Secondary battery

Abstract

This secondary battery includes: an electrode group in which a positive electrode, a negative electrode, and a separator are wound; an electrolyte; a bottomed cylindrical outer can that accommodates the electrode group and the electrolyte; a sealing plate that is disposed in the opening of the outer can with an insulating gasket interposed therebetween; a positive electrode lead that connects the positive electrode and the sealing plate; and a negative electrode lead that connects the negative electrode and the outer can. The negative electrode includes a negative electrode current collector, and a negative electrode mixture layer supported on the negative electrode current collector. In the outermost periphery of the negative electrode, the negative electrode mixture layer faces the inner surface of the outer can, and the negative electrode lead is disposed further to the inner peripheral side than the positive electrode lead. When the radius of the electrode group is R, the positive electrode lead is disposed within a region whose distance in the radial direction from the winding axis of the electrode group is less than 0.9 R. In an external short circuit, a heat generation amount Q1 of the positive electrode lead and a heat generation amount Q2 of the negative electrode lead satisfy the relationship Q1 < Q2.

Description

secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-051882, filed on March 27, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a secondary battery including a wound electrode group.

[0003] The secondary battery includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, an electrolyte, a cylindrical outer can with a bottom that houses the electrode group and the electrolyte, a sealing plate that is placed at the opening of the outer can via an insulating gasket, a positive electrode lead that connects the positive electrode to the sealing plate, and a negative electrode lead that connects the negative electrode to the inner bottom surface of the outer can. The sealing plate also serves as a positive electrode terminal. The bottom of the outer can also serves as a negative electrode terminal.

[0004] Patent Document 1 describes a battery comprising: a positive electrode plate having a positive electrode mixture layer containing a positive electrode active material formed on a positive electrode current collector; a negative electrode plate having a negative electrode mixture layer containing a negative electrode active material formed on a negative electrode current collector; a separator; a non-aqueous electrolyte; an outer can; and a sealing body, the positive electrode plate and the negative electrode plate being wound together with the separator interposed therebetween; the positive electrode active material containing a lithium nickel composite oxide; and the lithium nickel composite oxide having a general formula Li ａ Ni ｂ Co ｃ Al ｄ O ２ (0<a≦1.2, 0.8≦b<1, 0<c<0.2, 0<d<0.05, b+c+d=1), the negative electrode active material contains graphite and a silicon material, the negative electrode plate has negative electrode current collector exposed portions at both ends in the longitudinal direction where the negative electrode active material layer is not formed, and a negative electrode tab is connected to each of the negative electrode current collector exposed portions.

[0005] International Publication No. 2016 / 136227

[0006] There is a demand for improved safety in the event of an external short circuit in a secondary battery.

[0007] One aspect of the present disclosure relates to a battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to an inner bottom surface of the outer can; the negative electrode mixture layer faces the inner surface of the outer can at the outermost periphery of the negative electrode, the negative electrode lead is arranged more inward than the positive electrode lead, and when a radius of the electrode group is R, the positive electrode lead is arranged in a region whose radial distance from a winding axis of the electrode group is less than 0.9R, and in the event of an external short circuit, a heat generation amount Q1 of the positive electrode lead and a heat generation amount Q2 of the negative electrode lead satisfy the relationship Q1<Q2.

[0008] Another aspect of the present disclosure relates to a battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to an inner bottom surface of the outer can; the negative electrode lead is disposed more inward than the positive electrode lead; and when a radius of the electrode group is R, the positive electrode lead is disposed in a region whose radial distance from a winding axis of the electrode group is less than 0.9R; and in the event of an external short circuit, a heat generation amount Q1 of the positive electrode lead, a heat generation amount Q2 of the negative electrode lead, and a heat generation amount Q3 of the negative electrode current collector exposed portion satisfy the relationships Q1<Q2 and Q3<Q2.

[0009] Yet another aspect of the present disclosure relates to a battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to an inner bottom surface of the outer can; the negative electrode lead has a first layer and a second layer disposed on at least a part of a surface of the first layer, the first layer containing a first metal element, and a resistivity ρa of the first metal element being equal to or greater than a resistivity of copper and smaller than a resistivity of nickel, the second layer containing a second metal element, and a resistivity ρb of the second metal element being equal to or greater than a resistivity of nickel, the negative electrode lead having a thickness of 60 μm or greater, and an area ratio of the second layer to a cross section of the negative electrode lead in the thickness direction is 51% or greater and less than 100%.

[0010] According to the present disclosure, the safety of a secondary battery in the event of an external short circuit can be improved.

[0011] 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.

[0012] Fig. 1 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; Fig. 2 is a top view schematically showing an example of a positive electrode of a secondary battery according to an embodiment of the present disclosure; Fig. 3 is a top view schematically showing an example of a negative electrode of a secondary battery according to an embodiment of the present disclosure; Fig. 4 is a top view schematically showing another example of a negative electrode of a secondary battery according to an embodiment of the present disclosure; Fig. 5 is a schematic top view of one end face of an electrode group as viewed from the direction of the winding axis.

[0013] Below, embodiments according to the present disclosure will be described 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 expression "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 numerical values ​​for specific physical properties or conditions are exemplified as lower and upper limits, 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.

[0014] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0015] The secondary battery includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, an electrolyte, a cylindrical outer can with a bottom that houses the electrode group and the electrolyte, a sealing plate that is placed at the opening of the outer can via an insulating gasket, a positive electrode lead that connects the positive electrode to the sealing plate, and a negative electrode lead that connects the negative electrode to the inner bottom surface of the outer can. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer carried on the surface of the negative electrode current collector. The inventors have conducted extensive research into secondary batteries with the above structure and have found that batteries X1 to X3 described below can suppress a temperature increase on the battery surface during an external short circuit.

[0016] In a secondary battery (battery X1) according to an embodiment of the present disclosure, the negative electrode mixture layer faces the inner surface of the outer can at the outermost periphery of the negative electrode. That is, the negative electrode does not have a negative electrode current collector exposed portion (described below) that contacts the inner surface of the outer can at the outermost periphery of the negative electrode. The negative electrode mixture layer that faces the inner surface of the outer can at the outermost periphery of the negative electrode may contact the inner surface of the outer can, or a separator may be interposed between the negative electrode mixture layer and the inner surface of the outer can. The negative electrode lead is disposed more inward than the positive electrode lead. When the radius of the electrode group is R, the positive electrode lead is disposed in a region where the radial distance from the winding axis of the electrode group is less than 0.9R. During an external short circuit, the heat generation amount Q1 of the positive electrode lead and the heat generation amount Q2 of the negative electrode lead satisfy the relationship Q1<Q2.

[0017] In this case, a temperature rise on the battery surface during an external short circuit can be suppressed, improving safety. In the secondary battery disclosed herein, the negative electrode lead, which generates a large amount of heat, is positioned more inward than the positive electrode lead to ensure a sufficient distance from the side surface of the outer can, and the amount of heat generated by the positive electrode lead, which is closer to the side surface of the outer can than the negative electrode lead, is made smaller than the amount of heat generated by the negative electrode lead, thereby suppressing a temperature rise on the side surface of the outer can during an external short circuit. In this case, the resistance of the entire cell can be reduced while suppressing a temperature rise on the side surface of the outer can during an external short circuit.

[0018] Q1 / Q2 may be 4 / 5 or less, or may be 1 / 3 or less.

[0019] In a secondary battery (battery X2) according to another embodiment of the present disclosure, the negative electrode has a negative electrode current collector exposed portion (hereinafter also referred to as a "second negative electrode current collector exposed portion") on at least a portion of the outermost periphery of the negative electrode, and the negative electrode current collector exposed portion is in contact with the inner surface of the outer can. The negative electrode lead is disposed more inward than the positive electrode lead. When the radius of the electrode group is R, the positive electrode lead is disposed in a region where the radial distance from the winding axis of the electrode group is less than 0.9R. During an external short circuit, the amount of heat generated by the positive electrode lead Q1, the amount of heat generated by the negative electrode lead Q2, and the amount of heat generated by the negative electrode current collector exposed portion Q3 satisfy the relationships Q1 < Q2 and Q3 < Q2. The amount of heat generated by the negative electrode current collector exposed portion Q3 is the amount of heat generated by the negative electrode current collector at the negative electrode current collector exposed portion.

