A lithium iron phosphate cathode material with high rate and high compaction performance and a preparation method thereof

Abstract

This invention relates to the field of lithium-ion battery cathode material preparation technology, specifically to a lithium iron phosphate cathode material with both high rate capability and high compaction performance, and its preparation method. Ferrous sulfate is dissolved and filtered to remove impurities, yielding an iron salt solution. Vanadium-doped lithium iron phosphate precursor material A and manganese-doped ferrous phosphate octahydrate precursor material B are synthesized via hydrothermal and co-precipitation methods, respectively. The two precursor materials are mixed with a lithium source, a carbon source, and titanium dioxide as a dopant, and then subjected to graded grinding, spray drying, and sintering to obtain the lithium iron phosphate cathode material. This invention utilizes the high reactivity of the ferrous phosphate octahydrate precursor, combined with the grain-regulating effect of vanadium, manganese, and titanium ternary co-doping, to prepare a material with a compaction density of 2.58 g / cm³. The synergistic doping of vanadium, manganese, and titanium, along with carbon coating, constructs a highly efficient conductive network, achieving a discharge specific capacity ≥158 mAh / g at 0.1C and ≥147 mAh / g at 1C, demonstrating excellent discharge rate performance.

Description

Technical Field

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

[0002] Lithium iron phosphate (LiFePO4, LFP) with olivine structure has become one of the most widely used cathode materials in the lithium-ion battery field due to its excellent cycle stability, high safety, and low cost. It has been widely used in new energy vehicles, energy storage power stations, and consumer electronics. However, current lithium iron phosphate materials have significant shortcomings: firstly, their low electronic and ionic conductivity leads to poor rate performance; secondly, the ion diffusion rate decreases significantly at low temperatures, resulting in a lower discharge rate; and thirdly, the uneven particle morphology and particle size distribution make it difficult to improve the compaction density, thus limiting further increases in battery energy density.

[0003] To address the aforementioned issues, existing technologies primarily focus on doping modification, carbon coating, morphology control, and particle size distribution. Regarding doping modification, vanadium doping is one of the effective methods to improve the electronic conductivity of lithium iron phosphate, through V... 3+ / V 4+ Valence state pair with Fe 2+ / Fe 3+ The synergistic effect of vanadium and sulfur optimizes the charge transport channel, but traditional vanadium doping often employs solid-state mixing methods. For example, patent CN120895620A discloses a vanadium-sulfur-doped lithium iron phosphate cathode material, its preparation method, and its application. This method involves mixing vanadium pentoxide powder with a lithium iron phosphate precursor, ball milling, and then sintering to obtain the vanadium-doped lithium iron phosphate precursor. However, this approach may result in uneven vanadium source dispersion, easily leading to localized enrichment and impurity formation. Titanium doping, on the other hand, can be achieved through Ti... 4+ Occupying lattice sites lowers the lithium-ion diffusion barrier, thereby improving electrochemical performance. However, single titanium doping struggles to simultaneously achieve both compaction density and low-temperature performance, and high titanium content can inhibit primary particle growth. Patent CN119674025A discloses a method for preparing carbon-coated titanium-doped lithium iron phosphate cathode material, but the use of a single iron source makes it difficult to form effective particle gradation to improve the material's compaction density. Regarding particle gradation and process optimization, patent CN120039852A discloses a method for preparing high-compact lithium iron phosphate cathode material, but this involves secondary milling and sintering, increasing the material's preparation cost. Patent CN120117581A discloses a method for preparing high-compact lithium iron phosphate cathode material using a dual-iron-source composite gradation, where the precursor and auxiliary materials are milled separately, sintered, and then mixed again for a second sintering; however, this process is complex and costly.

[0004] Furthermore, each mainstream synthesis route has its own advantages and disadvantages, making it difficult to balance overall performance and production cost. Hydrothermal synthesis of lithium iron phosphate (LFP) results in high crystallinity, excellent rate capability, and superior low-temperature performance; however, its primary particle size is small, and the particle distribution tends to be uniform, leading to lower compaction density and thus limiting energy density improvement. It is also prone to lithium iron phosphate antisite defects, which can block lithium-ion diffusion channels, further deteriorating overall performance. While solid-state synthesis of LFP using iron phosphate as a raw material can effectively improve the compaction density, it typically requires high-temperature sintering above 800°C, resulting in high energy consumption. Moreover, iron phosphate is a trivalent iron source, requiring the addition of a reducing agent, increasing process complexity and cost.

