/z M S Mx/zS

S.

S.

wherein M is any metal that can function as an active component in a negative electrode in a

S.

S' battery cell wherein active-sulfur is the active component of the positive electrode; x 0 through x 2; z the valence of the metal; and S is sulfur.

M is preferably selected from the group consisting of alkali metals, alkaline earth 0 metals, and transition metals. M is more preferably selected from the group consisting of alkali metals, and still more preferably lithium or sodium. M is most preferably lithium.

More specifically, for example, in a preferred embodiment of this invention wherein the negative electrode contains lithium, the overall cell reaction wherein z 1 can be described as follows: xLi S LiXS.

When x 2, 100% of the theoretical specific energy of the system has been released.

Upon discharge, the positive electrode becomes a combination of sulfur, metal sulfides and polysulfides, and during the discharging process the proportions of those sulfurcontaining components will change according to the state of charge. The charge/discharge

M

process in the positive electrode is reversible. Similarly, upon recharging, the percentages of the sulfur-containing ingredient will vary during the process.

The positive electrode is thus made from an electrode composition comprising active-sulfur, an electronically conductive material intermixed with the active-sulfur in a manner that permits electrons to move between the active-sulfur and the electronically conductive material, and an ionically conductive material intermixed with the active-sulfur in a manner that permits ions to move between the ionically conductive material and the sulfur.

The ionically conductive material of said composite positive electrode is preferably a polymeric electrolyte, more preferably a polyalkylene oxide, and further, preferably 1 0 polyethylene oxide in which an appropriate salt may be added. Additional ionically conductive materials for use in the positive electrode include the components described below in the solidstate and gel-state electrolyte separator. Preferred ionic conductors are selected from the group consisting of a positive electrode according to any one of claims 1 to 9 wherein the ionic conductor is selected from the group consisting of polymeric electrolytes, ceramic electrolytes, glass electrolytes, beta alumina compounds, and combinations thereof.

Preferably the ionic conductor comprises a positive electrode wherein the ionic conductor comprises an electrolyte salt that form a complex with compounds selected from the group S* consisting of polyether compounds, polyamine compounds, polythioether compounds, polyphosphazene compounds, and combinations thereof.

20 Exemplary electronically conductive materials of the composite positive electrode include carbon black, electronically conductive compounds with conjugated carbon-carbon and/or carbon-nitrogen double bonds, for example but not limited to, electronically conductive polymers, such as, polyaniline, polythiophene, polyacetylene, polypyrrole, and combinations of such electronically conductive materials. The electronically conductive materials of the positive :electrode may also have electrocatalytic activity.

The composite sulfur-based positive electrode may further optionally comprise RA performance enhancing additives, such as, binders; electrocatalysts, for example, phthalocyanines, metallocenes, brilliant yellow (Reg. No. 3051-11-4 from Aldrich Catalog i 0II.R N 3 2-M 5 6 4 7 16 4 99 -7A- Handbook of Fine Chemicals; Aldrich Chemical Company, Inc., 1001 West Saint Paul Avenue, Milwaukee, WI 53233 (USA)) among other electrocatalysts; surfactants; dispersants (for example, to improve the homogeneity of the electrode's ingredients); and protective layer forming additives (for example, to protect a lithium negative electrode), such as, organosulfur compounds, phosphates, iodides, iodine, metal sulfides, nitrides, and fluorides, for example Lil, PbS, and HF, The range of active-sulfur in such electrodes in the theoretically fully charged state of from about 20% to about 80% by weight. Said active-sulfur-based composite electrode is preferably -o 8 processed such that the component p aresre homogeneously distributed, and segregation and/or agglomeration of the component particles is avoided.

A metal-sulfur battery system constructed with said active-sulfur-based composite positive electrode of this invention should have at least and more preferably at least 10% availability of the active-sulfur. That availability corresponds to a minimum of 168 mAh per gram of sulfur included in the positive electrode. This is based on the theoretical value of 1675 mAh/gm of sulfur at 100% availability.

The electrolyte separator used in combination with the positive electrodes of this invention functions as a separator for the electrodes and as a transport medium for the metal 1 0 ions. Any electronically insulating and ionically conductive material which is electrochemically stable may be used. For example, it has been shown that polymeric, glass and/or ceramic materials are appropriate as electrolyte separators, as well as other materials known to those of skill in the art, such as, porous membranes and composites of such materials. Preferably, however, the solid-state electrolyte separator is any suitable ceramic, glass, or polymer 5 electrolyte such as, polyethers, polyimines, polythioethers, polyphosphazenes, polymer blends, and the like, in which an appropriate electrolyte salt may be added. In the solid-state, the electrolyte separator may contain an aprotic organic liquid wherein said liquid constitutes from about 0. 1% to about 20% (weight percentage) of the total weight of the electrolyte I separator.

In the gel-state, the electrolyte separator contains at least 20% (weight percentage) 0 of an aprotic organic liquid wherein the liquid is immobilized by the inclusion of a gelling agent.

Any gelling agent, for example, polyacrylonitrile, PVDF, or PEO, can be used.

The liquid electrolyte for the liquid format batteries using the positive electrode of this invention, is also preferably an aprotic organic liquid. The liquid format battery cells constructed using the positive electrodes of this invention would preferably further comprise a separator which acts as an inert physical barrier within the liquid electrolyte. Exemplary of such separators include glass, plastic, ceramic, polymeric materials, and porous membranes thereof RA among other separators known to those in the art.

Solid-state and gel-state positive electrodes of this invention can be used in solidrJy state or liquid format batteries, depending on the specific format of the electrolyte separator and WO 96/16450 PCT/US95/12671 r 9 negative electrode. Regardless of the format of the batteries using the positive electrode of this invention, the negative electrode can comprise any metal, any mixture of metals, carbon or metal/carbon material capable of functioning as a negative electrode in combination with the active-sulfur-based composite positive electrode of this invention. Accordingly, negative electrodes comprising any of the alkali or alkaline earth metals or transition metals for example, (the polyether electrolytes are known to transport divalent ions such as in combination with the positive electrode of this invention are within the ambit of the invention, and particularly alloys containing lithium and/or sodium.

Preferred materials for said negative electrodes include Na, Li and mixtures of Na or Li with one or more additional alkali metals and/or alkaline earth metals. The surface of such negative electrodes can be modified to include a protective layer, such as that produced on the negative electrode by the action of additives, including organosulfur compounds, phosphates, iodides, nitrides, and fluorides, and/or an inert physical barrier conductive to the metal ions from the negative electrode, for example, lithium ions transport in lithium phosphate, or silicate glasses, or a combination of both.

Also preferred materials for said negative electrodes include carbon, carbon inserted with lithium or sodium, and mixtures of carbon with lithium or sodium. Here, the negative electrode is preferably carbon, carbon inserted with lithium or sodium, and/or a mixture of carbon with lithium or sodium. When the negative electrode is carbon, the positive electrode is in the fully discharged state, comprising lithium or sodium sulfides and polysulfides.

Particularly preferred negative electrodes for batteries are lithium inserted within highly disordered carbons, such as, poly p-phenylene based carbon, graphite intercalation compounds, and LiyC 6 wherein y 0.3 to 2, for example, LiC 6 Li 2

C

6 and LiC 12 When the negative electrode is carbon, the cells are preferably assembled with the positive electrode in the fully discharged state comprising lithium or sodium sulfides and/or polysulfides. The use of negative electrodes of the carbon, carbon inserted with lithium or sodium, and mixtures of carbon with lithium or sodium with the solid-state and gel-state positive electrodes of this invention are especially advantageous when the battery is in the liquid format.

WO 96/16450 PCT/US95/12671 In another aspect, the present invention provides methods of forming an active-sulfurcontaining electrode. Such methods may be characterized as including the following steps: (a) combining active-sulfur, an electronic conductor, and an ionic conductor to form a mixture; (b) homogenizing the mixture to form a homogeneous mixture; and forming the active-sulfurcontaining electrode from the homogeneous mixture. The method is conducted in a such a manner that the resulting active-sulfur-containing electrode has at least about 5% (and more preferably at least about 10%) of its active-sulfur available for electrochemical reaction. In many embodiments, the method will involve a step of forming a slurry in order to facilitate formation the electrode. A thin layer of such slurry is then deposited on a substrate and allowed to dry. In other embodiments, no slurry is formed and, instead, the step of homogenizing comprises homogenizing a solid phase mixture containing the active-sulfur, the electronic conductor, and the ionic conductor. In some preferred embodiments, the resulting homogeneous mixture is converted to an electrode by a process such as extrusion, calendaring, or a process analogous to the solid phase rubber processing methods conventionally used in that art. In other preferred embodiments, the homogeneous mixture is deposited on a substrate by a process such as electrostatic deposition, sputtering, vapor deposition, printing, transfer printing, laminating, or coating.

In preferred embodiments, the step of forming the active-sulfur-containing electrode involves a step of depositing a layer of the homogeneous mixture on a substrate by a technique that does not rely on capillary action. If the homogeneous mixture is provided as a slurry, it is believed that deposition without capillary action helps to ensure that the resulting film will not segregate and therefore provide good contact between the active-sulfur, the ionic conductor, and the electronic conductor, thus allowing greater than 5% utilization of the active-sulfur.

When a slurry is employed to prepare the electrode, a further step of drying must be employed to form the electrode. The slurry may be dried on either a non-adhesive substrate or on a current collector. In the latter case, the electrode is essentially completely fabricated upon drying. In the former case, the dried electrode must be first removed from the non-adhesive substrate, and then affixed to a current collector such that the active-sulfur-containing electrode is in electrical contact with the current collector.

WO 96/16450 PCT/US95/12671 11 These and other features of the invention will further described and exemplified in the drawings and detailed description below.

Brief Description of the Drawings Figure 1 provides a flow chart showing the important steps employed in preparing an electrode in accordance with this invention.

Figure 2 illustrates a fixed tube apparatus for depositing a film of slurry on a substrate in accordance with one embodiment of this invention.

Figure 3 illustrates apparatus for continuous slurry film deposition in accordance with one embodiment of this invention.

