JP5952673B2 - Protective element and battery pack - Google Patents

Description

  The present invention relates to a protection element that protects a circuit connected on a current path by fusing the current path.

  Many secondary batteries that can be charged and used repeatedly are processed into battery packs and provided to users. In particular, in lithium ion secondary batteries with high weight energy density, in order to ensure the safety of users and electronic devices, in general, several protection circuits such as overcharge protection and overdischarge protection are built in the battery pack, It has a function of shutting off the output of the battery pack in a predetermined case.

  In many electronic devices using lithium ion secondary batteries, an overcharge protection or an overdischarge protection operation of the battery pack is performed by turning on / off the output using an FET switch built in the battery pack. However, when the FET switch is short-circuited for some reason, a lightning surge or the like is applied, and an instantaneous large current flows, or the output voltage drops abnormally due to the life of the battery cell. The battery pack and the electronic device must be protected from accidents such as ignition even when the is output. Accordingly, in order to safely shut off the output of the battery cell in any possible abnormal state, a protection element made of a fuse element having a function of cutting off the current path by an external signal is used.

  As a protection element of such a protection circuit for a lithium ion secondary battery or the like, as described in Patent Document 1, a heating element is provided inside the protection element. A structure that melts a molten conductor is generally used.

JP 2010-3665 A

  In the protective element described in Patent Document 1, the fusible conductor (fuse) has a current capacity of about 15 A at the maximum because it is used for applications having a relatively low current capacity such as a mobile phone or a notebook computer. doing. Applications of lithium ion secondary batteries have been expanding in recent years, and their use in higher current applications such as electric tools such as electric drivers, transportation equipment such as hybrid cars, electric vehicles, and electric power assisted bicycles has been studied. Part recruitment has begun. In these applications, particularly when starting up, a large current exceeding several tens of A to 100 A may flow. The realization of a protective element corresponding to such a large current capacity is desired.

  In order to realize a protection element corresponding to a large current, the cross-sectional area of the soluble conductor may be increased. When Sn / Ag / Cu solder molded into a 1.6 mmφ line is used, a current capacity of about 50 A can be obtained. However, the protective element detects an overvoltage state of the battery cell in addition to the case where the battery is blown by an overcurrent state, and causes a current to flow through the heating element formed of the resistor, thereby cutting the soluble conductor by the heat generation. There is a need. However, in the case of a “thick” soluble conductor, there is a problem that heat conduction from the heating element is lowered and it is difficult to stably melt the soluble conductor.

  Accordingly, it is an object of the present invention to provide a protective element that can be stably melted by heat generated by a heating element while securing a current capacity during overcurrent protection.

  As means for solving the above-described problems, a protection element according to the present invention includes an insulating substrate, a heating element stacked on the insulating substrate, and an insulating member stacked on the insulating substrate so as to cover at least the heating element. The first and second electrodes are stacked on the insulating member so as to overlap the heating element, and are electrically connected to the current path between the first and second electrodes and one terminal of the heating element. And a soluble conductor that is laminated from the heating element extraction electrode to the first and second electrodes and that melts the current path between the first electrode and the second electrode by heating. Prepare. The fusible conductor is a thin-walled portion with a thin portion in which the portion superimposed on the heating element has a concave shape, the other portion is thicker than the thin-walled portion, and has the same current capacity as the thin-walled portion. The thin-walled portion can be easily melted by the heat generated by the heating element.

  Preferably, the protective element according to the present invention further includes a support member having a metal layer on at least a surface, which is disposed so as to support at least a part of the thick part adjacent to the thin part with respect to the insulating substrate. The support member is thermally insulated from the insulating substrate.

  Preferably, the protective element according to the present invention is in contact with the thin portion of the soluble conductor, passes through the insulating member, reaches the insulating substrate, and is formed on the insulating substrate, and is connected to the molten solder discharging electrode. A storage electrode is further provided.

