JPH03203159A - Battery - Google Patents

Abstract

PURPOSE:To maintain excellent safety by specifying the ratio of internal impedance, at a temperature higher by a specified value than a given temperature, to internal impedance at a maximum temperature, and by making infinite air permeability in a temperature range higher by a specified value than a given temperature. CONSTITUTION:A battery basically comprising a positive electrode 11 and a negative electrode 13 has internal impedance transition temperature t1 deg.C in a temperature range of 95-160 deg.C. Even if internal impedance maximum temperature t2 deg.C is or is not in a temperature range of (t1+10) deg.C, the ratio of internal impedance at (t2+5) deg.C to internal impedance at t2 deg.C is specified to 0.25 or more but less than 1.0. The battery has air permeability transition temperature in a temperature range of 95-160 deg.C and retains the infinity of air permeability in a temperature range higher by 5 deg.C than the air permeability transition temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a primary battery and a secondary battery, and particularly to a battery with excellent separator safety.

[Conventional technology]

In recent years, electrical energy storage devices such as secondary batteries, secondary batteries, capacitors, and condensers have been increasing in capacity and output. Along with this, safety problems that occur when an abnormality such as a short circuit occurs, especially in batteries, have been attracting attention.

For example, in the case of lithium batteries, whose usage has been increasing significantly in recent years, if a short circuit occurs inside or outside the battery, the temperature of the battery will rise rapidly, causing the contents of the battery to eject and even cause an explosion.

In order to solve this problem, attempts have been made to add various ideas to the separator for separating the positive electrode and the negative electrode.

For example, in Japanese Patent Application Laid-open No. 60-23,954, Separa l/
- It has been proposed to use a synthetic resin film having micropores as the film. Compared to conventional non-woven fabric separators, this method is actually effective to some extent when an external short circuit occurs in a single cell; It has not been effective to use a synthetic resin film with micropores as a separator for short circuits under more severe conditions such as the above.

Furthermore, as a further improvement, JP-A-1-186,751 describes applying a low melting point wax to the above-mentioned synthetic resin film having micropores. In this case, internal resistance increases at low temperatures, that is, in the actual operating temperature range, which is undesirable, and being covered with such a wax-like insulating film impairs basic performance even at room temperature, which is undesirable.

On the other hand, JP-A-63-308-866 proposes the use of two types of microporous films, polyethylene and polypropylene, in a superimposed manner.

In this case, an improvement in safety is expected, but since two separators are used, there are problems in that the assembly process becomes more complicated, the battery volume increases, and the cost increases.

On the other hand, in JP-A-60-52, JP-A-61-232-560, JP-A-62-283-553, and JP-A-1-258-358, non-woven fabric separators were somehow improved. Attempts are being made to do so. However, when a nonwoven fabric with a large pore diameter is used as a base material, the thickness of the separator becomes large, which does not meet the purpose of making the battery smaller and lighter. In addition, the temperature rise during short circuits was not sufficiently suppressed, and it was not effective against short circuits under severe conditions.

[Problems to be Solved by the Invention] Although the conventional improvement means as described above showed some improvement effects, they were insufficient in the following points.

For example, in the case of an external short circuit, although troubles such as rupture or explosion can be prevented by the conventional improvements described above, short circuits under more severe conditions, such as: ■ Assembled batteries with multiple cells connected in parallel or series. short circuit.

■ Internal short circuit accompanied by red heat.

■ Short circuit under high temperature.

■ Short circuit due to instantaneous damage such as nail puncture or crushing.

■ Short circuit when the separator deteriorates.

■　Dendrite short circuit.

■ Short circuit due to internal contact between positive and negative electrode tabs.

If such a severe short circuit were to occur, a phenomenon such as rupture or explosion would occur, causing damage to surrounding equipment, buildings, and even the human body.

Particularly in recent years, accidents due to such causes have been occurring frequently, and ensuring safety under conditions even more severe than before has become an urgent social need. For this purpose, further improvement of the separator is required.

An object of the present invention is to solve the above-mentioned problems and provide a battery that can maintain safety even in abnormal situations by using a separator with excellent safety.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors conducted a detailed study on phenomena that occur during abnormalities such as short circuits, and found that by using a separator with a specific thermal deformation behavior, severe We have discovered that a battery can be obtained that can maintain safety even under abnormal conditions.