Figure 4 provides a schematic of a Li/ electrolyte separator! active-sulfur electrode cell of this invention.

Figure 5 illustrates the reversible cycling performance of a lithium cell (Li/ amorphous PEO/ active-sulfur) of this invention evaluated at 30 0 C at an active-sulfur capacity 1 5 of 330 mAh/gm for each cycle.

Figure 6 illustrates the availability of the active-sulfur in the positive electrode of a lithium cell (Li/ amorphous PEO/ active-sulfur) of this invention evaluated at 30 0

C.

Figure 7 illustrates the availability of the active-sulfur in the positive electrode of a lithium cell (Li/ gel-state electrolyte separator/ active-sulfur) of this invention evaluated at 30 0

C.

Figure 8 illustrates the availability of the active-sulfur in the positive electrode of a lithium cell (Li/ PEO/ active-sulfur) of this invention evaluated at 90 0

C.

Figure 9 illustrates the reversible cycling performance of a lithium cell (Li/ PEO/ active-sulfur) of this invention evaluated at 90 0 C at an active-sulfur capacity of 400 mAh/gm for each cycle.

Figure 10 illustrates the reversible cycling performance of a lithium cell (Li/ PEO/ active-sulfur) of this invention evaluated at 90 0

C.

Figure 11 illustrates the peak power performance of a lithium cell (Li/ PEO/ active-sulfur) of this invention evaluated at WO 96/16450 PCT/US95/12671 12 Figure 12a is a table illustrating the performance of the cells prepared and operated as described in examples 1-8.

Figure 12b is a table illustrating the performance of the cells prepared and operated as described in examples 9-15.

Figure 13 illustrates the peak power performance of a lithium cell (Li/ PEO/ active-sulfur) of this invention evaluated at Best Modes for Carrying out the Invention 1. Abbreviations aPEO -amorphous polyethylene oxide (oxy-methylene linked polyoxy-ethylene) cm centimeter DEC diethyl carbonate DMC dimethyl carbonate DME dimethyl ether EC ethylene carbonate E.W. equivalent weight F.W. formula weight GICs graphite intercalation compounds gm gram mAh milliampere hour mm millimeter MW molecular weight OCV open circuit voltage PC propylene carbonate P.E.D. practical energy density PEO polyethylene oxide PEG polyethylene glycol PPP poly (p-phenylene) WO 96/16450 PCTIUS95/12671 psi

PVDF

S

T.E.D.

gA pm

WE

W/kg Wh/kg W/l wt.

V

pounds per square inch polyvinylidene fluoride sulfur theoretical energy density microampere micrometer working electrode watts per kilogram watthours per kilogram watts per liter weight volts 2. Definitions "Metals" are defined herein to be elements whose atoms usually lose electrons in the formation of compounds.

The phrase "alkali metals" is herein defined as the alkali family of metals located in Group IA of the periodic table, including lithium sodium potassium rubidium cesium (Cs) and francium (Fr).

The phrase "alkaline earth family" is herein defined as the Group IIA elements, including beryllium magnesium calcium strontium barium (Ba) and radium (Ra).

The phrase "transition metals" is defined herein to include the following metals: the scandium family: scandium yttrium lanthanum (La) and the lanthanide series, and actinium (Ac) and the actinide series; the titanium family: titanium zirconium and hafnium (Hf); the vanadium family: vanadium niobium and tantalum (Ta); WO 96/16450 PCT/US95/12671 14 the chromium family: chromium molybdenum and tungsten the manganese family: manganese technetium and rhenium (Re); the iron family: iron cobalt and nickel (Ni); the platinum family: ruthenium rhodium palladium (Pd), iridium and platinum (Pt); the copper family: copper silver and gold (Au); the zinc faily: zinc cadmium and mercury (Hg); the aluminum family: aluminum gallium indium and osmium (Os), 1 0 thallium and (11) the germanium family: germanium tin and lead (Pb).

The term "active-sulfur" is defined herein to be elemental sulfur or sulfur that would be elemental if the positive electrode were in its theoretically fully charged state.

1 5 The term "solid-state" is defined herein to be a material which contains less than by weight of a liquid.

The term "gel-state" is defined herein to be a material containing at least 20% by weight of a liquid wherein said liquid is immobilized by the presence of a gelling agent.

The term "component" is defined herein to be positive electrode, (b) electrolyte separator, or negative electrode.

WO 96/16450 PCT/US95/12671 r 3. Detailed Description The instant invention provides a positive electrode for solid-state and liquid format battery systems, wherein the positive electrode is based on active-sulfur which provides high specific energy and power, exceeding that of highly developed systems now known and in use. Solid-state format battery cell means all the components of the battery are either solid-state or gel-state. It further means that no component is in a liquid state. The equivalent weight of the active-sulfur used in the redox reactions within the battery cells of this invention is 16 grams/equivalent (with a lithium metal as the negative electrode, active-sulfur in its theoretically fully discharged state is Li2S), leading to a theoretical specific energy of 2800 watthours per kilogram (Wh/kg) for a lithium cell having a average OCV of 2.4 volts. Such an exceedingly high specific energy is very unusual and highly attractive.

Further, the batteries containing the positive electrode of this invention can operate at room temperature. The battery systems of this invention provide energy to weight ratios far in excess of the present demands for load leveling and/or electric vehicle applications, and can be reliably fabricated into units with reproducible performance values.

This invention can be incorporated in a battery cell which includes solid-state or gel-electrolyte separators. This embodiment excludes the problem of a battery cell in the liquid format that may suffer electrolyte leakage. For example, in lithium cells wherein a liquid electrolyte is used, leakage of the electrolyte can leave lithium exposed to the air, where it rapidly reacts with water vapor. Substantive casing can prevent such reactions and protects users and the environment from exposure to solvents but adds unwanted weight to the battery. Using a solid-state or gel-state format battery cells greatly reduces such problems of electrolyte leakage and exposure of lithium, and can cut down on the weight of the battery.

Another embodiment concerns battery cells in a liquid format, which have a solid active-sulfur-based positive electrode of this invention, and which have a solid negative electrode that contains carbon (when in the fully discharged state), carbon inserted with lithium or sodium and/or a mixture of carbon with lithium or sodium. Such an embodiment can overcome the problem of lithium depletion described in the prior art, for example, Rauh et al., supra.

16 In accordaince with tis inventionIU, ue acutiv-suiLr-ubas composite positive electrode and a battery system constructed with said positive electrode are provided. The positive electrodes of this invention are preferably reversible, and the metal-active-sulfur battery cells are preferably secondary batteries, and more preferably thin film secondary batteries.

The invention relates in one aspect to the positive electrode of battery cells.

wherein both the positive and negative electrodes are solid-state or gel-state and the electrolyte separator is either a solid-state or a gel-state material (see Definition). In another aspect, as indicated above, the positive electrode of this invention is used in a battery cell which contains a liquid electrolyte wherein the negative electrode is solid or gel-state and contains carbon, carbon 1 0 inserted with lithium or sodium, or mixtures of carbon with lithium or sodium. However, whatever the format of the battery cells made with the positive electrodes of this invention, said positive electrode comprises elemental sulfur as the active component when in the theoretically fully charged state.

5 Positive Electrode The active-sulfur of the novel positive electrodes of this invention is preferably uniformly dispersed in a composite matrix, for example, the active-sulfur can be mixed with a polymer electrolyte (ionically conductive), preferably a polyalkylene oxide, such as polyethylene oxide (PEO) in which an appropriate salt may be added, and an electronically conductive 20 material. Furthermore, the ionically conductive material may be either solid-state or gel-state format. In most cases it will be necessary or desirable to include a suitable polymeric electrolyte, for rapid ion transport within the electrode as is done with intercalation materials based electrodes. Furthermore, because the active-sulfur is not electrically conductive, it is important to disperse some amount of an electronically conductive material in the composite electrode.

Preferred weight percentages of the major components of the active-sulfur-based Spositive electrodes of this invention in a theoretically fully charged state are: from about r 20% to about 80% active-sulfur; from about 15% to about 75% of the ionically S conductive material (which may be gel-state or solid-state), such as PEO with salt, and S from about 5% to about 40% of an electronically conductive 17 material, such as carbon black, electronically conductive polymer, such as polyaniline. More preferably, those percentages are: from 30% to 75% of active-sulfur; from 15% to 60% of the ionically conductive material; and from 10% to 30% of the electronically conductive material.

Even more preferable percentages are: from 40% to 60% of active-sulfur; from 25% to 45% of the ionically conductive material; and from 15% to 25% of the electronically conductive material.

Another preferred percentage by weight range for the electronically conductive material is from about 8 to about 24 Methods of Making a Positive Electrode: An important feature of this invention is the ability to provide electrodes having active material (usually active-sulfur and/or a polydisulfide polymer) in intimate contact with both an ionic conductor and an electronic conductor. This facilitates ion and electron transport to and from the active material to allow nearly complete utilization of the active material. To this end, the invention provides a method of producing electrodes which ensures that at least about 5% of the active material in the resulting electrode will be available for electrochemical reaction.

No prior method produces electrodes having such high availability of active-sulfur.

A preferred method of making electrodes in accordance with this invention is illustrated in the flow chart of Fig. 1. The method begins with a step 100 of combining the electrode components (including an electrochemically active material, an electronic conductor, *Jog 20 and an ionic conductor). Next, at a step 102, the mixture is homogenized (and deagglomerated as necessary) such that the electrode components are well mixed and free of agglomerates.

Typically, a slurry will be formed by combining the electrode components with a liquid at either step 100 or step 102.

After the electrode components are homogenized and in slurry form, the slurry is coated on a substrate to form a thin film at a step 104. Best results will generally be obtained if the slurry is homogenized immediately before the film formation at step 104. This ensures that the slurry components have not settled or separated to any significant degree, thus providing a uniform film with the desired ratio of electrode components. Finally, at a step 106, the coated T film is dried to form the electrode. The film preferably will be sufficiently thin to allow for rapid WO 96/16450 PCT/US95/12671 18 drying so that the electrode components do not significantly redistribute during drying step 106.

