A preparation method and application of lithium manganese iron phosphate cathode material

Abstract

This invention relates to the field of lithium-ion battery cathode material technology, specifically to a method for preparing and applying lithium manganese iron phosphate cathode material. The method for preparing the lithium manganese iron phosphate cathode material includes the following steps: (a) performing a first milling on a mixture containing a manganese source, a phosphorus source, a dispersant, and a ball milling aid to obtain a first slurry; performing a second milling on a mixture containing an iron source, a lithium source, and a carbon source to obtain a second slurry; (b) mixing the first slurry and the second slurry, followed by ball milling and drying to obtain a lithium manganese iron phosphate precursor; and (c) subjecting the lithium manganese iron phosphate precursor to two-stage sintering and pulverization under an inert atmosphere. The method for preparing the lithium manganese iron phosphate cathode material has advantages such as simple synthesis, low pollution, low process requirements, and good uniformity and conductivity of the prepared material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and more specifically, to a method for preparing and applying lithium manganese iron phosphate cathode material. Background Technology

[0002] With the further development of new energy electric vehicles, the market has placed an even more urgent demand on high-energy-density lithium-ion batteries. With the energy density of lithium iron phosphate nearing its limit, lithium manganese iron phosphate has emerged as a replacement product and gained market favor. Lithium manganese phosphate possesses the advantages of lithium iron phosphate, including high safety, long cycle life, low cost, and environmental friendliness. Furthermore, it features a dual-voltage platform, enabling it to provide higher energy density for batteries, making it a key focus for the future development of the cathode material market.

[0003] However, the synthesis of lithium manganese iron phosphate (LFP) is difficult. The hydrothermal-based liquid-phase method requires sophisticated equipment (high temperature and high pressure) and causes significant pollution. The solid-phase method, based on sand milling and calcination, suffers from poor particle size control and uniformity due to the introduction of manganese and iron precursors. Furthermore, LFP has lower electrical conductivity than lithium iron phosphate, all of which hinder its development.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing lithium manganese iron phosphate cathode material. This method has advantages such as simple synthesis, low pollution, low process requirements, and good uniformity and conductivity of the prepared material.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] One aspect of the present invention relates to a method for preparing a lithium manganese iron phosphate cathode material, comprising the following steps:

[0008] (a) A mixture containing a manganese source, a phosphorus source, a dispersant and a ball milling aid is subjected to a first sand milling to obtain a first slurry; a mixture containing an iron source, a lithium source and a carbon source is subjected to a second sand milling to obtain a second slurry;

[0009] (b) The first slurry and the second slurry are mixed and then ball-milled and dried to obtain lithium manganese iron phosphate precursor;

[0010] (c) The lithium manganese iron phosphate precursor is subjected to two-stage sintering and pulverization under an inert atmosphere.

[0011] The preparation method of the lithium manganese iron phosphate cathode material has the advantages of simple synthesis, low pollution, low process requirements, and good uniformity and conductivity of the prepared material.

[0012] Another aspect of the present invention relates to a positive electrode sheet, which is mainly made of lithium manganese iron phosphate positive electrode material prepared by the aforementioned method for preparing lithium manganese iron phosphate positive electrode material.

[0013] Another aspect of the present invention relates to a lithium-ion battery, including the aforementioned positive electrode.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The method for preparing lithium manganese iron phosphate cathode material provided by this invention is simple, has low process requirements, low pollution, and low cost. It adopts a two-step grinding process, in which the manganese source and the iron source are sand-milled separately and then mixed, avoiding uneven particle size and uneven mixing caused by the different processing performance of the manganese source and the iron source. The introduction of dispersant and ball milling aid accelerates the sand milling efficiency of the manganese source, and the ball milling aid and carbon source enhance the conductivity of the lithium manganese iron phosphate material. The two-stage sintering improves the integrity of the crystal structure and the uniformity of particle growth of the material. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 The image shows the XRD results of the lithium manganese iron phosphate material prepared in Example 1.

[0018] Figure 2 The image shows the SEM results of the lithium manganese iron phosphate material prepared in Example 1.

[0019] Figure 3 The graph shows the electrical performance test results of the lithium manganese iron phosphate material prepared in Example 1;

[0020] Figure 4 SEM image of lithium manganese iron phosphate material prepared in Comparative Example 1;

[0021] Figure 5 The image shows the SEM results of the lithium manganese iron phosphate material prepared in Comparative Example 2.

