Preparation method of lithium iron phosphate positive electrode material and lithium iron phosphate positive electrode material
By preparing lithium iron phosphate nanofibers through electrospinning and chemical modification, the problems of insufficient conductivity and lithium-ion diffusion performance of lithium iron phosphate cathode materials were solved, and high-performance lithium iron phosphate cathode materials were realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN YUNENG NEW ENERGY BATTERY MATERIALS CO LTD
- Filing Date
- 2026-06-10
- Publication Date
- 2026-07-10
AI Technical Summary
Existing lithium iron phosphate cathode materials have low discharge capacity, insufficient electronic conductivity, and inadequate lithium-ion diffusion performance, which limits their commercial application.
Lithium iron phosphate nanofibers were prepared using electrospinning technology. By introducing amylopectin groups and silver ions into the fiber material, an amorphous carbon layer was formed by polymer pyrolysis. Combined with the porous structure of aminated iron-based MOFs, the conductivity and lithium ion transport pathway of the material were improved.
It significantly enhances the conductivity and cycle stability of lithium iron phosphate cathode materials, and improves discharge capacity and rate performance.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for preparing lithium iron phosphate cathode material and the lithium iron phosphate cathode material itself. Background Technology
[0002] With the rapid rise of the new energy industry, lithium-ion batteries have been widely used. Lithium iron phosphate (LiFePO4) not only possesses a high theoretical specific capacity (171 mAh / g), but also boasts numerous advantages such as stable voltage platform, high safety, long cycle life, and no pollution, and has been widely applied in new energy industries such as base station energy storage, electric vehicles, and electric ships. However, lithium iron phosphate has relatively low electronic conductivity and a small Li-ion content. + The diffusion rate limits its further commercial application.
[0003] Currently, in order to improve the problems of low electronic conductivity and low lithium-ion diffusion performance of lithium iron phosphate materials, existing technologies mainly focus on ion doping and carbon coating modification of lithium iron phosphate. Although some progress has been made, the resulting lithium iron phosphate materials are all powder materials. However, in the process of using lithium batteries, powdered lithium iron phosphate materials cause lithium ions to have a long diffusion path and slow electrode reaction kinetics, which makes the final improvement effect unsatisfactory.
[0004] Because the fibers obtained by electrospinning have small diameters and short diffusion paths, selecting appropriate precursor materials and using electrospinning technology to prepare lithium iron phosphate nanofibers is expected to yield high-performance lithium iron phosphate cathode materials. This is because electrospinning fibers have a high area-to-mass ratio, enabling faster lithium-ion intercalation kinetics. Electrospinning fiber materials also provide a relatively large number of lithium intercalation sites, which can relatively reduce the surface charge transfer resistance between the electrolyte and the active electrode material. For example, the paper "Preparation and Electrochemical Performance Study of LiFePO4 / C / GO" (Yang Huhou, Zhen Qing, Ma Yuxin) discloses the preparation of LiFePO4 / C / GO cathode composite materials by electrospinning using graphene oxide, polyacrylonitrile, lithium acetate, phosphoric acid, and iron nitrate as raw materials. Although some progress has been made, the discharge capacity of the obtained battery material at 0.1C rate is only 118.4 mAh / g, indicating that there is still much room for optimization. Summary of the Invention
[0005] This invention provides a method for preparing lithium iron phosphate cathode material and the lithium iron phosphate cathode material itself, which can solve the problem of low discharge capacity in existing lithium iron phosphate cathode materials.
[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a lithium iron phosphate cathode material includes the following steps: S1. Add lithium source, iron source and phosphorus source to solvent and stir evenly to obtain lithium iron phosphate precursor solution; S2. Add polymers, namely epoxidized polyvinylidene fluoride and polyacrylonitrile, to the lithium iron phosphate precursor solution, stir evenly to obtain spinning solution, and obtain precursor fibers through electrospinning process. S3. Add hydroxylamine hydrochloride to deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add the precursor fiber to the treatment solution and stir the reaction at 65-75℃ for 4-6 hours. After the reaction is completed, filter the solution, wash and dry the filter cake to obtain the amylated precursor fiber. S4. Add the amylated precursor fiber to silver nitrate solution, stir for 1.5-2 hours, remove, dry, heat treat and calcinate to obtain lithium iron phosphate cathode material.
