Continuous manufacturing system and method of modified sodium vanadium phosphate

Abstract

The invention discloses a continuous manufacturing system and method for modified sodium vanadium phosphate, and the system comprises five base solution introduction pipelines which are respectively used for introducing a vanadium source solution, a reducing agent, a phosphorus source solution, a sodium source solution and a dopant; the pre-reaction mechanism is connected with two roadbed liquid introduction pipelines for introducing a vanadium source solution and a reducing agent, and can perform injection-compression catalytic reduction reaction on the vanadium source solution and the reducing agent introduced into the pre-reaction mechanism; and the homogeneous reactor is communicated with the pre-reaction mechanism by adopting a continuous phase liquid injection pipeline. In the system, a pre-reaction mechanism is used for treating a catalytic reduction reaction of a vanadium source and a reducing agent, and a homogeneous reactor is used for uniformly mixing a pre-reaction product with a phosphorus source, a sodium source and a doping agent to generate a modified sodium vanadium phosphate precursor; the staged reaction design avoids severe reaction or precipitation possibly caused by direct mixing, so that the reaction is more controllable.

Description

Technical Field

[0001] This invention specifically relates to the field of manufacturing technology of modified sodium vanadium phosphate, and more specifically to a continuous manufacturing system and method for modified sodium vanadium phosphate. Background Technology

[0002] Sodium vanadium phosphate (PVP) is widely used in sodium-ion battery production due to its stable three-dimensional sodium ion transport channels, high operating voltage, and theoretical specific capacity. However, its low electronic conductivity limits its rate performance and practical applications. Therefore, elemental doping (modification) is used to improve its electrochemical performance.

[0003] However, the preparation process of modified sodium vanadium phosphate has the following drawbacks: For key catalytic reduction reactions (such as reducing pentavalent vanadium to trivalent or tetravalent), the traditional mixing method has low mass transfer efficiency, and the reducing agent cannot diffuse into the vanadium source quickly and fully, resulting in slow reaction rate, low conversion rate, and easy generation of unreacted residues. These residues not only reduce the purity of the precursor, but may also become impurity phases in the final material, damaging its electrochemical performance. Summary of the Invention

[0004] Therefore, the present invention proposes a continuous manufacturing system and method for modified sodium vanadium phosphate to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a continuous manufacturing system for modified sodium vanadium phosphate, comprising:

[0006] The base liquid inlet pipeline has five channels, which respectively introduce vanadium source solution, reducing agent, phosphorus source solution, sodium source solution and dopant;

[0007] The pre-reaction mechanism is connected to two base liquid inlet pipelines for introducing vanadium source solution and reducing agent, and is capable of performing a pressure-injected catalytic reduction reaction on the vanadium source solution and reducing agent introduced into it;

[0008] The homogeneous reactor is connected to the pre-reaction mechanism via a continuous phase injection pipeline, and the homogeneous reactor is connected to the three base liquid introduction pipelines for introducing phosphorus source solution, sodium source solution and dopant via a dispersed phase injection pipeline.

[0009] And a coil reactor, into which a modified sodium vanadium phosphate precursor prepared by a homogenizing reactor is injected and continuously carbothermicly reduced to complete the crystallization of modified sodium vanadium phosphate.

[0010] Optionally, a metering pump and two valves are sequentially arranged on the base liquid inlet pipeline along its flow direction, wherein a preheater is arranged between the two valves, and a temperature gauge is arranged at the outlet of the preheater.

[0011] Optionally, a temporary storage container, valve 2, pressure gauge and booster pump are sequentially provided on the continuous phase injection pipeline and the dispersed phase injection pipeline along their respective flow directions.

[0012] Optionally, the upper port of the coil reactor is connected to an exhaust mechanism, and the lower port of the coil reactor is connected to a discharge mechanism.

[0013] Optionally, the pre-reaction mechanism includes:

[0014] The reaction shell is sealed at its outlet with an electrically controlled liquid outlet device;

[0015] A continuous injection mechanism is located at the tail of the reaction shell and is capable of continuously suctioning, pressurizing and discharging the mixture in the inner cavity of the reaction shell.

