CN114583388A - High-hydrophilicity polyolefin film and preparation method thereof - Google Patents

High-hydrophilicity polyolefin film and preparation method thereof Download PDF

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CN114583388A
CN114583388A CN202210169054.5A CN202210169054A CN114583388A CN 114583388 A CN114583388 A CN 114583388A CN 202210169054 A CN202210169054 A CN 202210169054A CN 114583388 A CN114583388 A CN 114583388A
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polyolefin
multilayer
melt
organic compound
hydrophilicity
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CN114583388B (en
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李志平
陈平绪
叶南飚
陈延安
程文超
张引龙
谭亚辉
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Shanghai Kingfa Science and Technology Co Ltd
Jiangsu Kingfa New Material Co Ltd
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Shanghai Kingfa Science and Technology Co Ltd
Jiangsu Kingfa New Material Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H01M50/406—Moulding; Embossing; Cutting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Cell Separators (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Abstract

The invention discloses a high-hydrophilicity polyolefin film and a preparation method thereof, belonging to the technical field of polyolefin materials. The product prepared by the method has good hydrophilicity, is stable after being soaked in electrolyte, has high ionic conductivity, has high specificity on target ion transmission when being applied to a new energy battery diaphragm, can improve the charge and discharge performance and capacity of the battery, and prolongs the service life of the battery.

Description

High-hydrophilicity polyolefin film and preparation method thereof
Technical Field
The invention relates to the technical field of polyolefin materials, in particular to a high-hydrophilicity polyolefin film and a preparation method thereof.
Background
Polyolefins generally refer to a generic term for thermoplastic resins obtained by polymerizing or copolymerizing an α -olefin such as ethylene or propylene, and some cyclic olefins, among which polyethylene and polypropylene are most common. The polyolefin has the characteristics of small relative density, good chemical resistance and water resistance, good mechanical strength, good electrical insulation property and the like, and can be used for various products such as films, pipes, plates, wires and cables and the like.
The lithium ion battery mainly comprises an electrode material, an electrolyte, a diaphragm and a battery shell packaging material. The diaphragm is an important component of the lithium ion battery and is used for separating the positive electrode from the negative electrode so as to prevent the internal short circuit of the battery, allow electrolyte ions to freely pass through and complete the function of the electrochemical charge-discharge process. The performance of the diaphragm determines the interface structure, internal resistance and the like of the battery, directly influences the capacity, cycle performance, safety performance and other characteristics of the battery, and the diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery.
In the lithium ion battery diaphragm category, the polyolefin microporous membrane has the advantages of low cost, controllable size and aperture, stable chemical stability, good mechanical strength and electrochemical stability, and high-temperature self-closing performance, and ensures the safety performance of daily use of the lithium ion secondary battery. The commercial lithium ion battery diaphragm material mainly adopts a Polyethylene (PE) and polypropylene (PP) microporous membrane.
When the polyolefin film is used as a battery diaphragm, the wettability between the electrolyte and the diaphragm is important, and the better wettability is favorable for improving the affinity between the diaphragm and the electrolyte and expanding the contact surface between the diaphragm and the electrolyte, so that the ionic conductivity is increased, and the charge and discharge performance and capacity of the battery are improved; however, the membrane of the existing commercially available new energy battery (especially lithium ion battery) has poor hydrophilicity and lower ionic conductivity, and meanwhile, the stability after soaking in the electrolyte is not enough, although some researches adopt a surface modifier to modify the membrane to properly improve the hydrophilicity of the surface of the membrane and improve the electrolyte wettability of the membrane, the ion transmission rate and the battery capacity after actual use still have larger promotion space, and the properties such as micropore and the like of the membrane are not changed by the surface modification method; the polyolefin film cannot maintain long-term stability in the electrolyte, and the polyolefin film is easy to react with the electrolyte and electrode substances, so that the performance of the battery is seriously influenced, and therefore, the hydrophilicity of the existing polyolefin film still needs to be further improved.