[0005] In summary, current technologies cannot simultaneously achieve high rate capability and high compaction density of lithium iron phosphate materials through a simple process while maintaining low cost and low energy consumption. Therefore, developing a lithium iron phosphate material and its preparation method that combines excellent low-temperature performance, good rate capability, high compaction density, low preparation cost, and low energy consumption has significant industrial application value. Summary of the Invention

[0006] To address the challenges of simultaneously achieving high rate capability, high compaction density, and low-temperature performance in existing lithium iron phosphate (LFP) preparation technologies, as well as the issues of poor uniformity, high cost, and high energy consumption associated with vanadium, manganese, and titanium doping, this invention provides a lithium iron phosphate cathode material and its preparation method that combine high rate capability and high compaction density. This invention prepares vanadium-doped lithium iron phosphate via a hydrothermal method, ensuring uniformity and regular morphology of vanadium doping, thus laying the foundation for high rate capability and low-temperature performance. A co-precipitation method is used to prepare highly crystalline ferrous octahydrate doped with manganese in situ, enhancing its low-temperature performance potential. Furthermore, the vanadium-doped lithium iron phosphate, highly crystalline ferrous octahydrate doped with manganese in situ, a lithium source, a carbon source, and titanium dioxide dopant are combined to achieve synergistic optimization of vanadium-manganese-titanium doping, ensuring doping uniformity and effectiveness. Simultaneously, carbon coating and particle size distribution are combined to achieve multiple performance synergistic effects, ultimately yielding a high-rate, high-compact, and stable lithium iron phosphate material.

[0007] The technical solution of this invention is as follows: In a first aspect, the present invention provides a method for preparing a lithium iron phosphate cathode material that combines high rate capability and high compaction performance, comprising the following steps: S1. After dissolving and filtering ferrous sulfate to remove impurities, adjust the iron content in the solution to obtain an iron salt solution; S2. Add lithium source solution, phosphate salt solution and dopant vanadium source to iron salt solution, adjust the pH value of the solution with triethylamine, and then transfer it to high pressure reactor for hydrothermal reaction to obtain vanadium-doped lithium iron phosphate precursor material A. S3. Add the phosphate salt solution and the manganese dopant source to the iron salt solution, mix them evenly, and then adjust the pH value with ammonia water to make the precipitation reaction complete. The resulting precipitate is washed and dried to obtain manganese-doped ferrous phosphate octahydrate precursor material B. S4. The precursor material B obtained in step S3 is mixed with the lithium source, carbon source and dopant titanium dioxide, and subjected to first-stage grinding. Then, the precursor material A obtained in step S2 is added and subjected to second-stage grinding to obtain a mixed slurry. The obtained mixed slurry is subjected to spray granulation, sintering, crushing and packaging to obtain lithium iron phosphate cathode material.

[0008] The iron salt solution obtained in step S1 is used in steps S2 and S3 respectively. The amount used will be measured according to actual needs to meet different material ratio requirements.

[0009] Furthermore, in step S1, the pH of the ferric salt solution is 1.0-3.5, and the iron content of the ferrous sulfate is 55-85 g / L. Maintaining the pH of the ferric salt solution within the range of 1.0-3.5 is beneficial for inhibiting Fe... 2+ The oxidation and hydrolysis processes ensure the stability of the solution system, improving the controllability of subsequent reactions from the source. Maintaining an iron content of 55-85 g / L ensures reaction efficiency while avoiding solutions that are too dilute or too concentrated. When the iron content is below 55 g / L, the ion concentration in the system is insufficient, affecting the rate of subsequent precipitation or hydrothermal reactions; when it is above 85 g / L, local supersaturation easily occurs, leading to particle aggregation.

[0010] Furthermore, in step S2, the lithium source solution is one or more of lithium hydroxide, lithium carbonate, and lithium phosphate; the phosphate salt solution is one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate; the vanadium dopant source is ammonium metavanadate; and the molar ratio of lithium, iron, phosphorus, and vanadium sources is (2.1-3):1:1:(0.01-0.05).

