A method for preparing titanium-niobium-doped lithium iron phosphate materials

Abstract

This invention discloses a method for preparing titanium-niobium-doped lithium iron phosphate material, comprising the following steps: mixing phosphorus source, lithium source, iron source, titanium source, niobium source and carbon source and grinding to obtain a total slurry; taking half of the total slurry mass as large particle slurry; grinding the remaining slurry a second time to obtain small particle slurry; mixing the large particle slurry and the small particle slurry to obtain a precursor slurry; and drying, calcining and cooling the precursor slurry to obtain lithium iron phosphate material, whose general formula is LiFe. 1‑x‑y Ti x Nb y PO4, where 0 < x + y ≤ 0.08. This invention controls the total doping amount of titanium and niobium to below 0.08, achieving full solid solution of elements without high-temperature sintering. This effectively avoids the problems of particle melting and adhesion and the formation of iron phosphide impurity phases caused by high-temperature sintering, ensuring the integrity of the material's crystal structure and particle morphology. Furthermore, through slurry gradation process and particle size distribution control, it synergistically compensates for insufficient density that may be caused by low-temperature sintering.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium iron phosphate material, and more particularly to a method for preparing lithium iron phosphate material doped with titanium and niobium. Background Technology

[0002] LiFePO4 (LFP) has become the mainstream cathode material for power lithium-ion batteries and energy storage batteries due to its advantages such as low cost, long cycle life, good thermal stability, and excellent safety performance. However, traditional lithium iron phosphate has drawbacks such as low electronic conductivity, slow lithium-ion diffusion rate, and low compaction density, especially since the compaction density is usually only 2.0~2.4 g / cm³. 3 This limits the improvement of its volumetric energy density.

[0003] In existing doping modification techniques, doping elements are often used to overcome the above-mentioned defects. CN121800165A discloses a niobium-titanium co-doped lithium iron phosphate electrode material, its preparation method and application. By preparing three lithium iron phosphate precursor slurries with different particle sizes, and wet-milling them with a niobium-titanium source mixed solution obtained by hydrochloric acid dissolution, LiFePO4-Nb / Ti material is obtained at a final calcination temperature of 730℃. However, wet milling cannot accurately control the doping amount of niobium and titanium, and the improvement on the compaction density of lithium iron phosphate material is not explored.

[0004] CN117810423A discloses a lithium iron phosphate material, its preparation method, and its application. It adopts gradient niobium doping combined with three different particle sizes of lithium iron phosphate to improve the compaction density and electrochemical performance of the lithium iron phosphate material. However, it requires three sintering processes, making the preparation process relatively complicated. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing lithium iron phosphate materials by simultaneously improving compaction density and electrochemical performance through titanium-niobium doping.

[0006] Technical Solution: The present invention provides a method for preparing titanium-niobium-doped lithium iron phosphate material, comprising the following steps: mixing phosphorus source, lithium source, iron source, titanium source, niobium source and carbon source and grinding to obtain a total slurry; taking half of the total slurry mass as large particle slurry; grinding the remaining slurry a second time to obtain small particle slurry; mixing the large particle slurry and the small particle slurry to obtain a precursor slurry; and drying, calcining and cooling the precursor slurry to obtain lithium iron phosphate material, whose general formula is LiFe. 1-x- y Ti x Nb y PO4, where 0 < x + y ≤ 0.08.

[0007] The condition 0 < x ≤ 0.04 indicates that introducing titanium doping can improve the compaction density of lithium iron phosphate (LFP) materials. However, when x is too large, i.e., the titanium doping amount is too high, LFP materials require a higher sintering temperature (above 750°C) for sufficient titanium dissolution. Insufficient dissolution will affect lithium-ion transport and reduce the electrochemical performance of the material. Furthermore, when the sintering temperature is too high, LFP particles will melt and agglomerate, forming iron phosphide (Fe3P) impurities. This promotes grain boundary movement and merging of adjacent particles, causing abnormal growth of the originally small primary grains. Excessively large grains shorten the grain boundary ratio, increasing the solid-phase diffusion distance of lithium ions. Simultaneously, the internal stress cannot be released during grain growth, leading to numerous dislocations and microcracks, further damaging the crystal integrity and the crystal structure and morphology of the finished material. This results in rapid capacity decay, not only reducing the electrochemical performance of the material but also further affecting the improvement of compaction density, making it difficult to simultaneously achieve high compaction and excellent electrochemical performance.

