JP2002280068A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having superior stability in high-temperature circumstances during overcharge. SOLUTION: A plate group having a positive electrode 2 and a negative electrode 3 rolled together with a separator 4 is sealed in a case 5 together with a nonaqueous electrolyte to which an overcharge resistant additive such as 2-biphenylmethyl carbonate is added. The separator 4 between plates has an air permeation reaistivity of 400-1500 sec/100 ml and a total pore volume of 0.3-1.5 cm<3> /g after held in the atmosphere for 15 minutes at 115 deg.C in the state of giving a tensile load of 25 kg/cm<2> to MD.

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 having high safety in a high-temperature environment at the time of overcharging, and more particularly to an additive and a separator for improving safety at the time of overcharging. The present invention relates to a non-aqueous electrolyte secondary battery used.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries can be maintained in a high-temperature environment during overcharge by using a safety device that is broadly incorporated into the battery or by using overcharge-resistant characteristics of the power generation element itself. Is provided. Further, as a specific example of providing the latter power generation element itself with overcharge resistance, a method of improving the characteristics of a separator, a method of adding an overcharge resistance additive to an electrolyte, and the like have been proposed.

Conventionally, as a configuration for improving safety during overcharge, a configuration utilizing a separator shutdown function which is a function unique to a separator of a non-aqueous electrolyte secondary battery is widely used. Normally, the separator plays the role of preventing short circuit between the positive electrode and the negative electrode.However, the separator using porous polyolefin etc. softens when the battery temperature rises significantly due to excessive current etc. due to external short circuit. By doing so, it has a so-called shutdown function that becomes substantially non-porous and does not allow current to flow.

[0004] If the battery temperature rises even after the shutdown function, the separator may melt and form a large hole, resulting in a short circuit between the positive electrode and the negative electrode (hereinafter, this phenomenon is referred to as meltdown). . It can be said that the higher the temperature at which the meltdown occurs, the higher the safety of the battery. However, in order to enhance the shutdown function, when the heat melting property is increased, the meltdown temperature is lowered, and the safety is reduced.

On the other hand, in a configuration in which an overcharge-resistant additive is added to an electrolytic solution, various methods for improving safety during overcharge have been proposed. For example, a method of increasing the internal resistance of a battery by polymerizing an additive during overcharge and protecting the battery from overcharge (Japanese Patent No. 3061756, etc.), and a method of generating gas at overcharge and operating at a predetermined internal pressure A method of reliably operating the internal electric cutting device (Japanese Patent No. 3061759, etc.) and a method of producing a conductive polymer during overcharge abuse,
A method of generating a short circuit inside a battery and automatically discharging the battery
No. 0-32258), among others, an additive comprising a carbonate derivative having a biphenyl group has attracted attention (Japanese Patent No. 3080609). When the battery voltage reaches an overcharged state, the additive made of this derivative starts a decomposition reaction to generate gas and starts a polymerization reaction to produce a polymer. In addition to the polymer acting as a resistor, it is a substance that does not easily redissolve in the electrolyte,
It works effectively against overcharging.

[0006] Due to recent development competition, there is a strong demand for high capacity non-aqueous electrolyte secondary batteries. Higher capacity has a performance improvement by improving the active material of the electrode.
The capacity has been increased by reducing the volume of members that do not contribute to the electromotive reaction and increasing the substantial amount of the active material filled in a limited battery container. For this reason, the thicknesses of the current collectors and separators of the positive and negative electrodes tend to be thin. When the separator becomes thinner, the safety against short circuits and the like tends to worsen, but since the amount of the active material is substantially increased,
Conversely, the demands on security increase.

