Iron phosphate dihydrate slurry, iron phosphate particles and preparation method

Abstract

The invention discloses iron phosphate dihydrate slurry, iron phosphate particles and a preparation method. The preparation method of the iron phosphate dihydrate slurry comprises the following steps: respectively flowing a ferrous dihydrogen phosphate solution and an oxidizing agent into a mixing cavity of a tubular reactor from a first feeding channel and a second feeding channel of the tubular reactor; the feeding flow ratio of the ferrous dihydrogen phosphate solution to the oxidizing agent is (30-1): 1; the feeding flow of the ferrous dihydrogen phosphate solution is 200-4000 mL / min, and the inner diameter ratio of the first feeding channel to the mixing cavity is (25-56): 175; and the inner diameter ratio of the second feeding channel to the mixing cavity is (75-546): 1750. The superfine iron phosphate particles with controllable and uniform size are prepared by the preparation method of the iron phosphate particles, and the lithium iron phosphate positive electrode material prepared from the superfine iron phosphate particles has excellent electrochemical performance.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to ferric phosphate dihydrate slurry, ferric phosphate particles and a preparation method. Background Art

[0002] Since Goodenough et al. first proposed the intercalated lithium polyanion compound LiMPO4 (M = Fe, Co, Ni, Mn) in 1997, lithium iron phosphate (LiFePO4) has been widely used in the new energy vehicle industry, energy storage market, uninterruptible power supply and power tool fields due to its advantages such as low raw material cost, environmental friendliness, stable structure, stable discharge platform, high specific capacity (170mAh / g), good thermal stability and outstanding cycle performance. The market prospect is very broad.

[0003] Currently, lithium iron phosphate has been widely promoted and applied, but research on its performance improvement, quality improvement and cost reduction has been ongoing. The main methods for industrially synthesizing lithium iron phosphate are: ferrous oxalate process, iron red process, full wet process, iron phosphate process, etc.

[0004] The ferrous oxalate process was the most widely used in the early days. Its main advantages are simple process and easy industrialization. The process is to grind ferrous oxalate, diammonium hydrogen phosphate and lithium carbonate in proportion and mix them evenly, and then calcine them at high temperature under the protection of inert gas to obtain lithium iron phosphate material. The materials prepared by this process have poor consistency and the process requires multiple calcinations. The synthesis cycle is long and the energy consumption is high. During the pre-burning process, waste gas will be discharged to pollute the environment, and the environmental pressure is relatively high. When the ferrous oxalate method is used to prepare LiFePO4 positive electrode materials, the ferrous oxalate precursor has a great influence on the structure and electrochemistry of its product. Since the preparation cost of ferrous oxalate is relatively high, the cost of lithium iron phosphate positive electrode materials prepared by this process is relatively high.

[0005] The iron red process uses iron oxide and lithium dihydrogen phosphate as raw materials, grinds and mixes with a carbon source, and prepares lithium iron phosphate positive electrode materials through a carbon thermal reduction method. The iron red process is relatively environmentally friendly, has abundant raw material resources, and is inexpensive, but the cost of lithium dihydrogen phosphate raw materials is high and not very stable. The particle size of lithium iron phosphate prepared by the iron red process is difficult to control, the product morphology is uneven, and the electrochemical performance is poor.

[0006] The full wet process (hydrothermal or solvent thermal) refers to a process in which ferrous sulfate, lithium hydroxide and phosphoric acid are dissolved in water or other solvents as reaction solvents in a high-temperature and high-pressure reactor to synthesize lithium iron phosphate under hydrothermal or solvent thermal conditions. Its advantages are: the synthesized material has good rate performance, small and uniform particle size, and uniform phase, but this reaction requires high-temperature and high-pressure equipment, which is costly and difficult to promote industrially.

[0007] The iron phosphate process uses iron phosphate as a precursor, evenly mixes it with a lithium source and a carbon source, and then undergoes a high-temperature carbon thermal reduction reaction to synthesize lithium iron phosphate positive electrode materials. The process has loose reaction conditions and is simple to operate. It can also achieve precise control of the target product by regulating the morphology, structure, and composition of the iron phosphate precursor. Its advantages have been gradually recognized.

