JP5958140B2 - Clad foil, battery active material current collector using the same, and method for producing negative electrode current collector of lithium ion secondary battery - Google Patents

Description

  The present invention relates to a clad foil suitable for a battery active material current collector of a secondary battery such as a lithium ion secondary battery, a battery active material current collector using the same, and a negative electrode current collector of a lithium ion secondary battery. The present invention relates to a method of manufacturing an electric body.

  With the spread of medium- and large-sized batteries for mobile objects such as hybrid EV cars, plug-in hybrid EV cars, and pure EV cars, stationary medium and large-sized batteries for distributed power supplies, and portable information terminals, mobile phones, and notebook computers Demand for high-capacity secondary batteries is growing. Among secondary batteries, lithium ion secondary batteries, whose lithium ions in the electrolyte are responsible for electrical conduction, are used in many fields because of their light weight and high energy density, and the market scale is expected to grow further in the future. ing.

A lithium ion secondary battery uses a foil strip coated with an active material as an electrode plate. Generally, the positive electrode is made of aluminum foil coated with a compound such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , and the negative electrode is made of graphitic carbon, hard carbon, Si-based alloy, Sn-based. In many cases, an alloy, Li ₄ Ti ₅ O ₁₂ and a mixture thereof are applied as active materials to copper foil or copper alloy foil.

  The copper foil or copper alloy foil used for the negative electrode is a material that is extremely excellent in terms of electrical conductivity and corrosion resistance (corrosion resistance by an electrolytic solution or the like). Since the electrical conductivity of copper foil or copper alloy foil in the vicinity of room temperature is the second highest after that of silver and has low resistance, heat loss during energization is small. For this reason, the negative electrode which consists of copper foil or copper alloy foil has the big merit of low loss and low heat_generation | fever for the use which handles a large current.

  Copper foil includes electrolytic copper foil produced by electrolysis and rolled copper foil that finishes an ingot obtained by casting into a foil strip by rolling. In the manufacturing process of the rolled copper foil, after the ingot is hot-rolled, cold rolling and annealing are repeated to finish to a predetermined thickness of about 7 to 35 μm. The rolled copper foil is superior to the electrolytic copper foil in that a high strength exceeding 400 MPa can be imparted by performing temper rolling that finishes while leaving distortion in cold rolling.

  Generally, the negative electrode of a lithium ion secondary battery is manufactured through processes shown as (1) to (4) below.

  (1) A conductive additive is added to an active material (graphitic carbon, Si-based alloy, Sn-based alloy, etc.) as necessary, mixed with a binder, and a paste kneaded and dispersed in a solvent is mixed with a current collector. This is applied to the surface of the copper foil to be a base material for the negative electrode plate material.

  (2) In order to bind the active material to the copper foil, heating is performed at a temperature of 120 to 350 ° C. for several hours to several tens of hours. The heating atmosphere may be an inert gas atmosphere in order to prevent copper foil oxidation and alloy negative electrode oxidation. In the case of an alloy-based negative electrode, an imide-based or polyamide-imide-based binder having a high binding force may be used. In this case, the heating temperature tends to be higher than the recrystallization temperature of pure Cu, 250 ° C.

  (3) When necessary, pressurization is performed with a roll press or the like to enhance the binding property and finish to a predetermined electrode plate thickness.

  (4) A predetermined negative electrode shape is finished by cutting with shearing and slitting with a slitter.

  In the conventional rolled copper foil, the copper foil recrystallizes during the heating process (2), and the strength of the copper foil is reduced. If the strength of the copper foil is reduced, the following problems may occur.

  (A) A negative electrode active material (especially alloy type) breaks through the copper foil during pressurization by a roll press or the like. After the battery configuration, the protruding active material may penetrate the separator and cause a short circuit with the positive electrode.

  (B) Although tension (tension) is applied in the negative electrode winding and winding process in the battery manufacturing process, the copper foil whose strength has been reduced by recrystallization may cause foil breakage.

  (C) The negative electrode active material of the lithium ion secondary battery expands in volume with charge and decreases in volume due to discharge. The copper foil is subjected to mechanical repeated stress due to repeated charging and discharging. The copper foil softened by recrystallization is easily deformed, so that the active material mixed with the binder and applied easily falls off the copper foil.

