阅读说明：本技术 一种功能涂层隔膜及其制备方法和应用 (Functional coating diaphragm and preparation method and application thereof ) 是由 刘向春 唐丽 于 2021-08-10 设计创作，主要内容包括：本申请公开了一种功能涂层隔膜及其制备方法和应用,其中该功能涂层隔膜由以下组分按重量份组成：PVDF粉体10份、碱溶液100份～500份、氧化剂溶液1份～10份、接枝改性单体0.01份-1份、极性高分子材料颗粒0.5份～3份和分散溶剂6～30份。本发明采用先消除反应后氧化工艺对PVDF材料进行改性,制备出改性PVDF功能浆料,然后涂覆在隔膜基材上,通过油性水洗工艺制得一种功能涂层隔膜,使制备的功能涂层隔膜同时具有油性工艺的优良极片粘结特性和水性涂布的低堵孔特性,另外,极性高分子材料颗粒和用于改性的亲水基团可以吸收微量水分,二者分布在网络结构的涂层中,可实现三维立体导静电的效果,有效降低功能涂层隔膜产生静电的概率,提高功能涂层隔膜产品和电芯的成品率。(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 aqueous alkali, 1-10 parts of oxidant solution, 0.01-1 part of graft modified monomer, 0.5-3 parts of polar high polymer material particles and 6-30 parts of dispersing solvent. The invention adopts the technology of eliminating reaction firstly and then oxidizing to modify PVDF material, prepare modified PVDF functional slurry, then coat on the diaphragm substrate, prepare a functional coating diaphragm through the oily water washing technology, make the functional coating diaphragm prepared have excellent pole piece adhesive property of the oily technology and low pore blocking property of aqueous coating at the same time, in addition, polar high molecular material granule and hydrophilic group used for modifying can absorb trace moisture, the two are distributed in the coating of the network structure, can realize the three-dimensional static-conducting effect, reduce the probability that the functional coating diaphragm produces static effectively, improve the yield of diaphragm products and electric core of functional coating.)

1. The functional coating diaphragm is characterized by being prepared from the following functional coating slurry in parts by weight:

2. the functional coated separator according to claim 1, wherein the molecular weight M of the PVDF powder is_wComprises the following steps: 3.7X 10⁵≤M_W≤8.0×10⁵The 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.

3. The functional coated separator according to claim 2, wherein 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 spheroidal, and the particle size is 50-500 nm.

4. The functionally coated membrane of claim 3, wherein the alkali solution comprises a solute comprising at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and sodium ethoxide, and a solvent comprising at least one of methanol, ethanol, water, NMP, and DMAc; the mass concentration of the alkali solution is 1-10%.

5. The functionally coated membrane of claim 4 wherein the oxidizer solution has solutes comprising at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate, and a solvent comprising at least one of NMP, DMAc, DMSO, and DMF; the mass concentration of the oxidant solution is 0.5-5%.

6. The functionally coated membrane of claim 5, wherein the dispersing solvent comprises at least one of methanol, ethanol, water, NMP, DMAc, DMSO, and DMF.

7. A method for preparing the functional coating separator as defined in any one of claims 1 to 6, comprising the steps of,

s1: modifying a PVDF material, namely sequentially adding an alkali solution and an oxidant solution into PVDF powder, performing alkali treatment to remove the PVDF powder, and then adding a grafting modification monomer containing a hydrophilic group for oxidative grafting to prepare the hydrophilic group grafting modified PVDF material;

s2: preparing functional coating slurry, adding polar high polymer material particles into a dispersion solvent to prepare a suspension, adding the suspension into a solution containing a PVDF material, and uniformly stirring to prepare the functional coating slurry;

s3: and (3) coating to prepare a membrane, namely coating the functional coating slurry on two sides of the membrane substrate, and preparing the antistatic functional coating membrane through solidification pore-forming, washing pore sizing, drying and rolling.

