CN114243213B - Ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles and preparation method thereof - Google Patents
Ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high-load ceramic particle ultrathin high-strength multilayer composite diaphragm and a preparation method thereof, wherein the battery diaphragm comprises a supporting layer with a microporous structure and at least one functional layer, wherein the supporting layer contains 0-20 parts of inorganic ceramic particles, 20-40 parts of low molecular weight polyethylene and 40-80 parts of ultrahigh molecular weight polyethylene, and the functional layer contains 65-95 parts of inorganic ceramic particles and 5-35 parts of ultrahigh molecular weight polyethylene. The preparation method comprises the steps of preparing mixed materials of all layers according to a set proportion, then adding a pore-foaming agent to prepare a blend, preparing a melt by utilizing the blend, forming a multilayer composite film, stretching, heat setting, and finally extracting by using an organic solvent and drying to obtain the battery diaphragm. The invention can effectively reduce the thermal shrinkage rate of the battery diaphragm under the high-temperature condition, has strong thermal stability and better absorption wettability and adsorptivity, and is suitable for large-scale industrial production.
Description
Technical Field
The invention relates to the technical field of polyethylene battery diaphragms, in particular to an ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles and a preparation method thereof.
Background
Lithium Ion Batteries (LIBs) have become the main energy storage devices in modern society, and are widely applied to various new energy devices, from portable electronic devices such as digital cameras, mobile phones and notebook computers to electric vehicles and emerging smart grids. There has been a constant effort to improve the macroscopic performance of LIBs. Despite anode and cathode related studies, separator optimization has proven to be the most effective strategy to improve LIBs performance, including safety, cycle life, power density, and energy density, among other aspects. The main function of the separator is to avoid physical contact between the electrodes. The separator allows ions to migrate during charge and discharge, but does not directly promote any cell reactions. Conventional LIBs separators are used on a large scale as polyolefin separators, i.e., polyethylene (PE) and polypropylene (PP) or a multi-layer structure thereof. At present, with the progress of science and technology, an ultra-high molecular weight polyethylene (UHMWPE) separator, which is a polyolefin film, is widely used in lithium ion batteries due to its advantages such as good chemical stability, excellent corrosion resistance, high tensile strength, and economy. However, most polyolefin separators (including UHMWPE separators) exhibit high thermal shrinkage and low affinity for liquid electrolytes in size due to their electrophilic behavior and poor electrolyte retention during cycling, thereby limiting their application in high temperature, high capacity and high power LIBs.
In order to solve the above problems of the conventional polyolefin separator, research researchers at home and abroad have conducted a great deal of research work in recent ten years, wherein the preparation of the multilayer ceramic composite separator by surface coating or graft modification of the conventional polyolefin separator is one of the most effective means for improving the overall performance of the separator, and the multilayer ceramic composite separator has high strength of the conventional polyolefin layer and high thermal stability and electrolyte affinity of the inorganic layer. At present, a series of ceramic materials and modified materials thereof are used for modifying traditional polyolefin diaphragms, such as SiO2, al2O3, zrO2 and the like, and the content of ceramic particles is generally higher than 60wt%. The selection of the ceramic filler binder is crucial in the process of preparing the multilayer composite diaphragm by adopting direct surface coating, the currently widely used binders mainly comprise PVDF, cellulose Diacetate (CDA), polyurethane (PU) and the like, and sometimes, a plurality of binders are also used in combination in order to further improve the bonding effect. The multilayer ceramic composite separator prepared by surface coating can improve the thermal stability and the electrolyte affinity of the separator to a certain extent, but can also cause some adverse results, such as: 1) Resulting in an increase in the thickness of the separator (the total thickness of the composite separator substantially exceeds 30 μm), thereby increasing the weight of the battery and reducing the energy density; 2) The polymer binder causes substrate micropore blockage, reducing battery ionic conductivity and high power capability; 3) Because the polarity difference exists between the polyolefin substrate layer and the coating layer, the coating layer can be separated from the polyolefin diaphragm in the charging and discharging process, so that the cycle life of the battery is shortened and the performance of the battery is reduced. In order to improve the adhesion between the ceramic particles and the polyolefin diaphragm, researchers adopt methods such as adhesive crosslinking modification, direct chemical grafting of a polyolefin substrate with a ceramic filler and the like to prepare the multilayer composite diaphragm. Generally, electron beam irradiation, ultraviolet ozone (UVO) plasma treatment, chemical agent treatment, etc. are often used to increase the grafting rate of the ceramic particles prior to chemically grafting the ceramic filler. The surface chemical grafting method overcomes the problem of poor adhesion of the surface coating method and improves the performance of the multilayer ceramic composite membrane, but the technical process is complex and high in cost, special energy-consuming equipment is required, and the large-scale practical application of the surface chemical grafting method is hindered.
