Metal organic conjugated polymer material Zn-MOF, synthesis method thereof and application of metal organic conjugated polymer material Zn-MOF in sodium metal battery

Abstract

The invention discloses a metal organic conjugated polymer material Zn-MOF, a synthesis method thereof and application of the metal organic conjugated polymer material Zn-MOF in a sodium metal battery. Research results show that the material has relatively high actual discharge capacity (400 mAh g <-1 >), and can stably circulate for 300 circles in a sodium metal battery. Sodium ions can be efficiently and reversibly combined / separated through a specific two-dimensional net structure and rich active sites, and the Zn-MOF material shows a relatively high capacity retention ratio. The material effectively solves the problems of structural collapse and low capacity of a traditional inorganic layered material in the circulation process, and is not easy to dissolve in a liquid electrolyte. The sodium metal battery taking the Zn-MOF material as a negative electrode can still show relatively high discharge capacity and cycling stability even if the sodium metal battery runs under high current density.

Description

Technical Field

[0001] The present invention belongs to the field of preparation and synthesis of organic electrode materials, and specifically relates to a metal-organic conjugated polymer material Zn-MOF, a synthesis method thereof, and an application thereof in a sodium metal battery. Background Art

[0002] For alkali metal ion batteries, the electrode material is one of the most important components. However, the current commercial inorganic electrode materials have disadvantages such as short cycle life, slow charge and discharge speed, and low power density, which limit their wide application in electric vehicles and intelligent renewable energy grids. Organic materials are considered as new electrode materials because of their adjustable structure, light weight, good flexibility, and reversible redox active sites. Therefore, developing efficient organic cathode materials is one of the effective methods to commercialize sodium ion batteries.

[0003] Nowadays, there are two obstacles restricting the practical application of organic electrode materials: one is that organic materials are easily soluble in the electrolyte, and the other is that the conductivity of organic materials is poor and cannot meet the commercial requirements of high current. Therefore, designing and constructing electrode materials with controllable structures is still the main challenge for obtaining high-performance sodium metal batteries.

[0004] The above two problems can be effectively solved by polymerizing to increase the molecular weight to reduce dissolution and by increasing the conjugated structure to improve the conductivity of the material. In this application, a novel metal-organic conjugated polymer material is designed as the negative electrode material of a high-performance sodium metal battery. An aromatic π-conjugated precursor OHTAPQ is obtained through a simple condensation reaction, and then a central metal atom is introduced to coordinate with it to form a two-dimensional network structure Zn-MOF material with multiple active sites. The Zn-MOF prepared according to this strategy shows a high discharge capacity in the rate test. At the same time, the macromolecular structure connected by coordination bonds makes it stable in the organic electrolyte and not easily soluble; the abundant active sites in Zn-MOF endow it with high reversibility and structural stability during sodium ion insertion / extraction; the extended conjugated aromatic structure can improve the electronic conductivity of Zn-MOF, enabling it to still exhibit a high discharge capacity under high current. Summary of the Invention

[0005] To solve the deficiencies of the existing electrode materials, the purpose of the present invention is to design and synthesize a metal-organic conjugated polymer material Zn-MOF, a synthesis method thereof, and an application thereof in a sodium metal battery.

[0006] Based on the above purpose, the present invention adopts the following technical solutions: A synthesis method of a metal-organic conjugated polymer material Zn-MOF, comprising the following steps: (1) Take octahydroxy-tetraazapentacenequinone (OHTAPQ) and Zn(NO3)2 with a molar ratio of 1: (1 - 3), and dissolve them in N,N-dimethylformamide and deionized water respectively; (2) Transfer the above two solutions to a reaction tube, add ethylenediamine and methanol, and mix them evenly and disperse; (3) Place the reaction tube in liquid nitrogen and freeze it until it solidifies, then evacuate the air, and then thaw it. Repeat this process one to five times; (4) Let the reaction tube stand and react under heating conditions; (5) After cooling to room temperature, filter by suction, wash the solid until the filtrate is colorless, and dry it to obtain the metal-organic conjugated polymer material Zn-MOF.

