Fibrous NH4V3O8 electrode material and preparation method thereof

Abstract

The invention relates to the field of batteries, and discloses a fibrous NH4V3O8 electrode material and a preparation method thereof, and the method comprises the following steps: S1, dissolving urea in a vanadium-containing solution to obtain a mixed solution; s2, adjusting the pH value of the mixed solution to 2-5, and carrying out precipitation reaction at 60-85 DEG C to obtain slurry; and S3, adding a morphology regulator into the slurry, carrying out a reaction at a temperature of 90-100 DEG C to obtain a reacted material, and carrying out post-treatment on the reacted material to obtain the fibrous NH4V3O8 electrode material. The fibrous NH4V3O8 electrode material which is regular in morphology, uniform in particle size, high in purity and excellent in electrochemical performance can be prepared.

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 / hydrothermal method [J]. Journal of Xiamen University (Natural Science Edition), 2014, 53(03):383-389" studied the preparation of NH4V3O8 nanoribbons using a combination of sol-gel and hydrothermal methods. The specific steps included: first, V2O5 and 10% H2O2 solution were stirred in a water bath at 25℃ for 1 hour to form a sol, which was then aged in the dark for 12 hours and centrifuged; then, 2 mL of the sol was mixed with 1 mmol of (NH4)2SO4 and diluted to a final volume, transferred to a hydrothermal reactor, and hydrothermally reacted at 180℃ for 24 hours to generate a suspension; finally, the product was obtained by centrifugation, washing with deionized water and ethanol, and vacuum drying at 80℃ for 6 hours. During the process, parameters such as precursor concentration, ammonium salt concentration, solution pH, hydrothermal temperature, and time were optimized to achieve the synthesis of nanoribbons with regular morphology. However, this method has obvious drawbacks: the products are prone to stacking and agglomeration, and the process is highly sensitive; moreover, it relies on complex synergistic control of multiple parameters, making industrial scale-up difficult, and further solutions are needed to address the issues of dispersion and stability.

[0006] While hydrothermal methods can yield nanomaterials with controllable morphology and high purity through precise control of reaction parameters, a series of unavoidable problems remain at present. For example, the equipment is expensive, requiring specialized reactors (such as Hastelloy) and supporting temperature and pressure control systems to withstand high temperatures and pressures (above 200°C and tens of megapascals), increasing equipment investment and maintenance difficulty; process control is complex and carries significant safety risks, as the reaction process is extremely sensitive to parameters such as temperature, pressure, and time, and even minor deviations can lead to uncontrolled product morphology or phase structure, while the high-temperature, high-pressure, and confined environment may trigger explosions; the reaction often results in a solid-liquid mixture, requiring multiple centrifugation and washing, and solid-liquid separation is extremely difficult; large-scale production faces bottlenecks, with long reaction cycles (from several hours to several days), and poor product consistency due to uneven heat transfer and unstable pressure control during industrial scale-up; the reaction process is unobservable, as the closed high-pressure reactor cannot monitor crystal nucleation and growth in real time, relying on indirect inference. All these problems severely restrict the application and development of NH4V3O8 electrode materials.

[0007] Therefore, it is necessary to study a preparation scheme for NH4V3O8 electrode materials based on primary vanadium-containing raw materials, which has the advantages of simplified process, controllable cost, high purity output and strong industrial adaptability. Summary of the Invention

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

[0009] According to one aspect of the present invention, 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 carrying out a precipitation reaction at 60-85°C to obtain a slurry; S3, adding a morphology modifier to the slurry, and carrying out a reaction at 90-100°C to obtain a post-reaction material, and performing post-treatment on the post-reaction material to obtain the fibrous NH4V3O8 electrode material.

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

[0011] According to one embodiment of the present invention, the vanadium-containing solution is selected from at least one of the following: vanadium nitride solution obtained by sodium roasting-water leaching process, vanadium calcide solution obtained by calcification roasting-acid leaching process, and vanadium extraction solution from coal shale.

[0012] According to one embodiment of the present invention, 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 invention, the morphology modifier is cationic polyacrylamide.

