Cell current cutoff mechanism

[0002] 1. Field of the Invention

[0003] The present invention relates to a current cutoff mechanism of a cell, particularly relates to a current cutoff mechanism of a cell used for securing safety when pressure inside a cell case is increased

[0004] 2. Description of the Related Art

[0005] Heretofore, a sealed lithium ion secondary cell inside the case of which an electrolyte including an organic solvent for example is injected and which can be charged are widely used for a power source for portable equipment such as a mobile telephone and a personal computer

[0006] However, if such a cell is excessively charged when it is charged again or is charged with larger current than defined current, abnormality occurs in the cell, gas is generated in a cell case, pressure and temperature in the cell case rise, the cell case is swollen, further a crack is formed, an inside electrolyte leaks outside and the leaked electrolyte sometimes has an adverse effect on equipment in which the cell is built.

[0007] If the use of the above cell is continued in the above abnormal state even if the above leaked electrolyte does not have an adverse effect on the equipment, the swell of the cell progresses, the cell case may burst and the use of the abnormal cell is required to be stopped promptly.

[0008] A conventional type current cutoff mechanism of a cell for preventing the burst of such a cell will be described as a circular cell shown in FIGS. 10 and 11 below. First, in a cell case 1, a cell lid 3 attached by riveting the periphery of the cell lid via a gasket 2 or welding in order to seal the inside of the cell case 1 and an actuator 4 which can be displaced above and below in the lower part of the cell lid 3 are respectively arranged.

[0009] An air vent 3ais formed in the cell lid 3 and when the actuator 4 in the lower part is displaced and cleaves its way upward air in a part between the cell lid 3 and the actuator 4 is emitted outside from the air vent 3a.

[0010] In the actuator 4, a circular relief valve 4ais formed by drawing and in the relief valve 4a, a projection 4bprotruded downward in the drawings is formed in the center and a radial groove 4cis formed on the surface around the projection 4b.

[0011] An insulating plate 5 is arranged below the actuator 4 and in the insulating plate 5, a hole 5afor inserting the projection 4bof the relief valve 4aand an air vent 5bare formed.

[0012] A lead fixing member 6 is arranged below the above insulating plate 5 and in the lead fixing member 6, a hole 6afor communicating with the above hole 5aof the insulating plate 5 and an air vent 6bcommunicating with the air vent 5bof the insulating plate 5 are respectively provided.

[0013] The projection 4bof the relief valve 4ais inserted into the respectively holes 5aand 6aof the above insulating plate 5 and the lead fixing member 6 and a thin lead 7 made of a metallic plate is attached to the end of the projection 4b.

[0014] The thin lead 7 is provided with a junction 7abonded to the end of the projection 4bby welding, and the actuator 4 and the lead 7 are electrically connected. The other end of the lead 7 is connected to a generating element 8 in the lower part in the drawings and a conductive path is formed between the generating element 8 and the cell lid 3.

[0015] If an abnormality occurs inside the cell and pressure inside the cell case 1 is increased, the pressure of gas is increased and the gas flows from the air vents 5band 6bas shown by an arrow A in FIG. 11. The application force which pushes up the rear of the relief valve 4ais applied.

[0016] When concentrated stress is applied to the junction 7aof the lead 7 by application force applied to the relief valve 4aand the concentrated stress is larger than the shearing stress of the junction 7a, the junction 7ais disconnected from the lead 7, electrical connection between the lead 7 and the actuator 4 is cut off and the conductive path of the above cell is cut off.

[0017] The flow of current inside the cell is cut off by the above cutoff of the conductive path, the increase of pressure inside the cell case 1 is prevented and the cell can be prevented from bursting beforehand.

[0018] Portable equipment using such a conventional type cell (such as a mobile telephone) has become more and more miniaturized and the need has increased for the miniaturization and the thinning of the cell used for such portable equipment.

