Patent Publication Number: US-2011052948-A1

Title: Cell Cap Assembly with Desirable Safety Performance

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present patent invention claims priority to Chinese Patent Application No. CN 200920193726.6 filed Aug. 31, 2009, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The present patent invention generally relates to cell cap assemblies and, more particularly, relates to a cell cap assembly with desirable safety performance. 
     BACKGROUND OF THE INVENTION 
     Recently, with the development of science and technology, portable electronic devices, such as video cameras, laptop personal computers, portable DVDs and personal digital assistants are becoming increasingly popular in people&#39;s daily life. To meet the requirement of being convenient for carrying, desirable high-energy power source, such as lithium-ion batteries are being widely used. 
     High-energy batteries can supply enough energy for mobile electronic devices anytime and anywhere. However, due to the use of high-energy chemical materials and energy concentration, safety performance of high-energy batteries is not satisfactory. For instance, in charging or discharging process of lithium-ion batteries, short-circuit possibly occur due to compression, collision or other unexpected incidents, which will inevitably produce large current and, therefore, generate a lot of heat. The heat accumulation may cause the lithium-ion batteries to burn or explode and, therefore, damage the electronic devices and even injure the users. 
     To solve the technical problem as previously discussed, cell cap assemblies which can prevent the batteries from burning or exploding are widely used in the art. Typically, a cell cap assembly which can prevent the battery from burning or exploding generally includes an grommet defining a stepped through hole, a stripper contact plate defining at least one gas hole, an rupture plate electrically connected with the stripper contact plate via spot welding, and an end cap electrically connected with the rupture plate. The stripper contact plate, the rupture plate and the end cap are orderly and tightly received in the through hole of the grommet. In use, when short-circuit in the battery occurs due to overcharge or unsuitable operation, the expanding gas in the battery flows through the gas hole of the stripper contact plate and actuates the rupture plate to reverse upwardly. If the gas pressure achieves a predetermined pressure value, the welding spots between the rupture plate and the stripper contact plate are ruptured. The current path of the battery is cut off to prevent the battery from burning or exploding. 
     However, the cell cap assemblies as disclosed in the prior art at least have the following shortcoming. The stiffness of the rupture plate is not adjustable or controllable. The current path of the battery is difficult to cut off accurately when unexpected incidents occur and, therefore, the safety performance of the battery is still not desirable enough. 
     What is needed, therefore, is to provide a cell cap assembly having desirable safety performance which can avoid the safety accidents as previously discussed. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a cell cap assembly with desirable safety performance which can avoid safety accidents of the battery. 
     According to one embodiment of the present invention, a cell cap assembly includes a grommet defining a through hole, a stripper contact plate defining at least one gas hole securely received in the through hole, an rupture plate securely positioned in the through hole and electrically connected with the stripper contact plate, and an end cap electrically connected with the rupture plate. The rupture plate includes an outer ring portion, a bent portion extending from the outer ring portion and a recessed portion defining a recess formed at an end of the bent portion. 
     According to the embodiment of the present invention, the recess defined in the recessed portion of the rupture plate can adjust and control the stiffness of the rupture plate, so that the rupture plate can reverse controllably and easily. When an unexpected incident occurs, the current path through the battery can be cut off quickly and accurately. 
     Preferably, the recess has a shape of closed circular, square, trapezoid, oval or rectangle. 
     Preferably, a positive temperature coefficient (PTC) is sandwiched between the rupture plate and the end cap. The PTC defines a center hole for receiving at least part of the reversed rupture plate. 
     Preferably, a groove is disposed adjacent the boundary area of the outer ring portion and the bent portion of the rupture plate. 
     Preferably, the recess and the groove are disposed concentrically. 
     Preferably, the end cap has an annular flange, a sidewall extending upwardly from the annular flange and a round top formed at a top of the sidewall. At least one perforation is defined in the sidewall and/or the round top. 
     Preferably, the rupture plate and the stripper contact plate are in electrical connection with each other via welding spots at the recessed portion, and are separated from each other by an insulative gasket at the other area. 
     Preferably, the bent portion of the rupture plate is provided with at least one relief groove at a central area thereof. 
