JP4497141B2 - PTC element and battery protection system - Google Patents

Description

  The present invention relates to a PTC element used for the purpose of protecting a battery or an electronic circuit from an overcurrent, and a battery protection system having the PTC element.

  A PTC (positive temperature coefficient) element has a characteristic that the resistance value of the element increases when the temperature of the element rises in a predetermined temperature region. In particular, when the temperature of the PTC element reaches the Curie temperature, the resistance of the PTC element increases rapidly. Such a property is called a PTC characteristic.

  The PTC element is incorporated in an electric circuit such as an electronic device. If an excessive current flows in the circuit for some reason during use of the electronic device, the temperature of the electronic device rises, and the temperature of the PTC element itself rises accordingly. When the temperature of the PTC element reaches the Curie temperature, the resistance value of the PTC element increases rapidly. As a result, the PTC element blocks excess current in the electric circuit. Therefore, it is possible to prevent the electrical device from being damaged due to excessive current.

  Thus, the PTC element is used as a safety protection device against overheating and excessive current. Specifically, the PTC element is incorporated in a circuit (protection circuit) for protecting a secondary battery that is a power source of the mobile phone from excessive current. When an excessive current flows during charging or discharging of the secondary battery, the PTC element cuts off the current and protects the secondary battery.

  An example of such a PTC element is a structure in which an element body (polymer positive temperature coefficient resistor) in which conductive particles are dispersed in a polymer material (crystalline polymer) is sandwiched between electrode plates (or metal foils). There is known a polymer PTC element having the following (see Patent Document 1).

  Conventionally, the polymer PTC element is manufactured by the following method. First, a polymer (such as high-density polyethylene) containing a conductive filler such as metal particles and carbon black is extruded to form an element body. Next, the polymer PTC element is completed by thermocompression bonding the electrode plate to the front and back surfaces of the element body.

  When this polymer PTC element is incorporated in a predetermined protection circuit, the electrode plate of the polymer PTC element is joined to a terminal board electrically connected to the protection circuit. This joining is conventionally performed by soldering, welding, or the like.

  When performing soldering, welding, etc., it is necessary to heat at least a part of the electrode plate and the terminal plate to a high temperature. Since the electrode plate (or metal foil) of the polymer PTC element is very thin, heat applied to the electrode plate during soldering and welding is immediately conducted to the element body. As a result, the element body becomes high temperature and may be thermally deteriorated (softened or melted). When the element body is softened or melted, the dispersibility of the conductive particles in the polymer becomes non-uniform. In a polymer PTC element that has undergone such a thermal history, the resistance value at room temperature (room temperature resistance value) is greatly increased compared to that before this thermal history.

  Furthermore, if the temperature is repeatedly increased and decreased with respect to such a polymer PTC element, the room temperature resistance value of the polymer PTC element becomes higher. In such a polymer PTC element having a high room temperature resistance value, the power consumption increases.

As described above, the increase in the room temperature resistance value of the polymer PTC element caused by heating at the time of joining the electrode plate and the terminal plate is a waste of power or a short battery life when mounted on a small device such as a mobile phone. It leads to problems such as conversion.
International publication WO2004 / 023499

  An object of the present invention is to provide a PTC element capable of preventing the element body from being thermally deteriorated when the electrode plate and the terminal plate are joined together by welding or the like. Another object of the present invention is to provide a battery protection system capable of effectively protecting a battery when an excessive current flows.

In order to achieve the above object, the PTC element according to the present invention includes:
An element body whose resistance value increases as the temperature rises in a predetermined temperature range;
A PTC element having two electrode plates bonded to the front and back surfaces of the element body,
At least one of the electrode plates has a joint portion with a terminal plate for connecting to a predetermined circuit in a portion where the electrode plate and the element body overlap.
The joint protrudes from the surface of the electrode plate;
The protruding surface of the joint (surface to be joined to the terminal board) is flattened.

  Preferably, the element body is a conductive polymer having a positive temperature coefficient.

