JP2017027837A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy-to-manufacture lithium ion secondary battery in which the temperature difference between the inner periphery and outer periphery of a wound electrode body, occurring when the wound electrode body generates heat, is relaxed sufficiently.SOLUTION: A lithium ion secondary battery includes a wound electrode body constituted by laminating and winding a positive electrode sheet, a negative electrode sheet and a separator. Any one of the positive electrode sheet or negative electrode sheet is provided with a collector exposed part, where an active material layer is not formed in the full width of the collector, at one end in the longitudinal direction. The collector exposed part is the start of winding part of the wound electrode body, only the collector exposed part is wound multiple number of turns at the innermost periphery of the wound electrode body, and the lamination part of the positive electrode sheet, separator and the negative electrode sheet is wound at the farther outer periphery than the innermost periphery. A collector is provided at the opposite ends of the wound electrode body in the winding axis direction, and a plurality of ends of the collector exposed part are overlapping at the collector.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries are lighter and have a higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. Lithium-ion secondary batteries are expected to become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Yes.

  As one form of a lithium ion secondary battery, a positive electrode sheet having a positive electrode active material layer on a long positive electrode current collector, a negative electrode sheet having a negative electrode active material layer on a long negative electrode current collector, and the positive electrode A wound electrode body formed by laminating a sheet and a separator interposed between the negative electrode sheet and having a configuration in which the sheet electrode is housed in a battery case together with a non-aqueous electrolyte (for example, patent document) 1).

  The charging / discharging of the lithium ion secondary battery is performed through a chemical reaction and generates heat. Therefore, when the lithium ion secondary battery is charged and discharged, the temperature of the wound electrode body rises, but when the wound electrode body does not have sufficient heat dissipation, the inner peripheral portion of the wound electrode body There is a disadvantage in that a temperature difference occurs between the outer peripheral portion and the chemical reaction during charge / discharge occurs unevenly.

  Further, it is known that when an abnormality such as overcharge occurs, the active material of the electrode and the non-aqueous electrolyte react to cause abnormal heat generation. As a countermeasure against this abnormal heat generation, the separator is given a function of interrupting current (so-called “shutdown”) by closing the pores of the separator by melting the constituent material of the separator such as polyolefin. When the temperature difference is generated between the inner peripheral portion and the outer peripheral portion of the wound electrode body, there is a disadvantage that the progress of the shutdown becomes non-uniform.

  In order to alleviate the temperature difference between the inner peripheral portion and the outer peripheral portion of the wound electrode body, a technique of introducing a metal shaft center into the wound electrode body and radiating heat through the shaft center has been proposed (for example, (See Patent Documents 2 and 3). However, in such a technique, a complicated process is required when manufacturing a lithium ion secondary battery, such as joining and fixing a metal shaft center to an electrode or the like so that a short circuit due to the metal shaft center does not occur. It is.

JP 2010-049967 A JP 2011-113895 A JP 2011-192476 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lithium ion secondary battery in which the temperature difference between the inner peripheral portion and the outer peripheral portion of the wound electrode body that occurs when the wound electrode body generates heat is sufficiently mitigated, and is easy to manufacture.