[0008] There are few reports on the relevant process research of the iron method for producing precursor iron phosphate, especially the continuous process, which can simplify the process flow, ensure product consistency and reduce the preparation cost. CN114644327A discloses a method for preparing intermittent iron phosphate, which uses ferrous dihydrogen phosphate as raw material and performs oxidation precipitation reaction with hydrogen peroxide in a reactor. However, due to the fast reaction rate of the iron method, high requirements for the control accuracy of mass transfer, heat transfer and reaction conditions are required, and it is difficult to synthesize iron phosphate with stable quality and controllable particle size and morphology through traditional kettle reaction. CN116534824A discloses a method for preparing iron phosphate by a continuous oxidation process, in which ferrous dihydrogen phosphate is continuously oxidized and overflowed in a multi-grid oxidation tank, but this method still has a large reactant concentration gradient and temperature gradient and a static dead angle of the reaction, and the nucleation and growth of the reactant cannot be accurately controlled, thereby affecting the particle size, morphology, elemental composition and roasting structure of the iron phosphate product. CN116443834A discloses a method for continuously synthesizing ferric phosphate using a microreactor. A ferrous dihydrogen phosphate solution synthesized by an iron method is placed in a dynamic environment microreactor to react with an oxidant to obtain a product slurry. During this period, disturbance sources such as stirring, shaking, and ultrasound are introduced to ensure the strengthening effect of the microchannel on the precipitation reaction and the smooth transportation of solid particles in the channel. This process can reduce the particle size of anhydrous ferric phosphate after roasting, but this method is difficult to manufacture equipment and is not easy to scale up for production. It also requires the introduction of a disturbance source, which increases the complexity of the process. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of the prior art in that the equipment for preparing iron phosphate particles is difficult to manufacture, it is not easy to scale up production, the preparation method is complicated, the iron phosphate particles have a large particle size, and the electrochemical performance is poor, and a dihydrate iron phosphate slurry, iron phosphate particles and a preparation method are provided. The preparation method of the dihydrate iron phosphate slurry provided by the present invention can continuously discharge the generated dihydrate iron phosphate slurry in a tubular reactor, so that the particles are not easy to block the outlet. The preparation method of the iron phosphate particles provided by the present invention can control the nucleation rate of the iron phosphate particles by controlling the inlet temperature and the inlet flow rate of the tubular reactor; the growth rate of the iron phosphate particles can be controlled by controlling the reaction temperature and the stirring rate in the aging kettle; and the size-controllable and uniform ultrafine iron phosphate particles can be obtained by controlling the inlet temperature and the inlet flow rate of the tubular reactor and the reaction temperature and the stirring rate in the aging kettle.

[0010] The technical problem to be solved by the present invention is achieved through the following technical solutions.

[0011] The present invention provides a method for preparing ferric phosphate dihydrate slurry, which comprises the following steps:

[0012] The ferrous dihydrogen phosphate solution and the oxidant flow into the mixing chamber of the tubular reactor from the first feed channel and the second feed channel of the tubular reactor respectively;

[0013] Wherein, the feed flow ratio of the ferrous dihydrogen phosphate solution to the oxidant is (30-1):1; the feed flow rate of the ferrous dihydrogen phosphate solution is 200-4000mL / min;

[0014] Among them, the inner diameter ratio of the first feed channel and the mixing chamber is (25-56):175; the inner diameter ratio of the second feed channel and the mixing chamber is (75-546):1750.

[0015] In the present invention, preferably, the first feed channel and the second feed channel are respectively arranged on both sides close to one end of the mixing chamber along a direction perpendicular to the central axis of the mixing chamber.

[0016] In the present invention, preferably, a discharge port is provided at the other end of the mixing chamber away from the first feed channel and the second feed channel.

[0017] In the present invention, preferably, the inner diameter of the first feed channel is greater than the inner diameter of the second feed channel.

[0018] In the present invention, preferably, the mixing chamber is cylindrical. More preferably, when the mixing chamber is cylindrical, the inner diameter of the mixing chamber may be 7-25 mm. More preferably, when the mixing chamber is cylindrical, the height of the mixing chamber may be 15-50 mm.

[0019] In the present invention, preferably, the volume of the mixing chamber is 500-25000mm 3 .

[0020] In the present invention, preferably, the first feed channel is used to introduce ferrous dihydrogen phosphate solution. Preferably, the second feed channel is used to introduce an oxidant. The ferrous dihydrogen phosphate solution and the oxidant flow back and disturb in the mixing chamber.

[0021] In the present invention, preferably, the tubular reactor includes a heating element, and more preferably, the heating element is arranged around the outside of the first feed channel. More preferably, when the tubular reactor includes a heating element, by adjusting the heating element of the first feed channel, the temperature of the ferrous dihydrogen phosphate solution when entering the mixing chamber of the reactor is 50-95°C, preferably 60-90°C.

[0022] In the present invention, preferably, the tubular reactor is a microchannel reactor.

[0023] In the present invention, the preparation method of the ferrous dihydrogen phosphate solution comprises: mixing an iron source and a phosphoric acid solution, performing an oxidation-reduction reaction, and filtering to obtain the ferrous dihydrogen phosphate solution.

[0024] The container for mixing the iron source and the phosphoric acid solution may be an iron-making kettle.

[0025] The iron source may be any form of iron-containing metal solid, preferably one or more of iron blocks, iron bars, iron rods and iron powder.

[0026] Wherein, the purity of the iron source can be above 99.5%.

[0027] The concentration of the phosphoric acid solution may be 12%-35%, preferably 20%-30%, such as 25%, where the percentage is the mass percentage of the phosphoric acid in the phosphoric acid solution.

