Lithium iron phosphate and its preparation method and application

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate, a preparation method and application thereof. A preparation method of lithium iron phosphate is provided, which comprises the following steps: after a transition metal source and a lithium iron phosphate slurry are subjected to first mixing treatment, calcination treatment is carried out, so that a transition metal oxide layer coated lithium iron phosphate precursor is obtained; the transition metal oxide layer coated lithium iron phosphate precursor, a lithium iron phosphate precursor, a lithium source and a carbon source are subjected to second mixing treatment, and then drying and sintering treatment are carried out, so that lithium iron phosphate is obtained. Since the coating layer in the transition metal oxide layer coated lithium iron phosphate precursor inhibits the growth of crystal grains, the obtained lithium iron phosphate is a finished product in which small-particle-size lithium iron phosphate and large-particle-size lithium iron phosphate are fully mixed, and the packing density and the rate performance of the finished product material are significantly improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and particularly relates to a lithium iron phosphate, its preparation method and application. Background Technology

[0002] Lithium iron phosphate (LFP) is a safe, long-cycle-life, and low-cost cathode material for lithium-ion batteries, making it a research hotspot in recent years, with its market share continuously increasing. Compared to ternary materials, LFP has a lower true density, resulting in a significant drawback in energy density. Furthermore, due to the low lithium-ion conductivity and electronic conductivity, it must be fabricated into nanoparticles for practical applications to achieve usable rate performance and low-temperature performance. However, the large specific surface area and low compaction density of nanoparticles limit the energy density of LFP batteries.

[0003] Currently, the main methods for industrializing the improvement of energy density in lithium iron phosphate batteries include: preparing multi-peak lithium iron phosphate powder, and improving the charge-discharge performance of the powder through carbon coating and doping modification. However, in some doping processes, most of the dopants are distributed in a dotted pattern on the surface of lithium iron phosphate particles, which inhibits particle growth. However, high temperatures are required to prepare lithium iron phosphate materials with dopants distributed on them. Under the influence of high temperatures, the particles are easily induced to melt and grow into micron-sized particles, making it difficult to maintain the number and proportion of small nanoparticles. This can easily lead to the generation of excessively large single-crystal particles, which will affect the rate performance and DC resistance (DCR).

[0004] Therefore, a simple preparation process for producing high-performance lithium iron phosphate is still lacking. Summary of the Invention

[0005] The purpose of this application is to provide a lithium iron phosphate, its preparation method and application, aiming to solve the problem of the lack of a simple preparation process for producing high-performance lithium iron phosphate in the prior art.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a method for preparing lithium iron phosphate, comprising the following steps:

[0008] After a first mixing treatment of the transition metal source and the iron phosphate slurry, a calcination treatment is performed to obtain an iron phosphate precursor coated with a transition metal oxide layer; wherein, the temperature of the first mixing treatment is 80-180℃ and the time is 3-5 hours; the temperature of the calcination treatment is 500-700℃ and the time is 7-10 hours.

[0009] The iron phosphate precursor, lithium source, and carbon source coated with the transition metal oxide layer are subjected to a second mixing treatment, followed by drying and sintering to obtain lithium iron phosphate.

[0010] In some embodiments, the mass of the transition metal source is 0.1 wt% to 0.8 wt% of the mass of the iron phosphate slurry.

[0011] In some embodiments, the content of the transition metal oxide layer in the iron phosphate precursor coated with the transition metal oxide layer is 3500 ppm to 6000 ppm.

[0012] In some embodiments, the mass ratio of the transition metal oxide-coated iron phosphate precursor to the iron phosphate precursor is 0.1 to 10:1.

[0013] In some embodiments, the mass of the lithium source is 24.8% to 25.3% of the mass of the iron phosphate precursor.

[0014] In some embodiments, the mass of the carbon source is 9% to 12% of the mass of the iron phosphate precursor.

[0015] In some embodiments, the transition metal source includes any one of transition metal oxides, transition metal chlorides, and organometallic compounds.

[0016] In some embodiments, the lithium source includes any one of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide.

[0017] In some embodiments, the carbon source includes any one of glucose, polyethylene glycol, citric acid, urea, graphite, and graphite oxide.

[0018] In some embodiments, the preparation method further includes: providing an additive for a second mixing treatment; wherein the mass of the additive is 0.1% to 0.5% of the mass of the iron phosphate precursor, and the additive includes at least one of a titanium source, nickel source, cadmium source, molybdenum source, manganese source, zinc source, vanadium source, tin source, cerium source, lanthanum source, and tungsten source.

[0019] In some embodiments, the drying is performed by spray drying, wherein the temperature of the spray drying is 180–260°C and the outlet air temperature is 90–150°C.

[0020] In some embodiments, the sintering conditions are as follows: heating from room temperature to 700-800°C at an average heating rate of 1.2-2°C / min, and holding at that temperature for 7-11 hours.

[0021] Secondly, this application provides a lithium iron phosphate, which includes a first lithium iron phosphate and a second lithium iron phosphate, wherein the first lithium iron phosphate is a lithium iron phosphate containing a transition metal oxide layer, and the particle size D of the first lithium iron phosphate is... 50 The particle size D of the second lithium iron phosphate particle is 100-150 nm. 50 The wavelength is 500–800 nm.

