A rigid-flexible adjustable triangular COF material and a preparation method and application thereof

Abstract

The application relates to the technical field of battery positive electrode materials, in particular to a rigid-flexible adjustable triangular COF material and a preparation method and application thereof. The preparation method comprises the following steps: dissolving flexible unit material and rigid unit material in a mixed solvent of 1,2-dichlorobenzene and n-butanol according to a molar ratio of 9:1, adding acetic acid as a catalyst to obtain a mixed solution; transferring the mixed solution into a pressure-resistant reaction kettle, sealing, reacting at 120 DEG C, carrying out centrifugal treatment after the reaction is completed, and collecting the product; sequentially washing the centrifugal product with tetrahydrofuran, acetone and methanol, vacuum drying at 80 DEG C after the washing, and obtaining a powder-shaped CTP-COF; mixing the powder-shaped CTP-COF with sulfur powder according to a mass ratio of 1:2, melting and diffusing in a closed container under an argon atmosphere at 155 DEG C after the mixing, grinding the melted product after the cooling, and obtaining a triangular COF material. The application improves the performance of the battery by regulating the proportion of the rigid unit material and the flexible unit material in the COF skeleton.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, and in particular to a triangular COF material with adjustable rigidity and flexibility, its preparation method and application. Background Technology

[0002] Lithium-sulfur batteries are considered one of the next-generation high-energy-density rechargeable battery systems due to the high theoretical specific capacity and high theoretical energy density of their sulfur cathode. However, in practical applications, lithium-sulfur batteries still face problems such as the polysulfide shuttle effect, poor conductivity of sulfur and its discharge products, and volume expansion during charge and discharge, which severely limit their cycle stability and rate performance. To suppress the diffusion of polysulfides, existing technologies typically employ porous carbon materials or metal-organic framework materials to physically confine or chemically adsorb sulfur.

[0003] However, carbon-based materials mainly rely on physical confinement, making it difficult to effectively suppress the migration of long-chain polysulfides. While metal-organic frameworks possess some chemisorption capacity, they are prone to structural collapse during electrochemical cycling, affecting long-term stability. Furthermore, traditional covalent organic frameworks have a rigid skeleton and lack the dynamic adaptability to configurational changes of polysulfide molecules during charge and discharge. Excessive introduction of flexible units can lead to channel disorder or even collapse, thereby reducing ion transport efficiency and structural stability.

[0004] Therefore, there is a need for a method for preparing COF materials and its applications that can maintain the stability of the COF pore structure while achieving synergistic control of the material's rigidity and flexibility. Summary of the Invention

[0005] The main objective of this invention is to provide a triangular COF material with adjustable rigidity and flexibility, its preparation method, and its application, aiming to solve the problems of insufficient stability of the pore structure and difficulty in controlling rigidity and flexibility in existing COF materials.

[0006] To achieve the above objectives, this invention proposes a method for preparing a triangular COF material with adjustable rigidity and flexibility, the method comprising the following steps:

[0007] The flexible unit material and the rigid unit material were dissolved in a mixed solvent of 1,2-dichlorobenzene and n-butanol in a molar ratio of 9:1, and 0.2 mL of acetic acid was added as a catalyst to obtain a mixed solution.

[0008] The mixed solution was transferred to a pressure-resistant reactor, sealed, and reacted at 120°C for 72 hours. After the reaction was completed, the mixture was centrifuged and the product was collected.

[0009] The centrifuged product was washed sequentially with tetrahydrofuran, acetone and methanol, and then vacuum dried at 80°C for 12 h to obtain powdered CTP-COF.

[0010] Powdered CTP-COF and sulfur powder were mixed at a mass ratio of 1:2. After mixing, the mixture was transferred to a sealed container and melted and diffused at 155°C for 12 hours under an argon atmosphere. After cooling, the melted product was ground to obtain triangular COF material.

[0011] Furthermore, the flexible unit material is CTP-6-CHO, and the rigid unit material is one of short-chain rigid aromatic diamines (PPD), benzidine (BD), and methyldiamine (MDA).

[0012] Furthermore, the flexible unit material is a flexible molecular unit with multiple connecting arms, the number of connecting arms being no less than 3, and the rigid unit material is a multifunctional connector with an aromatic skeleton.

[0013] Furthermore, the molecular chain length of the rigid unit material is 0.5~2.0 nm.

