Preparation Method of Lithium Iron Manganese Phosphate Composite Material and Lithium Iron Manganese Phosphate Composite Material Prepared thereby

Abstract

The present invention provides a preparation method of a lithium iron manganese phosphate composite material and the lithium iron manganese phosphate composite material. The preparation method of the lithium iron manganese phosphate composite material comprises the steps of: (I) heating a lithium iron manganese phosphate product and then performing liquid-phase mixing with a first lithium source and a first additive to obtain a first suspension, and then adding a first carbon source and mixing to form a second suspension; (II) performing spray granulation on the second suspension and then performing heat treatment and post-treatment to obtain lithium iron manganese phosphate; (III) performing liquid-phase mixing of the lithium iron manganese phosphate, a second lithium source, a second additive, a second carbon source, a phosphorus source and an iron source to obtain a third suspension, and then performing a hydrothermal reaction and filtering to obtain a filter cake; (IV) taking the filter cake and a third carbon source and performing liquid-phase mixing to obtain a fourth suspension, and performing spray drying on the fourth suspension and then performing heat treatment and post-treatment. The prepared lithium iron manganese phosphate composite material ensures high capacity and tap density, retains the advantages of the dual voltage platforms of lithium iron manganese phosphate, and has a great breakthrough in energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a preparation method of a lithium iron manganese phosphate composite material and the lithium iron manganese phosphate composite material. Background Art

[0002] In recent years, due to the continuous maturity of raw materials and processes, lithium iron phosphate batteries have almost equally shared the lithium-ion battery market with ternary battery cells, and have shined brightly in the field of large cylindrical batteries with high safety. However, with continuous development, the energy density of lithium iron phosphate battery cells has been increased to nearly the limit, and the upgraded version of lithium iron phosphate - lithium iron manganese phosphate has emerged as the times require.

[0003] In lithium iron manganese phosphate (LMFP), iron and manganese exist in the form of a solid solution, combining the advantages of lithium iron phosphate (LFP) and lithium manganese phosphate (LMP), and having good development prospects. Compared with lithium iron phosphate, lithium iron manganese phosphate has a higher voltage platform, a similar specific capacity, a greater breakthrough in energy density, and rich raw material sources, so its development meets the requirements of economy. Although lithium iron manganese phosphate inherits the advantages of low cost and high safety, it has problems of poor conductivity, poor cycling performance, and low tap density. The main reason is the Jahn-Teller effect of lithium iron manganese phosphate. Mn with a +3 valence is prone to disproportionation reaction to generate Mn with a +2 valence and Mn with a +4 valence. Mn with a +2 valence is easily dissolved in the electrolyte, consuming the electrolyte, and additionally causing oxygen vacancies, resulting in lattice distortion, structure collapse, poor cycling stability, and poor thermal stability.

[0004] In view of this, it is necessary to modify lithium iron manganese phosphate. Currently, methods such as carbon coating, nanosizing, and doping processes are used to improve conductivity, or surface coating is carried out to reduce its contact with the electrolyte and reduce the dissolution of manganese, thereby improving the cycling performance. However, the current modification processes all have deficiencies and it is difficult to obtain lithium iron manganese phosphate materials with excellent electrochemical performance. Summary of the Invention

[0005] In view of the above problems, the present invention provides a preparation method of a lithium iron manganese phosphate composite material and the lithium iron manganese phosphate composite material. The prepared lithium iron manganese phosphate composite material ensures high capacity and tap density, retains the double voltage platform advantage of lithium iron manganese phosphate, has a greater breakthrough in energy density, can promote the application of lithium iron manganese phosphate in battery cells, and accelerate the process of replacing lithium iron phosphate.

[0006] To achieve the above object, the first aspect of the present invention provides a preparation method of a lithium iron manganese phosphate composite material, including the steps:

[0007] (I) Pretreatment of iron manganese phosphate

[0008] The manganese iron phosphate product is heat-treated and then mixed with a first lithium source and a first additive in a liquid phase to obtain a first suspension, and then a first carbon source is added and mixed to form a second suspension;

[0009] (II) Preparation of lithium iron manganese phosphate

[0010] The second suspension is spray granulated and then heat-treated and post-treated to obtain lithium iron manganese phosphate;

[0011] (III) Hydrothermal synthesis of lithium iron phosphate

[0012] Lithium iron manganese phosphate, a second lithium source, a second additive, a second carbon source, a phosphorus source and an iron source are mixed in a liquid phase to obtain a third suspension, and then hydrothermal reaction is carried out and filtered to obtain a filter cake;

[0013] (IV) Carbon coating

[0014] The filter cake and a third carbon source are mixed in a liquid phase to obtain a fourth suspension, and the fourth suspension is spray-dried and then heat-treated and post-treated.

[0015] In the preparation method of the lithium iron manganese phosphate composite material of the present invention, by doping lithium source, first additive and first carbon source into manganese iron phosphate for heat treatment, and then adding second lithium source, second additive, second carbon source, phosphorus source and iron source for hydrothermal reaction, a composite material with lithium iron manganese phosphate as the core and lithium iron phosphate as the coating layer can be synthesized, which can improve the conductivity, optimize the lithium ion deintercalation channels and increase the tap density.

