CN115498363A - Composite diaphragm, preparation method thereof and electrochemical device - Google Patents
Composite diaphragm, preparation method thereof and electrochemical device Download PDFInfo
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- CN115498363A CN115498363A CN202211320922.1A CN202211320922A CN115498363A CN 115498363 A CN115498363 A CN 115498363A CN 202211320922 A CN202211320922 A CN 202211320922A CN 115498363 A CN115498363 A CN 115498363A
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- thermal expansion
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- 238000002360 preparation method Methods 0.000 title abstract description 12
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- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical compound CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 claims description 14
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- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 claims description 6
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- 239000002174 Styrene-butadiene Substances 0.000 claims description 2
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- MTAZNLWOLGHBHU-UHFFFAOYSA-N butadiene-styrene rubber Chemical compound C=CC=C.C=CC1=CC=CC=C1 MTAZNLWOLGHBHU-UHFFFAOYSA-N 0.000 claims description 2
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- DMEGYFMYUHOHGS-UHFFFAOYSA-N heptamethylene Natural products C1CCCCCC1 DMEGYFMYUHOHGS-UHFFFAOYSA-N 0.000 claims description 2
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- QXLPXWSKPNOQLE-UHFFFAOYSA-N methylpentynol Chemical compound CCC(C)(O)C#C QXLPXWSKPNOQLE-UHFFFAOYSA-N 0.000 claims 1
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- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 description 1
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Images
Classifications
-
- 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
-
- 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
-
- 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
-
- 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
- H01M50/497—Ionic conductivity
-
- 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
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Cell Separators (AREA)
Abstract
The invention provides a composite diaphragm, a preparation method thereof and an electrochemical device. The composite diaphragm comprises a base film and a reversible thermal expansion polymer microsphere coating coated on at least one side of the base film; the thermal shutdown temperature of the composite membrane is 90-110 ℃. The composite diaphragm provided by the invention has excellent reversible thermal shutdown performance, good heat-resistant stability and air permeability, and the prepared electrochemical device has higher safety performance and cycle performance.
Description
Technical Field
The invention belongs to the technical field of diaphragm materials, and particularly relates to a composite diaphragm, a preparation method thereof and an electrochemical device.
Background
The lithium ion battery has the advantages of high specific capacity, low self-discharge rate, high cost performance and the like, so that the lithium ion battery is widely applied to the fields of portable electronic products and electric automobiles. Among them, the separator is one of the key components in the lithium battery structure.
The diaphragm plays a main role in separating the positive and negative pole pieces, preventing short circuit in the battery, and simultaneously ensuring that the battery promotes the normal passing of lithium ions when the battery is charged and discharged normally, thereby ensuring the normal work of the battery. The quality of the performance is closely related to the safety performance of the battery.
Currently, porous polyolefin separators are mostly used in lithium ion batteries, and the main materials of the separators include polyethylene and polypropylene. However, the melting points of polyethylene and polypropylene are low, 130 ℃ and 150 ℃, respectively, so that a lithium battery may release a large amount of heat due to short circuit when being overcharged, impacted, heated, and the like, so that a polyolefin separator is heated to shrink or melt, short circuit occurs between charged positive and negative electrode materials, heat in the battery is further out of control, and further serious safety accidents such as fire or explosion occur. Therefore, it is important to improve the thermal stability and safety of the separator material so as to avoid the above safety problem.
In recent years, researchers generally adopt a method of coating a layer of ceramic material (such as alumina, boehmite and the like) on the surface of the separator to further improve the heat resistance of the separator, but the polyolefin separator is melted at the melting point (> 130 ℃) of the polyolefin separator, so that micropores of lithium ions disappear, and the conduction of the lithium ions is blocked, which is called a thermal shutdown closed-cell effect. Due to the high closing temperature of the polyolefin membrane, the thermal shutdown effect cannot be realized in time.
In the prior art, a low-melting-point polymer is coated on one side or two sides of a base membrane or a ceramic membrane, so that when the internal temperature of a battery reaches the melting point of a polymer microsphere, the molten polymer enters micropores of a polyolefin base membrane to block lithium ion channels, and the internal short circuit is prevented from continuously occurring. Meanwhile, the polymer microspheres are melted to block the ion channels to realize diaphragm closed pores, and the measure has irreversibility, so that the battery cannot be reused after diaphragm closed pores.
