A method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste.

Abstract

This invention discloses a method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste. This method uses extremely inexpensive iron oxide red waste as an iron source and effectively utilizes the unique high solubility characteristics of strong acids to synthesize iron phosphate precursors with high sphericity in a homogeneous system. Compared with the traditional iron phosphate process, this invention achieves a significant reduction in cost while maintaining excellent electrochemical performance of the synthesized lithium iron phosphate material, which is of great significance for cost reduction and profit enhancement of lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste. Background Technology

[0002] In today's increasingly electrified world, lithium iron phosphate batteries are continuously expanding their market share due to their excellent electrochemical performance and cost advantages. Faced with the ever-increasing market demand, low-cost production is of great significance for the lithium iron phosphate industry to reduce costs and increase profits.

[0003] Currently, the production processes for lithium iron phosphate include the iron oxalate process, the iron oxide red process, the hydrothermal process, and the iron phosphate process. Among these, the iron oxalate process generates a large amount of waste gas during sintering, resulting in significant environmental pressure and low yield; the iron oxide red process requires high purity and particle size of the raw material iron oxide, leading to generally lower overall performance of the produced lithium iron phosphate; the hydrothermal process poses certain safety hazards and requires a phosphoric acid purification process, resulting in higher costs; the iron phosphate process produces lithium iron phosphate with good overall performance, but also suffers from higher costs.

[0004] Therefore, this invention provides a method for synthesizing iron phosphate precursors from iron oxide red waste from steel mills through purification and acid hydrolysis. The product has uniform element distribution, good crystallinity, excellent electrical properties, and extremely cheap iron source, which can significantly reduce the production cost of lithium iron phosphate. Summary of the Invention

[0005] In view of the defects and shortcomings of existing processes, the purpose of this invention is to provide a method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste. This method aims to reduce the manufacturing cost of iron phosphate precursor materials.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste, comprising the following steps:

[0007] Step (1): The crude iron oxide red is purified, which is mainly divided into two steps: First, the pH value is adjusted by using a strong acid solvent under liquid-phase stirring so that the insoluble carbonates and hydroxides are decomposed in an acidic environment; Second, the ionic impurities are washed and removed with deionized water in one go, filtered and dried to obtain refined iron oxide red.

[0008] Step (2): Add strong acid solvent and demineralized water to step (1), and dissolve the refined iron oxide red into a ferric ion solution under certain stirring and temperature conditions;

[0009] Step (3): Add a certain proportion of phosphate-containing solution to the ferric ion liquid in step (2), control a certain iron-to-phosphorus ratio, heat to a certain temperature and maintain for a period of time to obtain a slurry containing ferric phosphate precipitate.

[0010] Step (4): Add alkali solution to the slurry in step (3) to adjust the pH value of the reaction system so that the ferric phosphate precipitation crystallizes completely;

[0011] Step (5): Wash the slurry from step (4) multiple times, and take the filter cake for drying and sintering dehydration to obtain the ferric phosphate precursor;

[0012] Step (6): The obtained iron phosphate and carbon composite is mixed with a certain proportion of lithium source and carbon source, and ball milling-sand milling-spraying-sintering process is used to obtain lithium iron phosphate cathode material.

[0013] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0014] In this invention, extremely inexpensive iron oxide red waste is used as the iron source, and the unique high solubility of strong acid is effectively utilized to synthesize a sphericity-high iron phosphate precursor in a homogeneous system. Compared with the traditional iron phosphate process, this invention achieves a significant reduction in cost while maintaining excellent electrochemical performance of the synthesized lithium iron phosphate material, which is of great significance for cost reduction and profit enhancement of lithium iron phosphate. Attached Figure Description

[0015] Figure 1 Here is a SEM image of the iron phosphate precursor prepared in Example 1;

[0016] Figure 2 The XRD pattern of the iron phosphate precursor prepared in Example 1;

[0017] Figure 3 The first charge-discharge curve of the lithium iron phosphate prepared in Example 1 is shown.

[0018] Figure 4 The graph shows the charge-discharge cycle curves of the lithium iron phosphate prepared in Example 1. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1

[0021] like Figures 1 to 4 As shown, a method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste includes the following steps:

[0022] Step (1): Stir the crude iron oxide red thoroughly in deionized water at 60°C for 30 minutes, then slowly add 98% concentrated sulfuric acid until the pH value drops to 1.00-1.10, and continue stirring for another 30 minutes;

[0023] Step (2): Filter the slurry from step (1) to obtain a filter cake;

[0024] Step (3): Add the filter cake from step (2) to 60℃ desalinated water and stir and wash for 30 minutes. Filter the slurry to obtain the filter cake. Dry the filter cake at 120℃ for 12 hours to obtain refined iron oxide red.

