Preparation method and application of COFs with three-element molecular junction

Abstract

The invention discloses a symmetrical all-organic battery (SAPBs) prepared based on the same organic electrode material, the COFs electrode material with a three-element molecular junction is obtained through in-situ polymerization under the solvent-free condition by an organic fluxing method, the three elements are azo, triazine and anhydride functional groups respectively, the accumulation mode is ABC accumulation, and the COFs electrode material with the three-element molecular junction is obtained. The electrode has the characteristics of excellent electrode compatibility, compensable volume change, complete discharge capacity, low preparation cost, simple operation procedure and the like. The assembled symmetric all-organic battery shows excellent rate capability, high energy density and excellent long cycle performance, and the feasibility of practical application is verified by successfully assembling a soft package battery.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation and application of covalent organic framework composites, and specifically refers to a three - element molecular junction COFs material, a preparation method thereof, and an application thereof. Background Art

[0002] Compared with traditional metal - containing inorganic electrode materials, organic electrode materials have the advantages of environmental friendliness, light weight, high energy density, and good intrinsic flexibility. It is possible to replace commercial graphite anodes or transition metal oxide materials. With the development of organic electrode materials, Nishide's group first proposed the concept of all - organic batteries (AOBs) based on poly(p - type) cathodes and poly(n - type) anodes in 2009. However, the low working voltage and low capacity limit the performance of the batteries. So far, many breakthroughs have been made in organic electrode materials, which can be mainly divided into p - type, n - type, or bipolar. Generally speaking, p - type materials are mainly used as cathodes, n - type organic materials can be used as cathodes or anodes, and bipolar materials have both of these characteristics in battery applications. With the rapid development of battery technology, the requirements for organic electrode materials will be more complex, which requires specific designs to integrate various functions to maximize the overall advantages of organic electrode materials in batteries.

[0003] As a unique type of AOBs, symmetric all - organic batteries (SAOBs) that use the same organic electrode material for both the cathode and the anode have been widely developed in the past decade. They have the advantages of high active - site utilization rate, simplified assembly process, good electrode compatibility, low manufacturing cost, and compensable volume change. In addition, SAOBs have the potential to discharge to 0V to achieve full discharge and higher capacity. Nevertheless, the design of dual - electrode available materials for SAOBs still faces the following challenges: (1) The organic electrode material should contain dual - electrode active functions to meet the voltage requirements of both the cathode and the anode to ensure proper voltage output; (2) Excellent negative - electrode and cathode compatibility are required to ensure that SAOBs can achieve fast charge - discharge, full discharge, and satisfactory cycle stability; (3) The synthesis procedure of organic battery materials is preferably simple and low - cost for large - scale preparation. Therefore, new dual - electrode available materials must be developed to overcome the above - mentioned challenges. So far, some organic small molecules and covalent organic polymers have been used as anode and cathode materials in SAOBs. However, the high solubility of organic small molecules or the unmet functions triggered by the limited mono - motif or bi - motif units of covalent organic polymers hinder their application in SAOBs. In this regard, it is very necessary to explore new heterogeneous electrode materials with multiple functions and high stability to expand the limits of SAOBs.

[0004] Covalent organic frameworks (COFs) combine the characteristics of low density, excellent stability, and tunable functions, making them a superior platform for constructing promising SAOBs electrode materials. Compared with the reported SAOBs organic materials, COFs have the following advantages in the application of SAOBs: (1) The tunability of COFs can achieve the coupling of dual-electrode active functional substituents to endow high specific capacity, while meeting the requirements of both the cathode and the anode; (2) The low density may bring high theoretical capacity and high stability of COFs, which may avoid dissolution and structural damage during repeated cycling; (3) Uniform pore channels and abundant redox-active sites can accelerate Li+ or electron transport, achieving excellent rate performance; (4) Some simple COFs synthesis methods, such as the machine-assisted melting method, can achieve the large-scale synthesis of COFs, promoting the potential industrial-scale application of COF-based electrode materials. In the past few decades, COFs have been applied as single positive or negative electrode materials in organic batteries. However, due to the lack of COFs with bifunctional available functional groups, the application of COFs in SAOBs is rare.

[0005] In view of the reported work on p-type, n-type, or bipolar electrode materials, we propose to design a three-motif molecular junction COF containing positive electrode active n-type functional groups, negative electrode active n-type functional groups, and bipolar functional groups, which can provide a tunable voltage sensing effect and greatly increase the compatibility between the positive and negative electrodes of SAOBs. However, to the best of our knowledge, the application of three-motif molecular junction COF in SAOBs has not been reported and is a research direction to be explored.

