Vanadium-based electrode material, preparation method thereof and lithium ion battery positive pole piece

Abstract

The invention belongs to the technical field of electrode materials, and particularly relates to a vanadium-based electrode material, a preparation method thereof and a lithium ion battery positive pole piece. The invention provides a novel vanadium-based electrode material Li < x > Na < y > VO < 3-z > M < w >, and M is selected from F, Cl or Br. The preparation method comprises the following steps: firstly mixing a vanadium source with a soluble sodium salt aqueous solution, preparing beta-NaVO3 powder by adopting a solution-freeze drying method, then mixing the beta-NaVO3 powder with lithium halide, and realizing ion exchange by adopting a solvothermal method to obtain the vanadium-based electrode material. The vanadium-based electrode material is prepared from cheap and easily available raw materials, has good electrochemical performance, structural stability and thermal stability, and overcomes the problems of low ionic conductivity and low electronic conductivity of the vanadium-based electrode material in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and particularly relates to a vanadium-based electrode material, a preparation method thereof, and a positive electrode sheet of a lithium-ion battery. Background Art

[0002] To address the issues of energy shortage and environmental deterioration, the development and utilization of environmentally friendly renewable energy have become a hot topic of concern for researchers. Lithium-ion batteries have the advantages of high specific energy, high working voltage, and good cycling performance, and are widely used in portable mobile devices and electric vehicles.

[0003] The positive electrode material has an important impact on the performance of lithium-ion batteries. However, the key element resources in the raw materials required for preparing the positive electrode material are limited, such as nickel, cobalt, and manganese metals. Continuous consumption will inevitably lead to cost increases and resource shortages. Therefore, it is particularly important to develop positive electrode materials with excellent performance, low cost, and environmental friendliness.

[0004] The content of vanadium element in the earth's crust is much higher than that of nickel, cobalt, and manganese elements. Using vanadium-based compounds has the advantage of low cost. At the same time, the multiple valence states of vanadium elements can achieve multi-electron redox reactions, making vanadium-based electrode materials have a high theoretical specific capacity. This makes vanadium-based compounds show great research prospects and value in the field of lithium-ion battery energy storage materials. However, the ionic conductivity and electronic conductivity of existing vanadium-based electrode materials are both low, which affects the application of vanadium-based electrode materials. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a vanadium-based electrode material, a preparation method thereof, and a positive electrode sheet of a lithium-ion battery. The present invention provides a novel vanadium-based electrode material Li x Na y VO 3-z M w , wherein M is selected from F, Cl, or Br. In the present invention, a vanadium source is first mixed with an aqueous solution of soluble sodium salt, and β-NaVO 3 powder is prepared by a solution-freeze drying method. Then, the β-NaVO 3 powder is mixed with lithium halide, and ion exchange is achieved by a solvothermal method to obtain a vanadium-based electrode material. The vanadium-based electrode material of the present invention is made of cheap and easily available raw materials, and while having good electrochemical performance, structural stability, and thermal stability, it overcomes the problem of low ionic conductivity and electronic conductivity of existing vanadium-based electrode materials.

[0006] The present invention is realized through the following technical solutions: The present invention protects a vanadium-based electrode material, and the chemical formula of the vanadium-based electrode material is: Li x Na y VO 3-zM w , wherein M is selected from F, Cl or Br.

[0007] When M is selected from F, 0 < x < 0.1, 0 < y < 1, 0 < z < 0.1, 0 < w ≤ 0.1.

[0008] When M is selected from Cl or Br, 0 < x < 1, 0 < y < 1, 0 < z < 0.2, 0.1 ≤ w ≤ 1.

[0009] Preferably, the crystal structure of the vanadium-based electrode material belongs to the orthorhombic system.

[0010] Preferably, when M is selected from F, 0.01 ≤ x ≤ 0.098, 0.093 ≤ y ≤ 0.98, 0.02 ≤ z ≤ 0.09, 0.01 ≤ w ≤ 0.1.

[0011] Preferably, when M is selected from Cl, 0.1 ≤ x ≤ 0.98, 0.08 ≤ x ≤ 0.95, 0.05 ≤ z ≤ 0.19, 0.1 ≤ w ≤ 1.

[0012] Preferably, when M is selected from Br, 0.1 ≤ x ≤ 0.88, 0.48 ≤ x ≤ 0.95, 0.07 ≤ z ≤ 0.1, 0.1 ≤ w ≤ 1.