[0008] Preferably, both x and y are 0.01~0.04. Introducing niobium doping can lower the sintering temperature of lithium iron phosphate materials and improve their electrochemical performance. However, when y is too large, i.e., the amount of niobium doping is too high, it will reduce the compaction density of lithium iron phosphate materials.

[0009] The x:y=1:(0.5~3) range can fully accommodate the high real density of titanium doping and the excellent electrochemical performance of niobium doping, and significantly reduce the sintering temperature.

[0010] Preferably, the molar ratio of the lithium source to the iron source is Li:Fe = 1.02~1.05:1, which ensures sufficient compensation of lithium element and meets the solid solution requirements of the sintering temperature.

[0011] Preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium phosphate; the iron source is at least one of ferrous oxalate, ferrous carbonate, ferric nitrate, and ferric phosphate; and the phosphorus source is ferric phosphate.

[0012] Preferably, the carbon source is at least one of polyethylene glycol 2000, glucose, sucrose, citric acid, polyvinyl alcohol, starch, and polyvinylidene fluoride, and the amount used is such that the carbon content of the final sintered product is 1.3-1.5%.

[0013] The large particle slurry has a particle size of D50 = 0.75~1.55μm. The large particle slurry acts as a framework to provide structural support and improve the structural stability of lithium iron phosphate materials.

[0014] Preferably, the particle size of the large particle slurry is D50 = 0.8~1.5μm.

[0015] The particle size of the small-particle slurry is D50 = 0.15~0.45μm. The small-particle slurry acts as a filler phase, filling the gaps between the large-particle slurry and promoting the solid solution of dopant elements during sintering.

[0016] Preferably, the particle size of the small particle slurry is D50 = 0.2~0.4μm.

[0017] The mass ratio of the large particle slurry to the small particle slurry is (5~7):(5~3), which is used to achieve sufficient gradation of large and small particles and improve the compaction density of lithium iron phosphate material.

[0018] The titanium source is at least one of titanium dioxide, tetrabutyl titanate, tetraethyl titanate, and isopropyl titanate.

[0019] The niobium source is at least one of niobium oxalate, niobium pentoxide, and niobium oxyphosphate. Since niobium oxyphosphate readily forms impurities, leading to an imbalance in the P element ratio at the front end, niobium pentoxide and niobium oxalate are preferred niobium sources.

[0020] Preferably, the drying is spray drying, and the inlet air temperature is 180~200℃.

[0021] The calcination temperature is 680~740℃, the heating rate is 2~4℃ / min, and the duration is 6~10 hours.

[0022] Preferably, the finished product obtained after calcination and cooling is subjected to air jet milling, and the D50 of the final product after air jet milling is 0.7~1.5μm.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention controls the total doping amount of titanium and niobium to below 0.08, and can achieve full solid solution of elements without high-temperature sintering, effectively avoiding the problems of particle melting and adhesion and the generation of iron phosphide impurity phase caused by high-temperature sintering, ensuring the integrity of the material crystal structure and particle morphology, and through the slurry gradation process and particle size distribution control, it synergistically compensates for the insufficient density that may be caused by low-temperature sintering, and achieves 2.48 g / cm under lower temperature sintering conditions. 3 The above high density; (2) The synergistic doping of titanium and niobium achieves simultaneous improvement of electronic conductivity and ion diffusion rate at low addition amount. The specific capacity of the material at 0.1C is ≥159.3mAh / g, and the specific capacity at 1C discharge rate is ≥141.7mAh / g; (3) The slurry gradation, spray drying and low temperature sintering adopted in this invention are all mature industrial technologies. No special equipment is required. Low temperature sintering reduces energy consumption, extends the kiln life, improves production efficiency and reduces industrial production costs. Attached Figure Description

[0024] Figure 1This is a scanning electron microscope image of the lithium iron phosphate material prepared in Example 1;

[0025] Figure 2 This is a scanning electron microscope image of the lithium iron phosphate material prepared in Comparative Example 6. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the embodiments and comparative examples. Unless otherwise stated, all reagents used are commercially available and are used directly without purification.

