Current interrupt apparatus for electrochemical cells

FIELD OF THE INVENTION

This invention relates generally to electrochemical cells and more particularly to current interrupt and vent apparatus used for such cells responsive to various adverse conditions.

BACKGROUND OF THE INVENTION

Electrochemical cells, especially high energy density cells such as those in which lithium is an active material, are subject to leakage or rupture by various abusive treatment, which, in turn, can cause damage to the device which is powered by the cell or to the surrounding environment. In the case of rechargeable cells self-heating occurs as such cells are charged. Charging at too rapid a rate or overcharging can lead to an excessive increase in temperature. When the temperature exceeds a certain point, which varies depending upon the chemistry and structure of the cell, an undesirable and uncontrollable thermal runaway condition begins. In addition, because of the overheating and/or chemical reaction, internal pressure builds up, and electrolyte may suddenly be expelled from the cell.

Conventional cell designs employ an end cap fitting which is inserted into an open ended cylindrical casing after the cell's active material, appropriate separator material and electrolyte have been inserted therein. The end cap is in electrical contact with one of the anode or cathode material and the exposed portion of the cap forms one of the cell terminals. A portion of the cell casing forms the other terminal. Typically, various loose components are received in the end cap to provide over-pressure, short circuit and/or over-temperature protection. The typical header includes one or more seals to prevent leakage of the electrolyte through the header. However, these seals tend to leak over time due to temperature and pressure conditions and the like. Conventional cells frequently employ polymer PTC (positive temperature coefficient of resistivity) components for over-current protection which are susceptible to deformation when the header is crimp sealed to the electrochemical cell during manufacture. Deformation of the PTC component adversely effects its performance. Further, polymer PTC inherently results in relatively low ampere capacity and high resistance.

Copending U.S. Pat. No. (Ser. No. 08/720,585- A40743), which is incorporated herein by this reference, shows a current interrupt device responsive to over-temperature and over-pressure conditions which is incorporated into an end cap assembly which, in turn, is welded into the open end of the casing of an electrochemical cell to form a hermetic seal. This end cap assembly has particular application to rechargeable (secondary) cells, such as lithium-ion, nickel metal hydride, nickel cadmium and the like, to overcome the danger of the cell over-heating and pressure building up in the cell during exposure to high temperatures, excessive or improper charging, or shorting of the cell. While the current interrupt device of the patent is very effective, it would be desirable to provide an end cap assembly which has fewer component parts and which can be crimped into the casing of the electrochemical cell to lower the cost of the device while forming an effective hermetic seal. Additionally, it would be desirable to integrate an additional safety feature relating to low rate overcharge and overdischarge protection.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide end cap apparatus for an electrochemical cell which includes improved safety features which is an assembled unit to which an electrode tab or strap can be easily welded to effect electrical connection and, as a single calibrated unit, can be deposited in the open end of a cell casing and crimped thereto in hermetically sealed relation to the casing without the danger of upsetting or changing the preset calibration of the safety features. Another object of the invention is the provision of end cap apparatus for such a cell incorporating a thermally responsive member adapted to interrupt current flow in response to over-temperature due to heat received through a heat transfer path from the interior of the cell to the thermally responsive member as well as heat generated by l

2

r heating of components within the end cap apparatus. Yet another object is the provision of end cap apparatus for such a cell having a pressure responsive diaphragm disposed in pressure receiving communication with the atmosphere inside the cell in which welding of the cell's electrode tab to the end cap apparatus is facilitated. Yet another object is the provision of end cap apparatus which has improved electrolyte leak protection as well as providing venting in response to selected over-pressure conditions. Another object is the provision of electrochemical cell end cap apparatus which is easily handled and installed and which is small in size and mass. Yet another object of the invention is to provide an end cap apparatus which has increased ampere capacity over a broad ambient temperature range, e.g., −20° to 80° C., to serve high power applications and allow fast charging utilizing higher energy density cell chemistries.

Briefly, in accordance with the invention, end cap apparatus for electrochemical cells particularly useful with lithium-ion cell chemistry, comprises a header which allows the cell manufacturer to attach the end cap apparatus utilizing existing crimp technology to produce an electrolyte seal with the header also serving as a vehicle to mount several condition sensing mechanisms for a single action, safety protection device. End cap apparatus made in accordance with the invention provides the capability of opening the electrical charging circuit across a broad range of incremental cell pressure, without venting, as well as venting upon a high predetermined pressure level. The safety protection features include high rate overcharge protection (over-temperature and/or low pressure switch), low rate overcharge/overdischarge protection (low pressure switch), extended short circuit protection (thermally sensitive switch) and explosion protection (high pressure vent). The apparatus can be modified to include all or selective ones of the safety protective features, as desired.

The end cap apparatus in the preferred embodiments is of positive polarity and is electrically isolated from the negative polarity of the cell's casing by means of a polymer gasket which is compressed between the inside diameter of the cell casing and the outside diameter of the end cap apparatus. An electrical strap, typically aluminum, from the cell plates is welded to a portion of the bottom surface of the header forming the positive current path. The header is formed with a rigid, circumferential flange extending about the periphery thereof which allows the end cap apparatus to be crimped to the cell as well as cell pressurization to occur, both without changing the calibration of the safety protection features. In selected embodiments, the header is suitably formed of aluminum by machining, forging or the like to form a centrally disposed recess with a thin diaphragm portion, e.g., 0.008 inches thick extending across the recess, the diaphragm having a frangible portion which ruptures at a predetermined pressure level to prevent cell explosion. Suitable vent holes are formed through the header and ancillary components to allow the pressurized fluid, i.e., electrolyte, to escape upon venting. In certain other embodiments a diaphragm cap member, typically aluminum, is attached to the circumferential flange and extends over the lower half of the header, i.e., over the portion which will be exposed to electrolyte in the cell forming a leak proof seal. A corresponding diaphragm portion and frangible portion is formed in the diaphragm cup member.

