A method for the continuous production of nanoscale iron phosphate

Abstract

The application discloses a kind of preparation methods of continuous nanoscale iron phosphate, it is related to lithium battery positive electrode material preparation field.The method includes the following steps: step S101, configuration phosphorus source and iron source solution;Step S102, phosphorus source and iron source solution are continuously added in two reactors in series and finally obtained iron phosphate slurry;Two reactors in series are kettle type stirred reactor and tubular reactor in turn, reaction temperature is 70-98 DEG C, average residence time is 1-100 min;Step S103, iron phosphate slurry in step S102 is washed, filtered, dried, and battery-grade iron phosphate is obtained by calcining.The combination of two reactor types in series shortens the actual reaction time, and the consistent performance of the product is enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation of lithium battery positive electrode materials, and relates to a continuous preparation method of nanoscale iron phosphate. BACKGROUND

[0002] In the development process of lithium battery materials in recent years, lithium iron phosphate and ternary materials account for more than 80% of the market share. Compared with ternary materials, the advantages of lithium iron phosphate materials such as low cost, long cycle life, and green environmental protection gradually appear. Iron phosphate, as an important raw material of lithium iron phosphate, determines the physical and chemical parameters of lithium iron phosphate to a certain extent. The current market production method of iron phosphate is intermittent reaction, and the consistency of the product material has always been a difficult problem. The primary particles of the prepared and synthesized iron phosphate are relatively large (>200 nm), and the rate performance of the lithium iron phosphate is general. Therefore, a new preparation method of iron phosphate is urgently needed to meet the increasingly strict requirements of the market for products.

[0003] At present, the methods for continuously preparing nanoscale iron phosphate include micro-channel reaction method. For example, the patent application for invention with the publication number CN107473196A discloses a method for continuously producing battery-grade high-pressure density nanoscale iron phosphate. The method is aimed at obtaining iron phosphate product by passing iron phosphate slurry through a three-stage micro-channel reactor. However, in this method, the slurry viscosity is large when the slurry has not formed iron phosphate, and the micro-channel volume is small and easy to be blocked by solid particles, which is difficult to clean. In addition, the iron phosphate slurry itself is strongly acidic, and the corrosion of the equipment is very strong when the reaction temperature exceeds 110℃. Moreover, the processing cost of the micro-channel equipment is also expensive, which is not conducive to industrialization.

[0004] For another example, the patent application for invention with the publication number CN104555975A discloses a continuous preparation device and method for lithium iron phosphate. The method discloses a continuous preparation method of iron phosphate in which the material is sequentially passed through a material conveying system, a tubular reactor, and a kettle reactor. Although this method can realize continuous production, the mixing and stirring in the tubular reactor is general, and the material consistency is strong. However, when industrialized, the kettle reactor cannot be too small due to the demand for production, which leads to the fact that the stirring rate cannot be fast enough, the reaction between ions is not intense enough, and the crystal nucleus slowly accumulates to form larger primary particles. Therefore, this method cannot prepare nanoscale primary particles of iron phosphate. SUMMARY

[0005] 1. Problems to be solved

[0006] In order to solve the above problems, the application provides a continuous preparation method of nanoscale iron phosphate, which can reduce the equipment area and investment cost, and prepare nanoscale iron phosphate, so that the rate performance of prepared lithium iron phosphate is greatly improved.

[0007] 2. Technical scheme

[0008] In order to solve the above problems, the application adopts the following technical scheme:

[0009] The continuous preparation method of nanoscale iron phosphate provided by the application comprises the following steps:

[0010] Step S101, configure a phosphorus source solution and an iron source solution;

[0011] Step S102, continuously add the phosphorus source solution and the iron source solution into two reactors in series to react, and finally obtain an iron phosphate slurry; the two reactors in series are a kettle type stirring reactor and a tubular reactor in sequence, the reaction temperature of each reactor is 70-98 DEG C, and the average residence time is 1-100 min;

[0012] Step S103, wash, filter, dry and calcine the iron phosphate slurry in step S102 to obtain a battery-grade iron phosphate.

[0013] In a possible embodiment of the application, in step S101, the phosphorus source is one or more of sodium monohydrogen phosphate, sodium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate and ammonium phosphate.

[0014] In a possible embodiment of the application, in step S101, the iron source is one or more of iron sulfate, iron hydroxide and iron chloride.

[0015] In a possible embodiment of the application, the mass concentration of iron in the iron source solution is 10-100 g / L, and the mass concentration of phosphorus in the phosphorus source solution is 20-500 g / L.

