JPH03283259A - Battery - Google Patents

Abstract

PURPOSE:To maintain safety even during abnormalities under severe conditions by using a synthetic resin microporous film as a separator, and covering at least one side of the film with a resin porous powder aggregate whose softening temperature is in a specific range. CONSTITUTION:A separator 12 is a microporous film of a synthetic resin and at least one side of the film is covered with a resin porous powder aggregate whose softening temperature is above 90 deg.C and below 160 deg.C. For example, chemical pearl M-200 which is low-density polyethylene dispersion is applied to a poly. ethylene microporous film by bar coater method using a wire bar of No.12 and is dried by hot air at 80 deg.C so as to obtain a separator.

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.

[Prior Art] In recent years, electrical energy storage devices such as rechargeable batteries, secondary batteries, capacitors, and condensers have been increasing in capacity and output. Along with this, safety problems that occur during abnormalities such as short circuits, especially in batteries, are becoming more and more important.

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, Japanese Patent Application Laid-Open No. 60-23954 proposes the use of a synthetic resin film having micropores as a separator. 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 having micropores as a separator to prevent short circuits under more severe conditions such as the above.

Furthermore, as a further improvement, JP-A-1-186751 describes partially applying a low-melting wax to the above-mentioned synthetic resin film having micropores.

In this case, the coated area has no iodine permeability and an increase in internal resistance occurs at low temperatures, i.e., in the actual operating temperature range, which is undesirable, and because it is covered with such a wax-like insulating film, basic performance is maintained even at room temperature. This is not desirable as it damages the quality of the product.

On the other hand, JP-A No. 60-52 proposes a separator in which polyethylene powder particles are attached to the surface of a polypropylene nonwoven fabric, and JP-A No. 61-232,560 proposes a separator in which polyethylene powder particles are attached to the surface of a polypropylene nonwoven fabric. Separators using nonwoven fabric made of composite fibers with a heavy structure have been proposed, but since the nonwoven fabric is used as the base material, the pores are large and it takes time for the resin to melt and close the pores. The occlusion is not complete and is not desirable.

Furthermore, in Japanese Patent Application Laid-Open No. 1-283585, it is proposed to use a microporous membrane made of a low-melting point resin and a non-woven fabric in a superimposed manner, which improves safety, but does not prevent problems such as internal short circuits in batteries. It is insufficient for short circuits under severe conditions.

Furthermore, as long as a non-woven fabric is used, the membrane is thick and the volume inevitably increases, which is a problem in that it goes against the trend of making batteries smaller and lighter.

[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.

That is, the battery of the present invention has a positive electrode, a negative electrode, and a separator as basic components, and the separator is a microporous synthetic resin membrane, and at least one side of the separator is a porous resin membrane with a softening temperature of 95°C or more and 160°C or less. [Function] Traditionally, in the event of an abnormality such as a short circuit, a large short-circuit current flows and the internal temperature of the battery rises, causing the separator to soften and melt. The idea was to ensure safety by blocking the pores to reduce ion permeability, thereby reducing short-circuit current and preventing temperatures 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 as described above when the internal temperature rises. It is true that this happens, 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 found out.

This phenomenon is particularly noticeable when the internal temperature rise is uneven (or has a temperature distribution), or when there is a localized temperature rise. This phenomenon has been found to be a major cause of the loss of safety.

As mentioned above, the present inventors have achieved a significant improvement over the above problems by using a separator in which a synthetic resin microporous membrane is coated with a resin porous powder aggregate having a softening temperature of 95°C or higher and 160°C or lower. I found out.

In the present invention, the synthetic resin microporous membrane is not particularly limited, but for example, a microporous membrane having a network structure consisting of fine communicating pores as described in JP-A No. 54-52167. can be mentioned.

In addition, the material is not particularly limited, but
For example, polyethylene, polypropylene, polybutene,
Examples include polyvinyl chloride, polyethylene terephthalate, nylon, polytetrafluoroethylene, and mixtures or copolymers thereof.

In the present invention, the porous resin powder aggregate is a continuous body in which resin particles are present alone or together at contact points, and is an aggregate having voids between the particles in a single layer or multilayer state.

The softening temperature of the resin porous powder aggregate in the present invention is 95°C, which has a glass transition temperature (Tg) and a melting point (Tm).
160°C or less, preferably 110°C or more and 15°C or more
The temperature is 0°C or less, more preferably 110°C or more and 145°C or less.

