JP2006164773A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To structurally prevent the heat generation of a battery when mechanical pressure is applied to the battery toward the inside of the battery, in a nonaqueous secondary battery composed by housing, in an armoring case, an electrode body formed by spirally rolling, by interposing a separator, a positive electrode formed by applying positive electrode active materials to both surfaces of at least a part of a strip-like positive electrode collector, and a negative electrode formed by applying negative electrode active materials to both surfaces of at least a part of a strip-like negative electrode collector and by applying the negative electrode active material on one-side surface of the at least a part continuously to the negative electrode active material both-surface application layers. <P>SOLUTION: This lithium ion secondary battery is so structured that ends of the negative electrode active material both-surface application layers and the end of the negative electrode active material one-side-surface application layer arranged at the peripheral part of the negative electrode 6 in an electrode body A having a rolled structure are so arranged that a relative angle with respect to the center point of the electrode body A at each region is set not smaller than 5° on a cross section of the electrode body A. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium ion secondary battery excellent in safety such as short circuit resistance.

  2. Description of the Related Art In recent years, consumer electronic devices have become increasingly portable and cordless, and there is a strong demand for higher energy density, smaller size, and lighter weight of secondary batteries serving as driving power sources for these electronic devices. Under such circumstances, the demand for lithium ion secondary batteries using non-aqueous electrolytes having characteristics such as high voltage, high capacity, and light weight has increased, and further higher energy density has been demanded. ing.

A lithium ion secondary battery currently on the market uses a lithium composite oxide (for example, LiCoO ₂ ) that exhibits a high charge / discharge voltage as a positive electrode active material, and a material that can hold lithium such as a carbon material in the negative electrode active material. In general, an electrolyte using a nonaqueous solvent is used. The active material is generally a paste dispersed in an organic or aqueous dispersion medium together with a binder and the like, and the paste is applied to a positive electrode current collector such as aluminum and a negative electrode current collector such as copper, respectively. It is used after being processed into a coated strip-shaped electrode plate. A battery is constructed by inserting an electrode body obtained by winding these strip electrode plates in a spiral shape with a separator interposed therebetween into an outer case.

  Ensuring battery safety is an important issue in achieving higher capacities, and various efforts have been made to ensure safety.

  As a problem related to the safety of the nonaqueous secondary battery, when the battery is crushed, there is a problem that the positive and negative electrode plates are internally short-circuited in the battery, and the battery temperature rises abnormally.

  The cause of such an abnormal temperature rise is that when the battery is crushed, the active material portions of the positive and negative electrodes directly cause an internal short circuit, and the active material is thermally decomposed by the generated Joule heat.

In order to solve this problem, a proposal has been made to arrange an electrode plate having a pole different from that of the battery case on the outermost periphery of the electrode body to expose a current collector portion to which no active material is applied. This is because when the battery is crushed, the battery case and the current collector on the outermost periphery of the electrode body are short-circuited to generate heat, but there is no active material for the positive and negative electrodes. This is because a thermal decomposition reaction does not occur and abnormal heat generation can be suppressed (for example, see Patent Document 1).
JP 09-259926 A

  In order to achieve further increase in capacity of the lithium ion secondary battery, items such as (1) reducing the thickness of the separator and (2) increasing the thickness of the mixture coating layer including the positive electrode and the negative electrode active material are necessary. Yes. Under such circumstances, according to the study by the present inventors, even if a current collector not coated with an active material is disposed on the outermost periphery of the electrode body as in Patent Document 1, the safety of the battery during crushing It has been found that the property cannot always be sufficiently secured.

  As described above, (1) by reducing the thickness of the separator, the physical strength is lowered, and (2) the thickness of the mixture coating layer containing the positive electrode and the negative electrode active material is increased. By increasing the stress applied to the separator by the mixture coating layer containing the positive electrode and the negative electrode active material in the electrode body, the outermost active material is coated separately from the intention shown in Patent Document 1. This is probably because a short circuit occurs in the mixture coating layer containing the positive electrode active material or the negative electrode active material before the current collector portion that is not formed, and abnormal heat generation of the battery due to a thermal decomposition reaction of the active material occurs. As a result of further studies by the present inventors, it has been found that such a short circuit occurs almost at the end of the mixture coating layer. This is due to the fact that the end portions of the mixture coating layer that are structurally susceptible to concentrated stress from the outside are close to each other in the electrode body, so that the strain stress received by the electrode body is concentrated and amplified at one point. This is considered to cause breakage.