[0007] Further, in step (1), the concentration of octahydroxy-tetraazapentacenequinone in N,N-dimethylformamide is 0.02 - 0.03 mmol / mL, the concentration of Zn(NO3)2 in water is 0.1 - 0.15 mmol / mL, and for every 0.1 - 0.2 mmol of Zn(NO3)2, 70 - 100 μL of ethylenediamine and 80 - 150 μL of methanol need to be added.

[0008] In step (3), the evacuation time is 3 - 5 minutes; in step (4), the temperature for the standing reaction is 75 - 85 °C, and the reaction duration is more than 100 hours. In step (5), wash the solid successively with N,N-dimethylformamide, deionized water, acetone and methanol; for every 0.1 - 0.2 mmol of Zn(NO3)2, the washing volume with the above N,N-dimethylformamide, deionized water, acetone and methanol is 30 - 50 mL each time, and each washing liquid is washed at least 2 times; the drying temperature is 100 - 150 °C, and the drying duration is 10 - 15 hours.

[0009] The preparation process of the above OHTAPQ is as follows: S1. Weigh 2,3,5,6-tetraaminobenzoquinone (TABQ) and tetrahydroxy-1,4-benzoquinone hydrate (THBQ) with a molar ratio of 1: (1.5 - 2.5) respectively, and transfer them to a round-bottom flask; add acetic acid to the round-bottom flask, seal it well and dissolve; S2. Connect a circulating cooler to the round-bottom flask, turn on the switch of the circulating cooler until the water temperature cools down; S3. Carry out reflux stirring reaction for 45 - 50 hours, cool to room temperature, and then centrifuge to remove the upper clear liquid and retain the lower precipitate; S4. Filter by suction the lower precipitate obtained in step S3, wash it until the filtrate is colorless, and dry it to synthesize octahydroxy-tetraazapentacenequinone.

[0010] Preferably, the mass fraction of acetic acid in step S1 is above 95%; the water temperature in step S2 is cooled to 5 - 15°C.

[0011] In step S3, the reflux temperature is 130 - 150°C, and the stirring rate is 50 - 150 rmp; in step S4, it is washed successively with dilute hydrochloric acid with a volume fraction of 15 - 25%, deionized water, methanol, and acetone.

[0012] When the molar amount of 2,3,5,6 - tetraaminobenzoquinone is 1.5 - 2.0 mmol, the volume of each of the above 15 - 25% dilute hydrochloric acid, deionized water, methanol, and acetone for washing is 30 - 50 mL each time, and each washing solution is washed at least 2 times.

[0013] The metal - organic conjugated polymer material Zn - MOF obtained by the above synthesis method.

[0014] The application of the above metal - organic conjugated polymer material Zn - MOF in a sodium metal battery, using sodium as the positive electrode, the Zn - MOF electrode sheet as the negative electrode, glass fiber as the separator, and after adding the electrolyte and encapsulating, it is obtained.

[0015] The preparation process of the Zn - MOF electrode sheet is as follows: Take Zn - MOF, Ketjen black, and PVDF and mix them evenly according to a mass ratio of 8:(2 - 3):1, add an appropriate amount of N - methyl - 2 - pyrrolidone and grind until there are no obvious particles in the slurry, and evenly coat it on carbon paper with a spatula, and dry to obtain the Zn - MOF electrode sheet. The loading amount of Zn - MOF on the electrode is 1 - 1.5 mg cm -2 。

[0016] The preparation process of the electrolyte is as follows: Dissolve sodium hexafluorophosphate (NaPF6) in the solvent of diethylene glycol dimethyl ether (G2), and the concentration of sodium hexafluorophosphate in the solvent is 0.5 - 5 mol L -1 。

[0017] The sodium metal full battery assembled with the Zn - MOF electrode sheet obtained by the above method, using sodium as the positive electrode, the negative electrode being the above - prepared Zn - MOF electrode sheet, glass fiber as the separator, and after adding the electrolyte and encapsulating, it is obtained. The addition amount of the electrolyte is 100 - 200 μL cm -2 。