[0028] The molar ratio of the iron source to the phosphorus source in the phosphoric acid solution (Fe:P) may be 1:(2.2-3.5), preferably 1:(2.5-3.5), for example 1:3. The molar ratio of the iron source to the phosphorus source in the phosphoric acid solution is controlled to ensure sufficient dissolution of the iron source.

[0029] The temperature of the redox reaction may be 50-95°C, preferably 60-90°C, such as 60°C.

[0030] The time of the redox reaction may be 1-10 h, preferably 1-2 h.

[0031] In the present invention, the oxidant may be one or more of sodium chlorate, hydrogen peroxide, potassium chlorate, and sodium chlorate, preferably hydrogen peroxide.

[0032] In the present invention, the oxidant may be an aqueous solution. Preferably, the concentration of the aqueous solution is 5%-35%, preferably 10%-30%, where the percentage is the mass percentage of the oxidant in the aqueous solution of the oxidant.

[0033] In the present invention, the flow rate ratio of the ferrous dihydrogen phosphate solution to the oxidant feed can be (20-1):1, for example, 13.5:1.

[0034] In the present invention, the feed flow rate of the ferrous dihydrogen phosphate solution may be 400-4000 mL / min, such as 500 mL / min, 2000 mL / min or 4000 mL / min.

[0035] The present invention also provides an aging method for ferric phosphate dihydrate slurry, which comprises the following steps:

[0036] S1. Using the above-mentioned method for preparing ferric phosphate dihydrate slurry, prepare ferric phosphate dihydrate slurry;

[0037] S2. Passing the ferric phosphate dihydrate slurry into an aging kettle for aging to obtain aged ferric phosphate dihydrate slurry.

[0038] In the present invention, the aging temperature may be 50-98°C, preferably 60-95°C, such as 60°C, 75°C or 90°C.

[0039] In the present invention, the aging time may be 10 min-12 h, preferably 30 min-4 h, such as 1 h.

[0040] In the present invention, the aging process may be accompanied by stirring.

[0041] The stirring speed may be 10-1500 rpm, preferably 50-900 rpm, such as 300 rpm, 600 rpm or 900 rpm.

[0042] The present invention also provides a method 1 for preparing iron phosphate particles, which comprises the following steps:

[0043] S1. Using the above-mentioned method for preparing ferric phosphate dihydrate slurry, prepare ferric phosphate dihydrate slurry;

[0044] S2, aging the ferrous phosphate dihydrate material using the aforementioned aging method for ferrous phosphate dihydrate slurry to obtain aged ferrous phosphate dihydrate slurry;

[0045] S3. The aged ferric phosphate dihydrate slurry is post-treated to obtain the ferric phosphate particles.

[0046] In the present invention, the post-treatment may include solid-liquid separation, water washing, drying and roasting.

[0047] Wherein, the target object of the water washing may be the filter cake after the solid-liquid separation.

[0048] The water washing may be performed until the conductivity of the ferric phosphate dihydrate slurry is no more than 0.5 μs / cm.

[0049] Wherein, the water washing can be performed until the ferric phosphate dihydrate slurry does not contain water-soluble impurities;

[0050] The drying temperature may be 100-160°C, preferably 105-140°C, such as 120°C.

[0051] The drying time may be 30-120 min, preferably 30-90 min, for example 60 min.

[0052] The calcination temperature may be 480-800°C, preferably 500-650°C, such as 600°C.

[0053] The calcination time may be 2-6 hours, preferably 2-4 hours, for example 2 hours.

[0054] The present invention also provides a method 2 for preparing iron phosphate particles, which comprises the following steps:

[0055] The iron phosphate particles are obtained by drying and calcining the iron phosphate dihydrate slurry with an electrical conductivity of no more than 0.5 us / cm.

[0056] In the present invention, preferably, the ferric phosphate dihydrate slurry with an electrical conductivity of no more than 0.5 us / cm is prepared by the above-mentioned method 1 for preparing ferric phosphate particles.

[0057] In the present invention, the drying temperature may be 100-160°C, preferably 105-140°C, for example 120°C.

[0058] In the present invention, the drying time may be 30-120 min, preferably 30-90 min, for example 60 min.

[0059] In the present invention, the calcination temperature may be 480-800°C, preferably 500-650°C, such as 600°C.

[0060] In the present invention, the calcination time may be 2-6 hours, preferably 2-4 hours, for example 2 hours.

[0061] In the present invention, preferably, the ferric phosphate dihydrate slurry does not contain water-soluble impurities.

[0062] The present invention also provides an iron phosphate particle, wherein the iron phosphate particle is prepared by the above-mentioned method 1 for preparing the iron phosphate particle or the above-mentioned method 2 for preparing the iron phosphate particle.

[0063] The present invention also provides a ferric phosphate dihydrate slurry, wherein the conductivity of the ferric phosphate dihydrate slurry is not greater than 0.5 us / cm.

[0064] In the present invention, preferably, the ferric phosphate dihydrate slurry with an electrical conductivity of no more than 0.5 us / cm is prepared by the above-mentioned method 1 for preparing ferric phosphate particles.

