A high-density lithium iron phosphate cathode material for lithium batteries and a preparation method thereof

Abstract

The application relates to the technical field of lithium iron phosphate positive electrode material preparation, in particular to a high-compaction lithium iron phosphate positive electrode material for lithium batteries and a preparation method thereof. The preparation method comprises the following steps: respectively preparing titanium-doped small-particle precursors (A) and ammonium metavanadate-doped large-particle precursors (B) as vanadium sources; grading and mixing A and B at a ratio of 1-9:1; and then sintering and crushing to obtain a final product. Through the correlation design of specific doping elements (Ti / V) and specific particle sizes in the precursor stage, and the unique role of ammonium metavanadate in the sintering process, the physical grading and chemical modification are synergized, and the lithium iron phosphate positive electrode material with a compaction density of greater than or equal to 2.64 g / cm3 and high capacity and excellent rate performance is successfully prepared. The material is particularly suitable for high-energy-density lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium iron phosphate positive electrode material preparation, and particularly relates to a high-compaction lithium iron phosphate positive electrode material for lithium batteries and a preparation method thereof. BACKGROUND

[0002] Lithium iron phosphate (LiFePO4) positive electrode material has outstanding advantages in safety and service life, but is limited by its inherent low conductivity and low compaction density, and the volume energy density has been difficult to meet market demand. Therefore, developing a lithium iron phosphate material with high compaction density and excellent electrochemical performance through the synergy of process and design and a simplified preparation method thereof has become an urgent demand of the industry.

[0003] Existing improvement schemes mainly focus on chemical doping and physical optimization. In terms of physical optimization, there are technologies for preparing particles of different particle sizes and mixing them for multiple times of sintering to improve the density. For example, CN120841473A discloses a method: first, independently complete the synthesis and sintering of small particles (containing titanium doping) and large particles (without doping) respectively to obtain two kinds of intermediate products (samples A and B) with complete crystallization, and then mix the two intermediate products for a third sintering. The method has a long and complex process route (three times of sintering) and high energy consumption, and its essence is still a third sintering after physical mixing. More importantly, the technology only performs doping in small particles, and the large particles are “blank” particles without doping, and does not involve the design idea of functionalizing specific doping elements and particles of specific particle sizes, so it cannot build the synergy of chemical modification and physical grading, and improving the compaction density often sacrifices the conductivity and structural uniformity.

[0004] In terms of chemical doping, the conventional “finished product doping method” or “co-precipitation method” generally has the problems of poor uniformity or complex process. More importantly, in the selection of vanadium sources, the conventional vanadium pentoxide (V2O5) has poor solubility, and vanadyl sulfate (VOSO4) will introduce harmful impurities, and neither of the two vanadium sources can ensure the uniformity of doping while maintaining the structural purity of the material.

[0005] The root cause is that the existing technologies generally separate the “chemical doping” and “physical grading” or simply superimpose them without correlation. Especially the technology described in CN120841473A, although the particle size is controlled, due to the “mixing after separate sintering” process path and the “large particles without doping” design, the “physical grading” and “chemical modification” are disconnected, and cannot form a functional complementary synergistic network in the material, so it is difficult to simultaneously solve the technical problems of “high compaction density”, “high conductivity” and “high structural stability”. SUMMARY

[0006] The application aims to provide a high-compaction lithium iron phosphate cathode material and a preparation method thereof, which are simple in process and realize physical and chemical synergistic strengthening through element-particle size correlation design.

[0007] The technical solution of the application is as follows: in a first aspect, the application provides a high-compaction lithium iron phosphate cathode material, which is composed of secondary particles of titanium-doped primary small particles and vanadium-doped primary large particles through grading; the vanadium doping is derived from ammonium metavanadate; and the powder compaction density of the cathode material is greater than or equal to 2.64 g / cm3.

[0008] Preferably, the D50 of the primary small particles is 0.2-0.6 μm, and the D50 of the primary large particles is 0.8-1.6 μm.

