CA1155918A

CA1155918A - Electrochemical cell

Info

Publication number: CA1155918A
Application number: CA000376101A
Authority: CA
Inventors: Cyril Morgan; Franz Goebel
Original assignee: GTE Products Corp
Current assignee: Osram Sylvania Inc
Priority date: 1980-04-29
Filing date: 1981-04-23
Publication date: 1983-10-25
Also published as: JPS57500533A; EP0050631A1; WO1981003243A1; US4347293A; EP0050631A4

Abstract

ELECTROCHEMICAL CELL
ABSTRACT OF THE DISCLOSURE
A primary electrochemical cell having a carbon current collector cathode structure of improved design The electrochemical cell includes an elongated housing containing an electrolyte solution and a battery stack in contact with the electrolyte solution. The battery stack includes a concentric arrangement of an anode, a porous separator, and a carbon current collector cath-ode structure. The carbon current collector cathode structure in accordance with the invention includes a vertical stacked array of annular-shaped porous carbon elements having coaxially -aligned openings therein.
An elongated, hollow, metal current collector tube having a large number of small openings formed therein for its entire length is disposed within and along the openings in the array of carbon elements and in direct physical contact with the carbon elements. The electrolyte solution in the cell is supplied directly to the array of carbon elements and also by way of the openings in the current collector tube. The carbon elements have a network of electrolyte-conducting channels therein and respond to the electro-lyte solution received thereby to swell or expand out-wardly against the porous separator and anode. As a result, constituent particles of the carbon elements fill the openings in the current collector tube, thereby permanently locking the array of carbon elements to the tube.

Description

FLECTR_CHE I AL CELL
CROSS-REFERENCE TO REL~TED APPI,ICATION
_ _ _ . _ _ _ In co-pendiny appllca-tion numher 376,051-1, filed concurrently herewi-th in the names of Franz Goebel and Ibsen R. Hansen, and entitled "METHOD FOR ASSEl~LING
AN ELECTROCHEMICAL CELL", there is disclosed and claimed a method for assembling a battery stack as utilized within an elec-trochemical cell as disclosed and claimed in the present application.
BACKGROUND OE THE INVENTIO~I
The present invention relates to an electrochemical cell and, more particularly/ to a primary electrochemical cell having a carbon cathode structure of improved design. - -Primary elec-trochemical cells are utilized for a wide variety of applications and are commonly available in a large assor-tmen-t of sizes and shapes. Furthermore, a number of electrochemical systems are known for incorporation in-to such primary electrochemical cells.
Many of these electrochemical cells utilize a carbon cathode structure. By way of example, in U.S. Patent~
No. 4,060,668, in the name of Franz Goebel and assigned to GTE Laboratories Incorporated, -there is disclos~d an electrochemical system includin~ an anode, a carbon :25 current collector cathode structure, and an electro-lyte solution in contact with the anode and the carbon current collector ca-thode structure. The carbon current collector cathode structure employed in -this eIectro-chemical system i.ncludes a preformed porous cylindrical carbon s-l:ructure of a speci.fied length (as determined by the si~e of the cell), and a twlsted metal cathode curren-t collector impressed in-to and alon~ the carbon -struc-ture. Th~: porous carbon structure comprises an a~c~re~ation of a large number o~ porous semi-ri.~:id ~, : . . ..

: ' :', ~L ~55~8 A ) ~ 2~1 2 globul.~ ich are pressed together in a manner to define a multi-plicity of eLec.-rolyt2 channe1.s. By virtue bE these channels, t.he electrolyte solution can diffuse -throu~hout the porous carbon st.ructure and con-tac-t the cathodic particles of the structure.
~hi~.e carbon cathode current collector cathode structures as de.scrlbecl hereinabo~e can be constructed and successfullv employed within electrochemical cells, they nonetheless are . subject to numerolls possibie problems and disadvantages. More part:icularly, the preformecl porou.s carbon structuxes are i.nherently fragile and there~ore diffi.cl1lt to produce in any - reasonable or substantial length (eOgO, 2 inch~s or mor~
without breaklng or fallin~ apart. E'ur-ther even when a carbon struc1ure is successfullv formed to t11e desired length, the subséque11t act of irnpressin~ a metal cathode current collector into the preformed carbon structure, either by twlsting or.
forciny the metal cathode current collector longitudi.nal:ly .into the preformed carbon structure, cannot be contro~.led with yreat accuracy. As a result, the mechanical ancl electrical .:
contact between the twisted metal cathode current collector and the preformed carbon structure may be ina~equate t~
satisfy the str:ingent requirements and specificaticns of the electxochemic~l cell in which such structure is to be used.
BRIEF SU~ ~RY OF THE INVENTIOM
__________ _ Accordingly, the present invention provides a carbon cu.rrent collectox cathode structure or use with an electroi.y-tic solution Orc an electrochemical system of a primary electxochemical cell, said carbon current co]lector cathode structure comprising: a pluralit~ o individual porou~ carbon elements superi.mposed one above the other in a stacked array ancl each havirlg a networ~ of electrolyte- --conductin~ channels formec; therein for receivin~ an e:l.ectrol.~ti.c so:Lution ~y ~hich the carbon element can be permea.ted b~r the elec~rolyt.i.c ~sol.ution, each oE said carbon ele~nents ha~in~ an opening e~tendl'~ complete3y thereth:rough;
and an elongated, hollow, metal current collec-tor tuhe havinc~

