Production process and equipment for preparing iron phosphate based on oxygen micro-interface reaction gas oxidation method and iron phosphate

Abstract

The invention relates to the technical field of iron phosphate production, in particular to a production process and equipment for preparing iron phosphate based on an oxygen micro-interface reaction gas oxidation method and iron phosphate. The micro-nano bubble oxygen is used for replacing hydrogen peroxide to serve as an oxidizing agent, so that the production process of iron phosphate is optimized, and the reaction efficiency and the product quality are remarkably improved. The special property of the micro-nano bubble oxygen enables the micro-nano bubble oxygen to effectively improve the mass transfer efficiency and the reaction rate of the oxygen under the conditions of higher temperature and lower concentration, so that the efficient oxidation of ferrous in the raw material and the crystal form control of ferric phosphate are promoted. Oxygen is injected into the reaction liquid and forms superfine bubbles through the micro-nano bubble generator, so that the oxygen solubility and the reaction speed at a gas-liquid phase interface are enhanced. The oxygen generator is used for uniformly distributing bubbles in the whole reaction system by precisely controlling the gas flow and the bubble size, so that the uniformity and efficiency of the reaction are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of ferric phosphate production, and in particular to a production process, equipment and ferric phosphate for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method. Background Art

[0002] As an important inorganic compound, iron phosphate is widely used in energy storage devices such as lithium batteries and is one of the key materials in the battery industry. According to the industry standard (HG / T4701-2021), battery-grade iron phosphate is divided into type I anhydrous iron phosphate (FePO4) and type II dihydrate iron phosphate (FePO4·2H2O). The iron-phosphorus molar ratio must be strictly controlled at 0.95-1.05, and the impurity content (such as Fe2O3) must be less than 300ppm. The traditional production process relies on hydrogen peroxide (H2O2) as an oxidant to convert divalent iron (Fe 2+ ) is oxidized to ferric iron (Fe 3+ ), thereby promoting the precipitation of iron phosphate.

[0003] First, the use of hydrogen peroxide results in a low reaction efficiency. Although the strong oxidizing property of hydrogen peroxide can promote the conversion of divalent iron to trivalent iron, it has poor stability and is easy to decompose. In addition, there are difficulties in controlling the temperature and concentration during the reaction. In conventional processes, the reaction temperature is usually controlled between 50-70°C, but the decomposition of hydrogen peroxide limits the reaction temperature range and reaction time, resulting in a low reaction rate and difficulty in achieving the ideal conversion rate. Especially in large-scale production, the high cost of hydrogen peroxide further increases the economic burden of production.

[0004] Secondly, the use of hydrogen peroxide produces a large amount of byproducts during the reaction, making it difficult to achieve complete conversion, resulting in poor crystal quality of the iron phosphate. The iron phosphate precipitate formed is often amorphous, requiring an additional aging step to improve its crystal form. This process not only increases the complexity of the process, but also brings additional energy consumption and time costs. In addition, the strong corrosiveness and instability of hydrogen peroxide make it a certain environmental safety hazard in the reaction, further affecting the sustainability and environmental friendliness of the production process.

[0005] While some improved ferric phosphate production methods have been developed to reduce the use of hydrogen peroxide, they still rely on traditional oxidants or complex reaction steps, failing to achieve fundamental breakthroughs in terms of reaction efficiency, production costs, and environmental friendliness. Therefore, improving reaction efficiency, reducing costs, and ensuring product quality in the ferric phosphate production process remain pressing challenges.

[0006] This invention aims to address the low reaction efficiency, high cost, and poor product quality issues inherent in traditional ferric phosphate production processes. It proposes a novel ferric phosphate production process that utilizes micro-nanobubble oxygen instead of hydrogen peroxide. By improving oxidation reaction conditions and increasing oxygen utilization efficiency, this process enables efficient oxidation at higher temperatures, improving ferric phosphate conversion and crystal quality, and significantly reducing production costs. Summary of the Invention

[0007] (1) Technical problems solved

[0008] To address the shortcomings of the existing technology, the present invention relates to a production process, equipment, and ferric phosphate for preparing ferric phosphate based on an oxygen microinterface reaction gas oxidation method. The process aims to improve ferric phosphate production efficiency, reduce production costs, and enhance product quality. By using micro-nano bubble oxygen instead of the traditional hydrogen peroxide oxidation agent, combined with efficient reaction conditions and an improved process flow, the present invention effectively addresses the problems of low efficiency, low quality, and high cost associated with existing ferric phosphate production.

[0009] (2) Technical solution

[0010] To achieve the above object, the present invention provides the following technical solution: a production process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0011] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at 30 to 90 ° C, and the reaction solution was formed after pretreatment to remove impurities, and the mixture was injected into the reactor at a molar ratio of ferrous sulfate and ammonium dihydrogen phosphate of 1:1 to 1:2;

[0012] S2. Using oxygen as an oxidant, oxygen is generated by a micro-nano bubble generator or a micro-interface reaction generator to generate ultrafine oxygen bubbles with a particle size of 1 nm to 10 μm. The pump circulates the reaction solution within the reactor and drives the oxygen and the reaction solution through a micro-nano bubble generator or a micro-interface reaction generator into the reactor together for oxidation reaction;

[0013] S3. The pH of the reaction solution was adjusted to 1 to 2.5 using aqueous ammonia;

[0014] S4. During the oxidation reaction, the reaction temperature is controlled to be 30 to 90°C, the oxygen partial pressure is 0.02 MPa to 1 MPa, and the oxidation reaction time is 1 to 6 hours;

[0015] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0016] Furthermore, in step S1, at least one of ammonium monohydrogen phosphate, sodium phosphate or phosphoric acid is used as a phosphorus source, and at least one of ferrous sulfate, ferrous chloride, ferric chloride or ferric nitrate is used as an iron source, and the phosphorus source and the iron source are reacted through a precipitation reaction to generate the ferric phosphate.

[0017] Furthermore, in step S2, oxygen or air is preferentially used for gas oxidation. When the ferrous ion concentration in the reaction solution drops to below 20 g / L, hydrogen peroxide is added for further oxidation according to the oxidation effect. At this time, the amount of hydrogen peroxide added is 1-1.4 times the theoretical stoichiometric molar ratio of the residual ferrous concentration to hydrogen peroxide. Hydrogen peroxide is added alone or simultaneously with oxygen / air microinterface oxidation until the ferrous ions are completely converted into trivalent ferrous ions to generate ferric phosphate.

