A method for preparing a high-compaction, low-manganese-leaching, long-circulation lithium iron manganese phosphate cathode material

Abstract

The application discloses a method for preparing a high-compaction, low-manganese dissolution, long-cycle lithium manganese iron phosphate positive electrode material. 2+ The lithium manganese iron phosphate positive electrode material prepared by the method has low dissolution rate, excellent structural stability, a compaction density higher than 2.4 g / cm3, excellent volume energy density and low cycle attenuation rate, and can meet the long-term use requirement of a power battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium manganese iron phosphate cathode material preparation, and particularly relates to a method for preparing high-pressure, low-manganese-dissolution, long-cycle lithium manganese iron phosphate cathode material. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x Lithium iron phosphate (LFP) (PO4, LMFP) is a core upgrade material for lithium iron phosphate (LFP), and with its high voltage platform of 3.8~4.1V and energy density advantage of 15%~20%, it has become a key technology direction in the fields of power batteries and energy storage. However, its industrialization process faces three major bottlenecks: manganese leaching leading to cycle degradation, low intrinsic conductivity limiting rate performance, and low compaction density limiting cell energy density. Specifically:

[0003] (1) Manganese leaching leads to cycle decay: Mn in LMFP 2 Mn²⁺ readily induces the Jahn-Teller effect, leading to lattice distortion. Under high-voltage, high-temperature cycling conditions, large amounts of Mn²⁺ dissolve in the electrolyte and migrate to the negative electrode surface for deposition. This process not only causes the loss of active material but also disrupts the stability of the solid electrolyte interphase (SEI) at the negative electrode, catalyzing electrolyte decomposition, causing active lithium loss, a surge in interfacial impedance, and ultimately resulting in rapid capacity decay and gas generation problems.

[0004] (2) Low intrinsic conductivity limits rate performance: The intrinsic electronic conductivity of LMFP is only 10⁻ 9 ~10⁻¹ 0 With a capacity of S / cm, the narrow ion diffusion channels cause a lag in Li⁺ migration rate during high-rate charge and discharge, leading to increased polarization and a sharp drop in capacity. While traditional single carbon coating can improve electron transport, it offers limited improvement in ion conductivity, making it insufficient for fast-charging applications. Furthermore, manganese leaching further exacerbates interfacial impedance, creating a vicious cycle of poor conductivity – intensified leaching – increased impedance, limiting the performance of LMFPs at high rates and significantly falling short of the industrial requirements for fast charging and high-power energy storage.

[0005] (3) Low compaction density limits cell energy density: LMFP particles have uneven morphology and large specific surface area. Under conventional processes, the compaction density is only 2.2~2.3 g / cm³, far lower than LFP's 2.65 g / cm³. Low compaction density leads to excessively high electrode porosity and insufficient active material loading, directly reducing the cell energy density and making it difficult to match the volumetric energy density requirements of high-end vehicles and energy storage power stations. Existing processes have problems such as poor particle size controllability, unreasonable particle gradation, and coating layer affecting packing density. They cannot improve compaction density without sacrificing electrochemical performance, becoming a key bottleneck restricting the breakthrough of system energy density.

[0006] Based on this, we now study a novel preparation process for lithium manganese iron phosphate cathode material. Starting from the synergistic optimization of multiple indicators, we have prepared a high-pressure, low-manganese-dissolution, long-cycle lithium manganese iron phosphate cathode material. Summary of the Invention

[0007] Purpose of the invention: This invention provides a method for preparing a composite lithium manganese iron phosphate cathode material, which simultaneously achieves high compaction, low manganese leaching, and long-cycle stability.

[0008] Technical solution: The present invention provides a method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode materials, comprising the following steps:

[0009] (1) Preparation of ion-doped spherical lithium manganese iron phosphate cathode material;

[0010] (2) Disperse the spherical lithium manganese iron phosphate cathode material from step (1) in an organic solvent, add ferrocene and dispersant, stir and dry, and then keep it in an inert atmosphere at 600-700℃ for 2-5 hours to obtain spherical lithium manganese iron phosphate cathode material powder A.

[0011] (3) Disperse the spherical lithium manganese iron phosphate cathode material powder A from step (2) in an organic solvent, add tetrabutyl titanate and lithium dihydrogen phosphate, stir to form a sol-gel system, and obtain a dry gel powder after static aging and drying; keep the dry gel powder at 200-300℃ for 1-5h, and then keep it at 600-800℃ for 4-6h to obtain spherical lithium manganese iron phosphate cathode material powder B;

[0012] (4) The spherical lithium manganese iron phosphate cathode material powder B obtained in step (3) is kept in an inert atmosphere at 800-850℃ for 3-5 h to obtain a composite lithium manganese iron phosphate cathode material with high compaction, low manganese dissolution and long cycle life.

