High-compaction and high-capacity lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, and discloses a high-compaction and high-capacity lithium iron phosphate positive electrode material and a preparation method thereof, the positive electrode material has a three-level particle grading structure composed of large, medium and small particles, and the material contains a titanium element. The preparation method comprises the following steps: S1, mixing first iron phosphate and second iron phosphate with different iron-phosphorus molar ratios with a lithium source, a carbon source and an additive, then carrying out first sintering, and generating a stacking framework composed of large and medium particles in situ by utilizing the difference of internal growth activity of raw materials; and S2, mixing the sintered material obtained in the step S1 with titanium-containing iron phosphate, a lithium source and a carbon source in a specific ratio, and then carrying out secondary sintering to generate small particles to fill gaps of the frame, thereby finally forming the three-stage particle grading structure. Through programmed design of chemical properties of raw materials, accurate construction of a physical structure of a final product is achieved, the technological process is simplified, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery cathode material, in particular to a high-compaction high-capacity lithium iron phosphate cathode material and a preparation method thereof. BACKGROUND

[0002] Lithium iron phosphate (LiFePO4) has become one of the most widely used cathode materials in the field of power batteries and energy storage due to its stable olivine structure, excellent thermal stability, low cost, and environmental friendliness. With the rapid development of new energy vehicle and consumer electronics market, there is a growing demand for the volumetric energy density of lithium ion batteries. For lithium iron phosphate material system, its gravimetric capacity is close to the theoretical value. Therefore, improving the compaction density of the cathode material itself and then achieving higher compaction density at the electrode level is a key technical approach to improve the volumetric energy density of the battery.

[0003] To improve the compaction density of lithium iron phosphate material, the existing technology usually adopts the strategy of increasing the particle size of the material or optimizing the particle morphology. However, simply increasing the particle size will significantly prolong the diffusion path of lithium ions in the solid phase, leading to deterioration of the kinetic performance of the material, especially under high-rate charging and discharging and low-temperature environment, the capacity decay problem is particularly prominent. This makes the compaction density and rate performance of the material form a mutually restrictive relationship, which is difficult to improve simultaneously.

[0004] Another technical approach is to build a wide particle size distribution or multi-modal particle size distribution, and use small particles to fill the gaps between large particles to improve the packing density. Although this approach is effective in theory, it faces the problems of process complication and cost increase in actual production. To achieve this specific particle grading, different particle size materials need to be prepared in batches and then compounded by mechanical mixing. This process not only increases the independent production and processing procedures, but also requires high precision in equipment and process control, and the uniformity of physical mixing is difficult to guarantee, which affects the stability and batch consistency of the final product performance.

[0005] Therefore, the existing technology still has technical problems to be solved in how to prepare lithium iron phosphate cathode material with high compaction density and excellent electrochemical performance through a simple process, cost controllable and high product consistency method. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a high-compaction high-capacity lithium iron phosphate cathode material and a preparation method thereof, which solves the problem that the compaction density and electrochemical performance of the existing lithium iron phosphate cathode material are difficult to balance, and the preparation process of high-compaction density material is complex and costly.

[0007] To achieve the above object, the application is implemented by the following technical solutions: A high-compaction and high-capacity lithium iron phosphate positive electrode material, the positive electrode material has a three-stage particle grading structure composed of large, medium and small particles, and the particle size distribution curve has: a first particle size peak in the range of 0.1-0.5 μm; a second particle size peak in the range of 0.5-1.0 μm; and a third particle size peak in the range of 1.0-1.5 μm; and the positive electrode material preparation raw materials include iron phosphate A and iron phosphate B, a first lithium source and a first carbon source, an additive, titanium-containing iron phosphate, a second carbon source, and a second lithium source.

[0008] Preferably, the content of titanium element in the titanium-containing iron phosphate is 5000-10000 ppm.

[0009] Preferably, the powder particle size distribution D50 of the positive electrode material is 1.0-1.5 μm.

[0010] Preferably, the residual carbon content of the positive electrode material is 1.1-1.4%.