[0016] Intermittent injection mechanism, which can intermittently inject a quantitative reducing agent into the inner cavity of the reaction shell;

[0017] And the oscillating fluid assembly, which is driven to oscillate by the impact force generated by the injection of solution into the reaction shell by the continuous injection mechanism and the intermittent injection mechanism;

[0018] The reaction shell has four injection channels arranged in a matrix on its inner wall, and a vibrating liquid assembly is provided between each pair of opposite injection channels.

[0019] Optionally, the vibrating fluid assembly consists of a vibrating spring and two sealing balls, wherein the two sealing balls are connected by a vibrating spring, and under the tension of the vibrating spring, each sealing ball seals the corresponding injection groove.

[0020] The sealing ball has multiple hemispherical protrusions arranged in a circumferential array on its side wall, and each protrusion slides in contact with the inner wall of the liquid injection channel.

[0021] Optionally, the continuous injection mechanism includes:

[0022] There are two plunger cylinders, which are symmetrically fixed on the reaction shell, and each plunger cylinder has a plunger slidably connected inside;

[0023] There are two shaft disks, which are rotatably mounted at the front and rear ends of the reaction shell drive cavity respectively;

[0024] A connecting post is connected between the edges of two shaft discs. The connecting post is rotatably connected to one end of two pressure handles, and the other end of each pressure handle is rotatably connected to its corresponding plunger.

[0025] The driven gear meshes with the driving gear for transmission, and the driven gear is connected to its corresponding shaft disc by a coupling.

[0026] And a motor, which is fixed to the reaction shell by a bracket, and the drive end of the motor is connected to the drive gear;

[0027] The two plunger cylinders are connected to two injection channels located on the rear side by pressure pipes.

[0028] Optionally, the two liquid injection channels located on the rear side are connected to the inner cavity of the reaction shell by a liquid flow channel, and a one-way valve is provided in the liquid flow channel to inject liquid into the liquid injection channel.

[0029] Optionally, the intermittent injection mechanism consists of an injection pipe one, a contact and a contact solenoid valve, and an injection pipe two. The contact solenoid valve is filled with a reducing agent through the injection pipe one, and the outlet end of the contact solenoid valve is connected to its corresponding injection groove through the injection pipe two.

[0030] The contact is fixed on its corresponding shaft disc and is driven by the shaft disc to rotate to the pressing position of the contact solenoid valve.

[0031] The present invention also provides a continuous method for manufacturing modified sodium vanadium phosphate, comprising the following steps:

[0032] Step 1: In-situ complexation. Specifically, the vanadium source solution and reducing agent are preheated to 80°C and then introduced into the pre-reaction mechanism. The reducing agent reduces the vanadium in the vanadium source solution from "+5" valence to one of "+4" or "+3" valence.

[0033] Step 2: The vanadium source solution after pre-reaction reduction is injected into the homogenizing reactor under pressure through a continuous phase injection pipeline. At the same time, the phosphorus source solution, sodium source solution, and dopant are injected into the homogenizing reactor in a measured amount.

[0034] Step 3: In a homogenizing reactor at a constant temperature of 80–100°C, vanadium source solution, reducing agent, phosphorus source solution, sodium source solution, and dopant are mixed to generate modified sodium vanadium phosphate precursor.

[0035] Step 4: The modified sodium vanadium phosphate precursor is fed into the coil reactor and crystallized at a gradually increasing temperature of 100–700°C.

[0036] The present invention employs the above technology and has the following beneficial effects compared with the existing technology: In the system of the present invention, the pre-reaction mechanism is used to process the catalytic reduction reaction of vanadium source and reducing agent, and utilizes the working effect of continuous injection mechanism and intermittent liquid injection mechanism to realize the synergistic effect of "pressurization + vibration" of the vibrating liquid component. Among them, "pressurization" provides large-amplitude turbulent kinetic energy, while "vibration" introduces small-amplitude turbulent kinetic energy. The superposition of the two makes the mixing more thorough. For the catalytic reduction reaction, this mixing method ensures that the reducing agent diffuses rapidly into the vanadium source, improves the reaction conversion rate, reduces unreacted residues, and thus improves the quality of the precursor. Attached Figure Description

[0037] Figure 1 A schematic diagram of a continuous manufacturing system for modified sodium vanadium phosphate;

[0038] Figure 2 for Figure 1 Schematic diagram of the pre-reaction mechanism;

[0039] Figure 3 for Figure 1 Schematic diagram of the internal structure of the pre-reaction mechanism;

[0040] Figure 4 for Figure 3 An enlarged schematic diagram of part A in the middle;

[0041] Figure 5 for Figure 3 A schematic diagram of the structure of the intermediate vibration fluid assembly.

