Lithium iron phosphate material, preparation method thereof, positive electrode sheet, battery and power utilization system

Abstract

The application discloses a lithium iron phosphate material and a preparation method thereof, a positive plate, a battery and an electric system. The lithium iron phosphate material comprises: lithium iron phosphate particles, part of the outer surface of the lithium iron phosphate particles is recessed to form a pit to the inside of the lithium iron phosphate particles; and / or the inside center position of the lithium iron phosphate particles has a hollow hole structure.

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, and an electrical system. Background Technology

[0002] Currently, the main cathode material used in lithium-ion batteries is lithium iron phosphate, which has an olivine crystal structure and good safety and stability. Lithium batteries increasingly pursue large-capacity cells. Using high-compact or high-capacity lithium iron phosphate materials in the cathode within the same volume can achieve higher volumetric energy density. Therefore, it is necessary to develop a high-capacity lithium iron phosphate material with long cycle performance.

[0003] However, to improve the compaction density, lithium iron phosphate materials currently require a certain proportion of large particles, but the capacity performance of large particles is questionable. In addition, as the number of cycles increases, the crystal structure of the cathode material undergoes continuous lithium ion insertion and extraction, causing partial lattice distortion and microcracks. Coupled with the corrosion of the electrolyte, the particles are prone to breakage, ultimately leading to a sharp deterioration in the cycle performance of the lithium battery. Summary of the Invention

[0004] 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, its preparation method, a positive electrode, a battery, and a power system thereof. The lithium iron phosphate material of this application can achieve high capacity performance while maintaining good long-cycle performance.

[0005] 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:

[0006] Lithium iron phosphate particles, wherein a portion of the outer surface of the lithium iron phosphate particles is recessed into the interior of the lithium iron phosphate particles to form pits;

[0007] And / or, the lithium iron phosphate particles have a hollow pore structure at their internal center.

[0008] According to the lithium iron phosphate material of this application embodiment, a portion of the outer surface of the lithium iron phosphate particles is recessed into the interior of the particles, forming pits. This not only helps to shorten the migration distance of lithium ions within the lithium iron phosphate particles but also expands the wetting range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and giving it high capacity performance. And / or, the central position of the lithium iron phosphate particles has a hollow porous structure, which helps to disperse the internal stress concentration caused by lattice distortion during the continuous insertion and extraction of lithium ions, thus helping to suppress the breakage of the lithium iron phosphate particles and effectively improving the long-cycle performance of the lithium iron phosphate material. Therefore, the lithium iron phosphate material of this application can achieve high capacity performance while maintaining good long-cycle performance.

[0009] In addition, the lithium iron phosphate material according to the above embodiments of this application may also have the following additional technical features:

[0010] In some embodiments of this application, the lithium iron phosphate particles are secondary particles.

[0011] In some embodiments of this application, the average depth of the pits on the surface of the lithium iron phosphate particles does not exceed 42% of the major diameter of the lithium iron phosphate particles.

[0012] In some embodiments of this application, the average depth of the pits on the surface of the lithium iron phosphate particles is 10% to 42% of the major diameter of the lithium iron phosphate particles.

[0013] In some embodiments of this application, the average cross-sectional area of ​​the hollow pore structure of the lithium iron phosphate particles does not exceed 30% of the maximum cross-sectional area of ​​the lithium iron phosphate particles.

[0014] In some embodiments of this application, the particle size Dv50 of the lithium iron phosphate particles is 6μm to 8μm.

[0015] In some embodiments of this application, the lithium iron phosphate particles include titanium, and the chemical structural formula of the lithium iron phosphate particles is LiFe. x Ti y PO4, where x + y = 1, 0 <y≤0.05。

[0016] In a second aspect, this application provides a method for preparing the above-mentioned lithium iron phosphate material, comprising:

[0017] (1) Preparation of porous hollow carbon microspheres;

[0018] (2) Weigh the iron source, phosphorus source and lithium source according to the required stoichiometric ratio in LiFePO4, and prepare a mixed metal salt solution;

[0019] (3) The mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution are placed in a reaction vessel and reacted to obtain the lithium iron phosphate material precursor.

[0020] (4) The lithium iron phosphate material precursor and dispersant are mixed and then ground and crushed;

[0021] (5) Spray dry the ground and crushed material;

[0022] (6) Under a protective atmosphere, the spray-dried material is calcined at high temperature, ground and crushed to obtain lithium iron phosphate material.

[0023] The method for preparing the above-mentioned lithium iron phosphate material according to the embodiments of this application allows for the formation of pits on the outer surface of some of the lithium iron phosphate particles, which not only shortens the migration distance of lithium ions inside the lithium iron phosphate particles but also expands the wetting range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and giving it high capacity performance. And / or, this method can also create a hollow pore structure at the center of the formed lithium iron phosphate particles, which helps to disperse the internal stress concentration caused by lattice distortion during the continuous insertion and extraction of lithium ions, thus helping to suppress the breakage of the lithium iron phosphate particles and effectively improving the long-cycle performance of the lithium iron phosphate material. Therefore, the lithium iron phosphate material prepared by this method can achieve high capacity performance while maintaining good long-cycle performance.