[0022] In some embodiments, the thickness of the transition metal oxide layer of the first lithium iron phosphate is 20–50 nm.

[0023] Thirdly, this application provides an electrode comprising a positive electrode material, wherein the positive electrode material is selected from the aforementioned lithium iron phosphate.

[0024] Fourthly, this application provides a battery including the aforementioned electrodes.

[0025] The first aspect of this application provides a method for preparing lithium iron phosphate. This method uses a transition metal source and iron phosphate slurry as raw materials. First, a short-term mixing treatment is performed at low temperature to form a preliminary precursor with a surface-coated metal oxide. Then, calcination is performed to allow the transition metal oxide to tightly coat the surface of the iron phosphate material through physical thermal melting, forming a transition metal oxide layer. This two-step method for preparing the transition metal oxide-coated iron phosphate precursor provides a basis for controlling the structure and properties of the finished lithium iron phosphate product. Further, the transition metal-coated iron phosphate precursor, along with iron phosphate, a lithium source, and a carbon source, are used... In the preparation of lithium iron phosphate (LFP) through a mixed process, the transition metal oxide (TMO) layer tightly binds to the surface of the LFP precursor, inhibiting the growth of LFP grains. This results in smaller LFP particle sizes, while the LFP precursor reacts to produce larger LFP particles. Therefore, the resulting LFP is a product of a thorough mixture of small and large LFP particles. This mixing of different LFP particle sizes significantly improves the packing density and rate performance of the final material, meeting the requirements of high-electrode compaction battery designs. Furthermore, the preparation method described in this application is simple, with controllable reaction conditions, and can produce LFP at low cost.

[0026] The lithium iron phosphate provided in the second aspect of this application is prepared by the aforementioned method for preparing lithium iron phosphate. Based on the characteristics of the aforementioned preparation method, the obtained lithium iron phosphate has a particle size of D. 50 The first lithium iron phosphate with a transition metal oxide layer and a particle size of 100-150 nm and D 50It is obtained by mixing 500-800nm ​​second lithium iron phosphate, which gives lithium iron phosphate high compaction density and high rate performance, significantly improves electron and ion diffusion performance, and has high discharge specific capacity and volumetric specific capacity. It is a high-performance positive electrode material active material that is beneficial for wide application.

[0027] The electrode provided in the third aspect of this application includes a positive electrode material selected from the aforementioned lithium iron phosphate. Due to the high compaction density and high rate performance of the provided lithium iron phosphate, the resulting electrode exhibits stable and excellent performance.

[0028] The fourth aspect of this application provides a battery including the aforementioned electrodes; the provided electrodes contain lithium iron phosphate, resulting in a battery with good performance and low cost. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a SEM image of lithium iron phosphate provided in Example 1 of this application;

[0031] Figure 2 This is a SEM image of the lithium iron phosphate material provided in Comparative Example 1 of this application. Detailed Implementation

[0032] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] In this application, the term "and / or" describes 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, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0036] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0037] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0038] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0039] In the traditional process of preparing lithium iron phosphate, iron source, lithium source, carbon source and additives are directly mixed and then calcined. The reaction process is prone to particle melting and growth due to high temperature calcination. The additives are doped into the lithium iron phosphate in a doping manner and cannot form a separate coating layer. As a result, it is difficult to maintain the number and proportion of small-sized nanoparticles in the subsequent calcination reaction, and it is easy to produce single crystal particles with excessively large size. The material obtained by mixing larger single crystal particles has low compaction density, which is not conducive to improving the rate performance of the material.

[0040] The first aspect of this application provides a method for preparing lithium iron phosphate, comprising the following steps:

[0041] S01. After the transition metal source and the iron phosphate slurry are subjected to a first mixing treatment, the mixture is then calcined to obtain an iron phosphate precursor coated with a transition metal oxide layer; wherein the temperature of the first mixing treatment is 80-180°C and the time is 3-5 hours; the temperature of the calcination treatment is 500-700°C and the time is 7-10 hours.

[0042] S02. The iron phosphate precursor, lithium source, and carbon source coated with the transition metal oxide layer are subjected to a second mixing treatment, followed by drying and sintering to obtain lithium iron phosphate.

