CN115974042B - Continuous production method of sodium battery-level nano sodium iron phosphate - Google Patents
Continuous production method of sodium battery-level nano sodium iron phosphate Download PDFInfo
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Abstract
The invention relates to a continuous production method of sodium battery-level nano sodium iron phosphate, which comprises the following steps: s1, dissolving high-purity ferrous sulfate heptahydrate crystals to obtain a ferrous sulfate solution, and mixing the ferrous sulfate solution with hydrogen peroxide and sulfuric acid to obtain a ferric sulfate solution; s2, reacting the ferric sulfate solution with disodium hydrogen phosphate, aging, separating, washing with cold water, and filtering to obtain a ferric phosphate crystal filter cake; s3, dispersing the ferric phosphate crystal filter cake into water to prepare ferric phosphate suspension, simultaneously pumping the ferric phosphate suspension and sodium carbonate solution into a multi-medium continuous flow reactor for reaction at normal temperature and normal pressure, carrying out solid-liquid separation, washing and filtering to obtain a high-purity ferric phosphate crystal filter cake; and S4, drying the sodium iron phosphate crystal filter cake, calcining in an inert atmosphere, and grinding to obtain the battery-grade nano sodium iron phosphate. The invention does not use complexing agent or template agent, can realize continuous production, does not need to purchase expensive equipment, and further improves the production efficiency and reduces the production cost on the premise that the production meets the technical index of battery level.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a continuous production method of sodium battery-level nano sodium iron phosphate.
Background
With the rapid development of new energy automobiles and energy storage lithium ion batteries in recent years, the lithium iron sulfate serving as a battery anode material of the lithium ion batteries is rapidly developed, the price of lithium source lithium carbonate is increased, the current market price reaches 50 ten thousand yuan/ton, the development of the lithium ion batteries and the new energy industry is severely restricted, sodium serves as a same group element of the lithium elements, the physical and chemical properties of the lithium ion batteries are quite close, besides the defect that the battery capacity density of the sodium ion batteries is slightly low, other safety properties and the use temperature range of the sodium ion batteries are far higher than those of the lithium ion batteries, the charge and discharge times of the sodium ion batteries are quite close, and the lithium ion batteries have wide application in the aspects of energy storage, low-speed electric automobiles, electric bicycles, electric tricycles, electric tools and the like, and can completely replace the lithium ion batteries in the fields.
The sodium ion battery is produced by using nano sodium ferric orthophosphate as a raw material of the positive electrode material, and the positive electrode material is usually prepared by doping carbon and the like with the raw material. The positive electrode material for manufacturing the sodium ion battery has strict requirements on nano sodium iron phosphate, and the technical indexes are as follows:
the prior art for preparing the battery-level nano sodium iron phosphate is commonly used for a template agent or a complexing agent, the template agent or the complexing agent needs to be removed after the production is finished, and the electrochemical performance of the nano sodium iron phosphate can be influenced if the removal is incomplete. Other prior art adopts spray drying equipment to produce, and this technology not only production efficiency is low, and industrial grade spray drying equipment acquisition cost and maintenance cost are high, are unfavorable for reducing product cost.
Disclosure of Invention
First, the technical problem to be solved
In view of the above-mentioned shortcomings and disadvantages of the prior art, the invention provides a continuous production method of sodium battery-level nano sodium iron phosphate, which does not use complexing agent or template agent, can realize continuous production, does not need to purchase expensive equipment, has high production efficiency, and further reduces the product cost on the premise of producing nano sodium iron phosphate products meeting battery-level technical indexes.
