CA1154820A

CA1154820A - Method for assembling an electrochemical cell

Info

Publication number: CA1154820A
Application number: CA000376051A
Authority: CA
Inventors: Franz Goebel; Ibsen R. Hansen
Original assignee: GTE Products Corp
Current assignee: Osram Sylvania Inc
Priority date: 1980-04-29
Filing date: 1981-04-23
Publication date: 1983-10-04
Also published as: US4309817A; EP0050630A4; EP0050630A1; JPS57500535A; WO1981003242A1

Abstract

METHOD FOR ASSEMBLING AN ELECTROCHEMICAL CELL

ABSTRACT OF THE DISCLOSURE

A method for assembling a primary electrochemical cell including a carbon cathode structure. The carbon cathode structure is assembled by arranging a selected number of individual annular-shaped porous carbon elements, each having an opening extending therethrough, together with an elongated, hollow, cylindrical metal current collector tube so that the carbon elements are in a stacked array and the tube is loosely disposed within and along the openings in the array of carbon elements. The current collector tube is an expandable member and is initially in a non-expanded state and loosely surrounded by the stacked array of carbon elements. A porous separator and an anode structure are then placed around the aforementioned assembly of the carbon elements and the current collector tube, and the resultant assembly, representing a battery stack, is placed within an elongated housing of an electro-chemical cell. A tool is then employed to permanently expand the current collector tube outwardly so that the tube makes direct physical contact with the array of carbon elements. An electrolyte solution is placed within the cell in contact with the battery stack and the hollow opening of the tube. The electrolyte solution permeates the carbon elements directly and also by way of a large number of small holes formed in the tube, causing the porous carbon elements to be permeated with the electrolyte solution and expand outwardly. The expansion of the carbon elements causes constituent particles thereof to fill the openings in the current collector tube thereby permanently locking the carbon elements to the current collector tube.

Description

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METHOD FOR ASSEMBLING AN ELECTROC _ MICA~ CEL~
CROSS-REFERENCE TO RELATED APPLICATION
-In co-pending patent application No. 376,101, filecl concurren-tly herewith in the names oE Franz Goebel and Cyril Moryan, and entitled "ELECTROCHEMICAL CELL", there is disclosed and claimed a battery stac'c assembled in accordance with the method disclosed and claimed in the present application.
BACXGROUND OF THE INVENTION
~ .
The present invention relates to a method for assem-hling an electrochemical cell and, more particularly, to a method for assembling a primary electrochemical celL
having a carbon cathode structure.
Primary electrochemical cells are utilized for a wide var-ety of applications and are commonly available in a large assortment of sizes and shapes. Furthermore, a number of electrochemical systems are known for incorpora-tion into such primary electrochemical cells. klany of these eiectrochemical cells utilize a carbon cathode structure. By wa~ of e~ample, in UOS~ Patent Mo.
4,060,668, in the name of Franz Goebel and assigned to GrrE
Laboratories Incorporated, there is disclosed an electro-chemical system including an anode, a carbon currsnt collector cathode structure, and an electrolyt~ solution in contact with the anode and the carbon current collector cathode structure. The carbon current cathode collector structure employed in this electrochemical system includes a preformed porous cyl~ndrical carbon structure o~ a specified lenyth (as determined by the slze of the cell~, and a ~wisted metal cathode current collector impressed into and along the carbon structure. The carbon siructure comprises an ayyregation of a large number of porous semi-rigid ylobules which are pressed together in a manner -to c~efine a multiplicity of electrolyte-conductiny channels~
By virtue oE these channels, the electrolyte solutlon can --. 22883CN -2-diffuse throughout the porous carbon structure and contact the cathodic particles o the structure.
While carbon current collector cathode structu~es as described hereinabove can be constructed and successfully employed within electrochemical cells, they nonetheless are subject to numerous possible problems and disadvan-tages. More particularly, the preformed porous carbon structures are inherently ~ragile and therefore difficult to produce in any reasonable or substantial length (e.g.,