[0019] However, as the above conventional type current cutoff mechanism is formed by one plate though the lead 7 is thin, the application force of the actuator 4 varies widely depending upon variation in the thickness of the lead 7 and it is difficult to securely disconnect the junction 7afrom the lead 7 when the internal pressure of the cell is increased up to a predetermined value.

[0020] As the junction 7ais disconnected as if it were torn off when the internal pressure of the cell is increased and the junction 7ais disconnected from the lead 7, a burr like a beard is made on the section of a disconnected hole 7bof the junction 7aafter the junction is disconnected from the lead and it is difficult to precisely and completely cut off the conductive path between the actuator 4 displaced upward and the lead 7.

[0021] The present invention is made to solve the above problems and the object is to provide a high performance current cutoff mechanism of a cell wherein the miniaturization and the thinning are enabled and when pressure inside the cell is increased up to a predetermined value, a conductive path inside the cell can be securely cut off.

[0022] A current cutoff mechanism according to the present invention of a cell as first arrangement for solving the above problems is provided with a cell case in which a generating element is housed, a cell lid for airtightly shielding the inside of the cell case, a diaphragm connected to the cell lid, displaced according to the internal pressure of the cell case and provided with a convex portion in a part and an internal electrode provided with a fitted part for fitting the above convex portion of the diaphragm at the base, and is characterized in that the convex portion of the diaphragm is press-fitted into the above fitted part, a conductive path is formed between the cell lid and the generating element via the diaphragm and the internal electrode and when the internal pressure of the cell case is increased over a predetermined value and the diaphragm is displaced, the convex portion of the diaphragm is pulled out from the fitted part and the above conductive path is cut off.

[0023] A current cutoff mechanism according to the present invention as second arrangment for solving the above problems is characterized in that plural slits radially extended from the center of the base are formed, each triangular tongue is provided in a part between these plural slits, these plural tongues are protruded approximately in a conic shape, the above fitted part is formed by the tops of these plural tongues and the convex portion of the diaphragm is press-fitted into the fitted part.

[0024] A current cutoff mechanism according to the present invention as third arrangment for solving the above problems is characterized in that the above convex portion is formed so that the end is wider than the base fitted into the fitted part.

[0025] A current cutoff mechanism according to the present invention as fourth arrangment for solving the above problems is characterized in that the above fitted part is formed in the shape of a bag having a hollow part whose entrance is narrow and the inside is wider than the entrance and the wider end of the convex portion is press-fitted into the hollow part of the fitted part.

[0026] FIG. 1 is a top view according to the present invention;

[0027] FIG. 2 is a sectional view showing a main part according to the present invention;

[0028] FIG. 3 is a bottom view according to the present invention;

[0029] FIG. 4 is a sectional side view showing the main part according to the present invention;

[0030] FIG. 5 is a sectional view in which a diaphragm according to the present invention is enlarged;

[0031] FIG. 6 is a sectional view in which the main part is enlarged for explaining the operation of the diaphragm according to the present invention;

[0032] FIGS. 7A and 7B are schematic drawings for explaining another embodiment of the present invention;

[0033] FIG. 8 is a schematic drawing for explaining further another embodiment of the present invention;

[0034] FIG. 9 is a schematic drawing for explaining the other embodiment of the present invention;

[0035] FIG. 10 is a sectional view showing the main part of a conventional type current cutoff mechanism of a cell; and

[0036] FIG. 11 is a sectional view showing the main part for explaining the operation of the conventional type current cutoff mechanism of the cell.

[0037] An embodiment of a current cutoff mechanism of a cell according to the present invention will be described below. FIG. 1 is a top view according to the present invention, FIG. 2 is the sectional view of the main part according to the present invention in a state in which the current cutoff mechanism is attached to a cell case, FIG. 3 is a bottom view according to the present invention, FIG. 4 is a sectional side view of the main part according to the present invention, FIG. 5 is a sectional view in which the main part of a diaphragm according to the present invention is enlarged, FIG. 6 is a sectional view in which the main part is enlarged for explaining its operation and FIGS. 7 to 9 are schematic drawings for explaining the other embodiments according to the present invention.