[0018] Furthermore, in step S2, the oxidant is oxygen or air. When air is used, the oxygen partial pressure is controlled to be 0.02 MPa to 1 MPa by pressurization.

[0019] Furthermore, in step S2, the micro-nano bubble generator generates oxygen ultrafine bubbles through one or a combination of a jet system, a hydrodynamic cavitation system, a static mixer and a pressurized dissolution system; the micro-interface reaction generator can react the gas with the material through a microchannel device, wherein: the jet system adopts a traditional ejector structure or a jet structure of an improved channel, which includes a solution inlet, a solution outlet and a gas inlet, wherein the liquid flow rate to gas flow rate ratio is 1:1 to 20:1; the hydrodynamic cavitation system includes a core component, a cavitator, which is divided into two forms with an air inlet and without an air inlet, and the effect of gas-liquid mixing micro-reaction is achieved by pre-intake of the cavitator or intake of the cavitator.

[0020] Furthermore, in step S2, by controlling the partial pressure of the ultrafine oxygen bubbles to 0.1-1 MPa, the reaction time to 1-6 hours, and the temperature to 30-95° C., the oxidation reaction and the crystal growth are completed synchronously, thereby achieving one-step in-situ crystallization.

[0021] Furthermore, in the step S4, the optimal reaction temperature controlled in the oxidation reaction process is 30°C to 90°C, and the optimal reaction temperature is 50°C to 70°C.

[0022] Furthermore, in the step S4, in the step S4, the oxygen partial pressure controlled during the oxidation reaction process is 0.02 MPa to 1 MPa, and the optimal controlled oxygen partial pressure is 0.02 MPa to 0.6 MPa.

[0023] Furthermore, in step S4, during the oxidation reaction, gradient temperature control is adopted, and oxidation is first carried out at 30-60°C for 1-2 hours to promote the nucleation of amorphous iron phosphate, and then the temperature is raised to 60-100°C and oxidation is continued for 1-4 hours, and oxidation simultaneously drives the crystal transformation.

[0024] Furthermore, the crystal form includes a monoclinic phase (P21 / c), an orthorhombic phase (Pnma) and a mixed phase thereof, the grain size is 20-200 nm, and the grain size distribution deviation is ≤20%.

[0025] Furthermore, in the step S5, the aging treatment is carried out under stirring conditions, the stirring speed is 50 to 400 rpm, and the temperature is controlled at 40°C to 100°C.

[0026] Furthermore, in step S5, the aging treatment time is shortened to less than 1 hour or no further aging is required to obtain a crystallinity greater than 95%.

[0027] Based on the same technical concept, the present invention also provides a production device for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, which is used to implement the above-mentioned production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, and includes the following components:

[0028] a) a batching tank for storing ferrous sulfate and ammonium dihydrogen phosphate solutions of respective prepared concentrations;

[0029] b) a micro-nano bubble or micro-interface reaction generating device for generating ultrafine bubbles with a particle size of 1 nm to 10 μm, enhancing the reaction efficiency at the gas-liquid interface and ensuring uniform distribution of oxygen or air in the reaction liquid;

[0030] d) a reaction tank, used for carrying out oxidation reaction and controlling pH, temperature, oxygen partial pressure and reaction time;

[0031] e) a solid-liquid separation device for sedimentation, filter pressing or centrifugal drying of the crystallized slurry;

[0032] f) an aging tank, used to perform an aging process at 40° C. to 100° C. on the separated iron phosphate;

[0033] g) a heat treatment device for treating ferric phosphate dihydrate at 100° C. to 700° C. to convert it into anhydrous ferric phosphate.

[0034] Furthermore, the micro-nano bubbles or micro-interface reaction generating device generates ultrafine bubbles with a diameter of 1 nm to 10 μm through a jet system, a hydrodynamic cavitation system, a static mixer or a pressurized dissolution system.

[0035] Based on the same technical concept, the present invention also provides a high-purity iron phosphate, which is prepared by the above-mentioned production process for preparing iron phosphate based on the oxygen micro-interface reaction gas oxidation method. The iron phosphate is dihydrate iron phosphate or anhydrous iron phosphate, and its chemical formula is FePO4·2H2O or FePO4, the iron-phosphorus molar ratio is 0.95-1.1, and the iron oxide impurity content is less than 300ppm, which is suitable for lithium-ion battery positive electrode materials.

[0036] Furthermore, the compacted density of the ferric phosphate dihydrate is 1.13-1.59 g / cm 3 .

[0037] Furthermore, the anhydrous ferric phosphate has an initial discharge specific capacity of greater than 150 mAh / g at a rate of 0.1 C, and a capacity retention rate of greater than 95% after 100 cycles, under test conditions of 25° C. and a voltage range of 2.0-4.2 V.

[0038] (3) Beneficial effects

[0039] Compared with the prior art, the present invention provides a production process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method, which has the following beneficial effects:

[0040] 1. By using micro-nano bubble oxygen instead of hydrogen peroxide as an oxidant, this invention optimizes the production process of ferric phosphate and significantly improves reaction efficiency and product quality. The unique properties of micro-nano bubble oxygen enable it to effectively improve oxygen mass transfer efficiency and reaction rate under conditions of higher temperature and lower concentration, thereby promoting the efficient oxidation of ferric phosphate and controlling its crystal form.

[0041] 2. During the oxidation process, oxygen is injected into the reaction solution and formed into ultrafine bubbles by a micro-nano bubble generator, enhancing oxygen solubility and reaction speed at the gas-liquid interface. The oxygen generator precisely controls gas flow and bubble size, evenly distributing bubbles throughout the reaction system and ensuring uniformity and efficiency. Compared to traditional hydrogen peroxide applications, micro-nano bubble oxygen maintains greater stability at the reaction temperature and pressure, making the reaction process more controllable and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a process diagram of Example 1 of the present invention;

[0043] Figure 2 This is a process diagram of Example 2 of the present invention;

[0044] Figure 3 This is a process diagram of Example 2 of the present invention;

[0045] Figure 4 This is a process diagram of Example 3 of the present invention;

[0046] Figure 5 Schematic diagram of the process of Examples 5, 6, and 7 of the present invention;

[0047] Figure 6 This is a process diagram of Example 8 of the present invention. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] The key technical points of the production process of the present invention for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method include the following aspects:

[0050] 1. Batching Process: During this process, ferrous sulfate (FeSO4) and ammonium dihydrogen phosphate (NH4H2PO4) dissolve under specific temperature conditions to form a reaction solution. The molar ratio of ferrous sulfate to ammonium dihydrogen phosphate is 1:1-1:2, ensuring an appropriate ratio of iron to phosphorus, thereby obtaining a stable iron phosphate precipitate. During the batching process, ammonia is used to adjust the pH of the solution, keeping it in the acidic range of 1.0 to 2.5 to ensure a smooth reaction. This batching reaction must be carried out in warm water (30-90°C) to ensure effective dissolution and a smooth reaction.