[0022] Figure 6 The image shows the XRD results of the lithium manganese iron phosphate material prepared in Comparative Example 2. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] One aspect of the present invention relates to a method for preparing a lithium manganese iron phosphate cathode material, comprising the following steps:

[0025] (a) A mixture containing a manganese source, a phosphorus source, a dispersant and a ball milling aid is subjected to a first sand milling to obtain a first slurry; a mixture containing an iron source, a lithium source and a carbon source is subjected to a second sand milling to obtain a second slurry;

[0026] (b) The first slurry and the second slurry are mixed and then ball-milled and dried to obtain lithium manganese iron phosphate precursor;

[0027] (c) The lithium manganese iron phosphate precursor is subjected to two-stage sintering and pulverization under an inert atmosphere.

[0028] The preparation method of the lithium manganese iron phosphate cathode material adopts a two-step grinding process, in which the manganese source and the iron source are ground separately and then mixed. This avoids the uneven particle size and uneven mixing caused by the different processing performance of the manganese source and the iron source. The introduction of dispersant and ball milling aid accelerates the grinding efficiency of the manganese source. The ball milling aid and carbon source enhance the conductivity of the lithium manganese iron phosphate material. The two-stage sintering improves the integrity of the crystal structure and the uniformity of particle growth of the material.

[0029] The preparation method of the lithium manganese iron phosphate cathode material has the advantages of simple synthesis, low pollution, low process requirements, and good uniformity and conductivity of the prepared material.

[0030] Preferably, the amount of the dispersant added is 5% to 15% of the mass of the manganese source (e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%).

[0031] Preferably, the dispersant comprises at least one of polyethylene glycol, polyvinyl alcohol, or polyacrylic acid.

[0032] Preferably, the amount of the ball milling aid added is 0.1% to 3% of the mass of the manganese source (e.g., 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%).

[0033] Preferably, the ball milling aid includes at least one of titanium dioxide, aluminum oxide, or magnesium oxide.

[0034] Preferably, the two-stage sintering specifically includes:

[0035] The first stage of sintering is held at 300–400℃ (e.g., 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃) for 2–5 hours (e.g., 2h, 3h, 4h or 5h), and the second stage of sintering is held at 700–800℃ (e.g., 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃ or 800℃) for 4–7 hours (e.g., 4h, 5h, 6h or 7h).

[0036] Preferably, the heating rate of the first sintering stage is 1 to 5 °C / min (e.g., 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min).

[0037] Preferably, the heating rate of the second sintering stage is 3 to 15 °C / min (e.g., 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min or 15 °C / min).

[0038] Preferably, the molar ratio of iron to manganese in the mixture of the first slurry and the second slurry is (4-6):(4-6) (e.g., 4:6, 5:5 or 6:4).

[0039] Preferably, the molar ratio of lithium to phosphorus in the mixture of the first slurry and the second slurry is (1.00 to 1.20):1 (e.g., 1.00:1, 1.05:1, 1.10:1, 1.15:1 or 1.20:1).

[0040] Preferably, the molar ratio of the sum of the molar amounts of iron and manganese to the molar ratio of phosphorus in the mixture of the first slurry and the second slurry is (0.93 to 0.99):1 (e.g., 0.93:1, 0.94:1, 0.95:1, 0.96:1, 0.97:1, 0.98:1 or 0.99:1).

[0041] Preferably, the D of the particles in the first slurry50 The micrometer size is 0.30–0.45 μm (e.g., 0.30 μm, 0.33 μm, 0.35 μm, 0.38 μm, 0.40 μm, 0.43 μm or 0.45 μm).

[0042] Preferably, the D of the particles in the second slurry 50 The micrometer size is 0.30–0.45 μm (e.g., 0.30 μm, 0.33 μm, 0.35 μm, 0.38 μm, 0.40 μm, 0.43 μm or 0.45 μm).

[0043] Preferably, the particle size D in the ball-milled slurry is... 50 The micrometer size is 0.30–0.45 μm (e.g., 0.30 μm, 0.33 μm, 0.35 μm, 0.38 μm, 0.40 μm, 0.43 μm or 0.45 μm).

[0044] Preferably, the particle size of the pulverized particles is 0.8 to 1.5 μm (e.g., 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm).

[0045] Preferably, the manganese source includes manganese dioxide and / or manganese tetroxide.

