Preparation method and application of a two-dimensional single crystal conductive Co-HITP material

Abstract

The invention discloses a preparation method and application of a two-dimensional single crystal conductive Co-HITP material. Co(NO3)2·6H2O and a ligand HITP are ultrasonically dispersed in deionized water to obtain a mixed solution; then heated in a water bath at 50-70°C, concentrated ammonia water is added and reacted; after the reactants are cooled to room temperature, they are washed with acetone and deionized water respectively, centrifuged for multiple times to obtain a precipitate, and dried to obtain a precursor Co-HITP-P; the precursor Co-HITP-P is used as a negative electrode material to be assembled into a sodium ion button battery CR2032 in a glove box, and a nano-sheet-shaped two-dimensional single crystal conductive Co-HITP material is obtained in situ during the electrochemical reaction process. When the two-dimensional single crystal conductive Co-HITP material is used as a negative electrode material for SIBs, it exhibits high capacity, ultra-long cycle stability and excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for sodium ion batteries, and in particular relates to a preparation method and application of a two-dimensional single crystal conductive Co-HITP material. Background Art

[0002] In recent years, sodium-ion batteries (SIBs) have attracted extensive attention and research due to their abundant sodium resources, environmental friendliness, and low cost. Anode materials have an important impact on the performance of SIBs, so the development of high-performance anode materials is an important task in the development of SIBs. The development of new high-performance anode materials, integrating multiple structures and functions into one by expanding the interlayer spacing, creating abundant active sites, improving conductivity, and achieving a robust structure / composition, is a necessary condition for achieving high-performance SIBs.

[0003] In the development of new SIBs anode materials, MOFs materials with porous structures have been widely studied in recent years. MOFs are assembled from metal ions or clusters and organic ligands, which can provide multiple active sites. Most MOFs are unstable in certain environments (such as acidic, alkaline, organic solvents or pressurized conditions), resulting in reduced reactivity of active sites. Therefore, improving the inherent structural stability and conductivity of MOFs-based anode materials is a necessary condition for improving their electrochemical performance. High-temperature calcination is usually used to improve the conductivity and structural stability of MOFs, but high temperatures often cause MOFs to react to form derivatives. Compared with the original MOFs, it is difficult for derivatives to maintain the framework structure of the original MOFs, and the specific surface area of ​​the derivatives will also be reduced due to the destruction of their pore structure and the reduction of active sites. Combining MOFs with conductive carbon materials or with other coating materials is also a common method to improve the conductivity and stability of the anode, but this method also has some disadvantages. On the one hand, the additional materials will affect the exposure of MOFs active sites; on the other hand, when MOFs are combined with external materials, there are different orientation interfaces or low composite degree, which will affect the effective transport of electrons and ions during battery cycling. It is still necessary to further improve the stability, active sites and conductivity of MOFs-based SIBs anode materials. Therefore, constructing d-π conjugated two-dimensional conductive MOFs structures with high-density active sites and stable single crystal structures is an effective strategy to improve their electrochemical performance. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for preparing a two-dimensional single crystal conductive Co-HITP material. When the two-dimensional single crystal conductive Co-HITP material prepared by the method is used as a negative electrode material for SIBs, it can be used as a negative electrode material for Na + The storage provides extended spacing layers and abundant sites, thus achieving high capacity, that is, at 0.2A g -1After 200 cycles, it can still reach 366.1mA hg -1 At the same time, the stable structure ensures ultra-long cycle stability and excellent rate performance, that is, at 8A g -1 The ultra-low attenuation rate of each cycle is less than 0.001% after 15,000 cycles. The synthetic strategy established by the present invention can provide guidance for the development of new SIBs negative electrode materials with ultra-high cycle stability.

[0005] The present invention aims at the problems existing in the current MOFs negative electrode materials, and successfully synthesizes the conductive single crystal two-dimensional nanosheet Co-HITP for SIBs negative electrode materials through in-situ electrochemical reconstruction. The tetragonal coordination structure formed by the metal ions and the π-π conjugated organic ligands unfolds along the ab plane to form a two-dimensional planar network structure with a graphene-like structure. The d-π hybrid orbits of the metal ions and the ligands allow the electrons to be delocalized in the whole system, and these two-dimensional planes can be further stacked along the c axis to form a porous structure with a one-dimensional open channel through π-π interactions. The two-dimensional plane and the one-dimensional open channel can realize the rapid transport of electrons in and out of the plane, so that the material has a higher intrinsic conductivity. The high intrinsic conductivity can make the electrons quickly transfer to the redox active site, thereby improving the reactivity of the active site. The large electron delocalization system can make the free radicals generated by the redox reaction stable, effectively prevent the self-polymerization of the free radicals, and provide a stable framework for realizing reversible charge and discharge. The open one-dimensional pores can store more sodium ions and provide channels for ion transport, thereby improving the reaction kinetics of the active site.

