Lithium iron phosphate materials and their preparation methods, cathode sheets, batteries, energy storage devices and energy storage systems

Abstract

This application discloses lithium iron phosphate materials and their preparation methods, positive electrode sheets, batteries, energy storage devices, and energy storage systems. The lithium iron phosphate materials include: secondary lithium iron phosphate particles and bulk lithium iron phosphate particles, wherein the bulk lithium iron phosphate particles are adhered to and / or embedded in the surface of the secondary lithium iron phosphate particles.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion batteries, specifically relating to a lithium iron phosphate material and its preparation method, a positive electrode, a battery, an energy storage device, and an energy storage system. Background Technology

[0002] Currently, the primary cathode material used in lithium-ion batteries is lithium iron phosphate (LFP), which has an olivine crystal structure and good safety and stability. Lithium batteries increasingly strive for high capacity; however, one method to improve the capacity performance of LFP is to reduce the particle size range and achieve smooth, predominantly spherical particle surfaces. These characteristics are beneficial for shortening the Li-Phase Ionization Cycle. + Migration paths enhance material dynamics, thereby enabling high capacity utilization. However, this material characteristic easily causes particle slippage and deformation, leading to excessive electrode elongation during rolling of the manufactured positive electrode, resulting in processing problems such as roller idling and electrode edge cracking, thus affecting the industrial application of the material. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to provide a lithium iron phosphate material and its preparation method, a positive electrode, a battery, an energy storage device, and an energy storage system. Thus, this application ensures that the lithium iron phosphate material has high capacity performance while effectively hindering particle deformation and slippage, thereby reducing the elongation of the positive electrode formed from the lithium iron phosphate material.

[0004] In one aspect of this application, a lithium iron phosphate material is provided. According to an embodiment of this application, the lithium iron phosphate material comprises:

[0005] Lithium iron phosphate secondary particles and blocky lithium iron phosphate particles, wherein the blocky lithium iron phosphate particles are adhered to and / or embedded in the surface of the lithium iron phosphate secondary particles.

[0006] The lithium iron phosphate material according to embodiments of this application includes secondary lithium iron phosphate particles and bulk lithium iron phosphate particles, with the bulk lithium iron phosphate particles adhered to and / or embedded on the surface of the secondary lithium iron phosphate particles. The secondary lithium iron phosphate particles facilitate the high capacity performance of the lithium iron phosphate material; the adhesion and / or embedding of the bulk lithium iron phosphate particles on the surface of the secondary lithium iron phosphate particles effectively hinders particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed from the lithium iron phosphate material, and thus effectively avoiding processing problems that occur during rolling of the positive electrode sheet. Therefore, this application ensures high capacity performance of the lithium iron phosphate material while effectively hindering particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed from the lithium iron phosphate material.

[0007] In addition, the lithium iron phosphate material according to the above embodiments of this application may also have the following additional technical features:

[0008] In some embodiments of the present application, the lithium iron phosphate secondary particles are formed from lithium iron phosphate primary nanoparticles.

[0009] In some embodiments of the present application, the average contact area between the lithium iron phosphate secondary particles and the massive lithium iron phosphate particles does not exceed 35% of the plane area of the lithium iron phosphate secondary particles.

[0010] In some embodiments of the present application, the average contact area between the lithium iron phosphate secondary particles and the massive lithium iron phosphate particles is 10% to 30% of the plane area of the lithium iron phosphate secondary particles.

[0011] In some embodiments of the present application, the massive lithium iron phosphate particles are elongated lithium iron phosphate particles.

[0012] In some embodiments of the present application, the average long diameter of the massive lithium iron phosphate particles is not greater than 6.2 μm, preferably not greater than 5 μm.

[0013] In some embodiments of the present application, the particle size Dv50 of the lithium iron phosphate material is 6 μm to 9.5 μm, preferably 6 μm to 8.5 μm.

[0014] In some embodiments of the present application, the lithium iron phosphate material comprises titanium element, and the chemical structural formula of the lithium iron phosphate material is LiFe x Ti y PO4, wherein x+y=1, 0<y≤0.05, preferably 0<y≤0.04.

[0015] In a second aspect of the present application, the present application provides a method for preparing the above lithium iron phosphate material, comprising:

[0016] (1) Weighing an iron source, a phosphorus source and a lithium source according to the required stoichiometric ratio for LiFePO4, and preparing a mixed metal salt solution;

[0017] (2) Placing the mixed metal salt solution, a precipitant solution and a complexing agent solution in a reaction kettle for reaction to obtain massive lithium iron phosphate;

[0018] (3) Weighing an iron source, a phosphorus source and a lithium source according to the required stoichiometric ratio for LiFePO4, weighing a carbon source and mixing them uniformly, adding a dispersant, and performing ball milling;

[0019] (4) Performing spray drying on the ball-milled material;

[0020] (5) Performing first sintering on the spray-dried material under a protective atmosphere, and crushing the same to obtain a first sintered material;

[0021] (6) mixing the first sintered material with the bulk lithium iron phosphate, and conducting spray drying to obtain a mixed powder;

[0022] (7) performing second sintering on the mixed powder under a protective atmosphere, and grinding and crushing to obtain a lithium iron phosphate material.

[0023] According to an embodiment of the present application, there is provided a method for preparing the above lithium iron phosphate material. In the method, bulk lithium iron phosphate particles are first formed, primary lithium iron phosphate particles are then formed, and finally the primary lithium iron phosphate particles are agglomerated to form secondary lithium iron phosphate particles, and the bulk lithium iron phosphate particles are adhered and / or embedded on the surface of the secondary lithium iron phosphate particles, so as to finally obtain the lithium iron phosphate material with special particle surface morphology. Accordingly, the method can effectively hinder particle deformation and slip while ensuring that the lithium iron phosphate material has high capacity performance, thereby reducing the elongation of a positive electrode sheet formed from the lithium iron phosphate material.

[0024] In some embodiments of the present application, in step (1), according to LiFe x Ti y PO₄, an iron source, a phosphorus source, a lithium source and a titanium source are weighed according to a required stoichiometric ratio, and the mixed metal salt solution is prepared, wherein x+y=1 and 0<y≤0.05.

[0025] In some embodiments of the present application, in step (2), the reaction temperature of the mixed metal salt solution, the precipitant solution and the complexing agent solution in a reaction kettle is 180°C to 220°C, the reaction time is 8h to 10h, and the pH of the reaction system is 9 to 11; and / or, in step (2), the precipitant solution comprises a strong alkali solution of 0.5mol / L to 1.5mol / L; and / or, in step (2), the complexing agent solution comprises an ammonia water solution of 0.5mol / L to 1.5mol / L.

[0026] In some embodiments of the present application, in step (3), according to LiFe x Ti y PO₄, an iron source, a phosphorus source, a lithium source and a titanium source are weighed according to a required stoichiometric ratio, wherein x+y=1 and 0<y≤0.05; and / or, in step (3), the mass of the carbon source is 20% to 25% of the total mass of the iron source, the phosphorus source, the lithium source and the titanium source.

