Current interrupter for electrochemical cells

• US 6,037,071 A
• Filed: 11/06/1997
• Issued: 03/14/2000
• Est. Priority Date: 04/10/1996
• Status: Expired due to Term

• Current Assignee: Duracell U.S. Operations, Inc. (Berkshire Hathaway Incorporated)
• Original Assignee: Duracell Incorporated (Berkshire Hathaway Incorporated)
• Inventors: McDermott, Michael, Cheeseman, Paul, Patel, Bhupendra, Vu, Viet, Kouznetsova, Yelena, Fontaine, Lucien P., Cantave, Reynald, Poirier, Jeffrey, Pinault, Robert J., McHugh, William T., Blasi, Jane A., Kaplan, Alex, Hewes, Jeffrey
• Primary Examiner(s): Nuzzolillo, Maria
• Assistant Examiner(s): WILLS, MONIQUE M
• Application Number:
  US08/965,494
• Time in Patent Office: 859 Days
• Field of Search: 429/53, 429/54, 429/56, 429/57, 429/61, 429/62, 429/72, 429/7, 429/163, 429/170, 429/171, 429/172, 429/89
• US Class Current: 429/7
• CPC Class Codes: H01H 2037/769 characterised by the composition of insulating fusible materials, e.g. for use in the thermal pellets
• CPC Class Codes: H01H 35/34 actuated by diaphragm
• CPC Class Codes: H01H 37/323 making use of shape memory materials in thermal relays H01H61/0107; release mechanism H01H71/145; treatment of SMF alloys C22F1/006; for control of temperature G05D23/024
• CPC Class Codes: H01H 37/54 wherein the bimetallic element is inherently snap acting
• CPC Class Codes: H01H 37/764 in which contacts are held closed by a thermal pellet
• CPC Class Codes: H01M 2200/10 Temperature sensitive devices
• CPC Class Codes: H01M 2200/101 Bimetal
• CPC Class Codes: H01M 2200/108 Normal resistors
• CPC Class Codes: H01M 2200/20 Pressure-sensitive devices
• CPC Class Codes: H01M 50/3425 in the form of rupturable membranes or weakened parts, e.g. pierced with the aid of a sharp member
• CPC Class Codes: H01M 50/574 Devices or arrangements for the interruption of current
• CPC Class Codes: H01M 50/578 in response to pressure
• CPC Class Codes: H01M 50/581 in response to temperature
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A current interrupt mechanism for electrochemical cells is disclosed. A thermally activated current interrupt mechanism is integrated into an end cap assembly for an electrochemical cell. The thermally responsive mechanism preferably includes a free floating bimetallic disk or shape memory alloy member which deforms when exposed to elevated temperature causing a break in an electrical pathway within the end cap assembly. This prevents current from flowing through the cell and effectively shuts down an operating cell. The thermally responsive mechanism may include a heat producing electrical resistance means, preferably a Zener diode, to enhance thermal sensitivity. The end cap assembly may include a pressure responsive mechanism which ruptures when there is extreme gas pressure buildup. Gas is allowed to escape from the cell interior to the external environment through a series of vent apertures within the end cap assembly.

Claims

1. An end cap assembly for application to an electrochemical cell having a positive and a negative terminal and a pair of electrodes (anode and cathode), said end cap assembly comprising a housing and an exposed end cap plate, said plate functional as a cell terminal, said end cap assembly having an electrically conductive pathway therethrough permitting the end cap plate to be electrically connected to a cell electrode when said end cap assembly is applied to a cell, said end cap assembly further including thermally responsive means for preventing current from flowing through said electrical pathway and electrical resistance means in proximity to said thermally responsive means, said resistance means causing heating as current passes therethrough, said resistance means exhibiting decreasing resistance as voltage applied thereto increases, wherein said thermally responsive means activates when the temperature within said end cap assembly rises causing a break in said electrical pathway.

2. The end cap assembly of claim 1 wherein said resistance means comprises a diode located within said housing, said diode having a positive and a negative terminal for parallel electrical connection to the positive and negative terminals, respectively, of said cell.

3. The end cap assembly of claim 1 wherein said resistance means comprises a diode subassembly having a Zener diode located within said housing, said Zener diode having a positive and a negative terminal for parallel electrical connection to the positive and negative terminals, respectively, of said cell.

4. The end cap assembly of claim 3 wherein a terminal of said Zener diode is electrically connected to said exposed end cap plate of said assembly.

