A honeycomb porous structure iron phosphate material, a preparation method and application thereof

Abstract

The application provides a kind of iron phosphate composite material, including honeycomb porous carbon framework and its supported graphene quantum dot doped iron phosphate;The particle size of the iron phosphate composite material is D50=700nm~1μm;The porosity of the honeycomb porous carbon framework is 55%~60%;The particle size of the graphene quantum dot is 5nm~10nm.The material of this structure has larger specific surface area, more reaction active sites and rich mass transfer channels, which enables the electrode material to be in full contact with the electrolyte, shortens the diffusion path of lithium ions, enhances the transmission and migration of electrons, and promotes the lithiation / delithiation process, thereby improving the rate performance of the lithium iron phosphate battery.In addition, the honeycomb porous structure is also beneficial to alleviate the volume change of the electrode material during charging and discharging, and enhances its structural stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a honeycomb porous iron phosphate material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are the most widely used energy storage devices in recent years, and improving their energy density is a crucial direction for lithium battery development. The structure and composition of the cathode material significantly impact the energy density of lithium batteries. Lithium iron phosphate (LiFePO4), as one of the cathode materials for lithium-ion batteries, is favored by the power battery industry due to its stable charge-discharge platform, long cycle life, high specific capacity, and excellent safety performance. However, lithium iron phosphate suffers from poor electronic conductivity and low lithium-ion diffusion rate, which greatly affects its rate performance. Iron phosphate (FePO4) is an important precursor material for the synthesis of lithium iron phosphate, and its structure and morphology have a significant impact on the performance of lithium iron phosphate products. Therefore, macroscopically controlling the specific surface area of ​​the iron phosphate precursor material and microscopically controlling its nucleation and growth is beneficial for improving the electrochemical performance of lithium iron phosphate cathode materials.

[0003] Currently, methods such as ion doping, carbon coating, particle size reduction, and morphology control are commonly used to modify iron phosphate. However, the current preparation process generally involves solution crystallization, washing, filtration, and sintering. The resulting iron phosphate products often suffer from severe agglomeration, large particle size, and small specific surface area. This leads to a long lithium ion diffusion path during subsequent reaction with a lithium source, resulting in poor electrical performance of the corresponding lithium iron phosphate. Therefore, developing a simple and economical method to prepare iron phosphate precursors with special microstructures that facilitate lithium ion diffusion and interfacial electrolyte penetration is of great significance for obtaining high-performance lithium iron phosphate cathode materials. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a honeycomb porous structure iron phosphate material and its preparation method, which can be used to prepare lithium iron phosphate cathode materials with excellent performance.

[0005] According to a first aspect of the present invention, an iron phosphate composite material is provided, comprising a honeycomb porous carbon framework and graphene quantum dot-doped iron phosphate supported thereon.

[0006] The particle size of the iron phosphate composite material is D50 = 700 nm to 1 μm;

[0007] The porosity of the honeycomb porous carbon skeleton is 55% to 60%.

[0008] The particle size of the graphene quantum dots is 5nm to 10nm.

[0009] In some embodiments, the content of the honeycomb porous carbon skeleton is 12wt% to 20wt%.

[0010] In some preferred embodiments, the content of the honeycomb porous carbon skeleton is 13.4 wt% to 17.2 wt%.

[0011] The honeycomb porous structure and the doping of graphene quantum dots are beneficial to synergistically promote the rapid diffusion of lithium ions and electrolytes, improve the conductivity of cathode materials, and enhance the overall electrochemical performance of lithium batteries.

[0012] According to a second aspect of the present invention, a method for preparing an iron phosphate composite material as described in the first aspect of the present invention is provided, comprising the following steps:

[0013] S1: Methyl methacrylate monomer is mixed with water and emulsifier, heated and then an initiator is added to react. The resulting emulsion is centrifuged and dried to obtain PMMA microsphere colloidal template.

[0014] S2: Disperse ferrous salt and imidazole compound in alcohol, add surfactant and organic carbon source and stir, then add PMMA microsphere colloidal template obtained in step S1 and continue stirring to obtain PMMA-carbon source / iron-based zeolite imidazole framework (Fe-ZIF) material.

[0015] S3: After removing PMMA from the PMMA-carbon source / Fe-ZIF material obtained in step S2, calcine it at a temperature containing oxygen and nitrogen to obtain Fe2O3 / C material.