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

In addition, if the softening temperature exceeds 160°C, as described above (
This is not preferable since the internal temperature of the battery will rise to this temperature, making it impossible to ensure safety.

Resins having a softening point in the range of 95 to 160°C are not particularly limited, but examples thereof include polyolefin resins such as low density polyethylene, linear low density polyethylene, high density polyethylene, and polybutene. , polystyrene resins such as polystyrene and styrene/acrylonitrile copolymers.

Examples include polyacrylic resins such as polyethyl methacrylate and polymethyl methacrylate. Among these, particularly preferred are low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

The particle size of the particles of the resin porous powder aggregate is not particularly limited, but is 0.01 to 50 μm, preferably 0.1 to 50 μm.
20 μm, more preferably in the range of 0.5 to 1104z. If the particle size is less than 0.01 μm, it is so small that it will enter the pores of the synthetic resin microporous membrane, thereby impairing its normal function as a separator, which is undesirable. If the particle size exceeds 50 μm, the thickness of the covering layer increases and the volume increases, which is not preferable from the viewpoint of reducing the size and weight of the battery.

As mentioned above, in order to ensure safety against abnormalities under all conditions, it is essential to use a resin porous powder aggregate that has a softening temperature within the above temperature range.
More importantly, in a temperature range exceeding the softening temperature, the resin porous powder aggregate softens and melts, blocking the pores of the synthetic resin microporous membrane, increasing the battery's internal impedance and maintaining high resistance. It is to be.

In the present invention, the coating thickness of the resin porous powder aggregate is 0.
The thickness is 1 to 100 μm, preferably 0.5 to 50 μm, and more preferably 0.5 to 30 μm. This coating thickness is 0.
If it is less than 1 um, when the resin porous powder aggregate softens and melts, the pores of this synthetic resin microporous membrane are insufficiently covered, reducing short circuit current and suppressing temperature rise, thereby increasing safety. This is not desirable as it is not possible to ensure If the film thickness exceeds 100 μm, the volume of the separator increases, which is not preferable from the viewpoint of reducing the size and weight of the battery.

In the present invention, the method of coating the synthetic resin microporous membrane with the resin porous powder aggregate is not particularly limited, but for example, an aqueous dispersion or an oil dispersion of resin particles may be used. A method in which a resin dispersion containing a soluble substance is coated onto a synthetic resin microporous membrane using various coating methods, a method in which a resin dispersion containing a soluble substance is uniformly applied onto a synthetic resin microporous membrane, and then the soluble substance is extracted with a extraction agent; Examples include a method of uniformly applying and fusing dry powder onto a synthetic resin microporous membrane.

Further, after coating, the resin particles and the synthetic resin microporous membrane can be dried at a temperature that does not significantly deform, and depending on the case, it is acceptable even if the particles are partially thermally fused to each other.

However, what is important is that in either method, the resin porous powder aggregate has porosity. For this purpose, in the drying step after coating, the resin particles must be handled at a temperature lower than the lowest film forming temperature. If the resin particles are dried at a temperature higher than the minimum film forming temperature, thermal melting of the resin particles will proceed and film formation will occur, which is not preferable since the porosity of the resin will be lost.

Therefore, the air permeability of the separator in the present invention is not particularly limited, but at 25°C, the air permeability is 300 seconds/
It is 100 cc or less, preferably 200 seconds/100 cc or less, more preferably 150 seconds/100 cc or less.

The air permeability transition temperature range of the separator is 95℃ or higher16
The temperature is 0°C or less, preferably 110°C or more and 155°C or less.

Also, although it is not particularly limited, the membrane resistance value (R25) at 25°C is preferably as low as possible, but is usually 0.5 to 50 Ω·cm2, preferably 0.5 to 20 Ωc.
m2. More preferably, it is in the range of 0.5 to 10 Ω·Cm2.

The thickness of the separator is also not particularly limited, but is usually 10 to 100 μm, preferably 15 to 80 μm.
m, more preferably in the range of 15 to 50 μm. 1
If it is less than 0 μm, it is too thin and the insulation function is impaired, which is not preferable. If it exceeds 100 μm, the volume is thick (
This is not preferable from the viewpoint of making the battery smaller and lighter.

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.