[0038] To explain a current cutoff mechanism T according to the present invention of a cell using a square cell for example, a cell lid 11 for shielding the inside of a cell case K airtightly is attached to the cell case K in which a generating element not shown is housed by welding as shown in FIGS. 1 to 4.

[0039] The above cell lid 11 is held between an insulating member 12 attached under the cell lid and a pressing member 13 attached on the cell lid, is fastened to a rivet 14 in the center, and the cell lid 11, the insulating member 12 and the pressing member 13 are integrated.

[0040] A positive terminal 15 is attached under the rivet 14 and a conducting washer 16 is attached on the rivet. An external positive electrode 17 which conducts to the positive terminal 15 is touched to the conducting washer 16 on the above rivet 14. An internal electrode 18 provided with a lead 18aand composed of a negative terminal is riveted on the right side in the drawings of the insulating member 12.

[0041] To explain the details of the above current cutoff mechanism T of a cell, the shape of the cell lid 11 is approximately rectangular and the cell lid is made of a conductive metallic plate such as stainless steel. The cell lid 11 is composed of a hooked part 11ain its outside part and a flat bottom plate 11bformed by protruding the inside of the hooked part 11adownward by drawing.

[0042] In a part of the above bottom plate 11b, for example, a diaphragm D shown on the right side in FIG. 2 and a relief valve Z shown on the left side are integrated with the cell lid 11.

[0043] As for the above diaphragm D, as shown in a sectional view shown in FIG. 5 in which the main part is enlarged, a thin part 11dis provided by a circular concave portion 11cformed by grinding from the side of the lower surface of the bottom plate 11b. The above thin part 11dis pressed downward inside the cell case K in FIG. 5 so that the thin part is in the shape of a bowl and a convex portion 11eis protruded downward in FIG. 5 from the center of the protruded thin part 11d.

[0044] The above diaphragm D is composed of the convex portion 11eprotruded from the center and the thin part 11dformed by the concave portion 11caround the convex portion 11e, and the convex portion 11ein the center can be displaced above and below using the base of the thin part 11don the outside of the concave portion 11cas a fulcrum.

[0045] The relief valve Z is composed of a flat thick protruded part 11fthe shape of which is circular and which is protruded upward and a coupling part 11gformed by thinning the base of the protruded part 11f.

[0046] The insulating member 12 which is formed so that the insulating member is smaller than the outer shape of the cell lid 11 and which is formed by rectangular resin is attached to the lower surface of the bottom plate 11bof the above cell lid 11. In the above insulating member 12, a lead inserting hole 12ais formed below the convex portion 11e of the diaphragm D and first air vents 12bare formed in four locations around the lead inserting hole 12a.

[0047] A second air vent 12cwhich is larger than the outer diameter of the relief valve Z is formed under the relief valve Z. A cylindrical part 12eprovided with a central hole 12dinto which a rivet 14 is inserted is protruded upward from the center of the above insulating member 12.

[0048] A riveted part 12fis protruded downward near the right end of the insulating member 12.

[0049] A pressing member 13 is arranged on the bottom plate 11bof the cell lid 11 so that the cell lid 11 is supported by the insulating member 12 and the pressing member 13 between them.

[0050] The above pressing member 13 is made of insulating material and in the center, a central hole 13afor inserting the cylindrical part 12eof the insulating member 12 is formed In the pressing member 13 over the diaphragm D, a first concave portion 13bis formed as a relief hole when the diaphragm D is displaced upward and a third air vent 13cis formed over the first concave portion 13b. As air in the first concave portion 13bis emitted outside because of the above third air vent 13cwhen the thin part lid of the diaphragm D is displaced upward, the diaphragm D can be displaced smoothly.

