JP3489381B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the safety of a non-aqueous electrolyte secondary battery provided with an electrode group composed of long electrode plates.

[0002]

2. Description of the Related Art Hitherto, as a lithium secondary battery, a battery system using a transition metal oxide or sulfide such as manganese dioxide or molybdenum disulfide as a positive electrode active material and a metal lithium as a negative electrode active material has been proposed. It has been. However, in this battery, the shape of the negative electrode lithium that deposits during charging becomes needle-like or mossy, which penetrates the separator and contacts the positive electrode, causing internal short circuits and ignition, which is a safety issue. .

Therefore, batteries using a compound for intercalating and deintercalating lithium in the negative electrode have been proposed. In this battery, lithium is not deposited on the negative electrode during charging and it can be expected that the safety is improved and the battery is also excellent in rapid charging characteristics.

In the above battery, Li is used as the positive electrode active material.
A lithium-containing metal oxide such as CoO ₂ or LiNiO ₂ is used, and a carbon material capable of reversibly intercalating and deintercalating lithium is used as a negative electrode active material.

However, since these batteries use an organic electrolytic solution having a low conductivity, it is necessary to increase the electrode area in order to ensure discharge characteristics at a large current. A long thin electrode plate in which a substance is applied on a metal foil is formed in a spiral shape via a separator made of a polyolefin resin.

[0006]

When a fully-charged battery is crushed assuming that it is caught in a garbage truck or trampled by an automobile, an experiment of crushing the battery reveals that among many batteries Some were ignited or exploded. It was because when the cause of ignition was investigated, the battery was crushed, the separator broke, the positive electrode plate and the negative electrode plate contacted each other, and a short circuit was generated to generate heat.

The present invention is intended to solve this problem, and provides a non-aqueous electrolyte secondary battery which is excellent in safety and does not ignite or burst even when the battery is crushed.

[0008]

According to the present invention, a lithium-containing transition metal oxide is used as a positive electrode active material, a carbon material is used as a negative electrode, and a positive electrode plate and a negative electrode plate, each of which is coated on a metal foil, together with a separator. In a non-aqueous electrolyte secondary battery wound in a spiral shape, the outermost peripheral side of the positive electrode plate is less than the outermost peripheral side.
Metal foil with no active material layer on both sides over the above length
It is an exposed part, and when the side of the battery is pressed,
The exposed portion of the metal foil and the negative electrode plate are configured to be in contact with each other by breaking the separator (however, the negative electrode plate is not coated with the negative electrode active material at the winding end portion thereof, and the metal foil is not applied thereto). The negative electrode current collector has a bare non-coated portion, and the non-coated portion of the negative electrode plate is wound around the outer periphery of the electrode group while facing the positive electrode plate with the separator interposed therebetween. Except when).

[0009]

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a non-aqueous electrolyte secondary battery of the present invention containing a positive electrode plate and a negative electrode plate and a separator, which is spirally wound, a part of the positive electrode active material of the positive electrode plate is used. Even if the battery is crushed and a short circuit occurs inside the battery, the uncoated part has extremely low electrical resistance compared to the part coated with the positive electrode active material, so heat generation due to Joule heat is suppressed and the battery ignites. There is nothing to do. Furthermore, even when the battery is crushed by setting the length of the portion not coated with the positive electrode active material to be the outermost circumference of the electrode plate group or more,
Since a short circuit occurs at this portion, heat generation due to Joule heat is suppressed and the battery does not ignite. Therefore, the battery configured by using the positive electrode plate in which the positive electrode active material is not applied to a part of the positive electrode plate does not ignite even when the battery is crushed and an internal short circuit occurs, and thus the safety is improved. You can

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a cylindrical lithium secondary battery prototyped to show the effect of the present invention. The battery has a diameter of 20 mm and a total height of 70 mm.

(Example) In FIG. 1, the positive electrode plate 1 is composed of lithium carbonate (Li ₂ CO ₃ ) and tricobalt tetroxide (Co).
₃ O ₄₎ were mixed with lithium cobalt oxide calcined at 900 ° C. in air (LiCo ₃ O ₂₎ as an active material, which after mixing the artificial graphite 5 wt% as a conductive agent, poly as a binder A mixture of 5% by weight of an aqueous dispersion of a tetrafluoroethylene resin was kneaded into a paste to apply the mixture on both sides of a core material made of aluminum foil, and after drying and rolling, a width of 57 mm and a length of 520 mm. It is cut into a size. However, in the positive electrode plate 1, as shown in FIG. 2, the positive electrode active material 2 is formed on both surfaces of the electrode plate at a portion 57 mm from the end in the length direction.
Is not applied and the exposed portion 3 of the aluminum foil is provided. The positive electrode lead piece 4 is spot-welded to the opposite end of this portion.