Therefore, aiming at the problems of large thickness, poor bonding property, easy blockage of micropores, complex process, high cost and the like in the coating or chemical grafting manufacturing process of the multilayer ceramic composite diaphragm, if a common polyolefin biaxial tension forming method is directly adopted to prepare the polyolefin/inorganic nanoparticle multilayer composite diaphragm, the problems are solved, a brand new diaphragm and a manufacturing method thereof are formed, and the advantages of the battery diaphragm can be better improved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles, when the diaphragm is applied to a lithium ion battery, the thermal shrinkage rate of the lithium ion battery under the high-temperature condition can be effectively reduced, the thermal stability of the lithium ion battery is high, the diaphragm has better absorption wettability and adsorbability on electrolyte, the battery performance can be effectively improved, and the diaphragm is suitable for large-scale industrial production.
The invention also aims to provide a preparation method of the ultrathin high-strength multilayer composite diaphragm with the high-load ceramic particles.
The technical scheme of the invention is as follows: the ultrathin high-strength multilayer composite diaphragm comprises a supporting layer and at least one functional layer, wherein the functional layer covers one side or two sides of the supporting layer, and microporous structures are arranged in the supporting layer and the functional layer; the support layer comprises the following main components in parts by weight: 0-20 parts of inorganic ceramic particles, 20-40 parts of low molecular weight polyethylene and 40-80 parts of ultrahigh molecular weight polyethylene; the functional layer comprises the following main components in parts by mass: 65-95 parts of inorganic ceramic particles and 5-35 parts of ultrahigh molecular weight polyethylene. The battery diaphragm adopts a structure of a multilayer composite membrane, a microporous membrane formed by low-molecular-weight polyethylene and ultrahigh-molecular-weight polyethylene or a microporous membrane of low-molecular-weight polyethylene and ultrahigh-molecular-weight polyethylene with low content of inorganic ceramic particles in the middle layer is formed by a biaxial stretching technology and is called a supporting layer, so that good mechanical support is provided for the whole battery diaphragm, and the ultrahigh-molecular-weight polyethylene has good tensile property and mechanical property in the supporting layer; the two sides or one side of the supporting layer are provided with the ultra-high molecular weight polyethylene microporous membrane with high content of inorganic ceramic particles, which is called as a functional layer, so that the battery diaphragm is provided with good electrolyte wettability, thermal stability, electrochemical stability and battery performance.
Preferably, the molecular weight of the ultra-high molecular weight polyethylene is 150 to 600 ten thousand; the molecular weights of the ultra-high molecular weight polyethylene used by the supporting layer and the functional layer are the same or different, and the molecular weights of the ultra-high molecular weight polyethylene used by different functional layers are the same or different.
Preferably, the low molecular weight polyethylene has a molecular weight of 15 to 60 ten thousand.
The inorganic ceramic particles are SiO 2 、Al 2 O 3 、TiO 2 、BaSO 4 Or PZT, or other inorganic nano materials with high temperature resistance and electrophilic electrolyte.
In the supporting layer and the functional layer, the porosity of the microporous structure is 50-90%, and the pore size distribution is 0.01-10 μm; the porosity of the support layer and the functional layer may be the same or different, and the porosity may be the same or different between different functional layers.
