JP2003231772A - Microporous film made of polyolefin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microporous film made of a polyolefin which is used as a separator exhibiting excellent battery characteristics and having safety in a battery. <P>SOLUTION: The microporous film made of the polyolefin comprises at least 10-85 wt.% of a polyethylene PEa solely composed of an ethylene unit and having a viscosity-average molecular weight (hereinafter referred to as Mv) of at least 100,000 but less than 500,000, 10-85 wt.% of a polyethylene PEb solely composed of an ethylene unit and having an Mv of at least 500,000 but at most 5,000,000 and 5-50 wt.% of a polyethylene PEc having an Mv of more than 100,000 but less than 5,000,000 obtained by copolymerizing ethylene with a comonomer, and the magnitude of these Mv's are in the order of PEa< PEc<PEb. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin microporous membrane, and more particularly to a polyolefin microporous membrane suitable for a battery separator. Furthermore, the present invention relates to a microporous polyolefin membrane having excellent ion permeability, mechanical properties, and safety, which is used as a separator in a battery using a carbon material into which lithium ions can be inserted, metallic lithium, lithium alloys, etc. as a negative electrode. Is.

[0002]

2. Description of the Related Art With the recent remarkable development of information-related devices such as mobile phones, notebook type personal computers and PDAs, there has been a demand for batteries which are small in size and light in weight and have a high energy capacity. While various batteries are being researched, developed, and sold, lithium-ion batteries are expanding the market,
A polyolefin microporous film is used as a separator used for this purpose.

As a separator for this lithium-ion battery, high ion permeability capable of exhibiting excellent battery characteristics, excellent mechanical characteristics capable of withstanding stress during battery assembly and battery use, overcharge, etc. There is no short circuit between positive and negative electrodes (short-circuit resistance) when the temperature rises, the holes block and block the flow of ions to stop the flow of electric current (fuse characteristics), and even when heated at high temperatures, contraction and film breakage occur. ) Such as high safety is required, and improvements are being continued.

Specific requirements for battery characteristics include "higher capacity" for realizing longer-time driving in electronic devices, and "charging with large current" for completing charging in a short time. Improvement of "characteristics", improvement of "discharge characteristics at large current" accompanying increase in power consumption, and further improvement of "cycle characteristics at large current" to withstand severe charge / discharge. As a matter of course, as the battery characteristics are improved, the demand for improvement in safety is becoming stricter, and as the improvement means, for example, methods such as Patent Documents 1, 2, and 3 are known; In addition, there is a continuous demand for a polyolefin microporous membrane as a separator that can achieve both superior battery characteristics and higher safety, and vigorous research and development is still underway.

[0005]

[Patent Document 1] Japanese Patent No. 2657434

[Patent Document 2] Japanese Patent No. 3113287

[Patent Document 3] Japanese Patent No. 3177744

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polyolefin microporous membrane which is used as a separator in a battery, which exhibits excellent battery characteristics and high safety. .

[0007]

Means for Solving the Problems The present invention comprises (1) at least 10 to 85% by weight of polyethylene PEa having a viscosity average molecular weight (hereinafter Mv) of 100,000 or more and less than 500,000 and consisting only of ethylene units, and having a Mv of Polyethylene PEb consisting of only ethylene units in the range of 500,000-5,000,000
Polyethylene P obtained by copolymerizing ethylene and a comonomer with 85% by weight and Mv of more than 100,000 and less than 5 million.
A microporous polyolefin membrane comprising a composition containing 5 to 50% by weight of Ec and having a Mv size of PEa <PEc <PEb, (2) the polyethylene PEc is ethylene. Is a copolymer of an α-olefin having 3 or more carbon atoms, and (3) a microporous polyolefin membrane, (3) polyethylene PEa, PE according to (1) or (2) above.
b, a microporous membrane made of polyolefin, comprising a composition containing PEc and polypropylene, wherein the polypropylene content is 1 to 30% by weight.
(4) The polyolefin microporous membrane according to any one of (1) to (3), wherein the calculated average pore diameter is in the range of 0.030 to 0.060 μm, and (5) the porosity is 20.
˜80%, the hole bending ratio calculated from the air permeability and the water permeability is 1.50 to 3.50, and the number of holes is 55 to 300.
The microporous film made of polyolefin according to any one of (1) to (4), characterized in that the number is per unit / μm ² .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below, focusing on its preferred embodiments. The polyolefin microporous membrane of the present invention has an Mv of at least 1.
10 to 85% by weight of polyethylene PEa consisting of only ethylene units and having an Mv of 100,000 to less than 500,000 and 10 to 85% by weight of polyethylene PEb consisting of only ethylene units having an Mv of 5 million to 5 million and having an Mv of 100,000. Over 50
A composition containing 5 to 50% by weight of polyethylene PEc obtained by copolymerizing ethylene and a comonomer in an amount of less than 0,000, and the magnitude of Mv thereof is PEa <PEc.
<PEb is a feature.