[0011] A preparation method of a high-compaction and high-capacity lithium iron phosphate positive electrode material, comprising the following steps: S1: iron phosphate A and iron phosphate B with different iron-phosphorus molar ratios are mixed with a first lithium source, a first carbon source and an additive to perform first sintering, to obtain a lithium iron phosphate sintered material, the additive is one or more of magnesium sulfate, magnesium oxide, titanium dioxide, tetrabutyl titanate and niobium pentoxide; S2: the lithium iron phosphate sintered material is mixed with titanium-containing iron phosphate, a second lithium source and a second carbon source to perform second sintering, to obtain the lithium iron phosphate positive electrode material.

[0012] Preferably, in step S1, the iron-phosphorus molar ratio of the iron phosphate A and the iron phosphate B is in the range of 0.95-0.98.

[0013] Preferably, in step S1, the mass ratio of the iron phosphate A to the iron phosphate B is (0.3-3):1.

[0014] Preferably, in step S2, the molar ratio of the lithium iron phosphate sintered material to the titanium-containing iron phosphate is (6-8):(4-2).

[0015] Preferably, the temperature of the first sintering is 770-800℃, and the temperature of the second sintering is not higher than 750℃.

[0016] Preferably, in step S2, the mixture is sand milled until its particle size distribution curve forms first, second and third particle size peaks before the second sintering is performed.

[0017] The application provides a high-compaction high-capacity lithium iron phosphate cathode material and a preparation method thereof. 1. The application realizes the synergistic improvement of material compaction density and electrochemical performance by constructing a specific three-level particle grading structure composed of large, medium and small particles. In this structure, large and medium particles accumulate to form a high-density framework, and small particles effectively fill the gaps between the framework, thereby significantly reducing the porosity of particle accumulation, enabling the material to obtain a high compaction density of 2.6 g / cm 3 The above high compaction density. At the same time, the presence of small particles shortens the lithium ion diffusion path and increases the electrochemical reaction active site, ensuring that the material still has high discharge capacity and excellent rate performance under high compaction density.

[0018] 2. The preparation method of the application significantly simplifies the production process of high-compaction materials and reduces costs. In the first step of sintering, the use of two different iron-phosphorus molar ratio iron phosphate raw materials forms a large and medium particle grading in situ due to the difference in intrinsic "growth activity", avoiding the complex process of batch, separate line sanding and processing of different particle materials in the prior art. This design not only simplifies the process flow, but also reduces the production cost due to the increase of equipment and the complexity of process control.

[0019] 3. The front-end doping technology used in the application improves the uniformity of the modified elements and the performance of the final product. By introducing titanium elements in the form of co-precipitation during the synthesis of the iron phosphate precursor, it ensures that the titanium elements are uniformly distributed in the precursor particles at the atomic or near-atomic scale. Compared with the external mixing and doping method during sintering, this method avoids element agglomeration, making the modification of titanium elements in the final lithium iron phosphate product more sufficient and stable, and the performance improvement more obvious.

[0020] 4. The two-step sintering process of the application realizes precise control of particle growth and reduces energy consumption. The first step is carried out at a higher temperature (770-800℃) to promote the growth of large and medium particles to form a dense skeleton; the second step is carried out at a lower temperature (not more than 750℃) to convert titanium-containing iron phosphate into small particles and complete the final structure construction. This step-by-step temperature control meets the formation conditions of particles of different sizes, and avoids the high energy consumption problem caused by high temperature throughout the traditional two-step sintering process.

[0021] 5、The technical scheme has high process controllability and product consistency. The core physical structure (three-stage particle size distribution) of the final product is inherently determined by the chemical properties (iron-phosphorus molar ratio, titanium content) of the starting raw material. This programmed construction from chemical composition to physical structure provides strong repeatability of the process and high batch consistency of the product. Compared with the traditional method of relying on external physical parameters such as mechanical sanding time and speed to control particle size, the internal regulation mechanism of the present application provides higher process stability and product quality assurance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM images of the lithium iron phosphate material prepared for the present application example 1 at different sizes; Figure 2 SEM images of the lithium iron phosphate material prepared for the present application comparative example 1 at different sizes. DETAILED DESCRIPTION

