Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-11-21
2004-05-11
Tsang-Foster, Susy (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
Reexamination Certificate
active
06733924
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of lithium anodes for use in electrochemical cells. More particularly, the present invention pertains to an anode for use in an electrochemical cell comprising a first layer comprising lithium metal and a second layer of a temporary protective metal. The present invention also pertains to methods of forming such anodes, electrochemical cells comprising such anodes, and methods of making such cells.
BACKGROUND
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
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 of electrochemical cells because of its extremely light weight and high energy density, compared for example to anodes, such as lithium intercalated carbon anodes, where the presence of non-electroactive materials increases the weight and volume of the anode, thereby reducing the energy density of the cells, and to other electrochemical systems with, for example, nickel or cadmium electrodes. 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. Unfortunately, the reactivity of lithium and the associated cycle life, dendrite formation, electrolyte compatibility, fabrication and safety problems have hindered the commercialization of lithium cells.
The separation of a lithium anode from the electrolyte of the cell is desirable for reasons including the prevention of dendrites during recharging, reaction with the electrolyte, and cycle life. For example, reactions of lithium anodes with the electrolyte may result in the formation of resistive film barriers on the anode. This film barrier increases the internal resistance of the battery and lowers the amount of current capable of being supplied by the battery at the rated voltage.
Many different solutions have been proposed for the protection of lithium anodes including coating the lithium anode with interfacial or protective layers formed from polymers, ceramics, or glasses, the important characteristic of such interfacial or protective layers being to conduct lithium ions. For example, U.S. Pat. Nos. 5,460,905 and 5,462,566 to Skotheim describe a film of an n-doped conjugated polymer interposed between the alkali metal anode and the electrolyte. U.S. Pat. No. 5,648,187 to Skotheim and U.S. Pat. No. 5,961,672 to Skotheim et al. describe an electrically conducting crosslinked polymer film interposed between the lithium anode and the electrolyte, and methods of making the same, where the crosslinked polymer film is capable of transmitting lithium ions. U.S. Pat. No. 5,314,765 to Bates describes a thin layer of a lithium ion conducting ceramic coating between the anode and the electrolyte. Yet further examples of interfacial films for lithium containing anodes are described, for example, in: U.S. Pat. Nos. 5,387,497 and 5,487,959 to Koksbang; U.S. Pat. No. 4,917,975 to De Jonghe et al.; U.S. Pat. No. 5,434,021 to Fauteux et al.; U.S. Pat. No. 5,824,434 to Kawakami et al.; and U.S. Pat. No. 6,025,094 to Visco et al.
The reactivity of lithium can be a hindrance to the deposition of interfacial or protective layers on lithium surfaces. For example, during deposition of a protective layer reactions between the protective layer precursors or materials and the lithium surface may occur. Although, this may be desirable for some protective layers, in other cases this has undesirable results, for example, increasing the resistance of the interfacial layer or changing the desired morphology of the deposited layer. This is a particular concern when the lithium layer is very thin, for example, below 25 microns in thickness, as is highly desirable in cells with a thin film design where excess lithium is kept to a minimum to reduce unnecessary weight and volume in order to provide cells with higher energy and volumetric capacities.
Despite the various approaches proposed for methods for forming lithium anodes and the formation of interfacial or protective layers, there remains a need for improved methods, which will allow for increased ease of fabrication of cells, while providing for cells with long cycle life and high energy density.
SUMMARY OF THE INVENTION
The anode of the present invention for use in an electrochemical cell, comprises an anode active layer, which anode active layer comprises: (i) a first layer comprising lithium metal; and (ii) a second layer of a temporary protective material in contact with a surface of the first layer. In one embodiment, the temporary protective material is a temporary protective metal that is capable of forming an alloy with lithium metal or is capable of diffusing into lithium metal.
In one embodiment, the temporary protective metal is selected from the group consisting of copper, magnesium, aluminum, silver, gold, lead, cadmium, bismuth, indium, germanium, gallium, zinc, tin, and platinum. In one embodiment, the temporary protective metal is copper.
In one embodiment, the thickness of the first layer is 2 to 100 microns.
In one embodiment, the thickness of the second layer is 5 to 500 nanometers. In one embodiment, the thickness of the second layer is 20 to 200 nanometers.
In one embodiment, the anode further comprises a substrate, wherein the substrate is in contact with a surface of the first layer on the side opposite to the second layer. In one embodiment, the substrate comprises a current collector. In one embodiment, the substrate is selected from the group consisting of metal foils, polymer films, metallized polymer films, electrically conductive polymer films, polymer films having an electrically conductive coating, electrically conductive polymer films having an electrically conductive metal coating, and polymer films having conductive particles dispersed therein.
In one embodiment, the anode further comprises a third layer, the third layer comprising a single ion conducting layer, wherein the third layer is in contact with the second layer on the side opposite to the first layer. In one embodiment, the single ion conducting layer of the third layer comprises a glass selected from the group consisting of lithium silicates, lithium borates, lithium aluminates, lithium, phosphates, lithium phosphorus oxynitrides, lithium silicosulfides, lithium germanosulfides, lithium lanthanum oxides, lithium tantalum oxides, lithium niobium oxides, lithium titanium oxides, lithium borosulfides, lithium aluminosulfides, and lithium phosphosulfides and combinations thereof. In one embodiment, the third layer is a lithium phosphorus oxynitride.
In another embodiment, the anode further comprises a third layer, the third layer comprising a polymer, and wherein the third layer is in contact with the second layer on the side opposite to the first layer. In one embodiment, the polymer of the third layer is selected from the group consisting of electrically conductive polymers, ionically conductive polymers, sulfonated polymers, and hydrocarbon polymers. In one embodiment, the electrically conductive polymer is selected from the group consisting of poly(p-phenylene), polyacetylene, poly(phenylenevinylene), polyazulene, poly(perinaphthalene), polyacenes, and poly(naphthalene-2,6-diyl). In one embodiment, the polymer of the third layer is a crosslinked polymer.
In one embodiment, the anode further comprises a fourth layer,
Mikhaylik Yuriy V.
Sheehan Christopher J.
Skotheim Terje A.
Moltech Corporation
Nicol Jacqueline M.
Rogers David E.
Squire Sanders & Dempsey L.L.P.
Tsang-Foster Susy
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