Preparation method of lithium iron phosphate particles

Abstract

The invention relates to the technical field related to lithium ion battery processing, in particular to a preparation method of lithium iron phosphate particles. The preparation method of the lithium iron phosphate particles comprises the following steps: providing a mixed aqueous dispersion of a lithium source, an iron source and a carbon source; preparing a spherical material by using the mixed aqueous dispersion; placing the spherical material in a protective gas atmosphere, raising the temperature to a first sintering temperature, then raising the first sintering temperature to a second sintering temperature step by step, keeping the temperature at the raised temperature for a set duration after each step of temperature raising, and then continuing to raise the temperature to the temperature of the next step, and keeping the temperature for a set time length at the second sintering temperature until the temperature is raised to the second sintering temperature. According to the method, the temperature is firstly increased to the first sintering temperature and then increased to the second sintering temperature step by step, and heat preservation is performed after each step of temperature increase, so that overhigh crystallinity can be avoided, the roundness of particles can be improved, the compaction performance can be improved, uniform coating of carbon can be promoted, and the electrical performance of the prepared battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery processing, and particularly to a lithium iron phosphate particle preparation method. BACKGROUND

[0002] As a green energy source, lithium ion batteries have developed rapidly in recent years and are widely used in mobile phones, computers, new energy vehicles, energy storage stations, etc.

[0003] Among them, lithium iron phosphate (LFP, LiFePO4) stands out due to its low cost, good safety performance, light weight, stable structure, good cycle performance and other advantages, and is recognized as one of the most important materials for the new generation of lithium ion batteries. The lithium iron phosphate material industry and lithium iron phosphate battery industry have also grown rapidly with the market.

[0004] With the continuous expansion of the lithium ion battery market, people have put forward higher and higher requirements for the energy density of the battery. However, lithium iron phosphate is an olivine structure, and Li + can only be transported along a one-dimensional channel, so its ion diffusion coefficient (10 - 14 cm 2 / s) is low, and the electronic conductivity is also low (about 10 -9 s / cm), which makes the electrochemical performance of lithium iron phosphate not fully developed. Therefore, improving the electrochemical performance of lithium iron phosphate has become a key technical difficulty in the development of positive electrode materials.

[0005] The prior art usually adopts a two-step sintering method to prepare lithium iron phosphate, and the highest temperature holding time curve is unchanged, and then a crushing process is performed. However, the particles prepared by this method grow too fast, resulting in poor carbon coating effect. Once the particles are crushed, the carbon coating layer may be damaged, forming free carbon, which leads to a significant decrease in performance during the later cycle and storage process, thereby resulting in low electrical performance of the battery. SUMMARY

[0006] The purpose of the present application is to provide a lithium iron phosphate particle preparation method to improve the electrical performance of the battery.

[0007] To solve the above technical problems, the present application provides a lithium iron phosphate particle preparation method.

[0008] The lithium iron phosphate particle preparation method of the present application comprises:

[0009] providing a mixed aqueous dispersion of a lithium source, an iron source and a carbon source;

[0010] preparing spherical material using the mixed aqueous dispersion;

[0011] The spherical material is placed in a protective atmosphere, and then the temperature is raised to a first sintering temperature, and then the first sintering temperature is raised to a second sintering temperature in steps, after each step of temperature rise, the temperature after the temperature rise is kept for a set time length, and then the temperature is continuously raised to the temperature of the next step, until the temperature is raised to the second sintering temperature and kept at the second sintering temperature for a set time length.

[0012] Further, the first sintering temperature is 580-620 DEG C, and the second sintering temperature is 740-820 DEG C.

[0013] Further, the first temperature is raised to the second sintering temperature in two steps.

[0014] Further, the temperature rise range in the first step is 150-200 DEG C, and the temperature rise range in the second step is 5-15 DEG C.

[0015] Further, the time length of keeping the temperature after the first step of raising to the set temperature is equal to the time length of keeping the temperature after the second step of raising to the set temperature, and both are 5 hours.