[0023] The technical scheme in the embodiments of the present application will be described below in conjunction with the drawings in the specification of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0024] The present application provides a high-compaction, high-capacity lithium iron phosphate cathode material, which has a three-stage particle size distribution structure composed of large, medium and small particles, and its particle size distribution curve has: a first particle size peak in the range of 0.1-0.5 μm; a second particle size peak in the range of 0.5-1.0 μm; and a third particle size peak in the range of 1.0-1.5 μm; And the preparation raw material of the cathode material includes phosphorus acid iron A and phosphorus acid iron B, first lithium source and first carbon source, additive, titanium-containing phosphorus acid iron, second carbon source, second lithium source, wherein the content of titanium element in the titanium-containing phosphorus acid iron is 5000-10000 ppm, the powder particle size distribution D50 of the cathode material is 1.0-1.5 μm, and the residual carbon content of the cathode material is 1.1-1.4%.

[0025] In the present application, titanium-free anhydrous phosphorus acid iron is used as a framework support, and titanium-containing phosphorus acid iron provides nanoscale particle filling gaps to achieve "closest packing" in cooperation. If the proportion of titanium-free anhydrous phosphorus acid iron is too high, the capacity of the lithium iron phosphate powder prepared will be low; if the proportion of titanium-containing phosphorus acid iron is too high, the compaction density will be low. Therefore, reasonable selection of the proportion of phosphorus acid iron in the composite precursor is conducive to balancing the high compaction density and high capacity of lithium iron phosphate.

[0026] In titanium-doped iron phosphate, Ti replaces Fe sites to form LiFe. 1x Ti x PO4 solid solution is beneficial for improving conductivity and structural stability; at the same time, Ti doping can refine LiFePO4 grains, avoid excessive grain growth during sintering, and help maintain a multi-level distribution structure.

[0027] By using anhydrous iron phosphate and titanium-containing iron phosphate with different growth activities to form a composite precursor, lithium iron phosphate materials that balance high compaction and high capacity performance can be obtained without multiple sintering and batch milling processes. Specifically, since titanium-containing iron phosphate mainly forms small particles, the titanium doping amount is relatively large in order to suppress the excessive growth of lithium iron phosphate generated from iron phosphate during sintering; conversely, titanium-free iron phosphate mainly forms a large and medium particle framework. The difference in growth activity caused by the different iron-phosphorus ratio can initially form a secondary particle gradation, so the titanium doping amount is relatively low. The features and performance of the present invention will be further described in detail below with reference to specific embodiments.

[0028] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0029] Ferrous sulfate heptahydrate, CAS No.: 7782-63-0.

[0030] Phosphoric acid, 85% by mass, CAS No.: 7664-38-2.

[0031] Ammonia Hydroxide, CAS No.: 1336-21-6.

[0032] Anhydrous ethanol, CAS No.: 64-17-5.

[0033] Tetrabutyl Titanate, CAS No.: 5593-70-4.

[0034] Lithium carbonate, battery grade, CAS number: 554-13-2.

[0035] Glucose (D-Glucose), analytical grade, CAS No.: 50-99-7.

[0036] Polyethylene glycol (PEG), CAS No.: 25322-68-3.

[0037] Titanium dioxide, nanoscale, anatase type, CAS No.: 13463-67-7.

[0038] Acetylene Black, a conductive agent, CAS No.: 1333-86-4.

[0039] Polytetrafluoroethylene (PTFE), adhesive, CAS No.: 9002-84-0.

[0040] Lithium metal foil, battery grade, CAS No.: 7439-93-2.

[0041] Lithium hexafluorophosphate (LiPF6), an electrolyte salt, CAS No.: 21324-40-3.

[0042] Ethylene carbonate (EC), battery grade, CAS No.: 96-49-1.

[0043] Dimethyl carbonate (DMC), battery grade, CAS No.: 616-38-6.

[0044] Diethyl Carbonate (DEC), battery grade, CAS No.: 105-58-8.

[0045] Celgard 2400, a polypropylene microporous membrane diaphragm.