[0018] The present invention synthesizes the OHTAPQ precursor by a solvothermal synthesis method, and the metal group is connected to the organic conjugate polymer OHTAPQ in the form of a coordination bond, enhancing the stability of the precursor structure. The introduction of the central Zn metal enables the material to have more sodium ion adsorption and desorption sites, showing excellent specific capacity in sodium metal batteries. Its macromolecular structure can also effectively solve the problem of electrode material dissolution, greatly reducing the consumption and loss of active substances, which is beneficial to improving the capacity retention rate of the battery during the cycling process.

[0019] Compared with the prior art, the present invention has the following advantages and effects.

[0020] (1) The synthesis monomers of the present invention are easily available, and the synthesis method conditions are simple, solving the problems of low capacity and easy collapse of traditional layered materials.

[0021] (2) The central metal atom and the precursor of the present invention are combined with hydroxyl groups in the form of coordination bonds, increasing the sodium storage sites of the material and reducing the solubility of the material in the organic electrolyte.

[0022] (3) The sodium metal battery assembled by the present invention has excellent cycling performance, and the actual capacity and retention rate are much higher than those of existing sodium storage materials. At a current density of 5 A g -1 , its initial capacity can reach 250 mAh g -1 , and the capacity retention rate is 84.9% after 1200 cycles. Even at a current density of 10 A g -1 , its capacity can still reach 220 mAh g -1 . Description of the Drawings

[0023] Figure 1 is a schematic diagram of the synthesis of Zn-MOF; Figure 2 is a schematic diagram of the insertion and extraction sites of Na + in Zn-MOF; Figure 3 is the Fourier infrared spectrum of OHTAPQ and Zn-MOF; Figure 4 is the X-ray photoelectron spectroscopy (XPS) spectrum of OHTAPQ and Zn-MOF; (a) XPS full spectrum of OHTAPQ and Zn-MOF; (b) XPS C 1s spectrum of OHTAPQ; (c) XPS O 1s spectrum of OHTAPQ; (d) XPS Zn 2p spectrum of Zn-MOF; (e) XPS C1s spectrum of Zn-MOF; (f) XPS O 1s spectrum of Zn-MOF; Figure 5Chinese: (a) X-ray diffraction (XRD) pattern of OHTAPQ; (b) XRD pattern of Zn-MOF; Figure 6 Chinese: (a) Carbon-13 nuclear magnetic resonance ( 13 13C NMR) spectrum of OHTAPQ; (b) 13 13C NMR spectrum of Zn-MOF; Figure 7 Chinese: (a) Scanning electron microscopy (SEM) image of OHTAPQ; (b) SEM image of Zn-MOF; Figure 8 Chinese: (a) Cycling performance of Zn-MOF||Na full cell at 50 mA g -1 -1; (b) Charge-discharge curves of Zn-MOF||Na full cell at 1, 2, 3; (c) Cycling performance at 0.1 A g -1 -1; (d) Cycling performance at 1 A g -1 -1; (e) Cycling performance at 5 A g -1 -1; (f) Rate performance of Zn-MOF||Na full cell. Detailed implementation manners

[0024] To make the technical objectives, technical solutions and excellent effects of the present invention clearer, the technical solutions of the present invention will be further described below with reference to the accompanying drawings and specific implementation cases.

[0025] Material sources: 2,3,5,6-tetra(amino)benzoquinone (TABQ) was directly purchased from Jilin Zhongke Yanshen Technology Co., Ltd., tetrahydroxy-1,4-benzoquinone hydrate (THBQ) was directly purchased from Macklin, polyvinylidene fluoride (PVDF), N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP) were purchased from Aladdin. Acetic acid was purchased from Luoyang Haohua Chemical Reagent Co., Ltd., ethylenediamine, methanol, sodium hexafluorophosphate (NaPF6) and G2 (diethylene glycol dimethyl ether) were purchased from Suzhou Duoduo Chemical Technology Co., Ltd., China. The glass fiber membrane (GF) is a battery-grade separator with the model No. 1822-047.