Furthermore, we have discovered that when the internal impedance changes when the temperature of the battery is raised at a constant rate, it exhibits excellent safety when certain specific conditions are met.

Furthermore, it has been found that the specific conditions satisfied by the change in internal impedance match the conditions satisfied by the change in the air permeability value of the separator.

In other words, the battery of the present invention has a positive electrode, a negative electrode, and a separator as its basic structure, and has a temperature of 95°C or higher and 16°C.
The internal impedance transition temperature (1
+°C) and does not have an internal impedance maximum temperature (12°C) in a temperature range of at least (t++lO)'C, or has the internal impedance maximum temperature in a temperature range of (t, +10)°C. Even so
The internal impedance at (ta+5)℃ 12
It is characterized in that the ratio to the internal impedance at °C is 0.25 or more and less than 1.0.

Further, in the battery of the present invention, the film forming the separator has 9
The air permeability transition temperature (1
+°C), and the air permeability value remains infinite in a temperature range of at least (t, +5)°C.

[Function] Traditionally, when a large short circuit current flows during an abnormality such as a short circuit, and the internal temperature of the battery rises, the separator softens and melts, blocking the pores and reducing ion permeability, resulting in a short circuit. The idea was to ensure safety by reducing the current to prevent the temperature from reaching a certain level. However, in the conventional method, as mentioned above, an abnormality such as a short circuit under severe conditions still results in a rupture or explosion.

As a result of a detailed study of this phenomenon, the present inventors found that when a conventionally known separator is used, the pores of the separator become clogged due to softening and melting of the separator when the internal temperature rises. It is true that this occurs, but at the same time, as the separator melts and flows, it loses its original function of electrically insulating the positive and negative electrodes, resulting in a more severe short circuit. I discovered that.

This phenomenon is particularly noticeable when the internal temperature rise is not uniform and there is a temperature distribution, or when a local temperature rise occurs. This phenomenon was found to be a major cause of the loss of safety.

In the present invention, the temperature at which the internal impedance value of the battery increases when the battery temperature increases is extremely important. The internal impedance transition temperature is a value uniquely defined by measuring the internal impedance of a battery using the same measurement method as the membrane resistance transition temperature.

The temperature at which the internal impedance value of the battery increases when the battery temperature increases is extremely important.

The internal impedance transition temperature is a value uniquely defined by measuring the internal impedance of a battery using the same measurement method as the membrane resistance transition temperature.

The internal impedance transition temperature will be explained below, but the definition of the membrane resistance transition temperature is the same except that the measurement target is different, so the explanation thereof will be omitted.

It is defined as the temperature at which the internal impedance value initially becomes 10 times the resistance value at 25°C when the temperature is increased from 25°C. In other words, internal impedance resistance transition rate Rt defined by the following formula + internal impedance value R2 at an arbitrary temperature t'C
5: This is the temperature at which the internal impedance value at 25° C. becomes 10 for the first time.

According to the invention, the internal impedance transition temperature (t+°C)
is 95°C or higher and 160° or lower, preferably 110°C or higher and 15°C or higher
5 or less.

It is preferable that the internal impedance transition temperature is less than 95°C from the viewpoint of ensuring safety, but it is not preferable because the resistance value increases in the temperature range in which the battery is normally used, which impairs the performance of the battery. .

Furthermore, if the internal impedance transition temperature exceeds 160° C., the internal temperature of the battery will rise to this temperature as described above, making it impossible to ensure safety, which is not preferable.

As mentioned above, in order to ensure safety against abnormalities under all conditions, it is essential to have an internal impedance transition temperature (t, 'c) within the temperature range of the above conditions, but what is more important is that It has a high resistance value even in a temperature range exceeding the internal impedance transition temperature (1+°C).

The air permeability transition temperature (tloC) of the present invention is sepa l/-
This value represents the temperature at which the pores of the filter begin to become clogged, and is uniquely defined by measuring the change in air permeability as the temperature rises using the method described below. That is, separate lake
It is defined as the temperature at which the air permeability value first reaches infinity when the temperature is increased from 25°C.

According to the present invention, the air permeability transition temperature (tloC) is 95°C or more and 160°C or less, preferably 110°C or more and 155°C or less.

Although it is preferable for the air permeability transition temperature to be less than 95°C from the viewpoint of ensuring safety, the air permeability of the separator increases in the temperature range in which the battery is normally used, so the performance of the battery may be affected. It is damaged and undesirable.