[0016] Further, the first temperature is raised to the second sintering temperature in three steps.

[0017] Further, the temperature rise range in the first step is 150-200 DEG C, the temperature rise range in the second step is 5-15 DEG C, and the temperature rise range in the third step is 5-15 DEG C.

[0018] Further, the temperature rise range in the second step is the same as the temperature rise range in the third step.

[0019] Further, the time length of keeping the temperature after the first step of raising to the set temperature is equal to the time length of keeping the temperature after the second step of raising to the set temperature, and both are 3 hours, and the time length of keeping the temperature after the third step of raising to the set temperature is greater than the time length of keeping the temperature after the second step of raising to the set temperature, and the time length of keeping the temperature after the third step of raising to the set temperature is 4 hours.

[0020] Further, the temperature rise rate in each step of temperature rise is the same, and the temperature rise rate is 1.5-2.5 DEG C / min.

[0021] Compared with the prior art, the application has at least the following beneficial effects:

[0022] The core innovation of the application is to propose a calcination method combining stepwise temperature rise and keeping, by raising the temperature to a first sintering temperature first, and then raising the temperature to a second sintering temperature in steps, and keeping the temperature after each step of temperature rise, the crystallization process and morphology of the lithium iron phosphate particles can be more accurately controlled, this method can help to avoid too high crystallinity, improve the roundness of the particles, improve the compaction performance, and promote uniform coating of carbon, thereby improving the electrical performance of the prepared battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of an embodiment of a method for preparing lithium iron phosphate particles of the present invention;

[0024] Figure 2 is a scanning electron microscope image of lithium iron phosphate particles obtained in the comparative example;

[0025] Figure 3 This is a scanning electron microscope image of the lithium iron phosphate particles obtained in Example 1. DETAILED DESCRIPTION

[0026] The following description of the energy storage battery liquid cooling test system of the present invention is provided with reference to a schematic diagram, which illustrates a preferred embodiment of the present invention. It should be understood that those skilled in the art may modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as a general guideline for those skilled in the art and is not intended to limit the present invention.

[0027] The serial numbers of the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings). In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0028] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0029] The inventors have found that in the preparation process of lithium iron phosphate cathode materials, there are some key technical problems in the traditional calcination method. Specifically, these problems mainly manifest in the aspects of too high crystallinity, insufficient particle roundness, poor compaction performance, and poor carbon coating effect, etc. These problems directly affect the electrochemical performance of lithium iron phosphate materials and the overall performance of the battery.

[0030] For example, in a typical lithium iron phosphate battery production line, after the raw materials go through the processes of mixing, granulation, and calcination, the final lithium iron phosphate particles often exhibit sharp-edged morphology rather than the ideal spherical structure. This irregular morphology leads to a decrease in the packing density between particles, which in turn affects the compaction density of the electrode. At the same time, due to the lack of precise temperature control in the traditional calcination process, it is easy to cause the material to have too high crystallinity, which not only limits the deintercalation ability of lithium ions, but also reduces the electrochemical activity of the material.

[0031] Specifically, during the battery assembly process, when these irregularly shaped lithium iron phosphate particles are coated on the current collector, more voids are formed, resulting in a decrease in the content of active materials per unit volume. In addition, due to the uneven carbon coating on the surface of the particles, during the charge and discharge cycle, some areas may have carbon layer peeling off, forming free carbon, which not only cannot effectively improve the conductivity of the material, but may hinder the transmission of lithium ions.

[0032] If these technical problems cannot be effectively solved, it will have a serious impact on the performance of lithium iron phosphate batteries. First, the energy density of the battery will be significantly limited, which cannot meet the demand of high energy density applications. Second, due to the lack of compaction density, the mechanical strength of the electrode may be reduced, affecting the long-term service life of the battery. Third, uneven carbon coating may lead to an increase in internal impedance of the battery, a decrease in power performance, and even cause safety hazards in extreme cases. Therefore, developing a new calcination method that can simultaneously solve these problems is of great significance to improve the overall performance of lithium iron phosphate batteries and market competitiveness.