[0013] Furthermore, in step (2) of the preparation method, the amount of ferrocene added is 3-8% of the mass of the spherical lithium manganese iron phosphate cathode material.

[0014] Furthermore, in step (2) of the preparation method, the dispersant is selected from polyvinylpyrrolidone or polyethylene glycol, and its addition amount is 0.5-1% of the mass of the spherical lithium manganese iron phosphate cathode material.

[0015] Furthermore, in step (3) of the preparation method, the amount of tetrabutyl titanate added is 3-8% of the mass of spherical lithium manganese iron phosphate cathode material powder A, and the amount of lithium dihydrogen phosphate added is 3-8% of the mass of spherical lithium manganese iron phosphate cathode material powder A.

[0016] Furthermore, in step (1) of this preparation method, the ion doping is high-entropy doping of Mg, Ti, and V elements, which is obtained by the following steps:

[0017] (a) Manganese source, iron source, phosphorus source and lithium source are mixed in a molar ratio a:(1-a):b:c to prepare a slurry. After grinding and drying, the slurry is reacted at 400-500℃ for 3-8 hours to obtain pre-calcined manganese iron lithium phosphate material; wherein 0.05≤a≤0.95, 1≤b≤1.05, 1≤c≤1.08;

[0018] (b) A slurry is prepared by mixing pre-burned lithium manganese iron phosphate, carbon source, magnesium source, titanium source and vanadium source. After grinding and drying, the slurry is reacted at 720-800℃ for 12-20h to obtain ion-doped spherical lithium manganese iron phosphate cathode material.

[0019] Furthermore, in step (a) of the present invention for preparing ion-doped spherical lithium manganese iron phosphate cathode material, the manganese source is selected from manganese carbonate, manganese tetroxide, manganese sulfate, manganese dioxide or manganese oxide;

[0020] The iron source is selected from at least one of ferrous sulfate, ferric sulfate, ferric nitrate, ferric chloride, or ferric ammonium citrate;

[0021] The phosphorus source is selected from phosphoric acid, ammonium dihydrogen phosphate, lithium phosphate, or monoammonium phosphate;

[0022] The lithium source is selected from lithium carbonate, lithium hydroxide, lithium sulfate, lithium nitrate or lithium chloride.

[0023] Furthermore, in step (b) of the present invention for preparing ion-doped spherical lithium manganese iron phosphate cathode material, the magnesium source is selected from magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium acetate or magnesium oxide, and its addition amount is 0.2-0.5% of the mass of the lithium manganese iron phosphate pre-calcined material.

[0024] Furthermore, in step (b) of the present invention for preparing ion-doped spherical lithium manganese iron phosphate cathode material, the titanium source is selected from tetrabutyl titanate, tetraethyl titanate, isopropyl titanate, titanium oxysulfate, or titanium dioxide, and its addition amount is 0.2-0.5% of the mass of the pre-calcined lithium manganese iron phosphate material.

[0025] Furthermore, in step (b) of the present invention for preparing ion-doped spherical lithium manganese iron phosphate cathode material, the vanadium source is selected from ammonium metavanadate, sodium vanadate, ammonium vanadate or vanadium pentoxide, and its addition amount is 0.2-0.5% of the mass of the lithium manganese iron phosphate pre-calcined material.

[0026] Furthermore, in step (b) of the present invention for preparing ion-doped spherical lithium manganese iron phosphate cathode material, the carbon source is selected from at least one of glucose, sucrose, starch, cellulose, polyvinyl alcohol, soluble starch, cellulose, ascorbic acid or phenolic resin, and the amount added is 8-20% of the theoretical mass of the generated spherical lithium manganese iron phosphate cathode material.

[0027] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are:

[0028] 1) Significantly inhibits manganese leaching: The composite lithium iron phosphate cathode material prepared by this process exhibits excellent Mn content. 2+ The first-cycle dissolution rate of 1C is less than 1ppm, which can effectively avoid lattice collapse and significantly improve the structural stability of the material.

[0029] 2) Significantly improved compaction density: The composite lithium iron phosphate cathode material prepared by this process has a compaction density higher than 2.4 g / cm³, which significantly improves the volumetric energy density of the battery.

[0030] 3) Excellent cycle stability: The composite lithium manganese iron phosphate cathode material prepared by this process can retain a capacity of >91% after 1000 cycles at 25℃ and 1C rate, and a capacity retention of >86% after 500 cycles at 55℃. The cycle decay rate is significantly reduced, which meets the long-term use requirements of power batteries.