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

[0015] According to one embodiment of the present invention, in step S3, the ratio of the amount of morphology modifier added to the volume of slurry is 0.1~0.5 g / L.

[0016] According to one embodiment of the present invention, in step S3, the reaction is carried out under stirring conditions for a reaction time of 60-120 min.

[0017] According to one embodiment of the present invention, 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.

[0018] According to another aspect of the present invention, a fibrous NH4V3O8 electrode material is provided, which is prepared by the method described above. The fibrous NH4V3O8 electrode material has a purity greater than 99.5% and a fibrous microstructure.

[0019] In the technical solution of this invention, 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 conditions of 60-85°C are applied. At this temperature, urea undergoes hydrolysis 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 precipitates slowly and uniformly throughout the solution, avoiding particle agglomeration or impurity co-precipitation caused by local supersaturation. Furthermore, with the help of morphology modifiers, nanofiber-like materials with regular morphology, uniform particle size, and high purity are obtained. Moreover, highly polymerized vanadates have 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 and adsorb fewer impurity ions. Therefore, the method of this invention can not only prepare nanofiber-like NH4V3O8 electrode materials but also effectively improve the purity of the material. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating a method for preparing a fibrous NH4V3O8 electrode material according to an embodiment of the present invention is shown. Figure 2 The X-ray diffraction pattern of the NH4V3O8 electrode material prepared in Example 1 of the present invention is shown. Figure 3 The image shows a SEM image of the NH4V3O8 electrode material prepared in Example 1 of the present invention; Figure 4 Another SEM image of the NH4V3O8 electrode material prepared in Example 1 of the present invention is shown; Figure 5 The cycle performance test results of the battery assembled using the NH4V3O8 electrode material prepared in Example 1 of the present invention are shown. Figure 6 The results of rate testing are shown for a battery assembled using the NH4V3O8 electrode material prepared in Example 1 of this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0023] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0024] refer to Figure 1 This invention proposes a method for preparing fibrous NH4V3O8 electrode material, comprising 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 the precipitation reaction at 60~85℃ to obtain slurry; S3, add morphology modifier to slurry, react at 90~100℃ to obtain reacted material, and then perform post-processing on the reacted material to obtain fibrous NH4V3O8 electrode material.

[0025] In the technical solution of this invention, 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 conditions of 60-85°C are applied. At this temperature, urea undergoes hydrolysis 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.

[0026] 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-Vanadium exists in polymeric form. The vanadium-containing solution can be selected from at least one of the following: vanadium nitride solution obtained by sodium roasting-water leaching process, vanadium calcide solution obtained by calcification roasting-acid leaching process, and vanadium extraction solution from coal shale. Of course, the present invention is not limited to this, and other suitable vanadium-containing solutions can also be selected. The sodium roasting-water leaching process may include: mixing vanadium-containing materials (such as vanadium-titanium magnetite, vanadium slag, petroleum coke ash, etc.) with sodium salts (such as sodium carbonate, sodium sulfate, or sodium chloride), roasting at a high temperature (e.g., 750~850℃) to oxidize the insoluble low-valent vanadium in the vanadium-containing materials and convert it into water-soluble high-valent sodium vanadate; then leaching the roasted clinker with water, so that the soluble sodium vanadate salt enters the solution and is separated from most of the insoluble solid residue, and the leachate obtained after filtration is the vanadium nitride solution. The calcination-roasting-acid leaching process may include: mixing vanadium-containing materials (such as vanadium-titanium magnetite, vanadium slag, vanadium-containing coal shale, etc.) with calcium salts (such as CaO or CaCO3), roasting at high temperature (e.g., 800~950℃) to convert vanadium into acid-soluble calcium metavanadate (Ca(VO3)2), etc., and then leaching with an acid solution (e.g., dilute sulfuric acid, carbonic acid) to allow vanadium to enter the solution in ionic form, resulting in vanadium calcination solution. Vanadium extraction extract from coal shale can be a vanadium-containing extract obtained by selectively extracting vanadium from coal shale using a specific extractant.

[0027] In some embodiments, the morphology modifier is cationic polyacrylamide (CPAM).

