Preparation method of high-compaction and high-multiplying lithium manganese iron phosphate positive electrode material
Patent Information
- Application Number
- CN202610799065.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-04
- Publication Date
- 2026-08-21
AI Technical Summary
[0004]然而，采用单一改性，例如：仅采用碳包覆或仅采用离子掺杂，难以同时提高电导率压实密度以及结构稳定性
[0021] Beneficial effects: Compared with the prior art, the significant advantages of this invention are: the lithium iron phosphate cathode material not only has high conductivity (resistivity ≤10Ω·cm) and high rate performance (0.1C discharge specific capacity ≥157mAh/g, 0.5C discharge specific capacity ≥146.7mAh/g, 1C discharge specific capacity ≥141.2mAh/g), but also has excellent high compaction properties (compaction density ≥2.60g/cm³). 3 The compaction degree reaches the standard of fourth-generation high-compact lithium iron phosphate cathode material, achieving simultaneous improvement in compaction density, battery rate performance and structural stability.
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Figure CN122607998A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of lithium iron phosphate cathode materials, and particularly relates to a high-pressure, gradient-doped lithium iron phosphate material. Background Technology
[0002] Lithium iron phosphate (LiFePO4) has become one of the mainstream cathode materials for lithium-ion batteries due to its advantages such as low cost, environmental friendliness, long cycle life, and high safety performance. However, its low electronic conductivity (approximately 10⁻⁶ ppm) is a significant drawback. -9 Its low density (S / cm) and low lithium-ion diffusion coefficient, as well as its low compaction density, limit its application in high-rate, high-energy-density scenarios (such as fast charging of electric vehicles), which is also a difficult problem for researchers to overcome.
[0003] To overcome the aforementioned shortcomings, existing technologies mainly focus on modification through carbon coating, ion doping, nano-sizing, and precursor improvement. For example, boron / nitrogen co-doped single-walled carbon nanotubes are introduced before secondary sintering to form a three-dimensional conductive network on the material surface, thereby improving the material's electronic conductivity. Alternatively, bilayer carbon nanotubes can be used to coat the surface of lithium iron phosphate, forming a core-shell structure. Furthermore, methods for in-situ growth of carbon nanotubes within lithium iron phosphate particles and methods for in-situ synthesis of lithium iron phosphate and carbon nanotube composites have been disclosed. These methods involve mixing catalysts with raw materials and growing carbon nanotubes during sintering to form an internal conductive network.
[0004] However, using a single modification, such as carbon coating or ion doping alone, is insufficient to simultaneously improve conductivity, compaction density, and structural stability. While surface coating can improve conductivity, its effect on bulk conductivity is limited and may hinder lithium-ion transport. Simple bulk doping, although improving structural stability, usually comes at the cost of reduced capacity. Furthermore, existing ion doping techniques can only address specific issues such as structural stability or improved lithium-ion transport efficiency; however, doping introduces other problems, such as variations in cathode particle morphology and various surface and internal issues (e.g., surface side reactions, internal stress concentration).
[0005] Therefore, developing a lithium iron phosphate material that can simultaneously achieve high electronic conductivity, high compaction, and high structural stability, and controlling its morphology, is a technical problem that urgently needs to be solved. Summary of the Invention
[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a lithium iron phosphate material that simultaneously improves conductivity and compaction, thereby obtaining a lithium iron phosphate material with high electronic conductivity, fast lithium-ion transport and high structural stability.
[0007] Technical solution: The high-pressure, gradient-doped lithium iron phosphate cathode material of the present invention is prepared by the following steps:
[0008] (1) Disperse carbon nanotubes in an ethylene glycol solution containing a surfactant and a first dopant source, so that the first dopant is anchored on the carbon nanotubes to obtain a uniform dispersion.
[0009] (2) Using the dispersion as the reaction base liquid, heat it to 50-80℃, keep the pH of the system at 2.5-3, and under stirring conditions, first add iron source, phosphorus source and oxidant to the reaction base liquid at a rate of 5-10 mL / min and a time of 20-30 min to generate precursor crystal nuclei of the first doping element gradient on carbon nanotubes; then add iron source, phosphorus source, oxidant and second doping element source to the reaction base liquid at a rate of 5-15 mL / min and a time of 1-3 h to generate a double-doped primary particle precursor slurry with a concentration gradient using carbon nanotubes as the framework structure;
[0010] (3) Add a pore-forming agent to the primary particle precursor slurry and heat treat it, then filter to obtain the modified precursor;
[0011] (4) After washing and drying the modified precursor, it is mixed with lithium source and carbon source, and pre-sintered at 320-460℃ for 2-4h under an inert atmosphere, and then sintered at 660-780℃ for 6-10h to obtain high-compact, gradient-doped lithium iron phosphate material.
