Protective elements and battery pack

Abstract

To provide a protection element and a battery pack that can respond to high responsiveness and high reliability by preventing fast melting and insulation breakdown of fuse elements.SOLUTION: A protection element 1 has an insulating substrate 2, first and second electrodes 4a, 4b on the insulating substrate 2, a heating element 5 formed on the insulating substrate 2, a heating element draw-out electrode 4c electrically connected to the heating element 5, a fusible conductor 3 mounted over the first electrode 4a to the second electrode 4b via the heating element draw-out electrode 4c, and an insulation protection layer 7 covering the heating element 5. The insulation protection layer 7 contains a thermal conductive filler 10.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present technology relates to a protection element that cuts off a current path during an abnormality such as overcharging or over-discharging, and a battery pack using this protection element.

Background Art

[0002] Many secondary batteries that can be charged and repeatedly used are processed into battery packs and provided to users. Especially in lithium-ion secondary batteries with high weight energy density, in order to ensure the safety of users and electronic devices, generally, several protection circuits such as overcharge protection and over-discharge protection are built into the battery pack, and it has a function of cutting off the output of the battery pack in a predetermined case.

[0003] As a protection element of such a protection circuit for lithium-ion secondary batteries and the like, a structure is used in which a heating element is provided inside the protection element, and the heating of this heating element melts a soluble conductor on the current path.

[0004] In recent years, the applications of lithium-ion secondary batteries have been expanding, and their adoption in applications with larger currents, such as power tools like electric drivers, and devices such as drones, electric bikes, hybrid cars, electric vehicles, and electric assist bicycles, has started. Thus, with the expansion of the applications of lithium-ion secondary batteries, the protection element also needs to satisfy various requirements. Among them, the characteristics related to high response and high reliability are one of the most important indicators in terms of the nature of the protection element that ensures safety.

[0005] Figure 12 shows an example of a configuration of a conventional protective element, where (A) is a plan view with the cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view. The protective element 100 shown in Figure 12 comprises an insulating substrate 101, first and second electrodes 102 and 103 formed on the surface of the insulating substrate 101, a heating element 104 formed on the surface of the insulating substrate 101, an insulating layer 105 covering the heating element 104, a heating element lead electrode 106 laminated on the insulating layer 105 and connected to the heating element 104, and a fuse element 107 which is a fusible conductor mounted via connecting solder across the first electrode 102, the heating element lead electrode 106, and the second electrode 103.

[0006] The first and second electrodes 102 and 103 are terminals connected to the current path of the external circuit to which the protection element 100 is connected. The first electrode 102 is connected via castellation to the first external connection electrode 102a formed on the back surface of the insulating substrate 101, and the second electrode 103 is connected via castellation to the second external connection electrode 103a formed on the back surface of the insulating substrate 101. The protection element 100 is incorporated into a part of the current path formed on the external circuit board by the connection of the first and second external connection electrodes 102a and 103a to connection electrodes provided on the external circuit board to which the protection element 100 is mounted.

[0007] The heating element 104 is a conductive material with relatively high resistance that generates heat when energized, and is made of materials such as nichrome, W, Mo, Ru, or materials containing these materials. The heating element 104 is connected to a heating electrode 108 formed on the surface of the insulating substrate 101. The heating electrode 108 is connected via castellation to a third external connection electrode 108a formed on the back surface of the insulating substrate 101. The protective element 100 is connected to an external power supply provided in the external circuit by the third external connection electrode 108a being connected to a connection electrode provided on the external circuit board on which the protective element 100 is mounted, thereby connecting the heating element 104 to an external power supply provided in the external circuit. The heating element 104 is constantly controlled in terms of energization and heat generation by a switch element or the like (not shown).

[0008] The heating element 104 is covered with an insulating layer 105 made of glass or the like, and a heating element lead electrode 106 is formed on the insulating layer 105, so that it is superimposed on the heating element lead electrode 106 via the insulating layer 105. In addition, a fuse element 107 is connected to the heating element lead electrode 106, extending between the first and second electrodes 102 and 103.

[0009] As a result, the protective element 100 is thermally connected by the superposition of the heating element 104 and the fuse element 107, and when the heating element 104 generates heat due to the flow of current, it can melt the fuse element 107.

[0010] The fuse element 107 is formed from a low-melting-point metal such as Pb-free solder, or a high-melting-point metal such as Ag, Cu, or an alloy mainly composed of these, or it has a laminated structure of a low-melting-point metal and a high-melting-point metal. The fuse element 107 is connected from the first electrode 102 through the heating element lead electrode 106 to the second electrode 103, thereby forming part of the current path of the external circuit into which the protection element 100 is incorporated. The fuse element 107 melts due to self-heating (Joule heating) when a current exceeding its rating flows through it, or melts due to the heat generated by the heating element 104, thereby interrupting the connection between the first and second electrodes 102 and 103.

[0011] Then, when it becomes necessary to interrupt the current path of the external circuit, the protection element 100 energizes the heating element 104 via a switch element. As a result, the heating element 104 is heated to a high temperature, and the fuse element 107 incorporated on the current path of the external circuit melts. The molten conductor of the fuse element 107 is attracted to the highly wettable heating element lead electrode 106 and the first and second electrodes 102 and 103, causing the fuse element 107 to melt. Therefore, the protection element 100 can melt the connection between the first electrode 102, the heating element lead electrode 106, and the second electrode 103, thereby interrupting the current path of the external circuit. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2015-35281 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The insulating layer 105 is formed, for example, using thick-film printing technology. The thickness of the glass that can be formed by the printing process is generally about 10 to 60 μm, and since it can be formed very thinly, the heat generated by the heating element 104 can be efficiently transferred to the fuse element 107.

[0014] However, as the applications of secondary batteries are moving towards higher voltages, the voltage applied to the heating element 104 is now routinely exceeding 42V, which is considered a safe and low voltage. Furthermore, as mentioned above, the insulating layer 105 is formed very thinly, which can lead to the formation of pinholes or other defects within the glass layer during printing. As a result, as shown in Figure 13, when a high voltage is applied to the heating element 104, dielectric breakdown can occur at locations where the insulating performance is degraded, such as pinholes, causing the heating element 104 to be destroyed before it can generate sufficient heat.

[0015] One countermeasure is to increase the number of printing cycles to increase the thickness of the insulating layer 105. In order to prevent dielectric breakdown when current is supplied to the heating element 104, the insulating layer 105 is generally formed with a film thickness of 20 μm or more.

[0016] However, increasing the thickness of the insulating layer 105 reduces the heat conduction efficiency to the fuse element 107, and if the thickness of the fuse element 107 is increased to realize a protective element that can handle large currents, it becomes impossible to quickly fuse the fuse.

