JP2002124238A - Heat resistant separator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a low-resistance heat-resistant separator in which the separator does not melt even when left at high temperatures and the electrodes do not short-circuit. SOLUTION: The average fiber diameter is 1 to 20 µm and the basis weight is 5 to 5 µm.
120 g / m ² , air permeability of 1 to 100 cc / cm ² / s
ec, a heat-resistant separator made of a melt-blown nonwoven fabric of polymethylpentene having a thickness of 0.01 to 1.0 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-resistance and heat-resistant separator made of a polymethylpentene melt-blown nonwoven fabric.

[0002]

2. Description of the Related Art Meltblown nonwoven fabrics of polyolefins, especially polypropylene, have been used for various separation membranes, battery separators, electrolytic capacitor separators, capacitor separators, polymer battery separators, etc., taking advantage of their properties. Especially lithium batteries (primary,
Secondary) is often used as a separator which is insoluble in an organic solvent and stable to an electrolyte or an electrode active material.

In general, when a short circuit occurs inside and outside of a battery, a large current is discharged, whereby the separator between the opposed positive and negative electrodes thermally shrinks due to Joule heat or heat of chemical reaction or the separator is shrunk. Heat melting,
As a result of the direct shorting of the positive and negative electrodes, there is a problem that the internal short circuit is enlarged, a large amount of heat is released to the surroundings, and a large amount of gas may be ejected. In order to solve such problems, it has been desired to have a function of shutting off the current by blocking the passage of ions and a function of preventing the separator itself from shrinking or melting.

A conventionally used separator made of a nonwoven fabric of polyolefin such as polyethylene or polypropylene has a melting point of polyethylene of about 125 to 140 ° C and a melting point of polypropylene of about 160 to 180 ° C. In use, a short circuit was likely to occur due to the dissolution of the separator. Recent lithium ion battery separators include high capacity, battery characteristics,
In addition to improving productivity, safety is required.When the electrodes are short-circuited and the temperature inside the battery rises, in order to prevent accidents such as ignition from occurring, lithium must be melted before ignition. It has the function of clogging the holes and shutting down the current, and even if the temperature rises further after the shutdown, the separator itself does not melt and break down (melt down) and suppresses the ignition and explosion of the battery. It is required to suppress thermal runaway during a heat storage test.

[0005] Also, at present, the safety of a heat-resistant electrolyte, an external short-circuit protection circuit, a highly safe polymer electrolyte, and the like has been improved, so that it operates at a high temperature and does not require a shutdown or is substituted by another safety mechanism. Accordingly, a secondary battery having high heat resistance and not causing a short circuit has been required.

[0006] In recent years, batteries and electric double-layer capacitors used near the engine room of vehicles have
Conventional batteries such as polyethylene and polypropylene separators may operate above their melting point,
Since some batteries need to be soldered,
Further, a separator having heat resistance and low resistance has been required.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low-resistance heat-resistant separator which satisfies the above-mentioned objects and which does not melt even when left at a high temperature and does not short-circuit the electrodes. That is.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a low-resistance heat-resistant separator can be obtained by using a melt-blown nonwoven fabric of polymethylpentene. The present invention has been completed.

That is, according to the present invention, the average fiber diameter is 1 to 2
0 μm, basis weight 5 to 120 g / m ² , air permeability 1 to 10
0 cc / cm ² / sec, thickness 0.01 to 1.0 mm
A heat-resistant separator comprising a polymethylpentene melt-blown nonwoven fabric.

Also, the present invention provides a frequency of 10 KH at room temperature.
The heat-resistant separator described above, wherein the real-part impedance at z is 20 Ω · cm ² or less.

[0011] Further, the present invention relates to a method for manufacturing a semiconductor device, comprising:
The maximum value of the real part impedance at a frequency of 10 KHz up to 100 times or less the real part impedance at room temperature and the absolute value is 200 Ω · cm ² or less.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below.
Polymethylpentene used in the present invention is a polyolefin obtained by polymerizing 4-methylpentene-1 obtained by dimerization of propylene. For example, TPX from Mitsui Chemicals, Inc.
Commercially available under the name of
Melting point.

The polymethylpentene resin of the present invention may contain, if necessary, a polyolefin resin having a shutdown function, a thermoplastic elastomer and various additives, a surfactant, a compatibilizer, a pigment, an inorganic filler and the like. Can be added.

The polymethylpentene melt-blown nonwoven fabric constituting the present invention can be used as a battery separator for lithium ion batteries or a separator for electric double layer capacitors. For example, propylene carbonate, ethylene carbonate, It can be used as a separator impregnated with γ-butyrolactone, a mixed system thereof, a mixed solvent of the electrolytic solution and a low-viscosity solvent, or an electrolytic solution which is another organic solvent such as fluorinated carbonate. In order to be used as such a separator, it is necessary to have the following physical properties.

