Vanadium-containing ore Na + Method for preparing lithium vanadium phosphate lithium-ion battery cathode material by in-situ doping

Abstract

The invention discloses a method for preparing lithium vanadium phosphate lithium battery cathode material by in-situ doping of Na<supgt;+< / supgt; in vanadium-containing ore. Using vanadium-containing ore as the initial raw material, through a hydrometallurgical process, a vanadium-containing sodium compound is prepared, and then it is mixed with lithium carbonate and ammonium dihydrogen phosphate and directly calcined. Through the method of in-situ doping in the liquid phase, sodium element is directly doped into the lithium vanadium phosphate material to produce a lithium vanadium phosphate material with good electrochemical performance. The sodium salt in this patent is the original one in the vanadium-containing ore and does not require additional addition; the sodium element is mixed and added in the liquid phase, which is easy to be evenly distributed, thus facilitating the electrochemical uniformity of the lithium vanadium phosphate electrode; using lithium carbonate as the lithium source has a lower cost compared with lithium fluoride. The invention organically combines the traditional metallurgical production process with the production process of the cathode material of new energy lithium-ion batteries, and has many advantages such as simplifying the preparation process of the material, reducing the production cost of the material, and being suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering technology, and particularly relates to a method for preparing a lithium vanadium phosphate cathode material for lithium-ion batteries by in-situ doping of vanadium-containing ore Na + in the cathode material. Background Art

[0002] Lithium-ion secondary batteries have a relatively high working voltage, high energy density and power density, and thus occupy a dominant position in the battery field of consumer electronic products. However, electric vehicle batteries and energy storage batteries, which have received great attention for solving energy and environmental problems, put forward higher requirements for current lithium-ion batteries, which also pose higher requirements for the anode and cathode materials that restrict the performance and cost of lithium-ion batteries. Lithium vanadium phosphate has a high theoretical specific capacity (3.0 - 4.3V, theoretical capacity 133 mAh / g; 3.0 - 4.8V, theoretical capacity up to 197 mAh / g), good cycling performance, high working voltage and outstanding low-temperature performance, and is a new generation of lithium-ion battery cathode material with great potential. Li3V2(PO4)3 is a typical polyanion-type cathode material. In this polyanion structure, larger phosphate ions replace oxygen ions in traditional metal oxide-type cathode materials. On the one hand, it improves the structural stability of the material, but on the other hand, it increases the distance between metal vanadium ions and reduces the electronic conductivity of Li3V2(PO4)3. Currently, to solve the problem of the low conductivity of Li3V2(PO4)3, researchers mainly solve it by two methods: surface modification and ion doping. For example, in the patent document "A Sodium-Doped Lithium Vanadium Fluorophosphate Material, Its Preparation Method and Use" with the publication number CN111072004A, the general formula of the sodium-doped lithium vanadium fluorophosphate material described therein is: Li (1-x) / Na x VPO4F, where 0 < x ≤ 0.3; the preparation method of the sodium-doped lithium vanadium fluorophosphate material includes: mixing a vanadium source, a phosphorus source, and a carbon source at 60 - 100°C, drying; placing the product in an inert atmosphere for calcination to obtain carbon-doped vanadium phosphate; mixing the carbon-doped vanadium phosphate, LiF, and a sodium source, and dry ball-milling to obtain a uniformly mixed powder; calcining the powder to obtain the sodium-doped lithium vanadium fluorophosphate material, where the calcination temperature is 650 - 800°C and the calcination time is 1 - 6h, and the sodium-doped lithium vanadium fluorophosphate material is prepared. The above patent method uses Na ion doping in an external doping manner, which requires additional addition of sodium salts, such as adding sodium carbonate, sodium fluoride, sodium chloride, etc., which will lead to the complication of the production process and the increase in production cost; secondly, the doping process uses dry ball-milling, and there will be uneven distribution of sodium elements, which will result in poor uniformity of the produced lithium vanadium fluorophosphate material; thirdly, it uses lithium fluoride as the lithium salt, which will corrode the production equipment and thus reduce the controllability of the production process. Summary of the Invention

