Preparation method of MOF-derived porous carbon thin layer coated lithium manganese iron phosphate material
By preparing MOF-derived porous carbon thin-layer coated lithium manganese iron phosphate materials, the problems of conductivity and manganese ion precipitation in lithium manganese iron phosphate were solved, and the high conductivity and excellent electrochemical performance of the materials were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YIDU XINGFA CHEMICAL CO LTD
- Filing Date
- 2023-03-22
- Publication Date
- 2026-06-02
AI Technical Summary
Lithium manganese iron phosphate materials have poor conductivity and low lithium-ion diffusion rate, resulting in poor rate performance and cycle performance, and the deposition of manganese ions leads to electrochemical instability.
Metal-organic framework (MOF) materials were synthesized by hydrothermal method. They were then mixed with lithium manganese iron phosphate precursor and prepared by centrifugation and calcination to form MOF-derived porous carbon thin layer coated lithium manganese iron phosphate material. The nitrogen-containing heteroatom MOF was used as a carbon precursor to form a carbon-nitrogen co-doped porous carbon thin layer, which improved the conductivity and suppressed the precipitation of manganese ions.
It improves the electrical conductivity and rate performance of lithium manganese iron phosphate materials, inhibits manganese ion deposition, and improves electrochemical performance and cycle life.
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Figure CN116344762B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery cathode material preparation, specifically to a method for preparing lithium manganese iron phosphate coated with a porous carbon thin layer derived from a metal-organic framework (MOF) material. Background Technology
[0002] The core of lithium-ion battery operation lies in the insertion and extraction of lithium ions. The cathode material, as the source of lithium ions, is crucial for improving battery performance, and its cost accounts for the largest proportion of the overall cost of a lithium-ion battery. Therefore, the cost of the cathode material determines the cost of the lithium-ion battery. Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) possesses higher voltage, higher energy density, and better low-temperature performance. In terms of capacity, both have a theoretical capacity of 170 mAh / g, but LFP's voltage plateau is only 3.4V, while LFP can reach 4.1V, resulting in a 15% increase in energy density for LMFP compared to LFP. Regarding low-temperature performance, various nano-lithium iron phosphates retain approximately 67% of their capacity at -20℃, while LFP can maintain 71%. While theoretically, lithium manganese iron phosphate (LFP) possesses the safety and cycle advantages of lithium iron phosphate (LFP) and has a higher energy density, its hexagonal close-packed structure, with FeO6 and MnO6 located on octahedra and interconnected via PO4 tetrahedra, lacks a continuous FeO6 (MnO6) edge-sharing octahedral network, resulting in poor conductivity. Furthermore, the PO4 tetrahedra positioned between the FeO6 (MnO6) octahedra obstruct lithium-ion diffusion channels, restricting their movement to one-dimensional channels and leading to a low lithium-ion diffusion rate and poor rate performance. These drawbacks prevent LFP from fully realizing its electrochemical performance, thus limiting its large-scale application. Additionally, the presence of both Fe and Mn elements introduces two different operating voltages, and the dual-voltage plateau is unstable. Manganese ions are also affected by the Jahn-Teller effect, leading to dissolution and deposition on the negative electrode surface, damaging the SEI film.
[0003] Carbon is a commonly used conductive material. Constructing a fast-conducting network with conductive carbon and lithium manganese iron phosphate allows electrons to migrate rapidly between active materials during charging and discharging, reducing battery internal resistance and polarization during charging and discharging. Simultaneously, carbon coating reduces the contact surface area between the active material and the electrolyte, thus preventing side reactions and improving high-temperature and cycle performance. Furthermore, surface carbon coating effectively inhibits the aggregation and growth of modified material particles, maintaining the nanostructure of the particles and effectively reducing Li... + The diffusion distance within the active particles gives the material superior rate performance.
