Preparation method of V2O5 sodium ion battery positive electrode material

Abstract

The invention discloses a preparation method of a V2O5 sodium-ion battery positive electrode material, which comprises the following steps: mixing ethylene glycol and vanadyl oxalate hydrate, carrying out heating reaction in an oxygen supply atmosphere, and carrying out proper hydrothermal temperature control and annealing treatment to generate a yellow vanadium pentoxide sodium-ion battery positive electrode material with an obvious layered structure. And the obtained sodium ion battery positive electrode material is not easy to dissolve in the use process, so that the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of sodium-ion batteries and relates to a method for preparing a cathode material for a V2O5 sodium-ion battery. Background Art

[0002] As a new energy storage technology, sodium-ion batteries have advantages compared with traditional lithium-ion batteries due to their resource abundance, environmental friendliness, and high safety. ① Sodium is the sixth most abundant element in the earth's crust, with a wide distribution and relatively low price. In contrast, although lithium resources are not scarce, their distribution is uneven, the extraction cost is high, and with the growth of demand, there may be a problem of tight supply; ② Sodium-ion batteries can be more environmentally friendly in material selection. For example, using aqueous electrolytes instead of organic electrolytes can reduce environmental hazards and safety risks; in addition, the acquisition and processing of sodium-based materials are usually more environmentally friendly than those of lithium-based materials; ③ Since the working voltage of sodium-ion batteries is relatively low, this helps to improve the safety performance of the battery and reduce the risk of thermal runaway; at the same time, sodium-ion batteries can work in a relatively wide temperature range, further improving their safety and applicability. With the in-depth research and technological progress, sodium-ion batteries are expected to become an important energy storage solution in the future.

[0003] However, at present, the energy density of sodium-ion batteries is still lower than that of lithium-ion batteries. Currently, materials scientists are constantly exploring new cathode and anode materials for sodium-ion batteries in order to improve the electrochemical performance of sodium-ion batteries, including energy density, cycle life, etc. Moreover, its commercial application still faces some challenges, such as the need to further improve the energy density, reduce the cost, and improve the production process.

[0004] Existing cathode materials for sodium-ion batteries include V2O5 and its related materials. The reasons for choosing vanadium pentoxide are as follows: ① High theoretical capacity: Vanadium pentoxide has a relatively high theoretical specific capacity, which can provide a relatively high energy density for sodium-ion batteries. ② High working voltage: The working voltage of V2O5 is relatively high, usually between 3.4 and 3.9V, which helps to improve the output power of the battery. ③ Abundant resources and low cost: Vanadium resources are widely distributed in nature, with a relatively low price, and the preparation process is relatively simple, which gives vanadium pentoxide a cost advantage in large-scale energy storage applications. ④ Good structural stability: Some vanadium-based compounds, such as vanadium-based polyanion compounds, have a relatively stable crystal cell structure, and the sodium ion diffusion rate is relatively fast, which helps to improve the cycle stability and rate performance of the battery. ⑥ Environmentally friendly: Compared with some cathode materials containing heavy metals such as nickel and cobalt, vanadium-based materials have obvious advantages in environmental health and safety.

[0005] However, the electronic conductivity of existing sodium-ion battery cathode materials related to vanadium pentoxide is not ideal. Since vanadium pentoxide itself is a narrow-bandgap semiconductor material with a low intrinsic electronic conductivity, this will limit the charge and discharge speed and rate performance of the battery; moreover, the structural stability is insufficient. During the repeated sodium-ion insertion / extraction process, V2O5 is prone to structural changes, resulting in relatively fast capacity decay; during the charge and discharge process, vanadium pentoxide may undergo a large volume expansion, further affecting the structural stability and cycle life of the electrode; V2O5 may dissolve in the electrolyte, resulting in the loss of active materials and affecting the long-term stability of the battery. As a result, the cycle life of vanadium pentoxide-based cathode materials is usually short and difficult to meet the requirements of battery life for application scenarios such as large-scale energy storage.

[0006] To address the above problems and overcome the disadvantages of vanadium pentoxide, researchers have proposed some modification methods:

[0007] Nanostructuring: By constructing nanoscale materials such as nanosheets and nanowires, the transport path of sodium ions can be effectively shortened, improving the rate performance and cycle stability of the materials.

[0008] Composite materials: Composite with other conductive materials (such as carbon materials, conductive polymers, etc.) can improve the electronic conductivity of the materials. For example, by coating with TiO2 or composite with carbon nanotubes, the electrochemical performance of V2O5 can be significantly improved.

[0009] Crystal structure modification: Optimize the crystal structure of the materials by means of chemical pre-insertion, doping, etc. to improve its stability and electrochemical performance.

[0010] The present invention plans to provide a method for improving the properties of vanadium pentoxide as a sodium-ion battery cathode material, which can overcome its inherent defects through a suitable preparation method to meet the needs of practical applications. Summary of the Invention

[0011] Aiming at the disadvantages of the prior art, the present invention provides a preparation method for a V2O5 sodium-ion battery cathode material.

