Phosphated ionogel composite separator for lithium-sulfur batteries

Abstract

The application discloses a phosphatized ion gel composite diaphragm for a lithium-sulfur battery, which has a sandwich structure, a polyolefin diaphragm as a middle layer and a phosphatized ion gel as an outer layer, and the thickness of the composite diaphragm is not more than 30 microns; the phosphatized ion gel is loaded on the polyolefin diaphragm, and covalent grafting of phosphoric acid groups is realized based on ultraviolet light curing. The composite diaphragm prepared by the application has good ion conductivity and electrolyte wettability, and the introduction of strong negative phosphoric acid groups effectively inhibits the shuttle effect of intermediate product polysulfide anions, and significantly improves the cycle life of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention pertains to functional materials for lithium-sulfur batteries, specifically relating to a phosphorylated ion gel composite separator for lithium-sulfur batteries. Background Technology

[0002] Among numerous novel energy storage devices, lithium-sulfur batteries possess immense development prospects and potential due to their extremely high theoretical specific capacity and energy density, as well as the abundant and inexpensive nature of sulfur. However, the development of lithium-sulfur batteries has encountered many challenges, primarily including the low conductivity of sulfur, significant electrode volume changes during charge and discharge, the shuttle effect of soluble polysulfides, slow reaction kinetics, and lithium dendrites. Among these, the shuttle effect significantly impacts the performance of lithium-sulfur batteries, leading to a substantial decrease in cycle performance. In the battery, the separator, as the intermediate component connecting the positive and negative electrodes, is undoubtedly a crucial structure for preventing polysulfide shuttle. Currently, commercially available lithium-sulfur battery separators are mainly based on porous polypropylene and polyethylene materials. These separators have a weak ability to suppress the polysulfide shuttle effect and poor affinity with the electrolyte, resulting in unsatisfactory battery performance.

[0003] Therefore, developing novel separators with superior performance, or modifying and functionalizing existing separators using appropriate methods, is crucial for suppressing the shuttle effect and improving the electrochemical performance of lithium-sulfur batteries. Ion gels possess advantages such as high ionic conductivity, good interfacial contact, and excellent thermal and chemical stability. Furthermore, their diverse polymer structures provide excellent structural tunability, making them ideal composite separator materials. For lithium-sulfur battery systems, ion gel composite separators also possess many excellent properties: good flexibility, optimizing interfacial contact, adapting to the volume expansion of the cathode, and preventing lithium dendrite puncture; and excellent liquid absorption, restricting the free movement of the electrolyte to suppress polysulfide shuttle. In addition, polysulfides can be physically or chemically adsorbed and captured by polymer structures to suppress their shuttle behavior, but the capture sites are limited, and the captured polysulfides are difficult to re-participate in the reaction, leading to the loss of active materials. Ion gel composite separators based on electrostatic repulsion are one of the more effective means of suppressing the shuttle effect. These separators typically have certain ion selectivity characteristics, allowing lithium ions while repelling the passage of polysulfide anions, thereby blocking the transport path. Summary of the Invention

[0004] To address the problem that existing separators cannot effectively suppress the shuttle effect, and taking into account factors such as manufacturing cost and ion repulsion effect, this invention provides a phosphorylated ion gel composite separator, which is then used in lithium-sulfur batteries to improve the shuttle effect and enhance battery performance.

[0005] The technical solution to achieve the purpose of this invention is:

[0006] In a first aspect, the present invention provides a method for preparing a phosphorylated ion gel composite membrane, comprising the following steps:

[0007] (1) Using polyethylene glycol methyl ether methacrylate and ethylene phosphoric acid as functional monomers, ethoxylated trimethylolpropane triacrylate as crosslinking agent, and diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide as photoinitiator, a uniform ion gel precursor solution was obtained by stirring in tetrahydrofuran solvent at room temperature for a period of time.

[0008] (2) The ion gel precursor solution is uniformly impregnated with the polyolefin membrane and cured under ultraviolet light. After vacuum drying for a period of time, the phosphorylated ion gel composite membrane is obtained.

[0009] Preferably, the mass ratio of polyethylene glycol methyl ether methacrylate, ethylene phosphoric acid, ethoxylated trimethylolpropane triacrylate, and diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide is 7:4:3:1.