[0051] 2. Oxidation process: The oxidation process is the core of the present invention. The traditional iron phosphate oxidation process usually uses hydrogen peroxide for oxidation reaction, while the present invention uses micro-nano bubble oxygen instead of hydrogen peroxide, which significantly improves the dissolution efficiency and reaction rate of oxygen. Micro-nano bubble oxygen increases the contact area and mass transfer efficiency between gas and liquid through micro bubbles (size ranging from tens of nanometers to hundreds of nanometers), so that the oxidation reaction can continue at a higher temperature (50-90 ° C) without worrying about the decomposition of oxygen. The addition of micro-nano bubble oxygen can effectively increase the efficiency of divalent iron (Fe 2+ ) to ferric iron (Fe 3+ ) conversion efficiency, and improve the precipitation rate and conversion rate of iron phosphate.

[0052] During the oxidation process, oxygen is injected into the reaction solution and formed into ultrafine bubbles by a micro-nano bubble generator, enhancing oxygen solubility and reaction speed at the gas-liquid interface. The micro-nano bubble generator precisely controls gas flow and bubble size, evenly distributing bubbles throughout the reaction system and ensuring uniformity and efficiency. Compared to traditional hydrogen peroxide applications, micro-nano bubble oxygen maintains greater stability at reaction temperature and pressure, making the reaction process more controllable and efficient.

[0053] The micro-nano bubbles in the jet system generate negative pressure through the contraction and expansion of the flow channel structure, and passively inhale gas. The negative pressure generated when the fluid passes through the narrow flow channel at high speed inhales the gas, and the inhaled gas is completely crushed due to the cavitation effect when the downstream channel widens, forming micro bubbles. The core components of the jet system include an ejector, a liquid inlet and a gas inlet. The hydrodynamic cavitation system includes a core component, a cavitator, which is divided into two forms: one with an air inlet and one without an air inlet. The effect of gas-liquid mixing micro-reaction is achieved by pre-intake of the cavitator or intake of the cavitator. The UltraRUltraR series micro-nano bubble generator used in the present invention ensures that the size of the generated bubbles is at the nanometer level (1-200 nanometers) and the bubbles are evenly distributed through precise flow channel design, control of gas flow and liquid flow rate, and pressure control, thereby significantly improving the contact area of ​​the gas-liquid interface and the oxygen transfer efficiency.

[0054] Characteristics of micro- and nano-bubbles include uniform size, an average bubble size coefficient of variation of less than 5.0%, and the ability to remain stable in liquids for extended periods. These bubbles are generated using a variety of methods, including cyclonic systems, static mixers, and pressurized dissolution systems. For example, a cyclonic system involves high-speed rotation of liquid within a cylinder, reducing pressure near the central axis. This draws in gas and pulverizes it into fine bubbles. The core component of a cyclonic system is the cyclonic cylinder, whose internal design allows centrifugal force to separate the liquid and gas. Gas is concentrated in the center, while liquid is pushed toward the cylinder walls, ultimately pulverizing the gas into fine bubbles through shear forces. The efficiency of a cyclonic system depends on the liquid's rotational speed and the cylinder's geometry. Optimizing the design can significantly improve the uniformity and stability of bubble generation. Static mixers, on the other hand, use complex flow structures to generate vortexes, utilizing viscous shear forces to pulverize the gas. Static mixers typically consist of multiple guide vanes and baffles. These structures generate intense turbulence as the liquid and gas flow through them, breaking large bubbles into finer ones. The flow channel design of the static mixer is the key. Complex flow channels can increase the contact area between liquid and gas, thereby improving the efficiency of bubble generation.

[0055] The pressurized dissolution system uses a pressure pump to suck the liquid in. The gas is sucked into the pipe under negative static pressure and mixed with the liquid. The pressure is eventually restored to normal at the nozzle, prompting the bubble nuclei to form and grow into micro-bubbles. The key components of the pressurized dissolution system include the pressure pump, nozzle and pressure reducing valve. Through the coordinated work of these components, the system can dissolve the gas in the liquid under high pressure and generate a large number of micro-bubbles when the pressure is released. The operating pressure and gas-liquid ratio of the pressurized dissolution system are important factors affecting the bubble generation effect. The appropriate pressure and ratio can ensure that the gas reaches a saturated state in the liquid, thereby generating a large number of uniform micro-bubbles when the pressure is reduced. In addition, the pressurized dissolution system is usually equipped with a residual gas separator or a gas dissolving tank to separate the undissolved gas and ensure the stable operation of the system.

[0056] The stability of micro-nanobubbles is closely related to their surface charge and the liquid environment. The surface of micro-nanobubbles usually carries a negative charge, which helps prevent the bubbles from coalescing and thus maintain their dispersed state. The ionic strength and pH value in the liquid also affect the stability of micro-nanobubbles. An appropriate liquid environment can significantly extend the life of micro-nanobubbles. For example, in solutions with low ionic strength, the stability of micro-nanobubbles is higher, while in solutions with high ionic strength, the electrostatic repulsion between bubbles is weakened, which may lead to bubble coalescence. In addition, surfactants in the liquid can further reduce the gas-liquid interfacial tension, thereby reducing bubble size and improving stability. The concentration of surfactants should be greater than the critical micelle concentration to ensure that they effectively reduce the interfacial tension.