[0012] Furthermore, the doping element in the first doping element source of the lithium iron phosphate cathode material is selected from Nb and / or V, and the doping element in the second doping element source is selected from Mn and / or Co.
[0013] Furthermore, the number of moles of the first doping element source used in this lithium iron phosphate cathode material is 1-2% of the number of moles of ferrous sulfate, and the number of moles of the second doping element source is 1-1.5% of the number of moles of ferrous sulfate.
[0014] Furthermore, the mass of carbon nanotubes added to this lithium iron phosphate cathode material is 0.1-0.8% of the theoretically generated iron phosphate mass.
[0015] Furthermore, the first doping element source used in this lithium iron phosphate cathode material is selected from at least one of niobium ammonium oxalate monohydrate, niobium ethanol, ammonium metavanadate, and vanadium acetylacetonate; the second doping element source is selected from at least one of manganese sulfate, manganese acetate, manganese nitrate, cobalt sulfate, and cobalt acetate.
[0016] Furthermore, the surfactant used in this lithium iron phosphate cathode material is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, and hexadecyltrimethylammonium bromide, and the mass ratio of the surfactant to carbon nanotubes is (1-1.5):1.
[0017] Furthermore, the lithium iron phosphate cathode material uses a lithium source, iron source, and phosphorus source with a Li:Fe:P molar ratio of (1.01-1.05):1:1; wherein the iron source is selected from ferrous sulfate, ferrous nitrate, or ferrous chloride, the phosphorus source is selected from phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate, and the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium nitrate.
[0018] Furthermore, the oxidant used in this lithium iron phosphate cathode material is selected from hydrogen peroxide or ammonium persulfate, and its molar amount is 0.5-1 times the total molar amount of iron source.
[0019] Furthermore, the carbon source used in this lithium iron phosphate cathode material is selected from at least one of glucose, sucrose, and citric acid, and its added mass is 6-8% of the theoretical mass of the primary particle precursor.
[0020] Furthermore, the pore-forming agent used in this lithium iron phosphate cathode material is selected from at least one of polyethylene glycol, hexadecyltrimethylammonium bromide, and polymethyl methacrylate, and its added mass is 2-6% of the theoretical mass of the primary particle precursor.
[0021] Beneficial effects: Compared with the prior art, the significant advantages of this invention are: the lithium iron phosphate cathode material not only has high conductivity (resistivity ≤10Ω·cm) and high rate performance (0.1C discharge specific capacity ≥157mAh / g, 0.5C discharge specific capacity ≥146.7mAh / g, 1C discharge specific capacity ≥141.2mAh / g), but also has excellent high compaction properties (compaction density ≥2.60g / cm³). 3 The compaction degree reaches the standard of fourth-generation high-compact lithium iron phosphate cathode material, achieving simultaneous improvement in compaction density, battery rate performance and structural stability. Attached Figure Description
[0022] Figure 1 This is an electron microscope image of the lithium iron phosphate cathode material prepared in Example 1;
[0023] Figure 2 This is an electron microscope image of the lithium iron phosphate cathode material prepared in Example 8. Detailed Implementation
[0024] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.
[0025] In the following examples and comparative examples, all carbon nanotubes were single-walled carbon nanotubes with a diameter of 2-4 nm and a length of 10 μm. All surfactants used were polyvinylpyrrolidone (PVP), and the mass of PVP added was consistent with the mass of the carbon nanotubes. All pore-forming agents used were polyethylene glycol (PEG-400). The oxidant used was hydrogen peroxide, added at a rate equal to one mole of the total amount of iron source added. All reagents used were commercially available.
[0026] Example 1 - Nb, Mn dual doping
[0027] In this embodiment, the amount of carbon nanotubes added is 0.6% of the theoretically generated iron phosphate mass. The Li:Fe:P molar ratio in the lithium, iron, and phosphorus sources is 1.05:1:1. The iron source is a 2 mol / L ferrous sulfate solution, the phosphorus source is a 2 mol / L phosphoric acid solution, and the lithium source is lithium carbonate. The first dopant source is niobium ammonium oxalate monohydrate, and the second dopant source is manganese sulfate.