[0009] In a second aspect, a preparation method of the high-compaction lithium iron phosphate cathode material is provided, which includes the following steps:

[0010] (1) preparing a titanium-doped small particle precursor: mixing iron phosphate, lithium carbonate, sucrose, a dispersing agent and a titanium source in water, sand grinding to slurry A with a D50 of 0.2-0.45 μm, and then drying to obtain solid powder A;

[0011] (2) preparing a vanadium-doped large particle precursor: mixing iron phosphate, lithium carbonate, sucrose, a dispersing agent and ammonium metavanadate in water, sand grinding to slurry B with a D50 of 0.7-1.6 μm, and then drying to obtain solid powder B;

[0012] (3) grading and mixing: mixing the solid powder A and the solid powder B at a mass ratio of 1-9:1 to obtain a mixture;

[0013] (4) one-time synergistic sintering: one-time synergistic sintering of the mixture in an inert atmosphere at 600-780 ℃ to obtain a sintered product;

[0014] (5) crushing: air flow crushing of the sintered product to obtain the high-compaction lithium iron phosphate cathode material.

[0015] Preferably, in step (1), the molar ratio of iron to phosphorus in the iron phosphate is 0.95-1:1, the molar ratio of lithium in the lithium carbonate to iron in the iron phosphate is 1.03-1.08:1, the addition amount of the sucrose is 6-10 wt% based on the theoretical output mass of lithium iron phosphate, the addition amount of the dispersing agent is 1-5 wt%, the addition amount of the titanium source is 0.2-2 wt%, and the solid content of the prepared slurry is controlled to be between 30% and 60%.

[0016] Preferably, in step (2), the molar ratio of iron to phosphorus of the iron phosphate is 0.96-0.98:1; the molar ratio of lithium in the lithium carbonate to iron in the iron phosphate is 1.02-1.06:1; the amount of the sucrose added is 4-10 wt%, the amount of the dispersant added is 1.5-6 wt%, the amount of the ammonium metavanadate added is 0.025-0.1 wt%, and the solid content of the prepared slurry is controlled to be between 30-60% based on the theoretical output mass of the lithium iron phosphate.

[0017] Preferably, in steps (1) and (2), the dispersant is polyethylene glycol; and in step (1), the titanium source is titanium dioxide.

[0018] Preferably, in step (3), the mass ratio of the solid powder A to the solid powder B is (3-8):2.

[0019] Preferably, in step (4), the sintering temperature is 600-780°C, the heating rate is 4-8°C / min, and the holding time is 2-12h.

[0020] Preferably, in step (5), the final product D50 after the jet milling is 0.95-1.5μm.

[0021] In a third aspect, a lithium ion battery is provided, which comprises the high-compacted lithium iron phosphate positive electrode material.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The "element-particle size" correlation design and "one-time synergistic sintering" process are established, and deep coupling of physics and chemistry is achieved. The present application does not simply imitate the existing particle grading idea, but creatively gives small particles the function of stabilizing structure and promoting lithium ion diffusion by doping titanium. For sub-micron small particles (0.2-0.45μm), the specific surface area is large, the lithium ion diffusion path is short, but the crystal structure is relatively unstable at high temperature. Ti 4+ (ion radius and Fe 2+Doping, preferentially entering the small particle lattice, can effectively stabilize the olivine structure, inhibit excessive growth or agglomeration in the sintering process, and provide additional charge carriers that are more easily transported in a short range, significantly improving the lithium ion diffusion coefficient of the small particle region; vanadium doping from the ammonium metavanadate source is used to endow the large particles with the function of improving electronic conductivity. For micron-sized large particles (0.7-1.6 pm), as the accumulation skeleton, the long electronic conduction path becomes the key to limiting their performance, and the introduction of high-valence V ions from ammonium metavanadate (NH4VO3) for doping can achieve uniform modification of the large particle body due to its excellent water solubility and uniform dispersibility. V doping not only introduces electron carriers in LiFePO4 to improve electronic conductivity, but more importantly, the NH3 local reducing atmosphere produced by the decomposition of NH4VO3 in sintering can precisely act on the sucrose pyrolysis process wrapped around the large particles to promote the generation of a conductive carbon layer with higher graphitization degree, thereby building an efficient electron conduction network covering the surface of the large particles. Subsequently, by mixing the two functional precursors and performing one-time sintering, the small particles fill the gaps between the large particles to achieve physical compaction, and the two doping elements play a synergistic modification role in their respective optimized particle size environment. This completely solves the problem of the disconnection between physical mixing and chemical modification in existing technologies such as CN120841473A, and the process path is more concise and efficient.

