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

Abstract

The invention belongs to the technical field of battery materials, and particularly discloses a preparation method and application of a modified diaphragm based on photopolymerization discotic liquid crystal, and the preparation method comprises the following steps: uniformly mixing and grinding photopolymerization discotic liquid crystal and a conductive agent, adding a photoinitiator and a solvent to obtain uniformly dispersed coating slurry, and drying to obtain the modified diaphragm based on the photopolymerization discotic liquid crystal. Coating a diaphragm substrate with the coating slurry to obtain a coating diaphragm; and carrying out ultraviolet light illumination polymerization on the coating diaphragm, and drying to finally obtain the photopolymerization-based discotic liquid crystal modified diaphragm. According to the invention, the diaphragm is modified by adopting the photopolymerization discotic liquid crystal, the improved coating diaphragm is coated with the discotic liquid crystal, so that the lithium-sulfur battery has good conductivity, migration between positive and negative electrodes of polysulfide ions can be effectively prevented, and a good channel is provided for lithium-sulfur reaction among the discotic layers of the liquid crystal; and the reaction activity 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 discotic liquid crystals and its application in lithium-sulfur batteries. Background Art

[0002] With the increasing demand for renewable energy, new energy battery technology is gaining attention. Lithium-sulfur batteries have attracted widespread attention due to their high energy density, wide temperature range, and low cost. Currently, Japan is using them for nuclear submarine propulsion, and British companies are also promoting them in vehicles. The enormous potential of lithium-sulfur batteries in electric vehicles and their environmentally friendly nature make them a mainstream choice for the future. Compared to lithium-ion batteries, lithium-sulfur batteries are more environmentally friendly and contain no heavy metals. This characteristic has made them highly sought after amidst growing global environmental awareness. Despite their many advantages, lithium-sulfur batteries still require further research and improvement in terms of stability during charge and discharge and cycle life. Furthermore, sulfur undergoes significant volume expansion and contraction during charge and discharge, potentially causing battery damage. Furthermore, polysulfide ions can migrate between the positive and negative electrodes, resulting in loss of active material and wasted energy. Dissolved polysulfides can diffuse across the separator to the negative electrode, reacting with it and damaging the solid electrolyte interface membrane. These issues continue to hamper the continued development of lithium-sulfur batteries.

[0003] As a crucial component of lithium-sulfur batteries, the separator acts as a barrier between the positive and negative electrodes, separating them. On the one hand, it prevents direct contact between the positive and negative electrodes, which could cause a short circuit. On the other hand, it fully absorbs the electrolyte, allowing ion transport and ensuring the normal redox reaction in lithium-sulfur batteries. Therefore, lithium-sulfur batteries require separator materials to possess certain mechanical and electronic insulation properties, as well as good ionic conductivity and electrolyte wettability. Traditional polyolefin separators are simple to prepare and offer high strength, but their functionality is poor. On the one hand, their high porosity prevents the transport of polysulfides dissolved in the electrolyte. On the other hand, their poor hydrophilicity prevents close contact between the positive and negative electrode materials, leading to significant polarization. Such separators cannot operate continuously at high current densities, nor can they effectively conduct ions or prevent the diffusion of polysulfides. Therefore, they require optimization and modification. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention provides a method for preparing a modified separator using photopolymerized discotic liquid crystals. By modifying the separator using photopolymerized discotic liquid crystals, the improved coated separator can better encapsulate sulfur, preventing sulfur dissolution and loss during the battery's charge and discharge cycles, thereby improving the battery's cycle stability and cycle life. Furthermore, the improved separator can effectively prevent the migration of polysulfide ions between the positive and negative electrodes, thereby reducing active material loss and energy waste.

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

[0006] A method for preparing a modified diaphragm based on photopolymerized discotic liquid crystals comprises the following steps:

[0007] Step (1): mixing and grinding photopolymerized discotic liquid crystals 4a, 4b, 8a, 8b, 12a, 12b (hexahydrotriphenylene-2,3,6,7,10,11-hexadecylhexyl (4-(6-(acryloyloxy)hexyl)oxy)benzoate)) and a conductive agent in a certain proportion, and then adding a photoinitiator and a solvent to obtain a uniformly dispersed coating slurry. The coating slurry is evenly coated on a 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 discotic liquid crystal.

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

[0010] The mass ratio of the conductive agent, the photoinitiator and the polymerized discotic liquid crystal is 1:0.1-0.2:2-6.

[0011] Preferably, the mass ratio of the conductive agent, the photoinitiator and the polymerized discotic liquid crystal is 1:0.12:4.

[0012] Furthermore, the conductive agent is one or a mixture of two or more of conductive carbon black, acetylene black, Ketjen black, carbon fiber or graphite conductive agent.

[0013] Furthermore, the photoinitiator 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, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

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

[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 discotic 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] The present invention uses photopolymerized discotic liquid crystals 4a, 4b, 8a, 8b, 12a, 12b - hexahydrotriphenylene-2,3,6,7,10,11-hexadecylhexyl (4-(6-(acryloyloxy)hexyl)oxy)benzoate) to modify the diaphragm. The improved coated diaphragm, coated with the discotic liquid crystals, enables the lithium-sulfur battery to have good electrical conductivity and effectively prevents the migration of polysulfide ions between the positive and negative electrodes. In addition, the liquid crystal disc layers provide good channels for the lithium-sulfur reaction, thereby increasing the reaction activity of the lithium-sulfur battery.

