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

Abstract

This invention discloses a high-compact, high-capacity lithium iron phosphate cathode material and its preparation method. Using iron phosphate and iron hydroxide as a mixed iron source, a two-step synthesis method is employed. First, the two raw materials are ground to one large particle size and one small particle size. The large particle size is sintered at two different temperatures to prepare large and medium particles, while the small particle size is sintered at two different temperatures to prepare small and ultra-small particles. Then, the large and medium particles are mixed and ground to a large particle size, and the small and ultra-small particles are mixed and ground to a small particle size. The mixing of large and small particle sizes increases the particle size distribution, and sintering yields the high-compact, high-capacity lithium iron phosphate cathode material. The mixing and grinding of multiple particles in this invention further increases the particle size distribution and improves the compaction density of the cathode material. The use of a low-molecular-weight carbon source in the first sintering stage is beneficial for particle coating and improves particle roundness. The use of a high-molecular-weight carbon source in the second sintering stage constructs a continuous conductive network, ensuring the material's capacity is fully realized.

Description

Technical Field

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

[0002] With the global energy structure transformation and the advancement of "dual carbon" goals, lithium-ion batteries are increasingly widely used in new energy vehicles, large-scale energy storage systems, and portable electronic devices. Among them, lithium iron phosphate has become the mainstream cathode material for power batteries and energy storage batteries due to its core advantages such as high theoretical specific capacity, excellent thermal stability, low cost, environmental friendliness, and long cycle life. However, the rapid development of the new energy industry has placed higher demands on battery performance, which is determined by the compaction density and capacity performance of the cathode material. Compaction density directly determines the amount of active material filled per unit volume and is a key indicator for improving battery energy density, while high capacity is a core prerequisite for ensuring range and energy storage efficiency.

[0003] Currently, high-performance lithium iron phosphate is commonly prepared using a single precursor. However, the material reaction mechanisms and temperatures of the same precursor process are similar, which significantly affects the design particle size distribution and prevents the optimal performance from being achieved. This invention uses a composite product of iron phosphate and iron hydroxide as a precursor. Due to the inherent material properties of iron phosphate and iron hydroxide, the precursor already exhibits particle size distribution. Furthermore, by utilizing the difference in their reaction temperatures, the particle size distribution is increased, significantly improving the performance of the lithium iron phosphate cathode material. Summary of the Invention

[0004] The purpose of this invention is to provide a high-pressure, high-capacity lithium iron phosphate cathode material and its preparation method. Using iron phosphate and iron hydroxide as a mixed iron source, a two-step synthesis method is employed. First, the two raw materials are ground to a large particle size and a small particle size, respectively. The large particle size is then sintered at two different temperatures to prepare large and medium particles, while the small particle size is sintered at two different temperatures to prepare small and extremely small particles. Next, the large and medium particles are mixed and ground to a large particle size, and the small and extremely small particles are mixed and ground to a small particle size. The mixing of large and small particles increases the particle size distribution, and sintering yields the high-pressure, high-capacity lithium iron phosphate cathode material.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a high-pressure, high-capacity lithium iron phosphate cathode material, comprising the following steps: A first iron source, lithium source, phosphorus source, carbon source, dopant, and deionized water are mixed in a certain proportion, and after a first grinding and spray drying, a first precursor powder is obtained; a portion of the first precursor powder is sintered at a first temperature and then pulverized by airflow to obtain a first intermediate; another portion of the first precursor powder is sintered at a second temperature and then pulverized by airflow to obtain a second intermediate. The second iron source, lithium source, phosphorus source, carbon source, dopant, and deionized water are mixed in proportion, and after a second grinding and spray drying, a second precursor powder is obtained; a portion of the second precursor powder is sintered at a third temperature and then pulverized by airflow to obtain a third intermediate; another portion of the second precursor powder is sintered at a fourth temperature and then pulverized by airflow to obtain a fourth intermediate. The first intermediate, the second intermediate, the third carbon source, and deionized water are mixed in a certain proportion and then ground in a third process to obtain a first slurry. The third intermediate, the fourth intermediate, the fourth carbon source, and deionized water are mixed in a certain proportion and then ground in a fourth process to obtain a second slurry. The first and second slurries are mixed and spray-dried to obtain a third precursor powder, which is then sintered at a fifth temperature and pulverized by airflow to obtain the high-pressure, high-capacity lithium iron phosphate cathode material with a D50 particle size of 0.8~1.4μm. The first intermediate has an average primary particle size of 1500~2000nm; the second intermediate has an average primary particle size of 800~1200nm; the third intermediate has an average primary particle size of 300~600nm; and the fourth intermediate has an average primary particle size of 50~150nm. The first and second iron sources include iron phosphate and iron oxide hydroxide, wherein the specific surface area of ​​the iron phosphate is 4-16 m². 2 / g, with an Fe / P molar ratio of 0.960–0.980, and the specific surface area of ​​the ferric hydroxide is 20–300 m² / g. 2 / g, wherein the ratio of ferric phosphate to ferric hydroxide is 9:1 to 1:9.