[0003] In order to overcome the defects existing in the above-mentioned prior art, the present invention aims at the problems such as low electronic conductivity of lithium vanadium phosphate cathode materials in the existing methods. Using vanadium-containing ore as the initial raw material, a vanadium-containing sodium compound is prepared, and through the liquid-phase in-situ doping method, sodium elements are directly doped into the lithium vanadium phosphate material, effectively improving the electrochemical performance of lithium vanadium phosphate. The prepared lithium vanadium phosphate cathode material has significantly higher rate performance and cycling performance.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides a method for preparing a lithium vanadium phosphate lithium battery cathode material by in-situ doping of vanadium-containing ore Na + The method comprises the following steps:

[0005] ① Using converter vanadium slag as the basic raw material, putting the vanadium slag into a ball mill for ball milling, and obtaining refined vanadium slag after magnetic separation. Taking the refined vanadium slag and sodium carbonate and mixing them evenly according to the mass ratio of Na2CO3 / V2O5 of 1.6 - 1.8. The mixing process of this raw material is to evenly mix the converter vanadium slag and the roasting assistant sodium carbonate together to facilitate the reaction.

[0006] ② Putting the mixture obtained in step ① into a muffle furnace for roasting, the roasting temperature is 770 - 790 °C, in an air atmosphere, and the roasting time is 30 - 60 min to obtain clinker. Through oxidative roasting, the vanadium element in the converter vanadium slag and sodium carbonate jointly generate soluble vanadium sodium oxide.

[0007] ③ Ball milling the clinker obtained in step ② to a particle size of about 120 mesh, then adding an appropriate amount of water, heating to 80 - 90 °C, reacting for 15 - 30 min, with the stirring speed during the leaching process being 100 - 300 r / min, and filtering after the leaching is completed to obtain a vanadium-containing leachate. Through aqueous solution leaching, the soluble vanadium and sodium elements in the vanadium sodium oxide enter the solution.

[0008] ④ Taking the vanadium-containing leachate obtained in step ③, adding ammonium sulfate according to the mass ratio of (NH4)2SO4:V of 1.2 - 2.0, and then using dilute sulfuric acid with a volume ratio of 1:1 to adjust the pH value of the solution from 9 - 10 to 1.8 - 2.0, heating to 90 - 100 °C, and precipitating for 30 - 60 min to obtain a vanadium-containing compound. This step is the precipitation process of the vanadium-containing sodium oxide, which is to generate a vanadium-containing sodium compound by precipitation reaction of the soluble vanadium generated in the above step ③.

[0009] ⑤ Mixing the vanadium-containing compound obtained in step ④ with lithium carbonate, ammonium dihydrogen phosphate, and sucrose; putting the evenly mixed substances into a vacuum tube furnace, under an argon atmosphere, at a temperature of 300 - 400 °C, roasting for 3 - 5 h; then raising the temperature to 800 - 850 °C and roasting for 8 - 12 h to obtain an in-situ Na + doped lithium vanadium phosphate material.

[0010] In the above technical solution, further, the particle size of the vanadium slag after ball milling in step ① is greater than 80% of -120 mesh.

[0011] In the above technical solution, further, the liquid-solid ratio (volume / mass) in step ③ is 1.5 - 2.0:1.

[0012] In the above technical solution, further, the mass ratio of the vanadium-containing compound: lithium carbonate: ammonium dihydrogen phosphate: sucrose in step ⑤ is 1:0.592:1.755:0.326.

[0013] A lithium-ion battery cathode material prepared by the above method.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The present invention uses vanadium-containing ore as the initial raw material, prepares vanadium-containing sodium compound through a hydrometallurgical process, and then directly calcines it after mixing with lithium carbonate and ammonium dihydrogen phosphate. Through the liquid-phase in-situ doping method, sodium element is directly doped into the lithium vanadium phosphate material to produce a lithium vanadium phosphate material with good electrochemical performance. The sodium salt in this patent is the original one in the vanadium-containing ore and does not need to be added additionally, which can simplify the production process and reduce the production cost. In addition, the sodium element is added in the liquid phase, which is very conducive to the uniform distribution of the sodium element and the electrochemical homogeneity of the lithium vanadium phosphate electrode. Again, using lithium carbonate as the lithium salt, compared with lithium fluoride, it has a lower cost and is more conducive to the long-term operation of production equipment. The present invention organically combines the traditional metallurgical production process with the production process of the positive electrode material of new energy lithium-ion batteries, and has many advantages such as simplifying the preparation process of the material, reducing the production cost of the material, and being suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a micrograph of the vanadium-containing sodium compound in Example 3;

