A method for precisely and controllably preparing high-pressure high-capacity lithium manganese iron phosphate

Abstract

The application provides a method for preparing high-pressure high-capacity lithium manganese iron phosphate precisely and controllably, and the method is characterized in that: a high-concentration manganese iron sulfate solution is used as a reaction bottom solution, ammonium hydrogen phosphate is used as a complexing precipitant, the slow drop method is combined with precise pH control of the system, the reversible complexing effect of ammonium ions and manganese iron ions is used to realize uniform and slow co-precipitation of metal ions, and a low-defect high-dense manganese iron phosphate precursor is generated in a directional manner; the precursor synthesis is divided into two independent stages of crystal nucleus formation and crystal growth, the number of nuclei and the initial particle size are controlled by adjusting the concentration of the bottom solution, the crystal growth state is precisely controlled by adjusting the temperature and the rotating speed in stages, the precursor particles with uniform particle size and dense crystal are obtained, and high-pressure high-capacity lithium manganese iron phosphate positive electrode materials are obtained through lithiation sintering. The lithium manganese iron phosphate material prepared by the method has the characteristics of high compaction density, large electrochemical capacity, excellent cycle stability and good batch consistency.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery cathode material preparation, specifically relating to a method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is a new generation of lithium-ion battery cathode material with great industrialization potential. It combines the high safety and long cycle life of lithium iron phosphate with the high voltage and high energy density of ternary materials. With its high operating voltage and large theoretical capacity, it is a core candidate material for power lithium batteries and large-scale energy storage batteries. The electrochemical performance of LMFP materials is highly dependent on the microstructure and particle physical properties of the powder. Among these, particle compaction density, crystal integrity, particle size distribution uniformity, and crystal purity are the core factors restricting its actual capacity, rate performance, and cycle stability. Compaction density directly determines the energy density of a single battery cell, while crystal integrity and particle size uniformity determine the material's ion transport efficiency and cycle life. Therefore, achieving precise and controllable synthesis of high-compact, high-capacity LMFP particles is currently the core technological breakthrough for the industrialization of high-end LMFP materials.

[0003] Currently, traditional lithium manganese iron phosphate synthesis processes mostly employ solid-state sintering or single-stage liquid-phase co-precipitation methods, which have significant technical shortcomings. Solid-state methods suffer from uneven raw material mixing and incomplete reactions, resulting in products with numerous crystal defects, loose particles, low compaction density, high impurity content, and limited material capacity. Conventional liquid-phase co-precipitation processes often use a single-stage integrated reaction mode, failing to distinguish the differentiated reaction mechanisms of nucleation and crystal growth. The nucleation and growth processes are coupled and overlapped, making it impossible to independently control the number of nuclei, initial particle size, and grain growth rate. This easily leads to problems such as uneven particle size, localized agglomeration, grain breakage, and high internal porosity. The final product exhibits a wide particle size distribution, poor batch consistency, and low compaction density, making it difficult to achieve high capacity characteristics.

[0004] Furthermore, existing processes lack the ability to coordinate the control of supersaturation, pH of the reaction system, staged stirring speed, and reaction temperature. Low saturation leads to uneven nucleation and incomplete crystal nuclei; high stirring speed throughout the process easily shears and breaks the crystals, while low stirring speed throughout the process easily causes large-scale agglomeration. Moreover, the industry lacks a precise pH control scheme adapted to the ammonium hydrogen phosphate buffer system, making it impossible to achieve a precise match between manganese iron ion complexation precipitation and crystal directional growth, easily generating impurity crystals and defective lattices, further reducing material purity and electrochemical stability. In summary, existing technologies cannot simultaneously achieve high compaction density, high reversible capacity, high crystal integrity, and high batch consistency in lithium manganese iron phosphate materials, failing to meet the stringent application requirements of high-end power batteries and long-cycle energy storage batteries for cathode materials. Based on the above-mentioned defects in existing technologies and the gaps in industrial technology, this invention proposes a precise synthesis method for high-compact, high-capacity lithium manganese iron phosphate with controllable staged parameters and complexation-assisted directional precipitation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate.