[0017] Therefore, this technology aims to provide a protective element and battery pack that can prevent rapid melting and dielectric breakdown of fuse elements, and that can meet high responsiveness and high reliability requirements. [Means for solving the problem]

[0018] To solve the above-mentioned problems, the protective element according to this technology comprises an insulating substrate, first and second electrodes provided on the insulating substrate, a heating element formed on the insulating substrate, a heating element lead electrode electrically connected to the heating element, a fusible conductor mounted from the first electrode to the second electrode via the heating element lead electrode, and an insulating protective layer covering the heating element, wherein the insulating protective layer contains a thermally conductive filler.

[0019] Furthermore, the battery pack according to this technology comprises one or more battery cells, a protective element connected to the charge / discharge path of the battery cell and blocking the charge / discharge path, and a current control element that detects the voltage value of the battery cell and controls the supply of current to the protective element. The protective element comprises an insulating substrate, first and second electrodes provided on the insulating substrate, a heating element formed on the insulating substrate, a heating element lead electrode electrically connected to the heating element, a fusible conductor mounted from the first electrode to the second electrode via the heating element lead electrode, and an insulating protective layer covering the heating element, wherein the insulating protective layer contains a thermally conductive filler. [Effects of the Invention]

[0020] According to this technology, by increasing the thermal conductivity of the insulating layer, the heat transfer rate from the heat-generating element to the fusible conductor is increased, and dielectric breakdown can be prevented, providing a protective element that offers high responsiveness and high reliability. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 shows an example configuration of a protective element to which this technology is applied, where (A) is a plan view with the cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view. [Figure 2] Figure 2 shows a state where the soluble conductor is blown in the protection element shown in Figure 1. (A) is a plan view showing the cover member omitted, and (B) is a cross-sectional view. [Figure 3] Figure 3 is a conceptual diagram showing heat conduction in the insulating protection layer. [Figure 4] Figure 4 is a graph showing the correspondence between the thermal conductivity and the aluminum oxide volume fraction of the insulating protection layer in which aluminum oxide (thermal conductivity: 40 W / mK) is dispersed in glass (thermal conductivity: 1 W / mK). [Figure 5] Figure 5 is a graph showing the correspondence between the thermal conductivity and the aluminum nitride volume fraction of the insulating protection layer in which aluminum nitride (thermal conductivity: 285 W / mK) is dispersed in glass (thermal conductivity: 1 W / mK). [Figure 6] Figure 6 is a cross-sectional view of the soluble conductor. [Figure 7] Figure 7 is a circuit diagram showing a configuration example of a battery pack. [Figure 8] Figure 8 is a circuit diagram of the protection element. [Figure 9] Figure 9 is a cross-sectional view showing a modified example of the protection element to which the present technology is applied. [Figure 10] Figure 10 shows a configuration example of a protection element provided with a heating element on the back surface of an insulating substrate. (A) is a plan view showing the cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view. [Figure 11] Figure 11 shows a state where the soluble conductor is blown in the protection element shown in Figure 10. (A) is a plan view showing the cover member omitted, and (B) is a cross-sectional view. [Figure 12] Figure 12 shows a conventional protection element. (A) is a plan view, (B) is a cross-sectional view, and (C) is a bottom view. [[ID=3〗2 [Figure 13] Figure 13 is a plan view showing a state where a spark has occurred in the protection element shown in Figure 12.

Embodiments for Carrying Out the Invention

[0022] The protective elements and battery packs to which this technology is applied will be described in detail below with reference to the drawings. It should be noted that this technology is not limited to the embodiments described below, and various modifications are possible within the scope of the gist of this technology. Furthermore, the drawings are schematic, and the proportions of dimensions may differ from those of reality. Specific dimensions should be determined by referring to the following explanation. It should also be noted that there may be differences in the relationships and proportions of dimensions between different drawings.

[0023] As shown in Figures 1(A) to (C), the protective element 1 to which this technology is applied comprises an insulating substrate 2, a fusible conductor 3 supported on the insulating substrate 2, a first electrode 4a, a second electrode 4b, and a heating element lead electrode 4c connected to the fusible conductor 3, a heating element 5 provided on the insulating substrate 2 that generates heat when energized, a heating element electrode 6 connected to the heating element 5 and serving as a power supply terminal to the heating element 5, and an insulating protective layer 7 covering the heating element 5.

[0024] In the protective element 1 shown in Figure 1, a heating element 5 and an insulating protective layer 7 covering the heating element 5 are formed on the surface 2a of the insulating substrate 2 on which the fusible conductor 3 is supported. Furthermore, on the surface 2a of the insulating substrate 2, a first electrode 4a connected to one end of the fusible conductor 3 and a second electrode 4b connected to the other end of the fusible conductor 3 are formed as energizing parts. In addition, a heating element lead electrode 4c is formed on the surface 2a side of the insulating substrate 2, which is electrically connected to the heating element 5 and is superimposed on the insulating protective layer 7 and also connected to the fusible conductor 3.

[0025] Here, the insulating protective layer 7 is made of an insulating material such as glass and contains a thermally conductive filler. As a result, the insulating protective layer 7 has improved thermal conductivity and efficiently transfers the heat generated by the heating element 5 to the fusible conductor 3. This eliminates the need to form the insulating protective layer 7 extremely thin to increase thermal conductivity, and it can be formed thick enough to prevent the occurrence of pinholes, etc., while suppressing dielectric breakdown. Furthermore, the fusible conductor 3 can be quickly cut even without forming the insulating protective layer 7 extremely thin, thus preventing the heating element 5 from being damaged before the fusible conductor 3 is cut.

[0026] Such a protective element 1 is incorporated into an external circuit, where the fusible conductor 3 forms part of the current path of the external circuit. The current path is interrupted by melting due to heat generated by the heating element 5 or by an overcurrent exceeding its rating. The components of the protective element 1 will be described in detail below.

[0027] [Insulating substrate] The insulating substrate 2 is formed from an insulating material such as alumina, glass ceramics, mullite, or zirconia. Alternatively, the insulating substrate 2 may be made from materials used for printed circuit boards, such as glass epoxy substrates or phenolic substrates.

[0028] [First and second electrodes] First and second electrodes 4a and 4b are formed at opposing ends of the insulating substrate 2. The first and second electrodes 4a and 4b are each formed by conductive patterns such as Ag and Cu. Preferably, the surfaces of the first and second electrodes 4a and 4b are coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by known methods such as plating. This prevents oxidation of the first and second electrodes 4a and 4b in the protective element 1 and prevents fluctuations in the rating due to an increase in conductivity resistance. Furthermore, when the protective element 1 is reflow mounted, it is possible to prevent the first and second electrodes 4a and 4b from being dissolved (solder erosion) by the connecting solder that connects the fusible conductor 3.

[0029] The first electrode 4a is continuous with the first external connection electrode 11 formed on the back surface 2b of the insulating substrate 2 via castellation from the front surface 2a. The second electrode 4b is continuous with the second external connection electrode 12 formed on the back surface 2b of the insulating substrate 2 via castellation from the front surface 2a. When the protective element 1 is mounted on an external circuit board, the first and second external connection electrodes 11 and 12 are connected to connection electrodes provided on the external circuit board, thereby incorporating the fusible conductor 3 into a part of the current path formed on the external circuit board.

