Wound cell stack design for enhanced battery performance

Abstract: An electrochemical cell comprising an electrode assembly in which the electrodes are wound together in a bi-directional fashion yielding a high energy density cell stack with low internal impedance. The electrode assemblies are such that either a single cathode is paired with two anodes or a single anode is paired with two cathodes prior to winding of the cell stack assembly. The cell stack assembly is formed by overlapping the two anode electrodes on opposite sides of the cathode electrode across a midportion and then winding the electrode strips bi-directionally about the midportion to form a cell stack assembly.

Description: FIELD OF INVENTION The present invention generally relates to the art of electrochemical energy, and more particularly, to an electrode assembly, electrochemical cells in which the electrode assembly is used, and a method for making the electrode assembly. BACKGROUND OF THE INVENTION Batteries or electrochemical cells are typically volumetrically constrained systems that cannot exceed the available volume of the battery case. The size and resulting volume of the battery case are dictated by the space requirements available for the particular application. The components that make up a battery, namely, the cathode electrode, the anode electrode, the separator, the current collectors, and the electrolyte all have to fit into the limited space defined by the battery case. Therefore, the arrangement of the components impacts on the amount of active electrode material that can be fit into the case and the ease of manufacturing the unit. Some typical electrode assemblies include the "Z" folded electrode assembly that is disclosed in U.S. Patent No. 3,663,721 to Blondel et al. In the "Z" folded electrode, a unitary and continuous lithium anode is folded back and forth in a zigzag fashion. The length of the individual folds determines the width of the electrode assembly. Individual cathode plates are positioned between pairs of the pleated anode electrode and electrically connected to one another. The design has some drawbacks, including the requirement that separate cathode plates be inserted between each pair of adjacent layers of anode electrode and the requirement that electrical connections be made between all of the inserted cathode plates. This arrangement increases the time and costs associated with manufacturing. Another typical electrode assembly configuration is the "jelly roll" design in which the anode electrode, the cathode electrode, and the separator are overlaid with respect to each other and coiled up. Such an electrode configuration is desirable because the continuous anode and cathode electrodes require a minimal number of mechanical connections to their respective terminal leads, and the jelly roll assembly is generally recognized as preferred for high discharge . and current pulse applications. However, in some applications, a cylindrically shaped electrode assembly is not desired because of other factors, such as the shape of the battery case. U.S. Patent No. 4,761,352 to Bakos et al. discloses yet another electrode assembly design comprising an accordion folded electrode assembly with unitary members for both the anode and cathode strips. The cathode strip is approximately half the length of the anode strip, and the anode strip is folded over the cathode strip to "sandwich" the cathode between two layers of the anode. The resulting form is then manually folded in an alternating series of "V" folds (best shown in Fig. 4 of the patent). However, that design provides some undesirable gaps which reduce the volumetric density of the electrochemically active materials. What is needed is an improved multi-layer, folded electrode assembly design for high energy devices that includes many of the desirable features of the jelly roll design, such as unitary anode and cathode electrodes. SUMMARY OF THE INVENTION The present invention fills the above-described need by providing an electrochemical cell comprising an electrode assembly in which the electrodes are wound together in a bi-directional fashion, yielding a high energy density cell with low internal impedance. The anode and cathode electrodes are arranged in the cell in such a fashion that provides efficient utilization of the active components. The resultant wound assembly is configured such that it can be conveniently packaged in either a cylindrical or prismatic housing. The electrode assemblies are disposed such that either a single cathode is paired with two anodes or a single anode is paired with two cathodes prior to winding of the cell stack assembly. The cell stack assembly is formed by winding the electrodes starting at the centralmost portion of the assembly. The electrodes can be configured such that the two anodes (or two cathodes) are independent of each other or are electrically connected prior to winding. The resulting electrodes are then electrically connected to the battery housing. In one embodiment of the electrochemical cell, the electrodes are provided as two anode assemblies and one cathode assembly configured such that each anode is positioned on either side of the cathode assembly, and extending in opposing directions. At the centermost portion of the assembly there is an overlap of anodes. This assembly is then wound about the overlapping region in a bi-directional fashion. The resultant assembly produces a wound cell stack configuration with a uniform contact of anode and cathode, such that the cell is balanced electrochemically and provides for optimum volume utilization within the battery enclosure. Each anode has one or more tabs that can be welded to the case. Alternately, two cathode assemblies can be paired with one anode assembly, with a resultant cathode tab welded to the case. In both of the above configurations, the opposite electrode may contain one or more tabs which are then electrically connected to the battery feedthrough pin. An alternate embodiment of this invention provides for an anode electrode and a cathode electrode, wherein the electrodes are slotted. The electrodes are inserted, one into the other, essentially