[0042] In the diagram: 1. Valve 1; 2. Thermometer; 3. Pre-reaction mechanism; 4. Valve 2; 5. Valve 3; 6. Discharge mechanism; 7. Coil reactor; 8. Exhaust mechanism; 9. Homogenizing reactor; 10. Booster pump; 11. Temporary storage container; 12. Preheater; 13. Metering pump; 14. Pressure gauge;

[0043] 301. Plunger cylinder; 302. Driven gear; 303. Driven gear; 305. Motor; 306. Vent; 307. Injection pipe one; 308. Pressure pipe; 309. Reaction shell; 310. Electrically controlled liquid outlet; 311. Injection port; 312. Plunger; 313. Pressure handle; 314. Connecting column; 315. Shaft disc; 316. Sealing ball; 317. Block; 318. Injection channel; 319. Check valve; 320. Liquid flow channel; 321. Vibrating spring; 322. Contact; 323. Contact solenoid valve. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example: Please refer to the appendix Figure 1-5 This invention provides a technical solution: a continuous manufacturing system for modified sodium vanadium phosphate, comprising:

[0046] The base liquid inlet pipeline has five channels, which respectively introduce vanadium source solution, reducing agent, phosphorus source solution, sodium source solution and dopant;

[0047] The pre-reaction mechanism 3 is connected to two base liquid inlet pipelines for introducing vanadium source solution and reducing agent, and can perform pressure injection catalytic reduction reaction on the vanadium source solution and reducing agent introduced therein;

[0048] Specifically, the pre-reaction mechanism injects pressure to catalytically reduce the vanadium source solution and reducing agent, which helps to pre-treat key components before they enter the main reaction and improves reaction efficiency.

[0049] The homogenizing reactor 9 is connected to the pre-reaction mechanism 3 via a continuous phase injection pipeline, and the homogenizing reactor 9 is connected to the three-way base liquid introduction pipeline for introducing phosphorus source solution, sodium source solution and dopant via a dispersed phase injection pipeline.

[0050] Specifically, the homogeneous reactor mixes the pre-reaction products with other components (phosphorus source, sodium source, dopants) through continuous phase and dispersed phase injection pipelines to ensure uniform mixing and provide a uniform precursor for subsequent reactions;

[0051] And a coil reactor 7, with a valve 3 5 installed on the pipeline between it and the homogenizing reactor 9. The coil reactor 7 is injected with the modified sodium vanadium phosphate precursor mixed by the homogenizing reactor 9 and undergoes continuous carbothermic reduction to complete the crystallization of modified sodium vanadium phosphate.

[0052] It should be noted that the pre-reaction mechanism is used to handle the catalytic reduction reaction of vanadium source and reducing agent, while the homogenizing reactor is used to uniformly mix the pre-reaction product with phosphorus source, sodium source and dopant to generate modified sodium vanadium phosphate precursor. This staged reaction design avoids the violent reaction or precipitation that may be caused by direct mixing, making the reaction more controllable.

[0053] In this embodiment, a metering pump 13 and two valves 1 are sequentially arranged on the base liquid inlet pipeline along its flow direction. A preheater 12 is arranged between the two valves 1, and a temperature gauge 2 is arranged at the outlet of the preheater 12.

[0054] In this embodiment, a temporary storage container 11, a valve 4, a pressure gauge 14, and a booster pump 10 are sequentially arranged on the continuous phase injection pipeline and the dispersed phase injection pipeline along their respective flow directions.

