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

Abstract

This invention relates to a current collector foil with a conductive adhesive layer, a negative electrode current collector, and a secondary battery, and provides a novel current collector foil with a conductive adhesive layer for an anode-free battery. The current collector foil with a conductive adhesive layer comprises a current collector foil and a conductive adhesive layer. The conductive adhesive layer has a matrix comprising at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix. Relative to the total mass of the conductive adhesive layer, it comprises 85% to 95% by mass of the matrix and 5% to 15% by mass of the conductive material. The matrix comprises a polyisobutylene-based adhesive, which comprises a first polyisobutylene and a second polyisobutylene. The first polyisobutylene has a weight-average molecular weight of 30,000 to 200,000, and the second polyisobutylene has a weight-average molecular weight of 500,000 to 5,000,000. Relative to the total mass of the conductive adhesive layer, it comprises 35% to 85% by mass of the first polyisobutylene and 5% to 60% by mass of the second polyisobutylene.

Description

Technical Field

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

[0002] In recent years, the importance of secondary batteries as power sources has been increasing. Research and development are actively underway on secondary batteries, ranging from small batteries for portable electronic devices to medium and large batteries for electric vehicles or household use.

[0003] Generally, a secondary battery has a pair of electrodes containing active materials and an electrolyte disposed between the electrodes. As electrodes, it is known that there is a structure consisting of an active material layer containing either a positive or negative active material and a current collector with excellent conductivity.

[0004] In contrast, in recent years, researchers have been studying batteries with a structure known as "anode-free batteries" that do not have a negative electrode active material layer during battery assembly (see, for example, Patent Document 1). Compared to conventional batteries with a negative electrode, anode-free batteries can reduce weight corresponding to the absence of a negative electrode active material layer such as graphite, thereby increasing gravimetric energy density. Moreover, by removing the negative electrode active material layer, manufacturing costs can also be reduced in anode-free batteries.

[0005] Patent Document 1: Japanese Patent Publication No. 2022-542314 Summary of the Invention

[0006] Anode-less batteries differ from conventional rechargeable batteries in the structure of the negative electrode (the counter electrode of the positive electrode). Therefore, by using novel materials not previously used in rechargeable battery research on the negative electrode side, it is expected that manufacturing can be simplified.

[0007] The present invention was made in view of this situation, and its object is to provide a novel current collector foil with a conductive adhesive layer for use in anode-free batteries. Furthermore, its object is to provide a novel negative electrode current collector using this current collector foil with a conductive adhesive layer as a material, and a novel secondary battery having this negative electrode current collector.

[0008] To address the aforementioned issues, the present invention includes the following solutions.

[0009] [1] A current collector foil with a conductive adhesive layer, comprising a current collector foil and a conductive adhesive layer disposed on one side of the current collector foil, the conductive adhesive layer having a matrix comprising at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix, comprising, relative to the total mass of the conductive adhesive layer, 85% by mass and 95% by mass of the matrix, and comprising, 5% by mass and 15% by mass of the conductive material, the matrix comprising the polyisobutylene-based adhesive, the polyisobutylene-based adhesive comprising a first polyisobutylene and a second polyisobutylene, the first polyisobutylene having a weight-average molecular weight of 30,000 or more and 200,000 or less, the second polyisobutylene having a weight-average molecular weight of 500,000 or more and 5,000,000 or less, and comprising, relative to the total mass of the conductive adhesive layer, 35% by mass and 85% by mass of the first polyisobutylene, and comprising, 5% by mass and 60% by mass of the second polyisobutylene.

[0010] [2] The current collector foil with a conductive adhesive layer according to [1], wherein the thickness of the conductive adhesive layer is more than 2 μm and less than 30 μm.

[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 more than 4 μm and less than 15 μm.

[0012] [4] A 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], wherein a release film is formed on the surface of the conductive adhesive layer.

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

[0015] [7] A secondary battery comprising: [6] a negative current collector; a positive electrode; and a separation layer sandwiched between the conductive adhesive layer of the negative current collector and the positive electrode, and for the conductive adhesive layer of the negative current collector to adhere to, wherein the separation layer is a separator or a solid electrolyte membrane.

