JP2011165388A - Electrode for lithium ion secondary battery, electrode group for lithium ion secondary battery using the electrode and lithium ion secondary battery using the electrode group - Google Patents

Abstract

An object of the present invention is to provide an electrode group for a lithium ion secondary battery that is not affected by the distance from the center of winding of the electrode group and in which the liquid retaining property of the electrolyte is uniform throughout the electrode group. .
SOLUTION: A long current collector sheet and an electrode active material layer formed on the surface of the current collector sheet, the electrode active material layer having electrode active material particles that occlude and release lithium ions, and a conductive material. Contains an auxiliary agent and a binder that binds the electrode active material particles and the conductive auxiliary agent, and in the longitudinal direction of the electrode active material layer, the half side in the longitudinal direction is upstream, and the other half side is downstream. In this case, the porosity on the upstream side is higher than the porosity on the downstream side, and the content ratio of the conductive additive to the electrode active material is higher on the upstream side than on the downstream side.
[Selection] Figure 2

Description

  The present invention relates to a lithium ion secondary battery. Specifically, the present invention relates to an improvement in an electrode used for manufacturing a wound electrode group excellent in liquid retention of a non-aqueous electrolyte.

  With the downsizing and multi-functionalization of portable electronic devices, lithium ion secondary batteries used as power sources are required to be lighter, larger in capacity, longer in life, and the like.

  A general lithium ion secondary battery includes a positive electrode having a positive electrode active material layer formed on the surface of the positive electrode current collector, a negative electrode having a negative electrode active material layer formed on the surface of the negative electrode current collector, and a separator separating the positive electrode and the negative electrode As a battery component.

  The positive electrode active material layer is rolled after, for example, applying a positive electrode mixture containing a positive electrode active material such as lithium cobaltate, a conductive additive, and a binder to the surface of the positive electrode current collector such as an aluminum foil. Is obtained. Similarly, the negative electrode active material layer is applied to the surface of the negative electrode current collector such as a copper foil with a roll type coating machine containing a negative electrode active material such as graphite, a conductive additive, and a binder. It is obtained by rolling.

  By the way, in recent years, as a method for forming an active material layer on the surface of a current collector, an active material is used by using an ink jet coating apparatus using a so-called ink jet method, which is used in the printing field, instead of the roll type coating machine described above. A method of forming a layer has been proposed.

  Patent Document 1 below discloses a method of forming an active material layer using an electrode ink for ink jet coating, wherein the electrode active material and the conductive auxiliary agent particle size are 1 μm or less. Patent Document 1 describes that such an electrode electrode for ink-jet coating is capable of producing a thin film electrode with good reproducibility and accuracy because precipitation of the active material is unlikely to occur over time.

  Further, the following Patent Document 2 uses an ink jet coating apparatus to eject a liquid containing an active material on the current collector surface as a large number of particles, and attach the particles to the current collector surface, thereby reducing the thickness. And it discloses that an electrode with high uniformity of film thickness can be obtained.

  Furthermore, the following Patent Document 3 discloses that on the active material layer of at least one of the positive electrode active material layer and the negative electrode active material layer for the purpose of improving safety at the time of internal short-circuiting of the lithium ion battery and nail penetration safety. Discloses a method of forming a porous insulating layer forming region and a non-forming region with an inkjet coating apparatus.

JP 2006-172959 A JP 2005-11656 A JP 2005-174792 A

  A wound type lithium ion secondary battery is configured such that a wound electrode group including a positive electrode plate, a negative electrode plate, a positive electrode plate, and a separator that separates the negative electrode plate is enclosed in a battery case together with a non-aqueous electrolyte.

  In the wound electrode group, the radius of curvature of the electrode plate is smaller as it is closer to the center of winding, and the radius of curvature of the electrode plate is larger as it is farther from the center of winding. In a lithium ion secondary battery, the positive electrode active material or the negative electrode active material expands or contracts with the insertion or extraction of lithium ions during charge / discharge. In such a case, in the portion close to the winding center where the radius of curvature of the electrode plate is small, it is difficult to relieve stress associated with deformation when the active material expands or contracts. Accordingly, the surface pressure increases as the active material expands at a portion near the winding center of the electrode plate group, and conversely, the surface pressure decreases at a portion far from the winding center. Therefore, in the portion near the winding center of the electrode, the liquid retaining property of the electrolytic solution tends to be relatively low during charging and discharging, and in the portion far from the winding center of the electrode, the liquid retaining property of the electrolytic solution is relatively low. It tends to be expensive.

  It is an object of the present invention to provide an electrode group for a lithium ion secondary battery that is not affected by the distance from the center of winding of the electrode group and in which the electrolyte solution retainability is uniform throughout the electrode group. To do.

  The inventors of the present invention have studied various means for causing a charge / discharge reaction uniformly in the electrode plate for the purpose of further improving the battery life. The present invention has been completed by paying close attention to the fact that the difference in liquid retention between the electrode plate and the separator occurs depending on the distance from the winding center of the electrode group.

  That is, an electrode for a lithium ion secondary battery according to one aspect of the present invention includes a long current collector sheet and an electrode active material layer formed on the surface of the current collector sheet, and the electrode active material layer is a lithium ion battery. An electrode active material particle that occludes and releases ions, a conductive auxiliary agent, and a binder that binds the electrode active material particle and the conductive auxiliary agent, in the longitudinal direction of the electrode active material layer, When the half side is the upstream side and the other half side is the downstream side, the porosity on the upstream side is higher than the porosity on the downstream side, and the content ratio of the conductive additive to the volume ratio of the electrode active material is the downstream side. The upstream side is formed to be higher than the side.

  The electrode group for a lithium ion secondary battery according to another aspect of the present invention is an electrode group for a lithium ion secondary battery obtained by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. And at least one of a positive electrode or a negative electrode uses the electrode mentioned above, and has arrange | positioned the upstream side to the winding center side, It is characterized by the above-mentioned.

