A method for preparing high-rate precursor by continuous oxidation complex precipitation reaction

Abstract

The application relates to a method for preparing a high-rate precursor through a continuous oxidation complex precipitation reaction and belongs to the technical field of lithium ion battery preparation. The method comprises arranging three-stage oxidation zones in a continuous flow reaction kettle, gradually increasing the oxidant concentration and pH value, and gradiently injecting a complexing agent, so that Fe2+ is preferentially complexed and slowly oxidized, and Mn2+ is subsequently synchronously oxidized and precipitated. According to the method, the multistage oxidation zones are arranged in the continuous flow reaction kettle, the oxidant concentration and the pH value are gradually increased, and the complexing agent is gradiently injected, so that Fe2+ is preferentially partially complexed and slowly oxidized in the front section, Mn2+ is synchronously oxidized and precipitated in the rear section, phase separation is inhibited, spherical precursor particles with uniform composition, compact structure and regular morphology are obtained, and the spherical precursor particles are suitable for high-rate lithium battery positive electrode material preparation.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery preparation technology, specifically relating to a method for preparing high-rate precursors via a continuous oxidation-complexation-precipitation reaction. Background Technology

[0002] In the preparation of lithium-ion battery cathode material precursors, co-precipitation is one of the mainstream processes. Its core lies in controlling the reaction conditions of metal salts, alkaline solutions, and complexing agents to obtain spherical precursor particles with regular morphology, narrow particle size distribution, and high tap density. However, in systems involving easily oxidized metal ions such as Mn²⁺ or Fe²⁺, traditional co-precipitation processes often face the problem of asynchronous metal ion oxidation, leading to localized phase separation and component segregation, which in turn affects the structural uniformity and electrochemical performance of the precursor.

[0003] In the prior art, CN114920305B discloses a method for preparing a ternary precursor, which improves product repeatability and tap density by controlling the flow rate and pH value of the metal salt solution in stages (nucleation period → pH reduction period → growth period). Although this method optimizes the particle growth process to some extent, it is still based on the conventional co-precipitation path and does not actively intervene in the oxidation kinetics of Mn²⁺ / Fe²⁺. The lack of effective control over the redox potential in the reaction system may lead to premature precipitation of high-valence metal hydroxides, resulting in uneven nucleus composition or rough surface.

[0004] Another related technology, CN115745026B, proposes a method for preparing precursors for sodium-ion batteries. This method involves introducing urea and polyethylene glycol to induce the uniform deposition of a nickel-manganese-iron co-precipitate on the crystal nucleus surface, forming a nanosheet structure. While this approach focuses on the uniformity of the multi-metal co-precipitation, it relies on organic additives to control the morphology and does not clearly address the issue of simultaneous oxidation of Mn²⁺ / Fe²⁺ in an alkaline environment. Under continuous production conditions, if the oxidation rate does not match the precipitation rate, local supersaturation or phase separation may still occur, affecting the formation of the dense spherical structure required for high-rate performance.

[0005] In summary, although the two closest existing technologies have made some improvements in precursor morphology control and composition uniformity, neither has systematically integrated the synergistic mechanism of oxidation-complexation-precipitation in a continuous reaction system. In particular, they lack precise temporal and territorial control of the Mn²⁺ / Fe²⁺ oxidation process, making it difficult to effectively suppress phase separation caused by asynchronous oxidation and limiting the stable preparation of high-rate performance precursors. Summary of the Invention

[0006] To overcome the problems in the prior art, this application provides a method for preparing high-rate precursors through a continuous oxidation-complexation-precipitation reaction. The method aims to construct multi-stage oxidation zones in a continuous flow reactor, progressively increase the concentration of oxidant and pH value, and combine this with gradient injection of complexing agents. This allows Fe²⁺ to preferentially undergo partial complexation and slow-release oxidation in the front region, while Mn²⁺ achieves simultaneous oxidation and precipitation in the rear region. This suppresses phase separation and yields spherical precursor particles with uniform composition, dense structure, and regular morphology.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, this application provides a method for preparing high-rate precursors via a continuous oxidative complexation precipitation reaction, comprising the following steps: S10: A mixed metal salt solution containing Mn²⁺ and Fe²⁺, an alkaline solution, an oxidant solution, and a complexing agent solution are fed into a continuous flow reactor via independent metering pumps. The interior of the continuous flow reactor is divided into at least three oxidation-precipitation reaction zones in series along the material flow direction, namely the first oxidation zone, the second oxidation zone, and the third oxidation zone. S20: In the first oxidation zone, the instantaneous oxidant concentration of the mixed slurry in the first oxidation zone is controlled to be 0.05 to 0.2 mol / L, and the pH value is maintained at 8.0 to 9.0. At the same time, a first gradient complexing agent solution accounting for 30% to 50% of the total complexing agent is injected, so that Fe²⁺ preferentially forms a partial complex with the complexing agent, which slows down its oxidation rate, while Mn²⁺ remains unoxidized in this stage; S30: After the material enters the second oxidation zone, the concentration of oxidant is increased to 0.2 to 0.5 mol / L, the pH value is adjusted to 9.0 to 10.0, and a second gradient complexing agent solution accounting for 20% to 40% of the total complexing agent is injected to promote the gradual dissociation of Fe²⁺ complex and complete the oxidation to Fe³⁺, while starting the initial oxidation process of Mn²⁺. S40: After the material enters the third oxidation zone, the concentration of oxidant is further increased to 0.5 to 1.0 mol / L, the pH value is maintained at 10.0 to 11.0, and the remaining 10% to 30% of the third gradient complexing agent solution is injected. The sum of the three is 100%, so that Mn²⁺ and Fe³⁺ are oxidized simultaneously and co-precipitated as hydroxides or hydroxy oxides, forming spherical precursor particles with uniform composition. S50: The slurry from the outlet of the third oxidation zone is subjected to solid-liquid separation, washing, and drying to obtain a high-ratio performance precursor.

