WO1999005896A1

WO1999005896A1 - Hermetic seal for an encased power source

Info

Publication number: WO1999005896A1
Application number: PCT/US1998/015277
Authority: WO
Inventors: Thomas A. Turgeon
Original assignee: Minnesota Mining And Manufacturing Company; Hydro-Quebec Corporation
Priority date: 1997-07-25
Filing date: 1998-07-23
Publication date: 1999-02-04
Also published as: AU8509898A; WO1999005896A9

Abstract

An apparatus and method for sealing a perimeter of a hole defined in a planar surface. A hermetic seal for sealing a hole provided in the cover of a housing includes a first seal body contacting a first surface of the cover and has a central passage. The first seal body includes a collar that extends through the hole in the cover and has an outer surface which bears against an inner surface of the hole. The collar has an inner surface that tapers away from the central passsage. A second seal body of the hermetic seal contacts the second surface of the cover and has a central passage. The second seal body includes a groove having an inner surface tapering toward the central passage. Upon engagement of the first and second seal bodies, a portion of the collar is received by the groove such that the tapering surface of he collar bears against the tapering surface of the groove. A conduit passes through the respective central passages of the first and second seal bodies and includes a first end, a second end opposing the first end, and a flange extending outwardly from the first end which contacts the first seal body. A fastener is coupled to the second end of the conduit and produces a compressive force on the first and second seal bodies sufficient to cause a portion of the outer surface of the collar to cold flow against the inner surface of the hole thereby sealing the perimeter of the hole in the cover.

Description

HERMETIC SEAL FOR AN ENCASED POWER SOURCE

FIELD OF THE INVENTION

This invention relates generally to hermetic seals, and more particularly, to a hermetic seal for use with an encased power source .

BACKGROUND OF THE INVENTION

The demand for new and improved electronic and electro-mechanical systems has placed increased pressure on the manufacturers of energy storage devices to develop battery technologies that provide for high energy generation in a safe, low-volume package. A number of advanced battery technologies have recently been developed, such as metal hydride (e.g., Ni-MH) , lithium-ion, and lithium polymer cell technologies, which would appear to provide the requisite level of energy production and safety margins for many commercial and consumer applications. Such advanced energy storage systems, however, often employ power sources that operate properly only in an air free, moisture free environment .

In applications in which power sources are encased in a housing, it is necessary to permit electrical leads and other lines to pass through the housing in order to provide external connectivity with the power sources and other components disposed in the housing. Such passages in the housing provide an access pathway through which air and moisture my pass into the housing. Also, gaseous and particulate contaminants may be passed into and out of the housing through such passages .

There is a general need for a simple and low- cost hermetic seal that can effectively seal an opening provided in a planar surface, such as a plate or a housing. There exists a particular need in the battery manufacturing industry for an apparatus and method for effectively sealing an access passage provided in the housing of a power generating system. The present invention fulfills these and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method for sealing a perimeter of a hole defined in a planar surface. A hermetic seal for sealing a hole provided in the cover of a housing includes a first seal body contacting a first surface of the cover and has a central passage. The first seal body includes a collar that extends through the hole in the cover and has an outer surface which bears against an inner surface of the hole. The collar has an inner surface that tapers away from the central passage. A second seal body of the hermetic seal contacts the second surface of the cover and has a central passage. The second seal body includes a groove having an inner surface tapering toward the central passage. Upon engagement of the first and second seal bodies, a portion of the collar is received by the groove such that the tapering surface of the collar bears against the tapering surface of the groove. A conduit passes through the respective central passages of the first and second seal bodies and includes a first end, a second end opposing the first end, and a flange extending outwardly from the first end which contacts the first seal body. A fastener is coupled to the second end of the conduit and produces a compressive force on the first and second seal bodies sufficient to cause a portion of the outer surface of the collar to cold flow against the inner surface of the hole thereby sealing the perimeter of the hole in the cover.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a depiction of an embodiment of a hermetic sealing apparatus for sealing a passage provided in a cover of a housing; Figs. 2-3 illustrate a pre-sealed configuration and a post-sealed configuration of the hermetic sealing apparatus shown in Fig. 1

Fig. 4 is an exploded view of a power generating module disposed in a housing that incorporates a hermetic seal in accordance with an embodiment of the present invention;

Fig. 5 is an illustration of a prismatic electrochemical cell which represents one embodiment of a power source which may be encased in a housing incorporating a hermetic seal in accordance with an embodiment of the present invention; and

