Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-06-16
2001-02-13
Chaney, Carol (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S094000, C429S211000
Reexamination Certificate
active
06187062
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, this invention is directed to a technique for improving the current collection capability in an electrochemical cell by depositing a connection coating onto the exposed ends of the electrodes in a spirally wound electrochemical cell.
In a typical spirally wound electrochemical cell, a first conductive layer and a second conductive layer are separated by insulating layers which alternate with the conductive layers. The conductive layers are offset from one another, so that the first conductive layer extends beyond the insulating layers and the second conductive layer in one direction. The second conductive layer extends beyond the insulating layers and first conductive layer in an opposite direction. The layers are then rolled together to form a jelly-roll style electrode stack wherein the first conductive layer forms a positive electrode at one end of the stack, and the second conductive layer forms a negative electrode at a second end of the stack opposite the stack first end.
A first spiral space is defined in the first end of the jelly-roll by the portion of the first conductive sheet which is not layered with either insulation or the second conductive sheet. A second spiral space is defined in the second end of the jelly-roll by the portion of the second conductive sheet which is not layered with either insulation or the first conductive sheet. The electrodes are then connected to terminals of a fluid tight casing for use as a battery. Before the casing is sealed shut, an electrolyte is put into the casing, surrounding the electrodes. The electrolyte aids in the development of an electrical potential difference between the electrodes in the cell.
In the typical electrochemical cell, the electrodes are connected to the terminals of the battery by tabs extending from the electrode sheet itself, or by tap straps. Another method of connection is to edge weld the tabs to the spiral end of the electrodes. These methods, however, suffer the problem of only being capable of carrying a limited amount of current from the cell. The tabs do not connect to a sufficient area of the electrode to carry larger currents associated with bigger batteries. Moreover, welding additional tabs presents problems in manufacture of the batteries, such as limiting the area by which electrolyte can be introduced into the electrode, and increasing the cost as well as production time of the battery.
SUMMARY OF THE INVENTION
One object of the present invention is to improve the current collection capacity from an electrochemical cell by overcoming the problems associated with the present current collection methods.
Another object of the present invention is to improve the current collection capacity from an electrochemical cell by providing an improved method of attaching a contact to a spirally wound electrode.
Yet another object of the present invention is to improve the current collection capacity from an electrochemical cell by providing increased contact area between the contact and a spirally wound electrode.
The present invention achieves these and other objects through a process of fabricating a conductive coating on the spirally wound electrode. The contact area is increased because the coating contacts the electrode over more than merely the spirally wound edge of the electrode sheet. The conductive coating can be formed onto selected areas of a spirally wound electrode by a thermal spray process.
The coating is deposited onto the spirally wound electrode in such a manner that it only coats one of the electrodes, without any of the coating particles contacting the insulating layer or the other electrode. This objective is accomplished by spraying the coating in a direction at an angle to the longitudinal axis of the electrode jelly-roll.
The angle of spray, with respect to the electrode stack longitudinal axis, depends upon the distance by which the two electrode substrates of the cell are offset. The angle of spray can be varied between about 20° and about 80°. Best results are achieved when the angle of spray is between about 45° and about 70°. By spraying at a suitable angle, the need for applying an insulating material to the jelly-roll ends, to protect against unwanted contact between the spray coating and the alternate electrode, is eliminated.
The conductive coating is made of metal particles or the like. Any metallic or cermet materials can be used for the spray coating including, but not limited to, aluminum, copper, zinc, zinc-aluminum alloy, and tin alloys. Conductive or loaded polymers can also be used. Zinc is an economical metal to use for the coating, and can be applied with either combustion wire or two wire arc thermal spray processes. The material of the conductive coating should be matched to that of the electrode onto which it is formed.
Any number of techniques can be used to deposit the conductive coating onto the spirally wound electrodes, including but not limited to, using a combustion wire thermal spray gun, using a two wire arc gun, or using an Arc Plasma thermal spray system. However, the spray coating must be applied in such a manner that the temperature of the cell ends remains below the thermal melting point of the insulating layer between the electrodes. If the temperature of the cell is raised above the insulating layer melting point, a short between electrode layers may result which can decrease the capacity of the battery or even make it inoperative.
Further, a mask or shield is used to cover areas of the electrode end so that the coating is applied to only a selected portion of the electrode. The mask can be flexible as for example when made of any suitable tape. Alternatively, the mask can be a rigid shell shaped to fit over one end of the electrode stack. The mask can be designed to allow any shaped coating to be applied to the electrode stack by covering any desired areas of the electrode to thus leave uncoated portions. Uncoated portions of the electrode are necessary for insertion of liquid, electrolyte, or chemical slurry, into the spiral space of the electrode for proper operation of the battery. The mask can be inserted into the spray path at any point between the spray outlet and the electrode surface.
Additionally, suitable electrically conductive wires, tabs strips, or the like, can be welded onto the thermally sprayed layers by laser welding, for example. Alternatively, the electrically conductive wires, tabs, strips, or the like, can be embedded into the coating during the thermal spray process for electrical connection to the spirally wound electrode substrate edges.
To improve the bond strength between the spray coating and the areas to be coated on the electrode ends, conductive wires, tabs, strips, or the like, the areas to be coated can be provided with a texture, either before or after arranging in a stack, e.g., by brushing with a wire brush, grit blasting, perforation, providing with a dimple or waffle pattern, etc. The material from which the electrically conductive wires, tabs, strips, or the like, are made is compatible with that of the electrode substrate to which they are attached and with the spray material with which they are attached so as to avoid formation of a galvanic cell.
The invention may be used in, but is not limited to, the production of lithium-ion cells. One example of a lithium-ion cell uses an aluminum foil substrate for the positive electrode, and a copper foil substrate for the negative electrode. The invention may be used in manufacturing other types of cells including, but not limited to, nickel metal hydride cells and nickel cadmium cells. The invention can be practiced on any size of cell, but is particularly useful in manufacturing cells for electric vehicles.
The foregoing objects of the present invention, together with the features and advantages thereof, will be made apparent from the following description, in which like reference characters designate the same or similar parts throughout the drawings.
REFERENCES:
patent: 3891901 (1975-06-01), Booe et al.
patent: 448
Chagnon Guy
Oweis Salah
Rigobert Gerard
Souliac Laurent
Zatorski Raymond A.
Alcatel
Chaney Carol
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tsang Susy
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