The negative electrode plate 5 is made of artificial graphite (average grain size: 3 μm).
m) as an active material, and 5% by weight of styrene-butadiene rubber as a binder with respect to the active material is mixed, and then suspended in an aqueous solution of carboxymethylcellulose to form a paste, which is a core material made of copper foil. Is coated on both sides of the above, dried and rolled, and cut into a size of 0.2 mm in thickness, 59 mm in width and 550 mm in length. A negative electrode lead piece 7 is spot-welded to the end of the negative electrode plate.

As the separator 6, a porous film made of polypropylene was used after being cut wider than the positive electrode plate 1 and the negative electrode plate 5.

The positive electrode plate 1 is attached to the negative electrode plate 5 from the side of the lead piece 4.
Was spirally wound together with the separator around the side opposite to the lead piece 7 so that the separator covered the outer peripheral portion of the electrode plate group once. The diameter of this plate group is 1
It is 8 mm.

Next, the upper and lower parts of the electrode plate group are heated with warm air,
After heat-shrinking the separator 6, a lower insulating ring 8 was attached to the lower side of the electrode plate group, housed in a battery case 9 having a diameter of 20 mm and a height of 70 mm, and the negative electrode lead piece 7 was spot-welded to the battery case 9. . In addition, after mounting the upper insulating ring 10 on the upper side of the electrode plate group and making a groove in the upper part of the battery case 9,
A non-aqueous electrolyte was injected. The electrolyte used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 and 1 mol / 1 of lithium hexafluorophosphate (LiPF ₆ ) dissolved therein. After spot welding the assembled sealing plate 11 having a gasket incorporated therein and the positive electrode lead piece 4, the assembled sealing plate 11 was mounted in the battery case 9 and sealed to obtain the battery A of the present invention.

Example 2 A battery similar to that of Example 1 was constructed except that the length of the portion of the positive electrode plate 1 not coated with the positive electrode active material was 30 mm as shown in FIG. Battery B
And

(Embodiment 3) As shown in FIG. 4, a positive electrode lead piece 4 was formed on the same end of the positive electrode plate as the positive electrode plate 1 prepared by the same method as that of the first embodiment on the side not coated with the positive electrode active material. Using a spot-welded positive electrode plate, the positive electrode plate 1 and a negative electrode plate 5 produced by the same method as in Example 1 are centered on the positive electrode plate 1 from the lead piece side and the negative electrode plate 5 on the opposite side to the lead piece. As
The electrode plate group was constructed by spirally winding the whole together with the separator. After that, a battery was constructed in the same manner as in (Example 1) to obtain Battery C of the invention.

Example 4 A battery was constructed in the same manner as in Example 3 except that the length of the portion of the positive electrode plate 1 not coated with the positive electrode active material was 30 mm as shown in FIG. This is battery B of the invention.

(Comparative Example) As shown in FIG. 6, the positive electrode plate 1 was coated with a mixture prepared by the same method as in (Example 1) on both sides of a core material made of aluminum foil, dried and rolled,
After cutting into a width of 57 mm and a length of 520 mm, the positive electrode lead piece 4 was spot-welded to the end portion. The positive electrode plate 1 and the negative electrode plate 5 and the positive electrode plate 1 produced by the same method as in Example 1 are spirally wound together with the separator from the lead piece side to the negative electrode plate 5 centered on the side opposite to the lead piece. It was rotated to form a plate group. After that, a battery was constructed by a method similar to that of (Example 1) to obtain a battery E of a comparative example.

50 cells of each of the batteries A, B, C and D of the present invention and the battery E of the comparative example were prepared, and the charging voltage was 4.2 at 20 ° C.
V, charging time was 2 hours, and constant voltage / constant current charging with a limiting current of 800 mA was performed to perform a battery crush test.

In the crush test, a cylindrical metal round bar having a diameter of 10 mm was used, and the center part of the battery was placed so that the round bar was parallel to the direction perpendicular to the direction in which the outer dimension of the battery was the longest. It was pressed against and crushed until the thickness of the battery became half.
(Table 1) shows the ignition rate of the battery by the crush test.