The lithium ion secondary battery disclosed herein includes a positive electrode sheet having a positive electrode active material layer on a long positive electrode current collector, a negative electrode sheet having a negative electrode active material layer on a long negative electrode current collector, A wound electrode body is provided in which a separator interposed between the positive electrode sheet and the negative electrode sheet is laminated and wound. The positive electrode sheet has a positive electrode active material layer in which the positive electrode active material layer is not formed at one end in the width direction, which is a direction orthogonal to the long direction of the positive electrode current collector, along the long direction. The negative electrode sheet has a forming portion, and the negative electrode active material layer is formed along the longitudinal direction at one end in the width direction, which is a direction orthogonal to the longitudinal direction of the negative electrode current collector. It has a negative electrode active material layer non-formed part. On one electrode sheet of either the positive electrode sheet or the negative electrode sheet, a current collector exposure in which an active material layer is not formed over the entire width of the current collector at one end in the longitudinal direction of the electrode sheet. Is provided. In the wound electrode body, the positive electrode sheet, the negative electrode sheet, and the separator leave at least a part of the current collector exposed portion of the one electrode sheet without overlapping with the other electrode sheet and separator. The positive electrode active material layer non-formed part of the positive electrode sheet and the negative electrode active material layer non-formed part of the negative electrode sheet are laminated so as to protrude on opposite sides in the width direction of the separator. The current collector exposed portion is a winding start portion, and only the current collector exposed portion is wound around the innermost peripheral portion of the wound electrode body, and the positive electrode is disposed on the outer periphery from the innermost peripheral portion. A laminated portion of the sheet, the separator, and the negative electrode sheet is wound. The wound electrode body has a wound core portion in which the positive electrode sheet, the negative electrode sheet, and the separator overlap each other, and one end portion of the current collector exposed portion in the winding axis direction is the wound core. The positive electrode sheet and the negative electrode sheet protrude from the winding core portion from the winding core portion, and the positive electrode sheet and the negative electrode sheet are respectively wound from the winding core portion. It protrudes so as to overlap and overlap one end and the other end in the direction. When the positive electrode sheet includes the current collector exposed portion, the end portion of the current collector exposed portion protruding so as to overlap and the positive electrode active material layer non-forming portion protruding so as to overlap each other are gathered together. And the negative electrode active material layer non-forming part protruding so as to overlap with each other to form a negative electrode current collector that is in contact with each other, and the negative electrode sheet is exposed to the current collector The positive electrode active material layer non-forming portions protruding so as to overlap each other, and the positive electrode current collectors contacting each other, and the end portions of the current collector exposed portions protruding so as to overlap with each other, and The negative electrode active material layer non-forming portions protruding so as to overlap with each other are formed to form a negative electrode current collector portion that is in contact with each other, and in the current collector portion, a plurality of end portions of the current collector exposed portion are provided. We have each other now.
According to such a configuration, the current collector exposed portion wound around the innermost peripheral portion of the wound electrode body serves as a heat conductor, and is generated at the inner peripheral portion of the wound electrode body. Heat can be efficiently discharged to the outside, and the temperature difference between the inner peripheral portion and the outer peripheral portion of the wound electrode body can be sufficiently relaxed. In addition, compared with the conventional method of manufacturing a wound electrode body, a wound electrode body can be manufactured only by changing the position where the active material layer is applied and the position where the positive electrode sheet, the negative electrode sheet and the separator are laminated. Therefore, the lithium ion secondary battery can be easily manufactured without adding a complicated process.

It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a typical exploded view of the winding electrode body of the lithium ion secondary battery concerning one embodiment of the present invention. It is a perspective view which shows typically the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the structure of the negative electrode current collection part vicinity of the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. 6 is a diagram schematically showing a structure in the vicinity of a negative electrode current collector of a wound electrode body of a lithium ion secondary battery according to Example 2. FIG. 6 is a diagram schematically showing a structure in the vicinity of a negative electrode current collector of a wound electrode body of a lithium ion secondary battery according to Example 3. FIG. It is a graph which shows the temperature measurement result of the lithium ion secondary battery at the time of the overcharge in an Example.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a lithium ion secondary battery that does not characterize the present invention) are as follows. Therefore, it can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  The structure of the lithium ion secondary battery 100 according to this embodiment will be briefly described with reference to FIGS. In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a power storage element such as a so-called storage battery and an electric double layer capacitor. Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes.

  In the lithium ion secondary battery 100 shown in FIG. 2, roughly speaking, a flat battery case (that is, an outer container) in which a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) are flat. 30). The battery case 30 has a box-shaped (that is, bottomed rectangular parallelepiped) case main body 32 having an opening at one end (corresponding to the upper end in a normal use state of the battery), and the opening of the case main body 32 is sealed. And a lid 34 to be stopped. As a material of the battery case 30, for example, a light metal material having a good thermal conductivity such as aluminum, stainless steel, or nickel-plated steel can be preferably used.

  Further, as shown in FIG. 2, the lid 34 is set to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or more, and the positive terminal 42 and the negative terminal 44 for external connection. A thin safety valve 36 and an injection port (not shown) for injecting a non-aqueous electrolyte are provided. In addition, a current interrupt device (CID) that operates when the internal pressure of the battery case 30 is increased may be provided inside the battery case 30.

  The wound electrode body 20 includes a positive electrode sheet 50 having a positive electrode active material layer 54 on a long positive electrode current collector 52, and a negative electrode sheet 60 having a negative electrode active material layer 64 on a long negative electrode current collector 62. The separator 70 is interposed between the positive electrode sheet 50 and the negative electrode sheet 60.