[0020] In the secondary battery described in Patent Document 1, negative electrode tabs (leads) are connected to one longitudinal end (innermost circumferential side) and the other longitudinal end (outermost circumferential side) of the negative electrode, respectively, and the two negative electrode leads are prone to heat generation in the event of an external short circuit. Each of the two negative electrode leads is connected to the bottom of the outer can, and the outermost negative electrode lead in particular is located near the side of the outer can. This can cause the temperature of the battery surface (side surface of the outer can) to rise abnormally in the event of an external short circuit. An abnormal rise in temperature on the side surface of the outer can can damage the battery or, in the case of a cell module made up of multiple batteries, cause the shutdown of adjacent batteries.

[0021] In contrast, in the present disclosure, by satisfying the above configuration, it is possible to suppress a temperature rise on the battery surface during an external short circuit, thereby improving safety. The negative electrode lead, which generates a large amount of heat, is positioned more inward than the positive electrode lead to ensure a sufficient distance from the side surface of the outer can. The positive electrode lead and the exposed portion of the negative electrode current collector, which are closer to the side surface of the outer can than the negative electrode lead, generate less heat than the negative electrode lead, thereby suppressing a temperature rise on the side surface of the outer can during an external short circuit. In this case, it is possible to suppress a temperature rise on the side surface of the outer can during an external short circuit while reducing the resistance of the entire cell.

[0022] If the positive electrode lead is arranged in a region where the radial distance from the winding axis of the electrode group is 0.9 R or more, the positive electrode lead will be located near the side of the outer can, and the temperature of the battery surface (side of the outer can) may rise in the event of an external short circuit.

[0023] Q1 / Q2 may be 4 / 5 or less, or may be 1 / 3 or less.

[0024] Q3 / Q2 may be 4 / 5 or less, or may be 1 / 3 or less.

[0025] The calorific value Q is the amount of heat generated per unit time by the current flowing through the conductor, and is calculated by using the current I flowing through the conductor and the resistance R of the conductor. ２ The resistance R of a conductor is calculated by the resistivity ρ × (effective length L / cross-sectional area S). Hereinafter, the resistivity will also be referred to as "volume resistivity." The resistivity can be measured by the four-probe method.

[0026] (Heat generation amount Q1) The heat generation amount Q1 of the positive electrode lead is I1 ２ × R1, where I1 is the current flowing through the positive lead and R1 is the resistance of the positive lead.

[0027] The resistance R1 of the positive electrode lead is calculated by ρ1 × (L1 / S1), where ρ1 is the resistivity of the positive electrode lead, L1 is the effective length of the positive electrode lead, and S1 is the cross-sectional area of ​​the positive electrode lead. The effective length L1 of the positive electrode lead is the length of the portion of the positive electrode lead that protrudes from the positive electrode (excluding the connection portion with the sealing plate).

[0028] (Heat generation amount Q2) The heat generation amount Q2 of the negative electrode lead is I2 ２ ×R2, where I2 is the current flowing through the negative lead, and R2 is the resistance of the negative lead.

[0029] The resistance R2 of the negative electrode lead is calculated by ρ2 × (L2 / S2), where ρ2 is the resistivity of the negative electrode lead, L2 is the effective length of the negative electrode lead, and S2 is the cross-sectional area of ​​the negative electrode lead. The effective length L2 of the negative electrode lead is the length of the portion of the negative electrode lead that protrudes from the negative electrode (excluding the connection portion with the inner bottom surface of the outer can).

[0030] (Heat generation amount Q3) The heat generation amount Q3 of the negative electrode current collector exposed portion (heat generation amount of the negative electrode current collector at the negative electrode current collector exposed portion) is I3 ２ × R3, where I3 is the current flowing through the negative electrode current collector at the exposed portion of the negative electrode current collector, and R3 is the resistance of the negative electrode current collector at the exposed portion of the negative electrode current collector.

[0031] The resistance R3 of the negative electrode current collector at the negative electrode current collector exposed portion is calculated by ρ3 × (L3 / S3), where ρ3 is the resistivity of the negative electrode current collector, L3 is the effective length of the negative electrode current collector at the negative electrode current collector exposed portion, and S3 is the cross-sectional area of ​​the negative electrode current collector at the negative electrode current collector exposed portion. The effective length L3 of the negative electrode current collector at the negative electrode current collector exposed portion is the dimension in the width direction of the strip-shaped negative electrode current collector. The cross-sectional area S3 of the negative electrode current collector at the negative electrode current collector exposed portion is calculated by multiplying the dimension in the length direction of the negative electrode at the negative electrode current collector exposed portion by the thickness dimension of the negative electrode current collector.

[0032] When the negative electrode does not include the above-described negative electrode current collector exposed portion, I1=I2 is satisfied.

[0033] In a battery in which the negative electrode does not include the above-described negative electrode current collector exposed portion, when the short-circuit current flowing between the positive and negative electrodes during an external short circuit is I, the heat generation amounts Q1 to Q2 during an external short circuit can be calculated by the following equation using the short-circuit current I and the resistances R1 and R2.

[0034] Q1=I ２ ×R1 Q2 = I ２ ×R2

[0035] When the negative electrode includes the above-described negative electrode current collector exposed portion, I1, I2, and I3 satisfy the following relationship: In this case, there are two paths through which current flows between the negative electrode and the outer can (negative electrode terminal): a path through the negative electrode lead and a path through the negative electrode current collector exposed portion.

[0036] I1=I2+I3 I2=I1×(R3 / (R2+R3)) I3=I1×(R2 / (R2+R3))

[0037] In a battery in which the negative electrode includes the above-described negative electrode current collector exposed portion, when the short-circuit current flowing between the positive and negative electrodes during an external short circuit is I (= I1 = I2 + I3), the amounts of heat generated during an external short circuit Q1 to Q3 can be calculated by the following equation using the short-circuit current I and the resistances R1 to R3.

[0038] Q1=I ２ ×R1 Q2=(I×(R3 / (R2+R3)) ２ ×R2 Q3=(I×(R2 / (R2+R3)) ２ ×R3

[0039] During an external short circuit, it is sufficient that the relationship Q1<Q2 is satisfied for battery X1 (Q1<Q2 and Q3<Q2 for battery X2). For example, it is preferable that the relationship Q1<Q2 is satisfied for battery X1 (Q1<Q2 and Q3<Q2 for battery X2) when the temperature of each component is in the range from room temperature to around 100°C (or around 90°C). The heat generation amount of each component at a given temperature can be calculated using the resistivity of each component at the given temperature.

[0040] In a secondary battery (battery X3) according to yet another embodiment of the present disclosure, the negative electrode has a negative electrode current collector exposed portion (hereinafter also referred to as a "second negative electrode current collector exposed portion") on at least a portion of the outermost periphery of the negative electrode, and the negative electrode current collector exposed portion is in contact with the inner surface of the outer can. The negative electrode lead includes a first layer and a second layer disposed on at least a portion of the surface of the first layer. The first layer includes a first metal element, and the resistivity ρa of the first metal element is lower than the resistivity of nickel. The second layer includes a second metal element, and the resistivity ρb of the second metal element is equal to or higher than the resistivity of nickel. The thickness of the negative electrode lead is 60 μm or greater. The area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is 51% or greater but less than 100%.

[0041] That is, instead of the feature of battery X2 that "the negative electrode lead is arranged more inward than the positive electrode lead, and the positive electrode lead is arranged in a region where the radial distance from the winding axis of the electrode group is less than 0.9R, where R is the radius of the electrode group, and the relationships Q1 < Q2 and Q3 < Q2 are satisfied during an external short circuit," battery X3 has the following feature: "the negative electrode lead includes a first layer and a second layer, the first layer contains a first metal element, and the resistivity ρa of the first metal element is smaller than the resistivity of nickel, the second layer contains a second metal element, and the resistivity ρb of the second metal element is equal to or greater than the resistivity of nickel, the thickness of the negative electrode lead is 60 μm or more, and the area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is 51% or more and less than 100%."