[0027] In some embodiments of the present application, in step (5), the temperature of the first sintering is 650°C to 720°C, and the time of the first sintering is 5h to 8h.

[0028] In some embodiments of the present application, in step (6), the mass of the bulk lithium iron phosphate is 5% to 35% of the mass of the first sintered material.

[0029] In some embodiments of this application, in step (7), the temperature of the second sintering is 760°C to 800°C, and the time of the second sintering is 6h to 14h.

[0030] In a third aspect, this application proposes a positive electrode sheet. According to embodiments of this application, the positive electrode sheet comprises the lithium iron phosphate material of the first aspect of this application, or the lithium iron phosphate material prepared using the method of the second aspect. This allows the positive electrode sheet to maintain good high-rate performance while reducing its elongation. It should be noted that the features and advantages described above for the lithium iron phosphate material and its preparation method also apply to this positive electrode sheet.

[0031] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes a positive electrode sheet as described in the third aspect. This allows the battery to maintain good high-rate performance while reducing the elongation of the positive electrode sheet. In an embodiment of this application, the battery can be a lithium-ion battery.

[0032] A fifth aspect of this application discloses an energy storage device. According to an embodiment of this application, the energy storage device includes the battery described in the above embodiments. Therefore, the energy storage device possesses all the advantages of the battery described in the above embodiments, which will not be repeated here.

[0033] A sixth aspect of this application discloses an energy storage system. According to an embodiment of this application, the energy storage system includes: the battery or the energy storage device described in the above embodiments. Therefore, the energy storage system possesses all the advantages of the battery or the energy storage device, which will not be elaborated further here.

[0034] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0035] Figure 1 This is a surface morphology diagram of the lithium iron phosphate material prepared in Example 1;

[0036] Figure 2 This is an enlarged surface morphology image of the lithium iron phosphate material prepared in Example 1;

[0037] Figure 3 The surface morphology of the lithium iron phosphate material prepared in Comparative Example 1 is shown.

[0038] Figure 4 This is an enlarged surface morphology image of the lithium iron phosphate material prepared in Comparative Example 1;

[0039] Figure 5This is a schematic diagram of the particle size distribution of lithium iron phosphate materials prepared in Example 1 and Comparative Example 1;

[0040] Figure 6 This is a schematic diagram of the positive electrode rolling process and a schematic diagram of the positive electrode elongation measurement method;

[0041] Figure 7 This is a schematic diagram of the structure of an energy storage system according to some embodiments of this application;

[0042] Figure 8 This is a schematic diagram of the structure of an energy storage system according to some embodiments of this application;

[0043] Figure 9 This is a schematic diagram of the structure of an energy storage system according to some embodiments of this application. Detailed Implementation

[0044] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0045] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In one aspect of this application, a lithium iron phosphate material with a special particle surface morphology is proposed. According to an embodiment of this application, the lithium iron phosphate material includes: secondary lithium iron phosphate particles and bulk lithium iron phosphate particles, wherein the bulk lithium iron phosphate particles are adhered to and / or embedded on the surface of the secondary lithium iron phosphate particles. Therefore, this application, while ensuring high capacity performance of the lithium iron phosphate material, can also effectively prevent particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed by the lithium iron phosphate material.

[0047] It should be noted that "blocky" refers to three-dimensional, independent, and clearly defined entities (in contrast to spherical particles), with irregular or regular geometric shapes, such as... Figure 2 The material that adheres to and / or is embedded in the surface of the lithium iron phosphate secondary particles can be in the form of long strips or non-long strips.

[0048] The principle by which the lithium iron phosphate material proposed in this application achieves the above-mentioned beneficial effects will be explained in detail below:

[0049] The lithium iron phosphate material of this application includes secondary lithium iron phosphate particles and bulk lithium iron phosphate particles, with the bulk lithium iron phosphate particles adhered to and / or embedded on the surface of the secondary lithium iron phosphate particles. The secondary lithium iron phosphate particles facilitate the high-capacity performance of the lithium iron phosphate material; the adhesion and / or embedding of the bulk lithium iron phosphate particles on the surface of the secondary lithium iron phosphate particles effectively hinders particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed from the lithium iron phosphate material, and thus effectively avoiding processing problems that occur during the rolling process of the positive electrode sheet.

[0050] According to some specific embodiments of this application, the above-mentioned secondary lithium iron phosphate particles are formed by the agglomeration of primary lithium iron phosphate nanoparticles, which further facilitates the high capacity performance of lithium iron phosphate materials.

[0051] Furthermore, the aforementioned secondary lithium iron phosphate particles are spherical particles formed by the agglomeration of primary lithium iron phosphate nanoparticles, which further enhances the high capacity performance of lithium iron phosphate materials.

[0052] According to some specific embodiments of this application, the average contact area between the secondary lithium iron phosphate particles and the bulk lithium iron phosphate particles does not exceed 35% of the planar area of ​​the secondary lithium iron phosphate particles. For example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or any range between the two. By limiting the average contact area between the secondary lithium iron phosphate particles and the bulk lithium iron phosphate particles to the above range, while ensuring that the lithium iron phosphate material has high capacity performance, it can further effectively prevent particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed by the lithium iron phosphate material.

[0053] According to some preferred embodiments of this application, the average contact area between the secondary lithium iron phosphate particles and the bulk lithium iron phosphate particles does not exceed 10% to 30% of the planar area of ​​the secondary lithium iron phosphate particles. By limiting the average contact area between the secondary lithium iron phosphate particles and the bulk lithium iron phosphate particles to the above range, it is possible to further ensure that the lithium iron phosphate material has high capacity performance, while further effectively preventing particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed by the lithium iron phosphate material.

[0054] In this application, instruments and methods known in the art can be used to determine the proportion of the average contact area between the lithium iron phosphate secondary particles and the blocky lithium iron phosphate particles in the planar area of ​​the lithium iron phosphate secondary particles. As a specific example, a scanning electron microscope is used to take photographs at several magnifications (e.g., 5,000x), and image recognition software (e.g., ImageJ) is used to measure the large particles (i.e., lithium iron phosphate secondary particles). The planar area of ​​the large particles (i.e., lithium iron phosphate secondary particles) and the cumulative planar area of ​​the elongated particles (i.e., blocky lithium iron phosphate particles) on the surface of the large particles (i.e., lithium iron phosphate secondary particles) are calculated to obtain the planar area value. The ratio of the two is the proportion of the average contact area between the lithium iron phosphate secondary particles and the blocky lithium iron phosphate particles in the planar area of ​​the lithium iron phosphate secondary particles. Photographs from multiple (e.g., 5) different regions are selected, the operation is repeated, and the average value is calculated.

[0055] It should be noted that, since the above-mentioned test method for the average contact area ratio between secondary lithium iron phosphate particles and blocky lithium iron phosphate particles uses scanning electron microscopy to take photographs and image recognition software to measure and calculate the planar area of ​​the secondary lithium iron phosphate particles, this application limits the measurement to the proportion of the average contact area between secondary lithium iron phosphate particles and blocky lithium iron phosphate particles in the planar area of ​​the secondary lithium iron phosphate particles. Furthermore, in the test method, since photographs of multiple different areas are taken repeatedly and the average value is calculated, the calculated result is the average contact area.