  By increasing the porosity of the active material layer in the portion near the winding center of the wound electrode group and lowering the porosity of the active material layer in the portion far from the winding center, electrolysis in the portion near the winding center The liquid retention of the liquid can be preferentially improved. Therefore, even when a portion close to the winding center is subjected to a high surface pressure due to the expansion of the active material, it is not affected by the distance from the winding center, and the liquid retention of the electrolyte is uniform throughout the entire electrode group. An electrode group for a lithium ion secondary battery is obtained. On the other hand, when the porosity is high, since the conductive path between the electrode active material particles becomes poor, charging / discharging of a large current becomes difficult. In this case, the conductive path between the electrode active material particles can be sufficiently ensured by increasing the blending ratio of the conductive additive in the portion close to the winding center. As a result, with such a configuration, a uniform charge / discharge reaction can be maintained throughout the electrode group without being affected by the distance from the winding center.

  The objects, features, aspects and advantages of the present invention will become more apparent by referring to the following detailed description and attached drawings.

  According to the present invention, it is possible to obtain an electrode group for a lithium ion secondary battery that is not affected by the distance from the winding center of the electrode group and in which the electrolyte solution retainability is uniform over the entire electrode group. A lithium ion secondary battery including such an electrode group has a long life because of high uniformity of charge / discharge reaction in the electrode plate.

A schematic perspective sectional view of a lithium ion secondary battery 100 of the present embodiment is shown. The schematic longitudinal cross-sectional view of the positive electrode plate 10a which comprises the electrode group 10 accommodated in the lithium ion secondary battery 100 of this embodiment is shown. The graph explaining the ratio of the porosity in an electrode active material layer with respect to the distance from the winding center which is an upstream edge part, and the content rate of the conductive support agent with respect to positive electrode active material particle is shown. It is a schematic explanatory drawing explaining the method to manufacture the electrode plate for lithium ion secondary batteries. The partial cross section schematic diagram of the electrode group 10 of this embodiment is shown.

  Preferred embodiments of an electrode for a lithium ion secondary battery, an electrode group including such an electrode, and a lithium ion secondary battery according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic perspective sectional view of a cylindrical lithium ion secondary battery 100 as an example of the lithium ion secondary battery of the present embodiment. For convenience of explanation, FIG. 1 also shows a partial element exploded view in which the electrode group 10 accommodated in the lithium ion secondary battery 100 is exploded.

  A lithium ion secondary battery 100 shown in FIG. 1 includes an electrode group 10 and a non-aqueous electrolyte (not shown) enclosed in a battery case 40. The electrode group 10 is formed by winding a positive electrode plate 10 a and a negative electrode plate 10 b with a separator 9 interposed therebetween. A positive electrode lead 43 is drawn from the positive electrode plate 10 a and connected to the sealing plate 41, and a negative electrode lead 44 is drawn from the negative electrode plate 10 b and connected to the bottom of the battery case 40. Insulating rings (not shown) are respectively provided on the upper and lower portions of the electrode group 10. Then, the non-aqueous electrolyte is injected, and the battery case 40 is sealed by the sealing plate 41 through the gasket 42.

  FIG. 2 is a schematic longitudinal sectional view of the positive electrode plate 10a constituting the electrode group 10.

  As shown in FIG. 2, the positive electrode plate 10a includes a long positive electrode current collector sheet 1a and a positive electrode active material layer 2a formed on the surface of the positive electrode current collector sheet 1a. The positive electrode active material layer 2a contains positive electrode active material particles 3a, a conductive additive 4a, and a binder 5a.

  The positive electrode active material particles 3a and the conductive additive 4a are bound to each other with a small amount of the binder 5a partially attached to the surface. And the space | gap v for electrolyte solution to pass through is formed between the positive electrode active material particle 3a and the conductive support agent 4a which were bound in this way.

  In the positive electrode active material layer 2a formed on the surface of the positive electrode plate 10a, when the half side in the longitudinal direction is the upstream side U and the other half side is the downstream side L, the porosity of the upstream side U is downstream. It is formed so that the porosity of the side L is higher and the content ratio of the conductive additive 4a to the positive electrode active material particles 3a is higher on the upstream side than on the downstream side.

  As an example, in FIG. 2, the porosity gradually increases as the distance from the upstream end surface arranged on the side closer to the winding center in the electrode group 10 increases, and the conductive auxiliary agent 4 a with respect to the positive electrode active material particles 3 a The positive electrode active material layer 2a is formed so that the weight ratio gradually increases.

  The positive electrode active material layer 2a is formed such that the upstream porosity of the wound positive electrode plate 10a is higher than the downstream porosity. As a result, the liquid retention in the portion near the winding center where the liquid retention of the electrolytic solution decreases due to the increase in the surface pressure applied to the electrode plate during charging and discharging is improved. Thus, in the part which improved the porosity, since the electroconductive path between positive electrode active material particles becomes scarce, there exists a possibility that charging / discharging of a large current may become difficult. In this case, the conductive path between the positive electrode active material particles can be sufficiently ensured by increasing the content ratio of the conductive additive on the upstream side. As a result, even when charging and discharging a large current, the charge / discharge reaction rate can be made uniform by making the liquid retention property uniform over the entire electrode group 10.

  The porosity of the positive electrode active material layer can be adjusted by increasing the density of the constituent components of the upstream positive electrode active material layer and increasing the density of the constituent components of the downstream positive electrode active material layer. Specifically, for example, when the thickness of the positive electrode active material layer is uniform, the constituent component composition is changed in the longitudinal direction so that the packing density of the upstream constituent component is lower than the downstream packing density. Thus, the porosity on the upstream side can be made higher than the porosity on the downstream side. As another method, for example, by increasing the pressing pressure during rolling when forming the positive electrode active material layer, the pressing pressure on the downstream side is higher than the pressing pressure on the upstream side, thereby increasing the packing density on the upstream side. It can be made lower than the packing density on the downstream side. Furthermore, the thickness of the coating film for forming the upstream positive electrode active material layer is reduced, and the thickness of the coating film on the downstream side is reduced and rolled by a roll press that maintains a constant gap interval. You can make a difference. In these cases, the content ratio of the conductive additive to the positive electrode active material particles is selected such that the upstream side is higher than the downstream side.