The actual film thickness will, of course, depend upon the amount of liquid used in the slurry.

The components that are combined at step 100 include at least an electrochemically active insulator elemental sulfur or a polydisulfide), an electronically conductive material, and an ionically conductive material. Appropriate ratios of these materials are presented above for the resulting electrodes. Generally the same ratios may be employed in the mixture used to make the electrodes. The electrochemically active insulator is preferably active-sulfur, but any electrochemically active insulator or moderately conductive material may benefit from the inventive method. The ionic conductor is, as noted, preferably a polymeric ion 1 0 conductor such as a polyalkylene oxide, and more preferably PEO or amorphous PEO. To increase the conductivity of the ion conductor, it typically will be provided with a salt containing the transported ion a lithium salt such as lithium trifluoromethanesulfonimide or lithium perchlorate as described herein in connection with the electrolyte). The electronic conductor is preferably a carbon black or an electronically conductive polymer such as a polyaniline, polythiophene, polyacetylene, polypyrrole, etc. In an especially preferred embodiment, the electrochemically active material is active-sulfur, the ionic conductor is PEO (possibly with a small amount of an appropriate salt), and the electronic conductor is a carbon black.

In addition to the three above-mentioned "necessary" electrode components, other components that may be added to the mixture include materials to catalyze the transfer of electrons from the electronically conductive material to the active material, additives to protect an active metal electrode surface lithium or sodium electrode surfaces) in cells that employ such electrodes, dispersants, binders, and surfactants.

Materials that catalyze electron transport between the electrochemically active material and the electronic conductor are known in the art and include, for example, phthalocyanines, metallocenes, and brilliant yellow. Additives to protect an active metal electrode surface include, for example, organosulfur compounds such as 1,3,4-thiadiazole, phosphates, iodides, iodine, metal sulfides, nitrides, and fluorides. These materials are believed to provide a protective layer on the metal electrode surface. By casting them in the active-sulfur (or other insulator) electrode, small amounts of these protective agents WO 96/16450 PCT/US95/12671 19 will diffuse across the electrolyte to react with the metal electrode and provide the protective layer. Further, a dispersant (or dispersants) such as Brij or PEG may also be added to the mixture. Such materials reduce a tendency to agglomerate exhibited by some of the necessary components such as carbon black. Agglomeration, of course, degrades the quality of the resulting electrode by preventing thorough mixing of the components. Other additives are widely used in fabricating positive electrodes and are known in the art to have various benefits.

The use of such additives in formation of electrodes is within the scope of this invention.

As noted, the components of the electrode mixture will typically be dispersed in a slurry. Various liquids may be employed in the slurry. Typically, but not necessarily, the liquid 1 0 will not dissolve active-sulfur or carbon black. It may, however, dissolve polymeric components such as PEO or a polymeric electronic conductor. Preferred liquids evaporate quickly so that the resulting film dries completely and before redistribution of the components can occur. Examples of acceptable liquids for the slurry system include water, acetonitrile, methanol, ethanol, tetrahydrofuran, etc. Mixtures of liquid compounds may also be employed.

1 5 In large-scale continuous processes, it may be desirable to use a relatively low volatility liquid such as water to facilitate liquid recovery for recycling.

The relative amounts of solid and liquid in the slurry will be governed by the viscosity required for subsequent processing. For example, electrodes formed by a tape casting apparatus may require a different viscosity slurry than electrodes formed with a Mayer rod. The slurry viscosity will, of course, be governed by such factors as the composition and amounts the slurry components, the slurry temperature, and the particle sizes in the slurry. When the mixture includes a soluble ionic conductor such as PEO, the slurry ratio is conventionally defined in terms of the amount of soluble material to liquid. Amounts of the remaining insoluble components are then pegged to the amount of soluble material. For PEO-containing electrodes, a preferred range of concentrations is between about 30 and 200 milliliters of solvent per gram of PEO.

The exact ordering in which components are added to the slurry is not critical to the invention. In fact, as illustrated in examples 18 to 20 below, various approaches have been found to work with this invention. In one embodiment, for example, the soluble components WO 96/16450 PCT/US95/12671 such as PEO and brij are first dissolved in the liquid solvent before the insoluble components are added. In another exemplary embodiment, all components except crystalline PEO are dispersed and dissolved before the crystalline PEO is added. The insoluble components may be added to the slurry sequentially or in a premixed form the solid insolubles are mixed before addition to the slurry).

The process of homogenizing the electrode components (step 102 of Fig. 1) may take a variety of forms in accordance with the present invention. The process may vary depending upon whether electrode fabrication is performed batchwise or continuous. For smallscale batch operations, suitable slurry homogenization apparatus includes stir bars (preferably cross-type stir bars), paint mixers such as rotary blade mixers, paint shakers, and shear mixers.

Further, any mixing apparatus conventionally used to make "slips" in the ceramic processing arts will be sufficient for use with this invention. By way of example, some other batch mixing systems employ ball milling, tumble mixing, shear mixing, etc. The amount of time required to obtain a suitably homogenous mixture can be determined by routine experimentation with each of these pieces of mixing equipment.

Suitably homogenous mixtures are evidenced by high availability of active electrode material in the resulting electrode. It has been found that with stir bars, homogenization typically requires about 2 days, whereas with paint mixers and paint shakers homogenization requires less time (on the order of a few hours). In scaling up agitators for suspending solid particles, the torque per unit volume generally should be kept constant. Even so, blending times typically are significantly longer in larger vessels than in smaller ones and this should be factored into any scale-up.

In large-scale and/or continuous electrode fabrication systems, an industrial agitator will generally be preferable. Design criteria for such systems are well known in the art and are discussed at, for example, pages 222-264 of McCabe and Smith "Unit Operations of Chemical Engineering" Third Edition, McGraw Hill Book Company, New York (1976), which reference is incorporated by reference herein for all purposes. Suitable systems include turbine agitators and axial-flow or radial-flow impellers in tanks or vessels with rounded bottoms. In general, the vessels should not have sharp corners or regions where fluid currents cannot easily WO 96/16450 PCT/US95/12671 21 penetrate. Further, the system should be designed to prevent circulatory currents which throw solid particles to the outside of the vessel where they move downward and concentrate.

Circulatory currents can be mitigated by employing baffles in the system vertical strips perpendicular to the wall of the vessel). Shrouded impellers and diffuser rings can also be used for this purpose.

Very soon after the slurry is homogenized, it is deposited as a film on a substrate (step 104 of Fig. The exact amount of time between homogenization and deposition will depend upon the physical character of the slurry (viscosity, solids concentration, solids particle sizes, etc.). Significant settling and separation of the solids in the slurry is to be avoided.

Settling can be slowed by employing small particles of low density solids, high concentrations of the solids, and/or highly viscous liquids. Further the particles of the various solids components of the slurry can be chosen so that they all settle at about the same rate, thereby avoiding the problem of segregation. To the extent possible, the slurry, should be delivered to a substrate immediately after homogenization. For example, slip conditioning and supply systems such as these provided by EPH Associates, Inc. of Orem, Utah may be used to deliver slurry from a homogenizer directly to a substrate.

Preferably, the step of slurry film deposition does not rely on centrifugal, capillary or other forces that tend to exacerbate separation of the solid slurry components. Thus, for example, procedures involving dipping of a substrate into the slurry generally will not be suitable for use in the present invention.

In accordance with this invention, preferred film formation procedures include deposition onto a substrate via a fixed tube or structure temporarily defining a chamber above the substrate, spreading via a Mayer rod, and spreading via a doctor blade.

Deposition via a fixed tube is illustrated in Fig. 2 where a tube 122 is placed against a substrate 124 with sufficient force to prevent slurry solids from leaking outside of deposition region 120.

The tube 122 preferably is made from inert materials such as glass tube. It should have a smooth bottom so that it makes good contact and a reasonably impervious seal with substrate 124. An amount of slurry sufficient to cover region 120 is provided through the top of tube 122.

WO 96/16450 PCT/US95/12671 r 22 The slurry film also may be applied by spreading. In batch processes, a Mayer rod which is rod of about 1/2 to 1 inch in diameter wound with thin wires may profitably be used to roll out a thin layer of slurry film on the substrate. In continuous or batch processes, a doctor blade may be employed to deliver a thin layer of slurry to a moving sheet of substrate, as explained in more detail below. Still further, the slurry film may be applied by a laminating process, or by a printing process such as a screen printing process analogous to silk screen printing.

Regardless of how the slurry film is applied, it should have a primary dimension, thickness, that allows for rapid drying. This thickness will, of course, depend upon such factors as slurry concentration and liquid volatility. In addition, the slurry film thickness should be chosen so as to produce electrodes of appropriate thickness for the ultimate battery application. For example, low power, high energy applications, such as batteries for pacemakers, may use thicker electrodes, up to a few millimeters. In contrast, high power applications, such as batteries for power tools or hybrid vehicles should employ thinner electrodes, no more than about 100 gtm thick. It should be noted that electrodes of appropriate thickness for low power applications may be made by laminating two or more thinner electrodes. In this manner, the problem of slow drying associated with thick electrodes can be avoided.

Preferably the substrate on which the slurry is applied is a current collector such as a sheet of stainless steel, aluminum, copper, titanium, metallized PET, or other conductive material which will not react at operating cell conditions. Suitable current collectors may also take the form of expanded metals, screens, meshes, foams, etc. as is known in the art. In alternative embodiments, the substrate may be a sheet of inert material that does not adhere to dried electrode material. One such suitable substrate material is Teflon®. After the electrode film is dried, it is peeled away from such substrate and later contacted to a current collector such as one of the above-mentioned materials. Contacting to the current collector may be accomplished by hot pressing, crimping, etc. Alternatively, the current collector can be formed directly on the electrode material by a technique such as metal spraying, sputtering, or other technique known to those of skill in the art.