(II) technical scheme
In order to achieve the above purpose, the main technical scheme adopted by the invention comprises the following steps:
in a first aspect, the present invention provides a continuous production method of sodium battery-level nano sodium iron phosphate, comprising:
s1, dissolving ferrous sulfate heptahydrate crystals with purity of over 99.9% with water to obtain a ferrous sulfate solution, mixing the ferrous sulfate solution with hydrogen peroxide and sulfuric acid for reaction, and oxidizing ferrous ions to obtain a ferric sulfate solution;
s2, reacting the ferric sulfate solution with disodium hydrogen phosphate, standing for ageing, filtering, washing with cold water, and filtering (removing sodium salt) to obtain a ferric phosphate crystal filter cake and a sodium sulfate solution;
s3, adding the ferric phosphate crystal filter cake into desalted water to prepare ferric phosphate suspension, pumping the suspension and sodium carbonate solution into a multi-medium continuous flow reactor at the same time, reacting at normal temperature and normal pressure, performing solid-liquid separation after the reaction, washing and filtering to obtain an ultrapure ferric sodium phosphate crystal filter cake; meanwhile, sodium sulfate mixed in the ferric phosphate crystal filter cake is washed out to generate sodium sulfate solution;
s4, drying the ultra-pure sodium iron phosphate crystal filter cake to remove free water, calcining at high temperature under the protection of inert gas to enable the ultra-pure sodium iron phosphate crystal filter cake to lose crystal water, and grinding to obtain sodium battery-level nano sodium iron phosphate.
According to a preferred embodiment of the invention, in S1, the concentration of the ferrous sulfate solution is 190-210g/L, water is heated to 40 ℃ before dissolution, and the temperature is raised to 48-51 ℃ during dissolution.
According to the preferred embodiment of the invention, in S1, ferrous sulfate heptahydrate crystals are dissolved in a dissolution tank, the pumping speed is set, ferrous sulfate solution is pumped into an oxidation reaction tank, and sulfuric acid and hydrogen peroxide are pumped into the oxidation reaction tank; oxidizing ferrous sulfate to ferric sulfate in the oxidation reaction tank by utilizing sulfuric acid and hydrogen peroxide; the pumping speed of the sulfuric acid and the hydrogen peroxide is calculated according to the pumping speed of the ferrous sulfate solution and the metering ratio required by complete oxidation.
According to a preferred embodiment of the present invention, in S1, the sulfuric acid concentration is 27-31wt.%, the hydrogen peroxide concentration is 27-31wt.%, and the oxidation reaction temperature is 50-55 ℃; during the reaction, detecting whether the oxidation reaction is finished or not by using phenanthroline; and (3) leading out the ferric sulfate solution generated after the oxidation reaction is completed and temporarily storing the ferric sulfate solution in a ferric sulfate solution storage tank.
According to a preferred embodiment of the invention, the reaction conditions of S2 are 75-85 ℃ and the reaction time is 1.5-2h to produce ferric phosphate (dissolved in hot water); and then standing and aging for more than 2 hours to obtain ferric phosphate crystals. The ferric phosphate is insoluble in cold water, flocculent suspended matters are generated in the solution along with the temperature reduction in the aging process, and solid-liquid separation is carried out to obtain ferric phosphate crystal solid phase matters, and the solid phase matters are required to be further washed.
According to the preferred embodiment of the invention, in S2, the procedure of cold water washing and filtering adopts Moire filtering water washing or membrane filter press water washing, the water washing is carried out twice, after the primary water washing, the filter disc is adjusted to 15% slurry concentration for carrying out the secondary water washing, the secondary water washing waste water is used as the primary water washing water, and the water washing temperature is 15-25 ℃. The sodium content of the iron phosphate crystals is reduced by water washing.
According to the preferred embodiment of the invention, in S3, the ferric phosphate crystal filter cake after the secondary water washing in the step S2 is added into cold desalted water to prepare ferric phosphate suspension (ferric phosphate is insoluble in cold water), the suspension and sodium carbonate solution are pumped into a multi-medium continuous flow reactor at the same time, and the continuous reaction is carried out at normal temperature and normal pressure, and the solid-liquid separation is carried out, so as to obtain the sodium ferric phosphate crystal. The sodium iron phosphate is white or yellowish white powder, odorless and tasteless, and insoluble in water. Therefore, flocculent suspended matters are generated after the reaction is finished, and solid-liquid separation is carried out to obtain solid phase matters of sodium iron phosphate crystals, and the solid phase matters are required to be further washed.