Fig. 6 is a depiction of various film layers constituting an electrochemical cell in accordance with the embodiment shown in Fig. 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, and more particularly to Figs. 1-3, there is illustrated a hermetic seal apparatus in accordance with an embodiment of the present invention. A seal constructed in accordance with the principles of the present invention may be employed to provide hermetic sealing between a conduit, such as an electrical feed-through provided in a housing cover of a power generating system, and a passage in the housing. Power and communication lines, for example, may be passed through the conduit to provide external conductivity with power and electronic components contained within the hermetic environment of an encased power generating system. It is to be understood that a hermetic seal constructed in accordance with the principles of the present invention may be employed in applications other than those described herein. The hermetic seal 20 shown in Figs. 1-3 includes a first seal body 22 having a central passage which is in general alignment with a hole provided through a substantially planar plate 21, such as a cover of a power generating system housing. A second seal body 24 of the seal 20 also includes a central passage which is in general alignment with the hole of the cover 21 and the central passage of the first seal body 22. The first seal body 22 is disposed on an upper surface of the cover 21, and the second seal body 24 is disposed on a lower surface of the cover 21.

In one embodiment, the first seal body 21 includes a collar 33 which extends through the hole of the cover 21 and bears against an inner surface 39 of the hole. The collar 33 includes a tapered inner surface 38 which tapers away from the central passage of the first seal body 22. The second seal body 24 includes a groove 35 having an inner tapered surface 40 which tapers toward the central passage of the second seal body 24.

As is best illustrated in the pre-sealed and post-sealed depictions provided in Figs. 2 and 3, respectively, the collar 33 of the first seal body 22 is received by the groove 35 provided in the second seal body 24 such that the tapered surfaces 38, 40 of the first and second seal bodies 22, 24 slidably engage one another as the collar 33 is forced into the groove 35. Engagement of the opposing tapered surfaces 38, 40 of the first and second seal bodies 22, 24 in a fully installed configuration forces a portion 37 of the outer surface of the collar 33 to cold flow against the inner surface 39 of the hole provided in the cover 21. Those skilled in the art will appreciate that cold flowing one material against another material forms an extremely tight seal between the two materials. As such, a hermetic seal is provided between the inner surface 39 of the hole and the collar 33 through slidable engagement between the collar 33 of the first seal body and the groove 35 provided in the second seal body 24. As is further shown in Figs. 1-3, a conduit

26, having a first end 23 and an opposing second end 27, passes through the hole in the cover 21 and the central passages of the first and second seal bodies 22, 24. The conduit 26 includes a central passage through which electrical and communication lines may pass into the internal hermetic environment of a housing to which the cover 21 is mounted. The conduit 26 includes a flange 25 which extends outwardly from the first end 23 of the conduit 26 and contacts a surface of the first seal body 22. The conduit 26 has a diameter which is substantially equivalent to the diameter of the central passages of the first and second seal bodies 22, 24 such that an outer surface 42 of the conduit 26 forms a tight, smooth fit with the inner diameter surfaces of the first and second seal body central passages.

A portion of the second end 27 of the conduit

26 is threaded so that a nut 34 may be secured thereon. The seal 20 also includes a thrust washer 28 that abuts a lower surface of the second seal body 24. A wave washer 30 is disposed between the thrust washer 28 and a second thrust washer 32. A nut 34, in abutment with the second thrust washer 32, exerts an axially directed compressive force on the elements of the hermetic seal 20 as the nut 34 is tightened on the threaded second end

27 of the conduit 26.

As is best seen in Fig. 3, a compressive force, F_c, produced by the tightened nut 34 causes the wave washer 30 to compress which, in turn, forces the inwardly tapered inner surface 40 of the second seal body 24 into slidable engagement with the outwardly tapered inner surface 38 of the first seal body 22. Application of the compressive force, F_c, drives the inner diameter surface 41 of the second seal body 24 inwardly against the outer surface 42 of the conduit 26. Slidable engagement between the two tapered surfaces 38, 40 also drives a portion 37 of the collar 33 into tight engagement with the inner surface 39 of the hole provided in the cover 21. After tightening the nut 34 to generate an appropriate level of compressive force,

Fc, the wave washer 30 continues to apply the compressive force, F_c, so as to maintain the integrity of the hermetic seal 20 over the service life of the seal. It is understood that the compressive force, F_c, may be produced by a fastener apparatus other than that shown in Fig. 1. By way of example, a spring- loaded metal keeper may be used as an alternative to the threaded nut 34. Other retention devices which are capable of maintaining a continuous compressive force, Fc, may also be employed.

In one embodiment, the hole provided in the cover 21 is circular and the first and second seal bodies 22, 24, as well as the conduit 26, each have a geometry that complements the geometry of the hole provided through the cover 21. It is understood that a hermetic seal constructed in accordance with the principles of the present invention may have a configuration other than that illustrated in the

Figures, and that the configuration of the seal may be modified to complement the geometry of the passage provided in the cover 21.

