Modified lithium iron manganese phosphate material and preparation method thereof
By using a first carbon source composite consisting of polyethylene glycol and pitch, and a second carbon source composite consisting of carbon nanotubes and cellulose, a gradient coating structure is formed in lithium iron manganese phosphate materials, which solves the crystal instability problem caused by manganese and significantly improves the cycling stability and capacity retention of the materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 湖南泓原新能源科技有限公司
- Filing Date
- 2026-05-11
- Publication Date
- 2026-06-05
AI Technical Summary
The addition of manganese to lithium iron manganese phosphate materials leads to instability in the crystal structure. Especially during high temperature and long-term charge and discharge processes, manganese ions are prone to detach from the crystal structure, resulting in capacity decay and service life loss.
A first carbon source composite consisting of polyethylene glycol and asphalt, and a second carbon source composite consisting of carbon nanotubes and cellulose, are used to enhance the cycling stability of the material by forming a gradient coating system.
It significantly improves the cycle stability of modified lithium iron manganese phosphate materials during high temperature and long-term charge-discharge processes, and enhances the capacity retention of the materials.
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Abstract
Description
Technical Field
[0001] This application relates to the field of lithium iron manganese phosphate materials technology, and more specifically, to a modified lithium iron manganese phosphate material and its preparation method. Background Technology
[0002] Lithium batteries are a type of battery that uses lithium metal or lithium alloy as the positive / negative electrode material and a non-aqueous electrolyte solution. They are mainly divided into two categories: lithium metal batteries and lithium-ion batteries. Their positive electrode materials are mostly lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, ternary materials, etc. Different materials affect voltage, capacity and safety.
[0003] Lithium iron manganese phosphate (LMP) is a novel cathode material for lithium-ion batteries. By doping LMP with manganese to form a solid solution, it exhibits significant advantages in energy density, safety, and cost. The addition of manganese increases the cathode material's voltage platform from 3.4V to 4.1V, theoretically increasing the energy density by 15%-20% compared to LMP, with some products reaching 180-230 Wh / kg, approaching the level of ternary lithium batteries. Moreover, for the same battery weight, LMP batteries can extend the driving range by about 20%, effectively alleviating the "range anxiety" of electric vehicles. At the same time, LMP inherits the olivine structure of LMP, achieving a thermal runaway temperature exceeding 600℃ and a needle-puncture non-flammability rate of up to 98.7%, significantly superior to ternary lithium batteries. Furthermore, it does not require precious metals such as cobalt and nickel, and its cost is 20-30% lower than that of ternary lithium batteries.
[0004] Regarding the aforementioned technologies, the inventors believe that while the addition of manganese can bring about the above-mentioned application advantages, the addition of manganese can also lead to instability in the crystal structure. Especially during high temperature and long-term charge and discharge processes, manganese ions are prone to detach from the crystal structure, resulting in severe capacity decay and ultimately causing a significant loss in service life.
[0005] Therefore, there is an urgent need to propose a solution to address the aforementioned technical problems. Summary of the Invention
[0006] To improve the cycle stability of lithium iron manganese phosphate materials during high temperature and long-term charge-discharge processes, this application provides a modified lithium iron manganese phosphate material and its preparation method.
[0007] In a first aspect, this application provides a method for preparing a modified lithium iron manganese phosphate material, employing the following technical solution: A method for preparing a modified lithium iron manganese phosphate material includes the following steps: (1) Add iron source, lithium source, manganese source and phosphorus source to ethylene glycol solution, mix, dry and sinter to obtain precursor material; (2) The precursor material obtained in step (1) is ball-milled, sieved and mixed with the first carbon source compound. After ball milling, dispersion, drying and sintering, a primary coating product is obtained. (3) The primary coating product obtained in step (2) is mixed with the second carbon source compound, and after ball milling dispersion, drying and sintering, modified lithium iron manganese phosphate material is obtained; The first carbon source compound is composed of polyethylene glycol and asphalt; The second carbon source compound is composed of carbon nanotubes and cellulose.
