High-voltage lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a high-voltage lithium iron phosphate positive electrode material and a preparation method thereof, and the preparation method comprises the following steps: carrying out wet pretreatment on an iron phosphate raw material by using a soluble titanium source to realize lattice internal doping; pulping the pretreated material, and dynamically adding a second titanium source in the spray drying process to prepare precursor particles of which the titanium concentration is distributed in a gradient manner; the precursors with different gradients are shunted and subjected to differential temperature sintering, and two intermediate products with the particle size and the performance regulated and controlled are obtained; and finally mixing the two intermediate products. According to the preparation method, a unique structure in which a titanium element is in heterogeneous gradient distribution in crystal lattices and on the surfaces of particles is prepared through a double-path synergistic titanium doping strategy, scientific particle gradation is constructed, and the problem that compaction density and rate capability are difficult to consider at the same time is solved; therefore, the final product has high compaction density and excellent high rate performance and cycling stability.

Description

Technical Field

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

[0002] Lithium iron phosphate (LiFePO4) has become an important cathode material in the field of lithium-ion batteries due to its stable olivine structure, excellent thermal stability, long cycle life, and cost advantages, especially in power batteries and energy storage systems. However, the inherent low electronic conductivity and slow lithium-ion diffusion coefficient of lithium iron phosphate material limit its performance under high-rate charge and discharge conditions, which has become a technical bottleneck restricting its further application.

[0003] To improve the electrochemical performance of lithium iron phosphate (LFP), existing technologies typically employ various modification strategies. Among these, elemental doping to enhance the intrinsic conductivity and structural stability of the material is a common and effective method. For example, introducing high-valence metal ions such as titanium (Ti) into the LFP lattice can effectively improve the material's conductivity. Conventional doping processes often employ homogeneous mixing, where the dopant source is mixed with the LFP precursor material in a single step followed by differential temperature sintering. While this homogeneous doping method can improve the rate performance of the material to some extent, it also introduces new technical challenges. On the one hand, the uniform distribution of the dopant element may disrupt the crystal structure integrity of LFP, leading to a loss of specific capacity. On the other hand, the nano-sizing strategies commonly used to promote doping often result in low tap density and compaction density, thereby reducing the battery's volumetric energy density.

[0004] Therefore, existing technologies generally face a technical dilemma: modification methods aimed at improving rate performance often come at the cost of sacrificing the material's compaction density, and vice versa. How to effectively improve the rate performance and cycle stability of lithium iron phosphate cathode materials without sacrificing or even increasing compaction density remains a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-voltage lithium iron phosphate cathode material and its preparation method, solving the problem that it is difficult to simultaneously achieve high actual density and excellent rate performance in existing lithium iron phosphate modification technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing high-voltage lithium iron phosphate cathode material, comprising the following steps: (a) Soluble titanium source a is mixed with iron phosphate to prepare pre-titanium iron phosphate. This step utilizes the high dispersibility of soluble titanium source in the liquid phase to make it uniformly attached to the surface of iron phosphate particles at the molecular or nanoscale. After low-temperature treatment, a uniform active titanium oxide pre-doped layer is formed, which provides favorable conditions for the subsequent diffusion of titanium elements into the lithium iron phosphate lattice.

[0007] (b) The pre-titanium iron phosphate, lithium source and carbon source are mixed to prepare a precursor slurry; (c) Spray drying the precursor slurry, and during the drying process, continuously supplying titanium source b to the slurry, and by controlling the supply rate of titanium source b, obtaining at least two gradient-doped precursors with gradient titanium concentrations in stages; this step dynamically introduces titanium source b during the formation of secondary particles, so that titanium elements form a concentration gradient in the near-surface region of the secondary particles, which is used to control the growth of grains during the subsequent differential temperature sintering process, and lays the foundation for the formation of a continuous particle size distribution in the final product.

