CN115974042A - Continuous production method of sodium battery grade nano sodium iron phosphate - Google Patents
Continuous production method of sodium battery grade nano sodium iron phosphate Download PDFInfo
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Abstract
The invention relates to a continuous production method of sodium battery grade 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 iron phosphate crystal filter cake into water to prepare an iron phosphate suspension, pumping the iron phosphate suspension and a sodium carbonate solution into a multi-medium continuous flow reactor simultaneously, reacting at normal temperature and normal pressure, carrying out solid-liquid separation, washing and filtering to obtain a high-purity iron phosphate sodium 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 indexes 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-grade nano sodium iron phosphate.
Background
In recent years, with the rapid development of new energy automobiles and energy storage lithium ion batteries, lithium iron sulfate serving as a battery anode material is rapidly developed, the price of lithium source lithium carbonate rises sharply, the market price reaches 50 ten thousand yuan/ton at present, the development of lithium ion batteries and new energy industries is severely restricted, sodium element is taken as a family element of lithium element, the physical and chemical properties of the sodium element and the lithium element are very close, meanwhile, the sodium ion batteries have the defect of slightly low battery capacity density, other safety performance and use temperature ranges are far higher than those of the lithium ion batteries, the charging and discharging times are also very close, the lithium ion batteries are widely applied in the aspects of energy storage, low-speed electric automobiles, electric bicycles, electric tricycles, electric tools and the like, and the lithium ion batteries can be completely replaced in the fields.
In the production of sodium ion batteries, nano sodium ferric phosphate is used as a raw material of a positive electrode material, and the raw material is usually doped with carbon and the like to prepare the positive electrode material. The anode material for manufacturing the sodium ion battery has strict requirements on the nano sodium iron phosphate, and the technical indexes are as follows:
the prior art for preparing battery-grade nano sodium iron phosphate generally uses a template agent or a complexing agent, the template agent or the complexing agent needs to be removed after production is finished, and the electrochemical performance of the nano sodium iron phosphate is affected due to incomplete removal. In other prior art, spray drying equipment is adopted for production, the process is low in production efficiency, and the acquisition cost and the maintenance cost of industrial-grade spray drying equipment are extremely high, so that the product cost is not reduced.
Disclosure of Invention
Technical problem to be solved
In view of the defects and shortcomings of the prior art, the invention provides a continuous production method of sodium battery grade nano sodium iron phosphate, which does not use a complexing agent or a 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 the battery grade technical indexes.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
in a first aspect, the invention provides a continuous production method of sodium battery grade nano sodium iron phosphate, which comprises the following steps:
s1, dissolving ferrous sulfate heptahydrate crystals with purity of more than 99.9% by using 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, aging, 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 iron phosphate crystal filter cake into desalted water to prepare an iron phosphate suspension, pumping the suspension and a sodium carbonate solution into a multi-medium continuous flow reactor simultaneously, reacting under the conditions of normal temperature and normal pressure, and carrying out solid-liquid separation, washing and filtering after reaction to obtain an ultra-pure iron phosphate sodium crystal filter cake; meanwhile, sodium sulfate mixed in the iron phosphate crystal filter cake is washed out to generate a sodium sulfate solution;
and S4, drying the filter cake of the ultrapure sodium iron phosphate crystal to remove free water, then calcining at high temperature under the protection of inert gas to remove crystal water, and grinding to obtain the sodium battery-grade nano sodium iron phosphate.
According to the preferred embodiment of the invention, in S1, the concentration of the ferrous sulfate solution is 190-210g/L, water is heated to 40 ℃ before dissolving, and the temperature is raised to 48-51 ℃ during dissolving.
According to the preferred embodiment of the invention, in S1, ferrous sulfate heptahydrate crystals are dissolved in a dissolving tank, the pumping speed is set, the ferrous sulfate solution is pumped into an oxidation reaction tank, and meanwhile, sulfuric acid and hydrogen peroxide are pumped into the oxidation reaction tank; oxidizing ferrous sulfate into ferric sulfate in the oxidation reaction tank by using sulfuric acid and hydrogen peroxide; wherein 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 invention, in the step S1, the sulfuric acid concentration is 27-31wt.%, the hydrogen peroxide concentration is 27-31wt.%, and the oxidation reaction temperature is 50-55 ℃; in the reaction process, detecting whether the oxidation reaction is finished by using phenanthroline; and (4) leading out the ferric sulfate solution generated after the oxidation reaction is finished and temporarily storing the ferric sulfate solution in a ferric sulfate solution storage tank.