  Further, when the copper foil is heated, there is a problem that the negative electrode active material formed by oxidizing and binding the copper foil surface easily falls off due to the influence of oxygen remaining in the atmosphere.

  For this reason, there is a need for a copper foil that has high tensile strength after the final temper rolling and that does not recrystallize or soften in the drying / heating step and that is difficult to oxidize. In order to solve these problems, a rolled copper foil made of a copper alloy instead of a rolled copper foil made of pure copper has been proposed.

  In Patent Document 1, a copper material containing 0.01 to 0.20% by mass of Zr with the balance being Cu and inevitable impurities is rolled, and the copper foil obtained by the rolling is, for example, 450 ° C. By carrying out the heat treatment for 4 hours, it has an appropriate elongation even before the heat treatment during electrode production, can maintain a tensile strength of 300 MPa or more after being subjected to the heat treatment, and is 80% or more of pure copper. A rolled copper foil for a secondary battery negative electrode current collector having electrical conductivity is disclosed.

  Non-Patent Document 1 includes Cr: 0.20 to 0.30 mass%, Sn: 0.23 to 0.27 mass%, and Zn: 0.18 to 0 together with the rolled copper foil disclosed in Patent Document 1. A rolled copper foil (product number: HCL-64T) for a lithium ion secondary battery that contains .26 mass% and has a strength of 500 MPa even when heated to 400 ° C. after rolling is disclosed.

  Patent Document 2 discloses a copper foil for a current collector for a lithium ion secondary battery in which the surface of the copper foil is subjected to rust prevention treatment by silane coupling treatment. However, Patent Document 2 describes that the copper foil discolors when heated to 150 ° C. or higher, and the upper limit of the heating temperature of the current collector copper foil disclosed in Patent Document 2 is considered to be about 150 ° C. It is done.

  Although using copper alloy-based rolled foil as described above, recrystallization occurs in the heating and drying process, and various problems caused by softening of the material are being solved, the foil during the high temperature heating and drying process The present situation is that the essential solution with respect to the problem which arises from the oxidation of the surface is not established.

JP 2003-217595 A JP 2011-23303 A

Hitachi Cable Catalog “CAT. NO. C300B Hitachi Rolled Copper Foil "

  An object of the present invention is to provide a current collector foil material having two characteristics I and II listed below.

(I) The strength reduction is small in the heating process at the time of electrode manufacture When tension is applied in the negative electrode winding / winding process of the battery manufacturing process, which occurs due to the strength reduction of the current collector foil This is to solve the problems that the copper foil is cut off due to a decrease in strength and that the negative electrode active material (particularly the alloy system) breaks through the copper foil due to softening when pressed by a roll press or the like.

(II) In order to solve the phenomenon that the formation of an oxide film on the electrode surface reduces the adhesion of the active material and the active material is easily peeled off during the heating process during electrode production. is there.

  So far, although proposals have been made to individually provide the current collector foil materials with the above-mentioned properties, no means for simultaneously solving them has been proposed.

The present invention is listed below.
(1) It has a three-layer structure consisting of a base layer made of Cu or Cu alloy and a surface layer made of Ni or Ni alloy formed by clad on both surfaces of the base layer, and has a tensile strength at room temperature of 485 MPa or more and 586 MPa A clad foil strip for a negative electrode for a battery, characterized in that the tensile strength after holding at 450 ° C. for 4 hours is 300 MPa or more and 474 MPa or less and the total thickness is 35 μm or less.

(2) It has a three-layer structure consisting of a base layer made of Cu or Cu alloy and a surface layer made of Ni or Ni alloy formed by clad on both sides of the base layer, and has a tensile strength at room temperature of 485 MPa or more and 586 MPa A clad foil strip for a negative electrode for a battery, having the following strength, a tensile strength after holding at 450 ° C. for 4 hours: 400 MPa to 474 MPa, and a total thickness of 35 μm or less .

(3) The ratio of the thickness of the base layer made of Cu or Cu alloy to the total thickness is 68% or more and 90% or less, and the conductivity is 80% or more and 83% or less of IACS or (1) The clad foil strip described in the item (2).