In one embodiment, the cover 21 is constructed from a metallic material, such as aluminum, and the first and second seal bodies 22, 24 are fabricated from a plastic material, such as polypropylene plastic. Alternatively, the cover 21 may be fabricated from any suitable material that facilitates air-tight sealing between the cover 21 and the first and second seal bodies 22, 24. The conduit 26 may be fabricated from a metallic or a plastic material. It is noted that gaps 46,47 may be provided in the first and second seal bodies 22, 24, respectively, to accommodate positional shifting between the first and second seal bodies 22, 24 occurring from forced engagement of the two tapered surfaces 38, 40. Also, a notch 51 may be provided in the first seal body 22 to facilitate movement of the collar 33 in a direction toward the inner surface of the hole of the cover 21 in response to slidable engagement between the two tapered surfaces 38, 40.

It can be appreciated that employment of the two tapered surfaces 38, 40 of the first and second seal bodies 22, 24 that facilitate hermetic sealing of the hole of the cover 21 with respect to the conduit 26 eliminates the need to tightly control key tolerances in the design and manufacturing of the hermetic seal 20, thereby reducing the cost of the seal 20 and improving the overall reliability of the seal 20 over its intended service life.

In Fig. 4, there is illustrated an exploded view of a power generating module 100 that includes an inner shell 101 which contains a stack 105 of electrochemical cells 80 and various electronic boards. An inner shell cover 108 incorporates a hermetic seal 115, such as that described previously with respect to Figs. 1-3, that seals various feed-throughs provided in the inner shell cover 108. In accordance with one embodiment, the module

100 includes a stack 105 of electrochemical cells 80 which are interconnected through use of a power board 104. The stack 105 of electrochemical cells 80 are segregated into six cell packs 82, all of which are banded together by use of two bands 92 and two opposing end plates 90. The 48 electrochemical cells 80 are subjected to a continuous compressive force generated by use of the bands 92 and a foam or spring-type element disposed within or adjacent each of the cells 80. It is noted that the foam or spring-type element serves to distribute pressure evenly between the cells 80, which is of particular importance during cell discharge.

The volume of one embodiment of an electrochemical cell 80 varies during charge and discharge cycling due to the migration of lithium ions into or out of the cathode material. This creates a corresponding increase or decrease in cell volume on the order of approximately 5 percent during charging and discharging, respectively. A foam or spring-type element incorporated within each cell 80 is maintained at approximately 10 to 40 percent compression with respect to its original thickness, which produces pressure variations ranging between approximately 10 and 35 psi during charge/discharge cycling. A pressure management apparatus, such as a stack banding apparatus, in combination with foam or spring-type elements 22, provides for constant pressures ranging between approximately 15 and 100 psi during operation to accommodate changes in cell volume which generally improves cell cycleability and heat transfer characteristics .

Each electrochemical cell 80 includes a bus bar which is spot welded or otherwise attached respectively to one or both of the positive and negative sprayed-on metal contacts. The positive and negative contacts of the bus bars 81 carry current from the cells 80 to the power board 104. The bus bars 81 also conduct heat from the cells to a metallic inner shell 101 which serves as a heat sink. The bus bars 81 include a spring portion which deforms when the cell 80 is inserted into the inner shell 101, accommodating tolerances in cell length and changes in separation distances between the cells 80 and the inner shell 101. The inner shell 101 has a thickness of approximately 1 mm and is fabricated from deep drawn aluminum. The interior sides of the inner aluminum shell 101 include an anodized coating having a thickness of approximately 0.64 mm. The anodized surface of the inner shell 101 provides electrical insulation between adjacent cells 80., yet provides for the efficient transfer of heat generated from the cells 80 through contact with the bus bars 81. The power board 104 is situated above the cell stack 105 and includes control circuitry for each of the respective six cell packs 82 constituting the cell stack 105. Each cell pack control unit 113 includes a short circuit protection device (SCPD) 107, a by-pass device 109, and an equalizer circuit 111 which cooperate to control the operation of the cell pack 82 while charging and discharging. Accordingly, each of the cell packs 82 is monitored and controlled by a respective cell pack control unit 113. A control board 106, situated above the power board 104, includes a processor that monitors and controls each of the six cell pack control units

113. As such, the control board 106 provides for cell pack and module level monitoring and control during charging and discharging operations.