[0046] Preferably, the phosphorus source includes monoammonium phosphate and / or diammonium hydrogen phosphate.

[0047] Preferably, the iron source includes at least one of ferric phosphate, ferric phosphate dihydrate, or ferric citrate.

[0048] Preferably, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, or butyllithium.

[0049] Preferably, the drying method includes, but is not limited to, spray drying.

[0050] Preferably, the pulverization method includes, but is not limited to, airflow pulverization.

[0051] The solvent used in this invention is deionized water.

[0052] Another aspect of the present invention relates to a positive electrode sheet, which is mainly made of lithium manganese iron phosphate positive electrode material prepared by the aforementioned method for preparing lithium manganese iron phosphate positive electrode material.

[0053] Another aspect of the present invention relates to a lithium-ion battery, including the aforementioned positive electrode.

[0054] The embodiments of the present invention will now be described in detail with reference to specific examples and comparative examples.

[0055] Example 1

[0056] The preparation method of lithium manganese iron phosphate cathode material provided in this embodiment includes the following steps:

[0057] (1) Weigh 751.9g of manganese dioxide, 1015.2g of monoammonium phosphate, 90.4g of polyethylene glycol and 7.6g of titanium dioxide and mix them in 3kg of pure water. Then place them in a sand mill 1 and grind them until the average particle size D50 of the slurry is 0.43μm. Weigh 2000g of iron phosphate, 824.8g of lithium carbonate and 467.1g of sucrose and mix them in 5kg of pure water. Then place them in a sand mill 2 and grind them until the average particle size D50 of the slurry is 0.43μm. Mix the slurries from sand mills 1 and 2 evenly in a ball mill with zirconium beads to obtain slurry 3. The particle size D50 of slurry 3 is 0.40μm.

[0058] (2) The slurry 3 obtained in step (1) is spray-dried at an inlet air temperature of 240°C and an outlet air temperature of 90°C to obtain lithium manganese iron phosphate precursor.

[0059] (3) The lithium manganese iron phosphate precursor was placed in a box-type atmosphere furnace and calcined at 350°C for 3 hours at a rate of 2°C / min under the protection of flowing nitrogen atmosphere. Then, it was calcined at 750°C for 6 hours at a rate of 5°C / min. After natural cooling, it was crushed to an average particle size D50 of 1.1 μm to obtain lithium manganese iron phosphate material.

[0060] Samples were taken for SEM, XRD, and electrical performance testing, and the results are as follows: Figure 1 , Figure 2 and Figure 3 As shown in the figure. XRD patterns show that the diffraction peaks of the synthesized material correspond to the standard card representing lithium manganese iron phosphate (JCPDS#01-073-7355), with sharp peak shapes and good crystal growth. SEM indicates that the primary particles of this lithium iron phosphate material have a spherical morphology, with a particle size of approximately 100–200 nm. Electrical performance tests show that the material exhibits a distinct dual-voltage plateau, with an initial charge specific capacity of 159.2 mAh / g and a discharge specific capacity of 152.2 mAh / g.

[0061] Example 2

[0062] The preparation method of lithium manganese iron phosphate cathode material provided in this embodiment includes the following steps:

[0063] (1) Weigh 676.7g of manganese dioxide, 1048.9g of diammonium hydrogen phosphate, 81.9g of polyethylene glycol and 6.8g of titanium dioxide and mix them in 2.5kg of pure water. Then place them in a sand mill 1 and grind them until the average particle size D50 of the slurry is 0.42μm. Weigh 1800g of iron phosphate, 742.3g of lithium carbonate and 420.3g of sucrose and mix them in 4.5kg of pure water. Then place them in a sand mill 2 and grind them until the average particle size D50 of the slurry is 0.44μm. Mix the slurries from sand mills 1 and 2 evenly in a stirred ball mill with zirconium beads to obtain slurry 3. The particle size D50 of slurry 3 is 0.41μm.

[0064] (2) The slurry 3 obtained in step (1) is spray-dried at an inlet air temperature of 240°C and an outlet air temperature of 90°C to obtain lithium manganese iron phosphate precursor.

[0065] (3) The lithium manganese iron phosphate precursor was placed in a box-type atmosphere furnace and calcined at 400°C for 3 hours at a rate of 2°C / min under the protection of a flowing nitrogen atmosphere. Then, it was calcined at 770°C for 6 hours at a rate of 5°C / min. After natural cooling, it was crushed to an average particle size D50 of 1.2 μm to obtain lithium manganese iron phosphate material.