[0016] In a possible embodiment of the application, in step S102, the molar ratio of the phosphorus source to the iron source in the continuous reaction feeding process is 1.01-2.0, and the molar ratio is preferably 1.02-1.50.

[0017] In a possible embodiment of the application, the average residence time of the kettle type stirring reactor is 10-100 min, and the average residence time of the tubular reactor is 1-20 min.

[0018] In a possible embodiment of the application, the stirring speed in the kettle type stirring reactor and the tubular reactor is 100-4500 r / min.

[0019] In a possible implementation of the present application, the stirring speed of the stirred tank reactor is 100-2000 r / min, and the stirring speed of the tubular reactor is 2000-4500 r / min.

[0020] In a possible implementation of the present application, in the step S103, the drying temperature is 80-150℃, the calcination temperature is 550-700℃, and the time is 1-4h.

[0021] 3. Advantages

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The continuous preparation method of the iron phosphate of the present application shortens the actual reaction time by combining two types of reactors in series, and the continuous reaction reduces the steps of charging and discharging, and the consistent performance of the product is enhanced.

[0024] (2) The iron phosphate preparation method reduces equipment investment and land use, and improves the level of industrial integration.

[0025] (3) The method separates the material mixing stage and the material molecular level reaction stage in two reactors in series, which is more conducive to the regulation of the parameters of the iron phosphate product.

[0026] (4) The method prepares nano-scale iron phosphate by regulating the molecular level reaction process, and the rate performance of the prepared lithium iron phosphate is improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] The technical solutions of the present application will be further described in detail below in combination with the drawings and examples, but it should be understood that these drawings are designed only for explanatory purposes, and therefore do not limit the scope of the present application. In addition, unless specifically indicated, these drawings are only intended to conceptually illustrate the structural configuration described herein, and are not necessarily drawn to scale.

[0028] Figure 1 400nm SEM image of the dehydrated iron phosphate in Example 1 of the present application;

[0029] Figure 2 2nm SEM image of the dehydrated iron phosphate in Example 1 of the present application. DETAILED DESCRIPTION

[0030] The detailed description and example embodiments of the present application below can be better understood in combination with the drawings, in which the elements and features of the present application are identified by reference numerals.

[0031] The continuous preparation method of nano-scale iron phosphate of the present application comprises the following steps:

[0032] Step S101, configure a phosphorus source solution and an iron source solution; the phosphorus source is one or more of sodium monobasic phosphate, sodium dibasic phosphate, ammonium monobasic phosphate, ammonium dibasic phosphate, sodium phosphate, and ammonium phosphate, the mass concentration of phosphorus in the phosphorus source solution is 20-500 g / L; the iron source is one or more of iron sulfate, iron hydroxide, and iron chloride, the mass concentration of iron in the iron source solution is 10-100 g / L.

[0033] Step S102, continuously add the phosphorus source solution and the iron source solution into two reactors in series to react, and finally obtain an iron phosphate slurry; the molar ratio of the phosphorus source to the iron source in the continuous reaction feeding process is 1.01-2.0, and the molar ratio is preferably 1.02-1.50; the two reactors in series are a stirred tank reactor and a tubular reactor in sequence, the reaction temperature is 70-98℃, and the average residence time is 1-100 min;

[0034] The average residence time T1 of the stirred tank reactor is 10-100 min, the average residence time T2 of the tubular reactor is 1-20 min, and T1=(5-10)T2 is satisfied; the stirring speed in the stirred tank reactor and the tubular reactor is 100-4500 r / min, the stirring speed R1 of the stirred tank reactor is preferably 100-2000 r / min, the stirring speed R2 of the tubular reactor is 2000-4500 r / min, and R2=(10-15)R1 is satisfied. Further, the inventors have found that, in certain specific cases, the iron phosphate obtained by the present application has better performance than commercially available iron phosphate, the specific case is that the residence time T in the reactor and the stirring speed have a certain relationship, for example: T1 / R2=T2 / R1, the inventors have tried to analyze the possible reasons, but no feasible conclusion has been reached so far, however, the iron phosphate obtained in the related examples has a relatively concentrated and uniform particle size and good consistency.

[0035] Step S103, wash, filter, dry, and calcine the iron phosphate slurry in step S102, the drying temperature is 80-150℃, the calcining temperature is 550-700℃, and the time is 1-4 h, to obtain a battery-grade iron phosphate.

[0036] 1) stirred tank reactor

[0037] It is composed of a stirrer and a tank body, the stirrer includes a transmission device, a stirring shaft (including a shaft seal), and an impeller (stirring paddle); the tank body includes a cylinder, a jacket, internal parts, a coil, a draft tube, etc.; there are hundreds of thousands of stirring tank reactors used in industry, which can be divided into two categories of homogeneous reactors and heterogeneous reactors according to the phase state of the reaction materials. The heterogeneous reactor includes a solid-liquid reactor, a liquid-liquid reactor, a gas-liquid reactor, and a gas-liquid-solid three-phase reactor.