[0016] Specifically, after the heat treatment of lithium iron manganese phosphate, the lattice of manganese iron phosphate itself is stable, and the iron and manganese are uniformly mixed at the molecular level, which can fully exert the iron-manganese synergistic effect. By doping with the second additive during the preparation, the structure of the material can be optimized, which is beneficial to the intercalation of lithium ions into the lattice and the subsequent deintercalation during the heat treatment, and also enhances the conductivity of lithium iron manganese phosphate, overall improving the electrochemical performance of lithium iron manganese phosphate. Then, by forming a suspension and combining with the carbothermal reduction reaction, carbon and lithium can be distributed around iron and manganese. After synthesis, the core lithium iron manganese phosphate has excellent electrical properties and a high compaction. And then, after forming a suspension, the surface coating layer of lithium iron phosphate is synthesized by hydrothermal method and heat-treated. The material has good consistency, controllable morphology, and helps to stabilize the structure of lithium iron manganese phosphate, reduce the manganese dissolution, and reduce the side reaction with the electrolyte. That is, the composite material synthesized by the preparation method of the present invention has the characteristics of high compaction of the carbothermal reduction reaction, consistency of hydrothermal synthesis and high capacity, forming a composite material with lithium iron manganese phosphate as the core and lithium iron phosphate as the coating layer in structure, ensuring high capacity and compaction density, retaining the double voltage platform advantage of lithium iron manganese phosphate, and having a great breakthrough in energy density.

[0017] In addition, in the preparation method of the present invention, there are carbon layers formed by carbon reduction and doping of additives in both the core of lithium iron manganese phosphate and the coating layer of lithium iron phosphate. The doped elements are evenly distributed in the composite material, which can greatly improve its conductivity, thereby exerting its high-capacity characteristics.

[0018] As a technical solution of the present invention, the lithium iron manganese phosphate product is lithium iron manganese phosphate or its hydrate. The iron-manganese ratio in the lithium iron manganese phosphate product is 3-7:7-3, the particle size D50 is 1-9 μm, and the tapped density ≤ 2 g / cm 3 , and the specific surface area ≤ 50 m 2 / g.

[0019] As a technical solution of the present invention, the temperature for heat treatment of the lithium iron manganese phosphate product is 300-700 °C, the time is 2-12 h, and the atmosphere used is air, oxygen, nitrogen or helium.

[0020] As a technical solution of the present invention, the first lithium source and the second lithium source each independently include at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium dihydrogen phosphate.

[0021] As a technical solution of the present invention, the first carbon source and the second carbon source each independently include at least one of glucose, starch, sucrose, polyvinyl alcohol, ascorbic acid, citric acid, phenolic resin, cellulose, lemon sugar, graphite and carbon nanotubes.

[0022] As a technical solution of the present invention, the first additive and the second additive each independently include compounds containing Mg, Al, Nb, Ti, W or Zr.

[0023] As a technical solution of the present invention, the solvents used for liquid-phase coating in steps (I), (III) and (IV) include at least one of water, ethanol, ethylene glycol, glycerol, acetone and isopropanone.

[0024] As a technical solution of the present invention, the molar ratio of lithium in the first lithium source, metal in the first additive to lithium iron manganese phosphate in the lithium iron manganese phosphate product is 1.0-1.2:0.001-0.6:1.0, the first carbon source is 5-20 wt.% of the lithium iron manganese phosphate product, and the solid content of the second suspension is 20-60%.

[0025] As a technical solution of the present invention, in the pretreatment of lithium iron manganese phosphate in step (I), the first carbon source is added to the first suspension and stirred and ground to form a second suspension. The stirring frequency is 20-40 HZ, and the grinding is carried out until the particle size ≤ 800 nm.

[0026] As a technical solution of the present invention, in the preparation of lithium iron manganese phosphate in step (II), the inlet air temperature for spray drying is 200-290 °C, and the outlet air temperature is 90-150 °C.

[0027] As a technical solution of the present invention, in the preparation of lithium iron manganese phosphate in step (II), the equipment used for heat treatment is a pusher kiln or a roller hearth kiln, the heat treatment temperature is 600 - 800 °C, the time is 5 - 20 h, and the atmosphere introduced is nitrogen, helium or argon.

[0028] As a technical solution of the present invention, the post-treatment in the preparation of lithium iron manganese phosphate in step (II) includes crushing, classification and grinding in sequence, crushing to a particle size ≤ 5 μm, and grinding to a particle size ≤ 800 nm.

[0029] As a technical solution of the present invention, the post-treatment in carbon coating in step (IV) includes crushing, classification and demagnetization in sequence, crushing to a particle size ≤ 3 μm.

[0030] As a technical solution of the present invention, the phosphorus source is phosphoric acid, and the iron source is at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferric sulfate, ferric chloride and ferric nitrate.

[0031] As a technical solution of the present invention, the preparation of the third suspension includes first making the iron source into a solution with a concentration of 0.01 - 4.0 mol / L, then successively adding the second carbon source and the second additive and stirring and mixing to form a suspension, making the second lithium source into a solution with a concentration of 0.03 - 12.0 mol / L, mixing it with the suspension and the phosphorus source, and then mixing it with lithium iron manganese phosphate.

[0032] As a technical solution of the present invention, the molar ratio of lithium in the second lithium source, metal in the second additive, phosphorus in the phosphorus source, and iron in the iron source is (1.0 - 1.8):(0.001 - 0.5):(3.0 - 5.4):1, the second carbon source is 0.2 - 40 wt.% of the phosphorus source, and the molar ratio of lithium iron manganese phosphate to the second lithium source is 1:(0.001 - 0.3).

[0033] As a technical solution of the present invention, the temperature of the hydrothermal reaction is 100 - 220 °C, the time is 0.5 - 36 h, and the internal air pressure of the reaction vessel is 0.2 - 2 Mpa.