[0030] The first and second electrodes 4a and 4b are electrically connected via a fusible conductor 3, which is mounted on the electrodes via a conductive connecting material such as solder. Furthermore, as shown in Figures 2(A) and 2(B), the connection between the first and second electrodes 4a and 4b is broken when a large current exceeding the rating flows through the protection element 1, causing the fusible conductor 3 to melt due to self-heating (Joule heating), or when the heating element 5 heats up in response to the current, causing the fusible conductor 3 to melt.

[0031] [Heating element] The heating element 5 is a conductive material with relatively high resistance that generates heat when current is passed through it, and is made of materials such as nichrome, W, Mo, Ru, or materials containing these materials. The heating element 5 can be formed by mixing powdered alloys, compositions, or compounds of these materials with a resin binder to form a paste, forming a pattern on the insulating substrate 2 using screen printing technology, and then firing it. As an example, the heating element 5 can be formed by adjusting a mixed paste of ruthenium oxide paste, silver, and glass paste according to a predetermined voltage, forming a film over a predetermined area at a predetermined position on the surface 2a of the insulating substrate 2, and then firing it under appropriate conditions. The shape of the heating element 5 can be designed as appropriate, but as shown in Figure 1, it is preferable to make it substantially rectangular in accordance with the shape of the insulating substrate 2 in order to maximize the heating area.

[0032] Furthermore, the heating element 5 has one end 5a connected to the first lead electrode 15 and the other end 5b connected to the second lead electrode 16. The first lead electrode 15 is formed by drawing out from the heating element electrode 6 along the one end 5a of the heating element 5, and in the protective element 1 shown in Figure 1, it extends along one side edge of the substantially rectangular heating element 5, and the other side edge of the heating element 5 is superimposed on it. Similarly, the second lead electrode 16 is formed by drawing out from the intermediate electrode 8 along the other end 5b of the heating element 5, and in the protective element 1 shown in Figure 1, it extends along the other side edge of the substantially rectangular heating element 5, and the other side edge of the heating element 5 is superimposed on it.

[0033] The heating element electrode 6 and the intermediate electrode 8 are formed on opposite side edges of the insulating substrate 2, distinct from the side edges on which the first and second electrodes 4a and 4b are provided. The heating element electrode 6 is a power supply electrode to the heating element 5 and is connected to one end 5a of the heating element 5 via the first lead electrode 15, and is also continuous with a third external connection electrode 13 formed on the back surface 2b of the insulating substrate 2 via castellation.

[0034] The heating element electrode 6, the first and second lead electrodes 15 and 16, and the intermediate electrode 8 can be formed by printing and firing conductive paste such as Ag or Cu, similar to the first and second electrodes 4a and 4b. Furthermore, by constructing each of these electrodes formed on the surface 2a of the insulating substrate 2 from the same material, they can be formed in a single printing and firing process.

[0035] Furthermore, the heating element electrode 6 may be provided with a restricting wall to prevent the connecting solder provided on the electrode of the external circuit board connected to the third external connection electrode 13 from melting during reflow mounting, etc., and spreading onto the heating element electrode 6 via castellation. Similarly, the first and second electrodes 4a and 4b may also be provided with restricting walls. The restricting walls can be formed using insulating materials that do not wet with solder, such as glass, solder resist, or insulating adhesive, and can be formed on the heating element electrode 6 by printing or the like. By providing restricting walls, it is possible to prevent the molten connecting solder from spreading to the heating element electrode 6 and the first and second electrodes 4a and 4b, and to maintain connectivity between the protective element 1 and the external circuit board.

[0036] The intermediate electrode 8 is an electrode provided between the heating element 5 and the heating element lead electrode 4c which is laminated on the insulating protective layer 7. It is connected to the other end 5b of the heating element 5 and also to the heating element lead electrode 4c. The heating element lead electrode 4c is superimposed on the heating element 5 via the insulating protective layer 7 and is connected to the fusible conductor 3.

[0037] [Insulating protective layer] Furthermore, the heating element 5, the first lead electrode 15, and the second lead electrode 16 are covered with an insulating protective layer 7. In addition, a heating element lead electrode 4c is formed on the insulating protective layer 7, and a fusible conductor 3 is superimposed on it.

[0038] The insulating protective layer 7 is provided to protect and insulate the heating element 5, and to efficiently transfer the heat from the heating element 5 to the heating element lead electrode 4c and the fusible conductor 3. As shown in Figure 3, it is composed of an insulating material 9 such as glass that has heat resistance to the heating temperature of the heating element 5, and this insulating material 9 contains a thermally conductive filler 10. Examples of glass raw materials that make up the insulating material 9 include silica-based glass overcoat glass paste and insulating glass paste.

[0039] The insulating protective layer 7 can be formed, for example, by applying a glass-based paste using screen printing and then firing it. In the protective element 1 shown in Figure 1, the insulating protective layer 7 is formed to cover the heating element 5 formed on the surface 2a of the insulating substrate 2.

[0040] The thickness of the insulating protective layer 7 is determined from the viewpoint of the applicability of the glass paste and the break-off time of the fusible conductor 3. Specifically, the viscosity of the glass paste changes depending on the content of the thermally conductive filler 10, and depending on the application thickness, pinholes that cause dielectric breakdown may occur, or in the case of fine opening patterns, the paste may become difficult to peel off from the mask, causing defects in the pattern. In addition, as the thickness of the insulating protective layer 7 increases, the distance to the heating element lead electrode 4c and the fusible conductor 3 increases, so depending on the thermal conductivity of the insulating protective layer 7, the break-off time of the fusible conductor 3 may increase. For this reason, the thickness of the insulating protective layer 7 is appropriately set according to the applicability of the material such as the glass paste and the required break-off time of the fusible conductor 3, and is, for example, thicker than 10 μm and 40 μm or less, preferably between 20 μm and 40 μm.

[0041] [Thermal conductive filler] The thermally conductive filler 10 contained in the insulating material 9 has a higher thermal conductivity than the insulating material 9 that constitutes the insulating protective layer 7. Therefore, by including the thermally conductive filler 10, the thermal conductivity of the insulating protective layer 7 is improved, and the heat generated by the heating element 5 is efficiently transferred to the fusible conductor 3 (see Figure 3). This allows the insulating protective layer 7 to be formed thick enough to prevent the occurrence of pinholes, etc., thereby suppressing dielectric breakdown, and also efficiently transfers the heat generated by the heating element 5 to the fusible conductor 3, enabling rapid melting. Furthermore, by rapidly melting the fusible conductor 3, it is possible to prevent the heating element 5 from being damaged before the fusible conductor 3 melts.