Therefore, it is highly desirable to develop a composite separator for realizing reversible thermal shutdown, which not only has good high temperature resistance and low impedance, but also has good safety and cycle performance of the prepared battery.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a composite separator, a preparation method thereof and an electrochemical device. The composite diaphragm provided by the invention has reversible thermal shutdown performance and good heat-resistant stability and air permeability, so that the electrochemical device has higher rate performance and cycle performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a composite separator comprising a base film and a coating of reversible thermal expansion polymeric microspheres coated on at least one side of the base film;
the thermal shutdown temperature of the composite diaphragm is 90-110 ℃.
In the present invention, the thermal shutdown temperature of the composite separator is 90 to 110 ℃, and may be, for example, 90 ℃, 92 ℃, 95 ℃, 97 ℃, 100 ℃, 102 ℃, 105 ℃, 107 ℃, 110 ℃.
In the invention, the reversible thermal expansion polymer microsphere is a polymer which has a boiling point near a set thermal shutdown temperature and is immiscible with water.
The composite diaphragm is prepared by coating a reversible thermal expansion polymer microsphere coating on the surface of a base film. The heat expansion polymer microspheres are coated on the surface of the porous base membrane, so that the porous base membrane has better air permeability and the internal resistance of the battery cannot be obviously improved. Meanwhile, the heat-resistant stability of the base film at a temperature of more than 200 ℃ is achieved, the heat shrinkage rate of the composite diaphragm at a high temperature is reduced, and the phenomenon that the diaphragm is thermally shrunk due to the fact that the inside of the battery is still subjected to side reaction after thermal shutdown response is avoided, and the aggravation of the side reaction further promotes the temperature to continue rising, so that the positive electrode and the negative electrode are in direct contact, and the battery is in a short circuit in a large area. The battery prepared by the composite diaphragm within the specific thermal shutdown temperature range has higher safety performance and electrochemical performance, and realizes reversible thermal shutdown effect at lower temperature, namely the battery can be reused after thermal shutdown and temperature reduction.
According to the invention, the thermal shutdown temperature of the composite diaphragm is controlled, so that the composite diaphragm has lower closed pore temperature, and the blocking of ion transmission and the interruption of battery reaction are facilitated.
Preferably, the reversible thermal expansion polymer microsphere coating comprises reversible thermal expansion polymer microspheres and an auxiliary agent.
Preferably, the reversibly thermally expandable polymeric microspheres comprise any two or a combination of at least three of polystyrene, polybutadiene, cis-1, 4-polyisoprene, ethylene-propylene rubber, butyl rubber, polyisobutylene, polyethylene-polybutylene copolymer, non-crystalline polyethylene, polyether, polyester-polystyrene copolymer, polypropylene, syndiotactic 1, 2-polybutadiene, trans-1, 4-polyisoprene, polyurethane, polyester or polyamide.
Preferably, the reversible thermal expansion polymer microsphere comprises any two or at least three of styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer, polystyrene-polyethylene-polybutylene-polystyrene copolymer or polystyrene-polyethylene-polypropylene-polystyrene copolymer.
In the invention, two or more reversible thermal expansion polymer microspheres are combined, so that the advantage of better thermal response shutoff is achieved.
Preferably, the auxiliary agent comprises any one of a binder, a dispersant or a thickener or a combination of at least two thereof.
Preferably, the reversible thermal expansion polymer microsphere coating comprises the following components in parts by weight: 80-100 parts (for example, 80 parts, 85 parts, 90 parts, 95 parts and 100 parts) of reversible thermal expansion polymer microspheres and 0.1-25 parts (for example, 1 part, 5 parts, 10 parts, 15 parts and 25 parts) of auxiliary agents.