[0043] The first aspect of this application provides a method for preparing lithium iron phosphate. This method first prepares a transition metal oxide-coated iron phosphate precursor in two steps, and then mixes and reacts it with the iron phosphate precursor, lithium source, carbon source, etc. to obtain a finished lithium iron phosphate product with different particle sizes. Specifically, in the preparation process, the transition metal source and iron phosphate slurry are first mixed at 80–180°C for 3–5 hours. Since the transition metal source will enter the iron phosphate precursor in the form of doping under higher temperatures, a lower temperature is used for the mixing process in this step. Under this temperature, on the one hand, the transition metal source can be coated on the outer surface of the iron phosphate precursor in the form of a coating layer, and on the other hand, a uniformly coated transition metal oxide layer can be obtained through low-temperature mixing. The reaction time is controlled at 3–5 hours, at which the thickness of the coating layer is moderate, which can form a uniform and complete transition metal oxide layer without affecting the chemical properties of the iron phosphate precursor itself. Then, a calcination treatment is carried out at 500–700°C for 7–10 hours. The first low-temperature treatment only forms a preliminary surface transition metal oxide layer. The calcination treatment at a higher temperature allows the surface transition metal oxide to be tightly coated on the surface of the iron phosphate material by physical thermal melting. The resulting transition metal oxide layer is tightly bonded and not easy to fall off. Furthermore, the iron phosphate precursor coated with a transition metal oxide layer, the lithium source, and the carbon source are mixed and reacted. During the reaction, the transition metal oxide layer is tightly bonded to the surface of the iron phosphate precursor coated with the transition metal oxide layer, which inhibits the growth of iron phosphate grains. This results in smaller particle size of the lithium iron phosphate containing the transition metal oxide layer obtained from the reaction. Meanwhile, the iron phosphate precursor reacts to obtain lithium iron phosphate with larger particle size. Therefore, the resulting lithium iron phosphate is a finished product of lithium iron phosphate with a thorough mixture of small-sized and large-sized lithium iron phosphate particles. The finished lithium iron phosphate is dominated by large-sized lithium iron phosphate particles, with small-sized lithium iron phosphate particles filling the gaps, which better improves the compaction density of the finished lithium iron phosphate.

[0044] In summary, the preparation method of this application enables the synthesis of lithium iron phosphate materials with different particle sizes in a short process and at low cost. The resulting lithium iron phosphate material is a mixture of large and small particle sizes, with high compaction density and rate performance. Moreover, the process is simple and the reaction conditions are mild, allowing for the low-cost preparation of lithium iron phosphate.

[0045] In some embodiments, in step S01, the mass of the transition metal source in the first mixing treatment with the iron phosphate slurry is 0.1 wt% to 0.8 wt% of the mass of the iron phosphate slurry. If too much transition metal source is added, the proportion of transition metal source in the resulting lithium iron phosphate product will be excessive, which is not conducive to the role of lithium iron phosphate as the main component; if too little transition metal source is added, the amount of coating layer formed will be too small, the coating effect will be poor, and it will be difficult to control the growth size of the particles. In some specific embodiments, the mass of the transition metal source added is, but is not limited to, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, and 0.8 wt% of the mass of the iron phosphate slurry.

[0046] In some embodiments, the temperature of the first mixing treatment is 80–180°C, and the time is 3–5 hours. The provided temperature for the first mixing treatment includes, but is not limited to, 80–120°C, 100–160°C, or 120–180°C; reactions conducted at these temperatures can form a coating-like transition metal oxide layer. The provided time for the first mixing treatment includes, but is not limited to, 3–4 hours, or 4–5 hours; reactions conducted within these timeframes can form a complete coating layer.

[0047] In some embodiments, the transition metal source includes any one of transition metal oxides, transition metal chlorides, and organometallic transition metal compounds. In some embodiments, the transition metal can be selected from metals with relatively mild properties, ensuring that the resulting transition metal oxide layer is stable as a coating material. On the one hand, it is not easily reacted under high-temperature calcination conditions; on the other hand, as a coating material, it is not easily reacted with oxygen, moisture, etc., in the air, thus ensuring the stability of the material. In some specific embodiments, the transition metal is selected from at least one of titanium, nickel, cadmium, molybdenum, manganese, zinc, vanadium, tin, cerium, lanthanum, and tungsten.

[0048] In some embodiments, a calcination treatment is then performed. The calcination temperature is 500–700°C, and the time is 7–10 hours. The calcination temperature includes, but is not limited to, 500–600°C or 600–700°C; the calcination time includes, but is not limited to, 7–8 hours, 8–9 hours, or 9–10 hours. Under these temperature and time conditions, the transition metal oxide on the surface can be tightly coated onto the surface of the iron phosphate material through physical thermal melting, ensuring that the formed transition metal oxide layer is tightly bonded and not easily detached. If the calcination temperature is too high, the transition metal source will melt into the iron phosphate, making it impossible to maintain the formation of a transition metal coating layer on the iron phosphate surface; this is detrimental to controlling grain growth. If the calcination temperature is too low, the prepared transition metal coating layer cannot tightly coat the surface of the iron phosphate, and is prone to detachment, which is also detrimental to controlling grain growth.

[0049] Furthermore, the calcination process can be carried out in a roller kiln or a rotary kiln.

[0050] In some embodiments, the content of the transition metal oxide layer in the transition metal oxide-coated iron phosphate precursor is 3500 ppm to 6000 ppm. By synergistically controlling the amount of transition metal source added, the time and temperature of the first mixing treatment, and the temperature and time of the calcination treatment, the content of the transition metal in the transition metal-coated iron phosphate precursor can be controlled. By controlling the content of the transition metal, the thickness of the transition metal oxide layer can be further controlled, thereby achieving control over the particle size of lithium iron phosphate. A higher content of transition metal oxide results in a denser transition metal coating layer, which better restricts grain growth during the preparation of lithium iron phosphate particles. Therefore, the resulting lithium iron phosphate particles have a smaller particle size and can better fill the gaps between large lithium iron phosphate particles, thereby improving the overall compaction density of the finished lithium iron phosphate material. In some specific embodiments, the content of the transition metal in the transition metal-coated iron phosphate precursor includes, but is not limited to, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, and 6000 ppm.