[0024] (2) Creative selection of key raw materials: The present application specifically selects ammonium metavanadate (NH4VO3) with good water solubility and no foreign anions as the vanadium source of the large particle precursor, replacing poorly soluble vanadium pentoxide or vanadyl sulfate which can introduce sulfate impurities. The excellent water solubility of NH4VO3 ensures the uniform dispersion of vanadium elements at the molecular level in the liquid phase, achieving efficient and uniform bulk doping. The local reducing atmosphere (NH3) that may be produced during the sintering decomposition process not only protects Fe 2+ from oxidation, but also optimizes the graphitization degree of the carbon coating layer and the particle morphology, further improving the overall conductivity, producing an unexpected synergistic effect.

[0025] (3) Excellent comprehensive performance, solving the contradiction between high compaction and high rate. Thanks to the above-mentioned integrated design and synergistic effect, the material prepared by the present application not only has a high compaction density of ≥2.64 g / cm3, but also maintains excellent lithium ion diffusion and electronic conduction capacity, thereby exhibiting high specific capacity and excellent rate performance. This successfully solves the problem of sacrificing kinetic performance in traditional grading technology to improve density. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described below in conjunction with the drawings and examples:

[0027] Figure 1This is a scanning electron microscope image of the lithium iron phosphate cathode material described in this invention;

[0028] Figure 2 The X-ray diffraction pattern of the lithium iron phosphate cathode material prepared in Example 1 of the present invention is shown below.

[0029] Figure 3 The charge-discharge curve of the lithium iron phosphate cathode material prepared in Example 1 of the present invention is shown. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments:

[0031] In this invention, the particle size distribution D50 value refers to the volume median diameter measured by using a laser diffraction particle size analyzer with water as the dispersion medium and after ultrasonic dispersion.

[0032] Example 1

[0033] (1) Preparation of titanium-doped small particle precursor A: Iron phosphate with an iron-to-phosphorus molar ratio of 0.98:1 was selected. This ratio is close to the stoichiometric ratio, and the crystal structure is complete, which is beneficial to Ti 4+ Ions stably enter the crystal lattice, improving conductivity while avoiding excessive lithium vacancies. Lithium carbonate is added at a lithium to iron molar ratio (Li / Fe) of 1.04:1 to provide a slight excess of lithium to compensate for volatilization losses during high-temperature sintering. 8% sucrose is added as a carbon source, 2% polyethylene glycol (PEG ~ molecular weight 4000) as a dispersant, and 0.5% titanium dioxide (TiO2) as a titanium source. The above raw materials are mixed in water, controlling the slurry solid content to 45%. After mechanical dispersion for 1 hour, the slurry is milled using zirconia beads until the particle size D50 = 0.30 μm. Milling to the submicron level significantly increases reactive sites and ensures uniform dispersion of TiO2, laying the foundation for the subsequent formation of uniform Ti-doped LiFePO4. The resulting powder is then spray-dried to obtain solid powder A.

