WO2018209794A1

WO2018209794A1 - Polymer composition for forming battery isolation membrane, battery isolation membrane and preparation method therefor

Info

Publication number: WO2018209794A1
Application number: PCT/CN2017/093654
Authority: WO
Inventors: 程跃; 熊磊
Original assignee: 上海恩捷新材料科技股份有限公司
Priority date: 2017-05-15
Filing date: 2017-07-20
Publication date: 2018-11-22
Also published as: CN107200901A

Abstract

A polymer composition for forming a battery isolation membrane, a battery isolation membrane and a preparation method therefor. The polymer composition for forming the battery isolation membrane comprises: high molecular weight polyethylene with an average molecular weight of 1.0x105-10.0x106 and a density of 0.940-0.976 g/cm3, a pore forming agent, and an antioxidant. If the high molecular weight polyethylene is calculated in 100 parts by weight, the pore forming agent is 500-2000 parts by weight, and the antioxidant is 0.1-10 parts by weight. The polymer composition for forming a battery isolation membrane is used for forming a battery isolation membrane. The battery isolation membrane formed by using the polymer composition has a low micro-pore aperture, uniform and centralized aperture distribution, and good porosity and membrane strength, and two surfaces of the formed battery isolation membrane have closer microscopic appearances.

Description

Polymer composition forming battery separator, battery separator and preparation method thereof

Technical field

The present invention relates to the field of lithium battery technology, and in particular to a polymer composition for forming a battery separator, a battery separator, and a preparation method.

Background technique

Lithium-ion batteries are usually composed mainly of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. In lithium-ion battery construction, the diaphragm is one of the key inner layer components. The main function of the separator is to separate the positive and negative electrodes of the battery to prevent direct contact between the positive and negative electrodes and short circuit. At the same time, the electrolyte ions can pass smoothly during the charging and discharging process of the battery to form a current, and the battery operating temperature is abnormal. When rising, the electrolyte ion migration channel is turned off, and the current is cut off to ensure battery safety. It can be seen that the performance of the diaphragm determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. The separator with excellent performance plays an important role in improving the overall performance of the battery. Currently, commercially available lithium ion battery separators generally employ a polyolefin porous membrane.

The main performance parameters of the battery separator include thickness, porosity, pore size, pore size distribution, strength, heat shrinkage, closed cell temperature and membrane rupture temperature. In order to reduce the internal resistance of the battery, the electrode area must be as large as possible, so the thickness of the diaphragm is required to be as thin as possible. Although the battery separator itself is not electrically conductive, the conductive ions need to migrate through the diaphragm. This requires that the diaphragm itself needs a certain number of pores, that is, porosity, but the porosity is too high, which will cause the strength of the diaphragm to decrease, affecting the overall reliability of the battery. In addition, the wettability of the electrolyte on the separator directly affects the resistance of ion migration. The better the wettability, the smaller the resistance of ions to migrate through the separator, and the smaller the internal resistance of the battery. Generally, in the case where the pore diameter is not very large, the more uniform the pore size distribution, the better the wettability of the electrolyte. The battery assembly needs to pull the diaphragm during its production and assembly process. After the assembly is completed, it is also necessary to ensure that the diaphragm is not pierced by the electrode material, so the diaphragm not only needs sufficient tensile strength but also requires a certain piercing strength. The polymer separator will undergo heat shrinkage under certain heating conditions. In order to avoid internal short circuit caused by direct contact between the positive and negative electrodes caused by heat shrinkage, the heat shrinkage rate of the separator is also required. Under abnormal conditions, such as when a short circuit occurs on an external line, the internal temperature of the battery rises sharply due to excessive current, which requires the diaphragm to close the migration path of the conductive ions in time. Therefore, the temperature at which the micropores of the battery separator are melt-closed is referred to as a closed-cell temperature. When the temperature continues to rise, the isolation film is broken and the fracture temperature is called the film breaking temperature. From the perspective of the safety of lithium-ion batteries, the closed-cell temperature and the membrane-breaking temperature of the diaphragm must have a certain temperature difference to ensure that even if the temperature continues to rise after the diaphragm is closed, the diaphragm will not rupture.