[0024] In some embodiments of this application, step (1) includes: preparing a first carbon source solution, spray drying the first carbon source solution to obtain a carbon microsphere precursor; and calcining the carbon microsphere precursor to obtain the porous hollow carbon microspheres.

[0025] In some embodiments of this application, in step (2), 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。

[0026] In some embodiments of this application, in step (3), the temperature at which the mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution, and the complexing agent solution react in the reactor 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 (3), the mass of the porous hollow carbon microspheres is 1% to 13% of the mass of the mixed metal salt in the mixed metal salt solution; and / or, in step (3), the precipitant solution comprises a strong alkaline solution of 0.5mol / L to 1.5mol / L; and / or, in step (3), the complexing agent solution comprises an aqueous ammonia solution of 0.5mol / L to 1.5mol / L.

[0027] In some embodiments of this application, in step (4), during the mixing of the lithium iron phosphate material precursor and the dispersant, the process further includes: mixing the lithium iron phosphate material precursor, the second carbon source and the dispersant, and then grinding and crushing them.

[0028] In some embodiments of this application, the mass ratio of the lithium iron phosphate material precursor to the second carbon source is (92:8) to (85:15).

[0029] In some embodiments of this application, in step (5), the outlet temperature of the spray drying of the ground and crushed material is 180°C to 230°C.

[0030] In some embodiments of this application, in step (6), the temperature at which the spray-dried material is subjected to high-temperature calcination is 650°C to 710°C; and / or, in step (6), the time for high-temperature calcination of the spray-dried material is 5h to 12h.

[0031] 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. 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, and will not be repeated here.

[0032] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes a positive electrode plate as described in the third aspect. This allows the battery to maintain good long-cycle performance while increasing its rate discharge capacity.

[0033] In a fifth aspect of this application, an electrical system is proposed. According to an embodiment of this application, the electrical system includes: an electrical system itself, and an energy storage device that supplies power to the electrical system. The energy storage device includes the battery described in the above embodiments. Thus, the electrical system possesses all the advantages of the battery, 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 Here is a surface morphology image of the lithium iron phosphate particles prepared in Example 1;

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

[0037] Figure 3 This is a cross-sectional morphology diagram of the lithium iron phosphate particles prepared in Example 1;

[0038] Figure 4 The surface morphology of lithium iron phosphate particles prepared in Comparative Example 1 is shown.

[0039] Figure 5 This is a cross-sectional morphology diagram of the lithium iron phosphate particles prepared in Comparative Example 1;

[0040] Figure 6 This is a schematic diagram of the particle size distribution of lithium iron phosphate materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] In one aspect of this application, a lithium iron phosphate material is proposed. According to an embodiment of this application, the lithium iron phosphate material includes: lithium iron phosphate particles, wherein a portion of the outer surface of the lithium iron phosphate particles is recessed into the interior of the lithium iron phosphate particles to form pits; and / or, the interior center of the lithium iron phosphate particles has a hollow pore structure. Therefore, the lithium iron phosphate material of this application can achieve high capacity performance while maintaining good long-cycle performance.

[0044] 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:

[0045] In the lithium iron phosphate material of this application, a portion of the outer surface of the lithium iron phosphate particles is recessed into the interior of the particles, forming pits. This not only shortens the migration distance of lithium ions within the lithium iron phosphate particles but also expands the wetting range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and giving it high capacity performance. And / or, the central position of the lithium iron phosphate particles has a hollow porous structure, which helps to disperse the internal stress concentration caused by lattice distortion during the continuous insertion and extraction of lithium ions, thus helping to suppress particle breakage and effectively improving the long-cycle performance of the lithium iron phosphate material. Therefore, the lithium iron phosphate material of this application can achieve high capacity performance while maintaining good long-cycle performance.

[0046] According to some specific embodiments of this application, lithium iron phosphate particles are secondary particles, which are formed from primary nanoparticles. The pits on the surface of the lithium iron phosphate particles are formed during the process of primary nanoparticles forming secondary particles. At the same time, the hollow pore structure at the center of the internal part of the lithium iron phosphate particles is also formed during the process of primary nanoparticles forming secondary particles.

[0047] According to some specific embodiments of this application, the average depth of the pits on the surface of lithium iron phosphate particles does not exceed 42% of the major diameter of the lithium iron phosphate particles. For example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 42%, or any range between the two. By limiting the average depth of the pits on the surface of lithium iron phosphate particles to the above range, it is possible to further shorten the migration distance of lithium ions inside the lithium iron phosphate particles and further expand the wetting range of the electrolyte, thereby further improving the kinetics of lithium iron phosphate materials and giving them more superior high-capacity performance.

[0048] As some preferred embodiments, the average depth of the pits on the surface of lithium iron phosphate particles is 10% to 42% of the major diameter of the lithium iron phosphate particles. By limiting the average depth of the pits on the surface of lithium iron phosphate particles to the above range, it is possible to further shorten the migration distance of lithium ions inside the lithium iron phosphate particles and further expand the wetting range of the electrolyte, thereby further improving the kinetics of lithium iron phosphate materials and giving them more superior high-capacity performance.

