JPH1050292A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the rise of battery internal pressure due to the sudden rise of battery temperature at the time of a short circuit or overcharge, or the leakage of an electrolyte due to the rise of the battery internal pressure, by constituting the separator of a specific microporous film, in this secondary battery equipped with positive and negative electrodes, the separator arranged between these electrodes, and a nonaqueous electrolyte. SOLUTION: A separator 1 is constituted of a polyolefine fine porous film which is a microporous film wherein heat absorbing quantity to a unit area at 70-150 deg.C is 0.07cal/cm<2> or more, a thickness of 15-30μm, preferably PE alone, or a composite film where a PE microporous coat and a PP microporous film and a PP microporous coat are made multilayer. In this secondary battery, it is preferable to use an Li containing transition metal oxide to a positive electrode 2, carbon capable of storing and emitting Li to a positive electrode 3, one or more selected from ethylene, propylene, dimethyl, diethyl, and ethyl- methyl-carbonate, etc., to the solvent of a nonaqueous electrolyte, and lithium phosphate hexafluoride to the solvent of the nonaqueous electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a separator thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices such as personal computers and mobile phones have been rapidly reduced in size and weight and become cordless.
Development of a secondary battery having a high energy density has been required for these driving power supplies. As a battery meeting such a demand, LiCoO ₂ or L
Lithium-containing transition metal oxides exhibiting a 4V-class voltage with respect to lithium such as iNiO ₂ and LiMn ₂ O ₄ , and lithium in which lithium is used as an active material for a carbon material capable of intercalating and deintercalating lithium. Secondary batteries are particularly expected as batteries having high voltage and high energy density.

[0003] A separator used in a lithium secondary battery is poorly soluble in organic solvents such as ethers and esters used in an electrolytic solution, and is a porous material through which an electrolytic solution can sufficiently penetrate and lithium ions can move quickly. It must be a membrane. On the other hand, in order to achieve a high energy density of the battery, it is necessary to pack the battery active material as much as possible in the case, and it is required to reduce the thickness of the separator. However, when the battery is charged at a very low temperature, lithium ions do not move quickly and dendritic lithium is generated on the surface of the negative electrode, which may penetrate the separator and cause an internal short circuit. And it is necessary to reduce the diameter of the holes in the separator to some extent. Therefore, as a separator for a lithium secondary battery, a thickness of 20
A polyethylene resin having a porosity of 〜50 μm and a porosity of 40 to 70%, a polypropylene resin, or a composite film of a polyethylene resin and a polypropylene resin has been used.

[0004]

SUMMARY OF THE INVENTION A lithium secondary battery is
Due to its very high energy,
The reaction between the electrode active material and the electrolytic solution occurs, and the heat inside the battery greatly increases the temperature inside the battery. As the temperature rises, the volatilization of the organic solvent in the electrolytic solution and the generation of gas due to the reaction between the battery active material and the electrolytic solution are promoted, and the internal pressure of the battery rises. As a result, when the battery internal pressure exceeds a predetermined value,
The safety valve on the sealing plate was activated and the electrolyte leaked with the release of gas.

The present invention has been made to solve such a problem, and it is an object of the present invention to prevent a sudden rise in the battery temperature in the event of a short circuit or overcharging, thereby improving the safety of the battery.

[0006]

In order to solve this problem, the present invention provides a separator in which the heat absorption per unit area due to heat of fusion is at least 70-150 ° C.
A polyolefin-based microporous membrane of 0.07 cal / cm ² and a thickness of 15 to 30 μm is used.

Thus, when the battery temperature rises during overcharge or short circuit, the separator efficiently absorbs heat generated by the heat of the positive and negative electrodes and the reaction between the active material of the electrode plate and the electrolyte. This suppresses the volatilization of the solvent in the electrolyte due to the rise in battery temperature and the rapid generation of gas due to the reaction between the active material and the electrolyte, and the leakage of the electrolyte from the battery due to the rapid rise in battery internal pressure. Liquid can be prevented.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION
It shows a heat absorption of 0.07 cal / cm ² or more in a temperature range of ° C., and uses a separator made of a polyolefin-based microporous membrane having a thickness of 15 μm or more and 30 μm or less, preferably a polyethylene film alone, or a polyethylene film and polypropylene. A composite film having a multilayered film is used. With this configuration, it is possible to effectively absorb the heat generated by the positive electrode and the negative electrode, which cause the battery temperature to rise, and to suppress an increase in the battery internal pressure. Therefore, the safety valve of the sealing plate does not operate, and it is possible to prevent the electrolyte from leaking.