[0006] In a first aspect, the present invention provides the following technical solution: a method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate, comprising: S1. Prepare a high-concentration manganese-ferric sulfate base solution: Dissolve the manganese source and iron source in deionized water according to the preset manganese-iron molar ratio, stir evenly to prepare a mixed manganese-ferric sulfate base solution, and let it stand to stabilize for later use. S2. Prepare ammonium hydrogen phosphate reaction solution: Dissolve the phosphorus source in deionized water to prepare a homogeneous ammonium hydrogen phosphate solution as a complexing precipitant. S3, Crystal nucleus formation stage reaction: Ammonium hydrogen phosphate solution is slowly added dropwise to the mixed base solution of manganese iron sulfate at a constant low rate. In the system, ammonium ions preferentially complex with manganese and iron ions to form uniform and stable manganese iron complex ions, which slows down the precipitation rate of metal ions, achieves uniform co-precipitation, and initially forms manganese iron phosphate precursor crystal nuclei; the pH value of the system is monitored and stabilized throughout the process. S4. Crystal growth stage control: After the crystal nuclei are formed, continue to add ammonium hydrogen phosphate solution, switch the stirring speed and synthesis temperature, and enter the independent crystal growth and maintenance stage; control the uniform growth of crystal nuclei through constant temperature and constant speed precise maintenance. S5. Post-processing and lithiation sintering: After the reaction is completed, the mixture is allowed to stand for aging, filtered, washed and dried to obtain a high-density manganese iron phosphate precursor. The high-density manganese iron phosphate precursor is uniformly mixed with a lithium source and conductive additives, and then subjected to high-temperature sintering to finally prepare a high-compact, high-capacity, and high-stability lithium manganese iron phosphate cathode material.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: Innovative complexation precipitation mechanism with high particle density: The controlled precipitation mechanism assisted by ammonium hydrogen phosphate complexation effectively slows down the instantaneous precipitation rate of manganese iron ions, avoiding the formation of loose and amorphous precipitates. The metal ion precipitation is uniform and the utilization rate is high. The precursor particles are dense and have low porosity, fundamentally solving the industry pain point of low compaction density of traditional lithium manganese iron phosphate materials. Combined with precise pH control, pure phase precursors are generated in a directional manner, free of impurities and impurities, ensuring high capacity performance of the material. Dual-stage independent controllability, excellent product consistency: The dual-stage differentiated parameter control process of nucleation and crystal growth precisely controls the nucleation characteristics by controlling the supersaturation of the bottom liquid and the crystal growth characteristics by controlling the temperature and rotation speed. This completely solves the problems of uncontrolled nucleation and growth coupling, uneven particle size, and agglomeration and breakage in traditional processes. The finished lithium manganese iron phosphate has a concentrated particle size distribution and highly consistent batch performance. The core performance of the material is greatly improved: The lithium manganese iron phosphate cathode material prepared by this invention has complete crystal structure, few lattice defects, and significantly improved particle compaction density, which effectively improves the energy density of the battery cell; at the same time, the material has high ion conduction efficiency, high electrochemical reversible capacity, and slow cycle decay, which perfectly meets the application requirements of high-end power lithium batteries and long-cycle energy storage batteries. Wide process adaptability: The overall synthesis process is mild, highly controllable, and simple to operate, making it suitable for both laboratory-scale trials and large-scale industrial production, with high value for industrialization and promotion.

[0008] Preferably, in step S1, the molar concentration of the manganese-ferric sulfate mixed base solution is 1.0 to 3.0 mol / L, and the molar ratio of manganese to iron in the manganese-ferric sulfate mixed base solution is 1:1 to 2:1; the manganese source includes at least one of manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese chloride, and manganese acetate; the iron source includes at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous oxalate.

