Lithium iron phosphate positive electrode material, preparation method thereof, lithium ion battery and electric device

Abstract

The application belongs to the technical field of batteries, and particularly relates to a lithium iron phosphate positive electrode material and a preparation method thereof, a lithium ion battery and an electric device, the lithium iron phosphate positive electrode material has a pore density coordination balance coefficient X=S1x D 50 x phi x p, and satisfies: 4<=X<=16; wherein S1 is a BET specific surface area of the lithium iron phosphate positive electrode material, in units of m 2 / g, D 50 is a volume distribution median particle size of the lithium iron phosphate positive electrode material, in units of mu m, phi is a total porosity of the lithium iron phosphate positive electrode material, and p is a true density of the lithium iron phosphate positive electrode material, in units of g / cm 3 The lithium iron phosphate positive electrode material can realize the unification of high compaction, high rate, long cycle, low temperature performance and good processing performance, and the preparation method is simple and convenient for large-scale production.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to lithium iron phosphate cathode materials and their preparation methods, lithium-ion batteries, and electrical devices. Background Technology

[0002] Lithium iron phosphate (LFP) is a core cathode material for my country's new energy vehicle and energy storage industries, currently accounting for over 75% of the market. With the increasing range of electric vehicles, the growing demand for longer lifespans in energy storage systems, and the expansion of applications in extreme environments, existing LFP material systems are no longer sufficient to meet future needs. The LFP industry is gradually shifting its strategic focus from "capacity expansion" to "technology leadership." Developing high-performance LFP materials has profound industrial significance and strategic value. Currently, the industry is accelerating innovation along routes focusing on high compaction density, improved kinetics, and enhanced energy efficiency. How to control the processing and electrical properties of LFP materials under high compaction conditions, thereby improving their overall performance, remains one of the current challenges. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a lithium iron phosphate cathode material and its preparation method, a lithium-ion battery, and an electrical device. This lithium iron phosphate cathode material can achieve a balance between high compaction and electrochemical performance, resulting in better overall performance.

[0004] In a first aspect, this application provides a lithium iron phosphate cathode material. According to embodiments of this application, the pore density synergistic balance coefficient X of the lithium iron phosphate cathode material is X = S1 × D. 50 ×φ×ρ, and satisfying: 4≤X≤16; where S1 is the BET specific surface area of ​​the lithium iron phosphate cathode material, in m². 2 / g,D 50 The median particle size of the lithium iron phosphate cathode material is given in μm, φ is the total porosity of the lithium iron phosphate cathode material, and ρ is the true density of the lithium iron phosphate cathode material in g / cm³. 3 .

[0005] This application achieves a balance between high compaction and electrochemical performance by controlling X within the range of 4 to 16, thus ensuring both the unobstructed ion migration channels and electrolyte wettability in the lithium iron phosphate cathode material. If X is too high, side reactions intensify and cycle performance deteriorates; if X is too low, rate performance worsens.

[0006] According to embodiments of this application, in the lithium iron phosphate cathode material, the volume percentage P of mesopores is... mes Satisfy: 45%≤P mes ≤70%.

[0007] According to an embodiment of this application, the increase in compaction density of the lithium iron phosphate cathode material is ΔP = (P 3T -P 1T ) / P 1T ×100, and satisfying: 4.5≤△P≤6.5, preferably 5.0≤△P≤6.3; where P 3T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 3T, expressed in g / cm³. 3 P 1T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 1T, expressed in g / cm³. 3 .

[0008] According to embodiments of this application, the lithium iron phosphate cathode material satisfies at least one of the following conditions: The compaction density P of the lithium iron phosphate cathode material is 2.10 g / cm³. 3 ~2.90 g / cm 3 The preferred value is 2.60 g / cm³. 3 ~2.90 g / cm 3 ; Median particle size D in the volume distribution of lithium iron phosphate cathode materials 50 The micrometer size is 0.7μm to 2.5μm, preferably 0.8μm to 2.4μm; The BET specific surface area S1 of the lithium iron phosphate cathode material is 10m². 2 / g~15m 2 / g; The total porosity φ of the lithium iron phosphate cathode material is 8%~25%.

[0009] According to embodiments of this application, the lithium iron phosphate cathode material includes a lithium iron phosphate matrix and a carbon coating layer covering its surface, and satisfies at least one of the following conditions: The lithium iron phosphate matrix includes the compound shown in Formula 1: Li a Fe b M c (PO4) d Formula 1 In Formula 1, 0.97≤a≤1.07, 0.93≤b≤1, 0≤c≤0.1, 0.98≤d≤1.08; M includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na; The thickness of the carbon coating layer is 1 nm to 8 nm; The carbon content of the lithium iron phosphate cathode material is 1.05 wt% to 1.6 wt%.

[0010] A second aspect of this application provides a method for preparing the aforementioned lithium iron phosphate cathode material. According to an embodiment of this application, the method includes: mixing an iron source, a phosphorus source, a lithium source, an optional first M source, and a carbon source; grinding the resulting first mixture to obtain a precursor slurry; sequentially spray-drying and sintering the precursor slurry to obtain a first-sintered product; crushing the first-sintered product and classifying and screening the crushed product to remove particles with a particle size >20 μm and a particle size <1 μm, obtaining a graded and screened product, which is used as the lithium iron phosphate cathode material; wherein the first M source includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na. This method is simple and convenient to operate, easy to scale up for production, and the obtained lithium iron phosphate cathode material has excellent comprehensive performance.

[0011] According to embodiments of this application, the method for preparing the aforementioned lithium iron phosphate cathode material may further include: mixing the graded screening product with an optional second M source, and subjecting the resulting second mixture to secondary sintering to obtain a secondary sintered product, wherein the secondary sintered product serves as the lithium iron phosphate cathode material; wherein the second M source includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na.

[0012] According to an embodiment of this application, the iron source includes a first iron source and a second iron source, wherein the specific surface area of ​​the second iron source is greater than that of the first iron source. Preferably, the specific surface area of ​​the first iron source is 5m². 2 / g~9m 2 / g, the specific surface area of ​​the second iron source is 8m². 2 / g~14m 2 / g; Preferably, the iron source includes iron phosphate, and the iron-phosphorus molar ratio Fe / P of the first iron source and the second iron source are each independently 0.945~0.985.

