A functional separator and a preparation method and use thereof

Abstract

The application belongs to the technical field of battery materials, and provides a functional diaphragm, a preparation method and application thereof.The functional diaphragm comprises a diaphragm base and a modified coating arranged on the surface of the diaphragm base; the modified coating comprises a polymer, and monomers of the polymer comprise a compound with a specific structural formula, the compound comprising an acrylic acid group connected with a benzene ring, and at least one cyano group and at least one hydroxyl group connected on the benzene ring and / or the acrylic acid group.Through the synergistic optimization of the cyano group, the hydroxyl group, the carboxyl group and the benzene ring, the wettability of the functional diaphragm is effectively improved, the interface impedance is reduced, the liquid retention capacity is improved, the mechanical strength and the thermal stability of the modified coating are improved, the puncture resistance is improved, and the short circuit probability is reduced.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a functional separator, its preparation method and application. Background Technology

[0002] Since their commercialization in the 1990s, lithium-ion batteries have rapidly become the core energy storage component in portable electronic devices, electric vehicles, and large-scale energy storage systems. In recent years, with the continuous advancement of power battery technology, the driving range of electric vehicles has significantly improved, gradually alleviating users' anxiety about range. However, correspondingly, charging speed has become a new bottleneck affecting user experience and widespread adoption. Therefore, developing lithium-ion battery systems with fast charging capabilities has become one of the key directions of current technological development.

[0003] To achieve fast-charging performance targets, it is necessary to further improve the energy density and power density of lithium-ion batteries. Therefore, improvement measures mainly focus on the positive and negative electrode materials.

[0004] In terms of cathode materials, high-nickel ternary materials (such as NCM811 and NCA) have become one of the mainstream choices for high-energy-density power batteries due to their high specific capacity and energy density. The theoretical specific capacity of high-nickel ternary materials can reach over 200 mAh / g, far exceeding that of traditional cathode materials such as lithium iron phosphate (approximately 160 mAh / g) and lithium manganese oxide (approximately 120 mAh / g). However, high-nickel materials suffer from poor structural stability, low thermal stability, and numerous interfacial side reactions under high voltage. Especially under fast charging conditions, they are prone to local lithium deposition and interfacial instability, which in turn affect the cycle life and safety of the battery.

[0005] In terms of anode materials, silicon-based anodes possess a high theoretical specific capacity, making them a strong competitor to graphite anodes. Graphite anodes are approaching their theoretical upper limit of 372 mAh / g, while silicon-based anodes boast a theoretical specific capacity as high as 4200 mAh / g, approximately 10 times that of graphite anodes. Furthermore, silicon-based anode materials exhibit a lower lithium insertion / extraction potential (~0.4V vs. Li / Li). + Slightly higher than graphite (~0.05V vs. Li / Li) + During fast charging, lithium plating on the surface can be avoided. However, the huge volume expansion (over 300%) that occurs in silicon-based materials during repeated lithium insertion / extraction processes leads to the destruction of the electrode material structure, particle pulverization, and breakage of the conductive network, resulting in rapid capacity decay and reduced cycle life.

[0006] Besides improvements in material systems, the separator, as an indispensable key component of lithium-ion batteries, directly affects the battery's ion transport capacity, thermal stability, and safety performance. Currently, commercially available lithium-ion batteries commonly use polyolefin separators (such as polyethylene (PE), polypropylene (PP), and their composite multilayer structures). These separators exhibit poor thermal shrinkage at high temperatures; for example, the shrinkage rate typically exceeds 10% at 150°C. This can easily lead to separator melting and pore closure during thermal runaway or localized high temperatures, resulting in internal short circuits. Furthermore, the porosity of polyolefin separators is usually below 40%, resulting in poor electrolyte wettability and high ion transport resistance. Under high-rate charge-discharge conditions, uneven deposition of lithium ions on the electrode surface can easily occur, inducing lithium dendrite growth and increasing the risk of short circuits.

[0007] Therefore, when constructing high-nickel ternary / silicon-carbon composite systems, especially in high-energy-density battery systems composed of high-nickel ternary cathodes and silicon-carbon composite anodes, higher requirements are placed on the performance of the separator. Furthermore, it is necessary to develop separator material solutions with high ion conductivity, excellent heat resistance, and good interfacial stability to meet the future development needs of high-performance lithium-ion batteries in fast-charging applications. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of this invention is to provide a functional diaphragm, its preparation method and uses. The functional diaphragm includes a diaphragm substrate and a modified coating disposed on the surface of the diaphragm substrate. The modified coating includes a polymer, wherein the monomer of the polymer includes a compound having a specific structural formula, the compound including an acrylic group linked to a benzene ring, and at least one cyano group and at least one hydroxyl group are attached to the benzene ring and / or the acrylic group. Through the synergistic optimization effect of the cyano group, hydroxyl group, carboxyl group and benzene ring, the wettability of the functional diaphragm is effectively improved, the interfacial impedance is reduced, the liquid retention capacity is enhanced, and the mechanical strength and thermal stability of the modified coating are improved, the puncture resistance is improved, which is beneficial to reducing the probability of short circuit.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a functional diaphragm, comprising a diaphragm substrate and a modified coating disposed on the surface of the diaphragm substrate; the modified coating comprises a polymer, wherein the monomer of the polymer comprises a compound having the structure shown in Formula I:

[0011]

[0012] R1, R2, R3, R4, R5 and R6 are each independently selected from hydrogen, cyano, hydroxyl or methoxy, and include at least one cyano and at least one hydroxyl.

[0013] In the monomers of the polymer described in this invention, the cyano group (-CN), as a strongly polar group, can improve the wettability of carbonate electrolytes, reduce interfacial impedance, and promote lithium-ion transport; the hydroxyl group (-OH) can combine with the surface hydroxyl groups of the negative electrode material, especially silicon material, through hydrogen bonding, effectively enhancing the interfacial adhesion between the separator and the silicon negative electrode, alleviating the interfacial failure problem caused by silicon expansion, increasing hydrophilicity, improving the separator's liquid retention capacity, and alleviating the problem of electrolyte drying during cycling; the benzene ring structure can enhance the mechanical strength of the coating, improve puncture resistance, and reduce the probability of short circuits; the carboxyl group (-COOH) can improve electrolyte wettability and promote Li+ transport. Therefore, through the synergistic optimization of cyano, hydroxyl, carboxyl, and phenyl groups, the functional separator can meet the application requirements in fast-charging batteries.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0015] As a preferred embodiment of the present invention, the monomer of the polymer includes at least one compound having the structure shown in Formula II, Formula III or Formula IV:

[0016]

[0017] In Formula II, R1, R2, R5, and R6 are all hydrogen, one of R3 and R4 is a cyano group, and the other is a hydroxyl group; in Formula III, R1 is a cyano group, R2, R5, and R6 are all hydrogen, one of R3 and R4 is a hydroxyl group, and the other is selected from hydrogen, cyano, hydroxyl, or methoxy; in Formula IV, R1, R2, and R6 are all hydrogen, R3, R4, and R5 are each independently selected from cyano, hydroxyl, or methoxy, and include at least one cyano group and at least one hydroxyl group.

