Chemistry: electrical current producing apparatus – product – and – Fluid active material or two-fluid electrolyte combination... – Active material in molten state
Reexamination Certificate
2000-10-18
2002-04-23
Bell, Bruce F. (Department: 1741)
Chemistry: electrical current producing apparatus, product, and
Fluid active material or two-fluid electrolyte combination...
Active material in molten state
C429S105000, C429S212000, C429S213000, C429S218100
Reexamination Certificate
active
06376123
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to positive electrodes characterized by active-sulfur. 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) and energy density (Wh/l). All references cited in this application are incorporated by reference for all purposes.
The rapid proliferation of portable electronic devices in the international marketplace has led to a corresponding increase in the demand for advanced secondary batteries. 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.
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 modern 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 electric vehicles and load leveling. Of course, such batteries are also suitable for use in lower power applications such as cameras or portable recording devices.
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. Pat. Nos. 4,833,048 and 4,917,974; and Visco et al., U.S. Pat. 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, P., “Polymere Carbone-Soufre Synthèse et Propriètes Electrochimiques,” Doctoral Thesis at the
Institut National Polytechnique de Grenoble
(date of defense of thesis: Jun. 19, 1986) at page 117.)
Similarly, Rauh et al., “A Lithium/Dissolved Sulfur Battery with an Organic Electrolyte,”
J. Electrochem. Soc.,
126 (4): 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 (Aug. 20, 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 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 liquid-electrolyte lithium batteries (that is, in liquid formats) is known. For example, Peled and Yamin, U.S. Pat. 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. Pat. No. 4,469,761; Farrington and Roth, U.S. Pat. No. 3,953,231; Nole and Moss, U.S. Pat. No. 3,532,543; Lauck, H., U.S. Pat. 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 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 466467 (1974).)
DeGott, supra, 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° C. to 180° C. and 300° C. to 350° C., DeGott state 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
Bell Bruce F.
Beyer Weaver & Thomas LLP
PolyPlus Battery Company
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