JP6613082B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries are used in a wide range of applications such as portable information terminals and electric vehicles, and research and development are being conducted to improve energy density and output. A high energy density, high output lithium ion secondary battery is extremely attractive because it can improve the convenience of a device in which it is mounted, but ensuring safety is even more important. If a part of the battery is damaged and the positive and negative electrodes are locally short-circuited due to an abnormal situation such as a strong impact on the battery or gas generation inside the overcharged battery, an excessive current will be locally applied in a short time. There is concern that it will flow and fire. For this reason, a lithium ion secondary battery manufacturer is required to perform an appropriate safety confirmation test and to inspect beforehand that no ignition occurs.

  In Patent Document 1, in a test in which a battery is deformed and destroyed due to gas generation due to intentional overcharge and an internal short circuit occurs, a safe short circuit occurs after a temperature increase after the internal short circuit occurs and before a fire occurs. A lithium ion secondary battery having a mechanism for forming a path has been proposed. The battery is provided with a spare electrode pair which is normally not used, insulated by a separator having a low melting temperature. The initial temperature rise due to the internal short circuit melts the separator, the electrode pair is brought into conductive contact, and the positive electrode and the negative electrode are quickly short-circuited. This short circuit of the electrode pair provides a mechanism for quickly releasing battery energy by the low resistance electrode pair before the temperature rises to a temperature at which the high resistance electrode active material ignites.

JP 2003-243037 A

  However, in recent lithium ion secondary batteries, where energy is increasingly increased, the temperature of the electrode active material rapidly increases after an internal short circuit. For this reason, the time difference between the melting of the low melting point separator proposed in Patent Document 1 and the ignition of the electrode active material is extremely short, and there is a concern that the ignition cannot be completely prevented.

  The present invention has been made in view of the above circumstances, and provides a lithium ion secondary battery provided with a mechanism for more actively operating a short circuit as a safety mechanism without depending on a temperature rise after an internal short circuit. Is an issue.

[1] A positive electrode in which an active material layer is formed on at least one surface of a positive electrode current collector, and a negative electrode in which an active material layer is formed on at least one surface of a negative electrode current collector, A lithium ion secondary battery comprising an electrode laminate laminated via a first metal foil electrically connected to the positive electrode current collector at the outermost layer of the electrode laminate, and the negative electrode current collector A metal foil laminate is provided in which a second metal foil conducted to the body is laminated via an insulating sheet, and the tensile strength of the insulating sheet is 80 MPa or less in the largest A direction, the A direction. And a tensile elongation of the insulating sheet is 20% or less in the A direction and 20% or less in the B direction.
[2] The lithium ion secondary battery according to [1], wherein the insulating sheet has different tensile strength and tensile elongation in the A direction and the B direction.
[3] The lithium ion according to [1] or [2], wherein the first metal foil is made of the same metal as the positive electrode current collector, and the second metal foil is made of the same metal as the negative electrode current collector. Secondary battery.
[4] The lithium ion secondary battery according to any one of [1] to [3], wherein the electrode laminate and the metal foil laminate are accommodated in a laminate film.
[5] The insulating sheet, wherein the metal foil laminate is installed on each of the first end and the second end of the electrode laminate, and constitutes the metal foil laminate provided on the first end. of the the a direction, and the a direction of the insulating sheets constituting the metal foil laminated body provided on the second end portion, but, as viewed in the thickness direction of the electrode stack, of 30 to 90 ° The lithium ion secondary battery according to any one of [1] to [4], wherein the lithium ion secondary battery is disposed so as to have an intersection angle.
[6] The insulating material according to any one of [1] to [5], wherein the insulator is an insulating layer including inorganic particles formed on a surface of at least one of the positive electrode and the negative electrode. Lithium ion secondary battery.
[7] The lithium ion secondary battery according to any one of [1] to [6], wherein the energy density of the electrode stack is 700 Wh / L or more.

  According to the lithium ion secondary battery of the present invention, when a strong impact is applied from the outside, the insulating sheet of the metal foil laminate provided as a safety mechanism tears before the electrode laminate is short-circuited, and the positive electrode and the negative electrode A pair of metal foils connected to each other come into contact with each other, and a short circuit can be formed safely and quickly. That is, a safe short circuit can be formed almost simultaneously with the impact without waiting for the temperature of the electrode active material to rise. As a result, ignition can be prevented more reliably than before.

