HIGH DURABILITY LITHIUM-ION CELLS
A rechargeable battery and a method of fabricating which includes stacking a plurality of electrode pages having an uncoated portion between portions coated with an active electrode material. The electrode pages are arranged in a stack and an overall current collector is connected at the uncoated portion in order to form an electrode booklet. The overall current collector maintains the arrangement of the electrode pages and electrically connects all of the uncoated portions of the electrode pages. A tilted stack of electrode pages is utilized when a large number of electrodes are desired to result in a battery cell having a vertical orientation.
This application is a Division of prior application Ser. No. 12/381,167 filed Mar. 9, 2009.
FIELD OF THE INVENTIONThe purpose is to make high durability lithium ion cells for high power applications such as electric and hybrid electric vehicles.
BACKGROUNDConventionally, lithium ion cells are cylindrical in shape and are composed of winding structured electrodes. However, the winding technology has disadvantages that limit the size (capacity) and integrity of the cells as outlined below:
-
- 1. Electrode smoothness problem at a certain length: This problem becomes more serious when cell size is increased. If the electrode smoothness or the variation of the thickness can not be maintained at a certain level, the size of the wound electrodes will not be consistent and that leads to the failure in fitting into the battery can.
- 2. Electrode swelling problem: This limits the electrode design, processing method, and thus the yield.
- 3. Current collector positioning problem: Large wound cells with long electrodes need multiple current collector tabs for high power applications. Proper alignment of the tabs is always a problem for large cylindrical wound cells. Electrode thickness variation with a long electrode winding causes poor alignment of the tabs. Poor alignment makes welding of the current tabs to the cell top difficult and induces poor reliability of the cell.
- 4. Heat dissipation problem: This factor limits the final size of the cell owing to the difficulty of heat dissipation in a radial heat diffusion path. Nonetheless, owing to the requirement of a high C-rate for high power applications, the heat dissipation problem will affect the applicability of the cylindrical cells in high power applications. It may also cause serious safety problems.
Although stacking structured cells have advantages over the disadvantages outlined above, the stacking precision and labor intensive nature of the stacking process make the stacking structured batteries expensive and difficult in maintaining high yield while the size (corresponding to the number of layers) is increased.
A conventional stacking structured cell is shown in
-
- 1. The electrodes are single pieces. This leads to the difficulty in each stacking process, as precision control is necessary during each stacking process.
- 2. The current collecting tab on each single electrode is either punched out from the uncoated portion of the metal substrate foil or a separated metal strip is welded to the electrode. Either way adds complications and cost to the assembling process.
- 3. Difficulty is encountered when welding the multiple electrode tabs together and attaching them to the main negative and positive posts under the battery cap within the limited headspace. This difficulty becomes more severe when the number of stacking layers is increased. If one of the electrodes is not welded properly, or if one of the electrode's current collector part (i.e. the uncoated substrate such as copper or aluminum foil) is broken, the performance and reliability of the resultant cell will be affected drastically. Owing to this reason, the consistency of the stacked cell becomes unpredictable especially when a vibration test is conducted.
- 4. For electrodes of a large surface area, if the current collector on each electrode is made too small, it will give poor current distribution and make the resultant cell perform poorly owing to the high resistance originating from each electrode.
In the present invention, the electrode stacking problems mentioned above can be solved with more advantages obtainable compared to the conventional stacking technologies.
SUMMARY OF THE INVENTIONThe present invention is an electrode booklet for a rechargeable battery, having a plurality of electrode pages, each electrode page is a foil having a shape symmetric about a center line and having a top and bottom surface coated with an active electrode material at symmetric portions other than a central uncoated portion which extends between edges of the foil and includes the center line. At least one overall current collector is disposed along the uncoated portion of at least one of the plurality of electrode pages. The electrode pages are in a stack arrangement and similarly oriented, with the at least one overall current collector being connected to the uncoated portion of all of the plurality of electrode pages to maintain the plurality of electrode pages in the stack arrangement and to provide an electrical connection between all of the plurality of electrode pages.
