A method for continuously and rapidly preparing battery-grade iron phosphate by microwave heating

Abstract

The application provides a method for rapidly preparing battery-grade iron phosphate by microwave heating, which comprises the following steps: adding iron powder into a phosphoric acid solution, adjusting pH after the iron powder is dissolved, collecting filtrate and heating to a set temperature range; carrying out oxidation reaction on the collected filtrate and an oxidizing agent, pumping the obtained reaction slurry into a tubular reactor for microwave heating reaction; filtering and washing the obtained product, and drying the filter cake after the washing by microwave to obtain hydrous iron phosphate; and calcining the obtained dihydrate iron phosphate after ball milling to obtain battery-grade anhydrous iron phosphate. The application adopts a combination of a kettle reactor and a tubular reactor for reaction, the kettle reactor buffers the violent reaction in the initial contact process of the material, and reduces the particle size of the primary reaction; the tubular reactor enables the material to be more fully contacted, further improves the crystal structure of the material, and improves the conversion rate of the material.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of lithium-ion battery material precursor iron phosphate, specifically relating to a method for rapid preparation of battery-grade iron phosphate by microwave heating. Background Technology

[0002] With the deterioration of the global ecological environment, people are paying increasing attention to the development and utilization of clean energy. Lithium-ion batteries, as a new type of energy storage device, mainly rely on the electrochemical insertion / extraction of lithium ions in electrode materials to store energy, boasting a high energy density (150–200 Wh / kg). -1 It is favored by the market for its high efficiency (over 90%) and conversion efficiency, and has been widely used in electric vehicles, energy storage power stations and small electronic devices.

[0003] LiFePO4, as one of the cathode materials for lithium-ion batteries, is favored by electric vehicles and energy storage markets due to its advantages such as good structural stability, long service life, good thermal stability, low hygroscopicity, and excellent discharge cycle performance. Among the various methods for preparing lithium iron phosphate, the iron phosphate process has gradually become the mainstream process due to its advantages such as simple synthesis method, high raw material utilization, good reproducibility, high cathode material activity, and mature and stable production technology. Currently, the main synthesis method for LiFePO4 is to use iron phosphate as the iron source, combined with lithium source compounds, carbon sources, and additives.

[0004] The disadvantages of lithium iron phosphate materials are also obvious. Among them, the low conductivity and low diffusion coefficient of lithium ions limit the high power output of the battery and also affect the low temperature performance of the battery. Changing the synthesis characteristics of iron phosphate is a feasible way to improve the performance of lithium iron phosphate, such as (1) nano-sized iron phosphate: nano-sized iron phosphate can improve the uniformity of material mixing and reduce the primary particle size of lithium iron phosphate; (2) high-purity iron phosphate: reducing the types and contents of impurity elements in iron phosphate can reduce side reactions in the battery reaction process; (3) high iron-phosphorus ratio iron phosphate: the higher the iron-phosphorus ratio in the iron phosphate structure, the more complete the lattice is, and the higher the lithium it can accommodate. Conventional processes are limited by the raw materials and reaction process. The prepared iron phosphate has a large particle size, high impurity content and low iron-phosphorus ratio. The performance of lithium iron phosphate prepared using it as a precursor is also poor. Summary of the Invention

[0005] This invention addresses the problems encountered in the preparation of iron phosphate, such as large particle size leading to poor mixing uniformity and conductivity, the introduction of impurity ions in conventional processes reducing product quality, and the difficulty in controlling the iron and phosphorus content of the product. It provides a method for the continuous and rapid preparation of battery-grade iron phosphate using microwave heating.

[0006] To achieve the above-mentioned objective, this invention provides a method for the continuous and rapid preparation of battery-grade iron phosphate using microwave heating, the method comprising the following steps:

[0007] (1) Take iron powder, phosphoric acid and water and heat them to react. After the iron powder is basically dissolved and the solution reaches a fixed pH, filter it, collect the filtrate and keep it constant at a certain temperature.

[0008] (2) Add the filtrate from step (1) and the oxidant to the batch reactor simultaneously, and control the Fe... 2+ The feed molar ratio of the oxidant and the slurry is rapidly stirred while the slurry is discharged from the bottom and transported to the tubular reactor.

[0009] (3) The reaction slurry obtained in step (2) is pumped into a tubular reactor for microwave heating and isothermal reaction;

[0010] (4) The product obtained in step (3) is filtered and washed, and the filter cake after washing is dried by microwave to obtain hydrated ferric phosphate.