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] A preparation method for a V2O5 sodium-ion battery cathode material, comprising the following steps:

[0014] 1) Grind and mix vanadyl oxalate hydrate C2O5V·xH2O with ethylene glycol C2H6O2, and heat and stir thoroughly in an oxygen-supplying atmosphere;

[0015] 2) After raising the temperature to the reaction temperature, heat steadily for 1 - 1.5 h;

[0016] 3) After adjusting the pH to 7 - 7.5, continue to hydrothermally heat up in the reaction kettle, slowly raise the temperature step by step to 500 °C, and then keep it warm for 2 - 3 h;

[0017] 4) Filter and dry the product after heat preservation to obtain a black dried product;

[0018] 5) Transfer the black dried product in step 4) to a muffle furnace for annealing treatment to obtain the cathode material.

[0019] Adopting the above technical solution, under the condition of a high - temperature aerobic atmosphere, ethylene glycol, as a combustible reducing agent, can first compete for coordination with the oxalate in vanadyl oxalate, and then ethylene glycol itself is oxidized to CO2 / H2O, while releasing heat, which can further promote the oxidation of vanadium, and the released heat drives the conversion of vanadium from +4 valence (VO 2+ ) to +5 valence (V2O5).

[0020] Preferably, the reaction process equation of the preparation method is as follows:

[0021]

[0022] Preferably, in step 1), the molar ratio of C2O5V·xH2O to ethylene glycol is 1:1.5 - 1:2.

[0023] Adopting the above technical solution, VO(C2O4)·xH2O and ethylene glycol are ground and mixed to form a wet gel, which is beneficial for both sides to fully contact with each other and promote the forward progress of the reaction.

[0024] Preferably, in step 2), the reaction temperature is 180 - 220 °C.

[0025] Preferably, the substance for adjusting pH in step 3) is ammonia water.

[0026] Adopting the above technical solution, oxalic acid is a relatively strong organic acid, and ammonia water has strong volatility. Using ammonia water as a pH regulator can avoid introducing sodium ions in advance.

[0027] Preferably, in step 3), the rate of step - by - step slow heating is 5 - 10 °C / min.

[0028] Preferably, in step 5), the conditions for annealing treatment are to control the temperature at 450 °C - 550 °C under the protection of an inert gas, and the duration is 1.5 - 2.5 h.

[0029] Adopting the above technical solution, the temperature control conditions can ensure that the annealing temperature is uniform and stable, avoiding local overheating or temperature fluctuations during the process; using inert gas protection during the annealing process can prevent the material from being oxidized or reduced, and promote the formation of a layered structure of vanadium pentoxide.

[0030] Preferably, the positive electrode material is yellow layered vanadium pentoxide.

[0031] The invention also provides a layered V2O5 positive electrode material, which is prepared by the preparation method of the vanadium pentoxide positive electrode material.

[0032] The present invention also provides an application of a layered V2O5 positive electrode material in the field of sodium ion batteries.

[0033] Beneficial effects of the present invention:

[0034] The invention generates a V2O5 positive electrode material with an obvious layered structure by adjusting the hydrothermal temperature condition and the annealing condition. VO(C2O4)·xH2O and ethylene glycol are first ground and mixed to form a wet gel. During the reaction, the oxidation reaction is controlled by increasing the temperature in stages to remove free water and part of the ethylene glycol that affect the reaction process and ensure the full progress of the reaction. Ammonia water is used to adjust the pH of the reaction environment without introducing sodium ions in advance. After that, the temperature is slowly increased to 500° C. in steps and then kept warm for 2-3 hours to avoid local carbon residue. The annealing treatment conditions are controlled to make the microstructure of the finally generated high-purity vanadium pentoxide more uniform, improve the consistency of its performance, and alleviate the dissolution phenomenon of the vanadium pentoxide in an electrolyte when used as a positive electrode material for a sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the preparation process of layered V2O5;

[0036] Figure 2 Schematic diagram of the structure of layered V2O5. DETAILED DESCRIPTION

[0037] The present invention is further described below by means of specific examples, but the scope of the present invention is not limited thereto.

[0038] Embodiment 1:

[0039]

[0040] Preparation method:

[0041] 1) Grind and mix vanadyl oxalate hydrate C2O5V·xH2O and ethylene glycol C2H6O2, and fully heat and stir in an oxygen atmosphere; the molar ratio of C2O5V·xH2O to ethylene glycol is 1:2.

[0042] 2) Heat to 200°C and heat steadily for 1.2h;

[0043] 3) After adding ammonia water to adjust the pH to 7-7.5, continue to hydrothermally heat the reactor, slowly increase the temperature to 500°C at a rate of 5°C / min, and keep it warm for 2 hours;

[0044] 4) Filter and dry the product after heat preservation under negative pressure vacuum to obtain a black dried product;

[0045] 5) Transfer the black dried product in step 4) to a muffle furnace for annealing treatment at a temperature of 520 °C for a duration of 2 h to obtain the positive electrode material.

