Mof-based nano positive electrode material, preparation method thereof, positive electrode sheet and battery

Abstract

The application relates to the technical field of batteries, in particular to a MOFs-based nano positive electrode material, a preparation method thereof, a positive electrode sheet and a battery. The preparation method of the MOFs-based nano positive electrode material comprises the following steps: preparing nanofibers by using a spinning solution formed by an organic ligand, a high-molecular polymer, a conductive salt and an organic solvent; immersing the nanofibers in a soluble iron salt solution, and then performing ultrasonic treatment and first heat treatment to obtain a precursor; mixing the precursor with a lithium source and a phosphorus source, and then performing second heat treatment to obtain the MOFs-based nano positive electrode material. The MOFs material is combined with the electrostatic spinning technology, the in-situ growth method is adopted to make the Fe element grow uniformly and firmly on the surface layer of the fiber network, more uniform and consistent crystal particles can be induced, and after high-temperature carbonization, a conductive network is formed, so that the conductivity of the prepared positive electrode material precursor is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a MOFs-based nano cathode material, its preparation method, cathode sheet, and battery. Background Technology

[0002] In recent years, passenger vehicles powered by lithium-ion batteries have been widely used, and the performance of cathode materials is particularly important in power battery systems. Among the many cathode materials, lithium iron phosphate cathode materials have attracted attention and development due to their good stability, high safety, low cost, and non-toxicity and environmental friendliness. However, they still have problems such as poor conductivity and easy agglomeration.

[0003] Currently, the preparation methods for lithium iron phosphate have gradually matured. In industrial production, the low-cost high-temperature solid-state method is mostly used. However, this method is prone to problems such as powder agglomeration and severe agglomeration, which reduces efficiency and is not conducive to the full performance of the battery. At the same time, in order to improve the poor conductivity of lithium iron phosphate cathode materials, a carbon coating process is generally required to improve its conductivity. However, since the carbon content and distribution are difficult to control, the uniformity after coating is poor, which affects the microstructure, particle size distribution and subsequent processing of the material.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing MOFs-based nano cathode materials, thereby overcoming the technical problems in the prior art where the preparation of cathode materials using high-temperature solid-state methods easily leads to severe powder agglomeration and agglomeration, reducing efficiency and hindering the full utilization of battery performance.

[0006] Another objective of this invention is to provide a method for preparing MOFs-based nano cathode materials, as described above, to obtain MOFs-based nano cathode materials.

[0007] Another object of the present invention is to provide a positive electrode sheet comprising the aforementioned MOFs-based nano-positive electrode material.

[0008] Another object of the present invention is to provide a battery comprising the aforementioned positive electrode.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] The preparation method of MOF-based nano cathode materials includes the following steps:

[0011] Nanofibers are prepared using a spinning solution formed from organic ligands, polymers, conductive salts, and organic solvents. The nanofibers are then immersed in a soluble iron salt solution and subjected to ultrasonic treatment and a first heat treatment to obtain a precursor. The precursor is mixed with a lithium source and a phosphorus source and then subjected to a second heat treatment to obtain MOF-based nano cathode materials.

[0012] In one embodiment, the organic ligand comprises at least one of pyromellitic acid, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine, ethylenediaminetetraacetic acid and its sodium salt, and azotetracarboxylic acid.

[0013] In one embodiment, the polymer comprises at least one of polyacrylonitrile, polyvinylpyrrolidone, polycaprolactone, and polymethyl methacrylate.

[0014] In one embodiment, the conductive salt includes at least one of lithium chloride and sodium chloride.

[0015] In one embodiment, the organic solvent includes at least one of N,N-dimethylformamide and dimethyl sulfoxide.

[0016] In one embodiment, the mass ratio of the organic ligand, the polymer, and the conductive salt is (0.35-0.5):(2.8-5.5):(0.001-0.03).

[0017] In one embodiment, the ratio of the organic ligand to the organic solvent is (0.35–0.5) g: (15–25) mL.

