CN113644378B - Functional coating diaphragm and preparation method and application thereof - Google Patents
Functional coating diaphragm and preparation method and application thereof Download PDFInfo
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- CN113644378B CN113644378B CN202110914743.XA CN202110914743A CN113644378B CN 113644378 B CN113644378 B CN 113644378B CN 202110914743 A CN202110914743 A CN 202110914743A CN 113644378 B CN113644378 B CN 113644378B
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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
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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
- 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
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/426—Fluorocarbon polymers
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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- 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
Abstract
The application discloses a functional coating diaphragm and a preparation method and application thereof, wherein the functional coating diaphragm comprises the following components in parts by weight: 10 parts of PVDF powder, 100-500 parts of alkali solution, 1-10 parts of oxidant solution, 0.01-1 part of grafting modification monomer, 0.5-3 parts of polar polymer material particles and 6-30 parts of dispersing solvent. The invention adopts a process of eliminating reaction and oxidizing to modify PVDF material to prepare modified PVDF functional slurry, then coats the modified PVDF functional slurry on a membrane substrate, and prepares the functional coating membrane through an oily water washing process, so that the prepared functional coating membrane has excellent pole piece bonding property of the oily process and low pore blocking property of water-based coating, in addition, polar polymer material particles and hydrophilic groups for modification can absorb trace water, and the polar polymer material particles and the hydrophilic groups can be distributed in a coating of a network structure, thereby realizing three-dimensional static conduction effect, effectively reducing the probability of generating static electricity of the functional coating membrane, and improving the yield of functional coating membrane products and electric cores.
Description
Technical Field
The invention relates to the preparation of a diaphragm in the field of batteries, in particular to a functional coating diaphragm, and a preparation method and application thereof.
Background
When the lithium battery is assembled, a layer of diaphragm is required to be coated outside the lithium battery, so that the use safety of the lithium battery is improved, the diaphragm of the existing lithium battery can be divided into a wet PE diaphragm and a dry PP diaphragm according to the process, because the liquid absorption and the cohesiveness of the PE and PP coated diaphragms are poor, an oily PVDF coating is usually coated on a diaphragm base film, and the oily PVDF coated diaphragm is obtained through water washing pore-forming.
The PVDF organic functional polymer is generally prepared by pulping through an oily or aqueous process, then coating on a diaphragm, and directly drying and forming. Although the process is simple and is also suitable for large-scale production and application, the following defects exist when the oily or aqueous process is adopted for pulping independently: the oily direct drying process uses flammable and explosive organic solvents which are easy to prepare toxins, is not environment-friendly, and the product prepared by the process has obvious hole blocking, can influence the multiplying power and the cycle performance of a battery, and has the problems of large electrostatic of a coating and adverse processing and application; secondly, although the water-based process has no environmental protection and economical problems, the prepared product has insufficient adhesive force, and the problems of higher water content, poor adhesive force of pole pieces and the like when the product is applied to batteries.
For example, in the invention, through designing a multi-layer structure, aramid fiber coating is carried out on one side of a treated base film, polyvinylidene fluoride coating is carried out on the same side of the base film, and finally inorganic particle coating treatment is carried out on the other side of the base film, so that the heat resistance and the bonding property of a pole piece are both achieved, although the heat resistance and the electrostatic property of the side can be improved by the inorganic particle coating on one side of the base film, the problems of difficult processing and large electrostatic property of the coating are caused by the aramid fiber coating on the other side and PVDF coating on the aramid fiber coating, meanwhile, the overall electrostatic property of the product is not improved due to the fact that the electrostatic property is necessarily caused on one side of the diaphragm, and the patent product has the advantages of multiple and complex coating structures, multiple processing times, low production efficiency and no guarantee of finished product rate. Thus, the prior art has yet to be developed.
Disclosure of Invention
The application provides a functional coating diaphragm and a preparation method thereof, and aims to provide a functional coating diaphragm with small static electricity, high coating porosity and good bonding performance so as to improve the processing and application performances of the functional coating diaphragm.
The PVDF modification technology reported in the prior art is mostly an inorganic blending modification technology, namely, an organic-inorganic composite material is formed by adding inorganic silicon dioxide or aluminum oxide materials for mixing, but the method has the problems of uneven dispersion of the inorganic materials and weak organic-inorganic acting force. Some techniques also use chemical grafting, but in a manner that is significantly different from the present application. In the method, PVDF powder is firstly subjected to alkali treatment, the PVDF material is subjected to elimination reaction, then a grafting modification monomer containing hydrophilic groups is added for oxidation grafting, so that the hydrophilic group grafting modified PVDF material is prepared, meanwhile, due to the proportion of different additives and the synergistic effect of the hydrophilic group grafting modification monomer, a three-dimensional conductive network structure can be formed inside the prepared functional coating membrane, static electricity is reduced, and the optimization of the performance of the functional coating membrane is realized.