[0011] Furthermore, in step S2, the solution pH is 4.0-6.5, the reaction temperature is 150-200℃, and the reaction time is 4-8 hours. Conducting the hydrothermal reaction at pH 4.0-6.5 is beneficial for controlling the crystal nucleation and growth rate, allowing vanadium to uniformly enter the crystal lattice. A reaction temperature of 150-200℃ and a reaction time of 4-8 hours yield a precursor with high crystallinity and suitable particle size. Insufficient temperature or time results in incomplete crystallization, affecting rate performance; excessively high or long temperatures can easily lead to particle coarsening, reducing specific surface area and reactivity.

[0012] Furthermore, in step S3, the phosphate salt solution is one or more of phosphoric acid, diammonium hydrogen phosphate, and disodium hydrogen phosphate; the manganese dopant source is manganese sulfate; the pH value is 5.5-6.5; and the molar ratio of iron, phosphorus, and manganese sources is 3:2:(0.03-0.06). Controlling the pH within the range of 5.5-6.5 is beneficial for the complete precipitation of ferrous phosphate octahydrate and the formation of its crystal structure; controlling the manganese doping amount within this ratio range can effectively expand the lithium-ion migration channels while ensuring lattice stability; when the manganese content is too low, the improvement on low-temperature performance is limited; when it is too high, it may introduce excessive lattice distortion or impurity phase formation, affecting structural stability.

[0013] Furthermore, in step S4, the lithium source is one or more of lithium phosphate, lithium hydroxide, and lithium carbonate; the carbon source is one or more of glucose, citric acid, polyethylene glycol, and sucrose; the molar ratio of precursor material B to lithium source is n(Li):n(Fe):n(P) = (1.005-1.02):(0.963-0.968):1. By precisely controlling the ratio of lithium, iron, and phosphorus, the system is made close to the ideal stoichiometry. At the same time, appropriate compensation for lithium loss and regulation of iron content are beneficial to reducing Li / Fe antisite defects and improving lithium-ion diffusion efficiency. When Li is insufficient, lithium defects are easily generated, reducing capacity, while excessive or high amounts may form impurity phases (such as Li3PO4). Furthermore, in step S4, the average particle size after the first-stage grinding is 0.35-0.50 μm. Controlling the particle size of the first-stage particles within the range of 0.35-0.50 μm helps to maintain a high specific surface area to improve rate performance while avoiding the decrease in compaction density caused by excessively fine particles. When the particle size is less than 0.35 μm, the porosity between particles increases, which is not conducive to compaction; when it is greater than 0.50 μm, the specific surface area decreases, affecting the electrochemical reaction kinetics.

[0014] Furthermore, in step S4, the sintering temperature is 730-810℃, and the sintering time is 540-600 min. Sintering within the 730-810℃ range ensures both a well-developed crystal structure and the formation of carbon coating, resulting in a stable conductive network. Controlling the sintering time to 540-600 min facilitates the full diffusion of dopant elements into the crystal lattice. If the temperature is too low or the time is insufficient, incomplete crystallization and poor conductivity will occur; if the temperature is too high or the time is too long, abnormal grain growth can easily occur, reducing rate performance and compaction performance.

[0015] Furthermore, in step S4, the mass ratio of precursor material A to precursor material B is 1:4 to 1:9. By controlling the ratio of A to B, a multi-level particle gradation structure is achieved, effectively filling the gaps between particles and increasing the bulk density; at the same time, the rate performance advantage brought by small particles is also taken into account. When the proportion of A is too low, the high rate performance is insufficient; when it is too high, the gradation effect weakens and the compaction density decreases.

[0016] Secondly, the present invention provides a lithium iron phosphate cathode material, which is prepared by the method described above.

[0017] Compared with existing technologies, the advantages of this invention are as follows: In this invention, the water of crystallization in octahydrate ferrous phosphate gradually dehydrates during sintering, forming pores in the material, reducing the diffusion resistance between the lithium source and dopant elements, and promoting atomically uniform mixing. Its fixed iron-phosphorus atomic ratio avoids the problem of uneven element distribution in traditional mixed raw materials, laying the foundation for subsequent precise doping and composition control. The preparation process of the manganese-doped ferrous phosphate precursor in this invention eliminates the need for oxidation and high-temperature sintering processes, reducing the use of oxidants such as hydrogen peroxide and lowering sintering energy consumption, thus significantly reducing production costs while improving production efficiency. Compared to traditional iron phosphate preparation processes, it has the advantages of a shorter process, lower energy consumption, and lower cost.