[0018] As a preferred embodiment of the present invention, the monomer of the polymer includes at least one compound having the following structural formula:

[0019]

[0020] The compound represented by Formula IIA is 3-(4-cyano-3-hydroxyphenyl)acrylic acid, with the chemical formula C. 10 H7NO3, CAS number 262018-87-0; the compound shown in formula IIIA is α-cyano-3-hydroxycinnamic acid, chemical formula C 10 H7NO3, CAS number 54673-07-3; the compound shown in formula IIIB is α-cyano-4-hydroxycinnamic acid, chemical formula C 10H7NO3, CAS number 28166-41-8; the compound represented by formula IVA is 3-(3-cyano-4-hydroxy-5-methoxyphenyl)acrylic acid, chemical formula C 11 H9NO4, CAS number 1708115-46-1.

[0021] In this invention, the monomer of the polymer is preferably a compound with the structure shown in Formula II or Formula IV, and more preferably a compound shown in Formula IIA and Formula IVA, because the cyano group and hydroxyl group in the molecular structure are located on the benzene ring, which can form a conjugated system, enhance molecular rigidity, and further improve thermal stability and mechanical strength.

[0022] Preferably, in this invention, the ratio of cyano groups to hydroxyl groups on the benzene ring of the polymer monomer is 1:1 to form a stable conjugated structure. A deviation in this ratio may lead to an imbalance in molecular polarity, affecting the bonding force with the silicon anode and the ion transport efficiency. For example, in poly3-(4-cyano-3-hydroxyphenyl)acrylic acid, the cyano group is located at position 4 of the benzene ring, the hydroxyl group at position 3, and the carboxyl group at the end of the acrylic acid chain, forming a "cyano-hydroxy-carboxyl" conjugated system.

[0023] As a preferred embodiment of the present invention, the weight-average molecular weight Mw of the polymer is 50,000 to 300,000 Da, for example, it can be 50,000, 80,000, 100,000, 130,000, 150,000, 180,000, 200,000, 220,000, 240,000, 260,000, 280,000, or 300,000.

[0024] In this invention, if the weight-average molecular weight of the polymer is too low, the film-forming properties and interfacial adhesion will be insufficient, and the mechanical strength will be insufficient. If the molecular weight is too high, the viscosity will increase, the coating uniformity will decrease, and the high molecular weight polymer will have higher crystallinity, higher melting temperature, but increased brittleness.

[0025] Preferably, the modified coating is disposed on one or both sides of the diaphragm substrate, and the thickness of the modified coating is 1 to 4 μm, such as 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3 μm, 3.3 μm, 3.5 μm, 3.8 μm or 4 μm.

[0026] In this invention, the functional coating is too thin and unevenly distributed, resulting in insufficient buffering / protection against the expansion of the silicon anode and limited improvement in thermal stability. + The improvement in transport efficiency is not significant; excessive thickness will increase the total thickness and internal resistance of the functional separator, reduce the battery energy density and power density, may lead to excessively high permeability (Gurley value) affecting electrolyte wetting and ion transport, and increase costs.

[0027] Preferably, the membrane substrate is made of PP (polypropylene) and / or PE (polyethylene).

[0028] Preferably, the thickness of the membrane substrate is 7–16 μm, such as 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, and the porosity is 40%–60%, such as 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58% or 60%.

[0029] In this invention, the membrane substrate can be a three-layer composite PP / PE / PP membrane, preferably a PE membrane. If the membrane substrate is too small, the mechanical strength is low, and the membrane is easily punctured. If the thickness is too large, the ion transport distance increases, leading to a decrease in energy density and a decline in rate performance. If the membrane porosity is too high, the high-temperature shrinkage rate is large; if the porosity is low, the liquid absorption rate is low, and rate performance is affected.

[0030] As a preferred embodiment of the present invention, the modified coating further includes inorganic particles, and the polymer is mixed with and / or encapsulates the inorganic particles.

[0031] In this invention, inorganic oxide particles are preferably introduced to form a modified coating. The inorganic particles are mixed with or "encapsulated" with the polymer to form a strong organic-inorganic network. The polymer provides adhesion and stress buffering, while the inorganic particles (especially high-melting-point Al2O3) provide rigid support and a thermal barrier, synergistically resisting high-temperature thermal shrinkage and silicon expansion stress, thereby further reducing the thermal shrinkage rate of the functional membrane.

[0032] Preferably, the inorganic particles include silicon oxide (SiO2) and / or aluminum oxide (Al2O3).

[0033] Preferably, the silicon oxide comprises mesoporous silicon oxide with a pore volume of 1.2–1.5 cm³. 3 / g, for example, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc.; specific surface area of ​​200-300m² 2 / g, for example 200m 2 / g、210m 2 / g、220m 2 / g、230m 2 / g、240m 2 / g、250m 2 / g、260m 2 / g、270m 2 / g、280m 2 / g、290m2 / g or 300m 2 / g etc.

[0034] Preferably, the inorganic particles have a D 50 The particle size is 5–50 nm, such as 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm.

[0035] Preferably, the D of alumina 50 A particle size of 5–25 nm can improve the puncture resistance of the coating, while Al 3+ It can adsorb HF, which helps to inhibit electrolyte decomposition.

[0036] Preferably, the D of mesoporous silica 50 With a particle size of 25–50 nm, the large pore volume can adsorb electrolyte and improve the liquid absorption rate. At the same time, the low dielectric constant of silicon oxide helps to reduce interfacial polarization and improve fast charging performance.

[0037] In this invention, if the particle size of the inorganic particles is too large, it is difficult for them to form a coating with or be coated by the polymer, and it will increase the coating thickness. If the particle size is too small, they are prone to agglomeration, which will reduce the coating strength and may block the pores of the base film.