[0051] Step S02, the second mixing process of the transition metal oxide-coated iron phosphate precursor, lithium source, and carbon source includes: mixing the transition metal oxide-coated iron phosphate precursor, lithium source, and carbon source to obtain a mixed slurry, controlling the solid content of the mixed slurry to be 32%–40%. If the solid content is too high, the uniformity of the particles in the mixed slurry will be poor, and the materials will easily agglomerate, which is not conducive to particle preparation. If the solid content is too low, the yield of lithium iron phosphate will be too low, and too few particles will be prepared. In some specific embodiments, the solid content of the mixed slurry includes, but is not limited to, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%.

[0052] In some embodiments, the mass ratio of the transition metal oxide-coated iron phosphate precursor to the iron phosphate precursor is 0.1 to 10:1. Controlling the mass ratio of the transition metal oxide-coated iron phosphate precursor to the iron phosphate precursor ensures that the resulting lithium iron phosphate product is a mixture of large and small particles of lithium iron phosphate. The specific amounts of large and small particles added can be determined according to actual needs. A higher mass ratio of transition metal oxide-coated iron phosphate precursor to iron phosphate precursor results in a higher compaction density of the resulting lithium iron phosphate product. In some specific embodiments, the mass ratio of the transition metal-coated iron phosphate precursor to the iron phosphate precursor includes, but is not limited to, 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, and 10:1.

[0053] In some embodiments, the preparation method of the ferric phosphate precursor includes: washing and removing impurities from ferric phosphate slurry, drying it to obtain ferric phosphate dihydrate, and sintering it at 650-700°C to obtain a pure ferric phosphate precursor.

[0054] In some embodiments, the lithium source includes any one of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide, and the mass of the lithium source is 24.8% to 25.3% of the mass of the iron phosphate precursor.

[0055] In some embodiments, the carbon source includes any one of glucose, polyethylene glycol, citric acid, urea, graphite, and graphite oxide; the mass of the carbon source is 9% to 12% of the mass of the iron phosphate precursor.

[0056] In some embodiments, the preparation method further includes: providing an additive for a second mixing treatment; wherein the mass of the additive is 0.1% to 0.5% of the mass of the iron phosphate precursor, and the additive includes at least one selected from titanium, magnesium, nickel, cadmium, molybdenum, manganese, zinc, vanadium, tin, cerium, lanthanum, and tungsten sources. The purpose of adding the additive is to dope a small amount of transition metal into the lithium iron phosphate to improve the voltage platform and increase the energy density, while retaining the advantages of low cost, high safety, and long cycle life. Furthermore, the additive can be selected from a metal source consistent with the transition metal source to ensure that the obtained lithium iron phosphate has high purity and is free of excessive impurities.

[0057] Furthermore, the obtained mixed slurry is placed in a sand mill for grinding, which can uniformly coat the carbon source onto the surface of the precursor material. The solvent used for grinding can be at least one of water, alcohol, and ketone solvents. The grinding beads include zirconia beads with a particle size of 1–5 mm and zirconia beads with a particle size of 0.05–0.5 mm; such grinding media have better grinding effects. Furthermore, the grinding can be carried out in a sand mill.

[0058] Next, the ground slurry is dried. In some embodiments, spray drying is used, wherein the spray drying temperature is 180–260°C and the outlet air temperature is 90–150°C. Spray drying ensures that the solvent in the ground material is fully dried, resulting in a uniformly dispersed material.

[0059] Further, the dried mixture is sintered to prepare large-particle lithium iron phosphate material and small-particle lithium iron phosphate material. In some embodiments, the sintering conditions are as follows: heating from room temperature to 700-800°C at an average heating rate of 1.2-2°C / min, and holding at that temperature for 7-11 hours. In this step, the sintering temperature is controlled at 700-800°C. If the temperature is too low, the sintering reaction will be incomplete, and the purity of the sintered product will be too low, which is not conducive to the preparation of subsequent materials; if the temperature is too high, the coated material will also undergo a melting reaction, which is not conducive to controlling the particle size of lithium iron phosphate.

[0060] A second aspect of this application provides a lithium iron phosphate, comprising a first lithium iron phosphate and a second lithium iron phosphate, wherein the first lithium iron phosphate is a lithium iron phosphate containing a transition metal oxide layer, and the particle size D of the first lithium iron phosphate is... 50 The particle size D of the second lithium iron phosphate particle is 100-150 nm. 50 The wavelength is 500–800 nm.

[0061] The lithium iron phosphate provided in the second aspect of this application is prepared by the aforementioned method for preparing lithium iron phosphate. Based on the characteristics of the aforementioned preparation method, the obtained lithium iron phosphate has a particle size of D. 50 The first lithium iron phosphate with a transition metal oxide layer and a particle size of 100-150 nm and D 50 It is obtained by mixing 500-800nm ​​second lithium iron phosphate, which gives lithium iron phosphate high compaction density and high rate performance, significantly improves electron and ion diffusion performance, and has high discharge specific capacity and volumetric specific capacity. It is a high-performance positive electrode material active material that is beneficial for wide application.