The present invention includes a method of fabricating an electrode booklet for a rechargeable battery. The method includes providing a plurality of electrode pages, each being a foil having a shape symmetric about a center line and having a top and bottom surface coated with an active electrode material at two similar portions other than a central uncoated portion which extends between edges of the foil and includes the center line, arranging the plurality of electrode pages in a stack with the electrode pages being similarly oriented, providing at least one overall current collector disposed along the uncoated portion of at least one of the plurality of stacked electrode pages and connecting all the plurality of electrode pages to maintain the plurality of electrode pages in the stack arrangement and to provide an electrical connection between all of the plurality of electrode pages.
The stacking method of the present invention can be visualized from
However, for a thick electrode stack (greater than about 2 cm in overall electrode stack), a front edge of an electrode booklet may not superimpose well enough to provide a vertical stacked electrode assembly owing to the numerous layers being stacked together while the layers are constrained by a certain length. The position of the front edge of each electrode in a stacked electrode assembly is important in the sense of making sure of the capacity consistency of the final cells, as well as the maximization of the cell capacity. A method of preparing electrode booklets with numerous layers and the method of forming a vertical stacked electrode assembly, with electrode edges and thus coated portions being stacked vertically above each other, are described as follows:
A second embodiment of the invention is disclosed for making stacked electrodes of the same symmetry obtainable by a single cutting. Taking the electrode booklet as shown in
In addition to the methods disclosed above for making a thick stacked electrode assembly, a thick stacked electrode assembly can be made by stacking several thin anode and cathode booklets as shown in
Features and advantages of the present invention include:
1. Electrode booklets are always prepared as a first step.
2. Pertinent electrode booklets can be constructed using electrode pages without further cutting or with only one cutting in forming two symmetric stacks, no matter how thick the final electrode stack is. This is very important not only to the cost reduction but also to the enhancement in quality assurance.
3. The full length of the uncoated portion of each electrode can be welded to the overall current collector and it provides uniform current distribution even with electrodes having a large surface area. This is very important for obtaining high rate capability and reducing heat generation.
4. The welding of electrode layers to the overall current collector is conducted prior to stacking anode booklets with cathode booklets. This makes the welding process more reliable with higher yield.
5. Electrode stacking can be very efficient without precision control. Short time stacking, thus cost reduction is expected.
6. High yield of an overall electrode stack results owing to the reduction of risks in undesirable stacking precision and stacking sequencing, unreliable welding, and damaging of electrodes during welding (especially the current collector part during the welding process).
7. The longitudinal direction of the separator material helps stabilizing the electrode stack thus enhances the durability of the cell, especially when vibrated in up and down directions (please refer to
The cell structure and assembly method disclosed above is to enhance the durability and yield of the resultant cell utilizing the electrode booklets described above. The method and the structure of cell assembly are described using the following examples:
Example IFor only one anode booklet and one cathode booklet (please refer to the structure shown in
1. Stabilizing the overall current collectors (including the cathode and anode) on an insulating base with a determined width. The insulating base is indicated in
2. Weld (or using bolts and nuts or other methods) the stabilized overall current collectors to the current collecting posts constructed on a battery cap (please refer to
3. Insert the whole structure including the battery cap and the stabilized stacked electrode assembly into the battery can (please refer to
4. Seal the battery can using laser welding or other equivalent methods.
5. Fill up the electrolyte to the battery through a filling port on the battery cap followed by final sealing of the filling port (please refer to
For a plurality of anode booklets and cathode booklets (please refer to the structure shown in
1. Stabilizing the overall current collectors (including the cathode and anode) of the booklets on an insulating base with a determined width. The insulating base is indicated in
2. Weld (or using bolts and nuts or other methods) the stabilized stacked electrode assembly to the main conducting plates (please refer to
3. Weld (or using bolts and nuts or other methods) the main conducting plates to the current collecting posts constructed on the battery cap.