[0014] The present invention also proposes a COF material, which is obtained by the preparation method of the rigid-flexible triangular COF material described in any of the above technical solutions. The COF material includes rigid unit materials and flexible unit materials, and the rigid unit materials and the flexible unit materials cooperate to form a topological structure. The topological structure includes at least one of polygonal topological structure, star topological structure, and through-type mesh structure.

[0015] Furthermore, the topology is a triangular topology.

[0016] Furthermore, the COF material has an average pore size of 1.2~4.0 nm and a specific surface area of ​​200~800 m². 2 / g.

[0017] The present invention also proposes the application of the rigidity-flexibility adjustable triangular COF material described in any of the above technical solutions in the preparation of electrode materials.

[0018] Furthermore, the application of the method for preparing the rigid-flexible triangular COF material in the preparation of electrode materials also includes an active substance loaded in the pores of the COF material, wherein the active substance is sulfur and the sulfur loading is 50~80wt%.

[0019] The present invention also proposes the application of the rigidity-flexibility adjustable triangular COF material of any of the above technical solutions in the preparation of electrochemical devices.

[0020] This invention constructs a triangular topological COF material that combines structural stability and dynamic adaptability by adjusting the ratio of rigid to flexible unit materials in the COF framework. This synergistically enhances the confinement capability of polysulfides and ion transport performance of the lithium-sulfur battery cathode, thereby improving the cycle stability and rate performance of the battery. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the processes shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart illustrating a method for preparing a rigid-flexible triangular COF material according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of a COF structure with a triangular topology provided in an embodiment of the present invention;

[0024] Figure 3 XRD patterns of COF in Examples 1-3 of this invention; wherein, Figure 3 (a) XRD pattern of COF in Example 1 provided by the present invention; Figure 3 (b) XRD pattern of COF in Example 2 provided by the present invention; Figure 3 (c) The XRD pattern of COF in Example 3 provided by the present invention;

[0025] Figure 4 The variable-temperature in-situ XRD characterization of the stiffness-flexibility gradient changes in Examples 1-3 of this invention are provided; wherein, Figure 4 (a) A variable-temperature in-situ XRD characterization of the rigidity-flexibility gradient variation of Example 1 provided by the present invention; Figure 4 (b) A variable-temperature in-situ XRD characterization of the rigidity-flexibility gradient variation of Example 2 provided by the present invention; Figure 4 (c) is a variable-temperature in-situ XRD characterization of the rigidity-flexibility gradient in Example 3 provided by the present invention;

[0026] Figure 5 The first-cycle performance curves of the cathode materials prepared in Examples 1-3 of this invention are shown in the figure; wherein, Figure 5 (a) First-cycle performance curve of the cathode material prepared in Example 1 of the present invention; Figure 5 (b) A graph showing the first cycle performance of the cathode material prepared in Example 2 of this invention; Figure 5 (c) A graph showing the first cycle performance of the cathode material prepared in Example 3 of this invention;

[0027] Figure 6 Rate performance curves of the cathode materials prepared in Examples 1-3 of this invention are provided; wherein, Figure 6 (a) Rate performance curve of the cathode material prepared in Example 1 of the present invention; Figure 6 (b) Rate performance curve of the cathode material prepared in Example 2 of the present invention; Figure 6 (c) A rate performance curve of the cathode material prepared in Example 3 of the present invention;

[0028] Figure 7 This is a performance comparison diagram of the COF materials prepared in Examples 1, 2, and 3 of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0031] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0032] It is understandable that traditional covalent organic frameworks (COFs) have a rigid skeleton and lack the ability to dynamically adapt to the configurational changes of polysulfide molecules during charging and discharging. If it is necessary to improve the dynamic adaptability of COFs, flexible unit materials need to be introduced. However, excessive introduction of flexible unit materials into COFs can lead to channel disorder or collapse, reducing ion transport efficiency and structural stability.

[0033] This invention utilizes polygonal topological design to control the rigidity-flexibility ratio of covalent organic framework (COF) materials. Using multi-arm flexible unit materials (n≥3) as the structural core, rigid aromatic polyamine linkers of varying chain lengths are introduced. Through dynamic covalent bonding, a COF material with a triangular topological structure is formed. By adjusting the molecular chain length of the linkers, precise control of the pore size of the COF material is achieved, resulting in an adjustable rigidity-flexibility pore structure within the COF material. The rigid unit materials maintain the regularity and structural stability of the pores, while the flexible unit materials dynamically adapt to the configurational changes of polysulfide molecules during electrochemical cycling, thereby achieving effective confinement and stable transport of polysulfides. The BET specific surface area of ​​the COF material involved in this invention is 200~800 m². 2 / g, with an average pore size of 1.2~4.0nm.

