A method for rapidly synthesizing lithium iron phosphate positive electrode material by using hydrated iron phosphate as raw material

Abstract

The present application relates to a kind of quick thermal shock synthesis of lithium iron phosphate anode material with hydrated iron phosphate as raw material.The method includes obtaining nanometer level trihydrogen iron phosphate by coprecipitation method, mixing the trihydrogen iron phosphate directly with lithium source and carbon source to obtain LiFePO4 precursor, and finally synthesizing LiFePO4 anode material by rapid thermal shock to the precursor.When using rapid thermal shock method to synthesize LiFePO4, it is not necessary to remove the crystal water in trihydrogen iron phosphate before mixing raw materials, and the short-time sintering process can effectively save the energy consumption generated in the process of removing crystal water at high temperature sintering.The LiFePO4 synthesized by the present application is nanometer level, with good crystal form and no impurity phase.And, as the rapid removal of crystal water can widen the lithium ion transmission path, the synthesized LiFePO4 has good electrochemical performance, with a discharge specific capacity of 164mAh / g at 0.1C, and also shows good rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate cathode material technology, specifically to a method for rapidly thermally shock synthesizing lithium iron phosphate cathode material using hydrated iron phosphate as raw material. Background Technology

[0002] Oil, coal, and natural gas, due to their non-renewable nature and irreversible pollution to the environment, are insufficient to meet our needs, while green renewable energy sources such as solar, wind, and hydropower suffer from temporal and spatial unpredictability in their application. Therefore, vigorously developing efficient, environmentally friendly, and renewable new energy sources, and promoting energy conservation, environmental protection, and resource recycling are imperative. Chemical batteries, as devices for storing and converting chemical energy into electrical energy, have been widely used in various fields. Lithium-ion batteries possess advantages such as high specific energy density, high efficiency, good cycle life, and low environmental pollution. Currently, key indicators of lithium-ion batteries, such as energy density, charge / discharge rate, and safety, are mainly constrained by the cathode material. Therefore, the focus of lithium-ion battery development is on researching and developing low-cost and high-performance cathode materials.

[0003] LiFePO4 is one of the most widely studied polyanionic cathode materials. LiFePO4 belongs to the orthorhombic crystal system, such as... Figure 1-7 As shown, Li occupies the 4a position of the octahedron in the crystal, Fe occupies the 4c ​​position, and O is arranged in a slightly distorted, near-hexagonal close-packed form. Fe and O form the FeO6 octahedron, and P and O form the PO4 tetrahedron, together constituting the spatial framework of LiFePO4. Lithium ions intercalate and deintercalate in the material in a one-dimensional manner. Its crystal structure contains strong P–O covalent bonds, forming stable (PO4)3– units, thus giving LiFePO4 high structural stability. The lithium ion intercalation and deintercalation mechanism of LiFePO4 is a two-phase reaction (LiFePO4 / FePO4). FePO4 is the most advantageous raw material for production, and its purity, structure, and physicochemical properties are the decisive factors in the properties of the final LiFePO4 product.

[0004] Currently, FePO4 is mainly prepared industrially using liquid-phase synthesis. The crude product is filtered, washed, and dried to obtain FePO4·xH2O containing water of crystallization. In current research, when using FePO4 containing water of crystallization as a raw material for LiFePO4 preparation, sol-gel methods or solid-liquid phase methods are often required to embed lithium ions into FePO4, which is not conducive to large-scale industrial applications. If FePO4·xH2O containing water of crystallization is used as a raw material for high-temperature solid-phase synthesis of LiFePO4, the slow heating process leads to incomplete removal of water of crystallization, resulting in LiFePO4 with poor crystallinity and electrochemical performance. Therefore, in industrial applications, FePO4·xH2O containing water of crystallization needs to be calcined at high temperature for a long time to remove the water of crystallization before being mixed with a lithium source and a carbon source, and finally, a high-temperature carbothermal reduction method is used to prepare LiFePO4. However, high-temperature sintering for several hours not only results in huge energy consumption, but also inevitably causes grains to grow and agglomerate during the heating process, leading to a loss of the electrochemical performance of the final product, LiFePO4.