[0011] (5) Ferric phosphate is rapidly heated and dried in a microwave drying oven via a conveyor belt to obtain anhydrous ferric phosphate. After being crushed, it is calcined at 450-700℃ for 3-5 hours to obtain anhydrous ferric phosphate.

[0012] In step (1), the iron powder has an iron content of over 99% and a particle size between 200 and 500 mesh; the phosphoric acid is food-grade phosphoric acid with a phosphorus pentoxide content greater than 85%, and the molar ratio of iron powder to phosphoric acid is controlled between 0.9 and 1.5:1; the iron-phosphorus mixed solution is prepared through an acid-base reaction without the addition of any other additives, thus avoiding the introduction of impurity ions at the source, and the filtrate can be reused. The iron-phosphorus molar ratio is one of the important indicators for measuring the quality of iron phosphate. The iron-phosphorus molar ratio in the feed can be changed by altering the molar ratio of reduced iron powder to phosphoric acid. The initial iron-phosphorus molar ratio affects the reaction time of iron dissolution and the iron and phosphorus content in the solution. Because the phosphoric acid in the reaction solution is a moderately strong acid, the reaction with the iron powder is slow and incomplete. Allowing a slight excess of iron powder during feeding can promote the reaction.

[0013] During iron dissolution, the reaction temperature is generally controlled at 50–60℃ and the reaction pH at around 1.6. When the pH is too high, a dark gray precipitate will form, and this precipitate will continuously increase as the reaction proceeds. This is because as the pH increases, the H₂PO₄ in the solution… - A large amount of PO4 is ionized. - It will react with Fe 2+ The combination produces a large amount of Fe3(PO4)2 precipitate, and pH values ​​above this level will affect the preparation of ferric phosphate.

[0014] In step (1), the pH value of the mixed solution is adjusted to the range of 1.5 to 3.0 during the reaction process, and the pH adjuster is a phosphoric acid solution.

[0015] In step (2), the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide used is related to the amount of Fe in the iron and phosphorus solution. 2+ The molar ratio is 0.4 to 1:1. Hydrogen peroxide has strong oxidizing properties under acidic conditions and can oxidize Fe. 2+ Completely oxidized to Fe 3+ This process avoids introducing other impurity ions. The feed method involves simultaneous feeding of hydrogen peroxide and iron-phosphorus solution. The reactor uses a stirring paddle to disperse the solution, and a spiral discharge port is located at the bottom of the reactor. The reacted slurry is discharged from the bottom and transported to a tubular reactor for further heating and reaction.

[0016] Based on the solubility product theory and calculations of the ionization equilibrium constants of phosphate at each stage, the precipitation of hydrated iron phosphate depends on H2PO4. - Concentration and Fe 3+ The lower the concentration and pH, the more PO4 is ionized. 3- The smaller the quantity, the more the hydrated ferric phosphate generated under acidic conditions will partially dissolve in the phosphoric acid solution, significantly reducing the product yield. Based on the chemical equation, the oxidation reaction consumes hydrogen ions, while the ferric phosphate formation process generates hydrogen ions. To achieve equilibrium or raise the pH, the amounts of hydrogen peroxide and water used throughout the reaction are critical control points. Furthermore, the molar ratio of hydrogen peroxide to ferric salt needs to be controlled at approximately 0.5–1.0, and the reaction pH at approximately 1.5–3.0. Increasing the reaction pH helps improve the yield; here, the pH is controlled above 1.5. A value below this will lead to a significant decrease in product yield, resulting in raw material loss.

[0017] In step (2), the microwave heating reaction zone of the tubular reactor operates at a frequency of 1000-10000MHz and a power of 10-70kW. The material in the tubular reactor is heated to 80-90℃ in the microwave heating section and kept warm in the microwave heat preservation section for 5-30 minutes.

[0018] A further preferred embodiment is that the operating frequency in the heating section of the tubular reactor is 5000–10000 MHz, and the operating power is 30–70 kW; while the operating frequency in the insulation section of the tubular reactor is 1000–5000 MHz, and the operating power is 10–30 kW. The heating section needs to rapidly raise the temperature to a specific temperature, and this process requires relatively high frequency and power.