8. The method for preparing the functional coating separator according to claim 7, wherein in the step S1, the stirring speed is 10-100 rpm, the reaction temperature is 40-80 ℃, the reaction time is 0.1-1.5 h during the alkali treatment, the stirring speed is 5-50 rpm, the reaction temperature is 35-60 ℃, and the reaction time is 0.1-1.0 h during the oxidative grafting; in step S2, in preparing the suspension, the dispersion is performed by mechanical stirring, ultrasound or sand milling.

9. The method for preparing a functional coated membrane according to claim 8, wherein in the PVDF material modified by grafting 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 μm.

10. The application of the functional coating diaphragm of any one of claims 1 to 6 or the functional coating diaphragm prepared by the preparation method of any one of claims 7 to 9 in a lithium ion battery diaphragm.

Technical Field

The invention relates to diaphragm preparation 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 needs to be coated outside the lithium battery, so that the use safety of the lithium battery is improved, the diaphragm of the conventional lithium battery can be divided into a wet-method PE diaphragm and a dry-method PP diaphragm according to the difference of process procedures, because the liquid absorption rate and the caking property of the PE and PP coating diaphragms are poor, an oily PVDF coating is usually coated on a diaphragm base film, and an oily PVDF coating diaphragm is obtained by washing and forming holes, compared with the traditional PE/PP diaphragm, the caking property of the diaphragm and a pole piece is obviously improved, the cycle life, the rate capability and the safety of the battery can be greatly improved, the oily PVDF coating diaphragm in the current market has large static electricity, the diaphragms are easily adhered to each other and adsorb dust in the production and use processes, and meanwhile, the diaphragm is easy to cause poor winding of a battery core, difficult to draw a needle and low yield in the rear-stage production and processing, the problem of high static electricity of the oily PVDF coating diaphragm is urgently needed to be solved so as to improve the processing and application performance of the diaphragm.

The PVDF organic functional polymer is generally prepared by an oil-based or water-based process, is coated on a diaphragm, and is directly dried and molded. Although the process is simple and is suitable for large-scale production and application, the oil-based or water-based process is adopted for pulping independently, and the following defects exist: firstly, the oily direct drying process uses flammable, explosive and toxic organic solvents, is not environment-friendly, and the product prepared by the process is obviously blocked, can affect the multiplying power and the cycle performance of the battery, and has the problems of large static electricity of a coating and being not beneficial to processing and application; and secondly, although the water-based process has no problems of environmental protection and economy, the prepared product has insufficient adhesive force, and the problems of high moisture, poor pole piece adhesive force and the like exist when the water-based process is applied to batteries.

For example, a composite coating-treated lithium ion battery separator and a preparation method thereof (with the patent number of CN106252565B), the invention designs a multilayer structure, one side of the processed base film is coated with aramid fiber, the same side of the base film is coated with polyvinylidene fluoride, and the other side of the base film is coated with inorganic particles, so that the product has both heat resistance and pole piece bonding property, although the coating of inorganic particles on one side of the substrate can improve the heat resistance and electrostatic characteristics of this side, the coating of aramid on the other side, and the coating of PVDF on the aramid coating layer have problems in that the processing is difficult and the coating static electricity is large, and at the same time, since one side of the separator is inevitably problematic in that the static electricity is large, the electrostatic characteristics of the product as a whole are not improved, moreover, the coating of the product has the advantages of multiple and complex structures, multiple processing times, low production efficiency and incapability of ensuring the rate of finished products. Therefore, the prior art has yet to be developed.

Disclosure of Invention

The application provides a functional coating diaphragm and a preparation method thereof, aiming at providing a functional coating diaphragm with small static electricity, high coating porosity and good adhesive property so as to improve the processing and application properties of the diaphragm.

The PVDF modification technology reported in the prior art is mostly inorganic blending modification technology, i.e. inorganic silica or alumina material is added for mixing to form an organic-inorganic composite material, but the method has the problems of uneven dispersion of inorganic material 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 application, the PVDF powder is subjected to alkali treatment, the PVDF material undergoes an elimination reaction, and then a grafting modification monomer containing a hydrophilic group is added for oxidation grafting to prepare the hydrophilic group grafting modified PVDF material.