[0049] According to some specific embodiments of this application, the average cross-sectional area of ​​the hollow pore structure of the lithium iron phosphate particles does not exceed 30% of the maximum cross-sectional area of ​​the lithium iron phosphate particles. For example, it can be 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, or any range between the two. By limiting the average cross-sectional area of ​​the hollow pore structure of the lithium iron phosphate particles to the above range, it is further beneficial to disperse the internal stress concentration caused by lattice distortion during the continuous insertion and extraction of lithium ions in the crystal structure of the lithium iron phosphate material, and further beneficial to suppress the breakage of lithium iron phosphate particles, thereby further effectively improving the long-cycle performance of lithium iron phosphate materials.

[0050] In this application, instruments and methods known in the art can be used to determine the average pit depth and the proportion of the cross-sectional area of ​​internal pores on the surface of lithium iron phosphate particles. As a specific example, a positive electrode sample is selected, the positive electrode is cut using a focused ion beam, and the cross-section of the positive electrode is observed using a scanning electron microscope. Then, a 2,000x magnification photograph is taken. Then, the image recognition software ImageJ is used to statistically analyze the proportion of the pit depth and the cross-sectional area of ​​internal pores of 50 particles to the total cross-sectional area of ​​the particles, and finally, the average value is calculated.

[0051] According to some specific embodiments of this application, the particle size Dv50 of lithium iron phosphate particles is 6μm to 8μm, for example, it can be 6μm, 6.2μm, 6.5μm, 6.8μm, 7μm, 7.2μm, 7.5μm, 7.8μm, 8μm, or any range between the two. By limiting the particle size Dv50 of lithium iron phosphate particles to the above range, it is further beneficial to form pits on the outer surface of lithium iron phosphate particles and to form a hollow pore structure at the internal center of lithium iron phosphate particles. This further helps the lithium iron phosphate material to achieve high capacity performance while maintaining good long-cycle performance. Here, Dv50 refers to the particle size corresponding to when the cumulative volume percentage of lithium iron phosphate particles reaches 50%.

[0052] In the present application, the particle size Dv50 of lithium iron phosphate particles can be measured by instruments and methods well known in the art. 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 particles according to the laser diffraction method for particle size distribution GB / T19077-2016.

[0053] According to still other specific embodiments of the present application, the lithium iron phosphate particles include titanium element, and the chemical structural formula of the lithium iron phosphate particles is LiFe x Ti y PO4, wherein x+y=1, 0<y≤0.05, preferably 0<y≤0.04, that is, titanium element is doped in the lithium iron phosphate particles. By doping titanium element in the lithium iron phosphate particles, the high-capacity performance of the lithium iron phosphate material can be further effectively improved.

[0054] According to still other specific embodiments of the present application, a carbon coating layer is provided on the surface of the lithium iron phosphate particles, thereby effectively improving the electrical conductivity of the lithium iron phosphate particles.

[0055] 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:

[0056] S100: preparing porous hollow carbon microspheres;

[0057] According to some specific embodiments of the present application, the method for preparing the above porous hollow carbon microspheres comprises:

[0058] S110: preparing a first carbon source solution with a suitable concentration, and performing spray drying on the first carbon source solution to obtain a carbon microsphere precursor;

[0059] As some specific embodiments, the concentration of the first carbon source solution may be 2 mol / L to 5 mol / L, for example, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, etc.

[0060] In the embodiments of the present application, the specific type of the above first carbon source solution is not particularly limited, and those skilled in the art can select according to actual needs. For example, the first carbon source solution may be a sucrose solution.

[0061] S120: roasting the carbon microsphere precursor to allow the first carbon source to undergo thermal shrinkage, so as to obtain the porous hollow carbon microspheres.

[0062] In some specific embodiments, the calcination temperature of the carbon microsphere precursor may be 180°C to 220°C (for example, it may be 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, etc.), and the calcination time is 3h to 5h (for example, it may be 3h, 3.5h, 4h, 4.5h, 5h, etc.).

[0063] S200: Weighing an iron source, a phosphorus source and a lithium source according to the required stoichiometric ratio of LiFePO4 to prepare a mixed metal salt solution;

[0064] According to some further specific embodiments of the present application, according to LiFe x Ti y PO4, weigh the iron source, phosphorus source, lithium source and titanium source according to the required stoichiometric ratio to prepare a mixed metal salt solution, wherein x+y=1, 0<y≤0.05, preferably 0<y≤0.04. That is, titanium element is doped in lithium iron phosphate particles, and doping titanium element in lithium iron phosphate particles can further effectively improve the high capacity performance of the lithium iron phosphate material.

[0065] In the embodiments 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. In some specific embodiments, the iron source may be ferrous oxalate, ferric sulfate, ferric chloride, etc. In some further specific embodiments, the phosphorus source may be phosphoric acid, ammonium dihydrogen phosphate, etc. In still some other specific embodiments, the lithium source may be lithium carbonate, lithium hydroxide, etc. In still some other specific embodiments, the titanium source may be titanium tetrachloride, titanium oxalate, etc.

