An organic nanoelectrode material for sodium ion batteries and a preparation method and application thereof

Abstract

The application discloses an organic nanoelectrode material for a sodium ion battery and a preparation method and application thereof. The organic nanoelectrode material has a smaller molecular weight and a higher theoretical capacity than a naphthalimide sodium salt small molecule reported in the current literature, and is very stable to water and air. The organic nanoelectrode material exhibits extremely poor solubility in an organic electrolyte, can be dissolved in water and simultaneously assembled to form a uniform nanofiber morphology, thereby exhibiting strong conductivity and a high ion diffusion coefficient. Therefore, the application uses water as a dispersion medium, and through compounding of the organic nanoelectrode material with a binder and a conductive agent, a high-performance nanoelectrode is simply and efficiently prepared, the application of a high-performance sodium ion battery is realized, and high specific capacity, excellent rate performance and an ultralong cycle life are exhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of organic electrode materials of sodium ion batteries, and particularly relates to an organic nano electrode material for sodium ion batteries, a preparation method thereof and application of the organic nano electrode material in preparation of high-performance sodium ion batteries. BACKGROUND

[0002] Under the background of facing a bottleneck in lithium resource supply and the rising price of lithium ion batteries, sodium ion batteries (SIBs) are favored due to abundant sodium resources, wide distribution, low cost, higher safety and good high and low temperature performance, and have broad application prospects in the fields of power batteries and large-scale energy storage. However, due to the large radius of sodium ions, the volume change of traditional inorganic electrode materials is large during the charging and discharging process, which leads to the destruction of the material structure. This has a very significant impact on inorganic electrodes with rigid structures, resulting in poor cycle stability of the battery.

[0003] Organic materials have better flexibility, adjustable lattice spacing, and no significant volume effect during repeated cycles. In addition, organic electrode materials have the advantages of abundant resources, adjustable molecular structure, high specific capacity, and low cost, and have become a hot spot in the research of sodium-ion batteries (SIBs). At present, many organic materials have been developed, but most of them exist in the form of bulk or powder materials, and the electrode morphology regulation is still a great challenge. Compared with bulk electrode materials, nanostructured electrode materials have the smallest ion / electron transport diffusion length and more exposed redox active sites, resulting in higher actual capacity and enhanced rate performance. On the other hand, organic electrode materials often exhibit high solubility and low conductivity in electrolyte, especially small molecules, which are easy to dissolve in organic electrolyte. The salt formation strategy is an effective method to reduce the solubility of small molecules, but most of them are through the formation of carboxylate or sulfonate (Adv. Energy Mater. 2021, 11, 2101972, Electrochem. Commun. 2017, 76, 47-50, ChemSusChem 2019, 12, 2181-2185). The team of Professor Xun Yunhua from Tianjin University realized the long cycle life of sodium-ion batteries by introducing carboxylate into the structure of N,N'-dihydroxynaphthalimide small molecules (Adv. Energy Mater. 2021, 11, 2101972). The team of Professor Fang Cong from University of Electronic Science and Technology of China introduced sodium sulfonate into the structure of small molecule 9,10-anthraquinone, which is a highly stable organic cathode in sodium-ion batteries and can provide a capacity of about 120 mAhg (ChemSusChem 2019, 12, 2181-2185). However, the non-active groups introduced by the above salt formation method have a large molecular weight, resulting in a relatively low specific capacity. Therefore, the development of high-performance organic electrode materials urgently needs the coordinated regulation of molecular structure and morphology. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application provides an organic nano-electrode material for sodium-ion batteries with small molecular weight and high stability, which solves the problem of solubility and improves the specific capacity of the battery. At the same time, using water as the dispersion medium, a high-performance nano-electrode is prepared by self-assembly of amphiphilic molecules, which promotes the transmission performance of electrons and ions, greatly improves the rate performance and long-life cycle stability in the battery.

[0005] The present application also provides a preparation method and application of the above-mentioned organic nano-electrode material.

[0006] The organic nano-electrode material provided by the present application is any one of the following PMI-ONa, NDI-ONa, and PDI-ONa:

[0007]

[0008] In the above structural formula, R represents any one of a hydrogen atom, a halogen atom, a cyano group, and a nitro group.

