Preparation method of lithium manganese iron phosphate positive electrode material

Abstract

The invention discloses a preparation method of a lithium manganese iron phosphate positive electrode material, which comprises the following steps: mixing a manganese iron phosphate precursor, a lithium source and a carbon source to prepare slurry, grinding, spray-drying and sintering to prepare the lithium manganese iron phosphate positive electrode material, adding a dispersing aid into the slurry, grinding, and drying to obtain the lithium manganese iron phosphate positive electrode material. The mass of the dispersing aid is 1-2% of that of the ferromanganese phosphate precursor, and the dispersing aid is a mixture of phytic acid and polyvinylpyrrolidone in a mass ratio of (1-4): 1. According to the preparation method, 1-2% of phytic acid and polyvinylpyrrolidone dispersing auxiliaries are introduced into the slurry in the preparation process of the lithium manganese iron phosphate positive electrode material, so that charges on the surfaces of particles are increased, the reaction force among the particles is improved, meanwhile, the pH value of the slurry is adjusted, the initial efficiency of the obtained lithium manganese iron phosphate positive electrode material is ensured to be greater than 95.7%, and meanwhile, the service life of the lithium manganese iron phosphate positive electrode material is prolonged. The compaction density is not less than 1.994 g / cm < 3 >, and the 1C specific discharge capacity is not less than 145.1 mAh / g.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron manganese phosphate cathode materials, and in particular to a preparation method of lithium iron manganese phosphate cathode materials. Background Art

[0002] Due to its advantages such as cycle performance, manufacturing cost, and non-toxic raw materials, lithium iron phosphate is widely used in energy storage, power and other fields. However, its low-temperature performance and energy density are poor. Lithium iron manganese phosphate is to replace a part of the iron element in lithium iron phosphate with manganese element to improve the discharge voltage and energy density. At present, lithium iron manganese phosphate is mainly mixed with ternary materials. However, with the continuous research and development of the industry insiders, its tap density and cycle performance will be further improved, and it can replace lithium iron phosphate as the next-generation widely used cathode material.

[0003] If using lithium iron manganese phosphate precursor as the phosphorus source, iron source and manganese source, and then adding lithium source and carbon source for grinding, lithium iron manganese phosphate is prepared by the solid-phase method. Under the above conditions, as the grinding time prolongs, the specific surface area of the slurry will become larger and larger, and the slurry will become viscous with the decrease of the grinding particle size, resulting in poor processability of the slurry, and even situations such as uneven slurry and blockage of the spray drying equipment, which will affect the subsequent process and production capacity. At present, in order to ensure the uniformity and fluidity of the slurry, dispersing aids such as polyvinylpyrrolidone, polyacrylamide, sodium dodecyl sulfate and polyethylene glycol are usually added to the slurry. However, the inventor found in actual production that although the above dispersing aids can improve the uniformity and fluidity of the slurry, they have little effect on the electrochemical performance and tap density of the cathode material. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of lithium iron manganese phosphate cathode materials, which can improve the uniformity and fluidity of the slurry while improving the electrochemical performance and tap density of the lithium iron manganese phosphate cathode materials.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a preparation method of lithium iron manganese phosphate cathode materials, in which the lithium iron manganese phosphate precursor, lithium source and carbon source are mixed to form a slurry, and then ground, spray-dried and sintered to obtain the lithium iron manganese phosphate cathode materials. After adding a dispersing aid to the slurry, it is ground. The mass of the dispersing aid is 1-2% of the mass of the lithium iron manganese phosphate precursor, and the dispersing aid is a mixture of phytic acid and polyvinylpyrrolidone with a mass ratio of 1-4:1.

[0006] Further, the mass ratio of phytic acid to polyvinylpyrrolidone in the dispersing aid is 1.5-3:1.

[0007] Further, titanium dioxide as an additive is added to the slurry, and the mass of the titanium dioxide is 1400 - 1600 ppm of the mass of the iron manganese phosphate precursor.

[0008] Further, the lithium source is lithium carbonate, and the molar ratio of the iron manganese phosphate precursor to lithium carbonate is 1:1.015.

[0009] Further, the carbon source is an organic carbon source such as sucrose, polyethylene glycol or a mixture of both; the carbon source is 6 - 10 wt% of the mass percentage of the iron manganese phosphate precursor.