It is a cross-sectional schematic diagram which shows an example of the lithium ion secondary battery of this invention.

In the first embodiment of the present invention, as shown in FIG. 1, a positive electrode 4 in which an active material layer (positive electrode active material layer) 3 is formed on at least one surface of a positive electrode current collector 2, and a negative electrode current collector A lithium ion secondary battery comprising an electrode laminate 9 in which an active material layer (negative electrode active material layer) 6 is formed on at least one surface of 5 and an insulator 8 is laminated via an insulator 8 1.
In the present embodiment, the positive electrode active material layer 3 is formed on one surface and the other surface of the positive electrode current collector 2, and the negative electrode active material layer 6 is formed on one surface and the other surface of the negative electrode current collector 5. Is formed.

  In the electrode laminate 9, a positive electrode 4 and a negative electrode 7 that are arranged to face each other with a porous separator 8 that is an insulator 8 are laminated in a four-layer set. Lead tabs 2a are drawn out from each of the positive electrode current collectors 2 made of aluminum foil having the positive electrode active material layer 3 formed on both surfaces, and are electrically connected to each other. Similarly, lead tabs 5a are drawn out from the respective negative electrode current collectors 5 made of copper foil in which the negative electrode active material layers 6 are formed on both surfaces, and are electrically connected to each other.

The electrode laminate 9 has two outermost layer portions of a first end portion and a second end portion as viewed in the stacking direction. In this embodiment, for convenience, the first end is referred to as the uppermost portion, and the second end is referred to as the lowermost portion.
Metal foil laminates 11 separated by separators 8 are installed at two places, the uppermost part and the lowermost part, which are the outermost layer parts of the electrode laminate 9. The metal foil laminate 11 is a first metal foil 12 which is an aluminum foil conducted to the positive electrode current collector 2 via the lead tab 2a, and a copper foil conducted to the negative electrode current collector 5 via the lead tab 5a. The second metal foil 15 is laminated via the insulating sheet 10. The electrode active material is not laminated on the surfaces of the first metal foil 12 and the second metal foil 15, and the insulating sheet 10 is sandwiched between the exposed metal surfaces.

  The metal foil laminated body 11 should just be provided in at least any one of the uppermost part which is the outermost layer part of the lithium ion secondary battery 1, and the lowest part, and the structure provided only in either one may be sufficient. Absent. If there is a possibility that an unexpected impact may be applied from both above and below, it is preferable that both are provided.

The direction in which the tensile strength of the insulating sheet 10 included in the metal foil laminate 11 is the largest is defined as the A direction, and the direction perpendicular to the A direction on the sheet plane is defined as the B direction.
The tensile strength of the insulating sheet 10 is 80 MPa or less in the A direction and 20 MPa or less in the B direction, and the tensile elongation is 20% or less in the A direction and 20% or less in the B direction.
When the insulating sheet 10 is stretched at the time of manufacture, the MD direction (longitudinal direction) is often the A direction, and the TD direction (lateral direction) is often the B direction.

  When an impact is applied to the metal foil laminate 11 from the outside with respect to the metal foil laminate 11 provided with the insulating sheet 10 having the above physical properties, the porous separator 8 (insulator 8) constituting the electrode laminate 9 is more affected. Preferentially, the insulating sheet 10 is cleaved and the exposed metal surfaces of the first metal foil 12 and the second metal foil 15 are in physical contact with each other. When the positive electrode 4 and the negative electrode 7 are short-circuited through the short circuit of the first metal foil 12 and the second metal foil 15 formed by this contact, the battery energy is safely released. Since the electrode active material layer that causes ignition is not formed on the surfaces of the first metal foil 12 and the second metal foil 15, the electrical resistance is low, and an excessive temperature rise hardly occurs. As a result, even when the energy density of the lithium ion secondary battery 1 is 700 Wh / L or more, the battery energy can be dissipated safely and quickly without causing ignition.