[0038] Preferably, the inorganic particles comprise alumina and silicon oxide in a mass ratio of (0.2 to 3):1, such as 0.2:1, 0.5:1, 0.8:1, 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, or 3:1.

[0039] In this invention, the combination of inorganic particles should form a reasonable packing pore structure; for example, large particles form a skeleton, and small particles fill the gaps.

[0040] Preferably, the mass ratio of the polymer to the inorganic particles is (1-7):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1 or 7:1, etc.

[0041] In this invention, the combination of inorganic particles and polymers should form a reasonable organic-inorganic network.

[0042] In a second aspect, the present invention provides a method for preparing the functional diaphragm described in the first aspect, wherein a polymer is formulated into a coating slurry, coated on the surface of a diaphragm substrate and dried to form a modified coating, thereby obtaining a functional diaphragm.

[0043] As a preferred technical solution of the present invention, the method for preparing the polymer includes: mixing monomers, organic solvents and initiators, and carrying out a polymerization reaction to obtain the polymer.

[0044] Preferably, the organic solvent includes at least one of benzene, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), or dimethylformamide (DMF).

[0045] Preferably, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

[0046] Preferably, the initiator accounts for 0.5% to 1% of the total mass of the monomer, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0047] Preferably, the polymerization reaction is carried out under the protection of an inert atmosphere, and the temperature of the polymerization reaction is 60-120°C, such as 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the time is 10-36h, such as 10h, 13h, 15h, 18h, 20h, 23h, 25h, 28h, 30h, 33h or 36h.

[0048] Preferably, after the polymerization reaction is completed, a polymer solution is obtained. The polymer solution is mixed with the precipitation solvent to precipitate the polymer. The precipitate is then washed and dried to obtain the polymer.

[0049] Preferably, the precipitation solvent includes at least one of propanol, isopropanol, or acetone.

[0050] As a preferred embodiment of the present invention, the preparation method further includes preparing the coating slurry by combining the polymer with inorganic particles.

[0051] Preferably, the process of preparing the coating slurry includes: first stirring and mixing the dispersant with water, then adding inorganic particles for a second stirring and mixing, and then adding polymer, organic solvent, thickener and wetting agent for a third stirring and mixing to obtain the coating slurry.

[0052] Preferably, the mass ratio of the inorganic particles, dispersant, and water is 1:(2.2~13.2):(0.005~0.06). For example, when the mass ratio of the inorganic particles is 1, the mass ratio of the dispersant can be 2.2, 2.6, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or 13.2, etc., and the mass ratio of water can be 0.005, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, or 0.06, etc.

[0053] Preferably, the mass ratio of the polymer, organic solvent, thickener, and wetting agent is 1:(0.06-0.25):(0.06-0.3):(0.0006-0.004). For example, when the mass ratio of the polymer is 1, the mass ratio of the organic solvent can be 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, or 0.25, etc.; the mass ratio of the thickener can be 0.06, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, or 0.3, etc.; and the mass ratio of the wetting agent can be 0.0006, 0.0008, 0.001, 0.0013, 0.0015, 0.0018, 0.002, 0.0023, 0.0026, 0.003, 0.0033, 0.0035, 0.0038, or 0.004, etc.

[0054] Preferably, the organic solvent includes at least one of ethanol, isopropanol, n-propanol, or propylene glycol methyl ether (PGME).

[0055] In this invention, organic solvents can also act as dispersants. Specifically, they can improve the dispersibility of polymers in aqueous systems (polymers contain hydrophobic groups, and using water alone can easily lead to agglomeration); they can adjust the viscosity of the slurry (reducing surface tension and making the slurry easier to spread); and they can promote subsequent drying efficiency (they have a moderate boiling point, form an azeotrope with water, and accelerate water evaporation). Therefore, low-boiling-point polar organic solvents with good water compatibility can be selected.

[0056] Preferably, the dispersant includes at least one of silicates, sodium polyacrylate, or sodium citrate.

[0057] In this invention, the dispersant can uniformly disperse inorganic particles that are difficult to dissolve in liquid, while also preventing the sedimentation and aggregation of inorganic particles to form a stable suspension.

[0058] Preferably, the thickener includes at least one of carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), or polyvinyl alcohol (PVA).

[0059] In this invention, the thickener increases the viscosity of the slurry through molecular chain entanglement, preventing component sedimentation and ensuring coating uniformity.

[0060] Preferably, the wetting agent includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate.

[0061] In this invention, the wetting agent mainly functions to reduce surface tension, enhance the fluidity of the slurry, and prevent "pinholes" from occurring during coating.

[0062] It should also be noted that when preparing a coating slurry that does not contain the aforementioned inorganic particles, it should contain the above-mentioned polymer, water (as the main dispersion medium), organic solvent, thickener, and wetting agent.

[0063] Preferably, the rotation speed of the first stirring and mixing is 2000-3100 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm or 3100 rpm; the revolution speed is 20-40 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm or 40 rpm; and the stirring time is 5-45 min, such as 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min or 45 min.

[0064] Preferably, the rotation speed of the second stirring and mixing is 2000-3100 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm or 3100 rpm; the revolution speed is 20-50 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm, 40 rpm, 43 rpm, 48 rpm or 50 rpm; and the stirring time is 10-30 min, such as 10 min, 15 min, 20 min, 25 min or 30 min.

[0065] Preferably, the first stirring and blending and the second stirring and blending are performed under ultrasound, and the ultrasound frequency is 20 to 50 kHz, such as 20 kHz, 23 kHz, 25 kHz, 28 kHz, 30 kHz, 33 kHz, 35 kHz, 38 kHz, 40 kHz, 43 kHz, 45 kHz, 48 kHz or 50 kHz.

[0066] Preferably, the rotation speed of the third stirring and mixing process is 1000-3000 rpm, such as 1000 rpm, 1300 rpm, 1500 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, or 3000 rpm; the revolution speed is 20-40 rpm, such as 20 rpm, 25 rpm, 28 rpm, 30 rpm, 33 rpm, 36 rpm, or 40 rpm; and the stirring time is 15-30 min, such as 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, or 30 min.

[0067] Preferably, the third stirring and mixing is performed simultaneously with ultrasonic vacuum oscillation, the frequency of which is 5 to 60 kHz, such as 5 kHz, 10 kHz, 15 kHz, 20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, 45 kHz, 50 kHz, 55 kHz or 60 kHz.