  In other words, in a high energy density lithium ion secondary battery in which the stress applied to the separator by the mixture application layer becomes more pronounced, the specific stress strain is alleviated by controlling the arrangement of the mixture application layer. It is necessary to suppress the preferential short circuit of the coating layer.

  In order to solve the above-described problems, the present invention provides a positive electrode in which at least a part of a strip-shaped positive electrode current collector is coated with a positive electrode active material on both surfaces, and at least a part of the strip-shaped negative electrode current collector on both surfaces. An electrode body in which a negative electrode active material is coated on the negative electrode electrode, and a negative electrode having at least a part of the negative electrode active material coated on one side of the negative electrode active material double-sided coating layer is wound in a spiral shape through a separator. In the non-aqueous secondary battery in which the outer casing is housed, the negative electrode active material double-side coated layer end X and the negative electrode active material disposed on the outer periphery of the negative electrode in the electrode body A are shown in FIG. The non-aqueous secondary battery is characterized in that the relative angle θ with respect to the center point O of the electrode body A of the material single-side coated layer end X ′ is 5 ° or more and 180 ° or less. As described above, by controlling the distance between the two ends of the negative electrode active material coating layer, the concentrated amplification effect of the strain stress received by the electrode body is avoided, and the preferential short circuit of the mixture coating layer is suppressed. Is.

  The present invention also provides a negative electrode in which at least a part of a strip-like negative electrode current collector is coated with a negative electrode active material on both sides, and at least a part of a belt-like positive electrode current collector is coated with a positive electrode active material on both sides. In addition, an electrode body in which a positive electrode having at least part of a positive electrode active material coated on one side of the positive electrode active material double-sided coating layer is wound in a spiral shape through a separator is accommodated in an outer case. In the non-aqueous secondary battery, the positive electrode active material double-sided coating layer end Y and the positive electrode active material single-sided coated layer end Y disposed on the outer periphery of the positive electrode in the electrode body B as shown in FIG. The non-aqueous secondary battery is arranged such that the relative angle θ ′ to the center point O ′ of the electrode body B is 5 ° or more and 180 ° or less. As described above, by controlling the distance between the two ends of the positive electrode active material coating layer, the concentrated amplification effect of the strain stress received by the electrode body is avoided, and the preferential short circuit of the mixture coating layer is suppressed. It is.

  In the non-aqueous secondary battery according to the present invention, by controlling the arrangement of the mixture coating layer, the specific stress strain generated inside the electrode body when subjected to external stress such as a crush test is alleviated, The short circuit of the mixture coating layer containing the positive and negative electrode active materials can be prevented, and abnormal heat generation of the battery can be prevented. Therefore, according to the present invention, a high quality and high safety lithium ion secondary battery can be provided.

  As shown in FIG. 1, the non-aqueous secondary battery of the present invention comprises at least part of a strip-shaped positive electrode current collector, a positive electrode having a positive electrode active material applied on both sides, and at least a strip-shaped negative electrode current collector. Part of the negative electrode active material is coated on both sides, and the negative electrode made of at least part of the negative electrode active material coated on one side of the negative electrode active material double-sided coating layer is spirally wound through a separator. A non-aqueous secondary battery in which the rotated electrode body A is housed in an outer case, and the negative electrode active material double-side coated layer end X and the negative electrode disposed on the outer periphery of the negative electrode in the wound electrode body A It arrange | positions so that the relative angle (theta) with respect to the center point O of the electrode body A may be 5 to 180 degree | times. By controlling the arrangement of the negative electrode active material coating layer in this way, the specific stress strain generated inside the electrode body when subjected to external stress such as a crush test is alleviated, and the local positive and negative electrodes An internal short circuit of the active material portion can be prevented, and abnormal heat generation of the battery can be prevented.