According to the preferred embodiment of the invention, the reaction conditions of S2 are 75-85 ℃, and the reaction time is 1.5-2h to generate iron phosphate (dissolved in hot water); then standing and aging for more than 2h to obtain iron phosphate crystals. The ferric phosphate is insoluble in cold water, flocculent suspended matters are generated in the solution along with the reduction of the temperature in the aging process, a ferric phosphate crystal solid phase object can be obtained through solid-liquid separation, and the solid phase object needs to be further washed.
According to the preferred embodiment of the present invention, in S2, the step of washing and filtering the cold water is performed by mohr filtration washing or membrane filter press washing, the washing is performed in two steps, the filter disc is adjusted to a slurry concentration of 15% after the primary washing, the secondary washing is performed, and the secondary washing wastewater is used as the primary washing water, wherein the washing temperature is 15 ℃ to 25 ℃. The sodium content in the iron phosphate crystals is reduced by washing with water.
According to a preferred embodiment of the invention, in S3, the iron phosphate crystal filter cake obtained after the secondary water washing in step S2 is added into cold desalted water to prepare an iron phosphate suspension (iron phosphate is insoluble in cold water), the suspension and a sodium carbonate solution are simultaneously pumped into a multi-medium continuous flow reactor for continuous reaction at normal temperature and normal pressure, and solid-liquid separation is performed to obtain iron phosphate sodium crystals. The sodium ferric phosphate is white or yellowish white powder, odorless, tasteless, and insoluble in water. Therefore, flocculent suspended matters are generated after the reaction is finished, and the solid-liquid separation is carried out to obtain the solid phase substance of the sodium ferric phosphate crystal, which needs to be further washed.
According to a preferred embodiment of the present invention, in S3, the washing and filtering process is performed in two or more times, the next washing wastewater is used as the washing water for the previous washing, the last washing is performed with pure deionized water, the washing is performed until the sodium sulfate content in the sodium iron phosphate crystals is less than 30ppm, which is the washing end point, and the washing and filtering are performed in a mohr filter or a membrane filter press.
According to the preferred embodiment of the invention, in S4, the water content in the filter cake of the ultra-pure sodium iron phosphate crystal 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 present invention, in S4, the calcination conditions are: calcining at 550-650 ℃ in a calcining kiln under the protection of inert gas, losing crystal water, and grinding to obtain the sodium battery grade nano sodium iron phosphate powder.
(III) advantageous effects
The continuous production method of sodium battery grade nano sodium iron phosphate takes high-purity ferrous sulfate heptahydrate as a raw material, ferric sulfate is obtained after oxidation, then the ferric sulfate is mixed with disodium hydrogen phosphate to generate ferric phosphate floccule, and the ferric phosphate floccule is subjected to solid-liquid separation, full washing and filtration to obtain ferric phosphate crystals without sulfate; and then preparing the iron phosphate crystals into turbid liquid, adding a sodium carbonate solution to enable sodium ions to be uniformly embedded into iron phosphate suspended particles to generate sodium ferric phosphate, carrying out solid-liquid separation to further obtain sodium ferric phosphate crystals, fully washing and filtering to obtain a sodium ferric phosphate crystal filter cake with the sodium sulfate content of less than 30ppm, drying and calcining to obtain the battery-grade nano sodium ferric phosphate powder.
The invention utilizes the characteristic that ferric phosphate is insoluble in cold water and ferric sodium 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 grade. The ferric phosphate is dispersed into water to react with a sodium carbonate solution in the form of flocculent suspended particles (suspension), so that sodium ions freely move and are uniformly embedded into suspended particles of the ferric phosphate at a heating reaction temperature to generate ferric phosphate sodium suspended particles, the distribution uniformity of the sodium ions embedded into a ferric phosphate sodium product is favorably ensured, and the product quality and the stability of the electrochemical performance of the product are improved. Compared with a template method, a complexing method and a hydrothermal coprecipitation method, the production method does not need to remove the template or complexing agent, and is easier to obtain a product with the microscopic morphology (particle size, specific surface area and tap density) meeting the technical indexes of a battery grade.