According to the preferred embodiment of the present invention, in S3, the washing filtration step is performed twice or more, the next washing wastewater is used as the last washing water, the last washing is performed with pure deionized water, the washing is performed until the sodium sulfate content in the sodium iron phosphate crystal is less than 30ppm as the washing end point, and the washing filtration is performed in the moire filter or the membrane filter press.
According to the preferred embodiment of the invention, in S4, water content in the ultra-pure sodium iron phosphate crystal filter cake obtained by washing and filtering is 40% -45%, and the filter cake is dried at 120-125 ℃ to remove free water.
According to a preferred embodiment of the invention, in S4, the calcination conditions are: calcining at 550-650 ℃ under the protection of calcining kiln and inert gas, losing crystal water, grinding to obtain sodium battery-level nano sodium iron phosphate powder.
(III) beneficial effects
The invention relates to a continuous production method of sodium battery-level nanometer sodium iron phosphate, which takes high-purity ferrous sulfate heptahydrate as a raw material, obtains ferric sulfate after oxidation, then mixes the ferric sulfate with disodium hydrogen phosphate to generate ferric phosphate floccules, and carries out solid-liquid separation, full washing and filtration to obtain ferric phosphate crystals without sulfate; and then preparing ferric phosphate crystals into suspension, adding sodium carbonate solution to uniformly embed sodium ions into ferric phosphate suspended particles to generate ferric sodium phosphate, carrying out solid-liquid separation to further obtain ferric sodium phosphate crystals, washing and filtering to obtain ferric sodium phosphate crystal filter cakes with sodium sulfate content less than 30ppm, and then drying and calcining to obtain the battery-level nano ferric sodium phosphate powder.
The invention uses the characteristic that ferric phosphate is insoluble in cold water and sodium ferric phosphate is insoluble in water, can remove impurities by adopting a water washing mode, and improves the purity of the product, so that the product meets the use requirement of a battery level. The ferric phosphate is dispersed into water to react with sodium carbonate solution in the form of flocculent suspended particles, so that sodium ions are freely moved and uniformly embedded into suspended particles of the ferric phosphate at the heating reaction temperature to generate suspended particles of the ferric phosphate, the uniformity of the distribution of the embedded sodium ions in a ferric phosphate sodium product is guaranteed, and the product quality and the stability of the electrochemical performance of the product are improved. Compared with a template agent method, a complexation method and a hydrothermal coprecipitation method, the production method does not need to remove the template agent or complexing agent, and can more easily obtain a product with microscopic morphology (particle size, specific surface area and tap density) meeting the technical index of the battery level.
The invention takes ferrous sulfate heptahydrate as a raw material, and ferrous sulfate heptahydrate is a main byproduct of titanium dioxide production by the unit sulfuric acid method of the applicant, so that the process can be coupled with the process of titanium dioxide production by the sulfuric acid method to form a large production line, the battery grade ferric sodium orthophosphate is prepared by using the byproduct (ferrous sulfate heptahydrate) of the process of titanium dioxide production by the sulfuric acid method, and the byproducts ferric sulfate and sodium sulfate produced by the ferric sodium orthophosphate production can be used for producing ferric sodium sulfate, and the ferric sodium sulfate is also a cathode material raw material of a sodium ion battery.
In addition, in the production method, the product obtained after each step of reaction is immediately led out of a storage tank or a reaction tank which is transferred to the reaction tank so as to empty the original reaction tank, and the next batch of reaction materials are conveniently received to enter the reaction tank so as to complete the reaction, thereby realizing the continuous production process of the sodium battery-level nano sodium iron phosphate in the whole process line.
Drawings
FIG. 1 is a flow chart of the continuous production of sodium battery grade nano sodium iron phosphate of the present invention.
Detailed Description
The invention will be better explained by the following detailed description of the embodiments with reference to the drawings.
