Cathode material Mn-PTO for sodium-ion batteries, preparation method and application thereof

Abstract

This application provides a metal-organic framework sodium-ion battery cathode material Mn-PTO, a preparation method and applications, belonging to the technical field of battery development. This material selects the organic ligand pyromellitic dianhydride with conjugated extension, and synthesizes 2,7-dicarboxy-4,5,9,10-pyromellitic dianhydride PTO-(COOH)2 through a series of reactions. It has four energy storage sites and can provide a high specific capacity. At a current of 0.1 A g −1 a high reversible specific capacity of 160.1 mAh g −1 is achieved; even at a current of 5 A g −1 after 7000 cycles, a reversible specific capacity of 118.1 mAh g −1 can still be realized. It can stably cycle 10000 times at a high current of 10 A g −1 . Therefore, this material has great potential in being used as the cathode of sodium-ion batteries.

Description

Technical Field

[0001] The present invention relates to a metal-organic framework sodium-ion battery cathode material Mn-PTO, a preparation method and an application thereof, belonging to the technical field of battery development. Background Art

[0002] Benefiting from high energy density and long cycle life, lithium-ion batteries have occupied the main market of secondary batteries. At present, most advanced energy storage systems adopt lithium-ion battery technology. Nevertheless, with the price fluctuations of lithium-ion batteries, especially the consumption and future shortage of lithium resources, the development of lithium-ion batteries also has certain limitations. Therefore, sodium with rich resources has attracted much attention. Sodium is in the same group as lithium and has similar electrochemical properties; compared with lithium-ion batteries, sodium-ion batteries have many potential advantages such as low cost and good safety, and are suitable for large-scale energy storage, and will surely become a new type of green and environmentally friendly energy storage battery with great development prospects.

[0003] In recent years, metal-organic framework materials (MOFs) with superior properties such as large specific surface area porous crystal structure, highly adjustable composition and controllable functionality have been considered as promising electrode materials in sodium-ion batteries (SIBs).

[0004] Chinese Patent with publication number CN116102561A discloses a tricyclic quinazolinyl two-dimensional conductive metal-organic framework material based on amino coordination. As the cathode of a sodium-ion battery, in the voltage range of 1.0 - 3.6V and at a current density of 1 A g −1 the discharge specific capacity after 1000 cycles is only 88 mAh g −1 . The specific capacity of the sodium battery cathode material described in this scheme is relatively low, and the long-cycle performance and stability at a larger current are not good enough to meet the market demand. Summary of the Invention

[0005] In order to solve the above-mentioned defects and deficiencies in the prior art, the present invention provides a preparation method and an application of a metal-organic framework sodium-ion battery cathode material Mn-PTO.

[0006] To solve the above technical problems:

[0007] The first object of the present invention is to provide a metal-organic framework sodium-ion battery cathode material Mn-PTO, which is a three-dimensional cross-linked metal-organic framework formed by coordination of 2,7-dicarboxy-4,5,9,10-pyrenetetrone PTO-(COOH) 2 and Mn 2+ Using the rigid carboxylic acid ligand 2,7-dicarboxy-4,5,9,10-pyrenetetrone (PTO-(COOH) 2)( ) and manganese acetate were used to synthesize a three-dimensional metal-organic framework. Hydrogen bonds connect adjacent polymer chains, thus forming a strong three-dimensional metal-organic framework named Mn-PTO. When Mn-PTO is used as the positive electrode for sodium ions, it exhibits excellent rate performance and long cycle performance, providing new ideas and solutions for the development of positive electrode materials for sodium-ion batteries.

[0008] The second object of the present invention is to provide a preparation method of a metal-organic framework sodium-ion battery positive electrode material Mn-PTO, which includes the following steps:

[0009] Step 1. Synthesis of 2,7-dibromo-pyrene-4,5,9,10-tetrone (PTO-Br 2 ) : Add pyrene-4,5,9,10-tetrone PTO, concentrated sulfuric acid and N-bromosuccinimide into a round-bottom flask, heat and stir to mix, and then cool to room temperature; slowly drop it into deionized water, filter under vacuum, collect the precipitate, wash with deionized water, transfer the collected product to dimethyl sulfoxide (DMSO) for heat treatment, naturally cool for recrystallization, and filter by suction; after repeating the recrystallization process (3 times), wash the filtrate with dichloromethane and ether and dry to obtain the compound PTO-Br 2 ;