Moreover, Li _x M _y O ₂ (wherein M in the positive electrode C
at least one metal selected from the group consisting of o, Ni, and Mn; a transition metal oxide containing lithium represented by the following formula: 0.5 ≦ x ≦ 1.0; 1.0 ≦ y ≦ 2.0); The plane distance d (002) by X-ray diffraction is less than 3.38Å, and the specific surface area by the BET method is 2.0 m ² / g or more and 8.0 m ² / g.
Less than carbon, and further used as a solvent for the electrolyte solution is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propionate, at least one selected from the group consisting of ethyl propionate, solute phosphorus hexafluoride It is more preferable to use lithium oxide.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view showing the structure of a nonaqueous electrolyte secondary battery used in this embodiment. As shown in FIG. 1, a positive electrode plate 2 and a negative electrode plate 3 are separated by a separator 1, and these are spirally wound a plurality of times and housed in a nickel-plated iron battery case 4. And
An aluminum positive electrode lead 5 is drawn out of the positive electrode plate 2 and connected to the sealing plate 6, and a nickel negative electrode lead 7 is drawn out of the negative electrode plate 3 and connected to the bottom of the battery case 4. Reference numeral 8 denotes a polyethylene insulating ring provided at the upper bottom of the electrode plate group. Hereinafter, the positive and negative electrode plates will be described in detail.

The positive electrode plate is prepared by mixing Li ₂ CO ₃ and Co ₃ O ₄ and baking at 900 ° C. for 10 hours to synthesize 100 parts by weight of LiCoO ₂ , 3 parts by weight of acetylene black as a conductive material, and a binder. 7 parts by weight of a fluororesin binder as
1% carboxymethylcellulose aqueous solution to CoO ₂ 100
The paste is suspended in parts by weight as a positive electrode mixture paste, and this paste is applied to both sides of a 30 μm thick aluminum foil,
Drying and rolling by a rolling roller were performed, and cut into predetermined dimensions to obtain a positive electrode plate.

The negative electrode plate is obtained by graphitizing mesophase spheres at 2800 ° C., pulverizing and classifying the particles into an average particle size of about 3 μm (d (002) = 3.360 °, BET specific surface area = 4.0 m ² / g). ) And styrene / butadiene rubber 5 as a binder.
After mixing by weight, the mixture was suspended in 100 parts by weight of a 1% aqueous solution of carboxymethyl cellulose with respect to graphite to prepare a negative electrode paste. This paste was coated on a copper foil having a thickness of 20 μm on both sides with a negative electrode paste, dried, rolled using a rolling roller, and cut into predetermined dimensions to obtain a negative electrode plate.

An aluminum lead is attached to the positive electrode plate and a nickel lead is attached to the negative electrode plate.
As a result of measurement using a (differential thermal analyzer), a separator made of a polyethylene microporous film having a heat of fusion of 0.03 cal / cm ² and a thickness of 25 μm in a temperature range of 70 to 150 ° C. was spirally wound. ,
It was housed in a cylindrical battery case having a diameter of 17 mm and a height of 50 mm. As the electrolytic solution, a solution prepared by dissolving 1.5 mol / l of LiPF ₆ in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 was used, injected, and sealed. This was designated as Battery A of the present invention.

(Example 2) As a result of measurement using DSC,
A battery similar to (Example 1) was produced except that a separator having a heat of fusion of 0.04 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery B of the present invention.

(Example 3) As a result of measurement using DSC,
A battery similar to (Example 1) was produced except that a separator having a heat of fusion of 0.05 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery C of the present invention.

(Example 4) As a result of measurement using DSC,
A battery similar to (Example 1) was prepared except that a separator having a heat of fusion of 0.06 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery D of the present invention.

Example 5 As a result of measurement using DSC,
A battery similar to (Example 1) was prepared except that a separator having a heat of fusion of 0.07 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery E of the present invention.

(Example 6) Results of measurement using DSC
A battery similar to (Example 1) was prepared except that a separator having a heat of fusion of 0.08 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery F of the present invention.

(Example 7) As a result of measurement using DSC,
A battery similar to (Example 1) was produced except that a separator having a heat of fusion of 0.09 cal / cm ^{2 in} a temperature range of 70 to 150 ° C. was used. This was designated as Battery G of the present invention.

