Preparation method and application of nematic liquid crystal modified diaphragm based on photopolymerization fluorenone-phenyl ester-acrylate

Abstract

The invention belongs to the technical field of battery materials, and particularly discloses a preparation method and application of a nematic phase liquid crystal modified diaphragm based on photopolymerization fluorenone-phenyl ester-acrylate. The preparation method comprises the following steps: mixing 2, 7-diylbis (4-((6-(acryloyloxy) hexyl) oxy) benzoate), a conductive agent and an initiator in a solvent to obtain uniformly dispersed coating slurry, and coating a diaphragm substrate with the coating slurry to obtain a coating diaphragm; and carrying out ultraviolet light illumination polymerization and vacuum drying on the coating diaphragm to obtain the modified diaphragm based on the nematic phase liquid crystal. According to the invention, an orderly arranged nematic phase liquid crystal structure is introduced into the modified diaphragm, the improved coating diaphragm has very strong chemical adsorption on polysulfide formed in the charging and discharging process, the shuttle effect and lithium dendrite growth of the polysulfide in the charging and discharging process of the lithium-sulfur battery can be inhibited, meanwhile, the binding power between lithium electrode materials can be enhanced, and the service life of the lithium-sulfur battery is prolonged. And the cycle performance and the capacity performance of the lithium-sulfur battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to the preparation of lithium-sulfur battery separators, and in particular to a preparation method of a separator based on photopolymerized fluorenone-phenyl ester-acrylate nematic phase liquid crystal modified and its application in lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries, with their exceptional high energy density and low cost, are considered a highly promising next-generation technology in energy storage applications such as new energy vehicles. Global environmental protection policies, actively supporting new energy technologies, have also created a highly favorable external environment for the development of lithium-sulfur batteries. Lithium-sulfur batteries use sulfur, a resource abundant and affordable on Earth, as their positive electrode material. Their theoretical energy density far exceeds that of traditional lithium-ion batteries, making them significantly more cost-competitive. However, despite their numerous advantages, lithium-sulfur batteries still face a series of challenges in terms of technological maturity, number of recyclable cycles, and safety, requiring further research and improvement.

[0003] To address these issues, researchers are actively researching new electrolytes, separators, cathode materials, and safety devices to improve the electrochemical performance, cycle life, and safety of lithium-sulfur batteries. The design of modified materials for lithium-sulfur batteries aims not only to enhance overall electrochemical performance but also to address several major challenges facing the sulfur cathode: poor conductivity, the dissolution and shuttle effect of polysulfides in the electrolyte, and significant volume changes during charge and discharge. To this end, ideal modified materials must possess excellent conductivity, be able to effectively adsorb polysulfides to mitigate the shuttle effect, and maintain structural stability during charge and discharge cycles.

[0004] As a key component in batteries, the separator plays a vital role in preventing internal short circuits and providing a transport pathway for ions. Developing functional separators to inhibit the shuttling of polysulfides has become a research hotspot. Currently, separators are modified with metals, carbons, and polymers, each exhibiting varying performance characteristics. While some progress has been made in research on functional separators for lithium-sulfur batteries, much more work is needed to rapidly bring lithium-sulfur batteries to the commercial market. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a method for preparing a modified diaphragm based on a photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal. The present invention introduces an ordered nematic liquid crystal structure into the modified diaphragm. The improved coated diaphragm has strong chemical adsorption for polysulfides formed during the charge and discharge process, and can inhibit the "shuttle effect" of polysulfides and the growth of lithium dendrites during the charge and discharge process of lithium-sulfur batteries. At the same time, it can enhance the bonding force between lithium electrode materials and improve the cycle performance and capacity performance of lithium-sulfur batteries.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a nematic liquid crystal modified membrane based on photopolymerized fluorenone-phenyl ester-acrylate comprises the following steps:

[0008] Step (1): mixing and grinding nematic liquid crystal 9-oxo-9H-fluorene-2,7-diylbis(4-((6-(acryloyloxy)hexyl)oxy)benzoate) and a conductive agent in a certain proportion, then adding an initiator and a solvent to obtain a uniformly dispersed coating slurry, and uniformly coating the coating slurry on a diaphragm substrate to obtain a coated diaphragm;

[0009] Step (2): subjecting the above-mentioned coating membrane to ultraviolet light polymerization and vacuum drying to finally obtain a modified membrane based on the nematic liquid crystal of fluorenone-phenyl ester-acrylate.

[0010] A further improvement of the present invention is:

[0011] The mass ratio of the initiator, the conductive agent and the nematic liquid crystal is 0.1:0.5:3 to 0.2:1.5:5.

[0012] Furthermore, the initiator is one or a mixture of two or more of 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0013] Furthermore, the conductive agent is one or a mixture of two or more of conductive carbon black, acetylene black or Ketjen black.

