Preparation method of high-conductivity manganese iron phosphate precursor and application thereof

Abstract

The application relates to the field of battery positive electrode material production, and discloses a preparation method and application of a high-conductivity manganese iron phosphate precursor, which comprises the following steps: preparing a mixed salt solution with a total metal ion molar concentration of 2.0 mol / L to 4.0 mol / L according to a molar ratio of manganese ions to iron ions of 2:8 to 8:2; placing the mixed salt solution in a reaction device with a shearing force field adjustment function under a protective atmosphere and maintaining the temperature at 55 DEG C to 60 DEG C; adding ammonia water into the solution to adjust the pH value to 6.0 to 7.5, and continuously stirring and wet sand milling the solution at a high speed during the period; aging, washing and reslurry of the precipitated product in sequence, adding a lithium source and a carbon source to uniformly disperse the product, and then spray drying to obtain the precursor with a size of 15 microns to 40 microns; the application utilizes the coupling mechanism of precipitation and sand milling to ensure the atomic-level uniform distribution of manganese and iron elements, solves the problems of low intrinsic conductivity of manganese-based materials and slow ion diffusion kinetics, and enhances the structural stability of active substances.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material production technology, and particularly relates to a method for preparing a highly conductive manganese iron phosphate precursor and its application. Background Technology

[0002] Currently, lithium-ion batteries, as devices that directly convert chemical energy into electrical energy, have their energy density and rate performance limited by the charge transfer efficiency of the positive electrode active material. Liquid phase coprecipitation is the mainstream method for preparing manganese iron phosphate precursors. It uses metal salts and precipitants to produce a precipitation reaction under specific acid-base conditions, generating secondary particles with spherical morphology.

[0003] During precursor growth, the supersaturation and shear force distribution of the reaction system determine the formation rate and spatial assembly mode of primary nuclei. Besides the physical field distribution and hardware parameter fine-tuning, reaction kinetic control strategies are a key dimension affecting precursor quality. For example, Chinese invention patent application CN118026129A discloses a method for preparing battery-grade manganese iron phosphate based on co-precipitation. The scheme involves conventional limitations on reaction temperature, rotation speed, and stoichiometry. However, the feeding process relies on static addition at a preset ratio, failing to penetrate the underlying physical limitations of supersaturation instability caused by the nonlinear consumption of ion concentration in the co-precipitation system. Furthermore, the lack of real-time characterization and dynamic feedback of the crystallization driving force makes... In long-range reactions, the system is prone to disordered homogeneous nucleation induced by local concentration polarization. It is difficult to eliminate the segregation of manganese and iron elements at the atomic scale, and it is impossible to constrain the growth of crystal nuclei along specific high-conductivity crystal planes. Due to the limited control logic lag, the precursor synthesized by existing technology exhibits phase disorder characteristics, making it difficult to solidify the high-speed electron conduction path that penetrates the particle. With the increasing requirements for high-current charging and discharging, the existing process shows physical limitations in balancing charge conduction rate and surface structure stability. The industry has tried to optimize the morphology by increasing the stirring intensity or adjusting the feeding sequence, but such linear improvement methods cannot solve the underlying logic of component distribution and structural arrangement at the crystal plane orientation level.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve the directional assembly of primary particles and eliminate metal element segregation through surface dynamics regulation, and construct a precursor structure with efficient charge transport channels. Summary of the Invention

[0005] The present invention aims to solve the problem of slow electrochemical kinetics caused by disordered surface structure and uneven component distribution of manganese iron phosphate precursor.

[0006] In this technical solution, a method for preparing a highly conductive manganese iron phosphate precursor includes the following steps: Step 101: Prepare a mixed salt solution with a total metal ion molar concentration of 2.0 mol / L to 4.0 mol / L by mixing manganese source, iron source, phosphorus source and deionized water according to a manganese ion to iron ion molar ratio of 2:8 to 8:2. Step 102: Place the mixed salt solution in a reaction apparatus with shear force field regulation function, and adjust the temperature of the mixed salt solution to 55°C to 60°C under a protective atmosphere; Step 103: Ammonia solution with a concentration of 0.5 mol / L to 1.0 mol / L is continuously added dropwise to the mixed salt solution as a pH adjuster; the pH value of the mixed salt solution is gradually adjusted to between 6.0 and 7.5, while maintaining continuous high-speed stirring and wet sand milling; based on the continuous addition of ammonia solution as a pH adjuster, sodium hydroxide solution or potassium hydroxide solution is added to the mixed salt solution to limit the pH fluctuation within the preset error range corresponding to 6.0 to 7.5, and to construct a uniformly distributed shear force field within the reaction device; Step 104 involves aging, washing, and re-slurrying the precipitated product sequentially; lithium source, organic carbon source, and inorganic carbon source are added to the re-slurry and homogenized and dispersed; finally, the slurry is spray-dried to obtain the average particle size. It is a highly conductive lithium manganese iron phosphate precursor with a diameter of 15 μm to 40 μm; the specific surface area of ​​the lithium manganese iron phosphate precursor is 5 m² / g to 15 m² / g, and the ratio of the diffraction peak intensity of the secondary spheres on the 010 crystal plane to the diffraction peak intensity on the 100 crystal plane is greater than 1.5.