Next, the batteries A, B, C, D, E,
F and G were prepared for each 5 cells, and the battery was charged at a constant temperature of 630 mA for 2 hours at an ambient temperature of 20 ° C., an upper limit voltage of 4.2 V.

The discharging is performed by discharging the battery in the charged state with a discharging current of 720 m.
A, constant current discharge at a discharge termination potential of 3.0 V was performed. After repeating the above charge / discharge cycle for 20 cycles, heating was performed in a fully charged state. The heating test was performed under the condition that the temperature was raised from room temperature to 150 ° C. at 5 ° C./min and maintained at 150 ° C. for 10 minutes. The temperature inside the battery and the liquid leakage rate are shown in (Table 1).

[0023]

[Table 1]

From Table 1, it can be seen that the use of a separator having a large heat of fusion has the effect of suppressing the temperature rise of the battery and preventing the electrolyte from leaking. This is because the heat generated by the reaction between the battery active material and the electrolytic solution is effectively absorbed by the heat of fusion of the separator, thereby suppressing gas generation accompanying the reaction.

When a separator having the same heat of fusion per unit area is used, the total heat absorbed by the separator increases as the thickness of the separator increases, and a good effect is obtained. There are inconveniences such as the absence. As a result of this experiment, the thickness of the separator was preferably 30 μm or less. Therefore, in order to secure the energy density of the battery to some extent, the thickness of the separator is preferably 30 μm or less.

When the thickness of the separator was 10 μm or less, the amount of gas generated increased because the amount of the separator contained in the battery was very small and the heat absorbed by the separator was small. Further, when the separator is thin, there is a risk of internal short circuit or the like. Therefore, in consideration of safety, a thickness of 15 μm or more is preferable.

In this experimental example, the case where the polyethylene microporous membrane was used alone for the separator was shown.
The same effect was obtained even with a multilayer of a polyethylene microporous membrane and a polypropylene microporous membrane.

(Embodiment 8) LiOH.H ₂ O and N
i (0H) ₂ and 100 parts by weight of LiNiO ₂ fired at 750 ° C. for 10 hours in a dry air atmosphere, 3 parts by weight of acetylene black as a conductive material, and 4 parts by weight of polyvinylidene fluoride as a binder. The mixture was mixed and suspended in 100 parts by weight of methylpyrrolidone to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied on both sides of a 30 μm-thick aluminum foil, dried, and then rolled using a rolling roller. This was used as a positive electrode plate having a predetermined size.

The negative electrode was obtained by graphitizing a mesophase spheroid at 3000 ° C. and pulverizing and classifying the sphere to an average particle size of about 3 μm (d (002) = 3.355 °, BET specific surface area = 4.0 m ² / g). Was used. Here, d (002) was obtained by X-ray diffraction. Further, after mixing 3% by weight of styrene / butadiene rubber as a binder, 1% aqueous solution of carboxymethyl cellulose is added to graphite.
It was suspended in 100 parts by weight to make a paste. This negative electrode paste was applied on both sides of a copper foil having a thickness of 15 μm, dried, and then rolled to prepare a negative electrode plate.

A lead made of aluminum is attached to the positive electrode plate, and a lead made of nickel is attached to the negative electrode plate.
As a result of the measurement using
A polyethylene separator with a thickness of 25 μm at 0.07 cal / cm ²
The coil was spirally wound and delivered to a cylindrical battery case with a diameter of 17 mm and a height of 50 mm. As the electrolytic solution, a solution prepared by dissolving 1.5 mol / l of LiPF ₆ in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 was used, injected, and sealed. This was designated as Battery H of the present invention.

(Example 9) Mesophase small spheres were used for the negative electrode.
Graphitized at 2800 ° C and pulverized so that the average particle size becomes about 3 μm,
Classified (d (002) = 3.360Å, BET specific surface area = 4.0m
² / g) was prepared in the same manner as in (Example 8), except that ² / g) was used. This was designated as Battery I of the present invention.

(Example 10) Mesophase small spheres were graphitized at 2500 ° C on the negative electrode, pulverized and classified so as to have an average particle size of about 3 μm (d (002) = 3.370 °, BET specific surface area =
(Example 8) except that 4.0 m ² / g) was used. This was designated as Battery J of the present invention.