(4) Any one of items (1) to (3) manufactured by hot rolling, strain relief annealing, and cold rolling with a reduction rate of 90% or more after this strain relief annealing. The manufacturing method of the clad foil strip described in the item.

(5) The method for producing a clad foil strip according to (4), which is produced by annealing at 400 ° C. to 500 ° C. after the cold rolling.

(6) The clad foil strip described in any one of the items (1) to ( 3 ), and a coating film containing an active material formed on the surface of the clad foil strip A method for producing a battery active material current collector.

(7) A coating film containing an active material is formed on the surface of the clad foil strip described in any one of items (1) to ( 3 ), and then heated to a temperature of 120 to 350 ° C. And processing to a predetermined shape after pressurizing to a predetermined thickness, and a method for producing a negative electrode current collector of a lithium ion secondary battery.

  “Clad” in the present invention means that a base layer made of Cu or Cu alloy and a surface layer made of Ni or Ni alloy are bonded together, and the boundary surface between these base layers and the surface layer is diffusion-bonded (has an alloy layer). means.

  The clad foil strip for collecting the active material for a battery according to the present invention covers the surface of pure copper or copper alloy with Ni metal, specifically, it is not a state obtained by plating or surface treatment, but hot working As a result, the Ni and Cu coating layers diffused together, and the Ni coating layer on the surface is a clad foil body with a thickness that contributes to increasing the strength of the material. The above-mentioned two problems that could not be achieved, that is, the decrease in strength in the heating process during electrode manufacturing is small, and the decrease in the adhesion of the active material due to oxidation of the electrode surface in the heating process during electrode manufacturing can be prevented become.

  Under the most appropriate conditions, a clad foil strip having a tensile strength at room temperature of 485 MPa or more, a strength of 400 MPa even after heat treatment at 450 ° C. for 4 hours, and a conductivity of 80% or more of IACS is obtained. Can be provided.

  High-capacity type electrode manufactured using a polyamide-imide-based binder that obtains high binding properties at high temperatures by applying the clad foil strip according to the present invention to a negative electrode current collector of a lithium ion secondary battery Occurrence of a problem that the negative electrode active material breaks through the negative electrode current collector when pressurizing with a roll press or the like can be prevented. In addition, it is possible to prevent the problem that the copper foil is torn due to the tension in the negative electrode winding and winding process of battery manufacture.

  By using the clad foil strip according to the present invention, it becomes possible to manufacture a high-capacity type using carbon and a high-capacity lithium ion secondary battery using an alloy-based negative electrode. This can contribute to longer battery driving time and longer mileage per charge of an electric vehicle.

It is explanatory drawing which shows an example of the manufacturing process of the clad foil strip which concerns on this invention in a model type. It is the cross-sectional observation photograph of Example number 8 observed and image | photographed in order to investigate the ratio for which a Cu layer or Cu alloy layer occupied to a cladding layer thickness.

1. Knowledge Based on the Present Invention The following new knowledge AD based on the present invention will be described.

(A) Antioxidation of the surface It is inevitable that the surface of the rolled foil of copper or copper alloy is oxidized by heating in the drying process. Therefore, it is effective to coat both surfaces of copper or copper alloy with another metal that has excellent oxidation resistance and does not cause an alloying reaction with Li.

  Metals suitable for coating are Ti, Ni, Co, Fe, and Cr because they are metals that do not alloy with Li, but high conductivity is required from the viewpoint of securing the high conductivity required for the negative electrode current collector foil. Co, Ni, etc. having a rate are suitable.

(B) Suppression of strength reduction If the metal covering the surface of the rolled foil of copper or copper alloy is a metal having a recrystallization temperature higher than 350 ° C., the strength of the rolled foil of copper or copper alloy coated with this metal Is determined by a composite rule of copper or copper alloy rolled foil and the metal covered, and by coating this metal, it is possible to suppress a decrease in strength even when heated to about 400 ° C. .

  That is, a metal suitable for coating is a metal that can maintain high strength without recrystallization when heated at about 400 ° C. after temper rolling.