[0008] By adopting the above technical solutions, in the application of the first carbon source composite, polyethylene glycol has a low-temperature pore-forming effect. During sintering, the oxygen-containing functional groups formed by its initial decomposition can chemically bond with the surface of lithium iron manganese phosphate, forming nanoscale pores. Then, the dense carbon layer formed after the asphalt carbonization fills the nanoscale pores formed by polyethylene glycol, forming a soft-hard bonded carbon layer structure. This not only reduces the dissolution of manganese ions at high temperatures but also effectively inhibits lattice collapse. In the application of the second carbon source composite, cellulose, as a bio-based carbon source, forms a porous carbon structure after high-temperature pyrolysis, enhancing lithium ion diffusion. The carbon nanotubes, while constructing a three-dimensional conductive network, can penetrate the porous carbon structure, which not only enhances the structural toughness and stability, effectively constrains the displacement of carbon nanotubes during charging and discharging, and helps suppress lattice strain, but also effectively disperses heat during charging and discharging, reducing the adverse effects of high temperature during subsequent charging and discharging. Furthermore, the combination of the first carbon source complex and the second carbon source complex forms a gradient coating system, which exerts excellent synergistic enhancement effect, thereby significantly improving the cycle stability of modified lithium iron manganese phosphate materials during high temperature and long-term charging and discharging.
[0009] Preferably, the first carbon source compound is composed of polyethylene glycol and asphalt in a weight ratio of 1:(1-2).
[0010] By adopting the above technical solution and within the above ratio range, the porous carbon layer formed by polyethylene glycol and the dense carbon network formed by pitch can establish an excellent complementary structure, and they exhibit strong compatibility during sintering, thereby enabling the first carbon source compound to exert a stable and better corresponding effect.
[0011] Preferably, the first carbon source compound is 4-6% of the weight of the precursor material.
[0012] By adopting the above technical solution and the above proportion of addition, while forming a continuous conductive network, it is also possible to avoid excessive addition that would result in an excessively thick carbon layer after the second carbon source compound takes effect, which would not easily have an adverse effect on lithium ion diffusion. In this way, under the premise that polyethylene glycol and asphalt play an excellent synergistic role, excellent conductivity and cycle stability are taken into account. After being combined with the carbon layer structure formed by the application of the second carbon source compound, the cycle stability of modified lithium iron manganese phosphate material can be significantly improved during high temperature and long-term charge and discharge.
[0013] Preferably, the second carbon source compound is composed of carbon nanotubes and cellulose in a weight ratio of 1:(2.5-4).
[0014] By adopting the above technical solution, when the weight ratio of carbon nanotubes and cellulose is lower or higher than the above range, the structural toughness enhancement effect brought by carbon nanotubes will be insignificant and cellulose will have difficulty forming a uniform and stable porous carbon structure, which will greatly reduce the effect of the combination of the two. Therefore, within the above ratio range, the second carbon source compound can be guaranteed to exert a stable and better corresponding effect.
[0015] Preferably, the second carbon source compound is 3-5% of the weight of the primary coating product.
[0016] By adopting the above technical solution, when the amount of the second carbon source compound is lower than the above range, the density of the complex structure formed between carbon nanotubes and cellulose is insufficient, while when it is higher than the above range, it is easy to induce the aggregation of carbon nanotubes. Therefore, at the above ratio, not only can the above application defects be overcome, but the synergistic effect between carbon nanotubes and cellulose can also be better, and the carbon layer structure formed by the interaction with the first carbon source compound can show excellent stable complex synergistic effect, thereby improving the cycle stability of modified lithium iron manganese phosphate material at high temperature and during long-term charge and discharge.
[0017] Preferably, the iron source is one or a combination of several of ferrous sulfate, ferric nitrate, ferric acetate and ferric chloride; The lithium source is one or a combination of several of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium acetate, lithium oxalate, lithium carbonate, and lithium citrate. The manganese source is one or a combination of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride; The phosphorus source is one or a combination of several of the following: phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate.
[0018] By adopting the above technical solutions, the aforementioned types of iron, lithium, manganese, and phosphorus sources are all suitable for the preparation of modified lithium iron manganese phosphate materials.
[0019] Preferably, the iron source, lithium source, manganese source, and phosphorus source are provided in a Fe:Li:Mn:P molar ratio of 1:(1.8-2.6):(1.4-2.0):(1.8-2.4).
[0020] By adopting the above technical solution, under the above ratio, iron, lithium, manganese and phosphorus can fully combine and interact, lithium can promote phase transformation, manganese and iron can balance structural stability, and phosphorus can suppress side reactions, which is conducive to finally obtaining high-quality and stable modified lithium iron manganese phosphate material.
[0021] Preferably, in step (2), the sintering operation is as follows: first sintering at 400-500℃ for 0.5-1h, and then sintering at 700-800℃ for 2-4h.