[0068] Preferably, the first stirring and blending, the second stirring and blending, and the third stirring and blending all employ planetary mixing equipment.

[0069] As a preferred embodiment of the present invention, the coating method includes microgravure printing coating, wherein the anilox roller of the microgravure printing coating has a line count of 150-200 lines / cm, such as 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm, or 200 lines / cm, etc.; and the coating speed is 10-29 m / min, such as 10 m / min, 13 m / min, 15 m / min, 18 m / min, 20 m / min, etc. The printing speed is m / min, 23m / min, 25m / min or 29m / min, etc.; the printing gap is 0.1 to 0.3 mm, such as 0.1 mm, 0.130 mm, 0.15 mm, 0.18 mm, 0.2 mm, 0.23 mm, 0.25 mm, 0.28 mm or 0.3 mm, etc.; the squeegee angle is 45° to 65°, such as 45°, 48°, 50°, 53°, 55°, 58°, 60°, 62° or 65°, etc.

[0070] Preferably, the drying process involves the material being pulled into a drying device by a traction roller.

[0071] Preferably, the drying temperature is 40-80°C, such as 40°C, 50°C, 60°C, 70°C or 80°C; and the drying time is 1-5 min, such as 1 min, 2 min, 3 min, 4 min or 5 min.

[0072] Preferably, the air velocity during drying is controlled at 15-25 m / s, such as 15 m / s, 16 m / s, 18 m / s, 20 m / s, 22 m / s, or 25 m / s.

[0073] Preferably, the product is wound up after drying, and the winding tension is 10-15 N / m, such as 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m or 15 N / m.

[0074] Thirdly, the present invention provides a battery comprising the functional separator described in the first aspect.

[0075] It should be noted that this invention does not specifically limit the selection of the positive electrode and positive electrode material, negative electrode and negative electrode material, or electrolyte in the battery. All materials widely used in the field are applicable to this invention. The functional separator described in this invention is particularly suitable for batteries in fast-charging systems. For example, the positive electrode material can be selected as a high-nickel ternary material, and the negative electrode material can be selected as silicon or silicon-carbon composite material, etc. Conductive agents and binders are also used in the positive and negative electrodes, which will not be elaborated here.

[0076] For electrolytes, conventional electrolytes contain solvents, lithium salts, and additives. To better meet the demands of fast charging and improve high-rate performance, LiFSI at a mass ratio of 1% to 3% can be added to the electrolyte, such as 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, or 3%, which can further reduce interfacial impedance and achieve a synergistic effect with the functional separator. If tris(4-nitrophenyl)phosphate is added as an additive to the electrolyte, its proportion can be controlled. The electrolyte content is 0.5% to 1.5% of the electrolyte mass, for example, 0.5%, 0.6%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, or 1.5%, and more preferably 1.0%. If a low-resistance additive such as LiBOB is added, its content is controlled to be 0.1% to 0.4% of the electrolyte mass, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, or 0.4%, and more preferably 0.2%, to further improve rate performance.

[0077] It should also be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0078] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0079] The modified coating of the functional diaphragm of the present invention comprises a specific polymer, wherein the monomer of the polymer adopts a compound with a specific structural formula, the compound comprising an acrylic group attached to a benzene ring, and at least one cyano group and at least one hydroxyl group are attached to the benzene ring and / or the acrylic group. Through the synergistic optimization effect of the cyano group, hydroxyl group, carboxyl group and benzene ring, the wettability of the functional diaphragm is effectively improved, the interfacial impedance is reduced, the liquid retention capacity is enhanced, and the mechanical strength and thermal stability of the modified coating are improved, the puncture resistance is improved, which is beneficial to reducing the probability of short circuit. Detailed Implementation

[0080] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0081] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0082] Example 1

[0083] This embodiment provides a functional diaphragm, including a diaphragm substrate and a modified coating disposed on both sides of the diaphragm substrate; the diaphragm substrate is made of PE diaphragm with a thickness of 12 μm and a porosity of 50%; the modified coating on each side has a thickness of 2.6 μm; the modified coating comprises a polymer and inorganic particles in a mass ratio of 4:1, wherein the polymer and the inorganic particles are mixed and / or encapsulated together;

[0084] The inorganic particles comprise alumina and mesoporous silica in a mass ratio of 2:1; the mesoporous silica has a pore volume of 1.32 cm³. 3 / g, specific surface area is 265m² 2 / g,D 50 The particle size is 39 nm; the D of alumina 50 The particle size is 17nm;

[0085] The polymer has a weight-average molecular weight (Mw) of 180,000 Da, and its monomer is 3-(4-cyano-3-hydroxyphenyl)acrylic acid, represented by formula IIA, with chemical formula C. 10 H7NO3, CAS number 262018-87-0:

[0086]

[0087] This embodiment also provides a method for preparing the functional diaphragm, including:

[0088] S1. Polymer preparation: The monomer 3-(4-cyano-3-hydroxyphenyl)acrylic acid was added to the organic solvent NMP, and 0.7% of the total monomer mass of the initiator azobisisobutyronitrile was added. The polymerization reaction was carried out at 96°C for 24 hours under argon protection to generate the polymer poly(4-cyano-3-hydroxyphenyl)acrylic acid, and a polymer solution was obtained. The polymer solution was added to the precipitation solvent isopropanol and mixed to precipitate. The precipitate was washed and dried to obtain the polymer.

[0089] S2. Preparation of coating slurry: In a planetary mixing device, dispersant sodium polyacrylate and water are first stirred and mixed, and the mass ratio of dispersant to water is controlled at 54:0.2. The rotation speed of the first stirring and mixing is controlled at 2600 rpm, the revolution speed is controlled at 30 rpm, and the stirring time is 20 min. Ultrasonic mixing is performed simultaneously with the first stirring and mixing, and the ultrasonic frequency is 35 kHz.

[0090] Inorganic particles are then added for a second stirring and mixing process. The mass ratio of the inorganic particles, dispersant and water is controlled to be 12:54:0.2. The rotation speed of the second stirring and mixing process is controlled to be 2700 rpm, the revolution speed is controlled to be 32 rpm, and the stirring time is controlled to be 24 min. Ultrasonication is performed simultaneously with the first stirring and mixing process at a frequency of 35 kHz.