[0051] In the pressing member 13, a second concave portion 13dis formed over the relief valve Z and a fourth air vent 13eis formed over the second concave portion 13d.

[0052] A rivet 14 made of aluminum is inserted into the central hole 12dof the above insulating member 12 and in the rivet 14, its head 14ais formed in the lower part and the end 14bprotruded from the cylindrical part 12eis formed in the upper part.

[0053] A positive terminal 15 bent approximately in the shape of a letter L is held between the head 14aof the rivet 14 and the insulating member 12 on the lower side of the insulating member 12, the end 14bof the rivet 14 is riveted on the upper side of the pressing member 13 and a conducting washer 16 made of a metallic plate and approximately in the shape of a bowl is attached to the end of the rivet.

[0054] An external positive electrode 17 is arranged on the riveted end 14bof the rivet 14. The external positive electrode 17 is attached to a hooked part in the outside part of the conducting washer 16 by spot welding. The above external positive electrode 17 is made of a steel plate, nickeling are applied to the surface, and the external positive electrode 17 and the positive terminal 15 are electrically connected via the rivet 14.

[0055] As for the above internal electrode 18, its lead 18ais formed to be flat and as shown in FIG. 4, a terminal 18bis formed by bending the end of the lead 18adownward in the shape of a letter.

[0056] A cylindrical projection 18cprotruded in the lead inserting hole 12aabove the above lead 18ais formed on the left side shown in FIG. 5 by drawing.

[0057] In the above projection 18c, a base 18ewhich is also a ceiling is formed in the upper part and a fitted part 18fwhich is a through hole formed by press working is formed in the vicinity of the center which is a part of the base 18e.

[0058] As for the internal electrode 18, the projection 18cis inserted into the lead inserting hole 12a, the convex portion 11eof the diaphragm D is press-fitted into the fitted part 18fin this state, and the convex portion 11eand the fitted part 18fare electrically connected.

[0059] In four locations of the lead 18aaround the above projection 18c, as shown in FIG. 3, a notch 18gcommunicating with the first air vent 12bof the insulating member 12 is formed.

[0060] On the right side of the lead 18ashown in FIG. 3, a rivet hole 18his formed, the rivet hole 18his fitted to the riveted part 12fof the insulating member 12 and as a result, the internal electrode 18 is attached to the insulating member 12.

[0061] In the current cutoff mechanism T composed as described above of a cell, as shown in FIG. 2, the hooked part 11ain the outside part of the cell lid 11 is attached to the cell case K in which a generating element not shown is housed by welding and the inside of the cell case K is airtightly shielded.

[0062] In a cell to which the current cutoff mechanism T is attached, a conductive path is formed between the cell lid 11 and a negative element not shown of the above generating element via the diaphragm D and the internal electrode 18.

[0063] As for the operation of the above current cutoff mechanism T of a cell according to the present invention, when an abnormality occurs inside the cell and pressure inside the cell is increased, the pressure of gas inside the cell is increased enters the concave portion 11cfrom four first air vents 12bas shown by an arrow B in FIG. 6.

[0064] Then, application force which pushes up the thin part lid upward is applied to the diaphragm D by the gas whose pressure is increased.

[0065] When pressure inside the cell exceeds a predetermined value, force which pulls out the convex portion 11epress-fitted into the fitted part 18fupward is applied to the thin part lid by application force applied to the diaphragm D.

[0066] The convex portion 11eis pulled out from the fitted part 18fand the thin part 11dof the diaphragm D is displaced upward at a stroke and is inverted.

[0067] The diaphragm D and the internal electrode 18 are separated by the upward inversion of the diaphragm D and a conductive path between the cell lid 11 and the negative element not shown of the generating element inside the cell is cut off. The increase of pressure inside the cell case K is prevented by the above cutoff of the conductive path and the cell can be prevented from bursting beforehand.