The average fiber diameter of the melt blown nonwoven fabric of polymethylpentene is 1 to 20 μm, preferably 1 to 8 μm.
It is. If the average fiber diameter is less than 1 μm, the internal resistance of the battery becomes too large, and if it exceeds 20 μm, the risk of internal short circuit increases.

The basis weight is 5 to 120 g / m ² , preferably 10 to 60 g / m ² . If the basis weight is less than 5 g / m ² , the strength of the separator is insufficient, and the reliability in assembly is reduced, or short-circuit is apt to occur, which is not preferable. On the other hand, when the basis weight exceeds 120 g / m ² , the internal resistance of the battery increases.

The air permeability is 1 to 100 cc / cm²/ Se
c, preferably 3 to 60 cc / cm ²/ Sec.
Air permeability is 1cc / cm²/ Sec, the internal resistance
High resistance, 100cc / cm²/ Sec,
The risk of internal short circuit increases.

The thickness is 0.01 to 1.0 mm, and within this range, it can be used after calendering to a desired thickness. When the thickness is less than 0.01 mm, film formation becomes intense, and when the thickness exceeds 1.0 mm, fluff is apt to occur.

Measured by immersing the nonwoven fabric in the electrolyte, at room temperature
Real impedance at a frequency of 10 KHz is 2
0Ωcm²The following is preferable, and more preferably 10Ω ·
cm ²It is as follows. Real part impedance is 20Ω ・ cm
²If it exceeds, the internal resistance becomes too high, which is not preferable.
No. Low apparent resistance of battery due to low internal resistance
Enlarge, reduce heat generation and extend service life
You. In addition, frequency 10KH from 100 ° C to 180 ° C
The maximum value of the real impedance at z
Less than 100 times the impedance of the part and the absolute value is 20
0Ωcm²The following is preferred. From 100 ° C
The maximum value of the real part impedance up to 180 ° C is
More than 100 times the real part impedance or its absolute
Value is 200Ω · cm²Exceeds, the internal resistance increases.
This makes it difficult to use the battery at high temperatures. In addition, 10
The real part impedance at a high frequency such as kHz is
Equivalent to the solution resistance through the separator and separated
It corresponds to the internal resistance caused by the data.

The tensile strength of the nonwoven fabric in the MD direction is 10 N /
50 mm or more is preferable. Tensile strength in MD direction is 10
If it is less than N / 50 mm, it may break or open when incorporated into a battery.

The polymethylpentene nonwoven fabric having the above-mentioned properties used in the present invention is obtained by a melt blow method. As the melt blow method, a known method can be adopted. For example, the molten polymethylpentene is discharged from a plurality of nozzle holes arranged in a line, and a high-temperature and high-speed air is injected from an injection gas port provided adjacent to an orifice die to discharge the discharged molten polymer. This is a method of forming a nonwoven fabric by forming a fine fiber and then collecting the fiber stream on a conveyor net as a collector. In the melt blow method, in the present invention, a method of producing under the following conditions is particularly preferable.

In the melt blow apparatus die, the nozzle hole diameter is preferably 0.2 to 0.8 mmφ, and the number of nozzles is preferably 5 to 15 / cm. If the nozzle hole diameter is less than the above range, the pressure of the discharged resin increases, and if the nozzle hole diameter exceeds the above range, the fibers cannot be thinned. When the number of nozzles is less than the above range, the resin discharge pressure becomes high,
If it exceeds the above range, the fibers are fused together too much, and the uniformity of the nonwoven fabric is lost.

Under the conditions of the melt blow method, the resin extrusion temperature is preferably 280 to 420 ° C., the resin discharge amount is preferably 0.2 to 3 g / min / hole, and the high-speed air temperature is 280 to 400 ° C. preferable. If the extrusion temperature of the resin is too low, the pressure of the discharged resin will be low, and if it is too high, the deterioration of the resin will be accelerated. When the resin discharge amount is too low, the discharge resin pressure becomes low, and a uniform nonwoven fabric cannot be obtained. When the resin discharge amount is high, fine fibers cannot be obtained. If the high-speed air temperature is too low, fine fibers cannot be obtained, and if it is high, continuous fibers cannot be obtained, and it is difficult to cut and collect on a conveyor net.

The heat-resistant separator of the present invention is made of the above-mentioned melt-blown non-woven fabric of polymethylpentene, and is generally used after being calendered to have a constant thickness. Further, depending on the application, it can be used as a laminate with an embossed or polyolefin-based or nylon-based melt-blown nonwoven fabric. Further, depending on the purpose, it can be used by improving the lyophilicity of the surface of the nonwoven fabric by graft polymerization, application of a surfactant, or the like.