  When joining the electrode plate and the terminal plate, the electrode rod for spot welding is brought into contact only with the portion of the terminal plate that overlaps the joint portion. As a result, the current flowing during welding is concentrated near the joint. Therefore, Joule heat is generated only in the vicinity of the joint. As a result, Joule heat generated during welding can be minimized. Therefore, heat conduction from the welded part to the element body is suppressed, and thermal deterioration of the element body due to heat conduction can be prevented.

  Further, since the joint portion protrudes from the surface of the electrode plate, a gap is generated between the terminal plate and the surface of the electrode plate (portion other than the joint portion) during welding. Joule heat generated at the welding site (joint) during welding is radiated from this gap. As a result, heat conduction to the element body is suppressed, and thermal deterioration of the element body can be prevented.

  Furthermore, it is possible to improve the welding efficiency by limiting the welding point to only the joint portion and flattening the surface of the joint portion. Although it is difficult to weld if the surface of the joint, which is a welding point, is rough, when the surface of the joint is flattened, the joint and the terminal plate come into close contact with each other, so that welding becomes easy.

  Preferably, on the surface of the electrode plate having the joint portion, a portion other than the joint portion is roughened.

  On the surface of the electrode plate, by roughening the portion other than the joint (hereinafter referred to as the roughened portion), the substantial surface area of the portion other than the joint is larger than that when the surface is not roughened. Become. Therefore, by roughening the surface of the electrode plate, the effect of dissipating heat generated during welding from the surface of the electrode plate can be improved. As a result, thermal deterioration of the element body due to heat conduction can be prevented.

  Preferably, a clad plate is bonded to an electrode plate different from the electrode plate having the bonding portion, out of the two electrode plates.

  Preferably, the terminal plate is composed of a Ni terminal plate mainly containing Ni.

  By using a terminal plate containing Ni as a main component, the strength of spot welding with an electrode plate containing Ni as a main component can be improved.

  Preferably, a protective film is formed on a surface of the element body exposed to the outside.

  By forming a protective film on the surface of the element body that is exposed to the outside, it is possible to suppress oxidation of the element body due to oxygen in the atmosphere and prevent deterioration of the element body.

The battery protection system according to the present invention is:
The PTC element;
A protection circuit electrically connected to one of the electrode plates of the PTC element;
A battery electrically connected to the other electrode plate not connected to the protection circuit among the electrode plates of the PTC element.

  When the battery protection system includes the PTC element that has no thermal deterioration and has a low room temperature resistance value, the power consumption of the battery protection system and the entire electronic device including the battery protection system can be reduced.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a schematic diagram showing a connection relationship of a polymer PTC element, a secondary battery, and a protection circuit according to an embodiment of the present invention;
FIG. 2 is a schematic cross-sectional view of a polymer PTC element according to an embodiment of the present invention.
3 is an enlarged schematic view of the surface (roughened portion) of the first electrode plate in the vicinity of the joint shown in FIG.
FIG. 4 is an external view of a polymer PTC element according to an embodiment of the present invention viewed in the IV direction of FIG.
FIG. 5 is a schematic cross-sectional view of a polymer PTC element according to an embodiment of the present invention as viewed in the direction V in FIG. Schematic showing the positional relationship of the electrode rod for welding,
6 and 7 are schematic cross-sectional views of a polymer PTC element according to another embodiment of the present invention.

Overall Configuration of Polymer PTC Element First, a polymer PTC element for protecting a secondary battery cell used as a power source of a mobile phone will be described as an embodiment of a PTC element according to the present invention.

As shown in FIG. 1, the polymer PTC element 2 is disposed on a spacer 36 formed on a secondary battery cell 32 that is a power source of a mobile phone. The polymer PTC element 2 is incorporated between a secondary battery cell 32 and a protection circuit 30 (predetermined circuit) for protecting the secondary battery cell 32 from overcurrent. The polymer PTC element 2 cuts off the current between the protection circuit 30 and the secondary battery cell 32 when an overcurrent that cannot be controlled by the protection circuit 30 flows during charging or discharging of the secondary battery cell 32. Thus, the secondary battery cell 32 is protected.
Below, the whole structure of a polymer PTC element is demonstrated.

