GB2121596A

GB2121596A - Feedthrough terminal

Info

Publication number: GB2121596A
Application number: GB08309197A
Authority: GB
Inventors: Thomas David Kaun
Original assignee: US Department of Energy
Current assignee: US Department of Energy
Priority date: 1982-05-28
Filing date: 1983-04-05
Publication date: 1983-12-21
Also published as: GB2121596B; CA1191890A; FR2527840A1; DE3318307A1; JPS58216357A

Abstract

A feedthrough terminal for a high power electrochemical storage cell providing low resistance coupling to the conductive elements therein while isolating the terminal electrode from the highly corrosive environment within the cell is disclosed. A large diameter, cylindrical copper electrode 40 is enclosed in a stainless steel tube 42 with a BN powder feedthrough seal 52 maintained around the stainless steel tube by means of facing insulative bushings 50A,50B and an outer sleeve 48. One end of the copper conductor is silver-brazed directly to a flat, "butterfly" bus bar 18 within the cell, with the adjacent end of the surrounding outer feedthrough sleeve welded to the bus bar. A threaded seal is fixedly positioned on a distal portion of the stainless steel tube immediately adjacent the distal insulative bushing so as to compress the feedthrough seal in tight fitting relation around the stainless steel tube in providing a rugged, leak-proof electrical feedthrough terminal for the power cell. <IMAGE>

Description

SPECIFICATION Feedthrough terminal for high power This invention relates generally to electrochemical storage cells and more particularly is directed to a feedthrough terminal for a high specific power storage cell containing highly corrosive internal reactants.

In pursuit of cheaper, more efficient sources of energy, a substantial amount of work is being done in the development of high temperature, high specific power cells. These energy sources are generally rated in terms of the ratio of power output to weight, with high specific power cells generally considered to be those which are capable of providing more than 180 watts per kg. These cells typically include alkali metals and their alloys as negative electrodes and chalcogens or metal chalcogens as positive electrode materials. These cells also typically utilize a highly corrosive molten salt electrolyte and operate at high temperatures. Separation betvveen cell components is maintained by chemically unreactive, high temperature resistant, electrically inert materials.

While large amounts of energy may be generated in these electrochemical cells, great care must be taken in confining these highly reactive materials in the cell and isolating from these materials the electrical conductors used for removing the electrical energy thus generated in these cells. Isolating these conductors from the corrosive materials within the cell is essential for cell operation and reliability since these conductive elements themselves are generally highly susceptible to damage and deterioration when exposed to these corrosive materials. In addition, electrical coupling between the terminal conductors and the electrodes within a cell must possess high electrical efficiency for maximizing cell output.In prior art multiplate cells of the general configuration as described above, more than 50% of the cell's overall resistance is attributed to electrical connections external to the cell's internal electrodes.

The hostile environment internal to high specific power cells has imposed other demands on their design. For example, internal cell temperatures during operation may rise substantially. This not only affects the resistance of the cell's terminals, which of course is to be minimized for optimum performance, but also affects the physical configuration of the outer cell components in terms of their expansion and contraction at these extreme temperatures. Thus, the cell designer seeks to incorporate a terminal conductor of increased conductivity at elevated temperatures, such as by increasing the cross sectional area of the conductor. But increasing terminal conductor size also increases the surface area of the cell in the vicinity of the terminal from which the hot electrolytes in the cell may escape.

One way of course to avoid these problems is by utilizing exotic materials which are highly inert and structurally strong. However, this approach would eliminate any possibility of widespread commercial use of this type of energy source.

Still another design goal in high specific power cells necessary for their widespread acceptance and usage is that they must be structurally rugged and capable of being utilized in a variety of environments. For example, one potential field of use for these new electrochemical cells is that of electrical vehicle propulsion. These cells are particularly attractive in this field because of their high energy output per unit weight (specific energy). Thus, energy cells of this type should ideally be capable of operating in an automobile environment.

The following patents illustrate developments in the general field of high specific power electroche mical cells. Arntzen, U.S. Patent No. 4,110,517, discloses an electrochemical cell employing frangible forms of boron nitride and other ceramic materials as an electrically insulative cell separator.