[0034] As a technical solution of the present invention, the third carbon source accounts for 0.02 - 10 wt.% of the filter cake, and the solid content of the fourth suspension is 10 - 60%.

[0035] As a technical solution of the present invention, the inlet air temperature for spray drying in carbon coating in step (IV) is 200 - 300 °C, and the outlet air temperature is 80 - 150 °C.

[0036] As a technical solution of the present invention, the equipment used for heat treatment in carbon coating in step (IV) is a pusher kiln or a roller hearth kiln. The heat treatment temperature is 300-800 °C, the time is 0.5-8 h, and the atmosphere introduced is nitrogen, helium or argon.

[0037] The second aspect of the present invention provides a lithium iron manganese phosphate composite material, which includes a core and a coating layer covering the core. The core includes doped lithium iron manganese phosphate, and the coating layer includes doped lithium iron phosphate. The lithium iron manganese phosphate composite material has a high capacity and a tap density. Detailed implementation mode

[0038] The lithium iron manganese phosphate composite material of the present invention includes a core and a coating layer covering the core. The core includes doped lithium iron manganese phosphate, and the coating layer includes doped lithium iron phosphate. The doping elements in the core include the metal elements in the first additive, and the doping elements in the coating layer include the metal elements in the second additive. After heat treatment, the first carbon source forms a carbon layer distributed on the surface of the doped lithium iron manganese phosphate, and the second carbon source forms a carbon layer distributed on the surface of the doped lithium iron phosphate after heat treatment.

[0039] The preparation method of the lithium iron manganese phosphate composite material of the present invention includes step (I) pretreatment of iron manganese phosphate, (II) preparation of lithium iron manganese phosphate, (III) hydrothermal synthesis of lithium iron phosphate, and (IV) carbon coating.

[0040] Among them, the pretreatment of iron manganese phosphate in step (I) includes heating the iron manganese phosphate product and then performing liquid-phase mixing with a first lithium source and a first additive to obtain a first suspension, and then adding a first carbon source and mixing to form a second suspension.

[0041] As a technical solution, the iron manganese phosphate product is iron manganese phosphate or its hydrate. The iron-manganese ratio in the iron manganese phosphate product is 3-7:7-3, the particle size D50 is 1-9 μm, the tap density ≤ 2 g / cm 3 , and the specific surface area ≤ 50 m 2 / g, preferably the specific surface area ≤ 15 m 2 / g. The heating treatment temperature of the iron manganese phosphate product is 300-700 °C, preferably 400-700 °C, the time is 2-12 h, and the atmosphere used is air, oxygen, nitrogen or helium.

[0042] As a technical solution, the first lithium source includes at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium dihydrogen phosphate. The first lithium source can be a lithium source with crystal water or a dehydrated lithium source, preferably dehydrated lithium carbonate.

[0043] As a technical solution, the first carbon source includes at least one of glucose, starch, sucrose, polyvinyl alcohol, ascorbic acid, citric acid, phenolic resin, cellulose, lemon sugar, graphite, and carbon nanotubes. Preferably, the first carbon source includes at least one of glucose, starch, sucrose, phenolic resin, cellulose, lemon sugar, graphite, and carbon nanotubes.

[0044] As a technical solution, the first additive includes a compound containing Mg, Al, Nb, Ti, W, or Zr.

[0045] As a technical solution, the solvent used for liquid-phase coating includes at least one of water, ethanol, ethylene glycol, glycerol, acetone, and isopropyl acetone, preferably water.

[0046] As a technical solution, the molar ratio of lithium in the first lithium source, metal in the first additive, and lithium iron manganese phosphate in the lithium iron manganese phosphate product is 1.0 - 1.2:0.001 - 0.6:1.0, preferably 1.0 - 1.06:0.01 - 0.2:1.0. Selecting this molar ratio can optimize the material structure and facilitate the insertion and later extraction of lithium ions into the lattice after heat treatment. The first carbon source is 5 - 20 wt.% of the lithium iron manganese phosphate product, and the solid content of the second suspension is 20 - 60%, preferably 30 - 50%.

[0047] As a technical solution, in the pretreatment of lithium iron manganese phosphate in step (I), the first carbon source is added to the first suspension and stirred and ground to form a second suspension. The stirring frequency is 20 - 40 HZ, and it is ground to a particle size ≤ 800 nm, preferably ground to a particle size of 100 - 600 nm.

[0048] Step (II) for the preparation of lithium iron manganese phosphate includes spray granulating the second suspension and then performing heat treatment and post-treatment to obtain lithium iron manganese phosphate.

[0049] As a technical solution, the inlet air temperature for spray drying is 200 - 290 °C, and the outlet air temperature is 90 - 150 °C. The equipment used for heat treatment is a pusher kiln or a roller hearth kiln. The stacking method of the crucibles containing the material is single-row multi-column or multi-layer multi-column, and the loading amount in each crucible is 2 - 6 kg. The heat treatment temperature is 600 - 800 °C, the time is 5 - 20 h, and the atmosphere introduced is nitrogen, helium, or argon.

[0050] As a technical solution, the post-treatment includes sequential crushing, classification, and grinding. It is crushed to a particle size ≤ 5 μm, and the grinding is to a particle size ≤ 800 nm.

[0051] Step (III) for the hydrothermal synthesis of lithium iron phosphate includes liquid-phase mixing of lithium iron manganese phosphate, the second lithium source, the second additive, the second carbon source, the phosphorus source, and the iron source to obtain a third suspension, and then performing a hydrothermal reaction and filtering to obtain a filter cake.