[0008] (d) The at least two gradient-doped precursors obtained in step (c) are subjected to high-temperature treatment under different sintering temperature conditions to obtain at least two intermediate products; different heat treatment regimes are applied to the precursors with different titanium concentration gradients, so as to precisely control their crystallinity and final particle size, thereby obtaining intermediate products suitable for framework construction and interstitial filling respectively.

[0009] (e) The at least two intermediate products obtained in step (d) are mixed to obtain the final high-pressure lithium iron phosphate cathode material.

[0010] Preferably, the soluble titanium source a in step (a) is tetrabutyl titanate and / or chelated titanium citrate.

[0011] Preferably, the mixing process in step (a) specifically includes wet sand milling, drying and sintering steps, wherein the sintering temperature is set to 300-500℃, and the titanium content in the pre-titanium iron phosphate obtained after the process is controlled at 500-1500ppm.

[0012] Preferably, the titanium source b in step (c) is a suspension containing nano-titanium dioxide and a dispersant to ensure its rapid and uniform dispersion in the slurry.

[0013] Preferably, in step (d), the sintering temperature of the first gradient-doped precursor is 750-800℃, and the sintering temperature of the second gradient-doped precursor is 755-805℃.

[0014] Preferably, in the high-pressure lithium iron phosphate cathode material finally obtained in step (e), the total titanium content is controlled at 1500-3000 ppm.

[0015] A high-voltage lithium iron phosphate cathode material is disclosed, in which titanium is distributed heterogeneously. Specifically, some titanium is distributed within the lattice of the primary lithium iron phosphate grains through lattice doping to improve the intrinsic ionic conductivity of the material; other titanium is enriched on the surface and near-surface region of the secondary spherical particles formed by the aggregation of primary grains, creating a concentration gradient distribution to regulate the microstructure and packing behavior of the particles.

[0016] Preferably, the cathode material is composed of a mixture of at least two types of lithium iron phosphate particles with different physicochemical properties, including a first lithium iron phosphate particle as a framework structure and a second lithium iron phosphate particle for filling the gaps between them. The second lithium iron phosphate particle has a smaller average particle size than the first lithium iron phosphate particle, and its particle surface has a higher concentration of titanium.

[0017] Preferably, the compacted density of the positive electrode material powder is not less than 2.60 g / cm³. 3 Furthermore, the discharge specific capacity at a 5C rate is not less than 120mAh / g.

[0018] This invention provides a high-voltage lithium iron phosphate cathode material and its preparation method. It has the following beneficial effects: 1. This invention achieves uniform pre-coating of titanium at the molecular / nanoscale by wet mixing and low-temperature pre-sintering of a soluble titanium source with iron phosphate in the early stages of preparation. Compared to traditional solid-phase mixing, this method makes it easier for titanium to enter the crystal lattice during subsequent high-temperature synthesis of lithium iron phosphate, effectively improving the intrinsic ionic and electronic conductivity of the material and laying the foundation for improving the rate performance of the material.

[0019] 2. In the spray drying process, this invention dynamically and continuously adds a second titanium source to the slurry, and by controlling the addition rate, prepares precursor particles with a gradient distribution of titanium concentration. This innovative "gradient doping" process ensures that the distribution of titanium in the final product changes continuously from the particle core to the surface, effectively suppressing excessive grain growth during differential temperature sintering and providing the possibility for forming a continuous particle size distribution, thus avoiding the interface incompatibility problem caused by the simple mixing of particles of different sizes in traditional methods.

[0020] 3. This invention involves the separate and differential temperature sintering of precursors with different titanium concentrations. Precursors with lower surface titanium concentrations are sintered at relatively lower temperatures to obtain large skeletal particles, while precursors with higher surface titanium concentrations are sintered at relatively higher temperatures to obtain small filler particles. This synergistic control strategy of titanium concentration and sintering temperature enables precise control of the crystallinity and particle size of different functional particles, ensuring the overall performance of the final mixed product.