Therefore, when a battery using a thin separator falls into an overcharged state and becomes a high temperature state due to heat generation, the overcharged state is reduced rather than a method of electrically avoiding the overcharged state. It is effective to adopt a method for solving the problem. Specifically, in the method described above,
A method to increase the internal resistance of the battery by polymerizing the additive when the separator is shut down or when the additive is overcharged, to protect the battery from overcharge, and to generate a gas at the time of overcharge and operate at a predetermined internal pressure. The method of reliably operating the cutting device avoids the continuation of the overcharge state by limiting or cutting off the current applied to the battery.
On the other hand, in the method of causing a short circuit inside the battery and automatically discharging, the battery is forcibly discharged inside the battery, and the overcharging state is stopped from the point that the power generating element inside the battery is released from the overcharge state. This method is preferable to the method described above. In particular, when an additive that generates gas at the time of overcharging is added to a configuration in which an internal electric disconnecting device that operates at a predetermined internal pressure is not provided in a rectangular battery or the like, the internal pressure of the battery container increases, and the safety is increased. It is not preferable in terms of sex.

[0008]

However, when an additive comprising a carbonate derivative having a biphenylyl group is used as the additive, the amount of the additive, the relationship with the electrolyte salt, the non-aqueous solvent, and other components, and Under the influence of various factors such as the deterioration state, the function of avoiding the above-described conventional overcharge state is mixed. For this reason,
Conductive polymer is generated at the time of overcharging, and there is a possibility that gas may be generated or the internal resistance of the battery may be increased in preference to the function of ensuring safety by internal short circuit. There is a problem in terms of reliability that protection is ensured.

The present invention solves the above-mentioned conventional problems. By using a combination of a suitable additive and a separator, a high-capacity non-aqueous electrolyte secondary having excellent safety in a high-temperature environment is provided. It is intended to provide a battery.

[0010]

In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention comprises a non-aqueous electrolyte comprising 2-biphenylylmethyl carbonate, 4-biphenylylmethyl carbonate, 4-biphenylylbutyl. An overcharge-resistant additive selected from carbonate and 3-biphenylmethyl carbonate is added, and immediately after applying a high temperature and a stress expected to be exposed to the separator at the time of overcharging, the air permeability resistance becomes 400. From 1500 seconds / 10
0 ml and a total pore volume of 0.3 to 1.5 cm ³ /
g. In addition, the said air resistance is based on Japanese Industrial Standard (JISP8117-1998 or less, J
The measurement method specified in IS is applied mutatis mutandis, and is expressed by the time (seconds / 100 ml) at which 100 ml of air passes through a separator having an area of 642 mm ² at 23 ° C. ± 1 ° C. Generally, this value is also called a Gurley number, and a smaller value indicates that air passes better, that is, a lower air resistance.

According to the constitution of the present invention, 2-biphenylylmethyl carbonate and 4-biphenylyl carbonate are used as overcharge additives.
By using at least one selected from biphenylyl methyl carbonate, 4-biphenylyl butyl carbonate, 3-biphenylmethyl carbonate and 4-biphenylyl phenyl carbonate, and further combining a separator having the above-mentioned characteristic parameters, the battery is overheated. When the charged polymer enters the charged state, the conductive polymer penetrates the separator to cause an internal short circuit, thereby eliminating the overcharged state. This makes it possible to provide a non-aqueous electrolyte secondary battery with high capacity and excellent reliability.

[0012]

Embodiments of the present invention will be described below.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and a separator. , 2-biphenylylmethylcarbonate, 4-biphenylylmethylcarbonate, 4-biphenylylbutylcarbonate, 3-biphenylmethylcarbonate, and at least one overcharge-resistant additive. After holding at a temperature of 115 ° C. in the atmosphere for 15 minutes in a state where a tensile load of 25 kg / cm ² was applied in a stretched longitudinal direction (hereinafter, this direction is referred to as MD), the air permeability resistance was 600.
From 2000 seconds / 100 ml, with a total pore volume of 0,1 s.
The one at 3 to 1.5 cm ³ / g is used.

As the separator according to the present invention, an electronically insulating microporous thin film having high ion permeability and appropriate mechanical strength is used. As the material, it is preferable to use a porous polyolefin such as a polypropylene resin, a polyethylene resin alone or a laminate or a mixture or composite of these, from the viewpoints of organic solvent resistance and hydrophobicity and having a shutdown function. .