The thickness of the support layer is 1-10 μm, and the thickness of the functional layer is 1-10 μm.
The invention discloses a preparation method of the ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles, which adopts a coextrusion-biaxial stretching preparation method and specifically comprises the following steps:
(1) A dry mixing stage: according to a set proportion, inorganic ceramic particles, low molecular weight polyethylene and ultrahigh molecular weight polyethylene or low molecular weight polyethylene and ultrahigh molecular weight polyethylene are put into a high-speed mixer for dispersion and mixing to form a support layer mixed material; placing inorganic ceramic particles and ultrahigh molecular weight polyethylene into a high-speed mixer for dispersion and mixing to form a functional layer mixed material;
(2) A wet mixing stage: respectively adding pore-foaming agents into the supporting layer mixed material and the functional layer mixed material, fully mixing and uniformly dispersing, and standing or stirring for 6-72 hours at the temperature of 25-100 ℃ to respectively form a supporting layer blend and a functional layer blend;
(3) Preparation stage of multilayer composite gel film: respectively putting the supporting layer blend and the functional layer blend into corresponding extruders for melt blending, plasticizing and conveying to form corresponding supporting layer melt and functional layer melt; extruding and molding the supporting layer melt and the functional layer melt through a co-extrusion die head to form a multi-layer composite gel film;
(4) And (3) a biaxial stretching stage: adopting asynchronous biaxial stretching (namely transverse stretching and longitudinal stretching or longitudinal stretching and transverse stretching) or synchronous biaxial stretching (namely transverse stretching and longitudinal stretching are carried out synchronously) to carry out heat setting treatment;
(5) A battery diaphragm preparation stage: and sequentially carrying out organic solvent extraction and drying on the biaxially oriented multilayer composite membrane to form a microporous membrane, and finally obtaining the ultrathin high-strength multilayer composite membrane with high-load ceramic particles.
In the step (2), the mass of the pore-foaming agent added into the supporting layer mixed material or the functional layer mixed material accounts for 50-90% of the total mass of the blend formed after mixing; the pore-forming agent is polymer pore-forming agent (such as PVP, PEG, PVA, etc.) or small molecule pore-forming agent (such as mineral oil, kerosene, decalin, sodium chloride, potassium carbonate, lithium chloride, ADC foaming agent, water, etc.).
In the step (3), when the support layer mixed material and the pore-foaming agent or the functional layer mixed material and the pore-foaming agent are blended, the adopted blending equipment is a multi-screw extruder, a single-shaft eccentric rotor extruder or a double-shaft eccentric rotor extruder, and the plasticizing melting temperature is 180-230 ℃.
In the step (4), the stretcher is an asynchronous biaxial stretching machine or a synchronous biaxial stretching film machine, the transverse stretching ratio of the film is 3-10 times, the longitudinal stretching ratio of the film is 3-10 times, the stretching temperature is 90-120 ℃, the heat setting temperature is 100-140 ℃, and the heat setting time is 1-20 minutes.
In the step (5), the solvent used in the extraction is n-hexane, acetone, chloroform, water or alcohol and other substances capable of removing the pore-forming agent.
In the step (5), the thickness of the film is 3-30 μm, wherein the thickness of the supporting layer is 1-10 μm, the thickness of the functional layer is 1-10 μm, the diameter distribution of micropores is 0.01-10 μm, and the porosity is 50-90%.
Compared with the prior art, the invention has the following beneficial effects:
in the ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles and the preparation method thereof, the battery diaphragm is in a multilayer composite structure, the low-molecular-weight polyethylene and the ultrahigh-molecular-weight polyethylene are utilized to form a supporting layer through a better proportioning and forming process, a mechanical supporting effect is achieved, the mechanical and mechanical properties of the battery diaphragm are enhanced, one or more layers of functional layers can be arranged, and the ultrahigh-molecular-weight polyethylene film with high inorganic ceramic particle content is adopted, so that the battery diaphragm has good electrolyte wettability, good thermal stability, small thermal shrinkage, and excellent electrochemical stability and electrochemical performance. In addition, in the preparation method of the battery diaphragm, the thickness of the battery diaphragm and the distribution of the microporous structure in the battery diaphragm are adjustable by a biaxial tension technology, so that the battery diaphragm meeting the requirements can be better obtained.