[0025] Step (4): Add concentrated sulfuric acid and deionized water to the oxide red in step (3), heat to 90°C and stir continuously. After 4 hours, discharge the material, filter off the residue, and obtain a ferric ion solution.

[0026] Step (5): Mix the ferric ion solution from step (4) with a certain proportion of phosphoric acid, with a molar ratio of phosphorus to iron of 1.03:1, heat to 95℃ and stir continuously for 1 hour, slowly add sodium hydroxide solution, adjust the pH of the solution to 1.0-1.1, so that the ferric phosphate is completely precipitated.

[0027] Step (6): Filter the slurry obtained in step (5), wash the filter cake with deionized water 4 times, and dry it at 120°C for 12 hours to obtain ferric phosphate dihydrate.

[0028] Step (7): Calcine the ferric phosphate dihydrate obtained in step (6) at 500℃ for 3 hours to obtain anhydrous ferric phosphate;

[0029] Step (8): The anhydrous iron phosphate and carbon composite obtained in step (7) is mixed with a certain proportion of lithium phosphate and 12wt% starch relative to the composite, and ball milling-sand milling-spraying-sintering process is combined to obtain lithium iron phosphate material.

[0030] SEM image of the product of iron phosphate precursor is shown below. Figure 1 As shown, the product has excellent sphericity, and the primary particles are in the form of nano-fine strips.

[0031] Figure 2 XRD patterns show that iron phosphate has good crystallinity and no impurities.

[0032] Electrochemical performance testing: The lithium iron phosphate cathode material prepared in Example 1, acetylene black, and binder were mixed uniformly at a mass ratio of 8:1:1. Using NMP as a solvent, the mixture was manually ground to obtain a homogeneous slurry. The slurry was coated onto aluminum foil and dried in a vacuum oven at 120°C for 12 hours. It was then punched into a disc-shaped electrode with a diameter of 12 mm and assembled into a CR2025 coin cell in a pure argon glove box. At 25°C, with a charge / discharge cutoff voltage of 2.5–4.1 V, the 0.1C specific capacity reached 159.5 mAh / g, and the initial charge / discharge efficiency reached 97.5%. After 200 cycles of a 1C constant current charge / discharge cycle test, the lithium iron phosphate still maintained a specific capacity of 148 mAh / g, with a capacity retention rate of 99%.

[0033] The process route of this application mainly uses iron oxide waste from steel mills as the iron source, with a ferric oxide content of 60-90% and containing 10-40% impurities. The main components of the impurities are combined salts of calcium, magnesium, sodium, and zinc. Acidic adjustment is performed in the liquid phase system to degrade insoluble precipitates of carbonates and oxides. Then, all soluble impurity ions are removed in one step by water washing. After drying, high-purity ferric oxide is obtained. Further, using the purified ferric oxide as the iron source, a strong acidic solvent is used to process the ferric oxide at high temperature. The iron ions dissolve to form a ferric ion solution. Further, using the acid-hydrolyzed molten iron as the iron source, and adding a phosphorus source in a corresponding proportion, the mixture is thoroughly mixed in a liquid-phase synthesizer. A certain stirring speed is employed, and the mixture is heated to a specific temperature and given a suitable nucleation time. An alkaline source is used as a pH adjuster to gradually precipitate the iron phosphate product. After filtration, drying, and dehydration, the iron phosphate precursor product is obtained. The iron phosphate precursor is then mixed with a lithium source and a carbon source in a certain proportion, and after ball milling, sand milling, spray drying, and inert atmosphere sintering, lithium iron phosphate cathode material is obtained.

[0034] The process of preparing iron phosphate materials has the advantages of low cost and high purity, and the lithium iron phosphate batteries obtained after lithium-ion sintering have excellent performance.