[0042] The thermally conductive filler 10 is not particularly limited as long as it is a filler with excellent thermal conductivity. For example, the thermally conductive filler 10 can be metal oxides such as aluminum oxide, magnesium oxide, alumina, magnesia, and silicon dioxide, or nitrides such as aluminum nitride and boron nitride. Among these, aluminum oxide or aluminum nitride is preferred from the viewpoint of heat resistance (high thermal reliability), low specific gravity, and cost reduction. The thermally conductive filler 10 may be treated with a silane coupling agent for the purpose of strengthening the interface and improving dispersibility. Furthermore, the thermally conductive filler 10 may be used alone, or two or more types may be used in combination, such as by including a filler with high thermal conductivity, to adjust the volume capacity of the thermally conductive filler 10 necessary for the insulating protective layer 7 to have the desired heat transfer efficiency.

[0043] Furthermore, the shape of the thermally conductive filler 10 is not particularly limited, and examples include spherical, powdery, granular, flattened, or flaky thermally conductive fillers.

[0044] The higher the thermal conductivity of the thermal conductive filler 10, the less thermal conductivity is required to improve the thermal conductivity of the insulating protective layer 7. Furthermore, the higher the thermal conductivity of the thermal conductive filler 10, the less thermal conductivity is required to ensure the desired thermal conductivity in the insulating protective layer 7, thereby suppressing an increase in the coating viscosity of the insulating material 9 constituting the insulating protective layer 7 and providing good coatability.

[0045] Figure 4 is a graph showing the correspondence between the thermal conductivity and the volume fraction of aluminum oxide in an insulating protective layer 7 in which aluminum oxide (thermal conductivity: 40 W / mK) is dispersed in glass (thermal conductivity: 1 W / mK). Figure 5 is a graph showing the correspondence between the thermal conductivity and the volume fraction of aluminum nitride in an insulating protective layer 7 in which aluminum nitride (thermal conductivity: 285 W / mK) is dispersed in glass (thermal conductivity: 1 W / mK).

[0046] The thermal conductivity of the insulating protective layer 7 can be determined, for example, by Bruggeman's equation for the thermal conductivity of a composite material containing fillers. Bruggeman's equation, shown below, takes into account the thermal conductivity of the resin and fillers, the filling density of the fillers in the composite resin, the effects of the filler shape (spherical) and size, and the influence of the temperature distribution between adjacent fillers.

[0047]

number

[0048] It is preferable that the difference in thermal conductivity between the thermally conductive filler 10 and the insulating material 9 constituting the insulating protective layer 7 be 19 W / mK or more. For example, when glass (thermal conductivity: 1 W / mK) is used as the insulating material 9 and alumina (content 96%) (thermal conductivity: 20 W / mK) is used as the thermally conductive filler 10, the difference in thermal conductivity is 19 W / mK. Also, when glass (thermal conductivity: 1 W / mK) is used as the insulating material 9 and magnesium oxide (thermal conductivity: 50 W / mK) is used as the thermally conductive filler 10, the difference in thermal conductivity is 49 W / mK. As will be described later, by using a thermally conductive filler 10 with high thermal conductivity, the volume of thermally conductive filler 10 required to achieve the desired thermal conductivity of the insulating protective layer 7 is reduced, resulting in good coatability and improved manufacturing efficiency.

[0049] The content of the thermal conductive filler 10 in the insulating protective layer 7 is set based on the thermal conductivity of the thermal conductive filler 10, the desired thermal conductivity of the insulating protective layer 7, and the applicability of the insulating material 9. Preferably, the content of the thermal conductive filler 10 in the insulating protective layer 7 is more than 20 volume% and less than 60 volume%. If the content of the thermal conductive filler 10 is less than 20 volume%, the thermal conductivity of the insulating protective layer 7 cannot be improved, and depending on the thickness of the insulating protective layer 7 and the fusible conductor 3, rapid melting of the fusible conductor 3 becomes difficult. Also, if the content of the thermal conductive filler 10 exceeds 60 volume%, the application viscosity of the insulating material 9 increases, and depending on the application thickness, the applicability may be impaired. For example, the content of the thermal conductive filler 10 to ensure a thermal conductivity of 2 W / mK in the insulating protective layer 7 is 20 to 25 volume%, using a thermal conductive filler 10 with a high thermal conductivity of 20 W / mK or more.

[0050] The average particle size of the thermal conductive filler 10 can be, for example, in the range of 0.5 to 20 μm. Furthermore, in order to aim for high packing (closest packing) of the thermal conductive filler 10 and to further improve the thermal conductivity of the insulating protective layer 7, two or more types of thermal conductive fillers 10 with different average particle sizes may be used. When a single thermal conductive filler 10 is used, gaps may form between the particles, but by using two or more types of thermal conductive fillers 10 with different average particle sizes, the gaps between the particles are more easily filled, and as a result, the insulating protective layer 7 can be made to have higher thermal conductivity. For example, from the viewpoint of dispersibility and high thermal conductivity, it is preferable to use a combination of a small-diameter filler with an average particle size of 0.5 to 5 μm and a large-diameter filler with an average particle size of 5 to 20 μm as the thermal conductive filler 10.

[0051] Furthermore, when using two types of thermally conductive fillers 10 with different average particle sizes, the volume ratio of the relatively small-diameter thermally conductive filler 10 to the relatively large-diameter thermally conductive filler 10 (small-diameter thermally conductive filler: large-diameter thermally conductive filler) can be, for example, in the range of 15:85 to 90:10, or in the range of 40:60 to 60:40.

[0052] The protective element 1 is mounted on an external circuit board, thereby connecting the heating element 5 to a current control element formed in the external circuit via a third external connection electrode 13. Under normal conditions, the heating element 5 is restricted from energizing and generating heat, but at a predetermined timing when the energizing path of the external circuit is interrupted, it is energized via the third external connection electrode 13 and generates heat.

[0053] The protective element 1 allows the heat from the heating element 5 to be transferred to the fusible conductor 3 via the insulating protective layer 7 and the heating element lead electrode 4c, thereby melting the fusible conductor 3 that connects the first and second energized parts 4a and 4b. In this case, the protective element 1 contains a thermally conductive filler 10 in the insulating material 9 that constitutes the insulating protective layer 7, so the heat from the heating element 5 is efficiently transferred to the fusible conductor 3. This allows the fusible conductor 3 to be quickly melted. The insulating protective layer 7 has high heat transfer efficiency, so it does not need to be formed extremely thin in order to quickly transfer heat to the fusible conductor 3, preventing the occurrence of pinholes and suppressing dielectric breakdown. In addition, by quickly melting the fusible conductor 3, it is also possible to prevent the heating element 5 from being damaged before the fusible conductor 3 is melted.

[0054] The molten conductor 3a of the fusible conductor 3 condenses on the heating element lead electrode 4c and on the first and second energized sections 4a and 4b, thereby interrupting the current path between the first and second energized sections 4a and 4b (Figure 2). As will be described later, the heating element 5 stops generating heat because its own energized path is also interrupted when the fusible conductor 3 melts.