According to a first aspect, the present application provides a functional coating separator prepared from a functional coating slurry comprising, by weight:
in one embodiment, the PVDF powder has a molecular weight M w The method comprises the following steps: 3.7X10 5 ≤M W ≤8.0×10 5 The melting point Tm is: tm is more than or equal to 140 ℃ and less than or equal to 160 ℃; the graft-modifying monomer includes at least one of acrylic acid, methacrylic acid, 2-ethylhexyl acrylate, and enamine.
In one embodiment, the polar polymeric material particles comprise at least one of polyvinyl alcohol, carboxylated modified polystyrene, carboxylated modified polypropylene, polyethylene oxide, PS-PMMA copolymerized crosslinked microspheres, and PS-polyurethane copolymerized crosslinked microspheres; the polar polymer material particles are spherical or spheroidic, and the particle size is 50-500 nm.
In one embodiment, in the alkaline solution, the solute comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide and sodium ethoxide, and the solvent comprises at least one of methanol, ethanol, water, NMP and DMAc; the mass concentration of the alkali solution is 1-10%.
In one embodiment, the oxidizer solution comprises at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate, and the solvent comprises at least one of NMP, DMAc, DMSO and DMF; the mass concentration of the oxidant solution is 0.5-5%.
In one embodiment, the dispersing solvent comprises at least one of methanol, ethanol, water, NMP, DMAc, DMSO, and DMF.
According to a second aspect, the present application also provides a method for preparing a functional coated separator according to the first aspect, comprising the steps of,
s1: modifying the PVDF material, sequentially adding an alkali solution and an oxidant solution into the PVDF powder, and preparing a PVDF material grafted and modified by hydrophilic groups by an alkali treatment and then an oxidation grafting mode and then adding a grafting modification monomer containing hydrophilic groups;
s2: preparing functional coating slurry, adding polar polymer material particles into a dispersion solvent to prepare suspension, adding the suspension into a solution containing PVDF material, and uniformly stirring to prepare the functional coating slurry;
s3: coating and forming a film, coating the functional coating slurry on two sides of a diaphragm substrate, and performing solidification pore forming, water washing pore shaping, drying and rolling to obtain the antistatic functional coating diaphragm.
In one embodiment, in the step S1, during alkali treatment, the stirring speed is 10-100 rpm, the reaction temperature is 40-80 ℃, the reaction time is 0.1-1.5 h, during oxidative grafting, the stirring speed is 5-50 rpm, the reaction temperature is 35-60 ℃, and the reaction time is 0.1-1.0 h; in step S2, the dispersion is performed by means of mechanical stirring, ultrasound or sanding, when preparing the suspension.
In one embodiment, in the PVDF material grafted and modified by the hydrophilic group, the hydrophilic group includes at least one of a carboxyl group, a hydroxyl group, an ester group, an amine group and a sulfonic acid group; the grafting ratio is 0.5-10%, wherein the grafting ratio is 100 percent of [ the mass of grafted modified monomer/(the mass of grafted modified monomer+the mass of grafted modified monomer homopolymer) ].
In one embodiment, the membrane substrate is a PP or PE membrane with a thickness of 5-20 μm; the thickness of the single-side coating of the functional coating slurry is 0.5-2 mu m.
According to a third aspect, the application further provides an application of the functional coating membrane in the first aspect or the functional coating membrane prepared by the preparation method in the second aspect in a lithium ion battery membrane. The functional coating diaphragm has small static electricity and higher porosity (a three-dimensional network structure is formed inside), so that dust or adhesion can be effectively reduced, and the yield of products is improved.
The beneficial effects are that: according to the functional coating diaphragm prepared by the preparation method, as hydrophilic groups in the coating are arranged outwards, the functional coating diaphragm and polar polymer material particles can absorb trace moisture in the environment, so that a water conducting layer is formed on the surface of the coating, and the functional coating diaphragm has an electrostatic conducting effect; in addition, the polar polymer material particles form network nodes in the coating network structure, so that three-dimensional static electricity conduction is realized. The functional coating diaphragm has less static electricity in the production process, is not easy to form bonding or adsorb dust, has higher porosity and good uniformity, and can effectively improve the processing performance of the coating diaphragm. When the high-voltage battery is applied to the battery field such as high-end 3C and power soft package batteries, the yield of diaphragm products and battery core products can be effectively improved.
Drawings
FIG. 1 is a schematic structural view of a functional coated separator according to an embodiment of the present application; wherein 1 represents a coating; 2 represents polar polymer material particles; 3 represents a separator substrate.
