Lead wire and power storage device

Abstract

This lead wire comprises a conductor and an insulating film that covers an outer peripheral surface of the conductor between both ends of the conductor while exposing both ends in a first direction of the conductor. The conductor is made of aluminum or an aluminum alloy. The conductor includes a first region in contact with the insulating film. The first region includes a second region. The development interface area ratio Sdr of the second region defined by JIS B 0681-2:2018 is 0.5 or more.

Description

Lead wire and energy storage device

[0001] The present disclosure relates to a lead wire and an electricity storage device. This application claims priority to Japanese Patent Application No. 2023-137049, filed on August 25, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] As electronic devices become smaller and lighter, there is a demand for smaller and lighter electrical components, such as batteries and capacitors, used in these devices. To achieve this, for example, a technique has been adopted in which a positive electrode, a negative electrode, and an electrolyte are enclosed in a bag-like sealed container.

[0003] Sealed containers are required to have properties that prevent gas permeation and moisture penetration from the outside. For this reason, laminated films, in which a metal layer such as aluminum foil is coated with resin, are used as materials for sealed containers. Sealed containers are formed by heat-sealing the edges of two sheets of laminated film.

[0004] One end of the sealed container is an opening, and the positive electrode, negative electrode, electrolyte, etc. are enclosed inside this opening. Furthermore, lead conductors (hereinafter also referred to as "conductors"), one end of which is connected to the positive electrode and the negative electrode, are arranged so as to extend from the inside to the outside of the sealed container. The opening is then closed by heat sealing (thermal fusion), and the sealed container and the conductor are bonded to seal the opening.

[0005] The surface of the enclosure is made of resin, while the conductor is made of metal, so the materials are different. As a result, the interface between the enclosure and the conductor has weak adhesion. For this reason, technologies to improve the adhesive strength between the enclosure and the conductor are being investigated.

[0006] Patent Document 1 discloses a lead wire for a nonaqueous electrolyte battery, which is characterized in that a composite coating layer is formed on the metal surface of the lead wire by applying a treatment liquid containing a resin component including polyacrylic acid and a metal salt, and an insulator is provided on the outside of the composite coating layer and sealed to an enclosure. Hereinafter, the insulator will also be referred to as an insulating film.

[0007] Japanese Patent Application Laid-Open No. 2006-128096

[0008] The lead wire of the present disclosure includes a conductor and an insulating film that covers an outer surface of the conductor between both ends of the conductor while exposing both ends of the conductor in a first direction, wherein the conductor is made of aluminum or an aluminum alloy, the conductor includes a first region that contacts the insulating film, the first region includes a second region, and the second region has a developed interface area ratio Sdr of 0.5 or more as defined in JIS B 0681-2:2018.

[0009] Fig. 1 is a schematic overview of an example of a lead wire according to embodiment 1. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Fig. 4 is a front view schematically showing an example of an electricity storage device according to embodiment 2. Fig. 5 is a partial cross-sectional view taken along line V-V in Fig. 4.

[0010] [Problem to be Solved by the Present Disclosure] In recent years, in response to demands for shorter charging times and longer driving ranges for electric vehicles, in-vehicle power storage devices are being required to have high output characteristics that enable them to charge and discharge large currents in a short time. As the power output of power storage devices increases, the environment in which the power storage devices are used becomes hotter, and the pressure inside the power storage device increases more than before when the power storage device is in use. In order to maintain the performance of the power storage device, it is necessary for the conductor and the insulating film to be bonded with high adhesive strength even when the pressure inside the power storage device increases. Therefore, there is a demand for lead wires that have excellent adhesive strength between the conductor and the insulating film at high temperatures.

[0011] Therefore, an object of the present disclosure is to provide a lead wire that has excellent adhesive strength between a conductor and an insulating film at high temperatures, and an electricity storage device including the lead wire.

[0012] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a lead wire that has excellent adhesive strength between a conductor and an insulating film at high temperatures, and an electricity storage device that includes the lead wire.

[0013] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described. (1) A lead wire of the present disclosure includes a conductor and an insulating film covering an outer peripheral surface of the conductor between both ends of the conductor while exposing both ends of the conductor in a first direction, wherein the conductor is made of aluminum or an aluminum alloy, the conductor includes a first region in contact with the insulating film, the first region includes a second region, and the second region has a developed interface area ratio Sdr of 0.5 or more as defined in JIS B 0681-2:2018.

[0014] According to the present disclosure, it is possible to provide a lead wire having excellent adhesive strength between a conductor and an insulating film even at high temperatures. The developed interfacial area ratio (Sdr) defined in JIS B 0681-2:2018 is a composite parameter indicating the ratio of the difference between the area of ​​the interface of a contoured surface and the area of ​​the reference region to the area of ​​the reference region. If the contoured surface within the reference region to be evaluated has no surface irregularities, the area of ​​the interface of the contoured surface is the same as the area of ​​the reference region, and therefore Sdr = 0%. The developed interfacial area ratio (Sdr) is also defined in ISO 25178-2:2022.

[0015] (2) In the above (1), the second region may have an arithmetic mean height Sa defined in JIS B 0681-2:2018 of 0.1 μm or more, and the second region may have a maximum height Sz defined in JIS B 0681-2:2018 of 1.0 μm or more.

[0016] This improves the adhesive strength between the conductor and the insulating film.

[0017] (3) In the above (1) or (2), the percentage (S2 / S1)×100 of the area S2 of the second region to the area S1 of the first region may be 40% or more.

[0018] This improves the adhesive strength between the conductor and the insulating film.

[0019] (4) In any one of the above (1) to (3), the conductor may have an aluminum content of 99 mass % or more, thereby improving the corrosion resistance of the conductor.