In order to quickly form a safe short-circuit path in the metal foil laminate 11 to which an external impact has been applied, it is desirable that the insulating sheet 10 is rapidly cleaved.
From this viewpoint, it is preferable that the insulating sheet 10 has different tensile strength and tensile elongation in the A direction and the B direction orthogonal thereto. The tensile strength in the A direction of the insulating sheet 10 is more preferably larger than that in the B direction. Furthermore, it is particularly preferable that the tensile strength in the A direction of the insulating sheet 10 is larger than that in the B direction, and the tensile elongation in the A direction of the insulating sheet 10 is larger than that in the B direction.
Moreover, it is preferable that each physical property of the insulating sheet 10 is as follows.

The tensile strength and tensile elongation in the A direction of the insulating sheet 10 are
1 MPa to 75 MPa and 1 to 19% are preferable,
30 MPa to 70 MPa and 5 to 18% are more preferable,
More preferably, it is 40 MPa to 65 MPa and 10 to 17%.
When it is at least the lower limit of the above range, it is possible to prevent unnecessarily cleaving when a weak impact that frequently occurs in normal use is applied. When it is below the upper limit of the above range, it becomes easy to cleave quickly when an abnormally strong impact is applied.

The tensile strength and tensile elongation in the B direction of the insulating sheet 10 are
0.1 MPa to 18 MPa and 0.1 to 15% are preferable,
1 MPa to 15 MPa and 1 to 12% are more preferable,
5 MPa to 12 MPa and 2 to 9% are more preferable.
When it is at least the lower limit of the above range, it is possible to prevent unnecessarily cleaving when a weak impact that frequently occurs in normal use is applied. When it is below the upper limit of the above range, it becomes easy to cleave quickly when an abnormally strong impact is applied.

The difference between the tensile strength in the A direction and the tensile strength in the B direction of the insulating sheet 10 is preferably 10 MPa to 70 MPa, more preferably 20 MPa to 60 MPa, and further preferably 30 MPa to 50 MPa.
When it is at least the lower limit of the above range, it is possible to prevent unnecessarily cleaving when a weak impact that frequently occurs in normal use is applied. When it is below the upper limit of the above range, it becomes easy to cleave quickly when an abnormally strong impact is applied.

The difference between the tensile elongation in the A direction and the tensile elongation in the B direction of the insulating sheet 10 is preferably 1% to 18%, more preferably 3% to 15%, and even more preferably 6% to 12%.
When it is at least the lower limit of the above range, it is possible to prevent unnecessarily cleaving when a weak impact that frequently occurs in normal use is applied. When it is below the upper limit of the above range, it becomes easy to cleave quickly when an abnormally strong impact is applied.

  In the present invention, the tensile strength of the insulating sheet 10 is a numerical value measured by a method according to JIS K 7127, and the tensile elongation of the insulating sheet 10 is a numerical value measured by a method according to JIS K 7127. .

In the present invention, the method of determining the A direction and the B direction of the insulating sheet 10 first confirms the A direction by measuring the tensile strength, and when viewed from above the sheet plane, the direction orthogonal to the A direction is determined. B direction is defined.
When there are a plurality of directions in which the tensile strength is the same, an arbitrary direction of the plurality is temporarily set as the A ′ direction, and the B direction orthogonal to the A ′ direction satisfies the above-described conditions of the tensile strength and the tensile elongation. If this is confirmed, the A ′ direction is determined to be the true A direction.

  The material of the insulating sheet 10 may be any material that can form an insulating sheet having the above physical properties, and for example, synthetic resin, paper, and the like can be applied. Examples of the synthetic resin include known thermoplastic resins such as polyolefin resins, polyester resins, polyimide resins, and aramid resins. In addition, a thermosetting resin may be used.

  The thickness of the insulating sheet 10 is not particularly limited as long as it has the above physical properties, and can be set to a thickness of about 1 μm to 100 μm, for example. From the viewpoint of reducing the thickness of the metal foil laminate 11 and reducing the thickness of the battery cell, the thinner one is preferable. In addition, it is preferable that the thickness of the insulating sheet 10 is thinner than that of the insulator 8 from the viewpoint that the insulating sheet 10 is easily cleaved preferentially over the insulator 8 when an external impact is applied.