[0008] According to this application, a multi-stage oxidation zone is set up in a continuous flow reactor. The concentration of oxidant, pH value, and injection amount of complexing agent are independently controlled in each stage, so that the oxidation process of Fe²⁺ and Mn²⁺ is carried out stepwise in time and space, avoiding premature precipitation or phase separation due to differences in oxidation potential. The first oxidation zone, through the synergistic effect of low concentration of oxidant and high proportion of complexing agent, enables Fe²⁺ to form a kinetically stable complex intermediate, inhibiting its rapid oxidation to Fe³⁺ and precipitation. The second oxidation zone, by increasing the concentration of oxidant and pH value, triggers the controllable dissociation and oxidation of Fe²⁺ complex, and simultaneously initiates the oxidation of Mn²⁺. The third oxidation zone, under strong oxidation and high alkalinity conditions, achieves the synchronous precipitation of Mn²⁺ and Fe³⁺, ensuring uniform element distribution and complete crystal structure within the precursor particles.

[0009] In some embodiments, the continuous flow reactor is any one of a tubular reactor, a multi-stage stirred tank reactor in series, or a microchannel reactor, and a static mixer or dynamic stirring device is provided between each oxidation zone to ensure uniform mixing and mass transfer efficiency of materials during the transition between zones.

[0010] In some embodiments, the molar ratio of Mn²⁺ to Fe²⁺ in the mixed metal salt solution is 1:1 to 4:1, the total metal ion concentration is 1.0 to 2.5 mol / L, the solvent is deionized water, and the metal salt is selected from at least one of sulfate, chloride, or nitrate.

[0011] In some embodiments, the alkaline solution is at least one of sodium hydroxide, potassium hydroxide, or ammonia water, with a concentration of 2.0 to 6.0 mol / L, and is injected into each oxidation zone at a set flow rate via an independent metering pump to maintain the target pH value in each zone.

[0012] In some embodiments, the oxidant solution is at least one of hydrogen peroxide, air, oxygen, or sodium hypochlorite, wherein the hydrogen peroxide concentration is 3% to 30% (mass fraction), and the gaseous oxidant is introduced into the bottom of each oxidation zone by bubbling, with a gas flow rate of 0.1 to 1.0 L / min.

[0013] In some embodiments, the complexing agent is at least one of ammonia, ethylenediaminetetraacetic acid (EDTA), sodium citrate, potassium sodium tartrate, or polyacrylic acid, the molar ratio of total complexing agent to total metal ions is 0.8:1 to 1.5:1, and the concentration of the complexing agent solution is 0.5 to 2.0 mol / L.

[0014] In some embodiments, the residence time in the first oxidation zone is 10 to 30 minutes, the residence time in the second oxidation zone is 15 to 40 minutes, and the residence time in the third oxidation zone is 20 to 50 minutes. The residence time in each zone is controlled by adjusting the reactor volume and the total feed flow rate.

[0015] In some embodiments, the first oxidation zone, the second oxidation zone, and the third oxidation zone are each equipped with an independent pH online monitoring and feedback control system. Each oxidation zone adjusts the pH value through an incremental PID algorithm using the control system, with the proportional coefficient Kp set to 1.2, the integral time Ti to 45s, and the derivative time Td to 10s. When the pH is detected to deviate from the set value by 0.05, the control system outputs a pulse signal to drive the stepper motor of the alkali metering pump to change its speed.

[0016] In some embodiments, the first oxidation zone, the second oxidation zone, and the third oxidation zone are respectively equipped with an online oxidation-reduction potential (ORP) monitoring device, and the ORP values ​​are controlled at +200 to +350 mV, +350 to +500 mV, and +500 to +700 mV, respectively, and the target oxidation intensity is maintained by adjusting the oxidant flow rate.

[0017] In some embodiments, the injection site of the first gradient complexing agent solution is located 10% to 30% downstream of the inlet of the first oxidation zone, the injection site of the second gradient complexing agent solution is located 20% to 40% downstream of the inlet of the second oxidation zone, and the injection site of the third gradient complexing agent solution is located 30% to 50% downstream of the inlet of the third oxidation zone, thereby achieving a spatial gradient distribution of the complexing agent in each region.

[0018] In some embodiments, the inner wall of the continuous flow reactor is coated with an alkali-resistant and oxidation-resistant ceramic coating or a polytetrafluoroethylene coating to prevent metal ions from being adsorbed on the vessel wall or from undergoing side reactions.

[0019] In some embodiments, in step S50, solid-liquid separation is performed by centrifugation or pressure filtration, washing is performed by repeated countercurrent washing with deionized water until the conductivity of the filtrate is lower than 50 μS / cm, drying temperature is 80 to 120°C, and drying time is 4 to 12 hours.

[0020] In some embodiments, the method is applicable to the preparation of lithium-ion battery cathode material precursors, including but not limited to hydroxide or hydroxyl oxide precursors of nickel-manganese-iron (Ni-Mn-Fe), cobalt-manganese-iron (Co-Mn-Fe), or nickel-cobalt-manganese-iron (Ni-Co-Mn-Fe) systems.

[0021] In some embodiments, in the first oxidation zone, the complex formed by Fe²⁺ and the complexing agent is a [Fe(L)_n]²⁺ type complex, where L is the complexing agent ligand and n is 1 to 4. This complex has a high stability constant (log K ≥ 6) under pH conditions of 8.0 to 9.0, which can effectively inhibit the spontaneous oxidation of Fe²⁺ to Fe³⁺.

[0022] In some embodiments, in the second oxidation zone, as the pH increases to 9.0 to 10.0, the [Fe(L)_n]²⁺ complex undergoes partial hydrolysis, releasing free Fe²⁺, which is then oxidized to Fe³⁺ by the oxidant. Fe³⁺ immediately combines with OH⁻ to form FeOOH crystal nuclei, which serve as nucleation centers for subsequent co-precipitation.