  A polymer PTC element 2 shown in FIG. 2 includes an element body 4 having a positive resistance temperature characteristic (PTC characteristic). The element body 4 has front and back surfaces (a first surface 6 and a second surface 8 facing each other). A first electrode plate 10 and a second electrode plate 12 are joined to the first surface 6 and the second surface 8, respectively. Therefore, the element body 4 is disposed so as to be sandwiched between the first electrode plate 10 and the second electrode plate 12.

  The shape of the element body 4 is not particularly limited, and examples thereof include a rectangular parallelepiped type and a cylindrical type. When the shape of the element body 4 is a rectangular parallelepiped, the dimensions of the element body 4 are L1 (3.0 to 1.0) mm × W1 (2.0 to 6.0) mm × H1 thickness (0.2). .About.1.0) mm (see FIGS. 2 and 5).

  The first electrode plate 10 has a joint portion 14 in a portion where the first electrode plate 10 and the element body 4 overlap. The joint portion 14 protrudes from the surface of the first electrode plate 10. The surface of the protruding joint portion 14 is flattened. In the joint portion 14, the first electrode plate 10 and the terminal plate 16 are joined.

  A protective film 3 is formed on the exposed surface of the element body 4 as needed. By forming the protective film 3, it is possible to suppress the oxidation of the element body 4 due to oxygen in the atmosphere and to prevent the element body 4 from being deteriorated. The type of the protective film 3 is not particularly limited as long as it has a function of shielding oxygen, and examples thereof include an epoxy resin and an ethylene-vinyl alcohol copolymer resin. Note that the protective film 3 is not necessarily formed.

  Preferably, on the surface of the first electrode plate 10, a portion (roughened portion 24) other than the joint portion 14 is roughened. That is, irregularities are intentionally formed on the surface of the roughened portion 24.

  Although the uneven | corrugated difference (surface roughness Ry) of the roughening site | part 24 is not specifically limited, Preferably, it is about 100-200 micrometers. By setting the surface roughness Ry within this range, the substantial surface area of the roughened portion 24 is appropriately increased as compared with the case where the surface is not roughened. As a result, it is possible to improve the effect of radiating Joule heat generated during spot welding of the first electrode plate 10 and the terminal plate 16 from the surface of the first electrode plate 10 (roughened portion 24).

The surface roughness Ry (maximum height) is determined according to the JIS standard as shown below. In the measurement of the surface roughness Ry, as shown in FIG. 3, a region that falls within the reference length L ₀ including the joint 14 and a part of the first electrode plate 10 located in the vicinity thereof is defined as a measurement region. . Then, the roughened portion 24 in the measurement region, the mean line _{L average,} determine the distance Yp to the highest part to the average line _{L average} (top part 5). Further, from the average line _{L average,} determine the distance Yv of the most to a low site (valley 7) relative to the mean line _{L average.} The surface roughness Ry (maximum height) is calculated by the formula Ry = Yp + Yv.

In the present invention, the bonding portion 14 in FIG. 2 protrudes from the surface of the first electrode plate 10 because the protruding height H ₀ of the bonding portion 14 shown in FIG. 3 satisfies H ₀ > Ry = Yp + Yv. It is synonymous. The height _{H 0} projection of the joint 14 is not particularly limited, preferably, with respect to the troughs 7 of FIG. 3, is about 250～500Myuemu. By setting the protrusion height H ₀ of the joint portion 14 within this range, the flattened surface of the joint portion 14 and the terminal plate 16 are brought into close contact with each other without being disturbed by the unevenness of the roughened portion 24. It is possible to join (spot welding). Furthermore, in spot welding, an appropriate interval is generated between the roughened portion 24 and the terminal plate 16, and Joule heat generated during welding can be radiated into the atmosphere from this interval. As a result, heat conduction from the welded portion to the element body 4 can be suppressed, and thermal deterioration of the element body 4 can be prevented.