[0028] It is specifically prepared through the following steps:
[0029] (1) Carbon nanotubes were added to an ethylene glycol solution containing PVP and niobium oxalate monohydrate and ultrasonically dispersed for 2 hours to obtain a uniform dispersion.
[0030] (2) The dispersion was transferred to the reaction vessel as the reaction base liquid and nitrogen gas was purged throughout the reaction. The pH value was adjusted to 2.5-3 with ammonia water. The mixture was heated to 60°C and ferrous sulfate solution, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 10 mL / min under stirring conditions for 20 min. Ferrous sulfate solution, manganese sulfate, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 15 mL / min for 2 h to obtain a primary particle precursor slurry.
[0031] (3) PEG-400 of 2% of the theoretical precursor mass was added to the primary particle precursor slurry, transferred to a high-pressure reactor, and hydrothermally treated at 180℃ for 12h to obtain the reaction product. The product was then washed and dried to obtain the modified precursor.
[0032] (4) The modified precursor was mixed with lithium carbonate and glucose, wherein the amount of glucose added was 7% of the precursor mass; after ball milling, the mixture was pre-calcined at 400°C for 2 hours under a nitrogen atmosphere at 5°C / min, and then sintered at 700°C for 6 hours at 5°C / min. Finally, after natural cooling, the mixture was crushed and sieved to obtain high-compact, gradient-doped lithium iron phosphate material.
[0033] Example 2 - V, Co dual doping
[0034] This embodiment 2 is basically the same as embodiment 1, except that the first doping element source is ammonium metavanadate and the second doping element source is cobalt acetate.
[0035] Example 3 - V, Mn dual doping
[0036] This embodiment 3 is basically the same as that of embodiment 1, except that the first dopant element source is ammonium metavanadate.
[0037] Example 4 - Nb, Co dual doping
[0038] Example 4 is basically the same as Example 1, except that the second dopant element source is cobalt acetate.
[0039] Example 5 - Nb, Mn dual doping
[0040] Example 5 is basically the same as Example 1, except that the amount of carbon nanotubes added is 0.3% of the theoretically generated iron phosphate mass.
[0041] Example 6 - Nb, Mn dual doping
[0042] Example 6 is basically the same as Example 1, except that the amount of carbon nanotubes added is 0.5% of the theoretically generated iron phosphate mass.
[0043] Example 7 - Nb, Mn dual doping
[0044] Example 7 is basically the same as Example 1, except that the amount of carbon nanotubes added is 0.7% of the theoretically generated iron phosphate mass.
[0045] Example 8 - V, Co dual doping
[0046] In this embodiment, the amount of carbon nanotubes added is 0.2% of the theoretically generated iron phosphate mass. The Li:Fe:P molar ratio in the lithium, iron, and phosphorus sources is 1.05:1:1. The iron source is a 2 mol / L ferrous sulfate solution, the phosphorus source is a 2 mol / L phosphoric acid solution, and the lithium source is lithium carbonate. The first dopant source is ammonium metavanadate, and the second dopant source is cobalt acetate.
[0047] It is specifically prepared through the following steps:
[0048] (1) Carbon nanotubes were added to an ethylene glycol solution containing PVP and ammonium metavanadate and ultrasonically dispersed for 2 hours to obtain a uniform dispersion.
[0049] (2) The dispersion was transferred to the reaction vessel as the reaction base liquid and nitrogen gas was purged throughout the reaction. The pH value was adjusted to 2.5-3 with ammonia water. The mixture was heated to 60°C and ferrous sulfate solution, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 5 mL / min with stirring for 30 min. Ferrous sulfate solution, cobalt acetate, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 5 mL / min for 3 h to obtain a primary particle precursor slurry.
[0050] (3) PEG-400 of 2% of the theoretical mass of the primary particle precursor was added to the primary particle precursor slurry, transferred to a high-pressure reactor, and hydrothermally treated at 180°C for 12 h to obtain the reaction product. The product was then washed and dried to obtain the modified precursor.
[0051] (4) The modified precursor was mixed with lithium carbonate and glucose, wherein the amount of glucose added was 7% of the precursor mass; after ball milling, the mixture was pre-calcined at 400°C for 2 hours under a nitrogen atmosphere at 5°C / min, and then sintered at 700°C for 6 hours at 5°C / min. Finally, after natural cooling, the mixture was crushed and sieved to obtain high-compact, gradient-doped lithium iron phosphate material.
