Magnesium vanadium oxide positive electrode material with spinel structure and preparation method of magnesium vanadium oxide positive electrode material

Abstract

The invention relates to the related technical field of magnesium ion batteries, and particularly discloses a magnesium vanadium oxide positive electrode material with a spinel structure and a preparation method of the magnesium vanadium oxide positive electrode material. The preparation method comprises the following steps: step 1, mixing vanadium pentoxide and magnesium oxide according to a molar ratio of vanadium pentoxide to magnesium oxide of 1: (3-3.2), and grinding to obtain mixed powder; 2, the mixed powder is heated to 900 DEG C to 1200 DEG C, heat preservation is conducted for 2 h to 24 h, and magnesium orthovanadate is obtained; and 3, heating magnesium orthovanadate in a reducing atmosphere of a mixed gas composed of hydrogen and argon for 4-16 h at 450-900 DEG C to obtain the positive electrode material. The positive electrode material prepared by the preparation method disclosed by the invention has a spinel structure, and the problem of dynamic retardation of a water-based magnesium ion battery is solved.

Description

Technical Field

[0001] The present invention relates to the technical field related to magnesium ion batteries, and in particular to a magnesium vanadium oxide positive electrode material with a spinel structure and a preparation method thereof. Background Art

[0002] Fuel-powered vehicles are prone to environmental pollution, while batteries offer a more efficient and environmentally friendly green energy source. Traditionally, lithium batteries are limited by the scarcity of lithium resources, energy density, cycle life, and safety, prompting a pursuit of lower-cost, higher-capacity, and safer batteries. Magnesium-ion batteries, due to their abundant magnesium resources, are the most promising electrochemical energy storage devices to replace lithium batteries.

[0003] Aqueous magnesium-ion batteries are mainly composed of embedded electrode materials and aqueous electrolytes. They have the advantages of being green, environmentally friendly, low-cost, safe and have high energy density. However, current aqueous magnesium-ion batteries generally have a low voltage platform and low specific capacity. In addition, the migration energy barrier of Mg2+ in the embedded electrode materials is large, which often leads to voltage hysteresis and sluggish kinetics in the battery, which greatly limits the application of aqueous magnesium-ion batteries. Summary of the Invention

[0004] The present invention aims to provide a magnesium vanadium oxide positive electrode material with a spinel structure and a preparation method thereof, so as to solve the problem of slow kinetics of aqueous magnesium ion batteries.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, comprising the following steps: Step 1: Mix vanadium pentoxide and magnesium oxide in a molar ratio of vanadium pentoxide:magnesium oxide = 1:3-3.2 and grind to obtain a mixed powder; Step 2: heating the mixed powder to 900-1200° C. and keeping the temperature for 2-24 hours to obtain magnesium orthovanadate; Step 3: Heat magnesium orthovanadate at 450-900° C. in a reducing atmosphere of a mixed gas consisting of hydrogen and argon for 4-16 hours to obtain a positive electrode material.

[0006] The beneficial effects of this program are: 1. Vanadates have a high valence of vanadium and the amount of oxygen deficiency is difficult to control. They often exhibit two phases on the surface and inside of the material, resulting in a high number of impurities in the material, making it difficult to apply to magnesium batteries. However, the inventors accidentally discovered that when the raw materials are sintered by the solid-phase sintering method in this solution and reduced by the atmosphere reduction method, the resulting magnesium vanadium oxide has a pure-phase spinel structure, and the size and morphology of the microstructure of the material are basically the same. In addition, in the materials of this solution, the valence of vanadium is +3, at which time the vanadium is in a completely reduced state, and the electrochemical performance of the material is better.

[0007] At the same time, the material prepared in step 3 has three-dimensional ion channels, which effectively reduces the migration barrier of magnesium ions. After adopting the positive electrode material prepared by this scheme, the battery will not have problems of voltage hysteresis and kinetic sluggishness.