[0057] 3. Optimization of the aging process: During the synthesis of iron phosphate, the iron phosphate precipitate generated after the oxidation reaction is usually amorphous, and the transformation of the crystal structure needs to be achieved through the aging process. In traditional processes, this process relies on long-term heat treatment (usually 12-24 hours, with the temperature maintained at 60-80°C), which is not only time-consuming but also energy-intensive. The present invention achieves directional regulation of the crystal structure during the oxidation stage by optimizing the oxidation process parameters. Specifically, by precisely controlling the oxygen partial pressure (0.02-1MPa), reaction temperature (30-90°C) and reaction time (1-6 hours) in the reaction system, Fe is simultaneously achieved during the oxidation process. 2+ Fe 3+Complete transformation and directional growth of the crystal structure. This in situ crystallization mechanism effectively reduces the content of iron oxide impurities (<0.5wt%) and directly promotes the transformation of the amorphous state to the monoclinic form (Monoclinic, space group P21 / c). X-ray diffraction (XRD) analysis confirmed that the crystallinity of the obtained product reached more than 95%, and the grain size distribution was uniform (50-200nm). Compared with the traditional process, this method shortens the aging time by 60-70%, reduces energy consumption by 40-50%, and significantly improves the electrochemical performance of the product, providing a more economical solution for the large-scale preparation of positive electrode materials for lithium-ion batteries.

[0058] The present invention innovatively realizes the in-situ coupling of oxidation reaction and crystal growth in the preparation process of ferric phosphate by constructing a dynamic synergistic system of oxygen partial pressure, temperature and time. Under the action of the micro-nano bubble generator, the gradient oxygen partial pressure environment of 0.1-1MPa significantly enhances the gas-liquid mass transfer efficiency, making Fe 2+ The oxidation rate is increased by 3-5 times, and the heat released by the oxidation reaction provides energy support for the crystal transformation. By designing a gradient temperature field of 30-95°C, a high-density nanocrystalline nucleus (20-50nm) is induced to form in the low-temperature range (30-60°C), and then the directional growth of grains to 50-200nm is promoted in the high-temperature range (60-100°C), synchronously completing the crystal transformation from the amorphous phase to the monoclinic phase (P21 / c) or orthorhombic phase (Pnma).

[0059] This synergistic mechanism breaks through the process fragmentation problem of traditional technology and integrates the oxidation, aging and other processes that originally needed to be carried out step by step into a single reaction system. Experimental data show that this technology shortens the aging time from 12-24 hours in traditional technology to less than 1 hour, and improves the crystallinity to more than 95% (XRD half-peak width <0.2°), while achieving precise control of the grain size distribution deviation ≤20%. It is particularly noteworthy that by adjusting the combination of 0.5-1MPa oxygen partial pressure and 70-90℃ temperature, a monoclinic phase product (compacted density 1.35-1.59g / cm3) can be prepared in a directionally; while the combination of 0.1-0.5MPa and 60-80℃ is conducive to the formation of an orthorhombic phase structure (1.13-1.40g / cm 3 ), providing adaptation options for different battery systems.

[0060] The optimized design of process parameters is based on in-depth analysis of reaction kinetics: the lower limit of oxygen partial pressure of 0.1MPa ensures that the oxidation rate exceeds the nucleation rate, while the upper limit of 1MPa avoids the attenuation of mass transfer efficiency caused by bubble coalescence; the setting of a temperature gradient of 30-100°C avoids kinetic hysteresis in the low-temperature section and suppresses high-temperature dehydration side reactions. In practical applications, this technology has demonstrated excellent industrial adaptability - only by adding a micro-nano bubble micro-reaction equipment module to the existing reactor can 10,000-ton mass production be achieved, with crystallinity fluctuations of <2% and grain size deviations of <10% between pilot batches, and comprehensive energy consumption reduced by 40-50% compared to traditional processes. The LiFePO4 positive electrode prepared from the resulting iron phosphate material has a discharge capacity of 185mAh / g at a rate of 0.1C, and a capacity retention rate of over 95% after 100 cycles, verifying the dual advantages of this synergistic control system in improving material performance and reducing production costs.

[0061] IV. Byproduct Treatment: Ammonium sulfate is produced as a byproduct during the ferric phosphate production process and can be recycled as fertilizer. Recycling ammonium sulfate not only reduces waste emissions during production but also provides additional economic benefits for the company. Equipment used in the byproduct treatment process (such as filters and coolers) effectively removes impurities from the solution, ensuring the purity of the ferric phosphate product.

[0062] Example 1:

[0063] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0064] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 85 ° C, and the reaction solution was pretreated to form 1.2 mol / L and injected into the reactor;

[0065] S2. Using oxygen bubbles of micro-nano bubble size as an oxidant, oxygen is generated by an UltraR micro-nano bubble generator with a diameter of less than 300 nm, and the oxygen flow rate is 50 L / h. The reaction solution is circulated within the reactor by a metering pump, and the oxygen is injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0066] S3. The pH of the reaction solution was adjusted to 2.0 using aqueous ammonia;

[0067] S4. During the oxidation reaction, the reaction temperature was controlled to 85 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0068] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0069] In the above process, the stirring speed was 250 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.15 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0070] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly monoclinic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 1.8 microns and D90 of 2.5 microns.

[0071] Results: In Example 1, the highly stable oxygen provided by the micro-nano bubbles effectively increased the reaction rate. However, since the conversion rate did not reach 100% when using the micro-nano bubbles alone, the addition of hydrogen peroxide further accelerated the reaction. This synergistic approach reduced the amount of hydrogen peroxide used by approximately 70%, resulting in a corresponding reduction in production costs of approximately RMB 300 per ton.

[0072] Example 2:

[0073] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0074] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 85 ℃, and the reaction solution was pretreated to form 1.0 mol / L and injected into the reactor;

[0075] S2. Using micro-nano bubble-sized oxygen bubbles as an oxidant, oxygen is generated by an UltraR micro-nano bubble generator with a diameter of less than 400 nm, and the oxygen flow rate is 60 L / h. The reaction solution is circulated within the reactor by a metering pump, and the oxygen is injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0076] S3. The pH of the reaction solution was adjusted to 1.8 using aqueous ammonia;

[0077] S4. During the oxidation reaction, the reaction temperature was controlled to 90 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0078] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0079] In the above process, the stirring speed was 200 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.2 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0080] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly monoclinic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 2.2 microns and D90 of 2.8 microns.