(C) Bondability with Cu Metal coating is performed before cold rolling, and then the metal to be coated is work hardened in a process of cold rolling to increase the strength. In order to increase the strength, it is desirable to perform cold rolling with a high reduction ratio. In order to prevent the metal from peeling during cold rolling, it is effective that the interface between the metal to be coated and the rolled foil of copper or copper alloy is firmly fixed before cold rolling. For this reason, in order to promote strengthening of interfacial bonding in the pre-process for performing cold rolling, it is desirable to perform hot working for promoting bonding by diffusion.

  (D) Furthermore, considering the material cost, the recrystallization temperature of 400 ° C. or higher, and the bondability with the rolled foil made of copper or copper alloy, the optimum metal for coating the surface of the rolled foil made of copper or copper alloy is Ni and Ni alloy. Furthermore, Ni forms an alloy of a solid solution with Cu and there is no possibility that a brittle compound is generated at the interface. That is, there is little risk of peeling between the base layer made of Cu or Cu alloy and the surface layer made of Ni or Ni alloy formed by clad on both surfaces.

2. Clad foil strip according to the present invention The clad foil body according to the present invention is based on these novel findings A to D, and a base layer made of Cu or Cu alloy and Ni or clad formed on both surfaces of the base layer by clad. Since there are three layers consisting of a surface layer made of Ni alloy, these will be described.

(I) Coated metal species The conductivity of the metal not alloyed with Li described above is Co>Ni>Fe>Cr> Ti. Since the present invention is a current collector, it is desirable to use a material having a high conductivity, and Fe, Cr, Ti which is significantly inferior to copper is not desirable from the viewpoint of current collection efficiency. Organize from the perspective of material costs. The market price is Fe <Cr <Ni <Co <Ti, and Co and Ti cause a cost increase.

  Therefore, Ni and Ni alloy are used as the metal material for covering both surfaces of the base layer made of Cu or Cu alloy.

(II) Recrystallization temperature The recrystallization temperature of pure copper is 200 to 250 ° C. (machine / metal material for young engineers, page 63, Maruzen 1979). In a general manufacturing process of a negative electrode of a lithium ion secondary battery, recrystallization occurs when heated at a temperature of 120 ° C. to 400 ° C. for several hours to several tens of hours in order to bind the active material to the rolled copper foil. In some cases, the foil made of copper or a copper alloy may have problems such as elongation, breakage, and tearing of the foil.

  On the other hand, the recrystallization temperature is Fe; 350 to 500 ° C., Ni; 530 to 660 ° C., etc., and Ni has a recrystallization temperature exceeding 450 ° C. Therefore, from this point of view, Ni and Ni alloy are used as the metal material for covering both surfaces of the base layer made of Cu or Cu alloy.

(III) The ratio of the thickness of the base layer of Cu or Cu alloy to the total thickness The clad foil strip according to the present invention has been adopted internationally as a standard for IACS (internationally annealed copper standard) electrical resistance (or electrical conductivity) 80% or higher conductivity of annealed standard annealed copper (reference volume resistivity is defined as 100% of 1.7241 × 10 ⁻² μΩm, conductivity 58.0 × 10 ⁶ S / m) Have

  In order to achieve this conductivity, it is necessary to compensate the conductivity, which is decreased by the surface layer made of Ni or Ni alloy formed by the clad on both surfaces of the base layer made of Cu or Cu alloy, with pure Cu or Cu alloy of the base layer. is there. The proportion of pure Cu or Cu alloy necessary to achieve an IACS of 80% or more is 68% or more, preferably 70% or more, as a proportion of the thickness of the base layer of Cu or Cu alloy in the total thickness. is there.

  On the other hand, if the thickness of the base layer of Cu or Cu alloy exceeds 90%, a thin portion is generated due to the thickness variation of the surface layer after rolling, and the surface layer may be exposed to the surface by surface care during the manufacturing process. Since the significance of providing a surface layer made of Ni or Ni alloy is lost, the ratio of the thickness of the base layer of Cu or Cu alloy to the total thickness is preferably 90% or less.

(IV) Tensile strength at normal temperature The clad foil strip according to the present invention preferably has a surface layer made of Ni or Ni alloy formed by clad on both surfaces of a base layer made of Cu or Cu alloy of 90% or less. The tensile strength at room temperature has a strength of 485 MPa or more. Further, the lower limit of the base layer is desirably 68% or more, and more desirably 81% or less.

