A lithium manganese iron phosphate material and a preparation method thereof
By employing solvothermal synthesis and hot-pressing sintering processes, the conductivity and cycle stability issues of lithium manganese iron phosphate materials have been resolved, enabling the efficient preparation of high-performance lithium manganese iron phosphate materials suitable for lithium-ion battery cathode materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEFEI GUOXUAN HIGH TECH POWER ENERGY
- Filing Date
- 2024-11-07
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional methods for preparing lithium manganese iron phosphate materials suffer from low production efficiency, poor conductivity, and poor cycle stability. In particular, the uneven dispersion of elements and uneven carbon coating lead to obstructed lithium-ion transport and excessively large material particle size.
A ternary metal-glycerate precursor of manganese iron was prepared by solvothermal synthesis. Combined with high-energy ball milling and hot pressing sintering processes, the uniformity of element distribution and carbon coating effect were achieved by combining primary CVD-like sintering and secondary hot pressing sintering, thereby controlling the particle size and density of the material.
The conductivity and cycle stability of lithium manganese iron phosphate materials were improved, the difficulty of the nano-sizing process was reduced, the production efficiency was increased, and high solid density and excellent electrical conductivity were obtained.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery cathode materials, and in particular to a lithium manganese iron phosphate material and its preparation method. Background Technology
[0002] With the continuous development of portable electronic devices, electric vehicles, and large-scale energy storage equipment markets, improving the performance of lithium-ion batteries has become increasingly important. The cathode is a key component of lithium-ion batteries, and the performance of the cathode material plays a decisive role in the battery's performance. Olivine-type cathode materials offer advantages in terms of high safety and low cost. Lithium manganese iron phosphate (LFP) and lithium iron phosphate (LFP) are both olivine-type cathode materials. While LFP exhibits good safety and cycle stability, its relatively low voltage plateau makes it difficult to meet the ever-increasing energy density requirements. Compared to LFP, the high voltage characteristic of manganese gives LFP a higher voltage plateau, resulting in a 10%–20% increase in energy density while maintaining the same specific capacity. Furthermore, LFP combines the high safety, long cycle life, low cost, and environmental friendliness of LFP, making it one of the most researched cathode materials for lithium-ion batteries.
[0003] While the introduction of manganese brings the advantage of high voltage, it also leads to poor conductivity in lithium manganese iron phosphate (LMP) materials. To address this, nano-sizing of the raw materials is typically achieved through sand milling, shortening the lithium-ion transport path. This is then supplemented with appropriate carbon coating methods, such as high-temperature sintering after mixing with a carbon source, to improve the material's electronic conductivity. However, traditional sand milling processes are difficult and time-consuming to achieve nano-sizing quickly, resulting in low efficiency in actual production. Furthermore, the uneven dispersion of raw materials during milling significantly impacts the performance of LMP materials. Uneven dispersion of manganese and iron during milling not only distorts the crystal structure, hindering lithium-ion transport and reducing conductivity, but also exacerbates manganese leaching due to the Jahn-Teller effect, worsening the cycle stability of LMP materials. In addition, traditional high-temperature sintering methods suffer from uneven carbon coating and excessively large particle sizes after sintering, resulting in less than ideal improvements in the conductivity of LMP materials. In summary, developing a preparation process that is highly efficient and can effectively improve the conductivity of lithium manganese iron phosphate materials is of great practical significance. Summary of the Invention
[0004] Based on the technical problems existing in the background technology, the present invention proposes a lithium manganese iron phosphate material and its preparation method.
[0005] This invention proposes a method for preparing lithium manganese iron phosphate material, comprising the following steps:
[0006] S1. A manganese-iron M ternary metal-glycerate precursor was prepared by solvothermal synthesis, wherein M is magnesium, nickel, cobalt or aluminum;
[0007] S2. The manganese iron M ternary metal-glycerate precursor is mixed with a phosphorus source and a lithium source and then subjected to high-energy ball milling to obtain a lithium manganese iron phosphate precursor.