(Example 11) Mesophase small spheres were graphitized at 2300 ° C for the negative electrode, pulverized and classified so that the average particle size became about 3 µm (d (002) = 3.380 °, BET specific surface area =
(Example 8) except that 4.0 m ² / g) was used. This was designated as Battery K of the present invention.

(Example 12) Mesophase small spheres were graphitized at 2100 ° C on the negative electrode, pulverized and classified so as to have an average particle size of about 3 μm (d (002) = 3.390 °, BET specific surface area =
(Example 8) except that 4.0 m ² / g) was used. This was designated as Battery L of the present invention.

A test was carried out using different negative electrodes having the same d (002) but different BET specific surface areas.

Example 13 The negative electrode had an average particle size of about 50 μm.
Flake graphite (d (002) = 3.360Å, BET specific surface area = 0.5m
² / g) was prepared in the same manner as in (Example 8), except that ² / g) was used. This was designated as Battery M of the present invention.

Example 14 A negative electrode having an average particle size of about 30 μm
Flake graphite (d (002) = 3.360Å, BET specific surface area = 2.0m
² / g) was prepared in the same manner as in (Example 8), except that ² / g) was used. This was designated as Battery N of the present invention.

Example 15 A negative electrode having an average particle size of about 20 μm
Flake graphite (d (002) = 3.360Å, BET specific surface area = 6.0m
² / g) was prepared in the same manner as in (Example 8), except that ² / g) was used. This was designated as Battery O of the present invention.

Example 16 A negative electrode having an average particle size of about 10 μm
Flake graphite (d (002) = 3.360Å, BET specific surface area = 8.0m
² / g) was prepared in the same manner as in (Example 8), except that ² / g) was used. This was designated as Battery P of the present invention.

(Example 17) Scaly graphite having an average particle size of about 5 μm (d (002) = 3.360 °, BET specific surface area = 10.0 m ²⁾
/ g), except that (g) was used. This was designated as Battery Q of the present invention.

Next, the batteries H, I, J, K, L,
M, N, O, P, Q are prepared for each 5 cells, and environmental temperature
At 20 ° C, set the upper limit voltage to 4.2V, and set
Charged for hours. For discharging, the battery in this charged state was subjected to constant current discharge at a discharge current of 720 mA and a discharge termination potential of 3.0 V. The discharge capacity at the 20th cycle was used as the initial capacity. After repeating the above charge / discharge cycle, heating was performed in a 100% charged state. The heating test is 150 ° C at 5 ° C / min from room temperature.
The temperature was raised to 150 ° C. and the temperature was maintained at 150 ° C. for 10 minutes. The temperature inside the battery and the liquid leakage rate are shown in (Table 2).

[0042]

[Table 2]

From Table 2, it can be seen that there was no difference between the graphite layers between the graphite layers in terms of the liquid leakage rate. However, from the viewpoint of the initial capacity of the battery, when d (002) becomes 3.38 ° or more, the initial capacity is significantly reduced. This is because if the interlayer distance of graphite is too large, the amount of lithium that can be intercalated decreases. Also, the smaller the d (002), the higher the temperature in the battery. This is because the higher the degree of graphitization, the higher the reactivity with the electrolytic solution and the larger the calorific value. Therefore, d (002) is preferably not less than 3.350 ° and less than 3.380 °.

Further, from the batteries M to Q in (Table 2), BE
As the T specific surface area increases, the reaction area with the electrolyte increases, the calorific value increases, and the battery internal temperature increases. Here, when the BET specific surface area is 8 m ² / g or more, the temperature inside the battery rises greatly, gas generation accompanying the reaction with the electrolytic solution also increases, and liquid leakage starts to occur. Therefore, the BET specific surface area is 8 m ² / g
Must be less than. Therefore, the BET specific surface area is 8m
If it is less than ² / g, it is considered good from the viewpoint of the liquid leakage rate.
However, similar to the above, from the viewpoint of the initial capacity of the battery,
When the specific surface area is 0.5 m ² / g, the initial capacity is significantly reduced. This is due to a decrease in rate characteristics due to a decrease in the reaction area. Therefore, the BET specific surface area does not have to be small, and it must be 2.0 m ² / g or more.

