The purpose is to make high durability lithium ion cells for high power applications such as electric and hybrid electric vehicles.
Conventionally, 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:
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
In the present invention, the electrode stacking problems mentioned above can be solved with more advantages obtainable compared to the conventional stacking technologies.
The 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.
a) and 1(b) are examples of stacked electrodes of the prior art;
a) is an elongated foil of the present invention having two portions with an active electrode material and an uncoated central portion, with lines indicated for cutting electrode pages;
b) is a stack of electrode pages of the invention with coated portions stacked in a vertical orientation;
c) is an electrode booklet of the invention having stacked electrode pages connected to an overall current collector;
d) is the electrode booklet of
a) is an anode booklet and a cathode booklet of the invention in an initial stage of fabricating a stacked electrode assembly having a separator material between coated portions of anodes and cathodes;
b) is the stacked electrode assembly of
a) is a stack of electrode pages of the invention with coated portions stacked with a selected angle from vertical, the selected angle being toward the left or right as shown in the drawing;
b) is an electrode booklet of the invention fabricated with the stack of electrode pages of
c) is the electrode booklet of
d) is the electrode booklet as in
e) is the electrode booklet of
f) shows two electrode booklets of the invention in a folded condition, one as an anode booklet and one as a cathode booklet;
g) is a stacked electrode assembly of the invention fabricated with the anode booklet and cathode booklet of
h) is the electrode booklet of
i) is a semi anode booklet and a semi cathode booklet of the invention resulting from cutting an anode booklet and a cathode booklet as shown in
j) is a cell of a battery having alternating anodes and cathodes fabricated from the semi of anode booklet and semi cathode booklet of
a) shows electrode booklets of the invention with overall current collectors disposed in an insulating base for support; and
b) shows an assembled rechargeable battery of the invention fabricated with use of the supported overall current collectors and electrode booklets of
The stacking method of the present invention can be visualized from
c) shows an overall current collector that is welded (or connected by other methods) on the uncoated area of at least one of the electrode pages in the electrode stack shown in
a) shows the shuffling nature of stacking electrode pages of the booklets. The separator material is implemented as a continuous strip with a longitudinal edge of the strip being parallel to the center line with respected to the cathode and anode layers. With the movement of the separator roll moving back and forth, the separator material is placed continuously in between each anode and cathode layer coming from the cathode and anode booklets.
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) shows a stack of electrode pages placed in a tilted manner, that is the coated portions are stacked at a selected angle from vertical. The tilting of the initial electrode stack is to solve the non-superposition problem for the final stacked electrode assembly.
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:
For 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.