Furthermore, if the air permeability transition temperature exceeds 160°C, the internal temperature of the battery will rise to this temperature as described above, making it impossible to ensure safety, which is not preferable.

As mentioned above, in order to ensure safety against abnormalities under all conditions, the air permeability transition temperature (1+
℃) is an essential condition, but what is more important is (t,,+5)℃ or higher, preferably (t++
io) The air permeability value remains infinite in a temperature range of 0.degree. C. or higher, more preferably (t+15)'C or higher.

If the temperature range in which the air permeability value can be maintained is less than (t++5)'C, safety cannot be ensured, which is not preferable. Here, the air permeability value being infinite means that the pores of the separator are closed. Furthermore, an air permeability value of O means that the separator is torn.

It is a trade-off for a separator to satisfy the above two conditions at the same time, and there have been many difficulties in realizing this.

That is, as mentioned above, when a large short-circuit current flows and the internal temperature of the battery rises, the separator softens and melts and closes the pores, reducing ion permeability and short-circuit current. This is an extremely important requirement for ensuring safety.

This phenomenon occurs near the air permeability transition temperature (t° C.) in the present invention. At the same time, the separator softens and melts, loses its original function of electrically insulating the positive and negative electrodes, and conversely increases internal short circuits, which has a rather negative effect on safety. It's coming.

In particular, this phenomenon is exposed as a major problem when it often occurs in actual battery abnormalities, such as when the internal temperature rise is not uniform, there is a temperature distribution, or there is a localized temperature rise, resulting in problems such as rupture or explosion. will occur.

With conventionally known separators, it has been impossible to satisfy these antinomic requirements at the same time.

As a result of various studies, the present inventors have found the following methods for obtaining a battery that satisfies the requirements of the present invention, although they are not particularly limited.

■ Method using a specific separator.

■ A substance that has the property of absorbing electrolyte at a certain temperature or higher (three-dimensional methacrylate).

A method in which acrylic resin, etc.) is present inside the battery, inside the positive and negative electrodes, inside the separator, etc.

■ A method in which a substance that thickens the electrolyte at a certain temperature or higher is present inside the battery, inside the positive and negative electrodes, inside the separator, etc.

■ Micro-encapsulated mineral oil, wax, and other insulating substances inside the battery.

A method of making it exist inside the positive and negative electrodes and inside the separator.

Regarding (2), there are no particular limitations, but the selection of the separator material 5 molecular weight or molecular weight distribution, the shape of the pores of the separator, the thickness of the separator, the surface structure of the separator 5 surface condition, the degree of stretching or anisotropy of the separator This is achieved by combining various factors such as.

Although not particularly limited, an example will be shown. The material selection for the separator is particularly important depending on the air permeability transition temperature (t l 'C
) is important as an element that falls within the scope of the present invention.

One of the criteria for material selection is, for example, glass transition temperature (
A material having a temperature range of 95° C. to 160° C. can be selected. -For example,
Low density polyethylene (Ll) PE), linear low density polyethylene (LLDPE) and high density polyethylene (LLDPE)
HDPE), etc.

The molecular weight distribution, the shape of the separator pores, the degree of stretching, anisotropy, etc. are important in maintaining the air permeability value in the temperature range exceeding the air permeability transition temperature (t+℃). . As a guideline for these selection criteria, the higher the molecular weight, the better. However, the higher the molecular weight, the more the moldability is sacrificed, so it is naturally necessary to devise a film forming method and a pore opening method. For example, it may be necessary to take measures such as using a plasticizer in combination, or widening the molecular weight distribution by mixing a high molecular weight substance and a low molecular weight substance.

In addition, the shape of the holes in the separator may be such that the holes are formed linearly in the thickness direction (for example, by the drawing method known as the manufacturing method of the product name Celguard (manufactured by Celanese Corporation, USA)). obtained) is not desirable. A net-like pore shape obtained by production such as an extraction method is preferred. Furthermore, with regard to stretching, a separator that has been excessively stretched is also undesirable because of its large degree of thermal shrinkage.

In addition, although not particularly limited in the present invention, the air permeability at 25°C as a basic performance is 300 seconds/10
It is 0 cc or less, preferably 200 seconds/7100 cc or less, more preferably 150 seconds/100 cc or less.