[0042] When the above configuration is satisfied, the resistance of the entire cell can be reduced while suppressing a temperature rise on the battery surface during an external short circuit.The resistance of the negative electrode lead can be reduced while suppressing a temperature rise on the side surface of the outer can.

[0043] The negative electrode lead may be a laminated member in which the second layer is laminated on one or both sides of the first layer. That is, the negative electrode lead may have a laminated structure of (first layer / second layer) or (second layer / first layer / second layer). The second layer can be formed on the surface of the first layer by, for example, a plating method.

[0044] The first layer includes a first metal element. The first metal element has a lower resistivity than the second metal element. Examples of the first metal element include copper, aluminum, etc. The first layer may include one type of the first metal element, or may include two or more types of the first metal element. The resistivity ρa of the first metal element may be lower than the resistivity of nickel, greater than or equal to the resistivity of copper, and less than the resistivity of nickel. Copper has a lower resistivity than nickel. For example, the resistivity ρa of the first metal element at 100°C may be 2.23 μΩ·cm or greater, or may be 2.23 μΩ·cm or greater and less than 10.3 μΩ·cm.

[0045] The second layer includes a second metal element. Examples of the second metal element include nickel, iron, and chromium. The second layer may include one type of the second metal element, or may include two or more types of the second metal element. The resistivity ρb of the second metal element is equal to or greater than the resistivity of nickel. For example, the resistivity ρb of the second metal element at 100°C may be 10.3 μΩ cm or greater.

[0046] The first layer reduces the cell resistance, while the second layer suppresses the temperature rise on the side surface of the outer can. Furthermore, the second layer ensures reliable connection between the negative electrode lead and the negative electrode and the inner bottom surface of the outer can by welding. The area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is 51% or more and less than 100%, and may be 51% or more and 90% or less. The area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is the area ratio of the second layer to the total area of ​​the first layer and the second layer in the cross section of the negative electrode lead in the thickness direction.

[0047] When the area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is 51% or more, the temperature rise on the side surface of the outer can is likely to be suppressed. Furthermore, in this case, the negative electrode lead and the negative electrode can be reliably connected by welding the negative electrode lead to the negative electrode current collector. The second layer can contain a second metal element that is easily welded to the negative electrode and the outer can. For example, even if the first layer of the negative electrode lead and the negative electrode current collector are made of the same material, the negative electrode lead can be reliably connected to the negative electrode current collector by resistance welding if the negative electrode lead contains a sufficient proportion of the second layer (second metal element).

[0048] When the area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is less than 100%, the presence of the first layer is advantageous in reducing the resistance of the entire cell. However, if the area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is less than 51%, and the first layer and the negative electrode current collector are made of the same material, the connection between the negative electrode lead and the negative electrode current collector becomes insufficient, and in the event of an external short circuit, the short-circuit current flowing from the outermost exposed portion of the negative electrode current collector to the side of the outer can increases, which may make the temperature of the side of the outer can more likely to rise.

[0049] Typically, the negative electrode lead and the negative electrode are connected by a welding method (e.g., resistance welding). That is, a weld is formed between the negative electrode lead and the negative electrode current collector. Since the negative electrode lead has a second layer containing the second metal element, the weld contains the second metal element. The weld is preferably formed in a region that is 3 mm or more away from the edge of the negative electrode current collector. In this case, the negative electrode lead can be stably connected to the negative electrode current collector. The negative electrode lead is typically connected to the inner bottom surface of the outer can by resistance welding, and a weld containing the second metal element is also formed between the negative electrode lead and the inner bottom surface of the outer can.

[0050] The thickness of the negative electrode lead is 60 μm or more, may be 70 μm or more, or may be 80 μm or more. The thickness of the negative electrode lead may be, for example, 500 μm or less, 300 μm or less, or 200 μm or less. The thickness of the negative electrode lead is the total thickness of the first layer and the second layer. When the thickness of the negative electrode lead is 60 μm or more, the strength of the negative electrode lead is easily ensured, and the negative electrode lead and the negative electrode current collector can be reliably welded together.

[0051] From the viewpoint of easily ensuring a sufficient thickness of the second layer, the thickness of the second layer may be 25 μm or more, preferably 30 μm or more. Also, from the viewpoint of easily ensuring a sufficient thickness of the first layer, the thickness of the second layer may be 60 μm or less, or may be 50 μm or less. Note that, when the negative electrode lead has a laminated structure of (second layer / first layer / second layer), the thickness of the second layer refers to the total thickness of the two second layers.

[0052] The negative electrode of the battery X3 may be, for example, a negative electrode 12 having a first negative electrode current collector exposed portion 120a and a second negative electrode current collector exposed portion 120b as shown in FIG.

[0053] The negative electrode leads of the batteries X1 and X2 may be made of a clad material having the first and second layers. The first layer reduces the cell resistance, while the second layer, which has a high resistivity, makes it easy to construct the battery X1 such that Q1<Q2, and the battery X2 such that Q1<Q2 and Q3<Q2 are easy to construct.

[0054] Examples of components of the secondary battery are described below, but the secondary battery is not limited to the examples described below.

[0055] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. Materials for the positive electrode current collector and the positive electrode mixture layer are not particularly limited, and any material used in the positive electrodes of known non-aqueous electrolyte secondary batteries may be used.

[0056] Examples of the material of the positive electrode current collector include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0057] The positive electrode active material can be a material that reversibly absorbs and releases lithium ions. Examples of positive electrode active materials include composite oxides containing lithium and a metal element Me other than lithium, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. The composite oxide containing lithium and the metal element Me may be a lithium-containing transition metal oxide containing at least a transition metal as the metal element Me. Lithium-containing transition metal oxides are preferably used as the positive electrode active material because of their low production cost and high average discharge voltage.

[0058] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain only one type of transition metal element, or two or more types. The lithium-containing transition metal oxide preferably contains at least one element selected from the group consisting of Ni, Co, Mn, and Al.

[0059] Additives other than the positive electrode active material (binder, conductive material) are not particularly limited, and known additives may be used. A conductive carbon material may be used as the conductive material. Examples of conductive carbon materials include carbon black, carbon nanotubes, and graphite. Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0060] The manufacturing method of the positive electrode is not limited, and the positive electrode may be manufactured by a known method. In one example of the manufacturing method, first, a positive electrode mixture slurry is prepared by mixing a positive electrode active material, additives (conductive material, binder, etc.), and a dispersion medium (e.g., organic solvent). Next, the positive electrode mixture slurry is applied to a positive electrode current collector to form a laminate of the positive electrode current collector and a coating film of the positive electrode mixture slurry. Next, the coating film is dried, and then the laminate is rolled. In this manner, a positive electrode is obtained. The method of forming the positive electrode current collector exposed portion is not particularly limited. The positive electrode current collector exposed portion may be formed by removing a portion of the positive electrode mixture layer after forming the positive electrode.

[0061] (Negative Electrode) The negative electrode includes a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The materials for the negative electrode current collector and the negative electrode mixture layer are not particularly limited, and materials used in the negative electrodes of known non-aqueous electrolyte secondary batteries may be used. The thickness of the negative electrode current collector may be 5 μm or more or 10 μm or more, and may be 50 μm or less or 30 μm or less. The thickness of the negative electrode may be 100 μm or more or 150 μm or more, and may be 300 μm or less or 200 μm or less.

[0062] Examples of materials for the negative electrode current collector include copper and copper alloys. The negative electrode current collector may be a copper foil or a copper alloy foil.

[0063] The negative electrode active material may be a material that reversibly absorbs and releases lithium ions. Examples of the negative electrode active material include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material or a combination of two or more types. Examples of the carbonaceous material include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon).

[0064] The additives (binder, conductive material) other than the negative electrode active material are not particularly limited, and known additives may be used. The conductive material and binder may be the same materials as those exemplified as the conductive material and binder for the positive electrode mixture layer.

[0065] The method for manufacturing the negative electrode is not particularly limited, and the negative electrode may be manufactured by a known method. In one example of the manufacturing method, first, a negative electrode mixture slurry is prepared by mixing a negative electrode active material, additives (conductive material, binder, etc.), and a dispersion medium (e.g., organic solvent). Next, the negative electrode mixture slurry is applied to a negative electrode current collector to form a laminate of the negative electrode current collector and a coating film of the negative electrode mixture slurry. Next, the coating film is dried, and then the laminate is rolled. In this manner, the negative electrode is obtained. The method for forming the negative electrode current collector exposed portion is not particularly limited. The negative electrode current collector exposed portion may be formed by removing a portion of the negative electrode mixture layer after forming the negative electrode.