FIG. 2 is a schematic view of the internal structure of a functional coated membrane according to an embodiment of the present application under a microscope; it can be seen from the figure that the interior forms a three-dimensional network structure.
Detailed Description
The invention will be described in further detail below with reference to the drawings by means of specific embodiments. Wherein like elements in different embodiments are numbered alike in association. In the following embodiments, numerous specific details are set forth in order to provide a better understanding of the present application. However, one skilled in the art will readily recognize that some of the features may be omitted, or replaced by other elements, materials, or methods in different situations. In some instances, some operations associated with the present application have not been shown or described in the specification to avoid obscuring the core portions of the present application, and may not be necessary for a person skilled in the art to describe in detail the relevant operations based on the description herein and the general knowledge of one skilled in the art.
Furthermore, the described features, operations, or characteristics of the description may be combined in any suitable manner in various embodiments. Also, various steps or acts in the method descriptions may be interchanged or modified in a manner apparent to those of ordinary skill in the art. Thus, the various orders in the description and drawings are for clarity of description of only certain embodiments, and are not meant to be required orders unless otherwise indicated.
In the present invention, the term "room temperature" means a temperature range of 25±5 ℃. All ranges cited herein are inclusive unless clearly indicated to the contrary. The numbers in the present invention are approximations, by use of the antecedent "about" or "about" herein. The numerical values of the numbers may differ by 1%, 2%, 5%, 7%, 8%, 10%, etc. Whenever a number is disclosed having a value of N, any number having a value of N+/-1%, N+/-2%, N+/-3%, N+/-5%, N+/-7%, N+/-8% or N+/-10% will be explicitly disclosed, where "+/-" means plus or minus, and a range between N-10% and N+10% is also disclosed.
As shown in fig. 1, the present application discloses a functional coated separator, which is composed of a separator substrate 3 and a coating 1 (made of functional coating slurry) coated on both sides of the separator substrate 3, and further has inside the coating 1 polar polymer material particles 2 that can be supported as network nodes. Specifically, the functional coating slurry for preparing the coating comprises the following components in parts by weight:
the functional coating membrane in the application refers to a PVDF coating membrane (also called an oily PVDF coating membrane) prepared by an oily water washing process, and the coating is added with polar polymer material particles and modified and grafted PVDF material (prepared from PVDF powder, grafted modified monomer and other components). The polar polymer material particles in the functional coating diaphragm provide skeleton support and network nodes, and simultaneously the polar functional groups in the polar polymer material particles and hydrophilic groups grafted on the PVDF powder can absorb trace moisture in the environment at the same time to form a conductive layer, so that static electricity generated in the preparation process of the functional coating diaphragm is led out from a three-dimensional network structure, and the static voltage of the coating is reduced. The functional coating diaphragm can effectively avoid the phenomena of mutual adhesion and dust adsorption of PVDF coating diaphragms in the preparation process, and simultaneously avoid the problems of poor winding and difficult needle extraction of the battery core and low yield caused by large static electricity in the subsequent production and processing.
In addition, the above components are generally understood to be parts by weight, and represent a proportional relationship, not representing a specific weight of each substance. That is, the above ratio is calculated by calculating the ratio range of the other components based on 10 parts of PVDF powder (1 g may be represented by one part by weight or 1kg may be represented by the other mass). Any solution modified based on the technical idea of the present application shall be within the protection scope of the present application.
For example, in one embodiment, the functional coating slurry comprises the following components in parts by weight:
in another specific embodiment, the functional coating slurry comprises the following components in parts by weight:
preferably, the PVDF powder has a molecular weight M w The method comprises the following steps: 3.7X10 5 ≤M W ≤8.0×10 5 The melting point Tm is: tm is more than or equal to 140 ℃ and less than or equal to 160 ℃. PVDF, chinese polyvinylidene fluoride not only has good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance and radiation resistance, but also has special properties such as piezoelectricity, dielectric property, thermoelectric property and the like. In the embodiment of the application, the oily PVDF powder coating is coated on the membrane substrate, and the membrane is subjected to water washing pore-forming treatment, so that the prepared oily PVDF coated membrane has the excellent pole piece bonding characteristic of an oily process and the low pore-blocking characteristic of water-based coating, and has the advantages of small static electricity and good processability.
In the present application, the graft-modifying monomer includes at least one of acrylic acid, methacrylic acid, 2-ethylhexyl acrylate, and enamine. The grafting modification monomer is added to provide hydrophilic groups for PVDF powder, the grafted hydrophilic groups after modification are arranged outwards, and the hydrophobic groups in the coating are attached to the surface of the diaphragm material. The hydrophilic group can absorb water, and the water is liquid with high dielectric constant, so that the hydrophilic group forms a conductive layer in the coating after absorbing water, and static electricity generated in the preparation process of the functional coating diaphragm can be led out, and the static electricity in the functional coating diaphragm is reduced.