[0005] Therefore, a method for rapidly synthesizing lithium iron phosphate cathode materials using hydrated iron phosphate as a raw material via thermal shock is needed. Summary of the Invention

[0006] This invention relates to the field of lithium iron phosphate cathode materials, and in particular to a method for rapidly thermally shock synthesizing lithium iron phosphate cathode materials using hydrated iron phosphate as a raw material.

[0007] Traditional liquid-phase synthesis of FePO4·xH2O requires prolonged high-temperature sintering to remove crystal water before it can be mixed with lithium and carbon sources to obtain the LiFePO4 precursor. Traditional industrial preparation of LiFePO4 involves single or multiple sintering processes at 600-800℃ under a protective atmosphere for 8-20 hours, significantly increasing energy and time consumption. This process also easily leads to excessive growth or agglomeration of LiFePO4 particles during sintering, affecting the rate performance of LiFePO4. This invention utilizes a co-precipitation method to prepare FePO4·3H2O, which is then directly mixed with lithium and carbon sources to obtain the LiFePO4 precursor. By applying direct current to both ends of the load, the precursor powder can be rapidly heated, allowing it to acquire sufficient energy for reaction in a short time, ultimately yielding a LiFePO4 cathode material with excellent electrochemical performance. This method effectively avoids the energy consumption associated with removing crystal water and prolonged sintering during high-temperature solid-phase reactions in traditional methods. Furthermore, the generated LiFePO4 particles are small, with a particle size of only 50-200nm and a small specific surface area; the rapid heating process can completely remove the water of crystallization in the precursor, which widens the lithium-ion transport channels during the removal process, giving the synthesized LiFePO4 good rate performance.

[0008] To achieve the above objectives of this invention, the following technical solution is adopted:

[0009] A method for rapidly thermally shock synthesizing lithium iron phosphate cathode material using hydrated iron phosphate as a raw material includes the following steps:

[0010] Step 1: Prepare hydrated ferric phosphate using the co-precipitation method;

[0011] FeSO4·7H2O is dissolved in water to obtain solution A, and NH4H2PO4 is dissolved in water to obtain solution B.

[0012] Solution A and solution B are mixed with a molar ratio of iron to phosphorus of 1:(1.00-1.40). The mixture is heated and stirred in a water bath during the mixing process. H2O2 (30%) is added dropwise to the mixed solution to carry out an oxidation reaction. An alkaline solution is added to adjust the pH value to obtain an iron phosphate precipitate.

[0013] The ferric phosphate precipitate was subjected to solid-liquid separation. The resulting solid material was washed and dried in an oven to obtain nano-sized ferric phosphate trihydrate.

[0014] Step 2: The iron phosphate trihydrate obtained in Step 1 is ball-milled and mixed with lithium source and carbon source. The solution is then dried in a vacuum oven to obtain LiFePO4 precursor.

[0015] Step 3: In an inert atmosphere, the LiFePO4 precursor obtained in Step 2 is placed on a heated substrate, and the LiFePO4 precursor powder is subjected to rapid thermal shock by an electric current to obtain the LiFePO4 cathode material.

[0016] Furthermore, in step 1, the heating temperature of the water bath for heating and stirring is 60-90℃, and the stirring speed is 400-900ppm.

[0017] Furthermore, in step 1, the amount of H2O2 (30%) added is 0.7-1 times the amount of the iron source material; in step 1, the alkaline solution is one or more combinations of sodium hydroxide solution, potassium hydroxide solution, and ammonia (30%).

[0018] Furthermore, the pH value in step 1 is adjusted within the range of 2-3.5.

[0019] Furthermore, in step 1, the drying temperature is 100-120℃ and the drying time is 12-24h.

[0020] Furthermore, the nanoscale iron phosphate trihydrate obtained in step 1 has a particle size of 30-100 nm.

[0021] Furthermore, in step 2, the molar ratio of lithium element to iron phosphate trihydrate in the lithium source is (1.00-1.08):1, and the lithium source is one or more combinations of lithium carbonate, lithium hydroxide, lithium oxalate, lithium nitrate, and lithium chloride.

[0022] Furthermore, in step 2, the mass of the carbon source added is 10-30% of the mass of the LiFePO4 precursor powder, and the carbon source is one or more combinations of glucose, oxalic acid, citric acid, malic acid, ascorbic acid, maltose, adipic acid, ethylene glycol, sucrose, conductive carbon black, Ketjen black, graphene, and carbon nanotubes.

