Functional coating, functional coating diaphragm as well as preparation method and application of functional coating diaphragm

Abstract

The invention discloses a functional coating, a functional coating diaphragm as well as a preparation method and application of the functional coating diaphragm, and belongs to the technical field of coatings. The functional coating is prepared from the following components in parts by weight: 800 to 1200 parts of ceramic particles, 150 to 300 parts of nano cellulose, 50 to 200 parts of a conductive additive and 4000 to 6000 parts of a solvent. Through cooperation of the conductive additive, the nano cellulose and the ceramic powder, the surface of the polyolefin diaphragm is coated with the functional coating, and a conductive network with a porous structure is formed, so that the thermal stability, the ionic conductivity and the lithium dendrite inhibition capability of the diaphragm are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and in particular relates to a functionalized coating, a functionalized coating diaphragm, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] With the rapid development of lithium-ion batteries in high-energy-density and high-power-density applications, the performance of separators, as a crucial component of batteries, directly impacts their safety, cycle life, and rate capability. While traditional polyolefin separators offer excellent mechanical properties and chemical stability, they suffer from poor thermal stability and are prone to shrinkage at high temperatures, leading to battery short circuits. Furthermore, the low ionic conductivity of traditional separators limits the battery's rapid charge and discharge capabilities.

[0004] In recent years, researchers have sought to improve separator performance by applying functional coatings to the surface. For example, ceramic particles can be applied to enhance thermal stability and mechanical strength, while polymer coatings can improve electrolyte wettability and ionic conductivity. However, these approaches still suffer from several challenges, such as poor coating uniformity, insufficient adhesion to the base membrane, and limited effectiveness in suppressing lithium dendrites during high-rate charge and discharge.

[0005] Therefore, developing a functionalized coating separator with excellent thermal stability, high ionic conductivity and the ability to effectively inhibit the growth of lithium dendrites is a technical problem that needs to be urgently solved in the field of lithium-ion batteries. Summary of the Invention

[0006] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a functionalized coating, a functionalized coating diaphragm, and a preparation method and application thereof. The present invention forms a composite coating by coating a conductive additive, nanocellulose, and ceramic powder on the surface of the diaphragm to form a conductive network with a porous structure, thereby improving the thermal stability, ionic conductivity, and lithium dendrite inhibition ability of the diaphragm.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] The first aspect of the present invention provides a functional coating comprising, in parts by weight:

[0009] 800-1200 parts of ceramic particles, 150-300 parts of nanocellulose, 50-200 parts of conductive additives, and 4000-6000 parts of solvents.

[0010] To address the deficiencies of traditional diaphragms in terms of thermal stability and ionic conductivity, the present invention provides a functional coating of nanocellulose-conductive additive-ceramic powder, a functional coated diaphragm, and a preparation method thereof. By coating a composite coating formed by nanocellulose, a conductive additive, and ceramic powder on the surface of the diaphragm, a conductive network with a porous structure is formed, thereby improving the thermal stability, ionic conductivity, and lithium dendrite inhibition ability of the diaphragm.

[0011] In some embodiments of this embodiment, the functional coating further includes a binder. After the addition of the binder, the viscosity of the functional coating is 500-2000 mPa·s.

[0012] In some embodiments of this embodiment, the binder includes any one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber, and polytetrafluoroethylene.

[0013] In some embodiments of this embodiment, the functional coating further includes: 0.1-0.5 parts of a wetting agent, 1-5 parts of a dispersant, and 1-5 parts of a thickening agent.

[0014] Preferably, the wetting agent includes, but is not limited to, alkylphenol polyoxyethylene ether compounds or sodium alkylbenzene sulfonate.

[0015] Preferably, the dispersant includes, but is not limited to, polyacrylamide.

[0016] Preferably, the thickening agent includes, but is not limited to, carboxymethyl cellulose (CMC).