[0056] According to some specific embodiments of this application, the above-mentioned blocky lithium iron phosphate particles are elongated lithium iron phosphate particles, thereby further effectively hindering particle deformation and slippage, and thus reducing the elongation of the positive electrode sheet formed by lithium iron phosphate material.

[0057] According to some specific embodiments of this application, the average major diameter of the aforementioned bulk lithium iron phosphate particles is no greater than 6.2 μm, and can be, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.2 μm, or any range between the two. By limiting the average major diameter of the aforementioned bulk lithium iron phosphate particles to the above range, particle deformation and slippage can be effectively prevented, while avoiding easy breakage caused by excessively large average major diameter of the bulk lithium iron phosphate particles, thereby further facilitating the reduction of the elongation of the positive electrode sheet formed from lithium iron phosphate material. Preferably, the average major diameter of the aforementioned bulk lithium iron phosphate particles is no greater than 5 μm.

[0058] In the present application, instruments and methods well known in the art can be used to measure the average major diameter of the above-mentioned blocky lithium iron phosphate particles. As a specific example, photographs at several magnifications (e.g., 3000× magnification) are taken with a scanning electron microscope, the major diameters of the blocky lithium iron phosphate particles on large particles (i.e., secondary lithium iron phosphate particles) are measured using graphic recognition software (e.g., ImageJ), the operation is repeated to count a number of particles (e.g., 100 particles), and the average value is calculated.

[0059] It should be noted that the major diameter of the above-mentioned blocky lithium iron phosphate particle refers to the maximum displayable size of the blocky lithium iron phosphate particle on a large particle (i.e., secondary lithium iron phosphate particle) in a photograph taken by a scanning electron microscope. In addition, in the testing method, since the operation is repeated to count the major diameters of the blocky lithium iron phosphate particles on a number of large particles (i.e., secondary lithium iron phosphate particles) and the average value is calculated, the result obtained is the average major diameter.

[0060] According to some other specific embodiments of the present application, the particle size Dv50 of the above lithium iron phosphate material is 6 μm to 9.5 μm, for example, it can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or a range between any two of the above values. By limiting the Dv50 of the lithium iron phosphate material within the above range, it is further beneficial to improve the capacity performance of the lithium iron phosphate material. Preferably, the particle size Dv50 of the above lithium iron phosphate material is 6 μm to 8.5 μm. Wherein, Dv50 refers to the corresponding particle size when the cumulative volume percentage of the lithium iron phosphate material reaches 50%.

[0061] In the present application, instruments and methods well known in the art can be used to measure the particle size Dv50 of the lithium iron phosphate material. As a specific example, a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000) is used to measure the particle size distribution of the lithium iron phosphate material in accordance with the national standard GB / T19077-2016 for particle size distribution laser diffraction method.

[0062] According to some other specific embodiments of the present application, the lithium iron phosphate material includes titanium element, and the chemical structural formula of the lithium iron phosphate material is LiFe x Ti y PO4, wherein x+y=1, 0<y≤0.05 (for example, y can be 0.01, 0.02, 0.03, 0.04, 0.05, or a range between any two of the above values), preferably 0<y≤0.04. That is, titanium element is doped into the lithium iron phosphate material, and by doping titanium element into the lithium iron phosphate material, the high capacity performance of the lithium iron phosphate material can be further effectively improved.

[0063] According to some other specific embodiments of the present application, the surface of the lithium iron phosphate material is provided with a carbon coating layer, thereby effectively improving the electrical conductivity of the lithium iron phosphate material.

[0064] In a second aspect of the present application, the present application provides a method for preparing the above lithium iron phosphate material. According to an embodiment of the present application, the method comprises:

[0065] S100: weighing an iron source, a phosphorus source and a lithium source according to the required stoichiometric ratio in LiFePO4, and preparing a mixed metal salt solution;

[0066] According to some specific embodiments of the present application, according to LiFe x Ti y weighing an iron source, a phosphorus source, a lithium source and a titanium source according to the required stoichiometric ratio in PO4, and preparing a mixed metal salt solution, wherein x+y=1, 0<y≤0.05, preferably 0<y≤0.04. Thereby, titanium element can be doped in bulk lithium iron phosphate, and by doping titanium element in bulk lithium iron phosphate, the high capacity performance of bulk lithium iron phosphate can be further effectively improved.

[0067] In the embodiment of the present application, the specific types of the above-mentioned iron source, phosphorus source, lithium source and titanium source are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the iron source may be ferrous oxalate, ferric sulfate, ferric chloride, or the like. As some other specific embodiments, the phosphorus source may be phosphoric acid, ammonium dihydrogen phosphate, or the like. As some other specific embodiments, the lithium source may be lithium carbonate, lithium hydroxide, or the like. As some other specific embodiments, the titanium source may be titanium tetrachloride, titanium oxalate, or the like.

[0068] In the embodiment of the present application, the specific type of the solvent of the mixed metal salt solution is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific embodiments, the solvent of the mixed metal salt solution may be deionized water.

[0069] S200: placing the mixed metal salt solution, the precipitant solution and the complexing agent solution in a reaction vessel, and reacting to obtain bulk lithium iron phosphate;

[0070] In this step, the mixed metal salt solution, the precipitant solution and the complexing agent solution are placed in a reaction kettle, continuously stirred, synthesized through precipitation combination reaction, and bulk lithium iron phosphate is prepared after solid-liquid separation, washing and drying.

[0071] According to some specific embodiments of this application, the reaction temperature of the mixed metal salt solution, precipitant solution, and complexing agent solution in the reactor is 180℃~220℃ (e.g., 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.), the reaction time is 8h~10h (e.g., 8h, 8.5h, 9h, 9.5h, 10h, etc.), and the pH of the reaction system is 9~11 (e.g., 9, 9.5, 10, 10.5, 11, etc.). By limiting the reaction temperature, time, and pH of the reaction system in the reactor to the above ranges, it can be further ensured that the mixed metal salt solution, precipitant solution, and complexing agent solution react fully in the reactor to obtain blocky lithium iron phosphate material, preferably strip-shaped lithium iron phosphate material.

[0072] In the embodiments of this application, the specific type of the precipitant solution is not particularly limited. Those skilled in the art can select it according to actual needs. As some specific embodiments, the precipitant solution includes a strong alkaline solution of 0.5 mol / L to 1.5 mol / L, such as a sodium hydroxide solution or potassium hydroxide solution of 0.5 mol / L to 1.5 mol / L.

