Low-cost lithium iron phosphate and preparation method and application thereof

Abstract

The application provides a low-cost lithium iron phosphate and a preparation method and application thereof, and belongs to the field of lithium battery materials, wherein an intermediate is obtained by mixing a ferrous salt solution with a lithium source, a phosphorus source, a reducing agent and a homogeneous precipitant; the intermediate is mixed with a carbon source to obtain a mixed slurry; and the mixed slurry is subjected to spray drying, calcination and crushing treatment to obtain lithium iron phosphate. The intermediate is prepared by directly reacting the ferrous salt solution with the lithium source, the phosphorus source, the reducing agent and the homogeneous precipitant, the synthesis of an expensive iron source precursor and the complicated nanometer grinding process in the traditional process are omitted, the process flow is greatly shortened, and the raw material cost and energy consumption are significantly reduced; in combination with the spray drying and calcination process, the introduction of impurities is effectively avoided, the prepared lithium iron phosphate has the characteristics of low cost, good consistency and excellent electrochemical performance, and effectively promotes the cost reduction and efficiency increase of new energy automobile power batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, specifically to a low-cost lithium iron phosphate, its preparation method, and its applications. Background Technology

[0002] With the accelerated global energy transition and green transportation initiatives, new energy vehicles have become a crucial development direction for the automotive industry. Lithium iron phosphate (LFP), as one of the mainstream cathode materials for power batteries, is widely used in electric vehicles, hybrid vehicles, and energy storage systems due to its advantages such as high safety, long cycle life, environmental friendliness, and relatively low cost. However, as the new energy vehicle market continues to expand, higher demands are being placed on cost control of power batteries. Reducing the manufacturing cost of LFP has become a key factor in enhancing the competitiveness of vehicles and promoting the widespread adoption of new energy vehicles.

[0003] Currently, the main preparation processes for lithium iron phosphate include: 1. Ferrous oxalate route: Using ferrous oxalate, phosphate, and lithium salt as raw materials, it is prepared through alcohol solvent grinding, spraying, and high-temperature calcination. This process requires the additional synthesis of ferrous oxalate and the decomposition of oxalate during calcination, increasing raw material and energy costs; it also requires nano-grinding, further increasing production costs. 2. Iron oxide red route: Using iron oxide red as the iron source, it is mixed with phosphorus and lithium sources, followed by slurrying, nano-grinding, and calcination. This process requires high raw material purity and has complex grinding steps, resulting in relatively high costs. 3. Iron phosphate route: Using iron phosphate and lithium sources as raw materials, it is prepared through mixing, water slurrying, nano-grinding, and calcination. Although this process is relatively mature, it still requires multiple grinding and drying steps, resulting in high energy consumption and significant challenges in overall cost control.

[0004] While the aforementioned processes can produce lithium iron phosphate with acceptable performance, they all involve energy-intensive grinding, drying, and multi-step synthesis processes, resulting in high production costs and making it difficult to meet the urgent demand of the new energy vehicle industry for continuous cost reduction in battery materials. Furthermore, some raw materials used in existing processes, such as ferrous oxalate and iron oxide red, are expensive, and impurities are easily introduced during processing, affecting material consistency and electrochemical performance. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a low-cost lithium iron phosphate, its preparation method and application, aiming to solve the technical problems of long process flow, high energy consumption and high cost of existing lithium iron phosphate preparation process.

[0006] In a first aspect, embodiments of this application provide a low-cost method for preparing lithium iron phosphate, comprising the following steps: The ferrous salt solution was mixed with a lithium source, a phosphorus source, a reducing agent, and a homogeneous precipitant, and the intermediate was obtained by reaction. The intermediate is mixed with a carbon source and slurryed to obtain a mixed slurry; The mixed slurry was spray-dried, calcined, and pulverized to obtain lithium iron phosphate.

[0007] In the technical solution of this application embodiment, the intermediate is prepared by directly reacting ferrous salt solution with lithium source, phosphorus source, reducing agent and homogeneous precipitant. This eliminates the expensive iron source precursor synthesis and complex nano-grinding process in traditional processes, greatly shortening the process flow and significantly reducing raw material costs and energy consumption. Combined with spray drying and calcination processes, the introduction of impurities is effectively avoided. The prepared lithium iron phosphate has the characteristics of low cost, good consistency and excellent electrochemical performance, which strongly promotes cost reduction and efficiency improvement of power batteries for new energy vehicles.

