Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-02-17
2001-12-11
Maples, John S. (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S094000
Reexamination Certificate
active
06328769
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, this invention is directed to an electrochemical cell exhibiting improved current collection capability, and a method of making such an electrochemical cell. In one instance the electrochemical cell is a spirally wound cell, but the cell can be of any variety.
In a typical spirally wound electrochemical cell, a first conductive layer and a second conductive layer are separated by insulation. The conductive layers are offset from one another, so that the first conductive layer extends beyond the insulation and the second conductive layer in one direction. The second conductive layer extends beyond the insulation and the 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 positive and negative 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 electric potential difference between the electrodes in the cell.
In the typical electrochemical cell, the electrodes are connected to the terminals of the battery by connection portions extending from the electrode sheet itself, or by tap straps. Another method of connection is to edge weld the connection portions 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 connection portions 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 for the battery.
SUMMARY OF THE INVENTION
One object of the 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 invention is to improve the current collection capacity from an electrochemical cell by providing an improved method of attaching a current collection tab to an electrode, which may be a spirally wound electrode. The invention also includes an electrochemical cell having one or more current collection tabs attached thereto in such a manner as to increase the current collected from the cell.
Yet another object of the present invention is to improve the current collection capacity from an electrochemical cell by providing increased contact area between a current collection tab and an electrode, including a spirally wound electrode. By increasing the contact area between each contact tab and the electrode, fewer contact tabs are necessary which thus leaves sufficient space on the electrode for introduction of electrolyte.
The present invention achieves these and other objects by slitting selected portions of the electrode that are not covered by insulation. Slits are made in the end of the electrode stack and extend down through the electrode in a direction parallel to the electrode stack longitudinal axis, and in a radial direction from the periphery of the electrode stack towards the longitudinal axis. The slits may be either parallel to one another, converge, or diverge. The slits do not extend the entire length of the electrode portion which is uncovered by insulation. The slits define a tab connection portion of the spirally wound electrode therebetween which is subsequently folded over so that the sections of the electrode extend in a radial direction. The folded portions of the electrode can extend substantially perpendicular to the longitudinal axis of the electrode. The folded portions of the electrode may extend from their bend toward the longitudinal axis, that is in an inward direction. Alternatively, the folded portions can extend from their bend in a direction away from the longitudinal axis, i.e., in an outward direction. In either case, the folded portions of the electrode extend in a radial direction and can be substantially perpendicular to the longitudinal axis.
The folded portions of the electrode define a contact tab connection portion. Each electrochemical cell electrode can have one or more contact tab connection portions. Each contact tap connection portion includes a plane which is recessed from the end plane of the electrode stack. The plan of the contact tab connection portion can be substantially parallel to the end plane of the electrode stack, but can also form an angle therewith. The folded portions may be covered by a conductive material in order to provide a flatter surface to which the contact tab is connected. For example, a thermally sprayed coating of conductive material that is compatible with the material of the electrode can be sprayed onto the folded portions before the contact tab is attached.
A contact tab, of conductive material, is connected to each connection portion by any suitable method. The contact tab can be made either of the same or different material than the electrode to which it is attached. The contact tab should have a geometry and dimensions compatible with the electric current to be collected from the respective cell.
One suitable method for connecting the contact tab to the connection portion is welding, for example sonic welding or laser welding. However, laser welding is preferred. Proper precautions are taken so that the temperature of the electrode stack can be controlled to prevent the insulation from being heated beyond its melting point. Further, high electric conductivity is achieved between the current collection tab and the electrode while minimizing the internal resistance drop between the electrodes, i.e., shorts between the positive and negative electrodes are minimized. When a conductive coating is applied to the folded portions of the electrode, the current collection tab is welded directly to the conductive coating. The coating layer creates a flat surface with controlled height. This helps to fix the welding process parameters, speed up the welding process, and improve the quality of the weld.
Further, in the case of a spirally wound electrode, the invention can include a hollow thin walled mandrel around which the conductive sheets and insulation are wound to form the jelly-roll. This construction results in a tubular cell having a hollow core. The diameter of the hollow mandrel is selected according to the winding, thermal, and fabrication considerations of the cell. The hollow mandrel can then be welded to top and bottom covers of the cell casing, which act as thermal links between the outer case of the cell and the electrode stack. The hollow core design improves the dissipation of heat generated along the central core of the cell. The relatively large radius of the tubular cell minimizes the cracking of any coated layers on the electrodes of the jelly-roll.
Additionally, the hollow mandrel can have longitudinal grooves on its outer surface, i.e., the surface on which the jelly-roll is wound. The longitudinal grooves on the outer surface of the tube help to properly evacuate and fill the cell during the electrolyte filling process.
The electrochemical cell of the present invention may be, but is not limited to, a rechargeable lithium-ion cell of either the standard or scaled up high power type. The substrate material for the positi
Alunans Peter
Chagnon Guy
Oweis Salah
Romero Antonio
Alcatel
Maples John S.
Sughrue & Mion, PLLC
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