KR20140021593A - Protective element - Google Patents

Abstract

The present invention provides a protection element capable of flowing a larger current while providing protection against excess current. Such a protection element is formed of an insulating resin and is located on a side element defining at least one of the layered element having at least one through opening, the conductive metal foil layer located on each major surface of the layered element, and the through opening. And a fuse layer for electrically connecting the conductive metal foil layer.

Description

Protective element {PROTECTIVE ELEMENT}

The present invention relates to a protective element for protecting an electrical device, and more particularly, to a protective element for protecting an electrical element or a circuit included in the electrical device. For example, when an excess current flows in an electric device such as a secondary battery, the present invention relates to a protection element that blocks the flow of the current, that is, an overcurrent protection element.

As a protection element that blocks the flow of current when an excessive current flows during charging or discharging of a cylindrical lithium ion secondary battery, a thermal fuse element, a current fuse element, a polymer PTC element, and the like are used. Especially, since a polymer PTC element can be built-in and arrange | positioned in the sealing plate of a secondary battery, it is especially useful at the point which the battery pack comprised by many secondary batteries becomes compact.

However, a commercially available PTC element cannot carry a large current (for example, a current of 20 A). When the PTC element is removed and the temperature is lowered, the PTC element has a resilience that becomes low resistance, but such resilience may cause problems depending on the application. For example, in the case of using a PTC element in a cylindrical lithium ion secondary battery cell used in parallel, the cell continues to generate heat unless the shorted cell using the PTC element is removed. As a result, the battery cell may rupture.

In view of such a problem, it is proposed to use a spacer instead of a PTC element inside a sealing plate, for example in a cylindrical lithium ion secondary battery cell (refer nonpatent literature 1 below). However, when spacers are used, there is a problem in that protection against excess current cannot be ensured.

Matsushita Technical Journal Vol. 52 N0. 4 Aug. 2006 pp31-35

Accordingly, the problem to be solved by the present invention is to provide a protection element capable of providing a larger current while allowing protection against excess current.

In a first aspect, the present invention

A layered element formed of an insulating resin and having at least one through opening,

A conductive metal foil layer located on each major surface of the layered element, and

A fuse layer located on a side surface defining at least one of the through openings, the fuse layer electrically connecting the conductive metal foil layer.

It provides, comprising a protective element.

In a second aspect, the present invention provides an electric device, for example, a secondary battery, comprising the protection element of the present invention as described above and below. More specifically, a secondary battery cell, a secondary battery cell assembly or a secondary battery pack in combination thereof is provided.

The protective element of the present invention includes a layered element formed of an insulating resin, and the layered element has at least one through opening. The opening extends along the thickness direction of the layered element and penetrates the layered element. The cross-sectional shape in the direction perpendicular to the thickness direction is not particularly limited, but is preferably circular. In this case, the through opening is a cylindrical space part. However, other shapes may be used, for example square, rhombus, rectangle, oval. The number of through openings is at least one. That is, one, two or more, for example, two, three, four, five may be sufficient, but it can select suitably according to the degree of protection calculated | required by a protection element. In the case of having one through opening, the through opening is preferably located at the center of the layered element, more specifically, at the center of the cross-sectional shape in the direction perpendicular to the thickness direction.

The insulating resin constituting the layered element is not particularly limited as long as it is an electrically insulating resin. For example, resin, such as polyethylene, a polypropylene, a polycarbonate, a fluororesin, can be illustrated. In particular, it is preferable to use a resin such as polyethylene or polyvinylidene fluoride, and such a resin has the same flexibility as that of the polymer used in the polymer PTC device, and the protective device of the present invention is replaced with the secondary battery. It is advantageous in that it can be incorporated in the sealing plate of a cell, and can be used reliably in general in an electric apparatus. In another embodiment, the protection element of the present invention can be used in place of the spacer used inside the sealing plate of the secondary battery cell described above. In that case, the protection element can be used as a washer.

The layered element comprises a conductive metal foil layer disposed on each major surface thereof, that is, on the major surfaces of both sides thereof. The metal foil layer is not particularly limited as long as it is a thin layer of conductive metal (for example, a layer having a thickness of about 0.1 μm to about 100 μm). For example, the metal foil layer is composed of metal such as copper, nickel, aluminum, and gold. can do.