[0013] According to an embodiment of this application, the amount of carbon source used is 7% to 10% of the theoretical yield of lithium iron phosphate cathode material.

[0014] According to an embodiment of this application, the primary sintering includes sequentially performing a first-stage sintering, a second-stage sintering, and a third-stage sintering, and satisfies at least one of the following conditions: The constant temperature for the first sintering stage is 350℃~400℃; The holding time for the first sintering stage is 2h~3h; The constant temperature for the two-stage sintering is 500℃~600℃; The holding time for the two-stage sintering is 3h~5h; The constant temperature for the three-stage sintering is 730℃~850℃; The holding time for the three-stage sintering is 6h to 14h.

[0015] According to embodiments of this application, the above method satisfies at least one of the following conditions: The crushing pressure is 350 kPa to 450 kPa; The grading and screening process involves sequentially grading the crushed product using grading sieves with mesh sizes of 20μm, 10μm, and 5μm to obtain a first product with a particle size of 5μm to 20μm and a second product with a particle size of less than 5μm. The second product is then subjected to airflow sieving to obtain a third product with a particle size of 1μm to 5μm. The first product and the third product are then combined to obtain the graded and screened product.

[0016] According to embodiments of this application, the secondary sintering satisfies at least one of the following conditions: The constant temperature for the secondary sintering is 700℃~850℃; The holding time for the secondary sintering is 4h to 14h.

[0017] A third aspect of this application provides a lithium-ion battery. According to embodiments of this application, the lithium-ion battery includes the lithium iron phosphate cathode material described above. This lithium-ion battery exhibits high energy density, good low-temperature performance, good cycle stability, and good rate performance, demonstrating excellent overall performance.

[0018] In a fourth aspect, this application provides an electrical device. According to an embodiment of this application, the electrical device includes the lithium iron phosphate cathode material or the lithium-ion battery described above. This electrical device possesses all the features and advantages of the lithium iron phosphate cathode material or the lithium-ion battery described above, which will not be repeated here. Attached Figure Description

[0019] Figure 1 This is a SEM image of the lithium iron phosphate cathode material of Example 1 of this application.

[0020] Figure 2 This is a SEM image of the lithium iron phosphate cathode material of Comparative Example 1 of this application.

[0021] Figure 3 These are the cumulative pore size and volume distribution curves of the lithium iron phosphate cathode materials of Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In a first aspect, this application provides a lithium iron phosphate cathode material. According to embodiments of this application, the pore density synergistic balance coefficient X of the lithium iron phosphate cathode material is X = S1 × D. 50 ×φ×ρ, and satisfying: 4≤X≤16; where S1 is the BET specific surface area of ​​the lithium iron phosphate cathode material, in m². 2 / g,D 50 The median particle size of the lithium iron phosphate cathode material is given in μm, φ is the total porosity of the lithium iron phosphate cathode material, and ρ is the true density of the lithium iron phosphate cathode material in g / cm³. 3 .

[0024] Specifically, the pore density synergistic balance coefficient X of lithium iron phosphate (LFP) cathode materials can quantitatively reflect the actual effective surface area of ​​the LFP cathode material that can be effectively contacted by the electrolyte and participate in interfacial interactions, reflecting the overall surface utilization efficiency of the LFP cathode material from its outer surface and internal channels. A larger X value indicates a more developed pore structure, a more significant contribution to the internal specific surface area, more fully exposed active sites, and a higher effective specific surface area utilization rate. Conversely, a smaller X value indicates a denser structure, less developed channels, a lower effective surface area for interfacial interactions, and a lower surface utilization efficiency. This application controls X within the range of 4 to 16, enabling the LFP cathode material to balance ion migration channel unobstructedness and electrolyte wettability, achieving a balance between high compaction and electrochemical performance. If X is too high, side reactions intensify and cycle performance decreases; if X is too low, rate performance deteriorates.

[0025] In this paper, S1 can be tested using a Microt TriStar 3030 instrument: 1–3 g of sample, degassed at 300 ℃ for 1 h, the relative pressure P / P0 is measured to be 0.01–0.995, and the specific surface area is obtained, which is S1; D 50 It can be detected using a Marvern Mastersizer 3000 laser particle size analyzer; φ can be measured using V. 孔 A surface area analyzer is used to test the pore volume and distribution of the material to determine the pore volume. An X-ray diffractometer is then used to analyze the material structure and calculate the structural density, thereby calculating the sample's framework volume V. 骨 Porosity = V 孔 / (V) 孔 +V 骨 ); ρ can be detected using an X-ray diffractometer.

[0026] In some embodiments, the lithium iron phosphate cathode material described herein has a hierarchical pore structure, specifically referring to the lithium iron phosphate cathode material having pores with different pore sizes, which may include micropores (pore size less than 2nm), mesopores (pore size 2-50nm), macropores (pore size greater than 50nm), etc.

[0027] According to embodiments of this application, in the lithium iron phosphate cathode material, the volume percentage P of mesopores is... mes The percentage of mesopore volume to total pore volume in lithium iron phosphate cathode materials satisfies: 45% ≤ P mes ≤70%, specifically such as 45%, 50%, 55%, 60%, 65%, 70%, or any two of these ranges. The volume fraction of mesopores reflects the proportion of effectively connected ion transport channels within the single crystal. Within the above range, efficient electrolyte wetting can be maintained, thereby achieving better electrochemical performance.

[0028] In this article, P mes The distribution of mesopore and macropore sizes from 2 to 300 nm can be analyzed by using the BJH model (with both adsorption and desorption branches selected) and comparing the tables. Based on the pore size classification standard, the pore volume of mesopores from 2 to 50 nm and the total pore volume are extracted, and the proportion of mesopore volume is calculated.

[0029] According to an embodiment of this application, the increase in compaction density of the lithium iron phosphate cathode material is ΔP = (P 3T -P 1T ) / P 1T ×100, and satisfying: 4.5≤△P≤6.5, specifically, 5.0≤△P≤6.3; as a specific example, △P can be 4.5, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.5, or any two of them. Where P 3T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 3T, expressed in g / cm³. 3 P 1T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 1T, expressed in g / cm³. 3 .

