PTC DEVICE AND SECONDARY BATTERY HAVING SAME

Abstract

A PTC device as well as an electrical device such as a battery pack or a dry-cell type secondary cell containing a PTC device and a secondary cell is made more compact. The PTC device includes (1) a PTC component including a laminar polymer PTC element having an electrically conductive filler and a polymer material, and a metal electrode disposed on a surface of each side of the polymer PTC element; and (2) a lead positioned at least in part on the metal electrode of the PTC component, and connected to the metal electrode by an electrically conductive material An exposed part of the electrically conductive material is covered by a protective member including a polypropylene resin, a nylon resin or an epoxy resin.

Claims

1. A secondary battery which comprises a positive electrode, a negative electrode, and a separator and an electrolyte disposed therebetween, characterized by a PTC device being disposed within a positive electrode tab space between the positive electrode and a terminal of the positive electrode, said PTC device comprising: (1) a PTC component comprising: (A) a laminar polymer PTC element comprising (a) an electrically conductive filler, and (b) a polymer material, and (B) a metal electrode disposed on a surface of each side of the polymer PTC element; and (2) a lead positioned at least in part on the metal electrode of the PTC component, and connected to the metal electrode by an electrically conductive material; wherein an exposed part of said electrically conductive material is covered by a protective member comprising a polypropylene resin, a nylon resin or an epoxy resin.

2. A secondary battery according claim 1 which is in the form of a battery pack, wherein the PTC device, together with a protection circuit, is disposed outside of the battery.

3. The secondary battery according to claim 1, wherein the electrically conductive material contains tin.

4. The secondary battery according to claim 1, wherein the protective member is in the form of a molded member enclosing the PTC component and the lead, while an end portion of the lead protrudes outwardly from the molded member.

5. The secondary battery according to claim 1, wherein the protective member is in the form of a film enclosing the PTC component and the lead, while an end portion of the lead protrudes outwardly from the molded member.

6. The secondary battery according to claim 5, wherein the film is a laminated material of a layer of the polypropylene resin, the nylon resin or the epoxy resin and a layer of ethylene vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer or polyvinylidene fluoride.

7. The secondary battery according to claim 1, wherein the polypropylene resin, the nylon resin or the epoxy resin has alkali resistance.

8. The secondary battery according to claim 1, wherein the secondary battery is a size AA battery or a size AAA battery.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0044] FIG. 1 shows a cross-sectional view of a secondary battery with its internal structure illustrated schematically;

[0045] FIG. 2 shows a PTC device according to one embodiment of the present invention schematically in its cross-section;

[0046] FIG. 3 shows a PTC device according to another embodiment of the present invention schematically in its cross-section;

[0047] FIG. 4 shows a PTC device according to a further embodiment of the present invention schematically in its cross-section;

[0048] FIG. 5 shows the secondary battery illustrated in FIG. 1 having a PTC device of the present invention in a cross-sectional view; and

[0049] FIG. 6 shows the measured results of the resistance-temperature property (R-T property) of the PTC device A of the present invention produced in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0050] The present invention is described in more detail below with reference to the drawings. FIG. 2 shows a PTC device according to one embodiment of the present invention. The illustrated PTC device 10 comprises a PTC component 22 having a laminar polymer PTC element 12 containing an electrically conductive filler and a polymer material, and metal electrodes (e.g. metal foil electrodes) 18 and 20 on the surfaces 14 and 16 on the both sides of the PTC element, and the leads 24 and 26.

[0051] The lead 24 is connected electrically to a part of the metal electrode 18 by an electrically conductive material 28, and the lead 26 is connected electrically to the entire metal electrode 20 by an electrically conductive material 30. As a result, the electrically conductive material has an exposed part on the side surface 32 of the PTC component 22 if there is no protective member present.

[0052] In the PTC device 10 of the present invention, such exposed parts of the electrically conductive material are covered by the protective members as a protective coating 34 comprising a polypropylene resin, a nylon resin or an epoxy resin.

[0053] The protective coating may be in any form; in the embodiment shown in FIG. 2, a side part 32 of the electrically conductive material as the exposed part and a relatively narrow region(s) above and/or below the side part are covered by the protective coating 34. Such a protective coating may be formed by applying a protective coating forming material (e.g. an epoxy resin or a solution or dispersion containing it) by brushing, spraying, etc., and hardening it, and further removing the solvent as needed. Needless to say, the protective coating may cover substantially the entire PTC component and the leads with the exception of the lead end. In this case, the protective coating may be substantially in a similar form as films (58, 60) in FIG. 4 below.

