JP3480190B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the technical field of thermal stability in a non-aqueous electrolyte secondary battery such as a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, with the rapid progress of portable and cordless electronic devices such as information-related devices or personal computers, secondary devices having small size, light weight and high energy density as power sources for driving these devices have been developed. The demand for batteries is increasing. Against this background, non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, are greatly expected as batteries having high voltage and high energy density.

As described above, as the expectation for the lithium secondary battery increases, the reliability such as the thermal stability required for the lithium secondary battery also increases, and particularly the thermal stability when the battery is short-circuited under various conditions. Is getting closer.

For example, attention has been paid to the thermal stability when a short circuit occurs due to a malfunction of an internal circuit of an electronic device incorporating a lithium secondary battery, or a short circuit occurs inside the battery due to a shock applied from the outside of the battery. ing.

In order to solve the problem of the thermal stability, the melting point of polyethylene, polypropylene or the like has a melting point of 2 as the core of the spiral electrode body in the non-aqueous electrolyte secondary battery.
It has been proposed that a polymer compound having a temperature of 00 ° C. or lower is used, and the core melts before the battery temperature starts to rise sharply to remove the heat of the battery as heat of fusion to suppress the temperature rise of the battery (for example, a special method). See Kaihei 7-192753).

However, when a short circuit actually occurs inside or outside the battery, the temperature of the positive electrode and the negative electrode first rise due to the Joule heat, and the rising speed is considerably large immediately after the short circuit occurs. There is a problem that the temperature of the electrode plate rises sharply before the heat of is diffused into the core and is absorbed as heat of fusion, and as a result, the temperature of the entire battery also rises and leads to liquid leakage. there were.

Therefore, in order to solve this problem, a high molecular compound having a large heat of fusion, for example, an olefinic thermoplastic polymer is directly added as a heat absorbing material to the electrode plate of the non-aqueous electrolyte secondary battery. There has been a proposal to suppress the temperature rise of the electrode plate (for example, JP-A-63-26).
676).

[0008]

In the conventional non-aqueous electrolyte secondary battery, the polymer compound added as a heat absorbing material in the electrode plate is once melted to prevent the formation of the electrode plate during the formation process. It is preferable if the function as a binder can also be expressed, but once the polymer compound once melted is not reversibly recrystallized even when returned to room temperature, the heat of fusion is reduced, and the heat absorption material There was a problem that the function was impaired.

[0009]

In order to solve the above problems, in the present invention, a heat absorbing material and a binder are added to the positive electrode so that the heat absorbing material has a melting point of 90 to 130 ° C. A low-molecular-weight polymer compound having a large heat of fusion of 30 J / g or more is added, and a polymer compound having a binding property without high-temperature treatment is used as the binder. Even if a short circuit occurs inside and outside the battery and Joule heat is generated, this heat can be absorbed as the heat of fusion of the added polymer compound that is the heat absorbing material, so that an increase in the battery temperature can be suppressed.

In addition to the polymer compound added as a heat absorbing material, styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-6-fluorine, which have binding properties without high temperature treatment, are also available. reduction since added to the positive electrode mixture at least one as a binding agent selected from propylene copolymers, without the function of the heat absorbing material is impaired to use, it can improve the thermal stability, if It is possible to prevent the drug from falling off.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention comprises:
In a positive electrode using a lithium-containing composite oxide as an active material, a heat absorbing material having a melting point of 90 to 130 ° C. and a heat of fusion of 30 J /
g or more, preferably having a melting point of 90 to 110 ° C. and a heat of fusion of 50 J / g or more, and containing a polymer compound, styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene as a binder. It contains at least one substance selected from the group consisting of a propylene hexafluoride copolymer and an acrylonitrile-butadiene rubber.

Further, as the polymer compound used as the heat absorbing material, polyethylene, polypropylene, ethylene-
At least one substance selected from the group of ethyl acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer is preferable.

The shape of the heat absorbing material is spherical with an average particle size of 1 to 12 μm, preferably 3 to 12.
A spherical shape of μm is effective.