[0010] Preferably, the total mass ratio of the functional monomer and crosslinking agent to the tetrahydrofuran is 5:4.

[0011] Preferably, stir at room temperature for 1 hour.

[0012] Preferably, the loading of the ionogel precursor solution on the polyolefin membrane is 4.8 μL / cm. 2 .

[0013] Ideally, it should be cured under ultraviolet light for 3 minutes.

[0014] Preferably, vacuum drying is performed at 60 °C for 1 h.

[0015] Secondly, the present invention provides a phosphorylated ion gel composite membrane prepared by the method described in the first aspect.

[0016] Preferably, the composite membrane has a sandwich structure, with a polyolefin membrane as the middle layer and a phosphorylated ion gel as the outer layer.

[0017] Preferably, the thickness of the composite diaphragm is no more than 30 μm.

[0018] Thirdly, the present invention also provides the use of the phosphorylated ion gel composite separator described in the second aspect for use as a separator in lithium-sulfur batteries.

[0019] The technical solution of the present invention has the following advantages compared with the prior art:

[0020] (1) This invention achieves covalent anchoring of phosphate groups through a one-step ultraviolet curing method. In this process, the utilization rate of phosphate groups is close to 100%. It is easier to control the degree of phosphorylation, and the resulting phosphorylated ion gel is uniform and stable. The material can be prepared at room temperature and normal pressure.

[0021] (2) The synthesis method of this invention is simpler and more efficient, the experimental parameters are easier to control, and the repeatability is good, which is more conducive to reducing production costs and has good economic efficiency and scalability. In addition, the structure of the obtained material is well preserved. Compared with previous studies, this invention has higher yield and safety reliability.

[0022] (3) The phosphorylated ion gel composite separator of the present invention has a sandwich structure with a thickness of only about 30 μm, exhibiting good flexibility and electrolyte wettability, ensuring resistance to dendrite puncture and ion transport performance. Phosphate ions are uniformly distributed throughout the structure, establishing a barrier rich in negative charge, effectively inhibiting the migration of polysulfides to the negative electrode; while its strong lithiophilicity promotes the dissociation of lithium salt and rapid lithium ion transport, thereby significantly increasing the lithium ion transfer number. This dual regulation function effectively suppresses the shuttle effect while maintaining rapid sulfur conversion kinetics, overcoming the problem of difficulty in balancing sulfur inhibition and lithium conduction in traditional separators, and effectively improving the actual capacity and cycle performance of lithium-sulfur batteries. Attached Figure Description

[0023] Figure 1 The Fourier transform infrared spectra are those of the composite membranes prepared in Example 1 and Comparative Example 1 of this invention.

[0024] Figure 2 Scanning electron microscope images and phosphorus energy dispersive spectra of the phosphorylated ion gel composite membrane and polyolefin membrane prepared in Example 1 of this invention.

[0025] Figure 3 The cycling performance of lithium-sulfur batteries equipped with the composite separators prepared in Example 1 and Comparative Example 1 of the present invention, as well as ordinary polyolefin separators, at 0.2 C was measured. Detailed Implementation

[0026] The present application will be further described below with reference to specific embodiments.

[0027] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0029] Unless otherwise specified in the examples, the procedures were performed under standard conditions or conditions recommended by the manufacturer. All reagents and instruments used, unless otherwise specified, were commercially available products. The polyolefin membrane used was model Celgard 2400.

[0030] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0031] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0032] Example 1

[0033] Add 7 g of polyethylene glycol methyl ether methacrylate, 4 g of ethylene phosphoric acid, and 3 g of ethoxylated trimethylolpropane triacrylate to a beaker. Mix the sample thoroughly by stirring. Then add 1 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 11 g of tetrahydrofuran. Seal the beaker and continue stirring for 1 h to obtain a homogeneous precursor solution. (The solution is in a 24 cm² area.) 2 115 μL of precursor solution (4.8 μL / cm²) was uniformly dropped onto the polyolefin membrane. 2 The membrane was placed between two glass plates with polytetrafluoroethylene (PTFE) films on their surfaces and clamped in place. It was allowed to stand for 10 minutes to allow the precursor solution to completely wet the polyolefin membrane. Then, it was irradiated under a UV light source for 3 minutes to initiate a copolymerization reaction. The membrane was then removed and dried in a vacuum drying oven at 60 °C for 1 hour to allow the tetrahydrofuran to completely evaporate. The resulting phosphorylated ion-gel composite membrane was collected, and its thickness was measured to be approximately 30 μm using a micrometer.

