JP2015167149A - Rectangular lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rectangular lithium secondary battery in which exfoliation and cracking of a negative electrode active material on the innermost periphery of a wound electrode group are prevented without lowering the productivity.SOLUTION: A rectangular lithium secondary battery includes a flat wound electrode group formed by winding a sheet-like positive electrode and a sheet-like negative electrode while sandwiching a separator, and having corners at both ends, and a battery container for housing the wound electrode group. The negative electrode is arranged on the inner peripheral side of the positive electrode on the center side of the wound electrode group. A negative electrode active material mixture layer having a single side thickness of 50 μm or less is formed on both sides of the metal foil of the negative electrode. Adhesion strength of the negative electrode active material mixture layer and negative electrode metal foil is set to 0.05 N/mm or more, and the radius of curvature with reference to the inner surface of the metal foil of the negative electrode at the corner is set to 0.15 mm or more.

Description

  The present invention relates to a prismatic lithium secondary battery.

Conventionally, small-sized consumer lithium secondary batteries having a high energy density have been widely used for mobile phones and notebook computers. In recent years, lithium secondary batteries with high capacity and high output, for example, non-aqueous lithium secondary batteries having a high voltage have attracted attention as power sources for electric vehicles (EV) and hybrid electric vehicles (HEV). In particular, since the prismatic lithium secondary battery has excellent volumetric efficiency when packed, expectations for development of a high capacity prismatic lithium secondary battery for HEV or EV are increasing.

In order to increase the capacity, that is, to increase the electrode occupancy per volume of the flat wound electrode group, a flat wound electrode group having no space in the inner periphery is generally adopted as the electrode group. There is a problem that the active material mixture layer at the corner portion of the peripheral electrode breaks or falls off. The active material mixture thus cracked and dropped may penetrate the separator and cause a short circuit.

Therefore, in order to prevent the active material mixture layer from cracking or falling off, a method (Patent Document 1) has been proposed in which a wound electrode group is prepared by previously missing and peeling off the active material mixture layer at the corner. .

Japanese Patent Laid-Open No. 10-253263

The prismatic lithium secondary battery of Patent Document 1 is missing only a few millimeters at the time of electrode production.
It is extremely difficult to produce a peeled electrode, and disposing the missing / peeled portion at the innermost peripheral corner of the wound electrode group is extremely low in productivity from the viewpoint of positional accuracy.

(1) A rectangular lithium secondary battery according to the present invention is a flat wound electrode group in which a sheet-like positive electrode and a sheet-like negative electrode are wound into a flat shape via a separator, and corner portions are formed at both ends; A negative electrode is disposed on the inner peripheral side of the positive electrode at the center side of the wound electrode group, and the thickness of one side is 50 μm or less on both surfaces of the metal foil of the negative electrode. The negative electrode active material mixture layer is formed, the adhesion strength between the negative electrode active material mixture layer and the negative electrode metal foil is 0.05 N / mm or more, and the inner surface of the negative electrode metal foil at the corner is used as a reference The curvature radius is 0.15 mm or more.
(2) The invention according to claim 2 is the prismatic lithium secondary battery according to claim 1, wherein a radius of curvature with respect to the inner surface of the negative electrode metal foil in the corner portion is 0.5 mm or more. To do.
(3) The invention according to claim 3 is the prismatic lithium secondary battery according to claim 1, characterized in that the one-side thickness of the negative electrode active material mixture layer is 30 μm or more.

According to the present invention, it is possible to provide a prismatic lithium secondary battery in which the innermost negative electrode active material of the wound electrode group is prevented from dropping and cracking without reducing productivity.

It is a perspective view which shows embodiment of the square lithium battery by this invention. The perspective view which shows the flat wound electrode group of embodiment of the square lithium battery by this invention. It is a disassembled perspective view which shows embodiment of the square lithium battery by this invention. It is a fragmentary schematic sectional view showing the corner portion of the flat wound electrode group of the same embodiment. Tables 1 to 3 showing specifications of Examples 1 to 7 and Comparative Examples 1 to 5 of the same embodiment. Tables 4 to 6 showing evaluation results of Examples 1 to 7 and Comparative Examples 1 to 5 of the same embodiment. It is a perspective view which shows the flat wound electrode group in the modification of the embodiment.