[0008] S3. The lithium manganese iron phosphate precursor is placed in a reactor, and a mixture of carbon source gas and protective gas is introduced for sintering to obtain a primary sintering product.
[0009] S4. The first sintering product is cold-pressed into shape, and then hot-pressed and sintered under a protective atmosphere to obtain the lithium manganese iron phosphate material.
[0010] This invention synthesizes a manganese-iron M ternary metal-glycerate precursor via a solvothermal method, achieving excellent elemental distribution uniformity in the precursor, thereby improving the elemental distribution uniformity in lithium manganese iron phosphate materials and effectively enhancing their conductivity and cycle stability. Furthermore, the smaller particle size of the metal-organic composite precursor synthesized via the solvothermal method significantly reduces the difficulty of subsequent milling to reduce particle size, enabling nano-sizing of the material in a shorter time. By combining primary CVD-like sintering with secondary hot-pressing sintering, optimal carbon coating effect is achieved with limited carbon content, effectively limiting the particle size growth of lithium manganese iron phosphate materials and imparting good electrical conductivity. Hot-pressing sintering also improves the material's density, resulting in a good compaction density level.
[0011] Preferably, in the manganese-iron M ternary metal-glycerate precursor, the molar ratio of manganese, iron and M is (0.55-0.75):(0.40-0.20):0.05.
[0012] Preferably, the preparation steps of the manganese-iron M ternary metal-glycerate precursor include: fully dissolving manganese salt, iron salt, and M metal salt in isopropanol, adding glycerol and mixing evenly, and then carrying out a solvothermal reaction to obtain the precursor. Through the above specific solvothermal synthesis steps, the uniformity of elemental distribution in the precursor can be improved, thereby further improving the conductivity and cycle stability of lithium manganese iron phosphate materials.
[0013] Preferably, the manganese salt is manganese nitrate tetrahydrate, and the iron salt is ferric nitrate nonahydrate.
[0014] Preferably, the M metal salt is a nitrate of the M metal.
[0015] Preferably, the ratio of the sum of the molar amounts of manganese in the manganese salt, iron in the iron salt, and M in the M metal salt to the molar amount of glycerol is 1:2 to 5.
[0016] Preferably, the solvothermal reaction is carried out at a temperature of 150–180°C for 10–20 hours. By controlling the temperature and time of the solvothermal reaction, a precursor with suitable particle size and high uniformity can be obtained, thereby further improving the conductivity and cycle stability of lithium manganese iron phosphate materials.
[0017] Preferably, in the preparation step of the manganese-iron M ternary metal-glycerate precursor, glycerol is added and mixed evenly under stirring. The stirring speed is 200-300 r / min and the stirring time is 1-3 h.
[0018] In the preparation steps of the manganese-iron M ternary metal-glycerate precursor, after the solvothermal reaction is completed, conventional post-processing steps may also be included, such as centrifuging the product, washing and drying the precipitate; the washing process includes rinsing with deionized water and ethanol 3-5 times in sequence; the drying temperature is 80-100℃ and the time is 10-20h.
[0019] Preferably, in S2, the ratio of the sum of the molar amounts of manganese, iron and M elements in the manganese-iron M ternary metal-glycerate precursor to the molar amount of phosphorus source and the molar amount of lithium in lithium source is 1:(0.95~1.05):(1~1.1), preferably 1:1:(1.01~1.05).
[0020] Preferably, the phosphorus source is at least one selected from ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and phosphoric acid.
[0021] Preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium chloride, and lithium acetate.
[0022] Preferably, in step S2, the high-energy ball milling speed is 300–500 r / min, and the time is 5–10 h. Controlling the conditions of high-energy ball milling can give the precursor a suitable particle size and excellent uniformity, improve the carbon coating effect, and thus further enhance the electrical conductivity and cycle performance of the material.
[0023] Preferably, in S2, the high-energy ball milling is carried out in a solvent, which is anhydrous ethanol. After the ball milling is completed, the solvent is removed by drying.