The positive electrode of the present invention has a conventionally known structure, but is a mixture comprising a lithium-containing composite oxide such as lithium cobalt oxide, lithium nickel oxide, and manganese spinel as an active material, and a mixture of a conductive agent and a binder. Is applied to the current collector.

In the negative electrode of the present invention, carbon such as natural graphite or artificial graphite is used as a main active material.
Various alloys mainly composed of aluminum and aluminum, various metal oxides including tin oxide and the like, conventionally known ones such as metal nitrides, and like the positive electrode, mixed with a conductive agent and a binder The mixture is produced by coating the current collector.

In the non-aqueous electrolyte (hereinafter referred to as an electrolytic solution) in the present invention, non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) and dimethyl carbonate (DM).
C), a mixture of two or more kinds of chain carbonates such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) is preferable. As the electrolyte salt, a conventionally known lithium salt such as LiPF ₆ or LiBF ₄ can be used.

In the battery of the present invention, an internal short circuit is caused by the overcharge-resistant additive and the separator in a high temperature environment at the time of overcharge, and the mechanism of the internal short circuit is as follows.

When the voltage of the battery exceeds the maximum operating voltage during overcharge, the overcharge-resistant additive polymerizes and grows on the surface of the positive electrode to form a polymer layer having a high resistance value. When the voltage further increases, the polymer layer becomes a conductive polymer. If the overcharge state continues, the conductive polymer grows inside the pores of the separator, and eventually penetrates to the negative electrode, causing an internal short circuit. As a result, in the battery using the separator and the overcharge-resistant additive according to the present invention, the conductive polymer is formed from a relatively early stage of the overcharge process, and the charge depth of the positive electrode and the negative electrode is excessively excessive. Does not reach
The risk of overcharging can be reduced.

In the mechanism described above, the overcharge resistant additive is not added, or the additive amount is 0.1% by weight.
If it is less than 1, the overcharge state will progress to a serious state before the conductive polymer grows sufficiently. When the amount of the additive is large, for example, when it is more than 10% by weight, the effect of suppressing the overcharged state can be exerted.
This is unsuitable because normal battery characteristics, especially during high-temperature storage, deteriorate.

Further, as a result of diligent studies, the present inventors have found that there are suitable values for the air resistance and the porosity of the separator. If there are many through holes in the separator,
That is, when the air permeability is low, a large amount of the conductive polymer penetrates to reach the negative electrode, so that a short-circuit current increases and a dangerous situation occurs. Conversely, when the separator has few through-holes, that is, when the degree of air permeability is high, the overcharge state further progresses before the conductive polymer penetrates and reaches the negative electrode.

Furthermore, even if the air permeability resistance is almost the same, when the separator has a large number of pores, that is, when the total pore volume is large, the rate at which the generated conductive polymer stays in the separator increases, and the conductivity increases. The overcharge state further progresses before the conductive polymer penetrates and reaches the negative electrode. Conversely, when the separator has a small number of pores, that is, when the total pore volume is small, the generated conductive polymer is efficiently filled in the through-holes of the separator and reaches the negative electrode in a large amount. That is, an overcharged state is promoted. In addition, when either separator is used, the amount of polymerization of the overcharge-resistant additive and the increase in internal resistance due to the lack of electrolyte, or the gas generation of the additive functions normally, and the overcharge suppression effect or the internal electric disconnection device Works reliably. However, when the shutdown function does not function sufficiently because the separator thickness is thin, or when the internal electric disconnection device is not provided, the overcharge additive does not function and the overcharge state of the battery may be continued. As such, there is a suitable degree of air resistance and porosity.

The separator according to the present invention described above has an MD
Immediately after being held at a temperature of 115 ° C. in the atmosphere for 15 minutes while applying a tensile load of 25 kg / cm ^{2 to} the
It is measured based on a measurement method based on IS, and has an air resistance of 400 to 1500 seconds / 100 ml and a total pore volume of 0.3 to 1.5 cm ³ / g.