[0066] In the embodiments of the present application, the specific type of the solvent for the mixed metal salt solution is not particularly limited, and those skilled in the art can select it according to actual needs. In some specific embodiments, the solvent of the mixed metal salt solution may be deionized water.

[0067] S300: Placing the mixed metal salt solution, porous hollow carbon microspheres, precipitant solution and complexing agent solution in a reaction kettle for reaction to obtain a lithium iron phosphate material precursor;

[0068] In this step, the mixed metal salt solution, porous hollow carbon microspheres, precipitant solution and complexing agent solution are placed in a reaction kettle, continuously stirred, synthesized through precipitation combination reaction, and the lithium manganese iron phosphate material precursor is prepared after solid-liquid separation, washing and drying. Wherein, during the subsequent high-temperature calcination process, the porous hollow carbon microspheres can be cracked and shrunk to form pits and / or pores.

[0069] According to some specific embodiments of this application, the reaction temperature of the mixed metal salt solution, porous hollow carbon microspheres, 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, porous hollow carbon microspheres, precipitant solution, and complexing agent solution react fully in the reactor to obtain the lithium iron phosphate material precursor.

[0070] According to some specific embodiments of this application, the mass of the porous hollow carbon microspheres is 1% to 13% of the mass of the mixed metal salt in the mixed metal salt solution, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or any range between the two. By limiting the amount of porous hollow carbon microspheres within the above range, it can be further ensured that the average depth of the pits on the surface of the finally prepared lithium iron phosphate particles does not exceed 42% of the long diameter of the lithium iron phosphate particles, and the average cross-sectional area of ​​the hollow pore structure of the lithium iron phosphate particles does not exceed 30% of the maximum cross-sectional area of ​​the lithium iron phosphate particles. This further ensures that the prepared lithium iron phosphate material can achieve high capacity performance while maintaining good long cycle performance. If the amount of porous hollow carbon microspheres is too large, it will lead to an excessively large average depth of pits on the surface of lithium iron phosphate particles or an excessively large average cross-sectional area of ​​the hollow pore structure. This results in a very loose structure of lithium iron phosphate particles, making them prone to cracking under rolling pressure during the fabrication of the cathode, leading to a sharp deterioration in the material's capacity performance. Preferably, the mass of the porous hollow carbon microspheres is 1% to 10% of the mass of the mixed metal salt in the mixed metal salt solution.

[0071] 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.

[0072] 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.

[0073] S400: After mixing the lithium iron phosphate material precursor and dispersant, the mixture is ground and crushed;

[0074] According to some specific embodiments of this application, the process of mixing the lithium iron phosphate material precursor and the dispersant further includes: mixing the lithium iron phosphate material precursor, the second carbon source, and the dispersant, followed by grinding and crushing. The role of the second carbon source is to form a carbon coating layer on the surface of the lithium iron phosphate particles during the subsequent calcination process, thereby effectively improving the conductivity of the lithium iron phosphate particles.

[0075] According to some specific embodiments of this application, the mass ratio of the lithium iron phosphate material precursor and the second carbon source is (92:8) to (85:15), thereby further ensuring the formation of a carbon coating layer on the surface of the lithium iron phosphate particles, and further ensuring the effective improvement of the conductivity of the lithium iron phosphate particles.

[0076] In the embodiments of this application, the specific type of dispersant is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific embodiments, the dispersant can be deionized water.

[0077] S500: Spray drying of the ground and crushed material;

[0078] In this step, the ground and crushed material is spray-dried to form powder with a certain particle size.

[0079] According to some specific embodiments of this application, the outlet temperature for spray drying of the ground and crushed material is 180℃ to 230℃, for example, it can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, or any range between the two. Increasing the spray drying outlet temperature will increase the drying speed of the particles, causing the pit depth on the surface of the lithium iron phosphate particles to increase. By limiting the spray drying outlet temperature within the above range, it can be further ensured that the average depth of the pits on the surface of the finally prepared lithium iron phosphate particles does not exceed 42% of the long diameter of the lithium iron phosphate particles, thereby further ensuring that the prepared lithium iron phosphate material can achieve high capacity performance while maintaining good long-cycle performance. If the spray drying outlet temperature is too high, the average depth of the pits on the surface of the lithium iron phosphate particles will be too large, which will cause the material particles to be easily crushed under roller pressure, resulting in a decrease in material capacity performance. Preferably, the outlet temperature for spray drying of the ground and crushed material is 180℃~220℃.

[0080] S600: Under a protective atmosphere, the spray-dried material is calcined at high temperature, ground and crushed to obtain lithium iron phosphate material.

[0081] In this step, the spray-dried material is calcined at high temperature under a protective atmosphere. During the high-temperature calcination process, the porous hollow carbon microspheres decompose and shrink to form pits and / or pores. The second carbon source forms a carbon coating layer (coating the surface of the lithium iron phosphate particles) during the calcination process. After grinding and crushing, the lithium iron phosphate material is finally obtained.