[0028] In step S1, urea can be added to the vanadium-containing solution and stirred to ensure complete dissolution of the urea to obtain a mixed solution. In some embodiments, the mass ratio of urea to vanadium in the vanadium-containing solution in step S1 is (0.8~3):1, preferably (1~2):1. If the amount of urea used is too low, the product yield will be low; if the amount of urea used is too high, it will cause the solution pH to rise, leading to secondary dissolution of the product and preventing the acquisition of the target product.

[0029] In step S2, the pH of the mixed solution is adjusted to 2-5, preferably 3-4, and the temperature of the mixed solution is set to 60-85°C. At this point, urea undergoes hydrolysis to provide NH4. + During hydrolysis, urea releases hydroxide ions, causing the pH to rise to 4-6, creating a slightly acidic environment. The pH can be adjusted by adding an acid (e.g., sulfuric acid) or a base (e.g., sodium hydroxide). The reaction equation for the hydrolysis of urea is:

[0030]

[0031] Under conditions of 60-85℃ and pH 4-6 (urea hydrolysis causes pH to rise from 2-5 to 4-6), with decavanadate (V 10 O 28 6- Vanadium ions, existing in the form of NH4)4Na2V, can rapidly combine with ammonium and sodium ions to form sodium decavanadate (NH4)4Na2V. 10 O 28 The reaction formula is as follows:

[0032] In step S2, the sodium decavanadate precipitation reaction is carried out under stirring conditions for 30-120 min, preferably 60 min. If the reaction time is too short, the reaction will not be complete, resulting in a low product yield; if the reaction time is too long, the product yield remains unchanged, but the process energy consumption increases. The slurry obtained after the reaction is not treated and directly proceeds to the next reaction step.

[0033] In step S3, the slurry is kept at a temperature of 90-100℃ (preferably 100℃, as this results in a fast reaction rate and high product yield). Under these conditions, in an acidic environment, driven by heating, and accompanied by the redistribution of ammonium ions and the release of sodium ions, vanadate ions transform from a highly polymerized state (decapanoate) to a less polymerized state (trivanadate). Simultaneously, a morphology modifier is added to selectively guide the growth of specific crystal faces, thereby achieving morphology self-assembly and generating fibrous NH4V3O8 vanadium precipitation. The specific reaction formula is as follows:

[0034] In step S3, a morphology modifier is added to the slurry and stirred. In some embodiments, the ratio of the amount of morphology modifier added to the volume of the slurry in step S3 is 0.1~0.5 g / L, preferably 0.1~0.2 g / L. If the amount of morphology modifier is too small, the guiding effect is weak and insufficient to effectively inhibit isotropic crystal growth; if the amount of morphology modifier is too large, it excessively inhibits and hinders the growth of all crystal faces, leading to crystal structure destruction.

[0035] In some embodiments, in step S3, the reaction is carried out under stirring conditions for a reaction time of 60-120 min, preferably 90 min. A shorter reaction time results in incomplete reaction and uneven product morphology; a longer reaction time increases energy consumption. In some embodiments, the post-processing of the reacted material in step S3 includes: filtering the reacted material to obtain vanadium precipitate, and washing and drying the vanadium precipitate to obtain the fibrous NH4V3O8 target product.

[0036] In summary, this invention provides a method for preparing high-purity fibrous NH4V3O8 electrode materials using vanadium-containing solution as raw material, characterized by low temperature, low cost, simple operation, and scalability. Compared with existing technologies, the method of this invention has the following advantages: 1. It can realize the low-temperature (90~100℃) large-scale preparation of fibrous NH4V3O8 electrode materials, which has significant advantages over the traditional hydrothermal synthesis method: mild reaction conditions (no need for high temperature and high pressure equipment), simplified process (easy operation and good repeatability), and high safety (eliminating high pressure safety hazards), making it particularly suitable for industrial production applications.

[0037] 2. It has a dual advantage in terms of raw material selection: on the one hand, it uses the most basic primary raw materials in the vanadium industry chain, which greatly reduces production costs; on the other hand, it has a wide adaptability to raw materials, which provides strong support for commercial promotion.

