Zn single atom modified hard carbon material and preparation method and application thereof

Abstract

The present invention is applicable to the field of sodium ion battery technology and provides Zn single-atom modified hard carbon materials and their preparation methods and applications. Electrode sheets are prepared using Zn-N4 carbon nanosheets, which are then cut to obtain circular electrode sheets. The circular electrode sheets are used as negative electrodes, and metallic sodium sheets are used as counter electrodes. The electrodes are assembled together with a separator and an electrolyte to form a sodium ion battery. The Zn-N4 carbon nanosheets prepared by the present invention are used as negative electrode materials for sodium ion batteries and exhibit extremely high reversible capacity (0.05A g ‑1 321.4mAh g ‑1 ), excellent rate performance (5A g ‑1 190.2mAh g ‑1 ) and ultra-long cycle life (at 2A g ‑1 The single-atom modification method proposed in this invention provides a reasonable and effective solution to the challenges of slow storage kinetics and poor cycling stability of sodium-ion battery anodes.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a Zn single atom modified hard carbon material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs) are considered a promising next-generation energy storage device due to their abundant sodium reserves and similar chemical properties to lithium. Although graphite is currently widely used as a carbonaceous anode material, its shortcomings, such as its small interlayer spacing and its tendency to form unstable compounds with sodium, limit its large-scale application in SIBs. In contrast, hard carbon materials are considered one of the most promising anode candidates due to their low voltage platform, chemical stability, low cost, and ease of preparation.

[0003] Existing technologies employ modification strategies such as introducing defects and functional groups and increasing specific surface area to increase the adsorption capacity contribution of sodium ions. However, these modification strategies also present challenges, such as irreversible adsorption at defect sites and irreversible decomposition of the electrolyte, which can lead to the formation of an uneven solid electrolyte interface (SEI). This can lead to problems in sodium-ion batteries, such as low initial coulombic efficiency, poor rate performance, and unsatisfactory cycling stability. To address this issue, the present invention proposes Zn single-atom modified hard carbon materials, their preparation methods, and applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a Zn single atom modified hard carbon material and a preparation method and application thereof, aiming to solve the problems raised in the above background technology.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The preparation method of Zn single atom modified hard carbon material comprises the following steps:

[0007] Dicyandiamide, benzenetricarboxylic acid, zinc oxide and ammonium nitrate are weighed and placed in a ball mill; the raw materials are mixed evenly and ground; after the grinding is completed, the resulting product is centrifuged, then washed with ethanol, and then dried in a vacuum oven to obtain a precursor; the precursor is placed in high-purity argon gas and subjected to high-temperature carbonization to obtain the final product, which is recorded as Zn-N4 carbon nanosheets.

[0008] Furthermore, the dicyandiamide is replaced by melamine or urea; the ammonium nitrate is replaced by N,N-dimethylformamide or ethanol; and the zinc oxide is replaced by zinc chloride, zinc nitrate, zinc acetylacetonate, cobalt trioxide, nickel trioxide, antimony trioxide or molybdenum trioxide.

[0009] Furthermore, the following specific steps are included:

[0010] 6 g of dicyandiamide, 0.6 g of benzenetricarboxylic acid, 108 mg of zinc oxide and 50 mg of ammonium nitrate were weighed and placed in a ball mill; the raw materials were mixed evenly and ground at a speed of 500 rpm for 2 hours; after grinding, the resulting product was centrifuged, then washed three times with ethanol, and then dried in a vacuum oven at 60°C for 12 hours to obtain a precursor; the precursor was placed in high-purity (99.99%) argon and high-temperature carbonized at 800°C for 2 hours to obtain the final product, which was recorded as Zn-N4 carbon nanosheets.

[0011] The Zn single atom modified hard carbon material is prepared according to the above-mentioned preparation method of the Zn single atom modified hard carbon material.

[0012] According to the above-mentioned application of Zn single atom modified hard carbon material in the preparation of sodium ion batteries.

[0013] Furthermore, the sodium ion battery is prepared according to the following steps:

[0014] Electrode sheets were prepared using Zn-N4 carbon nanosheets, which were then cut to obtain circular electrode sheets with a diameter of 12 mm. The circular electrode sheets were used as negative electrodes, and the metallic sodium sheets were used as counter electrodes, and were assembled together with the diaphragm and electrolyte to form a sodium ion battery.

[0015] Furthermore, the specific process of the step of preparing the electrode sheet using Zn-N4 carbon nanosheets is as follows:

[0016] Zn-N4 carbon nanosheets were mixed with a binder and a conductive agent in a ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent. The mixture was stirred thoroughly to form a slurry. The slurry was coated and placed in a vacuum drying oven and dried at 60°C to obtain an electrode sheet.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The Zn-N4 carbon nanosheets prepared in the present invention are used as negative electrode materials for sodium ion batteries and exhibit extremely high reversible capacity (0.05Ag -1 321.4mAh g -1 ), excellent rate performance (5Ag -1 190.2mAh g -1 ) and ultra-long cycle life (at 2A g -1 The single-atom modification method proposed in this invention provides a reasonable and effective solution to the challenges of slow storage kinetics and poor cycling stability of sodium-ion battery anodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Scanning electron microscopy (SEM) characterization of Zn-N4 carbon nanosheets.