The Mv of PEa in the present invention is 100,000 or more and less than 500,000. The Mb of PEb in the present invention is 50.
10,000 to 5 million, preferably 500 to 4
It is, 000,000 or less, more preferably 500,000 or more and 2,500,000 or less, and further preferably 500,000 or more and 1,500,000 or less. From the viewpoint of polyethylene dispersibility, it is preferably 5 million or less. Mv of PEc in the present invention is 1
It is more than 0,000 and less than 5 million, preferably more than 100,000 and less than 2.5 million, more preferably more than 100,000 and less than 1,500,000, and even more preferably more than 100,000.
It is less than 0,000. 500 from the viewpoint of polyethylene dispersibility
It is preferably 10,000 or less.

The melting point of PEc in the present invention is preferably 100 ° C. or higher and 133 ° C. or lower, more preferably 110 ° C. or higher and 133 ° C. or lower, and further preferably 120 ° C.
It is above 133 ° C. PEc in the present invention is a copolymer of ethylene and a comonomer, but a copolymer of ethylene and an α-olefin having 3 or more carbon atoms is particularly preferable. The α-olefin preferably has 3 to 6 carbon atoms, and particularly preferably 3 carbon atoms. Further, the content of the α-olefin unit is preferably 0.1 to 4 mol%.

In the present invention, polyethylene PEa and PEb consisting only of two kinds of ethylene units having different Mv
It was revealed that the object can be achieved by blending polyethylene PEc in which ethylene having a Mv between the two types and a comonomer are blended with each other to prepare a microporous membrane. For this reason, different M
The molecular weight distribution can be appropriately widened by blending three types of polyethylene having v. At this time, the presence of PEa having a relatively low Mv has a broad molecular weight distribution on the low molecular weight side, which is advantageous in film-forming properties and leads to an improvement in quality, thereby providing excellent battery characteristics. The physical properties of the film can be stably obtained, and in addition, the fuse temperature can be lowered and the effect of improving the battery safety can be expected. Also, PE with a relatively high Mv
The presence of b improves short-circuit resistance, which can also be expected to be effective in improving battery safety. Another reason is that PEc, which is a low-melting point component, has an Mv between PEa and PEb, so that it is effectively dispersed in the microporous membrane and uniform physical properties of the microporous membrane are obtained. It is also possible to expect the effect of producing a fuse in a uniform state.

The polyolefin microporous film of the present invention is preferably composed of a composition containing polyethylene PEa, PEb, PEc and polypropylene (PP), and the PP content is 1 to 30% by weight. It is preferable. This can be expected to have the effect of increasing the short-circuit resistance, but the content is preferably 1 to 15% by weight from the viewpoint of the balance between physical properties of puncture strength and air permeability.
Also, from the viewpoint of improving short-circuit resistance, Mv of PP
Is preferably 150,000 or more, and is preferably 700,000 or less from the viewpoint of quality.

The average pore size of the polyolefin microporous membrane of the present invention is 0.030 to 0.060 μm, preferably 0.030 to 0.055 μm, and more preferably 0.0.
It is 30 to 0.050 μm. Moreover, the pore bending ratio of the polyolefin microporous membrane of the present invention is preferably in the range of 1.50 to 3.50. The length of the hole can be obtained by multiplying the hole bending rate by the film thickness. In addition, the number of holes is 55-30
0 / μm ² is preferable, and more preferably 80 to 300.
Pieces / μm ² , more preferably 100 to 300 pieces / μm
It is ² .

When the polyolefin microporous membrane has the average pore diameter, pore bending ratio, and pore number in such ranges, the lithium ion battery exhibits excellent charge / discharge characteristics. The reason for this is presumed to be as follows. During the charge / discharge process, the electrolyte is electrochemically decomposed inside the battery to produce solid by-products containing organic substances and gases such as ethylene, propylene, carbon dioxide, and hydrogen. These products obstruct ion conduction by closing the pores of the separator, leading to deterioration of charge / discharge characteristics. At this time, if the porosities of the separators are the same, the ion conduction path between the positive electrode and the negative electrode is blocked when there are a small number of large diameter holes rather than when there are a large number of small diameter holes. It is easy to cause a situation where Even if this difference only causes a slight decrease in charging / discharging efficiency in the initial stage, this difference causes new deterioration, and such a deterioration is more likely to occur as the current during charging is larger. It is estimated that deterioration will progress.

Regarding the method for obtaining the average pore diameter of the microporous polyolefin membrane, a method of calculating from a scanning electron microscope photograph, as in JP 2001-89593 A,
A method using adsorption / desorption of nitrogen as in JP 2001-205709 A and a method using a mercury porosimeter are known. In the present invention, the average pore diameter, the pore bending ratio, the number of pores measured by the method described below are It was found that there is a large correlation between battery characteristics.