With reference to FIGS. 1-4, the structure of Examples 1-7 of the square lithium secondary battery by this invention is demonstrated. The prismatic lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 are prismatic lithium secondary batteries shown in FIGS. 1 to 4 except for the detailed configuration of the wound electrode group.

FIG. 1 shows the external shape of a prismatic lithium secondary battery 200 of Examples 1-7. The prismatic lithium secondary battery 200 is configured by storing the wound electrode group 20 as a power generation element shown in FIG. 2 in a battery can 19 while being covered with an insulating bag 18 as shown in FIG. The wound electrode group 20 includes a sheet layer in which a sheet-like negative electrode 22, a sheet-like separator 21, a sheet-like positive electrode 24, and a sheet-like separator 23 are sequentially laminated. Located on the innermost circumference of
The wound electrode group 20 is wound in a flat shape so that arc portions (hereinafter also referred to as corner portions) 20T are formed at both ends.

The separators 21 and 23 are interposed between the positive electrode 24 and the negative electrode 22, and the separator 23
Constitutes the outer peripheral surface of the wound electrode group 20.

The outer shape of the wound electrode group 20 formed by winding the sheet layer described above is shown in FIGS.
As shown in FIG. 4, the flat shape is defined by an arc portion (hereinafter also referred to as a corner portion) 20T formed at both ends and a flat portion 20P positioned between the both end arc portions 20T.

FIG. 4 shows a cross-sectional view of the arc portion 20T of the wound electrode group 20. A sheet layer in which the negative electrode 22, the separator 21, the positive electrode 24, and the separator 23 are laminated in this order from the innermost periphery of the wound electrode group 20 is wound. The negative electrode 22 is configured by applying a negative electrode mixture layer 22b to the front and back surfaces of the negative electrode metal foil 22a. The positive electrode 24 is configured by applying a positive electrode mixture layer 24b to the front and back surfaces of the positive electrode metal foil 24a.
In FIG. 4, the radius of curvature at the arc portion 20T of the innermost negative electrode 22 of the wound electrode group 20, that is, the radius of curvature based on the inner surface of the negative electrode metal foil 22a is represented by r. Reference numeral 20 in FIG.
c is the center of curvature. This curvature radius r is determined in Examples 1 to 3 and 7 and Comparative Examples 1 and 4 described later.
, 5 is 0.15 mm, Example 4 is 0.30 mm, Example 5 is 0.50 mm, Example 6 is 1.00 mm, and Comparative Examples 2 and 3 are 0.05 mm.

When winding, the positive electrode 24, the negative electrode 22, and the separators 21 and 23 are all 1 in the sheet longitudinal direction.
While extending by applying a load of 0 N, meandering control was performed so that the electrode end face and the separator end face were at fixed positions. Prior to winding, a separator was wound a plurality of times around the center of the flat wound electrode group 20 to replace the innermost axis.

The wound electrode group 20 will be described in more detail with reference to FIGS. 2 and 4.
The positive electrode 24 is a sheet in which the positive electrode mixture layer 24b is disposed on both sides of a metal current collector, for example, an aluminum foil 24a, and the positive electrode mixture layer 24b is disposed from the winding start end to the winding end end. A positive electrode uncoated portion 24c to which the positive electrode mixture layer 24b is not applied is formed on one end edge extending in the longitudinal direction of the copper aluminum foil 24a, and is used as a positive electrode lead. The negative electrode 22 is a sheet in which the negative electrode mixture layer 22b is disposed on both sides of a metal current collector, for example, a copper foil 22a, and the negative electrode mixture layer 22b is disposed from the winding start end to the winding end end. A negative electrode uncoated portion 22c to which the negative electrode mixture layer 22b is not applied is formed on the other end edge extending in the longitudinal direction of the copper foil 22a, and is used as a negative electrode lead.

Referring to FIG. 3, the joint 11 of the positive electrode current collector lead 9 made of aluminum is connected to the positive electrode uncoated portion 24c of the wound electrode group 20 by ultrasonic welding, and the negative electrode uncoated portion 22c is connected to the negative electrode uncoated portion 22c. ,
The joint portion 12 of the copper negative electrode current collecting lead portion 10 is connected by ultrasonic welding. The current collecting leads 9 and 10 are respectively connected to the positive electrode terminal 13 and the negative electrode terminal 14 attached to the battery lid 17, whereby the wound electrode group 20 is supported by the battery lid 17 and the positive electrode terminal 13. And charging / discharging from the negative electrode terminal 14 is attained.

