JP2009259749A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable nonaqueous electrolyte secondary battery in which excellent safety is secured at the time of an external short circuit even though a negative electrode lead is used. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes: an electrode group which has a belt-like positive electrode and a belt-like negative electrode rolled up by interposing a belt-like separator between them, wherein the positive electrode has a positive collector and a positive electrode mix layer formed on the positive collector and the negative electrode has a negative collector and a negative electrode mix layer formed on the negative collector; a nonaqueous electrolyte; a negative electrode lead for electrically connecting the negative electrode and a negative electrode terminal; and a positive electrode lead for electrically connecting the positive electrode and a positive electrode terminal. The negative electrode has a negative electrode collector exposed part connected to the negative electrode lead at the outermost periphery of the electrode group. The electrode collector exposed part has an extension part further extending in the lengthwise direction from a connecting part with the negative electrode lead. The negative electrode lead directly contacts with the extension part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery excellent in safety at the time of an external short circuit.

  As electronic devices become more portable and cordless, a small and lightweight non-aqueous electrolyte secondary battery having a high energy density is used as a power source. In recent years, with higher functionality and higher power of electronic devices, there has been a demand for higher energy density of non-aqueous electrolyte secondary batteries. Among non-aqueous electrolyte secondary batteries, lithium ion secondary batteries Expectations are rising.

  In a non-aqueous electrolyte secondary battery, in order to prevent a significant temperature increase at the time of an external short circuit or overcharge, for example, a battery pack including a plurality of non-aqueous electrolyte secondary batteries has an overcurrent such as a PTC element or a thermo stud. And a protection mechanism against temperature rise. However, when assuming abnormal use of various batteries, an external short circuit that does not go through the protection function may occur, and the battery may run out of heat.

  Hereinafter, the thermal runaway of the battery will be described. When an external short circuit is made without a protection mechanism against overcurrent or temperature rise such as PTC or thermostud, excessive current flows in the battery, large Joule heat is generated, and the battery generates heat. Of the region where the short-circuit current flows, the amount of heat generated by the high resistance portion is particularly large. In the case of a general cylindrical battery, the nickel negative electrode lead connecting the negative electrode and the battery case in the battery has a high resistance and the largest amount of heat generation. The separator shrinks and melts due to the heat generated by the negative electrode lead to cause an internal short circuit, and the battery is thermally runaway due to the internal short circuit. Further, the battery runs out of heat when the heat generation temperature of the negative electrode lead exceeds the heat resistance temperature of the active material.

As a method for preventing thermal runaway due to heat generation of the negative electrode lead, for example, in Patent Document 1, in a non-aqueous electrolyte secondary battery including an electrode group in which a positive electrode and a negative electrode are wound through a separator, Without using, a portion where the metal foil as the negative electrode current collector is exposed (hereinafter referred to as a metal foil exposed portion) is provided on the outermost periphery of the electrode group (on the winding end side of the negative electrode), and this metal foil exposed portion is used as the battery case. It has been proposed to improve the heat dissipation of the battery by directly contacting the inner surface of the battery.
JP-A-6-150973

  However, in the method described in Patent Document 1, if the electrode group diameter is smaller than the inner diameter of the battery case, the contact state between the exposed metal foil portion and the inner surface of the battery case becomes uneven, and the safety tends to vary. In order to make the contact state between the exposed metal foil portion and the inner surface of the battery case uniform, the electrode group diameter needs to be substantially the same as the inner diameter of the battery case. However, in this case, since the insertion pressure of the electrode group is increased, a shift or deformation of the exposed portion of the metal foil having a low strength occurs when the electrode group is inserted, which easily causes a process failure. Even if the battery can be manufactured, an internal short circuit may occur. Thus, it is extremely difficult in the manufacturing process to obtain a good contact state between the exposed metal foil portion and the battery inner surface without using the negative electrode lead.

  Therefore, the present invention aims to provide a highly reliable non-aqueous electrolyte secondary battery that is excellent in safety at the time of external short-circuiting, even when a negative electrode lead is used, in order to solve the above conventional problems. To do.