Vissers et al. U.S. Patent No. 4,029,860, describes a compartmented or honeycombed structure used as a current collector and to support electrochemically active material within the electrode of an eiectrochemical cell. Kaun, U.S. Patent No.4,011,374, describes the use of a thermosetting resin as a moldable material into which electrochemically active material is blended for preparing electrodes. Cooper et al, U.S. Patent No. 4,087,905 and Mathers et al, U.S.

Patent No. 4,086,396 disclose an electrochmeical cell including a layer of powdered electrically insulative material between electrodes of opposite polarity.

In addition, Kaun et al., U.S. patent application Serial No. 148,312, allowed June 1981,entitled "Electrode for Electrochemical Cell", discloses an electrode structure for a secondary electrochemical cell which includes a rigid electrically conductive metal sheet with perforated openings therein defining a compartment containing electrochemically active material. The enclosure can be assembled as first and second trays each with a rigid sheet of perforated electrically conductive metal at major side surfaces with the positive and negative electrodes arranged in an alternating array with interelectrode separators inserted therebetween. The terminals extend through and are electrically insulated from a top wall of the cell's housing by insulative feed-throughs.Electrical bus bars are spaced lengthwise from one another within the cell housing and are each connected to individual electrodes by respective electrical conductors.

Therefore, in view of the above it is an object of the present invention to provide an improved electrical terminal structure for a high specific power cell.

It is another object of the present invention to provide a feedthrough terminal for a high energy electrochemical cell offering a low resistance path to the power generating electrical components therein in enhancing cell energy recovery.

Still another object is to provide an electrically conductive feedthrough path for an electrochemical power cell containing electrochemically active materials for confining those materials therein while isolating the conductor from the corrosive/destructive effects of these materials.

A further object is to provide a compact, rugged, low cost easily installed feedthrough terminal for a high specific power electrochemical cell containing a flat bus bar coupled to a plurality of current collector elements within the cell.

A still further object of the present invention is to provide a temperature compensating feedthrough terminal for a high specific power cell for maintaining the cell in a sealed condition even at extremely high operating temperatures while providing a low resistance electrical path for the cell.

The present invention contemplates a conductive feedthrough terminal for a high specific power electrochemical storage cell providing low resistance coupling to the cell's internal electrodes and isolation of the conductive terminal electrode from the highly corrosive materials within the power cell.

A large diameter, cylindrical copper electrode is sealably enclosed in a stainless steel tube extending through an opening in the cell's cover assembly and over a portion of the length of the copper electrode.

A BN powder feedthrough seal is provided in sealing relation coaxially around the stainless steel tube by means of facing proximal and distal insulative bushings and an outerfeedthrough sleeve also coaxially positioned with respect to the stainless steel tube. One end portion of the copper conductor is silver-brazed directly to a flat, "butterfly" bus bar within the cell, with the adjacent end of the surrounding outer feedthrough sleeve securely welded to the same bus bar. A threaded seal is fixedly positioned on a distal portion of the stainless steel tube immediately adjacent the distal insulative bushing so as to compressively confine the BN powderfeedthrough seal in providing a rugged, leak-proof electrical feedthrough for the terminal conductor.

The appended claims set forth those novel features believed characteristic of the invention.

However, the invention itself, as well as further objects and advantages thereof will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures in which: Figure 1 is a partially cut away perspective view of a high specific power electrochemical cell having a feedthrough terminal in accordance with the present invention; Figure 2 is a cross-sectional view of the feedthrough terminal for a high specific power cell of the present invention as shown in Figure 1; and Figure 3 is a sectional view taken along line 3-3 in Figure 2 showing the connection between the feedthrough terminal and a bus bar within the power cell.

Referring to Figure 1, there is shown a high specific power cell 10 for converting electrochemical energy into an electrical output. The power cell includes a housing 12 comprised of a plurality of coupled lateral walls, a base (now shown) and a cover assembly 54 (shown partially cut away).

Included in housing 12 are a plurality of plate-like alternately spaced negative and positive electrodes 28,30. The rectilinear shaped housing 12 includes at least two end walls 19 and at least two side walls 21.