As shown in figure 1, the method is a process for continuously producing sodium battery-level nano sodium iron phosphate, and the production method takes ferrous sulfate heptahydrate crystals with purity of more than 99.9% as a starting material, and the ferrous sulfate solution is obtained by dissolving the ferrous sulfate heptahydrate crystals with water. The ferrous sulfate heptahydrate crystal is dissolved in a dissolving tank, the concentration of the ferrous sulfate heptahydrate crystal is kept at 190-210g/L after dissolution, water is heated to 40 ℃ before dissolution, and the temperature is raised to 48-51 ℃ during the dissolution process. The concentration of ferrous sulfate is not too high, and aggregation is easy to form due to the too high concentration, so that the particle size of the product is increased, and the iron and sodium elements in the product are unevenly distributed. The ferrous sulfate solution is led to a storage tank for storage. And then setting the discharge speed of the ferrous sulfate solution, leading the ferrous sulfate solution into an oxidation reaction tank according to the set speed, and simultaneously pumping hydrogen peroxide and sulfuric acid into the oxidation reaction tank to oxidize the ferrous sulfate to obtain the ferric sulfate solution. The concentration of sulfuric acid is 27-31 wt%, the concentration of hydrogen peroxide is 27-31 wt%, and the oxidation reaction temperature is 50-55 ℃. In the reaction process, the pumping speed of sulfuric acid and hydrogen peroxide is calculated according to the pumping speed of ferrous sulfate solution and the metering ratio required by complete oxidation. In an oxidation reaction tank, detecting whether the oxidation reaction is finished or not by using phenanthrene ortho-dinitrogen; and (3) leading out the ferric sulfate solution generated after the oxidation reaction is completed and temporarily storing the ferric sulfate solution in a ferric sulfate solution storage tank. And then pumping the ferric sulfate solution and disodium hydrogen phosphate in a ferric sulfate solution storage tank into a ferric phosphate reaction tank at the same time, mixing the ferric sulfate solution and the disodium hydrogen phosphate, heating to 75-85 ℃, carrying out heat preservation reaction for 1.5-2h, stopping heating, standing and aging for more than 2h, generating flocculent suspended matters in the solution along with the reduction of the temperature, and carrying out solid-liquid separation to obtain the ferric phosphate crystal solid phase matters. And washing and filtering with cold water to remove sodium sulfate mixed in the solid phase substance and obtain a pure ferric phosphate crystal filter cake. The cold water washing is performed by adopting water at normal temperature or below. The washing step is preferably carried out by using a moire filter washing or a membrane filter press washing, the washing is carried out in two steps, after the primary washing, the filter sheet is adjusted to 15% slurry concentration to carry out the secondary washing, the secondary washing wastewater is used as the primary washing water, the washing temperature is 15-25 ℃, and the sodium content in the ferric phosphate crystal is reduced by the washing. And adding the ferric phosphate crystal filter cake after the secondary water washing into cold desalted water, and stirring at a high speed to prepare ferric phosphate suspension. The ferric phosphate suspension is stored in the ferric phosphate storage tank, the storage tank is provided with a stirring device, and the stirring device continuously performs high-strength disturbance on the suspension to avoid standing and precipitation of the suspension. Pumping the suspension and sodium carbonate solution into a multi-medium continuous flow reactor at the same time to perform a mixing reaction, continuously reacting at normal temperature and normal pressure, generating flocculent suspended matters after the reaction is finished, carrying out solid-liquid separation to obtain a solid phase matter of sodium iron phosphate crystals, washing the solid phase matter with water, filtering, and washing with water to remove sodium sulfate and sodium carbonate. The water washing and filtering process is carried out for two times or more, the next water washing waste water is used as the water for the last water washing, the last water washing is carried out by pure deionized water, the water washing is carried out until the sodium sulfate content in the sodium iron phosphate crystal is less than 30ppm as the water washing end point, and the water washing and filtering are carried out in a Moire filter or a membrane filter press. Washing and filtering to obtain an ultrapure sodium iron phosphate crystal filter cake (the water content is 40% -45%); and meanwhile, sodium sulfate and sodium carbonate which are mixed in the ferric phosphate crystal filter cake are washed out. Continuously drying the ultrapure sodium iron phosphate crystal filter cake with hot air at 120-125 ℃ to remove free water, transferring to a calcining kiln, calcining at 550-650 ℃ under the protection of inert gas to remove crystal water, and crushing and grinding to obtain sodium battery-level nano sodium iron phosphate powder. The organic impurities and carbonate ions contained in the product can be removed by calcination, so that the purity of the product is improved, and the product meets the use requirement of a battery level.