According to a first aspect, the present application provides a functional coating membrane, which is prepared from functional coating slurry comprising, by weight:

in one embodiment, the molecular weight M of the PVDF powder_wComprises the following steps: 3.7X 10⁵≤M_W≤8.0×10⁵The 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 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 spheroidal, and the particle size is 50-500 nm.

In one embodiment, the base solution comprises a solute comprising at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and sodium ethoxide, and a solvent comprising 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 includes a solute comprising at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate, and a solvent comprising at least one of NMP, DMAc, DMSO, and DMF; the mass concentration of the oxidant solution is 0.5-5%.

In one embodiment, the dispersion 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 the functional coated separator as described in the first aspect, comprising the steps of,

s1: modifying a PVDF material, namely sequentially adding an alkali solution and an oxidant solution into PVDF powder, adding a grafting modification monomer containing a hydrophilic group in a manner of firstly performing alkali treatment and then oxidizing and grafting to prepare the PVDF material grafted and modified by the hydrophilic group;

s2: preparing functional coating slurry, adding polar high polymer material particles into a dispersion solvent to prepare a suspension, adding the suspension into a solution containing a PVDF material, and uniformly stirring to prepare the functional coating slurry;

s3: and (3) coating to prepare a membrane, namely coating the functional coating slurry on two sides of the membrane substrate, and preparing the antistatic functional coating membrane through solidification pore-forming, washing pore sizing, drying and rolling.

In one embodiment, in step S1, the stirring speed is 10-100 rpm, the reaction temperature is 40-80 ℃, the reaction time is 0.1-1.5 h during the alkali treatment, the stirring speed is 5-50 rpm, the reaction temperature is 35-60 ℃, and the reaction time is 0.1-1.0 h during the oxidation grafting; in step S2, in preparing the suspension, the dispersion is performed by mechanical stirring, ultrasound or sand milling.

In one embodiment, in the PVDF material graft-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 grafting ratio is 0.5-10%, wherein the grafting ratio is [ mass of grafted modified monomer/(mass of grafted modified monomer + mass of grafted modified monomer homopolymer) ]. 100%.

In one embodiment, the membrane substrate is a PP or PE membrane, and the thickness of the membrane substrate is 5-20 μm; the thickness of the single-side coating of the functional coating slurry is 0.5-2 μm.

According to a third aspect, the application also provides an application of the functional coating diaphragm of the first aspect or the functional coating diaphragm prepared by the preparation method of the second aspect in a lithium ion battery diaphragm. The functional coating diaphragm has small static electricity and high porosity (a three-dimensional network structure is formed inside), can effectively reduce dust or bonding conditions, and improves the yield of products.

Has the advantages that: according to the functional coating diaphragm prepared by the preparation method, because the hydrophilic groups in the coating are arranged outwards, the hydrophilic groups and the polar polymer material particles can adsorb trace moisture in the environment, so that a water conducting layer is formed on the surface of the coating, and the coating has an electrostatic conducting effect; in addition, the polar polymer material particles form network nodes in the coating network structure, and three-dimensional static conduction is realized. The functional coating diaphragm has less static electricity in the production process, is not easy to form adhesion or adsorb dust, has higher porosity and good uniformity, and can effectively improve the processing performance of the coating diaphragm. When the film 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 as described in the examples of the present application; wherein, 1 represents a coating; 2 represents polar polymer material particles; and 3 represents a separator substrate.

FIG. 2 is a schematic view of the internal structure of the functional coating diaphragm under a microscope in the embodiment of the application; the inside of the structure forms a three-dimensional network structure as can be seen from the figure.

Detailed Description

The present invention will be described in further detail with reference to the following detailed description and accompanying drawings. Wherein like elements in different embodiments are numbered with like associated elements. In the following description, numerous details are set forth in order to provide a better understanding of the present application. However, those skilled in the art will readily recognize that some of the features may be omitted or replaced with other elements, materials, methods in different instances. In some instances, certain operations related to the present application have not been shown or described in detail in order to avoid obscuring the core of the present application from excessive description, and it is not necessary for those skilled in the art to describe these operations in detail, so that they may be fully understood from the description in the specification and the general knowledge in the art.