The physical properties of the polyolefin raw material used in the present invention are evaluated by the following test methods; Based on Mv ASTM D4020 of polyethylene, the intrinsic viscosity [η] is measured in a 135 ° C. decalin solution and determined by the following formula: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 2. Based on Mv ASTM D4020 of polypropylene, the intrinsic viscosity [η] is measured in a 135 ° C. decalin solution and determined by the following formula: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80

3. This refers to the temperature at which the melting endothermic curve obtained by the measurement of the melting point differential scanning calorimeter (DSC) of polyethylene has a maximum, and is measured by the following method; [Measuring device] DSC220 (manufactured by Seiko Instruments) [ Sample preparation] Approximately 3 mg of polyethylene is placed in an open sample pan made of aluminum having a diameter of 5 mm, and a clamping cover is put on and sealed with a sample sealer. As a reference, make a polyethylene-free one. [Measurement conditions] 30 ° C to 180 ° C at a speed of 10 ° C / min
The temperature is raised to 180 ° C. and kept for 5 minutes. Then speed 1
The temperature is lowered to 30 ° C. at 0 ° C./min, and the temperature is kept at 30 ° C. for 5 minutes. Then, the temperature is raised again at a rate of 10 ° C./min, and the melting point is obtained from the melting endothermic curve shown at that time.

4. Content of α-olefin unit in polyethylene obtained by copolymerizing ethylene and α-olefin In the ¹³ C-NMR spectrum, the molar conversion amount (A) of the integrated value of the signal intensity derived from the α-olefin unit is
The value obtained by dividing by the sum of (A) and the molar conversion amount (B) of the integral value of the signal intensity derived from the ethylene unit is multiplied by 100 to obtain the value.

For example, in the case of copolymerized polyethylene using propylene as an α-olefin, the following structural model

[0020]

[Chemical 1]

In, I ₁ , I _{1 ′} , I ₂ , I ₃ , I
_alpha, I _beta, I _gamma, the _{I m,} and the ¹³ C-NMR signal intensity of a spectrum derived from the _{I M} to the corresponding carbon, the content of α- olefin unit (mol%) = (A) /
((A) + (B)) × 100 where (A) = (I _{1 ′} + I _m + I _α / 2) / 3, (B) = (I ₁ + I ₂ + I ₃ + I _M + I _α / 2 + I _β +
I _γ ) / 2, so the signal strengths I ₁ and I ₂ derived from the terminal carbons are obtained.
And I ₃ are disregarded and the above formula is arranged, the content of the α-olefin unit (mol%) = I _m / (I
_m + (I _M + 5I _m ) / 2) × 100.

Next, the method for producing the microporous polyolefin membrane of the present invention will be described. First, mix the raw material polyolefin, in the extruder equipped with a die,
It is melted and kneaded by being dissolved in a plasticizer at a temperature equal to or higher than the melting point and lower than the decomposition temperature. This is extruded from a die lip and cast on a cooling roll to form a sheet having a thickness of several tens of μm to several mm to obtain a gel composition. The plasticizer referred to here is an organic compound capable of forming a uniform solution with polyolefin at a temperature equal to or lower than the boiling point. Specifically, liquid paraffin, decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane and the like are mentioned, and liquid paraffin and decalin are particularly preferable. preferable.

The concentration of polyolefin in the plasticizer is 10-8.
0 wt% is preferable, more preferably 20 to 60 wt%
Is the range. From the viewpoint of easily forming a continuous sheet, it is preferably 10% by weight or more, and from the viewpoint of obtaining an appropriate porosity, it is preferably 80% by weight or less. In addition, it is preferable to add an antioxidant in order to prevent the oxidation of the polyolefin during heating and melting.

This gel composition is heated and stretched,
It is a stretched film. The stretching temperature is preferably from room temperature to the melting point of the polymer gel, more preferably 80 to 130 ° C, and further preferably 100 to 125 ° C. The stretching method is a tenter method, a roll method, an inflation method, a rolling method, or a combination of these methods at a predetermined magnification. It may be uniaxially stretched or biaxially stretched, but biaxially stretched is preferable. In the case of biaxially stretched, both longitudinal and transverse simultaneous stretching or sequential stretching may be performed. The stretching ratio is preferably in the range of 4 to 400 times, more preferably 8 to 200 times, and further preferably 16 to 100 times in terms of area ratio. The stretching ratio is preferably 4 times or more from the viewpoint of high strength, and is preferably 400 times or less from the viewpoint of production stability.

Next, a plasticizer is extracted from the stretched film to form a microporous film. As an extraction method, there is extraction with an organic solvent. As the solvent at this time, methyl ethyl ketone, methylene chloride, hexane, diethyl ether and the like are preferably used, and thereafter, it is preferable to dry by heating and air drying. When a low boiling point compound such as decalin is used as the plasticizer, it can be removed by heating and drying. In any case, in order to prevent the physical properties from being deteriorated due to the contraction of the film, it is desirable to carry out the process with the film constrained.