  Specific examples of the positive electrode current collector include foils and sheets made of aluminum, stainless steel, nickel, titanium, and the like. Although the thickness of a positive electrode electrical power collector is not specifically limited, Usually, it is preferable that it is the range of 1-500 micrometers.

  Specific examples of the positive electrode active material particles include lithium-containing transition metal oxides such as lithium cobaltate, lithium nickelate, and lithium manganate. A part of the transition metal of the lithium-containing transition metal oxide may be substituted with another element. For example, a modified product obtained by substituting a part of cobalt of lithium cobaltate with aluminum or magnesium, or a modified product obtained by replacing part of nickel of lithium nickelate with cobalt or manganese may be used.

  As a content rate of a positive electrode active material, it is preferable that it is the range of 60-98 mass% with respect to the whole component of a positive electrode active material layer, Furthermore, 70-98 mass%, Especially 80-98 mass%. .

  The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 0.001 to 2 μm, more preferably 0.01 to 1 μm.

  Further, the average particle diameter of the positive electrode active material particles is 2 to 20 times, more preferably 5 to 10 times the average particle diameter of the conductive auxiliary agent described later, and the adjustment of the porosity becomes easy. It is preferable from the point.

  As a specific example of the conductive auxiliary agent, any conductive material that is chemically stable in the battery can be used without particular limitation. For example, graphite such as natural graphite (such as flake graphite), artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and conductive such as carbon fiber and metal fiber Conductive fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide whisker and potassium titanate whisker, conductive metal oxides such as titanium oxide, organic conductive materials such as polyphenylene derivatives, carbon fluoride, etc. Can be used.

  As a content rate of a conductive support agent, it is preferable that it is 1-40 mass% with respect to the whole component of a positive electrode active material layer, Furthermore, it is 1-30 mass%, Especially, it is preferable that it is the range of 1-20 mass%. .

  In addition, the conductive auxiliary agent can adjust the steric hindrance that contributes to the control of the porosity in the rolling process when forming the active material layer described later by selecting the particle shape and particle diameter. it can. That is, in the case of using conductive particles or conductive fibers of non-spherical shape such as wedge shape, flat shape, flake shape, etc. with a high aspect ratio as the particle shape of the conductive auxiliary agent, the rolling process at the time of forming the active material layer The rolling force can be applied to the mixture layer uniformly due to the steric hindrance. Therefore, the porosity can be adjusted by selecting the particle shape.

  The average particle diameter of the conductive assistant is preferably 0.001 to 1 μm, and more preferably 0.01 to 0.5 μm from the viewpoint of easy adjustment of the porosity.

  Specific examples of the binder include polytetrafluoroethylene (PTFE), modified polyacrylic acid rubber particles (such as “BM-500B (trade name)” manufactured by Nippon Zeon Co., Ltd.), and polyvinylidene fluoride (PVDF). Etc. Further, PTFE and rubber particles may be used in combination with carboxymethyl cellulose (CMC), polyethylene oxide, and soluble modified acrylonitrile rubber (such as “BM-720H (trade name)” manufactured by Nippon Zeon Co., Ltd.) having a thickening effect. Good.

  As a content rate of a binder, it is preferable that it is 1-30 mass parts with respect to 100 mass parts of positive electrode active materials, Furthermore, 1-20 mass parts, Especially it is the range of 1-10 mass parts.

  In the positive electrode active material layer 2a, as shown in the graph of FIG. 3, the porosity in the positive electrode active material layer increases as it approaches the winding center of the electrode group 10, and the conductivity with respect to the positive electrode active material particles is increased. The content of auxiliary agent is high.

  The porosity on the upstream side of the positive electrode active material layer is preferably in the range of 20 to 50%, more preferably 25 to 40%. If the upstream porosity is too low, the liquid retention property of the portion near the winding center tends to be insufficient. Further, when the upstream porosity is too high, the constituent components of the positive electrode active material layer are relatively reduced, and thus the capacity secured on the upstream side tends to decrease.

  The porosity on the downstream side of the positive electrode active material layer is preferably 10 to 40%, more preferably 15 to 30%. When the porosity on the downstream side is too high, the constituent components of the positive electrode active material layer are relatively reduced, so that the capacity secured on the downstream side tends to decrease. On the other hand, when the downstream porosity is too low, the liquid retention property of the portion far from the winding center tends to be insufficient.

  Moreover, as a difference of the porosity of the downstream of a positive electrode active material layer, and the porosity of an upstream, it is preferable that it is about 2 to 30%, Furthermore, it is about 5 to 20%.

  The porosity can be measured by a mercury intrusion method using a mercury porosimeter (for example, Autopore III9410 manufactured by Shimadzu Corporation).

  On the upstream side containing the conductive auxiliary agent in a high ratio, the mass ratio of the conductive auxiliary agent to the positive electrode active material particles is positive electrode active material particles: conductive auxiliary agent = 30: 1 to 1: 1, and further 20: 1 to 1. 3: 1 is preferred. When the content ratio of the conductive additive on the upstream side is too low, the conductive path between the positive electrode active material particles tends to be poor when the porosity is high. Moreover, when the content rate of a conductive support agent is too high, since the porosity and the ratio of positive electrode active material particle fall relatively, it is unpreferable. On the other hand, on the downstream side containing the conductive auxiliary agent at a low ratio, the mass ratio of the conductive auxiliary agent to the positive electrode active material particles is positive electrode active material particles: conductive auxiliary agent = 200: 1 to 5: 1, and further 100: It is preferable that it is 1-20: 1.

  On the upstream side, it is preferable that the content ratio of the conductive assistant with respect to the entire constituent components of the positive electrode active material layer is in a relatively high ratio range such as 3 to 45 mass%, further 5 to 30 mass%. On the other hand, on the downstream side, it is preferable to set a relatively low ratio range such as 0.5 to 15% by mass, and further 1 to 5% by mass.