Furthermore, the features, operations, or characteristics described in the specification may be combined in any suitable manner to form various embodiments. Also, the various steps or actions in the method descriptions may be transposed or transposed in order, as will be apparent to one of ordinary skill in the art. Thus, the various sequences in the specification and drawings are for the purpose of describing certain embodiments only and are not intended to imply a required sequence unless otherwise indicated where such sequence must be followed.

In the present invention, the term "room temperature" means a temperature range of 25. + -. 5 ℃. All ranges cited herein are inclusive, unless expressly stated to the contrary. The numbers in this disclosure are approximate, regardless of whether the word "about" or "approximately" is used. The numerical value of the number may have differences of 1%, 2%, 5%, 7%, 8%, 10%, etc. Whenever a number with a value of N is disclosed, any number with a value of N +/-1%, N +/-2%, N +/-3%, N +/-5%, N +/-7%, N +/-8% or N +/-10% is explicitly disclosed, wherein "+/-" 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 comprises a separator substrate 3 and coating layers 1 (made of functional coating slurry) coated on both sides of the separator substrate 3, wherein the coating layers 1 further have polar polymer material particles 2 capable of serving as network nodes for supporting. Specifically, the functional coating slurry for preparing the coating comprises the following components in parts by weight:

it should be noted that the functional coating membrane in the present application refers to a PVDF coating membrane (also called as an oily PVDF coating membrane) prepared by an oily water washing process, and polar polymer material particles and a modified and grafted PVDF material (prepared from PVDF powder, a graft modification monomer, and the like) are added in the coating. The polar high polymer material particles in the functional coating diaphragm provide framework support and network nodes, and meanwhile, polar functional groups in the polar high polymer material particles and hydrophilic groups grafted on PVDF powder can simultaneously adsorb trace moisture in the environment 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 the PVDF coating diaphragm in the preparation process, and simultaneously avoid the problems of poor winding of a battery core, difficult needle drawing and low yield caused by large static electricity in the back-end production and processing.

In addition, it should be noted that the above components are generally understood as parts by weight, which are proportional and do not represent the specific weight of each substance. That is, the above ratio is a ratio range part calculated for other components assuming that 10 parts (one part may represent 1g or 1kg, etc. by weight) of PVDF powder are used. Any variant based on the technical idea of the present application should fall within the protection scope of the present application.

For example, in one embodiment, the functional coating paste 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 molecular weight M of the PVDF powder_wComprises the following steps: 3.7X 10⁵≤M_W≤8.0×10⁵The melting point Tm is: tm is more than or equal to 140 ℃ and less than or equal to 160 ℃. PVDF and Chinese polyvinylidene fluoride have good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance and ray radiation resistance, and also have special properties such as piezoelectricity, dielectricity, pyroelectricity and the like. In the embodiment of the application, the oily PVDF powder coating is coated on the diaphragm substrate, and the pore-forming treatment is carried out through water washing, so that the prepared oily PVDF coating diaphragm 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 purpose of adding the grafting modification monomer is to provide hydrophilic groups for PVDF powder, the modified grafted hydrophilic groups 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, 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, acrylic acid has the chemical formula C₃H₄O₂Is an unsaturated carboxylic acid; methacrylic acid has the formula C₄H₆O₂The liquid is colorless crystal or transparent liquid and has pungent smell; 2-ethylhexyl acrylate of formula C₁₁H₂0O₂The liquid is colorless and transparent liquid, and is odorless and tasteless; enamines are unsaturated compounds formed by dehydration condensation of aldehydes or ketones and secondary amines, and have the general formula R₂C＝CR-NR₂. The chemical components used are all chemical substances generally understood in the art, and any concept based on the technical scheme is within the protection scope of the present application.

In the embodiment of the present application, the polar polymer material particles include 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 spheroidal, and the particle size is 50-500 nm. In the present application, the role of the polar polymer material particles is mainly two-fold: firstly, polar high polymer material particles are dispersed in functional coating slurry, and when a coating is formed, the polar high polymer material particles can become network nodes and play a supporting role in the coating with a three-dimensional network structure; and secondly, polar functional groups in the polar high molecular material particles also have hydrophilicity and can adsorb trace moisture in the environment, and static electricity can be led out through a three-dimensional network structure through a conducting layer formed by the trace moisture, and the surface static voltage of the coating can be effectively reduced by the structure shown in fig. 2.