[0082] According to some specific embodiments of this application, the high-temperature calcination temperature for the spray-dried material is 650℃ to 710℃, for example, it can be 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, or any range between the two. By limiting the high-temperature calcination temperature within the above range, it can be further ensured that the average depth of the pits on the surface of the finally prepared lithium iron phosphate particles does not exceed 42% of the long diameter of the lithium iron phosphate particles, thereby further ensuring that the prepared lithium iron phosphate material can achieve high capacity performance while maintaining good long-cycle performance. If the high-temperature calcination temperature is too high, the average depth of the pits on the surface of the lithium iron phosphate particles will be too large, which will cause the material particles to be easily crushed under roller pressure, resulting in a decrease in material capacity performance. Preferably, the high-temperature calcination temperature for the spray-dried material is 650℃ to 700℃.

[0083] According to some specific embodiments of this application, the high-temperature calcination time for the spray-dried material is 5h to 12h, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any range between the two. By limiting the high-temperature calcination time within the above range, it can be further ensured that the average depth of the pits on the surface of the finally prepared lithium iron phosphate particles does not exceed 42% of the major diameter of the lithium iron phosphate particles, thereby further ensuring that the prepared lithium iron phosphate material can achieve high capacity performance while maintaining good long-cycle performance. If the high-temperature calcination time is too long, the average depth of the pits on the surface of the lithium iron phosphate particles will be too large, which will make the material particles easily crushed under roller pressure, resulting in a decrease in material capacity performance. Preferably, the high-temperature calcination time for the spray-dried material is 5h to 10h.

[0084] The method for preparing the above-mentioned lithium iron phosphate material according to the embodiments of this application allows for the formation of pits on the outer surface of some of the lithium iron phosphate particles, which not only shortens the migration distance of lithium ions inside the lithium iron phosphate particles but also expands the wetting range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and giving it high capacity performance. And / or, this method can also create a hollow pore structure at the center of the formed lithium iron phosphate particles, which helps to disperse the internal stress concentration caused by lattice distortion during the continuous insertion and extraction of lithium ions, thus helping to suppress the breakage of the lithium iron phosphate particles and effectively improving the long-cycle performance of the lithium iron phosphate material. Therefore, the lithium iron phosphate material prepared by this method can achieve high capacity performance while maintaining good long-cycle performance.

[0085] 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. 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, and will not be repeated here.

[0086] 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.

[0087] 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).

[0088] 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.

[0089] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes a positive electrode plate as described in the third aspect. This allows the battery to maintain good long-cycle performance while increasing its rate discharge capacity. In an embodiment of this application, the battery can be a lithium-ion battery.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.).

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] In a fifth aspect of this application, an electrical system is proposed. According to an embodiment of this application, the electrical system includes: an electrical system itself, and an energy storage device that supplies power to the electrical system. The energy storage device includes the battery described in the above embodiments. Thus, the electrical system possesses all the advantages of the battery, which will not be elaborated further here.

[0102] The aforementioned energy storage device can be powered by an electrical system or by an energy storage unit within that system. The aforementioned electrical system can include, but is not limited to, portable electronic devices such as mobile phones, tablets, laptops, desktop computers, smart bracelets, smartwatches, e-readers, and game consoles. It can also include, but is not limited to, vehicles such as cars, trucks, sedans, freight cars, bullet trains, high-speed trains, and electric vehicles. Furthermore, it can power various household appliances, including but not limited to refrigerators, lights, and air conditioners.

[0103] In addition, the energy storage device of this application may include at least one of the following: a power energy storage device for the generation side of a power system, a power energy storage device (e.g., an electrochemical energy storage device) for the distribution side of a power system, and a power energy storage device for the user side of a power system.

[0104] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0105] 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.

[0106] Example 1

[0107] 1) Lithium iron phosphate materials

[0108] ① Prepare a 3 mol / L sucrose solution, use spray drying to obtain carbon microsphere precursor, and then calcine (calcine temperature is 200℃, time is 4h) to make the sucrose shrink due to heat to form porous hollow carbon microspheres.

[0109] ②According to LiFe 0.99 Ti 0.01 To prepare a mixed metal salt solution for PO4, weigh out the required stoichiometric ratio of iron source (ferrous oxalate), phosphorus source (phosphate), lithium source (lithium carbonate), and titanium source (titanium tetrachloride). Use deionized water as the solvent, with a titanium molar concentration of 3 mol / L. Then, prepare a 1 mol / L strong alkali solution as a precipitant solution and a 1 mol / L ammonia solution as a complexing agent solution. Finally, weigh out and add porous hollow carbon microspheres, with the mass of the porous hollow carbon microspheres being 1% of the mass of the mixed metal salt.

[0110] ③ 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 maintained at 9.5 and the reaction temperature is 180℃. The reaction is carried out for 10 hours. The precursor of lithium manganese iron phosphate material is obtained by precipitation and combination reaction, followed by solid-liquid separation, washing and drying.