  A clad plate 18 is joined to the second electrode plate 12.

  The material of the first electrode plate 10 and the second electrode plate 12 is not particularly limited as long as it is a conductive material, and examples thereof include Ni, Cu, and Cu foil plated with Ni. Preferably, Ni plates are used as the first electrode plate 10 and the second electrode plate 12. By using a Ni plate as each electrode plate, the strength of spot welding with a terminal plate containing Ni as a main component can be improved. The thickness of each of the first electrode plate 10 and the second electrode plate 12 is not particularly limited, but is usually about 100 to 500 μm.

  The material of the terminal plate 16 is not particularly limited as long as it is a conductive material, but preferably the terminal plate 16 mainly contains Ni. The thickness of the terminal board 16 is not particularly limited, but is usually about 100 to 300 μm. The length L2 of the terminal board 16 is not particularly limited and can be freely designed according to the application.

  The clad plate 18 is not particularly limited, but the clad plate 18 is preferably composed of a nickel layer 20 and an aluminum layer 22. The nickel layer 20 is joined to the second electrode plate 12. Moreover, the aluminum layer 22 is joined to the electrode terminal 34 of the secondary battery cell 32 as shown in FIG. The thickness of the clad plate 18 is not particularly limited, but is usually about 100 to 500 μm. The length L3 of the clad plate 18 is not particularly limited and can be freely designed according to the application.

Manufacturing Method of Polymer PTC Element 2 Next, a manufacturing method of the polymer PTC element 2 will be described.

(Formation of element body 4)
The element main body 4 of FIG. 2 is normally comprised from the polymer (high molecular compounds, such as a thermosetting resin and a thermoplastic resin) which are a main component, and the resin composition (conductive polymer) containing electroconductive particle. Note that the element body 4 may include both a thermosetting resin and a thermoplastic resin.

  In forming the element body 4, first, a polymer compound (thermosetting resin, thermoplastic resin, etc.), conductive particles (metal powder, carbon black, etc.), a low molecular organic compound, and a polymer compound are cross-linked. Weigh and knead the reaction initiator and the like to adjust the PTC composition. The kneading method is not particularly limited, and examples thereof include a kneader, an extruder, and a mill. Further, as the conductive particles to be contained in the PTC composition, only conductive particles having a predetermined particle diameter are classified using a sieve or the like. Next, this PTC composition is shape | molded and the element main body 4 is obtained.

  Although it does not specifically limit as a thermosetting resin, An epoxy resin, a polyimide resin, unsaturated polyester resin, a silicon resin, a polyurethane resin, a phenol resin, etc. are mentioned. Preferably, an epoxy resin is used as the thermosetting resin. By using an epoxy resin, the polymer PTC element can have a sufficient resistance change amount and heat resistance. As for the molecular weight of the thermosetting resin, the weight average molecular weight Mw is usually about 300 to 10,000. Said thermosetting resin may be used independently and multiple types of resin may be used. Moreover, you may use the compound which has a structure where different kinds of thermosetting resins were bridge | crosslinked.

  Although it does not specifically limit as a thermoplastic resin, Preferably, a crystalline polymer is used. The melting point of the thermoplastic resin is not particularly limited, but is preferably about 70 to 200 ° C. By using a resin having a melting point within this range, it is possible to prevent the thermoplastic resin from melting, flowing, and deformation of the element body during the operation of the polymer PTC element.

  The thermoplastic resin is not particularly limited, but polyolefins such as polyethylene, copolymers such as ethylene-vinyl acetate copolymer, vinyl halides such as polyvinyl chloride, polyvinyl fluoride, and polyvinylidene fluoride, and vinylidene polymers, 12- Examples thereof include polyamide such as nylon, polystyrene, polyacrylonitrile, thermoplastic elastomer, polyethylene oxide, polyacetal, thermoplastic modified cellulose, polysulfones, polymethyl (meth) acrylate and the like.