[0009] Preferably, in step S2, the molar concentration of the ammonium hydrogen phosphate solution is 1.2–3.0 mol / L; the phosphorus source includes at least one of diammonium phosphate, phosphoric acid, and monoammonium phosphate.

[0010] Preferably, the precise control parameters for the crystal nucleation stage are: the dropping rate of ammonium hydrogen phosphate solution is 4-15 mL / min, the stirring speed of the system is 200-700 r / min, the pH value of the reaction system is stably controlled at 2.0-6.5, the reaction time for crystal nucleation is 15-30 min, and the temperature of the reaction system is 30-120℃.

[0011] Preferably, the control parameters for the crystal growth stage are as follows: after the crystal nucleation stage, the crystal growth stage begins, the reaction time is controlled at 50–180 min, the stirring speed is adjusted to 300–500 rpm, the reaction system temperature is maintained at 40–80 °C, the ammonium hydrogen phosphate solution is continuously added dropwise at a rate of 4–15 mL / min, and the pH value is 2.0–7.0.

[0012] Preferably, in step S5, the static aging time is 80–360 min, the drying process adopts vacuum drying at 80℃–150℃, and the drying and heat preservation time is 8–24 h.

[0013] Preferably, in step S5, the calcination temperature of the high-density manganese iron phosphate precursor is 400–600℃, and the time is 4–10 h.

[0014] Preferably, the lithium source is lithium carbonate, and the conductive additive is glucose.

[0015] Preferably, in step S5, the atmosphere for high-temperature sintering is an inert nitrogen atmosphere, the sintering temperature is 650℃, and the sintering time is 12h.

[0016] Preferably, in step S5, the washing process includes washing three times with deionized water and washing once with anhydrous ethanol. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a particle size distribution diagram of the lithium manganese iron phosphate cathode material prepared in Example 3 of the present invention; Figure 2 The crystal structure diffraction pattern of the lithium manganese iron phosphate cathode material prepared in Example 3 of this invention; Figure 3 This is a scanning electron microscope image of the lithium manganese iron phosphate cathode material prepared in Example 3 of the present invention.

[0019] The embodiments of the present invention will be further described below with reference to the accompanying drawings. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain embodiments of the present invention, and should not be construed as limiting the present invention.

[0021] This invention provides a method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate, comprising: S1. Prepare a high-concentration manganese-ferric sulfate base solution: Dissolve the manganese source and iron source in deionized water according to the preset manganese-iron molar ratio, stir evenly to prepare a mixed manganese-ferric sulfate base solution, and let it stand to stabilize for later use. S2. Prepare ammonium hydrogen phosphate reaction solution: Dissolve the phosphorus source in deionized water to prepare a homogeneous ammonium hydrogen phosphate solution as a complexing precipitant. S3, Crystal nucleus formation stage reaction: Ammonium hydrogen phosphate solution is slowly added dropwise to the mixed base solution of manganese iron sulfate at a constant low rate. In the system, ammonium ions preferentially complex with manganese and iron ions to form uniform and stable manganese iron complex ions, which slows down the precipitation rate of metal ions, achieves uniform co-precipitation, and initially forms manganese iron phosphate precursor crystal nuclei; the pH value of the system is monitored and stabilized throughout the process. S4. Crystal growth stage control: After the crystal nuclei are formed, continue to add ammonium hydrogen phosphate solution, switch the stirring speed and synthesis temperature, and enter the independent crystal growth and maintenance stage; control the uniform growth of crystal nuclei through constant temperature and constant speed precise maintenance. S5. Post-processing and lithiation sintering: After the reaction is completed, the mixture is allowed to stand for aging, filtered, washed and dried to obtain a high-density manganese iron phosphate precursor. The high-density manganese iron phosphate precursor is uniformly mixed with a lithium source and conductive additives, and then subjected to high-temperature sintering to finally prepare a high-compact, high-capacity, and high-stability lithium manganese iron phosphate cathode material.