[0020] Figure 2 X-ray diffraction (XRD) characterization of Zn-N4 carbon nanosheets.

[0021] Figure 3 Transmission electron microscopy (TEM) characterization of Zn-N4 carbon nanosheets.

[0022] Figure 4 Element distribution map of Zn-N4 carbon nanosheets.

[0023] Figure 5 High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Zn-N4 carbon nanosheets.

[0024] Figure 6 N1s and Zn 2p images of Zn-N4 carbon nanosheets from X-ray photoelectron spectroscopy (XPS).

[0025] Figure 7 X-ray absorption fine structure (XAFS) characterization of Zn-N4 carbon nanosheets; (a) is the near-edge absorption structure spectrum, (b) is the extended-edge absorption structure spectrum, and (c) is the extended-edge structure fitting curve.

[0026] Figure 8 Characterization of the cyclic voltammetry curves of Zn-N4 carbon nanosheets as the negative electrode of sodium ion batteries.

[0027] Figure 9 Characterization of the rate performance of Zn-N4 carbon nanosheets as anode for sodium ion batteries.

[0028] Figure 10 Characterization of the cycling performance of Zn-N4 carbon nanosheets as anode for sodium ion batteries. DETAILED DESCRIPTION

[0029] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided. However, this description should not be construed as limiting the scope of the present invention. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0030] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0031] Example 1, Preparation of Zn-N4 carbon nanosheets;

[0032] First, 6g of dicyandiamide, 0.6g of benzenetricarboxylic acid, 108mg of zinc oxide, and 50mg of ammonium nitrate were accurately weighed and placed in a ball mill. The raw materials were mixed thoroughly and ground at 500 rpm for 2 hours. After grinding, the resulting product was centrifuged and then washed three times with ethanol to remove impurities. It was then dried in a vacuum oven at 60°C for 12 hours to obtain the precursor. The precursor was placed in high-purity argon and carbonized at 800°C for 2 hours to obtain the final product, which was named Zn-N4 carbon nanosheets.

[0033] In an embodiment of the present invention, the present invention uses a high-energy ball milling method to prepare a zinc-containing precursor. In this process, the combined action of lateral shear force and vertical extrusion pressure destroys the zinc-oxygen bonds in zinc oxide, converting them into molten zinc ions, which then synergistically self-assemble with benzenetricarboxylic acid to form a zinc-based metal-organic framework (MOF). In the subsequent high-temperature pyrolysis process, the zinc ions are reduced to metallic zinc by carbon and volatilize in gaseous form. The volatilized single atoms are captured and anchored on the carbon support by four nitrogen atoms on the carbon support to form Zn-N4 carbon nanosheets. The advantages of Zn-N4 carbon nanosheets include:

[0034] 1) Increase Na + The storage capacity of Na + The reversible adsorption / desorption at the complementary atomic sites and the enhanced conductivity enhance the charge transfer kinetics between these sites, leading to improved storage capacity.

[0035] 2) Reduce the diffusion barrier: The optimized electrode surface configuration improves the ion affinity and reduces the ion migration resistance, thereby accelerating the ion storage kinetics and significantly improving the rate performance of the electrode material.

[0036] 3) Construction of a robust SEI: Single-atom sites significantly enhance the redox activity of the electrode surface, catalyzing the preferential decomposition of electrolyte salts to form a uniform, stable, and inorganic-rich SEI, thereby effectively preventing further electrolyte decomposition and the occurrence of side reactions.

[0037] Example 2, Preparation of Sodium Ion Battery;

[0038] Zn-N4 carbon nanosheets are mixed with polyvinylidene fluoride (PVDF) and a conductive agent (superP) in a ratio of 8:1:1. N-methylpyrrolidone (NMP) is used as a solvent and the mixture is stirred thoroughly to form a slurry. The slurry is coated and placed in a vacuum drying oven and dried at 60°C to obtain an electrode sheet. The electrode sheet is cut to obtain a circular electrode sheet with a diameter of 12 mm. The circular electrode sheet is used as the negative electrode, the metal sodium sheet is used as the counter electrode, and they are assembled together with a diaphragm and an electrolyte to form a sodium ion battery.

[0039] Example 3, various characterizations and performance tests of Zn-N4 carbon nanosheets;

[0040] Scanning electron microscopy (SEM) characterization: Results are shown in Figure 1 , it can be seen that the prepared material is a stacked nanosheet structure.

[0041] X-ray diffraction (XRD) characterization: the results are shown in Figure 2 It can be seen that the XRD diffraction peaks of the prepared material only have a broad peak of carbon at about 2θ=26°, and there is no characteristic diffraction peak of Zn, indicating that Zn is distributed in an amorphous state.