After the above, it is desirable to carry out heat setting (heat setting) for the purpose of enhancing dimensional stability and reducing heat shrinkage. As the temperature at this time,
It is preferable to carry out in the range of the crystal dispersion temperature to the melting point. Further, during heat setting, stretching in the width direction (usually stretching to the maximum draw ratio and then relaxing to the final draw ratio) may be performed at the same time, and the normal draw ratio is the maximum draw ratio of 1.01 to 2.00. It is preferable that the range of the final magnification is 0.70 to 1.80 times. The physical properties of the polyolefin microporous film obtained as described above are described below.

The film thickness is preferably in the range of 1 to 100 μm,
More preferably, it is 5 to 50 μm. The thickness is preferably 1 μm or more from the viewpoint of mechanical strength, and is preferably 100 μm or less from the viewpoint of winding property and battery capacity in the battery manufacturing process. 20-80% of porosity is preferable,
It is more preferably 30 to 55%. The porosity is preferably 20% or more from the viewpoint of ion permeability, and is preferably 80% or less from the viewpoint of mechanical strength. Air permeability is 1 to 2000 sec. / 100 cm ³ , and more preferably 30 to 1500 sec. / 100c
m ³ , more preferably 50 to 1000 sec. / 10
It is 0 cm ³ . 2000se from the viewpoint of ion permeability
c. It is preferably / 100 cm ³ or less.

The puncture strength is preferably 0.4 N / 20 μm or more, more preferably 0.8 N / 20 μm or more, still more preferably 2.4 N / 20 μm or more. From the viewpoint of the yield during battery production, it is preferably 0.4 N / 20 μm or more. Further, the fuse temperature and the short-circuit temperature are important as indexes for evaluating safety. The fuse temperature is preferably 143 ° C. or lower, and the short circuit temperature is preferably 150 ° C. or higher.

Various physical properties of the polyolefin microporous membrane of the present invention are evaluated by the following test methods; Thin film thickness gauge (manufactured by Toyo Seiki; trademark "KBM", terminal diameter φ5)
mm, measurement pressure 62.47 kPa), room temperature 23 ±
Measure at 2 ° C. 2. Air permeability digital type Oken type air permeability tester (made by Asahi Seiko; trademark "EG
01 "). 3. Porosity The obtained polyolefin microporous membrane is cut into a rectangular shape to obtain a sample, and the sample is calculated by the following formula: Porosity = {1- (10000 × M / 0.95) / (X ×
Y × T)} × 100 In the above formula, X, Y: length and width of sample (cm) T: sample thickness (μm), M: sample weight (g) 4. Puncture strength Handy compression tester (made by Kato Tech: trademark "KES-
G5 "), a needle with a diameter of 1 mm and a tip curvature radius of 0.5 mm is attached, the temperature is 23 ± 2 ° C, and the moving speed of the needle is 0.2 cm /
A puncture test is performed in sec. 2 for the obtained piercing strength (N)
20 μm by multiplying 0 (μm) / film thickness (μm)
The puncture strength (N / 20 μm) in terms of film thickness is calculated.

5. Fuse temperature and short-circuit temperature Two sheets of nickel foil (A, B) having a thickness of 10 μm were prepared, one nickel foil A was placed on a slide glass, and the length was 10 mm.
Teflon (registered trademark) leaving a 10 mm wide square part
Fix with tape masking. Another nickel foil B was placed on a ceramic plate to which a thermocouple was connected, and LiBF ₄ was added as a solute to a mixed solvent of propylene carbonate: ethylene carbonate: γ-butyrolactone = 1: 1: 2 (volume ratio). The microporous membrane of the measurement sample was immersed in an electrolytic solution dissolved to have a concentration of 1.0 mol / liter for 3 hours and sufficiently impregnated with the electrolytic solution.
On top of that, slide glass with nickel foil A attached is placed, and then silicone rubber is placed. This is set on a hot plate and heated at a rate of 20 ° C./min while applying a pressure of 1.5 MPa with a hydraulic press. The impedance change at this time is measured by an LCR meter under the conditions of AC 1V and 1 kHz. In this measurement, the temperature when the impedance reached 1000Ω was defined as the fuse temperature, and then the impedance was 1000Ω.
The temperature at the time of falling below is the short-circuit temperature.