[0016] S4: The Fe2O3 / C material obtained in step S3 is mixed with urea, graphene dispersion and phosphoric acid solution in an aqueous phase, and heated to react to obtain iron phosphate / graphene quantum dot material.

[0017] In this invention, "x / y material" represents a composite material composed of x and y, such as "iron phosphate / graphene quantum dot material"; "ab" represents that a and b are in a blended state, such as "PMMA-carbon source"; "Fe-ZIF" specifically refers to the iron-based zeolite imidazole framework.

[0018] In some implementations, step S1 satisfies one or more of the following conditions:

[0019] a. The volume ratio of the methyl methacrylate monomer, water and the initiator is (10-16) mL: 350 mL: (30-40) mL;

[0020] b. The emulsifier is at least one of sodium dodecyl sulfate or sodium dodecylbenzene sulfonate;

[0021] c. The liquid-to-solid ratio of the methyl methacrylate monomer to the emulsifier is (10-16) mL:1 g;

[0022] d. The concentration of the initiator is 0.02 mol / L to 0.05 mol / L;

[0023] e. The heating temperature is 65–70°C, and the reaction time is 2–3 hours;

[0024] f. The centrifugation speed is 3000 r / min to 5000 r / min, and the centrifugation time is 4 to 7 h.

[0025] In some embodiments, the methyl methacrylate monomer is further subjected to a washing treatment to remove the polymerization inhibitor.

[0026] In some embodiments, in step S1, the mixing process and the reaction process are carried out under a nitrogen atmosphere.

[0027] In some embodiments, in step S1, the emulsion is further filtered to remove clumps before centrifugation.

[0028] In some embodiments, in step S1, the drying temperature is 65-70°C and the time is 20-30 hours.

[0029] The temperature of emulsion polymerization needs to be controlled within the range of 65-75℃. Too high or too low a temperature will affect the polymerization rate and the stability of the emulsion. After removing the clumps, the resulting emulsion is centrifuged and dried to obtain regular, ordered and tightly arranged PMMA microsphere colloidal templates.

[0030] In some implementations, step S2 satisfies one or more of the following conditions:

[0031] g. The ferrous salt is at least one of ferrous sulfate or ferrous chloride, and the mass molar ratio of the PMMA microsphere colloidal template to the ferrous salt is 1 g: (0.001~0.002) mol;

[0032] h. The imidazole compound is 2-methylimidazole, and the molar ratio of the 2-methylimidazole to the ferrous salt is (3.5-4.5):1;

[0033] i. The surfactant is at least one of polyvinylpyrrolidone (PVP) or polyvinyl alcohol;

[0034] j. The mass of the surfactant is 9 wt% to 12 wt% of the mass of the ferrous salt;

[0035] k. The organic carbon source is carboxymethyl cellulose;

[0036] l. The mass of the organic carbon source is 18wt% to 25wt% of the mass of the ferrous salt.

[0037] The addition of surfactants can prevent particle aggregation and improve the uniformity of the synthesized product. The purpose of adding organic carbon source is to generate carbon skeleton in the subsequent high-temperature calcination process. Since the subsequent preparation steps require washing with anhydrous acetone to remove PMMA template, the selected carboxymethyl cellulose can exist stably in anhydrous acetone, thus forming carbon skeleton structure.

[0038] In some embodiments, in step S2, the alcohol is anhydrous methanol.

[0039] In some embodiments, in step S2, the organic carbon source is first dispersed and dissolved in deionized water before use.

[0040] In some embodiments, step S2 is performed at room temperature, and the stirring is continued for 20 to 30 hours.

[0041] In some embodiments, step S2 further includes centrifuging, washing, and drying the PMMA-carbon source / Fe-ZIF material, wherein the drying temperature is 60-65°C and the drying time is 12-15 hours.

[0042] In some embodiments, in step S3, the purity specifications of the oxygen-containing nitrogen atmosphere are: N2: 99%, O2: 0.7%–1%, and other impurity gases: 0%–0.3%. The nitrogen contains a small amount of oxygen to remove Fe from the metal-organic framework complex Fe-ZIF. 2+ Fe2O3 is generated during high-temperature calcination.

[0043] In some embodiments, in step S3, the calcination temperature is 450–600°C and the time is 1–2 hours.