[0013] The present invention also protects a method for preparing a vanadium-based electrode material, comprising the following steps: Adding a vanadium source to an aqueous solution of soluble sodium salt and mixing evenly, then heating to obtain a sample. The heating process promotes the uniform mixing of each raw material on the one hand and evaporates water on the other hand. The heating conditions are: heating and stirring at 50 °C to 70 °C for 1 h to 10 h to obtain a sample.

[0014] Freeze-drying the sample, that is, adopting the solution-freeze drying method, to obtain β-NaVO 3 powder; this method is obtained by laboratory exploration. β-phase sodium metavanadate cannot be obtained by the high-temperature solid-phase method, and the solution method directly dried at low temperature often contains impurities. The freeze-drying method can obtain β-NaVO with higher purity 3 , and the β-NaVO prepared by the solution-freeze drying method 3 has oxygen vacancies, which is beneficial to ion diffusion.

[0015] Adding the β-NaVO 3 powder to an alcoholic solution of lithium halide, and performing solvothermal treatment by the solvothermal method. At this time, ion exchange occurs, so that Na + and Li + are exchanged, and M - and VO 3 - are ion-exchanged to obtain a vanadium-based electrode material.

[0016] Among them, the lithium halide is selected from lithium fluoride, lithium chloride or lithium bromide.

[0017] Preferably, the molar ratio of the vanadium source to the soluble sodium salt is 0.9-1.2:1. Experimental results show that if the molar ratio of the vanadium source to the soluble sodium salt is less than 0.9:1, impurities will appear in the β-NaVO 3 powder.

[0018] Preferably, the concentration of the soluble sodium salt aqueous solution is greater than 0.1 mol / L. If it is lower than 0.1 mol / L, the pH value cannot be guaranteed to be greater than 10, which is not conducive to the formation of VO 3 - groups. The maximum value of the concentration of the soluble sodium salt aqueous solution is its saturation concentration.

[0019] Preferably, the soluble sodium salt is selected from one or more of Na 2 CO 3 , NaHCO 3 , NaOH.

[0020] Preferably, the vanadium source is selected from one or more of V 2 O 5 , NH 4 VO 3 , V 2 O 3 .

[0021] Preferably, the conditions of the solvothermal treatment are: heating at 50°C to 120°C for 3 h to 48 h.

[0022] Preferably, the molar ratio of the lithium halide to the β-NaVO 3 powder is 5-10:1.

[0023] Preferably, the solvent of the alcohol solution of the lithium halide is one or a mixture of two of ethanol, propanol, and pentanol.

[0024] The present invention also protects a positive electrode plate of a lithium-ion battery. The positive electrode plate of the lithium-ion battery is prepared from a vanadium-based electrode material, a conductive agent, a binder, and a current collector. The vanadium-based electrode material, the conductive agent, and the binder are mixed in a solvent to obtain a slurry, and the slurry is uniformly coated on the current collector and dried to evaporate the solvent to obtain the positive electrode plate of the lithium-ion battery.

[0025] Preferably, the conductive agent is selected from one or several of Super P conductive carbon black, conductive acetylene black, ordered mesoporous carbon CMK-3, carbon nanotubes, and graphene; the binder is selected from polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, polytetrafluoroethylene, or polyvinyl alcohol; the solvent is selected from N-methylpyrrolidone; the current collector is selected from aluminum foil or copper foil.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a novel vanadium-based electrode material Li x Na y VO 3-z M w , wherein M is selected from F, Cl or Br; the crystal structure of the vanadium-based electrode material Li x Na y VO 3-z M w belongs to the orthorhombic system, and the orthorhombic system is the crystal system of β-NaVO 3 . After ion exchange, the obtained product Li x Na y VO 3-z M w retains the original crystal system of β-NaVO 3 ; in orthorhombic NaVO 3 , VO 5 polyhedra are connected into VO 3 chains, extending along the b-axis direction, the crystal structure is open, with multi-dimensional ion diffusion channels, so after ion exchange, Li x Na y VO 3-z M w retains the original structure, which is beneficial to ion diffusion. The introduction of halogen atoms does not change the open crystal structure of the parent phase, but due to the difference in atomic radius, lattice distortion occurs, resulting in defects, and the defects change the band structure of Li x Na y VO 3-z M w , improving the electronic conductivity of Li x Na y VO 3-z M w ; in addition, a certain degree of lattice distortion effectively expands the lithium ion diffusion path, thereby improving the ionic conductivity.