[0010] Step 2. Synthesis of 2,7-dibromo-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-Br 2 ) : Add the compound PTO-Br obtained in Step 1 2 , ethylene glycol, p-toluenesulfonic acid monohydrate and toluene into a round-bottom flask, heat under reflux, cool to room temperature, filter under vacuum to collect the precipitate, wash with deionized water and dry to obtain the compound PTO-Me-Br 2 ;

[0011] Step 3. Synthesis of 2,7-dicyano-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-CN 2 ) : Add PTO-Me-Br 2 , cuprous cyanide and N-methylpyrrolidone into a three-necked flask, heat and stir under an argon atmosphere, slowly cool to room temperature, add ammonia water, wash the obtained crude product with ammonia water and deionized water and dry to obtain PTO-Me-CN 2 ;

[0012] Step 4. Synthesis of 2,7-dicarboxy-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-(COOH) 2 ) : PTO-Me-CN 2, A 10% sodium hydroxide solution and ethanol are heated under reflux in a round-bottom flask, cooled to room temperature, acidified with hydrochloric acid, the precipitate is collected by centrifugation, washed with deionized water, and dried to obtain PTO-Me-(COOH). 2 ;

[0013] Step Five, Synthesis of 2,7-dicarboxy-pyrene-4,5,9,10-tetrone (PTO-(COOH)) 2 ): PTO-Me-(COOH) is added to a round-bottom flask 2 and stirred and mixed with 60% perchloric acid. The precipitate is collected by centrifugation, washed with deionized water, and dried to obtain the yellow powdery compound PTO-(COOH). 2 ;

[0014] Step Six, Synthesis of Mn-PTO: Dissolve PTO-(COOH) 2 in DMSO, dissolve manganese acetate in deionized water. Under stirring conditions, the PTO-(COOH) 2 -DMSO solution is dropped into the manganese acetate aqueous solution; stir and ultrasonically treat at room temperature; then transfer to a high-pressure reaction kettle, naturally cool down, and then centrifuge to obtain a precipitate, which is washed and dried successively with DMSO, absolute ethanol, and deionized water to obtain the product Mn-PTO.

[0015] Further, the reaction temperature of the high-pressure reaction kettle is 120°C - 200°C, and the reaction time is 40 - 100 hours.

[0016] Further, the reaction temperature of the high-pressure reaction kettle is 160°C, and the reaction time is 72 hours.

[0017] Further, the stirring speed at room temperature is 500 rpm, and the stirring time is 4 hours.

[0018] Further, the ultrasonic time is 30 minutes.

[0019] The third object of the present invention is to provide an application of the above-mentioned positive electrode material Mn-PTO, or the positive electrode material Mn-PTO prepared by using the above-mentioned preparation method, in the preparation of sodium ion batteries.

[0020] Further, the positive electrode material Mn-PTO is mixed and ground with conductive carbon black and polyvinylidene fluoride, N-methylpyrrolidone is added as a solvent, and the slurry is stirred for 8 - 12 hours. After the slurry is ultrasonically treated, it is coated on carbon-coated aluminum foil and cut into pieces after drying in a vacuum oven.

[0021] Further, the mass ratio of the positive electrode material Mn-PTO, conductive carbon black, and polyvinylidene fluoride is 6:3:1.

[0022] Further, the negative electrode material is a sodium metal tablet, and the electrolyte is NaPF 6It is prepared by dissolving in 1,3 - epoxy pentane / ethylene glycol dimethyl ether.

[0023] The beneficial technical effects achieved by the present invention: This application provides a metal - organic framework sodium - ion battery cathode material Mn - PTO, its preparation method and application. By selecting the organic ligand pyrene tetrone with conjugated extension, 2,7 - dicarboxy - 4,5,9,10 - pyrene tetrone PTO-(COOH) is synthesized through a series of reactions 2 , which has four energy storage sites and can provide a high specific capacity. Due to the unique cross - linked three - dimensional structure of this material, it can be used as the cathode material for SIBs. Through electrical performance tests, it can be known that the sodium - ion battery made with this material as the cathode material reaches a high reversible specific capacity of 160.1 mAh g −1 under the current condition of 0.1 A g −1 . This may be because the moderate interlayer distance (2.06 Å) has strong π - π stacking, which can form a continuous ion transport channel, reduce the ion migration resistance, and facilitate the de - intercalation and inter - calation of Na + , with good stability, thus improving the rate performance. Even under the current condition of 5 A g −1 , an excellent reversible specific capacity of 118.1 mAh g −1 can be achieved after 7000 cycles. In addition, it can stably cycle 10000 times at a high current of 10 A g −1 , and the specific capacity still reaches 83.5 mAh g −1 . Therefore, this cathode material Mn - PTO has great potential in the field of sodium - ion battery cathodes. Brief Description of the Drawings

