A kind of π-d conjugated covalent organic framework material and its preparation method and application

Abstract

The application belongs to the technical field of electrochemistry, and discloses a kind of π-d conjugated covalent organic framework material, and its preparation method includes the following steps: 2,5-hydroxy terephthalic acid, 2,3,5,6-tetra (amino) p-benzoquinone and nickel acetate tetrahydrate are added into a container, then N-methyl pyrrolidone is added, and after ultrasonic for 0.5h, it is transferred into a hydrothermal reaction kettle, and sealed reaction is carried out for 2-5 days; after reaction, it is naturally cooled to room temperature; the obtained precipitate is collected by filtration, washed, and vacuum dried to obtain the π-d conjugated covalent organic framework material. The covalent organic framework material is rich in N / O chemical adsorption sites and Ni 2+ catalytic sites, which can effectively inhibit the shuttle of polysulfides; on the other hand, it promotes the catalytic conversion of polysulfides, further accelerates the reaction kinetics of lithium-sulfur batteries, greatly improves the electrical conductivity compared with traditional covalent organic frameworks, and improves the transmission ability of electrons.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology and relates to a π-d conjugated covalent organic framework material, its preparation method, and its application. Background Technology

[0002] With the increasing demand for portable devices and electric vehicles, the development of high-energy-density rechargeable batteries has become urgent. However, the energy density of currently used lithium-ion batteries is gradually failing to meet the needs of practical applications. Lithium-sulfur batteries have an energy density of 1675 mAh g⁻¹. -1 High theoretical specific capacity and 2600Wh / kg -1 The high theoretical energy density, abundant and low-cost sulfur resources, and environmental friendliness of lithium-sulfur batteries offer enormous potential for next-generation energy storage systems. However, sulfur and its discharge product, lithium sulfide, are insulators of both electrons and lithium ions, severely hindering the efficient transport of electrons and ions during electrochemical reactions. This results in reduced utilization of the active material sulfur and a slower kinetic process. During charging and discharging, sulfur at the positive electrode produces polysulfide intermediates, which dissolve in the electrolyte, cross the separator, and diffuse towards the negative electrode. These intermediates can directly react with the lithium metal at the negative electrode, ultimately leading to irreversible loss of the active material and even posing safety hazards. Therefore, lithium-sulfur batteries suffer from low conductivity of sulfur and discharge products, the tendency of polysulfides to exhibit shuttle effects, and safety hazards caused by lithium dendrite formation, hindering their large-scale commercial application.

[0003] In recent decades, significant progress has been made in the modification of traditional separators, primarily focusing on carbon materials, inorganic materials, and polymer materials. The introduction of these modified materials has provided new possibilities for improving separator performance. However, in practical applications, modified separators face considerable challenges, including complex processes, high costs, and stability issues. Covalent organic frameworks (COFs) are functional porous materials composed of organic ligands linked by covalent bonds. They possess advantages such as low density, tunable structure, and high porosity, thus attracting considerable attention globally, especially in the battery field. They can be used for targeted design to address functional requirements in lithium-sulfur batteries, such as rapid lithium-ion / electrolyte transfer, polysulfide suppression, and electrode protection, thereby improving lithium-sulfur battery performance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a π-d conjugated covalent organic framework material rich in N / O chemisorption sites and Ni. 2+The catalytic sites serve two purposes: firstly, as adsorption sites, they can effectively inhibit the shuttle of polysulfides; secondly, as catalytic sites, they can promote the catalytic conversion of polysulfides, further accelerating the reaction kinetics of lithium-sulfur batteries. When the modified membrane is applied to lithium-sulfur batteries or symmetric batteries, it can enhance electron conductivity and improve the electrochemical performance of the battery.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a π-d conjugated covalent organic framework material, the structural formula of which is as follows:

[0007]

[0008] Secondly, the present invention provides a method for preparing the above-mentioned π-d conjugated covalent organic framework material, comprising the following steps: adding 2,5-hydroxyterephthalic acid, 2,3,5,6-tetra(amino)-p-benzoquinone and nickel acetate tetrahydrate into a container, followed by adding N-methylpyrrolidone, sonicating for 0.5 h, and then transferring to a hydrothermal reactor, sealing and reacting at 100-150°C for 2-5 days, and after the reaction is completed, naturally cooling to room temperature, collecting the obtained precipitate by filtration, washing, and vacuum drying at 60-120°C to obtain the π-d conjugated covalent organic framework material.