[0044] In some embodiments, in step S3, anhydrous acetone is used to remove PMMA from the PMMA-carbon source / Fe-ZIF material. The PMMA template can be removed by washing with anhydrous acetone, and after vacuum drying, a honeycomb-structured carbon source / Fe-ZIF precursor material is obtained. The precursor material is then calcined in an oxygen-nitrogen atmosphere to obtain an amorphous carbon skeleton / Fe2O3 composite material retaining a porous structure.

[0045] In some implementations, step S4 satisfies one or more of the following conditions:

[0046] m. The mass ratio of urea to the Fe2O3 / C material is (2-2.5):1;

[0047] n. The mass concentration of the graphene dispersion is 10 g / L to 15 g / L, wherein the mass of graphene is 10 wt% to 15 wt% of the mass of the Fe2O3 / C material;

[0048] o. The molar ratio of phosphorus in the phosphoric acid solution to iron in the Fe2O3 / C material is (1-1.2):1;

[0049] p. The heating reaction is carried out at a temperature of 120–150°C for a time of 12–24 hours.

[0050] During the heating process of urea, ammonia gas is generated and dissolved in a solvent to form ammonia water, thereby adjusting the pH value of the reaction solution to prevent it from becoming too low.

[0051] In some embodiments, in step S4, the concentration of the phosphoric acid solution is 0.8–1.0 mol / L.

[0052] In some embodiments, step S4 further includes heating and dehydrating the iron phosphate / graphene quantum dot material; the heating and dehydration temperature is 500–750°C, and the time is 4–10 hours. After the above treatment removes the water of crystallization, anhydrous iron phosphate / graphene quantum dot material is obtained.

[0053] This invention first involves the self-assembly of polymethyl methacrylate (PMMA) microspheres, formed by the emulsion polymerization of monomeric methyl methacrylate (MMA), into a three-dimensional ordered template. This template is then placed in a mixed solution of Fe-ZIF precursor and organic carbon source. Under room temperature conditions, Fe-ZIF crystals grow orderly along the three-dimensional template, yielding a PMMA-carbon source / Fe-ZIF composite hybrid material. Further, this material is placed in anhydrous acetone solvent to remove the PMMA template, resulting in a honeycomb-structured carbon source / Fe-ZIF hybrid material. Subsequently, the carbon source / Fe-ZIF hybrid material is calcined in an oxygen-nitrogen atmosphere to obtain an amorphous carbon skeleton / Fe2O3 composite material retaining a porous structure, i.e., Fe2O3 / C material. This material is then mixed with graphene dispersion and phosphoric acid, and prepared via hydrothermal method and high-temperature calcination to obtain an anhydrous FePO4 / GQDs (graphene quantum dots) composite material with a honeycomb porous structure.

[0054] This invention employs a colloidal template method to first prepare a honeycomb-structured carbon source / Fe-ZIF precursor material, which is then calcined at high temperature to obtain a porous Fe2O3 / C composite material. The introduction of carboxymethyl cellulose as the carbon source not only provides amorphous carbon, but the carbon skeleton formed after pyrolysis and carbonization also maintains its honeycomb morphology. Simultaneously, during the pyrolysis process, the Fe in the Fe-ZIF material... 2+Fe2O3 particles will be deposited on the surface of the carbon skeleton, and organic ligands will form nitrogen-doped carbon that adheres to the surface of the carbon wall to support the carbon skeleton. Subsequently, after the porous Fe2O3 / C material is mixed with phosphoric acid, the phosphoric acid solution can freely enter these pores and fully react with the Fe2O3 on the inner wall of the carbon material. The resulting iron phosphate self-assembles in situ along the carbon wall plane and eventually inherits its porous framework structure.

[0055] In the synthesis of iron phosphate, the strong acid phosphoric acid first oxidizes graphene nanosheets, then removes the oxygen-containing groups on their surface and chemically cleaves them in a high-temperature hydrothermal environment, forming graphene quantum dots (GQDs) deposited on the surface of the generated iron phosphate. This quantum dot material has an ultra-small size, a large surface area, and a higher electron mobility. After being compounded with FePO4 and then mixed with a lithium source and calcined at high temperature, LiFePO4 / GQDs cathode material is obtained, which can effectively improve the rate performance and cycle life of lithium batteries. In addition, the carbon skeleton formed after the pyrolysis and carbonization of the organic carbon source and the nitrogen-doped residual carbon formed after the organic ligands of the Fe-ZIF precursor material are calcined at high temperature can also improve the electronic / ionic conductivity of the cathode material.