The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode current collector and a strip-shaped positive electrode having a positive electrode mixture layer formed on the positive electrode current collector, a negative electrode current collector, and the negative electrode current collector. An electrode group obtained by winding a band-shaped negative electrode having a formed negative electrode mixture layer with a band-shaped separator interposed therebetween, a non-aqueous electrolyte, a negative electrode lead electrically connecting the negative electrode and the negative electrode terminal portion, and Comprising a positive lead for electrically connecting the positive electrode and the positive terminal portion;
The negative electrode has a negative electrode current collector exposed portion connected to the negative electrode lead in the outermost peripheral portion of the electrode group,
The negative electrode current collector exposed portion further has an extension portion extending in a longitudinal direction from a connection portion with the negative electrode lead,
The negative electrode lead is in direct contact with the extension.

The extension is wound in the same direction as the winding direction of the electrode group,
The negative electrode lead is preferably connected to the outer peripheral surface of the negative electrode current collector exposed portion and directly covered with the extension portion.

The extension has a folded portion formed by being bent in a direction opposite to the winding direction of the electrode group,
The negative electrode lead is preferably connected to the outer peripheral surface of the negative electrode current collector exposed portion and directly covered with the folded portion.

  According to the present invention, it is possible to suppress a significant increase in battery temperature due to an increase in the amount of heat generated at the negative electrode lead, which is a high resistance portion at the time of an external short circuit, and a highly reliable and excellent safety at the time of an external short circuit. A non-aqueous electrolyte secondary battery can be provided.

  The present invention provides a strip-shaped positive electrode having a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, and a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. An electrode group obtained by winding a strip-shaped negative electrode with a strip-shaped separator interposed therebetween, a non-aqueous electrolyte, a negative electrode lead for electrically connecting the negative electrode and the negative electrode terminal portion, and the positive electrode and the positive electrode terminal portion. The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode lead that is electrically connected. The negative electrode has a negative electrode current collector exposed portion connected to the negative electrode lead at an outermost peripheral portion of the electrode group, and the negative electrode current collector exposed portion further extends from a connection portion with the negative electrode lead. The negative electrode lead is characterized in that the negative electrode lead is in direct contact with the extension. The negative electrode lead is disposed so as to be surrounded by a connection portion and an extension portion of the negative electrode current collector exposed portion.

  As a result, even when an external short circuit that does not involve a protection mechanism against an overcurrent or temperature rise such as PTC or thermostud occurs, an increase in local heat generation at the negative electrode lead, which is a high resistance part in the battery, is suppressed. The water electrolyte secondary battery can be reliably prevented from thermal runaway.

Embodiment 1
Hereinafter, the structure of a cylindrical lithium ion secondary battery which is an embodiment of the non-aqueous electrolyte secondary battery of the present invention will be described with reference to FIG. FIG. 1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery which is an embodiment of the non-aqueous electrolyte secondary battery of the present invention.

  A substantially cylindrical electrode group 4 is accommodated in a bottomed cylindrical battery case 1. The electrode group 4 is configured by winding a belt-like positive electrode 5 and a belt-like negative electrode 6 with a belt-like separator 7 interposed therebetween.

  The positive electrode 5 has a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. A part of the positive electrode 5 is provided with a portion where the positive electrode current collector is exposed without forming a positive electrode mixture layer on the positive electrode current collector (hereinafter, referred to as a positive electrode current collector exposed portion). One end of the positive electrode lead 9 is connected to the current collector exposed portion. The other end of the positive electrode lead 9 is connected to the lower surface of the battery lid 2 that also serves as a positive electrode terminal portion.

  Separators 7 are also arranged on the innermost and outermost sides of the electrode group 4 (between the electrode group 4 and the battery case 1). Insulating rings 8a and 8b are disposed on the upper and lower portions of the electrode group 4, respectively. The opening portion of the battery case 1 is sealed by caulking the opening end portion of the battery case 1 to the peripheral portion of the battery lid 2 via the gasket 3.

Here, FIG. 2 shows a cross-sectional view of the main part of the electrode group of the lithium ion secondary battery of FIG. 1 (cross-sectional view perpendicular to the winding direction of the electrode group 4). In FIG. 2, only the outermost peripheral part of the electrode group (negative electrode winding end side) is shown, and the parts other than the outermost peripheral part of the electrode group are omitted. A front view of the negative electrode is shown in FIG.
As shown in FIGS. 2 and 3, the negative electrode 6 has a negative electrode mixture layer 6a formed on both surfaces of the negative electrode current collector 6b and the negative electrode current collector 6b. The negative electrode 6 is a portion where the negative electrode current collector 6b is exposed at the end of the outermost peripheral portion of the electrode group 4 without forming the negative electrode mixture layer 6a on both surfaces of the negative electrode current collector 6b (negative electrode current collector exposure). Part 11), and one end of the negative electrode lead 10 is connected to the outer peripheral surface (surface facing the battery case) of the negative electrode current collector exposed part 11. The other end of the negative electrode lead 10 is connected to the inner bottom surface of the battery case 1 that also serves as the negative electrode terminal portion.