[0019] The feed and discharge rates affect the product particle size. The reaction process adopts a continuous feed and discharge method, with a total feed rate of 1 to 15 L / min and a discharge rate of 1 to 10 L / min.

[0020] Microwaves are electromagnetic waves with both absorption and penetrating power. Due to their strong penetrating ability, materials can directly absorb microwave energy, generating heat from within. Liquid molecules that absorb microwave energy become polarized and change their direction of motion following the continuous shifts in the polarity of the microwave energy field, thereby increasing the ionization degree and ion activity of the liquid molecules. Under the microwave thermal effect, liquid molecules generate microwave "thermal effects" and "non-thermal effects" through friction and stirring. This process increases the probability of contact between liquid molecules and accelerates the diffusion rate of reaction products into the bulk liquid phase.

[0021] Microwave power plays a crucial role in the reaction. Under certain conditions, microwaves can accelerate the reaction rate and increase the conductivity of the liquid phase in the reaction system. As microwave power increases, water molecules absorb more energy, resulting in more dissociated water molecules, more significant water molecule polarization, and consequently, increased conductivity. After microwave treatment, aqueous solutions exhibit decreased association, increased unimolecular water, and higher conductivity. This property is maintained for a period after the microwave field is removed and the temperature is lowered, resulting in ionic nano-water, which exhibits enhanced diffusion and permeation capabilities. This process is beneficial for synthesis reactions.

[0022] In step (3), the temperature of the slurry transported from the reactor is maintained at approximately 80–85°C. The microwave heating section of the tubular microwave reactor needs to rapidly heat the slurry to 85–95°C before a constant-temperature reaction is carried out. In this region, the flow rate of the reaction slurry pumped into the tubular reactor is 1–15 L / min.

[0023] Both the secondary reaction heating stage and the isothermal stage are carried out by microwave heating. Compared with ordinary heating methods, its advantages are as follows: (1) Microwave heating can accelerate the deposition and precipitation of reaction crystals without changing the crystal system, lattice structure and crystal composition; (2) Microwave heating does not affect the crystal particle size distribution and porosity distribution. During the crystal transformation process, the crystal growth direction and stacking structure will change over time. Under microwave action, the relative change rate of fractal dimension is low, and fractal can maintain a high degree of self-similarity, so the crystal stacking structure does not change much; (3) Microwave action also leads to the homogenization of crystal particles, avoiding the low porosity caused by the nesting of particles of different sizes. However, under heating action, the formed crystal particles have low uniformity and are nested with each other. This characteristic will form a denser crystal stacking structure, which is easy to block ion transport channels.

[0024] In step (3), the reacted material is cooled and then transported to a filter press for filtration. The filtrate is recycled. The filter cake is washed until its conductivity is sufficiently low, such as below 1 mS / cm, below 0.5 mS / cm, or below 0.2 mS / cm. This filtration and washing is a standard procedure in the art. After washing and pressing, the filter cake is transported to a microwave dryer for drying. After drying, it is pulverized in a pulverizer and calcined at 450–600°C to obtain anhydrous ferric phosphate.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention employs a microwave heating reaction device, using high-power microwaves for heating, which greatly improves the reaction rate and reduces the heating time. Furthermore, microwave heating can accelerate the slurry crystallization process and has the effect of refining and homogenizing crystallization; however, the microwave action does not change the crystal system, lattice structure, or crystal composition, thus resulting in small product particles with uniform particle size distribution and regular morphology.

[0027] 2. This invention directly uses a solution obtained by dissolving high-purity iron powder in food-grade phosphoric acid as both the iron and phosphorus sources, without introducing other impurity ions at the raw material stage, thus resulting in a high-purity product. Furthermore, the process exhibits minimal pH fluctuations, leading to a smaller particle size in the prepared product compared to conventional methods, significantly improving its processing performance.

[0028] 3. This innovative process combines a batch reactor and a tubular reactor for the reaction. The batch reactor buffers the intense reaction process during the initial contact of the materials, reducing the particle size of the primary reaction particles; the tubular reactor allows for more complete contact of the materials, further improving the conversion rate. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A simplified process flow diagram for the production of iron phosphate provided by this invention.

[0031] Figure 2 The image shows the XRD pattern of ferric phosphate in Example 1 of this invention.

