Lithium iron phosphate-based positive electrode material, preparation method thereof and battery

Abstract

The invention discloses a lithium iron phosphate-based positive electrode material, a preparation method thereof and a battery. The particle size distribution curve of the lithium iron phosphate-based positive electrode material has a single peak or similar single peak type, the particle size Dp corresponding to the peak value of the single peak or similar single peak is greater than or equal to 7.5 microns, the total volume ratio Vp of particles corresponding to the peak value is greater than or equal to 6.0%, and the quantity ratio of particles with the primary particle size d greater than or equal to 600nm in the lithium iron phosphate-based positive electrode material is greater than or equal to 35%. The lithium iron phosphate-based positive electrode material disclosed by the invention is relatively large in particle size, narrow in particle size distribution and uniform in particle size, and the capacity and the rate capability are improved. The preparation method of the lithium iron phosphate-based positive electrode material can realize industrialization of the lithium iron phosphate-based positive electrode material, and the positive plate in the battery contains the lithium iron phosphate-based positive electrode material.

Description

Technical Field

[0001] This application belongs to the field of electrode materials, and particularly relates to a lithium iron phosphate-based cathode material, a preparation method thereof, and a battery containing the lithium iron phosphate-based cathode material. Background Art

[0002] Lithium iron phosphate (LiFePO 4 ) cathode materials have been widely used in the field of energy storage due to their high theoretical specific capacity, stable working voltage, excellent structural stability, good cycling performance, low raw material cost, and environmental protection characteristics. With the rapid development of mobile electronic devices, electric vehicles, and renewable energy fields, the market's requirements for the energy density and other performance of batteries are constantly increasing.

[0003] However, currently, the performance of lithium iron phosphate batteries in terms of energy density is gradually unable to meet the growing market demand. Especially in electric vehicle applications, the existing energy density is difficult to meet consumers' high requirements for driving range. This problem directly restricts the wide application of lithium iron phosphate in the field of electric vehicles and affects its market competitiveness.

[0004] In order to improve the energy density of lithium iron phosphate batteries, in recent years, researchers have begun to explore the grading strategy of using different particle size particles in order to improve the tap density of lithium iron phosphate cathode materials. This strategy aims to improve the overall performance of the material by optimizing the particle size distribution. However, in practical applications, it is found that introducing larger particles, although helpful for improving the tap density of the cathode material, often leads to a decline in its electrical performance, such as a decrease in capacity and a deterioration in rate performance. This decline in electrical performance may offset the energy density gain brought about by the increase in tap density and even lead to a loss of overall energy density.

[0005] Therefore, improving the capacity and rate performance of large particle lithium iron phosphate has become a key problem that needs to be solved urgently by researchers in this field. Summary of the Invention

[0006] The purpose of this application is to overcome the above deficiencies of the prior art, and provide a lithium iron phosphate-based cathode material, a preparation method thereof, and a battery containing the lithium iron phosphate-based cathode material, so as to solve the technical problem that the electrical properties such as capacity and rate of the existing large particle lithium iron phosphate cathode material are not ideal.

[0007] In order to achieve the above application purpose, in the first aspect, this application provides a lithium iron phosphate-based cathode material. The particle size distribution curve of the lithium iron phosphate-based cathode material of this application has a single peak or a quasi-single peak type, and the particle size D corresponding to the peak of the single peak or quasi-single peak p ≥7.5 μm, and the total volume ratio V of the particles corresponding to the peak p≥6.0%, and the proportion of particles with a primary particle size d≥600nm in the lithium iron phosphate-based cathode material is ≥35%.

[0008] The particle size distribution of the lithium iron phosphate-based cathode material of this application has the above characteristics. Its particle size is relatively large, the particle size distribution is narrow, and the particle size is uniform. Further testing found that the capacity and rate performance of the lithium iron phosphate-based cathode material with this particle size distribution and particle size characteristics have been significantly improved compared to traditional large-particle lithium iron phosphate cathode materials. Based on the particle size characteristics and electrical properties of the lithium iron phosphate-based cathode material of this application, it can be blended with small-particle lithium iron phosphate-based cathode materials to improve the tap density of the lithium iron phosphate-based cathode material.

[0009] In the second aspect of this application, a preparation method of the lithium iron phosphate-based cathode material of this application is provided. The preparation method of the lithium iron phosphate-based cathode material of this application includes the following steps:

[0010] The mixed material including iron phosphate precursor, first lithium source, and first carbon source is subjected to a first grinding treatment and then a first sintering treatment to obtain a lithium iron phosphate precursor;

[0011] The lithium iron phosphate precursor, second lithium source, and second carbon source are subjected to a second grinding treatment in a solvent to obtain a precursor slurry;

[0012] The precursor slurry is subjected to spray drying treatment and then a second sintering treatment to produce a lithium iron phosphate-based cathode material;

[0013] Wherein, during the first sintering treatment, the mixed material after the first grinding treatment is divided into multiple portions and placed in a longitudinally stratified sintering cavity respectively; and / or, during the second sintering treatment, the mixture particles formed by the spray drying treatment are divided into multiple portions and placed in a longitudinally stratified sintering cavity respectively.

[0014] The preparation method of the lithium iron phosphate-based cathode material in this application adopts two grindings combined with two sintering treatments. Moreover, the sintered material in the process of at least one sintering treatment among the two sintering treatments is divided into multiple portions, and each portion of the sintered material is respectively placed in a longitudinally layered sintering cavity for sintering treatment, so that each portion of the sintered material contacts the sintering cavity wall as much as possible, thereby reducing the proportion of the material at the central position of the sintered material, improving the uniformity of heat reception of each portion of the sintered material, significantly improving the consistency of the sintering temperature from the outer layer to the inside of each portion of the sintered material, thus significantly improving the consistency of the particle size of the lithium iron phosphate-based cathode material and having the characteristics of large particles, making the particle size of the generated lithium iron phosphate-based cathode material have the particle size characteristics of the lithium iron phosphate-based cathode material in the embodiment of this application above, and the capacity and rate performance have been significantly improved compared with the traditional large-particle lithium iron phosphate cathode material. Moreover, the sintered material in at least one sintering treatment is divided into multiple portions for simultaneous sintering treatment, effectively reducing the sintering at too high a temperature, reducing the content of impurity phases and magnetic substances in the lithium iron phosphate-based cathode material, and having high purity; it can also enable the preparation method of the lithium iron phosphate-based cathode material in this application to achieve large-scale industrial production under the existing production line of lithium iron phosphate cathode materials, improving the quality stability and efficiency of the preparation of the lithium iron phosphate-based cathode material, and reducing the production cost.

[0015] In the third aspect of this application, a battery is provided. The battery in this application includes a positive electrode sheet, and the positive electrode active material layer of the positive electrode sheet includes the lithium iron phosphate-based cathode material in this application or the lithium iron phosphate-based cathode material prepared by the preparation method in this application.