  The negative electrode current collector exposed portion 11 has a connection portion 12 with the negative electrode lead 10 and an extension portion 13 further extending in the longitudinal direction from the connection portion 12. The extension 13 is wound in the same direction as the winding direction of the electrode group 4 and directly covers the negative electrode lead 10. The extension 13 only needs to have a length corresponding to at least one turn in the outermost periphery of the electrode group in the longitudinal direction. Therefore, the negative electrode lead 10 is in contact with not only the connection portion 12 but also the extension portion 13, and the negative electrode lead 10 is in contact with the negative electrode current collector 6 b so that the negative electrode lead 10 is surrounded by the negative electrode current collector 6 b. Thereby, the heat generated in the negative electrode lead during an external short circuit can be efficiently dissipated to the negative electrode current collector, and the local increase in the amount of heat generated in the negative electrode lead can be suppressed.

The positive electrode mixture layer includes, for example, a positive electrode active material, a binder, and a conductive material.
As the positive electrode active material, for example, a lithium-containing composite oxide is used. Examples of the lithium-containing composite oxide include lithium cobaltate (LiCoO ₂ ), modified LiCoO ₂ , lithium nickelate (LiNiO ₂ ), modified LiNiO ₂ , lithium manganate (LiMnO ₂ ), or LiMnO ₂ . Examples include modified products. Examples of each modified body include those containing elements such as aluminum (Al) and magnesium (Mg). Further, examples of each modified body include those containing at least two of cobalt (Co), nickel (Ni), and manganese (Mn).

As the positive electrode binder, for example, polytetrafluoroethylene (PTFE), modified acrylonitrile rubber particles (for example, BM-500B (trade name) manufactured by Nippon Zeon Co., Ltd.), or PVDF is used. PTFE and modified acrylonitrile rubber particles are carboxymethylcellulose (CMC), polyethylene oxide (PEO), or modified acrylonitrile rubber (for example, BM-720H manufactured by Nippon Zeon Co., Ltd.) (product) It is preferable to use in combination with a thickener such as name)). PVDF functions as both a binder and a thickener.
As the conductive material, for example, carbon black such as acetylene black and ketjen black, or graphite material such as natural graphite and artificial graphite is used. These may be used alone or in combination of two or more.

As the negative electrode lead 10, for example, nickel, copper, a clad material of nickel and copper, or a nickel plating material of copper is used. Nickel is preferred in that it can be easily welded to the battery case. Copper is preferred because of its low resistance.
The negative electrode mixture layer 6b includes, for example, a negative electrode active material and a binder. As the negative electrode active material, for example, natural graphite, artificial graphite, silicon-containing composite materials such as silicide, or various alloy materials can be used. As the negative electrode binder, for example, PVDF or a modified product thereof is used.

  The separator 7 is made of, for example, a single layer of polypropylene resin or polyethylene resin, or a laminate in which a plurality of single layers are stacked. From the viewpoint of maintaining insulation between the electrodes and maintaining the electrolyte solution, the thickness of the separator is preferably 10 μm or more. From the viewpoint of maintaining the design capacity of the battery, the thickness of the separator is more preferably 30 μm or less.

The electrode group 4 includes a non-aqueous electrolyte. The non-aqueous electrolyte is composed of, for example, a non-aqueous solvent and a lithium salt that dissolves in the non-aqueous solvent. For example, lithium hexafluorophosphate (LiPF ₆ ) or lithium tetrafluoroborate (LiBF ₄ ) is used as the lithium salt. As the non-aqueous solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC) is used, and these may be used alone. Alternatively, two or more kinds may be used in combination. Further, vinylene carbonate (VC), cyclohexyl benzene (CHB), or a modified product thereof may be added to the nonaqueous electrolytic solution.