[0066] (Separator) A porous sheet having ion permeability and insulating properties is used for the separator. Examples of porous sheets include thin films, woven fabrics, nonwoven fabrics, etc. having micropores. The material of the separator is not particularly limited, and a polymeric material may be used. Examples of polymeric materials include olefin resins, polyamide resins, cellulose, etc. Examples of olefin resins include polyethylene, polypropylene, and ethylene-propylene copolymers. The separator may contain additives (such as inorganic fillers) as necessary. The thickness of the separator is not particularly limited, and may be 10 μm or more, or 16 μm or more, or 30 μm or less, or 20 μm or less.

[0067] (Electrolyte) A non-aqueous electrolyte having lithium ion conductivity can be used as the electrolyte. The non-aqueous electrolyte is not particularly limited, and a non-aqueous electrolyte used in a known non-aqueous electrolyte secondary battery can be used. The non-aqueous electrolyte contains, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0068] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0069] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain only one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted derivatives include fluorides. Examples of lithium salts include LiPF ６ The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less.

[0070] (Positive electrode lead, negative electrode lead) For the positive electrode lead, a lead made of a metal that can be used for a positive electrode lead can be used. For example, for the positive electrode lead, a metal thin plate made of aluminum or an aluminum alloy can be used. Furthermore, for the positive electrode lead, a clad material made of multiple metal layers can be used, for example, a clad material having a laminated structure of an aluminum layer / nickel layer / aluminum layer can be used.

[0071] The thickness T1 of the positive electrode lead may be 100 μm or more, or 120 μm or more, and may be 200 μm or less, or 180 μm or less. The width W1 of the positive electrode lead may be 1 mm or more, or 2 mm or more, and may be 5 mm or less, or 4 mm or less. A secondary battery usually includes only one positive electrode lead.

[0072] The negative electrode lead can be a lead made of a metal that can be used for a negative electrode lead. For example, the negative electrode lead can be a thin metal plate made of copper or a copper alloy. Alternatively, the negative electrode lead can be a clad material made of multiple metal layers, for example, a clad material having a laminated structure of a nickel layer / copper layer / nickel layer.

[0073] The thickness T2 of the negative electrode lead may be 60 μm or more, 80 μm or more, or 200 μm or more. The thickness T2 of the negative electrode lead may be 500 μm or less, or 300 μm or less. The width W2 of the negative electrode lead may be 1 mm or more, or 2 mm or more, and may be 5 mm or less, or 4 mm or less. A secondary battery typically includes only one negative electrode lead.

[0074] The method for connecting the positive electrode lead to the positive electrode current collector and the method for connecting the negative electrode lead to the negative electrode current collector are not limited, and a known method (e.g., welding) may be used. The positive electrode lead may be connected to either the inner surface or the outer surface of both sides of the positive electrode current collector. The negative electrode lead may be connected to either the inner surface or the outer surface of both sides of the negative electrode current collector.

[0075] (Exterior Body) The exterior body (battery case) houses the electrode group and the electrolyte. There are no particular limitations on the exterior body, and any known exterior body may be used. The exterior body typically includes a cylindrical exterior can with a bottom and a sealing member that seals the opening of the exterior can. The exterior can functions as a negative electrode terminal, and the sealing member functions as a positive electrode terminal. The sealing member includes a sealing plate and an insulating gasket that is interposed between the sealing plate and the exterior can.

[0076] The method for manufacturing a secondary battery is not particularly limited, and the secondary battery may be manufactured using steps used in known manufacturing methods. In one example of the manufacturing method, first, each component is prepared. A negative electrode lead is connected to the negative electrode, and a positive electrode lead is connected to the positive electrode. Next, an electrode assembly is prepared by winding the positive electrode, the negative electrode, and the separator. Next, the electrode assembly and the non-aqueous electrolyte are housed in an outer casing. At this time, one end of the positive electrode lead is connected to a sealing body, and one end of the negative electrode lead is connected to an outer casing can. When the negative electrode has a second negative electrode current collector exposed portion described below, the second negative electrode current collector exposed portion is brought into contact with the inner surface of the outer casing can.

[0077] An example of a secondary battery according to the present disclosure will be described below with reference to the drawings. The components described above can be applied to the components of the example described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the example described below, components that are not essential for the secondary battery according to the present disclosure may be omitted.

[0078] (Embodiment 1) FIG. 1 is a cross-sectional view schematically illustrating an example of a nonaqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) according to Embodiment 1. The nonaqueous electrolyte secondary battery 10 in FIG. 1 is a cylindrical battery. The secondary battery 10 includes a cylindrical exterior body (battery case) 30 with a bottom, and a wound electrode group 14 and a nonaqueous electrolyte (not shown) housed within the exterior body 30. The exterior body 30 includes an exterior can 38 and a sealing body (sealing plate 31 and gasket 37) that seals the opening of the exterior can 38. The exterior can 38 is a cylindrical case with a bottom made of metal. A gasket 37 is disposed between the exterior can 38 and the sealing plate 31. Within the exterior can 38, insulating plates 17 and 18 are disposed at both ends of the electrode group 14, respectively.

[0079] The sealing plate 31 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. All of the members except for the insulating member 34 are electrically connected to one another.

[0080] The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 13 so that the separator 13 is disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11, the negative electrode 12, and the separator 13 are each strip-shaped. The positive electrode 11 includes a positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector. The negative electrode 12 includes a negative electrode current collector and negative electrode mixture layers formed on both sides of the negative electrode current collector.

[0081] One end of the positive electrode lead 19 is connected to the positive electrode 11, and the other end is connected to the filter 32. That is, the positive electrode 11 is electrically connected to a cap 36 that also serves as a positive electrode terminal. One end of the negative electrode lead 20 is connected to the negative electrode 12, and the other end is connected to an outer can 38 that also serves as a negative electrode terminal.

[0082] 2 is a top view schematically illustrating an example of a positive electrode. X and Y in the figure indicate the length and width directions of the strip-shaped positive electrode, respectively. The figure is a schematic illustration, and the ratio of the dimensions of each member in the X and Y directions does not necessarily reflect the actual ratio.

[0083] The strip-shaped positive electrode 11 includes a positive electrode current collector 110 and a positive electrode mixture layer 111 carried on both sides of the positive electrode current collector 110. The positive electrode 11 has a part 11a thereof (positive electrode current collector exposed part 110a) where the positive electrode mixture layer 111 is not carried on the surface of the positive electrode current collector 110 and the positive electrode current collector is exposed. The positive electrode current collector exposed part 110a is usually formed on both surfaces of the positive electrode 11.

[0084] A positive electrode lead 19 is attached to the positive electrode 11. One end of the positive electrode lead 19 is connected to the positive electrode current collector exposed portion 110a by welding or the like. Note that, for convenience, the other end of the positive electrode lead 19, which is connected to the sealing plate 31, is not shown in FIG.

[0085] The resistance R1 of the positive electrode lead 19 is calculated by ρ1 × (L1 / S1). Here, ρ1 is the resistivity of the positive electrode lead 19 and can be adjusted appropriately depending on the material of the positive electrode lead 19. L1 is the effective length L1 of the positive electrode lead 19 in FIG. 2. The effective length L1 of the positive electrode lead 19 is the length of the portion of the positive electrode lead 19 that protrudes from the positive electrode 11 (excluding the connection portion with the sealing plate 31). S1 is the cross-sectional area of ​​the positive electrode lead 19. The cross-sectional area S1 of the positive electrode lead 19 is calculated by W1 × T1 using the width W1 of the positive electrode lead 19 and the thickness T1 of the positive electrode lead 19 in FIG. 2.

[0086] 3 is a top view schematically illustrating an example of a negative electrode (not including a second negative electrode current collector exposed portion). X and Y in the figure indicate the length direction and width direction of the strip-shaped negative electrode, respectively. The figure is a schematic illustration, and the ratio of the dimensions of each member in the X and Y directions does not necessarily reflect the actual ratio.