[0022] In step S1, the molar concentration of the manganese-ferric sulfate mixed base solution is 1.0 to 3.0 mol / L, and the molar ratio of manganese to iron in the manganese-ferric sulfate mixed base solution is 1:1 to 2:1; the manganese source includes at least one of manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese chloride, and manganese acetate; the iron source includes at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous oxalate.

[0023] In step S2, the molar concentration of the ammonium hydrogen phosphate solution is 1.2–3.0 mol / L; the phosphorus source includes at least one of diammonium phosphate, phosphoric acid, and monoammonium phosphate.

[0024] The precise control parameters for the crystal nucleation stage are as follows: the dropping rate of ammonium hydrogen phosphate solution is 4–15 mL / min, the stirring speed of the system is 200–700 r / min, the pH value of the reaction system is stably controlled at 2.0–6.5, the reaction time of crystal nucleation is 15–30 min, and the temperature of the reaction system is 30–120℃.

[0025] The control parameters for the crystal growth stage are as follows: after the crystal nucleation stage, the crystal growth stage begins; the reaction time is controlled at 50–180 min; the stirring speed is adjusted to 300–500 rpm; the reaction system temperature is maintained at 40–80℃; the ammonium hydrogen phosphate solution is continuously added dropwise at a rate of 4–15 mL / min; and the pH value is 2.0–7.0.

[0026] In step S5, the static aging time is 80-360 min, the drying process adopts vacuum drying at 80℃-150℃, and the drying and heat preservation time is 8-24 h.

[0027] In step S5, the high-density manganese iron phosphate precursor is calcined at a temperature of 400–600℃ for 4–10 hours.

[0028] The lithium source is lithium carbonate, and the conductive additive is glucose.

[0029] In step S5, the atmosphere for high-temperature sintering is an inert nitrogen atmosphere, the sintering temperature is 650℃, and the sintering time is 12h.

[0030] In step S5, the washing process includes washing with deionized water three times and washing with anhydrous ethanol once.