[0031] 4) Strong process adaptability: The preparation process is simple and controllable, requires no complex equipment, and can be directly adapted to existing industrial production lines of lithium manganese iron phosphate; the doping sources are rich in variety and can be flexibly selected, the production cost is controllable, the mass production feasibility is high, and it has good industrial application prospects. Attached Figure Description

[0032] Figure 1 SEM image of the composite lithium iron phosphate cathode material prepared in Example 1;

[0033] Figure 2 SEM image of the composite lithium iron phosphate cathode material prepared in Example 2;

[0034] Figure 3 The image shows a SEM image of the composite lithium iron phosphate cathode material prepared in Example 3. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] The composite lithium iron phosphate cathode material of Example 1 was prepared by the following steps:

[0038] (1) Preparation of ion-doped spherical lithium manganese iron phosphate cathode material:

[0039] 1) Weigh manganese sulfate, ferric nitrate, ammonium dihydrogen phosphate, and lithium nitrate according to the molar ratio of Mn, Fe, P, and Li of 0.45:0.55:1.03:1.03 and place them in deionized water. Stir for 0.5 h at a stirring temperature of 25℃ and a stirring frequency of 20 Hz to obtain a uniformly mixed slurry I. The amount of water added is sufficient to prepare the slurry.

[0040] 2) Grind slurry I for 2 hours to obtain lithium manganese iron phosphate precursor slurry I, and dry it at 150°C to obtain lithium manganese iron phosphate precursor powder I;

[0041] 3) The lithium manganese iron phosphate precursor powder I was reacted at 400°C under a nitrogen atmosphere for 8 hours and then naturally cooled to obtain lithium manganese iron phosphate pre-calcined material I.

[0042] 4) Pre-calcined lithium manganese iron phosphate material I was placed in deionized water with glucose, magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide. The mixture was stirred at 25°C and 20Hz for 0.5 hours to obtain a homogeneous slurry II. The amounts of magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide added were all 0.3% of the mass of pre-calcined lithium manganese iron phosphate material I; the amount of glucose added was 10% of the theoretical mass of lithium manganese iron phosphate cathode material.

[0043] 5) Grind slurry II for 2 hours to obtain lithium manganese iron phosphate pre-calcined material slurry II, and dry it at 150°C to obtain lithium manganese iron phosphate pre-calcined material II;

[0044] 6) The pre-calcined lithium manganese iron phosphate material II was kept at 800℃ under nitrogen atmosphere for 12 hours and then naturally cooled to obtain spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti and V elements.

[0045] (2) Preparation of composite lithium manganese iron phosphate cathode material

[0046] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements prepared in step (1) is dispersed in anhydrous ethanol, ferrocene and dispersant polyvinylpyrrolidone are added, and the mixture is stirred until homogeneous. The anhydrous ethanol is removed by rotary evaporation to obtain a mixed powder. The amount of ferrocene added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of dispersant added is 0.5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0047] 2) The mixed powder was heated to 600℃ under a nitrogen atmosphere and kept at that temperature for 4 hours to obtain spherical lithium manganese iron phosphate cathode material powder A;

[0048] 3) Disperse the spherical lithium manganese iron phosphate cathode material powder A from step 2) in anhydrous ethanol, add tetrabutyl titanate and lithium dihydrogen phosphate, stir to form a sol-gel system, allow to stand for aging for 1 hour, and then spray dry or vacuum dry to obtain a dry gel powder; wherein, the amount of tetrabutyl titanate added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material, and the amount of lithium dihydrogen phosphate added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material;

[0049] 4) After the dry gel powder is kept at 200℃ for 1 hour to remove organic solvents and residual organic matter, the temperature is raised to 600℃ and kept at 6 hours to allow the dry gel precursor to fully crystallize and obtain spherical lithium manganese iron phosphate cathode material powder B.

[0050] 5) Spherical lithium manganese iron phosphate cathode material powder B was placed under a nitrogen atmosphere and reacted at 800℃ for 5 hours to finally obtain a high-performance composite lithium manganese iron phosphate cathode material. The SEM image of the obtained cathode material is shown below. Figure 1 As shown, a two-step sintering process was employed, involving low-temperature nucleation followed by high-temperature crystallization, which improved the sphericity of the primary lithium manganese iron phosphate particles, resulting in smoother and more rounded particle surfaces. By coating and modifying the surface with ferrocene, tetrabutyl titanate, and lithium dihydrogen phosphate, L-shaped particles were formed on the surface under high-temperature calcination. i2 The thin layer of TiO3 coating simultaneously forms a Ti-doped lithium iron phosphate phase, which, together with the spherical lithium manganese iron phosphate cathode material, forms a particle size distribution during subsequent calcination, further improving the density.

[0051] Comparative Example 1-1

[0052] Comparative Example 1-1 is basically the same as Example 1, except that only the spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements in step (1) is prepared. And this step is the same as in Example 1.