[0065] The invention also provides an iron phosphate particle, the particle size of which is as small as 1 μm to 7 μm.

[0066] The present invention also provides a method for preparing lithium iron phosphate, wherein the raw materials include the above-mentioned iron phosphate particles, a carbon source and a lithium source.

[0067] In the present invention, the carbon source may be a conventional carbon source in the art, such as glucose.

[0068] In the present invention, the lithium source may be a conventional lithium source in the art, such as lithium carbonate.

[0069] In the present invention, preferably, the preparation method of lithium iron phosphate comprises the following steps: mixing, sand-milling, drying, granulating and thermally reducing the raw materials, wherein the drying is preferably carried out by spray drying.

[0070] In one embodiment of the present invention, the method for preparing lithium iron phosphate comprises the following steps:

[0071] The iron phosphate particles, glucose and lithium carbonate are mixed and poured into deionized water, and sand-milled by a horizontal sand mill for 40 minutes. The obtained slurry is dried and granulated by a spray drying method, and is kept at 400°C for 2 hours in a box-type furnace under a flowing nitrogen atmosphere, and then heated to 730°C for 4 hours to thermally reduce the carbon source to prepare the lithium iron phosphate.

[0072] The present invention also provides a lithium iron phosphate, which is prepared by the above-mentioned preparation method of lithium iron phosphate.

[0073] The present invention also provides a method for preparing positive electrode slurry, the raw materials of which include the lithium iron phosphate, conductive agent, binder and solvent as described above.

[0074] In the present invention, the conductive agent may be a conventional conductive agent in the art, such as conductive carbon black.

[0075] In the present invention, the binder may be a conventional binder in the art, such as polyvinylidene fluoride (PVDF).

[0076] In the present invention, the binder may be a conventional solvent in the art, such as N-methylpyrrolidine.

[0077] In the present invention, preferably, the method for preparing the positive electrode slurry comprises mixing the raw materials.

[0078] In the present invention, preferably, the mass ratio of the lithium iron phosphate, the conductive agent, and the binder is 8:1:1.

[0079] In one embodiment of the present invention, the method for preparing the positive electrode slurry comprises the following steps: mixing lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1, and adding N-methylpyrrolidone to prepare the positive electrode slurry.

[0080] The present invention also provides a positive electrode slurry, which is prepared by the positive electrode slurry preparation method described above.

[0081] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0082] The reagents and raw materials used in the present invention are commercially available.

[0083] The positive and progressive effects of the present invention are:

[0084] (1) The method for preparing ferric phosphate dihydrate slurry of the present invention can continuously discharge the generated ferric phosphate dihydrate slurry in a tubular reactor, so that particles are not easy to block the outlet, and the complexity of the equipment and process is reduced compared with the scheme of introducing disturbances such as stirring, shaking, and ultrasound.

[0085] (2) The method for preparing iron phosphate particles of the present invention can control the nucleation rate of iron phosphate particles by controlling the inlet temperature and inlet flow rate of the tubular reactor; can control the growth rate of iron phosphate particles by controlling the reaction temperature and stirring rate in the aging kettle; can obtain size-controllable and uniform ultrafine iron phosphate particles by controlling the inlet temperature and inlet flow rate of the tubular reactor and controlling the reaction temperature and stirring rate in the aging kettle.

[0086] (3) The iron phosphate particles provided by the present invention are ultrafine iron phosphate particles with a particle size as small as 1 μm to 7 μm.

[0087] (4) The ferric phosphate dihydrate slurry provided by the present invention contains low water-soluble impurities, and further has an electrical conductivity of no more than 0.5 μs / cm.

[0088] (5) The iron phosphate provided by the present invention is of high quality, and the lithium iron phosphate positive electrode material obtained through subsequent processing has excellent electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 Schematic diagram of the structure of the microchannel reactor of Example 1.

[0090] Figure 2 This is a vertical cross-sectional view of the first feed channel of the microchannel reactor of Example 1.

[0091] Figure 3 This is a flow chart of the method for preparing iron phosphate particles in Example 2.

[0092] Description of reference numerals:

[0093] A first feed channel 1 , a second feed channel 2 , a mixing chamber 3 , a discharge channel 4 , a discharge port 5 , a heat medium outlet 6 , a heat medium inlet 7 , and a heat medium channel 8 . DETAILED DESCRIPTION

[0094] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0095] Test method for conductivity of ferric phosphate dihydrate slurry:

[0096] Use a beaker to take the ferrous phosphate dihydrate slurry, insert the Leici DDSJ-318T conductivity meter under the liquid surface of the ferrous phosphate dihydrate slurry for testing and reading.

[0097] Example 1

[0098] This embodiment provides a microchannel reactor, and its structural schematic diagram is as follows Figure 1 As shown, it includes a first feed channel 1 , a second feed channel 2 , a mixing chamber 3 , a discharge channel 4 , and a discharge port 5 .