[0017] Figure 2 It is a micrograph of the sodium-doped lithium vanadium phosphate material prepared in Example 3;

[0018] Figure 3 It is the phase structure of the lithium vanadium phosphate material prepared in Example 3;

[0019] Figure 4 It is a CV curve test chart of the lithium vanadium phosphate material prepared in Example 3;

[0020] Figure 5 It is an electrochemical performance chart of the lithium vanadium phosphate material prepared in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be further described below in conjunction with specific embodiments, but it is not limited in any way. To avoid repetition, the raw materials in the following embodiments are commercially available without special instructions, and the quality grades are all industrial grades; the methods used are all conventional methods without special instructions. The components of vanadium slag and leaching solution are all measured using the national standard method of chemical titration. The electrochemical performance tests are all carried out according to the test standards prevailing in the lithium-ion battery industry.

[0022] The prevailing button cell test standard in the lithium-ion battery industry: The prepared LVP cathode material is mixed with the conductive agent Super P and the binder PVDF according to a mass ratio of 8:1:1, and an appropriate amount of NMP is added to adjust the viscosity of the slurry. The slurry is stirred at a constant temperature for 10 h with a constant temperature magnetic stirrer to make the slurry evenly dispersed. It is evenly coated on the aluminum foil with a thickness of 90 μm using a coater, transferred to a vacuum oven and dried at 120 °C for 12 h under vacuum conditions to remove the solvent NMP. The dried electrode sheet is made into a 14 mm round sheet using a punching machine. In an inert gas atmosphere in a glove box, a CR2025 button cell is made with metallic lithium as the anode and LVP as the cathode to test the electrochemical performance. The electrolyte used is 1 M LiPF6 in EC:DEC:EMC = 1:1:1 (v), and the activation process is all completed at a current of 0.1 C at room temperature.

[0023] Example 1

[0024] Vanadium-containing ore Na + A method for in-situ doping to prepare a lithium vanadium phosphate lithium battery cathode material, comprising the following steps:

[0025] Using converter vanadium slag as the basic raw material, an appropriate amount of vanadium slag is put into a ball mill for ball milling until the particle size of the ball-milled vanadium slag -120 mesh is greater than 80%. After magnetic separation, refined vanadium slag is obtained, and its composition is shown in Table 1. Take the above refined vanadium slag and mix it evenly with an appropriate amount of sodium carbonate according to the mass ratio of Na2CO3 / V2O5 being 1.6; put the above mixture into a muffle furnace for roasting, the roasting temperature is 770 °C, in an air atmosphere, and the roasting time is 30 min to obtain clinker; ball mill the clinker to a particle size of about 120 mesh, then add an appropriate amount of water to make the liquid-solid ratio 1.5:1 (volume ml / mass g), heat up to 80 °C, react for 15 min, the stirring speed during the leaching process is 100 r / min, and filter after the leaching is completed to obtain a vanadium-containing leaching solution, whose composition is shown in Table 2; take the vanadium-containing leaching solution, according to the proportional coefficient (mass ratio) of (NH4)2SO4 / V being 1.2, add ammonium sulfate, and then use dilute sulfuric acid with a volume ratio of 1:1 to adjust the pH value of the solution from 9 - 13 to 1.8, heat to 90 °C, precipitate for 30 min to obtain a vanadium-containing compound; take 0.49 g of the vanadium-containing compound and mix it with 0.29 g of lithium carbonate, 0.86 g of ammonium dihydrogen phosphate, and 0.16 g of sucrose. After mixing evenly, put the above substances into a vacuum tube furnace, under an argon atmosphere, at 300 °C, roast for 3 h, and then raise the temperature to 800 °C, roast for 8 h to obtain in-situ Na + doped lithium vanadium phosphate material.