[0020] (5) In any of the above (1) to (4), at least a portion of the surface of the conductor may contain one or both of silicon and iron. The silicon and iron present on the surface of the conductor are considered to be impurities contained in the aluminum or aluminum alloy that constitutes the conductor.

[0021] (6) In any one of the above (1) to (5), at least a portion of the surface of the conductor may contain trivalent chromium, thereby improving the corrosion resistance of the conductor.

[0022] (7) In any one of the above (1) to (6), at least a portion of the surface of the conductor may contain zirconium, thereby improving the corrosion resistance of the conductor.

[0023] (8) In any of the above (1) to (7), the insulating film may include a first insulating layer arranged in contact with the conductor and a second insulating layer provided on the surface of the first insulating layer opposite the conductor, the first insulating layer being an acid-modified polypropylene layer, and the second insulating layer being a heat-resistant resin layer.

[0024] This allows the insulating film to have good adhesiveness and sealing properties with the conductor.

[0025] (9) The presently disclosed electricity storage device comprises: an enclosed container; and a lead wire according to any one of (1) to (8) above, which is arranged so as to extend from the inside to the outside of the enclosed container; and the insulating film is fused to the enclosed container.

[0026] According to the present disclosure, even if the pressure inside the electricity storage device increases at high temperatures, the conductor and the insulating film can be bonded with high adhesive strength, and therefore the electricity storage device can maintain its performance even at high temperatures.

[0027] [Details of the embodiments of the present disclosure] Specific examples of the lead wire and the electricity storage device of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0028] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0029] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0030] In the present disclosure, when one or more numerical values ​​are recited as the lower limit and the upper limit of a numerical range, a combination of any one numerical value recited as the lower limit and any one numerical value recited as the upper limit is also considered to be disclosed. For example, when a1 or more, b1 or more, and c1 or more are recited as the lower limit and a2 or less, b2 or less, and c2 or less are recited as the upper limit, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are considered to be disclosed.

[0031] [Embodiment 1: Lead Wire] A lead wire 10 according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to FIGS. 1 to 3. FIG. 1 is a schematic overview of an example of a lead wire according to Embodiment 1. FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. In this disclosure, the direction along line II-II is also referred to as the width direction of the lead wire. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. In this disclosure, the direction along line III-III is also referred to as the longitudinal direction of the lead wire.

[0032] As shown in FIG. 1 , the lead wire 10 according to the first embodiment includes a conductor 3 and an insulating film 1 that covers the outer surface of the conductor 3 between both ends of the conductor 3 while exposing both ends of the conductor 3 in a first direction, wherein the conductor 3 is made of aluminum or an aluminum alloy, the conductor 3 includes a first region that contacts the insulating film 1, the first region includes a second region, and the second region has a developed interface area ratio Sdr of 0.5 or more as defined in JIS B 0681-2:2018.

[0033] In the lead wire 10 of the present disclosure, the developed interface area ratio Sdr, as defined in JIS B 0681-2:2018, of the second region of the conductor 3 that contacts the insulating film 1 is 0.5 or more. This means that at least a portion of the outer peripheral surface of the conductor 3 that contacts the insulating film 1 is roughened, which improves the adhesive strength between the conductor 3 and the insulating film 1 due to the anchor effect. Therefore, the lead wire 10 of the present disclosure has excellent adhesive strength between the conductor 3 and the insulating film 1 even at high temperatures.

[0034] The lead wire 10 of the present disclosure may be a lead wire for a non-aqueous electrolyte battery or a lead wire for an all-solid-state battery.

[0035] <Conductor> In the lead wire 10 of the first embodiment, the conductor 3 is made of aluminum or an aluminum alloy. This improves the conductivity of the conductor 3. In this disclosure, "the conductor is made of aluminum" means that the conductor 3 is made of pure aluminum containing 99% or more by mass of aluminum. Examples of aluminum alloys include aluminum alloys containing aluminum and at least one element selected from the group consisting of copper, manganese, silicon, magnesium, and zinc. The aluminum content of the aluminum alloy can be 90% or more by mass. Examples of aluminum alloys include aluminum-manganese alloys (A3000 series). The conductor 3 may contain impurity elements in addition to the aluminum or aluminum alloy, as long as the effects of the present disclosure are not impaired. Examples of impurity elements include iron, chromium, titanium, nickel, lead, and bismuth. The aluminum content of the conductor 3 is measured by inductively coupled plasma (ICP) emission spectroscopy.

[0036] The conductor 3 may have, for example, a first main surface, a second main surface opposite the first main surface, and two side surfaces, a first side surface and a second side surface, connecting the first main surface and the second main surface. The first main surface and the second main surface may have, for example, a rectangular planar shape. In the first embodiment, the direction in which a pair of parallel sides of the first main surface of the conductor 3 extend is defined as a first direction, the direction in which another pair of parallel sides extend is defined as a second direction, and the normal direction of the first main surface is defined as a third direction. The dimension of the conductor 3 in the first direction may be larger or smaller than the dimension of the conductor 3 in the second direction. The dimension of the conductor 3 in the first direction may be the same as the dimension of the conductor 3 in the second direction. The two side surfaces of the conductor 3 may be parallel to the third direction. In the first embodiment, the first and second main surfaces of the conductor 3 are each rectangular, but the shape of the conductor 3 is not limited thereto and any conventionally known shape may be adopted. For example, the corners of the first and second main surfaces of the conductor 3 may be tapered, and the first and second main surfaces do not have to be perfectly rectangular.

[0037] The conductor 3 may have a strip shape. The dimensions of the conductor 3 are set appropriately depending on the application. For example, the length of the conductor 3 in the first direction may be 10 mm or more and 150 mm or less, 20 mm or more and 100 mm or less, or 30 mm or more and 50 mm or less. The length of the conductor 3 in the second direction may be 5 mm or more and 200 mm or less, 15 mm or more and 140 mm or less, or 25 mm or more and 80 mm or less. The thickness of the conductor 3 in the third direction may be 50 μm or more and 1500 μm or less, 100 μm or more and 1000 μm or less, or 150 μm or more and 500 μm or less.