5. The end cap assembly of claim 1 where said assembly is a self-contained structure.

6. The end cap assembly of claim 3 wherein said diode subassembly comprises a conductive member connected to one of the terminals of said diode, said conductive member extending from the diode for electrical connection to a cell terminal of like polarity.

7. The end cap assembly of claim 6 wherein said conductive member is surrounded by electrical insulation.

8. The end cap assembly of claim 3 wherein the Zener diode has a wattage between about 100 and 500 microwatts.

9. The end cap assembly of claim 8 wherein the Zener diode has a Zener voltage of less than about 5 volts.

10. The end cap assembly of claim 3 wherein said Zener diode is a wafer chip.

11. The end cap assembly of claim 6 wherein said diode subassembly is in the form of a wafer having a polygonal or oval shape.

12. The end cap assembly of claim 1 further comprising a pressure responsive means comprising a member capable of rupture located at the end of said end cap assembly opposite said end cap plate, said member rupturing when gas pressure on the side thereof farthest from said end cap plate rises producing a rupture in said member allowing gas to pass therethrough.

13. The end cap assembly of claim 1 wherein said cell has a cylindrical casing and the end cap assembly is applied to the cell by inserting it into the open end of the cylindrical casing and welding the end cap assembly to the casing.

14. The end cap assembly of claim 1 wherein said thermally responsive means comprises a chamber within said end cap assembly having a bimetallic member and a resilient electrically conductive member, the resilient member forming a portion of said electrical pathway, wherein when the cell temperature within said assembly rises, the bimetallic member deforms thereby pushing against said resilient metallic member causing a break in said electrical pathway.

15. The end cap assembly of claim 14 wherein the bimetallic member rests freely on a surface of an electrically insulating member within said end cap assembly.

16. The end cap assembly of claim 15 wherein a portion of said resilient metallic member is sandwiched between a portion of said end cap plate and a portion of said electrically insulating member and wherein the end cap assembly comprises a contact plate which forms part of said electrical pathway, wherein said resilient member is in electrical contact with said contact plate.

17. The end cap assembly of claim 12 further comprising a separation member placed across the interior width of the end cap assembly and between said end cap plate and said member capable of rupture, said separation member separating said thermal responsive means from said pressure responsive means.

18. The end cap assembly of claim 17 wherein said separation member comprises a metallic plate having at least one aperture therein so that when said member capable of rupture ruptures, gas passes through said aperture and into said chamber within said end cap assembly.

19. The end cap assembly of claim 18 wherein said end cap plate has at least one aperture therethrough so that when said member capable of rupture ruptures, gas collected from said chamber passes through said end cap aperture and to the external environment.

20. The end cap assembly of claim 17 wherein said member capable of rupture comprises a diaphragm.

21. The end cap assembly of claim 16 wherein when the temperature of said bimetallic member rises it deforms causing the resilient conductive member to sever its electrical connection with said contact plate, thereby causing a break in said electrical pathway.

22. The end cap assembly of claim 20 further comprising an electrically insulating grommet in contact with the peripheral edge of the end cap plate and the peripheral edge of the diaphragm, said end cap assembly further comprising a metallic member (crimping member) mechanically crimped around said grommet to hold said diaphragm plate and said end cap plate under mechanical compression.

23. The end cap assembly of claim 22 further comprising a metallic cover around said crimping member.

24. The end cap assembly of claim 23 wherein the end cap assembly is applied to a cell by inserting it into the open end of a cylindrical casing for the cell and welding the outside surface of said cover to the inside surface of said casing, whereupon the end cap assembly becomes tightly sealed within the cylindrical case with the end cap plate comprising a terminal of the cell being exposed to the external environment.

25. The end cap assembly of claim 1 wherein the thermally responsive means comprises a resilient conductive member in electrical contact with said end cap plate, and a meltable mass of material holding said resilient conductive member in electrical connection between said end cap plate and another conductive portion of the end cap assembly, said other conductive portion adapted to be electrically connected to a cell electrode when the end cap assembly is applied to a cell thereby providing an electrical connection between said end cap plate and said electrode during cell operation, wherein when the cell temperature rises said mass of material melts thereby causing movement in said resilient metallic member to sever the electrical connection between said end cap plate and said cell electrode thereby preventing operation of the cell.