[0055] In this embodiment, the upper port of the coil reactor 7 is connected to an exhaust mechanism 8, and the lower port of the coil reactor 7 is connected to a discharge mechanism 6.

[0056] In this embodiment, the pre-reaction mechanism 3 includes:

[0057] The reaction shell 309 is provided with a liquid injection port 311, and an electrically controlled liquid dispenser 310 is sealed at the outlet of the reaction shell 309.

[0058] A continuous injection mechanism is located at the tail of the reaction shell 309 and is capable of continuously suctioning, pressurizing and discharging the mixture in the cavity of the reaction shell 309.

[0059] Intermittent injection mechanism, which can intermittently inject a quantitative reducing agent into the inner cavity of the reaction shell 309;

[0060] And the oscillating fluid assembly, which is driven to oscillate by the impact force generated by the injection of solution into the reaction shell 309 by the continuous injection mechanism and the intermittent injection mechanism;

[0061] The inner wall of the reaction shell 309 is provided with four liquid injection channels 318 arranged in a matrix, and a liquid vibration assembly is provided between each pair of liquid injection channels 318 arranged in opposite directions.

[0062] In this embodiment, the vibrating fluid assembly consists of a vibrating spring 321 and two sealing balls 316. The two sealing balls 316 are connected by the vibrating spring 321, and under the tension of the vibrating spring 321, each sealing ball 316 is sealed at its corresponding injection groove 318.

[0063] Among them, the side wall of the sealing ball 316 is provided with a circumferential array of multiple hemispherical protrusions, and each protrusion is slidably connected to the inner wall of the liquid injection channel 318.

[0064] It should be noted that the pre-reaction mechanism utilizes the working effects of the continuous injection mechanism and the intermittent injection mechanism to achieve the synergistic effect of "pressurization + vibration" of the vibrating fluid assembly;

[0065] Specifically, during pressurized injection, the continuous injection mechanism continuously draws and pressurizes the mixture in the reaction shell through the plunger cylinder 301, plunger 312 and motor drive system. During the alternating upper and lower pressurized injection, the solution can enter the reaction shell at high speed, generating high shear force, breaking the laminar flow state and forming turbulent flow. This increases the contact area between the vanadium source and the reducing agent, and accelerates the catalytic reduction reaction rate. Especially for solutions with high viscosity, pressurization can effectively overcome flow resistance.

[0066] When the vibrating liquid assembly is driven to vibrate under the injection pressure, when the solution impacts the sealing ball through the injection channel, the elastic deformation of the vibrating spring causes the sealing ball to periodically displace, generating high-frequency vibration. This vibration further agitates the reaction liquid, preventing excessively high local concentrations or precipitation formation, ensuring uniform dispersion of reactants. In addition, the hemispherical protrusions on the sealing ball slide against the inner wall of the injection channel, which also plays a self-cleaning role and reduces the risk of scaling.

[0067] In summary, "pressurization" provides a large amount of turbulent kinetic energy, while "mixing and vibration" introduces a small amount of turbulent kinetic energy. The combination of the two makes the mixing more thorough. For catalytic reduction reactions, this mixing method ensures that the reducing agent diffuses rapidly into the vanadium source, improves the reaction conversion rate, reduces unreacted residues, and thus improves the quality of the precursor.

[0068] In this embodiment, the continuous injection mechanism includes:

[0069] There are two plunger cylinders 301, which are symmetrically fixed on the reaction shell 309, and each plunger cylinder 301 has a plunger 312 slidably connected inside it;

[0070] Two shaft disks 315 are provided and are rotatably mounted at the front and rear ends of the driving cavity of the reaction shell 309 respectively. The side wall of the reaction shell 309 is provided with a vent 306 that communicates with the driving cavity.

[0071] A connecting post 314 is connected between the edges of two shaft discs 315. One end of the connecting post 314 is rotatably connected to one end of two pressure handles 313, and the other end of each pressure handle 313 is rotatably connected to its corresponding plunger 312.

[0072] Driven gear 302 meshes with driving gear 303 for transmission, and driven gear 302 is connected to its corresponding shaft disk 315 by a coupling.