The size of the insulating sheet 10 may be a size that can insulate the first metal foil 12 and the second metal foil 15 in a normal state. For example, the area is slightly larger than the first metal foil 12 and the second metal foil 15. It is preferable to have.
The insulating sheet 10 may be porous or non-porous.

The first metal foil 12 is preferably made of the same metal as the positive electrode current collector 2. When the first metal foil 12 and the positive electrode current collector 2 are the same metal, when the short circuit of the metal foil laminate 11 is formed, the electrochemical energy of the positive electrode 4 is passed through the metal foil laminate 11. It can be opened quickly. If the first metal foil 12 is a metal having a higher electrical resistance than the positive electrode current collector 2, the electrochemical energy may not be released quickly or excessive heat may be generated.
Similarly, the lead tab 2 a that electrically connects the first metal foil 12 and the positive electrode current collector 2 is preferably made of the same metal as the first metal foil 12 and the positive electrode current collector 2.

  From the viewpoint of forming a safer short circuit with low electrical resistance, it is preferable that at least one of the thickness and area of the first metal foil 12 is equal to or greater than that of the positive electrode current collector 2. Furthermore, it is preferable that at least one of the thickness and area of the lead tab 2 a is equal to or greater than that of the positive electrode current collector 2.

From the same viewpoint as described above, the second metal foil 15 is preferably made of the same metal as the negative electrode current collector 5. Further, the lead tab 5 a that electrically connects the second metal foil 15 and the negative electrode current collector 5 is also preferably made of the same metal as the second metal foil 15 and the negative electrode current collector 5.
From the viewpoint of forming a safer short circuit with low electrical resistance, it is preferable that at least one of the thickness and area of the second metal foil 15 is equal to or greater than that of the negative electrode current collector 5. Furthermore, it is preferable that at least one of the thickness and area of the lead tab 5 a is equal to or greater than that of the negative electrode current collector 5.

In the lithium ion secondary battery 1, metal foil laminates 11 are respectively installed at the uppermost part (first end part) and the lowermost part (second end part) of the electrode laminate 9, and these are further laminated films 16. Is housed in. Since the laminate film 16 is in close contact with the second metal foil 15 constituting the metal foil laminate 11, when an external impact is applied, the impact is transmitted to the metal foil laminate 11 without delay.
In addition, it may replace with this embodiment and the structure which reversed the positional relationship of the 1st metal foil 12 and the 2nd metal foil 15 may be employ | adopted. In this case, the first metal foil 12 adheres to the laminate film 16.

  The relative orientation between the A direction in plan view of the metal foil laminate 11 installed at the top of the electrode laminate 9 and the A direction of plan view of the metal foil laminate 11 installed at the bottom is the electrode When viewed in the thickness direction of the laminate 9, they may be the same or different, but are preferably different. The insulating sheet 10 having the above physical properties may have different easiness of tearing when compared in the A direction and the B direction. For this reason, when an impact is applied from an external direction by arranging the metal foil laminates 11 provided at two locations so that the directions in the A direction are relatively different, the two metal foils are provided. At least one of the laminates 11 may be able to form a short circuit more quickly than the other. As a result, not only when an impact is applied from a specific direction, safety against an impact from an arbitrary direction can be further enhanced.

  Specifically, for example, the A direction of the insulating sheet 10 constituting the metal foil laminate 11 provided at the uppermost portion and the A of the insulating sheet 10 constituting the metal foil laminate 11 provided at the lowermost portion. The direction is preferably arranged so as to have an intersection angle of 30 to 90 ° when viewed in the thickness direction of the electrode laminate 9. The crossing angle is more preferably 60 to 90 °, further preferably 85 to 90 °. When the crossing angle is in the above range, safety against an impact from an arbitrary external direction can be further enhanced.

  Here, the crossing angle determines the A direction of the insulating sheet 10 constituting each metal foil laminate 11 by the method described above, and in the state where the electrode laminate 9 is installed in the lithium ion secondary battery 1, It is measured by finding the acute angle side of the crossing angle between the A direction of the uppermost insulating sheet 10 and the A direction of the lowermost insulating sheet 10 when viewed in the thickness direction.