[0023] In some embodiments, in the third oxidation zone, Mn²⁺ is oxidized to Mn³⁺ or Mn at pH 10.0 to 11.0 and high oxidant concentrations. 4 ⁺, and undergo heterogeneous nucleation with the FeOOH crystal nucleus surface to form a Mn-Fe-O-OH composite phase, which grows into dense spherical particles through the Ostwald ripening mechanism.

[0024] In some embodiments, the total feed flow rate of the continuous flow reactor is 50 to 500 mL / min, and the flow rate ratio of each solution is precisely controlled by a mass flow meter. The volume ratio of the metal salt solution, alkali solution, oxidant solution and complexing agent solution is 1:0.8 to 1.5:0.1 to 0.5:0.05 to 0.3.

[0025] In some embodiments, the method further includes setting a seed crystal circulation loop at the outlet of the third oxidation zone, returning a portion of the slurry to the inlet of the first oxidation zone after screening, with a circulation ratio of 5% to 20%, to regulate the particle size distribution so that D50 is controlled at 8 to 15 μm and the particle size distribution span is less than 1.0.

[0026] In some embodiments, the gradient injection of the complexing agent solution is achieved by a multi-channel peristaltic pump, with each channel independently programmed. The injection flow rate decreases in a stepwise or linear manner as the reaction progresses, ensuring that the complexation strength matches the oxidation process.

[0027] In some embodiments, each oxidation zone of the continuous flow reactor is equipped with a jacketed temperature control system to maintain the reaction temperature at 40 to 70°C, with temperature fluctuations not exceeding ±1°C, so as to ensure the kinetic consistency of the oxidation and precipitation reactions.

[0028] Secondly, this application provides a high-rate precursor, which is prepared according to the method described in any embodiment of the first aspect.

[0029] According to this application, since the high-magnification precursor is prepared according to the method described in any embodiment of the first aspect, its particles are regularly spherical, with a primary particle size of 180 to 300 nm, a secondary spherical particle D50 of 8 to 15 μm, a tap density greater than 2.0 g / cm³, and an X-ray diffraction pattern showing a single β-Ni(OH)2 or α-FeOOH / MnOOH composite phase without impurity phase peaks, and elemental surface scan results showing that Mn and Fe are uniformly distributed with an atomic ratio deviation of less than ±3%.

[0030] Compared with the prior art, the present invention has the following significant advantages: 1. Precise temporal and territorial control of Mn / Fe oxidation kinetics was achieved, effectively suppressing phase separation and component segregation. This invention achieves active intervention in the oxidation process of metal ions by constructing three tandem oxidation-precipitation reaction zones in a continuous flow reactor and coordinating with gradient injection of complexing agents. In the first oxidation zone, high concentration of complexing agent and low concentration of oxidant preferentially stabilize Fe²⁺, delaying its oxidation rate; subsequently, the oxidation environment is progressively improved and the complexation strength is reduced, so that the dissociation oxidation of Fe²⁺ and the oxidation precipitation of Mn²⁺ are matched in time and space. Example data show that the precursor Mn / Fe atomic ratio deviation prepared by this invention is only ±1.5% to ±2.5%, far superior to the ±6.3% to ±7.8% of the comparative example, ensuring uniform elemental distribution at the microscale.

[0031] A spherical precursor with high tap density and dense structure was obtained, which significantly improved the volumetric energy density of the material. By progressively controlling the pH value and oxidant concentration, this invention effectively controls the formation and growth rate of crystal nuclei, avoiding explosive nucleation or agglomeration caused by excessive local supersaturation. Combined with the Ostwald ripening mechanism and seed crystal circulation loop in the third oxidation region, it promotes the close packing of primary particles, forming regular spherical secondary particles. Test results show that the precursor obtained by this invention is free of impurities (such as Fe2O3 or MnO2), has uniform primary particle size (180-250 nm), and a tap density of 2.02 to 2.21 g / cm³, which is more than 20% higher than the prior art (approximately 1.7 g / cm³), providing a high-quality basic material for the design of high-energy-density batteries.

[0032] Significantly improved the high-rate charge-discharge performance and cycle stability of the cathode material Thanks to the highly uniform elemental distribution and dense crystal structure of the precursor, the cathode material prepared by sintering has a more complete crystal lattice structure and more unobstructed lithium-ion transport channels, effectively reducing polarization impedance at high rates. Electrochemical test results show that the material prepared by this invention can achieve a capacity retention of 82.0% to 85.4% at 10C ultra-high rates, while the comparative ratio using traditional methods is only 44.8% to 52.7%, solving the industry pain point of severe capacity decay of traditional manganese-rich iron-based materials at high current densities.

[0033] High process control precision, good production stability, suitable for industrial continuous production This invention employs a continuous flow reaction system, with each oxidation zone equipped with an independent online monitoring and feedback control system for pH and ORP. An incremental PID algorithm is used to adjust the flow rates of the alkali solution and oxidant in real time, controlling pH fluctuations within ±0.1 and ORP within the set range. This segmented independent control strategy significantly broadens the process operating window and eliminates batch-to-batch instability. Examples show that under different raw material ratios and process parameters, product performance fluctuations are minimal, demonstrating excellent process robustness. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the continuous flow reaction system in an embodiment of the present invention; Figure 2 This is a process flow diagram of the connected flow reactor system in an embodiment of the present invention; Figure 3 This is a process flow diagram of the continuous oxidative complexation precipitation reaction preparation method in an embodiment of the present invention; In the diagram: 1-Continuous flow reactor; 1a-First oxidation zone; 1b-Second oxidation zone; 1c-Third oxidation zone; 2-Mixed metal salt solution storage tank; 3-Alkali solution storage tank; 4-Oxidizing agent solution storage tank; 5-Complexing agent solution storage tank; 6-Metering pump set; 7-Static mixer; 8-pH / ORP online monitoring unit; 9-Jacket temperature control system; 10-Seed crystal circulation loop; 11-Post-processing unit. Detailed Implementation

