CN113023700A - Preparation method of high-purity nanoscale iron phosphate - Google Patents
Preparation method of high-purity nanoscale iron phosphate Download PDFInfo
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- CN113023700A CN113023700A CN201911347607.6A CN201911347607A CN113023700A CN 113023700 A CN113023700 A CN 113023700A CN 201911347607 A CN201911347607 A CN 201911347607A CN 113023700 A CN113023700 A CN 113023700A
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/37—Phosphates of heavy metals
- C01B25/375—Phosphates of heavy metals of iron
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
Abstract
The invention discloses a preparation method of high-purity nanoscale iron phosphate, which comprises the following steps: mixing an iron source and dilute sulfuric acid, and reacting until the iron source is completely dissolved to obtain a light green ferrous sulfate solution A, wherein the iron source is one or a mixture of any two or three of iron powder, iron sheets and iron strips; adding a certain amount of phosphoric acid into the solution A obtained in the step (1), and controlling the molar ratio of phosphorus to iron to obtain a mixed solution B; heating the mixed solution B in the step (2) to a certain temperature, and starting to add H2O2Continuing to react for a period of time after the reaction is finished, and then performing the procedures of washing, filter pressing, drying and the like to obtain an iron phosphate precursor; and (4) calcining the iron phosphate precursor obtained in the step (3) to obtain nanoscale flaky iron phosphate powder. Through the mode, the invention provides a preparation method of high-purity nanoscale iron phosphate.
Description
Technical Field
The invention belongs to the technical field of inorganic chemistry, and particularly relates to a method for preparing high-purity iron phosphate for a nanoscale battery by reacting iron powder, sulfuric acid and phosphoric acid.
Background
Iron phosphateThe lithium iron phosphate battery has the advantages of safety, low cost, environmental friendliness and the like, and is an important positive electrode material of the lithium ion battery, so that the lithium iron phosphate battery has stable high-temperature performance, is not exploded when punctured, is easy to be used in series, can meet the requirements of frequent charging and discharging of an electric vehicle and an energy storage battery, and is more popular in the market. FePO4As a process for preparing LiFePO4The base material is an ideal electrode material for producing batteries of electric vehicles and energy storage batteries, has the characteristics of environmental protection, low cost, stable structure and the like, and is prepared from Li FePO4Can maintain FePO4The microstructure of the lithium iron phosphate has great influence on the electrochemical performance of the lithium iron phosphate material, so the lithium iron phosphate is prepared into Li FePO4The key to the performance of the battery is good and bad.
At present, the production process of iron phosphate mainly uses ferrous sulfate as an iron source and iron powder as the iron source to prepare battery-grade iron phosphate through reaction, the process cost is high due to the fact that ferrous sulfate heptahydrate is used as the iron source, the cost for producing the iron phosphate is high, the process can reduce the iron source cost to a great extent in the iron powder and phosphoric acid, but hydrogen ions in the phosphoric acid cannot be completely ionized, and negative and positive ions including H have H+、H2PO4 -、H2PO4 2-、 PO4 3-The filtrate is recycled and circularly added with phosphoric acid, although the production cost can be reduced to a great extent, ions H in the solution can be generated along with excessive circulation times2PO4 -、H2PO4 2-、PO4 3-The ratio of (A) is greatly changed, so that the stability of the material composition and the reaction environment cannot be ensured, thereby affecting the stability between batches and further affecting the FePO4Stability of quality. On the other hand, the filtrate can cause impurity element enrichment after long-term recycling, and can also influence the quality of battery-grade iron phosphate.
At present, pure iron powder and diluted phosphoric acid are adopted as raw materials to prepare iron phosphate on the market, and the reaction of iron and phosphoric acid is relatively complex, so that the generated product Fe (H) is2PO4)2、FeHPO4Extremely unstable, over-high temperature, easy decomposition, little part of FePO generated in the reaction process of iron and phosphoric acid4The precipitate covers the surface of the pure iron, which influences the reaction to continue, prolongs the reaction time, influences the production efficiency and is difficult to ensure the stable quality of the iron phosphate.