[0034] Based on this, the present invention proposes a method for preparing a triangular COF material with adjustable rigidity and flexibility, referring to... Figures 1-2 As shown, the preparation method involves the following steps:

[0035] Step S10: Dissolve the flexible unit material and the rigid unit material in a molar ratio of 9:1 in a mixed solvent of 1,2-dichlorobenzene and n-butanol, and add 0.2 mL of acetic acid as a catalyst to obtain a mixed solution;

[0036] Step S20: Transfer the mixed solution to a pressure-resistant reactor, seal it, and react at 120°C for 72 hours. After the reaction is completed, centrifuge and collect the product.

[0037] In step S30, the centrifuged product was washed sequentially with tetrahydrofuran, acetone and methanol, and then vacuum dried at 80°C for 12 h to obtain powdered CTP-COF.

[0038] Step S40: Powdered CTP-COF and sulfur powder are mixed at a mass ratio of 1:2. After mixing, the mixture is transferred to a sealed container and melted and diffused at 155°C for 12 hours under an argon atmosphere. After cooling, the melted product is ground to obtain triangular COF material.

[0039] The flexible unit material involved in this invention is CTP-6-CHO, which is hexa(4-formyl-phenoxy)cyclotriphosphonic cyclic alkene, wherein the specific structural formula of CTP is as follows:

[0040]

[0041] The rigid unit materials involved in this invention are PPD (p-phenylenediamine), BD (benzidine), and MDA (4,4'-diaminodiphenylmethane), with the following specific structural formulas:

[0042] PPD:

[0043]

[0044] BD:

[0045]

[0046] MDA:

[0047]

[0048] This invention discloses a method for preparing a triangular COF material with adjustable rigidity and flexibility, and provides the following three sets of examples and two sets of comparative examples, as detailed below:

[0049] Example 1

[0050] Preparation steps:

[0051] Step S1: Using a multi-arm flexible unit (CTP-6-CHO) and a short-chain rigid aromatic diamine (PPD) as the substrate, the six-arm flexible unit CTP-6-CHO (0.2 mmol) and phenylenediamine (PPD, chain length 0.5 nm) are dissolved in a mixed solvent of 1,2-dichlorobenzene and n-butanol (volume ratio 3:1) at a molar ratio of 9:1, and 0.2 mL of acetic acid is added as a catalyst to carry out the reaction, and a mixed solution is obtained.

[0052] Step S2: Transfer the mixed solution to a pressure-resistant reactor, seal it, and react at 120 °C for 72 hours. After the reaction is completed, collect the product by centrifugation, wash it three times with tetrahydrofuran, acetone and methanol in sequence, and dry it under vacuum at 80 °C for 12 hours to obtain a light yellow powder CTP-COF-1.

[0053] Step S3: CTP-COF-1 and sulfur powder are mixed at a mass ratio of 1:2, placed in a sealed quartz tube, and melted and diffused at 155°C for 12 hours under argon protection. After cooling, the mixture is ground uniformly to obtain S@CTP-COF-1 composite material with a sulfur loading of 62 wt%.

[0054] This embodiment illustrates the feasibility of constructing triangular topological covalent organic framework materials using short-chain rigid connectors, and the pore characteristics of the material under a semi-rigid framework structure and their impact on the performance of lithium-sulfur batteries.

[0055] This embodiment uses a rigid aromatic diamine with a short molecular chain as a linker. The resulting covalent organic framework material has a small pore size and high skeletal stability, enabling the formation of a regular and stable pore structure. This embodiment, as a representative of a relatively rigid structure, provides a benchmark for comparing the rigid-flexible synergistic regulation effect in subsequent embodiments, thus demonstrating that relying solely on a rigid pore structure is insufficient to simultaneously achieve both the dynamic adaptation of polysulfides and ion transport performance.