[0038] 2) Tubular reactor

[0039] A kind of continuous operation reactor with tubular shape, very large aspect ratio. This reactor can be very long, such as the reactor tube length of propylene dimerization is in kilometers. The structure of the reactor can be single tube, or multiple tubes in parallel; can be empty tube, such as tubular cracking furnace, or packed tube filled with granular catalyst in the tube, to carry out multiphase catalytic reaction, such as fixed bed reactor in tube. Generally, the aspect ratio of the empty tube is greater than 50 when the reactant flow is in turbulent flow; the ratio of the length of the packed section to the particle size is greater than 100 (for gas) or 200 (for liquid), and the flow of the material can be approximately regarded as a plug flow.

[0040] It should be noted that whether the kettle type stirring reactor or the tubular reactor is used alone, the ferric phosphate product can be obtained, but the consistency of the obtained ferric phosphate product is poor, which cannot meet the production requirements.

[0041] Surprisingly, the inventors of the present application first stir the material through the kettle type stirring reactor, and then react in the tubular reactor, and the final effect is better than that disclosed in patent CN104555975A. The inventors analyze the reasons: the present application divides the reaction process into space, and carries out the full mixing stage of the material and the molecular level reaction stage in different reactors, and combines the kettle type stirring reactor and the tubular reactor before and after respectively, the kettle type stirring reactor provides a larger volume, which can greatly reduce the reaction time, so that the material mixing is more uniform, and the tubular reactor can be fast in and fast out, so that the volume of the reactor can be smaller, and the stirring rate can be fast enough, so that the reaction of the ferric phosphate in the generation stage is greatly accelerated, the number of generated ferric phosphate crystal nucleus is more, the number of primary particles is more, and the particle size is smaller, finally reaching the nanometer level, and the whole process realizes the scale and continuity.

[0042] Example 1

[0043] (1) Prepare a ferric sulfate solution with an iron content of 75 g / L, and an ammonium dihydrogen phosphate solution with a phosphorus content of 200 g / L;

[0044] (2) The iron source and the phosphorus source in (1) are continuously fed into the kettle type stirring reactor according to the mass ratio of the phosphorus source to the iron source of 1.05, the stirring rate is 400 r / min, the average residence time is 30 min, and the reaction temperature is 80℃, then the reaction material continuously enters the tubular reactor, the stirring rate is 4000 r / min, the average residence time is 3 min, and the reaction temperature is 95℃, and the obtained discharge is white ferric phosphate slurry;

[0045] (3) The white ferric phosphate slurry obtained in (2) is washed, filtered, dried at 90°C for 2h, and the dihydrate material is calcined at 680°C for 3h to obtain the nanoscale ferric phosphate product.

[0046] As shown in Figure 1 and Figure 2 The primary particle size of the ferric phosphate obtained in this example is 65nm.

[0047] Example 2

[0048] (1) An iron chloride solution with an iron content of 100g / L and an ammonium monohydrogen phosphate solution with a phosphorus content of 300g / L are prepared;

[0049] (2) The iron source and the phosphorus source in (1) are continuously fed into a stirred tank reactor for reaction at a mass ratio of phosphorus source to iron source of 1.0, a stirring rate of 500r / min, an average residence time of 25min, and a reaction temperature of 78°C, and then the reaction material is continuously fed into a tubular reactor at a stirring rate of 5000r / min, an average residence time of 6min, and a reaction temperature of 90°C to obtain a white ferric phosphate slurry as the output;

[0050] (3) The white ferric phosphate slurry obtained in (2) is washed, filtered, dried at 100°C for 2h, and the dihydrate material is calcined at 680°C for 3h to obtain the nanoscale ferric phosphate product.

[0051] Example 3

[0052] (1) An iron sulfate solution with an iron content of 20g / L and an ammonium phosphate solution with a phosphorus content of 100g / L are prepared;

[0053] (2) The iron source and the phosphorus source in (1) are continuously fed into a stirred tank reactor for reaction at a mass ratio of phosphorus source to iron source of 1.3, a stirring rate of 400r / min, an average residence time of 30min, and a reaction temperature of 85°C, and then the reaction material is continuously fed into a tubular reactor at a stirring rate of 4000r / min, an average residence time of 3min, and a reaction temperature of 90°C to obtain a white ferric phosphate slurry as the output;

[0054] (3) The white ferric phosphate slurry obtained in (2) is washed, filtered, dried at 150°C for 1h, and the dihydrate material is calcined at 650°C for 3h to obtain the nanoscale ferric phosphate product.