Embodiment 2
A cylindrical lithium ion secondary battery which is another embodiment of the non-aqueous electrolyte secondary battery of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of an essential part of an electrode group of a cylindrical lithium ion secondary battery which is another embodiment of the non-aqueous electrolyte secondary battery of the present invention. FIG. 4 shows only a part of the outermost peripheral part of the electrode group (near the negative electrode current collector exposed part on the winding end side of the negative electrode), and the other parts are omitted. Further, FIG. 5 shows a front view of the negative electrode constituting the electrode group of FIG. Except for the outermost periphery of the electrode group, it has the same structure as the battery of the first embodiment.

  As shown in FIG. 4, the electrode group 14 includes a positive electrode (not shown) and a negative electrode 16 via a separator (not shown). The negative electrode 16 includes a negative electrode current collector 16b and a negative electrode mixture layer 16a formed on both surfaces of the negative electrode current collector 16b. The negative electrode 16 has a portion where the negative electrode current collector 16b is exposed without forming the negative electrode mixture layer 16a on both surfaces of the negative electrode current collector 16b at the end of the outermost peripheral portion of the electrode group (negative electrode current collector exposed portion). 21), and one end of the negative electrode lead 10 is connected to the outer peripheral surface (the surface facing the battery case 1) of the negative electrode current collector exposed portion 21. The other end of the negative electrode lead 10 is connected to the inner bottom surface of the battery case 1.

  The negative electrode current collector exposed portion 21 has a connection portion 22 to the negative electrode lead 10 and an extension portion 23 that further extends in the longitudinal direction from the connection portion 22. The extension part 23 has a folded part 24 formed by bending a part of the extension part 23 in a direction opposite to the winding direction of the electrode group (connection part 22) along the broken line in the extension part 23 of FIG. . The folded portion 24 directly covers the negative electrode lead 10. The portion where the extension portion 23 is bent may be a position where the folded portion 24 can cover the negative electrode lead. Therefore, the negative electrode lead 10 is in contact with not only the connecting portion 21 but also the folded portion 24, and the negative electrode lead 10 is in contact with the negative electrode current collector 16b so that the negative electrode lead 10 is surrounded by the negative electrode current collector 16b.

  Thereby, the heat generated in the negative electrode lead during an external short circuit can be efficiently dissipated to the negative electrode current collector, and the local increase in the amount of heat generated in the negative electrode lead can be suppressed. The battery of the second embodiment including the electrode group shown in FIG. 3 is inferior in heat dissipation because the length of the extension portion in the longitudinal direction is shorter than that of the battery of the first embodiment including the electrode group shown in FIG. However, the cost can be reduced.

Examples of the present invention will be described in detail below, but the present invention is not limited to the examples.
Example 1
A cylindrical lithium ion secondary battery having the same structure as that shown in FIG. 1 was produced by the following procedure.

(1) Production of positive electrode A positive electrode 5 was produced by the following procedure. 3 kg of lithium cobaltate as a positive electrode active material and “# 1320 (trade name)” (made by Kureha Chemical Co., Ltd.) as a binder (N-methyl-2-pyrrolidone containing 12% by weight of PVDF (hereinafter referred to as NMP) (Omitted) 1 kg of solution), 90 g of acetylene black as a conductive material, and an appropriate amount of NMP were stirred with a double-arm kneader to obtain a positive electrode mixture paste. This positive electrode mixture paste is applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode mixture layer on both surfaces of the positive electrode current collector, thereby obtaining a sheet-like positive electrode. It was. At this time, the thickness of the positive electrode composed of the positive electrode current collector and the positive electrode mixture layer was 160 μm.

  Thereafter, the positive electrode was cut into a strip shape into a size that can be inserted into the battery case (length in the width direction is 56 mm and length in the longitudinal direction is 610 mm). A positive electrode current collector exposed portion was provided on a part of the positive electrode. The positive electrode lead 9 (70 mm in the thickness direction and 3.5 mm in the width direction) was spot welded to the exposed portion of the positive electrode current collector.

(2) Production of negative electrode A negative electrode 6 was produced by the following procedure. An aqueous dispersion containing 3 kg of artificial graphite as a negative electrode active material and 40% by weight of “BM-400B (trade name)” (styrene-butadiene copolymer (rubber particles)) manufactured by Nippon Zeon Co., Ltd. as a binder. ) 75 g, 30 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water were stirred with a double-arm kneader to prepare a negative electrode mixture paste. This negative electrode mixture paste is applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode mixture layer on both sides of the negative electrode current collector, thereby obtaining a sheet-like negative electrode. It was. At this time, the thickness of the negative electrode comprising the negative electrode current collector and the negative electrode mixture layer was 180 μm.

