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

Abstract

The invention provides a lithium iron phosphate positive electrode material and a preparation method and a battery thereof, m, Nx, dx and rho of the lithium iron phosphate positive electrode material meet the condition that omega is more than or equal to 1.0 and less than or equal to 1.1, m is the mass of the lithium iron phosphate positive electrode material, and the unit is g; dx is the particle size value of particles in the lithium iron phosphate positive electrode material, the unit is [mu] m, Nx is the number of particles with the particle size value of dx in the lithium iron phosphate positive electrode material under m mass, and the unit is one; rho is the true density of the lithium iron phosphate positive electrode material, and the unit is g / cm < 3 >. The lithium iron phosphate positive electrode material omega meets a specific range, and the lithium iron phosphate positive electrode material has relatively high compaction density, so that the battery has relatively high capacity.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a lithium iron phosphate cathode material, its preparation method, and a battery. Background Technology

[0002] As the electrification of automobiles accelerates globally, the development of power batteries is accelerating. Lithium iron phosphate (LFP) cathode materials, with their advantages of high safety and low cost, have become the primary cathode material for lithium-ion batteries. Since the energy density of the power battery determines the driving range of a vehicle, the main development direction for power-grade LFP batteries is currently to increase their compaction density.

[0003] Based on the above research, there is a need to provide a high-density lithium iron phosphate cathode material. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium iron phosphate cathode material, its preparation method, and a battery thereof, wherein the lithium iron phosphate cathode material has a mass m and a particle size d. x Particle size d under mass m x The corresponding number of particles N x And the true density ρ satisfies 1.0 ≤ At a density of ≤1.1, lithium iron phosphate cathode material has a high compaction density, which enables the battery to have a high capacity.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a lithium iron phosphate cathode material, wherein the m and N of the lithium iron phosphate cathode material are... x d x And ρ satisfy:

[0007] Where 1.0≤ω≤1.1;

[0008] ω can be, for example, 1.00, 1.02, 1.04, 1.05, 1.08 or 1.10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0009] Where m is the mass of the lithium iron phosphate cathode material, in grams; d x The particle size value of the lithium iron phosphate cathode material is expressed in μm or N. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 .

[0010] This represents the total volume of all particles in a mass m lithium iron phosphate cathode material.

[0011] The particle size and the number of particles of each corresponding size in the lithium iron phosphate cathode material of the present invention can be obtained by particle size testing of the lithium iron phosphate cathode material.

[0012] The compaction density of lithium iron phosphate (LFP) materials is mainly related to particle morphology, particle size, and particle size distribution. When the particle morphology, particle size, and particle size distribution are well-matched, it is easier to achieve a denser packing of the material, thereby increasing the compaction density. The true density of LFP materials is the density under completely dense conditions. The ratio of the total volume of all particles in a given mass of LFP material to the volume of the material under true density conditions reflects the compactness of the packing. The closer the ratio (ω) is to 1, the denser the packing and the higher the compaction density. This invention improves the compaction density of LFP materials by controlling the particle morphology and particle size distribution, ensuring that 1.0 ≤ ω ≤ 1.1.

[0013] In the above-mentioned relational expression of the present invention, no specific limit is made on the specific value of m, and any value of m satisfies the above-mentioned relational expression.

[0014] Preferably, 3.62 g / cm³ 3 ≤ρ≤3.68g / cm 3 For example, it could be 3.625 g / cm³. 3 3.628 g / cm 3 3.65g / cm 3 3.657 g / cm 3 3.676 g / cm 3 3.679 g / cm 3 Or 3.680 g / cm 3 However, this does not limit the values ​​listed; other unlisted values ​​within the range also apply. The higher the true density of lithium iron phosphate materials, the higher their solid skeleton density, and consequently, the higher their compacted density.

[0015] Preferably, 3×10 9 pcs / g≤N≤10×10 12 pcs / g, for example, could be 3×10 9 pcs / g, 5×10 9 Units / g, 1×10 10 pcs / g, 5×10 10 Units / g, 1×10 11 pcs / g, 5×10 11 Units / g, 1×10 12 pcs / g, 5×10 12 pcs / g or 10×10 12The value is per gram, but not limited to the listed values; other unlisted values ​​within the range also apply. N represents the number of particles per unit mass of lithium iron phosphate cathode material, expressed as particles per gram.