  The thickness of the positive electrode active material layer is not particularly limited, but is preferably 10 to 100 μm, more preferably about 20 to 70 μm. Further, the thickness on the upstream side and the thickness on the downstream side may be constant or different.

  An example of a preferable method for manufacturing the positive electrode as described above will be described in detail with reference to FIG.

  In FIG. 4, a positive electrode active material layer is formed on the surface of the positive electrode current collector 1 a by using an inkjet coating apparatus 20 including a plurality of inkjet nozzles 11 a, 11 b, and 11 c whose supply amounts are independently controlled. It is a schematic explanatory drawing explaining the process of apply | coating a component. The inkjet nozzle 11a ejects the positive electrode active material ink 13 containing the positive electrode active material particles 3a. The inkjet nozzle 11b ejects the conductive assistant ink 14 containing the conductive assistant 4a. The inkjet nozzle 11c ejects the binder ink 15 containing the binder 5a. Ink jet nozzles 11a, 11b, and 11c are independently controlled in injection amount, and each component constituting the positive electrode active material layer is applied by supplying each component to the surface of positive electrode current collector 1a according to the control. be able to.

  The components constituting the positive electrode active material layer are applied to the surface of the positive electrode current collector 1a conveyed at a constant speed from the inkjet nozzles 11a, 11b, and 11c, respectively, and the positive electrode active material ink 13, the conductive auxiliary ink 14, and This is performed by spraying the binder ink 15 and applying it by inkjet.

  Inkjet application is a method in which ink is applied as droplets to the surface of a substrate (in the present embodiment, the positive electrode current collector 1a) from nozzles of an inkjet application apparatus that is widely used as printing means.

  As a method for inkjet application, any of a piezo element method, a thermal inkjet method, and a continuance method may be used. Among these, it is particularly desirable to use a piezo element method. In the piezo element method, the amount of ink ejected can be adjusted using a nozzle composed of a piezo element that is deformed by applying a voltage. The piezo element method is preferable because it does not require heating unlike the thermal ink jet method, and is excellent in thermal stability.

  As shown in FIG. 4, liquid chambers 16a, 16b, and 16c that store independent inks are connected to the inkjet nozzles 11a, 11b, and 11c of the inkjet coating apparatus 20, respectively. The liquid chambers 16a, 16b, and 16c communicate with independent ink jet nozzles 11a, 11b, and 11c via ink supply lines 17a, 17b, and 17c, respectively. Then, by independently controlling the liquid discharge operations of the ink jet nozzles 11a, 11b, and 11c, the positive electrode active material ink 13 and the conductive auxiliary ink 14 are independently controlled on the surface of the positive electrode current collector 1a. , And a binder ink 15 are applied.

  A method for independently controlling the liquid ejection operations of the inkjet nozzles 11a, 11b, and 11c is not particularly limited. Specifically, for example, the inkjet coating apparatus 20 is electrically connected to a computer 21 having a central processing unit (CPU) and a random access memory (RAM). Then, a program for controlling the ink jet coating apparatus 20 is installed in the computer 21. Then, the positive electrode active material ink 13, the conductive auxiliary ink 14, and the binder ink 15 are independently jetted from the inkjet nozzles 11a, 11b, and 11c onto the surface of the positive electrode current collector 1a that is conveyed at a constant speed. Inject with program control. The ink application method for forming the positive electrode active material layer using an ink jet coating apparatus is a mixture of cyan, magenta, and yellow at a predetermined ratio in a wide color space in order to express a desired image. It is possible to apply a conventionally known ink jet printer technology that expresses each of the colors.

  Next, the positive electrode active material ink 13, the conductive additive ink 14, and the binder ink 15 supplied to the ink jet coating apparatus 20 in the present embodiment will be described in detail.

  The positive electrode active material ink 13 is obtained, for example, by mixing the positive electrode active material particles 3a, a solvent (dispersion medium), a thickener, and the like at a predetermined blending ratio.

  Specific examples of the solvent include deionized water, ethanol, methanol, butanol, isopropyl alcohol, isobutyl alcohol, N-methyl-2-pyrrolidone and the like. These may be used alone or in combination of two or more.

  The mixing means is not particularly limited as long as it is various mixing methods that can sufficiently uniformly disperse the positive electrode active material particles 3a in a solvent. Specific examples thereof include a method using a homogenizer or a stirring deaerator.

  The viscosity of the positive electrode active material ink 13 adjusted in this way is preferably 100 cP or less, and more preferably 20 cP or less. If the viscosity of the positive electrode active material ink 13 exceeds 100 cP, there is a possibility that an inkjet nozzle clogging may occur.

  The positive electrode active material ink 13 may be used alone or in combination of two or more positive electrode active material inks ejected from inkjet nozzles having different types of positive electrode active material particles.

  In the conductive auxiliary ink 14 containing the conductive auxiliary 4a, for example, the conductive auxiliary 4a and the same solvent as described above are mixed at a predetermined mixing ratio by the same method as the mixing method of the positive electrode active material ink 13. Can be obtained. The conductive auxiliary ink 14 may be used alone or in combination of two or more types of conductive auxiliary inks ejected from inkjet nozzles having different types of conductive auxiliary agents.

  The conductive assistant ink 14 containing the binder ink 15 is also obtained by mixing the binder 5a, the solvent, and the like at a predetermined blending ratio in the same manner as the mixing method of the positive electrode active material ink 13. The binder ink 15 may be used alone or in combination of two or more binder inks ejected from inkjet nozzles having different types of binder.

  In the adjustment of the positive electrode active material ink 13, the conductive auxiliary ink 14, and the binder ink 15, as necessary, a thickener for adjusting the viscosity, a humectant for suppressing drying of the ink, and an appropriate pH. You may mix | blend the buffering agent for maintaining, etc.

  Examples of the thickener include carboxymethylcellulose (CMC), examples of the humectant include ethylene glycol, and examples of the buffer include maleic acid, but are not limited thereto.