[0021] 4. This invention mixes two intermediate products prepared by the above method, with optimized particle size and performance, to obtain a lithium iron phosphate cathode material with a scientifically proportioned particle size distribution. The smaller particles can efficiently fill the gaps between the larger particles, significantly improving the tap density and compaction density of the powder, thereby contributing to an increase in the volumetric energy density of the battery. Attached Figure Description

[0022] Figure 1 SEM of the lithium iron phosphate cathode material of the present invention Figure 1 ; Figure 2 SEM of the lithium iron phosphate cathode material of the present invention Figure 2 ; Figure 3 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] See appendix Figure 1-3 A method for preparing high-pressure lithium iron phosphate cathode material, comprising the following steps: (1) Mix 2000g of ferric phosphate, 14.22g of tetrabutyl titanate and 3000g of pure water and grind them until D50 is 300nm. Spray dry, sinter at 400℃ for 5h and pulverize to prepare pre-titanium ferric phosphate.

[0026] (2) Mix 1000g of pre-titanium iron phosphate, 250g of lithium carbonate, 80g of anhydrous glucose, and 15g of PEG2000 obtained in step (1) and grind them to 350nm to prepare a precursor slurry.

[0027] (3) Prepare a titanium source suspension by ultrasonic stirring of 1.7g nano titanium dioxide, 1g PVP, and 100g water. The precursor slurry prepared in step (2) is subjected to high-speed stirring and spraying, while the titanium source suspension is added to the precursor slurry at a speed of 10ml / min to prepare gradient-doped precursor 1. The titanium source spraying speed is increased to 15ml / min to continue preparing gradient-doped precursor 2.

[0028] (4) The gradient-doped precursor 1 was sintered at 780℃ and then gas-powdered to obtain product 1; the gradient-doped precursor 2 was sintered at 785℃ and then gas-powdered to obtain product 2.

[0029] (5) High-pressure compaction high-ratio lithium iron phosphate material is obtained by mixing product 1 and product 2 in a mixer. Example 2:

[0030] A method for preparing high-pressure lithium iron phosphate cathode material, comprising the following steps: (1) 2000g of ferric phosphate, 7.2g of citric acid chelated titanium, and 3000g of pure water were mixed and milled until D50 was 350nm, spray dried, sintered at 400℃ for 5h, and pulverized to prepare pre-titanium ferric phosphate.

[0031] (2) Mix 1000g of pre-titanium iron phosphate, 250g of lithium carbonate, 70g of anhydrous glucose, and 25g of PEG2000 obtained in step (1) and grind them to 350nm to prepare a precursor slurry.

[0032] (3) Prepare a titanium source suspension by ultrasonic stirring of 1.7g nano titanium dioxide, 1g PVP, and 100g water. The precursor slurry prepared in step (3) is subjected to high-speed stirring and spraying, while the titanium source suspension is added to the precursor slurry at a speed of 10ml / min to prepare gradient-doped precursor 1. The titanium source spraying speed is increased to 15ml / min to continue preparing gradient-doped precursor 2.

[0033] (4) The gradient-doped precursor 1 was sintered at 785℃ and then gas-powdered to obtain product 1; the gradient-doped precursor 2 was sintered at 790℃ and then gas-powdered to obtain product 2.

[0034] (5) High-pressure compaction high-ratio lithium iron phosphate material is obtained by mixing product 1 and product 2 in a mixer. Example 3:

[0035] A method for preparing high-pressure lithium iron phosphate cathode material, comprising the following steps: (1) Mix 2000g of ferric phosphate, 14.22g of tetrabutyl titanate and 3000g of pure water and grind them until D50 is 250nm. Spray dry, sinter at 400℃ for 5h and pulverize to prepare pre-titanium ferric phosphate.

[0036] (2) Mix 1000g of pre-titanium iron phosphate, 250g of lithium carbonate, 80g of anhydrous glucose, and 15g of PEG2000 obtained in step (1) and grind them to 400nm to prepare a precursor slurry.