[0046] This invention provides a method for preparing a high-capacity, high-density lithium iron phosphate cathode material, comprising the following steps: Iron phosphate A and iron phosphate B, with different iron-phosphorus molar ratios, were mixed with a first lithium source, a first carbon source, and additives, and then subjected to a first sintering to obtain lithium iron phosphate sintered material. The additives were one or more of magnesium sulfate, magnesium oxide, titanium dioxide, tetrabutyl titanate, and niobium pentoxide. The first sintering temperature was 770-800℃, the iron-phosphorus molar ratio of iron phosphate A and iron phosphate B was in the range of 0.95-0.98, and the mass ratio of iron phosphate A to iron phosphate B was (0.3-3):1. The lithium iron phosphate sintering material is mixed with titanium-containing iron phosphate, a second lithium source, and a second carbon source, and then subjected to a second sintering to obtain the lithium iron phosphate cathode material. The temperature of the second sintering does not exceed 750℃, and the molar ratio of the lithium iron phosphate sintering material to the titanium-containing iron phosphate is (6-8):(4-2). Before the second sintering, the mixture is milled until its particle size distribution curve forms the first, second, and third particle size peaks. The first lithium source is any one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium dihydrogen phosphate; the second lithium source is any one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium dihydrogen phosphate. The first carbon source is one or more of glucose, polyethylene glycol, sucrose, β-cyclodextrin, and polyacrylonitrile; the second carbon source is at least one of glucose, polyethylene glycol, sucrose, β-cyclodextrin, and polyacrylonitrile.

[0047] Preparation Example 1: Preparation of Iron Phosphate A with an iron-to-phosphorus molar ratio of 0.960 This preparation example aims to provide an iron phosphate precursor with a molar ratio of iron to phosphorus of 0.960:1 (hereinafter referred to as composite iron phosphate).

[0048] In a reaction vessel equipped with a mechanical stirrer, temperature controller and dropping device, 2000 mL of deionized water was added, followed by 266.9 g of ferrous sulfate heptahydrate (FeSO4·7H2O, equivalent to 0.960 moles of iron). The mixture was stirred until completely dissolved to form solution A, and the solution temperature was raised to 60°C.

[0049] In another beaker, dissolve 115.3 g of 85% phosphoric acid (H3PO4, equivalent to 1.00 mole of phosphorus) in 1000 mL of deionized water to form solution B.

[0050] Solution B was slowly added dropwise to solution A in the reactor at a rate of 20 mL / min using a peristaltic pump while stirring at 300 rpm. Throughout the addition, ammonia was added simultaneously to maintain the pH of the reaction system precisely within the range of 2.5 ± 0.5. After the addition was complete, the reaction was continued at 60°C and 300 rpm for 2 hours to ensure complete reaction.

[0051] After the reaction was complete, the resulting white suspension was filtered, and the precipitate was collected. The precipitate was washed three times with deionized water and then once with anhydrous ethanol to thoroughly remove residual sulfate ions and other impurities. Finally, the washed precipitate was placed in a vacuum drying oven and dried at 80°C for 12 hours. After pulverization, white powdered iron phosphate A was obtained.

[0052] Preparation Example 2: Preparation of Ferric Phosphate B with an iron-to-phosphorus molar ratio of 0.974 This preparation example aims to provide an iron phosphate precursor with a molar ratio of iron to phosphorus of 0.974:1.

[0053] The preparation method was basically the same as in Preparation Example 1, except for the amount of ferrous sulfate heptahydrate. Specifically, 270.8 g of ferrous sulfate heptahydrate (FeSO4·7H2O, equivalent to 0.974 moles of iron) was weighed and dissolved in 2000 mL of deionized water. The amount of phosphoric acid and all other operational steps, including reaction temperature, pH control, aging, washing, and drying conditions, were consistent with those specified in Preparation Example 1. Finally, white powdered ferric phosphate B was obtained.

[0054] Preparation Example 3: Preparation of front-end doped titanium-containing iron phosphate with a titanium content of 8000 ppm This preparation example aims to provide a titanium-containing iron phosphate precursor with uniform titanium element distribution via co-precipitation.