[0027] 2. The vanadium-based electrode material of the present invention is Li x Na y VO 3-z M w , and has good electrochemical compatibility with halide solid electrolytes with similar compositions and structures.

[0028] 3. Li x Na y VO 3-z M w prepared by the method of the present invention has oxygen vacancy defects, which is beneficial to lithium ion diffusion.

[0029] 4. The vanadium-based electrode material of the present invention Lix Na y VO 3-z M w It has good electrochemical performance, structural stability and thermal stability, and is a cathode material with research value and application potential.

[0030] 5. The present invention provides a preparation method of a vanadium-based electrode material. The raw materials used in the preparation process are simple, inexpensive, the reaction conditions are simple and mild, and it does not involve complex preparation process flows. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a cyclic performance diagram of the vanadium-based electrode materials of Examples 1 to 4 and Comparative Example 1 of the present invention.

[0032] Figure 2 It is a rate performance diagram of the vanadium-based electrode materials of Examples 1 to 4 and Comparative Example 1 of the present invention.

[0033] Figure 3 It is the first charge-discharge curve diagram of the vanadium-based electrode materials of Examples 1 to 4 and Comparative Example 1 of the present invention.

[0034] Figure 4 It is the EIS diagram of the vanadium-based electrode materials of Example 4 and Comparative Example 1 of the present invention; Figure 4 In FIG. (a), it is the EIS diagram of the vanadium-based electrode material of Comparative Example 1, Figure 4 In FIG. (b), it is the EIS diagram of the vanadium-based electrode material of Example 4, Figure 4 In FIG. (c), it is the real part impedance of the vanadium-based electrode materials of Example 4 and Comparative Example 1 and ω −1 / 2 linear relationship diagram, Figure 4 In FIG. (d), it is the comparison diagram of the lithium ion diffusion coefficients of the vanadium-based electrode materials of Example 4 and Comparative Example 1.

[0035] Figure 5 It is the thermogravimetric curve diagram of the vanadium-based electrode materials of Example 4 and Comparative Example 1 of the present invention.

[0036] Figure 6 It is the SEM image and element analysis diagram of the vanadium-based electrode material of Example 4 of the present invention; Figure 6 In FIG. a, it is the SEM diagram, Figure 6 In FIG. b, it is the element analysis diagram.

[0037] Figure 7 It is the electron spin resonance diagram of the vanadium-based electrode material of Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the protection scope of the present invention is not limited by the specific embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0039] Considering the problem that the ionic conductivity and electronic conductivity of the existing vanadium-based electrode materials are both low, the present invention provides a novel vanadium-based electrode material Li x Na y VO 3-z M w , where M is selected from F, Cl or Br. When M is selected from F, 0 < x < 0.1, 0 < y < 1, 0 < z < 0.1, 0 < w ≤ 0.1; when M is selected from Cl or Br, 0 < x < 1, 0 < y < 1, 0 < z < 0.2, 0.1 ≤ w ≤ 1. The present invention first prepares orthorhombic β-NaVO 3 , and then uses β-NaVO 3 to perform ion exchange with F - , Cl - or Br - of lithium halide to obtain the vanadium-based electrode material Li x Na y VO 3-z M w . The vanadium-based electrode material Li x Na y VO 3-z M w not only maintains the original orthorhombic system of β-NaVO 3 , but also has a high ionic conductivity and electrochemical compatibility due to the structure and composition similar to those of halide solid electrolytes. In addition, the introduction of halogen atoms causes lattice distortion, which improves the electronic conductivity of Li x Na y VO 3-z M w . Experimental results show that NaVO 3 or LiVO 3 of other crystal systems will not undergo ion exchange under the conditions of the technical solution of the present invention, thus obtaining the product Li x Na y VO 3-z M w .

[0040] The following uses examples and comparative examples to study the technical solution of the present invention. In the examples, different ion exchange times result in differences in the final chemical components. The specific research methods and results are as follows: Example 1 Preparation method of vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this embodiment is: Li 0.1 Na 0.95 VO 2.95 Cl 0.1 , including the following steps: S1. Weigh 0.01 mol of Na 2 CO 3 , added to a beaker containing 100 mL of deionized water, stirred at 300 r / min for 15 min, and 0.1 mol / L of Na 2 CO 3 Solution.

[0041] S2, weigh 0.01 mol of V 2 O 5 , added to Na 2 CO 3 After magnetic stirring for 30 min, the beaker was placed in a 70°C water bath to heat the Na 2 CO 3 With V 2 O 5 The reaction was continued for 3 h, during which water was gradually evaporated, and heating and stirring were continued for 4 h.