  The battery pack according to the present invention includes one or more battery cells, a protection element connected to cut off a current flowing through the battery cell, and a current for detecting the voltage value of each battery cell and heating the protection element. A current control element to be controlled. The protective element includes an insulating substrate, a heating element stacked on the insulating substrate, an insulating member stacked on the insulating substrate so as to cover at least the heating element, first and second electrodes, and a heating element. A heating element extraction electrode that is stacked on the insulating member so as to overlap and is electrically connected to one terminal of the heating element and the current path between the first and second electrodes, and the heating element extraction electrode from the heating element extraction electrode The soluble conductor is laminated over the first and second electrodes, and has a soluble conductor that blows off a current path between the first electrode and the second electrode by heating. A battery pack characterized in that a portion positioned overlapping the body is formed of a thin portion formed in a concave shape with a thin thickness and a flat shape.

  In the present invention, the fusible conductor is a thin-walled portion with a thickness where the portion positioned overlapping the heating element has a concave shape, and the other portion is thicker than the thin-walled portion and is substantially the same as the thin-walled portion. Since the thick portion has a current capacity, the soluble conductor can be easily blown by the heat generated by the heating element without reducing the current capacity of the soluble conductor.

  In addition, since at least the surface has a metal layer and further includes a support member that is thermally insulated from the insulating substrate, the heat generated by the heating element is concentrated on the thin portion of the soluble conductor, The fusing of the fusible conductor is promoted, and further, the solder melted by the heat generated by the heating element is guided and accommodated by the wettability of the support member, so that stable fusing characteristics can be realized.

  Further, since the solder melted by the heat generated by the heating element can be induced by the wettability of the molten solder discharge electrode and can be accommodated in the accommodating electrode, stable fusing characteristics can be realized.

(A) is a top view of the protection element to which this invention was applied. (B) is a sectional view taken along line AA ′ in FIG. (C) is sectional drawing which shows the state which the meltable conductor cut out. It is a block diagram which shows the application example of the protection element to which this invention was applied. It is a figure which shows the circuit structural example of the protection element to which this invention was applied. (A) is a top view of the protection element of other embodiment of this invention. (B) is a sectional view taken along line AA ′ in FIG. (C) is sectional drawing which shows the state which the meltable conductor is fuse | melting. (A)-(C) are top views for demonstrating the manufacturing process of the protection element of other embodiment of this invention. (A) is a top view of the protection element which combined two embodiment of this invention. (B) is a sectional view taken along line AA ′ in FIG. (A) is a top view of the protection element of the modification of this invention. (B) is a sectional view taken along line AA ′ in FIG. It is sectional drawing which shows notionally a mode that the soluble conductor of the protection element of the modification of this invention blows out. (A) is a figure which shows the state which the thin part of the soluble conductor began to melt | dissolve, it is a figure which shows a mode that the melt | dissolved solder flows in the direction of the arrow, and (B) is a figure which shows the state which the thin part melted | fused It is. (A)-(C) are sectional drawings for demonstrating the procedure which produces the soluble conductor used for the protection element of the modification of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited only to the following embodiment, Of course, a various change is possible in the range which does not deviate from the summary of this invention.

[Configuration of protection element]
As shown in FIGS. 1A and 1B, the protection element 10 includes an insulating substrate 11, a heating element 14 laminated on the insulating substrate 11 and covered with an insulating member 15, and both ends of the insulating substrate 11. Electrodes 12 (A1) and 12 (A2) formed on the heating member 14 and the heating element lead electrode 16 laminated on the insulating member 15 so as to overlap the heating element 14, and both ends of the electrodes 12 (A1) and 12 (A2). ) And a soluble conductor 13 having a central portion connected to the heating element extraction electrode 16. At both ends of the heating element 14, heating element electrodes 18 (P1) and 18 (P2) are connected to which a power source is connected in order to cause the heating element to generate current and generate heat. The fusible conductor 13 is thick so that the thickness thereof is substantially uniform at the position where the portion facing the heating element 14 overlaps the heating element 14 with a 1.6 mmφ round wire-like thick part 13a, for example. It consists of a thin portion 13b which is thinner and flatter than the portion 13a. The thickness of the thin portion 13b is, for example, 1/2 of the thickness (thickness) of the thick portion 13a. In addition, it is preferable that the cross-sectional area of the thick part 13a and the thin part 13b is substantially the same. The thin portion 13 b of the soluble conductor 13 is electrically connected to the heating element extraction electrode 16.