2 inches or more) without breaking or falling apart.
Further, even when a carbon structure is successfully formed to the desired length, the subsequent act of impressing a metal cathode current collector into the preformed carbon structure, either by twisting or forcing the metal cathode current collector longitudinally into the preformed carbon structure, cannot be controlled with great accuracy. As a result, the mechanical and elec-trical contact between the twisted metal cathode current collector and the preformed carbon structure may be inadequate to satisfy the stringent requirements and specifications of the electrochemical cell in which such structure is to be used.
BRIEF SUMMARY OF THE INVENTION
Accordingly, the present invention provides a me-thod for assembling a carbon cathode structure for an electro- :
chemical cell, comprising the steps of: arranging a selected number of individual porous carbon elements, each having an opening eY~tending there-through defining an interior wall portion, wi-thin and relative to a housing for an electrochemical cell and also relative to an elon~ated metal current collector so that the current collector is loosely disposed within and along the open-ings ln the carbon elements and the carbon elements loosely surround the current collector in a stacked array within the housing of the cell, said current collector being a hollow elongated metal tube having a central ,, :, .:. ., :, : . .:
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_ 22883CN -3-openin~ alon~ its length and -~urther being permanently expandable and being initially in a non-expancled state in which it is spaced from the interior wall portions o~ the :;
stacked array of carbon e.ements, said current collector further having a plurality of openin~s formed therein along its len~th; and expanding the elongated current collector outwardly ~rom its initial non-expanded state ~o a permanently expanded state by an amount to cause the :
current collector to make direct physical contact with the interior wall portions of the stacked array of carbon elements thereby to secure the array of carbon elements to `
the current collector, said step of expanding the current collector comprising the steps of: inse:rting and progres-sively advancing a tool into and along the central opening of the elongated current collector tube to permanently expand the tube outwardly to cause the expanded tube to ma~e direct physical contact with the interior wall :
portions o the array of stacked carbon elements; and withdrawing the tool from the opening in the current collector.
The present invention Eurther provides a method for assembling an electrochemical cell comprising the steps ;
of: arranging a selected number of individual porous carbon elements, each having an opening extendi~g there-through de~ining an interior wall portion, relative to an elongated hollow me.tal current collector so that the current collector is loosely disposed within and along the openings in the carbon elements and the carbon elements loosely surround the current collector in a stacked array, each of said carbon elements including a network of electrolyte-conducting ~hannels ~herein for receiving and being permeated by an electrolytic solution and to expand outwardly in response to said electrolytic solution, said current collector bein~ a permanently expandable tube and being initially in a non-expanded state in which it is spac~cl lrom the interior wall portions of the stac~ed .
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array o~ carbo:n elements, said current collector tube further having a plurality of openings formed -therein along its length; positioning a porous separator, an anode structure and the assembly o ~.he stacked array of carbon elements and current collector tube relative to each other and within an elongated hou~ing o~ the electrochemical cell with the anode structure being in con-tact with the porous separator and -the porous separator being in contact with the assembly of the stacke~ array of carbon elements and the current collector tube; expandin~ the current collector tube outwardly against the other aforesaid componen-ts of the cell to cause the current collector tube to make direct permanent physical contact with the inter-ior wall portions of the stacked array o carbon elements -thereby to secure the array oE carbon elements to the current collector tube, said step of expanding the current collector tube comprising the steps oE: inserting and progressively advancing a tool into and along the central,, opening of the elongated current collector tube to perma-nently expand the tube outwardly to cause the expandedtube to make direct physical contact with the interior wall portions of tne array of stacked carbon elements; and withdrawing the tool from the opening in the current collector tube; and placing an electrolytic solution into the cell in contact with the aforesaid components of the cell and within -the hollow cllrrent collector tube, whereby the electrolytic solution is supplied to the electrolyte-conducti.ng channels of the array of carbon elements directly and by way of the openings in the current collec-tor tube, causing the carbon elements to expand outwardlyand fill the openings in the current collector tube with constituent particl~s -thereof thereby permanently locking the array o. carbon elements to the current collector tube.