[0008] At present, the battery positive electrode material including magnesium elements, as shown in the patent application number 202410642318.3, needs to be sintered with a dispersant. And the above-mentioned prior art mainly improves the performance of the positive electrode material by manganese, but the raw materials of this scheme are only magnesium source and vanadium source, so that no other elements are introduced into the prepared positive electrode material, the impurity phase in the material is small, and the sintering yield is high. Secondly, the two elements of magnesium and vanadium are abundant in domestic resources and have low transportation costs, which makes the cost of the prepared positive electrode material low.

[0009] Moreover, this solution further reduces the particle size of vanadium pentoxide and magnesium oxide by ball milling, and can fully mix vanadium pentoxide and magnesium oxide. After the particle size of vanadium pentoxide and magnesium oxide is reduced, the contact surface is larger, making the reaction activity stronger during heating, which can further reduce the reaction temperature and improve the reaction efficiency.

[0010] 2. Currently, spinel-structured materials are typically prepared using a hydrothermal method, which is difficult, energy-intensive, and produces low yields. The present method effectively increases yields, and steps 2 and 3 require only controlling the temperature within the heating device, resulting in a low level of preparation and high yields.

[0011] Compared with the current single-shot sintering method, this solution performs two sintering steps, step 2 and step 3, so that the temperature during each sintering is lower, effectively reducing energy consumption. At the same time, it can also reduce the difficulty of production in large-scale production and facilitate the overall control of the reaction progress.

[0012] 3. Since only vanadium pentoxide and magnesium oxide are used in this scheme, hydrogen and argon can be used as the reducing atmosphere in step 3 of this scheme. The presence of argon makes the reaction in step 3 safer, thereby effectively improving the safety of large-scale processing.

[0013] Furthermore, the grinding time of step 1 is 5 to 30 minutes.

[0014] The beneficial effect of this solution is that it can fully mix vanadium pentoxide and magnesium oxide, thereby making the phase in the prepared positive electrode material more uniform.

[0015] Furthermore, in step 2, the heating rate during heating is 5-20°C / min.

[0016] Furthermore, in step 3, the heating rate during heating is 1-10°C / min.

[0017] The beneficial effects of this solution are: vanadium pentoxide and its reduction products are highly volatile at high temperatures. Rapid heating will cause them to dissolve, causing some of them to volatilize and some to adhere to the reaction vessel, thereby generating a small amount of impurities. This solution controls the heating rate to effectively suppress this volatilization, reduce impurities, and simultaneously improve the yield of the material.

[0018] Furthermore, in the mixed gas used in step 3, the hydrogen content is 5-30%, and the argon content is 70-95%.

[0019] The beneficial effect of this solution is that the argon content in this solution is higher, making the sintering safer.

[0020] A magnesium vanadium oxide positive electrode material with a spinel structure, prepared by the method of any one of claims 1 to 5, with a chemical formula of Mg3V2O6.

[0021] Furthermore, the material has a spinel structure, and grooves exist on the surface of the structure.

[0022] The beneficial effects of this solution are as follows: the positive electrode material prepared by the present invention has an irregular spinel structure, and the presence of gullies effectively increases the specific surface area of ​​the material, allowing the material to expose more active sites capable of electrochemical reactions, thereby effectively increasing the reaction rate and specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a preparation flow chart of an embodiment of the present invention; Figure 2 This is the XRD analysis pattern of the magnesium orthovanadate prepared in Example 1; Figure 3 This is the XRD analysis diagram of the positive electrode material prepared in Example 1; Figure 4 This is a scanning electron microscope image of the positive electrode material prepared in Example 1; Figure 5 SEM-EDS image of the cathode material; Figure 6 The cyclic voltammogram of the positive electrode material electrode in the first three cycles; Figure 7 This is the rate performance diagram of the cathode material at different rates; Figure 8 The rate performance diagram of the cathode material at different rates in the voltage window of 0-1.9V; Figure 9 Specific capacity and coulombic efficiency of the positive electrode material at different cycle times. DETAILED DESCRIPTION

[0024] The following is further described in detail through specific implementation methods: Example A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, combined with Figure 1 , including the following steps: Step 1: Mix vanadium pentoxide and magnesium oxide in a molar ratio of vanadium pentoxide:magnesium oxide = 1:3 and grind for 5-30 minutes to obtain a mixed powder; Step 2: heating the mixed powder to 900-1200°C at a heating rate of 5-20°C / min and keeping the temperature for 2-24 hours to obtain magnesium orthovanadate; Step 3: Heat magnesium orthovanadate to 450-900°C in a reducing atmosphere of a mixed gas consisting of hydrogen and argon, wherein the heating rate is 1-10°C / min, the hydrogen content in the mixed gas is 5-30%, the argon content is 70-95%, the heating time is 4-16 hours, and after naturally cooling to room temperature, a positive electrode material is obtained.