The layered element in which the conductive metal foil layer is located on each main surface is, for example, coextruded the insulating resin constituting the layered element together with the metal sheet (or metal foil) constituting the metal foil layer, thereby forming a metal sheet (or metal foil). It can manufacture by obtaining the extrudate of the state in which the insulating resin was sandwiched in between. In another aspect, it can also manufacture by obtaining the layered material of insulating resin by extrusion, for example, sandwiching this layered material between metal sheets (or metal foil), and thermocompressing them integrally and obtaining a crimping | compression-bonding material. Such extrudates (or crimps) are in a state where a plurality of layered elements of insulating resin having conductive metal foil layers on both main surfaces are adjacent to each other, and the extrudate (or crimps) is cut out to a predetermined shape and dimension, A single, layered element having a conductive thin layer on each major surface can be obtained.

In another embodiment, the conductive metal foil layer may be formed on the main surfaces of both sides by plating the conductive metal on the layered element of the insulating resin. Also in this case, it is preferable to obtain the thing in the aggregated state as described above, and then divide into individual layered elements.

Thus, in the case of plating, it is preferable that the layered element be brought into close contact with the layered element in advance by extrusion or thermocompression of another metal layer, particularly preferably metal foil, for example, as described above on the main surface thereof. Particularly preferred. In this case, it is preferable to form a conductive metal foil layer by plating on this other metal layer. Thus, when forming a conductive metal foil layer by plating, it is advantageous at the point that the plating layer as a conductive metal foil layer can adhere to the other metal layer which is already in close contact with a layered element. For example, the protection element of this invention has nickel foil as another metal layer in the main surface on both sides of a layered element, and has a conductive metal foil layer and fuse layer formed by nickel plating. That is, it is advantageous in that a conductive metal foil layer and a fuse layer can be formed simultaneously.

The form of the layered element is not particularly limited as long as the dimension in the thickness direction is smaller than other dimensions, and preferably considerably smaller (for example, in the form of a sheet). Planar shape of the layered element (figure when the layered element is viewed directly from above, for example, contour shape of the protective element shown in FIG. 2, and thus shape of the main surface) or cross-sectional shape in the direction perpendicular to the thickness direction of the layered element It is preferable that they are geometrically linear symmetrical and / or point symmetrical shapes, for example, circular, square, rectangular, rhombus, annular (especially annular, so-called donut shape) and the like.

Especially, it is preferable that a layered element is annular, especially annular. In the case of the annular shape, the through-opening part of the present invention may be the central opening part, for example, the central circular opening part in the case of the annular shape. Further, the layered element may have one or more additional through openings, eg through openings having a circular cross section, in the portion (for example, the middle portion) between the inner and outer circumferences defining the annular shape. do. Thus, the layered element has at least one through opening.

The protection element of this invention has a fuse layer located on the side surface which defines at least one of such through openings. When the fuse layer electrically connects the conductive metal foil layers located on both main surfaces of the layered element, and an excessive current flows from the conductive metal foil layer on one main surface toward the conductive metal foil layer on the other main surface. As a result, excessive current flows through the fuse layer, and as a result, it melts and opens the circuit, thereby blocking the flow of such current (so-called fuse). Both fuse layers are formed on the side surface defining at least one through opening. More specifically, as long as the conductive metal foil layers on both sides can be electrically connected, a fuse layer may be formed on at least a part of such side surfaces, but it is preferable that the fuse layers are formed over the entire side surfaces. Although the formation method is not specifically limited, It is especially preferable to form by electroplating (for example, electrolytic plating or electroless plating), for example, nickel plating. Although the thickness of a fuse layer can be controlled by plating conditions, it is preferable that it is 0.001-0.02 mm, for example.

In the case of forming one through opening having a fuse layer on the side, the layered element is circular or other suitable, original holeless flat plate shape, and its central portion (like a layered element whose plane shape is circular (i.e., discotic)). It is preferable to form a through opening (also referred to as a "center through opening") in such a central portion. As a result, the layered element is strictly annular in shape. The current flowing through the conductive metal foil layer on one main surface of the layered element having such an annular shape flows toward one end of the through opening, and then passes through the fuse layer to form another portion of the layered element from the other end of the through opening. Radially flows on the conductive metal foil layer on the main surface.

Thus, in the form in which one through opening is formed in the layered element, a larger through opening is formed at the center of the annular element as a center through opening as compared with the form in which a plurality of through openings will be described later. Preferably, a fuse layer is formed on the side of the through opening. Such a protection element can reduce the resistance value, and thus can be suitably used in the case where a large current (preferably larger than 20 A, for example, 30 to 40 A or larger, for example, 50 A) flows. have. In addition, since only one through opening is formed, the production of the protection element is simplified.