  Although the weight average molecular weight Mw of a thermoplastic resin is not specifically limited, Preferably, it is 10000-5 million. These thermoplastic resins may be used alone or a plurality of types of resins may be used. Moreover, you may use the compound which has a structure where different types of thermoplastic resins were bridge | crosslinked.

  Although it does not specifically limit as electroconductive particle contained in the element main body 4, Metal powder, carbon black, etc. are illustrated. Preferably, metal powder is used as the conductive particles. As the metal powder, a powder mainly composed of nickel is preferably used. The average particle diameter of the metal powder is preferably 0.1 μm or more, and more preferably about 0.5 to 4.0 μm.

  In the element body 4, the content of the conductive particles in the resin composition is preferably 20 to 80% by mass with respect to the entire resin composition. By setting the content of the conductive particles within this range, the room temperature resistance value during non-operation can be sufficiently lowered, and a large resistance change amount can be obtained. Furthermore, variation in element resistance can be sufficiently reduced.

  The resin composition constituting the element body 4 further includes, for example, a low-molecular organic compound such as wax, oil, fatty acid, and higher alcohol in addition to the above-described thermosetting resin, thermoplastic resin, and conductive particles. But you can. As a result, it is possible to increase the resistance change amount accompanying the temperature rise of the element body 4.

  The element body 4 may include a base material that has a gap inside and can fill the gap with the resin composition. Such a substrate is not particularly limited as long as it can play the above role, and examples thereof include woven fabrics, nonwoven fabrics, and continuous porous bodies.

(Formation of the first metal plate 10 and the second electrode plate 12)
The first metal plate 10 and the second metal plate 12 are formed by punching a nickel metal plate or a nickel alloy plate having a predetermined thickness.

(Formation of joint 14 and roughened portion 24)
Next, the joint portion 14 is formed on the surface of the first electrode plate 10 (the surface to which the terminal plate 16 is later joined). In the formation of the joint portion 14, the joint portion 14 is protruded from the surface of the first electrode plate 10, and the surface of the protruded joint portion 14 is flattened. Furthermore, on the surface of the first electrode plate 10 having the joint 14, the portion other than the joint 14 is roughened. That is, the roughened portion 24 is formed. Hereinafter, the formation of the joint portion 14 and the roughening of the roughened portion 24 will be described with reference to FIG.

  First, the entire surface of the first electrode plate 10 is flattened.

  Next, on the surface of the first electrode plate 10, the first electrode plate 10 and the element body 4 are located in a part where they overlap, and the two portions (joining portions 14) to which the terminal plate 16 will be joined later. ) Is masked.

  Next, a roughening process is performed with respect to the area | region (roughening site | part 24) which was not masked. As a result, only the surface of the roughened portion 24 is roughened. The surface roughening method is not particularly limited, and examples thereof include acid surface treatment, cutting, blasting, and etching.

  Next, by removing the masking, the bonding portion 14 having a flattened surface is formed.

As a result of the roughening treatment, the joint 14 protrudes from the surface of the first electrode plate 10 (that is, the roughened portion 24). In other words, as a result of the roughening treatment, a relationship of H ₀ > Ry is established between the protrusion height H ₀ of the joint portion 14 and the surface roughness Ry of the roughened portion 24 (FIG. 3).

(Thermocompression bonding of the first metal plate 10 and the second electrode plate 12)
Next, the first electrode plate 10 and the second electrode plate 12 are joined to the front and back surfaces (first surface 6 and second surface 8) of the element body 4 by a hot press or the like.

  The heating temperature when the first electrode plate 10 and the second electrode plate 12 are thermocompression bonded to the element body 4 by a hot press or the like depends on the material of the element body 4, but is preferably 130 to 200. It is about ℃. The pressure during thermocompression bonding is preferably about 0.1 to 2.5 MPa.

