Electrode current collector for secondary batteries, and secondary battery

Abstract

This electrode current collector for secondary batteries includes a metal foil that contains aluminum. The elongation at break D1 of the metal foil at the tensile speed of 5.0 mm / min and the elongation at break D2 of the metal foil at the tensile speed of 0.1 mm / min satisfy the relational expression 1.3 ≤ D2 / D1, and the tensile strength T1 of the metal foil at the tensile speed of 5.0 mm / min and the tensile strength T2 of the metal foil at the tensile speed of 0.1 mm / min satisfy the relational expression 0.85 ≤ T2 / T1.

Description

Electrode current collector for secondary battery and secondary battery

[0001] The present disclosure relates to an electrode current collector for a secondary battery and a secondary battery.

[0002] The secondary battery includes, for example, an electrode group and an electrolyte. The electrode group is configured by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween. The negative electrode current collector is made of, for example, copper foil, and the positive electrode current collector is made of, for example, aluminum foil.

[0003] Patent Document 1 proposes "an electrolytic copper foil for a secondary battery, which is manufactured using a drum with a plating solution containing TOC, cobalt, and iron, and is coated with a cathode active material, wherein the ratio of TOC, cobalt, and iron contained in the electrolytic copper foil satisfies the following formula 1. Formula 1 is TOC / (cobalt + iron) = 1.3 to 1.5."

[0004] Special table 2019-536212 publication

[0005] Cracks or breaks in the aluminum foil used as the current collector may cause a decrease in the performance of the secondary battery.

[0006] One aspect of the present disclosure relates to an electrode current collector for a secondary battery, comprising a metal foil containing aluminum, wherein a breaking elongation D1 of the metal foil at a tensile speed of 5.0 mm / min and a breaking elongation D2 of the metal foil at a tensile speed of 0.1 mm / min satisfy the relationship of 1.3≦D2 / D1, and a tensile strength T1 of the metal foil at a tensile speed of 5.0 mm / min and a tensile strength T2 of the metal foil at a tensile speed of 0.1 mm / min satisfy the relationship of 0.85≦T2 / T1.

[0007] Another aspect of the present disclosure relates to a secondary battery including: an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on both sides of the positive electrode current collector, and the positive electrode current collector of the positive electrode is the above-mentioned electrode current collector for a secondary battery.

[0008] According to the present disclosure, it is possible to suppress deterioration in performance of a secondary battery.

[0009] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] 1 is a schematic perspective view of a secondary battery according to an embodiment of the present disclosure, with a portion cut away;

[0011] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0012] (Secondary Battery Electrode Current Collector) An electrode current collector for a secondary battery according to an embodiment of the present disclosure includes a metal foil containing aluminum (Al) (hereinafter also referred to as an "Al-containing foil"). The Al-containing foil satisfies the following conditions (i) and (ii). The Al-containing foil here refers to a foil containing Al as a main component, with an Al content of 98 mass% or more.

[0013] (i) The breaking elongation D1 of the metal foil at a pulling speed of 5.0 mm / min and the breaking elongation D2 of the metal foil at a pulling speed of 0.1 mm / min satisfy the relationship of 1.3≦D2 / D1. (ii) The tensile strength T1 of the metal foil at a pulling speed of 5.0 mm / min and the tensile strength T2 of the metal foil at a pulling speed of 0.1 mm / min satisfy the relationship of 0.85≦T2 / T1.

[0014] When the conditions (i) and (ii) are satisfied, breakage or cracking (hereinafter also referred to as "breakage, etc.") of the electrode current collector can be suppressed both during battery production and during battery use, and deterioration of secondary battery performance (such as a decrease in initial capacity and a decrease in cycle characteristics) due to breakage, etc. of the electrode current collector can be suppressed.

[0015] Cracks may occur in the Al-containing foil during charge and discharge, resulting in a deterioration in charge and discharge characteristics. To prevent cracks, it is conceivable to use an Al-containing foil with high tensile strength, but this may result in a decrease in the elongation at break (ductility), which may lead to breakage during battery production. The tensile strength and the elongation at break are in a relationship in which the elongation at break decreases (increases) as the tensile strength increases (decreases).