[0007] This invention first prepares a lithium iron phosphate precursor solution, then adds epoxidized polyvinylidene fluoride and polyacrylonitrile to the lithium iron phosphate precursor solution to form a spinning solution. By electrospinning, precursor fibers are obtained. Then, the nitrile groups on the polyacrylonitrile molecules react with hydroxylamine hydrochloride to form precursor fibers carrying amylopectin groups. Since amylopectin groups have excellent adsorption capacity for silver ions, fiber materials with silver ions on their surface are obtained. Finally, lithium iron phosphate cathode materials are obtained through heat treatment and calcination.
[0008] Furthermore, in S1, the molar ratio of Li, Fe, and P in the lithium, iron, and phosphorus sources is 1:1:1, and the amount of solvent used is 8-13 times the sum of the masses of the lithium, iron, and phosphorus sources.
[0009] Furthermore, the lithium source is at least one of lithium acetate, lithium nitrate, and lithium hydroxide.
[0010] Furthermore, the phosphorus source is at least one of phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate.
[0011] Furthermore, the iron source is an amino-iron-based MOF.
[0012] Furthermore, the solvent is N,N-dimethylformamide.
[0013] Further, the iron-amined MOF is at least one of Fe-MIL-101-NH2 (CAS: 1189182-85-1), Fe-MIL-88B-NH (CAS: 1341134-09-5), and Fe-MIL-53-NH2 (CAS: 1291088-77-1).
[0014] Furthermore, the amount of polymer used in S2 is 5-15% of the mass of the lithium iron phosphate precursor solution, and the mass ratio of epoxidized polyvinylidene fluoride to polyacrylonitrile in the polymer is 0.2-0.5:1.
[0015] Furthermore, the epoxidized polyvinylidene fluoride is polyvinylidene fluoride grafted with glycidyl methacrylate.
[0016] In some embodiments, the method for preparing epoxidized polyvinylidene fluoride includes the following steps: exist 60 In a Co source chamber, polyvinylidene fluoride was irradiated in air for 10-15 minutes at a dose rate of 0.32 KGy / h to obtain irradiated polyvinylidene fluoride. Irradiated polyvinylidene fluoride, ferrous ammonium sulfate hexahydrate, glycidyl methacrylate and methanol were added to a flask, and nitrogen gas was purged for oxygen removal for 15 min. The mixture was then stirred at 45-55 °C for 5-6 h. After the reaction was completed, the mixture was filtered, and the filter cake was washed with methanol and dried to obtain epoxidized polyvinylidene fluoride.
[0017] In the above preparation process, the mass ratio of irradiated polyvinylidene fluoride, ferrous ammonium sulfate hexahydrate, and glycidyl methacrylate is 5:0.05:14-16. 60 Polyvinylidene fluoride (PVDF) is pre-irradiated with Co-γ rays, then free radicals are trapped, which then initiates a polymer reaction between PVDF and glycidyl methacrylate to generate a graft copolymer, yielding epoxidized PVDF.
[0018] Furthermore, in the electrospinning process of S2, the spinning voltage is 10-20kV, the receiving distance is 15-25cm, the spinning temperature is 25-30℃, and the relative humidity is 90±5%.
[0019] Furthermore, the ratio of hydroxylamine hydrochloride to deionized water in S3 is 1.32-1.98 g: 100 mL, and the ratio of precursor fiber to treatment solution is 1 g: 50-100 mL.
[0020] Furthermore, the concentration of silver nitrate solution in S4 is 0.1-1 mol / L, and the ratio of the amount of oxime-modified precursor fiber to silver nitrate solution is 1 g: 10-20 mL.
[0021] Furthermore, the S4 heat treatment operation steps are as follows: heat to 300-400℃ at a heating rate of 0.5-1℃ / min, and hold in air for 4-8 hours.
[0022] Furthermore, the S4 calcination treatment procedure is as follows: 600-800℃, in a nitrogen or argon protective atmosphere, for 10-24 hours.
