A Bi-MOF@rGO material and its preparation method and application

Abstract

This invention discloses a Bi-MOF@rGO material, its preparation method, and its applications, belonging to the field of alkali metal battery technology. First, Bi-MOF is obtained by reacting an organic solvent containing dissolved bismuth salt and trimesic acid at high temperature. Then, the Bi-MOF is dispersed in an aqueous GO solution and reacted at high temperature to obtain the Bi-MOF@rGO material. In the Bi-MOF@rGO material of this invention, Bi can undergo alloying reactions with alkali metal ions. Simultaneously, the alkali metal ions can reversibly intercalate into the pores of the metal framework, serving as alkali metal host sites. Furthermore, rGO provides a three-dimensional conductive network for the Bi-MOF, exhibiting excellent electrochemical performance and showing broad application prospects as a cathode in alkali metal ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of alkali metal batteries, and in particular relates to a Bi-MOF@rGO material and a preparation method thereof, as well as an application thereof as a negative electrode material for alkali metal batteries. Background Art

[0002] Sodium-ion batteries (LIBs) and next-generation metal-ion batteries (low-cost and abundant potassium, sodium, magnesium, zinc, and aluminum battery systems) are expected to dominate high-energy density applications. During the discharge process, positive ions migrate from the anode to the cathode to produce electrons, while the charging process is the opposite. Electrode materials, as the core components in metal-ion batteries, are the main electrochemical redox reaction substances in this reversible process. Its physicochemical properties and electrochemical properties are closely related to the performance and state of energy storage devices. Therefore, the development of novel, highly active, and multifunctional electrode materials has become a key issue to achieve efficient energy storage and conversion.

[0003] Compared with traditional inorganic anode materials, organic porous polymer anode materials, especially metal-organic framework materials (MOFs), are in an emerging period and have attracted the interest of contemporary researchers for energy storage systems. In the past 10 years, chemists and material scientists have conducted intensive research on the application of MOFs in batteries. MOFs have significant advantages as electrode materials directly. MOFs have a well-defined structure, which helps to gain a deep understanding of the operating mechanism of metal-ion batteries. In addition, their structural versatility and functional tunability at the molecular level provide a material platform for changing the electrochemical reaction behavior. In many cases, MOF-based electrode materials cause structural and morphological changes during repeated electrochemical cycles due to the instability of active sites and crystal structures, resulting in rapid capacity decay. Therefore, to become a qualified electrode material, MOF must be able to withstand electrochemical reactions in which mixed-valence metal centers or organic structural units are oxidized / reduced to a certain extent. In other words, the topology of MOF-based electrodes may undergo countless reversible insertion / deinsertion of metal ions (low residual metal ion content) transformation processes. In addition, due to the poor conductivity of MOF, there are few MOF electrode materials with good electrochemical activity reported. And the reported MOF electrode materials basically rely on their large porous specific surface area to show good electrochemical performance, while the metal ions in MOF often do not participate in the reaction to provide capacity. Therefore, improving the conductivity of MOF materials and developing a MOF that can not only utilize its pore structure but also allow the metal center to participate in electrochemical reactions are of great scientific significance for the research and application of MOF materials. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a Bi-MOF@rGO material and a preparation method thereof, as well as an application as a negative electrode material for alkali metal batteries.

[0005] The object of the present invention is to achieve the following:

[0006] A method for preparing Bi-MOF@rGO material mainly comprises the following steps:

[0007] (1) Preparation of Bi-MOF: Add bismuth salt or its hydrate to an organic solvent, stir and dissolve, add trimesic acid, continue stirring for 10 to 60 minutes, transfer to a reactor, react at 100 to 150° C. for 10 to 48 hours, and wash and dry the obtained product to obtain Bi-MOF;

[0008] (2) Preparation of Bi-MOF@rGO: The Bi-MOF prepared in step (1) is dispersed in a GO aqueous solution and transferred to a reactor, and reacted at 150-200° C. for 6-24 h. The obtained product is freeze-dried to obtain Bi-MOF@rGO material.