[0016] In order to ensure good battery performance, it is necessary to prevent breakage of the Al-containing foil both during battery production and during battery use (charge and discharge). During battery production, tensile stress is generated in the Al-containing foil during the electrode production process (transporting the Al-containing foil to an electrode slurry applicator, winding the produced electrode, etc.), the wound electrode group production process, etc. During use of a battery including a wound electrode group, tensile stress is generated in the wound Al-containing foil due to expansion and contraction of the electrode mixture layer during charge and discharge. The load rate applied to the Al-containing foil is 5 mm / min or less during battery production and 0.1 mm / min or less during battery use. In order to prevent breakage of the Al-containing foil both during battery production and battery use, constant tensile strength and breaking elongation are required for different load rates.

[0017] Based on the above findings, the present inventors conducted extensive research, focusing on the tensile strengths T1 and T2 and the elongation at break D1 and D2 at tension speeds of 5.0 mm / min and 0.1 mm / min. As a result, they newly discovered that when D2 / D1 is 1.3 or more and T2 / T1 is 0.85 or more, breakage of the Al-containing foil can be suppressed both during battery production and battery use. In this case, appropriate strength and elongation can be simultaneously ensured both during battery production and battery use.

[0018] If D2 / D1 is less than 1.3, a decrease in D2 and / or an increase in D1 (a decrease in T1) may cause breakage, etc. If T2 / T1 is less than 0.85, a decrease in T2 and / or an increase in T1 (a decrease in D1) may cause breakage, etc.

[0019] T2 / T1 may be 0.85 or more and 1.00 or less, and D2 / D1 may be 1.3 or more and 2.0 or less.

[0020] From the viewpoint of suppressing breakage of the Al-containing foil during battery production, the tensile strength T1 is preferably 150 MPa or more and 300 MPa or less. When the tensile strength T1 is 150 MPa or more, breakage of the Al-containing foil during electrode production is easily suppressed. When the tensile strength T1 is 300 MPa or less, breakage of the Al-containing foil during production of a wound electrode group is easily suppressed. From the same viewpoint, the breaking elongation D1 may be 2.0% or more, and is preferably 3.0% or more.

[0021] From the viewpoint of suppressing breakage of the Al-containing foil during charge and discharge, the tensile strength T2 may be 130 MPa or more and 300 MPa or less. From the same viewpoint, the breaking elongation D2 may be 2.5% or more, preferably 4.0% or more.

[0022] From the viewpoint of achieving a high energy density, the thickness of the Al-containing foil may be 30 μm or less, or may be 25 μm or less. From the viewpoint of ensuring strength, etc., the thickness of the Al-containing foil may be 5 μm or more. The thickness range of the Al-containing foil may be, for example, 5 μm or more and 30 μm or less, or 5 μm or more and 25 μm or less.

[0023] The Al-containing foil may be an Al metal foil or an Al alloy foil. The Al-containing foil may contain metals other than Al (e.g., Fe, Si, Mn, Cu, etc.). The content of metals other than Al is, for example, 1% by mass or less. The Al content in the Al-containing foil may be 99% by mass or more. Increasing the purity of Al can ensure the ductility of the Al-containing foil. The Al-containing foil may contain iron (Fe) and silicon (Si) as metals other than Al. In this case, the Al content in the Al-containing foil may be 98% by mass or more and less than 99% by mass, and the total content of Fe and Si in the Al-containing foil may be 1.20% by mass or more and 1.85% by mass or less. When the Al content is relatively low, the ductility of the Al-containing foil can be ensured by including Fe and Si.

[0024] (Elongation at break and tensile strength) The terms "elongation at break" and "tensile strength" used herein refer to the elongation at break (A) and tensile strength (Rm), respectively, determined by a tensile test in accordance with JIS Z 2241. The tensile speed is the crosshead displacement speed.

