Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-11-15
2003-03-25
Bell, Bruce F. (Department: 1741)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231900, C429S206000, C429S207000, C429S101000, C429S105000, C429S303000, C429S307000, C429S314000, C429S319000, C429S325000, C429S328000, C429S329000, C429S337000, C429S339000, C029S623500
Reexamination Certificate
active
06537701
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electrochemical batteries, and, more specifically, to lithium-metal batteries. More particularly, the present invention relates to methods and compositions that enhance the cycle life and shelf life of lithium-metal batteries, and, especially, lithium-active sulfur batteries. The present invention has applications in the fields of electrochemistry and battery technology.
Lithium battery technology continues to be an attractive option for providing light-weight, yet powerful energy sources. Lithium-sulfur secondary batteries are especially well suited to continuing market demands for more powerful and highly portable electronic devices. Examples of such batteries include those disclosed by De Jonghe, et al., in U.S. Pat. Nos. 4,833,048 and 4,917,974; and by Visco, et al., in U.S. Pat. No. 5,162,175. Nevertheless, the batteries described in these, and other references, have serious limitations (Rauh 1979; De Gott 1986). In particular, batteries using sulfur or polysulfide electrodes in combination with lithium, such as the Li
2
S
x
, batteries described by Peled and Yamin in U.S. Pat. No. 4,410,609, have suffered from poor cycling efficiencies (Rauh 1989).
Many of these difficulties are addressed by the batteries described in U.S. Pat. Nos. 5,523,179 and 5,532,077, both to Chu, each of which is incorporated herein by reference in its entirety and for all purposes. Briefly, the '179 and '077 patents describe solid-state batteries that comprise a lithium electrode in combination with an active sulfur-containing electrode. An “active sulfur” electrode is an electrode comprising elemental sulfur, or sulfur in an oxidation state such that the sulfur would be in its elemental state if the electrode was fully charged. The technology described in these patents is an important advance in lithium battery technology, in particular by describing batteries having large energy densities and good cycling performance.
The cycle life and shelf life of lithium-sulfur batteries is limited by the slow degradation of the lithium electrode surface arising from the formation of dendritic and/or high surface area “mossy lithium”. To compensate for active lithium loss, extra lithium must be provided for the lithium electrode increasing the cost and weight of the battery. The use of additional metals also increases the burden of disposing the battery as additional toxic materials must be processed. Mossy lithium can also present a fire hazard by creating fine particles of lithium metal that can ignite on contact with air.
Various attempts have been made to provide lithium batteries having long cycle life and improved stability of the lithium metal anode. To minimize the growth of lithium dendrites, stabilize a lithium metal anode, and improve lithium cycling efficiency, one approach has been to add a metal to the lithium to form a solid metal-lithium alloy electrode. For example, aluminum may be added to the lithium to form a solid aluminum-lithium alloy electrode (Rao 1977). However, as described in Huggins, et al., U.S. Pat. No. 4,436,796, solid lithium-metal alloys such as Li—Al or Li—Si exhibit lower surface kinetics and lose there charge capacities after prolonged cycling. In particular, some types of solid Li—Al alloy electrodes, suffer from problems of shape and mechanical instabilities as well as manufacturing difficulties. Further, as described in Kawakami, et al., U.S. Pat. No. 5,698,339, for use in a rechargeable lithium battery, use of a lithium alloy such as lithium-aluminum alloy as an anode is not practical because the lithium alloy is difficult to fabricate into a spiral form. Therefore, it is difficult to produce a spiral-wound cylindrical rechargeable battery. Further, desirable charging and discharging cycle life or energy density for a rechargeable battery is not easily obtained using lithium-alloys as the anode.
Thus, to. take advantage of the stabilizing properties of lithium-metal alloys, which may improve battery cycle life and shelf-life, there remains a need to improve the utilization of lithium-metal alloys in the design of lithium electrodes. The present invention meets these and other needs.
SUMMARY OF THE INVENTION
The present invention provides anode material stabilized with a metal-lithium alloy including aluminum-lithium alloy and battery cells comprising such anodes. In one embodiment, the present invention includes an electrochemical cell having a negative electrode (anode) and a sulfur electrode including at least one of elemental sulfur, lithium sulfide, and a lithium polysulfide. The anode includes a lithium core and an aluminum-lithium alloy layer over the lithium core. In another embodiment, a surface coating, which is effective to increase lithium cycling efficiency and anode stability towards electrolyte components during cell storage, is formed on the electrode. In a more particular embodiment, the lithium electrode is in an electrolyte solution, and, more particularly, an electrolyte solution including either elemental sulfur, a sulfide, or a polysulfide where the surface coating is comprised of Al
2
S
3
.
One aspect of the present invention provides an electrochemical cell that generally can be characterized as including: 1) a lithium anode and 2) a sulfur electrode including at least one of elemental sulfur, lithium sulfide, and a lithium polysulfide, where the anode has an aluminum-lithium metal alloy layer including a surface coating that is effective to increase lithium cycling efficiency and anode stability towards components of electrolyte during storage of said electrochemical cell. Typically, the anode may be in an electrolyte solution where the electrolyte solution contains elemental sulfur, a sulfide or a polysulfide. In a specific embodiment, the electrolyte solution may contain dioxolane. In some embodiments, the surface coating comprises Al
2
S
3
, a film based on poly(dioxolane), products of electroreduction of electrolyte components or a reaction product of aluminum-lithium metal alloy and polysulfides or elemental sulfur.
Another aspect of the present invention provides a lithium anode for use in an electrochemical cell that may be generally characterized as including: 1) a lithium metal layer and 2) a metal-lithium alloy layer substantially thinner than the lithium metal layer where the metal-lithium alloy layer is effective to increase the lithium cycling efficiency and anode stability during prolonged storage of the electrochemical cell. Additionally, the anode may include a surface coating on the metal-lithium alloy layer where the surface coating is a reaction product of aluminum, elemental sulfur and polysulfides, a reaction product of aluminum-lithium alloy, elemental sulfur and polysulfides, or an Al
2
S
3
. In a particular embodiment, the metal-lithium alloy layer is between 0.05 and 10 microns thick. In specific embodiments, the metal in the metal-lithium alloy layer is selected from the group consisting of Al, Mg, Bi, Sn, Pb, Cd, Si, In, Ag, and Ga and the anode may be in an electrolytic solution containing elemental sulfur or polysulfides.
Another aspect of the invention provides a method of forming a lithium anode with a lithium metal alloy layer including a surface coating. The method may be characterized as including: 1) depositing a metal layer on an outer surface of the lithium foil sheet, 2) alloying the lithium electrode and the metal layer on the outer surface of the lithium foil to form a metal-lithium alloy layer and 3) forming a surface coating on the metal-lithium alloy layer, wherein the anode is effective to increase the cycling efficiency of lithium and anode stability towards components of electrolyte during storage the electrochemical cell. In a specific embodiment, the metal layer is aluminum and the metal-lithium alloy layer is an aluminum-lithium alloy layer. In other embodiments, the metal layer is selected from the group consisting of Mg, Bi, Sn, Pb, Cd, Si, In, Ag, and Ga and the metal-lithium alloy layer is a Mg—Li alloy layer, a Bi—Li al
Chu May-Ying
Nimon Yevgeniy S.
Visco Steven J.
Bell Bruce F.
Beyer Weaver & Thomas LLP
PolyPlus Battery Company, Inc.
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