Disclosure of Invention
The invention mainly solves the technical problem of providing a preparation method of high-purity nanoscale iron phosphate, which can solve the problems of high process cost caused by taking ferrous sulfate heptahydrate as an iron source and instability between batches of iron phosphate prepared by reacting pure iron powder with phosphoric acid.
In order to solve the technical problems, the invention adopts a technical scheme that: mixing a certain amount of pure iron powder with a sulfuric acid solution with a certain concentration until the pure iron powder is dissolved, reacting to generate a light green ferrous sulfate solution A, calculating the amount of a phosphorus source according to the amount of an iron source in the solution A, adding phosphoric acid into the solution A, stirring, mixing and demagnetizing to obtain a solution B, heating the solution B to a reasonable range, and adding H2O2Oxidizing to generate ferric phosphate precipitate, filtering, washing, drying and calcining to obtain the high-purity nanoscale flaky ferric phosphate.
On the basis of adopting the technical scheme, the invention can also adopt the following optimized technical scheme, which comprises the following steps:
the method comprises the following steps: dissolving iron powder in dilute sulfuric acid, wherein the mass percentage of the dilute sulfuric acid is 10-30%, and the molar ratio of Fe to S is controlled to be 1.0-2.0;
step two: until the iron powder is completely dissolved, filtering out insoluble black solid impurities, and treating by a demagnetizer to obtain a light green ferrous sulfate solution A;
step three: adding phosphoric acid into the ferrous sulfate solution A, and controlling the proportion of phosphorus and iron to be 1.0-2.0;
step four: at a temperature between 25 ℃ and 95 ℃ with H2O2Oxidizing ferrous salt to obtain a ferric phosphate precursor;
step six: and washing, filtering, drying and calcining the obtained iron phosphate precursor to obtain the nanoscale iron phosphate powder.
Preferably, the iron source comprises one or two or three of pure iron strips, iron powder and iron sheets with the mass percentage of iron being more than or equal to 99.0 percent.
Further, in order to avoid introducing new impurities and influencing the quality of the iron phosphate, the oxidant is preferably a green oxidant H2O2。
Further, the mass percentage content of the dilute sulfuric acid is controlled to be 10-30 percent, and preferably 20-25 percent;
further, the molar ratio of Fe to S is controlled to be between 1.0 and 2.0, preferably between 1.0 and 1.5;
further, the molar ratio of Fe to P is controlled to be between 1.0 and 2.0, preferably between 1.0 and 1.5;
further, the addition of H was started2O2The temperature of (A) is controlled between 25 ℃ and 95 ℃, preferably between 85 ℃ and 95 ℃;
further, H2O2Controlling the crystallization temperature to be 65-105 ℃ after the addition is finished, and preferably to be 95-105 ℃;
further, the crystallization time is controlled to be H2O20.5h to 2h after the addition is finished, preferably 1h to 1.5 h;
further, compared with the prior art, the invention has the following advantages:
the method has the advantages that: the optimal reaction conditions determined by the invention, the initial concentration of the sulfuric acid, the mole ratio of the iron source to the sulfur source, the mole ratio of the phosphorus source to the iron source, and the addition of H2O2Temperature of (a) and H2O2The process for preparing iron phosphate by reacting iron with phosphoric acid has the following disadvantages, a: because phosphoric acid can not be completely ionized, the composition of each batch of materials is inconsistent by circularly adding phosphoric acid, so that the quality instability of the ferric phosphate is influenced, and b: the filtrate is recycled in the system, so that impurity metal elements are enriched, the content of the impurity metal elements in the product is higher, and the reaction of pure iron powder and sulfuric acid can completely ensure that the material composition starts at the beginningBefore the reaction is consistent; c: in the reaction process of iron and phosphoric acid, phosphoric acid can not be completely ionized, the reaction end point is not easy to control, the pH value needs to be adjusted before the reaction, the production time is prolonged, the components of the process are relatively constant, iron and sulfuric acid can completely react, the reaction end point is determined, the pH value does not need to be adjusted before the reaction, and the reaction time can be greatly saved.