[0056] Example 2

[0057] Preparation steps:

[0058] Step S1: Using a multi-arm flexible unit (CTP-6-CHO) and benzidine diamine (BD, chain length 1.05 nm) as the substrate, the six-arm flexible unit CTP-6-CHO (0.2 mmol) and benzidine diamine (BD, chain length 1.05 nm) are dissolved in a mixed solvent of 1,2-dichlorobenzene and n-butanol (volume ratio 1:1) at a molar ratio of 9:1, and 0.2 mL of acetic acid is added as a catalyst to carry out the reaction, and a mixed solution is obtained.

[0059] Step S2: Transfer the mixed solution to a pressure-resistant reactor, seal it, and react at 120°C for 72 hours. After the reaction is completed, collect the product by centrifugation, wash it three times with tetrahydrofuran, acetone and methanol in sequence, and dry it under vacuum at 80°C for 12 hours to obtain light yellow powder CTP-COF-2.

[0060] Step S3: CTP-COF-2 and sulfur powder are mixed at a mass ratio of 1:2 and placed in a sealed quartz tube. Under argon protection, the mixture is melted and diffused at 155°C for 12 hours. After cooling, it is ground uniformly to obtain an S@CTP-COF-2 composite material with a pore size of 1.8 nm and a sulfur loading of 65 wt%.

[0061] This embodiment illustrates the technical effect of synergistically controlling the rigidity-flexibility ratio of covalent organic framework materials by adjusting the linker chain length. Compared to Embodiment 1, this embodiment uses a medium-length rigid aromatic diamine linker. While maintaining the stability of the triangular topological framework structure, it introduces appropriate structural flexibility, allowing the material channels to dynamically adapt to changes in polysulfide chain length during electrochemical processes. Through this rigid-flexible synergistic structural design, the resulting covalent organic framework material significantly improves the confinement ability of polysulfides and lithium-ion transport efficiency while ensuring channel continuity and structural stability, thus exhibiting excellent cycle stability and rate performance in lithium-sulfur batteries. This embodiment is used to verify the preferred embodiment of the technical solution of the present invention and serves as a main supporting example of the technical effect of the present invention.

[0062] Example 3

[0063] Preparation steps:

[0064] Step S1: Using a multi-arm flexible unit (CTP-6-CHO) and methyldiamine (MDA, chain length 1.1 nm) as substrates, the six-arm flexible unit CTP-6-CHO (0.2 mmol) and methyldiamine (MDA, chain length 1.1 nm) are dissolved in a mixed solvent of 1,2-dichlorobenzene and n-butanol (volume ratio 1:1) at a molar ratio of 9:1, and 0.2 mL of acetic acid is added as a catalyst to carry out the reaction, resulting in a mixed solution.

[0065] Step S2: Transfer the mixed solution to a pressure-resistant reactor, seal it, and react at 120 °C for 72 hours. After the reaction is completed, collect the product by centrifugation, wash it three times with tetrahydrofuran, acetone and methanol in sequence, and dry it under vacuum at 80 °C for 12 hours to obtain light yellow powder CTP-COF-3.

[0066] Step S3: CTP-COF-3 and sulfur powder are mixed at a mass ratio of 1:2 and placed in a sealed quartz tube. Under argon protection, the mixture is melted and diffused at 155°C for 12 hours. After cooling, it is ground uniformly to obtain an S@CTP-COF-3 composite material with a pore size of 2.0 nm and a sulfur loading of 65 wt%.

[0067] This embodiment illustrates the adverse effects on the structural stability and electrochemical performance of materials when the linker chain length is further increased and the flexible proportion of the covalent organic framework material is too high.

[0068] While using longer linkers can further increase the material pore size and enhance its flexible response, excessive flexibility leads to a decrease in pore regularity and a weakening of local structural stability, thereby affecting the effective confinement of polysulfides and the continuity of ion transport.

[0069] This embodiment, compared with Embodiment 2, further demonstrates the necessity of achieving synergistic regulation of rigidity and flexibility by reasonably controlling the length of the connector chain in this invention, illustrating that a higher flexibility ratio is not necessarily more beneficial to improving the performance of lithium-sulfur batteries.

[0070] Comparative Example 1

[0071] Preparation materials: Multi-walled carbon nanotubes were used as carriers with a sulfur loading of 60 wt%.

[0072] Preparation steps: Multi-walled carbon nanotubes (CNTs) and sulfur powder were mixed at a mass ratio of 1:2 and placed in a sealed quartz tube. The mixture was melted and diffused at 155°C for 12 hours under argon protection. After cooling, the mixture was ground uniformly to form an S@CNT composite material with a sulfur loading of 60wt%.