[0008] In some embodiments, the molar ratio of iron in the ferrous salt solution, lithium in the lithium source, and phosphorus in the phosphorus source is 1:(1.03~1.05):(1.03~1.06); and / or, the ferrous salt in the ferrous salt solution is selected from one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the concentration of the ferrous salt solution is 1~2.5 mol / L; and / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate; and / or, the phosphorus source is selected from one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0009] In this embodiment, by precisely controlling the molar ratio of iron, lithium, and phosphorus, the loss of lithium volatilization during high-temperature calcination is effectively compensated, ensuring the accuracy of the product's stoichiometry and the integrity of its crystal structure. The selection of low-cost, readily available ferrous salts, lithium sources, and phosphorus sources helps to reduce production costs while ensuring the uniformity of the reaction system and the efficient utilization of raw materials, ultimately resulting in a stable and cost-competitive lithium iron phosphate material.

[0010] In some embodiments, the homogeneous precipitant is urea; and / or, the amount of the homogeneous precipitant added is 30-50% of the mass of the ferrous salt in the ferrous salt solution.

[0011] In this embodiment, urea is selected as a homogeneous precipitant. Utilizing its controllable hydrolysis under heating conditions, the pH value of the solution can be adjusted uniformly and slowly, thereby achieving synchronous precipitation throughout the entire solution system. This effectively avoids the problems of impurity introduction or uneven particle size caused by excessively high local concentrations in traditional processes, significantly improving the purity and structural consistency of the intermediate. At the same time, controlling the amount of urea within an appropriate range ensures the completeness of the precipitation reaction and the control of raw material costs, which is conducive to further reducing production process costs.

[0012] In some embodiments, the reducing agent is selected from one or more of ascorbic acid, phosphorous acid, and phosphite; and / or, the amount of the reducing agent added is 3 to 10% of the mass of the ferrous salt in the ferrous salt solution.

[0013] In this embodiment, a suitable type of reducing agent can effectively inhibit the oxidation of ferrous ions during the reaction process, which helps the iron source to participate in the reaction in the form of ferrous iron, thereby ensuring the stability of the product structure and electrochemical performance. A suitable amount of reducing agent avoids the generation of ferric iron impurities due to insufficient addition, while also preventing the waste of raw materials and increased costs caused by excessive addition, thus achieving a balance between performance optimization and cost control.

[0014] In some embodiments, the reaction temperature is 110~150°C and the reaction time is 1~3h.

[0015] In this embodiment, by controlling the reaction temperature and time, suitable thermodynamic and kinetic conditions are provided for the complete hydrolysis and precipitation reaction of urea, which effectively promotes the formation and growth of intermediate crystal nuclei, ensures the crystallinity and purity of the intermediate, and improves the preparation efficiency.

[0016] In some embodiments, the carbon source comprises a crude glucose solution that has not been purified and concentrated for crystallization, with a concentration of 100-200 g / L.

[0017] In this embodiment, a crude glucose solution without impurity removal and concentration crystallization is used as the carbon source, eliminating the high-energy-consuming processes such as glucose purification, crystallization and drying in traditional processes, which significantly reduces the cost of carbon source raw materials. At the same time, the appropriate concentration range is conducive to its uniform dispersion and effective coating in the mixed slurry, which reduces production costs while ensuring the integrity and uniformity of the carbon coating layer, thereby improving the conductivity and electrochemical performance of lithium iron phosphate materials.

[0018] In some embodiments, the inlet air temperature of the spray drying is 260~320℃ and the outlet air temperature is 80~95℃; and / or, the D50 particle size of the powder obtained by the spray drying is 5~25μm and the moisture content is less than 0.5%.

[0019] In this embodiment, by optimizing the inlet and outlet air temperatures of the spray dryer, rapid drying and effective granulation of the slurry are achieved, ensuring drying efficiency while avoiding damage to the material structure caused by high temperature. The resulting powder has a suitable D50 particle size and extremely low moisture content, which not only provides good flowability and facilitates subsequent calcination reactions, but also effectively avoids sintering agglomeration and impurity generation caused by excessive moisture, ensuring the consistency and electrochemical stability of the final product.