[0024] Figure 1 It is the infrared spectrum and yield statistics of each intermediate in the preparation process of the embodiment of the present invention;

[0025] Figure 2 It is the nuclear magnetic 1 1H spectrum and 13 13C spectrum of each intermediate in the preparation process of the embodiment of the present invention;

[0026] Figure 3 It is the infrared spectrum of the products obtained with different solvents in the synthesis step of Mn - PTO in the embodiment of the present invention;

[0027] Figure 4 It is the X - ray diffraction spectrum of the products obtained with different solvents in the synthesis step of Mn - PTO in the embodiment of the present invention;

[0028] Figure 5 It is the infrared spectrum of the products obtained at different reaction temperatures in the synthesis step of Mn - PTO in the embodiment of the present invention;

[0029] Figure 6 X-ray diffraction spectrogram of the product obtained at different reaction temperatures in the synthesis step of Mn-PTO in the embodiment of the present invention;

[0030] Figure 7 X-ray diffraction spectrogram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0031] Figure 8 Infrared spectrogram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0032] Figure 9 Raman spectrogram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0033] Figure 10 Structure schematic diagram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0034] Figure 11 Three-dimensional structure schematic diagram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0035] Figure 12 Scanning electron micrograph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0036] Figure 13 Element mapping diagram of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0037] Figure 14 Cycling performance graph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention at a current density of 0.2 A g −1 ;

[0038] Figure 15 Cycling performance graph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention in pure DMSO solvent at a current density of 0.2 A g −1 ;

[0039] Figure 16 Rate performance graph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention;

[0040] Figure 17 Long cycling graph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention at a large current of 5 A g −1 ;

[0041] Figure 18 Long cycling graph of the Mn-PTO product obtained by the preparation method of the embodiment of the present invention at a large current of 10 A g −1 ; Detailed implementation manners

[0042] The present invention will be further described below in conjunction with specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0043] The present invention patent will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] The present invention provides a metal-organic framework sodium-ion battery cathode material Mn-PTO. This cathode material is a three-dimensional cross-linked metal-organic framework formed by coordinating 2,7-dicarboxy-4,5,9,10-pyrenetetrone PTO-(COOH) 2 and Mn 2+ A three-dimensional metal-organic framework was synthesized using the rigid carboxylic acid ligand 2,7-dicarboxy-4,5,9,10-pyrenetetrone (PTO-(COOH) 2 ). Hydrogen bonds connect adjacent polymer chains, thus forming a strong three-dimensional metal-organic framework, named Mn-PTO. Its structural schematic diagram is as shown in Figure 10 and Figure 11 shown: It is composed of one-dimensional coordination polymer chains and triple hydrogen bonds. Three types of O−H···O hydrogen bonds are formed between C=O, COOH, and H 2 O, with lengths of 1.88 Å, 1.94 Å, and 2.04 Å. The one-dimensional chains are connected by hydrogen bonds to form a cross-linked three-dimensional structure. Therefore, this material has high stability; the three-dimensional cross-linked structure makes the layer spacing between parallel layers 2.06 Å, indicating that the material has strong π-π stacking, which is conducive to the formation of continuous ion transport channels; the overlapping angle between layers is 71.228°, and the cross-linked three-dimensional structure is conducive to the exposure of active sites and improves the utilization rate of active sites. When Mn-PTO is used as the sodium-ion cathode, it exhibits excellent rate performance and long cycle performance, providing new ideas and solutions for the development of sodium-ion battery cathode materials. Table 1 shows the crystallographic data of Mn-PTO.

[0045] Table 1

[0046]

[0047] It can be seen from Table 1 that Mn-PTO belongs to the monoclinic system, P 1 2 1 / c 1 space group, with lattice parameters a = 13.8122 Å, b = 10.8118 Å, c = 5.5750 Å, α = γ = 90°, and β = 96.910°.