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

In FIG. 1(A), IA and IB are lOμ thick N
It is an i-foil and is connected to the impedance measuring device 7. As shown in Fig. 1 fc), the Ni foil IA 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 IB, 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, two glass plates and 2B, a separator 3, and a thermocouple 5 are used while being housed in a case 4 shown in FIG. 1(B). 8 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 cmX L, 5cm (
Unit: Ω・cn+2) The membrane resistance change shown in Figure 3 was measured using the membrane resistance measuring device shown in Figure 1 at 2℃/min from 25℃ to 175℃ while continuously measuring impedance. Heat the battery in an oven set at a heating rate of .

Porosity The porosity is calculated using the following formula.

Pore volume = water content weight - bone dry weight x air permeability> As shown in Figure 2, a sample for air permeability measurement with a separator 9 set in a Teflon holder lO was heated at 2'C/min.
The temperature was raised in an oven set at a rate of 1. When each temperature was reached, the sample was taken out and the air permeability was measured at 25°C by the method described below.

Measured by ASTM D-726 Method A. The unit is second/100cc/sheet.

In addition, due to the accuracy of the air permeability measuring device, 5000 seconds/
100cc/sheet or more is considered to be infinite (■).

K construction site This example shows an example of manufacturing a separator.

Chemipearl M-200 (average particle size 6 μm, manufactured by Mitsui Petrochemicals), which is a low-density polyethylene dispersion, was placed on a polyethylene microporous membrane Ni-878 (manufactured by Celanese) using a No. 12 wire bar. Coating was performed using a bar coater.

After coating, hot air drying was performed at 80°C to obtain a separator exhibiting the characteristics shown in Table 1. Table 2 shows the change in air permeability of this separator as the temperature increases. Curve A in FIG. 3 shows the temperature change in membrane resistance as the temperature increases.

From Table 2, the air permeability transition temperature of this separator is 12
It can be seen that the temperature is 5°C. In addition, the air permeability is infinite (oo
) means that the pores of the separator are closed, and the air permeability of O means that the separator has burst.

1 Arashi ± Yu This example shows an example of manufacturing a separator.

The same operation as in Example 1 was performed except that Chemipearl W-500 (average particle size 2.5 μm, manufactured by Mitsui Petrochemicals), which is a low molecular weight polyethylene dispersion, was used. Table 1 shows the properties of the obtained separator. Table 2 shows the change in air permeability of this separator as the temperature increases. Curve B in FIG. 3 shows the temperature change in film resistance as the temperature increases.

husbandry godan This example shows an example of manufacturing a separator.

High Bore 4030Ll (polyethylene microporous membrane)
The same operation as in Example 1 was carried out except that a material (manufactured by Asahi Kasei Kogyo Co., Ltd.) was used. Table 1 shows the properties of the obtained separator. Table 2 shows the change in air permeability of this separator as the temperature increases. Curve C in FIG. 3 shows the temperature change in membrane resistance as the temperature increases. Figures 4A and 4 show electron micrographs of the surface condition of the separator before and after this measurement, respectively.
Shown in Figure B.

Next, a comparative example will be shown to confirm the characteristics of the films obtained in Examples 1, 2, and 3.

Chemivar M-200, a low-density polyethylene dispersion similar to that used in Example 1, was coated on a polypropylene nonwoven fabric (manufactured by Nippon Vilene Co., Ltd.) using a dip coater method, and dried with hot air at 80°C. A separator having the characteristics shown in Table 1 was obtained. Table 2 shows the change in air permeability of this separator as the temperature increases. Further, the temperature change in film resistance during temperature rise is shown by the curved line in FIG. Electron micrographs of the surface state of the separator before and after this measurement are shown in FIGS. 5A and 5B, respectively.

L comparison■U-polyethylene microporous membrane -878 (manufactured by Celanese)
On top, ethylene-vinyl acetate copolymerization (vinyl acetate-containing j
180wt%) emulsion (average particle size 0.5μm) was coated with a bar coater using a N096 wire bar and dried with hot air at 80°C to obtain a separator exhibiting the characteristics shown in Table 1. .

Table 2 shows the change in air permeability of this separator as the temperature increases. Curve E in FIG. 3 shows the temperature change in membrane resistance as the temperature increases.

-878 (manufactured by Celanese)
Polyvinylidene chloride emulsion was applied on top using a No. 6 wire bar using a one-way bar coater.
Hot air drying was performed at ℃ to obtain a separator exhibiting the characteristics shown in Table 1. Table 2 shows the change in air permeability of this separator as the temperature increases. In addition, the temperature change in film resistance during temperature rise is
This is shown by curve F in the figure.