Preferably, the reversible thermal expansion polymer microsphere coating comprises the following components in parts by weight: the reversible thermal expansion polymer microsphere is 80 to 100 parts (for example, 80 parts, 82 parts, 84 parts, 85 parts, 88 parts, 90 parts, 92 parts, 94 parts, 98 parts, 100 parts), preferably 84 to 94 parts (for example, 84 parts, 86 parts, 88 parts, 90 parts, 92 parts, 94 parts), the dispersant is 0.1 to 3 parts (for example, 0.1 part, 0.8 part, 1 part, 2 parts, 3 parts), preferably 0.1 to 1 part (for example, 0.1 part, 0.3 part, 0.5 part, 0.8 part, 1 part), the binder is 3 to 20 parts (for example, 3 parts, 8 parts, 10 parts, 12 parts, 14 parts, 15 parts, 20 parts), preferably 4 to 14 parts (for example, 4 parts, 8 parts, 10 parts, 12 parts, 14 parts), the thickener is 0.1 to 2 parts (for example, 0.1 part, 0.8 part, 1 part, 2 parts), preferably 0.3 to 1.5 parts, 0.1 part).
In the invention, the composite diaphragm has better thermal response shutdown function by controlling the weight parts of the components.
Preferably, the dispersing agent comprises any one or a combination of at least two of polyacrylate, polyethylene glycol ether, phosphate compounds, sodium tripolyphosphate, sodium hexametaphosphate, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, polyacrylamide or fatty acid polyethylene glycol ester, and is preferably sodium tripolyphosphate and/or sodium hexametaphosphate.
Preferably, the binder comprises any one or a combination of at least two of styrene-butadiene latex, styrene-acrylic emulsion, vinyl acetate-acrylic emulsion, polyvinyl alcohol or polymethyl methacrylate, preferably vinyl acetate-acrylic emulsion and/or polyvinyl alcohol.
Preferably, the thickener comprises any one or a combination of at least two of sodium carboxymethyl cellulose, sodium alginate or polyacrylamide, preferably sodium carboxymethyl cellulose.
In the present invention, the above-mentioned preferred auxiliary components can improve the dispersibility and uniformity of the slurry.
Preferably, the base film comprises a polyimide base film or a multi-layer polyolefin base film.
In the invention, the polyimide base film can work for a long time at 200 ℃; the multi-layer polyolefin-based film has high temperature stability at 170 ℃.
In the present invention, the polyimide-based film is prepared as follows: the electrostatic spinning is prepared by adopting electrostatic spinning, and the high polymer solution or melt is stretched into superfine fibers at the conical top of a capillary tube Taylor under the action of an electric field force under the action of a high-voltage electric field; the electric field intensity is moderate, the viscosity of the molten mass is 0.1-2000cps, preferably 10-200cps; the diameter of the nozzle is 0.01-5 μm, preferably 0.1-0.7 μm; the prepared polyimide basal membrane with the aperture of 0.1-1 μm, preferably 0.2-0.5 μm.
The preparation method of the multilayer polyolefin base film comprises the following steps: adopting a three-layer co-extrusion processing technology to crosslink polyethylene and then perform a diaphragm manufacturing technology to form a diaphragm with polyethylene in the middle and mixed material or polypropylene with higher molecular weight on two sides; the multi-runner die head is used for perfecting the function of the auxiliary extruder, and a three-layer co-extrusion processing technology is adopted to process the multi-layer polyolefin diaphragm on the premise of ensuring the thickness of the diaphragm; the main extruder and the auxiliary extruder are made of conventional ultrahigh molecular weight polypropylene, the extruded materials are compounded on a die head, then uniform sheets are formed on the surface of the substrate, and the subsequent procedures are like the processing technology of the wet diaphragm in the prior art.
Preferably, the thickness of the base film is 5 to 12 μm, preferably 8 to 10 μm, and may be, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm; the porosity is between 55% and 90%, preferably between 55% and 70%, and may be, for example, 55%, 60%, 65%, 70%, 80%, 90%.
Preferably, the thickness of the reversible thermal expansion polymer microsphere coating is 1-8 μm, preferably 2-6 μm, and for example, may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm.
In the invention, the reversible thermal expansion polymer microsphere coating cannot achieve the technical effect of reversible thermal shutdown when being too thin, and the internal resistance of the battery and the air permeability of the diaphragm can be increased when being too thick.
Preferably, the porosity of the composite separator is 40% to 60%, preferably 40% to 48%, and may be, for example, 40%, 42%, 45%, 48%, 50%, 55%, 60%.
In the invention, the porosity of the composite membrane is adjusted, so that the composite membrane has good air permeability and lower impedance.