[0073] And motor 305, which is fixed on reaction shell 309 by bracket, and the drive end of motor 305 is connected to drive gear 303;

[0074] The two plunger cylinders 301 are connected to the two injection channels 318 located on the rear side by pressure pipes 308 respectively.

[0075] In this embodiment, the two liquid injection channels 318 located on the rear side are connected to the inner cavity of the reaction shell 309 by a liquid flow channel 320, and a one-way valve 319 is provided in the liquid flow channel 320 to inject liquid into the liquid injection channel 318.

[0076] In this embodiment, the intermittent injection mechanism consists of an injection pipe 307, a contact 322, a contact solenoid valve 323, and an injection pipe 2. The contact solenoid valve 323 is filled with a reducing agent through the injection pipe 307, and the outlet end of the contact solenoid valve 323 is connected to the corresponding injection groove 318 through the injection pipe 2.

[0077] The contact 322 is fixed on the corresponding shaft disk 315 and is driven by the shaft disk 315 to rotate to the pressing position of the contact solenoid valve 323.

[0078] It should be noted that the intermittent injection mechanism achieves quantitative and intermittent injection of the reducing agent through a contact solenoid valve and contact design. This pulse-type addition avoids over-reduction or side reactions that may be caused by continuous injection, making the reaction more controllable.

[0079] It should be added that a plug 317 is sealed inside the injection channel 318 opposite to the injection channel 318 for injecting reducing agent.

[0080] The present invention also provides a continuous method for manufacturing modified sodium vanadium phosphate, comprising the following steps:

[0081] Step 1: In-situ complexation. Specifically, the vanadium source solution and reducing agent are preheated to 80°C and then introduced into the pre-reaction unit 3. The reducing agent reduces the vanadium in the vanadium source solution from "+5" valence to one of "+4" or "+3" valence.

[0082] Step 2: The vanadium source solution after pre-reaction reduction is injected into the homogenizing reactor 9 under pressure through a continuous phase injection pipeline. At the same time, the phosphorus source solution, sodium source solution, and dopant are injected into the homogenizing reactor 9 in a quantitative manner.

[0083] Step 3: In homogenizing reactor 9, vanadium source solution, reducing agent, phosphorus source solution, sodium source solution and dopant are mixed at a constant temperature of 80-100℃ to generate modified sodium vanadium phosphate precursor;

[0084] Step 4: The modified sodium vanadium phosphate precursor is fed into the coil reactor 7, and the modified sodium vanadium phosphate is crystallized at a gradually increasing temperature of 100-700℃.

[0085] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A continuous manufacturing system of modified sodium vanadium phosphate, characterized by, It includes: The base fluid introduction pipeline is provided with five ways, and is respectively introduced into vanadium source solution, reducing agent, phosphorus source solution, sodium source solution and dopant; The pre-reaction mechanism (3) is connected with two base fluid introduction pipelines for introducing vanadium source solution and reducing agent, and can perform pressure catalytic reduction reaction on the vanadium source solution and reducing agent introduced therein; The homogeneous reactor (9) is connected with the pre-reaction mechanism (3) through a continuous phase injection pipeline, and the homogeneous reactor (9) is connected with three base fluid introduction pipelines for introducing phosphorus source solution, sodium source solution and dopant through a dispersed phase injection pipeline; And the coil reactor (7) is injected with the modified vanadium sodium phosphate precursor mixed by the homogeneous reactor (9), and continuous carbothermal reduction is performed to complete the crystallization of the modified vanadium sodium phosphate.

2. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 1, characterized in that: The base fluid introduction pipeline is provided with a metering pump (13) and two valves (1) in sequence and along the liquid flow direction thereof, wherein a preheater (12) is arranged between the two valves (1), and a temperature table (2) is arranged at the outlet of the preheater (12).

3. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 2, characterized in that: The continuous phase injection pipeline and the dispersed phase injection pipeline are provided with a temporary storage container (11), a valve two (4), a pressure gauge (14) and a booster pump (10) in sequence and along the liquid flow direction thereof.

4. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 3, characterized in that: The upper side of the coil reactor (7) is connected with an exhaust mechanism (8), and the lower side of the coil reactor (7) is connected with a discharge mechanism (6).

5. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 1, characterized in that: The pre-reaction mechanism (3) includes: A reaction shell (309) is provided with an electrically controlled liquid outlet device (310) at the outlet thereof; A continuous pressure injection mechanism is arranged at the tail of the reaction shell (309) and can continuously suck and pressurize the mixed liquid in the cavity of the reaction shell (309); An intermittent liquid injection mechanism can intermittently inject a quantitative reducing agent into the cavity of the reaction shell (309); And a liquid vibration assembly is driven to oscillate by the continuous pressure injection mechanism and the intermittent liquid injection mechanism under the action of the stamping of the solution injected into the reaction shell (309); The reaction shell (309) is provided with four liquid injection slots (318) arranged in a matrix on the inner wall thereof, and a liquid vibration assembly is arranged between each pair of two liquid injection slots (318).

6. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 5, characterized in that: The liquid vibration assembly is composed of a vibration spring (321) and two sealing balls (316), wherein the vibration spring (321) is connected between the two sealing balls (316), and each sealing ball (316) is sealed at the corresponding liquid injection slot (318) under the tension of the vibration spring (321); The side wall of the sealing ball (316) is circumferentially provided with a plurality of semispherical protrusions, and each protrusion is in sliding connection with the inner wall of the liquid injection slot (318).

7. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 5, characterized in that: The continuous pressure injection mechanism includes: Two plunger barrels (301) are symmetrically fixed on the reaction shell (309), and each plunger barrel (301) is slidably connected with a plunger (312); Two shaft discs (315) are rotatably installed at the front and rear ends of the driving cavity of the reaction shell (309). Connecting column (314) is connected between the edge of two axis discs (315), the connecting column (314) is rotatably connected with one end of two pressing handles (313), and the other end of each pressing handle (313) is rotatably connected with the corresponding plunger (312); Driven gear (302) is meshed with driving gear (303), the driven gear (302) is connected with the corresponding axis disc (315) by shaft connection; And motor (305) is fixed on the reaction shell (309) by support, the driving end of the motor (305) is connected with the driving gear (303); Wherein, two plunger barrels (301) are connected with two liquid injection grooves (318) located on the rear side by pressure pipes (308).

8. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 7, characterized in that: The liquid flow channel (320) is communicated between the two liquid injection grooves (318) located on the rear side and the inner cavity of the reaction shell (309), and the one-way valve (319) for injecting liquid into the liquid injection groove (318) is arranged in the liquid flow channel (320).

9. The continuous manufacturing system of modified sodium vanadium phosphate according to claim 7, characterized in that: The intermittent liquid injection mechanism is composed of liquid injection pipe one (307), contact (322) and contact electromagnetic valve (323) and liquid injection pipe two, wherein the contact electromagnetic valve (323) is injected with reducing agent through the liquid injection pipe one (307), and the outlet end of the contact electromagnetic valve (323) is connected with the corresponding liquid injection groove (318) by the liquid injection pipe two; The contact (322) is fixed on the corresponding axis disc (315) and is driven to rotate to the pressing position of the contact electromagnetic valve (323) by the axis disc (315).

10. A continuous production method of modified sodium vanadium phosphate, characterized by, It includes the following steps: Step 1: in situ complexation, specifically, after preheating the vanadium source solution and reducing agent at 80 DEG C, input into the pre-reaction mechanism (3), reduce vanadium in vanadium source solution from "+5 valence" to "+4 valence" and "+3 valence" by reducing agent; Step 2: the reduced vanadium source solution is injected into the homogeneous reactor (9) through the continuous phase liquid injection pipeline, at the same time, the phosphorus source solution, sodium source solution and dopant are quantitatively injected into the homogeneous reactor (9); Step 3: the homogeneous reactor (9) generates modified vanadium sodium phosphate precursor by mixing vanadium source solution, reducing agent, phosphorus source solution, sodium source solution and dopant at constant temperature of 80-100 DEG C; Step 4: input the modified vanadium sodium phosphate precursor into the coil reactor (7), and generate modified vanadium sodium phosphate crystals by crystallization at 100-700 DEG C.

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