[0091] Then, polymer, isopropanol, thickener CMC, and wetting agent sodium hexametaphosphate are added for a third stirring and mixing. The mass ratio of polymer to inorganic particles is controlled at 4:1, and the mass ratio of polymer, isopropanol, thickener, and wetting agent is controlled at 28:3.5:4:0.05. The rotation speed of the third stirring and mixing is controlled at 2000 rpm, the revolution speed is controlled at 30 rpm, and the stirring time is controlled at 22 min. During the third stirring and mixing, ultrasonic vacuum oscillation is performed at a frequency of 30 kHz to obtain the coating slurry.

[0092] S3. Coating: Microgravure printing is used for coating. The anilox roller line count is controlled at 180 lines / cm, the coating speed is 20m / min, the printing gap is 0.2mm, and the squeegee angle is 55°. The coating slurry is applied to the diaphragm substrate and then pulled into the drying equipment by the traction roller for drying. The drying temperature is controlled at 60℃, the time is 3min, and the air speed is controlled at 20m / s. After drying, the diaphragm is wound up with a tension of 11.8N / m to obtain the functional diaphragm.

[0093] Example 2

[0094] This embodiment provides a functional membrane, wherein the monomer of the polymer in the modified coating of the functional membrane is α-cyano-3-hydroxycinnamic acid, represented by formula IIIA, with chemical formula C. 10H7NO3, CAS number 54673-07-3:

[0095]

[0096] Apart from the above, all other conditions are exactly the same as in Example 1.

[0097] Example 3

[0098] This embodiment provides a functional membrane, wherein the monomer of the polymer in the modified coating of the functional membrane is α-cyano-4-hydroxycinnamic acid, represented by formula IIIB, chemical formula C. 10 H7NO3, CAS number 28166-41-8:

[0099]

[0100] Apart from the above, all other conditions are exactly the same as in Example 1.

[0101] Example 4

[0102] This embodiment provides a functional diaphragm, wherein the monomer of the polymer in the modified coating of the functional diaphragm is 3-(3-cyano-4-hydroxy-5-methoxyphenyl)acrylic acid, represented by formula IVA, with chemical formula C. 11 H9NO4, CAS number 1708115-46-1:

[0103]

[0104] Apart from the above, all other conditions are exactly the same as in Example 1.

[0105] Example 5

[0106] This embodiment provides a functional diaphragm in which the weight-average molecular weight (Mw) of the polymer in the modified coating of the functional diaphragm is adjusted from 180,000 Da to 20,000 Da. Apart from the above, the other conditions are exactly the same as in Example 1.

[0107] Example 6

[0108] This embodiment provides a functional diaphragm in which the weight-average molecular weight (Mw) of the polymer in the modified coating of the functional diaphragm is adjusted from 180,000 Da to 50,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0109] Example 7

[0110] This embodiment provides a functional diaphragm in which the weight-average molecular weight (Mw) of the polymer in the modified coating of the functional diaphragm is adjusted from 180,000 Da to 300,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0111] Example 8

[0112] This embodiment provides a functional diaphragm in which the weight-average molecular weight (Mw) of the polymer in the modified coating of the functional diaphragm is adjusted from 180,000 Da to 350,000 Da. Except for the above, the other conditions are exactly the same as in Example 1.

[0113] Example 9

[0114] This embodiment provides a functional diaphragm, wherein the thickness of the modified coating of the functional diaphragm is adjusted from 2.6 μm to 0.3 μm, and all other conditions are exactly the same as in Embodiment 1.

[0115] Example 10

[0116] This embodiment provides a functional diaphragm, wherein the thickness of the modified coating of the functional diaphragm is adjusted from 2.6 μm to 1 μm, and all other conditions are exactly the same as in Embodiment 1.

[0117] Example 11

[0118] This embodiment provides a functional diaphragm, wherein the thickness of the modified coating of the functional diaphragm is adjusted from 2.6 μm to 4 μm, and all other conditions are exactly the same as in Embodiment 1.

[0119] Example 12

[0120] This embodiment provides a functional diaphragm, wherein the thickness of the modified coating of the functional diaphragm is adjusted from 2.6 μm to 5 μm, and all other conditions are exactly the same as in Embodiment 1.

[0121] Example 13

[0122] This embodiment provides a functional diaphragm. The modified coating of the functional diaphragm does not contain inorganic particles, but only polymers. Except for the above, the other conditions are exactly the same as those in Example 1.

[0123] Example 14

[0124] This embodiment provides a functional diaphragm in which the mass ratio of polymer to inorganic particles in the modified coating is adjusted from 4:1 to 0.5:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0125] Example 15

[0126] This embodiment provides a functional diaphragm in which the mass ratio of polymer to inorganic particles in the modified coating is adjusted from 4:1 to 1:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0127] Example 16

[0128] This embodiment provides a functional diaphragm in which the mass ratio of polymer to inorganic particles in the modified coating is adjusted from 4:1 to 7:1. Except for the above, the other conditions are exactly the same as in Example 1.

[0129] Example 17

[0130] This embodiment provides a functional diaphragm in which the mass ratio of polymer to inorganic particles in the modified coating is adjusted from 4:1 to 8:1. Except for the above, the other conditions are exactly the same as in Embodiment 1.

[0131] Comparative Example 1

[0132] This comparative example uses the separator substrate from Example 1 for subsequent battery assembly and related testing.

[0133] Comparative Example 2

[0134] This comparative example provides a functional diaphragm, wherein the polymer monomer in the modified coating of the functional diaphragm is 3-hydroxycinnamic acid, with the chemical formula C9H8O3 and CAS number 14755-02-3, and the structural formula is as follows:

[0135]

[0136] Apart from the above, all other conditions are exactly the same as in Example 1.

[0137] Comparative Example 3

[0138] This comparative example provides a functional diaphragm, wherein the polymer monomer in the modified coating of the functional diaphragm is 4-hydroxycinnamic acid, with the chemical formula C9H8O3 and CAS number 501-98-4, and the structural formula is as follows:

[0139]

[0140] Apart from the above, all other conditions are exactly the same as in Example 1.

[0141] Comparative Example 4

[0142] This comparative example provides a functional diaphragm, wherein the polymer monomer in the modified coating of the functional diaphragm is α-cyanocinonic acid, with the chemical formula C. 10 H7NO2, CAS number 1011-92-3, has the following structural formula:

[0143]

[0144] Apart from the above, all other conditions are exactly the same as in Example 1.