[0031] To further illustrate the effects of the present invention, the following embodiments and comparative examples are provided: Example 1 In Embodiment 1 of the present invention, a method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 1.5 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 7.5 for later use; S3. Control the system temperature to be constant at 50℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 50℃, adjust the stirring speed to 500r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0032] Example 2 The difference between Embodiment 2 and Embodiment 1 provided by this invention lies in the concentration of the manganese iron sulfate mixed substrate in step S1. A method for precisely and controllably preparing high-pressure compaction high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 7.5 for later use; S3. Control the system temperature to be constant at 50℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 50℃, adjust the stirring speed to 500r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0033] Example 3 The difference between Embodiment 3 and Embodiment 2 provided by this invention lies in the different stirring speeds during the crystal growth stage in step S4. A method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 7.5 for later use; S3. Control the system temperature to be constant at 50℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 50℃, adjust the stirring speed to 300r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0034] Example 4 The difference between Embodiment 4 and Embodiment 3 provided by this invention lies in the different reaction temperatures of steps S3 and S4. A method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 7.5 for later use; S3. Control the system temperature to be constant at 60℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 60℃, adjust the stirring speed to 300r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0035] Example 5 The difference between Embodiment 5 and Embodiment 4 provided by this invention lies in the different pH values ​​of the ammonium hydrogen phosphate solution in step S2. A method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 8.0 for later use; S3. Control the system temperature to be constant at 60℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 60℃, adjust the stirring speed to 300r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0036] Example 6 The difference between Example 6 and Example 5 provided by this invention lies in the different pH values ​​of the ammonium hydrogen phosphate solution in step S2 and the different reaction temperatures in steps S3 and S4. A method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate includes: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 8.5 for later use; S3. Control the system temperature to be constant at 50℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, react for 25min to complete the formation of uniform crystal nuclei; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 50℃, adjust the stirring speed to 300r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0037] Comparative Example 1 This comparative example uses a low-concentration base solution combined with a high-speed rotation process throughout, specifically including: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 0.5 mol / L manganese-iron sulfate mixed base solution (low supersaturation). Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 8.5 for later use; S3. Control the system temperature to be constant at 60℃, slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min, stir at 700r / min throughout the process, monitor and maintain the overall pH value of the system in real time, and react for 25min; the low supersaturation base solution has fewer nuclei and larger differences in crystal nuclei size; S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 60℃, adjust the stirring speed to 700r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0038] Comparative Example 2 This comparative example uses a high-concentration base solution combined with a low-speed process throughout, specifically including: S1. Dissolve manganese sulfate and ferrous sulfate in deionized water according to a manganese-iron molar ratio of 1:1 to prepare a 2.0 mol / L manganese-iron sulfate mixed base solution. Stir for 30 min until completely dissolved and let stand for 15 min to stabilize the system. S2. Prepare a 1.2 mol / L ammonium hydrogen phosphate solution, stir well, and adjust the pH of the solution to a stable value of 8.5 for later use; S3. Control the system temperature to be constant at 60℃, and slowly add ammonium hydrogen phosphate solution to the manganese ferric sulfate mixed base solution at a constant rate of 5mL / min. Stir at 300r / min throughout the process, monitor and maintain the overall pH value of the system in real time, and react for 25min. The low supersaturation base solution has fewer nuclei and larger differences in crystal nuclei size. S4. Continue to add ammonium hydrogen phosphate solution dropwise at a constant rate, keep the system temperature constant at 60℃, adjust the stirring speed to 300r / min, and stop adding ammonium hydrogen phosphate solution dropwise after 95min. S5. After the reaction is completed, let it stand for 120 minutes, filter and collect the solid product, wash it 3 times with deionized water and 1 time with anhydrous ethanol, dry it under vacuum at 80℃ for 8 hours, collect the product and calcine it at 450℃ for 6 hours to obtain high-density manganese iron phosphate precursor powder; disperse the precursor powder with lithium carbonate and glucose in deionized water, stir evenly and spray dry, place it in a tube furnace under nitrogen inert atmosphere, sinter at constant temperature of 650℃ for 12 hours, cool with the furnace and then crush and sieve to finally obtain lithium manganese iron phosphate cathode material.

[0039] To further verify the beneficial effects of the present invention, the powder resistivity, carbon content, specific surface area, compaction density, and electrochemical performance of the cathode materials in each embodiment and comparative example were tested. The results are shown in Table 1. Table 1

[0040] As shown in Table 1, the lithium manganese iron phosphate cathode materials prepared in each embodiment of the present invention have significantly higher compaction densities and lower powder resistivity than the comparative example, and their initial efficiency all reach over 92%, which is significantly better than the comparative example. Among them, Example 3 has the best overall performance, and its particle size distribution diagram is shown in [Figure 1]. Figure 1 The crystal structure diffraction pattern is shown below. Figure 2 Scanning electron microscope image (see) Figure 3 The results show that this invention successfully prepared high-compact, high-capacity, and high-crystal-integrity lithium manganese iron phosphate cathode materials through the synergistic effect of dual-stage independent regulation and complexation-assisted co-precipitation. This solves the technical problems of loose particles, low compaction density, numerous crystal defects, insufficient capacity utilization, and poor batch consistency in traditional processes. The following is a detailed analysis of the various embodiments of this invention and Comparative Examples 1 and 2: 1. Compacted density and particle compactness: The compacted density of all embodiments of the present invention reaches 2.15 g / m³ or higher, with Examples 2-4 reaching as high as 2.35-2.45 g / m³. In contrast, the compacted density of Comparative Example 1 is only 2.02 g / m³, and that of Comparative Example 2 is 2.05 g / m³, significantly lower than the embodiments. Meanwhile, the specific surface areas of Comparative Examples 1 and 2 are as high as 26.45 m² / g and 27.45 m² / g, respectively, while the specific surface areas of the embodiments remain consistently at a low level of 12.85-13.85 m² / g. This fully demonstrates that the comparative examples, due to the failure to distinguish between the nucleation and growth stages (Comparative Example 1 had insufficient nucleation at low saturation and high-speed shearing throughout; Comparative Example 2 had agglomeration due to low speed throughout), resulted in loose particles and high internal porosity. In contrast, the present invention, through independent dual-stage control, especially by optimizing the rotation speed during the crystal growth stage, effectively promotes the orderly and dense growth of grains, significantly reduces the internal porosity of the particles, and thus significantly improves the compaction density.

