Wide-temperature-range thermal management composite battery separator and preparation method thereof

Abstract

The application belongs to the technical field of battery materials, and relates to a wide-temperature-range thermal management composite battery diaphragm and a preparation method thereof. The preparation method comprises the following steps: (S1) dispersing mercaptoized nano hexagonal boron nitride in a solvent, adding a functional monomer and an initiator, and then performing first-stage ultraviolet irradiation to obtain modified nano hexagonal boron nitride; (S2) dispersing the modified nano hexagonal boron nitride in a solvent, dissolving a fluorine-containing linear polymer therein, and then adding a phosphorus-containing monomer, an ether oxygen-containing monomer and an initiator to form a mixed slurry; coating the mixed slurry on an inert peelable base material, and then performing second-stage ultraviolet irradiation to obtain the wide-temperature-range thermal management composite battery diaphragm. The functional monomer has the following structural formula: wherein m is an integer of 1-5, and n is an integer of 1-3. The diaphragm has high ion conductivity and high thermal conductivity, and has the functions of heat dissipation under normal working conditions and active flame retardation at high temperatures, that is, the diaphragm has a wide-temperature-range thermal management capability.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a wide-temperature-range thermal management composite battery separator and its preparation method. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and large-scale energy storage systems due to their high energy density and long cycle life. However, the frequent occurrence of battery thermal runaway accidents in recent years has seriously restricted their further development towards higher energy density and safety. Internal heat accumulation in the battery is the direct cause of thermal runaway. The main causes include: the decomposition of organic electrolyte at high temperature, releasing flammable gases and triggering a chain exothermic reaction, and the high-temperature thermal shrinkage of traditional polyolefin separators leading to internal short circuits in the battery, thereby aggravating the generation and accumulation of heat. In order to improve the thermal safety of batteries, researchers have developed a variety of strategies, mainly the following three categories: (1) Heat-resistant modification of separators: By coating the surface of polyolefin separators with ceramic layers (such as Al2O3, SiO2) or using heat-resistant polymers (such as polyimide PI, aramid) to prepare separators, the aim is to improve the thermal stability of the separators. However, in such methods, there is often a mismatch in the coefficient of thermal expansion between the coating and the separator, and uneven phase transitions and deformations are prone to occur when heated. (2) Electrolyte flame retardancy: Adding phosphate ester flame retardants to the electrolyte aims to interrupt the combustion chain reaction by capturing gaseous free radicals. However, these flame retardant additives usually have poor compatibility with graphite anodes, leading to instability of the solid electrolyte interface film and deterioration of the battery's electrochemical performance. (3) Solid / quasi-solid electrolyte: Replacing liquid electrolytes with solid electrolytes that have high mechanical strength and are non-flammable eliminates the risk of flammability at the source. However, solid electrolytes face problems such as high solid-solid interface contact resistance and severe interfacial side reactions, making it difficult for the battery's cycle stability to meet practical application requirements.

[0003] In recent years, the construction of smart separators with thermal management functions by combining high thermal conductivity fillers (such as hexagonal boron nitride) with functional polymers has become a research hotspot. Hexagonal boron nitride (h-BN) is considered an ideal functional filler due to its excellent in-plane intrinsic thermal conductivity, superior electrical insulation, and chemical stability. Theoretically, the thermally conductive network it constructs in the polymer matrix can quickly homogenize the temperature distribution inside the battery, suppress local hot spots, and delay the heat accumulation process. However, h-BN has strong surface chemical inertness and strong van der Waals forces between its layers, making it prone to agglomeration in the polymer matrix. This results in a large number of voids and weak interfacial bonding between the filler and the polymer matrix, leading to a large amount of phonon scattering and persistently high interfacial thermal resistance, which fails to fully realize the high thermal conductivity potential of h-BN. In addition, blindly increasing the amount of h-BN added (usually >50 wt%) in pursuit of high thermal conductivity will severely block the lithium-ion transport channels, causing a sharp drop in the ionic conductivity of the separator, while also making the separator embrittled and less flexible. How to construct an efficient thermally conductive network while maintaining or enhancing the ion conduction pathway with low filler content has become a technical challenge in this field.

[0004] Therefore, there is an urgent need to develop a new material and preparation method to break through the above-mentioned technical bottlenecks, achieve a synergistic improvement in thermal conductivity and ionic conductivity, and enable the battery to achieve all-round thermal management from heat dissipation under normal operating conditions to high-temperature flame retardancy. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor dispersion of high thermal conductivity fillers in battery separator substrates, high interfacial thermal resistance, and difficulty in simultaneously achieving thermal conductivity and ionic conductivity. The invention provides a thermal management composite separator and its preparation method that can simultaneously achieve efficient thermal conductivity and ion conduction with low thermal conductivity filler content, and has both heat dissipation under normal operating conditions and active flame retardancy at high temperatures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a wide-temperature-range thermal management composite battery separator includes the following steps:

[0008] (S1) Thiolized nano-hexagonal boron nitride (h-BN-SH) was dispersed in a polar aprotic solvent, and the functional monomer and initiator shown in Formula I were added to form a mixture. The mixture was subjected to the first stage of ultraviolet light irradiation. After the irradiation was completed, it was purified to obtain modified nano-hexagonal boron nitride (h-BN-P).

[0009] (Formula I),

[0010] In Equation I, m is an integer from 1 to 5, and n is an integer from 1 to 3;

[0011] (S2) Modified nano-hexagonal boron nitride (h-BN-P) is dispersed in a polar aprotic solvent, a fluorinated linear polymer is dissolved in it, and then a phosphorus-containing monomer, an ether-containing oxygen monomer, and an initiator are added to form a mixed slurry. The mixed slurry is coated on an inert peelable substrate and subjected to a second stage of ultraviolet light irradiation. After the irradiation is completed, it is dried and peeled off from the substrate to obtain a wide-temperature-range thermal management composite battery separator.

[0012] The functional monomer of Formula I of this invention contains both highly reactive double bonds (acrylate groups) and less reactive double bonds (allyl groups). The highly reactive alkenyl group undergoes a click chemical reaction with the thiol groups modified on the surface of hexagonal boron nitride, thereby grafting the functional monomer onto the surface of hexagonal boron nitride to form functional monomer-modified hexagonal boron nitride (h-BN-P), while the less reactive double bonds are retained. Subsequently, in step (S2), h-BN-P copolymerizes with the phosphorus-containing monomer and the ether-oxygen-containing monomer through its retained less reactive double bonds to form a phosphorus-based flame-retardant copolymer, thereby anchoring hexagonal boron nitride (h-BN) in the copolymer crosslinking network. The fluorinated linear polymer serves as the linear polymer backbone, physically interpenetrating with the copolymer crosslinking network, providing film-forming properties, mechanical strength, and excellent electrochemical stability. Furthermore, the functional monomer of Formula I is also a phosphonate compound, meaning it is also a phosphorus source and possesses flame-retardant properties.

[0013] Preferably, in Formula I, m is 1 or 2, and n is 1 or 2.

[0014] Furthermore, the functional monomer shown in Formula I is prepared by the following method:

[0015] (1) Phosphorus trihalomethanes are dissolved in solvent I to form a solution. The hydroxy C1-C5 alkyl ester of (meth)acrylic acid and the acid-binding agent are mixed and added dropwise to the above solution and reacted at 0~5℃. The molar ratio of phosphorus trihalomethanes to hydroxy C1-C5 alkyl ester of (meth)acrylic acid is 1~1.5:1. After the reaction is completed, the intermediate is obtained by purification.

[0016] (2) Dissolve the intermediate in solvent II to form a solution, add C3-C5 enyl alcohol and acid-binding agent dropwise to the solution, and react at 0~5℃. The molar ratio of C3-C5 enyl alcohol to intermediate is 2~2.5:1. After the reaction is completed, the solution is purified to obtain the functional monomer of formula I.

[0017] Taking hydroxyethyl methacrylate, phosphorus oxychloride, allyl alcohol, and triethylamine (EtN3) as acid-binding agents as an example, the reaction was carried out at 0°C for 4 hours, and the reaction formula is as follows:

[0018]

[0019] Further, in step (1), the molar ratio of phosphorus trihalomethane to (meth)acrylic acid hydroxy C1-C5 alkyl ester is 1.3~1.5:1. By controlling the molar ratio of phosphorus trihalomethane to (meth)acrylic acid hydroxy C1-C5 alkyl ester, the reaction generates a monosubstituted intermediate, and the obtained intermediate is mainly a monosubstituted product (as shown in Formula II-2).

[0020] Further, in step (1), the trihalomethane is selected from phosphorus oxychloride and / or phosphorus oxybromide; the hydroxy C1-C5 alkyl ester of (meth)acrylate is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and pentyl methacrylate; the solvent I is selected from anhydrous diethyl ether or dichloromethane; the acid-binding agent is selected from at least one of triethylamine and pyridine, and the molar ratio of the acid-binding agent to the hydroxy C1-C5 alkyl ester of (meth)acrylate is 1~1.3:1; the reaction time is 4~6h; the purification process is as follows: the reaction solution is filtered, the filtrate is extracted and washed with water, the aqueous phase is discarded, the organic phase is retained, the organic phase is dried with anhydrous sodium sulfate, filtered, and the solvent is removed by vacuum evaporation of the filtrate to obtain the intermediate.

[0021] Furthermore, in step (2), the molar ratio of C3-C5 enyl alcohol to intermediate is 2.2~2.5:1 to ensure that the halogen in the intermediate is fully substituted.

[0022] Further, in step (2), the C3-C5 enyl alcohol is allyl alcohol, enebutanol, or enepentanol; solvent II is selected from anhydrous diethyl ether or dichloromethane; the reaction time is 4-6 h. The purification process is as follows: the reaction solution is successively extracted and washed with dilute hydrochloric acid, saturated sodium bicarbonate solution, and saturated brine, the aqueous phase is discarded, and the organic phase is retained; the organic phase is then dried with anhydrous sodium sulfate, filtered, and the filtrate is evaporated under reduced pressure to remove the solvent, yielding the crude product; the crude product is then subjected to silica gel column chromatography using a petroleum ether / ethyl acetate mixed solvent as the eluent.

[0023] Furthermore, the thiolized nano-hexagonal boron nitride is prepared by a method including the following steps: after hydroxylation treatment of nano-hexagonal boron nitride, surface modification is performed using a coupling agent containing thiol groups to obtain thiolized nano-hexagonal boron nitride (h-BN-SH).

[0024] Furthermore, the nano-hexagonal boron nitride has a size of 100-300 nm and a thickness of 1-5 nm; the hydroxylation treatment conditions are as follows: the nano-hexagonal boron nitride is immersed in an inorganic alkaline aqueous solution of 4-7 mol / L or an aqueous solution of 3-5 wt% hydrogen peroxide, and hydrothermally reacted at 70-90 °C for 8-12 h, followed by centrifugation, washing with pure water to neutralize, and drying at 60-80 °C for 12-24 h; the mercapto-containing coupling agent is selected from at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; the surface modification conditions are as follows: the hydroxylated nano-hexagonal boron nitride and the mercapto-containing coupling agent are dispersed in alcohol at a mass ratio of 1:0.2-0.4, and reacted at 60-80 °C for 4-7 h under the action of a catalyst, followed by centrifugation, washing with alcohol 2-4 times, and drying at 60-80 °C for 6-12 h.

[0025] Furthermore, the alcohol is selected from at least one of ethanol, propanol, and isopropanol, and the catalyst is selected from acetic acid or ammonia, and its amount is 3-5 wt% of hydroxylated hexagonal boron nitride nanosheets.

[0026] Further, in step (S1), the mass ratio of the thiolized nano-hexagonal boron nitride, the functional monomer, and the initiator is 10:(2~4):(0.01~0.03); the polar aprotic solvent is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), and N,N-dimethylformamide (DMF); the initiator is selected from at least one of 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone; the ultraviolet irradiation conditions in the first stage are: irradiation at 500~800W for 3~5 min; the purification process is: centrifugation, washing the solid portion 2~3 times with a polar aprotic solvent, and drying at 60~80℃ for 6~24 h. During ultraviolet irradiation, the thiol groups on the h-BN-SH surface undergo selective click chemistry with the highly reactive alkenyl groups in the functional monomer, grafting the functional monomer onto the h-BN-SH surface while retaining the less reactive alkenyl groups. Because the double bonds in the acrylate groups of the functional monomer are highly reactive, the first stage of step S1 uses relatively mild ultraviolet irradiation conditions—low power and short time—to allow the highly reactive acrylate double bonds to react while retaining the less reactive allyl groups.

[0027] Further, in step (S2), the mass ratio of the phosphorus-containing monomer, the ether-oxygen-containing monomer, the initiator, and the fluorinated linear polymer is 1:(2~4):(0.02~0.1):(3~5), preferably 1:(2~3):(0.02~0.1):(3~4); the amount of the modified nano-hexagonal boron nitride (h-BN-P) is 5~15wt% of the total mass of the phosphorus-containing monomer, the ether-oxygen-containing monomer, and the fluorinated linear polymer, preferably 7.5~12.5wt%. The low-activity alkenyl groups retained on the surface of h-BN-P copolymerize with the phosphorus-containing monomer and the ether-oxygen-containing monomer, anchoring h-BN-P in the formed three-dimensional phosphorus-based copolymer network by covalent bonds, and the fluorinated linear polymer is dispersed in the copolymer network.

[0028] Further, in step (S2), the phosphorus-containing monomer is selected from phosphonate or phosphonic acid compounds containing carbon-carbon double bonds, specifically from at least one of vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, dimethyl allylphosphonate, diethyl allylphosphonate, dipropyl allylphosphonate, and diethyl isopropenylphosphonate, preferably diethyl allylphosphonate. It provides a phosphorus source in the copolymer network, which is crucial for generating flame-retardant free radicals at high temperatures. In the early stages of battery thermal runaway, the phosphonate can decompose to generate phosphorus-containing free radicals, interrupting the electrolyte chain combustion reaction. The phosphorus-containing monomer selected in this invention has relatively small steric hindrance and is easily introduced into the copolymer.

[0029] Further, in step (S2), the ether-oxygen-containing monomer is an acrylate compound containing an ether oxygen group, selected from at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate, preferably ethoxylated trimethylolpropane triacrylate; the initiator is selected from at least one of 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone. The ether-oxygen-containing monomers selected in this invention contain a large number of oxygen-containing substituents, and multiple double bonds in their molecules can serve as crosslinking points. Simultaneously, the ether oxygen group can improve the toughness of the polymer chain and its affinity for the electrolyte.

[0030] Further, in step (S2), the fluorinated linear polymer is selected from at least one of poly(vinylidene fluoride-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkyl vinyl ether), and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether), preferably poly(vinylidene fluoride-co-hexafluoropropylene).

[0031] Further, in step (S2), the inert peelable substrate is a polytetrafluoroethylene sheet or a polyimide sheet; the ultraviolet irradiation conditions in the second stage are: irradiation at 1500~2500W for 8~12 minutes; the drying is at 60~80℃ for 12~24 hours. The double bonds in the allyl groups retained in the phosphorus-containing monomers grafted onto the h-BN-SH surface have low activity. The ultraviolet irradiation conditions in step S2 are stronger than in step S1, ensuring that the allyl groups fully participate in the copolymerization reaction.

[0032] Secondly, the present invention also provides a wide-temperature-range thermal management composite battery separator, which is prepared by the above-described preparation method.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention designs a functional monomer with intramolecular differentially active double bonds, containing both highly active and less active double bonds. Through a stepwise reaction process, the thiol-alkenyl click reaction selectively occurs on the highly active double bonds of the functional monomer, thereby grafting this functional monomer onto the surface of hexagonal boron nitride (h-BN). Simultaneously, the less active double bonds are retained for subsequent copolymerization and crosslinking with phosphorus-containing monomers and ether-oxygen-containing monomers to form a three-dimensional polymer network, thus anchoring h-BN within the covalently crosslinked network. This fundamentally solves the problems of poor dispersibility and weak interfacial bonding between h-BN and the polymer matrix, thereby fully utilizing the high thermal conductivity potential of h-BN.

[0035] 2. Thanks to the chemical anchoring structure between the filler and the polymer matrix, this invention can construct a uniform and efficient thermally conductive network with a low filler addition amount (5~15wt%), while maintaining excellent ionic conductivity, effectively solving the contradiction between high thermal conductivity and high ionic conductivity in traditional battery separators.

[0036] 3. The composite separator of the present invention integrates the dual mechanisms of heat dissipation under normal operating conditions and active flame retardancy at high temperatures. When the battery is working normally, the hexagonal boron nitride thermal conductive network can quickly homogenize the temperature field and suppress local hot spots (heat dissipation); when the internal temperature of the battery rises sharply due to an anomaly to near the threshold of electrolyte decomposition or separator melting, the phosphorus-based flame retardant copolymer network decomposes under heat, releasing phosphorus-containing free radicals to quench the chain reaction and interrupt the thermal runaway process (active flame retardancy), realizing full-process thermal management from heat homogenization to chemical intervention in a wide temperature range. Attached Figure Description

[0037] Figure 1 Infrared spectra of the functional monomers prepared in Example 1.

[0038] Figure 2 An optical photograph of the composite battery separator prepared in Example 1.

[0039] Figure 3 This is a SEM image of the composite battery separator prepared in Example 1.

[0040] Figure 4 The infrared thermal imaging shows the heat distribution of the battery separators prepared in Example 1 and the blank example. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials are all commercially available.

[0042] The nano-hexagonal boron nitride was purchased from Shanghai McLean Biochemical Technology Co., Ltd., with a size of 150~200nm and a thickness of 2~3nm.

[0043] Preparation of functional monomers

[0044] Preparation Example 1

[0045] (1) Under nitrogen protection, 0.15 mol of phosphorus oxychloride (POCl3) was dissolved in anhydrous diethyl ether to form a solution. The solution was cooled to 0~3℃ in an ice bath. 0.1 mol of hydroxyethyl methacrylate and 0.12 mol of triethylamine were mixed and added dropwise to the solution under stirring. The addition was completed in 60 min, and the temperature was maintained at 0~3℃ during the addition process. After the addition was completed, the reaction was stirred for 4 h. After the reaction was completed, the reaction solution was filtered. The filtrate was extracted and washed three times with water. The aqueous phase was discarded and the organic phase was retained. The organic phase was dried with anhydrous sodium sulfate and filtered to remove the desiccant. The solvent was removed by vacuum evaporation of the filtrate to obtain the intermediate shown in formula II-2.

[0046] (2) Dissolve 0.1 mol of the intermediate in anhydrous diethyl ether to form a solution. Then, mix 0.25 mol of allyl alcohol and 80 mL of triethylamine and add the mixture dropwise to the solution under stirring. The addition is completed within 60 min, and the temperature is maintained at 0-3℃ during the addition process. After the addition is completed, continue stirring for 4 h. After the reaction is completed, transfer the reaction solution to a separatory funnel and extract and wash it successively with dilute hydrochloric acid, saturated sodium bicarbonate solution and saturated brine. Discard the aqueous phase and retain the organic phase. Dry the organic phase with anhydrous sodium sulfate, filter to remove the desiccant, and evaporate the solvent from the filtrate under reduced pressure to obtain the crude product. Purify the crude product by silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 3 / 1) to obtain a colorless oily liquid, which is the functional monomer a.

[0047] The infrared spectrum of functional monomer a is shown in Figure 1. The spectrum shows a region located at ~960 cm⁻¹. -1 and ~1030 cm -1The P–O–C stretching vibration has two peaks, with a peak at ~1270 (P=O) and a peak at ~1661 cm⁻¹. -1 (C=C) peak, ~1810 cm -1 (C=O-O) peak. Based on the aforementioned reaction mechanism and reaction formula, the structural formula of functional monomer a is deduced as follows:

[0048]

[0049] Preparation Example 2

[0050] The rest is the same as in Preparation Example 1, except that in step (1), hydroxymethyl acrylate is used in place of hydroxyethyl methacrylate in equimolar form; and in step (2), allyl butanol is used in place of allyl alcohol in equimolar form to obtain functional monomer b. Based on the aforementioned reaction mechanism and reaction formula, the structural formula of functional monomer b is deduced as follows:

[0051]

[0052] Preparation Example 3

[0053] The rest is the same as in Preparation Example 1, except that in step (1), hydroxyamyl methacrylate is used in equimolar substitution for hydroxyethyl methacrylate, and the reaction temperature is 3-5℃; in step (2), pentyl alcohol is used in equimolar substitution for allyl alcohol to obtain functional monomer c, and the reaction temperature is 3-5℃. Based on the aforementioned reaction mechanism and reaction formula, the structural formula of functional monomer c is deduced as follows:

[0054]

[0055] Example 1

[0056] (S1) 2g of nano-hexagonal boron nitride was added to 400mL of 5mol / L sodium hydroxide aqueous solution and stirred at 80℃ for 12 hours. After the reaction was completed, the mixture was centrifuged, washed with pure water until neutral, and dried in a vacuum drying oven at 60℃ for 12 hours to obtain hydroxylated nano-hexagonal boron nitride. Subsequently, 1g of hydroxylated nano-hexagonal boron nitride was dispersed in 20mL of anhydrous ethanol, sonicated for 30min, and 0.2g of 3-mercaptopropyltrimethoxysilane and 0.05mL of acetic acid catalyst were added. The mixture was stirred and refluxed at 70℃ for 6 hours. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, and dried in a vacuum drying oven at 60℃ for 6 hours to obtain mercaptolated nano-hexagonal boron nitride (h-BN-SH).

[0057] 5g of mercapto-modified nano-hexagonal boron nitride (h-BN-SH) was dispersed in N-methylpyrrolidone (NMP), 2g of functional monomer a and 10mg of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added, and the mixture was stirred until homogeneous to form a solution. The solution was then irradiated under ultraviolet light (365nm, 500W, 30cm) for 3min. After irradiation, the solution was centrifuged, washed three times with NMP to remove unreacted free functional monomers, and dried under vacuum at 60℃ for 12h to obtain modified nano-hexagonal boron nitride (h-BN-P).

[0058] (S2) 0.24g of modified nano-hexagonal boron nitride (h-BN-P) was dispersed in NMP, and 1.2g of poly(vinylidene fluoride-co-hexafluoropropylene) was dissolved in it. Then, 0.4g of allyl phosphonate diethyl ester, 0.8g of ethoxylated trimethylolpropane triacrylate, and 10mg of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added. The mixture was stirred at 600rpm for 1h to form a mixed slurry (i.e., h-BN-P is 10wt% of the total mass of phosphorus-containing monomers, ether-containing monomers, and fluorine-containing linear polymers, and the mass ratio of phosphorus-containing monomers, ether-containing monomers, and fluorine-containing linear polymers is 1:2:3). After vacuum degassing for 30min, the mixed slurry was coated onto a polytetrafluoroethylene (PTFE) substrate and irradiated under ultraviolet light (2000W power, 30cm distance) for 10min. After irradiation, the substrate was dried in a vacuum oven at 60℃ for 12h and then peeled off to obtain a wide-temperature-range thermal management composite battery separator (optical photograph as shown). Figure 2 (As shown).

[0059] Example 2

[0060] The rest is the same as in Example 1, except that in step (S1), functional monomer b is used to replace functional monomer a.

[0061] Example 3

[0062] The rest is the same as in Example 1, except that in step (S1), functional monomer c is used to replace functional monomer a.

[0063] Example 4

[0064] The rest is the same as in Example 1, except that the amount of h-BN-P used in step (S2) is 0.12g (i.e., h-BN-P is 5wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer).

[0065] Example 5

[0066] The rest is the same as in Example 1, except that the amount of h-BN-P used in step (S2) is 0.18g (i.e., h-BN-P is 7.5wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer).

[0067] Example 6

[0068] The rest is the same as in Example 1, except that the amount of h-BN-P used in step (S2) is 0.3g (that is, h-BN-P is 12.5wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer).

[0069] Example 7

[0070] The rest is the same as in Example 1, except that the amount of h-BN-P used in step (S2) is 0.36g (that is, h-BN-P is 15wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer).

[0071] Example 8

[0072] The rest is the same as in Example 1, except that the amount of functional monomer a in step (S1) is 1g.

[0073] Example 9

[0074] The rest is the same as in Example 1, except that the amount of each raw material used in step (S2) is different. Specifically, the amount of h-BN-P is 0.32g, the amount of poly(vinylidene fluoride-co-hexafluoropropylene) is 1.6g, the amount of allyl phosphonate diethyl ester is 0.4g, the amount of ethoxylated trimethylolpropane triacrylate is 1.2g, and the amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone is 15mg (h-BN-P is 10wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer, and the mass ratio of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer is 1:3:4).

[0075] Example 10

[0076] The rest is the same as in Example 1, except that the amount of each raw material used in step (S2) is different. Specifically, the amount of h-BN-P is 0.4g, the amount of poly(vinylidene fluoride-co-hexafluoropropylene) is 2.0g, the amount of allyl phosphonate diethyl ester is 0.4g, the amount of ethoxylated trimethylolpropane triacrylate is 1.6g, and the amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone is 15mg (i.e., h-BN-P is 10wt% of the total mass of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer, and the mass ratio of phosphorus-containing monomer, ether-containing oxygen-containing monomer and fluorine-containing linear polymer is 1:4:5).

[0077] Comparative Example 1

[0078] The rest is the same as in Example 1, except that step (S1) is omitted and in step (S2) nano-hexagonal boron nitride (h-BN) is used to replace the modified nano-hexagonal boron nitride (h-BN-P) by mass.

[0079] Comparative Example 2

[0080] The rest is the same as in Example 1, except that the thiolized nano-hexagonal boron nitride (h-BN-SH) in step (S1) is not modified, but is directly replaced by an equal mass of the modified nano-hexagonal boron nitride (h-BN-P) in step (S2). Specifically:

[0081] (S1) 2g of nano-hexagonal boron nitride was added to 400mL of 5mol / L sodium hydroxide aqueous solution and stirred at 80℃ for 12 hours. After the reaction was completed, the mixture was centrifuged, washed with pure water until neutral, and dried in a vacuum drying oven at 60℃ for 12 hours to obtain hydroxylated nano-hexagonal boron nitride. Subsequently, 1g of hydroxylated nano-hexagonal boron nitride was dispersed in 20mL of anhydrous ethanol, sonicated for 30min, and 0.2g of 3-mercaptopropyltrimethoxysilane and 0.05mL of acetic acid catalyst were added. The mixture was stirred and refluxed at 70℃ for 6 hours. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, and dried in a vacuum drying oven at 60℃ for 6 hours to obtain mercaptolated nano-hexagonal boron nitride (h-BN-SH).

[0082] (S2) 0.24g of mercapto-modified nano-hexagonal boron nitride (h-BN-SH) was dispersed in NMP, 1.2g of poly(vinylidene fluoride-co-hexafluoropropylene) was dissolved in it, and then 0.4g of allyl phosphonate diethyl ester, 0.8g of ethoxylated trimethylolpropane triacrylate and 10mg of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added. The mixture was stirred at 600rpm for 1h to form a mixed slurry (i.e., h-BN-SH is 10wt% of the total mass of phosphorus-containing monomers, ether-containing oxygen-containing monomers and fluorine-containing linear polymers, and the mass ratio of phosphorus-containing monomers, ether-containing oxygen-containing monomers and fluorine-containing linear polymers is 1:2:3). After vacuum degassing for 30min, the mixed slurry was coated onto a polytetrafluoroethylene vinyl plate and irradiated under ultraviolet light (power 2000W, distance 30cm) for 10min. After irradiation, it was dried in a vacuum oven at 60℃ for 12h and peeled off from the substrate to obtain a wide-temperature-range thermal management composite battery separator.

[0083] Comparative Example 3

[0084] The rest is the same as in Example 1, except that in step (S2), poly(vinylidene fluoride-co-hexafluoropropylene) is not added. The specific raw materials and amounts are: 0.12g modified nano-hexagonal boron nitride (h-BN-P), 0.4g allyl phosphonate diethyl ester, and 0.8g ethoxylated trimethylolpropane triacrylate. That is, h-BN-P accounts for 10wt% of the total polymer mass, consistent with Example 1.

[0085] Blank example

[0086] The rest is the same as in Example 1, except that step (S2) does not use modified nano-hexagonal boron nitride (h-BN-P), i.e., a pure polymer film.

[0087] Testing and Analysis

[0088] 1) Microscopic morphology analysis

[0089] SEM image of the composite battery separator prepared in Example 1 is shown below. Figure 3 As shown in the figure, hexagonal boron nitride is uniformly dispersed in the polymer matrix without obvious agglomeration and is tightly bonded to the matrix interface.

[0090] 2) Ionic conductivity test

[0091] The room-temperature ionic conductivity was measured by electrochemical impedance spectroscopy using the blocked electrode method (stainless steel | separator immersed in electrolyte | stainless steel). All separators were fully immersed in 1M LiPF6 electrolyte (solvent prepared in a volume ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1:1:1) before testing. Ionic conductivity (σ) = d / (R*S) (where d and S represent the separator thickness and facing area, respectively, and R represents the bulk resistance of the separator conductivity system), and the ionic conductivity was calculated. Specific data on the room-temperature ionic conductivity of the battery separators in the examples and comparative examples are shown in Table 1.

[0092] 3) Thermal shrinkage rate

[0093] To evaluate the heat resistance of the battery separator, the heat shrinkage rate of the battery separators prepared in the examples and comparative examples was tested. The specific method was as follows: the battery separator was placed between two clean flat glass plates and clamped, then placed on a programmable temperature-controlled heating stage. Under an argon atmosphere, it was held at 100℃, 120℃, 140℃, and 160℃ for 30 minutes each. After reaching each set temperature and holding at that temperature, the dimensional change in length (or width) was measured. The heat shrinkage rate (S) was calculated using the formula: S = (L0 - L1) / L0 × 100%; where L0 is the initial length (or width), and L1 is the length (or width) after heating. The heat shrinkage rate data of the battery separators in the examples and comparative examples are shown in Table 1.

[0094] Table 1 Ionic conductivity and thermal shrinkage

[0095]

[0096] Table 1 shows that the room temperature ionic conductivity of the composite battery separators prepared in the examples is significantly higher than that of the pure polymer membranes in Comparative Example 1, Comparative Example 2, and the blank example, all exceeding 1.20 mS / cm, with the preferred examples exceeding 1.30 mS / cm. It is evident that the addition of modified nano-hexagonal boron nitride (h-BN-P) actually promotes ion conduction, mainly due to its uniform dispersion and chemical bonding anchoring within the polymer network.

[0097] As can be seen from Table 1, the thermal shrinkage rate of the composite battery separator of the present invention at 160°C is 1-2%, which is significantly lower than that of the polymer membrane in the blank example, far lower than that of the commercial Celgard separator, and also lower than that of Comparative Example 1 and Comparative Example 2. This indicates that anchoring the filler in the polymer network through chemical bonds significantly increases the thermal stability of the polymer, providing a guarantee for the separator to maintain structural integrity at high temperatures and prevent internal short circuits induced by thermal shrinkage.

[0098] Comparative Example 3, lacking the physical interpenetrating structure of the fluorinated linear polymer, exhibited a higher thermal shrinkage rate and slightly lower ionic conductivity than the Example. This indicates that the introduction of the fluorinated linear polymer promotes the synergistic effect of achieving both high ionic conductivity and excellent thermal stability.

[0099] 4) Thermal management capability test

[0100] The battery separator samples (circular pieces with a diameter of 1.6 cm) prepared in the examples and comparative examples were placed under vacuum conditions, with a miniature thin-film heating element (simulating a local heat source) fixed at the center, and heated with a constant power (7 W). The surface temperature field distribution over time was then recorded using an infrared thermal imager. The thermal distribution of the battery separators prepared in Example 1 and the blank example is shown in the infrared thermal imaging as follows. Figure 4 As shown. From Figure 4 As can be seen, compared with the pure polymer separator of the blank example, the battery separator prepared in Example 1 has a faster thermal conduction speed, reflecting the improvement of in-plane thermal conductivity, which can avoid the formation of local hot spots, and thus has excellent thermal conduction and heat dissipation capabilities.

[0101] To further verify the flame-retardant properties of the battery separator, a flame contact test was conducted on the composite separator prepared in Example 1. Specifically, the separator sample was exposed to the outer flame of an alcohol lamp for approximately 3 seconds and then removed, with continuous observation of its combustion behavior. The results showed that the separator sample of Example 1 self-extinguished rapidly after being removed from the flame source, and there was no significant melting or dripping during combustion. In contrast, the pure polymer membrane of the blank example burned violently upon contact with the flame, accompanied by severe melting and dripping. This indicates that the separator of the present invention triggers a chemical flame-retardant mechanism at high temperatures, endowing it with active flame-retardant properties.

[0102] In summary, the composite battery separator of the present invention has both high ionic conductivity and high thermal conductivity, as well as good flame retardant properties. It integrates the dual functions of heat dissipation under normal operating conditions and active flame retardancy at high temperatures, thus possessing wide-temperature-range thermal management capabilities.

Claims

1. A method for preparing a wide-temperature-range thermal management composite battery separator, characterized in that, Includes the following steps: (S1) Thiolized nano-hexagonal boron nitride is dispersed in a polar aprotic solvent, and the functional monomer and initiator shown in Formula I are added to form a mixture. The mixture is subjected to the first stage of ultraviolet light irradiation. After the irradiation is completed, it is purified to obtain modified nano-hexagonal boron nitride. (Equation I), In Equation I, m is an integer from 1 to 5, and n is an integer from 1 to 3; (S2) Modified nano-hexagonal boron nitride is dispersed in a polar aprotic solvent, a fluorinated linear polymer is dissolved in it, and then a phosphorus-containing monomer, an ether-containing oxygen monomer, and an initiator are added to form a mixed slurry. The mixed slurry is coated on an inert peelable substrate and subjected to a second stage of ultraviolet irradiation. After the irradiation is completed, it is dried and peeled off from the substrate to obtain a wide-temperature-range thermal management composite battery separator.

2. The preparation method according to claim 1, characterized in that, In Equation I, m is 1 or 2, and n is 1 or 2.

3. The preparation method according to claim 1, characterized in that, The functional monomers shown in Formula I are prepared by the following method: (1) Phosphorus trihalomethanes are dissolved in solvent I to form a solution. The hydroxy C1-C5 alkyl ester of (meth)acrylic acid and the acid-binding agent are mixed and added dropwise to the above solution and reacted at 0~5℃. The molar ratio of phosphorus trihalomethanes to hydroxy C1-C5 alkyl ester of (meth)acrylic acid is 1~1.5:

1. After the reaction is completed, the intermediate is obtained by purification. (2) The intermediate is dissolved in solvent II to form a solution. C3-C5 enyl alcohol and acid-binding agent are added dropwise to the solution and reacted at 0~5℃. The molar ratio of C3-C5 enyl alcohol to intermediate is 2~2.5:

1. After the reaction is completed, the solution is purified to obtain the functional monomer of formula I.

4. The preparation method according to claim 3, characterized in that, In step (1), the molar ratio of phosphorus trihalomethane to hydroxy C1-C5 alkyl methacrylate is 1.3-1.5:1; the phosphorus trihalomethane is selected from phosphorus oxychloride and / or phosphorus tribromide; the hydroxy C1-C5 alkyl methacrylate is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and pentyl methacrylate; the solvent is selected from anhydrous diethyl ether or dichloromethane; the acid-binding agent is selected from at least one of triethylamine and pyridine, and the molar ratio of the acid-binding agent to the hydroxy C1-C5 alkyl methacrylate is 1-1.3:1; the reaction time is 4-6 hours; the purification process is as follows: the reaction solution is filtered, the filtrate is extracted and washed with water, the aqueous phase is discarded, the organic phase is retained, the organic phase is dried with anhydrous sodium sulfate, filtered, and the solvent is removed by vacuum distillation of the filtrate to obtain the intermediate; and / or, In step (2), the molar ratio of C3-C5 enyl alcohol to intermediate is 2.2~2.5:1; the C3-C5 enyl alcohol is allyl alcohol, enebutanol, or enepentanol; solvent II is selected from anhydrous diethyl ether or dichloromethane; the reaction time is 4~6 h. The purification process is as follows: the reaction solution is successively extracted and washed with dilute hydrochloric acid, saturated sodium bicarbonate solution, and saturated brine, the aqueous phase is discarded, and the organic phase is retained; the organic phase is then dried with anhydrous sodium sulfate, filtered, and the filtrate is evaporated under reduced pressure to remove the solvent, yielding the crude product; the crude product is then subjected to silica gel column chromatography using a petroleum ether / ethyl acetate mixed solvent as the eluent.

5. The preparation method according to claim 1, characterized in that, The thiolized nano-hexagonal boron nitride is prepared by a method including the following steps: after hydroxylation treatment of nano-hexagonal boron nitride, surface modification is performed by a coupling agent containing thiol groups to obtain thiolized nano-hexagonal boron nitride. Preferably, the nano-hexagonal boron nitride has a size of 100-300 nm and a thickness of 1-5 nm; the hydroxylation treatment conditions are as follows: the nano-hexagonal boron nitride is immersed in an inorganic alkaline aqueous solution of 4-7 mol / L or an aqueous solution of 3-5 wt% hydrogen peroxide, and hydrothermally reacted at 70-90°C for 8-12 h, followed by centrifugation, washing with pure water to neutralize, and drying at 60-80°C for 12-24 h; the mercapto-containing coupling agent is selected from at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; the surface modification conditions are as follows: the hydroxylated nano-hexagonal boron nitride and the mercapto-containing coupling agent are dispersed in alcohol at a mass ratio of 1:0.2-0.4, and reacted at 60-80°C for 4-7 h under the action of a catalyst, followed by centrifugation, washing with alcohol 2-4 times, and drying at 60-80°C for 6-12 h. Preferably, the alcohol is selected from at least one of ethanol, propanol, and isopropanol, and the catalyst is selected from acetic acid or ammonia, and its amount is 3-5 wt% of the hydroxylated hexagonal boron nitride nanosheets.

6. The preparation method according to claim 1, characterized in that, In step (S1), the mass ratio of the thiolized nano-hexagonal boron nitride, the functional monomer, and the initiator is 10:(2~4):(0.01~0.03); the polar aprotic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; the initiator is selected from at least one of 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone; the ultraviolet irradiation conditions in the first stage are: irradiation at 500~800W for 3~5 min; the purification process is: centrifugation, washing the solid part 2~3 times with a polar aprotic solvent, and drying at 60~80℃ for 6~24 h.

7. The preparation method according to claim 1, characterized in that, In step (S2), the mass ratio of phosphorus-containing monomer, ether-oxygen-containing monomer, initiator and fluorine-containing linear polymer is 1:(2~4):(0.02~0.1):(3~5), preferably 1:(2~3):(0.02~0.1):(3~4); the amount of modified nano-hexagonal boron nitride is 5~15wt% of the total mass of phosphorus-containing monomer, ether-oxygen-containing monomer and fluorine-containing linear polymer, preferably 7.5~12.5wt%.

8. The preparation method according to claim 1, characterized in that, In step (S2), the phosphorus-containing monomer is selected from phosphonate or phosphonic acid compounds containing carbon-carbon double bonds, specifically from at least one of vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, dimethyl allylphosphonate, diethyl allylphosphonate, dipropyl allylphosphonate, and diethyl isopropenylphosphonate, preferably diethyl allylphosphonate; the ether-oxygen-containing monomer is an acrylate compound having an ether-oxygen-containing group, selected from at least one of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate. The preferred initiator is ethoxylated trimethylolpropane triacrylate; the initiator is selected from at least one of 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone; the fluorinated linear polymer is selected from at least one of poly(vinylidene fluoride-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkyl vinyl ether), and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether), preferably poly(vinylidene fluoride-co-hexafluoropropylene).

9. The preparation method according to claim 1, characterized in that, In step (S2), the inert peelable substrate is a polytetrafluoroethylene sheet or a polyimide sheet; the conditions for ultraviolet irradiation in the second stage are: irradiation at 1500~2500W for 8~12 minutes; the drying is drying at 60~80℃ for 12~24 hours.

10. A wide-temperature-range thermal management composite battery separator, which is prepared by the preparation method according to any one of claims 1-9.

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