  The amount of the positive electrode active material ink 13, the conductive auxiliary ink 14, and the binder ink 15 ejected by the inkjet coating apparatus 20 is the same as that of the positive electrode active material 3 a in the composition of the positive electrode active material layer 2 a finally obtained. The ratio of the auxiliary agent 4a and the binder 5a is determined in advance, and the program is controlled.

  Then, the positive electrode active material ink 13, the conductive additive ink 14, and the binder ink 15 applied to the surface of the positive electrode current collector 1a are dried. As a means for drying, it may be carried out in a normal atmosphere, preferably a reduced pressure atmosphere, at 20 to 200 ° C., preferably 80 to 150 ° C., for 1 minute to 8 hours, preferably 3 minutes to 1 hour. In addition, the thickness of the positive electrode active material layer 2a may be insufficient with respect to the target thickness due to limitations on the ink concentration to be used and the amount of ink ejected per process. In some cases, it is necessary to partially change the thickness in order to adjust the porosity. In such a case, the coating film may be further coated on the surface of the coating film formed in advance using an inkjet coating apparatus. By coating in this way, a coating film having a desired thickness can be formed.

  And the positive electrode active material layer 2a formed by applying and drying in this way is usually rolled. The density of the obtained positive electrode active material layer 2a can be increased by rolling. Although the apparatus and conditions used for rolling are not particularly limited, a conventionally known roll press or the like can be appropriately used.

  In addition, the density of the component which comprises the positive electrode active material layer of an upstream and a downstream can be adjusted also at the time of rolling. That is, when a coating film having the same thickness is formed, the upstream gap is made higher than the downstream porosity by increasing the gap distance on the upstream side and decreasing the gap distance on the downstream side. be able to. In addition, when the thickness after rolling is made constant, the thickness is made thinner than the thickness of the coating film on the downstream side than the thickness of the coating film on the upstream side, and pressed with a roll press having the same gap interval. Is constant, but a positive electrode active material layer having a high upstream porosity is obtained.

  The positive electrode plate 10a can be manufactured by the above method.

  As described above, the configuration and the manufacturing method of the positive electrode plate 10a constituting the electrode group 10 have been described in detail. However, the negative electrode plate 10b constituting the electrode group 10 is also different in that the type of the current collector and the constituent components of the active material layer are different. The same configuration and manufacturing method can be applied.

  Next, the configuration and manufacturing method of the negative electrode plate 10b will be described, but detailed description of common parts will be omitted in order to avoid duplication of description.

  The negative electrode plate 10b includes a long negative electrode current collector sheet and a negative electrode active material layer formed on the surface of the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material, a conductive additive, and a binder.

  Specific examples of the negative electrode current collector sheet include foils and sheets made of copper, stainless steel, nickel, titanium, and the like. Although the thickness of a negative electrode collector is not specifically limited, Usually, it is preferable that it is the range of 5-20 micrometers.

Specific examples of the negative electrode active material include carbon materials such as various natural graphite, coke, graphitizing carbon, carbon fiber, spherical carbon, various artificial graphite, and amorphous carbon; SiO _x (0.05 <x <1.95), and silicon compounds such as alloys, compounds and solid solutions containing silicon; tin compounds such as Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _y (0 <y <2), SnO ₂ , and SnSiO ₃ ; Etc.

  The average particle size of the negative electrode active material is not particularly limited, but is preferably 0.001 to 2 μm, and more preferably 0.01 to 2 μm.

  As a content rate of a negative electrode active material, it is preferable that it is the range of 60-99 mass% with respect to the whole component of a negative electrode active material layer, Furthermore, 80-99 mass%, Especially 90-99 mass%. .

  Further, as the conductive additive for the negative electrode, the same conductive aid as that for the positive electrode can be used.

  As a content rate of a conductive support agent, it is 0.5-30 mass% with respect to the whole component of a negative electrode active material layer, Furthermore, 0.5-20 mass%, Especially 0.5-10 mass% A range is preferable.

  Specific examples of the negative electrode binder include PVDF and styrene-butadiene rubber (SBR).

  Although the content rate of a binder is not specifically limited, 0.5-30 mass parts with respect to 100 mass parts of negative electrode active materials contained in the whole negative electrode active material layer, Furthermore, 0.5-20 masses Part, particularly in the range of 0.5 to 10 parts by mass.

  In the negative electrode plate 10b as well, as the positive electrode plate 10a described above, the porosity in the negative electrode active material layer increases as it approaches the winding center of the electrode group 10, and the conductive auxiliary agent for the negative electrode active material particles. The content ratio of is high.

  The porosity on the upstream side of the negative electrode active material layer is preferably in the range of 20 to 50%, more preferably 25 to 40%. If the upstream porosity is too low, the liquid retention property of the portion near the winding center tends to be insufficient. Further, when the upstream porosity is too high, the constituent components of the negative electrode active material layer are relatively reduced, and thus the capacity secured on the upstream side tends to decrease.

  The porosity on the downstream side of the negative electrode active material layer is preferably 10 to 40%, more preferably 15 to 30%. When the porosity on the downstream side is too high, since the constituent components of the negative electrode active material layer are relatively reduced, the capacity secured on the downstream side tends to decrease. On the other hand, when the downstream porosity is too low, the liquid retention property of the portion far from the winding center tends to be insufficient.

  The difference between the downstream porosity and the upstream porosity of the negative electrode active material layer is preferably 2 to 30%, and more preferably about 5 to 20%.

  On the upstream side containing the conductive auxiliary agent in a high ratio, the content ratio of the conductive auxiliary agent to the negative electrode active material particles is as follows: negative electrode active material particles: conductive auxiliary agent = 100: 1 to 1: 1, and further, 100: 1 to 2: 1 is preferred. When the content ratio of the conductive additive on the upstream side is too low, the conductive path between the negative electrode active material particles tends to be poor when the porosity is high. Moreover, when the content rate of a conductive support agent is too high, since the porosity and the ratio of negative electrode active material particle fall relatively, it is unpreferable. On the other hand, on the downstream side containing the conductive auxiliary agent at a low ratio, the mass ratio of the conductive auxiliary agent to the negative electrode active material particles is negative electrode active material particles: conductive auxiliary agent = 1: 0 to 5: 1, and further 1: It is preferably 0 to 20: 1.