[0052] As a technical solution, the second lithium source includes at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium dihydrogen phosphate. The second carbon source includes at least one of glucose, starch, sucrose, polyvinyl alcohol, ascorbic acid, citric acid, phenolic resin, cellulose, lemon sugar, graphite, and carbon nanotubes, preferably at least one of glucose, sucrose, polyvinyl alcohol, ascorbic acid, and citric acid. The second additive includes a compound containing Mg, Al, Nb, Ti, W, or Zr.

[0053] As a technical solution, the solvent used for liquid-phase coating in step (III) includes at least one of water, ethanol, ethylene glycol, glycerol, acetone, and isopropanone. The phosphorus source is phosphoric acid, and the mass concentration can be 40-90%. The iron source is at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferric sulfate, ferric chloride, and ferric nitrate.

[0054] As a technical solution, the preparation of the third suspension includes first making the iron source into a solution with a concentration of 0.01-4.0 mol / L, then sequentially adding the second carbon source and the second additive and stirring and mixing to form a suspension. The second lithium source is made into a solution with a concentration of 0.03-12.0 mol / L, and after mixing with the suspension and the phosphorus source, it is then mixed with lithium iron manganese phosphate. The molar ratio of lithium in the second lithium source, metal in the second additive, phosphorus in the phosphorus source, and iron in the iron source is (1.0-1.8):(0.001-0.5):(3.0-5.4):1. The second carbon source is 0.2-40 wt.% of the phosphorus source, and the molar ratio of lithium iron manganese phosphate to the second lithium source is 1:(0.001-0.3).

[0055] As a technical solution, the temperature of the hydrothermal reaction is 100-220 °C, and the time is 0.5-36 h. Preferably, the temperature is 120-180 °C, and the time is 2-12 h. The internal air pressure of the reaction vessel is 0.2-2 Mpa.

[0056] Step (IV) carbon coating includes taking the filter cake and the third carbon source for liquid-phase mixing to obtain a fourth suspension, and then spray-drying the fourth suspension followed by heat treatment and post-treatment.

[0057] As a technical solution, the solvent used for liquid-phase coating includes at least one of water, ethanol, ethylene glycol, glycerol, acetone, and isopropanone. The post-treatment includes sequential crushing, classification, and demagnetization, and the crushing is to a particle size of ≤3 μm.

[0058] As a technical solution, the third carbon source accounts for 0.02-10 wt.% of the filter cake, and the solid content of the fourth suspension is 10-60%. The inlet air temperature of the spray drying is 200-300 °C, and the outlet air temperature is 80-150 °C. The equipment used for heat treatment is a pusher kiln or a roller hearth kiln. The temperature of the heat treatment is 300-800 °C, the time is 0.5-8 h, and the atmosphere introduced is nitrogen, helium, or argon.

[0059] To better illustrate the objectives, technical solutions, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0060] Example 1

[0061] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0062] (I) Pretreatment of iron manganese phosphate

[0063] Iron manganese phosphate (Mn 0.4 Fe 0.6 PO 4 , with a particle size D50 of 3.6 μm, a tapped density of 0.76 g / cm 3 , and a specific surface area of 6.3 m 2 / g) is treated in a nitrogen atmosphere at 500 °C for 5 h, then 150 kg is taken and put into water containing 39 kg of lithium carbonate and 2.6 kg of TiO 2 for liquid-phase mixing to obtain a first suspension. Then, after stirring at 30 HZ for 0.5 h, 17.5 kg of glucose is added to obtain a slurry with a solid content of 40%, and after stirring for 1 h, it is ground with a sand mill to a particle size of 300 nm to form a second suspension.

[0064] (II) Preparation of lithium iron manganese phosphate

[0065] After spray granulating the second suspension at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C, the spray material is loaded into a bowl at a rate of 3.5 kg and sent into a roller hearth kiln filled with nitrogen protection. The arrangement is 1 layer and 4 columns. The high-temperature temperature of the roller hearth kiln is 700 °C, and the high-temperature holding time is 8 h. The material is cooled by air cooling, transported to a crusher, the crushing frequency is 30 HZ, the classification frequency is 26 HZ, and at the same time, magnetic separation and sieving are carried out to obtain lithium iron manganese phosphate with a particle size of 1.6 μm. Then, it is continuously transported, and the solid content in pure water is 35%, and it is ground to a slurry with a particle size of 600 nm.

[0066] (III) Hydrothermal synthesis of lithium iron phosphate

[0067] Dissolve FeSO 4 in water to form a 0.2 mol / L solution, and sequentially add 0.2 kg of Al 2 O 3, 4 kg of ascorbic acid was stirred to obtain a suspension. LiOH was dissolved in water to form a 0.6 mol / L solution. Then, 250 L of the suspension, 250 L of the solution, and 9.8 kg of phosphoric acid solution (concentration: 50%) were mixed evenly. The slurry prepared in step (II) was slowly added and mixed to obtain a third suspension. A hydrothermal reaction was carried out in a closed container under an anaerobic environment, with a pressure of 0.8 MPa, a temperature of 170 °C, and a time of 5 h. After the reaction ended, filtration, washing, and drying were carried out to obtain a filter cake.

[0068] (IV) Carbon coating

[0069] The filter cake and starch were dispersed in water. After mixing evenly, a fourth suspension was obtained. The fourth suspension was spray-dried at an inlet air temperature of 240 °C and an outlet air temperature of 110 °C, and then heat-treated in a roller hearth furnace filled with nitrogen. The maximum temperature was 600 °C, and the time was 5 h. After discharging, it was crushed and classified, and the particle size was controlled to be 1.2 μm to obtain a lithium iron manganese phosphate composite material coated with lithium iron phosphate.