  Thereafter, the negative electrode was cut into a strip shape so as to be inserted into the battery case (a length in the width direction of 58 mm and a length in the longitudinal direction of 640 mm). A negative electrode current collector exposed portion 11 (length in the longitudinal direction: 70 mm) was provided on the outer periphery of the negative electrode. In the negative electrode current collector exposed portion 11, the length of the connection portion 12 in the longitudinal direction was 25 mm, and the length of the extension portion 13 in the longitudinal direction was 45 mm. The negative electrode lead 10 (70 mm in the thickness direction and 3 mm in the width direction) was spot welded to the connection portion 12 of the negative electrode current collector exposed portion 11.

(3) Preparation of Nonaqueous Electrolyte Solution A nonaqueous electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a nonaqueous solvent in which EC and MEC were mixed at a volume ratio of 1: 3.

(4) Battery Assembly The positive electrode 5 and the negative electrode 6 obtained above were wound through a separator 7 made of a polypropylene microporous film having a thickness of 16 μm to constitute an electrode group 4. At this time, the negative electrode lead 10 was directly covered with the extended portion 13 of the negative electrode current collector exposed portion 11 in the outer peripheral portion of the electrode group 4.
This electrode group 4 was inserted into a bottomed cylindrical battery case 1 (18 mm in diameter and 65 mm in height). At this time, insulating rings 8a and 8b were disposed on the upper and lower portions of the electrode group 4, respectively. 5.5 g of the nonaqueous electrolytic solution obtained above was injected into the battery case 1. The negative electrode lead 10 was welded to the inner bottom surface of the battery case 1, and the positive electrode lead 9 was welded to the lower surface of the battery lid 2. The opening end of the battery case 1 was caulked to the peripheral edge of the battery lid 2 via the gasket 3 to seal the opening of the battery case 1. In this way, a 18650 size cylindrical lithium ion secondary battery (18 mm in diameter and 65 mm in height) was produced.

Example 2
The same plate-like negative electrode as in Example 1 was cut into a strip shape so that it could be inserted into the battery case (length in the width direction was 58 mm and length in the longitudinal direction was 630 mm). A negative electrode current collector exposed portion 21 (length in the longitudinal direction: 60 mm) was provided on the outer periphery of the negative electrode. In the negative electrode current collector exposed portion 21, the length of the connecting portion 22 in the longitudinal direction was set to 15 mm, and the length of the extending portion 23 in the longitudinal direction was set to 45 mm. In this way, the same negative electrode 16 as in FIG. 5 was obtained.
The negative electrode 16 and the positive electrode 5 were wound through the separator 7 to configure the same electrode group 14 as that in FIG. At this time, the negative electrode lead 10 was connected to the connection portion 22 of the negative electrode current collector exposed portion 21. A part of the extension 23 was bent in a direction opposite to the winding direction of the electrode group 14 to form a folded part 24 (length in the longitudinal direction 30 mm), and the negative electrode lead 10 was directly covered with the folded part 24.
A battery was fabricated in the same manner as in Example 1 except for the above.

<< Comparative Example 1 >>
A battery was produced in the same manner as in Example 1 except that a negative electrode without an extension portion was provided on the negative electrode current collector exposed portion.

[Evaluation]
About each battery produced above, the external short circuit test was implemented with the following method.
Each battery was precharged / discharged in the order of (A) to (E) shown below, and stored in a 45 ° C. environment for 3 days.
(A) Constant current charging: 400 mA (end voltage 4.0 V)
(B) Constant current discharge: 400 mA (end voltage 3.0 V)
(C) Constant current charging: 400 mA (end voltage 4.0 V)
(D) Constant current discharge: 400 mA (end voltage 3.0 V)
(E) Constant current charging: 400 mA (end voltage 4.0 V)

Then, it charged / discharged in order of the following (F) and (G) in 25 degreeC environment.
(F) Predischarge
Constant current discharge: 400 mA (end voltage 3.0 V)
(G) First pattern
Constant current charge: 1400mA (end voltage 4.2V)
Constant voltage charge: 4.2V (end current 100mA)
Constant current discharge: 400 mA (end voltage 3.0 V)