[0026] Table 1 Composition of vanadium slag

[0027] TV TFe CaO MgO <![CDATA[SiO2]]> Cr Vanadium slag / % 9.12 28.7 1.85 3.94 15.95 0.21

[0028] Table 2 Composition of leaching solution

[0029] V P Na Cr Leaching solution / (g / l) 33.7 <0.01 26.9 1.12

[0030] Assemble the lithium vanadium phosphate material obtained in Example 1 into a button battery and test its electrochemical performance. The test voltage range is 3.0 - 4.3 V, and the test results are shown in Table 3.

[0031] Example 2

[0032] Vanadium-containing ore Na + Method for in-situ doping to prepare lithium vanadium phosphate lithium-ion battery cathode material, comprising the following steps:

[0033] Using converter vanadium slag as the basic raw material, put an appropriate amount of vanadium slag into a ball mill for ball milling until the particle size of the ball-milled vanadium slag -120 mesh is greater than 80%. After magnetic separation, refined vanadium slag is obtained. Take the above refined vanadium slag and mix it evenly with an appropriate amount of sodium carbonate according to the mass ratio of Na2CO3 / V2O5 of 1.7; put the above mixture into a muffle furnace for roasting at a roasting temperature of 780 °C, in an air atmosphere, and the roasting time is 40 min to obtain clinker; ball mill the clinker to a particle size of about 120 mesh, then add an appropriate amount of water to make the liquid-solid ratio 1.8:1 (volume ml / mass g), heat up to 85 °C, react for 30 min, the stirring speed during the leaching process is 200 r / min, and filter after the leaching is completed to obtain a vanadium-containing leaching solution; take the vanadium-containing leaching solution, add ammonium sulfate according to the proportional coefficient (mass ratio) of (NH4)2SO4 / V = 1.6, and then use dilute sulfuric acid with a volume ratio of 1:1 to adjust the pH value of the solution from 9 - 13 to 2.0, heat to 100 °C, precipitate for 60 min to obtain a vanadium-containing compound; take 0.98 g of the vanadium-containing compound and mix it with 0.58 g of lithium carbonate, 1.72 g of ammonium dihydrogen phosphate, and 0.32 g of sucrose. After mixing evenly, put the above substances into a vacuum tube furnace, under an argon atmosphere, at 400 °C, roast for 5 h, and then raise the temperature to 850 °C, roast for 12 h to obtain in-situ Na + doped lithium vanadium phosphate material.

[0034] Assemble the lithium vanadium phosphate material obtained in Example 2 into a button battery and test its electrochemical performance. The test voltage range is 3.0 - 4.3 V, and the test results are shown in Table 1.

[0035] Example 3

[0036] Vanadium-containing ore Na + Method for in-situ doping to prepare lithium vanadium phosphate lithium battery cathode material, comprising the following steps:

[0037] Using converter vanadium slag as the basic raw material, the vanadium slag is put into a ball mill for ball milling until the particle size of the ball-milled vanadium slag is greater than 80% at -120 mesh. After magnetic separation, refined vanadium slag is obtained. Take the above refined vanadium slag and mix it evenly with an appropriate amount of sodium carbonate according to the mass ratio of Na2CO3 / V2O5 being 1.8; put the above mixture into a muffle furnace for roasting, the roasting temperature is 790 °C, in an air atmosphere, and the roasting time is 60 min to obtain clinker; ball mill the clinker to a particle size of about 120 mesh, then add an appropriate amount of water so that the liquid-solid ratio is 2.0:1 (volume ml / mass g), heat up to 90 °C, react for 30 min, the stirring speed during the leaching process is 300 r / min, and after the leaching is completed, filter to obtain a vanadium-containing leaching solution; take the vanadium-containing leaching solution, according to the proportional coefficient (mass ratio) of (NH4)2SO4 / V = 2.0, add ammonium sulfate, and then use dilute sulfuric acid with a volume ratio of 1:1 to adjust the pH value of the solution from 9 - 13 to 2.0, heat to 100 °C, precipitate for 60 min to obtain a vanadium-containing compound; take 1.47 g of the vanadium-containing compound and mix it with 0.87 g of lithium carbonate, 2.58 g of ammonium dihydrogen phosphate, and 0.48 g of sucrose. After mixing evenly, put the above substances into a vacuum tube furnace, under an argon atmosphere, at 400 °C, roast for 5 h, and then raise the temperature to 850 °C, roast for 12 h to obtain in-situ Na + -doped lithium vanadium phosphate material.