[0016] The positive electrode sheet of the battery in this application contains the above-mentioned lithium iron phosphate-based cathode material in this application. Therefore, the battery in the embodiment of this application has an energy density. Description of the Drawings

[0017] In order to more clearly illustrate the specific implementation manners of this application or the technical solutions in the prior art, the following will briefly introduce the drawings required to be used in the description of the specific implementation manners or the prior art. Obviously, the drawings in the following description are some implementation manners of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a scanning electron microscope (SEM) picture of the lithium iron phosphate precursor in Example A1;

[0019] Figure 2 It is a scanning electron microscope (SEM) picture of the lithium iron phosphate-based cathode material in Example A1;

[0020] Figure 3It is a transmission electron microscope (TEM) image of the lithium iron phosphate precursor A in Example A1;

[0021] Figure 4 It is a particle size distribution curve graph of the lithium iron phosphate-based cathode material in Example A1;

[0022] Figure 5 It is a discharge curve graph of the coin cell in Example B1 at 0.1C and 1C. Detailed implementation manners

[0023] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer and more understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] In the present application, the term "and / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0025] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression below refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0026] It should be understood that in various embodiments of the present application, the magnitude of the serial numbers of the above processes does not mean the sequence of execution. Some or all of the steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms of "a", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] In the description of the embodiments of the present application, the weight of the relevant components mentioned not only refers to the specific content of each component, but also represents the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the description of the embodiments of the present application is scaled up or down proportionally, it is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass described in the description of the embodiments of the present application may be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX. Similarly, the second XX may also be referred to as the first XX. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0030] [Lithium iron phosphate-based cathode material]

[0031] In a first aspect, the embodiments of the present application provide a lithium iron phosphate-based cathode material. In some embodiments, the particle size distribution curve of the lithium iron phosphate-based cathode material in the embodiments of the present application has a single peak or a quasi-single peak type; wherein, the particle diameter D corresponding to the single peak or quasi-single peak of the particle size distribution curve p ≥7.5 μm, and the total volume proportion V of the particles corresponding to the peak p ≥6.0%; and the proportion of the number of particles with a primary particle size d≥600 nm in the lithium iron phosphate-based cathode material is ≥35%.

[0032] In the lithium iron phosphate-based cathode material of the embodiments of the present application, its particle size distribution curve is also called a particle size distribution frequency curve, which is a curve plotted with the particle size of the lithium iron phosphate-based cathode material as the abscissa and the volume percentage content (or cumulative percentage) as the ordinate. The particle size distribution curve having a single peak or a quasi-single peak indicates that the particle size distribution on the particle size distribution curve is mainly concentrated in a specific particle size range and forms a significant and single peak. The primary particle size refers to the particle size detected by scanning electron microscopy for the lithium iron phosphate-based cathode material.

[0033] In some embodiments, the particle diameter D corresponding to the single peak or quasi-single peak of the particle size distribution curve is 7.5 μm≤D p ≤8.0 μm, and the total volume proportion V of the particles corresponding to the peak is 6.0%≤V p ≤7.5%. Optionally, D pIt can be typical but non-limiting particle size values such as 7.5μm, 7.6μm, 7.7μm, 7.8μm, 7.9μm, 8.0μm, or a range between any two particle size values. Optionally, V p It can be typical but non-limiting volume percentage values such as 6.0%, 6.2%, 6.5%, 6.7%, 7.0%, 7.4%, 7.5%, 7.8%, etc., or a range between any two volume percentage values.

[0034] The particle size distribution of the lithium iron phosphate-based cathode material in the embodiments of the present application has the above characteristics. For example, D p ≥7.5μm, V p ≥6.0% range and further ranges. Its particle size is relatively large, and the particle size distribution is narrow, and the particle sizes are uniform. After further testing, it is found that the capacity and rate performance of the lithium iron phosphate-based cathode material with this particle size characteristic have been significantly improved compared to traditional large-particle lithium iron phosphate cathode materials. Based on the particle size characteristics and electrical properties of the lithium iron phosphate-based cathode material in the embodiments of the present application, it can be blended with small-particle lithium iron phosphate-based cathode materials to improve the tap density of the lithium iron phosphate-based cathode material.

[0035] In some embodiments, the proportion of the total number of particles with a primary particle size d≥600nm in the lithium iron phosphate-based cathode material of the embodiments of the present application is ≥35%, and optionally it is 35% - 50%. Optionally, the proportion of the total number of particles with a primary particle size d≥600nm in the lithium iron phosphate-based cathode material can be typical but non-limiting volume percentage values such as 35%, 38%, 40%, 42%, 45%, 48%, 50%, etc., or a range between any two volume percentage values. Of course, the proportion of the total number of particles with a primary particle size d≥600nm in the lithium iron phosphate-based cathode material can also be more than 50%, such as it can reach 60%, 70%, 80%, etc.

[0036] In the embodiments, the average particle size of this primary particle size is 350nm - 550nm. In the exemplary embodiments, it can be typical but non-limiting particle sizes such as 350nm, 400nm, 450nm, 500nm, 550nm, etc., or a range between any two particle size values. When the proportion of the total number of particles with a primary particle size d≥600nm in the lithium iron phosphate-based cathode material is higher, the average particle size of this primary particle size is relatively larger. Containing primary particle sizes within this particle size and proportion range can improve the performance such as the tap density of the lithium iron phosphate-based cathode material and regulate the electrical properties such as the rate performance, thereby further improving the capacity and rate performance of the lithium iron phosphate-based cathode material.

[0037] In some embodiments, the D 50 particle size of the lithium iron phosphate-based cathode material is 1.0μm - 1.5μm. In the exemplary embodiments, this D50 The particle size can be typical but non-limiting particle sizes such as 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc. or the range between any two particle size values. From this D 50 particle size range, it can be seen that the particle size of the lithium iron phosphate-based cathode material in the embodiments of the present application is relatively large, and the particle size distribution of the particles is narrow, and the particle sizes are uniform. Of course, the D 50 particle size of the lithium iron phosphate-based cathode material can be controlled to be greater than 550 nm, such as it can be controlled to 570 nm, 580 nm, 600 nm, etc.

[0038] In some embodiments, the lithium iron phosphate-based cathode material in the above embodiments further contains a doping element. In the embodiments, the content of the doping element in the lithium iron phosphate-based cathode material can be 3000 ppm to 10000 ppm, optionally 4000 ppm to 8000 ppm. In exemplary embodiments, it can be typical but non-limiting contents such as 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, etc. or the range between any two content values. In the embodiments, the doping element includes at least one of Ti, V, Mg, and Nb. By doping lithium iron phosphate with these doping elements and further controlling the content and type of the doping elements within the above ranges respectively, the content of each element and its lattice arrangement in the lithium iron phosphate-based cathode material can be adjusted, thereby improving the capacity and crystal stability of the lithium iron phosphate-based cathode material. Moreover, these doping elements have good electrical conductivity and can improve the rate performance of the lithium iron phosphate-based cathode material. Of course, the content of the doping element in the lithium iron phosphate-based cathode material can also be less than 3000 ppm, such as 1000 ppm, 2000 ppm, etc., or greater than 10000 ppm, such as 11000 ppm, 12000 ppm, etc.

[0039] In some embodiments, the lithium iron phosphate-based cathode material in the above embodiments further contains carbon. The mass content of the carbon in the lithium iron phosphate-based cathode material can be 1.3% to 1.8%, optionally 1.4% to 1.5%. In exemplary embodiments, it can be typical but non-limiting contents such as 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or the range between any two content values. Setting carbon in the lithium iron phosphate-based cathode material can effectively improve the electrical conductivity of the lithium iron phosphate-based cathode material, thereby improving the rate performance of the lithium iron phosphate-based cathode material. In the embodiments, the carbon forms a carbon coating layer in the lithium iron phosphate-based cathode material, coating the lithium iron phosphate-based material particles; wherein, the thickness of the carbon coating layer can be determined by the mass content of the carbon in the lithium iron phosphate-based cathode material, such as 1.3% to 1.8%. The formation of the carbon coating layer by carbon can effectively improve the electrical conductivity of the lithium iron phosphate-based cathode material, and can also play a protective role to improve the structural stability of the lithium iron phosphate-based cathode material particles. In addition, this thickness range does not affect the large particle size characteristics of the lithium iron phosphate-based cathode material.

[0040] In some embodiments, the lithium iron phosphate-based cathode material in the above embodiments has the above particle size characteristics, or further contains doping elements or carbon. Compared with the traditional large particle lithium iron phosphate cathode material, its rate performance has been significantly improved. For example, after testing, the electrical conductivity of the lithium iron phosphate-based cathode material can be 1.1×10 -9 S / cm to 9.9×10 - 8 S / cm, and further can be 1.5×10 -8 S / cm to 8.5×10 -8 S / cm.