[0033] In solving the technical problems existing in the preparation process of lithium iron phosphate particles, the present application first considers the limitations of the traditional method. The traditional calcination method usually adopts a single high-temperature sintering, which is simple but difficult to accurately control the crystallization process and particle morphology.

[0034] In order to improve this situation, the present application proposes a step-by-step heating idea. Specifically, the temperature is first raised to a lower first sintering temperature, and then raised to a higher second sintering temperature in steps. The advantage of this method is that it can better control the crystallization process, avoid too high crystallinity, and at the same time be conducive to the formation of round particle morphology.

[0035] However, simply increasing the temperature in steps is not enough to completely solve the problem. This application further adds a holding stage after each heating step. This holding stage allows the material sufficient time to adjust its internal structure, helping to form a more uniform crystal structure and particle morphology. This improves the roundness of the particles and the compaction performance of the material, facilitates uniform carbon coating, reduces the generation of free carbon, and ultimately improves the performance of the battery product.

[0036] Taking the above factors into consideration, this application proposes a method for preparing lithium iron phosphate particles, such as Figure 1 As shown, the following steps are included:

[0037] S100: providing a mixed aqueous dispersion of a lithium source, an iron source, and a carbon source;

[0038] S200: preparing a spherical material using the mixed aqueous dispersion;

[0039] S300: placing the spherical material into a protective gas atmosphere, first raising the temperature to a first sintering temperature, then raising the first sintering temperature to a second sintering temperature in steps, keeping the temperature at the raised temperature for a set time after each step of heating, then continuing to raise the temperature to the next step, until the temperature reaches the second sintering temperature and keeping the temperature at the second sintering temperature for a set time.

[0040] The lithium source refers to a compound containing lithium, specifically lithium carbonate, lithium hydroxide, or lithium phosphate. The iron source refers to a compound containing iron, specifically ferrous sulfate, ferrous chloride, or ferrous oxalate. The carbon source refers to a compound containing carbon, specifically one or more of glucose, sucrose, starch, citric acid, or polyethylene glycol.

[0041] When utilizing the mixed aqueous dispersion to prepare spherical materials, the mixed aqueous dispersion can be first sand-milled to a set particle size, and then the sand-milled mixed aqueous dispersion is spray-dried and granulated into spherical particles. Wherein, sand-milling refers to the process of grinding the mixed solution by mechanical force, which can be achieved by a horizontal sand mill or a vertical sand mill. Spray drying granulation refers to the process of atomizing a liquid into fine droplets through a high-speed rotating nozzle and rapidly drying the resulting particles in a hot air flow, which can be achieved by a centrifugal spray dryer or a pressure spray dryer. The protective gas is preferably nitrogen, but can also be argon or other protective gases that do not participate in the reaction.

[0042] The core innovation of the present application is to propose a calcination method combining step-by-step heating and holding. By first heating to a first sintering temperature, then step-by-step heating to a second sintering temperature, and holding after each step of heating, the crystallization process and morphology of lithium iron phosphate particles can be more accurately controlled. This method helps to avoid excessive crystallinity, improve particle roundness, improve compaction performance, and promote uniform carbon coating, thereby improving the electrical performance of the prepared battery.

[0043] In addition, the step-by-step heating method of the present application, combined with the aforementioned mixing, sanding, spray drying, and nitrogen atmosphere sintering steps, can produce a synergistic effect. Specifically, step-by-step heating can better control the crystallization and growth of the spherical material prepared in the early stage during the sintering process, thereby making full use of the uniform mixing and ideal particle morphology formed in the early preparation step, and ultimately obtaining a lithium iron phosphate material with better performance.

[0044] In the present application, first, the lithium source, iron source, and carbon source are mixed into deionized water in a set proportion to obtain a mixed solution. The use of deionized water can reduce the introduction of impurities and improve the purity of the raw materials. The mixed solution is treated by sanding to control the particle size within a set particle size range, for example, 0.4 microns to 1 micron. This step can improve the uniformity and reactivity of the raw materials, laying the foundation for the subsequent reaction process.