  On the upstream side, the content ratio of the conductive assistant to the entire constituent components of the negative electrode active material layer is preferably 1 to 40% by mass, and more preferably 1 to 30% by mass. On the other hand, on the downstream side, a relatively low ratio such as 0 to 15% by mass, and further 0 to 5% by mass is preferable.

  The thickness of the negative electrode active material layer is not particularly limited, but is preferably 10 to 100 μm, and more preferably about 20 to 80 μm. Further, the thickness on the upstream side and the thickness on the downstream side may be constant or different.

  In the above, the positive electrode and negative electrode of this embodiment were demonstrated. Such a positive electrode and a negative electrode of this embodiment may be applied to both the positive electrode and the negative electrode of the wound electrode group, or may be applied to only one of them. Furthermore, when the active material layer is formed on both surfaces of the current collector, the current collector may be applied to only one surface. In particular, since the radius of curvature of the winding inner side of the winding is smaller than the curvature radius of the outer surface of the winding, it is more preferable to apply to the inner side of the winding.

  That is, when the positive electrode plate 10a of the wound electrode group 10 is described as an example, as shown in FIG. 5, only the inner surface (A in FIG. 5) of the wound positive electrode plate 10a is wound. The surface (B in FIG. 5) of the wound positive electrode plate 10a is formed so that the porosity and the mass ratio of the conductive additive 4a to the positive electrode active material particles 3a increase as approaching the center. A positive electrode active material layer having a uniform composition may be formed. In a wound electrode plate, the radius of curvature of the inner surface of the electrode plate is smaller than the radius of curvature of the outer surface. For this reason, the surface pressure applied to the inner side of the electrode plate is particularly increased due to the volume change accompanying the occlusion / release of lithium as the active material, and the liquid retaining property of the electrolytic solution is particularly lowered. Accordingly, the positive electrode active material layer 2a is applied only to the inner side of the winding so that the porosity of the positive electrode active material layer 2a increases as the winding center is approached, and the content ratio of the conductive additive 4a to the positive electrode active material particles 3a increases. By doing so, a positive electrode plate can be obtained at a relatively low cost and capable of sufficiently ensuring the liquid retention of the electrolytic solution even on the side close to the winding center.

  Next, other elements of the battery 100 will be described.

  As a material constituting the positive electrode lead, the negative electrode lead, and the like, aluminum that has been conventionally used as a material for the positive electrode lead, nickel, aluminum, and the like that have been used as a material for the negative electrode lead are not particularly limited.

  As the battery case, for example, an aluminum case, an iron case whose inner surface is nickel-plated, a case made of an aluminum laminate film, or the like can be used. The shape of the battery case may be any shape such as a cylindrical shape or a square shape. As the cross section of the electrode group, a shape such as a circle or an ellipse is selected according to the shape of the battery case.

  As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in a non-aqueous solvent is preferably used. Specific examples of the non-aqueous solvent include, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, γ-butyrolactone, γ-valerolactone, etc. Lactones, chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, Dimethylsulfoxy 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl -2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methyl-2-pyrrolidone and the like. These may be used alone or in combination of two or more.

Specific examples of the lithium salt dissolved in the non-aqueous solvent include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, lithium imide salt and the like. These may be used alone or in combination of two or more. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L.

  In addition, various additives may be further added to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics of the battery. Specific examples of such additives include, for example, vinylene carbonate, vinyl ethylene carbonate, phosphazene and fluorobenzene, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphate triamide, nitrobenzene derivatives, Examples include crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ethers, and the like. These additives are preferably blended in an amount of about 0.5 to 10% by mass of the non-aqueous electrolyte.

  The lithium ion secondary battery using the electrode group of the present embodiment described above can maintain a high capacity even after repeating many cycles of charge / discharge. Such a lithium ion secondary battery exhibits a particularly high effect in a battery including an electrode plate group having a long overall length, which is used as a power source for an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle and the like. The lengths of the positive electrode plate, the negative electrode plate, and the separator constituting such an electrode plate group are preferably 800 to 10000 mm, and more preferably 2000 to 8000 mm.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, the scope of the present invention is not limited at all by the following examples.

[Example 1: Production of positive electrode plate]
A lithium-containing composite oxide represented by a composition of LiNi _0.85 Co _0.12 Al _0.03 O _{2 having} an average particle diameter of 0.8 μm was used as the positive electrode active material. A positive electrode active material ink is prepared by adding 5 parts by mass of a positive electrode active material to 100 parts by mass of N-methyl-2-pyrrolidone (NMP), which is a solvent (dispersion medium), and sufficiently stirring and mixing the mixture. did.

  On the other hand, PVDF “# 1320 (trade name)” (N-methyl-2-pyrrolidone (NMP) solution containing 12% by mass of PVDF) manufactured by Kureha Chemical Co., Ltd. was used as a binder. A positive electrode binder ink was prepared by adding 5 parts by mass (solid content) of PVDF to 100 parts by mass of NMP, which is a solvent, and sufficiently stirring and mixing them to dissolve.

  In addition, acetylene black having an average particle diameter of 50 nm was used as a conductive aid. A positive electrode conductive additive ink was prepared by sufficiently stirring and mixing 5 parts by mass of acetylene black with respect to 100 parts by mass of NMP as a solvent (dispersion medium).