[0055] [Heating element extraction electrode] The heating element lead electrode 4c, formed on the insulating protective layer 7, is connected at one end to the intermediate electrode 8 and is superimposed on the heating element 5 via the insulating protective layer 7. Furthermore, a fusible conductor 3 is connected between the first and second electrodes 4a and 4b of the heating element lead electrode 4c via a joining material such as connecting solder.

[0056] Furthermore, the heating element extraction electrode 4c can be formed by printing and firing a conductive paste such as Ag or Cu, similar to the first and second electrodes 4a and 4b. It is also preferable that the surface of the heating element extraction electrode 4c is coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by known methods such as plating.

[0057] [Fusable conductor] Next, the fusible conductor 3 will be described. The fusible conductor 3 is mounted between the first and second electrodes 4a and 4b, and melts due to heat generated by the energization of the heating element 5, or due to self-heating (Joule heating) when a current exceeding the rating is passed through it, thereby interrupting the current path between the first electrode 4a and the second electrode 4b.

[0058] The fusible conductor 3 can be any conductive material that melts due to the heat generated by the current flowing through the heating element 5 or due to an overcurrent condition. For example, SnAgCu-based Pb-free solder, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc., can be used.

[0059] Furthermore, the fusible conductor 3 may be a structure containing a high-melting-point metal and a low-melting-point metal. For example, as shown in Figure 6, the fusible conductor 3 is a laminated structure consisting of an inner layer and an outer layer, with a low-melting-point metal layer 18 as the inner layer and a high-melting-point metal layer 19 laminated on the low-melting-point metal layer 18 as the outer layer. The fusible conductor 3 is connected to the first and second electrodes 4a, 4b and the heating element lead electrode 4c via a joining material such as connecting solder.

[0060] The low-melting-point metal layer 18 is preferably solder or a metal mainly composed of Sn, and is a material commonly called "Pb-free solder". The melting point of the low-melting-point metal layer 18 does not necessarily need to be higher than the reflow temperature, and may melt at around 200°C. The high-melting-point metal layer 19 is a metal layer laminated on the surface of the low-melting-point metal layer 18, and is, for example, a metal mainly composed of Ag or Cu, and has a high melting point that does not melt even when the connection between the first and second electrodes 4a, 4b and the heating element lead electrode 4c and the fusible conductor 3 or the mounting of the protective element 1 onto the external circuit board is performed by reflow.

[0061] Such a fusible conductor 3 can be formed by depositing a high-melting-point metal layer onto a low-melting-point metal foil using plating technology, or by using other well-known lamination or film formation technologies. Furthermore, the fusible conductor 3 may have a structure in which the entire surface of the low-melting-point metal layer 18 is covered by the high-melting-point metal layer 19, or it may have a structure in which it is covered except for a pair of opposing sides. In addition, the fusible conductor 3 may be configured with the high-melting-point metal layer 19 as the inner layer and the low-melting-point metal layer 18 as the outer layer, or it may be a multilayer structure of three or more layers in which the low-melting-point metal layer 18 and the high-melting-point metal layer 19 are alternately laminated, or it may be formed in various configurations such as providing an opening in a part of the outer layer to expose a part of the inner layer.

[0062] The fusible conductor 3 maintains its shape as a fusible conductor 3 even when the reflow temperature exceeds the melting temperature of the low-melting-point metal layer 18, by laminating a high-melting-point metal layer 19 as an outer layer onto a low-melting-point metal layer 18 as an inner layer, and does not melt and break. Therefore, the connection between the first and second electrodes 4a, 4b and the heating element lead electrode 4c and the fusible conductor 3, as well as the mounting of the protective element 1 onto the external circuit board, can be efficiently performed by reflow. Furthermore, fluctuations in melting characteristics, such as not melting at a predetermined temperature or melting below a predetermined temperature due to localized high or low resistance values ​​caused by deformation of the fusible conductor 3 during reflow, can be prevented.

[0063] Furthermore, the fusible conductor 3 will not melt due to self-heating as long as a predetermined rated current is flowing through it. However, if a current higher than the rated value flows through it, it will melt due to self-heating, interrupting the current path between the first and second electrodes 4a and 4b. Additionally, the heating element 5 will melt when energized and generates heat, interrupting the current path between the first and second electrodes 4a and 4b.

[0064] In this case, the fusible conductor 3 melts at a temperature lower than its melting point because the molten low-melting-point metal layer 18 erodes (solder erosion) the high-melting-point metal layer 19. Therefore, the fusible conductor 3 can be melted and cut in a short time by utilizing the erosive action of the low-melting-point metal layer 18 on the high-melting-point metal layer 19. Furthermore, since the molten conductor 3a of the fusible conductor 3 is separated by the physical pulling action of the heating element lead electrode 4c and the first and second electrodes 4a and 4b, the current path between the first and second electrodes 4a and 4b can be quickly and reliably interrupted (Figure 2).

[0065] Furthermore, it is preferable that the fusible conductor 3 has a volume of low-melting-point metal layer 18 greater than the volume of high-melting-point metal layer 19. The fusible conductor 3 is heated by self-heating due to overcurrent or by the heating element 5, and the low-melting-point metal melts, corroding the high-melting-point metal, thereby allowing for rapid melting and cutting. Therefore, by forming the fusible conductor 3 with a volume of low-melting-point metal layer 18 greater than the volume of high-melting-point metal layer 19, this corroding action is promoted, and the connection between the first and second electrodes 4a and 4b can be quickly blocked.

[0066] Furthermore, since the fusible conductor 3 is constructed by laminating a high-melting-point metal layer 19 onto a low-melting-point metal layer 18 that forms the inner layer, the melting temperature can be significantly reduced compared to conventional chip fuses made of high-melting-point metals. Therefore, the fusible conductor 3 can have a larger cross-sectional area compared to chip fuses of the same size, and its current rating can be significantly improved. In addition, it can be made smaller and thinner than conventional chip fuses with the same current rating, and it has excellent rapid melting properties.

[0067] Furthermore, the fusible conductor 3 can improve resistance to surges (pulse resistance) when an abnormally high voltage is instantaneously applied to the electrical system into which the protective element 1 is incorporated. In other words, the fusible conductor 3 must not melt even when a current of, for example, 100A flows for several milliseconds. In this regard, since large currents that flow for a very short time flow through the surface layer of the conductor (skin effect), the fusible conductor 3 has a high melting point metal layer 19 such as Ag plating with low resistance as an outer layer, so that the current applied by the surge can easily flow and melting due to self-heating can be prevented. Therefore, the fusible conductor 3 can significantly improve resistance to surges compared to conventional fuses made of solder alloy.