[0042] S3. Pour the sample into a culture dish and place it in a freeze dryer cold trap for pre-freezing for 3 hours. After it is completely frozen, freeze-dry it for 12 hours to obtain β-NaVO 3 powder.

[0043] S4. Add lithium chloride into ethanol and stir thoroughly to dissolve, to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0044] S5. Add β-NaVO to the ethanol solution of lithium chloride 3 powder, and control LiCl:β-NaVO 3 The molar ratio was 10:1 and magnetic stirring was performed for 30 min to obtain a mixed solution.

[0045] S6. The mixed solution is transferred to a reactor and placed in an oven at 80°C for ion exchange reaction for 3 hours to obtain an ion exchange product. After the reaction is completed, the reactor is cooled, the ion exchange product is washed with ethanol, centrifuged 4 times to remove excess lithium chloride, and then placed in an oven at 50°C for drying to obtain a vanadium-based electrode material.

[0046] Example 2 The preparation method of the vanadium-based electrode material is the same as the preparation steps of Example 1, except that the time of the ion exchange reaction is replaced by 6 hours from 3 hours. The chemical formula of the vanadium-based electrode material in this example is: Li 0.2 Na0.8 VO 2.9 Cl 0.2 , including the following steps: S1. Weigh 0.01 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.1 mol / L Na 2 CO 3 solution.

[0047] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, stir magnetically for 30 min, then place the beaker in a water bath at 70 °C and heat it to react Na 2 CO 3 with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction, and continuously heat and stir for 4 h.

[0048] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h, and then perform freeze drying for 12 h after complete freezing to obtain β-NaVO 3 powder.

[0049] S4. Add lithium chloride to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0050] S5. Add β-NaVO 3 powder to the ethanol solution of lithium chloride, and control the molar ratio of LiCl:β-NaVO 3 to be 10:1, and stir magnetically for 30 min to obtain a mixed solution.

[0051] S6. Transfer the mixed solution to a reaction kettle, place it in an oven at 80 °C for an ion exchange reaction for 6 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium chloride, and then place it in an oven at 50 °C to dry, that is, obtain the vanadium-based electrode material.

[0052] Example 3 The preparation method of the vanadium-based electrode material is the same as the preparation steps of Example 1, except that the ion exchange reaction time is replaced by 12 h instead of 3 h. The chemical formula of the vanadium-based electrode material in this example is: Li 0.5 Na 0.5 VO 2.9 Cl 0.5 , including the following steps: S1. Weigh 0.01 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir vigorously at 300 r / min for 15 min to obtain a 0.1 mol / L Na 2 CO 3 solution.

[0053] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution. After magnetic stirring for 30 min, place the beaker in a water bath at 70 °C and heat it to allow Na 2 CO 3 to react with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction, and continue heating and stirring for 4 h.

[0054] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, perform freeze drying for 12 h to obtain β-NaVO 3 powder.

[0055] S4. Add lithium chloride to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0056] S5. Add β-NaVO 3 powder to the ethanol solution of lithium chloride, and control the molar ratio of LiCl:β-NaVO 3 to be 10:1, and stir magnetically for 30 min to obtain a mixture.

[0057] S6. Transfer the mixture to a reaction kettle, place it in an oven at 80 °C for an ion exchange reaction for 12 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium chloride, and then place it in an oven at 50 °C to dry, that is, obtain the vanadium-based electrode material.

[0058] Example 4 The preparation method of the vanadium-based electrode material is the same as the preparation steps of Example 1, except that the ion exchange reaction time is replaced by 24 h. The chemical formula of the vanadium-based electrode material in this example is: Li 0.77 Na 0.68 VO 2.84 Cl 0.67 , including the following steps: S1. Weigh 0.01 mol of Na 2 CO 3, added to a beaker containing 100 mL of deionized water, stirred vigorously at 300 r / min for 15 min to obtain a 0.1 mol / L Na 2 CO 3 solution.

[0059] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution. After magnetic stirring for 30 min, place the beaker in a water bath at 70 °C and heat it to allow Na 2 CO 3 to react with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction, continuously heating and stirring for 4 h.

[0060] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, perform freeze drying for 12 h to obtain β-NaVO 3 powder.

[0061] S4. Add lithium chloride to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0062] S5. Add β-NaVO 3 powder to the ethanol solution of lithium chloride, and control the molar ratio of LiCl:β-NaVO 3 to be 10:1. Stir magnetically for 30 min to obtain a mixed solution.