[0062] In some embodiments, the first lithium iron phosphate is lithium iron phosphate containing a transition metal oxide layer, the thickness of which is 20–50 nm. Controlling the thickness of the transition metal oxide layer of the first lithium iron phosphate is moderate ensures that the transition metal oxide layer can completely coat the outer surface of the iron phosphate grains, limiting the growth of the iron phosphate grains and thus obtaining small-particle-size lithium iron phosphate; at the same time, it ensures that the lithium iron phosphate material can exert its own properties without being affected by the coating layer.

[0063] In some embodiments, the mass ratio of the first lithium iron phosphate and the second lithium iron phosphate containing the transition metal oxide layer is 0.1 to 10:1. A higher mass ratio of the first lithium iron phosphate to the second lithium iron phosphate containing the transition metal oxide layer results in a higher compaction density of the final lithium iron phosphate product. The specific amounts of the first and second lithium iron phosphate produced can be determined according to actual needs. In some specific embodiments, the mass ratio of the first lithium iron phosphate to the second lithium iron phosphate includes, but is not limited to, 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, and 10:1.

[0064] A third aspect of this application provides an electrode, including a positive electrode material, wherein the positive electrode material is selected from the aforementioned lithium iron phosphate.

[0065] The electrode provided in the third aspect of the embodiments of this application includes a positive electrode material selected from the aforementioned lithium iron phosphate. Since the provided lithium iron phosphate has a high compaction density and high rate performance, the resulting electrode has stable and excellent performance.

[0066] A fourth aspect of this application provides a battery including the aforementioned electrodes.

[0067] A fourth aspect of this application provides a battery including the aforementioned electrodes; the provided electrodes contain lithium iron phosphate, resulting in a battery with good performance and low cost.

[0068] The following description is based on specific embodiments.

[0069] Example 1

[0070] Lithium iron phosphate and its preparation method

[0071] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0072] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0073] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate containing a transition metal oxide layer. The particle size of the first lithium iron phosphate was 50–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0074] Example 2

[0075] Lithium iron phosphate and its preparation method

[0076] Titanium dioxide is provided. 0.8% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0077] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0078] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain lithium iron phosphate products containing a transition metal oxide layer, specifically lithium iron phosphate with a first and second lithium iron phosphate. The particle size of the first lithium iron phosphate was 50–250 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0079] Example 3

[0080] Lithium iron phosphate and its preparation method

[0081] Titanium dioxide is provided. 0.1% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0082] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0083] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain lithium iron phosphate products containing a transition metal oxide layer, specifically lithium iron phosphate with a first and second lithium iron phosphate. The particle size of the first lithium iron phosphate was 150–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0084] Example 4

[0085] Lithium iron phosphate and its preparation method

[0086] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 600°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0087] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0088] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held at that temperature for 11 hours, cooled, and sieved at a temperature below 100°C before air-jetting to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 100–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0089] Example 5

[0090] Lithium iron phosphate and its preparation method

[0091] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 700°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0092] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0093] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 150–350 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0094] Example 6

[0095] Lithium iron phosphate and its preparation method

[0096] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 8 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0097] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0098] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 100–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0099] Example 7

[0100] Lithium iron phosphate and its preparation method

[0101] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 10 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0102] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0103] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 150–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0104] Example 8

[0105] Lithium iron phosphate and its preparation method

[0106] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 130°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0107] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0108] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 100–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0109] Example 9

[0110] Lithium iron phosphate and its preparation method

[0111] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 180°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0112] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0113] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 200–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0114] Example 10

[0115] Lithium iron phosphate and its preparation method

[0116] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 4 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0117] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0118] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate containing a transition metal oxide layer. The particle size of the first lithium iron phosphate was 50–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0119] Example 11

[0120] Lithium iron phosphate and its preparation method

[0121] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 5 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0122] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0123] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 100–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0124] Example 12

[0125] Lithium iron phosphate and its preparation method

[0126] Nickel oxide is provided. 0.4% by mass of nickel oxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain nickel oxide-coated ferric phosphate precursor.

[0127] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0128] Nickel oxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 100–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0129] Example 13

[0130] Lithium iron phosphate and its preparation method

[0131] Zinc oxide is provided. 0.4% zinc oxide by mass is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain zinc oxide-coated ferric phosphate precursor.

[0132] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0133] Zinc oxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 150–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0134] Example 14

[0135] Lithium iron phosphate and its preparation method

[0136] Manganese dioxide is provided. 0.4% manganese dioxide by mass is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain manganese dioxide-coated ferric phosphate precursor.

[0137] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0138] A manganese dioxide-coated iron phosphate precursor and an iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held at that temperature for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate containing a transition metal oxide layer. The particle size of the first lithium iron phosphate was 50–200 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0139] Example 15

[0140] Lithium iron phosphate and its preparation method

[0141] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0142] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0143] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 0.5 / 1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held at that temperature for 11 hours, cooled, and sieved at a temperature below 100°C before air-jetting to obtain lithium iron phosphate products containing a transition metal oxide layer (lithium iron phosphate first and lithium iron phosphate second). The particle size of lithium iron phosphate first was 50–300 nm, and the particle size of lithium iron phosphate second was 1–3 μm.