[0073] In the embodiments of this application, the specific type of complexing agent solution is not particularly limited. Those skilled in the art can select it according to actual needs. As some specific embodiments, the complexing agent solution includes an ammonia solution of 0.5 mol / L to 1.5 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0074] According to some specific embodiments of this application, step S200 further includes the following steps:

[0075] A certain amount of carbon source is weighed and uniformly mixed with the blocky lithium iron phosphate obtained in step S200. The mixture is then placed in an inert atmosphere (e.g., nitrogen atmosphere) sintering furnace for calcination, and after crushing, blocky lithium iron phosphate material is obtained, preferably elongated lithium iron phosphate material. In this step, the role of the carbon source is to form a carbon coating layer on the surface of the blocky lithium iron phosphate during calcination, thereby effectively improving the conductivity of the blocky lithium iron phosphate. Furthermore, the mass of the added carbon source is 10% to 15% of the mass of the blocky lithium iron phosphate obtained in step S200, for example, 10%, 11%, 12%, 13%, 14%, 15%, etc., which further contributes to improving the conductivity of the lithium iron phosphate material.

[0076] The specific type of carbon source in the above steps is not particularly limited, including but not limited to at least one of glucose and sucrose.

[0077] S300: Weigh an iron source, a phosphorus source, and a lithium source according to the required stoichiometric ratio in LiFePO4, weigh the carbon source, mix them uniformly, add a dispersant, and perform ball milling;

[0078] In this step, weigh the iron source, phosphorus source, and lithium source according to the required stoichiometric ratio in LiFePO4, then weigh a certain amount of carbon source and mix them uniformly, add the mixture to a ball mill for uniform mixing, then add an appropriate amount of dispersant (such as water), and then perform high-energy ball milling to ball mill the raw materials into particles of a suitable size. Among them, the iron source, phosphorus source, and lithium source form primary lithium iron phosphate particles in the subsequent first sintering. The carbon source in this step can inhibit the growth of primary lithium iron phosphate particles during the subsequent first sintering, which is conducive to the formation of nano-sized primary particles. Meanwhile, the carbon source in this step can also form a carbon coating layer on the surface of the primary particles during the subsequent first sintering.

[0079] According to some other specific embodiments of the present application, according to the required stoichiometric ratio in LiFe x Ti y PO4, weigh an iron source, a phosphorus source, a lithium source, and a titanium source, wherein x+y=1 and 0<y≤0.05. Thus, titanium element can be doped into the primary lithium iron phosphate particles formed in subsequent steps. Doping titanium element into the primary lithium iron phosphate particles can further effectively improve the high-capacity performance of the primary lithium iron phosphate particles, thereby facilitating the exertion of the high-capacity performance of the secondary lithium iron phosphate particles.

[0080] According to some other specific embodiments of the present application, the mass of the above carbon source is 20% to 25% of the total mass of the iron source, phosphorus source, lithium source and titanium source, for example, it can be 20%, 21%, 22%, 23%, 24%, 25% or a range between any two of the above values. Therefore, it is further favorable for inhibiting the growth of primary lithium iron phosphate particles, further favorable for forming nano-sized primary particles, meanwhile further favorable for forming a carbon coating layer on the surface of the primary particles, and further favorable for improving the electrical conductivity of the lithium iron phosphate material.

[0081] The specific type of the carbon source in the above step S300 is not particularly limited, including but not limited to at least one of glucose and sucrose.

[0082] S400: Perform spray drying on the ball-milled material;

[0083] In this step, the ball-milled material is subjected to spray drying to form powder with a certain particle size.

[0084] S500: Under a protective atmosphere, the spray-dried material is subjected to the first sintering, and after being crushed by ball milling, the first sintered material is obtained;

[0085] In this step, the spray-dried material is subjected to a first sintering under a protective atmosphere (e.g., nitrogen atmosphere), and then ball-milled to obtain the first sintered material. During the first sintering process, iron, phosphorus, and lithium sources form primary lithium iron phosphate particles. Titanium is doped into the lithium iron phosphate lattice. The carbon source can inhibit the growth of primary lithium iron phosphate particles during this process, which is beneficial to the formation of nanoscale primary particles. At the same time, the carbon source can also form a carbon coating layer on the surface of the primary particles during the first sintering process.

[0086] According to some specific embodiments of this application, the first sintering temperature is 650℃~720℃ (e.g., it can be 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃ or any range between two), and the first sintering time is 5h~8h (e.g., it can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h or any range between two). This further facilitates the formation of primary lithium iron phosphate particles.

[0087] S600: The first sintering material and blocky lithium iron phosphate are mixed and spray-dried to obtain a mixed powder;

[0088] In this step, the first sintering material and the bulk lithium iron phosphate are mixed evenly and then spray-dried to obtain a mixed powder with a certain particle size. The first sintering material can form secondary lithium iron phosphate particles in the subsequent second sintering process, with the bulk lithium iron phosphate particles adhering to and / or embedded on the surface of the secondary lithium iron phosphate particles.

[0089] According to some specific embodiments of this application, the mass of the bulk lithium iron phosphate is 5% to 35% of the mass of the first sintering material, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or any range between the two. By limiting the mass of the bulk lithium iron phosphate to the above range, it can be further ensured that a suitable amount of bulk lithium iron phosphate particles adhere to and / or embed on the surface of the secondary lithium iron phosphate particles, thereby further improving the capacity performance of the lithium iron phosphate material while effectively preventing particle deformation and slippage, and further reducing the elongation of the positive electrode sheet formed by the lithium iron phosphate material. Preferably, the mass of the bulk lithium iron phosphate is 5% to 30% of the mass of the first sintering material.

[0090] S700: Under a protective atmosphere, the mixed powder is subjected to a second sintering, then ground and crushed to obtain lithium iron phosphate material.

[0091] In this step, the mixed powder is subjected to a second sintering under a protective atmosphere (e.g., nitrogen atmosphere), followed by ball milling to obtain lithium iron phosphate material with a special particle surface morphology. During the second sintering process, primary lithium iron phosphate particles agglomerate to form secondary lithium iron phosphate particles, and blocky lithium iron phosphate particles adhere to and / or embed on the surface of the secondary lithium iron phosphate particles.

[0092] According to some specific embodiments of this application, the second sintering temperature is 760℃~800℃ (e.g., it can be 760℃, 765℃, 770℃, 775℃, 780℃, 785℃, 790℃, 795℃, 800℃, or any range between the two), and the second sintering time is 6h~14h (e.g., it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or any range between the two). By limiting the temperature and time of the second sintering within the above ranges, it is further ensured that the primary lithium iron phosphate particles agglomerate to form secondary lithium iron phosphate particles, and it is further ensured that the blocky lithium iron phosphate particles adhere to and / or embed on the surface of the secondary lithium iron phosphate particles. Preferably, the second sintering temperature is 760℃~790℃, and the second sintering time is 6h~12h.

[0093] The method for preparing the above-mentioned lithium iron phosphate material according to embodiments of this application involves first forming bulk lithium iron phosphate particles, then forming primary lithium iron phosphate particles, and finally agglomerating the primary lithium iron phosphate particles to form secondary lithium iron phosphate particles. The bulk lithium iron phosphate particles are then adhered to and / or embedded on the surface of the secondary lithium iron phosphate particles, ultimately yielding a lithium iron phosphate material with a unique particle surface morphology. Therefore, this method ensures high capacity performance of the lithium iron phosphate material while effectively preventing particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed from the lithium iron phosphate material.