[0016] According to the present invention, a novel current collector foil with a conductive adhesive layer for use in anode-free batteries can be provided. Additionally, a novel negative electrode current collector using this current collector foil with a conductive adhesive layer as a material, and a novel secondary battery having this negative electrode current collector, can also be provided. Attached Figure Description

[0017] Figure 1This is a schematic diagram showing the current collector foil 10 with a conductive adhesive layer according to this embodiment.

[0018] Figure 2 This is a schematic diagram showing the secondary battery 100 of this embodiment.

[0019] (Explanation of reference numerals in the attached diagram)

[0020] 10…Current collector foil with conductive adhesive layer

[0021] 10A… Negative current collector

[0022] 11,11A…Conductive adhesive layer

[0023] 12,12A…Current collector foil

[0024] 19… Peel-off membrane

[0025] 20…positive electrode

[0026] 22… collector

[0027] 30…Separation layer

[0028] 100…rechargeable battery

[0029] 111… matrix

[0030] 112…Conductive materials Detailed Implementation

[0031] [Current collector foil with conductive adhesive layer, negative electrode current collector, secondary battery]

[0032] Figure 1 This is a schematic diagram showing the current collector foil 10 with a conductive adhesive layer according to this 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 disposed on one side of the current collector foil 12. The negative electrode current collector made from the current collector foil 10 with a conductive adhesive layer is used as the structure of the negative electrode side of a lithium secondary battery.

[0033] "Current collector foil with conductive adhesive layer" refers to a strip-shaped long-sized shaped body formed by stacking conductive adhesive layer 11 and current collector foil 12, or a sheet-shaped shaped body obtained by cutting such strip-shaped shaped body.

[0034] Figure 1 The current collector foil 10 with a conductive adhesive layer shown has a release film 19 laminated on the surface of the conductive adhesive layer 11. The release film 19 can be a known material such as a PET film that has been demolded with silicone resin, fluorinated silicone resin, or non-silicone resin.

[0035] <Conductive adhesive layer>

[0036] The conductive adhesive layer 11 has the property of being able to adhere to an object without the need for solvents or heat, but simply by applying pressure. The conductive adhesive layer 11 is a layer of so-called pressure-sensitive adhesive. The conductive adhesive layer 11 has a matrix 111 and a conductive material 112 dispersed in the matrix 111.

[0037] (Matrix)

[0038] The matrix 111 contains at least a polyisobutylene-based binder as a material. Polyisobutylene-based binders have fewer side reactions during charge-discharge reactions and their glass transition temperature is not within the range of commonly used operating temperatures of secondary batteries, making them suitable as materials for the matrix 111.

[0039] The polyisobutylene-based adhesive comprises a first polyisobutylene and a second polyisobutylene with different molecular weights. It should be noted that, to the extent that it does not impair the effectiveness of the invention, a third polyisobutylene may also be included.

[0040] Furthermore, the first polyisobutylene, the second polyisobutylene, and the third polyisobutylene can each be either a single type or multiple types. More specifically, one type of first polyisobutylene and multiple types of second polyisobutylene can also be used.

[0041] The first polyisobutylene has a weight average molecular weight of 30,000 or more and 200,000 or less, or it may have a weight average molecular weight of 40,000 or more and 100,000 or less.

[0042] The second polyisobutylene has a weight average molecular weight of 500,000 or more and 5,000,000 or less, or it can be 1,000,000 or more and 4,000,000 or less.

[0043] Weight-average molecular weight is a value determined using gel permeation chromatography (GPC) and converted based on polystyrene. Examples of chromatographic columns used for determining weight-average molecular weight using GPC and based on polystyrene conversion include the Shodex LF-804 (manufactured by Showa Denko Corporation).

[0044] When a polyisobutylene-based adhesive containing a first polyisobutylene and a second polyisobutylene is subjected to GPC determination under the conditions of determining the weight-average molecular weight, multiple detection peaks are observed.