The advantages are two: compared with the process taking ferrous sulfate heptahydrate as an iron source, on one hand, the process reduces the crystallization process of ferrous sulfate and reduces energy consumption to a certain extent, thereby reducing the cost of the iron source; on the other hand, the use of alkali liquids such as sodium hydroxide, ammonia water and the like is avoided, and the introduction of new impurity ions into a reaction system is effectively avoided, so that the quality of the iron phosphate is ensured.
The advantages are three: the ferric phosphate produced by the process is sheet ferric phosphate, the secondary structure of the ferric phosphate is 80-100nm, each data index reaches the requirement standard of preparing the lithium iron phosphate anode material, and the method is a method for preparing anhydrous ferric phosphate stably and feasible in batches at low cost.
Drawings
Fig. 1 is an X-ray diffraction pattern of the iron phosphate prepared in example 1.
Fig. 2 is an SEM image of iron phosphate dihydrate prepared in example 1.
Detailed Description
The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.
Example 1: adding 50g of sulfuric acid (98%) into 117.9g of deionized water, stirring uniformly to prepare dilute sulfuric acid with the mass content of 21.5%, adding 28.28g of iron powder (99.0%), keeping the temperature to 80-85 ℃ until the iron powder is completely dissolved, filtering out insoluble black solid particles, and treating by a demagnetizer to obtain a light green solution A. 59.95g of phosphoric acid (85%) was added to the solution, and after stirring uniformly, a mixed solution B was obtained, and the solution B was heated to 85 ℃ to start the addition of the oxidizing agent 31.48g H2O2After the addition, the temperature is kept between 95 ℃ and 105 DEG CAnd continuously reacting for 30min, washing, filtering and drying to obtain an iron phosphate precursor, and calcining the iron phosphate precursor to obtain the nano flaky anhydrous iron phosphate powder.
As can be seen from fig. 1, the positions of diffraction peaks of the anhydrous iron phosphate crystals prepared in example 1 are substantially consistent with those of standard cards 84-875, and no diffraction peak of other impurities appears, which indicates that the purity of the product is high, the diffraction peaks are sharp, and the crystal form of the product is good.
As can be seen from FIG. 2, the sample is composed of relatively regular lamellar particles, the size is relatively regular, the dispersibility is good, and the average thickness of the lamellar structure is determined to be 80nm-100 nm.
Example 2: adding 50g of sulfuric acid (98%) into 117.9g of deionized water, stirring uniformly to prepare dilute sulfuric acid with the mass content of 21.5%, adding 28.28g of iron powder (99.0%), keeping the temperature to 80-85 ℃ until the iron powder is completely dissolved, filtering out insoluble black solid particles, and treating by a demagnetizer to obtain a light green solution A. Adding 61.1g phosphoric acid (85%) into the solution, stirring and mixing uniformly to obtain a mixed solution B, heating the solution B to 85 ℃, and starting to add 31.48g H oxidant2O2And after the addition is finished, keeping the temperature between 95 ℃ and 105 ℃, continuing to react for 30min, washing, filtering and drying to obtain an iron phosphate precursor, and then calcining the iron phosphate precursor to obtain the nano flaky anhydrous iron phosphate powder.