[0032] Figure 3 This is a SEM image of ferric phosphate from Example 1 of the present invention. Specific Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0034] like Figure 1 As shown, this invention provides a method for the continuous and rapid preparation of battery-grade iron phosphate using microwave heating. First, the phosphorus content of the phosphoric acid is adjusted, and iron powder is added for a heating reaction. After the reaction reaches a fixed pH, the mixture is filtered, and the filtrate is collected and heated to a constant temperature for later use. The filtrate and hydrogen peroxide are added to a reaction vessel through a nozzle for further reaction. The resulting slurry is pumped into a microwave-heated reactor, where continuous microwave heating and constant-temperature reaction are carried out. After the reaction is complete, the resulting slurry is filtered, washed, microwave-dried, and calcined to obtain the finished anhydrous iron phosphate. In this embodiment, the iron powder used has an iron content of over 99% and a particle size between 400 and 500 mesh; the phosphoric acid is food-grade phosphoric acid with a phosphorus pentoxide content greater than 85%.

[0035] The process for preparing iron phosphate using the above-mentioned iron and phosphorus sources is described in the following examples:

[0036] Example 1

[0037] A1: Accurately weigh food-grade phosphoric acid and add it to the reaction vessel, then dilute with water to a concentration of 1.2 mol / L. Add iron powder with an iron-to-phosphorus molar ratio of 1.2:1, heat the solution to 60°C to carry out the iron dissolution reaction, and stop the reaction when the pH reaches 1.6. Filter and collect the filtrate, then store the filtrate at a constant temperature of 70°C.

[0038] A2: Take the filtrate and oxidant for oxidation reaction, and control the Fe content in the mixed solution. 2+ The feed ratio of hydrogen peroxide is 1:0.7, and the feed is simultaneously fed through a nozzle. The stirring speed is 500 r / min, and the reaction is carried out while the product is being discharged. The feed rate is 3 L / min and the discharge rate is 2.5 L / min.

[0039] A3: Turn on the microwave-heated reactor. Pump the slurry from step A2 into the tubular reactor using a screw pump. Adjust the operating frequency of the microwave reaction in the heating section of the tubular reactor to 5000.0MHz and the power control to 50.0kW. Use a microwave heating box to heat the slurry to 85℃. Adjust the operating frequency of the microwave reaction in the isothermal section of the tubular reactor to 2450.0MHz and the power control to 30.0kW. Use feedback regulation to maintain the temperature at around 85℃ and continue the reaction for 10 minutes.

[0040] A4: Filter the slurry from the end of the reaction in step A3, wash it until the conductivity is less than 1 mS / cm, press the washed filter cake dry, and the filtrate and wash water can be reused in step A1 iron dissolution after treatment.

[0041] A5: Take the above-washed filter cake, send it to a microwave drying oven to dry, and crush and collect the powder to obtain ferric phosphate dihydrate.

[0042] A6: After filling the dried material into a sagger, calcination is carried out. The calcination temperature is set to 600℃ and the calcination time is set to 4.0h. After calcination, nano-anhydrous iron phosphate can be obtained. The dehydration rate of the product after drying is about 19.3%.

[0043] Examples 2-4

[0044] Examples 2-4 involve changing the pH at the reaction endpoint in step A1, while keeping all other conditions the same as in Example 1. Specifically, the pH at the reaction endpoint in Example 2 is 1.0, the pH at the reaction endpoint in Example 3 is 0.5, and the pH at the reaction endpoint in Example 4 is 2.5. The iron-phosphorus solution obtained at the end of the reaction is used as the reaction solution to prepare the iron phosphate product.

[0045] Examples 5-6

[0046] Examples 5 and 6 involve changing the operating frequency of the microwave reaction in the heating section of the tubular reactor in step A3, while keeping all other conditions the same as in Example 1. In Example 5, the operating frequency is 4000MHz, and in Example 6, the operating frequency is 6000MHz. The iron phosphate product is prepared through the above reaction.

[0047] Examples 7-8

[0048] Examples 7 and 8 involve changing the operating power of the microwave reaction in the heating section of the tubular reactor in step A3, while keeping all other conditions the same as in Example 1. In Example 7, the operating power was 30kW, and in Example 8, the operating power was 70kW. The iron phosphate product was prepared through the above reaction.

[0049] Examples 9-12

[0050] Examples 9-12 involve changing the feed flow rate of the reactor in step A3, while keeping all other conditions the same as in Example 1. Specifically, the feed flow rate in Example 9 is 2.5 L / min, in Example 10 it is 1 L / min, in Example 11 it is 3.5 L / min, and in Example 12 it is 4.0 L / min. Ferric phosphate is prepared through the above reaction.