Also, although not particularly limited to the same, 25
The lower the membrane resistance value (R25) at °C, the lower the better, but it is usually 0.5 to 50 Ω・cm" and preferably 0.5 to 50.
20Ω'cm2. More preferably 0.5 to 1[)Ω・
cm” range.

6 The thickness of the separator is also not particularly limited, but it is usually 5 to 500μ, preferably 10 to 100μ,
More preferably, it is in the range of 10 to 50μ. If it is less than 5μ, it is too thin and the insulation function is impaired, which is not preferable. If it exceeds 500μ, the volume increases, which is not preferable from the viewpoint of making the battery smaller and lighter.

The pore diameter of the separator pores is not particularly limited either, but the average pore diameter is usually 0.01 to 10μ, preferably 0.05 to 5μ, more preferably 0.05 to 0.5μ.
It is.

Porosity is not particularly limited, but is 35 to 85%, preferably 45 to 80%, more preferably 50 to 80%.
It is.

The term "battery" used in the present invention is not particularly limited, but examples include primary batteries such as lithium batteries, manganese-zinc batteries, and silver-zinc batteries, nickel-cadmium batteries, and nickel-zinc batteries. Examples include secondary batteries such as batteries, nickel-metal hydride batteries, polymer batteries, lithium secondary batteries, carbon secondary batteries, and the like.

By using a separator that satisfies the requirements of the present invention, the safety of batteries is dramatically improved, and phenomena such as rupture or explosion will not occur even in abnormal situations such as short circuit, reverse charging, or overcharging under severe conditions. disappears.

[Examples] Examples are shown below to explain the present invention in detail, but
The present invention is not particularly limited to the following examples.

In addition, various physical properties were measured according to the following measurement method.

Internal impedance transition temperature (1t°C) and maximum impedance temperature (1t°C)> Attach a thermocouple to the wall of the battery can, and while continuously measuring impedance at a frequency of 1kHz, Heat the battery in an oven set at a heating rate.

The temperature at which the impedance first reaches a value 10 times the impedance at 25° C. is measured, and this temperature is defined as the internal impedance transition temperature (t,° C.). The temperature continued to rise further until t1℃ (
t, +xo)' If the impedance has a maximum value in the temperature range c, this temperature is measured and set as the internal impedance maximum temperature (tz° C.).

Film Resistance> FIG. 1 shows an apparatus for measuring film resistance as defined in the present invention. The membrane resistance of the separator is measured using this measuring device.

In Figure 1(A), LA and IB are lOμ thick N
It is an i-foil and is connected to the impedance measuring device 8. As shown in FIG. 1(B), the Ni foil 1A is
Leave a rectangle 5mm wide and 10mm wide with Teflon tape 6.
is masked. A separator 3 is impregnated with a specified electrolytic solution, and is placed between IA and 1B, and its four sides are fixed with Teflon tape. 5 is a thermocouple for measuring temperature, which is attached to the glass plate 2B with Teflon tape. Glass plates 2A and 2B
The space between them is filled with a specified electrolyte.

Ni foils IA and IB, glass plates 2A and 2B, separator 9, and thermocouple 5 are used while being housed in case 4 shown in FIG. 1(C). 9 is a recording device for recording the temperature and measured impedance.

An IM-lithium borofluoride/propylene carbonate solution is used as the electrolyte. The measurement was performed at 25°C and the measurement frequency was 1kHz, and the membrane resistance R2 at 25°C was calculated by the following formula.
Find 5.

R25 = Measured value (Ω) x 1 cm x 1.5 cm (
Unit: Ω・cm") Air permeability transition temperature> As shown in Figure 2, a sample for air permeability measurement with a separator 21 set in a Teflon holder 22 was heated at 2°C/min.
The temperature was raised in an oven set at a rate of 1, and when each temperature was reached, the sample was taken out and the air permeability was measured at 25°C by the method described below.

<Molecular Weight> Weight average molecular weight (Mw) and number average molecular weight (Mn) are measured under the following conditions.

GPC measurement device - Waters Model 200
0 Column - Toyo Soda G 7000S - G 3000
S solvent - trichlorobenzene measurement temperature - 135°C Porosity> The porosity is calculated by the following formula.

Pore volume = Water content weight - Absolute dry weight / Average pore diameter> Calculated by taking a weighted average of the average length and breadth of 200 pores observed in a scanning electron micrograph of the surface of the porous membrane.