[0009] The preparation method of the organic nanoelectrode material provided by the application is as follows: under an air or nitrogen atmosphere, PMI-OH or NDI-OH or PDI-OH is dehydrogenated and sodium saltized by using sodium methoxide; after the reaction is completed, the precipitate is collected by suction filtration, and the target product PMI-ONa or NDI-ONa or PDI-ONa is obtained after washing and vacuum drying; the synthesis reaction route is as follows:

[0010]

[0011] In the above preparation method, the reaction molar ratio of the sodium methoxide and PMI-OH or NDI-OH or PDI-OH is 2-10:1; the solvent used for dehydrogenation and sodium saltization is any one of water, methanol and ethanol, the reaction temperature is 20-60°C, and the reaction time is 12-24 hours.

[0012] The application further provides an application of the organic nanoelectrode material in preparing a sodium ion battery. By using the excellent self-assembly performance of PMI-ONa or NDI-ONa or PDI-ONa in water, a slurry is prepared by compounding PMI-ONa or NDI-ONa or PDI-ONa with a binder and a conductive agent in water as a dispersion medium, then the slurry is uniformly coated on an aluminum foil, and an electrode sheet is obtained by vacuum drying. After the electrode sheet is cut, it is used as a positive electrode, sodiumized carbon paper is used as a negative electrode, the two electrodes are separated by a separator, an electrolyte is added, and a sodium ion battery is assembled under nitrogen protection. In the application, the electrolyte in the electrolyte is sodium hexafluorophosphate, the solvent is diethylene glycol dimethyl ether, the conductive agent is any one of carbon black and a carbon nanotube, the binder is sodium alginate, and the separator is a propylene polymer film. In the application, the total mass of PMI-ONa or NDI-ONa or PDI-ONa, the conductive agent and the binder is 100%, PMI-ONa or NDI-ONa or PDI-ONa accounts for 60%-90% of the total mass, the conductive agent accounts for 0%-30% of the total mass, and the rest is the binder. The temperature of the vacuum drying is 60-80°C, and the time is 20-28 hours.

[0013] The application has the following beneficial effects:

[0014] The present application constructs three kinds of conjugated imide sodium salt with small molecular weight and stability, simple synthesis, low cost, solves the solubility problem, and improves the specific capacity of the battery. Through experiments, it is found that PMI-ONa or NDI-ONa or PDI-ONa not only shows poor solubility in organic electrolyte, but also can be dissolved in water and simultaneously assembled to form uniform nanofiber morphology, thereby showing strong conductivity and high ion diffusion coefficient, so we use water as a dispersing agent, and by compounding with a binder and a conductive agent, a high-performance nanoelectrode is prepared, which shows high specific capacity, excellent rate performance and super-long cycle life in a sodium ion battery. In the 0.05Ag -1 and 3.0Ag -1 current density, the specific capacity of PMI-ONa is 157mA h g -1 and 80mA h g -1 , the specific capacity of NDI-ONa is 171mA h g -1 and 153mAhg -1 , and the specific capacity of PDI-ONa is 155mAhg -1 and 126mAhg -1 , wherein the NDI-ONa has a capacity retention of up to 93% after 20000 cycles at a large current density of 3.0Ag -1 . These data are the best results of naphthalimide-based small molecule positive electrode materials in sodium ion batteries at present. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the nuclear magnetic hydrogen spectrum of NDI-ONa prepared in Example 1.

[0016] Figure 2 is the SEM diagram of NDI-ONa prepared in Example 1.

[0017] Figure 3 is the nuclear magnetic hydrogen spectrum of PMI-ONa prepared in Example 2.

[0018] Figure 4 is the SEM diagram of PMI-ONa prepared in Example 2.

[0019] Figure 5 is the SEM diagram of PDI-ONa prepared in Example 3.

[0020] Figure 6 is the cyclic voltammogram (the scan rate is 0.2mVs -1 ) of the sodium ion battery assembled by NDI-ONa prepared in Example 1.

[0021] Figure 7is a cyclic voltammogram of the assembled sodium-ion battery of PMI-ONa prepared in Example 2 (the scan rate is 0.2 mVs -1 ).

[0022] Figure 8 is a cyclic voltammogram of the assembled sodium-ion battery of PDI-ONa prepared in Example 3 (the scan rate is 0.2 mVs -1 ).

[0023] Figure 9 is a rate performance graph of the assembled sodium-ion batteries of NDI-ONa, PMI-ONa, and PDI-ONa prepared in Examples 1-3 (the current density is 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 Ag -1 ).

