Fibrous nh4v3o8 electrode material and method for preparing the same

Abstract

The application relates to the field of batteries, and discloses a fibrous NH4V3O8 electrode material and a preparation method thereof, which comprises the following steps: S1, dissolving urea in a vanadium-containing solution to obtain a mixed solution; S2, adjusting the pH of the mixed solution to 2-5, and performing a precipitation reaction under the condition of 60-85 DEG C to obtain a slurry; S3, adding a morphology adjusting agent into the slurry, performing a reaction under the condition of a temperature of 90-100 DEG C to obtain post-reaction materials, and performing post-treatment on the post-reaction materials to obtain the fibrous NH4V3O8 electrode material. The fibrous NH4V3O8 electrode material prepared by the method has regular morphology, uniform particle size, high purity and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a fibrous NH4V3O8 electrode material and a preparation method thereof. BACKGROUND

[0002] NH4V3O8 is a layered vanadate material composed of V3O8 - layers and interlayer NH4 + ions, can provide lithium ion intercalation and deintercalation channels, exhibits high specific capacity and good rate performance, and is considered as an ideal lithium battery cathode material due to its unique structure and excellent electrochemical performance. At present, the preparation method of NH4V3O8 mainly adopts a hydrothermal method.

[0003] Chinese patent CN104701517B discloses a preparation method of NH4V3O8 cathode material for lithium ion batteries. In the method, ammonium metavanadate is dissolved in deionized water to prepare an NH4VO3 solution, 1-3 mm pre-oxidized short carbon fibers are added, the pH value is adjusted, and then the solution is transferred into a reaction kettle for forced stirring. After the reaction kettle is sealed, it is placed in a hydrothermal induction heating instrument, and a suspension is obtained after heating reaction. The suspension is centrifuged to obtain a powder product, which is then soaked in deionized water and anhydrous ethanol and repeatedly washed, and then dried and ground to obtain NH4V3O8. The method can obtain NH4V3O8 nanostructures with specific morphology by accurately controlling parameters, but has the problems of poor structural stability, strict process control, and high cost.

[0004] Chinese patent CN110255616A discloses a method for preparing ultra-thin nanosheet-shaped NH4V3O8 nanomaterial by superhigh pressure. First, 1-methyl-3-ethyl imidazole chloride is dissolved in water to form a mixed solution by adding ethylenediaminetetraacetic acid. Then, a solvent is added to the mixed solution to obtain an NH4VO3 solution, which is then subjected to microwave treatment in a microwave generator. Subsequently, the microwave-treated solution is transferred into a reaction kettle and subjected to hydrothermal reaction in a superhigh pressure hydrothermal reactor to obtain a suspension. Finally, the suspension is subjected to centrifugal separation, cleaning and drying to obtain the ultra-thin nanosheet-shaped NH4V3O8 nanomaterial. The nanosheet-shaped NH4V3O8 nanomaterial prepared by the method exhibits excellent electrochemical performance when used as a lithium ion battery cathode material, but has the problems of complex process, high equipment requirement and high raw material cost.

[0005] The article "Wei Chuang, Li Hongyi, Deng Dunyong, et al. Preparation of NH4V3O8 nanoribbons by sol-gel method and hydrothermal method [J]. Journal of Xiamen University (Natural Science Edition), 2014, 53(03): 383-389." studies the preparation of NH4V3O8 nanoribbons by combining sol-gel method and hydrothermal method. The specific steps include: first, V2O5 and 10% H2O2 solution are stirred in a 25°C water bath for 1 hour to form a sol, which is centrifuged after 12 hours of light aging; then 2mL of the sol is mixed with 1mmol (NH4)2SO4 and constant volume, and transferred to a hydrothermal kettle, and a suspension is generated after hydrothermal reaction at 180°C for 24 hours; finally, the product is obtained by centrifugal separation, deionized water and ethanol washing, and vacuum drying at 80°C for 6 hours. During the process, by optimizing the precursor concentration, ammonium salt concentration, solution pH, hydrothermal temperature and time, etc. parameters, the synthesis of nanoribbons with regular morphology is realized. However, this method has obvious shortcomings, the product is easy to stack and aggregate, the process is sensitive, and the industrialization is difficult to scale up, and the dispersion and stability need to be further solved.