[0025] The elongation at break and tensile strength can be determined by a tensile test in accordance with JIS Z 2241. A rectangular test piece of a predetermined size is taken from the Al-containing foil for the tensile test. The size of the test piece is, for example, 120 mm in the longitudinal direction and 15 mm in the transverse direction. The test is performed in an environment of 25°C. The test piece is pulled in the longitudinal direction at a predetermined crosshead displacement rate, and the maximum stress until the test piece breaks is determined as the tensile strength.

[0026] Also, the gauge length before the test (original gauge length) Lo and the gauge length at the time of break (final gauge length after break) Lu are determined. The ratio (percentage) of the difference between the gauge length at the time of break and the gauge length before the test to the gauge length before the test is determined as the breaking elongation. That is, (Lu - Lo) / Lo x 100 is calculated as the breaking elongation (%).

[0027] In the above, the tensile strength T1 and the breaking elongation D1 are determined when the crosshead displacement rate is 5 mm / min, and the tensile strength T2 and the breaking elongation D2 are determined when the crosshead displacement rate is 0.1 mm / min. The test pieces are taken from several arbitrarily selected locations (e.g., 3 to 6 locations) on the Al-containing foil. D1, D2, T1, and T2 are each determined by averaging the measured values ​​of multiple test pieces.

[0028] (Secondary Battery) A secondary battery according to an embodiment of the present disclosure includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and an electrolyte. The electrode group is fabricated by spirally winding a strip-shaped positive electrode and a strip-shaped negative electrode with the separator interposed therebetween. The wound electrode group may be cylindrical, or may be flattened by compressing the cylindrical electrode group in the radial direction. The positive electrode includes a positive electrode current collector and positive electrode mixture layers supported on both sides of the positive electrode current collector. The positive electrode current collector is the above-described electrode current collector for a secondary battery. Use of the above-described electrode current collector for a secondary battery suppresses performance degradation of the secondary battery due to breakage of the positive electrode current collector, etc.

[0029] The amount of the positive electrode mixture layer carried on one side of the positive electrode current collector is 240 g / m ２ Above, 400g / m ２ It is preferable that the amount of the positive electrode mixture layer is less than or equal to 1000. When the amount of the positive electrode mixture layer is within the above range, a high capacity can be easily achieved. Furthermore, since the amount of the positive electrode mixture layer is large, a load is likely to be applied to the positive electrode current collector that is in close contact with the positive electrode mixture layer when the electrode is wound and when the battery is charged and discharged, and breakage or the like is likely to occur, the use of the above secondary battery electrode current collector significantly suppresses breakage or the like of the positive electrode current collector.

[0030] Secondary batteries include non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, lithium metal secondary batteries, and solid-state batteries containing gel electrolytes or solid electrolytes. That is, secondary batteries may be liquid-type secondary batteries containing an electrolytic solution as an electrolyte, or all-solid-state secondary batteries containing a solid electrolyte. Secondary batteries are described in detail below.

[0031] (Positive Electrode) The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The above-mentioned electrode current collector for secondary batteries can be used as the positive electrode current collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry, in which the positive electrode mixture is dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying it. The dried coating film may be rolled if necessary.

[0032] The positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a conductive agent, and the like as optional components.

[0033] The positive electrode active material can be a material capable of absorbing and releasing lithium ions, and known materials can be used. Examples of the positive electrode active material include composite oxides containing lithium and transition metals. Examples of such composite oxides include Li a CoO2, Li a NiO2, Li a MnO2, Li a Co b Ni 1-b O2, Li a Co 1-b M b O c , Li a Ni 1-b M b O c , Li a Mn2O4, Li a Mn 2-b M b Examples of the lithium-ion battery include Li2O4, LiMePO4, and Li2MePO4F. Here, M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Me contains at least a transition element (e.g., at least one selected from the group consisting of Mn, Fe, Co, and Ni). Here, 0≦a≦1.2, 0≦b≦0.9, and 2.0≦c≦2.3. The value a, which indicates the molar ratio of lithium, increases or decreases with charge and discharge.