In a preferable embodiment, the layered element is an annular shape defined by the inner circumference 30 and the outer circumference 34 as shown in FIG. 2 or FIG. 4 described later. The diameter of the circle defining the inner perimeter of the layered element is, for example, 6 to 10 mm, and the diameter of the circle defining the outer perimeter is preferably 13 to 17 mm, for example. As a protection element in the case of flowing an electric current of 30-40 A, it is preferable that the diameter of the circle | round | yen of an inner perimeter is 6.5 mm, for example, and the thickness of a fuse layer is 0.01 mm, for example.

In the case of forming a plurality of through openings, it is preferable to arrange the through openings so that the current passing through the layered elements flows through the fuse layer of each through opening as evenly as possible. For example, a through opening having the same cross-sectional shape and size in a circumferential portion of the annular layered element having a center through opening (that is, the body portion of the layered element defined by the inner circumference and the outer circumference) (the “peripheral A plurality of through openings " For example, two through openings are formed every 180 °, three every 120 °, four every 90 °, and every 60 °. However, depending on the conditions of use of the protection element, the layered element may have only one peripheral through opening. Therefore, the number of the circumferential through openings may be one to six, for example.

If the diameter of the circle around the inner circumference, ie the cross-sectional circle of the central through opening, which defines an annular layered element is equal to or less than the diameter of the other through opening, ie the peripheral through opening, define such a central through opening. A fuse layer may also be formed on the side surface. Conversely, when the diameter of the cross section circle of the center through opening is larger than the diameter of the cross section circle of the peripheral through opening, it is preferable not to form a fuse layer on the side defining the center through opening.

Thus, whether or not a fuse layer is formed in the center through opening is determined depending on whether or not the current flowing through the fuse layer formed in each through opening of the protective element is substantially equal. Briefly, if the central through opening has a circular cross section larger than the peripheral through opening, forming a fuse layer in the central through opening makes it possible to substantially flow the fuse layer substantially over most of the current flowing through the protection element, and to form a smaller circular cross section. Since it is difficult for an electric current to flow through the fuse layer formed in the other through opening which has the cross section, the meaning of forming a fuse layer in the other through opening is faded.

In a preferable embodiment, the layered element is an annular element defined by the outer circumference and the inner circumference, the through opening is defined as the center through opening by the inner circumferential surface, and the other through opening is the inside of the layered element, that is, It may exist as a peripheral through opening penetrating between the inner periphery which defines a layered element, and the outer periphery (that is, the part of insulating resin which defines a layered element). In this case, therefore, the layered element has one central through opening defined by the inner circumference and at least one through opening (corresponding to the peripheral through opening described above) passing through the body portion of the layered element.

In this form, the fuse layer is present on the side surface (i.e. wall) defining the peripheral through opening. When the diameter of the center through opening is not significantly different from that of the peripheral through opening, and a fuse layer is present in the center through opening, the current flows in the fuse layer as well as the fuse layer of the peripheral through opening. In this case, a fuse layer may also be formed in the center through opening. If the diameter of the central through opening is larger than the diameter of the peripheral through opening, and it is assumed that a fuse layer exists in the central through opening, a much larger amount of current is expected to flow through the fuse layer than that of the peripheral through opening. Since there is no meaning of forming a fuse layer in the peripheral through opening, a fuse is not provided in the central through opening.

Therefore, in one embodiment of a protective element having an annular layered element having a plurality of through openings, for example, an annular layered element, there is no fuse layer in the center through opening, and a plurality of peripheries arranged around the periphery. It has a through opening. It is preferable that the circumference forming the peripheral through opening is usually one ply, but in some cases, the circumference of the plural ply may be sufficient, for example, the circumference of two ply or three ply. In this manner, in the form of forming the fuse layer only in the peripheral through opening, the resistance value of the protection element can be controlled according to the number of the peripheral through openings to be formed. Basically, increasing the number of peripheral through openings decreases the resistance value, and conversely, decreasing the number increases the resistance value. Therefore, there is an advantage that the resistance value of the protection element can be easily and precisely changed by simply changing the number of through openings to be provided, compared with the form of forming the fuse layer only in the above-described center through opening.