[0006] In some possible implementations, the first and second lithium sources are battery-grade lithium sources, including one or more of lithium carbonate, lithium phosphate, lithium hydroxide, and lithium dihydrogen phosphate, and the first and second phosphorus sources are battery-grade phosphorus sources, including one or more of iron phosphate, lithium phosphate, lithium dihydrogen phosphate, phosphoric acid, and ammonium monohydrogen phosphate. The amount of the first and second lithium sources added is determined based on the Fe / P molar ratio of the high-pressure, high-capacity lithium iron phosphate cathode material being 0.965 to 0.975, and the amount of the first and second phosphorus sources added is determined based on the Li / Fe molar ratio of the high-pressure, high-capacity lithium iron phosphate cathode material being 1.01 to 1.05.

[0007] In some possible implementations, the first and second carbon sources include one or more of glucose, PEG, citric acid, and sucrose, and the carbon content of the first and second precursor powders is 0.02~0.7wt%. The third and fourth carbon sources include one or more of polyethylene, PVP, PVDF, starch, PET, and polyamide; the carbon content of the high-pressure, high-capacity lithium iron phosphate cathode material is 1.1~1.5wt%.

[0008] In some possible implementations, the first and second dopants each include one or more of titanium dioxide, ammonium metavanadate, niobium pentoxide, and manganese oxide; the content of the doping element in the first precursor powder is 1500~4000ppm, and the content of the doping element in the second precursor powder is 5000~9000ppm.

[0009] In some possible implementations, the first intermediate and the second intermediate are mixed in a ratio of 2~4:2~4, and the third intermediate and the fourth intermediate are mixed in a ratio of 1~3:1~3.

[0010] In some possible implementations, the spray drying specifically includes: setting the inlet temperature to 180–240°C and the outlet temperature to 80–140°C; controlling the D50 particle size of the first, second, and third precursor powders to be 20–60 μm and the moisture content to be ≤1.5%.

[0011] In some possible implementations, the sintering at the first, second, third, fourth, and fifth temperatures is all carried out under a protective gas, which is an inert gas. The first temperature sintering specifically includes: setting the temperature to 800~840℃ and the holding period to 7~11h; The second temperature sintering specifically includes: setting the temperature to 740~780℃ and holding the temperature for 7~11 hours; The third temperature sintering specifically includes: setting the temperature to 660~700℃ and holding the temperature for 4~7 hours; The fourth temperature sintering specifically includes: setting the temperature to 500~600℃ and holding the temperature for 4~7 hours; The fifth temperature sintering specifically includes setting the temperature to 760~800℃ and the holding period to 6~10h.

[0012] In some possible implementations, the first grinding specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.8–1.2 μm, and a solid content of 30–50 wt%. The second grinding process specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.2–0.5 μm, and a solid content of 30–50 wt%. The third grinding process specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.8–1.2 μm, and a solid content of 30–50 wt%. The fourth grinding process specifically includes: setting the temperature to 10-45℃, grinding to a D50 particle size of 0.1-0.4μm, and a solid content of 30-50wt%.