[0099] The first feed channel 1 and the second feed channel 2 are respectively arranged on both sides of one end of the mixing chamber 3 in a direction perpendicular to the central axis of the mixing chamber 3, and a discharge port 5 is arranged at the other end of the mixing chamber 3 away from the first feed channel 1 and the second feed channel 2. The inner diameter of the first feed channel 1 is greater than the inner diameter of the second feed channel 2.

[0100] The inner diameter of the first feed channel 1 is 3 mm and the length is 30 mm; the inner diameter of the second feed channel 2 is 0.9 mm and the length is 30 mm; the inner diameter of the discharge channel 4 is 3.9 mm and the length is 30 mm; the volume of the mixing chamber 3 is 4618 mm 3 , inner diameter is 14mm and height is 30mm.

[0101] The first feed channel 1, the second feed channel 2, the discharge channel 4 and the mixing chamber 3 are all cylindrical.

[0102] One end of the mixing chamber 3 close to the first feed channel 1 and the second feed channel 2 is arc-shaped and closed.

[0103] The discharge port 5 is in the shape of an inverted frustum, and is used to connect to the discharge channel 4. The inverted frustum is in a structure that is wide at the top and narrow at the bottom.

[0104] The microchannel reactor includes a heating element, which is arranged outside the first feed channel 1. The vertical cross-sectional view of the first feed channel 1 of the microchannel reactor is as follows: Figure 2 As shown, the heating element includes a heat medium channel 8 , and the heat medium channel 8 includes a heat medium inlet 7 and a heat medium outlet 6 . The heating element is used to provide heat to the material in the first feed channel 1 .

[0105] The material of the microchannel reactor is S2205 stainless steel.

[0106] This embodiment also provides a reaction device, which includes the above microchannel reactor and an aging kettle, wherein the discharge channel 4 of the microchannel reactor is connected to the aging kettle, wherein the aging kettle can be used for heating and stirring.

[0107] Example 2

[0108] A kind of iron phosphate particles, the flow chart of the preparation method is shown in Figure 3 , using the reaction device of Example 1, the preparation method comprises the following steps:

[0109] (1) Preparation of ferrous dihydrogen phosphate solution: Place an iron block with a purity of more than 99.5% in an iron-making kettle, and add a dilute phosphoric acid solution with a concentration of 25%. The molar ratio of the iron source to the phosphorus source is 1:3. The temperature during the reaction is ensured to be 60° C. The reaction time is 1-2 hours. Filter the remaining residue of the reaction to make the solution clear and transparent to obtain a ferrous dihydrogen phosphate solution.

[0110] (2) Preparation of ferrous phosphate dihydrate slurry: The inlet temperature of the ferrous dihydrogen phosphate solution was set to 90° C., the feed flow ratio of the ferrous dihydrogen phosphate solution to the 30% hydrogen peroxide solution was 13.5:1, and the feed flow rate of the ferrous dihydrogen phosphate solution was set to 4000 mL / min to obtain ferrous phosphate dihydrate slurry.

[0111] (3) Aging of ferric phosphate dihydrate slurry: The ferric phosphate dihydrate slurry was transferred to an aging kettle at an aging temperature of 90° C., a stirring rate of 900 rpm, and an aging time of 1 h.

[0112] (4) Water washing: The ferrous phosphate dihydrate slurry is subjected to solid-liquid separation, and the filter cake is washed with water. The end point of the water washing is that the conductivity of the ferrous phosphate dihydrate slurry is not greater than 0.5 μs / cm.

[0113] (5) Drying and calcining: The obtained product was dried at 120° C. for 60 min, and then heated to 600° C. for calcination for 2 h to obtain iron phosphate particles.

[0114] Example 3

[0115] A kind of iron phosphate particles, which differ from Example 1 only in that, in step (2), the feed flow rate of ferrous dihydrogen phosphate solution is set to 2000 mL / min, and the other steps and conditions are the same as those in Example 2.

[0116] Example 4

[0117] A kind of iron phosphate particles, which differ from Example 1 only in that, in step (2), the feed flow rate of ferrous dihydrogen phosphate solution is set to 500 mL / min, and the other steps and conditions are the same as those in Example 2.

[0118] Example 5

[0119] An iron phosphate particle, which is different from Example 1 only in that in step (3), the aging temperature is 75° C., and the other steps and conditions are the same as Example 2.

[0120] Example 6

[0121] An iron phosphate particle, which is different from Example 1 only in that in step (3), the aging temperature is 60° C., and the other steps and conditions are the same as those in Example 2.

[0122] Example 7

[0123] A kind of iron phosphate particles, which is different from Example 1 only in that in step (3), the stirring rate is 600 rpm, and the other steps and conditions are the same as those in Example 2.

[0124] Example 8

[0125] A kind of iron phosphate particles, which is different from Example 1 only in that in step (3), the stirring rate is 300 rpm, and the other steps and conditions are the same as Example 2.