Specifically, the chemical formula of the acrylic acid is C 3 H 4 O 2 Is an unsaturated carboxylic acid; methacrylic acid has a chemical formula of C 4 H 6 O 2 Is colorless crystal or transparent liquid, and has pungent smell; 2-ethylhexyl acrylate of formula C 11 H 2 0O 2 Is colorless transparent liquid, odorless and tasteless; enamines are unsaturated compounds formed by dehydration condensation of aldehydes or ketones with secondary amines, and have the general formula R 2 C＝CR-NR 2 . Without any particular description of the present application, the chemical components employed are those commonly understood in the art, and any concepts based on the present technical solution fall within the scope of the present application.
In the embodiment of the application, the polar polymer material particles comprise at least one of polyvinyl alcohol, carboxylated modified polystyrene, carboxylated modified polypropylene, polyethylene oxide, PS-PMMA copolymerized crosslinked microspheres and PS-polyurethane copolymerized crosslinked microspheres; the polar polymer material particles are spherical or spheroidic, and the particle size is 50-500 nm. In the present application, the effect of the polar polymeric material particles is mainly two aspects: the polar polymer material particles are dispersed in the functional coating slurry, and can become network nodes to support the inside of the coating with a three-dimensional network structure when the coating is formed; and the polar functional groups in the polar polymer material particles also have hydrophilicity, so that trace moisture in the environment can be adsorbed, static electricity can be led out through a three-dimensional network structure through a conductive layer formed by the trace moisture, and the surface static voltage of the coating can be effectively reduced through the structure shown in fig. 2.
Specifically, the chemical formula of the polyvinyl alcohol is [ C 2 H 4 O] n The average molecular weight is 20000-200000; carboxylated modified polystyrene and carboxylated modified polypropylene are prepared through carboxylation modification treatment; polyethylene oxide is also called polyethylene oxide, and has the chemical formula of H (OCH) 2 CH 2 ) n OH, a crystalline, thermoplastic, water-soluble polymer; the PS-PMMA copolymerized crosslinked microsphere is prepared by polymerization reaction of Polystyrene (PS) and polymethyl methacrylate (PMMA); the PS-polyurethane copolymerization crosslinking microsphere is prepared by polymerization reaction of Polystyrene (PS) and polyurethane.
In an embodiment of the present application, the dispersing solvent includes at least one of methanol, ethanol, water, NMP, DMAc, DMSO, and DMF. Adding polar polymer material particles into the dispersion solvent, uniformly dispersing the polymer material particles (serving as solute) into the dispersion solvent by means of strong mechanical stirring, ultrasonic or sand grinding to prepare a suspension containing the polar polymer material particles, and mixing and stirring the suspension with grafted PVDF material to obtain the functional coating slurry, thereby preparing the functional coating diaphragm.
Specifically, NMP is also called N-methyl pyrrolidone and 1-methyl-2-pyrrolidone, and has a molecular formula of C 5 H 9 NO, a colorless transparent liquid; DMAc also known as dimethylacetamide, of the formula CH 3 CON(CH 3 ) 2 Is colorless transparent liquid; DMSO, also known as dimethyl sulfoxide, is a sulfur-containing organic compound of the formula (CH) 3 ) 2 SO; DMF is also known as N, N-dimethylformamide and has the molecular formula of C 3 H 7 NO。
In an embodiment of the present application, the solute in the alkaline solution includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide and sodium ethoxide, and the solvent includes at least one of methanol, ethanol, water, NMP and DMAc; the concentration of the alkali solution is 1-10%. The purpose of the alkali solution addition is to perform alkali treatment on the PVDF powder, so as to prepare for the subsequent oxidation grafting step. Lithium hydroxide, sodium hydroxide and potassium hydroxide all contain hydroxyl (OH) - ) Has strong alkalinity; sodium ethoxide contains C 2 H 5 O - Also has the characteristic of strong alkalinity. Preferably, the mass concentration of the alkali solution is 1-10%; further, the mass concentration of the alkali solution is 4 to 7%, and further, the mass concentration of the alkali solution is 5%.
In an embodiment of the present application, the solute in the oxidizer solution comprises at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate, and the solvent comprises at least one of NMP, DMAc, DMSO and DMF. The purpose of the oxidant solution is to graft hydrophilic groups to PVDF through oxidation treatment, so as to prepare the PVDF material after modification treatment. Preferably, the mass concentration of the oxidant solution is 0.5-5%; further, the mass concentration of the oxidant solution is 2-4%; still further, the mass concentration of the oxidizing agent is 3%.