The unit is μ.

Air permeability> Measured by ASTM D-726 Method A. The unit is second/1oocc.sheet.

X Breath Team Yu This example shows an example of manufacturing a separator.

13% by volume of finely divided silicic acid and 61.5% by volume of dioctyl phthalate were mixed in a Henschel mixer, and 25.5% by volume of a high-density polyethylene resin having a weight average molecular weight (Mw) of 600,000 and Mw/Mn = 15 was added thereto. Mixing was performed again using the Henschel mixer.

This mixture was kneaded into pellets using a twin-screw extractor with a diameter of 30 m/m. This pellet was molded into a film with a thickness of 100 μm in a film manufacturing apparatus comprising a twin-screw extruder with a diameter of 30 m/m and a T-die with a width of 450 m/m.

The formed membrane was immersed in 1.1.1-trichloroethane for 5 minutes to extract the DOP, dried, and then dried for 70 minutes.
It was immersed in 20% caustic soda at a temperature of 0.degree. C. for 30 minutes to extract fine powder silicic acid, and then dried to obtain a porous membrane.

Next, this porous membrane. It was stretched 2.7 times in the warp direction using a roll stretching machine heated to 115°C, and then stretched to 120°C.
Heat treatment was performed for 10 seconds in an atmosphere of .degree. Table 1 shows the properties of the film obtained through the above steps. Table 2 shows the change in air permeability as the temperature increases.

Trap Healing Team Yu This example shows an example of manufacturing a separator.

The same operation as in Example 1 was performed except that high-density polyethylene with a weight average molecular weight of 850,000 and Mw/Mn = 1.5 was used. The properties of the obtained film are shown in Table 1. Table 2 shows the change in air permeability as the temperature rises.

Next, a comparative example will be shown to confirm the characteristics of the films obtained in Examples 1 and 2.

comparative type This comparative example shows an example of producing a separate lake.

The same operation as in Example 1 was performed except that high-density polyethylene with a weight average molecular weight of 80,000 and Mw/Mn = 13 was used. The properties of the obtained film are shown in Table 1. Table 2 shows the change in air permeability as the temperature rises.

Yoshibanyu This example shows an example of manufacturing a separator.

The same operation as in Example 1 was performed except that low density polyethylene with a weight average molecular weight of 430,000 and Mw/Mn = 13 was used. The properties of the obtained film are shown in Table 1. The change in air permeability as the temperature rises is shown in Table 2 below.

3 4 Manganese dioxide is used as a positive electrode active material, graphite and acetylene black are used as conductive agents, tetrafluoroethylene is used as a binder, and each manganese dioxide: graphite: acetylene black: tetrafluoroethylene = 85:5 + 5:
A water paste was prepared by mixing the mixture in a weight ratio of 5:5, and a sheet coated and dried on a stainless steel plate was used as a positive electrode, and a lithium metal foil was used as a negative electrode, to produce a AA battery as shown in FIG. FIG. 3 is a half-cut sectional view of a spiral-wound battery. Here, 11 is a positive electrode, 12 is a separator, 13 is a negative electrode, 14 is an insulating plate, 15 is a negative electrode lead, 16 is a positive electrode lead, and 17 is a gasket.

The membrane obtained in Example 1 was used as the separator 3, and lithium perchlorate was adjusted to a concentration of 1.0M in a mixed solvent of propylene carbonate and dimethoxyethane (volume ratio 1:1) as the electrolyte. liquid was used. The internal impedance transition temperature (ti) of this battery was 135°C, and there was no internal impedance maximum temperature (t2) in the range of 135° to 145'. Table 3 shows the results of various tests and evaluations of this battery.

LiCoO2 was used as the positive electrode active material, graphite and acetylene black were used as the conductive agents, and fluororubber was used as the binder.The weight of each LiCo0□; graphite: acetylene black: fluororubber = 88 nia, 5:2.5:2. A dimethylformamide paste was prepared by mixing the mixture at the same ratio as dimethylformamide paste, a sheet coated and dried on Aj2 foil was used as the positive electrode, needle coke powder was used as the negative electrode active material, and fluororubber was used as the binder, with a weight ratio of needle coke:fluororubber = 95 + 5. The mixture was applied as a dimethylformamide paste to a Cu foil, and a dried sheet was used as a negative electrode to produce a AA battery as shown in FIG. 3.