[0018] In one embodiment, the method for preparing the spinning solution specifically includes: mixing the organic ligand and the organic solvent, then adding the polymer and the conductive salt, and mixing them under heating conditions.

[0019] In one embodiment, the heating temperature is 35–45°C, and the heating time is 10–15 hours.

[0020] In one embodiment, the nanofibers are prepared from the spinning solution using electrospinning technology; during the electrospinning process, the voltage is 18-24 kV and the feed rate is 0.1-2 mL / h.

[0021] In one embodiment, the mass ratio of the polymer to the soluble iron salt is (2.8–5.5):(0.24–3).

[0022] In one embodiment, the soluble iron salt includes at least one of FeCl3·6H2O, Fe(NO3)3, and Fe2(SO4)3.

[0023] In one embodiment, the concentration of the soluble iron salt in the soluble iron salt solution is 0.05 g / mL to 0.2 g / mL.

[0024] In one embodiment, the ultrasonic treatment time is 1 to 6 hours.

[0025] In one embodiment, the first heat treatment is carried out in a high-pressure reaction apparatus.

[0026] In one embodiment, the temperature of the first heat treatment is 140–180°C, and the duration of the first heat treatment is 6–12 hours.

[0027] In one embodiment, after the first heat treatment, the process involves sequential cooling, washing, drying, and grinding.

[0028] In one embodiment, the lithium source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate.

[0029] In one embodiment, the phosphorus source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium dihydrogen phosphate.

[0030] In one embodiment, the mass ratio of the precursor, the lithium source, and the phosphorus source is (2.5–3.5):(0.5–3):(0.5–3).

[0031] In one embodiment, the temperature of the second heat treatment is 700–800°C, and the duration of the second heat treatment is 9–12 hours.

[0032] In one embodiment, the second heat treatment is performed in a protective gas (nitrogen or argon).

[0033] In one embodiment, the soluble iron salt may be partially or wholly replaced by at least one of a soluble cobalt salt, a soluble nickel salt, and a soluble manganese salt.

[0034] The MOFs-based nano cathode material was prepared by the method described above.

[0035] A positive electrode, comprising the aforementioned MOFs-based nano-positive electrode material.

[0036] A battery, including the aforementioned positive electrode.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) This invention combines MOFs materials with electrospinning technology. Taking the characteristics of its organic ligands as the starting point, the in-situ growth method is used to make Fe elements grow uniformly and firmly on the surface of the fiber network. On the one hand, it can induce the generation of more uniform crystal particles. On the other hand, after high-temperature carbonization, a conductive network is formed, which improves the conductivity of the obtained positive electrode material.

[0039] (2) The MOFs-based nano cathode material obtained by this invention has a solid and stable conductive structure, and the uniform particle size reduces the agglomeration effect, which is more conducive to the performance of electrical properties.

[0040] (3) The MOFs-based nano cathode material of the present invention can be further used to prepare cathode sheets and batteries, and has excellent cycle stability and rate performance. Detailed Implementation

[0041] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0042] According to one aspect of the present invention, the present invention relates to a method for preparing MOFs-based nano cathode materials, comprising the following steps:

[0043] Nanofibers were prepared using a spinning solution formed from organic ligands, polymers, conductive salts, and organic solvents. The nanofibers were then immersed in a soluble iron salt solution and subjected to ultrasonic treatment and a first heat treatment to obtain a precursor. The precursor was mixed with a lithium source and a phosphorus source and then subjected to a second heat treatment to obtain MOFs (metal-organic framework) based lithium iron phosphate cathode nanomaterials.

