Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
1999-04-21
2001-06-26
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S502000, C429S231950
Reexamination Certificate
active
06252762
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electrical energy storage systems which may be recharged over numerous cycles to provide reliable power sources for a wide range of electrical utilization devices. The invention is directed in particular to a rechargeable storage system which is capable of exhibiting both high energy density normally associated with batteries, and high power density and long operative life typical of supercapacitors.
In the present invention, such a system comprises a multi-layer energy storage device structure which incorporates respective positive and negative electrode elements comprising pseudocapacitor or double-layer supercapacitor materials and rechargeable intercalation battery materials in a unitary, flexible structure which may be sized and shaped as desired to be most compatible with utilization devices while providing advantageously high energy and power densities.
Modern applications requiring mobile electrical energy sources, ranging from personal telecommunications devices to electric vehicles, are proliferating at an exponential rate. The demands of these applications range widely, for example, in voltage or power level, but all are preferably served by light-weight storage devices which can rapidly provide consistently high energy density over long time spans and can be quickly recharged to operational energy levels. To date, these extensive mobile energy needs are being met, in a fashion, by one or the other of the two available types of storage devices, viz., rechargeable batteries, such as lithium-ion intercalation systems, or supercapacitors of either faradic pseudocapacitive or non-faradic double-layer reaction type.
The choice between these battery or supercapacitor systems is normally dictated by the more pressing of the application's demand for high energy density, available from batteries, or for the rapid delivery of high power, provided by supercapacitors. Attempts to meet requirements for both high energy and high power densities in a single application have led in some instances to the utilization of both device types arranged together in such a manner that the battery is available to recharge the supercapacitor between periods of high power demand. The disadvantage of such a practice in the excessive weight factor alone is clearly apparent. Additional limitations on this expedient are reflected in the time requirement for battery charging, as well as in the multiplicity of cells and in battery life cycle which may often be shortened by the physical rigors of the intercalation battery charging operation.
The system of the present invention represents a remarkable advancement in means for meeting the requirements of mobile electrical energy utilization in that it combines the desirable characteristics of both the battery and the supercapacitor in a single integrated device of light weight and extended energy capacity. Comprising opposing electrodes of, for example, an activated carbon supercapacitor element and an intercalatable battery composition, particularly a transition metal oxide spinel material having a structure which exhibits rapid ion diffusion and little physical distortion from intercalation, the system is able to exhibit both the high energy storage capability of batteries and the high speed power delivery and exceptional cycle life of supercapacitors. An additional advantage of this unique combination of faradic battery intercalation and capacitive surface charging is the realization of intercalation systems which would not otherwise be available due to the sparsity of receptive counter-electrode materials able, for instance, to accommodate cations of considerable size, e.g., alkaline earth cations.
The hybrid systems of the present invention can utilize most of the respective compositions of previous rechargeable intercalation batteries and supercapacitor devices. Such earlier devices are typically represented, e.g., in U.S. Pat. Nos. 5,418,091 and 5,115,378. As in these earlier systems, intercalating electrodes may comprise metallic sulfides, oxides, phosphates, and fluorides, open-structured carbonaceous graphites, hard carbons, and cokes, and alloying elements, such as aluminum, tin, and silicon. Similarly, surface-active capacitor materials, typically high surface area closed-structure activated carbon powders, foams, fibers, and fabrics may be used in the counter-electrodes. The additional active electrolyte element of the hybrid systems may likewise be formulated of prior available materials, with particular utility being enjoyed in the non-aqueous solutions of intercalatable alkali and alkaline earth cations, usually incorporated in significantly fluid form in fibrous or polymer matrix containment materials, thus maintaining an environment conducive to mobility of both species of electrolyte ions. The laminated polymeric layer format typified by the secondary batteries described in U.S. Pat. No. 5,460,904 and related publications serves well for the structures of the present invention.
SUMMARY OF THE INVENTION
A hybrid battery/supercapacitor structure of the present invention comprises, in essence, negative and positive electrode members with an interposed insulative ion-transmissive separator member containing a fluid electrolyte. These functional members are preferably in the form of individual layers or membranes laminated together to form a flexible, unitary structure. The negative “battery” electrode member layer comprises a composition of an intercalatable material, preferably a spinel compound dispersed in a polymeric matrix of, for example, a copolymer of poly(vinylidene fluoride-co-hexafluoropropylene). To provide low resistance electrical current conduction between electrodes, the battery layer may be thermally laminated to a conductive current collector element, such as a reticulated metal foil. The positive “supercapacitor” counter-electrode member layer is similarly fabricated of an activated carbon composition in a matrix of the copolymer along with a current collector foil.
Interposed between the electrode members is the separator member which may comprise any of the previously employed high-porosity, microporous, or absorptive polymer film layers or membranes within which is dispersed a solution of electrolyte salt comprising an intercalatable cation, e.g., 1 M solution of LiPF
6
in a mixture of 2 parts ethylene carbonate and 1 part dimethyl carbonate. Such an electrolyte ensures essential ionic conductivity and mobility within the system structure. In the present invention this mobility serves the notable purpose of enabling the rapid flow of both ion species of the electrolyte salt to and from the respective electrodes during charge and discharge of the device. The high degree of fluidity enables a relatively unrestricted migration of the larger, previously inactive and unutilized anion species to adsorption at the positive electrode where they participate in the capacitive charging at that system member.
Thus the usual cation migration to effect intercalation within the negative electrode during a charging cycle, which normally serves as the sole mode of energy storage in prior battery structures, is augmented by anion migration from the electrolyte to the positive electrode surface to effect a capacitive charging, e.g., of the non-faradic double-layer type. This combined effect of faradic intercalation battery charging and non-faradic capacitor charging rapidly builds a high energy density which may be recovered in an equally rapid manner to yield high power density upon application demand. By judicial choice of electrode materials, that is, those respective intercalation and capacitor electrode member compounds presenting desired electrical charging potential differences, varied voltage levels may be achieved in the hybrid storage device.
REFERENCES:
patent: 5460904 (1995-10-01), Gozdz et al.
patent: 5545468 (1996-08-01), Koshiba et al.
patent: 5635138 (1997-06-01), Amatucci et al.
patent: 5953204 (1999-09-01), Suhara et al.
patent: 195 48 005 (1996-07-
Hey David A.
Reichard Dean A.
Telcordia Technologies Inc.
Thomas Eric
LandOfFree
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