[0048] Example 1 Preparation of the Cathode Material Mn-PTO for a Metal-Organic Framework Sodium-Ion Battery

[0049] 1) Synthesis of 2,7-dibromo-pyrene-4,5,9,10-tetrone (PTO-Br 2 ) In a 500 mL round-bottom flask, pyrene-4,5,9,10-tetrone (PTO) (1200 mg, 4.58 mmol), concentrated sulfuric acid (30 mL), and N-bromosuccinimide (1800 mg, 10.11 mmol) were added. The mixture was stirred at 45 °C for 2 hours and then cooled to room temperature. The mixture was slowly added dropwise to 400 mL of deionized water at 0 °C. The precipitate was collected by vacuum filtration and washed with deionized water. The collected product was heated in 100 mL of dimethyl sulfoxide (DMSO) at 130 °C for 3 hours and then allowed to cool naturally for recrystallization. The product was obtained by suction filtration. After recrystallization three times, the filtrate was washed with dichloromethane and ether. The product was dried at 80 °C to obtain the target compound (1500.2 mg, 3.59 mmol, 125%).

[0050] 2) Synthesis of 2,7-dibromo-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-Br 2 ) (-Me represents -CH 3 ) In a 500 mL round-bottom flask, PTO-Br 2 (1500.4 mg, 3.59 mmol), ethylene glycol (36 mL), p-toluenesulfonic acid monohydrate (1364.2 mg, 7.18 mmol), and toluene (36 mL) were added. The mixture was stirred under reflux at 120 °C for 24 hours and then cooled to room temperature. The precipitate was collected by vacuum filtration, washed with deionized water, and dried at 80 °C to obtain the target compound (1678.2 mg, 2.82 mmol, 112%).

[0051] 3) Synthesis of 2,7-dicyano-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-CN 2 ) In a 500 mL three-necked flask, PTO-Me-Br 2 (1678.2 mg, 2.82 mmol), cuprous cyanide (2328.2 mg, 26.0 mmol), and N-methylpyrrolidone (56 mL) were added. The mixture was heated and stirred at 190 °C under an argon atmosphere for 12 hours and then slowly cooled to room temperature. 200 mL of ammonia water was added to remove the remaining Cu +, the crude product obtained after centrifugation was washed with ammonia water and deionized water. The collected product was dried at 80 °C to obtain the target compound (1214.0 mg, 2.49 mmol, 72%).

[0052] 4) Synthesis of 2,7-dicarboxy-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxane) (PTO-Me-(COOH) 2 ) In a 500 mL round-bottom flask, PTO-Me-CN 2 (1214.0 mg, 2.49 mmol), 10% sodium hydroxide solution (30 mL) and ethanol (60 mL) were added. The mixture was stirred at reflux temperature of 80 °C for 4 hours, cooled to room temperature, and acidified with 1 M hydrochloric acid (80 mL). The precipitate was collected by centrifugation, washed with deionized water, and dried at 80 °C to obtain the target compound (1137.5 mg, 2.16 mmol, 94%).

[0053] 5) Synthesis of 2,7-carboxy-pyrene-4,5,9,10-tetraone (PTO-(COOH) 2 ) In a 500 mL round-bottom flask, PTO-Me-(COOH) 2 (1137.5 mg, 2.16 mmol) and 60% perchloric acid (95 mL) were added. The mixture was stirred at 0 °C for 12 hours. The precipitate was collected by centrifugation, washed with deionized water, and dried at 80 °C to obtain the target compound as a yellow powder (731.1 mg, 1.81 mmol, 64%).

[0054] 6) Synthesis of Mn-PTO: The prepared PTO-(COOH) 2 (105 mg, 0.3 mmol) was dissolved in 45 mL of DMSO, and manganese acetate (98 mg, 0.3 mmol) was dissolved in 45 mL of deionized water. Under stirring, the PTO-(COOH) 2 -DMSO solution was dropped into the manganese acetate aqueous solution. The reaction was stirred at 500 rpm at room temperature for 4 hours and sonicated for 30 minutes. Then, it was transferred to a high-pressure reaction kettle and heated at a temperature of 160 °C for 72 hours. The precipitate was separated by centrifugation. The powder was then washed with DMSO (50 mL × 2), absolute ethanol (50 mL × 2) and deionized water (50 mL × 2), and dried at 80 °C. Yield: 85.1 mg (81%, based on PTO-(COOH) 2 ).