[0068] Furthermore, the fusible conductor 3 may be coated with flux (not shown) to prevent oxidation and improve wettability during melting. The protective element 1 is protected internally by the insulating substrate 2 being covered by the case 17. The case 17 can be formed using insulating materials such as various engineering plastics, thermoplastics, ceramics, or glass epoxy substrates. The case 17 also has sufficient internal space on the surface 2a of the insulating substrate 2 for the fusible conductor 3 to expand spherically when melted, and for the molten conductor 3a to aggregate on the heating element extraction electrode 4c and the first and second electrodes 4a and 4b.

[0069] [Circuit Configuration Example] Such a protective element 1 is used, for example, by being incorporated into the circuitry of a lithium-ion secondary battery pack 20. As shown in Figure 7, the battery pack 20 has, for example, a battery stack 25 consisting of a total of four lithium-ion secondary battery cells 21a to 21d.

[0070] The battery pack 20 includes a battery stack 25, a charge / discharge control circuit 26 that controls the charging and discharging of the battery stack 25, a protection element 1 to which the present invention is applied that shuts off the charge / discharge path in the event of an abnormality in the battery stack 25, a detection circuit 27 that detects the voltage of each battery cell 21a to 21d, and a current control element 28 that acts as a switch element that controls the operation of the protection element 1 according to the detection result of the detection circuit 27.

[0071] The battery stack 25 consists of battery cells 21a to 21d connected in series, each requiring control to protect against overcharging and over-discharging. It is detachably connected to the charging device 22 via the positive terminal 20a and negative terminal 20b of the battery pack 20, and a charging voltage is applied from the charging device 22. The battery pack 20, once charged by the charging device 22, can power electronic equipment by connecting its positive terminal 20a and negative terminal 20b to the electronic equipment that operates on the battery.

[0072] The charge / discharge control circuit 26 comprises two current control elements 23a and 23b connected in series in the current path between the battery stack 25 and the charging device 22, and a control unit 24 that controls the operation of these current control elements 23a and 23b. The current control elements 23a and 23b are composed of, for example, field-effect transistors (hereinafter referred to as FETs), and the control unit 24 controls the conduction and interruption of the current path of the battery stack 25 in the charging direction and / or the discharge direction by controlling the gate voltage. The control unit 24 operates by receiving power from the charging device 22, and controls the operation of the current control elements 23a and 23b to interrupt the current path when the battery stack 25 is over-discharged or overcharged, according to the detection result by the detection circuit 27.

[0073] The protection element 1 is connected, for example, to the charge / discharge current path between the battery stack 25 and the charge / discharge control circuit 26, and its operation is controlled by the current control element 28.

[0074] The detection circuit 27 is connected to each battery cell 21a to 21d and detects the voltage value of each battery cell 21a to 21d, supplying each voltage value to the control unit 24 of the charge / discharge control circuit 26. The detection circuit 27 also outputs a control signal to control the current control element 28 when any one of the battery cells 21a to 21d reaches an overcharge voltage or over-discharge voltage.

[0075] The current control element 28 is composed of, for example, an FET, and when the voltage value of the battery cells 21a to 21d exceeds a predetermined over-discharge or overcharge state based on the detection signal output from the detection circuit 27, it activates the protection element 1 to control the charging and discharging current path of the battery stack 25 to be interrupted regardless of the switching operation of the current control elements 23a and 23b.

[0076] The protective element 1 to which the present invention is applied, used in the battery pack 20 having the above configuration, has the circuit configuration shown in Figure 8. Specifically, the protective element 1 has a first external connection electrode 11 connected to the battery stack 25 side, and a second external connection electrode 12 connected to the positive terminal 20a side, thereby connecting the fusible conductor 3 in series on the charge / discharge path of the battery stack 25. In addition, the protective element 1 has a heating element 5 connected to the current control element 28 via the heating element electrode 6 and the third external connection electrode 13, and the heating element 5 is connected to the open end of the battery stack 25. Thus, one end of the heating element 5 is connected to the fusible conductor 3 and one open end of the battery stack 25 via the heating element lead electrode 4c, and the other end is connected to the current control element 28 and the other open end of the battery stack 25 via the third external connection electrode 13. This forms a power supply path to the heating element 5, whose energization can be controlled by the current control element 28.

[0077] [Protection of protective element] When the detection circuit 27 detects an abnormal voltage in any of the battery cells 21a to 21d, it outputs a cutoff signal to the current control element 28. The current control element 28 then controls the current to energize the heating element 5. The protection element 1 receives current from the battery stack 25 to the heating element 5, causing the heating element 5 to start generating heat. The protection element 1 then cuts off the charge and discharge path of the battery stack 25 as the fusible conductor 3 melts due to the heat generated by the heating element 5. Furthermore, the protection element 1 is formed by incorporating a high-melting-point metal and a low-melting-point metal into the fusible conductor 3. The low-melting-point metal melts before the high-melting-point metal melts, and the molten low-melting-point metal corrodes the high-melting-point metal, allowing the fusible conductor 3 to melt in a short time.

[0078] In this case, the protective element 1 has improved thermal conductivity due to the inclusion of a thermally conductive filler 10 in the insulating protective layer 7. As a result, the insulating protective layer 7 efficiently transfers the heat generated by the heating element 5 to the fusible conductor 3, allowing it to melt and cut quickly. Furthermore, the insulating protective layer 7 does not need to be formed extremely thin, preventing the occurrence of pinholes, etc., thus preventing dielectric breakdown (sparking) between the heating element electrode 6, the first lead electrode 15, or the heating element 5 and the heating element lead electrode 4c. Moreover, by quickly melting the fusible conductor 3, it is possible to prevent the heating element 5 from being damaged before the fusible conductor 3 melts, allowing the current path to be safely and quickly interrupted.

[0079] When the fusible conductor 3 of the protective element 1 melts, the power supply path to the heating element 5 is also cut off, and thus the heating of the heating element 5 stops.

[0080] Furthermore, even if an overcurrent exceeding the rated current is supplied to the battery pack 20, the protective element 1 can shut off the charge and discharge path of the battery pack 20 by melting the fusible conductor 3 due to self-heating.

[0081] Thus, in the protection element 1, the fusible conductor 3 melts due to heat generated by the energization of the heating element 5 or self-heating of the fusible conductor 3 due to overcurrent. As described above, the protection element 1 has a structure in which a low-melting-point metal is covered with a high-melting-point metal, which suppresses deformation of the fusible conductor 3 even when reflow mounting to a circuit board or when the circuit board on which the protection element 1 is mounted is further exposed to high-temperature environments such as reflow heating. Therefore, fluctuations in melting characteristics caused by changes in resistance due to deformation of the fusible conductor 3 are prevented, and melting can be performed quickly by a predetermined overcurrent or heat generated by the heating element 5.

[0082] The protective element 1 according to the present invention is not limited to use in lithium-ion secondary battery packs, but can of course be applied to various other applications that require interruption of the current path by an electrical signal.