According to a feature of the invention, a motion transfer member of electrically insulative material is movably mounted in the recess and is adapted to transfer motion from the diaphragm portion to a movable contact normally biased into engagement with a stationary contact portion to force the movable contact out of electrical engagement with the stationary contact portion upon a selected increase in pressure within the cell. The movable contact is part of an electrically conductive spring member which is mounted in the recess formed in the header and electrically separated therefrom, in certain embodiments, by an annular insulative member. A top cap is mounted on an annular insulative member and is clamped to the header by means of a lip of the header which is rolled over with a portion of the annular insulative member disposed therebetween to electrically separate the header from the top cap. A thermally responsive, snap acting disc having a centrally located aperture is also mounted on the annular insulative member and is adapted to move from a first dished configuration in which a stationary contact is received through the aperture in the disc and the movable contact is biased into engagement with the stationary contact, to a second, oppositely dished configuration upon being heated to predetermined temperature to thereby drive the movable contact out of electrical engagement with the stationary contact. The disc is selected, in the preferred embodiments, to have such a low reset temperature, e.g., −20° C., that it becomes, in effect, a non-resettable safety device.

According to a feature of certain embodiments of the invention, the header is provided with a solid portion having substantial thickness at a location intermediate to the diaphragm and the circumferential flange which facilitates the welding operation of the electrode tab of the aluminum strap lo the header.

The header, formed of highly heat conductive aluminum, also serves as an effective heat conductive path from the interior of the cell to the thermally responsive disc thereby allowing a disc with a relatively high actuation temperature, that is, a disc having a minimized delta temperature between the disc actuation temperature and the temperature of the cell's core used as the reference for actuation of the thermal protection feature. The higher actuation temperature of the disc results in minimizing the possibility of a nuisance trip of the cell.

One embodiment is shown which includes only pressure protective features. Certain embodiments use an annular disc and spring mounting member comprising a high modulus material, e.g., metal, laminated with a low modulus electrically insulative plastic to provide a predictable seating surface as well as optimized clamping by the rolled lip of the header.

According to another feature of certain embodiments of the invention, protrusions are formed about the frangible portion of the diaphragm which protect that portion from damage during handling. The protrusions can be in the form of a continuous rib or they can be slotted, as by extending radially, in effect forming slots to permit radial venting in the event that the cell's plates are forced into blocking engagement with the bottom of the end cap apparatus.

According to another feature of the invention, a small circumferential bead can be formed on the flange to provide localized, high compression for clamping the annular insulative member and its components to the header.

According to yet another feature of the invention, the diaphragm portion can be formed with a dish shape to provide instantaneous displacement of the diaphragm at a selected pressure level. This feature can also be provided by locating the frangible portion of the diaphragm inboard of a support or strengthened area. Several diaphragm cap members are provided having improved snap action diaphragm portions which include an inclined, either straight or curved surface or truncated conical portion which serves as a calibration surface to compensate for differences in material properties and thicknesses as well as to enhance the driving force upon snapping of the diaphragm portion. Welding of the electrochemical cell's rolled cathode or anode electrode tab can be enhanced by providing a flat to convex surface either by a separate cup member or by an offset portion formed in the diaphragm portion.

According to another feature of the invention, the annular insulative member is formed of a first annular electrical portion of relatively high modulus to serve as a seating surface and a second electrically insulative portion of relatively low modulus, low strength which is insert molded on the top cap and which extends over the vent holes in the top cap. The second portion serves as an optimized clamping medium as well as a seal of the vent holes to permit rinsing of the cell after assembly without interfering with the venting function, i.e., the material covering the vent holes will yield at pressure levels well below venting pressure allowing the pressurized electrolyte to escape. In yet another embodiment the annular insulative member combines additional functions of seating the thermally responsive disc as well as providing motion transfer between the diaphragm portion and the movable contact.

According to still other features, stamped parts can be utilized in making the end cap apparatus while still providing the same functional operation of the safety features as well as the feature of avoiding calibration changes upon crimping and pressurization of the cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description, serve to explain the objects, advantages and principle of the invention. Dimensions may have been altered for purposes of illustration. Corresponding reference numerals refer to like parts throughout the views of the drawings.

In the drawings:

FIG. 1

is an exploded front elevational view of a casing of an electrochemical cell, a gasket and a schematic representation of an end cap apparatus prior to assembly shown with the cell and gasket in cross section;

FIG. 2

is a front elevational view showing the

FIG. 1

end cap apparatus and gasket assembled in the cell;

FIG. 3

is an elevational view, in cross section, of an end cap apparatus made in accordance with a first embodiment of the invention;

FIGS. 3

a

and

3

b

are top and bottom views, respectively, of the

FIG. 3

apparatus;

FIGS. 4-11

,

14

and

17

are views similar to

FIG. 3

of end cap apparatus made in accordance with alternate embodiments of the invention;

FIGS. 4

a

and

4

b

are top and bottom views, respectively, of the

FIG. 4

apparatus;

FIGS. 5

a

and

5

b

are top and bottom views, respectively, of the

FIG. 5

apparatus;

FIG. 5

c

is a view taken on line

5

c—

5

c

of

FIG. 5

, with the diaphragm removed for purposes of illustration, showing a motion transfer member having three legs;