[0044] The organic ligands in this invention have two functions. First, the properties of the organic ligands are compatible with the polymer matrix in electrospinning, which is beneficial for preparing a uniform spinning solution. Second, by utilizing the coordination of the organic ligands with Fe metal ions, an in-situ growth method is used to uniformly grow them on the surface of nanofibers, obtaining a metal source precursor with metal ions on the surface and nanofibers at the bottom. Subsequently, lithium source and phosphate are mixed evenly and spread on the fiber membrane. After high-temperature calcination, the bottom polymer matrix is ​​carbonized to form a uniform and stable two-dimensional conductive network. The resulting lithium iron phosphate material not only has a strong and stable conductive structure, but also has uniform particle size and reduced agglomeration effect, which is more conducive to the performance of electrical properties. It also saves the step of adding dispersants and coating agents in batches.

[0045] In one embodiment, the organic ligand contains ≥3 carboxylic acid groups. The organic ligand comprises at least one of pyromellitic acid, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine, ethylenediaminetetraacetic acid and its sodium salt, and azotetracarboxylic acid.

[0046] In one embodiment, the polymer comprises at least one selected from polyacrylonitrile (PAN), polyvinylpyrrolidone, polycaprolactone, and polymethyl methacrylate. In one embodiment, the polymer may be replaced with other polymeric materials that can be carbonized at temperatures ranging from 200 to 800°C. In one embodiment, the polymer has a weight-average molecular weight of 20,000 to 300,000, such as 20,000, 50,000, 80,000, 100,000, 120,000, 150,000, 200,000, 250,000, 270,000, or 300,000.

[0047] In one embodiment, the conductive salt includes at least one of lithium chloride and sodium chloride.

[0048] In one embodiment, the organic solvent includes at least one of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0049] In one embodiment, the mass ratio of the organic ligand, the polymer, and the conductive salt is (0.35–0.5):(2.8–4.2):(0.001–0.03). For example, 0.35:2.8:0.02, 0.38:3:0.024, 0.4:3.2:0.026, 0.43:3.5:0.026, 0.5:4.2:0.03, etc.

[0050] In one embodiment, the ratio of the organic ligand to the organic solvent is (0.35–0.5) g:(15–25) mL. For example, 0.35 g:15 mL, 0.37 g:18 mL, 0.4 g:20 mL, 0.5 g:25 mL, etc.

[0051] In one embodiment, the method for preparing the spinning solution specifically includes: mixing the organic ligand and the organic solvent, then adding the polymer and the conductive salt, and mixing them under heating conditions. In one embodiment, the heating temperature is 35–45°C, for example, 35°C, 37°C, 40°C, 42°C, 45°C, etc.; the heating time is 10–15 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours, etc. By using suitable heating temperature and time, the above-mentioned raw materials are thoroughly mixed.

[0052] In one embodiment, an appropriate amount of spinning solution is placed in a syringe, and the spinning solution is prepared into nanofibers using electrospinning technology. During the electrospinning process, a voltage of 18-24 kV is applied at the injection needle, such as 18 kV, 19 kV, 20 kV, 21 kV, 22 kV, 23 kV, 24 kV, etc., and the propulsion speed is 0.1-2 mL / h, such as 0.1 mL / h, 0.3 mL / h, 0.5 mL / h, 0.8 mL / h, 1 mL / h, 1.2 mL / h, 1.5 mL / h, 2 mL / h, etc., and the nanofibers are received by an aluminum foil as the receiving end.

[0053] In one embodiment, the mass ratio of the polymer to the soluble iron salt is (2.8–5.5):(0.24–3), for example, 2.8:0.24, 3:1, 3.5:2, 4:2.5, 4.5:3, 5:3.4, 5.5:3, etc.

[0054] In one embodiment, the soluble iron salt includes at least one of FeCl3·6H2O, Fe(NO3)3, and Fe2(SO4)3.

[0055] In one embodiment, the concentration of the soluble iron salt in the soluble iron salt solution is 0.05 to 0.2 g / mL, for example, 0.05 g / mL, 0.07 g / mL, 0.08 g / mL, 0.1 g / mL, 0.12 g / mL, 0.15 g / mL, 0.18 g / mL, etc.