[0035] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for synthesizing spherical iron phosphate precursors and lithium iron phosphate cathode materials using iron oxide red waste, characterized in that: It comprises the following steps: Step (1): iron red ferric oxide coarse powder and desalted water are put into a stirring reaction kettle according to a certain proportion, a strong acid solvent is slowly dropped at a certain stirring revolution and a certain temperature, the material is discharged when the PH value reaches a certain range, and a filter cake is obtained after filtration for later use; Step (2): the filter cake obtained in step (1) is taken and added into a stirring reaction kettle, a certain amount of desalted water is matched, water washing is carried out at a certain stirring revolution and a certain temperature, the material is discharged after a certain water washing time, a filter cake is obtained after filtration, and the filter cake is dried at a certain temperature to obtain refined iron oxide red; Step (3): a certain amount of refined iron oxide red is taken, matched with a certain proportion of strong acid solvent and desalted water, and added into a stirring reaction kettle for dissolution at a certain revolution and a certain temperature, the material is discharged after a certain dissolution time, the insoluble matter is filtered out, and a trivalent iron ion solution is reserved for later use; Step (4): a certain amount of trivalent iron ion solution is taken, matched with a certain proportion of phosphorus source solution, and added into a stirring reaction kettle for synthesis at a certain revolution and a certain temperature, a certain amount of alkali source is added after a certain synthesis time, the iron phosphate precipitate is completely removed, the material is discharged after filtration and water washing, and an iron phosphate filter cake is reserved for later use; Step (5): the iron phosphate filter cake is put into an oven for drying at a certain temperature range to remove free water to obtain iron phosphate dihydrate; Step (6): the iron phosphate dihydrate is put into a muffle furnace for high-temperature sintering at a certain temperature range to remove crystal water to obtain anhydrous iron phosphate precursor product; Step (7): a certain amount of iron phosphate precursor is taken, matched with a certain proportion of lithium source and carbon source for ball milling, sand milling, spray drying, sintering in a certain inert atmosphere at a certain temperature and for a certain time, and the lithium iron phosphate positive electrode material is obtained after grinding and crushing after discharging; In step (1), the content of iron oxide red ranges from 60% to 90%, the proportion of desalted water and iron oxide red ranges from 1:1 to 10:1, the proportion of strong acid solvent and iron oxide red ranges from 0.1:1 to 1:1, the revolution ranges from 50 to 500 revolutions per minute, the temperature ranges from 20 to 99 DEG C, the reaction time ranges from 1 to 5 hours, the final point adjusted PH value ranges from 0.50 to 2.50, and the strong acid solvent is one of nitric acid, sulfuric acid and hydrochloric acid or a mixed acid of any two thereof; In step (3), the proportion of desalted water and iron oxide red ranges from 1:1 to 10:1, the proportion of strong acid solvent and iron oxide red ranges from 1:1 to 10:1, the revolution ranges from 50 to 500 revolutions per minute, the temperature ranges from 20 to 99 DEG C, the reaction time ranges from 1 to 5 hours, and the strong acid solvent is any one of nitric acid, sulfuric acid and hydrochloric acid or a mixed acid of any two thereof.

2. The method for synthesizing spherical iron phosphate precursor and lithium iron phosphate positive electrode material by using iron oxide red waste according to claim 1, characterized in that: In step (2), the proportion of desalted water and iron oxide red ranges from 1:1 to 10:1, the revolution ranges from 50 to 500 revolutions per minute, the temperature ranges from 20 to 99 DEG C, and the reaction time ranges from 1 to 5 hours.

3. The method for synthesizing spherical iron phosphate precursor and lithium iron phosphate positive electrode material by using iron oxide red waste according to claim 1, characterized in that: The phosphorus source in the step (4) is any one of phosphoric acid, ammonium dihydrogen phosphate, monohydrogen ammonium phosphate, the molar ratio of the phosphorus source and the iron source is 1.05:1-1.01:1, the rotation speed is 50-500 rpm, the temperature is 20-99℃, and the synthesis time is 1-5 h, and the base source is any one of sodium hydroxide, potassium hydroxide and ammonia.

4. The method for synthesizing spherical iron phosphate precursor and lithium iron phosphate positive electrode material by using iron oxide red waste according to claim 1, characterized in that: The drying temperature in the step (5) is 70-120℃, and the drying time is 2-15 h.

5. The method for synthesizing spherical iron phosphate precursor and lithium iron phosphate positive electrode material by using iron oxide red waste according to claim 1, characterized in that: The sintering temperature in the step (6) is 400-650℃, and the sintering time is 2-8 h.

6. The method for synthesizing spherical iron phosphate precursor and lithium iron phosphate positive electrode material by using iron oxide red waste according to claim 1, characterized in that: The carbon source in the step (7) is at least one of starch, glucose, PEG and cyclodextrin, the proportion of the carbon source is 5wt%-20wt% relative to the precursor, the sintering atmosphere is at least one of nitrogen and argon, the sintering temperature is 650-800℃, and the sintering time is 6-15 h.

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