[0017] In some embodiments of this embodiment, the conductive additive is at least one of graphene, carbon nanotubes, or polypyrrole.

[0018] In some embodiments of this embodiment, the nanocellulose is at least one of cellulose nanofibers (CNF) and cellulose nanocrystals (CNC), with a diameter of 5-20 nm and a length of 100-500 nm.

[0019] In some embodiments of this embodiment, the ceramic powder is one of alumina (Al2O3), boehmite (Al-OOH), or silica (SiO2), and the D50 is 0.7-1.5 μm.

[0020] In some embodiments of this embodiment, the solvent is at least one of water and ethanol.

[0021] In some embodiments of this embodiment, by weight, the functional coating includes:

[0022] 800 - 1100 parts of ceramic particles, 150 - 250 parts of nanocellulose, 50 - 150 parts of conductive additive, 4000 - 5500 parts of solvent.

[0023] In some embodiments of this embodiment, by weight, the functionalized coating includes:

[0024] 850 - 1050 parts of ceramic particles, 150 - 275 parts of nanocellulose, 50 - 125 parts of conductive additive, 4100 - 5300 parts of solvent.

[0025] In a second aspect of the present invention, there is provided a method for preparing the above - mentioned functionalized coating, including:

[0026] Mix the ceramic particles, nanocellulose with a part of the solvent to obtain a nanocellulose solution;

[0027] Mix the conductive additive with the remaining solvent to obtain a conductive additive solution;

[0028] After mixing the nanocellulose solution and the conductive additive solution, a functionalized coating is obtained.

[0029] It should be noted that in the nanocellulose solution, the concentration of the ceramic particles is 25 - 35 wt%, and the concentration of the nanocellulose solution is 5 - 10 wt%; in the conductive additive solution, the concentration of the conductive additive is 5 - 10 wt%.

[0030] The method for preparing the functionalized coating provided by the present invention is simple and efficient, and is suitable for industrial production.

[0031] In some embodiments of this embodiment, after mixing the nanocellulose solution and the conductive additive solution, a binder, a wetting agent, a dispersing agent and a thickening agent are added.

[0032] In a third aspect of the present invention, there is provided a functionalized coating diaphragm, including a diaphragm and a porous coating provided on the surface of the diaphragm; the porous coating is a porous coating formed by the above - mentioned functionalized coating.

[0033] The principle of the present invention is as follows:

[0034] Improved Thermal Stability: Nano-cellulose (CNF / CNC) has a high thermal decomposition temperature (>200 °C), and its crystal structure remains stable at high temperatures, providing good thermal support for the separator. The dense coating formed can effectively block the transfer of heat sources and reduce the shrinkage rate of the separator at high temperatures. Conductive additives (such as graphene and carbon nanotubes) have excellent thermal conductivity and can quickly and evenly disperse local heat, avoiding local melting of the separator caused by heat concentration. Through the composite coating of nano-cellulose and conductive additives, the thermal stability of the separator is significantly improved, making it not easy to shrink at high temperatures and reducing the risk of battery short circuit. Ceramic particles have a high melting point and can inhibit the melting and shrinkage of traditional polyolefin separators (PE / PP) at high temperatures, avoiding thermal runaway. Moreover, the addition of ceramic particles can reduce the shrinkage rate of the separator at high temperatures, maintain the isolation between electrodes, and improve battery safety.

[0035] Increased Ionic Conductivity: The surface of nano-cellulose is rich in hydroxyl groups (-OH), which can form hydrogen bonds with polar solvents (such as EC and DMC) in the electrolyte, improving the wettability of the electrolyte. Conductive additives (such as graphene and carbon nanotubes) form a continuous conductive network in the coating, significantly reducing the interfacial impedance of the separator. The porous structure of nano-cellulose combined with the conductive network of conductive additives forms an efficient ion transport channel, significantly enhancing the ionic conductivity of the separator and making the battery perform better during high-rate charge and discharge. The surface of ceramic particles often carries polar groups, enhancing the wettability of the electrolyte and promoting ion transport. Ceramic materials have stable chemical properties, reducing side reactions with the electrolyte and prolonging the battery cycle life. It can stabilize the electrode / electrolyte interface and reduce the excessive growth of the SEI film. The porous ceramic structure adsorbs more electrolyte, reducing the interfacial resistance and improving the battery rate performance.