[0035] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0036] In the description of this specification, the references to terms such as "an embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an implementation or example is included in at least one implementation or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] like Figure 1 and Figure 2As shown, the continuous flow reaction system used in this application includes a continuous flow reactor 1, a mixed metal salt solution storage tank 2, an alkali solution storage tank 3, an oxidant solution storage tank 4, a complexing agent solution storage tank 5, a metering pump set 6, a static mixer 7, a pH / ORP online monitoring unit 8, a jacket temperature control system 9, a seed crystal circulation loop 10, and a post-processing unit 11. The continuous flow reactor 1 is divided into three oxidation zones: a first oxidation zone 1a, a second oxidation zone 1b, and a third oxidation zone 1c, along the material flow direction. These zones are connected by a static mixer 7. Each storage tank 2 to 5 is connected to a metering pump group 6 via an independent pipeline, and then flows into the corresponding inlet of the continuous flow reactor 1. A pH / ORP online monitoring unit 8 is installed inside each oxidation zone, providing real-time feedback signals to the control system to adjust the injection volume of alkali and oxidant. A jacketed temperature control system 9 surrounds the entire continuous flow reactor 1 and maintains the reaction temperature through circulating heat transfer oil. A seed crystal circulation loop 10 draws out a portion of the slurry from the outlet of the third oxidation zone 1c, which is then screened and returned to the inlet of the first oxidation zone 1a. The post-processing unit 11 includes a centrifuge, a washing tank, and a drying box, used to complete the solid-liquid separation, washing, and drying processes.

[0038] In a first aspect, this application provides a method for preparing high-rate precursors via a continuous oxidative complexation precipitation reaction, comprising the following steps: S10: A mixed metal salt solution containing Mn²⁺ and Fe²⁺, an alkaline solution, an oxidant solution, and a complexing agent solution are fed into a continuous flow reactor 1 via independent metering pumps. The interior of the continuous flow reactor 1 is divided into at least three oxidation-precipitation reaction zones in series along the material flow direction, namely the first oxidation zone 1a, the second oxidation zone 1b, and the third oxidation zone 1c. The oxidation zones of the continuous flow reactor are connected by a one-way overflow weir, an interstage isolation valve, or a high-resistance microchannel to suppress material backmixing and ensure that the pH gradient of each zone is independently controllable. S20: In the first oxidation zone 1a, the instantaneous oxidant concentration of the mixed slurry in the first oxidation zone is controlled to be 0.05 to 0.2 mol / L. The calculation formula is: Cmixed = (Coriginal × Qoxidant) / ∑Qtotal. The pH value is maintained at 8.0 to 9.0. At the same time, a first gradient complexing agent solution accounting for 30% to 50% of the total complexing agent is injected, so that Fe²⁺ preferentially forms a partial complex with the complexing agent, which slows down its oxidation rate, while Mn²⁺ remains unoxidized in this stage. S30: After the material enters the second oxidation zone 1b, the oxidant concentration is increased to 0.2 to 0.5 mol / L, the pH value is adjusted to 9.0 to 10.0, and a second gradient complexing agent solution accounting for 20% to 40% of the total complexing agent is injected to promote the gradual dissociation of Fe²⁺ complex and complete the oxidation to Fe³⁺, while starting the initial oxidation process of Mn²⁺. S40: After the material enters the third oxidation zone 1c, the concentration of oxidant is further increased to 0.5 to 1.0 mol / L, the pH value is maintained at 10.0 to 11.0, and the remaining 10% to 30% of the third gradient complexing agent solution is injected. The sum of the three is 100%, so that Mn²⁺ and Fe³⁺ are oxidized simultaneously and co-precipitated as hydroxides or hydroxy oxides, forming spherical precursor particles with uniform composition. S50: The slurry from the outlet of the third oxidation zone 1c is subjected to solid-liquid separation, washing, and drying to obtain a high-ratio performance precursor.

[0039] In some embodiments, the continuous flow reactor 1 is any one of a tubular reactor, a multi-stage stirred tank reactor in series, or a microchannel reactor. When a multi-stage stirred tank reactor in series is used, the first oxidation zone 1a, the second oxidation zone 1b, and the third oxidation zone 1c are each equipped with an independent stirring paddle, with rotation speeds controlled at 200 to 400 rpm, 300 to 500 rpm, and 400 to 600 rpm, respectively, to ensure uniform mass transfer within each zone; a static mixer 7 is provided between each oxidation zone, which is filled with spiral or cross-shaped mixing elements with a length of 10 to 30 cm to ensure thorough mixing of materials during transition between zones.

[0040] In some embodiments, the molar ratio of Mn²⁺ to Fe²⁺ in the mixed metal salt solution is 1:1 to 4:1, the total metal ion concentration is 1.0 to 2.5 mol / L, the solvent is deionized water, and the metal salt is selected from at least one combination of manganese sulfate and ferrous sulfate, manganese chloride and ferrous chloride, and manganese nitrate and ferrous nitrate. For example, a mixed sulfate solution with Mn²⁺:Fe²⁺ = 3:1 and a total concentration of 2.0 mol / L can be prepared, placed in storage tank 2, and pumped to the inlet of the first oxidation zone 1a at a flow rate of 100 mL / min using a metering pump.

[0041] In some embodiments, the alkaline solution is at least one of sodium hydroxide, potassium hydroxide, or ammonia water, with a concentration of 2.0 to 6.0 mol / L. The alkaline solution is stored in storage tank 3 and injected into the three oxidation zones at set flow rates via metering pumps to maintain the target pH value in each zone. For example, in the first oxidation zone 1a, the alkaline solution injection flow rate is 80 mL / min; in the second oxidation zone 1b, it is 100 mL / min; and in the third oxidation zone 1c, it is 120 mL / min. The specific flow rates are dynamically adjusted based on feedback signals from the online pH monitoring unit 8.