[0022] By adopting the above technical solution, the polyethylene glycol is first sintered at 400-500℃ for 0.5-1h to allow it to decompose completely, and then sintered at 700-800℃ for 2-4h. At this time, the asphalt carbonizes to form a continuous conductive network, which synergistically combines with the porous carbon layer derived from polyethylene glycol, thereby ensuring that the first carbon source compound can play a full role in the application process.
[0023] Preferably, in step (3), the sintering operation is as follows: first sinter at 400-500℃ for 0.5-1h, and then sinter at 700-800℃ for 2-3h.
[0024] By adopting the above technical solution, sintering at 400-500℃ for 0.5-1h first can completely decompose cellulose, and the carbon dioxide gas generated by pyrolysis can form nanoscale pores. Then, sintering at 700-800℃ for 2-4h can form a uniform and stable composite carbon layer between carbon nanotubes and cellulose-derived porous carbon structure, thereby ensuring that the second carbon source compound can play a full role in the application process.
[0025] Secondly, this application provides a modified lithium iron manganese phosphate material, which adopts the following technical solution: A modified lithium iron manganese phosphate material, prepared by the above method, exhibits excellent cycle stability when used at high temperatures and during long-term charge-discharge processes.
[0026] In summary, this application has the following beneficial effects: In the preparation of modified lithium iron manganese phosphate materials, this application sequentially uses a first carbon source composite composed of polyethylene glycol and asphalt, and a second carbon source composite composed of carbon nanotubes and cellulose. By forming a gradient coating system and exerting excellent synergistic effects, the modified lithium iron manganese phosphate material can be significantly improved in terms of cycle stability during high temperature and long-term charge and discharge processes. Detailed Implementation
[0027] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.
[0028] Unless otherwise specified, all raw materials used in the preparation examples, embodiments and comparative examples of this application are commercially available.
[0029] Polyethylene glycol was purchased from Shanghai Kaisheng New Materials Co., Ltd. as PEG6000; The asphalt was purchased from Hebei Lumao Energy Technology Co., Ltd., and the modified asphalt model was CF001. The carbon nanotube raw material was purchased from Beijing Deco Island Gold Technology Co., Ltd., and the model was CNT-202. The cellulose was purchased from Nanjing Qinhai Trading Co., Ltd. as Ashland cellulose, model HHBER250.
[0030] Example Example 1
[0031] A modified lithium iron manganese phosphate material is prepared by the following steps: (1) Add iron source, lithium source, manganese source and phosphorus source to ethylene glycol solution. The ethylene glycol solution is 18 times the total mass of iron source, lithium source, manganese source, phosphorus source, functional additives and carbon nanotubes. The volume ratio of ethylene glycol to water in the ethylene glycol solution is 1:2. After mixing, drying at 105℃ for 1.5h, sintering at 375℃ for 1.5h, and then sintering at 750℃ for 4h, the precursor material is obtained. (2) The precursor material obtained in step (1) is ball-milled, sieved through a 300-mesh sieve, and mixed with the first carbon source compound. After ball milling and dispersion for 1 hour, drying at 105°C for 2 hours, and sintering, a primary coating product is obtained. (3) The primary coating product obtained in step (2) is mixed with the second carbon source compound, dispersed by ball milling for 1 hour, dried at 105°C for 2 hours and sintered to obtain the modified lithium iron manganese phosphate material.