[0016] Preferably, 0.01μm≤d x ≤15μm, for example, can be 0.01μm, 0.05μm, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 10μm, 12μm, 13μm, 14μm or 15μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, as long as they can be detected.

[0017] Preferably, the lithium iron phosphate cathode material comprises LiFePO4 and carbon, wherein the carbon content is 0.5wt%-3wt%, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, or 3wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable. By controlling the carbon content within this range, the conductivity of the lithium iron phosphate cathode material can be improved without significantly reducing the material's compaction density.

[0018] Furthermore, the compaction density of the lithium iron phosphate cathode material is not less than 2.4 g / cm³. 3 The preferred value is 2.4 g / cm³. 3 -2.7g / cm 3 For example, it could be 2.4 g / cm³ 3 2.5g / cm 3 2.6g / cm 3 Or 2.7g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range also apply. The lithium iron phosphate cathode material of this invention has a high compaction density.

[0019] Secondly, the present invention provides a method for preparing the lithium iron phosphate cathode material as described in the first aspect, the method comprising the following steps:

[0020] (1) Mix the iron source, phosphorus source, solvent and surfactant to obtain a mixture, adjust the pH of the mixture to obtain a gel;

[0021] (2) Heat-treat the gel obtained in step (1) to obtain ferric phosphate, and grind the ferric phosphate to obtain crushed ferric phosphate;

[0022] (3) The crushed ferric phosphate described in step (2) is subjected to a hydrothermal reaction to obtain a hydrothermal reaction material;

[0023] (4) The hydrothermal reactant, lithium source and carbon source described in step (3) are mixed and calcined to obtain the lithium iron phosphate cathode material.

[0024] The preparation method of the present invention first prepares dumbbell-shaped iron phosphate, then breaks the dumbbell-shaped iron phosphate and continues hydrothermal growth into spherical iron phosphate, and finally prepares lithium iron phosphate that inherits the high sphericity of iron phosphate. Since the higher the sphericity of the material under the same composition and similar particle size distribution, the higher the compaction density of the material, the preparation method of the present invention obtains a lithium iron phosphate cathode material with high compaction density and satisfies the above relationship.

[0025] In this invention, iron phosphate is first prepared under the induction of a surfactant. The surfactant can interact with the highly active surface of iron phosphate, inhibiting the growth of the highly active surface. Since the crystal facets of low-activity surfaces grow slowly, this provides a kinetic basis for the formation of dumbbell-shaped iron phosphate. Specifically, iron ions and phosphate groups slowly generate iron phosphate crystals. Initially formed nanoparticles, in order to reduce surface energy, will directionally aggregate by sharing a common crystal facet. Surfactant molecules adsorb onto specific crystal faces, guiding these nanoparticles to connect and fuse with each other in a specific orientation. In the later stages of growth, particles with large radii of curvature gradually dissolve, while particles with small radii of curvature further... The iron phosphate grows step by step, eventually forming a dumbbell-shaped structure. After grinding in step (2), the dumbbell-shaped iron phosphate breaks down during the grinding stage because the connection of the dumbbell structure is relatively weak and easy to break. This results in a near-spherical iron phosphate. The subsequent hydrothermal process allows the part of the iron phosphate with small curvature to gradually dissolve, while the part with large curvature continues to grow, thereby further increasing the sphericity of the iron phosphate and improving the particle size distribution of the iron phosphate. This yields iron phosphate with high sphericity and appropriate particle size distribution. Since the morphology of lithium iron phosphate inherits that of iron phosphate, this invention yields a lithium iron phosphate cathode material with high sphericity and appropriate particle size distribution.

[0026] Preferably, the surfactant in step (1) includes any one or a combination of at least two of succinic acid, L-leucine, or polypeptide.

[0027] Preferably, the amount of surfactant added in step (1) is 0.5wt%-5wt% of the iron source mass, for example, it can be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1wt%-3.5wt%.

[0028] The amount of surfactant added in step (1) of this invention will affect the formation of dumbbell-shaped ferric phosphate. If the amount of surfactant added is too small, it will be difficult to form dumbbell-shaped ferric phosphate. If the amount of surfactant added is too large, ferric phosphate will be difficult to continue to grow.

[0029] Preferably, the iron source in step (1) includes any one or a combination of at least two of ferric nitrate, ferric sulfate, ferric chloride, or ferric acetate.

