Preparation method of pyridyl two-dimensional covalent-organic framework material and application thereof as positive electrode material of lithium-iodine battery

Abstract

The application discloses a preparation method of a pyridyl two-dimensional covalent-organic framework material and application of the material as a positive electrode material of a lithium-iodine battery. The application realizes effective anchoring of multi-valence iodine species in a lithium-iodine battery system by integrating a protonatable pyridyl unit into a rigid covalent-organic framework skeleton. The obtained material shows high specific capacity, excellent long cycle stability and excellent rate characteristics. The strategy opens up a new way for rational design of covalent-organic framework materials and application of the materials in electrode materials of lithium-iodine batteries.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and electrochemical energy storage devices, specifically relating to a method for preparing a pyridine-based two-dimensional covalent-organic framework material with an ordered nanoporous structure and its application as a cathode material for lithium-iodine batteries. Background Technology

[0002] Lithium-iodine (Li-I2) batteries are based on iodine cathodes. - / I 0 Redox reaction, with high theoretical specific capacity (211 mAh·g) -1 ), with a moderate operating voltage (approximately 2.9 V, relative to Li / Li + With its advantages of being environmentally friendly and highly safe, it is an electrochemical energy storage system with great application potential. Further development of I... 0 / I + Through high-valence-state conversion, the theoretical specific capacity of lithium-iodine batteries can be increased to 422 mAh. . g -1 This technology holds promise for breaking through the current energy density bottleneck in batteries. However, different valence states of iodine species (including I) - I3 - I5 - I2 and I + The high solubility of iodides in organic electrolytes can trigger a severe shuttle effect, leading to the loss of active materials and degradation of battery performance. Existing inorganic carbon materials mainly employ physical confinement strategies (such as MXene intercalation and porous carbon loading), which rely on weak physical adsorption and are difficult to effectively suppress the dissolution and migration of iodides. Therefore, developing materials with strong chemical anchoring sites to construct a stable host-guest interface is key to improving the cycle stability and energy density of lithium-iodine batteries.

[0003] Covalent organic frameworks (COFs) are a class of crystalline porous materials formed by organic structural units linked by covalent bonds. They possess characteristics such as tunable porosity, designable structure, and atomically precise structure. Introducing specific functional groups into COFs can achieve precise chemical anchoring of iodine species, thereby effectively inhibiting the dissolution and shuttle of polyiodides. The pyridine group, as a strong electron-donating group, allows nitrogen atoms to interact with I₂ / I₂ through Lewis acid-base interactions. + Formation of charge-transfer complexes; protonated pyridine nitrogen (HN) + Then it can interact with I through electrostatic action. - / I3 - Strong Coulomb interactions are generated, thereby confining active iodine species within the material system and effectively suppressing the shuttle effect. However, research on the application of pyridine-based COFs in the field of lithium-iodine battery cathode materials is still insufficient. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for synthesizing a pyridyl covalent-organic framework material (BPY-COF-HI).

[0005] A second objective of this invention is to provide a method for synthesizing pyridine-based covalent-organic framework@carbon nanotube composite materials (BPY-COF@CNT-HI).

[0006] The third objective of this invention is to provide an application of a pyridyl covalent-organic framework as a cathode material for lithium-iodine batteries.

[0007] The fourth objective of this invention is to provide an application of a pyridine-based covalent-organic framework@carbon nanotube composite material as a cathode material for lithium-iodine batteries.

[0008] The technical solution of this invention is summarized as follows:

[0009] The structure of the pyridine-based covalent-organic framework material (BPY-COF-HI) provided by this invention is shown in Formula I below.