[0030] Specifically, ΔP can reflect the particle rearrangement ability, crushing resistance and densification efficiency of lithium iron phosphate cathode material during the pressurization process. If ΔP meets the above range, it indicates that the lithium iron phosphate cathode material has moderate plasticity. During the compaction process with pressure of 1T to 3T, the particles can be effectively rearranged and are not easily crushed. This avoids the risk of cycle decay and gas expansion caused by the surge of new surface during the compaction process. At the same time, it widens the electrode processing window and improves the consistency of rolling.

[0031] In this article, P 3T and P 1T The compaction density value can be obtained by weighing a 1±0.01g sample and selecting a pressure of 3T and 1T.

[0032] In some specific examples, the lithium iron phosphate cathode material simultaneously satisfies X = 4~16 and 4.5 ≤ ΔP ≤ 6.5. These two factors form a strong synergistic and mutually supportive causal relationship. The carbon coating structure and the suitable X range fundamentally construct a reasonable particle system, providing a foundation for the stable compaction behavior and micro-compaction efficiency optimization of the lithium iron phosphate cathode material. A suitable ΔP parameter range can control the stability of the compaction process, avoiding ESR caused by abnormal compaction behavior. Together, these two factors enable the lithium iron phosphate cathode material to simultaneously possess excellent rate performance, long-cycle stability, high safety, and good electrode processing performance under high compaction conditions, solving the technical challenge of existing technologies that struggle to achieve multiple performance aspects.

[0033] According to an embodiment of this application, the BET specific surface area S1 of the lithium iron phosphate cathode material is 10 m². 2 / g~15m 2 / g, specifically 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g or any two of the above ranges. This range is beneficial for increasing the active sites of lithium iron phosphate cathode materials, further improving the overall performance of the battery.

[0034] According to embodiments of this application, the total porosity φ of the lithium iron phosphate cathode material is 8% to 25%, specifically 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, or any two of these ranges. This porosity allows for suitable wetting with the electrolyte, which is beneficial for improving the overall performance of the battery.

[0035] According to an embodiment of this application, the compaction density P of the lithium iron phosphate cathode material is 2.10 g / cm³. 3 ~2.90g / cm 3 Specifically, it can be 2.60 g / cm³. 3 ~2.90 g / cm 3 For example, P can specifically be 2.10 g / cm³. 3 2.20g / cm 3 2.30g / cm 3 2.40 g / cm3 2.50g / cm 3 2.60 g / cm 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 2.85g / cm 3 2.90 g / cm 3 Or a range between or equal to both of these. The aforementioned compaction density range is beneficial for increasing the energy density of the battery and further enhancing its overall performance.

[0036] In this paper, the compaction density P of lithium iron phosphate cathode material can be measured using a Sansi Zongheng (UTM7305) compaction density meter. The compaction density value is obtained by weighing 1±0.01g of sample and selecting a pressure of 3T.

[0037] According to embodiments of this application, the median particle size D in the volume distribution of the lithium iron phosphate cathode material is... 50 The particle size ranges from 0.7 μm to 2.5 μm, specifically from 0.8 μm to 2.4 μm. As an example, the median particle size D in the volume distribution of lithium iron phosphate cathode materials... 50 Specifically, the particle size can be 0.7μm, 1.0μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2.0μm, 2.2μm, 2.4μm, 2.5μm, or any combination thereof. This particle size range facilitates the construction of a reasonable particle system, thereby providing a foundation for optimizing the stable compaction behavior and micro-compaction efficiency of lithium iron phosphate cathode materials.

[0038] In this paper, the median particle size D of the volume distribution of lithium iron phosphate cathode material is... 50 The median particle size (D) of the lithium iron phosphate cathode material refers to the particle size corresponding to 50% of the total volume of the lithium iron phosphate cathode material. Particles larger and smaller than this value both account for 50% of the total volume of the lithium iron phosphate cathode material. 50 Specifically, it can be detected using a laser particle size analyzer.

[0039] According to embodiments of this application, the lithium iron phosphate cathode material includes a lithium iron phosphate matrix and a carbon coating layer covering its surface, wherein the lithium iron phosphate matrix includes the compound shown in Formula 1: Li a Fe b M c (PO4) d Formula 1 In Formula 1, 0.97≤a≤1.07, 0.93≤b≤1, 0≤c≤0.1, and 0.98≤d≤1.08; M includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na.

[0040] In some specific examples, 'a' can be 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, or any two of them; 'b' can be 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any two of them; 'c' can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any two of them; and 'd' can be 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, or any two of them.

[0041] According to embodiments of this application, the thickness of the carbon coating layer of the lithium iron phosphate cathode material is 1 nm to 8 nm, specifically within the range of 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, or any two of these ranges. This thickness range facilitates the construction of a reasonable particle system, thereby providing a basis for optimizing the stable compaction behavior and micro-compaction efficiency of the lithium iron phosphate cathode material.

[0042] In this paper, the thickness of the carbon coating layer can be detected by transmission electron microscopy.

[0043] According to embodiments of this application, the carbon content of the lithium iron phosphate cathode material is 1.05 wt% to 1.60 wt%, specifically within the ranges of 1.05 wt%, 1.10 wt%, 1.15 wt%, 1.20 wt%, 1.25 wt%, 1.30 wt%, 1.35 wt%, 1.40 wt%, 1.45 wt%, 1.50 wt%, 1.55 wt%, 1.60 wt%, or any two of these ranges. This carbon content range facilitates the construction of a reasonable particle system, thereby providing a basis for optimizing the stable compaction behavior and micro-compaction efficiency of the lithium iron phosphate cathode material.

[0044] In this paper, the carbon content of the lithium iron phosphate cathode material was tested using a Beijing Wanlianda CS-901B carbon-sulfur analyzer. Specifically, 0.2g of sample was prepared, and 2g of combustion improver was added together into a special high-purity crucible, which was then placed in the carbon-sulfur analyzer for testing.

[0045] A second aspect of this application provides a method for preparing the aforementioned lithium iron phosphate cathode material. According to embodiments of this application, the method includes: S10: Mix an iron source, a phosphorus source, a lithium source, an optional first M source, and a carbon source, and grind the resulting first mixture to obtain a precursor slurry, wherein the first M source includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na.

