Preparation method and application of modified diaphragm based on photopolymerization phenyl ester liquid crystal

Abstract

The invention belongs to the technical field of battery materials, and particularly discloses a preparation method of a modified diaphragm based on photopolymerization phenyl ester liquid crystal and application of the modified diaphragm in a lithium-sulfur battery, photopolymerization liquid crystal RM257, a conductive agent, a photoinitiator and a solvent are mixed to obtain coating slurry, and a diaphragm substrate is coated with the coating slurry to obtain a coating diaphragm; and carrying out ultraviolet irradiation polymerization on the coating diaphragm, and drying to obtain the phenyl ester liquid crystal modified diaphragm based on photopolymerization. The photo-polymerization phenyl ester liquid crystal is adopted as a lithium-sulfur battery diaphragm modified material, and the order of the liquid crystal is lower than that of a completely regular crystal and higher than that of an isotropic disordered liquid, so that the surface appearance of a common diaphragm can be improved, an ion channel required by a lithium-sulfur battery system can be provided, and the service life of the lithium-sulfur battery is prolonged. The shuttle effect of polysulfide and the growth of lithium dendrites can be inhibited; due to the good cohesiveness of the photopolymerization phenyl ester liquid crystal, additional addition of a binder can be avoided, a battery material system is optimized, and the performance of the lithium-sulfur battery is 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 modified by photopolymerized phenyl ester liquid crystal and its application in lithium-sulfur batteries. Background Art

[0002] In today's society, with the ever-increasing demand for energy and the increasing emphasis on environmental protection, the search for efficient and environmentally friendly energy storage devices has become a key research focus for researchers worldwide. Electrochemical energy storage, particularly lithium-sulfur batteries, is considered the most promising next-generation high-energy-density energy storage system due to its high theoretical energy density, abundant sulfur resources, and low cost. However, lithium-sulfur batteries still face a series of technical challenges in their commercial application, especially the short battery life caused by the poor cycling stability of the sulfur cathode and dissolved polysulfides, which has become an unresolved issue.

[0003] To overcome this bottleneck, researchers have proposed various strategies, among which modified separators have proven to be an effective approach. Separators are also a crucial component in lithium-sulfur batteries because they are insulating and porous, allowing for rapid ion transport. The shuttling of polysulfides results in a decrease in the utilization of active materials. Therefore, through the design and modification of multiple separators, the shuttling of polysulfides can be effectively inhibited. To achieve this design, carbon paper sheets with an intermediate functional layer were used as lithium-sulfur battery separators, effectively inhibiting the shuttling of polysulfides and successfully improving the performance of lithium-sulfur batteries. Subsequently, various substances that can chemically bond with polysulfides or undergo mutual adsorption were used to modify the separators. However, due to the inherent structural characteristics of lithium-ion batteries, most new modified materials are still concentrated on traditional inorganic materials. The preparation of most of these inorganic modified separators is complex, requires a large number of materials, is difficult to implement, and is difficult to promote and apply. Therefore, it is necessary to develop simpler, more effective, and scalable preparation methods. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a method for preparing a modified separator based on photopolymerized phenyl ester liquid crystals. This method utilizes acrylate groups, which possess the unique orderliness of the liquid crystal molecular structure, high adhesion, and photopolymerization efficiency, to prepare the modified separator. This molecular order improves the surface morphology of conventional separators, forms efficient ion transport channels within the battery, and inhibits the shuttling effect of polysulfides and the growth of lithium dendrites, thereby improving the interfacial properties between the electrolyte and the electrodes and enhancing the battery's stability and cycle life. Furthermore, the self-assembly properties of the liquid crystal material and its ability to regulate ion transport pathways offer new insights into the performance optimization of lithium-sulfur batteries.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal comprises the following steps:

[0007] Step (1): mixing and grinding photopolymerized liquid crystal 4-(3-acryloyloxypropoxy)benzoic acid-2-methyl-1,4-phenyl ester (RM257) and a conductive agent in a certain proportion, then adding a photoinitiator and a solvent to obtain a uniformly dispersed coating slurry, and uniformly coating the coating slurry on the diaphragm substrate to obtain a coated diaphragm;

[0008] Step (2): subjecting the above-mentioned coating membrane to ultraviolet light polymerization and drying, and finally obtaining a modified membrane based on photopolymerized phenyl ester liquid crystal material.