When the ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles is applied to a lithium ion battery, the thermal shrinkage rate of the battery diaphragm under the high-temperature condition can be effectively reduced, the thermal stability is high, the absorption wettability and the adsorbability to electrolyte are better, the battery performance can be effectively improved, and the diaphragm is suitable for large-scale industrial production.
In addition, in the ultrathin high-strength multilayer composite membrane of the high-load ceramic particles, due to the unique properties of the inorganic nanoparticles, including good wettability and remarkable high thermal stability due to the affinity of the inorganic nanoparticles with a liquid electrolyte, the battery membrane can effectively reduce the limit of UHMWPE membranes and prolong the service life of LIBs. Compared with commercial diaphragms in the prior art and PE composite materials of other experimental researches, the multilayer composite diaphragm has more excellent performance as a battery diaphragm. Furthermore, it combines the manufacture of UHMWPE nanofibrous membranes with the modification of inorganic particles at one time, reducing the cost and time of preparation and post-treatment. The mechanical property of the diaphragm can be enhanced by adopting a multi-layer composite structure. The inorganic nano particles are added into the UHMWPE structure, so that the absorption and wettability of electrolyte can be improved, the thermal stability is enhanced, the mechanical property is maintained, and the electrochemical stability and the battery performance are ensured.
Drawings
FIG. 1 is an electron microscope image of the cross-sectional structure of the ultra-thin high-strength multilayer composite membrane with bilateral enrichment of ceramic particles prepared in example 1.
Fig. 2 is a schematic view of the contact angle of the electrolyte of the ultra-thin high-strength multilayer composite membrane with bilateral enrichment of ceramic particles prepared in example 1.
FIG. 3 is a schematic view showing the contact angle of the electrolyte of the ultra-thin high-strength multi-layer composite membrane with single-side enriched ceramic particles prepared in example 2.
FIG. 4 is a schematic view showing the contact angle of the electrolyte of the ultra-thin high-strength multi-layer composite membrane with single-side enriched ceramic particles prepared in example 3.
Fig. 5 is a schematic view showing an electrolyte contact angle of a conventional ultra-high molecular weight polyethylene battery separator manufactured in a comparative example.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Example 1
The embodiment of the invention relates to a preparation method of an ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles (bilateral enrichment of ceramic particles), which comprises the following steps:
(1) Inorganic particles SiO of functional layer material 2 Fully dispersing 180 ten thousand of supermolecule molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a high-speed mixer according to the mass ratio of 80 to 20, and fully dispersing 180 ten thousand of supermolecule molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a supporting layer material in a high-speed mixer according to the mass ratio of 60;
(2) And (2) respectively pouring the two groups of mixed materials obtained in the step (1) into a liquid paraffin pore-foaming agent, wherein the mass ratio of each mixed material to the liquid paraffin is 20. Fully stirring and uniformly dispersing, and standing for 24 hours at room temperature to obtain a functional layer and supporting layer blend;
(3) Melting, blending and plasticizing and conveying the blend of the functional layer and the supporting layer obtained in the step (2) at the temperature of 210 ℃ through an eccentric rotor extruder, feeding the blend into a three-layer co-extrusion die, feeding the blend of the functional layer into the outer two sides, feeding the blend of the supporting layer into the inner side, and forming a three-layer composite gel film after tape casting and cooling;
(4) Stretching the three-layer composite gel film obtained in the step (3) on a synchronous biaxial stretching machine, wherein the stretching ratio is 5 multiplied by 5, the stretching temperature is 100 ℃, and then, performing heat setting at 120 ℃ for 5min;
(5) And (5) subjecting the biaxially oriented film obtained in the step (4) to n-hexane ultrasonic extraction, alcohol soaking, deionized water leaching and drying to finally obtain the ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles.