[0038] In Example 3, the microscopic morphology photograph of the obtained vanadium-containing sodium compound during the precipitation process is as shown in Figure 1 shown, which is composed of flaky or needle-like particles and has a disordered microstructure.

[0039] In Example 3, the scanning electron microscope image of the prepared sodium-doped lithium vanadium phosphate material is as shown in Figure 2 shown. It can be seen from the scanning electron microscope image that after mixing and roasting with lithium carbonate, ammonium dihydrogen phosphate, and sucrose, the microscopic morphology of the vanadium-containing sodium compound changes from a flaky particle needle-like disordered structure to small irregular spherical particles.

[0040] In Example 3, the phase structure diagram of the prepared sodium-doped lithium vanadium phosphate material is as shown in Figure 3 shown. Each diffraction peak in the LVP sample diagram corresponds to the JCPDS card: 01 - 072 - 7074, indicating that this substance is a lithium vanadium phosphate material.

[0041] Assemble the lithium vanadium phosphate material obtained in Example 3 into a button battery and test its electrochemical performance. The test voltage range is 3.0 - 4.3 V, and the test results are shown in Table 3.

[0042] Table 3 Electrochemical performance test results of button batteries assembled with lithium vanadium phosphate materials in each example

[0043]

[0044] The CV curve test of the lithium vanadium phosphate material prepared in Example 3 is as follows Figure 4 shown; the electrochemical performance of the lithium vanadium phosphate material prepared in Example 3 is as follows Figure 5 shown.

[0045] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. Vanadium-containing ore Na + Method for preparing lithium vanadium phosphate cathode material for lithium battery by in-situ doping, characterized in that The method includes the following steps: ① Using converter vanadium extraction vanadium slag as the basic raw material, ball-milling the vanadium slag, with the particle size of the ball-milled vanadium slag being greater than 80% of -120 mesh, and obtaining refined vanadium slag after magnetic separation; taking the refined vanadium slag and sodium carbonate and mixing them evenly according to the mass ratio of Na2CO3 / V2O5 of 1.6 - 1.8; ② Roasting the mixture obtained in step ①, with the roasting temperature being 770°C - 790°C, in an air atmosphere, and the roasting time being 30 - 60 min, to obtain clinker and generate soluble vanadium sodium oxide; ③ Ball-milling the clinker obtained in step ② to a particle size of 120 mesh, then adding water with a liquid-solid ratio of 1.5 - 2.0:1; then heating to 80°C - 90°C and reacting for 15 - 30 min, with the stirring speed during the leaching process being 100 - 300 r / min, and filtering after the leaching is completed to obtain a vanadium-containing leaching solution; ④ Taking the vanadium-containing leaching solution obtained in step ③, adding ammonium sulfate according to the mass ratio of (NH4)2SO4:V of 1.2 - 2.0, then using dilute sulfuric acid with a volume ratio of 1:1 to adjust the pH value of the solution from 9 - 10 to 1.8 - 2.0, heating to 90°C - 100°C, and precipitating for 30 - 60 min to generate a vanadium-containing sodium compound; ⑤Mix the vanadium-containing sodium compound obtained in step ④ with lithium carbonate, ammonium dihydrogen phosphate, and sucrose; the mass ratio of the vanadium-containing sodium compound: lithium carbonate: ammonium dihydrogen phosphate: sucrose is 1: 0.592: 1.755: 0.326; put the above-mentioned uniformly mixed substances into a vacuum tube furnace, under an argon atmosphere, at a temperature of 300 °C to 400 °C, calcine for 3 to 5 h; then raise the temperature to 800 °C to 850 °C, and calcine for 8 to 12 h to obtain in-situ Na + -doped lithium vanadium phosphate material.

2. A lithium-ion battery cathode material prepared by the method according to claim 1.

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