  The relative angle θ is more preferably in the range of 25 ° to 45 °. When θ is less than 25 °, the specific stress strain generated inside the electrode body when subjected to external stress such as a crush test is not sufficiently relaxed. An internal short circuit occurs, and abnormal heat generation of the battery may not be prevented. Conversely, when θ exceeds 45 °, it is not preferable because a specific stress strain relaxation limit is reached and the battery capacity decreases.

  In addition, as shown in FIG. 2, the non-aqueous secondary battery of the present invention includes a negative electrode in which at least a part of a strip-shaped negative electrode current collector is coated with a negative electrode active material on both sides, and a strip-shaped positive electrode current collector. The positive electrode active material is applied on both sides of the positive electrode active material on both sides, and the positive electrode formed by applying at least a part of the positive electrode active material on one side of the positive electrode active material double-sided coating layer is spirally formed through a separator. A non-aqueous secondary battery in which the wound electrode body B is housed in an outer case, and the positive electrode active material double-sided coating layer end Y disposed on the outer periphery of the positive electrode in the wound electrode body B And the relative angle θ ′ of the positive electrode active material single-side coated layer end Y ′ with respect to the center point O ′ of the electrode body B is 5 ° or more and 180 ° or less. By controlling the arrangement of the positive electrode active material coating layer in this way, as described above, the specific stress strain generated inside the electrode body when subjected to external stress such as a crush test is alleviated and localized. It is possible to prevent internal short circuit of the positive and negative electrode active material parts, and to prevent abnormal heat generation of the battery.

In a preferred embodiment of the present invention, the positive electrode includes at least a positive electrode active material, a binder, and a conductive agent. As the positive electrode active _{material, Li x M y N 1-} y O 2 (x: 1.05 ≧ x ≧ 0.95, M ≠ N, M, N are Co, Ni, Mn, Cr, Mg, Al, Zn Or a composite oxide represented by y: 1 ≧ y ≧ 0 (specifically, lithium cobaltate, modified lithium cobaltate, lithium nickelate, lithium nickelate) Preferred is a modified product of the above, lithium manganate, a modified product of lithium manganate, etc. Each modified product may contain an element such as aluminum or magnesium, and at least two of cobalt, nickel and manganese. You may use what contains.

When x exceeds 1.05, Li ₂ O, Li ₂ CO _{3 and the} like are generated and decomposed to generate gases such as O ₂ and CO ₂ . Conversely, when x is less than 0.95, the crystal structure is not sufficiently stabilized, and the cycle characteristics are deteriorated.

  When Cr, Mg, Al, Zn is used as M and the proportion thereof is increased, the crystal structure can be strengthened, but since the capacity is reduced, y is preferably in the range of 0.01 to 0.2. When Co, Ni, and Mn are used as (M ≠ N) and the ratio is increased, a part of N can be replaced, or all may be replaced.

  The binder used for the positive electrode is not particularly limited, and polytetrafluoroethylene, modified acrylonitrile rubber particles, polyvinylidene fluoride, and the like can be used. The polytetrafluoroethylene and modified acrylonitrile rubber particles are preferably used in combination with carboxymethyl cellulose, polyethylene oxide, modified acrylonitrile rubber and the like that serve as a thickener for the raw material paste of the positive electrode mixture layer. Polyvinylidene fluoride has a single function as both a binder and a thickener.

  As the conductive agent, acetylene black, ketjen black, various graphites and the like can be used. These may be used alone or in combination of two or more.

  The negative electrode includes at least a negative electrode active material and a binder. As the negative electrode active material, various natural graphites, various artificial graphites, silicon-containing composite materials such as silicide, and various alloy materials can be used. As the binder, various binders such as polyvinylidene fluoride and modified products thereof can be used.

Various lithium salts such as lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) can be used as the solute in the non-aqueous electrolyte. As the non-aqueous solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used, but are not limited thereto. Although a nonaqueous solvent can also be used individually by 1 type, it is preferable to use 2 or more types in combination. Moreover, as an additive, vinylene carbonate, cyclohexylbenzene, diphenyl ether, etc. can also be used.