The amount of the heat absorbing material added is such that the endothermic heat of fusion is 1 J or more per 1 g of the positive electrode mixture, and the weight fraction of the positive electrode mixture is 10% or less, preferably the positive electrode mixture 1
3% or more per gram, 7% in weight fraction with respect to the positive electrode mixture
The following are effective:

Further, lithium-containing composite oxide can be cited as the positive electrode active material, preferably Li _x M _y Ni _1-y
O ₂ (1.10 ≧ x ≧ 0.50, M is one or more of Co and Mn, 1 ≧ y ≧ 0) is good.

Examples of the negative electrode active material include carbon materials that occlude and release lithium, and metal oxides, lithium alloys, and lithium metals. Among them, carbon materials that occlude and release lithium are preferable, and more preferable are carbon materials. Is artificial graphite.

Further, as a solvent for the electrolytic solution, carbonates such as ethylene carbonate, ethylmethyl carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate, ethers such as 1,2-dimethoxyethane and 2-methyltetrahydrofuran, and propionic acid. An aliphatic carboxylic acid such as methyl or ethyl acetate, or a mixed solvent thereof is preferable, and the electrolyte of the electrolytic solution is LiBF ₄ , LiClO ₄ , LiPF ₆ , L.
iCF ₃ SO ₃ is preferred.

In the non-aqueous electrolyte secondary battery of the present invention configured as described above, even if the heat absorbing material short-circuits and Joule heat is generated due to the presence of the heat absorbing material, the heat absorbing material generates the heat of fusion. Since it absorbs heat, it is possible to prevent the battery temperature from rising, and the presence of the binder prevents the mixture from falling off, improving thermal stability and satisfying the battery characteristics.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a vertical sectional view of a cylindrical lithium secondary battery used in the embodiment.

An electrode plate group 4 formed by spirally winding a sheet-shaped positive electrode plate 2 and a sheet-shaped negative electrode plate 3 facing each other with a separator 1 in between is subjected to an organic electrolytic solution resistant treatment. It is stored in a battery case 5 made of stainless steel. Insulating rings 6 are provided on the upper and lower portions of the electrode plate group 4, respectively. A sealing plate 7 having a safety valve is fitted in the opening of the battery case 5 with an insulating packing 8 sandwiched therebetween. The positive electrode lead 9 drawn from the positive electrode plate 2 is connected to the sealing plate 7, and the negative electrode lead 10 drawn from the negative electrode plate 3 is connected to the bottom of the battery case 5.

The positive electrode plate and the negative electrode plate will be described in detail below. First, a method for synthesizing the positive electrode active material will be described. The powders of nickel hydroxide, cobalt hydroxide and lithium hydroxide were mixed with each other in which the atomic ratio of Ni, Co and Li was 0.
It was weighed so as to be 8: 0.2: 1.0 and thoroughly mixed with a ball mill. This mixture was placed in an alumina crucible, heat-treated in dry air at 750 ° C. for 10 hours, then naturally cooled, pulverized and classified to obtain a positive electrode active material having an average particle size of about 10 μm.

Positive electrode active material 10 obtained as described above
0 parts by weight, 4 parts by weight of artificial graphite powder having an average particle diameter of 4 μm as a conductive material, 4 parts by weight of various polyethylene powders having different melting points and heats of fusion shown in Table 1 as a heat absorbing material, and polyvinylidene fluoride as a binder. 4 in the state of being dissolved in a solvent
Parts by weight were added and kneaded to form a paste. Then
This paste was applied on both sides of an aluminum foil having a thickness of 0.02 mm, dried at 80 ° C., and rolled to obtain a positive electrode sheet. This positive electrode sheet was cut into a length of 380 mm and a width of 37 mm to obtain a positive electrode plate 2. The thickness was 0.14 mm. Further, in manufacturing the positive electrode plate, a series of steps after kneading were performed in dry air.