  Thus, by making the position where the fusible conductor 13 overlaps the heating element 14 into the thinned part 13b, the heat conduction in the thickness direction in the thinned part 13b is improved. The soluble conductor 13 can be easily blown out. Further, by molding the thin portion 13b into a flat shape, the contact area with the overlapping portion of the heating element 14 can be increased, heat from the heating element 14 can be efficiently transmitted, and stable fusing The characteristics can be realized. In addition, when the cross-sectional area of the thick part 13a and the thin part 13b is substantially the same, the current capacity of the soluble conductor 13 does not change, the cross-sectional area in the energizing direction of the soluble conductor 13 and the material of the soluble conductor 13 ( It is possible to pass a current corresponding to the specific resistance.

  The insulating substrate 11 is formed of an insulating member such as alumina, glass ceramics, mullite, zirconia, and the like. In addition, although the material used for printed wiring boards, such as a glass epoxy board | substrate and a phenol board | substrate, may be used, it is necessary to pay attention to the temperature at the time of fuse blowing.

  The two electrodes 12 (A1) and 12 (A2) connect the fusible conductor 13 inside the protective element 10, and are connected to an external circuit through the two electrodes 12 (A1) and 12 (A2). To do. The two electrodes 12 (A 1) and 12 (A 2) may be formed on the insulating substrate 11, or may be formed on an insulating material made of an epoxy resin or the like integrated with the insulating substrate 11.

  The heating element 14 is a conductive member that has a relatively high resistance value and generates heat when energized, and is made of, for example, W, Mo, Ru, or the like. These alloys, compositions, or compound powders are mixed with a resin binder or the like to form a paste on the insulating substrate 11 by patterning using a screen printing technique and firing.

  An insulating member 15 is disposed so as to cover the heating element 14, and a heating element extraction electrode 16 is disposed so as to face the heating element 14 through the insulating member 15. Of course, the insulating member 15 may be a laminated substrate in which the heating elements 14 are integrally laminated.

  One end of the heating element extraction electrode 16 is connected to one end of the heating element electrode 18 (P1) and the heating element 14. The other end of the heating element 14 is connected to the other heating element electrode 18 (P2).

  The fusible conductor 13 may be any conductive material that melts and melts due to the overcurrent state and the heat generated by the heating element 14. For example, in addition to SnAgCu-based Pb-free solder, BiPbSn alloy, BiPb alloy, BiSn An alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, or the like can be used.

  Further, the soluble conductor 13 may be a laminate of a high melting point metal made of a metal mainly composed of Ag or Cu or Ag or Cu and a low melting point metal such as Pb-free solder mainly composed of Sn. Good.

  In the protection element according to the present invention, a soluble conductor having a large cross-sectional area is used in order to cope with a large current capacity. When the fusible conductor is melted, the amount of solder to be melted is large, so that it is difficult to reliably shut off the circuit. Therefore, it is necessary to guide to a space that can accommodate the melted solder. In addition, since the thin conductor 13b is provided in the soluble conductor 13, there is a problem that stress is easily concentrated on the boundary position between the thick portion 13a and the thin portion 13b, and mechanical damage is likely to occur.

  Therefore, as shown in FIGS. 1A to 1C, the metal support member 3 is formed on the independent electrode 2 insulated from the other part of the insulating substrate 11 in a thermal circuit manner. The support member 3 is connected so as to support the soluble conductor 13 in the vicinity of the connection portion between the thick portion 13a and the thin portion 13b of the soluble conductor 13.