[0006] In the present invention, we designed a three-motif molecular junction COF (i.e., TAT-AZO-COF) by the organic melting method, which can be used as the negative and positive electrode materials of SAOBs. This work focuses on the concept of motif molecular junction COF, which may promote the development of porous crystalline materials in SAOBs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a preparation method of a COFs electrode material with a three-motif molecular junction and its application in symmetric all-organic batteries.

[0008] To solve the above technical problems, the technical solution provided by the present invention is: A preparation method of a COFs with a three-motif molecular junction, comprising the following steps:

[0009] Step 1: Prepare organic ligands;

[0010] Step 2: In-situ polymerize the organic ligands by the organic melting method to obtain a COFs electrode material with a three-motif molecular junction.

[0011] Preferably, the organic ligand includes 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 4,4'-(1,2-diazanedicarbonyl)bis-1,2-benzenedicarboxylic acid, and the organic flux is benzoic acid.

[0012] Preferably, the organic ligand and benzoic acid are mixed and frozen by pumping. After the reaction is completed, the product is filtered by suction to obtain a three-component molecular junction COFs electrode material.

[0013] Preferably, the organic flux method includes:

[0014] The organic ligand and benzoic acid are mixed into a Pyrex tube and vacuum-sealed at a temperature of 220 °C for 72 hours;

[0015] The obtained product is filtered and soaked in tetrahydrofuran for 24 hours. After soaking, the product is dried under vacuum at 120 °C for 12 h to obtain a three-component molecular junction COFs electrode material.

[0016] Preferably, the ratio of the organic ligand to benzoic acid is: 2,4,6-tris(4-aminophenyl)-1,3,5-triazine: 4,4'-(1,2-diazanedicarbonyl)bis-1,2-benzenedicarboxylic acid: benzoic acid = 0.1 mmol, 35.4 mg: 0.15 mmol, 53.7 mg: 0.6 mmol, 73.3 g.

[0017] On the other hand, the present invention discloses a three-component molecular junction COFs, the three components are azo, triazine and anhydride functional groups respectively, the structure stacking mode is ABC stacking, and the COF is TAT-AZO-COF.

[0018] On the other hand, the present invention discloses the application of a three-component molecular junction COFs in a symmetric all-organic battery.

[0019] Preferably, the application of the three-component molecular junction COFs in the negative and positive electrode materials of a symmetric all-organic battery is disclosed.

[0020] The advantages of the present invention compared with the prior art are as follows:

[0021] The present invention adopts an organic flux method and successfully prepares a three-component molecular junction COFs (i.e., TAT-AZO-COF), which can be used as the dual-electrode active material of a symmetric all-organic battery. TAT-AZO-COF has high stability and abundant redox sites, which can meet the requirements of SAOBs at the same time;

[0022] The material provided by the present invention exhibits excellent battery performance, can be used as a prospective electrode material for symmetric all-organic batteries, and will stimulate the research and development of organic materials with better electrochemical performance.

[0023] The three - building - block molecular - knot COF electrode material has high porosity, high stability, and abundant redox sites, which can meet most of the important parameters required for practical applications. As an electrode material for symmetric all - organic batteries, it has excellent battery performance. Description of the Drawings

[0024] Figure 1 PXRD pattern of the TAT - AZO - COF obtained in the present invention;

[0025] Figure 2 FTIR, nitrogen adsorption, SEM, and TEM images of the TAT - AZO - COF obtained in the present invention;

[0026] Figure 3 Performance graphs of the TAT - AZO - COF obtained in the present invention for symmetric all - organic batteries. Detailed Description of the Invention

[0027] The present invention will be further described in detail below with reference to the accompanying drawings.

[0028] The present invention will be further illustrated by the following specific examples.

[0029] Example 1:

[0030] TAT - AZO - COF was prepared by a simple melt - polycondensation method ( Figure 1 ) In a typical protocol, 4,4',4”-(1,3,5 - triazine - 2,4,6 - triyl) triphenylamine (TAT), 4,4'-(diazene - 1,2 - diyl) dibenzoic acid (AZO), and benzoic acid were mixed in a Pyrex tube and heated at 220 °C for 3 days to obtain an orange - black sample.

[0031] The crystal structure of TAT - AZO - COF was analyzed by powder X - ray diffraction (PXRD) ( Figure 1 ); the types of COFs functional groups were analyzed by Fourier transform infrared spectrometer (FTIR) ( Figure 2 ); the specific surface area and pore size distribution of COFs were tested by nitrogen adsorption; the size, morphology, and microstructure of the obtained TAT - AZO - COF were analyzed by transmission electron microscopy (TEM) and high - resolution transmission electron microscopy (HRTEM).

