JP2003173820A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] [Problem] To prevent a rapid temperature rise during overcharge,
An object of the present invention is to provide a non-aqueous electrolyte secondary battery that is safe and can maintain battery characteristics even after storage at high temperatures. SOLUTION: A positive electrode composed of a lithium-containing transition metal composite oxide containing at least one selected from the group consisting of cobalt, nickel and manganese, and a negative electrode composed of a carbon material capable of absorbing and releasing lithium are separated by a separator. A non-aqueous electrolyte secondary battery comprising an electrode group and a non-aqueous electrolyte laminated through the intermediary, wherein the amount of water contained in the electrode group is 50 ppm or less;
0.2 to 5 parts by weight of at least one selected from the group consisting of diphenylene oxide and a diphenylene oxide derivative is added to 0 parts by weight.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte contained therein.

[0002]

2. Description of the Related Art In recent years, electronic devices such as personal computers and mobile phones are rapidly becoming smaller and lighter and cordless.
A secondary battery having a high energy density is required as a power source for driving these. Among them, the non-aqueous electrolyte secondary battery using lithium as an active material is expected as a battery having particularly high voltage and high energy density. Conventionally, metallic lithium is used for the negative electrode of this battery, and molybdenum disulfide, manganese dioxide, or vanadium pentoxide is used for the positive electrode, and a 3V class battery has been realized.

However, when metallic lithium is used for the negative electrode, dendritic lithium is deposited on the negative electrode plate during charging.
Therefore, when charging and discharging are repeated, the dendritic lithium deposited on the negative electrode plate separates from the negative electrode plate and floats in the electrolytic solution, and contacts the positive electrode to cause a minute short circuit.
Therefore, there is a problem that the charging efficiency is lowered and the cycle life is shortened. Further, since dendritic lithium has a large surface area and high reactivity, there is a problem in terms of safety.

Therefore, recently, a lithium ion secondary battery using a carbon material instead of metallic lithium for the negative electrode and a lithium-containing composite oxide for the positive electrode has been actively studied and commercialized. In the negative electrode of this battery, since lithium ions are present in the carbon material in a state of being occluded in the carbon material, there is no problem as described above when metallic lithium is used for the negative electrode, and it is safe.

However, the lithium ion secondary battery, when overcharged, generates heat due to decomposition of the non-aqueous electrolyte, deposition of metallic lithium on the negative electrode plate, and destruction of the layer structure of the lithium-containing transition metal composite oxide on the positive electrode, resulting in heat generation. Causes problems such as. In particular, the rapid rise in battery temperature due to heat generation is an important issue related to battery reliability.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous electrolyte secondary battery which prevents a rapid temperature rise during overcharge, is safe, and can maintain battery characteristics even after storage at high temperature. And

[0007]

In order to solve the above-mentioned problems, a non-aqueous electrolyte secondary battery of the present invention is a lithium-containing transition metal composite oxide containing at least one selected from the group consisting of cobalt, nickel and manganese. A non-aqueous electrolyte secondary battery including a positive electrode made of a material and a negative electrode made of a carbon material capable of absorbing and desorbing lithium, with a separator interposed therebetween, and a non-aqueous electrolyte secondary battery comprising the electrode group. Has a water content of 50 ppm or less, and 0.2 to 5 parts by weight of at least one selected from the group consisting of diphenylene oxide and diphenylene oxide derivatives is added to 100 parts by weight of the non-aqueous electrolyte. Characterize.

The non-aqueous electrolyte preferably comprises a non-aqueous solvent composed of ethylene carbonate and a chain ester and a solute. Further, the chain ester is preferably at least one selected from the group consisting of dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, at least one selected from the group consisting of diphenylene oxide and diphenylene oxide derivatives (hereinafter abbreviated as diphenylene oxide group) is added to a non-aqueous electrolyte. It is based on the finding that it is possible to suppress a rapid temperature rise of the battery during overcharge. The diphenylene oxide group has a function of promoting a gas generation reaction due to decomposition of the non-aqueous electrolyte and increasing a gas generation amount when the battery is overcharged. As a result, the internal pressure of the battery rises, the current cutoff mechanism operates at an early stage, and charging ends before the battery temperature rises sharply.

However, if the amount of the diphenylene oxide group added exceeds 5 parts by weight per 100 parts by weight of the non-aqueous electrolyte,
When the charged non-aqueous electrolyte secondary battery is stored at high temperature, the diphenylene oxide group itself is decomposed to generate a by-product. This becomes an obstacle, and the discharge capacity is significantly reduced.

If the amount of the diphenylene oxide group added is less than 0.2 parts by weight per 100 parts by weight of the non-aqueous electrolyte, the effect of accelerating gas generation during overcharging becomes insufficient, so that the current interrupting mechanism is sufficient. Does not work. Therefore, 0.2 to 5 parts by weight of the diphenylene oxide group is added to 100 parts by weight of the non-aqueous electrolyte.