[0018] Furthermore, V 4+ Mn 2+ and Ti 4+ Cooperative substitution of Fe in the lattice 2+ The advantages of Mn doping are threefold: first, it broadens lithium-ion diffusion channels through lattice distortion, improving ion conductivity and electrochemical reaction kinetics; second, it forms a stable doped solid solution, effectively suppressing abnormal grain growth during sintering, promoting uniform grain size and rounded morphology, and providing a good structural basis for high-compact stacking; third, Mn doping broadens lithium-ion migration channels through lattice expansion, allowing Li to achieve higher lithium-ion conductivity at low temperatures. + The migration space resistance is reduced, that is, the Li + The migration barrier enhances the lithium-ion diffusion rate, and Mn 2+ Fe replacement 2+ This can induce local charge imbalance, generating additional electron / hole carriers and further improving electron conduction efficiency at low temperatures. Compared to single-element doping, multi-element synergy enables more precise control of lattice parameters while improving electronic conductivity and structural stability.

[0019] Based on the aforementioned advantages of precursors and the multi-element synergistic regulation mechanism, the lithium iron phosphate cathode material prepared by this invention achieves significant improvements in both compaction density and electrochemical performance. The compaction density of the material can reach 2.58 g / cm³, reaching the level of fourth-generation lithium iron phosphate, thereby effectively improving the volumetric energy density of the battery. At the same time, by constructing a highly efficient conductive network through vanadium-manganese-titanium synergistic doping and carbon coating, the material achieves a discharge specific capacity ≥158 mAh / g at 0.1C rate, close to the theoretical capacity, and can still reach ≥147 mAh / g at 1C rate, exhibiting excellent rate performance.

[0020] The preparation process of this invention can be achieved using conventional industrial equipment. The control window for each process parameter is wide. The precursor of ferrous octahydrate phosphate is widely available and its cost is lower than that of the traditional ferric phosphate system. The product has good batch consistency and high stability, making it suitable for large-scale continuous production and showing good prospects for industrial application. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1 of this invention.

[0023] Figure 2 This is a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention.

[0024] Figure 3 This is a charge-discharge curve of the lithium iron phosphate cathode material prepared in Example 1 of the present invention.

[0025] Figure 4 This is a charge-discharge curve of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention.

[0026] Figure 5 This is the charge-discharge curve of the lithium iron phosphate cathode material prepared in Comparative Example 2 of this invention.

[0027] Figure 6 This is a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention.

[0028] Figure 7 This is a scanning electron microscope image of the lithium iron phosphate cathode material prepared in Comparative Example 2 of this invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0030] Example 1 A method for preparing a lithium iron phosphate cathode material that combines high rate capability and high compaction performance, comprising the following steps: S1. Dissolve ferrous sulfate in deionized water, stir until completely dissolved, and then filter to remove insoluble impurities to obtain an iron salt solution with an iron content of 70 g / L. This solution is then set aside. The iron salt solution obtained in step S1 is used in steps S2 and S3, with the amount measured according to actual needs to meet different material ratio requirements.

[0031] S2. Lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metavanadate were added to an iron salt solution at a molar ratio of lithium:iron:phosphorus:vanadium = 2.6:1:1:0.03. The pH was adjusted to 6.5 with triethylamine. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180°C for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally. The grayish-white precipitate was collected, washed, dried, and used for later use to obtain vanadium-doped lithium iron phosphate precursor material A. The precursor material A was grayish-white in color.

[0032] S3. Add diammonium hydrogen phosphate and manganese sulfate to the iron salt solution at a molar ratio of iron:phosphorus:manganese = 3:2:0.045. Adjust the pH of the system to 6.5 with ammonia water. Stir the reaction continuously for 2 hours under nitrogen protection. The precipitate is washed with deionized water and dried at low temperature to obtain manganese-doped ferrous phosphate octahydrate precursor material B. The color of precursor material B is blue-gray.