[0023] Furthermore, in step 2, the ball milling aid is one of water, ethanol, or acetone, the ball-to-material ratio is 40:3, and the ball milling time is 5-10 hours.

[0024] Furthermore, in step 2, the temperature of the vacuum oven is 80°C, and the drying time is 12 hours.

[0025] Furthermore, the inert atmosphere in step 3 is nitrogen or argon.

[0026] Furthermore, the heating substrate in step 3 is carbon cloth, carbon felt, stainless steel sheet, or nickel foil.

[0027] Furthermore, the rapid thermal shock current in step 3 is 14-17A, and the duration is 20-40s.

[0028] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0029] The method of the present invention can directly use ferric phosphate trihydrate as a precursor of LiFePO4, reducing the step of removing the water of crystallization of ferric phosphate at high temperature and avoiding the energy consumption and time required for long-term high-temperature heating.

[0030] The method of this invention can greatly reduce the time required to synthesize LiFePO4, thereby saving energy consumption in this process.

[0031] The method of the present invention can completely remove the water of crystallization in the precursor during the LiFePO4 phase formation process, and the removal of the water of crystallization broadens the lithium ion transport channel, so that the synthesized LiFePO4 has excellent electrochemical performance.

[0032] This method can reduce the large amount of energy consumed in the traditional method of removing the water of crystallization of ferric phosphate trihydrate at high temperature, and the resulting lithium iron phosphate particles are small and have good electrochemical performance.

[0033] This invention employs a rapid thermal shock synthesis method that directly uses FePO4·3H2O containing water of crystallization as a raw material for a high-temperature solid-state method. During the rapid phase formation of LiFePO4, the water of crystallization in the precursor is completely removed. This not only simplifies the production process and saves energy, but also prevents the aggregation and growth of FePO4 particles during the removal of water of crystallization. Furthermore, the removal of water of crystallization can broaden the lithium-ion transport channels, resulting in LiFePO4 cathode materials with excellent electrochemical performance. Attached Figure Description

[0034] Figure 1 This is the thermogravimetric curve of hydrated ferric phosphate of the present invention;

[0035] Figure 2 This is the XRD pattern of FePO4·3H2O, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as raw material according to the present invention.

[0036] Figure 3 This is a scanning electron microscope image of FePO4·3H2O, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as a raw material, according to the present invention. The magnification is 30,000 times.

[0037] Figure 4 This is the XRD pattern of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as a raw material according to the present invention.

[0038] Figure 5 This is a scanning electron microscope image of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as a raw material, according to the present invention. The magnification is 30,000 times.

[0039] Figure 6 This is the XRD pattern of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as a raw material according to the present invention.

[0040] Figure 7 This is a charge-discharge curve of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as raw material, under 0.1C conditions.

[0041] Figure 8 This is a charge-discharge curve of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as raw material, under 0.1C conditions.

[0042] Figure 9 This is a rate performance diagram of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as raw material, according to the present invention.

[0043] Figure 10This is a cycling performance diagram of LiFePO4, a lithium iron phosphate cathode material synthesized by rapid thermal shock using hydrated iron phosphate as raw material, under 1C conditions.

[0044] Figure 11 This is a rate performance diagram of LiFePO4, a lithium iron phosphate cathode material synthesized using hydrated iron phosphate as a raw material, through conventional tube furnace heating. Detailed Implementation

[0045] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0046] Example 1

[0047] The rapid synthesis of lithium iron phosphate cathode material using hydrated iron phosphate as a raw material is carried out according to the following steps:

[0048] Step 1: Dissolve a certain amount of FeSO4·7H2O in water to obtain solution A, and dissolve a certain amount of NH4H2PO4 in water to obtain solution B. The concentration of solutions A and B is 0.1 mol / L, and the molar ratio of iron to phosphorus in the added raw materials is 1:1. Mix solutions A and B, heating in a 60°C water bath and stirring at 400 ppm during the mixing process. Add 0.7 times the amount of iron source material (30%) of H2O2 to the mixed solution to carry out the oxidation reaction. Add sodium hydroxide solution to adjust the pH of the solution to 3.5 to obtain ferric phosphate precipitate. Separate the ferric phosphate precipitate into solid and liquid components, wash the obtained solid material, and dry it in an oven at 120°C for 12 hours to obtain nano-sized FePO4·3H2O.