[0004] Porous coordination polymers formed by organic bridging molecules (i.e., ligands) and metal ions / clusters are commonly referred to as metal-organic frameworks (MOFs). MOFs are crystalline solid compounds, typically with relatively long organic ligands acting as connectors, allowing them to achieve porosity and surface area far exceeding that of other materials. Furthermore, through rational molecular design and synthetic assembly methods, a wide variety of coordination structures can be obtained between the organic bridging ligands and metal ions / clusters. MOF derivatives refer to nanoporous materials (porous carbon, metal oxides, etc.) with different properties obtained by using MOFs as templates and through physical or chemical treatments. MOF derivatives retain some of the unique structures of MOFs, making them highly advantageous for use as electrode materials. Patent CN104124453A improves conductivity and rate performance through nanostructuring and graphylene composite methods. Patent CN105226273A uses the sol-gel method to prepare nanoscale lithium iron phosphate gel and lithium manganese phosphate sol, respectively, which reduces the lithium ion diffusion path and improves the rate performance. The sol-gel method can uniformly coat the carbon source on the surface of the active material and can uniformly mix the two transition metal elements to obtain uniform lithium manganese iron phosphate. However, the method is complicated and the experiment is difficult.
[0005] Based on this, the development of a modified lithium manganese iron phosphate material with excellent conductivity and simple preparation is of great significance in solving the current outstanding problems and accelerating the application of lithium manganese iron phosphate. Summary of the Invention
[0006] To address the problems existing in the prior art, the present invention aims to provide a method for preparing lithium manganese iron phosphate. A conductive material (carbon material) is uniformly coated onto the particle surface to improve conductivity, prevent particle growth and agglomeration, and effectively inhibit manganese ion precipitation, thereby improving electrochemical performance and cycle life. Metal-organic framework (MOF) materials are synthesized via a hydrothermal method. Subsequently, lithium manganese iron phosphate is uniformly dispersed in a phosphate buffer solution, and the MOF material is mixed in. After centrifugation and calcination, MOF-derived porous carbon thin-layer coated lithium manganese iron phosphate material is finally obtained. Using MOF materials containing nitrogen heteroatoms as carbon precursors not only allows the material surface to be influenced by functional groups but also yields self-doped bulk carbon materials. The doped nitrogen element can cause adjacent carbon atoms to generate partial positive charges due to electron affinity, improving the electronic state density, conductivity, and electrochemical activity of the carbon material.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] A method for preparing MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material includes the following steps:
[0009] S1. Weigh the metal salt, organic ligand, and solvent accurately according to the ratio, place them in a glass container, mix and stir evenly, then transfer them to a polytetrafluoroethylene-lined stainless steel reactor, place them in a high-temperature oven and react at a certain temperature for a period of time, and then obtain the metal-organic framework (MOF) material through washing, centrifugation, drying and other steps.
[0010] S2. Weigh the iron source, lithium source, manganese source and phosphorus source accurately according to the proportion, mix them evenly in the solvent, stir and react for a certain time to obtain a mixed slurry, and obtain the precipitate by centrifugation, which is the precursor of lithium manganese iron phosphate.
[0011] S3. The products from S1 and S2 are uniformly dispersed in phosphate buffer solution and then mixed by low-temperature ultrasonication to obtain a homogeneous slurry. The obtained slurry is then ground, and the grinding method can include, but is not limited to, ball milling and sand milling. The ground slurry is then spray-dried to obtain powder.
[0012] S4. Place the powder in a graphite sagger, raise it to a certain temperature in an inert atmosphere and sinter for a period of time, then cool it naturally to room temperature to obtain a carbon-nitrogen co-doped lithium manganese iron phosphate material coated with a MOF-derived porous carbon thin layer.
[0013] As a preferred embodiment, the metal salt in S1 is a metal nitrate (including but not limited to zinc nitrate hexahydrate, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate) or a metal chloride (including but not limited to zinc chloride, cobalt chloride, and nickel chloride).
[0014] As a preferred embodiment, the organic ligands in S1 include, but are not limited to, 2-methylimidazole, pyromellitic acid, 3-amino-1,2,4-triazole, thiophene-2,5-dicarboxylic acid, and 1H-1,2,4-triazole.
[0015] As a preferred embodiment, the solvent in S1 is an organic solvent, including but not limited to methanol, anhydrous ethanol, DMF, or a mixture of organic solvent and water as a mixed solvent.
[0016] As a preferred embodiment, in step S1, the mixing and stirring time of the metal salt, organic ligand, and solvent should be no less than 60 minutes. When the solid has poor solubility, ultrasonic or heating dissolution should be used, and the temperature should be controlled below 60°C to prevent excessive solvent evaporation.
[0017] In the above scheme, in step S1, the reaction temperature is 120-200℃ and the reaction time is 12-72h; the washing uses water, methanol, anhydrous ethanol, DMF or a mixture of several; the drying uses a vacuum oven at a temperature of 60-80℃ for a time of not less than 8h.