[0007] Preferably, the continuous high-speed stirring and wet sand milling in step 103 refers to: using the grinding media in the sand mill to perform in-situ crushing and activation of the primary particles generated by co-precipitation under high-speed shear force, so as to suppress agglomeration and maintain the homogeneous distribution of metal ions in the reaction system.

[0008] Preferably, in step 101, the manganese source includes one or more of manganese sulfate, manganese chloride, or manganese acetate; the iron source includes one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate; and the phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid.

[0009] Preferably, in step 102, the rotation speed of the reaction device is set to 400 rpm to 500 rpm, and the temperature fluctuation inside the reaction device is limited to within ±0.5℃.

[0010] Preferably, the aging process in step 104 includes: keeping the precipitated product in a reaction solution at 60°C for 4 to 8 hours under stirring to reconstruct the surface pore structure of the secondary spheres and form electrolyte permeation channels.

[0011] Preferably, the washing in step 104 includes: washing the precipitated product multiple times with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, thereby removing sodium or potassium ions adsorbed on the surface of the secondary spheres.

[0012] Preferably, the drying in step 104 includes: granulating and drying the washed precipitate product using a spray drying device, with the inlet air temperature set to 180°C to 250°C and the outlet air temperature set to 80°C to 110°C.

[0013] Application of a method for preparing a highly conductive manganese iron phosphate precursor: The manganese iron phosphate precursor prepared by the method is used to produce battery cathode materials.

[0014] Compared with existing technologies, the method for preparing highly conductive manganese iron phosphate precursor of the present invention has the following advantages: 1. In the preparation of high-conductivity manganese iron phosphate precursor, a coupled mechanism of continuous high-speed stirring and wet sand milling is used to in-situ crush and activate the primary particles generated by co-precipitation under high-speed shear force through the grinding media in the sand mill. This effectively breaks the spontaneous agglomeration of primary particles caused by concentration fluctuations, ensuring that manganese and iron elements achieve uniform distribution at the atomic level during crystallization. This fundamentally inhibits phase separation, thereby establishing a high-speed electron conduction path and unobstructed ion migration channels throughout the particles in the active material formed by subsequent conversion. In principle, this solves the constraint between the inherently low electronic conductivity of manganese-based materials and the sluggish lithium-ion diffusion kinetics, enabling the battery to exhibit lower electrochemical polarization during charge transfer.

[0015] 2. By simultaneously introducing lithium source, organic carbon source and inorganic carbon source and homogeneously dispersing them during the re-slurry stage, the inorganic carbon source is interspersed inside the particles, and the organic carbon source forms a coating during subsequent sintering. The two work together to construct a continuous point-line-plane three-dimensional high-speed electron conduction channel inside the secondary sphere, thereby suppressing phase separation caused by local element enrichment and structural distortion caused by the Jahn-Teller effect, enhancing the lattice stability after precursor conversion, avoiding the collapse of active material structure due to stress concentration during multiple charge-discharge cycles, and ensuring the long-term cycle stability of the battery.

[0016] 3. A control strategy combining a high-concentration metal salt system (2.0 mol / L to 4.0 mol / L) with spray drying granulation process is employed. This strategy not only achieves dense particles with a uniform average particle size by adjusting the inlet and outlet air temperatures during spray drying, but also... Large-sized spherical precursors ranging from 15μm to 40μm significantly improve the flowability and volumetric compaction density of powders. This structure ensures rapid penetration of electrolyte into the particle interior and enhances the system's energy density by maintaining high particle compaction density. While ensuring high-rate output characteristics, it also improves the volumetric energy efficiency of active materials in practical applications. Attached Figure Description

[0017] Figure 1 This is a flowchart of the overall preparation process of the high conductivity manganese iron phosphate precursor of the present invention; Figure 2 This is the dynamic feedback logic diagram of the feeding rate based on the instantaneous slope of conductivity in this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0019] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0020] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0021] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0022] A method for preparing a highly conductive manganese iron phosphate precursor includes the following steps: Step 101: Prepare a mixed salt solution with a total metal ion molar concentration of 2.0 mol / L to 4.0 mol / L by mixing manganese source, iron source, phosphorus source and deionized water according to a molar ratio of manganese ions to iron ions of 2:8 to 8:2. Step 102: Place the mixed salt solution in a reaction apparatus with shear force field regulation function, and adjust the temperature of the mixed salt solution to 55°C to 65°C under a protective atmosphere; Step 103: Ammonia solution with a concentration of 0.5 mol / L to 1.0 mol / L is continuously added dropwise to the mixed salt solution as a pH adjuster; the pH value of the mixed salt solution is gradually adjusted to between 6.0 and 7.5, while maintaining continuous high-speed stirring and wet sand milling; based on the continuous addition of ammonia solution as a pH adjuster, sodium hydroxide solution or potassium hydroxide solution is added to the mixed salt solution to limit the pH fluctuation within the preset error range corresponding to 6.0 to 7.5, and to construct a uniformly distributed shear force field within the reaction device; Step 104 involves aging, washing, and re-slurrying the precipitated product sequentially; lithium source, organic carbon source, and inorganic carbon source are added to the re-slurry and homogenized and dispersed; finally, the slurry is spray-dried to obtain the average particle size. It is a highly conductive lithium manganese iron phosphate precursor with a diameter of 15 μm to 40 μm; the specific surface area of ​​the lithium manganese iron phosphate precursor is 5 m² / g to 15 m² / g, and the ratio of the diffraction peak intensity of the secondary spheres on the 010 crystal plane to the diffraction peak intensity on the 100 crystal plane is greater than 1.5.