[0063] S6. Transfer the mixed solution to a reaction kettle and place it in an oven at 80 °C for an ion exchange reaction for 24 h to obtain an ion exchange product. After the reaction is completed and the reaction kettle is cooled, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium chloride, and then place it in an oven at 50 °C to dry, thus obtaining the vanadium-based electrode material.

[0064] Example 5 Preparation method of vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.98 Na 0.08 VO 2.81 Cl, including the following steps: S1. Weigh 0.012 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, stir vigorously at 300 r / min for 15 min to obtain a 0.12 mol / L Na 2 CO 3 solution.

[0065] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, stir magnetically for 30 min, then place the beaker in a water bath at 50 °C and heat it to allow Na 2 CO 3 to react with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction, continuously heat and stir for 4 h.

[0066] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, perform freeze drying for 12 h to obtain β-NaVO 3 powder.

[0067] S4. Add lithium chloride to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0068] S5. Add β-NaVO 3 powder to the ethanol solution of lithium chloride, and control the molar ratio of LiCl:β-NaVO 3 to be 5:1, stir magnetically for 30 min to obtain a mixed solution.

[0069] S6. Transfer the mixed solution to a reaction kettle, place it in an oven at 50 °C for an ion exchange reaction for 48 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium chloride, and then place it in an oven at 50 °C to dry, thus obtaining the vanadium-based electrode material.

[0070] Example 6 Preparation method of vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.098 Na 0.093 VO 2.91 F 0.1 , and it includes the following steps: S1. Weigh 0.012 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, stir well at 300 r / min for 15 min to obtain a 0.12 mol / L Na 2 CO 3 solution.

[0071] S2. Weigh 0.01 mol of V 2 O 5 , add it to Na 2 CO 3In the solution, after magnetic stirring for 30 min, the beaker was placed in a water bath at 70 °C and heated to react Na 2 CO 3 with V 2 O 5 for 6 h, and water was gradually evaporated during the reaction, and continuous heating and stirring were carried out for 10 h.

[0072] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, carry out freeze drying for 12 h to obtain β-NaVO 3 powder.

[0073] S4. Add lithium fluoride to ethanol and stir well to dissolve it to obtain a saturated ethanol solution of lithium fluoride.

[0074] S5. Add β-NaVO 3 powder to the saturated ethanol solution of lithium fluoride, and control the molar ratio of LiF:β-NaVO 3 to be 7:1, and stir magnetically for 30 min to obtain a mixed solution.

[0075] S6. Transfer the mixed solution to a reaction kettle, and place it in an oven at 70 °C for an ion exchange reaction. The reaction time is 48 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium fluoride, and then place it in an oven at 50 °C to dry, that is, the vanadium-based electrode material is obtained.

[0076] Example 7 A method for preparing a vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.88 Na 0.48 VO 2.93 Br 0.9 , and the method includes the following steps: S1. Weigh 0.012 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.12 mol / L Na 2 CO 3 solution.

[0077] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution. After magnetic stirring for 30 min, place the beaker in a water bath at 50 °C and heat it to react Na 2 CO 3 with V 2 O 5React for 3 h, and gradually evaporate water during the reaction to obtain a sample.

[0078] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, carry out freeze drying for 12 h to obtain β-NaVO 3 powder.

[0079] S4. Add lithium bromide to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium bromide with a concentration of 5 mol / L.

[0080] S5. Add β-NaVO 3 powder to the ethanol solution of lithium bromide, and control the molar ratio of LiBr:β-NaVO 3 to be 6:1, and magnetically stir for 30 min to obtain a mixed solution.

[0081] S6. Transfer the mixed solution to a reaction kettle, and place it in an oven at 50 °C for an ion exchange reaction. The reaction time is 26 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium bromide, and then place it in an oven at 50 °C to dry, thus obtaining the vanadium-based electrode material.

[0082] Example 8 A preparation method of a vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.1 Na 0.95 VO 2.9 Br 0.1 , and it includes the following steps: S1. Weigh 0.009 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.09 mol / L Na 2 CO 3 solution.

[0083] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, after magnetic stirring for 30 min, place the beaker in a water bath at 60 °C and heat it to make Na 2 CO 3 react with V 2 O 5 for 10 h, and gradually evaporate water during the reaction to obtain a sample.

[0084] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, carry out freeze drying for 12 h to obtain β-NaVO 3 powder.