Disclosure of Invention
Based on the defects in the prior art, the invention aims to provide the preparation method of the high-hydrophilicity polyolefin membrane, the diaphragm prepared by the method has good hydrophilicity and is stable after being soaked in electrolyte, so that the contact area between the diaphragm and the electrolyte is enlarged, the ionic conductivity is improved, the charge and discharge performance and capacity of the battery can be improved when the diaphragm is used for a new energy battery diaphragm, and the service life of the battery is prolonged.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of a high-hydrophilicity polyolefin membrane comprises the following steps:
(1) taking a polyolefin material, crushing, transferring the polyolefin material to an extruder, and performing melt extrusion to form a polyolefin melt;
(2) introducing the polyolefin melt into a multilayer co-extrusion composite distributor for layering and stacking treatment, adding an anti-sticking agent and extruding to obtain a composite multilayer melt; the mass ratio of the polyolefin melt to the anti-sticking agent is (96.5:3.5) - (97.5: 2.5); the anti-sticking agent is polyolefin master batch containing a filler component, and the mass content of the filler component in the polyolefin master batch is 4-6%;
(3) sequentially cooling and forming, annealing and unidirectionally stretching the composite multilayer melt to form a multilayer polyolefin microporous membrane;
(4) and (3) soaking the multilayer polyolefin microporous membrane in the active copolymer for modification, cleaning and drying to obtain the high-hydrophilicity polyolefin membrane.
The polyolefin material is the same as the polyolefin in the polyolefin master batch.
According to the preparation method of the high-hydrophilicity polyolefin film, the polyolefin material is used for preparing the melt, then the melt is subjected to layering and stacking treatment in the co-extrusion composite distributor, and compared with the existing single diaphragm, the composite multi-layer product can effectively inhibit substances except target ions (such as lithium ions in a lithium ion battery) from participating in ion transportation, so that the ion transmission rate of the obtained product is improved; the anti-sticking agent with higher compatibility is introduced into the composite multilayer melt, so that the uniformity of the product is not influenced, the connection of the die holes of the final product is tighter, the water flux is increased, and the hydrophilicity is enhanced; after the composite multilayer melt is subjected to cooling forming, annealing and unidirectional stretching pore-forming treatment, the pore size distribution, pore density and porosity of the film layer obtained by optimization can effectively improve the adsorption effect of the electrolyte, and meanwhile, the specific transmission of target ions (namely other metal ions cannot pass through simultaneously) can be realized, so that the charging capacity of the battery is influenced; the active copolymer is adopted to soak the multilayer polyolefin microporous membrane, so that polar groups such as hydroxyl, carbonyl and the like can be generated on the surface of the multilayer polyolefin microporous membrane, meanwhile, the membrane layer can be coarsened to a certain degree, and the final product has higher hydrophilicity.
Meanwhile, the inventor finds through experiments that the content of the filler in the anti-sticking agent cannot be too high, otherwise, the compatibility of the anti-sticking agent and the polyolefin melt is influenced, and the uniformity of the product is reduced to a certain extent, so that the micropores are unevenly distributed, and the hydrophilicity and the conductivity of the product are weakened; on the other hand, the filler has insufficient components, insufficient product connectivity and insufficient hydrophilicity.
Preferably, the filler component is at least one of natural silica, calcium carbonate, and kaolin.
Preferably, the average particle size of the filler is 10 to 50 nm.
The too large particle size easily influences the size distribution of the diaphragm aperture, the too small particle size easily causes agglomeration, and further influences the diaphragm aperture, so that the hydrophilicity and the conductivity of the product are changed.
Preferably, the multilayer polyolefin microporesThe membrane has a pore size distribution of 30 to 50nm and a pore density of 8.5 to 9X 109Per cm3The porosity is 8-10%.
The pore size distribution, pore density and porosity of the multilayer polyolefin microporous membrane were measured with reference to astm f316-03(2019), standard test method for characterizing pore size of membrane filters by bubble point and mean flow pore test.
Preferably, the thickness of the multi-layer polyolefin microporous membrane is 10-30 μm.
The thickness is measured according to GB/T6672-2001 Plastic film and sheet thickness measuring Measure method.