In a second aspect, the present invention provides a method of making the composite separator of the first aspect, the method comprising the steps of:
coating reversible thermal expansion polymer microsphere slurry on at least one side of the base film to form a reversible thermal expansion polymer microsphere coating, and drying to obtain the composite diaphragm.
Preferably, the reversible thermal expansion polymer microsphere slurry comprises reversible thermal expansion polymer microspheres and an organic solvent.
In the invention, the reversible thermal expansion polymer microsphere slurry also comprises an auxiliary agent.
In the present invention, the auxiliary agent includes any one of a binder, a dispersant or a thickener, or a combination of at least two thereof.
Preferably, the mass percentage of the reversible thermal expansion polymeric microspheres in the reversible thermal expansion polymeric microsphere slurry is 10% to 90%, preferably 55% to 86%, and may be, for example, 10%, 20%, 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, 90%.
In the invention, the composite diaphragm has good reversible thermal expansion performance and lower thermal shutdown temperature by controlling the mass percentage of the reversible thermal expansion polymer microspheres.
Preferably, the mass percentage of the organic solvent in the slurry of reversible thermal expansion polymer microspheres is 15% to 90%, preferably 20% to 55%, and may be, for example, 15%, 20%, 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, 90%.
Preferably, the organic solvent comprises a C3-C5 linear alkane and/or a C3-C5 cycloalkane.
In the present invention, the term "C3-C5" refers to the number of main chain carbon atoms, for example, 3, 4, 5, etc.
In the present invention, the organic solvent can improve the reversible thermal expansion properties of the composite separator.
Preferably, the organic solvent comprises any one of propane, n-pentane or cyclopentane, or a combination of at least two thereof, preferably n-pentane.
Preferably, the coating is a spot coating.
Preferably, the dot coating temperature is 0-100 ℃, for example 10 ℃, 30 ℃, 50 ℃, 80 ℃, 100 ℃.
Preferably, the coating process further comprises a drying process.
Preferably, the drying temperature is 50-70 deg.C, such as 50 deg.C, 60 deg.C, 70 deg.C.
In the invention, the coating and unreeling tension is 0.01-100N, the reeling tension is 0-100N, the drawing speed is 0.01-80m/min, and the contact pressure is 0.01-30N.
In a third aspect, the present invention provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the separator is the composite separator according to the first aspect.
Preferably, the electrochemical device comprises a lithium ion battery or a sodium ion battery.
The composite diaphragm provided by the invention not only improves the safety performance of an electrochemical device, but also can improve the rate capability and the cycling stability of the electrochemical device.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a composite diaphragm, which improves the following performances of the diaphragm:
the composite diaphragm is prepared by coating a reversible thermal expansion polymer microsphere coating on the surface of a base membrane. The heat expansion polymer microspheres are coated on the surface of the porous base membrane, so that the porous base membrane has better air permeability and the internal resistance of the battery cannot be obviously improved. Meanwhile, the heat-resistant stability of the base film at a temperature of more than 200 ℃ is achieved, the heat shrinkage rate of the composite diaphragm at a high temperature is reduced, and the phenomenon that the diaphragm is thermally shrunk due to the fact that the inside of the battery is still subjected to side reaction after thermal shutdown response is avoided, and the aggravation of the side reaction further promotes the temperature to continue rising, so that the positive electrode and the negative electrode are in direct contact, and the battery is in a short circuit in a large area.
The battery prepared by the composite diaphragm within the specific thermal shutdown temperature range has higher safety performance and electrochemical performance, and realizes reversible thermal shutdown effect at lower temperature, namely the battery can be reused after thermal shutdown and temperature reduction.
Drawings
Fig. 1 is a schematic structural diagram of a composite separator provided in example 1;
FIG. 2 is a schematic diagram of the expansion of the reversibly thermally expandable polymeric microspheres at different temperatures.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the detailed description. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitation of the present invention.
Example 1
This example provides a composite membrane with a thermal shutdown temperature of 100 ℃ and a preparation method thereof, as shown in fig. 1, the composite membrane includes a polyimide base membrane (with a thickness of 9 μm and a porosity of 60%) and a reversible thermal expansion polymer microsphere coating (with a thickness of 4 μm) coated on both sides of the polyimide base membrane.