[0024] Preferably, in S3, the flow rate of the mixed gas of carbon source gas and protective gas is 70 mL / min to 120 mL / min, and the volume ratio of carbon source gas to protective gas is (2 to 4): 10. Under the specified gas flow rate and ratio, a uniform and thin coating layer can be formed on the surface of lithium manganese iron phosphate material, which improves conductivity while reducing the proportion of inactive carbon, thus improving the conductivity and cycle performance of the material.
[0025] Preferably, the carbon source gas is at least one of methane, ethane, and propane.
[0026] Preferably, in S3, the sintering temperature is 500-600℃ and the holding time is 4-6h. Under the sintering conditions described above, the lithium manganese iron phosphate material can form phases with high particle size uniformity, which is beneficial to improving the conductivity and cycle stability of the material.
[0027] Preferably, in S4, the sintering temperature of the hot pressing sintering is 720-750℃, the holding time is 8-10h, and the applied pressure is 30-50MPa. Under the hot pressing conditions, the material can have both excellent compaction performance and a suitable specific surface area, further improving the wetting effect of the electrolyte.
[0028] Preferably, in step S4, the pressure applied during cold pressing is 10–20 MPa.
[0029] In this invention, a protective atmosphere refers to an atmosphere formed by a protective gas. The protective gas may be, for example, nitrogen, helium, or argon.
[0030] The present invention also discloses a lithium manganese iron phosphate material, which is prepared by the aforementioned preparation method.
[0031] The beneficial effects of this invention are as follows:
[0032] This invention utilizes a solvothermal synthesis of a manganese-iron M ternary metal-glycerate precursor, achieving excellent elemental distribution uniformity in the precursor and thus improving the elemental distribution uniformity of lithium manganese iron phosphate (LMP) materials. This effectively enhances the conductivity and cycle stability of LMP materials. Furthermore, the smaller particle size of the metal-organic composite precursor synthesized by the solvothermal method significantly reduces the difficulty of subsequent milling to reduce particle size, enabling nano-sizing of the material in a shorter time. By combining primary CVD-like sintering with secondary hot-pressing sintering, optimal carbon coating is achieved with limited carbon content, effectively limiting the particle size growth of LMP materials and imparting excellent conductivity. Hot-pressing sintering also improves the material's density, resulting in a good compaction density. In summary, the preparation process of this invention can yield LMP materials with high compaction density, excellent conductivity, and excellent cycle stability, and it boasts high production efficiency, making it valuable for industrial applications. Detailed Implementation
[0033] The technical solution of the present invention will now be described in detail through specific embodiments.
[0034] Example 1
[0035] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0036] S1. Dissolve 1.76g manganese nitrate tetrahydrate, 1.01g ferric nitrate nonahydrate, and 0.13g magnesium nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 200r / min for 3h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 170℃ for 18h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 100℃ for 15h to obtain the manganese-iron-magnesium ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 52.0%, the mass fraction of iron was 18.9%, and the mass fraction of magnesium was 1.6%).
[0037] S2. Mix 2g of manganese iron magnesium ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.05g of lithium carbonate, and then ball mill at 500r / min for 8h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0038] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 2:10) was introduced at a flow rate of 80 mL / min. The mixture was sintered at 550 °C for 5 h to obtain the first sintered product.
[0039] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa. Then, under an argon atmosphere, it is hot-pressed at 750°C for 9 hours at a pressure of 30 MPa to obtain lithium manganese iron phosphate material.
[0040] Example 2
[0041] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0042] S1. Dissolve 1.76g manganese nitrate tetrahydrate, 1.01g ferric nitrate nonahydrate, and 0.15g cobalt nitrate hexahydrate thoroughly in 150mL of isopropanol. Add 3g glycerol and stir at 300r / min for 2h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 150℃ for 15h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 90℃ for 18h to obtain the manganese-iron-cobalt ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 52.0%, the mass fraction of iron was 18.9%, and the mass fraction of cobalt was 4.0%).