[0144] Example 16

[0145] Lithium iron phosphate and its preparation method

[0146] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0147] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0148] Titanium oxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 10 / 1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain lithium iron phosphate products containing a transition metal oxide layer, specifically lithium iron phosphate with a first and second lithium iron phosphate. The particle size of the first lithium iron phosphate was 50–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0149] Comparative Example 1

[0150] Preparation method of lithium iron phosphate

[0151] Iron phosphate was added to pure water, along with 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol, resulting in a slurry with a solid content of 33%. After spray drying, the dried material was fed into a roller kiln and heated to 790°C at an average heating rate of 1.5°C / min. After holding at this temperature for 11 hours, the material was cooled and sieved until the temperature dropped below 100°C. The resulting lithium iron phosphate was then subjected to air jet milling to obtain a particle size of 300 nm to 3 μm.

[0152] Comparative Example 2

[0153] Preparation method of lithium iron phosphate

[0154] Titanium-coated iron phosphate was added to pure water, along with 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol, resulting in a slurry with a solid content of 33%. After spray drying, the dried material was fed into a roller kiln and heated to 790°C at an average rate of 1.5°C / min. After holding at this temperature for 11 hours, the material was cooled until its temperature dropped below 100°C, then sieved and subjected to air-jet milling to obtain lithium iron phosphate with a particle size of 50–300 nm.

[0155] Comparative Example 3

[0156] Lithium iron phosphate and its preparation method

[0157] Titanium dioxide is provided. 2% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0158] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0159] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 50–150 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0160] Comparative Example 4

[0161] Lithium iron phosphate and its preparation method

[0162] Titanium dioxide is provided, and 0.4% by mass of titanium dioxide is added to iron phosphate slurry and calcined at 550℃ for 7 hours to obtain titanium dioxide-coated iron phosphate precursor;

[0163] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0164] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 150–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0165] Comparative Example 5

[0166] Lithium iron phosphate and its preparation method

[0167] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 1000°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0168] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0169] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 3:1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 300–450 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0170] Comparative Example 6

[0171] Lithium iron phosphate and its preparation method

[0172] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0173] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0174] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 15 / 1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held at that temperature for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 50–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0175] Comparative Example 7

[0176] Lithium iron phosphate and its preparation method

[0177] Titanium dioxide is provided. 0.4% by mass of titanium dioxide is added to ferric phosphate slurry and mixed at 100°C for 3 hours. After washing to remove impurities and flash drying, ferric phosphate dihydrate is obtained. Then, it is calcined at 550°C for 7 hours to obtain titanium dioxide-coated ferric phosphate precursor.

[0178] The ferric phosphate conversion slurry was washed to remove impurities and dried to obtain ferric phosphate dihydrate, which was then sintered at 650℃ to obtain the ferric phosphate precursor.

[0179] Titanium dioxide-coated iron phosphate precursor and iron phosphate precursor were added to pure water at a mass ratio of 0.05 / 1. 25.1% lithium carbonate, 0.3% titanium dioxide, 0.3% ammonium metavanadate, 6% glucose, and 6% polyethylene glycol were added and mixed to form a slurry with a solid content of 33%. The resulting slurry was ground in a sand mill and then spray-dried at 180°C with an outlet air temperature of 100°C to obtain a dried and dispersed material. The material was then heated to 790°C at an average heating rate of 1.5°C / min, held for 11 hours, and then cooled. After the material temperature dropped below 100°C, it was sieved and subjected to air jet milling to obtain a finished lithium iron phosphate product containing a first lithium iron phosphate and a second lithium iron phosphate with transition metal oxide layers. The particle size of the first lithium iron phosphate was 50–300 nm, and the particle size of the second lithium iron phosphate was 1–3 μm.

[0180] Property Testing and Result Analysis

[0181] (a) The lithium iron phosphate materials prepared in Examples 1-16 and Comparative Examples 1-7 were tested for compaction density in a powder compaction tester at a pressure of 3 tons.

[0182] (II) The lithium iron phosphate prepared in Examples 1-16 and Comparative Examples 1-7 were used as active materials, acetylene black as conductive agents, and polyvinylidene fluoride as binders. They were mixed in a mass ratio of 95 / 2.5 / 2.5 and dissolved in N-methylpyrrolidone to obtain a slurry. The slurry was uniformly coated on aluminum foil, dried, and cut into positive electrode sheets. The negative electrode was directly made of lithium metal sheets, with a polypropylene membrane as the separator. The electrolyte was 1M LiPF6, and the solvent was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1. After assembling into CR2016 coin-type lithium-ion batteries, battery performance was tested. The charge and discharge test voltage window was 2.0-3.75V.

[0183] The SEM image of the lithium iron phosphate obtained in Example 1 is shown below. Figure 1 The image shows lithium iron phosphate obtained by mixing large and small particles. The large lithium iron phosphate particles have a particle size of 1–3 μm, and the small lithium iron phosphate particles have a particle size of 50–300 nm. The compaction density is 2.58 g / cm³. 3 It exhibits good compaction density and a discharge specific capacity of 157 mAh / g at 0.1C and 144.2 mAh / g at 1C, with a first-cycle efficiency of 98.2%.