[0023] Preferably, the continuous high-speed stirring and wet sand milling in step 103 refers to: using the grinding media in the sand mill to perform in-situ crushing and activation of the primary particles generated by co-precipitation under high-speed shear force, so as to suppress agglomeration and maintain the homogeneous distribution of metal ions in the reaction system.

[0024] Preferably, in step 101, the manganese source includes one or more of manganese sulfate, manganese chloride, or manganese acetate; the iron source includes one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate; and the phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid.

[0025] Preferably, in step 102, the rotation speed of the reaction device is set to 400 rpm to 500 rpm, and the temperature fluctuation inside the reaction device is limited to within ±0.5℃.

[0026] Preferably, the aging process in step 104 includes: keeping the precipitated product in a reaction solution at 60°C for 4 to 8 hours under stirring to reconstruct the surface pore structure of the secondary spheres and form electrolyte permeation channels.

[0027] Preferably, the washing in step 104 includes: washing the precipitated product multiple times with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, thereby removing sodium or potassium ions adsorbed on the surface of the secondary spheres.

[0028] Preferably, the drying in step 104 includes: granulating and drying the washed precipitate product using a spray drying device, with the inlet air temperature set to 180°C to 250°C and the outlet air temperature set to 80°C to 110°C.

[0029] Application of a method for preparing a highly conductive manganese iron phosphate precursor: The manganese iron phosphate precursor prepared by the method is used to produce battery cathode materials.

[0030] Example 1: When the system faces the interfacial thermodynamic phase repulsion dilemma between a highly conductive inorganic carbon source and a polar transition metal salt in an aqueous slurry, conventional physical blending methods are limited by the chemical inertness and strong hydrophobicity of the surface of multi-walled carbon nanotubes. This results in the carbon phase and the metal precursor maintaining physical contact only through van der Waals forces. In this metastable contact system, during the pre-sintering or high-temperature heat treatment process of the finished product, driven by the minimization of the system's free energy, the inorganic carbon phase spontaneously undergoes phase separation and secondary agglomeration, making it impossible for the final active material to solidify into a three-dimensional conductive framework that penetrates the grain boundaries.

[0031] To address the conductivity fluctuation problem caused by the instability of the heterogeneous phase interface, this embodiment, in the preparation of the carbon-containing manganese-iron phosphate precursor, simultaneously adds citric acid as a polycarboxylic acid polar bridging agent at 0.5% to 2.0% of the total molar amount of manganese and iron sources to a premixed slurry containing phosphorus, manganese, iron sources, and multi-walled carbon nanotubes at an addition amount of 0.01% to 1.5%. This slurry is then pumped into a sand mill, with the grinding rotor linear speed controlled at 10 m / s to 15 m / s and the sand milling system temperature controlled at 40°C to 55°C. The sand milling system utilizes the mechanochemical activation effect generated by a specific shear energy field to partially activate the surface of the multi-walled carbon nanotubes. When the hybrid structure undergoes local tearing, reactive carbon topological defects are generated. At this time, the carboxyl group at one end of the citric acid is anchored in situ at the carbon topological defect under mechanical force. The free carboxyl or hydroxyl group at the other end captures and fixes the free manganese and iron ions in the slurry through the multidentate chelation effect. Thus, the coordination complexation center connecting the carbon skeleton to oxygen atoms and then to the metal precursor is constructed simultaneously during the sand milling process. Although the overall grinding linear speed of the rotor is within the conventional physical and mechanical range, at this speed, the high-density zirconia grinding media with a specific particle size distribution undergoes high-frequency inelastic collisions in the extremely narrow stator-rotor gap. At the collision point, an extreme fluid micro-jet is generated instantaneously in the micro-region exceeding the local cavitation threshold. This synergistic energy field formed by the surface hydraulic shear force generated by the high-pressure collapse of cavitation bubbles and the instantaneous point thermal shock locally crosses the thermodynamic physical energy barrier of carbon-carbon double bond breaking. Thus, without destroying the overall long-range conductive framework structure of the carbon nanotube, highly reactive localized carbon topological defects are generated in situ on the tube wall.