[0094] In a third aspect, this application proposes a positive electrode sheet. According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes the lithium iron phosphate material of the first aspect of this application, or the lithium iron phosphate material prepared using the method of the second aspect. This allows the positive electrode sheet to maintain good high-rate performance while reducing its elongation. It should be noted that the features and advantages described above for the lithium iron phosphate material and its preparation method also apply to this positive electrode sheet.

[0095] According to embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes the aforementioned lithium iron phosphate material, a positive electrode binder, and a positive electrode conductive agent. In embodiments of this application, the positive current collector can be made of a material with good conductivity and mechanical strength, preferably aluminum foil.

[0096] In the embodiments of this application, the specific type of positive electrode conductive agent is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the positive electrode conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Similarly, the specific type of positive electrode binder is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0097] According to some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as lithium iron phosphate material, positive electrode conductive agent, positive electrode binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0098] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes a positive electrode sheet as described in the third aspect. This allows the battery to maintain good high-rate performance while reducing the elongation of the positive electrode sheet. In an embodiment of this application, the battery can be a lithium-ion battery.

[0099] Specifically, the battery includes a positive electrode, a separator, a negative electrode, and an electrolyte, with the separator disposed between the positive and negative electrode.

[0100] In some embodiments of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0101] In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0102] In some embodiments of this application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0103] In some embodiments of this application, the negative electrode active material layer may optionally include a negative electrode binder. The negative electrode binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0104] In some embodiments of this application, the negative electrode active material layer may optionally include a negative electrode conductive agent. The negative electrode conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In the embodiments of this application, the specific material of the diaphragm is not particularly limited. As some specific examples, the diaphragm includes at least one of PP diaphragm, PE diaphragm, single-sided ceramic diaphragm, double-sided ceramic diaphragm, non-woven fabric diaphragm, and glass fiber diaphragm.

[0106] In the embodiments of this application, the electrolyte includes lithium salt and organic solvent. The specific types and compositions of the lithium salt and organic solvent are conventional choices in the battery field and can be selected according to actual needs. As some preferred embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonate)imide, lithium hexafluoroarsenate, lithium perchlorate, and lithium bis(trifluoromethanesulfonate)imide. The above-mentioned types of lithium salts can further optimize the conductivity, charge / discharge performance, and safety performance of lithium-ion batteries.

[0107] According to some specific embodiments of this application, the concentration of lithium salt in the electrolyte is D, which satisfies 0.8 mol / L ≤ D ≤ 1.5 mol / L. For example, it can be 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc. Therefore, by limiting the concentration D of lithium salt in the electrolyte within the above range, the conductivity, charge-discharge performance and safety performance of lithium-ion batteries can be further optimized.

[0108] The battery of this application may be in the form of a battery cell, a battery module, or a battery pack. In some embodiments, battery cells may be assembled into a battery module, and the number of battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0109] It should be noted that the features and advantages described above for the positive electrode also apply to this battery, and will not be repeated here.

[0110] A fifth aspect of this application discloses an energy storage device. According to an embodiment of this application, the energy storage device includes the battery described in the above embodiments. Therefore, the energy storage device possesses all the advantages of the battery described in the above embodiments, which will not be repeated here.

[0111] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form based on future application needs. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels.

[0112] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0113] This application provides an energy storage device 440, which is applied to an energy storage system 400. The energy storage device 440 is equipped with a battery 200 as described in the above embodiments. It mainly uses the chemical elements in the battery 200 as the energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, it stores the electrical energy generated by wind and solar energy in the chemical battery. When the use of external electrical energy reaches its peak, the stored electrical energy is released for use, or transferred to places with scarce electricity for use.

[0114] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices 440 include:

[0115] (1) Large-scale energy storage power stations applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, energy storage power stations can achieve load matching of power in time and space, enhance the absorption capacity of renewable energy, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy power generation, and are of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0116] (2) Energy storage containers applied on the grid side mainly function as peak shaving, frequency regulation and grid congestion relief. In terms of peak shaving, they can achieve peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption.

[0117] (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices 440, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system 400 when the electricity price is low and discharging the energy storage system 400 when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use the energy storage system 400 to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity electricity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0118] Optionally, the energy storage device 440 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0119] Optionally, the energy storage device 440 may include, but is not limited to, a single battery cell, or a battery module, battery pack, battery cluster, power bank, energy storage cabinet / container, or other battery integrated system composed of single batteries. The actual application form of the energy storage device 440 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 440. This application embodiment only uses a multi-cell battery as an example for illustration.

[0120] Optionally, when the energy storage device 440 is a single battery, the energy storage device 440 can be, but is not limited to, at least one of cylindrical, square, prismatic, or other shaped batteries.

[0121] Optionally, the single battery cell can be a rechargeable battery, which refers to a battery cell that can be recharged after discharge to activate the active materials and continue to be used. The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0122] A sixth aspect of this application discloses an energy storage system. According to an embodiment of this application, the energy storage system includes: the battery or the energy storage device described in the above embodiments. Therefore, the energy storage system possesses all the advantages of the battery or the energy storage device, which will not be elaborated further here.

[0123] In the embodiments of this application, the above-mentioned energy storage device can be used as a power source for an energy storage system, or as an energy storage unit for an energy storage system.

[0124] In some embodiments, see Figure 7 , Figure 7 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 7 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 440 of this application is not limited to the home energy storage scenario.

[0125] This application provides an energy storage system 400, which includes a first power conversion device 410 (photovoltaic panel), a first user load 420 (household lighting fixture), a second user load 430 (e.g., household appliances such as air conditioners), and an energy storage device 440. The energy storage device 440 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 440 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 440 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0126] In some embodiments, see Figure 8 , Figure 8 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application, and this application Figure 8 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 440 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0127] This application provides an energy storage system 400, which includes: a high-voltage cable 450, a first power conversion device 410, a second power conversion device 460, and an energy storage device 440 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 460 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 440 through grid connection. The energy storage device 440 is connected to the high-voltage cable and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power... The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 440 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 440 together with the high-voltage cable 450 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0128] In some embodiments on the distribution network side, the first power conversion device 410 can be a photovoltaic power conversion device, and the energy storage device 440 is connected to the high-voltage cable 450 and installed downstream of the high-voltage cable 450 and between the user load. The power output of the photovoltaic power conversion device is stored in the energy storage device 440, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 450 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0129] Optionally, the first power conversion device 410 may include, but is not limited to, a wind power conversion device, and the second power conversion device 460 may include, but is not limited to, a photovoltaic power conversion device. The first power conversion device 410 and the second power conversion device 460 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0130] In some embodiments, see Figure 9 , Figure 9 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application, and this application Figure 9 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 440 of this application is not limited to its power generation / distribution side energy storage scenario.