[0010] Further, the solid content of the slurry is 35 - 40%, and the slurry is ground in a sand mill, and the grinding particle size is controlled at 250 - 350 nm.

[0011] Further, the inlet air temperature of the spray drying process is 220 - 240 °C, the outlet air temperature is 105 - 110 °C, and the atomizer frequency is 370 - 380 Hz.

[0012] Further, the sintering process is to first hold at 450 °C for 5 h, then heat up to 745 - 775 °C and hold for 9 h, and the heating rate is 2.5 °C / min.

[0013] Further, the preparation method of the dispersion aid is to add phytic acid and polyvinylpyrrolidone to deionized water and stir evenly. The mass ratio of the total mass of phytic acid and polyvinylpyrrolidone to the mass of deionized water is 5:16.

[0014] Further, the iron source, manganese source, and phosphorus source are reacted, and the iron manganese phosphate precursor MnxFe1-xPO4 is prepared through filtration, washing, and drying, where 0.5 ≤ x ≤ 0.65; the molar ratio of Fe:Mn:P in the mixture of the iron source, manganese source, and phosphorus source is (0.35 - 0.5):(0.65 - 0.5):1.

[0015] The beneficial effects of the present invention are as follows: By introducing 1 - 2% of phytic acid and polyvinylpyrrolidone dispersion aids into the slurry during the preparation process of the lithium iron manganese phosphate cathode material, the charge on the particle surface is increased, the reaction force between particles is improved, and the pH of the slurry is adjusted. The obtained lithium iron manganese phosphate cathode material ensures that the initial efficiency is greater than 95.7% while ensuring that the tap density is not less than 1.994 g / cm 3 , and the discharge specific capacity at 1C is not less than 145.1 mAh / g. Description of the Drawings

[0016] Figure 1 is the SEM image of the spray-dried material of the LMFP-64 cathode material obtained in Example 2;

[0017] Figure 2It is the charge-discharge curve of the LMFP-64 cathode material obtained in Example 2. Detailed implementation mode

[0018] The present invention will be further described below in conjunction with embodiments.

[0019] Example 1:

[0020] (1) Prepare raw materials: Mn 0.65 Fe 0.35 PO4 (2000 g), Li2CO3 (521.4 g), sucrose (80 g), PEG (40 g), TiO2 (4.9 g), and prepare the above substances into a slurry with a solid content of 40%;

[0021] Take 17.9 g of phytic acid solution (the mass percentage of phytic acid in the phytic acid solution is 70%), 12.5 g of PVP, and 80 g of deionized water to prepare a dispersion aid. Put the slurry and the dispersion aid into a vertical sand mill and grind it to a particle size D50 of 300 nm at a speed of 2400 rpm;

[0022] (2) Spray-dry the slurry obtained in step (1) at an inlet air temperature of 240 °C, an outlet air temperature of 110 °C, and an atomizer frequency of 370 Hz;

[0023] (3) Under the protection of a nitrogen atmosphere, heat the dried material obtained in step (2) to 450 °C at a heating rate of 2.5 °C / min, hold it at 450 °C for 7 h, then heat it to 745 °C at a heating rate of 2.5 °C / min and hold it for 9 h, and cool it to room temperature to obtain the LMFP-55 cathode material.

[0024] Example 2:

[0025] Only change the ratio of phytic acid and PVP in the dispersion aid. In this example, the ratio of phytic acid and PVP is 6:4, and the others are the same as in Example 1, to obtain the LMFP-64 cathode material.

[0026] Example 3:

[0027] Only change the ratio of phytic acid and PVP in the dispersion aid. In this example, the ratio of phytic acid and PVP is 7:3, and the others are the same as in Example 1, to obtain the LMFP-73 cathode material.

[0028] Example 4:

[0029] Only change the ratio of phytic acid and PVP in the dispersion aid. In this example, the ratio of phytic acid and PVP is 8:2, and the others are the same as in Example 1, to obtain the LMFP-82 cathode material.

[0030] Comparative Example 1:

[0031] Only change the ratio of phytic acid and PVP in the dispersing agent. In this comparative example, the ratio of phytic acid and PVP is 9:1, and the others are the same as in Example 1, obtaining the LMFP-91 cathode material.