[0055] During the preparation process, the intermediates of each step were characterized and the yields were counted. The results are as Figure 1 andFigure 2 as shown. Among them Figure 1 are the infrared spectra and yield statistics of each intermediate during the preparation process. It can be seen from the figure that the changes in characteristic groups indicate the success of the synthesis. Figure 2 are the nuclear magnetic 1 H spectra and 13 C spectra of each intermediate during the preparation process. The X-ray diffraction spectrum, infrared spectrum and Raman spectrum of the product Mn-PTO obtained by the above preparation method are respectively as Figures 7 - 9 shown. From Figure 7 it can be seen that the Mn-PTO product obtained by the above method shows high crystallinity. The peak shape and position of Mn-PTO are consistent with the single crystal simulation peak, proving that the material is a pure phase. From Figure 8 it can be seen that the disappearance of the OH characteristic peak proves the success of coordination. At the same time, three hydrogen bond characteristic peaks appear in Mn-PTO at 3600 - 3200 cm −1 , corresponding to three kinds of intermolecular hydrogen bonds. From Figure 9 it can be seen that the Mn-O peak appears at 650 cm −1 of the Mn-PTO product, further proving the success of coordination. Figure 12 is the scanning electron microscope image of the Mn-PTO product. It can be seen from the figure that it is a three-dimensional cross-linked fibrous rod-like structure. Figure 13 is the elemental mapping diagram of the Mn-PTO product. It can be seen that the distributions of C, O, and Mn elements are uniform.

[0056] Example 2 Influence of the reaction temperature of the autoclave on the product in the synthesis steps of Mn-PTO

[0057] The preparation process is the same as that of Example 1. The reaction temperatures of the autoclave are 120 °C, 140 °C, 160 °C, 180 °C, and 200 °C respectively. The products are characterized by infrared spectroscopy and X-ray diffraction spectroscopy, and the results are Figure 5 and Figure 6 shown. From Figure 5 it can be seen that for Mn-PTO reacted at 120 °C, 140 °C, 160 °C, 180 °C, and 200 °C, the disappearance of the OH characteristic peak at 2574 cm −1 in the infrared spectrum indicates the success of Mn coordination. The hydrogen bond peak is the most obvious in the sample synthesized at 160 °C, indicating that the hydrogen bond formed in the sample synthesized at 160 °C is the most stable. From Figure 6 it can be seen that the X-ray peaks appear the most and the peak shape is the sharpest in the sample synthesized at 160 °C, indicating that the sample synthesized at 160 °C has the best crystallinity.

[0058] Example 3 Assembly of the battery

[0059] The Mn-PTO prepared in Example 1 was ground with carbon black and polyvinylidene fluoride in a mass ratio of 6:3:1, and N-methylpyrrolidone was added as a solvent to stir the slurry. The mixture was stirred for 8 hours, and the slurry was coated on carbon-coated aluminum foil after ultrasonic treatment and then cut into pieces after drying in a vacuum oven at 80 °C. The diameter of the electrode was 10 mm. A CR2032 battery case was used for battery assembly, a sodium metal tablet was used as the negative electrode, and 0.5 M NaPF 6 was dissolved in 1,3-epoxypentane / ethylene glycol dimethyl ether (v:v = 1:1). The assembled battery was subjected to relevant tests, and the results are as follows:

[0060] Figure 14 was 0.2 A g −1 Cycling performance graph at a current density: After 500 cycles, the specific capacity hardly decayed, and there was still a specific capacity of 155 mAh g −1 . It showed excellent cycling stability. In contrast, for PTO-(COOH) 2 , capacity decay inevitably occurred. After 500 cycles, the specific capacity of PTO-(COOH) 2 decreased from 117.1 mAh g −1 to 81.2 mAh g −1 , and the specific capacity retention rate was relatively low, only 69.4%.