Specifically, the polyvinyl alcohol has the chemical formula of [ C₂H₄O]_nThe average molecular weight is 20000-200000; the carboxylated modified polystyrene and the carboxylated modified polypropylene are both prepared by carboxylation modification treatment; polyethylene oxide, also known as polyethylene oxide, has the chemical formula H (OCH)₂CH₂)_nOH, a crystalline, thermoplastic, water-soluble polymer; the PS-PMMA copolymerized crosslinked microspheres refer to copolymerized crosslinked microspheres prepared by polymerizing Polystyrene (PS) and polymethyl methacrylate (PMMA); the PS-polyurethane copolymerized crosslinked microspheres refer to copolymerized crosslinked microspheres prepared by polymerizing Polystyrene (PS) and polyurethane.

In the present embodiment, the dispersion solvent includes at least one of methanol, ethanol, water, NMP, DMAc, DMSO, and DMF. Adding polar high molecular material particles into the dispersing solvent, uniformly dispersing the high molecular material particles (as solute) in the dispersing solvent in a mode of strong mechanical stirring, ultrasound or sanding to prepare suspension containing the polar high molecular material particles, mixing and stirring the suspension and the grafted PVDF material to obtain functional coating slurry, and preparing the functional coating diaphragm.

Specifically, NMP is also called N-methyl pyrrolidone, 1-methyl-2-pyrrolidone, molecular formula C₅H₉NO, a colorless transparent liquid; DMAc is also called dimethylacetamide and has a molecular formula of CH₃CON(CH₃)₂Is colorless transparent liquid; DMSO, also known as dimethyl sulfoxide, is a sulfur-containing organic compound with a molecular formula of (CH)₃)₂SO; DMF is also known as N, N-dimethylformamide and has a molecular formula of C₃H₇NO。

In an embodiment of the present application, the solute in the alkali solution 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 concentration of the alkali solution is 1-10%. The purpose of adding the alkali solution is to carry out alkali treatment on PVDF powder for the subsequent stepIn preparation for the oxidative grafting step of (a). Lithium hydroxide, sodium hydroxide, potassium hydroxide all contain hydroxyl (OH)^-) Having strong basicity; sodium ethoxide contains C₂H₅O^-And also has strong basicity. Preferably, the mass concentration of the alkali solution is 1-10%; further, the mass concentration of the alkali solution is 4-7%, and further, the mass concentration of the alkali solution is 5%.

In an embodiment of the present application, the solute in the oxidizer solution includes at least one of hydrogen peroxide, sodium hypochlorite, sodium percarbonate, sodium perborate, and potassium perborate, and the solvent includes at least one of NMP, DMAc, DMSO, and DMF. The oxidant solution is added to graft hydrophilic groups onto the PVDF through oxidation treatment, so as to prepare the PVDF material subjected to 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%; further, the mass concentration of the oxidizing agent is 3%.

Specifically, hydrogen peroxide is also called hydrogen peroxide, and the molecular formula is H₂O₂(ii) a The molecular formula of the sodium hypochlorite is NaClO; sodium percarbonate is an addition compound of hydrogen peroxide and sodium carbonate, and has a molecular formula of Na₂CO₄(ii) a The sodium perborate is prepared from borax, sodium hydroxide, hydrogen peroxide and water, and has a molecular formula of NaBO₃·4(H₂O); potassium perborate having the molecular formula KBO₃。

In addition, the present application also provides a preparation method of the functional coating membrane, and the chemical components and the proportion thereof adopted in the preparation method are specifically referred to the content in the functional coating membrane, and are not described in detail below. The preparation method mainly comprises three steps: modifying a PVDF material, preparing functional coating slurry and coating to prepare a membrane.