[0020] In some embodiments, the calcination temperature is 700~800℃, the holding time is 3~6h, and the heating rate is 100~200℃ / h.

[0021] In this embodiment, by setting an appropriate calcination temperature and holding time, sufficient thermodynamic conditions are provided for the full growth and lattice perfection of lithium iron phosphate crystals, which effectively improves the crystallinity and structural stability of the material. At the same time, a reasonable heating rate avoids abnormal grain growth or structural defects caused by uneven heating, ensuring that the material has excellent electrochemical performance and tap density.

[0022] Secondly, embodiments of this application provide a lithium iron phosphate, which is prepared by the low-cost lithium iron phosphate preparation method described in the first aspect; the lithium iron phosphate has a D50 particle size of 0.5~1.5μm and a carbon content of 1.2~1.8wt%.

[0023] In the technical solution of this application embodiment, the lithium iron phosphate is prepared by the above-mentioned low-cost process, and has a suitable D50 particle size and optimized carbon content. The smaller particle size shortens the lithium ion transport path, and the appropriate amount of carbon coating layer significantly improves the electronic conductivity of the material and effectively improves the rate performance. At the same time, the carbon coating layer inhibits grain growth and agglomeration, ensuring the stability of the material structure and cycle life, and achieving an effective balance between low cost and high performance.

[0024] Thirdly, embodiments of this application provide a positive electrode sheet, including the lithium iron phosphate described in the second aspect.

[0025] In this embodiment, the positive electrode contains the aforementioned lithium iron phosphate, thus possessing advantages such as excellent rate performance, high capacity, and long cycle life.

[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0028] Figure 1 A flowchart illustrating a low-cost lithium iron phosphate preparation method provided in this application embodiment; Figure 2This is a SEM image of lithium iron phosphate provided in Example 1 of this application. Detailed Implementation

[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0035] With the rapid development of lithium iron phosphate in the power and energy storage fields, its annual production and sales volume has exceeded 2.4 million tons. The industry competition has also shifted from simple technology competition to comprehensive competition that emphasizes both technology and cost. At present, the mainstream processes mainly include the ferrous oxalate process, the iron oxide red process, and the iron phosphate process. However, these processes generally have the problem of complicated procedures, and all require high-energy-consuming processes such as grinding, dispersion, or slurry nano-sizing. In addition, the ferrous oxalate process also faces the waste of raw materials caused by the decomposition of oxalate, resulting in high production costs for existing technologies.

[0036] To address the technical problems of high cost and cumbersome procedures in existing lithium iron phosphate preparation processes, this application provides a lithium iron phosphate, its preparation method, and its application. By using a crude glucose solution of a specific concentration as a carbon source and optimizing the reaction and drying processes, the technical effects of significantly reducing raw material costs, simplifying the production process, and ensuring the crystallinity and purity of the material are achieved. Consequently, the rate performance, cycle life, and cost advantages of the positive electrode are also improved.

[0037] Please refer to Figure 1 In a first aspect, embodiments of this application provide a low-cost method for preparing lithium iron phosphate, comprising the following steps: S1. A ferrous salt solution is mixed with a lithium source, a phosphorus source, a reducing agent, and a homogeneous precipitant, and the intermediate is obtained by reaction. S2. Mix the intermediate with the carbon source and slurry to obtain a mixed slurry; S3. The mixed slurry is spray-dried, calcined and pulverized to obtain lithium iron phosphate.

[0038] In this application, by adding urea as a homogeneous precipitant to the reaction system to adjust the pH value, precipitation reactions of ferrous ions, lithium ions, and phosphate ions are induced in the liquid phase. This achieves uniform mixing and mutual coating of lithium, iron, and phosphorus at the microscale, eliminating the energy-intensive nano-grinding process in traditional methods. Simultaneously, the anions from the lithium source are used as an alkali source to participate in the reaction, reducing the cost of external alkali. The introduction of a carbon source for slurrying and spray drying achieves uniform carbon coating on the material surface. Calcination and pulverization promote the complete development of lithium iron phosphate crystals and the formation of a highly efficient conductive carbon network. Through the synergistic effect of homogeneous precipitation and carbon coating, this process simplifies the process, reduces costs, and significantly improves the crystallinity, conductivity, and electrochemical performance of the material.