  As shown in FIGS. 1 and 2, the positive electrode sheet 50 typically includes a long positive electrode current collector 52 and a positive electrode active material layer 54 provided on the positive electrode current collector 52. . The positive electrode current collector 52 is provided with a portion where the positive electrode active material layer 54 is formed and a positive electrode active material layer non-forming portion 56 where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being provided. It has been. The positive electrode active material layer non-forming portion 56 is provided at one end of the width direction (hereinafter simply referred to as the width direction; the same applies to the negative electrode side) which is a direction orthogonal to the longitudinal direction of the positive electrode current collector 52. . In the present embodiment, the positive electrode active material layer 54 is provided on both surfaces of the positive electrode current collector 52, but the positive electrode active material layer 54 may be provided only on one of the surfaces.

  The positive electrode active material layer 54 includes a positive electrode active material. The positive electrode active material layer 54 may typically have a form in which the positive electrode active material is bonded together with a conductive material together with a binder (binder) and bonded to the positive electrode current collector 52. Such a positive electrode sheet 50 typically includes, for example, a positive electrode mixture paste (including slurry, ink, and the like) in which a positive electrode active material, a conductive material, and a binder are dispersed in an appropriate solvent. After being supplied to the surface of the positive electrode current collector 52 excluding the active material layer non-forming portion 56, it can be produced by drying and removing the solvent. As the positive electrode current collector 52, a conductive member (typically an aluminum foil) made of a metal foil having good conductivity (eg, aluminum, nickel, titanium, stainless steel) can be preferably used.

The positive electrode active material may be any material that can occlude and release lithium ions. For example, a lithium-containing compound containing a lithium element and one or more transition metal elements (eg, lithium transition metal composite oxide) ) Can be suitably used. Preferable examples include lithium transition metal oxides having a layered rock salt type or spinel type crystal structure. Such a lithium transition metal oxide is, for example, a lithium nickel composite oxide (eg, LiNiO ₂ ), a lithium cobalt composite oxide (eg, LiCoO ₂ ), a lithium manganese composite oxide (eg, LiMn ₂ O ₄ ), or lithium. A ternary lithium-containing composite oxide such as a nickel cobalt manganese composite oxide (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). In addition, a polyanionic compound having a general formula represented by LiMPO _4, LiMVO _4, or Li ₂ MSiO ₄ (wherein M is at least one element of Co, Ni, Mn, and Fe) is used as the positive electrode. It may be used as an active material.

  The conductive material may be any material that is used in a general lithium ion secondary battery, and examples thereof include carbon materials such as carbon powder and carbon fiber. As the carbon powder, carbon powders such as various carbon blacks (eg, acetylene black, furnace black, ketjen black) and graphite powder can be used. The carbon powder is preferably acetylene black (AB). Such conductive materials can be used singly or in appropriate combination of two or more.

  As a binder, the thing similar to the binder used for the positive electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, when the positive electrode active material layer 54 is formed by supplying a paste, a polymer having a property that can be uniformly dissolved or dispersed in a solvent constituting the paste can be used as the binder. When using a non-aqueous paste, a polymer material that dissolves in an organic solvent, such as a vinyl halide resin such as polyvinylidene fluoride (PVdF) or polyvinylidene chloride (PVdC), or a polyalkylene oxide such as polyethylene oxide (PEO) is used. Can be used. Further, when an aqueous paste is used, a water-soluble polymer material or a water-dispersible polymer material can be preferably employed. Examples thereof include polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and the like.

  As the solvent for dispersing the material constituting the positive electrode active material layer 54, any of an aqueous solvent and a non-aqueous solvent (organic solvent) can be used as long as it is in accordance with the properties of the binder to be used. For example, as the aqueous solvent, water or a mixed solvent mainly composed of water can be used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (eg, lower alcohol, lower ketone) that can be uniformly mixed with water can be appropriately selected and used. As the non-aqueous solvent, for example, N-methyl-2-pyrrolidone (NMP) can be suitably used.

  As shown in FIGS. 1 and 2, the negative electrode sheet 60 typically includes a long negative electrode current collector 62 and a negative electrode active material layer 64 provided on the negative electrode current collector 62. . The negative electrode current collector 62 is provided with a portion where the negative electrode active material layer 64 is formed and a negative electrode active material layer non-forming portion 66 where the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 being provided. It has been. The negative electrode active material layer non-forming portion 66 is provided at one end in the width direction of the negative electrode current collector 62. Further, as shown in FIG. 2, at one end portion in the longitudinal direction, the negative electrode sheet 60 is provided with a current collector exposed portion 68 in which the negative electrode active material layer 64 is not formed over the entire width of the negative electrode current collector 62. It has been. That is, in the region from one end in the long direction to a predetermined length in the long direction, the negative electrode active material layer 64 is not provided on the entire surface, and the negative electrode current collector 62 is exposed. The predetermined length in the longitudinal direction from one end in the longitudinal direction of this region is a length that allows the current collector exposed portion 68 to be wound around a plurality of times. In the present embodiment, the negative electrode active material layer 64 is provided on both surfaces of the negative electrode current collector 62, but the negative electrode active material layer 64 may be provided only on one of the surfaces.