[0045] The polyisobutylene-based adhesive constituting the matrix 111 is a mixture of polyisobutylenes with different molecular weights, thereby allowing the properties of the polyisobutylene-based adhesive to be adjusted by controlling the mixing ratio. The matrix 111, relative to the total mass of the conductive adhesive layer 11, may contain 35% to 85% by mass of a first polyisobutylene and 5% to 60% by mass of a second polyisobutylene.

[0046] By including 35% to 85% by mass of a first polyisobutylene in the polyisobutylene-based adhesive, suitable adhesive properties can be imparted to the polyisobutylene-based adhesive. This suppresses positional displacement during secondary battery assembly, facilitating the assembly process. Furthermore, it ensures tight adhesion along the separation layer during charging and discharging, thereby suppressing uneven reactions.

[0047] The polyisobutylene-based adhesive contains 5% to 60% by mass of a second polyisobutylene, ensuring conductivity by allowing the conductive adhesive layer to recover in the thickness direction when the pressure inside the secondary battery temporarily rises and falls due to charging, discharging, or heating. Furthermore, the presence of appropriate elastic forces during charging and discharging suppresses uneven deposition of dendrites and other deposits during lithium metal precipitation, promoting uniform lithium metal deposition. This effect further improves the lifespan and safety of the secondary battery.

[0048] (Conductive materials)

[0049] The conductive material 112 imparts conductivity to the conductive adhesive layer 11. Examples of the conductive material 112 include at least one selected from carbon black such as acetylene black, carbon fibers, activated carbon, metal powder, carbon nanotubes (CNTs), and conductive polymers. The conductive material 112 does not need to possess the activity of an active substance; it only needs to be a material that improves the conductivity inside the electrode.

[0050] The conductive adhesive layer 11 may contain a matrix 111 comprising 85% to 95% by mass and a conductive material 112 comprising 5% to 15% by mass relative to the total mass of the conductive adhesive layer 11.

[0051] 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 also 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 arbitrarily combined.

[0052] <Cellular foil>

[0053] The current collector foil 12 is a metal component used to collect current at the battery terminals when a current collector formed from a current collector foil 10 with a conductive adhesive layer is used on the negative electrode side of a lithium secondary 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.

[0054] 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 also be 5 μm or more. Alternatively, 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 arbitrarily combined.

[0055] The current-conducting component used to draw electricity from or into the battery can be electrically connected to the current-collecting foil 12. Alternatively, a portion of the current-collecting foil 12 without a conductive adhesive layer can be provided as a current-conducting section electrically connected to an external structure of the battery.

[0056] Figure 2 This 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 current collector foil 10 with the conductive adhesive layer described above, a positive electrode 20, and a separation layer 30. The secondary battery 100 is an anode-free battery without a negative electrode active material layer.

[0057] The negative current collector 10A is a laminate of a conductive adhesive layer 11A and a current collector foil 12A, obtained by cutting the aforementioned current collector foil 10 with the conductive adhesive layer. The negative current collector 10A is attached to the release layer 30 via the conductive adhesive layer 11A.

[0058] The positive electrode 20 has a positive electrode active material layer 21 and a current collector 22. The positive electrode 20 is formed by stacking the positive electrode active material layer 21 and the separation layer 30 in a manner in which they are placed opposite each other.

[0059] The positive electrode active material layer 21 has a known positive electrode active material, binder and conductive material used in lithium secondary batteries.

[0060] 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 (NCA) active material (LiNi) x Co y Al z O2), etc.

[0061] As a 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 single cell without an electrolyte, a solid electrolyte can be mixed into the positive electrode active material layer 21. The solid electrolyte can be a known solid electrolyte such as a sulfide-based solid electrolyte like Li2S-P2S5, an oxide-based solid electrolyte, or a polymer electrolyte.

[0062] The separation layer 30 is disposed between the negative current collector 10A and the positive electrode 20, separating the negative current collector 10A from the positive electrode 20. The separation layer 30 is sandwiched between the conductive adhesive layer 11A of the negative current collector 10A and the positive electrode 20, and allows the conductive adhesive layer 11A of the negative current collector 10A to adhere.