[0027] Example 1

[0028] Lithium carbonate, iron phosphate, titanium dioxide, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.02:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.45 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.97 Ti 0.02 Nb 0.01 PO4.

[0029] Example 2

[0030] Lithium carbonate, iron phosphate, tetrabutyl titanate, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.15 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.35 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0031] Example 3

[0032] Lithium carbonate, iron phosphate, tetraethyl titanate, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.03:0.03:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.4 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.94 Ti 0.03 Nb 0.03 PO4.

[0033] Example 4

[0034] Lithium carbonate, iron phosphate, isopropyl titanate, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.04:0.04:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.15 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.45 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 720℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature with the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.92 Ti 0.04 Nb 0.04 PO4.

[0035] Example 5

[0036] Lithium carbonate, iron phosphate, titanium dioxide, niobium oxalate, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.04:0.02:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.45 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.94 Ti 0.04 Nb 0.02 PO4.

[0037] Example 6

[0038] Lithium carbonate, iron phosphate, tetrabutyl titanate, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.50 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.20 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature with the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0039] When the particle size of the large particle slurry is D50=1.5±0.05μm and the particle size of the small particle slurry is D50=0.2±0.05μm, the same effect as in this embodiment can be achieved.

[0040] Example 7

[0041] Lithium carbonate, iron phosphate, titanium dioxide, niobium oxyphosphate, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.525:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.35 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 6:4 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0042] Example 8

[0043] Lithium carbonate, iron phosphate, titanium dioxide, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.40 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 7:3 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0044] Example 9

[0045] Lithium carbonate, iron phosphate, titanium dioxide, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 0.80 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.15 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 740℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0046] When the particle size of the large particle slurry is D50=0.8±0.05μm and the particle size of the small particle slurry is D50=0.2±0.05μm, the same effect as in this embodiment can be achieved.

[0047] Example 10

[0048] Lithium carbonate, iron phosphate, titanium dioxide, niobium pentoxide, glucose, and polyethylene glycol 2000 were mixed in a molar ratio of 0.51:1:0.01:0.01:0.1:0.05. Water was added, and the mixture was stirred until homogeneous. The mixture was then milled for 10 minutes, controlling the particle size D50 to 1.25 μm. Half of the total slurry was collected as the large particle slurry, and the remaining slurry was milled for another 30 minutes, controlling the particle size D50 to 0.45 μm. The remaining slurry was collected as the small particle slurry. The large and small particle slurries were mixed at a mass ratio of 5:5 to form a precursor slurry. The precursor slurry was then centrifugally spray-dried at an inlet air temperature of 200℃. The dried material was transferred to a tube furnace and heated to 680℃ at a rate of 2℃ / min under a nitrogen atmosphere, held for 8 hours, and then cooled to room temperature in the furnace. The sintered material was then pulverized by air jet milling, controlling the D50 to 1.0 μm, to obtain the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0049] Comparative Example 1: In this example, titanium and niobium are not doped, and the remaining steps are the same as in Example 2 to obtain the finished product LiFePO4.

[0050] Comparative Example 2: In this example, niobium was not doped, and the molar ratio of titanium dioxide to iron phosphate was 0.02:1. To maintain consistency with Example 2 in the remaining steps, the final product LiFe was obtained.0.98 Ti 0.02 PO4.

[0051] Comparative Example 3: In this example, titanium was not doped, and the molar ratio of niobium pentoxide to iron phosphate was 0.02:1. To maintain consistency with the remaining steps in Example 2, the final product LiFe was obtained. 0.98 Nb 0.02 PO4.

[0052] Comparative Example 4: In this example, the molar ratio of titanium dioxide to niobium pentoxide was 0.1:0.01, the sintering temperature was 720℃, and the remaining steps were consistent with those in Example 2, yielding the finished product LiFe. 0.89 Ti 0.1 Nb 0.01 PO4.