[0030] Preferably, the phosphorus source in step (1) includes phosphoric acid and / or ammonium hydrogen phosphate.

[0031] Preferably, the concentration of iron ions in the mixture in step (1) is 1 mol / L-3 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the solvent in step (1) includes deionized water and organic solvents.

[0033] Preferably, the organic solvent includes ethylene glycol and / or glycerol.

[0034] Preferably, the volume ratio of the deionized water to the organic solvent is (0.2-5):1, for example, it can be 0.2:1, 1:1, 2:1, 3:1, 4:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, step (1) involves adjusting the pH of the mixture to 5-8, for example, 5, 6, 7 or 8, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, ammonia is used to adjust the pH of the mixture in step (1).

[0037] Preferably, the heat treatment temperature in step (2) is ≥400℃, for example, it can be 400℃, 420℃, 440℃, 460℃, 480℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 400℃-500℃.

[0038] This invention heat-treats the gel at a high temperature, not only to dry the gel but also to remove the water of crystallization from the ferric phosphate. Because the grinding process is viscous and inefficient when ferric phosphate contains water of crystallization, removing the water of crystallization from the ferric phosphate, i.e. converting dihydrate ferric phosphate into ferric phosphate, reduces the grinding viscosity and creates vacancies for water of crystallization, thereby reducing the difficulty of grinding and ensuring that the dumbbell shape is broken, forming a near-spherical ferric phosphate.

[0039] Preferably, the heat treatment time in step (2) is 2h-5h, for example, it can be 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the atmosphere for the heat treatment in step (2) is an air atmosphere.

[0041] Preferably, the grinding method in step (2) includes wet ball milling.

[0042] Preferably, the solid content of the material in the wet ball milling is 20wt%-40wt%, for example, it can be 20wt%, 25wt%, 30wt%, 35wt%, or 40wt%, and the grinding solvent used includes ethanol. That is, ferric phosphate is prepared into a material with a solid content of 20wt%-40wt% by placing it in ethanol before grinding.

[0043] Preferably, after grinding in step (2) and before hydrothermal reaction, the material is dried to obtain a dried material, which is then mixed with water to obtain a mixture with a solid content of 10-20wt%, for example, 10wt%, 15wt% or 20wt%, and then subjected to the hydrothermal reaction in step (3).

[0044] Preferably, the temperature of the hydrothermal reaction in step (3) is 180℃-220℃, for example, it can be 180℃, 190℃, 200℃, 210℃ or 220℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the hydrothermal reaction time in step (3) is 2h-6h, for example, it can be 2h, 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the amount of carbon source added in step (4) is 5 mol%-20 mol% of the molar amount of the hydrothermal reactant, for example, it can be 5 mol%, 10 mol%, 15 mol% or 20 mol%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the calcination temperature in step (4) is 650℃-750℃, for example, 650℃, 670℃, 690℃, 710℃, 730℃ or 750℃, and the time is 8h-12h, for example, 8h, 9h, 10h, 11h or 12h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the calcination atmosphere in step (4) is an inert atmosphere.

[0049] Preferably, the carbon source in step (4) includes sucrose and / or glucose.

[0050] Thirdly, the present invention provides a battery comprising the lithium iron phosphate cathode material as described in the first aspect.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The lithium iron phosphate cathode material of this invention satisfies 1.0≤ω≤1.1, and its particle morphology and particle size distribution are in a suitable state. During the compaction process, it can achieve close packing, thereby improving the compaction density of the lithium iron phosphate cathode material and thus increasing the capacity of the battery prepared from it. Attached Figure Description

[0053] Figure 1 This is a graph showing the relationship between the particle size distribution and the quantity of the lithium iron phosphate cathode material described in Example 1. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Example 1

[0056] This embodiment provides a lithium iron phosphate cathode material, which comprises LiFePO4 and carbon, wherein the carbon content is 2wt%, and the ω, m, N of the lithium iron phosphate cathode material are... x d x The specific values ​​of ρ are shown in Table 1, where, m is the mass of the lithium iron phosphate cathode material, in grams; d x N represents the particle size of the lithium iron phosphate cathode material, in μm. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 ;

[0057] The preparation method of the lithium iron phosphate cathode material includes the following steps:

[0058] (1) According to the formula, ferric chloride, ammonium dihydrogen phosphate (the molar ratio of ferric chloride and ammonium dihydrogen phosphate is 1:1.02) and deionized water are mixed to obtain a salt solution. A surfactant (specifically succinic acid) and an organic solvent (specifically ethylene glycol) are mixed to obtain a surfactant solution. The surfactant solution is added to the salt solution and stirred to obtain a mixture. The pH of the mixture is adjusted to 6.5 using ammonia water to obtain a gel.