[0023] A lithium iron phosphate cathode material is prepared by the above-described preparation method.
[0024] The beneficial effects of this invention are: 1. In the preparation process of lithium iron phosphate cathode material, this invention utilizes the reaction of nitrile groups on polyacrylonitrile molecules with hydroxylamine hydrochloride to form precursor fibers carrying amylopectin groups. These amylopectin groups have excellent adsorption capacity for silver ions, thereby obtaining fiber materials with silver ions on their surface. The adsorption of silver ions by the amylopectin groups helps to improve the uniformity of silver ion distribution in the precursor fibers. Finally, through heat treatment and calcination, the polymer is pyrolyzed to form an amorphous carbon layer, and silver ions are reduced to elemental silver through a carbothermal reduction reaction. Both are uniformly dispersed on the surface of the lithium iron phosphate material. Under the synergistic effect of the carbon layer and elemental silver, the conductivity of the lithium iron phosphate cathode material is significantly enhanced, enabling it to exhibit excellent capacity levels and cycle stability.
[0025] 2. This invention uses iron-based MOFs with amino groups as the iron source. Compared with existing inorganic iron sources, MOFs have the characteristics of large specific surface area and high porosity. While serving as an iron source, the derived carbon material formed by calcination inherits the porous structure of MOFs, which can provide more electron and lithium-ion transport paths, thereby improving the electrochemical performance of the material.
[0026] 3. This invention uses aminated iron-based MOF as the iron source and epoxidized polyvinylidene fluoride and polyacrylonitrile as spinning polymers. Through electrospinning, heat treatment, and calcination, lithium iron phosphate cathode materials are obtained. During heat treatment, aminated iron-based MOF and epoxidized polyvinylidene fluoride can form covalent bonds through the reaction of amino and epoxy groups, "anchoring" the aminated iron-based MOF to the polymer molecular chain. This effectively prevents the aggregation of aminated iron-based MOF, ensuring uniform dispersion of the MOF in the spinning solution. This uniformity directly leads to a uniform atomic distribution in the lithium iron phosphate crystals, greatly reducing component segregation and the formation of impurity phases. Compared to physical mixing, the fiber structure formed by covalent bonds is more complete and stable, which is beneficial for improving the cycle stability of the final lithium iron phosphate cathode material. Furthermore, epoxidized polyvinylidene fluoride can form a highly hydrophobic carbon network during the carbonization process, which helps reduce the hygroscopicity of the lithium iron phosphate cathode material. Detailed Implementation
[0027] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0028] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.
[0029] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.
[0030] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.
[0031] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.
[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0033] To address the problem of low discharge capacity in existing lithium iron phosphate cathode materials, this application provides a method for preparing a lithium iron phosphate cathode material, comprising the following steps: S1. Add lithium source, iron source and phosphorus source to solvent and stir evenly to obtain lithium iron phosphate precursor solution; S2. Add polymers, namely epoxidized polyvinylidene fluoride and polyacrylonitrile, to the lithium iron phosphate precursor solution, stir evenly to obtain spinning solution, and obtain precursor fibers through electrospinning process. S3. Add hydroxylamine hydrochloride to deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add the precursor fiber to the treatment solution and stir the reaction at 65-75℃ for 4-6 hours. After the reaction is completed, filter the solution, wash and dry the filter cake to obtain the amylated precursor fiber. S4. Add the amylated precursor fiber to silver nitrate solution, stir for 1.5-2 hours, remove, dry, heat treat and calcinate to obtain lithium iron phosphate cathode material.
[0034] In some embodiments, the molar ratio of Li, Fe, and P in the lithium source, iron source, and phosphorus source in S1 is 1:1:1, and the amount of solvent used is 8-13 times the sum of the masses of the lithium source, iron source, and phosphorus source.
[0035] In some specific embodiments, the lithium source is at least one of lithium acetate, lithium nitrate, and lithium hydroxide.
[0036] In some specific embodiments, the phosphorus source is at least one of phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate.
[0037] In some specific embodiments, the iron source is an iron-ammoniated MOF.
[0038] In some specific embodiments, the solvent is N,N-dimethylformamide.