[0041] In some embodiments, the lithium iron phosphate-based cathode material in the above embodiments has the above particle size characteristics, and its tap density has been significantly improved compared with the traditional large particle lithium iron phosphate cathode material. For example, after testing, the tap density of the lithium iron phosphate-based cathode material ≥2.50 g / cm 3 , and further can be 2.50 g / cm 3 to 2.65 g / cm 3 .

[0042] In some embodiments, the lithium iron phosphate-based cathode material in the above embodiments has the above particle size characteristics, and its capacity has been significantly improved compared with the traditional large particle lithium iron phosphate cathode material. For example, after testing, the discharge specific capacity of the lithium iron phosphate-based cathode material under 1C condition ≥135 mAh / g, and further can be 135 mAh / g to 150 mAh / g.

[0043] [Preparation Method of Lithium Iron Phosphate-Based Cathode Material]

[0044] Second aspect, embodiments of the present application also provide a method for preparing the above-mentioned lithium iron phosphate-based cathode material. The method for preparing the lithium iron phosphate-based cathode material according to the embodiments of the present application includes the following steps:

[0045] S10: The mixed material including the iron phosphate precursor, the first lithium source, and the first carbon source is subjected to a first grinding treatment and then a first sintering treatment to obtain a lithium iron phosphate precursor;

[0046] S20: The mixed material including the lithium iron phosphate precursor, the second lithium source, and the second carbon source is subjected to a second grinding treatment in a solvent to obtain a precursor slurry;

[0047] S30: The precursor slurry is subjected to spray drying treatment and then a second sintering treatment to generate a lithium iron phosphate-based cathode material.

[0048] In the method for preparing the lithium iron phosphate-based cathode material according to the embodiments of the present application, during the first sintering treatment in step S10, the mixed material including the iron phosphate precursor, the first lithium source, and the first carbon source is divided into multiple portions after the first grinding treatment and is respectively placed in a longitudinally stratified sintering cavity for the first sintering treatment. Or / and, in the second sintering treatment in step S30, the mixture particles formed by the spray drying treatment are divided into multiple portions and are respectively placed in a longitudinally stratified sintering cavity for the second sintering treatment. Herein, or / and means that either one of the first sintering treatment and the second sintering treatment or both sintering treatments divide the sintered material into multiple portions, and the multiple portions of the sintered material are placed in a longitudinally stratified sintering cavity for sintering. The fact that the mixed material in step S10 and the mixture particles in step S30 are divided into multiple portions means two or more portions, and correspondingly, the number of layers of the longitudinally stratified sintering cavity is also two or more, such that one portion of the sintered material is placed in each layer of the sintering cavity, such as one portion of the mixed material or mixture particles is placed in each layer of the sintering cavity. The longitudinally stratified sintering cavity can be understood as a sintering cavity that is divided into cavities arranged in a stacked manner in the vertical direction.

[0049] In the conventional methods for preparing large-particle lithium iron phosphate cathode materials, it is often achieved by increasing the sintering temperature. However, if the sintering temperature is too high, the risk of generating impurity phases and magnetic substances also increases. Generally, the raw material components are mixed in proportion and stacked together and then sent to a sintering furnace, such as an ordinary graphite crucible. However, due to the different actual heating temperatures at different positions in the sintering furnace and the significant differences in the outer and inner temperatures of the stacked materials, for example, when sintering in an ordinary graphite crucible, due to the good heat transfer effect of the graphite material, the materials near the crucible wall and the upper surface layer experience a higher actual temperature and are prone to generating large particles; while the materials at the center position of the crucible experience a lower actual temperature and are prone to generating small particles, which results in non-uniform particle sizes in the finished product. In this way, the particle size of the lithium iron phosphate cathode material in the finished product is non-uniform, and the proportion of large particles cannot be effectively increased, thus actually making it impossible to effectively prepare lithium iron phosphate cathode materials with large particles and relatively uniform particle sizes.

[0050] However, the method for preparing the lithium iron phosphate-based cathode material in the embodiment of the present application adopts two grindings combined with two sintering treatments, and divides the sintered material in the process of at least one of the two sintering treatments into multiple portions, and places each portion of the sintered material in a longitudinally stratified sintering cavity for sintering treatment, so that each portion of the sintered material contacts the sintering cavity wall as much as possible, reducing the proportion of the material at the center position of the sintered material, significantly improving the consistency of the sintering temperature from the outer layer to the inner part (the material at the center position) of each portion of the sintered material, enabling the sintered material to be sintered under the same sintering conditions as much as possible, improving the consistency of the particles formed by the sintered material after sintering treatment, thus significantly improving the consistency of the particle size of the lithium iron phosphate-based cathode material and the characteristics of having large particles, making the particle size of the generated lithium iron phosphate-based cathode material have the particle size characteristics of the lithium iron phosphate-based cathode material in the embodiment of the present application above, and the capacity and rate performance are significantly improved compared with the traditional large-particle lithium iron phosphate cathode material.

[0051] In addition, the method for preparing the lithium iron phosphate-based cathode material in the embodiment of the present application adopts two sintering treatments and divides the sintered material in at least one of the sintering treatments into multiple portions and places them in a longitudinally stratified sintering cavity for simultaneous sintering treatment, effectively avoiding the use of too high a sintering temperature, so that the content of impurity phases and magnetic substances in the lithium iron phosphate-based cathode material is low; and there is no need to carry out large-scale transformation on the existing production line of lithium iron phosphate cathode materials, enabling the method for preparing the lithium iron phosphate-based cathode material in the embodiment of the present application to achieve large-scale industrial production based on the existing production line of lithium iron phosphate cathode materials, improving the quality stability and efficiency of preparing the lithium iron phosphate-based cathode material, and reducing the production cost.

[0052] Step S10:

[0053] Preparing a lithium iron phosphate precursor from an iron phosphate precursor, a first lithium source, and a first carbon source provides a basis for preparing a large-particle lithium iron phosphate-based cathode material.

[0054] In some embodiments, the addition amount of the first carbon source in step S10 satisfies that the mass content of carbon in the generated lithium iron phosphate precursor is 0.2% to 0.8%; and / or, the generated lithium iron phosphate precursor has a core-shell structure, which includes an iron phosphate particle core and a carbon coating layer covering the iron phosphate particle core, and the thickness of the carbon coating layer ≤ 5 nm. That is, carbon is contained in the lithium iron phosphate precursor, and its content can be 0.2% to 0.8%, or further, carbon forms a carbon coating layer in the lithium iron phosphate precursor. Controlling the addition amount of the first carbon source within the above range can effectively improve the conductivity of the lithium iron phosphate precursor. On this basis, the lower carbon content and smaller carbon layer thickness have little restraint on the growth of the generated lithium iron phosphate precursor, which can make the particles of the lithium iron phosphate precursor grow relatively larger, improving the particle size and specific capacity of the lithium iron phosphate precursor.

[0055] In some embodiments, the first carbon source may include at least one of glucose, sucrose, polyethylene glycol, and starch. Optionally, the first carbon source is at least one of glucose and polyethylene glycol. These types of first carbon sources can be effectively carbonized to form carbon during the first sintering treatment, improving the conductivity of the lithium iron phosphate precursor, and at the same time, the generated carbon can act as a reducing agent to improve the performance such as the specific capacity of the lithium iron phosphate precursor.

[0056] In some embodiments, the molar ratio of the first lithium source to the iron phosphate precursor in step S10 is (0.980 - 1.000):1. Controlling the addition amount of the first lithium source within this range can increase the content of active lithium ions, thereby increasing the capacity of the lithium iron phosphate precursor.

[0057] In some embodiments, the first lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium oxalate, lithium oxide, and lithium dihydrogen phosphate. Optionally, it includes lithium carbonate and lithium hydroxide. These lithium sources are rich in lithium and can improve the purity of the lithium iron phosphate precursor.