The battery lid 17 is provided with a liquid injection port 15 for injecting an electrolytic solution, and further provided with a gas rupture valve 16 for releasing the pressure when the internal pressure rises above a reference value. . The liquid injection port 15 is closed by laser welding after the electrolyte injection. The battery can 19 is sealed by welding the battery lid 17 to the battery can 19 by laser welding.
The non-aqueous electrolyte includes ethylene carbonate and dimethyl carbonate in a volume ratio of 1
: A solution obtained by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / liter in a mixed solution mixed at a ratio of 2 was used.

In preparing the positive electrode 24, a lithium-containing double oxide powder as a positive electrode active material, scaly graphite as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 85: 1.
The mixture was mixed at 0: 5, N-methylpyrrolidone (NMP) as a dispersion solvent was added thereto, and a kneaded slurry was prepared and applied to both sides of an aluminum foil having a thickness of 20 μm.
Then, the width of the portion where the active material mixture layer is arranged by drying, pressing, and cutting is 80 mm.
A positive electrode 24 having a thickness of 100 μm and a length of 4 m was obtained.

In producing the negative electrode 22, amorphous carbon powder as the negative electrode active material and P as the binder are used.
As described later, VDF was kneaded at a weight ratio set for each example and comparative example, and a slurry obtained by adding NMP as a dispersion solvent to this was applied to both surfaces of a rolled copper foil having a thickness of 10 μm. did.
Then, the width 84mm of the portion where the active material mixture layer was arranged by drying press, cutting,
A negative electrode 22 having a length of 4.4 m, a predetermined thickness, and a predetermined adhesion strength was obtained.

An embodiment of the prismatic lithium battery 20 described with reference to FIGS. 1 to 4 will be described. In addition, it describes together about the battery of the comparative example produced for the comparison.
FIG. 5 (Tables 1 to 3) shows the specifications of the batteries of Examples and Comparative Examples.

[Example 1]
In Example 1, the weight ratio of amorphous carbon, which is a negative electrode active material, and PVDF, which is a binder, is 90%.
A negative electrode 22 having a negative electrode mixture layer 22b with a thickness of 30 μm (negative electrode thickness 70 μm) and an adhesion strength of the negative electrode metal foil 22a and the negative electrode mixture layer 22b of 0.05 N / mm is used. The corner portion 20T of the flat wound electrode group 20 is wound around as the innermost axis.
The radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a is 0.15 m.
A square lithium battery 20 was prepared as m.

[Example 2]
Example 2 is different from Example 1 in that the one-side thickness of the negative electrode mixture layer 22b is 40 μm (negative electrode thickness 90 μm), and the other is the same.

[Example 3]
Example 3 is different from Example 1 in that the one-side thickness of the negative electrode mixture layer 22b is 50 μm (negative electrode thickness 90 μm), and the others are the same.

[Comparative Example 1]
Comparative Example 1 is different from Example 1 in that the one-side thickness of the negative electrode mixture layer 22b is 60 μm (negative electrode thickness 90 μm), and the others are the same.

[Example 4]
Example 4 is different from Example 1 in that the radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 is 0.3 mm. And others are the same.

[Example 5]
Example 5 is different from Example 1 in that the radius of curvature r (see FIG. 4) with respect to the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 is 0.5 mm. And others are the same.

[Example 6]
Example 6 is different from Example 1 in that the radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 is 1.0 mm. And others are the same.

[Comparative Example 2]
In Comparative Example 2, the weight ratio of amorphous carbon, which is a negative electrode active material, and PVDF, which is a binder, is 90%.
A negative electrode 22 having a negative electrode mixture layer 22b having a thickness of 50 μm (negative electrode thickness 110 μm) and an adhesion strength of the negative electrode metal foil 22a and the negative electrode mixture layer 22b of 0.05 N / mm is used. The corner portion 20 of the flat wound electrode group 20 is wound around as the innermost axis.
A radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a at T is 0.05.
mm.
That is, the comparative example 2 is different from the example 3 in that the corner portion 2 of the flat wound electrode group 20 is different.
The curvature radius r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a at 0T is 0.0.
The point is 5 mm.