Example 3: adding 50g of sulfuric acid (98%) into 117.9g of deionized water, stirring uniformly to prepare dilute sulfuric acid with the mass content of 21.5%, adding 28.28g of iron powder (99.0%), keeping the temperature to 80-85 ℃ until the iron powder is completely dissolved, filtering out insoluble black solid particles, and treating by a demagnetizer to obtain a light green solution A. 59.95g of phosphoric acid (85%) is added to the solution, and after stirring and mixing uniformly, a mixed solution B is obtained, the solution B is heated to 85 ℃, and the oxidant 31.48g H is added2O2And after the addition is finished, keeping the temperature between 95 ℃ and 105 ℃, continuously reacting for 60min, washing, filtering and drying to obtain an iron phosphate precursor, and then calcining the iron phosphate precursor to obtain the nano flaky anhydrous iron phosphate powder.
Example 4: adding 50g of sulfuric acid (98%) into 117.9g of deionized water, stirring uniformly to prepare dilute sulfuric acid with the mass content of 21.5%, adding 28.28g of iron powder (99.0%), keeping the temperature to 80-85 ℃ until the iron powder is completely dissolved, filtering out insoluble black solid particles, and treating by a demagnetizer to obtain a light green solution A. 59.95g of phosphoric acid (85%) is added to the solution, and after stirring and mixing uniformly, a mixed solution B is obtained, the solution B is heated to 95 ℃, and the oxidant 31.48g H is added2O2And after the addition is finished, keeping the temperature between 95 ℃ and 105 ℃, continuing to react for 30min, washing, filtering and drying to obtain an iron phosphate precursor powder material, and then calcining the iron phosphate precursor to obtain the nano flaky anhydrous iron phosphate powder.
Claims (9)
1. A preparation method of high-purity nanoscale iron phosphate is characterized by comprising the following steps:
the method comprises the following steps: mixing an iron source and dilute sulfuric acid for reaction, filtering insoluble black solid particles to obtain a light green ferrous sulfate solution A, and controlling the end point of the reaction; the iron source is one or a mixture of any two or three of iron powder, iron sheets and iron strips;
step two: adding a certain amount of phosphoric acid into the solution A obtained in the step (1), and controlling the molar ratio of P to Fe to obtain a solution B;
step three: heating the solution B in the step (2) to a certain temperature, starting to add H2O2, and continuing to react for a period of time after the addition is finished to obtain an iron phosphate precursor;
and (4) calcining the iron phosphate precursor obtained in the step (3) to obtain the nanoscale anhydrous iron phosphate.
2. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein the purity of iron in step (1) is not less than 99.0%, and the iron is one or a mixture of any two or three of iron powder, iron sheet and iron bar.
3. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein the molar ratio of Fe to S in step (1) is 1.0-2.0.
4. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein the molar ratio of P to Fe in step (2) is 1.0-2.0.
5. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein H in step (3)2O2The mol ratio of the Fe to the Fe is 0.5-2.0.
6. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein H in step (3)2O2The mass percentage of the component (A) is 10-30%.
7. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein H is added in the step (3)2O2The temperature of the reaction solution is 65-95 ℃.
8. The method for preparing high-purity nanoscale iron phosphate according to claim 1, wherein H is added in the step (4)2O2After finishing, the temperature is kept between 95 and 105 ℃.