M

WO 96/16450 PCT/US95/12671 23 The process of forming an electrode concludes with a drying step (step 106 of Fig. In batch processes, this is preferably accomplished in two steps: evaporation under ambient conditions for 30 seconds to 12 hours, followed by drying under vacuum for about 4 to 24 hours at room temperature or an elevated temperature. In continuous processes, drying may be accomplished by passing a sheet of electrode/substrate through a drying chamber such as an IR drier. A typical resulting active-sulfur electrode layer will have a density between about 0.0016 and 0.012 grams per cm 2 A continuous process for preparing sheets of precipitated polymer will now be described with reference to Fig. 3. As shown in Fig. 3, a hopper 220 dispenses a sheet of homogenized slurry 228 of suitable composition as described above. The slurry is deposited on a moving substrate sheet 222 which passes under blade 226 to produce a thin evenly spread layer of slurry 230 on substrate 222. The lower tip of blade 226 and the substrate 222 should be spaced such that slurry layer 230 has a thickness facilitating rapid drying as described above.

The substrate sheet 222 which moved along in the continuous process by a roller 232 may be made from a variety of suitable materials including flexible Teflon or any other release agent. In addition, the substrate may be a material that is intended to be incorporated in the ultimately produced electrode. For example, the substrate may include a metal foil, metallized PET, or screen that is to form a current collector in the final electrode. The substrate 222 with slurry layer 230 is directed into a drying apparatus 248 operated at a temperature sufficient to remove much of the liquid from the slurry. This apparatus may include one or more dryers such as IR dryers, and it may also have a condenser or other system (not shown) for recovering evaporated slurry liquid.

If the substrate sheet 222 is not a current collector, it may be separated from the electrode or partially dried electrode after the substrate enters drying apparatus 248. The separation can then be accomplished by providing separate uptake reels for substrate 222 (outside drying apparatus 248) and for the resulting electrode sheet. Of course, if the substrate 222 is a current collector or is otherwise intended to be part of the electrode, no separation is necessary, and the substrate/electrode laminate is taken up on reel 232 as shown.

WO 96/16450 PCT/US95/12671 24 In alternative embodiments, the electrode is formed without first preparing-a slurry. Rather the electrode components including the electrochemically-active insulator, the ion conductor, and the electron conductor are homogenized in a solid state and formed into a sheet as by extrusion or calendaring. The solid state homogeneous mixture may also be coated onto a substrate by roll coating, blade coating, extrusion coating, curtain coating, or a related process. In each case, the solid state mixture is caused to flow by application of heat and/or pressure and the resulting viscous or viscoelastic mixture is passed though a die, a roller, or a blade. In such embodiments, the PEO or other polymeric components should be present in concentrations suitable to allow formation of a viscous or viscoelastic material under conditions 1 0 encountered in standard polymer processing apparatus. Details of suitable polymer processing techniques are found in Middleman, "FUNDAMENTALS OF POLYMER

PROCESSING",

McGraw-Hill, Inc. 1977 which is incorporated herein by reference in its entirety and for all purposes. In addition to these processing techniques involving flow, alternative techniques within the scope of this invention include electrostatic deposition as by processes analogous to 1 5 xerography, sputtering, vapor deposition, printing, laminating, and roll coating. Further, dry processes conventionally used in the rubber processing arts may be applied to form electrodes in accordance with this invention. Because each of the above "dry" techniques do not involve a slurry, no drying step is required. Thus, there is less opportunity for the solid electrode components to segregate or agglomerate after homogenization.

Electrolyte Separators and Liquid Electrolytes The electrolyte separator for solid-state format battery cells incorporating the positive electrode of this invention functions as a separator for the positive and negative 2 5 electrodes and as a transport medium for the metal ions. As defined above, the material for such an electrolyte separator is preferably electronically insulating, ionically conductive and electrochemically stable.

When the battery cell is in a solid-state format, all components are either solidstate or gel-state and no component is in the liquid state.

WO 96/16450 PCT/US95/12671 The aprotic organic liquids used in the electrolyte separators of this invention, as well as in the liquid electrolytes of this invention, are preferably of relatively low molecular weight, for example, less than 50,000 MW. Combinations of aprotic organic liquids may be used for the electrolyte separators and liquid electrolytes of the battery cells incorporating the positive electrode of this invention.

Preferred aprotic organic liquids of the battery cells incorporating the positive electrode of this invention include among other related aprotic organic liquids, sulfolane, dimethyl sulfone, dialkyl carbonates, tetrahydrofuran (THF), dioxolane, propylene carbonate ethylene carbonate dimethyl carbonate (DMC), butyrolactone,

N-

1 0 methylpyrrolidinone, tetramethylurea, glymes, ethers, crown ethers, dimethoxyethane

(DME),

and combinations of such liquids.

For the battery cells, incorporating the positive electrode of this invention, containing a liquid electrolyte wherein the negative electrode is carbon-containing, said liquid is also an aprotic organic liquid as described above. Such a format also preferably contains a 1 5 separator within the liquid electrolyte as discussed above.

An exemplary solid-state electrolyte separator combined with this invention is a ceramic or glass electrolyte separator which contains essentially no liquid. Polymeric electrolytes, porous membranes, or combinations thereof are exemplary of the type of electrolyte separator to which an aprotic organic plasticizer liquid could be added according to this invention for the formation of a solid-state electrolyte separator containing less than 20% liquid.

Preferably the solid-state electrolyte separator is a solid ceramic or glass electrolyte and/or solid polymer electrolyte. Said solid-state ceramic electrolyte separator preferably comprises a beta alumina-type material, Nasicon or Lisicon glass or ceramic. The solid-state electrolyte separator may include sodium beta alumina or any suitable polymeric electrolyte, such as polyethers, polyimines, polythioethers, polyphosphazenes, polymer blends, and the like and mixtures and copolymers thereof in which an appropriate electrolyte salt has optionally been added. Preferred polyethers are polyalkylene oxides, more preferably, polyethylene oxide.

WO 96/16450 PCT/US95/12671 26 Exemplary but optional electrolyte salts for the battery cells incorporating the positive electrode of this invention include, for example, lithium trifluoromethanesulfonimide (LiN(CF 3 S02) 2 lithium triflate (LiCF 3 S0 3 lithium perchlorate (LiC104), LiPF 6 LiBF 4 LiAsF 6 as well as, corresponding salts depending on the choice of metal for the negative electrode, for example, the corresponding sodium salts. As indicated above, the electrolyte salt is optional for the battery cells of this invention, in that upon discharge of the battery, the metal sulfides or polysulfides formed can act as electrolyte salts, for example, MxzS wherein x 0 to 2 and z is the valence of the metal.

Negative electrode For solid-state battery cells incorporating the positive electrode of this invention, the negative electrode may comprise any metal, any mixture of metals, or any carbon or metal/carbon material capable of functioning as an active component of a negative electrode in combination with said active-sulfur positive electrode. For example, any of the alkali or alkaline 1 5 earth metals or transition metals can be used, and particularly mixtures containing lithium and/or sodium.

Preferred materials for said negative electrode for the solid-state battery cell formats include sodium and/or lithium, and mixtures of sodium or lithium with one or more additional alkali metals and/or alkaline earth metals. Preferred materials for said negative electrode also include mixtures of sodium or lithium with one or more elements to form a binary or ternary alloy, such as, Na 4 Pb, lithium-silicon and lithium-aluminum alloys.

A particularly preferred metal for a negative electrode is sodium, or at least a sodium base alloy at least 90% by weight sodium) because of its low cost, low equivalent weight and its relatively low melting point of 97.8 0 C. However, other alkali metals such as Li or K, or mixtures of same with Na may also be used, as desired, to optimize the overall system.

Also preferred negative electrode materials for the solid-state battery cells incorporating the positive electrode of this invention include carbon, carbon inserted with lithium or sodium and/or a mixture of carbon with sodium or lithium. Exemplary and preferred are LiyC 6 (wherein y 0.3 to such as, LiC 6 negative electrodes which comprise graphite or WO 96/16450 PCT/US95/12671 27 petroleum coke, for example, graphite intercalation compounds (GICs), and carbon inserted within highly disordered carbons. The inserted carbon may also be that wherein some carbon has been alloyed with boron, or wherein the carbon has been prepared from low temperature pyrolysis (about 750 0 C) of carbon or carbon-silicon containing polymers such that the carbon product retains some hydrogen or silicon or both. (See, Sato et al., "A Mechanism of Lithium Storage in Disordered Carbons," Science. 264: 556 (22 April 1994), which discusses very good results with a preferred negative electrode of Li inserted within poly p-phenylene-based

(PPP-

based) carbon.) For battery cells using the positive electrode of this invention that are in liquid formats, the negative electrode is carbon, carbon inserted with lithium or sodium, or mixtures of carbon and lithium or sodium as described above in relation to solid-state formats, including the preferable versions of such carbon-containing electrodes. For whatever format, if the negative electrode contains only carbon, the cell is in the theoretically fully discharged state, and the positive electrode comprises lithium or sodium sulfides or polysulfides.

Battery Cells The battery cells containing the sulfur-based composite positive electrodes of this invention can be constructed according to conventional formats as described in the literature.

For example, De Jonghe et al., U.S. patent No. 4,833,048 and Visco et al., U.S. Patent No.

5,162,175. Such conventional formats are understood to be herein incorporated by reference.

The novel battery cells incorporating this invention, preferably secondary cells, more preferably thin film secondary cells, may be constructed by any of the well-known and conventional methods in the art. The negative electrode may be spaced from the positive sulfur electrode, and both electrodes may be in material contact with an ionically conductive electrolyte separator. Current collectors contact both the positive and negative electrodes in a conventional manner and permit an electrical current to be drawn by an external circuit.

Suitable battery constructions may be made according to the known art for assembling cell components and cells as desired, and any of the known configurations may be WO 96/16450 PCT/US95/12671 28 fabricated utilizing the invention. The exact structures will depend primarily upon the intended use of the battery unit.

A general scheme for the novel battery cells of this invention in a solid-state format may include a current collector in contact with the negative electrode and a current collector in contact with the positive electrode, and a solid-state electrolyte separator sandwiched between the negative and positive electrodes. In a typical cell, all of the components will be enclosed in an appropriate casing, for example, plastic, with only the current collectors extending beyond the casing. Thereby, reactive elements, such as sodium or lithium in the negative electrode, as well as other cell elements are protected.

