Current collector foil with conductive adhesive layer, negative electrode current collector, and secondary battery

Abstract

To provide a novel current collector foil with a conductive adhesive layer for use in anode-free batteries. [Solution] A current collector foil comprising a current collector foil and a conductive adhesive layer, wherein the conductive adhesive layer comprises a matrix containing at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix, the conductive adhesive layer contains 85% to 95% by mass of the matrix and 5% to 15% by mass of the conductive material relative to the entire conductive adhesive layer, the matrix contains a polyisobutylene-based adhesive, the polyisobutylene-based adhesive contains a first polyisobutylene and a second polyisobutylene, the weight-average molecular weight of the first polyisobutylene is 30,000 to 200,000 and the weight-average molecular weight of the second polyisobutylene is 500,000 to 5,000,000, and the conductive adhesive layer contains 35% to 85% by mass of the first polyisobutylene and 5% to 60% by mass of the second polyisobutylene relative to the entire conductive adhesive layer.

Description

Technical Field

[0001] The present invention relates to a current collector foil with a conductive adhesive layer, a negative electrode current collector, and a secondary battery.

Background Art

[0002] In recent years, the importance of secondary batteries used as power sources has been increasing. Secondary batteries are actively being researched and developed, ranging from small ones such as power sources for portable electronic devices to medium and large ones such as electric vehicles and household storage batteries.

[0003] Generally, a secondary battery has a pair of electrodes containing an active material and an electrolyte disposed between the electrodes. As an electrode, a configuration in which an active material layer containing a positive electrode active material or a negative electrode active material and a current collector excellent in conductivity are laminated is known.

[0004] On the other hand, in recent years, a battery having a configuration called an "anode-free battery" in which a negative electrode active material layer does not exist during battery assembly has been studied (see, for example, Patent Document 1). In an anode-free battery, compared with a general battery having a negative electrode, the weight can be reduced by the amount corresponding to the absence of a negative electrode active material layer such as graphite, and the weight energy density can be improved. Furthermore, in an anode-free battery, the manufacturing cost can also be reduced by eliminating the negative electrode active material layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In anode-free batteries, the negative electrode (the opposite electrode to the positive electrode) has a different configuration compared to conventional rechargeable batteries. Therefore, it is expected that manufacturing will become simpler by using new materials on the negative electrode side that were not used in the study of conventional rechargeable batteries.

[0007] The present invention has been made in view of these circumstances, and aims to provide a novel conductive adhesive layered current collector foil for use in anode-free batteries. It also aims to provide a novel negative electrode current collector made from such conductive adhesive layered current collector foil, and a novel secondary battery having such a negative electrode current collector. [Means for solving the problem]

[0008] To solve the above problems, one aspect of the present invention includes the following aspects.

[0009] [1] A current collector foil and a conductive adhesive layer provided on one surface of the current collector foil, wherein the conductive adhesive layer comprises a matrix containing at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix, wherein the matrix is ​​contained in an amount of 85% to 95% by mass and the conductive material in an amount of 5% to 15% by mass relative to the entire conductive adhesive layer, the matrix contains the polyisobutylene-based adhesive, and the polyisobutylene-based adhesive is first A current collector foil with a conductive adhesive layer, comprising polyisobutylene and a second polyisobutylene, wherein the weight-average molecular weight of the first polyisobutylene is 30,000 to 200,000, and the weight-average molecular weight of the second polyisobutylene is 500,000 to 5,000,000, and the conductive adhesive layer contains 35% to 85% by mass of the first polyisobutylene and 5% to 60% by mass of the second polyisobutylene relative to the entire conductive adhesive layer.

[0010] [2] The conductive adhesive layer thickness is 2 μm or more and 30 μm or less, the conductive adhesive layer with current collector foil as described in [1].

[0011] [3] The current collector foil with a conductive adhesive layer according to [1] or [2], wherein the thickness of the current collector foil is 4 μm or more and 15 μm or less.

[0012] [4] The current collector foil with a conductive adhesive layer according to any one of [1] to [3], wherein the material of the current collector foil is copper or nickel.

[0013] [5] A current collector foil with a conductive adhesive layer according to any one of [1] to [4], having a release film laminated on the surface of the conductive adhesive layer.