  At the time of thermocompression bonding, the element main body 4 is slightly crushed in the thickness direction due to pressure and may protrude slightly to the side of the electrode plates 10 and 12, but unnecessary portions can be easily removed.

  Preferably, in the first metal plate 10 and the second electrode plate 12, the surfaces to be joined to the element body 4 are roughened. Specifically, the joint surface of the first metal plate 10 and the second electrode plate 10 to the element body has a nodule (the middle part or the base part of the nodule has a concavity and convexity difference of about 5 to 15 μm with respect to the top of the nose) It is preferable that a large number of shapes are formed. As a result, the bonding strength between the first metal plate 10 and the second electrode plate 10 and the element body 4 can be improved. A method for roughening the surfaces of the first metal plate 10 and the second electrode plate 12 (a method for forming a nodule) is not particularly limited, but has the same composition as the first metal plate 10 and the second electrode plate 12. Examples thereof include electroplating with metal (Ni, Cu, etc.) or chemical plating.

  In the first metal plate 10, a roughening process (formation of nodules) on the surface bonded to the first surface 6 of the element body 4 is performed before the formation of the above-described joint portion 14 and roughened portion 24. It may be done later or later. Alternatively, the formation of the nodules and the formation of the roughened portion 24 may be performed simultaneously by the same method. The roughened portion 24 is formed before the first metal plate 10 is thermocompression bonded to the element body 4, but may be performed after thermocompression bonding.

(Crosslinking reaction)
Next, the element body 4 on which the first electrode plate 10 and the second electrode plate 12 are formed is irradiated with an electron beam. By this electron beam irradiation, the reaction initiator functions and the cross-linking reaction between the polymers is promoted. The energy source for the crosslinking reaction is not limited to electron beams, and gamma rays, ultraviolet rays, heat, and the like are also used. What is necessary is just to adjust suitably the acceleration voltage and electron beam irradiation amount of the electron beam to irradiate according to the kind of high molecular compound contained in the element main body 4, or the dimension of an element main body. The electron beam irradiation may be performed before the first electrode plate 10 and the second electrode plate 12 are joined.

(Junction of clad plate 18)
Next, the clad plate 18 is bonded to the second electrode plate 12. Although it does not specifically limit as a joining method, Spot welding etc. are illustrated.

(Formation of protective film 3)
Next, the protective film 3 is formed on the surface of the element body 4 exposed to the outside. A method for forming the protective film 3 is not particularly limited. For example, the protective film 3 is formed by applying the above-described resin.

  In this way, the polymer PTC element 2 according to this embodiment is completed.

Assembly method of polymer PTC element 2 (formation of battery protection system 1)
(Bonding of the second electrode plate 12 and the clad substrate 18)
As shown in FIG. 1, the polymer PTC element 2 is incorporated between the secondary battery cell 32 and the protection circuit 30. In order to connect the polymer PTC element 2 as shown in FIG. 1, for example, first, the tip of the second metal plate 12 in the polymer PTC element 2 is spot-welded to the nickel layer 20 side of the clad plate 18.

(Junction of the clad substrate 18 and the secondary battery cell 32)
Next or before and after that, the aluminum layer 22 on the clad plate 18 is spot-welded in contact with the electrode terminals 34 of the secondary battery cells 32. When a gap is formed between the polymer PTC element 2 and the secondary battery cell 32, a spacer 36 or the like is disposed between the polymer PTC element 2 and the secondary battery cell 32.

(Junction between the junction 14 and the terminal board 16)
Next, the joining part 14 and the terminal board 16 are joined. A method for joining the joint portion 14 and the terminal plate 16 is not particularly limited, but preferably spot welding (resistance welding) is used.

  In spot welding, first, as shown in FIG. 4, the terminal plate 16 is overlaid on the two joints 14.