[0013] In a second aspect, the present invention provides a high-pressure, high-capacity lithium iron phosphate cathode material, wherein the high-pressure, high-capacity lithium iron phosphate cathode material is prepared by the preparation method described in any one of the first aspects.

[0014] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising a lithium-ion battery cathode made based on the high-pressure, high-capacity lithium iron phosphate cathode material described in the second aspect.

[0015] The present invention provides a high-pressure, high-capacity lithium iron phosphate cathode material and its preparation method, which have the following advantages compared with the prior art: 1. This invention uses ferric phosphate and ferric hydroxide as a composite precursor and imposes restrictions on them. Due to the inherent material properties of ferric phosphate and ferric hydroxide, the precursor already exhibits particle size distribution. Furthermore, the difference in their reaction temperature is utilized to increase the quantity of particle size distribution. Simultaneously, more free phosphate ions are introduced into the system, which is beneficial for improving particle roundness. Figure 1 As shown.

[0016] 2. The preparation method of this invention involves two grinding and two sintering processes. First, extremely large and extremely small particles are mixed and combined to form two layers of packing. Second, the first sintering at four temperatures results in four layers of packing. During the second sintering, the particles are mixed and ground, again forming two to four layers of packing. Ultimately, the finished product exhibits six to eight layers of packing. As shown in Table 1, the powder compaction degree of this invention is ≥2.7 g / cm³. 3 The powder resistivity is as low as 4.5Ω·cm, and the first discharge capacity at 1.0C is higher than 142mAh / g, which reflects the characteristics of high pressure, high capacity and low internal resistance of this invention.

[0017] 3. In the first sintering of this invention, a low-molecular-weight carbon source is used to improve particle coating and enhance particle roundness; in the second sintering, a high-molecular-weight carbon source is used to construct a continuous conductive network to ensure the material's performance.

[0018] 4. The large particles of the first intermediate and the medium particles of the second intermediate are mixed and ground to a large particle size, and the small particles of the third intermediate and the extremely small particles of the fourth intermediate are mixed and ground to a small particle size, which further increases the particle size distribution and effectively improves production efficiency and reduces costs. Attached Figure Description

[0019] Figure 1Here is a SEM image of the lithium iron phosphate cathode material prepared in Example 1; Figure 2 The graph shows the charge-discharge performance of the lithium iron phosphate cathode material prepared in Example 1. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. At the same time, in the description of the embodiments of this application, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0021] Example 1 This embodiment provides a high-pressure, high-capacity lithium iron phosphate cathode material, the preparation method of which includes the following steps: S1, 3000g iron phosphate, 792g iron hydroxide, 1110.95g lithium phosphate, 21.8g lithium carbonate, 220g glucose, 23.1g titanium dioxide, and 7750g deionized water were mixed and ground at 20℃ until the D50 particle size was 1.0μm and the solid content was 40wt%. The mixture was then spray-dried to obtain a first precursor powder with a particle size of 1800nm. A portion of the first precursor powder was sintered at 820℃ for 9 hours and then pulverized using airflow to obtain a first intermediate with an average primary particle size of 1800nm. Another portion of the first precursor powder was sintered at 760℃ for 9 hours and then pulverized using airflow to obtain a second intermediate with an average primary particle size of 1000nm. S2, 3000g iron phosphate, 792g iron hydroxide, 1110.95g lithium phosphate, 21.8g lithium carbonate, 220g glucose, 49g titanium dioxide, and 7750g deionized water were mixed and ground in a second process at 20℃ until the D50 particle size was 0.35μm and the solid content was 40wt%. The mixture was then spray-dried to obtain a second precursor powder. A portion of the second precursor powder was sintered at a third temperature of 680℃ for 5.5h and then air-jet milled to obtain a third intermediate with an average primary particle size of 450nm. Another portion of the second precursor powder was sintered at a fourth temperature of 550℃ for 5.5h and then air-jet milled to obtain a fourth intermediate with an average primary particle size of 110nm. S3. Mix 1200g of the first intermediate, 1200g of the second intermediate, 74.4g of PVP, and 3600g of deionized water in a certain proportion, and grind them in a third process at a temperature of 20℃ until the D50 particle size is 1.0μm and the solid content is 40wt%, to obtain the first slurry. Mix 800g of the third intermediate, 800g of the fourth intermediate, 49.6g of PVP, and 2400g of deionized water in a certain proportion, and grind them in a fourth process at a temperature of 20℃ until the D50 particle size is 0.25μm and the solid content is 40wt%, to obtain the second slurry. Mix the first and second slurries, spray dry them to obtain the third precursor powder, and then sinter it at a fifth temperature of 780℃ for 8 hours, followed by air jet milling, to obtain a high-pressure, high-capacity lithium iron phosphate cathode material with a D50 particle size of 1.1μm and a carbon content of 1.3wt%.