[0034] Examples of binders include fluororesins, polyolefin resins, polyamide resins, polyimide resins, vinyl resins, styrene-butadiene copolymer rubber (SBR), polyacrylic acid and its derivatives, etc. Examples of fluororesins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, etc.

[0035] The conductive agent may be the same as those exemplified for the negative electrode. Graphite such as natural graphite or artificial graphite may also be used as the conductive agent.

[0036] (Negative Electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry, in which the negative electrode mixture is dispersed in a dispersion medium, to the surface of the negative electrode current collector and drying the applied layer. The dried coating may be rolled as necessary. The negative electrode may also include a negative electrode current collector and a lithium metal foil or lithium alloy foil supported on the surface of the negative electrode current collector.

[0037] The negative electrode mixture contains a negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, and the like as optional components.

[0038] Negative electrode active materials include materials capable of absorbing and releasing lithium ions, lithium metal, lithium alloys, etc. Materials capable of absorbing and releasing lithium ions include carbon materials, alloy-based materials, etc. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Of these, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity. Examples of alloy-based materials include those containing at least one metal capable of forming an alloy with lithium, such as silicon, tin, silicon alloys, tin alloys, and silicon compounds. Silicon oxides and tin oxides formed by bonding these with oxygen may also be used.

[0039] The silicon-containing alloy-based material may be a composite material comprising a lithium ion conductive phase and a silicon phase (silicon particles) dispersed in the lithium ion conductive phase. Examples of the lithium ion conductive phase include a silicon oxide phase, a silicate phase, and a carbon phase. The silicon oxide phase may be mainly composed of silicon dioxide (e.g., 95 to 100% by mass). A composite material in which the silicon oxide phase is mainly composed of silicon dioxide may be composed of SiO ｘ (0.5≦x≦1.6). The carbon phase may be composed of, for example, amorphous carbon with low crystallinity. The amorphous carbon may be, for example, hard carbon, soft carbon, or other. The composite material may be used together with a carbon material.

[0040] A silicate phase containing lithium (lithium silicate phase) is preferred because it has a small irreversible capacity and a high initial charge / discharge efficiency. The lithium silicate phase may be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may contain other elements. Examples of other elements include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al). The lithium silicate phase has the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). The lithium silicate phase may have a composition represented by Li ２ SiO ３ , Li ２ Si ２ O ５ etc.

[0041] Examples of the binder include those listed for the positive electrode. Examples of the conductive agent include carbon black, conductive fiber, carbon fluoride, and organic conductive materials. Examples of the thickener include carboxymethyl cellulose (CMC) and polyvinyl alcohol.

[0042] The negative electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0043] (Electrolyte) The electrolyte may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a salt dissolved in the non-aqueous solvent. The concentration of the salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0044] The gel electrolyte contains a salt and a matrix polymer, or a salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.

[0045] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.) can be used.

[0046] For example, a liquid non-aqueous electrolyte is prepared by dissolving a salt in a non-aqueous solvent. The salt is an electrolyte salt that ionizes in the electrolyte, and may include, for example, a lithium salt. The electrolyte may contain various additives. The electrolyte is usually used in its liquid state, but its fluidity may be restricted by a gelling agent or the like.

[0047] The solvent may be an aqueous solvent or a non-aqueous solvent. Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0048] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 Lithium salts that can be used include lithium salts of fluorine-containing acids (LiPF, LiPF0, LiBF, LiSbF, LiAsF, LiCFSO, LiCFCO, etc.), lithium salts of fluorine-containing acid imides (LiN(FSO), LiN(CFSO), LiN(CFSO)(CFSO), LiN(CFSO)), lithium halides (LiCl, LiBr, LiI, etc.). One type of lithium salt may be used alone, or two or more types may be used in combination.

[0049] The concentration of the lithium salt in the electrolyte may be 1 mol / L or more and 2 mol / L or less, or may be 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0050] (Separator) It is desirable to interpose a separator between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. As the separator, a microporous thin film, woven fabric, nonwoven fabric, etc. can be used. As the material of the separator, polyolefin such as polypropylene or polyethylene is preferred.