[0036] Lithium Dendrite Inhibition: The high conductivity of conductive additives can quickly transport electrons, reduce electrochemical polarization, and reduce the driving force for the growth of lithium dendrites. The dense layer structure of nano-cellulose effectively inhibits the growth of lithium dendrites and improves battery safety. Ceramic particles inhibit the growth of lithium dendrites by homogenizing the lithium ion flow and reducing the local current density. Moreover, nano-sized ceramic particles can adjust the pore distribution of the separator to form an efficient ion channel, balancing conductivity and mechanical strength.

[0037] Enhanced Mechanical Properties: The mechanical strength of nano-cellulose improves the overall mechanical properties of the separator, making it not easy to be damaged during battery assembly and use. The addition of ceramic particles (such as alumina and silica) significantly improves the mechanical strength of the separator, preventing lithium dendrites or electrode expansion from piercing the separator and reducing the short circuit risk. Moreover, as a rigid filler, ceramic particles support the polymer matrix, reduce deformation during cycling, and prolong the separator life.

[0038] In some embodiments of this embodiment, the thickness of the porous coating is 2-5 μm, specifically, it can be 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0039] The fourth aspect of the present invention provides a method for preparing the above functionalized coating diaphragm, including:

[0040] Form a coating on the surface of the diaphragm, dry and heat-treat the coating to cure it, and obtain the functionalized coating diaphragm.

[0041] In some embodiments of this embodiment, the drying and heat treatment are pre-drying at 50-80 °C for 10-20 min, and then heat treatment at 100-150 °C for 40-50 min to cure the coating. It can be understood that the heat treatment can significantly enhance the adhesion of the coating.

[0042] The fifth aspect of the present invention provides an application of the above functionalized coating or the above functionalized coating diaphragm in a lithium battery.

[0043] The present invention provides a functionalized coating diaphragm with excellent thermal stability, high ionic conductivity and capable of effectively inhibiting the growth of lithium dendrites. When used in a lithium battery, it can significantly improve the rate performance and cycling performance of the battery.

[0044] The beneficial effects of the present invention are:

[0045] The present invention provides a functionalized coating. Through the combined action of conductive additives, nanocellulose and ceramic powder, the improvement of the thermal stability of the diaphragm, the improvement of the ionic conductivity, the inhibition of lithium dendrites and the enhancement of the mechanical properties are realized.

[0046] Specifically, the ceramic powder and nanocellulose have a high thermal decomposition temperature (>200°C), and their crystal structures can remain stable at high temperatures, providing good thermal support for the separator. The dense coating formed can effectively block the transfer of heat sources and reduce the shrinkage rate of the separator at high temperatures. Conductive additives (such as graphene and carbon nanotubes) have excellent thermal conductivity and can quickly disperse local heat evenly, avoiding local melting of the separator caused by heat concentration. Through the composite coating of ceramic powder, nanocellulose and conductive additives, the thermal stability of the separator is significantly improved, making it not easy to shrink at high temperatures and reducing the risk of battery short circuit. The porous structure of nanocellulose combined with the conductive network of conductive additives forms an efficient ion transport channel, significantly enhancing the ionic conductivity of the separator, making the battery perform better during high-rate charge and discharge. The high conductivity of the conductive additive can quickly transport electrons, reduce electrochemical polarization, and reduce the driving force for the growth of lithium dendrites. The dense layer structure of ceramic powder and nanocellulose effectively inhibits the growth of lithium dendrites and improves the safety of the battery. Moreover, the mechanical strength of ceramic powder and nanocellulose enhances the overall mechanical properties of the separator, making it not easy to be damaged during battery assembly and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0048] Figure 1 SEM image of the functionalized coating separator prepared in Example 1 of the present invention, with a scale bar of 1 μm;

