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

Abstract

The invention discloses a lithium iron phosphate material and a preparation method thereof, a positive plate, a battery and a power utilization system, the lithium iron phosphate material comprises: lithium iron phosphate particles, a part of outer surfaces of the lithium iron phosphate particles are recessed towards the interior of the lithium iron phosphate particles to form pits; and / or a hollow hole structure is arranged in the center of the interior of the lithium iron phosphate particle.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a lithium iron phosphate material, a preparation method thereof, a positive electrode sheet, a battery and a power utilization system. BACKGROUND

[0002] At present, the main positive electrode material used by lithium ion batteries is lithium iron phosphate, and the crystal structure thereof belongs to olivine structure and has good safety and stability. Lithium batteries increasingly pursue large-capacity cells. In the same volume, the use of high-compactness or high-capacity lithium iron phosphate material in the positive electrode sheet can obtain higher volume energy density, and therefore it is necessary to develop a high-capacity lithium iron phosphate material with long cycle performance.

[0003] However, at present, in order to improve the compactness density, the lithium iron phosphate material must be matched with a certain proportion of large particles, and the capacity performance of the large particles is poor. In addition, with the increase of the cycle number of lithium batteries, the crystal structure of the positive electrode material is distorted due to the continuous deintercalation process of lithium ions, and micro-cracks are generated, and in addition to the corrosion of the electrolyte, the particles are prone to breakage, which eventually leads to the rapid deterioration of the cycle performance of the lithium battery. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art. To this end, the purpose of the present application is to propose a lithium iron phosphate material, a preparation method thereof, a positive electrode sheet, a battery and a power utilization system. The lithium iron phosphate material of the present application can realize the high-capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance.

[0005] In one aspect of the present application, the present application proposes a lithium iron phosphate material. According to the embodiments of the present application, the lithium iron phosphate material comprises:

[0006] 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;

[0007] and / or, the inside center position of the lithium iron phosphate particles has a hollow hole structure.

[0008] According to the lithium iron phosphate material of the embodiments of the present application, part of the outer surface of the lithium iron phosphate particles is recessed to form pits towards the inside of the lithium iron phosphate particles, which not only shortens the migration distance of lithium ions in the lithium iron phosphate particles, but also expands the infiltration range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and making the lithium iron phosphate material have high capacity performance. In addition, the lithium iron phosphate particles have a hollow hole structure at the central position of the inside, which is beneficial to dispersing the internal stress concentration caused by the lattice distortion of the crystal structure of the lithium iron phosphate material in the process of continuous deintercalation of lithium ions, and is beneficial to inhibiting the crushing of the lithium iron phosphate particles, thereby effectively improving the long cycle performance of the lithium iron phosphate material. Therefore, the lithium iron phosphate material of the present application can realize high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance.

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

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

[0011] In some embodiments of the present application, the average depth of the pits on the surface of the lithium iron phosphate particles is not more than 42% of the length diameter of the lithium iron phosphate particles.

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

[0013] In some embodiments of the present application, the average cross-sectional area of the hollow hole structure of the lithium iron phosphate particles is not more than 30% of the maximum cross-sectional area of the lithium iron phosphate particles.

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

[0015] In some embodiments of the present application, the lithium iron phosphate particles contain titanium elements, and the chemical formula of the lithium iron phosphate particles is LiFe x Ti y PO4, wherein x+y=1 and 0

[0016] In the second aspect of the present application, a method for preparing the above lithium iron phosphate material is provided, which comprises:

[0017] (1) preparing porous hollow carbon microspheres;

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

[0019] (3) placing the mixed metal salt solution, the porous hollow carbon microspheres, a precipitant solution and a complexing agent solution into a reaction kettle, and reacting to obtain a lithium iron phosphate material precursor;

[0020] (4) mixing the lithium iron phosphate material precursor and a dispersant, and then grinding and crushing;

[0021] (5) spray drying the material after grinding and crushing;

[0022] (6) under a protective atmosphere, high-temperature calcining the material after spray drying, and grinding and crushing to obtain a lithium iron phosphate material.

[0023] According to the method for preparing the lithium iron phosphate material in the embodiments of the present application, part of the outer surface of the lithium iron phosphate particles formed is recessed to form pits towards the inside of the lithium iron phosphate particles, which not only shortens the migration distance of lithium ions in the inside of the lithium iron phosphate particles, but also expands the infiltration range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and making the lithium iron phosphate material have high capacity performance. And / or, the inside center position of the lithium iron phosphate particles formed has a hollow hole structure, which is beneficial to dispersing the internal stress concentration of the crystal structure of the lithium iron phosphate material caused by lattice distortion in the process of continuous deintercalation of lithium ions, and is beneficial to inhibiting the crushing of the lithium iron phosphate particles, thereby effectively improving the long cycle performance of the lithium iron phosphate material. Thus, the lithium iron phosphate material prepared by the method can realize high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance.

[0024] In some embodiments of the present application, step (1) comprises: 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 the present application, in step (2), the lithium source, the iron source, the phosphorus source and the titanium source are weighed according to the stoichiometric ratio required in LiFeTiPO4. x Ti y The iron source, the phosphorus source, the lithium source and the titanium source are weighed according to the stoichiometric ratio required in LiFeTiPO4, and the mixed metal salt solution is prepared, wherein x+y=1, and 0<y≤0.05.

[0026] In some embodiments of the present 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 are reacted in the reaction kettle is 180-220 DEG C, the reaction time is 8-10 hours, and the pH of the reaction system is 9-11; and / or, in step (3), the mass of the porous hollow carbon microspheres is 1-13% of the mass of the mixed metal salt in the mixed metal salt solution; and / or, in step (3), the precipitant solution comprises a 0.5-1.5 mol / L strong alkali solution; and / or, in step (3), the complexing agent solution comprises a 0.5-1.5 mol / L ammonia solution.