[0009] In one technical solution, the molar ratio of 2,3,5,6-tetra(amino)-p-benzoquinone to 2,5-hydroxyterephthalic acid is 1:1 to 3.

[0010] Thirdly, the present invention provides an application of the above-mentioned π-d conjugated covalent organic framework material in a battery separator, wherein the battery separator is provided with a mixed coating composed of the above-mentioned π-d conjugated covalent organic framework material, conductive carbon black and polyvinylidene fluoride.

[0011] In one technical solution, the mass ratio of the π-d conjugated covalent organic framework material to the conductive carbon black is 1:0.6 to 1.

[0012] Fourthly, the present invention provides an application of the above-mentioned π-d conjugated covalent organic framework material in a lithium-sulfur battery, wherein the battery separator in the lithium-sulfur battery is provided with a mixture of the above-mentioned π-d conjugated covalent organic framework material, conductive carbon black and polyvinylidene fluoride.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. The π-d conjugated covalent organic framework material of this invention contains a quinone structure and is rich in N / O chemisorption sites and Ni. 2+The catalytic site serves two purposes: firstly, as an adsorption site, it can effectively inhibit the shuttle of polysulfides; secondly, as a catalytic site, it promotes the catalytic conversion of polysulfides, further accelerating the reaction kinetics of lithium-sulfur batteries. Compared with traditional covalent organic frameworks, it greatly improves conductivity and enhances electron transport capability.

[0015] 2. The Ni-BQ COF modified separator of the present invention has abundant N / O polar groups in the Ni-BQ COF structure, which not only facilitates the wetting of electrolyte, but also enables the chemical adsorption of polysulfides, effectively suppressing the shuttle effect of polysulfides, improving its cycle stability, and enhancing the electrochemical performance of lithium-sulfur batteries.

[0016] 3. The Ni-BQ COF-modified separator of this invention is applied in lithium-sulfur batteries. The π-d conjugated structure of Ni-BQ COF effectively promotes high electron delocalization and enhances its electronic conductivity. Furthermore, the large amount of Ni introduced into the Ni-BQ COF structure... 2+ It can serve as a catalytic site, promoting the catalytic conversion of polysulfides, accelerating the reaction kinetics of lithium-sulfur batteries, and enhancing rate performance.

[0017] 4. When the Ni-BQ COF-modified separator of this invention is applied in a symmetrical battery, the Ni-BQ COF-modified separator exhibits higher lithium-ion transference number and lithium-ion diffusion coefficient, as well as better electrolyte wettability, and has superior electrochemical performance. Attached Figure Description

[0018] Figure 1 The image shows the X-ray powder diffraction pattern of the Ni-BQ COF prepared in Example 1.

[0019] Figure 2 The infrared absorption spectrum of Ni-BQ COF prepared in Example 1 is shown.

[0020] Figure 3 Nitrogen adsorption-desorption curves and pore size distribution of Ni-BQ COF prepared in Example 1.

[0021] Figure 4 The X-ray powder diffraction patterns of Ni-BQ COF prepared in Example 1 after immersion in different solvents are shown.

[0022] Figure 5 X-ray powder diffraction patterns of Ni-BQ COF prepared in Examples 2 and 3.

[0023] Figure 6 This is an electron microscope image of the Ni-BQ COF modified membrane prepared in Example 4, wherein... Figure 5 -a represents a plan view. Figure 5 -b represents a cross-sectional view.

[0024] Figure 7 The image shows the electrochemical polarization test results of a lithium-lithium symmetric battery assembled using a commercial PP separator and a Ni-BQ COF modified separator, as shown in Example 5. The inset shows the impedance spectra before and after polarization.

[0025] Figure 8 The electrochemical impedance spectroscopy of the stainless steel-stainless steel symmetric cell assembled using a commercial PP separator and a Ni-BQ COF modified separator is shown in Example 6.