The reversible thermal expansion polymer microsphere coating comprises the following components: the adhesive comprises, by mass, reversible thermal expansion polymer microspheres (45 parts by mass of polystyrene and 45 parts by mass of a styrene-butadiene-styrene copolymer), a binder (vinyl acetate-acrylic emulsion) 9 parts by mass, a dispersant (sodium tripolyphosphate) 2.5 parts by mass, and a thickener (sodium carboxymethylcellulose) 1 part by mass.
The preparation method of the composite diaphragm comprises the following steps:
uniformly mixing reversible thermal expansion polymer microspheres, a binder, a dispersant and a thickener in an N-pentane solvent to obtain slurry of a reversible thermal expansion polymer microsphere coating, wherein the mass percent of the reversible thermal expansion polymer microspheres in the slurry is 70%, and the mass percent of the N-pentane solvent is 20.28%, dot-coating the slurry of the reversible thermal expansion polymer microspheres on two sides of a base film to form the reversible thermal expansion polymer microsphere coating, wherein the dot-coating temperature is 50 ℃, drying is carried out at 60 ℃ after coating, the coating unwinding tension is 50N, the winding tension is 50N, the stretching speed is 40m/min, and the contact pressure is 15N, so that the composite diaphragm with the porosity of 45% is obtained.
Example 2
This example provides a composite separator with a thermal shutdown temperature of 95 ℃ and a preparation method thereof, and as shown in fig. 1, the composite separator includes a polyimide base film (with a thickness of 8 μm and a porosity of 55%) and reversible thermal expansion polymer microsphere coatings (with a thickness of 2 μm) coated on both sides of the polyimide base film.
The adhesive comprises, by mass, reversible thermal expansion polymer microspheres (42 parts by mass of polybutadiene and 42 parts by mass of styrene-isoprene-styrene copolymer), a binder (7 parts by mass of polyvinyl alcohol and 7 parts by mass of vinyl acetate-acrylic emulsion), a dispersing agent (sodium hexametaphosphate) 1 part by mass, and a thickening agent (sodium alginate) 1 part by mass.
The preparation method of the composite diaphragm comprises the following steps:
uniformly mixing reversible thermal expansion polymer microspheres, a binder, a dispersant and a thickener in an N-pentane solvent to obtain slurry of a reversible thermal expansion polymer microsphere coating, wherein the mass percent of the reversible thermal expansion polymer microspheres in the slurry is 55%, the mass percent of the N-pentane solvent is 34.52%, dot-coating the slurry of the reversible thermal expansion polymer microspheres on two sides of a base film to form the reversible thermal expansion polymer microsphere coating, wherein the dot-coating temperature is 40 ℃, drying is carried out at 50 ℃ after coating, the coating unwinding tension is 50N, the winding tension is 50N, the stretching speed is 40m/min, and the contact pressure is 15N, so that the composite diaphragm with the porosity of 40% is obtained.
Example 3
This example provides a composite separator with a thermal shutdown temperature of 105 ℃ and a preparation method thereof, and as shown in fig. 1, the composite separator includes a polyimide base film (with a thickness of 10 μm and a porosity of 70%) and reversible thermal expansion polymer microsphere coatings (with a thickness of 6 μm) coated on both sides of the polyimide base film.
The adhesive comprises, by mass, reversible thermal expansion polymer microspheres (47 parts by mass of polybutadiene and 47 parts by mass of styrene-isoprene-styrene copolymer), a binder (2 parts by mass of polyvinyl alcohol and 2 parts by mass of vinyl acetate-acrylic emulsion), a dispersing agent (sodium hexametaphosphate) 0.1 part by mass, and a thickening agent (sodium alginate) 0.3 part by mass.
The preparation method of the composite diaphragm comprises the following steps:
the reversible thermal expansion polymer microsphere coating slurry is prepared by uniformly mixing reversible thermal expansion polymer microspheres, a binder, a dispersant and a thickener in an N-pentane solvent, wherein the mass percent of the reversible thermal expansion polymer microspheres in the slurry is 80%, the mass percent of the N-pentane solvent is 16.26%, the reversible thermal expansion polymer microsphere slurry is dot-coated on two sides of a base film to form the reversible thermal expansion polymer microsphere coating, the dot-coating temperature is 60 ℃, the drying is carried out at 70 ℃ after the coating, the coating unwinding tension is 50N, the winding tension is 50N, the stretching speed is 40m/min, and the contact pressure is 15N, so that the composite diaphragm with the porosity of 48% is obtained.