[0070] Example 2

[0071] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0072] (I) Pretreatment of lithium iron manganese phosphate

[0073] Lithium iron manganese phosphate (Mn 0.3 Fe 0.7 PO 4 , with a particle size D50 of 2.5 μm, a tapped density of 0.61 g / cm 3 , and a specific surface area of 7.9 m 2 / g) was treated in a nitrogen atmosphere at 500 °C for 5 h. Then, 150 kg was put into water containing 39 kg of lithium carbonate and 2.6 kg of TiO 2 for liquid-phase mixing to obtain a first suspension. After stirring at 30 HZ for 0.5 h, 17.5 kg of glucose was added to obtain a slurry with a solid content of 40%. After stirring for 1 h, it was ground with a sand mill to a particle size of 300 nm to form a second suspension.

[0074] (II) Preparation of lithium iron manganese phosphate

[0075] After spray granulating the second suspension at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C, the spray material is loaded into the pot at a quantity of 3.5 kg and sent into a roller hearth kiln filled with nitrogen protection. The arrangement is 1 layer and 4 columns. The high-temperature of the roller hearth kiln is 700 °C, and the high-temperature holding time is 8 h. The material is cooled by air cooling and then transported to a crusher. The crushing frequency is 30 HZ, and the classification frequency is 26 HZ. At the same time, magnetic separation and sieving are carried out to obtain lithium iron manganese phosphate with a particle size of 1.6 μm. Then, it is continuously transported and obtained in pure water with a solid content of 35%, and ground into a slurry with a particle size of 600 nm.

[0076] (III) Hydrothermal synthesis of lithium iron phosphate

[0077] Dissolve FeSO 4 in water to form a 0.2 mol / L solution. Sequentially add 0.1 kg of MgO and 4 kg of ascorbic acid and stir to obtain a suspension. Dissolve LiOH in water to form a 0.6 mol / L solution. Then, mix 250 L of the suspension, 250 L of the solution, and 9.8 kg of phosphoric acid solution (concentration of 50%) evenly, and slowly add the slurry prepared in step (II) and mix to obtain a third suspension. Carry out hydrothermal reaction in a closed and oxygen-free environment container, with a pressure of 0.8 MPa, a temperature of 170 °C, and a time of 5 h. After the reaction, filter, wash, and dry to obtain a filter cake.

[0078] (IV) Carbon coating

[0079] Take the filter cake and starch and disperse them in water. After mixing evenly, obtain a fourth suspension. Spray-dry the fourth suspension at an inlet air temperature of 240 °C and an outlet air temperature of 110 °C, and then enter a roller hearth kiln filled with nitrogen for heat treatment. The highest temperature is 630 °C, and the time is 4 h. After discharging, crush and classify to control the particle size to 1.35 μm to obtain a lithium iron manganese phosphate composite material coated with lithium iron phosphate.

[0080] Example 3

[0081] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0082] (I) Pretreatment of lithium iron manganese phosphate

[0083] Lithium iron manganese phosphate (Mn 0.4 Fe 0.6 PO 4 , with a D50 particle size of 3.6 μm, a tapped density of 0.76 g / cm 3 , and a specific surface area of 6.3 m 2 / g) is treated in a nitrogen atmosphere at 500 °C for 5 h, and then 150 kg is taken and put into a container containing 55 kg of lithium acetate and 2.6 kg of TiO 2The first suspension was obtained by performing liquid-phase mixing in water, and after stirring at 30 Hz for 0.5 h, 17.5 kg of glucose was added to obtain a slurry with a solid content of 40%. After stirring for 1 h, it was ground with a sand mill to a particle size of 200 nm to form the second suspension.

[0084] (II) Preparation of lithium iron manganese phosphate

[0085] After spray granulating the second suspension at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C, the spray material with a loading of 3.5 kg per pot was sent into a roller hearth kiln filled with nitrogen protection. The arrangement was 1 layer and 4 columns. The high-temperature of the roller hearth kiln was 670 °C, and the high-temperature holding time was 10 h. The material was cooled by air cooling, transported to a crusher, with a crushing frequency of 30 Hz and a classification frequency of 26 Hz. At the same time, magnetic separation and sieving were carried out to obtain lithium iron manganese phosphate with a particle size of 1.6 μm. Then it was continuously transported, and in pure water, a slurry with a solid content of 35% was obtained and ground to a particle size of 600 nm.

[0086] (III) Hydrothermal synthesis of lithium iron phosphate

[0087] Dissolve FeSO 4 in water to form a 0.2 mol / L solution, and successively add 0.2 kg of Al 2 O 3 , 4 kg of ascorbic acid and stir to obtain a suspension. Dissolve LiOH in water to form a 0.6 mol / L solution. Then, 250 L of the suspension, 250 L of the solution, and 9.8 kg of phosphoric acid solution (concentration 50%) were mixed evenly, and slowly added to the slurry prepared in step (II) to mix to obtain the third suspension. A hydrothermal reaction was carried out in a closed anaerobic environment container, with a pressure of 0.8 MPa, a temperature of 170 °C, and a time of 5 h. After the reaction ended, filtration, washing, and drying were carried out to obtain a filter cake.