[0085] S4. Add lithium bromide to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium bromide with a concentration of 5 mol / L.

[0086] S5. Add β-NaVO 3 powder to the ethanol solution of lithium bromide, and control the molar ratio of LiBr:β-NaVO 3 to be 6:1, and magnetically stir for 30 min to obtain a mixed solution.

[0087] S6. Transfer the mixed solution to a reaction kettle, and place it in an oven at 100 °C for an ion exchange reaction. The reaction time is 3 h to obtain an ion exchange product. After the reaction is completed, wait for the reaction kettle to cool. Wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium bromide, and then place it in an oven at 50 °C to dry, thus obtaining the vanadium-based electrode material.

[0088] Example 9 Preparation method of vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.98 Na 0.17 VO 2.81 Br, and it includes the following steps: S1. Weigh 0.012 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.12 mol / L Na 2 CO 3 solution.

[0089] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, after magnetic stirring for 30 min, place the beaker in a water bath at 50 °C and heat it to make Na 2 CO 3 react with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction to obtain a sample.

[0090] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h. After complete freezing, carry out freeze drying for 12 h to obtain β-NaVO 3 powder.

[0091] S4. Add lithium bromide to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium bromide with a concentration of 5 mol / L.

[0092] S5. Add β-NaVO 3 powder to the ethanol solution of lithium bromide, and control the molar ratio of LiBr:β-NaVO 3 to be 6:1, and magnetically stir for 30 min to obtain a mixture.

[0093] S6. Transfer the mixture to a reaction kettle and place it in an oven at 120 °C for an ion exchange reaction for 48 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium bromide, and then place it in an oven at 50 °C to dry, thus obtaining the vanadium-based electrode material.

[0094] Example 10 Preparation method of vanadium-based electrode material. The chemical formula of the vanadium-based electrode material in this example is: Li 0.01 Na 0.98 VO 2.98 F 0.01 , and it includes the following steps: S1. Weigh 0.012 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.12 mol / L Na 2 CO 3 solution.

[0095] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, after magnetically stirring for 30 min, place the beaker in a water bath at 70 °C and heat it to make Na 2 CO 3 react with V 2 O 5 for 6 h, and gradually evaporate the water during the reaction, and continuously heat and stir for 10 h.

[0096] S3. Pour the viscous sample into a petri dish, place it in the cold trap of a freeze dryer for pre-freezing for 3 h, and perform freeze drying for 12 h after complete freezing to obtain β-NaVO 3 powder.

[0097] S4. Add lithium fluoride to ethanol and stir well to dissolve it to obtain a saturated ethanol solution of lithium fluoride.

[0098] S5. Add β-NaVO to the saturated ethanol solution of lithium fluoride3 powder and control the molar ratio of LiF:β-NaVO 3 to 7:1, magnetically stir for 30 min to obtain a mixed solution.

[0099] S6. Transfer the mixed solution to a reaction kettle and place it in an oven at 50 °C for an ion exchange reaction for 12 h to obtain an ion exchange product; after the reaction is completed, wait for the reaction kettle to cool, wash the ion exchange product with ethanol, centrifuge 4 times to remove excess lithium fluoride, and then place it in an oven at 50 °C to dry to obtain the vanadium-based electrode material.

[0100] Comparative Example 1 The preparation method of the vanadium-based electrode material is the same as the preparation steps of Example 1, except that the time of the ion exchange reaction is replaced by 0 h instead of 3 h, and it includes the following steps: S1. Weigh 0.01 mol of Na 2 CO 3 , add it to a beaker containing 100 mL of deionized water, and stir well at 300 r / min for 15 min to obtain a 0.1 mol / L Na 2 CO 3 solution.

[0101] S2. Weigh 0.01 mol of V 2 O 5 , add it to the Na 2 CO 3 solution, magnetically stir for 30 min, then place the beaker in a water bath at 70 °C and heat it to make Na 2 CO 3 react with V 2 O 5 for 3 h, and gradually evaporate the water during the reaction to obtain a sample.

[0102] S3. Pour the sample into a petri dish, place it in the cold trap of a freeze dryer and pre-freeze for 3 h, and then perform freeze drying for 12 h after complete freezing to obtain β-NaVO 3 powder.

[0103] S4. Add lithium chloride to ethanol and stir well to dissolve it to obtain an ethanol solution of lithium chloride with a concentration of 5 mol / L.