[0068] If the increase of pressure inside the cell is not stopped and further, pressure inside the cell is increased though the conductive path between the cell lid 11 and the generating element not shown inside the cell is cut off, further increased pressure inside the cell is applied to the protruded part 11fof the relief valve Z, application force which pushes up the protruded part 11foperates, the coupling part 11gformed in the thin part is broken by the above application force, high pressure gas inside the cell is exhausted outside from the broken part and the cell can be prevented from bursting beforehand.

[0069] Referring to FIGS. 7 to 9, the other embodiments of the diaphragm D in the above current cutoff mechanism T of the cell according to the present invention and the internal electrode 18 will be described below.

[0070] First, as for the other first embodiment, as shown in FIGS. 7A and 7B, plural slits 28jextended radially from the center of a base 28eof a protruded part 28care formed, each tongue 28kis provided to a part between the plural slits 28j, these plural tongues 28kare protruded upward in a conic shape and a fitted part 28fis formed by the tops of these plural tongues 28k.

[0071] A jig not shown in the same shape is located on each lower surface of the plural tongues 28kin a conic shape and a convex portion 11eof a diaphragm is press-fitted into the fitted part 28f.

[0072] As for the other second embodiment, as shown in FIG. 8, the end 21fof a convex portion 21eof a diaphragm D is formed so that the end is wider than the base 21gfitted into a fitted part 18fand the wider end 21fmay be also press-fitted into the fitted part 18f.

[0073] For a method of forming the above wide end 21f, for example, first, the end 21fand the base 21gare formed so that each diameter is equal and the end is press-fitted into the fitted part 18f. Afterward, the end 21fis tapped using a tool not shown and the end 21fmay be also made wider than the base 21g.

[0074] As for the other third embodiment, as shown in FIG. 9, a fitted part 38fformed at the base 38eis formed by drawing in the shape of a bag having a hollow part 38hwhose entrance 38gis narrow and the inside is wider than the entrance 38g, a convex portion 31eof a diaphragm D is formed so that its end 31gis wider than the base 31fand the wider end 31gmay be also press-fitted into the hollow part 38hof the fitted part 38fin the shape of a bag.

[0075] As in the current cutoff mechanism according to the present invention of the cell, the above convex portion of the diaphragm is press-fitted into the above fitted part, a conductive path is formed between the above cell lid and the above generating element via the diaphragm and the above internal electrode, the above convex portion of the diaphragm is pulled out from the fitted part when the internal pressure of the above cell case exceeds a predetermined value and the diaphragm is displaced and the above conductive path is cut off, the cutoff mechanism of a cell wherein the strength of the application force of the diaphragm can be readily adjusted by regulating the depth of press fit in which the convex portion is press-fitted into the fitted part and optimum application force can be readily acquired can be provided.

[0076] The dispersion of the dimension can be reduced by forming the convex portion and the fitted part by press working and the dispersion of the application force of the diaphragm can be reduced.

[0077] As the convex portion is pulled out from the fitted part and the conductive path is cut off, no metallic powder like a beard is caused from the convex portion or the fitted part and the above conductive path can be securely cut off.

[0078] As plural slits are formed so that they are radially extended from the center of the base, each tongue is provided in a part between these plural slits, each tongue is protruded approximately in a conic shape, the fitting part is formed by the tops of the plural tongues and the convex portion of the diaphragm is press-fitted into the fitted part, the tops of the tongues eat into the convex portion of the diaphragm and the application force of the diaphragm can be increased.

[0079] As the convex portion is formed so that the end is wider than the base fitted into the fitted part, the convex portion is hardly pulled out from the fitted part and the application force of the diaphragm can be increased.

[0080] As the fitted part is formed in the shape of a bag having a hollow part whose entrance is narrow and the inside is wider than the entrance and the wider end of the convex portion is press-fitted into the hollow part of the fitted part, the end of the convex portion is wider and the convex portion is hardly pulled out from the fitted part having the hollow part in the shape of a bag and the application force of the diaphragm can be further increased.