[0022] The specific surface area of ​​iron phosphate is 10 m². 2 / g, its Fe / P molar ratio is 0.970, and the specific surface area of ​​ferric hydroxide is 150m². 2 / g.

[0023] Spray drying specifically includes: setting the inlet temperature to 210℃ and the outlet temperature to 110℃; controlling the D50 particle size of the first, second, and third precursor powders to be 40μm and the moisture content to be ≤1.5%.

[0024] Sintering at the first, second, third, fourth, and fifth temperatures is carried out under a protective gas, which in this embodiment is nitrogen.

[0025] Example 2 This embodiment provides a high-pressure, high-capacity lithium iron phosphate cathode material, the preparation method of which includes the following steps: 3000g ferric phosphate, 880g ferric hydroxide (specific surface area 300m²) 21107.8g of lithium phosphate, 30.3g of phosphoric acid, 207g of glucose, 10.8g of titanium dioxide, and 12000g of deionized water were mixed and ground at 10℃ until the D50 particle size was 0.8μm and the solid content was 30wt%. The mixture was then spray-dried to obtain a first precursor powder. A portion of the first precursor powder was sintered at a first temperature of 800℃ for 9 hours and then pulverized by air jet milling to obtain a first intermediate with an average primary particle size of 1600nm. Another portion of the first precursor powder was sintered at a second temperature of 780℃ for 7 hours and then pulverized by air jet milling to obtain a second intermediate with an average primary particle size of 800nm. 3000g ferric phosphate, 880g ferric hydroxide (specific surface area 200m²) 2 1107.8g of lithium phosphate, 30.3g of phosphoric acid, 207g of glucose, 14.3g of titanium dioxide, and 12000g of deionized water were mixed and then ground at 10℃ until the D50 particle size was 0.2μm and the solid content was 30wt%. The mixture was then spray-dried to obtain a second precursor powder. A portion of the second precursor powder was sintered at a third temperature of 660℃ for 7 hours and then pulverized by air jet milling to obtain a third intermediate with an average primary particle size of 300nm. Another portion of the second precursor powder was sintered at a fourth temperature of 500℃ for 7 hours and then pulverized by air jet milling to obtain a fourth intermediate with an average primary particle size of 60nm. 800g of the first intermediate, 1600g of the second intermediate, 50.4g of PVP, 48g of PET, and 5600g of deionized water were mixed in a certain proportion and then ground in a third process at a temperature of 10℃ until the D50 particle size was 0.8μm and the solid content was 30wt%, resulting in the first slurry. 1200g of the third intermediate, 400g of the fourth intermediate, 33.6g of PVP, 32g of PET, and 3733g of deionized water were mixed in a certain proportion and then ground in a fourth process at a temperature of 10℃ until the D50 particle size was 0.1μm and the solid content was 30wt%, resulting in the second slurry. The first and second slurries were mixed and spray-dried to obtain the third precursor powder, which was then sintered at a fifth temperature of 800℃ for 6 hours using airflow milling to obtain a high-pressure, high-capacity lithium iron phosphate cathode material with a D50 particle size of 0.8μm and a carbon content of 1.1wt%.