[0046] In this step, there are no particular restrictions on the specific method or order of mixing the iron source, phosphorus source, lithium source, optional first M source, and carbon source; they can be flexibly selected according to actual conditions. As an example, the iron source, phosphorus source, lithium source, optional first M source, and carbon source can be added to a high-speed mixer for mixing separately.

[0047] According to the embodiments of this application, the optional first M source means that the first M source can be added in this step or not, and the specific choice can be made according to actual needs; that is, this step can mix iron source, phosphorus source, lithium source and carbon source to obtain a first mixture; or iron source, phosphorus source, lithium source, first M source and carbon source can be mixed to obtain a first mixture.

[0048] According to embodiments of this application, the iron source may include a first iron source and a second iron source, wherein the specific surface area of ​​the second iron source is greater than that of the first iron source. The dual iron source combination can pre-build an internal pore gradient within the particles; the low specific surface area iron source ensures the compactness of the particle body, while the high specific surface area iron source provides sufficient reactive sites, avoiding the problems of disordered particle pores and incomplete reactions caused by a single iron source.

[0049] According to an embodiment of this application, the specific surface area of ​​the first iron source is 5m². 2 / g~9m 2 / g, specifically 5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m 2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g or a range between or equal to either of these. According to an embodiment of this application, the specific surface area of ​​the second iron source is 8m². 2 / g~14m 2 / g, specifically 8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g、11m 2 / g, 11.5m 2 / g、12m 2 / g, 12.5m 2 / g、13m 2 / g, 13.5m 2 / g、14m 2 / g or any combination thereof. Within this range, it is more conducive to forming a suitable hierarchical porous structure, further improving overall performance.

[0050] According to embodiments of this application, the iron source includes iron phosphate. The iron-to-phosphorus molar ratio (Fe / P) of the first iron source (i.e., the first iron phosphate) and the second iron source (i.e., the second iron phosphate) is independently controlled to be 0.945~0.985, specifically within the ranges of 0.945, 0.955, 0.96, 0.965, 0.97, 0.975, 0.98, 0.985, or any two of these ranges. The independent control of the iron-to-phosphorus molar ratio (Fe / P) of both iron phosphates within the range of 0.945~0.985 ensures precise elemental proportions at the raw material level, laying the foundation for subsequent lattice formation and doping.

[0051] According to embodiments of this application, the mass ratio of the first iron source to the second iron source is (2:1) to (1:2), for example, it can be 1:2, 1:1, 2:1, or any range between two of them. Therefore, the positive electrode active material has a better particle size distribution and higher compaction density, which is beneficial for improving the battery's capacity.

[0052] The lithium source, iron source, phosphorus source, and first M source mentioned above can all use conventional raw materials, and are not limited here. For example, the iron source may include at least one of ferric carbonate, ferrous oxide, ferric oxide, iron powder, ferric oxide, ferrous oxalate, and ferric phosphate; the lithium source may include at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium oxide, lithium dihydrogen phosphate, and lithium phosphate; the phosphorus source may include at least one of sodium phosphate, potassium phosphate, phosphoric acid, and monoammonium phosphate; the first M source may include at least one of oxides, hydroxides, carbonates, fluorides, sulfates, phosphates, and chlorides of element M; and the carbon source may include at least one of glucose, sucrose, PVP, oxalic acid, water-soluble phenolic resin, PAA, ascorbic acid, citric acid, starch, asphalt, PEG, and PVA.

[0053] According to embodiments of this application, the amount of carbon source used is 7% to 10% of the theoretical yield of lithium iron phosphate cathode material, specifically 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any two of these ranges. Within the above range, the lithium iron phosphate cathode material can be controlled to have a suitable BET specific surface area, while stabilizing the carbon content of the lithium iron phosphate cathode material, which is beneficial to improving the overall performance of the lithium iron phosphate cathode material.

[0054] According to embodiments of this application, an iron source, a phosphorus source, a lithium source, an optional first M source, and a carbon source can be mixed and dispersed in a solvent at a certain solid content to obtain a first mixture, which is then ground. The specific solvent is not particularly limited, as long as it provides good dispersion and does not chemically react with the iron source, phosphorus source, lithium source, or first M source during the grinding process. As a specific example, for manufacturing cost considerations, deionized water can be used as the solvent, and the solid content is preferably ≥35%.

[0055] According to embodiments of this application, the particle size of the precursor slurry can be 0.2 μm to 0.8 μm. This facilitates obtaining a suitable lithium iron phosphate cathode material and improves the overall performance of the lithium iron phosphate cathode material.

[0056] S20: The precursor slurry is sequentially spray-dried and sintered once to obtain a sintered product.

[0057] According to the embodiments of this application, there are no particular limitations on the specific operation steps and parameters of spray drying. By spray drying, the precursor slurry can be granulated to obtain lithium iron phosphate cathode materials with better particle size uniformity and particle morphology.

[0058] According to an embodiment of this application, the first sintering includes sequentially performing a first-stage sintering, a second-stage sintering, and a third-stage sintering.

[0059] According to an embodiment of this application, the isothermal temperature of the sintering section is 350°C to 400°C, specifically 350°C, 360°C, 370°C, 380°C, 390°C, 400°C or any two of these ranges.

[0060] According to an embodiment of this application, the holding time for the first sintering stage is 2h to 3h, specifically 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h or any two of them.

[0061] According to an embodiment of this application, the constant temperature for the two-stage sintering is 500℃~600℃, specifically such as 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃ or any two of them.

[0062] According to an embodiment of this application, the holding time for the two-stage sintering is 3h to 5h, specifically within any two of the following ranges: 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4.0h, 4.2h, 4.4h, 4.6h, 4.8h, and 5h.

[0063] According to the embodiments of this application, the constant temperature for the three-stage sintering is 730℃~850℃, specifically such as 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃ or any two of them.

[0064] According to the embodiments of this application, the holding time for the three-stage sintering is 6h to 14h, specifically 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or any two of them.