[0049] Figure 2 SEM image of the functionalized coating separator prepared in Example 1 of the present invention, with a scale bar of 100 nm;

[0050] Figure 3 DSC curve of the functionalized coating separator prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other examples improved or modified by those of ordinary skill in the art belong to the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical effects of the present invention, rather than to limit the scope of protection of the present invention. In the embodiments, the methods used are all conventional methods unless otherwise specified.

[0052] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0053] All raw materials used in the following embodiments of the present invention are commercially available products. The ceramic particle size used in the following examples and comparative examples is controlled to be 0.7 - 1.5 μm in D50 diameter. The size of the used cellulose nanocrystals (CNC) is controlled to be 5 - 20 nm in diameter, 100 - 500 nm in length, the crystallinity ≥ 70%, the specific surface area 100 - 300 m 2 / g, and the hydroxyl (-OH) content ≥ 5 mmol / g. The number of graphene layers used is 1 - 3 layers, the sheet diameter is 1 - 5 μm, the specific surface area ≥ 500 m 2 / g, the conductivity ≥ 10 6 S / m, and the carrier mobility is 2000 - 5000 cm 2 / (V·s). Here, the graphene is mildly oxidized and modified, and the content of oxygen-containing functional groups (-OH, -COOH) ≤ 5 at%.

[0054] Example 1

[0055] A preparation method of a functionalized coating diaphragm includes the following steps:

[0056] Preparation of nano-cellulose dispersion: Add 1 kg of ceramic particles and 187.5 g of CNC to 3.2 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 1 h to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure the full dispersion of CNC.

[0057] Pretreatment of conductive additive: Add 62.5 g of graphene to 1 L of ethanol / water (1:1 volume ratio) mixed solvent. Use an ultrasonic processor (power 200 W) to disperse for 1 h to obtain a uniform graphene suspension.

[0058] Slurry mixing: Mix the above CNC dispersion and graphene suspension, add 50 g of polyvinylidene fluoride as a binder, 0.3 g of alkylphenol polyoxyethylene ether compound as a wetting agent, 4 g of polyacrylamide as a dispersant, and 4 g of CMC as a thickener. Use a magnetic stirrer to stir at 800 rpm for 1 h to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0059] Coating process: Select a polyethylene diaphragm with a thickness of 9 μm as the base film. Use a gravure coater to uniformly coat the mixed slurry on the surface of the diaphragm, and the coating thickness is about 3 μm. Pre-dry the coated diaphragm in an oven at 70 °C for 15 min, and then heat-treat it at 130 °C for 45 min to cure the coating.

[0060] Example 2

[0061] A preparation method of a functionalized coating diaphragm, comprising the following steps:

[0062] Preparation of nano-cellulose dispersion: Add 937.5 g of ceramic particles and 250 g of CNC to 3.2 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 1 h to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure sufficient dispersion of CNC.

[0063] Pretreatment of conductive additive: Add 62.5 g of graphene to 1 L of ethanol / water (1:1 volume ratio) mixed solvent. Use an ultrasonic processor (power 200 W) to disperse for 1 h to obtain a uniform graphene suspension.

[0064] Slurry mixing: Mix the above CNC dispersion with the carbon nanotube suspension, add 50 g of polyvinylidene fluoride as a binder, 0.3 g of alkylphenol polyoxyethylene ether compound as a wetting agent, 4 g of polyacrylamide as a dispersant, and 4 g of CMC as a thickener. Use a magnetic stirrer to stir at 800 rpm for 1 h to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0065] Coating process: Select a polyethylene (PE) diaphragm with a thickness of 9 μm as the base film. Use a gravure coater to uniformly coat the mixed slurry on the surface of the diaphragm, and the coating thickness is about 3 μm. Pre-dry the coated diaphragm in an oven at 70 °C for 15 min, and then heat-treat at 130 °C for 45 min to cure the coating.