The heat-resistant separator of the present invention can be used as a separator for lithium-based primary and secondary batteries and the like, and is particularly used as a heat-resistant battery separator that can withstand use at a high temperature such as a vehicle-mounted battery and a reflow battery. be able to.

[0026]

The present invention will be described in detail with reference to the following examples and comparative examples. In addition, the measurement of the physical property was performed using the following methods. (1) Fiber diameter: Five arbitrary points on the test piece were examined with an electron microscope.
One photograph was taken, the diameter of 20 fibers was measured per photograph, and these five photographs were taken.
The average fiber diameter of 00 fibers was determined. (2) basis weight: sample than the length direction, collect specimens of 100 × 100 mm, measuring the weight of the moisture equilibrium, 1 m ²
It was calculated by converting to per hit. (3) Thickness: A 100 × 100 mm test piece was sampled from the sample length direction and measured with a dial thickness gauge. (4) Air permeability: 100 × 100 mm from the sample length direction
Was measured using a Frazier-type testing machine in accordance with JIS L 1096. (5) Tensile strength: Measured according to JIS L1085 at a grip interval of 100 mm and a tensile speed of 300 mm / min. (6) Real part impedance: A nonwoven fabric of 0.01 to 1.0 mm is immersed in an electrolytic solution between two 16 mmφ metal poles, and then measured at normal temperature and a frequency of 10 KHz at 100 to 180 ° C. with an impedance analyzer manufactured by Sortron. The partial impedance was measured. The electrolytic solution was prepared by adding 1 mol LiClO ₄ to propylene carbonate under an argon atmosphere:
A solution dissolved in a 1: 1 solution of 1,2-dimethoxyethane was used. (7) Heat resistance: The nonwoven fabric was placed in γ-butyrolactone, and after standing at 100 ° C. for 2 hours, the tensile strength was measured according to JIS L10.
Measured in accordance with No.85. (8) Short: 200 mm between two aluminum electrode plates
A current voltage of 400 V was applied between the electrodes with a separator of × 200 mm interposed therebetween. A short circuit occurred when a current flowed, and no short circuit occurred when no current flowed.

Example 1 Polymethylpentene (TPX-DX82 manufactured by Mitsui Chemicals, Inc.)
0) was melt blown at an extrusion temperature of 290 ° C. under the conditions shown in Table 1 to obtain an average fiber diameter of 4.1 μm and a basis weight of 19.8 g /
to obtain a polymethylpentene meltblown nonwoven m ^2. The obtained nonwoven fabric is calendered, and the air permeability is 98c.
A separator having c / cm ² / sec, a thickness of 0.49 mm, and a tensile strength in the MD of 10 N / 50 mm was obtained. The characteristics are shown in Table 1.

Examples 2 to 5 Melt blown nonwoven fabrics and separators were obtained in the same manner as in Example 1 except that the discharge amount, air temperature and basis weight under the conditions of melt blowing were changed as shown in Table 1. Table 1 shows the characteristics.
Shown in

Comparative Example 1 A separator was obtained in the same manner as in Example 1 except that the melt-blown polypropylene non-woven fabric shown in Table 1 was used instead of the melt-blown polymethyl pentene non-woven fabric. Table 1 shows the characteristics.
Shown in

Comparative Example 2 A separator was obtained in the same manner as in Example 1 except that the polymethylpentene nonwoven fabric according to the dry method shown in Table 1 was used instead of the meltblown polymethylpentene nonwoven fabric. The characteristics are shown in Table 1.

[0031]

[Table 1]

[0032]

The heat-resistant battery separator of the present invention is excellent in heat resistance as compared with a polypropylene separator, and therefore has high safety and can be used as a battery separator that can withstand use at a high temperature such as a vehicle-mounted battery or a reflow battery.
Further, it is excellent in dry polymethylpentene nonwoven fabric in short-circuit resistance. Furthermore, since it has low resistance, it is suitable as an organic solvent-based lithium battery separator having low conductivity.

Claims (3)

[Claims] An average fiber diameter of 1 to 20 μm and a basis weight of 5 to 1.
120 g / m ² , air permeability of 1 to 100 cc / cm ² / s
ec, a heat-resistant separator made of a melt-blown nonwoven fabric of polymethylpentene having a thickness of 0.01 to 1.0 mm. 2. The heat-resistant separator according to claim 1, wherein the real part impedance at a frequency of 10 KHz at room temperature is 20 Ω · cm ² or less. 3. Frequency 10 from 100 ° C. to 180 ° C.
The maximum value of the real part impedance at KHz is 100 times or less of the real part impedance at room temperature, and the absolute value is 200 Ω · cm ² or less.
Or the heat-resistant separator according to 2.