[0018] As a preferred embodiment, the iron source in S2 includes ferric phosphate and ferrous sulfate heptahydrate; the lithium source includes lithium carbonate and lithium hydroxide; the manganese source includes manganese carbonate, manganese oxide, and manganese tetroxide; and the phosphorus source includes phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.
[0019] A metal-organic framework-derived porous carbon thin-layer coated lithium manganese iron phosphate cathode material is expressed by the general formula LiMn. x Fe 1-x PO4 / C. Where x ranges from 5 to 9; that is, Mn 2+ Fe 2+ PO4 3- The molar ratio of the phosphate, manganese salt, and iron salt is calculated to be 1:(0.5-0.9):(0.1-0.5); with Li + The amount of lithium salt used is calculated in relation to PO4. 3- The molar ratio is 1.00-1.05:1; the molar amount is calculated based on carbon atoms to ensure that LiMn x Fe 1-x The carbon content in PO4 / C is 1.5-3.3% by weight.
[0020] As a preferred embodiment, the solvent in S2 is water; the mixture is stirred at room temperature for 0.5-6 hours at a stirring speed of 100-500 rpm.
[0021] As a preferred embodiment, the phosphate buffer in S3 is a weakly alkaline phosphate buffer with a pH of 7.8-9.0. The phosphate buffer is prepared by adding potassium dihydrogen phosphate solution to sodium hydroxide and adjusting the pH to 7.8-9.0.
[0022] As a preferred embodiment, the lithium manganese iron phosphate precursor in S3 is ultrasonically dispersed at low temperature (0-10℃) for 30-60 minutes; the concentration of the lithium manganese iron phosphate precursor is 50-150 mg / mL, such as 50 mg / mL, 60 mg / mL, 70 mg / mL, 80 mg / mL, 100 mg / mL, 120 mg / mL, 150 mg / mL, etc.
[0023] As a preferred embodiment, the mass ratio of lithium manganese iron phosphate precursor to MOF material in S3 varies depending on the type of material, and the mass ratio is 100:0.62-5:1, preferably 20:3-25:1.
[0024] As a preferred embodiment, the grinding process in S3 is performed using a Langling mechanical sand mill (NT-0.3L), with a mill speed of 1000-1300 rpm and a grinding time of 0.5-2.5 hours. Spray drying is performed using a Shanghai Shunyi spray dryer (SP-1500).
[0025] As a preferred embodiment, the material sintering in S4 is carried out in a tube furnace, with an inert atmosphere of either high-purity nitrogen or argon, a sintering temperature of 600-900℃, a heating rate of 2-10℃ / min, preferably 2-5℃ / min, a holding time of 5-15h, and after being pulverized to a qualified particle size, a carbon-nitrogen co-doped lithium manganese iron phosphate material with MOF-derived porous carbon thin film coating is obtained.
[0026] This invention provides a method for preparing a porous carbon thin-layer coated lithium manganese iron phosphate cathode material derived from a metal-organic framework (MOF). The method involves preparing a lithium manganese iron phosphate precursor material, mixing it with MOFs in different proportions in phosphate buffer solutions at different pH values to obtain a homogeneous slurry, and then drying and sintering to obtain a thin-layer coated modified lithium manganese iron phosphate material. This material can be divided into an inner layer and a coating layer. The main component of the inner layer is LiMnFePO4, and the coating layer is a bulk nitrogen-doped carbon coating layer.
[0027] It should be understood that this invention prepares MOF materials, then uniformly disperses lithium manganese iron phosphate in a phosphate buffer solution, mixes in the MOF materials, and obtains a MOF-derived porous carbon thin-layer coated carbon-nitrogen co-doped lithium manganese iron phosphate material through grinding, drying, and calcination. Using MOF materials containing nitrogen heteroatoms as carbon precursors not only allows the material surface to be influenced by functional groups, but also enables the acquisition of bulk nitrogen-self-doped carbon materials without additional steps. The doped nitrogen can cause adjacent carbon atoms to generate partial positive charges due to electron affinity, thereby improving the electronic state density, conductivity, and electrochemical activity of the carbon material.