[0009] Furthermore, the bismuth salt in step (1) is one or more of bismuth sulfate, bismuth chloride, and bismuth nitrate, and the final concentration of bismuth ions is 1 to 20 mmol / L, preferably 2.5 to 10 mmol / L.

[0010] Furthermore, the organic solvent in step (1) is CH3OH or a mixed solution of DMF and CH3OH, and the volume ratio of DMF to CH3OH is 4:1 to 0:1.

[0011] Furthermore, the final concentration of trimesic acid in step (1) is 10 to 200 mmol / L, 30 to 120 mmol / L.

[0012] Furthermore, the reaction conditions in step (1) are 120° C. for 24 hours.

[0013] Furthermore, the washing in step (1) is performed by rinsing with CH3OH twice or more.

[0014] Furthermore, the drying temperature in step (1) is in the range of 40 to 70°C.

[0015] Furthermore, the concentration of the GO aqueous solution in step (2) is 0.1 to 5 mg / mL, preferably 1 to 2.5 mg / mL.

[0016] Furthermore, in step (2), the mass ratio of GO to Bi-MOF is 1:7 to 1:1.

[0017] Furthermore, the reaction conditions in step (2) are 150-180° C. for 10-20 hours.

[0018] Another aspect of the present invention provides a Bi-MOF@rGO material prepared by the above preparation method.

[0019] The present invention also provides the use of the Bi-MOF@rGO material as a negative electrode material for alkali metal batteries.

[0020] Furthermore, the alkali metal battery includes a sodium ion battery, a potassium ion battery, a magnesium ion battery, a zinc ion battery, an aluminum ion battery or a lithium ion battery.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] 1. MOF materials have attracted widespread attention due to their rich porosity and large surface area. However, when used as electrode materials, traditional MOFs often have inactive metal central ions and very poor conductivity, which limits their application in the field of energy storage. The Bi in the Bi-MOF of the present invention can react with alkali metal ions (lithium ions, sodium ions and potassium ions) to form alloys. At the same time, the alkali metal ions can also reversibly penetrate into the pores of the metal skeleton and serve as alkali metal host sites, thereby providing more capacity. At the same time, rGO can provide a three-dimensional conductive network for Bi-MOF, so Bi-MOF@rGO exhibits good electrochemical performance. It shows broad application prospects as the cathode of alkali metal ion batteries.

[0023] 2. Usually, MOF-based electrode materials become amorphous during repeated electrochemical cycles due to unstable active sites and crystal structures, resulting in rapid capacity decay. The rGO in the Bi-MOF@rGO of the present invention can not only provide a three-dimensional conductive network but also inhibit the volume expansion of Bi-MOF to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0025] Figure 1 This is the XRD pattern of the synthesized Bi-MOF@rGO.

[0026] Figure 2 This is the scanning electron microscope image of the synthesized Bi-MOF@rGO.

[0027] Figure 3 This is the rate performance diagram of the synthesized Bi-MOF@rGO.

[0028] Figure 4The synthesized Bi-MOF@rGO has a -1 Circular diagram of . DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0030] Example 1

[0031] (1) Preparation of Bi-MOF: 150 mg Bi(NO3)3·5H2O was added to 60 ml DMF / CH3OH (volume ratio: 4:1), stirred for 30 minutes, and then 750 mg of trimesic acid was added. After stirring for 30 minutes, the mixture was transferred to a 100 mL reactor and reacted at 120°C for 24 hours. The product was washed three times with CH3OH and dried at 65°C to obtain Bi-MOF.

[0032] (2) Preparation of Bi-MOF@rGO: 0.2 g of Bi-MOF prepared in step (1) was dispersed in 40 mL of 1.5 mg / mL GO aqueous solution and transferred to a 50 mL reactor and reacted at 180 °C for 12 h. The resulting hydrogel column was then freeze-dried for one day to obtain the Bi-MOF@rGO composite.