6. Average Pore Diameter, Pore Flexibility, Pore Number It is known that the fluid inside the capillary follows Poiseuille flow when the mean free path of the fluid is smaller than the pore diameter of the capillary, and Knudsen flow when it is larger. Assuming that the air flow in the air permeability measurement is Knudsen flow and the water flow in the water permeability measurement at room temperature follows the Poiseuille flow, the average pore diameter d (m) and the pore bending ratio τ (dimensionless) Is the air permeation rate constant Rga
s, water permeation rate constant Rliq, water viscosity η (Pa · se
c), standard pressure Ps (101325 Pa), porosity ε
(Dimensionless), film thickness L (m), gas molecular velocity ν (m / s
ec), it can be obtained using the following formula: d = 2ν (Rliq / Rgas) (16η / 3) (1 / Ps) τ = (d × (ε / 100) × ν / (3L × Ps × Rga
s)) ^1/2 where Rgas is determined from the air permeability (sec) using the following formula: Rgas (m ³ / (m ² · sec · Pa)) = 0.000
1 / air permeability / 0.0006424 / (0.01276 ×
101325) Further, Rliq is the water permeability (cm ³ / (cm ² · sec · P
a)) is calculated using the following formula: Rliq (m ³ / m ² · sec · Pa) = water permeability / 100
0000 / 0.0001

The water permeability in the above formula is measured as follows: A stainless porous liquid cell having a diameter of 42 mm is set with a microporous membrane which has been immersed in ethanol in advance.
After the ethanol of the membrane was washed with water, about 50,000 Pa
The water permeation rate (cm ³ ) is calculated by calculating the water permeation rate (cm ³ / (cm ^2).・
sec · Pa)). Furthermore, ν is the gas constant R
(8.314 J / mol · K), absolute temperature T (K),
Circularity π, average molecular weight of gas M (= 2.896 × 10
^-2 ) (kg / mol) is calculated using the following formula: ν ² = 8RT / πM In addition, the number of holes B (number / μm ² ) is calculated from the following formula; B = 4 × (ε / 100) ) / (Π × d ² × τ)

[0033]

EXAMPLES The embodiments of the present invention will be further described below with reference to examples. Example 1 (1) Production of Polyolefin Microporous Membrane (Separator) The following three types were used as raw material polyethylene; Mv: 100,000, melting point: 135 ° C. 45% by weight polyethylene ... PEa 2. Polyethylene 40% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. Mv: 120,000, melting point: 131 ° C., and 15% by weight of copolymer polyethylene having an amount of α-olefin unit having 3 carbon atoms of 1.3 mol% ... PEc 0.3% by weight of the total weight of these raw materials. Amount of the antioxidant pentaerystyryl-tetrakis- [3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate] is added and dry blended using a tumbler mixer to obtain a polymer mixture. After thoroughly replacing the polymer mixture with nitrogen, the mixture is supplied to a twin-screw extruder by a feeder under a nitrogen atmosphere. In addition, liquid paraffin is injected into the extruder cylinder by a plunger pump. At this time, the feeder and the plunger pump are adjusted so that the liquid paraffin (kinematic viscosity at 37.78 ° C. 75.9 cSt) is 62% by weight with respect to 38% by weight of the polymer mixture. In this state, the temperature was set to 240 ° C. and the screw rotation speed was 120 rpm, and the mixture was melt-kneaded, extruded from a T die at a discharge rate of 12 kg / h, and cast on a cooling roll to obtain 1400.
A gel sheet having a thickness of μm is formed. This is simultaneously biaxially stretched by a simultaneous biaxial stretching machine in the range of 118 to 123 ° C. in a winding direction of 7 times and a width direction of 6.4 times. After that, liquid paraffin is extracted and removed in a methyl ethyl ketone tank, and then methyl ethyl ketone is removed by heat drying. Furthermore, the temperature 11
Heat setting is performed under the condition of 5 to 125 ° C. The polyolefin microporous membrane produced in this manner was judged to be good in quality from the viewpoints of pinholes, pores, and uniformity of physical properties. Table 1 shows the obtained physical property values.
Shown in.

(2) Preparation of positive electrode LiCoO ₂ lithium cobalt composite oxide as an active material
In an amount of 92.2% by weight, flaky graphite and acetylene black as a conductive agent in an amount of 2.3% by weight, and polyvinylidene fluoride (PVDF) in an amount of 3.2% by weight as a binder in N-methylpyrrolidone (NMP). To prepare a slurry. This slurry is applied on one surface of an aluminum foil having a thickness of 20 μm to be a positive electrode current collector by a die coater, dried at 130 ° C. for 3 minutes, and then compression molded by a roll press. At this time, the amount of the positive electrode active material applied is 250 g.
/ M ² , and the bulk density of the active material is 3.00 g / cm ³ . This is punched into a circle having an area of 2.00 cm ² .