  The negative electrode active material layer 64 includes a negative electrode active material. Typically, the negative electrode active materials may be bonded to each other by a binder (binder) and bonded to the negative electrode current collector 62. In such a negative electrode sheet 60, for example, a negative electrode paste obtained by dispersing a negative electrode active material and a binder in a suitable solvent (eg, water or N-methyl-2-pyrrolidone, preferably water) is used. It can be manufactured by supplying to the surface of the substrate and drying to remove the solvent. As the negative electrode current collector 62, a conductive member (typically copper foil) made of a metal having good conductivity (eg, copper, nickel, titanium, stainless steel) can be preferably used.

The negative electrode active material is not particularly limited, and one of various materials used as a negative electrode active material of a general lithium ion secondary battery is used alone, or two or more types are combined (mixed or composited). ) And the like. Preferable examples include carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotubes, or a combination of these. Among these, from the viewpoint of energy density, graphite-based materials such as natural graphite (graphite) and artificial graphite can be preferably used. As such a graphite-based material, a material in which amorphous carbon is disposed on at least a part of the surface can be preferably used. In addition to the carbon-based material, lithium transition metal composite oxides such as lithium titanium composite oxides such as Li ₄ Ti ₅ O ₁₂ and lithium transition metal composite nitrides can be used.

  As a binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, the same binder as in the positive electrode sheet 60 can be used. And as a preferable form, when using said aqueous solvent in order to form the negative electrode active material layer 64, rubbers, such as styrene butadiene rubber (SBR); water-solubles, such as a polyethylene oxide (PEO) and a vinyl acetate copolymer Or a water-dispersible polymer material is employed. More preferably, SBR is used. As the dispersion medium for the negative electrode active material, an aqueous solvent can be preferably used.

  Moreover, depending on the formation method of the negative electrode active material layer 64, a thickener may be included. As such a thickener, the same one as the above binder may be used, and for example, the following water-soluble polymer or water-dispersible polymer may be employed. Examples of the water-soluble polymer include cellulose polymers such as methyl cellulose (MC), carboxyl methyl cellulose (CMC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA).

  Two separators 70 interposed between the positive electrode sheet 50 and the negative electrode sheet 60 are usually used. The separator 70 only needs to insulate the positive electrode active material layer 54 and the negative electrode active material layer 64 and have a nonaqueous electrolyte holding function and a shutdown function. Preferable examples include porous resin sheets (films) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. From the viewpoint of exhibiting a shutdown function at an appropriate timing, a polyolefin-based porous resin sheet (for example, PE or PP) is preferable.

  The separator may have a single layer structure, or may have a structure in which two or more porous resin sheets having different materials and properties (such as thickness and porosity) are laminated. As the multilayer structure, for example, a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer (that is, a three-layer structure of PP / PE / PP) is suitable. The separator may include a porous heat-resistant layer on one or both surfaces (typically one surface) of the porous sheet.

  Next, the laminated form of the wound electrode body 20 will be described. In the wound electrode body 20, the positive electrode sheet 50, the negative electrode sheet 60, and the separator 70 are laminated so that at least a part of the current collector exposed portion 68 remains without overlapping with the positive electrode sheet 50 and the separator 70. Yes. In the present embodiment, as shown in FIG. 2, the negative electrode sheet 60, the positive electrode sheet, and the separator 70 are laminated in the region where the negative electrode active material layer 64 of the negative electrode sheet 60 is formed. On the other hand, the current collector exposed portion 68 of the negative electrode sheet 60 does not overlap the positive electrode sheet and the separator 70, and is in a state of being exposed protruding from the laminated portion of the positive electrode sheet 50, the negative electrode sheet 60 and the separator 70. Further, as shown in FIG. 1, the positive electrode sheet 50 and the negative electrode sheet 60 are laminated with a slight shift in the width direction, and the positive electrode active material layer non-forming portion 56 of the positive electrode sheet 50 and the negative electrode active material layer non-electrode of the negative electrode sheet 60 are stacked. The formation part 66 protrudes on the opposite side in the width direction of the separator 70.