[0053] Comparative Example 5: In this example, the molar ratio of titanium dioxide to niobium pentoxide is 0.01:0.1, and the remaining steps are consistent with those in Example 2, yielding the finished product LiFe. 0.89 Ti 0.01 Nb 0.1 PO4.

[0054] Comparative Example 6: In this example, niobium was not doped, the molar ratio of titanium dioxide to iron phosphate was 0.02:1, the sintering temperature was 800℃, and the remaining steps were the same as in Example 2, yielding the finished product LiFe. 0.98 Ti 0.02 PO4.

[0055] Comparative Example 7: In this example, only one sand milling was performed, and no slurry gradation was carried out. The remaining steps were consistent with those in Example 2, resulting in the finished product LiFe. 0.98 Ti 0.01 Nb 0.01 PO4.

[0056] Comparative Example 8: In this example, the mass ratio of large particle slurry to small particle slurry is 8:2, and the remaining steps are the same as in Example 2, yielding the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0057] Comparative Example 9: In this example, the mass ratio of large particle slurry to small particle slurry is 4:6, and the remaining steps are the same as in Example 2, yielding the finished product LiFe. 0.98 Ti 0.01 Nb 0.01 PO4.

[0058] Comparative Example 10: In this example, the grinding particle size D50 of the large particle slurry was 0.75 μm, and the grinding particle size D50 of the small particle slurry was 0.55 μm. The remaining steps were consistent with those in Example 2, resulting in the finished LiFe product. 0.98 Ti 0.01 Nb 0.01 PO4.

[0059] The lithium iron phosphate materials prepared in the examples and comparative examples were tested as follows, and the results are shown in Table 1:

[0060] (1) Powder compaction density: Tested using Shenzhen Sansi Zongheng UTM7305 electronic powder compaction tester according to GB / T 44330-2024 stepped compaction (three-stage) method;

[0061] (2) Electrochemical test: The 0.1C discharge specific capacity and 1C specific capacity were tested using the Blue Battery Test System Instrument according to the constant current charge-discharge method.

[0062] Table 1. Experimental results of the examples and comparative examples Example 1 2.567 162.54 145.19 Example 2 2.53 160.02 142.80 Example 3 2.545 160.18 144.32 Example 4 2.55 161.19 142.21 Example 5 2.559 162.15 145.03 Example 6 2.515 160.52 144.05 Example 7 2.525 159.98 142.93 Example 8 2.517 159.70 142.08 Example 9 2.495 159.32 141.76 Example 10 2.489 160.14 143.32 Comparative Example 1 2.216 156.31 128.87 Comparative Example 2 2.544 158.47 136.89 Comparative Example 3 2.307 160.36 143.23 Comparative Example 4 2.37 156.12 136.01 Comparative Example 5 2.578 158.3 136.49 Comparative Example 6 2.591 155.79 129.37 Comparative Example 7 2.422 158.62 141.14 Comparative Example 8 2.465 161.33 144.91 Comparative Example 9 2.484 159.62 142.50 Comparative Example 10 2.428 159.34 142.57

[0063] As can be seen from Table 1, the powder compaction in Example 1 reached 2.567 g / cm³. 3 The 0.1C discharge specific capacity is 162.54 mAh / g, and the 1C discharge specific capacity is 145.19 mAh / g, while the compaction densities of comparative examples 1-3 are 2.216 g / cm³, respectively. 3 2.591 g / cm 3 2.422 g / cm 3The 0.1C discharge specific capacities were 156.31 mAh / g, 155.79 mAh / g, and 158.62 mAh / g, respectively, and the 1C discharge specific capacities were 128.87 mAh / g, 129.37 mAh / g, and 141.14 mAh / g, respectively. Comparing with Comparative Example 1, it can be seen that the combination of titanium-niobium dual doping with slurry gradation and low-temperature sintering significantly improved the compaction and rate performance of the material. In Comparative Example 1, the undoped lithium iron phosphate sample, due to its low intrinsic conductivity and poor particle packing, exhibited significantly inferior performance. Comparing with Comparative Example 6, although the compaction density was slightly higher due to the high titanium doping and high-temperature sintering formulation, the electrochemical performance was poor. Possible reasons include: high-temperature sintering generating iron phosphide, which exacerbated side reactions leading to poor electrochemical performance; particle melting disrupting the morphology, thus hindering lithium-ion diffusion paths; and high doping causing lattice distortion, limiting capacity utilization. Example 1 achieved a similar compaction density, but its capacity and rate performance far exceeded those of Comparative Example 6, demonstrating the superiority of the present invention. In Comparative Example 2, using the same sintering temperature as Example 2 with high titanium doping as in Comparative Example 6, the lower sintering temperature prevented sufficient solidification of titanium, thus affecting lithium-ion transport and reducing the electrochemical performance of the lithium iron phosphate material. This further illustrates that the present invention can achieve a balance between compaction density and electrochemical performance at lower sintering temperatures. Comparing the data with Comparative Example 3, slurry gradation not only increased the compaction density by approximately 0.145 g / cm³, but also improved the conductive network inside the electrode, slightly enhancing capacity and rate performance. This sufficiently demonstrates that single titanium and single niobium doping modifications are less effective than dual doping; Ti and Nb synergistic doping can both improve powder compaction density and optimize ion and electron conduction, effectively improving electrochemical performance.