[0009] A further improvement of the present invention is:

[0010] The mass ratio of the RM257, the conductive agent and the photoinitiator is 1:0.1-0.5:0.01-0.05.

[0011] Preferably, the mass ratio of the RM257, the conductive agent and the photoinitiator is 1:0.25:0.03.

[0012] Furthermore, the diaphragm substrate is a common polypropylene diaphragm substrate.

[0013] Furthermore, the photoinitiator includes but is not limited to 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone.

[0014] Furthermore, the conductive agent includes but is not limited to conductive carbon black.

[0015] Furthermore, the solvent includes but is not limited to N-methylpyrrolidone.

[0016] Furthermore, during the ultraviolet light polymerization, the wavelength of the ultraviolet light includes but is not limited to 365 nm or 254 nm, and the ultraviolet irradiation time is 1 min to 2 h.

[0017] Furthermore, the drying temperature is 35° C. to 60° C., and the drying time is 2 h to 12 h.

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

[0019] The application of the modified diaphragm based on photopolymerized phenyl ester liquid crystal material 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] The present invention uses a photopolymerizable phenyl ester acrylate liquid crystal as a diaphragm modification material, and improves the performance of lithium-sulfur batteries by combining the advantages of liquid crystal and photopolymerization. The photopolymerization process is a simple, clean, efficient, and convenient post-processing technology for preparing polymer materials. Compared with other polymerization methods, photopolymerization technology has the advantages of mild reaction conditions and high controllability. It can usually be carried out at room temperature without the need for high temperature or high pressure conditions, so the requirements for reaction equipment are relatively low. In addition, mild reaction conditions are conducive to maintaining the molecular structure and performance integrity of the polymer and preventing degradation. Photopolymerization technology can achieve precise control of the polymerization process by regulating parameters such as photoinitiator concentration, light source intensity, and exposure time, which makes photopolymerization technology highly controllable and repeatable. In addition, the present invention uses acrylate liquid crystals with high adhesion and photopolymerization efficiency, which can avoid the addition of additional adhesives.

[0022] The photopolymerized phenyl ester liquid crystal used in the coating membrane of the present invention is commercially available, cost-effective, and the coating modification process is simple to operate. The selected liquid crystal material for the lithium-sulfur battery coating membrane has unique molecular structural order and self-assembly properties, which can improve the surface morphology of ordinary membranes, form efficient ion transport channels within the battery, and inhibit the shuttling effect of polysulfides and the growth of lithium dendrites, thereby improving the interface performance between the electrolyte and the electrode, and enhancing the battery's stability and cycle life. The selected liquid crystal material has an acrylate with high photopolymerization efficiency and exhibits high adhesion, which can also avoid the addition of additional binders, optimize the performance parameter system of lithium-sulfur batteries, and improve lithium-sulfur battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of a lithium-sulfur battery using a liquid crystal modified diaphragm;

[0024] Figure 2 This is a graph showing the cycling performance of a lithium-sulfur battery assembled with a conventional separator and the liquid crystal modified separator of the present invention at a rate of 0.2C;

[0025] Figure 3 This is a comparison of the effects of a common diaphragm and the liquid crystal modified diaphragm of the present invention on inhibiting polysulfide shuttle;

[0026] Figure 4 This is a scanning electron microscope comparison of the surface morphology of a common diaphragm and the liquid crystal modified diaphragm of the present invention. DETAILED DESCRIPTION

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

[0028] The photopolymerizable liquid crystal 4-(3-acryloyloxypropoxy)benzoic acid-2-methyl-1,4-phenyl ester (RM257) used in the present invention has a CAS number of 174063-87-7 and can be purchased commercially.

[0029] Example 1

[0030] 80 mg of photopolymerized liquid crystal 4-(3-acryloyloxypropoxy)benzoic acid-2-methyl-1,4-phenyl ester (RM257) and 20 mg of conductive carbon black (Super-P) were mixed and ground evenly, and then 2.4 mg of initiator 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl) butanone and 2 mL of solvent N-methylpyrrolidone were added to obtain a uniformly dispersed coating slurry. The above coating slurry was evenly coated on an ordinary polypropylene diaphragm substrate with a coating thickness of 100 μm. The above coating diaphragm was polymerized under ultraviolet light with a wavelength of 365 nm for 30 min, and then vacuum dried at 40°C for 2 hours to obtain a coating diaphragm based on liquid crystal modification.