Since the diphenylene oxide group easily reacts with water, it reacts with water in the battery and is consumed. However, in the non-aqueous electrolyte secondary battery of the present invention, a positive electrode composed of a lithium-containing transition metal composite oxide,
A negative electrode made of a carbon material capable of inserting and extracting lithium and a negative electrode made of a carbon material were laminated with a separator interposed between them so that the water content was 50%.
Since it is controlled to be below ppm, such a problem is
Avoided.

The electrode group whose water content is reduced to 50 ppm or less is used, and the diphenylene oxide group is added to the non-aqueous electrolyte 100.
By adding 0.2 to 5 parts by weight with respect to parts by weight, a sufficient amount of gas necessary for operating the current interruption mechanism is generated at the time of overcharging, so that a rapid temperature rise of the battery can be prevented. it can. In this way, by reducing the amount of water in the electrode group, a small amount of diphenylene oxide group suppresses a rapid rise in battery temperature, enhances battery safety, and decomposes the diphenylene oxide group itself. It is possible to suppress the reduction of the discharge capacity due to the product. Therefore, the battery characteristics can be maintained even after storage at high temperature.

Diphenylene oxide is a compound having the structural formula shown below.

[0015]

[Chemical 1]

Examples of the diphenylene oxide derivative include compounds represented by the following formula.

[0017]

[Chemical 2]

The non-aqueous solvent used for the non-aqueous electrolyte preferably comprises ethylene carbonate and a chain ester.
The chain ester is preferably a chain carbonate ester such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, but a chain ester such as methyl propionate or methyl butyrate may be used.

The solute to be dissolved in the above non-aqueous solvent is not particularly limited, and those usually used in non-aqueous electrolyte secondary batteries can be used. For example, LiClO ₄ , LiA
sF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , Li
Examples thereof include lithium salts such as N (CF ₃ SO ₂ ) ₂ .
Among them, LiPF ₆ and LiBF ₄ are particularly preferable.

For the positive electrode forming the electrode group, a lithium-containing composite oxide containing at least one transition metal selected from the group consisting of cobalt, nickel and manganese is used. It is preferable to use a carbon material such as graphite capable of inserting and extracting lithium for the negative electrode forming the electrode group. It is preferable to use a polyolefin microporous membrane such as polyethylene or polypropylene for the separator that interposes the positive electrode and the negative electrode.

The amount of water in the electrode group can be controlled by drying the electrode group using a vacuum dryer. The water content in the electrode group can be measured by the Karl Fischer method using a water content meter. The battery may have any shape such as a cylindrical shape, a square shape, and a button shape. Further, the modes of the positive electrode and the negative electrode may be changed according to each.

[0022]

EXAMPLES Examples of the present invention will be described below. << Example 1 >> FIG. 1 shows a vertical cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery produced in this example. This battery was manufactured as follows.

(I) Preparation of positive electrode Lithium cobalt oxide (LiCoO ₂ ) 10 as an active material
3 parts by weight of acetylene black as a conductive agent was mixed with 0 parts by weight, and 7 parts by weight of an aqueous dispersion of polytetrafluoroethylene as a binder was added as a binder to the mixture and kneaded to obtain a paste-like positive electrode mixture. I got an agent. This paste-like positive electrode mixture was applied on both sides of a current collector made of aluminum foil, dried and rolled to obtain a positive electrode 12.

(Ii) Production of Negative Electrode To 100 parts by weight of a carbon material as an active material, 3 parts by weight of an aqueous dispersion of styrene-butadiene rubber as a binder in solid content was added and kneaded to obtain a paste-like negative electrode mixture. It was
The paste-form negative electrode mixture was applied on both sides of a current collector made of copper foil, dried, and rolled to obtain a negative electrode 14.

(Iii) Preparation of Battery The positive electrode 12 and the negative electrode 14 are spirally wound with a separator 13 made of polyethylene having a thickness of 30 μm interposed therebetween.
An electrode group was constructed. Then, in order to reduce the water content in the electrode group, the electrode group was dried at 60 ° C. for 12 hours using a vacuum dryer, and the water content in the electrode group was set to 50 ppm or less.
The amount of water in the electrode group is measured by the Karl Fischer method using a water content meter, and the weight of the electrode group before measurement is W
_A, the weight of the electrode group after measurement as W _B, the water content (pp
m) = (W _A −W _B ) / W _A × 10 ⁶ .