[0045] Next, the sanding mixed solution is subjected to spray drying granulation to form spherical material. This step is crucial for improving the roundness and uniformity of the final product. The spherical material is beneficial to improving the bulk density in the subsequent compaction process, thereby improving the compaction performance of the electrode.

[0046] In the sintering stage, the spherical material is placed in a nitrogen atmosphere with oxygen content strictly controlled at a set concentration, for example, less than 10 ppm. This low-oxygen environment can prevent the carbon source from being oxidized at high temperatures, which is beneficial to the formation of a uniform carbon coating layer. The sintering process uses a step-by-step heating method, first heating to a first sintering temperature, then step-by-step heating to a second sintering temperature. After each step of heating, the temperature after heating is held for a certain period of time until the temperature is raised to the second sintering temperature and held at the second sintering temperature for a set period of time. This step-by-step heating and holding method can better control the crystallization process, avoid excessive crystallinity, and facilitate the formation of round particle morphology and uniform carbon coating.

[0047] Through the process flow of the present application, the problems of excessive crystallinity, insufficient particle roundness, poor compaction performance, and poor carbon coating effect in the traditional lithium iron phosphate particle preparation process can be effectively solved, thereby improving the electrochemical performance of the final product.

[0048] In some embodiments, the first sintering temperature is 580°C-620°C, and the second sintering temperature is 740°C-820°C.

[0049] The first sintering temperature range of 580°C-620°C is used as the temperature control for the initial sintering stage, which facilitates the initial crystallization and particle formation of the material. The second sintering temperature range of 740°C-820°C is used as the temperature control for the subsequent sintering stage, which promotes further crystallization and performance optimization of the material.

[0050] Specifically, the first sintering temperature range of 580°C-620°C is based on the crystallization characteristics of lithium iron phosphate. Within this temperature range, the material begins to form a preliminary crystal structure, but the crystallization rate is relatively slow, which is conducive to the formation of uniform crystal nuclei. This temperature range may also facilitate the initial decomposition and coating of the carbon source, laying the foundation for the subsequent carbon coating process.

[0051] The second sintering temperature range of 740°C-820°C is designed to promote further crystallization and optimize the material's performance. Within this temperature range, the lithium iron phosphate crystal structure is further refined and the particle morphology is optimized. This temperature range also facilitates the formation and solidification of the carbon coating, thereby improving the material's electrical conductivity.

[0052] As a preferred embodiment, the present application can be carried out according to the following steps:

[0053] First, a lithium source, an iron source, and a carbon source were mixed into deionized water at a molar ratio of 1:1:0.05 to obtain a mixed solution.

[0054] Then, the mixture was sand-milled to an average particle size of 0.8 μm.

[0055] Next, the milled mixture is spray-dried and granulated into spherical materials.

[0056] Finally, sintering was performed under a nitrogen atmosphere with an oxygen content controlled at 5 ppm. The temperature was first raised to 600°C, then increased in three steps: the first step was from 180°C to 780°C and held for 3 hours; the second step was from 10°C to 790°C and held for 3 hours; and the third step was from 10°C to 800°C and held for 4 hours. The heating rate for each step was 2°C / min.

[0057] In some embodiments, the first temperature is raised to the second sintering temperature in two steps.

[0058] This step-by-step heating method allows for better control over the growth of lithium iron phosphate particles, fostering the formation of an ideal crystal structure and particle morphology. Compared to directly increasing the temperature from the first to the second temperature, this step-by-step heating method reduces the impact of temperature changes on the material structure, helping to improve the material's crystallinity and uniformity.

[0059] The two-step temperature rising method of the present application can be implemented in various ways. For example, the temperature rising range in the first step is 150-200°C, and the temperature rising range in the second step is 5-15°C.

[0060] Specifically, the design of the first step of temperature rising by 150-200°C can quickly raise the temperature to a range close to the target temperature. This larger temperature rising range helps to improve production efficiency and shorten the time of the entire calcination process. For example, the temperature can be raised by 170°C, which can raise the temperature from the first sintering temperature (580-620°C) to a level close to the second sintering temperature (740-820°C) in a relatively short time.