[0104] S5. Add β-NaVO 3 powder to the ethanol solution of lithium chloride, and control the molar ratio of LiCl:β-NaVO 3 to 10:1, magnetically stir for 30 min to obtain a mixed solution.

[0105] S6. Wash the mixed solution with ethanol, centrifuge 4 times to remove excess lithium chloride, and then place it in an oven at 50 °C to dry to obtain the vanadium-based electrode material.

[0106] In Examples 1 to 6 of the present invention, vanadium-based electrode materials with good electrochemical performance, structural stability and thermal stability were all prepared. Taking the vanadium-based electrode materials of Examples 1 to 4 as examples and comparing them with Comparative Example 1, the specific research methods and results are as follows: Assembly of lithium-ion batteries: The vanadium-based electrode materials obtained in Comparative Example 1 and Examples 1 to 4 were respectively ground and mixed with conductive agent carbon nanotubes and binder polyvinylidene fluoride according to a mass ratio of 7:2:1, then N-methylpyrrolidone was added for mixing to form a uniform slurry. The slurry was coated on an aluminum foil current collector with a scraper, dried and cut into circular pieces with a diameter of 10 mm, and then placed in a glove box to obtain the positive electrode plates of lithium-ion batteries.

[0107] The positive electrode plates of lithium-ion batteries prepared using Comparative Example 1 and Examples 1 to 4 were respectively assembled with lithium sheets, commercial polypropylene separators and lithium secondary electrolytes into 2032 button batteries. The cycle performance and rate performance of the positive electrode plates of lithium-ion batteries were tested through a Neware battery test system. The cycle performance test was carried out in a voltage range of 1.0 V to 3.5 V at 50 mAh·g -1 ; The rate performance test was carried out in a voltage range of 1.0 V to 3.5 V, and at current densities of 25 mA·g -1 , 50 mA·g -1 , 100 mA·g -1 , 150 mA·g -1 , 200 mA·g -1 and 20 mA·g -1 for ten cycles each. The test results are shown in Tables 1, Figure 1 and Figure 2 .

[0108] Table 1 Retention capacity of vanadium-based electrode materials in Comparative Example 1 and Examples 1 to 4 after 100 cycles

[0109] Table 1 shows the retention capacity of the vanadium-based electrode materials in Comparative Example 1 and Examples 1 to 4 after 100 cycles. The retention capacity after cycling in Comparative Example 1 was only 53 mAh·g -1 , and the retention capacities after cycling in Examples 1 to 4 were all higher than that in Comparative Example 1, indicating that the vanadium-based electrode materials in Examples 1 to 4 have better cycle performance and charge-discharge capacity.

[0110] Figure 1 is the cycle performance diagram of Comparative Example 1 and Examples 1 to 4. The discharge specific capacities of Examples 1 to 4 are all higher than that of Comparative Example 1, and the capacity decay rate is significantly less than that of Comparative Example 1, indicating that ion exchange improves the cycle stability of the vanadium-based electrode materials.

[0111] Figure 2 It is the rate performance graph of Comparative Example 1 and Examples 1 to 4. At each current density, the discharge specific capacity of Examples 1 to 4 is significantly higher than that of Comparative Example 1, indicating that the ion exchange reaction effectively improves the rate performance of the vanadium-based electrode material. In summary, it is considered that the vanadium-based electrode material provided by the present invention has good electrochemical performance.

[0112] Figure 3 It is the first charge-discharge curve graph of the vanadium-based electrode materials of Examples 1 to 4 and Comparative Example 1. Figure 3 The results show that during the first charge-discharge process, obvious charge-discharge platforms can be observed for the vanadium-based electrode materials of Examples 1 to 4, indicating that a stable two-phase reaction occurs in Examples 1 to 4, indicating that the vanadium-based electrode material has better structural stability. At the same time, the average discharge platform of Examples 1 to 4 is significantly higher than the average discharge potential of Comparative Example 1. Therefore, the vanadium-based electrode materials of Examples 1 to 4 have higher specific energy. The voltage difference between the charge-discharge platforms of the vanadium-based electrode materials of Examples 1 to 4 is significantly smaller than that of the vanadium-based electrode material of Comparative Example 1, indicating that the vanadium-based electrode materials of Examples 1 to 4 have higher electronic conductivity and smaller electrochemical polarization.