The conventional wet lithium ion battery separator needs to undergo an organic solvent extraction process in the production process, which is often a bottleneck restricting the production speed of the entire battery separator film, and there is also a significant gap between the two sides of the produced separator. Same In order to maintain the continuity of the entire production process, all heating components require external heat supply, high energy consumption and high production costs. An object of the present invention is to provide a semi-dry and semi-wet battery separator manufacturing process and a product thereof, which can eliminate the extraction process in the wet process, and at the same time, the battery separator has excellent comprehensive performance, such as The lower micropore diameter, uniform concentration of pore size distribution, good porosity and film strength, the two sides of the separator prepared by this method have a closer microscopic morphology.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a polymer composition, a battery separator, and a preparation method for forming a battery separator, which are used for solving a battery separator prepared by a wet process in the prior art. There is a need to extract the bottleneck that limits the production speed of the entire battery separator. The resulting micro-topography of the battery separator has significant differences, and in order to maintain the continuity of the entire production process, all heating components require external heat supply. The problem of high energy consumption and high production cost.

To achieve the above and other related objects, the present invention provides a polymer composition for forming a battery separator, the polymer composition forming the battery separator comprising: an average molecular weight of 1.0×10 ⁵ to 10.0×10 ⁶ and a high molecular weight polyethylene having a density of 0.940 to 0.976 g/cm ³ , a pore former, and an antioxidant, wherein

The pore former has a weight of 500 to 2000 parts by weight based on 100 parts by weight of the high molecular weight polyethylene, and the antioxidant has a weight of 0.1 to 10 parts.

As a preferred embodiment of the polymer separator for forming a battery separator of the present invention, the pore former comprises: natural mineral oil, C _6-15 alkane, C _8-15 aliphatic carboxylic acid C _1-4 alkyl ester , C _2-6 halogenated alkane, phthalate, trimellitate, adipate, sebacate, maleate, benzoate, epoxy vegetable oil, benzenesulfonamide, phosphoric acid At least one of a triester, a glycol ether, acetyl glyceryl monoacetate, a citric acid ester or a diisononyl cyclohexane-1,2-dicarboxylate.

As a preferred embodiment of the polymer separator for forming a battery separator of the present invention, the pore former has a kinematic viscosity at 40 ° C of 10 mm ² /s to 100 mm ² /s.

As a preferred embodiment of the polymer separator for forming a battery separator of the present invention, the pore former has an initial boiling point of greater than or equal to 110 °C.

As a preferred embodiment of the polymer separator for forming a battery separator of the present invention, the antioxidant comprises: 4,4-thiobis(6-tert-butylm-cresol), dibutylhydroxytoluene, sub- Phosphate ester, tert-butyl hydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate, 1,1,3-tris(2-methyl-) 4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl p-phenylenediamine, dilauryl thiodipropionate, At least one of tris(nonylphenyl)phosphite or triphenyl phosphite.

The invention also provides a method for preparing a battery separator, the method for preparing the battery separator comprises:

1) preparing a polymer composition as described in any of the above schemes, and continuously extruding the polymer composition;

2) the step 1) the continuously extruded polymer composition is subjected to vacuum distillation to cast the cast piece to obtain a ribbon;

3) the strip obtained in the step 2) is subjected to vacuum distillation to biaxially stretch into a film to remove the pore former in the ribbon;

4) heat-setting the film obtained in the step 3);

5) Winding the heat-set film.

As a preferred embodiment of the method for preparing a battery separator of the present invention, the step 1) comprises the following steps:

1-1) the high molecular weight polyethylene having an average molecular weight of 1.0 × 10 ⁵ to 10.0 × 10 ⁶ and a density of 0.940 to 0.976 g/cm ³ , the pore former and the antioxidant in a desired mass part Add into the continuous ingredient feeding kettle, stir and mix evenly;

1-2) adding the mixture obtained in the step 1-1) to the extruder, the high molecular weight polyethylene having an average molecular weight of 1.0×10 ⁵ to 10.0×10 ⁶ and a density of 0.940 to 0.976 g/cm ³ and The antioxidant is dissolved in the porogen and is continuously extruded from the extruder.