[0032] Note: In the above operations, the iron source is ferrous sulfate, the lithium source is lithium carbonate, the manganese source is manganese acetate, and the phosphorus source is ammonium dihydrogen phosphate. The iron, lithium, manganese, and phosphorus sources are in the Fe:Li:Mn:P molar ratio of 1:2.2:1.7:2.1. The first carbon source compound is composed of polyethylene glycol and asphalt in a weight ratio of 1:1.5, and the first carbon source compound accounts for 5% of the weight of the precursor material. The second carbon source compound is composed of carbon nanotubes and cellulose in a weight ratio of 1:3.25, and the second carbon source compound accounts for 4% of the weight of the primary coating product. In step (2), the sintering operation is as follows: first sinter at 450℃ for 0.75h, and then sinter at 750℃ for 3h. In step (3), the sintering operation is as follows: first sinter at 450℃ for 0.75h, and then sinter at 750℃ for 2.5h. Example 2
[0033] A modified lithium iron manganese phosphate material differs from Example 1 in that the iron source, lithium source, manganese source, and phosphorus source are in the Fe:Li:Mn:P molar ratio of 1:1.8:1.4:1.8. Example 3
[0034] A modified lithium iron manganese phosphate material differs from Example 1 in that the iron source, lithium source, manganese source, and phosphorus source are in the Fe:Li:Mn:P molar ratio of 1:2.6:2.0:2.4. Example 4
[0035] A modified lithium iron manganese phosphate material differs from Example 1 in that the first carbon source compound is composed of polyethylene glycol and asphalt in a weight ratio of 1:1. Example 5
[0036] A modified lithium iron manganese phosphate material differs from Example 1 in that the first carbon source compound is composed of polyethylene glycol and asphalt in a weight ratio of 1:2. Example 6
[0037] A modified lithium iron manganese phosphate material, which differs from Example 1 in that the first carbon source compound is 4% of the weight of the precursor material. Example 7
[0038] A modified lithium iron manganese phosphate material, which differs from Example 1 in that the first carbon source compound is 6% of the weight of the precursor material. Example 8
[0039] A modified lithium iron manganese phosphate material differs from Example 1 in that the second carbon source compound is composed of carbon nanotubes and cellulose in a weight ratio of 1:2.5. Example 9
[0040] A modified lithium iron manganese phosphate material differs from Example 1 in that the second carbon source compound is composed of carbon nanotubes and cellulose in a weight ratio of 1:4. Example 10
[0041] A modified lithium iron manganese phosphate material, which differs from Example 1 in that the second carbon source compound is 3% of the weight of the primary coating product. Example 11
[0042] A modified lithium iron manganese phosphate material, which differs from Example 1 in that the second carbon source compound is 5% of the weight of the primary coating product. Example 12
[0043] A modified lithium iron manganese phosphate material differs from Example 1 in that, in step (2), the sintering operation is: first sintering at 400°C for 1 hour, and then sintering at 800°C for 2 hours. Example 13
[0044] A modified lithium iron manganese phosphate material differs from Example 1 in that, in step (2), the sintering operation is: first sintering at 500°C for 0.5h, and then sintering at 700°C for 4h. Example 14
[0045] A modified lithium iron manganese phosphate material differs from Example 1 in that, in step (3), the sintering operation is: first sintering at 400°C for 1 hour, and then sintering at 800°C for 2 hours. Example 15
[0046] A modified lithium iron manganese phosphate material differs from Example 1 in that, in step (3), the sintering operation is: first sintering at 500°C for 0.5h, and then sintering at 700°C for 3h.
[0047] Comparative Example Comparative Example 1 A modified lithium iron manganese phosphate material, which differs from Example 1 in that it does not use a second carbon source compound.
[0048] Comparative Example 2 A modified lithium iron manganese phosphate material, which differs from Example 1 in that the first carbon source compound is not used.
[0049] Comparative Example 3 A modified lithium iron manganese phosphate material, which differs from Example 1 in that it does not use the first carbon source compound and the second carbon source compound.
[0050] Comparative Example 4 A modified lithium iron manganese phosphate material, which differs from Example 1 in that polyethylene glycol is not used in the first carbon source compound.
[0051] Comparative Example 5 A modified lithium iron manganese phosphate material, which differs from Example 1 in that no asphalt is used in the first carbon source compound.
[0052] Comparative Example 6 A modified lithium iron manganese phosphate material, which differs from Example 1 in that carbon nanotubes are not used in the second carbon source compound.
[0053] Comparative Example 7 A modified lithium iron manganese phosphate material, which differs from Example 1 in that cellulose is not used in the second carbon source compound.
[0054] Performance testing Test samples: The modified lithium iron manganese phosphate materials obtained in Examples 1-15 were selected as test samples 1-15, and the modified lithium iron manganese phosphate materials obtained in Comparative Examples 1-7 were selected as control samples 1-7.
[0055] Experimental method: Using N-methylpyrrolidone as a dispersant, modified lithium iron manganese phosphate material, carbon black, and PVDF (polyvinylidene fluoride) were mixed at a mass ratio of 80:10:10 to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto carbon-coated aluminum foil with a coating density of 3 cm³. 2 / mg, dried in an oven at 80℃ for 2h to obtain the positive electrode; under an argon atmosphere in a glove box, using a Celgard 2500 separator, lithium metal sheet as the negative electrode, and 1mol / L electrolyte (EC, EMC and DMC in a volume ratio of 1:1:1); CR2032 button half-cells were assembled in the order of negative electrode, electrolyte, separator, electrolyte, and positive electrode.