(3) Preparation of negative electrode 96.9% by weight of artificial graphite as an active material, 1.4% by weight of ammonium salt of carboxymethylcellulose and 1.7% by weight of styrene-butadiene copolymer latex as a binder are dispersed in purified water. To prepare a slurry. This slurry is used as a negative electrode current collector and has a thickness of 12 μm.
It is applied to one side of the copper foil of No. 1 by a die coater, dried at 120 ° C. for 3 minutes, and then compression molded by a roll press machine. At this time,
The amount of active material applied to the negative electrode is 106 g / m ² , and the bulk density of the active material is 1.35 g / cm ³ . Area 2.
Punch into a circle of 05 cm ² . (4) Preparation of non-aqueous electrolyte solution Ethylene carbonate: Ethyl methyl carbonate =
LiPF ₆ as a solute in a mixed solvent of 1: 2 (volume ratio)
Is dissolved and adjusted to a concentration of 1.0 mol / liter.

(5) Simple battery assembly A simple lithium ion battery is manufactured by incorporating the above-mentioned polyolefin microporous membrane separator, the positive electrode and the negative electrode punched in a circular shape, and the electrolytic solution into a cell made of aluminum and stainless steel. (6) Simple battery evaluation The simple battery assembled as described above was used in a 25 ° C. atmosphere at a current value of 3 mA (about 0.5 C) and a battery voltage of 4.2 V.
The battery is charged up to 4.2V, and the current value is started to be reduced from 3mA so that the battery voltage is 2.5V at a current value of 3mA. To discharge. Then, in a 25 ° C. atmosphere, the battery voltage is 4.2 V at a current value of 6 mA (about 1.0 C).
The battery is charged up to 4.2V, and then the current value is held down to 4.2V. Then, the current value is started to be reduced from 6mA, charging is performed for 3 hours in total, and the battery voltage is 2.5V at a current value of 6mA. Repeat times. The ratio (%) of the capacity at the 300th cycle to the capacity at the first cycle in this cycle was calculated as the capacity retention rate, and the value is shown in Table 1.

Example 2 As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 40% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. 15% by weight of copolymer polyethylene having a Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol%, PEc is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 1 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

Example 3 As a raw material polyethylene for producing a microporous polyolefin film, 1. Mv: 300,000, melting point: 135 ° C. 45% by weight polyethylene ... PEa 2. 40% by weight of polyethylene having Mv: 700,000 and melting point: 135 ° C. PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 400,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 1 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

Example 4 As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Mv: 400,000, melting point: 135 ° C. 45% by weight polyethylene ... PEa 2. Mv: 1,000,000, melting point: 135 ° C. 40% by weight polyethylene ... PEb 3. 15% by weight of copolymer polyethylene having a Mv of 500,000, a melting point of 125 ° C. and an α-olefin unit content of 3 carbon atoms of 1.3 mol% PEc is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 1 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Example 5] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight having Mv: 450,000 and melting point: 135 ° C .... PEa 2. Mv: 1.5 million, melting point: 135 ° C. 40% by weight polyethylene ... PEb 3. 15% by weight of copolymer polyethylene having a Mv of 1,000,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% PEc is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 2 shows the contents of the prepared polyolefin microporous membrane and the results of the simple battery evaluation.

[Example 6] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight having Mv: 450,000 and melting point: 135 ° C .... PEa 2. Mv: 2.5 million, melting point: 135 ° C. 40% by weight polyethylene ... PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 2,000,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 2 shows the contents of the prepared polyolefin microporous membrane and the results of the simple battery evaluation.

Example 7 As a raw material polyethylene for producing a polyolefin microporous film, 1. Polyethylene 50% by weight having Mv: 200,000 and melting point: 135 ° C .... PEa 2. 45% by weight of polyethylene having Mv: 600,000 and melting point: 135 ° C. PEb 3. 5% by weight of copolymer polyethylene PE having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 2 shows the contents of the prepared polyolefin microporous membrane and the results of the simple battery evaluation.

Example 8 As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 35% by weight having Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 35% by weight having Mv: 600,000 and melting point: 135 ° C. PEb 3. PEc of 30% by weight of copolymer polyethylene having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 2 shows the contents of the prepared polyolefin microporous membrane and the results of the simple battery evaluation.

[Example 9] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 25% by weight having Mv: 200,000 and melting point: 135 ° C. PEa 2. Polyethylene 25% by weight having Mv: 600,000 and melting point: 135 ° C. PEb 3. 50% by weight of copolymer polyethylene PEc having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 3 shows the contents of the produced polyolefin microporous film and the results of the simple battery evaluation.

[Example 10] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. 85% by weight of polyethylene having Mv: 200,000 and melting point: 135 ° C. PEa 2. Polyethylene 10% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. 5% by weight of copolymer polyethylene PE having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 3 shows the contents of the produced polyolefin microporous film and the results of the simple battery evaluation.

[Example 11] As a raw material polyethylene for the production of a polyolefin microporous film, 1. Polyethylene 10% by weight having Mv: 200,000 and melting point: 135 ° C .... PEa 2. 85% by weight of polyethylene having Mv: 600,000 and melting point: 135 ° C. PEb 3. 5% by weight of copolymer polyethylene PE having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 3 shows the contents of the produced polyolefin microporous film and the results of the simple battery evaluation.