[0014] A negative electrode current collector made of a current collector foil with a conductive adhesive layer as described in any one of items [6], [1] to [5].

[0015] A secondary battery comprising a negative electrode current collector as described in [7][6], a positive electrode, the conductive adhesive layer of the negative electrode current collector, and a separation layer sandwiched between the positive electrode and the negative electrode current collector, wherein the separation layer is a separator or a solid electrolyte membrane. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a novel current collector foil with a conductive adhesive layer for use in anode-free batteries. Furthermore, it is possible to provide a novel negative electrode current collector made from such a current collector foil with a conductive adhesive layer, and a novel secondary battery having such a negative electrode current collector. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a schematic diagram showing a current collector foil 10 with a conductive adhesive layer according to an embodiment. [Figure 2] Figure 2 is a schematic diagram showing a secondary battery 100 according to an embodiment. [Modes for carrying out the invention]

[0018] [Conductive adhesive foil current collector, negative electrode current collector, secondary battery] FIG. 1 is a schematic view showing a current collector foil 10 with a conductive adhesive layer according to the present embodiment. The current collector foil 10 with a conductive adhesive layer has a conductive adhesive layer 11 and a current collector foil 12. The conductive adhesive layer 11 is provided on one surface of the current collector foil 12. The negative electrode current collector produced from the current collector foil 10 with a conductive adhesive layer is used as a component on the negative electrode side of a lithium secondary battery.

[0019] The "current collector foil with a conductive adhesive layer" is a long-shaped molded body in which the conductive adhesive layer 11 and the current collector foil 12 are laminated and formed in a strip shape, or a sheet-shaped molded body obtained by processing such a strip-shaped molded body into single sheets.

[0020] In the current collector foil 10 with a conductive adhesive layer shown in FIG. 1, a release film 19 is laminated on the surface of the conductive adhesive layer 11. As the release film 19, known materials such as a PET film subjected to a release treatment with a silicone resin, a fluorine-containing silicone resin, or a non-silicone resin can be adopted.

[0021] 〈Conductive Adhesive Layer〉 The conductive adhesive layer 11 has the property of adhering to an object by applying pressure without requiring a solvent or heat when attaching to the object. The conductive adhesive layer 11 is a layer of a so-called pressure-sensitive adhesive. The conductive adhesive layer 11 has a matrix 111 and a conductive material 112 dispersed in the matrix 111.

[0022] (Matrix) The matrix 111 contains at least a polyisobutylene-based adhesive as a material. The polyisobutylene-based adhesive is suitable as a material for the matrix 111 because it has few side reactions during charge and discharge reactions and its glass transition temperature is not within the range of the normal operating temperature of the secondary battery.

[0023] The polyisobutylene-based adhesive contains a first polyisobutylene and a second polyisobutylene having different molecular weights. In addition, within a range that does not inhibit the effects of the invention, it may further contain a third polyisobutylene.

[0024] Furthermore, the first polyisobutylene, the second polyisobutylene, and the third polyisobutylene may each be of only one type or multiple types. More specifically, one type of first polyisobutylene and multiple types of second polyisobutylene can also be used.

[0025] The weight-average molecular weight of the first polyisobutylene is 30,000 or more and 200,000 or less, and may be 40,000 or more and 100,000 or less.

[0026] 5,000,000 The weight-average molecular weight of the second polyisobutylene is between 500,000 and 5,000,000, and may be between 1,000,000 and 4,000,000.

[0027] The weight-average molecular weight is determined by measuring it using gel permeation chromatography (GPC) and converting it to polystyrene equivalent. Examples of columns used when measuring the weight-average molecular weight in polystyrene equivalent using GPC include Shodex LF-804 (manufactured by Showa Denko Corporation).

[0028] Polyisobutylene-based adhesives containing primary polyisobutylene and secondary isobutylene preferably exhibit multiple detection peaks when GPC measurement is performed under the conditions for weight-average molecular weight measurement.

[0029] Since the polyisobutylene-based adhesive constituting the matrix 111 is a mixture of polyisobutylenes with different molecular weights, the physical properties of the polyisobutylene-based adhesive can be adjusted by controlling the mixing ratio. The matrix 111 preferably contains 35% to 85% by mass of primary polyisobutylene and 5% to 60% by mass of secondary polyisobutylene, relative to the entire conductive adhesive layer 11.