The current collectors can be sheets of conductive material, such as, aluminum or stainless steel, which remain substantially unchanged during discharge and charge of the cell, and which provide current connections to the positive and negative electrodes of the cell. The positive electrode film may be attached to the current collector by directly casting onto the current collector or by pressing the electrode film onto the current collector. Positive electrode mixtures cast directly onto current collectors preferably have good adhesion. Positive electrode films can also be cast or pressed onto expanded metal sheets. Alternately, metal leads can be attached to the positive electrode film by crimp-sealing, metal spraying, sputtering or other techniques known to those skilled in the art. The sulfur-based positive electrode can be pressed together with the electrolyte separator sandwiched between the electrodes. In order to provide good electrical conductivity between the positive electrode and a metal container, an electronically conductive matrix of, for example, carbon or aluminum powders or fibers or metal mesh may be used.

A particularly preferred battery cell comprises a solid lithium or sodium electrode, a polymeric electrolyte separator, either solid-state or gel, preferably a polyalkylene oxide, such as, polyethylene oxide, and a thin-film composite positive electrode containing an elemental sulfur electrode (that is in the theoretically fully charged state), and carbon black, dispersed in a polymeric electrolyte. Optionally the electrolyte separator in such a preferred battery call can comprise an electrolyte salt.

Operating Temperatures _29 The operating temperature of the battery cells incorporating the novel positive electrode of this invention is preferably from about -40°C to about 180°C. Preferred operating temperature ranges depend upon the application. Exemplary preferred operating temperature ranges include from 40°C to 145C; from -20°C to 145 0 C; from -20°C to 120°C; and from 0°C to 90°C. Most preferably for many applications, the cells incorporating this invention operate at ambient or above-ambient temperatures.

Different embodiments of this invention can provide different preferred operating temperature ranges. The choice of electrolyte can influence the preferred operating temperature ranges for the batteries incorporating the positive electrode of this invention. For example, when 1 0 conventional PEO is used the preferred operating range is 60 0 C to 120°C; whereas when amorphous PEO (aPEO) is used, the battery can be run at room temperature, or in a range of OOC to Gel formats also provide for lower operating temperature ranges. Exemplary battery cells using the positive electrode of this invention containing, for example, polymeric 5 electrolyte separators with increasingly greater percentage of a aprotic organic liquid immobilized by the presence of a gelling agent, can provide for increasingly lower operating temperature ranges. An exemplary operating temperature range for a solid-state battery having -gel-state components of this invention would be from about -20 0 C to about 60 0

C.

A battery with a liquid separator and an negative electrode comprising carbon, inserted carbon and/or a mixture of carbon and lithium or sodium can operate at a preferred temperature range of from -40 0 C to 60 0

C.

*i The high temperature operating range of the battery cells based on the positive electrode of this invention can be limited by the melting point of either a solid electrode or a solid electrolyte. Thus sodium negative electrodes are limited to temperatures below 97.8 0 C, but sodium alloy electrodes, such as Na 4 Pb, can be used in a solid form at well over 100 0

C.

WO 96/16450 PCT/US95/12671 Specific Energy and Specific Power The practical specific energies of the secondary cells utilizing this invention are preferably greater than 65 watt-hours per kilogram (Wh/kg), more preferably greater than 100 Wh/kg, still more preferably greater than 150 Wh/kg, even more preferably greater than 200 Wh/kg, and still even more preferably greater than 250 Wh/kg. While cells having specific energies in the above ranges are preferred for many applications, these ranges should not be viewed as limiting the invention. In fact, the cells of this invention can be expected to achieve specific energies in excess of 850 Wh/kg. Thus, for some applications, a preferred practical specific energy range of the batteries incorporating this invention is from about 100 Wh/kg to about 800 Wh/kg.

The practical steady-state specific power of the secondary cells utilizing this invention are preferably greater than 20 watts per kilogram more preferably greater than W/kg, still more preferably greater than 100 W/kg, even more preferably greater than 150 W/kg, and still even more preferably greater than 250 W/kg. It is envisioned that with battery 1 5 construction optimized for power, the steady-state power of this invention can exceed 750 W/kg.

A preferred practical specific energy range of the batteries incorporating this invention is from about 50 W/kg to about 500 W/kg. The peak and pulse power performances would be many times greater than the steady-state power.

Cells made with lithium negative electrodes, solid-state or gel-state electrolyte separators, and positive electrodes made with elemental sulfur, polyethylene oxide (or modified polyethylene oxide) and carbon particles were constructed to test the performance of the batteries of this invention. Examples of these tests will serve to further illustrate the invention but are not meant to limit the scope of the invention in any way.

Example 1 Solid-state cell: Cycling performance at an active-sulfur capacity of 330 mAh/gm for each recharge cycle evaluated at 30 0

C

WO 96/16450 PCT/US95/12671 31 A positive electrode film was made by mixing 45% (percentage by weight) elemental sulfur, 16% carbon black, amorphous polyethylene oxide (aPEO) and lithium trifluoromethanesulfonimide (wherein the concentration of the electrolyte salt to PEO monomer units (CH 2

CH

2 0) per molecule of salt was 49:1), and 5% 2 ,5-dimercapto-1,3,4-dithiadiazole in a solution of acetonitrile (the solvent to PEO ratio being 60:1 by weight). The components were stir-mixed for approximately two days until the slurry was well mixed and uniform. A thin positive electrode film was cast directly onto stainless steel current collectors, and the solvent was allowed to evaporate at ambient temperatures. The resulting positive electrode film weighed approximately 0.0028 gm per cm 2 1 0 The polymeric electrolyte separator was made by mixing aPEO with lithium trifluoromethanesulfonimide, (the concentration of the electrolyte salt to PEO monomer units

(CH

2

CH

2 0) per molecule of salt being 39:1) in a solution of acetonitrile (the solvent to polyethylene oxide ratio being 15:1 by weight). The components were stir-mixed for two hours until the solution was uniform. Measured amounts of the separator slurry were cast into a 1 5 retainer onto a release film, and the solvent was allowed to evaporate at ambient temperatures.

The resulting electrolyte separator film weighed approximately 0.0144 gm per cm 2 The positive electrode film and polymeric electrolyte separator were assembled under ambient conditions, and then vacuum dried overnight to remove moisture prior to being transferred into the argon glovebox for final cell assembly with a 3 mil (75 micron) thick lithium anode film (FMC/Lithco, 449 North Cox Road, Box 3925 Gastonia, NC 28054 (USA)).

A schematic of the cell layers are shown in Figure 4. Once assembled, the cell was compressed at 2 psi and heated at 40 0 C for approximately 6 hours. After heating the layers of lithium, electrolyte separator, and the positive electrode were well adhered.

The cell was then evaluated with a battery tester (Maccor Inc., 2805 West Street, Tulsa, OK 74107 (USA)) inside the glovebox at 30 0 C. That procedure was performed to eliminate any contamination problems of the lithium.

The cell was cycled to a constant capacity corresponding to delivering 330 mAh per gram of the active-sulfur in the positive electrode film. The rates used were 100-20 gA/cm 2 WO 96/16450 PCTfUS9512671 32 for discharging and 50 10 gtA/cm 2 for charging to cutoff voltages of 1.8 and 3.0 volts, respectively.

Figure 5 shows the end of the discharge voltage of the cell after each recharge cycle. As evident from the graph, the cell performance is very consistent.

Example 2 Solid-state cell: Total discharge capacity to 900 mAh/gm of active-sulfur evaluated at 30 0

C

1 0 A cell identical to the one described in Example 1 was discharged to 1.8 volts at current densities of 100 20 tA/cm 2 at 30 0 C to determine the total availability of the activesulfur in the film. The resulting discharge curve is seen in Figure 6. The total capacity delivered by this film was in excess of 900 mAh per gram of the active-sulfur, that is, a utilization of 54% of the available active-sulfur, wherein 100% would be 1675 mAh/gm.

Example 3 Solid-state cell having gel-state components: Total discharge capacity to 900 mAh/gm of active-sulfur evaluated at 30 0

C

A positive electrode film similar to the one described in Example 1 was made with a composition of 50% (percentage by weight) elemental sulfur, 16% carbon black, amorphous polyethylene oxide (aPEO) and lithium trifluoromethanesulfonimide (at a 49:1 concentration).

The electrolyte separator used was a gel made inside the glovebox to avoid moisture and oxygen contamination. A starting solution consisting of 10% (weight percentage) of lithium trifluoromethanesulfonimide and 90% of tetraethylene glycol dimethylether (tetraglyme) was made. Then a solvent of 90% tetrahydrofuran (THF) was mixed with 10% of the starting solution. 5.6% Kynar Flex 2801 (Elf Atochem of North America, Inc., Fluoropolymers Department, 2000 Market Street, Philadelphia, PA 19103 a gelling agent (PVDF), was added to the mixture.

WO 96/16450 PCT/US95/12671 33 The mixture was stirred for a few minutes and then left standing for 24 hours so that the components were absorbed into the Kynar,. The mixture was stirred again for a few minutes to homogenize the components and then heated for 1 hour at 60 0 C. Electrolyte separator films were cast onto a release film, and the THF solvent was allowed to evaporate at ambient temperatures. The resulting electrolyte separator film weighed approximately 0.0160 gm per cm 2 The resulting cell comprising the positive electrode film, the gel-state electrolyte separator film, and the lithium negative electrode was tested at the same conditions as the cell described in Example 2. The total capacity delivered by this film was also in excess of 900 1 0 mAh per gram of the active-sulfur, that is, a utilization of 54% of the available active-sulfur, wherein 100% would be 1675 mAh/gm as shown in Figure 7.

Example 4 Solid-state cell: Total discharge capacity to 1500 mAh/gm of sulfur evaluated at 90 0

C

A positive electrode film similar to the one described in Example 1 was made for use at above ambient temperatures with a composition of 50% (weight percentage) elemental sulfur, 16% carbon black, polyethylene oxide (900,000 molecular weight) and lithium trifluoromethane-sulfonimide (a 49:1 concentration).