9. The method for preparing high-purity nanoscale iron phosphate according to claim 1, characterized in that in the step (2), the temperature is kept between 0.5H and 2H after H2O2 is added.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113880062A (en) * | 2021-09-15 | 2022-01-04 | 四川省盈达锂电新材料有限公司 | Preparation method and application of iron phosphate |
| CN114162795A (en) * | 2021-11-08 | 2022-03-11 | 江苏涛立电子新材料有限公司 | Nano iron phosphate for synthesizing lithium battery anode material and preparation method thereof |
| CN114560455A (en) * | 2022-03-08 | 2022-05-31 | 四川大学 | Method for preparing battery-grade iron phosphate by using ferrous sulfate and phosphoric acid |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1567769B1 (en) * | 1965-06-16 | 1971-01-07 | Pfizer & Co C | Process for the production of white iron phosphate |
| CN101481104A (en) * | 2009-02-11 | 2009-07-15 | 刘世琦 | Method for producing high purity battery level ferric pyrophosphate from pickle liquor |
| CN103022482A (en) * | 2012-10-29 | 2013-04-03 | 北大先行科技产业有限公司 | Battery grade sheet hydrated iron phosphate and preparation method thereof |
| CN104817059A (en) * | 2015-04-29 | 2015-08-05 | 江西东华科技园有限责任公司 | Method for preparing battery-grade iron phosphate from reaction between iron powder and phosphoric acid |
| CN110294466A (en) * | 2019-08-19 | 2019-10-01 | 四川轻化工大学 | A kind of preparation method of nano-sheet ferric phosphate |
| WO2019200557A1 (en) * | 2018-04-18 | 2019-10-24 | 南通百川新材料有限公司 | Preparation method for iron phosphate |
| CN110436432A (en) * | 2019-07-22 | 2019-11-12 | 贵州大学 | A kind of low temperature preparation method of nano flaky lithium iron phosphate particle |
| CN110436427A (en) * | 2019-07-05 | 2019-11-12 | 合肥国轩高科动力能源有限公司 | The preparation method of high capacity high-pressure solid LiFePO4 composite construction ferric orthophosphate |
| CN110482512A (en) * | 2019-07-12 | 2019-11-22 | 乳源东阳光磁性材料有限公司 | A kind of preparation method of battery-grade iron phosphate |
-
2019
- 2019-12-24 CN CN201911347607.6A patent/CN113023700A/en active Pending
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1567769B1 (en) * | 1965-06-16 | 1971-01-07 | Pfizer & Co C | Process for the production of white iron phosphate |
| CN101481104A (en) * | 2009-02-11 | 2009-07-15 | 刘世琦 | Method for producing high purity battery level ferric pyrophosphate from pickle liquor |
| CN103022482A (en) * | 2012-10-29 | 2013-04-03 | 北大先行科技产业有限公司 | Battery grade sheet hydrated iron phosphate and preparation method thereof |
| CN104817059A (en) * | 2015-04-29 | 2015-08-05 | 江西东华科技园有限责任公司 | Method for preparing battery-grade iron phosphate from reaction between iron powder and phosphoric acid |
| WO2019200557A1 (en) * | 2018-04-18 | 2019-10-24 | 南通百川新材料有限公司 | Preparation method for iron phosphate |
| CN110436427A (en) * | 2019-07-05 | 2019-11-12 | 合肥国轩高科动力能源有限公司 | The preparation method of high capacity high-pressure solid LiFePO4 composite construction ferric orthophosphate |
| CN110482512A (en) * | 2019-07-12 | 2019-11-22 | 乳源东阳光磁性材料有限公司 | A kind of preparation method of battery-grade iron phosphate |
| CN110436432A (en) * | 2019-07-22 | 2019-11-12 | 贵州大学 | A kind of low temperature preparation method of nano flaky lithium iron phosphate particle |
| CN110294466A (en) * | 2019-08-19 | 2019-10-01 | 四川轻化工大学 | A kind of preparation method of nano-sheet ferric phosphate |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113880062A (en) * | 2021-09-15 | 2022-01-04 | 四川省盈达锂电新材料有限公司 | Preparation method and application of iron phosphate |
| CN114162795A (en) * | 2021-11-08 | 2022-03-11 | 江苏涛立电子新材料有限公司 | Nano iron phosphate for synthesizing lithium battery anode material and preparation method thereof |
| CN114162795B (en) * | 2021-11-08 | 2023-07-11 | 江苏涛立电子新材料有限公司 | Nanometer ferric phosphate for synthesizing lithium battery anode material and preparation method thereof |
| CN114560455A (en) * | 2022-03-08 | 2022-05-31 | 四川大学 | Method for preparing battery-grade iron phosphate by using ferrous sulfate and phosphoric acid |
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Application publication date: 20210625 |