[0028] Compared with the prior art, the present invention has the following advantages:
[0029] (1) This invention prepares a MOF material containing nitrogen heteroatoms, and through its interaction with a lithium manganese iron phosphate precursor, prepares a porous carbon-nitrogen co-doped lithium manganese iron phosphate modified material with a thin carbon coating. This material effectively reduces the resistivity of the cathode material and increases its conductivity through the thin carbon coating, preventing particle growth and agglomeration, thereby maintaining the nanostructure of the particles and effectively reducing Li + The increased diffusion distance within the active particles gives the material superior rate performance. It also effectively suppresses manganese ion release, improves electrochemical performance, and extends cycle life.
[0030] (2) After mixing and grinding the precursor material of lithium manganese iron phosphate with carbon source, it is calcined. The MOF-derived carbon source will dissolve first at high temperature. The dissolved material has good fluidity and can be uniformly penetrated and coated on the surface of the material to form a thin layer of carbon coating. Attached Figure Description
[0031] Figure 1Electrochemical performance curves of lithium manganese iron phosphate coated with porous carbon thin films derived from the metal-organic framework material prepared in Example 1.
[0032] Figure 2 This is a scanning electron microscope image of a porous carbon thin film coated with lithium manganese iron phosphate derived from the metal-organic framework material prepared in Example 1. Detailed Implementation
[0033] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.
[0034] Example 1
[0035] (1) Preparation of metal-organic framework (MOF) materials
[0036] Dissolve 6.92 g of zinc chloride, 2.11 g of sodium hydroxide, and 4.06 g of 2-methylimidazole in a mixed solvent of 300 mL of DMF and 300 mL of H2O. Place the solution in a 1000 mL stainless steel reactor lined with polytetrafluoroethylene and heat it to 120 °C in a constant temperature drying oven for 48 h. After cooling to room temperature, wash the solution three times repeatedly with a mixture of deionized water and DMF, and then vacuum dry it at 60 °C for 12 h to obtain pale yellow crystals.
[0037] (2) Preparation of lithium manganese iron phosphate precursor: 58.8g iron phosphate, 63.5g phosphoric acid, 45.6g manganese tetroxide and 37.8g lithium carbonate were dissolved in 425g water and mixed evenly. The stirring speed was set to 200rpm and the mixture was stirred for 2h to obtain a slurry. The precipitate was collected by centrifugation to obtain lithium manganese iron phosphate precursor.
[0038] (3) Preparation of LiMnFePO4 / C
[0039] A phosphate buffer solution with pH = 7.8 was prepared. 20 g of lithium manganese iron phosphate precursor, 6 g of MOF material, and 400 mL of the phosphate buffer solution were dispersed evenly and then ultrasonically mixed at 5°C for 30 min to obtain a homogeneous slurry. The slurry was then milled at 1200 rpm for 1.0 h, and finally spray-dried to obtain powder. Sintering was performed in a high-purity nitrogen atmosphere at a temperature of 650°C, a heating rate of 2°C / min, and a holding time of 8 h. Subsequent pulverization yielded a MOF-derived porous carbon-coated carbon-nitrogen co-doped lithium manganese iron phosphate material.
[0040] Example 1-1
[0041] The experimental scheme and procedures were the same as in Example 1, except that in Example 1-1, a phosphate buffer solution with pH=8.0 was used as the dispersion solution.
[0042] Examples 1-2
[0043] The experimental scheme and procedures were the same as in Example 1, except that in Examples 1-2, a phosphate buffer solution with pH = 8.2 was used as the dispersion solution.
[0044] Examples 1-3
[0045] The experimental scheme and procedures were the same as in Example 1, except that in Examples 1-3, a phosphate buffer solution with pH = 8.5 was used as the dispersion solution.
[0046] Examples 1-4
[0047] The experimental scheme and procedures were the same as in Example 1, except that phosphate buffer solution with pH=9.0 was used as the dispersion solution in Examples 1-4.
[0048] Examples 1-5
[0049] The experimental scheme and steps are the same as those in Examples 1-3, except that in step (3) of Examples 1-5, the material is ultrasonically dispersed at 0°C to form a homogeneous phase.
[0050] Examples 1-6
[0051] The experimental scheme and steps are the same as those in Examples 1-3, except that in step (3) of Examples 1-6, the material is ultrasonically dispersed at 10°C to form a homogeneous phase.
[0052] Examples 1-7
[0053] The experimental scheme and steps are the same as those in Examples 1-3. The difference is that in step (3) of Examples 1-7, the material is ultrasonically dispersed at 0°C to form a homogeneous phase, and the sintering temperature is 650°C.