[0055] In a reaction vessel identical to that used in Preparation Example 1, 278.0 g of ferrous sulfate heptahydrate (FeSO4·7H2O, equivalent to 1.00 moles of iron) and 2000 mL of deionized water were added, stirred and dissolved to form solution D, and the solution temperature was raised to 60 °C.

[0056] Separately, dissolve 8.5 g of tetrabutyl titanate (Ti(OC4H9)4, equivalent to 0.025 moles of titanium) in 200 mL of anhydrous ethanol to form solution E. Then, dissolve 115.3 g of 85% phosphoric acid (H3PO4, equivalent to 1.00 moles of phosphorus) in 1000 mL of deionized water to form solution F. The feeding ratio here is intended to achieve a titanium content of approximately 8000 ppm in the final product.

[0057] At a stirring speed of 300 rpm, solutions E and F were simultaneously and slowly added dropwise to solution D in the reactor at corresponding rates using two independent peristaltic pumps. Throughout the addition process, the pH of the reaction system was precisely maintained within the range of 2.5 ± 0.5 by simultaneously adding ammonia.

[0058] After the addition was complete, the subsequent aging, filtration, washing, and drying steps were exactly the same as in Preparation Example 1. The final product was a white powdery titanium-containing iron phosphate with titanium uniformly distributed within the particles. This front-end doping method ensured the uniform introduction of titanium during the formation of the iron phosphate lattice.

[0059] Example 1: Refer to Appendix Figure 1 A method for preparing a high-compact, high-capacity lithium iron phosphate cathode material, the specific steps of which are as follows: S1: Weigh ferric phosphate A obtained from Preparation Example 1 and ferric phosphate B obtained from Preparation Example 2, and mix them at a mass ratio of 3:1 to obtain mixed ferric phosphate. Then, add the mixed ferric phosphate, lithium carbonate, glucose, polyethylene glycol, and titanium dioxide to deionized water and stir to obtain a mixed slurry. The amount of lithium carbonate added makes the molar ratio of lithium to iron 1.02:1; the amount of glucose added is 9.2% of the total mass of the mixed ferric phosphate; the amount of polyethylene glycol added is 1.1% of the total mass of the mixed ferric phosphate; and the amount of titanium dioxide added is 0.18% of the total mass of the mixed ferric phosphate.

[0060] S2: Place the mixed slurry prepared in step S1 into a horizontal sand mill, set the rotation speed to 2000 rpm, and perform wet grinding for 2 hours, controlling the particle size distribution D50 of the slurry after grinding to be within the range of 0.38-0.43 μm. Dry and granulate the ground slurry using a spray dryer to obtain spherical dried powder.

[0061] S3: Under nitrogen atmosphere protection, the dried powder obtained in step S2 is placed in a box furnace, heated to 790°C and sintered at this temperature for 9 hours to obtain lithium iron phosphate sintered material.

[0062] S4: The lithium iron phosphate sintered material obtained in step S3 is mixed with the titanium-containing iron phosphate obtained from Preparation Example 3 at a molar ratio of 7:3. Lithium carbonate, glucose, and polyethylene glycol are added to the mixture, and deionized water is added to prepare a slurry. The amount of lithium carbonate added makes the total molar ratio of lithium to iron 1.02:1; the amount of glucose added is 2.2% of the mass of titanium-containing iron phosphate; and the amount of polyethylene glycol added is 8.4% of the mass of titanium-containing iron phosphate. The slurry is placed in a horizontal sand mill, the speed is set to 1500 rpm, and it is ground for 1.5 hours until its particle size distribution curve shows three separate particle size peaks.

[0063] S5: The slurry obtained in step S4 is spray-dried and then placed in a box furnace under nitrogen atmosphere protection. The temperature is raised to 750°C and sintered at this temperature for 6 hours. After cooling, the sintered product is deagglomerated using an air jet mill to obtain the final lithium iron phosphate cathode material.

[0064] Example 2:

[0065] The preparation method of this embodiment is basically the same as that of Example 1, except that in step S1, the mass ratio of iron phosphate A to iron phosphate B is adjusted to 1:1.