[0006] Although the hydrothermal method can obtain nanomaterials with controllable morphology and high purity by precise control of reaction parameters, there are still a series of unavoidable problems at present. For example, the cost of equipment is high, special reaction kettles (such as Hastelloy) and matching temperature control and pressure measurement systems are needed to withstand high temperature and high pressure (temperature greater than 200°C, pressure up to tens of megapascals), which increases the difficulty of equipment investment and maintenance; the process control is complex and the safety risk is high, the reaction process is extremely sensitive to temperature, pressure and time, and small deviations can easily lead to loss of control of product morphology or phase structure, and the high temperature and high pressure closed environment may cause explosion; after the reaction, a solid-liquid mixture is formed, which needs to be centrifuged and washed several times, and the solid-liquid separation is extremely difficult; the scale production bottleneck, the reaction period is long (several hours to several days), and the consistency of the product is poor due to uneven heat transfer and unstable pressure control during industrialization; the reaction process cannot be observed, and the closed high-pressure kettle cannot monitor the crystal nucleation and growth process in real time. The above problems seriously restrict the application and development of NH4V3O8 electrode materials.

[0007] Therefore, it is necessary to study a preparation scheme of NH4V3O8 electrode material based on primary vanadium-containing raw materials, which has the advantages of process simplification, cost control, high-purity output and strong industrialization adaptability. SUMMARY

[0008] The main purpose of the present application is to provide a fibrous NH4V3O8 electrode material and a preparation method thereof, so as to solve the problems of high equipment cost and complex process control in the prior art for preparing NH4V3O8 electrode material by hydrothermal method.

[0009] According to one aspect of the present application, a method for preparing a fibrous NH4V3O8 electrode material is provided, comprising the following steps: S1, dissolving urea in a vanadium-containing solution to obtain a mixed solution; S2, adjusting the pH of the mixed solution to 2-5, and performing a precipitation reaction under the condition of 60-85 DEG C to obtain a slurry; S3, adding a morphology adjusting agent to the slurry, and performing a reaction under the condition of a temperature of 90-100 DEG C to obtain a post-reaction material, and performing a post-treatment on the post-reaction material to obtain the fibrous NH4V3O8 electrode material.

[0010] According to one embodiment of the present application, the vanadium-containing solution contains pentavalent vanadium.

[0011] According to one embodiment of the present application, the vanadium-containing solution is selected from at least one of the following: a sodiumized vanadium solution obtained by a sodiumization roasting-water leaching process, a calcified vanadium solution obtained by a calcification roasting-acid leaching process, and a stone coal vanadium extraction solution.

[0012] According to one embodiment of the present application, in step S1, the mass ratio of urea to vanadium in the vanadium-containing solution is (0.8-3):1.

[0013] According to one embodiment of the present application, the morphology adjusting agent is a cationic polyacrylamide.

[0014] According to one embodiment of the present application, in step S2, the reaction time is 30-120 min.

[0015] According to one embodiment of the present application, in step S3, the ratio of the added amount of the morphology adjusting agent to the volume of the slurry is 0.1-0.5 g / L.

[0016] According to one embodiment of the present application, in step S3, the reaction is performed under stirring, and the reaction time is 60-120 min.

[0017] According to one embodiment of the present application, in step S3, the post-treatment on the post-reaction material comprises: filtering the post-reaction material to obtain a vanadium precipitation product, and washing and drying the vanadium precipitation product.

[0018] According to another aspect of the present application, a fibrous NH4V3O8 electrode material is provided, which is prepared by the method as described above, and the purity of the fibrous NH4V3O8 electrode material is greater than 99.5%, and the micro-morphology is fibrous.