[0111] ④ Weigh out the above precursor materials and carbon source (glucose) at a mass ratio of 85%:15%, mix them evenly, add an appropriate amount of deionized water as a dispersant, and then grind and crush them.

[0112] ⑤ Spray dry the ball-milled material (spray outlet temperature is 180℃) to form powder with a certain particle size.

[0113] ⑥ The dried powder is placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere is nitrogen, 650℃, 5h), and then ground and crushed to obtain lithium iron phosphate material.

[0114] 2) Positive electrode plate

[0115] 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.

[0116] ② The slurry is evenly coated onto the aluminum foil on the specified side by extrusion coating to form a positive electrode sheet.

[0117] 3) Manufacturing lithium-ion batteries

[0118] 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.

[0119] 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.

[0120] 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.

[0121] Example 2

[0122] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate material, the amount of porous hollow carbon microspheres added was controlled to be 3% of the mass of the mixed metal salt, as Example 2.

[0123] Example 3

[0124] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate material, the amount of porous hollow carbon microspheres added was controlled to be 5% of the mass of the mixed metal salt, as Example 3.

[0125] Example 4

[0126] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate material, the amount of porous hollow carbon microspheres added was controlled to be 7% of the mass of the mixed metal salt, as Example 4.

[0127] Example 5

[0128] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate material, the amount of porous hollow carbon microspheres added was controlled to be 10% of the mass of the mixed metal salt, as Example 5.

[0129] Example 6

[0130] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate material, the amount of porous hollow carbon microspheres added was controlled to be 13% of the mass of the mixed metal salt, as Example 6.

[0131] Example 7

[0132] Following a similar method to Example 1 above, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature was controlled at 190°C, as Example 7.

[0133] Example 8

[0134] Following a similar method to Example 1 above, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature is controlled at 200°C, as Example 8.

[0135] Example 9

[0136] Following a similar method to Example 1 above, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature was controlled at 210°C, as Example 9.

[0137] Example 10

[0138] Following a similar method to Example 1 above, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature was controlled at 220°C, as Example 10.

[0139] Example 11

[0140] Following a similar method to Example 1 above, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature was controlled at 230°C, as Example 11.

[0141] Example 12

[0142] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 660°C, as Example 12.

[0143] Example 13

[0144] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 670°C, as Example 13.

[0145] Example 14

[0146] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 680°C, as Example 14.

[0147] Example 15

[0148] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 690°C, as Example 15.

[0149] Example 16

[0150] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 700°C, as Example 16.

[0151] Example 17

[0152] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination temperature was controlled at 710°C, as Example 17.

[0153] Example 18

[0154] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination time was controlled to be 7 hours, as Example 18.

[0155] Example 19

[0156] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination time was controlled to be 10 hours, as Example 19.

[0157] Example 20

[0158] Following a similar method to Example 1 above, in step ⑥ of preparing lithium iron phosphate material, the high-temperature calcination time was controlled to be 12 hours, as Example 20.

[0159] Example 21

[0160] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate materials, LiFe... 0.98 Ti 0.02 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 21.

[0161] Example 22

[0162] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate materials, LiFe... 0.97 Ti 0.03 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 22.

[0163] Example 23

[0164] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate materials, LiFe... 0.96 Ti 0.04 The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 23.

[0165] Example 24

[0166] Following a similar method to Example 1 above, in step ② of preparing lithium iron phosphate materials, LiFe... 0.95 Ti 0.05The raw materials were weighed according to the stoichiometric ratio of PO4, as in Example 24.

[0167] Comparative Example 1

[0168] 1) Positive electrode material

[0169] 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 carbon source (glucose) at 15% of the total mass ratio of the above raw materials 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.

[0170] ② Spray dry the ball-milled material (spray outlet temperature is 180℃) to form powder with a certain particle size.

[0171] ③ The dried powder is placed in a vacuum atmosphere sintering furnace for sintering (protective atmosphere is nitrogen, 700℃, 10h), and then the lithium iron phosphate material is obtained by ball milling.

[0172] 2) Positive electrode plate

[0173] 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.

[0174] ② The slurry is evenly coated onto the aluminum foil on the specified side by extrusion coating to form a positive electrode sheet.

[0175] 3) Manufacturing lithium-ion batteries

[0176] 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.

[0177] 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.

[0178] 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.

[0179] Test example:

[0180] 1) Particle size distribution test

[0181] The particle size distribution of lithium iron phosphate particles 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 6 As shown.

[0182] 2) Test of average pit depth and cross-sectional area ratio of internal pores on the surface of lithium iron phosphate particles.

[0183] Positive electrode samples were selected, and the positive electrode sheets were cut using a focused ion beam. The cross-section of the positive electrode sheets was then observed using a scanning electron microscope, and images were taken at 2000x magnification. ImageJ image recognition software was then used to statistically analyze the proportion of the depth of 50 particle pits and the cross-sectional area of ​​internal pores to the total cross-sectional area of ​​the particle, and the average value was calculated. The test results are shown in Table 1 and below. Figures 1-5 As shown.

