Heterojunction vanadium oxide / three-dimensional graphite paper aqueous magnesium ion battery electrode material and preparation method thereof

Abstract

The application provides a preparation method of a heterojunction V02.xH2O@V2O5 magnesium storage electrode and belongs to the technical field of energy storage materials. VOSO4 is used as a vanadium source, CH3COONH4 is used as a buffer solution, and a heterojunction vanadium oxide composite is grown on the surface of a stripped three-dimensional graphite paper by controlling electrochemical reaction conditions. The prepared vanadium oxide is composed of a tunnel-shaped VO2.xH2O and a layered V2O5 composite, a variety of magnesium ion diffusion paths are provided, a three-dimensional graphite paper provides an electron conduction path, and the combination of the two makes the material have excellent magnesium storage performance. The heterojunction electrode can be expanded to other energy storage fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of aqueous energy storage materials, and in particular relates to a method for preparing a heterojunction VO2·xH2O@V2O5 magnesium storage electrode. Background Art

[0002] Aqueous magnesium-ion batteries (AMIBs) play an important role in large-scale energy storage due to their low cost, long cycle life, and high safety. AMIBs are primarily composed of electrode materials, separators, and aqueous electrolytes. Each component significantly impacts the AMIBs, with the electrode materials playing a decisive role in their performance. Vanadium oxide, a common transition metal oxide, offers advantages such as high theoretical specific capacity, structural diversity, and ease of preparation, making it a promising electrode material for AMIBs. However, its low electrical conductivity and strong Mg-O interaction severely limit its performance, resulting in limited application in AMIBs. Therefore, the development of vanadium oxide electrodes with excellent electrical conductivity and ion diffusion kinetics is of great significance.

[0003] At present, the main methods to improve the performance of vanadium oxide are material nano-sizing, heteroatom doping and carbon coating modification. For example, Fu et al. reported a hydrothermal synthesis of hydrated Ca 2+ AMIBs cathode materials doped with V2O5 achieve better rate performance by regulating the electrolyte (Energy Storage Materials 66 (2024) 103212). Xu et al. synthesized Mg by hydrothermal method. 2+ Mg co-doped with H2O 0.3 V2O5·1.1H2O AMIBs cathode material achieves good cycling performance (Chem 5(2019) 1194-1209). Although these methods have improved the performance of vanadium oxide to a certain extent, they are equipment-intensive and time-consuming. Therefore, it is necessary to develop a simple and rapid preparation technology for vanadium oxide electrode materials to achieve high-performance AMIBs. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the aforementioned preparation techniques by providing a rapid method for preparing a sea urchin-like nanostructured heterojunction vanadium oxide magnesium storage electrode, addressing the issues of vanadium oxide's low conductivity and slow magnesium ion diffusion. This method utilizes electrochemical techniques to prepare a three-dimensional graphite paper current collector. The heterojunction vanadium oxide (VO2·xH2O@V2O5) nanomaterial is then electrodeposited onto the surface of this three-dimensional graphite paper current collector. The method comprises the following steps:

[0005] 1. Preparation of 3D graphite paper current collector

[0006] In a three-electrode electrolytic cell system, graphite paper was used as the working electrode, a Pt sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrochemical stripping process consisted of three steps: (1) a primary stripping step using cyclic voltammetry in a low-concentration alkaline solution; (2) a secondary stripping step using constant voltage in a saline solution; and (3) a cyclic voltammetry scan in a saline solution to restore the conductivity and surface wettability of the graphite paper.

[0007] 2. Preparation of heterojunction VO2·xH2O@V2O5 electrode

[0008] In a three-electrode system, the vanadium oxide heterojunction material was electrodeposited using the three-dimensional graphite paper prepared in step 1 as the working electrode, unexfoliated graphite paper as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrolyte used for the electrodeposition was a mixed solution of sulfate and acetate, and cyclic voltammetry was used for electrodeposition. After the reaction was complete, the working electrode was removed, washed, and dried to obtain the heterojunction VO2·xH2O@V2O5 magnesium storage electrode material.

[0009] Wherein, the alkaline solution in (1) is NaOH or KOH with a solubility of 0.3~0.6 M; the scanning voltage range of the cyclic voltammetry is 0.5~1.7 V, the scanning rate is 10~30 mV / s, and the number of cycles is 5~10.