[0022] The discotic liquid crystals employed in the present invention effectively coat sulfur, thereby preventing sulfur dissolution and loss during the battery's charge-discharge cycle, thereby improving the battery's cycle stability and cycle life. The continuous disc-like layered structure provides efficient ion transport channels, resulting in excellent conductivity and effective charge transfer, providing a better electron transport pathway for lithium-sulfur batteries. Furthermore, the discotic liquid crystals attached to the coated separator effectively prevent the migration of polysulfide ions between the positive and negative electrodes, thereby reducing active material loss and energy waste, and effectively protecting the solid electrolyte interface membrane at the negative electrode. Furthermore, the discotic liquid crystals exhibit excellent electrochemical properties in lithium-sulfur batteries, resisting polarization and expansion problems that can occur in lithium-sulfur batteries, thereby slowing battery degradation and extending their service life.

[0023] The preparation method of the photopolymerized discotic liquid crystal modified lithium-sulfur battery separator provided by the present invention is simple to operate and can be easily popularized. The photopolymerization method is simple, clean, and does not introduce any by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of a lithium-sulfur battery with a photopolymerized discotic liquid crystal modified diaphragm according to the present invention;

[0025] Figure 2 The graphs show the cycling performance of lithium-sulfur batteries assembled with a common separator and a separator modified with a photopolymerized discotic liquid crystal prepared by the present invention at a rate of 0.2C.

[0026] Figure 3 This is a scanning electron microscope image of the photopolymerized discotic liquid crystal modified diaphragm prepared in the present invention. DETAILED DESCRIPTION

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

[0028] The photopolymerized discotic liquid crystal 4a, 4b, 8a, 8b, 12a, 12b used in the present invention - hexahydrotriphenylene-2,3,6,7,10,11-hexahydrohexyl (4-(6-(acryloyloxy)hexyl)oxy)benzoate) has the following structural formula:

[0029]

[0030] The preparation process thereof refers to the record of the applicant's prior application for Chinese patent No. 2025106115609.

[0031] Example 1

[0032] 80 mg of photopolymerized liquid crystal 4a, 4b, 8a, 8b, 12a, 12b - hexahydrotriphenyl-2,3,6,7,10,11-hexadecylhexyl (4-(6-(acryloyloxy)hexyl)oxy)benzoate) was mixed and ground evenly with 20 mg of acetylene black, 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 modified coating diaphragm based on polymerized discotic liquid crystal.

[0033] The obtained liquid crystal modified coating membrane is applied to the lithium sulfur battery. The battery is assembled in the order of negative electrode cover, lithium layer, liquid crystal coating membrane, lithium sheet, sulfur layer and positive electrode cover, wherein the liquid crystal coating of the membrane is located on the side close to the negative electrode in the battery (the structural diagram is 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.

[0034] Comparative Example 1

[0035] 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.

[0036] In order to study the effects of ordinary diaphragms and liquid crystal diaphragms on the charge and discharge performance of lithium-sulfur batteries, the present invention compares the charge and discharge specific capacity ( Figure 2 ).Depend on Figure 2It can be seen that when using ordinary separators, the specific capacity of lithium-sulfur batteries drops from 896 mAh / g to 332 mAh / g after 100 cycles; while when using liquid crystal modified separators, the specific capacity of lithium-sulfur batteries drops from 1189 mAh / g to 433 mAh / g after 100 cycles, and the coulombic efficiency always remains at 100%. The remaining specific capacity is 1.3 times that of ordinary separators, and the performance has been effectively improved. The data comparison is summarized in Table 1.

[0037] Table 1

[0038]

[0039] The improved performance of the modified separator of the present invention is primarily due to the continuous discotic layered liquid crystal structure providing efficient ion transport channels, thereby enhancing charge and discharge performance and efficiency. Furthermore, the introduction of the liquid crystal separator layer effectively blocks the shuttling effect of polysulfide ions between the positive and negative electrodes, reducing the loss of active materials and energy waste, effectively protecting the electrolyte interface membrane at the negative electrode, and improving the battery's cycle stability and lifespan. Furthermore, the discotic layered liquid crystal exhibits excellent electrochemical properties in lithium-sulfur batteries, resisting polarization and expansion problems that can occur in lithium-sulfur batteries, thereby slowing battery degradation and extending its service life.

[0040] 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 discotic liquid crystal, characterized in that: The following steps are involved: Step (1): mixing and grinding the photopolymerized discotic liquid crystal 4a, 4b, 8a, 8b, 12a, 12b--hexahydrotriphenylene-2,3,6,7,10,11-hexaylhexyl (4-(6-(acryloyloxy)hexyl)oxy)benzoate) and the conductive agent in a certain proportion, and 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 discotic liquid crystal.

2. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to claim 1, characterized in that: The mass ratio of the conductive agent, the photoinitiator and the polymerized discotic liquid crystal is 1:0.1-0.2:2-6.

3. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to claim 2, characterized in that: The mass ratio of the conductive agent, the photoinitiator and the polymerized discotic liquid crystal is 1:0.12:

4.

4. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to any one of claims 1 to 3, characterized in that: The conductive agent is one or a mixture of two or more of conductive carbon black, acetylene black, Ketjen black, carbon fiber or graphite conductive agent.

5. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to any one of claims 1 to 3, characterized in that: The photoinitiator 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, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

6. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to claim 1, characterized in that: The membrane matrix is ​​selected from aluminum oxide membrane, calcium oxide membrane or polypropylene membrane.

7. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to claim 1, characterized in that: The coating thickness of the coating membrane is 100 μm to 500 μm.

8. The method for preparing a modified diaphragm based on photopolymerized discotic liquid crystal according to claim 1, wherein: The illumination time is 5 minutes to 24 hours.

9. The method for preparing a modified diaphragm based on photopolymerized discotic 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.

10. Use of the modified diaphragm based on photopolymerized discotic liquid crystal prepared by the method according to claim 1 in the preparation of lithium-sulfur batteries.

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