[0043] S2. Mix 2g of manganese iron cobalt ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.03g of lithium carbonate, and then ball mill at 400r / min for 6h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain lithium manganese iron phosphate precursor.
[0044] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of methane and nitrogen (volume ratio of methane to nitrogen of 2:10) was introduced at a flow rate of 70 mL / min. The mixture was sintered at 600 °C for 6 h to obtain the first sintered product.
[0045] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 15 MPa. Then, under an argon atmosphere, it is hot-pressed at 750°C for 8 hours at a pressure of 50 MPa to obtain lithium manganese iron phosphate material.
[0046] Example 3
[0047] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0048] S1. Dissolve 1.38g manganese nitrate tetrahydrate, 1.62g ferric nitrate nonahydrate, and 0.15g nickel nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 200r / min for 3h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 180℃ for 10h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 80℃ for 15h to obtain the manganese-iron-nickel ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 40.9%, the mass fraction of iron was 30.4%, and the mass fraction of nickel was 4.0%).
[0049] S2. Mix 2g of manganese iron nickel ternary metal-glycerate precursor with 3.12g of ammonium dihydrogen phosphate and 1.05g of lithium carbonate, and then ball mill at 500r / min for 5h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0050] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of propane and nitrogen (the volume ratio of propane to nitrogen was 3:10) was introduced at a flow rate of 80 mL / min. The mixture was sintered at 600℃ for 6 h to obtain the first sintered product.
[0051] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 10 MPa. Then, under an argon atmosphere, it is hot-pressed at 720°C at a pressure of 30 MPa for 9 hours to obtain lithium manganese iron phosphate material.
[0052] Example 4
[0053] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0054] S1. Dissolve 1.88g manganese nitrate tetrahydrate, 0.81g ferric nitrate nonahydrate, and 0.19g aluminum nitrate nonahydrate completely in 150mL isopropanol. Add 3g glycerol and stir at 300r / min for 2h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 160℃ for 16h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 80℃ for 13h to obtain the manganese-iron-aluminum ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 55.7%, the mass fraction of iron was 15.2%, and the mass fraction of aluminum was 1.8%).
[0055] S2. Mix 2g of manganese iron aluminum ternary metal-glycerate precursor with 3.12g of ammonium dihydrogen phosphate and 1.03g of lithium carbonate, and then ball mill at 500r / min for 5h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain lithium manganese iron phosphate precursor.
[0056] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 2:10) was introduced at a flow rate of 90 mL / min. The mixture was sintered at 550 °C for 5 h to obtain the first sintered product.
[0057] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 15 MPa. Then, under an argon atmosphere, it is hot-pressed at 740°C for 10 hours at a pressure of 35 MPa to obtain lithium manganese iron phosphate material.
[0058] Example 5
[0059] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0060] S1. Dissolve 1.51g manganese nitrate tetrahydrate, 1.41g ferric nitrate nonahydrate, and 0.15g cobalt nitrate hexahydrate thoroughly in 150mL of isopropanol. Add 3g glycerol and stir at 250r / min for 3h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 170℃ for 13h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 95℃ for 17h to obtain the manganese-iron-cobalt ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 44.6%, the mass fraction of iron was 26.7%, and the mass fraction of cobalt was 4.0%).
[0061] S2. Mix 2g of manganese iron cobalt ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.06g of lithium carbonate, and then ball mill at 500r / min for 8h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0062] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 4:10) was introduced at a flow rate of 100 mL / min. The mixture was sintered at 600 °C for 5 h to obtain the first sintered product.
[0063] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 18 MPa. Then, under an argon atmosphere, it is hot-pressed at 740°C for 9 hours at a pressure of 50 MPa to obtain lithium manganese iron phosphate material.
[0064] Example 6
[0065] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0066] S1. Dissolve 1.38g manganese nitrate tetrahydrate, 1.62g ferric nitrate nonahydrate, and 0.13g magnesium nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 300r / min for 2h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 180℃ for 15h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 100℃ for 15h to obtain the manganese-iron-magnesium ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 40.9%, the mass fraction of iron was 30.4%, and the mass fraction of magnesium was 1.6%).