As the negative electrode active material, natural graphite having an average particle size of 6.0 μm was used. To 100 parts by weight of this natural graphite, 3 parts by weight of styrene-butadiene rubber as a binder dissolved in a solvent was added and kneaded to form a paste. Apply this paste to both sides of 0.025mm thick copper foil,
After drying at ℃, it was rolled to obtain a negative electrode sheet. This negative electrode sheet was cut into a length of 420 mm and a width of 39 mm to obtain a negative electrode plate 3. The thickness was 0.2 mm.

Then, the positive electrode lead 9 made of aluminum was attached to the positive electrode plate 2, and the negative electrode lead 10 made of nickel was attached to the negative electrode plate 3. The positive electrode plate 2 and the negative electrode plate 3 are stacked via a polyethylene separator 1 having a thickness of 0.025 mm, a width of 45 mm and a length of 1000 mm, and are spirally wound in the length direction to form a plate group 4. This electrode group 4
Was stored in a battery case 5 having a diameter of 17 mm and a height of 50 mm.

In the battery case 5, 2 parts of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are placed.
An electrolyte solution in which 1 mol / liter of LiPF ₆ was dissolved as an electrolyte was injected into a solvent mixed in a volume ratio of 0:80.
After that, the sealing plate 7 was fitted into the opening of the battery case 5 to seal the battery case 5 to obtain a lithium secondary battery.

For each of these batteries, the positive electrode plate 2
The negative electrode plate 3 and the negative electrode plate 3 were short-circuited using a conductor wire having a diameter of 0.8 mm and a length of 200 mm, and the maximum temperature reached on the surface of the battery after the short circuit was measured. At that time, the presence or absence of leakage was also examined. Also, regarding the battery capacity after the battery was left at 85 ° C. for 5 hours and then returned to room temperature, No. 1 to No. Each of the batteries of 7 specifications was measured. This is based on the assumption of a high temperature environment in which a battery is placed when used in a high performance notebook computer, and the respective results are shown in Table 1.

[0028]

[Table 1]

No. 1, No. 2 has a melting point of 90
If the temperature is lower than 0 ° C, the capacity will be impaired when the battery is placed in a high temperature environment (here, 85 ° C). This is probably because part of the polyethylene began to melt and coated part of the active material when it returned to room temperature.

No. 1, No. 3, No. Like 5,
When the heat of fusion is 30 J / g or less, the maximum temperature reaches a high level, which facilitates liquid leakage. In addition, No. Even if the heat of fusion is 30 J / g or more as in the case of 6, if the melting point is higher than 130 ° C., the maximum attainable temperature also becomes high and liquid leakage occurs.

When the heat absorbing material was not contained at all, the battery temperature rose to a considerably high temperature, which also led to liquid leakage.

Example 2 Another form of the positive electrode plate will be described in detail.

To 100 parts by weight of the positive electrode active material synthesized in the same manner as in Example 1, 4 parts by weight of artificial graphite powder having an average particle size of 4 μm as a conductive material and 4 parts by weight of polyethylene powder as a heat absorbing material were further combined. As a binder, 4 parts by weight of various organic compounds shown in Table 2 were dissolved in a solvent, and the mixture was kneaded to form a paste. Next, this paste was applied onto both sides of an aluminum foil having a thickness of 0.02 mm, dried at 80 ° C., and then rolled to obtain a positive electrode sheet. This positive electrode sheet was cut into a length of 380 mm and a width of 37 mm to obtain a positive electrode plate 2. The thickness was 0.14 mm. Further, in manufacturing the positive electrode plate, a series of steps after kneading were performed in dry air. The positive electrode plate 2 was wound around a winding core having a diameter of 10 mm, and the weight of the mixture dropped off was measured. In Table 2, the delaminating agent is expressed as a weight percentage with respect to the total weight of the mixture applied to the electrode plate.

[0034]

[Table 2]

From Table 2, styrene-butadiene rubber of the present embodiment, polyvinylidene fluoride, polytetrafluoroethylene,
It was found that the binding properties of the tetrafluoroethylene-hexafluoropropylene copolymer and the acrylonitrile-butadiene rubber were better than those of the acrylic resin and the ethylene-propylene-diene copolymer. When polyethylene is used without a binder, the binder is often dropped off, and the binder is required.