[0051] Examples 13-14

[0052] Example 13 involves changing the heating method in step A3. In Example 13, the heating method is steam heating, while in Example 14, the heating method is heat transfer oil heating. All other conditions remain the same as in Example 1. The ferric phosphate product is prepared through the above reaction.

[0053] Regarding the above embodiments 1 to 14, this application has verified the products described therein, wherein the solid content refers to the percentage by mass of the remaining part of the reaction slurry after drying under specified conditions.

[0054] Yield refers to the ratio of the actual product output obtained per unit quantity of raw material input to the theoretically calculated product output during the chemical reaction production of ferric phosphate. The same chemical reaction can have different yields under different reaction conditions.

[0055] The battery performance test refers to the following: The charge and discharge test of this invention uses the Xinwei Electrochemical Workstation. Specifically, the battery is connected to the tester, and the required current is set. In this invention, a charge and discharge current of 0.1C is used for testing (1C = 170mAh / g). The test voltage window is set on the microcomputer through relevant software. This paper uses a voltage range of 2 to 3.75V for testing. The charging or discharging stage of the battery is controlled by the microcomputer program, and the charging and discharging are performed in a constant current and constant voltage manner.

[0056] Table 1 Comparison of various process conditions and indicators in the embodiments.

[0057]

[0058] Comparative Example 1

[0059] A1: Take titanium dioxide, remove impurities, ferrous sulfate and monoammonium phosphate solution, with an iron-to-phosphorus molar ratio of 1:1. The overall mass is consistent with that in Example 1 above. Add the phosphate solution to the reaction vessel within 1 hour using a nozzle. Stir the reaction vessel while adding the material. The stirring speed is 350 r / min.

[0060] A2: After all the phosphate has been added, transfer it to an aging kettle for heating and stirring reaction. The stirring speed is 350 r / min, the reaction temperature is set to 60℃, and the reaction time is 0.5 h. After aging, wash until the conductivity is as low as 5 mS / cm.

[0061] A3: After washing, take the filter cake and slurry it. The solid content and aging reaction should be kept consistent. Adjust the pH of the slurry to about 1.7 with phosphoric acid. The crystallization reaction time is 1 hour. The stirring speed is set to 350 r / min and the reaction temperature is set to 95℃. After the reaction is completed, wash the filter cake until the conductivity is as low as 0.5 mS / cm.

[0062] A4: Take the cleaned filter cake and dry it with a spray dryer. After drying, the dehydration rate of the material is about 19.5%, forming ferric phosphate dihydrate.

[0063] A5: The dried material is crushed, then placed in a sagger and calcined under an inert atmosphere. The calcination temperature is set to 600℃ and the calcination time is set to 4h. After calcination, nano-sized anhydrous iron phosphate can be obtained.

[0064] Comparative Example 2

[0065] A1: Take titanium dioxide, remove impurities, ferrous sulfate and phosphoric acid solution, with an iron-to-phosphorus molar ratio of 1:1. Add the materials to the reactor while stirring to make the mixed solution uniform. The stirring speed is 350 r / min.

[0066] A2: Add hydrogen peroxide to the above mixed solution, with a molar ratio of hydrogen peroxide to iron salt of 1:1. Stir while adding the materials, with a stirring speed of 350 r / min, a reaction temperature of 50℃, and a reaction time of 0.1 h.

[0067] A3: Add ammonia water to the above oxidized mixed solution, control the pH value at the reaction endpoint to be around 1.5, add the material while stirring, the stirring speed is 600 r / min, and the reaction time is 0.1 h;

[0068] A4: After feeding, quickly heat to about 95℃ and keep the temperature for 2 hours. After the reaction is complete, filter and wash the filter cake until the conductivity is as low as 0.5mS / cm.

[0069] A5: Take the cleaned filter cake and dry it with a flash dryer. The inlet air temperature is controlled at about 140℃ and the outlet air temperature is controlled at above 80℃. After drying, the dehydration rate of the material is about 19.5%, forming ferric phosphate dihydrate.

[0070] A6: The dried material is crushed, then placed in a sagger and calcined under an inert atmosphere. The calcination temperature is set to 600℃ and the calcination time is set to 4h. After calcination, nano-sized anhydrous iron phosphate can be obtained.