[0061] Figure 16 is the rate performance graph: At current densities of 0.2, 0.5, 1, 2, 5, 10, and 20 A g −1 , the discharge capacities of Mn-PTO were 152.9, 149.5, 146.4, 142.6, 133.4, 127.3, and 124.1 mAh g −1 respectively, and its rate performance was better than that of the vast majority of reported MOF cathodes. Moreover, the specific capacity of Mn-PTO could be restored to the initial value at 0.2 A g −1 , indicating that Mn-PTO has excellent electrochemical stability even at high current densities during charge and discharge. In contrast, the discharge capacities of PTO-(COOH) 2 were 113.0, 101.5, 96.6, 91.9, 85.4, 80.1, and 74.8 mAh g −1 respectively. As the current density increased from 0.2 A g −1 to 20 A g −1 , the specific capacity significantly decayed and could not be restored to the initial value at 0.2 A g −1 .

[0062] Figure 17 is at 5 A g −1Long cycle diagram at high current: After cycling 7000 times at a current of 5 A g −1 , Mn-PTO shows an excellent discharge specific capacity retention rate of 118.1 mAh g −1 (the specific capacity retention rate is 86.8%). In contrast, PTO-(COOH) 2 The discharge specific capacity under the condition of 5 A g −1 remains at 62.4 mAh g after 3000 cycles −1 (the specific capacity retention rate is 65.8%).

[0063] Figure 18 is 10 A g −1 Long cycle diagram at high current: After 10000 cycles, the specific capacity of the Mn-PTO positive electrode decreases from 127.1 mAh g −1 to 83.5 mAh g −1 , and the specific capacity retention rate is 65.4%, which is equivalent to only a 0.00346% attenuation of the specific capacity per cycle. While PTO-(COOH) 2 Under the condition of 10 A g −1 The specific capacity drops from 88.0 mAh g after 4500 cycles −1 to 31.5 mAh g −1 (the specific capacity retention rate is 35.8%). This further proves the excellent cycle stability of Mn-PTO.

[0064] Example 4 Influence of solvent on the product in the synthesis steps of Mn-PTO

[0065] The preparation process is the same as that of Example 1, except that the prepared PTO-(COOH) 2 (105 mg, 0.3 mmol) was dissolved in 45 mL of DMSO, and manganese acetate (98 mg, 0.3 mmol) was dissolved in 45 mL of DMSO. The obtained Mn-PTO metal-organic framework was characterized by infrared spectroscopy and X-ray diffraction spectroscopy, and the results are as Figure 3 and Figure 4 shown. As can be seen from Figure 3 , the OH characteristic peak at 2574 cm −1 disappears, indicating successful Mn coordination. The Mn-PTO synthesized by the (DMSO + H 2 O) mixed solvent shows three O−H···O hydrogen bond characteristic peaks at 3600 cm −1 ; Figure 4 is the X-ray diffraction spectrum of Mn-PTO synthesized using different solvents. Using (DMSO + H 2O) The X-ray diffraction spectrum of Mn-PTO synthesized with a mixed solvent shows distinct peaks with sharp shapes and high intensities, indicating high crystallinity; while the X-ray diffraction spectrum of Mn-PTO synthesized with pure DMSO has only a broad diffraction peak, indicating that the material has little crystallinity.

[0066] Then, the product was assembled into a battery in the same manner as in Example 3, and its cycling performance at a current density of 0.2 A g −1 is as follows Figure 15 shown: The Mn-DMSO-PTO structure is disordered, the Coulomb efficiency fluctuates greatly, the specific capacity is unstable, and the specific capacity decays rapidly after 100 cycles.

[0067] The present invention has been disclosed in the above preferred embodiments, but it is not intended to limit the present invention. Any technical solutions obtained by adopting equivalent substitution or equivalent transformation shall fall within the protection scope of the present invention.

Claims

1. A metal organic framework sodium ion battery cathode material Mn-PTO, characterized in that: The positive electrode material is prepared by 2,7-dicarboxyl-4,5,9,10-pyrenetetraone PTO-(COOH)2 and Mn 2+ Coordination-formed three-dimensional cross-linked metal-organic frameworks.