[0010] The salt solution in (2) of 1 is NaNO3 or KNO3, with a solubility of 1~2.5 M, a voltage of 1.8 V, and a deposition time of 3-10 min.

[0011] The salt solution in (3) of 1 is KNO3 or LiNO3 with a concentration of 1~2.5 M. The surface of the working electrode needs to be cleaned with deionized water before operation.

[0012] The voltage range of the cyclic voltammetry in 1 (3) is -1~1 V, the scan rate is 10~30 mV / s, and the number of scan cycles is 20~30 cycles.

[0013] The sulfate in 2 is VOSO4 with a purity greater than 99% and a concentration of 0.1 to 0.5 M, and the acetate is CH3COONH4 with a concentration of 0.1 to 0.5 M. The volume ratio of VOSO4 to CH3COONH4 is 1:1 to 2.

[0014] The voltage range of the cyclic voltammetry method used in the second electrodeposition of heterojunction vanadium oxide is -1 to 1.5 V, the scan rate is 20 to 30 mV / s, and the number of scan cycles is 10 to 30 cycles.

[0015] The two washing solvents are ethanol and deionized water, and the drying method is vacuum freeze drying.

[0016] The composition of the heterojunction vanadium oxide in the second embodiment is a composite of V2O5 and VO2·xH2O, and its morphology is a three-dimensional sea urchin-like structure self-assembled by nanobelts, and the width of the nanobelts is 8-30 nm.

[0017] The basic principle of the present invention is

[0018] Electrochemical exfoliation of graphite paper is a highly efficient exfoliation method. It works by embedding electrolyte ions between graphite layers. Electrochemical oxidation, which introduces oxygen-containing functional groups and bubbles generated by water decomposition, weakens the van der Waals forces between the layers, thereby peeling the graphite layers apart. By adjusting the electrolyte concentration and exfoliation time, the degree of exfoliation is controlled, allowing a large number of graphite sheets or graphene to curl up from the surface of the graphite block. Electrochemical reduction then restores the conductivity of the rolled-up graphite oxide sheets, resulting in a three-dimensional graphite paper current collector.

[0019] Electrodeposition is a common method for preparing heterojunction materials. By controlling the electrodeposition conditions (voltage window, current density, and reaction time), heterojunctions can be fabricated and adjusted, offering advantages such as low cost and high efficiency. The heterojunction vanadium oxide prepared in this invention utilizes cyclic voltammetry. In this method, the deposition potential must be above the onset potential of the electrochemical reaction to initiate the deposition reaction, and the deposition rate gradually increases with increasing deposition potential. As a result, the prepared heterojunction material has a relatively uniform crystalline structure. Due to the wide positive voltage range, the deposited vanadium oxide is primarily in the high-valent state, V2O5. Furthermore, during the rapid oxidation / reduction process, the surface crystalline structure of the high-valent V2O5 rapidly changes, generating low-valent VO2. Since the electrolyte is an aqueous solution, water molecules readily intercalate within the vanadium oxide structure.

[0020] Compared with the prior art, the present invention has the following advantages

[0021] (1) The present invention uses electrochemical stripping technology and electrodeposition technology to prepare heterojunction composite materials. The equipment is simple, the operation is convenient, and harsh preparation conditions are avoided. Most importantly, the preparation time is short.

[0022] (2) Three-dimensional graphite paper as a current collector has a large specific surface area, high space utilization, and high conductivity.

[0023] (3) Vanadium oxide is grown on the surface of three-dimensional graphite paper using the COV force of chemical bonds, ensuring the stability of the electrode material structure.

[0024] (4) The heterojunction vanadium oxide consists of a layered structure of V2O5 and a tunnel structure of VO2·xH2O. This structure provides multiple ion diffusion paths and has high ion diffusion kinetics.

[0025] (5) The heterojunction VO2·xH2O@V2O5 material obtained in the present invention has excellent electrochemical magnesium storage performance and can be further applied in the field of energy materials such as zinc, calcium and aluminum storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope photograph of the three-dimensional graphite paper current collector prepared in Example 1;

[0027] Figure 2 This is a scanning electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 1;

[0028] Figure 3 This is a transmission electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 1;

[0029] Figure 4 This is the X-ray diffraction image of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 1;

[0030] Figure 5 Performance diagram of the heterojunction VO2·xH2O@V2O5 electrode prepared in Example 1;

[0031] Figure 6 This is a scanning electron microscope photograph of the three-dimensional graphite paper current collector prepared in Example 2;

