Indigo-based porous organic polymers, synthesis and their application in lithium-ion battery cathode materials

Abstract

The application belongs to the technical field of lithium ion battery cathode materials, and provides an indigo dye-based porous organic polymer, synthesis and application thereof in lithium ion battery cathode materials. Through a Sonogashira coupling reaction, an indigo molecule containing a carbonyl structure is copolymerized with 1,3,5-triethinyl benzene monomers to synthesize a novel porous organic polymer containing indigo dye in a molecular chain. The material has a large specific surface area, and is the first porous organic polymer based on an indigo structure. Then, a multi-walled carbon nanotube is used to in-situ polymerize the porous organic polymer to obtain a composite material with good electrical conductivity, and a novel indigo-based organic electrode material with high rate performance and good cycle performance is developed. Compared with traditional inorganic materials, the material has simple synthesis, does not need high temperature, is rich in dye material sources, is low in price and can be applied in industrialization.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials, and relates to the synthesis of an indigo dye molecule-based porous organic polymer and its application in lithium-ion battery positive electrode materials. Background Art

[0002] The growing demand for energy storage has driven the rapid development of lithium-ion batteries and has dominated the electronic product market. Electrodes, as the core components of battery equipment, not only determine the capacity of the battery, but are also an important factor affecting whether the battery can achieve long life, low cost and reliable safety. Currently, the electrode materials used in batteries are mainly divided into inorganic electrode materials and organic electrode materials. The synthesis of inorganic electrode materials (such as LiCoO2, LiMn2O4, LiFePO4) consumes mineral resources and produces carbon emissions, and the production is energy-intensive. Organic electrode materials usually store lithium based on the charge conversion of active functional groups. They are rich in sources, diverse in structure, easily regulated in function and have high theoretical specific capacity. They can simultaneously achieve high energy density, high cycle stability and high power density of the battery. In this case, organic materials are a better choice as electrode materials.

[0003] Among organic materials, porous organic polymers (POPs) possess large specific surface areas and pores. When used as electrodes, they can provide more active centers for ion storage and diffusion, thereby improving battery storage performance. They hold great potential for developing batteries with superior electrochemical performance. Dye-based POPs are particularly promising. Dyes containing carbonyl groups linked by functional conjugated bonds are both abundant and environmentally friendly. Carbonyl-containing porous polymers, combining the advantages of porous organic materials and reduced dyes, have garnered widespread attention in the fields of materials chemistry and organic electronics.

[0004] Indigo, pyrenetetraketone, pyrrolopyrroledione, naphthalene diimide, perylene diimide, and anthraquinone dyes are common dyes containing reactive carbonyl functional groups. In recent years, porous organic polymers based on these dyes with diverse structures have been developed and applied to battery electrode materials. However, indigo-based porous organic polymers are not currently available. Indigo dyes exhibit high open-circuit voltage, high carrier mobility, and a two-electron redox reaction mechanism. The introduction of nitrogen atoms makes the indigo structure more electron-deficient, resulting in a lower lowest unoccupied molecular orbital energy level and improved planarity, offering significant advantages as electron transport materials. Addressing this need, we have developed indigo-based porous organic polymer materials and used them as novel lithium-ion battery electrode materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing an indigo dye-based porous organic polymer, study its application in the positive electrode of a lithium-ion battery, and fill the gap in the application of indigo-based porous polymers in lithium-ion batteries.

[0006] The technical solution of the present invention:

[0007] An indigo dye-based porous organic polymer having the following structural formula:

[0008]

[0009] A method for preparing an indigo-based porous organic polymer comprises the following steps:

[0010] Step 1: Using 4-bromo-2-nitrobenzaldehyde, acetone, water and alkaline solution as raw materials to react and synthesize 6,6'-dibromoindigo;

[0011] Step 2: Using 6,6'-dibromoindigo, 4-dimethylaminopyridine, di-tert-butyl carbonate and N,N-dimethylformamide as raw materials to react and synthesize 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo;

[0012] Step 3: Using 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo as a building monomer, a Sonogashira coupling reaction is carried out with 1,3,5-triethynylbenzene in a mixed solvent in the presence of a catalyst. After the reaction, the reaction product is purified to prepare a porous organic polymer based on indigo molecules.