[0014] Furthermore, the diaphragm matrix is ​​selected from aluminum oxide diaphragm, calcium oxide diaphragm or polypropylene diaphragm.

[0015] Furthermore, the coating thickness of the coated diaphragm is 100 μm to 500 μm.

[0016] Furthermore, the illumination time is 5 minutes to 24 hours.

[0017] Furthermore, the vacuum drying temperature is 20° C. to 45° C., and the time is 2 h to 24 h.

[0018] A further improvement of the present invention is:

[0019] The application of the photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal modified diaphragm prepared by the above method in the preparation of lithium-sulfur batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention utilizes an ordered nematic liquid crystal structure as a modified lithium-sulfur battery separator. Its order lies somewhere between that of a crystal and a disordered liquid, optimizing the separator surface and providing ion channels while inhibiting polysulfide shuttling and lithium dendrite growth. Furthermore, fluorenone enhances the positive electrode reaction rate and battery cycle stability, while the excellent gel properties of acrylate enhance battery performance, achieving environmental sustainability.

[0022] The preparation method of the modified diaphragm provided by the present invention is simple to operate, the photopolymerization reaction process is convenient and clean, and no impurities are introduced into the battery system. The selected ordered nematic liquid crystal material can improve the surface morphology of ordinary diaphragms, can provide an efficient transmission channel for ions, and improve the conductivity. At the same time, the coated liquid crystal layer has a strong blocking effect on polysulfides, can effectively inhibit the shuttle effect and the growth of lithium dendrites, improve the interface performance of the battery, and enhance the stability and cycle life of the battery. In addition, the introduction of ester bonds and polyoxygen structures such as fluorenone-acrylate can enhance the bonding force between lithium electrode materials, improve battery safety, and significantly improve the adhesion between the positive electrode material or diaphragm and the electrolyte. At the same time, the cross-linked liquid crystal polymer electrolyte membrane prepared by photopolymerization technology has excellent thermal stability and chemical stability, which can improve the safety and operational stability of the battery under harsh conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the H NMR spectrum of nematic liquid crystal 9-oxo-9H-fluorene-2,7-diylbis(4-((6-(acryloyloxy)hexyl)oxy)benzoate);

[0024] Figure 2 Schematic diagram of the structure of a lithium-sulfur battery using a liquid crystal modified diaphragm

[0025] Figure 3 The graphs are the cycle performance of lithium-sulfur batteries assembled with a common separator and a liquid crystal modified separator prepared by the present invention at a rate of 0.2C;

[0026] Figure 4 This is a scanning electron microscope image of the liquid crystal modified membrane prepared in the present invention. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to specific embodiments.

[0028] Example 1: Preparation of Nematic Liquid Crystal 9-Oxo-9H-fluorene-2,7-diylbis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)

[0029]

[0030] Prepare a 100 mL single-necked round-bottom flask, dissolve compound 4-(6-(acryloyloxy)hexyloxy)benzoic acid (1) (1.5 g, 5.4 mmol) and compound 2,7-dihydroxy-9-fluorenone (2) (0.50 g, 2.3 mmol) in 20 ml of DCM, and add 4-dimethylaminopyridine (5.7 mg, 0.04 mmol), dicyclohexylcarbodiimide (1.1 g, 5.6 mmol), and 2,6-di-tert-butyl-p-cresol (0.1 g, 0.5 mmol). Place in a dark environment and react at 25°C for 48 h. The reaction is completed by plate counting. Filter to remove the salt generated by the reaction, and extract the filtrate three times with water and dichloromethane. Then, remove the water in the organic matter with sodium sulfate. The organic matter is dried by rotary evaporator, and silica gel is added for purification by column chromatography. The elution solvent is petroleum ether and dichloromethane (PE:Ea=15:1-2:1).

[0031] Target compound (3): 1.50 g, light yellow solid, reaction yield 89%.

[0032] 1 H NMR(600MHz,Chloroform-d)δ8.14(d,J=8.8Hz,4H),7.56-7.50(m,4H),7.34(dd,J=8.0,2.2Hz,2H),7.00-6.94(m,4H),6.41(dd,J=17.3,1.5Hz,2H ),6.13(dd,J=17.3,10.4Hz,2H),5.83(dd,J=10.4,1.4Hz,2H),4.18(t,J= 6.7Hz,4H),4.06(t,J=6.4Hz,4H),1.76-1.70(m,4H),1.62-1.43(m,12H).

[0033] Example 2

[0034] 80 mg of photopolymerized liquid crystal 9-oxo-9H-fluorene-2,7-diylbis(4-((6-(acryloyloxy)hexyl)oxy)benzoate) was mixed and ground evenly with 20 mg of conductive carbon black (Super-P). 2.4 mg of initiator 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone and 2 mL of solvent N-methylpyrrolidone were then added to obtain a uniformly dispersed coating slurry. The coating slurry was evenly coated on a common polypropylene diaphragm substrate with a coating thickness of 100 μm. The coating diaphragm was polymerized under ultraviolet light with a wavelength of 365 nm for 30 minutes, and then vacuum dried at 40°C for 2 hours to obtain a coating diaphragm based on liquid crystal modification.