[0063] Examples of separation layer 30 include an ion-conducting separator disposed between the positive and negative electrodes in a lithium secondary battery using an electrolyte, and an electrolyte layer (solid electrolyte membrane) disposed 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. Separation layer 30 can be composed of multiple layers to function properly. Among these multiple layers, a metal layer formed based on metal foil or metal vapor deposition may be included. Additionally, some layers may have a current-collecting function.

[0064] Regarding the structure of the anodeless battery used in the secondary battery 100, a known structure may be appropriately adopted.

[0065] The negative electrode current collector 10A can be easily formed by cutting the current collector foil 10 with a conductive adhesive layer as raw material. Furthermore, the resulting negative electrode current collector 10A is bonded to the separator 30 via the conductive adhesive layer 11A, thereby easily forming a laminated structure of the negative electrode current collector 10A and the separator 30. Therefore, by using the negative electrode current collector 10A, a secondary battery 100 as an anode-free battery can be easily manufactured.

[0066] It is presumed that when the obtained anode-free battery, i.e., secondary battery 100, is charged, metallic lithium is deposited near the interface between the conductive adhesive layer 11A and the separation layer 30 of the negative electrode current collector 10A, forming a lithium deposition layer (not shown).

[0067] Furthermore, the metallic lithium constituting the lithium deposition layer releases electrons by discharging the secondary battery 100, becoming lithium ions and remaining in the positive electrode active material layer 21. As a result, the lithium deposition layer is reduced or disappears.

[0068] As described above, when the lithium deposited layer in the secondary battery 100 is repeatedly formed and disappeared through charging and discharging, volume changes occur along with the formation and reduction of the lithium deposited layer. Therefore, the conductive adhesive layer 11A of the negative electrode current collector 10A is subjected to internal stress accompanying the formation and reduction of the lithium deposited layer.

[0069] Furthermore, in the secondary battery 100, the negative electrode current collector 10A is adhered to the separation layer 30 due to the adhesive force of the conductive adhesive layer 11A. Therefore, when a lithium deposition layer is deposited at the interface between the conductive adhesive layer 11A and the separation layer 30, there is a risk that the conductive adhesive layer 11A may peel off from the separation layer 30.

[0070] In order to address these changes that are expected to occur inside the battery during charging and discharging, the inventors believe that it is crucial that the conductive adhesive layer 11A possesses the following physical properties: (a) moderate flexibility that allows for volume changes accompanying the formation and disappearance of the lithium deposited layer without excessive deformation; and (b) maintaining the adhesive force between the conductive adhesive layer 11A and the separation layer 30 even if a lithium deposited layer is formed.

[0071] Based on the above concept, the inventors conducted in-depth research and found that by fabricating a current collector foil with a conductive adhesive layer having the structure described above, a preferred current collector foil 10 with a conductive adhesive layer that combines the physical properties of (a) and (b) above can be fabricated. That is, it was found that when the current collector foil 10 with a conductive adhesive layer having the conductive adhesive layer 11 of the above structure is used in the secondary battery 100, cycle life is easily maintained even with repeated charging and discharging.

[0072] In this specification, by evaluating (1) and (2) below, it can be confirmed that the current collector foil 10 with conductive adhesive layer has both the physical properties of (a) and (b) above.

[0073] (1) Effusion test

[0074] In the effusion test using condition 1 below, no serious effusion was detected.

[0075] (Condition 1)

[0076] The following laminate was fabricated: multiple sheets of the conductive adhesive layer of the current collector foil were stacked to a thickness of 300 μm. The laminate was then clamped between the current collector foil and the release film. The resulting laminate was punched into a circular plate with a diameter of 10 mm to prepare a test piece.

[0077] The obtained test piece was clamped between a pair of 25 μm thick, light-transmitting polyester films, and a weight was placed on the polyester films to apply a pressure of 4.5 psi (where 1 psi = 6.89476 kPa) for 5 minutes.

[0078] Remove the weights and observe the condition from above through the polyester film. Measure the area of ​​the conductive adhesive layer seeping from the current-collecting foil constituting the laminate using a microscope. A result meeting either (i) or (ii) below is considered acceptable.

[0079] (i) No conductive adhesive layer seeps out when viewed from above.