[0013] In step 1, the mass ratio of 4-bromo-2-nitrobenzaldehyde to water is 1:50, the volume ratio of acetone to water is 1:1-1:1.2, the alkaline solution is a 2M NaOH solution, and the amount added is to adjust the pH value to 9-10. The reaction conditions are 16-25°C for 10-15h;

[0014] In step 2, the molar ratio of 4-dimethylaminopyridine to 6,6'-dibromoindigo is 1:1.7-1:2, the molar ratio of 6,6'-dibromoindigo to di-tert-butyl carbonate is 1:2-1:5.3, and the mass ratio of 6,6'-dibromoindigo to N,N-dimethylformamide is 1:5.6-1:5.7; the temperature when adding di-tert-butyl carbonate is 0°C, and it needs to be added in two times. The reaction conditions are 16-25°C and the reaction is carried out for 20-24 hours;

[0015] The catalyst in step 3 is a mixture of tetrakis(triphenylphosphine)palladium and cuprous iodide, the molar ratio of the two catalysts is 1:40, and the mixed solvent is a mixture of N,N-dimethylformamide and triethylamine, and the volume ratio is 1:1; the molar ratio of 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo to 1,3,5-triethynylbenzene is 1.5:1, the molar ratio of cuprous iodide and 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo is 1:10, and the mass ratio of 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo and N,N-dimethylformamide is 1:15-1:16;

[0016] In step 3, the reaction conditions are degassing under freeze pump thawing, purging with argon, back and forth three times, heating to 80-110°C, and reacting for 48-96 hours. The purification treatment is washing with methanol, water, chloroform and acetone in sequence, Soxhlet extraction with anhydrous methanol, and drying.

[0017] A composite material of an indigo-based porous organic polymer and a conductive carbon material is used as a positive electrode material for lithium-ion batteries, wherein the conductive carbon material is a multi-walled carbon nanotube.

[0018] In the composite material, the mass percentage of the multi-walled carbon nanotubes is 20% to 40%.

[0019] Beneficial effects of the present invention: Through the Sonogashira coupling reaction, the present invention utilizes indigo molecules containing a carbonyl structure to copolymerize with 1,3,5-triethynylbenzene monomers to synthesize a new type of porous organic polymer containing indigo dye in the molecular chain. This material has a large specific surface area and is also the first porous organic polymer based on an indigo structure. The porous organic polymer is then in situ polymerized using multi-walled carbon nanotubes to obtain a composite material with good conductivity, developing a new indigo-based organic electrode material with high rate performance and good cycling performance. Compared with traditional inorganic materials, its synthesis is simple, does not require high temperature, and the dye material is abundant and inexpensive, making it suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 For the material in Example 2 1 H NMR spectrum;

[0021] Figure 2 is the infrared spectra of the materials in Example 3 and Example 4;

[0022] Figure 3 are scanning electron microscope (SEM) images of the materials in Examples 3 and 4, wherein (a) is the SEM image of the material in Example 3, and (b) is the SEM image of the material in Example 4;

[0023] Figure 4The XRD patterns in Examples 3 and 4 are shown below:

[0024] Figure 5 3 and 4 are nitrogen adsorption spectra of the materials in Examples 3 and 4, wherein (a) is the isothermal adsorption-desorption curve of the materials in Examples 3 and 4, and (b) is the pore size distribution of the materials in Examples 3 and 4;

[0025] Figure 6 The material in Example 4 is 0.1 mV s -1 Cyclic voltammetry test diagram under scanning rate;

[0026] Figure 7 This is a rate performance test diagram of the material in Example 4;

[0027] Figure 8 This is the cycle performance diagram of the material in Example 4 at 0.5C. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0029] Example 1

[0030] 4-Bromo-2-nitrobenzaldehyde (2 g, 8.7 mmol) was dissolved in acetone (90 mL), and then water (100 mL) was slowly added. The mixture was stirred at room temperature overnight and filtered. The solid was washed with excess acetone and deionized water, then vacuum dried to obtain 1.32 g of purple powder 6,6'-dibromoindigo (INO) with a yield of 72.1%. The reaction formula is as follows:

[0031]

[0032] Due to the poor solubility of INO, in order to increase the degree of polymerization, we used di-tert-butyl diformate group substitution protection to solubilize it to facilitate the occurrence of polymerization reaction, and then removed the protecting group and reduced it in the subsequent heating polymerization.