[0019] In the technical solution of the present application, urea is first dissolved in a vanadium-containing solution to obtain a mixed solution, then the pH of the mixed solution is adjusted to 2-5, and the condition of 60-85 DEG C is adopted, at which time the urea is hydrolyzed to provide NH4 +, hydrolysis while improving the solution pH value to form a weakly acidic environment, and a precipitation reaction occurs in the weakly acidic environment to obtain a slurry containing the precipitate, and vanadium in the precipitate exists in the form of decavanadate; then a morphology adjusting agent is added to the slurry, and the slurry is heated to 90-100 DEG C, at this time, by driving under an acidic environment, the vanadate is transformed from a high polymerization state (decavanadate) to a low polymerization state (trivanadate), and under the action of the morphology adjusting agent, specific crystal face growth is selectively guided to realize morphology self-assembly, and finally the fibrous NH4V3O8 electrode material is obtained. The fibrous electrode material has the advantages that the one-dimensional structure can provide a continuous electron conduction path and a shorter ion diffusion distance, thereby significantly improving the rate performance and cycle stability of the electrode, and is especially suitable for application scenarios requiring fast charging and discharging and resisting volume expansion. The fibrous material can be applied to high-power output and flexible devices (such as fast-charging batteries and flexible supercapacitors). In the present application, the slow-release effect of urea hydrolysis is utilized to realize uniform supply of NH4 + at the molecular scale, so that NH4V3O8 precipitates slowly and uniformly in the entire solution, avoiding local supersaturation and causing particle agglomeration or impurity co-precipitation, and under the action of the morphology adjusting agent, the nanofibrous material with regular morphology, uniform particle size and high purity is obtained. Moreover, the high-polymerization state vanadate has a larger molecular size and a more complex spatial structure, and more coordination unsaturated vanadium-oxygen bonds exist on the surface, which can adsorb more impurity ions through electrostatic action and coordination exchange. In comparison, the low-polymerization state vanadate can form pure ammonium vanadate, and fewer impurity ions are adsorbed. Therefore, the method of the present application can not only prepare the NH4V3O8 electrode material with a nanofibrous structure, but also effectively improve the purity of the material. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 A flow chart showing the preparation method of the fibrous NH4V3O8 electrode material according to the embodiment of the present application is shown;

[0022] Figure 2 An X-ray diffraction pattern of the NH4V3O8 electrode material prepared in Example 1 of the present application is shown;

[0023] Figure 3 An SEM image of the NH4V3O8 electrode material prepared in Example 1 of the present application is shown;

[0024] Figure 4 Another SEM image of the NH4V3O8 electrode material prepared in Example 1 of the present application is shown;

[0025] Figure 5 The cycle performance test results of the battery assembled using the NH4V3O8 electrode material prepared in Example 1 of the present application are shown;

[0026] Figure 6 The rate test results of the battery assembled using the NH4V3O8 electrode material prepared in Example 1 of the present application are shown. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to specific examples and the accompanying drawings.

[0028] It should be noted that all the expressions of "first" and "second" in the present application are used to distinguish two same-named different entities or different parameters, and it can be seen that "first" and "second" are only for the convenience of description and should not be understood as a limitation of the present application. The subsequent examples will not be described one by one.

[0029] Reference Figure 1 The present application proposes a preparation method of fibrous NH4V3O8 electrode material, which comprises the following steps:

[0030] S1, dissolving urea in a vanadium-containing solution to obtain a mixed solution;

[0031] S2, adjusting the pH of the mixed solution to 2-5, and performing a precipitation reaction under the condition of 60-85℃ to obtain a slurry;

[0032] S3, adding a morphology adjusting agent to the slurry, and performing a reaction under the condition of a temperature of 90-100℃ to obtain a post-reaction material, and performing a post-treatment on the post-reaction material to obtain the fibrous NH4V3O8 electrode material.