  Next, the wound state of the wound electrode body will be described. As shown in FIG. 3, in the wound electrode body 20, the current collector exposed portion 68 of the negative electrode sheet 60 is a starting portion, and only the current collector exposed portion 68 is present in the innermost peripheral portion 22 of the wound electrode body 20. It is wound several times. The current collector exposed portion 68 is preferably wound 2 to 15 times and more preferably 3 to 10 times in the innermost peripheral portion of the winding resistance 20. In the outer peripheral portion 24 outside the innermost peripheral portion 22, a laminated portion of the positive electrode sheet 50, the separator 70, and the negative electrode sheet 60 is wound. The winding is performed using the width direction orthogonal to the longitudinal direction of the positive electrode sheet 50, the negative electrode sheet 60, and the separator 70 as a winding axis. The wound electrode body 20 is preferably flattened by crushing and ablating.

  As shown in FIGS. 1 and 3, the wound electrode body 20 has a wound core portion 26 in which a positive electrode sheet 50, a negative electrode sheet 60, and a separator 70 overlap each other. As shown in FIG. 3, the current collector exposed portion 68 protrudes so that one end in the winding axis direction overlaps the winding core portion, and the positive electrode sheet 50 and the negative electrode sheet 60 are positive electrodes. Each of the active material layer non-forming portion 56 and the negative electrode active material layer non-forming portion 56 protrudes so as to overlap with one end and the other end in the winding axis direction.

  At one end of the wound electrode body 20 in the winding axis direction, a positive electrode current collecting part 59 is formed in which the positive electrode active material layer non-forming parts 56 protruding so as to overlap each other are gathered. Further, at the other end of the wound electrode body 20 in the winding axis direction, an end of the current collector exposed portion 68 protruding so as to overlap and a negative electrode active material layer non-forming portion 66 protruding so as to overlap are collected. Thus, negative electrode current collectors 69 that are in contact with each other are formed. Since only the current collector exposed portion 68 is wound around the innermost peripheral portion 22 of the wound electrode body 20, a plurality of ends of the current collector exposed portion 68 overlap in the negative electrode current collector 69. ing. FIG. 3 is a diagram drawn schematically and does not accurately represent the actual number of windings of the wound electrode body 20.

  FIG. 4 schematically shows the structure in the vicinity of the negative electrode current collector 69. In the innermost peripheral portion 22 of the wound electrode body 20, a plurality of current collector exposed portions 68 are overlapped. The negative electrode sheet 60 is located on the outer peripheral side of the innermost peripheral portion 22 (the outer periphery following the innermost peripheral portion 22) with the separator 70 interposed therebetween. The current collector exposed portion 68 is a part of the negative electrode sheet 60 because it is provided at the end of the negative electrode sheet 60. As described above, when the negative electrode sheet 60 is located on the outer peripheral side of the innermost peripheral portion 22 composed of the current collector exposed portion 68 of the negative electrode sheet 60 with the separator 70 interposed therebetween, the separator 70 is damaged. Even if the current collector occurs, the current collector exposed portion 68 and the negative electrode sheet 60 have the same potential, so that no problem occurs even if the current collector exposed portion 68 and the negative electrode sheet 60 come into contact with each other. The safety of the ion secondary battery 100 can be ensured.

  In FIG. 4, the current collector exposed portion 68 of the negative electrode sheet 60 extends from the innermost peripheral portion 22 of the wound electrode body 20 toward the outside of the wound electrode body 20, and End portions of the material layer non-forming portion 66 and the current collector exposed portion 68 are gathered together in the negative electrode current collecting portion 69. In the negative electrode current collector 69, a plurality of end portions of the current collector exposed portion 68 overlap each other. In this manner, in the wound electrode body 20, a heat conduction path is formed from the inside of the wound electrode body 20 to the outside by a plurality of overlapping current collector exposed portions 68. That is, a plurality of current collector exposed portions 68 are wound around the innermost peripheral portion 22 of the wound electrode body 20 to serve as a heat conductor having a sufficient volume. The heat generated in the inner peripheral portion can be efficiently discharged to the outside, and the temperature difference between the inner peripheral portion and the outer peripheral portion of the wound electrode body 20 can be sufficiently relaxed.