[0073] Comparative Example 1, prepared using conventional carbon-based materials, demonstrates the performance of porous carbon materials, commonly used in the prior art, as sulfur carriers in lithium-sulfur batteries. This comparative example primarily relies on physical confinement to suppress polysulfide diffusion, lacking chemical confinement and dynamic structural adaptation capabilities. During charge and discharge, polysulfides readily dissolve and migrate, leading to rapid capacity decay.

[0074] By comparing the performance of Examples 1-3 of the present invention with that of Comparative Example 1, it can be seen that the COF composite material of the present invention has significant advantages in polysulfide confinement capability and cycle stability compared with the prior art.

[0075] Comparative Example 2

[0076] Preparation materials: CNT-8 was used as the carrier, with a sulfur loading of 60 wt%.

[0077] Preparation steps: ZIF-8 and sulfur powder are mixed at a mass ratio of 1:2 and placed in a sealed quartz tube. Under argon protection, the mixture is melted and diffused at 155°C for 12 hours. After cooling, it is ground uniformly to form a S@ZIF-8 composite material with a sulfur loading of 60wt%.

[0078] Comparative Example 2 uses CNT-8 metal-organic frameworks (MOFs) to illustrate the application effect of porous framework materials without rigid-flexible synergistic regulation in lithium-sulfur batteries. Although such materials possess certain pore structures and chemisorption capabilities, their rigid or purely flexible framework structures make it difficult to simultaneously meet the requirements of structural stability and dynamic adaptability during electrochemical cycling, thus limiting cycle performance and rate performance. A comparison between Comparative Example 2 and Example 2 of this invention further verifies the significant advantages of this invention in improving the overall performance of lithium-sulfur batteries through polygonal topology design that achieves rigid-flexible synergistic regulation.

[0079] like Figures 3-6As shown, the present invention also discloses the structural characterization and electrochemical performance of Examples 1-3, as detailed below:

[0080] Example 1:

[0081] Structural characterization:

[0082] XRD analysis: such as Figure 3 As shown in (a), the XRD pattern of CTP-COF-1 shows a strong diffraction peak at 5°, corresponding to the (100) crystal plane. The secondary peaks are located at 3°, 5° and 6°, corresponding to the (200), (300) and (201) crystal planes, respectively, indicating that it has a triangular topological structure with AA stacking.

[0083] Variable temperature in-situ XRD: such as Figure 4 As shown in (a), the characteristic peak shift of CTP-COF-2 is Δ2θ=0.3° in the range of 25-150℃, indicating that it has a moderate stiffness-flexibility ratio.

[0084] Electrochemical performance:

[0085] First lap capacity: such as Figure 5 As shown in (a), at a current density of 0.1C, the first discharge capacity of the S@CTP-COF-1 battery (the battery prepared with the S@CTP-COF-1 composite material in Example 1) is 1337 mAh / g, and the plateau voltage is stable at 2.3V (reduction) and 2.4V (oxidation).

[0086] Cyclic stability: such as Figure 7 As shown, after 200 cycles at 0.1C, the capacity retention rate is 97.5%, and the capacity decay rate is 0.25%.

[0087] Ratio performance: such as Figure 6 As shown in (a), the reversible capacity of 434 mAh / g can still be maintained at a high rate of 2.0C, and the capacity recovers to 1135 mAh / g when restored to 0.1C.

[0088] Example 2:

[0089] Structural characterization:

[0090] XRD analysis: such as Figure 3 As shown in (b), the (100) crystal plane peak of CTP-COF-2 is located at 6°, and the secondary peaks (200) and (300) are shifted to the left, indicating that the pore size has been expanded to 1.8 nm;

[0091] Variable temperature in-situ XRD: such as Figure 4 As shown in (b), the characteristic peak shift of CTP-COF-2 is Δ2θ=0.6° in the range of 25-150℃, indicating that it has a moderate stiffness-flexibility ratio.

[0092] Electrochemical performance:

[0093] First lap capacity: such as Figure 5 As shown in (b), at a current density of 0.1C, the first discharge capacity of the S@CTP-COF-2 battery (the battery prepared with the S@CTP-COF-2 composite material in Example 2) is 1462 mAh / g, which is significantly higher than that of the S@CTP-COF-1 battery (1337 mAh / g).

[0094] Cyclic stability: such as Figure 7 As shown, after 200 cycles at 0.1C, the capacity retention rate is 99.1%, and the decay rate is only 0.079%.