[0025] The present invention also discloses a magnesium vanadium oxide positive electrode material with a spinel structure prepared by the above preparation method, the chemical formula of which is Mg3V2O6, the crystal phase of which is a spinel structure, and grooves exist on the surface of the crystal phase structure.

[0026] The present invention discloses Examples 1 to 4. The grinding time, heating temperature, heating rate, holding time in step 2 and step 3, and the content of hydrogen and argon in the mixed gas in Examples 1 to 4 are different, as shown in the following table:

[0027] The present invention characterizes and analyzes the structure and morphology of the magnesium orthovanadate prepared in Example 1 and the final cathode material using the following characterization methods: 1. XRD analysis Please refer to Figure 2 All diffraction peaks of the magnesium orthovanadate prepared in step 2 match the PDF standard card (JCPDS No.73-0207), with no obvious impurity peaks and good crystallinity, indicating that the product prepared by this method is pure magnesium orthovanadate with extremely low impurity content.

[0028] Please refer to Figure 3 All diffraction peaks of the prepared cathode material match the PDF standard card (JCPDS No.50-1895), proving that the cathode material prepared by this method has a spinel structure skeleton, no obvious impurity peaks and good crystallinity.

[0029] 2. SEM Characterization Please refer to Figure 4 The material prepared by this invention appears as irregular micron-sized particles with a particle size between 5 and 20 µm. Due to the lack of oxygen atoms, the surface of the positive electrode material is covered with grooves and large pores. The width of the grooves is generally above 90 nm, and can reach up to 170 nm. These large grooves provide a large number of active sites for magnesium ion and charge transfer, maximizing the material's specific capacity.

[0030] Please refer to Figure 5 , proving that the Mg, V and O elements in the sample are evenly distributed, indicating that the double sintering in steps 2 and 3 in the present invention makes the crystal phase in the obtained material evenly distributed, and the performance of the prepared positive electrode is the same everywhere, so that the performance of the battery can remain stable for a long time during use.

[0031] The present invention also installed the positive electrode material prepared in Example 1 into the following two battery systems, and tested the electrochemical performance: 1. The intrinsic electrochemical properties of the Mg3V2O6 electrode material were tested using a traditional three-electrode system (hereinafter referred to as "three-electrode"), with Mg3V2O6 electrode as the working electrode, platinum electrode as the counter electrode, Ag / AgCl as the reference electrode, and 2M Mg(CF3SO3)2 solution with polyethylene glycol (PEG):H2O=1:1 as the solvent as the electrolyte.

[0032] 2. A button cell double-electrode system (hereinafter referred to as "double electrode") was used, with Mg3V2O6 electrode as the positive electrode, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) electrode as the negative electrode, 2M Mg(CF3SO3)2 solution with polyethylene glycol (PEG):H2O=1:1 as the solvent as the electrolyte, and glass fiber filter paper (pore size of 1.0-1.6μm) as the separator. The system was assembled into a CR2430 button cell, and its electrochemical performance was tested.

[0033] Both the three-electrode and two-electrode systems were tested for cyclic voltammetry (CV) using a Chenhua electrochemical workstation (CHI660E), and constant current charge and discharge (GCD) and long cycle tests were performed on a Xinwei multi-channel battery tester (CT4008A).

[0034] The test results are as follows: 1. Cyclic voltammetry curve - three electrodes Please refer to Figure 6 Under conditions of a current density of 1 mV s⁻¹ and a voltage range of -1 to 1.2 V (vs. Ag / AgCl), a strong oxidation peak is observed at 0.33 V, and two reduction peaks are observed at -0.70 V and -0.22 V, indicating that the removal of Mg₂+ occurs in steps. In subsequent cycles, the insertion and removal of Mg₂+ gradually become reversible, and the CV curves maintain similar shapes and voltage positions, demonstrating good electrochemical reversibility.