[0034] (2) Preparation of vanadium-doped large-particle precursor B: Iron phosphate with an iron-to-phosphorus molar ratio of 0.96:1 was selected. This ratio was intentionally designed to create an appropriate amount of iron vacancies, providing more abundant and energy-friendly lattice sites for the incorporation of V, effectively reducing the difficulty of doping. Lithium carbonate was added at a Li / Fe ratio of 1.03:1. 8% sucrose, 2% PEG-4000, and 0.05% ammonium metavanadate (NH4VO3) were added as vanadium sources. The excellent water solubility of NH4VO3 ensured the vanadium... 3-Molecular dispersion of ions in the slurry is the prerequisite for achieving atomic-level uniform doping. Its non-ionic impurity characteristics are crucial compared to other vanadium sources. Control the solid content of the slurry to 45%, disperse for 2 hours, sand mill to a particle size of D50=1.00μm, and spray dry to obtain solid powder B.

[0035] (3) Gradation and mixing: Mix the dried solid powders A and B in a mass ratio of 7:3 in deionized water to prepare the slurry. This ratio is theoretically calculated and experimentally verified to achieve optimal filling of small particles in the gaps between large particles, thereby achieving the highest packing density. The mixed slurry is spray dried to obtain a uniformly graded precursor powder in terms of composition and particle size distribution.

[0036] (4) One-time synergistic sintering: Place the graded precursor powder in an atmosphere sintering furnace and perform one-time synergistic sintering under high-purity nitrogen protection. The sintering program is as follows: increase the temperature from room temperature to 770℃ at a rate of 5℃ / min, and maintain the temperature for 8 hours. The key point in this one-time synergistic sintering process is that the decomposition of ammonium metavanadate and the activation of the titanium source occur in the same heat treatment environment, synchronously with the pyrolysis of the carbon source, the crystallization reaction of LiFePO4, and the rearrangement and densification process of the particles, and promote each other. Specifically:

[0037] First, the local atmosphere generated by the decomposition of ammonium metavanadate, in conjunction with the pyrolysis process of the carbon source, optimizes the properties of the carbon coating layer on the particle surface, and is beneficial to maintaining the low valence state of iron elements; at the same time, the active vanadium species generated by its decomposition can be effectively doped into the crystal lattice of large particle precursors.

[0038] Second, the doping of titanium elements into small particle precursors helps to stabilize their crystal structure during sintering, inhibit their excessive growth, and thus maintain a small particle size that is beneficial to filling.

[0039] Finally, under the combined action of the above chemical processes, the large and small particle precursors exhibit good sintering compatibility, and are simultaneously converted into crystalline and complete LiFePO4 in a one-time sintering cycle. The in-situ synchronization and synergy of this series of processes is the key to achieving high density and high performance, and is also unattainable by the step-by-step sintering process in the prior art.

[0040] (5) Crushing: Crush the sintered block through an air jet crusher to obtain the final product with a particle size of D50=1.01μm by adjusting the air pressure and classifier speed.

[0041] Performance test:

[0042] The product compaction density is 2.65g / cm³ as tested by a powder compaction densitometer.

[0043] The carbon content was 1.21% as measured by a carbon-sulfur analyzer.

[0044] The morphology of the material was observed by a scanning electron microscope (SEM), as shown in FIG. 1, and the secondary spherical morphology composed of small particles and large particles in a grading distribution can be clearly observed, and the small and large particles are uniformly distributed, achieving close packing. Figure 1

[0045] The phase of the material was analyzed by an X-ray diffractometer (XRD), as shown in FIG. 2, and the diffraction peak is sharp, consistent with the standard olivine structure lithium iron phosphate, and there is no impurity phase peak, proving that the product has complete crystallinity and extremely high purity. Figure 2

[0046] The electrochemical performance was tested by a blue cell battery test system, and the charge-discharge curve is shown in FIG. 3, the initial discharge capacity at 0.1C is 160.09 mAh / g, the initial coulombic efficiency is 99.71%, and the discharge capacity at 1C is 142.04 mAh / g, showing excellent electrochemical performance. Figure 3

[0047] Example 2

[0048] (1) Preparation of titanium-doped small particle precursor A: iron phosphate with a molar ratio of iron to phosphorus of 0.98:1 was selected. Lithium carbonate was added according to a molar ratio of lithium to iron of 1.04:1. 9% sucrose, 2.5% PEG~4000, and 0.3% titanium dioxide (TiO2) were added. The above raw materials were mixed in water, the solid content of the slurry was controlled to be 45%, and mechanical dispersion was carried out for 2 hours, followed by sand milling to D50=0.30μm, and then spray drying to obtain solid powder A.