[0080] (ii) The area of ​​the conductive adhesive layer seeping from the current collector foil is less than 15% of the top-view area of ​​the test piece before the test.

[0081] It should be noted that the 4.5psi test pressure is set with reference to the constraint pressure of a typical automotive battery.

[0082] (2) Peel test

[0083] The peel strength obtained in the peel test based on the following condition 2 is ≥1.0 N / mm.

[0084] (Condition 2)

[0085] Three test pieces were prepared by cutting the current collector foil with a conductive adhesive layer into 15mm strips. The conductive adhesive of the test pieces was then attached to an SUS304 board that had been cleaned with ethanol. During attachment, a 2kg rubber roller was used to apply pressure by reciprocating the roller once to ensure a tight seal.

[0086] Subsequently, with the ends of the current collector foil with the conductive adhesive layer protected by paper, the foil was fixed in place using the sample gripper of a tensile testing machine. A peel of 100 mm was achieved at a peel speed of 300 mm / min and a peel angle of 180°, and the peel strength was measured. The arithmetic mean of the peel strengths measured for each of the three test pieces was used as the peel strength (N / mm).

[0087] The conductive adhesive layer 11A (conductive adhesive layer 11) that satisfies the above (1) becomes an adhesive layer with moderate flexibility without being too soft. Therefore, for example, when the secondary battery uses a negative electrode current collector made of current collector foil 10 with conductive adhesive layer, the negative electrode current collector will not be excessively compressed due to external stresses applied to the secondary battery (e.g., constraint stress when stacking secondary batteries (single cells)). Therefore, such a secondary battery can easily follow the deformation that accompanies the deposition and disappearance of metallic lithium during charging and discharging, thereby suppressing breakage.

[0088] Even if a lithium deposition layer is formed, the conductive adhesive layer 11A (conductive adhesive layer 11) that satisfies the above (2) can maintain good adhesion between the conductive adhesive layer 11A and the separation layer 30.

[0089] The structure of forming a resin film called a base layer on the surface of the current collector foil is known (e.g., WO2009 / 147989). The known base layer is used as a protective coating for the current collector foil and does not have the adhesive strength to adhere to adjacent layers as the conductive adhesive layer 11A (conductive adhesive layer 11) described above. Therefore, the known base layer does not have a matrix containing polyisobutylene-based adhesives or acrylic adhesives as the conductive adhesive layer 11A (conductive adhesive layer 11) of this embodiment, and can be said to be a completely different structure that does not satisfy (1) and (2) above.

[0090] [Manufacturing method of current collector foil with conductive adhesive layer]

[0091] A current collector foil with a conductive adhesive layer can be manufactured by applying a coating obtained by dissolving or dispersing the material of the conductive adhesive layer in a solvent onto the current collector foil and then removing the solvent.

[0092] The solvent used must be one that can dissolve the adhesive resin. Examples of solvents include hydrocarbon solvents, alcohol solvents, ether solvents, ketone solvents, ester solvents, amide solvents, halogen solvents, sulfur solvents, and inorganic solvents.

[0093] Examples of hydrocarbon solvents include heptane, cyclohexane, toluene, and xylene.

[0094] Examples of alcohol-based solvents include methanol and ethanol.

[0095] Examples of ether-based solvents include tetrahydrofuran and dioxane.

[0096] Examples of ketone solvents include acetone and methyl ethyl ketone.

[0097] Examples of ester-based solvents include ethyl acetate and ethyl lactate.

[0098] Examples of amide solvents include dimethylformamide and N-methyl-2-pyrrolidone.

[0099] Examples of halogen-based solvents include chloroform and dichloromethane.

[0100] Examples of sulfur-based solvents include dimethyl sulfoxide and sulfolane.

[0101] As an inorganic solvent, it can be used to extract water.

[0102] The solvents mentioned above can be used alone or in combination of two or more solvents.

[0103] There are no particular limitations on the method of preparing coatings. As long as one or more of the adhesive, conductive material and any added additives are mixed with the solvent at the same time and dissolved or dispersed in the solvent, the coating can be prepared.