The upper and lower parts of the dried electrode group were heated with warm air to heat-shrink the separator 13. Then, the lower insulating ring 19 was arranged below the electrode group, the electrode group was housed in the battery case 11, and the negative electrode lead plate 14a was spot-welded to the battery case 11. An upper insulating ring 18 was attached to the upper side of the electrode group, and a groove portion was formed on the upper portion of the battery case 11 to form an inwardly protruding step portion for receiving the gasket 16. The positive electrode lead plate 12a connected to the end portion of the positive electrode 12 was laser-welded to a predetermined portion of the sealing plate 17 in which the gasket 16 was incorporated in advance. Seal plate 17
Has a positive electrode terminal 15. The sealing plate 17 was attached to the battery case 11 and caulked and sealed to assemble the battery.

For the non-aqueous electrolyte, lithium hexafluorophosphate (LiPF ₆ ) was added in an amount of 1.25 mol / l in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 3. 1 was used after being dissolved. And
After adding 0.2 parts by weight of diphenylene oxide to 100 parts by weight of the non-aqueous electrolyte, the non-aqueous electrolyte was added to the battery case 11
Was poured into. The obtained battery has an outer diameter of 18 mm and a total height of 65 mm. The design capacity of the battery is 1700m.
It is Ah.

This battery has the following mechanism. In this battery, an upper metal plate 20 and a lower metal plate 21 are provided between the positive electrode terminal 15 and the sealing plate 17. The outer peripheral portion of the lower metal plate 21 is sandwiched between the sealing plate 17 and the insulating plate, and the upper metal plate 20 is further disposed via the insulating plate. And these metal plates 20
The central portions of and 21 are joined by welding and are in contact with each other so that they can be electrically conducted. However, when the internal pressure of the battery exceeds the set value due to the gas generated by the battery reaction, the joint portion of the lower metal plate 21 with the upper metal plate 20 is broken,
From there, gas enters the gap between the upper metal plate 20 and the lower metal plate 21, and the upper metal plate 20 is pushed upward. Thus, the contact between the upper metal plate 20 and the lower metal plate 21 is cut off, and the current is cut off. Then, when the battery internal pressure further rises and reaches the set value in the state where the current is cut off, the upper metal plate 20 is broken, and gas is discharged from the broken portion of the upper metal plate 20 through the gas discharge hole of the positive electrode terminal. It is configured to be released to the outside.

This battery was subjected to constant current charging up to 4.1 V at an ambient temperature of 20 ° C. and a charging current of 0.34 A.
After resting for 0 minutes, discharge current 0.34 A, final voltage 3.
Charging and discharging for discharging at 0 V were repeated. After that, the battery was charged to 4.1V with a charging current of 0.34A. This battery was used as the battery of Example 1.

Example 2 The above compound 2 was used as a diphenylene oxide derivative instead of diphenylene oxide.
A battery was prepared in the same manner as in Example 1 except that This battery was used as the battery of Example 2.

Example 3 A battery was manufactured in the same manner as in Example 1 except that 2.0 parts by weight of diphenylene oxide was added to 100 parts by weight of the non-aqueous electrolyte. This battery was used as the battery of Example 3.

Example 4 The above compound 2 was used as a diphenylene oxide derivative instead of diphenylene oxide.
A battery was produced in the same manner as in Example 3 except that This battery was used as the battery of Example 4.

Example 5 A battery was prepared in the same manner as in Example 1 except that 5.0 parts by weight of diphenylene oxide was added to 100 parts by weight of the non-aqueous electrolyte. This battery was used as the battery of Example 5.

Comparative Example 1 A battery was prepared in the same manner as in Example 1 except that 0.1 part by weight of diphenylene oxide was added to 100 parts by weight of the non-aqueous electrolyte. This battery was used as the battery of Comparative Example 1.

Comparative Example 2 A battery was manufactured in the same manner as in Example 1 except that 7.0 parts by weight of diphenylene oxide was added to 100 parts by weight of the non-aqueous electrolyte. This battery was used as a battery of Comparative Example 2.

Comparative Example 3 A battery was produced in the same manner as in Example 1 except that after the electrode group was formed, the electrode group was not dried to reduce the water content. This battery was used as a battery of Comparative Example 3.

Comparative Example 4 A battery was manufactured in the same manner as in Example 3 except that after the electrode group was formed, the electrode group was not dried to reduce the water content. This battery was used as the battery of Comparative Example 4.

Comparative Example 5 A battery was produced in the same manner as in Example 5 except that after the electrode group was formed, the electrode group was not dried to reduce the water content. This battery was used as the battery of Comparative Example 5. With respect to the batteries of Examples 1 to 5 and the batteries of Comparative Examples 1 to 5 manufactured as described above, the recovery rate of the discharge capacity after the overcharge test and the high temperature storage was measured.