If the layered element is annular, for example annular, the peripheral through opening is preferably located in contrast with respect to the center of the layered element. When there are a plurality of peripheral through openings, for example, from 2 to 12, preferably from 4 to 10, at the same angle around the center of the annular element, ie the figure defining the inner circumference, for example the center of the circle. More preferably 5 to 9, particularly preferably 6 to 8, for example 2 every 180 °, 3 every 120 °, 4 every 90 °, 6 every 60 °, 8 every 45 ° 9, every 40 degrees, 10 every 36 degrees, and may exist so that it may exist.

In a specific aspect, the diameter of the center through opening (not forming the fuse layer) is 6 to 10 mm, and the diameter of the cross-sectional circle of the peripheral through opening (forming the fuse layer) around it is 0.2 to 1 mm. In this aspect, the outer diameter of the layered element is preferably 13 to 17 mm, for example. As a protection element in the case of flowing a current of 20-30 A, four peripheral through openings of diameter 0.6mm are formed, for example, and it is preferable that the thickness of a fuse layer is 0.01 mm, for example.

In any of the aspects, the through opening may preferably have a circular cross-sectional shape (ie, a cross-sectional shape perpendicular to the thickness direction of the layered element), but may have any other suitable cross-sectional shape. It is preferable to have a cross section. In another embodiment, a square, rectangle, rhombus, triangle, or the like may be used. In that case, the above-mentioned diameter corresponds to the equivalent diameter of another cross-sectional shape.

When the fuse layer formed on the side surface (or circumferential surface) which defines the through-opening part electrically connects both main surfaces of a layered element, and an excessive current flows from one main surface to the other main surface. As a result, the excess current flows intensively in the fuse layer, and as a result, it melts and has a function of interrupting the flow of such current. The material constituting such a fuse layer is a conductive material, in particular a conductive metal layer. For example, it is preferable to form a fuse layer by a thin layer of metal, such as copper, nickel, aluminum, and gold. It is particularly preferable to form the fuse layer by plating the metal constituting the fuse layer.

Thus, the cross-sectional shape of the through opening, the size of the through opening (usually, the diameter) and the length of the through opening along the thickness direction of the layered element, the thickness of the material of the fuse and the layer thereof, and the through so as to melt according to the assumed excess current amount Various factors such as the number and arrangement of the openings are selected, and the numerical values and the like are selected as prescribed. This selection can be carried out by those skilled in the art by, for example, trial and error on these factors.

In a preferable embodiment, the conductive metal foil layer and the fuse layer are integrally formed by plating of the conductive metal, more preferably by nickel plating. In this case, it is advantageous because by plating such a layered element having through openings with such a metal, these layers can be formed simultaneously and integrally. That is, the fuse layer and the conductive metal foil layer are formed of the same kind of metal. As the plating method, an electrolytic plating or an electroless plating method can be used.

In a particularly preferred embodiment, there is a metal foil, preferably nickel foil, which is in close contact with the layered element between the main surface of the layered element and the conductive metal foil layer. In this case, the conductive metal foil layer formed as the plating layer can be in close contact with the metal foil, and as a result, there is an advantage that the conductive metal foil layer is firmly bonded to the layered element through the metal foil.

The protection element of the invention uses a second electrical element (e.g. a charger) as an electrical element different from the first electrical element (e.g. secondary battery) in order to protect the circuit to be protected or the electrical element constituting it. Positioned between them for electrical direct or indirect connection, so that one conductive metal foil layer is in direct or indirect contact with the first electrical element, and the other conductive metal foil layer is in direct or indirect contact with the second electrical element. Contact. Thus, there is provided an electrical device comprising the protection element of the invention and a circuit and / or an electrical element electrically connected thereby.

The protection element of this invention has a conductive metal foil layer on the main surface of both sides of a layered element, and makes it possible to flow a large electric current by connecting these fuse layers electrically, but when excess current flows, As a result of the intensive flow of excess current, the fuse layer melts and the circuit is interrupted, whereby the flow of excess current can be interrupted.

1 schematically shows the protection element of the present invention in a sectional view along its thickness direction.
FIG. 2 schematically shows the protection element shown in FIG. 1 in a plan view.
FIG. 3: shows typically the protection element of another form of this invention in sectional drawing along the thickness direction.
4 schematically shows the protection element shown in FIG. 3 in a plan view.

With reference to the drawings, the protection element of this invention is demonstrated in more detail. In FIG. 1, one aspect of the protection element of this invention is shown typically in sectional drawing along the thickness direction (the part shown as a cut surface is shown by A), and also the protection element shown in FIG. 2 in FIG. Is schematically shown in plan view (that is, when the protective element is viewed so as to be indicated by an arrow B from above in FIG. 1).