     According to another aspect of the present invention, an rupture plate for use in a cell cap assembly includes an outer ring portion, a bent portion extending obliquely and downwardly from an internal edge of the outer ring portion, and a recessed portion defining a recess formed at an end of the bent portion. 
     Preferably, the recess has a shape of closed circle, square, trapezoid, rectangle or oval. 
     Preferably, a groove is provided adjacent the boundary area of the outer ring portion and the bent portion. 
     Preferably, the rupture plate is provided with at least one relief groove at a central area thereof. 
     Other advantages and novel features will be drawn from the following detailed description of preferred embodiments with the attached drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a vertical sectional view of an assembled cap assembly according to one embodiment of the present invention, wherein a rupture plate thereof is in a normal state; 
         FIG. 2  depicts a perspective view of the rupture plate as shown in  FIG. 1 ; 
         FIG. 3  depicts a perspective view of a rupture plate for use in the cap assembly as shown in  FIG. 1  according to another embodiment of the present invention. 
         FIG. 4  depicts another vertical sectional view of the assembled cap assembly as illustrated in  FIG. 1 , wherein the rupture plate is in a reversed state; 
         FIG. 5  depicts a perspective view of the rupture plate in a reversed state as shown in  FIG. 4 ; and 
         FIG. 6  depicts another perspective view of the rupture plate in a reversed state as shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 to 6 , a cap assembly according to one embodiment of the present invention includes a grommet  20 , an end cap  30 , a rupture plate  40 , a positive temperature coefficient  50  (hereinafter referred as PTC), an insulative gasket  60  and a stripper contact plate  80 . 
     The grommet  20  is substantially a hollow cylinder. Upper end of the grommet  20  having a larger diameter defines a closed end  203 , and the lower end having a smaller diameter defines a holding end  205 . Stepped through hole  208  is defined in the grommet  20 . A first vertical wall  202 , a second vertical wall  204  and a third vertical wall  206  are provided at an inner surface of the grommet  20  from upper side to lower side. 
     The end cap  30  is a hollow cup including an annular flange  302 . An external diameter of the annular flange  302  is smaller than a diameter of the through hole  208  at the closed end  203 . A sloped sidewall (not labeled) protrudes from the internal edge of the annular flange  302  upwardly and obliquely. A planar round top  304  is provided at the top of the sloped sidewall. A number of circumferentially spaced perforations  306  are defined in the sloped sidewall, or the round top  304 , or both of them. 
     Referring particularly to  FIGS. 2 ,  3  and  5 ,  6 , the rupture plate  40  is a round plate having a planar recessed center area. The rupture plate  40  includes an outer ring portion  402 , a bent portion  404  protruding obliquely and downwardly from internal edge of the outer ring portion  402  and a planar recessed portion  406  formed at a contraction end of the bent portion  404 . An annular groove  403  is defined adjacent the boundary area of the outer ring portion  402  and the bent portion  404 . If a gas pressure in a battery exceeds a predetermined pressure value, the rupture plate  40  will be ruptured around the annular groove  403  to release the gas pressure and ensure the battery safety. 
     The recessed portion  406  is a planar plate which defines a closed recess  405  on an upper surface facing the end cap  30 . The recess  405  and the groove  403  are preferably arranged concentrically. The arrangement of the recess  405  can make the stiffness of the rupture plate  40  controllable and convenient, so that the rupture plate  40  can reverse easily and controllably. When unexpected incident occurs due to unsuitable operation, the current path through the battery can be cut off quickly and accurately. 
     It is noticeable that, in the embodiment of the present invention as illustrated, the recess  405  generally has a shape of closed circle. However, according to alternative embodiments of the present invention, the recess  405  may also has other shapes, such as closed square, trapezoid, rectangle or oval depending on accuracy and convenience of mechanical process. Additionally, the depth of the recess  405  is linear to the reversing pressure. 
     Additionally, referring particularly to  FIGS. 3 and 6 , to make sure the rupture plate  40  can be reversed more readily under the pressure of the expanding gas inside the battery, especially for the rupture plate made from hard material, such as hard aluminum, central area of the bent portion  404  is thinner than other areas thereof. In the embodiment as illustrated, the bent portion  404  is provided with a relief groove  407  at a central area thereof. 