[0054] FIG. 3 shows schematically a PTC device according to another embodiment of the present invention. In the embodiment shown, the PTC device 40 comprises a PTC component 42 and leads 44 and 46 on both its sides. This PTC device has a molded member 48 around it. In the embodiment shown, the PTC component 42 is illustrated as a whole for the sake of simplicity, and illustration of the electrically conductive materials positioned between the PTC component 42 and the leads 44, 46 is omitted.

[0055] Such a PTC device may be produced by inserting a PTC component connected to leads by a conductive material into a mold, then performing injection molding wherein a molding material containing or consisting of a polypropylene resin, a nylon resin or an epoxy resin in its molten state is injected into the mold and solidified, thereby forming the molded member 48 as a protective member so as to cover the exposed surface of the PTC component 42 including the exposed parts of the electrically conductive material. However, as shown in FIG. 3, the ends of the leads protrude from the molded member. Therefore, there is a need for forming the mold and inserting the PTC component in the mold so that the molded member will not be formed on the ends of the leads during the injection molding.

[0056] FIG. 4 shows a PTC device 50 according to a further embodiment of the present invention. In the embodiment shown, the PTC device comprises a PTC component 52 and leads 54 and 56 on both its sides. The PTC device is sandwiched between two pieces of film 58 and 60, with the ends of the leads 54 and 56 protruding outward. These films are formed of the material comprising a polypropylene resin, a nylon resin or an epoxy resin, and these films constitute the protective member of the PTC device of the present invention. As is easily understood, the films 58 and 60 cover the exposed surface of the PTC component and the exposed parts of the leads (excluding, however, their ends), including the exposed parts of the electrically conductive material, and can function as a protective member of the PTC device of the present invention. As in FIG. 3, in the embodiment shown, the PTC component 52 is illustrated as a whole for the sake of simplicity, and illustration of the electrically conductive materials positioned between the PTC component 52 and the leads 54 and 56 is omitted.

[0057] Such a PTC device may be produced by sandwiching a PTC component having leads electrically connected by a conductive material between two pieces of the films, with the ends of the leads protruding from the films, and then compression bonding, for example thermal compression bonding (i.e. heat sealing) the films together. In this embodiment, it is preferred that the film has an additional layer(s) on its inside to secure an improved adhesion between the film and the PTC component and the lead. As to the additional layer, the EVA layer, the EVOH layer, the PVDF layer as described above are suitably used.

[0058] FIG. 5 shows, schematically as in FIG. 1, a secondary battery of the present invention with a PTC device of the present invention incorporated therein. In the embodiment shown, the secondary battery 70 has the PTC device 74 of the present invention inside a positive electrode tab space 72, and is characterized by the end of one lead 76 being connected to a positive electrode terminal 80 via a sealing plate 78 and the other lead 82 being connected to a positive electrode 84. Thus, with the exception of the PTC device of the present invention being disposed instead of the positive electrode tab, the other parts of the secondary battery of the present invention may be the same as the known secondary battery.

[0059] In another embodiment, the secondary battery of the present invention has a protection circuit on its outside and comprises the PTC device of the present invention disposed on the outside of the secondary battery, for example, on the outside of the positive electrode. In this case, in such a secondary battery, the PTC device is disposed within the protection circuit. These together work to protect the secondary battery, and the secondary battery, the PTC device and the protection circuit constitute a battery pack. Thus, even when the PTC device is disposed outside of the secondary battery, if there is a slight leak of the electrolyte in the secondary battery, the adverse effects from the electrolyte to the electrically conductive material may be suppressed.

EXAMPLE 1

[0060] A PTC device A of the present invention as shown in FIG. 4 was produced by thermal compression-bonding a PTC component sandwiched by films (provided that the end of the lead was exposed). During the thermal compression bonding, only the film portion extending outside from around the PTC component was pressed so that force would not be applied to the PTC component (the lead section was pressed).

[0061] The film used was a laminated film of a polypropylene resin layer and a polyethylene resin layer (thickness: 100 μm). This film was used so that the polypropylene resin layer was on the outside.

[0062] Other conditions are shown below:

[0063] PTC component used (trade name: PolySwitch, manufactured by Tyco Electronics Japan G.K.)

[0064] Lead: nickel (trade name: NB201, manufactured by Neomax Co., Ltd., thickness: 150 μm)

[0065] Conductive Material: lead-free solder (alloy solder of tin, silver and copper)

[0066] Thermal compression bonding condition: Pressed for 10-40 seconds at a temperature of 160° C.-210° C. under a pressure of 0.4 MPa.