[0027] In some embodiments of the present application, in step (4), during the mixing of the lithium iron phosphate material precursor and the dispersant, the lithium iron phosphate material precursor, a second carbon source, and the dispersant are mixed, and then are ground and crushed.

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

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

[0030] In some embodiments of the present application, in step (6), the temperature of the high-temperature calcination of the spray-dried material is 650-710 DEG C; and / or, in step (6), the time of the high-temperature calcination of the spray-dried material is 5-12 hours.

[0031] In a third aspect of the present application, the present application provides a positive electrode sheet. According to embodiments of the present application, the positive electrode sheet comprises the lithium iron phosphate material of the first aspect of the present application, or the lithium iron phosphate material prepared by the method of the second aspect of the present application. It should be noted that the features and advantages described above for the lithium iron phosphate material and the preparation method thereof are also applicable to the positive electrode sheet, and will not be described here again.

[0032] In a fourth aspect of the present application, the present application provides a battery. According to embodiments of the present application, the battery comprises the positive electrode sheet of the third aspect of the present application. Thus, the battery can improve the rate discharge capacity of the battery on the basis of maintaining good long cycle performance.

[0033] In a fifth aspect of the present application, a power consuming system is provided. According to embodiments of the present application, the power consuming system comprises: a power consuming system, and an energy storage device, the energy storage device supplies power to the power consuming system, the energy storage device comprises the battery as described in the above embodiments. Thus, the power consuming system has all the advantages of the battery, which are not repeated here.

[0034] Additional aspects and advantages of the present application will be made apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a surface morphology of lithium iron phosphate particles prepared in Example 1;

[0036] Figure 2 is a magnified surface morphology of lithium iron phosphate particles prepared in Example 1;

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

[0038] Figure 4 is a surface morphology of lithium iron phosphate particles prepared in Comparative Example 1;

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

[0040] Figure 6 is a particle size distribution of lithium iron phosphate materials prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0041] Embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein the same or like reference numerals and letters in the drawing and the following description denote the same or functions elements throughout the several embodiments. The embodiments described below are merely exemplary for the purposes of explanation and are not intended to limit the application, which is limited only by the claims.

[0042] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate descriptions and are understood to include values approximately around or close to that endpoint or value as understood by persons of ordinary skill in the art. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to generate one or more new numeric ranges, which are to be considered as specifically disclosed herein.

[0043] In one aspect of the present application, the present application provides a lithium iron phosphate material. According to embodiments of the present application, the lithium iron phosphate material comprises: lithium iron phosphate particles, a part of the outer surface of the lithium iron phosphate particles is recessed towards the interior of the lithium iron phosphate particles to form a pit; and / or, the central position of the interior of the lithium iron phosphate particles has a hollow hole structure. Thus, the lithium iron phosphate material of the present application can realize high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance.

[0044] The principle that the lithium iron phosphate material of the present application can realize the above beneficial effects will be described in detail as follows:

[0045] In the lithium iron phosphate material of the present application, the part of the outer surface of the lithium iron phosphate particles is recessed towards the interior of the lithium iron phosphate particles to form a pit, which not only helps to shorten the migration distance of lithium ions inside the lithium iron phosphate particles, but also can expand the infiltration range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material, so that the lithium iron phosphate material has high capacity performance. And / or, the central position of the interior of the lithium iron phosphate particles has a hollow hole structure, which is beneficial to disperse the internal stress concentration caused by the lattice distortion of the crystal structure of the lithium iron phosphate material in the process of continuous deintercalation of lithium ions, and is beneficial to inhibit the crushing of the lithium iron phosphate particles, thereby effectively improving the long cycle performance of the lithium iron phosphate material. Thus, the lithium iron phosphate material of the present application can realize high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance.

[0046] According to some specific embodiments of the present application, the lithium iron phosphate particles are secondary particles formed by primary nanoparticles, the pits on the surface of the lithium iron phosphate particles are formed in the process of forming the secondary particles from the primary nanoparticles, and at the same time, the hollow hole structure of the central position of the interior of the lithium iron phosphate particles is also formed in the process of forming the secondary particles from the primary nanoparticles.

[0047] According to still some specific embodiments of the present application, the average depth of the pits on the surface of the lithium iron phosphate particles is not more than 42% of the length 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 any two of them, etc. By limiting the average depth of the pits on the surface of the lithium iron phosphate particles within the above range, the migration distance of lithium ions inside the lithium iron phosphate particles can be further shortened, and the infiltration range of the electrolyte can be further expanded, thereby further improving the kinetics of the lithium iron phosphate material, so that the lithium iron phosphate material has more excellent high capacity performance.

[0048] As some more preferred embodiments, the average depth of the pits on the surface of the lithium iron phosphate particles is 10% to 42% of the length-diameter of the lithium iron phosphate particles. By limiting the average depth of the pits on the surface of the lithium iron phosphate particles within the above range, the migration distance of lithium ions inside the lithium iron phosphate particles can be further shortened, and the infiltration range of the electrolyte can be further expanded, thereby further improving the kinetics of the lithium iron phosphate material and making the lithium iron phosphate material have more excellent high-capacity performance.

[0049] According to still some specific embodiments of the present application, the average cross-sectional area of the hollow hole structure of the lithium iron phosphate particles is not more than 30% of the maximum cross-sectional area of the lithium iron phosphate particles, for example, can be 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, or any range between any two of them, etc. By limiting the average cross-sectional area of the hollow hole structure of the lithium iron phosphate particles within the above range, the internal stress concentration caused by the lattice distortion of the crystal structure of the lithium iron phosphate material during the continuous deintercalation of lithium ions can be further dispersed, and the crushing of the lithium iron phosphate particles can be further inhibited, thereby further effectively improving the long cycle performance of the lithium iron phosphate material.