[0066] Example 3:

[0067] The preparation method of this embodiment is basically the same as that of Example 1, except that in step S1, the mass ratio of iron phosphate A to iron phosphate B is adjusted to 1:3.

[0068] Example 4:

[0069] The preparation method of this embodiment is basically the same as that of Example 1, except that the amount of titanium dioxide added in step S1 is adjusted to 0.1% of the total mass of mixed iron phosphate, and the sintering temperature in step S3 is adjusted to 780℃.

[0070] Example 5:

[0071] The preparation method of this embodiment is basically the same as that of Example 1, except that in step S4, the molar ratio of lithium iron phosphate sintering material to titanium-containing iron phosphate is adjusted to 6:4.

[0072] Example 6:

[0073] The preparation method of this embodiment is basically the same as that of Example 1, except that in step S4, the molar ratio of lithium iron phosphate sintering material to titanium-containing iron phosphate is adjusted to 8:2.

[0074] Example 7:

[0075] The preparation method of this embodiment is basically the same as that of Example 1, except that the titanium-containing iron phosphate used in step S4 has its titanium source input amount adjusted during the preparation process so that the titanium content in the final product is 6000ppm.

[0076] Comparative Example 1: See attached document Figure 1 The preparation method of this comparative example is basically the same as that of Example 1, except that in step S1, the two iron phosphate raw materials used are prepared by the method of Example 2, that is, the iron-phosphorus molar ratio of the two iron phosphate raw materials is 0.974.

[0077] Comparative Example 2: The preparation method of this comparative example is basically the same as that of Example 1, except that titanium dioxide is not added in step S1.

[0078] Comparative Example 3: The preparation method of this comparative example is basically the same as that of Example 1, except that in step S4, the ratio of the second carbon source is changed to: the amount of glucose added is 9.2% of the mass of titanium-containing iron phosphate, and the amount of polyethylene glycol added is 1.1% of the mass of titanium-containing iron phosphate.

[0079] Part Three: Performance Testing and Results Analysis Test Example 1: Compacted Density Test The compaction density of the lithium iron phosphate cathode material powders prepared in Examples 1-7 and Comparative Examples 1-3 was tested to evaluate their powder packing performance.

[0080] The specific testing steps are as follows: Using an electronic balance with an accuracy of 0.1 mg, accurately weigh 2.000 g of the positive electrode material powder sample to be tested, and record its mass as m.

[0081] The weighed powder sample is completely and evenly placed into a cylindrical steel mold with an inner diameter of 10.0 mm, and the mold is gently vibrated to flatten the powder surface. The inner diameter of the mold is recorded as d.

[0082] Place the mold containing the sample on the powder tablet press, set the program to apply a pressure of 20 MPa to the mold, and hold it at this pressure for 60 seconds.

[0083] After the pressure holding period is over, release the pressure and carefully remove the pressed circular sample from the mold.

[0084] Using a micrometer with an accuracy of 0.001 mm, the thickness of the circular sample was measured at four different locations evenly distributed along its center and edge. The arithmetic mean of the five thickness values ​​was taken as the final thickness of the sample. .

[0085] According to the formula Calculate the compacted density of the sample Each sample was tested three times, and the arithmetic mean was taken as the final report result.

[0086] The lithium iron phosphate cathode materials prepared in the above embodiments and comparative examples were tested according to the method of this test example, and the results are shown in Table 1.

[0087] Table 1. Compaction density test results of each embodiment and comparative example.

[0088] As shown in Table 1, the cathode materials prepared by the methods in Examples 1-7 all achieved a compaction density of 2.55 g / cm³. 3 Of the above, the compaction density of Examples 1, 6, and 7 exceeded 2.60 g / cm³. 3 This result demonstrates that the material provided by this technical solution possesses a high powder bulk density. The structural basis for achieving this high compaction density lies in the formation of a three-tiered particle size distribution within the material, consisting of large, medium, and small particles. In this structure, large and medium particles stack together to form a primary framework, while small particles fill the pores within this framework, thereby reducing the porosity between particles.