[0037] (3) Prepare a titanium source suspension by ultrasonic stirring of 1.2g nano titanium dioxide, 1g PVP, and 100g water. The precursor slurry prepared in step (3) is subjected to high-speed stirring and spraying, while the titanium source suspension is added to the precursor slurry at a speed of 10ml / min to prepare gradient-doped precursor 1. The titanium source spraying speed is increased to 15ml / min to continue preparing gradient-doped precursor 2.

[0038] (4) The gradient-doped precursor 1 was sintered at 780℃ and then gas-powdered to obtain product 1; the gradient-doped precursor 2 was sintered at 785℃ and then gas-powdered to obtain product 2.

[0039] (5) High-compaction, high-ratio lithium iron phosphate material is obtained by mixing product 1 and product 2 in a mixer.

[0040] Comparative Example 1: A method for preparing high-pressure lithium iron phosphate cathode material, comprising the following steps: (1) Mix 2000g of ferric phosphate, 14.22g of tetrabutyl titanate and 3000g of pure water and grind them until D50 is 250nm. Spray dry, sinter at 400℃ for 5h and pulverize to prepare pre-titanium ferric phosphate.

[0041] (2) The precursor slurry was prepared by mixing and grinding 1000g of pre-titanium iron phosphate, 250g of lithium carbonate, 80g of anhydrous glucose, 15g of PEG2000, and 1.2g of solid nano titanium dioxide obtained in step (1) to 400nm.

[0042] (3) The precursors are mixed evenly in a mixer, sintered at 780℃ for 8 hours, pulverized in an air jet mill, and then mixed again to prepare homogeneous doped high-pressure lithium iron phosphate material.

[0043] Comparative Example 2: Objective: To demonstrate the indispensability of the "dynamic gradient doping + split sintering" step in this invention for achieving the final superior performance.

[0044] Preparation method: (1) Preparation of pre-titanium-modified ferric phosphate: 2000g of ferric phosphate, 14.22g of tetrabutyl titanate, and 3000g of pure water were mixed and milled until D50 was 300nm, spray-dried, sintered at 400℃ for 5h, and pulverized to prepare pre-titanium-modified ferric phosphate. (This step is exactly the same as in Example 1, retaining the "pre-titanium-modified" feature.) (2) Preparation of homogeneous doped slurry: 1000g of pre-titanium iron phosphate, 250g of lithium carbonate, 80g of anhydrous glucose, 15g of PEG2000 and 1.7g of solid nano titanium dioxide (corresponding to the amount of titanium source b) obtained in step (1) are added at one time, mixed and milled to 350nm to prepare a homogeneous precursor slurry.

[0045] This step involves mixing the titanium source b into the slurry all at once during preparation, rather than adding it dynamically during spray drying.

[0046] (3) Preparation of the final product: The homogeneous precursor slurry prepared in step (2) is spray-dried to obtain the precursor. The obtained precursor is sintered at 785℃ (a compromise sintering temperature can be selected), and then subjected to gas powdering to obtain the final lithium iron phosphate material.

[0047] Comparative Example 3: Objective: To demonstrate the necessity of the "pre-titanium treatment" step in this invention for achieving the final superior performance.

[0048] Preparation method: (1) Preparation of homogeneous doped slurry: 2000g of untreated iron phosphate, 250g of lithium carbonate, 80g of anhydrous glucose, 15g of PEG2000, 14.22g of tetrabutyl titanate (corresponding to titanium source a) and 1.7g of solid nano titanium dioxide (corresponding to titanium source b) were added at one time, mixed and milled to 350nm to prepare a homogeneous precursor slurry.

[0049] Without a pre-titanium treatment step, all raw materials, including two forms of titanium sources, are mixed at the very beginning. (2) Preparation of the final product: The homogeneous precursor slurry prepared in step (1) is spray-dried to obtain the precursor. The obtained precursor is sintered at 785°C (the same compromise temperature as Comparative Example 2), and then gas-powdered to obtain the final lithium iron phosphate material.