[0054] Examples 1-8
[0055] The experimental scheme and steps are the same as those in Examples 1-3. The difference is that in step (3) of Examples 1-8, the material is ultrasonically dispersed at 0°C to form a homogeneous phase, and the sintering temperature is 750°C.
[0056] Examples 1-9
[0057] The experimental scheme and steps are the same as those in Examples 1-3. The difference is that in step (3) of Examples 1-9, the material is ultrasonically dispersed at 0°C to form a homogeneous phase, and the sintering temperature is 850°C.
[0058] Examples 1-10
[0059] The experimental scheme and steps are the same as those in Examples 1-3. The difference is that in step (3) of Examples 1-10, the material is ultrasonically dispersed at 0°C to form a homogeneous phase, and the sintering temperature is 950°C.
[0060] Example 2
[0061] (1) Preparation of metal-organic framework (MOF) materials
[0062] 3.735 g of terephthalic acid, 0.756 g of 3-amino-1,2,4-triazole, and 5.355 g of zinc nitrate hexahydrate were dissolved in a mixed solvent of 450 mL DMF and 180 mL H2O. The solution was then placed in a 1000 mL stainless steel reactor lined with polytetrafluoroethylene (PTFE) and heated to 120 °C in a constant temperature drying oven for 48 h. After cooling to room temperature, the solution was repeatedly washed five times with a mixed solvent of deionized water and DMF, filtered, and then vacuum dried at 60 °C for 12 h to obtain white crystals.
[0063] (2) Preparation of lithium manganese iron phosphate precursor
[0064] This step uses the same scheme as in Example 1 to prepare lithium manganese iron phosphate precursor powder.
[0065] (3) Preparation of LiMnFePO4 / C
[0066] A phosphate buffer solution with pH = 7.9 was prepared. 100 g of lithium manganese iron phosphate precursor, 7.63 g of MOF material, and 1000 mL of the phosphate buffer solution were dispersed evenly and then ultrasonically mixed at 5°C for 60 min to obtain a homogeneous slurry. The slurry was then milled at 1000 rpm for 1.0 h, followed by milling at 1200 rpm for 0.5 h. Finally, the slurry was spray-dried to obtain powder. Sintering was carried out in a high-purity nitrogen atmosphere at a temperature of 650°C, a heating rate of 2°C / min, and a holding time of 9 h. Subsequent pulverization yielded a MOF-derived porous carbon-coated carbon-nitrogen co-doped lithium manganese iron phosphate material.
[0067] Example 2-1
[0068] The experimental scheme and procedures were the same as in Example 2, except that in Example 2-1, a phosphate buffer solution with pH = 8.1 was used as the dispersion solution.
[0069] Example 2-2
[0070] The experimental scheme and procedures were the same as in Example 2, except that Example 2-2 used a phosphate buffer solution with pH=8.3 as the dispersion solution.
[0071] Example 2-3
[0072] The experimental scheme and procedures were the same as in Example 2, except that in Examples 2-3, a phosphate buffer solution with pH=8.8 was used as the dispersion solution.
[0073] Examples 2-4
[0074] The experimental scheme and procedures were the same as in Example 2, except that in Examples 2-4, a phosphate buffer solution with pH = 9.0 was used as the dispersion solution.
[0075] Examples 2-5
[0076] The experimental scheme and procedures were the same as in Example 2, except that in Examples 2-5, the mass ratio of lithium manganese iron phosphate precursor to MOF material was 10:1, that is, 100g of lithium manganese iron phosphate precursor, 10g of MOF material and 1000mL of phosphate buffer solution with pH=8.3 were taken and dispersed.
[0077] Examples 2-6
[0078] The experimental scheme and procedures were the same as in Example 2. The difference was that in Examples 2-6, the mass ratio of lithium manganese iron phosphate precursor to MOF material was 50:3, that is, 100g of lithium manganese iron phosphate precursor, 6g of MOF material and 1000mL of phosphate buffer solution with pH=8.3 were taken for dispersion.