Example 12 As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 40% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 300,000, a melting point of 120 ° C. and a content of α-olefin unit having 4 carbon atoms of 2.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 3 shows the contents of the produced polyolefin microporous film and the results of the simple battery evaluation.

[Example 13] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 40 wt% with Mv: 300,000 and melting point: 135 ° C .... PEa 2. 40% by weight of polyethylene having Mv: 700,000 and melting point: 135 ° C. PEb 3. 3. Mv: 400,000, melting point: 125 ° C., and 15% by weight of copolymer polyethylene having a carbon number 3 α-olefin unit content of 1.3 mol%. PEc In addition, as a raw material polypropylene, 4. Mv: 5% polypropylene by weight of 400,000 ... P
P is used. An amount of antioxidant equal to 1.0% by weight of the total weight of these raw materials is added. Except for these matters, the procedure is the same as in the first embodiment. Table 4 shows the contents of the prepared polyolefin microporous film and the results of the simple battery evaluation.

Example 14 As a raw material polyethylene for producing a microporous polyolefin film, 1. Polyethylene 35% by weight having Mv: 300,000 and melting point: 135 ° C .... PEa 2. Polyethylene 35% by weight having Mv: 700,000 and melting point: 135 ° C. PEb 3. 3. Mv: 400,000, melting point: 125 ° C., and 15% by weight of copolymer polyethylene having a carbon number 3 α-olefin unit content of 1.3 mol%. PEc In addition, as a raw material polypropylene, 4. Mv: 15% by weight of 400,000 polypropylene ...
PP is used. An amount of antioxidant equal to 1.0% by weight of the total weight of these raw materials is added. Except for these matters, the procedure is the same as in the first embodiment. Table 4 shows the contents of the prepared polyolefin microporous film and the results of the simple battery evaluation.

Example 15 As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 30% by weight having Mv: 300,000 and melting point: 135 ° C .... PEa 2. 25% by weight of polyethylene having Mv: 700,000 and melting point: 135 ° C. PEb 3. 3. Mv: 400,000, melting point: 125 ° C., and 15% by weight of copolymer polyethylene having a carbon number 3 α-olefin unit content of 1.3 mol%. PEc In addition, as a raw material polypropylene, 4. Mv: 400,000 polypropylene, 30% by weight ...
PP is used. An amount of antioxidant equal to 1.0% by weight of the total weight of these raw materials is added. Except for these matters, the procedure is the same as in the first embodiment. Table 4 shows the contents of the prepared polyolefin microporous film and the results of the simple battery evaluation.

[Comparative Example 1] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. 40% by weight of polyethylene having Mv: 500,000 and melting point: 135 ° C. PEb 3. 15% by weight of copolymer polyethylene having a Mv of 550,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% PEc is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 5 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 2] As a raw material polyethylene for producing a polyolefin microporous film, 1. Polyethylene 45% by weight having Mv: 450,000 and melting point: 135 ° C .... PEa 2. 40% by weight of polyethylene having Mv: 700,000 and melting point: 135 ° C. PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 400,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 5 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 3] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight having Mv: 550,000 and melting point: 135 ° C .... PEa 2. 40% by weight of polyethylene having Mv: 700,000 and melting point: 135 ° C. PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 600,000, a melting point of 125 ° C., and an α-olefin content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 5 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 4] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 40% by weight having Mv: 450,000 and melting point: 135 ° C .... PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 400,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 5 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 5] As a raw material polyethylene for producing a microporous polyolefin membrane, 1. Polyethylene 25% by weight having Mv: 200,000 and melting point: 135 ° C. PEa 2. 20% by weight of polyethylene having an Mv of 600,000 and a melting point of 135 ° C. PEb 3. 55% by weight of copolymer polyethylene PEc having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 6 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 6] As a raw material polyethylene for producing a microporous polyolefin film, 1. (PEa is not used) Polyethylene 50% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. 50% by weight of copolymer polyethylene PEc having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 6 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 7] As a raw material polyethylene for producing a microporous polyolefin film, 1. Polyethylene 50% by weight having Mv: 200,000 and melting point: 135 ° C .... PEa 2. (PEb is not used) 3. 50% by weight of copolymer polyethylene PEc having an Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 6 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Comparative Example 8] As a raw material polyethylene for producing a microporous polyolefin film, 1. Polyethylene 50% by weight having Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 50% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. (PEc is not used) is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 6 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Reference Example 1] As a raw material polyethylene for producing a polyolefin microporous film, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 40% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. PEc of 15% by weight of copolymer polyethylene having an Mv of 300,000, a melting point of 135 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol% is used. Except for these matters, the procedure is the same as in the first embodiment.
Table 7 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Reference Example 2] As a raw material polyethylene for producing a polyolefin microporous film, 1. Polyethylene 45% by weight with Mv: 200,000 and melting point: 135 ° C .... PEa 2. Polyethylene 40% by weight having Mv: 600,000 and melting point: 135 ° C .... PEb 3. 15% by weight of copolymer polyethylene having a Mv of 300,000, a melting point of 125 ° C., and an α-olefin unit content of 3 carbon atoms of 1.3 mol%, PEc is used. The heat setting is performed at a temperature of 115 to 130 ° C. Except for these matters, the procedure is the same as in the first embodiment. Table 7 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[Reference Example 3] As a raw material polyethylene for producing a microporous polyolefin film, 1. Polyethylene 25% by weight having Mv: 200,000 and melting point: 135 ° C. PEa 2. Polyethylene 25% by weight having Mv: 600,000 and melting point: 135 ° C. PEb 3. 3. 15% by weight of copolymer polyethylene having Mv: 300,000, melting point: 125 ° C., and content of α-olefin unit having 3 carbon atoms: 1.3 mol% PEc In addition, as a raw material polypropylene, 4. Mv: 35% by weight of polypropylene, which is 400,000, ...
PP is used. An amount of antioxidant equal to 1.0% by weight of the total weight of these raw materials is added. Except for these matters, the procedure is the same as in the first embodiment. Table 7 shows the contents of the produced polyolefin microporous membrane and the results of the simple battery evaluation.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