[0104] There are no restrictions on the order in which solid components (binders, conductive materials, and any other additives) are added relative to solvents.

[0105] Solvents can be added after the coating is prepared to adjust the viscosity of the coating.

[0106] The state of a coating can be adjusted through processes such as defoaming and filtration. Additives such as defoamers, viscosity modifiers, thickeners, diluents, surfactants, and stabilizers can be added to the coating. These additives can be commonly used substances.

[0107] There are no particular limitations on the methods of applying coatings; examples include scraper coating, dip coating, spray coating, gravure coating, rod coating, and mold coating.

[0108] A current-collecting foil with a conductive adhesive layer can be formed by removing the solvent from the coating film created by applying the coating material. The solvent can be removed by heating, depressurization, air supply, and combinations thereof.

[0109] When using long strip-shaped current collector foil, the current collector foil with a conductive adhesive layer can be rolled into a roll for storage and transportation, or it can be further slit to produce multiple sheet-shaped current collector foils with a conductive adhesive layer.

[0110] This yields a current collector foil with a conductive adhesive layer.

[0111] By using a current-collecting foil with a conductive adhesive layer having the structure described above and a negative electrode current collector to manufacture an anodeless battery (secondary battery), secondary batteries can be easily manufactured. Furthermore, the secondary battery with a negative electrode current collector, as described above, easily maintains cycle life and has high reliability even during charge-discharge cycles.

[0112] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to these examples. The shapes, combinations, etc. of the constituent components shown in the above examples are just examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

[0113] Example

[0114] The present invention will be described below using examples, but the present invention is not limited to these examples.

[0115] (Examples 1-7, Comparative Examples 1-4)

[0116] The materials used in the embodiments and comparative examples are shown below.

[0117] (Polyisobutylene)

[0118] PIB1: Tetrax 3T (Made with materials from ENEOS Co., Ltd., Mw41,000)

[0119] PIB2: Tetrax 6T (Made with materials from ENEOS Co., Ltd., Mw75,000)

[0120] PIB3: OPPANOL N50 (manufactured by BASF, Mw1,050,000)

[0121] PIB4: OPPANOL N80 (manufactured by BASF, Mw3,050,000)

[0122] PIB5: OPPANOL N150 (manufactured by BASF, Mw565,000)

[0123] The weight-average molecular weight (Mw) of each polyisobutylene was determined by gel permeation chromatography (GPC) and obtained by conversion to polystyrene. The GPC conditions were as follows.

[0124] (GPC conditions)

[0125] Column: Shodex LF-804 (manufactured by Showa Denko Corporation)

[0126] Solvent: Chloroform

[0127] Temperature: 40℃

[0128] PIB1 and PIB2 are equivalent to the first polyisobutylene in this invention, and PIB3, PIB4 and PIB5 are equivalent to the second polyisobutylene in this invention.

[0129] (Conductive materials)

[0130] Conductive carbon black: C-NERGY SUPER C65T (manufactured by Imerys)

[0131] (Current collector foil)

[0132] Cu foil

[0133] The adhesive was mixed at the ratios shown in Table 1 below to obtain a material solution. The resulting material solution was then mixed with a conductive material at the ratios shown in Table 1 to prepare a coating. Toluene was then added to adjust the viscosity.

[0134] The slurry was degassed and passed through a sieve with a pore size of 100 μm to obtain the coatings of the examples and comparative examples.

[0135] The obtained coating was applied to the current collector foil using a coating machine, resulting in a coating thickness of 5 μm after drying. After coating, the foil was placed in an intermittent dryer for 5 minutes to allow it to dry completely, thus obtaining the current collector.

[0136] [Table 1]

[0137]

[0138] (Evaluation 1)

[0139] The degree of oozing of the obtained conductive adhesive layer was tested using the method described in "(1) Exudation Test" above. Cases in which no oozing could be confirmed or where the area increase was less than 15% were considered acceptable, while cases in which there was oozing and the area increase was more than 15% were considered unacceptable.

[0140] (Evaluation 2)

[0141] The peel strength of the obtained conductive adhesive layer was tested using the method described in "(2) Peel Test" above. A peel strength of 1.0 N / mm or higher was considered acceptable, and a peel strength of less than 1.0 N / mm was considered unacceptable.