2. A method for preparing a metal organic framework sodium ion battery positive electrode material Mn-PTO, characterized in that The following steps are involved: Step 1, synthesis of 2,7-dibromo-pyrene-4,5,9,10-tetraone (PTO-Br2): add pyrene-4,5,9,10-tetraone PTO, concentrated sulfuric acid and N-bromosuccinimide into a round-bottom flask, heat and stir to mix, and then cool to room temperature; then slowly add dropwise into deionized water, vacuum filter, collect precipitate, wash with deionized water, transfer the collected product into dimethyl sulfoxide (DMSO) for heating treatment, cool naturally for recrystallization, and filter; after repeating the recrystallization process, wash the filtrate with dichloromethane and ether, and dry to obtain compound PTO-Br2; Step 2, synthesis of 2,7-dibromo-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxabutane) (PTO-Me-Br2): heat the compound PTO-Br2 obtained in step 1, ethylene glycol, p-toluenesulfonic acid monohydrate and toluene in a round-bottom flask under reflux, cool to room temperature, collect the precipitate by vacuum filtration, wash with deionized water and dry to obtain the compound PTO-Me-Br2; Step 3, synthesis of 2,7-dicyano-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxabutane) (PTO-Me-CN2): PTO-Me-Br2, cuprous cyanide and N-methylpyrrolidone were added to a three-necked flask, heated and stirred under an argon atmosphere, slowly cooled to room temperature, and ammonia water was added to obtain a crude product, which was washed with ammonia water and deionized water and dried to obtain PTO-Me-CN2; Step 4, synthesis of 2,7-dicarboxyl-pyrene-4,5-,4,5-9,10-,9,10-tetra(1,4-dioxabutane) (PTO-Me-(COOH)2): PTO-Me-CN2, 10% sodium hydroxide solution and ethanol were heated to reflux in a round-bottom flask, cooled to room temperature, acidified with hydrochloric acid, centrifuged to collect the precipitate, washed with deionized water, and dried to obtain PTO-Me-(COOH)2; Step 5, synthesis of 2,7-carboxy-pyrene-4,5,9,10-tetraone (PTO-(COOH)2): PTO-Me-(COOH)2 and 60% perchloric acid were added to a round-bottom flask and stirred to mix, and the precipitate was collected by centrifugation, washed with deionized water, and dried to obtain a yellow powder compound PTO-(COOH)2; Step 6. Synthesis of Mn-PTO: PTO-(COOH)2 is dissolved in DMSO and manganese acetate is dissolved in deionized water. Under stirring, the PTO-(COOH)2-DMSO solution is dropped into the manganese acetate aqueous solution; stirring and ultrasonic treatment are performed at room temperature; then the mixture is transferred to a high-pressure reactor, cooled naturally and centrifuged to obtain a precipitate, which is washed with DMSO, anhydrous ethanol and deionized water in turn, and dried to obtain the product Mn-PTO.

3. The method for preparing the metal organic framework sodium ion battery positive electrode material Mn-PTO according to claim 2, characterized in that: In step six, the reaction temperature of the high-pressure reactor is 120° C.-200° C., and the reaction time is 40-100 hours.

4. The method for preparing the metal organic framework sodium ion battery positive electrode material Mn-PTO according to claim 3, characterized in that: The reaction temperature of the autoclave was 160° C. and the reaction time was 72 hours.

5. The method for preparing the metal organic framework sodium ion battery positive electrode material Mn-PTO according to claim 3, characterized in that: The stirring speed was 500 rpm at room temperature and the stirring time was 4 hours.

6. The method for preparing the metal organic framework sodium ion battery positive electrode material Mn-PTO according to claim 3, characterized in that: The ultrasonication time was 30 minutes.

7. Use of the metal organic framework sodium ion battery positive electrode material Mn-PTO according to claim 1, or the metal organic framework sodium ion battery positive electrode material Mn-PTO prepared by the preparation method according to claim 2 in the preparation of sodium ion batteries.

8. The use according to claim 7, characterized in that: The positive electrode material Mn-PTO is mixed with conductive carbon black and polyvinylidene fluoride and ground, and N-methylpyrrolidone is added as a solvent to stir the slurry for 8-12 hours. The slurry is coated on a carbon-coated aluminum foil after ultrasonic treatment, and then cut into pieces after drying in a vacuum oven.

9. The use according to claim 8, characterized in that: The mass ratio of the positive electrode material Mn-PTO to the conductive carbon black and polyvinylidene fluoride is 6:3:

1.

10. The use according to claim 7, characterized in that: The negative electrode material is sodium metal pressed tablets, and the electrolyte is NaPF6 dissolved in 1,3-epoxypentane / ethylene glycol dimethyl ether.

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