[0032] Comparative Example 2:

[0033] Only change the ratio of phytic acid and PVP in the dispersing agent. In this comparative example, no phytic acid is added, and only PVP is added. The others are the same as in Example 1, obtaining the LMFP-91 cathode material.

[0034] Comparative Example 3:

[0035] Only change the ratio of phytic acid and PVP in the dispersing agent. In this comparative example, only phytic acid is added, and no PVP is added. The others are the same as in Example 1, obtaining the LMFP-91 cathode material.

[0036] Perform physical and chemical and electrical property tests and analyses on the cathode materials obtained in the examples and comparative examples. The electrical property test is the coin cell test method. The production and test process of the coin cell are as follows: (1) Preparation of the electrode sheet: Mix the active material, conductive agent, and binder in a mass ratio of 80:10:10. Stir the mixture evenly in NMP (N-methylpyrrolidone), coat it on the aluminum foil, then dry and press it in a vacuum drying oven. Cut the dried and pressed electrode sheet into the required size for subsequent assembly; the negative electrode is a lithium metal sheet; (2) Assembly process: Perform the assembly in a glove box to ensure an inert atmosphere in the environment. Use a separator and electrolyte for battery assembly. After assembly, let it stand in an incubator for 2 hours before testing; (3) Test conditions: The test temperature is 25°C. Perform charge and discharge tests at a current of 0.1C within a voltage range of 2.5 - 4.5V. Record the first charge capacity and the first discharge capacity during the test process, and calculate the first charge-discharge efficiency. Compaction density test method: Release pressure of 3t.

[0037] The addition amounts of phytic acid and PVP in the examples and comparative examples and the test parameters of the prepared cathode materials are shown in Table 1.

[0038] Table 1

[0039]

[0040] As can be seen from Table 1, Examples 1 - 4 ensure a compaction density greater than 1.994 g / cm 3 while ensuring the discharge specific capacity and the first efficiency. In Comparative Example 1, due to too much phytic acid in the ratio, although the first efficiency can be ensured, its discharge specific capacity and compaction density decrease significantly.

Claims

1. A method for preparing a lithium iron manganese phosphate positive electrode material, comprising mixing a manganese iron phosphate precursor, a lithium source, and a carbon source to form a slurry, and then grinding, spray drying, and sintering to obtain the lithium iron manganese phosphate positive electrode material, characterized in that: The slurry is ground after adding a dispersing aid, wherein the mass of the dispersing aid is 1-2% of the mass of the ferromanganese phosphate precursor, and the dispersing aid is a mixture of phytic acid and polyvinyl pyrrolidone in a mass ratio of 1-4:

1.

2. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The mass ratio of phytic acid to polyvinyl pyrrolidone in the dispersing aid is 1.5 to 3:

1.

3. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: Add titanium dioxide as an additive to the slurry, wherein the mass of the titanium dioxide is 1400-1600 ppm of the mass of the ferromanganese phosphate precursor.

4. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The lithium source is lithium carbonate, and the molar ratio of the ferromanganese phosphate precursor to the lithium carbonate is 1:1.

015.

5. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The carbon source is an organic carbon source of sucrose, polyethylene glycol or a mixture of the two; the carbon source is 6-10wt% of the mass percentage of the ferromanganese phosphate precursor.

6. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The solid content of the slurry is 35-40%. The slurry is ground in a sand mill, and the grinding particle size is controlled at 250-350nm.

7. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The spray drying process has an inlet air temperature of 220-240° C., an outlet air temperature of 105-110° C., and an atomizer frequency of 370-380 Hz.

8. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The sintering process is to first keep the temperature at 450° C. for 5 hours, then increase the temperature to 745-775° C. and keep the temperature for 9 hours, with the heating rate being 2.5° C. / min.

9. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The preparation method of the dispersing aid is to add phytic acid and polyvinyl pyrrolidone into deionized water and stir evenly, and the mass ratio of the total mass of phytic acid and polyvinyl pyrrolidone to deionized water is 5:

16.

10. The method for preparing a lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: The iron source, manganese source and phosphorus source are reacted, and the manganese ferrophosphate precursor MnxFe1-xPO4 is prepared by filtering, washing and drying, wherein 0.5≤x≤0.65; the molar ratio of Fe:Mn:P in the mixture of the iron source, manganese source and phosphorus source is (0.35~0.5):(0.65~0.5):1.

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