[0050] Test Example 1: (1) Compacted density test Accurately weigh 2.000 g of the cathode material powder prepared in the examples or comparative examples and place it in a steel mold with an inner diameter of 13.0 mm. Apply a pressure of 200 MPa to the mold using a press and hold the pressure for 1 minute to form a circular flattened object. After removing the flattened object, measure the thickness five times at different locations using a micrometer with an accuracy of 0.001 mm, and take the average value (h). According to the formula: ρ = m / [π*(1.3cm / 2)] 2 The compaction density (ρ) of the material is calculated using *h], where m is the mass of the powder.

[0051] (2) Electrochemical performance testing Electrode preparation: The positive electrode material powder, SuperP conductive carbon black, and polyvinylidene fluoride (PVDF) binder prepared in the examples or comparative examples were mixed at a mass ratio of 90:5:5 in N-methylpyrrolidone (NMP) solvent and subjected to high-speed mechanical stirring until a uniform, particle-free slurry was formed. This slurry was then uniformly coated onto a 15 μm thick aluminum foil current collector using a coating machine, controlling the wet coating thickness to be 100 μm. The coated electrode was then dried in a vacuum oven at 80°C for 12 hours. After drying, the electrode was rolled using a roller press to control the areal density of the positive electrode active material to be 5.0 ± 0.1 mg / cm³. 2 Finally, the rolled electrode sheet is punched into a circular electrode sheet with a diameter of 14.0 mm.

[0052] Battery assembly and testing: The CR2032 button cell was assembled in a glove box under an argon atmosphere with water and oxygen content below 0.1 ppm. The prepared electrode sheet was used as the working electrode, a lithium metal sheet as the counter electrode, and a Celgard 2400 polypropylene membrane as the separator. A mixed solution of 1.0 mol / L LiPF6 of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) (volume ratio 1:1:1) was injected as the electrolyte.

[0053] The assembled batteries were tested for electrochemical performance using a battery testing system (NEWARECT-4008) in a constant temperature environment of 25°C. The test procedure was as follows: First, the batteries were activated by initial charge-discharge at a constant current of 0.1C within a voltage range of 2.5V to 3.8V. Subsequently, constant current charge-discharge tests were performed at rates of 1.0C and 5.0C, and the discharge specific capacity was recorded. The current density corresponding to 1C was 170 mA / g.

[0054] The cathode materials prepared in Examples 1-3 and Comparative Example 1 were subjected to performance tests according to the above method, and the results are summarized in Table 1.

[0055] Table 1. Test results of physical and electrochemical properties of each sample

[0056] As shown in Table 1, the cathode materials prepared by the methods described in Examples 1-3 exhibit higher compaction density and higher discharge specific capacity at high rates than the cathode materials prepared by the comparative examples using conventional homogeneous doping methods. This result demonstrates that the preparation method described in this invention can effectively improve the overall performance of lithium iron phosphate materials.

[0057] The material prepared in this invention exhibits a higher compaction density due to the particle structure formed by its unique preparation process. By performing differential temperature sintering of precursors with different titanium concentration gradients in separate channels, two intermediate products with regulated particle size and properties were obtained. When these two products are mixed, smaller particles can effectively fill the gaps between larger particles, thereby forming a denser packing structure, ultimately leading to an increase in the macroscopic powder compaction density.

[0058] Meanwhile, the reason why the material prepared by this invention can maintain a high discharge capacity at high rates is due to the heterogeneous distribution of titanium elements within it. The pre-titanization treatment achieved in the early stages of preparation using a soluble titanium source promotes the incorporation of some titanium elements into the primary grain lattice of lithium iron phosphate, improving the material's intrinsic ion / electron transport capability. Combined with subsequent gradient doping to regulate the microstructure of secondary particles, this optimizes the electrochemical reaction kinetics and reduces polarization during high-rate charge and discharge, thereby achieving excellent rate performance.

[0059] Test Example 2: The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were used to prepare CR2032 type button batteries according to the method described in Test Example 1 (2) for electrochemical performance testing.