[0053] Comparative Examples 1-2

[0054] Comparative Examples 1-2 are basically the same as Example 1, except that only spherical lithium manganese iron phosphate cathode material powder A is prepared. The specific steps are as follows:

[0055] (1) Preparation of spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements:

[0056] The steps are the same as in Example 1.

[0057] (2) Preparation of spherical lithium manganese iron phosphate cathode material powder A

[0058] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements prepared in step (1) is dispersed in anhydrous ethanol, ferrocene and dispersant polyvinylpyrrolidone are added, and the mixture is stirred until homogeneous. The anhydrous ethanol is removed by rotary evaporation to obtain a mixed powder. The amount of ferrocene added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of dispersant added is 0.5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0059] 2) The mixed powder was heated to 800℃ under a nitrogen atmosphere and kept at that temperature for 5 hours to obtain spherical lithium manganese iron phosphate cathode material powder A.

[0060] Comparative Examples 1-3

[0061] Comparative Examples 1-3 are basically the same as Example 1, except that spherical lithium manganese iron phosphate cathode material powder A is not prepared in advance. Instead, spherical lithium manganese iron phosphate cathode material powder B is prepared directly based on spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements. The specific steps are as follows:

[0062] (1) Preparation of spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements:

[0063] The steps are the same as in Example 1.

[0064] (2) Preparation of spherical lithium manganese iron phosphate cathode material powder B

[0065] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements from step (1) is dispersed in anhydrous ethanol, tetrabutyl titanate and lithium dihydrogen phosphate are added, and stirred to form a sol-gel system. After standing and aging for 1 hour, the dry gel powder is obtained by spray drying or vacuum drying. The amount of tetrabutyl titanate added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of lithium dihydrogen phosphate added is 3% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0066] 2) After the dry gel powder is kept at 200℃ for 1 hour to remove organic solvents and residual organic matter, the temperature is raised to 600℃ and kept at 6 hours to allow the dry gel precursor to fully crystallize and obtain spherical lithium manganese iron phosphate cathode material powder B.

[0067] 3) By placing spherical lithium manganese iron phosphate cathode material B under a nitrogen atmosphere and at 800°C for 5 hours, lithium manganese iron phosphate cathode material B can be obtained.

[0068] Example 2

[0069] The composite lithium iron phosphate cathode material of Example 2 was prepared by the following steps:

[0070] (1) Preparation of ion-doped spherical lithium manganese iron phosphate cathode material:

[0071] 1) Weigh manganese sulfate, ferric nitrate, ammonium dihydrogen phosphate, and lithium nitrate according to the molar ratio of Mn, Fe, P, and Li of 0.65:0.35:1.01:1.05 and place them in deionized water. Stir at 25°C and 20Hz for 0.5 hours to obtain a uniformly mixed slurry I. The amount of water added is sufficient to prepare the slurry.

[0072] 2) Grind slurry I for 2 hours to obtain lithium manganese iron phosphate precursor slurry I, and dry it at 150°C to obtain lithium manganese iron phosphate precursor powder I;

[0073] 3) The lithium manganese iron phosphate precursor powder I was reacted under nitrogen atmosphere and at 450°C for 5.5 h, and then naturally cooled to obtain lithium manganese iron phosphate pre-calcined material I;

[0074] 4) Pre-calcined lithium manganese iron phosphate material I was placed in deionized water with glucose, magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide. The mixture was stirred at 25°C and 20Hz for 0.5 hours to obtain a uniformly mixed slurry II. The amounts of magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide added were all 0.4% of the mass of pre-calcined lithium manganese iron phosphate material I; the amount of glucose added was 10% of the theoretical mass of lithium manganese iron phosphate cathode material.

[0075] 5) Grind slurry II for 2 hours to obtain lithium manganese iron phosphate pre-calcined material slurry II, and dry it at 150°C to obtain lithium manganese iron phosphate pre-calcined material II;

[0076] 6) The pre-calcined lithium manganese iron phosphate material II was kept at 760℃ under nitrogen atmosphere for 16 hours and then naturally cooled to obtain spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti and V elements.