[0038] In the lead wire 10 of the first embodiment, the conductor 3 includes a first region that is in contact with the insulating film 1. That is, the insulating film 1 is provided on the first region, which is at least a part of the conductor 3.

[0039] In the conductor 3, the percentage of the area of ​​the first region relative to the entire surface area of ​​the conductor 3 is not particularly limited and can be set appropriately depending on the application and shape of the lead wire 10. The percentage may be, for example, 5% or more, 10% or more, or 20% or more. The percentage corresponds to the coverage of the conductor 3 by the insulating film 1.

[0040] The first region of the conductor 3 includes the second region. The developed interface area ratio Sdr of the second region, as defined in JIS B 0681-2:2018, is 0.5 or greater, and may be 0.8 or greater, 1.0 or greater, 1.2 or greater, 1.4 or greater, 2.0 or greater, or 2.4 or greater. The higher the developed interface area ratio Sdr of the second region, the more improved the anchoring effect, so there is no particular upper limit. From a manufacturing standpoint, the upper limit of the developed interface area ratio Sdr of the second region may be, for example, 15.0 or less, or 13.0 or less. The developed interface area ratio Sdr of the second region may be 0.5 or greater and 15.0 or less, 0.8 or greater and 15.0 or less, 1.2 or greater and 15.0 or less, 1.4 or greater and 15.0 or less, 2.0 or greater and 15.0 or less, or 2.4 or greater and 13.0 or less.

[0041] In the conductor 3, the percentage (S2 / S1) x 100 of the area S2 of the second region relative to the area S1 of the first region may be 40% or more. This means that the proportion of the area where the conductor 3 and the insulating film 1 are in contact with each other is sufficiently large. This further improves the adhesive strength between the conductor 3 and the insulating film 1. The larger the percentage (S2 / S1) x 100, the better the adhesive strength between the conductor 3 and the insulating film 1. The percentage (S2 / S1) x 100 may be 50% or more, 60% or more, 80% or more, 90% or more, or even 100%.

[0042] In the present disclosure, the developed interface area ratio Sdr of the second region and the percentage (S2 / S1)×100 are measured by the following procedure: First, in the state of the lead wire 10, the first region in the conductor 3 where the insulating film 1 is provided is identified.

[0043] The conductor 3 and the insulating film 1 of the lead wire 10 are peeled at 25°C using a 180° peel test to separate the conductor 3 and the insulating film 1, exposing the first region of the conductor 3. At this time, there is a possibility that a portion of the insulating film 1 remains in the first region of the conductor 3. To remove the remaining portion of the insulating film 1, the conductor 3 is immersed in a xylene solution at 120°C for 60 minutes.

[0044] The conductor 3 is removed from the xylene solution and dried, and then the developed interface area ratio Sdr of the first region of the conductor 3 is measured. A shape analysis laser microscope (Keyence Corporation's "VK-X100" (trademark)) is used for the measurement. The arithmetic mean height Sa and maximum height Sz, which will be described later, are also measured using the same measuring device.

[0045] First, the first region is divided into rectangular unit regions of 0.2 mm x 0.2 mm, and the developed interface area ratio Sdr is measured for each unit region. Depending on the size and shape of the first region, the first region cannot be divided into an integral number of unit regions, and the unit region may include the first region and an area adjacent to the first region. In such cases, the unit region consisting only of the first region is measured, and the unit region including the first region and an area adjacent to the first region is excluded from the measurement.

[0046] The percentage (N2 / N1) of the number N2 of unit regions having a developed interface area ratio Sdr of 0.5 or more relative to the number N1 of all unit regions is calculated. In the present disclosure, the percentage (N2 / N1) x 100 corresponds to the percentage (S2 / S1) x 100.

[0047] The developed interface area ratio Sdr is measured for the entire region A, which consists of all unit regions having a developed interface area ratio Sdr of 0.5 or more. The unit regions included in region A may or may not be in contact with each other. In the present disclosure, region A corresponds to the second region, and the developed interface area ratio of region A corresponds to the developed interface area ratio of the second region.

[0048] In the lead wire 10 of the first embodiment, when the second region of the conductor 3 is divided into rectangular unit regions of 20 μm × 20 μm, the developed interface area ratio Sdr of all the unit regions may be 0.5 or more. This makes the developed interface area ratio Sdr uniform throughout the entire second region, further improving the adhesive strength between the conductor 3 and the insulating film 1.

[0049] The arithmetic mean height Sa of the second region of the conductor 3, as defined in JIS B 0681-2:2018, may be 0.1 μm or more. This further improves the adhesive strength between the conductor 3 and the insulating film 1. The larger the arithmetic mean height Sa of the second region, the more improved the adhesive strength between the conductor 3 and the insulating film 1. The lower limit of the arithmetic mean height Sa of the second region may be 0.2 μm or more, 0.4 μm or more, or 0.6 μm or more. The upper limit of the arithmetic mean height Sa of the second region is not particularly limited, but may be set to 2.0 μm or less from a manufacturing standpoint, for example. The arithmetic mean height Sa of the second region may be 0.1 μm or more and 2.0 μm or less, 0.4 μm or more and 2.0 μm or less, or 0.6 μm or more and 2.0 μm or less.

[0050] The second region of the conductor 3 may have a maximum height Sz of 1.0 μm or more as defined in JIS B 0681-2:2018. This further improves the adhesive strength between the conductor 3 and the insulating film 1. The greater the maximum height Sz of the second region, the more improved the adhesive strength between the conductor 3 and the insulating film 1. The lower limit of the maximum height Sz of the second region may be 3.0 μm or more, or 6.0 μm or more. The upper limit of the maximum height Sz of the second region is not particularly limited, but may be set to 16.0 μm or less from a manufacturing standpoint, for example. The maximum height Sz of the second region may be 1.0 μm or more and 16.0 μm or less, 3.0 μm or more and 16.0 μm or less, or 6.0 μm or more and 16.0 μm or less.