The invention takes ferrous sulfate heptahydrate as raw material, the ferrous sulfate heptahydrate is the main by-product of the unit sulfuric acid method for producing titanium dioxide of the applicant, therefore, the process of the invention can be coupled with the process for producing titanium dioxide by the sulfuric acid method to form a large production line, the by-product (ferrous sulfate heptahydrate) of the process for producing titanium dioxide by the sulfuric acid method is used for preparing battery-grade sodium ferric phosphate, the by-products ferric sulfate and sodium sulfate produced by producing sodium ferric phosphate can be used for producing sodium ferric sulfate, and the sodium ferric sulfate is also a raw material of the anode material of a sodium ion battery.
In addition, in the production method, products obtained after the reaction in each step is finished are 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 finish the reaction, and the continuous production process of the sodium battery-grade nano iron sodium phosphate is realized 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
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
As shown in fig. 1, the continuous production process of sodium battery-grade nano sodium iron phosphate of the present invention is that ferrous sulfate heptahydrate crystal with purity of 99.9% or more is used as starting material, and is dissolved in water to obtain ferrous sulfate solution. The ferrous sulfate heptahydrate crystal is dissolved in a dissolving tank, the concentration of the ferrous sulfate heptahydrate crystal is kept between 190 and 210g/L after the ferrous sulfate heptahydrate crystal is dissolved, the water is heated to 40 ℃ before the ferrous sulfate heptahydrate crystal is dissolved, and the temperature is raised to 48 to 51 ℃ in the dissolving process. The concentration of the ferrous sulfate is not too high, and the excessive concentration is easy to form agglomeration, so that the particle size of the product is increased, and the distribution of the sodium iron element in the product is uneven. And guiding the ferrous sulfate solution to a storage tank for storage. And then setting the leading-out speed of the ferrous sulfate solution, leading the ferrous sulfate solution into an oxidation reaction tank according to the set speed, simultaneously pumping hydrogen peroxide and sulfuric acid into the oxidation reaction tank, and oxidizing the ferrous sulfate to obtain a ferric sulfate solution. The concentration of sulfuric acid is 27-31wt.%, the concentration of hydrogen peroxide is 27-31wt.%, and the temperature of oxidation reaction is 50-55 deg.C. In the reaction process, 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. In an oxidation reaction tank, detecting whether the oxidation reaction is finished or not by using phenanthroline; and (4) leading out the ferric sulfate solution generated after the oxidation reaction is finished and temporarily storing the ferric sulfate solution in a ferric sulfate solution storage tank. And pumping the ferric sulfate solution and the disodium hydrogen phosphate in the ferric sulfate solution storage tank into a ferric phosphate reaction tank simultaneously, 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 temperature reduction, and carrying out solid-liquid separation to obtain the ferric phosphate crystal solid phase. Washing and filtering with cold water, and washing off sodium sulfate mixed in the solid phase to obtain a pure ferric phosphate crystal filter cake. The cold water washing is carried out by adopting water at normal temperature or below. The washing procedure preferably adopts Mohr filtration washing or membrane filter press washing, the washing is carried out in two times, after one time of washing, the filter disc is adjusted to be 15% of slurry concentration for secondary washing, the secondary washing wastewater is used as the water for the primary washing, the washing temperature is 15-25 ℃, and the sodium content in the ferric phosphate crystal is reduced through washing. And adding the iron phosphate crystal filter cake after the secondary water washing into cold desalted water, and stirring at a high speed to prepare an iron phosphate suspension. During leaving the iron phosphate turbid liquid in the iron phosphate storage tank, the storage tank is equipped with agitating unit, and agitating unit constantly carries out the high strength disturbance to the turbid liquid, avoids its precipitate that stews. Pumping the turbid liquid and the sodium carbonate solution into a multi-medium continuous flow reactor simultaneously for 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 sodium iron phosphate crystal solid-phase substance, washing the solid-phase substance with water, and filtering to remove sodium sulfate and sodium carbonate. The washing and filtering process is carried out by two or more times, the next washing wastewater is used as the washing water for the previous washing, the last washing is carried out by pure deionized water, the washing is carried out until the content of sodium sulfate in the sodium ferric phosphate crystal is less than 30ppm, and the washing and filtering are carried out in a Mohr filter or a membrane filter press. Washing and filtering to obtain an ultra-pure sodium ferric phosphate crystal filter cake (the water content is 40-45%); and simultaneously washing out sodium sulfate and sodium carbonate which are mixed in the iron phosphate crystal filter cake. Continuously drying the ultra-pure sodium iron phosphate crystal filter cake by hot air at 120-125 ℃, removing free water, then transferring to a calcining kiln, calcining at 550-650 ℃ under the protection of inert gas, losing crystal water, crushing and grinding to obtain sodium battery grade nano sodium iron phosphate powder. Organic impurities and carbonate ions can be removed through calcination, and the purity of the product is improved, so that the product meets the use requirement of a battery level.