[0052] Comparative Example 1
[0053] Comparative Example 1 is basically the same as Example 1, except that the first and second doping element sources of the dual-doped material are loaded together on the carbon nanotubes. The specific steps are as follows:
[0054] (1) Carbon nanotubes were added to an ethylene glycol solution containing PVP, ammonium niobate monohydrate and manganese sulfate, and ultrasonically dispersed for 2 hours to obtain a uniform dispersion.
[0055] (2) The dispersion was transferred to the reaction vessel as the reaction base liquid and nitrogen gas was purged throughout the reaction. The pH value was adjusted to 2.5-3 with ammonia water. The mixture was heated to 60°C and ferrous sulfate solution, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 10 mL / min with stirring for 2.5 h to obtain a primary particle precursor slurry.
[0056] (3) PEG-400 of 2% of the theoretical precursor mass was added to the primary particle precursor slurry, transferred to a high-pressure reactor, and hydrothermally treated at 180℃ for 12h to obtain the reaction product. The product was then washed and dried to obtain the modified precursor.
[0057] (4) The modified precursor was mixed with lithium carbonate and glucose, wherein the amount of glucose added was 7% of the precursor mass; after ball milling, the mixture was pre-calcined at 400°C for 2 hours under a nitrogen atmosphere at 5°C / min, and then sintered at 700°C for 6 hours at 5°C / min. Finally, after natural cooling, the mixture was crushed and sieved to obtain high-compact, gradient-doped lithium iron phosphate material.
[0058] Comparative Example 2
[0059] Comparative Example 2 is basically the same as Example 1, except that the manganese source is added directly together with the iron and phosphorus sources. The specific steps are as follows:
[0060] (1) Carbon nanotubes were added to an ethylene glycol solution containing PVP and niobium oxalate monohydrate and ultrasonically dispersed for 2 hours to obtain a uniform dispersion.
[0061] (2) The dispersion was transferred to the reaction vessel as the reaction base liquid and nitrogen gas was purged throughout the reaction. The pH value was adjusted to 2.5-3 with ammonia water. The mixture was heated to 60°C and ferrous sulfate solution, manganese sulfate, phosphoric acid and hydrogen peroxide were added simultaneously at a rate of 10 mL / min with stirring. The addition time was 2.5 h to obtain a primary particle precursor slurry.
[0062] (3) PEG-400 of 2% of the theoretical precursor mass was added to the primary particle precursor slurry, transferred to a high-pressure reactor, and hydrothermally treated at 180℃ for 12h to obtain the reaction product. The product was then washed and dried to obtain the modified precursor.
[0063] (4) The modified precursor was mixed with lithium carbonate and glucose, wherein the amount of glucose added was 7% of the precursor mass; after ball milling, the mixture was pre-calcined at 400°C for 2 hours under a nitrogen atmosphere at 5°C / min, and then sintered at 700°C for 6 hours at 5°C / min. Finally, after natural cooling, the mixture was crushed and sieved to obtain high-compact, gradient-doped lithium iron phosphate material.
[0064] Performance testing
[0065] The lithium iron phosphate materials prepared in Examples 1-8 and Comparative Examples 1-2 were used as positive electrode active materials, mixed with conductive carbon black and PVDF at a mass ratio of 90:5:5, and coated onto aluminum foil to form a positive electrode sheet. A lithium sheet was used as the negative electrode to assemble CR2032 coin cells. Electrochemical performance was tested within a voltage range of 2.5-3.75V, and the results are shown in Table 1.
[0066] Table 1. Electrochemical performance test results of coin cells prepared in the examples and comparative examples.
[0067] As can be seen from Table 1, the material prepared in the embodiments of the present invention can form a gradient from the inside out: the concentration gradient of the first dopant element decreases and the concentration gradient of the second dopant element increases. While maintaining high capacity, its rate performance and cycle stability are significantly better than those of the comparative example.
[0068] The structural characterization of the lithium iron phosphate cathode materials prepared in Examples 1 and 8 was performed, and the results are as follows: Figure 1 and Figure 2 As shown. (Through) Figure 1 and Figure 2 It can be seen that the lithium iron phosphate cathode material prepared by the preparation process of the present invention forms a particle size distribution relationship, with small particles filling the spaces between large particles, which improves the compaction performance.