The solid-state electrolyte separator used was cast from a slurry of 900,000 MW PEO in acetonitrile without any additional electrolyte salts. The resulting electrolyte separator film weighed approximately 0.0048 gm per cm 2 The cell was assembled as described in Example 1. Once assembled, the cell was compressed at 2 psi and heated at 90 0 C for approximately 6 hours. The cell was tested at 0 C inside a convection oven located in the glovebox. The cell was discharged to 1.8V at rates of 500 to 100 gA/cm 2 The capacity relative to the active-sulfur versus the voltage during discharge is shown in Figure 8. The total capacity delivered by this film was also in excess of 1500 mAh WO 96/16450 WO 96/16450 PCT/US95/12671 34 per gram of the active-sulfur, that is, a utilization of 90% of the available active-sulfur, wherein 100% would be 1675 mAh/gm.

Example Solid-state cell: Cycling performance at a sulfur capacity of 400 mAh/gm for each cycle evaluated at 90 0

C

A positive electrode film similar to the one described in Example 4 was made with a composition of 50% (weight percentage) elemental sulfur, 24% carbon black, polyethylene oxide (900,000 molecular weight) and lithium trifluoromethanesulfonimide (a 49:1 concentration). The electrolyte separator is also the same as described in Example 4. The cell was tested at 90 0 C and cycled to a constant capacity corresponding to delivering 400 mAh/gm of the active-sulfur in the positive electrode film. The rate used was 500 gA/cm 2 for discharge to 1000 500 tA/cm 2 for charging at cutoff voltages of 1.8 and 2.6 volts, respectively.

Figure 9 shows the end of the discharge voltage of the cell after each recharge cycle. As evident from the graph, the cell performance is very consistent.

Example 6 Solid-state cell: Cycling performance for each cycle to a cutoff voltage of 1.8V evaluated at 90 0

C

A positive electrode film identical to the one described in Example 4 was made.

The electrolyte separator is also the same as described in Example 4. The cell was tested at 0 C and cycled between voltage limits between 1.8 2.6 volts. The rates used were 500 100 gtA/cm 2 for charging. Figure 10 shows the delivered capacity after each recharge. As evident from this graph most recharge cycles delivered above 1000 mAh per gram of the active-sulfur used in the cathode film.

WO 96/16450 PCT/US95/12671 Example 7 Solid-state cell: Peak power performance evaluated at 90 0

C

A positive electrode film similar to the one described in Example 4 was made with a composition of 50% (weight percentage) elemental sulfur, 16% carbon black, polyethylene oxide (900,000 molecular weight) and lithium trifluoromethanesulfonimide (a 49:1 concentration). The electrolyte separator is also the same as described in Example 4. The cell was tested at 90 0 C and pulse discharged for a 30 second duration or to a cutoff voltage of 1.2 V.

1 0 The discharge rates ranged from 0.1 3.5 mA/cm 2 The pulse power (W/kg) delivered by the cathode film versus the current density is shown in Figure 11. As seen from the plot, an extraordinarily high pulse power of 3000 W/kg is capable of being attained.

Example 8 A cell was tested under the conditions described in Example 5 above, except that the cell was cycled to a constant capacity corresponding to delivering 200 mAh/gm of the activesulfur in the positive electrode film. The electrode was prepared from 50% elemental sulfur, 16% carbon, and the balance 900,000 MW PEO. A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

Example 9 A cell was tested under the conditions described in Example 5 above, except that the cell was cycled to a constant capacity corresponding to delivering 300 mAh/gm of the activesulfur in the positive electrode film. The electrode was prepared from 45% elemental sulfur, 16% carbon, 5% 2,5-dimercapto-1,3,4-dithiadiazole, and the balance 900,000 MW PEO. A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

WO 96/16450 PCT/US95/12671 36 Example A cell was tested under the conditions described in Example 5 above, except that the cell was cycled to a constant capacity corresponding to delivering 400 mAh/gm of the activesulfur in the positive electrode film. The electrode was prepared from 45% elemental sulfur, 16% carbon, 5% 2 ,5-dimercapto-1,3,4-dithiadiazole, and the balance 900,000 MW PEO. A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

Example 11 1 0 A cell was tested under the conditions described in Example 5 above, except that the cell was cycled to a constant capacity corresponding to delivering 600 mAh/gm of the activesulfur in the positive electrode film. The electrode was prepared from 50% elemental sulfur, 24% carbon, 1% PbS, and the balance 900,000 MW PEO. A film of electrode material was directly cast onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

Example 12 A cell was tested under the conditions described in Example 6 above. The electrode was prepared from 50% elemental sulfur, 16% carbon, and the balance 900,000 MW PEO. A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 but with the addition of 1% PbS.

Example 13 A cell was tested under the conditions described in Example 6 above. The electrode was prepared from 50% elemental sulfur, 24% carbon, and the balance 900,000 MW PEO and lithium trifluoromethanesulfonimide (at a 49:1 weight ratio). A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

WO 96/16450 PCT/US95/12671 V 37 Example 14 A cell was tested under the conditions described in Example 4 above, but at The electrode was prepared from 50% elemental sulfur, 24% carbon, and the balance 900,000 MW PEO and lithium trifluoromethanesulfonimide (at a 49:1 weight ratio). A film of electrode material was formed with a Mayer rod onto a current collector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod.

Example A cell was tested under the conditions described in example 7, but with discharge rates ranging from 0.4 to 9 mA/cm 2 The electrode was prepared with 50% elemental sulfur, 16% carbon, and the balance 900,000 MW PEG. A film of the electrode material was formed with a Mayer rod onto a current coilector. The separator was like the one in example 4 with 900,000 MW PEO and formed with a Mayer rod. As seen from the plot, an extraordinarily high pulse power of 7400 W/kg of the positive electrode can be attained.

Table 1 presented in Figure 12a summarizes the performance of the representative battery cells of examples 1-7 under the specific testing conditions detailed in each example. Table 2 presented in Figure 12b summarizes the performance of the representative battery cells of examples 8-14 under the specific testing conditions detailed in each example.

The demonstrated specific energies and specific powers listed above are based on the entire composite positive electrode. The electrolyte separators and lithium foils used for the laboratory tests were not optimized for the final battery. The battery projections are based on using 5 gm thick polymeric electrolyte separators, 30 gm thick lithium foil and 2.5-5.0 gim thick current collectors. Additionally, there is a 10% weight increase allocated for the external casing assuming for batteries larger than 1 Amphour.

Depending on the exact size and configuration of the cell laminate, the finished battery performance is approximately 30 70% of the positive electrode film performance. For simplicity, 50% has been used for the conversion between positive electrode performance and battery projections (this is equivalent to 100% battery burden). The calculated density range of WO 96/16450 PCT/US95/12671 38 the battery ranged from 1.0 1.6 gm/cm 3 depending on the specific components and configurations. For simplicity, a density of 1.25 gm/cm 3 is used to calculate the projected energy density (Wh/l).

As evident from the table, the battery systems containing the positive electrode of this invention demonstrate exceptionally high specific energies and exceed all now known solidstate intercalation compound-based batteries. The cells of this invention also outperform cells which operate at much higher temperatures such as the Na/beta"-alumina/Na 2 Sx cell (350 0

C),

LiA/LiC, KCI/FeS 2 cell (450 0

C).

It is seen that the invention provides high specific energy and power cells, the performance of which exceeds that of highly developed systems now known and in use. At the same time, the high energy and power are available at room temperature or ambient operation.

Example 16 This example details one method of making active-sulfur electrodes of this invention.

Initially, a three inch long piece of stainless steel (Brown Metals) was cut off of a four inch wide spool. Both sides of the sheet were then abraded with a sanding sponge to remove any insulating coating and ensure better electrical contact between the film and the stainless steel current collector. The abraded stainless steel current collector was wiped with acetone and Kimwipe EX-L until the Kimwipe was clean. A tab for electrically connecting the battery was made by cutting a section out of the stainless steel. The resulting stainless steel current collector was then weighed.

Next, the current collector was placed on a flat sheet of glass, and a standard 13 cm 2 glass casting ring was placed on the center of a 3"X3" portion of the steel current collector.

Then a syringe was filled with a cathode slurry prepared according one of the examples above. Quickly 0.5ml of the slurry was squirted out (or the desired volume to obtain the desired capacity per area) onto the area inside the glass ring. Before the solvent evaporated, the bead of slurry was spread so as to cover the area inside the glass ring with a wet film of even thickness. Thereafter, the film was allowed to dry for several hours before removing the glass ring from the current collector. An X-acto knife was used to cut the film off of the WO 96/16450 PCT/US95/12671 39 glass ring. The current collector with the film was again weighed in order to obtain the weight of the cathode film.

Electrodes were also prepared on Teledyne stainless steel or aluminum foils as described above but without abrading the steel or aluminum since there are no insulating coatings as on the Brown Metals steel.

Example 17 A stainless steel current collector was prepared as described in example 15. The current collector was then placed on a smooth and flat glass sheet, and the middle of the Mayer rod RDS 075 is standard now), was centered on the edge of the current collector.

Several milliliters of slurry (as much as necessary so as to not run out of slurry) were poured in front of the rod. With one hand holding the substrate in place on the glass and the other holding the middle of the rod, the rod was dragged across the current collector leaving a wet film. The film was then dried and the process was repeated from the other end. The solvent content of the slurry was adjusted so that the wet film did not run (too much solvent) and did not have a ridged or raked appearance. When the film was dried, it was placed on a glass ring (at the center of the 3"x3" current collector), and a circular section was cut along the inside circumference of the ring. The excess film outside the circle was then scraped off and the weight of the film was determined.