[0079] Example 3
[0080] (1) Preparation of metal-organic framework (MOF) materials
[0081] 16.4 g of zinc nitrate hexahydrate and 0.4 g of cobalt nitrate hexahydrate were weighed and dissolved in 800 mL of methanol, and stirred until homogeneous. This solution is designated as solution A. 37 g of 2-methylimidazole was then weighed and dissolved in 800 mL of methanol, and stirred until homogeneous. This solution is designated as solution B. Solution B was added dropwise to solution A with stirring. A purple solution was observed to form. The solution was stirred rapidly at room temperature for 36 h, centrifuged, washed several times with methanol, and vacuum dried at 60 °C for 12 h to obtain a purple solid powder.
[0082] (2) Preparation of lithium manganese iron phosphate precursor
[0083] 60g of iron phosphate, 67.35g of ammonium dihydrogen phosphate, 44.6g of manganese tetroxide, and 36.85g of lithium carbonate were dissolved in 546g of water and mixed evenly. The stirring speed was set to 150rpm, and the mixture was stirred for 6 hours to obtain a slurry. The precipitate was collected by centrifugation to obtain the lithium manganese iron phosphate precursor.
[0084] (3) Preparation of LiMnFePO4 / C
[0085] A phosphate buffer solution with pH = 8.0 was prepared. 100 g of lithium manganese iron phosphate precursor, 8 g of MOF material, and 833.3 mL of the above phosphate buffer solution were taken, dispersed evenly, and then ultrasonically mixed at 5°C for 45 min to obtain a homogeneous slurry. The slurry was then milled at 1200 rpm for 1.2 h, and finally spray-dried to obtain powder. Sintering was carried out in a high-purity nitrogen atmosphere at a temperature of 700°C, a heating rate of 2°C / min, and a holding time of 9 h. Subsequent pulverization yielded a MOF-derived porous carbon-coated carbon-nitrogen co-doped lithium manganese iron phosphate material.
[0086] Example 3-1
[0087] The experimental scheme and procedures were the same as in Example 3, except that in Example 3-1, a phosphate buffer solution with pH=8.4 was used as the dispersion solution.
[0088] Example 3-2
[0089] The experimental scheme and procedures were the same as in Example 3, except that Example 3-2 used a phosphate buffer solution with pH=8.6 as the dispersion solution.
[0090] Example 3-3
[0091] The experimental scheme and procedures were the same as in Example 3, except that in Example 3-3, a phosphate buffer solution with pH=8.8 was used as the dispersion solution.
[0092] Examples 3-4
[0093] The experimental scheme and procedures were the same as in Example 3, except that in Examples 3-4, a phosphate buffer solution with pH=9.0 was used as the dispersion solution.
[0094] Examples 3-5
[0095] The experimental scheme and procedures were the same as in Example 3, except that in Examples 3-5, the mass ratio of lithium manganese iron phosphate precursor to MOF material was 10:1, that is, 100g of lithium manganese iron phosphate precursor, 10g of MOF material and 1000mL of phosphate buffer solution with pH=8.6 were taken for dispersion.
[0096] Examples 3-6
[0097] The experimental scheme and procedures were the same as in Example 3, except that in Examples 3-6, the mass ratio of lithium manganese iron phosphate precursor to MOF material was 25:1, that is, 100g of lithium manganese iron phosphate precursor, 4g of MOF material and 1000mL of phosphate buffer solution with pH=8.6 were taken for dispersion.
[0098] Comparative Example 1
[0099] The experimental scheme and procedures were the same as those in Example 1, except that water with pH 7.0 was used as the dispersion solution for MOF and lithium manganese iron phosphate precursor in Comparative Example 1.
[0100] Comparative Example 2
[0101] The experimental scheme and procedures were the same as in Example 2, except that water with pH=7.0 was used as the dispersion solution for MOF and lithium manganese iron phosphate precursor in Comparative Example 1.
[0102] Comparative Example 3
[0103] The experimental scheme and procedures were the same as those in Example 3, except that water with pH=7.0 was used as the dispersion solution for MOF and lithium manganese iron phosphate precursor in Comparative Example 3.
[0104] Comparative Example 4
[0105] The experimental scheme and procedures were the same as those in Example 1, except that Comparative Example 4 used glucose as a conventional carbon source, with an amount of 23.1g, and it was added directly during the grinding process.