[0087] The negative electrode 12 includes a negative electrode current collector 120 and a negative electrode mixture layer 121 supported on both sides of the negative electrode current collector 120. The negative electrode 12 has a portion (first negative electrode current collector exposed portion 120a) where the negative electrode mixture layer 121 is not supported on the surface of the negative electrode current collector 120 and the negative electrode current collector 120 is exposed. The first negative electrode current collector exposed portion 120a is usually formed on both surfaces of the negative electrode 12. The first negative electrode current collector exposed portion 120a is usually formed in predetermined locations excluding the outermost peripheral portion 12b. In the illustrated example, the first negative electrode current collector exposed portion 120a is formed on the end 12a on the winding start side (innermost peripheral side) of the negative electrode 12.

[0088] 3, a negative electrode mixture layer 121 is also supported on both sides of the outermost peripheral portion 12b of the negative electrode 12. The outermost peripheral portion 12b is the portion that becomes the outermost periphery of the negative electrode when the electrode group is constructed (the portion that faces the inner surface of the outer can when the battery is fabricated). In the battery, the negative electrode mixture layer 121 of the outermost peripheral portion 12b of the negative electrode faces the inner surface of the outer can.

[0089] A negative electrode lead 20 is attached to the negative electrode 12. One end of the negative electrode lead 20 is connected to the first negative electrode current collector exposed portion 120a by welding or the like. Note that, for convenience, the other end of the negative electrode lead 20, which is connected to the bottom of the outer can, is not shown in Fig. 3.

[0090] The resistance R2 of the negative electrode lead 20 is calculated by ρ2 × (L2 / S2). Here, ρ2 is the resistivity of the negative electrode lead 20 and can be adjusted appropriately depending on the material of the negative electrode lead 20. L2 is the effective length L2 of the negative electrode lead 20 in FIG. 3. The effective length L2 of the negative electrode lead 20 is the length of the portion of the negative electrode lead 20 that protrudes from the negative electrode 12 (excluding the connection portion with the inner bottom surface of the outer can). S2 is the cross-sectional area of ​​the negative electrode lead 20. The cross-sectional area S2 of the negative electrode lead 20 is calculated by W2 × T2 using the width W2 of the negative electrode lead 20 and the thickness T2 of the negative electrode lead 20 in FIG. 3.

[0091] 4 is a top view schematically illustrating another example of a negative electrode (including a second negative electrode current collector exposed portion). X and Y in the figure indicate the length direction and width direction of the strip-shaped negative electrode, respectively. The figure is a schematic illustration, and the ratio of the dimensions of each member in the X and Y directions does not necessarily reflect the actual ratio. Explanation of parts common to FIG. 3 will be omitted.

[0092] The negative electrode 12 has the first negative electrode current collector exposed portion 120a described above. The first negative electrode current collector exposed portion 120a is the same as described above.

[0093] The negative electrode 12 in Fig. 4 has a negative electrode current collector exposed portion 120b in contact with the inner surface of the outer can at the outermost peripheral portion 12b of the negative electrode 12. The outermost peripheral portion 12b is the portion that becomes the outermost periphery of the negative electrode when an electrode group is constructed (the portion that faces the inner surface of the outer can during battery fabrication). The negative electrode 12 in Fig. 4 has a portion (second negative electrode current collector exposed portion 120b) on one surface (the surface facing the outer can) of the outermost peripheral portion 12b where the negative electrode mixture layer 121 is not supported and the negative electrode current collector 120 is exposed.

[0094] 4, the second negative electrode current collector exposed portion 120b is formed over the entire outermost peripheral portion 12b, but it may be formed over at least a portion of the outermost peripheral portion. For example, the area ratio of the second negative electrode current collector exposed portion to the outermost peripheral portion may be 65% or more, or may be 70% or more. Furthermore, the area ratio of the second negative electrode current collector exposed portion to the outermost peripheral portion may be 95% or less, 90% or less, or may be 85% or less.

[0095] For example, in the case where the inner peripheral surface of the outermost periphery of the negative electrode faces the positive electrode and the outer peripheral surface faces the outer can, a negative electrode mixture layer is supported on the inner peripheral surface, and a second negative electrode current collector exposed portion is formed on the outer peripheral surface without a negative electrode mixture layer being supported on the outer peripheral surface. The outermost periphery of the negative electrode may include a region where the negative electrode protrudes beyond the positive electrode (negative electrode protruding region). That is, the outermost periphery of the negative electrode may include a region where the inner peripheral surface does not face the positive electrode. In the negative electrode protruding region, a negative electrode mixture layer may not be supported on either the outer peripheral side or the inner peripheral side of the negative electrode, and a second negative electrode current collector exposed portion may be formed on both sides of the negative electrode. The entire outermost periphery of the negative electrode may be a negative electrode protruding region.

[0096] When the electrode group 14 of the secondary battery 10 of FIG. 1 includes the negative electrode 12 of FIG. 4, the second negative electrode current collector exposed portion 120b is in contact with the inner surface of the outer can 38. In this case, current flows easily as indicated by the arrows in FIG. 4, flowing from the negative electrode 12 to the outer can 38 via two paths: the negative electrode lead 20 and the second negative electrode current collector exposed portion 120b. This also makes it easy to ensure a large contact area between the second negative electrode current collector exposed portion 120b and the outer can. From the viewpoints of reducing internal resistance and dispersing short-circuit current, it is preferable that the negative electrode 20 have the second negative electrode current collector exposed portion 120b.

[0097] The resistance R3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b is calculated by ρ3 × (L3 / S3). Here, ρ3 is the resistivity of the negative electrode current collector 120 and can be adjusted appropriately depending on the material of the negative electrode current collector 120. L3 is the effective length L3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in FIG. 4. S3 is the cross-sectional area of ​​the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b. The cross-sectional area S3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b is calculated by W3 × T3, where W3 is the width W3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in FIG. 4 and T3 is the thickness T3 of the negative electrode current collector 120.

[0098] From the viewpoint of suppressing a temperature rise on the battery surface during an external short circuit, the negative electrode lead 20 is disposed closer to the inner periphery than the positive electrode lead 19. From the same viewpoint, as shown in Figures 3 and 4, the negative electrode lead 20 is preferably connected to the end 12a on the winding start side of the negative electrode 12. Note that the end 12a on the winding start side of the negative electrode 12 is the end region to which the negative electrode lead 20 is connected, and is the region where the first negative electrode current collector exposed portion 120a is formed.

[0099] FIG. 5 is a schematic top view of one end face of a cylindrical wound electrode group as viewed from the winding axis direction. For convenience, FIG. 5 shows the positions of the positive electrode lead 19 and the negative electrode lead 20 within the electrode group 14. The electrode group 14 typically has a hollow portion, but this hollow portion is omitted. In FIG. 5 , C is the winding axis, and R is the radius of the electrode group 14 when one end face of the electrode group 14 is viewed from the winding axis C direction. Furthermore, D1 is the radial distance between the positive electrode lead 19 and the winding axis C when one end face of the electrode group 14 is viewed from the winding axis C direction, and D2 is the radial distance between the negative electrode lead 20 and the winding axis C when one end face of the electrode group 14 is viewed from the winding axis C direction. As shown in FIG. 5 , the negative electrode lead 20 is positioned more inward than the positive electrode lead 19. That is, D2 is smaller than D1.

[0100] From the viewpoint of suppressing a temperature rise on the battery surface during an external short circuit, the positive electrode lead 19 is disposed within a region where the radial distance from the winding axis C of the electrode group 14 is less than 0.9R. That is, D1 is less than 0.9R. The positive electrode lead 19 is preferably disposed within a region where the radial distance from the winding axis C of the electrode group 14 is 0.2R or more and 0.8R or less. That is, D1 is preferably 0.2R or more and 0.8R or less. When D1 is 0.8R or less, a sufficient distance is likely to be secured between the positive electrode lead 19 and the side of the outer can 38. When D1 is 0.2R or more, it is easy to dispose the negative electrode lead more inwardly than the positive electrode lead, and it is also easy to suppress an increase in cell resistance due to the positive electrode lead being disposed at one end of the positive electrode in the longitudinal direction. The positive electrode lead 19 is more preferably disposed within a region where the radial distance from the winding axis C of the electrode group 14 is 0.25R or more and 0.75R or less. That is, D1 is more preferably 0.25R or more and 0.75R or less.