The electrodes are aligned as illustrated in an alternating array of negative and positive electrodes each separated by an insulator 26. Insulator 26 is a frangible, porous electrically insulative material spaced between immediately adjacent electrodes of opposite polarity and is comprised of a felt-like composition of boron nitride (BN). In addition, a layer of the BN insulator 26 is positioned between the ends of the electrode array and the immediately adjacent, respective side walls 19 of the power cell's housing 12.

Each electrode includes an outer surface of electrically conductive material which includes a plurality of openings 22. The electrochemically active material 25 contained within the negative and positive electrodes 28, 30 may be of any suitable type to provide this alternativng electrical configuration.

Solid alloys of alkali metals or alloys of alkaline earth metals containing alloying materials of aluminum, silicon, magnesium and combinations thereof are utilized in the instant power cell. In a preferred embodiment of the cell, the negative electrodes 28 are comprised of an Li-Al alloy while the positive electrodes 30 are comprised of FeS. Cells containing the various alkaline metal alloys compatible with power cell 10 are well known in the art and described in the above cited patents as well as being extensively described in various other publications in the literature.

In the illustrated alternating array of electrodes, an odd number of electrodes is included within housing 12. The center electrode is of like polarity with that of the end electrodes in the spaced array of negative and positive electrodes 28,30. The end electrodes, which may be either positive or negative in potential, are of like polarity which minimizes the harmful consequence of insulation failure between the end electrodes 28 and the side walls 21 of housing 12.

Each negative electrode 28 in the power cell is coupled by means of a negative electrode terminal 16 to a negative bus bar 20. Similarly, each positive electrode 30 is coupled to a positive bus bar 18 by means of a positive electrode terminal 17. The positive and negative bus bars 18 and 20 are positioned within the housing 12 of the power cell immediately adjacent to the cover assembly 54 thereof. Each bus bar is comprised of nickel metal in a preferred embodiment. Nickel is well suited for the present application in that it possesses relatively high conductivity at high temperatures while being relatively inert to the highly corrosive environment within the power cell. The "butterfly" design of the bus bar plates shown in Figures 1 and 3 offers a wide connecting-weld area to provide a low resistance connection of the electrode terminals to an associated bus bar. The connections between negative bus bar 20 and each negative electrode terminal 16 and positive bus bar 18 and each positive electrode terminal 17 are made directly beneath respective negative and positive cell terminals 24, 14to minimize the current path between corresponding cell electrodes and terminals. In addition, the upper, flat surfaces of the respective bars provide a convenient and efficient means for coupling between respective bus bars and cell terminals.

In accordance with the present invention, Figure 1 shows a partially cut away view of a feedthrough/ positive cell terminal 14 for a high power cell in accordance with the present invention. Similarly, Figure 2 shows a cross sectional view of the feedthrough/positive cell terminal 14 depicted in Figure 1. The present invention is not limited to a positive cell terminal application, but may equally as well form the negative terminal of a high power cell.

Its principle advantages of providing a low resistance path from the power cell's bus bar and internal electrodes to an exterior terminal while maintaining the cell in a highly sealed condition may be used in the structure and installation of either a positive or negative cell terminal in a power cell as shown in Figure 1.

The cell terminal 14 includes an innermost positive terminal electrode 40 which is comprised of copper and is cylindrical in shape in a preferred embodi ment. The lower end portion, or base, of the positive terminal electrode 40 is physically and electrically connected to the upper, flat surface of the positive bus bar 18 by means of silver-brazing. As shown in Figures 2 and 3, the silver-brazed junction 56 extends over the entire base of the positive terminal electrode 40 forming a low resistance, structurally strong coupling between the positive terminal electrode 40 and the positive bus bar 18. Positioned immediately adjacent and coaxially with respect to the positive terminal electrode 40 is a hollowed-out, cylindrical terminal body 42.

The terminal body 42 extends over a portion of the length of the positive terminal electrode 40, allowing a portion of the distal end thereof with respect to the power cell to be electrically connected to an electrical lead (not shown) of the device to which the electrical energy is being provided. The terminal body 42 is positioned around the positive terminal electrode 40 in a tight fitting relation. The proximal end of the terminal body 42 is TIG welded via washer 60 to the upper, flat surface of the positive bus bar 18. The washer 60 is first welded to the base of terminal body 42 and then to the upper flat surface of bus bar 18 at 58. This couplinag method and configuration represents a substantial structural improvement over the direct fillet-weld of the lower portion of the terminal body 42 to the positive bus bar 18 previously utilized.