Step S1: modifying a PVDF material, namely adding an alkali solution and an oxidant solution into PVDF powder in sequence, performing alkali treatment to remove the PVDF powder, and then adding a grafting modification monomer containing a hydrophilic group for oxidation grafting to prepare the hydrophilic group grafting modified PVDF material.

The step mainly comprises alkali treatment and oxidation grafting processes. Wherein the alkali treatment comprises: putting PVDF powder into an alkaline solution for reaction, uniformly stirring, heating to a reaction temperature, preserving heat, and cooling to obtain a PVDF material containing unsaturated double bonds; the oxidative grafting comprises: and continuously adding an oxidant solution into the solution, uniformly stirring, heating, adding a grafting modification monomer, and carrying out heat preservation reaction for a period of time to obtain the hydrophilic group grafting modified PVDF material.

In the alkali treatment, after adding an alkali solution with the mass concentration of 1-10% into the PVDF powder, the PVDF powder is fully mixed in a mechanical stirring mode, 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 temperature reduction refers to the reduction to the 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 ℃, graft modification monomers such as acrylic acid, methacrylic acid, acrylic acid-2-ethylhexyl ester and/or enamine are continuously added under the condition, 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 groups, amine groups and sulfonic groups. The grafting rate is [ the mass of the grafted modified monomer/(the mass of the grafted modified monomer + the mass of the grafted modified monomer homopolymer) ]. 100%, and the grafting rate is 0.5-10%. The proportion relation of each component is as follows: assuming 10 parts of PVDF powder, 100-500 parts of alkali solution, 1-10 parts of oxidant solution and 0.01-1 part of grafting monomer.

It should be noted that the grafting ratio finally obtained in this step is 0.5-10%, and more specifically, in order to take into account the two functions of the PVDF material serving as the bonding pole piece and the modified grafted hydrophilic static conductive group, the grafting ratio should be controlled to be 3-5% optimal, the water content of the product can be effectively controlled within this range, and the product has good static conductive performance and reduces static on the premise of ensuring the product performance. 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 low, and insufficient groups and the polar high polymer material form a network static electricity conducting structure together, so that the static electricity conducting effect is poor, and the static electricity of the product is too high; too high a grafting ratio, however, leads to two undesirable consequences: firstly, the PVDF material has the problems of degradation and chain scission, damages the material structure, causes the reduction of the pole piece bonding property and influences the main functions; and secondly, the grafting rate is high, so that the hydrophilic group of the PVDF material is easily too high, and after the PVDF coating membrane is prepared, the water content of the product is too high, so that the ballooning problem occurs in the battery application, and the electrical property of the battery is influenced.

Step S2: preparing functional coating slurry, adding polar high polymer material particles into a dispersing solvent to prepare a suspension, adding the suspension into a solution containing a PVDF material, and uniformly stirring to prepare the functional coating slurry. The polar polymer material particles may be dispersed in the dispersion solvent by means of strong mechanical stirring, ultrasound or sand milling. As the particle size of the polar polymer material particles is smaller and is approximately within the range of 50-500 nm, the particles are easy to agglomerate, the method of sanding and dispersing is preferably adopted, 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. And adding the suspension obtained after dispersion into the PVDF material grafted and modified by the hydrophilic group, and stirring and mixing uniformly again to obtain the functional coating slurry, wherein the stirring time is usually 0.2-1.0 h, and the standard is that the mixture is completely and uniformly mixed.

Compared with the prior art, the functional coating slurry has the great difference that the PVDF material containing polar high polymer material particles and hydrophilic groups can absorb micro-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: and (3) coating to prepare a membrane, namely coating the functional coating slurry on two sides of the membrane substrate, and preparing the antistatic functional coating membrane through solidification pore-forming, washing pore sizing, drying and rolling.