[0033] Example 2

[0034] To a suspension of compound INO (0.842 g, 2.0 mmol) and 4-dimethylaminopyridine (0.147 g, 1.2 mmol) in N,N-dimethylformamide (DMF, 5 mL), di-tert-butyl carbonate (2.31 g, 10.6 mmol) was added twice at 0°C. The mixture was then stirred at room temperature for 20 hours, during which time the color of the suspension changed from dark red to bright red. The product was isolated by filtration, and the residue was washed with DMF and deionized water and dried. 1.03 g of pink powder 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl ester indigo (INO-BOC) was recrystallized from a mixture of chloroform / isopropanol with a yield of 82.7%. The reaction formula is as follows:

[0035]

[0036] The product prepared in this example 1 H NMR spectrum Figure 2 The characterization data are as follows: 1 H NMR (400MHz, CDCl3): δ = 8.26 (s, 2H), 7.61 (d, J = 8.1Hz, 2H), 7.37 (dd, J = 8.1, 1.6Hz, 2H), 1.61 (s, 18H).

[0037] Example 3

[0038] INO-BOC (310 mg, 0.5 mmol), TEB (38 mg, 0.25 mmol), tetrakis(triphenylphosphine)palladium(0) (15 mg) and cuprous iodide (10 mg) were dissolved in a mixture of DMF (5.0 mL) and Et3N (5.0 mL). The mixture was degassed under freeze pump thawing, purged with argon, and reacted at 100°C for 48 h. The mixture was then cooled to room temperature, the precipitated polymer was filtered, and the filter cake was washed with methanol, water, chloroform, and acetone, respectively. Soxhlet extraction was further performed with methanol for 48 h, and the product was vacuum dried at 70°C for 24 h to obtain yellow-green powder IN-TEB. The reaction formula is as follows:

[0039]

[0040] The infrared spectrum of the product prepared in this example is as follows Figure 2 As shown, the absorption peaks of -CH3, C=O and COC bonds in the protecting group di-tert-butyl diformate (respectively 3005-2925 cm -1 1767~1729cm -1 and 1295~1214cm -1 ) disappeared, indicating the successful synthesis of polymer IN-TEB. Figure 3As shown in a, the polymer IN-TEB has an irregular block morphology. Figure 4 As shown in the figure, it can be seen that IN-TEB has an amorphous structure. The nitrogen adsorption and pore size distribution diagrams are shown in Figure 5 As shown in the figure, it can be seen that the specific surface area of ​​IN-TEB is 576.536m 2 g -1 The pore size is 0.524 nm. These results indicate that IB-TEB is a porous organic polymer.

[0041] Example 4

[0042] The synthesis method of multi-walled carbon nanotube composite IB@CNT (i.e., indigo-based porous organic polymer composite material): INO-BOC (310 mg), TEB (38 mg), multi-walled carbon nanotubes (69 mg), tetrakis(triphenylphosphine)palladium (0) (15 mg) and cuprous iodide (10 mg) were dissolved in a mixture of DMF (5.0 mL) and Et3N (5.0 mL). Degassed under freeze pump thawing, purged with argon, and reacted at 100°C for 48 hours. The mixture was then cooled to room temperature, the precipitated polymer was filtered, and the filter cake was washed with methanol, water, chloroform and acetone, respectively. Soxhlet extraction was further performed with methanol for 48 hours, and the product was vacuum dried at 70°C for 24 hours to obtain black powder IB@CNT229 mg, of which the mass percentage of multi-walled carbon nanotubes (doping rate) was 30wt%. Infrared ( Figure 2 ) and XRD( Figure 4 ) test verified the successful synthesis of the material. SEM analysis was performed to obtain the morphology of the powder as shown below Figure 3 As shown in b, IB@CNT is a fiber network with a porous structure. The nitrogen adsorption and pore size distribution are shown in Figure 5 As shown in the figure, it can be seen that the specific surface area of ​​IN-TEB is 490.310m 2 g -1 , the pore size is 0.476nm.

[0043] The 2032-type lithium-ion battery was prepared using the following process. The prepared IB@CNT polymer was used as the active material, Super P as the conductive additive, and PVDF as the binder. These were stirred in a mortar at a mass ratio of 7:2:1 in N-methyl-2-pyrrolidone (NMP) solvent to form a uniform slurry. The slurry was then coated onto aluminum foil using an applicator and dried overnight in a vacuum drying oven. Finally, a cutting machine was used to cut the electrode sheet into circular pieces with a diameter of 12 mm for use as the working electrode. A metallic lithium sheet was used as the counter electrode, a 16mm diameter Ceglard 2400 membrane was used as the battery separator, and 1M lithium hexafluorophosphate (LiPF6) dissolved in a mixed solution of dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (1:1:1 Vol%) was used as the electrolyte. All the components were assembled in a glove box (O2≤0.1ppm, H2O≤0.1ppm), sealed on a sealing machine, and finally left to stand.