[0184] Compared with Example 1, the difference between Example 2 and Example 3 lies in the amount of titanium dioxide added. In Example 2, the amount of titanium dioxide added was 0.8%, and the resulting product had small lithium iron phosphate particles with a particle size of 50-250 nm and a compaction density of 2.54 g / cm³. 3In Example 3, the amount of titanium dioxide added was 0.1%. The resulting product contained lithium iron phosphate particles with a particle size of 150–300 nm and a compaction density of 2.55 g / cm³. 3 Therefore, by adjusting the amount of titanium dioxide added, the particle size of small lithium iron phosphate particles in the product can be controlled, thereby adjusting the overall compaction density of the product. The difference in Comparative Example 3 also lies in the amount of titanium dioxide added; in Comparative Example 3, the amount of titanium dioxide added was 2%, resulting in a compaction density of 2.46 g / cm³. 3 It can be seen that as the amount of titanium dioxide filler increases, the compaction density of the product decreases significantly, which further affects the discharge specific capacity and first-cycle efficiency of the product, and is not conducive to subsequent use.

[0185] Compared to Example 1, the differences between Examples 4, 5, and Comparative Example 5 lie in the calcination temperature, while the differences between Examples 6 and 7 lie in the calcination time. The calcination temperature for Example 4 was 600℃, for Example 5 it was 700℃, and for Comparative Example 5 it was 1000℃. It can be seen that under temperature conditions of 500–700℃, as the temperature increases, the particle size of lithium iron phosphate increases, thus affecting the compaction density of the finished product. An appropriate calcination temperature is beneficial for obtaining lithium iron phosphate with suitable particle size. Lithium iron phosphate products with suitable particle size can further control the overall density of the lithium iron phosphate product. When the calcination temperature exceeds 700℃, it leads to excessively large particle size of small lithium iron phosphate particles, affecting the specific capacity of the product. The calcination time for Example 6 was 8 hours, and for Example 7 it was 10 hours. With the increase in calcination time, the particle size of the obtained lithium iron phosphate increases, thereby adjusting the compaction density of the material. Calcination treatment can cause the transition metal oxides on the surface of the iron phosphate material to be tightly coated by physical thermal melting. The resulting transition metal oxide layer is tightly bonded and not easy to fall off. Therefore, by adjusting the temperature and time of calcination treatment, the particle size of the material can be adjusted, thereby affecting the density of the material.

[0186] Compared with Example 1, the difference between Example 8 and Example 9 is that the temperature of the first mixing process is different, and the difference between Example 10 and Example 11 is that the time of the first mixing process is different. As long as the adjustment is made within the provided temperature range and time range, a product with excellent performance can be obtained.

[0187] Compared with Example 1, Example 12 used nickel oxide, Example 13 used zinc oxide, and Example 14 used manganese dioxide. The products obtained are the same as those prepared in Example 1, which are a mixture of large-particle lithium iron phosphate and small-particle lithium iron phosphate. However, due to the different metal sources selected, the compaction density of the products obtained under a series of processing steps is lower than that of the products obtained in Example 1, and the discharge specific capacity and first-cycle efficiency are weaker.

[0188] Compared with Example 1, Examples 15 and 16, and Comparative Examples 6 and 7 provide different mass ratios of titanium oxide-coated iron phosphate precursor and iron phosphate precursor. As can be seen from Examples 16 and 6, as the mass ratio of titanium oxide-coated iron phosphate precursor to iron phosphate precursor increases, the overall compaction density of the material decreases. When the compaction density is too low, it is not conducive to use. As shown in Examples 15 and 7, as the mass ratio of titanium oxide-coated iron phosphate precursor to iron phosphate precursor decreases, although the overall compaction density of the material increases, its 1C discharge specific capacity decreases. Therefore, there is an imbalance between compaction density and specific capacity, which is not conducive to practical applications.

[0189] Comparative Example 1 uses lithium iron phosphate material prepared from pure iron phosphate precursor, which has a larger particle size (e.g., ...). Figure 2 As shown in the figure, the compacted density of the obtained product is 2.56 g / cm³. 3 Under 0.1C conditions, the discharge specific capacity is 154.8 mAh / g, and under 1C conditions, the discharge specific capacity is 135.9 mAh / g, with a first-cycle efficiency of 96.6%. Compared with the product obtained in the example, it can be seen that although the product of Comparative Example 1 has excellent compaction density, its electrical performance is poor, which is not conducive to its use in batteries.

[0190] Comparative Example 2 used titanium-coated iron phosphate as a precursor material to prepare lithium iron phosphate, resulting in a product with a smaller particle size and a compaction density of 2.07 g / cm³. 3 Under 0.1C conditions, the discharge specific capacity is 161.6 mAh / g, and under 1C conditions, the discharge specific capacity is 157.1 mAh / g, with a first-cycle efficiency of 100.3%. Compared with the product in the example, although the electrical performance is better, the compaction density is poor, which is not conducive to subsequent processing.

[0191] Compared with Example 1, the difference of Comparative Example 4 is that no low-temperature treatment was performed during the process, and high-temperature calcination was performed directly. Therefore, the product obtained is a doped material, and its compaction density and electrochemical properties are weaker than those of Example 1.

[0192] In summary, based on a comprehensive analysis of the overall compaction density, discharge specific capacity, and first-cycle efficiency of the materials, the compaction densities of the products obtained in Examples 1 and 10 are both higher than 2.5 g / cm³. 3 The 0.1C discharge specific capacity is higher than 156 mAh / g, and the 1C discharge specific capacity is higher than 1144 mAh / g. Therefore, Examples 1 and 10 can be regarded as preferred gradation schemes.