  Then, the obtained positive electrode active material ink, positive electrode conductive assistant ink, and positive electrode binder ink were supplied to independent liquid chambers 16a, 16b, and 16c of the inkjet coating apparatus 20 as shown in FIG. Then, each ink was applied to the surface of a long aluminum foil having a thickness of 15 μm, a width of 52 mm, and a length of 800 mm, which was a positive electrode current collector, using the ink jet coating apparatus 20. In addition, application | coating was repeated in multiple times in order to form the positive electrode active material layer of predetermined thickness. And the formed coating film was dried on 100 degreeC and the conditions for 1 hour. Similarly, a positive electrode active material layer was formed on the other surface. And the positive electrode active material layer with a one side thickness of 40 micrometers was formed by rolling the dried coating film using a roll press machine. In the formed positive electrode active material layer, the binder is uniformly contained in the positive electrode active material layer in an amount of 3% by mass. Further, the conductive auxiliary agent is controlled so that the conductive auxiliary agent in the positive electrode active material layer at the upstream end is 10% by mass (mass ratio of positive electrode conductive auxiliary agent to positive electrode active material is 87:10), and downstream. The concentration of the conductive auxiliary agent at the end on the side is controlled to be 2% by mass (same mass ratio 95: 2), and the concentration of the positive electrode conductive auxiliary agent gradually has a concentration gradient in the range of 10% to 2% by mass therebetween. The composition of the positive electrode active material layer was controlled so as to obtain such a composition. The positive electrode plate thus obtained is referred to as a positive electrode plate A1.

  The average porosity of the positive electrode active material layer formed on the positive electrode plate A1 was 35%, and the conductive agent concentration was 8% on average. Further, the porosity on the downstream side was 23% on average, and the conductive agent concentration was 4% on average.

[Example 2: Production of negative electrode plate]
Artificial graphite having an average particle diameter of 1 μm was used as the negative electrode active material. 5 parts by mass of artificial graphite was added to 100 parts by mass of deionized water as a solvent (dispersion medium), and the mixture was dispersed by sufficiently stirring and mixing. Then, an appropriate amount of a 1% by mass aqueous solution of carboxymethylcellulose (CMC) was added to prepare a negative electrode active material ink.

  On the other hand, styrene butadiene rubber (SBR) (an aqueous dispersion having a solid content of 40% by mass) manufactured by JSR Corporation was used as a binder. A binder ink was prepared by adding 1 part by mass of SBR to 100 parts by mass of deionized water as a solvent and dissolving the mixture by sufficiently stirring and mixing.

  Moreover, VGCF (gas phase method carbon fiber) manufactured by Showa Denko KK was used as a conductive additive. To 100 parts by mass of deionized water, which is a solvent (dispersion medium), 2 parts by mass of VGCF was sufficiently stirred and mixed to disperse, and an appropriate amount of a 1% by mass aqueous solution of carboxymethyl cellulose (CMC) was added to prepare a conductive auxiliary ink. .

  Then, the obtained negative electrode active material ink, conductive additive ink, and binder ink were supplied to independent liquid chambers 16a, 16b, and 16c of the inkjet coating apparatus 20 as shown in FIG. And each said ink was apply | coated to the surface of copper foil of thickness 10 micrometers, width 56mm, and length 900mm which is a negative electrode collector using the inkjet coating device 20. FIG. In addition, application | coating was repeated in multiple times in order to form the negative electrode active material layer of predetermined thickness. And the formed coating film was dried on 100 degreeC and the conditions for 1 hour. Similarly, a negative electrode active material layer was formed on the other surface. And the negative electrode active material layer with a thickness of 50 μm on one side was formed by rolling the dried coating film using a roll press machine. In the formed negative electrode active material layer, the negative electrode binder is uniformly contained in the active material layer in an amount of 1% by mass. In the formed negative electrode active material layer, the conductive auxiliary in the negative electrode active material layer at the upstream end is 5% by mass (mass ratio of negative electrode conductive auxiliary to negative electrode active material 94: 5). The concentration of the conductive auxiliary agent at the downstream end is controlled to 0.5% by mass (same mass ratio 98.5: 1), and the conductive auxiliary agent concentration is gradually reduced to 5 to 0.5% by mass therebetween. The negative electrode active material layer composition was controlled so as to have a composition having a concentration gradient in the above range. The negative electrode plate thus obtained is referred to as a negative electrode plate B1.

  The porosity on the upstream side of the negative electrode active material layer formed on the negative electrode plate B1 was an average of 36%, and the conductive agent concentration was an average of 4%. Further, the porosity on the downstream side was 24% on average, and the conductive agent concentration was 2% on average.

[Comparative Example 1: Production of positive electrode plate A2]
A positive electrode mixture paste was prepared by stirring 1 kg of lithium-containing composite oxide, 250 g of PVDF, 60 g of acetylene black, and an appropriate amount of NMP, which were the same as those used in Example 1, with a double-arm kneader. This paste was applied uniformly on both sides of an aluminum foil as a positive electrode current collector similar to that used in Example 1, using a die coater, dried and then roll-pressed to form a positive electrode active material layer having a thickness of 40 μm. Formed. The positive electrode plate thus obtained is referred to as a positive electrode plate A2. The positive electrode plate A2 uniformly contains 3% by mass of a binder and 6% by mass of acetylene black, which is a conductive additive, over the entire positive electrode active material layer. The composition of the positive electrode active material formed on the positive electrode plate A1 was the same.

  The porosity of the positive electrode active material layer formed on the positive electrode plate A1 was constant on the upstream side and the downstream side, and was 29%.

[Comparative Example 2: Production of negative electrode plate B2]
A paste was prepared by stirring 1 kg of artificial graphite, 25 g of styrene butadiene rubber (SBR), 27 g of VGCF, 10 g of CMC, and an appropriate amount of deionized water similar to those used in Example 2 in a double-arm kneader. did. This paste was applied uniformly on both sides of the paste used in Example 2 and a copper foil having a thickness of 10 μm as a negative electrode current collector using a die coater and dried. Thereafter, the coating film was roll-pressed to form a negative electrode active material layer. The negative electrode plate thus obtained is referred to as a negative electrode plate B2. The negative electrode plate B2 uniformly contains 1% by mass of binder and 2.7% by mass of VGCF, which is a conductive auxiliary agent, throughout the negative electrode active material layer. The composition of the negative electrode active material formed on the negative electrode plate B1 was the same.