[0044] The assembled batteries were tested for constant current charge and discharge curve and rate performance in the Xinwei battery test system with a voltage range of 1.5-4V (vs Li + The cyclic voltammetry curves (CV, scan rate of 0.1 mV s) were performed using a CHI660 electrochemical workstation. -1 )Measurement.

[0045] The prepared battery was subjected to electrochemical testing, and the test results were as follows: Figure 6 As shown in the figure, the cyclic voltammetry curve of the polymer IB@CNT battery has two pairs of redox peaks, indicating that the polymer has a two-electron redox mechanism. In the electrochemical performance test, the IB@CNT battery showed a high rate performance ( Figure 7 ) and excellent cycle performance ( Figure 8 ).

[0046] The above results indicate that the novel porous organic polymer described in the present invention can be used as a very potential positive electrode material in lithium-ion batteries.

Claims

1. An indigo dye-based porous organic polymer, characterized in that: The indigo dye-based porous organic polymer has the following structural formula: 。 2. A method for preparing an indigo dye-based porous organic polymer, characterized in that: Here are the steps: Step 1: Using 4-bromo-2-nitrobenzaldehyde, acetone, water and alkaline solution as raw materials to react and synthesize 6,6'-dibromoindigo; Step 2: Using 6,6'-dibromoindigo, 4-dimethylaminopyridine, di-tert-butyl carbonate and N,N-dimethylformamide as raw materials to react and synthesize 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo; Step 3: Using 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo as a building monomer, a Sonogashira coupling reaction is carried out with 1,3,5-triethynylbenzene in a mixed solvent in the presence of a catalyst. After the reaction, the reaction product is purified to prepare an indigo dye-based porous organic polymer.

3. The preparation method according to claim 2, characterized in that In step 1, the mass ratio of 4-bromo-2-nitrobenzaldehyde to water is 1:50, the volume ratio of acetone to water is 1:1-1:1.2, the alkaline solution is a 2M NaOH solution, and the amount added is to adjust the pH value to 9-10.

4. The preparation method according to claim 2, characterized in that In step 1, the reaction conditions are 16~25 o C for 10-15h.

5. The preparation method according to claim 2, characterized in that In step 2, the molar ratio of 4-dimethylaminopyridine to 6,6'-dibromoindigo is 1:1.7-1:2, the molar ratio of 6,6'-dibromoindigo to di-tert-butyl carbonate is 1:2-1:5.3, and the mass ratio of 6,6'-dibromoindigo to N,N-dimethylformamide is 1:5.6-1:5.

7.

6. The preparation method according to claim 2, characterized in that In step 2, the temperature when adding di-tert-butyl carbonate is 0 o C, and needs to be added twice, the reaction conditions are 16~25 o C for 20-24 hours.

7. The preparation method according to claim 2, characterized in that In step 3, the catalyst is a mixture of tetrakis(triphenylphosphine)palladium and cuprous iodide, the molar ratio of tetrakis(triphenylphosphine)palladium to cuprous iodide is 1:40, and the mixed solvent is a mixture of N,N-dimethylformamide and triethylamine, with a volume ratio of 1:1; the molar ratio of 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo and 1,3,5-triethynylbenzene is 1.5:1, the molar ratio of cuprous iodide to 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo is 1:10, and the mass ratio of 6,6'-dibromo-1,10-dicarboxylic acid di-tert-butyl indigo and N,N-dimethylformamide is 1:15-1:

16.

8. The preparation method according to claim 2, characterized in that In step 3, the reaction conditions are degassing under thawing with a freeze pump, purging with argon, back and forth three times, and then heating to 80-110 o C, reaction 48-96h; purification treatment is washing with methanol, water, chloroform and acetone in sequence, Soxhlet extraction with anhydrous methanol and drying.

9. The use of a composite material of an indigo dye-based porous organic polymer and a conductive carbon material as a positive electrode material for a lithium-ion battery according to claim 1.

10. The use according to claim 9, characterized in that The conductive carbon material is multi-walled carbon nanotubes, and the mass percentage of the multi-walled carbon nanotubes in the composite material is 20% to 40%.

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