[0126] Comparative Example 1

[0127] A method for preparing iron phosphate particles comprises the following steps:

[0128] (1) Preparation of ferrous dihydrogen phosphate solution: Place an iron block with a purity of more than 99.5% in an iron-making kettle, and add a dilute phosphoric acid solution with a concentration of 25%, with the molar ratio of the iron source to the phosphorus source being 1:3. Ensure that the temperature during the reaction is 60° C. and the reaction time is 1-2 hours. Filter the remaining residue of the reaction to make the solution clear and transparent to obtain a ferrous dihydrogen phosphate solution.

[0129] (2) Preparation and aging of ferrous phosphate dihydrate slurry: Ferrous dihydrogen phosphate solution and 30% hydrogen peroxide solution were directly introduced into the aging kettle, and the feed flow ratio of ferrous dihydrogen phosphate solution to oxidant was 13.5:1. The temperature in the aging kettle was ensured to be 90°C, the stirring rate was 900 rpm, and the reaction time was 1 h.

[0130] (3) Water washing: The ferrous phosphate dihydrate slurry is subjected to solid-liquid separation, and the filter cake is subjected to water treatment. The end point of the water washing is that the conductivity of the ferrous phosphate dihydrate slurry is not greater than 0.5 us / cm.

[0131] (4) Drying and calcining: The obtained product was dried at 120° C. for 60 min, and then heated to 600° C. for calcination for 2 h to obtain iron phosphate particles.

[0132] Comparative Example 2

[0133] An iron phosphate particle, which differs from Comparative Example 1 only in that, in step (3), the aging temperature is 75° C., and the other steps and conditions are the same as those in Comparative Example 1.

[0134] Comparative Example 3

[0135] An iron phosphate particle, which differs from Comparative Example 1 only in that, in step (3), the aging temperature is 60° C., and the other steps and conditions are the same as those in Comparative Example 1.

[0136] Comparative Example 4

[0137] A kind of iron phosphate particles, which is different from comparative example 1 only in that, in step (3), the stirring rate is 600 rpm, and the other steps and conditions are the same as those in comparative example 1.

[0138] Comparative Example 5

[0139] A kind of iron phosphate particles, which is different from comparative example 1 only in that, in step (3), the stirring rate is 300 rpm, and the other steps and conditions are the same as those in comparative example 1.

[0140] Effect Example 1

[0141] (1) The particle size D50 of the iron phosphate particles obtained in Examples 2-8 and Comparative Examples 1-5 was measured using a Malvern 3000 laser particle size analyzer. The measurement results are shown in Table 1.

[0142] (2) The iron-phosphorus molar ratio of the iron phosphate particles obtained in Examples 2-8 and Comparative Examples 1-5 was measured using an inductively coupled plasma spectrometer. The measurement results are shown in Table 1.

[0143] (3) The iron phosphate particles obtained in Examples 2-8 and Comparative Examples 1-5 were mixed with glucose and lithium carbonate and poured into deionized water. The mixture was sand-milled in a horizontal sand mill for 40 minutes. The obtained slurry was dried and granulated by spray drying. The mixture was kept at 400°C for 2 hours in a box furnace under a flowing nitrogen atmosphere and then heated to 730°C for 4 hours. The lithium iron phosphate (LiFePO4) prepared by the carbon thermal reduction method was mixed with the above powders in a mass ratio of LiFePO4: conductive carbon black: PVDF = 8:1:1. N-methylpyrrolidone was added to prepare a positive electrode slurry, which was evenly coated on a carbon-coated aluminum foil. After vacuum drying, the mixture was taken out and rolled and punched into an area of ​​2.01 cm 2 The pole piece has a surface density of 13 mg / cm 2Button cells were assembled in a glove box (high-purity Ar atmosphere), the electrolyte used was a commercial product (SS-SHRG004, Dongguan Shanshan Battery Materials Co., Ltd.), the negative electrode used a metal lithium sheet, and the separator used a Celgard 2400PE film. The button cells were subjected to constant current charge and discharge cycle tests at 25°C and 0.1C, with a charge and discharge voltage of 2.0 to 3.7V, and the first coulomb efficiency was tested; the test results are shown in Table 1.

[0144] Table 1

[0145]

[0146] As can be seen from Table 1, the iron-phosphorus molar ratio of the iron phosphate particles obtained in Examples 2-8 and Comparative Examples 1-5 all meet the industry standard of an iron-phosphorus ratio of 0.96 to 1.02.

[0147] The data of Example 2, Example 3, and Example 4 show that the particle size of the iron phosphate particles decreases with the increase of the feed flow rate. This is because with the increase of the feed flow rate, the disturbance of the solution in the reaction mixing chamber increases, and the microscopic mixing degree increases, thereby improving the reaction effect and the nucleation rate, which is conducive to promoting the reduction of the particle size of the iron phosphate particles.

[0148] The data of Example 2, Example 5, and Example 6, and the data of Comparative Example 1, Comparative Example 2, and Comparative Example 3 show that the particle size of the iron phosphate particles decreases as the aging temperature is increased. This is because increasing the aging temperature is conducive to further nucleation of crystals and reduces the particle size of the iron phosphate particles.