(Example 3) Example 1 other than the form of the positive electrode plate
A lithium secondary battery similar to the above was constructed and measured.
Hereinafter, other forms of the positive electrode plate will be described in detail.

To 100 parts by weight of the positive electrode active material synthesized in the same manner as in Example 1, 4 parts by weight of artificial graphite powder having an average particle size of 4 μm as a conductive material and various polymer compounds shown in Table 3 as a heat absorbing material. 4 parts by weight, and further 4 parts by weight of polyvinylidene fluoride as a binder dissolved in a solvent were added and kneaded to form a paste. Next, this paste was applied onto both sides of an aluminum foil having a thickness of 0.02 mm, dried at 80 ° C., and then rolled to obtain a positive electrode sheet. This positive electrode sheet was cut into a length of 380 mm and a width of 37 mm to obtain a positive electrode plate 2. The thickness was 0.14 mm. Further, in manufacturing the positive electrode plate, a series of steps after kneading were performed in dry air.

After the lithium secondary battery assembled using these positive electrode plates 2 was left at 85 ° C. for 5 hours, the internal resistance of the battery was measured.

No. 16 to No. A short circuit test similar to that in Example 1 was also performed for each of the lithium secondary batteries of specifications No. 22.

[0040]

[Table 3]

If a polymer compound having a melting point and a heat of fusion within the range of this embodiment is used, No. 16 to No. 22
As described above, the increase in battery temperature after a short circuit can be suppressed, but N
o. 21, No. As in No. 22, the internal resistance after storage at high temperature becomes large depending on the type, which is not preferable. It is considered that this is because a reaction between the polymer compound and the electrolytic solution occurred in a high temperature environment, and a polymer thin film was formed in the positive electrode plate. Therefore, the polymer compound used as the heat absorbing material is preferably polyethylene, polypropylene, ethylene-ethyl acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer.

Example 4 Another form of the positive electrode plate will be described in detail.

100 parts by weight of the positive electrode active material synthesized in the same manner as in Example 1, 4 parts by weight of artificial graphite powder having an average particle diameter of 4 μm as a conductive material, and polyethylene powder of each shape shown in Table 4 as a heat absorbing material. And 4 parts by weight of polyvinylidene fluoride dissolved in a solvent as a binder were added and kneaded to form a paste. Next, this paste is applied to both sides of 0.02 mm thick aluminum foil,
After drying at 0 ° C., the positive electrode plate 2 was rolled until the thickness of the electrode plate reached a certain value and remained unchanged, and the mixture density at this time is shown in Table 4.

[0044]

[Table 4]

No. As 23, the average particle size is 1μm or less, sometimes bulk density itself of polyethylene powder is reduced, the positive-electrode mixture density is reduced. Also, N
o. 27 as in the average particle size polyethylene powder is not placed in the gap of the positive <br/> electrode active material to become more 13 .mu.m, also positive-electrode mixture density is reduced. No. 28, No.
29 as in, for polyethylene fibers, the positive-electrode mixture density regardless of the length of the fibers becomes extremely small is not preferable.

(Example 5) Example 1 except for the form of the positive electrode plate
A lithium secondary battery similar to the above was constructed and measured.
Hereinafter, other forms of the positive electrode plate will be described in detail.

100 parts by weight of the positive electrode active material synthesized in the same manner as in Example 1, 4 parts by weight of artificial graphite powder having an average particle diameter of 4 μm as a conductive material, and various polyethylene powders shown in Table 5 as a heat absorbing material were used. Parts by weight, and further 4 parts by weight of polyvinylidene fluoride as a binder dissolved in a solvent were added and kneaded to form a paste. Next, this paste was applied onto both sides of an aluminum foil having a thickness of 0.02 mm, dried at 80 ° C., and then rolled to obtain a positive electrode sheet. This positive electrode sheet is cut into a length of 380 mm and a width of 37 mm, and the positive electrode plate 2 is cut.
And The thickness was 0.14 mm. Further, in manufacturing the positive electrode plate, a series of steps after kneading were performed in dry air.