The illustrated protection element 10 is formed of an insulating resin, and at least one through opening, in the illustrated form, two through openings of the central through opening 12 of the circular cross section and the peripheral through opening 14 of the circular cross section. It consists of an annular layered element (16) having a. It has conductive metal foil layers 22 and 24 located on major surfaces 18 and 20 on both sides of layered element 16. In addition, in the form shown, other metal layers 26 and 28 exist between the layered element 16 and the conductive metal foil layers 22 and 24.

In the form shown, a fuse layer is not present on the inner circumference 30 of the annular ring, that is, on the side of the inner side of the annular ring, which defines the center through opening 12. In the form shown, a fuse layer on the circumferential side surface 38 defining a peripheral through opening 14 located in the body portion 36 of the layered element between the inner circumference 30 and the outer circumference 34 of the annular ring. 40 is present.

In the illustrated embodiment, one peripheral through opening 14 having a fuse layer 40 is formed in the middle of the body portion 36 along a diameter (shown in broken lines in FIG. 2) passing through the center O of the layered element. However, such peripheral through openings may be formed on the opposite side along the radial direction. In that case, two peripheral through openings are formed every 180 degrees around the center O. In another embodiment, the peripheral through openings having preferably 3 to 12, more preferably 4 to 10 and particularly preferably 6 to 8 fuse layers, at the same angle, based on the center O of the circle. Peripheral through openings having three fuse layers every 120 °, four every 90 °, six every 60 °, or eight fuse layers every 45 ° may be provided at the same angle, for example.

In addition, in the form shown, since the diameter of the center through opening 12 is much larger than the diameter of the peripheral through opening 14, although a fuse layer does not exist on the side surface of the inner periphery 30 of a torus, the center through opening is not present. When the diameter of is equal to or smaller than the diameter of the peripheral through opening, a fuse layer may be formed on the side surface of the inner circumference 30 of the annular ring as necessary. Moreover, in one aspect, if the convex part corresponding to a center through opening is formed in the electrical device which should arrange | position a protection element, such a convex part will fit in the large diameter part of a center through opening, and positioning a protection element in an electrical device. There may be cases. For example, by forming such a convex portion in the sealing plate of the secondary battery cell and allowing the convex portion to fit in the center through opening, the protection element can be positioned in the sealing plate.

In another form, the layered element 16 does not have a central through opening 12 (thus the layered element is disc shaped) and has only at least one peripheral through opening 14, even if it has a fuse layer 40. do.

The protection element 10 'of another form of this invention is shown to FIG. 3 and FIG. 4 similarly to FIG. In addition, about the same element as FIG. 1 and FIG. 2, the same code | symbol is used. In the form shown, the layered element 16 does not have a peripheral through opening 14 of the protection element 10 of FIG. 1, but has only a central through opening 12, which has a fuse layer 32.

Example 1

The protection element of this invention shown in FIG. 1 and FIG. 2 was manufactured. Therefore, the protection element 10 which has only the fuse layer 40 and does not have the fuse layer 32 which the protection element 10 'of FIG. 3 has was manufactured. However, four peripheral through openings 14 were formed around the center O at the same angle in the circumferential shape.

First, the sheet of insulating resin (made of polyethylene, thickness 0.3mm, corresponding to the layered element 16) is prepared, and nickel foil (thickness: 22 micrometers, corresponding to the other metal layers 26 and 28) is arrange | positioned at both sides. Then, they were integrally pressurized under heating to obtain a crimped article in which nickel foil was attached to both main surfaces of the sheet of insulating resin.

A through hole (corresponding to the peripheral through opening 14) having a diameter of 0.6 mm was formed at a predetermined location of the compressed material, and the compressed material was then attached by nickel plating treatment by the electrolytic method. The thickness of the nickel layer (corresponding to the conductive metal foil layers 22 and 24) formed by plating was about 0.01 mm. Subsequently, the annular element was punched out from the crimped material, and the protection element 10 of the present invention in which four through holes are located at predetermined positions about 90 degrees around the center of the annular element was obtained.

The diameter of the outer circumferential circle 34 of the obtained annular element was 15 mm, and the diameter (that is, the diameter of the central through opening) of the inner circumferential circle 30 was 6.4 mm. This toroidal element has nickel foils functioning as the other metal layers 26 and 28 on both main surfaces of the insulated resin layer 16 as layered elements, and four in the middle part of the main body part 36 of the toroidal part. It has a peripheral through opening 14. Further, the toroidal element had plating layers as the conductive metal foil layers 22 and 24 on the nickel foil, and had a plating layer functioning as the fuse layer 40 on the inner circumferential surface defining the peripheral through opening.