An SEM cross-section of the ultra-thin high-strength multi-layer composite membrane with double-sided enriched ceramic particles obtained in this example is shown in fig. 1 (including one support layer 1 and two functional layers 2), the thickness of the functional layer is 10 μm, the thickness of the middle support layer is 5 μm, the tensile strength is 55mpa, the thermal shrinkage after being placed at 150 ℃ for 1 hour is 4.6%, and the contact angle of the electrolyte is 13.8 ° (as shown in fig. 2).
Example 2
The embodiment of the invention relates to a preparation method of an ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles (single-side enriched ceramic particles), which comprises the following specific steps:
(1) Inorganic particles SiO of functional layer material 2 Fully dispersing 180 ten thousand of supermolecule molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a high-speed mixer according to the mass ratio of 80 to 20, and fully dispersing 180 ten thousand of supermolecule molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a supporting layer material in a high-speed mixer according to the mass ratio of 60;
(2) Respectively pouring the mixed material obtained in the step (1) into a liquid paraffin pore-foaming agent, wherein the mass ratio of the mixed material to the liquid paraffin is 20. Fully stirring and uniformly dispersing, and standing for 24 hours at room temperature to obtain a functional layer and supporting layer blend;
(3) Melting, blending and plasticizing and conveying the blend of the functional layer and the support layer obtained in the step (2) at the temperature of 210 ℃ through an eccentric rotor extruder, feeding the blend into a double-layer co-extrusion die, and forming a double-layer composite gel film after casting and cooling;
(4) And (4) stretching the double-layer composite gel film obtained in the step (3) on a synchronous biaxial stretching machine, wherein the stretching ratio is 5 multiplied by 5, the stretching temperature is 100 ℃, and then, heat setting is carried out at 120 ℃ for 5min.
(5) And (4) subjecting the biaxially oriented film obtained in the step (4) to n-hexane ultrasonic extraction, alcohol soaking, deionized water leaching and drying to finally obtain the ultrathin high-strength multilayer composite diaphragm with solid content of 60% and 80% and with ceramic particles enriched on one side.
The thickness of the functional layer of the ultrathin high-strength multilayer composite diaphragm with the single-side enriched ceramic particles (the content of SiO2 is 80%) prepared by the method is 10 micrometers, the thickness of the supporting layer is 10 micrometers, the tensile strength is 49MPa, the thermal shrinkage rate is 14% after the diaphragm is placed at 150 ℃ for 1 hour, and the contact angle of electrolyte is 17.8 degrees (as shown in figure 3).
Example 3
The embodiment of the invention relates to a preparation method of an ultrathin high-strength multilayer composite diaphragm with high-load ceramic particles (single-side enriched ceramic particles), which comprises the following specific steps:
(1) Inorganic particles SiO of functional layer material 2 Fully dispersing 180 ten thousand of ultra-high molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a high mixing machine according to the mass ratio of 60;
(2) And (2) respectively pouring the mixed materials obtained in the step (1) into a liquid paraffin pore-foaming agent, wherein the mass ratio of the mixed materials to the liquid paraffin is 20. Fully stirring and uniformly dispersing, and standing for 24 hours at room temperature to obtain a functional layer and supporting layer blend;
(3) Melting, blending and plasticizing and conveying the blend of the functional layer and the support layer obtained in the step (2) at the temperature of 210 ℃ through an eccentric rotor extruder, feeding the blend into a double-layer co-extrusion die, and forming a double-layer composite gel film after casting and cooling;
(4) And (4) stretching the double-layer composite gel film obtained in the step (3) on a synchronous biaxial stretching machine, wherein the stretching ratio is 5 multiplied by 5, the stretching temperature is 100 ℃, and then, heat setting is carried out at 120 ℃ for 5min.