[0038] 3. The product has excellent morphological characteristics: The method of the present invention can prepare fibrous nanomaterials with high crystallinity and regular morphology, and the particle size distribution is uniform, showing good structural consistency.

[0039] 4. Product purity reaches industry-leading level: The purity of the final product is >99.5%, and the content of key impurities such as Si, Cr, and P that affect the electrochemical performance of the electrode are all controlled below 0.005%. This high purity characteristic makes it exhibit excellent electrochemical performance, making it an ideal choice for new energy materials.

[0040] The following description is based on specific embodiments.

[0041] Example 1 The vanadium-containing solution used was sodium vanadium leaching solution, which is a vanadium leachate obtained from vanadium slag through sodium roasting and water leaching. It was taken from Panzhihua Iron & Steel Group Vanadium Products Branch and its main components were: 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 leaching solution was measured and 18.95 g of urea was added, i.e., m(urea):m(V) ≈ 2:1. The mixture was stirred until the urea was completely dissolved to obtain a mixed solution. The pH of the solution was adjusted to 3.0 using sulfuric acid, and the reaction was carried out at 85℃ for 60 min. After the reaction was completed, a slurry was obtained. 0.04 g of cationic polyacrylamide (CPAM) was added to the slurry, with the ratio of CPAM added to slurry volume being 0.2 g / L. The mixture was stirred continuously at 100 °C for 60 min. After the reaction was complete, the vanadium precipitate was obtained by filtration. The precipitated vanadium product was washed twice with deionized water, filtered, and dried to obtain nanofiber-like NH4V3O8. The purity of NH4V3O8 was tested to be 99.87%, and the content of each impurity element by mass percentage was: K - 0.013%, Na - 0.0034%, Si - 0.0013%, Cr - 0.0017%.

[0042] XRD analysis was performed on the NH4V3O8 obtained in Example 1, and the resulting X-ray diffraction pattern is shown below. Figure 2 As shown, the product is a pure phase substance with high crystallinity.

[0043] The NH4V3O8 obtained in Example 1 was subjected to SEM testing, and the obtained SEM image is shown below. Figure 3 and Figure 4 As shown, the product is a fibrous nanomaterial with a uniform morphology.

[0044] Coin cells were assembled using NH4V3O8 obtained in Example 1 as the positive electrode material, and the assembled cells were subjected to cycle performance and rate testing. The assembly method for the coin cells included: mixing the NH4V3O8 active material with the conductive agent Super-P and the binder PVDF in a mass ratio of 7:2:1 in NMP solvent; and coating the mixture onto aluminum foil (area loading 2.5~4.0 mg / cm³). 2After drying, cutting, and rolling, the material was stored in an argon glove box to obtain the electrode. Using this electrode as the positive electrode, lithium metal as the negative electrode, Celgard 2400 as the separator, and 1.0M LiPF6 dissolved in an EC:DMC:EMC (mass ratio 1:1:1) mixture as the electrolyte, a CR2025 coin cell was assembled. Cyclic performance testing methods included: activating the coin cell three times at 30 mA / g, followed by constant current charge-discharge cycling at 300 mA / g (1.5~4.0V). Rate testing methods included: cycling five times each at current densities of 30, 90, 150, 300, 600, and 1000 mA / g, and finally restoring to 30 mA / g for cycling.

[0045] Figure 5 The results of the cycle performance test show 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%.

[0046] Figure 6 The rate test results show that the battery has excellent rate performance. When the current density is 30 mA / g, 90 mA / g, 150 mA / g, 300 mA / g, 600 mA / g, and 1000 mA / g, the discharge specific capacity is 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.