[0142] The evaluation results are shown in Table 2. If both Evaluation 1 and Evaluation 2 are satisfactory, the overall evaluation is considered satisfactory. In Table 2, satisfactory is recorded as A, and unsatisfactory is recorded as B.

[0143] [Table 2]

[0144] Rating 1 Rating 2 Overall evaluation Example 1 A A A Example 2 A A A Example 3 A A A Example 4 A A A Example 5 A A A Example 6 A A A Example 7 A A A Comparative Example 1 B A B Comparative Example 2 A B B Comparative Example 3 A B B Comparative Example 4 A B B

[0145] The evaluation results indicate that the current collector foils with conductive adhesive layers in Examples 1-7 possess both: (a) moderate flexibility that allows for volume changes accompanying the formation and disappearance of lithium deposits without excessive deformation, and (b) adhesive strength that maintains a tight bond between the conductive adhesive layer and the separation layer even when lithium deposits are formed. In secondary batteries using current collector foils with such conductive adhesive layers, it is expected that cycle life will be easily maintained.

[0146] In contrast, in Comparative Example 1, it failed in (Evaluation 1). Therefore, the current collector foil with a conductive adhesive layer in Comparative Example 1 can be evaluated as being too soft for the purposes of the invention.

[0147] Furthermore, in Comparative Examples 2-4, (Evaluation 2) the results were deemed unacceptable. It was determined that the current collector foil with a conductive adhesive layer, exhibiting excessively low peel strength in Evaluation 2, failed to follow the separation layer during volume changes due to the increase or decrease in lithium during charging and discharging, resulting in uneven reaction. Therefore, the current collector foils with conductive adhesive layers in Comparative Examples 2-4 are at risk of interfacial peeling 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, and can be evaluated as having difficulty maintaining cycle characteristics.

[0148] It should be noted that the negative electrode current collectors were fabricated using the current collector foils with conductive adhesive layers from the embodiments and comparative examples. Cyclic performance of secondary batteries equipped with these negative electrode current collectors was evaluated, and the results confirmed that the secondary batteries from the embodiments exhibited better cycle performance than the secondary batteries from the comparative examples. Specifically, the secondary battery using the current collector foil with conductive adhesive layer from Example 3...

[0149] When the negative current collector is made of foil, it exhibits the best cycle performance.

[0150] The results above show that the present invention is useful.

Claims

1. A current collector foil with a conductive adhesive layer, comprising: Current collector foil; and A conductive adhesive layer is disposed on one side of the current-collecting foil. The conductive adhesive layer has a matrix comprising at least a polyisobutylene-based adhesive and a conductive material dispersed in the matrix, comprising 85% to 95% by mass of the matrix and 5% to 15% by mass of the conductive material relative to the total mass of the conductive adhesive layer. The matrix comprises the polyisobutylene-based adhesive. The polyisobutylene-based adhesive comprises a first polyisobutylene and a second polyisobutylene. The first polyisobutylene has a weight-average molecular weight of 30,000 or more and 200,000 or less. The second polyisobutylene has a weight-average molecular weight of 500,000 or more and 5,000,000 or less. The conductive adhesive layer comprises, relative to its total mass, 35% to 85% by mass of the first polyisobutylene and 5% to 60% by mass of the second polyisobutylene.

2. The current collector foil with a conductive adhesive layer according to claim 1, wherein, The thickness of the conductive adhesive layer is greater than 2 μm and less than 30 μm.

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

5. The current collector foil with a conductive adhesive layer according to claim 1 or 2, wherein, A release film is formed on the surface of the conductive adhesive layer.

6. A negative current collector, using the current collector foil with a conductive adhesive layer as described in claim 1 or 2 as the material.

7. A secondary battery, comprising: The negative current collector as described in claim 6; Positive electrode; and A separation layer is sandwiched between the conductive adhesive layer of the negative current collector and the positive electrode, and provides a place for the conductive adhesive layer of the negative current collector to adhere. The separation layer is a diaphragm or a solid electrolyte membrane.

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