[0033] In the technical solution of the present application, first, urea is dissolved in a vanadium-containing solution to obtain a mixed solution, then the pH of the mixed solution is adjusted to 2-5, and the condition of 60-85℃ is adopted, at this time, urea is hydrolyzed to provide NH4 +Hydrolysis simultaneously raises the pH of the solution, creating a weakly acidic environment. A precipitation reaction occurs under this environment, yielding a slurry containing the precipitate, where vanadium exists as decavanadate. A morphology modifier is then added to the slurry, which is heated to 90-100°C. This acidic heating environment drives the transformation of vanadate from a highly polymerized state (decavanadate) to a less polymerized state (trivanadate). Under the influence of the morphology modifier, specific crystal planes are selectively guided to grow, leading to morphological self-assembly and ultimately yielding a fibrous NH4V3O8 electrode material. The advantage of this fibrous electrode material lies in its one-dimensional structure, which provides a continuous electron conduction path and a shorter ion diffusion distance, significantly improving the rate performance and cycle stability of the electrode. It is particularly suitable for applications requiring rapid charge / discharge and tolerance to volume expansion. The fibrous material can be applied to high-power output and flexible devices (such as fast-charging batteries and flexible supercapacitors). This invention utilizes the slow-release effect of urea hydrolysis to achieve NH4V3O8 at the molecular scale. + The uniform supply of NH4V3O8 allows for slow and uniform precipitation throughout the solution, preventing particle agglomeration or impurity co-precipitation caused by localized supersaturation. Furthermore, with the aid of a morphology modifier, a nanofiber-like material with regular morphology, uniform particle size, and high purity is obtained. Moreover, highly polymerized vanadates possess larger molecular sizes and more complex spatial structures, with more coordinate-unsaturated vanadium-oxygen bonds on their surface, enabling them to adsorb more impurity ions through electrostatic interactions and coordination exchange. In contrast, low-polymerized vanadate ions can form pure ammonium vanadate salts, adsorbing fewer impurity ions. Therefore, the method of this invention not only prepares nanofiber-like NH4V3O8 electrode materials but also effectively improves material purity. In some embodiments, the purity of the NH4V3O8 electrode material prepared by this invention is greater than 99.5%, with the content of key impurities (e.g., Si, Cr, P, etc.) controlled below 0.005%, and the microstructure of the NH4V3O8 electrode material is fibrous and uniform. NH4V3O8 electrode material has excellent electrochemical performance, and batteries assembled using it as a cathode material exhibit excellent cycle performance and rate performance.

[0034] In some embodiments, the vanadium-containing solution contains pentavalent vanadium, and under weakly acidic conditions, the vanadium in the vanadium-containing solution is mainly in the form of decavanadate (V1vanadate). 10 O 28 6-)polymer form. The vanadium-containing solution can be selected from at least one of the following: a sodium-roasted vanadium solution obtained by a sodium roasting-water leaching process, a calcium-roasted vanadium solution obtained by a calcium roasting-acid leaching process, a stone coal vanadium extraction solution. Of course, the present application is not limited thereto, and other suitable vanadium-containing solutions can also be selected. The sodium roasting-water leaching process can include: mixing a vanadium-containing material (such as vanadium-titanium magnetite, vanadium slag, petroleum coke ash, etc.) with a sodium salt (such as sodium carbonate, sodium sulfate or sodium chloride), roasting at a high temperature (such as 750-850°C) to oxidize the low-valence vanadium in the vanadium-containing material and convert it into high-valence sodium vanadate that is soluble in water; then leaching the roasted material with water to make the soluble sodium vanadate salt enter the solution and separate from most of the insoluble solid residue, and the leaching solution obtained after filtration is the sodium vanadium solution. The calcium roasting-acid leaching process can include: mixing a vanadium-containing material (such as vanadium-titanium magnetite, vanadium slag, stone coal containing vanadium, etc.) with a calcium salt (such as CaO or CaCO3), roasting at a high temperature (such as 800-950°C) to convert vanadium into calcium metavanadate (Ca(VO3)2) and other acid-soluble substances, and then using an acid solution (such as dilute sulfuric acid, carbonic acid) for acid leaching to make vanadium enter the solution in ionic form, obtaining the calcium vanadium solution. The stone coal vanadium extraction solution can be a vanadium-containing extraction solution obtained by selectively extracting vanadium in stone coal with a specific extractant.