[0050] In the present application, instruments and methods known in the art can be used to measure the average pit depth on the surface of the lithium iron phosphate particles and the cross-sectional area ratio of the internal holes. As a specific example, the positive electrode sheet sample is selected, the positive electrode sheet is cut using a focused ion beam, the cross section of the positive electrode sheet is observed using a scanning electron microscope, and then a 2,000 times magnification photo is taken. Then, the pit depth of 50 particles and the cross-sectional area ratio of the internal holes to the entire particle cross-sectional area are counted using the image recognition software ImageJ, and finally the average value is obtained.

[0051] According to still some specific embodiments of the present application, the particle size Dv50 of the lithium iron phosphate particles is 6 μm to 8 μm, for example, can be 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8 μm, or any range between any two of them, etc. By limiting the particle size Dv50 of the lithium iron phosphate particles within the above range, it is further beneficial to form pits on the outer surface of the lithium iron phosphate particles and hollow hole structures at the central position inside the lithium iron phosphate particles, thereby further benefiting the lithium iron phosphate material to realize high-capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance. Wherein, Dv50 refers to the particle size corresponding to the cumulative volume percentage of 50% of the lithium iron phosphate particles.

[0052] In the present application, instruments and methods known in the art can be used to measure the particle size Dv50 of the lithium iron phosphate particles. As a specific example, a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) is used to measure the particle size distribution of the lithium iron phosphate particles according to the particle size distribution laser diffraction method GB / T19077-2016.

[0053] According to some specific embodiments of the present application, the lithium iron phosphate particles further include titanium elements, and the chemical 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, i.e. the lithium iron phosphate particles are doped with titanium elements. By doping the lithium iron phosphate particles with titanium elements, the high-capacity performance of the lithium iron phosphate material can be further effectively improved.

[0054] According to some specific embodiments of the present application, the surface of the lithium iron phosphate particles is provided with a carbon coating layer, which can effectively improve the electrical conductivity of the lithium iron phosphate particles.

[0055] In a second aspect of the present application, a method for preparing the lithium iron phosphate material described above is provided. According to embodiments 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 porous hollow carbon microspheres described above 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 carbon microsphere precursors;

[0059] As some specific embodiments, the concentration of the first carbon source solution can 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 embodiments of the present application, the specific type of the first carbon source solution described above is not particularly limited, and can be selected according to actual needs by those skilled in the art, for example, it can be a sucrose solution.

[0061] S120: performing calcination on the carbon microsphere precursors, so that the first carbon source shrinks after being heated, to obtain the porous hollow carbon microspheres.

[0062] As some specific embodiments, the temperature for roasting the carbon microsphere precursor can be 180-220℃ (for example, can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.), and the time can be 3-5h (for example, can be 3h, 3.5h, 4h, 4.5h, 5h, etc.).

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

[0064] According to still some specific embodiments of the present application, the iron source, the phosphorus source, the lithium source, and the titanium source are weighed according to the stoichiometric ratio required in LiFePO4, and a mixed metal salt solution is prepared, wherein x+y=1, 0 x Ti y PO4, and a mixed metal salt solution is prepared, wherein x+y=1, 0

[0065] In the embodiments of the present application, the specific types of the above-mentioned iron source, the phosphorus source, the lithium source, and the titanium source are not particularly limited, and persons skilled in the art can select according to actual needs. As some specific embodiments, the iron source can be ferrous oxalate or iron sulfate or iron chloride, etc. As still some specific embodiments, the phosphorus source can be phosphoric acid or ammonium dihydrogen phosphate, etc. As yet some specific embodiments, the lithium source can be lithium carbonate or lithium hydroxide, etc. As yet some specific embodiments, the titanium source can be titanium tetrachloride or titanium oxalate, etc.

[0066] In the embodiments of the present application, the specific types of the solvent of the mixed metal salt solution are not particularly limited, and persons skilled in the art can select according to actual needs. As some specific embodiments, the solvent of the mixed metal salt solution can be deionized water.

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

[0068] In this step, the mixed metal salt solution, the porous hollow carbon microsphere, the precipitant solution, and the complexing agent solution are placed in a reaction kettle, and stirring is continuously carried out. The lithium iron phosphate material precursor is prepared by a precipitation reaction synthesis, followed by solid-liquid separation, washing, and drying. In the subsequent high-temperature roasting process, the porous hollow carbon microsphere can form pits and / or holes by cracking and shrinking.

[0069] According to still some specific embodiments of the present application, the temperature for the reaction of the mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution in the reaction kettle is 180-220℃ (for example, it can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.), the reaction time is 8-10h (for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, etc.), and the pH of the reaction system is 9-11 (for example, it can be 9, 9.5, 10, 10.5, 11, etc.). By limiting the temperature, the time and the pH of the reaction system in the reaction kettle in the above ranges, the reaction of the mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution in the reaction kettle can be further ensured, and the lithium iron phosphate material precursor is obtained.

[0070] According to still some specific embodiments of the present application, the mass of the porous hollow carbon microspheres is 1-13% 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 any two of them, etc. By limiting the amount of the porous hollow carbon microspheres in the above ranges, the average depth of the pits on the surface of the lithium iron phosphate particles prepared finally can be ensured to be not more than 42% of the length-diameter of the lithium iron phosphate particles, and the average cross-sectional area of the hollow pore structure of the lithium iron phosphate particles can be ensured to be not more than 30% of the maximum cross-sectional area of the lithium iron phosphate particles, so that the lithium iron phosphate material prepared can further ensure high capacity performance on the basis of maintaining good long cycle performance. If the amount of the porous hollow carbon microspheres is too large, the average depth of the pits on the surface of the lithium iron phosphate particles or the average cross-sectional area of the hollow pore structure will be too large, so that the structure of the lithium iron phosphate particles is very loose, and the material particles are easily cracked during the process of making the positive electrode sheet under the roller pressure, which leads to a sharp deterioration of the capacity performance of the material. Preferably, the mass of the porous hollow carbon microspheres is 1-10% of the mass of the mixed metal salt in the mixed metal salt solution.