[0101] The negative electrode lead 20 may be disposed in a region where the radial distance from the winding axis C of the electrode group 14 is 0.5 R or less or 0.3 R or less, for example. That is, D2 may be 0.5 R or less or 0.3 R or less. Alternatively, D2 may be 0.2 R or more, for example.

[0102] To fix the winding end of the electrode assembly, a winding stop tape may be applied to the outer peripheral surface of the electrode assembly (the surface of the negative electrode facing the outermost outer can) From the viewpoint of reducing cell resistance, for example, 10 to 30% of the area of ​​the outer peripheral surface of the cylindrical electrode assembly (the surface of the negative electrode facing the outermost outer can) may be covered with tape.

[0103] <<Appendix>> The above description of the embodiments discloses the following technology: (Technology 1) An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wound together; an electrolyte; a cylindrical outer can with a bottom that houses the electrode assembly and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to the outer can, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector, wherein the negative electrode mixture layer faces the inner surface of the outer can at the outermost periphery of the negative electrode, and the negative electrode lead is arranged more inward than the positive electrode lead, and wherein, when the radius of the electrode assembly is R, the positive electrode lead is arranged in a region that is radially spaced from the winding axis of the electrode assembly by less than 0.9R, A secondary battery, wherein, in the event of an external short circuit, the amount of heat generated by the positive electrode lead Q1 and the amount of heat generated by the negative electrode lead Q2 satisfy the relationship Q1<Q2. (Technology 2) An electrochemical device comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode and the sealing plate; and a negative electrode lead that connects the negative electrode to an inner bottom surface of the outer can, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector, the negative electrode has a negative electrode current collector exposed portion on at least a part of the outermost periphery of the negative electrode, the negative electrode current collector exposed portion being in contact with the inner surface of the outer can, the negative electrode lead being arranged more inward than the positive electrode lead, and wherein, when a radius of the electrode group is R, the positive electrode lead is arranged within a region that is radially spaced from a winding axis of the electrode group by less than 0.9R, A secondary battery in which, during an external short circuit, the amount of heat generated by the positive electrode lead Q1, the amount of heat generated by the negative electrode lead Q2, and the amount of heat generated by the negative electrode current collector exposed portion Q3 satisfy the relationships Q1<Q2 and Q3<Q2. (Technology 3) The secondary battery according to Technology 1 or 2, which satisfies Q1 / Q2≦4 / 5. (Technology 4) The secondary battery according to Technology 2 or 3, which satisfies Q3 / Q2≦1 / 3.(Technology 5) The secondary battery according to any one of Technologies 1 to 4, wherein the negative electrode lead is connected to an end of the negative electrode on a winding start side. (Technology 6) The secondary battery according to any one of Technologies 1 to 5, wherein the positive electrode lead is arranged within a region where the radial distance from the winding axis of the electrode group is 0.2 R or more and 0.8 R or less. (Technology 7) The secondary battery according to any one of Technologies 1 to 6, wherein the negative electrode lead includes a first layer and a second layer arranged on at least a part of a surface of the first layer, wherein the first layer contains a first metal element, wherein the resistivity ρa of the first metal element is lower than the resistivity of nickel, the second layer contains a second metal element, and the resistivity ρb of the second metal element is equal to or higher than the resistivity of nickel, the negative electrode lead has a thickness of 60 μm or more, and an area ratio of the second layer to a cross section of the negative electrode lead in the thickness direction is 51% or more and less than 100%. (Technology 8) The secondary battery according to Technology 7, wherein the negative electrode lead and the negative electrode are connected by forming a welded portion between the negative electrode lead and the negative electrode current collector, and the welded portion contains the second metal element. (Technology 9) The secondary battery according to Technology 8, wherein the welded portion is formed in a region that is 3 mm or more away from an edge portion of the negative electrode current collector. (Technology 10) The secondary battery according to any one of Technology 7 to 9, wherein the negative electrode lead is a laminated member in which the second layer is laminated on one or both sides of the first layer.(Technology 11) An electrochemical device comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode and the sealing plate; and a negative electrode lead that connects the negative electrode to an inner bottom surface of the outer can; wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector; the negative electrode has a negative electrode current collector exposed portion on at least a part of the outermost periphery of the negative electrode, the negative electrode current collector exposed portion being in contact with the inner surface of the outer can; and the negative electrode lead comprises a first layer and a second layer that is placed on at least a part of a surface of the first layer; the first layer contains a first metal element, and the resistivity ρa of the first metal element is lower than the resistivity of nickel, A secondary battery, wherein the second layer contains a second metal element, the resistivity ρb of the second metal element being equal to or greater than the resistivity of nickel, the thickness of the negative electrode lead being 60 μm or greater, and the area ratio of the second layer to a cross section of the negative electrode lead in the thickness direction being 51% or greater and less than 100%. (Technology 12) The secondary battery according to Technology 11, wherein the negative electrode lead and the negative electrode are connected by forming a welded portion between the negative electrode lead and the negative electrode current collector, and the welded portion contains the second metal element. (Technology 13) The secondary battery according to Technology 12, wherein the welded portion is formed in a region that is 3 mm or greater from an edge portion of the negative electrode current collector. (Technology 14) The secondary battery according to any one of Technology 11 to 13, wherein the negative electrode lead is a laminated member in which the second layer is laminated on one or both sides of the first layer. (Technology 15) The secondary battery according to any one of Technology 11 to 14, wherein the thickness of the second layer is 30 μm or greater.

[0104] [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.

[0105] Secondary Batteries A1 to A5, B1 to B4 (Preparation of Positive Electrodes) Positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone was added and stirred to prepare a positive electrode slurry. A lithium-containing transition metal oxide containing nickel, cobalt, and aluminum was used as the positive electrode active material. The positive electrode slurry was then applied to both sides of aluminum foil serving as a positive electrode current collector. The coating was dried and rolled with a roller to form a positive electrode mixture layer. The positive electrode current collector with the positive electrode mixture layer formed on both sides was then cut to a predetermined size to prepare a positive electrode.

[0106] Each battery used the positive electrode 11 shown in FIG. 2 . A positive electrode current collector exposed portion 110a was formed on both surfaces of a portion 11a of the positive electrode 11 without forming a positive electrode mixture layer. The location of the positive electrode current collector exposed portion was adjusted so that the positive electrode lead was positioned at the position shown in Table 1 when the electrode group was constructed. The positive electrode lead position in Table 1 is the radial distance between the positive electrode lead and the winding axis of the electrode group when the cylindrical electrode group is viewed from one end face (distance D1 in FIG. 5 ).

[0107] (Negative Electrode Fabrication) Graphite (negative electrode active material), styrene-butadiene copolymer rubber (SBR), and carboxymethyl cellulose Na salt (CMC-Na) were mixed in a mass ratio of 98:1:1, and an appropriate amount of water was added and stirred to prepare a negative electrode slurry. The negative electrode slurry was then applied to both sides of a negative electrode current collector, the coating was dried, and the mixture was rolled with a roller to form a negative electrode mixture layer. The negative electrode current collector with the negative electrode mixture layer formed on both sides was cut to a predetermined size to prepare a negative electrode. For the negative electrode current collector, brass foil (copper alloy foil) (70% by mass of Cu, 30% by mass of Zn) was used for Batteries A1 to A5, Cu foil was used for Batteries B1 and B2, and Al foil was used for Batteries B3 and B4.

[0108] Each battery used the negative electrode 12 shown in FIG. 4 . A first negative electrode current collector exposed portion was formed on both surfaces of a portion of the negative electrode 12 without forming a negative electrode mixture layer. The location of the first negative electrode current collector exposed portion was adjusted so that the negative electrode lead would be positioned at the position shown in Table 1 when the electrode group was constructed. The negative electrode lead position in Table 1 is the radial distance between the negative electrode lead and the winding axis of the electrode group when the cylindrical electrode group is viewed from one end face (distance D2 in FIG. 5 ). For example, as shown in FIG. 4 , when the first negative electrode current collector exposed portion 120 a was formed at the end 12 a on the winding start side of the negative electrode 12, the distance D2 when the electrode group was constructed was 0.2R.