[0035] In some embodiments, the morphology adjusting agent is cationic polyacrylamide (CPAM).

[0036] In step S1, urea can be added to the vanadium-containing solution and stirred to make the urea completely dissolved in the vanadium-containing solution to obtain a mixed solution. In some embodiments, in step S1, the mass ratio of urea to vanadium in the vanadium-containing solution is (0.8-3):1, and preferably, the mass ratio of urea to vanadium in the vanadium-containing solution can be (1-2):1. If the amount of urea is too low, the yield of the product is low; if the amount of urea is too high, it will cause the pH of the solution to rise, causing the product to be re-dissolved, and the target product cannot be obtained.

[0037] In step S2, the pH of the mixed solution is adjusted to 2-5, and preferably can be adjusted to 3-4, and the temperature of the mixed solution is 60-85°C. At this time, the urea is hydrolyzed to provide NH4 + , and the hydrolysis releases hydroxyl ions to cause the pH to rise to 4-6, forming a weakly acidic environment. The pH can be adjusted by adding an acid (such as sulfuric acid) or a base (such as sodium hydroxide). The reaction formula of the hydrolysis of urea is:

[0038]

[0039]

[0040] at a temperature of 60-85°C and a pH of 4-6 (urea hydrolysis causes the pH to rise from 2-5 to 4-6) to form vanadium ions in the form of decavanadate (V 10 O 28 6- Vanadium ions in the form of decavanadate can rapidly combine with ammonium ions and sodium ions to form sodium ammonium decavanadate (NH4)4Na2V 10 O 28 The reaction is as follows:

[0041]

[0042] In step S2, the sodium ammonium decavanadate precipitation reaction is carried out under stirring, and the reaction time is 30-120 min, preferably 60 min. If the reaction time is too short, the reaction is not complete and the product yield is low; if the reaction time is too long, the product yield does not change and the process energy consumption increases. The slurry obtained after the reaction is not treated and is directly used in the next step.

[0043] The slurry is then subjected to step S3 at a temperature of 90-100°C (preferably 100°C, at which the reaction rate is fast and the product yield is high). At this time, in an acidic environment, the transformation of vanadate from a high polymerization state (decavanadate) to a low polymerization state (trivanadate) is driven by heating, accompanied by redistribution of ammonium ions and release of sodium ions. A morphology adjustment agent is added to selectively guide the growth of specific crystal faces and achieve morphology self-assembly, thereby generating fibrous NH4V3O8 vanadium precipitation products. The specific reaction is as follows:

[0044]

[0045] In step S3, the morphology adjustment agent is added to the slurry and stirred. In some embodiments, in step S3, the ratio of the amount of the morphology adjustment agent to the volume of the slurry is 0.1-0.5 g / L, preferably 0.1-0.2 g / L. If the amount of the morphology adjustment agent is too small, the guiding effect is weak and is not sufficient to effectively inhibit the isotropic growth of crystal forms; if the amount of the morphology adjustment agent is too large, it excessively inhibits the growth of all crystal faces, leading to destruction of the crystal structure.

[0046] In some embodiments, in step S3, the reaction is carried out under stirring, and the reaction time is 60-120 min, preferably 90 min. If the reaction time is too short, the reaction is not complete and the product morphology is not uniform; if the reaction time is too long, the process energy consumption increases. In some embodiments, in step S3, the material after the reaction is subjected to post-treatment, including filtering the material after the reaction to obtain vanadium precipitation products, and washing and drying the vanadium precipitation products to obtain fibrous NH4V3O8 target products.