[0131] This application provides an energy storage system 400, which includes: an energy storage cabinet 470, a high-voltage cable 450, a factory equipped with a first power conversion device 410, a photovoltaic-energy storage-charging station 480 equipped with a second power conversion device 460, and a vehicle 490. In some embodiments of industrial and commercial scenarios, the first power conversion device 410 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage cabinet 470 of the factory. In the event of a power grid failure, the energy storage cabinet 470 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage cabinet 470 in conjunction with the high-voltage cable 450 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 460 can also be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage cabinet 470 of the photovoltaic-energy storage-charging station 480, directly charging the vehicle 490 through the photovoltaic-energy storage-charging station 480, which is fast and convenient.

[0132] Optionally, the first power conversion device 410 and the second power conversion device 460 may include, but are not limited to, photovoltaic power conversion devices. The first power conversion device 410 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0133] Optionally, the energy storage cabinet 470 may include, but is not limited to, energy storage application scenarios such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and is also used in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0134] Optionally, the energy storage cabinet 470 may include, but is not limited to, individual batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / containers, and other integrated battery systems composed of individual batteries. The actual application form of the energy storage cabinet 470 provided in this application embodiment can be, but is not limited to, the listed products, and can also be other application forms. This application embodiment does not strictly limit the application form of the energy storage cabinet 470. This application embodiment only uses a multi-cell battery in the energy storage cabinet 470 as an example for illustration.

[0135] Optionally, the individual battery 200 constituting the energy storage cabinet 470 can be, but is not limited to, at least one of cylindrical, square, prismatic, or other shaped batteries.

[0136] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0137] Example 1

[0138] 1) Lithium iron phosphate materials

[0139] Step 1: Long strip-shaped lithium iron phosphate material

[0140] ①According to LiFe 0.99 Ti 0.01 To prepare a mixed metal salt solution for PO4, weigh out the required stoichiometric ratio of iron (ferrous oxalate), phosphorus (phosphate), lithium (lithium carbonate), and titanium (titanium tetrachloride). Use deionized water as the solvent, with a titanium molar concentration of 5 mol / L. Then, prepare a 1 mol / L strong alkali solution as the precipitant and a 1 mol / L ammonia solution as the complexing agent.

[0141] ② The mixed metal salt solution, precipitant solution and complexing agent solution prepared above are placed in a reaction vessel and stirred continuously. The pH value of the reaction liquid is kept at 9 and the reaction temperature is 195℃. The reaction is carried out for 10 hours. The long strip-shaped lithium iron phosphate material is obtained by using precipitation and chemical reaction to synthesize the material. After solid-liquid separation, washing and drying, the material is obtained.

[0142] ③ Weigh a certain amount of carbon source (glucose) and mix it evenly with the elongated lithium iron phosphate material powder from step 2. The mass of the carbon source (glucose) is 10% of the elongated lithium iron phosphate material powder from step 2. Place it in a vacuum atmosphere sintering furnace for calcination (the protective atmosphere is nitrogen, the sintering temperature is 650℃, and the sintering time is 10h). After crushing, the elongated lithium iron phosphate material is obtained.

[0143] Step 2: The lithium iron phosphate material of this application

[0144] ①According to LiFe 0.99 Ti 0.01 To prepare PO4, weigh out the required stoichiometric ratio of iron source (ferrous oxalate), phosphorus source (phosphate), lithium source (lithium carbonate), and titanium source (titanium tetrachloride). Then, weigh out 20% of the total mass of the above raw materials as carbon source (sucrose) and add it to a ball mill for uniform mixing. Add an appropriate amount of pure water as a dispersant, and then perform high-energy ball milling (ball-to-material ratio of 4:1, rotation speed of 2000 r / min, and time of 12 h) to grind the raw materials into particles of a suitable size.

[0145] ② Spray dry the ball-milled material to form powder with a certain particle size.

[0146] ③ The dried powder is placed in a vacuum atmosphere sintering furnace for the first sintering (the protective atmosphere is nitrogen, the temperature is 650℃, and the time is 8h), and then the powder is crushed by ball milling to obtain the first sintered material.

[0147] ④ Weigh out 5% of the mass fraction of the first sintering material, add the strip-shaped lithium iron phosphate material, mix evenly, and then spray dry to form a powder with a certain particle size.

[0148] ⑤ The powder obtained in the previous step is placed in a vacuum atmosphere sintering furnace for a second sintering (the protective atmosphere is nitrogen, the temperature is 760℃, and the time is 6h), and then crushed by ball milling to obtain the lithium iron phosphate material with special particle surface morphology of this application.

[0149] 2) Positive electrode plate

[0150] ① Weigh the corresponding amounts of lithium iron phosphate material and polyvinylidene fluoride into a mixing tank at a mass ratio of 97%:3%, then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with suitable viscosity.

[0151] ② The slurry is evenly coated onto the aluminum foil on the specified side by extrusion coating to form a positive electrode sheet.

[0152] 3) Manufacturing lithium-ion batteries

[0153] ① Weigh the corresponding amounts of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mixing tank at a mass ratio of 95%:2.5%:2.5%, add an appropriate amount of deionized water, and stir for 6 hours to obtain a uniform slurry with suitable viscosity; then coat the slurry onto a copper foil with a thickness of 10μm, and place it in a vacuum oven to dry at 150℃ for 16 hours to obtain a negative electrode sheet.

[0154] ②Place the positive and negative electrode sheets into a press for pressing, and then use a punch to cut Φ15mm positive electrode discs and Φ18mm negative electrode discs respectively.

[0155] ③ The positive and negative electrode discs are placed in a glove box filled with argon protective atmosphere for battery assembly. The electrolyte is a solution obtained by dissolving 1 mol / L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1. The positive electrode disc, negative electrode disc, polyethylene separator and other components are assembled together, and then the electrolyte is injected to finally obtain a lithium-ion battery.

[0156] Example 2

[0157] Following a similar method to Example 1 above, in step ④ of step two of the preparation of lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 10%, as Example 2.

[0158] Example 3

[0159] Following a similar method to Example 1 above, in step 4 of step two of preparing lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 15%, as Example 3.

[0160] Example 4

[0161] Following a similar method to Example 1 above, in step 4 of step two of preparing lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 20%, as Example 4.

[0162] Example 5

[0163] Following a similar method to Example 1 above, in step ④ of step two of the preparation of lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 25%, as Example 5.

[0164] Example 6

[0165] Following a similar method to Example 1 above, in step ④ of step two of the preparation of lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 30%, as Example 6.

[0166] Example 7

[0167] Following a similar method to Example 1 above, in step ④ of step two of the preparation of lithium iron phosphate material, the amount of elongated lithium iron phosphate material added was controlled to be 35%, as Example 7.

[0168] Example 8

[0169] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering temperature was controlled to be 770°C, as Example 8.

[0170] Example 9

[0171] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering temperature was controlled to be 780°C, as Example 9.

[0172] Example 10

[0173] Following a similar method to Example 1 above, in step ⑤ of step two in the preparation of lithium iron phosphate material, the second sintering temperature was controlled to be 790°C, as Example 10.