(5) And (4) subjecting the biaxially oriented film obtained in the step (4) to n-hexane ultrasonic extraction, alcohol soaking, deionized water leaching and drying to finally obtain the ultrathin high-strength multilayer composite diaphragm with solid content of 60% and 80% and with ceramic particles enriched on one side.
The thickness of the functional layer of the ultrathin high-strength multilayer composite diaphragm with single-side enriched ceramic particles (SiO 2 content of 60%) prepared by the method is 10 microns, the thickness of the supporting layer is 10 microns, the tensile strength is 52MPa, the thermal shrinkage rate is 13.2% after the diaphragm is placed at 150 ℃ for 1 hour, and the contact angle of electrolyte is 30.3 degrees (as shown in figure 4).
Comparative example
The preparation method of the traditional ultra-high molecular weight polyethylene battery diaphragm comprises the following specific steps:
(1) Fully dispersing 180 ten thousand of supermolecule molecular weight polyethylene and 35 ten thousand of low molecular weight polyethylene in a high-speed mixer according to the mass ratio of 60;
(2) Pouring the mixed material obtained in the step (1) into a liquid paraffin pore-foaming agent, wherein the mass ratio of the mixed material to the liquid paraffin is 20. Fully stirring, uniformly dispersing, and standing at room temperature for 24h to obtain a blend;
(3) Melting, blending and plasticizing and conveying the blend obtained in the step (2) at the temperature of 210 ℃ through an eccentric rotor extruder, feeding the blend into a single-layer die, and forming a single-layer gel film after casting and cooling;
(4) And (4) stretching the single gel film obtained in the step (3) on a synchronous biaxial stretching machine, wherein the stretching ratio is 5x5, the stretching temperature is 100 ℃, and then, performing heat setting at 120 ℃ for 5min.
(5) And (4) subjecting the biaxially oriented film obtained in the step (4) to n-hexane ultrasonic extraction, alcohol soaking, deionized water leaching and drying to finally obtain the ultrathin high-strength multilayer composite diaphragm.
The ultra-high molecular weight polyethylene battery separator prepared by the method has the thickness of 15 mu m, the tensile strength of 48MPa, the heat shrinkage rate of 100% after being placed at 150 ℃ for 1 hour, and the contact angle of the electrolyte of 34 degrees (as shown in figure 5).
As mentioned above, the present invention can be realized well, and the above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention; all equivalent changes and modifications made according to the present disclosure are intended to be covered by the scope of the claims of the present invention.
Claims (8)
1. The ultrathin high-strength multilayer composite diaphragm is characterized by comprising a supporting layer and at least one functional layer, wherein the functional layer covers one side or two sides of the supporting layer, the supporting layer and the functional layer are respectively provided with a microporous structure, the supporting layer and the functional layer are formed by co-extrusion and subjected to bidirectional stretching, and during the co-extrusion, a supporting layer blend and a functional layer blend are respectively put into corresponding extruders for melting, blending, plasticizing and conveying to form a corresponding supporting layer melt and a corresponding functional layer melt, and then the supporting layer melt and the functional layer melt are subjected to extrusion forming through a co-extrusion die head to form a multilayer composite gel film; wherein the content of the first and second substances,
the main components and the parts by mass of the supporting layer are as follows: 0-20 parts of inorganic ceramic particles, 20-40 parts of low molecular weight polyethylene and 40-80 parts of ultrahigh molecular weight polyethylene;
the functional layer comprises the following main components in parts by mass: 65-95 parts of inorganic ceramic particles and 5-35 parts of ultrahigh molecular weight polyethylene;
the molecular weight of the ultra-high molecular weight polyethylene is 150-180 ten thousand, and the molecular weight of the low molecular weight polyethylene is 15-35 ten thousand;
in the supporting layer and the functional layer, the porosity of the microporous structure is 50-90%, and the pore size distribution is 0.01-10 μm; the porosity of the support layer and the functional layer may be the same or different, and the porosity may be the same or different between different functional layers.