[0065] A three-stage stepped temperature-controlled sintering process is adopted, which differs from the extensive sintering mode of one stage of constant temperature and two stages of simple heating. Through precise temperature control, the pore gradient of the dual iron sources can be accurately matched to achieve controllable shaping of the microstructure. The first stage of pre-firing removes impurities and carbon source volatiles from the raw materials, while the high activity of the high specific surface area iron source is used to initiate crystal nucleation. The second stage of medium-temperature sintering promotes uniform growth of crystal nuclei and avoids grain agglomeration. The third stage of high-temperature sintering completes the crystal formation, while the compactness of the low specific surface area iron source is used to optimize the particle structure, achieving uniform grain size and stable lattice structure.

[0066] S30: The first sintering product is crushed, and the crushed product is graded and screened to remove particles with a particle size >20μm and a particle size <1μm, so as to obtain graded and screened products. The graded and screened products can be directly used as lithium iron phosphate cathode materials.

[0067] In this step, the specific crushing methods include, but are not limited to, air jet mills, jaw crushers, roller crushers, and rotary mills. Therefore, the equipment is readily available, the crushing efficiency is high, and it is beneficial to quickly obtain products with the target particle size.

[0068] According to embodiments of this application, the crushing pressure is 350 kPa to 450 kPa, specifically 350 kPa, 360 kPa, 370 kPa, 380 kPa, 390 kPa, 400 kPa, 410 kPa, 420 kPa, 430 kPa, 440 kPa, 450 kPa, or any two of these ranges. This allows the lithium iron phosphate cathode material to have a suitable median particle size D in its volume distribution. 50 .

[0069] According to embodiments of this application, after crushing, the obtained crushed products need to be graded and screened to remove particles with a diameter >20 μm and a diameter <1 μm, resulting in graded and screened products. Thus, removing excessively large agglomerated particles (diameter >20 μm) and excessively fine particles (diameter <1 μm) can solve the problems of particle agglomeration and particle size polarization during sintering, unify the particle size range, and ensure uniform distribution of doped elements and regular carbon layer coating during subsequent secondary sintering; simultaneously, it directly controls the median particle size distribution (D) of the material. 50 This ensures that the X in the prepared lithium iron phosphate cathode material meets the requirements.

[0070] In some embodiments, the grading and screening can be performed using grading sieves. For example, grading sieves with mesh sizes of 20 μm, 10 μm, and 5 μm can be used for grading and screening. Specifically, the grading and screening includes sequentially grading and screening the crushed product using grading sieves with mesh sizes of 20 μm, 10 μm, and 5 μm to obtain a first product with a particle size of 5 μm to 20 μm and a second product with a particle size of less than 5 μm. The second product is then subjected to airflow sieving to obtain a third product with a particle size of 1 μm to 5 μm. The first product and the third product are then combined to obtain the graded and screened product.

[0071] As an example, the specific operation process for graded screening is as follows: First, the crushed product is passed through a 20μm sieve to intercept particles larger than 20μm, leaving particles ≤20μm as the sieve residue. Second, the ≤20μm sieve residue is passed through a 10μm sieve to intercept particles between 10 and 20μm (classified as the qualified range, i.e., the first product), leaving particles ≤10μm as the sieve residue. Third, the ≤10μm sieve residue is passed through a 5μm sieve to intercept particles between 5 and 10μm (classified as the qualified range, i.e., the first product), leaving fine particles <5μm as the sieve residue (i.e., the second product). Fourth, the <5μm fine particles are further processed... Airflow sieving (suitable for ultrafine particle separation, avoiding screen clogging) utilizes the fact that <1μm particles are lighter and more fluid than 1~5μm particles. A gentle airflow is introduced, and ultrafine powder <1μm is carried away and collected by the airflow (achieving removal). Fine particles of 1~5μm, due to their slightly larger mass and weaker fluidity, remain in the sieving device and are classified into the qualified range (i.e., classified as the third product). Finally, only qualified particles of 1~20μm are retained (i.e., the first and third products are combined), achieving precise removal of oversized and overfine particles. This solves the industry pain points of fine screen clogging and low efficiency, and also achieves precise classification.

[0072] According to some embodiments of this application, the above method may further include: S40: The graded screening product is mixed with an optional second M source, and the resulting second mixture is sintered a second time to obtain a secondary sintered product, which is used as the lithium iron phosphate cathode material. The second M source includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na.

[0073] According to the embodiments of this application, the optional second M source means that the second M source can be added in this step or not, and the choice of whether to add the second M source can be made according to actual needs; that is, this step can directly sinter the graded screening product in a second time; or the graded screening product can be mixed with the second M source to obtain a second mixture and the second mixture can be sintered in a second time.

[0074] According to embodiments of this application, the second M source includes at least one of the following: oxides, hydroxides, carbonates, fluorides, sulfates, phosphates, and chlorides of the M element.

[0075] In this step, there are no particular restrictions on the specific method or order of mixing the graded screening product with the second M source; the choice can be made flexibly based on actual conditions. For example, the graded screening product and the second M source can be added separately to a high-speed mixer for mixing.

[0076] According to an embodiment of this application, the constant temperature for the secondary sintering is 700℃~850℃, specifically such as 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃ or any two of them.

[0077] According to an embodiment of this application, the holding time for the secondary sintering is 4h to 14h, specifically 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or any two of these ranges.

[0078] Secondary sintering can repair crystal defects, precisely control the proportion of hierarchical pores and mesopores, thereby optimizing the pore density synergistic balance coefficient and simultaneously further improving the compaction density of the material.

[0079] A third aspect of this application provides a lithium-ion battery. According to embodiments of this application, the lithium-ion battery includes the lithium iron phosphate cathode material described above. This lithium-ion battery exhibits high energy density, good low-temperature performance, good cycle stability, and good rate performance, demonstrating excellent overall performance.

[0080] According to an embodiment of this application, the lithium-ion battery may include a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are all immersed in the electrolyte. During the charging and discharging process of the battery, active ions are inserted and extracted back and forth between the positive and negative electrodes. The electrolyte plays the role of conducting ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, mainly to prevent short circuits between the positive and negative electrodes, while allowing active ions to pass through.

[0081] According to an embodiment of this application, the lithium-ion battery can be a solid-state battery. In this case, the lithium-ion battery can include the positive electrode, negative electrode and solid electrolyte membrane mentioned above, wherein the solid electrolyte membrane is disposed between adjacent positive and negative electrode sheets.