26. An end cap assembly for application to an electrochemical cell having a positive and a negative terminal and a pair of internal electrodes (anode and cathode), said end cap assembly comprising a housing, a chamber within the housing, and an exposed end cap plate, said plate functional as a cell terminal, said end cap assembly having an electrically conductive pathway therethrough permitting the end cap plate to be electrically connected to a cell electrode when said end cap assembly is applied to a cell, said end cap assembly further comprising a) thermally responsive means for preventing current from flowing through said electrical pathway and a.1) electrical resistance means electrically connected to said cell terminals for causing heating as current passes therethrough, said resistance means exhibiting decreasing resistance as voltage applied thereto increases, wherein said thermally responsive means comprises a shape memory alloy member which activates when the temperature within said end cap assembly rises causing a break in said electrical pathway, and said end cap assembly further comprises b) a pressure responsive means comprising a member capable of rupture located at the end of said end cap assembly opposite said end cap plate, said member rupturing when gas pressure on the side thereof farthest from said end cap plate rises producing a rupture in said member allowing gas to pass therethrough.

27. The end cap assembly of claim 26 wherein said resistance means comprises a diode located within said housing, said diode having a positive and a negative terminal for parallel electrical connection to the positive and negative terminals, respectively, of said cell.

28. The end cap assembly of claim 26 wherein said resistance means comprises diode subassembly comprising a Zener diode located within said housing, said Zener diode having a positive and a negative terminal for parallel electrical connection to the positive and negative terminals, respectively, of said cell.

29. The end cap assembly of claim 28 wherein a terminal of said Zener diode is electrically connected to said exposed end cap plate of said assembly.

30. The end cap assembly of claim 26 where said assembly is a self-contained structure.

31. The end cap assembly of claim 28 wherein said diode subassembly comprises a conductive member connected to one of the terminals of said diode, said conductive member extending from the diode for connection to a cell terminal of like polarity.

32. The end cap assembly of claim 31 wherein the body of said conductive member is surrounded by electrical insulation.

33. The end cap assembly of claim 28 wherein the Zener diode has a wattage of between about 100 and 500 microwatts.

34. The end cap assembly of claim 33 wherein the Zener diode has a Zener voltage less than about 5 volts.

35. The end cap assembly of claim 28 wherein said Zener diode is a wafer chip.

36. The end cap assembly of claim 31 wherein said diode subassembly is in the form of a wafer having a polygonal or oval shape.

37. The end cap assembly of claim 26 wherein said shape memory alloy comprises a nickel-titanium alloy.

38. The end cap assembly of claim 26 wherein said cell has a cylindrical casing and the end cap assembly is applied to the cell by inserting it into the open end of the cylindrical casing and welding the end cap assembly to the casing.

39. The end cap assembly of claim 26 wherein said thermally responsive means comprises a chamber within said end cap assembly, the shape memory alloy member forming a portion of said electrical pathway, wherein when the cell temperature within said assembly rises, the shape memory alloy member deforms thereby causing a break in said electrical pathway.

40. The end cap assembly of claim 39 wherein said shape memory element comprises a flexible member of single piece construction having a bent surface wherein when the cell temperature within said assembly rises, the surface of said shape memory member deforms causing a break in said electrical pathway.

41. The end cap assembly of claim 39 wherein said shape memory member comprises a disk having an aperture therethrough, said disk having an outer edge with a flexible portion protruding into said aperture from a portion of the outer edge, wherein the outer edge rests on a surface of an insulating member within said end cap assembly, wherein said flexible portion has a bent surface, wherein when the cell temperature within said assembly rises, said bent surface deforms causing a break in said electrical pathway.

42. The end cap assembly of claim 41 wherein said outer edge of said shape memory member is sandwiched between a portion of said end cap plate and a portion of said electrically insulating member and wherein the end cap assembly comprises a contact plate which forms part of said electrical pathway, wherein said shape memory member is in electrical contact with said contact plate.

43. The end cap assembly of claim 26 further comprising a separation member placed across the interior width of the end cap assembly and between said end cap plate and said member capable of rupture, said separation member separating said thermal responsive means from said pressure responsive means.

44. The end cap assembly of claim 43 wherein said separation member comprises a metallic plate having at least one aperture therein so that when said member capable of rupture ruptures, gas passes through said aperture and into said chamber within said end cap assembly.

45. The end cap assembly of claim 43 wherein said end cap plate has at least one aperture therethrough so that when said member capable of rupture ruptures, gas collected from said chamber passes through said end cap aperture and to the external environment.