[0067] S2. Mix 2g of manganese iron magnesium ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.04g of lithium carbonate, and then ball mill at 450r / min for 7h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0068] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 2:10) was introduced at a flow rate of 120 mL / min. The mixture was sintered at 570 °C for 5 h to obtain the first sintered product.
[0069] S4. The first sintering product is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa. Then, under an argon atmosphere, it is hot-pressed at 745°C at a pressure of 40 MPa for 8 hours to obtain lithium manganese iron phosphate material.
[0070] Example 7
[0071] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0072] S1. Dissolve 1.76g manganese nitrate tetrahydrate, 1.01g ferric nitrate nonahydrate, and 0.15g nickel nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 300r / min for 2h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 170℃ for 15h. Centrifuge and wash the obtained precipitate five times with deionized water and ethanol, and dry it in an oven at 90℃ for 12h to obtain the manganese-iron-nickel ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 52.0%, the mass fraction of iron was 18.9%, and the mass fraction of nickel was 4.0%).
[0073] S2. Mix 2g of manganese iron nickel ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.03g of lithium carbonate, and then ball mill at 400r / min for 8h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0074] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 3:10) was introduced at a flow rate of 110 mL / min. The mixture was sintered at 600℃ for 6 h to obtain the first sintered product.
[0075] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa. Then, under an argon atmosphere, it is hot-pressed at 750°C for 9 hours at a pressure of 30 MPa to obtain lithium manganese iron phosphate material.
[0076] Comparative Example 1
[0077] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0078] S1. Mix 4.75g manganese nitrate tetrahydrate, 2.73g ferric nitrate nonahydrate, 0.35g magnesium nitrate hexahydrate, 3.11g ammonium dihydrogen phosphate, 1.05g lithium carbonate, and 0.44g glucose, and then ball-mill at 500r / min for 10h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain lithium manganese iron phosphate precursor.
[0079] S2. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 2:10) was introduced at a flow rate of 80 mL / min. The mixture was sintered at 550 °C for 5 h to obtain the first sintered product.
[0080] S3. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa. Then, under an argon atmosphere, it is hot-pressed at 750°C at a pressure of 30 MPa for 9 hours to obtain lithium manganese iron phosphate material.
[0081] Comparative Example 2
[0082] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0083] S1. Dissolve 1.76g manganese nitrate tetrahydrate, 1.01g ferric nitrate nonahydrate, and 0.13g magnesium nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 200r / min for 3h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 170℃ for 18h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 100℃ for 15h to obtain the manganese-iron-magnesium ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 52.0%, the mass fraction of iron was 18.9%, and the mass fraction of magnesium was 1.6%).
[0084] S2. Mix 2g of manganese iron magnesium ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.05g of lithium carbonate, and then ball mill at 500r / min for 8h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0085] S3. The lithium manganese iron phosphate precursor is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa. Then, under an argon atmosphere, it is hot-pressed and sintered at 750°C for 10 hours at a pressure of 30 MPa to obtain the lithium manganese iron phosphate material.
[0086] Comparative Example 3
[0087] A method for preparing lithium manganese iron phosphate material includes the following steps:
[0088] S1. Dissolve 1.76g manganese nitrate tetrahydrate, 1.01g ferric nitrate nonahydrate, and 0.13g magnesium nitrate hexahydrate thoroughly in 150mL isopropanol. Add 3g glycerol and stir at 200r / min for 3h to mix evenly. Then, in a hydrothermal reactor, carry out a solvothermal reaction at 170℃ for 18h. Centrifuge and wash the obtained precipitate three times with deionized water and ethanol, and dry it in an oven at 100℃ for 15h to obtain the manganese-iron-magnesium ternary metal-glycerate precursor (titration and elemental analysis showed that the mass fraction of manganese in the precursor was 52.0%, the mass fraction of iron was 18.9%, and the mass fraction of magnesium was 1.6%).