[0082] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes the lithium iron phosphate positive electrode material, positive conductive agent, and positive binder described above.

[0083] According to embodiments of this application, the positive current collector can be a metal current collector or a composite current collector. Metal current collectors include at least one of aluminum foil current collectors and carbon-coated aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0084] According to embodiments of this application, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0085] According to embodiments of this application, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] According to an embodiment of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode sheet. The negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0087] According to embodiments of this application, the negative electrode current collector includes copper foil, composite copper foil, etc.

[0088] According to embodiments of this application, the negative electrode active material may include carbon-based materials (such as artificial graphite), silicon-based materials, tin-based materials, etc.

[0089] According to embodiments of this application, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0090] According to embodiments of this application, the negative electrode conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] According to embodiments of this application, the diaphragm includes polyethylene diaphragm, polypropylene diaphragm, polyethylene / polypropylene composite diaphragm, etc.

[0092] In a fourth aspect, this application provides an electrical device. According to an embodiment of this application, the electrical device includes the lithium iron phosphate cathode material or the lithium-ion battery described above. This electrical device possesses all the features and advantages of the lithium iron phosphate cathode material or the lithium-ion battery described above, which will not be repeated here.

[0093] It is understood that there are no particular restrictions on the specific type of electrical device; it can be any device that uses a lithium-ion battery as a power source or energy storage unit. For example, electrical devices include, but are not limited to, electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (such as mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, and so on.

[0094] It is understandable that, in addition to the lithium-ion battery mentioned above, the electrical device also includes necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0095] The embodiments of this application are described in detail below.

[0096] Example 1 Step S1: Weigh lithium carbonate, ferric phosphate I, ferric phosphate II, titanium dioxide 1, magnesium oxide 1, titanium dioxide 2, zirconium oxide 2, and phosphoric acid in a molar ratio of Li, Fe, Ti1 (titanium element in titanium dioxide 1), Mg1 (magnesium element in magnesium oxide 1), Ti2 (titanium element in titanium dioxide 2), Zr2 (zirconium element in zirconium oxide 2), and P of 1.02:0.94:0.02:0.01:0.01:0.03:1.02. Add lithium carbonate, ferric phosphate I, ferric phosphate II, titanium dioxide 1, magnesium oxide 1, and glucose (accounting for 7.5% of the theoretical yield of lithium iron phosphate) to deionized water as the solvent, controlling the solid content to 40wt%. Grind using a ball mill (speed 2000 rpm). 50 The process was stopped when the thickness reached 0.35 μm, yielding precursor slurry I. Step S2: The precursor slurry I obtained in step S1 is fed into the feed port using an atomizing disc atomizing dryer (inlet temperature set to 225±℃, outlet temperature controlled at 100±5℃) to perform spray drying treatment, thereby obtaining spray-dried material II. Step S3: The spray-dried material II is heated to 380°C at a heating rate of 2°C / min under N2 atmosphere and held for 2.5h. Then it is heated to 580°C at a heating rate of 1.5°C / min and held for 3.5h. Then it is heated to 820°C at a heating rate of 0.8°C / min and held for 12h. Then it is naturally cooled to room temperature and cooled with the furnace to obtain the primary sintered material III. Step S4: The primary sintered material III is crushed using an air jet mill, and the resulting crushed product has a D... 50 When the particle size reaches 2.5μm, the machine is stopped. Grading and screening are carried out using grading sieves (sieve apertures of 20μm, 10μm, and 5μm). Specifically, the crushed product first passes through a grading sieve with a 20μm aperture, collects the undersize and passes it through a grading sieve with a 10μm aperture, collects the oversize as the target product, and the undersize continues to pass through a grading sieve with a 5μm aperture, collects the oversize as the target product, and the undersize enters an air classifier to remove particles smaller than 1μm. The product from the air classifier and the oversize collected from the first two times are combined to obtain graded screening product IV.

[0097] Step S5: Mix the graded screening product IV with titanium dioxide 2 and zirconium dioxide 2 to obtain a homogeneous mixture V.

[0098] Step S6: The mixture V is heated to 780°C at a heating rate of 0.8°C / min under N2 atmosphere, held at this temperature for 12 hours, and then cooled in the furnace before being crushed by an air jet mill to obtain lithium iron phosphate cathode material.

[0099] Example 2-13 Similar to Example 1 above, the specific differences are shown in Tables 1 and 2.

[0100] Example 14 Same as Example 1, the specific difference is: the grading and screening steps are as follows: the crushed product is first passed through a grading sieve with a screen aperture of 20μm, the undersize material is collected and passed through a grading sieve with a screen aperture of 5μm, the oversize material is collected as the target product, the undersize material enters an air classifier to remove particles with a particle size of less than 1μm, and the product of the air classifier and the oversize material collected previously are combined to obtain the grading and screening product IV.

[0101] Example 15 Same as Example 1, the specific difference is: the grading and screening steps are as follows: the crushed product is first passed through a grading sieve with a screen aperture of 20μm, the undersize material is collected and passed through a grading sieve with a screen aperture of 10μm, the oversize material is collected as the target product, the undersize material enters an air classifier to remove particles with a particle size of less than 1μm, and the product of the air classifier and the oversize material collected previously are combined to obtain the grading and screening product IV.

[0102] Comparative Example 1 Similar to Example 1 above, the specific differences are shown in Tables 1 and 2, and the grading and screening steps are as follows: the crushed product is passed through a grading sieve with a mesh size of 20μm, and the material collected from the sieve is the grading and screening product IV.

[0103] Comparative Example 2 Similar to Example 1 above, the specific differences are shown in Tables 1 and 2, and the grading and screening steps are as follows: the crushed product enters the air classifier to remove particles with a diameter of less than 1 μm, and the collected product is the grading and screening product IV.

[0104] Comparative Example 3 Similar to Example 1 above, the specific differences are shown in Tables 1 and 2, and no hierarchical screening is performed.

[0105] Table 1

[0106] Table 2

[0107] Performance testing: 1. S1: Tested using a Microt TriStar3030 instrument: 1-3 g of sample, degassed at 300 ℃ for 1 h, the relative pressure P / P0 was 0.01-0.995, and the specific surface area was obtained.