[0059] The surfactant is added at 1 wt% of the mass of ferric chloride, the volume ratio of deionized water to organic solvent is 0.25:1, and the concentration of iron ions in the mixture is 2 mol / L.

[0060] (2) The gel described in step (1) is heat-treated at 450°C for 2 hours in an air atmosphere to obtain ferric phosphate. The ferric phosphate is then wet-milled to obtain crushed ferric phosphate, and then dried at 150°C for 2 hours to obtain dried ferric phosphate.

[0061] The material solid content of the wet ball mill is 30 wt%, and the grinding solvent used includes ethanol.

[0062] (3) After mixing the dried ferric phosphate and water described in step (2), a mixture with a solid content of 10 wt% is obtained. The mixture is subjected to hydrothermal reaction at 200°C for 4 h. After washing, filtering and drying, a hydrothermal reaction material is obtained.

[0063] (4) Mix the hydrothermal reactant, lithium hydroxide (the molar ratio of hydrothermal reactant to lithium hydroxide is 1:1.05) and sucrose according to the formula amount, and then calcine at 700°C for 10 hours in an argon atmosphere to obtain the lithium iron phosphate cathode material; wherein, the amount of sucrose added is 15 mol of the molar amount of the hydrothermal reactant.

[0064] Example 2

[0065] This embodiment provides a lithium iron phosphate cathode material, which comprises LiFePO4 and carbon, wherein the carbon content is 3wt%, and the ω, m, N of the lithium iron phosphate cathode material are... x d x The specific values ​​of ρ are shown in Table 1, where, m is the mass of the lithium iron phosphate cathode material, in grams; d x The particle size value of the lithium iron phosphate cathode material is expressed in μm or N. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 ;

[0066] The preparation method of the lithium iron phosphate cathode material includes the following steps:

[0067] (1) According to the formula, ferric chloride, ammonium dihydrogen phosphate (the molar ratio of ferric chloride and ammonium dihydrogen phosphate is 1:1.02) and deionized water are mixed to obtain a salt solution. The surfactant (specifically succinic acid) and organic solvent (specifically glycerol) are mixed to obtain a surfactant solution. The surfactant solution is added to the salt solution and stirred to obtain a mixture. The pH of the mixture is adjusted to 5 using ammonia water to obtain a gel.

[0068] The surfactant is added at 2 wt% of the mass of ferric chloride, the volume ratio of deionized water to organic solvent is 1:1, and the concentration of iron ions in the mixture is 1 mol / L.

[0069] (2) The gel described in step (1) is heat-treated at 500°C for 2 hours in air atmosphere to obtain ferric phosphate. The ferric phosphate is then wet-milled to obtain crushed ferric phosphate, and then dried at 150°C for 2 hours to obtain dried ferric phosphate.

[0070] The material solid content of the wet ball mill is 20 wt%, and the grinding solvent used includes ethanol.

[0071] (3) After mixing the dried ferric phosphate and water as described in step (2), a mixture with a solid content of 15 wt% is obtained. The mixture is then subjected to hydrothermal reaction at 220°C for 2 hours. After washing, filtering and drying, a hydrothermal reaction material is obtained.

[0072] (4) Mix the hydrothermal reactant, lithium hydroxide (the molar ratio of hydrothermal reactant to lithium hydroxide is 1:1.05) and sucrose according to the formula amount, and then calcine at 650°C for 12 hours in an argon atmosphere to obtain the lithium iron phosphate cathode material; wherein, the amount of sucrose added is 20 mol of the molar amount of the hydrothermal reactant.