[0088] (IV) Carbon coating

[0089] Take the filter cake and starch and disperse them in water. After mixing evenly, the fourth suspension was obtained. The fourth suspension was spray-dried at an inlet air temperature of 240 °C and an outlet air temperature of 110 °C, and then entered a roller hearth kiln filled with nitrogen for heat treatment. The highest temperature was 600 °C, and the time was 5 h. After discharging, it was crushed and classified, and the particle size was controlled to be 1.01 μm to obtain a lithium iron phosphate-coated lithium iron manganese phosphate composite material.

[0090] Example 4

[0091] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0092] (I) Pretreatment of iron manganese phosphate

[0093] Iron manganese phosphate (Mn 0.4Fe 0.6 PO 4 , with a particle size D50 of 3.6 μm and a tapped density of 0.76 g / cm 3 , and a specific surface area of 6.3 m 2 / g) was treated in a nitrogen atmosphere at 500 °C for 5 h, and then 150 kg was put into water containing 39 kg of lithium carbonate and 2.6 kg of TiO 2 for liquid-phase mixing to obtain a first suspension. Then, after stirring at 30 Hz for 0.5 h, 10.8 kg of sucrose was added to obtain a slurry with a solid content of 40%. After stirring for 1 h, it was ground with a sand mill to a particle size of 450 nm to form a second suspension.

[0094] (II) Preparation of lithium iron manganese phosphate

[0095] The second suspension was spray granulated at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C. The spray material was loaded into the pot at 3.5 kg and sent into a roller hearth kiln filled with nitrogen protection. The arrangement was 1 layer and 4 columns. The high-temperature of the roller hearth kiln was 700 °C, and the high-temperature holding time was 8 h. The material was cooled by air cooling, transported to a crusher, with a crushing frequency of 35 Hz and a classification frequency of 36 Hz. At the same time, magnetic separation and sieving were carried out to obtain lithium iron manganese phosphate with a particle size of 1.6 μm. Then, it was continuously transported, and in pure water, the solid content was 35%, and it was ground to a particle size of 700 nm to form a slurry.

[0096] (III) Hydrothermal synthesis of lithium iron phosphate

[0097] Dissolve FeSO 4 in water to form a 0.2 mol / L solution, and successively add 0.2 kg of Al 2 O 3 and 4 kg of ascorbic acid and stir to obtain a suspension. Dissolve LiOH in water to form a 0.6 mol / L solution. Then, mix 250 L of the suspension, 250 L of the solution, and 9.8 kg of phosphoric acid solution (concentration of 50%) evenly, and slowly add the slurry prepared in step (II) to mix to obtain a third suspension. Carry out a hydrothermal reaction in a closed and oxygen-free environment container, with a pressure of 0.8 MPa, a temperature of 150 °C, and a time of 10 h. After the reaction, filter, wash, and dry to obtain a filter cake.

[0098] (IV) Carbon coating

[0099] Take the filter cake and starch and disperse them in water. After mixing evenly, a fourth suspension is obtained. The fourth suspension is spray-dried at an inlet air temperature of 240 °C and an outlet air temperature of 110 °C, and then enters a roller hearth kiln filled with nitrogen for heat treatment. The highest temperature is 600 °C, and the time is 5 h. After discharging, it is crushed and classified, and the particle size is controlled to be 0.96 μm to obtain a lithium iron phosphate-coated lithium iron manganese phosphate composite material.

[0100] Example 5

[0101] This example is a preparation method of lithium iron manganese phosphate composite material, which includes the following steps.

[0102] (I) Pretreatment of iron manganese phosphate

[0103] Iron manganese phosphate (Mn 0.4 Fe 0.6 PO 4 , with a D50 particle size of 3.6 μm, a tapped density of 0.76 g / cm 3 , and a specific surface area of 6.3 m 2 / g) is treated in a helium atmosphere at 400 °C for 9 h, then 150 kg is taken and put into water containing 39 kg of lithium carbonate and 2.6 kg of TiO 2 for liquid-phase mixing to obtain a first suspension. After stirring at 30 HZ for 0.5 h, 17.5 kg of glucose is added to obtain a slurry with a solid content of 40%. After stirring for 1 h, it is ground with a sand mill to a particle size of 300 nm to form a second suspension.

[0104] (II) Preparation of lithium iron manganese phosphate

[0105] After spray granulating the second suspension at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C, the spray material with a loading of 3.5 kg per pot is sent into a roller hearth furnace filled with nitrogen protection. The arrangement is 1 layer and 4 columns. The high-temperature of the roller hearth furnace is 700 °C, and the high-temperature holding time is 8 h. The material is cooled by air cooling, transported to a crusher, with a crushing frequency of 30 HZ and a classification frequency of 26 HZ, while demagnetizing and sieving to obtain lithium iron manganese phosphate with a particle size of 1.6 μm. Then it is continuously transported, and the solid content in pure water is 35%, and it is ground to a slurry with a particle size of 600 nm.

[0106] (III) Hydrothermal synthesis of lithium iron phosphate

[0107] Dissolve ferrous chloride in water to form a 1.5 mol / L solution, and successively add 0.2 kg of Al 2 O 3 and 4 kg of ascorbic acid and stir to obtain a suspension. Dissolve LiOH in water to form a 2.5 mol / L solution. Then mix 250 L of the suspension, 250 L of the solution, and 9.8 kg of phosphoric acid solution (concentration of 50%) evenly, and slowly add the slurry prepared in step (II) to mix to obtain a third suspension. Carry out hydrothermal reaction in a closed anaerobic environment container, with a pressure of 0.8 MPa, a temperature of 170 °C, and a time of 5 h. After the reaction, filter, wash, and dry to obtain a filter cake.