[0049] (2) Preparation of vanadium-doped large particle precursor B: iron phosphate with a molar ratio of iron to phosphorus of 0.96:1 was selected. Lithium carbonate was added according to Li / Fe=1.04:1. 9% sucrose, 2.5% PEG~4000, and 0.03% ammonium metavanadate (NH4VO3) were added. The solid content of the slurry was controlled to be 45%, and dispersion was carried out for 2 hours, followed by sand milling to D50=1.00μm, and then spray drying to obtain solid powder B.

[0050] (3) Grading and mixing: solid powders A and B were mixed in deionized water according to a mass ratio of 7:3, and spray drying was carried out.

[0051] (4) One-time co-sintering: the mixed powder was heated from room temperature to 750°C at a heating rate of 4°C / min under a nitrogen atmosphere, and kept at this temperature for 10 hours.

[0052] (5) Pulverization: the sintered product was subjected to air jet pulverization to obtain a final product with D50=1.17μm.

[0053] ​​​Performance test: the product has a tap density of 2.64 g / cm3, a carbon content of 1.36%, and a 1C discharge capacity of 141.5 mAh / g.

[0054] Example 3

[0055] (1) Preparation of titanium-doped small-particle precursor A: iron phosphate with a molar ratio of iron to phosphorus of 0.985:1 is selected. Lithium carbonate is added in a molar ratio of lithium to iron of 1.04:1. 8% sucrose, 2% PEG 4000, and 0.8% titanium dioxide (TiO2) are added. The above raw materials are mixed in water, the solid content of the slurry is controlled at 45%, and mechanical dispersion is performed for 2 hours, followed by sand milling to D50=0.40 μm, and then spray drying to obtain solid powder A.

[0056] (2) Preparation of vanadium-doped large-particle precursor B: iron phosphate with a molar ratio of iron to phosphorus of 0.955:1 is selected. Lithium carbonate is added in a molar ratio of Li / Fe=1.04:1. 8% sucrose, 2% PEG 4000, and 0.08% ammonium metavanadate (NH4VO3) are added. The solid content of the slurry is controlled at 45%, and dispersion is performed for 2 hours, followed by sand milling to D50=1.18 μm, and then spray drying to obtain solid powder B.

[0057] (3) Grading and mixing: solid powders A and B are mixed in a mass ratio of 6:4 in deionized water to form a slurry, and spray dried.

[0058] (4) One-time co-sintering: the mixed powder is heated from room temperature to 770°C at a rate of 5°C / min under a nitrogen atmosphere, and held at this temperature for 8 hours.

[0059] (5) Pulverization: the sintered product is subjected to air jet pulverization to obtain a final product with a D50 of 1.10 μm.

[0060] Performance test: the product has a tap density of 2.64 g / cm3, a carbon content of 1.25%, and a 1C discharge capacity of 142.8 mAh / g.

[0061] Comparative Example 1

[0062] This comparative example only prepares and sinters the precursor A (titanium-doped small particles) in Example 1, without grading and mixing with B. The process parameters are completely the same as steps (1) and (4) in Example 1.

[0063] Results and analysis: The product is fine particles with a single particle size. Its tap density is only 2.48 g / cm3, and the inter-particle porosity is large due to the lack of skeleton support of large particles and the filling effect of small particles. At the same time, due to the lack of enhancement of the overall conductive network by vanadium doping, its 1C discharge capacity is low, only 134.2 mAh / g. This comparison proves that single titanium doping cannot solve the high compaction problem, and the conductivity improvement is limited.

[0064] Comparative Example 2

[0065] In this comparative example, ammonium metavanadate in step (2) of Example 1 is replaced by an equal molar amount of vanadium pentoxide (V2O5), and the remaining steps and parameters are the same as Example 1.