EXAMPLE 2

[0067] A PTC device B of the present invention shown in FIG. 3 was produced by using the same PTC component as Example 1 and insert-molding a polypropylene resin. The polypropylene resin used was, the trade name: Prime Polypro, manufactured by Prime Polymer Co., Ltd. The conditions for the PTC device B were the same as for the PTC device A except for the protective member.

[0068] The PTC devices A and B thus obtained were subjected to an alkali immersion experiment which was conducted by immersing them in a KOH aqueous solution (1N) at 60° C. for 3 months. The condition of the interface between the protective member and the lead was observed to evaluate the effect of alkali. A holding current test (I-V test) was performed on the PTC devices after the immersion. Also, for comparison, the same test was conducted on other PTC components having the same specification as the PTC components used in the production of the PTC devices. The results are shown below:

TABLE-US-00001 PTC device A PTC device B R.sub.initial I.sub.max R.sub.initial I.sub.max After alkali immersion 5.5 2.979 5.0 3.332 PTC Component 1 5.3 3.366 5.5 2.983 PTC Component 2 5.7 3.047 5.1 3.345
In the table, R.sub.initial is the initial resistance (unit: mΩ), and I.sub.max is the maximum current (unit: Amps). The initial resistance was measured at 60° C. using Milliohm HiTester manufactured by HIOKI E.E. CORPORATION.

[0069] There was no difference that is visually determinable in the conditions of the interface between the protective member and the lead in the PTC devices A and B before and after the alkali immersion test.

[0070] In the above table, the measured results on the PTC components having the same specification as the PTC components used in the production of the PTC devices A and B (provided that, not immersed in alkali) are shown as “PTC Component 1” and “PTC Component 2”, and those immersed in the KOH aqueous solution (1N) at 60° C. for 3 months are shown as “After alkali immersion”.

[0071] “PTC Component 1” and “PTC Component 2” are the measured values as a component that has not been affected by alkali; in the PTC device A, the initial resistance values are 5.3 mΩ and 5.7 mΩ, and the initial resistance value of “After alkali immersion” is 5.5 mΩ. Thus, the resistance can be said to be substantially unchanged. Also, the I.sub.max values are 3.366 A and 3.047 A for PTC Component 1 and PTC Component 2 respectively, and 2.979 A for “After alkali immersion”. Therefore, the I.sub.max is also substantially unchanged. In the PTC device B, the initial resistance values for PTC component 1 and PTC component 2 are 5.5 mΩ and 5.1 mΩ, and 5.0 mΩ for “After alkali immersion”. In this case also, as in the previous case, these values can be said to be within a resistance range that is substantially unchanged. If it had been affected by immersion, it is predicted that the resistance would have increased greatly beyond the 5 mΩ range. With respect to the Imax, the values which were 3.345 A and 2.983 A for PTC Component 1 and PTC Component 2 respectively, was 3.332 A for “After alkali immersion”. Therefore, it can be also said that this is substantially unchanged.

[0072] From these results, it can be seen that the holding current property of the PTC device is substantially unaffected even if the protective member is provided around the PTC device as in the present invention.

[0073] For confirmation, the resistance-temperature (R-T) property of the PTC device A before and after the above alkali immersion experiment was measured. The result is shown in FIG. 6. In the chart of FIG. 6, the broken line is the measured result of the PTC device after the alkali immersion experiment, and the solid line is the measured result before the alkali immersion experiment. It can be seen that the PTC device of the present invention is substantially unaffected by alkali.

[0074] The PTC device of the present invention can suppress the effect of electrolyte in the battery to a minimum even when disposed in the extra space within the secondary battery.

EXPLANATION OF THE LEGENDS

[0075] 10—PTC device; 12—polymer PTC element; [0076] 14, 16—surface; 18, 20—metal electrode; [0077] 22—PTC component; 24, 26—lead; [0078] 28, 30—electrically conductive material; 32—side; [0079] 34—protective coating; 40—PTC device; [0080] 42—PTC component; 44, 46—lead; 48—molded member; [0081] 50—PTC device; 52—PTC component; 54, 56—lead; [0082] 58, 60—film; 70—secondary battery; [0083] 72—positive electrode tab space; 74—PTC device; [0084] 76—lead; 78—sealing plate; 80—positive electrode; [0085] 82—lead; 100—nickel hydride battery; [0086] 102—positive electrode; 104—negative electrode; [0087] 106—positive electrode tab; 108—sealing plate; [0088] 110—positive electrode terminal.