The diaphragm base material has a supporting function, is a PP or PE diaphragm, has a thickness of 5-20 micrometers, can be applied to the field of battery diaphragms, and has the advantages of good ductility, long service life and the like. Furthermore, functional coating slurry is coated on both sides of the diaphragm substrate, and the thickness of the single-side coating is 0.5-2 μm. And then preparing the antistatic functional coating diaphragm by a wet solidification pore-forming process. Specifically, the wet-type solidification pore-forming process mainly comprises the process flows of solidifying and fixing pores, washing pore sizing, drying and rolling. Specifically, the prepared modified PVDF functional slurry is coated on a diaphragm substrate through an oily diaphragm coating machine or a laboratory pilot scale, and then is soaked in a solidification solution (the solidification solution is a mixed solution, the ratio of a solvent to water is 10-50%, the solvent can be one or a combination of more of NMP, DMAc, DMF and DMSO), and is soaked for 1-5 min at the temperature of 20-40 ℃; then transferring and soaking in a pure water solvent for 5-10 min at the temperature of 20-40 ℃; and then putting the mixture into an oven, and drying the mixture for 1-3 min at the temperature of 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 alkali solution is added for the elimination reaction, the grafting modification monomer and the oxidant solution are added for the oxidation grafting reaction, the continuous operation is realized, and the processes of intermediate filtration, purification, aging and the like do not exist, so the production efficiency is greatly improved, and the yield is improved;

2. the selected aqueous alkali, the graft modified monomer and the oxidant solution are all materials suitable for a lithium battery system, and impurities which are unfavorable to 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 a polyvinylidene fluoride-hexafluoropropylene copolymer, and the grafting modification selectivity occurs in a hexafluoropropylene structural unit;

4. the hydrophilic group of the modified PVDF and the polar functional group of the polar high molecular material have strong interaction and can generate synergistic action, and the hydrophilic group and the polar functional group are distributed in the coating with a network structure, so that the three-dimensional static electricity conducting effect can be realized.

The technical solution of the present application is further illustrated by the following specific examples.

Example 1

A functional coating diaphragm and a preparation method thereof are provided, wherein the functional coating diaphragm is prepared from functional coating slurry comprising the following components in parts by weight: 10 parts of PVDF powder, 200 parts of alkali solution, 5 parts of oxidant solution, 0.55 part of graft modified monomer, 2 parts of polar high polymer material particles and 20 parts of dispersing solvent. Specifically, the method comprises the following steps:

step S1: modifying a PVDF material, sequentially adding 2000g of lithium hydroxide solution with the mass concentration of 5% into 100g of PVDF-HFP powder, heating to 50 ℃ at the stirring speed of 50rpm, and carrying out elimination reaction for 0.5 h; then 5.5g of methacrylic acid monomer and 50g of hydrogen peroxide solution with the mass concentration of 3 percent are added, the temperature and the stirring rate are kept, the reaction is continued for 0.5h, and the hydrophilic group graft modified PVDF-HFP material is prepared, wherein the grafting rate is 5 percent.

Step S2: preparing functional coating slurry, adding 20g of polyvinyl alcohol particles into 200g of NMP solvent, grinding the particles in a sand grinding and dispersing mode, wherein the particle size of the grinding beads is 0.3-0.4 mm, grinding the particles for 4 times for 1.0h to prepare suspension, adding the suspension into the solution containing the PVDF-HFP material obtained in the step S1, and uniformly stirring to prepare the functional coating slurry.

Step S3: coating and preparing a membrane, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking in a solidification solution (the proportion of NMP/water is 30%) at 25 ℃ for 2 min; then transferring and soaking in pure water solvent, and soaking for 5min at 25 ℃; and then, putting the membrane into an oven, and drying the membrane for 3min at 60 ℃ to obtain the functional coating membrane with the total thickness of the double-sided coating of 4 mu.

Example 2

A functional coating diaphragm and a preparation method thereof are provided, wherein the functional coating diaphragm is prepared from functional coating slurry comprising the following components in parts by weight: 10 parts of PVDF powder, 500 parts of alkali solution, 10 parts of oxidant solution, 1 part of graft modified monomer, 3 parts of polar high polymer material particles and 30 parts of dispersing solvent. Specifically, the method comprises the following steps:

step S1: modifying a PVDF material, sequentially adding 5000g of lithium hydroxide solution with the mass concentration of 3% into 100g of PVDF-HFP powder, heating to 60 ℃ at the stirring speed of 80rpm, and carrying out elimination reaction for 1.0 h; 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 to prepare the hydrophilic group graft modified PVDF-HFP material with the grafting rate of 9.1%.