[0033] S4. Precursor material B is mixed with lithium phosphate, lithium hydroxide (n(Li):n(Fe):n(P) = 1.01:0.965:1), carbon source (glucose, citric acid and polyethylene glycol) and titanium dioxide to obtain a mixture. The mixture is graded and ground to a particle size D50 of 0.40 μm, and then ground at a ratio of precursor material A to precursor material B of 1:9. Subsequently, it is spray granulated. Under nitrogen protection, it is sintered at 760℃ for 580 min. The sintered product is crushed and sieved to obtain the final lithium iron phosphate cathode material.

[0034] Example 2 A method for preparing a lithium iron phosphate cathode material that combines high rate capability and high compaction performance, comprising the following steps: S1. Dissolve ferrous sulfate in deionized water, stir until completely dissolved, and then filter to remove insoluble impurities to obtain an iron salt solution with an iron content of 75 g / L. This solution is then set aside. The iron salt solution obtained in step S1 is used in steps S2 and S3, with the amount measured according to actual needs to meet different material ratio requirements.

[0035] S2. Lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metavanadate were added to an iron salt solution at a molar ratio of lithium:iron:phosphorus:vanadium = 2.5:1:1:0.04. The pH was adjusted to 6.4 with triethylamine. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180°C for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally. The grayish-white precipitate was collected, washed, dried, and used for later use to obtain vanadium-doped lithium iron phosphate precursor material A. The precursor material A was grayish-white in color.

[0036] S3. Add diammonium hydrogen phosphate and manganese sulfate to the iron salt solution at a molar ratio of iron:phosphorus:manganese = 3:2:0.05. Adjust the pH of the system to 6.5 with ammonia water. Stir the reaction continuously for 2 hours under nitrogen protection. The precipitate is washed with deionized water and dried at low temperature to obtain manganese-doped ferrous phosphate octahydrate precursor material B. The color of precursor material B is blue-gray.

[0037] S4. Precursor material B is mixed with lithium phosphate, lithium hydroxide (n(Li):n(Fe):n(P) = 1.02:0.965:1), carbon source (glucose, citric acid and polyethylene glycol) and titanium dioxide to obtain a mixture. The mixture is graded and ground to a particle size D50 of 0.45 μm, and then ground at a ratio of precursor material A to precursor material B of 3:17. Subsequently, it is spray granulated. Under nitrogen protection, it is sintered at 780℃ for 580 min. The sintered product is crushed and sieved to obtain the final lithium iron phosphate cathode material.

[0038] Example 3 A method for preparing a lithium iron phosphate cathode material that combines high rate capability and high compaction performance, comprising the following steps: S1. Dissolve ferrous sulfate in deionized water, stir until completely dissolved, and then filter to remove insoluble impurities to obtain an iron salt solution with an iron content of 70 g / L. This solution is then set aside. The iron salt solution obtained in step S1 is used in steps S2 and S3, with the amount measured according to actual needs to meet different material ratio requirements.

[0039] S2. Lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metavanadate were added to an iron salt solution in a molar ratio of lithium:iron:phosphorus:vanadium = 3:1:1:0.03. The pH was adjusted to 6.5 with triethylamine. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180°C for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally. The grayish-white precipitate was collected, washed, dried, and used for later use to obtain vanadium-doped lithium iron phosphate precursor material A. The color of precursor material A was grayish-white.

[0040] S3. Add diammonium hydrogen phosphate and manganese sulfate to the iron salt solution at a molar ratio of iron:phosphorus:manganese = 3:2:0.04. Adjust the pH of the system to 6.5 with ammonia water. Stir the reaction continuously for 2 hours under nitrogen protection. The precipitate is washed with deionized water and dried at low temperature to obtain manganese-doped ferrous phosphate octahydrate precursor material B. The color of precursor material B is grayish-blue.

[0041] S4. Precursor material B is mixed with lithium phosphate, lithium hydroxide (n(Li):n(Fe):n(P) = 1.02:0.965:1), carbon source (glucose, citric acid and polyethylene glycol) and titanium dioxide to obtain a mixture. The mixture is graded and ground to a particle size D50 of 0.40 μm, and then ground at a ratio of precursor material A to precursor material B of 3:17. Subsequently, it is spray granulated. Under nitrogen protection, it is sintered at 770℃ for 580 min. The sintered product is crushed and sieved to obtain the final lithium iron phosphate cathode material.