[0010]

[0011] Ⅰ

[0012] This invention relates to a method for synthesizing pyridyl covalent-organic framework materials (BPY-COF-HI), comprising the following steps:

[0013] 2,4,6-Tricarboxymethyl phloroglucinol and 5,5'-diamino-2,2'-bipyridine were added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution and ultrasonically dispersed for several minutes. After several cycles of freezing-vacuuming-thawing to degas the mixture, the reaction tube was sealed and placed in an oven to react for several days. After the reaction was completed, the precipitate was collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone by Soxhlet extraction, and vacuum dried overnight to obtain BPY-COF. The BPY-COF material was dispersed in a mixed solution of methanol and hydroiodic acid (HI), stirred at room temperature in the dark, filtered to separate the solid powder, washed with methanol, and vacuum dried to obtain the protonated material BPY-COF-HI.

[0014] The pyridine-based covalent-organic framework@carbon nanotube composite material (BPY-COF@CNT-HI) provided by the present invention has the pyridine-based covalent-organic framework shown in Formula I.

[0015] The preparation method of pyridine-based covalent-organic framework@carbon nanotube composite material (BPY-COF@CNT-HI) provided by this invention includes the following steps:

[0016] 2,4,6-Tricarboxymethyl phloroglucinol, 5,5'-diamino-2,2'-bipyridine, and carbon nanotubes were added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution and ultrasonically dispersed for several minutes. After several cycles of freezing-vacuuming-thawing to degas the mixture, the reaction tube was sealed and placed in an oven to react for several days. After the reaction was completed, the precipitate was collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone by Soxhlet extraction, and vacuum dried overnight to obtain BPY-COF@CNT. The BPY-COF@CNT material was dispersed in a mixed solution of methanol and hydroiodic acid (HI), stirred at room temperature in the dark, filtered to separate the solid powder, washed with methanol, and vacuum dried to obtain the protonated material BPY-COF@CNT-HI.

[0017] Furthermore, this invention provides an application of pyridyl covalent-organic framework material (BPY-COF-HI) in the preparation of lithium-iodine battery cathodes, comprising the following steps:

[0018] A CR2032 coin cell was assembled using a mixture of pyridyl covalent organic framework BPY-COF-HI, carbon nanotubes, and polyvinylidene fluoride binder at a mass ratio of 6:3:1. An appropriate amount of N-methylpyrrolidone was added and stirred to form a homogeneous slurry. The slurry was coated onto hydrophilic carbon paper and vacuum dried at 80°C for 12 h. A lithium electrode was used as the counter electrode, a Celgard 2400 membrane was used as the separator, and a 1M lithium bis(trifluoromethanesulfonyl)imide solution in 1,3-dioxolane DOL and ethylene glycol dimethyl ether DME was used as the electrolyte. The electrolyte contained 1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane DOL, and ethylene glycol dimethyl ether DME in a volume ratio of 1:1:1, with 2% LiNO3 added by mass.

[0019] Furthermore, this invention also provides an application of pyridine-based covalent-organic framework@carbon nanotube composite material (BPY-COF@CNT-HI) in the preparation of lithium-iodine battery cathodes, comprising the following steps:

[0020] A CR2032 coin cell was assembled using a pyridine-based covalent-organic framework@carbon nanotube composite material BPY-COF@CNT-HI, carbon nanotubes, and polyvinylidene fluoride binder at a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone was added and the mixture was stirred to form a homogeneous slurry. The slurry was coated onto hydrophilic carbon paper and vacuum dried at 80°C for 12 h. A lithium electrode was used as the counter electrode, a Celgard 2400 membrane was used as the separator, and a 1M lithium bis(trifluoromethanesulfonyl)imide solution in 1,3-dioxolane DOL and ethylene glycol dimethyl ether DME was used as the electrolyte. The electrolyte contained 1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane DOL, and ethylene glycol dimethyl ether DME in a volume ratio of 1:1:1, with 2% LiNO3 added by mass.