[0058] In some embodiments, the iron phosphate precursor selected in step S10 uses a raw material with an atomic ratio of iron to phosphorus of (0.950 - 0.965):1.

[0059] In some embodiments, the specific surface area of the particles of the iron phosphate precursor in step S10 is 4m 2 / g to 10m 2 / g, and can be selected as 4.0m 2 / g to 8.0m 2 / g. In exemplary embodiments, it can be 4m 2 / g, 5m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 Typical but non-limiting specific surface areas such as / g, or the range between any two specific surface area values.

[0060] Selecting the iron-to-phosphorus atomic ratio range and specific surface area of the iron phosphate precursor as described above has relatively high structural stability and high wear resistance, which helps to obtain a relatively large particle size after the first grinding. After the first sintering treatment, the particle size of the generated lithium iron phosphate precursor is increased.

[0061] In some embodiments, in the mixture of step S10, a dopant is further mixed. The addition amount of the dopant is such that in the lithium iron phosphate precursor, the content of the doping element contained in the dopant is greater than 0 and less than or equal to 4000 ppm, optionally 1500 ppm to 2500 ppm. At this time, in the generated lithium iron phosphate precursor, a doping element is also contained, and the content of the doping element is greater than 0 and less than or equal to 4000 ppm.

[0062] In the embodiments, the doping element of the dopant may include at least one of titanium (Ti), vanadium (V), magnesium (Mg), and niobium (Nb). That is, the dopant may be at least one of a titanium-containing compound, a vanadium-containing compound, a magnesium-containing compound, a niobium-containing compound, etc. For example, in the exemplary embodiment, the titanium-containing compound dopant may include at least one of titanium dioxide, titanium sulfate, titanium fluoride, titanium nitride, titanium carbide, titanium boride, magnesium titanate, etc.; the vanadium-containing compound may include at least one of vanadium oxide, vanadium tetroxide, vanadium pentoxide, vanadium chloride, potassium metavanadate, sodium metavanadate, ammonium metavanadate, vanadium boride, vanadium carbide, vanadium diselenide, etc.; the magnesium-containing compound may include at least one of magnesium oxide, magnesium fluoride, magnesium nitrate, magnesium acetate, magnesium carbonate, magnesium titanate, magnesium nitride, magnesium carbide, magnesium boride, etc.; the niobium-containing compound may include at least one of niobium oxide, niobium fluoride, niobium nitride, niobium carbide, niobium oxalate, potassium niobate, magnesium niobate, niobium pentachloride, niobium hydroxide, niobium iodide, niobium selenide, ammonium hexafluoroniobate, etc.

[0063] By adding a dopant to the mixture and further controlling and adjusting the addition amount and type of the dopant, it is possible to make the doping element participate in the formation of the lithium iron phosphate precursor crystal, obtain a doped lithium iron phosphate precursor, thereby improving the performance such as the capacity and crystal structure stability of the lithium iron phosphate precursor, and also increasing the particle size of the lithium iron phosphate precursor particles.

[0064] Before the first sintering treatment of the mixed material in step S10, the first grinding treatment can effectively adjust and control the particle sizes of the raw materials. For example, it can make the particle sizes of the raw materials relatively uniform and improve the dispersion uniformity of the raw material particles. In some embodiments, the first grinding treatment in step S10 includes the following treatment steps:

[0065] S11: Grind the mixed material in a solvent to obtain a mixture slurry;

[0066] S12: Perform spray drying on the mixture slurry to obtain a ground mixed material.

[0067] In step S11, grinding the mixed material in a solvent can effectively improve the mixing uniformity of the components in the mixture and the uniformity of the particle sizes. In the embodiment, after the grinding treatment in step S11, the solid particles D in the mixture slurry 50 have a particle size of 0.4 μm to 0.8 μm. By adjusting the particle size of the particles in the mixture slurry within this range, the particle size of the mixed material can be increased, thereby increasing the particle size of the lithium iron phosphate precursor generated by the first sintering treatment and reducing the generation of small particle lithium iron phosphate precursors.

[0068] In the embodiment, the solvent for this grinding treatment can be the raw material solvent for conventional grinding of electrode materials, such as at least one of water and ethanol. Among them, the water meets the water requirements for applications in the battery field, such as pure water, etc.

[0069] In step S12, the spray drying treatment can effectively remove the solvent and can control the particle size of the mixed material, so as to control the particle size of the iron phosphate precursor, such as increasing the particle size of the iron phosphate precursor and improving the particle size uniformity.

[0070] During the first sintering treatment in step S10, the first carbon source will be carbonized to form carbon, or further form a coating layer. On the one hand, it can act as a reducing agent to improve the stability of the valence of iron elements; on the other hand, it can act as a conductive agent to improve the conductivity of the lithium iron phosphate precursor; at the same time, it can also adjust the particle size of the lithium iron phosphate precursor.

[0071] In some embodiments, when the mixed material is divided into multiple portions spaced from each other during the first sintering process in step S10, the multiple portions of the mixed material can be respectively placed in a sintering cavity with longitudinal layers, such as placing one portion of the mixed material in each layer of the sintering cavity. The sintering cavity with longitudinal layers can be multiple-layer saggers or formed by vertically stacking multiple saggers. Since each portion of the mixed material is respectively placed in each layer of the sagger, the contact area between the mixed material and the layered sagger is effectively increased, which is equivalent to increasing the temperature conduction area of the mixed material. It can quickly transfer the sintering temperature of the layered sagger to each portion of the mixed material, thereby improving the consistency between the outer temperature and the inner temperature of each portion of the mixed material, and thus increasing the particle size and uniformity of the lithium iron phosphate precursor. At the same time, the generation of impurity phases and magnetic substances caused by too high sintering temperature is avoided, thereby improving the purity of the lithium iron phosphate precursor.

[0072] In some embodiments, the first sintering process can be carried out in a continuous sintering cavity. Using a continuous sintering cavity for the first sintering process can improve the sintering efficiency of the mixed material and enable large-scale industrial continuous production. At the same time, since the mixed material is divided into multiple portions and placed respectively in the longitudinally layered sintering cavity, the consistency between the outer temperature and the inner temperature of each portion of the mixed material is improved, thereby increasing the particle size and uniformity of the lithium iron phosphate precursor.

[0073] In the embodiment, when the mixed material is separated into multiple portions, and each portion of the mixed material accounts for 1 / 9 - 1 / 2 of the total mass of the mixed material. At this time, the number of layers and quantity of the longitudinally layered sintering cavity, such as the layered sagger, can be determined according to the number of portions into which the mixed material is separated. In the demonstration example, the mixed material can be separated into 2 portions, 3 portions, 4 portions, 5 portions, 6 portions, 7 portions, 8 portions, 9 portions, 10 portions, or more portions. The more the mixed material is separated, the more uniform the sintering temperature of the mixed material during the sintering process, thereby further improving the uniformity of the generated lithium iron phosphate particles and increasing the particle size.

[0074] In some embodiments, the temperature of the first sintering can be 750°C - 820°C, and the holding time is 8h - 20h. The first sintering temperature and time can increase the particle size of the generated lithium iron phosphate precursor particles.

[0075] In some embodiments, through the above control of the conditions for preparing the lithium iron phosphate precursor in step S10, the particle size of the prepared lithium iron phosphate precursor can be 0.8μm ≤ D 50 ≤ 2.0μm, optionally 1.0μm ≤ D 50≤1.2 μm. In exemplary embodiments, it can be typical but non-limiting particle sizes such as 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, etc., or a range between any two particle size values. Controlling the particle size of the lithium iron phosphate precursor within this range can effectively adjust the particle size of the final lithium iron phosphate-based cathode material, such that the lithium iron phosphate-based cathode material has the particle size characteristics of the lithium iron phosphate-based cathode material in the embodiments of the present application above.