In the process, the product obtained after the reaction of each step or the solution or suspension obtained after the dispersion is immediately led out and transferred to a storage tank or a reaction tank to empty the original reaction tank, so that the next batch of reaction materials can be conveniently received to enter for completing the reaction; the obtained crystal filter cakes are also rapidly transferred to the next treatment process, such as dispersion into suspension or drying and calcining; therefore, the whole process circuit realizes the production process of continuous sodium battery-level nano sodium iron phosphate, improves the production efficiency of battery-level products and reduces the cost.
In the process, the water washing liquid generated by each step of water washing filtration is purified and desalted by adopting a nanofiltration composite membrane, and desalted water is used for dissolving ferrous sulfate heptahydrate crystals and dispersing ferric phosphate crystal filter cakes or preparing disodium hydrogen phosphate or sodium carbonate solution, so that water resources are saved, and pure deionized water is only used in the most critical water washing step, such as pure deionized water used in the last water washing filtration of ferric sodium phosphate crystals, so as to ensure that the product meets battery grade indexes.
A multi-medium continuous flow reactor is a device that continuously performs chemical reactions. During the reaction, the reactants and solvent flow continuously and the chemical reaction process is completed simultaneously. The continuous flow reactor comprises: stirring, mixing (or heating) system, temperature control system, etc. The stirring function is to ensure the uniformity of the reaction; preventing deactivation of the catalyst; promoting gas absorption and heat release; accelerating dissolution of solid particles and dispersion of liquid; and improves the mass transfer efficiency. The mixing makes the materials fully contacted to accelerate mass transfer speed, reduce energy consumption and reduce equipment resistance loss. The mixing operation is generally realized by adopting a mechanical stirring or mechanical-fluid combined circulation mode, and the rapid and uniform distribution of the mixed materials can be realized by adopting a chemical metering pump as an auxiliary means. Temperature control is very important for the whole process because different materials have different thermodynamic properties (such as latent heat of fusion, vaporization enthalpy value, evaporation heat absorption coefficient and the like), and different process conditions require corresponding optimal temperature parameters to meet production requirements (e.g., production of synthetic ammonia at high temperature and high pressure). The main function of pressure control is to ensure that a certain balance state is achieved between the liquid phase and the solid phase, and to avoid bursting accidents caused by local overpressure. The common methods mainly comprise: the balance between the liquid phase and the solid phase is adjusted by adjusting the opening of the valve; pumping the pressure reduction by using a vacuum pump to realize the balance between the liquid phase and the solid phase; controlling the pressure within a certain range by using an elastic element to reach a stable state; pressurizing by using a booster pump to improve the operation pressure of the system so as to meet the process requirements; the pressure is reduced by a pressure reducing valve to achieve the purpose of stabilizing the pressure; the operating temperature range of the system is changed by adjusting the amount of cooling water flow.
The scheme and product index of the present invention are described below with reference to specific examples.
Example 1
The embodiment is a continuous production method of sodium battery-level nano sodium iron phosphate, the flow of which adopts the continuous production process line described above, and specifically described as follows:
(1) The ferrous sulfate heptahydrate crystal with purity of 99.9% is dissolved in desalted water with the temperature of 40 ℃, and the temperature is raised to 50 ℃ while dissolving, so as to obtain ferrous sulfate solution with the concentration of 190 g/L. The ferrous sulfate solution is led to a storage tank for storage.