  The member which comprises the electrode laminated body 9 is not specifically limited, The member of a well-known lithium ion secondary battery is applied. Specific examples are shown below, but the lithium ion secondary battery of the present invention is not limited to those using these members.

  The material, area, and thickness of the negative electrode current collector 5 constituting the negative electrode 7 are not particularly limited. For example, an area of 40 × 20 cm subjected to punching processing made of a metal such as copper, titanium, nickel, stainless steel, Examples thereof include a rolled metal foil having a thickness of 5 to 50 μm.

  As a constituent material (negative electrode material) of the negative electrode active material layer 6 formed on one side or both sides of the negative electrode current collector 5, a negative electrode active material capable of occluding and releasing lithium ions is generally used. Can be mentioned. Examples of the metal oxide include metal oxides that can be alloyed with lithium such as silicon oxide. The silicon oxide is preferably in the form of powder or particles, and the average particle size is preferably, for example, 1 to 30 μm.

  As a method for forming the negative electrode active material layer 6, for example, after a negative electrode material containing a negative electrode active material is applied on the negative electrode current collector 5 with a thickness of about 5 to 100 μm, the solvent contained in the negative electrode material is removed by drying. Is mentioned. In addition to the negative electrode active material such as silicon oxide, the negative electrode material preferably contains a binder resin such as PVDF and SBR, and a conductive aid such as a carbon material and metal particles.

  The material, area, and thickness of the positive electrode current collector 2 constituting the positive electrode 4 are not particularly limited. For example, an area of 40 × 20 cm subjected to punching processing made of a metal such as aluminum, titanium, nickel, stainless steel, Examples thereof include a rolled metal foil having a thickness of 5 to 50 μm. The areas of the positive electrode 4 and the negative electrode 7 are preferably equal.

As a constituent material (positive electrode material) of the positive electrode active material layer 3 formed on one side or both sides of the positive electrode current collector 2, a positive electrode active material capable of inserting and extracting lithium ions is usually used. For example, lithium cobalt oxide ( LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), ternary positive electrode material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the like.

  As a method for forming the positive electrode active material layer 3, for example, after a positive electrode material containing a positive electrode active material is applied on the positive electrode current collector 2 to a thickness of about 5 to 100 μm, the solvent contained in the positive electrode material is removed by drying. Is mentioned. The positive electrode material preferably contains a binder resin and a conductive additive in addition to the positive electrode active material such as the lithium metal acid compound.

  The insulator 8 is not particularly limited as long as it has insulating properties and can hold or pass the electrolytic solution, for example, a known porous film made of an olefin resin, a nonwoven fabric, etc. A porous insulating layer containing insulating particles is also included.

  The porous insulating layer is a known thin layer that is formed on the surface of the positive electrode active material layer 3 or the surface of the negative electrode active material layer 6 and that can insulate the positive electrode 4 and the negative electrode 7 and allow the electrolyte solution to pass therethrough. As a forming method thereof, for example, a method in which a composition containing insulating inorganic particles such as silicon dioxide is applied to the surface of a negative electrode or a positive electrode and dried is known. The thickness of the porous insulating layer as the insulator 8 is preferably about 0.5 μm to 50 μm, for example.

  The lithium ion secondary battery of the present invention can be prepared by a conventional method. An example is shown below. First, an electrode laminate 9 having a desired number of stages, for example, 1 to 10 pairs of positive electrode 4 and negative electrode 7 is laminated by a conventional method, and a metal foil laminate 11 is placed on the outermost layer portion of the electrode laminate 9. After that, a laminate cell is obtained in which these are temporarily sealed with an outer package 16 such as a laminated aluminum film. When the cells were temporarily sealed, the lead wires connected to the lead tabs 2a of the respective positive electrode current collectors 2 and the first metal foil 12, and the lead tabs 5a of the respective negative electrode current collectors 5 and the second metal foil 15 were connected. The lead-out wiring is protruded outside the exterior body 16. Each lead-out wiring functions as an electrode terminal for connecting to an external circuit. Subsequently, the temporary sealing of the laminate cell is partially released, and a known electrolytic solution is injected and then completely sealed. The electrolyte solution may be a gel electrolyte that gels in the cell. With the above method, the lithium ion secondary battery of the present invention is obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
A rectangular positive electrode (total thickness: 100 μm) in which a positive electrode active material layer (layer thickness of 42.5 μm on one side) was coated on both surfaces of an aluminum foil (thickness: 15 μm) was produced by a conventional method.
A rectangular negative electrode (total thickness of 70 μm) in which a negative electrode active material layer (layer thickness of 30 μm on one side) was coated on both sides of a copper foil (thickness of 10 μm) was produced by a conventional method.
A positive electrode and a negative electrode were overlapped, and a porous polyethylene separator (thickness 10 μm) was sandwiched between them to obtain an electrode laminate.