[0064] from Figure 1 and Figure 2 The electron microscope images clearly show that when titanium is doped alone, high-temperature sintering leads to particle melting, which also verifies the statement in Table 1 above that the melting causes the lithium-ion diffusion path to be blocked, resulting in a significant difference in electrochemical performance compared to Example 1.

[0065] The data in the table shows that there is an optimal range for the doping ratio; excessive doping may lead to a decrease in performance. In Examples 2-3 and Comparative Examples 4-5, it can be seen that moderately increasing the doping amount of titanium and niobium can slightly optimize performance, but excessive doping easily causes lattice distortion, an increase in impurity phases, and a decrease in the material's discharge specific capacity.

[0066] The experimental results from Examples 7-9 and Comparative Examples 7-9 also show that particle size distribution control effectively improves powder compaction and electrochemical performance. When the particle size ratio is 5:5, the sample exhibits better compaction density and electrochemical performance. Single-size grinding and unbalanced particle size distribution result in larger particle packing voids, hindered ion transport, and a simultaneous decrease in compaction density and rate capacity. Examples 6 and 9 and Comparative Example 10 demonstrate that the particle size during grinding is also a key factor affecting various performance characteristics. A reasonable combination of particle size differences is more conducive to constructing a dense and stable electrode structure.

[0067] In summary, the sample in Example 1 has the highest compaction density and discharge specific capacity. The combination of titanium-niobium dual doping ratio, doping raw materials, particle size distribution and sintering process is optimal. The modification effect is far better than the control group samples that are undoped, doped with a single element, doped with excessive amount, and have deviated process parameters.

Claims

1. A method for preparing titanium-niobium-doped lithium iron phosphate material, characterized in that, Includes the following steps: A total slurry is obtained by mixing and grinding phosphorus, lithium, iron, titanium, niobium, and carbon sources. Half of the total slurry mass is taken as large particle slurry, and the remaining slurry is ground again to obtain small particle slurry. The large particle slurry and the small particle slurry are mixed to obtain a precursor slurry. The precursor slurry is dried, calcined, and cooled to obtain lithium iron phosphate material, with the general formula LiFe. 1-x- y Ti x Nb y PO4, where 0 < x + y ≤ 0.

08.

2. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The condition is 0 < x ≤ 0.

04.

3. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 2, characterized in that, Both x and y are between 0.01 and 0.

04.

4. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The x:y = 1:(0.5~3).

5. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The particle size of the large-particle slurry is D50 = 0.75~1.55μm.

6. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The particle size of the small particle slurry is D50 = 0.15~0.45μm.

7. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The mass ratio of the large-particle slurry to the small-particle slurry is (5~7):(5~3).

8. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The titanium source is at least one of titanium dioxide, tetrabutyl titanate, tetraethyl titanate, and isopropyl titanate.

9. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The niobium source is at least one of niobium oxalate, niobium pentoxide, and niobium oxyphosphate.

10. The method for preparing titanium-niobium-doped lithium iron phosphate material according to claim 1, characterized in that, The calcination temperature is 680~740℃.

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