[0174] Example 11

[0175] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering temperature was controlled to be 800°C, as Example 11.

[0176] Example 12

[0177] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering time was controlled to be 8 hours, as Example 12.

[0178] Example 13

[0179] Following a similar method to Example 1 above, in step ⑤ of step two in the preparation of lithium iron phosphate material, the second sintering time was controlled to be 10 hours, as Example 13.

[0180] Example 14

[0181] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering time was controlled to be 12 hours, as Example 14.

[0182] Example 15

[0183] Following a similar method to Example 1 above, in step ⑤ of step two of preparing lithium iron phosphate material, the second sintering time was controlled to be 14 hours, as Example 15.

[0184] Example 16

[0185] Following a similar method to Example 1 above, in step ① of step one of the preparation of lithium iron phosphate materials, the control is performed according to LiFe... 0.98 Ti 0.02 Weigh the raw materials according to the stoichiometric ratio of PO4, and simultaneously control the proportion of LiFe in step ① of step two. 0.98 Ti 0.02 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 16.

[0186] Example 17

[0187] Following a similar method to Example 1 above, in step ① of step one of the preparation of lithium iron phosphate materials, the control is performed according to LiFe... 0.97 Ti 0.03 Weigh the raw materials according to the stoichiometric ratio of PO4, and simultaneously control the proportion of LiFe in step ① of step two. 0.98 Ti 0.03 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 17.

[0188] Example 18

[0189] Following a similar method to Example 1 above, in step ① of step one of the preparation of lithium iron phosphate materials, the control is performed according to LiFe... 0.96 Ti 0.04 Weigh the raw materials according to the stoichiometric ratio of PO4, and simultaneously control the proportion of LiFe in step ① of step two. 0.98 Ti 0.04 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 18.

[0190] Example 19

[0191] Following a similar method to Example 1 above, in step ① of step one of the preparation of lithium iron phosphate materials, the control is performed according to LiFe... 0.95 Ti 0.05 Weigh the raw materials according to the stoichiometric ratio of PO4, and simultaneously control the proportion of LiFe in step ① of step two. 0.98 Ti 0.05 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 19.

[0192] Comparative Example 1

[0193] 1) Lithium iron phosphate materials

[0194] ①According to LiFe 0.99 T i0.01To prepare PO4 / C, weigh out the required stoichiometric ratio of iron source (ferrous oxalate), phosphorus source (phosphate), lithium source (lithium carbonate), and titanium source (titanium tetrachloride). Then, weigh out 20% of the total mass of the above raw materials and add them to a ball mill for uniform mixing. Add an appropriate amount of pure water as a dispersant, and then perform high-energy ball milling (ball-to-material ratio of 4:1, rotation speed of 2000 r / min, and time of 12 h) to grind the raw materials into particles of a suitable size.

[0195] ② Spray dry the ball-milled material to form powder with a certain particle size.

[0196] ③ The dried powder is placed in a vacuum atmosphere sintering furnace for sintering (protective atmosphere is nitrogen, 820℃, 10h), and then crushed by ball milling to obtain lithium iron phosphate material.

[0197] The other steps are the same as in Example 1.

[0198] Test example:

[0199] 1) Particle size distribution test

[0200] The particle size distribution of lithium iron phosphate materials was measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000) according to the laser diffraction method for particle size distribution (GB / T19077-2016). The test results are shown in Table 1 and... Figure 5 As shown.

[0201] 2) Powder compaction density test

[0202] The powder compaction density of lithium iron phosphate material under 3kN pressure was measured using a powder compaction tester (model LD43.305) from Shanghai Lisheng Company, in accordance with the standard method GBT 24533-2019.

[0203] 3) Electrode elongation test

[0204] like Figure 6 As shown, L1 is the distance between marks A and B before the positive electrode sheet is rolled, and L2 is the distance between marks A and B after the positive electrode sheet is rolled, that is, the distance from A' to B'. The elongation rate of the positive electrode sheet is calculated as S = (L2-L1) / L1*100%.

[0205] 4) Contact area between particle planes

[0206] A 5,000x magnification photograph was taken using a scanning electron microscope. The large particles (i.e., secondary lithium iron phosphate particles) were measured using the image recognition software ImageJ. The planar area of ​​the large particles (i.e., secondary lithium iron phosphate particles) and the cumulative planar area of ​​the elongated particles (i.e., blocky lithium iron phosphate particles) on the surface of the large particles (i.e., secondary lithium iron phosphate particles) were calculated. The ratio of the two is the proportion of the average contact area between the secondary lithium iron phosphate particles and the blocky lithium iron phosphate particles in the planar area of ​​the secondary lithium iron phosphate particles. The process was repeated for photographs taken from five different regions, and the average value was calculated.

[0207] 5) Average major diameter of elongated particles

[0208] A 3,000x image was taken using a scanning electron microscope. The major diameter of the elongated particles on the large particles (i.e., secondary lithium iron phosphate particles) was measured using the image recognition software ImageJ. The operation was repeated for 100 particles, and the average value was calculated.

[0209] 6) Rate discharge capacity test

[0210] At 25°C, the lithium batteries prepared in the examples and comparative examples were charged to 3.65V at a rate of 0.1C, and then discharged to 2.5V at a rate of 0.1C. The discharge capacity at this time was recorded as 0.1C.

[0211] The test results are shown in Table 1.

[0212] Figure 1 The image shows the surface morphology of the lithium iron phosphate material prepared in Example 1. Figure 2 This is a magnified surface morphology image of the lithium iron phosphate material prepared in Example 1. From... Figures 1-2 As can be seen, the lithium iron phosphate material prepared in Example 1 includes secondary lithium iron phosphate particles and bulk lithium iron phosphate particles, with the bulk lithium iron phosphate particles adhering to and / or embedded on the surface of the secondary lithium iron phosphate particles. It can also be seen that the secondary lithium iron phosphate particles in Example 1 are formed from primary nanoparticles. Furthermore, from... Figures 1-2 As can be seen from the above, the average contact area between the secondary lithium iron phosphate particles and the blocky lithium iron phosphate particles in Example 1 is about 10% of the planar area of ​​the secondary lithium iron phosphate particles, and the average major diameter of the blocky lithium iron phosphate particles is about 2 μm.

[0213] Figure 3 The image shows the surface morphology of the lithium iron phosphate material prepared in Comparative Example 1. Figure 4 This is a magnified surface morphology image of the lithium iron phosphate material prepared in Comparative Example 1. Figures 3-4 As can be seen from the data, the lithium iron phosphate material prepared in Comparative Example 1 is a primary particle and does not have blocky lithium iron phosphate particles.

[0214] Figure 5The diagram shows the particle size distribution of lithium iron phosphate materials prepared in Example 1 and Comparative Example 1. It can be seen that the particle size Dv50 of Comparative Example 1 is about 1.2 μm, and the particle size Dv50 of Example 1 is about 6 μm.