[0042] Transmission electron microscopy (TEM) characterization: Results are shown in Figure 3 , the carbon sheets are wrinkled and have a layered structure. Figure 4 This is an element distribution diagram, which shows that carbon, nitrogen, oxygen and zinc are evenly distributed.

[0043] High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images: Results are shown in Figure 5 The dense bright spots in the figure are Zn single atoms, which intuitively show the distribution of Zn on the amorphous carbon support.

[0044] X-ray photoelectron spectroscopy (XPS) images of N1s and Zn 2p: Results are shown in Figure 6 , indicating that single-atom Zn is bound to N, which is consistent with the results of HAADF-STEM.

[0045] X-ray absorption fine structure (XAFS) characterization: Results are shown in Figure 7 In (a), the near-edge absorption threshold of Zn-N4 carbon nanosheets is between Zn foil and ZnO and close to that of ZnO, proving that it exists in a valence state close to +2. Figure 7 The EXAFS spectrum in (b) shows that Zn single atoms are bound to N. Figure 7 The fitting data in (c) further confirm the existence of the ZnN4 configuration, in which a single Zn atom is stabilized by bonding with four surrounding nitrogen atoms.

[0046] Cyclic voltammetry curve characterization as a negative electrode for sodium ion batteries: see Figure 8 , at 0.1mV s -1 At a scan rate of 1.5 V, the voltage window is 0.01-3.0 V. During the first cycle, the appearance of the irreversible reduction peak indicates the formation of the solid electrolyte interface.

[0047] Characterization of rate performance as a negative electrode for sodium ion batteries: Results are shown in Figure 9 , at 0.05Ag -1 At a current density of 3.5, the sodium half-cell has a reversible capacity of 321.4 mAh g -1, and in 5Ag -1 At high current density, the capacity can still be maintained at 190.2mAhg -1 .

[0048] Cycling performance characterization as a negative electrode for sodium ion batteries: see Figure 10 , in 2Ag -1 At a current density of 1.5 GHz, after 4000 charge and discharge tests, the capacity retention rate was 92.1%.

[0049] Conclusion: The Zn-N4 carbon nanosheets prepared in this invention exhibited extremely high reversible capacity (0.05A g -1 321.4mAh g -1 ), excellent rate performance (5A g -1 190.2mAh g -1 ) and ultra-long cycle life (at 2Ag -1 The single-atom modification method proposed in this invention provides a reasonable and effective solution to the challenges of slow storage kinetics and poor cycling stability of sodium-ion battery anodes.

[0050] The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention. These should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. Application of Zn single atom modified hard carbon material in the preparation of sodium ion batteries, characterized in that: The preparation method of the Zn single atom modified hard carbon material comprises the following steps: Dicyandiamide, benzenetricarboxylic acid, zinc oxide and ammonium nitrate are weighed and placed in a ball mill; the raw materials are mixed evenly and ground; after the grinding is completed, the resulting product is centrifuged, then washed with ethanol, and then dried in a vacuum oven to obtain a precursor; the precursor is placed in high-purity argon gas and subjected to high-temperature carbonization to obtain the final product, which is recorded as Zn-N4 carbon nanosheets.

2. The use according to claim 1, characterized in that The dicyandiamide is replaced by melamine or urea; the ammonium nitrate is replaced by N,N-dimethylformamide or ethanol; and the zinc oxide is replaced by zinc chloride, zinc nitrate, or zinc acetylacetonate.

3. The use according to claim 1, characterized in that The preparation method of the Zn single atom modified hard carbon material comprises the following specific steps: Weigh 6 g of dicyandiamide, 0.6 g of benzenetricarboxylic acid, 108 mg of zinc oxide, and 50 mg of ammonium nitrate into a ball mill. Mix the ingredients thoroughly and grind at 500 rpm for 1-5 h. After grinding, the product was centrifuged, washed three times with ethanol, and then dried in a vacuum oven at 60°C for 12 hours to obtain a precursor; the precursor was placed in argon with a purity of 99.99% and carbonized at 800°C for 2 hours to obtain the final product, which was recorded as Zn-N4 carbon nanosheets.

4. The use according to claim 1, characterized in that The sodium ion battery is prepared according to the following steps: Electrode sheets were prepared using Zn-N4 carbon nanosheets, and the electrode sheets were cut to obtain circular electrode sheets with a diameter of 12 mm. The circular electrode sheets were used as negative electrodes, and the metallic sodium sheets were used as counter electrodes, and they were assembled together with the separator and electrolyte to form a sodium ion battery.

5. The use according to claim 4, characterized in that The specific process of the step of preparing the electrode sheet using Zn-N4 carbon nanosheets is as follows: Zn-N4 carbon nanosheets were mixed with a binder and a conductive agent in a ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent. The mixture was stirred thoroughly to form a slurry. The slurry was coated and placed in a vacuum drying oven and dried at 60°C to obtain an electrode sheet.

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