[0034] Comparative Example 1

[0035] 7 g of polyethylene glycol methyl ether methacrylate and 3 g of ethoxylated trimethylolpropane triacrylate were added to a beaker and stirred until the sample was homogeneous. Then, 1 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 8 g of tetrahydrofuran were added. The beaker was sealed and stirred for another 1 h to obtain a homogeneous precursor solution. (The solution was prepared in a 24 cm² area.) 2115 μL of precursor solution was uniformly dropped onto a polyolefin membrane, which was then clamped between two glass plates coated with a polytetrafluoroethylene film and allowed to stand for 10 min to allow the precursor solution to completely wet the polyolefin membrane. The membrane was then irradiated under a UV light source for 3 min to initiate a copolymerization reaction. The membrane was then removed and dried in a vacuum oven at 60 °C for 1 h to allow the tetrahydrofuran to completely evaporate. The resulting unphosphorylated ionogel composite membrane was collected, and its thickness was measured to be approximately 30 μm using a micrometer. Because the gel network was unphosphorylated, no phosphorus-related signals could be observed. Figure 1 As shown.

[0036] Comparative Example 2

[0037] Add 7 g of polyethylene glycol methyl ether methacrylate, 8 g of ethylene phosphoric acid, and 3 g of ethoxylated trimethylolpropane triacrylate to a beaker. Mix the sample thoroughly by stirring. Then add 1 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 11 g of tetrahydrofuran. Seal the beaker and continue stirring for 1 h to obtain a homogeneous precursor solution. (The solution is in a 24 cm² area.) 2 115 μL of precursor solution was uniformly dropped onto a polyolefin membrane, which was then clamped between two glass plates coated with a polytetrafluoroethylene film and allowed to stand for 10 min to allow the precursor solution to completely wet the polyolefin membrane. The membrane was then irradiated under a UV light source for 3 min to initiate a copolymerization reaction. The membrane was then removed and dried in a vacuum drying oven at 60 °C for 1 h to allow the tetrahydrofuran to completely evaporate. The resulting phosphorylated ion-gel composite membrane was collected, and its thickness was measured to be approximately 30 μm using a micrometer. Due to the introduction of excessive phosphate groups, the density of the ether oxygen segments used for lithium-ion transport decreased, resulting in slow lithium-ion transport.

[0038] Comparative Example 3

[0039] Add 7 g of polyethylene glycol methyl ether methacrylate, 4 g of ethylene phosphoric acid, and 3 g of ethoxylated trimethylolpropane triacrylate to a beaker. Mix the sample thoroughly by stirring. Then add 1 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 11 g of tetrahydrofuran. Seal the beaker and continue stirring for 1 h to obtain a homogeneous precursor solution. (The solution is in a 24 cm² area.) 2 160 μL of precursor solution (6.7 μL / cm²) was uniformly dropped onto the polyolefin membrane. 2 The membrane was placed between two glass plates coated with a polytetrafluoroethylene (PTFE) film and clamped in place. It was allowed to stand for 10 minutes to allow the precursor solution to completely wet the polyolefin membrane. It was then irradiated under a UV light source for 3 minutes to initiate a copolymerization reaction. The membrane was then removed and dried in a vacuum oven at 60 °C for 1 hour to allow the tetrahydrofuran to completely evaporate. The resulting phosphorylated ion-gel composite membrane was collected, and its thickness was measured to be approximately 30 μm using a micrometer. Due to the excessive amount of gel phase, the resulting composite membrane swelled significantly in the electrolyte, leading to interlayer separation.