[0026] Figure 9 The graph shows the rate performance of the lithium-sulfur battery assembled using a commercial PP separator and a Ni-BQ COF modified separator in Example 7.

[0027] Figure 10 The graph shows the long-cycle performance of the lithium-sulfur battery assembled using a commercial PP separator and a Ni-BQ COF modified separator in Example 7. Detailed Implementation

[0028] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0029] Example 1

[0030] 2,5-Hydroxyterephthalic acid (HBC, 1 mmol), 2,3,5,6-tetra(amino)-p-benzoquinone (TABQ, 0.5 mmol), and excess nickel acetate tetrahydrate (NiOAc·4H₂O, 1.5 mmol) were added to a 10 mL glass bottle, followed by the addition of N-methylpyrrolidone (NMP, 10 mL), and the mixture was sonicated for 0.5 h. The bottle was then transferred to a Teflon-lined stainless steel hydrothermal reactor, sealed, and heated at 120 °C for 72 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting black precipitate was collected by filtration and repeatedly washed with DMF and methanol. The product was then vacuum-dried at 80 °C for 12 h to obtain the π-d conjugated covalent organic framework material Ni-BQ COF.

[0031] The X-ray powder diffraction pattern of the π-d conjugated Ni-BQ COF material synthesized in Example 1 is shown below. Figure 1 As shown in the figure, three distinct characteristic peaks can be seen at 7.4°, 8.4°, and 11.3°, corresponding to the (100), (010), and (110) crystal planes, respectively, indicating that the Ni-BQ COF material synthesized in Example 1 is a covalent organic framework material with good crystallinity.

[0032] The infrared absorption spectrum of the π-d conjugated Ni-BQ COF material synthesized in Example 1 is shown below. Figure 2 As shown in the image, the NH peak at 3381 cm⁻¹ and the -OH peak at 3270 cm⁻¹ in the Ni-BQ COF infrared spectrum have significantly disappeared, indicating that the reaction can proceed fully via a simple one-step solvothermal method. Additionally, the peak at 1654 cm⁻¹ is clearly visible. -1 and 1570cm -1 The absorption peaks can be attributed to the stretching vibrations of C=O and the connecting group C=N, respectively, further indicating the successful synthesis of Ni-BQ COF.

[0033] The nitrogen adsorption-desorption curves of the π-d conjugated Ni-BQ COF material synthesized in Example 1 are shown below. Figure 3 As shown. Figure 3 -a exhibits a typical type I isotherm, indicating that Ni-BQ COF is a microporous material with a specific surface area of ​​51.45 m². 2 g -1 . Figure 3 The pore size distribution diagram shows that the pore size is mainly distributed at 1.088 nm, which is close to the theoretical pore size (1.1 nm), further demonstrating the successful construction of the Ni-BQ COF periodic microporous structure.

[0034] The π-d conjugated Ni-BQ COF material prepared in Example 1 was subjected to X-ray powder diffraction tests after being immersed in different solvents. The results are as follows: Figure 4 As shown in the figure, the PXRD pattern of Ni-BQ COF after immersion is almost unchanged compared with that of the initially synthesized Ni-BQ COF, indicating that Ni-BQ COF has stable chemical stability.

[0035] Example 2

[0036] 2,5-Hydroxyterephthalic acid (HBC, 1 mmol), 2,3,5,6-tetra(amino)-p-benzoquinone (TABQ, 0.5 mmol), and excess nickel acetate tetrahydrate (NiOAc·4H₂O, 2.0 mmol) were added to a 10 mL glass bottle, followed by the addition of N-methylpyrrolidone (NMP, 10 mL), and the mixture was sonicated for 0.5 h. The bottle was then transferred to a Teflon-lined stainless steel hydrothermal reactor, sealed, and heated at 120 °C for 72 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting black precipitate was collected by filtration and repeatedly washed with DMF and methanol. The product was then vacuum-dried at 80 °C for 12 h to obtain the π-d conjugated covalent organic framework material Ni-BQ COF.