[0056] According to a third aspect of the present invention, a lithium iron phosphate cathode material is provided, which is prepared from the iron phosphate composite material described in the first aspect of the present invention.

[0057] In some embodiments, the preparation method of the lithium iron phosphate cathode material includes the following steps:

[0058] The FePO4 / GQDs material was mixed with a lithium source and ball-milled, then dried and sintered to obtain a lithium iron phosphate / graphene quantum dot (LiFePO4 / GQDs) composite material.

[0059] In some preferred embodiments, the lithium source is at least one of lithium carbonate, lithium hydroxide, or lithium acetate.

[0060] In some preferred embodiments, the molar ratio of iron to lithium source in the FePO4 / GQDs material is 1:(1 to 1.05).

[0061] In some preferred embodiments, the sintering includes low-temperature pre-sintering and secondary sintering; the low-temperature pre-sintering temperature is 400-500°C and the holding time is 3-5 hours; and / or, the secondary sintering temperature is 650-750°C and the holding time is 6-10 hours.

[0062] According to one embodiment of the present invention, at least the following beneficial effects are achieved:

[0063] The lithium iron phosphate prepared by this invention has a honeycomb porous structure. Compared with irregular bulk materials, this structure has a larger specific surface area, more reactive sites, and abundant mass transfer channels. This allows the electrode material to fully contact the electrolyte, shortens the lithium-ion diffusion path, enhances electron transport and migration, and promotes the lithiation / delithiation process, thereby improving the rate performance of lithium iron phosphate batteries. Furthermore, the honeycomb porous structure also helps to mitigate the volume changes of the electrode material during charge and discharge, enhancing its structural stability. Attached Figure Description

[0064] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0065] Figure 1 The image shows the XRD pattern of the iron phosphate / graphene quantum dot composite material (FePO4 / GQDs) prepared in Example 1 of this invention.

[0066] Figure 2 This is a SEM image of the PMMA microsphere colloidal template prepared in Example 1 of the present invention;

[0067] Figure 3 This is a SEM image of the lithium iron phosphate / graphene quantum dot composite material (LiFePO4 / GQDs) prepared in Example 1 of this invention. Detailed Implementation

[0068] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention.

[0069] Unless otherwise specified, the raw materials, reagents or apparatus used in the following examples and comparative examples are available from conventional commercial sources or can be obtained by existing known methods.

[0070] In the examples and comparative examples, the methyl methacrylate monomers used were treated as follows: the methyl methacrylate monomers were placed in a spherical separatory funnel and washed several times with sodium hydroxide solution and distilled water to remove the polymerization inhibitor, so as to obtain a pretreated monomer solution for later use.

[0071] Example 1

[0072] This embodiment provides an iron phosphate composite material, comprising a honeycomb porous carbon skeleton and graphene quantum dot-doped iron phosphate. The particle size of the iron phosphate composite material is D50 = 870 nm; the porosity of the honeycomb porous carbon skeleton is 56.5%, and the content is 14.2 wt%; the particle size of the graphene quantum dots is 5.5 nm.

[0073] This embodiment also provides a method for preparing the iron phosphate composite material as described above, including the following steps:

[0074] (1) Take 10 mL of pretreated methyl methacrylate monomer and 350 mL of distilled water and add them to a 500 mL three-necked flask. Purge with nitrogen and add 1.0 g of emulsifier sodium dodecyl sulfate while stirring continuously. After stirring for 30 min, heat the reaction system to 70 °C and add 30 mL of initiator ammonium persulfate solution (0.03 mol / L) to the above mixture. Stir and reflux at a constant temperature for 2 h. After the reaction is complete, filter out the clumps in the emulsion to obtain PMMA microsphere emulsion. Then, centrifuge the above PMMA microsphere emulsion at 3000 r / min for 5 h. After centrifugation, discard the supernatant and dry the remaining sample in a 65 °C oven for 24 h to obtain a regularly ordered and tightly arranged PMMA microsphere colloidal template. The SEM of the PMMA microsphere colloidal template is shown in Figure 1. Figure 2 As shown. 0.02 mol FeSO4·7H2O and 0.08 mol 2-methylimidazole were ultrasonically dispersed in 100 mL of anhydrous methanol. Then, 0.56 g PVP and carboxymethyl cellulose solution (1.11 g CMC / 20 mL deionized water) were added to the dispersion. After stirring until homogeneous, 11.12 g of... The PMMA colloidal template was placed in the above mixture and stirred at room temperature for 24 hours. The product was then centrifuged, washed sequentially with deionized water and anhydrous ethanol, and dried in a vacuum oven at 60°C for 12 hours to obtain the PMMA-carbon source / Fe-ZIF material. Subsequently, the product was washed several times with anhydrous acetone to remove the PMMA template, and then dried under vacuum to obtain the carbon source / Fe-ZIF precursor material. The material was then placed in a muffle furnace and calcined at 500°C for 1 hour in an oxygen-nitrogen atmosphere (N2: 99%, O2: 0.7%, other impurity gases: 0.3%) to obtain an amorphous carbon skeleton / Fe2O3 composite material with a porous structure, i.e., Fe2O3 / C material.

[0075] (2) 0.7 g of Fe2O3 / C material was ultrasonically dispersed in 60 mL of deionized water, and then 1.4 g of urea was added. After stirring evenly, a graphene dispersion (10 g / L) with a graphene mass of 10 wt% of Fe2O3 / C material was added to the above mixture. Then, phosphoric acid solution (0.8 mol / L) was added according to a Fe / P ratio of 1:1. After stirring at room temperature for 30 min, the mixture was transferred to a 100 mL stainless steel autoclave and heated in an oven at 120 °C for 12 h. After cooling to room temperature, the product was collected by centrifugation, washed, and vacuum dried to obtain a honeycomb porous iron phosphate / graphene quantum dot composite material. Subsequently, the above product was placed in a muffle furnace and heated to 500 °C for 4 h to remove the water of crystallization, thus obtaining anhydrous FePO4 / GQDs material. The XRD pattern of the FePO4 / GQDs material is shown in the figure. Figure 1 As shown.

[0076] This embodiment also provides an application of the iron phosphate composite material as described above, and further includes the following steps:

[0077] (3) Lithium carbonate and FePO4 / GQDs were dispersed in anhydrous ethanol at a lithium source to iron source molar ratio of 1:1 and ball-milled for 3 hours until homogeneous. The mixture was then spray-dried to obtain precursor powder. Subsequently, the precursor powder was heated to 400℃ for 3 hours at a heating rate of 5℃ / min under an argon atmosphere, and then calcined at 700℃ for 8 hours to obtain a lithium iron phosphate / graphene quantum dot composite cathode material. The scanning electron microscope image of this composite cathode material is shown below. Figure 3 As shown.

[0078] Example 2

[0079] This embodiment provides an iron phosphate composite material, comprising a honeycomb porous carbon skeleton and graphene quantum dot-doped iron phosphate. The particle size of the iron phosphate composite material is D50 = 1 μm; the porosity of the honeycomb porous carbon skeleton is 55.3% and the content is 13.4 wt%; the particle size of the graphene quantum dots is 6.2 nm.

[0080] This embodiment also provides a method for preparing the iron phosphate composite material as described above, the only difference from Example 1 being:

[0081] In step (1), the amount of ammonium persulfate solution used as the initiator is 35 mL;

[0082] In step (2), the heating temperature of the oven is 150℃ and the heating time is 12h.

[0083] Example 3

[0084] This embodiment provides an iron phosphate composite material, comprising a honeycomb porous carbon skeleton and graphene quantum dot-doped iron phosphate. The particle size of the iron phosphate composite material is D50 = 920 nm; the porosity of the honeycomb porous carbon skeleton is 58.2%, and the content is 16.6 wt%; the particle size of the graphene quantum dots is 8.3 nm.

[0085] This embodiment also provides a method for preparing the iron phosphate composite material as described above, the only difference from Example 1 being:

[0086] In step (1), the amount of methyl methacrylate monomer pretreated to remove the polymerization inhibitor is 13 mL;

[0087] In step (2), the heating temperature of the oven is 150℃ and the heating time is 12h; the amount of graphene dispersion is 12wt%.