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228~3C~ 5-BRIEE' L~ESCR~PTION OF THE DRAWING
-Some embodiments of the invention will now be described, by way of example, with reEerence to the accompanying drawings, in which:
FIG. 1 is an elevational view, partly in cross section, of a primary electrochemical cell employing a carbon cathode structure as assembled in accordance with the method of th~ present invention;
FIGS. 2 and 3 are perspective views of componen-cs employed by the carbon cathode structure shown in FIG. 1;
FIG. 4 illustrates a tool employed in the assembly of the electrochemical cell of FIG. 1 in accordance with the method of the present invention; and FIG. 5 illustrates an assembly step in accordance with the method of the pxesen-t invention.
DETAILED DESCRIPTION OF THE T~VENTION
,.
Referring now to FIG. 1, there is shown a primary el~ctrochemical cell 1 as assembled in accordance with the method of the p-esent invention. As shown in FIG. 1, the electrochemical cell 1 generally includes an elongated metal casing or housing 2, for example, of a cylindrical configuration, within which a battery stack 3 is disposed adjacent to a bottom end thereof. An electrolyte solution 5, for example, in the form of a cathodelectrolyte solu-tion, is provided within the interior of the cell 1 to permeate various portions of the battery stack 3 r in a manner to be described in greater detail hereinafter. A
suitable and preferred form of -the electrolyte solution 5 which is usable with the components of the battery stack 3 (a preferred ~orm ~f which will be described in greater detail hereinafter), is a cathodelectrolyte solution including a reducible soluble cathode r such as thionyl chloride, and an electrolyte solute, such as lithium tetrachloroaluminate, dissolved in the thionyl chloxide.
The bat-tery stack 3 and the electrolyte solution 5 as discussed hereinabove collectively represent the ~ 3 22883CN -~-electrochemical s~stem of the cell 1. The battery stack 3 as sho~-n in FIG. i is insula-ted from the housing 2 of the cell 1 b~ a suitable insulaior 6, and ~enerally includes a concentric arrangement of an anode 7, a -thin Porous separator 8, and a cathode current collector electrode structure 9. The anode 7, which takes the form of a cylindrical sheet and which ma~ be of an oxidizable acti~7e alkaline metal such as lithium, is connected mechanically and electrically to the housing 2 by means oE a fine metal screen or grid 11 which is spot welded to the interior wall of the housing 2 and into which the lithium anode is physically pressed to secure the lithium anode to the screen 11. ~he electrical connection of the anode 7 to the housing 2 establishes the housin~ 2, which may be of stainless steel, as the ne~ative terminal for the cell l.
I'he aforementioned porous separator 8 is employed to electrically isolate the anode 7 from the cathode current collector electrode structure 9 and typically takes the form of a cylindrical sheet o~ a standard electrically-nonconductive material such as fiberglass.
The aforementioned cathode current collector elec-trode structure 9 generally comprises a plurality of annular, or disc-shaped, porous carbon elements 12 arranged directly above each other in a vertical stacked array, and an elongated perforated expandable metal tube 14 disposed within central openings of the elements 12.
The tube 14 is connected by a thin metal strip 15 spot welded thereto to a positive terminal 16 o~ the cell 1.
The metal strip 15, for example, of nickel, is connected (e.~., spot welded) to the terminal 16 by way o~ a stand-ard insulative ~lass or ceramic-to-metal seal 17 provided within an hermetically sealed cap 18 of the cell 1.
The pluralit~ of porous carbon elements 12, when used witll the a orementioned components and specific materials of the cell 1, act as a cathode current collector and as a catal~st where the reduction of the solvent (thionyl ,-... ~