[0113] Figure 4 It is the EIS graph of the vanadium-based electrode materials of Example 4 and Comparative Example 1 of the present invention. According to the calculation of the EIS spectrum, the lithium ion diffusion coefficients of Comparative Example 1 and Example 4 are 1.97×10 -8 cm 2. s -1 and 4.2×10 -8 cm 2. s -1 , respectively. According to the Nernst-Einstein equation, the ionic conductivity is proportional to the lithium ion diffusion coefficient, and it is obtained that Example 4 has higher ionic conductivity than Comparative Example 1. Comprehensive Figure 2 and Figure 4 The results show that the vanadium-based electrode material of Example 4 has higher ionic conductivity and thus exhibits more excellent rate performance.

[0114] Figure 5 It is the thermogravimetric curve graph of the vanadium-based electrode materials of Example 4 and Comparative Example 1. The results show that there is no obvious mass change in the vanadium-based electrode materials of Example 4 and Comparative Example 1 within the range of 300 °C, that is, there is no obvious decomposition phenomenon, indicating that the vanadium-based electrode material has good thermal stability. There is a small amount of mass change in the vanadium-based electrode material of Comparative Example 1 during the heating process, which is caused by a small amount of adsorbed water. There is almost no mass change in Example 4, indicating that after the ion exchange reaction, the hygroscopic property of the vanadium-based electrode material in the air decreases and it is more stable.

[0115] Figure 6 The results show that the morphology of the vanadium-based electrode material in Example 4 is nanosheet-like, with a relatively high specific surface area, which can shorten the ion and electron transport paths and enhance the reaction kinetics. Its elemental analysis shows that the vanadium-based electrode material in Example 4 contains elements Na, O, V, and Cl, and the content of Cl element is relatively high.

[0116] Figure 7 The results show that the vanadium-based electrode material in Example 4 has oxygen vacancies, and the existence of oxygen vacancies is beneficial to ion diffusion.

[0117] Obviously, those skilled in the art can make various changes and deformations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and deformations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and deformations. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention, and the scope of protection of the present invention is subject to the claims.

Claims

1. A vanadium-based electrode material, characterized in that: The chemical formula of vanadium-based electrode material is: Li x Na y VO 3-z M w , wherein M is selected from F, Cl or Br; When M is selected from F, 0<x<0.1, 0<y<1, 0<z<0.1, 0<w≤0.1; When M is selected from Cl or Br, 0<x<1, 0<y<1, 0<z<0.2, 0.1≤w≤1.

2. The vanadium-based electrode material according to claim 1, characterized in that The crystal structure of vanadium-based electrode materials belongs to the orthorhombic system.

3. A method for preparing the vanadium-based electrode material according to claim 1, characterized in that: The steps include: Add the vanadium source to the soluble sodium salt aqueous solution, mix well, and then heat and stir at 50°C to 70°C for 1h to 10h to obtain a sample; The sample was freeze-dried to obtain β-NaVO3 powder; β-NaVO3 powder is added to the alcohol solution of lithium halide and subjected to solvent thermal treatment. At this time, ion exchange occurs, making Na + With Li + Exchange, M - With VO3 - Ion exchange to obtain vanadium-based electrode materials; Wherein, the lithium halide is selected from lithium fluoride, lithium chloride or lithium bromide.

4. The method for preparing a vanadium-based electrode material according to claim 3, characterized in that: The molar ratio of the vanadium source to the soluble sodium salt is 0.9~1.2:

1.

5. The method for preparing a vanadium-based electrode material according to claim 3, characterized in that: The concentration of the soluble sodium salt aqueous solution is greater than 0.1 mol / L and less than or equal to the saturation concentration.

6. The method for preparing a vanadium-based electrode material according to claim 3, characterized in that: The conditions of solvent thermal treatment are: heating at 50°C~120°C for 3h~48h.

7. The method for preparing a vanadium-based electrode material according to claim 3, characterized in that: The molar ratio of lithium halide to β-NaVO3 powder is 5~10:

1.

8. The method for preparing a vanadium-based electrode material according to claim 3, characterized in that: The solvent of the alcohol solution of lithium halide is one of ethanol, propanol and pentanol or a mixture of two of them.

9. A positive electrode plate for a lithium-ion battery, characterized in that: The positive electrode sheet of a lithium-ion battery is made from the vanadium-based electrode material according to claim 1, a conductive agent, a binder and a current collector.

10. The positive electrode plate of a lithium-ion battery according to claim 9, characterized in that: The vanadium-based electrode material, the conductive agent and the binder are mixed together in a solvent to obtain a slurry, the slurry is evenly coated on a current collector, and after the solvent is evaporated, a positive electrode sheet of a lithium-ion battery is obtained.

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