As a preferred embodiment of the method for preparing a battery separator of the present invention, the step 2) comprises the following steps:

2-1) placing the polymer composition continuously extruded in step 1) into a slit die in a vacuum distillation chamber;

2-2) The polymer composition was extruded through a slit die onto a casting chill roll and cast into a ribbon at a casting temperature.

As a preferred embodiment of the method for preparing a battery separator of the present invention, the ribbon obtained in the step 2) is subjected to vacuum distillation to biaxially stretch into a film to remove the pore former in the ribbon. The specific method is as follows: the ribbon obtained in the step 2) is placed in a vacuum distillation chamber for vacuum distillation, and simultaneously fed to a biaxial stretching machine to stretch the ribbon.

As a preferred embodiment of the method for producing a battery separator of the present invention, in the step 4), the heat setting temperature is 100 to 150 ° C; and the heat setting time is 10 to 20 minutes.

The present invention also provides a battery separator obtained by the production method as described in any of the above schemes.

As a preferred embodiment of the battery separator of the present invention, the battery separator has a thickness of 5 to 30 μm, a pore diameter of 0.3 to 0.8 μm, and a porosity of 30% to 60%.

As described above, the polymer separator, battery separator, and preparation method for forming a battery separator of the present invention have the following beneficial effects:

The battery separator forming polymer composition of the present invention is used to form a battery separator, using the polymer composition The formed battery separator has a lower micropore diameter, a uniformly concentrated pore size distribution, a good porosity and a film strength, and the formed battery separator has a closer microscopic morphology on both sides;

The preparation method of the battery separator of the invention completely abandons the extraction process in the existing wet process, effectively breaks the bottleneck of the production speed of the existing battery separator, and the battery separator prepared by the method has excellent comprehensive performance: The invention has a lower micropore diameter, a uniformly concentrated pore size distribution, a good porosity and a film strength. At the same time, the battery separator formed by the battery separator prepared by the method has a closer microscopic morphology on both sides. In addition, the method for preparing a battery separator of the present invention has the advantages of low energy consumption and low production cost compared to the wet process in the prior art.

DRAWINGS

1 is a flow chart showing a method of preparing a battery separator provided by the present invention.

2 is a front and back photomicrograph of a battery separator prepared in Example 1 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

3 is a front and back photomicrograph of a battery separator prepared in Example 2 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

4 is a front and back photomicrograph of a battery separator prepared in Example 3 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

Figure 5 is a front and back photomicrograph of a battery separator prepared in Example 4 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

Figure 6 is a front and back photomicrograph of a battery separator prepared in Example 5 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

Figure 7 is a front and back photomicrograph of a battery separator prepared in Example 6 of the present invention, wherein a is a frontal photomicrograph and b is a reverse photomicrograph.

detailed description

The embodiments of the present invention are described below by way of specific embodiments, and those skilled in the art can readily understand other advantages and functions of the present invention from the disclosure.

Please refer to Figure 1 to Figure 7. It is to be understood that the structures, the proportions, the sizes, and the like, which are illustrated in the accompanying drawings, are merely used to facilitate the understanding and reading of those skilled in the art, and are not intended to limit the practice of the present invention. The conditions are limited, so it is not technically meaningful. Any modification of the structure, change of the proportional relationship or adjustment of the size should remain in the present invention without affecting the effects and the achievable purposes of the present invention. The disclosed technical content is within the scope of the disclosure. At the same time, such as "upper", "lower", "left", "right", "central" and "one" as quoted in this specification The terminology of the present invention is also considered to be in the scope of the invention, and is not intended to limit the scope of the invention, and the change or adjustment of the relative relationship is also considered to be within the scope of the invention.