Example 18 Initially, an aluminum foil current collector prepared as in example 15 was placed on a sheet of glass, and taped to the ends of the glass so that it did not move while moving the Mayer rod. A Mayer Rod was placed on one end of the current collector and enough slurry to cover the desired area of current collector was squirted from a syringe in front of the Mayer Rod and onto the current collector. When the film was dry, the process was repeated as before but processed with a Mayer rod from a different end. When the film was dry, unwanted film was scraped off, and the current collector was trimmed to the desired area.

WO 96/16450 PCT/US95/12671 Example 19 The following procedure was employed to prepare a cathode slurry having elemental sulfur, 16wt% acetylene black, 2wt% Brij 35, and 32wt% 900,000 MW PEO. A 38X38 mm stir cross was placed in an 8 oz. Quorpac bottle (BWR Scientific, Brisbane, CA) with a Teflon lined top. To the bottle the following were added: 230ml of acetonitrile.

(Aldrich HPLC grade), 6g of sublimed and ball milled sulfur powder (Aldrich), 1.93g of acetylene (Shawinigin) carbon black (Chevron Cedar Bayou Plant), and 0.24g of Brij (Fluka). The contents of the bottle were then stirred overnight on a magnetic stir plate. The stir-plate power was set to stir at as high an RPM as possible without splattering or sucking air. The next day, as the slurry was rapidly stirring, 3.85g of 900,000 MW PEO (Aldrich) was added in a stream so as not to form a few large lumps of solvent swollen PEO but rather many tiny lumps of solvent swollen PEO. During the next two days, the speed of the stir bar was adjusted to maintain as high as possible rpms, again without splattering or sucking air. After stirring for two nights, the PEO was dissolved and the slurry was used to prepare thin films by either ring casting or Mayer rod techniques.

Alternatively, sublimed and precipitated sulfurs were used instead of the ball milled sulfur described above, but instead of mixing for two nights, about two weeks of stirring were required. If the slurry is mixed for only two nights the resulting thin film was found to be porous and lumpy.

Example The following procedure was employed to prepare a cathode slurry having elemental sulfur, 24wt% acetylene black, 2wt% Brij 35, and the balance 900,000 MW PEO:lithium trifluoromethanesulfonimide (20:1) in acetonitrile (ml AN:gm PEO, 90:1). A 38X38 mm stir cross was placed in an 8 oz. Quorpac bottle (BWR Scientific, Brisbane, CA) with a teflon lined top. To the bottle the following were added: 0.59g lithium trifluoromethanesulfonimide (added in a dry box), 200ml of acetonitrile (Aldrich HPLC grade), 5g of sublimed and ball milled sulfur powder (Aldrich), 2.4g of acetylene (Shawinigin) carbon black (Chevron Cedar Bayou Plant), and 0.2g of Brij 35 (Fluka). The WO 96/16450 PCT/US95/12671 41 contents of the bottle were then stirred overnight on a magnetic stir plate. The stir-plate power was set to stir at as high an RPM as possible without splattering or sucking air. The next day, as the slurry was rapidly stirring, 1.8g of 900,000 MW PEO (Aldrich) was added in a stream so as not to form a few large lumps of solvent swollen PEO but rather many tiny lumps of solvent swollen PEO. During the next two days, the speed of the stir bar was adjusted to maintain as high as possible rpms, again without splattering or sucking air. After stirring for two nights, the PEO was dissolved and the slurry was used to prepare thin films by either ring casting or Mayer rod techniques.

Example 21 The following procedure was employed for various slurry compositions (identified below). Initially, a glass bottle and a stir bar were washed with acetone, and the stir bar was placed in the jar. Then an appropriate amount of acetonitrile (depending upon subsequent processing) was added to the jar and the bottle was capped. The bottle with its contents was placed onto a stir plate operated at sufficient power to create a vortex in the acetonitrile.

Next, PEO was measured and slowly added to the bottle while it was still on the stir plate. The PEO was introduced in very small amounts to maximize the contact with acetonitrile and promote rapid mixing. If salt was added, it was measured and added in the same fashion as the PEO. If there were other solubles (brij) to be added, they were also mixed in also at this point. All components were mixed until dissolved. Next, all insoluble materials including sulfur and carbon were measured and added to the mixture. Mixing was conducted for a minimum of two days.

The slurry combinations employed were as follows: elemental sulfur; 24% Carbon (Acetylene Black); 2% brij 35; 24% (20 moles PEO 900K to 1 mole lithium trifluoromethanesulfonimide) with 90 ml acetonitrile per gram of PEO.

50wt% elemental sulfur; 16% Carbon (Acetylene Black); 1% brij 35; 33% PEO 900K with 60 ml acrylonitrile per gram of PEO.

42 r Ranges of components used in.preparing various compositions in accordance with this example are as follows: 24%-55% wt elemental sulfur; 8%-24% wt Carbon (Acetylene Black); 30 ml acrylonitrile per gram PEO to 110 ml acetonitrile per gram PEO; and 40, and 90 ml water per gram PEO. Other compositions had various additives pegged to elemenal sulfur according to the following: 5wt% Brilliant Yellow Dye additive with elemental sulfur; 5% 2,5-dimercapto-l,3,4-dithiadiazole with 45% elemental sulfur; 2 wt% lithium iodide with 48% elemental sulfur; 5 wt% iodine with 50% sulfur; 1 wt% PbS with 49% elemental sulfur; and 5 wt% polyethylene dithiol with elemental sulfur.

1 0 The foregoing describes the instant invention and its presently preferred embodiments. Numerous modifications and variations in the practice of this invention are expected to occur to those skilled in the art. Such modifications and variations are encompassed within the following claims.

All references cited herein are incorporated by reference.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

*S

Claims (53)

1. A positive electrode comprising a mixture of a) active-sulfur; b) an electronic conductor mixed with the active-sulfur so that electrons can move between the active-sulfur and the electronic conductor; and c) an ionic conductor mixed with the active-sulfur so that ions can move between the ionic conductor and the active-sulfur, wherein the mixture has between and 100% of the active-sulfur available for electrochemical reaction.

2. A positive electrode according to claim 1 wherein the mixture is electrically connected to a current collector.

3. A positive electrode according to either claim 1 or claim 2 wherein the electrode is 15 operated between about -40 degrees Celsius and about 180 degrees Celsius.

4. A positive electrode according to any one of claims 1 to 3 wherein the mixture V. contains, between 20% by weight to 80% by weight, active-sulfur.

5. A positive electrode according to any one of claims 1 to 4 wherein the mixture contains, between 40% by weight to 60% by weight, active-sulfur.

6. A positive electrode according to any one of claims 1 to 5 wherein the electronic conductor is selected from the group consisting of carbon black, compounds with conjugated carbon-carbon or carbon-nitrogen double bonds, electronically conductive polymers, polyaniline compounds, polythiophene compounds, polyacetylene compounds, polypyrrole compounds, and combinations thereof.

7. A positive electrode according to any one of claims 1 to 6 wherein the mixture a 30 contains, between about 5% by weight to about 40% by weight, electronic conductor. P OPIK ILA 382 954 '47 6 4 99 -44-

8. A positive electrode according to any one of claims 1 to 7 wherein the mixture contains, between about 8% by weight to about 24% by weight, electronic conductor.

9. A positive electrode according to any one of claims 1 to 8 wherein the ionic conductor is a solid or a gel. A positive electrode according to any one of claims 1 to 9 wherein the ionic conductor is selected from the group consisting of polymeric electrolytes, ceramic electrolytes, glass electrolytes, beta alumina compounds, and combinations thereof.

11. A positive electrode according to any one of claims 1 to 10 wherein the ionic conductor comprises an electrolyte salt that form a complex with compounds selected from the group consisting of polyether compounds, polyamine compounds, polythioether compounds, polyphosphazene compounds, and combinations thereof. S* liquid. 20 13. A positive electrode according to any one of claims 12to 11 wherein the aprotic organic lid-state liquid. S 20 13. A positive electrode according to claim 12 wherein the aprotic organic liquid is selected from the group consisting of sulfolane compounds, dimethyl sulfone compounds, tetrahydrofuran compounds, propylene carbonate compounds, dialkyl carbonate compounds, ethylene carbonate compounds, dimethyl carbonate compounds, butyrolactone compounds, N-methylpyrrolidinone compounds, tetramethylurea compounds, dioxolane compounds, glyme compounds, ether compounds, crown ether compounds, dimethoxyethane compounds, and combinations thereof.

14. A positive electrode according to any one of claims 1 to 9 wherein the ionic conductor is a gel including a gelling agent selected from the group consisting of AZ 0 polyvinylidene fluoride compounds, hexafluorpropylene-vinylidene fluoride copolymers, P OPER MLA 3882-95 047 16 4 99 polyacrylinitrile compounds, cross-linked polyether compounds, polyalklyene oxide compounds, polyethylene oxide compounds and combinations thereof. A positive electrode according to any one of claims 1 to 14 wherein the mixture further comprises one or more of the following: binders, electrocatalysts, surfactants, dispersants, and protective layer forming additives.

16. A positive electrode according to any one of claims 1 to 15 wherein the mixture is in the form of a solid or a gel.

17. A battery cell which comprises: a) a positive electrode comprising a mixture of i) between 20% to 80% active-sulfur in percent by weight; ii) a gel-state or solid-state ionic conductor in percent by weight between 15 15% to 75%; and iii) an electronic conductor in a percent by weight between 5 and a current collector electrically connected to the positive electrode; c) a negative electrode; and 2d) an electrolyte separator; 20 wherein the mixture has between 10% and 100% of the active-sulfur available for electrochemical reaction.