(V) Tensile strength after holding at 450 ° C. for 4 hours Since the clad foil strip according to the present invention has a surface layer made of Ni or Ni alloy formed by clad on both surfaces of a base layer made of Cu or Cu alloy, 450 When the tensile strength after holding at 4 ° C. for 4 hours is 300 MPa or more, the base layer is made of a Cu alloy, and the proportion of the base layer is 68% or more, it is 400 MPa or more.

(VI) Adhesiveness of active material The clad foil strip according to the present invention has a surface layer made of Ni or Ni alloy formed by clad on both surfaces of a base layer made of Cu or Cu alloy, and is heated on the surface during heating. Unlike Cu or Cu alloys that produce a Cu oxide layer that is easy to drop off, even when oxidized, it has a property that the generated oxide is difficult to drop off from the surface. Have sex.

  Note that “excellent adhesion of the active material” specifically means that the active material does not fall off in the process of assembling the battery using an electrode using a clad foil strip coated with the active material. In this invention, the case where it is hard to peel by a tape adhesive force in the tape peeling test described in the column of the Example mentioned later is evaluated as the outstanding adhesiveness.

(VII) Total thickness The total thickness defines an upper limit for constituting a high capacity battery. The electrode foil strip itself does not have a power storage function, and collects the electric energy stored in the active material during discharge, and distributes the electric energy applied from the outside of the battery to the active material during charging. In order to play a role, it is desirable to be as thin as possible. For the above reasons, the total thickness is 35 μm or less.

3. Manufacturing method of clad foil strip according to the present invention (I) Hot working FIG. 1 is an explanatory view showing an example of a manufacturing process of a clad foil strip according to the present invention in a model form.

  As shown in FIG. 1, when manufacturing a clad foil strip according to the present invention, a laminate 4 is formed by laminating Ni or Ni alloy foil strips 2 and 3 on both sides of a Cu or Cu alloy foil strip 1. The laminated body 4 is temporarily fixed by appropriate means. As temporary fixing, it is exemplified that beam welding is performed with Ni protection around the end face.

  Here, the clad foil body according to the present invention is formed by clad on both sides of the base layer of Cu or Cu alloy even in a temperature environment of 200 to 250 ° C. or higher, which is a temperature range where Cu or Cu alloy is recrystallized. Strength is ensured by the surface layer made of Ni or Ni alloy formed. For this purpose, it is effective that the interface between the foil strip 1 of Cu or Cu alloy and the foil strips 2 and 3 of Ni or Ni alloy has a sufficient bonding strength.

  In order to obtain sufficient bonding strength, no compound is formed at this interface, and Cu or Cu alloy elements and Ni or Ni alloy elements are interdiffused, and interface separation does not occur when handling as a current collector foil. It is necessary to provide an interdiffusion distance. However, since a sufficient diffusion distance cannot be obtained by the cold welding method, it is difficult to stably obtain a state in which the interfacial separation does not occur over the entire length of several kilometers or more of the foil coil.

  For this reason, when manufacturing the clad foil strip which concerns on this invention, it is desirable to hot-process the laminated body 4 temporarily fixed. Examples of such hot working include hot rolling after holding the laminated body at 850 ° C. for 1 hour.

  The rolling reduction of hot rolling is preferably about 40 to 60% so that the interface between the Cu or Cu alloy foil strip 1 and the Ni or Ni alloy foil strips 2 and 3 has a sufficient bonding strength. .

  The laminate 4 is made into a cold-rolled material 5 by this hot rolling. The thickness of the cold-rolled material 5 is exemplified by about 20 mm.

(II) Cold working After hot working, cold working is performed to obtain high strength. An example of cold working is cold rolling. By cold rolling, strain is accumulated in the cold-rolled material 5 and high strength can be obtained.

  As shown in FIG. 1, cold rolling and annealing (for example, 750 ° C. × 30 minutes) are repeated on the cold rolled material 5 to obtain a final cold rolled material having a thickness of about 100 to 200 μm, and the final cold rolled material is finished. Cold rolling is performed to obtain a clad foil strip according to the present invention having a desired thickness (for example, 15 μm).