[0108] (IV) Carbon coating

[0109] The filter cake and starch are dispersed in water. After mixing evenly, a fourth suspension is obtained. The fourth suspension is spray-dried at an inlet air temperature of 230 °C and an outlet air temperature of 100 °C, and then heat-treated in a roller hearth kiln filled with nitrogen. The maximum temperature is 600 °C and the time is 5 h. After discharging, it is crushed and classified, and the particle size is controlled to be 1.2 μm to obtain a lithium iron manganese phosphate composite material coated with lithium iron phosphate.

[0110] Comparative Example 1

[0111] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0112] (I) Pretreatment of lithium iron manganese phosphate

[0113] Lithium iron manganese phosphate (Mn 0.4 Fe 0.6 PO 4 , with a particle size D50 of 3.6 μm, a tapped density of 0.76 g / cm 3 , and a specific surface area of 6.3 m 2 / g) is treated in a nitrogen atmosphere at 500 °C for 5 h, and then 150 kg is taken and put into water containing 39 kg of lithium carbonate and 2.6 kg of TiO 2 for liquid-phase mixing to obtain a first suspension. After stirring at 30 HZ for 0.5 h, 17.5 kg of glucose is added to obtain a slurry with a solid content of 40%. After stirring for 1 h, it is ground with a sand mill to a particle size of 300 nm to form a second suspension.

[0114] (II) Preparation of lithium iron manganese phosphate

[0115] After spray granulating the second suspension at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C, the spray material is loaded into the pot at a rate of 3.5 kg and sent into a roller hearth kiln filled with nitrogen for protection. The arrangement is 1 layer and 4 columns. The high-temperature of the roller hearth kiln is 700 °C, and the high-temperature holding time is 8 h. The material is cooled by air cooling, transported to a crusher, the crushing frequency is 30 HZ, the classification frequency is 26 HZ, and at the same time, magnetic separation and sieving are carried out to obtain lithium iron manganese phosphate with a particle size of 1.6 μm.

[0116] Comparative Example 2

[0117] This example is a preparation method of a lithium iron manganese phosphate composite material, including the following steps.

[0118] (I) Preparation of the first mixed solution

[0119] According to the chemical formula LiMn 0.4 Fe 0.6 PO 4 , manganese sulfate, ferrous sulfate, and phosphoric acid are taken and dissolved in water to obtain a first premixed solution, and then TiO 2(For LiMn 0.4 Fe 0.6 PO 4 (1.5% of the mass) in water and mix to obtain a first mixed solution.

[0120] (II) Prepare a second mixed solution

[0121] Dissolve FeSO 4 in water to form a 0.2 mol / L solution, add 0.2 kg of Al 2 O 3 to obtain a suspension, and mix 250 L of the suspension with 9.8 kg of phosphoric acid solution (concentration 50%) to obtain a second mixed solution.

[0122] (III) Prepare a third mixed solution

[0123] Dissolve lithium carbonate in water to obtain a third mixed solution.

[0124] (IV) Prepare the precursor

[0125] According to the chemical formula LiMn 0.4 Fe 0.6 PO 4 Add the third mixed solution to the first mixed solution to obtain a first suspension, then add the second mixed solution and mix to obtain a second suspension. According to the chemical formula LiFePO 4 Add the third mixed solution and mix to obtain a third suspension. Place the third suspension in an oil bath at 130 °C under the protection of an inert atmosphere, and keep it warm for 6 h. After the reaction is completed, cool the reaction solution and filter to obtain a filter cake.

[0126] (IV) Carbon coating

[0127] Take the filter cake and starch, disperse them in water, and mix evenly to obtain a fourth suspension. Spray-dry the fourth suspension at an inlet air temperature of 240 °C and an outlet air temperature of 110 °C, then enter a roller hearth furnace filled with nitrogen for heat treatment. The maximum temperature is 600 °C and the time is 5 h. After discharging, crush and classify it, and control the particle size to be 1.2 μm to obtain a lithium manganese iron phosphate composite material coated with lithium iron phosphate.

[0128] Comparative Example 3

[0129] This example is a method for preparing a lithium manganese iron phosphate composite material, including the following steps.

[0130] (I) Prepare lithium manganese iron phosphate

[0131] According to the chemical formula LiMn 0.4 Fe 0.6 PO 4 , take lithium carbonate, manganese sulfate, ferrous sulfate, and phosphoric acid, dissolve them in water to obtain a first premixed solution, and then add TiO2 (For LiMn 0.4 Fe 0.6 PO 4 (1.5% by mass) and glucose (for LiMn 0.4 Fe 0.6 PO 4 (5% by mass) were mixed and stirred in water for 1 h, and then ground with a sand mill to a particle size of 300 nm to form a slurry. The slurry was spray granulated at an inlet air temperature of 210 °C and an outlet air temperature of 100 °C. After that, the spray granulated material with a loading of 3.5 kg per pot was sent into a roller hearth kiln filled with nitrogen protection, arranged in a pattern of 1 layer and 4 columns. The high temperature of the roller hearth kiln was 700 °C, and the high temperature holding time was 8 h. The material was cooled by air cooling, transported to a crusher, with a crushing frequency of 30 HZ and a classification frequency of 26 HZ, while removing magnetism and sieving, to obtain lithium iron manganese phosphate with a particle size of 1.6 μm.