[0035] The prepared liquid crystal modified membrane is applied to lithium sulfur battery. Figure 2 The structure is assembled, with the liquid crystal coating of the modified separator located on the side of the battery closest to the positive electrode. After being pressed tightly with a battery sealer, the battery performance is tested on a Blue Electric test system. The entire lithium-sulfur battery assembly process is carried out in an argon-filled glove box.

[0036] Comparative Example 1

[0037] In this comparative example, an ordinary polypropylene separator was used instead of the liquid crystal modified separator prepared in Example 1 and was directly applied to a lithium-sulfur battery. The assembly process of the lithium-sulfur battery was the same as that in Example 1.

[0038] In order to compare the effects of ordinary diaphragms and liquid crystal modified diaphragms on the performance of lithium-sulfur batteries, the present invention compares the cycle performance of lithium-sulfur batteries at a 0.2C rate ( Figure 2 ).Depend on Figure 2 By comparison, it can be seen that when using ordinary diaphragms, the specific capacity of lithium-sulfur batteries drops from 819 mAh / g to 360 mAh / g after 100 cycles; while when using liquid crystal modified diaphragms, the specific capacity of lithium-sulfur batteries drops from 1135 mAh / g to 451 mAh / g after 100 cycles, and the coulombic efficiency always remains at 100%. The remaining specific capacity is almost 1.3 times that of ordinary diaphragms, and the performance has been effectively improved. The data comparison is summarized in Table 1.

[0039] Table 1

[0040] Specific capacity of the first cycle discharge (mAh / g) 100th cycle discharge capacity (mAh / g) Liquid crystal modified diaphragm 1135 451 Ordinary diaphragm 819 360

[0041] The significant improvement in lithium-sulfur battery performance is primarily due to the efficient ion transport network constructed by the ordered liquid crystal structure. This three-dimensional channel structure not only effectively enhances the charge carrier migration dynamics, significantly optimizing the electrode reaction kinetics, but also achieves comprehensive performance improvements through the following synergistic mechanisms: First, the directionally aligned liquid crystal molecules form a selective permeability barrier, effectively inhibiting the polysulfide shuttle effect; second, the structure stabilizes the SEI film through interfacial chemical bonding, resulting in improved initial specific capacity and specific capacity after 100 cycles; more importantly, the mechanical stability of the liquid crystal phase effectively buffers electrode volume changes. Combined with the advantages of its intrinsic anisotropic conductivity, this ultimately slows battery degradation and extends the battery life while maintaining 100% Coulombic efficiency.

[0042] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a nematic liquid crystal modified membrane based on photopolymerized fluorenone-phenyl ester-acrylate, characterized in that: The following steps are involved: Step (1): mixing and grinding nematic liquid crystal 9-oxo-9H-fluorene-2,7-diylbis(4-((6-(acryloyloxy)hexyl)oxy)benzoate) and a conductive agent in a certain proportion, and then adding an initiator and a solvent to obtain a uniformly dispersed coating slurry, and uniformly coating the coating slurry on a diaphragm substrate to obtain a coated diaphragm; Step (2): subjecting the above-mentioned coating membrane to ultraviolet light photopolymerization and vacuum drying to finally obtain a modified membrane based on photopolymerized fluorenone-phenyl ester-acrylate nematic phase liquid crystal material.

2. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1, characterized in that: The mass ratio of the initiator, the conductive agent and the nematic liquid crystal is 0.1:0.5:3 to 0.2:1.5:

5.

3. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1 or 2, characterized in that: The initiator is one or a mixture of two or more of 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-hydroxy-2-methyl-1-phenylacetone, 1-hydroxycyclohexylphenyl ketone or 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

4. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1 or 2, characterized in that: The conductive agent is one or a mixture of two or more of conductive carbon black, acetylene black or Ketjen black.

5. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1, characterized in that: The membrane matrix is ​​selected from aluminum oxide membrane, calcium oxide membrane or polypropylene membrane.

6. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1, characterized in that: The coating thickness of the coating membrane is 100 μm to 500 μm.

7. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1, characterized in that: The illumination time is 5 minutes to 24 hours.

8. The method for preparing a modified diaphragm based on photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal according to claim 1, characterized in that: The vacuum drying temperature is 20° C. to 45° C., and the time is 2 h to 24 h.

9. Use of the photopolymerized fluorenone-phenyl ester-acrylate nematic liquid crystal modified diaphragm prepared by the method of claim 1 in the preparation of lithium-sulfur batteries.

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