[0193] Table 1

[0194]

[0195]

[0196] In summary, the method for preparing lithium iron phosphate provided in this application uses a transition metal source and iron phosphate slurry as raw materials. First, a short-term mixing treatment is performed at low temperature to form a preliminary precursor with a surface-coated metal oxide. Then, calcination is performed to tightly coat the surface of the iron phosphate material with the transition metal oxide through physical thermal melting, forming a transition metal oxide layer. This two-step method for preparing the transition metal oxide-coated iron phosphate precursor provides a foundation for controlling the structure and properties of the finished lithium iron phosphate product. Furthermore, the transition metal-coated iron phosphate precursor, along with iron phosphate, a lithium source, and a carbon source, are then used... In the preparation of lithium iron phosphate (LFP) through a mixed process, the transition metal oxide (TMO) layer tightly binds to the surface of the LFP precursor, inhibiting the growth of LFP grains. This results in smaller LFP particle sizes, while the LFP precursor reacts to produce larger LFP particles. Therefore, the resulting LFP is a product of a thorough mixture of small and large LFP particles. This mixing of different LFP particle sizes significantly improves the packing density and rate performance of the final material, meeting the requirements of high-electrode compaction battery designs. Furthermore, the preparation method described in this application is simple, with controllable reaction conditions, and can produce LFP at low cost.

[0197] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing lithium iron phosphate, characterized in that, Includes the following steps: After a first mixing treatment of a transition metal source and an iron phosphate slurry, a calcination treatment is performed to obtain an iron phosphate precursor coated with a transition metal oxide layer. The content of the transition metal oxide layer in the iron phosphate precursor is 3500ppm~6000ppm. The transition metal source is one of titanium dioxide, nickel oxide, zinc oxide, and manganese dioxide. The iron phosphate slurry is a slurry prepared from iron phosphate dihydrate obtained by washing, removing impurities, and flash drying. The temperature of the first mixing treatment is 80~180℃ and the time is 3~5 hours; the temperature of the calcination treatment is 500~700℃ and the time is 7~10 hours. The iron phosphate precursor coated with the transition metal oxide layer, the iron phosphate precursor, the lithium source, and the carbon source are subjected to a second mixing treatment, and the solid content of the mixed slurry is 32%~40%; then it is dried and sintered, and after sintering, it is cooled, sieved and air-jet pulverized to obtain lithium iron phosphate; the mass ratio of the iron phosphate precursor coated with the transition metal oxide layer to the iron phosphate precursor is 0.1~10:1; The drying process employs spray drying, wherein the spray drying temperature is 180~260℃ and the outlet air temperature is 90~150℃. The sintering process involves heating the temperature to 700-800°C at an average heating rate of 1.2-2°C / min and holding it at that temperature for 7-11 hours. The lithium iron phosphate includes a first lithium iron phosphate and a second lithium iron phosphate. The first lithium iron phosphate is a lithium iron phosphate containing a transition metal oxide layer with a D50 of 100~150 nm, and the second lithium iron phosphate is a lithium iron phosphate without a transition metal oxide layer with a D50 of 500~800 nm.

2. The method for preparing lithium iron phosphate according to claim 1, characterized in that, The mass of the transition metal source is 0.1wt% to 0.8wt% of the mass of the iron phosphate slurry.

3. The method for preparing lithium iron phosphate according to any one of claims 1 to 2, characterized in that, The mass of the lithium source is 24.8% to 25.3% of the mass of the iron phosphate precursor; and / or, The mass of the carbon source is 9% to 12% of the mass of the iron phosphate precursor.

4. The method for preparing lithium iron phosphate according to any one of claims 1 to 2, characterized in that, The lithium source includes any one of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide; and / or, The carbon source includes any one of glucose, polyethylene glycol, citric acid, urea, graphite, and graphite oxide.

5. The method for preparing lithium iron phosphate according to any one of claims 1 to 2, characterized in that, The preparation method further includes: providing an additive for a second mixing treatment; wherein the mass of the additive is 0.1% to 0.5% of the mass of the iron phosphate precursor, and the additive includes at least one of titanium source, magnesium source, nickel source, cadmium source, molybdenum source, manganese source, zinc source, vanadium source, tin source, cerium source, lanthanum source, and tungsten source.

6. A lithium iron phosphate, characterized in that, The lithium iron phosphate includes first lithium iron phosphate and second lithium iron phosphate, wherein the first lithium iron phosphate is lithium iron phosphate containing a transition metal oxide layer, and the particle size D of the first lithium iron phosphate is... 50 The particle size D of the second lithium iron phosphate is 100~150 nm. 50 The wavelength is 500~800 nm.

7. The lithium iron phosphate according to claim 6, characterized in that, The thickness of the transition metal oxide layer of the first lithium iron phosphate is 20~50 nm.

8. An electrode, characterized in that, Includes a cathode material, wherein the cathode material is selected from lithium iron phosphate according to any one of claims 6-7.

9. A battery, characterized in that, Includes the electrode as described in claim 8.

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