46. The end cap assembly of claim 45 wherein said member capable of rupture comprises a diaphragm.

47. The end cap assembly of claim 46 further comprising an electrically insulating grommet in contact with the peripheral edge of the end cap plate and the peripheral edge of the diaphragm, said end cap assembly further comprising a metallic member (crimping member) mechanically crimped around said grommet to hold said diaphragm and said end cap plate under mechanical compression.

48. The end cap assembly of claim 47 further comprising a metallic cover around said crimping member.

49. The end cap assembly of claim 48 wherein the end cap assembly is applied to a cell by inserting it into the open end of a cylindrical casing for the cell and welding the outside surface of said cover to the inside surface of said casing, whereupon the end cap assembly becomes tightly sealed within the cylindrical case with the end cap plate comprising a terminal of the cell being exposed to the external environment.

50. The end cap assembly of claim 26 wherein said shape memory alloy member comprises a disk having an aperture through the thickness thereof, said shape memory member having a peripheral edge with a flexible portion protruding inwardly into said aperture from a portion of said peripheral edge, wherein said edge rests on a surface of an insulating member within said end cap assembly, wherein when the cell temperature within the cell assembly rises, said flexible portion deforms causing a break in said electrical pathway.

51. In an electrochemical cell of the type formed by an end cap assembly inserted into an open ended cylindrical case for the cell, said cell further having a positive and a negative terminal and a pair of internal electrodes (anode and cathode), wherein said end cap assembly has a housing and an exposed end cap plate, said end cap plate functional as a cell terminal, the improvement comprising said end cap plate being electrically connected to one of said electrodes through an electrically conductive pathway within said end cap assembly, wherein said end cap assembly comprises a) thermally responsive means comprising an electrically conductive shape memory alloy member for preventing current from flowing through the cell and a.1) electrical resistance means in proximity to said thermally responsive means, said resistance means causing heating as current passes therethrough, said resistance means exhibiting decreasing resistance as voltage applied thereto increases, wherein said shape memory member comprises a flexible member having a bent surface and a thickness smaller than its length, said flexible member oriented within said end cap assembly so that current passes substantially in a direction through the thickness of said flexible member, wherein when the cell temperature rises, said shape memory member deflects along said bent surface causing a break in said electrical pathway between said end cap plate and said electrode thereby preventing current from flowing through the cell.

52. The electrochemical cell of claim 51 wherein said resistance means comprises a diode located within said housing, said diode having a positive and a negative terminal electrically connected in parallel to the positive and negative terminals, respectively, of said cell.

53. The electrochemical cell of claim 51 wherein said resistance means comprises diode subassembly comprising a Zener diode located within said housing, said Zener diode having a positive and a negative terminal electrically connected in parallel to the positive and negative terminals, respectively, of said cell.

54. The electrochemical cell of claim 53 wherein a terminal of said Zener diode is electrically connected to said exposed end cap plate of said assembly wherein said connected terminal of the Zener diode is of same polarity as said exposed end cap plate.

55. The electrochemical cell of claim 51 where said assembly is a self-contained structure.

56. The electrochemical cell of claim 53 wherein said diode subassembly comprises a conductive member connected to one of the terminals of said diode, said conductive member extending from the diode and electrically connected to a cell terminal of like polarity.

57. The electrochemical cell of claim 56 wherein the body of said conductive member is surrounded by electrical insulation.

58. The electrochemical cell of claim 53 wherein the Zener diode has a wattage between about 100 and 500 microwatts.

59. The electrochemical cell of claim 58 wherein the Zener diode has a Zener voltage of less than about 5 volts.

60. The electrochemical cell of claim 53 wherein said Zener diode is a wafer chip.

61. The electrochemical cell of claim 56 wherein said diode subassembly is in the form of a wafer having a polygonal or oval shape.

62. The electrochemical cell of claim 51 wherein said shape memory member comprises a disk having an aperture through the thickness thereof, said disk having a peripheral outer edge with said flexible member protruding inwardly into said aperture from a portion of said peripheral edge, said flexible member having a bent surface which deflects when the cell temperature rises.

63. The electrochemical cell of claim 51 wherein said shape memory member comprises a nickel-titanium alloy.

64. The electrochemical cell of claim 51 further comprising b) pressure responsive means allowing gas from the interior of the cell to pass into the interior of said end cap assembly when internal gas pressure within the cell rises.

65. The electrochemical cell of claim 64 wherein said pressure responsive means comprises a diaphragm plate located at the end of said end cap assembly opposite said end cap plate, said diaphragm plate rupturing when gas pressure on the side thereof farthest from said end cap plate rises producing a rupture in said diaphragm allowing gas to pass therethrough.