[0037] Example 3

[0038] 2,5-Hydroxyterephthalic acid (HBC, 1 mmol), 2,3,5,6-tetra(amino)-p-benzoquinone (TABQ, 0.5 mmol), and excess nickel acetate tetrahydrate (NiOAc·4H₂O, 2.5 mmol) were added to a 10 mL glass bottle, followed by the addition of N-methylpyrrolidone (NMP, 10 mL), and the mixture was sonicated for 0.5 h. The bottle was then transferred to a Teflon-lined stainless steel hydrothermal reactor, sealed, and heated at 120 °C for 72 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting black precipitate was collected by filtration and repeatedly washed with DMF and methanol. The product was then vacuum-dried at 80 °C for 12 h to obtain the π-d conjugated covalent organic framework material Ni-BQ COF.

[0039] The X-ray powder diffraction patterns of the Ni-BQ COF prepared in Examples 2 and 3 are as follows: Figure 5 As shown in the figure, the prepared Ni-BQ COFs all exhibit good crystallinity.

[0040] Example 4

[0041] 40 mg of the Ni-BQ COF material synthesized in Example 1 was mixed with 40 mg of conductive carbon black and 20 mg of polyvinylidene fluoride (5 wt%) in an agate mortar, and NMP was added to adjust the viscosity of the slurry. The prepared slurry was then coated onto a PP diaphragm, and the coated diaphragm was placed in a vacuum oven at 50°C overnight. After drying, the diaphragms were cut into circular pieces using a manual cutting machine. Finally, the cut diaphragms were transferred to a glove box for later use.

[0042] The Ni-BQ COF-modified PP separator prepared in Example 4 was observed under an electron microscope, and planar and cross-sectional images were obtained. The results are as follows. Figure 5 As shown. From Figure 6 -a shows a dense layer of Ni-BQ COF material; from Figure 6 -b As can be seen, the thickness of the Ni-BQ COF modification layer on the membrane surface is approximately 15 μm. This dense Ni-BQ COF layer plays an important role in suppressing polysulfide shuttle.

[0043] Example 5

[0044] The commercial PP separator and the Ni-BQ COF-modified PP separator prepared in Example 4 were respectively assembled into symmetrical cells with lithium metal sheets, and electrochemical polarization tests were performed. The results are as follows: Figure 7 As shown in the figure. Based on the electrochemical polarization results, the calculated ion transference number of the commercial PP membrane is 0.32, while that of the Ni-BQ COF modified membrane is 0.76, which is significantly higher than that of the commercial PP membrane. The main reason is that the regular channels of Ni-BQ COF play an important role in ion transfer.

[0045] Example 6

[0046] Commercial PP separators and the Ni-BQ COF-modified PP separator prepared in Example 4 were respectively assembled into symmetrical cells with stainless steel sheets, and electrochemical impedance spectroscopy was performed. The results are as follows: Figure 8 As shown. The calculated ionic conductivity of the commercial PP membrane is 0.49 mS / cm. -1 The ionic conductivity of the Ni-BQ COF-modified PP membrane is 1.7 mS / cm. -1 The efficiency was significantly higher than that of commercial PP membranes, indicating that Ni-BQ COF can effectively promote the rapid transport of ions.

[0047] Example 7

[0048] Using an S@SP composite electrode as the positive electrode (conventional melt preparation method) and a lithium metal sheet as the negative electrode, a Ni-BQ COF-modified PP separator prepared in Example 2 was used. During battery assembly, the side coated with the Ni-BQ COF coating was placed facing the S@SP positive electrode, and an electrolyte consisting of 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (DOL:DME = 1 / 1, 0.1 M LiNO3) was added dropwise. A CR2032 battery case was used, and after assembly, the cells were compacted on a tablet press. Electrochemical performance was then tested after a certain period of time. A lithium-sulfur battery was also assembled using a commercial PP separator for comparison.