  In order for the clad foil strip according to the present invention to obtain a desired strength, it is desirable that cold rolling is performed at a cold working rate of 90% or more. The processing rate specified here is the final cumulative cold working rate after applying strain relief annealing, and there is no restriction on the working pass schedule of cold working.

4). Method for producing negative electrode current collector of lithium ion secondary battery Addition of conductive additive to active material (graphitic carbon, Si alloy, Sn alloy, etc.) as necessary on the surface of the clad foil strip according to the present invention A paste mixed with a binder and kneaded and dispersed in a solvent is applied to the surface of a copper foil serving as a current collector to form a base material for a negative electrode plate. In this way, a coating film containing an active material is formed on the surface of the clad foil strip according to the present invention.

  Thereafter, in order to bind the active material, heating is performed at a temperature of 120 ° C. to 350 ° C. for several hours to several tens of hours.

  The heating atmosphere may be an inert gas atmosphere in order to prevent oxidation of the Cu or Cu alloy foil and oxidation of the alloy-based negative electrode. In the case of an alloy-based negative electrode, an imide-based or polyamide-imide-based binder having a high binding force may be used, and in this case, the heating temperature tends to increase.

  When softening occurs in this heat treatment process, defects (flatness, poor thickness accuracy, etc.) and foil breakage due to a change in the shape of the foil may occur. For this reason, when it is necessary to prevent a shape change, it is desirable to heat-process beforehand.

  It is effective that the preferred temperature for the heat treatment is 500 ° C. or less and is the same as or slightly higher than the heat treatment temperature. When the temperature of the heat treatment exceeds 500 ° C., it is possible to reach 530 ° C. to 660 ° C., which is a temperature at which Ni recrystallization of the surface layer made of Ni or Ni alloy formed by clad on both surfaces of the base layer made of Cu or Cu alloy starts. It is because there is sex.

  The upper limit of the heating temperature for promoting the binding of the active material is 350 ° C. When a polyamide-imide binder is used, it may be carried out at about 350 ° C. Therefore, in the present invention, it is necessary to ensure a temperature of 400 ° C. or higher. There is.

  Then, it pressurizes with a roll press etc. as needed, and finishes to predetermined plate | board thickness while improving binding property.

  Finally, the negative electrode current collector of the lithium ion secondary battery is manufactured by finishing it into a predetermined negative electrode shape by cutting with shearing and slitting with slitter.

In order to demonstrate the effects of the present invention, the following tests were conducted to evaluate the effects.
[Test conditions]
(A) Conventional material used in Examples Three types of rolled copper foil and copper alloy foil available in the market as high-strength negative electrode current collectors for lithium batteries were obtained and used as conventional materials A to C. A plate thickness of 15 μm was used. Table 1 shows conventional materials.

(B) Material of the present invention As shown in FIG. 1, a plate 1 (120 mm length × 100 mm width × 40 mm thickness) made of oxygen-free pure Cu (C1020), a plate 1 made of copper alloy C15150 (120 mm length × 100 mm width × 40 mm thick) and pure Ni (JIS NW2201) 1 (120 mm length × 100 mm width × tmm thickness) was prepared, and each bonded surface was polished with a stainless steel wire and degreased. A pure Cu / copper alloy plate 1 and a pure Ni plate 2 are laminated in the order of 120 mm long × 100 mm wide, and are clamped so that the bonded parts are not displaced in the horizontal direction. The laminated body 4 was produced by joining by electron beam welding.

  In this embodiment, electron beam welding in a vacuum is used. However, the present invention is not limited to this welding method. However, welding with consideration to reduce oxygen remaining at the interface between Ni and pure Cu or Cu alloy is necessary.

  Hereinafter, the plate | board thickness structure used for this invention is shown. Table 2 shows rolling base materials for obtaining the inventive materials D to I.

  The inventive materials D to I were all 20 mm thick by hot rolling after heating at 850 ° C. for 1 hour. Thereafter, cold rolling and intermediate annealing at 750 ° C. × 30 minutes were repeated to obtain 0.2 mm thickness and 0.1 mm thickness for all materials, and thereafter annealing was performed at 750 ° C. × 30 minutes. This material was cold-rolled to 15 μm to obtain a base material.