[0035] 2. Rate Performance - Three Electrodes Please refer to Figure 7 When the rate is 0.05A g-1, its initial specific capacity output is 309.12mAh / g. When the rate increases to 4A g-1, it can still output a specific capacity of up to 82.23mAh / g. When the rate is restored to 0.05A g-1, its capacity immediately recovers to 288.57mAh / g, showing an excellent rate performance advantage. All curves under different current densities maintain similar shapes and platform voltages, indicating that it has excellent rate performance advantages at different current densities.

[0036] 3. Rate Performance - Dual Electrode Please refer to Figure 8 When the rate is 0.05A g-1, its initial specific capacity output is 92.94mAh / g. When the rate increases to 4A g-1, it can still output a specific capacity of up to 58.89mAh / g. When the rate is restored to 0.05A g-1, its capacity rises to 97.71mAh / g, also showing an excellent rate performance advantage.

[0037] 4. Cyclic Stability Test-Dual Electrode Mg3V2O6 / / PTCDA was subjected to constant current charge and discharge cycles for 2000 times at a current density of 4A g-1 and a voltage window of 0-1.9V to test its stability.

[0038] Please refer to Figure 9 The initial discharge capacity was 69.23 mAh / g. After 2000 cycles, it still delivered a specific capacity of 51.02 mAh / g, with a capacity retention rate of 73.70%. Its coulombic efficiency remained stable at around 100%, indicating that the Mg3V2O6 prepared in this invention has relatively good cycling stability as a positive electrode material, and the insertion and extraction of magnesium ions in the structure are highly reversible. This confirms that Mg3V2O6 is a potential vanadium-based positive electrode material for spinel-structured magnesium-ion batteries with excellent electrochemical performance.

[0039] The present invention also discloses Comparative Example 1 and Comparative Example 2: Comparative Example 1: The material was prepared by the method shown in Patent No. CN201610821168.8, and the obtained material was applied to the above-mentioned three-electrode system and tested, so that it was found that the voltage range of Comparative Example 1 was -0.7~0.8v, and the specific capacity at a smaller current density of 20mA / g was 150mAh / g; the capacity at a current density of 50mA / g was 310mAh / g; the specific capacity at a current density of 100mA / g was 100mAh / g; but using the three-electrode system of Example 1 of the present invention, the specific capacity at a current density of 100mA / g was 250mAh / g, and the performance was better than the three-electrode system using the material of Comparative Example 1.

[0040] Comparative Example 2: The material was prepared by the method shown in Patent No. CN201410384120.6. The obtained material was applied to the above-mentioned three-electrode system and tested. It was found that the voltage range of Comparative Example 2 was -0.4~0.7V, and the capacity was 30mAh / g at a current density of 50mA / g, which was much lower than that of Example 1.

[0041] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: The following steps are involved: Step 1: Mix vanadium pentoxide and magnesium oxide in a molar ratio of vanadium pentoxide:magnesium oxide = 1:3-3.2 and grind to obtain a mixed powder; Step 2: heating the mixed powder to 900-1200° C. and keeping the temperature for 2-24 hours to obtain magnesium orthovanadate; Step 3: Heat magnesium orthovanadate at 450-900° C. in a reducing atmosphere of a mixed gas consisting of hydrogen and argon for 4-16 hours to obtain a positive electrode material.

2. A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: The grinding time of step 1 is 5~30min.

3. A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: In step 2, the heating rate during heating is 5-20°C / min.

4. A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: In step 3, the heating rate during heating is 1-10°C / min.

5. A method for preparing a magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: In the mixed gas used in step 3, the hydrogen content is 5-30%, and the argon content is 70-95%.

6. A magnesium vanadium oxide positive electrode material having a spinel structure, characterized in that: Prepared by any one of the methods of claims 1 to 5, the chemical formula is Mg3V2O6.

7. The magnesium vanadium oxide positive electrode material having a spinel structure according to claim 6, characterized in that: The material has a spinel structure with grooves on the surface.

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