[0032] In the pre-sintering process at 300℃ to 780℃ under a nitrogen protective atmosphere, because transition metal ions are pre-pinned to the defect sites of the inorganic carbon framework, the metal precursor undergoes epitaxial growth using multi-walled carbon nanotubes as low-energy nucleation sites. This results in a dense chemical bond between the manganese iron phosphate grain boundaries and the highly conductive inorganic carbon. This embedded conductive network eliminates the interfacial barrier during charge transport across phases and utilizes the steric hindrance and bonding binding force generated by the carbon framework to lock the lattice ionization tendency of manganese ions during long-term charge-discharge cycles, ensuring that the precursor particles meet the average particle size requirement after granulation. With a micron-scale spherical distribution ranging from 15 μm to 40 μm, the side reaction area of ​​the material is significantly reduced, while maintaining a defined structural stability and electron dynamics conduction rate.

[0033] Example 2: A 50-liter continuous stirred tank reactor was used to prepare a manganese-iron phosphate precursor. The reactor was equipped with an online conductivity sensor with a measurement accuracy of 0.1 μS / cm and a peristaltic pump driven by a programmable logic controller. The raw conductivity data stream acquired by the sensor was superimposed with Gaussian white noise with an amplitude of 2% of the original signal and a 50Hz power frequency electromagnetic interference signal. To achieve uniform transmission of the shear force field within the physical entity, four sets of asymmetrically distributed fluid dynamic baffles were specially welded into the inner cavity of the reactor. A parabolic turbine propeller spanning three liquid level levels from bottom to top was fitted to the bottom of the rotating shaft. Through the millimeter-level forced gap between the blade angle of attack and the inner wall of the reactor, the radial ejection force of the fluid generated by unidirectional rotation was forcibly converted into an axially folded deep circulating flow. This eliminated the inherent laminar isolation zone and fluid dynamic blind zone in the flat-bottom flow field from a hardware mechanical construction perspective. Initially, a manganese-iron mixed salt solution with a total metal ion molar concentration of 2.0 mol / L was injected into the reactor. The pH of the system was maintained between 6.0 and 7.5, and the temperature was kept between 55°C and 60°C. Ammonia solution with a concentration of 0.8 mol / L was continuously added dropwise to the mixed salt solution as a pH adjuster. During this period, the circulating wet sand milling system connected to the reactor was activated, maintaining continuous high-speed stirring and wet sand milling. The grinding media in the sand mill continuously and in-situ crushed and activated the primary particles generated by co-precipitation under high-speed shear force. This mechanical force strongly sheared the primary particles to break up the spontaneous aggregation caused by concentration fluctuations, maintaining the atomically homogeneous distribution of metal ions in the reaction system. The programmable logic controller (PLC) acquired raw conductivity data containing noise, used a Kalman filter algorithm to filter out 50Hz power frequency electromagnetic interference signals, calculated the difference between the current conductivity measurement and the historical conductivity value of the previous sampling period, and divided this difference by the time interval of the sampling period to output the instantaneous slope of the conductivity decrease. The ion precipitation consumption rate in the isothermal liquid phase system showed a linear mapping with the overall conductivity decay. The preset slope threshold calculation formula was as follows: ,in, This represents a preset slope threshold for the standard crystal nucleus growth rate. The peak conductivity of the system is measured at the initial moment of a single quantitative injection of metal ions into the basic buffer solution. The steady-state conductivity of the system represents the state at which the precipitation reaction terminates when the free-state equilibrium is reached. Representing the time span from the initial peak value to complete equilibrium of the reaction, the pre-calibration offline procedure uses a conductivity sensor with a range of 0 to 200 mS / cm and a sampling frequency of not less than 10 Hz. Measurements are maintained at a background baseline of 60°C and a blank ammonia buffer solution free of transition metal ions. A predetermined molar amount of manganese-iron standard salt solution is injected into the container in a single injection. The microprocessor records the extreme conductivity value after the abrupt jump as... Sampling continues until the difference between two adjacent sampling periods is less than the sensor quantization noise boundary, and the final state average is extracted as... And record the corresponding time period. The crystallization kinetics requirements are transformed into physical boundary indices. In this transformation logic, to eliminate the dimensional mismatch and physical dimension contradiction caused by direct calculation, the system control firmware incorporates a normalized scalar dimensionality reduction protocol. This protocol forces the actual measured time span values ​​to be converted into purely digital dimensionless time coefficients by dividing them by the system's built-in reference cycle period, and simultaneously based on steady-state variables... The implicit unit-time decay weight mapping property ensures that its product with the dimensionless time coefficient still maintains the single absolute dimension of conductivity, thus providing a benchmark abrupt change value. Performing subtraction calibration according to mathematical rules provides a compliance basis, accurately defining the theoretical attenuation lower limit of crystal nucleus growth. Based on the instantaneous slope, the controller adjusts the peristaltic pump speed in real time to maintain the supersaturation in the reaction system within the range of 0.01 to 0.05. In this feedback regulation closed loop, the controller embeds a two-way coupled matrix model of acidity and supersaturation. Since ammonia acts as a complexing regulator to control the material flux of crystal growth and directly intervenes in the overall acidity-base balance of the system, the controller uses 8.0 as a dynamic baseline. When the supersaturation approaches the kinetic upper limit of 0.05, the model simultaneously issues a command to slow down the feeding rate and finely adjusts the compensation injection ratio of the bypass auxiliary sodium hydroxide solution. This precisely counteracts the transient drop in local pH caused by the limited addition of ammonia. Through this synergistic locking of the constant physical field of the weakly alkaline hydroxide ion concentration in the micro-region, the selective spatial steric hindrance shielding of the high-energy barrier region of the hydrated complex ion clusters on the 100 and 001 crystal planes of the crystal nucleus is forcibly maintained, ensuring that the driving energy barrier of chemical deposition is released only directionally along the 010 crystal plane, which lacks steric hindrance.