[0026] The specific surface area of ​​iron phosphate is 4 m². 2 / g, with a Fe / P molar ratio of 0.960.

[0027] Spray drying specifically includes: setting the inlet temperature to 240℃ and the outlet temperature to 140℃; controlling the D50 particle size of the first, second, and third precursor powders to 20μm and the moisture content to ≤1.5%.

[0028] Sintering at the first, second, third, fourth, and fifth temperatures is carried out under a protective gas, which in this embodiment is nitrogen.

[0029] Example 3 This embodiment provides a high-pressure, high-capacity lithium iron phosphate cathode material, the preparation method of which includes the following steps: 3000g of ferric phosphate, 883g of ferric hydroxide, 1158.4g of lithium phosphate, 43.3g of phosphoric acid, 273g of glucose, 28.8g of titanium dioxide, and 5360g of deionized water were mixed and ground at 30℃ until the D50 particle size was 1.2μm and the solid content was 50wt%. The mixture was then spray-dried to obtain a first precursor powder. A portion of the first precursor powder was sintered at a first temperature of 840℃ for 7 hours and then pulverized by air jet milling to obtain a first intermediate with an average primary particle size of 2500nm. Another portion of the first precursor powder was sintered at a second temperature of 740℃ for 11 hours and then pulverized by air jet milling to obtain a second intermediate with an average primary particle size of 1200nm. 3000g of ferric phosphate, 883g of ferric hydroxide, 1158.4g of lithium phosphate, 43.3g of phosphoric acid, 273g of glucose, 36g of titanium dioxide, and 5360g of deionized water were mixed and ground in a second process at 30℃ until the D50 particle size was 0.5μm and the solid content was 50wt%. The mixture was then spray-dried to obtain a second precursor powder. A portion of the second precursor powder was sintered at a third temperature of 700℃ for 4 hours and then pulverized by air jet milling to obtain a third intermediate with an average primary particle size of 600nm. Another portion of the second precursor powder was sintered at a fourth temperature of 600℃ for 4 hours and then pulverized by air jet milling to obtain a fourth intermediate with an average primary particle size of 150nm. 1200g of the first intermediate, 800g of the second intermediate, 46g of PVP, and 2000g of deionized water were mixed in a certain proportion and then ground in a third process at a temperature of 30℃ until the D50 particle size was 1.2μm and the solid content was 50wt%, resulting in the first slurry. 1200g of the third intermediate, 800g of the fourth intermediate, 46g of PVP, and 2000g of deionized water were mixed in a certain proportion and then ground in a fourth process at a temperature of 30℃ until the D50 particle size was 0.4μm and the solid content was 50wt%, resulting in the second slurry. The first and second slurries were mixed and spray-dried to obtain the third precursor powder, which was then sintered at a fifth temperature of 760℃ for 10 hours using airflow pulverization to obtain a high-pressure, high-capacity lithium iron phosphate cathode material with a D50 particle size of 1.2μm and a carbon content of 1.5wt%.

[0030] The specific surface area of ​​iron phosphate is 16 m².2 / g, its Fe / P molar ratio is 0.980, and the specific surface area of ​​ferric hydroxide is 20m². 2 / g.

[0031] Spray drying specifically includes: setting the inlet temperature to 180℃ and the outlet temperature to 80℃; controlling the D50 particle size of the first, second, and third precursor powders to 60μm and the moisture content to ≤1.5%.

[0032] Sintering at the first, second, third, fourth, and fifth temperatures is carried out under a protective gas, which in this embodiment is nitrogen.

[0033] Comparative Example 1 The only difference between this comparative example and Example 1 is that, in S1 and S2, when preparing the first and second precursor powders, iron hydroxide in the raw materials is replaced with iron phosphate, lithium phosphate is replaced with lithium carbonate, and the elemental molar ratio of the first and second precursor powders remains unchanged.