[0021] The advantages of this invention are:

[0022] This invention is the first to introduce hydroiodic acid into a pyridine-based covalent organic framework modification system, achieving the modification of I through the protonation effect of the pyridine group. - / I3 - This invention utilizes the chemisorption of iodine by pyridine groups to simultaneously achieve the physicochemical synergistic adsorption of nonpolar iodine and iodide ions, thus constructing a functional iodine adsorbent material. When applied to the cathode of a lithium-iodine battery, this material exhibits excellent cycle stability and rate performance. Furthermore, this invention employs an in-situ growth strategy to composite the pyridine-based covalent organic framework with carbon nanotubes, forming a COF@CNT composite host material. This structural design, on the one hand, utilizes the highly conductive network of carbon nanotubes to enhance the electron transport efficiency of the composite material, and on the other hand, enhances the dispersion uniformity of iodine active species in the host material through in-situ loading, thereby synergistically achieving a lithium-iodine battery cathode material with high specific capacity, excellent rate performance, and long cycle stability. This invention, through a multifunctional site synergistic adsorption mechanism, provides a new theoretical basis for the study of the structure-performance relationship of covalent organic framework materials in the field of electrochemical energy storage, and also provides a feasible technical path for the development of high-energy-density lithium-iodine battery electrode materials based on two-dimensional covalent organic framework materials.

[0023] Figure 1 The X-ray diffraction (XRD) patterns of BPY-COF-HI hydroiodic acid before and after protonation are shown.

[0024] Figure 2 The image shows the XRD patterns of BPY-COF@CNT-HI before and after protonation of hydroiodic acid.

[0025] Figure 3 The infrared spectra of BPY-COF-HI hydroiodic acid before and after protonation are shown.

[0026] Figure 4 The infrared spectra of BPY-COF@CNT-HI before and after protonation.

[0027] Figure 5 The images are scanning electron microscope (SEM) images of BPY-COF-HI hydroiodic acid before and after protonation.

[0028] Figure 6 The images are scanning electron microscope (SEM) images of BPY-COF@CNT-HI hydroiodic acid before and after protonation.

[0029] Figure 7 XPS spectra of BPY-COF-HI hydroiodic acid before and after protonation.

[0030] Figure 8 XPS spectra of BPY-COF@CNT-HI before and after protonation of hydroiodic acid.

[0031] Figure 9 Thermogravimetric analysis (TGA) results for BPY-COF-HI hydroiodic acid before and after protonation.

[0032] Figure 10 Thermogravimetric analysis (TGA) results for BPY-COF@CNT-HI hydroiodic acid before and after protonation.

[0033] Figure 11 A battery using BPY-COF-HI as the lithium-iodine cathode material at 300 mA g -1 Cyclic performance at current density.

[0034] Figure 12 Batteries using BPY-COF-HI as the lithium-iodine cathode material operate at 300-2000 mA g. -1 Rate performance test chart at current density.

[0035] Figure 13 A battery using BPY-COF@CNT-HI as the lithium-iodine cathode material at 300 mA g -1 Cyclic performance at current density.

[0036] Figure 14 Batteries using BPY-COF-HI as the lithium-iodine cathode material operate at 300-2000 mA g. -1 Rate performance test chart at current density. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] The preparation method of BPY-COF-HI includes the following steps:

[0040] 2,4,6-Tricarboxymethyl phloroglucinol (Tp, 12.6 mg, 0.1 mmol) and 5,5'-diamino-2,2'-bipyridine (27 mg, 0.15 mmol) were added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution (volume ratio 1.5 mL : 0.5 mL : 0.12 mL), ultrasonically dispersed for several minutes, and degassed by three cycles of freezing-vacuuming-thawing. The reaction tube was then sealed and placed in an oven at 120 °C for 3 days. After the reaction, the precipitate was collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone by Soxhlet for 24 h, and dried under vacuum at 100 °C overnight. The yield of BPY-COF was 85%. 40 mg of BPY-COF material was weighed and dispersed in a mixed solution of 2 mL methanol and 2 mL hydroiodic acid (HI), and stirred at room temperature in the dark for 72 h. The solid powder was separated by filtration and washed five times with methanol. It was then dried under vacuum at 60 °C for 12 h to obtain the protonated BPY-COF material BPY-COF-HI.