In the process, products obtained after the reaction in each step or solution or suspension obtained after dispersion are immediately led out and transferred to a storage tank or a reaction tank so as to empty the original reaction tank and facilitate receiving the next batch of reaction materials to complete the reaction; the obtained crystal cake is also quickly transferred to the next treatment process, such as dispersion into a suspension or drying and calcination; therefore, the whole process line realizes the continuous production process of the sodium battery grade nano sodium iron phosphate, improves the production efficiency of battery grade products and reduces the cost.
In the process, the washing liquid generated by each step of washing and filtering is purified and desalted by adopting a nanofiltration composite membrane, desalted water is used for dissolving ferrous sulfate heptahydrate crystals and dispersing ferric phosphate crystal filter cakes or is used for preparing disodium hydrogen phosphate or sodium carbonate solution, so that water resources are saved, and pure deionized water is used only in the most critical step of washing, for example, pure deionized water is used in the last washing and filtering of the ferric phosphate sodium crystals, so as to ensure that the product meets the cell-level index.
A multi-media continuous flow reactor is a device that continuously performs chemical reactions. During the reaction, the reactants and the solvent continuously flow, and the chemical reaction process is completed at the same time. 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; the catalyst is prevented from being deactivated; promoting gas absorption and heat release; accelerating the dissolution of solid particles and the dispersion of liquid; the mass transfer efficiency is improved. The materials are fully contacted by mixing to accelerate the mass transfer speed, reduce the energy consumption and reduce the resistance loss of equipment. The mixing operation is generally realized by adopting a mechanical stirring or mechanical-fluid combined circulation mode, and the rapid and uniform distribution of mixed materials can also be realized by adopting a chemical metering pump as an auxiliary means. The control of the temperature is very important for the whole process because different materials have different thermodynamic properties (such as latent heat of fusion, enthalpy of vaporization, endothermic coefficient of vaporization, etc.), and different process conditions require corresponding optimal temperature parameters to meet production requirements (for example, the production of synthetic ammonia at high temperature and high pressure). The main function of pressure control is to ensure that a certain equilibrium state is achieved between liquid and solid phases and to avoid bursting accidents due to local overpressure. The methods used are mainly of the following types: the balance between the liquid phase and the solid phase is adjusted by adjusting the opening of the valve; the balance between the liquid phase and the solid phase is realized by pumping and reducing pressure by a vacuum pump; the pressure is controlled within a certain range by utilizing an elastic element to achieve a stable state; the operating pressure of the system is increased by pressurizing with a booster pump to meet the process requirements; the pressure is reduced by a pressure reducing valve to achieve the purpose of pressure stabilization; the operation temperature range of the system is changed by adjusting the flow of the cooling water.
The scheme and the product index of the invention are described below with reference to specific examples.
Example 1
The present embodiment is a continuous production method of sodium battery grade nano sodium iron phosphate, the flow process of which adopts the continuous production process line described above, and is specifically described as follows:
(1) Dissolving ferrous sulfate heptahydrate crystal with purity of 99.9% in desalted water of 40 deg.C, heating to 50 deg.C while dissolving to obtain ferrous sulfate solution with concentration of 190 g/L. And guiding the ferrous sulfate solution to a storage tank for storage.
(2) Introducing a ferrous sulfate solution into an oxidation reaction tank, simultaneously introducing a 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 by using phenanthroline; and after the oxidation reaction is finished, the ferric sulfate solution is led out and temporarily stored to a ferric sulfate solution storage tank. Wherein, 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 the excess or deficiency is avoided, and the impurity content in the product is reduced.