[0061] In the second step, the design of temperature rising by 5-15°C allows more precise control of the final sintering temperature. This smaller temperature rising range can more accurately adjust the temperature, which is beneficial for the crystallization and performance optimization of lithium iron phosphate particles. For example, the temperature can be raised by 10°C, which can accurately adjust the temperature to the target sintering temperature based on the temperature rising in the first step.

[0062] The combination of the two steps not only achieves precise control of the sintering temperature, but also ensures production efficiency. The large temperature rise in the first step quickly approaches the target temperature, while the small temperature rise in the second step ensures the accuracy of the final temperature.

[0063] Further, this two-step temperature rising method can also be flexibly adjusted according to actual production needs. For example, the temperature rising range of each step can be fine-tuned according to the characteristics of different batches of raw materials or the performance requirements of the target product. In the first step, a suitable temperature rising range can be selected within the range of 150-200°C; in the second step, fine adjustment can be made within the range of 5-15°C. This flexibility allows the technical solution of the present application to adapt to different production conditions and requirements.

[0064] As a preferred embodiment, which is named as Example 1, in step S300, the present application can be carried out according to the following detailed steps:

[0065] First, the spherical material is sintered under a nitrogen atmosphere, with the oxygen content controlled to be less than 10 ppm. The temperature is raised to the first sintering temperature, for example, 600°C.

[0066] Then, the first step of temperature rising is carried out. In this step, the temperature is raised from 600°C to 770°C, with a temperature rising range of 170°C, and the temperature rising rate is controlled at 2°C / min. After the temperature rising is completed, the temperature is maintained for 5 hours.

[0067] Then, the second step of temperature increase is performed. In this step, the temperature is increased from 770°C to 780°C at a rate of 10°C, and the temperature increase rate is controlled at 2°C / min. After the temperature increase is completed, the temperature is maintained for 5 hours.

[0068] In this way, the temperature during the preparation of lithium iron phosphate particles can be precisely controlled. The first step of large temperature increase quickly approaches the target temperature, improving production efficiency. The second step of small temperature increase ensures the accuracy of the final temperature, which is beneficial to the crystallization and performance optimization of lithium iron phosphate particles. The two steps of temperature maintenance have equal time, which helps to evenly distribute the temperature and fully react the material.

[0069] The present application also provides a comparative example, which is different from the above-mentioned embodiment 1 in that, after the temperature is increased to 600°C, the temperature is directly increased to 780°C at a rate of 2°C / min, and the temperature is maintained for 10 hours after the temperature increase is completed.

[0070] In addition, the scanning electron microscope image of the lithium iron phosphate particles obtained by the comparative example is shown in FIG. 2, and the scanning electron microscope image of the lithium iron phosphate particles obtained by the embodiment 1 is shown in FIG. 3. By comparison, it can be found that the lithium iron phosphate particles obtained by the comparative example are relatively rough, have poor roundness, have poor size particle distribution, and have a large amount of free carbon on the particle surface, which affects the performance of the lithium iron phosphate particles. The lithium iron phosphate particles obtained by the embodiment 1 are smooth, have high roundness, and have no free carbon on the particle surface, and the carbon coating effect is good. The main reason is that the high-temperature calcination curve is segmented, the particle growth is slow, the carbon coating effect and particle growth are good, and the electrical performance is better. Figure 2 Figure 3

[0071] The temperature maintenance time in the first step and the temperature maintenance time in the second step can be equal or not equal.

[0072] In other embodiments, the first sintering temperature can also be 590°C, the temperature increase in the first step is 180°C, the temperature is increased to 770°C at a rate of 1.5°C / min, the temperature is maintained for 4.5 hours, the second sintering temperature can be 785°C, the temperature increase in the second step is 15°C, the temperature increase rate is controlled at 2°C / min, and the temperature is maintained for 5.5 hours.

[0073] In some embodiments, the first temperature is increased to the second sintering temperature in three steps.