[0032] Figure 7 This is a scanning electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 2;

[0033] Figure 8 This is a transmission electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 2;

[0034] Figure 9 Performance diagram of the heterojunction VO2·xH2O@V2O5 electrode prepared in Example 2;

[0035] Figure 10 This is a scanning electron microscope photograph of the three-dimensional graphite paper current collector prepared in Example 3;

[0036] Figure 11 This is a scanning electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 3;

[0037] Figure 12 This is a transmission electron microscope photograph of the heterojunction VO2·xH2O@V2O5 electrode material prepared in Example 3;

[0038] Figure 13Performance chart of the heterojunction VO2·xH2O@V2O5 electrode prepared for example 3. DETAILED DESCRIPTION

[0039] The application will be further described in detail below with examples.

[0040] (1) The scanning electron microscope is SU8010 of Japan Hitachi Company, which is used to observe the morphology and structural characteristics of the sample.

[0041] (2) The transmission electron microscope is JEM2100F of Japan Electronics Corporation, which is used to observe the internal microstructure of the sample.

[0042] (3) The X-ray diffractometer is PANalytical X'Pert PRO of Netherlands PANalytical Company, which is used to observe the crystal composition of the sample.

[0043] (4) The electrochemical test is carried out by using a three-electrode system, wherein the prepared VO2·xH2O@V2O5 electrode is a working electrode, a saturated mercury-mercury electrode is a reference electrode, a Pt sheet is a counter electrode, 4 M MgCl2 is an electrolyte, and the electrochemical test window is-0.3~1.0 V.

[0044] The chemical reagents used in the embodiment of the application are provided by Shanghai Aladdin Bio-Chem Technology Co., Ltd.

[0045] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, the technical scheme in the embodiments of the application will be clearly and completely described below by combining the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, but not all the embodiments of the application. Any technical scheme which does not deviate from the spirit and scope of the application should be covered in the application protection range.

[0046] Example 1

[0047] 1. Preparation of three-dimensional graphite paper current collector:

[0048] In a three-electrode electrolytic cell system, graphite paper was used as the working electrode, a Pt sheet was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode. The electrochemical stripping was performed in three steps: (1) a preliminary cyclic voltammetry stripping was performed in a three-electrode system using 0.5 M 30 mL KOH as the electrolyte, with the parameters set at a scan voltage range of 0.5–1.7 V, a scan rate of 20 mV / s, and a scan number of 10 cycles; (2) a secondary constant voltage stripping was performed in a three-electrode system using 1 M 30 mL KNO3 as the electrolyte, with the parameters set at a voltage value of 1.8 V and a reaction time of 10 min; (3) to restore the conductivity and surface wettability of the graphite paper, the working electrode was briefly cleaned and placed in 1 M 30 mL KNO3 for cyclic voltammetry treatment, with the parameters set at a scan voltage range of -1–1 V, a scan rate of 20 mV / s, and a scan number of 20 cycles. After the reaction is completed, the working electrode is removed, washed with deionized water, and then freeze-dried to obtain the final three-dimensional graphite paper current collector. The scanning electron microscope image is shown in FIG. Figure 1 shown.

[0049] 2. Preparation of heterojunction VO2·xH2O@V2O5 electrode

[0050] In a three-electrode system, the three-dimensional graphite paper prepared in 1 above was used as the working electrode, the unpeeled graphite paper was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to electrodeposit heterojunction VO2·xH2O@V2O5. The electrolyte for electrodeposition was 30 mL of a mixed solution of VOSO4 and CH3COONH4 with a volume ratio of 1:1, wherein VOSO4 provided a vanadium source with a concentration of 0.5 M, and CH3COONH4 was a buffer solution with a concentration of 0.5 M. The parameters of the cyclic voltammetry were set to a voltage range of -1~1.5 V, a scan rate of 20 mV / s, and 20 scans. After the reaction was completed, the working electrode was taken out, washed three times with deionized water and ethanol respectively, and freeze-dried to obtain the heterojunction VO2·xH2O@V2O5 electrode material. The scanning electron microscope image is shown in FIG. Figure 2 As shown, its morphology is a three-dimensional sea urchin-like structure self-assembled by nanobelts; the transmission electron microscope image is shown Figure 3 As shown, the width of the nanoribbon is 8~20 nm; the X-ray diffraction pattern is shown Figure 4 As shown, it is a mixed phase heterojunction composition.