[0051] In the present disclosure, the arithmetic mean height Sa and maximum height Sz of the second region are measured by the following procedure: The second region is identified in the conductor 3 using the same method as the method for measuring the developed interface area ratio Sdr of the second region described above. The arithmetic mean height Sa and maximum height Sz of the second region are measured.

[0052] The developed interface area ratio Sdr of a region of the surface of the conductor 3 other than the second region (hereinafter also referred to as the "third region"), as defined in JIS B 0681-2:2018, may be 0 or more and 0.2 or less, 0 or more and 0.1 or less, 0 or more and 0.05 or less, or 0 or more and 0.02 or less. The surface shape of the third region of the conductor 3 corresponds to the surface shape of the aluminum plate or aluminum alloy plate that is the raw material of the conductor 3. According to the lead wire manufacturing method of embodiment 1 described below, even if the developed interface area ratio Sdr of the third region of the conductor 3 is 0.2 or less, 0.1 or less, 0.05 or less, or 0, the developed interface area ratio Sdr of the second region of the conductor 3 can be 0.5 or more.

[0053] The arithmetic mean height Sa of the third region of the conductor 3, as defined in JIS B 0681-2:2018, may be 0 μm or more and 0.3 μm or less, 0 μm or more and 0.2 μm or less, or 0 μm or more and 0.1 μm or less. According to the lead wire manufacturing method of the below-described embodiment 1, even if the arithmetic mean height Sa of the third region of the conductor 3 is 0.3 μm or less, 0.2 μm or less, 0.1 μm or less, or 0 μm, the developed interface area ratio Sdr of the second region of the conductor 3 can be 0.5 or more.

[0054] The maximum height Sz of the third region of the conductor 3, as defined in JIS B 0681-2:2018, may be 0 μm or more and 10 μm or less, 0 μm or more and 3.2 μm or less, 0 μm or more and 2 μm or less, or 0 μm or more and 0.8 μm or less. According to the lead wire manufacturing method of the below-described embodiment 1, even if the maximum height Sz of the third region of the conductor 3 is 10 μm or less, 3.2 μm or less, 2 μm or less, or 0.8 μm or less, the developed interface area ratio Sdr of the second region of the conductor 3 can be 0.5 or more.

[0055] In the lead wire 10 of embodiment 1, at least a portion of the surface of the conductor 3 may contain one or both of silicon and iron. Silicon may exist as a crystallized product containing silicon. Iron may exist as a crystallized product containing iron. It is presumed that silicon and iron are contained in crystallized products formed by the elements contained in the conductor 3 crystallizing on the surface of the conductor 3. The presence of one or both of silicon and iron on the surface of the conductor 3 can be confirmed by performing X-ray photoelectron spectroscopy on the conductor 3 exposed to the outside.

[0056] In the lead wire 10 of the first embodiment, the conductor 3 may be subjected to a surface treatment such as a chromate treatment, a trivalent chromium treatment, a non-chromate treatment, or a roughening treatment in order to improve resistance to an electrolyte solution, etc. Such a surface treatment can improve the resistance of the conductor 3 to an electrolyte solution.

[0057] In the lead wire 10 of the first embodiment, at least a portion of the surface of the conductor 3 may contain trivalent chromium. This improves the electrolytic solution resistance of the conductor 3 and suppresses corrosion. In the present disclosure, whether the surface of the conductor 3 contains trivalent chromium can be confirmed by performing X-ray photoelectron spectroscopy on the conductor 3 that is exposed to the outside and not provided with the insulating film 1 in the lead wire 10.

[0058] In the lead wire 10 of the first embodiment, at least a portion of the conductor 3 may contain zirconium. This improves the electrolytic solution resistance of the conductor 3 and suppresses corrosion. In the present disclosure, whether the surface of the conductor 3 contains zirconium can be confirmed by performing X-ray photoelectron spectroscopy on the conductor 3 that is exposed to the outside and not provided with the insulating film 1 in the lead wire 10.

[0059] 1 , the insulating film 1 covers the entire outer peripheral surface of the conductor 3 between both end portions in a first direction while exposing both end portions of the conductor 3. For example, the insulating film 1 covers the first main surface, the second main surface, and the first side surface and the second side surface connecting the first main surface and the second main surface of the conductor 3 between both end portions while exposing both end portions of the conductor 3 in the first direction. The insulating film 1 is provided so as to cover the outer peripheral surface of a part of the region in the first direction, excluding the region including both end portions of the conductor 3 in the first direction.

[0060] 1 and 2 , the width of the insulating film 1 in the second direction of the conductor 3 is wider than the width of the conductor 3 in the second direction. The insulating film 1 is attached by adhesion or fusion to the outer peripheral surface of the conductor 3 so as to protrude beyond both ends of the conductor 3 in the second direction, and the insulating films 1 protruding from both ends of the conductor 3 are attached to each other by adhesion or fusion. The length of the conductor 3 in the first direction of the insulating film 1 is shorter than the length of the conductor 3 in the first direction. The insulating film 1 is not attached to both ends of the conductor 3 in the first direction.

[0061] The lower limit of the average thickness of the insulating film 1 may be 40 μm or more, 50 μm or more, 70 μm or more, 80 μm or more, 100 μm or more, or 120 μm or more. The upper limit of the average thickness may be 500 μm or less, 300 μm or less, or 250 μm or less. The average thickness may be 40 μm or more and 500 μm or less, 80 μm or more and 500 μm or less, 100 μm or more and 300 μm or less, or 120 μm or more and 250 μm or less.

[0062] In the present disclosure, the average thickness of the insulating film 1 is measured as follows. The lead wire 10 is filled with resin and polished along the normal direction of the main surface exposed to the outside of the insulating film 1 to expose the cross section of the lead wire 10. The cross section is observed at 500x magnification using a microscope, and the thickness of the insulating film 1 is measured at five points along the normal direction of the surface of the conductor 3. The average distance between the five points corresponds to the average thickness of the insulating film 1. In the present disclosure, the average thicknesses of the first insulating layer 1a, the second insulating layer 1b, and other layers described below are also measured in a similar manner.

[0063] <<First Insulating Layer>> In the lead wire 10 of embodiment 1, the insulating film 1 may include a first insulating layer 1a disposed in contact with the conductor 3. The first insulating layer 1a may be made of an acid-modified polypropylene layer. Examples of acid-modified groups include maleic anhydride. When the first insulating layer 1a is an acid-modified polypropylene layer, the first insulating layer 1a has good adhesion and sealing properties with the conductor 3. The acid-modified polypropylene layer may contain unmodified polypropylene as well as acid-modified polypropylene as a resin component, as long as the effects of the present disclosure are not impaired. Hereinafter, acid-modified polypropylene and unmodified polypropylene will also be collectively referred to as polypropylene.

[0064] The fact that the first insulating layer 1a contains an acid-modified group and that the first insulating layer 1a contains polypropylene can be confirmed by removing only the first insulating layer 1a from the lead wire 10 and performing transmission light analysis on the first insulating layer 1a using a Fourier transform infrared spectrophotometer.

[0065] In the insulating film 1 of embodiment 1, the average thickness of the first insulating layer 1a may be 20 μm or more and 150 μm or less. When the average thickness of the first insulating layer 1a is 20 μm or more, the first insulating layer 1a is less likely to be too thin and break, and good adhesion to the conductor 3 can be ensured. When the average thickness of the first insulating layer 1a is 150 μm or less, the insulating film 1 can be made thinner, and an electricity storage device including the insulating film 1 can be made smaller.

[0066] The lower limit of the average thickness of the first insulating layer 1a may be 20 μm or more, 25 μm or more, or 30 μm or more from the viewpoint of ensuring good adhesion to the conductor 3. The upper limit of the average thickness of the first insulating layer 1a may be 150 μm or less, 120 μm or less, or 100 μm or less from the viewpoint of miniaturizing the electricity storage device including the insulating film 1. The average thickness of the first insulating layer 1a may be 20 μm or more and 150 μm or less, 25 μm or more and 120 μm or less, or 30 μm or more and 100 μm or less.

[0067] In the lead wire 10 of the first embodiment, the first insulating layer 1a may contain various additives such as a flame retardant, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a lubricant, a colorant, etc. The types and amounts of these additives may be similar to those used in conventionally known acid-modified polypropylene layers.

[0068] <Second Insulating Layer> In the lead wire 10 of the first embodiment, the insulating film 1 may further include a second insulating layer 1b provided on the main surface of the first insulating layer 1a opposite to the main surface in contact with the conductor 3. The second insulating layer 1b may be made of a heat-resistant resin layer. If the second insulating layer 1b is a heat-resistant resin layer, the second insulating layer 1b will not melt during thermocompression bonding between the insulating film 1 and the conductor 3, making the second insulating layer 1b an excellent support.

[0069] Examples of heat-resistant resins constituting the second insulating layer 1b include polyolefin resins, polyethylene terephthalate, polyamide, and fluororesin. Among these, polyolefin resins have good adhesion to the acid-modified polypropylene layer constituting the first insulating layer 1a. Examples of polyolefin resins include polyethylene, polypropylene, cross-linked polypropylene, ionomer resin, and acid-modified polyolefin. In particular, the second insulating layer 1b may contain homopolypropylene, a type of polypropylene. Homopolypropylene does not melt during thermocompression bonding between the adhesive film and the conductor 3, and therefore functions well as a support. The second insulating layer 1b may also contain polyester nonwoven fabric.

[0070] The fact that the second insulating layer 1b contains a heat-resistant resin can be confirmed by removing only the second insulating layer 1b from the lead wire 10 and performing transmission light analysis on the second insulating layer 1b using a Fourier transform infrared spectrophotometer.

[0071] In the insulating film 1 of embodiment 1, the average thickness of the second insulating layer 1b may be 20 μm or more and 150 μm or less. When the average thickness of the second insulating layer 1b is 20 μm or more, the second insulating layer 1b is less likely to be too thin and break, and good adhesion to the conductor 3 can be ensured. When the average thickness of the second insulating layer 1b is 150 μm or less, the insulating film 1 can be made thinner, and an electricity storage device including the insulating film 1 can be made smaller.

[0072] The lower limit of the average thickness of second insulating layer 1b may be 20 μm or more, 25 μm or more, or 30 μm or more from the viewpoint of ensuring good adhesion to conductor 3. The upper limit of the average thickness of second insulating layer 1b may be 150 μm or less, 120 μm or less, or 100 μm or less from the viewpoint of miniaturizing the electricity storage device including insulating film 1. The average thickness of second insulating layer 1b may be 20 μm or more and 150 μm or less, 25 μm or more and 120 μm or less, or 30 μm or more and 100 μm or less.

[0073] In the present disclosure, the second insulating layer 1b may contain various additives such as a flame retardant, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a lubricant, a colorant, etc. The types and amounts of these additives may be the same as those used in conventionally known homopolypropylene layers.