[0071] In the embodiments of the present application, the specific type of the above-mentioned precipitant solution is not particularly limited, and those skilled in the art can select it according to the actual needs. As some specific embodiments, the precipitant solution includes a strong alkali solution of 0.5-1.5mol / L, for example, a sodium hydroxide solution or a potassium hydroxide solution of 0.5-1.5mol / L.

[0072] In the embodiments of the present application, the specific type of the complexing agent solution is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific embodiments, the complexing agent solution includes an ammonia solution with a concentration of 0.5 mol / L to 1.5 mol / L, for example, 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 the dispersant, grinding and crushing are performed.

[0074] According to some specific embodiments of the present application, during the mixing of the lithium iron phosphate material precursor and the dispersant, the lithium iron phosphate material precursor, a second carbon source and the dispersant are mixed, and then grinding and crushing are performed. The second carbon source is used to form a carbon coating layer on the surface of the lithium iron phosphate particles in the subsequent calcination process, thereby effectively improving the conductivity of the lithium iron phosphate particles.

[0075] According to still some specific embodiments of the present application, the mass ratio of the lithium iron phosphate material precursor to the second carbon source is (92:8) to (85:15), thereby further ensuring the formation of the 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 the present application, the specific type of the dispersant is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific embodiments, the dispersant can be deionized water.

[0077] S500: Spray drying is performed on the material after grinding and crushing.

[0078] In this step, spray drying is performed on the material after grinding and crushing to form a powder with a certain particle size.

[0079] According to some embodiments of the present application, the outlet temperature of the spray drying of the ground and crushed material is 180-230°C, for example, it can be 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, or any range between any two of them, etc. Increasing the outlet temperature of the spray drying increases the drying speed of the particles, and causes the depth of the pits on the surface of the lithium iron phosphate particles to be larger. By limiting the outlet temperature of the spray drying to the above range, the average depth of the pits on the surface of the lithium iron phosphate particles prepared finally can be further ensured to be not more than 42% of the length-diameter of the lithium iron phosphate particles, thereby further ensuring that the lithium iron phosphate material prepared can realize the high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance. If the outlet temperature of the spray drying is too high, the average depth of the pits on the surface of the lithium iron phosphate particles will be too large, thereby causing the particles of the material under the roller pressure to be easily cracked, resulting in a decrease in the capacity performance of the material. Preferably, the outlet temperature of the spray drying of the ground and crushed material is 180-220°C.

[0080] S600: under a protective atmosphere, high-temperature calcining the material after the spray drying, and grinding and crushing to obtain a lithium iron phosphate material.

[0081] In this step, under a protective atmosphere, high-temperature calcining the material after the spray drying, in the process of high-temperature calcining, the pits and / or holes can be formed by the cracking and shrinking of the porous hollow carbon microspheres, the second carbon source forms a carbon coating layer (coated on the surface of the lithium iron phosphate particles) in the process of calcining, and grinding and crushing to obtain a lithium iron phosphate material finally.

[0082] According to some embodiments of the present application, the temperature of the high-temperature calcining of the material after the spray drying is 650-710°C, for example, it can be 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, or any range between any two of them, etc. By limiting the temperature of the high-temperature calcining to the above range, the average depth of the pits on the surface of the lithium iron phosphate particles prepared finally can be further ensured to be not more than 42% of the length-diameter of the lithium iron phosphate particles, thereby further ensuring that the lithium iron phosphate material prepared can realize the high capacity performance of the lithium iron phosphate material on the basis of maintaining good long cycle performance. If the temperature of the high-temperature calcining is too high, the average depth of the pits on the surface of the lithium iron phosphate particles will be too large, thereby causing the particles of the material under the roller pressure to be easily cracked, resulting in a decrease in the capacity performance of the material. Preferably, the temperature of the high-temperature calcining of the material after the spray drying is 650-700°C.

[0083] According to still some embodiments of the present application, the high-temperature calcination time of the spray-dried material is 5h-12h, for example, can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or any range between any two of them. By limiting the high-temperature calcination time within the above range, the average depth of the pits on the surface of the finally prepared lithium iron phosphate particles is ensured to be no more than 42% of the length-diameter of the lithium iron phosphate particles, thereby further ensuring that the prepared lithium iron phosphate material can achieve high capacity performance on the basis of 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, thereby causing the material particles to be easily crushed under the roller pressure, resulting in a decrease in the capacity performance of the material. Preferably, the high-temperature calcination time of the spray-dried material is 5h-10h.

[0084] According to the method for preparing the above lithium iron phosphate material according to the embodiments of the present application, part of the outer surface of the formed lithium iron phosphate particles is recessed to form pits towards the inside of the lithium iron phosphate particles, which not only helps to shorten the migration distance of lithium ions inside the lithium iron phosphate particles, but also can expand the infiltration range of the electrolyte, thereby improving the kinetics of the lithium iron phosphate material and enabling the lithium iron phosphate material to have high capacity performance. And / or, the method can enable the central position inside the formed lithium iron phosphate particles to have a hollow hole structure, which is beneficial to dispersing the internal stress concentration caused by the lattice distortion of the crystal structure of the lithium iron phosphate material in the process of continuous deintercalation of lithium ions, and is beneficial to inhibiting the crushing of the lithium iron phosphate particles, thereby effectively improving the long cycle performance of the lithium iron phosphate material. Thus, the lithium iron phosphate material prepared by the method can achieve high capacity performance on the basis of maintaining good long cycle performance.