[0039] In some specific embodiments, the aminated iron-based MOF is at least one of Fe-MIL-101-NH2 (CAS: 1189182-85-1), Fe-MIL-88B-NH (CAS: 1341134-09-5), and Fe-MIL-53-NH2 (CAS: 1291088-77-1).
[0040] In some embodiments, the amount of polymer used in S2 is 5-15% of the mass of the lithium iron phosphate precursor solution, and the mass ratio of epoxidized polyvinylidene fluoride to polyacrylonitrile in the polymer is 0.2-0.5:1.
[0041] In some specific embodiments, the epoxidized polyvinylidene fluoride is polyvinylidene fluoride grafted with glycidyl methacrylate.
[0042] In some specific embodiments, the method for preparing epoxidized polyvinylidene fluoride includes the following steps: exist 60 In a Co source chamber, polyvinylidene fluoride was irradiated in air for 10-15 minutes at a dose rate of 0.32 KGy / h to obtain irradiated polyvinylidene fluoride. Irradiated polyvinylidene fluoride, ferrous ammonium sulfate hexahydrate, glycidyl methacrylate and methanol were added to a flask, and nitrogen gas was purged for oxygen removal for 15 min. The mixture was then stirred at 45-55 °C for 5-6 h. After the reaction was completed, the mixture was filtered, and the filter cake was washed with methanol and dried to obtain epoxidized polyvinylidene fluoride.
[0043] In the above preparation process, the mass ratio of irradiated polyvinylidene fluoride, ferrous ammonium sulfate hexahydrate, and glycidyl methacrylate is 5:0.05:14-16.
[0044] In some specific embodiments, the electrospinning process in S2 has a spinning voltage of 10-20kV, a receiving distance of 15-25cm, a spinning temperature of 25-30℃, and a relative humidity of 90±5%.
[0045] In some specific embodiments, the ratio of hydroxylamine hydrochloride to deionized water in S3 is 1.32-1.98 g: 100 mL, and the ratio of precursor fiber to treatment solution is 1 g: 50-100 mL.
[0046] In some specific embodiments, the concentration of silver nitrate solution in S4 is 0.1-1 mol / L, and the ratio of the amount of oxime-modified precursor fiber to silver nitrate solution is 1 g: 10-20 mL.
[0047] In some specific embodiments, the S4 heat treatment operation steps are as follows: heat to 300-400℃ at a heating rate of 0.5-1℃ / min, and keep in air atmosphere for 4-8 hours.
[0048] In some specific embodiments, the S4 calcination treatment operation steps are as follows: 600-800℃, in a nitrogen or argon protective atmosphere, heat treatment for 10-24 hours.
[0049] The second aspect of this application provides a lithium iron phosphate cathode material, which is prepared by the above-described preparation method.
[0050] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.
[0051] In this application, polyacrylonitrile (PAN) Mw=150000g / mol and polyvinylidene fluoride is PVDF-6020. Unless otherwise specified, all other raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.
[0052] Preparation Example 1 This preparation example provides an epoxidized polyvinylidene fluoride, and the preparation steps are as follows: exist 60In a Co source chamber, 10g of polyvinylidene fluoride was irradiated in air for 10 minutes at a dose rate of 0.32KGy / h to obtain irradiated polyvinylidene fluoride. 5g of irradiated polyvinylidene fluoride, 0.05g of ferrous ammonium sulfate hexahydrate, 14g of glycidyl methacrylate and 100mL of methanol were added to a flask. After purging with nitrogen for 15min, the mixture was stirred at 45℃ for 5h. After the reaction was completed, the mixture was filtered, the filter cake was washed with methanol and dried to obtain epoxidized polyvinylidene fluoride.
[0053] Preparation Example 2 This preparation example provides an epoxidized polyvinylidene fluoride, and the preparation steps are as follows: exist 60 In a Co source chamber, 10g of polyvinylidene fluoride was irradiated in air for 12 minutes at a dose rate of 0.32KGy / h to obtain irradiated polyvinylidene fluoride. 5g of irradiated polyvinylidene fluoride, 0.05g of ferrous ammonium sulfate hexahydrate, 15g of glycidyl methacrylate and 100mL of methanol were added to a flask. After purging with nitrogen for 15min, the mixture was stirred at 50℃ for 5.5h. After the reaction was completed, the mixture was filtered, the filter cake was washed with methanol and dried to obtain epoxidized polyvinylidene fluoride.