,~

. ' ' : , ' ~

1157~59~
r)-~2~3~ 3-a plure.lity o~' opel~incJs iormed therein along its length and posi-tio.rle-l T7itn:in and along the openings in the stacked array of carboll el.ements and in di.rect physical contact with -the porous carbon elements of the stac]ced array, said current co:Llector tu3~e being a~apted to rece:i.ve an electrolytic solution therein and to supply said electrol.ytic solution to the array of s-tacked carbon elements by way o:E the openin~s formed therein whereby the electrolytic solution can perrne2.te the carbon elements by way of the electrolvte-conducting channe.ls formed in the carbon elemen-ts~
The present invention further provides a pri~ary electro~
chemical cell comprising: an elongated housing; a~.d an eleetrochemica]. system containecl within the housing, said electrochem:ical sys-tem comprising: an electrolytic so].ution;
and a battery stack exposed to said el.ec-trolytic soIu~ion, saîd battery s-tack comprlsing: an e].ec-trode in direet contact ~ith the housincJ; a porous separator in direet contact with the electro~e; a plural it~T of i.ndividual. porous carbon elemen-ts supe.rin~posed one ahove the other i.n a stacked array and in direct contact with the separator, each o:E said porous carbon e:Lements havin~ a network of electrolyte-conducting channels formed there;.n for receiving an electrolytic solutlon by ~hich the earbon element can be permeated hy the electro-lytie solution and expand outwardly in response to said electrolytie solution~, each of said carbon elemen-ts further hav.incJ an openi.ng extending completely there-through; and an '~
elongated, hollow, metal current collector tube having a ' :
.plurality of openin~s formed therein along its length and positioned within and alon~ the openings ln the stacked array of carbon elements and in direct physical contact with the porous. carbon elements of the stacked array, said current col.lector tube be:ing adapted to rece:i~Te the el.ectrol~-tic sol.ution thereln ancl :irl conjullction with the electrolytic sollltion other~i.se reeived hy LIIe carhon e].ements, to ~supplV
the~ -.lectro.l.ytic solution i.n tlle tuhe~ to thee axray o.~ st.acked Cc'lrbOn elerne~ntC. hy ~Jay of the openin~s formed in the tube, ~, .

.. , . :

,:
, :.. ~: , I

1 1~5~i ~

whercby t}h~ el--Ac:trolvtic solution recei~ed hy the carh,on ele!nen-ts can p-ermeate the carbon elemerlts by way of the electro'l.yte-conducting channels :Eormed in the earbon elements, said c~.rbon elements respondirlg to t:he electrolytic sol.ution recei~ed thereby to e~pand outwardly against the porous separator and the electrode in contact with the housing and fill the openin~s in the current collector tube ~Jith con.stituent particles -thereof, thereby permanently locking the >
array of carbon e:Lements to the current collector tube~
BRIEF DESCRIPTION OF THE DRAI~IING
~ Some embodiments of the invention will now be described~
by wav of e~a~ple, with reference -to the accomp.-anying drawin~s, in which:
EIG. 1 is an elevational view, partly in cross section, o:E a primary el.ectrochemical cell employing a carbon cathode structure in accordance wi-th the:present invention; and '~
FIGS. 2 ancl 3 are perspective views o~ com~onen-ts employed by t-lle carbon cathode structure in accorclance with the pr'esent inven~:ion.
DET~ ED DE~SCRIPTION OF THE INVENTION
~eferring no~ to E`IG. 1, there is shown a pri..mar~
electrochemical cell 1 in accordance with the present ' invention. As shown in FIG. 1, t'he electrochemical cell l.generally includes an elongated metal casing or houslng ~5 2, for example, of a eylindrical configuration, w.ithin whlch a battery stack 3 i.n accordance with the i.nverltion is disposed. An electrolyte solution 5, `~ ' for example, in the form of a cathodelectrolyte solution, is provided within the interior of the sell 1 to permeate ~:.
various portions of the battery stack 3, in a manner to be describecl in detail he.re.inafter. A suitabIe and preferred fvrm o:E the el.ectrolyte so~-ution 5 ~hich iS
n.-.:ahle wit.h the com~onents of- the 'batterv stack 3 (a r?reEerre.c3.:Eornl o~ ~h:Lch will be clescribed in detail hereinaf-ter), is a eatho(~electrolyte solution includin~
a re~luc:i.ble sol-uble catllode, such as thionyl ehlori.de ~r ~, :
.