[0051] Examples of the structure of the secondary battery include, but are not limited to, a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is housed in an outer casing together with an electrolyte. The shape of the battery is also not limited, and may be, for example, a cylindrical type, a prismatic type, a laminate type, or the like.

[0052] Hereinafter, the structure of a prismatic secondary battery will be described as an example of a secondary battery according to the present disclosure with reference to FIG.

[0053] The battery includes a bottomed, rectangular battery case 4, and an electrode group 1 and an electrolyte (not shown) housed within the battery case 4. The electrode group 1 is composed of a long, strip-shaped negative electrode, a long, strip-shaped positive electrode, and a separator interposed between the positive and negative electrodes, wound together in a spiral shape. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. In other words, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an electrolyte injection hole, which is closed with a seal plug 8 after injection.

[0054] <<Appendix>> The above embodiments disclose the following technologies. (Technology 1) An electrode current collector for a secondary battery, comprising a metal foil containing aluminum, wherein the breaking elongation D1 of the metal foil at a pulling rate of 5.0 mm / min and the breaking elongation D2 of the metal foil at a pulling rate of 0.1 mm / min satisfy the relationship 1.3≦D2 / D1, and the tensile strength T1 of the metal foil at a pulling rate of 5.0 mm / min and the tensile strength T2 of the metal foil at a pulling rate of 0.1 mm / min satisfy the relationship 0.85≦T2 / T1. (Technology 2) The electrode current collector for a secondary battery according to Technology 1, wherein the tensile strength T1 of the metal foil is 150 MPa or more and 300 MPa or less. (Technology 3) The electrode current collector for a secondary battery according to Technology 1 or 2, wherein the thickness of the metal foil is 30 μm or less. (Technology 4) The electrode current collector for a secondary battery according to any one of Technologies 1 to 3, wherein the aluminum content in the metal foil is 99% by mass or more. (Technology 5) The electrode current collector for a secondary battery according to any one of Technologies 1 to 3, wherein the metal foil further contains iron and silicon, the aluminum content in the metal foil is 98% by mass or more and less than 99% by mass, and the total content of the iron and the silicon in the metal foil is 1.20% by mass or more and 1.85% by mass or less. (Technology 6) A secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode comprises a positive electrode current collector and positive electrode mixture layers supported on both sides of the positive electrode current collector, and the positive electrode current collector of the positive electrode is the electrode current collector for a secondary battery according to any one of Technologies 1 to 5. (Technology 7) The amount of the positive electrode mixture layer carried on one surface of the positive electrode current collector is 240 g / m ２ Above, 400g / m ２ The secondary battery according to Technology 6, which is as follows:

[0055] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0056] Secondary Batteries A1 to A4, B1 to B4 (Preparation of Positive Electrode) Lithium transition metal-containing composite oxide (LiNi ０．８ Co ０．１８ Al０．０２ O ２ To 95 parts by mass of the cellulose acetate copolymer, 2.5 parts by mass of acetylene black, 2.5 parts by mass of polyvinylidene fluoride, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were added and mixed to obtain a positive electrode slurry.

[0057] Next, the positive electrode slurry was applied to both sides of the positive electrode current collector, and the coating was dried and then rolled to form a positive electrode mixture layer, thereby obtaining a positive electrode.

[0058] A strip-shaped Al-containing foil was used as the positive electrode current collector. D2 / D1, T2 / T1, and T1 were set to the values ​​shown in Table 1. The thickness of the Al-containing foil was set to the value shown in Table 1. The tensile strength and breaking elongation were adjusted by changing the composition, thickness, etc. of the Al-containing foil.