[0184] 3) Rate discharge capacity test

[0185] 4) Cyclic performance test

[0186] At 25°C, the lithium batteries prepared in the examples and comparative examples were charged to 3.65V at a 1C rate and then discharged to 2.5V at a 1C rate. The capacity of the first cycle was taken as the initial capacity, and the capacity of the 200th cycle was divided by the initial capacity to obtain the retention rate value.

[0187] 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 point was recorded. The test results are shown in Table 1.

[0188] Figure 1 The image shows the surface morphology of the lithium iron phosphate particles prepared in Example 1. Figure 2 This is a magnified surface morphology image of the lithium iron phosphate particles prepared in Example 1. Figure 3 This is a cross-sectional morphology image of the lithium iron phosphate particles prepared in Example 1. From... Figures 1-3As can be seen, some of the outer surfaces of the lithium iron phosphate particles prepared in Example 1 are recessed into the interior of the lithium iron phosphate particles, forming pits, and the interior center of the lithium iron phosphate particles has a hollow pore structure. It can also be seen that the lithium iron phosphate particles prepared in Example 1 are secondary particles formed from primary nanoparticles.

[0189] Figure 4 The image shows the surface morphology of the lithium iron phosphate particles prepared in Comparative Example 1. Figure 5 This is a cross-sectional morphology image of the lithium iron phosphate particles prepared in Comparative Example 1. From... Figures 4-5 As can be seen, the outer surface of the lithium iron phosphate particles prepared in Comparative Example 1 is slightly concave towards the interior of the lithium iron phosphate particles, but not enough to form pits. Furthermore, the interior center of the lithium iron phosphate particles does not have a hollow pore structure. In addition, the lithium iron phosphate particles prepared in Comparative Example 1 are primary particles.

[0190] Figure 6 The 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 1.3 μm, and the particle size Dv50 of Example 1 is about 6.2 μm.

[0191] Table 1

[0192]

[0193]

[0194] As can be seen from Table 1, compared with Comparative Example 1, the rate discharge capacity and capacity retention of Examples 1-24 are effectively improved. It can be seen that by forming pits by recessing part of the outer surface of the lithium iron phosphate particles into the interior of the lithium iron phosphate particles, and by having a hollow pore structure in the center of the interior of the lithium iron phosphate particles, the battery can effectively improve its capacity performance while maintaining good long cycle performance.

[0195] As can be seen from Table 1, compared with Examples 6, 11, 17 and 20, the rate discharge capacity of Examples 1-5, Examples 7-10, Examples 12-16, Examples 18-19 and Examples 21-23 is further improved. It can be seen that by limiting the average depth of the pits on the surface of lithium iron phosphate particles to no more than 42% of the major diameter of lithium iron phosphate particles, lithium iron phosphate materials can be further made to have better high-capacity performance.

[0196] As can be seen from Table 1, compared with Example 6, the rate discharge capacity of Examples 1-5 and Examples 7-24 is further improved. It can be seen that by limiting the average cross-sectional area of ​​the hollow pore structure of lithium iron phosphate particles to no more than 30% of the maximum cross-sectional area of ​​lithium iron phosphate particles, lithium iron phosphate materials can be further made to have better high-capacity performance.

[0197] As can be seen from Table 1, compared with Examples 17, 20, and 24, the rate discharge capacity of Examples 1-5, 7-10, 12-16, 18-19, and 21-23 was further improved. It can be seen that by limiting the particle size Dv50 of lithium iron phosphate particles to the range of 6μm to 8μm, lithium iron phosphate materials can be further made to have better high-capacity performance.

[0198] As can be seen from Examples 1-6 in Table 1, in step ② of preparing lithium iron phosphate materials, gradually increasing the amount of porous hollow carbon microspheres increases the proportion of the average surface pit depth and the average internal pore cross-sectional area of ​​the material particles, thereby improving the rate discharge capacity of the battery. However, excessive addition of porous hollow carbon microspheres can lead to a sharp deterioration in the rate discharge capacity of the battery. Therefore, in step ② of preparing lithium iron phosphate materials, the amount of porous hollow carbon microspheres added is preferably ≤10%.

[0199] As can be seen from Examples 1 and 7-11 in Table 1, in step ⑤ of preparing lithium iron phosphate material, increasing the spray drying outlet temperature can increase the proportion of the average surface pit and the cross-sectional area of ​​the average internal pores of the material particles, and the corresponding rate discharge capacity of the battery is also improved. However, excessive pit depth will lead to a decrease in the rate discharge capacity of the battery. Therefore, in step ⑤ of preparing lithium iron phosphate material, the spray drying outlet temperature is preferably 180℃ to 220℃.

[0200] As can be seen from Examples 1 and 12-17 in Table 1, in step ⑥ of preparing lithium iron phosphate material, increasing the calcination temperature can increase the proportion of the average surface pit and the cross-sectional area of ​​the average internal pores of the material particles, and the corresponding rate discharge capacity of the battery is also improved. However, excessively large material particle pits will lead to a decrease in the rate discharge capacity of the battery. Therefore, the preferred high-temperature calcination temperature is 650℃ to 700℃.