[0054] Preparation Example 3 This preparation example provides an epoxidized polyvinylidene fluoride, and the preparation steps are as follows: exist 60 In a Co source chamber, 10g of polyvinylidene fluoride was irradiated in air for 15min at a dose rate of 0.32KGy / h to obtain irradiated polyvinylidene fluoride. 5g of irradiated polyvinylidene fluoride, 0.05g of ferrous ammonium sulfate hexahydrate, 16g of glycidyl methacrylate and 100mL of methanol were added to a flask. After purging with nitrogen for 15min, the mixture was stirred at 55℃ for 6h. After the reaction was completed, the mixture was filtered, the filter cake was washed with methanol and dried to obtain epoxidized polyvinylidene fluoride.
[0055] Example 1 This embodiment provides a method for preparing lithium iron phosphate cathode material, including the following steps: S1. Add 0.3 mol lithium acetate, 0.1 mol Fe-MIL-101-NH2, and 0.3 mol phosphoric acid to 1.56 L of N,N-dimethylformamide and stir until homogeneous to obtain a lithium iron phosphate precursor solution. S2. Add a polymer to the lithium iron phosphate precursor solution. The amount of polymer is 5% of the mass of the lithium iron phosphate precursor solution. The polymer is composed of epoxidized polyvinylidene fluoride and polyacrylonitrile from Preparation Example 1 at a mass ratio of 0.2:1. Stir evenly to obtain a spinning solution. Load the spinning solution into a syringe with a needle for electrospinning. Control the injection speed at 1 mL / h, the voltage at 10 kV, the temperature at 25 °C, the relative humidity at 90%, the receiving distance at 15 cm, and the spinning time at 2 h to obtain precursor fibers. S3. Add 13.2g of hydroxylamine hydrochloride to 1000mL of deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add 10g of precursor fiber to 500mL of the treatment solution and stir at 65℃ for 4h. After the reaction is complete, filter and wash and dry the filter cake with deionized water to obtain the amylated precursor fiber. S4. Add 10g of the ammonium oxime precursor fiber to 100mL of 0.1mol / L silver nitrate solution, stir for 1.5h, remove and dry. Place the dried product in a muffle furnace and heat to 300℃ at a heating rate of 0.5℃ / min. Keep it in air for 8h. Keep the heating rate constant and heat to 600℃. Keep it in argon atmosphere for 24h to obtain lithium iron phosphate cathode material.
[0056] Example 2 This embodiment provides a method for preparing lithium iron phosphate cathode material, including the following steps: S1. Add 0.3 mol lithium acetate, 0.1 mol Fe-MIL-101-NH2, and 0.3 mol phosphoric acid to 1.08 L of N,N-dimethylformamide and stir until homogeneous to obtain a lithium iron phosphate precursor solution. S2. Add a polymer to the lithium iron phosphate precursor solution. The amount of polymer is 10% of the mass of the lithium iron phosphate precursor solution. The polymer is composed of epoxidized polyvinylidene fluoride and polyacrylonitrile from Preparation Example 1 at a mass ratio of 0.4:1. Stir evenly to obtain a spinning solution. Load the spinning solution into a syringe with a needle for electrospinning. Control the injection speed at 1 mL / h, the voltage at 15 kV, the temperature at 28 °C, the relative humidity at 95%, the receiving distance at 20 cm, and the spinning time at 2 h to obtain precursor fibers. S3. Add 16.8g of hydroxylamine hydrochloride to 1000mL of deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add 10g of precursor fiber to 800mL of the treatment solution and stir at 70℃ for 4h. After the reaction is complete, filter and wash and dry the filter cake with deionized water to obtain the amylated precursor fiber. S4. Add 10g of the ammonium oxime precursor fiber to 150mL of 0.5mol / L silver nitrate solution, stir for 1.5h, remove and dry. Place the dried product in a muffle furnace and heat to 350℃ at a heating rate of 0.5℃ / min. Keep it in air for 6h. Keep the heating rate constant and heat to 700℃. Keep it in nitrogen or protective atmosphere for 16h to obtain lithium iron phosphate cathode material.