The ionic transmission efficiency of the final product can be influenced by the excessive or insufficient thickness of the multilayer polyolefin microporous membrane, and the thickness of the multilayer polyolefin microporous membrane is optimal to be 10-30 mu m through tests. The difference of the pore structure of the product can also cause the performance effect of the product to change: if the pore size distribution is low, the pore density is low or the porosity is small, the pore structure of the product is insufficient, a communicated target ion transmission network is difficult to form, the conductivity is low, the electrolyte is difficult to infiltrate, and the hydrophilicity is insufficient; too large hole structures (or increased hole surface density) may cause insufficient mechanical properties in application, and the electrolyte is prone to uneven stress or puncture after being soaked, and may also have a micro short circuit phenomenon, and the service performance is also difficult to guarantee.
Preferably, the temperature of the extruder in the step (1) during melt extrusion is 220-260 ℃.
Preferably, the temperature of the co-extrusion composite distributor in the step (2) is 200-240 ℃ when the layered superposition treatment is carried out, and the number of the flow channels is 2-8.
Under the conditions, the thickness of the layer of the obtained composite multilayer melt after cooling forming is moderate, and the multilayer structure effectively blocks the movement between the positive electrode and the negative electrode of other metal ions while not influencing the target ion transmission efficiency in the new energy battery.
Preferably, the cooling forming in the step (3) is carried out by adopting a cooling wheel, and the temperature of the cooling wheel is 30-100 ℃; the temperature during the annealing treatment is 100-150 ℃, and the time is 1-10 h.
When the product is cooled and formed, the selected parameters have certain influence on the hole structure and the thickness of the product, after the hole is formed by unidirectional stretching under the optimized parameters, the porosity and the hole density of the product are more optimized, the thickness is more moderate, the specificity of target ions is higher when the target ions are transmitted, the battery capacity is higher, and the stability of the product after the product is soaked in electrolyte is better.
Preferably, the multilayer polyolefin microporous membrane in the step (4) is also pretreated before being soaked and modified in the active copolymer, and the pretreatment comprises the following steps: and (3) adding the multilayer polyolefin microporous membrane into a potassium dichromate solution, soaking, washing and drying.
The multilayer polyolefin microporous membrane is soaked by potassium dichromate solution, so that the surface of the multilayer polyolefin microporous membrane can be oxidized to a certain extent, hydroxyl groups and other groups are generated on the surface in advance, the hydrophilicity of the product is further improved, and the subsequent active copolymer modification efficiency can be improved.
Preferably, the active copolymer in the step (4) is obtained by initiating a reaction of an initiator C on a copolymer precursor obtained by a copolymerization reaction of an organic compound A and an organic compound B;
more preferably, the mass ratio of the organic compound A to the organic compound B is (2.5-3.5): (1.5-2.5), wherein the organic compound A is an aromatic vinyl monomer, and the organic compound B is a vinyl monomer;
more preferably, the aromatic vinyl monomer is at least one of styrene, alpha-methyl styrene, 3-methyl styrene, 4-propyl styrene and 4-cyclohexyl styrene; the vinyl monomer is at least one of acrylic acid and 2-acrylamide.
More preferably, the mass ratio of the copolymer precursor to the initiator C is (4.5-5.5): 1;
more preferably, the initiator C is at least one of dimethylaminoethyl methacrylate and 2-acrylamide-2-methylpropanesulfonic acid.
Another object of the present invention is to provide a highly hydrophilic polyolefin film prepared by the method for preparing a highly hydrophilic polyolefin film.
The high-hydrophilicity polyolefin membrane prepared by the preparation method provided by the invention has strong hydrophilicity and high ionic conductivity, has high transmission specificity to target ions (such as lithium ions, sodium ions, potassium ions and the like) when being used in a new energy battery, can effectively improve the charge and discharge performance and capacity of the battery, and prolongs the service life.