(2) Introducing ferrous sulfate solution into an oxidation reaction tank, simultaneously introducing sulfuric acid solution with the concentration of 30wt.% and hydrogen peroxide with the concentration of 30wt.%, keeping the temperature at 55 ℃, reacting for 1.5h, and detecting whether the oxidation reaction is finished or not by using phenanthroline; after the oxidation reaction is completed, the ferric sulfate solution is led out and temporarily stored to a ferric sulfate solution storage tank. The pumping speed of the sulfuric acid and the hydrogen peroxide is calculated according to the pumping speed of the ferrous sulfate solution and the metering ratio required by complete oxidation, so that excessive or insufficient is avoided, and the impurity content in the product is reduced.
(3) And simultaneously pumping the ferric sulfate solution and 42wt.% of disodium hydrogen phosphate solution into a ferric phosphate reaction tank, mixing the ferric sulfate solution and the disodium hydrogen phosphate, heating to 80 ℃, carrying out heat preservation reaction for 1.5 hours, stopping heating, standing and aging for 2 hours, generating flocculent suspended matters in the solution along with the temperature reduction, and filtering to obtain a ferric phosphate crystal solid phase matter. The solid phase is washed by Moire filtration, the washing is carried out twice, after the primary washing, the filter disc is adjusted to 15 percent of slurry concentration, the secondary washing is carried out, the secondary washing wastewater is used as the primary washing water, the washing temperature is 20 ℃, and the sodium content in the ferric phosphate crystal is reduced by the washing. Washing with water to obtain ferric phosphate crystal filter cake, wherein the water washing liquid contains sodium sulfate.
(4) Dispersing the ferric phosphate crystal filter cake into cold (15-20 ℃) desalted water, and stirring at a high speed to prepare ferric phosphate suspension. The ferric phosphate suspension is stored in the ferric phosphate storage tank, the storage tank is provided with a stirring device, and the stirring device continuously performs high-strength disturbance on the suspension to avoid standing and precipitation of the suspension. And simultaneously pumping the ferric phosphate suspension and 15wt.% sodium carbonate solution into a multi-medium continuous flow reactor for mixed reaction, reacting for 2 hours at normal temperature and normal pressure, generating flocculent suspended matters in the solution after the reaction is finished, and filtering and separating to obtain a ferric sodium phosphate crystal solid-phase matter filter cake.
(5) And (3) carrying out twice washing filtration on the sodium iron phosphate crystal solid phase filter cake, wherein the washing filtration is carried out in a Moire filter, the washing liquid filtered by the twice washing filtration is used as primary washing liquid for recycling, and the secondary filtration washing liquid adopts pure deionized water. After washing with water, the filtration gives an ultrapure sodium iron phosphate crystal cake (water content 42%) with a sodium sulfate content of less than 30 ppm.
(6) And (3) drying the ultrapure sodium iron phosphate crystal filter cake by hot air at 120 ℃, transferring to a calcining kiln, calcining for 3 hours at 620 ℃ under the protection of inert gas, and crushing and grinding to obtain sodium iron phosphate powder. Among them, it is preferable that the drying is followed by pulverization and calcination, so that the calcination speed can be increased.
The sodium iron phosphate powder is yellowish powder, and the particle size of the product is medium diameter (D50) =77.5 nm and tap density is 1.14g/cm 3 The average specific surface area is 21.4 square meters per gram.
Example 2
The embodiment is a continuous production method of sodium battery-level nano sodium iron phosphate, the flow of which adopts the continuous production process line described above, and specifically described as follows:
(1) The ferrous sulfate heptahydrate crystal with purity of 99.9% is dissolved in desalted water with the temperature of 40 ℃, and the temperature is raised to 55 ℃ while dissolving, so as to obtain ferrous sulfate solution with the concentration of 200 g/L.
(2) The ferrous sulfate solution is led into an oxidation reaction tank, sulfuric acid solution with the concentration of 30wt.% and hydrogen peroxide with the concentration of 30wt.% are led into the oxidation reaction tank, the temperature is kept at 50 ℃, the reaction is carried out for 2 hours, and the product ferric sulfate solution is led out and temporarily stored into a ferric sulfate solution storage tank.