[0066] Results and analysis: Due to the extremely low solubility of V2O5 in water, there are still undissolved V2O5 agglomerates in the slurry after sanding, resulting in serious uneven vanadium doping in the final product. The particle morphology after sintering is irregular, and some areas grow excessively due to vanadium enrichment. Its tap density is 2.58 g / cm3, lower than Example 1. This comparison proves that V2O5 as a vanadium source will cause uneven doping and structural defects, seriously damaging the cycle stability of the material, and also proves the importance of choosing ammonium metavanadate (NH4VO3) for achieving uniform doping and obtaining synergistic effects.

[0067] Comparative Example 3

[0068] This comparative example prepares a single precursor containing both titanium and vanadium. That is, iron phosphate (Fe / P = 0.97), lithium carbonate, glucose, PEG, 0.25% TiO2 and 0.025% NH4VO3 are mixed at one time (the total doping amount is similar to Example 1), sanding to D50 = 0.6 μm, and then sintering and crushing.

[0069] Results and analysis: The product has a single particle size distribution, and the tap density is 2.52 g / cm3. XRD shows a small amount of impurities. Its 1C discharge capacity is 138.0 mAh / g. This comparison proves that simply mixing two doping elements cannot achieve the high density brought by particle size grading, and the elements may interfere with each other, resulting in a decrease in doping effect and even the formation of impurities, which cannot achieve the synergistic effect of the step-by-step and grading design of the present application.

[0070] Comparative Example 4

[0071] This comparative example aims to explore the necessity of the "Ti-doped small particles and vanadium-doped large particles" associated design of the present application. The preparation method is basically the same as Example 1, but the reverse design is performed: 0.5% TiO2 and 0.05% NH4VO3 are added simultaneously when preparing the small particle precursor in step (1); while in step (2) for preparing the large particle precursor, no dopant is added, and the rest of the parameters remain unchanged. The product has a compacted density of 2.56 g / cm³, which is significantly lower than that of the present application.

[0072] Theoretical analysis and conclusions:

[0073] For small particles: introduce V-doping. Due to the high reactivity of small particles, the local strong reducing atmosphere generated by the decomposition of NH4VO3 may cause excessive graphitization of the carbon on the surface of the small particles, even causing partial iron elements to be excessively reduced, destroying the surface structure. At the same time, the short lithium ion diffusion path of the small particles is relatively not urgent for the demand of improving electronic conductivity, and the benefit of V-doping is not maximized.

[0074] For large particles: introduce Ti-doping. Ti 4+ Although it can stabilize the structure, for large particles which are the bottleneck of electronic conduction, its direct effect on electronic conductivity is weaker than high-valence V-doping. And lacking the local atmosphere brought by the decomposition of NH4VO3, the graphitization degree of the carbon layer wrapping the large particles may be low, and the electronic conduction network is not good.

[0075] The results also show that: this reverse design disrupts the functional distribution set by the present application, and the compacted density of the final product is expected to decrease due to the mismatch of particle growth behavior, and the overall electronic conduction network is not ideal, resulting in a significant decrease in capacity at high rates, especially at high rates. The technical effect of the present application does not come from the simple superposition of Ti and V elements. When the specific "function-particle size" correlation rule of the present application is violated, even if the same elements and total content are used, excellent comprehensive performance cannot be obtained.

[0076] This comparison proves that the association of specific doping elements with specific particle sizes is not an arbitrary choice, but a precise design based on a deep understanding of the intrinsic scientific problems faced by particles of different sizes (small particles need structure stability and ion diffusion optimization, large particles need electronic conduction strengthening).

[0077] The key performance comparison of the above examples and comparative examples is shown in the following table:

[0078]

[0079] Based on the above data, the following conclusions are drawn:

[0080] (1) The embodiments 1~3 of the present application achieve and exceed the compaction density of 2.64g / cm3 by the correlation design of "Ti-doped small particles and NH4VO3(V)-doped large particles" and the one-time synergistic sintering process, and maintain excellent rate performance (1C discharge capacity is more than 142mAh / g), which proves the effectiveness and repeatability of the present application scheme.