  As shown in FIG. 1C, when the fusible conductor 13 is melted, the solder wettability of the support member 3 is larger than that of the insulating member 15 and the insulating substrate 11, so that the melted solder is shown in FIG. It is drawn in the direction of the arrow. Since there is a space 8 between the lower portion of the soluble conductor 13 and the insulating member 15 and the insulating substrate 11, a large amount of molten solder is accommodated by arranging the support member 3 and the independent electrode 2 in this space 8. Make it possible. Furthermore, by disposing the support member 3 in the vicinity of the boundary portion between the thin portion 13b and the thick portion 13a of the soluble conductor 13 where stress is likely to concentrate, the portion having low mechanical strength is supported and soluble. The strength of the conductor 13 is improved. In particular, it is possible to prevent the fusible conductor 13 from being damaged at the time of manufacturing the protective element 10, thereby contributing to an improvement in manufacturing yield of the protective element 10. The independent electrode 2 is formed, for example, by patterning with Cu or Ag paste, but the independent electrode 2 is not connected to other circuits so that the support member 3 is insulated from other parts in terms of thermal circuit. Moreover, since the support member 3 and the accommodation electrode 4 have a fixed heat capacity, a heat storage effect can be expected. When the fusible conductor 13 is melted, the heat generated by the heating element 14 reaches the thin portion 13 b of the fusible conductor 13 via the insulating member 15. Due to the heat storage effect of the support member 3 and the independent electrode 2, the generated heat flows into the support member 3 side and prevents the heat from flowing out to the thick portion 13a connected to the thin portion 13b. Therefore, the heat generated by the heating element 14 can be concentrated on the thin portion 13 b of the soluble conductor 13, and can contribute to stabilization of the melting of the soluble conductor 13.

The metal support member 3 may be any metal that easily wets solder, and may be formed integrally with the independent electrode 2 using Cu, Ag, Ni, or the like. The support member 3 can be easily manufactured by using solder having a melting point lower than that of the soluble conductor 13. That is, the independent electrode 2 is patterned on the insulating substrate 11 with Ag paste simultaneously with other electrodes using a normal alignment process, and the insulating member 15 is arranged and connected. Thereafter, the support member 3 made of low melting point solder is formed on the independent electrode 2 and can be easily connected to the soluble conductor 13 by passing through a reflow process.
[How to use protection elements]

  As shown in FIG. 2, the protection element 10 described above is used for a circuit in a battery pack of a lithium ion secondary battery.

  For example, the protection element 10 is used by being incorporated in a battery pack 20 having a battery stack 25 including battery cells 21 to 24 of a total of four lithium ion secondary batteries.

  The battery pack 20 includes a battery stack 25, a charge / discharge control circuit 30 that controls charge / discharge of the battery stack 25, a protection element 10 to which the present invention that protects the battery stack 25 and the charge / discharge control circuit 30 is applied, A detection circuit 26 that detects the voltages of the battery cells 21 to 24 and a current control element 27 that controls the operation of the protection element 10 according to the detection result of the detection circuit 26 are provided.

  The battery stack 25 includes battery cells 21 to 24 that need to be controlled to protect overcharge and overdischarge states. The battery stack 25 is detachable via the positive electrode terminal 20a and the negative electrode terminal 20b of the battery pack 20. Are connected to the charging device 35, and a charging voltage from the charging device 35 is applied thereto. The electronic device can be operated by connecting the battery pack 20 charged by the charging device 35 to the positive terminal 20a and the negative terminal 20b to the electronic device that is operated by the battery.

  The charge / discharge control circuit 30 includes two current control elements 31 and 32 connected in series to a current path flowing from the battery stack 25 to the charging device 35, and a control unit 33 that controls operations of the current control elements 31 and 32. Is provided. The current control elements 31 and 32 are configured by, for example, field effect transistors (hereinafter referred to as FETs), and control the gate voltage by the control unit 33 to control conduction and interruption of the current path of the battery stack 25. . The control unit 33 operates by receiving power supply from the charging device 35, and according to the detection result by the detection circuit 26, when the battery stack 25 is overdischarged or overcharged, current control is performed so as to cut off the current path. The operation of the elements 31 and 32 is controlled.