(3) And simultaneously pumping the ferric sulfate solution and 45wt.% of disodium hydrogen phosphate solution into a ferric phosphate reaction tank, mixing the ferric sulfate solution and the disodium hydrogen phosphate, heating to 85 ℃, carrying out heat preservation reaction for 1.5 hours, stopping heating, standing and aging for 2.5 hours, generating flocculent suspended matters in the solution along with the temperature reduction, and filtering to obtain a ferric phosphate crystal solid phase matter. The solid phase is washed by a membrane filter press, the washing is carried out twice, after the primary washing, the filter disc is adjusted to 15 percent of slurry concentration, the secondary washing is carried out, the secondary washing wastewater is used as the primary washing water, the washing temperature is 25 ℃, and the sodium content in the ferric phosphate crystal is reduced by the washing. Washing with water to obtain ferric phosphate crystal filter cake, wherein the water washing liquid contains sodium sulfate.
(4) Dispersing the ferric phosphate crystal filter cake into cold (15-20 ℃) desalted water, and stirring at a high speed to prepare ferric phosphate suspension. And simultaneously pumping the ferric phosphate suspension and 20wt.% sodium carbonate solution into a multi-medium continuous flow reactor for mixed reaction, reacting for 2 hours at normal temperature and normal pressure, generating flocculent suspended matters in the solution after the reaction is finished, and filtering and separating to obtain a ferric sodium phosphate crystal solid-phase matter filter cake.
(5) And (3) carrying out twice water washing filtration on the sodium iron phosphate crystal solid phase filter cake, wherein the water washing filtration is carried out in a membrane filter press, the water washing liquid filtered by the twice water washing filtration is used as primary water washing liquid for recycling, and the secondary water washing liquid is pure deionized water. After washing with water, the filtration gives an ultrapure sodium iron phosphate crystal cake (water content 45%) with a sodium sulfate content of less than 30 ppm.
(6) And (3) drying the ultrapure sodium iron phosphate crystal filter cake by hot air at 120 ℃, transferring to a calcining kiln, calcining for 3 hours at 650 ℃ under the protection of inert gas, and crushing and grinding to obtain sodium iron phosphate powder. Among them, it is preferable that the drying is followed by pulverization and calcination, so that the calcination speed can be increased.
The sodium iron phosphate powder is yellowish powder, and the particle size of the product is medium diameter (D50) =74.5 nm and tap density is 1.21g/cm 3 The average specific surface area is 24.7 square meters per gram.
Mixing sodium iron phosphate powder prepared in example 1 with sucrose powder with the mass of 1% of the sodium iron phosphate powder, ball milling and crushing the mixture for 1 hour by adopting a ball mill, and sieving the mixture by a 100-mesh sieve to obtain powder; and then pouring the powder into a sagger, placing the sagger into a muffle furnace, introducing argon for protection, sintering at 700 ℃ for 14 hours, and cooling to obtain the black sodium iron phosphate anode material.
Uniformly mixing a sodium iron phosphate anode material, a binder and a conductive agent with a solvent according to the weight ratio of 90:5:5 to prepare anode slurry (wherein the binder is PVDF, the conductive agent is SP, and the solvent is NMP), coating the anode slurry on an aluminum foil, drying, rolling and slicing to obtain an anode plate, taking a metal sodium plate as a negative electrode, and taking a polypropylene film as a diaphragm; the positive plate, the negative plate and the diaphragm are arranged in a button cell shell, and the electrolyte of the injected electrolyte is NaPF 6 The concentration is 1mol/L, the solvent is EC: DEC: DMC=1:1:1, and the sodium ion button half cell is obtained. The cycle performance of the battery was tested.