[0047] In summary, the present application provides a low-temperature, low-cost, simple operation, and scalable production method for high-purity fibrous NH4V3O8 electrode material using vanadium-containing solution as raw material. Compared with the prior art, the method of the present application has the following advantages:

[0048] 1. Low-temperature (90-100℃) scale production of fibrous NH4V3O8 electrode material can be achieved, which has significant advantages compared with traditional hydrothermal synthesis method: mild reaction conditions (no need for high temperature and high pressure equipment), simplified process (simple operation and good repeatability), high safety (eliminate high pressure safety hazard), especially suitable for industrial production application.

[0049] 2. Dual advantages in raw material selection: on the one hand, the most basic primary raw material in the vanadium industry chain is used, which greatly reduces the production cost; on the other hand, it has wide adaptability to raw materials, which provides strong support for commercialization.

[0050] 3. The product has excellent morphological characteristics: the method of the present application can prepare fibrous nanomaterials with high crystallinity and regular morphology, and the particle size distribution is uniform, showing good structural consistency.

[0051] 4. The product purity reaches the industry leading level: the purity of the final product is >99.5%, and the content of key impurities such as Si, Cr and P affecting the electrochemical performance of the electrode is controlled below 0.005%, which makes it show excellent electrochemical performance and is an ideal choice for new energy materials.

[0052] The following will be described according to specific examples.

[0053] Example 1

[0054] The vanadium-containing solution used is sodium vanadium solution, which is a vanadium leaching solution obtained by sodium roasting and water leaching of vanadium slag, taken from the Vanadium Products Branch of Panzhihua Steel, and the main components are: K-0.239 g / L, Na-47.22 g / L, Si-0.86 g / L, Cr-3.45 g / L, and TV-47.38 g / L. 200 mL of sodium vanadium solution is measured, 18.95 g of urea is added, i.e. m(urea):m(V)≈2:1, and stirred until the urea is completely dissolved to obtain a mixed solution. Sulfuric acid is used to adjust the pH of the solution to 3.0, and the reaction is carried out at 85°C for 60 min. After the reaction is completed, 0.04 g of cationic polyacrylamide (CPAM) is added to the slurry, and the ratio of the amount of cationic polyacrylamide (CPAM) added to the volume of the slurry is 0.2 g / L. The stirring is continued at 100°C for 60 min. After the reaction is completed, the vanadium precipitation product is obtained by filtration, and the vanadium precipitation product is washed with deionized water for two times, and then dried after filtration to obtain nanofibrous NH4V3O8. The purity of NH4V3O8 is 99.87% by testing, and the content of each impurity element is: K-0.013%, Na-0.0034%, Si-0.0013%, and Cr-0.0017% by mass percentage.

[0055] The NH4V3O8 obtained in Example 1 is subjected to XRD test, and the obtained X-ray diffraction pattern is as shown in Figure 2 , which shows that the product is a pure phase material with high crystallinity.

[0056] The NH4V3O8 obtained in Example 1 is subjected to SEM test, and the obtained SEM images are as shown in Figure 3 and Figure 4 , which shows that the product is a fibrous nanomaterial with uniform morphology.

[0057] The NH4V3O8 obtained in Example 1 is used as a positive electrode material to assemble a button cell, and the assembled battery is subjected to cycle performance test and rate test. The assembly method of the button cell includes: mixing NH4V3O8 active material, conductive agent Super-P, and adhesive PVDF in a mass ratio of 7:2:1 in NMP solvent, coating the mixture on an aluminum foil (surface loading 2.5~4.0 mg / cm 2), dried, cut, rolled, and stored in an argon glove box to obtain an electrode. The electrode was used as a positive electrode, lithium metal was used as a negative electrode, Celgard 2400 was used as a separator, and 1.0 M LiPF6was dissolved in a mixture of EC:DMC:EMC (mass ratio 1:1:1) to obtain an electrolyte. A CR2025 button cell was assembled. The cycle performance test method included: the button cell was first activated at 30 mA / g for 3 times, and then constant current charge-discharge cycling was performed at 300 mA / g (1.5-4.0 V).