  In the present embodiment, the negative electrode sheet has a current collector exposed portion. However, it is also possible for the positive electrode sheet to have a current collector exposed portion. The aspect in which the positive electrode sheet has a current collector exposed portion is the same as the above except that the positive electrode sheet has a current collector exposed portion and the negative electrode sheet does not have a current collector exposed portion. In such an embodiment, in the wound electrode body, the ends of the current collector exposed portions protruding so as to overlap with each other and the positive electrode active material layer non-forming portions protruding so as to overlap each other are gathered and contact each other. A negative electrode current collector part that is in contact with each other is formed by combining the electric part and the negative electrode active material layer non-forming part protruding so as to overlap. Here, generally, a material having better thermal conductivity than the positive electrode current collector is used for the negative electrode current collector (generally, a copper foil is used for the negative electrode current collector and a positive electrode current collector is used for the positive electrode current collector). Is aluminum foil). Therefore, it is preferable that the negative electrode sheet has a current collector exposed portion from the viewpoint of efficiently discharging the heat of the inner peripheral portion of the wound electrode body when the wound electrode body generates heat.

  As shown in FIG. 1, a positive electrode current collector plate 42 a is attached to the positive electrode current collector 59 of the wound electrode body 20 by ultrasonic welding or the like, and is electrically connected to the positive electrode terminal 42. A negative electrode current collector plate 44 a is attached to the negative electrode current collector 69 of the wound electrode body 20 by ultrasonic welding or the like, and is electrically connected to the negative electrode terminal 44.

A non-aqueous electrolyte (not shown) is injected into the battery case 30 of the lithium ion secondary battery 100. As the non-aqueous electrolyte, typically, a non-aqueous electrolyte solution in which a supporting salt is dissolved or dispersed in a non-aqueous solvent may be employed.
As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones that are used as electrolytes in general lithium ion secondary batteries can be used without any particular limitation. it can. Examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. Such a non-aqueous solvent can be used individually by 1 type or in mixture of 2 or more types.
As the supporting salt, various types used for general lithium ion secondary batteries can be appropriately selected and employed. For example, lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ can be used. Such supporting salts may be used singly or in combination of two or more. Such a supporting salt is preferably added so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

  With respect to the lithium ion secondary battery 100, the position of applying the active material layer and the position of stacking the positive electrode sheet 50, the negative electrode sheet 60 and the separator 70 with respect to the conventional method of manufacturing a wound electrode body are changed. The wound electrode body 20 can be manufactured. Therefore, the lithium ion secondary battery 100 can be easily manufactured without adding a complicated process.

  The lithium ion secondary battery 100 can be used for various applications. Suitable applications include drive power sources mounted on vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). The lithium ion secondary battery 100 can also be used in the form of an assembled battery in which a plurality of lithium ion secondary batteries are electrically connected.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are LNCM: AB: PVdF = 92: 5: 3 was mixed with NMP to prepare a positive electrode active material layer forming slurry. The slurry was applied to both sides of the aluminum foil in a strip shape, dried, and then pressed to prepare a positive electrode sheet having a positive electrode active material layer. The positive electrode sheet was provided with a positive electrode active material layer non-formation part in which the positive electrode active material layer was not formed along the longitudinal direction at one end in the width direction.
Further, graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass of C: SBR: CMC = 98: 1: 1. The slurry for negative electrode active material layer formation was prepared by mixing with ion exchange water in a ratio. The slurry was applied to both sides of the long copper foil in a strip shape from a position away from the end in the long direction of the copper foil, dried, and then pressed to prepare a negative electrode sheet. The negative electrode sheet is provided with a current collector exposed portion in which an active material layer is not formed over the entire width of the current collector at one end in the longitudinal direction, and is long at one end in the width direction. A negative electrode active material layer non-forming portion in which no negative electrode active material layer is formed is provided along the scale direction.
In addition, two long separator sheets (porous polyolefin sheets) were prepared.

As shown in FIG. 2, the prepared positive electrode sheet, the negative electrode sheet, and the prepared two separator sheets, while leaving the current collector exposed portion of the negative electrode sheet, the positive electrode active material layer non-forming portion and the negative electrode active material layer After overlapping so that the non-formed part protrudes on the opposite side in the width direction of the separator, it was wound to produce a wound electrode body. At this time, a separator was interposed between the positive electrode and the negative electrode. In addition, the current collector exposed portion is wound around a plurality of times at the beginning of rolling.
The produced wound electrode body was provided with a current collector as shown in FIG. 3, and a positive electrode terminal and a negative electrode terminal were electrically connected to the wound electrode body. The structure in the vicinity of the negative electrode current collector was the same as that shown in FIG.
The wound electrode body was accommodated in a battery case having an injection port.

Subsequently, a non-aqueous electrolyte was injected from the inlet of the battery case, and the inlet was hermetically sealed to produce a lithium ion secondary battery according to Example 1. The non-aqueous electrolyte is supported by a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 1: 1: 1. of LiPF ₆ as a salt were used as dissolved at a concentration of 1.0 mol / L.