The membrane obtained in Example 1 was used as the separator 3, and the electrolyte was a mixed solvent of propylene carbonate and butyrolactone (volume ratio = 1:1) with lithium fluoroborate adjusted to a concentration of 1.0M. Using. This battery was charged for 5 hours at a constant voltage of 4.2 . The tl of this cell was 135° and there was no t2. Table 3 shows the results of various tests and evaluations of this battery.

The same operation as in Example 4 was carried out except that the membrane obtained in Example 2 was used as the 1U separator. j+13 of this battery
7°C t2 was 144°C. Also 140℃ and 144℃
The impedance ratio was 0.83. Table 3 shows the results of various tests and evaluations of this battery.

The comparative examples described below are for confirming the performance of the batteries produced in each example.

The same operation as in Example 4 was performed except that the membrane obtained in Comparative Example 1 was used as the separator. The tl of this battery was 1.
33°C, t2 was 140°C, and the ratio of impedance at 145°C and 140°C was 0.15. Table 3 shows the results of various tests and evaluations of this battery.

The same operation as in Example 4 was performed except that the separator shown in Table 2 was used as the separator.

Table 3 shows the results of various tests and evaluations of this battery. The tl of this cell was 169°C, 137°C, and >175°C, respectively. Further, the impedance ratio of the battery of Comparative Example 4 at 142° C. and 137° C. 7 was 0.05. Table 2 shows the change in air permeability of the separator used at this time as the temperature rose.

The same operation as in Example 5 was performed except that the membrane obtained in Example 2 was used as the separator. The tl of this battery is 1
37°C + 72 was 144°C. Also, 149℃ and 1
The impedance ratio at 44°C was 0.83. Table 3 shows the results of various tests and evaluations of this battery.

Back side 1 The same operation as in Example 5 was performed except that the membrane obtained in Example 3 was used as a separator. The tl of this battery is 1
The temperature was 16°C, and t2 was 121°C. 126℃ and 121℃
The impedance ratio was 0.30.

Table 3 shows the results of various tests and evaluations of this battery.

Comparative Plate Danji 1 The same operation as in Example 5 was performed except that the separator shown in Table 2 was used as the separator.

Table 3 shows the results of various tests and evaluations of this battery. The tl of this cell was 169°C, 137°C, and >175°C, respectively. Further, the impedance ratio of the battery of Comparative Example 7 at 142° C. and 137° C. 8 was 0.05. Table 2 shows the change in air permeability of the separator used at this time as the temperature rose.

[Effects of the Invention] As explained above, the battery defined by the present invention does not explode or explode even in the event of an abnormality such as a short circuit under severe conditions, and has excellent safety and reliability. This has the effect of being able to exhibit superior performance.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a membrane resistance measuring device defined in the present invention, Fig. 2 is a diagram showing a sample for air permeability measurement in an embodiment of the present invention, and Fig. 3 is a diagram showing a sample for measuring air permeability in an embodiment of the present invention and a comparative example. FIG. 2 is a half-cut cross-sectional view of a candle-wound battery. IA, IB...Ni foil, 2A, 2B...Glass plate, 3.12.21...Separator 4...Case, 5...Thermocouple, 6...Teflon tape, 8...・Impedance measuring device, 3 9...Recorder, 11...Positive electrode, 13...Negative electrode, 14...Insulating plate, 15...Negative electrode lead, 16...Positive electrode lead, 17... Gasket, 22...Teflon holder 4 -400- ω 3-ku tatami 8-style

Claims (1)

[Claims] 1) A battery having a basic configuration of a positive electrode, a negative electrode, and a separator, which has an internal impedance transition temperature (t_1°C) in a temperature range of 95°C or more and 160°C or less, and at least (t_1+10) It does not have an internal impedance maximum temperature (t_2℃) in the temperature range of ℃ or (
Even if the internal impedance maximum temperature is in the temperature range of t_1+10)°C, the ratio of the internal impedance at (t_2+5)°C to the internal impedance at t_2°C is 0.25 or more and less than 1.0. Characteristic batteries. 2) The film forming the separator has a temperature of 95°C or higher and 160°C.
Claim 1, characterized in that it has an air permeability transition temperature (t_1°C) in a temperature range of 0.degree. Batteries listed.