[0074] <Other Layers> The insulating film 1 of embodiment 1 may include other layers in addition to the first insulating layer 1a and the second insulating layer 1b. Examples of the other layers include a layer (hereinafter also referred to as a "third insulating layer") that serves to improve adhesion to the sealed container 2 containing aluminum foil. The other layers may be a single layer or a combination of two or more layers. The positions of the other layers are appropriately selected depending on the types of the other layers.

[0075] The insulating film 1 includes a first insulating layer 1a, a second insulating layer 1b provided on one of the main surfaces of the first insulating layer 1a, and a third insulating layer provided on the main surface of the second insulating layer 1b opposite to the main surface facing the first insulating layer 1a. Here, the insulating film 1 refers to the insulating film 1 alone.

[0076] In the insulating film 1 of embodiment 1, the average thickness of the third insulating layer may be 20 μm or more and 100 μm or less, 30 μm or more and 70 μm or less, or 35 μm or more and 60 μm or less.

[0077] In the present disclosure, the other layers may contain various additives such as flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, lubricants, colorants, etc. The types and amounts of these additives may be similar to those used in other conventionally known layers.

[0078] <Method for Manufacturing Lead Wire> The lead wire of the first embodiment can be manufactured, for example, by the following method.

[0079] <<Preparation of Conductor>> A substrate made of aluminum or an aluminum alloy is prepared as the substrate. The size of the substrate is not particularly limited and can be appropriately set depending on the application of the lead wire. As a pretreatment, the substrate is immersed in a sodium metasilicate aqueous solution (25 g / L) at 25°C, and a current density of 5.0 A / dm ２ After degreasing, the substrate is washed with running water.

[0080] Next, polyethylene glycol 600 is mixed with hydrochloric acid (concentration 1.5% by mass) to a concentration of 500 g / L to obtain a surface-roughening solution. The substrate is immersed in the surface-roughening solution at 60°C, and a current density of 10 to 50 A / dm ２ The electrolysis is carried out for 10 to 60 seconds with an alternating current having a frequency of 10 to 1000 Hz. After the electrolysis, the substrate is washed with running water to obtain a conductor.

[0081] The surface of the conductor can be subjected to a surface treatment. Chromium chloride hexahydrate (5.0 g / L) and potassium formate (170 g / L) are mixed with pure water to obtain a surface treatment solution. The conductor is immersed in the surface treatment solution at 45°C, and a current density of 10 A / dm ２ After the cathodic electrolysis, the conductor is washed with running water. This allows at least a portion of the surface of the conductor to contain trivalent chromium.

[0082] Another example of surface treatment is described below. 1 part by mass of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd., molecular weight (Mw) 10,000) is dissolved in 87.77 parts by mass of pure water, and 0.5 parts by mass of ammonium zirconium carbonate is added to the solution. 0.01 parts by mass of 25% aqueous ammonia is then added as a pH adjuster to obtain a mixed solution. The mixed solution is applied to the surface of the conductor and then dried at 120°C for 5 minutes. This allows at least a portion of the conductor surface to contain zirconium.

[0083] <<Preparation of Insulating Film>> Prepare an acid-modified polypropylene as the raw material for the first insulating layer and a heat-resistant resin as the raw material for the second insulating layer. If at least one of the first insulating layer and the second insulating layer contains an additive, prepare the additive. Mix the raw materials for the first insulating layer and the second insulating layer using a known mixing device such as an open roll, pressure kneader, single-screw kneader, or twin-screw kneader to obtain a mixed raw material.

[0084] The mixed raw materials for the first insulating layer and the second insulating layer are extruded using a co-extrusion T-die extruder to obtain an insulating film 1 in which the first insulating layer and the second insulating layer are laminated.

[0085] If the insulating film 1 includes other layers, a coat hanger-type three-type three-layer T-die film forming machine equipped with three single-screw extruders can be used to feed the mixed raw materials for the first insulating layer into the first extruder, the mixed raw materials for the second insulating layer into the second extruder, and the mixed raw materials for the other layers into the third extruder, and co-extrude to obtain the insulating film 1.

[0086] <<Fabrication of Lead Wire>> Next, the obtained insulating film 1 is cut to a predetermined size and heat-sealed to the main surface of the conductor at a mold temperature of 260° C. and a surface pressure of 0.3 MPa, thereby obtaining a lead wire.

[0087] [Embodiment 2: Electricity storage device] An electricity storage device according to one embodiment of the present disclosure (hereinafter also referred to as "embodiment 2") will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a front view schematically illustrating an example of an electricity storage device according to embodiment 2. Fig. 5 is a partial cross-sectional view taken along line V-V in Fig. 4.

[0088] The electricity storage device 30 according to the second embodiment includes an enclosed container 2 and the lead wire 10 of the first embodiment arranged to extend from the inside to the outside of the enclosed container 2. The insulating film 1 is fused to the enclosed container 2. The lead wire 10 of the electricity storage device 30 according to the second embodiment has improved adhesion strength between the conductor 3 and the insulating film 1. Therefore, the electricity storage device 30 according to the second embodiment can maintain its performance even at high temperatures and has high reliability.

[0089] The power storage device 30 of the second embodiment includes a battery cell 15 including a positive electrode 20, a negative electrode 14, and an electrolyte 13 sandwiched between the positive electrode 20 and the negative electrode 14, a conductor 3 electrically connected to each of the positive electrode 20 and the negative electrode 14, and an enclosure 2 that seals the battery cell 15. A portion of the conductor 3 is exposed to the outside of the enclosure 2, and the insulating film 1 of the first embodiment is disposed between the conductor 3 and the enclosure 2. A first insulating layer 1a of the insulating film 1 is disposed in contact with the conductor 3.