  The separator is not particularly limited as long as it is made of a material that can withstand the use environment of the lithium ion secondary battery, but a microporous film made of a polyolefin-based resin such as polyethylene or polypropylene is generally used. The microporous film may be a single layer film made of one kind of polyolefin resin or a multilayer film made of two or more kinds of polyolefin resin. The thickness of the separator is preferably in the range of 5 μm to 30 μm from the viewpoint of physical strength and battery capacity.

  Examples of the present invention will be described below.

  FIG. 3 shows a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery which is an embodiment of the present invention. As shown in FIG. 3, an electrode plate group in which a positive electrode 5 and a negative electrode 6 are wound in a spiral shape with a separator 7 interposed therebetween is housed in a bottomed cylindrical battery case 8, and the negative electrode 6 is connected to the battery case 8 via the lower insulating plate 10, and the positive electrode lead 3 connected to the positive electrode 5 is connected to the inside of the sealing plate 1 via the upper insulating plate 4. It is electrically connected to a terminal, a nonaqueous electrolyte (not shown) is injected, and the sealing plate 1 and the battery case 8 are caulked and sealed via the insulating gasket 2.

  Hereinafter, a method for producing the positive electrode 5 will be described in detail. First, 3 kg of lithium cobaltate, 1 kg of polyvinylidene fluoride ((N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) solution having a solid content of 12% by weight)) as a binder, 90 g of acetylene black, and an appropriate amount Of NMP is stirred with a double-arm kneader to prepare a positive electrode mixture paste. This paste is applied to both sides or one side of a 0.015 mm thick aluminum foil, dried and rolled to form a positive electrode mixture layer. Under the present circumstances, the thickness of the electrode plate which consists of an aluminum foil and a positive electrode mixture double-sided coating layer shall be 0.150 mm. This electrode plate is cut into a width that can be inserted into a battery case 8 having a cylindrical battery diameter of 18 mm and a height of 65 mm to obtain the positive electrode 5.

  Hereinafter, a method for producing the negative electrode 6 will be described in detail. First, 3 kg of artificial graphite, 75 g of a styrene-butadiene copolymer (an aqueous dispersion having a solid content of 40% by weight) as a binder, 30 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water, Stir in a kneader to prepare a negative electrode mixture paste. This paste is applied to both sides or one side of a 10 μm thick copper foil, dried and rolled to form a negative electrode mixture layer. Under the present circumstances, the thickness of the electrode plate which consists of copper foil and a negative electrode mixture double-sided coating layer shall be 0.180 mm. Thereafter, the electrode plate is cut into a width that can be inserted into the battery case 8 to obtain the negative electrode 6.

Hereinafter, the method for preparing the electrolytic solution will be described in detail. Lithium hexafluorophosphate (LiPF ₆ ) is dissolved at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate are mixed at a volume ratio of 2: 3: 3. As a result, 3% by weight of vinylene carbonate was added to prepare an electrolytic solution.

  The battery assembly method will be described in detail below. The positive electrode 5 and the negative electrode 6 are wound through a separator 7 made of a polyethylene microporous film having a thickness of 20 μm and inserted into the battery case 8. Next, 5.5 g of the electrolytic solution is weighed and poured into the battery case 8, and the opening of the battery case 8 is sealed together with the sealing plate 1. In this way, a cylindrical lithium ion secondary battery is produced.

  Below, the structure on the cross section of an electrode group is demonstrated concretely.

<< Examples 1-7 >>
When producing the positive electrode 5 according to the production method described above, when producing the positive electrode 5 having the positive electrode mixture layer formed only on both surfaces of the aluminum foil and the negative electrode 6 according to the production method described above, A negative electrode 6 having a negative electrode mixture layer formed on both sides of a copper foil and continuously on one side was wound through a separator 7 to form an electrode body A having a cross-sectional structure as shown in FIG. At this time, by adjusting the length of the negative electrode mixture coating layer, the negative electrode active material double-sided coating layer end X and the negative electrode active material single-sided coating layer end X arranged on the outer periphery of the negative electrode 6 in the electrode body A The relative angle θ of ′ with respect to the electrode body center point O is adjusted within a range (5 ° ≦ θ ≦ 180 °) as shown in Table 1 to be described below, and the cylindrical lithium ion two of Examples 1-7 A secondary battery was produced.