[0042] In some embodiments, the oxidant solution is at least one of hydrogen peroxide, air, oxygen, or sodium hypochlorite. When using 30% hydrogen peroxide, it is stored in tank 4 and injected into the three oxidation zones via metering pumps at flow rates of 10 mL / min, 25 mL / min, and 40 mL / min, corresponding to oxidant concentrations of 0.15 mol / L, 0.35 mol / L, and 0.8 mol / L, respectively. When using a gaseous oxidant (such as oxygen), it is introduced from the bottom of each oxidation zone through a bubbling plate at a flow rate of 0.1 to 1.0 L / min, preferably 0.5 L / min, and is accompanied by stirring to enhance gas-liquid contact.

[0043] In some embodiments, the complexing agent is at least one selected from ammonia, ethylenediaminetetraacetic acid (EDTA), sodium citrate, potassium sodium tartrate, or polyacrylic acid, with a total complexing agent to total metal ion molar ratio of 0.8:1 to 1.5:1, and a complexing agent solution concentration of 0.5 to 2.0 mol / L. For example, a 1.0 mol / L sodium citrate solution is used as the complexing agent, with the total amount calculated based on a total metal ion molar ratio of 1.2:1, wherein the first gradient injection amount is 40% of the total, the second gradient is 30%, and the third gradient is 30%. In some embodiments, the residence time in the first oxidation zone 1a is 10 to 30 minutes, the residence time in the second oxidation zone 1b is 15 to 40 minutes, and the residence time in the third oxidation zone 1c is 20 to 50 minutes. The residence time of each zone is controlled by adjusting the reactor volume and the total feed flow rate. For example, when the total feed flow rate is 200 mL / min, the effective volume of the first oxidation zone 1a is set to 4 L, the second oxidation zone 1b to 6 L, and the third oxidation zone 1c to 8 L, with corresponding residence times of 20 min, 30 min, and 40 min, respectively.

[0044] In some embodiments, the first oxidation zone 1a, the second oxidation zone 1b, and the third oxidation zone 1c are each equipped with an independent online pH monitoring and feedback control system. The control system employs an incremental PID algorithm, setting the proportional coefficient Kp to 1.2, the integral time Ti to 45s, and the derivative time Td to 10s. When a pH deviation of 0.05 is detected, the PLC calculates and outputs a pulse signal to control the stepper motor of the alkali metering pump to change its speed and adjust the instantaneous flow rate of the alkali solution. The pH sensor is installed 50% downstream of the inlet of each zone.

[0045] In some embodiments, the first oxidation zone 1a, the second oxidation zone 1b, and the third oxidation zone 1c are each equipped with an online oxidation-reduction potential (ORP) monitoring device, with the ORP values ​​controlled at +200 to +350 mV, +350 to +500 mV, and +500 to +700 mV, respectively. The target oxidation intensity is maintained by adjusting the oxidant flow rate. An ORP-oxidant flow rate PID control model is established, with the ORP value as the controlled variable. When the ORP deviation is greater than 5 mV, the oxidant metering pump frequency is automatically adjusted by the control system in steps of 0.1-0.5 mL / min. For example, when the ORP value in the first oxidation zone 1a is below +250 mV, the hydrogen peroxide injection rate is automatically increased by 5%.

[0046] In some embodiments, the first gradient complexing agent solution is injected 10% to 30% downstream of the inlet of the first oxidation zone 1a, the second gradient complexing agent solution is injected 20% to 40% downstream of the inlet of the second oxidation zone 1b, and the third gradient complexing agent solution is injected 30% to 50% downstream of the inlet of the third oxidation zone 1c. Tubular reactors use length ratios; stirred tanks use liquid level ratios or radial distances. The injection points are connected to the reactor inner wall via tee fittings to ensure that the complexing agent forms a spatial gradient distribution within the region.

[0047] In some embodiments, the inner wall of the continuous flow reactor 1 is coated with an alkali-resistant and oxidation-resistant ceramic coating or a polytetrafluoroethylene coating, with a coating thickness of 50 to 200 μm, to prevent Fe²⁺ and Mn²⁺ from being adsorbed on the reactor wall or from undergoing side reactions that could lead to component segregation.

[0048] In some embodiments, in step S50, solid-liquid separation is performed by centrifugation or pressure filtration, with a centrifuge speed of 3000 to 5000 rpm and a centrifugation time of 10 to 20 minutes; washing is performed by multiple countercurrent washings with deionized water, with each washing water volume being 2 to 3 times the volume of the filter cake, and the number of washings being 3 to 5 times, until the conductivity of the filtrate is lower than 50 μS / cm; drying is carried out in a vacuum drying oven at a temperature of 80 to 120°C for 4 to 12 hours, with a vacuum degree of -0.08 to -0.1 MPa.

[0049] In some embodiments, the method is suitable for preparing precursors for lithium-ion battery cathode materials, including but not limited to hydroxide or hydroxyl oxide precursors of nickel-manganese-iron (Ni-Mn-Fe), cobalt-manganese-iron (Co-Mn-Fe), or nickel-cobalt-manganese-iron (Ni-Co-Mn-Fe) systems. When preparing Ni0.5Mn1.2Fe0.3(OH) x When preparing the precursor, nickel sulfate can be added to the mixed metal salt solution to make Ni²⁺:Mn²⁺:Fe²⁺ = 0.5:1.2:0.3.

[0050] In some embodiments, in the first oxidation zone 1a, the complex formed by Fe²⁺ and the complexing agent is a [Fe(L)_n]²⁺ type complex, where L is the complexing agent ligand and n is 1 to 4. For example, when EDTA is used, [Fe(EDTA)]²⁻ is formed (actually an anion, but coexists with a cation at high pH), whose stability constant logK ≥ 6 at pH 8.0 to 9.0, effectively suppressing the spontaneous oxidation of Fe²⁺ to Fe³⁺.

