Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Intracell assembly having cell electrode connector
Reexamination Certificate
1999-06-11
2001-06-12
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Intracell assembly having cell electrode connector
C429S163000, C429S170000, C429S211000, C429S121000, C429S122000
Reexamination Certificate
active
06245457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a bussing structure for bussing current within an electrochemical cell, wherein the bussing structure connects current collection tabs, extending from an electrode stack of the electrochemical cell, to terminals on the outside of the electrochemical cell case (which are used to connect the electrochemical cell to a desired application) such that the overall cell impedance is less than or equal to 1.5 milliohms.
2. Related Art
The related art includes electrochemical cells having electrode stacks with current collection tabs extending therefrom. The current collection tabs are connected to the bottom surface of a washer which is then riveted or otherwise connected to a terminal on the outside of the electrochemical cell, above the washer. The terminal is then used to connect the electrochemical cell to deliver electricity to a desired application. Because the current collection tabs are connected to the bottom of the washer, the connection is susceptible to shear and bending stress when the electrode stack moves within the electrochemical cell. That is, when the electrochemical cell shakes or vibrates during use, the electrode stack moves within the casing of the electrochemical cell. When the electrode stack moves, it produces forces on the current collection tabs, and thus directly on the connection between the current collection tabs and the washer. The forces produced tend to disconnect the current collection tabs from the washer, thus breaking the current path from the electrode stack to the outside of the electrochemical cell, thereby reducing or eliminating the current output from the electrochemical cell.
Additionally, the current collection tabs must be sufficiently long to enable an apparatus to be positioned between the electrode stack and the washer for connecting the tabs to the washer. Further, a plurality of tabs are at one time disposed adjacent to the bottom of the washer and are then connected thereto. Because there are many tabs it is difficult to keep them all adjacent to the washer for connection thereto. Therefore, it is difficult to ensure that all the current collection tabs are sufficiently connected to the washer. Because some tabs are not sufficiently connected to the washer, the current capacity of the electrochemical cell is decreased. Alternatively, if the tabs are connected one at a time, to ensure that they are all sufficiently connected, the process is time consuming and inefficient.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the problems of the related art. More specifically, an object of the present invention is to provide a bussing structure which allows use of current collection tabs having a short length. Another object of the present invention is to provide a bussing structure which maintains the integrity of the connection between current collection tabs of an electrode stack within an electrochemical cell, and terminals on the outside of the electrochemical cell. Another object of the present invention is to provide a bussing structure which has low impedance, for example less than or equal to 1.5 milliohms, and high conductivity. Another object of the present invention is to provide a bussing structure which facilitates assembly of the electrochemical cell, as well as protects the electrode stack during assembly.
The present invention includes a double plate bussing structure for bussing current from an electrode stack to terminals on the outside of an electrochemical cell, wherein the bussing structure provides low impedance and high conductivity as well as protection of the electrode stack and current collection tabs extending from the electrode stack p The use of a double plate structure allows the current collection tabs to be of a short length, guarantees that every tab will be connected to the bussing structure, and maintains the integrity of the connection between the current collection tabs and the terminals in the face of vibration and shock. Because the current collection tabs are connected at a point that is sandwiched between two plates, any relative movement between the plate structure and the electrode stack, due to vibration or shock, does not act on the connection. That is, there is no shear or bending stress on the connection. Further, the plate structure helps transfer heat from the electrode stack to the electrochemical cell case.
In an electrode stack of an electrochemical cell, a plurality of tabs is connected to each of the electrodes for current collection, and thus extends from opposite sides (positive and negative) of the electrochemical cell. The tabs, on each respective end of the electrode stack, are brought into engagement with the top surface of a first plate. A second plate is put on top thereof to sandwich the tabs between the plates. The plates are then connected together with the tabs therebetween. Each pair of plates is then connected to a terminal on the outside of the electrochemical cell case.
On the negative side of a lithium-ion electrochemical cell, for example, the first plate is preferably made of copper to match the copper material of the negative electrode. However, if another material is used for the negative electrode, as in a different type of electrochemical cell, the first plate may be made of a matching or otherwise compatible material. The use of a copper for the first plate protects the inner contents of the electrode stack from heat and light during the formation of the connection between the current collection tabs and the plate. Further, when the connection is made by welding, for example laser welding, the copper plate is particularly advantageous. The copper plate acts as a reflective surface and heat sink during welding.
In a lithium-ion electrochemical cell, for example, the second plate is preferably made of nickel to facilitate connection to the terminal on the outside of the electrochemical cell case. The use of nickel improves the weld connection to the electrochemical cell case when such is made of stainless steel, and improves the connection to the terminal on the outside of the electrochemical cell case, when the terminal includes a portion coated with nickel. The above choice of materials gives a low impedance, of less than or equal to 1.5 milliohms, and high conductivity between the electrode stack and the negative terminal of the electrochemical cell. Also, the second plate has a particularly advantageous shape. The second plate includes protrusions on the top surface thereof, which top surface faces away from the current collection tabs connected to the bottom of the second plate. The protrusions keep the top of the second plate from contacting the electrochemical cell case so as to maintain a fill space for electrolyte and a space for gasses to escape through a safety vent in the electrochemical cell case.
The second plate, as well as the first plate underneath thereof, include through holes (other than central holes when the plates are of a washer type) to be located beneath the safety vent. The through hole in the plate sandwich is sized relative to the size of the safety vent to promote turbulent flow of gasses through the safety vent upon its opening.
The second plate further includes two plateaus for welding to the electrochemical cell case and to the negative terminal on the electrochemical cell case. The plateaus extend from the second plate top surface in a location so as to match that of holes in the electrochemical cell case used to weld the negative terminal to the electrochemical cell case. The plateaus may have the same height above the second plate surface as that of the protrusions to thereby keep the plate parallel to the cell case.
On the positive side of a lithium-ion electrochemical cell, for example, aluminum plates are used, to match the aluminum material used for the positive electrode. However, if another material is used for the positive electrode, as in a different type of electrochemical cell, the plates may be made of
Alcatel
Brouillette Gabrielle
Dove Tracy
Sughrue Mion Zinn Macpeak & Seas, PLLC
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