[0109] Furthermore, a second negative electrode current collector exposed portion 120b was formed without forming a negative electrode mixture layer on one surface (the surface facing the inner surface of the outer can) of the outermost peripheral portion 12b of the negative electrode 12. The area ratio of the second negative electrode current collector exposed portion 120b to the entire outermost peripheral portion 12b of the negative electrode 12 was in the range of 90 to 100%.

[0110] The volume resistivity ρ3 and resistance R3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b were set to the values ​​shown in Table 1. The effective length L3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in Fig. 4 was 6.4 cm. The width W3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in Fig. 4 was 6.2 cm. The thickness T3 of the negative electrode current collector 120 was 0.008 cm.

[0111] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). ６ was dissolved in a solution at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0112] (Preparation of Electrode Group) As the positive electrode lead, a Cu lead was used for battery B2, and an Al lead was used for all batteries other than battery B2. As the negative electrode lead, a Cu lead was used for batteries A2 and B1, a Ni lead was used for battery B2, and an Al lead was used for batteries A1, A3 to A5, and B3 to B4. The positive electrode lead had a length L1 of 1.5 cm, a width W1 of 0.4 cm, and a thickness T1 of 0.02 cm. The negative electrode lead had a length L2 of 1 cm, a width W2 of 0.2 cm, and a thickness T2 of 0.01 cm.

[0113] One end of the positive electrode lead was attached to the exposed portion of the positive electrode current collector. One end of the negative electrode lead was attached to the exposed portion of the first negative electrode current collector. In an inert gas atmosphere, the positive electrode and negative electrode were spirally wound with a porous polyethylene film as a separator between them to produce an electrode assembly. The end of the electrode assembly was fixed with tape. 28% of the area of ​​the circumferential surface of the electrode assembly (the outermost periphery of the negative electrode) was covered with the stop tape.

[0114] (Assembly of Secondary Battery) A cylindrical stainless steel (SUS) outer can with a bottom was prepared. The electrode group was housed in the outer can. At this time, the other end of the positive electrode lead was connected to a sealing plate, and the other end of the negative electrode lead was connected to the inner bottom surface of the outer can. The exposed portion of the second negative electrode current collector at the outermost periphery of the negative electrode was brought into contact with the inner surface of the outer can. After injecting a nonaqueous electrolyte, the opening of the outer can was covered and sealed with a sealing plate. At this time, an insulating gasket was interposed between the sealing plate and the open end of the outer can. In this manner, a cylindrical nonaqueous electrolyte secondary battery was fabricated.

[0115] (External Short-Circuit Test) A fully charged secondary battery was charged at a constant current of 500 mA until the voltage reached 4.2 V, and the internal resistance was measured at room temperature. The fully charged secondary battery was then connected to a 10 mΩ fixed resistor to cause an external short circuit. The short-circuit current (maximum short-circuit current) I was calculated by dividing the cell voltage by the resistance of the fixed resistor. The temperature near the center of the side surface (outer surface of the outer can) of the cylindrical battery during an external short circuit was measured using a thermocouple, and the maximum temperature at this time was measured.

[0116] The evaluation results are shown in Table 1. In Table 1, A1 to A5 are the batteries of the example (Battery X2), and B1 to B4 are the batteries of the comparative examples. In Table 1, the heat values ​​Q1 to Q3 of each member are values ​​calculated based on the resistivity of each member at 100°C.

[0117]

[0118] In the secondary batteries A1 to A5, the internal resistance was reduced, and the maximum temperature of the side surface of the battery during an external short circuit was lower than that of the secondary batteries B1 to B4. In the batteries A1 to A5, the heat generation amounts Q1 to Q3 during an external short circuit satisfied the relationships Q1 < Q2 and Q3 < Q2, the negative electrode lead was located more inward than the positive electrode lead, and the position of the positive electrode lead was less than 0.9R.

[0119] In secondary battery B1, Q1 was greater than Q2, and the positive electrode lead, which was located closer to the outer periphery than the negative electrode lead, generated a larger amount of heat, which led to easier heat transfer to the outer can. In secondary battery B2, Q3 was greater than Q2, and the second negative electrode current collector exposed portion generated a larger amount of heat, which led to easier heat transfer to the outer can, which was in contact with the second negative electrode current collector exposed portion at its side. In secondary battery B3, the negative electrode lead, which was located closer to the outer periphery than the positive electrode lead, generated a larger amount of heat, which led to easier heat transfer to the outer can. In secondary battery B4, the position of the positive electrode lead was 0.9R, and the positive electrode lead was located near the side of the outer can, which led to easier rises in the temperature of the outer can.

[0120] Secondary Batteries E1-E5, R1-R2 (Preparation of Positive Electrode) Positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone was added and stirred to prepare a positive electrode slurry. A lithium-containing transition metal oxide containing nickel, cobalt, and aluminum was used as the positive electrode active material. The positive electrode slurry was then applied to both sides of an aluminum foil serving as a positive electrode current collector. The coating was dried and rolled with a roller to form a positive electrode mixture layer. The positive electrode current collector with the positive electrode mixture layer formed on both sides was then cut to a predetermined size to prepare a positive electrode.

[0121] Each battery used the positive electrode 11 shown in FIG. 2 . A positive electrode current collector exposed portion 110a was formed on both surfaces of a portion 11a of the positive electrode 11 without forming a positive electrode mixture layer. The location where the positive electrode current collector exposed portion was formed was adjusted so that the position of the positive electrode lead was 0.5R when the electrode group was constructed. The position of the positive electrode lead was the radial distance between the positive electrode lead and the winding axis of the electrode group when the cylindrical electrode group was viewed from one end face (distance D1 in FIG. 5 ).

[0122] (Fabrication of Negative Electrode) Graphite (negative electrode active material), styrene-butadiene copolymer rubber (SBR), and carboxymethyl cellulose Na salt (CMC-Na) were mixed in a mass ratio of 98:1:1, and an appropriate amount of water was added and stirred to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to both sides of a negative electrode current collector, the coating was dried, and the mixture was rolled with a roller to form a negative electrode mixture layer. The negative electrode current collector with the negative electrode mixture layer formed on both sides was cut to a predetermined size to fabricate a negative electrode. Copper foil was used for the negative electrode current collector.

[0123] Each battery used the negative electrode 12 shown in FIG. 4 . A first negative electrode current collector exposed portion was formed on both surfaces of a portion of the negative electrode 12 without forming a negative electrode mixture layer. The location where the first negative electrode current collector exposed portion was formed was adjusted so that the position of the negative electrode lead was 0.2R when the electrode group was constructed. Specifically, as shown in FIG. 4 , the first negative electrode current collector exposed portion 120a was formed on the winding start side 12a of the negative electrode 12. The position of the negative electrode lead is the radial distance between the negative electrode lead and the winding axis of the electrode group when the cylindrical electrode group is viewed from one end face (distance D2 in FIG. 5 ).

[0124] Furthermore, a second negative electrode current collector exposed portion 120b was formed without forming a negative electrode mixture layer on one surface (the surface facing the inner surface of the outer can) of the outermost peripheral portion 12b of the negative electrode 12. The area ratio of the second negative electrode current collector exposed portion 120b to the entire outermost peripheral portion 12b of the negative electrode 12 was in the range of 90 to 100%.

[0125] The effective length L3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in Fig. 4 was 6.4 cm. The width W3 of the negative electrode current collector 120 at the second negative electrode current collector exposed portion 120b in Fig. 4 was 6.2 cm. The thickness T3 of the negative electrode current collector 120 was 0.008 cm.

[0126] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). ６ was dissolved in a solution at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0127] (Preparation of Electrode Group) An Al lead was used as the positive electrode lead. The positive electrode lead had an overall length of 6 cm (length L1 in FIG. 2: 1.5 cm), a width W1 of 0.4 cm, and a thickness T1 of 200 μm.