[0076] In some embodiments, the percentage by number of particles with a primary particle size ≥ 600 nm in the lithium iron phosphate precursor prepared in step S10 in the lithium iron phosphate precursor ≥ 15%, optionally 15% - 25%. Having a primary particle size within this particle size range and content range can increase the proportion of the number of particles with a primary particle size d ≥ 600 nm in the lithium iron phosphate-based cathode material formed by subjecting the precursor to the second sintering treatment.

[0077] Step S20:

[0078] In step S20, grinding the lithium iron phosphate precursor, the second lithium source, and the second carbon source in a solvent can effectively improve the mixing uniformity of raw materials such as the lithium iron phosphate precursor, the second lithium source, and the second carbon source, as well as the uniformity of particle size.

[0079] In some embodiments, after the grinding treatment in step S20, the solid particles D in the precursor slurry 50 have a particle size of 0.80 μm - 1.2 μm. In exemplary embodiments, it can be typical but non-limiting particle sizes such as 0.80 μm, 0.90 μm, 1.0 μm, 1.1 μm, 1.2 μm, etc., or a range between any two particle size values. By adjusting the particle size of the particles in the precursor slurry within this range, the particle size of the lithium iron phosphate-based cathode material formed by the second sintering treatment can be increased.

[0080] In an embodiment, the solvent for the grinding treatment in step S20 can be a raw material solvent for conventional grinding of electrode materials, such as at least one of water and ethanol. Among them, the water meets the water requirements for applications in the battery field, such as pure water, etc.

[0081] In some embodiments, the addition amount of the second carbon source in step S20 is 0.5 wt.% to 1.2 wt.% of the mass of the lithium iron phosphate-based cathode material. Controlling the addition amount of the second carbon source within the above range can effectively improve the conductivity of the lithium iron phosphate-based cathode material, and on this basis, can improve the stability of the valence of iron element in the lithium iron phosphate precursor, and improve the specific capacity and particle size of the lithium iron phosphate-based cathode material. By controlling the addition and addition amount of the first carbon source in step S10 and the second carbon source in step S20, the total carbon mass content in the finally generated lithium iron phosphate-based cathode material can be 1.3 wt.% to 1.8 wt.% as described above, effectively improving the rate performance of the lithium iron phosphate-based cathode material.

[0082] In some embodiments, the second carbon source may include at least one of glucose, sucrose, polyethylene glycol, and starch. Optionally, the second carbon source is at least one of glucose and polyethylene glycol, which may be the same as or different from the first carbon source in step S10. These types of second carbon sources can be effectively carbonized to form carbon during the second sintering treatment, improving the conductivity of the lithium iron phosphate precursor, and at the same time, the generated carbon can act as a reducing agent to improve the stability of the valence of iron element during the second sintering process, thereby improving the performance such as the specific capacity of the lithium iron phosphate-based cathode material.

[0083] In some embodiments, the molar ratio of the second lithium source to the lithium iron phosphate precursor in step S20 is (0.02 - 0.05):1. Controlling the addition amount of the second lithium source within this range can further adjust the content of highly active lithium ions in the lithium iron phosphate-based cathode material, thereby improving the capacity of the lithium iron phosphate-based cathode material.

[0084] In some embodiments, the second lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium oxalate, lithium oxide, and lithium dihydrogen phosphate. Optionally, it includes lithium carbonate and lithium hydroxide. These lithium sources are rich in lithium and can improve the purity of the lithium iron phosphate-based cathode material.

[0085] In some embodiments, a dopant is further mixed in the mixture in step S20, and the addition amount of the dopant is such that the content of the doping element contained in the dopant in the lithium iron phosphate-based cathode material can be 4000 ppm to 6000 ppm, optionally 4000 ppm to 5000 ppm. At this time, in the generated lithium iron phosphate-based cathode material, the content of the doping element is 4000 ppm to 6000 ppm.

[0086] In the embodiments, the doping elements of the dopant may include at least one of titanium (Ti), vanadium (V), magnesium (Mg), and niobium (Nb). That is, the dopant may be at least one of a titanium-containing compound, a vanadium-containing compound, a magnesium-containing compound, a niobium-containing compound, etc. For example, in the exemplary embodiment, the titanium-containing compound dopant may include at least one of titanium dioxide, titanium sulfate, titanium fluoride, titanium nitride, titanium carbide, titanium boride, and magnesium titanate; the vanadium-containing compound may include at least one of vanadium oxide, vanadium dioxide, vanadium pentoxide, vanadium chloride, potassium metavanadate, sodium metavanadate, ammonium metavanadate, vanadium boride, vanadium carbide, and vanadium diselenide; the magnesium-containing compound may include at least one of magnesium oxide, magnesium fluoride, magnesium nitrate, magnesium acetate, magnesium carbonate, magnesium titanate, magnesium nitride, magnesium carbide, and magnesium boride; the niobium-containing compound may include at least one of niobium oxide, niobium fluoride, niobium nitride, niobium carbide, niobium oxalate, potassium niobate, magnesium niobate, niobium pentachloride, niobium hydroxide, niobium iodide, niobium selenide, and ammonium hexafluoroniobate. Additionally, the dopant in step S20 may be the same as or different from the dopant in step S10.

[0087] By further adding a dopant in step S20 and further controlling and adjusting the addition amount and type of the dopant, it is possible to enable the doping elements to participate in the formation of the lithium iron phosphate-based cathode material crystal, thereby improving the performance such as the capacity and crystal structure stability of the lithium iron phosphate-based cathode material, and also increasing the particle size of the lithium iron phosphate-based cathode material particles.

[0088] S30:

[0089] In step S30, spray drying treatment can effectively remove the solvent and can control the particle size of the precursor particles after drying, so as to control the particle size of the lithium iron phosphate-based cathode material, such as increasing the particle size of the lithium iron phosphate-based cathode material and improving the particle size uniformity.

[0090] During the second sintering treatment in step S30, the second carbon source will be carbonized to form carbon. Similar to the first carbon source in step S10, on the one hand, it can act as a reducing agent to maintain the stability of the iron element valence; on the other hand, it can act as a conductive agent to improve the conductivity of the lithium iron phosphate-based cathode material, and at the same time, it can also adjust the particle size of the lithium iron phosphate-based cathode material.

[0091] In some embodiments, when the mixture particles formed after spray drying the precursor slurry are divided into multiple portions spaced apart from each other during the second sintering process in step S30, the mixture particles can be divided into multiple portions in the same way as the method of dividing the mixed material into multiple portions for the first sintering process in step S10, and the multiple portions of mixture particles are respectively placed in a longitudinally layered sintering cavity such as a layered crucible, for example, one portion of the mixed material particles is placed in each layer of the crucible. Since each portion of the mixed material is respectively placed in each layer of the crucible, the contact area between the mixture particles and the layered crucible is effectively increased, which is equivalent to increasing the temperature conduction area of the mixture particles. It can quickly transfer the temperature in the sintering cavity to each portion of the mixture particles, thereby improving the consistency between the outer temperature and the inner temperature of each portion of the mixture particles, and thus increasing the particle size and uniformity of the lithium iron phosphate-based cathode material.

[0092] In some embodiments, the second sintering process can also be carried out in a continuous sintering cavity. Using a continuous sintering cavity for the second sintering can improve the sintering efficiency of the mixture particles and enable large-scale industrial continuous production. At the same time, since the mixture particles are divided into multiple portions and respectively placed in a longitudinally layered sintering cavity such as a layered crucible, the consistency between the outer temperature and the inner temperature of each portion of the mixture particles is improved, thereby increasing the particle size and uniformity of the lithium iron phosphate-based cathode material.