[0066] Example 3

[0067] The preparation method of lithium manganese iron phosphate cathode material provided in this embodiment includes the following steps:

[0068] (1) Weigh 751.9g of manganese dioxide, 1015.2g of monoammonium phosphate, 90.4g of polyethylene glycol and 7.6g of titanium dioxide and mix them in 3kg of pure water. Then place them in a sand mill 1 and grind them until the average particle size D50 of the slurry is 0.40μm. Weigh 2000g of iron phosphate, 824.8g of lithium carbonate and 467.1g of sucrose and mix them in 5kg of pure water. Then place them in a sand mill 2 and grind them until the average particle size D50 of the slurry is 0.40μm. Mix the slurries from sand mills 1 and 2 evenly in a ball mill with zirconium beads to obtain slurry 3. The particle size D50 of slurry 3 is 0.35μm.

[0069] (2) Same as Example 1;

[0070] (3) The lithium manganese iron phosphate precursor was placed in a box-type atmosphere furnace and calcined at 400°C for 2 hours at a rate of 1°C / min under the protection of flowing nitrogen atmosphere. Then, it was calcined at 700°C for 7 hours at a rate of 3°C / min. After natural cooling, it was crushed to an average particle size D50 of 0.8 μm to obtain lithium manganese iron phosphate material.

[0071] Example 4

[0072] The preparation method of lithium manganese iron phosphate cathode material provided in this embodiment includes the following steps:

[0073] (1) Weigh 676.7g of manganese dioxide, 1048.9g of diammonium hydrogen phosphate, 81.9g of polyethylene glycol and 6.8g of titanium dioxide and mix them in 2.5kg of pure water. Then place them in a sand mill 1 and grind them until the average particle size D50 of the slurry is 0.45μm. Weigh 1800g of iron phosphate, 742.3g of lithium carbonate and 420.3g of sucrose and mix them in 4.5kg of pure water. Then place them in a sand mill 2 and grind them until the average particle size D50 of the slurry is 0.45μm. Mix the slurries from sand mills 1 and 2 evenly in a ball mill with zirconium beads to obtain slurry 3. The particle size D50 of slurry 3 is 0.30μm.

[0074] (2) The slurry 3 obtained in step (1) is spray-dried at an inlet air temperature of 240°C and an outlet air temperature of 90°C to obtain lithium manganese iron phosphate precursor.

[0075] (3) The lithium manganese iron phosphate precursor was placed in a box-type atmosphere furnace and calcined at 300°C for 5 hours at a rate of 5°C / min under the protection of flowing nitrogen atmosphere. Then, it was calcined at 800°C for 4 hours at a rate of 15°C / min. After natural cooling, it was crushed to an average particle size D50 of 1.5 μm to obtain lithium manganese iron phosphate material.

[0076] Comparative Example 1

[0077] The only difference between Comparative Example 1 and Example 1 is that the two-step sanding process was not performed in step (1). Step (1) is as follows:

[0078] (1) Weigh 751.9g manganese dioxide, 1015.2g monoammonium phosphate, 90.4g polyethylene glycol, 7.6g titanium dioxide, 2000g iron phosphate, 824.8g lithium carbonate and 467.1g sucrose and mix them in 8kg pure water. Place them in a sand mill 1 and grind them until the average particle size D50 of the slurry is 0.40μm.

[0079] SEM images of the obtained finished products are as follows Figure 4 As shown, the particle growth is uneven, with obvious submicron-sized large particles, which is not conducive to the material's electrical performance (0.1C discharge specific capacity is only 144.4mAh / g).

[0080] Comparative Example 2

[0081] The only difference between this comparative example and the embodiment is that the two-stage sintering was not performed in step (3). Step (3) is as follows:

[0082] (3) The lithium manganese iron phosphate precursor was placed in a box-type atmosphere furnace and calcined at 750°C for 9 hours under a flowing nitrogen atmosphere. After natural cooling, it was pulverized to an average particle size D50 of 1.1 μm to obtain lithium manganese iron phosphate material.

[0083] Its SEM photos are displayed in Figure 5 The boundaries between particles are not clear enough, and there is a tendency for them to fuse and grow together. XRD test results are as follows: Figure 6 As shown, the diffraction peaks are weak in intensity and have a wide spectrum, indicating a relatively poor degree of crystallinity.