[0085] In a third aspect of the present application, a positive electrode sheet is provided. According to embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, and the positive electrode active material layer includes the lithium iron phosphate material of the first aspect of the present application or the lithium iron phosphate material prepared by the method of the second aspect. It should be noted that the features and advantages described above for the lithium iron phosphate material and the method for preparing the same also apply to the positive electrode sheet, which will not be described here.

[0086] According to embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer includes the above lithium iron phosphate material, a positive electrode binder and a positive electrode conductive agent. In embodiments of the present application, the positive electrode current collector can be made of a material having good electrical conductivity and mechanical strength, and is preferably an aluminum foil.

[0087] In embodiments of the present application, the specific type of the positive electrode conductive agent is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific examples, the positive electrode conductive agent includes at least one of graphite, super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Similarly, the specific type of the positive electrode binder is not particularly limited, and can be selected by those skilled in the art 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 the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the lithium iron phosphate material, the positive electrode conductive agent, the positive electrode binder, and any other components, in a solvent (e.g., N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode sheet can be obtained.

[0089] In a fourth aspect of the present application, a battery is provided. According to embodiments of the present application, the battery includes the positive electrode sheet of the third aspect. Thus, the battery can improve the rate discharge capacity of the battery while maintaining good long cycle performance. In embodiments of the present application, the above-mentioned battery can be a lithium ion battery.

[0090] Specifically, the above-mentioned battery includes the positive electrode sheet of the third aspect, a separator, a negative electrode sheet, and an electrolyte, and the separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0091] In some embodiments of the present 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, and the negative electrode active material layer includes a negative electrode active material.

[0092] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material can include at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0093] In some embodiments of the present 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 base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0094] In some embodiments of the present application, the negative electrode active material layer may further 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 the present application, the negative electrode active material layer may further include a negative electrode conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In the embodiments of the present application, the specific material of the diaphragm is not particularly limited. As some specific examples, the diaphragm includes at least one of a PP diaphragm, a PE diaphragm, a single-sided ceramic diaphragm, a double-sided ceramic diaphragm, a non-woven fabric diaphragm, and a glass fiber diaphragm.

[0097] In the embodiments of the present application, the electrolyte includes a lithium salt and an organic solvent, wherein the specific types and compositions of the lithium salt and the 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 difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, lithium perchlorate, and lithium bis(fluoromethanesulfonyl)imide. The above types of lithium salts can further optimize the conductivity, charge and discharge performance, and safety performance of lithium-ion batteries.

[0098] According to some specific embodiments of the present application, the concentration of lithium salt in the electrolyte is D, which satisfies 0.8mol / L≤D≤1.5mol / L, for example, it can be 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, etc. Therefore, by limiting the concentration D of lithium salt in the electrolyte to the above range, the conductivity, charge and discharge performance and safety performance of the lithium-ion battery can be further optimized.

[0099] The battery of the present application can include a battery cell form, a battery module form, and a battery pack form. In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0100] It should be noted that the features and advantages described above for the positive electrode sheet also apply to the battery, which will not be described here.

[0101] In a fifth aspect of the present application, a power utilization system is provided. According to embodiments of the present application, the power utilization system includes: a power utilization system, and an energy storage device, which supplies power to the power utilization system, and the energy storage device includes the battery described in the above embodiments. Thus, the power utilization system has all the advantages of the battery, which will not be described here.

[0102] The above-mentioned energy storage device can be used as a power source for a power utilization system, or as an energy storage unit for a power utilization system. The above-mentioned power utilization system can include, but is not limited to, portable electronic devices such as mobile phones, tablet computers, notebook computers, desktop computers, smart wristbands, smart watches, e-readers, game consoles, etc. It can also include, but is not limited to, vehicles such as cars, trucks, cars, trucks, bullet trains, high-speed trains, electric automatic cars, etc. In addition, it can also be various household appliances, such as refrigerators, electric lamps, air conditioners, etc.

[0103] In addition, the energy storage device of the present application can include at least one of a power storage device for the power generation side of a power system, a power storage device for the power distribution side of a power system (such as an electrochemical energy storage device), and a power 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 the power utilization device, which will not be described here.

[0105] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are intended to explain the present application only, and should not be construed as limiting the present application. If a specific technique or condition is not specified in the embodiments, it is performed according to the technique or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase on the market.

[0106] Example 1

[0107] 1) Lithium iron phosphate material

[0108] ①Prepare a 3 mol / L sucrose solution, use a spray drying method to obtain a carbon microsphere precursor, and then perform calcination (calcination temperature: 200°C, time: 4h) to form porous hollow carbon microspheres after the sucrose shrinks due to heat.

[0109] ②According to LiFe 0.99 Ti 0.01 Weigh the iron source (ferrous oxalate), the phosphorus source (phosphoric acid), the lithium source (lithium carbonate), and the titanium source (titanium tetrachloride) according to the stoichiometric ratio required in Li4Ti5PO12 to prepare a mixed metal salt solution, with deionized water as the solvent and a titanium molar concentration of 3 mol / L; then prepare a 1 mol / L strong base solution as a precipitant solution and a 1 mol / L ammonia solution as a complexing agent solution; then weigh the porous hollow carbon microspheres and add them, with the mass of the porous hollow carbon microspheres being 1% of the mass of the mixed metal salt.

[0110] ③Place the mixed metal salt solution, the precipitant solution, and the complexing agent solution prepared above in a reaction kettle, continuously stir them, maintain the pH value of the reaction liquid at 9.5, and maintain the reaction temperature at 180°C for 10h to synthesize using a precipitation reaction, and then perform solid-liquid separation, washing, and drying to obtain a lithium manganese iron phosphate material precursor.