[0056] In one embodiment, the ultrasonic treatment time is 1 to 6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours. By employing ultrasonic treatment, iron ions in the solution are uniformly loaded onto the nanofibers, which is beneficial for subsequent reactions.

[0057] In one embodiment, the first heat treatment is carried out in a high-pressure reactor. The ultrasonically treated nanofibers and a soluble iron salt solution are transferred into a polytetrafluoroethylene-lined high-pressure reactor for reaction. In one embodiment, the temperature of the first heat treatment is 140–180°C, for example, 140°C, 150°C, 160°C, 170°C, or 180°C; the duration of the first heat treatment is 6–12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0058] In one embodiment, the nanofibers after the first heat treatment are sequentially cooled, washed, and dried. The nanofibers after the first heat treatment are cooled to room temperature, washed by centrifugation with anhydrous ethanol, and then dried and ground to obtain an Fe-MOF lithium iron phosphate precursor with a two-dimensional conductive network.

[0059] In one embodiment, the lithium source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate.

[0060] In one embodiment, the phosphorus source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate, and lithium dihydrogen phosphate.

[0061] In one embodiment, the mass ratio of the precursor, the lithium source, and the phosphorus source is (2.5–3.5):(0.5–3):(0.5–3). For example, 2.5:1:1, 2.5:1.2:1.2, 2.8:1.5:1.5, 3:2:2, 3.5:3:3, etc.

[0062] In one embodiment, the temperature of the second heat treatment is 700–800°C, such as 700°C, 720°C, 750°C, 770°C, 790°C, or 800°C, and the time of the second heat treatment is 9–12 hours, such as 9 hours, 10 hours, or 11 hours. By employing suitable temperature and time for the second heat treatment, this invention ensures that the final cathode material exhibits excellent electrochemical performance.

[0063] In one embodiment, the second heat treatment is performed in a protective gas, such as nitrogen or argon.

[0064] In one embodiment, after the second heat treatment, the material is cooled to room temperature and then further ground thoroughly to eliminate lumps.

[0065] In one embodiment, the soluble iron salt may be partially or wholly replaced by at least one of a soluble cobalt salt, a soluble nickel salt, and a soluble manganese salt. In one embodiment, the soluble cobalt salt includes cobalt chloride. In one embodiment, the soluble nickel salt includes nickel sulfate. In one embodiment, the soluble manganese salt includes manganese chloride.

[0066] According to another aspect of the present invention, the present invention also relates to MOFs-based nano-cathode materials prepared by the aforementioned method for preparing MOFs-based nano-cathode materials.

[0067] The MOFs-based nano cathode material of the present invention exhibits excellent cycle performance.

[0068] According to another aspect of the invention, the invention also relates to a cathode material comprising the aforementioned MOFs-based nano-cathode material.

[0069] According to another aspect of the invention, the invention also relates to a battery comprising the aforementioned positive electrode. The battery of the present invention exhibits excellent cycle stability and rate performance.

[0070] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0071] Example 1

[0072] The preparation method of MOFs-based nano-lithium iron phosphate cathode material includes the following steps:

[0073] (1) First, weigh 0.42 g of pyromellitic acid (H3BTC) and dissolve it completely in 20 mL of DMF. Then weigh 3.58 g of polyacrylonitrile and 0.022 g of LiCl and add them to the above mixture to prepare an electrospinning solution with a mass fraction of 20 wt%. Stir at 40 °C for 12 h to mix it thoroughly.

[0074] (2) Take an appropriate amount of spinning solution after stirring into a syringe, apply a voltage of 20kV at the injection needle, set the propulsion speed to 1mL / h, peel off the nanofibers after spinning and place them in an aqueous solution containing 0.05g / mL FeCl3·6H2O, sonicate for 3h and then transfer them into a high-pressure reactor lined with polytetrafluoroethylene, heat at 150℃ for 12h, and after cooling to room temperature, wash with deionized water by centrifugation and dry to obtain Fe-MOF lithium iron phosphate precursor;

[0075] (3) Take 3g of Fe-MOF lithium iron phosphate precursor and 1g of lithium dihydrogen phosphate and mix them evenly. Then put them into a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750℃ for 12h. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and obtain MOFs-based nano lithium iron phosphate cathode material.