[0049] Thermogravimetric analysis was performed on the obtained hydrated ferric phosphate, such as... Figure 1 As shown, the total weight loss of the sample after heating to 800℃ was 27%, corresponding to the presence of 3 molecules of water of crystallization, confirming the chemical formula of the sample as FePO4·3H2O. The powder X-ray diffraction (XRD) pattern shows... Figure 2 The prepared FePO4·3H2O contains water of crystallization and exhibits an amorphous state. Figure 3 The scanning electron microscope (SEM) image of the obtained FePO4·3H2O shows that FePO4·3H2O consists of uniform spherical particles with a particle size of 30-100 nm.

[0050] Step 2, LiFePO4 precursor preparation process: FePO4·3H2O prepared by co-precipitation method is directly ball-milled and mixed with lithium carbonate and glucose. The molar ratio of lithium to ferric phosphate trihydrate in lithium carbonate is 1.00:1, and the glucose added is 25% of the mass of the LiFePO4 precursor powder. The ball-to-powder ratio is 40:3, and the ball-milling time is 6 hours. After ball milling, the resulting solution is placed in a vacuum oven and dried at 80℃ for 12 hours to obtain the LiFePO4 precursor.

[0051] Step 3: The rapid thermal shock process is carried out in an argon atmosphere, using a 5×2.5cm carbon cloth as the heating substrate. The LiFePO4 precursor is ground, and 150mg is placed on the heating substrate. A 15A current is applied for 25s to rapidly thermally shock the LiFePO4 precursor powder, yielding the finished LiFePO4 product.

[0052] Figure 4 The XRD pattern of the obtained LiFePO4 cathode material shows that the obtained LiFePO4 cathode material has a good crystal structure, and all peak positions can be matched with the PDF card of olivine-type LiFePO4. There are no impurity peaks. Figure 5 The image shows a SEM image of the obtained LiFePO4 cathode material. It can be seen that the particle size of the LiFePO4 cathode material is 50-200 nm and it is spherical.

[0053] Example 2

[0054] The rapid synthesis of lithium iron phosphate cathode material using hydrated iron phosphate as a raw material is carried out according to the following steps:

[0055] Step 1: Dissolve a certain amount of FeSO4·7H2O in water to obtain solution A, and dissolve a certain amount of NH4H2PO4 in water to obtain solution B. The concentration of solutions A and B is 0.1 mol / L, and the molar ratio of iron to phosphorus in the added raw materials is 1:1.40. Mix solutions A and B, heating in a 90℃ water bath and stirring at 700 ppm during the mixing process. Add 0.8 times the amount of iron source material of H2O2 (30%) to the mixed solution to carry out the oxidation reaction. Add ammonia solution to adjust the pH of the solution to 2 to obtain iron phosphate precipitate. Separate the iron phosphate precipitate into solid and liquid components, wash the obtained solid material, and dry it in an oven at 100℃ for 24 h to obtain nano-sized FePO4·3H2O.

[0056] Step 2, the preparation process of the LiFePO4 precursor: FePO4·3H2O prepared by the co-precipitation method was directly ball-milled and mixed with lithium carbonate and glucose. The molar ratio of lithium to ferric phosphate trihydrate in the lithium carbonate was 1.08:1, and the glucose added was 10% of the mass of the LiFePO4 precursor powder. The ball-to-powder ratio was 40:3, and the ball-milling time was 10 hours. After ball milling, the resulting solution was placed in a vacuum oven and dried at 80°C for 12 hours to obtain the LiFePO4 precursor.

[0057] Step 3: The rapid thermal shock process is carried out in an argon atmosphere, using a 5×2.5cm carbon cloth as the heating substrate. The LiFePO4 precursor is ground, and 150mg is placed on the heating substrate. A 17A current is applied for 40s to rapidly thermally shock the LiFePO4 precursor powder, yielding the finished LiFePO4 product.