[0058] Figure 5 The cycle performance test results are shown, indicating that the battery has excellent cycle performance. The initial capacity at a current density of 300 mA / g is 223.3 mAh / g, and the specific capacity is still 199.01 mAh / g after 300 cycles, with a capacity retention rate of 89.1%.

[0059] Figure 6 The rate test results are shown, indicating that the battery has excellent rate performance. When the current densities are 30 mA / g, 90 mA / g, 150 mA / g, 300 mA / g, 600 mA / g, and 1000 mA / g, the discharge specific capacities are 398.12 mAh / g, 271.42 mAh / g, 205.57 mAh / g, 157.47 mAh / g, 80.97 mAh / g, and 55.28 mAh / g, respectively. When the current density returns to 30 mA / g, the battery still has a specific capacity of 287.62 mAh / g.

[0060] Example 2

[0061] The vanadium-containing solution used is a calcified vanadium solution, which is a vanadium leaching solution obtained by calcification roasting-acid leaching of vanadium slag, taken from Pangang Xichang Vanadium Products Technology Co., Ltd., and the main components are: Na-0.477 g / L, Ca-0.442 g / L, Si-0.116 g / L, Mn-6.29 g / L, Mg-1.47 g / L, and TV-25.44 g / L. 200 mL of the calcified vanadium solution is measured, 7.63 g of urea is added, i.e. m(urea):m(V)≈1.5:1, and stirring is performed until the urea is completely dissolved to obtain a mixed solution. Sulfuric acid is used to adjust the pH of the solution to 4.0, and the reaction is carried out at 60°C for 120 min. After the reaction is completed, a slurry is obtained. 0.1 g of cationic polyacrylamide (CPAM) is added to the slurry, and the ratio of the amount of cationic polyacrylamide (CPAM) added to the volume of the slurry is 0.5 g / L. The stirring is continued at 95°C for 80 min. After the reaction is completed, the precipitate is filtered to obtain a precipitate product. The vanadium precipitate is washed with deionized water for two times, filtered and dried to obtain the nanofibrous NH4V3O8 target product. Test results show that the purity of NH4V3O8 is 99.72%, and the content of each impurity element is: Na-0.0065%, Si-0.0011%, Ca<0.001%, Mn-0.024%, and Mg-0.012% by mass percentage. The button cell is assembled and the electrochemical performance test is carried out according to the same method as in Example 1. The test results show that the capacity retention rate is 87.9% after 300 cycles at a current density of 300 mA / g, and the rate performance is excellent.

[0062] Example 3

[0063] The vanadium-containing solution used is the extraction solution in the vanadium extraction process from stone coal, and the main components are: Al-13.88 g / L, Fe-5.09 g / L, K-5.81 g / L, Mg-3.72 g / L, P-0.51 g / L, and TV-1.89 g / L. 2000 mL of the extraction solution is measured, 11.34 g of urea is added, i.e. m(urea):m(V)≈3:1, and the urea is stirred until it is completely dissolved to obtain a mixed solution. Sulfuric acid is used to adjust the pH of the solution to 5.0, and the solution is reacted at 75°C for 90 min. After the reaction is completed, a slurry is obtained. 0.2 g of cationic polyacrylamide (CPAM) is added to the slurry, and the ratio of the amount of cationic polyacrylamide (CPAM) added to the volume of the slurry is 0.1 g / L. The slurry is continuously stirred at 98°C for 120 min. After the reaction is completed, the precipitate is filtered to obtain a precipitate product. The vanadium precipitate product is washed with deionized water twice, filtered, and dried to obtain the nanofibrous NH4V3O8 target product. Testing shows that the purity of NH4V3O8 is 99.53%, and the content of each impurity element is: Fe-0.018%, Al-0.021%, K-0.031%, Mg-0.004%, and P-0.002% by mass percentage. The button cell is assembled and the electrochemical performance is tested according to the same method as in Example 1. The test results show that the capacity retention rate is 88.5% after 300 cycles at a current density of 300 mA / g, and the button cell has excellent rate performance.