[0041] Example 2

[0042] The preparation method of BPY-COF@CNT-HI includes the following steps:

[0043] 2,4,6-Tricarboxymethyl phloroglucinol (Tp, 12.6 mg, 0.1 mmol), 5,5'-diamino-2,2'-bipyridine (27 mg, 0.15 mmol), and 25 mg of carbon nanotubes were added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution (volume ratio 1.5 mL : 0.5 mL : 0.12 mL), ultrasonically dispersed for several minutes, and degassed by three cycles of freezing-vacuuming-thawing. The reaction tube was then sealed and placed in an oven at 120 °C for 3 days. After the reaction, the precipitate was collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone by Soxhlet extraction for 24 h, and dried under vacuum at 100 °C overnight to obtain BPY-COF@CNT. 40 mg of BPY-COF@CNT material was weighed and dispersed in a mixed solution of 2 mL methanol and 2 mL hydroiodic acid (HI), and stirred at room temperature in the dark for 72 h. The solid powder was separated by filtration and washed five times with methanol. It was then dried under vacuum at 60 °C for 12 h to obtain the protonated material BPY-COF@CNT-HI.

[0044] Figure 1 X-ray diffraction (XRD) patterns of BPY-COF and BPY-COF-HI. (Source: [Insert source here]) Figure 1 It can be seen that BPY-COF-HI treated with hydroiodic acid still retains its original crystal structure.

[0045] Figure 2 The X-ray diffraction (XRD) pattern of BPY-COF@CNT is shown. Figure 2 It can be seen that the X-ray diffraction data of BPY-COF@CNT are in good agreement with the simulated structural data, indicating that the composite of BPY-COF and carbon nanotubes was successful.

[0046] Figure 3 The images show the infrared spectra of BPY-COF and BPY-COF-HI. The data indicate that the structure of BPY-COF-HI remained unchanged after hydroiodic acid treatment.

[0047] Figure 4 The infrared spectra of BPY-COF@CNT and BPY-COF@CNT-HI are shown. The data indicate that BPY-COF@CNT-HI did not undergo structural changes after hydroiodic acid treatment.

[0048] Figure 5 The images show scanning electron microscope (SEM) images of BPY-COF-HI and BPY-COF-HI. The data indicate that the morphology of BPY-COF-HI did not change after treatment with hydroiodic acid.

[0049] Figure 6 Scanning electron micrographs of BPY-COF@CNT and BPY-COF@CNT-HI are shown. The data indicate that BPY-COF@CNT-HI did not undergo morphological changes after hydroiodic acid treatment.

[0050] Figure 7 XPS spectra of BPY-COF and BPY-COF-HI. The data indicate that BPY-COF-HI treated with hydroiodic acid was successfully loaded with hydrogen iodide.

[0051] Figure 8 XPS spectra of BPY-COF@CNT and BPY-COF@CNT-HI. The data indicate that BPY-COF@CNT-HI treated with hydroiodic acid was successfully loaded with hydrogen iodide.

[0052] Figure 9 The thermogravimetric analysis results for BPY-COF and BPY-COF show that the hydrogen iodide loading of BPY-COF-HI is 31.6%.

[0053] Figure 10 Thermogravimetric analysis (TGA) charts for BPY-COF@CNT and BPY-COF@CNT-HI are shown. The data indicate that the hydrogen iodide loading of BPY-COF@CNT-HI is 18.6%.

[0054] Example 3

[0055] The application of lithium-iodine battery cathodes based on pyridyl covalent-organic framework (BPY-COF-HI) includes the following steps:

[0056] The BPY-COF-HI prepared in Example 1 was mixed with carbon nanotubes and polyvinylidene fluoride binder at a mass ratio of 6:3:1. An appropriate amount of N-methylpyrrolidone was added and stirred to form a uniform slurry. The slurry was coated onto a 12 mm diameter circular hydrophilic carbon paper and vacuum dried at 80 °C for 12 h. A CR2032 coin cell was assembled using lithium as the counter electrode, Celgard 2400 as the separator, and 1M lithium bis(trifluoromethanesulfonyl)imide in 1,3-dioxolane (DOL): ethylene glycol dimethyl ether (DME) (1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane, and ethylene glycol dimethyl ether in a volume ratio of 1:1:1, with 2% LiNO3 added by mass) as the electrolyte.