Specifically, hydrogen peroxide is also called hydrogen peroxide, and has a molecular formula of H 2 O 2 The method comprises the steps of carrying out a first treatment on the surface of the Sodium hypochlorite has a molecular formula of NaClO; sodium percarbonate is an addition compound of hydrogen peroxide and sodium carbonate, and has a molecular formula of Na 2 CO 4 The method comprises the steps of carrying out a first treatment on the surface of the Sodium perborate is prepared from borax, sodium hydroxide, hydrogen peroxide and water, and has molecular formula of NaBO 3 ·4(H 2 O); potassium perborate of formula KBO 3 。
In addition, the application also provides a preparation method of the functional coating membrane, and chemical components adopted in the preparation method and the proportion thereof are specifically shown in the functional coating membrane, and are not described in detail below. The preparation method mainly comprises three steps: and modifying PVDF material, preparing functional coating slurry, and coating and film making.
Step S1: and (3) modifying the PVDF material, sequentially adding an alkali solution and an oxidant solution into the PVDF powder, performing alkali treatment to enable the PVDF powder to undergo an elimination reaction, and then adding a grafting modification monomer containing hydrophilic groups for oxidation grafting to obtain the hydrophilic group grafting modified PVDF material.
This step mainly comprises an alkaline treatment and an oxidative grafting process. Wherein the alkali treatment comprises: placing PVDF powder into an alkali solution for reaction, stirring uniformly, heating to the reaction temperature, preserving heat, and cooling to obtain a PVDF material containing unsaturated double bonds; the oxidative grafting comprises: continuously adding an oxidant solution into the solution, uniformly stirring, heating, adding a grafting modification monomer, and reacting for a period of time in a heat preservation way to obtain the PVDF material grafted and modified by hydrophilic groups.
In the alkali treatment, PVDF powder is fully mixed by a mechanical stirring mode after adding alkali solution with the mass concentration of 1-10%, the stirring speed is 10-100 rpm, the reaction temperature is 40-80 ℃, the reaction time (heat preservation time) is 0.1-1.5 h, and the cooling means cooling to room temperature. In the oxidation grafting, 0.5-5% of oxidant solution is added, the stirring speed is 5-50 rpm, the reaction temperature is 35-60 ℃, and under the condition, grafting modification monomers such as acrylic acid, methacrylic acid, 2-ethylhexyl acrylate and/or enamine and the like are continuously added, and the reaction time (heat preservation time) is 0.1-1.0 h. And (3) finishing the reaction to obtain the PVDF material grafted with hydrophilic groups, wherein the hydrophilic groups comprise at least one of carboxyl, hydroxyl, ester, amino and sulfonic acid groups. Grafting ratio = [ grafted modified monomer mass/(grafted modified monomer mass+grafted modified monomer homopolymer mass) ]. 100%, grafting ratio is 0.5-10%. The proportion relation of each component is as follows: assuming 10 parts of PVDF powder, the alkali solution is 100-500 parts, the oxidant solution is 1-10 parts, and the grafting monomer is 0.01-1 part.
It should be noted that, the grafting rate finally obtained in this step is 0.5-10%, more specifically, in order to take account of the two functions of the PVDF material, i.e. the bonding of the pole pieces, and the hydrophilic static conductive group through modification, the grafting rate should be controlled to be 3-5% optimally, so that the water content of the product can be effectively controlled within this range, and the product has good static conductive performance and reduces static electricity on the premise of ensuring the performance of the product. The addition amount of the grafting modification monomer directly influences the grafting rate, if the grafting rate is too low, the hydrophilic groups grafted by the PVDF material are too few, and insufficient groups and the polar polymer material form a network static electricity conducting structure together, so that the static electricity leading-out effect is poor, and the static electricity of the product is too large; too high a grafting ratio can lead to two undesirable consequences: firstly, the PVDF material has the problem of degradation and chain breakage, and damages the material structure, so that the bonding characteristics of the pole piece are reduced, and the main functions are affected; secondly, the high grafting rate easily causes too high hydrophilic groups of the PVDF material, and after the PVDF coating diaphragm is prepared, the moisture content of the product is too high, so that the problem of air expansion occurs in battery application, and the electric performance of the battery is affected.