  The porosity of the negative electrode active material layer formed on the negative electrode plate B2 was constant on the upstream side and the downstream side, and was 30%.

[Example 3: Production and evaluation of battery α]
(I) Preparation of electrolyte solution Lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / L in a mixed solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1: 3, and non-aqueous An electrolyte solution was prepared.
(II) Battery assembly The positive electrode plate A1 and the negative electrode plate B1 are wound through a microporous polyethylene sheet having a thickness of 20 μm, a width of 60 mm, and a length of 2000 mm to form a spiral electrode group as shown in FIG. Configured.

A positive electrode lead made of aluminum and a negative electrode lead made of nickel were attached to the positive electrode plate A1 and the negative electrode plate B1, respectively. An upper insulating plate was disposed on the upper surface of this electrode group, and a lower insulating plate was disposed on the lower surface. The electrode group was inserted into the battery case, and 5 g of nonaqueous electrolyte was injected into the battery case. Then, the sealing board which arranged the gasket around and the positive electrode lead were made to conduct, and the opening of the battery case was sealed with the sealing board. Thus, a battery α which is a cylindrical 18650 lithium ion secondary battery was completed.
(III) Evaluation of Battery The battery α was evaluated for battery life characteristics by the following method.

  The charge / discharge cycle test was conducted 500 cycles at 25 ° C. under the conditions shown in Table 1 below, and the capacity retention rate of the post-test battery before the cycle test was evaluated.

  The results are shown in Table 2.

[Examples 4 and 5, Comparative Example 1: Production of batteries β to δ]
As shown in Table 2, an electrode group was produced in the same manner as in Example 3 except that the positive electrode plate A2 or the negative electrode plate B2 described above was used instead of the positive electrode plate A1 or the negative electrode plate B1, respectively. A secondary battery was obtained. The obtained lithium ion secondary batteries are referred to as batteries β to δ, respectively. Then, the batteries β to δ were evaluated in the same manner as the evaluation of the battery α of Example 3. The results are shown in Table 2.

  As shown in the results of Table 2, the battery α of Example 3 using the positive electrode plate A1 obtained in Example 1 as the positive electrode and the negative electrode plate B1 obtained in Example 2 as the negative electrode was charged / discharged. The capacity retention rate after 500 cycles was 89%, and the battery had excellent life characteristics. Further, the positive electrode plate A1 was used as the positive electrode, the negative electrode plate B2 in which the homogeneous active material layer was formed over the entire surface as the negative electrode, the battery β of Example 4, and the negative electrode plate B1 as the negative electrode. All of the batteries γ of Example 5 using the positive electrode plate A2 on which the homogeneous active material layer was formed over the entire surface had a high capacity retention rate after 500 charge / discharge cycles.

  On the other hand, the battery δ using the positive electrode plate A2 and the negative electrode plate B2 having a uniform active material layer throughout the conductive agent composition has a capacity retention rate of 73% after 500 charge / discharge cycles, and the battery α˜ The life characteristics were inferior to γ. Further, when the electrode α was observed by disassembling the battery α and the battery δ after the cycle test, the color and peeling of the active material layer were not uniform over the active material layer in general in the electrode plate of the battery δ. The electrode plate of the battery α was relatively uniform.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which can maintain a high capacity | capacitance even after repeating many cycles charging / discharging can be obtained. Such a lithium ion secondary battery is, for example, a large lithium used as a power source for an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, etc., in order to exert a higher effect in a battery including a long electrode plate group. It is preferably used as an ion secondary battery. Further, it is also preferably used in a consumer lithium ion secondary battery that is further downsized and has a high packing density of the active material and a high tension rate of the electrode group.

DESCRIPTION OF SYMBOLS 1a Positive electrode collector, 2a Positive electrode active material layer, 3a Positive electrode active material, 4a Conductive support agent, 5a Binder, 7 Inorganic particle, 9 Separator, 10 Electrode group, 10a Positive electrode plate, 10b Negative electrode plate, 11a, 11b, 11c Inkjet nozzle, 13 Positive electrode active material ink, 14 Conductive auxiliary ink, 15 Binder ink, 16a, 16b, 16c Liquid chamber, 17a, 17b, 17c Ink supply line, 20 Inkjet coating device, 21 Computer, 40 Battery case , 41 Sealing plate, 42 Gasket, 43 Positive electrode lead, 44 Negative electrode lead, 100 Lithium ion secondary battery

Claims (8)

A long current collector sheet, and an electrode active material layer formed on the surface of the current collector sheet,
The electrode active material layer contains electrode active material particles that occlude and release lithium ions, a conductive aid, and a binder that binds the electrode active material particles and the conductive aid,
In the longitudinal direction of the electrode active material layer, when the half side in the longitudinal direction is the upstream side and the other half side is the downstream side, the porosity on the upstream side is higher than the porosity on the downstream side, and An electrode for a lithium ion secondary battery, wherein the content ratio of the conductive additive to the electrode active material is higher on the upstream side than on the downstream side.   From the downstream end to the upstream end of the current collector sheet, the porosity of the electrode active material layer gradually increases, and the content ratio of the conductive additive to the electrode active material gradually increases. It forms so that it may become high, The electrode for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned.   The electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the conductive additive has a non-spherical or fibrous shape.   The electrode for a lithium ion secondary battery according to claim 3, wherein the conductive additive has a fibrous shape.   The electrode for a lithium ion secondary battery according to claim 3, wherein the conductive additive has a non-spherical shape selected from a wedge shape, a flat shape, and a flake shape.   The electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the electrode active material particles have an average particle diameter of 2 to 20 times the average particle diameter of the conductive additive. An electrode group for a lithium ion secondary battery obtained by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,
At least one of the positive electrode or the negative electrode is the electrode according to any one of claims 1 to 6, wherein the upstream side is disposed on a winding center side, and the electrode for a lithium ion secondary battery group.   A lithium ion secondary battery, wherein the battery case contains the electrode group for a lithium ion secondary battery according to claim 7 and a nonaqueous electrolyte.

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