[0057] Figure 11 A lithium-iodine battery using BPY-COF-HI material as the positive electrode at 300 mA g -1 Cyclic performance graphs at current density, such as Figure 11 As shown, at 300 mA g -1 At current density, the discharge specific capacity using BPY-COF-HI as the positive electrode material can reach up to 141 mA hg. I -1 And it can still provide 130 mA hg after 100 cycles. -1 The discharge specific capacity and coulombic efficiency are close to 100%, indicating that it has good cycle stability.

[0058] Figure 12 For lithium-iodine batteries using BPY-COF-HI as the positive electrode material, the range is 300-2000 mA g. -1 Rate performance test graph at current density, as shown Figure 12 As shown, when the current density increases from 2000 mA g -1 Recovery time to 300 mA g -1 When the discharge specific capacity can quickly return to the initial state, it indicates that it has good rate performance.

[0059] Example 4

[0060] The application of lithium-iodine battery cathodes based on pyridyl covalent-organic framework composites (BPY-COF@CNT-HI) includes the following steps:

[0061] The BPY-COF@CNT-HI prepared in Example 2 was mixed with carbon nanotubes and polyvinylidene fluoride binder at a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone was added and stirred to form a uniform slurry. The slurry was coated onto a 12 mm diameter circular hydrophilic carbon paper and vacuum dried at 80 °C for 12 h. A CR2032 coin cell was assembled using lithium metal as the counter electrode, Celgard 2400 as the separator, and 1M lithium bis(trifluoromethanesulfonyl)imide in 1,3-dioxolane (DOL): ethylene glycol dimethyl ether (DME) (1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane, and ethylene glycol dimethyl ether in a volume ratio of 1:1:1, with 2% LiNO3 added by mass) as the electrolyte.

[0062] Figure 13 For lithium-iodine batteries using BPY-COF@CNT-HI as the positive electrode material, at 300 mA g -1 Cyclic performance diagram at flux density, as shown Figure 13 As shown, at 300 mA g -1 At current density, the highest discharge specific capacity using BPY-COF-HI as the lithium-iodine cathode material can reach 233 mA hg. I -1 And it can still provide 169 mA hg after 100 cycles. -1 The discharge specific capacity and coulombic efficiency are close to 100%, indicating that it has good cycle stability.

[0063] Figure 14 For lithium-iodine batteries using BPY-COF@CNT-HI as the positive electrode material, the performance at 300-2000 mA g -1 Rate performance test graph at current density, as shown Figure 14 As shown, when the current density increases from 2000 mA g -1 Recovery time to 300 mA g -1 When the energy density returns to its initial state, it indicates that it has good rate performance.

[0064] The above embodiments are merely illustrative examples of the implementation of the present invention and are not intended to limit the present invention in any other way. Any simple modifications, substitutions, equivalent changes and modifications made without departing from the design and construction principles and spirit of the present invention are included within the protection scope of the present invention.

Claims

1. A pyridyl covalent-organic framework, the structure of which is shown in the following formula, abbreviated as BPY-COF-HI 。 2. The method for preparing the pyridyl covalent-organic framework according to claim 1, characterized in that, The process includes the following steps: 2,4,6-tricarboxymethyl phloroglucinol and 5,5'-diamino-2,2'-bipyridine are added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution, ultrasonically dispersed for several minutes, and degassed by several cycles of freezing-vacuuming-thawing. The reaction tube is then sealed and placed in an oven to react for several days. After the reaction is complete, the precipitate is collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone using Soxhlet extraction, and vacuum dried overnight to obtain BPY-COF. The BPY-COF material is dispersed in a mixed solution of methanol and hydroiodic acid (HI), stirred at room temperature in the dark, filtered to separate the solid powder, washed with methanol, and vacuum dried to obtain the protonated BPY-COF material BPY-COF-HI.