[0060] The assembled button cell battery was subjected to cycle stability testing. The specific steps are as follows: Leave the battery in a constant temperature environment of 25°C for 2 hours.

[0061] The battery was subjected to one charge-discharge cycle at a constant current of 0.2C within a voltage range of 2.5V to 3.8V to record its actual capacity during the first cycle.

[0062] Subsequently, the battery was subjected to continuous charge-discharge cycle tests at a constant current of 1.0C, with a charging cutoff voltage of 3.8V and a discharging cutoff voltage of 2.5V.

[0063] The test was performed for a total of 500 cycles, and the discharge capacity was recorded after the 500th cycle.

[0064] Calculate and record the capacity retention rate of the battery after 500 cycles. The formula for calculating the capacity retention rate is: Capacity retention rate (%) = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0065] Test Results The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the above method, and the results are summarized in Table 2.

[0066] Table 2: Cyclic stability test results of each sample

[0067] As shown in Table 2, the cathode materials prepared using the methods described in Examples 1-3 exhibit significantly higher capacity retention after 500 charge-discharge cycles compared to comparative examples 1, 2, and 3, which used different simplified methods. This result demonstrates that the preparation method described in this invention can effectively improve the cycle stability of lithium iron phosphate materials.

[0068] The superior cycle stability of the material prepared in this invention is closely related to its unique heterogeneous elemental distribution and particle structure. The pre-titanization treatment performed in the early stage of preparation allows some titanium elements to enter the lithium iron phosphate lattice. This lattice-scale doping helps stabilize the olivine structure and suppresses lattice distortion or phase transitions caused by repeated lithium ion extraction / intercalation during long-term charge and discharge, thereby slowing down the structural degradation of the active material.

[0069] Comparing the results of the examples and comparative examples reveals that Comparative Example 3, lacking pre-titanium treatment and gradient doping, had an unoptimized crystal structure and particle packing structure, resulting in the worst cycling performance. Comparative Example 2, although employing pre-titanium treatment, lacked subsequent gradient doping and split-path sintering, failing to achieve a scientifically sound particle size distribution. This made the electrodes susceptible to structural damage due to mechanical stress during long-term cycling, thus its capacity retention was inferior to the examples. These comparative results collectively demonstrate that the combination of lattice stabilization through pre-titanium treatment and particle structure optimization through gradient doping / splitting is crucial for achieving high cycling stability in materials.

[0070] Test Example 3: The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were used to prepare CR2032 type button batteries according to the method described in Test Example 1 (2) for electrochemical performance testing.

[0071] The assembled button cell battery was subjected to a DC internal resistance test to characterize its dynamic properties. The specific steps are as follows: Charge the battery to 50% State of Charge (SOC) at a constant current of 0.5C in a constant temperature environment of 25℃, and then let it stand for 1 hour to allow the battery to stabilize.

[0072] Apply a constant current discharge pulse at a rate of 5.0C to the battery at 50% SOC, with a pulse duration of 10 seconds.

[0073] Accurately record the instantaneous voltage (V1) before the discharge pulse is applied and the instantaneous voltage (V2) at the end of the discharge pulse.

[0074] Calculate the battery's DC internal resistance during discharge based on the recorded voltage changes and pulse current values. The formula for calculating the DC internal resistance is: Discharge DCIR (mΩ) = (V1 - V2) / I discharge , among which, I discharge The current value (unit: A) corresponding to a 5.0C discharge pulse.

[0075] Test Results The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the above method, and the results are summarized in Table 3.

[0076] Table 3: DC internal resistance (DCIR) test results for each sample

[0077] As shown in Table 3, the cathode materials prepared using the methods described in Examples 1-3 have significantly lower DC internal resistance (DCIR) values ​​than those of Comparative Examples 1, 2, and 3, which used different simplified or conventional methods. DCIR is an important parameter for evaluating battery kinetic characteristics; a lower DCIR value indicates less polarization and better kinetic performance.