[0088] Example 4

[0089] This embodiment provides an iron phosphate composite material, comprising a honeycomb porous carbon skeleton and graphene quantum dot-doped iron phosphate. The particle size of the iron phosphate composite material is D50 = 700 nm; the porosity of the honeycomb porous carbon skeleton is 60%, and the content is 17.2 wt%; the particle size of the graphene quantum dots is 10 nm.

[0090] This embodiment also provides a method for preparing the iron phosphate composite material as described above, the only difference from Example 1 being:

[0091] In step (1), the amount of methyl methacrylate monomer pretreated to remove the polymerization inhibitor is 13 mL;

[0092] In step (2), 1.0 g of Fe2O3 / C material was ultrasonically dispersed in 60 mL of deionized water, and then 2.0 g of urea was added. After stirring evenly, a graphene dispersion (10 g / L) with a graphene mass of 12 wt% of Fe2O3 / C material was added to the above mixture. Then, phosphoric acid solution (0.8 mol / L) was added according to the Fe / P ratio of 1:1. After stirring at room temperature for 30 min, the mixture was transferred to a 100 mL stainless steel autoclave and placed in an oven at 150 °C for 24 h.

[0093] Example 5

[0094] This embodiment provides an iron phosphate composite material, comprising a honeycomb porous carbon skeleton and graphene quantum dot-doped iron phosphate. The particle size of the iron phosphate composite material is D50 = 720 nm; the porosity of the honeycomb porous carbon skeleton is 59.3%, and the content is 16.8 wt%; the particle size of the graphene quantum dots is 9.5 nm.

[0095] This embodiment also provides a method for preparing the iron phosphate composite material as described above, the only difference from Example 4 being:

[0096] In step (2), the amount of graphene fed is 15 wt% of the mass of the Fe2O3 / C material.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing an iron phosphate / graphene quantum dot composite material and its application (the difference from Example 1 is that a PMMA colloidal template is not prepared to synthesize the iron phosphate / graphene quantum dot composite material), including the following steps:

[0099] (1) 0.02 mol FeSO4·7H2O and 0.08 mol 2-methylimidazole were ultrasonically dispersed in 100 mL of anhydrous methanol, and then 1.67 g PVP was added to the above dispersion. The mixture was stirred at room temperature for 24 h. The product was centrifuged, washed with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum oven at 60 °C for 12 h to obtain the Fe-ZIF material. Subsequently, the above material was placed in a muffle furnace, heated to 500 °C in an oxygen-nitrogen atmosphere and calcined for 1 h to obtain the Fe2O3 / C material with nitrogen-doped carbon.

[0100] Steps (2) and (3) are the same as steps (2) and (3) in Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a honeycomb porous iron phosphate material, its preparation method, and its application (the difference from Example 1 is that the graphene quantum dot composite iron phosphate material is not prepared), including the following steps:

[0103] (1) is the same as step (1) in Example 1.

[0104] (2) The difference from step (2) of Example 1 is that no graphene dispersion is added when preparing the iron phosphate material.

[0105] (3) is the same as step (3) in Example 1.

[0106] Test case

[0107] The lithium iron phosphate cathode materials obtained in the above examples and comparative examples were formulated into coin cells for lithium-ion battery electrochemical performance testing (with charge and discharge voltage controlled between 2.5-4.5V). The results are shown in the table below.

[0108]

[0109] from Figure 1It can be seen that the XRD curve of the iron phosphate / graphene quantum dot (GQDs) material prepared in Example 1 has the same characteristic peaks as the FePO4 standard card, and the weak diffraction peak that appears at 2θ of 22.5° corresponds to the (002) crystal plane of GQD, indicating that graphene quantum dots exist in the FePO4 / GQDs composite material.

[0110] As shown in the table, the electrochemical performance of the lithium iron phosphate products prepared in the examples is significantly better than that of the comparative examples, especially in Example 4. Compared with the irregular iron phosphate bulk prepared in Comparative Example 1 and the porous iron phosphate prepared in Comparative Example 2, the iron phosphate prepared in the examples has a honeycomb porous structure and is loaded with graphene quantum dots. The lithium iron phosphate cathode material prepared with this precursor has a large specific surface area, high conductivity, short lithium-ion diffusion path, fast rate, and low deintercalation / intercalation resistance. Therefore, the electrochemical performance of the lithium-ion battery is superior.