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chloride~ in the ca~hodelectrolyte solution takes place.
Each O,c -the elQments 12, the form of which is shown in FIG. 2, is produced by compressing together a plurality o-E
discrete, semi-rigid, porous carbon conglomerates thereb~
to define a network of electrolyte-conducting channels throughout the element 12. The conglomerates generally contain a combination of carbon black, graphite, and a binder such as "Teflon" [trademark). By virtue of the small physical size of each of the elements 12, for example, one inch in diameter and one-half inch thickness for a t'D"-sized cell, a stacked array of carbon elements of any desirable length may be assembled by simply select-ing the required number of elements 12 for the particular size of cell and stacking the elements one atop the other as indicated in FIG. 1. For a "D"-sized cell, for exam-ple, eight elements 12 would be sufficient. The use of multiple carbon elements 12 in a stacked array further -avoids the fragility and breakage problems associated with the aforedescribed prior ar-t carbon structures in which the carbon s-tructures are formed in one piece, and often of substantlal length, and twistéd metal current collector elements are forced or screwed into the carbon structures.
Techniques for producing the conglomerates employed by the carbon elements 12 are described in detail in the a~ore-mentioned U.S. Patent No. 4,161,063 to which reference may be made for specific details.
The perforated expandable metal tube 14 employed with the multiple carbon elements 12 as discussed hereinabove takes the specific form as shown in ~IG. 3. As shown in FIG. 3, the perforated metal tube 14, which may be o~
nickel or stalnless steel, is split along its entire length to define a generally C-shaped cross section and includes a large number of small openings 20. The openings 20 may be produced by simple metal stamping operations. The -tube 14 as shown in FIG. 3 is assembled into the c211 1 together with the other components of the ,. . ~

22883CN ~8-batte.r stack 3 in the fo].lowing manner. First, the tube 14 and tlle re~uisite number of carbon elements 12 are assembled together so that the tube 14 is loosely disposed within the central openings in the elements 12 and loosely suxrounded by the elements 12. The porous separator 8 and the lithium anode 7 (within the grid 11) are then wrapp2d in succession around the tube/carbon element clssembly~
The resulting assembly.so formed is then placed into.the :
housing 2 of the cell on top of the insula.tor 6. The -tube 14 at this time is in its non-expanded position. A tool 30 as shown in FIG. 4 and including an elongated tapered rod 31 having an integral spherical ball 32 at its end is then used to expand the tube 14. The spherical ball 32 has a diameter larger than the non-expanded diametex o~
the tube 14 but approximately equal to the desired final expanded diameter of the tube 14. A holder unit 34 loosely carried on the rod 31 is placed and held on top of ::
the above-described assembly, and the rod 31 is progressively advanced down through and along -the opening in the tube 14 as generally indicated in FIG. 5, causing the tube 14 to expand outwardly permanently and physically contact adjoining interior wall portions of the carbon elements 12. The action of the tool 30, together with the confinement of the other parts of the battery stack 3 by the housing 2, results in a close physical union between the tube 14 and the array of carbon elements 12. Once the above-described sxpansion operation has been completed, and with the holder 34 stil]. held on top of the battery stack 3, the rod 31 is withdrawn completely from the tube 14.
Once the battery stack 3 has been assembled as . described hereinabove, and once the electrolyte solution 5 (e.g., cathodelectrolyte solution) has been added to the assembled cell 1, -the electrolyte solution i.s able to pass through the openings 20 and the widened slit in the tube 14 and permeate both the carbon elements 12 and the porous . . :
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22883CN ~9-separa-~.:or ~. In addition, the electrolYte solution causes the carbon elements 12 to eY~pand outwardly, or swell (by up to twenty percent), thereby ~illing the openings 20 in the tube 14 with constituent particles of the carbon elements and es-tablishing an even greater physical perma-nent union between the tube 14 and t'ne array o~ carbon elements 12 and also resulting in a more solid, compact, tight bat-tery stack 3 within the cell 1. Further, by virtue of the electrolyte channels in the elements 12, the electrolyte solution is able to penetrate the carbon elements 12 and contact interior cathodic particles, thereb-y providing substantial active sur.'~ace areas ~or increasing the rate capability and cell discharge capaci-ty of the cell 1. During the discharge o~ the cell 1, the tube 1~1 electrically contacts the interior portions o~ the carbon elements 12 to function as a current collector.
The battery stack 3 as described hereinabove, includ-ing the cathode current collector electrode structure 9,.
is disclosed and claimed in the aforementioned co-pending application No. 376,101.
While there has been descri.bed what is considered to be a preferred method o~ the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the invention as called for in the appended claims.