[0073] Example 3

[0074] This embodiment provides a lithium iron phosphate cathode material, the chemical formula of which is LiFePO4 and carbon, wherein the carbon content is 1 wt%, and the ω, m, N of the lithium iron phosphate cathode material are... x d x The specific values ​​of ρ are shown in Table 1, where, m is the mass of the lithium iron phosphate cathode material, in grams; d x The particle size value of the lithium iron phosphate cathode material is expressed in μm or N. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 ;

[0075] The preparation method of the lithium iron phosphate cathode material includes the following steps:

[0076] (1) According to the formula, ferric acetate, phosphoric acid (the molar ratio of ferric acetate and phosphoric acid is 1:1.02) and deionized water are mixed to obtain a salt solution. A surfactant (specifically succinic acid) and an organic solvent (specifically ethylene glycol) are mixed to obtain a surfactant solution. The surfactant solution is added to the salt solution and stirred to obtain a mixture. The pH of the mixture is adjusted to 8 using ammonia water to obtain a gel.

[0077] The surfactant is added at 3.33 wt% of the mass of ferric chloride, the volume ratio of deionized water to organic solvent is 1.5:1, and the concentration of iron ions in the mixture is 3 mol / L.

[0078] (2) The gel described in step (1) is heat-treated at 400°C for 5 hours in an air atmosphere to obtain ferric phosphate. The ferric phosphate is then wet-milled to obtain crushed ferric phosphate, and then dried at 150°C for 2 hours to obtain dried ferric phosphate.

[0079] The material solid content of the wet ball mill is 40 wt%, and the grinding solvent used includes ethanol.

[0080] (3) After mixing the dried ferric phosphate and water described in step (2), a mixture with a solid content of 20 wt% is obtained. The mixture is subjected to hydrothermal reaction at 180°C for 6 h. After washing, filtering and drying, a hydrothermal reaction material is obtained.

[0081] (4) Mix the hydrothermal reactant, lithium hydroxide (the molar ratio of hydrothermal reactant and lithium hydroxide is 1:1.05) and sucrose according to the formula amount, and then calcine at 750°C for 8 hours in an argon atmosphere to obtain the lithium iron phosphate cathode material; wherein, the amount of sucrose added is 5 mol of the molar amount of the hydrothermal reactant.

[0082] Example 4

[0083] This embodiment provides a lithium iron phosphate cathode material. Except for the method in which the amount of surfactant added is 0.5 wt% of the mass of ferric chloride, which changes the adaptability of the resulting lithium iron phosphate cathode material, the rest of the lithium iron phosphate cathode material is the same as in Example 1.

[0084] Example 5

[0085] This embodiment provides a lithium iron phosphate cathode material. Except for the method in which the amount of surfactant added is 5 wt% of the mass of ferric chloride, which changes the adaptability of the resulting lithium iron phosphate cathode material, the rest of the lithium iron phosphate cathode material is the same as in Example 1.

[0086] Example 6

[0087] This embodiment provides a lithium iron phosphate cathode material. Except for the heat treatment temperature of 300°C in its preparation method, which causes the lithium iron phosphate cathode material to change its adaptability, the rest is the same as in Example 1.

[0088] Comparative Example 1

[0089] This comparative example provides a lithium iron phosphate cathode material, the preparation method of which includes the following steps:

[0090] Ferric nitrate, phosphoric acid, and lithium hydroxide were mixed in a molar ratio of 1:1.02:1.05, and succinic acid was added to obtain a mixture, wherein the amount of succinic acid added was 30% of the amount of ferric nitrate. The mixture was transferred to an 80°C water bath and ammonia was added to adjust the pH to 3. The mixture was stirred continuously until a gel was formed. The gel was dried at 100°C and then transferred to a high-temperature furnace for calcination at 700°C for 6 hours. After demagnetization, the lithium iron phosphate cathode material was obtained.

[0091] Comparative Example 2

[0092] This comparative example provides a lithium iron phosphate cathode material, the preparation method of which includes the following steps:

[0093] Iron phosphate and lithium carbonate were mixed in a molar ratio of 1:0.52, and then glucose was added at 10 mol% of the iron phosphate content. The mixture was then ground to a solid content of 60 wt%. The ground material was dried and transferred to a reactor, where it was calcined at 700°C for 10 h in an argon atmosphere. After demagnetization, the lithium iron phosphate cathode material was obtained.

[0094] Comparative Example 3

[0095] This comparative example provides a lithium iron phosphate cathode material. Except for the fact that the wet ball milling step (2) was not performed in its preparation method, so as not to change the adaptability of the obtained lithium iron phosphate cathode material, the rest of the lithium iron phosphate cathode material is the same as that in Example 1.