[0033] Figure 1 is the XRD pattern of the synthesized Bi-MOF@rGO, indicating that Bi-MOF@rGO was successfully synthesized;

[0034] Figure 2 The rod-shaped Bi-MOF is shown to be wrapped by reduced graphene oxide sheets.

[0035] The prepared Bi-MOF@rGO was used as the active electrode material of the sodium ion half-cell, a sodium sheet with a diameter of 1.6 mm was used as the counter electrode, a glass fiber membrane was used as the separator, 1 M NaPF6 was used as the supporting electrolyte, and the solvent DIGLYME was used as the electrolyte to assemble the sodium / Bi-MOF@rGO half-cell. -1 , 0.2A g -1 , 0.5A g -1 , 1A g -1 , 2A g -1 , 5A g -1 , 10A g -1 and 20A g -1 The charge and discharge rate performance was tested at 5A g -1A high current long cycle test was carried out at a current density of .

[0036] Figure 3 It shows that Bi-MOF@rGO composite has good thermal conductivity at 10A g -1 At the rate of 64.2 mAh g -1 Specific capacity.

[0037] Figure 4 It shows that Bi-MOF@rGO composite has a -1 After 200 cycles at a current density of 443.6 mAh g -1 Specific capacity.

[0038] Example 2-19

[0039] The preparation process of Bi-MOF, the battery assembly process and the performance testing process are the same as those in Example 1, except that the concentration of Bi(NO3)3·5H2O, the concentration of trimesic acid, the volume ratio of DMF / CH3OH, the volume of DMF / CH3OH, the hydrothermal time of step one, the concentration of GO, the hydrothermal time of step two and other parameters are different. The relevant parameters and the performance test data of the prepared sodium ion battery are shown in Table 1.

[0040] Table 1. Preparation process parameters and performance test data of the composites of Examples 1-19

[0041]

[0042]

[0043] Comparative Examples 1-8

[0044] The preparation process of Bi-MOF, the battery assembly process and the performance testing process are the same as those in Example 1, except for the parameters such as the hydrothermal temperature in step 1, the hydrothermal time in step 1, the concentration of GO, the hydrothermal temperature in step 2, the hydrothermal time in step 2 and whether calcination is performed. The relevant parameters and the performance test data of the prepared sodium ion battery are shown in Table 2.

[0045] Comparative Example 9

[0046] (1) Preparation of Bi-MOF: 150 mg Bi(NO3)3·5H2O was added to 60 ml DMF / CH3OH (volume ratio: 4:1), stirred for 30 minutes, and then 750 mg of trimesic acid was added. After stirring for 30 minutes, the mixture was transferred to a 100 mL reactor and reacted at 120°C for 24 hours. The product was washed three times with CH3OH and dried at 65°C to obtain Bi-MOF.

[0047] (2) Preparation of Bi-MOF@rGO: 0.2 g of Bi-MOF prepared in step (1) was dispersed in 40 mL of 1.5 mg / mL rGO aqueous solution. After being evenly dispersed, the mixture was filtered, washed, and dried for one day to obtain the Bi-MOF@rGO composite.

[0048] Table 1. Preparation process parameters and performance test data of the composites of Comparative Examples 1-9

[0049]

[0050] It can be seen from the above experimental results that changes in the concentrations of Bi(NO3)3·5H2O and trimesic acid will not significantly change the electrochemical performance, mainly as metal salts and organic ligands of Bi-MOF. The preferred concentration of Bi(NO3)3·5H2O is 1.25-5 (mg / mL); the preferred concentration of trimesic acid is 6.25-25 (mg / mL).

[0051] It can be seen from the above experimental results that changes in the volume ratio of DMF / CH3OH and the volume (mL) of DMF / CH3OH do not cause changes in the electrochemical performance. Mainly as an organic reaction solvent for synthesizing Bi-MOF, the preferred volume ratio of DMF / CH3OH is 4:1 to 0:1; the preferred volume of DMF / CH3OH is 30-60 ml.