FIG. 5

d

is a view similar to

FIG. 5

c

showing a motion transfer member having two legs;

FIGS. 6

a

and

6

b

are top and bottom views, respectively, of the

FIG. 6

apparatus;

FIG. 6

c

is a view taken on line

6

c—

6

c

of

FIG. 6

with the diaphragm removed for purposes of illustration, showing a motion transfer member having a plurality of legs;

FIG. 9

a

is a bottom view of the

FIG. 9

apparatus shown with a diaphragm cup member partly removed for purposes of illustration;

FIG. 11

a

is a view taken on line

11

a—

11

a

of

FIG. 11

, shown with the diaphragm removed for purposes of illustration;

FIG. 12

is a graph showing displacement of the center of a diaphragm (inches) versus pressure (psi) applied to a face surface of the diaphragm for two different diaphragms;

FIGS. 12

a

and

12

b

are respective schematic representations of the two diaphragms of the type used in

FIG. 12

shown in solid lines in a deflected position prior to breaking of the frangible portion and in dashed lines prior to deflection;

FIG. 13

is an elevational view, in cross section, of another embodiment of an end cap apparatus prior to crimping into its assembled configuration;

FIG. 13

a

is an exploded view of the

FIG. 13

components;

FIG. 13

b

is a top plan view of a spring member used in the

FIG. 13

embodiment and

FIG. 13

c

is a cross section taken on line

13

c—

13

c

of

FIG. 13

b;

FIGS. 14

a

,

14

b

and

14

c

are views similar to

FIG. 14

showing different current interrupt and vent mechanisms;

FIGS. 15 and 15

a

are elevational and bottom plan views respectively of a modified end cap apparatus;

FIG. 16

is a cross section of a diaphragm cap useful in practicing the invention;

FIG. 16

a

is a top plan view of

FIG. 16

;

FIGS. 16

b

and

16

c

are alternative diaphragm caps useful in practicing the invention; and

FIG. 17

a

is a top plan view of the annular electrically insulative member used in

FIG. 17

with

FIG. 17

b

being a cross section taken on line

17

b—

17

b

of

FIG. 17

a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1

shows an end cap apparatus

2

made in accordance with the invention, along with a gasket

4

of electrically insulative material, and an open ended cylindrical casing

6

, prior to assembly, while

FIG. 2

shows the gasket and end cap apparatus after it has been received in the open end of casing

6

and sealingly crimped thereto. End cap apparatus

2

can be comprised of any one of several embodiments discussed below.

With reference to

FIGS. 3

,

3

a

and

3

b

, an end cap apparatus made in accordance with a first embodiment of the invention is identified by reference numeral

10

and comprises a generally circular, in top plan view, header

12

formed of suitable material by machining, forging or the like. When used with electrochemical cells which comprise lithium as an active material, aluminum, which is compatible with the electrolyte in such cells, serves as a suitable material in cells in which the core is of positive polarity and the casing of negative polarity. Header

12

is formed with a rigid, circumferentially extending flange

12

and a recess

12

b

to serve as a switch chamber. A platform

12

c

formed on header

12

receives an annular, electrically insulative member

14

, to be discussed. A thin preferably circular diaphragm

12

d

, e.g., 0.008 inches in thickness, is centrally formed in the bottom of header

12

and is formed with a frangible portion

12

e

formed as by coining, of a selected configuration, such as C-shaped as disclosed in U.S. Pat. No. (A40743), reference supra, as well as in

FIG. 9

a.

A generally disc shaped stationary contact plate

16

having an upstanding contact portion

16

a

is formed of suitably electrically conductive material, such as cold-rolled steel with a gold or silver plated contact face which is press fit into a cylindrical portion

12

f

of recess

12

b

. Stationary contact plate

16

is provided with one or more apertures

16

b

which serve to allow electrolyte to pass through in the event that the frangible portion of diaphragm

12

d

bursts due to an undesirable, selected increase in pressure. Contact member

16

is also provided with a bore

16

c

which extends through contact member

16

at the center thereof aligned with the center of diaphragm

12

d

. A motion transfer pin

18

of electrically insulative material, such as ceramic or plastic, is slidingly received in bore

16

c

. The length of pin

18

is selected to enable it to transfer motion from diaphragm

12

d

to a movable contact portion

20

a

to be discussed.

Electrically insulative annular member

14

is formed with a first thermally responsive disc seat

14

a

and second electrically conductive spring and top cap seat

14

b

spaced vertically above and outboard of seat

14

a

, as seen in FIG.

3

. Insulative member

14

may be composed of plastic material having a relatively high modulus to provide a predictable seat for disc

22

and at the same time sufficiently flexible to allow it to conform to the rolling over of lip

12

g

to be discussed. A thermostat metal (e.g. bimetal), snap acting disc

22

, movable from a first dished shaped configuration shown in

FIG. 3

to a second, opposite dished shaped configuration (not shown) when heated to a predetermined temperature, is disposed on disc seat

14

a

. Disc

22

is selected to have a very low reset temperature, e.g., approximately −20° C., so that, in effect, it becomes a single action or non-resettable device. Disc

22

is formed with an aperture through the disc at its center with stationary contact portion

16

a

extending up through the aperture when the disc is in the first configuration. Spring member

20

, formed of suitable electrically conductive material, such as beryllium copper, is received on spring and top cap seat

14

b

and has a contact tab

20

a

with a gold or silver plate or stripe on the contact tab aligned with and normally biased into engagement with stationary contact portion

16

a

. A top cap

24

formed of electrically conductive material such as a plated cold rolled steel has a circumferential flange

24

a

electrically connected to spring member

20

as by physical contact or by welding. Top cap

24

has a top wall

24

b

and a sidewall

24

c

through which one or more vent holes

24

d

are formed to allow pressurized electrolyte to escape in the event that frangible portion

12

e

of diaphragm

12

d

is broken due to over-pressure conditions.

Header

12

has a upstanding circumferential lip

12

g

which cooperates with an upstanding skirt

14

c

of annular insulative member

14

to clamp top cap

24

and spring member

20

on seat

14

b

when lip

12

g

is deformed or rolled from the dashed line to the solid line configuration with top cap

24

and spring member

20

electrically separated from header

12

.

The bottom portion of header

12

, as seen in

FIG. 3

, which serves as the inside surface of the end cap apparatus exposed to the electrolyte in casing

6

, is formed with a solid portion

12

h

which extends intermediate to diaphragm

12

d

and flange

12

a

which not only adds rigidity to the header which, along with the rigidity of flange

12

a

, prevents any bowing of the header body when the header is crimped into casing

6

or when the cell is pressurized, also advantageously serves as an excellent support for welding electrode tab

8

to the header, as by laser or ultra sonic welding, both of which require a pressurized engagement of the components being welded during the welding operation.

Header

12

serves as a receptacle for the several parts of the end cap apparatus and its rigidity allows the end cap apparatus to be manufactured and assembled having a selected calibration for the several protective functions which is not susceptible to shifts in calibration during crimping of the apparatus to the casing nor during pressurization of the cell. Electrode tab

8

can be welded to surface

12

h

of the header and the apparatus placed in the open end of casing

6

in gasket

4

and crimped thereto to form a hermetic seal without any danger of changing the calibration of the protection functions.

The safety or protective functions comprise temperature protection, pressure protection and short circuit protection by separating movable contact tab

20

a

from stationary contact portion

16

a

to interrupt current flow which normally extends through electrode tab

8

through header

12

, stationary contact plate

16

, spring

20

to top cap

24

. The temperature protection function utilizes bimetal disc

22

which is selected to snap from the configuration shown in

FIG. 3

to an opposite dished configuration (not shown) forcing movable contact tab

20

a

to move out of electrical engagement with stationary contact portion

16

a.

Header

12

, formed of aluminum, serves as a highly heat conductive path from tab

8

to disc

22

resulting in an optimized low delta temperature between the core of the cell and disc

22

. This permits a higher actuation temperature of the disc

22

while still using the same core temperature as the reference temperature. The result of this is that the cell can be subjected to higher ambient temperature environments without nuisance actuation of the temperature protection function.

Short circuit protection is afforded by means of l

2

r heating of top cap

24

, spring

20

, contact interface between tab

20

a

and contact portion

16

a

and contact plate

16

with the heat being transferred to disc

22

resulting in actuation of disc

22

.

Pressure increase within the cell will cause diaphragm

12

d

to bow inwardly. This bowing causes pin

18

to move toward movable contact tab

20

a

eventually lifting the tab off stationary contact portion

16

a

to interrupt current flow. This type of pressure increase can occur without a corresponding increase in temperature in certain situations such as upon low current overcharge or overdischarge. The amount of bowing as well as the pressure at which the bowing occurs can be controlled by the thickness of the diaphragm portion

12

d

as well as its hardness. Additional control is obtained by varying the length of pin

18

. As described, the protection function is characterized by a creep action mode of operation; however, as will be described below, this can be made into a snap action mode of operation, if desired.

In the event that pressure increases above a selected level, the frangible portion

12

e

will break allowing pressurized electrolyte to escape through apertures

16

b

in stationary contact

16

and

24

d

in top cap

24

.

FIGS. 4

,

4

a

and

4

b

show a modification of the

FIG. 3

embodiment in which diaphragm

32

of end cap apparatus

30

is formed as a separate member and is hermetically attached to header

12

′ as by laser welding. As shown in

FIG. 4

, a downwardly extending flange

32

a

is welded all around its circular periphery to a corresponding flange

12

j

. In this embodiment, stationary contact portion

12

i

, corresponding to

16

a

of

FIG. 3

, is formed integrally with header

12

′ in a transversely extending wall portion

12

k

of header

12

′. A bore

12

m

corresponding to bore

16

c

of

FIG. 3

, slidingly receives motion transfer pin member

18

and apertures

12

n

through wall portion

12

k

serve as vent apertures corresponding to aperture

16

b

of FIG.

3

. The operation of end cap apparatus

30

is the same as that of the

FIG. 3

embodiment.

FIGS. 5 and 5

a-

5

c

show another modification of the

FIG. 3

embodiment. End cap apparatus

40

comprises the same header

12

, top cap

24

, spring

20

, disc

22

and annular insulative member

14

; however, stationary contact plate

16

′ has been modified to accommodate a multi-leg motion transfer member

18

′. Motion transfer member

18

′, composed of suitable electrically insulative material such as ceramic or plastic, comprises a body portion

18

a

with three depending legs

18

b

which are slidingly received through aperture

16

c

.

FIG. 5

d

shows a modified motion transfer member

18

″ with two legs which can be used, if desired, with a stationary contact plate modified to include accommodating apertures.

FIGS. 6 and 6

a-

6

c

show another modification of the

FIG. 3

embodiment. End cap apparatus

50

comprises header

12

″ the same as in the

FIG. 3

embodiment except that platform

12

c

of

FIG. 3

has been modified to include a step portion

12

c′

to receive flange

24

a

of top cap

24

by itself with an annular gasket

52

of electrically insulative material to electrically isolate top cap

24

from header

12

″. Lip

12

g

is rolled over in the same manner as in the previous embodiments. Electrically conductive spring

20

′ is, in effect, suspended from and electrically connected to top cap

24

as by welding and is biased into electrical engagement with stationary contact portion

16

a

. Stationary contact plate

16

″ has a plurality of bores

16

e

which slidingly receive therethrough respective legs

18

d

which extend from body

18

a′

of motion transfer member

18

′″. This embodiment includes the pressure protection features of the above embodiments but does not include temperature protection and short circuit features.

FIG. 7

shows another modification of the

FIG. 3

embodiment. End cap apparatus

60

comprises a header

12

′″ in which flange

24

a

of top cap

24

and spring

20

are received on seat

60

b

of an annular metal member

60

a

of suitable high modulus material such as aluminum, nickel, stainless steel or the like providing a predictable disc seat

60

c

for thermally responsive, snap acting disc

22

. Member

60

a

is laminated with an electrically insulative material

60

d

such as thermoplastic preferably having a relatively low modulus to serve both to electrically separate spring

20

and top cap

24

from header

12

′″ and to provide an improved clamping engagement of lip

12

g

. Flange

12

a′

is formed with a bead

12

o

which serves as a localized high compression feature to enhance the crimping seal of casing

6

through gasket

4

. Although bead

12

o

is shown at the outer distal end of flange

12

a′,

it will be understood that the bead could be placed at other locations of flange

12

a′

to provide the improved localized high compression function. Yet another feature incorporated in header

12

′″ comprises radially extending protrusions

12

p

formed in the bottom surface of the header, as seen in

FIG. 7

, outboard of diaphragm portion

12

d

. The protrusions serve to provide protection for frangible portion

12

e

of the diaphragm during handling of the end cap apparatus prior to being crimped into casing

6

thereby preventing a potential leakage path allowing electrolyte through a damaged portion of the frangible portion. As shown in

FIG. 7

, the protrusions are spaced from one another to allow a radial venting path from the interior of casing

6

up through the diaphragm area in the event that increased pressure causes the diaphragm to rupture even if the cell plates are biased against the bottom of header

12

′″. Stationary plate

16

′″ is shown as a generally flat plate having an upwardly extending stationary contact portion

16

a

with venting apertures

16

b

and leg receiving apertures

16

c

for sliding reception of legs

18

b

of motion transfer member

18

′ as shown in the

FIG. 5

embodiment.

End cap apparatus

70

of

FIG. 8

is similar to the

FIG. 7

embodiment except that protrusion

12

q

forms a circular, continuous protection surface slightly outboard of frangible portion

12

e

and stationary plate

16

iv

is formed with a slightly greater bearing surface

16

f

for press fitting in bore

12

f

. Surface

12

h′

in both the

FIGS. 7 and 8

embodiments is used to weld electrode strap

8

(not shown) upon assembly when mounted in casing

6

.

FIGS. 9 and 9

a

show another embodiment in which a separate diaphragm cap

82

, formed of suitable material such as aluminum, is attached to flange

12

a″

of apparatus

80

, as by welding, press fitting or crimping thereto, and extends over the bottom half of header

12

v

. Radially extending protrusions

12

p

of the type shown in

FIG. 7

are formed in the lower surface of header

12

v

with corresponding protrusions

82

a

formed in diaphragm cap

82

. Header

12

v

is formed similar to that of

FIG. 4

having an open bottom and an integral transverse wall

12

k

which serves to mount stationary contact portion

12

i

. Since header

12

v

is shielded from the electrolyte of the electrochemical cell by diaphragm cap

82

, it can be formed of any suitable material, such as a higher strength cold rolled steel, if desired. Diaphragm portion

12

d

is formed as part of diaphragm cap

82

and covers the open bottom portion of header

12

v

. Frangible portion

12

e

is shown in

FIG. 9

a

formed in a C-shaped configuration as seen in the bottom plan view. Although other configurations could be utilized, the C-shaped configuration is a preferred configuration.

FIG. 10

shows another embodiment similar to that of

FIG. 9

in having a separate diaphragm cap

92

formed of suitable material such as aluminum. Diaphragm portion

12

d′

in the

FIG. 10

embodiment is recessed at

92

a

so that the bottom portion of header

12

vi

provides the protective feature for frangible portion

12

e

. Diaphragm portion

12

d′

is shown formed with a dish shaped portion

92

b

. Upon exposure to increasing pressure from within the cell, dish shaped portion

92

b

will snap to an oppositely dished configuration (not shown) to drive motion transfer member

18

′ upwardly, as seen in the figure, to move movable contact portion

20

a

, through disc

22

, away from stationary contact portion

12

i

. Continued pressure increase, should it occur, as in the other embodiments, will cause frangible portion

12

e

to break allowing the pressurized electrolyte to vent. Header

12

vi

is formed of material such as aluminum in the

FIG. 10

embodiment to provide a low weight end cap apparatus

90

and therefore peripheral flange

12

a′″

is made somewhat thicker than in the

FIG. 9

embodiment to provide the desired degree of rigidity, as discussed above. Top cap

24

′, formed of plated cold rolled steel, is formed with a radially extending flange

24

a′

which is welded to electrically conductive spring

20

, and has a plurality of vent apertures

24

d′

formed in sidewall

24

c′.

Top cap

24

′ is overmolded with electrically insulative material

94

having a low modulus and low strength, such as unfilled polypropylene, which serves as a low pressure seal for vent holes

24

d′,

electrical separator between top cap

24

′, spring

20

and header

12

vi

and an improved clamping connection with lip

12

g

once it is rolled over as shown in the figure. The top cap assembly, i.e., the overmolded cap

24

′ and spring

20

, is received on annular insulative member

96

formed of high modulus material, such as a mineral or glass filled thermoplastic, to provide a stable seat for the top cap assembly at

96

a

as well as disc

22

at

96

b

. By having vent holes

24

d′

covered with overmold material

94

, the assembled electrochemical cell can be rinsed of any electrolyte which may have been inadvertently deposited on the exterior, non-aluminum surface of casing

6

and end cap apparatus

90

thereby preventing corrosion of the internal components. In operation, should the pressure level in the cell increase to the point where frangible portion

12

e

breaks, the escaping pressurized fluid will easily break the seal of the low strength material

94

covering vent apertures

24

d′.

FIGS. 11 and 11

a

show yet another embodiment in which end cap apparatus

100

is formed out of stamped parts to provide the functional equivalent of the previously described embodiments. Support member

102

, formed of high modulus, strong material such as nickel, cold rolled steel or stainless steel has upstanding sidewalls

102

a

,

102

b

to enhance rigidity and an outwardly extending flange portion

102

c

. The outer portion

102

d

of flange

102

c

extends upwardly to provide added strength and rigidity to the composite flange to be described. Vent apertures

102

e

are formed in recessed wall portion

102

f

. Motion transfer leg apertures

102

g

are formed in wall portion

102

f

to slidingly receive respective legs

18

b″

of a two leg motion transfer member

18

″. An annular disc seat member

104

formed of high strength, high modulus material such as nickel, cold rolled steel, stainless steel or the like is received on flange portion

102

c

and is formed with a disc seat

104

a

for receipt of disc

22

. Ventilation holes

104

b

are formed in disc seat

104

to facilitate electrolyte venting. Electrically conductive spring

20

is received on top of disc seat member

104

along with flange

24

a″

of top cap

24

″. A suitable electrically insulative gasket

106

, such as Nomex, or thermoplastic, is placed around the stack of flange

24

a″,

the outer peripheral portion of spring

20

and annular disc seat member

104

to electrically separate the stack from support members

102

and diaphragm cap member

108

received over support

102

. Top cap

24

″ formed of suitable material such as nickel, stainless steel, cold rolled steel or the like is formed with suitable vent apertures

24

d″

in sidewall

24

c″.

Diaphragm cap member

108

is formed with a diaphragm portion

12

d

and frangible portion

12

e

as in the above described embodiments. Stationary contact

16

a

, integral with stationary contact plate

16

v

, is welded to wall

102

f

of support

102

. The composite flange is made up of flange

24

a″,

the outer periphery of spring

20

, annular disc seat member

104

, flange support

102

c

, the diaphragm cap member

108

and gasket

106

. The horizontal and vertical portions of diaphragm cap member

108

, and the horizontal and vertical portions of support member

102

are high modulus, high strength materials to provide a rigid composite flange structurally equivalent to the header flanges of the previously described embodiments.

As described above, end cap apparatus

90

of

FIG. 10

includes a snap acting, over-pressure feature provided by dished shaped portion

92

b

. This feature is advantageous in avoiding contact chattering if the pressure should hover around the level at which displacement of the diaphragm would drive contact portion

20

a

away from the stationary contact. A sudden large increase in deflection can also be obtained by moving the frangible portion

12

e

inboard of a supported portion of the diaphragm. With reference to

FIG. 12

a

, frangible portion

12

e

is located immediately adjacent a thicker portion of header

12

, for example, as shown in FIG.

3

. This results in displacement of the center of the diaphragm with increasing pressure along a generally straight line “a” of

FIG. 12

until the frangible portion

12

e

breaks at point “b”. However, if frangible portion

12

e

is moved inboard away from the thicker or supported portion of the header as shown in

FIG. 12

b

, the displacement of the center of diaphragm portion

12

d

follows trace “c” which includes the essentially instantaneous displacement at “d” followed by a further relatively gradual increase until the frangible portion breaks at “e”. This sudden displacement occurs when the portion of the diaphragm outboard of frangible portion

12

e

suddenly moves upwardly, as seen in the figure, hinging at the connection with the thicker or supported portion of the header. As shown in

FIG. 12

, the sudden increase in displacement occurred at 200 psi, however; the pressure level at which this occurs can be controlled by forming frangible portion

12

e

closer to the support to increase the pressure level at which the sudden displacement occurs or further from the support to decrease the pressure level at which the sudden displacement occurs.

As noted supra, snap action of the diaphragm is provided by dished portion

92

b

of FIG.

10

. However, even in diaphragm portion

12

d

of diaphragm cap member

108

of

FIG. 11

a certain amount of snap action is obtained. Although as shown in the drawing, diaphragm portion

12

d

is flat, when frangible section

12

e

is formed by coining, the material of the diaphragm is displaced causing the diaphragm portion to go into compression, resulting in a slightly concave curved surface of the diaphragm portion when viewed externally of the end cap (not shown). When subjected to pressure from within the electrochemical cell the center portion of the diaphragm will snap over to a concave configuration when the pressure reaches a level sufficient to overcome the compression forces.