[0096] Comparative Example 4

[0097] This comparative example provides a lithium iron phosphate cathode material. Except for the fact that the preparation method of the lithium iron phosphate cathode material does not carry out the hydrothermal reaction step (3), but instead dries the crushed iron phosphate at 100°C to change the adaptability of the obtained lithium iron phosphate cathode material, the rest is the same as in Example 1.

[0098] The above embodiments and comparative examples provide the ω, m, N values ​​of the lithium iron phosphate cathode materials. x d x The specific values ​​of ρ are shown in Table 1, where, m is the mass of the lithium iron phosphate cathode material, in grams; d x The particle size value of the lithium iron phosphate cathode material is expressed in μm or N. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 .

[0099] The lithium iron phosphate cathode materials provided in the above embodiments and comparative examples were respectively prepared into electrodes and assembled into batteries. The specific methods included: mixing the lithium iron phosphate cathode materials, conductive carbon black, and PVDF provided in the above embodiments and comparative examples at a mass ratio of 8:1:1; adding NMP solvent and magnetically stirring to form a uniform slurry; coating the slurry onto aluminum foil and vacuum drying at 100°C for 12 hours; cutting the prepared electrode sheet into 12mm circular pieces using a slicer and weighing them; controlling the load of each electrode at 2mg / cm². 2 The electrode sheet was used to assemble coin cells in a glove box. Specifically, lithium metal was used as the negative electrode, Celgrad 2400 as the separator, and a 1 mol / L LiPF6 organic solution (the solvent was a mixture of EC, DEC, and DMC in a 1:1:1 volume ratio) was used as the electrolyte to assemble CR2032 coin cells. The coin cells were then subjected to constant current charge-discharge tests using a Blue Battery testing cabinet. The voltage range for the charge-discharge tests was 2.5-3.6V. The 0.1C capacity test results are shown in Table 1.

[0100] In Table 1, N and d x N x The test methods and conditions were as follows: A nano-tracking analyzer (NTA) was used to test the particle size distribution and particle number. Specifically, lithium iron phosphate powder was dispersed in deionized water, ultrasonically dispersed, diluted 200 times, and then tested. The software automatically displayed the particle concentration (i.e., particle number) and particle size distribution (the test results of Example 1 are shown below). Figure 1As shown in the figure, the horizontal axis represents particle size, and the vertical axis represents particle number. Dividing the measured total particle number by the corresponding lithium iron phosphate powder mass gives the particle number per unit mass of lithium iron phosphate cathode material, d. x It is the particle size obtained by NTA instrument testing, N x The particle size is d x The number of particles.

[0101] True density ρ was tested using a Bestar physical adsorption analyzer-TD, in accordance with GB / T 24586-2009.

[0102] Taking Example 1 as an example, the calculation process of ω is as follows:

[0103]

[0104] The graph shows the total volume of each particle in the relationship between the particle size distribution and the quantity of lithium iron phosphate cathode material.

[0105] The test method and conditions for compaction density are as follows: the compaction density is tested using a powder compaction density meter under a pressure of 5t in accordance with GB / T 44330-2024.

[0106] Table 1

[0107]

[0108] As can be seen from Table 1 above:

[0109] As can be seen from Example 1 and Comparative Examples 1-4, the lithium iron phosphate cathode material provided in the embodiments of the present invention satisfies 1.0≤ω≤1.1, and the lithium iron phosphate cathode material has a high compaction density, thereby enabling the battery to have a high capacity.

[0110] This invention first prepares dumbbell-shaped iron phosphate, then breaks the dumbbell-shaped iron phosphate into near-spherical shapes, and further hydrothermally grows the near-spherical iron phosphate into spherical iron phosphate, finally obtaining a lithium iron phosphate cathode material with a high compaction density of 1.0≤ω≤1.1. As shown in Examples 1 and 4-5, in the preparation method of the lithium iron phosphate cathode material of this invention, the amount of surfactant added affects the morphology of iron phosphate, thereby affecting the morphology and compaction density of the lithium iron phosphate cathode material. As shown in Examples 1 and 6, the temperature of the gel heat treatment in this invention affects the grinding efficiency of the next step, affects the breaking of dumbbell-shaped iron phosphate, and thus affects the morphology and compaction density of the lithium iron phosphate cathode material.