[0090] As shown in FIG. 5 , the sealed container 2 is made of a three-layer laminate film 8, which includes a metal layer 16 and first and second resin layers 17 and 18 that cover the metal layer 16. The metal layer 16 is formed from a metal such as aluminum foil. The second resin layer 18, located on the exterior side of the sealed container 2, can be made of a polyamide resin such as 6,6-nylon or 6-nylon, a polyester resin, or a polyimide resin. The first resin layer 17, located on the interior side of the sealed container 2, is preferably made of an insulating resin that is insoluble in nonaqueous electrolytes and melts when heated. Examples of insulating resins include polyolefin resins, acid-modified polyolefin resins, and acid-modified styrene-based elastomers. The sealed container 2 is fabricated by overlapping two laminate films 8 and heat-sealing the three edges, excluding the edge through which the conductor 3 passes. At the outer periphery of the sealed container 2, the two metal layers 16 are bonded via the first resin layer 17.

[0091] The conductor 3 is bonded (thermally fused) to the sealed container 2 (laminate film 8) via the insulating film 1 at a seal portion 9. The electricity storage device 30 further contains a positive electrode 20, a negative electrode 14, and an electrolyte 13 connected to the ends of the conductor 3.

[0092] The electricity storage device 30 of the second embodiment may be an all-solid-state battery in which the electrolyte 13 is a solid electrolyte. This allows the high adhesive strength of the insulating film 1 to the conductor 3 to be maintained for a long period of time, further improving the reliability of the electricity storage device 30.

[0093] The electricity storage device 30 of the second embodiment may be a non-aqueous electrolyte battery in which the electrolyte 13 is a non-aqueous electrolyte. Examples of the non-aqueous electrolyte include LiPF ６ , LiBF ４ Examples of suitable lithium salts include those obtained by dissolving fluorine-containing lithium salts such as those mentioned above in diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), or the like.

[0094] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0095] The following substrates, substrate A and substrate B, were prepared as substrates. The substrates used for each sample are as shown in the "Type" column of "Substrate" in Table 1. Substrate A: Pure aluminum plate (A1050), aluminum content 99.5 mass%, developed interface area ratio of the main surface Sdr 0.1, arithmetic mean height Sa 0.04 μm, maximum height Sz 0.7 μm. Substrate B: Aluminum alloy plate, aluminum content 97 mass%, developed interface area ratio of the main surface Sdr 0.2, arithmetic mean height Sa 0.06 μm, maximum height Sz 0.7 μm.

[0096] As a pretreatment, the substrate was immersed in a sodium metasilicate aqueous solution (concentration: 25 g / L) at 25°C, and a current density of 5.0 A / dm ２ After the degreasing, the substrate was washed with running water.

[0097] Next, hydrochloric acid (concentration 1.5% by mass) was mixed with polyethylene glycol 600 to a concentration of 500 g / L to obtain a surface-roughening solution. The substrate was immersed in the surface-roughening solution at 60°C and subjected to electrolysis. The current density, frequency, and time during the electrolysis are shown in the "Electrolysis Conditions" column in Table 1. The substrate was washed with running water to obtain the aluminum conductor for each sample.

[0098] The values ​​in the "A2 / A1" column of the "Electrolysis Conditions" section of Table 1 indicate the percentage (A2 / A1) x 100 of the area A2 of the region to be electrolyzed relative to the total area A1, where the total area A1 (corresponding to the area S1 of the first region) of one main surface of the substrate in contact with the insulating film in the test sample described below is taken as 100%. For samples with a value in the "A2 / A1" column of less than 100%, the electrolysis was performed with a portion of the main surface of the substrate masked with a vinyl chloride plate to achieve the value in the "A2 / A1" column. For example, in Sample 1, the electrolysis was performed with 28% of the total area A1 of one main surface of the substrate in contact with the insulating film masked. As a result, the percentage (A2 / A1) x 100 of the area A2 of the region to be electrolyzed relative to the total area A1 of one main surface of the substrate in contact with the insulating film was 72%. In Sample 1, all unit areas in the electrolytically treated region have an Sdr of 0.5 or more, so (S2 / S1) is 72%. In the unmasked sample, the percentage (A2 / A1)×100 of the area A2 of the electrolytically treated region to the total area A1 is 100%.

[0099] For samples with "Cr" in the "Cr / Zr" column in Table 2, surface treatment was performed as follows: Chromium chloride hexahydrate (5.0 g / L) and potassium formate (170 g / L) were mixed with pure water to obtain a surface treatment solution. A conductor was immersed in the surface treatment solution at 45°C, and a current density of 10 A / dm ２ After the cathodic electrolysis, the conductor was washed with running water. As a result, at least a portion of the surface of the conductor contained trivalent chromium.

[0100] The samples with "Zr" in the "Cr / Zr" column in Table 2 were surface treated using the following procedure. One part by mass of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd., molecular weight (Mw) 10,000) was dissolved in 87.77 parts by mass of pure water, and 0.5 parts by mass of ammonium zirconium carbonate was added to the resulting aqueous solution. 0.01 parts by mass of 25% aqueous ammonia was then added as a pH adjuster to obtain a mixed solution. The mixed solution was applied to the surface of the conductor and then dried at 120°C for 5 minutes. This resulted in at least a portion of the conductor surface containing zirconium.

[0101] <<Preparation of insulating film>> Acid-modified polypropylene was prepared as the raw material for the first insulating layer, homopolypropylene as the raw material for the second insulating layer, and random polypropylene as the raw material for the other layers. The raw materials for the first insulating layer, the second insulating layer, and the other layers were each mixed using a mixer to obtain a mixed raw material.

[0102] Using a coat hanger-type three-kind, three-layer T-die film-forming machine equipped with three single-screw extruders, the mixed raw materials for the first insulating layer were fed into the first extruder, the mixed raw materials for the second insulating layer into the second extruder, and the mixed raw materials for the other layers into the third extruder, and co-extruded to obtain an insulating film in which an acid-modified polypropylene layer (corresponding to the first insulating layer), a homopolypropylene layer (corresponding to the second insulating layer), and a random polypropylene layer (corresponding to the other layers) were laminated in the above order. The average thickness of the acid-modified polypropylene layer was 50 μm, the average thickness of the homopolypropylene layer was 50 μm, and the average thickness of the other layers was 50 μm.