The overcharge test was conducted as follows. 20 ° C
In this environment, after discharging with a discharge current of 1 A and a cutoff voltage of 3.0 V, constant current and constant voltage charging was performed with a maximum current of 1 A and a set voltage of 4.2 V for 2 hours. The charging capacity at this time was defined as the specified capacity of the battery. Each battery charged to the specified capacity was discharged at a discharge current of 1 A and a final voltage of 3.0V.
After that, constant current charging was performed at a charging current of 3 A until the current cut-off mechanism was activated to bring the battery into an overcharged state, and the charge capacity rate and the maximum temperature of the battery at that time were measured. The charge capacity ratio is the ratio of the charge capacity in the overcharge test to the specified capacity.

Next, the recovery rate of the discharge capacity after high temperature storage was measured as follows. Using each battery charged to the specified capacity, discharge current 1
A, discharge was performed at a final voltage of 3.0 V, and the discharge capacity was measured. Then, the constant current constant voltage charging is performed for 2 hours at the maximum current of 1 A and the set voltage of 4.2 V, and then at the ambient temperature of 85 ° C.,
Stored for 3 days. After storage, discharge current 1A, final voltage 3.
The discharge was performed at 0V. The ratio of the discharge capacity after storage to the discharge capacity before storage was defined as the recovery rate of the discharge capacity after high temperature storage.

Table 1 shows the addition amount of diphenylene oxide or diphenylene oxide derivative in each battery, the charge capacity ratio in the overcharge test and the maximum temperature of the battery, and the recovery ratio of the discharge capacity after high temperature storage.

[0042]

[Table 1]

In Example 1 and Comparative Example 3, the non-aqueous electrolyte 1 was used.
The addition amount of diphenylene oxide was 0.2 parts by weight with respect to 00 parts by weight, but at the time of overcharge, Example 1 had a lower charge capacity ratio than Comparative Example 3 and an increase in battery temperature. Is suppressed.

This is because the water content of the electrode group is 5 in the first embodiment.
This is because by reducing the amount to 0 ppm or less, the side reaction of diphenylene oxide with water can be reduced, and that amount effectively acted to promote gas generation. Therefore, it is considered that the current cutoff mechanism operated at an early stage before the gas generation amount increased and the battery temperature rapidly increased. As described above, by reducing the water content of the electrode group, it was possible to suppress a rapid increase in battery temperature during overcharge with a small amount of diphenylene oxide added. Such an effect was similarly observed when the diphenylene oxide derivative was added as in Example 2.

Also, when comparing Examples 3 and 5 with Comparative Examples 4 and 5, the charging capacity ratios of Examples 3 and 5 were lower, and the current interruption mechanism operated at the time when the battery temperature was low. It turned out to be a safer battery.

It was found that the recovery rate of the discharge capacity after high temperature storage was lower as the amount of the diphenylene oxide or diphenylene oxide derivative added was larger. This is 85 ℃
It is considered that this is because the diphenylene oxide itself decomposes in the high temperature environment to generate a by-product, which becomes an obstacle and reduces the discharge capacity.

[0047]

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a non-aqueous electrolyte secondary battery that prevents a rapid temperature rise during overcharge, is safe, and can maintain battery characteristics even after storage at high temperature.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

11 battery case 12 Positive electrode 12a Positive lead plate 13 separator 14 Negative electrode 14a Negative electrode lead plate 15 Positive terminal 16 gasket 17 Seal plate 18 Upper insulation ring 19 Lower insulation ring 20 Upper metal plate 21 Lower metal plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyomi Kato             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shu Koshina             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kenji Okahara             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation (72) Inventor Noriko Shima             3-3-1 Chuo 8-chome, Ami Town, Inashiki District, Ibaraki Prefecture             Within Mitsubishi Chemical Corporation (72) Inventor, Hitoshi Suzuki             3-3-1 Chuo 8-chome, Ami Town, Inashiki District, Ibaraki Prefecture             Within Mitsubishi Chemical Corporation F-term (reference) 5H029 AJ04 AJ12 AK03 AL06 AM03                       AM05 AM07 BJ02 BJ14 DJ09                       EJ11 HJ01                 5H050 AA10 AA15 BA17 CA08 CA09                       CB07 DA13 EA22 HA01

Claims (3)

[Claims] 1. A positive electrode made of a lithium-containing transition metal composite oxide containing at least one selected from the group consisting of cobalt, nickel, and manganese, and a negative electrode made of a carbon material capable of inserting and extracting lithium. A non-aqueous electrolyte secondary battery comprising an electrode group and a non-aqueous electrolyte laminated via a separator, wherein the amount of water contained in the electrode group is 50 ppm or less, and 100 parts by weight of the non-aqueous electrolyte is mixed with dihydrate. A non-aqueous electrolyte secondary battery comprising 0.2 to 5 parts by weight of at least one selected from the group consisting of phenylene oxide and diphenylene oxide derivatives. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte comprises a non-aqueous solvent composed of ethylene carbonate and a chain ester and a solute. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the chain ester is at least one selected from the group consisting of dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate.