Polyarylene ether nitrile lithium battery diaphragm and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion battery materials, and relates to a polyarylene ether nitrile lithium battery diaphragm and a preparation method thereof. According to the preparation method, carboxyl-containing polyarylene ether nitrile is taken as a matrix, a non-solvent induced phase separation method is adopted to prepare a diaphragm main body, carboxyl coordination is utilized to guide in-situ growth of a metal organic framework (MOF) structure in the diaphragm main body, then a compact MOF coating is further coordinated and grown on the surface through an interface impregnation method, and a three-dimensional porous network structure with synergistic exterior and interior is formed. By regulating and controlling the MOF hybrid region and structure distribution, the influence of the MOF on the pore structure, electrolyte wettability and thermal stability of the diaphragm is systematically researched, and multi-dimensional optimization of the performance of the diaphragm is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and relates to a polyarylether nitrile lithium battery separator and a preparation method thereof, in particular to a preparation method of a gradient designed high-safety polyarylether nitrile lithium battery separator. BACKGROUND

[0002] Lithium metal batteries are widely regarded as a key technology for building a new generation of high-energy-density energy storage systems due to their extremely high theoretical specific capacity (3860 mAh·g⁻¹) and ultra-low reduction potential (-3.04 V vs SHE). However, its commercialization process is limited by poor safety, mainly manifested in the easy induction of lithium dendrite growth during the cycle process, which in turn pierces the separator to cause short circuit and even thermal runaway and other safety accidents. As a key component between the electrode and the electrolyte, the separator plays a crucial role in maintaining the electrochemical stability and structural safety of the battery.

[0003] The current commercial mainstream separator is mostly made of polypropylene (PP), polyethylene (PE) and other polyolefin materials, which have good mechanical strength and mature processing, but their low polarity and high crystallinity make them generally have poor electrolyte wettability, insufficient thermal stability, and difficulty in effectively inhibiting dendrite penetration. They are prone to serious shrinkage at high temperatures, leading to internal short circuit and further inducing thermal runaway.

[0004] Therefore, researchers have proposed various surface modification strategies, such as improving the heat resistance of the separator by ceramic coating. The manufacturing method of a composite separator for lithium ion power batteries disclosed in Chinese Patent No. 201810504179.2 coats an inorganic particle layer on the substrate to enhance the heat resistance of the separator by introducing functional groups into the non-woven fabric fiber layer made of a mixture of polyarylether nitrile and polyvinyl alcohol through an electrospinning process. However, this method easily leads to the closure of pores in the separator, and the manufacturing process is complex and difficult to control. In addition, the surface coating method is usually accompanied by problems such as poor interfacial adhesion, limited coating uniformity, and peeling of the coating during long-term cycling.

[0005] Therefore, how to provide a preparation method of a polyarylether nitrile lithium battery separator that can simultaneously construct stable functional structures inside and outside the separator, and also consider the thermal stability, wettability and dendrite inhibition capacity is a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0006] Therefore, the application discloses a polyarylether nitrile lithium battery separator and a preparation method thereof.

[0007] It should be noted that the present application aims at the synergistic control problem of the current diaphragm material in improving thermal stability, electrolyte affinity and microstructure-function regulation, and proposes a preparation method of surface-internal synergistic hybrid modified lithium battery diaphragm. The present application uses carboxyl-containing polyarylether nitrile as the matrix, uses the non-solvent induced phase separation method to prepare the diaphragm main body, and uses the carboxyl coordination to guide the in-situ growth of metal organic framework (MOF) structure in the inside, then further grows the dense MOF coating on the surface through the interface impregnation method, to form the three-dimensional porous network structure of surface and inside synergy. By adjusting the MOF hybrid area and structure distribution, the influence of the diaphragm pore structure, electrolyte wettability and thermal stability is systematically studied, and the multi-dimensional optimization of the diaphragm performance is realized.

[0008] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: The first technical purpose of the present application is to provide a preparation method of a gradient designed high safety polyarylether nitrile lithium battery diaphragm, comprising the following steps: Step 1, synthesis of carboxyl type polyarylether nitrile: 1.1 Add 4,4'-diphenol, 3,5-dihydroxybenzoic acid and 2,6-difluorobenzonitrile as reactants in a three-necked bottle, add potassium carbonate as a catalyst to obtain a mixture powder; inject toluene in a water separator; wherein the molar ratio of 3,5-dihydroxybenzoic acid, 4,4'-diphenol, 2,6-difluorobenzonitrile and potassium carbonate is 1:9:10:15; 1.2 Add a mixed solvent of N-methylpyrrolidone and toluene to the mixture powder obtained in step 1.1, stir and mix uniformly to obtain a mixed solution A; in the mixed solvent, the volume ratio of N-methylpyrrolidone to toluene is 3:1; wherein the molar ratio of toluene injected in the water separator in step 1.1 and toluene added in the mixture powder in step 1.2 is 1:(1.35~1.8); 1.3 Heat the mixed solution A obtained in step 1.2 to reflux at 140℃ for 2~3 h to release toluene in the water separator; then heat to 150~159℃ and keep at 150~159℃ for 0.5~1h, heat to 160~169℃ and keep at 160~169℃ for 0.5~1h, heat to 170~179℃ and keep at 170~179℃ for 0.5~1h, heat to 180~190℃ and keep at 180~190℃ for 0.5~1h, pour the obtained reaction liquid into deionized water and stir to obtain a strip-shaped solid; 1.4 After the strip-shaped solid obtained in step 1.3 is soaked in hydrochloric acid solution for 24 h, it is crushed and then washed with deionized water until it is neutral; the washed powder is dried in an oven to obtain a carboxylic acid type polyarylether nitrile powder; Step 2, preparation of a hot solution of carboxylate-type polyarylene ether nitrile for internal growth of MOF: In a three-necked flask, N-methylpyrrolidone and carboxylate-type polyarylene ether nitrile powder obtained in step 1 were added, and stirring was performed at 120-130℃ for 2-5h to obtain solution B; then, 10-15wt% of cobalt nitrate hexahydrate based on the amount of carboxylate-type polyarylene ether nitrile was added, and sufficient reaction was performed for 20-30min; then, 3.7-15wt% of 2-methylimidazole based on the amount of carboxylate-type polyarylene ether nitrile was added, and stirring was continued for 2-3h to obtain a MOF / carboxylate-type polyarylene ether nitrile hot solution; wherein the solid-liquid ratio of carboxylate-type polyarylene ether nitrile powder and N-methylpyrrolidone was 1g:(10-20)mL; Step 3, preparation of a carboxylate-type polyarylene ether nitrile porous lithium battery separator for internal growth of MOF by non-solvent induced phase separation method: 3.1 The MOF / carboxylate-type polyarylene ether nitrile hot solution obtained in step 2 was poured onto a clean and flat glass plate, and a wet film was cast using a four-side film applicator; 3.2 The glass plate with the wet film obtained in step 3.1 was immersed in a coagulation bath for 10-20min to form a separator with a porous structure, and then the separator was soaked in deionized water; wherein the coagulation bath was a mixture of anhydrous ethanol and deionized water in a volume ratio of 1:1; 3.3 The separator obtained after step 3.2 was air-dried at room temperature to obtain the carboxylate-type polyarylene ether nitrile porous lithium battery separator for internal growth of MOF; Step 4, preparation of a gradient-designed high-safety polyarylene ether nitrile lithium battery separator: The carboxylate-type polyarylene ether nitrile porous lithium battery separator for internal growth of MOF obtained in step 3 was immersed in a water / methanol solution containing cobalt nitrate hexahydrate for 0.5-1h, and then a water / methanol solution containing 2-methylimidazole was added and soaked for 6-24h to obtain a carboxylate-type polyarylene ether nitrile porous lithium battery separator for growth of MOF on the surface and inside, i.e. the gradient-designed high-safety polyarylene ether nitrile lithium battery separator; wherein the amount ratio in the water / methanol solution containing cobalt nitrate hexahydrate was 85:15, and the amount ratio in the water / methanol solution containing 2-methylimidazole was 85:15.

[0009] The present application realizes the integrated construction of functional structure by in-situ inducing growth of ZIF-67 metal organic framework inside and outside the carboxylate-type polyarylene ether nitrile matrix. Compared with the traditional surface-coated separator, this method can effectively improve the thermal stability, electrolyte wettability and dendrite inhibition ability of the separator, while avoiding the problems of coating falling off and pore blocking, simplifying the preparation process and enhancing the cycle stability, ensuring the safety performance while considering the electrochemical performance.

[0010] A second technical object of the present application is to provide a polyarylene ether nitrile lithium battery separator prepared by the method as described above.

[0011] Compared with the prior art, the beneficial effects of the present application are: 1) The present application provides a surface-internal synergistic hybrid modified lithium battery separator, which adopts a non-solvent induced phase separation method combined with a secondary immersion reaction to introduce a MOF structure in the interior of the separator, and simultaneously construct a dense MOF coating layer in situ on the surface thereof. The double structure design effectively improves the pore structure and thermal stability of the separator, and enhances the affinity to liquid electrolyte and lithium ion migration rate.

[0012] 2) The polyarylene ether nitrile matrix endows the separator with intrinsic high heat resistance and dimensional stability, the carboxyl groups in the matrix skeleton can coordinate with the MOF precursor to enhance the binding stability thereof in the matrix; the internal MOF network helps to optimize the pore size distribution, and the surface MOF layer significantly inhibits dendrite penetration.

[0013] 3) Compared with the existing single surface modification or blending modification method, the present application realizes the synergistic improvement of structural stability, electrochemical performance and thermal safety. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0015] Figure 1 The synthesis route of the carboxylic acid type polyarylene ether nitrile of step 1.

[0016] Figure 2 The electrolyte contact angle of the gradient designed high safety polyarylene ether nitrile lithium battery separator prepared in the examples and the comparative examples 1-4.

[0017] Figure 3 The thermal stability of the gradient designed high safety polyarylene ether nitrile lithium battery separator prepared in the examples and the comparative examples 1-4.

[0018] Figure 4 The battery rate performance of the gradient designed high safety polyarylene ether nitrile lithium battery separator prepared in the examples and the comparative examples 1-4.

[0019] Figure 5 The battery cycle performance of the gradient designed high safety polyarylene ether nitrile lithium battery separator prepared in the examples and the comparative example 4. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts are within the scope of the present application.

[0021] The special word "embodiment" in this paper is not necessarily interpreted as superior or better than other embodiments as "exemplary" described any embodiment. The performance index test in the embodiments of the present application adopts the conventional test method in the art, unless otherwise specified. It should be understood that the terms described in the present application are only for describing the specific embodiments, and are not used to limit the disclosure of the present application.

[0022] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as generally understood by those of ordinary skill in the art to which the present application belongs; as the test methods and technical means not specially noted in the present application refer to the experimental methods and technical means generally used by those of ordinary skill in the art.

[0023] In order to better illustrate the content of the present application, a large number of specific details are given in the specific embodiments below. Those skilled in the art should understand that without certain specific details, the present application can also be implemented. In the embodiments, some methods, means, instruments, equipment and the like which are well known to those skilled in the art are not described in detail, in order to highlight the main idea of the present application.

[0024] The technical features disclosed in the embodiments of the present application can be combined in any way without conflict, and the technical solutions obtained belong to the disclosure of the embodiments of the present application.

[0025] The present application discloses a preparation method of a gradient designed high safety polyarylether nitrile lithium battery separator.

[0026] In order to better understand the present application, the present application will be further specifically described by the following embodiments, but it should not be understood as limiting the present application. Some non-essential improvements and adjustments made by those skilled in the art according to the above disclosure are also regarded as falling within the scope of the present application. Embodiment 1

[0027] A preparation method of a gradient designed high safety polyarylether nitrile lithium battery separator, comprising the following steps: Step 1, synthesis of carboxyl type polyarylether nitrile: 1.1 A three-necked flask was charged with 4,4'-diphenol, 3,5-dihydroxybenzoic acid and 2,6-difluorobenzonitrile as reactants, and potassium carbonate as catalyst to obtain a mixture powder; to a water separator was injected toluene; wherein the molar ratio of 3,5-dihydroxybenzoic acid, 4,4'-diphenol, 2,6-difluorobenzonitrile and potassium carbonate was 1:9:10:15; 1.2 The mixture powder obtained in step 1.1 was added with a mixed solvent of N-methylpyrrolidone and toluene, and the mixture was stirred to obtain a mixed solution A; in the mixed solvent, the volume ratio of N-methylpyrrolidone to toluene was 3:1; wherein the molar ratio of toluene injected in the water separator in step 1.1 to toluene added in the mixture powder in step 1.2 was 1:1.5; 1.3 The mixed solution A obtained in step 1.2 was heated to reflux at 140℃ for 2 h to release toluene in the water separator; then the temperature was increased to 155℃ and kept for 0.5 h, increased to 165℃ and kept for 0.5 h, increased to 175℃ and kept for 0.5 h, increased to 185℃ and kept for 1 h, and the obtained reaction solution was poured into deionized water and stirred to obtain a strip-shaped solid; 1.4 The strip-shaped solid obtained in step 1.3 was soaked in hydrochloric acid solution for 24 h, then crushed and washed with deionized water until neutral; the washed powder was dried in an oven to obtain a carboxylic acid type polyarylether nitrile powder; Step 2, preparation of a carboxylic acid type polyarylether nitrile hot solution for internal growth of MOF: A three-necked flask was charged with N-methylpyrrolidone and the carboxylic acid type polyarylether nitrile powder obtained in step 1, and heated and stirred at 130℃ for 3 h to obtain a uniform solution B; then 14wt% cobalt nitrate hexahydrate was added and reacted for 25 min, and then 12wt% 2-methylimidazole was added and heated and stirred for another 3 h to obtain a MOF / carboxylic acid type polyarylether nitrile hot solution; wherein the solid-liquid ratio of the carboxylic acid type polyarylether nitrile powder to N-methylpyrrolidone was 1g:15mL; Step 3, preparation of a carboxylic acid type polyarylether nitrile porous lithium battery separator for internal growth of MOF by non-solvent induced phase separation method: 3.1 The carboxylic acid type polyarylether nitrile hot solution for internal growth of MOF obtained in step 2 was poured onto a clean and flat glass plate, and a wet film was cast out using a four-side film applicator; 3.2 The glass plate with the wet film obtained in step 3.1 was immersed in a coagulation bath for 20 min to form a separator with a porous structure, and then the separator was soaked in deionized water; wherein the coagulation bath was a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 1:1; 3.3 Dry the porous lithium battery separator of carboxylate type polyarylene ether nitrile with internal growth MOF obtained after step 3.2 at room temperature, to obtain the porous lithium battery separator of carboxylate type polyarylene ether nitrile with internal growth MOF.

[0028] Step 4, preparation of gradient design high safety polyarylene ether nitrile lithium battery separator: The porous lithium battery separator of carboxylate type polyarylene ether nitrile with internal growth MOF obtained in step 3 is immersed in a water / methanol solution containing cobalt nitrate hexahydrate for 0.5 h, and then a water / methanol solution containing 2-methylimidazole is added and soaked for 24 h, to obtain the porous lithium battery separator of carboxylate type polyarylene ether nitrile with MOF growth on the surface and inside, that is, the gradient design high safety polyarylene ether nitrile lithium battery separator. Example 2

[0029] The difference between this example and example 1 is that: The process of preparing the hot solution of MOF / carboxylate type polyarylene ether nitrile in step 2 is adjusted as follows: N-methylpyrrolidone and carboxylate type polyarylene ether nitrile powder obtained in step 1 are added to a three-necked flask, heated and stirred at 130 ℃ for 3 h to obtain a uniform solution B; then 12wt% cobalt nitrate hexahydrate is added and fully reacted for 25 min, and then 8wt% 2-methylimidazole is added and heated and stirred for 3 h to obtain the MOF / carboxylate type polyarylene ether nitrile hot solution; wherein the solid-liquid ratio of carboxylate type polyarylene ether nitrile powder and N-methylpyrrolidone is 1g:15mL. Example 3

[0030] The difference between this example and example 1 is that: The process of preparing the hot solution of MOF / carboxylate type polyarylene ether nitrile in step 2 is adjusted as follows: N-methylpyrrolidone and carboxylate type polyarylene ether nitrile powder obtained in step 1 are added to a three-necked flask, heated and stirred at 130 ℃ for 3 h to obtain a uniform solution B; then 12wt% cobalt nitrate hexahydrate is added and fully reacted for 25 min, and then 8wt% 2-methylimidazole is added and heated and stirred for 3 h to obtain the MOF / carboxylate type polyarylene ether nitrile hot solution; wherein the solid-liquid ratio of carboxylate type polyarylene ether nitrile powder and N-methylpyrrolidone is 1g:15mL.

[0031] In order to further prove the beneficial effects of the present application and better understand the present application, the technical features disclosed in the present application are further illustrated by the following comparative examples, but it should not be understood as a limitation of the present application. Other improvements without creative work made by those skilled in the art according to the above invention content are also considered to fall within the protection scope of the present application. Comparative Example 1

[0032] A carboxylic acid type polyarylether nitrile porous lithium battery separator, a preparation method thereof comprises the following steps: Step 1, synthesis of carboxylic acid type polyarylether nitrile: 1.1 A three-necked bottle is added with 4,4'-diphenol, 3,5-dihydroxybenzoic acid and 2,6-difluorobenzonitrile as reactants, and potassium carbonate as a catalyst to obtain a mixture powder; toluene is injected into a water separator; wherein the molar ratio of 3,5-dihydroxybenzoic acid, 4,4'-diphenol, 2,6-difluorobenzonitrile and potassium carbonate is 1:9:10:15; 1.2 The mixture powder obtained in step 1.1 is added with a mixed solvent of N-methyl pyrrolidone and toluene, and stirred to be uniformly mixed to obtain a mixed solution A; in the mixed solvent, the volume ratio of N-methyl pyrrolidone and toluene is 3:1; wherein the molar ratio of toluene injected into the water separator in step 1.1 and toluene added into the mixture powder in step 1.2 is 1:1.5; 1.3 The mixed solution A obtained in step 1.2 is heated to reflux at 140℃ for 2 h to release toluene in the water separator; then heated to 155℃ and kept for 0.5 h, heated to 165℃ and kept for 0.5 h, heated to 175℃ and kept for 0.5 h, heated to 185℃ and kept for 1 h, and the obtained reaction solution is poured into deionized water and stirred to obtain a strip-shaped solid; 1.4 The strip-shaped solid obtained in step 1.3 is soaked in a hydrochloric acid solution for 24 h, then crushed, and washed with deionized water until neutral; the washed powder is dried in an oven to obtain a carboxylic acid type polyarylether nitrile powder; Step 2, preparation of a carboxylic acid type polyarylether nitrile hot solution: A three-necked bottle is added with N-methyl pyrrolidone and the carboxylic acid type polyarylether nitrile powder obtained in step 1, and heated and stirred at 130℃ for 3 h to obtain a uniform solution B; the solid-liquid ratio of the carboxylic acid type polyarylether nitrile powder and N-methyl pyrrolidone is 1 g:15 mL.

[0033] Step 3, preparation of a carboxylic acid type polyarylether nitrile porous lithium battery separator by using a non-solvent phase separation method: 3.1 The carboxylic acid type polyarylether nitrile hot solution obtained in step 2 is poured onto a clean and flat glass plate, and a wet film is cast out by using a four-side film coater; 3.2 The glass plate with the wet film obtained in step 3.1 is immersed in a coagulation bath for 20 min to form a separator with a porous structure, and then the separator is soaked in deionized water; wherein the coagulation bath is a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 1:1; 3.3 The separator obtained after step 3.2 is air-dried at room temperature to obtain the carboxylic acid type polyarylether nitrile porous lithium battery separator. Comparative Example 2:

[0034] Step 1, preparation of MOF / carboxylate poly(arylene ether nitrile) hot solution: In a three-necked flask, N-methyl pyrrolidone and carboxylate poly(arylene ether nitrile) powder obtained in step 1 of Comparative Example 1 were added, and heated and stirred at 130 °C for 3 h to obtain a uniform solution B; then 14wt% cobalt nitrate hexahydrate was added and reacted for 30 min, and then 12wt% 2-methyl imidazole was added and heated and stirred for 3 h to obtain a MOF / carboxylate poly(arylene ether nitrile) hot solution; wherein the solid-liquid ratio of carboxylate poly(arylene ether nitrile) solid powder and N-methyl pyrrolidone was 1g:15 mL; Step 2, preparation of carboxylate poly(arylene ether nitrile) porous battery separator with MOF grown inside: The MOF / carboxylate poly(arylene ether nitrile) hot solution obtained in step 1 was subjected to the process in step 3 of Comparative Example 1 to obtain a carboxylate poly(arylene ether nitrile) porous battery separator with MOF grown inside. Comparative Example 3:

[0035] This comparative example added a step based on Comparative Example 1: The carboxylate poly(arylene ether) porous battery separator obtained in Comparative Example 1 was immersed in a water / methanol solution containing cobalt nitrate hexahydrate for 30 min, and then a water / methanol solution containing 2-methyl imidazole was added and immersed for 24 h to obtain a carboxylate poly(arylene ether nitrile) porous lithium battery separator with MOF grown on the surface, i.e. a carboxylate poly(arylene ether nitrile) porous battery separator with MOF grown on the surface. Comparative Example 4:

[0036] Commercially available Celgard 2400 separator.

[0037] The lithium battery separators prepared in the above examples and comparative examples were tested for various properties, and the results are shown in Table 1.

[0038] Table 1 Performance of battery separator

[0039] As can be seen from Table 1, the gradient design high-safety polyarylene ether nitrile lithium battery separator provided by the application has excellent performance in terms of pore structure regulation, electrolyte adsorption performance and lithium ion transmission characteristics. Specifically, the separator in the embodiment has a porosity of 82.63% and a liquid absorption rate of 510%, which is significantly better than the samples of Comparative Examples 1 to 4 (porosity of 29.17% to 76.44% and liquid absorption rate of 90.24% to 470%), indicating that the separator prepared by the application has a more developed porous structure and stronger electrolyte adsorption and retention capacity, which can effectively improve the wettability and interface contact performance of the separator. Further, the lithium ion conductivity of the separator reaches 2.02×10 -3 S / cm, which is much higher than the maximum value 1.383×10 -3 S / cm of the samples of the comparative examples, significantly improving the migration efficiency of lithium ions in the membrane. In addition, the lithium ion transference number of the separator is 0.78, which is also higher than all the samples of the comparative examples (the highest is 0.75 and the lowest is only 0.24), indicating that the separator can effectively improve the transmission selectivity of lithium ions while ensuring the total ion transmission capacity, suppress the polarization phenomenon caused by anion migration, and improve the cycle stability of the battery.

[0040] Figure 2 The electrolyte contact angles of the gradient design high-safety polyarylene ether nitrile lithium battery separator prepared in the embodiment and Comparative Examples 1 to 4 are as follows: Figure 2 It can be seen that, compared with Comparative Examples 1 to 2 and 4, the gradient design high-safety polyarylene ether nitrile lithium battery separator prepared in the embodiment has excellent electrolyte affinity, and the electrolyte contact angle is close to 0°, and the electrolyte can quickly spread on the separator. The electrolyte contact angles of Comparative Example 3 and the embodiment are both close to 0°. According to the data in Table 1, the liquid absorption rate of Comparative Example 3 is significantly lower than that of the embodiment, indicating that only surface modification cannot achieve the synergistic effect of internal rapid wetting channels.

[0041] Figure 3 The heat resistance stability of the gradient design high-safety polyarylene ether nitrile lithium battery separator prepared in the embodiment and Comparative Examples 1 to 4 is as follows: Figure 3 It can be seen that, compared with Comparative Example 4, the gradient design high-safety polyarylene ether nitrile lithium battery separator prepared by the application has a shrinkage rate of less than 4% at 180°C, has good heat resistance, and can meet the safety standards of lithium ions.

[0042] Figure 4 The battery rate performance of the gradient design high-safety polyarylene ether nitrile lithium battery separator prepared in the embodiment and Comparative Examples 1 to 4 is as follows: Figure 4It can be seen that the battery based on the embodiment has discharge capacities of 152, 150, 135, 118 and 152 mAh / g at 0.5 C, 1 C, 2 C, 3 C and back to 0.5 C, respectively, showing good rate performance and recovery ability. The performance of Comparative Examples 1-3 decreases slightly, while the battery based on Comparative Example 4 has a serious capacity loss at high current, providing only 87 mAh / g of discharge capacity at 3 C.

[0043] Figure 5 The battery cycle performance of the gradient designed high safety polyarylether nitrile lithium battery separator prepared for the embodiment and Comparative Example 4; both batteries initially exhibit similar discharge capacities, about 146.8 mAh / g. After activation, the discharge capacity of the battery using the embodiment increases to 156 mAh / g, while the battery using Comparative Example 4 decreases to 140 mAh / g, and the capacity rapidly decays after about 200 cycles, reflecting its poor cycle stability. Compared with Comparative Example 4, the embodiment exhibits significantly better capacity retention ability, maintaining 139.4 mAh / g after 504 cycles, with a capacity retention rate of 94.95%. The cycle curve remains smooth with minimal fluctuations. This indicates that the embodiment effectively suppresses the growth of lithium dendrites and stabilizes the solid electrolyte interface (SEI) film, thereby improving the long-term cycle performance and interface chemical stability of the battery and achieving high safety.

[0044] From the above description of the disclosed embodiments, Figure 5 It can be seen that, compared with Comparative Example 4, the battery specific capacity of the high heat-resistant polyether ketone nitrile / polyvinylidene fluoride lithium battery separator film prepared in the embodiment of the application has a relatively high specific capacity, reaching about 160 mAh g -1 The initial discharge specific capacity at a current density of 0.5 C is 169.1 mAh g -1 After 45 cycles, the capacity retention rate of the battery is 86.64%, and the battery discharge specific capacity is 146.5 mAh g -1 The high-temperature-resistant polyether ketone nitrile / polyvinylidene fluoride film of the application as a lithium ion battery separator has significantly better battery performance than Celgard 2400 separator film.

[0045] The above description of the disclosed embodiments enables those skilled in the art to implement or use the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-safety polyarylene ether nitrile lithium battery separator with a gradient design, comprising the following steps: Step 1, synthesis of carboxyl type polyarylene ether nitrile: 1.1 Add 4,4'-diphenol, 3,5-dihydroxybenzoic acid and 2,6-difluorobenzonitrile as reactants, and potassium carbonate as catalyst into a three-necked flask to obtain a mixture powder; inject toluene into a water separator; 1.2 Add a mixed solvent of N-methylpyrrolidone and toluene into the mixture powder obtained in step 1.1, stir and mix uniformly to obtain a mixed solution A; 1.3 Heat the mixed solution A obtained in step 1.2 to reflux, release toluene in the water separator, then perform gradient temperature rising, pour the obtained reaction solution into deionized water, and stir to obtain a strip-shaped solid; 1.4 After the strip-shaped solid obtained in step 1.3 is soaked in hydrochloric acid solution for 24 h, crush, and then washed with deionized water until neutral, the obtained powder is dried in an oven to obtain a carboxylic acid type polyarylether nitrile powder; Step 2, preparation of a carboxylic acid type polyarylether nitrile hot solution for internal growth of MOF: Add N-methylpyrrolidone and the carboxylic acid type polyarylether nitrile powder obtained in step 1 into a three-necked flask, heat and stir at 120-130 ℃ for 2-5 h to obtain a solution B; then add 10-15 wt% of cobalt nitrate hexahydrate, fully react for 20-30 min, and then add 3.7-15 wt% of 2-methylimidazole, continue to heat and stir for 2-3 h to obtain a MOF / carboxylic acid type polyarylether nitrile hot solution; Step 3, preparation of a carboxylic acid type polyarylether nitrile porous lithium battery separator for internal growth of MOF by using a non-solvent induced phase separation method: 3.1 Pour the carboxylic acid type polyarylether nitrile hot solution for internal growth of MOF obtained in step 2 on a clean and flat glass plate, and use a four-side coater to cast a wet film; 3.2 Soak the glass plate with the wet film obtained in step 3.1 into a coagulation bath to separate and form a porous separator, and then soak the separator in deionized water; 3.3 Dry the separator obtained after the treatment in step 3.2 at room temperature to obtain the carboxylic acid type polyarylether nitrile porous lithium battery separator for internal growth of MOF; Step 4, preparation of a gradient designed high-safety polyarylether nitrile lithium battery separator: Soak the carboxylic acid type polyarylether nitrile porous lithium battery separator for internal growth of MOF obtained in step 3 into a water / methanol solution containing cobalt nitrate hexahydrate, and then add a water / methanol solution containing 2-methylimidazole to obtain a carboxylic acid type polyarylether nitrile porous lithium battery separator for growth of MOF on the surface and inside, i.e. the gradient designed high-safety polyarylether nitrile lithium battery separator.

2. The method for preparing a gradient-designed high-safety polyarylene ether nitrile lithium battery separator according to claim 1, characterized in that, The molar ratio of 3,5-dihydroxybenzoic acid, 4,4'-diphenol, 2,6-difluorobenzonitrile and potassium carbonate is 1:9:10:

15.

3. The method for preparing a gradient-designed high-safety polyarylene ether nitrile lithium battery separator according to claim 1, characterized in that, In the mixed solvent, the volume ratio of N-methylpyrrolidone and toluene is 3:1; the molar ratio of toluene injected into the water separator in step 1.1 and toluene added into the mixture powder in step 1.2 is 1:(1.35-1.8).

4. The method of making a gradient designed high safety polyarylene ether nitrile lithium battery separator of claim 1, wherein, In step 1.3, the gradient temperature rising operation is as follows: The mixture A obtained in step 1.2 was heated to reflux at 140 °C for 2-3 h, releasing toluene in the water trap, then the temperature was increased to 150-159 °C and kept for 0.5-1 h, increased to 160-169 °C and kept for 0.5-1 h, increased to 170-179 °C and kept for 0.5-1 h, increased to 180-190 °C and kept for 0.5-1 h.

5. The method of making a gradient designed high safety polyarylene ether nitrile lithium battery separator of claim 1, wherein, In step 2, the solid-liquid ratio of carboxylic acid type poly (arylene ether nitrile) powder and N-methyl pyrrolidone was 1 g: (10-20) mL.

6. The method of making a gradient designed high safety polyarylene ether nitrile lithium battery separator of claim 1, wherein, In step 3.1, the coagulation bath was a mixture of anhydrous ethanol and deionized water at a volume ratio of 1:

1.

7. The method of making a gradient designed high safety polyarylene ether nitrile lithium battery separator of claim 1, wherein, In step 4, the amount ratio of the water / methanol solution containing cobalt nitrate hexahydrate was 85:15, and the amount ratio of the water / methanol solution containing 2-methyl imidazole was 85:

15.

8. The method for preparing a gradient-designed high-safety polyarylene ether nitrile lithium battery separator according to claim 1 or 7, characterized in that, In step 4, the soaking time in the water / methanol solution containing cobalt nitrate hexahydrate was 0.5-1 h, and the soaking time after adding the water / methanol solution containing 2-methyl imidazole was 6-24 h.

9. A poly (arylene ether nitrile) lithium battery separator prepared by the method of any one of claims 1-8.

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