[0111] ④Weigh the precursor material and the carbon source (glucose) according to a mass ratio of 85%:15%, uniformly mix them, then add an appropriate amount of deionized water as a dispersant, and then perform grinding and crushing.

[0112] ⑤Perform spray drying (spray outlet temperature: 180°C) on the ground material to form a powder with a certain particle size.

[0113] ⑥Place the dried powder in a vacuum atmosphere sintering furnace to perform high-temperature calcination (protective atmosphere: nitrogen, 650°C, 5h), and then perform grinding and crushing to obtain a lithium iron phosphate material.

[0114] 2) Positive electrode sheet

[0115] ①Weigh the corresponding amount of lithium iron phosphate material and polyvinylidene fluoride according to a mass ratio of 97%:3% in a stirring tank, then add an appropriate amount of N-methyl pyrrolidone (NMP) and stir for 6h to obtain a uniform slurry with suitable viscosity.

[0116] ②Uniformly coat the slurry on the aluminum foil on the specified side using an extrusion coating method to form a positive electrode sheet.

[0117] 3) Manufacture of lithium ion battery

[0118] ① Take the corresponding amount of artificial graphite, conductive carbon black and sodium carboxymethyl cellulose according to the mass ratio of 95%:2.5%:2.5% in a stirring tank, add an appropriate amount of deionized water and stir for 6h to obtain a uniform slurry with suitable viscosity; then coat the slurry on a copper foil with a thickness of 10μm, and put it into a vacuum oven, dry at 150℃ for 16h to obtain a negative electrode sheet.

[0119] ② Put 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 Put the positive and negative electrode discs into a glove box filled with argon protective atmosphere for battery assembly, wherein a solution of 1mol / L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate with a molar ratio of 1:1 is used as the electrolyte; assemble the positive and negative electrode discs, polyethylene separator and other components together, then inject the electrolyte, and finally prepare a lithium ion battery.

[0121] Example 2

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

[0123] Example 3

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

[0125] Example 4

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

[0127] Example 5

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

[0129] Example 6

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

[0131] Example 7

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

[0133] Example 8

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

[0135] Example 9

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

[0137] Example 10

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

[0139] Example 11

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

[0141] Example 12

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

[0143] Example 13

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

[0145] Example 14

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

[0147] Example 15

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

[0149] Example 16

[0150] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the high-temperature calcination temperature in step (vi) was controlled to 700°C, to obtain Example 16.

[0151] Example 17

[0152] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the high-temperature calcination temperature in step (vi) was controlled to 710°C, to obtain Example 17.

[0153] Example 18

[0154] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the high-temperature calcination time in step (vi) was controlled to 7h, to obtain Example 18.

[0155] Example 19

[0156] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the high-temperature calcination time in step (vi) was controlled to 10h, to obtain Example 19.

[0157] Example 20

[0158] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the high-temperature calcination time in step (vi) was controlled to 12h, to obtain Example 20.

[0159] Example 21

[0160] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the raw materials were weighed in stoichiometric ratio of LiFe 0.98 Ti 0.02 PO4, to obtain Example 21.

[0161] Example 22

[0162] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the raw materials were weighed in stoichiometric ratio of LiFe 0.97 Ti 0.03 PO4, to obtain Example 22.

[0163] Example 23

[0164] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the raw materials were weighed in stoichiometric ratio of LiFe 0.96 Ti 0.04 PO4, to obtain Example 23.

[0165] Example 24

[0166] A lithium iron phosphate material was prepared in the same manner as in Example 1, except that the raw materials were weighed in stoichiometric ratio of LiFe 0.95 Ti 0.05The raw materials are weighed in the stoichiometric ratio of PO4 as Example 24.

[0167] Comparative Example 1

[0168] 1) Cathode material

[0169] ① According to LiFe 0.99 Ti 0.01 The iron source (ferrous oxalate), phosphorus source (phosphoric acid), lithium source (lithium carbonate), titanium source (titanium tetrachloride) and other raw materials are weighed in the required stoichiometric ratio in PO4, and then the carbon source (glucose) is weighed according to 15% of the total mass ratio of the above raw materials and added to the ball mill for uniform mixing, and then an appropriate amount of pure water is added as a dispersant, and then high-energy ball milling is performed (ball-to-material ratio of 4:1, speed of 2000r / min, time for 12h) to ball mill the raw materials into particles of appropriate size.

[0170] ② The ball-milled material is spray-dried (the spray outlet temperature is 180°C) to form a powder with a certain particle size.

[0171] ③ The dried powder was placed in a vacuum atmosphere sintering furnace for sintering (protective atmosphere: nitrogen, 700°C, 10h), and then crushed by ball milling to obtain lithium iron phosphate material.

[0172] 2) Positive electrode

[0173] ① Weigh the corresponding amount of lithium iron phosphate material and polyvinylidene fluoride in a mass ratio of 97%:3% into a stirring tank, then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with appropriate viscosity.

[0174] ②Use extrusion coating to evenly apply the slurry on the specified side of the aluminum foil to form the positive electrode sheet.

[0175] 3) Making lithium-ion batteries

[0176] ① Weigh corresponding amounts of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mass ratio of 95%:2.5%:2.5% in a stirring tank, add appropriate amount of deionized water and stir for 6 hours to obtain a uniform slurry with appropriate viscosity; then coat the slurry on a copper foil with a thickness of 10μm, place it in a vacuum oven, and dry it at 150℃ for 16 hours to obtain the negative electrode sheet.