[0006] The present invention adopts the following technical solution to solve the above technical problems, a method for preparing a two-dimensional single crystal conductive Co-HITP material, characterized by the specific steps of:

[0007] Step S1: ultrasonically dispersing Co(NO3)2·6H2O and ligand HITP in deionized water to obtain a mixed solution;

[0008] Step S2: transfer the mixed solution obtained in step S1 to a reaction vessel and heat it in a water bath at 50-70° C., then add concentrated ammonia water and react for 1-3 hours;

[0009] Step S3: After the reactants of step S2 are cooled to room temperature, they are washed with acetone and deionized water respectively, and centrifuged multiple times to obtain a precipitate, and then the precipitate is dried to obtain the precursor Co-HITP-P;

[0010] Step S4: The precursor Co-HITP-P obtained in step S3 is used as a negative electrode material to assemble a sodium ion button battery CR2032 in a glove box, and a nanosheet-shaped two-dimensional single crystal conductive Co-HITP material is obtained in situ during the electrochemical reaction.

[0011] Furthermore, the mass ratio of Co(NO3)2·6H2O and ligand HITP in step S1 is 1.5~3:1

[0012] Furthermore, the voltage of the electrochemical reaction process in step S4 is 0.01~3V vs. (Na + / Na).

[0013] The application of the two-dimensional single crystal conductive Co-HITP material described in the present invention in the preparation of negative electrode materials for sodium ion batteries.

[0014] The advantages and beneficial effects of the present invention compared with the prior art are as follows: the tetragonal coordination structure of metal ions and π-conjugated organic ligands in the two-dimensional single crystal conductive Co-HITP material prepared by the present invention unfolds along the ab plane to form a two-dimensional planar network structure with a graphene-like structure, the d-π hybrid orbits of the metal ions and ligands allow electrons to be delocalized in the entire system, and the two-dimensional planar network structure can be further stacked along the c axis to form a porous structure with one-dimensional open channels through π-π interactions; the two-dimensional planar network structure and the one-dimensional open channels can realize the rapid transport of electrons in and out of the plane, so that the material has a higher intrinsic conductivity; the high intrinsic conductivity can enable electrons to be quickly transferred to the redox active sites, thereby improving the reactivity of the active sites; the large electron delocalization system can stabilize the free radicals generated by the redox reaction, effectively prevent the self-polymerization of the free radicals, and provide a stable framework for achieving reversible charging and discharging. The open one-dimensional pores can store more sodium ions and provide channels for ion transport, thereby improving the reaction kinetics of the active sites. The in-situ reconstructed conductive single crystal two-dimensional nanosheet Co-HITP is Na + The storage provides an extended spacing layer and abundant sites (C=N), which effectively improves the capacity, that is, at 0.2A g -1 After 200 cycles, it can still reach 366.1mA hg -1 At the same time, the stable structure ensures ultra-long cycle stability and excellent rate performance, that is, at 8A g -1 The product can be cycled for 15,000 times, and the ultra-low attenuation rate in each cycle is less than 0.001%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Field emission scanning electron microscope (FESEM) images, transmission electron microscope (TEM) images and corresponding element distribution images of samples at different stages in Example 1.

[0016] Figure 2 These are FESEM images of samples at different stages of Example 1, including (a) ground slurry, (b) slurry soaked in electrolyte, (c) coated on copper foil soaked in electrolyte, and (d) electrode after charge and discharge cycles.

[0017] Figure 3 The FESEM image, TEM image and corresponding element distribution map of the Co-HITP material prepared in Example 1 after 9999 cycles.

[0018] Figure 4 This is a cycle performance diagram of the Co-HITP material prepared in Example 1 at a current density of 0.2 A / g.

[0019] Figure 5 This is a cycle performance diagram of the Co-HITP material prepared in Example 1 at a current density of 8 A / g.

[0020] Figure 6 This is a radar chart comparing the electrochemical performance of the Co-HITP material prepared in Example 1 and MOFs reported in other literature as SIBs negative electrode materials. DETAILED DESCRIPTION

[0021] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example 1

[0022] Step S1: 0.0535 g Co(NO3)2·6H2O (0.184 mmol) and 0.0687 g ligand HITP (0.128 mmol) were dissolved in 80 mL deionized water and ultrasonicated for 30 min to obtain a mixed solution;

[0023] Step S2: The mixed solution obtained in step S1 was transferred to a round-bottom flask and heated in a water bath at 60°C, and 8 mL of concentrated ammonia water was added dropwise to react for 2 h;

[0024] Step S3: After the reactant of step S2 is cooled to room temperature, it is washed with acetone and deionized water and centrifuged three times respectively, and the obtained precipitate is vacuum dried at 60°C for 12 hours to obtain the precursor Co-HITP-P;

[0025] Figure 1 Figures a and b are FESEM images of Co-HITP-P at different magnifications. It can be seen from the figure that the Co-HITP-P sample is composed of many irregular nanosheets and exhibits a large number of micro-wrinkles, which are similar to the wrinkle morphology of stacked graphene. Figure 1 In the middle c, the wrinkled nanosheets can be clearly seen. This graphene-like structure of nanosheets can greatly promote the electrochemical performance. From the HR-TEM image of Co-HITP-P ( Figure 1No obvious lattice fringes were observed in (d), indicating that Co-HITP-P is amorphous, and the selected area electron diffraction (SAED) pattern can also prove this result. Figure 1 Figure (e) shows that Co, C, and N elements are uniformly distributed in the Co-HITP-P sample.