[0066] Example 3

[0067] A preparation method of a functionalized coating diaphragm, comprising the following steps:

[0068] Preparation of nano-cellulose dispersion: Add 875 g of ceramic powder and 250 g of cellulose nanocrystals (CNC) to 3.2 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 1 h to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure sufficient dispersion of CNC.

[0069] Pretreatment of conductive additive: Add 125 g of graphene to 2 L of ethanol / water (1:1 volume ratio) mixed solvent. Use an ultrasonic processor (power 200 W) to disperse for 1 h to obtain a uniform graphene suspension.

[0070] Slurry mixing: The above-mentioned CNC dispersion is mixed with the carbon nanotube suspension, and 50 g of polyvinylidene fluoride is added as a binder, 0.3 g of alkylphenol polyoxyethylene ether compound as a wetting agent, 4 g of polyacrylamide as a dispersant, and 4 g of CMC as a thickener. Use a magnetic stirrer to stir at 800 rpm for 1 h to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0071] Coating process: Select a polyethylene (PE) separator with a thickness of 9 μm as the base film. Use a gravure coater to uniformly coat the mixed slurry on the surface of the separator, and the coating thickness is about 3 μm. Pre-dry the coated separator in an oven at 70 °C for 15 min, and then heat-treat it at 130 °C for 45 min to cure the coating.

[0072] Comparative Example 1

[0073] A method for preparing a functionalized coating separator includes the following steps:

[0074] Slurry preparation: Add 1100 g of ceramic powder and 200 g of CNC to 3.8 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 40 min to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure the full dispersion of nanocellulose. Add 10.5 g of polyvinylidene fluoride as a binder, and use a magnetic stirrer to stir at 800 rpm for 1 hour to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0075] Coating process: Select a polyethylene separator with a thickness of 9 μm as the base film. Use a doctor blade coater to uniformly coat the mixed slurry on the surface of the separator, and the coating thickness is about 3 μm. Pre-dry the coated separator in an oven at 70 °C for 15 min, and then heat-treat it at 130 °C for 45 min to cure the coating.

[0076] Comparative Example 2

[0077] A method for preparing a functionalized coating separator includes the following steps:

[0078] Slurry preparation: Add 1250 g of ceramic particles to 3.2 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 1 h to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure the full dispersion of the ceramic particles, and obtain a ceramic particle slurry.

[0079] Pretreatment of conductive additive: Add 50 g of graphene to 1 L of ethanol / water (1:1 volume ratio) mixed solvent. Use an ultrasonic processor (power 200 W) to disperse for 1 h to obtain a uniform graphene suspension.

[0080] Slurry mixing: Mix the above-mentioned ceramic particle slurry with the graphene suspension, add 50 g of polyvinylidene fluoride as a binder, 0.3 g of alkylphenol polyoxyethylene ether compound as a wetting agent, 4 g of polyacrylamide as a dispersant, and 4 g of CMC as a thickener. Use a magnetic stirrer to stir at 800 rpm for 1 h to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0081] Coating process: Select a polyethylene diaphragm with a thickness of 9 μm as the base film. Use a doctor blade coater to evenly coat the mixed slurry on the surface of the diaphragm, and the coating thickness is about 3 μm. Pre-dry the coated diaphragm in an oven at 70 °C for 15 min, and then heat-treat it at 130 °C for 45 min to cure the coating.

[0082] Comparative Example 3

[0083] A method for preparing a functionalized coating diaphragm, comprising the following steps:

[0084] Slurry preparation: Add 1000 g of CNC to 1.5 L of deionized water. Use a high-speed disperser to stir at 4000 rpm for 40 min to form a uniform colloidal dispersion. Use an ultrasonic processor (power 300 W) to process for 40 min to ensure that the CNC is fully dispersed, and obtain a CNC dispersion.