[0083] [Example 1] A modified example of a protective element to which this technology is applied will be described below. In the following description, the same reference numerals may be used for the same components as those in the protective element 1 described above, and their details may be omitted. The protective element 30 shown in Figure 9 has an insulating protective layer 7 composed of a substrate-side protective layer 7a on which a heating element 5 is formed on its surface, and a covering protective layer 7b that covers the heating element 5 formed on the substrate-side protective layer 7a. The substrate-side protective layer 7a is formed on the surface 2a of the insulating substrate 2, and the heating element 5 and the first and second lead electrodes 15 and 16 are formed on it. The covering protective layer 7b is laminated on the substrate-side protective layer 7a, thereby covering the heating element 5 together with the substrate-side protective layer 7a. As a result, the insulating protective layer 7 has the heating element 5 inside. The covering protective layer 7b also has the heating element lead electrodes 4c laminated on it. The method of forming the substrate-side protective layer 7a and the covering protective layer 7b is the same as that of the insulating protective layer 7 described above.

[0084] It is preferable that the protective coating layer 7b has a higher thermal conductivity than the substrate-side protective layer 7a. This makes it more difficult for the heat generated by the heating element 5 to escape to the insulating substrate 2, and allows heat to be transferred to the protective coating layer 7b more quickly. This increases the amount of heat transferred to the protective coating layer 7b per unit time, and allows the fusible conductor 3 to be heated efficiently. Methods for making the thermal conductivity of the protective coating layer 7b higher than that of the substrate-side protective layer 7a include, for example, including the thermal conductive filler 10 only in the protective coating layer 7b and not in the substrate-side protective layer 7a. Alternatively, the thermal conductive filler 10 included in the protective coating layer 7b has a higher thermal conductivity than the thermal conductive filler 10 included in the substrate-side protective layer 7a. Another method is to include using a larger amount of thermal conductive filler 10 in the protective coating layer 7b than in the substrate-side protective layer 7a. This technology is not limited to these methods, as it is a method for making the thermal conductivity of the protective coating layer 7b higher than that of the protective coating layer 7a on the substrate side.

[0085] [Differentiation 2] Next, other variations of the protective element to which this technology is applied will be described. In the following description, the same reference numerals are used for the same components as those in the protective elements 1 and 30 described above, and their details may be omitted. As shown in Figures 10 and 11, the protective element 40 to which this technology is applied may have a heating element provided on the back surface of the insulating substrate. In the protective element 40, a heating element 5, first and second lead electrodes 15 and 16, and an insulating protective layer 7 covering them are formed on the back surface 2b of the insulating substrate 2, opposite to the front surface 2a. In addition, a heating element electrode 6, a back-side intermediate electrode 8b, and first and second external connection electrodes 11 and 12 are formed on the back surface 2b of the insulating substrate 2.

[0086] Furthermore, the surface 2a of the insulating substrate 2 has first and second electrodes 4a and 4b, a fusible conductor 3, a heating element lead electrode 4c, and a surface-side intermediate electrode 8a formed thereon.

[0087] The back-side intermediate electrode 8b has a second lead electrode 16 drawn out, similar to the intermediate electrode 8 described above. The front-side intermediate electrode 8a and the back-side intermediate electrode 8b are electrically connected by castellations formed on the side surface of the insulating substrate 2 or by conductive through-holes penetrating the insulating substrate 2. The front-side intermediate electrode 8a is connected to a heating element lead electrode 4c. The front-side intermediate electrode 8a and the back-side intermediate electrode 8b can be formed using the same materials and processes as the intermediate electrode 8 described above.

[0088] The heating element lead electrode 4c is electrically and thermally connected to the heating element 5 via the front-side intermediate electrode 8a and the back-side intermediate electrode 8b. In other words, the protective element 40 is able to heat the heating element lead electrode 4c when the heating element 5 heats the heating element lead electrode 4c via the insulating substrate 2, and when the heat from the heating element 4 is transferred to the heating element lead electrode 4c via the front-side intermediate electrode 8a and the back-side intermediate electrode 8b, which have excellent thermal conductivity, thereby heating and melting the fusible conductor 3 (Figure 11(A)(B)).

[0089] Furthermore, in the protective element 40, the heating element electrode 6 also serves as an external connection electrode that connects to the electrode of the external circuit board; therefore, the third external connection electrode 13 provided in the protective element 1 is not provided in the protective element 40.

[0090] In the protective element 40, the insulating protective layer 7 is composed of a substrate-side protective layer 7a on which the heating element 5 is formed on its surface, and a covering protective layer 7b formed on the substrate-side protective layer 7a that covers the heating element 5. The substrate-side protective layer 7a is formed on the back surface 2b of the insulating substrate 2, and the heating element 5 and the first and second lead electrodes 15 and 16 are formed on its surface. The covering protective layer 7b is laminated on the substrate-side protective layer 7a, thereby covering the heating element 5 together with the substrate-side protective layer 7a.

[0091] It is preferable that the protective coating layer 7b of the protective element 40 has a lower thermal conductivity than the protective coating layer 7a on the substrate side. This makes it more difficult for the heat generated by the heating element 5 to escape to the protective coating layer 7b side and allows heat to be transferred to the insulating substrate 2 side more quickly, increasing the amount of heat transferred to the protective coating layer 7a side per unit time and enabling efficient heating of the fusible conductor 3. Methods for making the thermal conductivity of the protective coating layer 7a higher than that of the protective coating layer 7b include, for example, including the thermal conductive filler 10 only in the protective coating layer 7a and not in the protective coating layer 7b. Alternatively, the thermal conductive filler 10 included in the protective coating layer 7a has a higher thermal conductivity than the thermal conductive filler 10 included in the protective coating layer 7b. Or, the amount of thermal conductive filler 10 included in the protective coating layer 7a is greater than the amount of thermal conductive filler 10 included in the protective coating layer 7b. This technology is not limited to these methods, as it is a method for making the thermal conductivity of the substrate-side protective layer 7a higher than that of the covering protective layer 7b. [Examples]

[0092] Next, Examples 1 and 2 of this technology will be described. In Example 1, a glass layer was formed as an insulating protective layer, and protective element samples were prepared with varying glass layer thickness and thermal conductivity. The time required from the application of current to the fusible conductor (interruption time) was measured. The configuration of the protective element was the same as that of protective element 30 described above. The heating element was formed from ruthenium oxide with a thickness of 15 μm. A current of 15 A was applied to the heating element at a voltage of 60 V.

[0093] The thickness of the glass layer refers to the thickness of the protective coating layer on top of the heating element, with thicknesses of 10 μm, 20 μm, 30 μm, and 40 μm for each sample. The thickness of the protective layer on the substrate side was 15 μm. Aluminum oxide (thermal conductivity: 40 W / mK) was used as the thermally conductive filler to be incorporated into the glass layer. The thermal conductivity of the glass layer was adjusted within the range of 1 W / mK to 20 W / mK by changing the volume fraction of the thermally conductive filler (see Figure 4).