(Left below) Manganese dioxide as the positive electrode active material, graphite and acetylene black as the conductive agent, tetrafluoroethylene as the binder, manganese dioxide, graphite: acetylene black: tetrafluoroethylene = 85 + 5 :5:
A water paste was prepared by mixing the mixture at 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, and an AA type battery as shown in FIG. 6 was manufactured. FIG. 6 is a half-cut sectional view of a thinly 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 12, and the electrolyte was a mixed solvent of propylene carbonate and dimethoxyethane (volume ratio 1:l) containing 1.0 liters of lithium perchlorate. A solution adjusted to the concentration of OM was used. Table 3 shows the results of various tests and evaluations of this battery.

Example 11: LiCo0□ was used as a positive electrode active material, graphite and acetylene black were used as conductive agents, and fluororubber was used as a binder. A dimethylformamide paste was prepared by mixing the mixture in a weight ratio of , a sheet coated and dried on Aβ foil was used as a positive electrode, needle coke powder was used as a negative electrode active material, and fluororubber was used as a binder.Needle coke:fluororubber = 95:5 A dimethylformamide paste was prepared by mixing the mixture in a weight ratio of 1 to 100 ml and was applied to a Co foil and dried. A sheet of the same was used as a negative electrode, and an AA-type battery as shown in FIG. 6 was manufactured.

The membrane obtained in Example 1 was used as the separator 12, 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 . 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 membrane obtained in Example 2 was used as the separator. Table 3 shows the results of various tests and evaluations of this battery.

! The same operation as in Example 5 was performed except that the membrane obtained in Example 3 was used as the blood-soil separator. 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.

L Comparison Plate A The same operation as in Example 4 was performed except that -878 (manufactured by Celanese Co., Ltd.) was used as the polyethylene microporous membrane Celgard as a separator. The air permeability of Celgard -878 is as shown in Table-2. Table 3 shows the results of various tests and evaluations of this battery. Curve G in FIG. 3 shows the temperature change in membrane resistance as the temperature of this separator increases.

The same operation as in Example 4 was performed except that a polypropylene nonwoven fabric (manufactured by Nippon Vilene Co., Ltd.) was used as the Hiji Etan separator. The air permeability of this polypropylene nonwoven fabric is as shown in Table-2. Table 3 shows the results of various tests and evaluations of this battery.
Shown below. Further, the temperature change in membrane resistance as the temperature of this separator increases is shown by curve H in FIG.

The same operation as in Example 4 was performed except that the membrane obtained in Comparative Example 1 was used as the L-interlaced separator. Table 3 shows the results of various tests and evaluations of this battery.

Comparison ■l The same operation as in Example 5 was performed except that the membrane obtained in Comparative Example 1 was used as the separator. Table 3 shows the results of various tests and evaluations of this battery.

Engineering Trial 1 The same operation as in Example 5 was performed except that the membrane obtained in Comparative Example 3 was used as the separator. Table 3 shows the results of various tests and evaluations of this battery.

The same operation as in Example 5 was performed except that the membrane obtained in Comparative Example 2 was used as the JLf skin tan separator. This battery is
As shown in 2, if the membrane resistance of the separator is high (normal charging and discharging will not occur, it cannot be used).

(The following is a blank space) As explained above, it can be seen that the batteries using the separators produced in Examples 1 to 3 have excellent characteristics.

[Effects of the Invention J As explained above, the battery limited by the present invention does not explode or explode even in abnormal situations such as short circuits 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 air permeability measurement samples in examples and comparative examples of the present invention, and Fig. 3 is a diagram showing examples and comparative examples of the present invention. Figures 4A and 4B are electron micrographs showing the particle structure of Example 3 of the present invention. Figures 5A and 5B are photographs of the present invention. FIG. 6 is a half-cut sectional view of a thinly wound battery in an example of the present invention and a comparative example. LA, IB...Ni foil, 2A, 2B...Glass plate, 3.9.12...Separator 4...Case, 5...Thermocouple, 6...Teflon tape, 7... - Impedance measuring device, 8... Recorder, 10... Teflon holder 11... Positive electrode, 13... Negative electrode, 14... Insulating plate, 15... Negative electrode lead, 16... Positive electrode lead , 17...gasket. The present invention's small JJP'131=b+γru Nerichiaatf<
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Claims (1)

[Claims] 1) In a battery whose basic components are a positive electrode, a negative electrode, and a separator, the separator is a synthetic resin microporous membrane, and at least one side thereof has a softening temperature of 95%.
A battery characterized by being coated with a resin porous powder aggregate having a temperature of 160°C or higher.