<< Comparative Examples 1-2 >>
When constructing the electrode body A in the same manner as in Examples 1 to 7, both sides of the negative electrode active material disposed on the outer periphery of the negative electrode 6 in the electrode body A by adjusting the length of the negative electrode mixture coating layer The relative angle θ between the coating layer end X and the negative electrode active material single-side coating layer end X ′ with respect to the electrode body center point O is adjusted within a range (θ <5 °) as shown in Table 1 described below. Thus, cylindrical lithium ion secondary batteries of Comparative Examples 1 and 2 were produced.

<< Examples 8 to 14 >>
When the negative electrode 6 is produced according to the production method described above, the negative electrode in which the negative electrode mixture layer is formed only on both surfaces of the copper foil, and when the positive electrode 5 is produced according to the production method described above, the positive electrode The positive electrode 5 in which the mixture layer was formed on both sides of the aluminum foil and continuously on one side thereof was wound through a separator 7 to form an electrode body B having a cross-sectional structure as shown in FIG. At this time, by adjusting the length of the positive electrode mixture coating layer, the positive electrode active material double-sided coating layer end Y and the positive electrode active material single-sided coating layer end Y arranged on the outer periphery of the positive electrode 5 in the electrode body B The relative angle θ ′ with respect to the electrode body center point O ′ is adjusted within a range (5 ° ≦ θ ′ ≦ 180 °) as shown in Table 1 described below, and the cylindrical shapes of Examples 8-14 A lithium ion secondary battery was produced.

<< Comparative Examples 3-4 >>
When the electrode body B is configured in the same manner as in Examples 8 to 14, both sides of the positive electrode active material disposed on the outer peripheral portion of the positive electrode 5 in the electrode body B by adjusting the length of the positive electrode mixture coating layer. The relative angle θ ′ of the coating layer end Y and the positive electrode active material single-sided coating layer end Y ′ with respect to the electrode body center point O ′ is within the range shown in Table 1 described below (θ ′ <5 °). The cylindrical lithium ion secondary batteries of Comparative Examples 3 to 4 were prepared by adjusting the above.

  100 test batteries were prepared, respectively, and a crush test was performed under the following conditions.

  After charging to 4.2 V at 400 mA in an environment of 20 ° C., a crush test was performed. In the crushing test, a metal cylindrical round bar with a diameter of 4 mm was used, and this round bar was pressed against the center of the battery so that it was parallel to the direction perpendicular to the direction in which the outer dimension of the battery was the longest, The battery was crushed until the thickness was halved.

  Table 1 below shows the results of the crush test. In Table 1, the denominator of the numerical value indicating the result is the number of batteries subjected to the test, and the numerator is the number of batteries that have abnormally heated. This abnormal heat generation indicates a case where the battery surface temperature is 100 ° C. or higher.

  From the results of Table 1, it can be seen that when the batteries of Examples 1 to 14 of the present invention are compared with the batteries of Comparative Examples 1 to 4, the abnormal heat generation frequency of the batteries is clearly low and it is safe.

  This is because, in the case of the electrode body A shown in FIG. 1, the negative electrode active material double-sided coating layer end X and the negative electrode active material single-sided coating layer end X ′ are structural change points, so that stress from the outside is originally concentrated. As the two points approach each other, the strain stress received by the electrode body is concentrated and amplified at one point, and the separator is easily broken, resulting in the results of Examples 1 to 7 and Comparative Examples 1 and 2. It is. From the results of Table 1, it can be seen that if the relative angle θ is 5 ° or more and 180 ° or less, the separator is not broken by concentrated amplification of strain stress, and safety is maintained. Furthermore, when the battery after the test was disassembled and the separator was observed for damage, the battery of Examples 2 to 7 showed almost no damage to the separator, whereas the battery of Example 1 was slightly damaged. Observed. From this result, it is considered that the relative angle θ (0 ° ≦ θ ≦ 180 °) is more preferably 25 ° or more from the viewpoint of relaxation of strain stress.