[0069] Based on the performance test data in Table 1, it can be seen that the lithium iron phosphate cathode materials prepared in Examples 1 to 8 of this invention are superior to Comparative Examples 1 and 2 in terms of electrochemical performance, cycle stability, and compaction performance. Based on the experimental results, further analysis reveals that this invention, based on metal ion dual doping, first anchors the first doping element Nb and / or V onto carbon nanotubes to form a base solution. Then, iron and phosphorus sources are simultaneously added and reacted for a period of time. Next, iron, phosphorus, and the second doping element Mn and / or Co are simultaneously added and reacted for another period. This avoids the interference of competition between doping elements, creating spatial order in the doping and achieving a seamless transition from external Mn and / or Co enrichment to internal Nb and / or V enrichment, effectively improving electronic conductivity. Furthermore, during this process, the pre-added iron and phosphorus sources react with the first doping element to generate crystal nuclei. The subsequently added phosphorus, iron, and second doping element sources then use these as nuclei to grow again, forming new crystal nuclei. This creates a gradation mechanism where small crystal nuclei continuously fill larger ones, thus improving the compaction performance of the prepared lithium iron phosphate cathode material.
[0070] Combining the electron micrographs of the cathode materials in Examples 1 and 8, it can be seen that through the distributed doping and the anchoring effect of carbon nanotubes in this invention, crystal nuclei with different sizes can be obtained, and after calcination, particles with different sizes are obtained, thus improving the compaction density.
[0071] In addition to the above embodiments, the recycling process and parameters of the present invention can achieve the technical effects claimed above, so no further testing is required to verify them.
Claims
1. A high-density, gradient dual-doped lithium iron phosphate cathode material, characterized in that, It is prepared by the following steps: (1) Disperse carbon nanotubes in an ethylene glycol solution containing a surfactant and a first dopant source, so that the first dopant is anchored on the carbon nanotubes to obtain a uniform dispersion. (2) Using the dispersion as the reaction base liquid, heat it to 50-80℃, keep the pH of the system at 2.5-3, and under stirring conditions, first add iron source, phosphorus source and oxidant to the reaction base liquid at the same time. The addition rate is 5-10mL / min and the addition time is 20-30min. The precursor crystal nuclei of the first doped element gradient doping are generated on the carbon nanotubes. Iron source, phosphorus source, oxidant and second doping element source are added to the reaction base solution at a rate of 5-15 mL / min and a time of 1-3 h to generate a double-doped primary particle precursor slurry with a concentration gradient using carbon nanotubes as the framework structure. (3) Add a pore-forming agent to the primary particle precursor slurry and heat treat it, then filter to obtain the modified precursor; (4) After washing and drying the modified precursor, it is mixed with lithium source and carbon source, and pre-sintered at 320-460℃ for 2-4h under an inert atmosphere, and then sintered at 660-780℃ for 6-10h to obtain high-compact, gradient-doped lithium iron phosphate material.
2. The high-density, gradient-doubly doped lithium iron phosphate cathode material of claim 1, wherein, The doping element in the first doping element source is selected from Nb and / or V, and the doping element in the second doping element source is selected from Mn and / or Co.
3. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, The number of moles of the doping element in the first doping element source is 1-2% of the number of moles of ferrous sulfate, and the number of moles of the doping element in the second doping element source is 1-1.5% of the number of moles of ferrous sulfate.
4. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The mass of the added carbon nanotubes is 0.1-0.8% of the theoretically generated iron phosphate mass.
5. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1 or 2, characterized in that, The first dopant source is selected from at least one of niobium ammonium oxalate monohydrate, niobium ethanol, ammonium metavanadate, and vanadium acetylacetonate; the second dopant source is selected from at least one of manganese sulfate, manganese acetate, manganese nitrate, cobalt sulfate, and cobalt acetate.
6. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The surfactant is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, and hexadecyltrimethylammonium bromide, and the mass ratio of the surfactant to carbon nanotubes is (1-1.5):
1.
7. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The Li:Fe:P molar ratio of the lithium source, iron source, and phosphorus source is (1.01-1.05):1:1; wherein the iron source is selected from ferrous sulfate, ferrous nitrate, or ferrous chloride, the phosphorus source is selected from phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate, and the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium nitrate.
8. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The oxidant is selected from hydrogen peroxide or ammonium persulfate, and its molar amount is 0.5-1 times the total molar amount of iron source.
9. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The carbon source is selected from at least one of glucose, sucrose, and citric acid, and its added mass is 6-8% of the theoretical mass of the primary particle precursor.
10. The high-pressure, gradient-doped lithium iron phosphate cathode material according to claim 1, characterized in that, The pore-forming agent is selected from at least one of polyethylene glycol, hexadecyltrimethylammonium bromide, and polymethyl methacrylate, and its added mass is 2-6% of the theoretical mass of the primary particle precursor.