In particular, when 2-biphenylylmethyl carbonate is used as the overcharge-resistant additive, the air resistance is 450 to 900 seconds / 100 ml, and the total pore volume is 0.5 to 1.0 cm. Those at ³ / g show a very good effect.

The air permeability resistance and the total pore volume of the above-mentioned separator are larger than those of the known separator in a normal temperature range. If the degree of air permeability increases in a normal use state, it adversely affects high-rate discharge characteristics and the like. In view of the above-mentioned adverse effects, the separator of the present invention is preferably a porous polyolefin having a small air resistance at normal temperature and a large air resistance at a high temperature. At this time, the porosity naturally changes with the air resistance.

Hitherto, the air resistance and the porosity have been studied in a normal temperature range, and various proposals have been made. However, when the battery falls into an overcharged state, each component is exposed to a high-temperature environment due to the heat generated by the battery itself, and thus the separator is required to have characteristics different from those in a normal temperature range. Against this background, the present inventors have obtained the knowledge that it is necessary to evaluate in a thermally and physically added state assumed in a high-temperature environment, and keep the evaluation under predetermined conditions. Immediately after that, it was concluded that the separator having the above-mentioned characteristics was suitable for the battery of the present invention. Hereinafter, the processing conditions applied to the separator in advance will be described.

The heating mechanism in the overcharged state of the battery is complicated
The state of the stress applied to the separator in the electrode group
It is difficult to reliably simulate. In particular, Sepa
The separator can be used as a separator even at the same high environmental temperature.
Consider the fact that the heat shrinkage condition changes due to the stress.
Is important. Therefore, the present inventors have found that the reproducibility is high.
Separator as processing condition
25kg / cm for MD ^TwoThe state where the tensile load is given
It has been found favorable. Usually wound in a spiral
When manufacturing electrode plates, the separator must have some tension.
Has been added and wound up. In other words, pull to MD
Placed in a wound electrode plate group with a load applied
Have been.

On the other hand, regarding the temperature condition, it is necessary to consider the ultimate temperature of the battery at the time of overcharging and the time required from when the battery is overcharged to when the overcharged state is eliminated by the conductive polymer. 115 ° C in air in form
It has been found that it is preferable to hold at a temperature of 15 minutes for 15 minutes. Here, the time of 15 minutes means that the separator has no change in the air permeability and the porosity at that temperature, that is, a time sufficient to reach saturation, and a longer time may be used, If the contraction in the machine-stretched width direction (hereinafter, this direction is referred to as TD) has reached saturation, the time may be shorter than this, but 15 minutes is preferable as the retention time with high reproducibility.

In the above-described battery of the present invention, the thickness of the separator is preferably from 8 μm to 18 μm. When the thickness exceeds 18 μm, it is disadvantageous in terms of battery characteristics such as high capacity and high rate discharge of the battery, and internal short circuit is unlikely to occur. If the thickness is less than 8 μm, the overcharge protection function may not operate normally even if an internal short circuit occurs in a high temperature environment during overcharge.

[0030]

Next, specific examples of the present invention will be described. First, separators having various characteristics described below were manufactured under different conditions.

(Production of Separator) In this example, a separator composed of a polyethylene (PE) film was produced by the method described below.

High density polyethylene (average molecular weight 280,000)
20 parts by weight and high density polyethylene (average molecular weight 360,000)
20 parts by weight and 60 parts by weight of liquid paraffin were melt-kneaded in a twin-screw extruder. A polymer gel sheet was prepared by extrusion casting from a coat hanger die onto a cooling roll. The thickness was 1.8 mm at this point. This polymer gel sheet was cured at 122 ° C. for 7 using a simultaneous biaxial stretching machine.
It was stretched by a factor of 7 before extraction. Then, it was immersed in methylene chloride to extract and remove liquid paraffin. Further, after stretching to TD twice at 125 ° C. using a tenter,
Heat treatment was performed while relaxing the stretching of D by 17%. Through the steps described above, a PE film having a thickness of 16 μm was prepared, and the separator A
And

Hereinafter, various characteristics of the separator A were measured.