A predetermined current 20A flows from the one conductive metal foil layer 22 to the other conductive metal foil layer 24 to the obtained protective element of the present invention, and the surface temperature of the conductive metal foil layer 22 of the protective element rises after 10 minutes. Was measured. In addition, the current interruption time (that is, the time until the fuse layer melted when a current of 100 A was flowed) as the fuse of the protection element was measured.

As a result, surface temperature rise was 10 degrees C or less in any place, and the current interruption time was 0.1 second or less.

Example 2

The protection element of this invention shown in FIG. 3 and FIG. 4 was manufactured. Therefore, the protection element 10 'which does not have a peripheral through opening and has only the fuse layer 32 around the center through opening was manufactured. In the manufacturing method, after forming an opening corresponding to the center through opening in the crimped material, the fuse layer is formed by plating, and then the protective element 10 'is obtained by punching out an annular element. Other implementation was carried out in the same manner as in Example 1. The diameter of the center through opening was 6.5 mm, and the thickness of the fuse layer was 0.1 mm.

The surface of the conductive metal foil layer 22 of the protection element which flows predetermined electric current 30-40 A from one conductive metal foil layer 22 to the other conductive metal foil layer 24 to the protective element of this invention obtained after 10 minutes. The temperature rise was measured. In addition, the current interruption time (that is, the time until the fuse layer melted when a current of 100 A flowed) as the fuse of the protection element was measured.

As a result, surface temperature rise was 10 degrees C or less in any place, and the current interruption time was about 0.1 second.

From these results, it can be seen that the protection element of the present invention can provide protection against excess current while allowing a larger current to flow. Therefore, in the protection element of this invention, when the electric current value which can be normally flowed is made extremely large, for example, in the cylindrical lithium ion secondary battery cell, the nickel washer embedded in the sealing plate and nickel plating on the stainless steel material It can also be used as a substitute for a washer or the like. In this case, since the protection element has a layered element formed of insulating resin, the function as a washer is improved by the elasticity of the resin. Accordingly, the present invention also provides a washer having the features of the above-described protective element of the present invention.

10, 10 ': protection device
12: center through opening
14: peripheral through opening
16: layered elements
18, 20: major surface
22, 24: conductive metal foil layer
26, 28: another metal layer
30: inner circumference
32: fuse layer
34: outer circumference
36: body part
38: side
40: fuse layer

Claims (12)

As a protective element,
A layered element formed of an insulating resin and having at least one through opening,
A conductive metal foil layer located on each major surface of the layered element, and
A fuse layer located on a side surface defining at least one of the through openings, the fuse layer electrically connecting the conductive metal foil layer.
Consisting of, comprising a. The method of claim 1,
The conductive metal foil layer and the fuse layer are integrally formed by plating metal, The protection element characterized by the above-mentioned. 3. The method of claim 2,
The metal to plate is a protective element characterized by the above-mentioned. The method according to claim 2 or 3,
A protective element, further comprising a metal foil positioned between the layered element and the conductive metal foil layer. 5. The method of claim 4,
The metal foil is a nickel foil, wherein the protection element. The method according to any one of claims 1 to 5,
The layered element is an annular element defined by the inner circumferential surface and the outer circumferential surface, and has a single through opening defined by the inner circumferential surface. The method according to any one of claims 1 to 5,
The layered element is an annular element defined by the inner circumferential surface and the outer circumferential surface and having at least two through openings, the through openings being the center through opening defined by the inner circumferential surface and the inner and outer circumferential surfaces. At least one peripheral through opening positioned in between, wherein the peripheral through opening has a fuse layer. The method of claim 7, wherein
In the layered element, six to eight peripheral through-holes are formed at the same angle around the center through-hole, and the protection element characterized by the above-mentioned. The method according to any one of claims 1 to 8,
The layered element has a toroidal shape. An electrical apparatus comprising the protective element according to any one of claims 1 to 9. A secondary battery cell comprising the protective element according to any one of claims 1 to 9. As a washer,
A layered element formed of an insulating resin and having at least one through opening,
A conductive metal foil layer located on each major surface of the layered element, and
A fuse layer located on a side surface defining at least one of the through openings, the fuse layer electrically connecting the conductive metal foil layer.
Consisting of, including.

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