[0040] Comparative Example 4

[0041] Add 7 g of polyethylene glycol methyl ether methacrylate, 4 g of ethylene phosphoric acid, and 3 g of ethoxylated trimethylolpropane triacrylate to a beaker. Mix the sample thoroughly by stirring. Then add 1 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 11 g of tetrahydrofuran. Seal the beaker and continue stirring for 1 h to obtain a homogeneous precursor solution. (The solution is in a 24 cm² area.) 2 60 μL of precursor solution (2.5 μL / cm²) was uniformly dropped onto the polyolefin membrane. 2 The membrane was placed between two glass plates coated with a polytetrafluoroethylene (PTFE) film and clamped in place. It was allowed to stand for 10 minutes to allow the precursor solution to completely wet the polyolefin membrane. It was then irradiated under a UV light source for 3 minutes to initiate a copolymerization reaction. The membrane was then removed and dried in a vacuum oven at 60 °C for 1 hour to allow the tetrahydrofuran to completely evaporate. The resulting phosphorylated ion-gel composite membrane was collected, and its thickness was measured to be approximately 30 μm using a micrometer. Due to insufficient loaded gel phase, the edges of the resulting composite membrane still had exposed polyolefin membrane, which could not effectively hinder the formation of polysulfides.

[0042] Figure 1 Fourier transform infrared spectra of the composite membranes prepared in Example 1 and Comparative Example 1. The phosphorylated ion gel composite membrane retains the basic spectral lines of the unphosphorylated gel composite membrane, while characteristic vibrational absorption peaks corresponding to phosphate groups appear at the marked locations, indicating successful grafting of phosphate groups without disrupting the basic framework structure of the gel network.

[0043] Figure 2 Scanning electron microscope images and phosphorus energy dispersive spectra of the phosphorylated ion gel composite membrane and the polyolefin membrane prepared in Example 1 are shown. It can be seen that the phosphorylated ion gel uniformly fills a large number of pores in the polyolefin membrane, and the surface is smooth without obvious impurities. The cross-section has a sandwich structure, and the overall thickness is about 30 μm. The phosphorus element is uniformly distributed throughout the surface and interior.

[0044] Figure 3 The cycling data at 0.2 C are for lithium-sulfur batteries equipped with the composite membranes prepared in Example 1 and Comparative Example 1, as well as a conventional polyolefin membrane. The results show that the lithium-sulfur battery based on the phosphorylated ion gel composite membrane exhibits higher initial capacity and more stable cycling performance, with slower capacity decay. This indicates that the phosphorylated ion gel composite membrane can effectively mitigate the shuttle effect and improve reaction reversibility, demonstrating certain practical value.

[0045] The above embodiments are merely preferred embodiments of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, or combinations made without departing from the spirit and principle of the present invention, such as various combinations of solutions in the embodiments, should be considered equivalent replacements and are all within the protection scope of the present invention.

Claims

1. A method for preparing a phosphorylated ion gel composite membrane, characterized in that, Includes the following steps: (1) Using polyethylene glycol methyl ether methacrylate and ethylene phosphoric acid as functional monomers, ethoxylated trimethylolpropane triacrylate as crosslinking agent, and diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide as photoinitiator, the above raw materials were stirred in tetrahydrofuran solvent at room temperature for a period of time to obtain a uniform ion gel precursor solution. (2) The ion gel precursor solution is uniformly impregnated with the polyolefin membrane and cured under ultraviolet light. After vacuum drying for a period of time, the phosphorylated ion gel composite membrane is obtained.

2. The method as described in claim 1, characterized in that, The mass ratio of polyethylene glycol methyl ether methacrylate, ethylene phosphoric acid, ethoxylated trimethylolpropane triacrylate, and diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide is 7:4:3:

1.

3. The method as described in claim 1, characterized in that, The total mass ratio of the functional monomer and crosslinking agent to the tetrahydrofuran is 5:

4.

4. The method as described in claim 1, characterized in that, Stir at room temperature for 1 hour.

5. The method as described in claim 1, characterized in that, The loading capacity of the ionogel precursor solution on the polyolefin membrane was 4.8 μL / cm. 2 .

6. The method as described in claim 1, characterized in that, Cured under ultraviolet light for 3 minutes.

7. The method as described in claim 1, characterized in that, Vacuum dry at 60 ℃ for 1 h.

8. A phosphorylated ion gel composite membrane prepared by the method according to any one of claims 1-7.

9. The composite diaphragm as described in claim 8, characterized in that, The composite membrane has a sandwich structure, with a polyolefin membrane as the middle layer and a phosphorylated ion gel as the outer layer. The thickness of the composite membrane is no more than 30 μm.

10. The use of a phosphorylated ion gel composite separator prepared by the method of any one of claims 1-7 for use as a separator in a lithium-sulfur battery.

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