(3) Pumping a ferric sulfate solution and a 42wt.% disodium hydrogen phosphate solution into a ferric phosphate reaction tank at the same time, mixing the ferric sulfate solution and the disodium hydrogen phosphate, heating to 80 ℃, carrying out heat preservation reaction for 1.5h, stopping heating, standing and aging for 2h, generating flocculent suspended matters in the solution along with the temperature reduction, and filtering to obtain a ferric phosphate crystal solid phase. And (3) carrying out Mohr filtration washing on the solid-phase substance, wherein the washing is carried out twice, the concentration of a filter disc is adjusted to be 15% of slurry concentration after primary washing, secondary washing is carried out, secondary washing wastewater is used as primary washing water, the washing temperature is 20 ℃, and the sodium content in the ferric phosphate crystal is reduced through washing. Washing with water to obtain iron phosphate crystal filter cakes, wherein the washing liquid contains sodium sulfate.
(4) And dispersing the iron phosphate crystal filter cake into cold (15-20 ℃) desalted water, and stirring at a high speed to prepare an iron phosphate suspension. Leave the iron phosphate turbid liquid in the iron phosphate storage tank, the storage tank is equipped with agitating unit, and agitating unit constantly carries out the high strength disturbance to the turbid liquid, avoids its sedimentation of stewing. And simultaneously pumping the iron phosphate suspension and 15wt.% of sodium carbonate solution into a multi-medium continuous flow reactor for mixing 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 filter cake of the sodium iron phosphate crystal solid-phase substance.
(5) And (3) washing and filtering the solid-phase filter cake of the sodium ferric phosphate crystal twice, wherein the washing and filtering are carried out in a Mohr filter, the washing liquid filtered by the secondary washing is used as the primary washing liquid for recycling, and the washing liquid filtered by the secondary washing is pure deionized water. After washing with water, filtration yielded a cake of ultrapure sodium iron phosphate crystals with a sodium sulfate content of less than 30ppm (water content 42%).
(6) Drying the ultra-pure sodium iron phosphate crystal filter cake by hot air at 120 ℃, transferring the filter cake 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 to dry the powder, pulverize it, and calcine it, thereby accelerating the calcination speed.
The sodium iron phosphate powder is yellowish powder, and tests show that the product has a particle size of medium diameter (D50) =77.5nm and a tap density of 1.14g/cm 3 The average specific surface area is 21.4 square meters per gram.
Example 2
The present embodiment is a continuous production method of sodium battery grade nano sodium iron phosphate, the flow of which adopts the continuous production process line described above, and is specifically described as follows:
(1) Dissolving ferrous sulfate heptahydrate crystal with purity of 99.9% in desalted water of 40 deg.C, heating to 55 deg.C while dissolving to obtain ferrous sulfate solution with concentration of 200 g/L.
(2) Introducing a ferrous sulfate solution into an oxidation reaction tank, simultaneously introducing a sulfuric acid solution with the concentration of 30wt.% and hydrogen peroxide with the concentration of 30wt.%, keeping the temperature at 50 ℃, reacting for 2 hours, and leading out a product ferric sulfate solution and temporarily storing the product ferric sulfate solution into a ferric sulfate solution storage tank.
(3) Pumping a ferric sulfate solution and a 45wt.% disodium hydrogen phosphate solution into a ferric phosphate reaction tank at the same time, mixing the ferric sulfate solution and the disodium hydrogen phosphate, heating to 85 ℃, carrying out heat preservation reaction for 1.5h, stopping heating, standing and aging for 2.5h, generating flocculent suspended matters in the solution along with the reduction of temperature, and filtering to obtain a ferric phosphate crystal solid phase. And (3) washing the solid phase by using a membrane filter press, wherein the washing is carried out twice, after primary washing, the filter disc is adjusted to be 15% of slurry concentration for secondary washing, secondary washing wastewater is used as primary washing water, the washing temperature is 25 ℃, and the sodium content in the ferric phosphate crystal is reduced by washing. Washing to obtain iron phosphate crystal filter cakes, wherein the washing liquid contains sodium sulfate.