forming an "X." Upon collapsing the electrodes, a variation of the above-described invention is obtained wherein the anode is approximately equally disposed about the cathode. This assembly is then wound from the center, resulting in a preferred cell stack assembly. This configuration. provides for the additional advantage of having the anode registered to the cathode, and mitigates the need for aligning two distinct anodes to the cathode. Other features and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the accompanying drawings and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of the cathode strip and separator of the present invention; Fig. 2 is a plan view of the anode strip and separator of the present invention; Fig. 3 is an elevational view of the cell stack assembly of the present invention; Fig. 4 is a plan view of the cell stack assembly of the present invention; Fig. 5 is an elevational view of the wound electrode assembly of the present invention; Fig. 6 is a perspective view of the alternate embodiment of the electrode strips of the present invention; Fig. 7 is a elevational view of the wound electrode assembly of the alternative embodiment; and Fig. 8 is an exploded view of an electrochemical cell of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is designed for high energy devices such as batteries and capacitors and is adaptable in a wide variety of electrode configurations and shapes for applications as capacitors and batteries, including aqueous and nonaqueous primary and secondary batteries. Referring to Fig. 1, an electrode strip 10 is preferably a continuous structure comprising an active material combined with a current collector. The active material for a cathode electrode is preferably comprised of a metal, a metal oxide, a metal sulfide, a mixed metal oxide, a carbonaceous material, or the like and is combined with a current collector of a conductive material such as a conductive screen. For an anode electrode the preferred active material is an alkali metal selected from Group lA of the Periodic Table of Elements and contacted to a nickel current collector. An insulating separator material 13 prevents contact between adjoining layers of electrodes. The electrode strip 10 is a cathode electrode 14. The cathode electrode 14 has a set of cathode tabs 15 that are provided for making an electrical connection. Turning to Figs. 2 and 3, a pair of electrode strips 16 are disposed on opposite sides of electrode strip 10. The electrode strips 16 overlap along a midportion 19 of electrode strip 10, as shown in Fig. 3. Electrode strip 16 is part of anode electrode 18. Anode electrode 18 is also provided with a layer of separator material 13, and the electrode strip 16 has anode tabs 22 that provide for electrical connection. Turning to Fig. 4, cathode electrode 14 and the two anode electrodes 18 are preferably elongate, flat, and rectangular. The anode electrodes 18 are disposed on opposite sides of the cathode and lined up such that they overlap across the midportion 19. The electrode strips 16 are approximately half the length of the electrode strip 10, and extend a short distance across the midportion 19 in order to overlap. Alternately, two cathode electrode assemblies could be paired with one anode electrode. From the alignment shown in Figs. 3 and 4, the electrode strips 10 and 16 are then folded about the overlapping region in bi-directional fashion to provide the electrode assembly 25, shown in Fig. 5. The term bi-directional refers to the fact that one side is folded downward and the opposite side is folded upward, in succession, to generate the electrode assembly 25 shown in Fig. 5. The electrode assembly 25 produces a wound cell stack configuration with uniform contact of anode and cathode such that the cell is balanced electrochemically and provides for optimum volume utilization within the battery enclose. The electrode assembly 25 provides several advantages, including producing a high energy density cell with low internal impedance. The anode and cathode electrodes 14, 18 are arranged in the cell in a way that provides efficient utilization of the active components. The resultant wound cell stack is configured such that it can be conveniently packaged in either a cylindrical or prismatic housing. The assembly 25 also provides a cell stack construction in which the anode and cathode are uniformly utilized during cell discharge. The assembly also provides for reduced internal cell resistance through the use of a dual anode (or dual cathode) configuration in combination with a single cathode (or anode). Also, the assembly 25 provides for a cell that has a high current rate capability, which is advantageous for use in applications such as powering an implantable defibrillator. An alternate embodiment of the present invention is shown in Fig. 6. A cathode electrode strip 50 has a slot 53 disposed in a midportion 56. An anode electrode strip 60 has a slot 63 disposed in a midportion 66. The strips 50 and 60 are inserted into each other to form a generally X-shaped member that is collapsible. Upon collapsing the electrode strips 50, 60, a variation of the above-described invention is obtained wherein the anode is approximately equally disposed about the cathode. The strips 50, 60 are then folded in bi-directional fashion from the center to produce the electrode assembly 75, shown in Fig. 7. The alternate embodiment provides the additional advantage of having the anode registered to the cathode and mitigates the need for aligning two distinct anodes to the cathode. Referring to Figs. 1, 2, and 8, the anode tabs 22 can be welded to the case 80 (negative). Alternately, two cathode assemblies can be paired with one anode assembly with the resultant cathode tabs (not shown) welded to the case 80 (positive). In both of the above configurations, the opposite electrode may contain one or more tabs (cathode tabs 15) that are electrically connected to the battery feedthrough pin 89. While the invention has been described in connection with certain preferred embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the scope of the invention, as defined by the appended claims.