Step S2: preparing functional coating slurry, adding polar polymer material particles into a dispersion solvent to prepare suspension, adding the suspension into a solution containing PVDF material, and uniformly stirring to prepare the functional coating slurry. The polar polymeric material particles may be dispersed in the dispersing solvent by means of strong mechanical agitation, ultrasound or sanding. Because the particle size of the polar polymer material particles is smaller and is approximately in the range of 50-500 nm, the polar polymer material particles are easy to agglomerate, and therefore, the polar polymer material particles are preferentially subjected to sand grinding and dispersing, the particle size of the grinding beads is 0.3-0.4 mm, the grinding is carried out for 1-10 times, and the time is 0.2-1.0 h. Adding the dispersed suspension into PVDF material grafted and modified by hydrophilic group, stirring again and mixing uniformly to obtain functional coating slurry, wherein the stirring time is usually 0.2-1.0 h, and the standard is that the functional coating slurry is completely and uniformly mixed.
Compared with the prior art, the functional coating slurry is greatly different in that PVDF material containing polar polymer material particles and hydrophilic groups can absorb trace moisture in the environment to form a water conducting layer, static electricity in the preparation process is led out through the water conducting layer, and static electricity on the coating is reduced.
Step S3: coating and forming a film, coating the functional coating slurry on two sides of a diaphragm substrate, and performing solidification pore forming, water washing pore shaping, drying and rolling to obtain the antistatic functional coating diaphragm.
The membrane substrate has a supporting function, the membrane substrate adopted in the application is a PP or PE membrane, the thickness is 5-20 mu m, and the membrane substrate can be applied to the field of battery membranes and has the advantages of good ductility, long service life and the like. Further, functional coating slurry is coated on both sides of the diaphragm substrate, and the thickness of one side coating is 0.5-2 mu m. And then preparing the antistatic functional coating diaphragm through a wet solidification pore-forming process. Specifically, the wet solidification pore-forming process mainly comprises the process flows of solidifying and fixing pores, washing the pores for shaping, drying and rolling. The preparation method comprises the steps of coating the prepared modified PVDF functional slurry on a membrane substrate through an oily membrane coater or a laboratory bench tester, and then soaking the modified PVDF functional slurry in coagulating liquid (the coagulating liquid is a mixed solution, the ratio of solvent to water is 10-50%, and the solvent can be one or a combination of a plurality of NMP, DMAc, DMF, DMSO), and soaking the modified PVDF functional slurry for 1-5 min at 20-40 ℃; then transferring and soaking in pure water solvent for 5-10 min at 20-40 ℃; then put into an oven and dried for 1-3 min at 40-90 ℃ to obtain the product.
The functional coating diaphragm and the preparation method thereof have the following characteristics:
1. the chemical grafting modification is carried out by a one-step method, the elimination reaction is carried out by adding an alkali solution, the oxidation grafting reaction is carried out by adding a grafting modification monomer and an oxidant solution, and the continuous operation is carried out without intermediate filtration, purification, ageing and other processes, so that the production efficiency is greatly improved, and the yield is improved;
2. the selected alkali solution, the grafting modified monomer and the oxidant solution are all materials suitable for a lithium battery system, and impurities which are unfavorable for a diaphragm or a lithium battery are not introduced, so that the method can be applied to the preparation of the lithium battery;
3. PVDF suitable for the application is a copolymer, namely polyvinylidene fluoride-hexafluoropropylene copolymer, and grafting modification selectively occurs in hexafluoropropylene structural units;
4. the hydrophilic group of the PVDF modified by the method has strong interaction with the polar functional group of the polar polymer material, can generate synergistic effect, and can realize the effect of three-dimensional static electricity conduction by distributing the hydrophilic group and the polar functional group in the coating of the network structure.
The technical scheme of the application is further described through specific examples.
Example 1
The functional coating diaphragm is prepared from the following functional coating slurry: 10 parts of PVDF powder, 200 parts of alkali solution, 5 parts of oxidant solution, 0.55 part of grafting modification monomer, 2 parts of polar polymer material particles and 20 parts of dispersing solvent. Specifically, the method comprises the following steps:
step S1: modifying PVDF material, sequentially adding 2000g of lithium hydroxide solution with mass concentration of 5% into 100g of PVDF-HFP powder, heating to 50 ℃ at a stirring speed of 50rpm, and carrying out elimination reaction for 0.5h; then 5.5g of methacrylic acid monomer and 50g of hydrogen peroxide solution with the mass concentration of 3% are added, the temperature and the stirring rate are kept, and the reaction is continued for 0.5h, so that the PVDF-HFP material grafted and modified by hydrophilic groups is prepared, and the grafting rate is 5%.
Step S2: preparing functional coating slurry, adding 20g of polyvinyl alcohol particles into 200g of NMP solvent, performing sand grinding and dispersing, grinding the particles with the particle size of 0.3-0.4 mm for 4 times and 1.0h to prepare suspension, adding the suspension into the solution containing PVDF-HFP material in the step S1, and uniformly stirring to obtain the functional coating slurry.