[0074] ​​Specifically, the first sintering temperature is raised to the second sintering temperature in three steps, and each step is followed by a predetermined holding time. This allows the lithium iron phosphate particles to fully react during the calcination process and form an ideal crystal structure. This precise temperature control method avoids structural defects caused by excessive material growth while also ensuring the uniformity and stability of the carbon coating, thereby improving the electrochemical performance and cycle stability of the final product.

[0075] For example, in the first heating step, the temperature is raised by 150°C-200°C from the first sintering temperature. This large temperature increase can quickly reach a basic reaction temperature, saving overall sintering time while avoiding excessively rapid temperature increases that could lead to uneven material structure. In the second and third steps, the temperature is increased by 5°C-15°C, respectively. This slow heating process allows for more precise control of the crystal growth rate, facilitates the formation of a uniform and stable crystal structure, improves the carbon coating effect, and allows the carbon source to better bond with the lithium iron phosphate particles.

[0076] Furthermore, in some embodiments, the present application employs the same temperature increase in the second and third steps. This design can ensure the continuity and stability of the crystal growth process. For example, the temperature can be increased by 10°C in both the second and third steps. This allows the crystal to maintain a relatively constant growth rate throughout the growth process, which is conducive to the formation of a uniform crystal structure.

[0077] In addition, the present application also optimizes the holding time after each heating step. Specifically, the holding time in the first and second steps is equal, 3 hours, while the holding time in the third step is increased to 4 hours. Increasing the holding time in the final step can improve the crystal structure and also facilitate the full reaction and uniform coating of the carbon source.

[0078] Through precise temperature control, this application avoids the problems of excessive crystallinity, hard particles, and low roundness mentioned in the prior art. This method can control the particle growth rate while maintaining the material's crystallinity, thereby obtaining more rounded and soft particles, which is conducive to increasing the material's compaction density and, in turn, improving the electrochemical performance of the resulting battery.

[0079] As a preferred embodiment, named as Example 2, in step S300, the present application can be carried out according to the following detailed steps:

[0080] First, the spherical material is sintered in a nitrogen atmosphere with the oxygen content controlled to be less than 10 ppm, and the temperature is raised to a first sintering temperature, for example, 600°C.

[0081] Then, the first step of heating is carried out. In this step, the temperature is increased from 600°C to 760°C in increments of 160°C at a rate of 2°C / min. After the heating is completed, the temperature is kept at this temperature for 3 hours.

[0082] Next, the second heating step was carried out. In this step, the temperature was increased from 760°C to 770°C in 10°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 3 hours.

[0083] Finally, the third heating step was carried out. In this step, the temperature was increased from 770°C to 780°C in 10°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 4 hours.

[0084] The present application also provides another preferred embodiment, which is named Example 3. In step S300, the present application can be performed according to the following detailed steps:

[0085] First, the spherical material is sintered in a nitrogen atmosphere with the oxygen content controlled to be less than 10 ppm, and the temperature is raised to a first sintering temperature, for example, 600°C.

[0086] Then, the first heating step is carried out. In this step, the temperature is increased from 600°C to 770°C, with a heating range of 170°C and a heating rate controlled at 2°C / min. After the heating is completed, the temperature is kept at this temperature for 3 hours.

[0087] Next, the second heating step was carried out. In this step, the temperature was increased from 770°C to 775°C in 5°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 3 hours.

[0088] Finally, the third heating step was carried out. In this step, the temperature was increased from 775°C to 780°C in 5°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 4 hours.

[0089] Compared to existing technologies, the three-step heating method of this application can better control the growth rate and crystallinity of lithium iron phosphate particles. Rapid heating in the first step promotes the formation of initial crystal nuclei; while smaller heating steps in the second and third steps allow for fine control of crystal growth rate. This method avoids the problems of excessive crystallinity, hard particles, and low roundness mentioned in the existing technology, resulting in more rounded, soft particles, which helps improve the material's compaction density and electrochemical performance.