  Next, as shown in FIG. 5, a pair of spot welding electrode rods 52 and 54 are pressed above the terminal plate 16. At this time, as shown in FIG. 5, the pair of spot welding electrode rods 52 and 54 are positioned directly above the two joint portions 14 via the terminal plate 16.

  Next, a current I is passed through the pair of spot welding electrode rods 52 and 54 while the terminal plate 16 is crimped to the joint portion 14. As a result, the joint 14 through which the current I flows and the portion of the terminal plate 16 that contacts the joint 14 are melted and joined by the generated Joule heat. That is, the first electrode plate 10 and the terminal plate 16 are bonded at the bonding portion 14.

  In spot welding, appropriate adjustment is made by appropriately adjusting the current, energization time, pressure applied to the terminal plate 16 and the like according to conditions such as the surface area of the joint portion 14 and the thickness of the terminal plate 16. Welding strength can be obtained.

  In this way, the polymer PTC element 2 is incorporated between the secondary battery cell 32 and the protection circuit 30 as shown in FIG. 1, and the battery protection system 1 is completed.

  In the present embodiment, as described above, when the first electrode plate 10 and the terminal plate 16 are joined, the spot welding electrode bars 52 and 54 are brought into contact with only the portion overlapping the joining portion 14 in the terminal plate 16. Let As a result, the current flowing during welding is concentrated near the joint. Therefore, Joule heat is generated only in the vicinity of the joint 14. Therefore, surreal heat generated during welding can be minimized. As a result, heat conduction from the welded part to the element body 4 is suppressed, and thermal deterioration of the element body 4 due to heat conduction can be prevented.

  Moreover, since the junction part 14 protrudes from the surface of the 1st electrode board 10, a clearance gap arises between the terminal board 16 and the surface (parts other than the junction part 14) of the 1st electrode board 10 at the time of welding. Joule heat generated during welding is radiated from the gap. As a result, heat conduction from the welded part to the element body 4 is suppressed, and thermal deterioration of the element body 4 due to heat conduction can be prevented.

  Furthermore, it is possible to improve the welding efficiency by limiting the welding point to only the joint 14 and flattening the surface of the joint 14. If the surface of the joint 14 that is a welding point is rough, it is difficult to weld the terminal plate. However, when the surface of the joint 14 is flattened, the surface of the joint 14 and the terminal plate 16 are in close contact with each other and welded together. It becomes easy.

  In the present embodiment, by roughening the roughened portion 24 (portion other than the joint portion 14) on the surface of the first electrode plate 10, the substantial surface area of the roughened portion 24 is roughened. It becomes larger than the case where it does not become. Therefore, the roughening of the roughened portion 24 can improve the effect of radiating Joule heat generated during spot welding from the surface of the first electrode plate 10 (roughened portion 24). As a result, thermal deterioration of the element body 4 due to heat conduction can be prevented.

  In the present embodiment, the battery protection system 1 (FIG. 1) having the polymer PTC element 2, the protection circuit 30, and the secondary battery cell 32 effectively protects the battery even when an excessive current flows. be able to.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, as shown in FIG. 6, in the polymer PTC element 2, the nickel layer 20 of the clad plate 18 may be directly bonded to the second surface 8 of the element body 4. That is, in the polymer PTC element 2 shown in FIG. 6, since the clad plate 18 also has the function of the second electrode plate, the second electrode plate is unnecessary. Even in this case, the same effect as the above-described embodiment can be obtained.

  Further, as shown in FIG. 7, a metal foil 60 may be formed on the front and back surfaces of the element body 4 (polymer layer made of a single conductive polymer). The element body 4 can be formed, for example, by hot pressing the metal foil 60 on both surfaces of a sheet-like polymer layer and then punching it out to a predetermined dimension. The nickel layer 20 of the first electrode plate 10 and the clad plate 18 and the metal foil 60 are joined via a solder layer 62. Even in this case, the same effect as the above-described embodiment can be obtained. The thickness of the metal foil 60 is thinner than the thicknesses of the first electrode plate 10 and the clad plate 18 and is generally about 25 to 30 μm.