18. A battery cell according to claim 17 wherein the electrolyte separator is a solid- state electrolyte separator.

19. A battery cell according to claim 17 wherein the electrolyte separator is a gel-state electrolyte separator. A battery cell according to claim 17 wherein the electrolyte separator is a liquid A, 0 electrolyte separator. P PLER MI.A 3-882 95 0"47 16 4 Q9 -46-

21. A battery cell according to claim 17 wherein the negative electrode is a solid-state negative electrode.

22. A battery cell according to claim 17 wherein the negative electrode is a gel-state negative electrode.

23. A battery cell according to claim 17 wherein the negative electrode is a liquid negative electrode.

24. A battery cell which comprises: a positive composite electrode comprising active-sulfur in a percentage by weight from 20% to 80%, an ionic conductor in a percentage by weight from 15% to and an electronic conductor in a percentage by weight from 5 to a negative electrode; and 15 a solid-state electrolyte separator or a gel-state electrolyte separator; wherein the positive electrode has between 10% and 100% of the active-sulfur available for electrochemical reaction. A battery cell according to claim 24 wherein said negative electrode is selected from the group consisting of alkali metals, alkaline earth metals, transition metals, mixtures of alkali, alkaline earth and transition metals, carbon, carbon inserted with lithium or sodium, and mixtures of carbon with lithium or sodium. "i 26. A battery cell according to claim 25 wherein said negative electrode is selected from the group consisting of lithium, sodium, a mixture of carbon with lithium or sodium, or carbon inserted with lithium or sodium.

27. A battery cell according to claim 25 wherein said negative electrode is selected from the group consisting of lithium, sodium, Na 4 Pb, lithium-silicon and lithium- 0 aluminium alloys. P OPER %LLA 3882 95 047 16 4 9 -47-

28. A battery cell according to any one of claims 24 to 27 wherein the electrolyte separator is a gel-state.

29. A battery cell according to any one of claims 24 to 27 wherein the electrolyte separator is solid-state. A battery cell which comprises: a negative electrode which comprises carbon, carbon inserted with lithium or sodium, or a mixture of carbon with lithium or sodium; and a positive composite electrode comprising active-sulfur in a percentage by weight of from 20% to 80%, an ionic conductor in a percentage weight of from 15% to and an electronic conductor in a percentage by weight from 5 to wherein the positive electrode has between 10% and 100% of the active-sulfur available for electrochemical reaction. p* 31. A battery cell according to claim 30 further comprising an electrolyte salt in a p liquid electrolyte. S

32. A battery cell according to claim 31 further comprising a separator within said 20 liquid electrolyte.

33. A battery cell according to any one of claims 30 to 32 wherein said negative electrode comprises lithium inserted within highly disordered carbons, graphite intercalation compounds, or LiyC 6 wherein y=0.3 to 2.

34. A positive electrode comprising: a) an electrochemically active material selected from the group consisting of elemental sulfur, a metal sulfide, a metal polysulfide, and combinations thereof, wherein said metal is selected from the group consisting of alkali metals, alkaline earth metals, and 0 mixtures of alkali and alkaline earth metals; P OPER NILA 3882 95 047 16 4 99 -48 b) an electronically conductive material mixed with the electrochemically active material so that electrons move between the electrochemically active material and the electronically conductive material; and c) an ionically conductive material mixed with the electrochemically active material so that ions move between the ionically conductive material and the electrochemically active material, wherein at least 10% of the electrochemically active material is accessible to electrons and ionic charge carriers, and wherein the ionically conductive material is a solid or gel state material and is not a sulfide or polysulfide.

35. A positive electrode according to claim 34, wherein the electrochemically active material is non-molten.

36. A positive electrode according to either claim 34 or claim 35 wherein the positive electrode contains between about 20% by weight to about 80% by weight 15 electrochemically active material. 0@

37. A positive electrode according to any one of claims 34 to 36, wherein the electronically conductive material is selected from the group consisting of carbon black, compounds with conjugated carbon-carbon or carbon-nitrogen double bonds, electronically 20 conductive polymers, polyaniline compounds, polythiophene compounds, polyacetylene compounds, polypyrrole compounds, and combinations thereof.

38. A positive electrode according to any one of claims 34 to 37, wherein the positive electrode contains between about 5 by weight to about 40% by weight, electronically conductive material.

39. A positive electrode according to any one of claims 34 to 38 wherein the ionically conductive material of the positive electrode is provided in a solid-state form. 30 40. A positive electrode according to claim 39 wherein the solid-state ionic conductor P OPER MI A 332 9 047 16 499 -49- comprises an electrolyte salt that form a complex with compounds selected from the group consisting of polyether compounds, polyimine compounds, polythioether compounds, polyphosphazene compounds, polyalkylene oxide compounds, polyethylene oxide compounds, amorphous polyethylene oxide compounds, and combinations thereof.

41. A positive electrode according to any one of claims 34 to 40 wherein at least of the electrochemically active material is accessible to electrons and ionic charge carriers.

42. A positive electrode according to any one of claims 34 to 41 wherein at least of the electrochemically active material is accessible to electrons and ionic charge carriers.

43. A battery cell comprising: a) a positive electrode comprising a mixture of i) an electrochemically active material, 15 ii) a gel-state or solid-state ionically conductive material, and iii) an electronically conductive material, the mixture having between 10% and 100% of the electrochemically active material accessible to electrons and ionic charge carriers; b) a current collector electrically connected to the positive electrode 20 c) a negative electrode including a metal or metal ion; and d) an electrolyte separator; 0.. wherein electrochemically active material is selected from the group consisting of elemental sulfur, sulfides of the metal, polysulfides of the metal, and combinations thereof.

44. A battery cell according to claim 43 wherein the electrochemically active material is present in the mixture in a weight percentage of between about 20% to about A battery cell according to either claim 43 or claim 44 wherein the ionically i R 0 conductive material is present in the mixture in a weight percentage of between about conuciv P 6 OPL MLA 39.5 0Y 7 16 4,99) to

46. A battery cell of claim 1, wherein the electronically conductive material is present in the mixture in a weight percentage of between about 5 and about

47. A battery cell of claim 1, wherein said negative electrode is selected from the group consisting of alkali metals, alkaline earth metals, transition metals, mixtures of alkali, alkaline earth and transition metals, lithium or sodium insertion materials, and mixtures of carbon with lithium or sodium.

48. A battery cell of claim 1, wherein the electrochemically active material is non- molten. oo

49. A battery cell comprising: 15 a) a negative electrode including a metal or an ion of the metal; a positive electrode comprising i) in electrochemically active material comprising sulfur in the form of at least one of elemental sulfur, a sulfide of the metal, and a polysulfide of the metal, and ii) an electronically conductive material; and 20 c) a gel-state or polymeric solid-state electrolyte separator electronically separating the positive and negative electrodes, d) wherein at least 10 of the sulfur is accessible to electrons and ionic charge carriers.

50. A battery cell according to claim 49, wherein the battery cell is rechargeable.

51. A battery cell according to either claim 49 to 50 wherein the metal of the negative electrode includes at least one of sodium and lithium. 0 52. A battery cell according to any one of claims 49 to 51 wherein the metal in the P OPRR'MIL\ i3482.-5 0-47 164W) -51 negative electrode is a lithium metal electrode.

53. A battery cell according to any one of claims 49 to 52 wherein the negative electrode is a lithium intercalation electrode.

54. A battery cell according to any one of claims 49 to 53 wherein the electronic conductor of the positive electrode is at least one of carbon and an electronically conductive polymer.

55. A battery cell according to any one of claims 49 to 54 wherein the electrolyte separator comprises a gel-state electrolyte separator including at least 20% by weight of an aprotic organic liquid immobilized by the presence of a gelling agent. o. 56. A battery cell according to any one of claims 49 to 55 wherein the electrolyte 15 separator comprises a polymeric solid-state electrolyte separator. 9. *9

57. A battery cell according to claim 56 wherein in the polymeric solid-state electrolyte seperator comprises a polymer of ethylene oxide. 20 58. A battery cell according to any one of claims 49 to 57 wherein the electrolyte separator comprises an aprotic organic liquid.

59. A method of forming an active-sulfur-containing electrode, the method comprising the following steps: combining active-sulfur, an electronic conductor, and an ionic conductor to form a mixture; homogenizing the mixture to form a homogenous mixture; and forming the active-sulfur-containing electrode from said homogenous mixture, wherein said active-sulfur-containing electrode has at least 10% of its active-sulfur l? 30 available for electrochemical reaction. P OPER NLA 3992-QP 047 !64 99 -52- A method according to claim 59 wherein the method includes a step of forming a slurry by combining the active-sulfur, the electronic conductor, and the ionic conductor with a liquid.

61. A method according to claim 60 wherein the slurry is formed from a dispersant in addition to the active-sulfur, the electronic conductor, the ionic conductor, and the liquid.

62. A method according to any one of claims 59 to 61 wherein said step of homogenizing involves deagglomerating the slurry to form said homogenous mixture.

63. A method according to any one of claims 59 to 62 wherein the step of forming the active-sulfur-containing electrode includes a step of applying a slurry layer of said homogenous mixture to a substrate. 15 64. A method according to claim 63 wherein said slurry layer is formed on a current collector. A method according to claim 63 wherein said slurry layer is formed on a non- adhesive substrate.

66. A method according to claim 65 further comprising the following steps: drying said slurry layer to form the active-sulfur-containing electrode; removing the active-sulfur-containing electrode from the non-adhesive substrate; and affixing the active-sulfur-containing electrode to a current collector such that the active-sulfur-containing electrode is in electrical contact with the current collector.

67. A method according to claim 63 further comprising a step of drying said slurry layer to form said active-sulfur-containing electrode. P OPER 11_l,38X2 95 047 16A 99 -53

68. A method according to claim 63 wherein the slurry layer is continuously formed on the substrate which is continuously contacted with a source of slurry.

69. A method according to any one of claims 59 to 68 wherein said step of homogenizing comprises homogenizing a solid phase mixture containing the active-sulfur, the electronic conductor, and the ionic conductor. A method according to any one of claims 59 to 69 wherein the electronic conductor employed in the step of combining is selected from the group consisting of carbon and conductive polymers.

71. A method according to any one of claims 59 to 70 wherein the ionic conductor is a polyalkylene oxide. Co 15 72. A method according to any one of claims 59 to 71 further comprising a step of preparing an electrochemical cell containing said active-sulfur-containing electrode. DATED this 16th DAY of APRIL, 1999 C 20 POLYPLUS BATTERY COMPANY, INC. by DAVIES COLLISON CAVE **.Patent Attorneys for the Applicant(s) Patent Attorneys for the Applicant(s) C