3. The method for preparing the pyridyl covalent-organic framework according to claim 1, characterized in that, The volume ratio of mesitylene, 1,4-dioxane, and 6 M acetic acid aqueous solution was 1.5 mL : 0.5 mL : 0.12 mL; the volume ratio of methanol to hydroiodic acid was 2 mL : 2 mL.

4. The application of the pyridyl covalent-organic framework according to claim 1, characterized in that, The preparation of the positive electrode for lithium-iodine batteries includes the following steps: pyridyl covalent organic framework BPY-COF-HI, carbon nanotubes, and polyvinylidene fluoride binder are mixed at a mass ratio of 6:3:

1. An appropriate amount of N-methylpyrrolidone is added and stirred to form a uniform slurry. The slurry is coated onto a circular hydrophilic carbon paper with a diameter of 12 mm and vacuum dried at 80°C for 12 h. A CR2032 coin cell is assembled using lithium as the counter electrode, Celgard 2400 as the separator, and 1M lithium bis(trifluoromethanesulfonyl)imide in 1,3-dioxolane DOL: ethylene glycol dimethyl ether DME as the electrolyte. The electrolyte contains 1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane DOL, and ethylene glycol dimethyl ether DME in a volume ratio of 1:1:1, and 2% LiNO3 is added by mass.

5. A pyridyl covalent-organic framework@carbon nanotube composite material, the pyridyl covalent-organic framework@carbon nanotube composite material is abbreviated as BPY-COF@CNT-HI, having the pyridyl covalent-organic framework shown in Formula I of claim 1.

6. The method for synthesizing the pyridyl covalent-organic framework@carbon nanotube composite material according to claim 5, characterized in that, The process includes the following steps: 2,4,6-tricarboxymethyl phloroglucinol, 5,5'-diamino-2,2'-bipyridine, and carbon nanotubes are added to a mixed solvent of mesitylene / 1,4-dioxane / 6 M acetic acid aqueous solution, ultrasonically dispersed for several minutes, degassed by several cycles of freezing-vacuuming-thawing, and then the reaction tube is sealed and placed in an oven to react for several days. After the reaction is completed, the precipitate is collected by centrifugation, washed with N,N-dimethylformamide (DMF), extracted with acetone using Soxhlet extraction, and vacuum dried overnight to obtain BPY-COF@CNT. The BPY-COF@CNT material is dispersed in a mixed solution of methanol and hydroiodic acid (HI), stirred at room temperature in the dark, filtered to separate the solid powder, washed with methanol, and vacuum dried to obtain the protonated material BPY-COF@CNT-HI.

7. The method for synthesizing pyridyl covalent-organic framework@carbon nanotube composite materials according to claim 6, characterized in that, The volume ratio of mesitylene, 1,4-dioxane, and 6 M acetic acid aqueous solution was 1.5 mL : 0.5 mL : 0.12 mL; the volume ratio of methanol to hydroiodic acid was 2 mL : 2 mL.

8. The application of the pyridine-based covalent-organic framework@carbon nanotube composite material according to claim 5, characterized in that, The preparation of the positive electrode for lithium-iodine batteries includes the following steps: pyridine-based covalent-organic framework@carbon nanotube composite material BPY-COF@CNT-HI, carbon nanotubes, and polyvinylidene fluoride binder are mixed at a mass ratio of 7:2:

1. An appropriate amount of N-methylpyrrolidone is added and stirred to form a uniform slurry. The slurry is coated onto a 12 mm diameter circular hydrophilic carbon paper and vacuum dried at 80°C for 12 h. A CR2032 coin cell is assembled using lithium as the counter electrode, Celgard 2400 as the separator, and 1M lithium bis(trifluoromethanesulfonyl)imide in 1,3-dioxolane DOL: ethylene glycol dimethyl ether DME as the electrolyte. The electrolyte contains 1M lithium bis(trifluoromethanesulfonyl)imide, 1,3-dioxolane DOL, and ethylene glycol dimethyl ether DME in a volume ratio of 1:1:1, and 2% LiNO3 is added by mass.

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