     The electrically insulative gasket  60  includes an annular main body  602 . An external diameter of the main body  602  is larger than a diameter of the third vertical wall  206  but is smaller than the diameter of the second vertical wall  204 . A downwardly extending side wall  604  is formed at an inner edge of the insulative gasket  60 . 
     The stripper contact plate  80  has a shape similar to that of the end cap  30  and is formed with a ring portion  802 , a connection portion  804  extending downwardly and obliquely from the ring portion  802  and a wafer  805  formed on a contraction end of the connection portion  804 . External diameter of the ring portion  802  is equal to or slightly smaller than the external diameter of the insulative gasket  60 . A depression  808  is defined in a lower surface of the wafer  805 , so that a disconnection portion  809  having a smaller thickness is formed. At least one gas holes  810  are defined in the wafer  805 . 
     To further improve the safety performance of the battery, a PTC  50  is disposed between the rupture plate  40  and the end cap  30 . The PTC  50  is a flat ring plate having a center hole  502  in a center thereof. The center hole  502  has a diameter slightly lager than an external diameter of the bent portion  404  of the rupture plate  40 . When the rupture plate  40  is reversed under the pressure of the gas in the battery, the bent portion  404  and part of the recessed portion  406  of the rupture plate  40  are received in the center hole  502  of the PTC  50 . 
     In assembly, the insulative gasket  60  is set on the ring portion  802  of the stripper contact plate  80 . The side wall  604  of the insulative gasket  60  abuts against an inner edge of the ring portion  802  of the stripper contact plate  80 , to prevent the stripper contact plate  80  from being movable relative to the insulating gasket  60 . The recessed portion  406  of the rupture plate  40  and the disconnection portion  809  of the stripper contact plate  80  are in electrical connection with each other by spot welding. The welded rupture plate  40  and the stripper contact plate  80  are received in the through hole  208  of the grommet  20 . Thereafter, the PTC  50  and the end cap  30  are assembled on the rupture plate  40  in order. 
     Please referring to  FIGS. 1 and 3 , in nipping process, the closed end  203  of the grommet  20  is deformed under the pressure of the housing  70 . The first vertical wall  202  of the closed end  203  presses the upper surface of the annular flange  302  of the end cap  30  tightly. The rupture plate  40 , the PTC  50  and the end cap  30  are mounted tightly and electrically connected to each other safely. The battery cell (not shown) is safely sealed off in the housing  70 . 
     During charging or discharging, if short-circuit occurs in the battery and the temperature of the battery rises, the expanding gas in the battery will flow through the gas hole  810  of the stripper contact plate  80  into the space between the stripper contact plate  80  and the rupture plate  40 . When the gas pressure in the battery exceeds a predetermined pressure value, the bent portion  404  and the recessed portion  406  of the rupture plate  40  are urged to deform upwardly. As the ring portion  802  of the stripper contact plate  80 , the main body  602  of the insulative gasket  60  and the outer ring portion  402  of the rupture plate  40  abutting against one another tightly, the disconnection portion  809  of the stripper contact plate  80  or the welding spots between the rupture plate  40  and the stripper contact plate  80  are ruptured. The current path of the battery is then cut off. If the pressure of the expanding gas is large enough, the rupture plate  40  will reverse and be ruptured at the groove  403 . The gas flows through the perforation  306  of the end cap  30  to prevent the battery from burning or exploding. 
     According to the embodiments of the present invention as previously detailed, the recess  405  defined in the recessed portion  406  of the rupture plate  40  can adjust the stiffness of the rupture plate  40  and, therefore, the rupture plate  40  can reverse easily and controllably. When an unexpected incident occurs, the current path through the battery can be cut off quickly and accurately. 
     While the present invention has been illustrated by the above description of the preferred embodiments thereof, while the preferred embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications within the spirit and scope of the present invention will readily appear to those ordinary skilled in the art. Consequently, the present invention is not limited to the specific details and the illustrative examples as shown and described.