[0106] Performance Testing: The lithium manganese iron phosphate cathode material, PVDF, and Super-p prepared in the examples and comparative examples were homogenized with N-methylpyrrolidone at a solid content of 30% (based on a 90:5:5 ratio). The resulting mixture was then coated, dried, and stamped to obtain circular electrode sheets. Finally, the circular electrode sheets, separator, and lithium foil were assembled into coin cells for testing in a glove box. The coin cells were charged and discharged within a voltage range of 2.0–4.3V.
[0107] Test results:
[0108]
[0109]
[0110] The test results above show that the embodiment, by using phosphate buffer solutions of different pH values and nitrogen-doped metal-organic framework materials to treat lithium manganese iron phosphate, prepared a MOF-derived porous carbon thin-layer coated lithium manganese iron phosphate material. This material exhibits significant improvements in discharge capacity at 0.1C, 0.33C, and 0.5C, demonstrating good overall performance.
Claims
1. A method for preparing MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material, characterized in that, Includes the following steps: (1) Metal salt, organic ligand and solvent are mixed and stirred evenly, and then subjected to solvothermal reaction to obtain metal-organic framework material; the metal salt is selected from at least one of zinc salt, cobalt salt and nickel salt; the organic ligand includes 2-methylimidazolium, 3-amino-1,2,4-triazole and 1H-1,2,4-triazole. (2) Mix the iron source, lithium source, manganese source and phosphorus source evenly in water, stir and react for a certain time to obtain a mixed slurry, and obtain the precipitate by centrifugation, which is the precursor of lithium manganese iron phosphate; The metal-organic framework material-derived porous carbon thin-layer coated lithium manganese iron phosphate cathode material has the general formula LiMn. x Fe 1-x PO4 / C; where x ranges from 0.5 to 0.9; with Mn 2+ Fe 2+ PO4 3- The molar ratio of the phosphorus source, manganese source, and iron source is calculated to be 1:(0.5-0.9):(0.1-0.5); with Li + The amount of lithium source used and PO4 3- The molar ratio is 1.00-1.05:1; LiMn x Fe 1-x The carbon content in PO4 / C is 1.5-3.3% by weight. (3) The products from steps (1) and (2) are uniformly dispersed in phosphate buffer and mixed by low-temperature ultrasonication to obtain a homogeneous slurry. The slurry is then ground and spray-dried to obtain powder. The phosphate buffer is a weakly alkaline phosphate buffer with a pH of 7.8-9.
0. The lithium manganese iron phosphate precursor is dispersed in the phosphate buffer by low-temperature ultrasonication at 0-10 °C for 30-60 min. The mass ratio of lithium manganese iron phosphate precursor to MOF material is 20:3-25:1; (4) The powder is placed in a graphite sagger, heated to a certain temperature in an inert atmosphere and sintered for a period of time, and then naturally cooled to room temperature to obtain a carbon-nitrogen co-doped lithium manganese iron phosphate material coated with MOF-derived porous carbon thin layer.
2. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (1), the zinc salt is selected from zinc nitrate hexahydrate and zinc chloride; the cobalt salt is selected from cobalt nitrate hexahydrate and cobalt chloride; and the nickel salt is selected from nickel nitrate hexahydrate and nickel chloride.
3. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (1), the solvent is an organic solvent including methanol, anhydrous ethanol, N,N-dimethylformamide; or an organic solvent and water are used together as a mixed solvent. The solvothermal reaction temperature is 120-200 °C, and the reaction time is 12-72 h.
4. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (2), the iron source includes ferric phosphate and ferrous sulfate heptahydrate; the lithium source includes lithium carbonate and lithium hydroxide; the manganese source includes manganese carbonate, manganese oxide, and manganese tetroxide; and the phosphorus source includes phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.
5. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (3), the concentration of the lithium manganese iron phosphate precursor is 50-150 mg / mL.
6. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 5, characterized in that, The concentration of the lithium manganese iron phosphate precursor is any one of 50 mg / mL, 60 mg / mL, 70 mg / mL, 80 mg / mL, 100 mg / mL, 120 mg / mL, or 150 mg / mL.
7. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (3), the grinding process is carried out at a speed of 1000-1300 rpm for 0.5-2.5 h.
8. The method for preparing a MOF-derived porous carbon thin-film coated lithium manganese iron phosphate material according to claim 1, characterized in that, In step (4), the material sintering is carried out in a tube furnace, with an inert atmosphere of either high-purity nitrogen or argon, a sintering temperature of 650℃, a heating rate of 2-10℃ / min, and a holding time of 5-15 h.