  Moreover, as a method of roughening the roughened portion 24 shown in FIG. 2, in addition to the method described above, a plating method or the like can be given.

  The polymer PTC element 2 according to the present invention is used not only as an overcurrent protection element but also as a self-control heating element, a temperature sensor, a current limiting element, an overcurrent protection element, and the like.

  In the present invention, the method for producing the polymer PTC element 2 is not particularly limited. For example, as in the above-described embodiment, the polymer PTC element 2 is manufactured as follows without joining the element body 4, the first electrode plate 10, and the second electrode plate 12 to each other alone. Also good. That is, an unnecessary portion after thermocompression bonding a sheet-like element body constituting the element body 4 after cutting and a pair of sheet-like electrodes that respectively constitute the first electrode plate 10 and the second electrode plate after cutting. The individual polymer PTC elements 2 may be formed by punching out the substrate with a press. In that case, the efficiency of the manufacturing process of the polymer PTC element 2 can be improved by joining the assembly of parts constituting the polymer PTC element 2 at a time.

FIG. 1 is a schematic diagram showing a connection relationship between a polymer PTC element, a secondary battery, and a protection circuit according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a polymer PTC element according to an embodiment of the present invention. FIG. 3 is an enlarged schematic view of the surface of the first electrode plate (roughened portion) in the vicinity of the joint shown in FIG. 2. FIG. 4 is an external view of a polymer PTC element according to an embodiment of the present invention viewed in the IV direction of FIG. 2, and is a schematic diagram illustrating a positional relationship between an electrode plate, a joint, and a terminal plate. FIG. 5 is a schematic cross-sectional view of a polymer PTC element according to an embodiment of the present invention viewed in the direction V of FIG. 4, and includes electrode plate joints, terminal boards, and spots in the manufacturing process of the polymer PTC element. It is the schematic which shows the positional relationship of the electrode rod for welding. FIG. 6 is a schematic cross-sectional view of a polymer PTC element according to another embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a polymer PTC element according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery protection system 2 ... Polymer PTC element 3 ... Protective film 4 ... Element main body 10 ... 1st electrode board 12 ... 2nd electrode board 14 ... Junction part 16 ... Terminal board 18 ... Cladding board 30 ... Protection circuit 24 ... Rough surface 32 ... Secondary battery cell 34 ... Electrode terminal

Claims (7)

An element body whose resistance value increases as the temperature rises in a predetermined temperature range;
A PTC element having two electrode plates bonded to the front and back surfaces of the element body,
At least one of the electrode plates, in a portion where the electrode plate and the element main body overlap, a spot welding joint with a terminal plate for connection to a predetermined circuit, the surface of the electrode plate, Having at least two so as to protrude from the surface opposite to the element body ;
A protruding PTC element, wherein the surface of the protruding spot welding joint is flattened. The PTC element according to claim 1, wherein the element body is a conductive polymer having a positive temperature coefficient. Wherein the surface of the electrode plate with the spot welding joint, the portion other than the joint portion for spot welding are roughened, surface roughness Ry of the roughened portions is 100-200 [mu] m, the 3. The PTC element according to claim 1 , wherein the relationship between the surface roughness Ry and the protrusion height Ho of the joint is Ho> Ry . 4. The PTC element according to any one of claims 1 to 3, wherein a clad plate is bonded to an electrode plate different from the electrode plate having the bonding portion among the two electrode plates. The PTC element according to any one of claims 1 to 4, wherein the terminal plate is composed of a Ni terminal plate mainly containing Ni. The PTC element according to claim 1, wherein a protective film is formed on a surface of the element body exposed to the outside. A PTC element according to any one of claims 1 to 6,
A protection circuit electrically connected to one of the electrode plates of the PTC element;
The battery protection system which has a battery electrically connected to the other electrode plate which is not connected to the said protection circuit among the electrode plates which the said PTC element has.

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