[0051] In some embodiments, in the second oxidation zone 1b, as the pH increases to 9.0 to 10.0, the [Fe(L)_n]²⁺ complex undergoes partial hydrolysis, releasing free Fe²⁺. Simultaneously, the oxidant oxidizes it to Fe³⁺, which immediately combines with OH⁻ to form FeOOH crystal nuclei, serving as nucleation centers for subsequent co-precipitation. This process is achieved by controlling the ORP at approximately +400 mV.

[0052] In some embodiments, in the third oxidation zone 1c, Mn²⁺ is oxidized to Mn³⁺ or Mn at a pH of 10.0 to 11.0 and a high oxidant concentration. 4 ⁺, and undergo heterogeneous nucleation with the FeOOH crystal nuclei to form a Mn-Fe-O-OH composite phase, which grows into dense spherical particles through the Ostwald ripening mechanism. The ripening time is ensured by the residence time in the third oxidation zone 1c.

[0053] In some embodiments, the total feed flow rate of the continuous flow reactor 1 is 50 to 500 mL / min, and the flow rate ratio of each solution is precisely controlled by a mass flow meter. The volume ratio of the metal salt solution, alkali solution, oxidant solution, and complexing agent solution is 1:0.8 to 1.5:0.1 to 0.5:0.05 to 0.3. For example, the flow rate is 100 mL / min for the metal salt solution, 120 mL / min for the alkali solution, 30 mL / min for the oxidant solution, and 20 mL / min for the complexing agent solution, resulting in a total volumetric flow rate of 270 mL / min.

[0054] In some embodiments, the method further includes setting a seed crystal circulation loop 10 at the outlet of the third oxidation zone 1c. The seed crystal circulation loop 10 includes an online vibrating screen and an intermediate storage tank. The slurry is continuously filtered through a 200-mesh stainless steel screen. The undersize material (particle size less than 75 μm) enters the intermediate storage tank and is pumped back by a peristaltic pump, while the oversize material is returned to the main reactor through the slag discharge port. An ultrasonic transducer with a working frequency of 40 kHz is installed below the screen. After screening through a screen of 325 mesh or larger (pore size ≤ 45 μm), a portion of the slurry is returned to the inlet of the first oxidation zone 1a by a peristaltic pump at a circulation ratio of 5% to 20%. The circulation ratio refers to the ratio of the return flow rate to the total discharge flow rate. This measure can control the particle size distribution, keeping D50 between 8 and 15 μm, and the particle size distribution span (Span = (D90 - D10) / D50) less than 1.0.

[0055] In some embodiments, the gradient injection of the complexing agent solution is achieved using a multi-channel peristaltic pump, with each channel independently programmed and the injection flow rate decreasing in a stepwise or linear manner as the reaction progresses. For example, the first gradient injection flow rate is constant at 8 mL / min, the second gradient at 6 mL / min, and the third gradient at 4 mL / min, ensuring that the complexation strength matches the oxidation process.

[0056] In some embodiments, each oxidation zone of the continuous flow reactor 1 is equipped with a jacketed temperature control system 9, maintaining the reaction temperature between 40 and 70°C, with temperature fluctuations not exceeding ±1°C. The heat transfer oil circulation temperature is set to 60°C, and the heating power is adjusted by a PID controller to ensure the kinetic consistency of the oxidation and precipitation reactions.

[0057] Secondly, this application provides a high-rate precursor, which is prepared according to the method described in any embodiment of the first aspect.

[0058] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0059] Example 1 Prepare 20 L of a sulfate mixed solution with a total concentration of 2.0 mol / L and a ratio of Mn²⁺:Fe²⁺ = 3:1, and place it in storage tank 2; Prepare a 4.0 mol / L sodium hydroxide solution and place it in storage tank 3; Prepare 10% hydrogen peroxide (approximately 2.94 mol / L) and place it in storage tank 4; Prepare a 1.0 mol / L sodium citrate solution and place it in storage tank 5.

[0060] Start the continuous flow reaction system and set the total feed flow rate to 200 mL / min, including 100 mL / min for metal salt solution, 100 mL / min for alkali solution, 20 mL / min for hydrogen peroxide, and 20 mL / min for complexing agent.

[0061] In the first oxidation zone 1a, the pH was controlled at 8.5±0.1, ORP was +300 mV, the residence time was 20 min, and 40% of the total complexing agent was injected (8 mL / min). In the second oxidation zone 1b, the pH was controlled at 9.5±0.1, ORP was +450 mV, the residence time was 30 min, and 30% complexing agent was injected (6 mL / min). In the third oxidation zone 1c, the pH was controlled at 10.5±0.1, ORP was +600 mV, the residence time was 40 min, and 30% complexing agent (6 mL / min) was injected.

[0062] The reaction temperature is 60±1℃. The seed crystal circulation loop 10 is activated, with a circulation ratio of 10%.

[0063] The slurry was centrifuged (4000 rpm, 15 min), washed four times countercurrently with deionized water (conductivity <50 μS / cm), and dried at 100℃ for 8 h to obtain spherical precursors.

[0064] Example 2 Except for replacing the complexing agent with a 0.8 mol / L EDTA solution, the total complexing agent / metal ion molar ratio with 1.0:1, and the gradient injection ratio with 50%:30%:20%, the other conditions were the same as in Example 1.

[0065] Example 3: Except that the oxidant was replaced with oxygen (0.5 L / min bubbled into the bottom of each oxidation zone), the alkali solution was replaced with 5.0 mol / L ammonia water, and no seed crystal circulation was used, the other conditions were the same as in Example 1.

[0066] Example 4: Except for Mn²⁺:Fe²⁺ = 1:1, total metal concentration of 1.5 mol / L, complexing agent of 1.2 mol / L potassium sodium tartrate, gradient injection ratio of 30%:40%:30%, and circulation ratio of 15%, the other conditions were the same as in Example 1.

[0067] Comparative Example 1 used a single-stage reactor, adding all the oxidant (final concentration 0.8 mol / L), alkali solution (pH 10.5), and complexing agent (total ratio 1.2:1) at once, with other conditions the same as in Example 1.