[0081] (2) The comparative examples 1 and 3 prove that simple titanium doping or simple blending doping without functional correlation cannot achieve the comprehensive performance realized by the "element-particle size" correlation design of the present application.

[0082] (3) The comparative example 2 proves that, compared with the conventional V2O5, the selection of ammonium metavanadate (NH4VO3) as the vanadium source has unexpected significant advantages in ensuring doping uniformity, obtaining higher compaction density and rate capacity, and the local atmosphere generated by its decomposition has a synergistic promotion effect on performance.

[0083] (4) In summary, the technical route proposed by the present application, which correlates specific doping elements with specific particle size particles in the precursor stage and realizes synergistic effect through one-time sintering, has essential differences and significant progress in technical concept, process path and final effect compared with the three-time sintering method disclosed in the prior art.

[0084] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and it cannot limit the protection scope of the present application. For those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application, therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

Claims

1. A method for preparing a high-pressure lithium iron phosphate cathode material, characterized in that, Includes the following steps: (1) Preparation of titanium-doped small particle precursor: Iron phosphate, lithium carbonate, sucrose, dispersant and titanium source are mixed in water and milled to a slurry A with D50 of 0.2~0.45μm, and then dried to obtain solid powder A; (2) Preparation of vanadium-doped large particle precursor: Iron phosphate, lithium carbonate, sucrose, dispersant and ammonium metavanadate are mixed in water, and milled into a slurry B with D50 of 0.7~1.6μm, and then dried to obtain solid powder B; (3) Grading and mixing: The solid powder A and the solid powder B are mixed at a mass ratio of 1 to 9:1 to obtain a mixture. (4) One-time co-sintering: The mixture is subjected to one-time co-sintering at 600~780℃ under an inert atmosphere to obtain the sintered product; (5) Pulverization: The sintered product is subjected to air jet pulverization to obtain the high-pressure lithium iron phosphate cathode material; The obtained cathode material is a secondary particle composed of titanium-doped primary small particles and vanadium-doped primary large particles through gradation; the D50 of the primary small particles is 0.2~0.6μm, and the D50 of the primary large particles is 0.8~1.6μm; the vanadium doping is derived from ammonium metavanadate; the powder compaction density of the cathode material is ≥2.64g / cm³.

2. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the molar ratio of iron to phosphorus in the iron phosphate is 0.95~1:1; the molar ratio of lithium in the lithium carbonate to iron in the iron phosphate is 1.03~1.08:1; based on the theoretical mass of lithium iron phosphate produced, the amount of sucrose added is 6~10wt%, the amount of dispersant added is 1~5wt%, the amount of titanium source added is 0.2~2wt%, and the solid content of the prepared slurry is controlled between 30~60%.

3. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the molar ratio of iron to phosphorus in the iron phosphate is 0.96~0.98:1; the molar ratio of lithium in the lithium carbonate to iron in the iron phosphate is 1.02~1.06:1; based on the theoretical mass of lithium iron phosphate produced, the amount of sucrose added is 4~10wt%, the amount of dispersant added is 1.5~6wt%, the amount of ammonium metavanadate added is 0.025~0.1wt%, and the solid content of the prepared slurry is controlled between 30~60%.

4. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In steps (1) and (2), the dispersant is polyethylene glycol; in step (1), the titanium source is titanium dioxide.

5. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the mass ratio of solid powder A to solid powder B is (3~8):

2.

6. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step (4), the sintering temperature is 600~780℃, the heating rate is 4~8℃ / min, and the holding time is 2~12h.

7. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The final product D50 after air jet milling in step (5) is 0.95~1.5μm.

8. A high-pressure lithium iron phosphate cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. A lithium-ion battery, characterized in that, It includes the high-pressure lithium iron phosphate cathode material as described in claim 8.

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