[0077] (2) Preparation of composite lithium manganese iron phosphate cathode material

[0078] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements prepared in step (1) is dispersed in anhydrous ethanol, ferrocene and polyethylene glycol dispersant are added, and the mixture is stirred until homogeneous. The anhydrous ethanol is removed by rotary evaporation to obtain a mixed powder. The amount of ferrocene added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of dispersant added is 0.7% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0079] 2) The mixed powder was heated to 650℃ under a nitrogen atmosphere and kept at that temperature for 5 hours to obtain spherical lithium manganese iron phosphate cathode material powder A;

[0080] 3) Disperse the spherical lithium manganese iron phosphate cathode material powder A from step 2) in anhydrous ethanol, add tetrabutyl titanate and lithium dihydrogen phosphate, stir to form a sol-gel system, allow to stand for aging for 2 hours, and then spray dry or vacuum dry to obtain a dry gel powder; wherein, the amount of tetrabutyl titanate added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material, and the amount of lithium dihydrogen phosphate added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material;

[0081] 4) After the dry gel powder is kept at 200℃ for 1 hour to remove organic solvents and residual organic matter, the temperature is raised to 700℃ and kept at 700℃ for 5 hours to allow the dry gel precursor to fully crystallize and obtain spherical lithium manganese iron phosphate cathode material powder B.

[0082] 5) High-performance composite lithium manganese iron phosphate cathode material can be obtained by placing spherical lithium manganese iron phosphate cathode material B under a nitrogen atmosphere and at 825℃ for 4 hours. The SEM image of the obtained cathode material is shown below. Figure 2 As shown, a two-step sintering process was employed, involving low-temperature nucleation followed by high-temperature crystallization, which improved the sphericity of the primary lithium manganese iron phosphate particles, resulting in smoother and more rounded particle surfaces. By coating and modifying the surface with ferrocene, tetrabutyl titanate, and lithium dihydrogen phosphate, L-shaped particles were formed on the surface under high-temperature calcination. i2 The thin layer of TiO3 coating simultaneously forms a Ti-doped lithium iron phosphate phase, which, together with the spherical lithium manganese iron phosphate cathode material, forms a particle size distribution during subsequent calcination, further improving the density.

[0083] Comparative Example 2-1

[0084] Comparative Example 2-1 is basically the same as Example 2, except that only the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements in step (1) is prepared. And this step is the same as in Example 2.

[0085] Comparative Example 2-2

[0086] Comparative Example 2-2 is basically the same as Example 2, except that only spherical lithium manganese iron phosphate cathode material powder A is prepared. The specific steps are as follows:

[0087] (1) Preparation of ion-doped spherical lithium manganese iron phosphate:

[0088] This step is the same as in Example 2.

[0089] (2) Preparation of spherical lithium manganese iron phosphate cathode material powder A

[0090] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements prepared in step (1) is dispersed in anhydrous ethanol, ferrocene and polyethylene glycol dispersant are added, and the mixture is stirred until homogeneous. The anhydrous ethanol is removed by rotary evaporation to obtain a mixed powder. The amount of ferrocene added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of dispersant added is 0.7% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0091] 2) The mixed powder was heated to 825°C under a nitrogen atmosphere and kept at that temperature for 4 hours to obtain spherical lithium manganese iron phosphate cathode material powder A.

[0092] Comparative Examples 2-3

[0093] Comparative Examples 2-3 are basically the same as Example 2, except that spherical lithium manganese iron phosphate cathode material powder A is not prepared in advance. Instead, spherical lithium manganese iron phosphate cathode material powder B is prepared directly based on spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements. The specific steps are as follows:

[0094] (1) Preparation of ion-doped spherical lithium manganese iron phosphate

[0095] This step is the same as in Example 2.

[0096] (2) Preparation of spherical lithium manganese iron phosphate cathode material powder B

[0097] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements from step (1) is dispersed in anhydrous ethanol, tetrabutyl titanate and lithium dihydrogen phosphate are added, and stirred to form a sol-gel system. After standing and aging for 2 hours, the dry gel powder is obtained by spray drying or vacuum drying. The amount of tetrabutyl titanate added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of lithium dihydrogen phosphate added is 5% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0098] 2) After the dry gel powder is kept at 200℃ for 1 hour to remove organic solvents and residual organic matter, the temperature is raised to 700℃ and kept at 700℃ for 5 hours to allow the dry gel precursor to fully crystallize and obtain spherical lithium manganese iron phosphate cathode material powder B.

[0099] 3) Place the spherical lithium manganese iron phosphate cathode material powder B under a nitrogen atmosphere and at 825°C for 4 hours to obtain the final lithium manganese iron phosphate cathode material.

[0100] Example 3

[0101] The composite lithium iron phosphate cathode material of Example 3 was prepared by the following steps:

[0102] (1) Preparation of ion-doped spherical lithium manganese iron phosphate:

[0103] 1) Weigh manganese sulfate, ferric nitrate, ammonium dihydrogen phosphate, and lithium nitrate according to the molar ratio of Mn, Fe, P, and Li of 0.95:0.05:1.01:1.05 and place them in deionized water. Stir for 0.5 h at a stirring temperature of 25℃ and a stirring frequency of 20Hz to obtain a uniformly mixed slurry I. The amount of water added is just enough to prepare the slurry.

