Coating apparatus – Solid applicator contacting work – With work-handling or work-supporting
Reexamination Certificate
1998-03-10
2001-10-23
Edwards, Laura (Department: 1734)
Coating apparatus
Solid applicator contacting work
With work-handling or work-supporting
C118S256000, C118S261000
Reexamination Certificate
active
06306215
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrochemical devices and, more particularly, to an apparatus and method for coating current collectors employed in non-aqueous electrochemical cells.
BACKGROUND OF THE INVENTION
Non-aqueous lithium electrochemical cells typically include an anode, a lithium electrolyte prepared from a lithium salt dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the lithium anode. Non-aqueous lithium electrochemical cells are discussed in U.S. Pat. Nos. 4,472,487, 4,668,595, 5,028,500, 5,441,830, 5,460,904, 5,540,741, and 5,584,893.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li
X
C. In operation of the cell, lithium passes from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abuse conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur.
Laminate cells and batteries have been developed which possess good performance characteristics. Typically, a laminate cell includes composite electrodes which refer to cathodes and anodes wherein the cathode is comprised of materials other than compatible cathodic materials and the anode is comprised of materials other than compatible anodic materials. Typically, the composite electrodes contains a polymer which acts to bind the composite materials together and an electrolytic solvent. Composite electrodes are well known in the art. For example, a composite cathode can comprise a compatible cathodic material, a conductive material, an electrolytic solvent, an alkali salt, and a solid matrix forming polymer. Similarly, for example, a composite anode can comprise a compatible intercalation anodic material, an electrolytic solvent and a solid matrix forming polymer.
In order to enhance the overall current produced by solid or liquid batteries, it is conventional to employ several electrochemical cells in a battery. When so employed, the current from each of the cells is accumulated so that the total current generated by the battery is roughly the sum of the current generated from each of the individual electrochemical cells employed in the battery. One method for accumulating the current from individual electrochemical cells is by using a current collector attached to the cathode or the anode of the electrochemical cell. Typically, the current collector is a metal foil or a conductive plastic which is coupled to other current collectors in the battery so that the current generated by each cell is collected and accumulated over all of the cells. Thus, the total current generated by the battery is a summation of the current generated by each of the electrochemical cells employed in the battery minus whatever current is lost due to resistance in the current collector. Current collectors are described, for example, in U.S. Pat. Nos. 4,925,752, 5,011,501, and 5,441,830. Notwithstanding the benefits of using current collectors in electrochemical cells, metal foil current collectors often do not adhere to the surface of composite electrodes. This inevitably reduces the electrochemical performance of the electrochemical cell and battery. U.S. Pat. No. 5,464,707 describes the use of an adhesion promoting layer that is applied onto the surface of a current collector. Thereafter, a cathode paste comprising monomers and/or prepolymers is coated onto the adhesion layer. Upon curing the monomers and/or prepolymers of the cathode paste, the cathode material becomes attached to the collector.
SUMMARY OF THE INVENTION
The invention is directed to an apparatus and efficient method of continuously coating a web of current collector with an adhesion material in the process of making electrochemical cells and batteries. Electrochemical cells are batteries produced by the inventive method are expected to exhibit high reactivity, good charge rate capabilities, life cycle, specific rate and stability.
In one aspect, the invention is directed to an apparatus for continuously coating a liquid adhesive promoter composition onto a surface of a web of current collector material which includes:
a source of the web of current collector material;
a reservoir containing the liquid composition;
a first rotatable roller having an exterior surface that is at least partially submerged in the liquid composition whereby liquid composition adheres to the exterior surface of the first rotatable roller that comes into contact with the liquid composition; and
a second rotatable roller that is positioned adjacent to the first rotatable roller and wherein an exterior surface of the second rotatable roller and an exterior surface of the first rotatable roller defines a nip through which the web of current collector material traverses.
In another aspect, the invention is directed to a method of continuously coating a liquid adhesion promoter composition that includes the steps of:
(a) providing a coating apparatus that includes:
(i) a source of the web of current collector material;
(ii) a reservoir containing the liquid composition;
(ii) a first rotatable roller having an exterior surface that is at least partially submerged in the liquid composition whereby liquid composition adheres to the exterior surface of the first rotatable roller that comes into contact with the liquid composition; and
(iv) a second rotatable roller that is positioned adjacent to the first rotatable roller and wherein an exterior surface of the second rotatable roller and an exterior surface of the first rotatable roller defines a nip through which the web of current collector material traverses;
(b) rotating the first rotatable roller to cause liquid composition to adhere to the exterior surface of the first roller; and
(c) rotating the second roller to cause at least a portion of the liquid composition from the exterior surface of the first roller to be transferred and coated onto a surface of the web.
In yet another aspect, the invention is directed to a method of preparing an electrode/current collector assembly that includes the steps of:
(a) providing a coating apparatus that includes:
(i) a source of a web of current collector material;
(ii) a reservoir containing the liquid composition;
(ii) a first rotatable roller having an exterior surface that is at least partially submerged in the liquid composition whereby liquid composition adheres to the exterior surface of the first rotatable roller that comes into contact with the liquid composition; and
(iv) a second rotatable roller that is positioned adjacent to the first rotatable roller and wherein an exterior surface of the second rotatable roller and an exterior surface of the first rotatable roller defines a nip through which the web of current collector material traverses.
(b) rotating the first rotatable roller to cause liquid composition to adhere to the exterior surface of the first roller;
(c) rotating the second roller to cause at least a portion of the liquid composition from the exterior surface of the first roller to be transferred and coated onto a surface of the web to form a layer of electrically conductive promoter thereon;
(d) applying an electrode layer comprising a mixture comprising a solvent, a polymeric binder, and an anodic material or cathodic material onto
Edwards Laura
Harness Dickey & Pierce
Valence Technology Inc.
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