[0057] Example 3 This embodiment provides a method for preparing lithium iron phosphate cathode material, including the following steps: S1. Add 0.3 mol lithium acetate, 0.1 mol Fe-MIL-101-NH2, and 0.3 mol phosphoric acid to 1.76 L of N,N-dimethylformamide and stir until homogeneous to obtain a lithium iron phosphate precursor solution. S2. Add a polymer to the lithium iron phosphate precursor solution. The amount of polymer is 15% of the mass of the lithium iron phosphate precursor solution. The polymer is composed of epoxidized polyvinylidene fluoride and polyacrylonitrile from Preparation Example 1 at a mass ratio of 0.5:1. Stir evenly to obtain a spinning solution. Load the spinning solution into a syringe with a needle for electrospinning. Control the injection speed at 1 mL / h, the voltage at 20 kV, the temperature at 30 °C, the relative humidity at 95%, the receiving distance at 25 cm, and the spinning time at 2 h to obtain precursor fibers. S3. Add 19.8g of hydroxylamine hydrochloride to 1000mL of deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add 10g of precursor fiber to 1000mL of the treatment solution and stir at 75℃ for 6h. After the reaction is complete, filter and wash and dry the filter cake with deionized water to obtain the amylated precursor fiber. S4. Add 10g of the ammonium oxime precursor fiber to 200mL of 1mol / L silver nitrate solution, stir for 2h, remove and dry. Place the dried product in a muffle furnace and heat to 400℃ at a heating rate of 1℃ / min. Keep it in air for 8h. Keep the heating rate constant and heat to 800℃. Keep it in nitrogen or argon atmosphere for 24h to obtain lithium iron phosphate cathode material.
[0058] Example 4 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that the epoxidized polyvinylidene fluoride in Example 1 is replaced with the product obtained in Example 2 by the same mass.
[0059] Example 5 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that the epoxidized polyvinylidene fluoride in Example 1 is replaced with the product obtained in Example 3 by the same mass.
[0060] Example 6 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that Fe-MIL-101-NH2 in Example 1 is replaced with an equimolar amount of Fe-MIL-88B-NH.
[0061] Example 7 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that Fe-MIL-101-NH2 in Example 1 is replaced with three times the molar amount of Fe-MIL-53-NH2.
[0062] Example 8 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that the concentration of silver nitrate solution in S4 of Example 1 is adjusted from 0.1 mol / L to 0.5 mol / L.
[0063] Comparative Example 1 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that Fe-MIL-101-NH2 in Example 1 is replaced with an equimolar amount of MIL-101(Fe) (CAS:1189182-67-9).
[0064] Comparative Example 2 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that Fe-MIL-101-NH2 in Example 1 is replaced with 3 times the molar amount of iron nitrate.
[0065] Comparative Example 3 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that the epoxidized polyvinylidene fluoride in Example 1 is replaced with an equal mass of polyvinylidene fluoride.
[0066] Comparative Example 4 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, the difference is that the epoxidized polyvinylidene fluoride in Example 1 is replaced with an equal mass of polyacrylonitrile.
[0067] Comparative Example 5 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, steps S1 and S2 are the same, except that the subsequent operations in S2 are different, as follows: The precursor fiber and silver nitrate were mixed evenly at a mass ratio of 10:1.7 and then ground through a 400-mesh sieve. The sieved product was placed in a muffle furnace and heated to 300°C at a heating rate of 0.5°C / min. It was then kept at this temperature in an air atmosphere for 8 hours. The heating rate was kept constant and the temperature was increased to 600°C. The product was then kept at this temperature in a nitrogen or argon atmosphere for 24 hours to obtain the lithium iron phosphate cathode material.