[0076] Example 2

[0077] The preparation method of MOFs-based nano-lithium iron phosphate cathode material includes the following steps:

[0078] (1) First, weigh 0.42 g of pyromellitic acid (H3BTC) and dissolve it completely in 20 mL of DMF. Then weigh 3.58 g of polyacrylonitrile and 0.022 g of LiCl and add them to the above mixture to prepare an electrospinning solution with a mass fraction of 20 wt%. Stir at 40 °C for 12 h to mix it thoroughly.

[0079] (2) After stirring, take an appropriate amount of spinning solution into a syringe, apply a voltage of 20kV at the injection needle, set the propulsion speed to 1mL / h, peel off the nanofibers after spinning and place them in an aqueous solution containing 0.1g / mL FeCl3·6H2O, sonicate for 3h and then transfer them into a high-pressure reactor lined with polytetrafluoroethylene, heat at 150℃ for 12h, and after cooling to room temperature, wash with deionized water by centrifugation and dry to obtain Fe-MOF lithium iron phosphate precursor;

[0080] (3) Take 3g of Fe-MOF lithium iron phosphate precursor and 1g of lithium dihydrogen phosphate and mix them evenly. Then put them into a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750℃ for 12h. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and finally obtain MOFs-based nano lithium iron phosphate cathode material.

[0081] Example 3

[0082] The preparation method of MOFs-based nano-lithium iron phosphate cathode material includes the following steps:

[0083] (1) First, weigh 0.42 g of pyromellitic acid (H3BTC) and dissolve it completely in 20 mL of DMF. Then weigh 3.58 g of polyacrylonitrile and 0.022 g of LiCl and add them to the above mixture to prepare an electrospinning solution with a mass fraction of 20 wt%. Stir at 40 °C for 12 h to mix it thoroughly.

[0084] (2) After stirring, take an appropriate amount of spinning solution into a syringe, apply a voltage of 20kV at the injection needle, set the propulsion speed to 1mL / h, peel off the nanofibers after spinning and place them in an aqueous solution containing 0.2g / mL FeCl3·6H2O, sonicate for 3h and then transfer them into a high-pressure reactor lined with polytetrafluoroethylene, heat at 150℃ for 12h, and after cooling to room temperature, wash with deionized water by centrifugation and dry to obtain Fe-MOF lithium iron phosphate precursor;

[0085] (3) Take 3g of Fe-MOF lithium iron phosphate precursor and 1g of lithium dihydrogen phosphate and mix them evenly. Then put them into a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750℃ for 12h. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and finally obtain MOFs-based nano lithium iron phosphate cathode material.

[0086] Example 4

[0087] The preparation method of MOFs-based nano-lithium iron phosphate cathode material includes the following steps:

[0088] (1) First, weigh 0.42 g of pyromellitic acid (H3BTC) and dissolve it completely in 20 mL of DMF. Then weigh 3.18 g of polyacrylonitrile and 0.022 g of LiCl and add them to the above mixture to prepare an electrospinning solution with a mass fraction of 18 wt%. Stir at 40 °C for 12 h to mix it thoroughly.

[0089] (2) After stirring, take an appropriate amount of spinning solution into a syringe, apply a voltage of 20kV at the injection needle, set the propulsion speed to 1mL / h, peel off the nanofibers after spinning and place them in an aqueous solution containing 0.1g / mL FeCl3·6H2O, sonicate for 3h and then transfer them into a high-pressure reactor lined with polytetrafluoroethylene, heat at 150℃ for 12h, and after cooling to room temperature, wash with deionized water by centrifugation and dry to obtain Fe-MOF lithium iron phosphate precursor;

[0090] (3) Take 3g of Fe-MOF lithium iron phosphate precursor and 1g of lithium dihydrogen phosphate and mix them evenly. Then put them into a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750℃ for 12h. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and finally obtain MOFs-based nano lithium iron phosphate cathode material.