[Comparative Example 3]
In Comparative Example 3, the weight ratio of amorphous carbon, which is a negative electrode active material, and PVDF, which is a binder, is 90%.
A negative electrode 22 having a negative electrode mixture layer 22b with a thickness of 30 μm (negative electrode thickness 70 μm) and an adhesion strength of the negative electrode metal foil 22a and the negative electrode mixture layer 22b of 0.05 N / mm is used. The corner portion 20T of the flat wound electrode group 20 is wound around as the innermost axis.
The radius of curvature r (see FIG. 4) with respect to the inner surface of the negative electrode metal foil 22a is 0.05 m.
A battery was fabricated in the same manner as in Example 1 except that m was set.
That is, Comparative Example 2 is different from Comparative Example 3 in that the thickness of one side of the negative electrode mixture layer 22b is 30 μm.
m (negative electrode thickness 70 μm).

[Example 7]
In Example 7, the weight ratio of amorphous carbon as the negative electrode active material and PVDF as the binder was 85.
A plurality of separators were used using a negative electrode 22 in which the negative electrode mixture layer 22b had a thickness of 50 μm (negative electrode thickness 110 μm) and the adhesion strength of the negative electrode metal foil 22a and negative electrode mixture layer 22b was 0.08 N / mm. The corner portion 20 of the flat wound electrode group 20 is wound around as the innermost axis.
The radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a at T is 0.15.
A battery was produced in the same manner as in Example 1 except that the thickness was mm.
That is, Example 7 is different from Example 3 in that the negative electrode metal foil 22a and the negative electrode mixture layer 22b.
This is the point where the adhesion strength of the steel was 0.08 N / mm.

[Comparative Example 4]
In Comparative Example 4, the weight ratio of amorphous carbon as the negative electrode active material and PVDF as the binder was 95.
A negative electrode 22 having a negative electrode mixture layer 22b having a thickness of 50 μm (negative electrode thickness 110 μm) and an adhesion strength of the negative electrode metal foil 22a and the negative electrode mixture layer 22b of 0.02 N / mm was used. The corner portion 20T of the flat wound electrode group 20 is wound around as the innermost axis.
The radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a is 0.15 m.
A battery was fabricated in the same manner as in Example 1 except that m was set.
That is, Comparative Example 4 is different from Example 7 in that the negative electrode metal foil 22a and the negative electrode mixture layer 22b.
This is the point at which the adhesion strength of 0.02 N / mm.

[Comparative Example 5]
In Comparative Example 5, the weight ratio of amorphous carbon as the negative electrode active material and PVDF as the binder was 95.
The thickness of one side of the negative electrode mixture layer 22b is 30 μm (negative electrode thickness 70 μm), and the negative electrode metal foil 2
In the corner portion 20T of the flat wound electrode group 20, the negative electrode 22 having an adhesion strength of 2a and the negative electrode mixture layer 22b of 0.02 N / mm is used, and a plurality of separators are wound to replace the innermost axis. The radius of curvature r (see FIG. 4) based on the inner surface of the negative electrode metal foil 22a is 0.15 mm.
A battery was fabricated in the same manner as in Example 1 except that.
That is, Comparative Example 5 is different from Example 7 in that the thickness of one side of the negative electrode mixture layer 22b is 30 μm.
m (negative electrode thickness 70 μm), and the adhesion strength between the negative electrode metal foil 22a and the negative electrode mixture layer 22b was 0.02 N / mm.

-Test and evaluation-
For the above examples and comparative examples, 10 batteries were manufactured, and charging was performed at a constant current rate of up to 4.1 V, and discharging was performed at a current of 1 hour rate. 5 charge / discharge cycle tests were conducted under constant current discharge conditions, and the battery after 5 cycles was 3.6V.
And then the amount of voltage drop for 30 days was measured. The battery voltage after 30 days is 3.
It was judged that batteries with a voltage of 55 V or more had no internal micro short circuit, and batteries with a battery voltage of less than 3.55 V had an internal micro short circuit.

Further, the batteries after the voltage drop amount measurement was disassembled and the inside and outside of the negative electrode active material mixture layer 22b of the negative electrode 22 arranged on the innermost periphery were externally observed, and the negative electrode metal foil 22a and the active material mixture layer 22b were observed. And the presence or absence of cracks in the active material mixture layer 22b were investigated.
The above test and evaluation results are shown in FIG. 6 (Tables 4 to 6).