  The protection element 10 is connected, for example, on a charge / discharge current path between the battery stack 25 and the charge / discharge control circuit 30, and its operation is controlled by the current control element 27.

  The detection circuit 26 is connected to each of the battery cells 21 to 24, detects the voltage value of each of the battery cells 21 to 24, and supplies each voltage value to the control unit 33 of the charge / discharge control circuit 30. Further, the detection circuit 26 outputs a control signal for controlling the current control element 27 when any one of the battery cells 21 to 24 becomes an overcharge voltage or an overdischarge voltage.

  The current control element 27 operates the protection element 10 when the voltage value of the battery cells 21 to 24 exceeds a predetermined overdischarge or overcharge state by the detection signal output from the detection circuit 26, Control is performed so that the charging / discharging current path of the battery stack 25 is cut off regardless of the switching operation of the current control elements 31 and 32.

  In the battery pack 20 having the above configuration, the configuration of the protection element 10 will be specifically described.

  First, the protection element 10 to which the present invention is applied has a circuit configuration as shown in FIG. 3, for example. That is, the protective element 10 generates heat by melting the soluble conductor 13 by causing the soluble conductor 13 connected in series via the heating element lead electrode 16 and the connection point of the soluble conductor 13 to generate heat. This is a circuit configuration comprising the body 14. In the protection element 10, for example, the fusible conductor 13 is connected in series on the charge / discharge current path, and the heating element 14 is connected to the current control element 27. Of the two electrodes 12 and 12 of the protective element 10, one is connected to A1, and the other is connected to A2. Further, the heating element extraction electrode 16 and the heating element electrode 18 connected thereto are connected to P1, and the other heating element electrode 18 is connected to P2.

  The protection element 10 having such a circuit configuration can surely melt the soluble conductor 13 on the current path by the heat generation of the heating element 14 while realizing a low profile.

[Other embodiments]
As shown in FIGS. 4A and 4B, the protection element 10 of the present invention includes a molten solder discharge electrode 5 formed on the insulating member 15 so as to be close to the thin portion 13b, and an insulating substrate. A housing electrode 4 that houses the molten solder induced by the molten solder discharge electrode 5 may be provided on the electrode 11. By providing the molten solder discharge electrode 5 and the accommodating electrode 4, it is possible to induce a large amount of molten solder of the soluble conductor using “thick” solder for dealing with a large current, and to reliably cut the soluble conductor 13. Can contribute.

  The molten solder discharge electrode 5 is formed on the same surface as the heating element extraction electrode 16 formed on the insulating member 15. The molten solder discharge electrode 5 is disposed along the longitudinal direction of the fusible conductor 13, is connected to the thin portion 13 b on the insulating member 15, passes through the side surface (side electrode) of the insulating member 15, and then the insulating substrate 11. It is connected to the accommodation electrode 4 formed on the top. The molten solder discharge electrode 5 may be formed by forming a through-hole electrode from the upper surface of the insulating member 15 toward the back surface side. The lower surface and the side surface of the side electrode of the insulating member 15 and the accommodating electrode 4 are connected by solder. Then, the surfaces of the molten solder discharge electrode 5 and the accommodating electrode 4 are soldered to form a solder fillet.

  As shown in FIG. 4C, when the thin portion 13b of the fusible conductor 13 is melted, a capillary inflow occurs between the thin portion 13b of the fusible conductor 13 and the insulating member 15, and the solder fillet is formed. The molten solder moves along the solder discharge electrode 5 and is guided in the direction of the accommodating electrode 4. If the area in which the storage electrode 4 is disposed is set large to some extent, the molten solder is stored on the storage electrode 4 in accordance with the wettability of the storage electrode 4. In this way, by arranging the path through which the melted solder is guided and the accommodation location, the melted solder is divided even in the case of the fusible conductor 13 for a large current using a large amount of solder. The circuit can be shut off.