[0071] Table 2 Comparison of various process conditions and indicators in the comparative examples

[0072] sample Comparative Example 1 Comparative Example 2 Fe:P 0.968 0.970 <![CDATA[Particle size D50 (μm)]]> 5.1 4.8 Al (ppm) 20.98 12.12 Co (ppm) 5.02 0.62 Cr (ppm) 22.12 3.39 Cu (ppm) 5.56 3.21 Ca (ppm) 8.32 6.01 Zn (ppm) 25.60 19.14 Mg (ppm) 37.56 32.56 S (ppm) 54.13 48.35 Button charge performance (mAh / g) 148.60 150.30

[0073] Key indicator testing methods:

[0074] In the iron-phosphorus ratio test method, the iron content is determined by chemical titration, and the phosphorus content is determined by gravimetric method. The elemental content test uses inductively coupled plasma atomic emission spectrometry (ICP-AES). Its working principle is to analyze the characteristic spectral lines emitted by the analyte atoms when they return to the ground state from the excited state, thereby qualitatively and quantitatively analyzing trace metal elements.

Claims

1. A method for rapid preparation of battery-grade iron phosphate using microwave heating, characterized in that, The main preparation steps are as follows: (1) Add iron powder to phosphoric acid solution, and adjust the pH after the iron powder dissolves; (2) Filter the reaction solution from step (1), collect the filtrate and keep it at a constant temperature, and add it to the batch reactor at the same time as the oxidant to carry out the oxidation reaction; the oxidant is selected from any one of hydrogen peroxide, sodium peroxide and sodium persulfate. (3) The reaction slurry obtained in step (2) is pumped into a microwave tubular reactor for reaction. In the microwave heating reaction zone of the microwave tubular reactor, the material in the microwave tubular reactor is heated to 80~90 ℃ in the microwave heating section and kept warm in the microwave heat preservation section for 5~30 min. The working frequency in the microwave heating section of the microwave tubular reactor is 5000~10000 MHz and the working power is 30~70 kW. The working frequency in the microwave heat preservation section of the microwave tubular reactor is 1000-5000 MHz and the working power is 10~30 kW. The reaction process adopts a continuous feeding and discharging method, with a total feeding rate of 1-10 L / min and a total discharging rate of 1-8 L / min. (4) The product obtained in step (3) is filtered and washed, and the washed filter cake is dried by microwave to obtain hydrated ferric phosphate; the filtrate and the water washing filtrate are all returned to step (1) for recycling, the filter cake is washed until the conductivity is as low as 5~10mS / cm, and pressed until the moisture content is as low as 60% or less. (5) The aqueous ferric phosphate obtained in step (4) is ball-milled and then calcined to obtain battery-grade anhydrous ferric phosphate.

2. The method for rapid preparation of battery-grade iron phosphate by microwave heating according to claim 1, characterized in that, The iron powder mentioned in step (1) has an iron content of more than 99.0% and a particle size between 200 and 500 mesh; the phosphoric acid is food-grade phosphoric acid with a phosphorus pentoxide content of more than 85%.

3. The method for rapid preparation of battery-grade iron phosphate by microwave heating according to claim 1, characterized in that, In step (1), the reaction temperature of the iron powder and phosphoric acid solution is controlled at 50~60 ℃, and the molar ratio of iron powder and phosphoric acid is controlled at (0.9~1.5):

1.

4. The method for rapid preparation of battery-grade iron phosphate by microwave heating according to claim 1, characterized in that, Fe in the filtrate collected in step (2) 2+ The molar ratio of feed to oxidant is (0.4~1):1, and the stirring rate is controlled at 500~800 r / min during the reaction.

5. The method for rapid preparation of battery-grade iron phosphate by microwave heating according to claim 1, characterized in that, In step (2), steam, circulating hot water, or heat transfer oil are used for heating, and the temperature is kept constant within the range of 70~80℃.

6. The method for rapid preparation of battery-grade iron phosphate by microwave heating according to claim 1, characterized in that, The filter cake after pressing in step (4) is conveyed to the microwave drying reaction chamber by a conveyor belt. The temperature of the microwave drying reaction chamber is controlled at 120~150 ℃. In step (5), the calcination temperature is set to 450~700 ℃ and the calcination time is 3~5 h.

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