[0031] The obtained liquid crystal modified membrane is applied to lithium sulfur battery, and the battery is assembled in the order of positive electrode shell, C / S pole piece, electrolyte, liquid crystal membrane, lithium sheet, nickel foam and negative electrode shell (structural diagram as shown in FIG. Figure 1 The battery is then sealed and sealed with a battery sealer, and then tested for performance on a BlueDian testing system. The entire lithium-sulfur battery assembly process is carried out in an argon-filled glove box.

[0032] Comparative Example 1

[0033] 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.

[0034] 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 rate of 0.2C ( Figure 2 ), the effect of inhibiting polysulfide shuttle ( Figure 3 ) and surface morphology analysis ( Figure 4 ).Depend on Figure 2 By comparison, it can be seen that when using ordinary diaphragms, the specific capacity of lithium-sulfur batteries drops from 1027mAh / g to 371mAh / g after 100 cycles; while when using RM257 liquid crystal modified diaphragms, the specific capacity of lithium-sulfur batteries drops from 1380mAh / g to 693mAh / g after 100 cycles, and the coulombic efficiency always remains at 100%. The remaining specific capacity is almost twice that of ordinary diaphragms, and the performance has been significantly improved. The data comparison is summarized in Table 1.

[0035] Table 1

[0036]

[0037]

[0038] Depend on Figure 3 By comparison, it can be seen that under the same time, the liquid crystal modified membrane has a better inhibitory effect on polysulfide shuttle than the ordinary membrane, that is, Figure 3 (fj) The color of the solution on the right is better than that of the solution under the corresponding time. Figure 3 (ae) The color of the solution on the right is lighter. Figure 4 By comparison, ordinary diaphragms ( Figure 4 a) The gap is large, and the effect of inhibiting polysulfide is poor, while the liquid crystal modified membrane ( Figure 4 b) It can effectively block gaps and inhibit the shuttling of polysulfides without hindering the passage of smaller ions. On the contrary, the ordered structure of the liquid crystal further promotes the ion transport performance.

[0039] 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 modified diaphragm based on photopolymerized phenyl ester liquid crystal, characterized in that: The following steps are involved: Step (1): mixing and grinding photopolymerized liquid crystal 4-(3-acryloyloxypropoxy)benzoic acid-2-methyl-1,4-phenyl ester and a conductive agent in a certain proportion, then adding a photoinitiator and a solvent to obtain a uniformly dispersed coating slurry, and uniformly coating the coating slurry on the diaphragm substrate to obtain a coated diaphragm; Step (2): subjecting the above-mentioned coating membrane to ultraviolet light polymerization and drying, and finally obtaining a modified membrane based on photopolymerized phenyl ester liquid crystal material.

2. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1, characterized in that: The mass ratio of the RM257, the conductive agent and the photoinitiator is 1:0.1~0.5:0.01~0.

05.

3. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 2, characterized in that. The mass ratio of the RM257, the conductive agent and the photoinitiator is 1:0.25:0.

03.

4. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1 or 2, characterized in that: The photoinitiator includes but is not limited to 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone.

5. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1 or 2, characterized in that: The conductive agent includes but is not limited to conductive carbon black.

6. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1 or 2, characterized in that: The solvent includes but is not limited to N-methylpyrrolidone.

7. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1, characterized in that: During the ultraviolet light polymerization, the wavelength of the ultraviolet light includes but is not limited to 365 nm or 254 nm, and the ultraviolet irradiation time is 1 min to 2 h.

8. The method for preparing a modified diaphragm based on photopolymerized phenyl ester liquid crystal according to claim 1, characterized in that: The drying temperature is 35° C. to 60° C., and the drying time is 2 h to 12 h.

9. Use of a modified diaphragm based on a photopolymerized phenyl ester liquid crystal material obtained by the method of claim 1 in the preparation of a lithium-sulfur battery.

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