' ~ :

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for assembling a carbon cathode structure for an electrochemical cell, comprising the steps of:
arranging a selected number of individual porous carbon elements, each having an opening extending therethrough defining an interior wall portion, within and relative to a housing for an electro-chemical cell and also relative to an elongated metal current collector so that the current collector is loosely disposed within and along the openings in the carbon elements and the carbon elements loosely surround the current collector in a stacked array within the housing of the cell, said current collector being a hollow elongated metal tube having a central opening along its length and further being permanently expandable and being initially in a non-expanded state in which it is spaced from the interior wall portions of the stacked array of carbon elements, said current collector further having a plurality of openings formed therein along its length; and expanding the elongated current collector outwardly from its initial non-expanded state to a perma-nently expanded state by an amount to cause the current collector to make direct physical contact with the interior wall portions of the stacked array of carbon elements thereby to secure the array of carbon elements to the current collector, said step of expanding the current collector comprising the steps of:
inserting and progressively advancing a tool into and along the central opening of the elongated current collector tube to permanently expand the tube outwardly to cause the expanded tube to make direct physical contact with the interior wall portions of the array of stacked carbon elements; and withdrawing the tool from the opening in the current collector.

2. A method in accordance with claim 1 wherein:
the porous carbon elements arranged to surround the current collector each comprise a plurality of compressed semi-rigid porous carbon conglomerates.

3. A method in accordance with claim 2 wherein:
the porous carbon elements are of like size and shape and are arranged in the stacked array directly on top of each other.

4. A method in accordance with claim 3 wherein:
the porous carbon elements are of an annular configu-ration.

5. A method in accordance with claim 3 wherein:
the elongated current collector tube is generally cylindrical and has a slit along its length defining a generally C-shaped cross section for the tube;
the openings in the carbon elements are circular; and the tool employed to expand the current collector tube includes a tube-expanding portion of a size greater than the diameter of the current collector tube in its non-expanded state, the size of said tube-expanding portion being selected to sufficiently permanently expand the current collector tube outwardly to make direct physical contact with the interior wall portions of the stacked array of carbon elements.

6. A method in accordance with claim 5 wherein:
the tube-expanding portion of the tool is of a generally spherical configuration.

7. A method for assembling an electrochemical cell comprising the steps of:
arranging a selected number of individual porous carbon elements, each having an opening extending therethrough defining an interior wall portion, relative to an elongated hollow metal current collector so that the current collector is-loosely disposed within and along the openings in the carbon elements and the carbon elements loosely surround the current collector in a stacked array, each of said carbon elements including a network of electrolyte-conducting channels therein for receiving and being permeated by an electrolytic solution and to expand outwardly in response to said electrolytic solution, said current collector being a permanently expandable tube and being initially in a non-expanded state in which it is spaced from the interior wall portions of the stacked array of carbon elements, said current collector tube further having a plurality of openings formed therein along its length;
positioning a porous separator, an anode structure and the assembly of the stacked array of carbon elements and current collector tube relative to each other and within an elongated housing of the electrochemical cell with the anode structure being in contact with the porous separator and the porous separator being in contact with the assem-bly of the stacked array of carbon elements and the current collector tube;
expanding the current collector tube outwardly against the other aforesaid components or the cell to cause the current collector tube to make direct permanent physical contact with the interior wall portions of the stacked array of carbon elements thereby to secure the array of carbon elements to the current collector tube, said step of expanding the current collector tube comprising the steps of:
inserting and progressively advancing a tool into and along the central opening of the elongated current collector tube to permanently expand the tube outwardly to cause the expanded tube to make direct physical contact with the interior wall portions of the array of stacked carbon elements; and withdrawing the tool from the opening in the current collector tube; and placing an electrolytic solution into the cell in contact with the aforesaid components of the cell:
and within the hollow current collector tube, whereby the electrolytic solution is supplied to the electrolyte-conducting channels of the array of carbon elements directly and by way of the openings in the current collector tube, causing the carbon elements to expand outwardly and fill the openings in the current collector tube with constituent particles thereof thereby permanently locking the array of carbon elements to the current collector tube.