[0056] The capacity retention rate of the battery was tested after 500 charge-discharge cycles at 55℃ and a current density of 3C (1C = 200mAh g-1). After performing the above tests on test samples 1-15 and control samples 1-7, the test results are recorded in Table 1.
[0057] Table 1. Test results of test samples 1-15 and control samples 1-7 As can be seen from Example 1 and Comparative Examples 1-3, and Table 1, in the preparation of modified lithium iron manganese phosphate materials, this application sequentially uses a first carbon source complex composed of polyethylene glycol and pitch, and a second carbon source complex composed of carbon nanotubes and cellulose. The combined use of these two compounds significantly improves the cycle stability of the modified lithium iron manganese phosphate material during high temperatures and long-term charge-discharge cycles. The capacity retention rate of the obtained modified lithium iron manganese phosphate material, as tested above, shows a significant improvement. While using only the first or second carbon source complex can improve the effect, the improvement is limited, and the sum of the improvements from using either compound alone is far less than the improvement from their combination. Therefore, the first and second carbon source complexes can bring a significant improvement effect (1+1>2) in the preparation of modified lithium iron manganese phosphate materials.
[0058] Based on Example 1 and Comparative Examples 2, 4-5, and Table 1, it can be seen that if only polyethylene glycol or asphalt is used in the first carbon source compound, the corresponding effect brought about by the combined use of the first carbon source compound and the second carbon source compound will be greatly reduced. Moreover, from the perspective of the improvement effect brought about by the application of polyethylene glycol or asphalt alone, it can be found that polyethylene glycol and asphalt have a compound synergistic effect, which can ultimately significantly improve the cycle stability of modified lithium iron manganese phosphate material during high temperature and long-term charge and discharge.
[0059] Based on Example 1 and Comparative Examples 1, 6-7, and Table 1, it can be seen that if only carbon nanotubes or cellulose are used in the second carbon source compound, the corresponding effect brought about by the combined use of the second carbon source compound and the first carbon source compound will be greatly reduced. Moreover, from the perspective of the improvement effect brought about by the application of single carbon nanotubes or cellulose, it can be found that there is a synergistic effect between carbon nanotubes and cellulose, which can ultimately significantly improve the cycle stability of modified lithium iron manganese phosphate materials during high temperature and long-term charge and discharge processes.
[0060] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A method for preparing a modified lithium iron manganese phosphate material, characterized in that, Includes the following steps: (1) Add iron source, lithium source, manganese source and phosphorus source to ethylene glycol solution, mix, dry and sinter to obtain precursor material; (2) The precursor material obtained in step (1) is ball-milled, sieved and mixed with the first carbon source compound. After ball milling, dispersion, drying and sintering, a primary coating product is obtained. (3) The primary coating product obtained in step (2) is mixed with the second carbon source compound, and after ball milling dispersion, drying and sintering, modified lithium iron manganese phosphate material is obtained; The first carbon source compound is composed of polyethylene glycol and asphalt; The second carbon source compound is composed of carbon nanotubes and cellulose.
2. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The first carbon source compound is composed of polyethylene glycol and asphalt in a weight ratio of 1:(1-2).
3. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The first carbon source compound is 4-6% of the weight of the precursor material.
4. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The second carbon source compound is composed of carbon nanotubes and cellulose in a weight ratio of 1:(2.5-4).
5. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The second carbon source compound is 3-5% of the weight of the primary coating product.
6. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The iron source is one or a combination of several of ferrous sulfate, ferric nitrate, ferric acetate and ferric chloride; The lithium source is one or a combination of several of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium acetate, lithium oxalate, lithium carbonate, and lithium citrate. The manganese source is one or a combination of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride; The phosphorus source is one or a combination of several of the following: phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate.
7. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: The iron source, lithium source, manganese source, and phosphorus source are supplied in a Fe:Li:Mn:P molar ratio of 1:(1.8-2.6):(1.4-2.0):(1.8-2.4).
8. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: In step (2), the sintering operation is as follows: first sinter at 400-500℃ for 0.5-1h, and then sinter at 700-800℃ for 2-4h.
9. The method for preparing the modified lithium iron manganese phosphate material according to claim 1, characterized in that: In step (3), the sintering operation is as follows: first sinter at 400-500℃ for 0.5-1h, and then sinter at 700-800℃ for 2-3h.
10. A modified lithium iron manganese phosphate material, characterized in that: Obtained by the preparation method according to any one of claims 1-9.