In a preferred embodiment, the terminal body is comprised of stainless steel. The surrounding stainless steel terminal body 42 thus isolates the copper electrode from the highly corrosive components within power cell 10. The welded junction thus formed also enhances the structural integrity of the terminal installation.

A ram-type feedthrough configuration is achieved by forcing (ramming) the terminal body 42 through a doughnut-shaped lower bushing SOB. The lower bushing SOB is positioned at the lower, or proximal, end portion of terminal body 42 and in direct contact with the washer 60 which is welded to the upper surface of the positive bus bar 18. As shown in Figure 2, the lower bushing SOB extends through the cover assembly 54 and just beyond the outer suface of the power cell.The circular aperture in the cover assembly 54 is in tight fitting relation to the lower bushing SOB. With the combination of the positive terminal electrode 40, the terminal body 42, and the lower bushing SOB positioned in a circular aperture in the cover assembly 54, an outer sleeve, or feedthrough housing, 48 is positioned in tight fitting relation to the outer periphery of the lower bushing SOB. An insulating material 52 is then inserted between the immediately adjacent portions of the terminal body 42 and the feedthrough housing 48. In a preferred embodiment, the insulating material 52 is comprised of a BN powder deposited in the annular space defined by terminal body 42 and feedthrough housing 48 and the ceramic bushings are comprised of BeO.

An upper bushing 50A is then positioned immedi ately adjacent the upper end portion feedthrough housing 48 and in tight fitting relation between the terminal body 42 and the feedthrough housing 48.

The insulating material 52 is then confined in the annular space defined by upper and lower bushings 50A, SOB and the terminal body 42 and feedthrough housing 48. The insulative seal 52 may then by hydraulically compressed within the annular space by conventional means with the upper and lower insulating bushings 50A, SOB fixedly positioned along the length of the terminal body 42 by means of a snap ring (not shown) or a ring welded in place along the length of the terminal body 42. The upper end portion of terminal body 42 includes a threaded portion 43 over which a spacer, or washer, 46 is positioned followed by the threaded positioning of a coupler, such as a nut, 44 thereon.By tightening the threaded coupler 44 on the terminal body 42, the washer 46 and upper bushing 50A may be displaced downward so as to tightly confine and compress the powder seal 52. Thus, the compression of the annular-shaped powder seal 52 is accomptished by means of a fastner such as a nut 44 rather than by means of a bushing containing the powder seal attached to the cell housing. This permits the seal to remain tight as the terminal electrode 40 and bushings 50A, 50B expand, possibly differentially, with increasing cell operating temperatures.In addition, by positioning the powder seal 52 in direct contact with upper and lower ceramic bushings 50A, SOB, irregularities in the surfaces thereof, e.g., offsets, indents, steps, etc., are accommodated and the risk of the ceramic insulator cracking is substantially decreased. Finally, the terminal electrode 40 can conveniently be displaced from the lower bushing SOB without incorporating elongated electrical insulation extending around the terminal electrode 40 as in prior implementations. The configuration of the terminal of the present invention thus provides an elongated, smooth extension from the power cell and avoids the use of fittings which may become crimped thus forming small crevices or spaces in which dirt or dust may build up eventually resulting in the shorting out of the power cell.

There has thus been described a low resistance, feedthrough terminal for a high specific power electro-chemical cell providing a highly secure seal for confining the highly corrosive reactants within the cell while isolating the terminal's conductor from those highly corrosive reactants. The confinement under high compression of a powdered seal reduces the tendency for the terminal's insulators to crack under high temperature stress while utilizing a low resistance conductor of high cross sectional area efficiently coupled to the electrical components within the cell.