[0078] The reason why the material prepared in this invention exhibits lower DC internal resistance is that the electron and ion transport paths within the material have been effectively optimized. The pre-titanization treatment using a soluble titanium source in the early stages of preparation induces some titanium elements to enter the primary grains of lithium iron phosphate in a doping form. This lattice-level elemental doping can improve the intrinsic conductivity of the material itself and lower the energy barrier for lithium ion migration in the solid matrix, which is the basis for reducing the material's internal resistance.

[0079] Furthermore, by dynamically introducing a second titanium source during the spray drying process to form a gradient doped structure, combined with a split-path differential temperature sintering process, the secondary particle morphology and particle packing of the final product are improved. This scientific particle size distribution not only increases the compaction density but also constructs a more efficient conductive network, reducing the contact resistance between particles. Comparison of the various comparative examples shows that the absence of any key step (e.g., comparative example 2 lacks gradient doping, and comparative example 3 has completely disordered doping) leads to an increase in the DCIR value. This demonstrates that the combined effect of improved intrinsic conductivity and optimized interparticle conductive network is the reason for the material's low internal resistance and excellent kinetic properties.

[0080] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-voltage lithium iron phosphate cathode material, characterized in that, Includes the following steps: (a) Pre-titanium-modified iron phosphate was prepared by mixing soluble titanium source a with iron phosphate. (b) The pre-titanium iron phosphate, lithium source and carbon source are mixed to prepare a precursor slurry; (c) The precursor slurry is spray-dried, and titanium source b is continuously added to the slurry during the spray-drying process. By controlling the addition rate of titanium source b, at least two gradient-doped precursors with gradient titanium concentrations are obtained stepwise. (d) The at least two gradient-doped precursors obtained in step (c) are subjected to differential temperature sintering under different conditions to obtain at least two intermediate products; (e) The at least two intermediate products obtained in step (d) are mixed to obtain the high-pressure lithium iron phosphate cathode material.

2. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, The soluble titanium source a mentioned in step (a) is tetrabutyl titanate and / or chelated titanium citrate.

3. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, In step (a), the mixing process includes wet sand milling, drying and sintering steps, wherein the sintering temperature is 300-500℃ and the titanium content in the obtained pre-titanium iron phosphate is 500-1500ppm.

4. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, The titanium source b mentioned in step (c) is a suspension of nano-titanium dioxide.

5. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, In step (c), a first gradient doped precursor is obtained by first adding it at a lower rate and then a second gradient doped precursor is obtained by adding it at a higher rate; the mass ratio of the first gradient doped precursor to the second gradient doped precursor is 1:(0.5-1.0).

6. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, In step (d), the first gradient doped precursor is sintered at a temperature of 750-800℃, and the second gradient doped precursor is sintered at a temperature of 755-805℃.

7. The method for preparing a high-voltage lithium iron phosphate cathode material according to claim 1, characterized in that, The total titanium content in the high-pressure lithium iron phosphate cathode material obtained in step (e) is 1500-3000 ppm.

8. A high-voltage lithium iron phosphate cathode material, prepared from the high-voltage lithium iron phosphate cathode material and its preparation method as described in any one of claims 1-7, characterized in that: The cathode material is composed of at least two types of lithium iron phosphate particles, wherein titanium is heterogeneously distributed in the cathode material and exists both inside the primary crystal lattice of lithium iron phosphate and in the surface gradient layer of the secondary spherical particles.

9. A high-voltage lithium iron phosphate cathode material according to claim 8, characterized in that, The material comprises first lithium iron phosphate particles and second lithium iron phosphate particles, wherein the average particle size of the second lithium iron phosphate particles is smaller than that of the first lithium iron phosphate particles, and the titanium concentration on the surface of the second lithium iron phosphate particles is higher than that of the first lithium iron phosphate particles.

10. A high-voltage lithium iron phosphate cathode material according to claim 8, characterized in that, The compacted density of the positive electrode material powder is not less than 2.60 g / cm³. 3 The discharge specific capacity at 5C rate is not less than 120mAh / g.

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