In

FIGS. 13

,

13

a

another variation of the

FIGS. 11

,

11

a

embodiment is shown which also includes an improved diaphragm

112

, to be described below. A pressure vent and current interrupt device in the form of end cap apparatus

110

comprises a top cap

124

formed of suitable material such as nickel plated cold rolled steel having a flat central portion

124

b

and circumferential flange

124

a

with frustoconical intermediate portion

124

c

. Vent holes

124

d

are provided in the top cap as in the above described embodiments. A spring member

120

including a movable contact

120

a

, best seen in

FIGS. 13

b

,

13

c

formed of suitable material such as nickel plated beryllium copper having a silver plated or inlayed contact portion

120

a

is disposed beneath the top cap. As seen in

FIG. 13

c

, contact portion

120

a

is offset from the body of member

120

. Spring member

120

is selected to have a low spring rate and therefore is formed to extend as long as space permits within the end cap with the frustoconical portion

124

c

of the end cap shaped so as not to constrict movement of the spring. Spring member

120

is preferably provided with tab portions

120

b

which extend radially inwardly from annular body portion

120

c

with their free distal ends extending to a location inboard of thermally responsive disc member

22

to be discussed. The tabs will serve as a reaction surface against which disc

22

can be loaded. Protrusions

120

d

extending toward the disc seat

114

a

may be formed on tabs

120

b

for this purpose.

Thermally responsive bimetallic disc member

22

, the same as that used in the previously described embodiments, is disposed beneath spring member

120

and is received on disc seat

114

of aluminum, nickel plated cold rolled steel or other suitable material. Disc seat

114

is formed with a slightly depressed portion

114

a

to seat disc

22

and has a central opening

114

b

and may be formed with apertures

114

c

around the periphery of the seat portion to enhance venting when the disc is positioned in the seat.

A support

122

which includes stationary contact

122

a

formed of suitable high strength material such as cold rolled steel, AISI 1008, nickel plated with a silver plate at the centrally located stationary contact

122

a

is formed with an annular strengthening rib

122

b

in bottom wall

122

c

and has an upwardly extending sidewall

122

d

. Openings

122

e

are formed through bottom wall

122

c

on opposite sides of stationary contact

122

a

which serve both as vent openings as well as to receive therethrough legs

118

a

depending from annular body portion

118

b

of motion transfer member

118

.

An electrically insulative gasket

116

of suitable material such as Nylon has an annular bottom wall

116

a

and an upstanding sidewall

116

b

, preferably formed with an attenuated free end

116

c

to facilitate bending as will be described. The attenuated portion can also include spaced vertical ribs (not shown) to compliantly center the several components and allow full seating even if any such components are slightly oversized without changing the distance which the motion transfer member must travel.

Diaphragm cap

112

is a generally cup-shaped member, similar to that of

108

in

FIG. 11

, but is formed with an inclined surface portion or truncated conical portion

112

a

which may be either straight or curved, disposed in the end of the cap extending between support section

112

b

aligned with rib

122

b

and the central portion

112

c

within franglible portion

12

e

. As noted above, when frangible

12

e

is coined, or stamped, the diaphragm material is displaced causing a slight curve, as indicated in

FIGS. 13

,

13

a

. The particular angle chosen for the truncated conical portion and the gap between central portion

112

c

and support section

112

b

(see FIG.

13

), that which creates a vertical offset of, e.g., 0.012 inch, can be adjusted to control the amount of snap movement which can be obtained upon actuation and the actuation pressure.

Diaphragm cap

112

, as illustrated in

FIG. 13

a

, receives the several components within its cup shaped configuration forming a leak proof end cap assembly which provides a significant advantage to the cell manufacturer. The parts are easily dropped in place as shown in FIG.

13

and then the sidewalls of the diaphragm cap member

112

, the support

122

and the gasket

116

are crimped over as shown in FIG.

14

.

As shown in

FIG. 14

, the current interrupt apparatus

110

is in the normal closed circuit position with movable contact

120

a

biased into electrical engagement with stationary contact

122

a

.

FIG. 14

a

shows current interrupt apparatus

110

when thermal responsive disc

22

has been heated to its actuation temperature, e.g., 80° C. for one type, 110° C. for another type, caused by l

2

r heating produced primarily from current flowing through spring member

112

during short circuit or by high ambient temperatures. Disc

22

snaps to its opposite dished configuration lifting movable contact portion

120

a

out of electrical engagement with stationary contact

122

a

. In

FIG. 14

b

the interrupt apparatus is shown in the contacts open position caused by internal cell pressure rising to a selected actuation level, e.g., 6 kg/cm

2

, which causes diaphragm center portion

112

c

and inclined surfaces

112

a

to buckle with a snap action thereby transferring motion through motion transfer member

118

to disc

22

which in turn moves movable contact

120

a

away from stationary contact

122

a

. Current is permanently interrupted without allowing electrolyte to leak from the header. In the event that internal call pressure continues to increase once it reaches a preselected level, e.g., 21 kg/cm

2

, the coined portion

12

e

fractures as shown in

FIG. 14

c

allowing gas and electrolyte to escape through vent openings.

As seen in

FIGS. 13 and 14

a-

14

c

, diaphragm portion

112

c

forms a slightly concave configuration when the frangible portion

12

e

is formed by coining making it somewhat difficult to provide a high production volume, effective welded joint at the unsupported portion of the diaphragm with electrode tab

8

shown in previous drawings. In order to facilitate such attachment of tab

8

, a separate cup

126

shown in

FIGS. 15

,

15

a

having a flat outer surface

126

a

(as shown) or slightly convex (not shown) can be placed over the unsupported portions of diaphragm cup member

112

. Fluid pressure receiving openings

126

b

are provided in surface

126

a

to allow pressurization of diaphragm cup member

112

. Cup

126

is provided with a sidewall

126

c

having an outwardly extending flange

126

d

at its free end which can be suitably attached to the supported portion of diaphragm cup member

112

as by welding.