First, the air resistance of the separator A at normal temperature was measured. JIS in a laboratory controlled at 23 ° C
The air resistance was measured using an A-type measuring device conforming to the standard. The measured value was 150 seconds / 100 ml. next,
The air resistance of the separator A after the heat treatment was measured.
Separator A was cut into a rectangle of 120 mm in MD and 50 mm in TD, and placed in a constant temperature layer set at a temperature of 115 ° C. in the air with a weight of 200 g in the MD at 25 kg / cm.
^It was set with a tensile load of ² applied and held for 15 minutes. (Hereinafter referred to as MD pretreatment.) After the MD pretreatment, the air permeability was measured using a type A measuring device conforming to JIS in a laboratory adjusted to 23 ° C. The measured value was 600 seconds / 100 ml.

Further, the total pore volume of the separator A at normal temperature was measured. The total pore volume was measured using a mercury porosimeter in a laboratory adjusted to 23 ° C. The measured value was 1.6 cm ³ / g. Next, the total pore volume of the separator A after the heat treatment was measured. Separator A
Was subjected to MD pretreatment under the same conditions as when the airflow resistance was measured. After the MD pretreatment, the total pore volume was measured using a mercury porosimeter in a laboratory adjusted to 23 ° C. The measured value was 0.6 cm ³ / g.

A separator B having the same thickness as the separator A but having a different air resistance and a total pore volume was produced.

High density polyethylene (average molecular weight 280,000)
20 parts by weight and high density polyethylene (average molecular weight 520,000)
20 parts by weight and 60 parts by weight of liquid paraffin were melt-kneaded in a twin-screw extruder. A polymer gel sheet was prepared by extrusion casting from a coat hanger die onto a cooling roll. The thickness was 1.8 mm at this point. This polymer gel sheet was treated at 130 ° C. for 7 times using a simultaneous biaxial stretching machine.
It was stretched × 4 times before extraction. Then, it was immersed in methylene chloride to extract and remove liquid paraffin. Further, after stretching to TD three times at 130 ° C. using a tenter,
Heat treatment was performed while relaxing the stretching of D by 17%. Through the steps described above, a PE film having a thickness of 16 μm was formed, and the separator B was formed.
And

First, the air resistance of the separator B at normal temperature was measured.

The air resistance was measured using a type A measuring device conforming to JIS in a laboratory adjusted to 23 ° C. The measured value was 150 seconds / 100 ml. Next, the air resistance of the separator B after the heat treatment was measured. Separator B was cut out in the same manner as separator A and subjected to MD pretreatment. After the pre-treatment, the air permeability was measured using a type A measuring device conforming to JIS in a laboratory adjusted to 23 ° C. The measured value was 450 seconds / 100 ml.

Next, the total pore volume of the separator B at normal temperature was measured. The total pore volume was measured using a mercury porosimeter in a laboratory adjusted to 23 ° C. The measured value was 1.6 cm ³ / g. Then, the total pore volume of the separator B after the heat treatment was measured. Separator B
Was cut into a rectangle of 120 mm in MD and 50 mm in TD in the same manner as in the case of the separator A, and subjected to MD pretreatment. After the MD pretreatment, the total pore volume was measured using a mercury porosimeter in a laboratory adjusted to 23 ° C. The measured value was 1.0 cm ³ / g.

Hereinafter, by changing the molecular weight and stretching conditions of polyethylene in the same manner as in the case of the separator A or the separator B, the air permeability resistance and the total pore volume at room temperature are all the same. 13 types of separators A to M having the air resistance, the total pore volume, and the thickness after the pre-treatment as shown in FIG.