[0041] 2. Electrochemical performance and crystal integrity: Although the 0.1C discharge capacity of Comparative Example 1 (154.7 mAh / g) is similar to that of Example 1 (155.5 mAh / g), its initial coulombic efficiency (first-time efficiency) is only 85.63%, far lower than the 92.15% of Example 1 and the 94% or higher of other examples. Meanwhile, the powder resistivity of the comparative example (26.65 Ω / cm and 24.73 Ω / cm) is significantly higher than that of the examples (19.37~20.15 Ω / cm). This indicates that although the material prepared in the comparative example exhibits acceptable capacity performance during initial electrolyte wetting due to its loose structure, it contains a large number of lattice defects and irreversible side-reaction active sites, leading to significant lithium ion consumption and hindered electron conduction during the first charge and discharge process. In contrast, the material prepared in this invention has high crystal integrity and few lattice defects, ensuring unobstructed lithium ion channels and excellent electronic conductivity, thereby achieving high initial efficiency and low polarization.

[0042] By comparing Examples 1 to 6 longitudinally, the regulation patterns of each key process parameter on the performance of the final product can be further revealed: 1. Effect of Base Solution Concentration (Comparison of Example 1 and Example 2): When the base solution concentration was increased from 1.5 mol / L to 2.0 mol / L, the supersaturation of the system increased, and the nucleation driving force was enhanced. The compaction density of Example 2 (2.35 g / m³) was significantly higher than that of Example 1 (2.15 g / m³), and the first-time efficiency also increased from 92.15% to 95.31%. This is because the high supersaturation promoted the instantaneous formation of a large number of uniform crystal nuclei, providing a large base of uniform crystal nuclei for subsequent growth, resulting in more compact sintered product particles. However, it is worth noting that the 0.1C discharge capacity of Example 1 (155.5 mAh / g) was slightly higher than that of Example 2 (151.2 mAh / g). This may be because the lower compaction density of Example 1 resulted in a more suitable microporous structure between particles, which is conducive to the full wetting of the electrolyte and the rapid migration of lithium ions. However, this was at the cost of sacrificing energy density and first-time efficiency. Considering all factors, the higher concentration base solution is better.

[0043] 2. Effect of stirring speed during crystal growth (comparing Example 2 and Example 3): After reducing the stirring speed from 500 r / min to 300 r / min during the crystal growth stage, the compaction density of Example 3 further increased to 2.41 g / m³, achieving a maximum initial efficiency of 95.67%. This is because, during the growth stage after crystal nucleation, a moderately low stirring speed effectively avoids the physical breakage and dislocation of newly formed grains due to high shear forces, providing conditions for slow and orderly deposition and growth of grains in a relatively stable microenvironment, which is beneficial for the self-repair of lattice defects and the smoothing of particle surfaces.