[0034] Multiple sample groups were prepared to evaluate the physical effects of the dynamic feedback mechanism on the surface morphology and overall density of the precursor. In the experimental group, continuous high-speed stirring and wet sand milling were maintained. After the precipitation reaction, the precipitate was successively aged, washed, and re-slurryed. Lithium source, organic carbon source, and inorganic carbon source were added to the re-slurry and dispersed homogeneously with high energy. Finally, granulation and drying were carried out using a spray drying device with the inlet air temperature set at 180℃ to 250℃ and the outlet air temperature set at 80℃ to 110℃. The high conductivity lithium manganese iron phosphate precursor was finally obtained, and the average particle size of the precursor was measured. The particle size was 28 μm, and the specific surface area was 5 m² / g to 15 m² / g. In the first control group, where the conductivity slope feedback loop was cut off and a constant feeding rate was maintained, the supersaturation of the reaction system climbed to 0.12 at the end of the reaction. The consumption of free metal ions triggered phase separation, and fragmented crystals precipitated in the precipitate. The tap density of the product in the first control group was measured to be 0.92 g / cm³. An out-of-range control group with supersaturation deviating from the specified range was prepared. In the second control group, where the judgment criteria of the programmable logic controller were modified to control the supersaturation to be constant at 0.005, the primary grains along the 010 crystal plane... Anisotropic growth of the primary crystal aggregates was halted, and the particles exhibited irregular polyhedral shapes. The tap density of this product was measured to be 1.05 g / cm³. In the third control group, where the supersaturation threshold was kept constant at 0.08, the high driving force in the early stage of the reaction caused the emergence of crystal nuclei, resulting in halted particle volume growth and the presence of micron-sized pores within the aggregates. The tap density of this product was measured to be 1.12 g / cm³. The tap density exhibited a nonlinear evolution of first increasing and then decreasing with increasing supersaturation. After the supersaturation exceeded 0.05, the increase in the volume of micron-sized pores within the primary crystal aggregates constituted a physical limitation that inhibited the increase in tap density.

[0035] A crystallization process that regulates the supersaturation of free metal ions filters out environmental electromagnetic disturbances and limits the driving force for metal ion precipitation, suppressing disordered nucleation defects caused by local concentration polarization in constant-rate co-precipitation. The in-situ activation process, coupled with sand milling, effectively suppresses disordered nucleation defects caused by local concentration polarization during co-precipitation, resulting in a higher average particle size. The precursor compound, with a large particle size ranging from 15μm to 40μm, exhibits a reaction mechanism that, under specific weakly acidic to neutral conditions with a pH of 6.0 to 7.5, strong mechanical shearing effectively breaks the tendency for spontaneous aggregation of primary particles, ensuring a uniform atomic-level distribution of manganese and iron during crystallization. In the subsequent resizing stage, lithium, organic, and inorganic carbon sources are simultaneously introduced for homogeneous dispersion and combined with spray drying. This allows the inorganic carbon source to penetrate the particles, while the organic carbon source forms a coating during subsequent sintering. Together, they construct a continuous point-line-plane three-dimensional high-speed electron conduction channel within the secondary spheres, fundamentally overcoming the limitation of extremely low intrinsic electronic conductivity in manganese-based cathode materials and maintaining the long-term stability of the system structure.

[0036] Example 3: In a coupled system consisting of a batch reactor and an external circulating high-energy sand mill assembled on a specific production line, a manganese-iron mixed salt solution with a total metal ion molar concentration of 3.0 mol / L is initially injected into the reactor. The temperature of the mixed salt solution is adjusted and maintained at 58°C under a nitrogen protective atmosphere. Ammonia solution with a concentration of 0.6 mol / L is continuously added dropwise to the mixed salt solution as a pH adjuster. The circulation pump is turned on, allowing the slurry in the batch reactor to continuously pass through the external high-energy sand mill at a flow rate of 30 L / min. The rotor linear velocity of the sand mill is set to 12 m / s. The primary particles generated by co-precipitation are subjected to high-frequency non-elastic grinding under high-speed shear force by the grinding media. The pH of the co-precipitation system was gradually adjusted between 6.5 and 7.0 through collision and in-situ fragmentation activation. After the precipitation reaction was complete, the precipitate was successively aged and washed with deionized water until the conductivity of the washing solution was lower than 50 μS / cm. Subsequently, the precipitate was put into a re-slurry tank for re-slurrying. Lithium carbonate as a lithium source, sucrose as an organic carbon source, and single-walled carbon nanotubes as an inorganic carbon source were added to the re-slurry in a stoichiometric ratio. The mixture was then homogenized and dispersed for 2 hours using a high-speed shear emulsifier. Finally, the mixed slurry was pumped into a spray drying granulation device, with the inlet air temperature controlled at 220℃ and the outlet air temperature at 95℃. The final dried product had an average particle size of [missing value]. The precursor for highly conductive lithium manganese iron phosphate consists of micron-sized spherical particles with a diameter of 25 μm. This process eliminates the interfacial conduction barrier within the particles, and the intrinsic conductivity of the precursor after processing remains stable at [value missing]. above.