After the above charging / discharging, the following charging was further performed.
Constant current charging: 1400mA (end voltage 4.25V)
Constant voltage charge: 4.25V (end current 100mA)
Under a 60 ° C. environment, a nickel lead plate (length 30 mm, width 4 mm, thickness 0.1 mm) was resistance-welded to the positive electrode terminal and the negative electrode terminal of the charged battery, respectively, and the nickel lead plate connected to both terminals was The battery was short-circuited externally by connecting to an external resistor.
At this time, using the thermocouple, the surface temperature (battery surface temperature) of the part where the negative electrode lead in the battery case opposes was measured, and the maximum battery temperature at the time of external short circuit was obtained.
In addition, as a criterion for judging the safety of the battery, the case where the maximum battery temperature was lower than 120 ° C. was determined as OK, and the case where the maximum battery temperature was 120 ° C. or higher was determined as NG. The test results are shown in Table 1.

  In the battery of Comparative Example 1 using the negative electrode in which the negative electrode current collector exposed portion is not provided with the extension portion, the maximum battery temperature is 150 ° C. or higher, whereas the negative electrode current collector exposed portion is provided with the extension portion. In the batteries of Examples 1 and 2 using the above, the maximum battery temperature was 120 ° C. or lower. Thus, in the batteries of Examples 1 and 2, as compared with the battery of Comparative Example 1, an increase in battery temperature due to heat generation during an external short circuit was significantly suppressed.

  When the batteries after the external short-circuit test were disassembled and examined, melting of the separator was confirmed in the vicinity of the negative electrode lead portion in all the batteries. In the batteries of Examples 1 and 2, the melting of the separator was negligible, whereas in the battery of Comparative Example 1, the melting range of the separator was wide, and it was confirmed that the separator was melted to some extent that could cause an internal short circuit. . From this, it was found that in the batteries of Examples 1 and 2, heat generation at the negative electrode lead was significantly suppressed as compared with the battery of Comparative Example 1.

  In the above examples, the case of a cylindrical lithium ion secondary battery was shown, but the same effect was confirmed even in a prismatic lithium ion battery. The non-aqueous electrolyte secondary battery of the present invention only needs to include an electrode group in which a positive electrode and a negative electrode are wound through a separator, and the shape of the non-aqueous electrolyte secondary battery of the present invention is not limited thereto. .

  The non-aqueous electrolyte secondary battery of the present invention is excellent in safety and is suitably used as a power source for electronic equipment such as information equipment and portable equipment.

It is a schematic longitudinal cross-sectional view of the cylindrical lithium ion secondary battery which is one Embodiment of the nonaqueous electrolyte secondary battery of this invention. It is a principal part cross-sectional view of the electrode group of the cylindrical lithium ion secondary battery of FIG. It is a front view of the negative electrode which comprises the electrode group of FIG. It is a principal part cross-sectional view of the electrode group of the cylindrical lithium ion secondary battery which is other embodiment of the nonaqueous electrolyte secondary battery of this invention. It is a front view of the negative electrode which comprises the electrode group of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Battery cover 3 Gasket 4, 14 Electrode group 5 Positive electrode 6, 16 Negative electrode 6a, 16a Negative electrode mixture layer 6b, 16b Negative electrode collector 7 Separator 8a, 8b Insulation ring 9 Positive electrode lead 10 Negative electrode lead 11, 21 Negative electrode Current collector exposed part 12, 22 Connection part 13, 23 Extension part 24 Folding part

Claims (3)

A strip-shaped positive electrode having a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, and a strip-shaped negative electrode having a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector A group of electrodes wound with a band-shaped separator interposed therebetween,
Non-aqueous electrolyte,
A negative electrode lead that electrically connects the negative electrode and the negative electrode terminal portion; and a positive electrode lead that electrically connects the positive electrode and the positive electrode terminal portion;
The negative electrode has a negative electrode current collector exposed portion connected to the negative electrode lead in the outermost peripheral portion of the electrode group,
The negative electrode current collector exposed portion further has an extension portion extending in a longitudinal direction from a connection portion with the negative electrode lead,
The non-aqueous electrolyte secondary battery, wherein the negative electrode lead is in direct contact with the extension. The extension is wound in the same direction as the winding direction of the electrode group,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode lead is connected on an outer peripheral surface of the negative electrode current collector exposed portion and is directly covered with the extension portion. The extension has a folded portion formed by being bent in a direction opposite to the winding direction of the electrode group,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode lead is connected on an outer peripheral surface of the negative electrode current collector exposed portion and is directly covered with the folded portion.

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