The present invention provides a polymer composition for forming a battery separator for preparing a battery separator, the polymer composition forming the battery separator comprising: an average molecular weight of 1.0×10 ⁵ to 10.0 × 10 ⁶ Daltons and a density of 0.940 ~ 0.976g / cm ³ of the high molecular weight polyethylene, an antioxidant porogen, wherein

Preferably, the high molecular weight polyethylene has an average molecular weight of 1.0 × 10 ⁵ to 5.0 × 10 ⁶ Daltons; more preferably, the high molecular weight polyethylene has an average molecular weight of 1.0 × 10 ⁵ to 2.0 × 10 ⁶ Dalton.

Preferably, the high molecular weight polyethylene has a density of from 0.940 to 0.966 g/cm ³ ; more preferably, the high molecular weight polyethylene has a density of from 0.950 to 0.966 g/cm ³ .

It should be noted that the high molecular weight polyethylene may be a high molecular weight polyethylene having an average molecular weight or a mixture of two or more average molecular weight high molecular weight polyethylene.

As an example, the pore former may comprise: natural mineral oil, C _6-15 alkane, C _8-15 aliphatic carboxylic acid C _1-4 alkyl ester, C _2-6 halogenated alkane, phthalate, Trimellitic acid ester, adipate, sebacate, maleate, benzoate, epoxy vegetable oil, benzenesulfonamide, phosphotriester, glycol ether, acetyl monoglyceride, At least one of a citrate or a diisononyl cyclohexane-1,2-dicarboxylate.

As an example, the natural mineral oil may include CAS: 8020-83-5, 8042-47-5; MDL: MFCD00131611; E1NECS: 232-455-8, and the like.

As an example, the C _6-15 alkane may include decalin, decane, undecane or dodecane, and the like.

As an example, the C _8-15 aliphatic carboxylic acid C _1-4 alkyl ester may include methyl decanoate, ethyl decanoate, propyl citrate, n-butyl decanoate, methyl undecanoate, eleven Ethyl carbonate, propyl undecacrylate, n-butyl undecanoate, methyl dodecyl carbonate, ethyl dodecyl carbonate, propyl dodecyl carbonate or n-butyl dodecyl carbonate.

As an example, the C _2-6 haloalkane may include dichloroethane, dichloropropane, fluorochloroethane or chlorofluoropropane, and the like.

As an example, the pore former has a kinematic viscosity at 40 ° C of 10 mm ² /s to 100 mm ² /s; preferably, the pore former has a kinematic viscosity at 40 ° C of 20 mm ² /s to 80 mm ² /s; more preferably The pore former has a kinematic viscosity at 40 ° C of 30 mm ² /s to 70 mm ² /s.

As an example, the porogen has an initial boiling point greater than or equal to 110 °C.

Preferably, the pore former has a weight of 700 to 1800 parts by weight of the high molecular weight polyethylene, and more preferably, the weight of the high molecular weight polyethylene is 100 parts. The pore former has a weight of 800 to 1600 parts.

As an example, the antioxidant may include: 4,4-thiobis(6-tert-butylm-cresol), dibutylhydroxytoluene, phosphite, tert-butyl hydroquinone, β-(3 , 5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate, 1,1,3-tris(2-methyl-4hydroxy-5-tert-butylphenyl)butane, 2- Tert-butyl-6-methylphenol, N,N'-di-β-naphthyl p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite or triphenyl phosphite At least one of the esters.

Preferably, the antioxidant has a weight of 0.5 to 8 parts by weight based on 100 parts by weight of the high molecular weight polyethylene; more preferably, the weight of the high molecular weight polyethylene is 100 parts, The antioxidant has a weight of 1 to 6 parts.

Referring to FIG. 1 , the present invention also provides a method for preparing a battery separator, and the method for preparing the battery separator includes:

4) heat-setting the film obtained in the step 3);

5) Winding the heat-set film.

In step 1), referring to step S1 in Figure 1, a polymer composition as described in any of the above schemes is prepared and the polymer composition is continuously extruded.