4. Insert the whole structure including the battery cap and the stabilized stacked electrode assembly in the battery can (please refer to
5. Seal the battery can using laser welding or other equivalent methods.
6. Fill up the electrolyte to the battery through a filling port on the battery cap followed by final sealing of the filling port (please refer to
In Example II., the sequence of step 1 and 2 can be switched according to the design of the processing facilities. The processes shown in Example I and II are demonstrating the ease and highly efficient nature of the present cell assembly method. The procedures are not limited to the above sequences, as well as methods, in conducting each process.
The advantages of the stabilized stacked electrode assembly made up of anode and cathode booklets and the assembling method are as follows:
1. The stabilized stacked electrode assembly structure helps in the prevention of disintegration of the stacked electrode booklets before connecting to the battery cap (e.g. during transferring process, or welding process).
2. The welding (or using bolts and nuts or other methods) of the stabilized stacked electrode assembly to the current collecting posts of the battery cap becomes easy and reliable compared to the conventional method. (Please refer to the disadvantages of conventional stacking method analyzed in the background section regarding difficulty exhibited when welding the multiple electrode tabs together and attaching them to the main negative and positive posts under the cell cap within the limited headspace).
3. The stabilized stacked electrode assembly structure helps in reducing the possibility of inaccurate welding (or using bolts and nuts or other methods) to the current collecting posts of the battery cap.
4. Owing to the advantage described in 2, the insertion of the whole structure including the battery cap and the stabilized stacked electrode assembly to the battery can becomes smooth and efficient.
5. Overall, excellent reliability and consistent cells can be constructed at high efficiency and high yield using the presently disclosed cell structure and method of processing.
While specific material, dimensions, fabricating steps, etc. have been set forth for purposes of describing embodiments of the invention, various modifications can be resorted to, in light of the above teachings, without departing from Applicants' novel contributions; therefore in determining the scope of the present invention, reference shall be made to the appended claims.
Claims
1. An electrode booklet for a rechargeable battery, comprising
- a plurality of electrode pages, each electrode page being a foil having a shape symmetric about a center line and having a top and bottom surface coated with an active electrode material at similar portions other than a central uncoated portion which extends between edges of the foil and includes the center line, and
- at least one overall current collector disposed along the uncoated portion of at least one of said plurality of electrode pages, said electrode pages being in a stack arrangement and similarly oriented, with said at least one overall current collector being connected to the uncoated portion of all of the plurality of electrode pages to maintain said plurality of electrode pages in the stack arrangement and to provide an electrical connection between all of the plurality of electrode pages.
2. A stacked electrode assembly of a battery, comprising:
- an electrode booklet of claim 1, wherein the active electrode material is an active anode material to form an anode booklet,
- an electrode booklet of claim 1, wherein the active electrode material is an active cathode material to form a cathode booklet, and
- a separator material for separating the active anode material from the active cathode material,
- said anode booklet and cathode booklet being substantially similar in size, shape and number of pages, and being in a folded condition about the uncoated portions,
- said at least one overall current collectors being connected to the uncoated portion of each of said plurality of electrode pages in a manner to form a vertical stack of coated portions,
- the booklets being arranged to alternate coated portions of said anode booklet with coated portions of said cathode booklet to result in a vertical stack with the separator material separating each coated portion, and
- the at least one overall current collector of the anode booklet being disposed on one side of the resulting vertical stack and the at least one overall current collector of the cathode booklet being disposed on the opposite side of the resulting vertical stack.