A short circuit test similar to that in Example 1 was conducted on the lithium secondary battery assembled using these positive electrode plates 2.

[0049]

[Table 5]

As can be seen from Table 5, the larger the heat of fusion of the heat absorbing material per 1 g of the positive electrode mixture, the lower the maximum temperature reached, which is more preferable. However , the specific gravity of the polymer compound used as the heat absorbing material is as small as around 1 g / cc, and No. It is not preferable to add 10% or more in weight fraction as in No. 36, because the loss of battery capacity becomes large.

[0051] Although using LiCo _0.2 Ni _0.8 O ₂ as the positive electrode active material in Example 1-5, the chemical formula Li _x M _y
Ni _1-y O ₂ (1.10 ≧ x ≧ 0.50, M is Co, M
one or more of n, Cr, Fe, Mg, Al, Zn,
Similar effects were obtained even when an active material represented by 1 ≧ y ≧ 0) was used.

Further, although natural graphite was used as the negative electrode active material in Examples 1 to 5, cokes, carbon fibers,
Similar effects were obtained even when artificial graphite, metal oxide, lithium alloy, lithium metal or the like capable of inserting and extracting lithium was used.

[0053]

The present invention is carried out in the form described above, and has the effects of satisfying the battery characteristics and suppressing the temperature rise of the battery when a short circuit occurs inside or outside the battery.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view in which a part of a lithium secondary battery according to an embodiment of the present invention is cut away.

[Explanation of symbols]

2 Positive plate 3 Negative electrode plate

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichiro Watanabe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 63-193463 (JP, A) JP 7- 192753 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/62 H01M 10/40

Claims (6)

(57) [Claims] 1. A positive electrode using a lithium-containing composite oxide as an active material, a negative electrode made of at least one material selected from the group consisting of a carbon material that absorbs and releases lithium, a metal oxide, a lithium alloy, and a lithium metal. The positive electrode contains a heat absorbing material and a binder, and the melting point of the heat absorbing material is 90 to 130 ° C. and the heat of fusion is 30 J /
At least a polymer selected from the group consisting of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and acrylonitrile-butadiene rubber as a binder. Non-aqueous electrolyte secondary battery using one substance. 2. The heat-absorbing polymer compound is selected from the group consisting of polyethylene, polypropylene, ethylene-ethyl acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer. The non-aqueous electrolyte secondary battery according to claim 1, comprising at least one kind of substance selected. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer compound serving as the heat absorbing material has a spherical shape having an average particle diameter of 1 to 12 μm. 4. The addition amount of the polymer compound as a heat absorbing material is such that the endothermic heat of fusion is 1 J or more per 1 g of the positive electrode mixture, and the weight fraction of the positive electrode mixture is 10% or less. Alternatively, the non-aqueous electrolyte secondary battery described in 2. 5. A positive electrode using a lithium-containing composite oxide as an active material, a negative electrode made of at least one material selected from the group consisting of a carbon material that occludes and releases lithium, a metal oxide, a lithium alloy, and a lithium metal. A non-aqueous electrolyte solution, and the positive electrode has a melting point of 90 to 130 as a heat absorbing material.
C, heat of fusion of 30 J / g or more, and shape of average particle size 1 to
12μm spherical polyethylene, polypropylene,
At least one substance selected from the group consisting of ethylene-ethyl acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer has an endotherm due to its heat of fusion of 1 J per 1 g of the positive electrode mixture. Thus, the non-aqueous electrolyte secondary battery contains 10% or less by weight of the positive electrode mixture and contains polyvinylidene fluoride as a binder. 6. A lithium-containing composite acid as a positive electrode active material.
Compound is Li_xM_yNi _1-yO₂(1.10 ≧ x ≧ 0.5
0, 1 ≧ y ≧ 0, M is Co, Mn, Cr, Fe, Mg,
Non-aqueous electrolysis according to claim 1, which is one or more of Al and Zn).
Liquid secondary battery.