[0103] <<Preparation of Test Samples>> Next, the obtained insulating film was cut into a size of 55 mm in length and 10 mm in width, and heat-sealed to one of the main surfaces of the conductor at a mold temperature of 260°C and a surface pressure of 0.3 MPa, thereby obtaining test samples for each sample.

[0104]

[0105]

[0106] <Evaluation> <Measurement of surface roughness of conductor> For each test sample, the conductor and insulating film were separated and exposed by performing a 180° peel test at 25° C. The conductor was then immersed in a xylene solution at 120° C. for 60 minutes to remove part of the insulating film remaining on the conductor surface.

[0107] The conductor was removed from the xylene solution and dried. The developed interface area ratio Sdr, percentage (S2 / S1) x 100, arithmetic mean height Sa of the electrolytically treated region of the conductor, and maximum height Sz of the electrolytically treated region of the conductor were measured. The specific measurement method was as described in embodiment 1. The results are shown in Table 2. In samples 1 to 5, all unit regions in the electrolytically treated region had an Sdr of 0.5 or more. Samples 101 and 102 did not include any unit regions with an Sdr of 0.5 or more, so Table 2 lists the Sdr of the electrolytically treated region of the conductor.

[0108] It was confirmed by X-ray photoelectron spectroscopy that the surface of the conductor of each sample contained either or both of silicon and iron.

[0109] <Evaluation of Initial Adhesion Strength> One hour after the production of the test specimen for each sample, the adhesion strength between the conductor and the insulating film was measured by a 180° peel test at 25°C and 120°C. The pulling speed was 50 mm / min. The results are shown in the "Initial 25°C" and "Initial 120°C" columns of "Peel Strength" in Table 3. In the present disclosure, it is determined that the higher the adhesion strength at 120°C, the better the adhesion strength between the conductor and the insulating film at high temperatures.

[0110]

[0111] Samples 1 to 5 correspond to examples, in which the developed interface area ratio Sdr of the region of the conductor that underwent electrolytic treatment (corresponding to the second region) was 0.5 or more. Samples 101 and 102 correspond to comparative examples, in which the conductor did not include a region where the developed interface area ratio Sdr was 0.5 or more. It was confirmed that Samples 1 to 5 had superior adhesive strength between the conductor and the insulating film compared to Samples 101 and 102, both at 25°C and 120°C (high temperature).

[0112] Evaluation of Adhesion Strength After Aging The following test was carried out for each sample. A mixed solution was prepared by mixing ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1. Lithium hexafluorophosphate (LiPF６ ) was dissolved to a concentration of 1.0 mol / L, and water was added to a moisture content of 1000 ppm to prepare a test solution. Each test specimen was immersed in the test solution and left in a thermostatic chamber at 80°C for four weeks. The test specimen was then removed from the test solution, and the adhesive strength between the conductor and the insulating film was measured by a 180° peel test at 25°C. The tensile speed was 50 mm / min. The results are shown in the "After 25°C Aging" column of "Peel Strength" in Table 3.

[0113] Samples 1 to 5 correspond to Examples. Samples 101 and 102 correspond to Comparative Examples. It was confirmed that Samples 1 to 5 maintained superior adhesive strength compared to Samples 101 and 102, even after being left in a thermostatic chamber at 80°C for four weeks.

[0114] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0115] REFERENCE SIGNS LIST 1 insulating film, 1a first insulating layer, 1b second insulating layer, 2 encapsulation container, 3 conductor, 8 laminate film, 9 sealing portion, 10 lead wire, 13 electrolyte, 14 negative electrode, 15 battery cell, 16 metal layer, 17 first resin layer, 18 second resin layer, 20 positive electrode, 30 electricity storage device.

Claims

1. A lead wire comprising a conductor and an insulating film covering an outer peripheral surface of the conductor between both ends of the conductor while exposing both ends of the conductor in a first direction, wherein the conductor is made of aluminum or an aluminum alloy, the conductor includes a first region in contact with the insulating film, the first region includes a second region, and the second region has a developed interface area ratio Sdr of 0.5 or more as defined in JIS B 0681-2:2018.

2. The lead wire as described in claim 1, wherein the arithmetic mean height Sa of the second region as defined in JIS B 0681-2:2018 is 0.1 μm or more, and the maximum height Sz of the second region as defined in JIS B 0681-2:2018 is 1.0 μm or more.

3. A lead wire as described in claim 1 or claim 2, wherein the percentage (S2 / S1) x 100 of the area S2 of the second region to the area S1 of the first region is 40% or more.

4. A lead wire as claimed in any one of claims 1 to 3, wherein the aluminum content of the conductor is 99 mass% or more.

5. A lead wire as claimed in any one of claims 1 to 4, wherein at least a portion of the surface of the conductor contains one or both of silicon and iron.

6. A lead wire as claimed in any one of claims 1 to 5, wherein at least a portion of the surface of the conductor contains trivalent chromium.

7. The lead wire according to any one of claims 1 to 6, wherein at least a portion of the surface of the conductor comprises zirconium.

8. A lead wire as described in any one of claims 1 to 7, wherein the insulating film includes a first insulating layer arranged in contact with the conductor and a second insulating layer provided on the surface of the first insulating layer opposite the conductor, the first insulating layer being an acid-modified polypropylene layer, and the second insulating layer being a heat-resistant resin layer.

9. An electricity storage device comprising: an enclosed container; and a lead wire described in any one of claims 1 to 8 arranged to extend from the inside to the outside of the enclosed container, wherein the insulating film is fused to the enclosed container.

Images