The preparation method of the high-hydrophilicity polyolefin membrane has the beneficial effects that the product prepared by the method has good hydrophilicity, is stable after being soaked in electrolyte, has high ionic conductivity, has high specificity on target ion transmission when being applied to a new energy battery diaphragm, can improve the charge and discharge performance and capacity of a battery, and prolongs the service life of the battery. The invention also provides the high-hydrophilicity polyolefin membrane prepared by the preparation method and a new energy battery containing the high-hydrophilicity polyolefin membrane.
Detailed Description
In order to better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to specific examples and comparative examples, which are intended to be understood in detail, but not intended to limit the invention. All other embodiments obtained by a person skilled in the art without making any inventive step are within the scope of protection of the present invention. The experimental reagents and instruments designed for the implementation of the present invention are common reagents and instruments unless otherwise specified.
Wherein, the raw materials used in each example and comparative example comprise:
polypropylene material: commercially available polypropylene resins;
polyethylene materials: commercially available polyethylene resins;
anti-sticking agent: self-control, the self-control step does: uniformly mixing commercially available polypropylene resin and a filler (commercially available natural silica or commercially available nano calcium carbonate) in a high-speed mixer, putting the mixture into a double-screw extruder, mixing, melting, granulating and drying to obtain the anti-sticking agent polyolefin master batch;
potassium dichromate solution: a commercially available potassium dichromate solution with a mass concentration of 10 wt% was prepared.
Example 1
In the embodiment of the highly hydrophilic polyolefin film and the method for preparing the same according to the present invention, the method for preparing the highly hydrophilic polyolefin film comprises the steps of:
(1) crushing a polypropylene material, transferring the crushed polypropylene material to an extruder, and performing melt extrusion at 240 ℃ to form a polyolefin melt;
(2) introducing the polyolefin melt into a multilayer co-extrusion composite distributor (the number of runners is 2-8), carrying out layering and overlapping treatment at 210 ℃, adding an anti-sticking agent, and extruding to obtain a composite multilayer melt; the mass ratio of the polyolefin melt to the anti-sticking agent is 97: 3; the anti-sticking agent is polyolefin master batch containing a commercial natural silica component, and the mass content of the filler component in the polyolefin master batch is 5%; the average particle size of the natural silica after screening is 30 nm;
(3) sequentially cooling and molding the composite multilayer melt (the temperature of a cooling wheel is 60 ℃), annealing (the temperature is 100 ℃ and the time is 5 hours) and performing unidirectional stretching pore-forming treatment to obtain a multilayer polyolefin microporous membrane; the thickness of the multi-layer polyolefin microporous membrane is 20 mu m, the average pore size distribution is 30nm, and the pore density is 9 multiplied by 109Per cm3The porosity is 10%;
(4) soaking the multilayer polyolefin microporous membrane in a potassium dichromate solution for 4min, washing, drying, then placing the multilayer polyolefin microporous membrane into an active copolymer at normal temperature, soaking for 2-4 h for modification, washing and drying at 30-50 ℃ to obtain the high-hydrophilicity polyolefin membrane; the active copolymer is obtained by initiating a reaction of an initiator C on a copolymer precursor obtained by carrying out a copolymerization reaction on an organic compound A and an organic compound B; the mass ratio of the organic compound A to the organic compound B is 3:2, and the organic compound A is commercially available alpha-methyl styrene; the organic compound B is commercially available acrylic acid; the mass ratio of the copolymer precursor to the initiator C is 5: 1; the initiator C is commercially available dimethylaminoethyl methacrylate.