[0067]

[Table 6]

[0068]

[Table 7]

The following are clear from Tables 1-6. The polyolefin microporous membranes of the present invention according to the methods of Examples 1 to 15 can be expected to have high quality, be highly safe from the values of the fuse temperature and the short-circuit temperature, and maintain the capacity of the simplified battery evaluation results. It is understood from the rate that excellent battery characteristics can be exhibited. On the other hand, it can be seen that the methods of Comparative Examples 1 to 10 have drawbacks in quality, fail to exhibit an appropriate fuse temperature or short-circuit temperature, or fail to exhibit excellent battery characteristics.

As is clear from the comparison between Reference Example 1 (Table 7) and Example 2 (Table 1), the melting point of PEc is 13
If it exceeds 3 ° C., the fuse temperature exceeds 143 ° C. even if the claim 1 is satisfied, and safety is concerned even if the excellent battery characteristics are exhibited. Further, as is clear from the comparison between Reference Example 2 (Table 7) and Example 2 (Table 1), the used polyolefin raw material compositions are the same and satisfy claim 1, but the average pore diameter and the number of pores are claimed. When the items 4 and 5 are not satisfied, the battery characteristics may be slightly inferior even if the fuse temperature and the short circuit temperature, which are expected to have high safety, are exhibited. In addition, as is clear from Reference Example 3 (Table 7), even if PEa, PEb, and PEc satisfy claim 1, if the PP content does not satisfy claim 3, the quality is poor and the battery is poor. The characteristics may be slightly inferior.

[0071]

The polyolefin microporous membrane of the present invention is
It can be used as a separator exhibiting excellent battery characteristics and high safety in batteries.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // H01M 2/16 H01M 2/16 P 10/40 10/40 Z F term (reference) 4F074 AA17 AA24 AA98 AB01 CB03 CB16 CC04X CC04Y CC04Z DA02 DA03 DA09 DA10 DA23 DA24 DA49 4J002 BB03W BB03X BB05Y BB11Z BB15Y GD00 GQ01 5H021 EE04 EE15 HH01 HH02 HH03 H0507H07H07H03H07H07H07H07H07H03H07H03

Claims (5)

[Claims] 1. At least a viscosity average molecular weight (hereinafter M
v) is 10 to 85% by weight of polyethylene PEa consisting of only ethylene units and having a Mv of 5 of 100,000 to less than 500,000.
10 to 85% by weight of polyethylene PEb consisting of only ethylene units in the range of 0,000 to 5 million and 5 to 50% by weight of polyethylene PEc obtained by copolymerizing ethylene and a comonomer when Mv exceeds 100,000 and less than 5 million. Of the composition containing them, and their Mv size is PEa.
<PEc <PEb, A microporous polyolefin membrane characterized by the following: 2. The polyolefin microporous membrane according to claim 1, wherein the polyethylene PEc is a copolymer of ethylene and an α-olefin having 3 or more carbon atoms. 3. The polyethylene P according to claim 1 or 2.
A polyolefin microporous membrane comprising a composition containing Ea, PEb, PEc and polypropylene, wherein the polypropylene content is 1 to 30% by weight. 4. The calculated average pore diameter is 0.030 to 0.060.
The polyolefin microporous film according to any one of claims 1 to 3, wherein the microporous film is in the range of µm. 5. A porosity of 20 to 80%, and a pore bending ratio of 1.50 calculated from air permeability and water permeability.
3.50, polyolefin microporous membrane according to claim 1, the number holes, characterized in that a 55 to 300 pieces / [mu] m ^2.