(4) And dispersing the iron phosphate crystal filter cake into cold (15-20 ℃) desalted water, and stirring at a high speed to prepare an iron phosphate suspension. And simultaneously pumping the iron phosphate suspension and 20wt.% of sodium carbonate solution into a multi-medium continuous flow reactor for mixing 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 filter cake of the sodium iron phosphate crystal solid-phase substance.
(5) And (3) washing and filtering the solid-phase filter cake of the sodium ferric phosphate crystal twice, wherein the washing and filtering are carried out in a membrane filter press, the washing liquid obtained by washing and filtering twice is used as the primary washing liquid for recycling, and the secondary filtering washing liquid adopts pure deionized water. After washing with water, filtration yielded an ultrapure sodium iron phosphate crystal cake (water content 45%) with a sodium sulfate content of less than 30 ppm.
(6) Drying the ultra-pure sodium iron phosphate crystal filter cake by hot air at 120 ℃, transferring the filter cake 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 to dry the powder, pulverize it, and calcine it, thereby accelerating the calcination speed.
The sodium iron phosphate powder is yellowish powder, and tests show that the particle size of the product is medium diameter (D50) =74.5nm, and the tap density is 1.21g/cm 3 The average specific surface area is 24.7 square meters per gram.
After the sodium ferric phosphate powder prepared in example 1 and sucrose powder with the mass of 1% of the sodium ferric phosphate powder are ground by a ball mill for 1 hour, the mixed powder is sieved by a 100-mesh sieve to obtain powder; and then pouring the powder into a sagger, placing the sagger in a muffle furnace, introducing argon for protection, sintering the sagger at a high temperature of 700 ℃ for 14 hours, and cooling to obtain the black ferric sodium phosphate cathode material.
Uniformly mixing a sodium iron phosphate positive electrode material, a binder and a conductive agent with a solvent according to the weight ratio of 90; the positive plate, the negative plate and the diaphragm are arranged in a button type battery shell, and electrolyte of electrolyte is injected to be NaPF 6 And the concentration is 1mol/L, the solvent is EC: DEC: DMC = 1. And testing the cycle performance of the battery.
The cycle performance test method comprises the following steps: under the normal temperature environment, the battery is charged to 3.9V by a constant current of 0.5C, then is charged by a constant voltage of 3.9V, and when the charging current is less than 0.05C, the charging is stopped; standing for 10min, and then discharging to 2.0V at constant current of 0.5C; standing for 10min. The above steps are repeated to complete 3000 cycles. And recording the discharge capacity of each time, and calculating the percentage of the 3000 th discharge capacity to the 1 st discharge capacity, wherein the capacity fading is 16% (the 3000 th capacity retention rate reaches 84%). Therefore, the sodium iron phosphate prepared by the method can completely meet the requirement of battery grade indexes.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A continuous production method of sodium battery grade nano sodium iron phosphate is characterized by comprising the following steps:
s1, dissolving ferrous sulfate heptahydrate crystals with purity of more than 99.9% by using 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, aging, separating, washing with cold water, and filtering to obtain a ferric phosphate crystal filter cake and a sodium sulfate solution;
s3, dispersing the iron phosphate crystal filter cake into water to prepare an iron phosphate suspension, pumping the suspension and a sodium carbonate solution into a multi-medium continuous flow reactor simultaneously, reacting under the conditions of normal temperature and normal pressure, and carrying out solid-liquid separation, washing and filtering after reaction to obtain an ultra-pure iron phosphate sodium crystal filter cake; meanwhile, sodium sulfate mixed in the iron phosphate crystal filter cake is washed out to generate a sodium sulfate solution;
and S4, drying the filter cake of the ultrapure sodium iron phosphate crystal to remove free water, then calcining at high temperature under the protection of inert gas to remove crystal water, and grinding to obtain the sodium battery-grade nano sodium iron phosphate.
2. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 1, wherein in S1, the concentration of ferrous sulfate solution is 190-210g/L, water is heated to 40 ℃ before dissolving, and the temperature is raised to 48-51 ℃ during dissolving.