~ ~5~gl~
~-228~4 _5_ and an electrolyte solute, such as lithium tetrachlo-roaluminate, dissolved in the thionyl chloride.
The battery stack 3 and the electrolyte solution ~ as discussed hereinabove collectively represent the electrochemical system of the cell 1~ The battery stack 3 in accordance with the invention and as shown in FIG. 1 is insulated from the housing 2 of the cell 1 by a suitable insulator 6 and generally includes a concen-tric 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 may be of an oxidizable active alkaline metal such as lithium, is connected mechanically and electrically to the housing 2 by means of 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. The electrical connection of the anode 7 to the housing 2 establishes the housing 2, which may be of stainless steel, as the negative terminal for the cell 1.
The aforementioned porous separator 8 is employed to electrically isolate the anode 7 from the cathode current collector electrode structure 9 and typically 25 takes the form of a cylindrical sheet of a standard ~
electrically-nonconductive material such as fiberglass.
The aforementioned cathode current collector electrode st~ucture 9 in accordance with the invention generally comprises a plurality of annular, or disc-shape~, porous carbon elements 12 arranged directlyabo~e each other in a vertical stacked array, and an elongated perforated expandable metal tube 14 disposed within circular central openings of the elements 12. The tube 14 is conllected by a thin metal strip 15 spotwelded .

: ~ . , . . -.. . .

5 5 ~ ;~ 8 D-228~ -6--thereto to a positive terminal 16 of the cell 1. The metal strip 15, for example, of nickel, is connected (e.g., spot welded) to the terminal 16 by means of a standard insulative glass or ceramic-to-metal seal 17 provided within an hermetically sea]ed cap 18 of the cell 1.
The plurality of porous carbon elements 12, when used with the aforementioned components and specific materials of the cell 1, act as a cathode current collector and as a catalyst where the reduction of the solvent (-thionyl chloride) in the cathodelectrolyte solution takes place. Each of the elements 12, a preferred form of which is shown in FIG. 2, is pro-duced by compressing together a plurality of discre-te, semi-rigid, porous carbon conglomerates thereby to de~ine 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" (trade ~ar~ Ey ~irtue of t~e ~mall physical size of each of the eléments 12, for example, one inch in diameter and one-half inch thickness for a "D"-sized cell, a stacked array of caxbon elements of any desirable length may be assembled by simply select-ing the required number of elements 12 for the particu-lar size o~ the cell and stackin~ the elements oneatop the other 2S indicated in FIG. 1. For a "D"-sized cell, for example, eight elements 12 would be sufficient.
The use of multiple carbon elements 12 in a stacked array further avoids the ~ragility and breakage problems 30~ associated with the aforedescribed prior art carbon structures in which the carbon structures are one-piece structures, and o~ten of substan-tial length, a~d twisted metal current collector elements are forced or screwed into the carbon structures. Techniques for producing ' ., ': ,: ' . , , P 1 5.~9 1 ~

the conglomerates employed by the carbon elements are described in detail in the aforementioned 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 here-inabove takes the specific form as shown in FIG. 3.
As shown in FIG. 3, the perforated metal tube 14, wh~ch may be of nickel or s-tainless steel, is split along its entire length to define a generally C-shaped cross section and includes a large number of small openings ~0 along its length. The openings 20 may be produced by simple me-tal stamping operations. In assembling the perforated metal tube 14 into the cell 1, the carbon elements 12 are first placed loosely around the tube l~
in its non-expanded state following which the porous separator 8 and the anode 7 (in the grid ll) are wrapped in succession around the tube/carbon element assembly. The complete assembly so formed is then placed into the housing 2 on top of the insulator 6 and the tube 14 is permanently expanded outwardly.
This expansion operation is accomplished by means of a suitable tool (not shown) which :is inserted into the hollow center of the tube 14 and advanced along the entire length of the tube 14 and then withdrawn. As the tube 14 expands outwardly, it establishes a close physical fit or contact with the interior wall portions of the carbon elements ]2 thereby securing the array of carbon elements 12 to the tube 14~ The openings 20 in the tube 14, together with the widened slit in the tube 14, serve to allow the electrolyte solution 5 (e.g., cathodelectrolyte solution) within the cell 1 to permeate and saturate the carbon elements 12, by way of the aforedescribed electrolyte conduc-ting channels 1 ~55~1 8 D-22~84 -~~