  A 0.2 mm (200 μm) and 0.1 mm (100 μm) thick material was cold rolled into a 15 μm thick clad foil strip and used in the examples.

(C) Strength Evaluation Method A 13B type test piece was taken in parallel with the rolling direction, and the tensile strength and elongation were measured according to JIS Z2241. The tensile speed was 25 mm / min.

(D) Measurement of conductivity The measurement was performed by a four-terminal method in accordance with JIS H 0505 (volume resistivity and conductivity measurement method of non-ferrous metal material) in an environment at a temperature of 22 ° C. ± 1 ° C.

Since the conductivity is expressed in IACS, the volume resistivity is 1.7241 × 10 ⁻² μΩm and the conductivity 58 × 10 ⁶ S / cm is 100%, which is expressed as a ratio (%) to this conductivity.

(E) Evaluation of active material adhesion The average amount of the natural graphite negative electrode active material of 10 μm and the polyamideimide binder (trade name SOXR) manufactured by Nippon Kogyo Paper Industries Co., Ltd. The mixture was mixed to 5%, and 20% by weight of NMP (N-methylpyrrolidone) was further added to form a slurry.

  This slurry was applied to the current collecting foil having a thickness of 15 μm of Example, dried at 80 ° C. for 1 hour, then pressure-formed with a roller press, and this electrode was dried at 350 ° C. × 4 hours for evaluation. Electrode.

  This electrode was cut into a 20 mm square, cuts were formed in a grid pattern with a cutter, a commercially available adhesive tape (registered trademark cello tape) was applied, and a 2 kg weight roller was placed to reciprocate once to pressure-bond the adhesive tape. Next, the adhesive tape was peeled off, the surface of the negative electrode current collector was taken as an image into a personal computer, and the metallic luster portion and the black portion where the active material remained were discriminated by binarization, and the active material remaining amount was calculated.

A residual rate of 80% or more was judged as ◯, and less than 80% was judged as ×.
(F) Ratio of the thickness of the base layer of Cu or Cu alloy in the total thickness The material is hardened with an embedding resin, the L cross section is polished, observed with a microscope, and an average Cu layer thickness is covered from five photographs taken The average Ni thickness was determined. Since it is difficult to observe at the final finishing thickness of 15 μm, the Cu, Cu alloy ratio was calculated based on the observation results at the stage of 200 μm or 100 μm before the final cold rolling. FIG. 2 is a cross-sectional observation photograph of Example No. 8 observed and photographed to investigate the ratio of the Cu layer or Cu alloy layer to the cladding layer thickness.

(G) Examples The conventional material shown in Table 1 is a rolled copper foil in which the A material is oxygen-free copper, the B material is a material disclosed by Patent Document 1, and the C material is described in Non-Patent Document 1. Material. These were used as conventional materials and compared with the present invention. The results are shown in Table 3.

(H) Conventional material A common problem is that the adhesion of the negative electrode active material is not excellent. Since the surface oxidation (copper oxidation) of the current collector foil occurs in the drying step after applying the active material, even if a strong binder is used, the adhesion is inferior. In addition, the problems of the individual conventional materials A to C are as follows.

  Since Example No. 1 has a recrystallization temperature of 200 to 250 ° C., the tensile strength decreases to 145 MPa when heated to 450 ° C. When the current collector coated with the active material is heated to 350 ° C. in order to dry it, there is a concern that dimensional change or foil breakage may occur in subsequent handling.

  Example No. 2 has excellent electrical conductivity, but when heated to 450 ° C., the strength decreases to 300 MPa or less.

  Example No. 3 is a material with a small decrease in strength even when heated to 450 ° C., but its conductivity is 72% IACS, which is not superior to the present invention.

  In Example No. 5, pure Cu having a recrystallization temperature lower than 450 ° C. is used for the base layer, and the degree of work hardening is small because the finish cold working rate% is smaller than those in Example Nos. 4 and 6. The strength after heat treatment was below 300 MPa.

  In Example No. 16-18, 81% of pure Cu having a recrystallization temperature lower than 450 ° C. was used for the base layer, and Cu was recrystallized and softened during the heat treatment.

  In Example No. 20, since the finish cold working rate was smaller than that in Example Nos. 19 and 21, the degree of work hardening was small, and the strength after heat treatment was less than 300 MPa.