[0081] Results: In Example 2, the highly stable oxygen provided by the micro-nano bubbles effectively increased the reaction rate. However, since the conversion rate did not reach 100% when using the micro-nano bubbles alone, the addition of hydrogen peroxide further accelerated the reaction. This synergistic approach reduced hydrogen peroxide usage by approximately 70%, correspondingly reducing the cost per ton of product by approximately RMB 300.

[0082] Example 3:

[0083] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0084] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 90 ℃, and the reaction solution was pretreated to form 1.3 mol / L and injected into the reactor;

[0085] S2 using micro-nano bubble size oxygen bubbles as an oxidant, oxygen generated by the UltraR micro-nano bubble generator diameter is controlled at 350nm or less, the oxygen flow rate is 100L / h, the reaction solution is circulated in the reactor by a metering pump, and the oxygen is injected into the reactor together with the circulating reaction solution pump oxidation reaction;

[0086] S3. The pH of the reaction solution was adjusted to 2.0 using aqueous ammonia;

[0087] S4. During the oxidation reaction, the reaction temperature was controlled to 85 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0088] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0089] In the above process, the stirring speed was 250 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.1 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0090] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly amorphous. SEM observation showed that the particles are regular particles with an average particle size D50 of 0.9 microns and D90 of 1.8 microns.

[0091] Results: In Example 3, by controlling the reaction time, temperature, and oxygen flow rate, the synergistic effect of micro-nano bubbles and hydrogen peroxide further optimized the reaction efficiency, improving the product's crystal stability and purity. The cost per ton of product was reduced by RMB 300, saving on hydrogen peroxide usage.

[0092] Example 4:

[0093] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0094] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 85 ℃, and the reaction solution was pretreated to form 1.0 mol / L and injected into the reactor;

[0095] S2. Using micro-nano bubble-sized oxygen bubbles as an oxidant, oxygen was generated by an UltraR micro-nano bubble generator with a diameter of less than 300 nm, and the oxygen flow rate was 50 L / h. The reaction solution was circulated within the reactor by a metering pump, and the oxygen was injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0096] S3. The pH of the reaction solution was adjusted to 2.0 using aqueous ammonia;

[0097] S4. During the oxidation reaction, the reaction temperature was controlled to 90 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0098] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0099] In the above process, the stirring speed was 250 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.15 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0100] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly monoclinic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 1.8 microns and D90 of 2.4 microns.

[0101] Results Analysis: In Example 4, the highly stable oxygen provided by the micro-nano bubbles effectively increased the reaction rate. However, since the conversion rate did not reach 100% when using the micro-nano bubbles alone, the addition of hydrogen peroxide further accelerated the reaction. This synergistic approach reduced the amount of hydrogen peroxide used by approximately 70%, correspondingly reducing the cost per ton of product by approximately RMB 300.

[0102] Example 5:

[0103] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0104] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 85 ℃, and the reaction solution was pretreated to form 1.0 mol / L and injected into the reactor;

[0105] S2. Using micro-nano bubble-sized oxygen bubbles as an oxidant, oxygen was generated by an UltraR micro-nano bubble generator with a diameter of less than 300 nm, and the oxygen flow rate was 50 L / h. The reaction solution was circulated within the reactor by a metering pump, and the oxygen was injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0106] S3. The pH of the reaction solution was adjusted to 2.0 using aqueous ammonia;

[0107] S4. During the oxidation reaction, the reaction temperature was controlled to 85 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0108] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0109] In the above process, the stirring speed was 250 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.10 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0110] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is orthorhombic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 2.0 μm and D90 of 2.7 μm.

[0111] Results Analysis: In Example 5, the highly stable oxygen provided by the micro-nano bubbles effectively increased the reaction rate. However, since the conversion rate did not reach 100% when using the micro-nano bubbles alone, the addition of hydrogen peroxide further accelerated the reaction. This synergistic approach reduced the amount of hydrogen peroxide used by approximately 70%, correspondingly reducing the cost per ton of product by approximately RMB 300.

[0112] Example 6:

[0113] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0114] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 85 ° C, and the reaction solution was pretreated to form 1.2 mol / L and injected into the reactor;

[0115] S2. Using micro-nano bubble-sized oxygen bubbles as an oxidant, oxygen was generated by an UltraR micro-nano bubble generator with a diameter of less than 400 nm and an oxygen flow rate of 80 L / h. The reaction solution was circulated within the reactor by a metering pump, and the oxygen was injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0116] S3. The pH of the reaction solution was adjusted to 2.2 using aqueous ammonia;

[0117] S4. During the oxidation reaction, the reaction temperature was controlled to 85 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0118] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0119] In the above process, the stirring speed was 250 rpm. After the oxygen with bubbles was injected for 30 minutes, 0.15 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 40 minutes, and the total reaction time was 70 minutes.

[0120] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly monoclinic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 2.1 microns and D90 of 2.8 microns.

[0121] Results Analysis: In Example 6, the highly stable oxygen provided by the micro-nano bubbles effectively increased the reaction rate. However, since the conversion rate did not reach 100% when using the micro-nano bubbles alone, the addition of hydrogen peroxide further accelerated the reaction. This synergistic approach reduced the amount of hydrogen peroxide used by approximately 70%, correspondingly reducing the cost per ton of product by approximately RMB 300.

[0122] Example 7:

[0123] This embodiment provides a production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, comprising the following steps:

[0124] S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at a temperature of 90 ℃, and the reaction solution was pretreated to form 1.1 mol / L and injected into the reactor;

[0125] S2. Using micro-nano bubble-sized oxygen bubbles as an oxidant, oxygen was generated by an UltraR micro-nano bubble generator with a diameter of less than 300 nm, and the oxygen flow rate was 90 L / h. The reaction solution was circulated within the reactor by a metering pump, and the oxygen was injected into the reactor together with the circulating reaction solution within the pump for oxidation reaction;

[0126] S3. The pH of the reaction solution was adjusted to 1.8 using aqueous ammonia;

[0127] S4. During the oxidation reaction, the reaction temperature was controlled to 90 ° C, the oxygen partial pressure was 0.05MPa to 1MPa, and the oxidation reaction time was 70 minutes;

[0128] S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

[0129] In the above process, the stirring speed was 300 rpm. After the oxygen with bubbles was injected for 40 minutes, 0.2 mol / L hydrogen peroxide was added for supplementary oxidation. The oxidation time was continued for 30 minutes, and the total reaction time was 70 minutes.