[0026] The purity of argon gas used in the experiment is 99.99%. All materials used for battery assembly are stored in a glove box filled with argon gas, with H2O < 0.1 ppm and O2 < 0.1 ppm.

[0027] Example 1: The synthesis process of Zn-MOF is as follows: (1)Take 24.2 mg (0.055 mmol) of OHTAPQ and 20 mg (0.11 mmol) of Zn(NO3)2, and dissolve them in 2 mL of DMF and 1 mL of H2O respectively. (2)Transfer the above two solutions to a 10 mL reaction tube, add 75 μL of ethylenediamine and 100 μL of methanol as the catalyst and co-solvent respectively, seal it well, and ultrasonicate for 15 minutes to mix and disperse evenly.

[0028] (3)Place the reaction tube in liquid nitrogen until it freezes, evacuate for 3 minutes, then thaw, and repeat this process three times.

[0029] (4)Transfer the reaction tube to an oven and let it stand and react at 80 °C for 120 hours.

[0030] (5)After cooling to room temperature, perform suction filtration. Wash the solid with DMF, deionized water, acetone, and methanol until the filtrate is colorless. Wash each washing liquid 3 times or more, with each usage of 30 - 50 mL. Transfer it to a vacuum oven and dry at 120 °C for 12 hours to obtain a black solid powder, namely the conjugated organic material Zn-MOF.

[0031] The preparation process of the above OHTAPQ is as follows: (1)Weigh 300 mg (1.78 mmol) of 2,3,5,6 - tetraaminobenzoquinone (TABQ, molecular weight 168.15) and 614 mg (3.23 mmol) of tetrahydroxy - 1,4 - benzoquinone hydrate (THBQ, molecular weight 190.11) respectively.

[0032] (2)Transfer the weighed monomer materials to a 50 mL round - bottom flask.

[0033] (3)Add 15 mL of concentrated acetic acid (mass fraction 95%) to the round - bottom flask, seal it well, and ultrasonicate for 15 minutes.

[0034] (4)Assemble the iron stand, fix the round - bottom flask, connect a spherical condenser to the flask, and connect a circulating cooler.

[0035] (5)Turn on the switch of the circulating cooler and the valves of the circulating inlet and outlet water. Cool the water temperature to 10 °C, turn on the heating and stirring switch of the oil bath, set the temperature to 140 °C, the stirring speed to 80 rpm, and reflux and react for 48 hours.

[0036] (6)After cooling to room temperature, centrifuge to remove the upper clear liquid; wash the lower precipitate with 20% (volume fraction) dilute hydrochloric acid, deionized water, methanol, and acetone respectively. Wash each solvent 3 times or more, with each usage of 30 - 50 mL until the washing liquid is colorless. Transfer it to a vacuum oven and dry at 120 °C for 12 hours to obtain OHTAPQ.

[0037] Example 2: Preparation of Zn-MOF electrode sheet: Take 24 mg of Zn-MOF, 9 mg of Ketjen black, and 3 mg of PVDF in a mortar and mix them evenly. Then, add N-methyl-2-pyrrolidone in portions until the slurry has a consistency that flows slowly when tilted. Coat it on carbon paper and spread it evenly with a spatula. Then transfer the coated electrode sheet to a vacuum oven and dry it at 80 °C for 12 hours. Weigh the dried electrode sheet and calculate the loading amount of Zn-MOF active material on the electrode sheet.

[0038] The diameter of the above carbon paper is 10 mm, and the blank carbon paper is weighed and recorded before coating.

[0039] The amounts of the above materials can approximately coat 20 electrode sheets, and the loading amount of active material on each electrode sheet is about 1 mg.

[0040] Example 3: Assembly of Zn-MOF full cell: The preparation process of the electrolyte is as follows: Dissolve sodium hexafluorophosphate (NaPF6) in diglyme (G2), and the concentration of the sodium salt is 1 M.