[0108] 2. D 50 The results were obtained directly using a Marvern Mastersizer 3000 laser particle size analyzer. Specifically, 0.03-0.04g of sample was prepared, and 1.0-1.1g of 10% NP40 was added dropwise while simultaneously sonicating. Water was then added to a final volume of 10.0-10.1g, and sonication was performed for 3 minutes. The sample was then transferred to the laser particle size analyzer for testing.

[0109] 3. φ: The pore volume V of the material is obtained by testing the pore volume and distribution using a surface area analyzer. 孔 The material structure was analyzed using an X-ray diffractometer. First, a full XRD spectrum scan of the sample was performed. The crystal structure model was corrected by fitting the Rietveld full spectrum, and the structure density was calculated using unit cell parameters (a, b, c, α, β, γ). This allowed for the calculation of the sample's framework volume V. 骨 The porosity of the material is obtained by dividing the pore volume by the sum of the pore volume and the skeleton volume, i.e., porosity = V. 孔 / (V) 孔 +V 骨 ).

[0110] 4. ρ: The material structure was analyzed using an X-ray diffractometer, specifically a Rigaku Smartlab 9KW powder X-ray diffractometer (1.54059Å) with a Cu target wavelength (1.54059Å), tube voltage of 40KV, tube current of 200mA, scanning speed of 5 / min, step size of 0.02°, and scanning range of 10°-90°. The measured data were then fitted using the WPPF full-spectrum fitting method. The theoretical density was obtained by software calculation and manually calculated using ρ=M / V / (NA / Z), where M is the molar mass of the cathode material, V is the lattice volume of the cathode material, NA is Avogadro's constant, and Z is the number of chemical units in the unit cell. V and Z can be directly read from the software, and the molar mass is calculated based on the chemical formula of the cathode material.

[0111] 5. P mes The distribution of mesopore and macropore sizes from 2 to 300 nm was analyzed using the BJH model (with both adsorption and desorption branches selected) and a comparison table. Pore types were classified according to pore size criteria, and the pore volume of mesopores from 2 to 50 nm and the total pore volume were extracted. The mesopore volume ratio, i.e., the volume percentage P of mesopores, was calculated. mes .

[0112] 6. P 3T P 1T P: The compaction density value was measured using a Sansi Zongheng (UTM7305) compaction density meter. A sample of 1 ± 0.01 g was weighed, and the test was conducted at a pressure of 3T. 3T P=P 3T The compaction density value obtained by selecting a pressure of 1T for testing is P. 1T .

[0113] 7. Carbon coating thickness: measured by transmission electron microscopy.

[0114] 8. Carbon content: Tested using a Beijing Wanlianda CS-901B carbon-sulfur analyzer. Specifically, 0.2g of sample was prepared, and 2g of combustion accelerant was added together into a special high-purity crucible, which was then placed in the carbon-sulfur analyzer for testing.

[0115] 9. Electrochemical performance: 9-1. 0.1C charging capacity, 0.1C discharging capacity, 0.1C initial efficiency, 0.5C discharging capacity, and 0.33C discharging capacity: The positive electrode active material, conductive agent Super P, and polyvinylidene fluoride (PVDF) prepared in the above examples and comparative examples were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2 to form a uniform slurry. This slurry was coated onto aluminum foil and dried at 120°C for 12 h. The electrode sheet was then compacted to 2.5 g / cm³. 3The positive electrode was then stamped to a diameter of 12 mm. In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into an R2025 coin cell and left to stand for 6 hours. The negative electrode used a 15.6 mm diameter, 0.45 mm thick lithium metal sheet; the separator used a 25 μm polypropylene microporous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC). The electrochemical performance of R2025 coin cells was tested using the Shenzhen Xinwei Battery Testing System. The initial charge-discharge capacity test conditions were: 25℃, voltage range 2.5V~4.2V, constant voltage cutoff current of 0.05C, 2 cycles of 0.1C charge-discharge, and 1 cycle each of 0.2C-0.33C-0.5C-1C. The 0.1C charge capacity, 0.1C discharge capacity, and 0.1C initial efficiency were obtained based on the first 0.1C charge-discharge cycle. The 0.33C discharge capacity was obtained based on the 0.33C charge-discharge cycle, and the 0.5C discharge capacity was obtained based on the 0.5C charge-discharge cycle.

[0116] 9-2. Low Temperature Performance: The battery assembly steps are the same as in 9-1. The specific testing steps are as follows: At 25℃, the battery is charged at a constant current of 0.33C to 4.2V, and then charged at a constant voltage of 4.2V until the current drops to 0.05C. The fully charged battery is then transferred to a low temperature test chamber set at -10±2℃ and left to stand for 10 hours to ensure the internal temperature of the battery reaches -10±2℃. Subsequently, at -10℃, the battery is discharged at a constant current of 0.33C to 2.5V, thus obtaining the discharge capacity at -10℃ with 0.33C. Low temperature performance = (Discharge capacity at -10℃ with 0.33C / Discharge capacity at 25℃ with 0.33C (obtained from test in 9-1)) × 100%.

[0117] 9-3 Cycle performance: The battery assembly steps are the same as in 9-1. The specific test steps are as follows: 45℃, 0.1C charge and discharge for 5 weeks, followed by 80 cycles of 1C charge and discharge, voltage range 2.5V~3.65V, charging constant voltage cutoff current is 0.05C, and the capacity retention rate after 80 cycles of 1C charge and discharge (i.e., the discharge capacity after 80 cycles of 1C charge and discharge / the discharge capacity after the first cycle of 1C charge and discharge) is used as the cycle performance.

[0118] Table 3

[0119] Table 4

[0120] As can be seen from the data in Table 2, when the pore density synergy coefficient X of the lithium iron phosphate cathode material is less than 4 and greater than 16, the discharge capacity, first efficiency, low temperature performance and cycle performance of the battery are significantly reduced. This indicates that controlling X to be between 4 and 16 can achieve a balance between high compaction, high rate, long cycle, low temperature performance and good processing performance.