[0111] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. An iron phosphate composite material, characterized by, The iron phosphate composite material comprises a honeycomb porous carbon framework and graphene quantum dots loaded thereon; The particle size of the iron phosphate composite material is D50=700nm-1μm; The porosity of the honeycomb porous carbon framework is 55%-60%; The particle size of the graphene quantum dots is 5nm-10nm.

2. The iron phosphate composite material of claim 1, wherein, The content of the honeycomb porous carbon framework is 12wt%-20wt%.

3. A process for the preparation of the iron phosphate composite material according to any one of claims 1-2, characterized in that, The method comprises the following steps: S1: mixing methyl methacrylate monomers with water and an emulsifier, adding an initiator after warming, and then performing a reaction, and obtaining PMMA microsphere colloidal templates by centrifuging and drying the obtained emulsion; S2: dispersing ferrous salt and an imidazole compound in alcohol, adding a surfactant and an organic carbon source for stirring, and then adding the PMMA microsphere colloidal templates prepared in step S1 for continuous stirring to obtain PMMA-carbon source / iron-based zeolite imidazole framework materials; S3: removing the PMMA in the PMMA-carbon source / iron-based zeolite imidazole framework materials prepared in step S2, and then performing calcination in an oxygen-containing nitrogen atmosphere after warming to obtain Fe2O3 / C materials; S4: mixing the Fe2O3 / C materials prepared in step S3 with urea, a graphene dispersion liquid, and a phosphoric acid solution in an aqueous phase, and then performing a heating reaction to obtain iron phosphate / graphene quantum dot materials.

4. The production method according to claim 3, characterized by, Step S1 meets one or more of the following conditions: a. The volume ratio of the methyl methacrylate monomers, water, and the initiator is (10-16)mL:350mL:(30-40)mL; b. The emulsifier is at least one of sodium dodecyl sulfate or sodium dodecyl benzene sulfonate; c. The liquid-solid ratio of the methyl methacrylate monomers and the emulsifier is (10-16)mL:1g; d. The concentration of the initiator is 0.02mol / L-0.05mol / L; e. The temperature of the warming is 65-70℃, and the reaction time is 2-3h; f. The centrifugation speed is 3000r / min-5000r / min, and the centrifugation time is 4-7h.

5. The preparation method according to claim 3, characterized in that, Step S2 meets one or more of the following conditions: g. The ferrous salt is at least one of ferrous sulfate or ferrous chloride, and the mass molar ratio of the PMMA microsphere colloidal templates and the ferrous salt is 1g:(0.001-0.002)mol; h. The imidazole compound is 2-methyl imidazole, and the molar ratio of the 2-methyl imidazole and the ferrous salt is (3.5-4.5):1; i. The surfactant is at least one of polyvinylpyrrolidone or polyvinyl alcohol; j. The mass of the surfactant is 9wt%-12wt% of the mass of the ferrous salt; k. The organic carbon source is carboxymethyl cellulose; l. The mass of the organic carbon source is 18wt%-25wt% of the mass of the ferrous salt.

6. The preparation method according to claim 3, characterized in that, In step S3, the purity specification of the oxygen-containing nitrogen atmosphere is: N2: 99%, O2: 0.7%-1%, and other impurity gases: 0%-0.3%.

7. The preparation method according to claim 3, characterized in that, In step S3, the temperature of the warming calcination is 450-600℃, and the time is 1-2h.

8. The preparation method according to claim 3, characterized in that, Step S4 meets one or more of the following conditions: m. the mass ratio of the urea to the Fe2O3 / C material is (2-2.5):1; n. the mass concentration of the graphene dispersion liquid is 10-15 g / L, wherein the mass of the graphene is 10-15 wt% of the mass of the Fe2O3 / C material; o. the molar ratio of phosphorus element in the phosphoric acid solution to iron element in the Fe2O3 / C material is (1-1.2):1; p. the heating reaction is at a temperature of 120-150 ℃ for 12-24 h.

9. The preparation method according to claim 3, characterized in that, Step S4 further comprises heating and dehydrating the iron phosphate / graphene quantum dot material; the heating and dehydrating is at a temperature of 500-750 ℃ for 4-10 h.

10. A lithium iron phosphate cathode material, characterized in that, The iron phosphate composite material is prepared by any one of claims 1-2.

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