(I) Invention Material The material according to the present invention has high conductivity and high strength after 450 ° C. × 4 hours (assuming a drying step after applying the negative electrode active material).

  When Example Nos. 2 and 5 are compared, none of them satisfies the 300 MPa of the present invention, but Example No. 2 which is a conventional material is superior in terms of conductivity.

  On the other hand, although Example No. 4 is the same material as Example No. 5, it has a strength of 300 MPa or more even after heating at 450 ° C. for 4 hours and is superior to Example No. 2. The difference between Nos. 4 and 5 is due to the difference in the finishing cold working rate. Since the recrystallization temperature of Ni is 530 ° C. or higher, high strength can be maintained with little decrease in Ni strength.

  From the comparison of Example No. 4 and Example No. 5, it can be seen that it is desirable that a cold working rate of 90% or more is desired after the strain relief annealing in the present invention.

  After heating at 450 ° C. × 4 hours, it is Nos. 10-15, 19, and 21 of the present invention example numbers that have a strength of 400 MPa or more. The conductivity of these materials is 74% or more, and it can be seen that Example No. 3 (conventional material) has a strength-conductivity balance superior to that of strength 370 MPa and conductivity 72%.

  Examples Nos. 4, 6, 11-13, 16-19, and 21 have a conductivity of 80% or more among the materials of the present invention. These materials are materials in which the ratio of pure copper or copper alloy in the cladding intermediate layer is 68% or more. In the present invention, the ratio of the Cu layer thickness or the Cu alloy layer thickness is preferably 68% or more with respect to the cladding layer thickness.

  Further, a material having a conductivity of 80% or more and a strength of 400 MPa or more is a material having a history of a finish cold working rate of 90% or more.

  From the above, the clad foil strip according to the present invention is coated with Ni or Ni alloy having excellent corrosion resistance, and therefore has little surface oxidation in the drying step and excellent active material adhesion. Moreover, since the ratio of the thickness of the base layer of Cu or Cu alloy in the total thickness of the clad foil strip according to the present invention is 70% or more, it is subjected to 90% or more cold work after strain relief annealing. Furthermore, it has high strength even after heating at 450 ° C. for 4 hours.

1 Cu or Cu alloy foil strip 2, 3 Ni or Ni alloy foil strip 4 Laminate 5 Cold rolled material

Claims (7)

It has a three-layer structure consisting of a base layer made of Cu or Cu alloy and a surface layer made of Ni or Ni alloy formed by clad on both sides of the base layer, and the tensile strength at normal temperature is 485 MPa or more and 586 MPa or less A clad foil strip for a negative electrode for a battery, wherein the tensile strength after holding at 450 ° C. for 4 hours is from 300 MPa to 474 MPa and the total thickness is 35 μm or less. It has a three-layer structure consisting of a base layer made of Cu or Cu alloy and a surface layer made of Ni or Ni alloy formed by clad on both sides of the base layer, and has a tensile strength at normal temperature of 485 MPa or more and 586 MPa or less A clad foil strip for a negative electrode for a battery having a tensile strength after holding at 450 ° C. for 4 hours and a strength of 400 MPa to 474 MPa and a total thickness of 35 μm or less. The ratio of the thickness of the base layer made of Cu or Cu alloy to the total thickness is 70% or more and 90% or less, and the conductivity is 80% or more and 83% or less of IACS. The clad foil strip described.   It was manufactured by hot rolling, strain relief annealing, and cold rolling with a reduction rate of 90% or more after the strain relief annealing. A method for producing a clad foil strip.   The method for producing a clad foil strip according to claim 4, wherein the clad foil strip is produced by annealing at 400 ° C to 500 ° C after the cold rolling.   An active for a battery comprising: the clad foil strip according to any one of claims 1 to 3; and a coating film containing an active material formed on a surface of the clad foil strip. A method for producing a current collector.   A coating film containing an active material is formed on the surface of the clad foil strip according to any one of claims 1 to 3, and then heated to 120 to 350 ° C and pressurized. A method for producing a negative electrode current collector for a lithium ion secondary battery, wherein the negative electrode current collector is processed into a predetermined shape after having a predetermined thickness.