[0030] By including 35% to 85% by mass of primary polyisobutylene in the polyisobutylene-based adhesive, appropriate tackiness can be imparted to the polyisobutylene-based adhesive. This suppresses misalignment during the assembly of secondary batteries, making the assembly process easier. Furthermore, this allows the adhesive to follow and adhere to the separation layer during charging and discharging, thereby suppressing reaction non-uniformity.

[0031] By incorporating 5% to 60% by mass of polyisobutylene-based adhesive, the conductive adhesive layer can be restored in the thickness direction, ensuring electrical conductivity when the pressure inside the secondary battery rises and then falls due to charging, discharging, or heat generation. Furthermore, the appropriate elasticity during charging and discharging suppresses the uneven deposition of dendrites and other structures during lithium metal deposition, thereby promoting uniform deposition of lithium metal. This effect further improves the lifespan and safety of the secondary battery.

[0032] (Conductive material) The conductive material 112 imparts conductivity to the conductive adhesive layer 11. The conductive material 112 can be at least one selected from carbon black such as acetylene black, carbon fibers, activated carbon, metal powder, carbon nanotubes (CNTs), conductive polymers, etc. The conductive material 112 does not need to have the activity of an active material; it only needs to be a material that improves conductivity within the electrode.

[0033] The conductive adhesive layer 11 contains 85% to 95% by mass of matrix 111 and 5% to 15% by mass of conductive material 112 relative to the entire conductive adhesive layer 11.

[0034] The thickness of the conductive adhesive layer 11 is preferably 2 μm or more and 30 μm or less. The thickness of the conductive adhesive layer 11 may be 5 μm or more. Alternatively, the thickness of the conductive adhesive layer 11 may be 25 μm or less. The upper and lower limits of the thickness of the conductive adhesive layer 11 can be any combination.

[0035] <Current collector foil> The current collector foil 12 is a metal component used to collect current to the terminals of a lithium secondary battery when a current collector formed from a current collector foil 10 with a conductive adhesive layer is used on the negative electrode side of the battery. The material of the current collector foil 12 can be selected from the group consisting of copper (Cu), Pt, Ti, Ni, and stainless steel. Copper or Ni is preferred as the material of the current collector foil 12.

[0036] The thickness of the current collector foil 12 is preferably 4 μm or more and 15 μm or less. The thickness of the current collector foil 12 may be 5 μm or more. Also, the thickness of the current collector foil 12 may be 10 μm or less. The upper and lower limits of the thickness of the current collector foil 12 can be any combination.

[0037] The current collector foil 12 may be electrically connected to lead members for guiding electricity from inside the battery or introducing electricity into the battery. Alternatively, the current collector foil 12 may have a portion without a conductive adhesive layer, which can serve as a lead portion for electrically connecting to components outside the battery.

[0038] Figure 2 is a schematic diagram showing the secondary battery 100 of this embodiment. The secondary battery 100 is a lithium secondary battery having a negative electrode current collector 10A made of the conductive adhesive layered current collector foil 10 described above, a positive electrode 20, and a separation layer 30. The secondary battery 100 is an anode-free battery that does not have a negative electrode active material layer.

[0039] The negative electrode current collector 10A is a laminate of a conductive adhesive layer 11A and a current collector foil 12A, and is obtained by cutting the current collector foil 10 with the conductive adhesive layer described above. The negative electrode current collector 10A is attached to the separation layer 30 by the conductive adhesive layer 11A.

[0040] The positive electrode 20 has a positive electrode active material layer 21 and a current collector 22. The positive electrode 20 is laminated with the positive electrode active material layer 21 facing the separation layer 30.

[0041] The positive electrode active material layer 21 comprises a known positive electrode active material for lithium secondary batteries, a binder, and a conductive material.

[0042] Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO4), lithium iron phosphate (LiFePO4), and Ni-Mn-Co ternary (NMC) active materials (LiNi x Mn y Co z O2), Ni-Co-Al ternary system (NCA system) active material (LiNi x Co y Al z Examples include O2, etc.

[0043] As the binder and conductive material, known materials used in the positive electrode active material layer for lithium secondary batteries can be used. In the case of a cell that does not use an electrolyte, a solid electrolyte may be mixed into the positive electrode active material layer 21. Known solid electrolytes such as sulfide-based solid electrolytes like Li2S-P2S5, oxide-based solid electrolytes, and polymer electrolytes can be used.