<Example 2>
A positive electrode sheet was produced in the same manner as in Example 1.
The negative electrode sheet was produced by applying the same slurry for forming a negative electrode active material layer as used in Example 1 to both sides of a long copper foil in a belt shape, drying it, and then pressing it. The negative electrode sheet was provided with a negative electrode active material layer non-formation part in which the negative electrode active material layer was not formed along the longitudinal direction at one end in the width direction. That is, in Example 2, unlike Example 1, the negative electrode sheet was not provided with the current collector exposed portion.
In addition, two long separator sheets (porous polyolefin sheets) were prepared.

The prepared positive electrode sheet, the negative electrode sheet, and two prepared separator sheets are aligned with the positions of the ends in the longitudinal direction, and the positive electrode active material layer non-formation part and the negative electrode active material layer non-formation part are separated. The wound electrode body was manufactured by overlapping and winding so as to protrude on the opposite sides in the width direction. At this time, a separator was interposed between the positive electrode and the negative electrode.
The prepared wound electrode body is provided with a current collecting part in which the overlapping positive electrode active material layer non-forming part and the overlapping negative electrode active material layer forming part are combined, and the positive electrode terminal and the negative electrode terminal are electrically connected to the wound electrode body. Connected. The structure in the vicinity of the negative electrode current collector had the structure shown in FIG. That is, the laminate of the positive electrode sheet 501, the negative electrode sheet 601, and the separator 701 is wound, and the negative electrode active material layer non-forming portion 661 protruding from the laminate portion of the positive electrode sheet 501, the negative electrode sheet 601, and the separator 701 is gathered. A current collector 691 was formed.
The wound electrode body was accommodated in a battery case having an injection port. Subsequently, the same nonaqueous electrolytic solution as used in Example 1 was injected from the injection port of the battery case, and the injection port was hermetically sealed to produce a lithium ion liquid secondary battery according to Example 2.

<Example 3>
A positive electrode sheet was produced in the same manner as in Example 1.
A negative electrode sheet was produced in the same manner as in Example 2.
In addition, two long separator sheets (porous polyolefin sheets) were prepared.
Furthermore, a metal shaft center was prepared. A shaft with a length not exceeding the width of the negative electrode sheet was selected.

The prepared positive electrode sheet, the negative electrode sheet, and the two prepared separator sheets are aligned with the positions of the end portions in the longitudinal direction, and the positive electrode active material layer non-forming portion and the negative electrode active material layer non-forming portion are the separators. The stacked electrode bodies were produced by superimposing them so as to protrude on opposite sides in the width direction, and winding them around the axis. At this time, the negative electrode active material layer non-formation part of the negative electrode sheet in the innermost periphery of the wound electrode body was joined to the shaft center by welding.
The prepared wound electrode body is provided with a current collecting part in which the overlapping positive electrode active material layer non-forming part and the overlapping negative electrode active material layer forming part are combined, and the positive electrode terminal and the negative electrode terminal are electrically connected to the wound electrode body. Connected. The structure near the negative electrode current collector had the structure shown in FIG. That is, a laminate of the positive electrode sheet 502, the negative electrode sheet 602, and the separator 702 is wound around a metal axis 802, and the negative electrode active portion protruding from the laminated portion of the positive electrode sheet 502, the negative electrode sheet 602, and the separator 702 is wound. The material layer non-forming portion 662 is gathered together with the metal shaft center 802 to form a current collecting portion 692. The metal axis 802 extended from the inside of the wound electrode body to the negative electrode collector 692 toward the outside.
The wound electrode body was accommodated in a battery case having an injection port. Subsequently, the same nonaqueous electrolytic solution as used in Example 1 was injected from the injection port of the battery case, and the injection port was hermetically sealed to produce a lithium ion secondary battery according to Example 3.

<Measurement of battery temperature during overcharge>
Temperature sensors (thermocouples) were attached to the innermost and outermost circumferences of the wound electrode bodies of the lithium ion secondary batteries according to Examples 1 to 3. Moreover, the temperature sensor was attached to the battery case of the lithium ion secondary battery which concerns on Examples 1-3.
The lithium ion secondary batteries according to Examples 1 to 3 were fully charged with SOC (State of Charge) 100% in a temperature environment of 25 ° C. Thereafter, the battery was continuously charged at a constant current of 1 C until the SOC reached 160%, and the temperature difference between the innermost and outermost parts of the wound electrode body (temperature difference between the inside and outside of the electrode) and the temperature of the battery case were measured. . The results are shown in FIG.