[0058] Figure 6 The XRD pattern of the obtained LiFePO4 cathode material shows that the obtained LiFePO4 cathode material has a good crystal structure, and all peak positions can be matched with the PDF card of olivine-type LiFePO4. There are no impurity peaks.

[0059] Example 3

[0060] The rapid synthesis of lithium iron phosphate cathode material using hydrated iron phosphate as a raw material is carried out according to the following steps:

[0061] Step 1: Dissolve a certain amount of FeSO4·7H2O in water to obtain solution A, and dissolve a certain amount of NH4H2PO4 in water to obtain solution B. The concentration of solutions A and B is 0.1 mol / L, and the molar ratio of iron to phosphorus in the added raw materials is 1:1.30. Mix solutions A and B, heating in an 80°C water bath and stirring at 700 ppm during the mixing process. Add H2O2 (30%), which is one times the amount of iron source material, dropwise to the mixed solution to carry out the oxidation reaction. Add ammonia solution to adjust the pH of the solution to 3 to obtain ferric phosphate precipitate. Separate the ferric phosphate precipitate into solid and liquid components, wash the obtained solid material, and dry it in an oven at 100°C for 24 hours to obtain nano-sized FePO4·3H2O.

[0062] Step 2, LiFePO4 precursor preparation process: FePO4·3H2O prepared by co-precipitation method is directly ball-milled and mixed with lithium carbonate and glucose. The molar ratio of lithium to ferric phosphate trihydrate in lithium carbonate is 1.03:1, and the glucose added is 30% of the mass of the LiFePO4 precursor powder. The ball-to-powder ratio is 40:3, and the ball-milling time is 5 hours. After ball milling, the resulting solution is placed in a vacuum oven and dried at 80℃ for 12 hours to obtain the LiFePO4 precursor.

[0063] Step 3: The rapid thermal shock process is carried out in an argon atmosphere, using a 5×2.5cm carbon cloth as the heating substrate. The LiFePO4 precursor is ground, and 150mg is placed on the heating substrate. A 14A current is applied for 20s to rapidly thermally shock the LiFePO4 precursor powder, yielding the finished LiFePO4 product.

[0064] Step 4: Assemble the materials into coin cells and test their electrochemical performance. Weigh Super P, PVDF, and the obtained LiFePO4 in a specific ratio, mix with a certain amount of 1-methyl-2-pyrrolidone (NMP), and stir on a magnetic stirrer for 2 hours to obtain a positive electrode slurry. Coat the slurry onto aluminum foil, vacuum dry it, and cut it into sheets to obtain the positive electrode. Assemble the coin cells in an argon atmosphere and test their electrochemical performance.

[0065] Figure 7 The charge-discharge curves of the obtained LiFePO4 cathode material at 0.1C are shown, with an initial discharge capacity of 153 mAh / g and a flat voltage plateau.

[0066] Example 4

[0067] The rapid synthesis of lithium iron phosphate cathode material using hydrated iron phosphate as a raw material is carried out according to the following steps:

[0068] Step 1: Dissolve a certain amount of FeSO4·7H2O in water to obtain solution A, and dissolve a certain amount of NH4H2PO4 in water to obtain solution B. The concentration of solutions A and B is 0.1 mol / L, and the molar ratio of iron to phosphorus in the added raw materials is 1:1.30. Mix solutions A and B, heating in a 90°C water bath and stirring at 900 ppm during the mixing process. Add H2O2 (30%), which is one times the amount of iron source material, to the mixed solution to carry out the oxidation reaction. Add ammonia solution to adjust the pH of the solution to 3 to obtain ferric phosphate precipitate. Separate the ferric phosphate precipitate into solid and liquid components, wash the obtained solid material, and dry it in an oven at 100°C for 12 hours to obtain nano-sized FePO4·3H2O.

[0069] Step 2, the preparation process of the LiFePO4 precursor, involves directly ball-milling and mixing FePO4·3H2O obtained by the co-precipitation method with lithium carbonate and glucose. The molar ratio of lithium to ferric phosphate trihydrate in the lithium carbonate is 1.05:1, and the glucose added is 20% of the mass of the LiFePO4 precursor powder. The ball-to-powder ratio is 40:3, and the ball-milling time is 6 hours. After ball milling, the resulting solution is placed in a vacuum oven and dried at 80°C for 12 hours to obtain the LiFePO4 precursor.