[0094] The protective element samples were evaluated based on the interruption time, with 0.2 seconds or less being rated as excellent (◎), between 0.2 seconds and 0.3 seconds being rated as good (○), and above 0.3 seconds being rated as poor (×). If dielectric breakdown occurred when voltage was applied, all protective element samples with that film thickness were evaluated as poor (×), regardless of the thermal conductivity of the glass layer.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] As shown in Table 1, dielectric breakdown occurred in the protective element sample with a glass layer thickness of 10 μm, and therefore all samples with this thickness were deemed defective.

[0100] As shown in Table 2, for protective elements with a glass layer thickness of 20 μm, the blocking time was 0.3 seconds or less for all samples.

[0101] As shown in Table 3, in protective elements with a glass layer thickness of 30 μm, the shut-off time exceeded 0.3 seconds for samples with a glass layer thermal conductivity of 1 W / mK and 1.25 W / mK, but the shut-off time was 0.3 seconds or less for samples with a glass layer thermal conductivity of 1.5 W / mK or higher.

[0102] As shown in Table 4, in protective elements with a glass layer thickness of 40 μm, the shutoff time exceeded 0.3 seconds for samples with a glass layer thermal conductivity of 1 W / mK to 1.75 W / mK, but the shutoff time was 0.3 seconds or less for samples with a glass layer thermal conductivity of 2 W / mK or higher.

[0103] As described above, the more thermally conductive fillers with high thermal conductivity are included to increase the thermal conductivity of the insulating protective layer, the thicker the insulating protective layer can be formed, providing a highly reliable protective element that prevents dielectric breakdown and also shortens the melting time. Furthermore, if the thickness of the insulating protective layer is the same, the higher the thermal conductivity of the insulating protective layer, the shorter the melting time can be, providing a more responsive protective element. [Examples]

[0104] In Example 2, a glass layer was formed as an insulating protective layer, and the volume capacity (%) of the thermal conductive filler required to achieve a thermal conductivity of 2 W / mK in the insulating protective layer was determined for each thermal conductivity of the thermal conductive filler, and the applicability of the glass paste was evaluated.

[0105] The insulating protective layer was formed by screen printing a glass paste onto an insulating substrate. The opening of the mask was 1000 × 100 μm, and the glass paste coating thickness was 20 μm.

[0106] The evaluation criteria for coating performance were as follows: ○ (Excellent) if the coating pattern was printed smoothly without pinholes or defects; △ (Average) if a good print quality was obtained by reducing the printing speed; and × (Poor) if pinholes or defects occurred even when the printing speed was reduced.

[0107] [Table 5]

[0108] As shown in Table 5, when the volume of the thermally conductive filler relative to the glass paste exceeds 35%, it leads to an increase in the viscosity of the glass paste constituting the insulating protective layer, resulting in a decrease in applicability.

[0109] In other words, the lower the thermal conductivity of the thermally conductive filler, the greater the volume of thermally conductive filler required to achieve a thermal conductivity of 2 W / mK in the insulating protective layer. This leads to an increase in the viscosity of the glass paste that constitutes the insulating protective layer, resulting in reduced applicability.

[0110] On the other hand, the higher the thermal conductivity of the thermally conductive filler, the less volume of thermally conductive filler is needed to achieve a thermal conductivity of 2 W / mK in the insulating protective layer, thereby suppressing the increase in viscosity of the glass paste and providing good applicability.

[0111] Example 2 shows that by limiting the volume of the thermally conductive filler to 25% or less, good applicability of the glass paste can be achieved. Therefore, it is found that to achieve a thermal conductivity of 2 W / mK for the insulating protective layer, it is effective to include a thermally conductive filler with a thermal conductivity of at least 20 W / mK. [Explanation of Symbols]

[0112] 1 Protective element, 2 Insulating substrate, 3 Fusible conductor, 4a First electrode, 4b Second electrode, 4c Heating element lead electrode, 5 Heating element, 6 Heating element electrode, 7 Insulating protective layer, 7a Substrate-side protective layer, 7b Covering protective layer, 8 Intermediate electrode, 9 Insulating material, 10 Thermally conductive filler, 11 First external connection electrode, 12 Second external connection electrode, 13 Third external connection electrode, 15 First lead electrode, 16 Second lead electrode, 18 Low melting point metal layer, 19 High melting point metal layer, 20 Battery pack, 21 Battery cell, 22 Charging device, 23 Current control element, 24 Control unit, 25 Battery stack, 26 Charge / discharge control circuit, 27 Detection circuit, 28 Current control element, 30 Protective element, 40 Protective element

Claims

1. Insulating substrate and The first and second electrodes provided on the insulating substrate, A heating element formed on the above insulating substrate, A heating element extraction electrode electrically connected to the above heating element, A fusible conductor mounted from the first electrode to the second electrode via the above-mentioned heating element extraction electrode, The above-mentioned heating element is covered by an insulating protective layer, The above insulating protective layer is a protective element containing a thermally conductive filler.

2. The protective element according to claim 1, wherein the insulating protective layer contains the thermally conductive filler that transmits the heat generated by the heating element to the fusible conductor.

3. The protective element according to claim 1 or 2, wherein the heating element, the insulating protective layer, the heating element lead electrode, and the fusible conductor are superimposed on each other.

4. The protective element according to any one of claims 1 to 3, wherein the above-mentioned thermally conductive filler comprises aluminum oxide and / or aluminum nitride.

5. The protective element according to any one of claims 1 to 4, wherein the insulating protective layer has a thickness of 20 μm or more.

6. The protective element according to any one of claims 1 to 5, wherein the thermal conductivity of the insulating protective layer is 1.5 W / mk or more.

7. The protective element according to any one of claims 1 to 6, wherein the volume capacity of the thermally conductive filler relative to the volume capacity of the insulating material constituting the insulating protective layer is 20% or more.

8. The protective element according to any one of claims 1 to 7, wherein the heating element and the insulating protective layer are formed on the surface of the insulating substrate on which the fusible conductor is mounted.

9. The protective element according to any one of claims 1 to 8, wherein the heating element and the insulating protective layer are formed on the side of the insulating substrate opposite to the side on which the fusible conductor is mounted.

10. One or more battery cells, A protective element connected to the charge / discharge path of the above-mentioned battery cell, which blocks the charge / discharge path, The system includes a current control element that detects the voltage value of the battery cell and controls the supply of power to the protection element, The above protective element is Insulating substrate and The first and second electrodes provided on the insulating substrate, A heating element formed on the above insulating substrate, A heating element extraction electrode electrically connected to the above heating element, A fusible conductor mounted from the first electrode to the second electrode via the above-mentioned heating element extraction electrode, The above-mentioned heating element is covered by an insulating protective layer, The above insulating protective layer contains a thermally conductive filler. Battery pack.

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