[0130] Characterization of the iron phosphate product obtained by the above process: XRD analysis confirmed that the iron phosphate crystal form of the final product is mainly monoclinic, with a crystal purity of 99%. SEM observation showed that the particles were regular particles with an average particle size D50 of 2.0 microns and D90 of 2.8 microns.

[0131] Results: In Example 7, by controlling the reaction time, temperature, and oxygen flow rate, the synergistic effect of micro-nano bubbles and hydrogen peroxide further optimized the reaction efficiency, improving the product's crystal stability and purity. The cost per ton of product was reduced by RMB 300, saving on hydrogen peroxide usage.

[0132] Comparative Example 1:

[0133] S1. Dissolve 1.2 mol / L ferrous sulfate solution in hot water at 85°C and adjust the pH to 2.0 with aqueous ammonia.

[0134] S2. The solution was delivered to the reactor by a metering pump. The reactor temperature was maintained at 85°C and the stirring speed was 250 rpm.

[0135] S3. Add 0.3 mol / L hydrogen peroxide for oxidation, and keep the oxidation time for 60 minutes.

[0136] S4. After the reaction is completed, the reaction solution is transferred to an aging tank and aged at 70°C for 12 hours.

[0137] Characterization of the ferric phosphate product obtained through the above process: XRD analysis confirmed that the final product was primarily amorphous ferric phosphate, with an average particle size D50 of 2.0 μm and D90 of 3.0 μm. The iron oxide impurity content was relatively high (approximately 1.5 wt%).

[0138] Analysis: The use of hydrogen peroxide in conventional processes leads to low reaction efficiency and requires a long aging time (12 hours) to improve the crystal structure. Due to incomplete decomposition and reaction of hydrogen peroxide, the iron oxide impurity content is high, affecting the purity and electrochemical performance of the product. The high hydrogen peroxide usage per ton of product increases production costs by approximately RMB 500.

[0139] Comparative Example 2:

[0140] S1. Dissolve 1.2 mol / L ferrous sulfate solution in hot water at 85°C and adjust the pH to 2.0 with aqueous ammonia.

[0141] S2. Ordinary bubble oxygen was added to the solution and delivered to the reactor via a metering pump. The reactor temperature was maintained at 85°C and the stirring speed was 250 rpm.

[0142] S3. Add 0.3 mol / L hydrogen peroxide for oxidation, and keep the oxidation time for 60 minutes.

[0143] S4. After the reaction is completed, the reaction solution is transferred to an aging tank and aged at 70°C for 12 hours.

[0144] Characterization of the ferric phosphate product obtained through the above process: XRD analysis confirmed that the final product was primarily amorphous ferric phosphate, with an average particle size D50 of 2.0 μm and D90 of 3.0 μm. The iron oxide impurity content was relatively high (approximately 1.5 wt%).

[0145] Results Analysis: In the conventional process of the existing technology, the use of hydrogen peroxide results in low reaction efficiency and requires a long aging time (12 hours) to improve the crystal structure. Due to the incomplete decomposition and reaction of hydrogen peroxide, the iron oxide impurity content is high, affecting the purity and electrochemical performance of the product. The mass transfer efficiency of ordinary bubble oxygen is low, resulting in a slow reaction rate. Hydrogen peroxide must still be added to complete the reaction. The amount of hydrogen peroxide used is reduced compared to the traditional process, but it is still higher than the micro-nano bubble process, resulting in an increase in production costs of approximately RMB 400.

[0146] The products obtained in Examples 1 to 7 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0147] Table 1 Performance data comparison:

[0148]

[0149] The following comparative analysis is performed on the embodiment and the comparative example:

[0150] 1. Reaction efficiency and conversion rate:

[0151] In Examples 1 to 7, the use of micro-nano bubble oxygen significantly improved the mass transfer efficiency and reaction rate of oxygen, so that the oxidation reaction was completed in a relatively short time and the conversion rate was close to 100%.

[0152] In Comparative Example 1, the reaction efficiency of the traditional hydrogen peroxide process is low, the conversion rate is insufficient, and a long aging time is required to improve the crystal form.

[0153] In Comparative Example 2, the mass transfer efficiency of ordinary bubble oxygen is low, resulting in a slow reaction rate, and hydrogen peroxide still needs to be added to complete the reaction.

[0154] 2. Product quality:

[0155] In Examples 1 to 7, due to the effect of micro-nano bubble oxygen, the crystallinity of the product reaches above 95%, the impurity content of iron oxide is less than 0.5 wt%, and the particle size distribution is uniform.

[0156] In Comparative Example 1, the product has a low crystallinity (about 85%) and a high iron oxide impurity content (about 1.5 wt %).

[0157] In Comparative Example 2, the crystallinity of the product was improved (about 90%), but the iron oxide impurity content was still relatively high (about 1.0 wt %).

[0158] 3. Production cost:

[0159] In Examples 1 to 7, the use of micro-nano bubble oxygen significantly reduced the amount of hydrogen peroxide used, and the cost per ton of product was reduced by approximately RMB 300.

[0160] In Comparative Example 1, the amount of hydrogen peroxide used was relatively high, resulting in an increase in production cost of approximately RMB 500.

[0161] In Comparative Example 2, the amount of hydrogen peroxide used is reduced compared to the traditional process, but is still higher than the micro-nano bubble process, resulting in an increase in production costs of approximately RMB 400.

[0162] 4. Energy consumption and time:

[0163] In Examples 1 to 7, the use of micro-nano bubble oxygen shortens the reaction time and aging time, and significantly reduces energy consumption.

[0164] In Comparative Example 1, the traditional process requires a long aging time (12 hours) and high energy consumption.

[0165] In Comparative Example 2, the reaction time is longer, and hydrogen peroxide still needs to be added, and the energy consumption is higher than that of the embodiment.

[0166] Example 8:

[0167] This embodiment provides a process for in-situ crystallization of ferric phosphate during the production process of ferric phosphate prepared by an oxygen micro-interface reaction gas oxidation method. The process adopts coordinated regulation of gradient oxygen partial pressure and temperature, and includes the following steps:

[0168] S1. Preparation of reaction materials

[0169] Mix ferrous sulfate (FeSO4) solution and ammonium dihydrogen phosphate (NH4H2PO4) solution in an oxidation tank / reactor at an iron to phosphorus molar ratio of 1:1.02 and stir.