[0039] Further, in some embodiments, the molar ratio of iron in the ferrous salt solution, lithium in the lithium source, and phosphorus in the phosphorus source is 1:(1.03~1.05):(1.03~1.06); and / or, the ferrous salt in the ferrous salt solution is selected from one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the concentration of the ferrous salt solution is 1~2.5 mol / L; and / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate; and / or, the phosphorus source is selected from one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0040] In this application, ferrous salt, lithium source, and phosphorus source are prepared in a specific molar ratio, and the concentration of ferrous salt is controlled to ensure sufficient contact between the components in the reaction system and the balance of stoichiometric coefficients. The appropriate excess of lithium source and phosphorus source not only compensates for losses during the reaction process but also promotes the efficient generation and mutual doping of lithium phosphate and ferrous phosphate during the liquid-phase precipitation process. The in-situ micro-mixing uniformity reaches the scale required for ion diffusion, eliminating the need for the energy-intensive nano-grinding process in traditional methods. At the same time, the optimized raw material combination and suitable concentration window effectively avoid the introduction of impurities, ensuring the precipitation reaction rate and the purity of intermediates, laying the material foundation for the low-cost preparation of high-performance lithium iron phosphate. Specifically, the molar ratio of iron in the ferrous salt solution, lithium in the lithium source, and phosphorus in the phosphorus source can be any value within the range of 1:1.03:1.03, 1:1.04:1.05, 1:1.05:1.06, or 1:(1.03~1.05):(1.03~1.06).

[0041] Furthermore, in some embodiments, the homogeneous precipitant is urea; and / or, the amount of homogeneous precipitant added is 30-50% of the mass of the ferrous salt in the ferrous salt solution.

[0042] In this application, urea was selected as a homogeneous precipitant and its addition amount was strictly controlled. The slow hydrolysis of urea under high temperature and pressure was utilized to promote a uniform and gentle increase in the pH value of the reaction system, avoiding precipitation and agglomeration caused by excessive local concentration. By inducing ferrous ions, lithium ions and phosphate ions to precipitate and dope in the liquid phase, a precursor with uniform particle size distribution and appropriate mixing scale was obtained. This eliminated the need for nano-grinding process and ensured the structural uniformity and electrochemical performance of the material.

[0043] Furthermore, in some embodiments, the reducing agent is selected from one or more of ascorbic acid, phosphorous acid, and phosphite; and / or, the amount of reducing agent added is 3 to 10% of the mass of ferrous salt in the ferrous salt solution.

[0044] In this application, by selecting a suitable reducing agent and controlling its addition amount, a stable reducing atmosphere is constructed in the reaction system by utilizing its strong reducing properties. This effectively inhibits the oxidative hydrolysis of ferrous ions during precipitation and filtration washing, ensuring the high purity and structural stability of the active iron source in the precursor, and avoiding the generation of impurities and performance degradation caused by changes in the valence state of iron ions.

[0045] Furthermore, in some embodiments, the reaction temperature is 110~150°C and the reaction time is 1~3h.

[0046] In this application, a suitable temperature range helps urea to decompose efficiently to adjust the pH value of the system, drive the homogeneous precipitation reaction of ferrous ions, lithium ions and phosphate ions, and ensure that the precursor crystals are complete and the particle size distribution is uniform. A suitable reaction time helps to ensure sufficient growth of solid-phase precipitation and microscopic uniform mixing between elements, so that the precursor can meet the size requirements required for subsequent sintering, thereby ensuring the structural stability and electrochemical performance of the final lithium iron phosphate material without the need for nano-grinding.

[0047] Furthermore, in some embodiments, the carbon source comprises a crude glucose solution that has not been purified and concentrated for crystallization, with a concentration of 100-200 g / L.

[0048] In this application, an unconcentrated and uncrystallized crude glucose solution is selected as the carbon source. Its liquid properties are used to directly slurry the intermediate, replacing the use of pure water or solvents. At the same time, the expensive concentration and crystallization processes in the production of finished glucose products are avoided, significantly reducing the cost of raw materials. The crude glucose solution of appropriate concentration has suitable viscosity and fluidity, which can achieve uniform dispersion and coating of the carbon source on the surface of the precipitate. After spray drying and calcination, a highly efficient conductive carbon network is formed, thereby ensuring the conductivity of the material while reducing costs.