Table 4 in FIG. 6 shows test results in the secondary batteries of Examples 1 to 3 and Comparative Example 1. Example 1
3. In the flat wound electrode group 20 of Comparative Example 1,
(A) The adhesion strength between the negative electrode metal foil and the negative electrode mixture layer 22b is 0.05 N / mm,
(B) The curvature radius with respect to the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 is set to 0.15 mm,
(C) The thickness of one side of the negative electrode mixture layer 22b was 30, 40, 50, and 60 μm, respectively.

In the secondary batteries of Examples 1 to 3 in which the one-side thickness of the negative electrode mixture layer 22b was 30 μm or more, the inner and outer negative electrode mixture layers 22b were not peeled off and there was no internal micro short circuit. In the secondary battery of Comparative Example 1, an internal micro short circuit occurred in two secondary batteries, and the outer mixture layer was peeled off in three secondary batteries. In all of Examples 1 to 3 and Comparative Example 1, in all the manufactured secondary batteries, cracks occurred in the inner mixture layer and the outer mixture layer.

Table 5 in FIG. 6 shows test results in the secondary batteries of Examples 3 to 6 and Comparative Examples 2 and 3. In the flat wound electrode group 20 of Examples 3 to 6 and Comparative Examples 2 and 3,
(A) The adhesion strength between the negative electrode metal foil 22a and the negative electrode mixture layer 22b is 0.05 N / mm,
(B) The one-side thickness of the negative electrode mixture layer 22b is 50 μm or less,
(C) The curvature radius with respect to the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 was set to 0.15 mm or more.

In the secondary batteries of Examples 3 to 6, it was found that neither an internal micro short circuit nor peeling of the inner and outer negative electrode mixture layers 22b occurred. In particular, it was found that when the radius of curvature was 0.50 mm or more as in Example 5 and Example 6, the inner and outer negative electrode mixture layers 22b were not cracked.

In the secondary battery of Example 3, cracks occurred in the inner mixture layer and the outer mixture layer in all the secondary batteries. In Example 4, cracks occurred in the inner mixture layer in four secondary batteries, and cracks occurred in the outer mixture layer in three secondary batteries.

In the secondary battery of Comparative Example 2, an internal micro short circuit occurred in two secondary batteries, and in the secondary battery of Comparative Example 3, an internal micro short circuit occurred in one secondary battery. In all the secondary batteries of Comparative Examples 2 and 3, the outer mixture layer was peeled off, and cracks occurred in the inner mixture layer and the outer mixture layer.

Table 6 in FIG. 6 shows the test results of the secondary batteries of Examples 3 and 7 and Comparative Examples 4 and 5. In the flat wound electrode group 20 of Examples 3 and 7 and Comparative Examples 4 and 5,
(A) The one-side thickness of the negative electrode mixture layer 22b is 50 μm or less,
(B) The curvature radius with respect to the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group is 0.15 mm,
(C) The adhesion strength between the negative electrode metal foil 22a and the negative electrode mixture layer 22b is 0.05 N / m in Example 3.
m, 0.08 N / mm in Example 7, and 0.03 N / mm in Comparative Examples 4 and 5.

In the secondary batteries of Examples 3 and 7, it was found that the inner and outer negative electrode mixture layers 22b were not peeled off and no internal micro short circuit occurred.
In the secondary battery of Comparative Example 4, internal micro short circuits occurred in three secondary batteries, and in the secondary battery of Comparative Example 5, internal micro short circuits occurred in two secondary batteries. In all the secondary batteries of Comparative Examples 4 and 5, the outer mixture layer was peeled off, and cracks occurred in the inner mixture layer and the outer mixture layer. In addition, the inner mixture layer was peeled off in the seven secondary batteries of Comparative Example 4, and the inner mixture layer was peeled off in the three secondary batteries of Comparative Example 5.

From the above, in the prismatic lithium secondary battery having the wound electrode group 20 in which the sheet layer obtained by laminating the positive electrode 24, the separators 21, 23, and the negative electrode 22 is wound into a flat shape,
(A) A negative electrode active material mixture layer having a thickness of 50 μm or less on one side is formed on both surfaces of the negative electrode metal foil 22a,
(B) The adhesion strength between the negative electrode active material mixture layer 22b and the negative electrode metal foil 22a is 0.05 N / mm or more,
(C) the negative electrode is located on the innermost circumference of the wound electrode group 20,
(D) By setting the radius of curvature based on the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 to 0.15 mm or more,
It is possible to provide a prismatic lithium secondary battery excellent in safety and productivity that does not peel off the negative electrode mixture layer 22b and does not cause an internal micro short circuit.