[0093] In the embodiment, when the mixture particles are divided into multiple portions, each portion of the mixture particles accounts for 1 / 9 to 1 / 2 of the total mass of the mixture particles. At this time, the number of layers and the quantity of the longitudinally layered sintering cavity such as the layered crucible can be determined according to the number of portions into which the mixture particles are divided. In the demonstration example, the mixture particles can be divided into 2 portions, 3 portions, 4 portions, 5 portions, 6 portions, 7 portions, 8 portions, 9 portions, 10 portions, or more portions. The more the mixture particles are divided, the more uniform the sintering temperature of the mixture particles during the second sintering process, thereby further improving the uniformity of the generated lithium iron phosphate-based cathode material and increasing the particle size.

[0094] In some embodiments, the temperature of the second sintering in step S30 can be 750 °C to 820 °C, and the holding time is 8 h to 20 h. This second sintering temperature and time can increase the particle size of the generated lithium iron phosphate precursor particles.

[0095] In some embodiments, after the second sintering process in step S30, it further includes a step of pulverizing the sintered material of the second sintering process to make the particles of the sintered material meet the application requirements. For example, in the embodiment, the pulverizing process can include a step of jet milling. Using jet milling can improve the particle size classification efficiency of the lithium iron phosphate-based cathode material and improve the large-scale industrial production of the lithium iron phosphate-based cathode material in the embodiments of the present application.

[0096] In the embodiments, the conditions for the jet milling treatment include at least one of the following (1) to (3):

[0097] (1) The classification frequency is 20 Hz to 50 Hz;

[0098] (2) The pressure intensity is 0.3 MPa to 0.5 MPa;

[0099] (3) The feeding rate is 2 kg / h to 10 kg / h.

[0100] These jet milling treatments can improve the efficiency of the milling treatment and the particle size classification efficiency of the lithium iron phosphate-based cathode material, thereby improving the particle size uniformity of the lithium iron phosphate-based cathode material.

[0101] [Battery]

[0102] In a third aspect, the embodiments of the present application further provide a battery. The battery in the embodiments of the present application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a separator or a solid electrolyte, and of course, other necessary or auxiliary components. Among them, the separator or the solid electrolyte is disposed between the positive electrode sheet and the negative electrode sheet. When the battery in the embodiments of the present application is an ion battery, it includes a separator; when the battery in the embodiments of the present application is a solid-state battery, it includes a solid electrolyte.

[0103] Among them, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer bonded to the surface of the positive electrode current collector. In the embodiments, the positive electrode current collector of the positive electrode sheet can be, but is not limited to, any one of copper foil and aluminum foil.

[0104] The positive electrode active material layer of the positive electrode sheet includes components such as a positive electrode active material, a binder, and a conductive agent, or further may include a lithium supplement material.

[0105] The positive electrode active material in the positive electrode active material layer includes the lithium iron phosphate-based cathode material in the above embodiments of the present application.

[0106] Since the positive electrode sheet of the battery in the embodiments of the present application contains the above-mentioned lithium iron phosphate-based cathode material of the embodiments of the present application, therefore, the battery in the embodiments of the present application has relatively high electrical properties such as capacity and rate performance. Further, the positive electrode active material in the positive electrode active material layer may further include other positive electrode active materials that are graded with the lithium iron phosphate-based cathode material in addition to the lithium iron phosphate-based cathode material, so as to improve the tap density of the positive electrode active material, thereby further improving the capacity of the battery.

[0107] In the embodiment, the content of the binder in the positive electrode active material layer can be 2 wt% to 4 wt%. In a specific embodiment, the content of the binder can be typical but non-limiting contents such as 2 wt%, 3 wt%, 4 wt%, etc. In a specific embodiment, the binder includes one or more of polyvinylidene fluoride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0108] In the embodiment, the content of the conductive agent in the positive electrode active material layer can be 3 wt% to 5 wt%. In a specific embodiment, the content of the conductive agent can be typical but non-limiting contents such as 3 wt%, 4 wt%, 5 wt%, etc. In a specific embodiment, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C 60 and carbon nanotubes.

[0109] In the embodiment, the preparation process of the positive electrode can be: mixing components such as positive electrode active material, conductive agent, and binder to obtain a positive electrode slurry, coating the positive electrode slurry on a current collector, and preparing the positive electrode through steps such as drying, rolling, and die-cutting.

[0110] The negative electrode sheet contained in the battery of the embodiment of the present application can be a conventional negative electrode sheet. When the negative electrode sheet is a lithium metal foil, the lithium battery of the embodiment of the present application can be a lithium metal battery.

[0111] The battery of the embodiment of the present application can be assembled according to the assembly methods of existing wound core batteries, cylindrical batteries, or stacked core batteries.

[0112] The following uses multiple specific embodiments to illustrate the lithium iron phosphate-based positive electrode material, its preparation method, battery, etc. of the embodiment of the present application.

[0113] 1. Embodiment of lithium iron phosphate-based positive electrode material and its preparation method:

[0114] Embodiment A1:

[0115] This embodiment provides a lithium iron phosphate-based positive electrode material and its preparation method. The particle size characteristics of the lithium iron phosphate-based positive electrode material are shown in Table 1 below.

[0116] The preparation method of the lithium iron phosphate-based positive electrode material in this embodiment includes the following steps:

[0117] S1. Prepare a lithium iron phosphate precursor:

[0118] S11: Weigh 100 kg of iron phosphate (the iron to phosphorus ratio is 0.965, and the specific surface area is 4.36 m 2 / g), 25.3 kg of lithium carbonate, 1 kg of glucose, 1 kg of polyethylene glycol and 0.25 kg of titanium dioxide are mixed and proportioned, and after being stirred evenly, the first sanding is carried out, and the particle size D of the sanding slurry is controlled 50 to be 0.50 μm, the mixture slurry;

[0119] S12: The mixture slurry prepared in step S11 is spray-dried, and the spray-dried mixture particles are respectively loaded into two graphite crucibles with dimensions of 340 mm × 340 mm × 160 mm. The loading amount of each crucible is 9 kg. Then, the two crucibles filled with materials are stacked vertically and put into a roller hearth kiln for the first high-temperature sintering treatment. The sintering temperature is 800 °C, and the heat preservation time is 10 h to obtain the lithium iron phosphate precursor;

[0120] S2. Sinter the lithium iron phosphate precursor to prepare the lithium iron phosphate-based cathode material:

[0121] Take 100 kg of the lithium iron phosphate precursor prepared in step S1, mix it evenly with 2.6 kg of lithium carbonate, 667.6 g of titanium dioxide, 7 kg of glucose and 4 kg of polyethylene glycol, and then carry out the second sanding, controlling the D50 of the sanding slurry to be 0.80 μm. Subsequently, spray drying is carried out, and then the dried mixed material is loaded into two graphite crucibles with the same dimensions as in step S12. The loading amount of each crucible is 9 kg. Then, the two graphite crucibles filled with materials are stacked vertically and put into a roller hearth kiln for the second sintering treatment. The sintering temperature is 780 °C, and the heat preservation time is 10 h; the cooled material is subjected to air flow pulverization, and the pulverization parameters are: the classification frequency is 20 Hz, the pressure intensity is 0.4 MPa, and the feeding rate is 5 kg / h. The product obtained after pulverization is the high-capacity large-particle lithium iron phosphate-based cathode material.

[0122] Example A2:

[0123] This Example A2 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference is that in the first sintering treatment in S1 and the second sintering treatment in S2 in Example A2, the materials are respectively put into three graphite crucibles with dimensions of 340 mm × 340 mm × 120 mm. The loading amount of each crucible is 6 kg. Then, the three crucibles filled with materials are stacked vertically and sent into a roller hearth kiln for sintering.