Claims: An electrode assembly, comprising: a first electrode strip (10) having a midportion (19) and a predetermined length; at least two second electrode strips (16) having a length shorter than the first electrode strip and disposed on opposite sides of the first electrode strip, the at least two second electrode strips disposed in overlapping fashion along the midportion of the first electrode strip, the at least two second electrode strips folded bi-directionally about the midportion of the first electrode strip such that a wound cell stack is formed; and a layer of an insulating separator material (13) disposed between the first electrode strip and the at least two second electrode strips. The electrode assembly of Claim 1, wherein the at least two second electrode strips have at least one tab for connection to a battery case (22). The electrode assembly of Claim 1, wherein the first electrode strip has a tab capable of connecting to a feedthrough pin (15). The electrode assembly of Claim 1, wherein the first electrode strip is an anode strip. The electrode assembly of Claim 1, wherein the first electrode strip is a cathode strip. The electrode assembly of Claim 1, wherein the at least two second electrode strips are anode strips. The electrode assembly of Claim 1, wherein the at least two second electrode strips are cathode strips. The electrode assembly of Claim 1, wherein the first electrode strip is a unitary member. The electrode assembly of Claim 1, wherein the at least two second electrode strips are unitary members. A battery, comprising: (a) a first electrode strip having a midportion and a predetermined length; (b) at least two second electrode strips having a length shorter than the first electrode strip and disposed on opposite sides of the first electrode strip, the at least two second electrode strips disposed in overlapping fashion along the midportion of the first electrode strip, the at least two second electrode strips disposed in overlapping fashion along the midportion of the first electrode strip, the at least two second electrode strips folded bi-directionally about the midportion of the first electrode strip such that a wound cell stack is formed; (c) a layer of an insulating separator material disposed between the first electrode strip and the at least two second electrode strips; and (d) an electrolyte activating and operatively associating the anode strip and the cathode strip. A battery comprising an electrode assembly according to any one of claims 1 to 9 and an electrolyte activating and operatively associating the anode strip and the cathode strip. A method of providing an electrode assembly, comprising the steps of: (a) providing a first' electrode strip having a midportion and a predetermined length; (b) providing at least two second electrodes strips having a length shorter than the first electrode strip; (c) providing a layer of insulating material adjacent to the first electrode strip and the at least two second electrode strips; (d) placing the at least two second electrode strips on opposite sides of the first electrode strip such that the at least two electrode strips overlap along the midportion; and (e) folding the at least two second electrode strips bi-directionally about the midportion of the first electrode strip to form a wound cell stack. An electrode assembly, comprising: (a) a first electrode strip (50) having a midportion (56) with a slot (53) defined therein; (b) a second electrode strip (60) having a midportion (66) with a slot (63) defined therein, the second electrode strip and the first electrode strip capable of mating through the slots such that an X-shaped combined electrode member is formed, the first and second electrode strips being folded bi-directionally to form a wound cell stack; and (c) a layer of an insulating separator material disposed between the first electrode strip and the second electrode strip. The electrode assembly of Claim 13, wherein the first electrode strip has a tab capable of connecting to a feedthrough pin. The electrode assembly of Claim 13, wherein the second electrode strip has at least one tab for connection to a battery case.

Inventors: FRUSTACI DOMINICK J, FRYSZ CHRISTINE A, HALLIFAX PAUL T, MOCERI KENNETH P, PAULOT WILLIAM M, FRUSTACI, DOMINICK J., FRYSZ, CHRISTINE A., HALLIFAX, PAUL T., MOCERI, KENNETH P., PAULOT, WILLIAM M.
Applicants: GREATBATCH W LTD, WILSON GREATBATCH LTD.
Application year: 2000
Main classification: H01M6
IPC codes: H01M6, H01G9, H01M2, H01M10, H01M4