The prismatic lithium secondary battery according to the present embodiment can prevent the active material mixture layer from being peeled off from the innermost electrode without adopting a complicated process as in Patent Document 1, and thus is produced in comparison with Patent Document 1. High nature. In addition, since the active material mixture layer is not dropped or cracked from the innermost negative electrode in the wound electrode group, the situation where the negative electrode active material mixture layer does not exist on the opposite surface of the positive electrode active material can be prevented. There is no possibility that lithium dendride will precipitate, and therefore an internal short circuit can be prevented and a highly safe lithium secondary battery can be provided.

In particular, if the radius of curvature with respect to the inner surface of the negative electrode metal foil 22a in the corner portion 20T of the flat wound electrode group 20 is 0.5 mm or more, in addition to dropping off of the active material mixture layer, cracks are generated. Therefore, it is possible to provide an excellent prismatic lithium secondary battery having both higher safety and productivity.

The prismatic lithium secondary battery described above can be modified as follows.
(1) The shapes of the positive electrode lead 24c and the negative electrode lead 22c are not limited to the present embodiment. As shown in FIG. 7, the positive electrode mixture layer uncoated portion 22c is periodically formed in the winding circumferential direction. A plurality of positive electrode lead pieces 24H and negative electrode lead pieces 22H may be formed in a so-called comb shape.

(2) The appearance and configuration of the prismatic lithium battery according to the present invention are not limited to the examples. As long as the lithium battery has a configuration in which the flat wound electrode group is housed in a thin container, it may have any configuration.

(3) In this embodiment, PVDF is exemplified as the binder, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose Various types of latex, polymers such as acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof may be used.

(4) In the present embodiment, a non-aqueous electrolyte solution in which LiPF6 is dissolved in a mixed solution of EC, DEC, and DMC is exemplified. However, a non-aqueous electrolyte in which a general lithium salt is used as an electrolyte and this is dissolved in an organic solvent. An electrolytic solution may be used, and the present invention is not particularly limited to the lithium salt or organic solvent used.
For example, as an electrolyte, LiClO4, LiAsF6, LiBF4, LiB (C6H
5) 4, CH3SO3Li, CF3SO3Li, etc., or a mixture thereof can be used.
Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-
Dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propiontonyl, etc. or two or more of these The mixed solvent may be used, and the mixing ratio is not limited.

The prismatic lithium secondary battery according to the present invention is excellent in safety and productivity, and can be used for portable electronic devices such as UPS and mobile phones in addition to hybrid vehicles and electric vehicles.

DESCRIPTION OF SYMBOLS 13 Positive electrode external terminal 14 Negative electrode external terminal 18 Insulation bag 19 Battery can 20 Flat-shaped wound electrode group 21, 23 Separator 22 Negative electrode 22a Copper foil 22b Negative electrode mixture layer 22c Negative electrode lead 24 Positive electrode 24a Aluminum foil 24b Positive electrode mixture layer 24c Positive electrode Lead 200 prismatic lithium secondary battery

Claims (3)

A sheet-shaped positive electrode and a sheet-shaped negative electrode are wound into a flat shape via a separator, and a flat-shaped wound electrode group in which corner portions are formed at both ends,
A battery container that houses the wound electrode group;
The negative electrode is disposed on the inner peripheral side of the positive electrode on the center side of the wound electrode group,
A negative electrode active material mixture layer having a thickness of 50 μm or less on one side is formed on both surfaces of the metal foil of the negative electrode,
The adhesion strength between the negative electrode active material mixture layer and the negative electrode metal foil is 0.05 N / mm or more,
The radius of curvature based on the inner surface of the metal foil of the negative electrode at the corner is 0.15.
A prismatic lithium secondary battery characterized by having a thickness of at least mm. The prismatic lithium secondary battery according to claim 1,
The radius of curvature based on the inner surface of the negative electrode metal foil at the corner is 0.5 mm.
A prismatic lithium secondary battery characterized by the above. The prismatic lithium secondary battery according to claim 1,
One side thickness of the said negative electrode active material mixture layer is 30 micrometers or more, The square lithium secondary battery characterized by the above-mentioned.

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