[0145] Characterization and testing:

[0146] I. Heat shrinkage rate test of functional diaphragm at 150℃ / 30min:

[0147] Referring to the standard test method (GB / T 36363), the dimensional changes of the diaphragm sample in the free state were measured at the specified temperature (150℃) and time (30min), and the transverse (TD) and longitudinal (MD) thermal shrinkage rates were calculated.

[0148] Equipment and materials include: a high-temperature furnace with a temperature control accuracy of ±1℃ and an internal atmosphere of air or an inert gas (such as N2); sample clamps: a stainless steel frame or quartz glass plate to ensure unrestrained free shrinkage of the sample; measuring tools: a vernier caliper with an accuracy of 0.02mm or an optical projector (suitable for micron-level diaphragms); and graph paper or a laser rangefinder (for marking initial dimensions).

[0149] Test Procedure: Sample Preparation: Cut samples to 100mm × 100mm, avoiding the diaphragm edge by 10mm; Marking: Draw cross lines on the sample surface and record the initial transverse (TD) and longitudinal (MD) lengths L0 (accurate to 0.1mm); Pretreatment: Place the sample in an environment of 23±2℃ and 50±5%RH for 24h; High-Temperature Treatment: Place the sample flat on a fixture and put it in the center of a high-temperature furnace preheated to 150℃, ensuring the sample does not contact the furnace wall. After holding at this temperature for 30min, quickly remove the fixture and cool at room temperature for 10min; Dimensional Measurement: Measure the length L1 of the cross lines on the cooled sample (measured separately in the TD and MD directions); Final Calculation: Test 3 parallel samples for each sample and take the average value. Calculate the heat shrinkage rate (in %) as follows: (L0-L1) / L0×100%, and obtain the transverse (TD) and longitudinal (MD) shrinkage rates.

[0150] II. The preparation of lithium-ion batteries includes the following steps:

[0151] 1) Preparation of positive electrode sheet

[0152] The ternary material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active material. It is mixed with binder PVDF (polyvinylidene fluoride), conductive agent SP (super-P conductive carbon black), and SWCNT (single-walled carbon nanotubes) in a mass ratio of 96:2:1.9:0.1 to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil through a coating process. After drying and cold pressing, a positive electrode sheet is obtained.

[0153] 2) Preparation of negative electrode sheet

[0154] Silicon-carbon anode material, conductive agent SP, SWCNT, binder PAA (polyacrylic acid) and SBR are mixed and stirred evenly in a mass ratio of 90:2:0.5:5:2.5 to obtain anode slurry. The solid content is controlled at 30%. Then, the anode slurry is coated onto copper foil current collector through a coating process. After vacuum drying and cold pressing, anode sheet is obtained.

[0155] 3) Selection of electrolyte

[0156] Solvents and additives include EC:PC:DMC:DEC:FEC in a volume ratio of 15:20:25:30:10, and LiPF6 with a lithium salt concentration of 1 mol / L.

[0157] 4) Manufacturing lithium-ion batteries

[0158] The functional separators from Examples 1-17 and Comparative Examples 1-4 are stacked sequentially with the positive and negative electrode sheets, respectively. The separators are positioned between the positive and negative electrode sheets to act as a separator. The cells are then wound to obtain bare cells. The bare cells are placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0159] III. Electrochemical Performance Testing

[0160] The LAND battery test system of Wuhan Jinno Electronics Co., Ltd. was tested at room temperature (25℃), and the charge and discharge voltage was limited to 2.5V to 4.2V.

[0161] 1) First Coulomb efficiency

[0162] At 25°C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 1 minute. The initial coulombic efficiency of the lithium-ion battery was calculated.

[0163] Initial coulombic efficiency (in %) = Total capacity of lithium-ion battery during initial discharge at 0.33C / Total capacity of lithium-ion battery during initial charge at 0.33C × 100%.

[0164] 2) Capacity retention rate after 1000 cycles at room temperature (1°C / 2°C)

[0165] At 25℃, the lithium-ion battery was charged at a 1C rate using constant current and constant voltage to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery was discharged at a 2C rate using constant current to 2.5V, followed by a 10-minute rest. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1000 charge-discharge cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles using 1C / 2C was calculated. The capacity retention rate (%) after N cycles is calculated as follows: (Discharge capacity of the Nth cycle / Initial discharge capacity) × 100%, where N is the number of cycles.

[0166] 3) Room temperature 6C rate performance - constant current charge ratio

[0167] At 25℃, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the lithium-ion battery were recorded. The constant current charge ratio of the 6C rate charging was calculated according to the following formula: 6C rate charging constant current charge ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0168] 4) Cell thermal runaway ARC test

[0169] The ARC adiabatic thermal runaway test begins (the test sample is heated from room temperature to 45±2℃ inside the chamber, left to stand for 90 minutes, and the change in battery temperature rise rate is monitored). If the temperature rise exceeds 0.2℃ within 10 minutes (i.e., SHR>0.02℃ / min), it is considered that a self-heating reaction has occurred inside the battery, and the adiabatic environment is maintained until the battery experiences thermal runaway; if the temperature rise does not exceed 0.2℃ within 10 minutes (i.e., SHR≤0.02℃ / min), the next temperature rise step test continues; each temperature step is 5℃, and the steps are repeated at each step. The ARC test temperature range is 45℃~300℃, the self-heating initiation temperature is T1 (temperature rise rate SHR>0.02℃ / min), and the thermal runaway initiation temperature is T2 (temperature rise rate SHR>1℃ / min). SHR refers to the self-heating rate (SHR).

[0170] The above data is recorded in Table 1.

[0171] Table 1

[0172]

[0173] As can be seen from Table 1:

[0174] Example 1 vs. Comparative Example 1: Comparative Example 1 is only a PE base film without functional groups of the modified coating, and has the following defects: ① strong hydrophobicity, poor electrolyte wettability (liquid absorption rate <200%), and high interfacial impedance (>100Ω·cm). 2 ① The coating lacks cyano / carboxyl groups to guide lithium-ion transport, resulting in a low ion transference number (<0.5) and poor rate performance. ② The coating lacks a benzene ring to provide rigidity, making it prone to shrinkage at high temperatures (shrinkage rate >10% at 150℃), posing a high risk of thermal runaway. In contrast, the modified coating in Example 1 achieves comprehensive performance improvement through synergistic optimization of "cyano (wetting) + hydroxyl (hydrogen bonding) + carboxyl (ion transport) + benzene ring (rigidity)".