[0049] Furthermore, in some embodiments, the inlet air temperature of the spray dryer is 260~320°C, and the outlet air temperature is 80~95°C; and / or, the D50 particle size of the powder obtained by spray drying is 5~25μm, and the moisture content is less than 0.5%.

[0050] In this application, suitable inlet and outlet air temperatures help ensure that the moisture inside the particles evaporates fully, while ensuring that the carbon source does not undergo excessive oxidation or coking, forming spherical particles with a suitable particle size distribution and good flowability, thereby improving the permeability and reaction uniformity of subsequent calcination processes.

[0051] Furthermore, in some embodiments, the calcination temperature is 700~800℃, the holding time is 3~6h, and the heating rate is 100~200℃ / h.

[0052] In this application, suitable temperature and sufficient holding time ensure the complete conversion of the precursor into lithium iron phosphate with high crystallinity and complete lattice structure, while promoting the pyrolysis of glucose carbon source on the particle surface to form a uniform and dense conductive carbon layer. A reasonable heating rate effectively avoids the reduction in specific surface area caused by excessive grain growth. While ensuring high crystallinity and excellent conductivity of the material, it significantly improves the diffusion rate and electrochemical performance of lithium ions. Specifically, during the calcination process, the furnace pressure is controlled at 5~25 Pa. Air vents are installed in the heating and cooling sections, and exhaust gases generated during calcination are discharged by induced draft fans. Simultaneously, dry inert gases (such as nitrogen, argon, etc.) are introduced to ensure that the humidity in the holding section is ≤0.5%.

[0053] Secondly, this application provides a lithium iron phosphate, which is prepared by the low-cost lithium iron phosphate preparation method described in the first aspect; the lithium iron phosphate has a D50 particle size of 0.5~1.5μm and a carbon content of 1.2~1.8wt%.

[0054] In this application, lithium iron phosphate is prepared by the above-mentioned low-cost process. Its moderate particle size distribution ensures that the material has high compaction density and excellent processing performance. The appropriate carbon content constructs an efficient conductive network, which significantly reduces the contact resistance between particles. Through the optimized combination of morphology and composition, the lithium iron phosphate still has excellent ion diffusion rate and electronic conductivity without the need for nano-grinding, thereby ensuring high capacity and long cycle life.

[0055] Thirdly, embodiments of this application provide a positive electrode sheet, including the lithium iron phosphate described in the second aspect.

[0056] In this application, the positive electrode contains the aforementioned lithium iron phosphate, thus possessing the advantages of excellent rate performance, high capacity, and long cycle life.

[0057] The following are some specific embodiments. It should be noted that 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 shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0058] I. Preparation Method Example 1 This embodiment provides a low-cost method for preparing lithium iron phosphate, including the following steps: S1. After dissolving the ferrous sulfate crystals, a byproduct of titanium dioxide production, iron powder was added and reacted until the pH reached 5.0. The solution was then filtered to obtain a ferrous sulfate solution with a concentration of 1.8 mol / L. Ferrous sulfate solution was mixed with industrial-grade lithium carbonate (purity 99.43%, Ca content 123 ppm, sulfate content 1125 ppm, Na content 769 ppm), monoammonium phosphate, ascorbic acid, and urea, and placed in a high-pressure reactor. The mixture was reacted at 130℃ for 1.5 h. After filtration, the mixture was washed until the sulfate content of the reactants was below 200 ppm to obtain an intermediate. The mass of urea added was 40% of the mass of ferrous sulfate, the mass of ascorbic acid added was 6% of the mass of ferrous sulfate, and the molar ratio of ferrous sulfate to iron, lithium, and phosphorus in lithium carbonate and monoammonium phosphate was 1:1.04:1.05. After the intermediate was dried, samples were taken and tested. The results are shown in Table 1. Table 1 Intermediate detection results S2. Mix the intermediate with the carbon source and slurry to obtain a mixed slurry; the carbon source is a crude glucose solution obtained during the glucose production process without purification and concentration crystallization, with a concentration of 150 g / L. S3. The mixed slurry is spray-dried at an inlet air temperature of 280℃ and an outlet air temperature of 90℃, maintaining the final sprayed material particle size at 18μm and a moisture content below 0.5%. The sprayed material is then calcined at a heating rate of 150℃ / h, reaching 750℃ and holding at this temperature for 4.5h. It is then cooled to a material temperature ≤100℃ before being discharged. The furnace pressure is controlled at 20Pa during calcination. Air inlets are installed in the heating and cooling sections to exhaust the calcination waste gas using a blower. Simultaneously, dry nitrogen is introduced to maintain a humidity level ≤0.5% in the holding section. The calcined material is then pulverized to a particle size of 1.0μm and vacuum-packed in a constant temperature and humidity chamber to obtain lithium iron phosphate. Its SEM image is shown below. Figure 2 As shown, the particles are mainly submicron in size, with a small number of larger particles or agglomerates, but the overall particle size distribution is relatively concentrated. The particle surface exhibits a layered structure, indicating that the glucose carbon source forms a uniform conductive carbon network after calcination.