[0044] The separation layer 30 is positioned between the negative electrode current collector 10A and the positive electrode 20, and is a layer that separates the negative electrode current collector 10A and the positive electrode 20. The separation layer 30 is sandwiched between the conductive adhesive layer 11A of the negative electrode current collector 10A and the positive electrode 20, and the conductive adhesive layer 11A of the negative electrode current collector 10A adheres to the separation layer 30.

[0045] Examples of the separation layer 30 include a separator that is ion-conductive and placed between the positive and negative electrodes in a lithium secondary battery using an electrolyte, and an electrolyte layer (solid electrolyte membrane) that is placed between the positive and negative electrodes in a lithium secondary battery using a gel-like or solid electrolyte. The electrolyte or electrolyte layer contains an electrolyte containing lithium ions. The separation layer 30 may be composed of multiple layers as long as it performs its function. Among these multiple layers, there may be a metal layer made of metal foil or metal vapor deposition. In addition, some of the layers may have a current-collecting function.

[0046] Regarding the configuration of the anode-free battery used in the secondary battery 100, any known configuration can be adopted as appropriate.

[0047] The negative electrode current collector 10A can be easily formed by cutting the current collector foil 10 with a conductive adhesive layer, which is the raw material. Furthermore, the obtained negative electrode current collector 10A can be easily bonded to the separation layer 30 via the conductive adhesive layer 11A to form a laminated structure of the negative electrode current collector 10A and the separation layer 30. Therefore, by using the negative electrode current collector 10A, a secondary battery 100, which is an anode-free battery, can be easily manufactured.

[0048] Here, it is estimated that when the resulting anode-free secondary battery 100 is charged, metallic lithium is deposited near the interface between the conductive adhesive layer 11A of the negative electrode current collector 10A and the separation layer 30, forming a lithium deposition layer (not shown).

[0049] Furthermore, the metallic lithium constituting the lithium deposition layer releases electrons when the secondary battery 100 is discharged, becoming lithium ions which are then retained in the positive electrode active material layer 21. As a result, the lithium deposition layer decreases or disappears.

[0050] In the secondary battery 100 described above, as the lithium deposition layer is repeatedly formed and destroyed by charging and discharging, a volume change occurs due to the formation and decrease of the lithium deposition layer. Therefore, the conductive adhesive layer 11A of the negative electrode current collector 10A is subjected to internal stress due to the formation and decrease of the lithium deposition layer.

[0051] In addition, in the secondary battery 100, the negative electrode current collector 10A is bonded to the separation layer 30 due to the adhesive force of the conductive adhesive layer 11A. Therefore, if a lithium deposition layer is deposited at the interface between the conductive adhesive layer 11A and the separation layer 30, the conductive adhesive layer 11A may peel off from the separation layer 30.

[0052] To address the changes expected to occur inside the battery during charging and discharging, the inventors considered it important that the conductive adhesive layer 11A possess (a) moderate softness that allows for volume changes associated with the formation and disappearance of the lithium deposition layer without excessive deformation, and (b) adhesive strength that maintains close contact between the conductive adhesive layer 11A and the separation layer 30 even after the lithium deposition layer is formed.

[0053] Based on the above idea, the inventors conducted thorough research and found that by creating a current collector foil with a conductive adhesive layer having the above-described configuration, a suitable current collector foil 10 possessing the physical properties of (a) and (b) can be obtained. In other words, it was found that a current collector foil 10 with a conductive adhesive layer having the above-described configuration of a conductive adhesive layer 11 can easily maintain its cycle performance even after repeated charging and discharging when used in the secondary battery 100.

[0054] In this specification, it can be confirmed that the current collector foil 10 with a conductive adhesive layer possesses the physical properties of (a) and (b) described above by evaluating (1) and (2) below.

[0055] (1) Excessive testing In the overflow test conducted under condition 1 below, no extreme overflow was observed. (Condition 1) Multiple conductive adhesive layers of the fabricated conductive adhesive foil are stacked to a thickness of 300 μm, and then a laminate is created by sandwiching the conductive adhesive layer between the foil and a release film. The resulting laminate is punched out into a 10 mm diameter disc shape to produce a test specimen.