As described above, the surface spacing d (00
2) is 3.35Å or more and less than 3.38Å, and the specific surface area by the BET method is 2.0 m ² / g or more and less than 8.0 m ² / g,
Without reducing the initial capacity of the battery, gas generation due to the reaction between the battery active material and the electrolytic solution is small even when the temperature of the battery rises, and the rise in battery internal pressure can be suppressed. Therefore, the safety valve of the sealing plate does not operate, and the leakage of the electrolyte can be prevented.

In this experimental example, the case where mesophase small spheres, which are spherical graphite, was used as the negative electrode carbon was shown. However, the same effect was obtained for the bulk graphite within the scope of the present invention.

Example 18 The positive electrode was made of Li ₂ CO ₃ and MnO
₂ and 100 parts by weight of LiMn ₂ O ₄ fired at 800 ° C. for 30 hours in a dry air atmosphere, and 3 parts by weight of acetylene black as a conductive material and 7 parts by weight of a fluororesin binder as a binder Then, the mixture was suspended in 100 parts by weight of a 1% aqueous solution of carboxymethyl cellulose with respect to LiMn ₂ O ₄ to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied on both sides of a 30 μm-thick aluminum foil, dried, and then rolled using a rolling roller. This was used as a positive electrode plate having a predetermined size.

The negative electrode was obtained by graphitizing a mesophase spheroid at 2800 ° C. and pulverizing and classifying the sphere to an average particle size of about 3 μm (d (002) = 3.360 °, BET specific surface area = 4.0 m ² / g). Was used. In addition, styrene / butadiene rubber 5
After mixing by weight, the mixture was suspended in 100% by weight of a 1% aqueous solution of carboxymethyl cellulose with respect to graphite to form a paste. Apply a negative electrode paste on both sides to a copper foil of 20 μm thickness,
After drying, rolling was performed using a rolling roller. This was used as a negative electrode plate having a predetermined size.

A lead made of aluminum is attached to the positive electrode plate, and a lead made of nickel is attached to the negative electrode plate.
As a result of the measurement using
A polyethylene separator with a thickness of 25 μm at 0.07 cal / cm ²
The coil was spirally wound and delivered to a cylindrical battery case with a diameter of 17 mm and a height of 50 mm. As the electrolytic solution, a solution prepared by dissolving 1.5 mol / l of LiPF ₆ in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 was used, injected, and sealed. This was designated as Battery R of the present invention.

(Example 19) A battery similar to (Example 18) was prepared except that a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 3 was used. This was designated as Battery S of the present invention.

(Example 20) A battery similar to (Example 18) was prepared except that a solvent in which ethylene carbonate and dimethyl tyl carbonate were mixed at a volume ratio of 1: 3 was used. This was designated as Battery T of the present invention.

Example 21 A battery similar to (Example 18) was prepared except that a solvent in which ethylene carbonate, ethyl methyl carbonate, and propylene carbonate were mixed at a volume ratio of 1: 2: 1 was used. This was designated as Battery U of the present invention.

(Example 22) Ethylene carbonate, diethyl carbonate and methyl propionate in a ratio of 1: 2:
Example 1 except that a solvent mixed at a volume ratio of 1 was used.
A battery similar to 8) was prepared. This was designated as Battery V of the present invention.

Example 23: Ethylene carbonate, diethyl carbonate and ethyl propionate in a ratio of 1: 2:
Example 1 except that a solvent mixed at a volume ratio of 1 was used.
A battery similar to 8) was prepared. This was designated as Battery W of the present invention.

Example 24 Ethylene carbonate and 1,
A battery similar to (Example 18) was made except that a solvent in which 2-dimethoxyethane was mixed at a volume ratio of 1: 3 was used. This was designated as Battery X of the present invention.

(Example 25) A battery similar to (Example 18) was prepared except that a solvent in which ethylene carbonate and tetrahydrofuran were mixed at a volume ratio of 1: 3 was used.
This was designated as Battery Y of the present invention.

Next, the batteries R, S, T, U, V,
W, X, Y are prepared for each 5 cells, at an ambient temperature of 20 ° C.,
The upper limit voltage was set to 4.2 V, and charging was performed at a constant current of 630 mA for 2 hours. Discharge the battery in this charged state with a discharge current of 720m
A, constant current discharge at a discharge termination potential of 3.0 V was performed. After repeating the above charge / discharge cycle for 20 cycles, heating was performed in a 100% charged state. Heating test: 150 ° C at 5 ° C / min from room temperature
The temperature was raised to 150 ° C. for 10 minutes. Table 3 shows the temperature inside the battery and the liquid leakage rate.