[0024] Figure 10 is a long cycle graph of the assembled sodium-ion batteries of NDI-ONa, PMI-ONa, and PDI-ONa prepared in Examples 1-3 at a current density of 3 Ag -1 ).

[0025] Figure 11 is a long cycle graph of the assembled sodium-ion battery of NDI-ONa prepared in Example 1 at a current density of 3 Ag -1 ). DETAILED DESCRIPTION

[0026] The present application will be further described below in connection with specific embodiments, but the embodiments are only used to illustrate the principles of the present application and provide a proof of the feasibility of the present application, and do not constitute a limitation on the scope of the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be within the protection scope of the present application.

[0027] Example 1

[0028] Under an air atmosphere, 298 mg (1 mmol) of NDI-OH was dispersed in 10 mL of methanol, 0.75 mL of a 5.4 mol / L sodium methoxide solution was added, and the reaction was stirred at room temperature for 24 hours. After the reaction was completed, the obtained precipitate was washed with methanol and then dried at 80°C under vacuum for 12 hours to obtain a solid product of NDI-ONa. Figure 1 is a nuclear magnetic hydrogen spectrum of NDI-ONa. As can be seen from Figure 2 , the prepared NDI-ONa is composed of nanobands with uniform morphology and uniform size distribution, which is conducive to efficient electron and ion transmission.

[0029] Example 2

[0030] In Example 1, the NDI-OH used is replaced with an equal molar PMI-OH, and the other steps are the same as Example 1, to obtain a solid pure product PMI-ONa. Figure 3 The nuclear magnetic hydrogen spectrum of PMI-ONa is shown in Figure 2. Figure 4 As can be seen, the prepared PMI-ONa electrode sheet is composed of nanospherical particles, which is conducive to efficient electron and ion transmission.

[0031] Example 3

[0032] In Example 1, the NDI-OH used is replaced with an equal molar PDI-OH, and the other steps are the same as Example 1, to obtain a solid pure product PDI-ONa. Figure 5 As can be seen, the prepared PDI-ONa is composed of uniform nanorods, which is conducive to efficient electron and ion transmission.

[0033] Example 4

[0034] Application of NDI-ONa, PMI-ONa, and PDI-ONa prepared in Examples 1-3 in the preparation of sodium ion batteries

[0035] NDI-ONa, PMI-ONa, and PDI-ONa are respectively used as active materials to assemble sodium ion full batteries and perform performance tests, and the specific steps of battery assembly are as follows:

[0036] The active material, carbon black, and sodium alginate are weighed in a mass ratio of 6:3:1, and the weighed materials are placed in a mortar and ground and mixed uniformly. Water is added and continued to be ground to form a uniform slurry. The uniformly mixed slurry is uniformly coated on a clean aluminum foil using a film applicator, and the coated aluminum foil is dried at 80°C under vacuum for 12 hours. The dried coated aluminum foil is punched into a circular electrode sheet with a diameter of 12 mm using a battery puncher, and the mass of each electrode sheet is weighed. The mass of the coated active material is calculated by deducting the mass of the blank aluminum foil. In a glove box under nitrogen protection, the prepared electrode sheet is used as the positive electrode, the sodiumized carbon paper is used as the negative electrode, the Celgard 3501 polypropylene film is used as the battery separator, and the 2.0 mol / L sodium hexafluorophosphate solution in diethylene glycol dimethyl ether is used as the electrolyte. The electrode sheet, electrolyte, separator, sodiumized carbon paper, gasket, and spring are sequentially placed in the battery positive shell, and the battery negative shell is covered. The battery is packaged using a battery sealing machine to form a CR 2032 type button cell. After standing for 8 hours, the electrochemical performance is tested, and the results are shown in Table 1 and Figures 6 to 11 .

[0037] Table 1 Battery performance of sodium ion batteries assembled with PMI-ONa, NDI-ONa, and PDI-ONa at different current densities

[0038]

[0039] Depend on Figure 6 As can be seen, the sodium-ion battery assembled with NDI-ONa prepared in Example 1 has four reversible redox pairs (2.67 / 2.45, 2.54 / 2.30, 2.13 / 1.72, 1.67 / 1.48 V), indicating that NDI-ONa has excellent multi-electron storage performance. Figure 7 As can be seen, the sodium-ion battery assembled with PMI-ONa prepared in Example 2 has two sets of reversible redox pairs (1.78 / 2.16, 1.63 / 1.83V), indicating that PMI-ONa has good redox performance. Figure 8 As can be seen, the sodium-ion battery assembled with PDI-ONa prepared in Example 3 has four reversible redox pairs (2.20 / 2.52, 1.97 / 2.20, 1.46 / 1.88, 1.09 / 1.56V), indicating that PDI-ONa also has excellent multi-electron storage performance.