[0052] It can be seen from the above experimental results that the electrochemical performance of the final composite mainly depends on the concentration of GO, the temperature of the hydrothermal step 2 and the time of the hydrothermal step 2. The preferred GO concentration in the present invention is 1-2.5 mg / mL, the preferred temperature of the hydrothermal step 2 is 150-180°C, and the preferred time of the hydrothermal step 2 is 10-20h. When the concentration of GO used in the synthesis is too low, the content of rGO in the final composite is less, resulting in poor overall conductivity, and at the same time, rGO has insufficient inhibitory effect on Bi-MOF during the charge and discharge process, which leads to a decrease in the overall electrochemical performance. When the concentration of GO used in the synthesis is too high, although the conductivity of the entire composite is improved, the electrochemical performance is reduced due to the excessively high content of rGO. When the reaction temperature is too low or the reaction time is too short, insufficient GO reduction will result, resulting in relatively poor conductivity, which in turn leads to poor electrochemical performance.

[0053] From the above experimental results, it can be seen that when directly mixed with rGO (Comparative Example 9) or GO is replaced with carbon nanotubes (Comparative Example 7), the obtained electrode material, the rate performance and cycle stability of the battery are significantly reduced. This may be due to the lack of weak chemical force in the synthesized composite, resulting in poor electrochemical performance. At the same time, when the carbon composite is prepared by conventional high-temperature calcination and carbonization (Comparative Example 8), the electrochemical performance of the electrode is reduced due to the destruction of the special pore structure of Bi-MOF.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing Bi-MOF@rGO material, characterized in that: The following steps are involved: (1) adding a bismuth salt or its hydrate to an organic solvent, stirring and dissolving, adding trimesic acid, continuing stirring for 10 to 60 minutes, transferring to a reaction kettle, reacting at 100 to 150° C. for 10 to 48 hours, and washing and drying the obtained product to obtain Bi-MOF; (2) The Bi-MOF prepared in step (1) is dispersed in a GO aqueous solution and transferred to a reactor, reacted at 150-200° C. for 6-24 h, and the obtained product is freeze-dried to obtain a Bi-MOF@rGO material.

2. The preparation method according to claim 1, characterized in that: The bismuth salt in step (1) is one or more of bismuth sulfate, bismuth chloride and bismuth nitrate, and the final concentration of bismuth ions is 1 to 20 mmol / L.

3. The preparation method according to claim 2, characterized in that: The final concentration of bismuth ions in step (1) is 2.5 to 10 mmol / L.

4. The preparation method according to claim 1, characterized in that: The organic solvent in step (1) is CH3OH or a mixed solution of DMF and CH3OH, and the volume ratio of DMF to CH3OH is 4:1 to 0:

1.

5. The preparation method according to claim 1, characterized in that: The final concentration of trimesic acid in step (1) is 10 to 200 mmol / L.

6. The preparation method according to claim 5, characterized in that: The final concentration of trimesic acid in step (1) is 30 to 120 mmol / L.

7. The preparation method according to claim 1, characterized in that: The washing in step (1) is performed by rinsing with CH3OH twice or more; the drying temperature range is 40 to 70°C.

8. The preparation method according to claim 1, characterized in that: The concentration of the GO aqueous solution in step (2) is 0.1-5 mg / mL.

9. The preparation method according to claim 8, characterized in that: The concentration of the GO aqueous solution in step (2) is 1 to 2.5 mg / mL.

10. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of GO to Bi-MOF is 1:7 to 1:

1.

11. The preparation method according to claim 1, characterized in that: The reaction conditions in step (2) are 150-180° C. for 10-20 hours.

12. The Bi-MOF@rGO material obtained by the preparation method according to any one of claims 1 to 11.

13. Use of the Bi-MOF@rGO material according to claim 12 as a negative electrode material for alkali metal batteries.

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