[0068] Comparative Example 6 This embodiment provides a method for preparing lithium iron phosphate cathode material. Compared with Example 1, steps S1 and S2 are the same, except that the subsequent operations in S2 are different, as follows: The precursor fiber was placed in a muffle furnace and heated to 300°C at a heating rate of 0.5°C / min. It was then kept at this temperature in an air atmosphere for 8 hours. The heating rate was kept constant and the temperature was increased to 600°C. The mixture was then kept at this temperature in a nitrogen or argon atmosphere for 24 hours to obtain the lithium iron phosphate cathode material.
[0069] The performance of the lithium iron phosphate cathode materials obtained in Examples 1-8 and Comparative Examples 1-6 was tested, and the test process is as follows: (1) The conductivity of lithium iron phosphate cathode materials obtained in Examples 1-8 and Comparative Examples 1-6 was tested using a four-probe tester. Before the test, 0.15g of the sample to be tested was weighed and pressed into a cylinder with a diameter of 12mm under 5MPa. Each sample was measured three times at different positions. The average value was calculated as the final value of the electronic conductivity of the sample. (2) The lithium iron phosphate cathode materials obtained in Examples 1-8 and Comparative Examples 1-6 were ground and passed through a 400-mesh sieve. The screened material was used as the active material. The active material, acetylene black and binder PVDF were mixed in a mass ratio of 85:10:5. N-methylpyrrolidone (NMP) was added and stirred evenly. The ratio of N-methylpyrrolidone to binder PVDF was controlled to be 10mL:1g. The slurry was coated on aluminum foil to form a cathode sheet. The cathode sheet was vacuum dried at 110°C for 12h in a vacuum drying oven to obtain the cathode electrode sheet. Each group of positive electrode sheets was dried at 120℃ for 10 hours, and the mass was recorded as M0. Then, they were placed in an environment of 25℃ and 30% humidity for 24 hours, and the mass was recorded as M1. The water absorption rate was then calculated as follows: Water absorption rate (%) = (M1-M0) / M0×100%; (3) Using the positive electrode sheet obtained in step (2) as the positive electrode, the lithium metal sheet as the negative electrode, the polypropylene microporous membrane (Celgard 2400) as the separator, and the 1 mol / L LiPF6 mixed solution as the electrolyte, the solvent in the electrolyte is ethylene carbonate (EC) and diethyl carbonate (DEC), and the volume ratio of EC to DMC is 1:1, the cells are assembled into button cells in an argon-filled glove box. Constant current charge-discharge test is performed using a blue electric tester, with a charge-discharge voltage range of 2.0-3.75V. Cyclic voltammetry test is performed on the cells using an electrochemical workstation, with a scanning voltage range of 2.0-3.75V and a scanning rate of 0.1mV / s. The discharge specific capacity at 0.1C and 1C rates is calculated, and the discharge specific capacity retention rate after 500 cycles at 1C rate is tested. The test results are shown in Table 1: Table 1
[0070] Analysis of the data recorded in Table 1 shows that all three examples (Example 1, Example 2, and Example 3) used the epoxidized polyvinylidene fluoride prepared in Example 1 as raw material. However, the raw material ratio and preparation process parameters were different, resulting in significant differences in the performance of the final lithium iron phosphate cathode material. Among them, the lithium iron phosphate cathode material obtained in Example 2 had the best performance. The test results of Examples 1, 4 and 5 show that, under the same preparation parameters and process conditions, the lithium iron phosphate cathode materials prepared using epoxidized polyvinylidene fluoride prepared in Examples 1, 2 and 3 as raw materials have similar performance. The test results of Examples 1, 6 and 7 show that, under the same preparation parameters and process conditions, the performance of lithium iron phosphate cathode materials obtained by using Fe-MIL-101-NH2, Fe-MIL-88B-NH and Fe-MIL-53-NH2 as iron sources is not significantly different. The test results of Examples 1 and 8 show that adjusting the concentration of silver nitrate solution from 0.1 mol / L to 0.5 mol / L is beneficial to the formation of more elemental silver, which in turn is beneficial to the improvement of the electronic conductivity of lithium iron phosphate cathode material. Ultimately, the discharge capacity, rate performance and cycle performance of lithium iron phosphate cathode material are improved. As can be seen from the test results of Example 1 and Comparative Example 1, when Fe-MIL-101-NH2 