[0059] The amount of the positive electrode mixture layer carried on one side of the positive electrode current collector is 240 g / m ２ Above, 400g / m ２ The range was as follows:

[0060] (Preparation of Negative Electrode) 97.5 parts by mass of the negative electrode active material was mixed with 1 part by mass of carboxymethyl cellulose Na salt (CMC-Na), 1.5 parts by mass of styrene butadiene rubber (SBR), and an appropriate amount of water to obtain a negative electrode slurry. The negative electrode active material used was a composite material containing Si and graphite. The mass ratio of the composite material to the graphite was 10:90. The composite material contained SiO ｘ (0.5≦x≦1.6) was used.

[0061] Next, the negative electrode slurry was applied to both sides of a copper foil serving as a negative electrode current collector, and the coating was dried and then rolled to form a negative electrode mixture layer, thereby obtaining a negative electrode.

[0062] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 3:7). ６ was dissolved in a solution at a concentration of 1.0 mol / L to obtain a non-aqueous electrolyte.

[0063] (Fabrication of Non-Aqueous Electrolyte Secondary Battery) An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. The positive electrode and negative electrode were spirally wound with a polyolefin separator interposed therebetween and then pressed radially to produce a flat electrode assembly. A polyolefin microporous film was used as the separator. The electrode assembly was housed in an exterior body made of an aluminum laminate sheet, and after injecting a non-aqueous electrolyte, the opening of the exterior body was sealed. At this time, a portion of the leads attached to the positive electrode and negative electrode were exposed from the exterior body. In Table 1, secondary batteries A1 to A4 are examples, and secondary batteries B1 to B4 are comparative examples.

[0064] (Charge-Discharge Cycle Test) A cycle test was carried out on each battery under the following charge-discharge conditions in an environment of 25° C. The rest period between charge and discharge was 10 minutes.

[0065] (Charging) The battery was charged at a constant current of 0.3 C until the voltage reached 4.2 V.

[0066] (Discharge) Constant current discharge was carried out at a current of 0.5 C until the voltage reached 2.85 V.

[0067] Charge and discharge were repeated up to 100 cycles under the above conditions, and the ratio (percentage) of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the capacity retention rate.

[0068] The evaluation results are shown in Table 1.

[0069]

[0070] The secondary batteries A1 to A4 had a higher capacity retention rate than the secondary batteries B1 to B4, but the secondary batteries B1 to B4 had a lower capacity retention rate due to cracks or breaks in the positive electrode current collector.

[0071] The secondary battery according to the present disclosure is useful as a main power source for mobile communication devices, electric vehicles, hybrid vehicles, portable electronic devices, and the like.

[0072] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0073] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug

Claims

1. An electrode collector for a secondary battery comprising a metal foil containing aluminum, wherein a breaking elongation D1 of the metal foil at a tensile speed of 5.0 mm / min and a breaking elongation D2 of the metal foil at a tensile speed of 0.1 mm / min satisfy a relationship of 1.3≦D2 / D1, and a tensile strength T1 of the metal foil at a tensile speed of 5.0 mm / min and a tensile strength T2 of the metal foil at a tensile speed of 0.1 mm / min satisfy a relationship of 0.85≦T2 / T1.

2. The electrode collector for a secondary battery according to claim 1, wherein the metal foil has a tensile strength T1 of 150 MPa or more and 300 MPa or less.

3. The electrode collector for a secondary battery according to claim 1, wherein the thickness of the metal foil is 30 μm or less.

4. The electrode collector for a secondary battery according to claim 1, wherein the content of said aluminum in said metal foil is 99 mass % or more.

5. An electrode collector for a secondary battery as described in claim 1, wherein the metal foil further contains iron and silicon, the aluminum content in the metal foil is 98 mass% or more and less than 99 mass%, and the total content of the iron and silicon in the metal foil is 1.20 mass% or more and 1.85 mass% or less.

6. A secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte; wherein the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer supported on both sides of the positive electrode current collector; and the positive electrode current collector of the positive electrode is the electrode current collector for a secondary battery according to claim 1.

7. The amount of the positive electrode mixture layer carried on one side of the positive electrode current collector is 240 g / m ２ Above, 400g / m ２ The secondary battery according to claim 6, wherein:

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