A pair of quick connectors 115 pass through corresponding holes provided in an inner shell cover 108 and serve as the main power terminals. The quick connectors 115 are hermetically sealed to the inner shell cover 108 using a sealing apparatus in accordance with the principles of the present invention. When an outer shell cover 112 is positioned onto the inner shell cover 108, the quick connectors 115 are received into mating sockets 117 provided on the power board 104. Communication connectors 119, which pass through the inner shell cover 108 and are similarly hermetically sealed thereto, provide external access to the control board 106 and other electronic boards of the module 100. A hermetic seal is provided between the inner shell 101 and inner shell cover 108 by welding the inner shell cover 108 to the top of the inner shell 101. The sealed inner shell 101 is then inserted into an outer shell 102. The outer shell 102 is fabricated from glass filled polypropylene through use of an injection molding process, and has a thickness of approximately 2 mm. The outer shell 102 includes ribs on three sides of the inner surface which form flow channels when the inner shell 101 is installed in the outer shell 102 for the purpose of transporting a heat transfer fluid between the inner and outer shells 101, 102. The outer shell cover 110 is vibration welded to the top of the outer shell 102. Fluid connectors 112 are provided on the outer shell cover 110 and provide for the flow of heat transfer fluid into and out of the module 100.

In accordance with one embodiment of the present invention, the power sources shown in Fig. 4 may constitute solid-state, thin-film cells of the type shown in Figs. 5-6. Such thin-film electrochemical cells are particularly well-suited for use in the construction of high-current, high-voltage power generating modules and batteries, such as those used to power electric vehicles for example. In Fig. 5, there is shown an embodiment of a prismatic electrochemical cell 200 which includes an anode contact 201 and a cathode contact 203 formed respectively along opposing edges of the electrochemical cell 200. A bus bar 202 is spot welded or otherwise attached to each of the anode and cathode contacts 201, 203, respectively. A bus bar 202 is typically disposed along the length of the anode contact 201 and the cathode contact 203, and typically includes an electrical connection lead 204 for conducting current into and out of the electrochemical cell 200. The bus bar 202 may be fashioned from copper and have a substantially C-shaped, double C-shaped, Z- shaped, V-shaped, or 0-shaped cross-section. In this embodiment, the electrochemical cell 200 is fabricated to have a length L of approximately 135 mm, a height- H of approximately 149 mm, and a width W_ec of approximately 5.4 mm or approximately 5.86 mm when including a foam core element . The width W_c of the cathode contact 203 and the anode contact 201 is approximately 3.9 mm, respectively. Such a cell 200 typically exhibits a nominal energy rating of approximately 36.5 Wh, a peak power rating of 87.0 W at 80 percent depth of discharge (DOD) , and a cell capacity of 14.4 Ah at full charge. Each of the electrochemical cells 200 has a nominal operating voltage ranging between approximately 2.0 V and 3.1 V.

The electrochemical cell shown in Fig. 5 may have a construction similar to that illustrated in Fig. 6. In this embodiment, an electrochemical cell 180 is shown as having a flat wound prismatic configuration which incorporates a solid polymer electrolyte 186 constituting an ion transporting membrane, a lithium metal anode 184, a vanadium oxide cathode 188, and a central current collector 190. These film elements are fabricated to form a thin-film laminated prismatic structure, which may also include an insulation film, such as polypropylene film. A known sputtering metallization process is employed to form current collecting contacts along the edges 185, 183 of the anode and cathode current collector films 184, 190, respectively. It is noted that the metal-sprayed contacts provide for superior current collection along the length of the anode and cathode film edges 185, 183, and demonstrate good electrical contact and heat transfer characteristics. A spring-like thermal conductor or bus bar, such as the bus bar 202 shown in Fig. 5, is then spot-welded or otherwise attached to the metal-sprayed contact. The electrochemical cells illustrated in Figs. 4-6 may be fabricated in accordance with the methodologies disclosed in U.S. Patent Nos. 5,423,110, 5,415,954, and 4,897,917.

It will, of course, be understood that modifications and additions can be made to the various embodiments discussed herein above without departing from the scope or spirit of the present invention. By way of example, the hermetic seal disclosed herein may be employed for sealing passages having varying geometries in surfaces having varying configurations. Also, the components of the seal may be fabricated from suitable materials other than those specifically described above. Further, a hermetic seal constructed in accordance with the principles of the present invention may be incorporated into housing structures that contain power sources of a conventional design, such as wet and dry electrolytic cells, or an advanced design, such as those employing nickel metal hydride (Ni-MH) , lithium-ion, (Li-Ion) , or other high energy battery technologies. Accordingly, the scope of the present invention should not be limited by the particular embodiments discussed above, but should be defined only by the claims set forth below and equivalents thereof .