As an example, the composition and characteristics of the polymer composition are described in detail above with respect to the contents of the polymer composition, and are not described herein.

As an example, preparing the polymer composition and continuously extruding the polymer composition comprises the steps of:

1-1) the high molecular weight polyethylene having an average molecular weight of 1.0 × 10 ⁵ to 10.0 × 10 ⁶ and a density of 0.940 to 0.976 g/cm ³ , the pore former and the antioxidant in a desired mass part Adding to the continuous batching charging tank, stirring and mixing evenly; the stirring speed can be set according to actual needs. In an example, the stirring speed can be 50 rpm; of course, in other examples, the stirring speed can also be other Any value;

1-2) adding the mixture obtained in the step 1-1) to an extruder under a certain temperature condition (for example, 180 ° C), the high molecular weight polyethylene and the antioxidant are the continuous extruder is dissolved in the pore former; to be an average molecular weight of ^{1.0 × 10 5 ~ 10.0 × 10} 6 and a density of 0.940 ~ 0.976g / cm ³ of the high molecular weight polyethylene, and the anti- After the oxidant is dissolved in the porogen, it is continuously extruded by the extruder; the speed of continuous extrusion of the extruder can be set according to actual needs, and in an example, the extruder is continuously extruded The speed of the exit may be 200 rpm; of course, in other examples, the speed at which the extruder is continuously extruded may also be any other value.

It should be noted that the extruder may be a single screw extruder, a twin screw extruder or a multi-screw extruder, or may be any other existing extruder.

In step 2), referring to step S2 in Fig. 1, the polymer composition continuously extruded in step 1) is subjected to vacuum distillation casting to obtain a ribbon.

As an example, performing the step 1) continuous extrusion of the polymer composition by vacuum distillation casting the cast sheet comprises the following steps:

As an example, the casting temperature may be 50 to 100 ° C. Preferably, in the present embodiment, the casting temperature is 80 ° C.

In step 3), referring to the step S3 in FIG. 1, the ribbon obtained in the step 2) is biaxially drawn into a film by vacuum distillation to remove the pore former in the ribbon. .

As an example, the strip obtained in the step 2) is subjected to vacuum distillation biaxially to form a film, and the specific method for removing the pore former in the ribbon is: the step obtained in the step 2) The ribbon is placed in a vacuum distillation chamber for distillation under reduced pressure, and simultaneously fed to a biaxial stretching machine to stretch the ribbon to obtain a film from which the pore former is removed.

In step 4), referring to step S4 in Fig. 1, the film obtained in step 3) is heat set.

As an example, the heat setting temperature and heat setting time can be set according to actual needs; preferably, the heat setting temperature is 100 to 150 ° C; the heat setting time is 10 to 20 minutes; more preferably, the heat setting temperature is It is 120 ° C; the heat setting time is 15 minutes.

In step 5), referring to step S5 in Fig. 1, the heat-set film is wound up.

As an example, the heat-set film is placed in a winding device to be wound up to obtain the battery separator, which is a semi-dry and semi-wet battery separator.

As an example, the speed at which the heat-set film is wound may be set according to actual needs. Preferably, the speed of winding the heat-set film may be 20 to 100 m/min; more preferably, The heat-set film was wound at a speed of 50 m/min.

The above preparation method of the battery separator completely eliminates the extraction process in the existing wet process, effectively breaks the bottleneck of the production speed of the existing battery separator, and the battery separator prepared by the method has excellent comprehensive performance: for example, It has a low pore size, a uniform concentration of pore size distribution, good porosity and film strength. At the same time, the battery separator formed by the battery separator has a closer microscopic morphology on both sides. In addition, the method for preparing a battery separator of the present invention has the advantages of low energy consumption and low production cost compared to the wet process in the prior art.

The invention will now be further described in conjunction with specific embodiments. Before giving a specific embodiment, in order to facilitate understanding of the subsequent performance test structure, the test instruments and test methods used in each performance test are first described as follows:

Thickness

The German Malt film thickness gauge 1216 was measured according to the method for measuring the thickness of plastic film and sheet of GB/T6672-2001.