[0059] The obtained detection data for lithium iron phosphate are shown in Table 2: Table 2. Detection results of lithium iron phosphate Example 2 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the molar ratio of iron, lithium and phosphorus in ferrous sulfate, lithium carbonate and ammonium hydrogen phosphate is 1:1.03:1.03.

[0060] Example 3 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the molar ratio of iron, lithium and phosphorus in ferrous sulfate, lithium carbonate and ammonium hydrogen phosphate is 1:1.05:1.06.

[0061] Example 4 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of urea added is 30% of the mass of ferrous sulfate.

[0062] Example 5 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of urea added is 50% of the mass of ferrous sulfate.

[0063] Example 6 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the concentration of the crude glucose solution is 100 g / L.

[0064] Example 7 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the concentration of the crude glucose solution is 200 g / L.

[0065] Example 8 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of ascorbic acid added is 3% of the mass of ferrous sulfate.

[0066] Example 9 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of ascorbic acid added is 10% of the mass of ferrous sulfate.

[0067] Example 10 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the calcination temperature is 700°C.

[0068] Example 11 This embodiment provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the calcination temperature is 800°C.

[0069] Comparative Example 1 Comparative Example 1 provides a low-cost method for preparing lithium iron phosphate, comprising the following steps: S1. Ferrous sulfate, ammonium dihydrogen phosphate, and hydrogen peroxide were mixed and reacted in a molar ratio of 1:1.1:0.65 to obtain ferric phosphate. After drying, the mixture was calcined at 610℃ for 3 hours to obtain anhydrous ferric phosphate. S2. Anhydrous iron phosphate, lithium carbonate, and glucose (carbon source) were mixed in a molar ratio of 1:1.03:0.11, pure water was added to slurry the mixture, the solid content was controlled at 40%, and the mixture was nano-milled to a particle size D50 of 0.32 μm. After that, it was spray-dried and then calcined at 750℃ for 4.5 h under nitrogen protection to obtain lithium iron phosphate.

[0070] Comparative Example 2 Comparative Example 2 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that urea is not added.

[0071] Comparative Example 3 Comparative Example 3 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of urea added is 60% of the mass of ferrous sulfate.

[0072] Comparative Example 4 Comparative Example 4 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the concentration of the crude glucose solution is 50 g / L.

[0073] Comparative Example 5 Comparative Example 5 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the concentration of the crude glucose solution is 300 g / L.

[0074] Comparative Example 6 Comparative Example 6 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of ascorbic acid added is 1% of the mass of ferrous sulfate.

[0075] Comparative Example 7 Comparative Example 7 provides a low-cost method for preparing lithium iron phosphate. The only difference from Example 1 is that the amount of ascorbic acid added is 15% of the mass of ferrous sulfate.

[0076] II. Testing Methods 1. SEM testing The lithium iron phosphate prepared in Example 1 was examined using a scanning electron microscope; 2. Powder internal resistance The lithium iron phosphate prepared in the examples and comparative examples was detected using the four-probe method; 3. BET test The lithium iron phosphate prepared in the examples and comparative examples was tested using the nitrogen adsorption BET test method. 4. Compacted density test The lithium iron phosphate prepared in the examples and comparative examples was tested using a compaction density tester; 5. Capacity test Lithium iron phosphate was mixed with conductive agent Super-P, binder PVDF and NMP to form a slurry. The slurry was then uniformly coated on aluminum foil to form an electrode sheet. The negative electrode sheet was made of lithium metal. A simulated battery was assembled using 1 mol / L LiPF6 / (EC+DEC) mass ratio (1:1) as the electrolyte and charge-discharge tests were conducted.