[0064] Example 4

[0065] The vanadium-containing solution used is a high-chromium vanadium solution, and the main components are: Cr-4.39 g / L, Si-2.04 g / L, Fe-1.12 g / L, P-0.63 g / L, and TV-72.21 g / L. 200 mL of the high-chromium vanadium solution is measured, 11.55 g of urea is added, that is, m(urea):m(V)≈0.8:1, and stirring is performed until the urea is completely dissolved to obtain a mixed solution. Sulfuric acid is used to adjust the pH of the solution to 2.0, and the reaction is performed at 70°C for 30 min. After the reaction is completed, a slurry is obtained. 0.07 g of cationic polyacrylamide (PAM) is added to the slurry, and the ratio of the amount of cationic polyacrylamide (PAM) added to the volume of the slurry is 0.35 g / L. The stirring is continued at 90°C for 100 min. After the reaction is completed, the precipitate is filtered to obtain a precipitate product. The vanadium precipitate product is washed with deionized water for two times, filtered, and dried to obtain the nanofibrous NH4V3O8 target product. Testing shows that the purity of NH4V3O8 is 99.79%, and the content of each impurity element is: Cr-0.0044%, Si-0.0031%, Fe-0.0033%, and P-0.0012% by mass percentage. The button cell is assembled according to the same method as in Example 1, and the electrochemical performance test is performed. The test results show that the capacity retention rate is 89.2% after 300 cycles at a current density of 300 mA / g, and the rate performance is excellent.

[0066] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is merely exemplary and is not intended to suggest that the scope of the embodiments disclosed (including the claims) is limited to these examples; under the concept of the embodiments, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes of different aspects of the embodiments as described above. In order to be brief, they are not provided in detail. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principles of the embodiments should be included in the protection scope of the embodiments.

Claims

1. A method for preparing a fibrous NH4V3O8 electrode material, characterized in that, Includes the following steps: S1, Dissolve urea in a vanadium-containing solution to obtain a mixed solution; S2, adjust the pH of the mixed solution to 2-5, and carry out a precipitation reaction at 60-85℃ to obtain a slurry; S3, add a morphology modifier to the slurry, react at a temperature of 90~100℃ to obtain the reacted material, and perform post-processing on the reacted material to obtain the fibrous NH4V3O8 electrode material. The vanadium-containing solution is selected from at least one of the following: vanadium sodium solution obtained by sodium roasting-water leaching process, vanadium calcification solution obtained by vanadium calcification-acid leaching process, and vanadium extraction solution from coal shale; the morphology modifier is cationic polyacrylamide.

2. The method according to claim 1, characterized in that, The vanadium-containing solution contains pentavalent vanadium.

3. The method according to claim 1, characterized in that, In step S1, the mass ratio of urea to vanadium in the vanadium-containing solution is (0.8~3):

1.

4. The method according to claim 1, characterized in that, In step S2, the reaction time is 30~120 min.

5. The method according to claim 1, characterized in that, In step S3, the ratio of the amount of morphology modifier added to the volume of the slurry is 0.1~0.5 g / L.

6. The method according to claim 1, characterized in that, In step S3, the reaction is carried out under stirring conditions for 60-120 minutes.

7. The method according to claim 1, characterized in that, In step S3, the post-processing of the reaction material includes: filtering the reaction material to obtain vanadium precipitate, and washing and drying the vanadium precipitate.

8. A fibrous NH4V3O8 electrode material, characterized in that, The fibrous NH4V3O8 electrode material is prepared by the method described in any one of claims 1-7, and has a purity greater than 99.5% and a fibrous microstructure.

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