[0091] Example 5

[0092] The preparation method of MOFs-based nano-lithium iron phosphate cathode material includes the following steps:

[0093] (1) First, weigh 0.42 g of pyromellitic acid (H3BTC) and dissolve it completely in 20 mL of DMF. Then weigh 3.98 g of polyacrylonitrile and 0.022 g of LiCl and add them to the above mixture to prepare an electrospinning solution with a mass fraction of 22 wt%. Stir at 40 °C for 12 h to mix it thoroughly.

[0094] (2) After stirring, take an appropriate amount of spinning solution into a syringe, apply a voltage of 20kV at the injection needle, set the propulsion speed to 1mL / h, peel off the nanofibers after spinning and place them in an aqueous solution containing 0.1g / mL FeCl3·6H2O, sonicate for 3h and then transfer them into a high-pressure reactor lined with polytetrafluoroethylene, heat at 150℃ for 12h, and after cooling to room temperature, wash with deionized water by centrifugation and dry to obtain Fe-MOF lithium iron phosphate precursor;

[0095] (3) Take 3g of Fe-MOF lithium iron phosphate precursor and 1g of lithium dihydrogen phosphate and mix them evenly. Then put them into a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750℃ for 12h. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and finally obtain MOFs-based nano lithium iron phosphate cathode material.

[0096] Example 6

[0097] The preparation method of MOFs-based nano lithium iron phosphate cathode material is as follows: except in step (1), the mixture is stirred at 35°C for 15 hours to ensure thorough mixing; in step (2), after ultrasonic treatment for 1 hour, the mixture is transferred to a high-pressure reactor lined with polytetrafluoroethylene and heated at 180°C for 6 hours; except in step (3), 2.5 g of Fe-MOF lithium iron phosphate precursor and 0.9 g of lithium dihydrogen phosphate are mixed evenly and then placed in a high-temperature tube furnace filled with nitrogen or argon and heat-treated at 800°C for 9 hours; other conditions are the same as in Example 1.

[0098] Example 7

[0099] The preparation method of MOFs-based nano lithium iron phosphate cathode material is as follows: except in step (1), the mixture is stirred at 45°C for 10 hours to ensure thorough mixing; in step (2), after ultrasonic treatment for 6 hours, the mixture is transferred to a high-pressure reactor lined with polytetrafluoroethylene and heated at 140°C for 10 hours; except in step (3), 3.5 g of Fe-MOF lithium iron phosphate precursor and 1.1 g of lithium dihydrogen phosphate are mixed evenly and then placed in a high-temperature tube furnace filled with nitrogen or argon and heat-treated at 700°C for 10 hours; other conditions are the same as in Example 1.

[0100] Comparative Example 1

[0101] Weigh 3g of iron oxide and 1g of lithium dihydrogen phosphate and mix them thoroughly. Then, place them in a high-temperature tube furnace filled with nitrogen or argon and heat-treat them at 750°C for 8 hours. Then, add 0.1mol of glucose and keep at 750°C for 4 hours. After cooling to room temperature, grind them thoroughly to eliminate agglomeration and finally obtain the LFP cathode material.

[0102] Experimental Example 1

[0103] The average particle size, particle concentration, and powder conductivity of the lithium iron phosphate cathode materials prepared in each example and comparative example were characterized using a laser particle size analyzer and a powder resistivity meter. The results are shown in Table 1.

[0104] Table 1. Test results of different lithium iron phosphate cathode materials

[0105]

[0106] As shown in Table 1, this invention combines MOF materials with electrospinning technology and uses an in-situ growth method to grow Fe elements uniformly and firmly on the surface of the fiber network. On the one hand, this can induce the generation of more uniform crystal particles, and on the other hand, after high-temperature carbonization, a conductive network is formed, which improves the conductivity of the prepared cathode material.