3. The continuous production method of sodium battery grade nano ferric sodium phosphate according to claim 1, characterized in that in S1, ferrous sulfate heptahydrate crystal is dissolved in a dissolving tank, a pumping-out speed is set, a 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 into ferric sulfate in the oxidation reaction tank by using sulfuric acid and hydrogen peroxide; wherein 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 grade nano sodium iron phosphate according to claim 1, characterized in that in S1, the concentration of sulfuric acid is 27-31wt.%, the concentration of hydrogen peroxide is 27-31wt.%, and the oxidation reaction temperature is 50-55 ℃; in the reaction process, detecting whether the oxidation reaction is finished by using phenanthroline; and (4) leading out the ferric sulfate solution generated after the oxidation reaction is finished and temporarily storing the ferric sulfate solution in a ferric sulfate solution storage tank.
5. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 1, characterized in that the reaction conditions of S2 are 75-85 ℃ and the reaction time is 1.5-2h to produce iron phosphate; then standing and aging for more than 2h to obtain iron phosphate crystals.
6. The method for continuously producing sodium battery grade nano-ferric sodium phosphate according to claim 1, wherein in S2, the step of washing and filtering the cold water is performed by Mohr filtration washing or membrane filter press washing, the washing is performed in two steps, after one step of washing, the filter disc is adjusted to be 15% of slurry concentration for secondary washing, and the secondary washing wastewater is used as the primary washing water, wherein the washing temperature is 15-25 ℃.
7. The continuous production method of sodium battery grade nano-iron sodium phosphate according to claim 6, characterized in that in S3, the iron phosphate crystal filter cake after the secondary water washing in the step S2 is added into cold desalted water to prepare an iron phosphate suspension, the suspension and a sodium carbonate solution are simultaneously pumped into a multi-medium continuous flow reactor for continuous reaction at normal temperature and normal pressure, and solid-liquid separation is carried out to obtain the iron sodium phosphate crystal.
8. The method for continuously producing sodium battery grade nano-sized ferric sodium phosphate according to claim 7, wherein in S3, the washing filtering process is performed by two or more times, the next washing wastewater is used as the washing water for the previous washing, the last washing is performed by pure deionized water, the washing is performed until the sodium sulfate content in the ferric sodium phosphate crystal is less than 30ppm, and the washing is performed in a Mohr filter or a membrane filter press.
9. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 1, characterized in that in S4, the water content in the ultra-pure sodium iron phosphate crystal filter cake obtained by washing and filtering is 40% -45%, and the ultra-pure sodium iron phosphate crystal filter cake is dried at 120-125 ℃ to remove free water.
10. The continuous production method of sodium battery grade nano sodium iron phosphate according to claim 9, characterized in that in S4, the calcination conditions are as follows: calcining at 550-650 deg.C under the protection of calcining kiln and inert gas to remove crystal water, and grinding to obtain sodium battery grade nanometer sodium ferric phosphate powder.
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| FR3054541A1 (en) * | 2016-08-01 | 2018-02-02 | Centre National De La Recherche Scientifique | PROCESS FOR THE PREPARATION OF ARSENATES AND / OR PHOSPHATES OF OLIVIN STRUCTURE TRANSITION METALS |
| CN107902637A (en) * | 2017-12-19 | 2018-04-13 | 贵州大龙汇成新材料有限公司 | A kind of production method of high-purity phosphoric acid iron |
| CN109786744A (en) * | 2019-01-24 | 2019-05-21 | 中南大学 | A method of phosphoric acid ferrisodium electrode is prepared using industrial by-product ferrous sulfate |
| CN114843432A (en) * | 2022-04-22 | 2022-08-02 | 宁波市稻禾科技有限公司 | Low-iron-phosphorus-ratio sodium iron phosphate @ carbon nanotube cathode material and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| FR3054541A1 (en) * | 2016-08-01 | 2018-02-02 | Centre National De La Recherche Scientifique | PROCESS FOR THE PREPARATION OF ARSENATES AND / OR PHOSPHATES OF OLIVIN STRUCTURE TRANSITION METALS |
| CN107902637A (en) * | 2017-12-19 | 2018-04-13 | 贵州大龙汇成新材料有限公司 | A kind of production method of high-purity phosphoric acid iron |
| CN109786744A (en) * | 2019-01-24 | 2019-05-21 | 中南大学 | A method of phosphoric acid ferrisodium electrode is prepared using industrial by-product ferrous sulfate |
| CN114843432A (en) * | 2022-04-22 | 2022-08-02 | 宁波市稻禾科技有限公司 | Low-iron-phosphorus-ratio sodium iron phosphate @ carbon nanotube cathode material and preparation method thereof |
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