Grid placement in lithium ion bi-cell counter electrodes

Details Grid placement in lithium ion bi-cell counter electrodes Grid placement in lithium ion bi-cell counter electrodes

2000-05-11

2001-09-18

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Intracell assembly having cell electrode connector

C429S162000, C429S122000, C429S127000, C429S233000, C429S237000, C429S210000, C429S239000

Reexamination Certificate

active

06291097

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to batteries comprising one or an integrated series of polymer matrix bi-cell batteries. Each individual bi-cell comprises, sequentially, a first counter electrode, a film separator, a central electrode, a film separator, and a second counter electrode.
BACKGROUND OF THE INVENTION
A lithium ion electrolytic cell, such as a rechargeable lithium ion battery, is commonly constructed by means of the lamination of electrode and separator film cell elements which are individually prepared. Each of the electrodes and the film separator is formed individually, for example by coating, extrusion, or otherwise, from compositions including binder materials and a plasticizer.
Lithium ion electrolytic cells
101
may be of the traditional type, shown in
FIG. 1
, with an cathode
110
, a separator
112
, and an anode
114
sandwiched together.
A separator is positioned between a negative electrode and a positive electrode. The anode, separator, and cathode structures are then laminated to produce a standard unitary flexible electrolytic cell precursor structure. The precursor can be extracted and activated with electrolyte to form a functional battery.
A lithium ion battery typically comprises several solid, secondary electrolytic cells in which the current from each of the cells is accumulated by a conventional current collector, so that the total current generated by the battery is roughly the sum of the current generated from each of the individual electrolytic cells employed in the battery. In lithium ion batteries it is common to stack separate electrolyte cells to create the battery.
There is a trend to commercially develop “bi-cells”, in which a single central electrode has two counter electrodes, one positioned on either side of the central electrode. The central electrode has been an anode, the counter electrodes have been cathodes. Bi-cells are more complex than standard cells, and require the successful lamination of more layers.
A bi-cell
201
, for example that shown in
FIG. 2
a
, includes, sequentially, a first counter electrode
214
a
having a first medially positioned current collector
215
a
, a first separator
212
a
, a central electrode
210
having a centrally located current collector
215
a
, a second separator
212
b
, and a second counter electrode
214
b
having a second medially positioned current collector
215
a
. An electrode tab (not shown) connects the central electrode elements to the exterior of the package. A similar counter electrode tab (not shown) connects the counter electrode elements to the exterior of the package.
Lamination has been, and continues to be, a problem in the preparation of polymer batteries.
FIG. 2
b
shows an exploded graphic representation of the interface between at a current collector. The current collectors used are grids or perforated sheets
255
, which permit a direct contact interface region
248
between two sheets of polymer electrode
253
a,
253
b.
This electrode-electrode contact across the perforated current collector has proven to be critical in producing bi-cells which resist delamination during use.
It is preferred that a battery achieve the maximum energy potential and cycle life. It would therefore be preferred that the current collector in the anodic and cathodic electrode be positioned to provide optimum battery performance.
SUMMARY OF THE INVENTION
It has been unexpectedly discovered that the placement of the current collector within the counter electrodes can affect the electrochemical properties of the electrolytic cell. The positioning of the current collector within the counter electrode can be varied as desired within the outer half of the counter electrode. Improved battery performance is achieved in a bi-cell battery when the current collector of the counter electrodes are not positioned medially within the electrode, as with the prior art, or within the inner half, but are placed toward the outside of the counter electrodes, i.e., further removed from the central electrode. Optimally, current collectors are positioned at the outermost edges of the two counter electrodes.
Counter electrode materials are preferably attached to another film of similar material through the perforated current collector. When some percentage of the counter electrode material is external to the current collector, the counter electrode bonds to itself through the current collector grid. An optimal placement of the current collector in the counter electrode is at the outermost edge of a counter electrode, with 100% of the electrode material between the current collector and the central electrode. However, if all of the counter electrode is at one side of the current collector with no material at the opposite side of the current collector to which to bond during lamination, the counter electrode tends to delamninate relatively quickly, destroying battery life.
It has been discovered that providing an electrochemically inactive polymer matrix film of material similar to the electrode material distal to the current collector, to which the counter electrode material can adhere, provides both optimal positioning of the current collector within the counter electrode, and minimizes delamination of the counter electrode during battery use. This polymer matrix is a terminal film which provides improved lamination and battery life, but which does not provide electrochemical activity to the bi-cell. Film which is a polymer matrix similar to the electrode film, but which does not contain electrode active materials, is preferred. An excellent choice for this terminal film is polymer matrix separator film.


REFERENCES:
patent: 5587253 (1996-12-01), Gozdz et al.
patent: 5840087 (1998-11-01), Gozdz et al.
patent: 6063519 (2000-05-01), Barker et al.
patent: 0 602 976 A1 (1994-06-01), None
patent: 0 642 186 A1 (1995-03-01), None
patent: 0771040A2 (1997-05-01), None
patent: WO 97/08769 (1997-03-01), None
International Search Report Aug. 31, 1999.

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