Step S3: coating and film-forming, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking the functional coating slurry in a coagulating liquid (the proportion of NMP/water is 30 percent) for 2 minutes at 25 ℃; then transferring and soaking in pure water solvent at 25deg.C for 5min; then put into an oven and dried at 60 ℃ for 3min, thereby obtaining the functional coating diaphragm with the total thickness of the double-sided coating of 4 mu.
Example 2
The functional coating diaphragm is prepared from the following functional coating slurry: 10 parts of PVDF powder, 500 parts of alkali solution, 10 parts of oxidant solution, 1 part of grafting modification monomer, 3 parts of polar polymer material particles and 30 parts of dispersing solvent. Specifically, the method comprises the following steps:
step S1: PVDF material is modified, 5000g of lithium hydroxide solution with mass concentration of 3% is sequentially added into 100g of PVDF-HFP powder, the temperature is raised to 60 ℃ under the stirring speed of 80rpm, and the elimination reaction is carried out for 1.0h; then 10g of acrylic acid monomer and 100g of sodium percarbonate solution with the mass concentration of 1% are added, the temperature and the stirring rate are kept, and the reaction is continued for 1.0h, so that the PVDF-HFP material grafted and modified by hydrophilic groups is prepared, and the grafting rate is 9.1%.
Step S2: preparing functional coating slurry, adding 30g of carboxylated modified polystyrene particles into 300g of DMAc solvent, performing sand grinding and dispersing, grinding the particles with the particle size of 0.3-0.4 mm for 2 times and 0.5h to prepare suspension, adding the suspension into the solution containing PVDF-HFP material in the step S1, and uniformly stirring to obtain the functional coating slurry.
Step S3: coating and film-forming, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking the functional coating slurry in a coagulating liquid (the proportion of DMAc/water is 40 percent) for 1.5min at 30 ℃; then transferring and soaking in pure water solvent at 30deg.C for 4min; then put into an oven and dried at 70 ℃ for 2min, thereby obtaining the functional coating diaphragm with the total thickness of the double-sided coating of 4 mu.
Example 3
The functional coating diaphragm is prepared from the following functional coating slurry: 10 parts of PVDF powder, 100 parts of alkali solution, 1 part of oxidant solution, 0.1 part of grafting modification monomer, 0.5 part of polar polymer material particles and 6 parts of dispersion solvent. Specifically, the method comprises the following steps:
step S1: modifying PVDF material, sequentially adding 1000g of lithium hydroxide solution with mass concentration of 10% into 100g of PVDF-HFP powder, heating to 80 ℃ at stirring speed of 100rpm, and eliminating reaction for 1.5h; then adding 1g of acrylic acid-2-ethylhexyl ester monomer, 10g of sodium perborate solution with mass concentration of 5%, keeping the temperature and stirring speed, and continuing to react for 1.0h to obtain the PVDF-HFP material grafted and modified by hydrophilic groups, wherein the grafting rate is 0.99%.
Step S2: preparing functional coating slurry, adding 5g of carboxylated modified polypropylene particles into 60g of DMF solvent, performing sand grinding and dispersing, grinding the particles with the particle size of 0.3-0.4 mm for 8 times and the time of 0.8h to prepare suspension, adding the suspension into the solution containing PVDF-HFP material in the step S1, and uniformly stirring to prepare the functional coating slurry.
Step S3: coating and film-forming, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking the functional coating slurry in a coagulating liquid (the ratio of DMF/water is 20 percent) for 1min at 40 ℃; then transferring and soaking in pure water solvent at 40deg.C for 2min; then put into an oven and dried at 80 ℃ for 1.5min, thereby obtaining the functional coating diaphragm with the total thickness of the double-sided coating layer of 4 mu.
Comparative example 1
Comparative example 1 differs from example 1 in that: step S1 was omitted and unmodified PVDF-HFP material was used, the remainder of the composition and preparation being the same as in example 1.
Comparative example 2
Comparative example 2 is different from example 1 in that: step S2 was omitted, and the polar polymer particles were not used, and the remaining components and the preparation method were the same as in example 1.
Comparative example 3
Comparative example 3 is different from example 1 in that: in step S3, the coagulating liquid and the pure water solvent are not soaked, and the coating is directly carried out, so that the coating is prepared, and the rest components and the preparation method are the same as those in example 1.
Performance testing
Six sets of lithium battery separators in the above 3 examples and 3 comparative examples were fabricated into lithium ion batteries, and peel strength of the separators and the pole pieces were measured in a wet pressure environment (electrolyte: EC/emc=3/7 (v/v), 1m LiPF 6, VC 2%; temperature 70 ℃, pressure 1.0 MPa) and a dry pressure environment (temperature 70 ℃ + pressure 1.5 MPa).