[0121] A comparison of Example 11 and Examples 1-10 shows that further controlling ΔP to 4.5-6.5, with the synergistic effect of both, further improves the overall performance of the battery.

[0122] A comparison of Examples 12-13 and Examples 1-10 shows that further control of P mes The capacitance is 40%~70%, and the 0.1C charge / discharge capacity, 0.5C discharge capacity, low-temperature performance and cycle performance are further improved.

[0123] As can be seen from Comparative Example 1, when X is less than 4, the 0.1C charge / discharge capacity, 0.5C discharge capacity, low-temperature performance, and cycle performance deteriorate significantly.

[0124] Comparative examples 2 and 3 show that when X is greater than 16, the 0.1C charge / discharge capacity, 0.5C discharge capacity, low-temperature performance, and cycle performance deteriorate significantly.

[0125] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0126] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0127] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium iron phosphate cathode material, characterized in that, The pore density-coordinated equilibrium coefficient of the lithium iron phosphate cathode material is X = S1 × D 50 ×φ×ρ, and satisfy: 4≤X≤16; Wherein, S1 is the BET specific surface area of ​​the lithium iron phosphate cathode material, in m². 2 / g,D 50 The median particle size of the lithium iron phosphate cathode material is given in μm, φ is the total porosity of the lithium iron phosphate cathode material, and ρ is the true density of the lithium iron phosphate cathode material in g / cm³. 3 .

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, In the lithium iron phosphate cathode material, the volume percentage P of mesopores is... mes Satisfy: 45%≤P mes ≤70%.

3. The lithium iron phosphate cathode material according to claim 1, characterized in that, The increase in compaction density of the lithium iron phosphate cathode material ΔP=(P 3T -P 1T ) / P 1T ×100, and satisfy: 4.5≤△P≤6.5, preferably 5.0≤△P≤6.3; Among them, P 3T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 3T, expressed in g / cm³. 3 P 1T This is the compaction density of the lithium iron phosphate cathode material after applying a pressure of 1T, expressed in g / cm³. 3 .

4. The lithium iron phosphate cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: The compaction density P of the lithium iron phosphate cathode material is 2.10 g / cm³. 3 ~2.90 g / cm 3 The preferred value is 2.60 g / cm³. 3 ~2.90 g / cm 3 ; The median particle size D of the volume distribution of the lithium iron phosphate cathode material 50 The micrometer size is 0.7μm to 2.5μm, preferably 0.8μm to 2.4μm; The BET specific surface area S1 of the lithium iron phosphate cathode material is 10m². 2 / g~15m 2 / g; The total porosity φ of the lithium iron phosphate cathode material is 8%~25%.

5. The lithium iron phosphate cathode material according to claim 1, characterized in that, It includes a lithium iron phosphate matrix and a carbon coating layer covering its surface, and satisfies at least one of the following conditions: The lithium iron phosphate matrix includes the compound shown in Formula 1: Li a Fe b M c (PO4) d Formula 1 In Formula 1, 0.97≤a≤1.07, 0.93≤b≤1, 0≤c≤0.1, 0.98≤d≤1.08; M includes at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na; The thickness of the carbon coating layer is 1 nm to 8 nm; The carbon content of the lithium iron phosphate cathode material is 1.05 wt% to 1.6 wt%.

6. A method for preparing the lithium iron phosphate cathode material according to any one of claims 1 to 5, characterized in that, include: Iron source, phosphorus source, lithium source, optional first M source, and carbon source are mixed, and the resulting first mixture is ground to obtain precursor slurry; The precursor slurry was sequentially spray-dried and sintered once to obtain a single-sintered product. The first sintering product is crushed, and the crushed product is graded and screened to remove particles with a particle size >20μm and a particle size <1μm, so as to obtain graded and screened products, which are used as lithium iron phosphate cathode materials. Optionally, the method further includes: mixing the graded screening product with an optional second M source, and performing a second sintering on the resulting second mixture to obtain a second sintered product, wherein the second sintered product is used as the lithium iron phosphate cathode material; The first M source and the second M source each independently include at least one of Ti, V, Ta, W, Zn, Zr, Cu, Mg, Mn, Ca, Nb, Al, Sn, Sb, Mo, Si, Ni, and Na.

7. The method according to claim 6, characterized in that, The iron source includes a first iron source and a second iron source, wherein the specific surface area of ​​the second iron source is greater than that of the first iron source. Preferably, the specific surface area of ​​the first iron source is 5m². 2 / g~9m 2 / g, the specific surface area of ​​the second iron source is 8m². 2 / g~14m 2 / g; Preferably, the iron source includes iron phosphate, and the iron-phosphorus molar ratio Fe / P of the first iron source and the second iron source are each independently 0.945~0.

985.

8. The method according to claim 6, characterized in that, The amount of carbon source used is 7% to 10% of the theoretical yield of lithium iron phosphate cathode material.

9. The method according to claim 6, characterized in that, The primary sintering includes sequential primary sintering, secondary sintering, and tertiary sintering, and satisfies at least one of the following conditions: The constant temperature for the first sintering stage is 350℃~400℃; The holding time for the first sintering stage is 2h~3h; The constant temperature for the two-stage sintering is 500℃~600℃; The holding time for the two-stage sintering is 3h~5h; The constant temperature for the three-stage sintering is 730℃~850℃; The holding time for the three-stage sintering is 6h to 14h.

10. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The crushing pressure is 350 kPa to 450 kPa; The grading and screening process involves sequentially grading the crushed product using grading sieves with mesh sizes of 20μm, 10μm, and 5μm to obtain a first product with a particle size of 5μm to 20μm and a second product with a particle size of less than 5μm. The second product is then subjected to airflow sieving to obtain a third product with a particle size of 1μm to 5μm. The first product and the third product are then combined to obtain the graded and screened product.

11. The method according to claim 6, characterized in that, The secondary sintering satisfies at least one of the following conditions: The constant temperature for the secondary sintering is 700℃~850℃; The holding time for the secondary sintering is 4h to 14h.

12. A lithium-ion battery, characterized in that, The lithium iron phosphate cathode material includes any one of claims 1 to 5.

13. An electrical appliance, characterized in that, The lithium iron phosphate cathode material according to any one of claims 1 to 5 or the lithium-ion battery according to claim 12.

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