is replaced with an equimolar amount of MIL-101(Fe) in Example 1, the lack of amino functional groups prevents the iron source from being covalently connected with epoxidized polyvinylidene fluoride, which in turn leads to a decrease in the electronic conductivity, discharge capacity, rate performance, and cycle performance of the final lithium iron phosphate cathode material. As can be seen from the test results of Example 1 and Comparative Example 2, when Fe-MIL-101-NH2 in Example 1 is replaced by 3 times the molar amount of ferric nitrate, ferric nitrate cannot be covalently linked with epoxidized polyvinylidene fluoride, nor does it have the performance of MOF-derived carbon, which leads to a significant reduction in the electronic conductivity, discharge capacity, rate performance and cycle performance of the final lithium iron phosphate cathode material. The test results of Example 1 and Comparative Examples 3 and 4 show that replacing epoxidized polyvinylidene fluoride with an equal mass of polyvinylidene fluoride or polyacrylonitrile will significantly reduce the electronic conductivity, discharge capacity, rate performance and cycle performance of the final lithium iron phosphate cathode material. In particular, replacing epoxidized polyvinylidene fluoride with an equal mass of acrylonitrile will also cause an increase in the hygroscopicity of the lithium iron phosphate material, which is not conducive to the preparation of high-performance lithium batteries. As can be seen from the test results of Example 1 and Comparative Examples 5 and 6, changing the way silver nitrate is added or omitting the use of silver nitrate will result in a significant reduction in the electronic conductivity, discharge capacity, rate performance and cycle performance of the final lithium iron phosphate cathode material.
[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1. Add lithium source, iron source and phosphorus source to solvent and stir evenly to obtain lithium iron phosphate precursor solution; S2. Add polymers, namely epoxidized polyvinylidene fluoride and polyacrylonitrile, to the lithium iron phosphate precursor solution, stir evenly to obtain spinning solution, and obtain precursor fibers through electrospinning process. S3. Add hydroxylamine hydrochloride to deionized water and adjust the pH to 7.0 with sodium carbonate to obtain a treatment solution. Add the precursor fiber to the treatment solution and stir the reaction at 65-75℃ for 4-6 hours. After the reaction is completed, filter the solution, wash and dry the filter cake to obtain the amylated precursor fiber. S4. Add the amylated precursor fiber to silver nitrate solution, stir for 1.5-2 hours, remove, dry, heat treat and calcinate to obtain lithium iron phosphate cathode material.
2. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, In S1, the molar ratio of Li, Fe, and P in the lithium, iron, and phosphorus sources is 1:1:1, and the amount of solvent used is 8-13 times the sum of the masses of the lithium, iron, and phosphorus sources.
3. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, The lithium source is at least one of lithium acetate, lithium nitrate, and lithium hydroxide; the phosphorus source is at least one of phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate; and the solvent is N,N-dimethylformamide.
4. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, The iron source is an amino-iron-based MOF.
5. The method for preparing a lithium iron phosphate cathode material according to claim 4, characterized in that, The iron-based amino-amined MOF is at least one of Fe-MIL-101-NH2, Fe-MIL-88B-NH, and Fe-MIL-53-NH2.
6. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, The amount of polymer used in S2 is 5-15% of the mass of the lithium iron phosphate precursor solution, and the mass ratio of epoxidized polyvinylidene fluoride to polyacrylonitrile in the polymer is 0.2-0.5:
1.
7. A method for preparing a lithium iron phosphate cathode material according to claim 1 or 6, characterized in that, The epoxidized polyvinylidene fluoride is polyvinylidene fluoride grafted with glycidyl methacrylate.
8. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, In S3, the ratio of hydroxylamine hydrochloride to deionized water is 1.32-1.98 g: 100 mL, and the ratio of precursor fiber to treatment solution is 1 g: 50-100 mL.
9. The method for preparing a lithium iron phosphate cathode material according to claim 1, characterized in that, The concentration of silver nitrate solution in S4 is 0.1-1 mol / L, and the ratio of the amount of oxime-modified precursor fiber to silver nitrate solution is 1 g: 10-20 mL.
10. A lithium iron phosphate cathode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.