[0177] ② Place the positive and negative electrode sheets into a press for pressing, and then use a punch to cut out Φ15mm positive electrode discs and Φ18mm negative electrode discs respectively.

[0178] ③The positive and negative electrode discs are placed into a glove box filled with argon protective atmosphere for battery assembly, wherein a solution obtained by using 1 mol / L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1 is used as an electrolyte; the positive electrode disc, the negative electrode disc, a polyethylene diaphragm and other components are assembled together, then the electrolyte is injected, and finally the lithium ion battery is prepared.

[0179] Test Example:

[0180] 1) Particle size distribution test

[0181] A laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) is used to measure the particle size distribution of the lithium iron phosphate particles according to the particle size distribution laser diffraction method GB / T19077-2016. The test results are shown in Table 1 and Figure 6 .

[0182] 2) Average pit depth of the surface of the lithium iron phosphate particles and proportion of the cross-sectional area of the internal pores

[0183] The positive electrode disc sample is selected, the positive electrode disc is cut by a focused ion beam, the cross section of the positive electrode disc is observed by a scanning electron microscope, then a 2,000 times magnification photo is taken, then the proportion of the cross-sectional area of the internal pores in the entire particle cross-sectional area is counted by using a graphic recognition software ImageJ, and finally the average value is obtained. The test results are shown in Table 1 and Figures 1-5 .

[0184] 3) Rate discharge capacity test

[0185] 4) Cycle performance test

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

[0187] At 25°C, the lithium batteries prepared from the examples and the comparative examples are charged to 3.65V at a 0.1C rate, then discharged to 2.5V at a 0.1C rate, and the 0.1C discharge capacity at this time is recorded. The test results are shown in Table 1.

[0188] Figure 1 FIG. 1 is a surface morphology diagram of the lithium iron phosphate particles prepared in Example 1, Figure 2 FIG. 2 is an enlarged surface morphology diagram of the lithium iron phosphate particles prepared in Example 1, Figure 3 FIG. 3 is a cross-sectional morphology diagram of the lithium iron phosphate particles prepared in Example 1. From Figures 1-3It can be seen from the figure that the partial outer surface of the lithium iron phosphate particles prepared in Example 1 is recessed towards the inside of the lithium iron phosphate particles to form pits, and the inside center position of the lithium iron phosphate particles has a hollow hole structure. Meanwhile, it can also be seen that the lithium iron phosphate particles prepared in Example 1 are secondary particles formed by primary nanoparticles.

[0189] Figure 4 The surface morphology of the lithium iron phosphate particles prepared in Comparative Example 1 is shown in FIG. 2. Figure 5 The cross-sectional morphology of the lithium iron phosphate particles prepared in Comparative Example 1 is shown in FIG. 3. Figures 4-5 It can be seen from the figure that the partial outer surface of the lithium iron phosphate particles prepared in Comparative Example 1 is slightly recessed towards the inside of the lithium iron phosphate particles, but not enough to form pits, and the inside center position of the lithium iron phosphate particles does not have a hollow hole structure, and in addition, the lithium iron phosphate particles prepared in Comparative Example 1 are primary particles.

[0190] Figure 6 The particle size distribution of the lithium iron phosphate materials prepared in Example 1 and Comparative Example 1 is shown in FIG. 4. It can be tested 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] It can be seen from Table 1 that the discharge capacity at multiple rates and the capacity retention rate of Examples 1-24 are effectively improved compared with Comparative Example 1. It can be seen that by recessing the partial outer surface of the lithium iron phosphate particles towards the inside of the lithium iron phosphate particles to form pits, and the inside center position of the lithium iron phosphate particles has a hollow hole structure, the capacity performance of the battery can be effectively improved on the basis of maintaining good long cycle performance.

[0195] It can be seen from Table 1 that the discharge capacity at multiple rates of Examples 1-5, Examples 7-10, Examples 12-16, Examples 18-19 and Examples 21-23 are further improved compared with Examples 6, 11, 17 and 20. It can be seen that by limiting the average depth of the pits on the surface of the lithium iron phosphate particles to be not more than 42% of the length diameter of the lithium iron phosphate particles, the lithium iron phosphate material can have more excellent high capacity performance.

[0196] As can be seen from Table 1, compared with Example 6, the discharge capacity at various rates of Examples 1-5 and Examples 7-24 is further improved, which shows that by limiting the average cross-sectional area of the hollow hole structure of the lithium iron phosphate particles to be not more than 30% of the maximum cross-sectional area of the lithium iron phosphate particles, the lithium iron phosphate material can have more excellent high-capacity performance.

[0197] As can be seen from Table 1, compared with Examples 17, 20 and 24, the discharge capacity at various rates of Examples 1-5, Examples 7-10, Examples 12-16, Examples 18-19 and Examples 21-23 is further improved, which shows that by limiting the particle size Dv50 of the lithium iron phosphate particles to be in the range of 6-8 μm, the lithium iron phosphate material can have more excellent high-capacity performance.

[0198] As can be seen from Examples 1-6 in Table 1, in Step ② of preparing the lithium iron phosphate material, gradually increasing the amount of the porous hollow carbon microspheres added can make the average particle surface pit and the cross-sectional pit depth area ratio of the average particle internal hole of the material larger, and the discharge capacity at various rates of the corresponding battery also improves. However, too much addition of the porous hollow carbon microspheres can cause the discharge capacity at various rates of the battery to deteriorate sharply, and therefore, in Step ② of preparing the lithium iron phosphate material, the amount of the porous hollow carbon microspheres added is preferably ≤10%.

[0199] As can be seen from Examples 1 and Examples 7-11 in Table 1, in Step ⑤ of preparing the lithium iron phosphate material, increasing the spray drying outlet temperature can make the average particle surface pit and the cross-sectional pit depth area ratio of the average particle internal hole of the material larger, and the discharge capacity at various rates of the corresponding battery also improves. However, too large pit depth can cause the discharge capacity at various rates of the battery to decrease, and therefore, in Step ⑤ of preparing the lithium iron phosphate material, the spray drying outlet temperature is preferably 180-220°C.