[0085] Pretreatment of conductive additive: Add 50 g of graphene to 1 L of ethanol / water (1:1 volume ratio) mixed solvent. Use an ultrasonic processor (power 200 W) to disperse for 1 h to obtain a uniform graphene suspension.

[0086] Slurry mixing: Mix the above-mentioned CNC dispersion with the graphene suspension, add 50 g of polyvinylidene fluoride as a binder, 0.3 g of alkylphenol polyoxyethylene ether compound as a wetting agent, 4 g of polyacrylamide as a dispersant, and 4 g of CMC as a thickener. Use a magnetic stirrer to stir at 800 rpm for 1 h to form a mixed slurry with a viscosity of about 1200 mPa·s.

[0087] Coating process: Select a polyethylene (PE) diaphragm with a thickness of 9 μm as the base film. Use a doctor blade coater to evenly coat the mixed slurry on the surface of the diaphragm, and the coating thickness is about 3 μm. Pre-dry the coated diaphragm in an oven at 70 °C for 15 min, and then heat-treat it at 130 °C for 45 min to cure the coating.

[0088] Performance testing

[0089] Preparation of soft-pack lithium-ion batteries: The functionalized coating diaphragm prepared in the examples or comparative examples was used in a lamination process with a lithium iron phosphate positive electrode and a graphite negative electrode sheet to make a soft-pack battery of about 3Ah. The electrolyte was 1mol / LLiPF6 / EC+PC+DEC+EMC (volume ratio 1:0.3:1:1). The full battery performance was tested in the range of 2.5V-3.8V.

[0090] Table 1 Comparison of electrical performance of soft pack batteries of Example and Comparative Example

[0091]

[0092] From Table 1 and Figure 1 、 Figure 2 It can be seen that the nanocellulose coating has a uniform porous structure, which provides more transmission channels for lithium ions. Ceramic powder and conductive additives not only improve the transmission rate of electrons, but also interact with lithium ions through surface functional groups to promote the migration of lithium ions. The porous structure of nanocellulose is combined with the conductive network of the conductive additive to form an efficient ion transmission channel, which significantly improves the ionic conductivity of the diaphragm and enables the soft-pack battery to exhibit better rate performance and cycle performance.

[0093] Physical and chemical properties testing

[0094] Thermal shrinkage test: Place a 10cm*10cm membrane (L0*L0 = 10cm*10cm) with a layer of A4 paper between the top and bottom. Heat in an oven at 130°C for 1 hour. Measure the length of each side (L1) and calculate the difference between the front and back lengths (L0-L1). Thermal shrinkage = (L0-L1) / L0*100%.

[0095] Puncture test: Take L0*L0=10cm*10cm diaphragm and put it into the clamp of tensile testing machine and fix it. The steel needle pierced the septum at a speed of 250 mm / min, and the puncture strength data was read.

[0096] Wettability: 5 mL of electrolyte was dropped onto a 10 cm x 10 cm diaphragm with L0*L0=L0, and the wettability was measured using a 2D instrument for 60 seconds.

[0097] Membrane rupture temperature: Take a membrane with L0*L0=10cm*10cm and place it in the fixture of the closed-cell membrane rupture tester. Start the instrument to heat and test the impedance. After the test is completed, read the membrane rupture temperature.

[0098] Table 2 Comparison of physical and chemical properties of diaphragms

[0099]

[0100] Nanocellulose (CNF / CNC) has a relatively high thermal decomposition temperature (>200 °C), and its crystal structure can remain stable at high temperatures, providing good thermal support for the separator, thereby reducing the shrinkage rate of the separator at high temperatures. Conductive additives (such as graphene and carbon nanotubes) have excellent thermal conductivity and can quickly and evenly disperse local heat, avoiding local melting of the separator caused by heat concentration. Ceramic powders have excellent high-temperature resistance and mechanical properties, reducing the shrinkage rate of the separator at high temperatures, increasing the puncture strength and breakdown temperature, and the surfaces of ceramic particles often carry polar groups, which can enhance the wettability of the electrolyte, improve the wettability of the separator, adsorb more electrolyte, promote ion transport, reduce the interfacial resistance, and improve the battery rate performance.