[0042]

[Table 1]

(Production of Battery) In order to evaluate the temperature change during overcharging of the battery in this example, a cylindrical battery described below was produced. FIG. 1 shows a structural view (a partial cross-sectional view) of a cylindrical battery manufactured in this example.

In FIG. 1, a non-aqueous electrolyte secondary battery 1
The positive electrode 2, the negative electrode 3, and the separator 4 are wound and housed in a case 5 together with an electrolytic solution (not shown) in which an electrolyte salt is dissolved in a nonaqueous solvent, and are sealed with a sealing plate 6. .

In the sealing plate, in a general commercial battery,
Although safety elements such as a safety valve and a PTC element are incorporated, no safety mechanism is incorporated in the sealing plate 6 in the battery of the embodiment for a safety test.

The positive electrode 2 was prepared by mixing 10% by weight of carbon powder as a conductive agent and 5% by weight of polyvinylidene fluoride resin (PVdF resin) as a binder with respect to 85% by weight of lithium cobalt oxide powder, and dehydrated NMP. To prepare a slurry, applied on a positive electrode current collector made of aluminum foil, dried,
It was produced by rolling.

For the negative electrode 3, artificial graphite powder was used as the negative electrode active material, and the PVdF
A resin was mixed at 5% by weight, and these were dispersed in dehydrated NMP to prepare a slurry. The slurry was applied on a negative electrode current collector made of copper foil, dried, and then rolled. In the separator 4,
Thirteen types of separators A to M shown in Table 1 were used.

The electrolyte used was one obtained by dissolving 1 mol / l of LiPF _{6 in} a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1. The amount of the electrolyte is about 3.8 ml.

The manufactured cylindrical battery had a diameter of 18
mm and a height of 65 mm. This size, which is usually commercially available, has a design capacity of 1800 mAh, and the thickness of the separator 4 is generally 25 to 27 μm. The battery of this embodiment has a higher capacity of 2000 m.
Ah was set as the design capacity. For this reason, when the thickness of the separator 4 was more than 25 μm, the wound electrode plate group could not be reliably inserted into the case.

(Examples 1 to 42) A separator A was assembled into a battery together with 3.8 ml of an electrolytic solution containing 5% by weight of biphenyl. This battery is referred to as the battery of Example 1. Hereinafter, the 13 types of separators A to M shown in Table 1 described above, the overcharge-resistant additives and the amounts added were combined as shown in (Table 2) and (Table 3), and Examples 2 to 42 were used.
Was prepared.

(Comparative Examples 1 to 9) A battery was assembled in the same manner as in Example 1 using a separator A together with an electrolytic solution to which no overcharge-resistant additive was added. Further, in the same manner as in the example, 13 kinds of separators A to M shown in (Table 1) were combined with the overcharge-resistant additive and the addition amount as shown in (Table 2) and (Table 3), and the actual comparison example 2 From 9 were produced.

(Evaluation of Batteries) A total of 5
One was evaluated by the method described below.

The design capacity of the battery is 2000 mA.
First, a charge / discharge cycle of charging at a constant current of 1000 mA until reaching 4.2 V and then discharging at a constant current of 1000 mA until reaching 3.0 V was repeated 10 times. The discharge capacity at the 10th cycle was defined as the initial capacity of each battery. The initial capacity of all 51 batteries satisfied the design capacity. The charge and discharge were performed in a thermostat at 20 ° C. Thereafter, each battery was charged to 4.2 V at a constant current of 1000 mA, and further overcharged for 3 hours at a constant current of 2000 mA. In the course of the overcharge test, the surface temperature of the battery was measured, and the maximum temperature of the battery was evaluated. These results are also shown in (Table 2) and (Table 3).

[0054]

[Table 2]

[0055]

[Table 3]

As can be seen from Table 2, in the batteries of Examples, abnormal temperature rise was suppressed despite the thinner separator. In all of the batteries of Examples, current was flowing while voltage was applied, and a minute internal short circuit occurred in the separator. In contrast, the battery of the comparative example
Abnormal heating occurred in all cases.