The separator was placed on the uppermost portion which is the outermost layer of the electrode laminate, and the metal foil laminate was placed by placing the aluminum foil, the insulating sheet made of synthetic resin, and the copper foil in this order. Since the electrode active material layer is not formed on the aluminum foil and the copper foil constituting the metal foil laminate, the metal surfaces of the opposing foils are exposed, but the insulating sheet is sandwiched between them to insulate State is maintained.
The insulating sheet used here is a resin film made of PP resin with a thickness of 25 μm (manufactured by Sekisui Chemical Co., Ltd.), and its tensile strength is 62 MPa in the A direction and 10 MPa in the B direction orthogonal to the A direction. The tensile elongation was 15% in the MD direction and 5% in the TD direction. In addition, the A direction of the resin film used in this example coincided with the MD direction (Machine-Direction), and the B direction coincided with the TD direction (Transverse-Direction).

Subsequently, the aluminum foil lead tab (lead-out wiring) constituting the metal foil laminate and the aluminum foil lead tab constituting the positive electrode were fused with ultrasonic waves to electrically connect both aluminum foils. Similarly, the lead tab of the copper foil constituting the metal foil laminate and the lead tab of the copper foil constituting the negative electrode were fused with an ultrasonic wave to electrically connect both the copper foils.
By the above method, the 1st metal foil laminated body was installed in the uppermost part of the electrode laminated body.

Next, the 2nd metal foil laminated body was installed in the lowest method of the said electrode laminated body by the method similar to installation of a 1st metal foil laminated body. At this time, the A direction of the insulating sheet constituting the second metal foil laminate and the A direction of the insulating sheet constituting the first metal foil laminate are 0 ° when viewed in the thickness direction of the electrode laminate. It was installed so that it might become a crossing angle.
By the above method, the 2nd metal foil laminated body was installed in the lowest part of the electrode laminated body.

  Lead tabs were fused to each of the positive electrode and the negative electrode of the electrode laminate obtained above. Subsequently, the electrode laminate is housed inside the aluminum laminate packaging material, and further injected with an electrolyte, and sealed in a state where the positive electrode lead tab and the negative electrode lead tab are projected to the outside as terminals, thereby providing a flat battery. A cell was produced. The laminate cell was fully charged to 4.2 V by a conventional method, and the following collision test was performed.

<Collision test>
In accordance with the UL1642 standard established by UL (Underwriters Laboratories Inc.) in the United States, a stainless steel rod with a diameter of 15.8 mm is set at the center of the upper surface of the laminate cell, and a weight of 9.1 kg is set from a height of 61 ± 2.5 cm. A collision test was performed by dropping the stainless steel rod onto the stainless steel rod.
As a result of the collision test, there was no ignition and the voltage of the laminate cell dropped 0.3 seconds after the collision.
When the laminate cell after the collision test was disassembled, the insulating sheet constituting the first metal foil laminate installed on the uppermost part of the electrode laminate was torn at the collision location, constituting the first metal foil laminate It turned out that the circuit which short-circuits a positive electrode and a negative electrode safely is formed by the aluminum foil and copper foil to contact.

[Example 2]
90 ° crossing angle when the A direction of the insulating sheet constituting the second metal foil laminate and the A direction of the insulating sheet constituting the first metal foil laminate are viewed in the thickness direction of the electrode laminate. A battery cell was prepared in the same manner as in Example 1 except that the battery cell was installed so as to be. Table 1 shows the result of a collision test performed on this battery cell.

[Example 3]
A battery as in Example 2 except that the porous separator constituting the electrode laminate was replaced with a porous insulating layer containing inorganic particles formed on the surface of the positive electrode active material layer facing the negative electrode. Created a cell. Table 1 shows the result of a collision test performed on this battery cell.

  The insulating layer was formed as follows. First, the composition which mix | blended the silica (average particle diameter of 0.3 micrometer) which is inorganic particle by 75 mass parts, and the polyvinyl alcohol which is binder resin by 25 mass parts was prepared. Next, the composition was applied to the surface of the positive electrode active material layer by a doctor blade method, and then heated at 120 ° C. and dried to form a porous insulating layer having a thickness of 15 μm.

[Comparative Example 1]
As an insulating sheet constituting the metal foil laminate, the thickness is 25 μm, the tensile strength is 101 MPa in the longitudinal direction (MD direction), 11 MPa in the lateral direction (TD direction), and the tensile elongation is the longitudinal direction. A battery cell was prepared in the same manner as in Example 1 except that a separator made of PP resin (manufactured by Sekisui Chemical Co., Ltd.), which was 155% in the MD direction and 56% in the lateral direction (TD direction). . Table 1 shows the result of a collision test performed on this battery cell.

[Comparative Example 2]
A battery cell was prepared in the same manner as in Example 3 except that the insulating sheet used in Comparative Example 1 was used as the insulating sheet constituting the metal foil laminate. Table 1 shows the result of a collision test performed on this battery cell.

  From the above results, it was confirmed that the lithium ion secondary batteries of Examples 1 to 3 according to the present invention were safely short-circuited without firing even when a strong impact in accordance with UL1642 was applied.

  The present invention can be widely used in the field of lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... Positive electrode collector, 2a ... Lead tab, 3 ... Electrode active material layer (positive electrode active material layer), 4 ... Positive electrode, 5 ... Negative electrode collector, 5a ... Lead tab, 6 ... Electrode Active material layer (negative electrode active material layer), 7 ... negative electrode, 8 ... insulator (separator), 9 ... electrode laminate, 10 ... insulating sheet, 11 ... metal foil laminate, 12 ... first metal foil, 15 ... first Two-metal foil, 16 ... exterior body (laminate film)

Claims (6)

A positive electrode in which an active material layer is formed on at least one surface of a positive electrode current collector;
A negative electrode having an active material layer formed on at least one surface of a negative electrode current collector,
A lithium ion secondary battery comprising an electrode laminate that is laminated via an insulator,
In the outermost layer part of the electrode laminate,
A metal foil laminate is provided in which a first metal foil conducted to the positive electrode current collector and a second metal foil conducted to the negative electrode current collector are laminated via an insulating sheet,
The tensile strength of the insulating sheet is 80 MPa or less in the largest A direction, 20 MPa or less in the B direction orthogonal to the A direction, and
The tensile elongation of the insulating sheet is, the more than 20% in the direction A state, and are 20% or less in the direction B,
The lithium ion secondary battery in which the tensile strength and tensile elongation of the insulating sheet are different in the A direction and the B direction, respectively . The first metal foil is made of the same metal as the positive electrode current collector,
The lithium ion secondary battery according to claim 1 , wherein the second metal foil is made of the same metal as the negative electrode current collector. The lithium ion secondary battery according to claim 1 or 2 , wherein the electrode laminate and the metal foil laminate are accommodated in a laminate film. The metal foil laminate is installed on each of the first end and the second end of the electrode laminate,
The A direction of the insulating sheet constituting the metal foil laminate provided at the first end; and
The A direction of the insulating sheet constituting the metal foil laminate provided at the second end is such that the crossing angle is 30 to 90 ° when viewed in the thickness direction of the electrode laminate. The lithium ion secondary battery as described in any one of Claims 1-3 arrange | positioned. The lithium ion secondary battery according to any one of claims 1 to 4 , wherein the insulator is an insulating layer containing inorganic particles formed on a surface of at least one of the positive electrode and the negative electrode. . The lithium ion secondary battery according to any one of claims 1 to 5 , wherein an energy density of the electrode laminate is 700 Wh / L or more.

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