[0037] Example 4: When the system faces the condition of fluctuations in the initial rheological properties of the slurry due to cross-batch raw materials, the system constructs a multidimensional lookup table containing the quantitative relationships of the coefficients in the kinetic mapping equation through an offline calibration process. Multiple sets of reference manganese-iron mixed salt solutions with defined viscosity gradients are prepared and placed in a stirred tank reactor. A preset stirring power is applied to each set of solutions, and ammonia is continuously added dropwise to each solution. The actual supersaturation parameter of the corresponding free metal ions is determined by chemical titration of samples. Simultaneously record the instantaneous slope of conductivity corresponding to supersaturation. The controller uses the least squares method to calculate the ion mobility conversion coefficient under different combinations of viscosity and stirring power based on the acquired discrete data sequence. and compensation factors The mapped data is written into non-volatile memory to generate a multidimensional lookup table.

[0038] During the continuous preparation of the carbon-containing manganese ferric phosphate precursor, the monitoring unit collects real-time slurry viscosity data and electrical power data output by the stirring motor in the reactor. The controller traverses a multidimensional lookup table to extract the ion mobility conversion coefficient that matches the real-time operating conditions. and compensation factors Substitute it into the kinetic mapping equation to calculate the supersaturation parameter of free metal ions in the reaction system. The controller is based on this supersaturation parameter A frequency adjustment command is output to the peristaltic pump to ensure that the ammonia feed flux corresponds to the coordination and complexation rate on the surface of the multi-walled carbon nanotubes, suppressing deviations in ion concentration caused by changes in fluid physicochemical properties, and ultimately synthesizing an average particle size. It is a spherical manganese iron phosphate compound entity with a diameter of 15 μm to 40 μm and a tap density greater than or equal to 1.20 g / cm³.

[0039] Example 5: When the reaction device is in long-term continuous preparation mode, and the online conductivity sensor probe is attached with precipitates and the data baseline drift and fluid delivery delay are caused by fatigue of the peristaltic pump hose, the controller calls the preset adaptive baseline calibration procedure to reconstruct the underlying data of the kinetic mapping equation. The monitoring unit suspends ammonia injection according to the set production batch interval and collects the discrete sequence of static slurry conductivity in the reactor within the preset time window. The controller calculates the variance of the discrete sequence and compares it with the calibration reference variance registered in the non-volatile memory. If the difference between the real-time variance and the calibration reference variance is greater than the preset tolerance boundary, the controller extracts the real-time temperature signal and pH signal of the current reaction system as compensation variables and recalculates the compensation factor using a multiple linear regression algorithm. The value, using the updated compensation factor Correct the coordinate mapping nodes within the multidimensional lookup table, generate a real-time parameter matrix, and overwrite the historical lookup table records.

[0040] The controller extracts the corrected ion mobility conversion coefficient based on the overwritten multidimensional lookup table. and compensation factors Substituting this into the kinetic mapping equation, the real-time supersaturation parameter of free metal ions in the reaction system is calculated. The updated frequency adjustment command is output to the peristaltic pump, and the dynamic reconfiguration procedure eliminates the instantaneous slope introduced by hardware aging. Measurement deviations during the collection process are minimized, and the ammonia feed throughput is kept synchronized with the coordination and complexation rate on the surface of multi-walled carbon nanotubes to avoid secondary agglomeration caused by local supersaturation imbalance. This ensures the reactor continuously produces an average particle size distribution during long-term continuous operation. Spherical manganese iron phosphate compound entities with a tap density greater than or equal to 1.20 g / cm³ and ranging from 15 μm to 40 μm.