[0215] Table 1

[0216]

[0217] As can be seen from Table 1, compared with Comparative Example 1, the elongation of the positive electrode sheet in Examples 1-19 was significantly reduced, and the rate discharge capacity of the batteries in Examples 1-19 was significantly improved. It can be seen that by adhering and / or embedding blocky lithium iron phosphate particles on the surface of lithium iron phosphate secondary particles, this application can improve the capacity performance of lithium iron phosphate materials while effectively hindering particle deformation and slippage, thereby reducing the elongation of the positive electrode sheet formed by lithium iron phosphate materials.

[0218] As can be seen from Examples 1-7 in Table 1, in step 4 of step two of the preparation of lithium iron phosphate materials, as the amount of elongated lithium iron phosphate material added gradually increases, the material powder compaction and electrode elongation show a decreasing trend, the particle size increases slightly, and the corresponding material capacity performance decreases. This is because the capacity performance of elongated lithium iron phosphate material is lower than that of secondary agglomerated spherical particles; therefore, the preferred amount of elongated lithium iron phosphate material added is 5-30%.

[0219] As can be seen from Examples 1 and 8-11 in Table 1, in step 5 of step two in the preparation of lithium iron phosphate material, the second sintering temperature is gradually increased. The increased temperature accelerates particle growth, expands the contact area between particle planes, and simultaneously increases the average length and diameter of the elongated particles, resulting in a decrease in material capacity. Therefore, the preferred second sintering temperature is 760-790℃.

[0220] As can be seen from Examples 1 and 12-15 in Table 1, in step 5 of step two in the preparation of lithium iron phosphate material, the second sintering time is gradually increased. The increase in time accelerates particle growth and expands the contact area between particle planes. At the same time, the average length and diameter of the elongated particles also become longer, and the corresponding material capacity decreases. Therefore, the second sintering temperature is preferably 6-12h.

[0221] As can be seen from Examples 1 and 16-19 in Table 1, in order to improve the capacity performance of the material, as the content of titanium doping gradually increases, the powder pressing and electrode elongation decrease slightly, and the material capacity first increases and then decreases. The main reason is that excessive doping may cause the material to form impurity compounds, thereby reducing the capacity performance, and also has the effect of refining the grain size. Therefore, the lithium iron phosphate material (LiFe) of this application... x Ti yThe preferred Ti doping amount for PO4 / C is y≤0.04.

[0222] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0223] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A lithium iron phosphate material, characterized in that, include: Lithium iron phosphate secondary particles and blocky lithium iron phosphate particles, wherein the blocky lithium iron phosphate particles are adhered to and / or embedded in the surface of the lithium iron phosphate secondary particles. The average contact area between the secondary lithium iron phosphate particles and the blocky lithium iron phosphate particles does not exceed 35% of the planar area of ​​the secondary lithium iron phosphate particles; The particle size Dv50 of the lithium iron phosphate material is 6μm~9.5μm.

2. The lithium iron phosphate material according to claim 1, characterized in that, The secondary lithium iron phosphate particles are formed from primary lithium iron phosphate nanoparticles.

3. The lithium iron phosphate material according to claim 1, characterized in that, The lithium iron phosphate secondary particles are spherical.

4. The lithium iron phosphate material according to claim 1, characterized in that, The average contact area between the secondary lithium iron phosphate particles and the blocky lithium iron phosphate particles is 10% to 30% of the planar area of ​​the secondary lithium iron phosphate particles.

5. The lithium iron phosphate material according to claim 1, characterized in that, The blocky lithium iron phosphate particles are elongated lithium iron phosphate particles.

6. The lithium iron phosphate material according to claim 1, characterized in that, The average major diameter of the blocky lithium iron phosphate particles is no greater than 6.2 μm.

7. The lithium iron phosphate material according to any one of claims 1 to 5, characterized in that, The lithium iron phosphate material includes titanium, and the chemical structural formula of the lithium iron phosphate material is LiFe. x Ti y PO4, where x + y = 1, 0 <y≤0.05。 8. A method for preparing lithium iron phosphate material according to any one of claims 1 to 7, characterized in that, include: (1) Weigh the iron source, phosphorus source and lithium source according to the required stoichiometric ratio in LiFePO4, and prepare a mixed metal salt solution; (2) The mixed metal salt solution, precipitant solution and complexing agent solution are placed in a reaction vessel and reacted to obtain blocky lithium iron phosphate; (3) Weigh the iron source, phosphorus source, and lithium source according to the required stoichiometric ratio in LiFePO4, and weigh the carbon source. Mix them evenly, add the dispersant, and ball mill. (4) Spray dry the ball-milled material; (5) Under a protective atmosphere, the spray-dried material is subjected to a first sintering and crushed to obtain the first sintered material; (6) The first sintering material and the blocky lithium iron phosphate are mixed and spray-dried to obtain a mixed powder; (7) Under a protective atmosphere, the mixed powder is subjected to a second sintering, grinding and crushing to obtain lithium iron phosphate material.

9. The method according to claim 8, characterized in that, In step (1), according to LiFe x Ti y The required stoichiometric ratio of iron, phosphorus, lithium, and titanium sources is used to prepare the mixed metal salt solution, where x + y = 1, 0 <y≤0.05。 10. The method according to claim 8, characterized in that, In step (2), the temperature of the mixed metal salt solution, the precipitant solution and the complexing agent solution in the reactor is 180℃~220℃, the reaction time is 8h~10h, and the pH of the reaction system is 9~11; And / or, in step (2), the precipitant solution comprises a strong alkaline solution of 0.5 mol / L to 1.5 mol / L; And / or, in step (2), the complexing agent solution comprises an aqueous ammonia solution of 0.5 mol / L to 1.5 mol / L.

11. The method according to claim 8, characterized in that, In step (3), according to LiFe x Ti y The required stoichiometric ratio for PO4 is obtained by weighing iron, phosphorus, lithium, and titanium sources, where x + y = 1, 0 <y≤0.05; And / or, in step (3), the mass of the carbon source is 20% to 25% of the total mass of the iron source, phosphorus source, lithium source and titanium source.

12. The method according to any one of claims 8 to 11, characterized in that, In step (5), the temperature of the first sintering is 650℃~720℃, and the time of the first sintering is 5h~8h.

13. The method according to any one of claims 8 to 11, characterized in that, In step (6), the mass of the blocky lithium iron phosphate is 5% to 35% of the mass of the first sintering material.

14. The method according to any one of claims 8 to 11, characterized in that, In step (7), the second sintering temperature is 760℃~800℃, and the second sintering time is 6h~14h.

15. A positive electrode plate, characterized in that, The lithium iron phosphate material includes any one of claims 1 to 7 or the lithium iron phosphate material prepared by the method described in any one of claims 8 to 14.

16. A battery, characterized in that, The lithium iron phosphate material includes any one of claims 1 to 7, the lithium iron phosphate material prepared by the method described in any one of claims 8 to 14, or the positive electrode sheet described in claim 15.

17. An energy storage device, characterized in that, Includes the battery as described in claim 16.

18. An energy storage system, characterized in that, include: Includes the battery of claim 16 or the energy storage device of claim 17.

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