Although all the separators used had the same air permeability and normal pore volume at room temperature, there were some batteries that had an abnormal temperature rise and those that did not, as in the batteries of Examples and Comparative Examples. This is because, as described above, the air permeability at high temperatures and the total pore volume are different.

In all the additives of the examples (2-biphenylylmethyl carbonate, 4-biphenylylmethyl carbonate, 4-biphenylylbutyl carbonate, 3-biphenylmethyl carbonate and 4-biphenylylphenyl carbonate), the amount added was There was no difference in effect between the 2.5% by weight and the 5% by weight.

The twelve batteries (Examples 8, 9, 17, 18, 23, 24, 29, 3) with the highest temperature reached by the batteries
0, 35, 36, 41, and 42) all belonged to the separator J or the separator K. The separator J is
Because of low air permeability at high temperature, large total pore volume at high temperature and small thickness, many internal short circuits occur,
It is considered that the temperature rise due to the short-circuit current was large.
On the other hand, the separator K has a high air permeability at high temperatures, a small total pore volume at high temperatures, and a large thickness. The rise seems to have been significant.

The batteries of the comparative examples (Comparative Examples 3, 5, 7, and 9) using the separator G and the separator M, which seem to cause the internal short circuit more easily than the separator J, have too many internal short circuits, Since the temperature rise due to the short-circuit current was large, it is considered that abnormal temperature rise occurred. On the contrary, the batteries of the comparative examples (Comparative Examples 2, 4, 6, and 8) using the separator F and the separator L, which are considered to be less likely to cause an internal short circuit than the separator K, have too few internal short circuits. It is considered that abnormal temperature rise occurred because the overcharged state advanced to a dangerous state.

[0061]

As described above, according to the present invention, the safety of a non-aqueous electrolyte secondary battery under high-temperature conditions can be improved despite the use of a thin separator.

[Brief description of the drawings]

FIG. 1 is a schematic diagram (partially sectional view) of a cylindrical battery used in an example of the present invention.

[Description of Signs] 1 Non-aqueous electrolyte secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 5 Case 6 Sealing plate

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI theme Court Bu (reference) B29L 31:34 B29L 31:34 (72) inventor Shozo Takahashi Osaka Prefecture Kadoma Oaza Kadoma 1006 address Matsushita Electric industrial Inside (72) Inventor Yasuhiko Mitou 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Nobuo Eda 1006 Odaka, Kazuma, Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. ) 4F210 AA03 AA05 AB19 AG01 AG20 AH33 QC14 QG01 QG18 QW12 5H021 BB01 BB05 CC08 CC17 EE04 EE31 HH00 HH03 HH04 HH06 5H029 AJ03 AJ12 AK03 AL01 AL02 AL07 AL11 AM01 AM03 DJ02J14 DJ02J14 DJ02J14 HJ14

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and a separator, wherein the non-aqueous electrolyte is 2-biphenylylmethyl carbonate, At least one selected from biphenylylmethyl carbonate, 4-biphenylylbutyl carbonate, 3-biphenylmethyl carbonate and 4-biphenylylphenyl carbonate as an overcharge-resistant additive, wherein the separator is a porous polyolefin; After holding at a temperature of 115 ° C. in the atmosphere for 15 minutes in a state where a tensile load of 25 kg / cm ² is applied in the machine-stretched longitudinal direction, the air resistance is 400 to 1500 seconds / 100 ml. to have a non-aqueous to the total pore volume, characterized in that from 0.3 to 1.5 cm ³ / g Solution electrolyte secondary battery. 2. The overcharge additive is 2-biphenylylmethyl carbonate, and the air permeation resistance is from 450 to 90.
0 sec / 100 ml with a total pore volume of 0.5 to 1.
The non-aqueous electrolyte secondary battery according to claim 1, wherein in the 0 cm ³ / g. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the separator is from 8 to 18 μm.