[0090] The insulation time in the first step and the insulation time in the second step may be equal or unequal. For example, the insulation time in the first step is 3 hours, the insulation time in the second step is 3.5 hours, and the insulation time in the third step is 4.5 hours.

[0091] As a preferred embodiment, the heating rate can be dynamically adjusted throughout the calcination process. For example, a faster heating rate (e.g., 2.5°C / min) can be used in the initial stages to improve efficiency; as the target temperature is approached, the heating rate can be reduced (e.g., 1.5°C / min) to ensure more precise temperature control. This dynamic adjustment strategy can further optimize production efficiency while ensuring material quality.

[0092] For example, in one embodiment, the calcination process of lithium iron phosphate particles uses the following steps: First, the temperature is raised from room temperature to 600°C at a heating rate of 2.0°C / min. After reaching 600°C, it is kept at this temperature for 3 hours. Then, the temperature is raised to 780°C at a rate of 1.8°C / min and kept at this temperature for another 3 hours. Finally, the temperature is raised to 795°C at a rate of 1.5°C / min and kept at this temperature for 4 hours. The entire process is carried out under a nitrogen atmosphere with an oxygen content of 5 ppm.

[0093] A comparative example is provided below for comparison with the above-mentioned Example 1, Example 2 and Example 3, and lithium iron phosphate particles are prepared respectively.

[0094] The comparative example and the above three embodiments differ only in the sintering step, and the steps for granulating the spherical materials are the same, specifically:

[0095] First, a lithium source, an iron source, and a carbon source were mixed into deionized water at a molar ratio of 1:1:0.05 to obtain a mixed solution.

[0096] Then, the mixture was sand-milled to an average particle size of 0.8 μm.

[0097] Next, the milled mixture is spray-dried and granulated into spherical materials.

[0098] Wherein, the sintering steps of the comparative example are:

[0099] The spherical material was sintered in a nitrogen atmosphere with an oxygen content of 5 ppm. During the sintering process, the temperature was first raised to 600°C.

[0100] Then directly heat to 780℃, control the heating rate at 2℃ / min, and keep warm for 10 hours.

[0101] The sintering steps of Example 1 are:

[0102] First, the spherical material was sintered in a nitrogen atmosphere with the oxygen content controlled at 5 ppm, and the temperature was raised to 600°C.

[0103] Then, the first heating step was carried out. In this step, the temperature was increased from 600°C to 770°C in increments of 170°C at a rate of 2°C / min. After the heating was completed, the temperature was kept at this temperature for 5 hours.

[0104] Next, the second heating step was carried out. In this step, the temperature was increased from 770°C to 780°C in 10°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 5 hours.

[0105] The sintering steps of Example 2 are:

[0106] First, the spherical material was sintered in a nitrogen atmosphere with the oxygen content controlled at 5 ppm, and the temperature was raised to 600°C.

[0107] Then, the first step of heating is carried out. In this step, the temperature is increased from 600°C to 760°C in increments of 160°C at a rate of 2°C / min. After the heating is completed, the temperature is kept at this temperature for 3 hours.

[0108] Next, the second heating step was carried out. In this step, the temperature was increased from 760°C to 770°C in 10°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 3 hours.

[0109] Finally, the third heating step was carried out. In this step, the temperature was increased from 770°C to 780°C in 10°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 4 hours.

[0110] The sintering steps of Example 3 are:

[0111] First, the spherical material was sintered in a nitrogen atmosphere with the oxygen content controlled at 5 ppm, and the temperature was raised to 600°C.

[0112] Then, the first heating step is carried out. In this step, the temperature is increased from 600°C to 770°C, with a heating range of 170°C and a heating rate controlled at 2°C / min. After the heating is completed, the temperature is kept at this temperature for 3 hours.

[0113] Next, the second heating step was carried out. In this step, the temperature was increased from 770°C to 775°C in 5°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 3 hours.

[0114] Finally, the third heating step was carried out. In this step, the temperature was increased from 775°C to 780°C in 5°C increments at a rate of 2°C / min. After the heating was completed, the temperature was also kept at this temperature for 4 hours.