[0089] S2. Mix 2g of manganese iron magnesium ternary metal-glycerate precursor with 3.11g of ammonium dihydrogen phosphate and 1.05g of lithium carbonate, and then ball mill at 500r / min for 8h using anhydrous ethanol as solvent. After ball milling, dry to remove the solvent to obtain the lithium manganese iron phosphate precursor.
[0090] S3. The lithium manganese iron phosphate precursor was placed in a tube furnace, and a mixture of ethane and nitrogen (volume ratio of ethane to nitrogen of 2:10) was introduced at a flow rate of 80 mL / min. The mixture was sintered at 550 °C for 5 h to obtain the sintered product.
[0091] S4. The sintered product is loaded into a graphite mold and cold-pressed at a pressure of 20 MPa to obtain lithium manganese iron phosphate material.
[0092] The lithium manganese iron phosphate materials obtained in the examples and comparative examples were ground into powder, and then subjected to compaction, 0.1C first charge and first efficiency, discharge specific capacity, and 1C rate discharge specific capacity tests. The test methods were in accordance with the national standard GB / T 30835-2014 "Carbon Composite Lithium Iron Phosphate Cathode Materials for Lithium-ion Batteries" for relevant physicochemical and electrochemical performance tests. The mass ratio of lithium manganese iron phosphate material powder, conductive agent, and binder was 90:5:5, and the charge and discharge voltage range was 2.0–4.5V. The results are shown in Table 1.
[0093] Table 1
[0094]
[0095]
[0096] The results above show that the compaction density and electrical properties of the lithium manganese iron phosphate material prepared in the examples are significantly better than those in the comparative examples.
[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing lithium manganese iron phosphate material, characterized in that, Includes the following steps: S1. Dissolve manganese salt, iron salt and M metal salt completely in isopropanol, add glycerol and mix well, then carry out a solvothermal reaction to obtain manganese-iron M ternary metal-glycerate precursor, wherein M is magnesium, nickel, cobalt or aluminum; S2. The manganese iron M ternary metal-glycerate precursor is mixed with a phosphorus source and a lithium source and then subjected to high-energy ball milling to obtain a lithium manganese iron phosphate precursor. S3. The lithium manganese iron phosphate precursor is placed in a reactor, and a mixture of carbon source gas and protective gas is introduced for sintering to obtain a primary sintering product; the sintering temperature is 500~600℃, and the holding time is 4~6h. S4. The first sintering product is cold-pressed into shape, and then hot-pressed under a protective atmosphere to obtain the lithium manganese iron phosphate material; the sintering temperature of hot-pressing is 720~750 ℃, the holding time is 8~10h, and the applied pressure is 30~50MPa.
2. The method for preparing lithium manganese iron phosphate material according to claim 1, characterized in that, In the manganese-iron M ternary metal-glycerate precursor, the molar ratio of manganese, iron and M is (0.55~0.75):(0.40~0.20):0.
05.
3. The method for preparing lithium manganese iron phosphate material according to claim 1, characterized in that, The solvothermal reaction is carried out at a temperature of 150-180℃ for 10-20 hours.
4. The method for preparing lithium manganese iron phosphate material according to claim 1, characterized in that, In S2, the ratio of the sum of the molar amounts of manganese, iron and M elements in the manganese-iron M ternary metal-glycerate precursor to the molar amount of phosphorus source and the molar amount of lithium element in lithium source is 1:1:(1.01~1.05).
5. The method for preparing lithium manganese iron phosphate material according to claim 1, characterized in that, In S2, the high-energy ball mill rotates at a speed of 300~500 r / min for 5~10 h.
6. The method for preparing lithium manganese iron phosphate material according to claim 1, characterized in that, In S3, the flow rate of the mixed gas of carbon source gas and protective gas is 70 mL / min to 120 mL / min, and the volume ratio of carbon source gas to protective gas is (2~4):
10.
7. A lithium manganese iron phosphate material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.