[0070] Step 3: The rapid thermal shock process is carried out in an argon atmosphere, using a 5×2.5cm carbon cloth as the heating substrate. The LiFePO4 precursor is ground, and 150mg is placed on the heating substrate. A rapid thermal shock is applied to the LiFePO4 precursor powder with a current of 15.5A and a duration of 25s to obtain the finished LiFePO4.

[0071] Step 4: Assemble the materials into coin cells and test their electrochemical performance. Weigh Super P, PVDF, and the obtained LiFePO4 in a specific ratio, mix with a certain amount of 1-methyl-2-pyrrolidone (NMP), and stir on a magnetic stirrer for 2 hours to obtain a positive electrode slurry. Coat the slurry onto aluminum foil, vacuum dry it, and cut it into sheets to obtain the positive electrode. Assemble the coin cells in an argon atmosphere and test their electrochemical performance.

[0072] Figure 8 The charge-discharge curves of the obtained LiFePO4 cathode material at 0.1C are shown, with an initial discharge capacity of 164.5 mAh / g and a flat voltage plateau.

[0073] Figure 9 The discharge specific capacity of the obtained LiFePO4 cathode material at different rates was demonstrated. At 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, the discharge specific capacities of LFP25-3 were 164.5 mAh / g, 157.29 mAh / g, 146.67 mAh / g, 138.42 mAh / g, 129.97 mAh / g and 113.23 mAh / g, respectively. After the high-rate test, when the charge and discharge were returned to 0.1C, the discharge specific capacity of the battery could still reach 163.46 mAh / g.

[0074] Figure 10 The cycling performance of the obtained LiFePO4 cathode material at 1C was demonstrated. After 500 cycles, the discharge specific capacity of the battery still reached 139.83 mAh / g, and the capacity retention rate was always higher than 100%.

[0075] Comparative Example 1

[0076] The rapid synthesis of lithium iron phosphate cathode material using hydrated iron phosphate as a raw material is carried out according to the following steps:

[0077] Step 1: Dissolve a certain amount of FeSO4·7H2O in water to obtain solution A, and dissolve a certain amount of NH4H2PO4 in water to obtain solution B. The concentration of solutions A and B is 0.1 mol / L, and the molar ratio of iron to phosphorus in the added raw materials is 1:1.3. Mix solutions A and B, heating in a 90°C water bath and stirring at 900 ppm during the mixing process. Add H2O2 (30%), which is one times the amount of iron source material, to the mixed solution to carry out the oxidation reaction. Add ammonia solution to adjust the pH of the solution to 3 to obtain ferric phosphate precipitate. Separate the ferric phosphate precipitate into solid and liquid components, wash the obtained solid material, and dry it in an oven at 100°C for 12 hours to obtain nano-sized FePO4·3H2O.

[0078] Step 2, the preparation process of the LiFePO4 precursor: FePO4·3H2O prepared by the co-precipitation method was directly ball-milled with lithium carbonate and glucose. The molar ratio of lithium carbonate to ferric phosphate trihydrate was 1.03:2, and the mass of glucose added was 20% of the mass of the LiFePO4 precursor powder. The ball-to-powder ratio was 40:3, and the ball-milling time was 6 hours. After ball milling, the resulting solution was placed in a vacuum oven and dried at 80°C for 12 hours to obtain the LiFePO4 precursor.

[0079] Step 3: Heating in a tube furnace under an argon atmosphere. The LiFePO4 precursor is ground, and 150 mg of the precursor powder is placed in a boat. The sintering temperature is 700℃ and the sintering time is 8 h to obtain the finished LiFePO4.

[0080] Step 4: Assemble the materials into coin cells and test their electrochemical performance. Weigh Super P, PVDF, and the obtained LiFePO4 in a specific ratio, mix with a certain amount of 1-methyl-2-pyrrolidone (NMP), and stir on a magnetic stirrer for 2 hours to obtain a positive electrode slurry. Coat the slurry onto aluminum foil, vacuum dry it, and cut it into sheets to obtain the positive electrode. Assemble the coin cells in an argon atmosphere and test their electrochemical performance.