[0077] III. Analysis of Test Results for Each Embodiment and Comparative Example The test results of the examples and comparative examples are shown in Table 3.

[0078] Table 3. Performance data of lithium iron phosphate materials As shown in Table 1, the lithium iron phosphate prepared in this application through the synergistic effect of homogeneous precipitation and carbon coating has the characteristics of low cost, good consistency, and excellent electrochemical performance. Compared with the conventional process of Comparative Example 1, this application does not require drying and calcining of iron phosphate, nor grinding. At the same time, this application introduces syrup instead of glucose, which can save more than 2,000 yuan / ton in costs.

[0079] Specifically, based on the data from Examples 1, 4-5 and Comparative Examples 2-3, it can be seen that by controlling the amount of urea added, this application can obtain a lower powder internal resistance and a higher 1C discharge capacity. However, not adding urea or adding excessive urea will lead to an increase in internal resistance and a decrease in capacity. This indicates that an appropriate amount of urea can uniformly adjust the pH value, promote uniform mixing of the precipitate, and avoid local over-concentration or the introduction of impurities.

[0080] Specifically, based on the data from Examples 1, 6-7 and Comparative Examples 4-5, it can be seen that by using a crude glucose solution with a concentration of 100-200 g / L without purification and concentration as a carbon source, this application can reduce the internal resistance of the powder and increase the discharge capacity. However, both excessively low and excessively high carbon source concentrations lead to increased internal resistance and decreased rate performance, indicating that a suitable carbon source concentration is beneficial for forming a uniform and dense conductive carbon network.

[0081] Specifically, based on the data from Examples 1, 8-9 and Comparative Examples 6-7, it can be seen that by controlling the amount of reducing agent added, this application can effectively suppress ferrous oxidation, obtain low powder internal resistance and high discharge capacity and coulombic efficiency. Insufficient or excessive reducing agent will lead to a decrease in capacity and a decrease in coulombic efficiency, indicating that an appropriate amount of reducing agent helps to maintain the stability of the iron valence state and avoid the generation of impurities.

[0082] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A low-cost method for preparing lithium iron phosphate, characterized in that, Includes the following steps: The ferrous salt solution was mixed with a lithium source, a phosphorus source, a reducing agent, and a homogeneous precipitant, and the intermediate was obtained by reaction. The intermediate is mixed with a carbon source and slurryed to obtain a mixed slurry; The mixed slurry was spray-dried, calcined, and pulverized to obtain lithium iron phosphate.

2. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The molar ratio of iron in the ferrous salt solution, lithium in the lithium source, and phosphorus in the phosphorus source is 1:(1.03~1.05):(1.03~1.06); and / or, The ferrous salt in the ferrous salt solution is selected from one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, The concentration of the ferrous salt solution is 1~2.5 mol / L; and / or, The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate; and / or, The phosphorus source is selected from one or more of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

3. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The homogeneous precipitant is urea; and / or, The amount of homogeneous precipitant added is 30-50% of the mass of ferrous salt in the ferrous salt solution.

4. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The reducing agent is selected from one or more of ascorbic acid, phosphorous acid, and phosphites; and / or, The amount of reducing agent added is 3 to 10% of the mass of ferrous salt in the ferrous salt solution.

5. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The reaction temperature is 110~150℃, and the reaction time is 1~3h.

6. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The carbon source includes a crude glucose solution that has not been purified and concentrated for crystallization, with a concentration of 100~200g / L.

7. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The spray dryer has an inlet air temperature of 260~320℃ and an outlet air temperature of 80~95℃; and / or, The powder obtained by spray drying has a D50 particle size of 5~25μm and a moisture content of less than 0.5%.

8. The method for preparing low-cost lithium iron phosphate according to claim 1, characterized in that, The calcination temperature is 700~800℃, the holding time is 3~6h, and the heating rate is 100~200℃ / h.

9. A lithium iron phosphate, characterized in that, The lithium iron phosphate is prepared by the low-cost lithium iron phosphate preparation method according to any one of claims 1-8; the lithium iron phosphate has a D50 particle size of 0.5~1.5μm and a carbon content of 1.2~1.8wt%.

10. A positive electrode plate, characterized in that, Including the lithium iron phosphate as described in claim 9.

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