[0026] Figure 2 As shown in the figure, the precursor Co-HITP-P is mixed with Ketjen black and a binder (PVDF), and then added to N-methylpyrrolidone (NMP) and ground ( Figure 2 a), further immersed in electrolyte ( Figure 2 b) and further coated on copper foil ( Figure 2 The morphology after (c) does not transform into a grass-like nanosheet structure.

[0027] Step S4: The Co-HITP-P coated on copper foil was used as the negative electrode to assemble into a CR2032 sodium ion button cell in a glove box and then charged in a voltage range of 0.01~3V vs. (Na + / Na) conditions in a blue electricity test system to obtain the Co-HITP material.

[0028] from Figure 2 As can be seen in figure d, after the charge and discharge cycles, the morphology of the Co-HITP material has changed, and the morphology of the sample has begun to transform from wrinkled nanosheets with graphene-like structures to grass-like nanosheet structures. Figure 3 The morphology of the nanosheet-structured Co-HITP material after 9999 cycles. Figure 3 It can be seen from ac that the sample maintains a uniform nanosheet structure very well. During the cycle process, this grass-like nanosheet structure is more conducive to long-term cycle stability. Figure 3 The nanosheets have a layered structure, and the larger interlayer spacing is conducive to the storage of sodium ions. HR-TEM and SAED show that the amorphous precursor is transformed into a single crystal structure after electrochemical reaction. Figure 3 Figure g is the element distribution diagram of Co-HITP material. It can be seen from the figure that Co, C and N elements are evenly distributed in the grass-like nanosheets.

[0029] Figure 4 For Co-HITP materials at 0.2A g −1 The cycle performance diagram below shows that after 200 cycles, the specific capacity is 366.1 mA hg −1 , the Coulomb efficiency reaches 99.1%. Figure 5 As shown, the Co-HITP material is −1 After 15,000 cycles, the battery capacity is 192 mAh g −1The specific capacity of the electrode material is as high as 82.0%, and the capacity retention rate is as high as 82.0%, which indicates that the electrode material exhibits excellent cycle stability. Figure 6 The figure is a comparison of the electrochemical performance of Co-HITP material as a negative electrode material for sodium ion batteries and the MOFs negative electrode materials reported in the following literature [1]~[5]. It can be seen from the figure that the Co-HITP material prepared in Example 1 as a negative electrode material for sodium ion batteries exhibits excellent rate performance, high charge and discharge specific capacity and ultra-long cycle stability.

[0030] [1] L. Wang, Y. Ni, X. Hou, L. Chen, F. Li, J. Chen, A Two-Dimensional Metal-Organic Polymer Enabled by Robust Nickel-Nitrogen and Hydrogen Bonds for Exceptional Sodium-Ion Storage, Angew. Chem. Int. Ed., 2020, 59, 22126.

[0031] [2] B. Wang, J. Li, M. Ye, Y. Zhang, Y. Tang, X. Hu, J. He and CCLi, Dual-Redox Sites Guarantee High-Capacity Sodium Storage in Two-DimensionConjugated Metal-Organic Frameworks, Adv. Funct. Mater., 2022, 32, 2112072.

[0032] [3] Y. Wu, Y. Zhang, Y. Chen, H. Tang, M. Tang, S. Xu, K. Fan, C. Zhang, J. Ma, C. Wang, W. Hu, Heterochelation Boosts Sodium Storage in π-dConjugated Coordination Polymers, Energy Environ. Sci., 2021, 14, 6514.

[0033] [4] Y. Liu, 2463-2478.

[0034] [5] Y. Zhang, K. Chen, H. Guo, Y. Huang, W. Li, C. Wang and Y. Wang, Phase Transformation Induced Benzene Rings Activation in a Metal-OrganicFramework to Boost Sodium Storage Performance, Chem. Eng. J., 2022, 433,133508.

[0035] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional single crystal conductive Co-HITP material, characterized in that The specific steps are: Step S1: ultrasonically dispersing Co(NO3)2·6H2O and ligand HITP in deionized water to obtain a mixed solution, wherein the mass ratio of Co(NO3)2·6H2O to ligand HITP is 1.5-3:1; Step S2: the mixed solution obtained in step S1 is transferred to a reaction vessel and heated in a water bath at 50-70° C., and then concentrated ammonia water is added and reacted for 1-3 hours; Step S3: After the reactants of step S2 are cooled to room temperature, they are washed with acetone and deionized water respectively, and centrifuged multiple times to obtain a precipitate, and then the precipitate is dried to obtain the precursor Co-HITP-P; Step S4: The precursor Co-HITP-P obtained in step S3 is used as a negative electrode material to assemble into a sodium ion button battery CR2032 in a glove box, and a nanosheet-shaped two-dimensional single crystal conductive Co-HITP material is obtained in situ during the electrochemical reaction process. The voltage of the electrochemical reaction process is 0.01~3V. The two-dimensional single crystal conductive Co-HITP material is used to prepare a negative electrode material for a sodium ion battery.

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