[0149] The data of Example 2, Example 7, and Example 8, and the data of Comparative Example 1, Comparative Example 4, and Comparative Example 5 show that as the stirring rate is increased from 300rpm to 600rpm and then to 900rpm, the particle size of the obtained iron phosphate particles first increases and then decreases. This is because increasing the stirring rate first accelerates the mutual collision between the iron phosphate particles and accelerates the agglomeration process, so the particle size first increases with the increase of the stirring rate. As the stirring rate further increases, the turbine shear force in the flow field also increases, and the probability of particle breakage increases, so the agglomerate particle size will not increase indefinitely, so the particle size decreases with the increase of the stirring rate. Therefore, the particle size of the iron phosphate particles at a stirring rate of 900rpm under the same conditions is smaller than the particle size of the iron phosphate particles at a stirring rate of 600rpm.

[0150] The data of Example 2 and Comparative Example 1, Example 5 and Comparative Example 2, Example 6 and Comparative Example 3, Example 7 and Comparative Example 4, and Example 8 and Comparative Example 5 show that the particle size of the iron phosphate particles is greatly reduced to 1 μm to 7 μm by using a microchannel reactor. This is because the use of a microchannel reactor can increase the nucleation rate and greatly reduce the particle size of the iron phosphate particles. In addition, the possibility of blockage is reduced. At the same time, the ferrous dihydrogen phosphate solution and the oxidant achieve spontaneous backflow and disturbance in the mixing chamber, and the generated dihydrate iron phosphate slurry is continuously discharged in the microchannel reactor, which further reduces the risk of blockage and realizes continuous and controllable production of ultrafine iron phosphate.

[0151] The iron phosphate obtained by the above method has a small particle size (D50). The lithium iron phosphate positive electrode material prepared therefrom, when used in a battery, has an initial charge and discharge specific capacity higher than 153 mAh / g, and an initial coulombic efficiency higher than 98%, and has excellent electrochemical performance, indicating that the lithium iron phosphate prepared from the iron phosphate provided by the present invention has good electrical properties.

[0152] It should be understood that after reading the above content of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing ferric phosphate dihydrate slurry, characterized in that: It includes the following steps: The ferrous dihydrogen phosphate solution and the oxidant flow into the mixing chamber of the tubular reactor from the first feed channel and the second feed channel of the tubular reactor respectively; Wherein, the feed flow ratio of the ferrous dihydrogen phosphate solution to the oxidant is (30-1):1; the feed flow rate of the ferrous dihydrogen phosphate solution is 200-4000mL / min; Among them, the inner diameter ratio of the first feed channel and the mixing chamber is (25-56):175; the inner diameter ratio of the second feed channel and the mixing chamber is (75-546):1750.

2. The method for preparing ferric phosphate dihydrate slurry according to claim 1, characterized in that: The method for preparing the ferric phosphate dihydrate slurry satisfies one or more of the following conditions: (1) The first feed channel and the second feed channel are respectively arranged on both sides of one end of the mixing chamber in a direction perpendicular to the central axis of the mixing chamber; (2) a discharge port is provided at the other end of the mixing chamber away from the first feed channel and the second feed channel; (3) The inner diameter of the first feed channel is larger than the inner diameter of the second feed channel; (4) The mixing chamber is cylindrical; (5) The volume of the mixing chamber is 500-25000mm 3 ; (6) The first feed channel is used to introduce ferrous dihydrogen phosphate solution; (7) The second feed channel is used to introduce an oxidant; (8) The tubular reactor includes a heating element; (9) The tubular reactor is a microchannel reactor; (10) The method for preparing the ferrous dihydrogen phosphate solution comprises: mixing an iron source and a phosphoric acid solution, performing an oxidation-reduction reaction, and filtering to obtain the ferrous dihydrogen phosphate solution; (11) The oxidant is an aqueous solution; (12) The feed flow ratio of the ferrous dihydrogen phosphate solution to the oxidant is (20-1):1, for example, 13.5:1; (13) the feed rate of the ferrous dihydrogen phosphate solution is 400-4000 mL / min, for example, 500 mL / min, 2000 mL / min or 4000 mL / min; and, (14) The oxidant is one or more of sodium chlorate, hydrogen peroxide, potassium chlorate, and sodium chlorate, preferably hydrogen peroxide; Preferably, the preparation method of the ferric phosphate dihydrate slurry meets one or more of the following conditions: (1) When the mixing chamber is cylindrical, the inner diameter of the mixing chamber is 7-25 mm; (2) When the mixing chamber is cylindrical, the height of the mixing chamber is 15-50 mm; (3) The heating element is arranged on the outer side of the first feed channel; (4) When the tubular reactor includes a heating element, the temperature of the ferrous dihydrogen phosphate solution when entering the mixing chamber of the reactor is 50-95° C., preferably 60-90° C., by adjusting the heating element of the first feed channel; (5) The container for mixing the iron source and the phosphoric acid solution is an iron-making kettle; (6) The iron source is an iron-containing metal solid in any form, preferably one or more of an iron block, an iron bar, an iron rod and iron powder; (7) The purity of the iron source is above 99.5%; (8) The concentration of the phosphoric acid solution is 12%-35%, preferably 20%-30%, for example 25%, where the percentage is the mass percentage of the phosphoric acid in the phosphoric acid solution; (9) The molar ratio of the iron source to the phosphorus source in the phosphoric acid solution (Fe:P) is 1:(2.2-3.5), preferably 1:(2.5-3.5), for example 1:3; (10) The temperature of the redox reaction is 50-95°C, preferably 60-90°C, for example 60°C; (11) The oxidation-reduction reaction time is 1-10 hours, preferably 1-2 hours; and, (12) The concentration of the aqueous solution of the oxidant is 5%-35%, preferably 10%-30%, where the percentage is the mass percentage of the oxidant in the aqueous solution of the oxidant.