[0111] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium iron phosphate cathode material, characterized in that, The m and N of the lithium iron phosphate cathode material x d x And ρ satisfy: Where 1.0≤ω≤1.1; In the formula, m is the mass of the lithium iron phosphate cathode material, in grams; d x N represents the particle size of the lithium iron phosphate cathode material, in μm. x For a mass m, the particle size of the lithium iron phosphate cathode material is d. x The number of particles, expressed in units; ρ is the true density of the lithium iron phosphate cathode material, expressed in g / cm³. 3 .

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, 3.62g / cm 3 ≤ρ≤3.68g / cm 3 ; Preferably, 3×10 9 pcs / g≤N≤10×10 12 N is the number of particles per unit mass of lithium iron phosphate cathode material, in units of particles / g; Preferably, 0.01μm≤d x ≤15μm.

3. The lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, The lithium iron phosphate cathode material comprises LiFePO4 and carbon, wherein the carbon content is 0.5wt%-3wt%. Preferably, the compaction density of the lithium iron phosphate cathode material is not less than 2.4 g / cm³. 3 The preferred value is 2.4 g / cm³. 3 -2.7g / cm 3 .

4. A method for preparing the lithium iron phosphate cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) Mix the iron source, phosphorus source, solvent and surfactant to obtain a mixture, adjust the pH of the mixture to obtain a gel; (2) Heat-treat the gel obtained in step (1) to obtain ferric phosphate, and grind the ferric phosphate to obtain crushed ferric phosphate; (3) The crushed ferric phosphate described in step (2) is subjected to a hydrothermal reaction to obtain a hydrothermal reaction material; (4) The hydrothermal reactant, lithium source and carbon source described in step (3) are mixed and calcined to obtain the lithium iron phosphate cathode material.

5. The preparation method according to claim 4, characterized in that, The surfactant in step (1) includes any one or a combination of at least two of succinic acid, L-leucine, or polypeptides; Preferably, the amount of surfactant added in step (1) is 0.5wt%-5wt% of the iron source mass, and more preferably 1wt%-3.5wt%. Preferably, the iron source in step (1) includes any one or a combination of at least two of ferric nitrate, ferric sulfate, ferric chloride, or ferric acetate; Preferably, the phosphorus source in step (1) includes phosphoric acid and / or ammonium hydrogen phosphate; Preferably, the concentration of iron ions in the mixture in step (1) is 1 mol / L-3 mol / L; Preferably, the solvent in step (1) includes deionized water and an organic solvent; Preferably, the organic solvent includes ethylene glycol and / or glycerol; Preferably, the volume ratio of the deionized water to the organic solvent is (0.2-5):

1.

6. The preparation method according to claim 4 or 5, characterized in that, In step (1), the pH of the mixture is adjusted to 5-8; Preferably, ammonia is used to adjust the pH of the mixture in step (1).

7. The preparation method according to claim 4 or 5, characterized in that, The heat treatment temperature in step (2) is ≥400℃, preferably 400℃-500℃; Preferably, the heat treatment time in step (2) is 2h-5h; Preferably, the atmosphere for the heat treatment in step (2) is an air atmosphere; Preferably, the grinding method in step (2) includes wet ball milling; Preferably, the solid content of the material in the wet ball mill is 20wt%-40wt%, and the grinding solvent used includes ethanol.

8. The preparation method according to claim 4 or 5, characterized in that, After grinding in step (2) and before hydrothermal reaction, the material was dried to obtain a dried material. The dried material was then mixed with water to carry out the hydrothermal reaction in step (3). Preferably, the temperature of the hydrothermal reaction in step (3) is 180℃-220℃; Preferably, the hydrothermal reaction time in step (3) is 2h-6h.

9. The preparation method according to claim 4 or 5, characterized in that, The amount of carbon source added in step (4) is 5 mol%-20 mol% of the molar amount of the hydrothermal reactant. Preferably, the calcination temperature in step (4) is 650℃-750℃, and the time is 8h-12h; Preferably, the calcination atmosphere in step (4) is an inert atmosphere; Preferably, the carbon source in step (4) includes sucrose and / or glucose.

10. A battery, characterized in that, The battery includes the lithium iron phosphate cathode material as described in any one of claims 1-3.

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