[0068] Comparative Example 2 employed a two-stage reaction: the first stage was at pH 8.5 with an oxidant of 0.1 mol / L, and the second stage was at pH 10.5 with an oxidant of 0.8 mol / L. Gradient injection without complexing agent was used, and the remaining conditions were the same as in Example 1.

[0069] The precursors obtained from the above embodiments and comparative examples were tested, and the results are shown in the table below. sample D50 (μm) Tap density (g / cm³) Mn / Fe atomic ratio deviation (%) XRD impurity peaks Primary particle size (nm) Example 1 12.3 2.15 ±1.8 none 220 Example 2 11.7 2.08 ±2.1 none 200 Example 3 10.5 2.02 ±2.5 none 180 Example 4 13.1 2.21 ±1.5 none 250 Comparative Example 1 9.2 1.75 ±6.3 <![CDATA[There is Fe2O3]]> 150 (uneven) Comparative Example 2 8.7 1.68 ±7.8 <![CDATA[There is MnO2]]> 120 (Reunion)

[0070] The detection data of the precursors obtained in Examples 1-4 and Comparative Examples 1-2 were analyzed: 1. Regarding compositional uniformity: The Mn / Fe atomic ratio deviation in Examples 1 to 4 was only ±1.5% to ±2.5%, far superior to ±6.3% to ±7.8% in Comparative Examples 1 to 2. This significant difference demonstrates that the tertiary oxidation zone and gradient complexing agent injection strategy can effectively solve the problem of asynchronous Mn²⁺ / Fe²⁺ oxidation, ensuring that the two metal ions are uniformly distributed during precipitation and avoiding compositional segregation caused by differences in oxidation rates in traditional single-stage or two-stage reactions.

[0071] 2. Regarding structural compactness: The tap density of Examples 1-4 reached 2.02 to 2.21 g / cm³, significantly higher than the 1.68 to 1.75 g / cm³ of Comparative Examples 1-2. This indicates that the precursor particles prepared by the method of this invention have a more compact structure and a more ordered arrangement of primary particles. This structural characteristic is beneficial to improving the volumetric energy density and electronic conductivity of the cathode material, and is an important basis for achieving high-rate performance.

[0072] 3. Regarding phase purity: XRD results showed that no impurity phase peaks were observed in Examples 1 to 4, while Fe2O3 impurity phase appeared in Comparative Example 1 and MnO2 impurity phase appeared in Comparative Example 2. This confirms that the present invention effectively avoids the premature oxidation of Fe²⁺ to Fe³⁺ to form Fe2O3 and the excessive oxidation of Mn²⁺ to MnO2 in the intermediate stage by controlling the redox potential (ORP) in a stepwise manner, thus ensuring the uniformity and purity of the precursor phase.

[0073] 4. Regarding particle morphology: The primary particle sizes of Examples 1-4 were 180 to 250 nm and uniformly distributed, while Comparative Examples 1-2 showed "inhomogeneity" or "agglomeration". Combining the D50 data (0.5 to 13.1 μm in Examples 1 and 8.7 to 9.2 μm in Comparative Examples) and the difference in tap density, it can be inferred that the method of the present invention promotes the regular growth of spherical particles, with primary particles arranged in an orderly manner on the surface of secondary spheres rather than agglomerated randomly. This is consistent with the "Ostwald ripening mechanism" and is a key morphological feature for obtaining high-rate performance precursors.

[0074] 5. In terms of process robustness: Examples 1 to 4 maintained excellent performance under changes in parameters such as complexing agent type (pH adjuster), Mn / Fe ratio, and cycle ratio, indicating that the method of the present invention has a wide process window and good adaptability, which can meet the preparation requirements of precursors with different compositions and provide technical support for industrial applications.

[0075] In summary, the effectiveness of the method for preparing high-rate precursors through continuous oxidative complexation precipitation reaction demonstrated by this invention, with its significant advantages in terms of compositional uniformity, structural compactness, phase purity, and morphological regularity, provides a reliable technical path for the preparation of high-performance lithium-ion battery cathode materials.

[0076] To further verify the actual electrochemical performance of the precursors prepared in this invention in lithium-ion batteries, especially their high-rate charge-discharge performance, the precursors obtained in Examples 1-4 and Comparative Examples 1-2 were respectively prepared as cathode materials and assembled into coin cells for testing.

[0077] 1. Cathode material preparation and battery assembly The dried precursor powders obtained in the above embodiments and comparative examples were mixed uniformly with lithium carbonate (Li2CO3) at a molar ratio of Li:(Ni+Mn+Fe)=1.05:1. The mixture was sintered at 850℃ for 12 hours in an oxygen-containing atmosphere. After natural cooling, the powder was pulverized and sieved to obtain the positive electrode material powder. The positive electrode material, conductive agent (acetylene black), and binder (PVDF) were mixed at a mass ratio of 8:1:1, and NMP solvent was added to prepare a slurry. This slurry was coated onto aluminum foil and then vacuum dried, rolled, and stamped to form the positive electrode sheet. Using lithium metal sheet as the negative electrode, 1.0 mol / L LiPF6 / EC+DEC+EMC (volume ratio 1:1:1) as the electrolyte, and Celgard 2400 as the separator, a CR2032 type coin cell was assembled in an argon-filled glove box.