[0040] From Table 1 and Figure 9 , Figure 10 As can be seen, the specific capacities of the sodium-ion batteries assembled with NDI-ONa prepared in Example 1 were 171, 170, 169, 166, 163, 159, and 153 mAh g, respectively. -1 Even at very high current densities (5Ag) -1 Even at this speed, the specific capacity can still reach 153mAh. -1 This indicates that it has good rate performance; the specific capacities of the sodium-ion batteries assembled with PMI-ONa prepared in Example 2 were measured to be 157, 138, 131, 124, 117, 106, and 80 mAh g, respectively. -1 Moreover, when the current density increases from 5.0 Ag... -1 Gradually recovered to 0.05A g -1 At different current densities, its specific capacity can be almost completely recovered, indicating that it has excellent stability; the specific capacities of the sodium-ion batteries assembled with PDI-ONa prepared in Example 3 were measured to be 155, 145, 143, 141, 137, 131, and 126 mAh g, respectively. -1 Similarly, at high current density (5Ag) -1 Even at this capacity, it still has 126mAh g. -1 This proves its excellent rate capability.

[0041] Depend on Figure 11 As can be seen, the sodium-ion battery assembled with NDI-ONa prepared in Example 1 performs well at 3.0 Ag. -1 After 20,000 cycles at high current density, its specific capacity still remains at 148 mAh g.-1 The capacity retention rate was as high as 93%.

Claims

1. Application of an organic nanoelectrode material in the preparation of a sodium ion battery, characterized in that: The organic nanoelectrode material, the conductive agent and the binder are mixed uniformly in deionized water to prepare a slurry, and then the slurry is uniformly coated on an aluminum foil to obtain an electrode sheet through vacuum drying; the obtained electrode sheet is cut and used as a positive electrode, sodium carbon paper is used as a negative electrode, the two electrodes are separated by a separator, an electrolyte is added, and a sodium ion battery is assembled under nitrogen protection; The structural formula of the organic nanoelectrode material is NDI-ONa as shown below: In the above structural formula, R represents a hydrogen atom.

2. Use of the organic nano-electrode material according to claim 1 in the preparation of a sodium-ion battery, characterized in that: The preparation method of the organic nanoelectrode material is as follows: under an air or nitrogen atmosphere, NDI-OH is dehydrogenated with sodium methoxide, after the reaction is completed, the precipitate is collected by suction filtration, and the target product NDI-ONa is obtained after washing and vacuum drying; the synthesis reaction route is as follows: 。 3. Use of the organic nano-electrode material according to claim 2 in the preparation of a sodium-ion battery, characterized in that: The molar ratio of the sodium methoxide to NDI-OH is 2-10:

1.

4. Use of the organic nano-electrode material according to claim 2 in the preparation of a sodium-ion battery, characterized in that: The solvent used for the dehydrogenation is any one of water, methanol or ethanol.

5. Use of the organic nano-electrode material according to claim 2 in the preparation of a sodium-ion battery, characterized in that: The reaction temperature for the dehydrogenation is 20-60 DEG C, and the reaction time is 12-24 hours.

6. Use of the organic nano-electrode material according to claim 1 in the preparation of a sodium-ion battery, characterized in that: The electrolyte in the electrolyte is sodium hexafluorophosphate, the solvent is diethylene glycol dimethyl ether, the conductive agent is any one of carbon black or carbon nanotube, the binder is sodium alginate, and the separator is a propylene polymer film.

7. Use of the organic nano-electrode material according to claim 5 or 6 for the preparation of a sodium-ion battery, characterized in that: The total mass of the organic nanoelectrode material, the conductive agent and the binder is 100%, wherein the organic nanoelectrode material accounts for 60-90% of the total mass, the conductive agent accounts for 0-30% of the total mass, and the rest is the binder.

8. Use of the organic nano-electrode material according to claim 5 in the preparation of a sodium-ion battery, characterized in that: The temperature for the vacuum drying is 60-80 DEG C, and the time is 20-28 hours.

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