[0055] Example 4

[0056] (1) An iron chloride solution with an iron content of 100g / L and an ammonium phosphate solution with a phosphorus content of 500g / L are prepared;

[0057] (2) the iron source and the phosphorus source in (1) are continuously fed into a stirred tank reactor for reaction at a mass ratio of the phosphorus source to the iron source of 1.5, a stirring rate of 1000 r / min, an average residence time of 20 min, and a reaction temperature of 90℃, and then the reaction material is continuously fed into a tubular reactor, a stirring rate of 3000 r / min, an average residence time of 5 min, and a reaction temperature of 98℃, to obtain a white iron phosphate slurry as the output;

[0058] (3) the white iron phosphate slurry obtained in (2) is washed, filtered, dried at 120℃ for 2 h, and the dihydrate material is calcined at 650℃ for 3 h to obtain a nano-sized iron phosphate product.

[0059] Example 5

[0060] (1) an iron sulfate solution with an iron content of 50 g / L is configured, and an ammonium dihydrogen phosphate solution with a phosphorus content of 100 g / L is configured;

[0061] (2) the iron source and the phosphorus source in (1) are continuously fed into a stirred tank reactor for reaction at a mass ratio of the phosphorus source to the iron source of 1.02, a stirring rate of 100 r / min, an average residence time of 50 min, and a reaction temperature of 70℃, and then the reaction material is continuously fed into a tubular reactor, a stirring rate of 2000 r / min, an average residence time of 1 min, and a reaction temperature of 90℃, to obtain a white iron phosphate slurry as the output;

[0062] (3) the white iron phosphate slurry obtained in (2) is washed, filtered, dried at 80℃ for 4 h, and the dihydrate material is calcined at 600℃ for 4 h to obtain a nano-sized iron phosphate product.

[0063] Further, the above-mentioned continuous preparation method of the nano-sized iron phosphate can obtain an iron phosphate product with primary particles of 50-70 nm, the prepared iron phosphate lithium product has excellent rate performance, and the performance of each batch is relatively stable and has small fluctuation, which reflects that the iron phosphate has good consistency. Therefore, the present application can meet the requirements of battery-grade iron phosphate, and the process is simple, the reaction conditions are mild, and it is easy to produce on a large scale.

[0064] It should be noted that the consistency of the iron phosphate obtained in Example 1 and Example 3 is better than that of the iron phosphate obtained in other examples, which fully illustrates that when T1 / R2 = T2 / R1 is met, the purpose of the present application is scientific.

[0065] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. The embodiments should therefore be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. No reference signs in the claims should be considered as limiting the scope of the claims with respect to the figures of the patent document.

Claims

1. A method for preparing continuous nanoscale iron phosphate, comprising the following steps: Step S101, providing a phosphorus source solution and an iron source solution; Step S102, continuously adding the phosphorus source solution and the iron source solution into two reactors in series to react, and finally obtaining an iron phosphate slurry; Step S103, washing, filtering, drying, and calcining the iron phosphate slurry in step S102 to obtain a battery-grade iron phosphate; The two reactors in series are a kettle-type stirring reactor and a tubular reactor in sequence, the reaction temperature of each reactor is 70-98℃, and the average residence time is 1-100min.

2. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, In step S101, the phosphorus source is one or more of sodium monohydrogen phosphate, sodium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and ammonium phosphate.

3. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, In step S101, the iron source is one or more of iron sulfate, iron hydroxide, and iron chloride.

4. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, The mass concentration of iron in the iron source solution is 10-100g / L, and the mass concentration of phosphorus in the phosphorus source solution is 20-500g / L.

5. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, In step S102, the molar ratio of the phosphorus source to the iron source during the continuous reaction feeding process is 1.01-2.

0.

6. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, In step S102, the molar ratio of the phosphorus source to the iron source during the continuous reaction feeding process is 1.02-1.

50.

7. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, The average residence time of the kettle-type stirring reactor is 10-100min, and the average residence time of the tubular reactor is 1-20min.

8. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, The stirring speed in the kettle-type stirring reactor and the tubular reactor is 100-4500r / min.

9. The method of claim 7, wherein the method is continuous. The stirring speed in the kettle-type stirring reactor is 100-2000r / min, and the stirring speed in the tubular reactor is 2000-4500r / min.

10. The process for the preparation of continuous nanosized iron phosphates according to claim 1, characterized in that, In step S103, the drying temperature is 80-150℃, and the calcining temperature is 550-700℃, both for 1-4h.

Images