[0044] 3. Effect of Temperature on Crystal Growth (Comparison of Examples 3 and 4): After increasing the reaction temperature from 50°C to 60°C, Example 4 achieved the highest compaction density (2.45 g / m³) and the lowest specific surface area (12.89 m² / g) among all samples. The increased temperature accelerated the diffusion rate of reacting ions and the grain boundary migration rate, promoting further grain fusion and growth, eliminating grain boundary porosity, and resulting in a more compact structure. However, excessively high temperatures led to excessive grain growth, coarsening of primary particles, and an increase in the solid-phase diffusion path length of lithium ions, thus significantly reducing its 0.1C discharge capacity to 142.1 mAh / g. This indicates that there is an optimal temperature window, and higher is not always better; 50°C (Example 3) ensured high compaction while also achieving higher capacity.

[0045] 4. Effect of pH on the reaction system (comparing Examples 3 / 4 and Examples 5 / 6): When the pH of the ammonium hydrogen phosphate solution was increased from 7.5 to 8.0 (Example 5) and even 8.5 (Example 6), the compaction density of the material significantly decreased to 2.28 and 2.23, and the capacity also showed a downward trend. The reason for this is that while increasing the pH enhances the complexation ability of ammonium ions, an excessively high pH environment increases the concentration of hydroxide ions in the system, potentially leading to the formation of manganese hydroxide / iron precipitates locally. This disrupts the single-phase pure-phase reaction pathway of ammonium hydrogen phosphate-metal ion complexation precipitation, resulting in the introduction of impurities or component segregation in the precursor. Consequently, the integrity of the crystal structure is compromised after sintering, causing performance degradation. This verifies that precisely controlling the pH within a suitable range (such as pH 7.5 in Example 3) is crucial for ensuring the high performance of the material.

[0046] Based on the data in Table 1 and the above analysis, it can be seen that this invention, through its unique dual-stage independent and precise control strategy for crystal nucleation and crystal growth, combined with the complexation-assisted co-precipitation effect of ammonium hydrogen phosphate, achieves precise control over the number of precursor particles nucleation, growth rate, and densification degree. Specifically, the scheme represented by Example 3 (bottom solution concentration 2.0 mol / L, nucleation stage 700 r / min, growth stage 300 r / min, temperature 50℃, pH 7.5) achieved the best balance between compaction density (2.41 g / m³), discharge capacity (152.1 mAh / g), and initial efficiency (95.67%), demonstrating significantly better overall performance than traditional processes and making it fully suitable for large-scale applications in high-end power lithium batteries and energy storage batteries.

[0047] The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate provided in this invention has the following advantages: Innovative complexation precipitation mechanism with high particle density: The controlled precipitation mechanism assisted by ammonium hydrogen phosphate complexation effectively slows down the instantaneous precipitation rate of manganese iron ions, avoiding the formation of loose and amorphous precipitates. The metal ion precipitation is uniform and the utilization rate is high. The precursor particles are dense and have low porosity, fundamentally solving the industry pain point of low compaction density of traditional lithium manganese iron phosphate materials. Combined with precise pH control, pure phase precursors are generated in a directional manner, free of impurities and impurities, ensuring high capacity performance of the material. Dual-stage independent controllability, excellent product consistency: The dual-stage differentiated parameter control process of nucleation and crystal growth precisely controls the nucleation characteristics by controlling the supersaturation of the bottom liquid and the crystal growth characteristics by controlling the temperature and rotation speed. This completely solves the problems of uncontrolled nucleation and growth coupling, uneven particle size, and agglomeration and breakage in traditional processes. The finished lithium manganese iron phosphate has a concentrated particle size distribution and highly consistent batch performance. The core performance of the material is greatly improved: The lithium manganese iron phosphate cathode material prepared by this invention has complete crystal structure, few lattice defects, and significantly improved particle compaction density, which effectively improves the energy density of the battery cell; at the same time, the material has high ion conduction efficiency, high electrochemical reversible capacity, and slow cycle decay, which perfectly meets the application requirements of high-end power lithium batteries and long-cycle energy storage batteries. Wide process adaptability: The overall synthesis process is mild, highly controllable, and simple to operate, making it suitable for both laboratory-scale trials and large-scale industrial production, with high value for industrialization and promotion.