[0041] (1) Weigh the electrode sheet in Example 2 and calculate the loading amount of active material on the electrode sheet.

[0042] (2) Process the sodium block into a sodium metal disc with a diameter of 12 mm and a thickness of about 400 μm.

[0043] (3) Select sodium as the negative electrode, the electrode sheet in Example 2 as the positive electrode, select a glass fiber membrane as the separator, add 120 μL of NaPF6 / G2 electrolyte, and then assemble and package it to obtain the required full cell.

[0044] Perform cyclic voltammetry tests, long-term cycling tests, and rate performance tests on the above-assembled full cell using an electrochemical workstation.

[0045] Figure 1 is the synthesis schematic diagram of Zn-MOF. It can be found that Zn, as the central atom, coordinates with the precursor to form a conjugated network structure; Figure 2 is the schematic diagram of Na + insertion / extraction sites in Zn-MOF. It can be found that both the carbonyl and imine groups with electron-withdrawing effects in the structure can serve as sites for redox reactions; Figure 3The Fourier transform infrared spectra of OHTAPQ and Zn-MOF show that the characteristic groups of Zn-MOF and OHTAPQ are consistent, both of which have characteristic peaks of C=O, C=N and -OH, and the intensity of the -OH peak in Zn-MOF is significantly weakened, which is due to the consumption of part of -OH by coordination. Figure 4 Figure 4 is the X-ray photoelectron spectroscopy (XPS) spectra of OHTAPQ and Zn-MOF. As shown in Figure 4 (a), C 1s, N 1s and O 1s peaks appear in the XPS spectra of OHTAPQ and Zn-MOF, and Zn 2p peak appears in Zn-MOF, which indicates that the central atom Zn is successfully coordinated with OHTAPQ. As shown in Figures 4 (b) and (e), the XPS C 1s spectra of OHTAPQ and Zn-MOF are fitted to obtain the peaks of C=N, C=C, CO and C=O, respectively, which indicates that the Zn-MOF synthesized according to Examples 1 and 2 is compatible with the Zn-MOF synthesized according to Examples 1 and 2. Figure 1 The assumption is consistent; from the XPS O 1s spectra fitted by OHTAPQ in 4 (c) and (f), it can be found that due to the electron transfer caused by coordination, the electron cloud density around O is reduced, so that the peaks of CO and C=O shift to high binding energy; (d) XPS Zn 2p spectrum of Zn-MOF; Figure 5 (a) The X-ray diffraction (XRD) spectrum of OHTAPQ prepared in Example 1 shows no crystalline structure; (b) The XRD spectrum of Zn-MOF prepared in Example 1 shows obvious amorphous structure peaks; Figure 6 (a) C NMR spectrum of OHTAPQ ( 13 C NMR) spectrum; (b) Zn-MOF 13 C NMR spectra; the two show the same chemical shift, which indicates that the introduction of the central atom Zn still maintains the same skeleton as the precursor.

[0046] Figure 7 (a) The scanning electron microscope (SEM) image of OHTAPQ prepared in Example 1 shows that it is a pore structure of nanosheet stacking; (b) The SEM image of Zn-MOF prepared in Example 1 shows that its morphology is uniform micron-sized solid particles; Figure 8 (a) Zn-MOF||Na full cell assembled by Example 3 at 50 mA g -1 The specific capacity can reach 400 mAh g -1; (b) The relatively large discharge capacity in the first cycle of the charge-discharge curve may be due to the presence of a small number of irreversible active groups at the edge of the Zn-MOF molecular structure, and it remains stable in the second and third cycles; for the Zn-MOF||Na full cell (c), at a current density of 0.1 A g -1 , the capacity remains at 310 mAh g during 600 cycles -1 ; (d) At 1 A g -1 , its initial capacity can reach 300 mAh g -1 , and the capacity retention rate is 83% after 910 cycles; (e) At 5 A g -1 , its capacity can still reach 250 mAh g -1 ; (f) The Zn-MOF||Na full cell exhibits excellent rate performance. After undergoing charge-discharge cycles at a large current (10 A g -1 ), when returning to 0.1 A g -1 , it can still recover to a discharge capacity comparable to that before.