[0170] S2. Oxidation-crystallization coupling reaction

[0171] The reaction material solution is pumped from the reactor to the micro-nano bubble generator system (bubble diameter ≤ 300nm) and then returned to the reactor, and the temperature is gradient controlled by the heating system.

[0172] The first stage (0-40 minutes): the oxygen flow rate is 80m3 / h, the oxygen partial pressure is controlled at 0.2MPa, the temperature is uniformly increased from 30℃ to 50℃, the stirring speed is 250rpm, and the Fe 2+ Rapid oxidation and formation of high-density nanocrystalline cores (grain size of approximately 35±5nm, SEM observation);

[0173] The second stage (40-150 minutes): introduce oxygen at a flow rate of 40m3 / h, and adjust the oxygen partial pressure to 0.6MPa, raise the temperature to 75℃ and keep it constant, use the Ostwald ripening mechanism to make the grains grow directionally to 120±20nm (dynamic light scattering analysis), and at the same time complete the crystal transformation from amorphous phase to monoclinic phase (P21 / c).

[0174] S3. Post-processing optimization

[0175] After the reaction, plate filter pressing was performed directly, eliminating the traditional aging step. After the filter cake was washed, it was dried at 80°C for 2 hours and then calcined at 650°C in an argon atmosphere for 1.5 hours to obtain anhydrous iron phosphate (FePO4).

[0176] Characterization and result analysis:

[0177] Crystal form and purity: XRD spectrum shows that the main peak matches the monoclinic phase P21 / c standard card (PDF#83-0517), there is no impurity peak, crystallinity is 97.2% (Jade software full spectrum fitting), unit cell parameters β = 96.5°, consistent with the characteristics of monoclinic structure;

[0178] Morphology and size distribution: SEM showed that the particles were spherical, with a particle size distribution concentrated between 100-140 nm, D50 = 118 nm (laser particle size analyzer statistics), and a size deviation of ≤15%;

[0179] Electrochemical performance: The LiFePO4 / C cathode material synthesized with this product has an initial discharge capacity of 158 mAh / g at a 0.5C rate and a capacity retention rate of 98.3% after 500 cycles at 1C, which is better than the 93-95% achieved by traditional processes.

[0180] Crystal form regulation mechanism:

[0181] This example achieves monoclinic-dominated crystal form regulation through the synergistic effect of micro-nano bubble oxygen partial pressure and temperature:

[0182] Low temperature section: In the low temperature section (30-60℃), micro-nano bubble oxygen and 0.2MPa oxygen partial pressure are used to quickly oxidize ferrous ions to form high concentration Fe 3+ , inducing an increase in the density of iron phosphate nucleation sites;

[0183] High temperature section: In the low temperature section (60-90℃), by increasing the oxygen partial pressure of micro-nano bubbles to 0.5MPa, the oxidation rate of ferrous iron and oxygen is enhanced at low ferrous iron concentration, so that the grains grow preferentially along the monoclinic phase (001) plane, while suppressing the formation of FePO4·H2O impurity phase (no -OH vibration peak is detected by FT-IR).

[0184] Process advantages:

[0185] In-situ crystallization shortens the total reaction time to 2.5 hours, reducing the overall energy consumption by 64% compared with Example 2;

[0186] Micro-nano bubble and micro-reaction interface generators can produce ultra-fine oxygen bubbles with extremely high dissolved oxygen saturation, thereby creating an oxidizing environment with local high oxygen partial pressure in a normal pressure reactor;

[0187] By adjusting the oxygen partial pressure (0.1-0.2 MPa) and temperature gradient (30-60°C) in the first stage, amorphous ferric phosphate dihydrate or a two-phase mixed structure of amorphous and monoclinic phases can be obtained (XRD quantitative analysis shows that the monoclinic phase accounts for 20-45%).

[0188] By adjusting the oxygen partial pressure (0.2-0.6 MPa) and temperature gradient (60-90°C) in the second stage, amorphous ferric phosphate dihydrate or a two-phase mixed structure of amorphous and monoclinic phases can be obtained (XRD quantitative analysis shows that the monoclinic phase accounts for 70-95%).

[0189] The micro-nano bubble system is compatible with conventional reactors, and the grain size fluctuation of the pilot batch (single reactor 100 tons) is less than 5%, meeting the consistency requirements of power battery positive electrode materials.

[0190] Possible crystal modifications:

[0191] If the temperature of the second stage is adjusted to 85°C and the oxygen partial pressure is maintained at 0.3 MPa, XRD shows that the characteristic peak of the orthorhombic phase (Pnma) is enhanced (2θ=20.5°, 29.7°). At this time, the particle size is reduced to 80±15 nm, and the compaction density is increased to 1.45 g / cm 3 , which is suitable for high-power lithium-ion batteries. This phenomenon is attributed to the fact that low oxygen partial pressure suppresses the long-range ordered growth of the monoclinic phase, while moderate temperature promotes the formation of the orthorhombic metastable phase.

[0192] It should be noted that, if in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, it does not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including a..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements.

[0193] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A production process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method, characterized by: The following steps are involved: S1. The ferrous sulfate and ammonium dihydrogen phosphate were dissolved in warm water at 30 to 90 ° C, and the reaction solution was formed after pretreatment to remove impurities, and the mixture was injected into the reactor at a molar ratio of ferrous sulfate and ammonium dihydrogen phosphate of 1:1 to 1:2; S2. Using oxygen as an oxidant, oxygen is generated by a micro-nano bubble generator or a micro-interface reaction generator to generate ultrafine oxygen bubbles with a particle size of 1 nm to 10 μm. The pump circulates the reaction solution within the reactor and drives the oxygen and the reaction solution through a micro-nano bubble generator or a micro-interface reaction generator into the reactor together for oxidation reaction; S3. The pH of the reaction solution was adjusted to 1 to 2.5 using aqueous ammonia; S4. During the oxidation reaction, the reaction temperature is controlled to be 30 to 90°C, the oxygen partial pressure is 0.02 MPa to 1 MPa, and the oxidation reaction time is 1 to 6 hours; S5. After the oxidation reaction is completed, the crystallized slurry is separated from the solid by precipitation, filter pressing or centrifugal drying, and then aged at 40°C to 100°C for 1 to 6 hours to remove impurities and then separated from the solid again to obtain ferric phosphate dihydrate; the ferric phosphate dihydrate is heat-treated at 100°C to 700°C for 1 to 2 hours to obtain battery-grade anhydrous ferric phosphate.