[0124] Example A3:

[0125] Example A3 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference lies in that in the first sintering treatment in S1 and the second sintering treatment in S2 in Example A3, the materials are respectively placed into four graphite crucibles with dimensions of 340 mm × 340 mm × 90 mm, the loading amount in each crucible is 4.5 kg, and then the four loaded crucibles are stacked vertically and sent into a roller hearth kiln for sintering.

[0126] Example A4:

[0127] Example A4 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference lies in that in the first sintering treatment in S1 and the second sintering treatment in S2 in Example A4, the materials are respectively placed into five graphite crucibles with dimensions of 340 mm × 340 mm × 70 mm, the loading amount in each crucible is 3.6 kg, and then the five loaded crucibles are stacked vertically and sent into a roller hearth kiln for sintering.

[0128] Example A5:

[0129] This Example A5 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference lies in that 667.6 g of titanium dioxide in step S2 of Example A1 is changed to 803.9 g of vanadium pentoxide in this Example A5.

[0130] Example A6:

[0131] This Example A6 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference lies in that the iron-to-phosphorus ratio of iron phosphate in step S1 of Example A1 is changed to 0.955, and other parameters remain unchanged.

[0132] Example A7:

[0133] This Example A7 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the lithium iron phosphate-based cathode material in Example A1, the difference lies in that the addition amount of titanium dioxide in step S11 of Example A1 is controlled to be 416.7 g and the addition amount of titanium dioxide in step S2 is controlled to be 833.5 g, so that the Ti metal doping amount in the final lithium iron phosphate-based cathode material is 7500 ppm, and other parameters remain unchanged.

[0134] Example A8:

[0135] Example A8 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference is that the addition amount of titanium dioxide in step S1 of Example A1 is changed to 0.67 kg, and other parameters remain unchanged.

[0136] Example A9:

[0137] Example A9 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference is that the specific surface area of iron phosphate in step S1 of Example A1 is adjusted to 5.5 m 2 / g, and other parameters remain unchanged.

[0138] Example A10:

[0139] Example A10 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference includes:

[0140] The phosphorus-iron ratio in iron phosphate in step S1 of Example A1 is 0.950, and the specific surface area is 4.0 m 2 / g; the proportion of the number of primary particles of lithium iron phosphate with a size of ≥600 nm is 53.3%.

[0141] Comparative Example A1:

[0142] Comparative Example A1 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A1, the difference is that step S2 in Example A1 is not included, that is, the lithium iron phosphate-based cathode material in this Comparative Example A1 is the lithium iron phosphate precursor prepared in step S1 of Example A1.

[0143] Comparative Example A2:

[0144] Comparative Example A2 provides a lithium iron phosphate-based cathode material and a preparation method thereof. Compared with the preparation method of the lithium iron phosphate-based cathode material in Example A2, the difference is that during the first sintering in step S1 and the second sintering in step S2 of Example A1, the sintering treatment is carried out in a common single graphite crucible that is not layered.

[0145] 2. Detection of relevant properties of the lithium iron phosphate-based cathode material:

[0146] 2.1 Particle size detection method for lithium iron phosphate-based cathode materials (including lithium iron phosphate precursors): The lithium iron phosphate-based cathode materials (including lithium iron phosphate precursors) in the above-mentioned examples were respectively analyzed by scanning electron microscopy (SEM), and the particle size characteristics of the lithium iron phosphate-based cathode materials were measured according to the SEM images; among them, the SEM image of the lithium iron phosphate precursor in Example A1 is as shown in Figure 1 , and the SEM image of the lithium iron phosphate-based cathode material in Example A1 is as shown in Figure 2 . As can be seen from Figure 1 , the particle morphology of the lithium iron phosphate precursor prepared in Example A1 presents a spherical-like shape, and the proportion of particles with a primary particle size d≥600nm is 19.7%. As can be seen from Figure 2 and Figure 4 , the particle morphology of the lithium iron phosphate-based cathode material prepared in Example A1 presents a uniformly dispersed spherical-like structure, the proportion of particles with a primary particle size d≥200nm is 41.6%, and the average size of the primary particle size is 466.8nm.

[0147] 2.2 Transmission electron microscopy (TEM) analysis of lithium iron phosphate-based cathode materials (including lithium iron phosphate precursors): The lithium iron phosphate-based cathode materials (including lithium iron phosphate precursors) in the above-mentioned examples were respectively analyzed by TEM; among them, the TEM image of lithium iron phosphate precursor A in Example A1 is as shown in Figure 3 . As can be seen from Figure 3 and Table 1, the Ti doping amount in the lithium iron phosphate precursor prepared in Example A1 is 1398ppm, the carbon content is 0.23wt.%, and the carbon layer thickness is significantly ≤5nm. The thinner carbon layer can reduce the binding to the particles, and the lower doping amount and carbon content are beneficial to the growth of lithium iron phosphate particles.

[0148] 2.3 Particle size distribution analysis of lithium iron phosphate-based cathode materials: The lithium iron phosphate-based cathode materials in the above-mentioned examples were respectively analyzed for particle size distribution; among them, the particle size distribution curve of the lithium iron phosphate-based cathode material in Example A1 is as shown in Figure 4 . As can be seen from Figure 4 , the particle size D 50 of the lithium iron phosphate-based cathode material prepared in Example A1 is 1.17μm, and its particle size distribution curve presents a quasi-single peak type, where the particle size D p corresponding to the highest peak intensity is 7.64μm, and the volume proportion V p corresponding to the highest peak intensity is 6.20%.

[0149] Table 1

[0150]

[0151]

[0152] As can be seen from Table 1, the carbon content of the lithium iron phosphate-based cathode materials in Examples A1 to A10 was maintained at 1.3 wt.% to 1.5 wt.%, the total amount of doped metals detected by ICP was maintained at 4000 ppm to 8000 ppm, and the tap density was ≥2.50 g / cm 3 .

[0153] Further comparing Example A1, Example A7, and Example A9, it can be seen that as the iron-to-phosphorus ratio and the doping elements increase, the particle size of the lithium iron phosphate-based cathode material decreases instead, and the particle size D corresponding to the peak of the particle size distribution curve p and the tap density also decrease, but they are all better than the relevant performance data of the lithium iron phosphate-based cathode materials in Comparative Example A1 and Comparative Example A2.

[0154] Combined with Figure 2 、 Figure 4 and Table 2, it can be seen that for the lithium iron phosphate-based cathode materials in Examples A1 to A10, 1.0 μm ≤ D 50 ≤ 1.5 μm, and their particle size distribution curves show a single or quasi-single peak type. The particle size D corresponding to the highest peak intensity p ≥ 7.5 μm, and the volume fraction Vp corresponding to the highest peak intensity ≥ 6.0%; the proportion of the number of primary particle sizes d ≥ 600 nm ≥ 35%, and the average size of the primary particle sizes is 350 nm to 550 nm. However, the particles of the lithium iron phosphate-based cathode materials in Comparative Example A1 and Comparative Example A2 often do not meet the above particle size and distribution.