[0049] The lithium-sulfur battery assembled in Example 4 using a commercial PP membrane and a Ni-BQ COF-modified membrane was electrochemically tested at different current densities. The battery rate performance results are as follows: Figure 9 As shown in the figure, the discharge capacities of batteries assembled with commercial PP separators are 623.68, 532.91, 503.86, and 459.77 mAh g⁻¹ at current densities of 0.5, 1, 2, and 4C, respectively. -1 However, the discharge capacities of batteries assembled with Ni-BQ COF-modified separators reached as high as 926.36, 851.41, 771.78, and 720.17 mAh g, respectively. -1 At the same current density, the rate performance of cells assembled with Ni-BQ COF modified separators was significantly higher than that of commercial PP separators, indicating that Ni-BQ COF modified separators possess excellent rate performance. This is due to the introduction of a large amount of Ni into the separator in Ni-BQ COF. 2+ It can serve as a catalytic site, promoting the catalytic conversion of polysulfides, accelerating the reaction kinetics of lithium-sulfur batteries, and enhancing rate performance.

[0050] The lithium-sulfur batteries assembled in Example 4 using commercial PP membranes and Ni-BQ COF-modified membranes were subjected to long-cycle tests at a current density of 0.5C, respectively. The results are as follows: Figure 10 As shown. When using a commercial PP membrane, the initial capacity at a current density of 0.5C is 679.00 mAh g. -1 After 200 cycles, the capacity of the commercial PP membrane was 506.3 mAh g. -1 Commercial PP separators exhibit significant capacity decay, with a capacity decay rate of 0.13% per cycle. In contrast, the battery using a Ni-BQ COF-modified separator clearly demonstrates an initial capacity of 880.21 mAh g at a 0.5C current density. -1 It maintains 688.18 mAhg after 200 cycles. -1 The capacity retention rate was 78.2%, and the capacity decay rate per cycle was only 0.10%, significantly higher than that of commercial PP separators, further validating the superiority of the Ni-BQ COF modified separator. The excellent long-term cycling stability is attributed to the Ni-BQ COF material acting as a physicochemical barrier as a separator coating, effectively adsorbing polysulfides and making a significant contribution to the performance improvement of lithium-sulfur batteries.

[0051] In summary, the π-d conjugated Ni-BQ COF material of this invention is used as a membrane modification layer. Specifically, on the one hand, the π-d conjugated structure effectively promotes high electron delocalization, enhancing its electronic conductivity; on the other hand, a large amount of Ni... 2+ The abundant N / O polar groups in the Ni-BQ COF structure can act as catalytic sites, promoting the catalytic conversion of polysulfides, accelerating the reaction kinetics of lithium-sulfur batteries, and enhancing rate performance. On the other hand, the abundant N / O polar groups in the Ni-BQ COF structure can chemically adsorb polysulfides, effectively suppressing the shuttle effect of polysulfides and improving the cycle stability of lithium-sulfur batteries.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A π-d conjugated covalent organic framework material, characterized in that, Its structural formula is as follows:

2. The method for preparing the π-d conjugated covalent organic framework material according to claim 1, characterized in that, Includes the following steps: 2,5-hydroxyterephthalic acid, 2,3,5,6-tetra(amino)-p-benzoquinone, and nickel acetate tetrahydrate were added to a container, followed by N-methylpyrrolidone. After sonication for 0.5 h, the mixture was transferred to a hydrothermal reactor and reacted under sealed conditions at 100–150 °C for 2–5 days. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The resulting precipitate was collected by filtration, washed, and vacuum dried at 60–120 °C to obtain a π-d conjugated covalent organic framework material.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 2,3,5,6-tetra(amino)-p-benzoquinone to 2,5-hydroxyterephthalic acid is 1:1 to 3.

4. The application of a π-d conjugated covalent organic framework material in battery separators, characterized in that, The battery separator is provided with a mixed coating consisting of the π-d conjugated covalent organic framework material as described in claim 1, conductive carbon black, and polyvinylidene fluoride.

5. The application according to claim 4, characterized in that, The mass ratio of the π-d conjugated covalent organic framework material to the conductive carbon black is 1:0.6 to 1.

6. The application of a π-d conjugated covalent organic framework material in lithium-sulfur batteries, characterized in that, The battery separator in the lithium-sulfur battery is provided with a mixed coating composed of the π-d conjugated covalent organic framework material as described in claim 1, conductive carbon black, and polyvinylidene fluoride.

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