2. The process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method according to claim 1, characterized in that: In step S1, at least one of ammonium monohydrogen phosphate, sodium phosphate or phosphoric acid is used as a phosphorus source, and at least one of ferrous sulfate, ferrous chloride, ferric chloride or ferric nitrate is used as an iron source, and the phosphorus source and the iron source are reacted through a precipitation reaction to generate the ferric phosphate.

3. The process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method according to claim 1, characterized in that: In step S2, oxygen or air is preferentially used for gas oxidation. When the ferrous ion concentration in the reaction solution drops to below 20 g / L, hydrogen peroxide is added for further oxidation according to the oxidation effect. At this time, the amount of hydrogen peroxide added is 1-1.4 times the theoretical stoichiometric molar ratio of the residual ferrous ion concentration to hydrogen peroxide. Hydrogen peroxide is added alone or simultaneously with oxygen / air microinterface oxidation until the ferrous ions are completely converted into trivalent ferrous ions to generate ferric phosphate.

4. A production process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 1 or 3, characterized in that: In step S2, the oxidant is oxygen or air. When air is used, the oxygen partial pressure is controlled to be 0.02 MPa to 1 MPa by pressurization.

5. The process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method according to claim 1, characterized in that: In step S2, the micro-nano bubble generator generates ultrafine oxygen bubbles through one or a combination of a jet system, a hydrodynamic cavitation system, a static mixer, and a pressurized dissolution system; the micro-interface reaction generator can react the gas with the material in the form of a microchannel device, wherein: The jet system adopts a traditional ejector structure or a jet structure with an improved channel, which includes a solution inlet, a solution outlet and a gas inlet, wherein the ratio of liquid flow to gas flow is 1:1 to 20:1; The hydrodynamic cavitation system includes a core component, a cavitator, which is divided into two types: one with an air inlet and one without an air inlet. The effect of gas-liquid mixing micro-reaction is achieved by pre-intake of the cavitator or intake of the cavitator.

6. A production process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 1 or 5, characterized in that: In step S2, by controlling the partial pressure of the ultrafine oxygen bubbles to 0.1-1 MPa, the reaction time to 1-6 hours, and the temperature to 30-95° C., the oxidation reaction and the crystal growth are completed synchronously, thereby achieving one-step in-situ crystallization.

7. The process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method according to claim 1, characterized in that: In the step S4, the reaction temperature of the oxidation reaction process is controlled to be 30°C to 90°C, and the optimal reaction temperature is controlled to be 50°C to 70°C.

8. The process for preparing ferric phosphate based on oxygen microinterface reaction gas oxidation method according to claim 1, characterized in that: In the step S4, the oxygen partial pressure during the oxidation reaction is controlled to be 0.02 MPa to 1 MPa, and the optimal controlled oxygen partial pressure is 0.02 MPa to 0.6 MPa.

9. The process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 1 or 7, characterized in that: In step S4, during the oxidation reaction, gradient temperature control is adopted, and oxidation is first performed at 30-60°C for 1-2 hours to promote the nucleation of amorphous iron phosphate, and then the temperature is raised to 60-100°C and oxidation is continued for 1-4 hours, and oxidation simultaneously drives the crystal transformation.

10. The process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 9, characterized in that: The crystal forms include monoclinic phase (P21 / c), orthorhombic phase (Pnma) and mixed phases thereof, the grain size is 20-200 nm, and the grain size distribution deviation is ≤20%.

11. The process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 1, characterized in that: In the step S5, the aging treatment is carried out under stirring conditions with a stirring speed of 50 to 400 rpm and a temperature controlled at 40° C. to 100° C.

12. A production process for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 1 or 11, characterized in that: In step S5, the aging treatment time is shortened to less than 1 hour or no further aging is required to obtain a crystallinity greater than 95%.

13. A production device for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method, used for implementing the production process for preparing ferric phosphate based on an oxygen micro-interface reaction gas oxidation method according to any one of claims 1 to 12, characterized in that: Includes the following components: a) a batching tank for storing ferrous sulfate and ammonium dihydrogen phosphate solutions of respective prepared concentrations; b) a micro-nano bubble or micro-interface reaction generating device for generating ultrafine bubbles with a particle size of 1 nm to 10 μm, enhancing the reaction efficiency at the gas-liquid interface and ensuring uniform distribution of oxygen or air in the reaction liquid; d) a reaction tank, used for carrying out oxidation reaction and controlling pH, temperature, oxygen partial pressure and reaction time; e) a solid-liquid separation device for sedimentation, filter pressing or centrifugal drying of the crystallized slurry; f) an aging tank, used to perform an aging process at 40° C. to 100° C. on the separated iron phosphate; g) a heat treatment device for treating ferric phosphate dihydrate at 100° C. to 700° C. to convert it into anhydrous ferric phosphate.

14. The production equipment for preparing ferric phosphate based on oxygen micro-interface reaction gas oxidation method according to claim 13, characterized in that: The micro-nano bubbles or micro-interface reaction generating device generates ultrafine bubbles with a diameter of 1 nm to 10 μm through a jet system, a hydrodynamic cavitation system, a static mixer or a pressurized dissolution system.

15. A high-purity ferric phosphate prepared by the production process for preparing ferric phosphate based on an oxygen microinterface reaction gas oxidation method according to any one of claims 1 to 12, characterized in that: The iron phosphate is dihydrate iron phosphate or anhydrous iron phosphate, with a chemical formula of FePO4·2H2O or FePO4, an iron-phosphorus molar ratio of 0.95-1.1, and an iron oxide impurity content of less than 300ppm, and is suitable for lithium-ion battery positive electrode materials.

16. The high-purity ferric phosphate according to claim 15, characterized in that: The compacted density of the ferric phosphate dihydrate is 1.13-1.59 g / cm 3 .

17. The high-purity ferric phosphate according to claim 15, characterized in that: The anhydrous ferric phosphate has an initial discharge specific capacity of greater than 150 mAh / g at a rate of 0.1 C, and a capacity retention rate of greater than 95% after 100 cycles, with the test conditions being 25° C. and a voltage range of 2.0-4.2 V.

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