Example 4
This example is different from example 1 in that the reversible thermal expansion polymer microspheres were all replaced with polystyrene, and the other examples were the same as example 1.
Example 5
This example is different from example 1 in that the base film was replaced with a PP/PE/PP base film, and the others were the same as example 1.
Example 6
This example is different from example 1 in that cyclohexane is used as the organic solvent in the slurry of the coating layer of the reversible thermal expansion polymer microsphere, and the rest is the same as example 1.
Example 7
The difference between this example and example 1 is that the total weight part of the reversible thermal expansion polymer microspheres in the reversible thermal expansion polymer microsphere coating is 70 parts, the type and ratio of the polymer are not changed, and the rest are the same as example 1.
Example 8
The difference between this example and example 1 is that the total weight part of the reversible thermal expansion polymeric microspheres in the reversible thermal expansion polymeric microspheres coating is 120 parts, the type and proportion of the polymer are not changed, and the rest are the same as those in example 1.
Comparative example 1
The comparative example is different from example 1 in that the reversible thermal expansion polymer microsphere coating is replaced by an alumina coating, and the rest is the same as example 1.
Comparative example 2
The comparative example is different from example 1 in that the thermal shutdown temperature of the composite membrane is 80 ℃, specifically, the reversible thermal expansion polymer microspheres are replaced by the reversible thermal expansion polymer microspheres (10 parts by mass of polybutadiene and 10 parts by mass of styrene-isoprene-styrene copolymer), and the rest is the same as example 1.
Comparative example 3
The comparative example is different from example 1 in that the thermal shutdown temperature of the composite membrane is 160 ℃, specifically, the reversible thermal expansion polymer microspheres are replaced by the foaming microspheres with the foaming temperature of 160 ℃, wherein the core is the low-boiling point hydrocarbon, the shell of the foaming microspheres is the thermoplastic acrylonitrile copolymer, and the rest is the same as example 1.
Application examples 1-8 and comparative application examples 1-3
The composite separators provided in examples 1 to 8 and comparative examples 1 to 3 were prepared to obtain sodium ion batteries by the following method:
preparing a positive plate: mixing sodium ferric phosphate, acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 8;
preparing a negative plate: mixing hard carbon, sodium carboxymethylcellulose and styrene butadiene rubber according to the mass ratio of 88;
electrolyte solution: the dried sodium hexafluorophosphate was dissolved in a mixed solvent (ethylene carbonate/diethyl carbonate) at a volume ratio of 1.
Preparing a sodium ion battery: separating the positive and negative pole pieces of the composite diaphragm cut to a certain size in a winding mode, and winding the positive and negative pole pieces into an electric core body; then, performing short circuit evaluation on the electric core body, and screening high-quality electric cores; then the materials are put into a battery shell, a battery cover is covered, and the opening is sealed by welding; and injecting electrolyte into the battery shell, forming, sealing for the second time, baking the clamp and grading the volume to obtain the finished product of the sodium-ion battery.
Test conditions
The composite separators provided in examples 1 to 8 and comparative examples 1 to 3 were subjected to a performance test by the following method:
heat shrinkage ratio: placing a stainless steel plate and two pieces of quantitative filter paper in the middle position (near the position of a temperature probe) of an oven, and controlling the temperature to enable the stainless steel plate and the filter paper to reach (200 +/-1) DEG C. According to the longitudinal direction and the transverse direction of the diaphragm, respectively measuring the longitudinal length and the transverse length of a test sample by using a length measuring instrument with corresponding resolution ratio according to actual requirements, flatly placing the diaphragm on one quantitative filter paper on a stainless steel plate in the middle of the blast type constant temperature box, stacking no more than 10 diaphragms at most, pressing by using the other quantitative filter paper after the completion, placing a pressing block in the middle of the filter paper, closing the constant temperature box door, starting to calculate the time, and keeping for 1h at the temperature of 200 ℃.
The sodium ion batteries provided in application examples 1 to 8 and comparative application examples 1 to 3 were subjected to electrochemical performance tests by the following test methods:
(1) Cycle performance: at normal temperature, the current density is 1C/1C, the electrochemical window is 1.5V-4.0V, and the charge-discharge cycle is 1000 circles.