[0155] 2. Lithium-ion battery examples:

[0156] Examples B1 to B11 and Comparative Examples B1 to B2 of the present invention each provide a lithium-ion battery. Each lithium-ion battery is assembled into a sub-lithium-ion battery according to the following method:

[0157] 2.1 Positive electrode sheet:

[0158] Using the lithium iron phosphate-based cathode materials provided in Examples A1 to A11 and Comparative Examples A1 to A2 as the cathode materials of the lithium-ion batteries in Examples B1 to B11 and Comparative Examples B1 to B2 respectively, and preparing the positive electrode sheets of each example of the lithium-ion battery according to the following method:

[0159] (1) Preparation of the positive electrode slurry. 2.33 kg of the positive electrode active material, 0.012 kg of superconducting carbon black (SP), and 0.048 kg of the binder polyvinylidene fluoride (PVDF) are simultaneously added to an agate ball milling tank with a volume of 500 mL, and then 1.6 kg of the solvent N-methylpyrrolidone (NMP) is added. The mixture is ball milled at a rotation speed of 360 r / min for 4 h to obtain the positive electrode slurry;

[0160] (2) Coating of the positive electrode slurry: Adjust the scale of the doctor blade of the coater, and evenly coat the ball-milled slurry on the aluminum foil. Place the coated electrode sheet in a vacuum drying oven at a temperature of 130 °C and bake for 3 h;

[0161] (3) Rolling and punching: Place the aluminum foil coated with the slurry flat in the middle position between the rollers and roll the positive electrode sheet; Press the front side of the rolled positive electrode sheet tightly against the punched area and punch the sheets in sequence; Place the punched positive electrode sheet in a vacuum drying oven at a temperature of 130 °C and bake for 3 h;

[0162] 2.2 Negative electrode sheet: Lithium sheet;

[0163] 2.3 Electrolyte: Lithium hexafluorophosphate (LiPF 6 ) solution;

[0164] 2.4 Separator: 20μm - PP.

[0165] 2.5 Assembling the button cell: In the glove box, assemble the button cell in the order of the negative electrode case, spring piece, steel sheet, lithium sheet, separator, positive electrode sheet, and positive electrode case. Inject 10 μL of electrolyte during the process, and then use a sealer to seal the button cell.

[0166] 3. Related performance testing of the button cell:

[0167] Perform the related performance tests on the button cells assembled in each example in Section 2 as shown in Table 2 below, and the measured results are shown in Table 2 below.

[0168] Among them, the methods for the related performance tests in Table 2 are as follows:

[0169] Test method for discharge capacity: At room temperature of 25 °C, discharge each button cell at a constant current of 0.1C with a cut-off voltage of 2.0V; and discharge at a constant current of 1C with a cut-off voltage of 2.0V, and measure the discharge capacity of each button cell. Among them, the discharge curves of the button cell in Example B1 at 0.1C and 1C are as Figure 5 shown.

[0170] Test method for capacity retention rate: Under the condition of 25 °C, discharge at 1C, and after 100 cycles, calculate the capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity of the first cycle) × 100%.

[0171] Table 2

[0172]

[0173] From Figure 5As can be seen from Table 2, the button cells prepared in Examples B1 to B10 can still maintain a stable capacity of more than 135 mAh / g at 1C, showing excellent electrochemical performance and rate performance, and can also maintain good cycle stability. This reflects that the lithium iron phosphate-based cathode material contained in the button cell has excellent discharge capacity and rate performance.

[0174] The above embodiments only illustrate several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A lithium iron phosphate-based positive electrode material, characterized in that: The particle size distribution curve of the lithium iron phosphate-based positive electrode material has a single peak or a quasi-single peak type, and the particle size D corresponding to the peak value of the single peak or the quasi-single peak is p ≥7.5μm, the total volume of particles corresponding to the peak value accounts for V p ≥6.0%, and the number of particles with a primary particle size d≥600nm in the lithium iron phosphate-based positive electrode material accounts for ≥35%.

2. The lithium iron phosphate-based positive electrode material according to claim 1, characterized in that: The average particle size of the primary particles is 350nm to 550nm; and / or The lithium iron phosphate-based positive electrode material further contains a doping element, the content of the doping element in the lithium iron phosphate-based positive electrode material is 3000ppm to 10000ppm, and / or the doping element includes at least one of Ti, V, Mg, and Nb; and / or The lithium iron phosphate-based positive electrode material further comprises carbon, and the content of the carbon is 1.3 wt.% to 1.8 wt.%.

3. The lithium iron phosphate-based positive electrode material according to claim 1 or 2, characterized in that: The D of the lithium iron phosphate-based positive electrode material 50 Particle size is 1.0 μm to 1.5 μm; and / or The particle size D corresponding to the peak value of the single peak or quasi-single peak p 7.5 μm to 8.0 μm; and / or The total volume proportion of the particles corresponding to the peak value is V p 6.0% to 7.5%; and / or The number of particles with a primary particle size of d≥600 nm accounts for 35% to 50%.

4. A method for preparing a lithium iron phosphate-based positive electrode material, characterized in that: The steps include: Subjecting a mixture of a ferric phosphate precursor, a first lithium source and a first carbon source to a first grinding process and then to a first sintering process to obtain a lithium iron phosphate precursor; Performing a second grinding process on the lithium iron phosphate precursor, the second lithium source and the second carbon source in a solvent to obtain a precursor slurry; The precursor slurry is spray-dried and then subjected to a second sintering process to generate a lithium iron phosphate-based positive electrode material; Wherein, during the first sintering process, the mixed material after the first grinding process is divided into a plurality of portions and respectively placed in longitudinally layered sintering cavities; And / or, in the second sintering process, the mixture particles formed by the spray drying process are divided into a plurality of portions and respectively placed in longitudinally layered sintering cavities.

5. The preparation method according to claim 4, characterized in that: The longitudinally layered sintering chamber comprises a multi-layer sagger; and / or The sintering conditions of the first sintering process and the second sintering process are the same or different as follows: The sintering temperature is 750℃~820℃, and the holding time is 8h~20h.

6. The preparation method according to claim 4 or 5, characterized in that: The mixed material is divided into multiple portions, and each portion accounts for 1 / 9 to 1 / 2 of the total mass of the mixed material; and / or The mixture particles are divided into multiple portions, and each portion accounts for 1 / 9 to 1 / 2 of the total mass of the mixture particles.

7. The preparation method according to claim 4 or 5, characterized in that: The iron phosphate precursor includes at least one of the following (1) to (2): (1) The atomic ratio of iron to phosphorus in the iron phosphate precursor is (0.950-0.965):1; (2) The specific surface area of ​​the iron phosphate precursor particles is 4 m 2 / g~10m 2 / g; and / or The lithium iron phosphate precursor includes at least one of the following (3) to (5): (3) The lithium iron phosphate precursor contains carbon, and the mass content of the carbon in the lithium iron phosphate precursor is 0.2% to 0.8%; and / or the carbon forms a carbon coating layer, and the thickness of the carbon coating layer is ≤5nm; (4) containing a doping element, and the content of the doping element in the iron phosphate precursor is greater than 0 and less than or equal to 4000 ppm, and / or the doping element includes at least one of Ti, V, Mg, and Nb; (5) The percentage of particles with a primary particle size of ≥600 nm in the lithium iron phosphate precursor is ≥15%.

8. The preparation method according to claim 4 or 5, characterized in that: The mixture slurry after the first grinding treatment is subjected to spray drying treatment; and / or The first milled slurry D 50 Particle size is 0.40μm~0.8μm; and / or The mixed material is further mixed with a dopant, wherein the content of the doping element contained in the dopant in the iron phosphate precursor is greater than 0 and less than or equal to 4000 ppm; and / or The molar ratio of the first lithium source to the iron phosphate precursor is (0.980-1.000):

1.

9. The preparation method according to claim 4 or 5, characterized in that: A dopant is also added during the grinding process, wherein the doping element contained in the dopant includes at least one of Ti, V, Mg, and Nb; and / or the content of the doping element contained in the dopant in the iron phosphate precursor is 4000ppm to 6000ppm; and / or, The molar ratio of the lithium iron phosphate precursor to the second lithium source is 1:(0.02-0.05); and / or The amount of the second carbon source added is 0.5wt.% to 1.2wt.% of the mass of the lithium iron phosphate-based positive electrode material; and / or The second grinding slurry particle size D 50 0.80 μm to 1.2 μm; and / or After the second sintering process, the process further includes performing air flow crushing on the sintered material of the second sintering process.

10. A battery, comprising a positive electrode sheet, characterized in that: The positive electrode active material layer of the positive electrode sheet comprises the lithium iron phosphate-based positive electrode material according to any one of claims 1 to 3 or the lithium iron phosphate-based positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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