2. Resistance

The results were measured using a multimeter at two points where the separators were 10 cm apart, and the results were the average of 10 measurements at different measurement points.

3. Transmission rate

The Gurley permeability tester 4110 was used to measure according to the GB/T 1037 plastic film and sheet water vapor permeability test method.

4. Porosity

It was measured using a PMI AAQ-3K-A-1 automatic water press.

5. Aperture

It was measured using a PMI AAQ-3K-A-1 automatic water press.

6. Piercing strength

The Shanghai Jiaoji QJ210A universal testing machine was used to measure the peeling strength of the paper according to GB/T 2679.7.

7. Tensile strength

The test was carried out according to ASTM d882-2002 tensile standard test method for plastic sheets using a Shanghai TQ QJ210A universal testing machine.

8. Shrinkage rate

The distance L ₀ between the points on the diaphragm (23 ℃) measured at a normal temperature environment test, the sample was placed in an oven at 120 ℃ ± 1 ℃ stainless steel in adding, taken after 1h incubation, the separator to be cooled to room environment test When measuring the distance L ₁ between two points on the diaphragm, the shrinkage S is calculated according to the following formula: S = (L _{0 -} L ₁ ) / L ₀ × 100%.

The invention will now be further described in conjunction with specific embodiments.

Example 1

100 g of mineral oil with a density of 0.957 g/cm ³ , an average molecular weight of 3.0×10 ⁵ high molecular weight polyethylene, 0.5 g of antioxidant, 700 g of 40° C. kinematic viscosity of 50 mm ² /s was added to the continuous batching charging kettle. Stir at a speed of 50 rpm to mix the raw materials uniformly.

The mixture was continuously fed into an extruder, and at 180 ° C, the high molecular weight polyethylene, the antioxidant was continuously dissolved in mineral oil in an extruder, and then continuously extruded by an extruder at a speed of 200 rpm. Out.

The continuously extruded mixture was introduced into a slit die placed in a vacuum distillation chamber, and the mixture was extruded through a slit die to a casting cooling roll, and cast into a ribbon at 80 ° C to obtain a belt. The substance is placed in a vacuum distillation chamber for distillation under reduced pressure. At the same time, it is fed into a biaxial stretching machine for stretching to remove mineral oil from the ribbon. The obtained film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 50 m / min to finally obtain a semi-dry and semi-wet battery separator.

The battery separator obtained in the present embodiment was tested by the above test instrument and test method, and the test results are as follows:

A photomicrograph of the battery separator obtained in this example is shown in Fig. 2.

Example 2

100 g of mineral oil with a density of 0.953 g/cm ³ , an average molecular weight of 5.0×10 ⁵ high molecular weight polyethylene, 0.5 g of antioxidant, 700 g of 40° C. kinematic viscosity of 50 mm ² /s was added to the continuous batching charging kettle. Stir at a speed of 50 rpm to mix the raw materials uniformly.

The continuously extruded mixture was introduced into a slit die placed in a vacuum distillation chamber, and the mixture was extruded through a slit die to a casting cooling roll, and cast into a ribbon at 80 ° C to obtain a belt. The material is placed in a vacuum distillation chamber for distillation under reduced pressure, and simultaneously fed to a biaxial stretching machine for stretching to remove mineral oil from the ribbon. The obtained film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 50 m / min to finally obtain a semi-dry and semi-wet battery separator.

A photomicrograph of the battery separator obtained in this example is shown in FIG.

Example 3

100 g of mineral oil with a density of 0.951 g/cm ³ , an average molecular weight of 1.0×10 ⁶ high molecular weight polyethylene, 0.5 g of antioxidant, 800 g of 40° C. kinematic viscosity of 40 mm ² /s was added to the continuous batching charging kettle. Stir at a speed of 50 rpm to mix the raw materials uniformly.