  As shown in FIGS. 5A to 5C, the path for accommodating the molten solder in this embodiment can be easily formed by, for example, performing metal patterning using a printing technique.

  As shown in FIG. 5A, heating element electrodes 18 (P 1) and 18 (P 2) for supplying power to the heating element 14 are formed on the insulating substrate 11, and the accommodating electrode 4 is formed at the same time. These electrodes may form a Cu pattern or an Ag paste. As shown in FIG. 5B, an insulating member (laminated substrate) 15 having a heating element 14 laminated thereon is soldered to the electrode pattern formed on the insulating substrate 11. Electrodes 18a (P1) and 18a (P2) for supplying power to the heating element 14 are formed on a pair of opposing sides of the insulating member 15 formed in a square shape. Molten solder discharge electrodes 5 and 5 are formed. As shown in FIG. 5C, the fusible conductor 13 is placed on the mounted insulating member 15. When the fusible conductor 13 is placed, it is arranged so that the heating element extraction electrode 16 and the molten solder discharge electrode 5 are connected to the thin portion 13b.

A protective element can also be configured by combining this embodiment with the embodiment described in FIG. That is, as shown in FIGS. 6A and 6B, the supporting member 3 is formed on the independent electrode 2 formed on the insulating substrate 11, and the molten solder discharge electrode 5 is provided on the insulating member 15. Then, connection is made on the accommodation electrode 4 formed on the insulating substrate 11. Here, if the accommodating electrode 4 is formed in a ring shape and is patterned so that the independent electrode 2 is disposed at the center of the ring, the limited area on the insulating substrate 11 can be effectively utilized. Needless to say, the patterning of the electrodes is not limited to this and can be arbitrarily set.
[Modification]

  In the case of a protection element that can handle a large current, securing the space for accommodating a large amount of molten solder is the biggest problem. A modification for that purpose will be described.

  As shown in FIGS. 7A and 7B, the thin portion 13b of the fusible conductor 13 has a space (concave portion) in which the insulating member 15 mounted on the insulating substrate 11 is accommodated. By enlarging this space when viewed from the insulating member 15 side, it becomes possible to accommodate the molten solder more easily. That is, as shown in FIG. 7 (B), the shape of the thin portion 13b of the fusible conductor 13 is drawn from the central portion 13d, which is substantially the same distance from the boundary position 13c between the thin portion 13b and the thick portion 13a. It is bent so as to be connected to the electrode 16. Then, the distance in the vertical direction between the boundary position 13c and the insulating member 15 can be increased by bending upward from the central portion 13d toward the boundary position 13c.

  As shown in FIG. 8A, when the heating element 14 is energized, the thin portion 13b of the soluble conductor 13 is melted, and the melted solder is a space in which the distance between the boundary position 13c and the insulating member 15 is large. Is guided toward the support member 3 having high solder wettability. As shown in FIG. 8B, the melted solder is also accommodated on the heating element extraction electrode 16 while being drawn and accommodated toward the support members 3 on both sides.

  In this way, the soluble conductor 13 having the thin portion 13b whose cross section is molded in an “M” shape can be manufactured as follows, for example.

  As shown in FIG. 9A, the pressing pin 40 is disposed at a predetermined position where the thin portion 13b of the fusible conductor 13 is to be formed, and is moved in the direction of the arrow. As shown in FIG. 9B, when the pressing pin 40 is pressed against the fusible conductor 13 with a predetermined pressure, the thin portion 13b is linear when the pressing pin 40 is removed due to the ductility and rigidity of the metal. Even if it exists, the both ends of the soluble conductor 13 will bend to the side which received the pressure. As shown in FIG. 9C, when pressure is applied to both ends of the bent soluble conductor 13 in the direction of the arrow so that the thick portions 13a on both sides are linear, the shape of the thin portion 13b is substantially “ It becomes “M” shape. In addition, the longitudinal direction cross-sectional shape of the soluble conductor 13 of the thin-walled portion 13b is not limited to the above-mentioned “M” shape, and the purpose is to expand the space for accommodating molten solder in the direction of the thick-walled portion 13a of the soluble conductor 13. Needless to say, any similar shape may be used.