[0034] Comparative Example 2 The only difference between this comparative example and Example 1 is that 2400g of the first intermediate, 74.4g of PVP, and 3600g of deionized water were mixed in proportion, and then ground in a third process at a temperature of 20°C until the D50 particle size was 1.0μm and the solid content was 40wt%, thus obtaining the first slurry.

[0035] Comparative Example 3 The only difference between this comparative example and Example 1 is that 1600g of the fourth intermediate, 49.6g of PVP, and 2400g of deionized water were mixed in proportion, and then ground in a fourth process at a temperature of 20°C until the D50 particle size was 0.2μm and the solid content was 40wt%, thus obtaining the second slurry.

[0036] Comparative Example 4 The only difference between this comparative example and Example 1 is that the PVP in S3 is replaced with 137.1g of glucose.

[0037] The following tests were performed on Examples 1-3 and Comparative Examples 1-4: 1. Take 10kx scanning electron microscope images of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-4; 2. Weigh 1g of each of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 and place them into a compaction mold. Place the mold into the compaction equipment to start the test. Take the result under 30KN pressure as the powder compaction density. 3. The lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 were dispersed in NMP with Super-P and PVDF at a mass ratio of 80:10:10. After ball milling and uniform dispersion, the dispersion was coated on aluminum foil and vacuum dried to obtain the cathode sheet. The electrolyte was 1 mol / L LiPF6, with a solvent volume ratio of EC:DMC:EMC = 1:1:1 (volume ratio). The separator was Celgard polypropylene membrane, and the lithium metal sheet was used as the anode. All materials were assembled into a coin cell. The test voltage range was 2.0V-3.75V. The cells were charged to 3.75V using a constant current and constant voltage charging method, and discharged to 2.0V using a constant current discharging method. The charge / discharge current was 0.1C for 1 cycle; then, the cells were charged / discharged at 1C for 3 cycles, with the cutoff voltage condition the same as at 0.1C.

[0038] The test results are shown in Table 1: Table 1 Test Results As shown in Table 1, under the same test conditions, the lithium iron phosphate cathode materials prepared in Examples 1-3 of this invention exhibit significantly lower powder resistivity compared to Comparative Examples 1-4, and the powder compaction degree of the lithium iron phosphate cathode materials prepared in Examples 1-3 all reaches 2.7 g / cm³. 3 This meets the requirements of fifth-generation lithium iron phosphate materials for powder compaction. At the same time, the 1.0C first discharge capacity of the lithium iron phosphate cathode materials prepared in Examples 1-3 is also significantly higher than that of Comparative Examples 1-4.

[0039] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing a high-capacity lithium iron phosphate cathode material with high pressure and high density, characterized in that, Includes the following steps: A first iron source, lithium source, phosphorus source, carbon source, dopant, and deionized water are mixed in a certain proportion, and after a first grinding and spray drying, a first precursor powder is obtained; a portion of the first precursor powder is sintered at a first temperature and then pulverized by airflow to obtain a first intermediate; another portion of the first precursor powder is sintered at a second temperature and then pulverized by airflow to obtain a second intermediate. The second iron source, lithium source, phosphorus source, carbon source, dopant, and deionized water are mixed in proportion, and after a second grinding and spray drying, a second precursor powder is obtained; a portion of the second precursor powder is sintered at a third temperature and then pulverized by airflow to obtain a third intermediate; another portion of the second precursor powder is sintered at a fourth temperature and then pulverized by airflow to obtain a fourth intermediate. The first intermediate, the second intermediate, the third carbon source, and deionized water are mixed in a certain proportion and then ground in a third process to obtain a first slurry. The third intermediate, the fourth intermediate, the fourth carbon source, and deionized water are mixed in a certain proportion and then ground in a fourth process to obtain a second slurry. The first and second slurries are mixed and spray-dried to obtain a third precursor powder, which is then sintered at a fifth temperature and pulverized by airflow to obtain the high-pressure, high-capacity lithium iron phosphate cathode material with a D50 particle size of 0.8~1.4μm. The first intermediate has an average primary particle size of 1500~2000nm; the second intermediate has an average primary particle size of 800~1200nm; the third intermediate has an average primary particle size of 300~600nm; and the fourth intermediate has an average primary particle size of 50~150nm. The first and second iron sources include iron phosphate and iron oxide hydroxide, wherein the iron phosphate has a specific surface area of ​​4-16 m². 2 / g, with an Fe / P molar ratio of 0.960–0.980, and the specific surface area of ​​the ferric hydroxide is 20–300 m² / g. 2 / g, wherein the ratio of ferric phosphate to ferric hydroxide is 9:1 to 1:

9.