(2) Testing internal resistance: an electrochemical workstation is adopted for EIS test, the frequency range is 1-200KHz, and the amplitude is 5mV.
(3) And (3) hot box testing: and after the single battery is fully charged, putting the single battery into a temperature box at 25 ℃, heating the single battery to 150 +/-2 ℃ from room temperature at the speed of 5 ℃/min, keeping the temperature for 30min, and stopping heating. Observe for 1h
The results of the tests are shown in tables 1 and 2:
TABLE 1
TABLE 2
As can be seen from the data in tables 1 and 2, the composite separator provided by the present invention has a lower thermal shrinkage rate, a lower internal resistance, and is capable of preventing side reactions from occurring inside the battery after a response due to thermal shutdown. Fig. 1-2 show that the composite diaphragm provided by the invention can realize reversible thermal shutdown effect at a lower temperature, namely, the battery can be reused after thermal shutdown and temperature reduction.
Application example 4 is the case of replacing a single polymer microsphere, and the effect of the composite membrane is inferior to the comprehensive performance of the composite membrane provided by application example 1; application example 5 is a case of replacing the base film, the effect of application example 1 is better because the thermal stability of the PP/PE/PP base film is not as good as that of the polyimide base film, and although the thermal shrinkage rate of the separator provided in application example 5 at 200 ℃ is higher, the thermal shrinkage rate at 150 ℃ is very low, so that the normal temperature performance test and the heating internal resistance test are not affected; application examples 7 to 8 are cases where the weight parts of the polymeric microspheres exceed the range, indicating that the weight parts of the reversible thermal expansion polymeric microspheres are controlled, so that the composite diaphragm has a better thermal response shutdown function.
The comparison of application example 1 is a replacement coating type, and the comparison of application examples 2 to 3 is a situation that the thermal shutdown temperature exceeds the range, which shows that the performance of the prepared diaphragm and the lithium ion battery is different from that of application example 1, shows that the composite diaphragm of the thermal expansion microsphere with the overhigh thermal response temperature cannot exert the thermal response function in advance, and before the pore closing of the base film, the thermal runaway of the battery can be caused, and the hot box test cannot be performed.
The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.
Claims (10)
1. The composite diaphragm is characterized by comprising a base film and a reversible thermal expansion polymer microsphere coating coated on at least one side of the base film;
the thermal shutdown temperature of the composite diaphragm is 90-110 ℃.
2. The composite membrane of claim 1, wherein the reversible thermal expansion polymeric microsphere coating comprises reversible thermal expansion polymeric microspheres and an auxiliary agent;
preferably, the reversible thermal expansion polymer microsphere comprises any two or at least three of polystyrene, polybutadiene, cis-1, 4-polyisoprene, ethylene-propylene rubber, butyl rubber, polyisobutylene, polyethylene-polybutylene copolymer, non-crystalline polyethylene, polyether, polyester-polystyrene copolymer, polypropylene, syndiotactic 1, 2-polybutadiene, trans-1, 4-polyisoprene, polyurethane, polyester or polyamide;
preferably, the reversible thermal expansion polymer microsphere comprises any two or at least three of styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer, polystyrene-polyethylene-polybutylene-polystyrene copolymer or polystyrene-polyethylene-polypropylene-polystyrene copolymer;
preferably, the auxiliary agent comprises any one of a binder, a dispersant or a thickener or a combination of at least two thereof.
3. The composite membrane as claimed in claim 1 or 2, wherein the reversible thermal expansion polymeric microsphere coating comprises the following components in parts by weight: 80-100 parts of reversible thermal expansion polymer microsphere and 0.1-25 parts of auxiliary agent;
preferably, the reversible thermal expansion polymer microsphere coating comprises the following components in parts by weight: 80-100 parts of reversible thermal expansion polymer microsphere, 0.1-3 parts of dispersant, 3-20 parts of binder and 0.1-2 parts of thickener, preferably 84-94 parts of reversible thermal expansion polymer microsphere, 0.1-1 part of dispersant, 4-14 parts of binder and 0.3-1 part of thickener.
