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Polypropylene microporous membrane as well as preparation method and application thereof

A technology of polypropylene microporous membrane and polypropylene, which is applied in the direction of electrical components, electrochemical generators, circuits, etc., can solve the problem of high drafting conditions, reduced controllability of dry membrane production process, and large pore size distribution of membrane pores and other issues, to achieve excellent air permeability and mechanical strength, good industrial application prospects, and little difference in mechanical strength

Pending Publication Date: 2021-03-26
CHINA PETROLEUM & CHEM CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, this method requires high drawing conditions, and the polypropylene prepared by stretching still has a unidirectional crack-like pore structure, which is not conducive to the improvement of the comprehensive mechanical properties of the separator; patent CN 105633328B discloses a lithium-ion battery polypropylene A porous diaphragm and a preparation method thereof, which adopt an in-situ composite method, add a pore shape modifier and a pore size regulator to a polypropylene resin, and the mixture is melted and cast, biaxially stretched, and then heat-set to obtain a polypropylene porous diaphragm. The addition of additives and regulators is conducive to the improvement of membrane porosity and good air permeability
However, the addition of the two agents reduces the controllability of the dry membrane process, and the pore size distribution of the membrane is relatively large (60-300nm).
On the other hand, a large amount of organic solvents are used in the process, and the organic solvents are completely volatilized during the preparation process, which will cause serious pollution and hazards in the film-making process; patent CN102604203A discloses an improved microporous polymer film, Composed of polypropylene homopolymer, β crystal nucleating agent, polymer additives and inorganic modifiers
The film has good uniformity, high permeability and strong dimensional stability, but its puncture resistance is weak and the porosity is too high

Method used

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  • Polypropylene microporous membrane as well as preparation method and application thereof
  • Polypropylene microporous membrane as well as preparation method and application thereof
  • Polypropylene microporous membrane as well as preparation method and application thereof

Examples

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preparation example Construction

[0027] The invention provides a method for preparing a polypropylene microporous membrane, comprising: mixing polypropylene with a composite diluent to obtain a premix, wherein the polypropylene accounts for 25% to 60% by mass of the premix, The compound diluent accounts for 40% to 75% by mass of the premix; the premix is ​​melt-extruded and cooled to form a primary film; an extractant is used to remove the primary film Composite diluent, then heat-treated to obtain the polypropylene microporous membrane; wherein, the composite diluent includes a high-temperature good solvent and a high-temperature poor solvent, and the high-temperature good solvent is selected from myristyl alcohol, cetyl alcohol, stearyl alcohol, One or more of alcohol, eicosanol; the high-temperature poor solvent is selected from one or more of benzyl alcohol, diphenyl carbonate, benzophenone and dimethyl sulfone, preferably benzophenone ; The mass percentage of the high-temperature good solvent in the comp...

Embodiment 1

[0048] Polypropylene (number-average molecular weight 50,000Da, polydispersity coefficient is 6) is mixed with composite diluent cetyl alcohol and benzophenone to form a premix, wherein the mass percentage of polypropylene is 35%, and the mass percentage of cetyl alcohol is 38%, and the mass percentage of benzophenone is 27%. The premixed material was added into a screw extruder, melted and mixed uniformly to form a film-forming liquid, wherein the melting temperature was 190°C. The film-making solution is molded by an extruder and poured into cooling water to solidify to obtain a nascent film. The cooling temperature is 25°C. The obtained nascent film is stretched horizontally and vertically, and then immersed in ethanol for extraction to remove cetyl alcohol and benzophenone. The extracted film was heat-treated in water at 90° C. for 60 min to obtain a polypropylene microporous film.

[0049] figure 2 It is the scanning electron micrograph of the polypropylene microporou...

Embodiment 2

[0051] The polypropylene microporous membrane is prepared according to the method of Example 1, the difference is that the composite diluent is cetyl alcohol and diphenyl carbonate, wherein the mass percentage of polypropylene is 35%, the mass percentage of cetyl alcohol is 38%, and diphenyl carbonate The mass percentage of ester is 27%. There is a phenomenon of liquid-liquid phase separation in this system. The microporous membrane was tested for mechanical properties, air permeability and porosity. The results and the maximum polymer mass concentration corresponding to the liquid-liquid phase separation zone are shown in Table 1.

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Abstract

The invention provides a preparation method of a polypropylene microporous membrane, and the comprises the following steps: mixing polypropylene and a composite diluent to obtain a premix, wherein thepolypropylene accounts for 25-60wt% of the premix, and the composite diluent accounts for 40-75wt% of the premix; and carrying out melt extrusion and cooling molding on the premix, then removing thecomposite diluent by adopting an extraction agent, and then carrying out heat treatment to obtain a polypropylene microporous membrane, wherein the composite diluent comprises a high-temperature goodsolvent and a high-temperature poor solvent, the high-temperature good solvent is selected from one or more of tetradecanol, hexadecanol, octadecanol and eicosanol, the high-temperature poor solvent is selected from one or more of benzyl alcohol, diphenyl carbonate, benzophenone and dimethyl sulfone, the high-temperature good solvent accounts for 30wt%-60wt% of the composite diluent, and the high-temperature poor solvent accounts for 40wt%-70wt% of the composite diluent. By adopting the specific composite diluent, the obtained polypropylene microporous membrane has the advantages of pore sizedistribution, no macropore defect, enhanced mechanical strength, and small difference between transverse and longitudinal mechanical strength, and provides guarantee for the safety performance of themembrane, and is suitable for being used as a lithium battery membrane material.

Description

technical field [0001] The invention belongs to the technical field of polymer material preparation, and in particular relates to a polypropylene microporous membrane and its preparation method and application. Background technique [0002] Lithium battery separator is one of the core materials in lithium-ion batteries. Its main function is to separate the positive and negative electrodes of the battery, while ensuring that lithium ions can pass freely between the positive and negative electrodes. [0003] The currently marketed lithium-ion battery separators mainly include dry-process uniaxially stretched separators, dry-process biaxially stretched separators and wet-process separators. The main difference between these membrane preparation methods lies in the different pore-forming mechanisms of the micropores. In our country, the dry process diaphragm is almost self-sufficient. The dry process is to mix the polymer and additive raw materials, form a uniform melt at high...

Claims

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Application Information

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IPC IPC(8): H01M50/403H01M50/417H01M10/0525
CPCH01M10/0525Y02E60/10
Inventor 庞博杜泽学
Owner CHINA PETROLEUM & CHEM CORP
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