[0104] 2) Grind slurry I for 2 hours to obtain lithium manganese iron phosphate precursor slurry I, and dry it at 150°C to obtain lithium manganese iron phosphate precursor powder I;

[0105] 3) The lithium manganese iron phosphate precursor powder I was reacted at 500°C under a nitrogen atmosphere for 3 hours and then naturally cooled to obtain lithium manganese iron phosphate pre-calcined material I.

[0106] 4) Pre-calcined lithium manganese iron phosphate material I was placed in deionized water with glucose, magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide. The mixture was stirred at 25°C and 20Hz for 0.5 hours to obtain a uniformly mixed slurry II. The amounts of magnesium nitrate, tetrabutyl titanate, and vanadium pentoxide added were all 0.5% of the mass of pre-calcined lithium manganese iron phosphate material I; the amount of glucose added was 10% of the theoretical mass of lithium manganese iron phosphate cathode material.

[0107] 5) Grind slurry II for 2 hours to obtain lithium manganese iron phosphate pre-calcined material slurry II, and dry it at 150°C to obtain lithium manganese iron phosphate pre-calcined material II;

[0108] 6) The pre-calcined lithium manganese iron phosphate material II was kept at 800℃ under nitrogen atmosphere for 12 hours and then naturally cooled to obtain spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti and V elements.

[0109] (2) Preparation of composite lithium manganese iron phosphate cathode material

[0110] 1) The spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements prepared in step (1) is dispersed in anhydrous ethanol, ferrocene and polyethylene glycol dispersant are added, and the mixture is stirred until homogeneous. The anhydrous ethanol is removed by rotary evaporation to obtain a mixed powder. The amount of ferrocene added is 8% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements, and the amount of dispersant added is 1% of the mass of the spherical lithium manganese iron phosphate cathode material with high entropy doping of Mg, Ti, and V elements.

[0111] 2) The mixed powder was heated to 700℃ under a nitrogen atmosphere and kept at that temperature for 2 hours to obtain spherical lithium manganese iron phosphate cathode material powder A;

[0112] 3) Disperse the spherical lithium manganese iron phosphate cathode material powder A from step 2) in anhydrous ethanol, add tetrabutyl titanate and lithium dihydrogen phosphate, stir to form a sol-gel system, allow to stand for aging for 1.5 hours, and then spray dry or vacuum dry to obtain a dry gel powder; wherein, the amount of tetrabutyl titanate added is 8% of the mass of the spherical lithium manganese iron phosphate cathode material, and the amount of lithium dihydrogen phosphate added is 8% of the mass of the spherical lithium manganese iron phosphate cathode material;

[0113] 4) After the dry gel powder is kept at 200℃ for 1 hour to remove organic solvents and residual organic matter, the temperature is raised to 800℃ and kept at 800℃ for 4 hours to allow the dry gel precursor to fully crystallize and obtain spherical lithium manganese iron phosphate cathode material powder B.

[0114] 5) The high-performance composite lithium manganese iron phosphate cathode material can be obtained by placing spherical lithium manganese iron phosphate cathode material B under a nitrogen atmosphere and at 850℃ for 3 hours. The SEM image of the obtained cathode material is shown below. Figure 3 As shown, a two-step sintering process was employed, involving low-temperature nucleation followed by high-temperature crystallization, which improved the sphericity of the primary lithium manganese iron phosphate particles, resulting in smoother and more rounded particle surfaces. By coating and modifying the surface with ferrocene, tetrabutyl titanate, and lithium dihydrogen phosphate, L-shaped particles were formed on the surface under high-temperature calcination. i2 The thin layer of TiO3 coating simultaneously forms a Ti-doped lithium iron phosphate phase, which, together with the spherical lithium manganese iron phosphate cathode material, forms a particle size distribution during subsequent calcination, further improving the density.

[0115] Performance testing

[0116] The lithium manganese iron phosphate cathode materials obtained in the above examples and comparative examples were used to prepare coin cells and their electrochemical performance was evaluated. The lithium manganese iron phosphate cathode material, Super P, and PVDF were uniformly mixed in an NMP solution at a ratio of 8:1:1 to obtain a mixed slurry. The slurry was applied to bright aluminum foil by hand and then dried at 100°C. After the NMP had completely evaporated, the electrode sheet was cut into electrode sheets with a diameter of 13 mm. The electrode sheets were then dried overnight at 105°C in a vacuum oven. After weighing the electrode sheets, they were quickly transferred to a glove box. Using lithium metal as the counter electrode, Celgard 2400 as the separator, and 1 mol / L LiPF6 dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1), the assembled battery underwent electrochemical performance testing. The testing equipment was a Xinwei 4008 constant current test cabinet, and the test voltage range was 2.0-4.35V. The electrochemical performance results are shown in Table 1.