  In the case of the electrode body B shown in FIG. 2, the positive electrode active material double-sided coating layer end Y and the positive electrode active material single-sided coating layer end Y ′ are structural change points, so that stress from the outside is concentrated. As the two points approach each other, the strain stress received by the electrode body is concentrated and amplified at one point, and the separator easily breaks, resulting in the results of Examples 8 to 14 and Comparative Examples 3 to 4. is there. From the results of Table 1, if the relative angle θ ′ (0 ° ≦ θ ′ ≦ 180 °) is 5 ° or more and 180 ° or less, the separator is not broken due to concentrated amplification of strain stress, and safety is maintained. I understand. Furthermore, when the battery after the test was disassembled and the separator was observed for damage, the battery of Examples 9 to 14 showed almost no damage to the separator, whereas the battery of Example 8 was slightly damaged. Observed. From this result, it is considered that the relative angle θ ′ is more preferably 25 ° or more from the viewpoint of relaxation of strain stress.

  In the above example, evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape is different, such as a square battery.

  If the component by this invention is used, a high quality and highly safe lithium ion secondary battery can be provided. This lithium ion secondary battery is useful as a drive power source for electronic devices such as notebook computers, mobile phones, and digital still cameras.

Cross-sectional schematic diagram of a spiral electrode body A of a cylindrical battery of the present invention Cross-sectional schematic diagram of spiral electrode body B of cylindrical battery of the present invention 1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Insulating gasket 3 Positive electrode lead 4 Upper insulating plate 5 Positive electrode 6 Negative electrode 7 Separator 8 Battery case 9 Negative electrode lead 10 Lower insulating plate A, B Electrode body X Negative electrode active material double-sided coating layer end X 'Negative electrode active material End of single-sided coating layer O Center point of electrode body A θ Relative angle of negative electrode active material double-sided coating layer end X and negative electrode active material single-sided coating layer end X ′ with respect to central point O Y Positive electrode active material double-sided coating layer end Y 'Positive electrode active material single-sided coating layer end O' center point of electrode body B θ 'Relative angle of positive electrode active material double-sided coating layer end Y and positive electrode active material single-sided coating layer end Y' with respect to central point O '

Claims (4)

At least a part of the strip-shaped positive electrode current collector is coated with a positive electrode active material on both surfaces, and at least a part of the strip-shaped negative electrode current collector is coated with a negative electrode active material on both surfaces. A secondary battery in which an electrode case obtained by spirally winding a negative electrode having a negative electrode active material coated on at least a part of one side continuously with a substance double-sided coating layer is interposed in a case. The negative electrode active material double-sided coating layer end and the negative electrode active material single-sided coating layer end arranged on the outer periphery of the negative electrode in the wound structure electrode body are each in a cross section of the electrode body. The lithium ion secondary battery is disposed so that a relative angle with respect to the center point of the electrode body is 5 ° or more and 180 ° or less. At least a part of the strip-shaped negative electrode current collector is coated with a negative electrode active material on both surfaces, and at least a part of the strip-shaped positive electrode current collector is coated with a positive electrode active material on both surfaces. A secondary battery in which an electrode body obtained by spirally winding a positive electrode having a positive electrode active material coated on at least a part of one side thereof continuously with a substance double-sided coating layer via a separator is accommodated in an outer case. In the electrode structure having the wound structure, the positive electrode active material double-sided coating layer end and the positive electrode active material single-sided coating layer end arranged on the outer periphery of the positive electrode are arranged on the cross-section of the electrode body. The lithium ion secondary battery is disposed so that a relative angle with respect to the center point of the electrode body is 5 ° or more and 180 ° or less. The lithium ion secondary battery according to claim 1, wherein the relative angle is 25 ° or more and 45 ° or less. The positive electrode _{is, Li x M y N 1-} y O 2 (x: 1.05 ≧ x ≧ 0.95, M ≠ N, M, N are, Co, Ni, Mn, Cr , Mg, Al, Zn Any one or more of the above, wherein a positive electrode mixture mainly composed of an active material represented by y: 1 ≧ y ≧ 0) is applied on a positive electrode current collector. Item 3. A lithium ion secondary battery according to any one of Items 2 to 3.

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