3. A method for aging ferric phosphate dihydrate slurry, characterized in that: It includes the following steps: S1. Prepare ferric phosphate dihydrate slurry by the method for preparing ferric phosphate dihydrate slurry according to claim 1 or claim 2; S2. Passing the ferric phosphate dihydrate slurry into an aging kettle for aging to obtain aged ferric phosphate dihydrate slurry.

4. The aging method of ferric phosphate dihydrate slurry according to claim 3, characterized in that: The aging method of the ferric phosphate dihydrate slurry satisfies one or more of the following conditions: (1) The aging temperature is 50-98°C, preferably 60-95°C, for example 60°C, 75°C or 90°C; (2) the aging time is 10 min-12 h, preferably 30 min-4 h, for example 1 h; and, (3) The aging process is accompanied by stirring; preferably, the stirring speed is 10-1500 rpm, preferably 50-900 rpm, such as 300 rpm, 600 rpm or 900 rpm.

5. A method for preparing iron phosphate particles 1, characterized in that: It includes the following steps: S1. Prepare ferric phosphate dihydrate slurry by the method for preparing ferric phosphate dihydrate slurry according to claim 1 or claim 2; S2. Aging the ferrous phosphate dihydrate material using the aging method for ferrous phosphate dihydrate slurry according to claim 3 or claim 4 to obtain aged ferrous phosphate dihydrate slurry; S3. The aged ferric phosphate dihydrate slurry is post-treated to obtain the ferric phosphate particles.

6. The method for preparing iron phosphate particles according to claim 5, characterized in that: The post-treatment includes solid-liquid separation, water washing, drying and roasting; Preferably, the preparation method 1 of the iron phosphate particles satisfies one or more of the following conditions: (1) The target object of the water washing is the filter cake after the solid-liquid separation; (2) washing with water until the conductivity of the ferric phosphate dihydrate slurry is no more than 0.5 μs / cm; (3) washing with water until the ferric phosphate dihydrate slurry does not contain water-soluble impurities; (4) The drying temperature is 100-160°C, preferably 105-140°C, for example 120°C; (5) The drying time is 30-120 min, preferably 30-90 min, for example 60 min; (6) the calcination temperature is 480-800°C, preferably 500-650°C, for example 600°C; and, (7) The calcination time is 2-6 hours, preferably 2-4 hours, for example 2 hours.

7. A method for preparing iron phosphate particles 2, characterized in that: It includes the following steps: The iron phosphate dihydrate slurry with an electrical conductivity of no more than 0.5 us / cm is dried and roasted to obtain the iron phosphate particles; Preferably, the preparation method 2 of the iron phosphate particles satisfies one or more of the following conditions: (1) The ferric phosphate dihydrate slurry with an electrical conductivity of no more than 0.5 us / cm is prepared by the method 1 for preparing the ferric phosphate particles according to claim 5 or claim 6; (2) The drying temperature is 100-160°C, preferably 105-140°C, for example 120°C; (3) The drying time is 30-120 min, preferably 30-90 min, for example 60 min; (4) the calcination temperature is 480-800°C, preferably 500-650°C, for example 600°C; and, (5) the calcination time is 2-6 hours, preferably 2-4 hours, for example 2 hours; and, (6) The ferric phosphate dihydrate slurry does not contain water-soluble impurities.

8. An iron phosphate particle, characterized in that: The iron phosphate particles are prepared by the preparation method 1 of the iron phosphate particles according to claim 5 or 6 or the preparation method 2 of the iron phosphate particles according to claim 7.

9. A ferric phosphate dihydrate slurry, characterized in that: The electrical conductivity of the ferric phosphate dihydrate slurry is not greater than 0.5 us / cm; Preferably, the ferric phosphate dihydrate slurry is prepared by the preparation method 1 of the iron phosphate particles as described in claim 5 or 6.

10. An iron phosphate particle, characterized in that: Its particle size is as small as 1μm to 7μm.

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