[0117] Table 1 Compaction and electrochemical properties of the examples and comparative examples

[0118]

[0119] Combining Examples 1-3 and Comparative Examples 1-1 and 2-1, it can be seen that, based on spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements (the spherical shape is achieved through a two-step sintering process: the first step is pre-sintering nucleation; the second step is high-temperature sintering, resulting in more rounded particles, and the carbon layer coating on the particle surface further enhances the roundness), by performing composite modification of ferrocene, tetrabutyl titanate, and lithium dihydrogen phosphate respectively, not only is the dissolution of Mn effectively reduced, but the density and long-cycle stability are also improved, achieving synergistic optimization of multiple indicators. Furthermore, combining the data from Examples 1, 1-2, 1-3, 2, 2-2, and 2-3, it is clear that only through combined modification of both can the simultaneous improvement of excellent performance be achieved.

[0120] Based on the above performance results, further analysis of its mechanism reveals that this invention is based on spherical lithium manganese iron phosphate with high entropy doping of Mg, Ti, and V elements, with Mg... 2+ (Ionic radius 0.072 nm), Ti 4+ (Ionic radius 0.068 nm), V 5+ (Ionic radius 0.054 nm) Ternary doped ions can selectively occupy Mn in the LMFP lattice. 2+ / Fe 2+ The lattice sites form a solid solution structure, which, on the one hand, strengthens the bonding strength of MO (M=Fe, Mn, Ti, V, Mg) bonds through charge compensation, thereby improving the rigidity and structural integrity of the olivine lattice and suppressing lattice distortion and Mn during charging and discharging. 3+ The disproportionation reaction reduces the thermodynamic driving force for Mn dissolution at the bulk level; on the other hand, the introduction of dopant ions can tune the lattice electron cloud density, reducing Mn dissolution. 3+ The surface exposure reduces its reactivity with HF in the electrolyte. Furthermore, the solid solution structure formed by Mg, Ti, and V ternary doping effectively suppresses lattice phase transitions and volume expansion during charge and discharge processes, preventing lattice collapse and pulverization of active materials, thus providing a reliable structural basis for long-cycle performance.

[0121] Based on spherical lithium manganese iron phosphate cathode materials, ferrocene is first added to modify the spherical lithium manganese iron phosphate cathode material, thereby forming a thin layer of Fe3C-C conductive phase on its surface during sintering. On the one hand, the thin layer of Fe3C-C conductive phase does not increase the surface roughness of the particles or hinder the close packing between particles. On the contrary, it can improve the flowability of the particles through interfacial lubrication, enabling the particles to achieve a more compact arrangement during electrode pressing, thereby significantly improving the compaction density of the material and further improving the volumetric energy density of the battery to meet the practical application requirements of power batteries. On the other hand, this Fe3C-C conductive phase can construct a continuous three-dimensional conductive network on the material surface. Fe3C, as a highly conductive active phase, can significantly reduce electron transport resistance, while the C phase can improve the contact conductivity between particles. The two work synergistically to improve the electronic conductivity of the material and effectively reduce the polarization effect during cycling. Simultaneously, based on the prerequisite of this pre-modified Fe3C-C conductive phase, a mild sol-gel method was used to mix it with tetrabutyl titanate and lithium dihydrogen phosphate to form a thin-layer coating modification of Li2TiO3. On the one hand, the thin-layer coating modification of Li2TiO3, as an interfacial buffer layer, has excellent chemical stability and ion conduction characteristics. It can physically isolate the electrolyte from the LMFP matrix, avoid the erosion of the crystal lattice by HF in the electrolyte, and block Mn. 2+ The Li2TiO3 layer provides a dissolution and migration pathway; it also reduces interface defects and suppresses interface side reactions through the lattice matching between Li2TiO3 and the LMFP interface, further synergistically suppressing Mn dissolution and achieving long-term structural stability of the material. On the other hand, the thin-layer coating of Li2TiO3 does not increase the surface roughness of the particles, nor does it hinder the close packing between particles; moreover, the Fe in the Fe3C phase of the Fe3C-C conductive phase can act as an anchoring point, combining with Li and P elements in the sol-gel system and forming a Ti-doped lithium iron phosphate phase through sintering. This phase forms a particle size distribution with the spherical lithium manganese iron phosphate cathode material during subsequent calcination, further improving the density. Moreover, the formed lithium iron phosphate phase can further optimize the interfacial compatibility between Li2TiO3 and the spherical lithium manganese iron phosphate substrate, strengthen the interfacial bonding strength between the phases, reduce interfacial impedance, and improve the structural stability of the final prepared lithium manganese iron phosphate cathode material. This ensures that the material maintains lattice integrity, stable conductivity, and clean interface during long-term charge-discharge cycles, effectively suppressing capacity decay and significantly improving cycle stability.