The lithium ion battery separators of examples 1 to 3 and the separators of comparative examples 1 to 3 were measured for thickness, air permeability, peel strength, and static electricity value, and after the separators were fabricated into batteries, the battery resistance and cycle parameters of the batteries were measured.
Table 1 results of various tests on diaphragms prepared in examples and comparative examples
The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be limiting. Several simple deductions, modifications or substitutions may also be made by a person skilled in the art to which the invention pertains, based on the idea of the invention.
Claims (6)
1. The functional coating diaphragm is characterized by being prepared from the following functional coating slurry in parts by weight:
at least one of an acid, 2-ethylhexyl acrylate, and enamine; the grafting modification monomer is used for providing hydrophilic groups for PVDF powder, and the grafting rate is 0.5-10%; in the alkali solution, the solute comprises at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide and sodium ethoxide, and the solvent comprises at least one of methanol, ethanol, water, NMP and DMAc; the mass concentration of the alkali solution is 1-10%;
in the oxidant solution, the solute comprises at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate and potassium perborate, and the solvent comprises at least one of NMP, DMAc, DMSO and DMF; the mass concentration of the oxidant solution is 0.5-5%;
the dispersion solvent includes at least one of methanol, ethanol, water, NMP, DMAc, DMSO, and DMF.
2. The functional coated separator of claim 1 wherein the PVDF powder has a molecular weight M w The method comprises the following steps: 3.7X10 5 ≤M W ≤8.0×10 5 The melting point Tm is: tm is more than or equal to 140 ℃ and less than or equal to 160 ℃.
3. The functional coated separator of claim 2, wherein the polar polymeric material particles comprise at least one of polyvinyl alcohol, carboxylated modified polystyrene, carboxylated modified polypropylene, polyethylene oxide, PS-PMMA co-crosslinked microspheres, and PS-polyurethane co-crosslinked microspheres; the polar polymer material particles are spherical or spheroidic, and the particle size is 50-500 nm.
4. A method for producing a functional coated separator according to any one of claim 1 to 3, comprising the steps of,
s1: modifying the PVDF material, sequentially adding an alkali solution and an oxidant solution into the PVDF powder, performing alkali treatment, performing elimination reaction on the PVDF powder, and then adding a grafting modification monomer containing hydrophilic groups for oxidative grafting to obtain a hydrophilic group grafting modified PVDF material;
s2: preparing functional coating slurry, adding polar polymer material particles into a dispersion solvent to prepare suspension, adding the suspension into a solution containing PVDF material, and uniformly stirring to prepare the functional coating slurry;
s3: coating and filming, namely coating functional coating slurry on two sides of a diaphragm substrate, and performing solidification pore forming, water washing pore shaping, drying and rolling to obtain an antistatic functional coating diaphragm;
in the step S1, during alkali treatment, the stirring speed is 10-100 rpm, the reaction temperature is 40-80 ℃, the reaction time is 0.1-1.5 h, during oxidative grafting, the stirring speed is 5-50 rpm, the reaction temperature is 35-60 ℃, and the reaction time is 0.1-1.0 h; in step S2, the dispersion is performed by means of mechanical stirring, ultrasound or sanding, when preparing the suspension.
5. The method for preparing a functional coated separator according to claim 4, wherein in the PVDF material grafted and modified with hydrophilic groups, the hydrophilic groups include at least one of carboxyl groups, hydroxyl groups, ester groups, amine groups, and sulfonic acid groups; the diaphragm base material is a PP or PE diaphragm, and the thickness of the diaphragm base material is 5-20 mu m; the thickness of the single-side coating of the functional coating slurry is 0.5-2 mu m.
6. Use of a functional coated separator according to any one of claims 1 to 3 or a functional coated separator prepared by a preparation method according to any one of claims 4 to 5 in a lithium ion battery separator.
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| WO2023078409A1 (en) * | 2021-11-05 | 2023-05-11 | 珠海冠宇电池股份有限公司 | Separator and lithium ion battery comprising same |
| CN114142167B (en) * | 2021-11-30 | 2023-05-02 | 珠海冠宇电池股份有限公司 | Diaphragm and lithium ion battery containing same |
| CN116780102A (en) * | 2022-03-07 | 2023-09-19 | 深圳市星源材质科技股份有限公司 | Coating for battery separator, preparation method of coating, battery separator and battery |
| CN115044171A (en) * | 2022-06-30 | 2022-09-13 | 浙江华正新材料股份有限公司 | Resin composition, resin-based composite material and preparation method thereof |
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