[0132] (II) Hydrothermal synthesis of lithium iron phosphate

[0133] 158.0 g of lithium iron manganese phosphate was made into a 1.0 mol / L suspension and continuously stirred. 27.8 g of ferrous sulfate and 11.5 g of phosphoric acid were dissolved in water to form a 0.1 mol / L solution, 12.6 g of lithium hydroxide was dissolved in water to form a 0.3 mol / L solution, and 1.09 g of glucose was dissolved in water. Under the protection of a nitrogen atmosphere, the mixed solution of ferrous sulfate and phosphoric acid and the lithium hydroxide solution were simultaneously and slowly pumped into the lithium iron manganese phosphate at a rate of 30 ml / min. The glucose solution was added, and at the same time, an emulsifier was turned on for emulsification (the emulsification conditions included: a rotation speed of 2500 rpm, a time of 45 min, and a temperature of 30 °C). The emulsified mixed solution was heated to 180 °C, continuously reacted for 4 h, and then naturally cooled. It was filtered and washed 3 times with deionized water and a 1500-mesh filter cloth, and dried at 300 °C to obtain the target product.

[0134] The specific surface area, tapped density, pressed density, and 0.1C (2.0 - 4.2V) button cell capacity mAh / g of the lithium iron manganese phosphate composite materials prepared in Test Examples 1 - 5 and Comparative Examples 1 - 3 were tested, and the results are shown in Table 1.

[0135] Table 1 Performance of the lithium iron manganese phosphate composite materials prepared in Examples 1 - 5 and Comparative Examples 1 - 3

[0136]

[0137]

[0138] As can be seen from the results in Table 1, for the lithium iron manganese phosphate composite materials of Examples 1 to 4, during preparation, by forming a suspension and then spray-drying for carbothermal reduction reaction and hydrothermal reaction, they can have the high tap density characteristics of the carbothermal reduction reaction, the consistency of hydrothermal synthesis, and the characteristics of high capacity. Therefore, the prepared composite materials have high capacity and high density.

[0139] In Comparative Example 1, no lithium iron phosphate coating was carried out, so the capacity and density performance of the prepared material were poor. In Comparative Example 2, when synthesizing the lithium iron manganese phosphate core layer, the obtained first suspension mainly contained lithium phosphate and did not completely form the lithium iron manganese phosphate inner core. Continuing to add the second mixed solution increased the proportion of iron in the lithium iron manganese phosphate, and the coating effect of the outer shell lithium iron phosphate was not ideal, and the manganese dissolution was still relatively serious, so its performance was poor. The mixing uniformity of iron and manganese in the lithium iron manganese phosphate core of Comparative Example 3 was limited, so the electrical performance was poor.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the embodiments. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Preparation method of lithium iron manganese phosphate composite material Characterized in that Comprising the steps of (I) Pretreatment of iron manganese phosphate After heat-treating the iron manganese phosphate product, it is mixed with a first lithium source and a first additive in a liquid phase to obtain a first suspension, and then a first carbon source is added and mixed to form a second suspension; (II) Preparation of lithium iron manganese phosphate The second suspension is spray granulated and then subjected to heat treatment and post-treatment to obtain lithium iron manganese phosphate; (III) Hydrothermal synthesis of lithium iron phosphate The lithium iron manganese phosphate, a second lithium source, a second additive, a second carbon source, a phosphorus source and an iron source are mixed in a liquid phase to obtain a third suspension, and then subjected to a hydrothermal reaction and filtered to obtain a filter cake. The first additive and the second additive each independently include a compound containing Mg, Al, Nb, Ti, W or Zr; (IV) Carbon coating The filter cake and a third carbon source are mixed in a liquid phase to obtain a fourth suspension, and the fourth suspension is spray dried and then subjected to heat treatment and post-treatment.

2. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The manganese iron phosphate product is manganese iron phosphate or its hydrate. The iron to manganese ratio in the manganese iron phosphate product is 3-7:7-3, the particle size D50 is 1-9 μm, and the tapped density is ≤2 g / cm 3 , and the specific surface area is ≤50 m 2 / g.

3. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The temperature for heat-treating the iron manganese phosphate product is 300-700 °C, the time is 2-12 h, and the atmosphere used is air, oxygen, nitrogen or helium.

4. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The first lithium source and the second lithium source each independently include at least one of lithium oxide, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium dihydrogen phosphate.

5. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The first carbon source and the second carbon source each independently include at least one of glucose, starch, sucrose, polyvinyl alcohol, ascorbic acid, citric acid, phenolic resin, cellulose, lemon sugar, graphite and carbon nanotubes.

6. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The molar ratio of lithium in the first lithium source, the metal in the first additive to iron manganese phosphate in the iron manganese phosphate product is 1.0-1.2:0.001-0.6:1.0, the first carbon source is 5-20 wt.% of the iron manganese phosphate product, and the solid content of the second suspension is 20-60%.

7. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The phosphorus source is phosphoric acid, and the iron source is at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferric sulfate, ferric chloride and ferric nitrate.

8. The preparation method of the lithium iron manganese phosphate composite material according to claim 1 Characterized in that The preparation of the third suspension includes first making the iron source into a solution with a concentration of 0.01-4.0 mol / L, then sequentially adding the second carbon source and the second additive and stirring to form a suspension. The second lithium source is made into a solution with a concentration of 0.03-12.0 mol / L, mixed with the suspension and the phosphorus source, and then mixed with the lithium iron manganese phosphate.

9. The lithium iron manganese phosphate composite material prepared by the method for preparing a lithium iron manganese phosphate composite material according to any one of claims 1 to 8, characterized in that, it includes a core and a coating layer covering the core, the core includes doped lithium iron manganese phosphate, and the coating layer includes doped lithium iron phosphate.

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