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A hermetic seal for sealing a perimeter of a hole defined in a plate having a first surface and a second surface, the seal comprising: a first seal body contacting the first surface of the plate and defining a central passage, the first seal body including a collar extending through the hole, the collar having an outer surface bearing against an inner surface of the hole and an inner surface tapering away from the central passage; a second seal body contacting the second surface of the plate and defining a central passage, the second seal body including a groove having an inner surface tapering toward the central passage, a portion of the collar being received by the groove such that the tapering surface of the collar bears against the tapering surface of the groove; a conduit passing through the respective central passages of the first and second seal bodies and having a first end, a second end opposing the first end, and a flange extending outwardly from the first end and contacting the first seal body; and a fastener coupled to the second end of the conduit and producing a force on the first and second seal bodies sufficient to cause a portion of the outer surface of the collar to cold flow against the inner surface of the hole, thereby sealing the perimeter of the hole in the plate .

2. The seal of claim 1, wherein application of the force by the fastener causes slidable engagement between respective tapering surfaces of the collar and groove .

3. The seal of claim 1, wherein slidable engagement between respective tapering surfaces of the collar and groove produces a force transverse to the force produced by the fastener, the transverse force being imparted to the outer surface portion of the collar.

4. The seal of claim 1, wherein the slidable engagement between respective tapering surfaces of the collar and the groove produces a force transverse to the force produced by the fastener, the transverse force being imparted to the inner surface of the groove.

5. The seal of claim 1, wherein the force produced by the fastener is continuously applied to the first and second seal bodies to provide continuous sealing of the perimeter of the hole in the plate.

6. The seal of claim 1, wherein the central passage of the first and the second seal bodies has a diameter smaller than a diameter of the hole in the plate .

7. The seal of claim 1, wherein the first seal body comprises a notch adjacent the outer surface of the collar for facilitating movement of the collar toward the perimeter of the hole in the plate

8. The seal of claim 1, wherein the first and the second seal bodies are respectively fabricated from a plastic material.

9. The seal of claim 1, wherein the first and the second seal bodies are respectively fabricated from a cold flowable material.

10. A hermetic seal for sealing a perimeter of a hole defined in a plate, the seal comprising: a first seal body including a collar extending through the hole and having a tapered surface; a second seal body including a groove having a tapered surface, a portion of the collar being received by the groove such that the tapered surface of the collar bears against the tapered surface of the groove; a conduit passing through the hole and passages respectively provided in the first and second seal bodies; and a fastener coupled to the conduit and producing a force on the first and second seal bodies sufficient to cause a portion of the collar to cold flow against an inner surface of the hole, thereby sealing the perimeter of the hole in the plate.

11. The seal of claim 10, wherein the first and the second seal bodies are respectively fabricated from a cold flowable material .

12. The seal of claim 10, wherein application of the force by the fastener causes slidable engagement between respective tapering surfaces of the collar and the groove, the slidable engagement producing a force transverse to the force produced by the fastener which is imparted to the collar portion.

13. A hermetic seal for sealing a perimeter of a hole defined in a cover of a housing within which a power source is disposed, the cover having a first surface and a second surface, and the seal comprising: a first seal body including a collar extending through the hole and having a tapered surface; a second seal body including a groove having a tapered surface, a portion of the collar being received by the groove such that the tapered surface of the collar bears against the tapered surface of the groove; a conduit passing through the hole and passages respectively provided in the first and second seal bodies, the conduit defining a bore through which an electrical lead passes for externally connecting with the power source disposed in the housing; and a fastener coupled to the conduit and producing a force on the first and second seal bodies sufficient to cause a portion of the collar to cold flow against the inner surface of the hole, thereby sealing the perimeter of the hole in the cover.

14. The hermetic seal of claim 13, wherein the power source disposed in the housing comprises a plurality of thin-film electrochemical cells.

15. The hermetic seal of claim 13, wherein a power board is disposed in the housing and coupled to the power source, the electrical lead passing through the bore of the conduit and connecting with the power board.

1 . A metnoα or sealing a perimeter or a passage provided in a plate, comprising: extending a collar of a first seal body contacting a first surface of the plate through the passage in the plate; receiving a portion of the collar in a groove provided in a second seal body contacting a second surface of the plate; and producing a force to slidably engage a tapered surface of the collar with a tapered surface of the groove so that the portion of the collar cold flows against the perimeter of the passage.

17. The method of claim 16, wherein producing the force comprises producing an axially directed compressive force exerted on the first and second seal bodies.

18. The method of claim 16, wherein slidably engaging the tapered surfaces of the collar and groove produces a transverse force which is exerted on the portion of the collar.