[0056] The obtained test specimen is sandwiched between a pair of 25 μm thick light-transmitting polyester films, a weight is placed on top of the polyester films, and a pressure of 4.5 psi (where 1 psi = 6.89476 kPa) is applied and held for 5 minutes.

[0057] The weight is removed, and the condition is observed through the polyester film in a plan view. The area of ​​the conductive adhesive layer protruding from the current collector foil constituting the laminate is measured with a microscope. A result that meets either of the following criteria (i) or (ii) is considered acceptable. (i) No excess conductive adhesive layer is visible in plan view. (ii) The area of ​​the conductive adhesive layer that extends beyond the current collector foil is less than 15% of the planar area of ​​the test specimen before testing.

[0058] The test pressure of 4.5 psi was set based on the typical constraint pressure of automotive batteries.

[0059] (2) Peel test The peel strength required in the peel test under condition 2 below is 1.0 N / mm or higher. (Condition 2) Three test pieces are prepared by cutting a conductive adhesive foil into 15mm strips. The conductive adhesive of the test pieces is attached to a SUS304 plate that has been cleaned with ethanol. When attaching, a 2kg rubber roller is used, and the roller is moved back and forth once to apply pressure and ensure a tight bond.

[0060] Subsequently, with the edges of the conductive adhesive foil protected by paper, the conductive adhesive foil was fixed in the sample gripping section of a tensile testing machine, and peeled 100 mm at a peeling speed of 300 mm / min and a peeling angle of 180°, and the peel strength was measured. The arithmetic mean of the peel strength measured for each of the three test pieces was adopted as the peel strength (N / mm).

[0061] The conductive adhesive layer 11A (conductive adhesive layer 11) that satisfies the above (1) is an adhesive layer that is not too soft but has appropriate flexibility. Therefore, for example, when a negative electrode current collector manufactured from a current collector foil 10 with a conductive adhesive layer is used in a secondary battery, the negative electrode current collector will not be excessively crushed by external stresses applied to the secondary battery (for example, the constraint stress when the secondary battery (cell) is assembled). Therefore, such a secondary battery can easily follow the deformation associated with the deposition and disappearance of metallic lithium during charging and discharging, and damage can be suppressed.

[0062] The conductive adhesive layer 11A (conductive adhesive layer 11) that satisfies the above (2) can suitably maintain close contact between the conductive adhesive layer 11A and the separation layer 30 even when a lithium deposition layer is formed.

[0063] Here, a configuration in which a resin film called an undercoat layer is formed on the surface of the current collector foil is known (for example, WO2009 / 147989). However, the known undercoat layer is a layer used as a protective film for the current collector foil and does not have the adhesive strength to adhere to adjacent layers like the conductive adhesive layer 11A (conductive adhesive layer 11) described above. Therefore, the known undercoat layer does not have a matrix containing a polyisobutylene-based adhesive or an acrylic-based adhesive, like the conductive adhesive layer 11A (conductive adhesive layer 11) of this embodiment, and can be said to be a completely different configuration that does not satisfy the above (1) and (2).

[0064] [Manufacturing method for current collector foil with conductive adhesive layer] A current collector foil with a conductive adhesive layer can be manufactured by applying a coating, in which the conductive adhesive layer material is dissolved or dispersed in a solvent, onto the current collector foil, and then removing the solvent.

[0065] The solvent used should be one that can dissolve the adhesive resin at least. Examples of solvents include hydrocarbon solvents, alcohol solvents, ether solvents, ketone solvents, ester solvents, amide solvents, halogen solvents, sulfur solvents, and inorganic solvents.

[0066] Examples of hydrocarbon solvents include heptane, cyclohexane, toluene, and xylene.

[0067] Examples of alcohol-based solvents include methanol and ethanol.

[0068] Examples of ether-based solvents include tetrahydrofuran and dioxane.

[0069] Examples of ketone solvents include acetone and methyl ethyl ketone.

[0070] Examples of ester solvents include ethyl acetate and ethyl lactate.

[0071] Examples of amide solvents include dimethylformamide and N-methyl-2-pyrrolidone.

[0072] Examples of halogenated solvents include chloroform and dichloromethane.

[0073] Examples of sulfur-based solvents include dimethyl sulfoxide and sulfolane.

[0074] Water is an example of an inorganic solvent.