[0051] The performance of the electrode prepared under these conditions was tested in a three-electrode system. The results showed that the heterojunction VO2·xH2O@V2O5 electrode had a -1 The magnesium storage capacity is 510 mAh g -1 , at 5 A g -1 The magnesium storage capacity is 195.5 mAh g -1 ,like Figure 5 shown.

[0052] Example 2

[0053] 1. Preparation of three-dimensional graphite paper current collector:

[0054] In a three-electrode electrolytic cell system, graphite paper was used as the working electrode, a Pt sheet was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode. The electrochemical stripping was performed in three steps: (1) a preliminary cyclic voltammetry stripping was performed in the three-electrode system using 30 mL of 0.5 M KOH as the electrolyte, with the parameters set at a scan voltage range of 0.5–1.7 V, a scan rate of 20 mV / s, and a scan number of 10 cycles; (2) a secondary constant voltage stripping was performed in the three-electrode system using 30 mL of 1 M KNO3 as the electrolyte, with the parameters set at a voltage value of 1.8 V and a reaction time of 8 min; (3) to restore the conductivity and surface wettability of the graphite paper, the working electrode was briefly cleaned and placed in 30 mL of 2.5 M LiNO3 for cyclic voltammetry treatment, with the parameters set at a scan voltage range of -1–1 V, a scan rate of 20 mV / s, and a scan number of 30 cycles. After the reaction is completed, the working electrode is removed, washed with deionized water, and then freeze-dried to obtain the final three-dimensional graphite paper current collector. The scanning electron microscope image is shown in FIG. Figure 6 It can be seen that after a long period of peeling, the surface of the graphite paper is peeled to an increased degree and small local fragments are generated.

[0055] 2. Preparation of heterojunction VO2·xH2O@V2O5 electrode

[0056] In a three-electrode system, the three-dimensional graphite paper prepared in 1 above was used as the working electrode, the unpeeled graphite paper was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to electrodeposit heterojunction VO2·xH2O@V2O5. The electrolyte for electrodeposition was 30 mL of a mixed solution of VOSO4 and CH3COONH4 with a volume ratio of 1:2, wherein VOSO4 provided a vanadium source with a concentration of 0.5 M, and CH3COONH4 was a buffer solution with a concentration of 0.5 M. The parameters of the cyclic voltammetry were set to a voltage range of -1~1.5 V, a scan rate of 20 mV / s, and 30 scans. After the reaction was completed, the working electrode was taken out, washed three times with deionized water and ethanol respectively, and freeze-dried to obtain the heterojunction VO2·xH2O@V2O5 electrode material. The scanning electron microscope image is shown in FIG. Figure 7 As shown, its morphology is a three-dimensional sea urchin-like structure self-assembled by dense nanobelts; the transmission electron microscopy image is shown in Figure 8 As shown, it shows that its nanoribbons have an interwoven sea urchin-like structure and the width of the nanoribbons is 8~30 nm.

[0057] The performance of the electrode prepared under these conditions was tested in a three-electrode system. The results showed that the heterojunction VO2·xH2O@V2O5 electrode had a -1 The magnesium storage capacity is 450 mAh g -1 , at 5 A g -1 The magnesium storage capacity is 190 mAh g -1 ,like Figure 9 shown.

[0058] Example 3

[0059] 1. Preparation of three-dimensional graphite paper current collector:

[0060] In a three-electrode electrolytic cell system, graphite paper was used as the working electrode, a Pt sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrochemical stripping was performed in three steps: (1) a preliminary cyclic voltammetry stripping was performed in the three-electrode system using 0.5 M 30 mL KOH as the electrolyte, with the parameters set at a scan voltage range of 0.5–1.7 V, a scan rate of 20 mV / s, and a scan number of 5 cycles; (2) a secondary constant voltage stripping was performed in the three-electrode system using 2.5 M 30 mL KNO3 as the electrolyte, with the parameters set at a voltage value of 1.8 V and a reaction time of 3 min; (3) to restore the conductivity and surface wettability of the graphite paper, the working electrode was briefly cleaned and placed in 2.5 M 30 mL KNO3 for cyclic voltammetry treatment, with the parameters set at a scan voltage range of -1–1 V, a scan rate of 20 mV / s, and a scan number of 20 cycles. After the reaction is completed, the working electrode is removed, washed with deionized water, and then freeze-dried to obtain the final three-dimensional graphite paper current collector. The scanning electron microscope image is shown in FIG. Figure 10 As shown in the figure, it can be seen that due to the short peeling time, the surface of the graphite paper is slightly peeled off and a good three-dimensional structure cannot be produced.