[0046] Example 2:

[0047]

[0048] Preparation method:

[0049] 1) Grind and mix vanadyl oxalate hydrate C2O5V·xH2O with ethylene glycol C2H6O2, and heat and stir thoroughly in an oxygen-supplying atmosphere; according to the molar ratio of C2O5V·xH2O to ethylene glycol of 1:2.

[0050] 2) Raise the temperature to 180 °C and then heat stably for 1.5 h;

[0051] 3) Add ammonia water to adjust the pH to 7 - 7.5, and then continue to heat hydrothermally in a reaction kettle. Gradually raise the temperature at a rate of 10 °C / min to 500 °C and then keep warm for 3 h;

[0052] 4) Filter and dry the product after heat preservation under negative pressure vacuum to obtain a black dried product;

[0053] 5) Transfer the black dried product in step 4) to a muffle furnace for annealing treatment at a temperature of 550 °C for a duration of 1.5 h to obtain the positive electrode material.

[0054] Example 3:

[0055]

[0056] Preparation method:

[0057] 1) Grind and mix vanadyl oxalate hydrate C2O5V·xH2O with ethylene glycol C2H6O2, and heat and stir thoroughly in an oxygen-supplying atmosphere; according to the molar ratio of C2O5V·xH2O to ethylene glycol of 1:1.5.

[0058] 2) Raise the temperature to 220 °C and then heat stably for 1.2 h;

[0059] 3) Add ammonia water to adjust the pH to 7 - 7.5, and then continue to heat hydrothermally in a reaction kettle. Gradually raise the temperature at a rate of 5 °C / min to 500 °C and then keep warm for 2 h;

[0060] 4) Filter and dry the product after heat preservation under negative pressure vacuum to obtain a black dried product;

[0061] 5) The black dried product in step 4) is transferred into a muffle furnace for annealing at a temperature of 510° C. for 2.5 hours to obtain a positive electrode material.

[0062] Comparative Example 1:

[0063] 1) Vanadyl oxalate hydrate C2O5V·xH2O and ethylene glycol C2H6O2 are mixed, and heated and stirred in an oxygen atmosphere; the molar ratio of C2O5V·xH2O to ethylene glycol is 1:1.5.

[0064] 2) Heat to 150°C and heat steadily for 2 hours;

[0065] 3) Continue to hydrothermally heat the reactor to 500°C and keep it warm for 2h;

[0066] 4) The product after heat preservation is filtered and dried under negative pressure to obtain the positive electrode material.

[0067] The results of Examples 1 to 3 and Comparative Example 1 are shown in the table below:

[0068]

[0069]

[0070] From the comparison results of various indicators in the table, it can be seen that the finished vanadium pentoxide in Examples 1-3 is subjected to appropriate hydrothermal temperature control reaction and annealing treatment to obtain a yellow product with an obvious layered structure, which makes it less likely to dissolve in the process of serving as a positive electrode material for a sodium ion battery, thereby increasing the service life of the battery; while the untreated comparative example 1 has poor performance in various indicators, and no layered structure is generated, which is an obvious defect as a positive electrode material for a sodium ion battery.

Claims

1. A preparation method of a V2O5 sodium-ion battery cathode material, characterized in that The steps include: 1) Grind and mix vanadyl oxalate hydrate C2O5V·xH2O and ethylene glycol C2H6O2, and fully heat and stir in an oxygen supply atmosphere; 2) After heating to the reaction temperature, heat steadily for 1-1.5h; 3) After adjusting the pH to 7-7.5, continue to hydrothermally heat the reactor, slowly raise the temperature to 500°C in steps, and keep it warm for 2-3 hours; 4) filtering and drying the product after heat preservation to obtain a black dried product; 5) The black dried product in step 4) is transferred into a muffle furnace for annealing to obtain a positive electrode material.

2. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, characterized in that, The reaction process equation of the preparation method is as follows:

3. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, characterized in that, In step 1), the molar ratio of C2O5V·xH2O to ethylene glycol is 1:1.5-1:

2.

4. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, wherein The substance for adjusting pH in step 3) is aqueous ammonia.

5. The preparation method of a V2O5 sodium ion battery cathode material according to claim 1, characterized in that, The rate of the stepwise slow heating in step 3) is 5-10°C / min.

6. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, wherein The annealing treatment conditions in step 5) are to control the temperature at 450° C. to 550° C. under the protection of inert gas and the duration is 1.5-2.5 hours.

7. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, characterized in that, The positive electrode material is yellow layered vanadium pentoxide.

8. The preparation method of a V2O5 sodium-ion battery cathode material according to claim 1, characterized in that, The reaction temperature in step 2) is 180-220°C.

9. A layered V2O5 cathode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the layered V2O5 positive electrode material according to claim 9 in the field of sodium ion batteries.

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