Claims

1. A method for synthesizing a metal-organic conjugated polymer material Zn-MOF, characterized in that, It includes the following steps: (1) Take octahydroxy-tetraazapentacenequinone and Zn(NO3)2 with a molar ratio of 1:(1~3), dissolve them in N,N-dimethylformamide and water respectively; (2) Transfer the above two solutions to a reaction tube, add ethylenediamine and methanol, and mix them evenly and disperse; (3) Place the reaction tube in liquid nitrogen and freeze it until it solidifies, then evacuate, and then thaw. Repeat this process one to five times; (4) Let the reaction tube stand and react under heating conditions; (5) After cooling to room temperature, filter by suction, wash the solid until the filtrate is colorless, and dry it to obtain the metal-organic conjugated polymer material Zn-MOF.

2. The synthesis method according to claim 1, wherein The preparation process of octahydroxy-tetraazapentacenequinone described in step (1) is as follows: S1. Weigh 2,3,5,6-tetraaminobenzoquinone (TABQ) and tetrahydroxy-1,4-benzoquinone hydrate (THBQ) with a molar ratio of 1:(1.5~2.5) respectively, and transfer them to a round-bottom flask; add acetic acid to the round-bottom flask, seal it well and dissolve; S2. Connect a circulating cooler to the round-bottom flask, turn on the switch of the circulating cooler until the water temperature cools down; S3. React under reflux and stirring for 45~50 hours, cool to room temperature, then centrifuge to remove the upper clear liquid and retain the lower precipitate; S4. Filter the lower precipitate obtained in step S3 by suction, wash it until the filtrate is colorless, and dry it to synthesize octahydroxy-tetraazapentacenequinone.

3. The synthesis method according to claim 1, characterized in that, In step (1), the concentration of octahydroxy-tetraazapentacenequinone in N,N-dimethylformamide is 0.02~0.03 mmol / mL, the concentration of Zn(NO3)2 in water is 0.1~0.15 mmol / mL, and 70~100 μL of ethylenediamine and 80~150 μL of methanol need to be added for every 0.1~0.2 mmol of Zn(NO3)2.

4. The synthesis method according to claim 1, characterized in that, In step (3), the evacuation time is 3~5 minutes; in step (4), the static reaction temperature is 75~85 °C, and the reaction duration is more than 100 hours.

5. The synthesis method according to claim 1, characterized in that, In step (5), wash the solid successively with N,N-dimethylformamide, deionized water, acetone and methanol; the drying temperature is 100~150 °C, and the drying duration is 10~15 hours.

6. The synthesis method according to claim 2, wherein In step S1, the mass fraction of acetic acid is more than 95%; in step S2, the water temperature cools down to 5~15 °C.

7. The synthesis method according to claim 2, characterized in that, In step S3, the reflux temperature is 130~150 °C, and the stirring rate is 50~150 rmp; in step S4, wash successively with dilute hydrochloric acid with a volume fraction of 15~25%, deionized water, methanol, and acetone.

8. The metal-organic conjugated polymer material Zn-MOF obtained by the synthesis method according to any one of claims 1 to 7.

9. Use of the metal-organic conjugated polymer material Zn-MOF according to claim 8 in a sodium metal battery, characterized in that Using sodium as the positive electrode, the Zn-MOF electrode sheet as the negative electrode, and glass fiber as the separator, after adding the electrolyte and encapsulating, it can be obtained.

10. The application according to claim 9, characterized in that, The preparation process of the Zn-MOF electrode sheet is as follows: Zn-MOF, Ketjen black, and PVDF are dissolved in N-methyl-2-pyrrolidone, coated on carbon paper, and dried to obtain it. The loading amount of Zn-MOF on the electrode is 1~1.5 mg cm -2 , and the electrolyte is a diglyme solution of sodium hexafluorophosphate with a concentration of 0.5~5 mol L -1 .

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