[0042] Comparative Example 1 The preparation steps for Comparative Example 1 and Example 1 are the same, except that precursor material B is not synthesized. The specific steps are as follows: S1. Dissolve ferrous sulfate in deionized water, stir until completely dissolved, and then filter to remove insoluble impurities to obtain an iron salt solution with an iron content of 70 g / L. This solution is then set aside. The iron salt solution obtained in step S1 is used in steps S2 and S3, with the amount measured according to actual needs to meet different material ratio requirements.

[0043] S2. Lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metavanadate were added to the above iron salt solution in a molar ratio of lithium:iron:phosphorus:vanadium = 2.6:1:1:0.03. The pH value was adjusted to 6.5 with triethylamine. The mixed solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180°C for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally. The grayish-white precipitate was collected, washed, dried, and used for later use to obtain precursor material A.

[0044] S3. Precursor material A, carbon source (glucose, citric acid, and polyethylene glycol), and titanium dioxide are mixed to obtain a mixture. The mixture is then graded and ground to a particle size D50 of 0.40 μm, followed by spray granulation. Under nitrogen protection, it is sintered at 760℃ for 580 min. The sintered product is then pulverized and sieved to obtain the final lithium iron phosphate cathode material.

[0045] Comparative Example 2 The preparation steps for Comparative Example 1 and Example 1 are the same, except that precursor material A is not synthesized. The specific steps are as follows: S1. Dissolve ferrous sulfate in deionized water, stir until completely dissolved, and then filter to remove insoluble impurities to obtain an iron salt solution with an iron content of 70 g / L. This solution is then set aside. The iron salt solution obtained in step S1 is used in steps S2 and S3, with the amount measured according to actual needs to meet different material ratio requirements.

[0046] S2. Add diammonium hydrogen phosphate and manganese sulfate to the iron salt solution at a molar ratio of iron:phosphorus:manganese = 3:2:0.045. Adjust the pH of the system to 6.5 with ammonia water. Stir the reaction continuously for 2 hours under nitrogen protection. The precipitate is washed with deionized water and dried at low temperature to obtain precursor material B.

[0047] S3. Precursor material B is mixed with lithium phosphate, lithium hydroxide (n(Li):n(Fe):n(P)=1.01:0.965:1), carbon source (glucose, citric acid and polyethylene glycol) and titanium dioxide to obtain a mixture; the mixture is graded and ground to a particle size D50 of 0.40 μm, and then spray granulated; under nitrogen protection, it is sintered at 760℃ for 580 min, and the sintered product is crushed and sieved to obtain the final lithium iron phosphate cathode material.

[0048] Performance testing: Test 1: Electrochemical Performance Test The vanadium and titanium-doped high-pressure lithium iron phosphate cathode materials, PVDF, and Superp prepared in each embodiment and comparative example were dispersed in NMP at a ratio of 90:5:5 for homogenization, then coated, dried, and punched to obtain circular electrode sheets. Finally, the circular electrode sheets, separator, lithium sheet, gasket, and spring sheet were assembled into CR2032 coin cells in a glove box for testing.

[0049] The button cell batteries were charged and discharged within a voltage range of 2.0~3.75V. After two cycles at 0.1C, their electrochemical performance was tested at rates of 0.2C / 0.5C and 0.2C / 1C.

[0050] Test 2: Compacted Density Test The density was measured using a Sansi longitudinal and transverse compaction density meter under 3 tons of pressure.

[0051] The performance test data of each embodiment and comparative example of the present invention are shown in Table 1.

[0052] Table 1. Electrical properties and compaction test results of lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-2

[0053] The following conclusions can be drawn from the data in Table 1: The compaction densities of Examples 1-3 of this invention are all greater than 2.58 g / cm³, reaching a maximum of 2.613 g / cm³, which is comparable to the compaction density level of fourth-generation lithium iron phosphate. Furthermore, the 1C discharge specific capacity of Examples 1-3 is all within the range of 147.7-148.0 mAh / g. This demonstrates that Examples 1-3 of this invention, by changing the doping ratio and the mixing mass ratio of the precursors, can achieve a good particle size distribution, improving the compaction density of the material while ensuring its electrical performance. In contrast, Comparative Example 1, using only the hydrothermal precursor material A, has a compaction density of only 2.316 g / cm³, and Comparative Example 2, using only the co-precipitation precursor material B, has a compaction density of only 2.529 g / cm³, further confirming the indispensable role of the synergistic particle size distribution of the two precursors. In addition, the cathode materials prepared in these examples exhibit excellent low-temperature rate performance, maintaining a high discharge specific capacity even at -20℃.