[0075] The above solvents may be used individually, or a mixed solvent consisting of two or more solvents may be used.

[0076] The method for preparing the paint is not particularly limited, but it may be done by mixing the adhesive, conductive material, and any optional additives one by one or two or more simultaneously with a solvent and dissolving or dispersing them in the solvent.

[0077] There are no restrictions on the order in which solid components (adhesive, conductive material, and any optional additives) are added to the solvent.

[0078] After preparing the paint, a solvent may be added to adjust its viscosity.

[0079] The paint's condition may be adjusted by processes such as defoaming and filtration. Additives such as defoamers, viscosity modifiers, thickeners, diluents, surfactants, and stabilizers may be added to the paint. These additives can be those that are commonly used.

[0080] There are no particular limitations on the method of applying the paint, but examples include blade coating, dip coating, spray coating, gravure coating, bar coating, and die coating.

[0081] A conductive adhesive layer can be formed by removing the solvent from the coating film formed by applying the paint. The solvent can be removed by heating, reduced pressure, blowing air, or a combination thereof.

[0082] When a long, strip-shaped current collector foil is used, the current collector foil with a conductive adhesive layer may be stored and transported in a roll, or it may be further processed into multiple sheets of conductive adhesive foil.

[0083] In this way, a current collector foil with a conductive adhesive layer is obtained.

[0084] By using the conductive adhesive layer-coated current collector foil and negative electrode current collector configured as described above in the manufacture of anode-free batteries (secondary batteries), secondary batteries can be easily manufactured. Furthermore, secondary batteries having such a negative electrode current collector tend to maintain their cycle performance even after charging and discharging, resulting in high reliability.

[0085] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but the present invention is not limited to these examples. The shapes and combinations of the constituent members shown in the above examples are merely examples, and can be modified in various ways based on design requirements, etc., without departing from the spirit of the present invention. [Examples]

[0086] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0087] (Examples 1-7, Comparative Examples 1-3) The materials used in the examples and comparative examples are as follows:

[0088] (Polyisobutylene) PIB1: Tetrax 3T (manufactured by ENEOS Material Co., Ltd., Mw 41,000) PIB2: Tetrax 6T (manufactured by ENEOS Material Co., Ltd., Mw 75,000) PIB3: OPPANOL N50 (BASF, Mw 1,050,000) PIB4: OPPANOL N80 (BASF, Mw 3,050,000) PIB5: OPPANOL N150 (BASF, Mw 565,000)

[0089] The weight-average molecular weight (Mw) of each polyisobutylene was measured by gel permeation chromatography (GPC) and determined by converting it to polystyrene equivalent. The following GPC conditions were used. (GPC conditions) Column: Shodex LF-804 (manufactured by Showa Denko Corporation) Solvent: Chloroform Temperature: 40℃

[0090] PIB1 and PIB2 correspond to the first polyisobutylene in this invention, and PIB3, PIB4, and PIB5 correspond to the second polyisobutylene in this invention.

[0091] (Conductive material) Conductive carbon black: C-NERGY SUPER C65T (manufactured by Imerys)

[0092] (Current collector foil) Cu foil

[0093] The adhesive was mixed in the proportions shown in Table 1 below to obtain a material solution. The obtained material solution and the conductive material were mixed in the proportions shown in Table 1 to create a paint. Toluene was then added to adjust the viscosity.

[0094] The slurry was degassed and passed through a sieve with a mesh size of 100 μm to obtain the paints of the examples and comparative examples.

[0095] The paint obtained was applied to the current collector foil using an applicator to a coating thickness of 5 μm after drying. After application, the foil was placed in a batch-type dryer for 5 minutes to allow it to dry completely, thus obtaining the current collector.

[0096] [Table 1]

[0097] (Rating 1) The obtained conductive adhesive layer was subjected to a bleed test using the method described in "(1) Bleed Test" above. Samples in which no bleed was observed, or in which the increase in area was less than 15%, were deemed to pass, while samples with bleed and an increase in area of ​​15% or more were deemed to fail.

[0098] (Rating 2) The adhesion strength of the obtained conductive adhesive layer was tested using the method described in "(2) Peel Strength" above. A peel strength of 1.0 N / mm or higher was considered acceptable, while a peel strength of less than 1.0 N / mm was considered unacceptable.