[0058]

[Table 3]

As a solvent for the electrolytic solution, ethylene carbonate is excellent in thermal stability, but has a high melting point of 34 ° C. and a high viscosity, so that when the content is increased, the conductivity of lithium ions decreases. Therefore, in this experiment, the content of ethylene carbonate was kept constant at 25%.

As shown in Table 3, when the cyclic ether such as tetrahydrofuran was used as the solvent for the electrolytic solution, the temperature in the battery increased more than when the cyclic and chain carbonates such as ethylene carbonate and ethyl methyl carbonate were used. It was big. This is because, when a cyclic ether is used as the solvent of the electrolytic solution, heat generation due to the reaction between the battery active material and the solvent of the electrolytic solution is larger than that of the cyclic and chain carbonates, and gas generation easily occurs due to the temperature rise. It is. Also, when a chain ether such as 1,2-dimethoxyethane was used as the solvent for the electrolytic solution, the rise in the temperature inside the battery was suppressed as compared with the cyclic ether. But,
Even at such a temperature, the amount of gas generated by the reaction between the battery active material and the solvent of the electrolytic solution is larger than in the case of using cyclic and chain carbonates, so that the internal pressure of the battery rises and the electrolyte leaks. Furthermore, the oxidation potential of cyclic and chain ethers is lower than that of ester-based ethers, so that a decomposition reaction of the electrolyte occurs during charging, and the battery capacity is small. For these reasons, the use of cyclic and chain ethers as the solvent of the electrolytic solution is inappropriate because it lowers battery performance.

As described above, the solvent for the electrolytic solution is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propionate, and ethyl propionate. .

In this embodiment, the positive electrode is LiCo.
Although O ₂ , LiNiO ₂ , and LiMn ₂ O ₄ were used, Fe may be used, and M is one or more transition metals selected from the group consisting of Co, Ni, Fe, and Mn and 0.5 ≦ x ≦ 1.0, 1.0 ≤y
Similar effects if a Li _x M _y O ₂ ≦ 2.0 was obtained.

[0063]

As described above, in the present invention, the separator
In the temperature range of 70 to 150 ° C., an endothermic amount per unit area by heat of fusion of at least 0.07cal / cm ^2, thickness 15 to 3
Since the microporous polyolefin membrane of 0 μm is used, the heat generated when the battery temperature rises can be efficiently absorbed by the separator, preventing a sudden increase in battery internal pressure and liquid leakage caused by this. it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Positive electrode plate 3 Negative electrode plate 4 Battery case 5 Positive electrode lead 6 Sealing plate 7 Negative electrode lead 8 Insulation ring

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H01M 10/40 H01M 10/40 Z A (72) Inventor Hideshi Koshina 1006 Odakadoma, Kadoma City, Osaka Prefecture Address Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] A positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.
Endotherm per unit area is 0.07ca in the temperature range of ℃
l / cm ² or more, a non-aqueous electrolyte secondary battery using the separator thickness is a polyolefin microporous film is 15μm or more 30μm or less. 2. The non-aqueous solution according to claim 1, wherein the separator comprising the polyolefin-based microporous membrane is a polyethylene-only microporous membrane or a composite membrane obtained by multilayering a polyethylene microporous membrane and a polypropylene microporous membrane. Electrolyte secondary battery. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a lithium-containing transition metal oxide is used for a positive electrode, and carbon capable of occluding and releasing lithium is used for a negative electrode. 4. The lithium-containing transition metal composite oxide has a chemical formula of Li _{x MyO 2} (where M is one or more transition metals selected from the group consisting of Co, Ni, Fe, and Mn; 0.5 ≦ x ≦ 1.
4. The non-aqueous electrolyte secondary battery according to claim 3, represented by the following formula: (0, 1.0 ≦ y ≦ 2.0). 5. The method according to claim 1, wherein the carbon has an interplanar spacing d (002) of 3.
Less than 38Å and specific surface area by BET method of 2.0 m ² /
Non-aqueous electrolyte secondary battery according to claim 3, wherein g or more 8.0m is less than ² / g. 6. The solvent of the non-aqueous electrolyte is ethylene carbonate, propylene carbonate, dimethyl carbonate,
4. The non-aqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of diethyl carbonate, ethyl methyl carbonate, methyl propionate, and ethyl propionate. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the solute of the non-aqueous electrolyte mainly comprises lithium hexafluorophosphate.