[0128] In batteries E1 to E4 and R1 to R2, a laminated member (second layer / first layer / second layer) in which a second layer was formed on both sides of a first layer was used as the negative electrode lead. The thickness of the first layer was the value shown in Table 2. The thickness of the second layer was the value shown in Table 2. Note that the thickness of the second layer in Table 2 indicates the total thickness of the second layer formed on both sides of the first layer. The first metal element and the second metal element were the metal elements shown in Table 2. In battery R2, a Ni lead was used as the negative electrode lead. The negative electrode lead had an overall length of 7 cm (length L2 in FIG. 4: 1 cm), a width W2: 0.2 cm, and a thickness T2 (μm) shown in Table 2.

[0129] One end of the positive electrode lead was attached to the positive electrode current collector exposed portion. One end of the negative electrode lead was attached to the first negative electrode current collector exposed portion. At this time, the negative electrode lead was connected by resistance welding to a predetermined location on the first negative electrode current collector exposed portion 120a that was 3 mm or more away from the edge portion 12a. An electrode assembly was produced by spirally winding the positive electrode and negative electrode with a porous polyethylene film as a separator in an inert gas atmosphere. The end of the electrode assembly was fixed with tape. 28% of the area of ​​the circumferential surface of the electrode assembly (the outermost periphery of the negative electrode) was covered with stop tape.

[0130] (Assembly of Secondary Battery) A cylindrical stainless steel (SUS) outer can with a bottom was prepared. The electrode group was housed in the outer can. At this time, the other end of the positive electrode lead was connected to a sealing plate, and the other end of the negative electrode lead was connected to the inner bottom surface of the outer can. The exposed portion of the second negative electrode current collector at the outermost periphery of the negative electrode was brought into contact with the inner surface of the outer can. After injecting a nonaqueous electrolyte, the opening of the outer can was covered and sealed with a sealing plate. At this time, an insulating gasket was interposed between the sealing plate and the open end of the outer can. In this manner, a cylindrical nonaqueous electrolyte secondary battery was fabricated.

[0131] (External Short Circuit Test) A secondary battery was charged at a constant current of 500 mA until the voltage reached 4.2 V, and the internal resistance (cell resistance) was measured. The fully charged secondary battery was then connected to a fixed resistor of 10 mΩ to cause an external short circuit. The temperatures of the side (external surface of the outer can) and bottom (external bottom surface of the outer can) of the cylindrical battery during the external short circuit were measured using a thermocouple, and the maximum temperature was measured. The ratio of the temperature of the side to the temperature of the bottom was calculated. A larger ratio indicates a higher temperature on the side of the battery.

[0132] The evaluation results are shown in Table 2. In Table 1, E1 to E5 are the batteries of the example (battery X3), and R1 and R2 are the batteries of the comparative example.

[0133]

[0134] In Batteries E1 to E5, the internal resistance (cell resistance) was reduced, and the temperature rise on the side of the battery during an external short circuit was suppressed compared to Battery R1. It is believed that Batteries E1 to E5 satisfied the conditions Q1 < Q2 and Q3 < Q2 due to the significant effect of the second layer of the negative electrode lead.

[0135] In Battery R1, the area ratio of the second layer (Ni) to the cross section of the negative electrode lead in the thickness direction was small at 2%, so a large current flowed during an external short circuit, causing the temperature of the side of the battery to rise.In Battery R2, the negative electrode lead was a Ni lead and did not include the first layer, so the internal resistance (cell resistance) increased.

[0136] The present disclosure can be used in a secondary battery in which a wound electrode group is housed in an outer can.

[0137] 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.

[0138] 10: Secondary battery, 11: Positive electrode, 12: Negative electrode, 12a: End of negative electrode on winding start side, 12b: Outermost periphery of negative electrode, 13: Separator, 14: Electrode group, 19: Positive electrode lead, 20: Negative electrode lead, 31: Sealing plate, 38: Outer can

Claims

1. An electrode assembly comprising a wound electrode group including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that houses the electrode group and the electrolyte; a sealing plate that is placed at the opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to the inner bottom surface of the outer can, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector, the negative electrode mixture layer faces the inner surface of the outer can at the outermost periphery of the negative electrode, the negative electrode lead is arranged more inward than the positive electrode lead, and when the radius of the electrode group is R, the positive electrode lead is arranged within a region that is radially spaced from the winding axis of the electrode group by less than 0.9R, A secondary battery, wherein, in the event of an external short circuit, the amount of heat generated by the positive electrode lead Q1 and the amount of heat generated by the negative electrode lead Q2 satisfy the relationship Q1<Q2.

2. An electrolytic capacitor comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that contains the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode to the sealing plate; and a negative electrode lead that connects the negative electrode to the inner bottom surface of the outer can, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector, the negative electrode has a negative electrode current collector exposed portion on at least a part of the outermost periphery of the negative electrode, the negative electrode current collector exposed portion being in contact with the inner surface of the outer can, the negative electrode lead being located more inward than the positive electrode lead, and wherein, when the radius of the electrode group is R, the positive electrode lead is located within a region that is radially spaced from the winding axis of the electrode group by less than 0.9R, a secondary battery in which, during an external short circuit, a heat generation amount Q1 of the positive electrode lead, a heat generation amount Q2 of the negative electrode lead, and a heat generation amount Q3 of the negative electrode current collector exposed portion satisfy the relationships Q1<Q2 and Q3<Q2.

3. The secondary battery according to claim 1 or 2, wherein Q1 / Q2≦4 / 5 is satisfied.

4. The secondary battery according to claim 2, wherein Q3 / Q2≦1 / 3 is satisfied.

5. The secondary battery according to claim 1 or 2, wherein the negative electrode lead is connected to the end of the negative electrode at the winding start side.

6. The secondary battery according to claim 1 or 2, wherein the positive electrode lead is disposed within an area whose radial distance from the winding axis of the electrode group is 0.2R or more and 0.8R or less.

7. The secondary battery according to claim 1 or 2, wherein the negative electrode lead comprises a first layer and a second layer disposed on at least a portion of the surface of the first layer, the first layer containing a first metal element, the resistivity ρa of the first metal element being lower than the resistivity of nickel, the second layer containing a second metal element, the resistivity ρb of the second metal element being equal to or higher than the resistivity of nickel, the thickness of the negative electrode lead being 60 μm or greater, and the area ratio of the second layer to the cross section of the negative electrode lead in the thickness direction is 51% or greater but less than 100%.

8. The secondary battery according to claim 7, wherein a weld is formed between the negative electrode lead and the negative electrode current collector, and the weld contains the second metal element.

9. The secondary battery according to claim 8, wherein the welded portion is formed in an area that is 3 mm or more away from the edge of the negative electrode current collector.

10. The secondary battery according to claim 7, wherein the negative electrode lead is a laminated member in which the second layer is laminated on one or both sides of the first layer.

11. A battery comprising: an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; a cylindrical outer can with a bottom that contains the electrode group and the electrolyte; a sealing plate that is placed at an opening of the outer can via an insulating gasket; a positive electrode lead that connects the positive electrode and the sealing plate; and a negative electrode lead that connects the negative electrode to the inner bottom surface of the outer can; wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector; the negative electrode has a negative electrode current collector exposed portion on at least a part of the outermost periphery of the negative electrode, the negative electrode current collector exposed portion being in contact with the inner surface of the outer can; the negative electrode lead comprises a first layer and a second layer that is placed on at least a part of the surface of the first layer; the first layer contains a first metal element, and the resistivity ρa of the first metal element is lower than the resistivity of nickel; a second layer containing a second metal element, a resistivity ρb of the second metal element being equal to or greater than the resistivity of nickel; a thickness of the negative electrode lead being 60 μm or greater; and an area ratio of the second layer to a cross section of the negative electrode lead in the thickness direction being 51% or greater and less than 100%.

12. The secondary battery according to claim 11, wherein a weld is formed between the negative electrode lead and the negative electrode current collector, and the weld contains the second metal element.

13. The secondary battery according to claim 12, wherein the welded portion is formed in an area that is 3 mm or more away from the edge of the negative electrode current collector.

14. The secondary battery according to claim 11, wherein the negative electrode lead is a laminated member in which the second layer is laminated on one or both sides of the first layer.

15. The secondary battery according to claim 14, wherein the second layer has a thickness of 30 μm or more.

Images