3. A stacked electrode assembly of a battery, comprising:
- an electrode booklet of claim 1, wherein the active electrode material is an active anode material to form an anode booklet,
- an electrode booklet of claim 1, wherein the active electrode material is an active cathode material to form a cathode booklet, and
- a separator material for separating the active anode material from the active cathode material,
- said anode booklet and cathode booklet being substantially similar in size, shape and number of pages, and being in a folded condition about the uncoated portions,
- said at least one overall current collectors being connected to the uncoated portion of each of said plurality of electrode pages in a manner to form a stack of coated portions being at a selected angle from vertical,
- the booklets being arranged to alternate coated portions of said anode booklet with coated portions of said cathode booklet to result in a vertical stack with the separator material separating each coated portion, and
- the at least one overall current collector of the anode booklet being disposed on one side of the resulting vertical stack and the at least one overall current collector of the cathode booklet being disposed on the opposite side of the resulting vertical stack.
4. A stacked electrode assembly, comprising
- a semi anode booklet having a plurality of anode pages, each page having, at one end, an active anode material portion on the top and bottom surfaces thereof, an uncoated portion at the other end and at least one overall current collector disposed on the uncoated portion of at least one anode page and connecting the plurality of anode pages,
- a semi cathode booklet having a plurality of cathode pages, each page having, at one end, an active cathode portion on the top and bottom surfaces thereof, an uncoated portion at the other end and at least one overall current collector disposed on the uncoated portion of at least one cathode page and connecting the plurality of cathode pages, and
- a separator material for separating the active anode material from the active cathode material,
- said active anode material and active cathode material being substantially similar in size and shape, and arranged to alternate active anode material with active cathode material in a manner to result in the coated portions being in a vertical stack with the separator material separating each coated portion,
- the at least one overall current collector of the anode booklet being disposed on one side of the vertical stack and the at least one overall current collector of the cathode booklet being disposed on the opposite side of the vertical stack,
- said uncoated portions of said anode pages being of a progressively increasing size from an anode page closest to its overall current collector to an anode page furthest from its overall current collector, and
- said uncoated portions of said cathode pages being of a progressively increasing size from a cathode page closest to its overall current collector to a cathode page furthest from its overall current collector,
5. The stacked electrode assembly of a battery of claim 3, wherein the selected angle is between 1 and 80 degrees.
6. The stacked electrode assembly of a battery of claim 2, 3 or 4, wherein said separator material is in a continuous strip with a longitudinal edge of the strip being parallel to the center lines.
7. The stacked electrode assembly of a battery of claim 2, 3 or 4, further comprising
- an insulating base for supporting the overall current collectors of the anode booklet and the cathode booklet.
8. A multiple stacked electrode assembly of a battery, comprising
- a plurality of stacked electrode assemblies of claim 2, 3 or 4 arranged with the overall current collectors of the anode booklets in vertical alignment and the overall current collectors of the cathode booklets in vertical alignment,
- a main positive collecting plate electrically connecting the vertically aligned overall current collectors of the anode booklets,
- a main negative collecting plate electrically connecting the vertically aligned overall current collectors of the cathode booklets, and
- an insulating base for supporting the overall current collectors of the anode booklets and the cathode booklets.
9. A rechargeable battery, comprising
- a battery can,
- the stacked electrode assembly of claim 7 disposed in the battery can, the insulating base being adjacent the bottom of the battery can,
- a battery cap having current collecting posts, with the overall current collectors connected electrically to the current collecting posts, said battery cap being sealed to the battery can, and
- an electrolyte filling the battery can.
10. A rechargeable battery, comprising
- a battery can,
- the stacked electrode assembly of claim 8 disposed in the battery can, the insulating base being adjacent the bottom of the battery can,
- a battery cap having current collecting posts, with the overall current collectors connected electrically to the current collecting posts, said battery cap being sealed to the battery can, and
- an electrolyte filling the battery can.
Type: Application
Filed: Mar 19, 2012
Publication Date: Jul 12, 2012
Inventors: Han Cheng Kuo (Burlington, MA), Tsun-Yu Chang (Taichung), Chun-Chieh Chang (Ithaca, NY)
Application Number: 13/423,694
International Classification: H01M 4/64 (20060101); H01M 2/08 (20060101);