[0200] As can be seen from Examples 1 and Examples 12-17 in Table 1, in Step ⑥ of preparing the lithium iron phosphate material, increasing the calcination temperature can make the average particle surface pit and the cross-sectional pit depth area ratio of the average particle internal hole of the material larger, and the discharge capacity at various rates of the corresponding battery also improves. However, too large material particle pit can cause the discharge capacity at various rates of the battery to decrease, and therefore, the high-temperature calcination temperature is preferably 650-700°C.

[0201] As can be seen from Examples 1 and Examples 18-20 in Table 1, in Step ⑥ of preparing the lithium iron phosphate material, increasing the calcination time can make the average particle surface pit and the cross-sectional pit depth area ratio of the average particle internal hole of the material larger, and the discharge capacity at various rates of the corresponding battery also improves. However, too large material particle pit can cause the discharge capacity at various rates of the battery to decrease, and therefore, the high-temperature calcination time is preferably 5-10 h.

[0202] As can be seen from Table 1, with the gradual increase of the content of the doped titanium element, the particle size of the material becomes smaller, the average particle surface pit depth and the cross-sectional area proportion of the average particle internal hole increase slightly, and the rate discharge capacity of the corresponding battery first increases and then decreases. The main reason is that too high doping element may produce heterogeneous compounds in the material and reduce the capacity performance. Therefore, the titanium doping amount of the lithium iron phosphate material (LiFe x Ti y PO4) of the present application is preferably: y≤0.04.

[0203] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and modified by those skilled in the art without contradiction.

[0204] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A lithium iron phosphate material, characterized in that: include: Lithium iron phosphate particles, wherein a portion of the outer surface of the lithium iron phosphate particle is sunken toward the interior of the lithium iron phosphate particle to form a pit; And / or, the inner center of the lithium iron phosphate particle has a hollow hole structure.

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 does not exceed 42% of the major diameter of the lithium iron phosphate particles.

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

5. The lithium iron phosphate material according to claim 1, characterized in that 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.

6. The lithium iron phosphate material according to any one of claims 1 to 5, characterized in that The particle size Dv50 of the lithium iron phosphate particles is 6 μm to 8 μm.

7. The lithium iron phosphate material according to any one of claims 1 to 5, characterized in that The lithium iron phosphate particles include titanium element, and the chemical structure of the lithium iron phosphate particles is LiFe x Ti y PO4, where x+y=1, 0 <y≤0.05。 8. A method for preparing the lithium iron phosphate material according to any one of claims 1 to 7, characterized in that: include: (1) Preparation of porous hollow carbon microspheres; (2) Weighing an iron source, a phosphorus source, and a lithium source according to the stoichiometric ratio required in LiFePO4 to prepare a mixed metal salt solution; (3) placing the mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution in a reactor to react and obtain a lithium iron phosphate material precursor; (4) mixing the lithium iron phosphate material precursor and the dispersant, and then grinding and crushing the mixture; (5) spray drying the ground and crushed material; (6) Under a protective atmosphere, the spray-dried material is subjected to high-temperature calcination, grinding, and crushing to obtain lithium iron phosphate material.

9. The method according to claim 8, characterized in that Step (1) includes: preparing a first carbon source solution, and spray-drying the first carbon source solution to obtain a carbon microsphere precursor; The carbon microsphere precursor is calcined to obtain the porous hollow carbon microspheres.

10. The method according to claim 8, characterized in that In step (2), according to LiFe x Ti y The iron source, phosphorus source, lithium source and titanium source are weighed in the required stoichiometric ratio in PO4 to prepare the mixed metal salt solution, wherein x+y=1, 0 <y≤0.05。 11. The method according to claim 8, characterized in that In step (3), the temperature of the reaction of the mixed metal salt solution, the porous hollow carbon microspheres, the precipitant solution and the complexing agent solution in the reactor is 180° C. to 220° C., the reaction time is 8 h to 10 h, 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 0.5 mol / L to 1.5 mol / L strong base solution; And / or, in step (3), the complexing agent solution includes 0.5 mol / L to 1.5 mol / L ammonia solution.

12. The method according to claim 8, characterized in that In step (4), during the mixing of the lithium iron phosphate material precursor and the dispersant, the method further comprises: The lithium iron phosphate material precursor, the second carbon source and the dispersant are mixed and then ground and crushed.

13. The method according to claim 12, characterized in that The mass ratio of the lithium iron phosphate material precursor to the second carbon source is (92:8) to (85:15).

14. The method according to any one of claims 8 to 13, characterized in that In step (5), the outlet temperature of the spray-dried material after grinding and crushing is 180°C to 230°C.

15. The method according to any one of claims 8 to 13, characterized in that In step (6), the spray-dried material is calcined at a temperature of 650° C. to 710° C.; And / or, in step (6), the spray-dried material is subjected to high-temperature calcination for 5 hours to 12 hours.

16. A positive electrode sheet, characterized in that: The invention comprises the lithium iron phosphate material according to any one of claims 1 to 7 or the lithium iron phosphate material prepared by the method according to any one of claims 8 to 15.

17. A battery, characterized in that: The invention comprises the lithium iron phosphate material according to any one of claims 1 to 7, the lithium iron phosphate material prepared by the method according to any one of claims 8 to 15, or the positive electrode sheet according to claim 16.

18. An electricity system, characterized in that: include: electrical systems, and An energy storage device, wherein the energy storage device supplies power to the power system, and the energy storage device comprises the battery according to claim 17.

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