[0099] The evaluation results are shown in Table 2. A passing grade was determined to be an overall pass if both evaluations 1 and 2 were met. In Table 2, a pass is indicated by A and a fail by B.

[0100] [Table 2]

[0101] The evaluation results show that each current collector foil with a conductive adhesive layer in Examples 1 to 7 possesses both (a) moderate flexibility that allows for volume changes associated with the formation and disappearance of the lithium deposition layer without excessive deformation, and (b) adhesive strength that maintains close contact between the conductive adhesive layer and the separation layer even after the lithium deposition layer is formed. Secondary batteries employing current collector foils made from such conductive adhesive foils are expected to maintain their cycle life more easily.

[0102] In contrast, Comparative Example 1 failed in (Evaluation 1). Therefore, the conductive adhesive foil of Comparative Example 1 can be evaluated as being too soft for the purpose of the invention.

[0103] Furthermore, Comparative Examples 2-4 failed in (Evaluation 2). In Evaluation 2, current collector foils with conductive adhesive layers exhibited excessively low peel strength, which suggests that the conductive adhesive layer may not be able to follow the separation layer during volume changes caused by increases and decreases in lithium during charging and discharging, potentially leading to non-uniformity of the reaction. Therefore, the current collector foils with conductive adhesive layers in Comparative Examples 2-4 are at risk of interfacial delamination at the interface between the adhesive layer and the separation layer (separator or solid electrolyte membrane) due to the deposition and disappearance of metallic lithium during charging and discharging, making it difficult to maintain cycle characteristics.

[0104] Furthermore, negative electrode current collectors were fabricated from the conductive adhesive foils of the Examples and Comparative Examples, and the cycle performance of secondary batteries equipped with these negative electrode current collectors was evaluated. It was confirmed that the secondary batteries of the Examples exhibited better cycle performance than the secondary batteries of the Comparative Examples. In particular, the negative electrode current collector fabricated from the conductive adhesive foil of Example 3 showed the best cycle performance when used in a secondary battery.

[0105] From these results, it was found that the present invention is useful. [Explanation of symbols]

[0106] 10...Current collector foil with conductive adhesive layer, 10A...Negative electrode current collector, 11,11A...Conductive adhesive layer, 12,12A...Current collector foil, 19...Release film, 20...Positive electrode, 22...Current collector, 30...Separation layer, 100...Secondary battery, 111...Matrix, 112...Conductive material

Claims

1. Current collector foil and The current collector foil comprises a conductive adhesive layer provided on one surface, The conductive adhesive layer comprises a matrix containing at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix, wherein the matrix accounts for 85% to 95% by mass and the conductive material accounts for 5% to 15% by mass relative to the entire conductive adhesive layer. The matrix comprises the polyisobutylene-based adhesive, The aforementioned polyisobutylene-based adhesive comprises a first polyisobutylene and a second polyisobutylene. The weight-average molecular weight of the first polyisobutylene is 30,000 or more and 200,000 or less. The weight-average molecular weight of the second polyisobutylene is 500,000 or more and 5,000,000 or less. Current collector foil with a conductive adhesive layer, wherein the entire conductive adhesive layer contains 35% to 85% by mass of the first polyisobutylene and 5% to 60% by mass of the second polyisobutylene.

2. The conductive adhesive layer is 2 μm or more and 30 μm or less, wherein the thickness of the conductive adhesive layer is 2 μm or more and 30 μm or less, as described in claim 1.

3. The current collector foil with a conductive adhesive layer according to claim 1 or 2, wherein the thickness of the current collector foil is 4 μm or more and 15 μm or less.

4. The conductive adhesive layered current collector foil according to claim 1 or 2, wherein the material of the current collector foil is copper or nickel.

5. The conductive adhesive layer-equipped current collector foil according to claim 1 or 2, further comprising a release film laminated on the surface of the conductive adhesive layer.

6. A negative electrode current collector made of a current collector foil with a conductive adhesive layer as described in claim 1 or 2.

7. The negative electrode current collector according to claim 6, Positive electrode and, The negative electrode current collector has a conductive adhesive layer, and the positive electrode has a separation layer that is sandwiched between them and to which the conductive adhesive layer of the negative electrode current collector adheres. The separation layer is a separator or a solid electrolyte membrane in a secondary battery.

Images