Example 2
In the embodiment of the highly hydrophilic polyolefin film and the method for preparing the same according to the present invention, the method for preparing the highly hydrophilic polyolefin film comprises the steps of:
(1) crushing a polypropylene material, transferring the crushed polypropylene material to an extruder, and performing melt extrusion at 260 ℃ to form a polyolefin melt;
(2) introducing the polyolefin melt into a multilayer co-extrusion composite distributor (the number of runners is 2-8), carrying out layering and stacking treatment at 240 ℃, adding an anti-sticking agent, and extruding to obtain a composite multilayer melt; the mass ratio of the polyolefin melt to the anti-sticking agent is 97: 3; the anti-sticking agent is polyolefin master batch containing a commercially available natural silica component, and the mass content of the filler component in the polyolefin master batch is 5%; the average particle size of the natural silica after screening is 30 nm;
(3) sequentially cooling and molding the composite multilayer melt (the temperature of a cooling wheel is 100 ℃), annealing (the temperature is 150 ℃ and the time is 10 hours) and performing unidirectional stretching pore-forming treatment to obtain a multilayer polyolefin microporous membrane; the thickness of the multi-layer polyolefin microporous membrane is 10 mu m, the average pore size distribution is 40nm, and the pore density is 9 multiplied by 109Per cm3The porosity is 10%;
(4) soaking the multilayer polyolefin microporous membrane in a potassium dichromate solution for 4min, washing, drying, then placing the multilayer polyolefin microporous membrane into an active copolymer at normal temperature, soaking for 2-4 h for modification, washing and drying at 30-50 ℃ to obtain the high-hydrophilicity polyolefin membrane; the active copolymer is obtained by initiating a reaction of an initiator C on a copolymer precursor obtained by carrying out a copolymerization reaction on an organic compound A and an organic compound B; the mass ratio of the organic compound A to the organic compound B is 3.5:1.5, and the organic compound A is commercially available styrene; the organic compound B is commercially available 2-acrylamide; the mass ratio of the copolymer precursor to the initiator C is 5.5: 1; the initiator C is commercially available 2-acrylamide-2-methylpropanesulfonic acid.
Example 3
In the embodiment of the highly hydrophilic polyolefin film and the method for preparing the same according to the present invention, the method for preparing the highly hydrophilic polyolefin film comprises the steps of:
(1) crushing polyethylene materials, transferring the crushed polyethylene materials into an extruder, and performing melt extrusion at 220 ℃ to form a polyolefin melt;
(2) introducing the polyolefin melt into a multilayer co-extrusion composite distributor (the number of runners is 2-8), carrying out layering and stacking treatment at 200 ℃, adding an anti-sticking agent, and extruding to obtain a composite multilayer melt; the mass ratio of the polyolefin melt to the anti-sticking agent is 97: 3; the anti-sticking agent is polyolefin master batch containing nano calcium carbonate, and the mass content of the filler component in the polyolefin master batch is 5%; the average particle size of the nano calcium carbonate after screening is 30 nm;
(3) sequentially cooling and forming the composite multilayer melt (the temperature of a cooling wheel is 30 ℃), annealing (the temperature is 100 ℃ and the time is 5 hours) and performing unidirectional stretching pore-forming treatment to obtain a multilayer polyolefin microporous membrane; the thickness of the multi-layer polyolefin microporous membrane is 30 mu m, the average pore size distribution is 50nm, and the pore density is 8.5 multiplied by 109Per cm3The porosity is 8%;
(4) soaking the multilayer polyolefin microporous membrane in a potassium dichromate solution for 4min, washing, drying, then placing the multilayer polyolefin microporous membrane into an active copolymer at normal temperature, soaking for 2-4 h for modification, washing and drying at 30-50 ℃ to obtain the high-hydrophilicity polyolefin membrane; the active copolymer is obtained by initiating a reaction of an initiator C on a copolymer precursor obtained by carrying out a copolymerization reaction on an organic compound A and an organic compound B; the mass ratio of the organic compound A to the organic compound B is 2.5:2.5, and the organic compound A is commercially available alpha-methyl styrene; the organic compound B is commercially available acrylic acid; the mass ratio of the copolymer precursor to the initiator C is 4.5: 1; the initiator C is commercially available dimethylaminoethyl methacrylate.
Example 4
The difference between this example and example 1 is that the cooling wheel temperature for cooling and forming the multilayer melt is 110 ℃, the annealing temperature is 160 ℃ and the time is 1 h. The polyolefin microporous membrane obtained by the uniaxial tension pore-forming treatment has the thickness of 8um, the average pore size distribution of 60nm and the pore density of 8 multiplied by 109Per cm3The porosity is 10%
Example 5
The difference between this example and example 1 is that the cooling wheel temperature for cooling and forming the multilayer melt is 20 ℃, the annealing temperature is 90 ℃ and the time is 5 h. Polyolefin obtained by uniaxial tension pore-forming treatmentThe microporous membrane has a thickness of 40um, an average pore size distribution of 40nm, and a pore density of 7.5 × 109Per cm3The porosity was 8%.