[0032] The TAT - AZO - COF prepared in the above Example 1 was applied to a symmetric all - organic battery:

[0033] In a voltage window of 0.01 - 4.0 V (versus Li / Li + ), TAT - AZO - COF was used as the negative electrode and the positive electrode, and LiPF 6The EC / DMC / EMC solution was used as the electrolyte to construct the SAOBs of the symmetric all-organic battery ( Figure 3 A). Before assembling the SAOBs, the TAT-AZO-COF negative electrode was pre-lithiated to generate additional active Li + , and the influence of SEI growth was excluded. Then, the positive electrode and the pre-lithiated negative electrode were further assembled into SAOBs. During discharge, the cathodic active carbonyl and triazine groups of the positive electrode material received 6 Li + and 3 PF 6 - , while the azo group and triazine group of the negative electrode material released 6 Li + . In addition, the reverse process occurred during charging ( Figure 3 B).

[0034] The battery performance results are as Figure 3 shown. The SAOBs exhibited excellent electrochemical performance, with a high capacity of 215 mAh g -1 at 1 A g -1 . In addition, the SAOBs provided capacities of 210, 174, 158, 145, 133, and 128 mAh g -1 at different current densities (i.e., 1, 2, 3, 5, 8, and 10 A g -1 ) (Figure 4C). As the current density recovered to 1 A g -1 , the capacity recovered to 175 mAh g -1 . The energy density of the SAOBs was approximately 68.7, 61.2, 57.5, 54.3, 50, and 48 Wh kg -1 , and 312, 680, 1150, 2718, 3125, and 3840 W kg -1 , respectively, which were superior to most of the previously reported SAOBs or AOBs electrode materials. In addition, the long cycle performance of the SAOBs based on TAT-AZO-COF was investigated ( Figure 3 D).

[0035] At a high current density of 10 A g -1 , it provided a high capacity of 90 mAh g -1 , with an average Coulombic efficiency of 100% and a capacity retention rate of 69% after 10,000 cycles, showing the best performance among all organic electrode materials in the dual-electrode available SAOBs ( Figure 3 F). In addition, for assembling a flexible pouch battery, it could be used to light up a light-emitting diode, and the flexible pouch battery could still operate even in the folded state of 90° or 180° ( Figure 3 G). This study opened up a new way for exploring efficient symmetric all-organic batteries based on COFs.

[0036] The present invention and its implementation manners have been described above. Such description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, creatively design structural manners and embodiments similar to the technical solution, they shall fall within the protection scope of the present invention.

Claims

1. A method for preparing COFs with three-element molecular junctions, characterized in that: The following steps are involved: Step 1: Prepare organic ligand; Step 2: In situ polymerization of organic ligands through an organic flux method is used to obtain a COFs electrode material having a three-element molecular junction.

2. The method for preparing COFs having a three-element molecular junction according to claim 1, characterized in that: The organic ligand comprises 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 4,4'-(1,2-diazolyl)bis-1,2-phthalic acid, and the organic flux is benzoic acid.

3. The method for preparing COFs with a three-element molecular junction according to claim 2, characterized in that: The organic ligand and benzoic acid are mixed and frozen, and after the reaction is completed, the three-element molecular structure COFs electrode material is filtered out to obtain the electrode material.

4. The method for preparing COFs having a three-element molecular junction according to claim 3, characterized in that: The organic fluxing method comprises: The organic ligand and benzoic acid were mixed into a Pyrex tube and vacuum sealed at 220 °C for 72 h; The obtained product was filtered and soaked in tetrahydrofuran for 24 hours. After soaking, the product was dried at 120° C. under vacuum for 12 hours to obtain the three-element molecular junction COFs electrode material.

5. The method for preparing COFs with three-element molecular junctions according to claim 3, characterized in that: The ratio of the organic ligand to benzoic acid is: 2,4,6-tris(4-aminophenyl)-1,3,5-triazine:4,4'-(1,2-diazolyl)bis-1,2-phthalic acid:benzoic acid=0.1mmol, 35.4mg:0.15mmol, 53.7mg:0.6mmol, 73.3g.

6. COFs with three-element molecular junctions, obtained by the method according to any one of claims 1 to 5, characterized in that: The three basic units are azo, triazine and anhydride functional groups respectively, the structural stacking method is ABC stacking, and the COF is TAT-AZO-COF.

7. Application of the COFs with three-element molecular junctions as claimed in claim 6 in symmetrical all-organic batteries.

8. The application of the three-element molecular junction COFs in symmetrical all-organic batteries according to claim 7, characterized in that: Application in negative and positive electrode materials of symmetrical all-organic batteries.

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