[0041] Example 6: Mechanism verification and comparative experiments of precursor structure orientation and component homogeneity. This invention demonstrates the underlying regulatory logic of the co-precipitation and wet milling coupling mechanism and the dual-alkali synergistic feedback compensation mechanism on the preferred orientation (010 / 100 diffraction peak intensity ratio) and atomic-level elemental distribution of the manganese iron phosphate precursor. Comparative Examples 1 to 4 were prepared and systematically characterized for their microstructure, elemental distribution variance, and electrochemical performance. Comparative Example Preparation Process: Comparative Example 1 (post-reaction milling – simulating the process in Comparative Document 1): Except for step 103, co-precipitation... During the reaction, wet sand milling was not activated. All other process parameters, concentrations, and feeding sequences were identical to those in Example 3. After the co-precipitation reaction was complete and the mixture aged, the resulting slurry was pumped into an external high-energy sand mill and circulated at the same rotor linear speed (12 m / s) to achieve the same particle size distribution. Subsequently, the slurry was washed, re-slurried, had a carbon source added, and was spray-dried. Comparative Example 2 (Single Ammonia Water Adjustment System – No Strong Alkali Dynamic Compensation): Except for step 103, where pH was adjusted only through a single high-concentration ammonia water flow path, the bypass flow of sodium hydroxide or potassium hydroxide solution was cut off. The auxiliary compensation adjustment loop is used, and due to the lack of dynamic polarization cancellation by the dual-base matrix model, the pH fluctuation range cannot be locked within the preset error range. The other process parameters are exactly the same as in Example 3; Comparative Example 3 (low concentration metal salt system): except that in step 101, the total metal ion molar concentration is reduced to 1.0 mol / L (deviating from the 2.0 mol / L to 4.0 mol / L limit of this invention), the other process parameters are exactly the same as in Example 3. Due to the low supersaturation of the system, the crystallization driving force is insufficient, and the nucleation rate is extremely slow; Comparative Example 4 (normal Mechanical stirring without in-situ sand milling: Except for step 103, where wet sand milling is omitted, physical shearing and stirring are performed solely by the parabolic turbine propeller on the reactor at a conventional speed of 500 rpm. All other process parameters are identical to those in Example 3. Testing and characterization methods: Crystal plane orientation (010 / 100 ratio) test: The precursor powders prepared in each example and comparative example were scanned using a rotating target X-ray diffractometer. The integral intensities of the characteristic diffraction peaks of the 010 and 100 crystal planes were extracted, and their ratio was calculated. The elemental atomic-level component segregation (D...) seg Test: Using high-resolution transmission electron microscopy combined with high-angle dark-field scanning transmission and energy-dispersive X-ray spectroscopy, ten micro-regions of 50 nm × 50 nm were randomly selected within a single precursor sphere to determine the actual molar ratio of manganese to iron and calculate its segregation variance D. seg The closer the variance is to 0, the more uniform the atomic-level distribution of manganese iron. Volumetric energy density and rate polarization tests: The cathode material after precursor conversion was used to fabricate a lithium battery. Its volumetric energy density under compaction density was measured, and the electrochemical polarization voltage (ΔV) during 10C high-current charge-discharge was tested using an electrochemical workstation. Test results comparison table:

[0042] Analysis of the underlying control mechanism and synergistic effect: From the above test data, it can be seen that there is a strong kinetic causal chain between the various process parameters limited by the present invention and the microscopic crystal structure characteristics, which cannot be predicted by those skilled in the art through conventional process fine-tuning: (1) The non-equivalent mechanism of synchronous coupling of coprecipitation and in-situ sand milling: Comparative document 1 and Comparative Example 1 adopt the route of sand milling after reaction; Due to the significant difference in the intrinsic solubility product constants of manganese ions and iron ions, in the early stage of coprecipitation crystallization, if there is no interference from the in-situ high-energy shear force field, the thermodynamic spontaneous driving force will cause iron and manganese to nucleate first in the micro-region and form disordered aggregates with phase disorder. At this time, manganese and iron elements have undergone serious atomic-level component segregation. The segregation variance of Comparative Example 1 The specific surface area was as high as 0.145; after the reaction, sand milling was performed, which only mechanically crushed the disordered coarse particles that had already segregated, resulting in an abnormally large specific surface area of ​​18.2 square meters per gram. This could not reverse the phase separation of the solidified micro-regions, and the crystal orientation showed disordered and chaotic characteristics with a 010 / 100 ratio of only 0.82. However, the present invention applies simultaneous wet sand milling and crushing at the same time as co-precipitation. The fluid micro-jet and instantaneous point thermal shock generated by the grinding media at the collision point micro-region forcibly break the spontaneous disordered agglomeration caused by concentration polarization within milliseconds. This overcomes the thermodynamic energy barrier of heterogeneous nucleation of different metal ions, so that manganese and iron elements achieve atomic-level non-segregated uniform mixing in the very initial stage of crystallization. ; This intervention implemented in the very early stage of the nucleation reaction changed the spatial assembly trajectory of the subsequent crystal nuclei; (2) The directional locking constraint of the 010 high-efficiency conductive crystal plane by the dual-alkali synergistic feedback compensation: If the in-situ sand milling is not precisely controlled by the coordination environment, the primary grains still tend to grow along the thermodynamic isotropic direction. In Comparative Example 2, due to the lack of precise bypass synergistic feedback compensation of sodium hydroxide or potassium hydroxide solution, the pH value in the system under the high-energy fluid fluctuations brought about by sand milling and the local volatilization of ammonia water produced a transient and violent jump. This invention, through dual-alkali synergistic feedback compensation, while adding the complexing agent ammonia water, uses multiple linear regression and two-way coupled matrix model to supplement the instantaneous injection of strong alkali. Its deep chemical essence lies in: at 6.0 to 7.5 Within the dynamic ultra-narrow pH error window, free sodium or potassium ions and multidentate complexed hydrated ion clusters form a specific charge layer, which specifically and dynamically shields and strongly adsorbs onto the 100 and 001 crystal planes of the primary crystal nucleus, thereby greatly raising the growth energy barrier of the crystal plane and hindering its growth. In contrast, the 010 crystal plane, which lacks steric shielding, is the golden channel plane for long-distance rapid conduction of electrons and lithium ions inside the battery. Its lattice growth energy barrier is relatively low, and the crystallization driving force of chemical deposition can be released directionally along the 010 crystal plane. Therefore, only under the combined suppression of dual alkali synergistic control and in-situ sand milling will the secondary spheres exhibit the characteristic that the ratio of the diffraction peak intensity of the 010 crystal plane to the diffraction peak intensity of the 100 crystal plane is greater than 1.5. (3) The necessity of strong coupling in high-concentration metal salt systems (2.0 mol / L to 4.0 mol / L): Data from Comparative Example 3 shows that when the total metal ion molar concentration drops to 1.0 mol / L, even with simultaneous sand milling and a dual-alkali system, the 0.10 / 100 ratio drops sharply to 0.61. This is because the crystallization supersaturation in low-concentration systems is extremely low, which is a typical diffusion-controlled nucleation process. At this time, the high shear force field of in-situ sand milling will destroy the spontaneous directional agglomeration and assembly behavior of crystal nuclei. This invention constructs 2.0 mol / L to 4.0 mol / L metal salt systems. The fundamental purpose of the high concentration system of l / L is to create an extremely high crystal nucleation supersaturation (locked in the range of 0.01 to 0.05). Within this range, the nucleation driving force is extremely high and the emergence rate of primary grains is extremely fast. This provides the in-situ sand mill with an extremely high density of activation units. At this time, the high-density activated crystal nuclei spontaneously and efficiently carry out directional crystal plane epitaxial growth under the preferred orientation energy barrier of the dual-alkali manufacturing process. Finally, they can be granulated to obtain a dense micron-sized spherical precursor with an average particle size D50 of 15 to 40 micrometers and internal three-dimensional continuous conduction channels of points, lines and surfaces.