formed within thc elements 12, add also to permeate the porous separator ~. In addi-tion, the electrolyte solution causes the carbon elements 12 to expand out-wardly,or swell (by up to twenty percent), thereby fillin~ the openings 20 in the -tube 1~ with constituent particles thereof and establishing a permanent physical union between the tube 1~ and the elements 12. The e~pansion of the carbon elements 12 also result in a solid, compact battery 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, thereby providing substantial active surface areas ~or increasing the rate-capability and cell discharge capacity of the cell 1. During the discharge of the cell 1, the tube 1~ electrically con-tacts the interior portions of the carbon elements 12 to function as a current collector.
Details relative to the method of assemb].y of the battery stack 3, includin~ the assembly of the cathode current collector electrode structure 9, are disclosed and claimed in the aforementioned co-pending applica-tion, number 376,051-1.
Whlle there has been described what is considered 25: to be a preferred embodiment of the invention, it will be apparen-t 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 carbon current collector cathode structure for use with an electrolytic solution of an electrochemical system of a primary electrochemical cell said carbon current collector cathode structure comprising:
a plurality of individual porous carbon elements superimposed one above the other in a stacked array and each having a network of electrolyte-conducting channels formed therein for receiving an electrolytic solution by which the carbon element can be permeated by the electrolytic solution each of said carbon elements having an opening extending completely therethrough; and an elongated, hollow metal current collector tube having a plurality of openings formed therein along its length and positioned within and along the openings in the stacked array of carbon elements and in direct physical contact with the porous carbon elements of the stacked array said current collector tube being adapted to receive all electrolytic solution therein and to supply said electrolytic solution to the array of stacked carbon elements by way of the openings formed therein whereby the electrolytic solution can permeate the carbon elements by way of the electrolyte-conducting channels formed in the carbon elements.

2. A carbon current collector cathode structure in accordance with claim 1. wherein:
each of the plurality of carbon elements comprises a plurality of compressed semi-rigid porous carbon conglomerates defining a network of electrolyte-conducting channels.

3. A carbon current collector cathode structure in accordance with claim 2 wherein:
the plurality of carbon elements are of like size and of annular shape and are superimposed directly on each other.

4. A carbon current collector cathode structure in accordance with claim 3 wherein:
the current collector tube further has a split along its entire length by which electrolytic solution in the tube can be additionally supplied to the array of stacked carbon elements.

5. A primary electrochemical cell comprising: an elongated housing; and an electrochemical system contained within the housing, said electrochemical system comprising:
an electrolytic solution; and a battery stack exposed to said electrolytic solution, said battery stacked comprising:
an electrode in direct contact with the housing; a porous separator in direct contact with the electrode;
a plurality of individual porous carbon elements superimposed one above the other in a stacked array and in direct contact with the separator, each of said porous carbon elemtns having a network of electrolyte-conducting channels formed therein for receiving an electrolytic solution by which the carbon element can be permeated by the electrolytic solution and expand outwardly in response to said electrolytic solution, each of said carbon elements further having an opening extending completely therethrough; and an elongated. hollow, metal current collector tube having a plurality of openings formed therein along its length and positioned within and along the openings in the stacked array of carbon elements and in direct physical contact with the porous carbon elements of the stacked array, said current collector tube being adapted to receive the electrolytic solution therein and in conjunction with the electrolytic solution otherwise received by the carbon elements, to supply the electrolytic solution in the tube to the array of stacked carbon elements by way of the openings formed in the tube, whereby the electrolytic solution received by the carbon elements can permeate the carbon elements by way of the electrolyte-conducting channels formed in the carbon elements, said carbon elements responding to the electrolytic solution received thereby to expand outwardly against the porous separator and the electrode in contact with the housing 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.

6. A primary electrochemical cell in accordance with claim 5 wherein:
each of the plurality of carbon elements comprises a plurality of compressed semi-rigid porous carbon conglomerates defining a network of electrolyte-conducting channels.

7. A primary electrochemical cell in accordance with claim 6 wherein:
the plurality of carbon elements are of like size and of annular shape and are superimposed directly on each other.

8. A primary electrochemical cell in accordance with claim 7 wherein:
the current collector tube further has a slit along its entire length by which electrolytic solution in the tube can be additionally supplied to the array of stacked carbon elements.

9. A primary electrochemical cell in accordance with claim 8 wherein:
the electrode in contact with the housing and the separator are generally cylindrical in configuration and are arranged concentrically with each other and with the array of carbon elements and current collector tube.

10. A primary electrochemical cell in accordance with claim 9 wherein:
the electrode in contact with the housing is an anode structure including an oxidizable alkaline metal; and the electrolytic solution includes a reducible soluble cathode and an electrolyte solute dissolved in the soluble cathode.

11. A primary electrochemical cell in accordance with claim 10 wherein:
the oxidizable alkaline 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.