Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-08-04
2002-08-20
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S324000, C429S326000
Reexamination Certificate
active
06436583
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of electrochemical cells. More particularly, this invention pertains to lithium batteries in which the cathode comprises an electroactive sulfur-containing material and the electrolyte comprises components that reduce self-discharge of the lithium battery.
BACKGROUND
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
There has been considerable interest in recent years in developing high energy density batteries with lithium containing anodes. Lithium metal is particularly attractive as the anode active material of electrochemical cells because of its extremely light weight and high energy density, compared for example to anode active materials, such as lithium intercalated carbon anodes, where the presence of non-electroactive materials increases the weight and volume of the anode, and thereby reduces the energy density of the cells. Lithium metal anodes, or those comprising mainly lithium metal, provide an opportunity to construct cells which are lighter in weight, and which have a higher energy density than cells such as lithium-ion, nickel metal hydride or nickel-cadmium cells. These features are highly desirable for batteries for portable electronic devices such as cellular phones and laptop computers where a premium is paid for low weight.
Various types of cathode materials for the manufacture of thin film alkali-metal batteries are known in the art. Of considerable interest are cathode materials comprising sulfur-sulfur bonds, wherein high energy capacity and rechargeability are achieved by the electrochemical cleavage (via reduction) and reformation (via oxidation) of these bonds. For example, in combination with a lithium anode, elemental sulfur has a theoretical specific capacity of 1680 mAh/g, and sulfur-containing polymers with trisulfide and longer polysulfide groups in the polymers have shown theoretical specific capacities of more than 1200 mAh/g, as for example, described in U.S. patent application Ser. No. 08/995,122 to Gorkovenko et al. of the common assignee (PCT Publication No. WO 99/33130). Examples of sulfur-containing cathode materials disclosed for use in lithium and sodium batteries include, for example, elemental sulfur, organo-sulfur, and carbon-sulfur polymer compositions. Elemental sulfur is an attractive cathode material in alkali-metal batteries owing to its low equivalent weight, low cost, and low toxicity.
It is highly desirable that batteries retain their capacity during prolonged storage under ambient conditions. However, battery storage invariably leads to a loss of charge retention, often termed self-discharge. Factors which influence charge retention, as summarized in Linden,
Handbook of Batteries,
2
nd
Edition,
pp. 3.18-3.19, McGraw Hill, New York, 1995, include, for example, storage conditions such as temperature, length of storage, cell design, the electrochemical system, and discharge conditions. As self-discharge proceeds at a lower rate at reduced temperatures, refrigerated or low temperature storage extends shelf life and is recommended for some battery systems.
Several approaches have been used to improve battery shelf life. For example, in U.S. Pat. No. 5,443,930 to Shoji et al., the incorporation of fluorinated graphite in a MnO
2
cathode of a lithium/MnO
2
battery is reported to reduce self-discharge. In U.S. Pat. No. 4,195,123 to Jumel, a lithium battery with improved storage life is described in which the lithium anode surface is alloyed with a metal, such as, for example, lead, tin, antimony, or silver, to prevent selective localized deposition of cathode active material during storage. Dey in U.S. Pat. No. 4,326,014 describes cells having negligible self-discharge on storage at 55° C. for extended periods built from lithium anodes which have been treated with an electrolyte solution containing gases such as CO
2
, SO
2
, O
2
, and NH
3
. In Japanese Patent Publication No. 08-321312, published Dec. 3, 1996, Kamino et al. report that over 40 different compounds added to electrolyte solvents comprising organic carbonates at 1-20% by volume provide long battery shelf life for lithium/MnO
2
batteries.
Several problems with self-discharge properties of alkali metal/elemental sulfur battery cells have been reported. One pertains to alkali-metal sulfides, formed at the positive electrode on discharge, reacting with elemental sulfur to produce polysulfides that are soluble in the electrolyte causing self-discharge and loss of cell capacity.
Despite the various approaches to the reduction of self-discharge and increased shelf life, there still remains a need for improvements, particularly for alkali metal/sulfur batteries with high rate capability.
SUMMARY OF THE INVENTION
The present invention pertains to an electrochemical cell comprising: (i) a cathode comprising an electroactive sulfur-containing material; (ii) an anode comprising lithium; and (iii) a non-aqueous electrolyte interposed between the cathode and the anode, wherein the electrolyte comprises: (a) one or more lithium salts; (b) one or more non-aqueous solvents; and (c) a self-discharge inhibiting amount of one or more organic sulfites; wherein the cell is characterized by delivering or utilizing greater than 60% of the available discharge capacity of the electroactive sulfur-containing material upon initial discharge at a C/10 rate.
Suitable self-discharge inhibiting organic sulfites include, but are not limited to, dimethyl sulfite, diethyl sulfite, dipropyl sulfite, dibutyl sulfite, dicyclohexyl sulfite, ethylene sulfite, propylene sulfite, and butylene sulfite.
Suitable self-discharge inhibiting amounts of organic sulfites range from 0.1% to 10% by volume of the electrolyte. Preferred amounts of organic sulfites range from 0.4 to 7% by volume of the electrolyte. More preferred amounts of organic sulfites range from 0.5 to 5% by volume of the electrolyte.
Examples of suitable electroactive sulfur-containing cathode materials for use in the cathodes of the present invention include elemental sulfur and organic materials comprising both sulfur atoms and carbon atoms. Such electroactive sulfur-containing organic materials may or may not be polymeric, and preferably comprise polysulfide moieties. The anode preferably comprises lithium metal. In preferred embodiments, the electrolyte comprises one or more non-aqueous solvents selected from the group consisting of dimethoxymethane, trimethoxymethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and glymes, and one or more lithium salts selected from the group consisting of LiBr, LiI, LiSCN, LiBF
4
, LiPF
6
, LiAsF
6
, LiSO
3
CF
3
, LiN(SO
2
CF
3
)
2
, and LiC(SO
2
CF
3
)
3
.
In one embodiment, the cell is a primary cell. In one embodiment, the cell is a secondary cell.
In another aspect of the present invention, a method is provided for increasing the storage life of an electrochemical cell comprising the steps of: (a) providing a cathode comprising an electroactive sulfur-containing material; (b) providing an anode comprising lithium; and (c) providing a non-aqueous electrolyte interposed between the cathode and the anode, wherein the electrolyte comprises: (i) one or more lithium salts; (ii) one or more non-aqueous solvents; and (iii) a self-discharge inhibiting amount of one or more organic sulfites; wherein the cell is characterized by delivering or utilizing greater than 60% of the available discharge capacity of the electroactive sulfur-containing material upon initial discharge at a C/10 rate. In one embodiment, the increased storage life of the cell occurs prior to discharge, such as initial discharge, of the ce
Carlson Steven A.
Moltech Corporation
Nicol Jacqueline M.
Ruthkosky Mark
Ryan Patrick
LandOfFree
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