[0081] Figure 11The discharge specific capacity of LiFePO4 obtained by conventional tube furnace heating at different rates was demonstrated. At 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, the discharge specific capacities of LFP25-3 were 151.14 mAh / g, 140.99 mAh / g, 132.85 mAh / g, 122.30 mAh / g, 113.12 mAh / g, and 96.32 mAh / g, respectively. The capacity of the tube furnace sample at all different rates was significantly lower than that of the rapidly thermally shock synthesized sample, highlighting the superior rate performance of the rapidly thermally shock sample.

[0082]

[0083] Table 1. XRD patterns of the rapid thermal shock sample (Example 4) and the tube furnace sample (Comparative Example 1).

[0084] Comparison of Retouched Results

[0085] Table 1 shows a comparison of the XRD refinement results of the rapid thermal shock sample (Example 4) and the tube furnace sample (Comparative Example 1). The cell parameters a and b of the rapid thermal shock sample are both greater than those of the tube furnace sample, proving that the rapid thermal shock method can broaden the lithium ion transport channel while removing the water of crystallization, thus obtaining LiFePO4 cathode material with excellent electrochemical performance.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for synthesizing lithium iron phosphate cathode material by rapid thermal shock using hydrated iron phosphate as raw material, characterized in that, The method comprises the following steps: Step 1, preparing hydrated iron phosphate by using coprecipitation method; Dissolving FeSO4·7H2O in water to obtain solution A, and dissolving NH4H2PO4 in water to obtain solution B; Mixing solution A and solution B, the molar ratio of iron element to phosphorus element being 1:(1.00-1.40), and stirring in water bath during mixing, adding H2O2 dropwise to the mixed solution to perform oxidation reaction, and adding an alkaline solution to adjust the pH value, to obtain an iron phosphate precipitate solution; Performing solid-liquid separation on the iron phosphate precipitate solution, and drying the obtained solid material in an oven after washing to obtain nano-level iron phosphate trihydrate; Step 2, ball-milling the iron phosphate trihydrate obtained in step 1 with a lithium source and a carbon source, and drying the solution in a vacuum oven to obtain a LiFePO4 precursor; Step 3, placing the LiFePO4 precursor obtained in step 2 on a heating base in an inert atmosphere, and performing rapid thermal shock on the LiFePO4 precursor powder by electrifying to obtain a LiFePO4 positive electrode material.

2. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, wherein, The heating temperature of the water bath stirring in step 1 is 60-90℃, and the stirring speed is 400-900 rpm.

3. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, characterized in that, The amount of H2O2 added in step 1 is 0.7-1 times the amount of iron source material; the alkaline solution in step 1 is one or a combination of sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

4. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, characterized in that, The pH value in step 1 is adjusted to a range of 2-3.

5.

5. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, characterized in that, The drying temperature in step 1 is 100-120℃, and the drying time is 12-24 h; the temperature of the vacuum oven in step 2 is 80℃, and the drying time is 12 h.

6. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, characterized in that, The molar ratio of lithium element in the lithium source to iron phosphate trihydrate in step 2 is (1.00-1.08):1, and the lithium source is one or a combination of lithium carbonate, lithium hydroxide, lithium oxalate, lithium nitrate, and lithium chloride.

7. The method for synthesizing lithium iron phosphate cathode material by rapid thermal shock according to claim 1, characterized in that, The mass of the carbon source added in step 2 is 10%-30% of the mass of the LiFePO4 precursor powder, and the carbon source is one or a combination of glucose, oxalic acid, citric acid, malic acid, antiseptic acid, maltose, adipic acid, ethylene glycol, sucrose, conductive carbon black, ketjen black, graphene, and carbon nanotube. 8.The method of claim 1, wherein the iron phosphate hydrate is used as a raw material to synthesize the lithium iron phosphate cathode material through rapid thermal shock. The ball milling aid in step 2 is one of water, ethanol, and acetone, the ball-to-material ratio is 40:3, and the ball milling time is 5-10 h; the ball-to-material ratio is a mass ratio. 9.The method of claim 1, wherein the method is characterized by, The heating base in step 3 is carbon cloth, carbon felt, stainless steel sheet, or nickel foil. 10.The method of claim 1, wherein the method is characterized by, The electrification current for rapid thermal shock in step 3 is 14-17 A, and the duration is 20-40 s.

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