[0175] As can be seen from Example 1 versus Comparative Examples 2 to 4, the performance of the comparative examples is significantly worse than that of Example 1. This is because: in Comparative Examples 2 and 3, the strong polar cyano group is missing, resulting in decreased wettability (liquid absorption rate decreased by 15%–20%) and increased interfacial resistance (>60 Ω·cm). 2 The rate performance deteriorated; in Comparative Example 4, there were no hydroxyl groups: it could not form hydrogen bonds with the Si-OH of the silicon anode, the interfacial bonding force decreased by more than 30%, the interface was easily peeled off during cycling, and the capacity decay accelerated; all three comparative examples were unable to form a synergistic effect due to the lack of core groups, and their performance was far inferior to that of Example 1.

[0176] Example 1 vs Examples 2 to 4: The three monomers used in Examples 2 to 4 all contain complete cyano, hydroxyl, carboxyl, and benzene rings, with only slight differences in group positions (e.g., cyano in the acrylic acid chain or benzene ring), but their synergistic mechanisms are consistent: ① The cyano group provides polarity, resulting in similar wettability (liquid absorption rate 320%–330%); ② The hydroxyl group forms hydrogen bonds with the silicon anode, resulting in comparable interfacial bonding (peel force > 5 N / m); ③ The rigidity of the benzene ring ensures thermal stability (shrinkage rate < 0.6% at 150℃). All three compounds contain a core functional group—a benzene ring (providing rigidity), at least one cyano group (strong polarity, improving wettability), at least one carboxyl group (-COOH, promoting lithium-ion transport), and at least one hydroxyl group (-OH, forming hydrogen bonds with the silicon anode). Furthermore, the group positions are all located on the benzene ring or acrylic acid chain, forming a synergistic system of "cyano-hydroxyl-carboxyl-benzene ring," thus their performance is close to that of Example 1. Furthermore, compared with Formula IIA, the cyano group of Formula IIIA / IIIB is located in the acrylic acid chain (α position), and Formula IVA has an additional methoxy group (-OCH3, weakly polar), but the synergistic effect of the core groups is not destroyed: key indicators such as wettability (liquid absorption rate), interfacial bonding force (with silicon anode), and thermal stability (shrinkage rate at 150℃) only fluctuate slightly (difference ≤5%), and are still significantly better than the comparative example.

[0177] Example 1 vs Examples 5 to 8: Preferred range of polymer molecular weight (50,000 to 300,000 Da): Moderate molecular chain length, reasonable chain segment entanglement, good film-forming properties (mechanical strength > 30 MPa), and moderate viscosity (3,000 to 4,000 mPa·s), uniform coating, and unobstructed ion transport channels; Below the lower limit (e.g., 20,000 Da): Short chains with insufficient entanglement, coating is prone to cracking, electrolyte retention rate decreases (< 280%), and cycle resistance increases; Above the upper limit (e.g., 350,000 Da): Chains are too long and entangled too densely, viscosity > 5,000 mPa·s, uneven coating, lithium ion transport is hindered, and rate performance decreases.

[0178] Example 1 vs Examples 9 to 12: When the modified coating thickness is within the preferred range (1–4 μm), the thickness is sufficient to cover the base film (coverage > 99%) without increasing the internal resistance excessively (< 50 Ω·cm). 2 The thickness of the substrate needs to balance wettability and ion transport. If the thickness is too thin (e.g., 0.3 μm), uneven coverage (coverage <80%) occurs, exposing the hydrophobic surface of the base film locally, leading to uneven electrolyte wetting and localized lithium deposition during cycling. If the thickness is too thick (5 μm), the ion transport distance increases, and the total resistance rises (>60 Ω·cm). 2 Furthermore, it clogs the pores of the base film (reducing air permeability by 20%), leading to a deterioration in rate performance.

[0179] Example 1 vs Examples 13 to 17: When the mass ratio of polymer to inorganic particles is within the preferred range ((1-7):1): the polymer and inorganic particles can form an "organic-inorganic interpenetrating network"—the polymer provides adhesion (preventing coating peeling), and the inorganic particles (Al2O3 / SiO2) provide rigidity and thermal barrier, synergistically suppressing thermal shrinkage (shrinkage rate <1% at 150°C); when there are no inorganic particles (Example 13): only polymer coating, the chain segments are easy to loosen at high temperatures, and the thermal shrinkage rate increases to >1.5%; when the proportion of polymer is too low (e.g., 0.5:1, Example 14): insufficient polymer, inorganic particles cannot be encapsulated, the coating becomes brittle (puncture strength decreases by 20%), and it is easy to crack during cycling; when the proportion of polymer is too high (e.g., 8:1, Example 17), the proportion of inorganic particles is insufficient, the thermal barrier effect is weakened, and the improvement in thermal stability is limited.

[0180] In summary, the modified coating of the functional diaphragm of the present invention comprises a specific polymer, wherein the monomer of the polymer adopts a compound with a specific structural formula, the compound comprising an acrylic group attached to a benzene ring, and at least one cyano group and at least one hydroxyl group are attached to the benzene ring and / or the acrylic group. Through the synergistic optimization effect of the cyano group, hydroxyl group, carboxyl group and benzene ring, the wettability of the functional diaphragm is effectively improved, the interfacial impedance is reduced, the liquid retention capacity is enhanced, and the mechanical strength and thermal stability of the modified coating are improved, the puncture resistance is improved, which is beneficial to reducing the probability of short circuit.

[0181] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0182] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0183] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A functional diaphragm, characterized in that, Includes a diaphragm substrate and a modified coating disposed on the surface of the diaphragm substrate; The modified coating comprises a polymer having a weight-average molecular weight (Mw) of 50,000 to 300,000 Da, and the monomers of the polymer comprising compounds having the structure shown in Formula I: ； R1, R2, R3, R4, R5 and R6 are each independently selected from hydrogen, cyano, hydroxyl or methoxy, and include at least one cyano and at least one hydroxyl. The modified coating also includes inorganic particles, and the polymer is mixed with and / or encapsulates the inorganic particles.

2. The functional diaphragm according to claim 1, characterized in that, The monomers of the polymer include at least one compound having the structure shown in Formula II, Formula III or Formula IV: ； ； ； In Formula II, R1, R2, R5, and R6 are all hydrogen, one of R3 and R4 is a cyano group, and the other is a hydroxyl group; in Formula III, R1 is a cyano group, R2, R5, and R6 are all hydrogen, one of R3 and R4 is a hydroxyl group, and the other is selected from hydrogen, cyano, hydroxyl, or methoxy; in Formula IV, R1, R2, and R6 are all hydrogen, R3, R4, and R5 are each independently selected from cyano, hydroxyl, or methoxy, and include at least one cyano group and at least one hydroxyl group.