[0048] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate, characterized in that, include: S1. Prepare a high-concentration manganese-ferric sulfate base solution: Dissolve the manganese source and iron source in deionized water according to the preset manganese-iron molar ratio, stir evenly to prepare a mixed manganese-ferric sulfate base solution, and let it stand to stabilize for later use. S2. Prepare ammonium hydrogen phosphate reaction solution: Dissolve the phosphorus source in deionized water to prepare a homogeneous ammonium hydrogen phosphate solution as a complexing precipitant. S3, Crystal nucleus formation stage reaction: Ammonium hydrogen phosphate solution is slowly added dropwise to the mixed base solution of manganese iron sulfate at a constant low rate. In the system, ammonium ions preferentially complex with manganese and iron ions to form uniform and stable manganese iron complex ions, which slows down the precipitation rate of metal ions, achieves uniform co-precipitation, and initially forms manganese iron phosphate precursor crystal nuclei; the pH value of the system is monitored and stabilized throughout the process. S4. Crystal growth stage control: After the crystal nuclei are formed, continue to add ammonium hydrogen phosphate solution, switch the stirring speed and synthesis temperature, and enter the independent crystal growth and maintenance stage; control the uniform growth of crystal nuclei through constant temperature and constant speed precise maintenance. S5. Post-processing and lithiation sintering: After the reaction is completed, the mixture is allowed to stand for aging, filtered, washed and dried to obtain a high-density manganese iron phosphate precursor. The high-density manganese iron phosphate precursor is uniformly mixed with a lithium source and conductive additives, and then subjected to high-temperature sintering to finally prepare a high-compact, high-capacity, and high-stability lithium manganese iron phosphate cathode material.

2. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, In step S1, the molar concentration of the manganese ferric sulfate mixed base solution is 1.0 to 3.0 mol / L, and the molar ratio of manganese to iron in the manganese ferric sulfate mixed base solution is 1:1 to 2:1; the manganese source includes at least one of manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese chloride, and manganese acetate; the iron source includes at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous oxalate.

3. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, In step S2, the molar concentration of the ammonium hydrogen phosphate solution is 1.2–3.0 mol / L; the phosphorus source includes at least one of diammonium phosphate, phosphoric acid, and monoammonium phosphate.

4. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, The precise control parameters for the crystal nucleation stage are as follows: the dropping rate of ammonium hydrogen phosphate solution is 4–15 mL / min, the stirring speed of the system is 200–700 r / min, the pH value of the reaction system is stably controlled at 2.0–6.5, the reaction time for crystal nucleation is 15–30 min, and the temperature of the reaction system is 30–120℃.

5. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, The control parameters for the crystal growth stage are as follows: after the crystal nucleation stage, the crystal growth stage begins, the reaction time is controlled at 50-180 min, the stirring speed is adjusted to 300-500 rpm, the reaction system temperature is maintained at 40-80℃, the ammonium hydrogen phosphate solution is continuously added dropwise at a rate of 4-15 mL / min, and the pH value is 2.0-7.

0.

6. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, In step S5, the static aging time is 80-360 min, the drying process adopts vacuum drying at 80℃-150℃, and the drying and heat preservation time is 8-24 h.

7. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, In step S5, the high-density manganese iron phosphate precursor is calcined at a temperature of 400–600℃ for 4–10 hours.

8. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, The lithium source is lithium carbonate, and the conductive additive is glucose.

9. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 1, characterized in that, In step S5, the atmosphere for high-temperature sintering is an inert nitrogen atmosphere, the sintering temperature is 650℃, and the sintering time is 12h.

10. The method for precisely and controllably preparing high-pressure, high-capacity lithium manganese iron phosphate according to claim 9, characterized in that, In step S5, the washing process includes washing with deionized water three times and washing with anhydrous ethanol once.

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