[0107] Experiment Example 2

[0108] The positive electrode materials prepared using the examples and comparative examples were used to assemble button batteries in a glove box using lithium foil as the counter electrode. Specifically, a 12 μm thick carbon-coated aluminum foil was used as the current collector, and a slurry was prepared according to the mass ratio of positive electrode material: SP:PVDF = 96:2:2. The coating surface density of the electrode sheet was 15 mg / cm². 2 A lithium electrode was used as the counter electrode. The electrochemical performance was then tested using a Blue Electricity testing system and an electrochemical workstation, and the results are shown in Table 2.

[0109] Table 2. Results of Button Battery Performance Test

[0110]

[0111]

[0112] As shown in Table 2, the method used in this invention improves the specific capacity and cycle retention of lithium iron phosphate cathode materials at different rates.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing MOF-based nano-cathode materials, characterized in that, Includes the following steps: Nanofibers were prepared by electrospinning using a spinning solution formed from organic ligands, polymers, conductive salts, and organic solvents. The nanofibers were then immersed in a soluble iron salt solution and subjected to ultrasonic treatment and a first heat treatment to obtain a precursor. The precursor was mixed with a lithium source and a phosphorus source and then subjected to a second heat treatment to obtain MOFs-based nano cathode materials. The conductive salt includes at least one of lithium chloride and sodium chloride; The organic ligands include at least one of pyromellitic acid, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine, ethylenediaminetetraacetic acid and its sodium salt, and azotetracarboxylic acid; The polymer includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polycaprolactone, and polymethyl methacrylate; The mass ratio of the organic ligand, the polymer, and the conductive salt is (0.35~0.5):(2.8~5.5):(0.001~0.03). The first heat treatment is carried out in a high-pressure reaction device; The temperature of the first heat treatment is 140~180℃, and the time of the first heat treatment is 6~12h; The temperature of the second heat treatment is 700~800℃, and the time of the second heat treatment is 9~12h.

2. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The organic solvent includes at least one of N,N-dimethylformamide and dimethyl sulfoxide; (2) The ratio of the amount of organic ligand to the amount of organic solvent is (0.35~0.5) g: (15~25) mL.

3. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The method for preparing the spinning solution specifically includes: mixing the organic ligand and the organic solvent, then adding the polymer and the conductive salt, and mixing them under heating conditions; The heating temperature is 35~45℃, and the heating time is 10~15h; (2) During the electrospinning process, the voltage is 18~24kV and the feed rate is 0.1~2mL / h.

4. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, It includes at least one of the following features (1) to (3): (1) The mass ratio of the polymer to the soluble iron salt is (2.8~5.5):(0.24~3); (2) The soluble iron salt includes at least one of FeCl3•6H2O, Fe(NO3)3 and Fe2(SO4)3; (3) The concentration of soluble iron salt in the soluble iron salt solution is 0.05~0.2g / mL.

5. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The duration of the ultrasonic treatment is 1 to 6 hours; (2) After the first heat treatment, the heat treatment is carried out in sequence: cooling, washing, drying and grinding.

6. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, It includes at least one of the following features (1) to (4): (1) The phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate; (2) The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium oxalate and lithium dihydrogen phosphate; (3) The mass ratio of the precursor, the lithium source and the phosphorus source is (2.5~3.5):(0.5~3):(0.5~3); (4) The second heat treatment is carried out in a protective gas.

7. The method for preparing MOFs-based nano-cathode materials according to claim 1, characterized in that, The soluble iron salt may be partially or wholly replaced by at least one of the soluble cobalt salt, soluble nickel salt, and soluble manganese salt.

8. The MOFs-based nano cathode material prepared by the method described in any one of claims 1 to 7.

9. A positive electrode plate, characterized in that, Including the MOFs-based nano cathode material as described in claim 8.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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