Example 4

100 g of mineral oil with a density of 0.947 g/cm ³ , an average molecular weight of 2.0×10 ⁶ high molecular weight polyethylene, 1.0 g of antioxidant, 900 g of 40° C. kinematic viscosity of 40 mm ² /s was added to the continuous batching charging kettle. Stir at a speed of 50 rpm to mix the raw materials uniformly.

Example 5

100 grams of mineral oil with a density of 0.948 g/cm ³ , an average molecular weight of 5.0×10 ⁶ high molecular weight polyethylene, 1.0 g of antioxidant, 1000 g of 40 ° C kinematic viscosity of 40 mm ² /s was added to the continuous batching charging kettle. Stir at a speed of 50 rpm to mix the raw materials uniformly.

A photomicrograph of the battery separator obtained in this example is shown in Fig. 6.

Example 6

100 g of a density of 0.953 g/cm ³ , an average molecular weight of 5.0 × 10 ⁵ high molecular weight polyethylene, 200 g of a density of 0.940 g / cm ³ , an average molecular weight of 8.0 × 10 ⁶ high molecular weight polyethylene, 1.0 g of anti- Oxygen agent, 3600 g of mineral oil having a kinematic viscosity of 40 mm ² /s at 40 ° C was added to a continuous batching charging kettle, and stirred at a speed of 50 rpm to uniformly mix the raw materials.

Comparative example 1

100 g of a mineral having a density of 0.935 g/cm ³ , an average molecular weight of 5.0×10 ⁴ , 0.5 g of an antioxidant, 700 g of a 40° C. kinematic viscosity of 40 mm ² /s, is added to the continuous dosing tank. The mixture was stirred at a rate of 50 rpm to uniformly mix the raw materials.

Comparative example 2

100 g of a density of 0.935 g/cm ³ of polyethylene having an average molecular weight of 10.0×10 ⁶ , 1.0 g of an antioxidant, 2500 g of a 40° C. kinematic viscosity of 30 mm ² /s, and a mineral oil added to the continuous dosing tank. The mixture was stirred at a rate of 50 rpm to uniformly mix the raw materials.

It can be seen from the above experimental results that as the molecular weight of polyethylene increases, the strength of the battery separator increases, and the shrinkage rate also decreases. However, the excessive molecular weight is not conducive to the opening of the membrane, the pore size and porosity are relatively low, and the transmittance is relatively high. The lower molecular weight is easier to open the membrane, but the pore size and porosity are relatively larger. The strength is lower, the shrinkage rate is also higher, and the practical application advantage is lost. As can be further seen from Fig. 2 to Fig. 7, the microscopic topography of both sides of the diaphragm in all of the examples is very close, with no significant difference.

In summary, the present invention provides a polymer composition for forming a battery separator, a battery separator, and a preparation method, the polymer composition for forming a battery separator comprising: an average molecular weight of 1.0×10 ⁵ to 10.0× ¹⁰⁶ and a density of 0.940 ~ 0.976g / cm ³ of the high molecular weight polyethylene, an antioxidant porogen, wherein the high molecular weight polyethylene by weight of 100 parts of the weight of porogen 500 ～2000 parts, the antioxidant has a weight of 0.1 to 10 parts. The polymer separator forming battery separator of the present invention is used for forming a battery separator, and the battery separator formed using the polymer composition has a low pore diameter, a uniformly concentrated pore size distribution, a good porosity, and Membrane strength, and the formed battery separator has more close microscopic morphology on both sides; the preparation method of the battery separator of the invention completely abandons the extraction process in the existing wet process, effectively breaks through the production of the existing battery separator The bottleneck of speed, and the battery separator prepared by the method has excellent comprehensive properties: for example, having a low pore diameter, a uniformly concentrated pore size distribution, good porosity and film strength, and the battery isolation prepared by the method The battery separator formed by the film has a closer microscopic morphology on both sides. Further, the method for producing a battery separator of the present invention has the advantages of low energy consumption and low production cost as compared with the wet process of the prior art.

The above-described embodiments are merely illustrative of the principles of the invention and its effects, and are not intended to limit the invention. Modifications or variations of the above-described embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and scope of the invention will be covered by the appended claims.