[0115] The lithium iron phosphate particles prepared in the above comparative example, example 1, example 2 and example 3 were combined with a conductive agent (SP) and polyvinylidene fluoride (PVDF) as a positive electrode material to prepare a positive electrode sheet, and graphite as a negative electrode material to prepare a negative electrode sheet. The positive electrode sheet, a separator and the negative electrode sheet were assembled into a battery cell in a winding (button) manner, and then an electrolyte composed of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) was injected into the battery cell and sealed to obtain four lithium ion batteries.

[0116] After the positive electrode sheet was prepared, the four positive electrode sheets were subjected to a pressure test at a test pressure of 3 tons, and then the tap density after the pressure test was measured.

[0117] The four lithium ion batteries were subjected to a 1P / 1P cycle test at 35°C, and the specific test method was as follows:

[0118] (1) standing at 35°C for 30 min;

[0119] (2) 1P constant current charging to 3.65V;

[0120] (3) standing for 5 min;

[0121] (4) 1P discharging to 2.0V;

[0122] (5) standing for 5 min;

[0123] (6) repeating the above steps (2)-(5) to test the cycle until the capacity attenuation to 70% SOC (remaining capacity) of the initial capacity;

[0124] (7) standing for 5 min.

[0125] After the above test, the performance of the materials with different sintering curves at 780°C was as shown in Table 1:

[0126] Table 1

[0127]

[0128] As can be seen from the above Table 1, the positive electrode sheet prepared from the lithium iron phosphate shell obtained by the lithium iron phosphate particle preparation method of the present application has a higher tap density, and the electrical performance of the lithium battery prepared therefrom is obviously improved.

[0129] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing lithium iron phosphate particles, characterized in that: include: providing a mixed aqueous dispersion of a lithium source, an iron source, and a carbon source; preparing a spherical material using the mixed aqueous dispersion; The spherical material is placed in a protective gas atmosphere, and the temperature is first raised to a first sintering temperature, and then the first sintering temperature is gradually raised to a second sintering temperature. After each step of heating, the temperature is first kept at the heated temperature for a set time, and then the temperature is continued to be raised to the next step temperature until the temperature is raised to the second sintering temperature and kept at the second sintering temperature for a set time.

2. The method for preparing lithium iron phosphate particles according to claim 1, wherein: The first sintering temperature is 580°C-620°C, and the second sintering temperature is 740°C-820°C.

3. The method for preparing lithium iron phosphate particles according to claim 1, wherein: The first temperature is raised to a second sintering temperature in two steps.

4. The method for preparing lithium iron phosphate particles according to claim 3, wherein: The temperature is increased by 150°C to 200°C in the first step and by 5°C to 15°C in the second step.

5. The method for preparing lithium iron phosphate particles according to claim 3, wherein: The holding time after the first step of heating to the set temperature and the holding time after the second step of heating to the set temperature are equal, both of which are 5 hours.

6. The method for preparing lithium iron phosphate particles according to claim 1, wherein: The first temperature is raised to a second sintering temperature in three steps.

7. The method for preparing lithium iron phosphate particles according to claim 6, characterized in that: In the first step, the temperature is increased by 150°C to 200°C, in the second step, the temperature is increased by 5°C to 15°C, and in the third step, the temperature is increased by 5°C to 15°C.

8. The method for preparing lithium iron phosphate particles according to claim 6, characterized in that: The temperature increase in the second step is the same as that in the third step.

9. The method for preparing lithium iron phosphate particles according to claim 7, characterized in that: The insulation time after the first step is raised to the set temperature is equal to the insulation time after the second step is raised to the set temperature, both of which are 3 hours. The insulation time after the third step is raised to the set temperature is longer than the insulation time after the second step is raised to the set temperature. The insulation time after the third step is raised to the set temperature is 4 hours.

10. The method for preparing lithium iron phosphate particles according to claim 1, wherein: The heating rate during each heating step is the same, and the heating rate is 1.5°C / min-2.5°C / min.

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