In the lithium ion secondary battery according to Example 1, a heat conduction path for radiating heat generated inside the wound electrode body was formed by winding a plurality of copper foils around the innermost peripheral portion of the wound electrode body. In the lithium ion secondary battery according to Example 2, a heat conduction path is formed by introducing a metal shaft center into the center of the wound electrode body. The lithium ion secondary battery according to Example 3 is not provided with a special means for radiating heat generated inside the wound electrode body.
As shown in FIG. 7, compared with the lithium ion secondary battery according to Example 3, the lithium ion secondary battery according to Example 1 and the lithium ion secondary battery according to Example 2 It was confirmed that the temperature difference of In addition, the temperature difference between the inner periphery and the outer periphery of the wound electrode body was smaller in the lithium ion secondary battery according to Example 1 than in the lithium ion secondary battery according to Example 2.
Moreover, compared with the lithium ion secondary battery which concerns on Example 3, in the lithium ion secondary battery which concerns on Example 1, and the lithium ion secondary battery which concerns on Example 2, the fall of the battery case temperature at the time of overcharge was confirmed. In addition, the decrease in battery case temperature was smaller in the lithium ion secondary battery according to Example 1 than in the lithium ion secondary battery according to Example 2.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 20 Winding electrode body 30 Battery case 32 Battery case main body 34 Cover body 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collecting plate 44 Negative electrode terminal 44a Negative electrode current collecting plate 50 Positive electrode 52 Positive electrode current collector 54 Positive electrode active material layer 56 Positive electrode active material layer Non-formed part 60 Negative electrode 62 Negative electrode current collector 64 Negative electrode active material layer 66 Negative electrode active material layer non-formed part 70 Separator 100 Lithium ion secondary battery

Claims (1)

A positive electrode sheet having a positive electrode active material layer on a long positive electrode current collector, a negative electrode sheet having a negative electrode active material layer on a long negative electrode current collector, and interposed between the positive electrode sheet and the negative electrode sheet A lithium ion secondary battery comprising a wound electrode body formed by laminating and winding a separator,
The positive electrode sheet has a positive electrode active material layer in which the positive electrode active material layer is not formed at one end in the width direction, which is a direction orthogonal to the long direction of the positive electrode current collector, along the long direction. Has a forming part,
The negative electrode sheet has a negative electrode active material layer in which the negative electrode active material layer is not formed at one end in the width direction, which is a direction orthogonal to the long direction of the negative electrode current collector, along the long direction. Has a forming part,
On one electrode sheet of either the positive electrode sheet or the negative electrode sheet, a current collector exposure in which an active material layer is not formed over the entire width of the current collector at one end in the longitudinal direction of the electrode sheet. Part is provided,
In the wound electrode body, the positive electrode sheet, the negative electrode sheet, and the separator leave at least a part of the current collector exposed portion of the one electrode sheet without overlapping with the other electrode sheet and separator. The positive electrode active material layer non-formed part of the positive electrode sheet and the negative electrode active material layer non-formed part of the negative electrode sheet are laminated so as to protrude on opposite sides in the width direction of the separator. The current collector exposed portion is a winding start portion, and only the current collector exposed portion is wound around the innermost peripheral portion of the wound electrode body, and the positive electrode is disposed on the outer periphery from the innermost peripheral portion. The laminated portion of the sheet, the separator and the negative electrode sheet is wound,
The wound electrode body has a wound core portion in which the positive electrode sheet, the negative electrode sheet, and the separator overlap each other, and one end portion of the current collector exposed portion in the winding axis direction is the wound core. The positive electrode sheet and the negative electrode sheet protrude from the winding core portion from the winding core portion, and the positive electrode sheet and the negative electrode sheet are respectively wound from the winding core portion. Protruding so as to overlap one end and the other end of the direction,
When the positive electrode sheet includes the current collector exposed portion, the end portion of the current collector exposed portion protruding so as to overlap and the positive electrode active material layer non-forming portion protruding so as to overlap each other are gathered together. And the negative electrode active material layer non-forming part protruding so as to overlap with each other to form a negative electrode current collector that is in contact with each other, and the negative electrode sheet is exposed to the current collector The positive electrode active material layer non-forming portions protruding so as to overlap each other, and the positive electrode current collectors contacting each other, and the end portions of the current collector exposed portions protruding so as to overlap with each other, and The negative electrode active material layer non-forming portions protruding so as to overlap with each other are formed to form a negative electrode current collector portion that is in contact with each other, and in the current collector portion, a plurality of end portions of the current collector exposed portion are provided. We have each other now,
Lithium ion secondary battery.

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