[0084] The performance of the lithium manganese iron phosphate cathode materials prepared in the examples and comparative examples was tested. Specifically, the prepared lithium manganese iron phosphate, conductive agent, and binder were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 9:0.5:0.5 to obtain an electrode slurry. The slurry was coated onto aluminum foil, vacuum dried at 100°C for 12 hours, and then sliced ​​to obtain the cathode sheet. Using argon as a protective gas, the cathode sheet, anode sheet (lithium metal), separator, and electrolyte were assembled into a CR2032 type button cell using a glove box. The charge and discharge performance of the battery was tested using a Blue Electric testing system: constant current and constant voltage charging (cutoff voltage 4.5V, cutoff current 0.05A), and constant current discharging (cutoff voltage 2.5V). The results are shown in Table 1.

[0085] Table 1 Performance Comparison of Lithium Manganese Iron Phosphate

[0086]

[0087]

[0088] As can be seen from Table 1, the lithium manganese iron phosphate cathode material prepared in the embodiments of the present invention has good uniformity and excellent electrochemical performance, which is superior to that of the comparative example.

[0089] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a lithium iron manganese phosphate cathode material, characterized in that, The method comprises the following steps: (a) performing first sand milling on a mixed system containing a manganese source, a phosphorus source, a dispersing agent and a ball milling aid to obtain a first slurry; performing second sand milling on a mixed system containing an iron source, a lithium source and a carbon source to obtain a second slurry; D50 of the particles in the first slurry is 0.30-0.45 μm 50 0.30-0.45 μm; D50 of the particles in the second slurry is 0.30-0.45 pm 50 0.30-0.45 pm; (b) mixing the first slurry and the second slurry, then performing ball milling and drying to obtain a lithium iron manganese phosphate precursor; (c) performing two-stage sintering and crushing on the lithium iron manganese phosphate precursor in an inert atmosphere.

2. The method of claim 1, wherein the lithium iron manganese phosphate cathode material is prepared by the steps of: The method comprises at least one of the following technical features (1) to (4): ​ (1) The dispersing agent is added in an amount of 5% to 15% of the mass of the manganese source; (2) The dispersing agent comprises at least one of polyethylene glycol, polyvinyl alcohol or polyacrylic acid; (3) The ball milling aid is added in an amount of 0.1% to 3% of the mass of the manganese source; (4) The ball milling aid comprises at least one of titanium dioxide, aluminum oxide or magnesium oxide.

3. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The two-stage sintering specifically comprises: The first-stage sintering is performed at 300 to 400℃ for 2 to 5h, and the second-stage sintering is performed at 700 to 800℃ for 4 to 7h.

4. The method for preparing lithium manganese iron phosphate cathode material according to claim 3, characterized in that, The first-stage sintering has a heating rate of 1 to 5℃ / min; And / or, the second-stage sintering has a heating rate of 3 to 15℃ / min.

5. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The method comprises at least one of the following technical features (1) to (3): (1) The molar ratio of iron to manganese in the mixed system after mixing of the first slurry and the second slurry is (4 to 6):(4 to 6); (2) The molar ratio of lithium to phosphorus in the mixed system after mixing of the first slurry and the second slurry is (1.00 to 1.20):1; (3) The molar ratio of the sum of the molar amounts of iron and manganese to phosphorus in the mixed system after mixing of the first slurry and the second slurry is (0.93 to 0.99):

1.

6. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The D50 of the particles in the slurry after ball milling is 0.30 to 0.45μm.

7. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The particle size of the particles after crushing is 0.8 to 1.5μm.

8. The method for preparing lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The method comprises at least one of the following technical features (1) to (4): (1) The manganese source comprises manganese dioxide and / or trimanganese tetroxide; (2) The phosphorus source comprises monoammonium phosphate and / or dihydrogen ammonium phosphate; (3) The iron source comprises at least one of iron phosphate, dihydrogen iron phosphate or iron citrate; (4) The lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium oxalate or butyl lithium.

9. A positive electrode sheet characterized by comprising: The lithium iron manganese phosphate anode material is mainly prepared by the preparation method of the lithium iron manganese phosphate anode material according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized by, The anode sheet comprises the anode sheet according to claim 9.

Images