[0061] 2. Preparation of heterojunction VO2·xH2O@V2O5 electrode

[0062] In a three-electrode system, the three-dimensional graphite paper prepared in 1 above was used as the working electrode, the unpeeled graphite paper was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to electrodeposit heterojunction VO2·xH2O@V2O5. The electrolyte for electrodeposition was 30 mL of a mixed solution of VOSO4 and CH3COONH4 with a volume ratio of 1:2, wherein VOSO4 provided a vanadium source with a concentration of 0.2 M, and CH3COONH4 was a buffer solution with a concentration of 0.2 M. The parameters of the cyclic voltammetry were set to a voltage range of -1~1.5 V, a scan rate of 20 mV / s, and 10 scans. After the reaction was completed, the working electrode was taken out, washed with deionized water and ethanol three times respectively, and freeze-dried to obtain the heterojunction VO2·xH2O@V2O5 electrode material. The scanning electron microscope image is shown in FIG. Figure 11 As shown, its morphology is a nanobelt structure. Due to the low concentration of electrolyte and short deposition time, the nanobelts are not assembled into a three-dimensional structure; the transmission electron microscope image is shown in Figure 12 As shown, the width of the nanoribbons is 8~20 nm.

[0063] The performance of the electrode prepared under these conditions was tested in a three-electrode system. The results showed that the heterojunction VO2·xH2O@V2O5 electrode had a -1 The magnesium storage capacity is 300 mAh g -1 , at 5 A g -1 The magnesium storage capacity is 120 mAh g -1 ,like Figure 13 shown.

[0064] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a heterojunction VO2·xH2O@V2O5 magnesium storage electrode, characterized in that: The preparation method comprises the following steps: (1) Electrochemical preparation of three-dimensional graphite paper current collector: In a three-electrode system, graphite paper is used as the working electrode, Pt sheet is used as the counter electrode, and saturated calomel electrode is used as the reference electrode. Electrochemical stripping is divided into three steps: 1) Preliminary stripping by cyclic voltammetry in a low-concentration alkaline solution, wherein the alkaline solution is NaOH or KOH with a solubility of 0.3~0.6 M, the scanning voltage range of the cyclic voltammetry is 0.5~1.7 V, the scanning rate is 10~30 mV / s, and the number of cycles is 5~10; 2) Secondary stripping by constant voltage in a salt solution, wherein the salt solution is NaNO3 or KNO3 with a solubility of 1~2.5 M, the constant voltage stripping voltage is 1.8 V, and the deposition time is 3-10 min; 3) Restoration of the conductivity of graphite paper by cyclic voltammetry scanning in a salt solution, wherein the salt solution is KNO3 or LiNO3 with a concentration of 1~2.5 M, the voltage range of the cyclic voltammetry is -1~1 V, and the scanning rate is 10~30 mV / s, the scanning number of circles is 20~30 circles; (2) Preparation of heterojunction VO2·xH2O@V2O5 magnesium storage electrode: In a three-electrode system, the three-dimensional graphite paper prepared in (1) is used as the working electrode, the unpeeled graphite paper is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode to carry out electrodeposition of heterojunction VO2·xH2O@V2O5 material; the electrolyte for electrodeposition is a mixed solution of sulfate and acetate, wherein the sulfate is VOSO4, the acetate is CH3COONH4, and the volume ratio of VOSO4 to CH3COONH4 is 1:1~2; the electrodeposition is carried out by cyclic voltammetry, wherein the voltage range of the cyclic voltammetry is -1~1.5 V, the scan rate is 20~30 mV / s, and the number of scan cycles is 10~30 cycles; after the reaction is completed, the working electrode is taken out, washed and dried to obtain the heterojunction VO2·xH2O@V2O5 magnesium storage electrode.

2. The method for preparing a heterojunction VO2·xH2O@V2O5 magnesium storage electrode according to claim 1, characterized in that: The heterojunction VO2·xH2O@V2O5 is composed of a composite of V2O5 and VO2·xH2O, and has a morphology of nanoribbons self-assembled into a three-dimensional sea urchin-like structure, wherein the nanoribbon width is 8-30 nm.

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