[0201] As can be seen from Examples 1 and 18-20 in Table 1, in step ⑥ of preparing lithium iron phosphate material, increasing the calcination time can increase the proportion of the average surface pit and the cross-sectional area of ​​the average internal pores of the material particles, and the corresponding rate discharge capacity of the battery is also improved. However, excessively large material particle pits will lead to a decrease in the rate discharge capacity of the battery. Therefore, the preferred high-temperature calcination temperature is 5h to 10h.

[0202] As can be seen from Examples 1 and 21-24 in Table 1, as the content of titanium doping gradually increases, the particle size of the material decreases, while the average depth of surface pits and the proportion of cross-sectional area of ​​internal pores of the average particles increase slightly. Consequently, the rate discharge capacity of the battery first increases and then decreases. This is mainly because excessive doping may cause the material to form impurity compounds, thus reducing capacity performance. Therefore, the lithium iron phosphate material (LiFe) of this application... x Ti y The preferred Ti doping amount for PO4 is y≤0.04.

[0203] 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.

[0204] 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: The lithium iron phosphate particles have a portion of their outer surface recessed into their interior to form pits, wherein the average depth of the pits on the surface of the lithium iron phosphate particles does not exceed 42% of the major diameter of the lithium iron phosphate particles. The lithium iron phosphate particles have a hollow pore structure at their internal center, and the average cross-sectional area of ​​the hollow pore structure of the lithium iron phosphate particles does not exceed 30% of the maximum cross-sectional area of ​​the lithium iron phosphate particles; The particle size Dv50 of the lithium iron phosphate particles is 6μm~8μm.

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

3. The lithium iron phosphate material according to claim 1, characterized in that, The average depth of the pits on the surface of the lithium iron phosphate particles is 10% to 42% of the major diameter of the lithium iron phosphate particles.

4. The lithium iron phosphate material according to any one of claims 1 to 3, characterized in that, The lithium iron phosphate particles include titanium, and the chemical structural formula of the lithium iron phosphate particles is LiFe. x Ti y PO4, where x + y = 1, 0 <y≤0.05。 5. A method for preparing the lithium iron phosphate material according to any one of claims 1 to 4, characterized in that, include: (1) Preparation of porous hollow carbon microspheres; (2) Weigh each raw material according to the required stoichiometric ratio in lithium iron phosphate material and prepare a mixed metal salt solution; (3) The mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution are placed in a reaction vessel and reacted to obtain the lithium iron phosphate material precursor; (4) The lithium iron phosphate material precursor and dispersant are mixed and then ground and crushed; (5) Spray dry the ground and crushed material; (6) Under a protective atmosphere, the spray-dried material is calcined at high temperature, ground and crushed to obtain lithium iron phosphate material.

6. The method according to claim 5, characterized in that, Step (1) includes: A first carbon source solution was prepared, and the first carbon source solution was spray-dried to obtain a carbon microsphere precursor. The carbon microsphere precursor is calcined to obtain the porous hollow carbon microspheres.

7. The method according to claim 5, characterized in that, In step (2), 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。 8. The method according to claim 5, characterized in that, In step (3), the temperature of the mixed metal salt solution, the porous hollow carbon microspheres, 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 (3), the mass of the porous hollow carbon microspheres is 1% to 13% of the mass of the mixed metal salt in the mixed metal salt solution; And / or, in step (3), the precipitant solution comprises a strong alkaline solution of 0.5 mol / L to 1.5 mol / L; And / or, in step (3), the complexing agent solution comprises an aqueous ammonia solution of 0.5 mol / L to 1.5 mol / L.

9. The method according to claim 5, characterized in that, In step (4), during the mixing of the lithium iron phosphate material precursor and the dispersant, the following further steps are included: The lithium iron phosphate material precursor, the second carbon source, and the dispersant are mixed and then ground and crushed.

10. The method according to claim 9, characterized in that, The mass ratio of the lithium iron phosphate material precursor to the second carbon source is (92:8) to (85:15).

11. The method according to any one of claims 5 to 10, characterized in that, In step (5), the outlet temperature for spray drying of the ground and crushed material is 180℃~230℃.

12. The method according to any one of claims 5 to 10, characterized in that, In step (6), the high-temperature calcination temperature for the spray-dried material is 650℃~710℃; And / or, in step (6), the spray-dried material is subjected to high-temperature calcination for 5h to 12h.

13. A positive electrode plate, characterized in that, The lithium iron phosphate material includes any one of claims 1 to 4 or the lithium iron phosphate material prepared by the method described in any one of claims 5 to 12.

14. A battery, characterized in that, The lithium iron phosphate material includes any one of claims 1 to 4, the lithium iron phosphate material prepared by the method described in any one of claims 5 to 12, or the positive electrode sheet described in claim 13.

15. An electrical system, characterized in that, include: Electrical systems, and An energy storage device that supplies power to the electrical system, the energy storage device comprising the battery of claim 14.

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