[0078] 2. Electrochemical rate performance testing Charge-discharge tests were conducted at 25°C within a voltage range of 2.0V–4.6V. Activation was first performed at a 0.1C rate, followed by discharge capacity tests at 0.1C, 1C, 5C, and 10C rates (1C = 180 mA / g). The test results are shown in the table below. sample 0.1C discharge capacity (mAh / g) 1C discharge capacity (mAh / g) 5C discharge capacity (mAh / g) 10C discharge capacity (mAh / g) 10C / 0.1C Capacity Retention Rate (%) Example 1 168.5 162.4 151.2 142.8 84.7% Example 2 165.2 158.7 147.5 138.6 83.9% Example 3 162.8 155.1 143.2 133.5 82.0% Example 4 170.1 164.5 153.8 145.2 85.4% Comparative Example 1 148.6 132.4 105.7 78.3 52.7% Comparative Example 2 145.3 128.9 98.4 65.1 44.8%

[0079] Analyze the data in the table above: 1. Low-rate capacity At a low rate of 0.1C, the discharge capacities of Examples 1-4 (162.8-170.1 mAh / g) were generally higher than those of Comparative Examples 1-2 (145.3-148.6 mAh / g). This is mainly due to the higher tap density and more uniform elemental distribution of the precursor prepared by the method of this invention (as shown in the physical property table above), which results in a more complete crystal structure and more active sites in the sintered cathode material, thereby exhibiting a higher specific capacity.

[0080] 2. High-rate performance Significant rate capability improvement: When the discharge rate was increased to 10C, the capacity retention of Examples 1-4 remained between 82.0% and 85.4%, demonstrating excellent high-current discharge capability. In contrast, Comparative Examples 1 and 2 experienced a precipitous drop in capacity at 10C, with only 78.3 mAh / g and 65.1 mAh / g remaining, respectively, resulting in a retention rate of less than 55%.

[0081] Analysis of the causes: In Comparative Examples 1 and 2, the asynchronous oxidation of Mn²⁺ and Fe²⁺ during the precursor stage led to microscopic component segregation and impurity phases (such as Fe₂O₃) within the cathode material, hindering the rapid transport channels of lithium ions and resulting in severe polarization at high rates. In contrast, this invention (Examples 1-4) constructs a uniform and dense spherical structure and a homogeneous atomic-level mixed state through tertiary oxidation and gradient complexation control. This structure not only shortens the lithium ion diffusion path but also enhances the structural stability of the material under high voltage and high current impacts, thus demonstrating the significant technical advantages of the method of this invention in preparing "high-rate precursors".

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing high-rate precursors via a continuous oxidative complexation precipitation reaction, characterized in that, Includes the following steps: S10: A mixed metal salt solution containing Mn²⁺ and Fe²⁺, an alkaline solution, an oxidant solution, and a complexing agent solution are fed into a continuous flow reactor via independent metering pumps. The interior of the continuous flow reactor is divided into at least three oxidation-precipitation reaction zones in series along the material flow direction, namely the first oxidation zone, the second oxidation zone, and the third oxidation zone. S20: In the first oxidation zone, the instantaneous oxidant concentration of the mixed slurry in the first oxidation zone is controlled to be 0.05 to 0.2 mol / L, the pH value is maintained at 8.0 to 9.0, and a first gradient complexing agent solution accounting for 30% to 50% of the total complexing agent is injected at the same time; S30: After the material enters the second oxidation zone, the oxidant concentration is increased to 0.2 to 0.5 mol / L, the pH value is adjusted to 9.0 to 10.0, and a second gradient complexing agent solution accounting for 20% to 40% of the total complexing agent is injected. S40: After the material enters the third oxidation zone, the oxidant concentration is further increased to 0.5 to 1.0 mol / L, the pH value is maintained at 10.0 to 11.0, and the remaining 10% to 30% of the third gradient complexing agent solution is injected, with the sum of the three ratios being 100%. S50: The slurry from the outlet of the third oxidation zone is subjected to solid-liquid separation, washing, and drying to obtain a high-ratio performance precursor.

2. The method according to claim 1, characterized in that, The continuous flow reactor is any one of a tubular reactor, a multi-stage stirred tank reactor in series, or a microchannel reactor, with a static mixer or dynamic stirring device between each oxidation zone.

3. The method according to claim 1, characterized in that, The molar ratio of Mn²⁺ to Fe²⁺ in the mixed metal salt solution is 1:1 to 4:1, the total metal ion concentration is 1.0 to 2.5 mol / L, and the metal salt is selected from at least one of sulfate, chloride, or nitrate.

4. The method according to claim 1, characterized in that, The alkaline solution is at least one of sodium hydroxide, potassium hydroxide, or ammonia water, with a concentration of 2.0 to 6.0 mol / L.

5. The method according to claim 1, characterized in that, The oxidant solution is at least one of hydrogen peroxide, air, oxygen or sodium hypochlorite, wherein the concentration of hydrogen peroxide is 3% to 30% by mass, and the gaseous oxidant is introduced into the bottom of each oxidation zone by bubbling, with a gas flow rate of 0.1 to 1.0 L / min.

6. The method according to claim 1, characterized in that, The complexing agent is at least one of ammonia, ethylenediaminetetraacetic acid, sodium citrate, potassium sodium tartrate, or polyacrylic acid, and the molar ratio of total complexing agent to total metal ions is 0.8:1 to 1.5:1, and the concentration of the complexing agent solution is 0.5 to 2.0 mol / L.

7. The method according to claim 1, characterized in that, The residence time in the first oxidation zone is 10 to 30 minutes, the residence time in the second oxidation zone is 15 to 40 minutes, and the residence time in the third oxidation zone is 20 to 50 minutes.

8. The method according to claim 1, characterized in that, The first oxidation zone, the second oxidation zone, and the third oxidation zone are each equipped with an independent pH online monitoring and feedback control system, with pH fluctuation range not exceeding ±0.1; and each is equipped with an online oxidation-reduction potential monitoring device, with ORP values ​​controlled at +200 to +350 mV, +350 to +500 mV, and +500 to +700 mV, respectively.

9. The method according to claim 1, characterized in that, The injection site of the first gradient complexing agent solution is located 10% to 30% downstream of the inlet of the first oxidation zone, the injection site of the second gradient complexing agent solution is located 20% to 40% downstream of the inlet of the second oxidation zone, and the injection site of the third gradient complexing agent solution is located 30% to 50% downstream of the inlet of the third oxidation zone.

10. A high-rate precursor, characterized in that, Prepared according to the method according to any one of claims 1 to 9.

Images