[0023]

[Table 1]

From Table 1, the batteries A, B, C of the present invention,
The effect of the present invention is clear when the firing rate of D is compared with that of the battery E of the comparative example. The battery B manufactured by using the positive electrode plate in which the positive electrode active material is not applied on the outermost periphery of the positive electrode plate for a length of 30 mm has the effect of reducing the ignition rate of the battery when the battery is crushed. It was Further, the length of the portion not coated with the positive electrode active material is 57 mm, and the length of the portion without the positive electrode active material is longer than the outermost circumference of the electrode plate group (56.5 mm).
The battery A using the above-mentioned positive electrode plate did not ignite even when a crush test was performed, and the effect of the present invention was most exhibited. Further, the batteries C and D in which the positive electrode active material is not applied to the winding core of the positive electrode plate also had the effect of reducing the ignition rate of the battery.

In this embodiment, LiCo is used as the positive electrode active material.
O ₂ was used, but in addition to this, LiMnO ₂ , LiNiO ₂ ,
LiFeO ₂ or LiM ₂ O ₄ (M is Co, Mn, N
The same effect can be obtained with either i or Fe). Further, the effect of the present invention is not limited to the cylindrical battery, and the same effect can be obtained also in the prismatic battery.

[0026]

INDUSTRIAL APPLICABILITY As described above, the non-aqueous electrolyte secondary battery of the present invention is a positive electrode plate and a negative electrode plate, each of which is formed of a long metal foil and is spirally wound with a separator interposed therebetween. Group is used and the length of the outermost circumference of the positive electrode plate is equal to or longer than the outermost circumference.
Therefore, the metal foil exposed portion not coated with the positive electrode active material is provided on both sides, and when the battery side surface is pressed, the metal foil exposed portion of the positive electrode plate and the negative electrode plate are configured to contact the separator by breaking. (However, the negative electrode plate is provided with an uncoated portion where the negative electrode active material is not applied to the winding end portion of the negative electrode and the negative electrode current collector made of the metal foil is exposed. Except when the non-coated portion circulates around the outer periphery of the electrode group while facing the positive electrode plate with the separator interposed therebetween), even if the battery is crushed, the heat generated by Joule heat is small and the battery ignites. Can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a cylindrical battery containing a positive electrode plate of the present invention.

FIG. 2 is a diagram showing a positive electrode plate showing one embodiment of the present invention.

FIG. 3 is a diagram showing a positive electrode plate showing an embodiment of the present invention.

FIG. 4 is a diagram showing a positive electrode plate showing an embodiment of the present invention.

FIG. 5 is a diagram showing a positive electrode plate showing an embodiment of the present invention.

FIG. 6 is a diagram showing a positive electrode plate used in a comparative example.

[Explanation of symbols]

1 Positive plate 2 Positive electrode active material 3 Aluminum foil exposed part 4 Positive electrode lead pieces 5 Negative electrode plate 6 separator 7 Negative electrode lead piece 8 Lower insulation ring 9 battery case 10 Upper insulation ring 11 Assembly sealing plate

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Inoue 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hideshi Koshina 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In-house (56) References JP-A-9-180761 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/00-4/62 H01M 6/16

Claims (2)

(57) [Claims] 1. A positive electrode containing a lithium composite oxide containing at least one transition metal as an active material, a negative electrode containing a carbon material as an active material, a non-aqueous electrolytic solution, and a separator, wherein the positive electrode and the negative electrode are In a battery in which an active material layer is formed on a metal foil, and the positive and negative electrodes are spirally wound with a separator between them to form an electrode group, the positive electrode plate is
The outermost peripheral side is the active material on both sides over the length of the outermost periphery
A non-aqueous electrolyte solution that is a metal foil exposed portion that does not form a layer, and is configured such that the metal foil exposed portion and the negative electrode contact each other when the side surface of the battery is pressed and the separator is broken to contact the positive and negative electrodes. The secondary battery (provided that the negative electrode plate has an uncoated portion where the negative electrode active material is not coated at the winding end portion and the negative electrode current collector made of the metal foil is exposed, and (Excluding the case where the coating section circulates around the outer periphery of the electrode group while facing the positive electrode plate with the separator interposed therebetween). 2. The positive electrode active material is a lithium-containing composite oxide, which is a single compound of the general formula LiMO ₂ or LiM ₂ O ₄ (where M is at least one of cobalt, manganese, nickel and iron) or a mixture thereof. The non-aqueous electrolyte secondary battery according to claim 1.