Example 6
The difference between this example and example 1 is only that the content of the filler component in the polyolefin masterbatch in the step (2) is 4% by mass.
Example 7
The difference between this example and example 1 is only that the content of the filler component in the polyolefin masterbatch in the step (2) is 6% by mass.
Example 8
This example differs from example 1 only in that the ratio of the mass of polyolefin melt to antiblocking agent is 96.5: 3.5.
Example 9
This example differs from example 1 only in that the ratio of the mass of polyolefin melt to antiblocking agent is 97.5: 2.5.
Example 10
This example differs from example 1 only in that the natural silica has an average particle size of 10nm after screening.
Example 11
This example differs from example 1 only in that the natural silica has an average particle size of 50nm after screening.
Example 12
This example differs from example 1 only in that the natural silica has an average particle size of 8nm after screening.
Example 13
This example differs from example 1 only in that the natural silica has an average particle size of 70nm after screening.
Comparative example 1
The comparative example differs from example 1 only in that no antiblocking agent was added in step (2).
Comparative example 2
The comparative example differs from example 1 only in that the ratio by mass of polyolefin melt to antiblocking agent in step (2) is 94: 6.
Comparative example 3
The comparative example differs from example 1 only in that the ratio of the mass of polyolefin melt to antiblocking agent in step (2) is 98: 2.
comparative example 4
The comparative example is different from example 1 only in that the content of the filler component in the polyolefin mother particle in the step (2) is 10% by mass.
Comparative example 5
The comparative example is different from example 1 only in that the filler component is contained in the polyolefin masterbatch in an amount of 1% by mass in the step (2).
Comparative example 6
The comparative example differs from example 1 only in that the multilayer polyolefin microporous membrane obtained in the step (4) is not soaked with the active copolymer.
Effect example 1
To verify the performance of each product, each example and comparative example was cut into 6 x cm size (thickness measured for each sample) samples and the static water contact angle of the microporous membrane was measured directly with a HARKE-SPCA contact angle tester, distilled water; and simultaneously, adopting a Shanghai Hua CHI electrochemical workstation to carry out the test calculation of the product conductivity by an alternating current impedance method: each cut product is used as a conductive diaphragm, so that the conductivity of the diaphragm is calculated conveniently, the conductivity of the electrolyte is ignored, and a formula is adopted:
Figure BDA0003516059550000101
wherein: d-average thickness of the separator in cm;
Rs-membrane resistance in Ω;
area of S-electrode in cm2；
The diaphragm resistance is carried out in electrolyte, a diaphragm cut to be 6 x 6cm in size is soaked in the electrolyte for 10min, the electrolyte is 1MLiC10 system commercial electrolyte, the diaphragm soaked in the electrolyte is placed in a test fixture, and test electrodes are 2 metal flat plates which are slightly smaller than the diaphragm in size and coated with polytetrafluoroethylene at two ends. The average resistance calculated by testing the results of 3 times is the resistance of the diaphragm.
The results were counted and the test results are shown in table 1.