3. The functional diaphragm according to claim 1 or 2, characterized in that, The monomer of the polymer includes at least one compound having the following structural formula: ； ； ； 。 4. The functional diaphragm according to claim 1, characterized in that, The modified coating is disposed on one or both sides of the diaphragm substrate, and the thickness of the modified coating is 1~4μm.

5. The functional diaphragm according to claim 1, characterized in that, The membrane substrate is made of PP and / or PE.

6. The functional diaphragm according to claim 1, characterized in that, The thickness of the diaphragm substrate is 7~16μm, and the porosity is 40%~60%.

7. The functional diaphragm according to claim 1, characterized in that, The inorganic particles include silicon oxide and / or aluminum oxide.

8. The functional diaphragm according to claim 7, characterized in that, The silica includes mesoporous silica with a pore volume of 1.2~1.5 cm³. 3 / g, specific surface area of ​​200~300m² 2 / g.

9. The functional diaphragm according to claim 1 or 7, characterized in that, The inorganic particles' D 50 The particle size is 5~50nm.

10. The functional diaphragm according to claim 1 or 7, characterized in that, The inorganic particles comprise aluminum oxide and silicon oxide in a mass ratio of (0.2~3):

1.

11. The functional diaphragm according to claim 1 or 7, characterized in that, The mass ratio of the polymer to the inorganic particles is (1~7):

1.

12. A method for preparing the functional diaphragm according to any one of claims 1-11, characterized in that, The polymer is formulated into a coating slurry, coated on the surface of the diaphragm substrate, and then dried to form a modified coating, thus obtaining a functional diaphragm.

13. The method for preparing the functional diaphragm according to claim 12, characterized in that, The method for preparing the polymer includes: mixing monomers, organic solvents, and initiators, and carrying out a polymerization reaction to obtain the polymer.

14. The method for preparing the functional diaphragm according to claim 13, characterized in that, The organic solvent includes at least one of benzene, tetrahydrofuran, N-methylpyrrolidone, or dimethylformamide.

15. The method for preparing the functional diaphragm according to claim 13, characterized in that, The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide.

16. The method for preparing the functional diaphragm according to claim 13, characterized in that, The initiator accounts for 0.5% to 1% of the total mass of the monomer.

17. The method for preparing the functional diaphragm according to claim 13, characterized in that, The polymerization reaction is carried out under an inert atmosphere, at a temperature of 60-120°C, for a time of 10-36 hours.

18. The method for preparing the functional diaphragm according to claim 13, characterized in that, After the polymerization reaction is completed, a polymer solution is obtained. The polymer solution is mixed with the precipitation solvent to precipitate the polymer. The precipitate is then washed and dried to obtain the polymer.

19. The method for preparing the functional diaphragm according to claim 18, characterized in that, The precipitation solvent includes at least one of propanol, isopropanol, or acetone.

20. The method for preparing the functional diaphragm according to claim 12, characterized in that, The preparation method further includes preparing the coating slurry by combining the polymer with inorganic particles.

21. The method for preparing the functional diaphragm according to claim 20, characterized in that, The process of preparing the coating slurry includes: first stirring and mixing the dispersant with water, then adding inorganic particles for a second stirring and mixing, and then adding polymer, organic solvent, thickener and wetting agent for a third stirring and mixing to obtain the coating slurry.

22. The method for preparing the functional diaphragm according to claim 21, characterized in that, The mass ratio of the inorganic particles, dispersant and water is 1:(2.2~13.2):(0.005~0.06).

23. The method for preparing the functional diaphragm according to claim 21, characterized in that, The mass ratio of the polymer, organic solvent, thickener, and wetting agent is 1:(0.06~0.25):(0.06~0.3):(0.0006~0.004).

24. The method for preparing the functional diaphragm according to claim 21, characterized in that, The organic solvent includes at least one of ethanol, isopropanol, n-propanol, or propylene glycol methyl ether.

25. The method for preparing the functional diaphragm according to claim 21, characterized in that, The dispersant includes at least one of silicates, sodium polyacrylate, or sodium citrate.

26. The method for preparing the functional diaphragm according to claim 21, characterized in that, The thickener includes at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, or polyvinyl alcohol.

27. The method for preparing the functional diaphragm according to claim 21, characterized in that, The wetting agent includes at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate.

28. The method for preparing the functional diaphragm according to claim 21, characterized in that, The first stirring and mixing process has a rotation speed of 2000~3100 rpm, a revolution speed of 20~40 rpm, and a stirring time of 5~45 min.

29. The method for preparing the functional diaphragm according to claim 21, characterized in that, The second stirring and mixing process has a rotation speed of 2000~3100 rpm, a revolution speed of 20~50 rpm, and a stirring time of 10~30 min.

30. The method for preparing the functional diaphragm according to claim 21, characterized in that, The first stirring and blending and the second stirring and blending are carried out under ultrasound, and the ultrasound frequency is 20~50kHz.

31. The method for preparing the functional diaphragm according to claim 21, characterized in that, The rotation speed of the third stirring and mixing process is 1000~3000 rpm, the revolution speed is 20~40 rpm, and the stirring time is 15~30 min.

32. The method for preparing the functional diaphragm according to claim 21, characterized in that, The third stirring and mixing process is performed simultaneously with ultrasonic vacuum oscillation, the frequency of which is 5~60kHz.

33. The method for preparing the functional diaphragm according to claim 12, characterized in that, The coating method includes microgravure printing coating, wherein the anilox roller line count of the microgravure printing coating is 150~200 lines / cm, the coating speed is 10~29m / min, the printing gap is 0.1~0.3mm, and the squeegee angle is 45°~65°.

34. The method for preparing the functional diaphragm according to claim 12, characterized in that, The drying temperature is 40~80℃ and the time is 1~5min.

35. The method for preparing the functional diaphragm according to claim 12, characterized in that, The air velocity is controlled at 15~25m / s during the drying process.

36. The method for preparing the functional diaphragm according to claim 12, characterized in that, After drying, the material is wound up, and the winding tension is 10~15 N / m.

37. A battery, characterized in that, It contains the functional diaphragm as described in any one of claims 1-11.

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