Step S2: preparing functional coating slurry, adding 30g of carboxylated modified polystyrene particles into 300g of DMAc solvent, grinding the mixture for 2 times in a sand grinding and dispersing mode, grinding the mixture for 0.5h to obtain suspension, adding the suspension into the solution containing the PVDF-HFP material obtained in the step S1, and stirring the mixture uniformly to obtain the functional coating slurry.

Step S3: coating and film making, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking in a solidification solution (the DMAc/water ratio is 40%) for 1.5min at 30 ℃; then transferring and soaking in pure water solvent, and soaking for 4min at 30 ℃; and then, putting the membrane into an oven, and drying the membrane for 2min at 70 ℃ to obtain the functional coating membrane with the total thickness of the double-sided coating of 4 mu.

Example 3

A functional coating diaphragm and a preparation method thereof are provided, wherein the functional coating diaphragm is prepared from functional coating slurry comprising the following components in parts by weight: 10 parts of PVDF powder, 100 parts of alkali solution, 1 part of oxidant solution, 0.1 part of graft modified monomer, 0.5 part of polar high polymer material particles and 6 parts of dispersing solvent. Specifically, the method comprises the following steps:

step S1: modifying a PVDF material, sequentially adding 1000g of lithium hydroxide solution with the mass concentration of 10% into 100g of PVDF-HFP powder, heating to 80 ℃ at the stirring speed of 100rpm, and carrying out elimination reaction for 1.5 h; then 1g of acrylic acid-2-ethylhexyl ester monomer and 10g of sodium perborate solution with the mass concentration of 5 percent are added, the temperature and the stirring rate are kept, the reaction is continued for 1.0 hour, and the hydrophilic group graft modified PVDF-HFP material is prepared, wherein the grafting rate is 0.99 percent.

Step S2: preparing functional coating slurry, adding 5g of carboxylated modified polypropylene particles into 60g of DMF solvent, grinding in a sand grinding dispersion mode, grinding the beads for 8 times for 0.8h to obtain suspension, adding the suspension into the solution containing the PVDF-HFP material obtained in the step S1, and stirring uniformly to obtain the functional coating slurry.

Step S3: coating and preparing a membrane, namely coating the functional coating slurry in the step 2 on two sides of a 12 mu PE diaphragm substrate, and then soaking in a solidification solution (the proportion of DMF/water is 20%) at 40 ℃ for 1 min; then transferring and soaking in pure water solvent, soaking for 2min at 40 deg.C; and then, putting the membrane into an oven, and drying the membrane at 80 ℃ for 1.5min to obtain the functional coating membrane with the total thickness of the double-sided coating of 4 mu.

Comparative example 1

Comparative example 1 differs from example 1 in that: step S1 was omitted, and an unmodified PVDF-HFP material was used, and the remaining components and the preparation method were the same as in example 1.

Comparative example 2

Comparative example 2 differs from example 1 in that: step S2 was omitted, and the polar polymer material 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 differs from example 1 in that: in step S3, the coagulation liquid and the pure water solvent were not immersed, and the coating was directly dried, and the other components and the preparation method were the same as in example 1.

Performance testing

The six groups of lithium battery separators in the above 3 examples and 3 comparative examples were made into lithium ion batteries, and the peel strength of the separators and the electrode sheets was measured in a wet pressure environment (electrolyte: EC/EMC: 3/7(v/v), 1M LiPF 6, VC 2%; temperature 70 ℃, pressure 1.0MPa) 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 used to measure the thickness, air permeability, peel strength and static electricity value, and after the separators were used to prepare batteries, the battery resistance and cycle parameters of the batteries were measured.

Table 1 test results of separators prepared in examples and comparative examples

The present invention has been described in terms of specific examples, which are provided to aid understanding of the invention and are not intended to be limiting. For a person skilled in the art to which the invention pertains, several simple deductions, modifications or substitutions may be made according to the idea of the invention.