  Of course, this modified example may be used in combination with the support member 3 and / or the molten solder discharge electrode 5 described above, and a further molten solder discharge mechanism is secured, and stable fusing characteristics can be realized.

  2 independent electrodes, 3 support members, 4 accommodating electrodes, 5 molten solder discharge electrodes, 8 spaces, 10 protective elements, 11 insulating substrates, 12 (A1), 12 (A2) electrodes, 13 soluble conductors, 13a thick parts, 13b Thin part, 13c Boundary position, 13d Center part, 14 Heating element, 15 Insulating member, 16 Heating element extraction electrode, 17 Flux, 18 (P1), 18 (P2) Heating element electrode, 18a (P1), 18a (P2) ) Electrode, 20 Battery pack, 20a Positive terminal, 20b Negative terminal, 21-24 Battery cell, 25 Battery stack, 26 Detection circuit, 27, 31, 32 Current control element, 30 Charge / discharge control circuit, 33 Control unit, 35 Charging Device, 40 pressure pins

Claims (11)

An insulating substrate;
A heating element laminated on the insulating substrate;
An insulating member laminated on the insulating substrate so as to cover at least the heating element;
First and second electrodes;
A heating element extraction electrode laminated on the insulating member so as to overlap the heating element, and electrically connected to a current path between the first and second electrodes and one terminal of the heating element; ,
A laminate that extends from the heating element extraction electrode to the first and second electrodes, and includes a soluble conductor that melts a current path between the first electrode and the second electrode by heating;
The fusible conductor is composed of a thick part and a thin part that is formed in a flat and concave shape at a portion that overlaps with the heating element.   At least a part of the thick part adjacent to the thin part forms a space between the soluble conductor and the insulating substrate that is supported by the insulating substrate and accommodates the melted soluble conductor. The protective element according to claim 1, further comprising a support member having a metal layer on at least a surface disposed in such a manner.   The protection element according to claim 2, wherein the support member is thermally insulated from the insulating substrate.   The protection element according to any one of claims 1 to 3, further comprising a molten solder discharge electrode that approaches the thin portion of the soluble conductor, passes through the insulating member, and reaches the insulating substrate.   The protective element according to claim 4, further comprising a storage electrode formed on the insulating substrate and connected to the molten solder discharge electrode.   The fusible conductor is connected to the heating element extraction electrode at an intermediate portion of the thin-walled portion, and from the connected portion, the molten solder is moved toward the boundary position of the thin-walled portion and the thick-walled portion. The protective element according to claim 1, wherein a flow path is formed.   The protective element according to claim 6, wherein the thin-walled portion has an M-shaped cross section in the longitudinal direction and the laminating direction of the soluble conductor.   The protection element according to claim 2, wherein the support member has at least a surface of a metal material having a melting point lower than that of the soluble conductor.   9. The protective element according to claim 8, wherein the low melting point metal material is a low melting point solder.   The protective element according to claim 1, wherein the thin-walled portion and the thick-walled portion have substantially the same cross-sectional area. One or more battery cells;
A protective element connected to cut off the current flowing through the battery cell;
A current control element that detects a voltage value of each of the battery cells and controls a current for heating the protection element;
The protective element is
An insulating substrate;
A heating element laminated on the insulating substrate;
An insulating member laminated on the insulating substrate so as to cover at least the heating element;
First and second electrodes;
A heating element extraction electrode laminated on the insulating member so as to overlap the heating element, and electrically connected to a current path between the first and second electrodes and one terminal of the heating element; ,
A soluble conductor that is laminated from the heating element extraction electrode to the first and second electrodes and that melts a current path between the first electrode and the second electrode by heating;
The battery pack is characterized in that the fusible conductor includes a thick portion and a thin portion in which a portion overlapping with the heating element is formed in a concave shape with a thin thickness.

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