[0122] In other words, the composite lithium manganese iron phosphate cathode material of the present invention can achieve simultaneous improvement and optimization of high compaction, low manganese dissolution, and long cycle stability, realizing synergistic optimization of multiple indicators of lithium manganese iron phosphate cathode material. Furthermore, in addition to the above embodiments, the preparation steps, process parameters, and raw material selection of the present invention can all achieve the technical effects claimed above, therefore, further experimental verification is not required.

Claims

1. A method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: (1) Preparation of ion-doped spherical lithium manganese iron phosphate cathode material; (2) Disperse the spherical lithium manganese iron phosphate cathode material from step (1) in an organic solvent, add ferrocene and dispersant, stir and dry, and then keep it at an inert atmosphere and 600-700℃ for 2-5 h to obtain spherical lithium manganese iron phosphate cathode material powder A. (3) Disperse the spherical lithium manganese iron phosphate cathode material powder A from step (2) in an organic solvent, add tetrabutyl titanate and lithium dihydrogen phosphate, stir to form a sol-gel system, and obtain a dry gel powder after static aging and drying; keep the dry gel powder at 200-300℃ for 1-5h, and then keep it at 600-800℃ for 4-6h to obtain spherical lithium manganese iron phosphate cathode material powder B; (4) The spherical lithium manganese iron phosphate cathode material powder B obtained in step (3) is kept in an inert atmosphere at 800-850℃ for 3-5 h to obtain a composite lithium manganese iron phosphate cathode material with high compaction, low manganese dissolution and long cycle life.

2. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (2), the amount of ferrocene added is 3-8% of the mass of the spherical lithium manganese iron phosphate cathode material.

3. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (2), the dispersant is selected from polyvinylpyrrolidone or polyethylene glycol, and its addition amount is 0.5-1% of the mass of the spherical lithium manganese iron phosphate cathode material.

4. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (3), the amount of tetrabutyl titanate added is 3-8% of the mass of the spherical lithium manganese iron phosphate cathode material, and the amount of lithium dihydrogen phosphate added is 3-8% of the mass of the spherical lithium manganese iron phosphate cathode material.

5. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (1), the ion doping is high-entropy doping of Mg, Ti, and V elements, which is obtained by the following steps: (a) Manganese source, iron source, phosphorus source and lithium source are mixed in a molar ratio a:(1-a):b:c to prepare a slurry. After grinding and drying, the slurry is reacted at 400-500℃ for 3-8 hours to obtain pre-calcined manganese iron lithium phosphate material; wherein 0.05≤a≤0.95, 1≤b≤1.05, 1≤c≤1.08; (b) A slurry is prepared by mixing pre-burned lithium manganese iron phosphate, carbon source, magnesium source, titanium source and vanadium source. After grinding and drying, the slurry is reacted at 720-800℃ for 12-20h to obtain ion-doped spherical lithium manganese iron phosphate cathode material.

6. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step (a), the manganese source is selected from manganese carbonate, manganese tetroxide, manganese sulfate, manganese dioxide, or manganese oxide; The iron source is selected from one of ferrous sulfate, ferric sulfate, ferric nitrate, ferric chloride, or ferric ammonium citrate; The phosphorus source is selected from phosphoric acid, ammonium dihydrogen phosphate, lithium phosphate, or monoammonium phosphate; The lithium source is selected from lithium carbonate, lithium hydroxide, lithium sulfate, lithium nitrate or lithium chloride.

7. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step (b), the magnesium source is selected from magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium acetate or magnesium oxide, and its addition amount is 0.2-0.5% of the mass of the lithium manganese iron phosphate pre-burned material.

8. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step (b), the titanium source is selected from tetrabutyl titanate, tetraethyl titanate, isopropyl titanate, titanium oxysulfate, or titanium dioxide, and its addition amount is 0.2-0.5% of the mass of the lithium manganese iron phosphate pre-burned material.

9. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step (b), the vanadium source is selected from ammonium metavanadate, sodium vanadate, ammonium vanadate or vanadium pentoxide, and its addition amount is 0.2-0.5% of the mass of lithium manganese iron phosphate pre-burned material.

10. The method for preparing high-pressure, low-manganese-leaching, long-cycle lithium manganese iron phosphate cathode material according to claim 5, characterized in that, In step (b), the carbon source is selected from at least one of glucose, sucrose, starch, cellulose, polyvinyl alcohol, soluble starch, cellulose, ascorbic acid or phenolic resin, and its addition amount is 8-20% of the theoretical mass of spherical lithium manganese iron phosphate cathode material.

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