With reference to

FIG. 16

, a flat (or convex) surface of the diaphragm cap member

112

′ for effective welding of electrode tab

8

is provided by forming an offset portion

112

d

to provide isolation from the coined frangible portion

12

e

. The forming of offset

112

d

creates tensional forces which offset compression forces caused by coining so that the inclined surface

112

a

becomes important in providing effective snap action of the diaphragm cup member

112

′. The inclined surface

112

a

serves as an effective calibration surface by controlling the angle of inclination to provide the amount of translation obtained during snap action as well as actuation pressure and provides increased driving force which can even cause disc

22

to actuate during over-pressure to increase the gap between the contacts. Further adjustment can be obtained by selection of the placement of frangible portion

12

e

in a flat intermediate surface portion

112

f

, i.e., selection of the diameter of the frangible portion

12

e

, for example, the C-shaped portion shown in

FIG. 16

a

. The offset flat portion can be formed to project outwardly as shown in

FIG. 16

, i.e., away from the end cap apparatus, or inwardly as shown in cap member

112

″ at

112

d′

in

FIG. 16

b

. When formed as shown in

FIG. 16

b

a separate, relatively thick disc

128

of suitable material such as aluminum preferably at least as thick as the offset is deep, can be mounted within the offset and welded thereto prior to assembly of the current interrupt apparatus when a suitable anvil type support can be provided. An electrode strap can then be easily laser welded to the thicker disc

128

when the apparatus is installed in an electrochemical cell without the danger of perforating the diaphragm cap member.

Another variation of the diaphragm cap member is shown in

FIG. 16

c

in which inclined calibration surface

112

a

is placed inboard of frangible portion

12

e

in cap member

112

′″ and serves not only to promote snap action but also to form the offset flat welding portion

112

d″.

This modification allows the provision of a diaphragm cap member having a smaller overall diameter of wall portion

112

g

when it is needed in electrochemical cells having a reduced available internal space. With reference to

FIGS. 17

,

17

a

,

17

b

, a modified current interrupt apparatus

130

is shown in which the function of various components of the

FIG. 13

embodiment are combined to decrease the number of component parts and facilitate handling during assembly. As shown in

FIG. 17

, current interrupt apparatus

130

includes diaphragm cap member

112

′ of

FIG. 16

with a shortened flat portion

112

f

between offset portion

112

d

and inclined portion

112

a

, however, it will be appreciated that the other diaphragm cap members described above described above could be employed as well. Electrically insulative member

132

, formed of suitable material such as nylon, serves to provide electrical isolation between top cap

124

and diaphragm cap member

112

′, as a disc seat for thermally responsive snap acting disc

22

and as a motion transfer member to transfer motion from diaphragm cup member

112

′. With particular reference to

FIG. 17

a

, a top plan view, and

FIG. 17

b

, a cross section, member

132

comprises a generally circular annular base portion

132

a

having a structural support rib

132

b

which is received in the space formed by rib

122

b

of support

122

. Disc seat

132

c

is formed in base portion

132

a

and is shown with optional vent slots

132

d

formed around the periphery of disc seat

132

d

. First and second generally J-shaped motion transfer arms

132

e

extend inwardly into the bore of the annulus from base portion

132

a

and each has a respective end formed with a downwardly depending leg

118

a

. Preferably, a recessed groove

132

f

is formed across each motion transfer arm

132

e

to serve as a hinge enhancing flexibility. Base portion

132

a

is formed as a relatively thick wall which, with support rib

132

b

provides a stable seat for disc

22

. A somewhat thinner sidewall

132

g

extends upwardly from the outer periphery of base portion

132

a

which is attenuated at its upper portion

132

h

to facilitate bending when wall

122

d

of support

122

and the outer peripheral wall of diaphragm cap member

112

′ are rolled over to crimp the parts together. Preferably, a plurality of spaced vertically extending ribs

132

k

are formed in attenuated portion

132

h

on the inside facing surface to pliably accommodate the composite flange components as they vary in tolerance keeping them properly aligned and fully seated to ensure that the appropriate distance for the motion transfer member to move does not change. The remaining components, i.e., the top cap

124

, the spring member

120

, support

122

and thermally responsive disc

22

function as described above and need not be repeated.

The invention provides an end cap having a single component which provides a leak proof seal for an electrochemical cell utilizing an appropriate gasket, the component being formed of electrolyte compatible material incorporating a coined pressure diaphragm to actuate a current interrupt device in response to low pressure and vent the electrolyte at elevated pressure. The end cap is characterized in having sufficient structural integrity to allow crimping into a cell in sealed relation without affecting the calibration of safety features mounted within the end cap and is provided with a suitable surface to facilitate attachment of the cell's electrode tab.

Although the invention has been described with regards to specific preferred embodiments thereof, variations and modifications will become apparent to those skilled in the art. For example, in certain electrochemical cells resettable thermostatic discs may be preferred. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.

Number	Name	Date
4943497	Oishi et al.	Jul 1990
5171648	Beard	Dec 1992
5464705	Wainwright	Nov 1995
5567539	Takahashi et al.	Oct 1996
5707756	Inoue et al.	Jan 1998
5750277	Vu et al.	May 1998
5998051	Poirier et al.	Dec 1999

Current interrupt apparatus for electrochemical cells

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Parent Case Info

US Referenced Citations (7)

Foreign Referenced Citations (1)

Provisional Applications (1)