The method for testing the cycle performance comprises the following steps: under normal temperature environment, the battery is charged to 3.9V at constant current of 0.5C, then is charged at constant voltage of 3.9V, and when the charging current is less than 0.05C, the charging is stopped; standing for 10min, and discharging to 2.0V at constant current of 0.5 ℃; standing for 10min. Repeating the above steps to complete 3000 times of circulation. The discharge capacity was recorded each time, and the percentage of the 3000 th discharge capacity to the 1 st discharge capacity was calculated, and the capacity fade was 16% (3000 times capacity retention rate reached 84%). Therefore, the sodium iron phosphate prepared by the method can completely meet the battery grade index requirement.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (5)
1. The continuous production method of the sodium battery-level nano sodium iron phosphate is characterized by comprising the following steps of:
s1, dissolving ferrous sulfate heptahydrate crystals with purity of over 99.9% with water to obtain a ferrous sulfate solution, mixing the ferrous sulfate solution with hydrogen peroxide and sulfuric acid for reaction, and oxidizing ferrous ions to obtain a ferric sulfate solution;
wherein the concentration of the ferrous sulfate solution is 190-210g/L; the concentration of sulfuric acid is 27-31 wt%, the concentration of hydrogen peroxide is 27-31 wt%, and the oxidation reaction temperature is 50-55 ℃; during the reaction, detecting whether the oxidation reaction is finished or not by using phenanthroline; guiding and temporarily storing ferric sulfate solution generated after the oxidation reaction is completed to a ferric sulfate solution storage tank;
s2, reacting the ferric sulfate solution with disodium hydrogen phosphate, standing for aging, separating, washing with cold water, and filtering to obtain a ferric phosphate crystal filter cake and a sodium sulfate solution; the reaction condition is 75-85 ℃ and the reaction time is 1.5-2 hours to produce ferric phosphate; standing and aging for more than 2 hours to obtain ferric phosphate crystals;
s3, dispersing the ferric phosphate crystal filter cake into cold desalted water to prepare ferric phosphate suspension, pumping the suspension and sodium carbonate solution into a multi-medium continuous flow reactor at the same time, reacting at normal temperature and normal pressure, performing solid-liquid separation after the reaction, washing and filtering to obtain an ultrapure ferric sodium phosphate crystal filter cake; meanwhile, sodium sulfate mixed in the ferric phosphate crystal filter cake is washed out to generate sodium sulfate solution;
the washing filtration process is carried out for two or more times, the next washing wastewater is used as the water for the last washing, the last washing is carried out by pure deionized water, the washing is carried out until the sodium sulfate content in the sodium iron phosphate crystal is less than 30ppm as the washing end point, and the washing filtration is carried out in a Moire filter or a diaphragm filter press;
s4, drying the ultrapure sodium iron phosphate crystal filter cake to remove free water, calcining at a high temperature under the protection of inert gas to enable the ultrapure sodium iron phosphate crystal filter cake to lose crystal water, and grinding to obtain sodium battery-level nano sodium iron phosphate; the calcination conditions are as follows: calcining at 550-650 deg.c in the calcining kiln and under the protection of inert gas.
2. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 1, wherein in S1, before the ferrous sulfate heptahydrate crystal is dissolved, water is heated to 40 ℃, and the temperature is raised to 48-51 ℃ in the dissolving process.
3. The continuous production method of sodium battery-level nano sodium iron phosphate according to claim 1, wherein in S1, ferrous sulfate heptahydrate crystals are dissolved in a dissolution tank, the pumping speed is set, ferrous sulfate solution is pumped into an oxidation reaction tank, and sulfuric acid and hydrogen peroxide are pumped into the oxidation reaction tank; oxidizing ferrous sulfate to ferric sulfate in the oxidation reaction tank by utilizing sulfuric acid and hydrogen peroxide; the pumping speed of the sulfuric acid and the hydrogen peroxide is calculated according to the pumping speed of the ferrous sulfate solution and the metering ratio required by complete oxidation.
4. The continuous production method of sodium battery-level nano sodium iron phosphate according to claim 1, wherein in S2, the procedure of cold water washing and filtering adopts moire filtering water washing or membrane filter press water washing, the water washing is carried out twice, after the primary water washing, the filter disc is adjusted to 15% of slurry concentration for secondary water washing, the secondary water washing waste water is used as primary water washing water, and the water washing temperature is 15-25 ℃.
5. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 1, wherein in S4, water content in the ultra-pure sodium iron phosphate crystal filter cake is 40% -45% after washing and filtering, and the filter cake is dried under the condition of 120-125 ℃ to remove free water.
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