[0054] Figure 1 The image shows the XRD pattern of lithium iron phosphate prepared in Example 1 of this invention. The diffraction peaks of the prepared sample are consistent with the standard PDF card (PDF#83-2092), with space group Pnma. No impurity diffraction peaks were observed in the XRD pattern, indicating high sample purity. No impurity peaks for titanium, vanadium, or manganese were also found in the XRD pattern, indicating that the low doping content does not affect the crystal structure of the lithium iron phosphate cathode material, but rather that the doping is uniformly distributed within its lattice.

[0055] Figure 2 This is a SEM image of lithium iron phosphate prepared in Example 1 of the present invention. As can be seen from the image, the obtained particles are uniformly distributed, thus forming a good particle size distribution and increasing the compaction density of the material.

[0056] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing a lithium iron phosphate cathode material possessing both high rate capability and high compaction performance, characterized in that, Includes the following steps: S1. After dissolving and filtering ferrous sulfate to remove impurities, adjust the iron content in the solution to obtain an iron salt solution; S2. Add lithium source solution, phosphate salt solution and dopant vanadium source to iron salt solution, adjust the pH value of the solution with triethylamine, and then transfer it to high pressure reactor for hydrothermal reaction to obtain vanadium-doped lithium iron phosphate precursor material A. S3. Add the phosphate salt solution and the manganese dopant source to the iron salt solution, mix them evenly, and then adjust the pH value with ammonia water to make the precipitation reaction complete. The resulting precipitate is washed and dried to obtain manganese-doped ferrous phosphate octahydrate precursor material B. S4. The precursor material B obtained in step S3 is mixed with the lithium source, carbon source and dopant titanium dioxide, and subjected to first-stage grinding. Then, the precursor material A obtained in step S2 is added and subjected to second-stage grinding to obtain a mixed slurry. The obtained mixed slurry is subjected to spray granulation, sintering, crushing and packaging to obtain lithium iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the pH value of the iron salt solution is 1.0-3.5, and the iron content of ferrous sulfate is 55-85 g / L.

3. The preparation method according to claim 1, characterized in that, In step S2, the lithium source solution is one or more of lithium hydroxide, lithium carbonate, and lithium phosphate; the phosphate salt solution is one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate; the vanadium dopant source is ammonium metavanadate; and the molar ratio of lithium, iron, phosphorus, and vanadium sources is (2.1-3):1:1:(0.01-0.05).

4. The preparation method according to claim 1 or 3, characterized in that, In step S2, the solution pH is 4.0-6.5, the reaction temperature is 150-200℃, and the reaction time is 4-8h.

5. The preparation method according to claim 1, characterized in that, In step S3, the phosphate salt solution is one or more of phosphoric acid, diammonium hydrogen phosphate, and disodium hydrogen phosphate; the manganese dopant source is manganese sulfate; the pH value is 5.5-6.5; and the molar ratio of iron, phosphorus, and manganese sources is 3:2:(0.03-0.06).

6. The preparation method according to claim 1, characterized in that, In step S4, the lithium source is one or more of lithium phosphate, lithium hydroxide, and lithium carbonate; the carbon source is one or more of glucose, citric acid, polyethylene glycol, and sucrose; and the molar ratio of precursor material B to lithium source is n(Li):n(Fe):n(P) = (1.005-1.02):(0.963-0.968):

1.

7. The preparation method according to claim 1, characterized in that, In step S4, the average particle size after the first-stage grinding is 0.35-0.50 μm.

8. The preparation method according to claim 1, characterized in that, In step S4, the sintering temperature is 730-810℃ and the sintering time is 540-600min.

9. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of precursor material A to precursor material B is 1:4 to 1:

9.

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

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