2. The ultra-thin high-strength multilayer composite membrane with high load of ceramic particles as claimed in claim 1, wherein the ultra-high molecular weight polyethylene used in the support layer and the functional layers has the same or different molecular weight, and the ultra-high molecular weight polyethylene used in different functional layers has the same or different molecular weight.
3. The ultra-thin high-strength multilayer composite membrane with high load of ceramic particles as claimed in claim 1, wherein the inorganic ceramic particles are SiO 2 、Al 2 O 3 、TiO 2 、BaSO 4 Or PZT.
4. The ultrathin, high-strength and multilayer composite membrane with the high load of the ceramic particles as claimed in claim 1, wherein the thickness of the support layer is 1-10 μm, and the thickness of the functional layer is 1-10 μm.
5. A method for preparing the ultrathin high-strength multilayer composite membrane with the high load of the ceramic particles as claimed in any one of claims 1 to 4, which is characterized by comprising the following steps:
(1) A dry mixing stage: according to a set proportion, inorganic ceramic particles, low molecular weight polyethylene and ultrahigh molecular weight polyethylene or low molecular weight polyethylene and ultrahigh molecular weight polyethylene are put into a high-speed mixer for dispersion and mixing to form a support layer mixed material; placing inorganic ceramic particles and ultrahigh molecular weight polyethylene into a high-speed mixer for dispersion and mixing to form a functional layer mixed material;
(2) A wet mixing stage: respectively adding pore-foaming agents into the supporting layer mixed material and the functional layer mixed material, fully mixing and uniformly dispersing, and standing or stirring for 6-72 hours at the temperature of 25-100 ℃ to respectively form a supporting layer blend and a functional layer blend;
(3) Preparation stage of multilayer composite gel film: respectively putting the supporting layer blend and the functional layer blend into corresponding extruders for melt blending, plasticizing and conveying to form corresponding supporting layer melt and functional layer melt; extruding and molding the supporting layer melt and the functional layer melt through a co-extrusion die head to form a multi-layer composite gel film;
(4) And (3) a biaxial stretching stage: adopting asynchronous biaxial stretching or synchronous biaxial stretching to form a multilayer composite gel film, and then carrying out heat setting treatment;
(5) A battery diaphragm preparation stage: and sequentially carrying out organic solvent extraction and drying on the biaxially oriented multilayer composite membrane to form a microporous membrane, and finally obtaining the ultrathin high-strength multilayer composite membrane with high-load ceramic particles.
6. The method for preparing the ultrathin high-strength multilayer composite membrane with the high load of the ceramic particles as claimed in claim 5, wherein in the step (2), the mass of the pore-forming agent added into the support layer mixed material or the functional layer mixed material accounts for 50-90% of the total mass of the blend formed after mixing; the pore-foaming agent is a macromolecular pore-foaming agent or a micromolecular pore-foaming agent.
7. The method for preparing the ultrathin high-strength multilayer composite membrane with high loading of ceramic particles as claimed in claim 5, wherein in the step (3), when the support layer mixed material and the pore-forming agent or the functional layer mixed material and the pore-forming agent are blended, the adopted blending equipment is a multi-screw extruder, a single-shaft eccentric rotor extruder or a double-shaft eccentric rotor extruder, and the plasticizing melting temperature is 180-230 ℃.
8. The method for preparing the ultrathin high-strength multilayer composite membrane with the high load of the ceramic particles as claimed in claim 5, wherein in the step (4), the stretcher is an asynchronous biaxial stretcher or a synchronous biaxial stretching film machine, the transverse stretching ratio of the film is 3-10 times, the longitudinal stretching ratio of the film is 3-10 times, the stretching temperature is 90-120 ℃, the heat setting temperature is 100-140 ℃, and the heat setting time is 1-20 minutes.
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| CN106784528A (en) * | 2016-12-27 | 2017-05-31 | 深圳市星源材质科技股份有限公司 | A kind of preparation method of lithium battery diaphragm |
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