8. A method for assembling an electrochemical cell comprising the steps of:
arranging a selected number of individual porous carbon elements, each having an opening extending therethrough defining an interior wall portion, relative to an elongated hollow metal current collector so that the current collector is loosely disposed within and along the openings in the carbon elements and the carbon elements loosely surround the current collector in a stacked array, each of said carbon elements including a network of electrolyte-conducting channels therein for receiving and being permeated by an electrolytic solution and to expand outwardly in response to said electrolytic solution, said current collector being a permanently expandable tube and being initially in a non-expanded state in which it is spaced from the interior wall portions of the stacked array of carbon elements, said current collector tube further having a plurality of openings formed therein along its length;
positioning a porous separator in contact with the assembly of the stacked array of carbon elements and current collector tube;
positioning an anode structure in contact with the porous separator;
inserting the assembly of the anode structure porous separator, stacked array of carbon elements and current collector tube into an elongated housing of the electrochemical cell;
expanding the current collector tube outwardly against the other aforesaid components of the cell to cause the current collector tube to make direct permanent physical contact with the interior wall portions of the stacked array of carbon elements thereby to secure the array of carbon elements to the current collector tube, said step of expanding-the current collector tube comprising the steps of:
inserting and progressively advancing a tool into and along the central opening of the elongated current collector tube to permanently expand the tube outwardly to cause the expanded tube to make direct physical contact with the interior wall portions of the array of stacked carbon elements; and withdrawing the tool from the opening in the current collector tube; and placing an electrolytic solution into the cell in contact with the aforesaid components of the cell and within the hollow current collector tube, whereby the electrolytic solution is supplied to the electrolyte-conducting channels of the array of carbon elements directly and by way of the openings in the current collector tube, causing the carbon elements to expand outwardly and fill the openings in the current collector tube with constituent particles thereof thereby permanently locking the array of carbon elements to the current collector tube.

9. A method in accordance with claim 8 wherein:
the porous carbon elements arranged to surround the current collector each comprise a plurality of compressed semi-rigid porous carbon conglomerates defining a network of electrolyte-conducting channels.

10. A method in accordance with claim 9 wherein:
the porous carbon elements are of like size and shape and are arranged in the stacked array directly on top of each other.

11. A method in accordance with claim 9 wherein:
the porous carbon elements are of an annular configu-ration.

12. A method in accordance with claim 8 wherein:
the elongated current collector is a generally cylindrical tube and has a slit along its length defining a generally C-shaped cross section for the tube;
the openings in the carbon elements are circular; and the tool employed to expand the current collector tube includes a tube-expanding portion or a size greater than the diameter of the current collector tube in its non-expanded state, the size of said tube-expanding portion being selected to perma-nently expand the current collector tube outwardly by a sufficient amount to make direct physical contact with the interior wall portions of the stacked array of carbon elements.

13. A method in accordance with claim 12 wherein:
the tube-expanding portion of the tool is of a generally spherical configuration.

14. A method in accordance with claim 8 wherein:
the porous carbon elements arranged to surround the current collector are of an annular configuration and each comprise a plurality of compressed semi-rigid porous carbon conglomerates defining a network of electrolyte-conducting channels; and the anode structure and porous separator are gener-ally cylindrical in configuration and are arranged concentrically with each other and with the array of carbon elements and current collector.

15. A method in accordance with claim 14 wherein:
the anode structure includes an oxidizable alkali metal; and the electrolytic solution includes a reducible soluble cathode and an electrolyte solute dissolved in the soluble cathode.

16. A method in accordance with claim 15 wherein:
the oxidizable alkali metal of the anode structure is lithium;
the reducible soluble cathode of the electrolytic solution is thionyl chloride; and the electrolyte solute of the electrolytic solution is lithium tetrachloroaluminate.