Claims

A polymer composition for forming a battery separator, characterized in that the polymer composition for forming a battery separator comprises: an average molecular weight of 1.0×10 5 to 10.0×10 6 and a density of 0.940 to 0.976 g/cm. 3 high molecular weight polyethylene, pore former and antioxidant, wherein

The pore former has a weight of 500 to 2000 parts by weight based on 100 parts by weight of the high molecular weight polyethylene, and the antioxidant has a weight of 0.1 to 10 parts.
The polymer separator for forming a battery separator according to claim 1, wherein said pore former comprises: natural mineral oil, C 6-15 alkane, C 8-15 aliphatic carboxylic acid C 1-4 Alkyl esters, C 2-6 halogenated alkanes, phthalates, trimellitates, adipates, sebacates, maleates, benzoates, epoxy vegetable oils, benzenesulfonamides At least one of a phosphate triester, a glycol ether, acetyl glyceryl monoacetate, a citric acid ester or a diisononyl cyclohexane-1,2-dicarboxylate.
The polymer separator for forming a battery separator according to claim 1, wherein the pore former has a kinematic viscosity at 40 ° C of 10 mm 2 /s to 100 mm 2 /s.
A battery separator-forming polymer composition according to claim 1, wherein the pore former has an initial boiling point of greater than or equal to 110 °C.
The polymer separator for forming a battery separator according to claim 1, wherein the antioxidant comprises: 4,4-thiobis(6-tert-butylm-cresol), dibutylhydroxytoluene , phosphite, tert-butyl hydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate, 1,1,3-tris(2-A 4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl p-phenylenediamine, thiodipropionic acid double laurel At least one of an ester, tris(nonylphenyl) phosphite or triphenyl phosphite.
A method for preparing a battery separator, wherein the method for preparing the battery separator comprises:

1) preparing the polymer composition according to any one of claims 1 to 5, and continuously extruding the polymer composition;

2) the step 1) the continuously extruded polymer composition is subjected to vacuum distillation to cast the cast piece to obtain a ribbon;

3) the strip obtained in the step 2) is subjected to vacuum distillation to biaxially stretch into a film to remove the pore former in the ribbon;

4) heat-setting the film obtained in the step 3);

5) Winding the heat-set film.
The method of preparing a battery separator according to claim 6, wherein the step 1) comprises the following steps:

1-1) the high molecular weight polyethylene having an average molecular weight of 1.0 × 10 5 to 10.0 × 10 6 and a density of 0.940 to 0.976 g/cm 3 , the pore former and the antioxidant in a desired mass part Add into the continuous ingredient feeding kettle, stir and mix evenly;

1-2) Step 1-1) to give the mixture was added to an extruder to be an average molecular weight of 1.0 × 10 5 ~ 10.0 × 10 6 and a density of 0.940 ~ 0.976g / cm 3 of the high molecular weight polyethylene and The antioxidant is dissolved in the porogen and is continuously extruded from the extruder.
The method of preparing a battery separator according to claim 6, wherein the step 2) comprises the following steps:

2-1) placing the polymer composition continuously extruded in step 1) into a slit die in a vacuum distillation chamber;

2-2) The polymer composition was extruded through a slit die onto a casting chill roll and cast into a ribbon at a casting temperature.
The method for preparing a battery separator according to claim 6, wherein the ribbon obtained in the step 2) is biaxially stretched into a film by vacuum distillation to remove the The pore former is specifically prepared by subjecting the ribbon obtained in the step 2) to a vacuum distillation chamber for vacuum distillation while feeding to a biaxial stretching machine to stretch the ribbon.
The method for preparing a battery separator according to claim 6, wherein in the step 4), the heat setting temperature is 100 to 150 ° C; and the heat setting time is 10 to 20 minutes.
A battery separator, which is obtained by the production method according to any one of claims 6 to 10.
The battery separator according to claim 11, wherein the battery separator has a thickness of 5 to 30 μm, a pore diameter of 0.3 to 0.8 μm, and a porosity of 30% to 60%.