[0095] Ratio performance: such as Figure 6 As shown in (b), the reversible capacity of 850 mAh / g can still be maintained at a high rate of 2.0C, and the capacity recovers to 1190 mAh / g when restored to 0.1C.

[0096] Example 3

[0097] Structural characterization:

[0098] Variable temperature in-situ XRD: such as Figure 4 As shown in (c), CTP-COF-3 exhibits the largest characteristic peak shift (Δ2θ=0.8°) when the temperature changes, indicating that it has the highest flexibility.

[0099] Electrochemical performance:

[0100] First lap capacity: such as Figure 5 As shown in (c), at a current density of 0.1C, the first discharge capacity of the S@CTP-COF-3 battery (the battery prepared with the S@CTP-COF-3 composite material in Example 3) is 1099 mAh / g, which is lower than that of the S@CTP-COF-2 battery.

[0101] Cyclic stability: such as Figure 7 As shown, after 200 cycles at 0.1C, the capacity retention rate is 98.9% and the decay rate is 0.11%.

[0102] Ratio performance: such as Figure 6 As shown in (c), the reversible capacity of 432 mAh / g can still be maintained at a high rate of 2.0C, and the capacity recovers to 1049 mAh / g when restored to 0.1C.

[0103] Comparative Example 1:

[0104] Electrochemical performance:

[0105] First-cycle capacity: At a current density of 0.1C, the first-cycle discharge capacity of the battery in Comparative Example 1 (the battery prepared with the materials in Comparative Example 1) is 980 mAh / g.

[0106] Cyclic decay rate: After 100 cycles at 0.5 C, the decay rate reaches 1.2%, indicating insufficient physical confinement capability.

[0107] Comparative Example 2:

[0108] Electrochemical performance:

[0109] First-cycle capacity: At a current density of 0.1C, the first-cycle discharge capacity of the battery in Comparative Example 2 (the battery prepared with the materials in Comparative Example 1) is 1200 mAh / g, and at 0.1C it is 1200 mAh / g.

[0110] Cyclic stability: After 50 cycles at 0.5 C, the capacity retention rate is only 80%, and the channel collapse is significant.

[0111] The specific performance data of the samples prepared in Examples 1-3 and Control Examples 1-2 and the batteries prepared therefrom are shown in the table below:

[0112] Table 1. Performance of the samples prepared in Examples 1-3 and Control Examples 1-2 and the batteries prepared therefrom.

[0113]

[0114] In summary, the experimental data of this invention show that: the smaller the aperture (Examples 1-3), the higher the rigidity ratio, resulting in increased first-cycle capacity but slightly decreased cycle stability; the larger the aperture, the higher the flexibility ratio, resulting in enhanced cycle stability but decreased first-cycle capacity, with Example 2 being the optimal balance point. Furthermore, as... Figure 7 As shown, under a high current density of 0.5C, Example 2 also exhibits the same phenomenon. After 200 cycles, the capacity decay rate is only 0.079%, while the capacity decay rate of Example 1 is 0.25% and the capacity decay rate of Example 3 is 0.11%. This further proves that by adjusting the flexibility of the chain length structure, Example 2, which reaches the optimal balance point, can obtain the optimal first-cycle capacity and the best cycle stability.

[0115] The COF material in this invention is constructed through dynamic covalent bonds, which include at least one of imine bonds and borate ester bonds.

[0116] Furthermore, the flexible unit material is CTP-6-CHO, and the rigid unit material is one of the following: short-chain rigid aromatic diamine (PPD), benzidine (BD), and methyldiamine (MDA).

[0117] In detail, the flexible unit material in this invention is used to dynamically adapt to the configurational changes of the target molecule during the electrochemical reaction. By adjusting the structural parameters of the rigid unit material and the flexible unit material, the COF material can effectively confine the reaction intermediate while maintaining a continuous ion transport channel. The guest molecule is an active substance that undergoes configurational changes during the reaction. The active substance includes polysulfides, polyselenides or other soluble intermediates.

[0118] Furthermore, the flexible unit material is a flexible molecular unit with multiple connecting arms, the number of connecting arms being no less than 3, and the rigid unit material is a multifunctional connector with an aromatic skeleton.

[0119] Furthermore, the molecular chain length of the rigid unit material is 0.5~2.0 nm.