[0089] The results of Comparative Example 1 show that when the two iron phosphate raw materials used in the first sintering step have the same iron-to-phosphorus molar ratio, the compacted density of the resulting material (2.53 g / cm³) is... 3 The efficiency was significantly lower than in Examples 1-3. This indicates that utilizing two iron phosphate precursors with different iron-phosphorus molar ratios in the first sintering step is a prerequisite for effectively forming large and medium particle size differences and constructing a high-density packing framework. Without this condition, it is difficult to form an effective bimodal particle distribution in situ during sintering, ultimately leading to a decrease in particle packing efficiency.

[0090] The results of Examples 1, 5, and 6 further demonstrate that by controlling the molar ratio between the lithium iron phosphate sintered material formed in the first sintering step and the titanium-containing iron phosphate introduced in the second step, the relative quantities of large, medium, and small particles in the final product can be effectively controlled, thereby optimizing the particle packing pattern. When this ratio is within a specific range (as in Examples 1 and 6), small particles can fill the gaps formed by large and medium particles with high efficiency, resulting in a high overall packing density of the system and thus obtaining a final product with high compaction density.

[0091] Test Example 2: Electrochemical Performance Test Electrochemical performance tests were conducted on the lithium iron phosphate cathode materials prepared in Examples 1-7 and Comparative Examples 1-3 to evaluate their capacity and rate performance as cathode materials for lithium-ion batteries.

[0092] The specific testing steps are as follows: Electrode preparation: The lithium iron phosphate cathode material prepared in each example, acetylene black as a conductive agent, and polytetrafluoroethylene (PTFE) emulsion as a binder were mixed in a mass ratio of 90:5:5. An appropriate amount of anhydrous ethanol was added to the mixture as a solvent, and the mixture was thoroughly stirred in a planetary ball mill until a uniform electrode slurry without particle agglomeration was formed. This slurry was uniformly coated onto an aluminum foil current collector, and the coated aluminum foil was placed in a vacuum oven at 80°C and dried for 12 hours. After drying, the electrode sheet was rolled using a roller press and then punched into circular electrode sheets with a diameter of 12 mm.

[0093] Button cell assembly: In a glove box filled with high-purity argon (water and oxygen content both below 0.1 ppm), the electrode sheet prepared in step 1 is used as the positive electrode, the lithium metal sheet as the negative electrode, the Celgard 2400 polypropylene microporous membrane as the separator, and the solution obtained by dissolving 1 mol / L lithium hexafluorophosphate (LiPF6) in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) (volume ratio 1:1:1) is used as the electrolyte to assemble a CR2032 type button cell.

[0094] Performance Testing: The assembled coin cells were placed in a constant temperature environment at 25°C for 12 hours. A battery testing system was used to test the cells at 2.0-3.8 V (vs. Li / Li). + The battery was subjected to constant current charge-discharge tests within the voltage range specified in the test. First, two charge-discharge cycles were performed at a rate of 0.1C. Then, discharge tests were performed at rates of 0.1C and 1C, and the corresponding first discharge specific capacity was recorded.

[0095] The lithium iron phosphate cathode materials prepared in the above embodiments and comparative examples were tested according to the method of this test example, and the results are shown in Table 2.

[0096] Table 2. Electrochemical performance test results of each embodiment and comparative example.

[0097] As shown in Table 2, the cathode materials prepared by the methods in Examples 1-7 all exhibit high discharge specific capacity and excellent rate performance, with discharge capacities at 1C exceeding 140 mAh / g. This is attributed to the synergistic effect of the tertiary particle size distribution structure and titanium. In this structure, large and medium particles constitute the main electronic conductivity network, while the small particles filling the gaps significantly shorten the solid-phase diffusion path of lithium ions. Simultaneously, the incorporation of titanium enhances the intrinsic electronic conductivity of the material. These two effects together ensure efficient transport channels for both lithium ions and electrons within the material, enabling it to maintain high capacity and high rate performance even under high compaction density.