TABLE 1
Figure BDA0003516059550000102
Figure BDA0003516059550000111
As can be seen from the above data, the products of the examples have good hydrophilicity (contact angle < 6 ℃) and electrical conductivity (conductivity > 30mS cm) after immersion in the electrolyte-1) The method can be effectively used for replacing the existing product to prepare the lithium ion battery diaphragm. And the product of the comparative example 1 does not contain an anti-sticking agent in the preparation process, so that the microporous structure of the product is not ideal, and the hydrophilicity and the conductivity of the product are poor. From examples 1, 6 to 7 and comparative examples 4 to 5, it can be seen that the amount of the filler in the anti-adhesion agent of the product component has a direct influence on the hydrophilicity and conductivity of the product, and if the amount is too small, the hydrophilicity of the product is insufficient; if the content is too much, micropores of a final product are not uniformly distributed, and the hydrophilicity and the conductivity are both obviously reduced, and the product with the content in the preferable range of 4-6% can ensure ideal performance. As can be seen from the comparison of the product performances of the examples 10 to 13, the particle size of the filler also has certain influence on the product performances, and the effect is optimal when the average particle size is 10 to 50 nm. On the other hand, if the mass ratio of the polyolefin melt to the antiblocking agent in the product component is too small or too large, as shown in comparative examples 2 and 3, the product has difficulty in achieving the desired conductivity. The thickness of the product obtained in example 1 is within the range of 10 to 30 μm, the pore diameter distribution is within the range of 30 to 50nm, and the pore density is 8.5 to 9 × 109Per cm3In this range, the porosity is in the range of 8-10%, which is better hydrophilic and conductive than the non-preferred range of the products of examples 4 and 5.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims (9)

1. A preparation method of a high-hydrophilicity polyolefin membrane is characterized by comprising the following steps:
(1) taking a polyolefin material, crushing, transferring the polyolefin material to an extruder, and performing melt extrusion to form a polyolefin melt;
(2) introducing the polyolefin melt into a multilayer co-extrusion composite distributor for layering and stacking treatment, adding an anti-sticking agent and extruding to obtain a composite multilayer melt; the mass ratio of the polyolefin melt to the anti-sticking agent is (96.5:3.5) - (97.5: 2.5); the anti-sticking agent is polyolefin master batch containing a filler component, and the mass content of the filler component in the polyolefin master batch is 4-6%;
(3) sequentially cooling and forming, annealing and unidirectionally stretching the composite multilayer melt to form a multilayer polyolefin microporous membrane;
(4) and (3) soaking the multilayer polyolefin microporous membrane in the active copolymer for modification, cleaning and drying to obtain the high-hydrophilicity polyolefin membrane.
2. The method for producing a highly hydrophilic polyolefin film according to claim 1,
the thickness of the multilayer polyolefin microporous membrane is 10-30 mu m, the pore size distribution is 30-50 nm, and the pore density is 8.5-9 multiplied by 109Per cm3The porosity is 8-10%.
3. The method for preparing the highly hydrophilic polyolefin film according to claim 1, wherein the temperature of the co-extrusion composite distributor in the step (2) is 200-240 ℃ and the number of the flow channels is 2-8 when the layered stacking treatment is performed.
4. The method for preparing the highly hydrophilic polyolefin film according to claim 1, wherein the cooling molding in the step (3) is performed by using a cooling wheel, and the temperature of the cooling wheel is 30-100 ℃; the temperature during the annealing treatment is 100-150 ℃, and the time is 1-10 h.
5. The method of preparing the highly hydrophilic polyolefin film according to claim 1, wherein the filler has an average particle diameter of 10 to 50 nm.
6. The method for preparing the highly hydrophilic polyolefin membrane according to claim 1, wherein the multilayer polyolefin microporous membrane of step (4) is further subjected to a pretreatment before being modified by soaking in the active copolymer, and the pretreatment comprises the following steps: and (3) adding the multilayer polyolefin microporous membrane into a potassium dichromate solution, soaking, washing and drying.
7. The method for preparing a highly hydrophilic polyolefin film according to claim 1, wherein the reactive copolymer in the step (4) is obtained by initiating a reaction of an initiator C on a copolymer precursor obtained by copolymerization of an organic compound A and an organic compound B;
preferably, the mass ratio of the organic compound A to the organic compound B is (2.5-3.5): (1.5-2.5), wherein the organic compound A is an aromatic vinyl monomer, and the organic compound B is a vinyl monomer;
the mass ratio of the copolymer precursor to the initiator C is (4.5-5.5): 1;
the initiator C is at least one of dimethylaminoethyl methacrylate and 2-acrylamide-2-methylpropanesulfonic acid.
8. The highly hydrophilic polyolefin film produced by the method according to any one of claims 1 to 7.
9. A lithium ion battery comprising the highly hydrophilic polyolefin film according to claim 8.
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