[0101] Combining the characteristics of the three materials, the composite coating of nanocellulose, conductive additive and ceramic powder forms a stable porous structure at high temperatures, which can not only block the heat source but also dissipate heat quickly, significantly improving the thermal stability of the separator.

[0102] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A functional coating, characterized in that, Comprising, by weight parts: 800 - 1200 parts of ceramic particles, 150 - 300 parts of nanocellulose, 50 - 200 parts of conductive additive, and 4000 - 6000 parts of solvent.

2. The functionalized coating according to claim 1, wherein The functional coating further comprises a binder. After adding the binder, the viscosity of the functional coating is 500 - 2000 mPa·s; Preferably, the binder comprises any one of polyvinylidene fluoride, carboxymethyl cellulose, styrene - butadiene rubber, and polytetrafluoroethylene; Preferably, the functional coating further comprises: 0.1 - 0.5 part of wetting agent, 1 - 5 parts of dispersant, and 1 - 5 parts of thickener; Preferably, the wetting agent comprises an alkylphenol polyoxyethylene ether compound or sodium alkylbenzene sulfonate; Preferably, the dispersant comprises polyacrylamide; Preferably, the thickener comprises carboxymethyl cellulose.

3. The functionalized coating according to claim 1, wherein The conductive additive is at least one of graphene, carbon nanotubes, or polypyrrole; Preferably, the nanocellulose is at least one of cellulose nanofibers and cellulose nanocrystals, with a diameter of 5 - 20 nm and a length of 100 - 500 nm; Preferably, the ceramic powder is one of alumina, boehmite, or silica, with a D50 of 0.7 - 1.5 μm; Preferably, the solvent is at least one of water and ethanol.

4. The functionalized coating according to claim 1, wherein By weight parts, the functional coating comprises: 800 - 1100 parts of ceramic particles, 150 - 250 parts of nanocellulose, 50 - 150 parts of conductive additive, and 4000 - 5500 parts of solvent.

5. The functionalized coating according to claim 1, wherein By weight parts, the functional coating comprises: 850 - 1050 parts of ceramic particles, 150 - 275 parts of nanocellulose, 50 - 125 parts of conductive additive, and 4100 - 5300 parts of solvent.

6. A method for preparing the functionalized coating according to claim 1, characterized in that, Comprising: Mixing ceramic particles, nanocellulose with a part of the solvent to obtain a nanocellulose solution; Mixing the conductive additive with the remaining solvent to obtain a conductive additive solution; Mixing the nanocellulose solution and the conductive additive solution to obtain a functional coating; Preferably, a binder, a wetting agent, a dispersant, and a thickener are added after mixing the nanocellulose solution and the conductive additive solution.

7. A functionalized coating diaphragm, characterized in that, Comprising a separator and a porous coating provided on the surface of the separator; the porous coating is a porous coating formed by the functional coating according to any one of claims 1 - 5.

8. The functionalized coating diaphragm according to claim 7, wherein The thickness of the porous coating is 2 - 5 μm.

9. A method for preparing the functionalized coating diaphragm according to claim 7 or 8, characterized in that, Comprising: Forming a coating on the surface of the separator, drying and heat - treating the coating to cure it to obtain a functional coating separator; Preferably, the drying and heat - treatment are pre - drying at 50 - 80°C for 10 - 20 min, and then heat - treating at 100 - 150°C for 40 - 50 min to cure the coating.

10. Use of the functional coating according to any one of claims 1 - 5 or the functional coating separator according to claim 7 or 8 in a lithium battery.

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