[0047] Example 2 The vanadium-containing solution used was vanadium calcide solution, which is a vanadium leachate obtained from vanadium slag through calcification roasting and acid leaching. It was sourced from Panzhihua Iron & Steel Group Xichang Vanadium Products Technology Co., Ltd., and its main components were: 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 vanadium calcide solution was measured, and 7.63 g of urea was added, i.e., m(urea):m(V) ≈ 1.5:1. The mixture was stirred until the urea was completely dissolved to obtain a mixed solution. The pH of the solution was adjusted to 4.0 using sulfuric acid, and the reaction was carried out at 60℃ for 120 min. After the reaction was completed, a slurry was obtained. 0.1 g of cationic polyacrylamide (CPAM) was added to the slurry, with the ratio of CPAM added to slurry volume being 0.5 g / L. The mixture was stirred continuously at 95 °C for 80 min. After the reaction was complete, the precipitated product was obtained by filtration. The precipitated vanadium product was washed twice with deionized water, filtered, and dried to obtain the target product of nanofiber NH4V3O8. The purity of NH4V3O8 was tested to be 99.72%, and the content of each impurity element by mass percentage was: Na - 0.0065%, Si - 0.0011%, Ca < 0.001%, Mn - 0.024%, Mg - 0.012%. A coin cell was assembled according to the same method as in Example 1, and its electrochemical performance was tested. The test results showed that after 300 cycles at a current density of 300 mA / g, the capacity retention was 87.9%, and it exhibited excellent rate performance.

[0048] Example 3 The vanadium-containing solution used was the extract from the vanadium extraction process of coal shale, with the main components being: 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 extract was measured, and 11.34 g of urea was added, i.e., m(urea):m(V) ≈ 3:1. The mixture was stirred until the urea was completely dissolved to obtain a mixed solution. The pH of the solution was adjusted to 5.0 using sulfuric acid, and the reaction was carried out at 75℃ for 90 min. After the reaction was completed, a slurry was obtained. 0.2 g of cationic polyacrylamide (CPAM) was added to the slurry, with the ratio of CPAM added to slurry volume being 0.1 g / L. The mixture was stirred continuously at 98 °C for 120 min. After the reaction was complete, the precipitated product was obtained by filtration. The precipitated vanadium product was washed twice with deionized water, filtered, and dried to obtain the target product of nanofiber NH4V3O8. The purity of NH4V3O8 was tested to be 99.53%, and the content of each impurity element by mass percentage was: Fe - 0.018%, Al - 0.021%, K - 0.031%, Mg - 0.004%, P - 0.002%. A coin cell was assembled according to the same method as in Example 1, and its electrochemical performance was tested. The test results showed that after 300 cycles at a current density of 300 mA / g, the capacity retention was 88.5%, and it exhibited excellent rate performance.

[0049] Example 4 The vanadium-containing solution used was a high-chromium vanadium solution, with the main components being: 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 was measured, and 11.55 g of urea was added, i.e., m(urea):m(V) ≈ 0.8:1. The mixture was stirred until the urea was completely dissolved to obtain a mixed solution. The pH of the solution was adjusted to 2.0 using sulfuric acid, and the reaction was carried out at 70℃ for 30 min. After the reaction was completed, a slurry was obtained. 0.07 g of cationic polyacrylamide (PAM) was added to the slurry, with the ratio of added cationic polyacrylamide (PAM) to slurry volume being 0.35 g / L. The mixture was stirred continuously at 90℃ for 100 min. After the reaction was completed, the precipitate was obtained by filtration. The vanadium precipitate was washed twice with deionized water, filtered, and dried to obtain the target product of nanofiber NH4V3O8. The purity of NH4V3O8 was tested to be 99.79%, and the content of each impurity element by mass percentage was: Cr - 0.0044%, Si - 0.0031%, Fe - 0.0033%, P - 0.0012%. Coin cells were assembled using the same method as in Example 1, and electrochemical performance tests were conducted. The results showed that after 300 cycles at a current density of 300 mA / g, the capacity retention was 89.2%, and it exhibited excellent rate performance.

[0050] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

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.

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, 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 calcification roasting-acid leaching process, and vanadium extraction solution from coal shale.

4. 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.

5. The method according to claim 1, characterized in that, The morphology modifier is a cationic polyacrylamide.

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

7. 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.

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

9. 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.

10. A fibrous NH4V3O8 electrode material, characterized in that, The fibrous NH4V3O8 electrode material is prepared by the method described in any one of claims 1-9, and has a purity greater than 99.5% and a fibrous microstructure.

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