While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

1. In an electrochemical cell having a housing with an aperture therein and an electrode located within said housing, a feedthrough electrical terminal positioned in said aperture comprising: an elongated electrical conductor positioned within said aperture so as to extend through said housing, said electrical conductor having a first end portion electrically coupled to said electrode; a sleeve coaxially disposed around and in tight fitting relation to said electrical conductor and extending over a portion of the length thereof and through said aperture, said sleeve having a first end portion thereof sealingly coupled to said electrode; an insulative seal coaxially disposed around said sleeve and extending over a portion of the length threof and through said aperture; and compressive sealing means coaxially disposed around said insulator and said sleeve and abutting an outer portion of said housing immediately adjacent said aperture for maintaining said insulative seal in tight fitting relation around said sleeve.

2. The electrical terminal of claim 1 further comprising a conductive bus bar positioned within said electrochemical cell and connected between said electrical conductor and said electrode.

3. The electrical terminal of claim 2 wherein said electrochemical cell includes a first plurality of positive electrodes and a second plurality of negative electrodes and wherein said conductive bus bar is comprised of nickel and includes a plurality of outer edges and inner slots for metallurgically bonding to a flat surface of each of said first plurality of positive electrodes.

4. The electrical terminal of claim 1 wherein said sleeve is more electrochemically inert and has a lower conductivity than said electrical conductor.

5. The electrical terminal of claim 4 wherein said electrical conductor is comprised of copper and said sleeve is comprised of stainless steel.

6. The electrical terminal of claim 5 wherein the first end portion of said electrical conductor is coupled to said conductive bus bar by means of silver brazing and the first end portion of said sleeve is welded to said conductive bus bar.

7. The electrical terminal of claim 6 further including sealing means fixedly coupled between the first end portion of said sleeve and said conductive bus bar, said sealing means including an aperture therein through which said electrical conductor extends when coupled to said conductive bus bar in sealed relation thereto.

8. The electrical terminal of claim 1 wherein said compressive sealing means exerts a tensile force upon said sleeve along the axis of said electrical conductor toward said housing.

9. The electrical terminal of claim 1 wherein said insulative seal is comprised of an inert powder confined between said sleeve and said compressive sealing means.

10. The electrical terminal of claim 9 wherein said inert powder is boron nitride.

11. The electrical terminal of claim 1 wherein said compressive sealing means includes distal and proximal insulating bushings positioned immediately adjacent and on each side of said insulative seal and along said sleeve and a cylindrical housing in sealed contact with said distal and proximal insulating bushings so as to define an annular space coaxially positioned around said sleeve for confining said insulative seal therein.

12. The electrical terminal of claim 11 wherein said distal and proximal bushings are comprised of a ceramic material and wherein said proximal bushing is sealably coupled to the portion of said housing defining said aperture.

13. The electrical terminal of claim 12 wherein said compressive sealing means further includes locking means variably positioned along said sleeve in contact with said distal bushing for urging said distal bushing toward said housing in compressing said insulative seal and maintaining said insulative seal in tight fitting relation around said sleeve.

14. The electrical terminal of claim 13 wherein the outer, distal portion of said sleeve is threaded and said locking means includes a threaded nut and washer combination whereby rotation of said nut on said sleeve displaces said washer along said sleeve for tightening said outer bushing against and increasing the compressive force upon said insulative seal.

15. In an electrochemical cell having a housing including an upper panel having a circular aperture therein, said housing containing a plurality of electrochemical elements for generating electrical energy, a feedthrough electrical terminal comprising: an elongated, cylindrical, solid conductor positioned within said aperture and extending therethrough and electrically coupled to at least one of said electrochemical elements; an inner sleeve extending through said aperture and coaxially disposed in tight fitting relation around said conductor, said sleeve including a proximal end portion fixedly connected to at least said one electrochemical element and spaced so as to isolate said conductor from the internal portion of said electrochemical cell; ; an outer sleeve coaxially disposed in spaced relation around said inner sleeve so as to define an annular space therebetween, said outer sleeve including a proximal end portion positioned in abutting contact with the outer surface of said upper panel immediately adjacent said aperture; an insulative seal disposed in and extending over a portion of said annular space; and structural means disposed on each side of said insulative seal in said annular space for confining said insulative seal therein, said structural means including a portion thereof linearly displaceable along said inner sleeve so as to compress said insulative seal within said annular space.