[0120] This invention also proposes a COF material, which is obtained by any of the above technical solutions for preparing a rigid-flexible triangular COF material. The COF material includes rigid unit materials and flexible unit materials, and the rigid unit materials and flexible unit materials work together to form a topological framework structure.

[0121] Furthermore, the topology is a triangular topology.

[0122] Furthermore, the COF materials have an average pore size of 1.2–4.0 nm and a specific surface area of ​​200–800 m². 2 / g.

[0123] The present invention also proposes an electrode material, comprising a COF material prepared by any of the above-described methods for preparing a rigid-flexible triangular COF material, and an active substance loaded in the pores of the COF material.

[0124] Furthermore, the active substance is sulfur, with a sulfur loading of 50-80 wt%.

[0125] The present invention also proposes an electrochemical device comprising a COF material according to any of the above technical solutions.

[0126] In the electrochemical device involved in this invention, by adjusting the ratio of rigid unit materials to flexible unit materials in the COF framework, a triangular topological COF material with both structural stability and dynamic adaptability is constructed, thereby synergistically improving the confinement ability of lithium-sulfur battery cathode for polysulfides and ion transport performance, and improving the cycle stability and rate performance of the electrochemical device.

[0127] The COF material of this invention achieves synergistic regulation of the stability of rigid channels and the dynamic adaptability of flexible structures through polygonal topology design, effectively suppressing the polysulfide shuttle effect. The adjustable pore size structure involved in this invention provides continuous ion transport channels while ensuring polysulfide confinement capability, significantly improving electrode reaction kinetics performance. The preparation method is simple, the conditions are controllable, the material structure is stable, suitable for large-scale preparation, and has good prospects for industrial application.

[0128] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a triangular COF material with adjustable rigidity and flexibility, characterized in that, Includes the following steps: The flexible unit material and the rigid unit material were dissolved in a mixed solvent of 1,2-dichlorobenzene and n-butanol in a molar ratio of 9:1, and 0.2 mL of acetic acid was added as a catalyst to obtain a mixed solution. The mixed solution was transferred to a pressure-resistant reactor, sealed, and reacted at 120°C for 72 hours. After the reaction was completed, the mixture was centrifuged and the product was collected. The centrifuged product was washed sequentially with tetrahydrofuran, acetone and methanol, and then vacuum dried at 80°C for 12 h to obtain powdered CTP-COF. Powdered CTP-COF and sulfur powder were mixed at a mass ratio of 1:

2. After mixing, the mixture was transferred to a sealed container and melted and diffused at 155°C for 12 hours under an argon atmosphere. After cooling, the melted product was ground to obtain triangular COF material.

2. The method for preparing the rigid-flexible triangular COF material as described in claim 1, characterized in that, The flexible unit material is CTP-6-CHO, and the rigid unit material is one of short-chain rigid aromatic diamines (PPD), benzidine (BD), and methyldiamine (MDA).

3. The method for preparing the rigid-flexible triangular COF material as described in claim 2, characterized in that, The flexible unit material is a flexible molecular unit with multiple connecting arms, the number of connecting arms being no less than 3, and the rigid unit material is a multifunctional connector with an aromatic skeleton.

4. The method for preparing the rigid-flexible triangular COF material as described in claim 1, characterized in that, The molecular chain length of the rigid unit material is 0.5~2.0 nm.

5. A COF material, characterized in that, The COF material is obtained by the preparation method of the rigid-flexible triangular COF material according to any one of claims 1-4. The COF material includes rigid unit materials and flexible unit materials. The rigid unit materials and the flexible unit materials cooperate to form a topological structure. The topological structure includes at least one of polygonal topological structure, star topological structure, and through-type mesh structure.

6. The COF material as described in claim 5, characterized in that, The topology is a triangular topology.

7. The COF material as described in claim 6, characterized in that, The COF material has an average pore size of 1.2~4.0 nm and a specific surface area of ​​200~800 m². 2 / g.

8. The application of the rigidity-flexibility adjustable triangular COF material as described in any one of claims 1-4 in the preparation of electrode materials.

9. The application of the COF material as described in claim 8, characterized in that, The method for preparing the rigid-flexible triangular COF material also includes the application of an active substance loaded in the pores of the COF material in the preparation of electrode materials. The active substance is sulfur, and the sulfur loading is 50~80wt%.

10. The application of the rigid-flexible triangular COF material as described in any one of claims 1-4 in the preparation of electrochemical devices.

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