2. The preparation method according to claim 1, characterized in that, The first and second lithium sources are battery-grade lithium sources, including one or more of lithium carbonate, lithium phosphate, lithium hydroxide, and lithium dihydrogen phosphate; the first and second phosphorus sources are battery-grade phosphorus sources, including one or more of iron phosphate, lithium phosphate, lithium dihydrogen phosphate, phosphoric acid, and ammonium monohydrogen phosphate. The amount of the first and second lithium sources added is determined based on the Fe / P molar ratio of the high-pressure, high-capacity lithium iron phosphate cathode material being 0.965 to 0.975, and the amount of the first and second phosphorus sources added is determined based on the Li / Fe molar ratio of the high-pressure, high-capacity lithium iron phosphate cathode material being 1.01 to 1.

05.

3. The preparation method according to claim 1, characterized in that, The first and second carbon sources include one or more of glucose, PEG, citric acid, and sucrose, and the carbon content of the first and second precursor powders is 0.02~0.7wt%. The third and fourth carbon sources include one or more of polyethylene, PVP, PVDF, starch, PET, and polyamide; the carbon content of the high-pressure, high-capacity lithium iron phosphate cathode material is 1.1~1.5wt%.

4. The preparation method according to claim 1, characterized in that, Both the first and second dopants include one or more of titanium dioxide, ammonium metavanadate, niobium pentoxide, and manganese oxide; the content of the doping element in the first precursor powder is 1500~4000ppm, and the content of the doping element in the second precursor powder is 5000~9000ppm.

5. The preparation method according to claim 1, characterized in that, The first intermediate and the second intermediate are mixed in a ratio of 2~4:2~4, and the third intermediate and the fourth intermediate are mixed in a ratio of 1~3:1~3.

6. The preparation method according to claim 1, characterized in that, The spray drying specifically includes: setting the inlet temperature to 180-240℃ and the outlet temperature to 80-140℃; controlling the D50 particle size of the first, second, and third precursor powders to be 20-60μm and the moisture content to ≤1.5%.

7. The preparation method according to claim 1, characterized in that, The sintering at the first, second, third, fourth, and fifth temperatures is all carried out under a protective gas, which is an inert gas. The first temperature sintering specifically includes: setting the temperature to 800~840℃ and the holding period to 7~11h; The second temperature sintering specifically includes: setting the temperature to 740~780℃ and holding the temperature for 7~11 hours; The third temperature sintering specifically includes: setting the temperature to 660~700℃ and holding the temperature for 4~7 hours; The fourth temperature sintering specifically includes: setting the temperature to 500~600℃ and holding the temperature for 4~7 hours; The fifth temperature sintering specifically includes setting the temperature to 760~800℃ and the holding period to 6~10h.

8. The preparation method according to claim 1, characterized in that, The first grinding process specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.8–1.2 μm, and a solid content of 30–50 wt%. The second grinding process specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.2–0.5 μm, and a solid content of 30–50 wt%. The third grinding process specifically includes: setting the temperature to 10–45°C, grinding to a D50 particle size of 0.8–1.2 μm, and a solid content of 30–50 wt%. The fourth grinding process specifically includes: setting the temperature to 10-45℃, grinding to a D50 particle size of 0.1-0.4μm, and a solid content of 30-50wt%.

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

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a lithium-ion battery cathode made based on the high-pressure, high-capacity lithium iron phosphate cathode material as described in claim 9.

Images