4. The composite separator according to claim 2 or 3, wherein the dispersant comprises any one of or a combination of at least two of polyacrylate salts, polyethylene glycol ethers, phosphate-based compounds, sodium tripolyphosphate, sodium hexametaphosphate, triethylhexyl phosphoric acid, sodium dodecyl sulfate, methylpentanol, polyacrylamide or fatty acid polyglycol esters, preferably sodium tripolyphosphate and/or sodium hexametaphosphate;
preferably, the binder comprises any one or a combination of at least two of styrene-butadiene latex, styrene-acrylic emulsion, vinyl acetate-acrylic emulsion, polyvinyl alcohol or polymethyl methacrylate, preferably vinyl acetate-acrylic emulsion and/or polyvinyl alcohol;
preferably, the thickener comprises any one or a combination of at least two of sodium carboxymethyl cellulose, sodium alginate or polyacrylamide, preferably sodium carboxymethyl cellulose.
5. The composite separator of any of claims 1-4, wherein the base film comprises a polyimide base film or a multi-layer polyolefin base film;
preferably, the thickness of the base film is 5 to 12 μm, preferably 8 to 10 μm;
preferably, the porosity of the base film is 55% to 90%, preferably 55% to 70%;
preferably, the thickness of the reversible thermal expansion polymer microsphere coating is 1-8 μm, preferably 2-6 μm;
preferably, the porosity of the composite separator is 40% to 60%, preferably 40% to 48%.
6. A method of making the composite separator of any one of claims 1-5, comprising the steps of:
coating reversible thermal expansion polymer microsphere slurry on at least one side of the base film to form a reversible thermal expansion polymer microsphere coating, and drying to obtain the composite diaphragm.
7. The method of claim 6, wherein the slurry of reversibly thermally expandable polymeric microspheres comprises reversibly thermally expandable polymeric microspheres and an organic solvent;
preferably, the mass percentage of the reversible thermal expansion polymer microspheres in the reversible thermal expansion polymer microsphere slurry is 10% -90%, and preferably 55% -86%;
preferably, the mass percent of the organic solvent in the reversible thermal expansion polymer microsphere slurry is 15% -90%, and preferably 20% -55%;
preferably, the organic solvent comprises a C3-C5 linear alkane and/or a C3-C5 cycloalkane;
preferably, the organic solvent comprises any one of propane, n-pentane or cyclopentane, or a combination of at least two thereof, preferably n-pentane.
8. The method according to claim 6 or 7, characterized in that the coating is a spot coating;
preferably, the temperature of the spot coating is 0-100 ℃;
preferably, the coating process further comprises a drying process.
9. The method according to any one of claims 6 to 8, wherein the temperature of the drying is 50 to 70 ℃.
10. An electrochemical device, characterized in that the electrochemical device comprises a positive plate, a negative plate, an electrolyte and a separator, wherein the separator is a composite separator according to any one of claims 1 to 5;
preferably, the electrochemical device comprises a lithium ion battery or a sodium ion battery.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2024159733A1 (en) * | 2023-02-03 | 2024-08-08 | 湖北亿纬动力有限公司 | Composite separator and preparation method therefor, and lithium ion battery |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111653716A (en) * | 2020-06-19 | 2020-09-11 | 江苏卓高新材料科技有限公司 | Diaphragm with reversible thermal shutdown performance and preparation method and application thereof |
| CN113178663A (en) * | 2021-04-28 | 2021-07-27 | 惠州亿纬锂能股份有限公司 | Composite diaphragm and preparation method and application thereof |
| CN114374056A (en) * | 2022-01-07 | 2022-04-19 | 惠州亿纬锂能股份有限公司 | Polyimide composite diaphragm, preparation method thereof and lithium ion battery |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111653716A (en) * | 2020-06-19 | 2020-09-11 | 江苏卓高新材料科技有限公司 | Diaphragm with reversible thermal shutdown performance and preparation method and application thereof |
| CN113178663A (en) * | 2021-04-28 | 2021-07-27 | 惠州亿纬锂能股份有限公司 | Composite diaphragm and preparation method and application thereof |
| CN114374056A (en) * | 2022-01-07 | 2022-04-19 | 惠州亿纬锂能股份有限公司 | Polyimide composite diaphragm, preparation method thereof and lithium ion battery |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2024159733A1 (en) * | 2023-02-03 | 2024-08-08 | 湖北亿纬动力有限公司 | Composite separator and preparation method therefor, and lithium ion battery |
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