[0098] Comparing the test results of Example 1 and Comparative Example 2, without the addition of titanium dioxide, the 0.1C low-rate discharge capacity of the material did not change significantly, but its 1C high-rate discharge capacity decreased significantly from 144.2 mAh / g to 138.4 mAh / g. This indicates that the introduction of titanium is crucial for maintaining the electrochemical performance of the material at high current densities. The mechanism is that the absence of titanium leads to a decrease in the intrinsic electronic conductivity of the material. During high-rate charge and discharge, electron transport becomes the limiting step, resulting in more severe polarization and lower capacity utilization.

[0099] Comparing the test results of Example 1 and Comparative Example 3, when the ratio of the second carbon source in step S4 was inappropriate, the high-rate performance of the material also deteriorated significantly, with the 1C discharge capacity decreasing from 144.2 mAh / g to 138.6 mAh / g. This indicates that providing a specific ratio of carbon source for the newly generated titanium-containing lithium iron phosphate particles during the second sintering process is essential for constructing a complete and efficient conductive network. An inappropriate carbon source ratio leads to insufficient or poor-quality carbon coating of the small particles, disrupting the effective electrical contact between the small particles and the framework of large and medium-sized particles, thereby hindering the rapid transport of electrons throughout the particle packing system, ultimately resulting in a decrease in the material's rate performance.

[0100] 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 high-compact, high-capacity lithium iron phosphate cathode material, characterized in that, The cathode material has a three-level particle size distribution structure consisting of large, medium, and small particles, and its particle size distribution curve has the following characteristics: The first particle size peak is located in the range of 0.1-0.5 μm; The second particle size peak is located in the range of 0.5-1.0 μm; And a third particle size peak located in the range of 1.0-1.5 μm; Furthermore, the raw materials for preparing the cathode material include iron phosphate A and iron phosphate B, a first lithium source and a first carbon source, additives, titanium-containing iron phosphate, a second carbon source, and a second lithium source.

2. The high-pressure, high-capacity lithium iron phosphate cathode material according to claim 1, characterized in that, The titanium content in the titanium-containing ferric phosphate is 5000-10000 ppm.

3. The high-pressure, high-capacity lithium iron phosphate cathode material according to claim 1, characterized in that, The particle size distribution D50 of the cathode material is 1.0-1.5 μm.

4. The high-compact, high-capacity lithium iron phosphate cathode material according to claim 1, characterized in that, The residual carbon content of the cathode material is 1.1-1.4%.

5. A method for preparing a high-compact, high-capacity lithium iron phosphate cathode material, characterized in that, The application of a high-compact, high-capacity lithium iron phosphate cathode material according to any one of claims 1-4 includes the following steps: S1: Iron phosphate A and iron phosphate B with different iron-phosphorus molar ratios are mixed with a first lithium source, a first carbon source and additives and then sintered for the first time to obtain lithium iron phosphate sintered material. The additives are one or more of magnesium sulfate, magnesium oxide, titanium dioxide, tetrabutyl titanate and niobium pentoxide. S2: The lithium iron phosphate sintering material is mixed with titanium-containing iron phosphate, a second lithium source and a second carbon source, and then sintered for a second time to obtain the lithium iron phosphate cathode material.

6. The method for preparing a high-pressure, high-capacity lithium iron phosphate cathode material according to claim 5, characterized in that, In step S1, the iron-phosphorus molar ratio of iron phosphate A and iron phosphate B is in the range of 0.95-0.

98.

7. The method for preparing a high-compact, high-capacity lithium iron phosphate cathode material according to claim 5, characterized in that, In step S1, the mass ratio of iron phosphate A to iron phosphate B is (0.3-3):

1.

8. The method for preparing a high-pressure, high-capacity lithium iron phosphate cathode material according to claim 5, characterized in that, In step S2, the molar ratio of the lithium iron phosphate sintered material to the titanium-containing iron phosphate is (6-8):(4-2).

9. The method for preparing a high-pressure, high-capacity lithium iron phosphate cathode material according to claim 5, characterized in that, The temperature of the first sintering is 770-800℃, and the temperature of the second sintering does not exceed 750℃.

10. The method for preparing a high-pressure, high-capacity lithium iron phosphate cathode material according to claim 5, characterized in that, In step S2, before the second sintering, the mixture is sand-milled until its particle size distribution curve forms the first, second and third particle size peaks.

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