[0043] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a highly conductive manganese iron phosphate precursor, characterized in that, Includes the following steps: Step 101: Prepare a mixed salt solution with a total metal ion molar concentration of 2.0 mol / L to 4.0 mol / L by mixing manganese source, iron source, phosphorus source and deionized water according to a manganese ion to iron ion molar ratio of 2:8 to 8:

2. Step 102: Place the mixed salt solution in a reaction apparatus with shear force field regulation function, and adjust the temperature of the mixed salt solution to 55°C to 60°C under a protective atmosphere; Step 103: Continuously add ammonia water with a concentration of 0.5 mol / L to 1.0 mol / L as a pH adjuster to the mixed salt solution; gradually adjust the pH value of the mixed salt solution to between 6.0 and 7.5, while maintaining continuous high-speed stirring and wet sand milling. Based on the continuous addition of ammonia water as a pH adjuster, sodium hydroxide solution or potassium hydroxide solution is added to the mixed salt solution to limit the pH fluctuation within the preset error range of 6.0 to 7.5, and a uniformly distributed shear force field is constructed in the reaction device. Step 104 involves aging, washing, and re-slurrying the precipitated product sequentially; lithium source, organic carbon source, and inorganic carbon source are added to the re-slurry and homogenized and dispersed; finally, the slurry is spray-dried to obtain the average particle size. It is a highly conductive lithium manganese iron phosphate precursor with a diameter of 15 μm to 40 μm; the specific surface area of ​​the lithium manganese iron phosphate precursor is 5 m² / g to 15 m² / g, and the ratio of the diffraction peak intensity of the secondary spheres on the 010 crystal plane to the diffraction peak intensity on the 100 crystal plane is greater than 1.

5.

2. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, The continuous high-speed stirring and wet sand milling in step 103 refers to: using the grinding media in the sand mill to crush and activate the primary particles generated by co-precipitation under high-speed shear force, so as to inhibit agglomeration and maintain the homogeneous distribution of metal ions in the reaction system.

3. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, In step 101, the manganese source includes one or more of manganese sulfate, manganese chloride, or manganese acetate; the iron source includes one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate; and the phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid.

4. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, In step 102, the rotation speed of the reaction device is set to 400 rpm to 500 rpm, and the temperature fluctuation inside the reaction device is limited to within ±0.5℃.

5. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, The aging process in step 104 includes: keeping the precipitated product in a reaction solution at 60°C for 4 to 8 hours under stirring to reconstruct the surface pore structure of the secondary spheres and form electrolyte permeation channels.

6. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, The washing process in step 104 includes: washing the precipitated product multiple times with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, thereby removing sodium or potassium ions adsorbed on the surface of the secondary spheres.

7. The method for preparing a highly conductive manganese iron phosphate precursor according to claim 1, characterized in that, The drying process in step 104 includes: granulating and drying the washed precipitate product using a spray drying device, with the inlet air temperature set to 180°C to 250°C and the outlet air temperature set to 80°C to 110°C.

8. An application of a method for preparing a highly conductive manganese iron phosphate precursor, characterized in that, The manganese iron phosphate precursor prepared by the method for preparing a highly conductive manganese iron phosphate precursor according to claim 1 is used to produce battery cathode materials.

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